NOR-type ROM with LDD cells and process of fabrication

US5793086A · kind A · utility

Assignee

• SGS-Thomson Microelectronics S.A. · IT

Inventors

• Emilio Ghio · Milano, IT
• Giuseppe Meroni · Lecco, IT
• Danilo Re · Bernareggio, IT
• Livio Baldi · Carugate, IT

Key dates

• Filing date: Dec 23, 1996
• Grant date: Aug 11, 1998
• Expiry date: Dec 23, 2016

Classification

• Technology area (CPC H): Electricity
• CPC primary: H10B20/00

Abstract

ROM memories made in MOS or CMOS technology with LDD cells may be programmed advantageously in a relatively advanced stage of fabrication by decoupling an already formed drain region from the channel region of cells to be permanently made nonconductive (programmed) by implanting a dopant in an amount sufficient to invert the type of conductivity in a portion of the drain region adjacent to the channel region. In CMOS processes, the programming mask may be a purposely modified mask commonly used for implanting source/drain regions of transistors of a certain type of conductivity. By using high-energy implantation and a dedicated mask, the programming may be effected at even later stages of the fabrication process.