Investigation of poly-Si1-xGex for dual-gate CMOS technology

Poly-Si1-xGex-gated MOS capacitors were fabricated with x varying from 0 to 0.5. NMOS and PMOS C-V characteristics were measured. Reduced poly-gate depletion effect (PDE) was observed in PMOS devices with increasing Ge mole fraction; while for NMOS, devices with a Ge content similar to 20% exhibit the least PDE. Higher active dopant concentration and reduced gate-depletion width for devices featuring less PDE were confirmed. Work function difference (Phi(MS)) was found to, decrease slightly in N+ films and significantly in P+ films as Ge content increases. The shift in Phi(MS) for N+ poly-Si1-xGex is negligible while it is -0.13 V for P+ Si0.8Ge0.2 and -0.32 V for P+ Si0.5Ge0.5. The reduction in energy bandgap (Delta E-g) was also determined to increase from 0 to 0.26 eV as Ge content increases from 0 to 50%. For deep submicron dual-gate CMOS application, the shift in Phi(MS) should be minimized for low and symmetrical Vth as well as improved short-channel effect (SCE). A Ge content of similar to 20% therefore seems to offer the best tradeoff between SCE and PDE.