Cobalt CMP Development for 7nm Logic Device

This study presented the advancement of cobalt CMP development for 7nm logic device at GLOBALFOUNDRIES. Two-step CMP process was developed. Overburden cobalt was removed and polishing stopped on the liner via endpoint detection during the bulk CMP. Bulk CMP was followed by buff CMP, where the liner and a certain amount of ILD films were removed. At first, the effect of polish pressure on blanket cobalt removal rate was investigated during bulk CMP. Results showed the Prestonial relationship. Results also showed that bulk CMP had wide over polish time window due to good stop ability of the bulk slurry on the liner. During buff CMP, removal rate selectivity between cobalt, liner, and ILD films were studied and compared for different types of slurries. Higher liner removal rate and lower cobalt/ILD rate could be achieved by slurry screening. Finally, the cleaning solution was also evaluated. Defects post cobalt CMP are comparable to tungsten CMP.