System and method for printing semiconductor patterns using an optimized illumination and reticle

• US 6,563,566 B2
• Filed: 01/29/2001
• Issued: 05/13/2003
• Est. Priority Date: 01/29/2001
• Status: Active Grant

• Current Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Original Assignee: International Business Machines Corporation
• Inventors: Wong, Alfred K. K., Rosenbluth, Alan E., Bukofsky, Scott Josef
• Primary Examiner(s): Adams, Russell
• Assistant Examiner(s): Brown, Khaled
• Application Number:
  US09/771,793
• Publication Number:
  US 20020140920A1
• Time in Patent Office: 834 Days
• Field of Search: 355/67, 355/55, 355/77, 430/311, 430/312, 430/323, 250/492.2, 250/492.22
• US Class Current: 355/67
• CPC Class Codes: G03F 1/32 Attenuating PSM [att-PSM], e.g. halftone PSM or PSM having semi-transparent phase shift portion,; Preparation thereof
• CPC Class Codes: G03F 1/34 Phase-edge PSM, e.g. chromeless PSM; Preparation thereof
• CPC Class Codes: G03F 7/70125 Use of illumination settings tailored to particular mask patterns details of setting means G03F7/70091
• CPC Class Codes: G03F 7/70433 Layout for increasing efficiency or for compensating imaging errors, e.g. layout of exposure fields for reducing focus errors; Use of mask features for increasing efficiency or for compensating imaging errors
• CPC Class Codes: G03F 7/705 Modelling or simulating from physical phenomena up to complete wafer processes or whole workflow in wafer productions

Abstract

A system and method is described for lithographically printing patterns on a semiconductor using combinations of illumination and mask patterns which are optimized together to produce the desired pattern. The method of optimizing both illumination and mask pattern allows the development of mask patterns that are not constrained by the geometry of the desired pattern to be printed. Thus, the method provides high quality images even when the desired printed patterns have critical dimensions that approach the resolution limits of a lithographic system. The resulting mask patterns using the method do not obviously correspond to the desired patterns to be printed. Such masks may include phase-shifting technology that use destructive interference to define dark areas of the image and are not constrained to conform to the desired printed pattern.

Claims

1. A method for printing a desired pattern on a semiconductor wafer having a photoactive material thereon, the method comprising the steps of:

providing a diffraction relationship for determining at least one diffracted amplitude diffracted by a reticle having at least one diffraction parameter when said reticle is exposed to illumination energy from an illumination source having at least one source parameter;

providing a merit function for computing a merit value of an image pattern on a wafer plane as a function of variables including said at least one diffracted amplitude;

selecting at least one constraint on at least one of said variables;

determining an optimal value of said at least one diffracted amplitude so that said merit function attains a merit value that is optimized in accordance with said at least one constraint;

selecting a combination of at least one selected source parameter and at least one selected diffraction parameter to produce said optimal value of said at least one diffracted amplitude in accordance with said diffraction relationship;

forming an optimal reticle having a diffractive feature with said at least one selected diffraction parameter;

illuminating said optimal reticle with illumination energy from an illumination source having said at least one selected source parameter, so that said illumination energy is diffracted by said diffractive feature and projected through a lens aperture to form an optimal image pattern on the wafer plane in accordance with said at least one constraint;

exposing the photoactive material to said optimal image pattern; and

developing said exposed photoactive material to form the desired pattern.

2. The method of claim 1 wherein said at least one source parameter comprises both a source direction and a source intensity.

3. The method of claim 1 further comprising

forming an optimal reticle having at least one diffractive feature with said at least one selected diffraction parameter so that said optimal value of said at least one diffracted amplitude is produced when said diffractive feature is illuminated by an illumination source having said at least one selected source parameter.

4. The method of claim 1 wherein said at least one diffracted amplitude further comprises a first amplitude collected within a first quadrant of the lens aperture and a second amplitude collected within a second quadrant of the lens aperture, wherein said first amplitude is selected independently of said second amplitude.

5. The method of claim 1 wherein said at least one constraint includes a preselected image intensity at a selected point of the desired image pattern corresponding to an edge of an element of the desired image pattern.

