Metrology system with projection patterning for defocused point-based processes

Abstract

A metrology system is provided, which includes a projected pattern for a defocused point type process. The metrology system includes an objective lens portion, a light source, a pattern projection portion and a camera. Different lenses (e.g., objective lenses) with different magnifications and cutoff frequencies can be used in the system. The pattern projection portion includes a pattern component having a pattern. At least a majority of the area of ​​the pattern includes pattern portions that do not repeat on the pattern at regular intervals (e.g., corresponding to different spectra of spatial frequencies that produce a relatively flat power spectrum within a desired range and can be used with different lenses with different cutoff frequencies). The pattern is projected onto a workpiece surface (e.g., for contrast generation), and an image stack is acquired, from which focus curve data indicating the three-dimensional position of a workpiece surface point is determined.

Description

Technical Field

[0001] The present disclosure relates to precision metrology using non-contact workpiece surface measurement (eg, in a machine vision inspection system), and more particularly, to a process for determining the Z height of a point on a workpiece surface. Background Art

[0002] Precision non-contact metrology systems such as precision machine vision inspection systems (or simply "vision systems") can be used to obtain accurate dimensional measurements of objects and inspect various other object characteristics, and may include a computer, camera, and optical system, as well as a precision stage that moves to allow workpiece traversal and inspection. An exemplary prior art is the PC-based QUICK Series of vision systems and Software. QUICK Series of vision systems and The features and operation of the software are generally described, for example, in the QVPAK 3D CNC Vision Measuring Machine User's Guide, published January 2003, the entire contents of which are incorporated herein by reference. This type of system uses a microscope-type optical system and a moving stage to provide inspection images of small or relatively large workpieces.

[0003] General-purpose precision machine vision inspection systems are often programmable to provide automated video inspection. Such systems often include GUI features and predefined image analysis "video tools" so that "non-expert" operators can perform operations and programming. For example, U.S. Patent No. 6,542,180, the entire contents of which are incorporated herein by reference, teaches a vision system that uses automated video inspection, including the use of various video tools.

[0004] Accuracy in the micron or sub-micron range is often required in such systems. This is particularly challenging for Z height measurements. Z height measurements (along the optical axis of the camera system) are typically derived from a "best focus" position, such as the position determined by an autofocus tool. Determining the best focus position is a relatively complex process that typically relies on combining and / or comparing information derived from multiple images. Therefore, the level of accuracy and reliability achieved by Z height measurements is typically lower than that achieved by the X and Y measurement axes, where measurements are typically based on feature relationships within a single image. There is a need for technologies that can improve or otherwise enhance the accuracy, precision and / or reliability achieved by Z height measurements of points on a workpiece surface. Summary of the invention

[0005] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

[0006] A metrology system is provided, which includes an objective lens part, a light source, a pattern projection part, a camera, one or more processors and a memory. The objective lens part includes an objective lens selected from a group of objective lenses, wherein each of the group of objective lenses has a different magnification and a cutoff frequency, and the magnification state of the metrology system is configured to be changed by changing the objective lens included in the objective lens part. The pattern projection part includes a pattern component having a pattern, wherein at least a majority of the area of ​​the pattern contains a plurality of pattern parts, and the patterns do not appear repeatedly on the pattern at regular intervals, and wherein the light from the light source is configured to be transmitted toward the pattern to form pattern light, which is transmitted through the objective lens to form a projection pattern on a workpiece surface, and wherein the objective lens is configured to input image light generated from a workpiece surface including a projection pattern and transmit the image light along an imaging light path. The camera is configured to receive the image light transmitted along the imaging light path and provide an image of the workpiece surface including the projection pattern. The memory is coupled to the one or more processors and stores program instructions that, when executed by the one or more processors, cause the one or more processors to at least: control a light source to transmit light toward a pattern to form a projected pattern on a workpiece surface; acquire, using a camera, an image stack including a plurality of images of the workpiece surface having the projected pattern, wherein each image of the image stack corresponds to a different Z height; and determine focus curve data based at least in part on an analysis of images of the image stack, wherein the focus curve data indicates three-dimensional positions of a plurality of surface points on the workpiece surface.

[0007] According to another aspect, a plurality of pattern portions of the pattern correspond to spatial frequencies below a highest cutoff frequency of an objective in a set of objective lenses. According to another aspect, the set of objective lenses comprises: a lowest magnification lens corresponding to the lowest magnification of the set; a highest magnification lens corresponding to the highest magnification of the set; and a plurality of intermediate magnification lenses, each corresponding to a respective intermediate magnification, each intermediate magnification being between the lowest magnification and the highest magnification, and wherein the highest magnification is at least 10 times the lowest magnification. In various embodiments, at least some of the objective lenses in the set of objective lenses each correspond to a respective magnification of at least one of 0.5x, 1x, 2x, 2.5x, 5x, 10x, 20x, 25x, 50x, or 100x.

[0008] According to another aspect, the system further includes a turret having a plurality of turret lenses, wherein each turret lens corresponds to a different magnification, and the turret is configured to position one of the turret lenses in the imaging optical path. In various embodiments, the turret can have at least a first turret lens, a second turret lens, and a third turret lens, wherein the second turret lens corresponds to a magnification of at least 2 times that of the first turret lens, and the third turret lens corresponds to a magnification of at least 4 times that of the first turret lens, and the turret is configured to position one of the turret lenses in the imaging optical path.

[0009] According to another aspect, each of a plurality of surface points on the workpiece surface corresponds to a region of interest in each of the images of the image stack, and determining focus curve data includes determining focus curve data for each of the regions of interest based at least in part on an analysis of the images of the image stack, wherein for each of the surface points, a peak of the focus curve data corresponding to the region of interest indicates a corresponding Z height of the surface point, and wherein the peak is caused at least in part by a contrast provided by a pattern portion of the projection pattern.

[0010] According to another aspect, the pattern portions include darker pattern portions and lighter pattern portions. In various embodiments, the total area of ​​the pattern corresponding to the darker pattern portions and the total area of ​​the pattern corresponding to the lighter pattern portions are nominally equal (e.g., the ratio of the pattern is about 50 / 50). In various embodiments, the lighter pattern portions correspond to the intervals between the darker pattern portions. In various embodiments, the pattern is formed on the pattern components using a chrome-on-glass type process.

[0011] In various embodiments, the pattern portions include pattern portions of different sizes. In various embodiments, the pattern portions of different sizes include at least a first size pattern portion, a second size pattern portion, a third size pattern portion, and a fourth size pattern portion, wherein the size (e.g., length) of the second size pattern portion, the third size pattern portion, and the fourth size pattern portion is at least twice, three times, or four times the corresponding size of the first size pattern portion. In various embodiments, the pattern portions of different sizes further include at least a fifth size pattern portion, a sixth size pattern portion, a seventh size pattern portion, and an eighth size pattern portion, wherein the size of the fifth size pattern portion, the sixth size pattern portion, the seventh size pattern portion, and the eighth size pattern portion is at least five times, six times, seven times, or eight times the corresponding size of the first size pattern portion.

[0012] In various embodiments, a largest pattern portion in the plurality of pattern portions is less than twenty times the size of a smallest pattern portion in the plurality of pattern portions. In various embodiments, the pattern portion of the first size is the smallest pattern portion in the plurality of pattern portions and has an area of ​​at least 2 microns by 2 microns and at most 20 microns by 20 microns. In various embodiments, the camera comprises an array of pixels, wherein each pixel has an area of ​​at least 2 microns by 2 microns and at most 20 microns by 20 microns.

[0013] In various embodiments, adjacent darker and lighter pattern portions in a plurality of pattern portions are in a sequence that does not repeat at regular adjacent intervals on the pattern in the x-axis or y-axis direction of the pattern. In various embodiments, the pattern may include rows and columns of pattern elements (e.g., wherein the rows and columns may extend in the x-axis and y-axis directions, respectively). In various embodiments, each of the darker pattern portions may be composed of one or more darker pattern elements (e.g., each included in the corresponding rows and columns of the pattern). Similarly, each of the brighter pattern portions (e.g., which may correspond to the intervals between the darker pattern portions) may be composed of one or more brighter pattern elements (e.g., each included in the corresponding rows and columns of the pattern). In various embodiments, at least a majority of the area of ​​the pattern includes at least one of the rows or columns of the pattern, and the rows or columns include a plurality of pattern portions that do not repeat at regular intervals in the corresponding rows or columns of the pattern. In various embodiments, for at least a majority of the rows or columns of a pattern, all or a portion of each respective row or column can be unique in that it includes a unique sequence of darker and lighter pattern portions (e.g., of corresponding sizes) extending across all or a portion of the respective row or column (e.g., not repeated in other rows or columns of the pattern).

[0014] According to another aspect, the pattern projecting part further includes a pattern positioning part configured to be controlled to position the pattern component in an optical path between the light source and the objective lens.

[0015] A method for operating a metrology system is provided. The method includes controlling a light source to transmit light to a pattern included in an optical path with an objective lens to form a projected pattern on a workpiece surface, wherein at least a majority of the area of ​​the projected pattern includes a plurality of pattern portions that do not repeat on the pattern at regular intervals. A camera is used to acquire an image stack containing a plurality of images of the workpiece surface having the projected pattern, wherein each image of the image stack corresponds to a different Z height. Focus curve data is determined based at least in part on an analysis of an image of the image stack. The three-dimensional positions of a plurality of surface points on the workpiece surface are determined using the focus curve data. In various embodiments, the plurality of pattern portions of the projected pattern correspond to spatial frequencies that are lower than a highest cutoff frequency of an objective lens in an objective lens group. According to another aspect, the method further includes controlling a pattern positioning portion to position a pattern component in the optical path between the light source and the objective lens.

