AN EXPERIMENTAL-STUDY OF HIGH-PRESSURE SYNTHESIS OF DIAMOND FILMS USING A MICROWAVE CAVITY PLASMA REACTOR

Diamond film deposition on Si ''benchmark'' substrates is experimental ly investigated al high pressures using a microwave plasma disk reacto r and CH4/H-2 gas mixtures. In this microwave plasma reactor the plasm a is formed inside a 12.7 cm diameter disk-like discharge region locat ed at one end of an internally tuned cylindrical cavity applicator. A water cooling stage is employed to control substrate temperature. The input variables of the experimental evaluation are (1) methane concent ration, expressed as c=%CH4/H-2 from 1 similar to 8%, (2) total flow r ate, f(t), 200 similar to 1400 sccm, (3) substrate temperature T-s whi ch varies from 700 similar to 1125 degrees C, (4) deposition time, t, 5 similar to 100 h, (5) pressure, p, 80 similar to 140 Ton, (6) incide nt power, P-inc, 2 similar to 4.5 kW. The output films deposited on 2 in. diameter substrates were characterized by (1) growth rate in mu m/ h and mg/h, (2) film morphology, and (3) Raman spectra. In particular film growth rate versus CH4/H-2, flow rate, T-s and t were performed o n films deposited uniformly (<15%) over 2 in. diameter Si substrates. 5 h experiments indicated that the average him growth rate (over 2 in. diameter) varied from a few mu m/h with c=1% to 4.3 mu m/h at c=3% an d then decreased for high c ratios. Average growth rate also varied wi th flow rate with a maximum of over 5 mu m/h (similar to 35 mg/h). Gro wth rate increases as deposition time increases and reaches a maximum growth rate of 6.3 mu m/h (similar to 44 mg/h) at t=100 h. The film gr owth reaches a maximum around T-s=1100 degrees C for both 2 and 3% che mistries. (C) 1997 Elsevier Science S.A.