Thermal stability of CoSi2 film for CMOS salicide

We describe the relationship between the sheet resistance of Co-silcided po ly-Si and various doping elements. The surface condition of the poly-Si bef ore Co sputtering plays an important role in suppressing the "narrow line e ffect," in which the silicide sheet resistance degrades as the gate length decreases. Si-O and Si-C bonding takes place in the gate poly-Si during RIE processing for gate side-wall formation when there is no CVD SiO2 gate cap . This leads to the sheet resistance degradation of CoSi2 when the gate len gth is reduced. The degradation becomes less severe as the weight of the io ns implanted during gate poly-Si doping increases, because the bonding is i nhibited by heavier ions. The best way to suppress this degradation, howeve r, is to prevent exposure of gate poly-Si surface by implementing a CVD SiO 2 cap during gate side-wall formation. When this is done, the sheet resista nce degradation does not occur even when the gate length is 0.1 mum for all types of implanted ions. We also observed thermal stability of the sheet r esistance up to 1000 degreesC, That can be improved, as well as narrow line effect, by using this cap process, However, the thermal stability of gate oxide TDDB depends on the type of ion implantation. The temperature at whic h degradation of TDDB begins rises as the weight of the implanted ions incr eased, This degradation depends on the grain size, and grains increase in s ize as the weight increases. The highest temperature before the onset of TD DB degradation is seen with in-situ phosphorus-doped nt polysilicon, becaus e the grain size is greatest in this case.