Effects of substrate bias on current for varying argon intensity in a low-pressure hydrogen/argon plasma in chemical vapor deposition.

Studies have shown that in CVD, low substrate temperature often favors amorphous materials growth over crystalline. In a hydrogen/argon plasma acting on a negatively DC-biased silicon substrate, hydrogen alpha and bias current due to ion bombardment were monitored for temperature <1000^oC. The temperature was controlled through microwave power of 0.6kW, and pressure of 10 – 30 torr. The flow rate of argon was varied between 0 sccm and 500 sccm, and hydrogen's was 500 sccm. Optical Emission Spectroscopy (OES) of hydrogen line was found to be influenced by argon flow rate. Current was recorded for several values of the applied bias voltage from 100V to 340V. A decrease in current with decreasing hydrogen emission for glow discharge systems has been reported in the literature. Our results substantiate these results, and further show a peak in current at 10 and 20 torr. OES data was used to estimate the plasma electron temperature to be constant at approximately 0.5 eV. This suggests that the observed peak in current may be due to variation in plasma density as Ar flow changes between 0 sccm and 500 sccm. These results may be used to correlate plasma emission characteristics with substrate bias conditions in order to better predict and control MPCVD grown materials.