Off-axis leveling in lithographic projection apparatus
First Claim
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1. A lithographic projection apparatus comprising:
- a radiation system constructed and arranged to supply a projection beam of radiation;
a first object table provided with a mask holder constructed and arranged to hold a mask;
a second, movable object table provided with a substrate holder constructed and arranged to hold a substrate;
a measurement station having a first position detection system configured to measure the position of said second object table at said measurement station;
an exposure station having a projection system configured to image irradiated portions of the mask onto target portions of the substrate;
a second position detection system configured to measure the position of said second object table at said exposure station;
a first sensor at said measurement station, said first sensor being arranged to measure the position of the surface of the substrate in a first direction substantially perpendicular to the substrate surface; and
a second sensor at said exposure station, said second sensor being arranged to measure the position of the surface of the substrate in said first direction.
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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
11 Claims
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1. A lithographic projection apparatus comprising:
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a radiation system constructed and arranged to supply a projection beam of radiation; a first object table provided with a mask holder constructed and arranged to hold a mask; a second, movable object table provided with a substrate holder constructed and arranged to hold a substrate; a measurement station having a first position detection system configured to measure the position of said second object table at said measurement station; an exposure station having a projection system configured to image irradiated portions of the mask onto target portions of the substrate; a second position detection system configured to measure the position of said second object table at said exposure station; a first sensor at said measurement station, said first sensor being arranged to measure the position of the surface of the substrate in a first direction substantially perpendicular to the substrate surface; and a second sensor at said exposure station, said second sensor being arranged to measure the position of the surface of the substrate in said first direction. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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Specification