Effect of annealing on the gate effective work-function modulation for the Al/TiN/SiO<inf>2</inf>/P-Si structure

Abstract

In our work, we investigate the effective work function (EWF) modulation of the metal gate about the Al/TiN/SiO2/p-Si structure through the thermal annealing. Through different annealing temperature and different annealing time, we find the EWF of gate electrode shifts from 4.73 eV (suitable for PMOS) to 4.18 eV (suitable for NMOS). We think the diffusion of Al to the interface and the variation of the thin TiN film characteristic are responsible for the decrease of the EWF. BACKGROUNDWith the aggressive downscaling of complementary metal oxide semiconductor (CMOS) transistor, metal gate electrodes are required for 45nm node CMOS devices [1] to replace the conventional doped poly-Si gate electrodes due to the issues such as poly-Si depletion effect, boron penetration, Fermi level pinning with high-k gate dielectric [2] etc.. In order to satisfy the requirements of high performance devices, a series of research is intensively going along. Some requirements on the new metal gate material must be fulfilled, for instance, process integration with the traditional CMOS process flow, material compatibility, suitable work function (4.05 eV for NMOS, 5.17 eV for PMOS) etc.. TiN is widely studied because of its chemical inertness, tunable work function etc.. For the sake of using TiN as gate material simultaneously to NMOS and PMOS, we need to search some methods tuning the effective work function (EWF) of gate electrode. It is widely known that the EWF of the metal gate stack not only depends on the work function of the bulk metal but also on the interfacial properties between the metal electrode and the dielectric underneath. The impurity piled up at interface is considered to be a very effective way for the EWF modulation. Impurities could be introduced to the interface by means of annealing. The EWF modulation by annealing is fully compatible with the conventional CMOS flow. Further more, rapid thermal annealing (RTA) won't introduce interface damage and traps as ion implantation.In this work, our focus is on the EWF modulation of the metal gate about the Al/TiN/SiO2/p-Si structure through the