Ultra Low-k Materials: Challenges of Scaling

High porosity and carbon doing are required to achieve low dielectric constant, k values for ultra low-k (ULK) materials based on silicon dioxide. Those characteristics create new challenges in the integration of ULK materials that are being developed for future interconnect scaling. Four of those challenges based on electrical characterizations of ULK films will be presented in this paper. First, a high concentration of porogen residue is typically present in ULK materials fabricated by Plasma Enhanced Chemical Vapor Deposition (PECVD). The high porogen residue concentration leads to a high leakage current density. Second, ULK materials based on Spin-on Glass (SOG) process demonstrate a low leakage current density. But early dielectric breakdown has been observed in SOG k=2.2 material. Third, PVD TaNTa barrier process can introduce significant damage to ULK materials. The damage level increases as the k value decreases or porosity increases. Four, direct deposition of ALD Ru barrier on ULK films results in a high leakage current density.