Transient charging and slow trapping in ultrathin SiO2 films on Si during electron bombardment

Abstract

Surface charging and electron trapping in ultrathin (1.6 nm) SiO2 films on n-type silicon during bombardment by 350–600 eV electrons are observed by electric-field-induced optical second harmonic generation (SHG). Transient surface charging by fast dissipating electrons (<1 ms charge/discharge time) can be distinguished from oxide electron trapping occurring over hundreds of seconds. The maximum SHG enhancement corresponds to an areal density of trapped electrons of ∼6×1012 cm−2. The gradual recovery of the SHG following electron bombardment suggests the trap sites are “slow traps”, i.e., oxide traps which discharge via tunneling to the Si/SiO2 interface. The effective trap lifetime is about 500 s.