Group IVB oxides as high permittivity gate insulators

Increasing MOSFET performance requires scaling, the systematic reduction in device dimensions. Tunneling leakage, however, provides an absolute scaling limit for SiO₂ of about 1.5 nm. Power limitations and device reliability are likely to pose softer limits slightly above 2 nm. We have investigated the use of high permittivity materials such as TiO₂, ZrO₂, and their silicates as potential replacements for SiO₂. We have synthesized titanium nitrate (Ti(NO₃)₄ or TN), zirconium nitrate (Zr(NO₃)₄ or ZrN), and hafnium nitrate (Hf(NO₃)₄ or HfN) as hydrogen and carbon free deposition precursors. Several problems arise in the use of these films including the formation of an amorphous low permittivity interfacial layer. For TiO₂ this layer is formed by silicon up diffusion. Surface nitridation retards the formation of the interfacial layer. We discuss the effects of both thermal and remote plasma surface nitridation treatments on the properties of the film stack. ZrO₂ and HfO₂ appear to form a thermal layer of silicon oxide between the high permittivity film and the silicon and have excess oxygen in the bulk of the film.