Silicides for polysilicon TFT-LCD applications

Silicides are proposed for display applications in order to reduce the series and contact resistances of TFTs fabricated on thin polysilicon islands which would otherwise limit the on current of these transistors. The use of two likely candidates, nickel and cobalt silicide was investigated in order to determine their suitability for TFT-LCD applications. Cobalt silicide was formed at the boundary of the thermal budget by requiring annealing at 600 degrees C, but the silicide is stable and does not degrade with further anneals as would occur during an implant anneal after silicidation. Nickel silicide is formed at 400 degrees C but its sheet resistance was observed to degrade when subjected to a 600 degrees C anneal after the silicidation. This problem was partially over come by depositing enough nickel to completely consume the polysilicon contact area during silicidation, though the nickel silicide was still observed to grow in volume during prolonged post silicidation anneals. Comparisons between the relative abilities of cobalt and nickel silicide to act as silicon dioxide etchant stops have been made, and while cobalt silicide films are destroyed during both dry etching in CF4 and wet etching in HF, nicker silicide films demonstrated only a slow degradation. Devices with silicides have been made and their results compared to non-silicided counterparts.