Characteristic of Copper Films on Molybdenum Substrate by Addition of Titanium in an Advanced Metallization Process

Mo(Ti) alloy and pure Cu thin films were subsequently deposited on SiO2-coated Si wafers, resulting in Cu/Mo(Ti)/SiO2 structures. The multi -structures have been annealed in vacuum at 100-600 degrees C for 30 min to investigate the outdiffusion of Ti to Cu surface. Annealing at high temperature allowed the outdiffusion of Ti from the Mo(Ti) alloy underlayer to the Cu surface and then forming TiO2 on the surface, which protected the Cu surface against SiH4+NH3 plasma during the deposition of Si3N4 on Cu. The formation of TiO2 layer on the Cu surface was a strong function of annealing temperature and Ti concentration in Mo(Ti) underlayer. Significant outdiffusion of Ti started to occur at 400 degrees C when the Ti concentration in Mo(Ti) alloy was higher than 60 at.%. This resulted in the formation of TiO2/Cu/Mo(Ti) alloy/SiO2 structures. We have employed the as deposited Cu/Mo(Ti) alloy and the 500 degrees C-annealed Cu/Mo(Ti) alloy as gate electrodes to fabricate TFT devices, and then measured the electrical characteristics. The 500 C annealed Cu/Mo(Ti(6 >=)Oat.%) gate electrode TFT showed the excellent electrical characteristics (mobility = 0.488 - 0.505 cm(2)/Vs, on/off ratio = 2X 10(5)-1.85X 10(6), subthreshold = 0.733-1.13 V/decade), indicating that the use of Ti-rich(Ti6Oat.%) alloy underlayer effectively passivated the Cu surface as a result of the formation of TiO2 on the Cu grain boundaries.