IMPACT OF NITROGEN (N-2(-STABILITY OF COBALT SILICIDE FORMED ON POLYSILICON GATE()) IMPLANTATION INTO POLYSILICON GATE ON THERMAL)

A novel process which uses N-2(+) implantation into polysilicon gates to suppress the agglomeration of CoSi2 in polycide gated MOS devices i s presented, The thermal stability of CoSi2/polysilicon stacked layers can be dramatically improved by using N-2(+) implantation into polysi licon, The sheet resistance of the samples without N-2(+) implantation starts to increase after 875 degrees C RTA for 30 s, while the sheet resistance of CoSi2 film is not increased at all after 950 and 1000 de grees C RTA for 30 s if the dose of nitrogen is increased up to 2X10(1 5) cm(-2) and 6X10(15) cm(-2), respectively, and TEM photographs show that the agglomeration of CoSi2 film is completely suppressed. It is f ound that the transformation to CoSi2 from CoSi is impeded by N-2(+) i mplantation such that the grain size of CoSi2 with N-2(+) implantation is much smaller than that without N-2(+) implantation, As a result, t he thermal stability of CoSi2 is significantly improved by Na implanta tion into polysilicon.