Silicon oxide in Si-Si bonded wafers

The properties of surface and buried interface silicon oxide layers in low- and high-temperature Si-Si bonded wafers, were investigated using infrared spectroscopy, spectroscopic ellipsometry (SE) and high resolution transmis sion electron microscopy (HRTEM). Infrared transmission spectra show the ab sorption by Si-O-Si vibrations originating from surface and interface silic on oxide. To distinguish the contribution of surface and buried interfaces oxide in the spectra, the surface oxide was removed by chemical etching. Th e interface oxide thickness was calculated from curve fitting of infrared t ransmission spectra of the etched bonds. An excellent agreement of values o f the interface oxide thicknesses determined using this method with those o btained from HRTEM measurements was found. The behaviour of longitudinal an d transversal optical (LO and TO) phonons in surface silicon oxide was anal ysed. The frequency position of TO and LO modes shifts towards higher energ y and the LO-TO splitting decreases upon annealing. This behaviour can be e xplained in terms of a thermal relaxation model. (C) 2001 Elsevier Science B.V. All rights reserved.