| 摘要 |
PURPOSE:To shorten turn around time at an MOS type mask ROM by a method wherein ROM data are written by changing the threshold value of the specified cell transistor at the same time with formation of the gate electrodes of the MOS type mask ROM. CONSTITUTION:Width of the polycrystalline silicon gate electrode film 342 of a cell transistor 22 on the side to be written with ROM data is made narrower than width of the polycrystalline silicon gate electrode film 341 of a cell transistor 21 on another side. Then N type impurities, arsenic ions for example, are implanted into a silicon substrate 31 on both the side regions of the polycrystalline silicon gate electrode films 341, 342 thereof to form N type layers 351-354 to be used respectively as the sources and the drains of the cell transistors 21, 22. Accordingly, ROM data can be written at the same time with formation of the gate electrodes by changing widths of the respective polycrystalline silicon gate electrodes 341, 342 of the specified cell transistor 22 and the other cell transistor 21, and turn around time is shortened. |
