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

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 similar to1.0 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. (C) 2003 American Institute of Physics.