20 nm N ⁺ abrupt junction formation in Strained Si/Si _1-xGe _x MOS device

Abstract

In strained Si/Si 1-xGe x 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 + junction thus far; Xj ∼ 20nm & 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.