Method and system for improving focus accuracy in a lithography system
AssigneeASML Holding N.V.
InventorsMichael L. Nelson, Justin L. Kreuzer, Peter L. Filosi, Christopher J. Mason
Life of this patent
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Abstract
A focus system that includes a calibration subsystem and a control subsystem. The control subsystem, which includes a control sensor, is in close proximity to the exposing of an image. The calibration subsystem, which includes a calibration sensor and a control sensor, is located remotely from, or off-axis with respect to, the exposing of an image. By separating calibration and control functions, the functional requirements can be separated into two (or more) types of sensors.
Claims20
A system for improving focus accuracy in a lithography system, comprising:
- a calibration sensor having relatively high focus accuracy;
- a secondary control sensor having relatively low focus accuracy, wherein the focus accuracy of the secondary control sensor is related to the focus accuracy of the calibration sensor by a calibration value;
- a primary control sensor having substantially the same focus accuracy as the secondary control sensor and configured to measure a focal distance to a surface of a substrate;
- and
- a focal adjustment system configured to determine an actual focal distance of the surface of the substrate based on the focal distance measured by the primary control sensor and the calibration value and adjust a position of the substrate based on the actual focal distance.
A system for positioning a substrate for exposure in a lithography system, comprising:
- a calibration subsystem configured to position the substrate at a proper focal distance to a surface of the substrate, the calibration system comprising:
- a relatively high accuracy calibration sensor configured to determine the proper focal distance to the surface of the substrate;
- and
- a relatively low accuracy secondary sensor configured to measure the focal distance to the surface of the substrate when the substrate is positioned at the proper focal distance;
- and
- a control subsystem configured to position the substrate at a proper focal distance under an exposure area of the lithography system, the control subsystem comprising:
- a primary sensor having substantially the same accuracy as the secondary sensor and configured to measure the proper focal distance to the surface of the substrate based on the focal distance measured by the secondary sensor.
Dependencies are inferred from the claim text.