| 摘要 |
PURPOSE:To shorten the step after writing informaton in a mask ROM by forming all the MISFETs forming memory cells in an equal mode and then introducing an impurity to the channel region of a desired element to convert its mode. CONSTITUTION:A gate film 3 is formed, for example, on the element forming region of a P type Si substrate 1, then ions are injected to form an N<-> type layer 4, and a polysilicon layer 5 is accumulated on the overall surface. Subsequently, the steps of etching and forming a gate electrode 5', forming N<+> type diffused layers for source and drain regions 6 and forming a protective oxidized film 7 are sequentially performed, and all the films are preserved in this stage (in which all the elements are in a D mode state). Then, a specific element (such as, for example, an element 8) is converted into an E mode on the basis of necessary information pattern. For that purpose, a resist pattern 9 is so formed as to allow the gate part of the element 8 to be opened, ions are injected to covert the channel region into a P<-> type layer 10 and to convert it into an E mode. Thereafter, the steps of forming electrodes and wires are performed. This can remarkably shorten the step after writing (converting the mode). |
