Optical characteristics and UV modification of low-k materials

We present a study of optical characteristics in visible and vacuum ultra-violet range of porous low-k dielectric films (prepared by Chemical Vapor Deposition), and the constituent materials: Carbon doped oxide (SiCOH) matrix and organic porogen. The materials have been deposited as thin film samples and,cured by thermal annealing and UV irradiation for various times. The optical properties of the films have been studied by variable angle spectroscopic ellipsometry in range from 2 eV to 9 eV and the composition has been analyzed by Fourier-transformed infrared spectroscopy. The analysis of the optical response of the porous dielectric as a mixture of matrix material, porogen and voids shows existence of decomposed porogen residuals inside the pores, even for long curing times. It is observed that the variation of deposition and curing conditions can control the amount of porogen residuals and the final porosity.