Studies of the oxidation states of phosphorus gettered silicon substrates using X-ray photoelectron spectroscopy and transmission electron microscopy

Abstract

Phosphorus diffusion in p-type silicon wafers with Fe or Cr impurities has been investigated using X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy. Silicon wafers doped with phosphorous are heavily used in semiconductor devices. It is, therefore, of crucial importance to determine their compositions profile. The XPS P2p spectra revealed presence of elemental phosphorus (P0), donor ion (P+), and interstitial or substitutional diffused P− from phosphorus oxides P2O5 and P4O10 as residues of the diffusion process. The surface of the Si wafers was oxidized during the deposition of P2O5 and SiO2 (with a subsequent heating). This resulted in the formation of a 1.3–1.4 nm thick SiOx layer. Pile-up of elemental P was found near the surface of the wafer. This pile-up was larger for Fe contaminated samples compared to Cr contaminated ones. The pile-up may have been caused by a decrease in the diffusion length of P+ donor ions, which could only be found in the first few nm near the surface of the silicon wafer. The observed diffusion length was DLP+<DLP0<DLP−.