[0016] In various embodiments, the objective lens included in the objective lens portion is a first objective lens having a first cutoff frequency, and the projected pattern is a first projected pattern at least partially filtered by the first cutoff frequency, and the plurality of pattern portions are a first plurality of pattern portions, and the method further includes changing the magnification state of the metrology system by changing the objective lens included in the objective lens portion to a second objective lens having a second cutoff frequency different from the first cutoff frequency. Controlling the light source to transmit light to the pattern included in the optical path with the second objective lens to form a second projected pattern on the workpiece surface, wherein the second projected pattern is at least partially filtered by the second cutoff frequency, and at least a majority of the second projected pattern includes a second plurality of pattern portions that do not repeat on the pattern at regular intervals, and wherein the second plurality of pattern portions differ from the first plurality of pattern portions at least in part due to different filtering of the first cutoff frequency and the second cutoff frequency. The camera is used to acquire a second image stack, the second image stack including a second plurality of images of the workpiece surface having a second projection map, wherein each image of the second image stack corresponds to a different Z height. Determining second focus curve data based at least in part on an analysis of the images of the second image stack. The second focus curve data is used to determine the three-dimensional position of a plurality of surface points on the workpiece surface.

[0017] In various embodiments, a pattern projection portion for use with a metrology system is provided, and includes a pattern component and a pattern positioning portion. The pattern component includes a pattern, wherein at least a majority of the area of ​​the pattern includes a plurality of pattern portions that do not repeat on the pattern at regular intervals. The pattern positioning portion is configured to position the pattern component in an optical path between a light source and an objective lens. After the pattern component is positioned in the optical path, light from the light source is configured to be transmitted toward the pattern to form pattern light, which is transmitted through the objective lens to form a projected pattern on a workpiece surface, and wherein the objective lens is configured to input image light including the projected pattern generated from the workpiece surface and transmit the image light along the imaging optical path, and wherein the camera is configured to receive the image light transmitted along the imaging optical path, and capture an image stack of a plurality of images of the workpiece surface having the projected pattern, wherein each image of the image stack corresponds to a different Z height, and wherein the image is configured to be analyzed to determine focus curve data indicating the three-dimensional position of a plurality of surface points on the workpiece surface. In various embodiments, the plurality of pattern portions of the pattern correspond to spatial frequencies lower than the highest cutoff frequency of the objective lens in the objective lens group. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a schematic diagram showing various typical components of a general precision machine vision inspection system;

[0019] Figure 2 is with Figure 1 A block diagram of the control system portion and vision component portion of a machine vision inspection system similar to and including the pattern projection portion;

[0020] Figure 3 Yes Figure 2 A block diagram of an exemplary implementation of a pattern projection portion is shown;

[0021] Figure 4A and 4B is a schematic diagram illustrating contrast focus curves resulting from characteristics of a projection pattern in a corresponding region of interest;

[0022] Figure 5 is a schematic diagram showing a checkerboard pattern and a corresponding power spectrum diagram;

[0023] Figure 6 is a schematic diagram showing a section of a three-level fractal pattern and a corresponding power spectrum diagram;

[0024] Figure 7 is a schematic diagram illustrating various principles of pattern portions corresponding to different spatial wavelengths;

[0025] Figure 8 An enlarged section of a pattern, including portions of the pattern that do not repeat at regular intervals.

[0026] Fig. 9 It shows the Figure 8 A schematic diagram of a complete pattern of a pattern segment of , wherein the pattern portion does not repeat at regular intervals in the pattern and the corresponding power spectrum diagram; and

[0027] Fig.10 is a flow chart illustrating a method for operating a metrology system including a pattern projection portion according to principles disclosed herein. DETAILED DESCRIPTION

[0028] Figure 1 1 is a block diagram of an exemplary machine vision inspection system 10 that can be used as a metrology system and / or imaging system according to the principles described herein. The machine vision inspection system 10 includes a vision measuring machine 12, which is operably connected to exchange data and control signals with a control computer system 14. The control computer system 14 is further operably connected to exchange data and control signals with a monitor or display 16, a printer 18, a joystick 22, a keyboard 24, and a mouse 26. The monitor or display 16 can display a user interface suitable for controlling and / or programming the operation of the machine vision inspection system 10. It should be understood that in various embodiments, a touch screen tablet or other computing element, etc. can replace and / or redundantly provide the functionality of any or all of the elements 14, 16, 22, 24 and 26.

[0029] Those skilled in the art will appreciate that the control computer system 14 can generally be implemented using any suitable computing system or device, including distributed or networked computing environments, etc. Such computing systems or devices may include one or more general or special processors (e.g., non-customized or customized devices) that execute software to perform the functions described herein. The software may be stored in a memory such as a random access memory (RAM), a read-only memory (ROM), a flash memory, etc., or a combination of such components. The software may also be stored in one or more storage devices such as an optical disk, a flash memory device, or any other type of non-volatile storage medium for storing data. The software may include one or more program modules, which include routines, programs, objects, components, data structures, etc. that perform specific tasks or implement specific abstract data types. In a distributed computing environment, the functionality of the program modules may be combined or distributed across multiple computing systems or devices, and the functionality of the program modules may be accessed via service calls in a wired or wireless configuration.

[0030] The vision measuring machine 12 includes a movable workpiece stage 32 and an optical imaging system 34 that may include a zoom lens or an interchangeable objective lens. The zoom lens or the interchangeable objective lens typically provides various magnifications for the image provided by the optical imaging system 34. Various embodiments of the machine vision inspection system 10 are also described in U.S. Patent Nos. 7,454,053; 7,324,682; 8,111,905; and 8,111,938, each of which is incorporated herein by reference in its entirety.

[0031] Figure 2 is similar to Figure 1 A block diagram of a control system portion 120 and a vision component portion 200 of a machine vision inspection system 100 (i.e., a metrology system) of a machine vision inspection system of the present invention, including certain features disclosed herein. As will be described in more detail below, the control system portion 120 is used to control the vision component portion 200 and the pattern projection portion 300. The control system portion 120 can be arranged to exchange data and control signals with the vision component portion 200 and the pattern projection portion 300. The vision component portion 200 includes an optical assembly portion 205, light sources 220, 230, 240, and a workpiece stage 210 having a central transparent portion 212. The workpiece stage 210 can be controllably moved along an x-axis and a y-axis, which are located in a plane generally parallel to the surface of a stage on which the workpiece 20 can be positioned.

[0032] The optical assembly portion 205 includes a camera system 260 and an interchangeable objective lens 250 included in the objective lens portion 245. In some embodiments, the optical assembly portion 205 can optionally include a variable focus length (VFL) lens 270, such as a tunable acoustic gradient (TAG), as disclosed in U.S. Pat. No. 9,143,674, which is incorporated herein by reference in its entirety.

[0033] In various embodiments, the optical assembly portion 205 can further include a turret lens assembly 280 having lenses 286 and 288. As an alternative to the turret lens assembly, in various embodiments, a fixed or manually interchangeable magnification changing lens or zoom lens configuration, etc. can be included. In various embodiments, the interchangeable objective lens 250 in the objective lens portion 245 can be selected from a set of fixed magnification objective lenses included as part of the variable magnification lens portion (e.g., a set of objective lenses corresponding to magnifications such as 0.5x, 1x, 2x or 2.5x, 5x, 10x, 20x or 25x, 50x, 100x, etc., and wherein each objective lens has a cutoff frequency).

[0034] The optical assembly portion 205 can be controllably moved along a z-axis, which is generally orthogonal to the x-axis and y-axis, by using a controllable motor 294, which drives an actuator to move the optical assembly portion 205 along the z-axis to change the focus of the image of the workpiece 20. The controllable motor 294 is connected to the input / output interface 130 via a signal line 296, as will be described in more detail below, to change the focus of the image (e.g., to change the focal position of the objective lens 250 relative to the workpiece 20). The workpiece 20 can be located on a workpiece stage 210. The workpiece stage 210 can be controlled to move relative to the optical assembly portion 205 so that the field of view of the interchangeable objective lens 250 moves between various positions on the workpiece 20 and / or among multiple workpieces 20.

[0035] One or more of the stage light source 220, the coaxial light source 230, and the surface light source 240 (e.g., a ring light) may emit source light 222, 232, and / or 242, respectively, to illuminate one or more workpieces 20. For example, during image exposure, the coaxial light source 230 may emit source light 232 along a path including a beam splitter 290 (e.g., a partial reflector). The source light 232 is reflected or transmitted from the workpiece 20 as image light 255, and the image light for imaging passes through the interchangeable objective lens 250 and the turret lens assembly 280 and is collected by the camera system 260. The workpiece image exposure including the image of the workpiece 20 is captured by the camera system 260 (e.g., including a pixel array) and output to the control system portion 120 on a signal line 262.

[0036] Various light sources (e.g., light sources 220, 230, 240) may be connected to lighting control interface 133 of control system portion 120 via associated signal lines (e.g., buses 221, 231, 241, respectively). Control system portion 120 may control turret lens assembly 280 to rotate along axis 284 to change image magnification by selecting a turret lens (e.g., having a magnification of 1x, 2x, 4x, 6x, etc.) via signal line or bus 281.

[0037] like Figure 2 As shown, in various exemplary embodiments, the control system portion 120 includes a controller 125, an input / output interface 130, a memory 140, a workpiece program generator and actuator 170, and a power supply portion 190. Each of these components and the additional components described below can be interconnected through one or more data / control buses and / or application programming interfaces or through direct connections between various components. The input / output interface 130 includes an imaging control interface 131, a motion control interface 132, an illumination control interface 133, and a lens control interface 134.

[0038] The illumination control interface 133 may include illumination control elements 133a to 133n that control, for example, the selection, power, and on / off switching of various corresponding light sources for the machine vision inspection system 100. The illumination control interface 133 also includes a pattern projection control portion 133pp, which, in the illustrated embodiment, works in conjunction with the pattern projection portion 300 to provide a projected pattern during image acquisition, as described in more detail below. In short, the pattern projection portion 300 is controllable to move the pattern into or out of the path of the source light 232. If the pattern is not positioned in the path of the source light 232, the source light 232 travels as described above to be reflected from the surface of the workpiece 20 as image light 255. If the pattern is positioned in the path of the source light 232, the source light 232 is transmitted or reflected from the pattern as pattern light 232', which is reflected by the beam splitter 290 to be directed through the objective lens 250 to form a projected pattern on the surface of the workpiece 20. Reflected image light 255' (i.e., including the projected pattern) from the surface of the workpiece 20 passes through the interchangeable objective 250 and turret lens assembly 280 and is collected by the camera system 260. A workpiece image exposure including an image of the workpiece 20 with the projected pattern is captured by the camera system 260 (e.g., including a pixel array of the camera system 260) and output to the control system portion 120 on a signal line 262 and further processed as will be described in more detail below.

