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Advisory Committee Chair

Shane Aaron Catledge

Document Type

Thesis

Date of Award

2020

Degree Name by School

Master of Science (MS) College of Arts and Sciences

Abstract

This study involves an Ar/H2 plasma acting on a negatively DC-biased silicon sub-strate in a microwave plasma chemical vapor deposition. The flow rate of hydro-gen was constant at 500 sccm, and that of argon was varied between 0 sccm and 500 sccm. Bias current was recorded for several values of the applied bias voltage ranging from – 100V to – 340V. At 10 and 20 torr, a peak in the bias current was found as argon flow rate changed. A decrease in current with varied argon intensi-ty in glow discharge plasma has been reported in the literature. Our results sub-stantiate these results, and further show a peak in bias current. OES data was used to estimate the plasma electron temperature which was found to be constant at each pressure. This suggests that the observed peak in bias current may be due to variation in plasma density as Ar flow changes between 0 sccm and 500 sccm. Us-ing these results, substrate bias pre-treatment experiments were performed at 10 torr in an Ar/H2 plasma, yielding the maximum bias current. Nucleation density of boron deposits were measured after subsequent exposure to B2H6 in H2 plasma and found to be a factor of 200 times higher than when no bias and no argon was used. Experiments were repeated at 20 and 30 torr (fixed bias voltage and Ar flow rate) in order to test the effect of chamber pressure on the nucleation density. Compared to 30 torr, we find nearly 7 times higher boron nucleation densities for both 10 and 20 torr pressures when using DC bias in the Ar/H2 plasma. Results are explained by incorporating measurements of plasma optical emission and by use of heterogeneous nucleation theory. Overall, these results help identify optimal conditions for nucleating and potentially growing superhard boron-rich coatings.

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