Interfacial oxide formation from intrinsic oxygen in W–HfO2 gated silicon field-effect transistors

We report the effects of ultrahigh vacuum and nitrogen annealing on self-aligned W-gated HfO2 n-field-effect transistors. While rapid thermal annealing in a nitrogen ambient significantly improved the channel mobility, there is a corresponding increase in the gate dielectric thickness of up to 20Å. Here we show that this increase is due to the formation of interfacial oxides between the HfO2 and the silicon, caused by the diffusion of oxygen from the W gates. The results point to the importance of oxygen solubility in metals, which may be significant in many candidate gate electrodes.