Lithographic apparatus and method
A lithography method comprises: providing a substrate with a target region; determining a topology of the substrate within the target region; determining a correcting telecentricity profile based on the topology of the substrate within the target region; providing a radiation beam; and projecting the radiation beam onto the target region of the substrate so as to form an image on the substrate. The radiation beam is such that a net direction of the total radiation received by one or more points in the target region of the substrate is chosen in dependence on the determined correcting telecentricity. The correcting telecentricity profile is such that the net direction of the total radiation received by at least one point in the target region of the substrate is chosen so as to at least partially correct for an overlay error introduced by a curvature of a surface of the substrate at said point.
1. A lithography method comprising:
determining a topology of a substrate within a target region; and
projecting a radiation beam onto the target region of the substrate so as to form an image on the substrate, wherein the radiation beam is such that a net direction of total radiation received by a point in the target region of the substrate is chosen in dependence on the topology of the substrate so as to at least partially correct for an overlay error introduced by a curvature of a surface of the substrate at the point.
2. The method of claim 1 , wherein the net direction of the total radiation received by the point in the target region of the substrate is chosen so that the radiation which is incident on the point passes through a corresponding point in a focal plane of a projection system that is used to project the radiation beam onto the target region of the substrate so as to form the image, the corresponding point in the focal plane being the point in the focal plane where the point on the substrate would be disposed if the surface of the substrate was deformed such that it was flat and coincided with the focal plane.
3. The method of claim 1 , wherein the net direction of the total radiation received by the point in the target region is not perpendicular to the plane of the substrate.
4. The method of claim 1 , further comprising:
producing the radiation by adjusting intensity to attenuate the radiation beam on opposing sides of the radiation beam by using a plurality of movable fingers arranged in pairs, each pair comprising one finger on each side of the radiation beam, such that the net direction of the total radiation received by each point on the surface of the substrate is controlled by controlling the fingers of the intensity adjustor during exposure of those points.
5. The method of claim 1 , further comprising:
determining a correcting telecentricity profile based on the topology of the substrate within the target region, the correcting telecentricity profile describing variation in the net direction of the total radiation received by the point across the target region; and
wherein the radiation beam is such that the net direction of the total radiation received by the point in the target region of the substrate is chosen in dependence on the correcting telecentricity.
6. The method of claim 1 , wherein the net direction of the total radiation received by each point on the surface of the substrate varies across the exposure region.
7. The method of claim 6 , wherein the projecting the radiation beam onto the target region of the substrate so as to form an image on the substrate comprises moving the substrate along a scanning path relative to the radiation beam such that the radiation beam scans across the target region so as to form the image.
8. The method of claim 7 , wherein the net direction of the total radiation received by the surface of the substrate varies across the target region in a non-scanning direction.
9. The method of claim 7 , wherein the net direction of the total radiation received by the surface of the substrate varies across the target region in the scanning direction.
10. The method of claim 1 , further comprising:
imparting the radiation beam with a pattern in its cross-section prior to projecting the radiation beam onto the target region of the substrate.
11. The method of claim 10 , wherein the projecting the radiation beam onto the target region of the substrate so as to form an image on the substrate comprises moving the patterning device along a scanning path relative to the radiation beam such that the radiation beam scans across the patterning device.
12. The method of claim 1 , wherein the substrate comprises a plurality of target regions,
wherein the determining a topology of the substrate within the target region comprises determining a topology of the substrate within each of a plurality of target regions; and
wherein the projecting the radiation beam onto the target region of the substrate so as to form an image on the substrate comprises sequentially projecting the radiation beam onto each target region of the substrate so as to form an image.
13. The method of claim 1 , wherein the determining a topology of the substrate within a target region is performed before the substrate is clamped to a substrate table.
14. The method of claim 13 , wherein the determining a topology of the substrate within a target region further comprises modeling effects of clamping the substrate to a substrate table on the topology of the substrate.
15. The method of claim 1 , wherein the determining a topology of the substrate within a target region is performed after the substrate has been clamped to a substrate table.
16. The method of claim 11 , wherein the determining a topology of the substrate within a target region comprises determining a height of the substrate at a plurality of points on the surface of the substrate.
17. The method of claim 16 , comprising:
projecting a radiation beam onto the plurality of points on the surface of the substrate, detecting radiation reflected from the substrate; and
determining a height of the substrate from the detected reflected radiation.
18. A lithographic apparatus comprising:
an illumination system configured to condition a radiation beam;
a substrate table configured to hold a substrate;
a projection system configured to project the patterned radiation beam onto a target region of the substrate so as to form an image on the substrate; and
a controller operable to control a net direction of total radiation received by a point in the target region of the substrate, such that the net direction of the total radiation received by the point in the target region of the substrate is chosen so as to at least partially correct for an overlay error introduced by a curvature of a surface of the substrate at the point.
19. The lithographic apparatus of claim 18 , wherein the controller is operable to implement one or more of:
providing a substrate with a target region;
determining a topology of the substrate within the target region;
providing a radiation beam; and
projecting the radiation beam onto the target region of the substrate so as to form an image on the substrate;
wherein the radiation beam provided is such that a net direction of the total radiation received by the point in the target region of the substrate is chosen in dependence on the topology of the substrate so as to at least partially correct for an overlay error introduced by a curvature of a surface of the substrate at the point.
20. The lithographic apparatus of claim 18 , wherein the controller comprises a processor operable to determine a correcting telecentricity based on a topology of the substrate within the target region.