Non-uniformities in polysilicon/silicon interfaces, and in the polysilicon structure, were expected to produce a non-uniform diffusion front when As was diffused in from epitaxially aligned polysilicon. By using transmission electron microscopy, surprisingly uniform As diffusion fronts were found in the underlying Si substrate when As was implanted before annealing at high temperatures (in order to induce epitaxial alignment). Thinned specimens were examined, using cross-sectional transmission electron microscopy, before and after immersion in a junction-delineating etch. The latter consisted of 0.5%HF in HNO3. At As penetration depths which were greater than 50nm, uniform junctions were found; even when annealing caused a non-uniform break-up of the interfacial layer and an epitaxial alignment of the polysilicon with the (100) substrate. It was concluded that the use of high As concentrations and high-temperature rapid thermal annealing, in order to induce an epitaxial alignment of the polysilicon, remained a viable technique.

J.L.Hoyt, E.F.Crabbé, R.F.W.Pease, J.F.Gibbons, A.F.Marshall: Journal of the Electrochemical Society, 1988, 135[7], 1773-9