TRANSIENT CHARGING AND SLOW TRAPPING IN ULTRATHIN SIO2-FILMS ON SI DURING ELECTRON-BOMBARDMENT

Surface charging and electron trapping in ultrathin (1.6 nm) SiO2 film s on n-type silicon during bombardment by 350-600 eV electrons are obs erved by electric-field-induced optical second harmonic generation (SH G). Transient surface charging by fast dissipating electrons (< 1 ms c harge/discharge time) can be distinguished from oxide electron trappin g occurring over hundreds of seconds. The maximum SHG enhancement corr esponds to an areal density of trapped electrons of similar to 6 x 10( 12) cm(-2). The gradual recovery of the SHG following electron bombard ment suggests the trap sites are ''slow traps'', i.e., oxide traps whi ch discharge via tunneling to the Si/SiO2 interface. The effective tra p lifetime is about 500 s. (C) 1997 American Vacuum Society.