Speckle reduction method and system for EUV interferometry
AssigneeASML Holding N.V.
InventorsRichard A. Gontin, Yuli Vladimirsky
Life of this patent
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Abstract
A wavefront measurement system has a source of electromagnetic radiation. An imaging system focuses the electromagnetic radiation at an object plane. A first grating is positioned in the object plane and has a plurality of rulings with randomized height. A stage moves the first grating parallel to the rulings. A projection optical system projects an image of the first grating onto an image plane. A second grating is at the image plane. A detector behind the second grating receives a fringe pattern produced by the second grating.
Claims9
An interferometer system comprising:
- a first grating having a plurality of rulings of randomized height;
- an imaging system that focuses the electromagnetic radiation at the first grating;
- a second grating assembly, wherein the second grating assembly is located further away from a source of the electromagnetic radiation than the first grating assembly;
- an optical system that projects an image of the first grating onto the second grating assembly;
- and
- a detector that receives a fringe pattern produced by the second grating assembly.
An interferometer system comprising:
- a first grating having a plurality of rulings of randomized height;
- an imaging system that focuses electromagnetic radiation at the first grating;
- a second grating assembly, wherein the second grating assembly is located further away from a source of the electromagnetic radiation than the first grating assembly;
- an optical system that projects an image of the first grating onto the second grating assembly;
- and
- a detector that receives a fringe pattern produced by the second grating assembly,
- wherein the second grating assembly comprises:
- two gratings disposed, respectively, on top of one another, wherein each of the two gratings has a pitch configuration with a checkerboard-like interference pattern.
A method of measuring a wavefront of an optical system comprising:
- directing electromagnetic radiation to a first grating having a plurality of rulings of randomized heights;
- optically conjugating the first grating with an image plane;
- receiving reflected radiation from the first grating at a second grating located at the image plane while simultaneously moving the first grating parallel to the rulings;
- and
- determining wavefront parameters from the image.
Dependencies are inferred from the claim text.