Investigation of the band offsets caused by thin Al₂O₃ layers in HfO₂ based Si metal oxide semiconductor devices

Ultrathin dielectric capping layers are a prominent route for threshold voltage control in advanced Si devices. In this work the position of an Al₂O₃ layer inside a HfO₂-based stack is systematically varied and investigated following a low and a high temperature anneal. Electrical results are compared with a sub-nanometer resolution materials characterization, showing a diffusion of Al to the bottom HfO₂ interface. A correlation is found between the presence of Al at the bottom interface and a flatband voltage increase. Based on these findings, we propose to use the position of the Al₂O₃ for fine-tuning the threshold voltage.