Advances in high-k dielectric gate materials for future ULSI devices

This article discusses recent developments in high dielectric constant gate insulator materials for future ultra-large-scale integration devices below 100 nm. Since conventional gate oxide poses problems as device features ar e scaled down, it becomes necessary to develop new gate dielectric material s with properties similar to SiO2 and compatible with current complementary metal-oxide semiconductor technology. As the thickness of silicon dioxide approaches less than 1.5 nm, the leakage current becomes higher than 1 A/cm (2) and tunnel current increases significantly. Therefore, materials are ne eded to provide excellent electrical characteristics such as dielectric con stant higher than 30, interface-state-density less than 1 x 10(11)/ cm(2)-e V, tunneling current less than 10 mA/cm(2), and negligible hysteresis. Many high dielectric constant materials have been reported that could potential ly replace SiO2 These include SiOxNy Ta2O5, TiO2, Y2O3, CeO2, SrTiO3, Al2O3 , La2O3, and silicates of hafnium and zirconium. These materials exhibit th e desired high dielectric constants for applications as gate dielectrics in sub-100 nm silicon technology. However, detailed studies need to he perfor med to evaluate the compatibility of these materials with the rest of the s ilicon integrated-circuit manufacturing processes.