[0039] The memory 140 may include an image file memory portion 141, a workpiece program memory portion 142, which may include one or more part programs, etc., and a video tool portion 143. The video tool portion 143 includes a video tool portion 143a and other video tool portions (e.g., 143n) that determine a GUI, image processing operations, etc. for each of the corresponding video tools, and a region of interest (ROI) generator 143roi that supports automatic, semi-automatic, and / or manual operations that define various ROIs that can be operated in various video tools included in the video tool portion 143. Embodiments of the operation of such video tools for locating edge features and performing other workpiece feature inspection operations are described in more detail in certain previously incorporated references and in U.S. Pat. No. 7,627,162, which is incorporated herein by reference in its entirety.

[0040] The video tool portion 143 also includes an autofocus video tool 143af that determines a GUI, image processing operations, etc. for focus height measurement operations. In various embodiments, the autofocus video tool 143af may also include a high-speed focus height tool that can be used to measure focus height at high speed, as described in more detail in U.S. Patent No. 9,143,674, which is incorporated herein by reference in its entirety. In various embodiments, the high-speed focus height tool may be a special mode of the autofocus video tool 143af that may be additionally operated according to conventional methods of the autofocus video tool, or the operation of the autofocus video tool 143af may only include the operation of the high-speed focus height tool. High-speed automatic focus and / or focus position determination for one or more image regions of interest may be based on analyzing the image according to known methods to determine corresponding quantitative contrast metrics for each region. For example, such methods are disclosed in U.S. Patent Nos. 8,111,905; 7,570,795; and 7,030,351, each of which is incorporated herein by reference in its entirety.

[0041] In the context of the present disclosure, and as known by those of ordinary skill in the art, the term "video tool" generally refers to a relatively complex set of automated or programmed operations that a machine vision user can implement through a relatively simple user interface. For example, a video tool may include a complex set of pre-programmed image processing operations and calculations that are applied and customized in a specific instance by adjusting several variables or parameters that govern the operations and calculations. In addition to the underlying operations and calculations, the video tool also includes a user interface that allows the user to adjust those parameters for a specific instance of the video tool. It should be noted that sometimes visible user interface features are referred to as video tools while implicitly including the underlying operations.

[0042] One or more display devices 136 (e.g., Figure 1 16) and one or more input devices 138 (e.g., Figure 1 A joystick 22, keyboard 24, and mouse 26 (e.g., a joystick 22, keyboard 24, and mouse 26) are connected to the input / output interface 130. The display device 136 and input device 138 can be used to display a user interface, which can include various graphical user interface (GUI) features that can be used to perform inspection operations, and / or create and / or modify part programs, view images captured by the camera system 260, and / or directly control the vision component portion 200.

[0043] In various exemplary embodiments, when a user utilizes the machine vision inspection system 100 to create a part program for a workpiece 20, the user generates part program instructions by operating the machine vision inspection system 100 in a learning mode to provide a required image acquisition training sequence. For example, the training sequence may include locating a specific workpiece feature of a representative workpiece in a field of view (FOV), setting light levels, focusing or autofocusing, acquiring an image, and providing an inspection training sequence applied to the image (e.g., an instance of using one of the video tools for that workpiece feature). The learning mode operates so that the sequence is captured or recorded and converted into corresponding part program instructions. When the part program is executed, these instructions will cause the machine vision inspection system to reproduce the trained image acquisition and cause the inspection operation to automatically inspect that the specific workpiece features (i.e., corresponding features in corresponding positions) are located on one or more operating mode workpieces that match the representative workpiece used when creating the part program. In some embodiments, such techniques can be utilized to create part program instructions for analyzing reference object images to provide the functions and operations described in more detail below.

[0044] The video tools portion 143 also includes a Z height measurement tools portion 143z that provides various operations and features related to Z height measurement operations, as described in more detail below. In one embodiment, the Z height measurement tools portion 143z may include a Z height tool 143zt. For example, the Z height tool 143zt may include an auto focus tool 143af and a multi-point auto focus tool 143maf. The Z height tool 143zt can be combined with a Z height tool to manage certain aspects of image stack acquisition and related pattern projection operations and processing, and the Z height tool is configured based on the techniques further described below to determine a mode of optimal focus height and / or Z height measurement (e.g., as part of a point from focus type operation).

[0045] In short, the Z height measurement tool portion 143z can perform at least some operations similar to known Z height measurement tools, such as performing operations in a learning mode and a run mode to generate all or part of a focus curve, and finding a peak as a best focus position, etc. Additional Z height measurement tool operations corresponding to the principles and operations disclosed herein can also be performed. For example, in various embodiments, the auto focus tool 143af and / or other Z height tools of the Z height tool 143zt can be selected and used by a user to perform a focus-from-focus (PFF) type process on a workpiece surface, including controlling a pattern projection control portion 133pp for projecting a pattern on a workpiece surface, and capturing an image stack for determining the three-dimensional position (i.e., including the Z height) of multiple surface points on the workpiece surface.

[0046] Figure 3 is a diagram showing some of the principles disclosed herein. Figure 2 FIG. 2 is a block diagram of a portion of the vision system assembly portion 200 and includes additional details of an exemplary embodiment of the pattern projection portion 300. Figure 3 As shown, the objective lens portion 245 includes an objective lens 250-1 selected from a group of objective lenses 248, wherein each of the group of objective lenses (e.g., objective lenses 250-1, 250-2, 250-3, ... 250-n) has a different magnification and spatial resolution, or in other words, has a cutoff frequency (e.g., different objective lenses 250 thereof can each have a different cutoff frequency). The magnification state of the visual component portion 200 (e.g., an optical system including an optical device) of the metrology system 100 is configured to be changed by changing the objective lens 250 included in the objective lens portion 245 (e.g., it can also change the corresponding cutoff frequency of the system according to the selected objective lens). In various embodiments, the group 248 of interchangeable objective lenses 250 (e.g., fixed magnification objective lenses) can each correspond to different magnifications (e.g., including at least some of 0.5 times, 1 times, 2 times, 2.5 times, 5 times, 7.5 times, 10 times, 20 times, 25 times, 50 times, 100 times, etc.).

[0047] The pattern projection part 300 includes a pattern component 302, a pattern positioning part 330, a turning mirror 320 and a projection lens 325. The pattern component 302 includes a pattern 305 (eg, formed by a chrome-on-glass process or other manufacturing methods). Figure 8 and Fig. 9 As described in more detail, in various embodiments, at least a majority of the area (e.g., 50% or more) of the pattern 305 can include multiple pattern portions that do not repeat at regular intervals on the pattern. In operation, such a configuration can provide a wide spectrum of spatial frequencies in the power spectrum, which can be advantageous when used with different objective lenses 250 of the group 248, which can each have a different cutoff frequency. More specifically, as will be described in more detail below, even if some frequency components are filtered by the cutoff frequencies of some objective lenses, some lower frequency ranges can still make it through those objective lenses so as to be present in the projection image and provide sufficient contrast so that accurate / reliable focus curve data can be obtained.

[0048] The pattern positioning part 330 includes a controllable motor 332 and a group of rollers 334. The controllable motor 332 (e.g., controlled by a control signal from the pattern projection control part 133pp or otherwise controlled) drives an actuator to move a pattern component 302 with a pattern 305 into or out of a source light path SOP between the light source 230 and the object lens 250-1. In operation, once the pattern positioning part 330 has been controlled to position the pattern component 302 with a pattern 305 into the source light path SOP, the light source 230 is controlled to transmit light through the pattern 305 to form a projection pattern 305' on the workpiece surface of the workpiece 20. More specifically, the source light 232 from the light source 230 is transmitted through the pattern 305 to form a pattern light 232' transmitted along the source light path SOP including the steering mirror 320, the projection lens 325, the beam splitter 290 and the object lens 250-1. Specifically, the pattern light 232' is reflected by the deflection mirror 320 and passes through the projection lens 325, and is reflected by the beam splitter 290 to pass through the objective lens 250-1, thereby forming a projection pattern 305' on the surface of the workpiece 20'. The objective lens 250-1 inputs the image light 255' generated from the surface of the workpiece including the projection pattern 305', and transmits the image light 255' along the imaging optical path IOP (i.e., it includes the image light 255' that reaches the camera 260 through the lens of the beam splitter 290 and the turret 280). The camera 260 receives the image light 255' transmitted along the imaging optical path IOP (i.e., in the illustrated example, it also corresponds to the optical axis OA of the vision component part 200, such as the optical axis corresponding to the objective lens 250-1), and provides an image of the surface of the workpiece 20' including the projection pattern. The camera 260 includes a sensor SA (e.g., including a pixel array, which will be described in more detail below).

[0049] As will be discussed below Figure 4A and 4B As described in more detail, in various embodiments (e.g., as part of a point from focus type process), the camera 260 is used to acquire an image stack including a plurality of images of a workpiece surface having a projected pattern, wherein each image of the image stack corresponds to a different Z height. Focus curve data is determined based at least in part on an analysis of the images of the image stack (e.g., to which the projected pattern contributes contrast), wherein the focus curve data indicates three-dimensional positions of a plurality of surface points on the workpiece surface (e.g., including Z heights as well as relative x-axis and y-axis positions).

