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This is to certify that the

thesis entitled

OPTICAL EMISSION SPECTROSCOPY INVESTIGATION
OF MICROWAVE PLASMAS

presented by

Jayakumaran Sivagnaname

has been accepted towards fulﬁllment
of the requirements for

MASTER OF SCIENCE Electrical Engg.

degree in

 

 

 

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OPTICAL EMISSION SPECTROSCOPY INVESTIGATION OF
MICROWAVE PLASMAS

By

J ayakumaran Sivagnaname

A THESIS

Submitted to
Michigan State University
in partial fulﬁllment of the requirements
for the degree of

MASTER OF SCIENCE
Department of Electrical and Computer Engineering

1998

ABSTRACT

OPTICAL EMISSION SPECTROSCOPY INVESTIGATION OF MICROWAVE
PLASMAS

By

J ayakumaran Sivagnaname

Microwave cavity plasma reactors are being used for a range of materials process-
ing applications including the deposition of diamond thin ﬁlms and the etching/surface
treatment of semiconductor materials during device fabrication. For all these microwave
plasma processes a concise understanding of the plasma species concentration and ener-
gies are often still lacking. The plasma parameters like gas temperature and species con-
centration, H, C2 and CH, for some of the commonly used plasmas for diamond thin ﬁlm
deposition, namely H2 - CH4 and Ar - H2 - CH4 were analyzed using optical emission
spectroscopy.

The addition of small amounts of N2 has been shown to affect the deposition rate
and characteristics of the diamond film. Hence the effect of nitrogen on these plasmas was
also studied. With the 0.1 - 1% addition of nitrogen no change in the gas temperature was
observed. However an increase in the amount of atomic hydrogen was observed with
nitrogen concentration.

The density of high energy electrons in a compact ion source was also analyzed.
This was achieved by observing the doubly ionized argon emission lines. The results indi-
cate the presence of high energy electrons (greater than 27eV) in the plasma of a compact

ion source.

Dedicated to

Almighty

iii

ACKNOWLEDGEMENTS

I would like to express my profound gratitude to Dr. Timothy Grotjohn. It was his
constant encouragement, support and untiring help that led to the completion of this
project. He has given his knowledge, his time and his support to guide me through the
work presented here. I would also like to thank Dr. Jes Asmussen and Dr. Tim Hogan for
their constructive remarks on the project and for being a part of the examining committee.
Thanks are due to Dr. Anatoly Vikharev, Alexander(Sasha) Kolysko and Dmitry Radis-
chev of the Russian Academy of Sciences for their contribution to the project, especially
the gas temperature measurements. I wish to express my gratitude to my parents and fam-
ily members for their love and support. I would also like to thank Bo Keu Kim, Meng-Hua

Tsai, Mark Perrin, Amir Khan and Wen-Shin Huang for their advice and friendship.

iv

TABLE OF CONTENTS

List of Tables iii
List of Figures ix
1 Introduction 1
1.0 Motivation ................................................................................................................ 1

1.2 Objectives ................................................................................................................. 2

1.3 Thesis Outline ........................................................................................................... 3

2 Equipment and Experimental Method 4
2.1 Introduction to equipment used ................................................................................ 4
2.2 Multipolar ECR plasma reactor system .................................................................... 4
2.2.1 Description of the Plasma Source - the MPDR 610 ....................................... 4

2.2.2 The microwave apparatus ............................................................................... 7

2.2.3 Gas/vacuum systems ....................................................................................... 8

2.3 High power resonant cavity microwave reactor ..................................................... 10
2.4 Spectrometer- system #1 ........................................................................................ 12
2.5 Data acquisition and signal processing for spectrometer system #1 ...................... 13
2.6 Diode array detector - spectrometer system #2 ...................................................... 14
2.7 Collection Optics .................................................................................................... 16
2.7.1 Arrangement #1 ............................................................................................ 17

2.7.2 Arrangement #2 ............................................................................................ 17

2.7.3 Arrangement #3 ............................................................................................ 18

vi

3 Identiﬁcation and analysis of Argon Doubly-ionized atoms 19
3.1 Introduction ............................................................................................................ 19
3.2 Theory of the diagnostic technique ........................................................................ 19
3.4 Experimental method ............................................................................................. 22
3.3 Observation and measurement of the doubly ionized lines .................................... 23
3.5 Results and discussion ............................................................................................ 26
3.6 Conclusion .............................................................................................................. 33

4 Gas Kinetic Temperature of H2 - CH4 Microwave Plasma 34
4.1 Introduction ............................................................................................................ 34
4.2 Gas kinetic temperature measurement theory ........................................................ 34

4.2.1 Hund’s Coupling Cases ................................................................................. 38
4.3 Experimental setup ................................................................................................. 40
4.4 Hydrogen rotational temperature ............................................................................ 41
4.4.1 Estimation of the rotational temperature ....................................................... 41
4.5 Rotational temperature results ................................................................................ 43
4.6 Conclusion .............................................................................................................. 50

5 Study of H2 - CH4 - N2 Microwave Plasma 51
5.1 Introduction ............................................................................................................ 51
5.2 Experimental Setup ................................................................................................ 51
5.3 Results and discussions .......................................................................................... 52
5.4 Conclusion .............................................................................................................. 6O

6 Study of Ar - H2 - CH4 - N2 Microwave Plasma

6.1 Introduction ............................................................................................................
6.2 Experimental setup .................................................................................................
6.3 Results and discussion ............................................................................................

6.5 Conclusion ..............................................................................................................

7 Summary of results

7.1 Conclusion ..............................................................................................................

7.1.1 Argon Doubly-ionized atoms measurements ................................................

7.1.2 Gas Kinetic Temperature of H2 - CH4 Microwave Plasma ..........................

7.1.3 Study of H2 - CH4 - N2 Microwave Plasma .................................................

7.1.4 Study of Ar-H2 - CH4 - N2 Microwave Plasma ............................................

7.2 Recommendations for future work .........................................................................
Appendix A
Appendix B
Appendix C

References

vii

61

61

61

62

78

79

79

79

80

80

81

81

84

86

91

97

LIST OF TABLES

4 Gas Kinetic Temperature of H2 - CH4 Microwave Plasma 34
Table 4.1: Energy level for the R-branch rotational lines ................................................. 43
Appendix A 84
Table A: Identiﬁcation and analysis of argon doubly ionized atoms ................................. 84
Appendix B 86
Table B: Measurements of Ar - H2 - CH4 - N2 Microwave Plasma .................................. 86

viii

LIST OF FIGURES

Figure 2.1 MPDR 610 Plasma Source ................................................................................. 6
Figure 2.2 Top view of the chamber ................................................................................... 7
Figure 2.3 Vacuum system of the plasma source ............................................................... 9
Figure 2.4 High Power Microwave Plasma Reactor ......................................................... 10
Figure 2.5 High Power Microwave Plasma Reactor ......................................................... 11
Figure 2.6 Sketch of the spectrometer .............................................................................. 13
Figure 2.7 Sketch of the diode array detector ................................................................... 15
Figure 2.8 Optical set up for light collection - arrangement #1 ........................................ 17
Figure 2.9 Optical set up for light collection - arrangement #2 ........................................ 18
Figure 2.10 Optical set up for light collection — arrangement #3 ...................................... 18
Figure 3.1 Atomic states of the Ar atom ........................................................................... 20
Figure 3.2 Experimental Set-up for the identification of Ar“ lines ................................ 23

Figure 3.3 Emission spectra of krypton plasma. Pressure: 3 mT, Flow rate: lsccm, Input
Power: 90 W. .................................................................................................................... 24

Figure 3.4 Emission spectra of argon plasma. Pressure: 0.75 mT, Flow rate: lsccm, Input
Power: 100 W. .................................................................................................................. 25

Figure 3.5 Variation of Ar++ density with pressure for argon plasma. Flow rate: lsccm.
Input power: 40 W. ........................................................................................................... 29

Figure 3.6 Variation of Ar++ density with pressure for argon plasma. Flow rate: lsccm.
Input power: 100 W. ......................................................................................................... 30

Figure 3.7 Variation of Ar‘“+ density with input power for argon plasma. Flow rate: 1 sccm.
Pressure: 0.9 mT ............................................................................................................... 31

Figure 3.8 Variation of Ar++ density with flow rate of Ar for argon plasma. Pressure: 0.9
mT. Input power: 40 W ..................................................................................................... 32

ix

Figure 4.1 Diagram of the Observed Electronic States of the H2 Molecule ..................... 36
Figure 4.2 Energy Level Diagram for a Band with P and R Branches ............................. 37
Figure 4.3 Experimental Set-up for the measurement of rotational temperature of H2.... 40
Figure 4.4 Emission Spectra of the R-Branch rotational lines of H2 ................................ 42
Figure 4.5 Boltzmann plot for the lines R0 and R5-R10 .................................................. 42

Figure 4.6 Variation of rotational temperature of H2 with pressure for H2 plasma. Flow rate:
H2-200 sccm. Input power: 400 W ................................................................................... 45

Figure 4.7 Variation of rotational temperature of Hz with pressure for H2-CH4 plasma.
Flow rate: H2-200 sccm, CH4-4 sccm. Input power: 400 W ............................................ 46

Figure 4.8 Variation of rotational temperature of Hz with input power for H2-CH4 plasma.
Flow rate: H2-200 sccm, CH4-4 sccm. Pressure: 30 Torr ................................................. 47

Figure 4.9 Variation of rotational temperature of H2 with flow rate for H2 plasma. Pressure:
30 Torr. Input power: 400 W ............................................................................................ 48

Figure 4.10 Variation of rotational temperature of H2 with ﬂow rate of N2 for Hz-CH4-N 2
plasma. Flow rate: H2-200 sccm, CH4-43ccm. Pressure: 30 Torr. Input power: 400 W .. 49

Figure 5.1 Variation of HG line intensity with N2 concentration. Flow rates: CH4-4 sccm,
H2-200 sccm. Pressure: 30 Torr. Input Power: 0.8 kW .................................................... 54

Figure 5.2 Variation of HB line intensity with N2 concentration. Flow rates: CH4-4 sccm,
H2-200 sccm. Pressure: 30 Torr. Input Power: 0.8 kW .................................................... 55

Figure 5.3 Variation of HB/Ha ratio with N2 concentration. Flow rates: CH4-4 sccm, H2-
200 sccm. Pressure: 30 Torr. Input Power: 0.8 kW .......................................................... 56

Figure 5.4 Emission spectrum of Hz-CH4-N2 plasma. Flow rates: CH4-7.2 sccm, H2-144
sccm, N2-0.5 sccm. Pressure: 30 Torr. Input Power: 0.8 kW ........................................... 57

Figure 5.5 Variation of CH line intensity with N2 concentration. Flow rates: CH4-7.2 sccm,
H2-144 sccm. Pressure: 30 Torr. Input Power: 0.8 kW .................................................... 58

Figure 5.6 Variation of CN line intensity with N2 concentration. Flow rates: CH4-7.2 sccm,
H2-144 sccm. Pressure: 30 Torr. Input Power: 0.8 kW .................................................... 59

Figure 6.1 Emission spectrum. Flow rates: Ar- 600 sccm, CH4- 3 sccm, Hz- lZsccm, N2- 3
sccm. Pressure: 120 Torr. Input Power: 1.09 kW ............................................................ 64

Figure 6.2 Emission spectrum. Flow rates: Ar- 100 sccm, CH4- 8 sccm, Hz- 3008ccm, N2-
0 sccm. Pressure: 120 Torr. Input Power: 1.621 kW ....................................................... 65

Figure 6.3 Emission spectrum. Flow rates: Ar- 100 sccm, CH4- 8 seem, Hz- 300sccm, N2-
0 sccm. Pressure: 120 Torr. Input Power: 1.621 kW ....................................................... 66

Figure 6.4 Variation of species concentration with H2 flow rate. Flow rates: Ar- 600 sccm,
CH4- 8 sccm. Pressure: 120 Torr. Input Power: ~ 1.2 kW ............................................... 67

Figure 6.4a Variation of species concentration with H2 ﬂow rate. Flow rates: Ar- 600 sccm,
CH4- 8 sccm. Pressure: 120 Torr. Input Power: ~ 1.2 kW ............................................... 68

Figure 6.5 Variation of species concentration with CH4 flow rate. Flow rates: Ar- 600 sccm,
Hz- 0 seem. Pressure: 120 Torr. Input Power: ~ 1.2 kW .................................................. 69

Figure 6.53 Variation of species concentration with CH4 flow rate. Flow rates: Ar- 600
sccm, H2- 0 sccm. Pressure: 120 Torr. Input Power: ~ 1.2 kW ........................................ 70

Figure 6.6 Variation of species concentration with N2 flow. Flow rates: Ar- 600 sccm, H2-
12 sccm, CH4- 8 sccm. Pressure: 120 Torr. Input Power: ~ 1.1 kW ................................ 71

