A Comparative Study of n+/p Junction Formation for Deep Submicron Elevated Source/Drain Metal Oxide Semiconductor Field Effect Transistors

Ultrashallow elevated n'/p junctions (∼75 nm) incorporating selectively deposited epitaxial silicon layers were fabricated. The undoped epi layers (∼100 nm) were deposited on exposed diffusion areas in an Advanced Semiconductor Material Epsilon I system specifically designed for low thermal budget single-wafer processing. Shallow junctions (∼75 nm) were formed by ion implantation (As, 4 x 10 15 /cm 2 , 80 keV) into undoped epi layers and out-diffusion into the underlying substrate. Alternatively, an ion implanted (As, 4 x 10 15 /cm 2 , 60 keV) elevated layer was utilized to contact a shallow junction, which was formed (As, 1.5 x 10 15 /cm 2 , 15 keV) before the epi deposition. All junctions were annealed at 950°C for 10 s. Nonsilicided elevated junctions and conventional nonelevated (As, 1.5 x 10 15 /cm 2 , 15 keV) ones displayed very similar junction characteristics. Silicided nonelevated ultrashallow junctions, however, showed large reverse leakage current due to the substrate consumption. Both silicided elevated (post-epi and pre-epi) junctions exhibited excellent forward characteristics and low reverse leakage current. The difference in the reverse leakage characteristics of these two elevated junctions was attributed to the epi faceting formed at the sidewall edge of localized oxidation of silicon isolation. Deep submicron n = channel metal oxide semiconductor field effect transistors incorporating these junctions were also fabricated and electrically tested. Both elevated source/drain (S/D) devices show superior current driving capability compared to nonelevated ones as a result of much reduced parasitic resistance from contact source/drain junctions.