| 摘要 |
PURPOSE:To prevent the saturation of an NPN transistor in a PNP load mem ory cell, and to shorten the writing time by comparing impurity concentration in a base region with that in a collector region and relatively reducing impurity concentration in the base region. CONSTITUTION:An epitaxial layer 43 is thinned (formed in size thinner than half a conventional epitaxial layer 43 (normally 1.5mum or less)) only in a memory cell section. The epitaxial layer is shaped thinly, thus increasing impurity concen tration in a base region in a PNP transistor. It is because an impurity diffuses from a buried layer 42 in a heat treatment process. When impurity concentration in the base region in the PNP transistor is elevated, the speed of quenching of minority carriers (holes) injected to said base is also accelerated, and speed where the PNP transistor changes to a nonconductive state from a conductive state is increased. Accordingly, the writing time is shortened. |
