SPECTRAL SHAPE-ANALYSIS OF INFRARED-ABSORPTION OF THERMALLY GROWN SILICON DIOXIDE FILMS

The shape of the infrared absorption spectra of thermally grown silico n dioxide films on Si (100) is analyzed in order to characterize the o xide quality as a function of distance from the Si/SiO2 interface, The analysis includes (1) an exact extraction of the thickness-deconvolut ed dielectric function of the SiO2 films from the infrared absorption spectra measured on a series of etched-back SiO2 films. thereby elimin ating the multiple reflection effect at the surface and tile interface and (2) evaluation of the Si-O-Si bond angle distribution from the di electric function, assuming the central-force model. It is found that, as the distance from the Si/SiO2 interface decreases, a significant b roadening of the Si-O-Si bond angle distribution occurs only for the s mall bond angle region (less than 130 degrees). This means that an ave rage indicator of oxide quality such as the peak wave number of the in frared absorption spectrum is insufficient to describe the structural change inside the thermally grown SiO2 films. A possible model for the asymmetric broadening of the Si-O-Si bond angle distribution is that the thermally grown SiO2 films are essentially composed of two compone nts, i.e., one is locally existing regions with strained SiO2 structur e and the other is a region with the bulk oxide quality. It is conside red that the lattice mismatch at the Si/SiO2 interface is relaxed by c hanging, the volume ratio of the two components.