Interface states and electron spin resonance centers in thermally oxidized (111) and (100) silicon wafers

Interface states and electron spin resonance centers have been observed and compared in thermally oxidized (111) and (100) silicon wafers subjected to various processing treatments. The ESR Pb signal, previously assigned to interface ⋅Si≡Si3 defects on (111) wafers, was found to have two components on (100): an ⋅Si≡Si3 center oriented in accord with (100) face structure, and an unidentified center consistent with ⋅Si≡Si2O. The quantitative proportionality of Pb spin concentration to midgap interface trap density Dit is maintained on (100), and both are lower by a factor of about 3 compared to (111). This correlation persists over the range of oxidation temperatures 800–1200°C, for both n- and p-doped silicon, cooled by fast pull in oxygen, and cooled or annealed in nitrogen or argon. The correlation is independent of doping level. In samples with different oxide thickness, neither Pb nor Dit varied significantly over the range 100–2000 A, but Pb was smaller at 50 A. In general, ESR is judged to offer promise for further studies of specific interface features.