[0050] It should be understood that in the illustrated system, the pattern projection optics include projection and imaging optics. Typically, in the vision system component portion 200 of the system 100, there are at least three different clear apertures that fundamentally limit the frequencies that can be imaged, including the frequencies of the projection lens 325, the objective lens 250, and the lenses of the turret 280 (e.g., also referred to as a tube lens, which can be lens 286 or 288, and / or other lenses included in the turret 280). As described herein, in certain embodiments, the characteristics of different objective lenses 250 and corresponding cutoff frequencies may be particularly relevant. In some embodiments, the projection lens 325 may also have an associated cutoff frequency and may be similarly included in the associated system determinations (e.g., for minimum pattern element size, etc.) as discussed herein. It should be understood that in system 100, in various embodiments, turret lens 280 can be physically located just in front of camera 260 and in the imaging optical path IOP after objective 250, and may not significantly change the spectrum of the imaging system, although in other embodiments, the lens of turret 280 may play a greater role and the characteristics thereof (e.g., cutoff frequency, etc.) may also be included in relevant system determinations.

[0051] Figure 4A and 4B 4 is a schematic diagram depicting contrast focus curves 401 and 402 that may be generated by features of a projection pattern in a corresponding region of interest. In accordance with the principles disclosed herein, it is generally desirable that the projection pattern provide sufficient contrast so that the peak of the contrast curve can be accurately located and reliably distinguished from noise in all desired regions of interest. As will be described in greater detail below, focus curve data may be determined from analysis of an image stack (e.g., as part of a focus from focal point (PFF) type process / measurement operation) that indicates the three-dimensional location of a surface point on a workpiece surface.

[0052] Figure 4A and 4B Depicted is how an image stack obtained by the system 100 (e.g., including the pattern projection portion 300) can be used to determine the Z height of a point on a workpiece surface. In various embodiments, the image stack is obtained by the system 100 operating in a focus-from-focus (PFF) mode (or a similar mode) to determine the Z height of a point on a workpiece surface. The PFF image stack can be processed to determine or output a Z height coordinate map (e.g., a point cloud) that quantitatively indicates a set of three-dimensional surface coordinates (e.g., corresponding to a surface shape or contour of a workpiece).

[0053] In the PFF type analysis described herein, focus curves 401 and 402 (eg Figure 4AEach of the focus curves (shown) corresponds to a single point on the workpiece surface. That is, the peak of each focus curve represents the Z height of a single point along the direction of the optical axis OA of the vision component portion 200 of the system 100. In various embodiments, the PFF type analysis repeats the process for multiple surface points across the workpiece surface (e.g., each having a corresponding region of interest) so that the overall profile of the workpiece surface can be determined. In general, the process can be performed for multiple surface points within the field of view (i.e., as captured within images of an image stack), where for each image of the image stack, a particular ROI (i) corresponds to a particular point on the workpiece surface (e.g., a point at the center of the ROI).

[0054] Figure 4A and 4B Aligned relative to each other along the Z height axis shown in the figure. Figure 4A is a representative graph 400A showing two examples of fitted focus curves 401 and 402, and Figure 4B is a schematic diagram of a variable focus image stack 400B, which includes two different regions of interest ROI(k), specifically ROI(1) and ROI(2), which correspond to data points fm(1,i) and fm(2,i), respectively. Figure 4A Two different focus curves 401 and 402. A region of interest ROI(k) is included in the imaging surface area of ​​the workpiece.

[0055] With respect to the term "region of interest", it should be understood that some "single-point" autofocus tools return a single Z height corresponding to the entire region of interest. However, known "multi-point" type autofocus tools may return multiple Z heights corresponding to various "sub-regions of interest" (e.g., a grid of sub-regions of interest) within a global region of interest defined by the multi-point type autofocus tool. For example, such sub-regions of interest may be manually and / or automatically defined to be centered on each (or most) pixels within the global region of interest. Thus, in some cases, ROI (1) and ROI (2) may be viewed as representative sub-regions of interest within the global region of interest. However, the key point is that a Z height may be established for any defined autofocus region of interest, regardless of whether it is a region of interest of a single-point autofocus tool or a sub-region of interest within a global region of interest defined by a multi-point autofocus tool. Thus, it should be understood that when the term region of interest is used to establish a Z height, the sub-region of interest (e.g., within a global region of interest defined by a multi-point autofocus tool) may be included within the meaning of the term. For simplicity of the present illustration, regions of interest ROI(1) and ROI(2) are shown as being relatively small (e.g., 3x3 pixels), although it will be appreciated that larger regions of interest (e.g., 7x7 pixels, etc.) may be used as part of such a process, etc., in various embodiments.

[0056] like Figure 4B As shown, each of the images (1)-image (11) of the image stack image (i) includes a centrally located region of interest ROI (1), wherein the determined focus metric value corresponds to a focus metric data point fm (1, i) on the focus curve 401. The region of interest ROI (1) is located at Figure 4B 402 as including a relatively high level of contrast (e.g., in image (6)), corresponding to a relatively large focus metric value shown on focus curve 401. Similarly, each of images (1)-image (11) of image stack image (i) includes a peripherally positioned region of interest ROI (2), wherein the determined focus metric value corresponds to a focus metric data point fm(2,i) on focus curve 402. The region of interest ROI (2) is located at Figure 4B 4 is schematically represented as including a relatively low level of contrast (eg, in image (6)), corresponding to a relatively small focus metric value shown on focus curve 402. As shown in FIG.

[0057] like Figure 4A As shown, each focus metric value fm(1,i) or fm(2,i) can be regarded as a sampled continuous basic focus data 401S or 402S, respectively. Figure 4A As can be seen in FIG. 4 , the basic focus data 401S or 402S is relatively noisy (e.g., due to the small size of the corresponding region of interest). However, in the case of focus curve 401, due to the higher contrast in the corresponding region of interest, the focus metric value near the peak of the focus curve (e.g., near Zp401) is relatively large compared to the size of the "noise component" in the basic focus data. In contrast, in the case of focus curve 402, due to the low contrast in the corresponding region of interest, the focus metric value near the peak of the focus curve (e.g., near Zp402) is relatively similar to the size of the "noise component" in the basic focus data.

[0058] In one specific example, the higher focus metric value indicated in focus curve 401 can be at least partially attributed to a section of the pattern projected onto the surface area in the region of interest ROI(1) being "highly textured" and / or otherwise producing a high contrast in the focused image. In contrast, the lower focus metric value indicated in focus curve 402 can be at least partially attributed to a section of the pattern projected or partially projected (e.g., partially or completely filtered by a cutoff frequency of a lens) onto the surface area in the region of interest ROI(2) having a "small texture" and / or otherwise producing little contrast in the focused image. In any case, it should be understood that due to the low "signal-to-noise ratio" associated with the lower peak of the focus curve 402, compared to the relatively high signal-to-noise ratio associated with the peak of the focus curve 401, the estimated Z height of the focus peak Zp402 of the focus curve 402 is less reliable or more uncertain than the estimated Z height of the focus peak Zp401 of the focus curve 401 (e.g., in some cases, the data of the focus curve 402 can be considered to be unreliable and / or uncertain, so that the focus peak determination cannot be reliably made, which can be considered to correspond to a "gap" in the focus curve data of the workpiece surface).

[0059] It should be appreciated that the contrast regions indicated in the region of interest ROI (1) (e.g., in image (6)) may correspond to pattern portions of a projected pattern on the workpiece surface, wherein the pattern portions have a desired size and arrangement so as to (a) provide a desired amount of contrast in the region of interest ROI (1) at a current magnification (e.g., the magnification of a current lens including the turret 280), and (b) not be filtered by the cutoff frequency of the currently selected interchangeable objective 250 or other lenses of the system. In contrast, the region of interest ROI (2) may represent certain problems that may arise when at least a portion of the pattern does not have such desired characteristics. For example, low contrast in the region of interest ROI (2) may result from corresponding segments of the pattern where pattern portions have high spatial frequencies that are filtered by the cutoff frequency of the currently selected interchangeable objective 250, wherein these pattern portions may be little or not visible in the region of interest ROI (2). As another potential problem, the scale / size of the pattern portions may be such that a single pattern portion (e.g., a single darker pattern portion or a single lighter pattern portion) may cover the entire region of interest ROI(2), resulting in no contrast between different pixels within the region of interest ROI(2).

[0060] According to the principles disclosed herein, it is desirable to utilize a pattern having characteristics that will produce a focus curve similar to focus curve 401 (e.g., having a relatively high focus curve peak), and the pattern can be effectively used for different objective lenses with different cutoff frequencies, and for various magnifications (e.g., including magnifications of turret lenses, etc.). As will be described in more detail below, such characteristics can include a pattern having a wide range of spatial frequency content, so that even if for some objective lenses, some higher frequency content is filtered / lost, other lower spatial frequencies (i.e., corresponding to certain larger pattern portions) can make it through and still be visible in the captured images of the image stack. In some embodiments, it may be desirable that the power spectrum of the pattern is relatively constant (e.g., relatively flat) to the highest cutoff frequency of the optical projection system (e.g., as defined by the highest cutoff frequency of an objective lens in a set of objective lenses that can be utilized). In some embodiments, it may also be desirable to have a relatively limited or small number and / or maximum size of larger pattern portions (e.g., larger darker and / or lighter pattern portions corresponding to lower spatial frequencies below the lowest cutoff frequency of the set of objectives) because such pattern portions may occupy a significant area in the pattern and may cover a significant number of pixels when magnified, etc. As will be described in more detail below, in some embodiments, a pseudo-random pattern (e.g., such as blue noise, etc.) may be suitable for generating high-frequency texture.

[0061] Points from focus type operations (eg, including autofocus operations, etc.) associated with determining the Z height of a region of interest have been outlined previously. Figure 4A and 4B In brief summary, a camera may be moved along a z-axis (e.g., a focus axis or optical axis OA) over a range of Z height positions Z(i) and capture an image (i) at each position. For each captured image (i), a focus metric fm(k,i) may be calculated based on a region of interest or sub-region ROI(k) (e.g., a set of pixels) in the image, which is associated with the corresponding position Z(i) of the camera along the Z-axis when the image was captured. This results in focus curve data (e.g., a focus metric fm(k,i) at position Z(i), which is a type of focus peak determination data set), which may be referred to simply as a "focus curve" or "auto-focus curve". In one embodiment, the focus metric value may involve a calculation of the contrast or sharpness of the region of interest in the image. In various embodiments, the focus value or curve may be normalized. Various focus metric calculation techniques are described in detail in the incorporated references, and various suitable focus metric functions are also known to those of ordinary skill in the art.

