In this days, the thinner film of dielectric materials is required while its capacitance is required to be still large at the VLSI process. Most of such VLSI have MOS structures. For the research on this requirement, MOS capacitors were fabricated on the silicon wafer in four different thickness groups by RF sputtering method. SiO of the SiO/TiN film is used as the insulating layer and TiN is chosen as the barrier against the diffusion of Al which is the terminal connected by ohmic contact because TiN has the advantageous properties such as good thermal stability and very low diffusion rate in spite of its relatively low specific resistance. In this study their electrical and optical characteristics are investigated to find refractive index, absorption coefficient and Permittivity.