Measurement and analysis of water adsorption in porous silica films

The influence of water adsorption on dielectric constants of the porous silica low-k dielectric films was investigated. The amount of water adsorption inside pores was calculated by a capacitance value, a gas adsorption measurement, the BET (Brunauer, Emmett, and Teller) adsorption theory, and the Kirkwood microscopic theory of water dielectrics. A hexamethyldisilazane (HMDS) vapor treatment was introduced to make porous silica low-k films hydrophobic, and the effect of the HMDS vapor treatment was investigated quantitatively. The BET adsorption at a low partial pressure of water vapor (p/p(0) <= 0.31 for the HMDS-treated film, p/p(0) <= 0.17 for the nontreated film) was investigated by a capacitance value. The results showed that the BET adsorptions of the HMDS-treated and the nontreated films were almost the same. A water cluster formation inside pores, at a high partial pressure of water vapor (p/p(0) > 0.31 for the HMDS-treated film and p/p(0) > 0.17 for the nontreated film), was investigated by a capacitance value and a gas adsorption measurement. The results showed that the HMDS vapor treatment suppressed the water cluster formation, and this suppression could lower the dielectric constant for the porous silica film. (c) 2006 The Electrochemical Society.