6. The method of claim 1 wherein said merit function comprises a derivative of image intensity at a selected point on the wafer plane corresponding to an edge of an element of the desired image pattern, said derivative having a direction normal to said edge.

36. The method of claim 1 wherein said at least one source parameter comprises a source direction having a source amplitude, and said step of selecting a combination further comprises:

selecting a plurality of source directions having diffracted orders overlapping in direction space in accordance with the desired image pattern;

deriving a simplified function from said merit function;

computing a diffracted amplitude corresponding to each of said plurality of source directions having source amplitudes and selecting a first optimized combination of computed diffracted amplitudes, source directions and source amplitudes so that said simplified function is globally optimized;

selecting a final optimized combination of at least one selected source direction having a selected source amplitude and at least one selected diffracted amplitude so that said merit function is locally optimized using said first optimized combination as a starting solution, and so that said merit function is locally optimized in accordance with said at least one constraint; and

forming said diffractive feature so that said at least one selected diffracted amplitude is produced when said diffractive feature is illuminated by an illumination source having said at least one selected source direction having said selected source amplitude.

37. The method of claim 1 wherein the step of forming said optimal reticle further comprises approximating said diffractive feature using superimposed rectangular shapes.

7. A method for printing an integrated circuit pattern on a semiconductor wafer having a photoactive material thereon, the method comprising the steps of:

providing a desired wafer feature pattern having at least one wafer feature element;

deriving a merit function describing a relationship between an illumination source, a reticle, and an image, said source having at least one source parameter, said reticle having at least one diffractive feature, and said image having at least one image intensity;

selecting at least one constraint in relation to said desired wafer feature pattern that said at least one image intensity must satisfy;

selecting a combination of said at least one source parameter and said at least one diffractive feature so that said merit function is optimized in accordance with said at least one constraint;

illuminating said reticle with illumination energy from said illumination source, so that said illumination energy is diffracted by said reticle and projected through a lens aperture to form said at least one image intensity on the wafer;

exposing the photoactive material to said at least one image intensity; and

developing said exposed photoactive material to form a printed feature,

so that said printed feature conforms with said at least one wafer feature element of said desired wafer feature pattern in accordance with said at least one constraint, and wherein said at least one source parameter comprises a source direction having a source amplitude, wherein illumination from said source direction on said at least one diffractive feature produces at least one diffracted amplitude, and said step of selecting a combination further comprises

selecting a plurality of source directions having diffracted orders overlapping in direction space in accordance with said desired wafer feature pattern;

deriving a simplified function from said merit function;

computing a diffracted amplitude corresponding to each of said plurality of source directions at selected source amplitudes and selecting a first optimized combination of computed diffracted amplitudes, source directions and source amplitudes so that said simplified function is globally optimized;

selecting a final optimized combination of at least one source direction, at least one source amplitude and at least one diffracted amplitude so that said merit function is locally optimized using said first optimized combination as a starting solution, and so that said merit function is locally optimized in accordance with said at least one constraint; and

forming said selected at least one diffractive feature so that said at least one selected diffracted amplitude is produced when said selected at least one diffractive feature is illuminated by said source from said selected at least one source direction.

8. The method of claim 7 wherein the step of forming said selected at least one diffractive feature further comprises approximating said diffractive feature using superimposed rectangular shapes.

9. A method for selecting a combination of source illumination parameters and diffraction mask features for projecting energy through a lens aperture to form a desired image pattern on a wafer plane, the method comprising the steps of:

providing a diffraction relationship for determining at least one diffracted amplitude diffracted by a reticle having at least one diffraction parameter when said reticle is exposed to illumination energy from an illumination source having at least one source parameter;

providing a merit function for computing a merit value of the desired image pattern on the wafer plane as a function of variables including said at least one diffracted amplitude;

selecting at least one constraint on at least one of said variables;

determining an optimal value of said at least one diffracted amplitude so that said merit function attains a merit value that is optimized in accordance with said at least one constraint; and

selecting a combination of at least one selected source parameter and at least one selected diffraction parameter to produce said optimal value of said at least one diffracted amplitude in accordance with said diffraction relationship.