[0062] The Z height corresponding to the peak of the focus curve (e.g., Zp401 or Zp402), which corresponds to the best focus position along the Z axis, is the Z height of the region of interest used to determine the focus curve. The Z height corresponding to the peak of the focus curve can be found by fitting a curve (e.g., curve 401 or 402) to the focus curve data (e.g., data fm(1,i) or fm(2,i)) and estimating the peak position of the fitted curve. It should be understood that although the image stack image (i) is shown as including only eleven images for illustrative purposes, in actual embodiments (e.g., as part of a PFF-type process or otherwise), a greater number of images (e.g., 100 or 200 or more) may be utilized. Exemplary techniques for determining and analyzing image stacks and focus curves are taught in U.S. Patent Nos. 6,542,180 and 8,581,162, each of which is incorporated herein by reference in its entirety.

[0063] Figure 5 5 is a schematic diagram illustrating a checkerboard pattern 500A and corresponding power spectrum graphs 500B and 500C. As will be described in more detail below, each pattern shown herein (e.g., Figures 5 to 9 ) represents a pattern on a pattern component (e.g., a pattern 305 formed on a pattern component 302 using chrome-plated glass or other processes) and all or part of a projected pattern (e.g., a projected pattern 305′ achieved by directing light to the pattern component to project the pattern onto a workpiece surface, and wherein a corresponding image is captured by a pixel array of a camera). An enlarged section 510 of a checkerboard pattern 500A is depicted, wherein the pattern is shown to include pattern elements A and B, wherein pattern element A is a darker pattern element and pattern element B is a lighter pattern element. In an embodiment formed by chrome-plated glass or a similar process, the darker pattern element A may correspond to the chrome portion, and the lighter pattern element B may correspond to the space between the darker pattern elements A. Pattern elements A and B are each nominally the same size, each having a dimension x1 along the x-axis direction and a dimension y1 along the y-axis direction. Therefore, the corresponding spatial wavelength Wx in the x-axis direction is equal to 2x1, and the spatial wavelength Wy in the y-axis direction is equal to 2y1.

[0064] In various embodiments, each pattern element A can be designated as a darker pattern portion, and each pattern element B can be designated as a lighter pattern portion, wherein in the example of pattern 500A, each pattern portion can have a size of one pattern element. As shown, pattern portions (e.g., corresponding to pattern elements A and / or B) repeat at regular intervals on pattern 500A (e.g., in the x-axis and y-axis directions of pattern 500A). More specifically, the darker and / or lighter pattern portions repeat (e.g., periodically) at regular intervals (e.g., at equally spaced locations) in the x-axis and y-axis directions across the entire pattern.

[0065] As shown in power spectrum graphs 500B and 500C, the spatial frequency composition of checkerboard pattern 500A results in only a few frequencies in the power spectrum. More specifically, the power spectrum exhibits peaks at the dominant spatial frequencies (e.g., spatial frequencies Wx along the x-axis) of pattern elements A and B (e.g., a maximum peak occurs at frequency 0.2 corresponding to spatial wavelength Wx=2x1) and at higher harmonics. In contrast, a sinusoidal checkerboard pattern may exhibit only a single peak in the power spectrum.

[0066] As will be described in more detail below, relatively few frequencies in the power spectrum may be undesirable for various factors. As one such factor, different lenses (e.g., different objectives 250) that may be used by the system 100 may have different optical cutoff frequencies. For example, a high frequency checkerboard pattern that is below the cutoff frequency of a particular 2.5x magnification objective (and therefore suitable for use with that objective) may be above the cutoff frequency of a different magnification lens (e.g., a higher magnification objective) having a different optical cutoff frequency, in which case the entire pattern may be filtered such that no pattern may be visible when projected with the higher magnification objective.

[0067] Figure 6 6 is a schematic diagram depicting a segment of a three-level fractal pattern 600A and corresponding power spectrum graphs 600B and 600C. An enlarged segment 610 of pattern 600A is shown as including two types of pattern arrangements that are repeated (e.g., periodically) at regular intervals (e.g., at equally spaced positions) in the x-axis and y-axis directions over the entire pattern. As shown in power spectrum graphs 600B and 600C, pattern 600A has a more diverse power spectrum than checkerboard pattern 500A, but for it, only a few frequencies dominate the spectral range. For the reasons described above, such characteristics may also be undesirable in certain embodiments (e.g., the lowest corresponding spatial frequency of the pattern arrangement shown in segment 610 may still be higher than the cutoff frequency of some objective lenses, etc.).

[0068] Figure 7 is a schematic diagram illustrating various principles of pattern segments and portions corresponding to different spatial wavelengths and related to pixel size. Figure 7 As shown, the three checkerboard pattern segments 710, 720 and 730 have the same size, but each corresponds to a different spatial wavelength. More specifically, the pattern portion in pattern segment 720 is twice as large as pattern segment 710, while the pattern portion in pattern segment 730 is three times as large as pattern segment 710.

[0069] The pattern segment 710 includes a checkerboard arrangement of pattern elements A and B, where pattern element A is a darker pattern element and pattern element B is a lighter pattern element. For purposes of illustration, the pattern segment 710 may be considered similar to Figure 5 The pattern elements A and B are of equal size, each having a dimension x1 along the x-axis direction and a dimension y1 along the y-axis direction. Therefore, the corresponding spatial wavelength along the x-axis direction is 2x1, and the corresponding spatial wavelength along the y-axis direction is 2y1.

[0070] In pattern segment 720 (i.e., for which the pattern portion is twice as large as pattern segment 710), each pattern portion has an x-axis dimension of 2x1 and a y-axis dimension of 2y1, wherein the corresponding spatial wavelength along the x-axis direction is 4x1, and the corresponding spatial wavelength along the y-axis direction is 4y1. In pattern segment 730 (i.e., for which the pattern portion is three times as large as pattern segment 710), the pattern portion has a dimension along the x-axis direction of 3x1 and a dimension along the y-axis direction of 3y1, wherein the corresponding spatial wavelength along the x-axis direction is 6x1 and the corresponding spatial wavelength along the y-axis direction is 6y1.

[0071] With respect to possible pixel sizes, in one embodiment, pattern segment 710 also represents a portion of a pixel array, where each pattern element (e.g., corresponding to a projected pattern on a workpiece surface imaged by a camera's pixel array) can be the same size and aligned with a corresponding pixel, wherein a pixel array segment having 6x6 pixels (i.e., covered by pattern segment 710) is depicted. Based on such pixel sizes, pattern portions of pattern segment 720 can each cover an area of ​​four pixels, while pattern portions of pattern segment 730 can each cover nine pixels. These comparisons illustrate certain principles related to the magnification of projected patterns (e.g., magnification by a turret lens, etc.). For example, magnification of pattern segment 710 by a 2x turret lens will result in projected pattern portions that are the size of the pattern portions of pattern segment 720 at a 1x magnification (i.e., so each covers an area of ​​four pixels in the above example). A 3x magnification of pattern segment 710 (e.g., by a 3x turret lens) will result in projected pattern portions that are the size of the pattern portions of pattern segment 730 at a 1x magnification (i.e., where each pattern portion will cover an area of ​​nine pixels). As will be described in more detail below, such magnification may create certain problems related to the desired amount of contrast between pixels (eg, where a portion of a pattern covering a large group of pixels may prevent a desired amount of contrast determination for pixels in the middle of the group).

[0072] As further illustration of certain principles relating to pattern element size and spatial frequency, additional corresponding pattern segments 715, 725, and 735 are shown below each of pattern segments 710, 720, and 730. Pattern portion 715 includes pattern element A and pattern element B, designated as darker and lighter pattern portions A1x and B1x, respectively, each having an x-axis dimension x1 and a y-axis dimension y1, and a corresponding spatial wavelength designated as WxA1B1, which is equal to 2x1 (i.e., similar to the x-axis spatial wavelength of pattern segment 710). Pattern segment 725 includes darker pattern portion A2x and lighter pattern portion B2x. Each of pattern portions A2x and B2x has an x-axis dimension 2x1 and a y-axis dimension y1, and wherein the corresponding spatial wavelength WxA2B2 is equal to 4x1 (i.e., similar to the x-axis spatial wavelength of pattern segment 720). Pattern segment 735 includes darker pattern portion A3x and lighter pattern portion B3x, each having an x-axis dimension 3x1 and a y-axis dimension y1, and wherein the x-axis spatial wavelength WxA3B3 is equal to 6x1 (ie, similar to the x-axis spatial wavelength of pattern segment 730).

[0073] As above about Figure 5 As described, a checkerboard pattern having elements of a single size exhibits only a single main spatial frequency (and some subharmonic frequencies) in the power spectrum, and where little or no projected pattern is visible if used in a system having an objective lens with a frequency cutoff below the main spatial frequency. Pattern segments 750 conceptually illustrates a method for creating a combination of spatial frequencies in a pattern (e.g., including a weighted combination of pattern segments 715, 725, and 735). More specifically, pattern segments 750 includes six pattern segments 715, three pattern segments 725, and two pattern segments 735. Therefore, pattern segments 750 correspondingly include six spatial wavelengths WxA1B1, three spatial wavelengths WxA2B2, and two spatial wavelengths WxA3B3. Based on such combinations, pattern portions of different sizes may be adjacent to each other and may also be assigned different spatial wavelength combinations, as shown at the bottom of pattern segment 750 (e.g., spatial wavelengths WxB1A2, WxB2A1, WxB1A3, WxB3A1, etc. are depicted). Such combinations of spatial wavelengths in a pattern may have certain desired properties (e.g., added to the spectrum of spatial frequencies of the pattern in the power spectrum), as will be described below with respect to Figure 8 Described in more detail.

