Patent ID: 12204226

DETAILED DESCRIPTION

Referring toFIG.1, a metrology system100includes a vision components portion105and a control system portion120. The vision components portion105includes a front vision components portion105A, a back vision component portion105B, and a movement mechanism portion110. The movement mechanism portion110includes a front movement mechanism110A (e.g., configured to move the front vision components portion105A in a direction that is transverse to the optical axis OA of the front vision components portion105A) and a back movement mechanism110B (e.g., configured to move the back vision components portion105B in a direction that is transverse to the optical axis OA of the back vision components portion105B and to be aligned with the front vision components portion105A). A workpiece20includes a plurality of apertures (e.g., shown at different X-axis locations as represented by dotted lines, and for which additional apertures may be included in the workpiece20, such as approximately arranged in rows and/or columns, with each aperture having a unique X-axis and Y-axis location in the workpiece). Examples of apertures will be described in more detail below with respect toFIGS.2,6A and6B. The apertures (e.g., including through-holes) each extend along the Z-axis through the workpiece20. A particular example aperture AP is shown as aligned along an optical axis OA of the front vision components portion105A and the back vision components portion105B in the example ofFIG.1.

The movement mechanism portion110is utilized (e.g., including operation of the front movement mechanism110A) to adjust a relative position between the front vision components portion105A and the workpiece20to align the optical axis OA of the front vision components portion105A with an aperture AP of the workpiece20. The movement mechanism portion110is also utilized (e.g., including operation of the back movement mechanism110B) to align the optical axis OA of the back vision components portion105B with the aperture AP of the workpiece20such that light from the back vision components portion105B (e.g., including at least a portion of light from a light source that passes through a diffuser (LD) of the back vision components portion105B as will be described in more detail below with respect toFIG.2) passes through the aperture AP for providing at least part of the illumination for imaging the aperture AP.

More specifically, in various implementations the movement mechanisms110A and110B are controlled (e.g., by the control system portion120) to move the front vision components portion105A and the back vision components portion105B (e.g., back and forth and up and down in directions along the X-axis and the Y-axis) to acquire images of each aperture AP. For imaging each aperture, the optical axis OA of the front vision components portion105A and the optical axis OA of the back vision components portion105B are aligned with the aperture (e.g., similar to the aperture AP as shown inFIG.1), and at least some light from the back vision components portion105B passes through the aperture for imaging by a camera (CMOS) that is included in the front vision components portion105A. As noted above, the front and back vision components portions105A and105B may be moved by the movement mechanism portion110(e.g., to a unique X-axis and Y-axis location for imaging each aperture). Further details of the configuration and operation of the metrology system100are described with reference toFIGS.2and3below.

The apertures (e.g., including through-hole portions) as defined in a workpiece, can be advantageously imaged and measured according to the present invention. In various implementations, the apertures may have a relatively high aspect ratio (e.g., of greater than 2 to 1). Such apertures may include, for example, Through Silicon Vias (TSV), aircraft through-hole features for skin panel fastening, through-holes in any large and/or thick workpieces, etc.

The control system portion120includes one or more processors122and a memory124coupled 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 perform the functions described herein. Those skilled in the art will appreciate that the control system portion120(e.g., including or implemented in a computing system, etc.), and/or other processing or control systems described or usable with the elements and methods described herein, may generally be implemented using any suitable computing system or device, including distributed or networked computing environments, and the like. Such systems or devices may include one or more general purpose or special purpose processors122(e.g., non-custom or custom devices) that execute software (e.g., including stored program instructions) to perform the functions described herein. Such software may be stored in memory124, such as random access memory (RAM), read only memory (ROM), flash memory, or the like, or a combination of such components. Software may also be stored in other types of memory124, such as one or more storage devices, including optical based disks, flash memory devices, or any other type of non-volatile storage medium for storing data. Software may include program instructions implementing one or more program modules that include processes, routines, programs, objects, components, data structures, and so on that perform particular tasks or implement particular abstract data types. In distributed computing environments, the functionality of the program modules may be combined or distributed across multiple computing systems or devices and accessed via service calls, either in a wired or wireless configuration.

FIG.2is a schematic diagram of a metrology system200that may be operated according to principles disclosed herein. As will be described in more detail below, an imaging optical path OPATH (which may also be referenced herein as a workpiece imaging optical path) comprises various optical components arranged along a path that conveys image light from a workpiece220to a camera CMOS (e.g., a “CMOS” camera as part of an optical system of the metrology system200). The image light is generally conveyed along the direction of the optical axes OA of the various components. In the implementation shown inFIG.2, the optical axes OA of various components are aligned. However, it will be appreciated that this implementation is intended to be exemplary only and not limiting. More generally, the imaging optical path OPATH may include mirrors and/or other optical elements, and may take any form that is operational for imaging the workpiece220using the camera CMOS according to known principles. In the illustrated implementation, the imaging optical path OPATH includes a VFL lens L4and is utilized at least in part for imaging workpiece features of an aperture AP1of the workpiece220during workpiece image exposures, along the optical axis OA of the front vision components portion205A. As shown inFIG.2, the metrology system200includes the front vision components portion205A (e.g., which is coupled to and movable by a movement mechanism, such as the front movement mechanism110A ofFIG.1) and the back vision components portion205B (e.g., which is coupled to and movable by a back movement mechanism, such as the back movement mechanism110B ofFIG.1). The metrology system200also includes a control system portion (e.g., such as the control system portion120ofFIG.1) which, in the illustrated example, comprises a lens controller280, an exposure (strobe) time controller233es, an effective focus position (Z-coordinate) calibration portion273, and a workpiece focus signal processing portion275(optional), to be described later. In various implementations, additional components may also be included in the control system portion, for implementing the various functions as described herein. In various implementations, various components of the control system portion (e.g., including controllers, portions, etc.), and/or the front vision components portion205A and/or the back vision components portion205B may be interconnected by direct connections or one or more data/control busses (e.g., a system signal and control bus295), and/or application programming interfaces, etc., and/or may be implemented, controlled and/or utilized by program instructions stored in a memory (e.g., memory124) that are executed by one or more processors (e.g., processors122) to perform the functions described herein. As illustrated inFIG.2, the metrology system200is configured to have the workpiece220positioned between the front vision components portion205A and the back vision components portion205B. The back vision components portion205B includes a light source PLS1and a diffuser LD located in the path of the light from the light source PLS1. The diffuser LD may be at least one of an optical diffuser or a transparent light diffuser. In various embodiments, the diffuser LD is configured to receive collimated light CL and to output diffuse light DL as the light which passes through the aperture AP1of the workpiece220for providing at least part of the illumination for imaging the aperture AP1. The back vision components portion205B may further include a focusing lens L6and a collimating lens L7in the path of the light between the light source PLS1and the diffuser LD. The collimating lens L7may be provided and configured to provide the collimated light CL to the diffuser LD.

In various implementations, the front vision components portion205A includes the VFL lens L4, an objective lens L2, and the camera CMOS. In the illustrated example, the front vision components portion205A further includes relay optics L3(e.g., that may include, for example, a tube lens and/or a relay lens, etc.), and a tube lens L5.

