CVD-SiO2 and plasma-SiNx films as Zn diffusion masks for GaAs

Asymptotic analysis of some two-dimensional diffusion problems

“…(iv) Various physical mechanisms have been proposed for the apparent en hancem ent in lateral diffusion (see, for example, Baliga & G handhi 1979;Blaauw et al 1984;Vawter et al 1988). These include ( ) stress, ( ) im purity diffusion through the mask and (c) excess vacancy generation at the interface by semi conductor outdiffusion into the mask.…”

“…As already shown, this condition can lead to pronounced 'b ird 's beak' profiles since they arise in this model from the generation of vacancies on the surface, which allow interstitial im purity atom s to become substitutional below the mask. However, there is experim ental evidence (see, for example, Blaauw et al 1984) th a t the extent of the 'beak' depends on the natu re of the mask. A simple way to incorporate this into the model is to introduce a finite reaction rate for the generation of vacancies on the masked p art of the surface, which perm its the de pletion of the surface vacancy concentration below its equilibrium value.…”