10. The method of claim 9 wherein said at least one source parameter comprises both a source direction and a source intensity.

11. The method of claim 9 further comprising

designing a reticle having a diffractive feature with said at least one selected diffraction parameter so that said optimal value of said at least one diffracted amplitude is produced when said diffractive feature is illuminated b~ an illumination source having said at least one selected source parameter.

12. The method of claim 9 wherein said at least one diffracted amplitude further comprises a first amplitude collected within a first quadrant of the lens aperture and a second amplitude collected within a second quadrant of the lens aperture, wherein said first amplitude is selected independently of said second amplitude.

13. The method of claim 9 wherein said at least one constraint includes a preselected image intensity at a selected point of the desired image pattern corresponding to an edge of an element of the desired image pattern.

14. The method of claim 9 wherein said merit function comprises a derivative of image intensity at a selected point on the wafer plane corresponding to an edge of an element of the desired image pattern, said derivative having a direction normal to said edge.

38. The method of claim 9 wherein said at least one source parameter comprises a source direction having a source amplitude and said step of selecting a combination further comprises:

selecting a plurality of source directions having diffracted orders overlapping in direction space in accordance with the desired image pattern;

deriving a simplified function from said merit function;

computing a computed diffracted amplitude corresponding to each of said plurality of source directions at selected source amplitudes and selecting a first optimized combination of computed diffracted amplitudes, source directions and source amplitudes so that said simplified function is globally optimized;

selecting a final optimized combination of at least one selected source direction having a selected source amplitude and at least one selected diffracted amplitude so that said merit function is locally optimized using said first optimized combination as a starting solution, and so that said merit function is locally optimized in accordance with said at least one constraint; and

forming a reticle having a diffractive feature with said at least one selected diffraction parameter so that said at least one selected diffracted amplitude is produced when said diffractive feature is illuminated by an illumination source having said at least one selected source direction having said selected source amplitude.

43. The method of claim 11 wherein the step of designing a reticle further comprises approximating said diffractive feature using superimposed rectangular shapes.

15. A method for selecting a combination of source illumination parameters and diffraction mask features for projecting energy through a lens aperture to form an image pattern on a wafer, the method comprising the steps of:

providing a desired wafer feature pattern having at least one wafer feature element;

deriving a merit function describing a relationship between an illumination source, a reticle, and the image pattern, said source having at least one source parameter, said reticle having at least one diffractive feature, and said image pattern having at least one image intensity;

selecting at least one constraint in relation to said desired wafer feature pattern that said at least one image intensity must satisfy; and

selecting a combination of said at least one source parameter and said at least one diffractive feature,

so that said merit function is optimized in accordance with said at least one constraint, and wherein said at least one source parameter comprises a source direction having a source amplitude, wherein illumination from said source direction on said at least one diffractive feature produces at least one diffracted amplitude and said step of selecting a combination further comprises;

selecting a plurality of source directions having diffracted orders overlapping in direction space in accordance with said desired wafer feature pattern;

deriving a simplified function from said merit function;

computing a computed diffracted amplitude corresponding to each of said plurality of source directions at selected source amplitudes and selecting a first optimized combination of computed diffracted amplitudes, source directions and source amplitudes so that said simplified function is globally optimized;

selecting a final optimized combination of at least one source direction, at least one source amplitude and at least one diffracted amplitude so that said merit function is locally optimized using said first optimized combination as a starting solution, and so that said merit function is locally optimized in accordance with said at least one constraint; and

forming said selected at least one diffractive feature so that said at least one selected diffracted amplitude is produced when said selected at least one diffractive feature is illuminated by said source from said selected at least one source direction.

