Controlled cobalt recess for advanced interconnect metallization

We have developed a wet chemical etch process for the controlled recess of cobalt metal based on 'digital etching'. Digital etching is a cyclic process wherein each process cycle comprises an oxidation and oxide dissolution step. Due to the self-limiting cobalt oxide thickness, the total recess amount is tuned based on the total number of cycles. This results in nanometer control of the total recess amount as well as excellent within-wafer uniformity. We also evaluated the effect of different oxidation and oxide-dissolution solutions on the cobalt etch amount. Furthermore, the TiN barrier was successfully removed with commodity chemistries without attacking the previously recessed cobalt. This combined process is then used for 10 nm recess of cobalt for the fully self-aligned via (FSAV) advanced interconnect scaling booster. To conclude, we proof the effectiveness of this method by measuring the resistivity of recessed cobalt interconnect lines down to 21 nm.