20 nm N/sup +/ abrupt junction formation in strained Si/Si/sub 1-x/Ge/sub x/ MOS device

In strained Si/Si/sub 1-x/Ge, NMOS, As dopant diffusivity was found to increase exponentially with %Ge and this becomes a significant roadblock for ultra-shallow As junction formation for high %Ge(>20%). A new approach which uses a co-implant to retard As motion has been developed and is applicable for a range of %Ge (20-75%) and Si cap (5-20 nm). For 20% Ge with 20 nm Si cap, it has created one of the shallowest and most abrupt N/sup +/ junctions thus far; Xj/spl sim/20 nm & Xjs/spl sim/5 nm/dec. Importantly, junction activation is not affected by the new method. In addition, for As diffusion, the strain in the Si cap was found to have a minimal effect.