Scaling limits of hafnium–silicate films for gate-dielectric applications

Abstract

The scaling limits of hafnium–silicate (Hf–silicate) films for use as the gate dielectric material in complementary metal–oxide–semiconductor field-effect transistors are investigated. Scalability is gauged by a figure of merit taken from the analytical model for direct tunneling leakage current. Based on the compositional dependence of this figure of merit, pure HfO2 is more scalable than Hf–silicates. However, the formation of intermediate oxide layers at the Si interface can limit the scalability of HfO2 to ∼1.0 nm equivalent SiO2 thickness (EOT). The use of Si3N4 as a diffusion barrier can prevent the formation of these interfacial layers and thereby yield lower EOT. Alternatively, 20% Hf–silicate may be more scalable than pure HfO2 with interfacial oxide layers.