A method of manufacturing a semiconductor device having a porous, low-k dielectric layer is provided. A preferred embodiment comprises the steps of forming a porogen-containing, low-k dielectric layer, in the damascene process. In preferred embodiments, pore generation, by e-beam porogen degradation, occurs after the steps of CMP planarizing the damascene copper conductor and depositing a semipermeable cap layer. In alternative embodiments, the cap layer consists essentially of silicon carbide, silicon nitride, Co, W, Al, Ta, Ti, Ni, Ru, and combinations thereof. The semipermeable cap layer is preferably deposited under PECVD conditions such that the cap layer is sufficiently permeable to enable removal of porogen degradation by-products. Preferred embodiments further include an in-situ N.sub.2/NH.sub.3 treatment before depositing the semipermeable cap layer.