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

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We have investigated the effect of postdeposition annealing (PDA) of Al2O3-capped HfO2 films on the flatband voltage ($V_{\text{fb}}$) shift and threshold voltage ($V_{\text{t}}$) 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 $V_{\text{fb}}$, and high-temperature PDA immediately after Al2O3 deposition induces a positive $V_{\text{fb}}$ shift. Additional $V_{\text{t}}$ 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 $V_{\text{t}}$ 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 $V_{\text{t}}$, suppression of $V_{\text{t}}$ variation, and suppression of EOT increase, were obtained by performing PDA before Al2O3 deposition.
2009-04-25