Mobility enhancement of high-k gate stacks through reduced transient charging

We report a high performance NFET with a HfO₂/TiN gate stack showing high field (1 MV/cm) DC mobility of 194 cm²/V-s (80% univ. SiO₂) and peak DC mobility of 239 cm²/V-s at EOT=9.5Å. These mobility results are among the best reported for HfO₂ with sub-10 Å EOT and represent a potential gate dielectric solution for 45 nm CMOS technologies. A 2× mobility improvement was realized by thinning HfO₂ from T_phys=4.0 nm to 2.0 nm. The mechanism for mobility improvement is shown to be reduced transient charge trapping. Issues associated with scaling HfO₂ including film continuity, density and growth incubation are studied with low energy ion scattering (LEIS), X-ray reflectivity (XRR) and Rutherford backscattering (RBS) and indicate atomic layer deposition (ALD) HfO₂ can scale below T_phys= 2.0 nm. While the mobility advancement with 2.0 nm HfO₂ is important, an additional concurrent advancement is improved V_t stability. Constant voltage stress results show ΔV_t improves 2× after 1000s stress at 1.8V as thickness is reduced in the range 2.0-4.0 nm.