| 摘要 |
PURPOSE:To obtain a MIS transistor having excellent breakdown strength which is unaffected by a highly concentrated diffusion layer by forming a highly concentrated impurity diffusion layer to be used to compensate for ohmic contact through a polycrystalline semiconductor film located on source and drain diffusion layers. CONSTITUTION:A polycrystalline semiconductor film which is in contact with respective source and drain diffusion layers of a MIS transistor is formed and an impurity region for forming applications of ohmic contact having an impurity concentration which is thicker than those of the source and drain diffusion layers is selectively formed. For example, compensating diffusion layers 17 and 18 which make the contact of source and drain ohmic are formed through the second polysilicon films 15 and 16. Then, no diffusion layers 17 and 18 are formed to have depths which are deeper than those of the source and drain diffusion layers having a low concentration of impurities so as to keep breakdown strength to a high degree. As a result, a MOS transistor having excellent breakdown strength can be set univocally by the impurity concentration for forming applications of source and drain.
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