Thickness and material dependence of capping layers on flatband voltage (V-FB) and equivalent oxide thickness (EOT) with high-k gate dielectric/metal gate stack for gate-first process applications

Abstract

We investigated controllability and scalability of flatband voltage (V-FB) and equivalent oxide thickness (EOT) using various thin capping films such as single layers (Hf, La, Ti, Al, Ta) and mixed layers (Hf/Ti, Al/Ti, Ta/Ti) with high-k gate dielectric/metal gate stack for gate-first process. With increasing thickness, negative V-FB shift observed with Hf and La while Ti and Al provided positive shift in conjunction with EOT scaling down to 0.6 nm simultaneously. Ti-based mixed cap layers showed both positive V-FB shift and EOT scaling with increasing thickness and higher Ti ratio. Al cap exhibited turn-around effect in V-FB shift behaviors beyond 0.7 nm thickness, which is attributed to strong scavenging interfacial layer rather than dipole formation. Based on V-FB modulation and EOT scaling, we propose novel process integration scheme for the gate first CMOS by adjusting Al composition in TiAlN single metal gate.