The interaction between copper interconnects and low-k hydrogen silsesquioxane (HSQ) film was investigated using a Cu/HSQ/Si metal insulation semiconductor capacitor and deuterium plasma post-treatment. Owing to serious diffusion of copper atoms in HSQ film, the degradations of dielectric properties are significant with the increase of thermal stress. By applying deuterium plasma treatment to HSQ film, however, this degradation was alleviated. In addition, the phenomena of serious Cu penetration were not observed by means of electrical characteristic measurements and secondary ion mass spectroscopy (SIMS) analysis, even in the absence of diffusion barrier layers. This indicates that copper diffusion in low-k HSQ film can be effectively blocked by deuterium plasma post-treatment. Therefore, further improvement in RC reduction can be obtained due to the minimized thickness requirement for conventional barriers such as inorganic Si3N4 and metallic TaN layers.