In various implementations, the front vision components portion205A may further include a second light source PLS2(e.g., as may be utilized for certain illumination and imaging functions in relation to certain features of the workpiece220, such as in relation to a workpiece feature WPF1C, etc. as will be described later). In the general configuration shown inFIG.2, the second light source PLS2may be a “coaxial” or other light source configured to emit source light (e.g., with strobed/pulsed or continuous illumination) along an illumination path including a collimation lens L0, a reflecting mirror M1, a focus lens L1, a linear polarizer LP1, and a Non-Polarizing Beam Splitter NPBS, toward the objective lens L2to illuminate and image the workpiece220.

In the general configuration shown inFIG.2, the first light source PLS1(i.e., of the back vision components portion205B) may be configured to emit the source light (e.g., with strobed/pulsed or continuous illumination) along an illumination path to illuminate and image the workpiece220. In various implementations, strobed/pulsed illumination may be utilized in conjunction with the operation of the VFL lens L4(e.g., as will be described in more detail below). After the workpiece220is illuminated, the objective lens L2inputs the workpiece light arising from the workpiece220, and transmits the workpiece light along the workpiece imaging optical path OPATH that passes through the VFL lens L4. As shown, the objective lens L2defines the optical axis OA of the front vision components portion205A. In the illustrated example, the workpiece imaging optical path OPATH includes the objective lens L2, along with the Non-Polarizing Beam Splitter NPBS, a linear polarizer LP2, the relay optics L3, the VFL lens L4, the tube lens L5and the camera CMOS. In various alternative implementations, a Polarizing Beam Splitter PBS may be utilized in place of the Non-Polarizing Beam Splitter NPBS. The camera CMOS receives the workpiece light transmitted by the VFL lens L4along the imaging optical path OPATH and provides a corresponding workpiece image exposure, as will be more fully described below. It will be appreciated that the configuration of the imaging optical path OPATH is not limited to the particular example illustrated inFIG.2and may be adapted to include more or less components as well as different components to meet the physical and/or optical specifications of each application.

The VFL lens L4is controlled to periodically modulate optical power of the VFL lens over a range of optical powers that occur at respective phase timings within the periodic modulation. In various implementations, the VFL lens L4may be a tunable acoustic gradient (“TAG” or “TAGLENS”) lens that creates a lensing effect using sound waves in a fluid medium. The sound waves may be created by application of an electrical field at a resonant frequency to a piezoelectric tube surrounding the fluid medium to create a time varying density and index of refraction profile in the lens's fluid, which modulates its optical power and thereby the focal length (or effective focus position) of its optical system. A TAG lens may be used to periodically sweep a range of focal lengths (i.e., to periodically modulate its optical power) at a resonant frequency greater than 30 kHz, or greater than 70 kHz, or greater than 100 kHz, or greater than 400 kHz, up to 1.0 MHz for example, at a high speed. Such a lens may be understood in greater detail by the teachings of the article, “High speed varifocal imaging with a tunable acoustic gradient index of refraction lens” (Optics Letters, Vol. 33, No. 18, Sep. 15, 2008), which is hereby incorporated herein by reference in its entirety. TAG (aka TAGLENS) lenses and related controllable signal generators are available, for example, from Mitutoyo Corporation of Kanagawa, Japan. As a specific example, certain TAG lenses are capable of periodic modulation having a modulation frequency of up to 1.0 MHz. Various aspects of operating principles and applications of TAG lenses are described in greater detail in U.S. Pat. Nos. 10,178,321; 10,101,572; 9,930,243; 9,736,355; 9,726,876; 9,143,674; 8,194,307; and 7,627,162, each of which is hereby incorporated herein by reference in its entirety.

As will be described in more detail below, in various implementations, the VFL lens controller280may control a drive signal of the VFL lens L4to periodically modulate optical power of the VFL lens over a range of optical powers that occur at respective phase timings within the periodic modulation (e.g., as will be described in more detail below with respect toFIGS.4and5). The camera CMOS (e.g., including an imaging detector, such as a “CMOS” imaging detector) receives light transmitted along the imaging optical path OPATH through the VFL lens L4and provides a corresponding workpiece image exposure. An effective focus position EFP in front of the objective lens L2during an image exposure corresponds to the optical power of the VFL lens L4(i.e., as operated in combination with the objective lens L2) during that image exposure. The exposure time controller233esis configured to control an image exposure timing used for a camera image, as will be more fully described below.

InFIG.2, only a portion of the workpiece220is shown which includes an example aperture AP1amongst a potentially large number of apertures existing throughout the workpiece220. In some implementations there may be many hundreds or thousands of apertures in a workpiece, for which, as will be described in more detail below, the configurations as disclosed herein may enable relatively rapid imaging of the apertures as part of processes for inspecting such workpieces.

The example aperture AP1ofFIG.2comprises an entrance portion EN1, a through-hole portion TH1, and an exit portion EX1. The through-hole portion TH1comprises a first workpiece feature WPF1A (e.g., the entrance of the through-hole portion TH1) and a second workpiece feature WPF1B (e.g., the exit of the through-hole portion TH1). The illumination light from the first light source PLS1of the back vision components portion205B enters the aperture AP1via the exit portion EX1, and travels through the through-hole portion TH1via the second workpiece feature WPF1B and the first workpiece feature WPF1A, and exits the aperture AP1through the entrance portion EN1to be received by the front vision components portion205A. As will be described in more detail below, in various implementations, the second workpiece feature WPF1B may be regarded as presenting particular challenges for achieving a desired level of image contrast, as compared to the first workpiece feature WPF1A, for which achieving a desired level of image contrast may be regarded as relatively less complex, due in part to the nature of the respective workpiece features and their relative locations with respect to the camera CMOS and light from the light source PLS1, etc.

The objective lens L2of the front vision components portion205A inputs the image light (workpiece light) that is focused at an effective focus position EFP (e.g., within the aperture AP1), and outputs the image light to travel back through the Non-Polarizing Beam Splitter NPBS, the linear polarizer LP2and the relay optics L3to the VFL lens L4. The VFL lens L4receives the image light and outputs it to the tube lens L5. The tube lens L5receives the image light and outputs it to the camera CMOS. In various implementations, the objective lens L2may be an interchangeable objective lens. In various implementations, any of the lenses referenced herein may be formed from or operate in conjunction with individual lenses, compound lenses, etc.

In various implementations, the camera CMOS captures a camera image during an image exposure (e.g., during an integration period of the camera CMOS) also referred to as an image exposure period, and may provide the corresponding image data to the control system portion. Some camera images may include a workpiece image (e.g., including a workpiece feature of the aperture AP1of the workpiece220) provided during a workpiece image exposure. In some implementations, an image exposure (e.g., a workpiece image exposure) may be limited or controlled by a strobe timing of the first light source PLS1that falls within an image integration period of the camera CMOS. In various implementations, the camera CMOS may have a pixel array greater than 1 megapixel (e.g., 1.3 megapixel, with a 1280×1024 pixel array, with 5.3 microns per pixel). In the example ofFIG.2, the relay optics L3, the VFL lens L4and the tube lens L5may be in a configuration intended to maintain telecentricity at the workpiece220, and may minimize scale change and image distortion (e.g., including providing constant magnification for each effective focus position (Z-coordinate) of the workpiece220).

