| 摘要 |
PURPOSE:To improve software error preventing effect by alpha rays, by constituting the cell part of a substrate by arranging a high concentration region directly below a high concentration region furthermore. CONSTITUTION:A semiconductor memory cell is formed on a P type substrate 10. A P<+> layer 12 and a P<++> layer 11 are provided directly below the cell. An N layer 13 is provided in the vicinity of the upper surface, and a depletion layer D is expanded. The thickness of the P<+> layer 12 is determined so that the depletion layer D is included in the P<+> layer 12 and does not reach the inside of the P<++> layer 11. Thus the width of the depletion layer is sufficiently reduced in the P<+> layer 12. In the P<++> layer 11, high concentration is suffificiently imparted without restricted by junction breakdown. The concentration ratio Nn/Np of electrons and holes can be sufficiently reduced in the P type substrate. By the synergistic effect, the thickness of a region, wherein field funneling phenomenon, by which an electric field is temporarily expanded under the depletion layer occurs, is largely reduced. Therefore, the number of electrons, which are induced by the input of alpha rays and absorbed in the N layer, is decreased, and the software error preventing effect due to the alpha rays is improved. |
