Effect of interlayer on thermal stability of nickel silicide

The thermal stability of nickel silicide is improved significantly by adding a thin layer of Ir or Co at the Ni/Si interface. The sheet resistance remains low after 850 °C annealing. The thermal stability was evaluated by measuring the junction leakage of an ultra-shallow junction with a 40 nm junction depth. With Ir, the film was stable and the reverse leakage of both N + /P and P + /N junctions remained in the picoampere range at 3 V on 100 μm×100 μm feature after 850 °C annealing. With Co, the leakage from P + /N junctions was low when the temperature was as high as 850 °C; leakage from N + /P junction was in the picoampere range up to 750 °C. These films were characterized by x-ray diffraction. The improved stability and low junction leakage is attributed to a very smooth interface.