ESR CENTERS, INTERFACE STATES, AND OXIDE FIXED CHARGE IN THERMALLY OXIDIZED SILICON WAFERS

The ESR Pb center has been observed in thermally oxidized single-crystal silicon wafers, and compared with oxide fixed charge Q ss and oxidation-induced interface states Nst. The P b center is found to be located near the interface on (111) wafers. Its g anisotropy is very similar to that of known bulk silicon defects having SiIII bonded to three other Si atoms; the Pb unpaired electron orbital, however, is exclusively oriented normal to the (111) surface. The Pb center cannot be identified with any other known defect in Si or SiO2; in particular, it is totally unlike the common E′ center of SiO2. In contrast to Qss, both Pb and Nst were found to be greatly reduced by steam oxidation and hydrogen annealing. Both Pb and Nst may be regenerated by subsequent N2 anneals at 500 °C. In a graded series of samples, Pb and Nst are found to be proportional and nearly equal in concentration. This possible confirmation of SiIII at the interface, and correlation with Nst, support the theoretical indication of an SiIII band-gap energy level. The E′ center is unobservable, and if present, exists only in a concentration well below that of Qss. Thus, in addition to a lack of strong correlation with P b, Qss is evidently not due to E′ centers in their normal charge state. Overall, ESR is judged to be a useful technique for research on silicon wafer defects.