STUDY OF THIN-FILMS OF TRANSPARENT ELECTRONIC MATERIALS BY PHASE-MODULATED SPECTROELLIPSOMETRY

Although phase-modulated spectroellipsometry (PMSE) has been applied s uccessfully to the study of a wide range of thin film materials, there are few studies dealing with transparent films. The reason for this i s that measurements of transparent thin films with the usual procedure of PMSE intrinsically give a great amount of error associated with sp ecific values of ellipsometric angles. We present a study of optical p roperties in the UV-visible range of transparent thin films (low press ure chemically vapour-deposited amorphous SiO2 (a-SiO2), plasma-enhanc ed chemically vapour-deposited hydrogenated amorphous SiN(x) and hydro genated amorphous SiO(x)N(y)) using a new method, with which we perfor m the PMSE measurements with great accuracy. From the measured complex pseudodielectric functions of the whole air/film/substrate structure, we determine the complex dielectric function of these materials using the Bruggeman effective-medium approximation. The results show that t hese transparent materials can be considered as a mixture of standard fused a-SiO2, standard pyrolytic amorphous Si3N4 and voids. We have re lated the obtained volume fractions to the technological parameters of the deposition process. More generally, this study illustrates the ca pacity of the new ellipsometric method for the study of a wide range o f transparent materials.