IMPROVEMENTS IN THE MANUFACTURE OF SEMICONDUCTOR DEVICES

摘要

Two IGFETs Q2 and Q1 (or Q3) having different threshold voltages due to opposite doping of their gates are produced by depositing a layer 106 of undoped polysilicon over the gate oxide 105, patterning to form gate electrodes and masking (107a) and diffusing-in an impurity to form the source and drain regions 108, 113 and to dope the gate electrode of the second transistor Q1 (Q3) and the edges of the gate electrode of the first transistor Q2. The central part of the gate electrode of the first transistor Q2 is doped by diffusion of an opposite conductivity type impurity using a mask (109a). The devices may be used to provide a voltage reference.