Off-axis levelling in lithographic projection apparatus
First Claim
1. A method of measuring the response of a level sensor comprising:
- placing a substrate on a substrate table;
moving the substrate table to a known height;
measuring a height of an area of the substrate using the level sensor;
moving the substrate to a second known height;
measuring a height of the area of the substrate using the level sensor, and comparing the known heights with the measured heights using the level sensor to determine the response of the level sensor.
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Abstract
In an off-axis levelling procedure a height map of the substrate is generated at a measurement station. The height map is referenced to a physical reference surface of the substrate table. The physical reference surface may be a surface in which is inset a transmission image sensor. At the exposure station the height of the physical reference surface is measured and related to the focal plane of the projection lens. The height map can then be used to determine the optimum height and/or tilt of substrate table to position the exposure area on the substrate in best focus during exposure. The same principles can be applied to (reflective) masks.
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Citations
16 Claims
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1. A method of measuring the response of a level sensor comprising:
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placing a substrate on a substrate table;
moving the substrate table to a known height;
measuring a height of an area of the substrate using the level sensor;
moving the substrate to a second known height;
measuring a height of the area of the substrate using the level sensor, and comparing the known heights with the measured heights using the level sensor to determine the response of the level sensor. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
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Specification