Sub-30 nm P⁺ abrupt junction formation in strained Si/Si_1-xGe_x MOS device

Abstract

For junction formation in strained Si on relaxed Si1-xGex substrates with x=15-30%, shallower and more abrupt boron P+ extension junction is achieved as the %Ge in the relaxed Si1-xGex is increased. At x=30%, a factor of 2 improvement in both junction depth Xj and abruptness Xjs is achieved over that formed in bulk Si. Further reduction in Xj and Xjs were achieved by vacancy injection during RTA anneal with NH3 ambient. However, this approach was found effective only for Ge concentration below 30% above which the boron diffusion mechanism apparently changes over from interstitial to vacancy. With 6 nm Si cap on 30 % Si1-xGex layer, it creates one of the shallowest and most abrupt boron junction yet achieved with RTA ; Xj=23 nm and Xjs ∼ 4.5 nm/dec. Better boron junction activation (>10%) is also achieved in strained Si/Si1-xGex layer than in bulk Si.