Gate engineering for deep-submicron CMOS transistors

Gate depletion and boron penetration through thin gate oxide place directly opposing requirements on the gate engineering for advanced MOSFET's. In this paper, several important issues of deep-submicron CMOS transistor gate engineering are discussed. First, the impact of gate nitrogen implantation on the performance and reliability of deep-submicron CMOSFET's is investigated. The suppression of boron penetration is confirmed by the SIMS profiles, and is attributed mainly to the diffusion retardation effect in bulk polysilicon by the presence of nitrogen. The MOSFET' I-V characteristics, MOS capacitor quasi-static C-V curves, SIMS profiles, gate sheet resistance, and oxide Q/sub bd/ are compared for different nitrogen implant conditions. A nitrogen dose of 5/spl times/10/sup 15/ cm/sup -2/ is found to be the optimum choice at an implant energy of 40 keV in terms of the overall electrical behavior of CMOSFET's. Under optimum design, gate nitrogen implantation is found to be effective in eliminating boron penetration without degrading performance of either p/sup +/ gate p-MOSFET and n/sup +/ gate n-MOSFET. Secondly, the impact of gate microstructure on the performance of deep-submicron CMOSFET's is discussed by comparing poly and amorphous silicon gate deposition technologies. Thirdly, poly-Si/sub 1-x/Ge/sub x/ is presented as a superior alternative gate material. Higher dopant activation efficiently results in higher active-dopant concentration near the gate/SiO/sub 2/ interface without increasing the gross dopant concentration. This plus the lower annealing temperature suppress the dopant penetration. Phosphorus-implanted poly-Si/sub 1-x/Ge/sub x/ is gate is compared with polysilicon gate in this study.

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