Investigation of poly-Si 1-xGe x for dual-gate CMOS technology

Abstract

Poly-Si 1-xGe x-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 ∼20% exhibit the least PDE. Higher active dopant concentration and reduced gate-depletion width for devices featuring less PDE were confirmed. Work function difference (ΦMS) was found to decrease slightly in N + films and significantly in P + films as Ge content increases. The shift in ΦMS for N + poly-Si 1_xGex is negligible while it is -0.13 V for P + Si 0.8Ge 0.2 and -0.32 V for P + Si 0.5Ge 0.5. The reduction in energy bandgap (ΔE 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 ΦMS should be minimized for low and symmetrical V th as well as improved short-channel effect (SCE). A Ge content of ∼20% therefore seems to offer the best tradeoff between SCE and PDE.