Spectral shape analysis of infrared absorption of thermally grown silicon dioxide films

The shape of the infrared absorption spectra of thermally grown silicon dioxide films on Si (100) is analyzed in order to characterize the oxide quality as a function of distance from the Si/SiO, interface. The analysis includes (1) an exact extraction of the thickness-deconvoluted dielectric function of the SiO, films from the infrared absorption spectra measured on a series of etched-back SiO, films, thereby eliminating the multiple reflection effect at the surface and the interface and (2) evaluation of the Si-0-Si bond angle distribution from the dielectric function, assuming the central-force model. It is found that, as the distance from the Si/SiO, interface decreases, a significant broadening of the Si-0-Si bond angle distribution occurs only for the small bond angle region (less than 130”). This means that an average indicator of oxide quality such as the peak wave number of the infrared absorption spectrum is insufficient to describe the structural change inside the thermally grown SiO, films. A possible model for the asymmetric broadening of the Si-0-Si bond angle distribution is that the thermally grown SiO, films are essentially composed of two components, i.e., one is locally existing regions with strained SiO, structure and the other is a region with the bulk oxide quality. It is considered that the lattice mismatch at the Si/SiO, interface is relaxed by changing the volume ratio of the two components.