Memory cell of the eeprom type having its threshold set by implantation, and fabrication method

Abstract

A process forms a structure incorporating at least one circuitry transistor and at least one non-volatile memory cell of the EEPROM type with two self-aligned polysilicon levels having a storage transistor and an associated selection transistor in a substrate of semiconductor material including field oxide regions bounding active area regions. The process comprises the steps of, in the active area regions, forming a gate oxide layer and defining a tunnel oxide region included in the gate oxide layer; depositing and partly defining a first polysilicon layer; forming an interpoly dielectric layer and removing the interpoly dielectric layer at least at the circuitry transistor; depositing a second polysilicon layer; selectively etching away, through a first mask, at least the second polysilicon layer at the cell, and the first and second polysilicon layers at the circuitry transistor; and selectively etching away, through a second mask, the interpoly dielectric layer and the first polysilicon layer at the cell. After the selective etch through said second mask, an implantation step is only carried out through the second mask and at least at the channel region of the floating-gate storage transistor to set the transistor threshold.