Metrology system utilizing points-from-focus type processes with glare reduction
A metrology system is provided including a lighting configuration and camera which are controlled to acquire image stacks of a workpiece, wherein each image stack is acquired utilizing different lighting (e.g., corresponding to different lighting positions). Sets of pixel intensity values from the image stacks are utilized to determine a composite stack which includes one pixel intensity value for each pixel position and focus position. At least some of the pixel intensity values of the composite stack are determined according to a glare reduction process which determines a corresponding pixel intensity value for the composite stack that is less than a maximum pixel intensity value of the corresponding set of pixel intensity values. Focus curve data is determined based at least in part on the pixel intensity values of the composite stack, wherein the focus curve data indicates three dimensional positions of a plurality of surface points on the workpiece.
1. A metrology system, comprising:
an objective lens comprising an optical axis and configured to input image light arising from a workpiece and to transmit the image light along an imaging optical path;
a camera comprising a sensor array including pixels, wherein the camera is configured to receive image light transmitted along the imaging optical path and to provide images of the workpiece, wherein a focus position that corresponds to the focus of the images is configured to be variable along the optical axis;
a lighting configuration configured to provide light from a plurality of different lighting positions toward the workpiece, the plurality of lighting positions comprising at least first and second lighting positions;
one or more processors; and
a memory coupled to the one or more processors and storing program instructions that when executed by the one or more processors cause the one or more processors to at least:
control the lighting configuration and the camera to acquire a plurality of image stacks, the plurality of image stacks comprising at least first and second image stacks, wherein:
each image stack is acquired utilizing different corresponding workpiece lighting, including:
the first image stack is acquired utilizing first workpiece lighting which comprises light from the first lighting position; and
the second image stack is acquired utilizing second workpiece lighting which comprises light from the second lighting position;
each image stack includes a plurality of images of the workpiece for which each image corresponds to a different focus position along the optical axis; and
each image has associated pixel intensity values for which each pixel intensity value corresponds to a pixel position and the focus position of the respective image and for which the plurality of image stacks comprises a set of pixel intensity values for each pixel position and focus position with one pixel intensity value of the set coming from each image stack;
utilize the sets of pixel intensity values to determine a composite stack which includes one pixel intensity value for each corresponding pixel position and focus position, wherein at least some of the pixel intensity values of the composite stack are determined according to a glare reduction process which is configured to determine a corresponding pixel intensity value for the composite stack that is less than a maximum pixel intensity value of the corresponding set of pixel intensity values; and
determine focus curve data based at least in part on the pixel intensity values of the composite stack, wherein the focus curve data indicates three dimensional positions of a plurality of surface points on the workpiece.
2. The system of claim 1 , wherein the glare reduction process comprises utilizing an intensity determination process as applied to at least some of the pixel intensity values of the corresponding set of pixel intensity values to determine the corresponding pixel intensity values of the composite stack.
3. The system of claim 2 , wherein the intensity determination process comprises at least one of:
a selection process which selects a value of the set of pixel intensity values to be utilized as the corresponding pixel intensity value of the composite stack; or
a calculation process which utilizes two or more values of the set of pixel intensity values to determine a value to be utilized as the corresponding pixel intensity value of the composite stack.
4. The system of claim 1 , wherein the image stacks each image the same field of view and area of the workpiece.
5. The system of claim 1 , wherein for each focus position the plurality of image stacks includes a set of images with one image from each image stack corresponding to the respective focus position.
6. The system of claim 1 , wherein the plurality of different lighting positions further comprises at least third and fourth lighting positions.
7. The system of claim 6 , wherein the plurality of image stacks further comprises at least third and fourth image stacks acquired utilizing third workpiece lighting and fourth workpiece lighting, respectively, wherein the third workpiece lighting comprises light from the third lighting position and the fourth workpiece lighting comprises light from the fourth lighting position.
8. The system of claim 7 , wherein the plurality of different lighting positions further comprises at least fifth, sixth, seventh and eighth lighting positions.
9. The system of claim 8 , wherein the plurality of image stacks comprises at least fifth, sixth, seventh and eighth image stacks acquired utilizing fifth, sixth, seventh and eighth workpiece lighting, respectively, wherein the fifth, sixth, seventh and eighth workpiece lighting comprises light from the fifth, sixth, seventh and eighth lighting positions, respectively.
10. The system of claim 1 , wherein:
in the first image stack, glare from reflection of the light from the first lighting position results in a first pixel intensity value which is a first maximum pixel intensity value in a first set of pixel intensity values corresponding to a first pixel position and a first focus position; and
the glare reduction process determines a corresponding first pixel intensity value for the composite stack that is less than the first maximum pixel intensity value of the first set of pixel intensity values.
11. The system of claim 10 , wherein:
the plurality of image stacks further comprises at least third and fourth image stacks acquired utilizing third workpiece lighting and fourth workpiece lighting, respectively, wherein the third workpiece lighting comprises light from the third lighting position and the fourth workpiece lighting comprises light from the fourth lighting position; and
the first set of pixel intensity values includes second, third and fourth pixel intensity values that correspond to the second, third and fourth image stacks acquired utilizing light from the second, third and fourth lighting positions, respectively, and which do not produce glare at the first pixel position and first focus position and for which the second, third and fourth pixel intensity values are less than the first pixel intensity value.
