Alignment dip back oxide and code implant through poly to approach the depletion mode device character

摘要

A metal code process for a read-only memory (ROM) combines the alignment dip back process (to reduce the polyoxide thickness over the gate electrode and to protect the field oxide) with a double charge implant approach to provide the function of a depletion mode ROM cell. The alignment dip back process also avoids leakage current problems. A stable depletion mode device character is achieved by implant step energies greater than 150 keV.