Nonlinear optical diagnosis of oxide traps formed during reactive ion etching

Abstract

Oxide traps generated by reactive ion etching are studied using a pulsed femtosecond laser. The second harmonic generation ͑SHG͒ signal from the Si/SiO 2 interface is sensitive to charged traps in the oxide. The time evolution of the SHG signal indicates that positive traps predominate. The angular dependence of the polarized signal shows that the electric field generated by 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 V͒. Thicker oxides have smaller SHG signals, presumably because the Fowler-Nordheim tunneling currents induced by plasma charging of the oxide surface are smaller. Very thin oxides also exhibit reduced damage. The time dependent SHG signals depend on the temperature of the samples; these data provide information on the trapping and detrapping of substrate electrons by oxide holes.

Optical second harmonic generation studies of ultrathin high-k dielectric stacks

“…29 However, in a study of plasma etching of thermallygrown SiO 2 on Si͑100͒, SHG-RA patterns were found to "deteriorate" with oxide thinning. 22 "Deterioration" exhibited itself through a reduction of the anisotropic contribution in the SHG-RA signal, i.e. the ratio ͉A / B͉ increased with the etching time.…”

“…Remarkably, after a complete oxide removal, the ͉A / B͉ ratio again became close to the value determined on oxide prior to the plasma etch. 22 The "deterioration" of SHG-RA was attributed to the creation and non-uniform distribution of defects capable of charge trapping in the oxide layer. 22 Clearly, this study suggests that the ͉A / B͉ ratio can be affected by factors other than interface topological roughness.…”

“…29 SHG "roughness" may, therefore, reflect factors other than a pure physical morphology of the interface. 22,29 In particular, SHG, unlike AFM, averages the signal over the spot-size area ͑on the order of 30 µm͒ and is sensitive, unlike x-ray or ion scattering, to local electronic defects, like dangling bonds, 29 charge traps, 21 etc.…”

Second harmonic generation probing of dopant type and density at the Si/SiO2 interface

“…EFISH adds to the usual second harmonic field of the semiconductor in the absence of an electric field, as shown in Eq. ͑1͒: [7][8][9][10] I͑2͒ ϰ ͉P 2 + P 2 EFISH ͉ 2 = ͉ ͑2͒ + ͑3͒ E DC ͉ 2 I 2 ͑͒, ͑1͒…”

Spectroscopic second-harmonic generation duringAr+-ion bombardment of Si(100)

“…[11][12][13] Also the surface of clean and H terminated c-Si has been studied thoroughly with SHG. [14][15][16][17][18][19][20] In these studies the SHG signal from the c-Si surface has been shown to be sensitive to surface Si dangling bonds for photon energies in the range of ϳ1.0 to ϳ 1.3 eV.…”