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:
May. 21, 1991
Filed:
Feb. 23, 1989
Nippondenso Co., Ltd., Kariya, JP;
Abstract
A first polysilicon film serving as an erase gate is deposited on the major surface of a semiconductor substrate on which a field oxide film is formed, so that the surface of the first polysilicon film is roughened. The surface of the first polysilicon film is thermally oxidized to form a first thermal oxide film thereon. During the oxidation, the roughened surface of the first polysilicon film is flattened, and is duplicated by the surface of the first thermal oxide film. A second polysilicon film is deposited on the roughened surface of the first thermal oxide film. The back surface of the second polysilicon film is roughened by the roughened surface of the first thermal oxide film. In this case, the surface of the second polysilicon film is also roughened. The roughened surface of the second polysilicon film is thermally oxidized in the same manner as described above to flatten its surface and to form a second thermal oxide film, the surface of which is roughened. A third polysilicon film serving as a write gate is formed on the second thermal oxide film.