Lighting configuration for metrology system with images acquired at different focus positions
A lighting configuration is provided for utilization with a metrology system. The metrology system includes a camera that provides images of a workpiece at different focus positions (e.g., through operation of a variable focal length lens). The lighting configuration includes a plurality of lighting portions which illuminate the workpiece for the imaging. The lighting portions are distributed in an arrangement (e.g., an annular arrangement) in which an imaging lens portion of each lighting portion directs light toward a central volume (e.g., for which illumination in the central volume may be relatively uniform in X, Y and Z axis directions). Each imaging lens portion may include at least two lenses in a telecentric arrangement. Each lighting portion may comprise an optical homogenizer. The camera acquires a stack of images of the workpiece, from which focus curve data may be determined which indicates 3 dimensional positions of surface points on the workpiece.
1 . A metrology system, comprising:
an objective lens configured to input image light arising from a workpiece, wherein the objective lens is configured to transmit the image light along an imaging optical path and has an optical axis;
a camera 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 within a focus range along the optical axis;
a lighting configuration comprising a plurality of lighting portions configured to illuminate the workpiece for producing the image light, wherein:
the plurality of lighting portions comprises:
a first lighting portion comprising a first imaging lens portion, wherein the first imaging lens portion comprises at least two lenses in a first telecentric arrangement;
a second lighting portion comprising a second imaging lens portion, wherein the second imaging lens portion comprises at least two lenses in a second telecentric arrangement;
a third lighting portion comprising a third imaging lens portion, wherein the third imaging lens portion comprises at least two lenses in a third telecentric arrangement; and
a fourth lighting portion comprising a fourth imaging lens portion, wherein the fourth imaging lens portion comprises at least two lenses in a fourth telecentric arrangement;
the first, second, third and fourth lighting portions are distributed in an arrangement in which the first, second, third and fourth imaging lens portions are each configured to direct light toward a central volume for illuminating the workpiece;
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 to direct light toward the central volume for illuminating the workpiece; and
utilize the camera to acquire an image stack comprising a plurality of images of the workpiece, wherein each image of the image stack corresponds to a different focus position along the optical axis.
2 . The system of claim 1 , wherein the program instructions when executed by the one or more processors further cause the one or more processors to determine focus curve data based at least in part on an analysis of the images of the image stack, wherein the focus curve data indicates 3 dimensional positions of a plurality of surface points on the workpiece.
3 . The system of claim 1 , further comprising a variable focal length (VFL) lens, wherein the objective lens transmits the workpiece light along the imaging optical path that passes through the VFL lens to the camera.
4 . The system of claim 3 , wherein the system further comprises a VFL lens controller that is configured to control the VFL lens to periodically modulate the optical power of the VFL lens over a range of optical powers at an operating frequency so as to vary the focus position of the system over a plurality of positions within the focus range.
5 . The system of claim 4 , wherein for each image of the image stack, the lighting configuration is controlled to provide at least one instance of pulsed illumination timed to correspond with a respective phase timing of a periodically modulated focus position that corresponds to the respective focus position for that respective image of the image stack.
6 . The system of claim 4 , wherein the VFL lens is a tunable acoustic gradient (TAG) lens.
7 . The system of claim 1 , wherein:
the first lighting portion comprises a first light guide, for which the first imaging lens portion with the at least two lenses in the first telecentric arrangement images at least part of the first light guide to the central volume;
the second lighting portion comprises a second light guide, for which the second imaging lens portion with the at least two lenses in the second telecentric arrangement images at least part of the second light guide to the central volume;
the third lighting portion comprises a third light guide, for which the third imaging lens portion with the at least two lenses in the third telecentric arrangement images at least part of the third light guide to the central volume; and
the fourth lighting portion comprises a fourth light guide, for which the fourth imaging lens portion with the at least two lenses in the fourth telecentric arrangement images at least part of the fourth light guide to the central volume.
8 . The system of claim 1 , wherein:
the first lighting portion comprises a first light guide and a first optical homogenizer, for which the first light guide provides light through the first optical homogenizer to the first imaging lens portion with the at least two lenses in the first telecentric arrangement;
the second lighting portion comprises a second light guide and a second optical homogenizer, for which the second light guide provides light through the second optical homogenizer to the second imaging lens portion with the at least two lenses in the second telecentric arrangement;
the third lighting portion comprises a third light guide and a third optical homogenizer, for which the third light guide provides light through the third optical homogenizer to the third imaging lens portion with the at least two lenses in the third telecentric arrangement; and
the fourth lighting portion comprises a fourth light guide and a fourth optical homogenizer, for which the fourth light guide provides light through the fourth optical homogenizer to the fourth imaging lens portion with the at least two lenses in the fourth telecentric arrangement.
9 . The system of claim 8 , wherein a cross-section of each optical homogenizer comprises a plurality of non-linear edge portions.
10 . The system of claim 9 , wherein the non-linear edge portions meet at vertices.
11 . The system of claim 1 , wherein the light directed toward the central volume by the first, second, third and fourth imaging lens portions of the first, second, third and fourth lighting portions is configured to overlap and to form a nominally uniform intensity of illumination within at least part of the central volume, such that the intensity of the illumination within the central volume is configured to be nominally the same at a plurality of focus positions.