16. A computer program product for selecting a combination of source illumination parameters and diffraction mask features for projecting energy through a lens aperture to form a desired image, the computer program product comprising computer readable instructions for causing a computer to perform the method steps of:

storing a desired image pattern on a wafer plane;

storing a diffraction relationship for determining at least one diffracted amplitude diffracted by a reticle having at least one diffraction parameter when said reticle is exposed to illumination energy from an illumination source having at least one source parameter;

storing a merit function for computing a merit value of an image pattern on the wafer plane as a function of variables including said at least one diffracted amplitude;

storing at least one constraint on at least one of said variables;

determining an optimal value of said at least one diffracted amplitude so that said merit function attains a merit value that is optimized in accordance with said at least one constraint; and

selecting a combination of at least one selected source parameter and at least one selected diffraction parameter to produce said optimal value of said at least one diffracted amplitude in accordance with said diffraction relationship.

17. The computer program product of claim 16 wherein said at least one source parameter comprises both a source direction and a source intensity.

18. The computer program product of claim 16 wherein said method steps further comprise

computing characteristics of a reticle having a diffractive feature with said at least one selected diffraction parameter so that said optimal value of said at least one diffracted amplitude is produced when said diffractive feature illuminated by an illumination source having said at least one selected source parameter.

19. The method of claim 16 said at least one diffracted amplitude further comprises a first amplitude collected within a first quadrant of the lens aperture and a second amplitude collected within a second quadrant of the lens aperture, wherein said first amplitude is selected independently of said second amplitude.

20. The computer program product of claim 16 wherein said at least one constraint includes a preselected image intensity at a selected point of the desired image pattern corresponding to an edge of an element of the desired image pattern.

21. The computer program product of claim 16 wherein said merit function comprises a derivative of image intensity at a selected point on the wafer plane corresponding to an edge of an element of the desired image pattern, said derivative having a direction normal to said edge.

39. The computer program product of claim 16 wherein said at least one source parameter comprises a source direction having a source amplitude, and said step of selecting a combination further comprises:

storing a plurality of source directions having diffracted orders overlapping in direction space in accordance with said desired feature pattern;

computing a simplified function derived from said merit function;

computing a diffracted amplitude corresponding to each of said plurality of source directions at selected source amplitudes and selecting a first optimized combination of computed diffracted amplitudes, source directions and source amplitudes so that said simplified function is globally optimized;

selecting a final optimized combination of at least one selected source direction having a selected source amplitude and at least one selected diffracted amplitude so that said merit function is locally optimized using said first optimized combination as a starting solution, and so that said merit function is locally optimized in accordance with said at least one constraint; and

computing characteristics of a reticle having a diffractive feature with said at least one selected diffraction parameter so that said at least one selected diffracted amplitude is produced when said diffractive feature is illuminated by an illumination source having said at least one selected source direction having said selected source amplitude.

40. The method of claim 16 wherein the computer readable instructions for computing characteristics of said optimal reticle further comprises approximating said diffractive feature using superimposed rectangular shapes.

22. A computer program product for selecting a combination of source illumination parameters and diffraction mask features for projecting energy through a lens aperture to form a desired image, the computer program product comprising computer readable instructions for causing a computer to perform a method having the steps of:

storing a desired wafer pattern having at least one wafer feature element;

storing a merit function describing a relationship between an illumination source, a reticle, and an image pattern, said source having at least one source parameter, said reticle having at least one diffractive feature, and said image pattern having at least one image intensity;

storing at least one constraint in relation to said desired wafer feature pattern that said at least one image intensity must satisfy; and

selecting a combination of said at least one source parameter and said at least one diffractive feature,

so that said merit function is optimized in accordance with said at least one constraint, and wherein said at least one source parameter comprises a source direction having a source amplitude, wherein illumination from said source direction on said at least one diffractive feature produces at least one diffracted amplitude and said step of selecting a combination further comprises;

storing a plurality of source directions having diffracted orders overlapping in direction space in accordance with said desired feature pattern;

computing a simplified function derived from said merit function;

computing a diffracted amplitude corresponding to each of said plurality of source directions at selected source amplitudes and selecting a first optimized combination of computed diffracted amplitudes, source directions and source amplitudes so that said simplified function is globally optimized;

selecting a final optimized combination of at least one source direction, at least one source amplitude and at least one diffracted amplitude so that said merit function is locally optimized using said first optimized combination as a starting solution, and so that said merit function is locally optimized in accordance with said at least one constraint; and

computing characteristics of said selected at least one diffractive feature so that said at least one selected diffracted amplitude is produced when said selected at least one diffractive feature is illuminated by said source from said selected at least one source direction.