[0074] Figure 8 A segment of a pattern that includes pattern portions (e.g., darker and lighter pattern portions) that do not repeat at regular intervals on the pattern. As will be described in more detail below, Figure 8 The pattern segment 810 shows the Fig. 9An enlarged pattern segment of pattern 900A. Figure 8 As shown, different pattern portions of different sizes extend in the x-axis and y-axis directions. Figure 8 The pattern segment of is specified to include 30 columns and 26 rows (e.g., darker and lighter pattern portions), and may have some characteristics similar to the other patterns described above (e.g., and may be manufactured using chrome-plated glass or other manufacturing processes, etc.). Figure 8 As shown, the pattern segment 810 (i.e., as Fig. 9 The pattern 900A segment) is not limited to Figure 5 A single element or unit in the checkerboard pattern 500A may be a square of a certain size, etc., and may include pattern portions of multiple sizes extending in the x-axis and y-axis directions (e.g., including multiple pattern elements).

[0075] In various embodiments, the element size can be defined as the minimum element size for forming a pattern. Figure 8 and 9 In the example of a pattern of , the minimum element size can be the size of the smallest shown square (e.g., where the darker pattern element "A" can correspond to the chrome element). According to such a configuration, the maximum spatial frequency of the pattern is thus defined by 2 times the minimum element size. As will be described in more detail below, although Figure 5 A checkerboard pattern can provide high spatial frequencies, but it does not have certain desired properties (e.g., a flat power spectrum), and more complex patterns that do have such desired properties (e.g., pattern 900A including pattern segment 810) can be composed of various combinations of multiple pattern elements.

[0076] As some specific examples, darker and lighter pattern portions of different sizes are marked in the x-axis direction in the 26th row and the y-axis direction in the 30th column. For example, the 26th row is shown as including darker and lighter pattern portions (i.e., the darker pattern portion is represented by "A" and the lighter pattern portion is represented by "B", similar to the other representations described above for other figures). The 26th row is shown as including adjacent combinations of lighter and darker pattern portions of different sizes, such as a sequence of pattern portions B1x, A1x, B2x, A6x, B1x, A1x, B1x, A3x, B1x, A3x, B1x, A3x, B3x, A1x and B2x. Each of these pattern portions has a height of 1y along the y-axis direction (e.g., corresponding to 1 unit), and the number designation indicates the number of units along the x-axis direction (e.g., the size of pattern portion A6x along the x-axis direction is 6x or 6 units). As another example, column 30 is shown as including a sequence of pattern portions A1y, B1y, A6y, B1y, A1y, B2y, A1y, B1y, A2y, B3y, A1y, B2y, A3y, and B1y, each having a length along the x-axis of dimension 1x (e.g., corresponding to one unit) and a length along the y-axis corresponding to a numerical designation. Figure 7 As described, each of these adjacent combinations of pattern portions of different sizes can provide different spatial wavelength contributions to the spatial frequencies observed in the power spectrum of the pattern. As also described above, each of the darker pattern portions and each of the brighter pattern portions do not repeat on the pattern at regular intervals (e.g., at equidistant intervals). In various embodiments, the brighter pattern portions may correspond to the intervals between the darker pattern portions (i.e., the darker pattern portions separated by the brighter pattern portions do not repeat on the pattern at regular intervals).

[0077] like Figure 8As further shown, additional pattern portions of additional lengths (e.g., having a total of 8 or more different unit lengths) are also depicted. For example, as described above, pattern portions A1x and A3x are shown in row 26, pattern portion A2x is shown in row 3, pattern portion A4x is shown in row 1, pattern portion A5x is shown in row 4, pattern portion A6x is shown in row 26, pattern portion A7x is shown in row 15, and pattern portion A8x is shown in row 16. As a further example, as described above, pattern portions B1x, B2x, and B3x are shown in row 26, pattern portion B4x is shown in row 1, pattern portion B5x is shown in row 12, pattern portion B6x is shown in row 1, and pattern portion B8x is shown in row 10. As a further example, as described above, pattern portions A1y, A2y, and A3y are shown in column 30, pattern portion A4y is shown in column 2, pattern portion A5y is shown in column 7, pattern portion A6y is shown in column 1, pattern portion A7y is shown in column 6, and pattern portion A8y is shown in column 24. As a further example, as described above, pattern portions B1y, B2y, and B3y are shown in column 30, pattern portion B4y is shown in column 2, pattern portion B5y is shown in column 4, pattern portion B6y is shown in column 10, pattern portion B7y is shown in column 14, and pattern portion B9y is shown in column 6.

[0078] As mentioned above, it should be understood that each of the darker and brighter pattern parts of these different sizes adjacent to other brighter or darker pattern parts can provide different spatial wavelength contributions for the spatial frequency observed in the power spectrum of the pattern.It should be understood that such various adjacent combinations can be realized in the whole pattern in particular, and the pattern is not subject to the constraint of the requirement that the pattern part repeats at regular intervals on the pattern (e.g., non-periodic, pseudo-random, etc. patterns).According to these characteristics, the darker and brighter pattern parts of different sizes of smaller or larger number can provide spatial wavelengths of different densities, which depends on the required characteristics of the resulting pattern.As mentioned above, in some embodiments, it may also be desirable to have a relatively limited or smaller number and / or a larger pattern part of maximum size (e.g., corresponding to a larger darker and / or brighter pattern part of a lower spatial frequency lower than the lowest cut-off frequency of the group of object lenses), because such pattern parts may occupy a considerable area in the pattern, and may cover a considerable amount of pixels when enlarged, etc. This consideration may also affect the required number of different sizes of the pattern parts included in the pattern (e.g., the maximum size of the pattern part and / or the maximum number of different sizes, such as 15, 20, 30, 40, etc., may be required).

[0079] Fig. 9 is pattern 900A (ie, including Figure 8 Schematic diagram of pattern segment 810) and corresponding power spectrum graphs 900B and 900C. Figure 8 As described, in pattern 900A, darker and lighter pattern portions of different sizes do not repeat at regular intervals on the pattern. The corresponding power spectrum graphs 900B and 900C illustrate certain characteristics that may be advantageous for certain embodiments. For example, with respect to frequency response, the scale along the horizontal axis in graph 900B is labeled as being within a very limited range (e.g., the amplitude is between 6.16 and 6.30), and the power spectrum is labeled as being relatively constant / flat (e.g., the variation for at least most of its power spectrum over the desired range does not exceed 20%). Pattern 900A therefore has a spatial frequency characteristic that results in a wide frequency spectrum in the power spectrum. As described above, such wide frequency content may be desired for various applications in which different lenses (e.g., different objective lenses) with different cutoff frequencies may be utilized. More specifically, when projecting the pattern, even if some lenses lose some frequency content, the system can still project other lower frequencies that are present, thereby producing sufficient contrast in the image of the workpiece to determine a focus curve with relatively high peak values ​​(e.g., see Figure 4A With respect to the desired range, it may be desirable for the power spectrum to be relatively flat up to the highest cutoff frequency of the optical projection system (e.g., based on the highest cutoff frequency of different lenses, such as objectives, that may be used with the system).

[0080] In various embodiments, it is also desirable to have a pattern with a dark / light ratio of approximately 50 / 50 (e.g., where the total area percentage of the pattern consisting of darker pattern portions is nominally / approximately 50% and is therefore approximately equal to the total area percentage of the pattern consisting of lighter pattern portions, which is also nominally / approximately 50%). As used herein, the term "nominal" encompasses variations in one or more parameters that fall within acceptable tolerances (e.g., variations from the stated values ​​and / or specified configurations are less than 5%, etc.). In addition, in various embodiments, it may be desirable to have a pattern with a non-repeating structure to avoid aliasing problems as well as self-imaging problems. In general, a pattern having characteristics similar to pattern 900A (e.g., which in some cases may be defined as a pseudo-random pattern, having a white noise type power spectrum within a desired range, or otherwise) is desirable because it meets this purpose and does not preferentially reduce higher frequencies (e.g., as may be the case with some pink or brown noise patterns). In various embodiments, a similar pattern having blue noise characteristics may also produce desired results because more energy is provided at higher frequencies. In some embodiments, in addition to type A and type B pattern elements and / or pattern portions, patterns formed according to the principles disclosed herein may also include pattern elements and / or pattern portions of different chromaticities, tones, colors, etc., wherein each pattern element and / or pattern portion may be designated as a darker or lighter pattern element and / or pattern portion. For example, in such embodiments, the darker and lighter pattern elements and / or pattern portions may be referenced to an average value (e.g., average color, chromaticity, etc.) of the pattern, for which there may be multiple types, chromaticities, etc. of darker pattern elements and / or pattern portions (i.e., darker than the average value of the pattern), and / or multiple types, chromaticities, etc. of lighter pattern elements and / or pattern portions (i.e., lighter than the average value of the pattern).

[0081] In some embodiments, the pattern 900A can be composed of small square pattern elements (e.g., similar to Figure 7900A) of pattern segments 710. In such embodiments, adjacent pattern elements A in the x or y axis direction may form a darker pattern portion of a corresponding size, while adjacent pattern elements B in the x or y axis direction may form a lighter pattern portion of a corresponding size. In various embodiments, such pattern portions may be produced by certain positioning of pattern elements A and / or B (e.g., random positioning, etc.). As described above, in various embodiments, the lighter pattern portions may correspond to the spaces between the darker pattern portions (e.g., in embodiments formed by chrome-plated glass or similar processes, the darker pattern elements A may correspond to the chrome portions, while the lighter pattern elements B may correspond to the spaces between the darker pattern elements A). In a specific example embodiment, the total size of the pattern (e.g., similar to pattern 900A) may be approximately 9 mm x 9 mm (e.g., in some cases, it may be large enough to be larger than most CCD or CMOS pixel arrays of certain common camera image sensors). In such an embodiment where the pattern elements are approximately 5 microns, there may be a total of approximately 3.2 million pattern elements in the pattern (i.e., (9 mm / 0.005 mm)^2=3.2 million), with a dark / light ratio of approximately 50 / 50 corresponding to approximately 1.6 million darker pattern elements A (e.g., chrome pattern elements). As described above with respect to the highest cutoff frequency of the objective lens, due to the limited (e.g., lateral) resolution of the projection system (e.g., of system 100, such as due to the highest cutoff frequency of the lens used, etc.), it may be necessary for the pattern elements (e.g., the corresponding sizes of pattern elements A and B and / or various pattern portions) to be no smaller than a certain size (e.g., corresponding to a high spatial frequency). In other words, if the size of the pattern elements is below the minimum cutoff size, then when projected, the pattern elements may be averaged over an area of ​​limited projection resolution and may not be visible (e.g., may become blurred and therefore produce no contrast). In various embodiments, it may be desirable to have a minimum element size close to the size of the minimum projection resolution that the optical system can pass (e.g., in order to achieve / utilize the maximum amount of contrast possible when utilizing an objective lens with the highest cutoff frequency). In some embodiments, a slightly smaller element size may also be used, with some amount of averaging resulting in some loss of contrast.

