Patent ID: 7273782

Claim:
A method for manufacturing a nonvolatile memory comprising: forming first trenches having a designated depth and a second trench having a depth smaller than that of the first trenches, and filling the first and second trenches with an oxidation film; planarizing the oxidation film, and etching the oxidation film in the second trench so that the oxidation film remains at the central portion of the second trench; forming a tunnel oxidation film in the second trench from which the oxidation film is etched, and depositing a first polysilicon film thereon; etching the first polysilicon film back so that a 2-bit floating gate is formed in the second trench; removing the oxidation film in the second trench by wet etching, and forming a common source on the silicon substrate under the second trench by depositing a lower oxidation film and using the lower oxidation film as a buffer film; depositing a nitride film and an upper oxidation film on the resulting structure provided with the deposited common source; depositing a second polysilicon film on the entire surface of the upper oxidation film; and forming a control gate by etching the second polysilicon film.