23. The method of claim 22 wherein the step of computing characteristics of said selected at least one diffractive feature further comprises approximating said diffractive feature using superimposed rectangular shapes.

24. A machine readable storage medium having stored therein a program of instructions executable by the machine to perform method steps for selecting a combination of source illumination parameters and diffraction mask features for projecting energy through a lens aperture to form a desired image pattern on a wafer plane, said method steps comprising:

storing a desired image pattern;

storing a diffraction relationship for determining at least one diffracted amplitude diffracted by a reticle having at least one diffraction parameter when said reticle is exposed to illumination energy from an illumination source having at least one source parameter;

storing a merit function for computing a merit value of an image pattern on the wafer plane as a function of variables including said at least one diffracted amplitude;

storing at least one constraint on at least one of said variables;

determining an optimal value of said at least one diffracted amplitude so that said merit function attains a merit value that is optimized in accordance with said at least one constraint; and

selecting a combination of at least one selected source parameter and at least one selected diffraction parameter to produce said optimal value of said at least one diffracted amplitude in accordance with said diffraction relationship.

25. The machine readable storage medium of claim 24 wherein said at least one source parameter comprises both a source direction and a source intensity.

26. The machine readable storage medium of claim 24 wherein said method steps further comprise

computing characteristics of a reticle having a diffractive feature with said at least one selected diffraction parameter so that said optimal value of said at least one diffracted amplitude is produced when said diffractive feature is illuminated by an illumination source having said at least one selected source parameter.

27. The method of claim 24 wherein said at least one diffracted amplitude further comprises a first amplitude collected within a first quadrant of the lens aperture and a second amplitude collected within a second quadrant of the lens aperture, wherein said first amplitude is selected independently of said second amplitude.

29. The machine readable storage medium of claim 24 wherein said at least one constraint includes a preselected image intensity at a selected point of the desired image pattern corresponding to an edge of an element of the desired image pattern.

30. The machine readable storage medium of claim 24 wherein said merit function comprises a derivative of image intensity at a selected point of the desired image pattern corresponding to an edge of an element of the desired image pattern, said derivative having a direction normal to said edge.

41. The machine readable storage medium of claim 24 wherein said at least one source parameter comprises a source direction having a source amplitude, and said step of selecting a combination further comprises:

selecting a plurality of source directions having diffracted orders overlapping in direction space in accordance with said desired wafer feature pattern;

deriving a simplified function from said merit function;

computing a diffracted amplitude corresponding to each of said plurality of source directions at selected source amplitudes and selecting a first optimized combination of computed diffracted amplitudes, source directions and source amplitudes so that said simplified function is globally optimized;

selecting a final optimized combination of at least one selected source direction having a selected source amplitude and at least one selected diffracted amplitude so that said merit function is locally optimized using said first optimized combination as a starting solution, and so that said merit function is locally optimized in accordance with said at least one constraint; and

computing characteristics of said optimal reticle having said diffractive feature so that said at least one selected diffracted amplitude is produced when said diffractive feature is illuminated by an illumination source having said at least one selected source direction having said selected source amplitude.

42. The machine readable storage medium of claim 26 wherein the step of computing characteristics of a reticle further comprises approximating said diffractive feature using superimposed rectangular shapes.

28. A machine readable storage medium having stored therein a program of instructions executable by the machine to perform method steps for selecting a combination of source illumination parameters and diffraction mask features for projecting energy through a lens aperture to form a desired image, said method steps comprising:

storing a desired wafer feature pattern having at least one wafer feature element;

storing instructions for causing a computer to compute a merit function describing a relationship between an illumination source, a reticle, and an image pattern, said source having at least one source parameter, said reticle having at least one diffractive feature, and said image pattern having at least one image intensity;

storing at least one constraint in relation to said desired feature pattern that said at least one image intensity must satisfy; and

selecting a combination of said at least one source parameter and said at least one diffractive feature,

so that said merit function is optimized in accordance with said at least one constraint, and wherein the step of selecting a combination further comprises approximating said diffractive feature using superimposed rectangular shapes.

