The use of PSG films as diffusion masks for gallium arsenide

This paper describes the development of phospho-silicate glass (PSG) films as an effective mask against Zinc and Tin diffusions in Gallium Arsenide. Films with a high P2O5content (as much as 30% by weight) were formed by the oxidation of Silane-Phosphine gas mixtures in an inert carrier gas, and used to obtain adequate masks against these dopants. Mask thicknesses of up to 10,000 Å were shown to exhibit no tendency towards cracking during the diffusion cycle, unlike pure silicon dioxide at these thicknesses. Effective masking was obtained for diffusion depths (unmasked regions) up to 10 microns. Information on the kinetics of growth of doped oxide films is also presented.