In various implementations, the lens controller280may include a drive signal generator portion281, a timing clock281′, and imaging circuits/routines282. The drive signal generator portion281may operate (e.g., in conjunction with the timing clock281′) to provide a periodic drive signal to the VFL lens L4via a signal line280′ and may also generate and provide a synchronization signal to the first light source PLS1and/or the second light source PLS2. In various implementations, the lens controller280may generally perform various functions related to imaging the workpiece220in a manner synchronized with a desired phase timing of the VFL lens L4, as well as controlling, monitoring and adjusting the driving and response of the VFL lens L4. In various implementations, the image circuits/routines282perform imaging operations for the optical system (e.g., as may be synchronized with the phase timing of the VFL lens L4).

With respect to the general operations of the VFL lens L4, in various implementations as described above, the lens controller280may rapidly adjust or modulate the optical power of the VFL lens L4periodically, to achieve a high-speed VFL lens capable of a periodic modulation (i.e., at a VFL lens resonant frequency) such as 250 kHz, or 70 kHz, or 30 kHz, or the like. As shown inFIG.2, by using the periodic modulation of a signal to drive the VFL lens L4, the effective focus position EFP of the front vision components portion205A of the metrology system200(e.g., the focus position in front of the objective lens L2) may be rapidly moved within a range Refp (e.g., an autofocus search range or focus range, etc.) bound by an effective focus position EFPmax corresponding to a maximum optical power of the VFL lens L4in combination with the objective lens L2, and an effective focus position EFPmin corresponding to a maximum negative optical power of the VFL lens L4in combination with the objective lens L2. In various implementations, the effective focus positions EFPmax and EFPmin may approximately correspond to phase timings of 90 degrees and 270 degrees. In various implementations, an approximate middle of the range Refp may be designated as an effective focus position EFPnom, and may correspond to zero optical power of the VFL lens L4in combination with the nominal optical power of the objective lens L2. According to this description, the effective focus position EFPnom may approximately correspond to the nominal focal length of the objective lens L2in some implementations (e.g., which may correspond to a working distance of the objective lens L2).

In various implementations, the modulation of the VFL lens L4may be utilized to acquire an image stack, such as described in U.S. Pat. Nos. 9,143,674 and 9,830,694, each of which is hereby incorporated herein by reference in its entirety. As described in the incorporated references, a periodically modulated focus position of the metrology system200ofFIG.2may be controlled by periodically modulating the focal length of a VFL lens L4(e.g., a TAG lens) in the metrology system200. In various implementations, strobed illumination (e.g., from the light source PLS1as controlled by the exposure time controller233es) can be timed to correspond with a respective phase timing of the periodically modulated focus position to expose an image focused at a respective Z-coordinate. That is, while the camera CMOS is acquiring an image during an integration period, if a short strobe pulse is provided at a phase timing ϕ0, then the focus position will be at a height zϕ0, and any workpiece surface of a workpiece feature of the aperture AP1that is located at the height zϕ0 will be in focus in the resulting image. Similar principles are applied for other exemplary phase timings and Z-coordinates throughout the focus range.

In various implementations, such processes may be utilized for obtaining an image stack. For example, as the VFL lens L4and corresponding overall focus position of the optical system is modulated sinusoidally, different images of the workpiece are captured as corresponding to different phase timings and different corresponding Z-coordinates (different focus positions). As a simplified example, if the focus range Refp is 100 mm and images are captured in 1 mm steps, the image stack may include 100 images, with each captured image corresponding to a different Z-coordinate in 1 mm steps throughout the 100 mm focus range. U.S. Pat. No. 8,581,162 describes various techniques for the acquisition and utilization of image stacks, and is hereby incorporated herein by reference in its entirety. In various implementations, an image stack and/or images outside of an image stack may also be acquired in a system with or without a VFL lens (e.g., when a VFL lens is not utilized, the system may utilize a mechanical movement system to change a focus position along the Z-axis for obtaining an image of the workpiece feature).

In various implementations, the optional focus signal processing portion275may input data from the camera CMOS and may provide data or signals that are utilized to determine when an imaged surface region (e.g., of the aperture AP1of the workpiece220) is at an effective focus position. For example, in various implementations a group of images acquired by the camera CMOS at different effective focus positions (Z-coordinates), such as part of an image stack, may be analyzed using a known “maximum contrast” or “best-focus image” analysis to determine when an imaged surface region of the workpiece220is at a corresponding effective focus position (Z-coordinate). However, more generally, any other suitable known image focus detection configuration may be used. In any case, the workpiece focus signal processing portion275or the like may input an image or images acquired during the periodic modulation of the effective focus position (sweeping of multiple effective focus positions) of the front vision components portion205A (e.g., utilizing the VFL lens L4and/or a movement mechanism, etc.), and determine an image and/or image timing at which a target workpiece feature (e.g., of the aperture AP1of the workpiece220) is best-focused.

In some implementations, the focus signal processing portion275may determine a phase timing of the VFL lens L4corresponding to a best-focus of the target workpiece feature and output that “best-focus” phase timing value to the effective focus position calibration portion273. The effective focus position calibration portion273may provide effective focus position (Z-coordinate) calibration data that relates respective effective focus positions (Z-coordinates) to respective “best-focus” phase timings within a period of a standard imaging resonant frequency of the VFL lens L4, wherein in some instances the calibration data may generally correspond to operating the VFL lens L4according to a standard imaging drive control configuration or reference state. For example, in various implementations, the signal data from the camera CMOS may correspond to one or more images acquired by the camera (e.g., as part of an image stack), wherein contrast or other focus metric determinations as part of points-from-focus operations or other analysis may be performed to determine when an imaged surface region of a workpiece feature of the workpiece220is at a “best-focus” position. Exemplary techniques for the determination and analysis of image stacks and focus curves, and for points-from-focus operations, are taught in U.S. Pat. Nos. 6,542,180; 8,581,162 and 9,060,117, each of which is hereby incorporated herein by reference in its entirety.

Generally speaking, the effective focus position calibration portion273comprises recorded effective focus position (Z-coordinate) calibration data (e.g., as determined by calibration processes such as those disclosed in the incorporated references). As such, its representation inFIG.2as a separate element is intended to be an example schematic representation only, and not limiting. In various implementations, the associated recorded effective focus position (Z-coordinate) calibration data may be merged with and/or indistinguishable from the lens controller280, the workpiece focus signal processing portion275, or a host computer system connected to the system signal and control bus295, etc. In various implementations, the exposure (strobe) time controller233es, the effective focus position calibration portion273, the workpiece focus signal processing portion275, the lens controller280and/or any other portions utilized for control, etc., of the front and back vision components portions205A and205B may be included as part of a control system portion (e.g., the control system portion120ofFIG.1) of the metrology system200. In various implementations, such a control system portion or any portions thereof may be included as part of the front vision components portion205A and/or the back vision components portion205B.

