Method of making a read only memory device
US4904615A · kind A · utility
Assignees
Inventors
Key dates
| Filing date | Jan 26, 1989 |
| Grant date | Feb 27, 1990 |
| Priority date | — |
| Expiry date | Jan 26, 2009 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH10B20/383
Abstract
Disclosed are memory cells of a vertical-type read only memory (ROM) having a plurality of MISFETs connected in series. The MISFETs include gate electrodes formed with multiple conductive layers, in which some of the MISFETs are set to the depletion type and at least some of the remaining MISFETs are set to the enhancement type, so as to write information in the memory cells. The information write operation is conducted through at least two steps. Namely, in the first information write step, gate electrodes are used as a mask to implant an impurity; and in the second step, an impurity is implanted through the gate electrodes into the surface of the semiconductor substrate. These steps enable a semiconductor memory device, such as a vertical-type mask ROM having memory cells with a reduced series resistance and being suitable for a high degree of integration, to be produced. Furthermore, there is disclosed a memory structure of a semiconductor memory device suitable for a higher degree of integration through an arrangement of gate electrodes of multiple layers.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.