Work Function Setting in High-k Metal Gate Devices

Abstract

As transistor size continues to shrink, SiO 2 /polysilicon gate stack has been replaced by high-k/metal gate to enable further scaling. Two different integration approaches have been implemented in high-volume production: gate first and gate last; the latter is also known as replacement gate approach. In both integration schemes, getting the right work functions and threshold voltages for N-type metal-oxide-semiconductor (NMOS) and P-type metal-oxide-semiconductor (PMOS) devices is critical. A number of recent studies have shown that the threshold voltage of devices is highly dependent on not just the deposited material properties but also on subsequent device processing steps. This chapter contains a description on the different mechanisms of work function setting in gate last and gate first technologies, the sensitivities to different process conditions and special measurement techniques for gate stack analysis is shown.