Improvement of sheet resistance and gate oxide integrity using phosphorus ion implantation in tungsten polycide gate

An implantation of phosphorus is used in tungsten polycide gate process, an d the effects of implantation on the reduction of resistance and characteri stics of GOI (Gate Oxide Integrity) were investigated. The sheet resistance of gate electrode decreases with increase of phosphorus implant dose and e nergy as increase of grain size. The depletion effects of gate polysilicon at reverse biases were found in unimplanted tungsten polycide gate due to t he out-diffusion of dopant atoms in buffer polysilicon layers during activa tion anneals. However, the depletion effects of gate polysilicon were effec tively suppressed by the implantation of phosphorus. The lifetime of gate o xide was degraded several orders of magnitude for the high-energy implanted samples. Therefore, there is optimum energy for phosphorus implantation in to gate electrode ro Improve the resistance of tungsten polycide gate elect rode and the depletion effects of gate polysilicon. (C) 2000 Elsevier Scien ce Ltd. All rights reserved.