In various implementations, the exposure (strobe) time controller233escontrols an image exposure time of the back and front vision components portions205B and205A (e.g., relative to a phase timing of the periodically modulated effective focus position). More specifically, in some implementations, during an image exposure, the exposure (strobe) time controller233es(e.g., using the effective focus position (Z-coordinate) calibration data available in the effective focus position calibration portion273), may control the first light source PLS1of the back vision components portion205B to strobe at a respective controlled time (e.g., so that each image of an image stack will be acquired at a different focus position corresponding to a known Z-coordinate within a focus range). For example, the exposure (strobe) time controller233esmay control the first light source PLS1(e.g., a strobe light source) to strobe at a respective phase timing within a period of a standard imaging resonant frequency of the VFL lens L4, so as to acquire an image having a particular effective focus position (e.g., with a corresponding known Z-coordinate) within the sweeping (periodic modulation) range of the VFL lens L4. In other implementations, the exposure time controller233esmay control a fast electronic camera shutter of the camera CMOS of the front vision components portions205A to acquire an image at a respective controlled time and/or its associated effective focus position (Z-coordinate). In some implementations, the exposure (strobe) time controller233esmay be merged with or indistinguishable from the camera CMOS. It will be appreciated that the operations of the exposure time controller233esand other features and elements outlined above may be implemented to govern the image stack acquisition.

In certain implementations in which the second light source PLS2is included in the front vision components portion205A, the first linear polarizer LP1may convert the light from the second light source PLS2into linearly polarized light (e.g., with horizontal polarization). In various implementations, some or all of the polarization altering components of the system200(e.g., the first and second linear polarizers LP1and LP2of the front vision components portion205A) may be tuned (e.g., adjusted in terms of orientation and/or position) in order to achieve a maximum contrast for images at a desired Z-coordinate.

In various implementations, strobed/pulsed illumination from the second light source PLS2may be utilized in conjunction with the operation of the VFL lens L4(e.g., similar to the operations of the first light source PLS1). In various implementations, strobed/pulsed illumination and/or continuous illumination may also or alternatively be utilized as part of certain other operations (e.g., where the front vision components portion205A is mechanically moved along the Z-axis direction by the movement mechanism110A ofFIG.1, or other movement mechanism, to be closer to or further from the workpiece220so as to change the focus position, etc.).

As a specific example of potential operations of the second light source PLS2, in one implementation the third workpiece feature WPF1C (e.g., at an entrance to the entrance portion EN1of the aperture AP1, as may correspond to an outside surface of the workpiece220) is to be imaged. In such an implementation, a movement mechanism (e.g., the movement mechanism110A ofFIG.1and/or other movement mechanism) may be configured and utilized to move the front vision components portion205A along the Z-axis to change the focus position of the optical system relative to the workpiece220so that the third workpiece feature WPF1C will be in focus in a corresponding image that is to be acquired. In various implementations, a movement mechanism (e.g., the movement mechanism110A and/or110B) may include various controllable motors that drive actuators and/or other components for achieving motion of the vision components portion205A and/or205B along the X, Y and/or Z-axis directions.

A coordinate system ofFIG.2is indicated as including orthogonal X, Y and Z-axes. In various implementations, the optical axis OA of the front vision components portion205A and/or back vision components portion205B may define and/or be aligned or parallel with, the Z-axis. In some implementations, the coordinate system may be a local coordinate system of the front vision components portion205A and/or back vision components portion205B (e.g., for which the optical axis OA of the front vision components portion205A and/or back vision components portion205B may define the Z-axis). In other implementations, the coordinate system may be a local coordinate system of the workpiece220(e.g., for which it may be desirable to have the optical axis OA of the front vision components portion205A and/or back vision components portion205B aligned with and/or parallel to the Z-axis). In other implementations, the coordinate system may be a local coordinate system of a movement mechanism that moves the front vision components portion205A and/or back vision components portion205B (e.g., the movement mechanism110A and/or110B, for which it may be desirable to have the optical axis OA of the front vision components portion205A and/or back vision components portion205B aligned with and/or parallel to the Z-axis of the coordinate system, and for which the movement mechanism may control movement of the front vision components portion205A and/or back vision components portion205B along the directions of the X and Y axes). In other implementations, other local coordinate systems may also or alternatively be established (e.g., for the images of the image stack, etc.). In various implementations, it may be desirable for any such local coordinate systems to generally have their Z-axes at least approximately aligned and/or in parallel, etc., with each other. In various implementations, as part of a local coordinate system, in addition to or as an alternative to X, Y and Z coordinates, certain types of cylindrical coordinates, Cartesian coordinates, or other coordinates may be utilized (e.g., with respect to the orientation of the vision components portion205A and/or205B and/or the determination of the coordinates of measured surface points, such as surface points within a cylindrical portion of the aperture AP1of the workpiece220, such as surface points of workpiece features of the through-hole portion TH1of the aperture AP1, etc.).

In various implementations, it may be desirable to obtain an image stack that includes images of workpiece features located at different Z-coordinates (e.g., such as the first and second workpiece features WPF1A and WPF1B located at opposite ends of the through-hole portion TH1of the aperture AP1that is oriented along the Z-axis). In such implementations, an image stack may be acquired and operations may be performed, including determining first and second local focus peaks and/or other indicators (e.g., as indicating effective focus positions EFP corresponding to each of the first and second workpiece features WPF1A and WPF1B). In various implementations, an image stack for determining the focus positions of the first and second workpiece features WPF1A and WPF1B may include a sufficient number of images for determining focus positions of workpiece features with a high degree of accuracy (e.g., in some implementations at least 30 images, or at least 60 images, etc.).

In various implementations, the workpiece220(or the workpiece20inFIG.1) may have many apertures extending through the workpiece (e.g., at least 1000, or 10000, or 100000 apertures, etc.). In various implementations, the dimensions of the workpiece220along the X and Y axes may be relatively large (e.g., greater than 1 meter, etc.) and for which the thickness along the Z-axis may be relatively less (e.g., less than 5%, 2%, or 1% of the dimension along the X and/or Y axes). In various implementations, it may be desirable to measure various aspects of the apertures, such as diameters and distances between various workpiece features of the apertures (e.g., diameters and distance between the first and second workpiece features WPF1A and WPF1B, etc.).

In operation, the workpiece220is positioned between the front vision components portion205A and the back vision components portion205B. The movement mechanisms110A and110B are utilized to adjust a relative position between the front vision components portion205A and the workpiece220and between the back vision components portion205B and the workpiece220in a direction that is transverse to the optical axis OA of both the front and back vision components portions205A and205B, to thereby align the optical axis OA of both the front and back vision components portions205A and205B with the aperture AP1of the workpiece220. The back vision components portion205B is thus on the opposite side of the workpiece220from the front vision components portion205A.

In this arrangement, at least a portion of the light from the first light source PLS1of the back vision components portion205B that passes through the focusing lens L6and the collimating lens L7as collimated light CL, then passes through the diffuser LD as diffuse light DL, and then passes through the aperture AP1for providing at least part of the illumination for imaging the aperture AP1.

The camera CMOS of the front vision components portion205A is utilized to acquire an image stack comprising a plurality of images of the aperture AP1as illuminated at least in part by the diffuse light DL, wherein each image of the image stack corresponds to a different focus position along the optical axis OA of the front vision components portion205A as corresponding to a phase timing of the periodic modulation of the optical power of the VFL lens L4. A measurement related to a workpiece feature of the aperture AP1, such as a distance between workpiece features of the aperture (e.g., a distance D1between the first and second workpiece features WPF1A and WPF1B) and/or a diameter of the aperture AP1, etc., is determined based at least in part on an analysis of the image stack.

