Off-axis levelling in lithographic projection apparatus

• US 20050088638A1
• Filed: 10/29/2004
• Published: 04/28/2005
• Est. Priority Date: 03/08/1999
• Status: Active Grant

• Current Assignee: ASML Netherlands BV (ASML Holding NV)
• Original Assignee: ASML Netherlands BV (ASML Holding NV)
• Inventors: van Asten, Nicolaas A.A.J., Boonman, Marcus E.J., Castenmiller, Thomas J.M., Jasper, Johannes C.M., Geman, Jacobus, Heuts, Frederik T.E., Du Croo de Jongh, Richard J.H., Klinkhamer, Jacob F.F., Loopstra, Erik R., Modderman, Theodorus M., Nijmeijer, Gerrit J.
• Granted Patent: US 7,019,815 B2
• Time in Patent Office: Days
• US Class Current: 355/55
• CPC Class Codes: G03F 9/70 for microlithography measuring printed patterns for monitoring overlay G03F7/70633 or focus G03F7/70641; projection system adjustment G03F7/70258; position control G03F7/70775
• CPC Class Codes: G03F 9/7026 Focusing
• CPC Class Codes: G03F 9/7034 Leveling
• CPC Class Codes: G03F 9/7049 Technique, e.g. interferometric
• CPC Class Codes: G03F 9/7096 Arrangement, mounting, housing, environment, cleaning or maintenance of apparatus

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.

Claims

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.

2. An apparatus according to claim 1, wherein the first and second sensors are substantially static.

3. An apparatus according to claim 1, wherein the first and second sensors are configured to provide optimal measurements when said substrate is a reference substrate and to provide sub-optimal measurements when said substrate is a production substrate.

4. An apparatus according to claim 3, wherein said reference substrate is a bare silicon wafer.

5. An apparatus according to claim 4, wherein said bare silicon wafer has a surface that is polished.