12. The system of claim 11 , wherein:
the glare reduction process is configured to at least one of:
determine a median value of the first set of pixel intensity values as the corresponding first pixel intensity value for the composite stack;
select one of the second, third or fourth pixel intensity values from the first set of pixel intensity values as the corresponding first pixel intensity value for the composite stack; or
determine the corresponding first pixel intensity value for the composite stack according to an averaging process which utilizes at least two of the second, third and fourth pixel intensity values to determine an average pixel intensity value as the corresponding first pixel intensity value for the composite stack.
13. The system of claim 1 , wherein the lighting configuration comprises a plurality of lighting portions that provide the light from the plurality of different lighting positions, and an arrangement in which the lighting portions are distributed is an annular arrangement, with each lighting portion located at a different angular position within the annular arrangement.
14. The system of claim 13 , wherein the plurality of lighting portions comprises at least four lighting portions.
15. A method for operating a metrology system,
the metrology system comprising:
an objective lens comprising an optical axis and configured to input image light arising from a workpiece and to transmit the image light along an imaging optical path;
a camera comprising a sensor array including pixels, wherein the camera is configured to receive image light transmitted along the imaging optical path and to provide images of the workpiece, wherein a focus position that corresponds to the focus of the images is configured to be variable along the optical axis; and
a lighting configuration configured to provide light from a plurality of different lighting positions toward the workpiece, the plurality of lighting positions comprising at least first and second lighting positions;
the method comprising:
acquiring a plurality of image stacks, the plurality of image stacks comprising at least first and second image stacks, wherein:
each image stack is acquired utilizing different corresponding workpiece lighting, including:
the first image stack is acquired utilizing first workpiece lighting which comprises light from the first lighting position; and
the second image stack is acquired utilizing second workpiece lighting which comprises light from the second lighting position;
each image stack includes a plurality of images of the workpiece for which each image corresponds to a different focus position along the optical axis; and
each image has associated pixel intensity values for which each pixel intensity value corresponds to a pixel position and the focus position of the respective image and for which the plurality of image stacks comprises a set of pixel intensity values for each pixel position and focus position with one pixel intensity value of the set coming from each image stack;
utilizing the sets of pixel intensity values to determine a composite stack which includes one pixel intensity value for each corresponding pixel position and focus position, wherein at least some of the pixel intensity values of the composite stack are determined according to a glare reduction process which is configured to determine a corresponding pixel intensity value for the composite stack that is less than a maximum pixel intensity value of the corresponding set of pixel intensity values; and
determining focus curve data based at least in part on the pixel intensity values of the composite stack, wherein the focus curve data indicates three dimensional positions of a plurality of surface points on the workpiece.
16. The method of claim 15 , wherein the glare reduction process comprises utilizing an intensity determination process as applied to at least some of the pixel intensity values of the corresponding set of pixel intensity values to determine the corresponding pixel intensity values of the composite stack.
17. The method of claim 16 , wherein the intensity determination process comprises at least one of:
a selection process which selects a value of the set of pixel intensity values to be utilized as the corresponding pixel intensity value of the composite stack; or
a calculation process which utilizes two or more values of the set of pixel intensity values to determine a value to be utilized as the corresponding pixel intensity value of the composite stack.
18. The method of claim 15 , wherein the plurality of image stacks further comprises at least third and fourth image stacks acquired utilizing third workpiece lighting and fourth workpiece lighting, respectively, wherein the third workpiece lighting comprises light from a third lighting position and the fourth workpiece lighting comprises light from a fourth lighting position.
19. The method of claim 15 , wherein:
in the first image stack, glare from reflection of the light from the first lighting position results in a first pixel intensity value which is a first maximum pixel intensity value in a first set of pixel intensity values corresponding to a first pixel position and a first focus position; and
the glare reduction process determines a corresponding first pixel intensity value for the composite stack that is less than the first maximum pixel intensity value of the first set of pixel intensity values.
20. A method for determining focus curve data which indicates three dimensional positions of a plurality of surface points on a workpiece, the method comprising:
utilizing a lighting configuration and a camera to acquire a plurality of image stacks, the plurality of image stacks comprising at least first and second image stacks, wherein:
each image stack is acquired utilizing different corresponding workpiece lighting, including:
the first image stack is acquired utilizing first workpiece lighting which comprises light from a first lighting position; and
the second image stack is acquired utilizing second workpiece lighting which comprises light from a second lighting position;
each image stack includes a plurality of images of the workpiece for which each image corresponds to a different focus position along the optical axis; and
each image has associated pixel intensity values for which each pixel intensity value corresponds to a pixel position and the focus position of the respective image and for which the plurality of image stacks comprises a set of pixel intensity values for each pixel position and focus position with one pixel intensity value of the set coming from each image stack;
utilizing the sets of pixel intensity values to determine a composite stack which includes one pixel intensity value for each corresponding pixel position and focus position, wherein at least some of the pixel intensity values of the composite stack are determined according to a glare reduction process which is configured to determine a corresponding pixel intensity value for the composite stack that is less than a maximum pixel intensity value of the corresponding set of pixel intensity values; and
determining focus curve data based at least in part on the pixel intensity values of the composite stack, wherein the focus curve data indicates three dimensional positions of a plurality of surface points on the workpiece.