Titanium nitride (TiN) films are used as diffusion barrier layers in the semiconductor industry. There is a need for accurate data on optical properties, because film thickness are usually monitored by optical methods. There are further needs to characterize TiN/(interlayer dielectrics)/Si system simultaneously. Thus, TiN(35, 60, 90 and 105 nm)/SiO2(1000 nm)/Si samples were prepared using sputtering from a TiN target in argon and nitrogen atmosphere. Those samples were characterized using simultaneous fits of multiple angle of incidence spectroscopic ellipsometry and normal incidence spectroscopic reflectivity. TiN films partially transmit light that interferes in the thick thermal silicon oxide, which gives more detailed information on the optical properties of TIN. Consequently optical dielectric function of TiN as well as two thickness of TIN and SiO2 were successfully determined simultaneously.