Dependence of Sheet Resistance of CoSi2with Gate Length of 30 nm on Thickness of Titanium Nitride Capping Layer in Co-Salicide Process

Since the distribution of gate resistance using cobalt silicide (CoSi2) increases markedly for gate lengths of 30 nm or less, CoSi2 is now being replaced by NiSi. However, CoSi2 still has the advantages of a high thermal stability and a low degree of roughness at the interface between the silicide and silicon layers owing to the low degree of mismatch (1.2%) of between their lattice constants. We have achieved excellent sheet resistance (Rs) with a gate length Lg=30 nm by optimizing the thickness of a cobalt capping layer of titanium nitride. The results shows an abnormal Rs behavior, in which one σ of Rs increases with capping layer thickness in the range of 10–50 nm, while it decreases with increasing capping layer thickness in the range of 0–10 nm. Unlike the results of a previous report [K. Goto et al.: IEDM Tech. Dig., 1995, p. 449], the variation in the Rs with a gate length Lg=30 nm is small, even without a TiN capping layer thickness down to 5–10 nm. We suggest that the uniformity of Rs is determined by the thickness of the CoSi layer after selective etching and the titanium concentration in the CoSi layer for capping TiN thicknesses of 10–50 nm, while the uniformity is determined by the titanium concentration and the damage sustained during selective etching for TiN thickness of 0–10 nm. For this optimization, CoSi2 is applicable to the 65 nm node technology node or beyond.