Methods for fabricating semiconductor devices

1. A method for fabricating a semiconductor device comprising:

etching a semiconductor substrate to form a trench;

forming an ONO film on the semiconductor substrate and in the trench;

removing the ONO film from an upper surface of the semiconductor substrate while leaving the ONO film on an inside wall surface of the trench;

forming a gate oxide film on the semiconductor substrate adjacent the ONO film;

depositing polysilicon on the semiconductor substrate, the polysilicon filling the trench; and

selectively removing the polysilicon to form SONOS gate electrodes on the gate oxide film and the trench, respectively.

2. A method as claimed in claim 1 , wherein etching the semiconductor substrate to form the trench comprises forming the trench to a depth of about 5~100% of a height of the gate electrode.

3. A method as claimed in claim 1 , wherein the ONO layer on the inside wall surface of the trench has a height of about 5~100% of a height of the gate electrode.

4. A method as claimed in claim 1 , wherein selectively removing the polysilicon to form the SONOS gate electrodes comprises forming a BARC (Bottom Anti-Reflect Coating) film to a thickness of about 200~1300 Å on or beneath a photoresist film coated on the polysilicon.

5. A method as claimed in claim 1 , wherein the ONO film comprises:

a lower oxide film with a thickness of about 20~100 Å,

a trap nitride film with a thickness of about 30~200 Å, and

an upper oxide film with a thickness of about 50~200 Å.