Recent advances and current challenges in the search for high mobility band-edge high-k/metal gate stacks

Abstract

Continued miniaturization of the different physical elements of a Si MOSFET required in order to attain higher transistor performance and greater economies of scale have spurred the need for significant materials innovations. This is most apparent in the search for the ideal high-k/Metal Gate stack that would replace conventional SiON/Poly-Si gate stacks. In this paper, we will review some of the recent advances and remaining challenges for high-k/Metal Gate stacks. It is shown that significant progress has been made towards improving electron mobility in HfO2/Metal Gate stacks by a combination of high temperature processes, nitrogen free interfaces and optimized metal deposition processes which result in mobility values competitive with SiON/Poly-Si. In addition by inserting nanoscale layers that comprise strongly electropositive gp. IIA and IIIB elements in between the HfO2and metal electrode stack have resulted in high mobility, band-edge aggressively scaled High-k/Metal Gate stacks. While much progress has been made with nMOSFET stacks, it will also be shown that a number of roadblocks remain with obtaining a similar solution for pMOSFET stacks, primarily due to the presence of thermally activated oxygen vacancies that induce large negative threshold voltage shifts towards midgap in HfO2/high workfunction metal stacks. © 2007 Elsevier B.V. All rights reserved.