Method, program product and apparatus for model based scattering bar placement for enhanced depth of focus in quarter-wavelength lithography

• US 20060075377A1
• Filed: 08/22/2005
• Published: 04/06/2006
• Est. Priority Date: 08/24/2004
• Status: Active Grant

• Current Assignee: ASML Netherlands BV (ASML Holding NV)
• Original Assignee: ASML Masktools B.V. (ASML Holding NV)
• Inventors: Chen, Jang Fung, Broeke, Douglas Van Den
• Granted Patent: US 7,620,930 B2
• Time in Patent Office: Days
• US Class Current: 716/53
• CPC Class Codes: G03F 1/36 Masks having proximity correction features; Preparation thereof, e.g. optical proximity correction [OPC] design processes
• CPC Class Codes: G03F 7/70441 Optical proximity correction [OPC]

Abstract

A method of generating a mask having optical proximity correction features. The method includes the steps of: (a) obtaining a desired target pattern having features to be imaged on a substrate; (b) determining a first focus setting to be utilized when imaging the mask; (c) determining a first interference map based on the target pattern and the first focus setting; (d) determining a first seeding site representing the optimal placement of an assist feature within the mask relative to a feature to be imaged on the basis of the first interference map; (e) selecting a second focus setting which represents a predefined amount of defocus relative to the first focus setting; (f) determining a second interference map based on the target pattern and the second focus setting; (g) determining a second seeding site representing the optimal placement of an assist feature within the mask relative to the feature to be imaged on the basis of the second interference map; and (h) generating an assist feature having a shape which encompasses both the first seeding site and the second seeding site.

Claims

1. A method of generating a mask having optical proximity correction features disposed therein, said method comprising the steps of:

(a) obtaining a desired target pattern having features to be imaged on a substrate;

(b) determining a first focus setting to be utilized when imaging said mask;

(c) determining a first interference map based on said target pattern and said first focus setting;

(d) determining a first seeding site representing the optimal placement of an assist feature within said mask relative to a feature to be imaged on the basis of said first interference map;

(e) selecting a second focus setting which represents a predefined amount of defocus relative to said first focus setting;

(f) determining a second interference map based on said target pattern and said second focus setting;

(g) determining a second seeding site representing the optimal placement of an assist feature within said mask relative to said feature to be imaged on the basis of said second interference map; and

(h) generating an assist feature having a shape which encompasses both said first seeding site and said second seeding site.

2. The method of claim 1, wherein said first focus setting represents the optimal focus setting for imaging the target pattern.

3. The method of claim 1, wherein said assist feature has a size such that said assist feature is not imaged on said substrate.

4. The method of claim 1, further comprising the step of placing additional assist features within said target pattern, each of said additional assist features being generated by performing steps (b)-(h).

5. The method of claim 1, wherein said interference map defines areas of constructive interference and areas of destructive interference between at least one of said features to be imaged and a field area adjacent said at least one feature.

6. The method of claim 1, further comprising the steps of:

determining a maximum image intensity level for said assist feature, said maximum image intensity defining an imaging intensity that will not result in the imaging of said assist feature on said substrate; and

adjusting the size of said assist features such that an image intensity level associated with said assist feature is equal to or less than said maximum image intensity level.

7. The method of claim 4, further comprising the steps of:

determining a maximum image intensity level which defines an imaging intensity that will not result in the imaging of said assist features on said substrate;

initially sizing each of said assist features such that said assist features have an imaging intensity level which is below said maximum image intensity level; and

adjusting the size of each of said assist features such that the image intensity level associated with said each assist feature is equal to or less than said maximum image intensity level.

8. A method of optical proximity correction for use in a photolithography process, said method comprising the steps of:

(a) obtaining a desired target pattern having features to be imaged on a substrate;

(b) determining an interference map based on said target pattern and said first focus setting;

(c) analyzing said interference map to determine a magnitude of interference for each of a plurality of said features to be imaged; and

(d) categorizing each of said plurality of features to be imaged as either a strong feature or a weak feature based on whether or not said magnitude of interference corresponding to the given feature is greater than or less than a predefined interference value.

9. The method of claim 8, wherein the magnitude of interference of a given feature is determined by the level of interference at the location of the given feature on the interference map.

