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

• US 20020140920A1
• Filed: 01/29/2001
• Published: 10/03/2002
• Est. Priority Date: 01/29/2001
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: International Business Machines Corporation
• Inventors: Rosenbluth, Alan E., Wong, Alfred K. K., Bukofsky, Scott Josef
• Granted Patent: US 6,563,566 B2
• Time in Patent Office: Days
• 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 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 constraints.

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

3. The method of claim 1 wherein said at least one diffractive feature produces at least one diffracted amplitude when said illumination energy is diffracted by said reticle,

said merit function describes a relationship including said at least one diffracted amplitude, and

said step of selecting a combination of said source parameter and said diffractive feature further comprises:

selecting said at least one diffracted amplitude so that said merit function is optimized in accordance with said at least one constraint; and

forming said diffractive feature so that said selected at least one diffracted amplitude is produced when said diffractive feature is illuminated by said source in accordance with said selected source parameter.

4. The method of claim 3 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 said image corresponding to an edge of said at least one wafer feature element.

6. The method of claim 1 wherein said merit function comprises a derivative of said at least one image intensity at a selected point of said image corresponding to an edge of said at least one wafer feature element, said derivative having a direction normal to said edge.

7. The method of claim 1 wherein said at least one source parameter comprises a source direction having an 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 diffractive feature so that said at least one selected diffracted amplitude is produced when said 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 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 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 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.

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

11. The method of claim 9 wherein said at least one diffractive feature produces at least one diffracted amplitude when said illumination energy is diffracted by said reticle, and

said merit function relationship includes said at least one diffracted amplitude, and

said step of selecting a combination of said source parameter and said diffractive feature further comprises:

selecting said at least one diffracted amplitude so that said merit function is optimized in accordance with said at least one constraint; and

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

12. The method of claim 11 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 said image corresponding to an edge of said at least one wafer feature element.

14. The method of claim 9 wherein said merit function comprises a derivative of said at least one image intensity at a selected point of said image corresponding to an edge of said at least one wafer feature element, said derivative having a direction normal to said edge.

15. The method of claim 9 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 diffractive feature so that said at least one selected diffracted amplitude is produced when said diffractive feature is illuminated by said source from said selected at least one source direction.

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

18. The computer program product of claim 16 wherein said at least one diffractive feature produces at least one diffracted amplitude when said illumination energy is diffracted by said reticle,

said merit function relationship includes said at least one diffracted amplitude, and

said step of selecting a combination of said at least one source parameter and said at least one diffractive feature further comprises:

selecting said at least one diffracted amplitude so that said merit function is optimized in accordance with said at least one constraint; and

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

19. The method of claim 18 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 said image corresponding to an edge of said at least one wafer feature element.

21. The computer program product of claim 16 wherein said merit function comprises a derivative of said image at a selected point of said image corresponding to an edge of said at least one wafer feature element, said derivative having a direction normal to said edge.

22. The computer program product of claim 16 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 diffractive feature so that said at least one selected diffracted amplitude is produced when said diffractive feature is illuminated by said source from said selected at least one source direction.

23. The method of claim 22 wherein the computer readable instructions for computing characteristics of said adjustable diffractive feature further comprises approximating said diffractive feature using superimposed rectangular shapes.

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

26. The machine readable storage medium of claim 24 wherein said at least one diffractive feature produces at least one diffracted amplitude when said illumination energy is diffracted by said reticle, and

said merit function relationship includes said at least one diffracted amplitude, and

said step of selecting a combination of said source parameter and said diffractive feature further comprises:

selecting said at least one diffracted amplitude so that said merit function is optimized in accordance with said at least one constraint; and

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

27. The method of claim 26 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.

28. The machine readable storage medium of claim 24 wherein the step of forming said diffractive feature further comprises approximating said diffractive feature using superimposed rectangular shapes.

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 said image corresponding to an edge of said at least one wafer feature element.

30. The machine readable storage medium of claim 24 wherein said merit function comprises a derivative of said image at a selected point of said image corresponding to an edge of said at least one wafer feature element, said derivative having a direction normal to said edge.

31. The machine readable storage medium of claim 24 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 diffractive feature so that said selected at least one diffracted amplitude is produced when said diffractive feature is illuminated by said source from said selected at least one source direction.

32. The machine readable storage medium of claim 24 wherein the step of forming said diffractive feature further comprises approximating said diffractive feature using superimposed rectangular shapes.

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 performing a method having the following steps:

causing a computer to store a desired wafer pattern having at least one wafer feature element;

causing the 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 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.

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, 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 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.

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 diffractive feature; and

a lens;

said illumination source, said reticle and said lens being arranged so that said 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, the image having at least one image intensity and wherein

said at least one source parameter and said at least one diffractive feature are selected in accordance with a merit function describing a relationship between said at least one source parameter, said plurality of diffracted amplitudes, and said at least one image intensity and wherein said merit function is optimized in accordance with at least one constraint that said at least one image intensity must satisfy,

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

35. The reticle of claim 34 wherein said phase-shifting material comprises phase-shifting chrome material.

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