Process margin using discrete assist features

• US 20070082277A1
• Filed: 10/07/2005
• Published: 04/12/2007
• Est. Priority Date: 10/07/2005
• Status: Active Grant

• Current Assignee: Globalfoundries US Incorporated (GlobalFoundries, Inc.)
• Original Assignee: Advanced Micro Devices, Inc.
• Inventors: Singh, Bhanwar, Matthew, Itty
• Granted Patent: US 7,749,662 B2
• Time in Patent Office: Days
• US Class Current: 430/5
• CPC Class Codes: G03F 1/36 Masks having proximity correction features; Preparation thereof, e.g. optical proximity correction [OPC] design processes

Abstract

The subject invention provides a system and method for improving the process margin of a lithographic imaging system. The process margin improvement is achieved through the novel placement of discrete assist features and/or the use of forbidden pitches and specific pitch orientations. Novel geometries are utilized, which take advantage of line-end pull back and/or a lack of resolution of pitches perpendicular to an axis of a dipole illumination source. The strategic placement of a series of discrete scatterbar segments on a mask near positions of critical features, such as, for example, contacts, mitigates resist residue that can result from the use of a contiguous scatterbar.

Claims

1. A method of improving a process margin of a lithographic imaging system, comprising:

identifying a semi-isolated pattern feature on a mask as a potential limiting factor to a process margin for a lithographic imaging technique;

determining a resolution threshold for the imaging technique; and

placing one or more discretized sub-resolution assist features near the semi-isolated mask feature.

2. The method of claim 1, the one or more discretized sub-resolution assist features comprises one or more discretized scatterbars.

3. The method of claim 2, the one or more discretized scatterbar comprises more than one discrete scatterbar segments.

4. The method of claim 3, further comprising determining a maximum size threshold for discrete scatterbar segments based at least in part on at least one of the determined resolution threshold for the imaging system and a known amount line-end pull back that occurs at the resolution threshold, and constructing the more than one discrete scatterbar segments to be smaller than the maximum threshold size. line-end pull

5. The method of claim 3, further comprising constructing the more than one discrete scatterbar segments with a pitch outside of a range of pitches that can be resolved by the imaging system to mitigate discrete scatterbar segments resolution by the imaging system.

6. The method of claim 5, further comprising forming the pitch perpendicular to an axis of a dipole illumination source of the imaging system.

7. The method of claim 3, the at least one semi-isolated mask feature comprises a terminal feature in a series of mask features of uniform pitch.

8. The method of claim 7, the terminal feature comprises a mask pattern feature for imaging a wordline and the series of mask features comprises a series of mask pattern features for imaging a series of wordlines.

9. The method of claim 7, the terminal feature comprises a mask feature for imaging a bitline and the series of mask features comprises a series mask features for imaging a series of bitlines.

10. The method of claim 4, further comprising running a simulation for a depth of focus for the imaging system.

11. The method of claim 5, the one or more pitches comprising forbidden pitches of the imaging system.

12. A photomask comprising:

one or more semi-isolated mask features; and

one or more discretized scatterbars positioned near at least one of the one or more semi-isolated mask features, the discretized scatterbars alter a pitch of the one or more semi-isolated mask features and mitigate photoresist residue after an exposure period.

13. The mask of claim 12, the one or more discretized scatterbar comprises more than one discrete sub-resolution scatterbar segment.

14. The mask of claim 13, each of the more than one discrete sub-resolution scatterbar segments is constructed smaller than a predefined maximum segment size threshold, below which the imaging system does not generate an image line-end pull.

15. The mask of claim 13, wherein the more than one discrete sub-resolution scatterbar segments comprise a forbidden pitch that is not resolvable by the imaging system.

16. The mask of claim 13, wherein the more than one discrete sub-resolution scatterbar segments comprise a pitch formed in an axis perpendicular to an axis of a dipole illumination source employed to expose a photoresist through the mask.

17. The mask of claim 12, at least one of the one or more semi-isolated mask features comprises a last feature in a series of uniformly sized and spaced features.

18. The mask of claim 17, the mask features form a pattern through which an exposure source can illuminate a photoresist on a wafer to generate an image of a pattern of wordlines thereon.

19. A system that facilitates improving wafer yield and mitigating resist residue after a photoresist exposure technique, comprising:

means for identifying a potential yield-limiting pattern feature on a photomask; and

means for generating a plurality of discrete scatterbar segments that are of a sub-resolution size that can be reliably printed on the photomask and cannot be resolved by an exposure source employed to print photomask features on a resist layer on a wafer;

20. The system of claim 19, further comprising:

means for positioning the plurality of scatterbar segments adjacent to the identified pattern feature and adjusting the pitch of the identified pattern feature; and

means for exposing the resist layer on the wafer through the photomask.