公开(公告)号：DE19804248A1

公开(公告)日：1999-06-10

申请号：DE19804248

申请日：1998-02-04

Applicant: UNITED MICROELECTRONICS CORP

Inventor： CHUNG CHENG-HUI ,  SHENG YI-CHUNG

IPC: H01L21/8246 ,  H01L27/112

Abstract: The ROM is fabricated by providing a semiconductor substrate having a gate oxide layer, a first polysilicon layer, a plurality of source/drain regions, and a plurality of channel regions. By using a first photoresist to dope the channel regions, a first coding step is performed to obtain a transistor having 2 different threshold voltages. A thin film transistor oxide layer is formed over the substrate, patterned and etched to expose the source/drain regions. A second polysilicon layer is formed on the thin film transistor oxide, and a mask used to dope a part of it to form a plurality of doped regions. Using a second photoresist layer as a mask, a part of the second polysilicon layer corresponding to the channel regions is doped and a second coding step performed.