Improvement of Device Characteristics for TiN Gate p-Type Metal–Insulator–Semiconductor Field-Effect Transistor with Al₂O₃-Capped HfO₂ Dielectrics by Controlling Al₂O₃ Diffusion Annealing Process

We have investigated the effect of postdeposition annealing (PDA) of Al₂O₃-capped HfO₂ films on the flatband voltage (V_fb) shift and threshold voltage (V_t) variation in TiN gate p-type metal–insulator–semiconductor field-effect transistors (pMISFETs). We found that optimizing the PDA conditions to diffuse Al₂O₃ into the HfO₂ films is a key factor for controlling V_fb, and high-temperature PDA immediately after Al₂O₃ deposition induces a positive V_fb shift. Additional V_t variation was observed when the PDA temperatures after Al₂O₃ deposition were 850 and 950 °C. In contrast, a higher temperature PDA at 1050 °C after Al₂O₃ deposition can suppress V_t variation to almost the same level as that obtained in a HfO₂ film without an Al₂O₃-cap layer, although the equivalent oxide thickness (EOT) increases. We also found that superior device characteristics, such as low V_t, suppression of V_t variation, and suppression of EOT increase, were obtained by performing PDA before Al₂O₃ deposition.