Automatic focusing apparatus
First Claim
1. An automatic focusing apparatus comprising:
- a stage which holds a substrate and which is movable in a horizontal direction and a vertical direction;
an objective lens disposed facing a surface of the substrate;
a first illumination optics which illuminates the surface of the substrate with at least one spotted light beam from an oblique direction;
a first photodetector which detects reflected light from the surface of the substrate to output a first electrical signal;
a first position detection circuit which detects a vertical position of the surface of the substrate from the first electric signal to output a first position detection signal;
a correction circuit which monitors the first position detection signal in real time and which subtracts a surplus exceeding a signal change corresponding to a surface shape change of the substrate from the first position detection signal, when a change amount per unit time of the first position detection signal exceeds a first predetermined level, to output a corrected position signal; and
a stage control circuit which controls the vertical position of the stage based on the corrected position signal.
1 Assignment
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Accused Products
Abstract
An automatic focusing apparatus comprises a stage holding a substrate, an objective lens disposed facing the substrate surface, an illumination optics illuminating the substrate surface with a spotted light beam from an oblique direction, a photodetector detecting reflected light from the substrate surface, a position detection circuit detecting a vertical position of the substrate surface from an electric signal obtained from the photodetector to output a position signal, a correction circuit monitoring the position signal in real time and subtracting a surplus exceeding a signal change corresponding to a surface shape change of the substrate from the position signal, when a change amount per unit time of the position signal exceeds a predetermined level and outputting a corrected position signal, and a stage control circuit controlling the vertical position of the stage based on the corrected position signal.
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Citations
20 Claims
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1. An automatic focusing apparatus comprising:
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a stage which holds a substrate and which is movable in a horizontal direction and a vertical direction;
an objective lens disposed facing a surface of the substrate;
a first illumination optics which illuminates the surface of the substrate with at least one spotted light beam from an oblique direction;
a first photodetector which detects reflected light from the surface of the substrate to output a first electrical signal;
a first position detection circuit which detects a vertical position of the surface of the substrate from the first electric signal to output a first position detection signal;
a correction circuit which monitors the first position detection signal in real time and which subtracts a surplus exceeding a signal change corresponding to a surface shape change of the substrate from the first position detection signal, when a change amount per unit time of the first position detection signal exceeds a first predetermined level, to output a corrected position signal; and
a stage control circuit which controls the vertical position of the stage based on the corrected position signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 15)
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10. An automatic focusing apparatus comprising:
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a stage which holds a substrate and which is movable in a horizontal direction and a vertical direction;
an objective lens disposed facing the surface of the substrate;
an illumination optics which illuminates the surface of the substrate with a plurality of spotted light beams from an oblique direction at different incident angles or in different incident directions;
a plurality of photodetectors which detect a plurality of reflected lights from the surface of the substrate to output electric signals;
a position detection circuit which selects an electric signal having a minimum signal change amount from the electric signals to detect a vertical position of the surface of the substrate to output a position signal; and
a stage control circuit which controls the vertical position of the stage based on the position signal. - View Dependent Claims (11, 12, 13)
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14. An automatic focusing apparatus comprising:
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a stage which holds a substrate and which is movable in a horizontal direction and a vertical direction;
an objective lens disposed facing the surface of the substrate;
an illumination optics which illuminates the surface of the substrate with a spotted light beam from an oblique direction;
a wave plate which is disposed in the illumination optics to obtain a circular polarization of the light beam incident upon the surface of the substrate from the oblique direction;
a beam splitter which branches the reflected light from the surface of the substrate into two reflected beams in two directions;
a first polarizing beam splitter which branches one of the two reflected beams into a first and a second light beam whose polarization directions cross each other at a right angle;
a second polarizing beam splitter which branches the other of the two reflected beams into a third and a fourth light beam whose polarization directions cross each other at the right angle and whose polarization directions are different from those of the first and the second light beam by 45 degrees;
a first photodetector which detects the first light beam to output a first electric signal;
a second photodetector which detects the second light beam to output a second electric signal;
a third photodetector which detects the third light beam to output a third electric signal;
a fourth photodetector which detects the fourth light beam to output a fourth electric signal;
a position detection circuit which receives the first to the fourth electric signal and which selects an electric signal having a minimum change amount to detect a vertical position of the surface of the substrate and output a position signal; and
a stage control circuit which controls the vertical position of the stage based on the position signal. - View Dependent Claims (16)
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17. An automatic focusing apparatus comprising:
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a stage which holds a substrate and which is movable in a horizontal direction and a vertical direction;
an objective lens disposed facing the surface of the substrate;
an illumination optics which faces the substrate via the objective lens;
a first beam splitter which transmits a light beam emitted from the illumination optics to irradiate the surface of the substrate with a spotted light beam and receives a reflected light beam from the substrate to emit the reflected light beam out by reflection;
a condensing optics which converges the reflected light beam emitted from the first beam splitter to output a converged beam;
a second beam splitter which branches the converged beam into a first and a second branched light in two directions;
a first area sensor which is disposed on a light path of the first branched light and before a focal position of the condensing optics to detect the first branched light and output a first electric signal;
a second area sensor which is disposed on a light path of the second branched light and behind the focal position of the condensing optics to detect the second branched light and output a second electric signal;
a position detection circuit which processes the first and the second electric signal to detect a vertical position of the substrate and output a position signal; and
a stage control circuit which controls the vertical position of the stage based on the position signal. - View Dependent Claims (18, 19, 20)
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Specification