Lithographic apparatus, level sensor, method of inspection, device manufacturing method, and device manufactured thereby
First Claim
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1. A lithographic apparatus comprising a level sensor configured to measure a height of a wafer surface, said level sensor comprising:
- a first reflector having at least two layers and being configured to direct a beam from a light source toward the wafer surface; and
a second reflector having at least two layers and being configured to direct the beam from the wafer surface to a detector,wherein a magnitude of an apparent depression of the wafer surface due to translation of the beam at reflective surfaces of the first and second reflectors is less than thirty-five nanometers.
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Abstract
A level sensor for a lithographic projection apparatus according to one embodiment of the invention includes a light source, a first reflector, a second reflector and a detector. The first reflector is positioned to direct light from the light source towards a wafer surface, and the second reflector is positioned to direct light reflected from the wafer surface to the detector. The first and second reflectors are selected to incur a minimal process dependent apparent surface depression.
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Citations
24 Claims
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1. A lithographic apparatus comprising a level sensor configured to measure a height of a wafer surface, said level sensor comprising:
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a first reflector having at least two layers and being configured to direct a beam from a light source toward the wafer surface; and a second reflector having at least two layers and being configured to direct the beam from the wafer surface to a detector, wherein a magnitude of an apparent depression of the wafer surface due to translation of the beam at reflective surfaces of the first and second reflectors is less than thirty-five nanometers. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. A method comprising:
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positioning a first reflector of a level sensor of a lithographic apparatus to direct a light beam from a light source toward a surface of a wafer, wherein the first reflector includes at least two layers; positioning a second reflector of a level sensor of a lithographic apparatus to direct the beam from the surface of the wafer to a detector, wherein the second reflector includes at least two layers; and selecting the first and second reflectors to obtain a minimum total effective translation of the beam at the surfaces of the first and second reflectors. - View Dependent Claims (16, 17, 18)
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19. A lithographic method comprising:
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using a first reflector of a level sensor of a lithographic apparatus to direct a light beam from a light source toward a wafer surface, wherein the first reflector includes at least two layers; using a second reflector of the level sensor of the lithographic apparatus to direct the beam from the wafer surface to a detector, wherein the second reflector includes at least two layers; and determining a height of the surface of the wafer based on the beam incident on the detector, wherein a magnitude of an apparent depression of the surface of the wafer due to translation of the beam at reflective surfaces of the first and second reflectors is less than thirty-five nanometers. - View Dependent Claims (20, 21, 22, 23)
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24. A lithographic apparatus comprising a level sensor configured to measure a height of a wafer surface, said level sensor comprising:
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a first reflector configured to direct a beam from a light source toward the wafer surface, wherein the first reflector includes at least two layers; and a second reflector configured to direct the beam from the wafer surface to a detector, wherein the second reflector includes at least two layers, and wherein the first reflector and the second reflector are selected to obtain a minimum total effective translation of the beam at the surfaces of the first reflector and the second reflector.
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Specification