TaN/Ta bilayer barrier characteristics and integration for 90 and 65nm nodes

In the development of damascene copper interconnects for the 90 and 65 nm technology nodes, several diffusion barriers were considered. Among barrier films a TaN/Ta bilayer is preferred because of its excellent adhesion to dielectrics and good barrier properties. In a typical process, the bilayer deposition includes four steps: TaN deposition, target reconditioning, Ta deposition, and resputtering. In this study, we define critical process parameters and characterize thin barriers for improved effective line and via resistance. Results on blanket wafers indicate that the TaN deposition time directly influences barrier thickness while the Ta deposition time mainly influences sheet resistance and the full bilayer stack. Additionally, decreasing DC power and deposition time does not induce any change on Ta; however, TaN films are influenced by DC power and deposition as shown by XRD. Critical parameters influencing the 90 nm technology performance include deposition time of TaN and Ta. Gas flows or bias resputtering show no significant impact on sheet resistance or film properties within the scope of this study. Experiments on 65 nm node highlight the role played by the tantalum deposition on the via chain yield. These results presented in this paper clarify the role of individual process steps during the barrier deposition.