Laminated metal gate electrode with tunable work function for advanced CMOS

This paper presents a novel technique for tuning the work function of metal gate electrodes. Laminated metal gate electrodes consisting of 1∼3 ultra thin (∼10 Å) layers of Ta, TaN, Ti, TiN, Hf or HfN and bulk metal nitride gate electrodes were deposited on SiO₂, HfO₂ or HfON, followed by RTP annealing to evaluate their thermal stability. Our results show that the work function of the laminated metal gate electrodes is significantly different from their bulk electrodes counterpart. Through lamination, a TiTaN_x alloy gate is formed which exhibits NMOS compatible work function (4.35 eV) with good thermal stability up to 900°C. Laminated metal gates consisting of 3 components exhibit pMOS compatible work function (5,0∼5.2 eV) after 1000°C annealing and this value remains unchanged after subsequent thermal processing. Possible mechanism responsible for work function tuning using laminated gates is discussed.