In various implementations, after the image stack is obtained, analysis of the image stack may be performed (e.g., including evaluating contrast and/or other factors) in order to determine the relative focus positions (e.g., in terms of Z-coordinates) of the first and second workpiece features WPF1A and WPF1B. A distance D1between the workpiece features WPF1A and WPF1B may then be determined in accordance with a difference between the corresponding Z-coordinates. In further regard to such analysis, once an in-focus image for each workpiece feature WPF1A and WPF1B is determined (e.g., in accordance with an image in the image stack that is closest to the in-focus position for the respective workpiece feature), corresponding dimensions of the workpiece features may be determined utilizing the best focused images of the workpieces. For example, a diameter of each of the workpiece features may be determined by performing measurement operations on the respective in-focus image of the workpiece feature. In one implementation, an equivalent diameter may be determined by performing thresholding on an image, and determining a sum of the pixels within the threshold area (e.g., as representing an equivalent area of the workpiece feature), and from which an equivalent diameter may be determined (e.g., for which the equivalent area of the workpiece feature may be considered as a circular area with a corresponding equivalent diameter).

It will be appreciated that the disclosed configuration enables accurate measurements to be performed for workpiece features such as the second workpiece feature WPF1B, even when the workpiece220includes many such workpiece features as part of many apertures (e.g., over 1000 apertures, or over 100000 apertures, etc.) that need to be inspected/measured as part of an inspection/measurement process. For such workpieces, there may be some variances between the many apertures (e.g., in terms of lengths of various portions, diameters of various portions, etc.) for which it is advantageous to be able to quickly and accurately measure the desired workpiece features (e.g., to determine if the variances are within acceptable manufacturing tolerances, etc.). In this regard, the utilization of the disclosed configuration helps enable the system to accurately measure workpiece features such as the second workpiece feature WPF1B, even when such variances occur (e.g., as opposed to a system in which accurate measurements of workpiece features such as the second workpiece feature WPF1B depend on the workpiece features being within a narrow range of positions and/or sizes that the system is only configured to measure). More specifically, the configuration ofFIG.2(i.e., including the back vision components portion205B with the collimating lens L7and diffuser LD for providing the diffuse light DL for the imaging and measuring functions) enables workpiece features (e.g., such as the second workpiece feature WPF1B) to be imaged with acceptable levels of contrast over a relatively large range of possible positions (e.g., along the Z-axis) of such workpiece features.

In various implementations, the aspect ratio of the aperture AP1and/or certain portions thereof (e.g., the through-hole portion TH1) may be relatively high (e.g., greater than two to one) such that the dimension extending along the Z-axis is greater than the diameter or other cross dimension along the X and/or Y axis directions. In various implementations, the diffuser LD of the back vision components portion205B helps ensure that sufficient light is directed into the aperture AP1for the imaging (e.g., the imaging of the second workpiece feature WPF1B), even if there may be less than perfect alignment of the back vision component portion205B with the aperture AP1. More specifically, in implementations where there may be some misalignments, the diffuser LD helps ensure that a sufficient amount of the diffuse light DL will be directed into the aperture AP1for performing the desired imaging.

In various implementations, an image stack may be acquired for measuring the workpiece features WPF1A and WPF1B, as described herein, while for measuring the workpiece feature WPF1C, an autofocus cycle or other imaging process may be performed (e.g., which may in some implementations include utilizing a movement mechanism to move the front vision components portion205A along the Z-axis as part of the autofocus cycle). In certain alternative implementations, an image stack may be acquired for measuring the workpiece feature WPF1C or for measuring all three of the workpiece features WPF1A, WPF1B and WPF1C.

In various implementations, a movement mechanism (e.g., the movement mechanism110A ofFIG.1and/or other movement mechanism) may also or alternatively be configured to rotate or otherwise move a different objective lens into the position of objective lens L2, for which the different objective lens may have a lower magnification and/or otherwise provide a larger range Refp in combination with the operation of the VFL lens L4, so that the workpiece feature WPF1C may fall within the increased range (e.g., and may be imaged as part of an image stack or individual image as part of the operation of the VFL lens L4, etc.). In various implementations, certain other methods may also or alternatively be utilized for increasing the range Refp (e.g., so that the workpiece feature WPF1C may fall within the increased range). For example, the lens controller may be configured/utilized to increase the resonant frequency of the VFL lens L4, to increase the optical power of the VFL lens L4and correspondingly increase the range Refp. As another example, the lens controller280may be configured/utilized to increase the driving signal amplitude to the VFL lens L4, to increase the optical power of the VFL lens L4and correspondingly increase the range Refp.

FIG.3is a schematic diagram of a back vision components portion205B′ according to principles disclosed herein. The back vision components portion205B′ may be similar or identical to the back vision components portion205B ofFIG.2, and will be understood to have similar or identical components and to operate similarly unless otherwise described below. As illustrated inFIG.3, in various implementations, the back vision components portion205B′ (or the back vision components portion205B ofFIG.2) may be configured such that a cross section of the diffuse light DL has a dimension DDL (e.g., a diameter or equivalent diameter) at (e.g., proximate to) the opening of the exit portion EX1of the aperture AP1. In various implementations, the dimension DDL may be adjusted by adjusting the size of the illumination spot as produced by the collimated light CL on the diffuser LD.

In various implementations, the dimension DDL may be approximately equal to, or slightly larger than, a dimension DEX1(e.g., a diameter or equivalent diameter) of the opening of the exit portion EX1, in order to optimize the illumination efficiency (e.g., so that a majority of the diffuse light DL is received within the opening of the exit portion EX1for illuminating various parts of the aperture AP1, including the through-hole portion TH1, for imaging, etc.). In various implementations, the arrangement may be configured such that the dimension DDL is somewhat larger than the dimension DEX1(e.g., to allow for certain tolerances in the alignment of the back vision components portion205B′ and associated components with the aperture AP1, etc., in relation to varying positional and/or angular alignments, etc.). Such an arrangement may also provide advantages when many apertures are being imaged on a workpiece within a limited period of time and the movement mechanism portion110B is being utilized to quickly move the back vision components portion205B′ to be aligned with different apertures for which certain alignment tolerances may be desirable. It is noted that the disclosed configuration with the diffuse light DL does not require a precise alignment of an optical axis OA of the back vision components portion205B′ with an central axis of the aperture AP1(e.g., as might be required in certain alternative illumination/lighting configurations). In various implementations, the optical axis OA of the back vision components portion205B′ may be defined by an optical axis of a component of the back vision components portion (e.g., an optical axis of the collimating lens L7, etc.) or according to a central axis of the back vision components portion205B′, etc.

Some example operations of the metrology system100/200and associated components ofFIGS.1-3will be described in more detail below with respect toFIGS.4and5.