Figure 6.7 Variation of species concentration with Ar flow rate. Flow rates: H2 - 50-300
sccm, CH4- 8 sccm. Pressure: 120 Torr. Input Power: ~ 1.4 kW ...................................... 72

Figure 6.7a Variation of species concentration with Ar ﬂow rate. Flow rates: H2 - 50-300
sccm, CH4- 8 sccm. Pressure: 120 Torr. Input Power: ~ 1.4 kW ..................................... 73

Figure 6.8 Variation of C2/Ha ratio with H2 ﬂow rate. Flow rates: Ar - 600 sccm, CH4- 8
seem. Pressure: 120 Torr. Input Power: ~ 1.2 kW ............................................................ 74

Figure 6.9 Variation of C2/HQt ratio with CH4 flow rate. Flow rates: Ar - 600 sccm, Hz— 0
sccm. Pressure: 120 Torr. Input Power: ~ 1.2 kW ............................................................ 75

Figure 6.10 Variation of HB/Ha ratio with H2 ﬂow rate. Flow rates: Ar - 600 sccm, CH4- 8
sccm. Pressure: 120 Torr. Input Power: ~ 1.2 kW ............................................................ 76

Figure 6.11 Variation of HB/Ha ratio with H2 ﬂow rate. Flow rates: Ar - 600 sccm, H2- 0
sccm. Pressure: 120 Torr. Input Power: ~ 1.2 kW ............................................................ 77

xi

Chapter 1

Introduction

1.0 Motivation

Microwave cavity plasma reactors are being used for a range of materials process-
ing applications including the deposition of diamond thin ﬁlms and the etching/surface
treatment of semiconductor materials during device fabrication. The etching applications
are carried out in electron cyclotron resonance (ECR) microwave cavity reactors which
typically operated at low pressure below 10 mTorr. The deposition of diamond thin ﬁlms
use the microwave cavity reactor without the static magnetic ﬁelds and the pressure used
are much higher in the range of 10-120 Torr. For all these microwave plasma processes a
concise understanding of the plasma species concentration and energies are often still
lacking.

For example, during the diamond deposition process the addition of small amounts
(10-100 ppm) of nitrogen can signiﬁcantly change the deposit ﬁlm’s properties and growth
rate [1]. The reason for the importance of nitrogen in the deposition process is not under-
stood. One possible explanation is that the bulk plasma species concentration or plasma
temperature are changed by the nitrogen and that these bulk changes effect the deposition
process. Hence a study of the various species concentration in the diamond CVD plasma

with the addition of nitrogen would be helpful in understanding the role of nitrogen and

how it affects the plasma parameters.

A second example where additional understanding of a plasma process would be

useful is the deposition of nanocrystalline diamond using Ar-CH4-H2 gas mixture. For the

microcrystalline and nanocrystalline diamond growth, the ratio of argon to hydrogen has
been found to be a dominant factor [2]. Therefore an analysis of the species in the plasma
may shed some light on their role in the plasma deposition process.

A third example for additional understanding of plasmas being of interest that is
investigated in this study is the electron energy distribution function in low pressure ECR
plasmas. Speciﬁcally, in a compact ECR ion source used for generating plasmas in molec-
ular beam epitaxy machines, the excitation mechanism in the source is not fully under-
stood. Speciﬁcally the density of high energy electrons in the. excitation region needs

investigation.

1.2 Objectives

The main objective of this work is to investigate microwave plasma discharges
using optical emission spectroscopy(OES) in order to add to the understanding of these
discharges. The speciﬁc objectives are:

1. To study the basic Ar plasma and measure the amount of doubly ionized atoms and
hence high energy electrons present under various process conditions for plasmas cre-
ated in a compact ECR ion source.

2. To understand the variation of the plasma parameters like gas temperature and species
concentration under various process conditions for plasmas used in diamond CVD

deposition. Speciﬁc issues to be studied include the gas temperature of diamond CVD

plasma, the inﬂux of nitrogen gas addition on CH4-H2 diamond deposition plasmas,
and the species concentration variation in CH4-Ar-H2 plasmas used for nanocrystalline

diamond deposition.

1.3 Thesis Outline

The main part of the thesis has been divided into four chapters (Chapters 3-6) with
one chapter devoted to each of the plasmas mentioned in the objectives.

Chapter 2 discusses the equipment and the plasma reactors used in the experi-
ments. The relevant details needed to understand the experimental set up has been pro-
vided with careful attention to each instrument.

Chapter 3 explains the argon doubly ionized atom measurements carried out in the
microwave ECR plasma source. The results are presented along with the discussions.

Chapter 4 details the gas temperature measurements performed on the Hz-CH4 plasma. An

insight has been provided to the theoretical aspects involved. The observations are pre-

sented along with the interpretations. Chapter 5 elaborates the role of N2 in the deposition
process as a result of the study of the Hz-CH4-N2 plasmas. The inﬂuence of N 2 on the
hydrogen, CH and CN species concentration is given importance. Chapter 6 presents the
study of the Ar-Hz-CHz-NZ plasmas and the results obtained. The variation of the constit-
uent species concentration with the process parameters is discussed. Chapter 7 provides

the summary of the research and discusses future research work in this area.

Chapter 2

Equipment and Experimental Method
2.1 Introduction to equipment used

This chapter describes the features of the resonant cavity microwave discharge
apparatus, especially those features relevant to the optical emission spectroscopy experi-
ments. It includes descriptions of the microwave plasma reactor, spectrometer, data acqui-
sition system and the collection optics used in the experiments.

The experiments were performed on two different types of the resonant cavities.

The diamond CVD reactor measurements discussed in chapters 4, 5 and 6 were performed

in a resonant cavity suited for high power and moderate pressure. The Ar++ density mea-
surements discussed in chapter 3 were performed in the microwave ECR plasma source
[MPDR 610] suited for low power and very low pressure plasma formation. Accordingly,
the set-up is described in two sections due to the different conﬁgurations of the plasma

reactor.
2.2 Multipolar ECR plasma reactor system

2.2.1 Description of the Plasma Source - the MPDR 610

The Microwave Plasma Disk Reactor [MPDR] 610 is a compact coaxial electron
cyclotron resonance plasma source. A sketch of the plasma source is shown in Figure 2.1.
The cylindrical source is made of stainless steel, and it has an outer diameter of about 5.8

cm with an application speciﬁc overall length [3]. The vacuum seal at one end is made by

a standard 4.5 inch Conﬂat ﬂange with the entire length of the source inserted into the vac-
uum chamber. At the other end (near the discharge), metal-to-fused quartz vacuum seals
are made using specially designed ultra high vacuum compatible ring shaped Helicoﬂex
spring loaded seals. The discharge located at this end of the plasma source has a diameter
of 3.5 cm. The electromagnetic cavity excitation region consists of a coaxial coupling sec-
tion which is terminated at one end with a sliding short, and at the other end, by the dis-
charge. The region between the sliding short and the discharge is occupied by a coaxial
waveguide section and an evanescent circular waveguide section. The diameter of the
inner conductor comprising the coaxial section is 1.2 cm. A small loop antenna is attached
to the sliding short, and this loop excites the TEM mode in the microwave cavity. Between
the terminus of the center conductor and the discharge is an impedance matching circular
waveguide section that has a diameter which is too small to support any electromagnetic
propagating modes for the 2.45 GHz excitation frequency. The plasma is conﬁned in a
quartz discharge chamber with an inner diameter of 3.5 cm and a height of 4.7 cm. The
quartz tube is surrounded by three ring shaped axially magnetized permanent magnets
which provide the static magnetic ﬂux density within the plasma chamber for plasma con-
ﬁnement and the 875 Gauss ﬁeld strength for ECR. The magnets have an outer diameter of
4.95 cm, a height of 1.27 cm, and an inner diameter of 4.32 cm. They are aligned with like

poles facing each other.

TyPe N
Microwave

Connector

K Gas Feed

 

Gas Line

Loop Antenna

 

 

\ _4L

 

 

 

 

 

.=<'>

 

E

 

Plasma

 

 

 

 

ﬂag

 

 

#11
41

 

 

Region

—5

 

 

 

 

 

Air Cooling ‘
Standard \ \
4.5 inch / Sliding Center Permanent
Conﬂat Short Conductor Magnets

Figure 2.1 MPDR 610 Plasma Source

The quartz walls and the magnets are cooled by compressed air ﬂowing through

the center conductor and blowing onto the discharge chamber. The positions of the center

conductor and the sliding short can be independently adjusted in order to match the dis-

charge load to the input transmission line impedance. The discharge load changes as the

plasma varies with input power, gas ﬂow/pressure, gas type etc., and appropriate tuning

minimizes the reﬂected power and ensures maximum power transfer to the plasma load.

The cylindrical stainless steel processing chamber is 10inch high and has a diam-

eter of 18 inches. It has four ports one each connected to the vacuum pump and the plasma

source. The other two ports are used as viewing port for the optical diagnostics. The view-

ing ports and the port connected to the source are 8 inch in diameter. The transparent win-

dow of the viewing port has a diameter of 1.8 inches. The ports are orthogonal as shown in

Figure 2.2.

    
   
   
 
  
  
  

 

 

 

1
Air
Cooling'\‘- ,
50 Ohm Coaxial cable
MPDR 610 Tuning / - — from microwave source
Assembly

 

 

 

 

 

> Input gas

Discharge
Chamber

Processing Chamber

 

 

Viewport
To
Diffusion Pump

 

vViewport

Figure 2.2 Top view of the chamber

2.2.2 The microwave apparatus

Microwave energy is supplied by a 2.45 GHz microwave power supply (Raytheon
PGM10X1). The experiments described in Chapter 3 were performed with microwave
power ranging from 10 Watts to 100 Watts. This power range refers to the power absorbed

by the cavity which is found by subtracting the microwave power reﬂected by the cavity

from the power incident to the cavity. The microwave circuit includes a three port circula-
tor and dummy load to protect the power supply and a dual directional coupler for sam-
pling both the reﬂected and incident power.

A 50 ohm coaxial cable with type N connectors and a Teﬂon dielectric ﬁlling
material transfers power from the bi-directional couplers to the plasma source. The coaxial
structure of the cable is continued into the source body, terminating in the loop antenna as
shown in Figure 2.1. This loop excites the TEM mode in the coaxial cavity that stretches
from the end of the sliding short to the terminus of the center conductor, beyond which

evanescent ﬁelds are excited in the circular waveguide section of the source.

2.2.3 Gas/vacuum systems

The vacuum system connected to the plasma reactor used for the argon doubly
ionized atom identiﬁcation and measurement (discussed in chapter 3) can be represented
as shown in the Figure 2.3.

The vacuum chamber is connected to a 6 inch diameter oil diffusion pump and
backed by a mechanical pump. A gate valve isolates the vacuum chamber from the diffu-
sion pump stack. Between the gate valve and the diffusion pump is a gate conductance
valve and a water cooled cold trap that helps in keeping stray pump oil away from the vac-
uum chamber. The diffusion pump is ﬁlled with a hydrocarbon-free oil [Fomblin] to allow

the use of reactive gases. Normal chamber base pressures under optimal pumping condi-

tions were about 10"5 Torr.

Gate Ionization gauge tube
1
Conductance Gate Valve To ionization gauge

Valve r / _

 

 

 

 

 

 

 

 
   
  
 
 

 

 

 

 

 

 

 

 

Processing Chamber
Diffusion o I | 7
Pump \ A

 
   
   

 

Rou hin Valve
E h t IXIX g g
x aus I \Foreline Valve

1
‘———L__.
(Lr— ($433332:

Mechanical Pump . Dumrr’ry Load
Microwave Power
Su 1
(CB—as Tank pp y

Figure 2.3 Vacuum system of the plasma source

 

 

 

Circulator

 

 

 

 

 

 

The gate valve, roughing valve and the foreline valves are pneumatically con-
trolled through a specially designed switch box. The pressure of the processing chamber is
measured using an ionization gauge and a capacitance manometer (100 mTorr full range),
while the foreline and the diffusion pump stack pressure are measured using thermocou-
ples.

Gas ﬂow into the MPDR is controlled through an MKS 247C four channel read-
out/controller. Pressure conditions inside the vacuum chamber are controlled by a gate
conductance valve. All components of this system are made of Ultra High Vacuum [UHV]

compatible steel.

2.3 High power resonant cavity microwave reactor

The high power microwave cavity plasma reactor is a resonant cavity microwave
discharge operating in the TM013 mode. The reactor includes a 7 inch inside diameter
microwave cavity that can be electromagnetically tuned with a sliding short and an adjust-
able probe. The tuning process consists of matching the complex impedance of the cavity
(Zin=Rin+inn) to the transmission line impedance which carries the microwave power
source to the cavity. The cavity effectively directs intense microwave energy into the
plasma source region. A Cober model S6F/4503 2.45 GHz microwave power supply was

used to provide 0.2-2.0 kilowatts of microwave power.

