Lanthanoid implantation for effective work function control in NMOS high-k/metal gate stacks

Effective work function instability of high-K/metal gate MOS stacks after high temperature treatment results in device threshold voltage shifts and is one of the problems associated with the gate-first integration of high-K dielectrics in the CMOS process flow. The exact reason for this instability is subject of intense debate. In this paper it is shown that a positive threshold voltage shift due to thermal treatment can be compensated by implanting the lanthanoids lanthanum or dysprosium into the high-K stack.