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Silicon is a known trace contaminant in diamond grown by chemical vapor deposition (CVD) methods. Deliberately Si-doped diamond is currently attracting great interest because of the attractive optical properties of the negatively charged silicon-vacancy (SiV - ) defect. This work reports in-depth studies of microwave-activated H 2 plasmas containing trace (10-100 ppm) amounts of SiH 4 , with and without a few % of CH 4 , operating at pressures and powers relevant for contemporary diamond CVD, using a combination of experiment (spatially resolved optical emission (OE) imaging) and two-dimensional plasma chemical modeling. Key features identified from analysis and modeling of the OE from electronically excited H, H 2 , Si, and SiH species in the dilute Si/H plasmas include the following: (i) fast H-shifting reactions ensure that Si atoms are the most abundant silicon-containing species throughout the entire reactor volume, (ii) the low ionization potentials of all SiH  x  ( x ≤ 4) species and efficient ion conversion reactions ensure that even trace SiH 4 additions cause a change in the dominant ions in the plasma volume (from H 3  + o SiH  x   + ), with consequences for electron-ion recombination rates and ambipolar diffusion coefficients, and (iii) the total silicon content in the reactor volume can be substantially perturbed by silicon deposition and H atom etching reactions at the reactor walls. The effects of adding trace amounts of SiH 4 o a pre-existing C/H plasma are shown to be much less dramatic but include the following: (i) a Si substrate or fused silica components within the reactor are a ready (unintended) source of gas-phase Si-containing species, (ii) OE from electronically excited Si atoms should provide a reliable measure of the Si content in the hot plasma region, and (iii) Si atoms and/or SiC 2 species are the most abundant gas-phase Si-containing species just above the growing diamond surface and thus the most likely carriers of the silicon incorporated into CVD diamond.

the journal of physical chemistry a

Optical Emission Imaging and Modeling Investigations of Microwave-Activated SiH4/H2 and SiH4/CH4/H2 Plasmas