551. Near Si/SiO2 interfacial layer formation of uncompensated P states in B-doped Si by thermal oxidation, evidenced by ESR at low T
- Author
-
J. Braet and Andre Stesmans
- Subjects
Thermal oxidation ,chemistry.chemical_classification ,Silicon ,Chemistry ,Diffusion ,Doping ,Analytical chemistry ,chemistry.chemical_element ,Mineralogy ,Surfaces and Interfaces ,Atmospheric temperature range ,Condensed Matter Physics ,BORO ,Surfaces, Coatings and Films ,Electrical resistivity and conductivity ,Materials Chemistry ,Inorganic compound - Abstract
It has been found that thermal oxidation of B-doped (p-type) commercially obtained CZ-grown Si wafers of room temperature resistivity 8 ≲ ϱ RT ≲ 37 Ω cm creates P-rich near-interfacial Si layers. The piled-up P was detected via X- and K-band ESR carried out in the temperature range 1.5 ⩽ T ⩽ 77 K, displaying a spectrum which is shown to be identical to the one typical for 31P atoms dissolved in P-doped (n-type) Si. From signal-intensity calibrations and chemical-thinning sequences, the P was shown to be piled up in the Si/SiO2-interfacial top-Si layers revealing the existence of local bulk concentrations N ≳ 7.6×1016P atoms cm−3 in one sample, most of the phosphorus being accumulated in a 25 nm thick interfacial Si layer. For the other samples, even higher N values were derived. The observability by ESR of the piled-up P was subsequently shown to be allowed by the effective reversal of the semiconductor type, i.e. from p to n, of the interfacial Si layers by the high local P donor concentrations compared to the averaged B concentrations; surface charge induced band-bending effects are shown to be negligible. As to the physical origin of the P atoms, from several experimental facts and arguments the possibility of external input during thermal cycling was excluded. Instead, the P atoms are presumed to be inherently present as bulk impurities - thus referring to a non-negligible compensation ratio of the doped Si - the P being collected at the interface during thermal oxidation via vacancy-mediated diffusion, driven by the naturally-present interfacial strain field. Once the strain field has been released by an interfacial saturation concentration of P, the ordinary inwards-Si diffusing behaviour via the interstitialcy mechanism becomes dominant. Consequently, it is argued that P may diffuse via a dual mechanism.
- Published
- 1986