CN-121994139-A - Method and device for determining the local height of a sample surface

Abstract

A method and apparatus for determining the local height of a sample surface. The present invention relates to a method for determining the local height of a location on a sample surface. The invention also relates to a structured light microscope for determining the local height of a certain spot on the surface of a sample. The invention further relates to a computer-readable data carrier comprising a computer program which, when run on a processor of a structured light microscope according to the invention, causes the structured light microscope to perform a method according to the invention.

Inventors

• R. A. Sepuhanov
• N. KUMAR

Assignees

• 株式会社三丰

Dates

Publication Date

20260508

Application Date

20251024

Priority Date

20241106

Claims (15)

1. 1. A method for determining a local height of a location on a sample surface, wherein the method comprises: -projecting an optical pattern on the sample surface; -moving the sample surface relative to the structured light microscope between a plurality of measurement positions along an optical axis of the structured light microscope; -obtaining a contrast defocus relationship associated with the location of the sample surface by measuring the contrast of the optical pattern on the location at each of the plurality of measurement locations; -determining a local tilt angle of the sample surface at the location based on comparing the obtained contrast defocus relationship with a plurality of calibrated contrast defocus relationships, each of the calibrated contrast defocus relationships being associated with a tilt angle, and selecting one of the calibrated contrast defocus relationships based on the comparison; -obtaining a height correction of the location based on the obtained local tilt angle; -obtaining the local height by determining an in-focus position of the optical pattern along the optical axis and correcting with the height correction.
2. 2. The method of claim 1, wherein the plurality of calibrated contrast defocus relationships, associated tilt angles, and associated height corrections are obtained by: -measuring the contrast of the optical pattern on a flat test surface having a known height at each of the plurality of measurement positions with the structured light microscope to obtain the plurality of calibrated contrast defocus relations, wherein different calibrated contrast defocus relations are obtained by placing the test surface at different tilt angles with respect to the optical axis; Obtaining an associated height correction for each calibrated contrast defocus relationship by determining the height of a flat test surface based on the associated calibrated contrast defocus relationship and calculating the difference of the known height of the flat test surface from the determined height, and -Storing the calibrated contrast defocus relationship, the associated tilt angle and the associated height correction.
3. 3. The method of claim 1, wherein the plurality of calibrated contrast defocus relationships, associated tilt angles, and associated height corrections are obtained by: -measuring the contrast of the optical pattern on the test surface having a known three-dimensional shape and a known height profile at each of the plurality of measurement positions with the structured light microscope to obtain the plurality of calibrated contrast defocus relations, wherein different calibrated contrast defocus relations are obtained by placing the test surface at different lateral positions with respect to the optical axis; Obtaining an associated height correction for each of the calibrated contrast defocus relations by determining the height of a flat test surface based on the associated calibrated contrast defocus relations and calculating the difference of the height of the test surface from the determined height, and -Storing the calibrated contrast defocus relationship, the associated tilt angle and the associated height correction.
4. 4. The method of claim 1, wherein comparing the obtained contrast defocus relationship to a plurality of calibrated contrast defocus relationships and selecting one of the calibrated contrast defocus relationships based on the comparison comprises determining a similarity between the obtained contrast defocus relationship and each of the plurality of calibrated contrast defocus relationships and selecting one of the calibrated contrast defocus relationships based on the determined similarity.
5. 5. The method of claim 4, wherein the similarity between the obtained contrast defocus relationship and the plurality of calibrated contrast defocus relationships is based on a contrast defocus curve associated with the respective contrast defocus relationship.
6. 6. The method of claim 4, wherein determining the local tilt angle of the sample surface at the location comprises calculating a weighted average of a first tilt angle associated with a calibrated contrast defocus having a highest similarity to the obtained contrast defocus, and a second tilt angle adjacent to the first tilt angle and associated with a calibrated contrast defocus having a second highest similarity to the tilt angle adjacent to the first tilt angle, wherein the weight of the weighted average is based on the determined similarity.
7. 7. The method of claim 6, wherein determining the altitude correction comprises calculating a weighted average of altitude corrections associated with the first tilt angle and the second tilt angle, wherein a weight of the weighted average is based on the determined similarity.
