Silicon-carbon stressors with high substitutional carbon concentration and in situ doping formed in source/drain extensions of n-channel transistors

Abstract

We report the first demonstration of n-channel field-effect transistors (N-FETs) with in situ phosphorus-doped silicon-carbon (SiCP) stressors incorporated in the source/drain extension (SDE) regions. A novel process which formed recessed SDE regions followed by selective epitaxy of SiCP was adopted. High in situ doping contributes to low series resistance to channel resistance ratio and is important for reaping the benefits of strain. Substitutional carbon concentration Csub was varied, showing enhanced drive current with increased Csub for comparable off-state leakage, series resistance, and control of short-channel effects. A record high carbon substitutional concentration Csub of 2.1% was achieved. Use of heavily doped silicon-carbon stressor with large lattice mismatch with respect to Si and placed in close proximity to the channel region in the SDE regions is expected to be important for strain engineering in nanoscale N-FETs. © 2008 IEEE.