| 摘要 |
PURPOSE:To form a multivalued ROM by using a mask material, the thickness of which is changing with the data written into a mask for performing ion- implantation, thereby changing the current driving ability of a memory cell transistor. CONSTITUTION:The writing of data is made by performing ion-implantation according to the data as shown at H, I, J, K, The ion-implantation is performed by using a photo-resist as a mask. Since a gate film on a second channel 123 has smaller thickness than that on a first channel 121, ions come thereinto more deeply in the case where for instance, the ion such as B is injected thereinto with the same energy, so that the variation of a threshold voltage is larger. Injection energy and dosage are controlled to form a memory cell in such a manner that there appears a difference on threshold voltage between the first channel 121 and the second channel 123. A memory cell into which data is written acts as a circuit in which the source an the drain of a transistor having a different threshold voltage are connected in parallel with each other to form four kinds of transistors each having a different current driving ability. |
