Dielectric Properties of Hydrogen Silsesquioxane Films Degraded by Heat and Plasma Treatment

Hydrogen silsesquioxane (HSQ)-type spin-on-glass (SOG) is a very attractive candidate material for intermetal dielectric (IMD) in the semiconductor industry. The low dielectric property of HSQ materials helps to minimize interconnection delay. However, it was found that the chemical structure of HSQ film is damaged and hydrogen inside the film is displaced when treated by a thermal process or plasma-enhanced tetraethyl orthosilicate (PETEOS) capping oxide deposition. As these steps are essential in the integration process of IMD materials, the thermal and chemical stability of HSQ was evaluated. We investigated the dielectric properties of the HSQ/PETEOS bilayer as a function of the deposition sequence and thermal treatment using C – V measurement, refractive index measurement, and Fourier transform infrared (FTIR) spectra. The three polarization components (electronic, ionic, and orientation) of HSQ were identified by a Kramers-Kronig transformation of the IR absorbance. It was found that the polarization induced by the orientation of the permanent dipoles, which is related to the adsorbed water, was the most effective component in affecting the dielectric constant of the damaged HSQ. Also, the PETEOS capping layer was shown to play a role in protecting thermally damaged HSQ against moisture absorption.