Thermally robust HfN metal as a promising gate electrode for advanced MOS device applications

Abstract

A systematic study of thermally robust HfN metal gate on conventional SiO2 and HfO2 high-κ dielectrics for advanced CMOS applications is presented. Both HfN-SiO2 and HfN-HfO2 gate stacks demonstrates robust resistance against high-temperature rapid thermal annealing (RTA) treatments (up to 1000°C), in terms of thermal stability of equivalent oxide thickness (EOT), work function, and leakage current. This excellent property is attributed to the superior oxygen diffusion barrier of HfN as well as the chemical stability of HfN-HfO2 and HfN-SiO2 interfaces. For both gate dielectrics, HfN metal shows an effective mid-gap work function. Furthermore, the EOT of HfN-HfO2 gate stack has been successfully scaled down to less than 10 Å with excellent leakage, boron penetration immunity, and long-term reliability even after 1000°C annealing, without using surface nitridation prior to HfO2 deposition. As a result, the mobility is improved significantly in MOSFETs with HfN-HfO2 gate stack. These results suggest that HfN metal electrode is an ideal candidate for ultrathin body fully depleted silicon-on-insulator (SOI) and symmetric double-gate MOS devices.