[0082] According to the principles disclosed herein, for a set of objective lenses used with a system (e.g., system 100), the highest and lowest cutoff frequencies passed by different objective lenses can be calculated or otherwise determined, and appropriate element sizes can be selected / determined (e.g., the minimum pattern element / portion size can be selected / determined based at least in part on the highest cutoff frequency, and in some embodiments, the maximum desired pattern portion size can be selected / determined based at least in part on the lowest cutoff frequency). In such embodiments, a certain amount of contrast may be lost for an objective lens with a lower cutoff frequency relative to the minimum pattern portion / element size, but for which it has been experimentally determined that the remaining contrast may be sufficient for certain PFF-type processes, etc.

[0083] In one particular example embodiment, the cutoff frequencies of a set of objective lenses of the system may correspond to pattern element sizes that vary from 3.3 microns to 20 microns. Thus, a minimum pattern element size of 3.3 microns may be selected to match the highest projection frequency cutoff (e.g., and where smaller element sizes may result in a loss of contrast with little or no additional benefit). Additionally, as will be described in more detail below, a minimum element size that is close to the pixel size of the pixel array of the camera 260 may be desired (e.g., a 5 micron pixel size, or a 10 micron pixel size, etc.) so that magnification of the turret lens will result in as few gaps in the focus curve data as possible (e.g., as for a PFF type process). Additionally, a pattern element size that is less than the pixel size may result in a loss of contrast at 1x turret magnification (e.g., although in some embodiments this may be acceptable if it is not a significant loss of contrast and given that contrast may be slightly increased at 2x turret magnification, and may also depend on the minimum projection wavelength, etc.).

[0084] In various embodiments, the primary characteristic of the turret lens that is considered for selecting pattern element size is the corresponding increase in scale of the projected pattern (e.g., by a 2x turret lens, by a 6x turret lens, etc.), which in some embodiments is an important reason for keeping the minimum pattern element size relatively small. More specifically, with respect to the turret lenses (e.g., turret lenses 286 and 288 and / or other lenses of turret 280), in various embodiments, the magnification of these lenses may not change the frequency that can be projected, but rather serve to magnify the resulting pattern on the camera's pixel array. Because of this aspect, it may be desirable to have the pattern element size be as relatively small as possible so that it is not too large when magnified by the turret lens (e.g., for turret lenses with a magnification of 2x, 6x, etc.). For example, if the pattern element / portion size starts out relatively large and is then further magnified by the turret lens, contrast data may not be obtained within the interior of the projected pattern element / portion (e.g., because the magnified pattern element / portion covers more pixels than are used to calculate contrast, if 3x3 or 7x7 pixels are used to calculate contrast and the magnified pattern element / portion covers more pixels than that number of pixels). It will be appreciated that this may be another factor used to determine the desired minimum element size for the pattern, in addition to the highest cutoff frequency of the lens used, etc.

[0085] As a specific example, if a pattern element has x and y axis dimensions of 25 microns and is projected through a 2x or 6x turret lens, the resulting projected pattern element size will have dimensions of 50 microns or 150 microns along the x and y axis directions, which may be significantly larger than a 10 square micron sized pixel and for which gaps may result in the corresponding contrast data being generated. More specifically, in this example, for a pattern element size of 25 microns, some gaps in the contrast data may even be caused by a 2x turret lens and a magnified 50 micron x 50 micron pattern element, for which the camera pixel size is approximately 10 microns and the pattern element projected with the 2x turret lens will cover approximately 25 pixels (i.e., an area of ​​5 pixels x 5 pixels). In general, with respect to the area used by the system to calculate contrast (e.g., using a 3x3 or 7x7 pixel area of ​​interest to calculate contrast), gaps in the contrast data may occur depending on how many pixels are covered by the projected pattern element or portion (i.e., a darker or lighter pattern element or portion). In addition, if Figure 8 As shown, certain combinations of pattern portions may result in pattern elements of 4x4 blocks or larger, which at 2x and 6x turret lens magnifications may cover a large number of pixels for which gaps in contrast data may appear.

[0086] Further with respect to turret magnification, the frequency cutoff of the projection optics (e.g., including the objective lens) will limit the wavelength of the projected pattern before it reaches the turret lens, which will then amplify the resulting portion of the projected / filtered pattern. Figure 5 As described above for a chessboard pattern, if the pattern is regular and includes spatial frequencies higher than the cutoff frequency of the projection optics, there will be no contrast in the projected pattern to be magnified by the turret lens (i.e., all pattern elements / parts will be filtered out). Fig. 9 The characteristics of pattern 900A will depend on the cutoff frequency of the objective lens used, at least some contrast will make it through (e.g., at least some larger pattern portions will not be filtered out), and the minimum wavelength scale of the projected pattern will be approximately the wavelength cutoff of the projection optics, which will then be magnified by the turret lens onto the camera's pixel array. In various embodiments, the contrast can be a function of the camera's pixel size relative to the cutoff wavelength (i.e., multiplied by the magnification of the turret lens).

[0087] With respect to camera pixel size, if the pixel size is relatively large (e.g., 20 microns) and the pattern elements are small (e.g., 4 microns), a single pixel will average several pattern elements and at least some amount of contrast will be lost. However, as pixel technology continues to advance, the pixel size of cameras continues to decrease (e.g., below 10 microns, 5 microns, etc.), and in some embodiments the camera pixel size may be considered a relatively small limiting factor with respect to pattern element size to meet other desired characteristics of the system as described above. For example, in some practical embodiments, the minimum pattern element size may be about 4 microns, which may also be close to the pattern element size that can be easily manufactured by glass chrome plating techniques, etc., which may currently be in the range of about 1 square micron in some current embodiments.

[0088] With respect to the relationship of pixel size to pattern element size and the spatial frequencies that can be resolved accordingly, if the pattern wavelength is twice the pixel size (e.g., the pattern element size is the same as the pixel size), then the pattern wavelength can be resolved. In terms of frequency, in such an embodiment, the spatial frequency of the pattern is just at the limit of what the sampling frequency can resolve. Alternatively, if the pattern element size is half the size of the pixel, then the pattern wavelength can be one pixel long, where in terms of frequency, the spatial frequency of the pattern will be half the sampling frequency and cannot be resolved. In some embodiments, pattern element sizes that are smaller than the pixel size can still produce a certain amount of contrast because adjacent pixels may have different numbers of light and dark pattern elements covering their areas. However, the smaller the element size, the more the overall contrast within the pixel tends to be averaged out, and the less effective the pattern is for producing contrast. As described above, current pixel technology (e.g., pixel sizes equal to or less than 10 microns, 5 microns, etc.) can make this concern less of a problem because in various practical embodiments, the camera pixel can be as small as the minimum pattern element size required.

[0089] Fig.10 1 is a flow chart showing a method 1000 for operating a metrology system including a pattern projection portion according to the principles disclosed herein. At block 1010, a light source is controlled to transmit light to a pattern included in an optical path with an objective lens to form a projected pattern on a workpiece surface, wherein at least a majority area (e.g., 50% or more) of the projected pattern includes a plurality of pattern portions that do not repeat on the pattern at regular intervals. At block 1020, an image stack including a plurality of images of the workpiece surface having the projected pattern is acquired using a camera, wherein each image of the image stack corresponds to a different Z height. At block 1030, focus curve data is determined based at least in part on an analysis of images of the image stack. At block 1040, three-dimensional positions of a plurality of surface points on the workpiece surface are determined using the focus curve data.

[0090] In various embodiments, method 1000 can be repeated after changing the magnification state of the metrology system by changing the objective lens included in the objective lens section (e.g., as a second objective lens having a second cutoff frequency different from the cutoff frequency of the first objective lens previously used). For example, after changing to the second objective lens, the light source can be controlled to transmit light to the pattern included in the optical path with the second objective lens to form a second projected pattern on the workpiece surface (or a different workpiece surface), wherein the second projected pattern is partially filtered by the second cutoff frequency, and at least a majority of the area of ​​the second projected pattern includes a second plurality of pattern portions that do not repeat at regular intervals on the pattern. It should be understood that due to the different filtering of the second objective lens (i.e., according to the second cutoff frequency), the second plurality of pattern portions can be different from the corresponding first plurality of pattern portions when the first objective lens is used (e.g., more or less smaller pattern portions can be filtered out, etc.). However, based on a pattern having spatial frequency characteristics that result in a wide frequency spectrum in the power spectrum (e.g., pattern 305 on pattern component 302) (i.e., based on the principles disclosed herein), the first and second plurality of pattern portions in the corresponding first and second projection patterns may be sufficient / effective to produce a desired level of contrast in an image of the workpiece surface (e.g., for a PFF-type process, etc.).

[0091] A second image stack may then be acquired using the camera, comprising a second plurality of images of the workpiece surface having the second projection pattern, wherein each image of the second image stack corresponds to a different Z height. It should be appreciated that, depending on the different magnifications of the second objective lens, the area of ​​the workpiece surface included in the field of view (i.e., as part of the same workpiece surface or a different workpiece surface) may be different than the area of ​​the workpiece surface included in the field of view when the first objective lens is used (e.g., a second objective lens having a higher magnification than the first objective lens may result in a magnified area of ​​the workpiece surface and a correspondingly smaller amount of area in the field of view). Second focus curve data may then be determined based at least in part on an analysis of the images of the second image stack, and the second focus curve data may be used to determine the three-dimensional positions of a plurality of surface points on the workpiece surface (e.g., as part of a PFF-type process, etc.).

