Instability of Metal Barrier with Porous Methyl Silsesquioxane Films

Abstract

Integration of porous ultralow-κ dielectrics into advanced copper interconnect scheme has been a challenge. Among other issues, metal diffusion/drift into interconnected pores consequently leading to the degradation of dielectrics is a concern. In the present work, the electrical stability of the metal-insulator-semiconductor (MIS) capacitors with various metal electrodes on porous methyl silsesquioxane (MSQ) on thermal oxide/n-type silicon was investigated. Our results suggest that the tendency of various metal, , drift into porous MSQ under bias-temperature stress (BTS) corresponds to the order of metal oxidation tendency at the interface. It is noted that the metal barrier materials such as Ta and Ru perform worse than Cu itself. This behavior is similar to metal drift in organosiloxane polymer reported earlier [Appl. Phys. Lett., 79, 1855 (2001)]. Furthermore, as-prepared MIS capacitors with Cu electrodes show stable capacitance-voltage characteristics under a moderate BTS of and . Under the same BTS, a deterioration of the MIS capacitors with increasing exposure time in air is observed. The electrical stability is fully restored after being annealed at an elevated temperature of in a reducing ambient. The degradation of the MIS capacitors over time is attributed to the permeation of oxygen and moisture through interconnected pores, which consequently facilitate the formation of interfacial Cu oxide. The electrical stability of MIS capacitors with Ta electrodes however does not exhibit improvement by such annealing because of their greater heat of oxide formation. The MIS capacitors with Al electrodes on -plasma treated porous MSQ show less metal drift than Al on porous MSQ, suggesting that the intrinsic property of metal oxide determines whether the oxygen contained in the dielectrics assists or inhibits the metal-related activities.