Photolytic silicon nitride deposition for gallium arsenide by 193 nm excimer laser radiation

GaAs technology requires low temperature processes for any film deposition. Furthermore, processes without particle bombardment are also preferred, two conditions which photolytic deposition does fulfil. An excimer laser beam of 20 × 1 mm2 cross-section skimmed over the wafer surface at 0.2 mm distance. The feed gases used were monosilane, NH3 and NF3. At a temperature of 150°C, an oxide was obtained containing almost no nitrogen. With higher temperatures the nitrogen content of the film increased raising the index of refractive correspondingly, while the deposition rate decreased. The deposition per pulse was proportional to the pulse energy by a factor of 6.25 angstrom min-1 mJ-1, but decreased with increasing pulse frequency, indicating a diffusion-limited deposition rate. The films have been analysed by ellipsometry, by quantitative energy dispersive electron microprobe measurements and also by ir absorption. When 50% of NF3 was substituted for the same amount of the NH3 gasflow, the peak of the Si-Hn bond did not decrease. We conclude that this is due to the insufficent absorption of the laser radiation by the NF3, as the deposition rate reduced to almost zero when only NF3 and no NH3 was used.