Highly conductive composite polysilicon gate for CMOS integrated circuits

摘要

Many integrated circuits include a type of transistor known as a metal-oxide-semiconductor, field-effect transistor, or “mosfet,” which has an insulated gate member that controls its operation. Early mosfets had aluminum gates. But because the aluminum made the mosfets unreliable and difficult to manufacture, aluminum was abandoned in favor of polysilicon. Unfortunately, polysilicon has ten-times more electrical resistance than aluminum, which not only wastes power but also slows operation of the integrated circuits. Several efforts have been made to use materials less-resistive than polysilicon, but these have failed to yield a practical solution, since some of the materials have high electrical resistance and prevent low-voltage operation. Accordingly, one embodiment of the invention provides a gate structure that includes a doped polysilicon layer to facilitate low-voltage operation, a diffusion barrier to improve reliability, and a low-resistance aluminum, gold, or silver member to reduce gate resistance. Moreover, to overcome previous manufacturing difficulties, the inventors employ a metal-substitution fabrication technique, which entails formation of a polysilicon gate, and then substitution of metal for the polysilicon.