Phosphorus redistribution in the surface region of heavily phosphorus doped silicon

Heavily phosphorus doped samples of both Si(100) and polycrystalline silicon (poly-Si) together with nondoped poly-Si were examined using X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS). The surfaces were treated by HF or a mixed solution of HCl, H2O2 and H2O. The Si2p photoelectron spectra from the heavily P-doped samples showed a new peak at below 0.4 eV from the Si0 state, which suggests that the Si-P bond and/or activated Si atoms with dangling bond exist in the surface region of as large as several nanometers. This is further supported by the analysis of P2p spectra. A lots of P atoms diffused to the surface and broke the Si-Si bond, which caused the surfaces chemically unstable. Consequently, although the H-terminated nondoped poly-Si surface showed no oxide features, the heavily P-doped samples of both Si(100) and poly-Si exhibited 0.5–1 nm thick oxides. The sputter profiles of XPS and SIMS revealed that P atoms redistributed in the thin native oxide film and formed not P2O5 but Si-P and/or elemental-P, even without intentional heating. The P-segregation was much more pronounced for the single crystal Si than for the poly-Si.