Effective Channel Length Shortening and Mobility Increase of p-Channel Metal Oxide Semiconductor Transistors Resulting in Higher Drive Current Using Short Source–Drain Diffusion Length

Abstract

Local lattice strain around the channel in metal oxide semiconductor (MOS) transistors of 0.13 µm gate length using shallow trench isolation can be altered using different source–drain diffusion lengths (Lov). It is known that as Lov is reduced, the drive current of p-channel metal oxide semiconductor (PMOS) transistors can be increased due to stress-enhanced hole mobility. However, in this study, we found that as Lov is reduced below 0.62 µm, the effective channel length (Leff) of the PMOS transistors is also reduced. This unexpected Leff shortening effect for very small Lov has instead led to a reduction of µeff, as shown through our calculations. We thus propose that the drive current increase for Lov reduction is due to stress-enhanced hole mobility for larger Lov and that the Leff shortening due to stress-enhanced diffusion is the secondary and the more dominating mechanism for Lov values below 0.62 µm.