A VARIABLE-WORK-FUNCTION POLYCRYSTALLINE-SI1-XGEX GATE MATERIAL FOR SUBMICROMETER CMOS TECHNOLOGIES

P+ polycrystalline silicon-germanium (poly-Si1-xGe(x)) is an attractive alternative to polycrystalline silicon (poly-Si) for the gate material in submicrometer CMOS technologies. The work function of P+ poly-Si1-xGe(x) decreases with increasing Ge content, by more than 0.3 V from 0 to 60%. This allows the trade-off between the PMOS and NMOS channel-doping designs to be adjusted by varying the Ge content in a single P+ gate material. PMOS and NMOS surface-channel devices may be simultaneously realized by using this reduced-work-function gate material. Lower gate sheet resistances can be achieved using lighter anneals in a P+ poly-Si1-xGe(x) gate CMOS technology, since significantly lower temperatures are sufficient to activate boron implanted into Si1-xGe(x) films compared to Si films. Poly-Si1-xGe(x) films with Ge mole fractions up to 0.6 were found to be completely compatible with silicon VLSI fabrication processes, and their use as the gate material does not introduce significant additional process complexity.