Microwave plasma-assisted CVD polycrystalline diamond films deposition at higher pressure conditions.

摘要

This study investigated the growth of polycrystalline diamond films using pressures higher than 100 Ton., which is higher than the pressure nominally used for polycrystalline diamond film deposition. Under these higher pressure operating conditions, high optical quality freestanding films and substrates of polycrystalline diamond with thickness up to 200 microns have been uniformly deposited on 2 inch and 3 inch silicon wafers in a 2.45 GHz microwave plasma-assisted chemical vapor deposition (CVD) system. Several of these films were separated from the silicon substrate and then lapped and polished for window applications. The polycrystalline diamond films are grown in a microwave plasma-assisted CVD reactor using either a hydrogen/methane or a hydrogen/argon/methane chemistry without any other additive gases. The deposition reactor is a microwave cavity applicator with the plasma confined inside a 12 cm diameter fused silica dome. The methane percentage was nominally varied to between 1-2% when reactor deposition pressure varied between 100-180 Torr. The reactor was also modified to improve its performance for higher pressure deposition processing. The substrate temperature was controlled between 900 and 1100°C. The experimentally measured average linear growth rate of the polycrystalline diamond film is as large as 3-4 mum/h at 160 Torr reactor pressure and 2% methane in the feed gas.;The polycrystalline diamond samples were characterized to determine growth rate, optical quality, film thickness uniformity, and intrinsic stress Raman spectroscopy is used to identify the spectral width of the sp3 peak and the ratio of the sp2 to sp3 signals. The FWHM of the diamond peak from the Raman spectrum is used as one measure of the diamond quality and the optical transmission measurements was used as another measure. The diamond films were grown on silicon wafers and after the deposition process was completed, the bowing of the wafer and film was used to determine the stress in the diamond film. It was found that stress levels greater than a threshold value in the diamond film on the silicon wafer often result in the film breaking when the silicon is etched away from the diamond film. It was also determined that by controlling the substrate temperature lower film stress could be achieved.;Finally, the diamond film thickness uniformity was evaluated by percent deviation of film thickness in the radial and circumferential directions for samples deposited at higher pressure condition. An example of achieved thickness non-uniformity was +/-4.7% radially across a diameter of 2.5 inch (or 6.3 cm) and +/-4.0% along the circumference at a radius of 1.25 inch (or 3.15 cm) for a 3-inch diameter deposition area at 120 Torr reactor pressure with argon addition. The achieved thickness non-uniformity was reduced down to +/-4.3% radially and +/-6.7% along the circumference for a 2-inch diameter silicon substrate at 160 Ton reactor pressure without using argon gas The thickness uniformity was significantly improved by controlling the substrate temperature to be uniform and the addition of the argon in the feed gas.