EFFECTS OF COSI2 ON P(+) POLYSILICON GATES FABRICATED BY BF2+ IMPLANTATION INTO COSI AMORPHOUS SI BILAYERS

The integrity of thin gate oxide structures fabricated by implanting B F2+ ions into bilayered CoSi/amorphous silicon films and subsequent an nealing has been studied as a function of cobalt silicide thickness an d implantation energy. Significant degradation of gate oxide integrity and flatband voltage shifts were found with increasing cobalt silicid e thickness and annealing temperature. It is shown that although thinn er cobalt silicide can result in excellent gate dielectric integrity i t also leads to worse thermal stability at a high annealing temperatur e. Moreover, shallower implantation depth and lower annealing temperat ure can reduce the boron penetration, but depletion effects in polycry stalline silicon gates are caused accordingly. Hence, appropriate proc ess conditions, involving trade-offs among CoSi2 thickness, implantati on energy and annealing temperature, must be used to optimize the devi ce performance while retaining the thin dielectric reliability.