| 摘要 |
PURPOSE:To easily obtain an ROM having a multi value output level by selectively arranging memory cells consisting of MIS transistors whose effective channel widths are varied by impurity introduction. CONSTITUTION:The masking ROM is formed of the first cell transistor Tr1 having the lowest output level whose effective channel width W1 is prescribed by the interval of a field oxide film FL, the second and third ones Tr2 and Tr3 whose widths W2 and W3 become narrow by impurity introduced regions P1 and P2, and the forth one Tr4 of OFF-state whose width is prescribed to 0 by an impurity introduced region P3. Thus, since the output level can be selected according to the size of the impurity introduced regions after forming the field oxide film FL, the manufacturing process becomes simple. |
