Integration of nickel silicide: minimizing defect generation during formation

Nickel silicide is becoming the choice for sub 90 nm technology and is being utilized for emerging metal gate technologies. [(F.F.Zhao et al., 2004)(Z.Krivokapic et al., 2002]. During the formation processes, the diffusion of Ni in conjunction with the phase transition needs to be controlled to minimize defect formation as such defects contribute to current leakage within devices. It is shown that the initial heating rate of the wafer produces a variety of reactions that can result in defects. Through control of the heating rate during the formation process, such defects can be minimized as detected by measuring leakage current versus annealing temperature ramp rate. Ttie initial heating cycle diffuses the Ni to form Ni₂Si which is controlled through the heating ramp. A second anneal at higher temperature transforms Ni₂Si into the low resistivity NiSi with the availability of Ni controlled through the first cycle. If too much Ni is available, Ni may cluster leading to the formation of leakage current centers. Other defects attributed to excess silicidation are also controlled through timely application of heat. Similar control is also required for dopant depletion that occurs during silicidation. Understanding these multiple mechanisms that can generate defects has led to optimizing the silicidation process