The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Apr. 06, 1999
Filed:
Jan. 20, 1998
Applicant:
Inventors:
Cheng-Hui Chung, Hsinchu Hsien, TW;
Yi-Chung Sheng, Taichung, TW;
Assignee:
Attorney:
Primary Examiner:
Assistant Examiner:
Int. Cl.
CPC ...
H01L / ;
U.S. Cl.
CPC ...
438276 ; 438278 ;
Abstract
A method of fabricating a tetra-state mask read only memory. A memory device is fabricated. Using a first photo-resist to dope the channel regions, a first coding step is performed to obtain a transistor having two different threshold voltage. Covering a gate oxide layer, and etching the first photo-resist layer to form a via, a buried bit line is formed. A poly-silicon layer is formed on the gate oxide layer. Doping the second poly-silicon layer by implanting ions to the source/drain regions, and using a second photo-resist layer, a second coding step is performed. An inverse transistor with two different threshold voltage is formed.