Substrate, method of preparing a substrate, method of measurement, lithographic apparatus, device manufacturing method and device manufactured thereby, and machine-readable storage medium
In a method according to one embodiment of the invention, a plurality of markers are printed in resist on a substrate at a range of angles relative to a crystal axis of the substrate. The markers are etched in to the substrate using an anisotropic etch process, such that after the etch the apparent positions of the markers are dependent on their orientation relative to the crystal axis. The apparent positions of the markers are measured, and from this information the orientation of the crystal axis is derived.
1. A method of preparing a substrate, said method comprising:
exposing the substrate with a plurality of images, each of the plurality of images having a different orientation with respect to a crystal axis of the substrate; and
anisotropically etching the substrate to form a plurality of alignment markers, a location of at least a portion of each of the plurality of alignment markers substantially coinciding with a location of a corresponding portion of a corresponding one of the plurality of images,
wherein the orientation of each of the plurality of images is within four degrees of the orientation of each other one of the plurality of images.
2. The method of preparing a substrate according to claim 1 , wherein a distance between the orientations of each pair among the plurality of images is within the range of from (5×10 −6 ) degrees to four degrees.
3. The method of preparing a substrate according to claim 1 , wherein the orientation of at least one of the plurality of images is within the range of from 0.5 degrees to 2 degrees on one side of a nominal orientation of the crystal axis, and
wherein the orientation of at least one of the plurality of images is within the range of from 0.5 degrees to 2 degrees on the other side of a nominal orientation of the crystal axis.
4. The method of preparing a substrate according to claim 1 , said method further comprising:
measuring a position of each of the plurality of alignment markers; and
determining an orientation of the crystal axis based on the measured positions.
5. The method of preparing a substrate according to claim 4 , said method further comprising marking, on at least one of the substrate and another substrate cut from the same crystal, information indicative of the determined orientation.
6. The method of preparing a substrate according to claim 1 , wherein at least one of the plurality of alignment markers includes features selected from the group consisting of gratings, chevrons, and boxes.
7. The method of preparing a substrate according to claim 1 , wherein at least one of the plurality of alignment markers comprises at least one area having a plurality of small elements on a contrasting background.
8. The method of preparing a substrate according to claim 1 , wherein said alignment markers comprise a structure having a solid area, a clear area, and a striped area.
9. A method of preparing a substrate comprising: providing on a surface of the substrate a plurality of alignment markers, each of said plurality of alignment markers having a different orientation relative to a crystal axis of the substrate,
wherein, for each of said plurality of alignment markers, a distance between an apparent position of the marker and an actual position of an element of the marker is dependent on the orientation of the marker.
10. The method of preparing a substrate according to claim 9 , wherein a distance between the orientations of each pair among the plurality of alignment markers is within the range of from (5×10 −6 ) degrees to 4 degrees.
11. The method of preparing a substrate according to claim 9 , wherein the orientation of at least one of the plurality of alignment markers is within the range of from 0.5 degrees to 2 degrees on one side of a nominal orientation of the crystal axis, and
wherein the orientation of at least one of the plurality of alignment markers is within the range of from 0.5 degrees to 2 degrees on the other side of a nominal orientation of the crystal axis.
12. The method of preparing a substrate according to claim 9 , wherein providing said alignment markers comprises using an anisotropic etching process to etch said alignment markers into the substrate.