OPTICAL PROPERTIES OF LOW PRESSURE CHEMICALLY VAPOR DEPOSITED SILICON OXYNITRIDE FILMS FROM SICL_2H_2-NH_3-N_2O MIXTURES

摘要

Silicon oxynitride thin films were deposited on 4 in. (100) Si wafers in a conventional low pressure chemical vapor deposition reactor at 812℃ and 230 mTorr, using SiCl_2H_2-NH_3-N_2O gas mixtures. Depositions were carried out keeping the flows of SiCl_2H_2 and of NH_3 constants at 20 and 60 sccm respectively, while that of N_2O was varying between 0 and 180 sccm. The optical properties of deposits were studied with the aid of the Forouhi-Bloomer model (Phys. Rev. B34, 7018 (1986)) for amorphous semiconductors. From the analysis of the optical spectra the complex refractive index of the films as well as their thicknesses were derived. Moreover, an approximate picture of the energetic distribution of the density of electronic states near the absorption threshold of these films was obtained. This picture was found to be consistent with theoretical calculations found in the literature. Thus, the increase of oxygen content in films implies an increase of the Forouhi-Bloomer gap and a decrease of the energetic distance between the centers of gravity of valence and conduction bands.