E < E: Microwave Input Probe

 

/Sliding Short

    
 
   

 

 

 

 

Window

U

Air Cooling Plasma

 

 

 

Quartz Dome

 

 

 

   

Substrate Holder

Figure 2.4 High Power Microwave Plasma Reactor

10

The hydrogen discharge experiments discussed in chapter 4 and 5 were performed
in the same reactor as shown in Figure 2.4. The experiments discussed in chapter 6 were
carried out in the reactor shown in Figure 2.5. These reactors differ in the shape of the
quartz dome used and the other basic conﬁguration remains the same. All the experiments
were performed at pressures of 10—120 Torr. The MKS 247C four channel readout/control-

ler regulates the ﬂow of hydrogen, methane and nitrogen.

E « 1L “H Microwave Input Probe

/Sliding Short

 

 

 

 

Window

 

 

\- U

    

 

 

Air Cooling

    

Plasma Quartz Dome

 

 

 

 

Substr te
Substrate Holder

Figure 2.5 High Power Microwave Plasma Reactor

The source is designed to operate at high power and moderate pressure conditions.
Hence the vacuum system is not as complex as the previous system. The chamber is
directly connected to a mechanical pump. A throttle valve connected between the pump

and the chamber is used for ﬁne control of the chamber pressure. Since high powers are

11

involved the quartz dome gets heated. Air cooling is provided to the quartz dome by a duct
with a fan connected to the other end. The heated air ﬂows out through the mesh window,

which is also used as a viewing port.

2.4 Spectrometer- system #1

The spectrometer used for some of the measurements is a McPherson Model
216.5, 0.5 meter, f/8.7, plane grating scanning monochromator. It is designed to operate in
the wavelength from 1050 A to 160,000 A by interchanging the gratings. The 2400
grooves/mm grating can be used in the 1050 A - 5000 A wavelength range and the 1200
grooves/mm grating can be used in the 1050 A -10,000 A wavelength range. The spec-
trometer has a resolution of 0.2 A and 0.4 A for the 24001ine/mm and 12001ines/mm grat-
ing respectively with input and output slits of the spectrometer set at 10 um wide. The
optical system of the spectrometer consists of two concave mirrors and a plane grating.

A collimating mirror is 3” in diameter and has a 0.5 meter focal length. A focus-
sing mirror is 6” in diameter and has a 0.5 meter focal length with a 4” focal plane. The
mirrors are mounted in rigid aluminum holders. The input and the output slits are adjust-
able and are provided with a opening range of 10 microns to 2 mm.

A photomultiplier tube is mounted at the exit slit. The McPherson model scanning
monochromator houses a EGI—GENCOM RPI QL/20 photomultiplier tube. For all the

experiments a bias voltage of -800 V was applied to the photomultiplier tube in order to

12

get a good signal-to-noise ratio. An Oriel model 70705 photomultiplier power supply was

used for this purpose.

 

    
      

r—
L_ .

\ o
A .
a . Input sht
Concave mirrors ,
7! Output SIlt
/ 1

 

 

 

 

h-
i

Photomultiplier

Figure 2.6 Sketch of the spectrometer

The principle used in the operation of the monochromator is diffraction. The grat-
ing in the monochromator diffracts the incoming light. The angle of diffraction varies with
the wavelength. Hence at any time only the diffracted signal of a particular wavelength is
collected by the concave mirror and focussed on to the photomultiplier. The wavelength
scan is done by tilting the grating about its vertical axis as shown in Figure 2.6. The scan-
ning motor has ﬁxed speeds of 0.5, 1, 2, 10, 20, 50, 100, 200, 500, 1000, 2000 A per
minute. Usually the data acquisition system collects around 4 samples/sec. from the spec-
trometer. Depending on the wavelength range and accuracy desired, the speed of the scan-

ning motor is selected.

13

2.5 Data acquisition and signal processing for spectrometer system #1

The data acquisition and processing were done by a semi-automated system. The
spectrometer has a ﬁxed speed motor used for scanning, that needs to be operated manu-
ally. Except for the start-up of the scanning motor of the spectrometer, the rest of the pro-
cess was automated. The output current from the photomultiplier tube was read by a
Keithley 485 Autoranging picoammeter. The output current was usually in the range of a
few nanoarnperes, depending on the intensity of the signal. The picoammeter was con-
nected to a personal computer by a IEEE-488 interface. The [BEE-488 bus was connected
to a National Instruments GPIB card in the computer. The software consisted of a Quick-
BASIC program that was used to collect the data at the desired interval. The processing

was done using MATLAB. The code for the software part is included in Appendix A.

2.6 Diode array detector - spectrometer system #2

The spectroscopic measurements described in chapter 6 were performed using the
ORIEL Instaspec diode array detector. A spectrograph/diode array combination is a
replacement for a motor driven monochromator and photomultiplier tube. The light source
is reduced to a point or thin line at the entrance slit, and the spectral content of the image is
measured. The dispersed spectrum is then projected as a continuous band of wavelengths
onto a diode array placed at the focal plane.

The diode arrays have their own advantages and limitations compared to the pho-

tomultiplier tube. The most important difference between the photomultiplier tube and

14

diode arrays is the multichannel nature of the arrays. The large number of photodiodes
constitute a series of detectors in close proximity, and this results in the ability to detect a
number of independent events simultaneously. Thus, rather than being a single detector,
the diode array is a one dimensional array of detectors. This multichannel nature of the
diode array results in an increased rate of data acquisition for multiple data points and
eliminates the requirement to move the image relative to the detector as in the scanning

monochromator.

 

 

     
 

   

   

\

. ’ ‘ Grating
Concave mrrrors

Glass Plate

/

To Computer

 

 

 

 

 

Input Slit ‘/

 

Figure 2.7 Sketch of the diode array detector
The limiting spatial resolution of a diode array is the element spacing along the
detector. The wavelength resolution of the array is dependent on the dispersed wavelength

range over the array and the element size. The spectroscopic wavelength resolution is

15

dependent on the input slit width, the total bandpass over the array and the number of ele—
ments in the array. The diode array detection system is fully automated and is controlled

by the software provided by the manufacturer.

2.7 Collection Optics

The collection optics usually consisted of an arrangement of lenses of different
focal lengths depending on the strength of the signal and the amount of coupling desired.
Three different arrangements were used for the various experiments. For simplicity, the
positioning of the lenses and the selection of the focal lengths were based on the results of
the calculations obtained by considering the emission beam from the plasma source as
straight rays. Fine tuning of the output was done manually by viewing the focus of the out-
put beam on a sheet of white paper. The ﬁber optic cable of the spectrometer was aligned
so that the focussed beam had maximum coupled to the core of the ﬁber. Additional focus-
sing was not needed since the diameter of the core of the ﬁber optic cable was large [1-3
mm]. Since measurements were performed on the whole plasma, spatial resolution was
not required. This avoided the necessity of collecting light from speciﬁc parts of the
plasma. In cases where the signal was very weak, a black cloth was used to cover the
entire collection optics set up to the entrance of the ﬁber, to prevent interference from the
ambient light. The optical arrangements are presented below in the increasing order of

complexity along with the necessary details.

16

Two types of ﬁbers were used. One of them is an optical cable with a diameter of 3

mm and the other one consisted of a multimode ﬁber with a core diameter of 1 mm.

2.7.1 Arrangement #1
This arrangement is very simple and requires the direct focussing of the multi-
mode ﬁber to the plasma. This arrangement was used when the plasma discharge was very

bright and there was enough signal coupled through the multimode ﬁber.

Plasma Source

 

    

Substrate
Substrate holder

Optical Fiber/
Figure 2.8 Optical set up for light collection — arrangement #1
2.7.2 Arrangement #2
This arrangement involves a single biconvex lens of diameter 5.1 cm and focal

length 5 cm. The optical cable was used in this set up. The optical set up is shown in Fig—

ure 2.9. The distances S and S’ and the focal length f of the lens is governed by the relation

w»—
ll
Vali—
val»—

 

ﬂ Lens
Plasma Source

Substrate

Substrate holder
:= s + S’

 

 

 

 

Optical Fiber/
Figure 2.9 Optical set up for light collection - arrangement #2

2.7.3 Arrangement #3

This arrangement involves three biconvex lenses, two of them with diameter 6.3
cm and the third one with a diameter of 5.1 cm. They had focal lengths of 30 cm, 15 cm
and 5 cm respectively. Since the signal from the plasma was weak, the collected light was
directly focussed on to the input slit of the spectrometer system #1. The arrangement is

shown in Figure 2.10.

Source

f=30cm, $=6.3cm f=15cm, (13:6.3cm f=50m, (13:5 .lcm

 

   

 

 

 

l—lScm ! 200m i 20cm —l-3cm-|

Figure 2.10 Optical set up for light collection - arrangement #3

18

Chapter 3

Identiﬁcation and analysis of Argon Doubly-ionized
atoms

3.1 Introduction
This chapter deals with the identiﬁcation and analysis of the doubly-ionized Argon

atoms in a microwave ECR plasma discharge. This experiment is aimed at identifying the
Ar++ density variation and to a lesser extent the electron temperature variation with chang-
ing process parameters in a compact ECR ion source. The motivation for studying Ar‘L+
emission is that higher energy electrons in excess of 27 eV are required to produce Ar++

emission. Hence the observation of Ar++ emission intensities is a relative indicator of the

number of high energy electrons. The ﬁrst section brieﬂy discusses about the optical tech-

nique and the research literature used as a reference in identifying the Ari”+ emission lines.
The subsequent sections describe the experiment and the data obtained. The last section

contains a discussion of the results.

3.2 Theory of the diagnostic technique
The spectroscopic radiation is emitted when a bound electron makes a transition in
an atom or ion. The observed intensity of the radiation thus emitted depends on
1.the probability of there being a bound electron in the upper level of the transition,
2.the atomic probability of the transition in question, and
3.the probability of the photons thus produced escaping from the volume of the plasma

without being reabsorbed.

19

The relevant atomic states of the Argon atom can be represented as shown in Fig-

ure 3.1. As it could be seen from the ﬁgure, the ionization potential of the Ar atom is 15.76
eV. By imparting 27.628 eV to the Ar+ ion an electron from the valence shell of the Ar+

ion can be removed resulting in an Ar++ ion. To cause further ionization 40.9 eV is

required.

 

 

 

 

 

 

AI+++
40.9 eV
Ar++* 5
A: Mm A 333.6 nm
28.1 ev: 24.38 eV
AI++!' Y
A
§ 27.628 eV
+ V
Ar A ‘
15.76 eV
Ar Y

 

 

Figure 3.1 Atomic states of the Ar atom

20

Figure 3.1 depicts the observed 3336.13 A transition of the excited Ar++* ion. The

valence electron of the Ar++ ion is excited to an intermediate state by absorbing 28.1 eV

via an electron collision. This energy state is well below the ionization potential of the

valence electron of the Ar++ ion. From this intermediate state, the electron drops spontane-
ously to a lower intermediate state 3.72 eV below it, simultaneously radiating the excess

energy as a photon. It is this radiation which is observed as a 3336.13 A line in the spectra.
Also the energy separation between Ar““*-Ar+ and ACT-Ar“ are almost the same. This
shows that the intensity of the 3336.31 A is a good indicator of the density of the Ar“

ions since both Ar++* and Ar++ are created by electrons of similar energy. The doubly-ion-
ized Ar emission lines were identiﬁed using the data presented by Striganov et a1. [4]. The
spectral lines that are presented in this reference have been measured with an accuracy of
more than 1A.

For a better understanding of the principles involved in the measurement, let us
show that the transition that is considered is indeed indicative of the doubly ionized atom
density. The ion formation results due to the excitation of electrons to higher energy lev-
els. In an atom, the energy transfer required for the excitation of the bound electrons from
one energy level to the other takes place due to the collision of the free high energy elec-
trons with the bound electrons in the lower energy level. The collision frequency of the

free electrons at a given energy level is given by
V... = n.]o(E>f(E>dE
where E is the electron energy, 0 is the excitation cross section, ne is the electron density

and ﬂ E) is the free electron distribution function. For Ar+ to Ar++ transition, Vex can be

21

approximated as Vex~ C1"e( Eex), where C I is a constant. Hence basically the collision fre-

quency depends on the number of electrons at or above the given energy level Eex. Simi-
larly for the Ar++ to Ar++* transition, Vex can be approximated as Vex~ Czne(Eex), where
C2 is another constant. Thus the number of ions excited from Ar++ to AF” state depends

on the same set of higher energy free electrons that formed the Ar++ state. The 333.6 nm

transition that is observed occurs due to the loss of energy of the electrons as they move

from the Ar”" state to another APE" state. The observation of this transition is thus a

good indicator of the density of the electrons with energy above Ea and the density of
Ar“ ions.