FIG.4is a chart of a timing diagram400illustrating a periodically modulated focus position of the metrology system100/200ofFIGS.1and2as controlled by periodically modulating the focal length of the VFL lens L4in the front vision components portion105A/205A, as outlined above. In the illustrated example, each focus position has a corresponding Z-coordinate, for which an optical axis and/or focus axis of the front vision components portion105A/205A may define and/or otherwise be aligned (e.g., be coaxial or in parallel with, etc.) a Z-axis of a corresponding coordinate system (e.g., for which the Z-coordinates may alternatively be referenced as Z-axis coordinates). The periodically modulated focus position is represented by a sinusoidal curve410. The relationship of the focus position (i.e., as indicated by corresponding Z-coordinates) to the phase timing may be established by calibration according to known principles (e.g., by repeatedly stepping a surface to a known Z-coordinate, and then manually or computationally determining the phase timing that best focuses an image at the known Z-coordinate, and storing that relationship in a lookup table or the like).

The diagram400also qualitatively shows how strobed illumination can be timed to correspond with a respective phase timing (e.g., ϕ0, ϕ1, ϕ12, on, etc.) of the periodically modulated focus position to expose an image focused at a respective Z-coordinate (e.g., zϕ0, zϕ1, zϕ12, zϕ0n, etc.). That is, in the illustrated example, while the camera CMOS is acquiring an image during an integration period, if a strobe pulse is short relative to the period of the focus modulation and is provided at the phase timing ϕ0, then the focus position will be at the Z-coordinate zϕ0, and any workpiece surface that is located at the Z-coordinate zϕ0 will be in focus in the resulting image. A similar description applies for the other exemplary phase timings and Z-coordinates shown in the diagram400.

It will be understood that the phase timings shown in the diagram400are exemplary only and not limiting. More generally, any phase timing selected by a user or automatically selected by a control system will have an associated focus position within the range of Z-coordinates zϕ0-zϕn, which represent the minimum and maximum Z-coordinates of the periodically modulated focus position. It will also be understood that if one strobe pulse at a particular phase timing is not sufficient to provide a well exposed image, the strobe pulse may be repeated at that particular phase timing for any desired number of periods within the image integration period (as schematically illustrated by the repeated instances of any of the exemplary phase timings ϕ0, ϕ1, ϕ12 in the diagram400). For example, one, or several, or thousands, etc., of such pulses may be integrated in an integration period, in some embodiments or implementations. The effect will be to increase the image exposure corresponding to that particular phase timing and/or Z-coordinate in the resulting image. As one specific example implementation, for a variable focal length lens that modulates at a frequency of 72 kHz and an imaging array in a camera operating at 30 frames per second, a single camera frame acquisition time corresponds to 2,400 cycles of the variable focal length lens and the resulting focus position Z-coordinate. It will be appreciated that the exemplary phase timings ϕ1 and ϕ12 are shown on a rising slope of the focus position cycle. In some embodiments, pulses may also be integrated in an integration period which corresponds to the same Z-coordinates during a falling slope of the focus position cycle.

FIG.5is a chart500showing a horizontally expanded portion410′ of the sinusoidal curve410of the periodically modulated focus position shown inFIG.4, and phase timings corresponding to those usable to collect an image stack (e.g., represented by the phase timing positions of the vertical dashed lines in the chart500).FIG.5also qualitatively shows how first and second particular instances of strobed illumination that correspond with first and second phase timings (e.g., in this particular example exemplary phase timings ϕ10and ϕ27) of the periodically modulated focus position can be utilized to produce corresponding exposure images that provide image focus for workpiece features that are located at different Z-coordinates (e.g., such as a first workpiece feature located at a first Z-coordinate Zϕ10 and a second workpiece feature located at a second Z-coordinate Zϕ27).

Regarding the phase timings corresponding to those usable to collect an image stack (represented by the phase timing positions of the vertical dashed lines in the chart500), in accordance with principles disclosed herein, in one implementation an image stack (or multiple image stacks) may be acquired with respect to one or more regions of interest of a representative workpiece. For example, an image stack may be acquired by exposing a first image using one or more strobe illumination pulses (e.g., over one or more periods) coinciding with the phase timing ϕ0. A second image in the image stack may be similarly acquired using the phase timing ϕ1, and so on up to phase timing ϕ35 in the illustrated example. It will be understood that an image stack images a field of view using various focus positions, and generally can include any desired number of images with focus positions corresponding to desired Z-coordinates, acquired using corresponding phase timings.

As noted above,FIG.5illustrates in part how first and second particular instances of strobed illumination that correspond with first and second phase timings (e.g., the exemplary phase timings ϕ10 and ϕ27) of the periodically modulated focus position can be utilized to produce corresponding exposure images that provide image focus for workpiece features that are located at different Z-coordinates (e.g., such as the first workpiece feature WPF1A located at a first Z-coordinate zϕ10, and the second workpiece feature WPF1B located at a second Z-coordinate zϕ27). As a specific example with respect toFIG.2, the first and second workpiece features WPF1A and WPF1B at first and second Z coordinates could be an entrance and an exit, respectively, of the through-hole portion TH1of the aperture AP1.

As illustrated inFIG.5, the first and second workpiece features WPF1A and WPF1B in the field of view on a representative workpiece are indicated as having a sufficient image focus in respective images of an image stack. The first workpiece feature WPF1A is indicated as being best or sufficiently focused at a Z-coordinate Zϕ10 which corresponds to a phase timing of ϕ10, and the second workpiece feature WPF1B is indicated as being best or sufficiently focused at a Z-coordinate Zϕ27 which corresponds to a phase timing of ϕ27. In various implementations, the contrast in one or more regions of interest may be analyzed (e.g., according to known methods) in each image of an image stack. Utilizing such processes, the particular images and/or interpolated Z-coordinates indicated as providing the best or sufficient contrast and focus for the first and second workpiece features WPF1A and WPF1B, respectively, may be determined.

In various implementations, a determination of an image which has the best or sufficient image focus for a workpiece feature in a region of interest may be made according to various techniques. In one specific example implementation, a technique including an analysis of a focus curve may be utilized. A focus curve may be formed based on focus curve data points, which may be established according to known methods (e.g., as described in incorporated references). Briefly, in one exemplary method, for each captured image in the image stack, a focus metric value is calculated based on the respective region of interest in that image, and that focus metric value becomes a data point on the focus curve (e.g., related to the corresponding phase timing and Z-coordinate at which the image was captured). This results in focus curve data, which may be referred to simply as a “focus curve” or “autofocus curve.” Exemplary techniques for the determination and analysis of image stacks and focus curves are taught in U.S. Pat. Nos. 8,581,162; 9,060,117 and 10,880,468, each of which is hereby incorporated herein by reference in its entirety.

In various implementations, the analysis of an image stack includes determining focus curve data for the image stack which indicates a focus position at which a workpiece feature of the aperture AP1is in focus (e.g., as may correspond to a local peak or other characteristic of the focus curve). For example, the focus curve data may indicate a first focus position at which the first workpiece feature WPF1A of the aperture AP1is in focus, and a second focus position at which the second workpiece feature WPF1B of the aperture AP1is in focus. A measurement related to the first and second workpiece features WPF1A and WPF1B may be made based on an analysis of the focus curve data. For example, a distance D1between the first workpiece feature WPF1A and the second workpiece feature WPF1B may be determined based on an analysis of the focus curve data.

