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

• US 20050225859A1
• Filed: 06/13/2005
• Published: 10/13/2005
• 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.
• Granted Patent: US 7,158,238 B2
• Time in Patent Office: Days
• US Class Current: 359/520
• CPC Class Codes: G01J 9/0215 by shearing interferometric methods
• CPC Class Codes: G02B 26/0833 the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD G02B26/0825 takes precedence; micromechanical devices in general B81B
• 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 7/70591 Testing optical components

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 plurality of pixels in an object plane;

a projection optical system that images the pixels onto an image plane;

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

a controller that modulates the pixels.

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

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

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

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

6. The system of claim 1, wherein the projection optics resolves each pixel in the image plane.

7. The system of claim 1, wherein the controller modulates alternate columns of the pixels.

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

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

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

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 pixels.

13. The system of claim 1, wherein the pixels are reflective.

14. The system of claim 1, wherein the pixels are pistoning pixels.

15. The system of claim 1, wherein the pixels are tilting micromirror pixels.

16. The system of claim 1, wherein the pixels are transmissive pixels.

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

(a) modulating a plurality of pixels in an object plane;

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

(c) measuring interference fringes of the interference pattern; and

(d) repeating the steps (a)-(c) to calibrate the pixels.

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

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

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

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

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