Method for forming cornered images on a substrate and photomask formed thereby

• US 6,184,151 B1
• Filed: 03/24/1999
• Issued: 02/06/2001
• Est. Priority Date: 08/21/1997
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Adair, William J., Martino, Ronald M., Hakey, Mark C., Horak, David V., Leidy, Robert K., Holmes, Steven J., Peng, Song, Ma, William Hsioh-Lien, Ferguson, Richard A.
• Primary Examiner(s): Saadat, Mahshid
• Assistant Examiner(s): RICHARDS, NORMAN DREW
• Application Number:
  US09/275,541
• Time in Patent Office: 685 Days
• Field of Search: 438/736, 438/737, 438/738, 438/723, 438/724, 438/717, 438/743, 438/744, 438/386, 438/947
• US Class Current: 438/743
• CPC Class Codes: H01L 21/0332 characterised by their composition, e.g. multilayer masks, materials
• CPC Class Codes: H01L 21/0334 characterised by their size, orientation, disposition, behaviour, shape, in horizontal or vertical plane
• CPC Class Codes: H10B 12/0383 wherein the transistor is vertical
• CPC Class Codes: Y10S 438/942 Masking

Abstract

A method for forming square shape images in a lithographic process is disclosed wherein a first plurality of lines running in a first direction is defined in a first, usually sacrificial, layer, and then a second resist is defined wherein the lines run in an intersecting pattern to those of the first layer, thereby creating cornered images wherever the first and second layer intersect and in the open areas between the lines. Methods are proposed for developing the square intersecting areas and the square angle areas defined by the openings. Additionally, a photomask is disclosed in which the length and width of the cornered images are independently patterned using the two-exposure process.

Claims

1. A method of forming cornered images on a substrate comprising the steps of:

(a) providing a substrate having a first layer of selectively etchable material thereon;

(b) forming a plurality of parallel edged openings in the first layer of etchable material, the openings aligned to form pairs of straight-edged first regions;

(c) depositing a layer of selectively etchable material over the openings in said first layer of etchable material;

(d) forming a second plurality of parallel edged openings in the layer of patternable material, said second plurality of openings intersecting adjacent pairs of said straight-edged first regions forming a plurality of second regions bounded by two edges of one of said first regions and two edges of one of said second region; and

(e) processing the substrate in the second regions defined by said first and second openings.

2. The method of claim 1, wherein the substrate includes:

a blocking layer on a top surface; and

wherein the selectively etchable material is a layer of hard mask material; and

wherein the processing of the substrate includes removing the blocking layer from the top surface in the region defined by the first and second openings.

3. The method of claim 2, wherein the processing step includes etching the blocking layer and further comprising the step, after step (e) of:

(f) stripping the second layer of patternable material.

4. The method of claim 3 further comprising, after the second layer of patternable material is stripped, the step of:

(g) over-etching the blocking layer for an amount of time sufficient to form rim-type phase shifters.

5. The method of claim 1, wherein the substrate includes a second layer of selectively etchable material between an upper surface of the substrate and a lower surface of the first layer of selectively etchable material, further comprising, after step (d) and before step (e), the step of:

forming a plurality of cornered openings in the second layer or selectively etchable material in the second regions defined by the first and second openings.

6. The method of claim 5, wherein the first layer of selectively etchable material is selected from the group consisting of:

silicon nitride and silicon oxide, and wherein the second layer of selectively etchable material is selected from the remaining of;

silicon nitride and silicon oxide.

7. The method of claim 1 wherein the substrate further comprises:

a first layer of polysilicon on an upper surface of the substrate;

a first layer of silicon nitride on an upper surface of the first layer of polysilicon;

a first layer of silicon oxide on an upper surface of the first layer of silicon nitride;

a second layer of polysilicon on an upper surface of the first layer of silicon oxide;

a second layer of silicon nitride on an upper surface of the second layer of polysilicon; and

wherein the first layer of selectively etchable material is a second layer of silicon oxide on an upper surface of the second layer of silicon nitride; and

further comprising, after step (d) and before step (e), the step of;

(d1) forming a plurality of cornered openings in the second layer of silicon nitride in the second regions defined by the first and second openings.

8. The method of claim 7, further comprising, after step(d1), the steps of:

selectively etching the second layer of polysilicon to expose cornered areas of the first layer of silicon oxide;

selectively etching the first layer of silicon oxide to expose cornered areas of the first layer of silicon nitride, thereby removing any remaining portions of the second layer of silicon oxide;

selectively etching the first layer of silicon nitride to expose cornered areas of the first layer of polysilicon, thereby removing any remaining portions of the second layer of silicon nitride; and

selectively etching the first layer of polysilicon to expose cornered areas of the substrate, thereby removing remaining portions of the second layer of polysilicon.

9. The method of claim 8, wherein step (e) comprises:

processing the exposed cornered areas of the substrate to form deep trench capacitors.

10. The method of claim 7, wherein the second layer of polysilicon is deposited to a thickness less than the first layer of polysilicon, wherein the second layer of silicon nitride is deposited to a thickness less than the first layer of silicon nitride;

and wherein the second layer of silicon oxide is deposited to a thickness less than the first layer of silicon oxide.

11. The method of claim 7, wherein the thickness of the second layer of polysilicon is in the range of 500 Å

to about 1000 Å

, wherein the thickness of the second layer of silicon nitride is in the range of about 500 Å

to about 1000 Å and

wherein the thickness of silicon dioxide is in the range of about 500 Å

to about 1000 Å

.

12. The method of claim 1, wherein the second plurality of parallel edged openings is a non-grating pattern of lines having ends and wherein the ends of the lines fall within remaining portions of the first layer of photoresist material proximate the two edges of the first regions.

13. The method of claim 1, wherein the substrate includes:

a layer of gate polysilicon on a surface of the substrate;

a layer of an oxide on an upper surface of the gate polysilicon;

a layer of nitride on an upper surface of the layer of oxide;

a layer of organic material on an upper surface of the layer of nitride;

a thin layer of an oxide on an upper surface of the layer of organic material;

and wherein the first layer of selectively etchable material is a thin layer of nitride on an upper surface of the thin layer of oxide; and

further comprising, after step(d) and before step(e), the step of;

selectively etching the thin layer of an oxide in the plurality of second regions;

removing remaining areas of the patternable material;

selectively etching the layer of organic material in the plurality of second regions;

selectively etching the layer of nitride in the plurality of second regions, thereby removing remaining areas of the thin layer of nitride;

selectively etching the layer of oxide in the plurality of second regions, thereby removing remaining areas of the thin layer of oxide; and

selectively etching the layer of gate polysilicon, thereby exposing the substrate in the plurality of second regions.

14. The method of claim 13, wherein the processing of the substrate includes the steps of:

non-selectively etching the substrate in the plurality of second regions using the layer of organic material as a mask; and

stripping the layer of organic material, thereby forming a final structure.

15. The method of claim 13, further comprising, after exposing the substrate, the step of:

processing the exposed second regions of the substrate to form isolation trenches.

16. The method of claim 13, wherein the second pattern of lines is a non-grating pattern.

17. A method of exposing selected portions of buried conductors, comprising the steps of

forming conductive structures in a substrate, said conductive structures being separated from one another by first insulator structures and being covered with second insulator structures;

forming a first grating pattern of parallel openings in upper ones of said second insulator structures; and

covering portions of said upper ones of said second insulator structures with a mask having a second non-grating pattern of parallel openings crossing over to said first grating pattern, and etching areas of said first and second insulator structures defined by the intersections of said first grating pattern and said second non-grating pattern to expose portions of said conductive structures.