3.4 Experimental method

The experiments were performed using the MPDR 610 microwave plasma reactor.
The optical emission from the discharge was focused to a ﬁber using a lens. The arrange-
ment #2 of the collection optics shown in Figure 2.9 was used. The other end of the ﬁber
was focussed to the input slit of the spectrometer system #1 shown in Figure 2.6. The
entrance and exit slits of the spectrometer were 50 u. wide by 2 cm high. The resolution of
the spectrometer used was 1A with 50 p. slits. The 0.5 meter spectrometer contains a 2400
lines/mm grating. The wavelength range scanned during the experiments is 3320 A- 3550
A. The optical ﬁber used in the experiment allowed the signal in this wavelength range
without attenuation. The experimental setup is as shown in Figure 3.2. The data acquisi-

tion system is the same as that discussed in the chapter 2.

22

Microwave Power f=5cm

k l
Quartz Window Optical

Input Gas Fiber \

Monochromator
Photomultiplier

W. e i
C 3 \ 1

Computer

   
   

 

Processing Chamber

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Picoammeter
Figure 3.2 Experimental Set-up for the identiﬁcation of Ar++ lines

3.3 Observation and measurement of the doubly ionized lines

The intensity of the doubly ionized atom emission lines gives more details about
the parameters of the plasma. Ionization occurs when the high energy particles collide
with an atom or ion. For double ionization to occur the energy of the charged particles
needs to be particularly high. Hence the intensity of the doubly ionized lines in the spectra
is a direct representation of the presence of high energy electrons in the plasma.

For the measurements at least 10 doubly ionized lines of Ar were identiﬁed ini-
tially. In order to make sure that the identiﬁed lines belonged to Ar and not any other
impurity atom, argon was replaced by krypton and the same wavelength range was

scanned. By comparison, more than half the number of peaks were identiﬁed as impuri-

23

ties. More scans with greater resolution were taken in the wavelength range of the remain-

ing peaks to check for their presence. One such wavelength scan is shown in Figure 3.3.
Finally three lines were chosen for the Ar” measurements. In the measurements, doubly
ionized lines with wavelengths 3336.13 A(4s‘ 3D° [1:31- 4p‘ 3F[J=4]), 3344.72 A(4s‘ 313°

[J=2]- 4p‘ 3F [1:31) and 3358.49 A (4s: 313° [1:1]- 4p‘ 3F [1:21) were considered.

 

60 l l l l l r l

50,. ........... . ............ . ......................... _ ......................... . ....................... ._.

A
O
i

  
 
 
  

 

 

 

N
O

Emission intensity (arb. units)
U)
o

 

 

 

 

 

 

 

 

 

 

RA

i p
3380 3400 .

 

 

 

 

i
3360
Wavelength (A)

i i
3320 3340

Figure 3.3 Emission spectra of krypton plasma. Pressure: 3 mT, Flow rate: lsccm,

Input Power: 90 W.

24

 

140 ' F ? 1T: 3?

 

 

     

   

 

 

 

 

 

 

 

 

 

 

 

 

 

120-. .......... ........... ......... ............ ............ ............ ......... -
A100- ..................... ............................................................ _
‘E i
=3 :

g 80- ...................... .................................................................. q
a» §
§ i
E 60,. ....................... ........................................................... h ..... _
a i
.9 :
.3 3344.72}.
5 40- ........... : ............ E ........................................
3336.13A 3 E f f
3 g 5 335844913. ;
20-. ......... 3....\‘ ..... ........ ¢
O 3 i i i i
3320 3340 3360 3400
Wavelength (A)

Figure 3.4 Emission spectra of argon plasma. Pressure: 0.75 mT, Flow rate:
lsccm, Input Power: 100 W.

LS (Russel-Saunders coupling scheme) notation is used here to represent the quan-
tum states. In this scheme the quantum state of an atom is labeled in the following manner:

where L is the total orbital angular momentum quantum number, S the total spin quan-

tum number, and J the magnitude of the total angular momentum (J =L+S ). 25+] gives

25

the multiplicity of the quantum state. The number N denotes the orbit number (in the Bohr
sense), and l the angular momentum states of the last k active electrons

Measurements were made for different values of incident microwave power, pres-
sure and gas ﬂow rates. For greater accuracy, the area under the peak was calculated,
rather than the peak intensity after subtracting the background noise. The emission spec-
trum observed in the 3320-3400 A range is shown in Figure 3.4. The peaks corresponding
to the doubly ionized atoms are marked on the ﬁgure. For calculating the area of the peak,
the trapezoidal method [In this numerical integration method, the curve is approximated
by small trapezoids and the total area under the curve is obtained by adding the areas of
the individual trapezoids] was used. The QBASIC code that was used to carry out these

measurements is presented in Appendix C.

3.5 Results and discussion
The results of the experiments are presented in this section. The complete data

obtained for the various conditions are shown in Appendix A. The various table entries

show changes in Ar++* emissions produced by the plasma source input parameter changes.
The source parameters that were analyzed included pressure, input power, and gas ﬂow
rate. The pressure was varied from 0.4 to 3.0 mTorr, the input power from 10 to 100 watts,

and the ﬂow rate from 1 to 20 sccm argon.
Figure 3.5 and 3.6 show the variation in Ar++ emission versus pressure. The line

on these plots indicate the average intensity of the three emission lines. The higher Ar++
emission occur in these ﬁgures at the lower pressures. This is consistent with the electron
temperature increasing at low pressure. Basically, the increased electron temperature have

more electrons with 28 eV or more of energy. It is these electrons that are needed to pro-

26

duce Ar++ and Ar++* as shown earlier in Figure 3.1. Figure 3.5 is at a power of 40 watts.
The Arl'+ emissions at this power are seen to drop by a factor of 6 when the pressure

changes from 0.4 mTorr to 3 mTorr. Figure 3.6 is at a higher power of 100 watts. The Ar++
emission is seen at this power to drop by a factor of about 2 when the pressure changes

from 0.4 mTorr to 3 mTorr.

Figure 3.7 shows the inﬂuence of microwave power on the Ar++ emission. The

ﬂow rate was 1 sccm and the pressure was 0.9 mTorr for the data shown in this ﬁgure. The
Ar++ emission is seen to rise with input power to about 40-50 watts and then the emissions
appear to saturate. This implies that for input power levels of 50-100 watts the Ar“+ den-
sity is not changing signiﬁcantly.

The last ﬁgure shown is Figure 3.8. The Ar++ emission is plotted versus argon ﬂow

rate at a power of 40 watts and a pressure of 0.9 mTorr. The Ar"+ emission and hence its

density drops at the higher ﬂow rates. The effect is quite substantial with the emission

dropping by an average factor of 8 when the ﬂow rate changes from 1 sccm to 20 sccm.
The typical behaviors expected from a plasma are: 1) As the pressure is reduced

the electron temperature increases, and 2) as the input microwave power increases the ion
density Ar+ increases. The variation in the argon Ar++ emission follows the expected pres-
sure dependence. Speciﬁcally, Ar++ production requires high electron temperatures, and
the higher Ar++ emission at low pressures in Figure 3.5 and 3.6 support the presence of

more high energy electrons at low pressure. The data in Figure 3.7 shows that the Ar‘“+

density is increasing with input power from 10-50 watts. This is as expected since more

power increases Ar+ and hence more Ar+ can be ionized to Ar“. For the higher micro-

27

wave power, the Ar++ emission appears to saturate versus microwave power increases.
This effect is a deviation from the expected behavior and further, future investigation

would be needed to clarify the cause of this effect.
The data of Ar“+ emission versus argon ﬂow rate in Figure 3.8 shows a strong vari-

ation. It can be concluded from the data that at the large ﬂow rates, the Ar” density is
reduced. Two mechanisms could be possible explanations of the observed data. Mecha-

nism 1 is that at high ﬂow rates the residence time of the plasma particles in the plasma

source region is reduced. The reduction is enough that Ar++ ions do not have time to be
created and excited. The second mechanism is that at the low ﬂow rates, strong neutral gas

heating occurs which reduces the electron collision frequency. The reduced electron colli-

sions raises the average electron energy making Ar++ density and emission larger. Further
experimentation such as gas temperature measurements would help to clarify the responsi-

ble mechanism.

28

 

U) 5 L11 0‘
I I I I

Emission Intensity (arb. units)

N
I

 

 

 

0 3336.13 A
0 3344.72 A
0 3358.49 A

 

 

 

Figure 3.5 Variation of Ar++ density with pressure for argon plasma. Flow rate:

lsccm. Input power: 40 W

l .5
PreSsure (mT)

29

 

 

 

12 I r I I I

0 3336.13 A
9 3344.72 A
0 3358.49 A

 

 

 

 

y—s

OO O
I I
1

Al

Emission Intensity (arb. units)
if 9‘

 

 

 

 

2- o -
0
c
O l 1 1 1 r
0 0.5 1 1.5 2 2.5 3

Pressure (mT)

Figure 3.6 Variation of Ar++ density with pressure for argon plasma. Flow rate:

lsccm. Input power: 100 W

30

 

 

 

 

 

 

 

 

 

 

12 I I I I I I I f
03336.13 A
E13344.72A
o
10_ 3358.49A _
.g 8- _
.D'
3; o
5‘
a 6" 0 0 0 _
i5) 0
G
.2
E 4
U-I
2
>
0:)
10 20 3O 4O 50 60 7O 80 90 100

Input Power (W)

Figure 3.7 Variation of Ar” density with input power for argon plasma. Flow rate:

1 sccm. Pressure: 0.9 mT.

31

 

 

<> 3336.13 A

 

 

 

4.5.. o 3344.72/31 ~
0 3358.49A
4- _
3.5—

DJ
I

N
I

p—a
LII
I

Emission Intensity (arb. units)
N
U!

 

 

0 l l LWI l l l 16
0 2 4 6 810121416182

Flow rate (sccm)

 

 

Figure 3.8 Variation of Ar” density with ﬂow rate of Ar for argon plasma. Pres-

sure: 0.9 mT. Input power: 40 W

32

3.6 Conclusion
The experiments have shown the dependence of Ar“+ emissions on the process

parameters. It conﬁrms the presence of Ar++ ions in the system. Also the Ar++ ion density

has a large dependence on the ﬂow rate and the pressure. Both low ﬂow rates and low
pressures produce larger Ar“ emissions. The results obtained presents data for helping to

understand the Ar++ density variation and high energy electron density variation in the 610

compact ion source.

33

Chapter 4

Gas Kinetic Temperature of H2 - CH4 Microwave
Plasma

4.1 Introduction
This chapter introduces the experimental set-up used to carry out the diagnostic

experiments on Hz-CH4 plasma gas temperature and then describes the experimental

results. For both the growth rate and quality of the diamond ﬁlms the optimum tempera-
ture is between 1100 and 1300 K [5]. It is likely that the deposition process is sensitive to
the gas kinetic temperature. The gas temperature helps determine the concentration of var-
ious radicals, because many gas-phase reaction rates are strongly dependent on the gas
kinetic temperature. The ﬁrst section details the theory of optical emission spectroscopy
used in the gas temperature measurement. The subsequent sections describe the speciﬁc

details of the experimental setup. Finally the results obtained are discussed.

4.2 Gas kinetic temperature measurement theory
Optical emission spectroscopy (CBS) is used to measure the rotational temperature

of H2 neutral species. The energy separations between rotational levels in a given vibra-

tional and electronic state are typically small compared with the thermal translational
energy. Nearly all gas kinetic collisions produce a change in the rotational quantum num-
ber, whereas collisions producing a change in the vibrational or electronic quantum num-
bers usually occur much less frequently. Consequently, the relative rotational population
distribution in a sufﬁciently long-lived vibrational state has a Boltzmann distribution and

the rotational temperature reﬂects the gas kinetic temperature [6]. The rotational tempera-

34

ture is derived from measurement of the relative intensities of rotational lines within a sin-
gle vibrational band. The relative rotational line intensities I of a Boltzmann distribution

are described by [7]

4.1

 

BV.J'(J' + 1)}:
kT 3)

4
I = K1) Sunexp(

,
where K is a constant for all lines originating from the same electronic and vibrational

level, 1) is the frequency of the radiation, S J . J» is the appropriate HOnl-London factor,

B v' is the molecular rotational constant for the upper vibrational level, J is the rota-

tional quantum number, h is the Planck’s constant, c is the speed of light, k is the Boltz-

mann ’s constant and T, is the rotational temperature. Quantum numbers associated with

the upper level of a transition are indicated with a prime, those corresponding to the lower

level with a double prime. If the variation in V4 across the vibrational band is negligible,
then a Boltzmann plot of In[ I/( S J, J» ) ] versus 8er ’(J’+I) produces a line of slope -hc/(kT,)

from which the rotational temperature is determined. The above assumes that the radiative
decay rates for various rotational levels are the same. If a given vibrational-rotational level
is mixed with a different vibrational-rotational level then the radiative decay rate of that
level may be altered and the intensity of the line may be unusually strong or weak in com-
parison with those of others in the band.

