The effect of surfactant in a cleaning chemical solution on two types of porous low dielectric constant (low-k) materials was investigated. For the microporous film (mean pore diameter <= 2 nm), the material properties are not affected by the presence of surfactant, polyoxyethylene octyl phenyl ether. On the contrary, for mesoporous material where the mean pore size is in the order of 3 nm, a substantial change in optical properties of the film was recorded. Spectroscopic ellipsometry, ellipsometric porosimetry, Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy data point to the incorporation of surfactant molecules into the bulk. An alternative way to reduce the surface tension of the solution without compromising the initial properties of low-k consists of using isopropyl alcohol as an additive. The material properties remained unchanged after wet treatment. The results also indicate that the properties of porous film, which had been contaminated/degraded by the presence of the surfactant inside of the pores, can be recovered by using an alcohol-containing aqueous solution or pure alcohol such as isopropyl alcohol. (c) 2006 The Electrochemical Society.