20 nm N+ abrupt junction formation in strained Si/Si_1-xGe_x MOS device

摘要

In strained Si/Si_1-xGe, 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+ junctions thus far; Xj∼20 nm & Xjs∼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.