The chemical composition changes of silicon and phosphorus in the process of native oxide formation of heavily phosphorus doped silicon

The chemical composition changes of silicon and phosphorus in the process of native oxide formation of both heavily phosphorus-doped Si(1 0 0) and polycrystalline Si prepared by HF-treatment were monitored for a period of 1 year, using angle dependent X-ray photoelectron spectroscopy (XPS). Right after HF-treatment, significant amounts of unoxidized-P (P∗) and a new chemical state of Si (Si∗) having an unstable bond were detected in the surface region of heavily P-doped Si. With decreasing depth, the concentration of P∗ increased, whereas the Si∗ decreased. The surface segregated P∗ was larger for P-doped Si(1 0 0) than for P-doped poly-Si. During the growth of native oxide, the distributions of P∗ and Si∗ in the underlying Si surface did not change largely with oxide thickness. A part of P atoms also reacted with oxygen and incorporated into Si–O–P network in the native oxide, and the amount of P-oxide increased with the progress of oxidation. The decomposed Si 2p spectra of growing oxide films on both heavily P-doped Si showed that the dominant component was not the Si4+, but Si3+ state until the oxide thickness went up to over about 1.5 nm, while that for the low P-content Si was Si4+, except at the very narrow interface.