Porous silica xerogel processing and integration for ULSI applications

With a tunable ultra low dielectric constant, porous silica xerogel is an attractive dielectric material for ULSI interconnect applications and is potentially extendable to multiple future technology nodes. Porous silica xerogel films have been processed and integrated into device test structures as ultra low k intermetal dielectrics. A fully automated thin film deposition process is recently developed and gives high throughput and good repeatability. A surface modification technique is used to make the films hydrophobic. The film dielectric constant is measured to be less than 2, depending on porosity. Because of the small pore sizes, the films display high dielectric break down strength. With proper shrinkage control, porous silica xerogel shows excellent gapfill capabilities. Integration of the porous silica xerogel material into CMP planarized double level metal (DLM) test structures with both Al and W plugs in a gapfill scheme is successful. Porous silica xerogel structures provide 14% and 35% total capacitance reduction compared to structures with hydrogen silsesquioxane (HSQ) and high density plasma (HDP) oxide respectively. Reliability and current leakage data of porous silica xerogel are comparable to that of HSQ. Feasibility of integrating porous silica xerogel into Cu damascene structures is also demonstrated. Cu/xerogel damascene structures exhibit improvements in both resistance and capacitance compared with convention Al/Oxide gapfill structures.