12 . The system of claim 11 , wherein each image of the image stack corresponds to one of the focus positions of the plurality of focus positions.
13 . The system of claim 1 , wherein the 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 1 , wherein the plurality of lighting portions comprises at least six lighting portions.
15 . The system of claim 1 , wherein the arrangement in which the lighting portions are distributed is configured such that the light from each imaging lens portion is directed from a different azimuthal direction toward the central volume.
16 . A method for operating a metrology system,
the metrology system comprising:
an objective lens configured to input image light arising from a workpiece, wherein the objective lens is configured to transmit the image light along an imaging optical path and has an optical axis;
a camera 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 within a focus range along the optical axis; and
a lighting configuration comprising a plurality of lighting portions;
the method comprising:
controlling the lighting configuration including the plurality of lighting portions to direct light toward a central volume for illuminating the workpiece, wherein:
the plurality of lighting portions comprises:
a first lighting portion comprising a first imaging lens portion, wherein the first imaging lens portion comprises at least two lenses in a first telecentric arrangement;
a second lighting portion comprising a second imaging lens portion, wherein the second imaging lens portion comprises at least two lenses in a second telecentric arrangement;
a third lighting portion comprising a third imaging lens portion, wherein the third imaging lens portion comprises at least two lenses in a third telecentric arrangement; and
a fourth lighting portion comprising a fourth imaging lens portion, wherein the fourth imaging lens portion comprises at least two lenses in a fourth telecentric arrangement;
the first, second, third and fourth lighting portions are distributed in an arrangement in which the first, second, third and fourth imaging lens portions are each configured to direct light toward the central volume for illuminating the workpiece; and
utilizing the camera to acquire an image stack comprising a plurality of images of the workpiece, wherein each image of the image stack corresponds to a different focus position along the optical axis.
17 . The method of claim 16 , further comprising determining focus curve data based at least in part on an analysis of the images of the image stack, wherein the focus curve data indicates 3 dimensional positions of a plurality of surface points on the workpiece.
18 . The method of claim 16 , wherein for each image of the image stack, the lighting configuration is controlled to provide at least one instance of pulsed illumination timed to correspond with a respective phase timing of a periodically modulated focus position that corresponds to the respective focus position for that respective image of the image stack.
19 . A lighting configuration for utilization in a metrology system,
the metrology system comprising:
an objective lens configured to input image light arising from a workpiece, wherein the objective lens is configured to transmit the image light along an imaging optical path and has an optical axis;
a camera 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 within a focus range along the optical axis;
the lighting configuration comprising:
a plurality of lighting portions configured to illuminate the workpiece for producing the image light, wherein:
the plurality of lighting portions comprises:
a first lighting portion comprising a first imaging lens portion, wherein the first imaging lens portion comprises at least two lenses in a first telecentric arrangement;
a second lighting portion comprising a second imaging lens portion, wherein the second imaging lens portion comprises at least two lenses in a second telecentric arrangement;
a third lighting portion comprising a third imaging lens portion, wherein the third imaging lens portion comprises at least two lenses in a third telecentric arrangement; and
a fourth lighting portion comprising a fourth imaging lens portion, wherein the fourth imaging lens portion comprises at least two lenses in a fourth telecentric arrangement;
the first, second, third and fourth lighting portions are distributed in an arrangement in which the first, second, third and fourth imaging lens portions are each configured to direct light toward a central volume for illuminating the workpiece; and
wherein:
the lighting configuration is controlled to direct light toward the central volume for illuminating the workpiece; and
the camera is utilized to acquire an image stack comprising a plurality of images of the workpiece, wherein each image of the image stack corresponds to a different focus position along the optical axis.
20 . The lighting configuration of claim 19 , wherein focus curve data is determined based at least in part on an analysis of the images of the image stack, wherein the focus curve data indicates 3 dimensional positions of a plurality of surface points on the workpiece.
21 . The lighting configuration of claim 19 , wherein for each image of the image stack, the lighting configuration is controlled to provide at least one instance of pulsed illumination timed to correspond with a respective phase timing of a periodically modulated focus position that corresponds to the respective focus position for that respective image of the image stack.
22 . The system of claim 1 , wherein for each lighting portion, a direction of the light from the corresponding telecentric arrangement is off-axis and non-parallel relative to the optical axis of the objective lens.
23 . The system of claim 1 , further comprising an optical configuration included in the imaging optical path between the objective lens and the camera, wherein the optical configuration comprises a plurality of lenses and is configured to maintain a telecentricity at the workpiece.
24 . The lighting configuration of claim 19 , wherein:
the first lighting portion comprises a first light guide, for which the first imaging lens portion with the at least two lenses in the first telecentric arrangement images the first light guide into the central volume and onto the workpiece;
the second lighting portion comprises a second light guide, for which the second imaging lens portion with the at least two lenses in the second telecentric arrangement images the second light guide into the central volume and onto the workpiece;
the third lighting portion comprises a third light guide, for which the third imaging lens portion with the at least two lenses in the third telecentric arrangement images the third light guide into the central volume and onto the workpiece; and
the fourth lighting portion comprises a fourth light guide, for which the fourth imaging lens portion with the at least two lenses in the fourth telecentric arrangement images the fourth light guide into the central volume and onto the workpiece.