Effect of surface species concentrations and temperature on diamond film morphology in inductively coupled r.f. plasma CVD

An analysis of flow, temperature, and chemical composition distortion in gas sampling through an orifice during chemical vapor deposition

“…As described above, simulations including detailed chemistry corresponding to the diamond deposition experiments described by Lindsay, Larson, and Girshick 5 were performed to determine quantitatively the effect of the sampling disturbance in those experiments. Figure 3 shows results of calculations corresponding to deposition at a substrate temperature of 1200 K, a pressure of 1 atm, an orifice diameter of 70 m, and an input methane to hydrogen ratio of 2%.…”

“…This geometry corresponds to the sampling orifice used in the experiments presented in previous work from this laboratory. 4,5 For simulations used to obtain quantitative results corresponding to experiments performed in our laboratory ͑see above͒, detailed reaction mechanisms were used in both the gas phase and on the surface. In the gas phase, a mechanism consisting of 27 reactions among 16 species ͑H 2 , H, Ar, and the C 1 and C 2 hydrocarbons͒ was used.…”

“…Gas sampling through an orifice in the substrate, followed by gas chromatographic or mass spectrometric analysis of the sampled gases, has been used to investigate the chemistry of a wide range of chemical vapor deposition ͑CVD͒ processes. Systems where this technique has been applied include combustion CVD of diamond, 1 hot filament CVD of diamond, 2 atmospheric-pressure radio-frequency plasma CVD of diamond, [3][4][5] microwave plasma CVD of diamond, 6 plasma-enhanced CVD of diamondlike carbon, 7 laser-assisted CVD of germanium, 8 thermal CVD of AlN from ͑͑CH 3 ͒ 2 AlNH 2 ͒ 3 , 9 MOCVD of GaAs, 10,11 photoassisted CVD of Si 3 N 4 , 12 tungsten CVD, 13 and laser-induced CVD of amorphous hydrogenated silicon. 14 In several of these studies, 1,2,4 measured concentrations were explicitly compared to one-dimensional simulations of a chemically reacting stagnation point flow computed using the SPIN code 15 from Sandia National Laboratories.…”

“…Our interest in exploring the effect of these sampling distortions arises from the experimental and modeling studies of atmospheric-pressure radio-frequency plasma CVD of diamond performed previously in our laboratory. 4,5,16,17 In these experiments, diamond was deposited on a molybdenum substrate at atmospheric pressure using a radiofrequency induction plasma operating with argon as the main plasma gas. Methane and hydrogen were the reactants, with typical inlet CH 4 :H 2 :Ar ratios of 1:50:500.…”

“…To do this, we have performed two-dimensional simulations of the near-orifice region of a stagnation point flow in which there is critical flow through a small orifice located on the axis of the flow. For conditions corresponding to experiments from this laboratory that have been presented previously, 4,5 simulations that included detailed diamond CVD chemistry in both the gas phase and on the surface were carried out. To generalize the results, we also performed less computationally expensive simulations, including only three species and a single surface reaction, over a range of pressures, total flow rates, orifice diameters, and freestream and substrate temperatures.…”