Method of making a nonvolatile semiconductor memory apparatus wi

Details Method of making a nonvolatile semiconductor memory apparatus wi Method of making a nonvolatile semiconductor memory apparatus wi

1989-02-23

1991-05-21

Chaudhuri, Olik

Fishing, trapping, and vermin destroying

437 43, 437 51, 437193, 437195, 437228, 437233, 437235, H01L 2170

Patent

active

050175050

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.

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