| 摘要 |
PURPOSE: To provide a method which can control the threshold voltage after forming a field effect transistor, and to improve the yield rate of the field effect transistor. CONSTITUTION: In the first process, a field effect transistor 1 having a polysilicon gate 15 is made, and a supplementary impurities 17 are introduced into the upper-layer section 15a of the polysilicon gate 15. In the second process, the supplementary impurities 17b are diffused in the depth direction by applying furnace heat treatment at a specified temperature in the range of 600οC-800 deg.C, or applying a laser beam, and the concentration of impurities in the vicinity of the bottom face 15b of the polysilicon gate 15 is increased to change the value of the threshold voltage of the field effect transistor 1 into a specified value. Hereby, the threshold voltage is controlled by the heat treatment after formation of the field effect transistor.
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