INFRARED SPECTROSCOPIC ANALYSIS OF PHOSPHOSILICATE GLASS-FILMS FOR MICROMACHINING

Fourier transform infrared spectroscopy has been employed to investiga te the effect of both the deposition parameters and subsequent thermal processing on phosphosilicate glass (PSG) and how these modifications are reflected in the peaks corresponding to the Si-O, P-O, and P=O bo nds. The variation of the frequency shift of the Si-O main band with t he phosphorus content and the annealing of PSG has been clearly establ ished. Furthermore, it is suggested that there is no separate phosphor us pentaoxide or trioxide present in the glass and that both P=O and P -O bonds determine the properties of PSG. It has been determined that the high etch rate of as-deposited PSG is due mainly to its porosity, its distorted and disordered internal structure, and the initially hyd rolized P=O bonds. The decreased etch rate after annealing is due to t he decrease in porosity the restoration of the P=O bonds, and probably the formation of insoluble compounds. Annealing at 950 or 1000 degree s C yields significant changes in the structure of the PSG and a consi derable phosphorus out-diffusion. In contrast, annealing at 850 degree s C is sufficient to stabilize the structure of the PSG without import ant structural modifications.