Sub-30 NM abrupt junction formation in strained silicon/silicon-germanium CMOS device

Abstract

In strained Si/Si 1-xGe x MOS devices, the boron and arsenic dopant diffusivities were found to decrease and increase exponentially with the %Ge in the Si 1-xGe x respectively. Thus in comparison with those in bulk Si, this behavior facilitates the control of boron transient diffusion, but at the same time presents a new significant roadblock for ultra-shallow arsenic N + junction formation in strained Si/Si 1-xGe x where use of high %Ge(>20%) for higher electron and hole mobility is desirable. New approaches which use a new co-implant to retard As enhanced diffusion and combination of co-implant and vacancy injection by nitridation to further slow down the boron diffusion have been developed. In particular, these new approaches have created the shallowest and most abrupt P + and N + junction thus far in strained Si/Si 1-xGe x substrate i.e. for boron P + junction, Xj (junction depth)∼ 18 nm, Xjs (junction abruptness) ∼ 3 nm/dec and for arsenic N + junction, Xj ∼ 20 nm & Xjs ∼ 5 nm/dec. In comparison with bulk Si, junction activation is found to be > 10% better for boron and comparable for arsenic dopant. In addition, it was found that the strain in the Si cap has a minimal effect on both the boron and arsenic dopant diffusion.