In various implementations, apertures in a workpiece may be formed through a drilling process (e.g., laser drilling, mechanical drilling, etc.) or other machining process. As part of such processes, certain workpiece features (e.g., the first and second workpiece features WPF1A and WPF1B) may correspond to an entrance and exit of a drilling hole (e.g., an entrance and exit of a through-hole portion, such as the through-hole portion TH1). In regard to such workpiece features, certain aspects may be important to inspect (e.g., due to the possibility of debris, extra material, or other imperfections that may remain at such an entrance or exit after the drilling or other machining process is complete, for which the presence of such imperfections may affect the performance of the workpiece, etc.).

As will be described in more detail below with respect toFIGS.6A and6B, imperfections (e.g., such as debris, extra material, etc.) at the first or second workpiece feature WPF1A or WPF1B (i.e., at the entrance or exit of the through-hole portion TH1) may generally be visible in an image that is well focused at the Z-coordinate of the respective workpiece feature.

FIGS.6A and6Bare relatively in-focus images of the first and second workpiece features WPF1A and WPF1B captured, for example, at phase timings of ϕ10 and ϕ27 as illustrated inFIG.5, with the workpiece features WPF1A and WPF1B at Z-coordinates of ϕ10 and ϕ27, respectively. The through-hole portion TH1may be formed by a drilling process, for which both the entrance and the exit have certain imperfections/defects. More specifically, sections SEC1A and SEC1B of the first and second workpiece features WPF1A and WPF1B, respectively, each illustrate a small amount of material extending into the through-hole portion TH1as part of each respective workpiece feature (i.e., as an imperfection/defect relative to a desired perfectly round/circular workpiece feature at each end of the through-hole portion TH1, which may ideally be a perfectly cylindrical through-hole portion TH1). By obtaining in-focus images, imperfections in the sections SEC1A and SEC1B can be inspected, measured, etc., in the images ofFIGS.6A and6B(e.g., to determine if the imperfections are within acceptable manufacturing tolerances, etc.).

As described above, the example aperture AP1(e.g., ofFIG.2) comprises an entrance portion EN1, a through-hole portion TH1, and an exit portion EX1. The through-hole portion TH1comprises the first workpiece feature WPF1A (e.g., the entrance of the through-hole portion TH1) and the second workpiece feature WPF1B (e.g., the exit of the through-hole portion TH1). For quality control purposes (e.g., when manufacturing a workpiece with through-hole portions), it may be desirable to measure certain features of the through-hole portions, although in some instances such features may be difficult to illuminate and measure (e.g., due to limited access and/or restricted sizes/spaces of the through-hole portions, etc.) One such feature that may be desirable to measure is the distance D1between the first workpiece feature WPF1A (e.g., the entrance of the through-hole portion TH1) and the second workpiece feature WPF1B (e.g., the exit of the through-hole portion TH1). As described herein, this can be done, for example, by focusing the imaging system (e.g., of the front vision components portion205A) on the first workpiece feature WPF1A, determining/measuring its focus position (i.e., corresponding to a first Z-coordinate), and then focusing the imaging system on the second workpiece feature WPF1B, and determining/measuring its focus position (e.g., corresponding to a second Z-coordinate). Such processes may be performed as part of the acquisition and analysis of an image stack, etc. The difference between the focus positions (e.g., the Z coordinates) is the distance D1. The focus positions can each be found according to a peak of a contrast measurement, as described herein.

In an alternative implementation toFIG.2where a diffuser (e.g., diffuser LD) is not included in the path of the light from the light source (i.e., where the collimated light CL would continue to the exit portion EX1without passing through a diffuser), it has been experimentally determined that in some implementations the measuring of the distance D1may be relatively less accurate. As a specific numerical example, in some instances it has been experimentally determined that such a configuration may result in determinations of distances D1that may be 15-20% under sized (i.e., the determined distance D1may be 15-20% less than the actual distance D1). Such differences may result at least in part due to the fact that, for the second workpiece feature WPF1B, the peak contrast signal (i.e., as utilized for determining the focus position/Z-coordinate for the second workpiece feature WPF1B) may be smaller than desired. This may be due, for example, to collimated/non-diffused light resulting in images of the second workpiece feature WPF1B in the image stack which result in lower contrast values. In some implementations, the lower contrast values may be due at least in part to an illumination halo around or otherwise proximate to the second workpiece feature WPF1B (e.g., as resulting from the illumination configuration providing the light without a diffuser). Alternatively or additionally, the lower contrast values may be due to imperfections (e.g., debris, etc. such as may cause increased contrast at other Z coordinates where the debris, etc. is located and may skew the determination/calculation of the peak contrast for the location of the second workpiece feature WPF1B). Other factors may also contribute to the lower contrast values, as may result at least in part from a utilization of an illumination configuration without a diffuser.

As disclosed herein, to address such issues, a configuration is provided for the back vision components portion205B (e.g., including the diffuser LD as located in the path of the light from the light source PLS1), for which the resulting diffuse light DL results in a desirable imaging and a desirable peak contrast signal for determining the focus position/Z-coordinate for the second workpiece feature WPF1B, and also results in desirable peak contrast signals and imaging for other features (e.g., for the first workpiece feature WPF1A, any imperfections such as debris, etc. at various locations in the through-hole portion TH1, etc.). It will be appreciated that a single illumination configuration which enables such desirable imaging/peak contrast signals as part of a single image stack acquisition (e.g., utilizing the operations of the VFL lens) enables such data for all of the desired elements/features (e.g., the noted workpiece features, the corresponding positions/distances, imperfections such as debris, etc.) to be collected as part of a single continuous acquisition process (e.g., as part of acquiring a single image stack). This is in contrast to a process requiring utilization of multiple illumination configurations, which could require more time as well as raising issues of any changes that may occur when switching between use of the different illumination configurations, etc.

In accordance with the configuration for the back vision components portion205B as described above, in various implementations, the light source PLS1provides the light through the focusing lens L6, for which the light is then collimated by the collimating lens L7, and the collimated light CL is directed onto and forms an illumination spot on the diffuser LD (e.g., an optical diffuser, such as a transparent light diffuser), which provides the diffuse light DL (e.g., which may be referenced as diffuse collimated light) for illuminating and imaging (e.g., including shadow imaging) the aperture AP1, including the through-hole portion TH1which includes the associated workpiece features (e.g., WPF1A, WPF1B, any imperfections such as debris, etc.). The spreading of the light rays by the diffuser LD essentially provides an average dispersion over certain desirable illumination conditions (e.g., including providing converging light, diverging light and/or collimated light as may each be desirable for imaging certain of the workpiece features). This effectively provides a compromise between optimizing (e.g., utilizing only one of converging light, diverging light or collimated light) for imaging any particular workpiece feature(s), and enables a single image acquisition process to be performed, such as acquiring an image stack including images of all of the desired workpiece features.

