Metal Gate Electrodes

Metal gate electrodes are a vital enabler for the use of high-k gate dielectrics in advanced complimentary metal oxide semiconductor (CMOS) technology. This chapter will detail how metal gate electrodes were selected over poly-Si electrodes to be used in conjunction with high-k gate dielectrics, how metal gate electrodes are an important component of device scaling, and how the of the metal gate can be tuned to optimize the device performance. In this chapter you will see how the properties of the metal gate are inseparable from those of the high-k gate dielectric and how the metal gate can be manipulated to intentionally influence the properties of the dielectric material to produce a desired device response. This chapter will discuss the different ways in which metal gates can be used to change the effective work function of a MOS transistor, including the vacuum work function, dielectric/metal capping layers, and oxygen vacancy manipulation. In each of these cases there is a clear interplay between the metal gate and the gate dielectric and it is important to understand both materials systems in order to understand the device response. Finally, this chapter will detail the common approaches of integrating metal gate electrodes in a complimentary metal oxide semiconductor. Because there are various methods of modulating the effective work functions by using metal gate electrodes, there are multiple integration schemes that have been devised in order to produce optimized nMOS and pMOS transistors.