10. A computer program product for controlling a computer comprising a recording medium readable by the computer, means recorded on the recording medium for directing the computer to generate files corresponding to a mask for use in a lithographic imaging process, the generation of the files comprising the steps of:

(a) obtaining a desired target pattern having features to be imaged on a substrate;

(b) determining a first focus setting to be utilized when imaging said mask;

(c) determining a first interference map based on said target pattern and said first focus setting;

(d) determining a first seeding site representing the optimal placement of an assist feature within said mask relative to a feature to be imaged on the basis of said first interference map;

(e) selecting a second focus setting which represents a predefined amount of defocus relative to said first focus setting;

(f) determining a second interference map based on said target pattern and said second focus setting;

(g) determining a second seeding site representing the optimal placement of an assist feature within said mask relative to said feature to be imaged on the basis of said second interference map; and

(h) generating an assist feature having a shape which encompasses both said first seeding site and said second seeding site.

11. The computer program product of claim 10, wherein said first focus setting represents the optimal focus setting for imaging the target pattern.

12. The computer program product of claim 10, wherein said assist feature has a size such that said assist feature is not imaged on said substrate.

13. The computer program product of claim 10, further comprising the step of placing additional assist features within said target pattern, each of said additional assist features being generated by performing steps (b)-(h).

14. The computer program product of claim 10, wherein said interference map defines areas of constructive interference and areas of destructive interference between at least one of said features to be imaged and a field area adjacent said at least one feature.

15. The computer program product of claim 10, further comprising the steps of:

determining a maximum image intensity level for said assist feature, said maximum image intensity defining an imaging intensity that will not result in the imaging of said assist feature on said substrate; and

adjusting the size of said assist features such that an image intensity level associated with said assist feature is equal to or less than said maximum image intensity level.

16. The computer program product of claim 13, further comprising the steps of:

determining a maximum image intensity level which defines an imaging intensity that will not result in the imaging of said assist features on said substrate;

initially sizing each of said assist features such that said assist features have an imaging intensity level which is below said maximum image intensity level; and

adjusting the size of each of said assist features such that the image intensity level associated with said each assist feature is equal to or less than said maximum image intensity level.

17. A computer program product for controlling a computer comprising a recording medium readable by the computer, means recorded on the recording medium for directing the computer to generate files corresponding to a mask for use in a lithographic imaging process, the generation of the files comprising the steps of:

(a) obtaining a desired target pattern having features to be imaged on a substrate;

(b) determining an interference map based on said target pattern and said first focus setting;

(c) analyzing said interference map to determine a magnitude of interference for each of a plurality of said features to be imaged; and

(d) categorizing each of said plurality of features to be imaged as either a strong feature or a weak feature based on whether or not said magnitude of interference corresponding to the given feature is greater than or less than a predefined interference value.

18. The computer program product method of claim 17, wherein the magnitude of interference of a given feature is determined by the level of interference at the location of the given feature on the interference map.(d) determining a first seeding site representing the optimal placement of an assist feature within said mask relative to a feature to be imaged on the basis of said first interference map;

(e) selecting a second focus setting which represents a predefined amount of defocus relative to said first focus setting;

(f) determining a second interference map based on said target pattern and said second focus setting;

(g) determining a second seeding site representing the optimal placement of an assist feature within said mask relative to said feature to be imaged on the basis of said second interference map; and

(h) generating an assist feature having a shape which encompasses both said first seeding site and said second seeding site.

19. A device manufacturing method comprising the steps of:

(a) providing a substrate that is at least partially covered by a layer of radiation-sensitive material;

(b) providing a projection beam of radiation using an imaging system;

(c) using a pattern on a mask to endow the projection beam with a pattern in its cross- section;

(d) projecting the patterned beam of radiation onto a target portion of the layer of radiation-sensitive material,

wherein, in step (c), said mask is formed by a method comprising the steps of;

obtaining a desired target pattern having features to be imaged on said substrate;

determining a first focus setting to be utilized when imaging said mask;

determining a first interference map based on said target pattern and said first focus setting;

determining a first seeding site representing the optimal placement of an assist feature within said mask relative to a feature to be imaged on the basis of said first interference map;

selecting a second focus setting which represents a predefined amount of defocus relative to said first focus setting;

determining a second interference map based on said target pattern and said second focus setting;

determining a second seeding site representing the optimal placement of an assist feature within said mask relative to said feature to be imaged on the basis of said second interference map; and

generating an assist feature having a shape which encompasses both said first seeding site and said second seeding site.