31. A machine readable storage medium having stored therein a program of instructions executable by the machine to perform method steps for selecting a combination of source illumination parameters and diffraction mask features for projecting energy through a lens aperture to form a desired image, said method steps comprising:

storing a desired wafer feature pattern having at least one wafer feature element;

storing instructions for causing a computer to compute a merit function describing a relationship between an illumination source, a reticle, and an image pattern, said source having at least one source parameter, said reticle having at least one diffractive feature, and said image pattern having at least one image intensity;

storing at least one constraint in relation to said desired feature pattern that said at least one image intensity must satisfy; and

selecting a combination of said at least one source parameter and said at least one diffractive feature,

so that said merit function is optimized in accordance with said at least one constraint, and wherein said at least one source parameter comprises a source direction having a source amplitude, wherein illumination from said source direction on said at least one diffractive feature produces at least one diffracted amplitude and said step of selecting a combination further comprises;

selecting a plurality of source directions having diffracted orders overlapping in direction space in accordance with said desired wafer feature pattern;

deriving a simplified function from said merit function;

computing a diffracted amplitude corresponding to each of said plurality of source directions at selected source amplitudes and selecting a first optimized combination of computed diffracted amplitudes, source directions and source amplitudes so that said simplified function is globally optimized;

selecting a final optimized combination of at least one source direction, at least one source amplitude and at least one diffracted amplitude so that said merit function is locally optimized using said first optimized combination as a starting solution, and so that said merit function is locally optimized in accordance with said at least one constraint; and

designing said selected at least one diffractive feature so that said selected at least one diffracted amplitude is produced when said selected at least one diffractive feature is illuminated by said source from said selected at least one source direction.

32. A machine readable storage medium having stored therein a program of instructions executable by the machine to perform method steps for selecting a combination of source illumination parameters and diffraction mask features for projecting energy through a lens aperture to form a desired image, said method steps comprising:

storing a desired wafer feature pattern having at least one wafer feature element;

storing instructions for causing a computer to compute a merit function describing a relationship between an illumination source, a reticle, and an image pattern, said source having at least one source parameter, said reticle having at least one diffractive feature, and said image pattern having at least one image intensity;

storing at least one constraint in relation to said desired feature pattern that said at least one image intensity must satisfy; and

selecting a combination of said at least one source parameter and said at least one diffractive feature,

so that said merit function is optimized in accordance with said at least one constraint, and wherein the step of selecting a combination further comprises approximating said selected at least one diffractive feature using superimposed rectangular shapes.

33. A lithographic system for printing a desired wafer feature pattern on a semiconductor wafer including a photoactive material, the system comprising:

an illumination source having at least one source parameter;

a reticle having at least one diffraction parameter; and

a lens;

said illumination source, said reticle and said lens being arranged so that said illumination source illuminates said reticle so as to produce a plurality of diffracted amplitudes and said plurality of diffracted amplitudes are collected by said lens and projected to form a image on the semiconductor wafer and wherein

said at least one source parameter and said at least one diffraction parameter are selected so that a merit function, expressed as a function of variables including said plurality of diffracted amplitudes, attains an optimal merit value and wherein said merit function is optimized in accordance with at least one constraint on at least one of said variables,

so that exposing the photoactive material to said image and developing said exposed photoactive material forms a printed pattern that substantially conforms with the desired wafer feature pattern.

34. A reticle for diffracting illumination energy to form a desired image pattern having a pattern of intensities, the desired image pattern having a desired bright area in which the intensities within the desired bright area exceed a predetermined bright threshold and having a desired dark area in which the intensities within the desired dark area are less than a predetermined dark threshold, the reticle comprising a pattern of phase-shifting material arranged so that the desired dark area is formed completely by destructive interference of diffracted illumination energy diffracted by said pattern of phase-shifting material.

35. The reticle of claim 34 wherein said phase-shifting material comprises phase-shifting chrome material that transmits at least some illumination energy.