Parasitic Resistance Considerations of Using Elevated Source/Drain Technology for Deep Submicron Metal Oxide Semiconductor Field Effect Transistors

Abstract

Device drive current, parasitic resistance, and junction leakage current have been studied using silicided and non‐silicided deep submicron elevated source/drain (ESD) n‐channel metal oxide semiconductor field effect transistors (NMOSFETs). This study illustrated the effects of doping profile in the elevated S/D region, junction depth in the substrate, and doping level in the source/drain extension. Compared to devices having nonelevated junctions with the same substrate doping profile, MOSFETs with a profile‐doped elevated S/D, used to contact an ultrashallow junction formed before selective epitaxial growth, had higher drive currents and demonstrated the ability of the elevated junction to reduce the extrinsic resistance. Measurements of drive currents in ESD devices showed that (i) the lightly doped region at the bottom of a profile‐doped elevated layer introduces additional extrinsic resistance, and (ii) the locally deeper junction beneath the epi facets extends laterally toward the channel and shortens the drain extension length, thereby reducing the intrinsic resistance. Silicided devices had higher drive current and reduced parasitic resistance when the silicide/silicon interfacial dopant concentrations remained high (>1 × 1020/cm3) after silicidation. The lowest total parasitic resistance was achieved when the elevated S/D was used to give a small contact resistance to a shallow junction and a moderately doped drain extension was used to lower the resistance of the source/drain extension tab.