Lens heating compensation systems and methods

• US 8,570,485 B2
• Filed: 05/29/2009
• Issued: 10/29/2013
• Est. Priority Date: 06/03/2008
• Status: Active Grant

• Current Assignee: ASML Netherlands BV (ASML Holding NV)
• Original Assignee: ASML Netherlands BV (ASML Holding NV)
• Inventors: Ye, Jun, Liu, Peng, Cao, Yu
• Primary Examiner(s): Ton, Toan
• Assistant Examiner(s): Sanei, Mona M
• Application Number:
  US12/475,071
• Publication Number:
  US 20090296055A1
• Time in Patent Office: 1,614 Days
• Field of Search: 355/30, 355/52, 355/55, 355/67, 430/30, 250/548
• US Class Current: 355/30
• CPC Class Codes: G03F 7/70266 Adaptive optics, e.g. deformable optical elements for wavefront control, e.g. for aberration adjustment or correction
• CPC Class Codes: G03F 7/70441 Optical proximity correction [OPC]
• CPC Class Codes: G03F 7/705 Modelling or simulating from physical phenomena up to complete wafer processes or whole workflow in wafer productions
• CPC Class Codes: G03F 7/70504 Optical system modelling, e.g. lens heating models
• CPC Class Codes: G03F 7/706 Aberration measurement
• CPC Class Codes: G03F 7/70891 Temperature
• CPC Class Codes: G06F 30/00 Computer-aided design [CAD]

Abstract

Methods for calibrating a photolithographic system are disclosed. A cold lens contour for a reticle design and at least one hot lens contour for the reticle design are generated from which a process window is defined. Aberrations induced by a lens manipulator are characterized in a manipulator model and the process window is optimized using the manipulator model. Aberrations are characterized by identifying variations in critical dimensions caused by lens manipulation for a plurality of manipulator settings and by modeling behavior of the manipulator as a relationship between manipulator settings and aberrations. The process window may be optimized by minimizing a cost function for a set of critical locations.

Claims

1. A method of calibrating a photolithographic system, comprising:

generating a cold lens contour for a reticle design;

generating at least one hot lens contour for the reticle design;

characterizing aberrations induced by a corrective system in a correction model; and

optimizing a process window of the photolithographic system using the correction model, wherein optimizing the process window includes controlling the corrective system such that variations in parameters of one or more features of the reticle design obtained from the cold lens contour and the at least one hot lens contour lie within a predetermined limit over an optimal amount of photolithographic system process settings,

wherein generating the cold lens contour includes using a lens model based on measurements obtained while a lens of the photolithographic system is maintained within a nominal operating temperature range,

wherein each hot lens contour is generated using a corresponding lens heating model, wherein the lens heating model characterizes light-induced heating of the lens in a photolithographic process, and

wherein optimizing the process window includes minimizing variations in critical dimensions caused by lens heating by inducing other variations in critical dimensions caused by lens aberrations.

2. The method of claim 1, wherein generating the cold lens contour or the at least one hot lens contour includes performing diffraction calculations based on the reticle design.

3. The method of claim 1, wherein the at least one hot lens contour is generated after working portions of a lens of the photolithographic system have been heated by light transmission.

4. The method of claim 1, wherein the step of characterizing aberrations includes:

identifying variations in critical dimensions caused by lens aberrations for a plurality of correction settings for the corrective system; and

modeling behavior of the corrective system as a linear relationship between the correction settings and aberrations.

5. The method of claim 1, further comprising identifying first variations in critical dimensions caused by lens heating, wherein the step of characterizing aberrations includes:

modeling behavior of the corrective system as a linear relationship between correction settings and the induced aberrations; and

identifying second variations in the critical dimensions caused by the induced aberrations for a plurality of the correction settings.

6. The method of claim 5, wherein the critical dimensions are identified in an image of the reticle design.

7. The method of claim 5, wherein the first variations in critical dimensions are expressed as a function of lens heating.

8. The method of claim 5, wherein the second variations in critical dimensions are expressed as a function of the correction settings.

9. The method of claim 5, wherein the first and second variations in the critical dimensions are expressed as a function of Zernike coefficients.

10. The method of claim 9, wherein the Zernike coefficients represent perturbations in the critical dimensions caused by the corrective system.

11. The method of claim 9, wherein the Zernike coefficients characterize aberrations induced by the corrective system.

12. The method of claim 9, wherein the Zernike coefficients represent perturbations in the critical dimensions caused by lens heating.

13. The method of claim 5, wherein optimizing a process window includes generating a cost function for a set of critical locations.

14. The method of claim 5, wherein optimizing a process window includes generating a cost function for a set of critical hotspots.

