| 摘要 |
PURPOSE:To form a device whose threshold voltage is controlled accurately by a method wherein, after a high concentration epitaxial layer is formed, the epitaxial layer is removed except the part where a channel is to be formed and higher concentration epitaxial layers are made to grow. CONSTITUTION:After a high concentration P-type epitaxial layer 14 is formed on a P-type substrate 1, a mask is formed on the part corresponding to the channel region of a pass transistor and the layer 14 is etched to the depth reaching the surface of the substrate 1. Then P-type epitaxial layers 15 and 16, which have higher concentration than the layer 14, are made to grow to the same thickness as the layer 14. After that, the mask is removed and the 1st layer gate electrode 17 is formed and N<+> type impurity ions are implanted by utilizing the electrode 17 as a mask to form a charge storing region 6 and a bit line 7 and further the 1st layer gate electrode 18 is formed. |
