LOCOS NITRIDE CAPPING OF DEEP TRENCH POLYSILICON FILL

• US 20100252905A1
• Filed: 04/06/2009
• Published: 10/07/2010
• Est. Priority Date: 04/06/2009
• Status: Active Grant

• Current Assignee: Polar Semiconductor, LLC (Sanken Electric Co., Ltd.)
• Original Assignee: Polar Semiconductor, Inc. (Sanken Electric Company Limited)
• Inventors: Hoilien, Noel
• Granted Patent: US 8,461,661 B2
• Time in Patent Office: Days
• US Class Current: 257/505
• CPC Class Codes: H01L 21/76235 trench shape altered by a local oxidation of silicon process step, e.g. trench corner rounding by LOCOS
• CPC Class Codes: H01L 21/763 Polycrystalline semiconductor regions H01L21/76264 takes precedence

Abstract

A polysilicon-filled isolation trench in a substrate is effective to isolate adjacent semiconductor devices from one another. A silicon nitride cap is provided to protect the polysilicon in the isolation trench from subsequent field oxidation. The cap has lateral boundaries that extend between the side boundaries of the polysilicon and the sidewalls of the trench. Subsequent field oxide regions formed adjacent to the trench establish a gap dimension from the substrate to a top surface of the field oxide regions adjacent to the polysilicon side boundaries that is no less than half of the field oxide thickness.

Claims

1. A protection structure for a an isolation trench in a substrate having first and second opposite side walls and having polysilicon therein with first and second opposite side boundaries, the protection structure comprising:

an oxide layer on the polysilicon and the substrate; and

a silicon nitride cap on the oxide layer over the polysilicon, the silicon nitride cap having a first lateral boundary that extends no less than the first side boundary of the polysilicon and no further than the first side wall of the isolation trench, and having a second lateral boundary that extends no less than the second side boundary of the polysilicon and no further than the second side wall of the isolation trench.

2. The protection structure of claim 1, wherein the substrate is composed of silicon.

3. The protection structure of claim 1, wherein the isolation trench has a depth of at least 15 μ

m.

4. The protection structure of claim 1, wherein the isolation trench is lined with oxide material.

5. An isolation trench structure in a substrate for isolating adjacent semiconductor devices, the isolation trench structure comprising:

a trench in the substrate, the trench having first and second opposite sidewalls;

polysilicon material in the trench, the polysilicon material having first and second side boundaries;

an oxide layer lining the trench around the polysilicon and extending across the top of the polysilicon layer and the substrate; and

first and second field oxide regions adjacent to the trench, the field oxide regions having a field oxide thickness and establishing a gap dimension from the substrate to a top surface of the field oxide regions adjacent to a corresponding polysilicon side boundary that is no less than half of the field oxide thickness.

6. The isolation trench structure of claim 5, wherein the substrate is composed of silicon.

7. The isolation trench structure of claim 5, wherein the first and second field oxide regions extend toward the first and second side boundaries, respectively, of the polysilicon at least as far as the first and second sidewalls, respectively, of the trench in the substrate.

8. The isolation trench structure of claim 5, wherein the first and second field oxide regions do not penetrate the polysilicon material in the trench.

9. A method of forming an isolation trench filled with polysilicon in a substrate, the method comprising:

forming the isolation trench in the substrate, the isolation trench having first and second opposite side walls;

lining the isolation trench with a first oxide layer;

filling the oxide-lined isolation trench with polysilicon having first and second opposite side boundaries;

forming a second oxide layer over the substrate and the polysilicon-filled isolation trench;

forming a silicon nitride cap on the second oxide layer over the polysilicon-filled isolation trench, the silicon nitride cap having a first lateral boundary that extends no less than the first side boundary of the polysilicon and no further than the first side wall of the isolation trench, and having a second lateral boundary that extends no less than the second side boundary of the polysilicon and no further than the second side wall of the isolation trench; and

applying field oxidation to form first and second field oxide regions adjacent to the polysilicon-filled trench, the field oxide regions having a field oxide thickness and establishing a gap dimension from the substrate to a top surface of the field oxide regions adjacent to a corresponding polysilicon side boundary that is no less than half of the field oxide thickness.

10. The method of claim 9, wherein forming the isolation trench in the substrate comprises forming the trench with a depth of at least 15 μ

m.

11. The method of claim 9, further comprising:

removing the silicon nitride cap after applying the field oxidation.

12. The method of claim 9, wherein the first oxide layer lining the isolation trench is formed with a thickness of 500 nm.

13. The method of claim 9, wherein the second oxide layer over the substrate and the polysilicon-filled isolation trench is formed with a thickness of 20 nm.

14. The method of claim 9, wherein the field oxide thickness is 400 nm.