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Impact of nitrogen (N2+) implantation into polysilicon gate on thermal stability of cobalt silicide formed on polysilicon gate

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4 Author(s)
Wein-Town Sun ; Dept. of Electr. Eng., Nat. Tsing Hua Univ., Hsinchu, Taiwan ; Ming-Chi Liaw ; Kuang-Chien Hsieh ; Charles Ching-Hsiang Hsu

A novel process which uses N2+ implantation into polysilicon gates to suppress the agglomeration of CoSi2 in polycide gated MOS devices is presented. The thermal stability of CoSi2/polysilicon stacked layers can be dramatically improved by using N2+ implantation into polysilicon. The sheet resistance of the samples without N2+ implantation starts to increase after 875°C RTA for 30 s, while the sheet resistance of CoSi2 film is not increased at all after 950 and 1000°C RTA for 30 s if the dose of nitrogen is increased up to 2×1015 cm-2 and 6×1015 cm2, respectively, and TEM photographs show that the agglomeration of CoSi2 film is completely suppressed. It is found that the transformation to CoSi2 from CoSi is impeded by N2+ implantation such that the grain size of CoSi2 with N2+ implantation is much smaller than that without N2+ implantation. As a result, the thermal stability of CoSi2 is significantly improved by N2+ implantation into polysilicon

Published in:

IEEE Transactions on Electron Devices  (Volume:45 ,  Issue: 9 )