Equation 4.1 can be represented in a simpliﬁed form by

I _ hc 4.2
S“ ' “pi—Earlier?)

where E represents the energy level of the upper electronic state.

upper

35

Under typical operating conditions, the plasma with a neutral gas density of around

1017 cm‘3 is far from local thermodynamic equilibrium. However we can expect that, at
this pressure, the collision rate is high enough to equilibrate the rotational modes of the

long lived electronic excited states of Hz with the heavy particles kinetic one [8]. In this

case, the plasma heavy particle temperature can be determined from the rotational bands

of the radiative excited states of H2. The temperature was determined using the R branch
of the G1 X g 4'. _>B12u + (0,0) electronic transition, where G128 + and B12 u +denote

the upper and lower electronic levels involved in the transition. The (0,0) symbol repre—
sents a band of transitions occurring between the levels with 0 vibrational quantum num-
ber in the upper electronic state and the levels with 0 vibrational quantum number in the

lower electronic state.

 

 

 

 

 

 

 

 

 

 

 

Singlets
nso npo nprt ndo ndrI: ndo ,
1 + 1 + 1 1 + 1 doubly exerted 1
E (cm‘l) 28 2:11 ITu 2g Hg Ag levels 280380 28
n n n n n n 2pn31m12
120,000—4 4 4 4 4 //'(2so)212,g
3 3 3 —_\:(2p1t)2l288
100,000 — 2 =\\ 2po2pnln
_ 2 \(22p0)2‘}38g
50,000 —
0 -- -1-——————— ----------------------------------------------------------------------

 

 

 

Figure 4.1 Diagram of the Observed Electronic States of the H2 Molecule

36

The electron conﬁguration for this transition is lsoBdo. The observed electronic

states of the H2 molecule is shown in Figure 4.1. According to the selection rule for elec-

tronic transition, if both the upper and lower electronic state involved in the transition have
zero electronic angular momenta, only the transitions with A] = i: 1 are allowed, where A]
is the change in the rotational quantum number. The A] = +1 transition gives rise to the R

branch and A] = -1 transition gives rise to the P branch. Since the electronic angular

momentum of a 2 state is zero, the G1 2 g +__.>B 1 2 u + (0,0) electronic transition has the

R and P branches as shown in Figure 4.2

 

 

 

 

J’
8
7
6
5
3
0
J’
8
7
6
5
3
0
R P
J’I74ZQIF123456 7 8|
IIIIIIII .l I III I I I
1)0 A

Figure 4.2 Energy Level Diagram for a Band with P and R Branches

37

The B12“ + level is well described by Hund’s limiting case b approximation [A

brief discussion about the Hund’s coupling cases is included in Section 4.2.1]. This is not

the case for the G1 2g + level which is intermediate between the Hund’s limiting cases b

and d [9,10]. Then, the rotational energy is no longer a linear function of J( J +1 ). There-
fore, the exact numerical values of the rotational energy levels in the temperature Boltz-

mann plot has to be considered [11,12]. Although these levels are perturbed by the high

vibrational levels of the EF1 2{ g } +, the strength of most of the R branch rotational lines
can be well described by the HOnl-London formulae, i.e. Sk=(J+I) / 2.
Only ten emission lines (R0--R10) were identiﬁed. The R1, R4 and R2, R3 lines are

not resolved and were not used in the Boltzmann plot.

4.2.1. Hund’s Coupling Cases
The inﬂuence of rotational and electronic motions on each other is given by the
Hund’s coupling cases a to e. The different angular momenta in the molecule — electron

spin S, electronic orbital angular momentum L or A, angular momentum of nuclear

rotation N - form a resultant that is designated J [13]. If S and A are zero, as in the 12‘.
state, the angular momentum of nuclear rotation is identical with the total angular momen-
tum J.

In Hund’s case a it is assumed that the interaction of the nuclear rotation with the
electronic motion (spin as well as orbital) is very weak, whereas the electronic motion
itself is coupled strongly to the line joining the nuclei. The total electronic angular
momentum about the internuclear axis 52 and the angular momentum N of nuclear

rotation form the resultant J.

38

Case b describes the condition when A = 0 and S it 0 , the spin vector S is not

coupled to the internuclear axis at all. Sometimes, particularly for light molecules, even if

A 1: O , S may be only very weakly coupled to the internuclear axis. In this case the angu-

lar momenta A and N form a designated K, where K is the total angular momentum apart
from spin.

Case c discusses certain cases like heavy molecules, where the interaction between
L and S may be stronger than the interaction with the internuclear axis. In this case L and S

ﬁrst form a resultant 10 which is then coupled to the internuclear axis with a component 9.

£2 and N then form the resultant angular momentum J.

Case d arises if the coupling between L and the internuclear axis is very weak
while that between L and the axis of rotation is strong. In this case the angular momentum
of nuclear rotation which is called R (rather than N) is quantized. The angular momenta R
and L are added vectorially, giving the total angular momentum apart from spin, desig-
nated by K.

Case e occurs when L and S are strongly coupled. L and S form a resultant Ja which

is combined with R to form J.

Hund’s coupling cases represent idealized limiting cases. Nevertheless they do
often represent the observed spectra to a good approximation. However, small or even
large deviations from these limiting cases are observed. These deviations have their origin
in the fact that interactions which were neglected or regarded as small in the idealized cou-
pling cases really have an appreciable magnitude, and particularly that the relative magni-
tude of the interactions changes with the increasing rotation. Therefore, sometimes, with

increasing rotation, a transition takes place from one coupling case to another.

39

4.3 Experimental setup

The measurements were performed in the high power microwave cavity plasma
reactor shown in Figure 2.4. The collection optics arrangement #3 was used to focus the
optical emission from the discharge to the spectrometer system#1 described in chapter 2.

A spectrometer with a resolution of 0.2 A for a slit width of 10 p. m was used for the mea-

surements. The entrance and exit slits of the spectrometer were set to 50 [L m wide by 2cm

high in order to get the optimum spectral resolution and signal intensity.

 

 

    
 
  

 

 

 

 

   

Microwave Input Probe
‘ Monochromator
__ / Sliding Short Photomultrpller

E ‘ / f=15cm

_ _. Window f=5cm
f=30cm /
Plasma /’ ,/ //
/// 1 // /d/

 

 

 

 

 

5/

‘ Quartz Dome IEEE-488 bus
Substrate Holder 1
Air Cooling f

Computer Picoammeter

 

 

 

 

 

Figure 4.3 Experimental Set-up for the measurement of rotational temperature of

H2

40

The optical emission spectroscopy experiments were carried out using a McPher-
son 0.5 m, plane grating scanning monochromator with a 2400 grooves/mm grating and a
EGI-GENCOM RPI QL/20 photomultiplier tube. A voltage of -800 V was applied to the
photomultiplier tube. The output of the photomultiplier tube was connected to the Kei-
thley 485 Autoranging picoammeter, which was interfaced to a computer using the IEEE-
488 interface. The data acquisition and processing were performed by the computer. The
complete source code of the QBASIC program used in the processing is included in

Appendix C.

4.4 Hydrogen rotational temperature

A series of experiments were performed using pure H2, a mixture of H2 and CH4
and a mixture of H2, CH4 and N2. The parameters that were varied include input power,

pressure and ﬂow rate of the gases. The monochromator was scanned in the range of 4530

A to 4650 A, corresponding to the R0-R10 rotational band of H2 molecule.

4.4.1. Estimation of the rotational temperature

The calculation involved in the determination of the rotational temperature is out-
lined below for the Hz-CH4 plasma operated at 30 Torr pressure, 200 sccm ﬂow rate [H2],
4 sccm ﬂow rate [CH4] and a microwave input power of 400 W. The microwave input
power means the resultant power input to the system, i.e. the difference between the inci-
dent power and the reﬂected power. Figure 4.4 shows the emission spectrum obtained for
the above said operating conditions. The various rotational lines are marked on the plot.
As it could be seen, the R1, R4 and R2, R3 lines are not resolved. Hence they are not used

in the calculations.

41

 

Emission Intensity (arb. units)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

- ~ ‘ 1 R1, R4
R2,§R3
. R8 R5 .
. . . . . . ............... ........................................... ' ............. '. ...... .1
_ ....... 3 ............... ........................................... RS. .. l .......... _
Rio R? R7
I I .W
4540 4560 4580 4600 4620
Wavelength A

Figure 4.4 Emission Spectra of the R-Branch rotational lines of H2

 

 

 

 

 

_3 I T I I I
-3.5- -
A .4— a
CO
5
.5".
-4.5L _
-5_ _
R10
“5.5 1 l I r L O
O 500 1000 1500 2000 2500 3000

Relative upper level energy (cm’l)

Figure 4.5 Boltzmann plot for the lines R0 and R5-R10

42

Table 4.1: Energy level for the R-branch rotational lines

 

 

 

 

 

 

 

 

 

. Relative
Rotational Wavelength upper level S
Line A -1
energy cm
R0 4627.5 292.86 60.01
R5 4624.7 895.24 86.17
R6 4618.4 1150 315.83
R7 4598.1 1490.48 1 13.09
R8 4581.3 1835.71 356.69
R9 4557.4 2238.1 199.34
R10 4537.9 2666.67 642.39

 

 

 

 

 

 

Table 4.1 shows the upper energy level for the R-branch rotational lines and the
corresponding value of S, the HOnl-London factor. The value of ln(I/S) is calculated and

plotted against the upper level energy, as shown in Figure 4.5. The line of best ﬁt is
. . . hc .
obtained for the plot. The slope of this lrne corresponds to —a , where c IS the speed of

light in cm/s. From the value of the slope, the rotational temperature of H2 is obtained.

4.5 Rotational temperature results

The experimental results for the rotational temperature are presented below. The
accuracy of rotational temperature determined using this method is found to be within
1200 K. This is estimated from the reproducibility of the data obtained.

From Figure 4.6 it is seen that the rotational temperature T, of H2 increases with

pressure. The temperature ranges from 1200-2000 K. Also from Figure 4.7 it can be

observed that T, of H2 in Hz-CH4 mixture is higher than that of a pure H2 plasma dis-

43

charge. Figure 4.8 shows the increase in T, with increase of input power. As more power is

fed to the system, i.e. more energy is used to heat the gas and hence the kinetic energy of

the gas molecules increases resulting in the increase of T ,.

When the ﬂow rate of the gas through the system was varied with the other param-

eters held constant, a slight decrease in T, was observed with increasing ﬂow rate, espe-

cially at the lower rates below 100 sccm. With higher ﬂow rate the amount of time that a
gas molecule spends in the active region of the plasma decreases as more molecules ﬂow
through the system. Consequently, the molecules do not gain as much kinetic energy as

compared to the case when the ﬂow rate is less, wherein the gas molecules remain in the

active region of the plasmas for a longer time. Hence the rotational temperature T,

decreases slightly as shown in Figure 4.9.

Since the presence of nitrogen plays a major role in the diamond deposition pro-
cess [14], it is interesting to determine its effect on the rotational temperature of the gas.
Nitrogen was introduced into the gas mixture and its ﬂow rate was varied a small amount
as compared to the total ﬂow rate present in the actual diamond deposition system. As

seen in Figure 4.10, there is no signiﬁcant change in T,, indicating the absence of inﬂuence

of 0.1-1% nitrogen in determining the rotational temperature of the given gas mixture.

2400

2200 -

8

p—A
OO
O
O

Rotational Temperature T, (K)
8?
S

1400

1200

 

I

 

1000

 

 

 

 

 

'80 "‘ “4‘0 50
Pressure (Torr)

 

 

 

Figure 4.6 Variation of rotational temperature of H2 with pressure for H2 plasma.

Flow rate: H2-200 sccm. Input power: 400 W

45

 

2400 I I I I I I

2200 -

5

 

°87

 

 

 

Rotational Temperature T, (K)
I
I

 

 

 

 

 

 

1600 -
0 0
_l_
1400 -
1200 ~
1000 l l l l l l
10 20 35 40 50 60

Pressure (Torr)

Figure 4.7 Variation of rotational temperature of Hz with pressure for Hz-CH4

plasma. Flow rate: H2-200 sccm, CH4-4 sccm. Input power: 400 W

46

 

2400 I— I I I T I I l I

2200 ‘

g

1800* ‘

1600- ‘

 

 

Rotational Temperature T, (K)
|
|

 

1400- " —— .

 

 

1200' ‘

 

 

1 000 1 1 1 1 1 1 1 1 1
200 300 400 500 600

Input Power (W)

 

Figure 4.8 Variation of rotational temperature of H2 with input power for Hz-CH4

plasma. Flow rate: H2-200 sccm, CH4-4 sccm. Pressure: 30 Torr

47

2400

2200

3’

8°

1600

Rotational Temperature T, (K)

1400

1200

1000
0

 

I

 

 

 

 

 

 

 

 

50

100

150

200 2le
Flow rate (sccm)

300

350 400 450

Figure 4.9 Variation of rotational temperature of Hz with ﬂow rate for H2 plasma.