15. The method of claim 13 or 14, wherein optimizing a process window includes minimizing the cost function.

16. The method of claim 14, wherein minimizing the cost function includes calculating a gradient of the cost function using one of a steepest descent method and a conjugate gradient method.

17. The method of claim 1, wherein the parameters comprise critical dimensions.

18. A device manufacturing method of calibrating a photolithographic system, comprising:

using a projection system to expose a target portion of a layer of radiation sensitive material which at least partially covers a substrate with a projection beam of radiation having a cross section, comprising;

using patterning means to endow the projection beam with a pattern in the cross-section;

generating a cold projection system contour for the patterning means;

generating at least one hot projection system contour for the patterning means;

characterizing aberrations induced by a projection system correction system in a correction model; and

optimizing a process window using the correction model, wherein optimizing the process window includes calculating correction settings for the projection system correction system such that variations in parameters of one or more features of the reticle design obtained from the cold projection system contour and the at least one hot projection system contour lie within a predetermined limit over an optimal amount of photolithographic system process settings, and

manipulating the projection system of the photolithographic system according to the calculated correction settings,

wherein generating the cold projection system contour includes using a lens model based on measurements obtained while a lens of the photolithographic system is maintained within a nominal operating temperature range,

wherein each hot projection system contour is generated using a corresponding lens heating model, wherein the lens heating model characterizes light-induced heating of the lens in a photolithographic process, and

wherein optimizing the process window includes minimizing variations in critical dimensions caused by lens heating by inducing other variations in critical dimensions caused by lens aberrations.

19. A method according to claim 18, wherein the correction system is a manipulator.

20. A non-transitory computer readable medium bearing a computer program for calibrating a photolithographic system, the computer program, when executed, causing a computer to perform the steps of:

generating a cold lens contour for a reticle design;

generating at least one hot lens contour for the reticle design;

characterizing aberrations induced by a lens manipulator in a manipulator model; and

optimizing a process window of the photolithographic system using the manipulator model, wherein optimizing the process window includes controlling the lens manipulator such that variations in parameters of one or more features of the reticle design obtained from the cold lens contour and the at least one hot lens contour lie within a predetermined limit over an optimal amount of photolithographic system process setting,

wherein generating the cold lens contour includes using a model based on measurements obtained while the lens is maintained within a nominal operating temperature range,

wherein each hot lens contour is generated using a corresponding lens heating model,

wherein the lens heating model characterizes light-induced heating of the lens in a photolithographic process, and

wherein optimizing the process window includes minimizing variations in critical dimensions caused by lens heating by inducing other variations in critical dimensions caused by lens aberrations.

21. A computer readable medium of claim 20, wherein generating the cold lens contour or the at least one hot lens contour includes performing diffraction calculations based on the reticle design.

22. The computer readable medium of claim 20, wherein the at least one hot lens contour is generated after working portions of the lens have been heated by light transmission.

23. The computer readable medium of claim 20, wherein the step of characterizing aberrations includes:

identifying variations in critical dimensions caused by lens aberrations for a plurality of manipulator settings; and

modeling behavior of the manipulator as a linear relationship between manipulator settings and aberrations.

24. The computer readable medium of claim 23, wherein optimizing a process window includes generating a cost function for a set of critical hotspots.

25. The computer readable medium of claim 24, wherein optimizing a process window includes minimizing the cost function.

26. The computer readable medium of claim 24, wherein minimizing the cost function includes calculating a gradient of the cost function using one of a deepest descent method and a conjugate gradient method.

27. The computer readable medium of claim 20, wherein the computer program further causes the computer to perform the step of identifying first variations in critical dimensions caused by lens heating, wherein the step of characterizing aberrations includes:

modeling behavior of the manipulator as a linear relationship between manipulator settings and the induced aberrations; and

identifying second variations in the critical dimensions caused by the induced aberrations for a plurality of manipulator settings.

28. The computer readable medium of claim 27, wherein the critical dimensions are identified in an image of the reticle.

29. The computer readable medium of claim 27, wherein the first variations in critical dimensions are expressed as a function of lens heating.

30. The computer readable medium of claim 27, wherein the second variations in critical dimensions are expressed as a function of manipulator setting.

31. The computer readable medium of claim 27, wherein the first and second variations in the critical dimensions are expressed as a function of Zernikes.

32. The computer readable medium of claim 31, wherein Zernike coefficients represent perturbations in the critical dimensions caused by the manipulator.

33. The computer readable medium of claim 31, wherein Zernike coefficients characterize the manipulator induced aberrations.

34. The computer readable medium of claim 31, wherein Zernike coefficients represent perturbations in the critical dimensions caused by lens heating.