8. 8. A structured light microscope for determining the local height of a location on a sample surface, comprising: -a projector for projecting an optical pattern on the sample surface; -an optical sensor for obtaining a contrast of the optical pattern projected on the sample surface; A sample holder for holding the sample surface at different measurement positions relative to the optical sensor along the optical axis of the structured light microscope, and A processor functionally connected to the optical sensor, the sample holder and the projector, Wherein the processor is configured to: -obtaining a contrast defocus relationship associated with the location of the sample surface based on the contrast of the optical pattern measured by the optical sensor at each of the plurality of measurement locations and projected by the projector on the sample surface; -determining a local tilt angle of the sample surface at the location based on comparing the obtained contrast defocus relationship with a plurality of calibrated contrast defocus relationships, each of the calibrated contrast defocus relationships being associated with a tilt angle, and selecting one of the calibrated contrast defocus relationships based on the comparison; -obtaining a height correction of the location based on the obtained local tilt angle; -obtaining the local height by determining an in-focus position of the optical pattern along the optical axis and correcting with the height correction.
9. 9. The structured light microscope of claim 8, wherein the structured light microscope is configured to obtain the plurality of calibrated contrast defocus relationships, associated tilt angles, and associated height corrections by: -measuring, with the optical sensor at each of the plurality of measurement positions, a contrast of an optical pattern on a flat test surface having a known height to obtain the plurality of calibrated contrast defocus relations, wherein different calibrated contrast defocus relations are obtained by placing the test surface at different tilt angles with respect to the optical axis with the sample holder; -obtaining, by the processor and for each of the calibrated contrast defocus relations, an associated height correction by determining the height of a flat test surface based on the associated calibrated contrast defocus relations and calculating the difference of the known height of the flat test surface from the determined height, and -Storing, by the processor, the calibrated contrast defocus relationship, the associated tilt angle and the associated height correction.
10. 10. The structured light microscope of claim 8, wherein the structured light microscope is configured to obtain the plurality of calibrated contrast defocus relationships, associated tilt angles, and associated height corrections by: -measuring the contrast of an optical pattern on a test surface having a known three-dimensional shape and a known height profile with the optical sensor at each of the plurality of measurement positions to obtain the plurality of calibrated contrast defocus relations, wherein different calibrated contrast defocus relations are obtained by placing the test surface at different lateral positions with respect to the optical axis with the sample holder; -obtaining, by the processor and for each of the calibrated contrast defocus relations, an associated height correction by determining the height of a flat test surface based on the associated calibrated contrast defocus relations and calculating the difference of the height of the test surface from the determined height, and -Storing, by the processor, the calibrated contrast defocus relationship, the associated tilt angle and the associated height correction.
11. 11. The structured light microscope of claim 8, wherein the processor is further configured to compare the obtained contrast defocus relationship to a plurality of calibrated contrast defocus relationships and to select one of the calibrated contrast defocus relationships based on the comparison comprises determining a similarity between the obtained contrast defocus relationship and each of the plurality of calibrated contrast defocus relationships and to select one of the calibrated contrast defocus relationships based on the determined similarity.
12. 12. The structured light microscope of claim 11, wherein the processor is configured to base the similarity between the obtained contrast defocus relationship and the plurality of calibrated contrast defocus relationships on a contrast defocus curve associated with the respective contrast defocus relationship.
13. 13. The structured light microscope of claim 11, wherein the processor is further configured to determine the local tilt angle of the sample surface at the location by calculating a weighted average of a first tilt angle associated with the calibrated contrast defocus relationship having a highest similarity to the obtained contrast defocus relationship and a second tilt angle adjacent to the first tilt angle and associated with the calibrated contrast defocus relationship having a second highest similarity to the tilt angle adjacent to the first tilt angle, wherein the weight of the weighted average is based on the determined similarity.
14. 14. The structured light microscope of claim 11, wherein the processor is further configured to determine the height correction by calculating a weighted average of the height corrections associated with the first tilt angle and the second tilt angle, wherein a weight of the weighted average is based on the determined similarity.
15. 15. A computer readable data carrier comprising a computer program which, when run on a processor of a structured light microscope according to claim 8, causes the structured light microscope to perform the method according to claim 1.

