Igfet integrated circuit memory cell

Abstract

An IGFET integrated circuit memory cell structure utilizing a capacitor with increased charge storage capability, and a method making the same. The capacitor includes a high impurity concentration region having the same conductivity type as the substrate. An island of opposite conductivity type is inset in the region and a conductive field plate overlies the island. The structure also includes a transfer transistor in which the source region is adjacent the capacitor and overlaps the island region therein. Activation of the transistor serves to transfer the charge stored in the capacitor to the drain region where it can be read by external circuitry. In the method, the high concentration region and island in the capacitor are formed by successive ion implantation steps. A subsequent source and drain diffusion causes lateral migration of the conductive portions of the cell to increase the storage capacitance and to insure electrical contact between the island region of the capacitor and the source of the transfer transistor.