1. A method, implemented by a computer, of improving imaging performance of a mask pattern having a feature to be imaged, said method comprising the steps of:
(a) obtaining a model of a lithographic process for imaging said mask pattern onto a substrate;
(b) determining an optimal setting of said lithographic process to be utilized when imaging said mask pattern;
(c) determining, using said model, a first interference map based on said mask pattern and said optimal setting;
(d) determining a first seeding site representing the optimal placement of an assist feature within said mask pattern relative to said feature to be imaged on the basis of said first interference map;
(e) selecting a plurality of lithographic process settings that represent a predefined amount of variation relative to said optimal setting;
(f) determining, using said model, a plurality of interference maps respectively based on said mask pattern and said plurality of lithographic process settings;
(g) determining a plurality of seeding sites representing the optimal placement of an assist feature within said mask pattern relative to said feature to be imaged on the basis of said plurality of interference maps; and
(h) generating an assist feature having a shape which encompasses both said first seeding site and said plurality of seeding sites,
wherein one or more of steps (a)-(f) are performed using said computer.
2. The method of claim 1, wherein said optimal setting represents the optimal focus setting for imaging said mask 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 relative to additional features to be imaged within said mask pattern, each of said additional assist features being generated by performing steps (b)-(h).
5. The method of claim 1, wherein said interference maps define areas of constructive interference and areas of destructive interference between said feature to be imaged and a field area adjacent said 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 feature 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. The method of claim 1, wherein said lithographic process settings correspond to focus, and wherein said step of selecting said plurality of lithographic processing settings includes determining a plurality of defocus values in accordance with a numerical aperture of the lithographic process.
9. The method of claim 1, wherein said feature to be imaged has a dimension approximately one quarter of a wavelength of said lithographic process.
10. A computer program product for controlling a computer comprising a non-transitory recording medium readable by the computer, means recorded on the recording medium for directing the computer to perform a method of improving imaging performance of a mask pattern having a feature to be imaged, said method comprising the steps of:
(a) obtaining a model of a lithographic process for imaging said mask pattern onto a substrate;
(b) determining an optimal setting of said lithographic process to be utilized when imaging said mask pattern;
(c) determining, using said model, a first interference map based on said mask pattern and said optimal setting;
(d) determining a first seeding site representing the optimal placement of an assist feature within said mask pattern relative to said feature to be imaged on the basis of said first interference map;
(e) selecting a plurality of lithographic process settings that represent a predefined amount of variation relative to said optimal setting;
(f) determining, using said model, a plurality of interference maps respectively based on said mask pattern and said plurality of lithographic process settings;
(g) determining a plurality of seeding sites representing the optimal placement of an assist feature within said mask pattern relative to said feature to be imaged on the basis of said plurality of interference maps; and
(h) generating an assist feature having a shape which encompasses both said first seeding site and said plurality of seeding sites.
11. The computer program product of claim 10, wherein said optimal setting represents the optimal focus setting for imaging said mask 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 relative to additional features to be imaged within said mask 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 maps define areas of constructive interference and areas of destructive interference between said feature to be imaged and a field area adjacent said 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 feature 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. The computer program product of claim 10, wherein said lithographic process settings correspond to focus, and wherein said step of selecting said plurality of lithographic processing settings includes determining a plurality of defocus values in accordance with a numerical aperture of the lithographic process.
18. The computer program product of claim 10, wherein said feature to be imaged has a dimension approximately one quarter of a wavelength of said lithographic process.
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 mask pattern having a feature to be imaged 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 pattern is optimized by a method comprising the steps of:
obtaining a model of said imaging system for imaging said mask pattern onto said substrate;
determining an optimal setting of said imaging system to be utilized when imaging said mask pattern;
determining, using said model, a first interference map based on said mask pattern and said optimal setting;
determining a first seeding site representing the optimal placement of an assist feature within said mask pattern relative to said feature to be imaged on the basis of said first interference map;
selecting a plurality of imaging system settings that represent a predefined amount of variation relative to said optimal setting;
determining, using said model, a plurality of interference maps respectively based on said mask pattern and said plurality of imaging system settings;
determining a plurality of seeding sites representing the optimal placement of an assist feature within said mask pattern relative to said feature to be imaged on the basis of said plurality of interference maps; and
generating an assist feature having a shape which encompasses both said first seeding site and said plurality of seeding sites.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1-19. (canceled)
20. A suture anchor, which comprises:
an outer sleeve having a threaded portion and defining a longitudinal axis; and
an inner suture pin positionable within the outer sleeve, the suture pin including first and second bores for receiving respective first and second sutures, the bores each defining a bore axis extending in transverse relation to the longitudinal axis.
21. The suture anchor according to claim 20 wherein the suture pin includes grooves formed in an outer surface thereof and extending from respective transverse bores, the grooves dimensioned to accommodate suture portions extending from the transverse bores.
22. The suture anchor according to claim 21 wherein the bore axes of the first and second bores are in general parallel relation to each other.
23. The suture anchor according to claim 20 wherein the suture pin includes first and second pin sections having the first and second bores respectively, the first pin section defining a cross-sectional dimension greater than the second pin section.
24. The suture anchor according to claim 21 wherein the threaded portion of the outer sleeve includes flutes defined therein.
25. The suture anchor according to claim 20 wherein the inner suture pin includes a pin head and a pin shaft, the pin shaft having the first and second bores and at least partially positionable in the outer sleeve, the pin head having at least one chamfer defined in an outer surface thereof.
26. The suture anchor according to claim 25 wherein the pin head includes a pair of chamfers arranged in general diametrical opposed relation.