Pressure: 30 Torr. Input power: 400 W

48

 

2400 . . . .

I

2200 '

I—t I—t N
G 00 §
8 8
l
j
|
|

Rotational Temperature T, (K)
E
3
J
I

 

 

 

 

 

1200 - __ _

 

 

h

1000 l 1 l
0 0.5 1 1.5 2

Flow rate (sccm)

 

Figure 4.10 Variation of rotational temperature of H2 with ﬂow rate of N2 for H2-
CH4-N2 plasma. Flow rate: H2-200 sccm, CH4-48ccm. Pressure: 30 Torr. Input power: 400

W

49

4.6 Conclusion

The rotational temperature of H2, Hz-CH4 and Hz-CH4-N2 microwave plasma dis-

charge were measured. The temperature was measured to an accuracy of 1:200 K. The
results showed that both increase in pressure and increase in microwave input power
increase the temperature.

The results also showed that the rotational temperature varies only slightly with
the gas ﬂow rate. The variation in the rotational temperature with nitrogen concentration
was of particular interest, since small amount of nitrogen [0-25 ppm] present in the gas
mixture has been found to enhance the growth rate in CVD diamond deposition [15]. But

with the 0.1 - 1% addition of nitrogen no change in the rotational temperature was
observed. This concludes that either the change in rotational temperature due to N2 con-

centration was within the error limit, or there was no change at all.

50

Chapter 5

Study of H2 - CH4 - N2 Microwave Plasma

5.1 Introduction

This chapter measures using OES the inﬂuence of nitrogen on Hz-CH4 diamond

deposition plasmas. The changes in various species emissions from the plasma are mea-
sured as nitrogen of controlled amounts is added. The motivation for this set of measure-
ments is that in the plasma-assisted chemical vapor deposition of diamond ﬁlms, the
addition of small amounts of nitrogen changes the deposition rate and the characteristics
of the diamond ﬁlm [1, 14, 15]. The reason for this strong inﬂuence is as yet not under-

stood. One possible inﬂuence of the N2 addition is it produces changes in the bulk plasma

properties and another reason is the nitrogen has a deposition surface inﬂuence. The mea-
surements taken here by OES is directed at looking for bulk plasma species changes. In

the previous chapter the inﬂuence of N2 addition to diamond deposition plasma gas tem-

perature was measured. The result was that no detectable gas temperature change was
observed as nitrogen was added in small amounts (less than 2%). The ﬁrst section of this
chapter gives a brief detail of the experimental setup. The second section presents the
results and a discussion of the results. The results are summarized in the concluding sec-

tion.

5.2 Experimental Setup
The experiments were performed in the high power microwave cavity reactor as
shown in Figure 2.4. The 0.5 meter spectrometer with 1200 lines/mm grating was used.

The optical emission from the discharge was collected using a lens arrangement as shown

51

in Figure 4.3. Three lenses were used to focus the optical emission from the discharge on
to the entrance slit of the spectrometer. The lens arrangement is shown in detail in Figure
4.4. The entrance and exit slits of the spectrometer were set to 50 [L m wide by 2 cm high.

The setup is identical to that used in chapter 4.

For the Ha and the HB measurements, the spectrometer was not scanned over the

wavelength range, as was done in other experiments. Instead, the spectrometer was set to

the wavelength corresponding to the peak of the Ha line at 656.28 mm (486.13 nm for H3).
With the spectrometer ﬁxed at this position the ﬂow rate of N2 was varied to give N2 con-

centration of 0-5%. The corresponding variation in the intensity of the signal from the

picoammeter was recorded by the computer and plotted. The CH and CN intensity mea-
surements were obtained by scanning over a range of 3800 to 4400 A°. The CH band at

4300 A0 and the CN band at 3880 A0 were used for the measurements are shown in Figure

5.4.

5.3 Results and discussions

From Figures 5.1 and 5.2 it is observed that the intensity of the atomic hydrogen
(Ha and H5) increases with the percentage of N2 in the gas mixture. The increase in the Ha
and HB emission is by a factor of greater than 3 as the amount of N2 is increased from 0 to
5%. The increase in the Ha and H5 emissions could occur due to either an increase in the
atomic hydrogen concentration [H] or an increase in the plasma electron temperature. A
higher electron temperature in the plasma would mean that a larger portion of the elec-
trons are capable of exciting the atomic hydrogen to the H(n=3) and H(n=4). These are the

states that the H0‘ and H13 emissions originate from.

52

The ratio of HB/Ha for different percentage of N2 as shown in Figure 5.3 gives an
idea of the change in electron temperature with N2 ﬂow. The H5 line involves the transi-
tion of electrons from the n=4 to n=2 state and the Ha line involves the transition of the
electrons from the n=3 to n=2 state. Hence an intense H5 line is indicative of the presence

of high temperature electrons in the gas. The electron temperature shows only a small

change as indicated by the ratio Hﬁ/Ha changing less than 4%. Hence, the strong changes
in Ha and H3 emissions is believed to be due to increases in atomic hydrogen concentra-
tion as the N2 is added, rather than a change of the electron temperature.

A typical CN and CH emission spectrum is shown in Figure 5.4. The CH line
intensity shows a dependence similar to that exhibited by the hydrogen lines versus N2
concentration as shown in Figure 5.5. However the dependence is not linear or as large as
shown by the hydrogen lines. The CH emission intensity increases by a factor of approxi-
mately 2 as the N2 concentration changes from 0-5%. The CN line intensity shows a larger
variation with N2 compared to the other species. The CN radicals as shown in Figure 5.6
tend to be promoted by adding nitrogen to the reactant gases. This could be attributed to
the reactions of nitrogen with methane and carbon atoms in the gas phase, which formed
the CN radicals. Alternatively, atomic nitrogen may remove carbon atoms from the grow-
ing surface and thus produce CN radicals [16]. The plots of CH and CN show that the

addition of N2 to the plasma in amounts of less than 1% produce changes in the CH and

CN concentrations in the plasma.

53

 

2.2

p—r
00

t"
as

3"
N

Ha line intensity (arb. units)
p—I
A

t—i

0.8

 

 

 

0,6 l l l l l l l l l
0 1 2 3 4 5

% Of N2

 

Figure 5.1 Variation of Ha line intensity with N2 concentration. Flow rates: CH4-

4 sccm, H2-200 sccm. Pressure: 30 Torr. Input Power: 0.8 kW

54

 

  
  
  

I" f" I"
v—t N h 0\
I I I

H3 line intensity (arb. units)

.9
oo

.9
ox

 

 

l l l l l

% Of N2

.—
F
.—

 

Figure 52 Variation of H5 line intensity with N2 concentration. Flow rates: CH4-4

sccm, H2-200 sccm. Pressure: 30 Torr. Input Power: 0.8 kW

55

8.8

9° 9° 9°
N A as

00

.“
co

>1
05

HB /Ha line intensity ratio

>3
A

>1
N

\l

 

 

 

 

 

I I I I I I I m I
1 1 1 1 1 1 1 1 1
O 1 2 3 4 5
% Of N2

Figure 5.3 Variation of H5 / Ha ratio with N2 concentration. Flow rates: CH4-4

sccm, H2-200 sccm. Pressure: 30 Torr. Input Power: 0.8 kW

56

 

12 I 0
CN 3880 :A

H
O
I

00
I

Emission intensity (arb. units)
I: as

 

 

 

 

 

 

0 1 1 i 1 1
3800 3900 4000 4100 4200 4300 4400
Wavelength (A0)

 

Figure 5.4 Emission spectrum of Hz-CH4-N2 plasma. Flow rates: CH4-7.2 sccm,

H2-144 sccm, N2-0.5 sccm. Pressure: 30 Torr. Input Power: 0.8 kW

57

1.8

r—t v—t
A O\

p—s
N

.o .o
O\ 00 H

CH line intensity (arb. units)

.3
.Is

0.2

 

 

 

 

L
L

p—

 

% Of N2

Figure 5.5 Variation of CH line intensity with N2 concentration. Flow rates: CH4-

7.2 sccm, H2-144 sccm. Pressure: 30 Torr. Input Power: 0.8 kW

58

 

I

250

§

§

CN line intensity (arb. units)
UI
o

 

 

 

OJ 1 L 1 1 1 J I 1 1

% Of N2

Figure 5.6 Variation of CN line intensity with N2 concentration. Flow rates: CH4-

7.2 sccm, H2-144 sccm. Pressure: 30 Torr. Input Power: 0.8 kW

59

5.4 Conclusion

The results presented above show a strong dependence of Ha, H5, CH and CN
emissions on the N2 concentration. An increase in the amount of atomic hydrogen is

observed with increase of nitrogen. Since it is believed that atomic hydrogen plays an

important role both in the gas phase and on the growing surface during diamond deposi-
tion, our observation shows that N2 does change the bulk plasma properties. The HIS/Ha
ratio shows no signiﬁcant change in the electron temperature as the nitrogen is added to

Hz-CH4 plasma. The variation of CH shows a similar trend as that of the atomic hydrogen.

60

Chapter 6

Study of Ar - H2 - CH4 - N2 Microwave Plasma

6.1 Introduction

This chapter extends the analysis presented in chapter 5 to Ar - H2 - CH4 - N2 plas-

mas used to deposit diamond. The addition of noble gases such as Ar has been found to
inﬂuence the growth rate of diamond, and they were found to have a profound effect on
the plasma chemistry, including ionization and dissociation [16]. This experiment is aimed

at studying Ar - H2 - CH4 plasmas and the effect of nitrogen on Ar - H2 - CH4 plasmas.

The motivation for studying this plasma stems from the fact that the surface morphology,
the grain size and the growth mechanism of the diamond ﬁlm can be controlled by varying

the Ar/Hz ratio in the Ar - H2 - CH4 plasma [2, 17]. The results of chapter 5 show that the

addition of nitrogen varies the amount of atomic hydrogen in the plasma. Hence it would

be interesting to observe the effect in the Ar - H2 - CH4 - N2 plasmas.The ﬁrst section

gives an overview of the experimental setup. The subsequent section describes the results
and presents a discussion of them. The concluding section highlights the signiﬁcant results

obtained.

6.2 Experimental setup

The experiments were carried out in the high power microwave reactor shown in
Figure 2.5. This system is semi-automated so that the ﬂow of the gases and the pressure
are monitored and controlled by a computer. Microwave power used in the experiment is
in the range of 1-1.7 kW. This resulted in the formation of a very bright plasma, which

eliminated the need for any optical arrangement to focus the emission into the core of the

61

ﬁber. The optical arrangement #1 shown in Figure 2.8 was used. The signal was detected
using the spectrometer system #2 shown in Figure 2.7. The input slit width was set to 0.4
mm. The exposure time of the diode array detector was varied to prevent saturation of the
detector. The maximum exposure time needed was 0.328 - 4 seconds. The center wave-

length was varied by tuming the grating of the diode array detector manually.

6.3 Results and discussion
The emission from the plasma was scanned at three regions, whose center wave-
lengths are 410, 485 and 650 nm. The main emission lines that were observed are CH, CN,

C2, Ha and H3. In the case of CN and C2, a band was observed due to the presence of var-

ious rotational and vibrational levels associated with the molecules. Since the exposure
time of the diode array detector was varied throughout the experiment to prevent the satu-
ration of the detectors, the results presented here are normalized to an exposure time of 1

second. For the CN and C2 molecules, both the peak intensities and the area under the

band are presented after taking background noise into consideration. The species identi-'

ﬁed and their wavelengths are as follows: CN (383 nm), CH (430 nm), C2(472 nm, 516
nm), H5 (486 nm) and Ha (656 nm), same as those studied by Clay et a1. [18]. The C2
bands at 472 nm and 516 nm are labeled as C2_a and C24, respectively. For area measure-

ments, the sufﬁx “area” is attached to the species name. 2% nitrogen gas was used in the
experiments. The process values and the associated data ﬁle names are provided in Appen-
dix B.

The source parameter that was analyzed included the gas ﬂow rate of H2, CH4, N2
and Ar. The Figures 6.1, 6.2 and 6.3 show the emission spectrum with center wavelengths

of 410, 485 and 650 nm. Figures 6.4 and 6.4a show the variation of the various species

62

concentrations with hydrogen ﬂow. The concentration of all the observed species tend to

decrease with increase in ﬂow of H2. Although at high H2 ﬂow rates HB and CH increase
slightly, CN radical concentration was observed to decrease by a factor of 4 as H2 ﬂow
rate varies from 0-100 sccm. This is followed by the C2 which decreased by a factor of 3

for the same ﬂow rate range. The presence of CN radical in the spectrum though nitrogen
was not added to the gas mixture, can be attributed to the impurity present in the input

gases or in the chamber. The result suggest that a lower amount of CH4 dissociates to form
C2 or CH with increased ﬂow of H2.

