The organic silsesquioxane, methylsilsesquioxane (MSQ), exhibits a low dielectric constant because of its lower film density compared with thermal oxide. In this study, boron implantation treatment is investigated in order to improve the quality of MSQ. The small size of boron atoms do not damage the chemical bonding of the MSQ film. In addition, the formation of densified surfaces after boron implantation can reduce the probability of moisture uptake into the MSQ. Therefore, the leakage current of MSQ film is significantly decreased and the low-k properties of MSQ film can be maintained.