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

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.