Influence of in situ applied ultrasound during Si~+ implantation in SiO_2 on paramagnetic defect generation

摘要

Electron spin resonance (ESR) results are presented on the influence of in situ ultrasound treatment (UST) during implantation at 300 K of Si~+ ions into thermal SiO_2 on (100)Si before and after subsequent high-temperature (T) annealing (1100 ℃) intended to promote the formation of embedded Si nanoparticles. The as-implpnted state exhibits high densities of three prominent types of point defects, including the SiO_2-specific S and E'_γ O-vacancy type centers, and an unknown broad (≈20 G) signal at g ≈ 2:0026 denoted IS. The high-intensity S signal shows demagnetization shape effects, pointing to a distribution of high local density of defects over a thin layer. UST is observed to effectuate a drastic reduction in S and E'_γ centers, and elimination of IS beyond detection. This reveals a strong healing influence of in situ transferred ultrasound (US) energy on implantation-induced damage, here quantified and identified on atomic level in terms of mainly intrinsic paramagnetic point defects elimination, viz., Frenkel pair elimination, while all three initial signals disappear. Other types of defects surface after annealing of the non-US treated sample, including the SiO_2-specific EX defect signal and P_b-type Si/SiO_2 interface centers, the appearance of the latter providing direct ESR evidence for crystallization of the excess Si nanoparticles. The influence of the UST healing effect is kept up after subsequent annealing, now resulting in the absence of virtually all ESR-active centers. The drop in P_b-type centers below the detection level in the UST annealed sample indicates improvement of the nanocrystalline-Si/SiO_2 interface quality. The combination of UST with high-T annealing emerges as a highly efficient means to eradicate ion implantation damage in terms of intrinsic point defects.