System and method for calibrating a spatial light modulator array using shearing interferometry

• US 6,965,436 B2
• Filed: 11/05/2004
• Issued: 11/15/2005
• Est. Priority Date: 01/29/2004
• Status: Active Grant

• Current Assignee: ASML Holding NV
• Original Assignee: ASML Holding NV
• Inventors: Latypov, Azat M., Poultney, Sherman K.
• Primary Examiner(s): Epps, Georgia
• Assistant Examiner(s): CHOI, WILLIAM C
• Application Number:
  US10/981,706
• Publication Number:
  US 20050168791A1
• Time in Patent Office: 375 Days
• Field of Search: 356/121, 356/520, 356/521, 250/201.9
• US Class Current: 356/520
• CPC Class Codes: G03F 7/70291 Addressable masks, e.g. spatial light modulators [SLMs], digital micro-mirror devices [DMDs] or liquid crystal display [LCD] patterning devices
• CPC Class Codes: G03F 7/70516 Calibration of components of the microlithographic apparatus, e.g. light sources, addressable masks or detectors

Abstract

A system for calibrating a spatial light modulator array includes an illumination system and a spatial light modulator array that reflects or transmits light from the illumination system. A projection optical system images the spatial light modulator array onto an image plane. A shearing interferometer creates an interference pattern in the image plane. A controller controls modulation of elements of the spatial light modulator array. The shearing interferometer includes a diffraction grating, a prism, a folding mirror or any other arrangement for generating shear. The shearing interferometer can be a stretching shearing interferometer, a lateral shearing interferometer, or a rotational shearing interferometer. The shearing interferometer may include a diffraction grating with a pitch corresponding to a shear of the light by an integer number of elements. The projection optics resolves each element of the spatial light modulator array in the image plane. The controller can modulate alternate columns of elements of the spatial light modulator array.

Claims

1. A system for calibrating a spatial light modulator array comprising:

a spatial light modulator array;

a projection optical system that images the spatial light modulator array onto an image plane;

a shearing interferometer that generates an interference pattern in the image plane; and

a controller that modulates the spatial light modulator array.

2. The system of claim 1, wherein the shearing interferometer comprises any of a diffraction grating, a prism, and a folding mirror for generating shear.

3. The system of claim 1, wherein the shearing interferometer is a lateral shearing interferometer.

4. The system of claim 1, wherein the shearing interferometer is a stretching shearing interferometer.

5. The system of claim 1, wherein the shearing interferometer is a rotational shearing interferometer.

6. The system of claim 1, wherein the projection optics resolves each element of the spatial light modulator array in the image plane.

7. The system of claim 1, wherein the controller modulates alternate columns of elements of the spatial light modulator array.

8. The system of claim 1, wherein the shearing interferometer comprises a diffraction grating with a pitch corresponding to a shear of the light by an integer number of elements of the spatial light modulator array.

9. The system of claim 1, wherein the shearing interferometer comprises a diffraction grating with a pitch corresponding to a shear of the light by a fractional number of elements of the spatial light modulator array.

10. The system of claim 1, wherein the controller controls any of tilting, pistoning, and deformation of the elements.

11. The system of claim 1, further including a CCD detector in the image plane for detecting the interferogram.

12. The system of claim 11, wherein the CCD detector comprises a plurality of detector cells corresponding to each element of the spatial light modulator array.

13. The system of claim 1, wherein the spatial light modulator array is a reflective spatial light modulator array.

14. The system of claim 1, wherein the spatial light modulator array is a pistoning spatial light modulator array.

15. The system of claim 1, wherein the spatial light modulator array is a tilting micromirror spatial light modulator array.

16. The system of claim 1, wherein the spatial light modulator array is a transmissive spatial light modulator array.

17. A method for calibrating a spatial light modulator array comprising:

(a) modulating a spatial light modulator array;

(b) imaging the spatial light modulator onto an image plane;

(c) shearing the light so as to create an interference pattern in the image plane;

(d) measuring interference fringes; and

(e) repeating the steps (a)–

(d) to calibrate the spatial light modulator array.

18. The method of claim 17, wherein step (c) comprises shearing the light using any of a diffraction grating, a prism and a folding mirror.

19. The method of claim 17, wherein step (c) comprises shearing the light using a stretching shearing interferometer.

20. The method of claim 17, wherein step (c) comprises shearing the light using a rotational shearing interferometer.

21. The system of claim 17, wherein step (c) comprises shearing the light using a diffraction grating with a pitch corresponding to a shear of the light by an integer number of spatial light modulator array elements.

22. The system of claim 17, wherein step (c) comprises shearing the light using a diffraction grating with a pitch corresponding to a shear of the light by an fractional number of spatial light modulator array elements.