| 摘要 |
PROBLEM TO BE SOLVED: To raise the uniformity of the concentration of impurities for setting the thresold voltages of MIS transistors constituting a DRAM in the surface of a semiconductor substrate, by a method wherein, after a polysilicon film for gate electrode formation is deposited on the semiconductor substrate, the impurities for setting the threshold voltages are introduced in the substrate. SOLUTION: A polysilicon film 34 is deposited on a semiconductor substrate 1 by a CVD method or the like. Subsequently, impurities for adjusting the threshold voltages of N-channel MOSFETs in a peripheral circuit region are introduced in the substrate 1. That is, after such a photoresist 32c as an N-channel MOSFET formation region is exposed is formed on the film 34, boron of P-type impurities, for example, is ion-implanted in the substrate 1 using this photoresist 32c as a mask via the film 34 and a gate insulating film 8i. As a result, the concentration distribution of the impurities in the surface of the substrate 1 can be uniformized and a setting accuracy of the threshold voltages of the MOSFETs Q for memory cell selection, other MOSFETs Qn and Qp and the like can be enhanced. |
