Nonlinear optical diagnosis of oxide traps formed during reactive ion etching

Oxide traps generated by reactive ion etching are studied using a pulsed fe mtosecond laser. The second harmonic generation (SHG) signal from the Si/Si O2 interface is sensitive to charged traps in the oxide. The time evolution of the SHG signal indicates that positive traps predominate. The angular d ependence of the polarized signal shows that the electric field generated b y the oxide traps alters the symmetry of the sample. The damage is greatest for an oxide thickness of 13 nm (for a plasma dc bias of 300 V). Thicker o xides have smaller SHG signals, presumably because the Fowler-Nordheim tunn eling currents induced by plasma charging of the oxide surface are smaller. Very thin oxides also exhibit reduced damage. The time dependent SHG signa ls depend on the temperature of the samples; these data provide information on the trapping and detrapping of substrate electrons by oxide holes. (C) 2000 American Institute of Physics. [S0021-8979(00)02918-2].