Description

Method and device for determining the local height of a sample surface Technical Field The present invention relates to a method for determining the local height of a location (position) on a sample surface. The invention also relates to a structured light microscope for determining the local height of a location on a sample surface. The invention further relates to a computer-readable data carrier comprising a computer program which, when run on a processor of a structured light microscope according to the invention, causes the structured light microscope to perform a method according to the invention. Background The structured light microscope may project an optical pattern onto the sample surface and measure its contrast at a location of the sample surface as the sample surface is at different measurement positions relative to the microscope along its optical axis to obtain a contrast defocus relationship. The maximum value of the contrast defocus relationship may be associated with a local height of the location of the sample surface. A height map of the sample surface may be obtained by performing these measurements on multiple locations of the sample surface. The optical system is affected by aberrations. Aberration can be defined as the deviation of a wavefront from an ideal shape. In a structured light microscope, aberrations may distort an image in a lateral direction, for example, perpendicular to the optical axis, and aberrations may also distort the shape of the obtained contrast defocus relationship, which may shift its maximum value. Thus, the aberration causes a measurement error in the height measurement. In general, the effects of aberrations can be minimized by using multiple optical surfaces. In the case of a structured light microscope, minimizing the effect of aberrations is complex because the sample has a three-dimensional shape. The way the sample reflects the optical pattern depends on the shape of the sample and affects the height measurement via the aberrations of the system. For example, this may result in obtaining a non-planar height map of a planar sample surface. Disclosure of Invention It is an object of the present invention to provide a method for reducing the effect of aberrations on a height map obtained by a structured light microscope. The object of the invention is achieved by a method according to claim 1. The method of the invention allows to determine the local height of a certain spot on the sample surface. The local height may be a relative local height, for example, relative to another location on the sample surface, for example, a baseline point. By collecting a plurality of local heights at a plurality of locations on the sample surface, a height map of the sample surface can be obtained. For each location on the sample surface, the method of the present invention may be used to obtain the relevant local height. The location of the sample surface may also be referred to herein as a sample surface location. The sample surface location may be associated with a pixel or group of pixels of the structured light microscope. The sample surface may be the surface of a semiconductor or optical element. The sample surface may be a product obtained from a manufacturing process. The method of the invention can be used for quality control of the production process. The method includes projecting an optical pattern on a sample surface and moving the sample surface relative to the structured light microscope between a plurality of measurement positions along an optical axis of the structured light microscope. The structured light microscope may comprise a projector for projecting an optical pattern and an optical sensor for measuring light reflected from the sample surface. The sample surface may be held in a sample holder during measurement. The sample surface may be movable between a plurality of measurement positions. The structured light microscope or a part thereof, such as an optical sensor or a lens of an optical sensor, can be moved relative to the sample surface between different measurement positions. The effective distance between the sample surface and the optical sensor may be different at different measurement locations. Since the measured contrast or focus of the optical pattern projected on the sample surface depends on the effective distance, the measured contrast may be different between different measurement positions. The maximum contrast of the optical pattern (i.e., when the optical pattern is in focus) may be related to the height of the sample surface. The method includes obtaining a contrast defocus relationship associated with a sample surface location by measuring the contrast of an optical pattern on the sample surface location at each measurement location. The contrast defocus relationship can establish an association between effective distance and measured contrast. The contrast defocus relationship may be a set of data points, where each data p