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

Abstract

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 are scaled down, it becomes necessary to develop new gate dielectric materials 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/cm² and tunnel current increases significantly. Therefore, materials are needed to provide excellent electrical characteristics such as dielectric constant higher than 30, interface-state-density less than 1 × 10¹¹/cm²-eV, tunneling current less than 10 mA/cm², and negligible hysteresis. Many high dielectric constant materials have been reported that could potentially replace SiO₂. These include SiO_xN_y, Ta₂O₅, TiO₂, Y₂O₃, CeO₂, SrTiO₃, Al₂O₃, La₂O₃, and silicates of hafnium and zirconium. These materials exhibit the desired high dielectric constants for applications as gate dielectrics in sub-100 nm silicon technology. However, detailed studies need to be performed to evaluate the compatibility of these materials with the rest of the silicon integrated-circuit manufacturing processes.