Non-volatile semiconductor memory device and process of manufacturing the same
In device isolation trenches, a first device-isolation insulator film is formed to have recesses thereon and a second device-isolation insulator film is formed in the recesses. The uppermost portions at both ends of the first device-isolation insulator film are located higher than the uppermost portions at both ends of the second device-isolation insulator film.
1. A non-volatile semiconductor memory device, comprising:
a semiconductor substrate having device formation regions defined by device isolation trenches;
a first gate insulator film formed over said device formation regions; a floating gate formed on said first gate insulator film;
a first device-isolation insulator film formed in said device isolation trenches and having recesses thereon; a second device-isolation insulator film formed in said recesses;
a second gate insulator film formed over a surface of said floating gate and said first and second device-isolation insulator films; and
a control gate formed above said floating gate and said first and second device-isolation insulator films via said second gate insulator film, wherein the uppermost portions at both ends of said first device-isolation insulator film are located higher than the uppermost portions at both ends of said second device-isolation insulator film,
wherein said second device-isolation insulator film is higher in etching rate than said first device-isolation insulator film under a certain etching condition.
2. The non-volatile semiconductor memory device according to claim 1 , wherein said uppermost portion of said second device-isolation insulator film is located higher than a lower surface of said floating gate.
3. The non-volatile semiconductor memory device according to claim 2 , wherein said uppermost portion of said first device-isolation insulator film is located lower than the uppermost portion of said floating gate.
4. The non-volatile semiconductor memory device according to claim 1 , wherein said first device-isolation insulator film comprises a silicon oxide film, and wherein said second device-isolation insulator film comprises a polysilazane film.
5. The non-volatile semiconductor memory device according to claim 1 , wherein said device isolation trench and said floating gate are etched through an identical etching mask to form aligned sides thereof.
6. The non-volatile semiconductor memory device according to claim 1 , further comprising side insulator films formed on at least sides of said device isolation trenches and sides of said floating gate.
7. The non-volatile semiconductor memory device according to claim 1 , wherein said second gate insulator film comprises a triple-layered lamination of a first silicon oxide film, a silicon nitride film and a second silicon oxide film.
8. The non-volatile semiconductor memory device according to claim 1 , further comprising a selection transistor formed in said device formation region and connected via a bit line to a memory cell,
wherein said device isolation trench for defining said device formation region employed to form said selection transistor therein is similarly structured as said device isolation trench for defining said device formation region employed to form said memory cell therein.
9. The non-volatile semiconductor memory device according to claim 1 , further comprising a peripheral semiconductor device formed in said device formation region and connected to a memory cell,
wherein said device isolation trench for defining said device formation region employed to form said peripheral semiconductor device therein is similarly structured as said device isolation trench for defining said device formation region employed to form said memory cell therein.