Figures 6.5 and 6.5a represent the variation of Ha, HB’ CN and C2 with methane
ﬂow. Ha, H5, CN and C2 increases with the increase in ﬂow of CH4, with C2 and CH

increase being more prominent. This result agrees with the general expectations of an
increased carbon species with an increased ﬂow of methane.
Figure 6.6 indicate the variation of CN and CH with the concentration of nitrogen.

CH remains unaffected by the changes in N2 while CN shows a linear increase by a factor
of 20 with increase in concentration of N2 by a factor of 10. Nitrogen forms CN readily

with increased ﬂow, while not affecting the amount of CH in the system. This is in agree-

ment with the results of the work done by Clay et a]. [18] in a CH4/N2 plasma.The CN

spectral lines are readily seen in the spectrum due to its low activation energy.
The inﬂuence of argon on the concentration of the other species is shown in Fig-

ures 6.7 and 6.7a. C2 and Ha increase by a factor of 3.5 and 1.5 respectively with increase
in Ar concentration from 24- 92%. CN, HB and CH show slight increase with the Ar con-

centration.

63

In addition to the above plots, the ratios of C2 and HB with Ha are plotted in Fig-

ures 6.8-6.11. The C2/Ha ratio decreases with increase in H2 ﬂow and increases with

increase in CH4 ﬂow. The ratio of HB/Ha gives some information about the electron tem-

perature of the system. With increase in the ﬂow of H2, the HB/Ha ratio decreases. The Hﬂ/

Ha ratio increases steadily with the ﬂow of CH4, suggesting a large increase in the elec-

tron temperature with increase in methane concentration.

Emission intensity (arb. units)

 

3500 i I I I I I T

3000 ........................................................................ _

2500 j .CH ............. .—
430 nm band 3

g

1500

i

 

0

 

500 .......................... _ ........................... , ............................................. .1

 

 

 

I .

.......................................................................

 

 

 

 

l

 

370

l
380

l 1 L J l
390 400 410 420 430 440
Wavelength (nm)

Figure 6.1 Emission spectrum. Flow rates: Ar- 600 sccm, CH4- 3 sccm, H2-

12sccm, N2- 3 sccm. Pressure: 120 Torr. Input Power: 1.09 kW

64

 

450 ;' F l :' F F F

400 ........ ............. .............. ............. ......
,5, ............. ............. .............. ............. ......
3..- ..... ........... ........... .......... ............. ______

o . . . ,
. l i , 8
. . . . o
o . . . .
b ........................................................................................... q...
p i . . o
o o . a
o . . . . .
o o

 

     

o

200

150

Emission intensity (arb. units)

 

 

100

 

 

50'

 

 

l l J l l l
450 460 470 480 490 500 5 10
Wavelength(nm)

0 i

 

Figure 6.2 Emission spectrum. Flow rates: Ar- 100 sccm, CH4- 8 sccm, H2-

300sccm, N2- 0 sccm. Pressure: 120 Torr. Input Power: 1.621 kW

65

 

900 T I I I I I
300- .......... ............... .............. ...... . ........ ............ [130,656 .nm . ............. 3

7mi— .......... .............. .............. ............... ..... T

600___ ........ f .............. ............. ............... ....... .............. ......... -

Emission intensity (arb. units)

300_ ...... ........... .............. ............... ............ .............. ............. _

200_.. ..... ............... .............. .............. ............ .............. ............. _

 

 

 
       

()0 W L i L i i
620 630 640 650 660 670 680
Wavelength (nm)

 

 

 

Figure 6.3 Emission spectrum. Flow rates: Ar— 100 sccm, CH4- 8 sccm, H2-

3008ccm, N2- 0 seem. Pressure: 120 Torr. Input Power: 1.621 kW

66

 

 

 

 

Emission Intensity (arb. units)

 

 

 

1111.1:
[Ur—1,8. . :3

 

 

 

v 4 l L l I
0 20 40 60 80 100 120 140 160 180 200

H2 ﬂow rate (sccm)

Figure 6.4 Variation of species concentration with H2 ﬂow rate. Flow rates: Ar-

600 sccm, CH4- 8 sccm. Pressure: 120 Torr. Input Power: ~ 1.2 kW

67

 

45 I ﬂ I I I I I I 1

 

 

 

 

b)
LII

DJ

Emission intensity (arb. units)
N
LII

 

 

 

 

 

 

 

 

H2 ﬂow rate (sccm)

Figure 6.4a Variation of species concentration with H2 ﬂow rate. Flow rates: Ar-

600 sccm, CH4- 8 sccm. Pressure: 120 Torr. Input Power: ~ 1.2 kW

68

 

20' F I F l I F i l I

18'

 

p—s
0)

y—d
P

p—t
N

p—L
O

 

 

 

9°

 

 

2‘

Emission Intensity (arb. units)

 

 

 

 

 

 

 

 

 

 

CH4 ﬂow rate (sccm)

Figure 6.5 Variation of species concentration with CH4 ﬂow rate. Flow rates: Ar-

600 sccm, Hz- 0 sccm. Pressure: 120 Torr. Input Power: ~ 1.2 kW

69

 

0.5I

 

.9

 

.........................................................

.o
1:8
I

 

 

 

.9
t9

  

Emission Intensity (arb. units)

 

 

 

 

 

' i i i 3
10 12 14 16 18 20 22 24
CH4 ﬂow rate (sccm)

Figure 6.5a Variation of species concentration with CH4 ﬂow rate. Flow rates: Ar-

600 sccm, Hz— 0 seem. Pressure: 120 Torr. Input Power: ~ 1.2 kW

70

 

2.5' I I: I I T: I; I I T.

 

+ CN i i i i 5

 

 

 

.................................................................

g—n
E"
I

p.—
I

Emission Intensity (arb. units)

 

.- 43 Z 3 3 3 f
7 i V 7 v
" l l 1 J L l l
I

l 2 3 4 5 6 7 8 9 10
N2 ﬂow rate (sccm)

h—n:.. .. .

Figure 6.6 Variation of species concentration with N2 ﬂow. Flow rates: Ar- 600

sccm, H2- 12 sccm, CH4- 8 sccm. Pressure: 120 Torr. Input Power: ~ 1.1 kW

71

 

 

 

1.4 I I T I l I I
CN . . . , .

 

 

 

Emission Intensity (arb. unitsO

 

 

 

 

20 30 40 50 60 70 80 90 100
% Argon

Figure 6.7 Variation of species concentration with Ar ﬂow rate. Flow rates: H2 -

50-300 sccm, CH4- 8 sccm. Pressure: 120 Torr. Input Power: ~ 1.4 kW

72

 

 

0.03 T I I I I I r

 

 

 

—A— CN
—6— CNarea
3 E f f f —lk— CH
0.025.. ........... ............ ............. ............ ............ , ...... H B d
a i j 3 i j
'E
5
'9' I i I I I . .
a 0.02.. ........... ............ : ............. . . .I ........ ............ ............ ............ .......... _
w
I:
B
E
.30015
m

0.01

 

0.005

 

 

 

 

 

. , i _
20 30 40 50 60 70 80 90 100
% Argon

Figure 6.7a Variation of species concentration with Ar ﬂow rate. Flow rates: H2 -

50-300 sccm, CH4- 8 sccm. Pressure: 120 Torr. Input Power: ~ 1.4 kW

73

 

20 I I I j I I T I I

 

183‘ ....... ....... .......... ..... ....... . . ..... ........... C2-aarca/I_Ia .—4

 

 

 

 

l6h....\....:. ....................................................... —1
\I
\: . . . . . . . .
........ \...
14b :\ ; : : : : : : 1
. \ . . . . . . . .
' \ : : : i ' ' ' ‘
\i i : i
.g 12.. ............... ...:.\ ........ : ........ : .......... '. ................................................. _
CU \ . . .
H \ . . .
\. . .
.g‘ $\ :
m ‘ \ ' ' .............................................. _
:10- ................................... V; ......... in”
8 :\\ :
c \.
H S

 

 

 

 

' ' ‘ a i ' '1 i i
0 20 40 60 80 100 1&0 140 160 180 200
H2 ﬂow rate (sccm)

Figure 6.8 Variation of CZ/I-Ia ratio with H2 ﬂow rate. Flow rates: Ar - 600 sccm,

CH4- 8 sccm. Pressure: 120 Torr. Input Power: ~ 1.2 kW

74

 

40 T I. .I I I I I I I

 

 

35... ----- C2_a area/Ha ...... .......... .......... .......... .......... ......... ’H’.’.),—4

 

 

 

. . . . . ’ . . , .
b- .............................................. ’ .............................................. .1
. . . . ’ . . . . .
f

25- ........ ... ........ ........ : ..... /....: .......... i .......... .......... f .......... ........ _

............................................................

N
O
l
\
l

p—A

{It
I

\'
l

Intensity ratio

 

 

 

 

 

CH4 ﬂow rate (sccm)

Figure 6.9 Variation of C2/Ha ratio with CH, ﬂow rate. Flow rates: Ar - 600 sccm,

H2- 0 sccm. Pressure: 120 Torr. Input Power: ~ 1.2 kW

75

 

0.08

 

 

 

 

0.07 '

0.06 .

p
O
m

 

.........

Intensity ratio
o
E
I

0.03- ........ .......... ......... ........ .......... .......... .......... .......... ......... ........ _
0002-..... .......... ......... ........ ......... .......... ..... .......... .......... ........ ..

0.01- ...... ..... ..... Z .......... ......... g. ......... .......... .......... .......... ........ 4

 

 

0 i P i i i 1 4 l L
0 20 40 60 80 100 120 140 160 180 200
H2 ﬂow rate (sccm)

 

Figure 6.10 Variation of Hall-Ia ratio with H2 ﬂow rate. Flow rates: Ar - 600 sccm,

CH4- 8 sccm. Pressure: 120 Torr. Input Power: ~ 1.2 kW

76

 

 

0.14 I I I 1 I I I I .I

 

 

 

0.12

0.1

.o
o
oo

Intensity ratio

9
8

0.04

 

002.... ........................... , .......... , ......... , .......... , .......... , ............................. _.
. n n u l n n l o -

 

 

i i i i i
14 16 18 20 22 24
CH4 ﬂow rate (sccm)

 

A
O\
p—
O
b—n
N

Figure 6.11 Variation of Hﬁ/Ha ratio with H2 ﬂow rate. Flow rates: Ar - 600 sccm,

H2- 0 sccm. Pressure: 120 Torr. Input Power: ~ 1.2 kW

77

6.5 Conclusion

The emissions from several species including H, CH, CN and C2 were measured

versus variation in source operating parameter including input gas ﬂow composition. The

results indicate that in Ar-Hz-CH4 plasmas the increase in argon ﬂow percentage produces
more C2 species in the plasma. The C2 species is important since it is believed to be a key

precursor for nanocrystalline growth [2]. The amount of argon was found to affect the
atomic hydrogen emission.

The inﬂuence of nitrogen on the Ar-HZ-CH4 plasmas was also examined. The
amount of N2 added was 0-300 ppm. As expected the CN emission was seen to depend
strongly on the N2 concentration. The CH emission was not affected by nitrogen concen-

tration.

78

Chapter 7

Summary of results
7.1 Conclusions

The experiments were performed in accordance with the objectives, which is to
investigate the microwave plasma discharges using optical emission spectroscopy. The
work was started with the aim of studying the Ar plasma and measuring the amount of

doubly ionized atoms, and studying the variation of gas temperature of H2 - CH4 micro-
wave plasma and the effect of N2 addition to the plasma. The above objectives were real-

ized by performing various experiments as discussed in the preceding chapters. This
chapter presents a brief summary of all the results obtained and how they have helped in

the realization of the goals set forth in chapter 1.

7.1.1 Argon Doubly-ionized atoms measurements
The experiments were carried out in a compact ion source. The results conﬁrmed
the presence of Ar“+ ions in the compact ion source. Experiments to determine the depen-

dence of the Ar++ emission on the source operating conditions were performed. The Ar++

ion density was found to increase as the ﬂow rate and the pressure decreases. The results

presented gives an idea of the Ar++ density variation in a compact ion source. And, it pro-

vides a relative indication of the high energy (>28eV) electron density.

79

7.1.2 Gas Kinetic Temperature of H2 - CH4 Microwave Plasma

The gas temperature measurements are important in understanding the plasma
since the gas temperature helps determine the concentration of various radicals. The gas
temperature was obtained from the rotational temperature, which was derived from the
measurement of the relative intensities of rotational lines within a single vibrational band.
The temperature obtained ranges from 1200-2000 K. The rotational temperature is found
to vary slightly with the gas ﬂow rate. The rotational temperature tends to increase with
the pressure of the gas mixture. Interestingly, the 0.1 - 1% addition of nitrogen did not

change the rotational temperature by an observable value.

