A low dielectric constant material, hydrogen silsesquioxane (FOx-16), can successfully suppress Cu diffusion without barrier metal by using NH3 plasma treatment. After NH3 plasma treatment, the hydrogen silsesquioxane film with lower leakage current and better barrier ability was achieved. This film almost keeps the same dielectric constant after different plasma exposure times. The decrease in leakage current with more exposure time is due to dangling bonds passivated by -H bonds on porous hydrogen silsesquioxane. The better barrier ability is due to a thin nitride film formed on the dielectric.