ABSTRACTGROWTH AND CHARACTERIZATION OF LARGE, HIGH QUALITY SINGLE CRYSTAL DIAMOND SUBSTRATES VIA MICROWAVE PLASMA ASSISTED CHEMICAL VAPOR DEPOSITIONByShreya NadSingle crystal diamond (SCD) substrates can be utilized in a wide range of applications. Important issues in the chemical vapor deposition (CVD) of such substrates include: shrinking of the SCD substrate area, stress and cracking, high defect density and hence low electronic quality and low optical quality due to high nitrogen impurities. The primary objective of this thesis is to begin to address these issues and to find possible solutions for enhancing the substrate dimensions and simultaneously improving the quality of the grown substrates.The deposition of SCD substrates is carried out in a microwave cavity plasma reactor via the microwave plasma assisted chemical vapor deposition technique. The operation of the reactor was first optimized to determine the safe and efficient operating regime. By adjusting the matching of the reactor cavity with the help of four internal tuning length variables, the system was further matched to operate at a maximum overall microwave coupling efficiency of ~ 98%. Even with adjustments in the substrate holder position, the reactor remains well matched with a coupling efficiency of ~ 95% indicating good experimental performance over a wide range of operating conditions. SCD substrates were synthesized at a high pressure of 240 Torr and with a high absorbed power density of 500 W/cm3. To counter the issue of shrinking substrate size during growth, the effect of different substrate holder designs was studied. An increase in the substrate dimensions (1.23 – 2.5 times) after growth was achieved when the sides of the seeds were shielded from the intense microwave electromagnetic fields in a pocket holder design. Using such pocket holders, high growth rates of 16 – 32 μm/hr were obtained for growth times of 8 – 72 hours. The polycrystalline diamond rim deposition was minimized/eliminated from these growth runs, hence successfully enlarging the substrate size. Several synthesized CVD SCD substrates were laser cut and separated from the underlying seeds, and then polished to form CVD diamond plates. These plates were characterized with various techniques and were determined to be of type IIa quality or better with a high optical transmission. Etch pits were observed to occur at the edges of growth terraces after etching experiments. By exploiting such an observation along with long growth times, the electronic quality of the substrates was improved upon by reducing the etch pit density of the grown substrates by 1 – 3 orders of magnitude over the commercially available seeds.This research has thus developed new process methods for enlarging the CVD SCD dimensions at high growth rates while improving their quality. These process methods were demonstrated by using electrically efficient, cost effective reactor designs. These process methods and reactor designs can now be used in the future for the synthesis of even larger and better quality substrates.
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