7.1.3 Study of H2 - CH4 - N2 Microwave Plasma

The experiments were performed in conditions similar to that of an actual diamond
deposition system. Typical values of input power, pressure and ﬂow rates were 0.8 kW, 30

Torr and 200 sccm, 4 sccm and 0-5 sccm for H2, CH4 and N2 respectively. Basically the
variation of Ha, HB’ CH and CN emissions produced by N2 concentration variations was

observed.

The results show a strong dependence of the observed species on the N 2 concen-

tration. An increase in the amount of atomic hydrogen is observed with increase of nitro-

gen. The HB/Ha ratio shows almost no change in the electron temperature of the mixture
with the inclusion of N2. The variation of CH shows a similar trend as that of the atomic

hydrogen.

80

7.1.4 Study of Ar-H2 - CH4 - N2 Microwave Plasma

The Ar—HZ - CH4 - N2 microwave plasma is used in the deposition of nanocrystal-

line and microcrystalline diamond thin ﬁlms. The experiments were carried out in the high

power microwave reactor. The typical values of power, pressure and the ﬂow rates of Hz,
Ar, CH4 and 2% N2 in H2 are 1.8 kW, 120 Torr, 0-300 sccm, 600 sccm, 3-24 sccm and 0-

10 sccm respectively. Some signiﬁcant results that were obtained are mentioned here.

The increase in the argon ﬂow produces more C2 in the plasma. The C2 species is

important since it is believed to be a key precursor for nanocrystalline growth. The amount
of argon was also found to affect the atomic hydrogen emission. Unlike the previous
experiments the CH emission was not affected by the nitrogen concentration change in the

0-300 ppm range.

7.2 Recommendations for future work
This study has contributed to the understanding of a few plasmas used in diamond
deposition and low pressure plasma processing of materials. The results obtained were

within our expectations. But some anomalies are found to exist, which need further careful
study. One such example is the variation of Ar++ density with power. Even though, the

Ar++ density was supposed to increase with power, it tends to saturate at higher power as
shown by the experiments. Another study of interest would be the comparison of the tem-
perature measurements with other methods like doppler broadening. An attempt was made

to measure the same using a Fabry-Perot cavity, but due to inadequate signal, the measure-

81

ments were not carried out. For a more complete understanding of the plasma species con-
centration, the plasma can be modeled theoretically and the plasma parameter variations
predicted by the model can be used to compare the validity of the experimental results. For
example, the plasma parameters in the low pressure source are found to exhibit a large
dependence on the ﬂow rate of the process gases. A theoretical model should be able to
help explain this dependence. Also to understand the variation of species concentration
and the plasma parameters with time, the DES experiments can be performed in an actual
diamond deposition process. This would also facilitate the study of the characteristics of

the deposited diamond ﬁlm under the various processing conditions.

82

APPENDICES

83

APPENDIX A

Table : A Identiﬁcation and analysis of argon doubly ionized atoms

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Expt. # 1:231; Pressure Flow rate Intensities (arbitrary units)
(W) mm (mm) 3336.13A 3344.72/K 3358.49A
l 40 0.3 1 7.29e-11 5.94e—ll 6.05e-11
2 40 0.5 1 6.55e-1 l 6.38e-11 5.10e-11
3 40 0.75 1 4.50e-11 3.09e-11 3.11e-11
4 40 0.9 l 4.90e-11 3.09e-11 2.86e-ll
5 40 0.9 8 3.16e-l l 1.74e-1 l 2.48e-ll
6 40 0.9 20 0 0 5.68e-12
7 40 2 l 2.90e-1 l 1.46e-ll 1.88e-11
8 40 3 l 1.04e-ll 5.14e-ll 9.12e-ll
9 40 3 8 1.lSe-ll 5.99e-12 1.24e-11
10 40 3 20 0 0 7.20e-12
21 100 0.3 l 8.81e-11 5.74e-11 6.93e-11
22 100 0.5 1 5.77e—ll 3.69e-11 4.31e-1 l
23 100 0.75 l 4. I 8e-11 4.59e-11 4.39e-1 1
24 100 0.9 1 4.96e-1 l 3.42e-11 4.22e—ll
25 100 0.9 8 2.9le-11 2.28e-11 2.68e-11
26 100 0.9 20 5.03e-11 3.43e-11 3.88e-ll
27 100 2 l 1.59e-ll 6.23e-11 2.04e-1 l
28 100 3 1 7.67e-11 3.15e-ll 1.26e-ll
29 100 3 8 4.23e-11 3.32e-11 8.29e-ll
30 100 3 20 1.28e-11 1.46e-11 0
31 10 0.9 1 1.56e-11 1.12e-11 4.88e-1l
32 20 0.9 1 2.66e-ll 3.74e-11 1.48e-11

 

84

 

Table: A (contd.)

 

Input

Intensities (arbitrary units)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Expt. # Power 1)::ng 122(5):: :3?

(w) 3336.13A 3344.72A 3358.49A
33 30 0.9 1 3.236-11 2.896-11 1.726-11
34 50 0.9 1 5.89e-ll 3.096-11 3.496-11
35 60 0.9 1 5.716-11 3.686-11 3.426-11
36 70 0.9 1 6.156-11 3.356-11 4.426-11
37 80 0.9 1 5.87e-ll 4.46e-11 3446-11
38 90 0.9 1 6.976-11 4.416-11 4.596—11

 

 

Input Power = Incident Power - Reﬂected Power

Intensities were calculated by measuring the area under the peaks at 3336.13, 3344.72 and

3358.49A.

85

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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90

 

APPENDIX C

QBASIC program to read data from the picoammeter connected to the monochro-
mator :

‘Author : Jayakumaran Sivagnaname ; Date: July 1998
‘Monochromator Spec: 2400 lines/mm grating: offset: 23.5 angstrom
‘Mcpherson Monochromator must be scanned with increasing wavelength ONLY

DECLARE SUB FILEWRTU ()
DECLARE SUB FILEWRTD (=)
‘$INCLUDE: ‘qbdecl4.bas’

CONST black = 0
CONST blue = l
CONST green = 2
CONST cyan = 3

CON ST red = 4

CONST magenta = 5
CONST brown 2 6
CONST white = 7
CONST grey = 8
CONST lightblue = 9
CONST lightgreen = 10
CONST lightcyan = 11
CONST lightred = 12
CON ST lightmagennta = 13
CONST yellow = 14
CONST brightwhite = 15

COMMON resoli, cyc%, count!, pico%, i%, stalnl, tottim%, sec%, buff$, temp$, prev

stl$ = “waveln=[“

st2$ = “value=[“

EN$ = “1;”

path$ = “c:\jay\spec\data”

10 CLS

20 SCREEN 0

30 LOCATE l, 3

40 PRINT “Enter the last few digits [mmddtrialno] of the data ﬁle”;

91

50 INPUT ﬁlenm$

60 PRINT “ Is the ﬁlename correct [y/n]”;
70 INPUT conﬁrm$

80 IF conﬁrm$ = “n” GOTO 10

CALL IBDEV(0, 3, 0, 10, 1, l, pico%)

OPEN path$ + “\W” + ﬁlenm$ + “.m” FOR OUTPUT AS #1 ’store wavelength value
PRINT #1, st1$
OPEN path$ + “\D” + ﬁlenm$ + “.”m FOR OUTPUT AS #2’store current value
PRINT #2, st2$

LOCATE 2, 3

PRINT “Values of wavelength stored in “; path$ + “\W” + ﬁlenm$ + “.m”; “ ﬁle”

LOCATE 3, 3

PRINT “Values of current stored in “; path$ + “\D” + ﬁlenm$ + “.m”; “ ﬁle”

mm = SPACE$(40)

temp$ = SPACE$(40)

cycle! = 4
count! = 1
prev = lE-ll

COLOR green, black

LOCATE 4, 3

PRINT “Program used for the spectrometer with 24001ines/mm grating”
COLOR white, black

LOCATE 5, 3

PRINT “Enter the initial scan wavelength [A]”;

INPUT staln!

COLOR yellow, blue

LOCATE 7, 3

PRINT “Set the counter to”; staln! + (47/2)

COLOR white, black

LOCATE 9, 3

PRINT “Enter the ﬁnal scan wavelength [A]”;

INPUT endln!

LOCATE 10, 3

PRINT “End point as observed from the counter [A]”; endln! + (47/2);
LOCATE ll, 3

PRINT “Enter the speed of scanning drive [A/min]”;

INPUT speed!

LOCATE 13, 3

PRINT “Maximum resolution that can be obtained [A]”; speed! / (cycle! * 60);
LOCATE 15, 3

PRINT “Enter the resolution required [A]-(default”; speed! / (cycle! * 60); “A)”;

92

INPUT resol!
IF resol! = 0 THEN resol! = speed! / (cycle! * 60)
sec! = resol! * (cycle! * 60) / speed!
sec% = sec!
IF (sec% - sec!) > .000001 THEN
COLOR white, red
LOCATE l6, 3
PRINT “Error in calculation is more likely to occur”;
END IF
COLOR white, black
LOCATE 17, 3
PRINT “Data acquisition interval [seconds]”; sec%;
temp% = endln! - staln!
IF temp% < 0
LOCATE l9, 3
PRINT “Please scan the spectrometer with increasing value of wavelength”
GOT O 200
ELSE
LOCATE l9, 3
tottim% = (endln! - staln!) * 60 / speed!
PRINT “Total time taken [seconds]”; tottim%;
endtim% = tottim% / sec%
LOCATE 21, 3
PRINT “No. of samples to be taken”; endtim% * cycle!;
LOCATE 22, 3
COLOR white, red
PRINT “Set Scan drive scanning switch to H”;
LOCATE 23, 3
PRINT “Start the Program and the Scan drive simultaneously”;
COLOR white, black
LOCATE 24, 3
PRINT “Hit any key to start”;
WHILE IN KEY$ = ““
WEND
COLOR green, black
1% = l
TIMER ON
ON TIIVIER(sec%) GOSUB disp
CLS
LOCATE 1, 1
PRINT “Program reads data from Picoammeter in”; sec% / cycle!; “second interval”:
LOCATE 2, 1
PRINT “No. of samples to be taken”; endtim% * cycle!;

93

LOCATE 3, 1

PRINT “Total time taken “; tottim%; “ seconds”;

LOCATE 5, l

PRINT “Wavelength[A] Current[amps] Sample No. Cycle/Sec. Time remaining[sec.]
start! = TIMER

DO

LOOP WHILE i% < endtim% + I

ﬁnish! = TIMER

TIMER OFF

PRINT “Total Execution time=”; ﬁnish! - start!

PRINT #1, EN$

PRINT #2, EN$

OPEN path$ + “\X” + ﬁlenm$ + “.m” FOR OUTPUT AS #3’store matlab EXE ﬁle
PRINT #3, “clear all;clc;”

PRINT #3, “W” + ﬁlenm$

PRINT #3, “D” + ﬁlenm$

PRINT #3, “plot(waveln,abs(value),’g’);pause(3);sm5;x1abel(‘Wavelength A’);yla-
bel(‘Current amps’);”

PRINT #3, “title(‘Emission Spectrum’);grid;”

PRINT “Execute “; path$ + “\X” + ﬁlenm$ + “.m”; “in matlab to view plot”
CLOSE

GOT O 200

END

6‘

disp:
FOR cyc% = 1 TO cycle!
CALL FILEWRT
count! = count! + 1
NEXT cyc%
1% = i% + 1
RETURN

200 COLOR white, red
PRINT “Switch off the Spectrometer drive”;
COLOR white, black
PRINT “ Press any key to end.”;
WHILE INKEY$ = ““
HTONE = 2000: LTONE = 550: DELAY = 500
FOR count = HTONE TO LTONE STEP -10
SOUND count, DELAY / count
NEXT count
HTONE = 780: RANGE = 650
FOR count = RANGE TO -RANGE STEP -4

94

SOUND HT ONE - ABS(count), .3
count = count - 2 / RANGE
NEXT count
WEND

END IF

END

SUB FILEWRT

SHARED prev, pico%, cyc%, i%, staln!, resol!, tottim%, sec%, temp$, buff$, count!
CALL [BRD(pico%, buff$)

temp$ = MID$(buff$, 5. 40)

y = VAL(RTRIM$(temp$))

IF (y > .00001) THEN

y = prev

END IF

prev = y

staln! = staln! + resol!

WRITE #1, 2 * staln!

WRITE #2, y

LOCATE 7, l

PRINT 2 * staln!, y, count!, cyc%, tottim% - (sec% * i%)
END SUB

SUB ReportError (fd%, errmsg$) STATIC
PRINT “Error = “, IBERR%; errmsg$
IF (fd% 0 -1) THEN
PRINT (“Cleanupz taking board off-line”)
CALL IBONL(fd%, 0)
END IF
STOP ‘ Abort program
END SUB

95

REFERENCES

96

REFERENCES

[1] J. Asmussen, J. Mossbrucker, S. Khatami, W. S. Huang, B. Wright and V. Ayres, “The
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