In various implementations, the size of the illumination spot as produced by the collimated light CL on the diffuser LD may be adjusted/configured to optimize the illumination efficiency (e.g., as depending on a numerical aperture (NA) restriction of the system, etc.). It is noted that there may be various components that may restrict the numerical aperture (NA) of the light/illumination in the configuration ofFIG.2(e.g., such as the NA of the objective lens L2, the dimensions of the exit portion EX1, through-hole portion TH1and/or entrance portion EN1, etc.) As a specific numerical example, in one implementation if the NA restriction of the system is 0.1 (6 degrees), then a 16 mm illumination spot on the diffuser LD which is placed 80 mm from the exit portion EX1may be sufficient for the desired imaging/measurements. In various implementations, polarized imaging (e.g., including one or more polarizers such a polarizer LP2in the front vision components portion205A) may be utilized to suppress scattered light from the side walls of the through-hole portion TH1(e.g., for which the scattered light may be reduced in some implementations by approximately ½, assuming the scattering is mostly random polarization).

It is noted that for imaging/measuring certain imperfections (e.g., debris, etc.), in various implementations it may be desirable to have at least some illumination that approximates collimated illumination/light (e.g., for shadow imaging which may provide desirable imaging of certain imperfections such as debris etc. within the through-hole portion TH1, for which any debris etc. may appear as dark areas in contrast to the bright center of the through-hole portion TH1in the images). For such imaging, some amount of divergence of the illumination may also be desirable (e.g., to reduce sensitivity to mechanical alignment, such as the angular alignment of the optical axis of the back vision components portion205B relative to the axis of the through-hole portion TH1).

It is further noted that for imaging/measuring the first workpiece feature WPF1A, in various implementations it may be desirable to have at least some illumination that approximates diverging illumination/light (e.g., for shadow imaging, such as of a knife edge type, that may provide high contrast for the location and size of the first workpiece feature WPF1A). It may be desirable for the numerical aperture (NA) corresponding to at least some of the illumination/light to be matched (e.g., may be slightly exceeding) to the NA restriction in the system (mechanical NA, the NA of the objective lens L2, etc.). This ensures that at least some of the light rays approaching first workpiece feature WPF1A at the largest angles (e.g., knife edge configuration) will be captured by the imaging system of the front vision components portion205A. Thus, in certain implementations the contrast at the first workpiece feature WPF1A may be desirable (e.g., sufficiently large contrast) if the illumination passes the first workpiece feature WPF1A in a “knife edge” configuration (e.g., as may be achieved by having at least some illumination/light that approximates diverging illumination, as noted above).

It is further noted that for imaging/measuring the second workpiece feature WPF1B, in various implementations it may be desirable to have at least some illumination that approximates converging illumination/light (e.g., for shadow imaging, such as of a knife edge type, that may provide high contrast for the location and size of the second workpiece feature WPF1B). It may be desirable for the numerical aperture (NA) corresponding to at least some of the illumination/light to be matched (e.g., may be slightly exceeding) to the NA restriction in the system (mechanical NA, the NA of the objective lens L2, etc.). This ensures that at least some of the light rays approaching the second workpiece feature WPF1B at the largest angles (e.g., knife edge configuration) will be captured by the imaging system of the front vision components portion205A. Thus, in certain implementations the contrast at the second workpiece feature WPF1B may be desirable (e.g., sufficiently large contrast) if the illumination passes the second workpiece feature WPF1B in a “knife edge” configuration (e.g., as may be achieved by having at least some illumination/light that approximates converging illumination, as noted above).

It is noted that an alternative illumination configuration (e.g., utilizing only collimated light and not utilizing a diffuser DL for illuminating an aperture AP1) has been experimentally determined in some implementations to produce less desirable imaging/measurements in particular of the second workpiece feature WPF1B (e.g., and in relation to the corresponding determined distance D1between the workpiece features WPF1A and WPF1B). This may be contrasted with the disclosed configuration ofFIG.2, for which the back vision components portion205B utilizing the illumination configuration including the diffuser LD for diffusing the collimated light CL to produce diffuse light DL produces more desirable and highly accurate imaging/measurements of the second workpiece feature WPF1B (e.g., and the corresponding distance D1between the workpiece features WPF1A and WPF1B). In general, as noted above, the diffuser LD essentially provides an average dispersion over certain desirable illumination conditions, which enables a single image acquisition process such as acquiring an image stack including images of all of the noted workpiece features and results in desirable and highly accurate imaging/measurements of each of the noted workpiece features (e.g., including WPF1A, WPF1B, D1, any imperfections such as debris, etc.).

FIG.7is a flow diagram showing one example of a method for operating a metrology system100,200including a front vision components portion105A,205A and a back vision components portion105B,205B to determine a measurement related to a workpiece feature of an aperture AP, according to principles disclosed herein.

Step702includes adjusting relative positions between a workpiece20,220and front and back vision components portions105A,105B,205A,205B of a metrology system100,200to align an optical axis OA of the front vision components portion105A,205A with an aperture AP, AP1of the workpiece and to also align an optical axis OA of the back vision components portion105B,205B with the aperture AP, AP1of the workpiece, such that at least a portion of light from a light source PLS1of the back vision components portion105B,205B that passes through a diffuser LD of the back vision components portion105B,205B passes through the aperture AP, AP1for providing at least part of the illumination for imaging the aperture. The front vision components portion105B,205B comprises a variable focal length (VFL) lens L4, an objective lens L2that defines the optical axis OA of the front vision components portion105A,205A, and a camera CMOS.

Step704includes acquiring an image stack comprising a plurality of images of the aperture AP, AP1as illuminated at least in part by light from the light source PLS1that has passed through the diffuser LD, wherein each image of the image stack corresponds to a different focus position along the optical axis OA of the front vision components portion105A,205A as corresponding to a phase timing ϕn of a periodic modulation of the optical power of the VFL lens L4.

Step706includes determining a measurement related to a workpiece feature WPF1A, WPF1B of the aperture AP, AP1based at least in part on an analysis of the image stack. In various implementations, the analysis of the image stack comprises determining focus curve data for the image stack which indicates a focus position at which the workpiece feature is in focus. In various implementations, the workpiece feature is a first workpiece feature WPF1A of the aperture AP, AP1and the focus position is a first focus position, and the focus curve data further indicates a second focus position at which a second workpiece feature WPF1B of the aperture AP, AP1is in focus, wherein the measurement comprises a distance D1between the first workpiece feature WPF1A and the second workpiece feature WPF1B. In various implementations, the aperture AP, AP1comprises a through-hole portion TH1, and the first and second workpiece features WPF1A and WPF1B correspond to an exit and entrance of the through-hole portion TH1, respectively.

As described above, for each image of the image stack, the light source PLS1may be controlled to provide at least one instance of strobed illumination timed to correspond with a respective phase timing on of a periodically modulated focus position that corresponds to the respective focus position for that respective image of the image stack.

While preferred implementations of the present disclosure have been illustrated and described, numerous variations in the illustrated and described arrangements of features and sequences of operations will be apparent to one skilled in the art based on this disclosure. Various alternative forms may be used to implement the principles disclosed herein.

All of the U.S. patents and U.S. patent applications referred to in this specification are incorporated herein by reference, in their entirety. Aspects of the implementations can be modified, if necessary to employ concepts of the various patents and applications to provide yet further implementations. These and other changes can be made to the implementations in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific implementations disclosed in the specification and the claims, but should be construed to include all possible implementations along with the full scope of equivalents to which such claims are entitled.