Lateral Uniformity of n+/p Junctions Formed by Arsenic Diffusion from Epitaxially Aligned Polycrystalline Silicon on Silicon

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Abstract
Nonuniformities in the polycrystalline silicon (polysilicon)/silicon interface and in the polysilicon structure are expected to produce a nonuniform diffusion front when arsenic is diffused from epitaxially aligned polysilicon. Using transmission electron microscopy, we find surprisingly uniform arsenic diffusion fronts in the underlying silicon substrate when arsenic is implanted prior to a high temperature anneal which induces epitaxial alignment. Thinned specimens were examined by cross‐sectional transmission electron microscopy (XTEM) before and after immersion in a junction‐delineating etch consisting of 0.5% in . For arsenic penetration depths greater than 500Å, uniform junctions are found even when the anneal causes nonuniform break‐up of the interfacial layer and epitaxial alignment of the polysilicon with the (100) substrate. We conclude that the use of high arsenic concentrations and high temperature rapid thermal annealing to intentionally induce epitaxial alignment of the polysilicon remains a viable technique for n+/p junction formation.

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