The degradation of a low-k material surface during the exposure to plasma etching is one of the most serious problems to be solved for the realization of high speed semiconductor devices. In this study, the factors causing the degradation of a low-k material surface during the etching using fluorine-based plasma etching have been investigated by using XPS. As the plasma factors, active radicals, bombardment energy, and charge of the ions were considered and, as the low-k material, methyl silsesquioxane (MSQ) has been used. The XPS results showed that the ion bombardment during the plasma etching of MSQ affects the breaking of MSQ bone structure by changing the Si-O bonds and Si-C bonds to Si-F mostly, while fluorine-based radicals in the plasma mostly affect the change of Si-CH3 bonds to Si-CH(x)F(y). By removing the charge of the ions during the bombardment, the MSQ properties were further improved. When F intensity which is related to the damage of the MSQ surface is estimated, the bombardment energy, reactive radical density, and charge of the ions were responsible for -18%, -53%, -19% of the F intensity in the MSQ. Therefore, by using the neutral beam etching instead of a conventional ICP etching, the degradation on the MSQ surface estimated by the F intensity remaining on the MSQ surface could be decreased to 10%.