[0092] In general, a pattern having properties according to principles such as those disclosed herein (e.g., similar to Fig. 9 For example, as described above, a pattern having a wide range of spatial frequencies may be desired because a pattern having a single spatial frequency may not be compatible with all objective lens sets and / or other lenses that may be used in a system (e.g., system 100). Figure 5 and 6 As shown in the example of Fig. 9Similar characteristics of pattern 900A. In some embodiments, for a desired range (e.g., determined in part by the cutoff frequency of the objective lens and / or other lenses used), it may be desirable that the power spectrum (e.g., which can be characterized as being equal to the Fourier transform of the pattern squared) be a nominally / approximately constant value within the desired range. In some embodiments, this may also correspond to an approximate definition of white noise within the desired range. In some embodiments, pseudo-random patterns such as blue noise may appropriately create high-frequency textures on an object. In various embodiments, a type of pseudo-random pattern (e.g., a pseudo-random bitmap pattern, etc.) may approximately meet such criteria, and the desired range of its minimum pattern element size and / or pattern portion size may be determined based on criteria such as those described above.

[0093] With respect to the minimum pattern element size, as described above, it is generally desirable that the pattern not contain spatial frequencies higher than a desired range (e.g., where the minimum element size for the pattern is desired to be no less than a certain size). More specifically, due to the highest cutoff frequency as described above, the optics will not project any higher spatial frequencies of the pattern even when the system uses a lens (e.g., an objective lens) with the highest cutoff frequency. Such higher frequencies (e.g., corresponding to smaller pattern portions that will not appear in the projected pattern) will effectively reduce the available contrast of the pattern by not being projected, which may generally be undesirable in certain embodiments. In some embodiments, it is also possible to utilize a slightly smaller element size, subjecting it to a certain amount of averaging, resulting in a certain amount of loss of contrast.

[0094] Although preferred embodiments of the present disclosure have been shown and described, based on the present disclosure, those skilled in the art will appreciate the many variations of the illustrated and described arrangements of features and the sequence of operations. Various alternatives may be used to implement the principles disclosed herein. In addition, the various embodiments described above may be combined to provide further embodiments. All U.S. patents mentioned in this specification are hereby incorporated herein by reference in their entirety. If it is necessary to adopt the concepts of various patents and applications to provide other embodiments, the various aspects of the embodiments may be modified.

[0095] These and other changes can be made to the embodiments in light of the above detailed description. In general, in the following claims, the terms used should not be interpreted to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be interpreted to encompass all possible embodiments and the full scope of equivalents to which such claims are entitled.

Claims

1. A metering system comprising: an objective lens section including an objective lens selected from a group of objective lenses, wherein each of the objective lenses in the group has a different magnification and a cutoff frequency, and a magnification state of the metering system is configured to be changed by changing the objective lenses included in the objective lens section; light source; a pattern projection portion, comprising a pattern component having a pattern, wherein at least a majority of the area of ​​the pattern comprises a plurality of pattern portions, the plurality of pattern portions not repeating at regular intervals on the pattern, wherein the pattern portion comprises a darker pattern portion and a lighter pattern portion, wherein the pattern portion comprises pattern portions having different sizes, wherein the pattern portions of different sizes comprise at least a pattern portion of a first size, a pattern portion of a second size, a pattern portion of a third size, and a pattern portion of a fourth size, wherein the lengths of the pattern portions of the second size, the third size, and the fourth size are each at least two, three, or four times the corresponding lengths of the pattern portions of the first size, respectively, and wherein light from the light source is configured to be transmitted toward the pattern to form pattern light, the pattern light is transmitted through the objective lens to form a projection pattern on a workpiece surface, and wherein the objective lens is configured to input image light generated from the workpiece surface including the projection pattern and transmit the image light along an imaging light path; a camera configured to receive image light transmitted along the imaging light path and provide an image of the workpiece surface including the projection pattern; one or more processors; as well as 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: Controlling the light source to transmit light toward the pattern to form the projection pattern on the workpiece surface; acquiring, with the camera, an image stack comprising a plurality of images of the surface of the workpiece having the projected pattern, wherein each image of the image stack corresponds to a different Z height; as well as 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 is indicative of three-dimensional positions of a plurality of surface points on a surface of the workpiece.

2. The system of claim 1, wherein the plurality of pattern portions of the pattern correspond to spatial frequencies below a highest cutoff frequency of the objective in the set of objective lenses.

3. The system of claim 1 , wherein the set of objective lenses comprises: a lowest magnification lens corresponding to the lowest magnification of the set; a highest magnification lens corresponding to the highest magnification of the set; and a plurality of intermediate magnification lenses, each corresponding to a respective intermediate magnification, each intermediate magnification being between the lowest magnification and the highest magnification, and wherein the highest magnification is at least 10 times greater than the lowest magnification.

4. The system of claim 3, wherein at least some of the objective lenses in the set of objective lenses each correspond to a respective magnification of at least one of 0.5x, 1x, 2x, 2.5x, 5x, 10x, 20x, 25x, 50x, or 100x.

5. The system of claim 1, further comprising a turret having a plurality of turret lenses, wherein each turret lens corresponds to a different magnification, and the turret is configured to position one of the turret lenses in the imaging optical path.

6. The system of claim 1 , wherein each of the plurality of surface points on the workpiece surface corresponds to a region of interest in each of the images of the image stack, and the determining of the focus curve data comprises determining focus curve data for each of the regions of interest based at least in part on an analysis of the images of the image stack, wherein for each of the surface points, a peak of the focus curve data corresponding to the region of interest indicates a corresponding Z height of the surface point, and wherein the peak is produced at least in part by contrast provided by a pattern portion of the projection pattern.

7. The system of claim 1, wherein a total amount of area of ​​the pattern corresponding to the darker pattern portion differs from a total amount of area of ​​the pattern corresponding to the lighter pattern portion by less than 5%.

8. The system of claim 1, wherein the lighter pattern portions correspond to spaces between the darker pattern portions.

9. The system of claim 8, wherein the pattern is formed on the pattern component using a chrome-on-glass type process.

10. The system of claim 1 , wherein the pattern portions of different sizes further comprise at least a fifth sized pattern portion, a sixth sized pattern portion, a seventh sized pattern portion, and an eighth sized pattern portion, wherein the lengths of the fifth sized pattern portion, the sixth sized pattern portion, the seventh sized pattern portion, and the eighth sized pattern portion are each at least five, six, seven, or eight times the corresponding lengths of the first sized pattern portion.

11. The system of claim 1, wherein a largest pattern portion of the plurality of pattern portions is less than twenty times the size of a smallest pattern portion of the plurality of pattern portions.

12. The system of claim 1, wherein the pattern portion of the first size is the smallest pattern portion of the plurality of pattern portions and has an area of ​​at least 2 microns by 2 microns and at most 20 microns by 20 microns.

13. The system of claim 12, wherein the camera comprises an array of pixels, wherein each pixel has an area of ​​at least 2 microns by 2 microns and at most 20 microns by 20 microns.

14. The system of claim 1, wherein adjacent darker and lighter pattern portions of the plurality of pattern portions are in a sequence that does not repeat on the pattern at regular adjacent intervals in an x-axis or y-axis direction of the pattern.

15. The system according to claim 1, wherein the pattern projection part further comprises a pattern positioning part, and the pattern positioning part is configured to be controlled to position the pattern component in an optical path between the light source and the objective lens.

16. A method for operating a metering system, The metering system comprises: an objective lens section including an objective lens selected from a group of objective lenses, wherein each of the objective lenses in the group has a different magnification and a cutoff frequency, and a magnification state of the metering system is configured to be changed by changing the objective lenses included in the objective lens section; light source; a pattern projection section included in an optical path with the objective lens section and containing a pattern component having a pattern configured to be projected onto a surface of a workpiece; a camera that receives image light transmitted along an imaging light path from the objective lens and provides an image of the workpiece surface including the projection pattern; The method comprises: Controlling the light source to transmit light to the pattern included in the optical path with the objective lens to form a projection pattern on the workpiece surface, wherein at least a majority of the projection pattern includes a plurality of pattern portions, the plurality of pattern portions do not appear repeatedly on the pattern at regular intervals, wherein the pattern portions include darker pattern portions and lighter pattern portions, wherein the pattern portions include pattern portions with different sizes, wherein the pattern portions with different sizes include at least a pattern portion of a first size, a pattern portion of a second size, a pattern portion of a third size, and a pattern portion of a fourth size, wherein the lengths of the pattern portions of the second size, the pattern portions of the third size, and the pattern portions of the fourth size are respectively at least two, three, or four times the corresponding lengths of the pattern portions of the first size; acquiring, with the camera, an image stack comprising a plurality of images of the surface of the workpiece having the projected pattern, wherein each image of the image stack corresponds to a different Z height; determining focus curve data based at least in part on an analysis of the image of the image stack; as well as The three-dimensional positions of a plurality of surface points on the surface of the workpiece are determined using the focus curve data.

17. The method of claim 16, wherein the plurality of pattern portions of the projected pattern correspond to spatial frequencies below a highest cutoff frequency of the objective in the set of objective lenses.

18. The method according to claim 16, wherein a pattern projection part comprises a pattern positioning part, and the method further comprises controlling the pattern positioning part to position the pattern component in the optical path between the light source and the objective lens.

19. The method of claim 16, wherein the objective lens included in the objective lens portion is a first objective lens having a first cutoff frequency, and the projection pattern is a first projection pattern at least partially filtered by the first cutoff frequency, and the plurality of pattern portions is a first plurality of pattern portions, the method further comprising: changing the magnification state of the metering system by changing the objective lens included in the objective lens section to a second objective lens having a second cutoff frequency different from the first cutoff frequency; controlling the light source to transmit light to the pattern included in the optical path with the second objective lens to form a second projection pattern on the surface of the workpiece, wherein the second projection pattern is at least partially filtered by the second cutoff frequency, and at least a majority of the area of ​​the second projection pattern includes a second plurality of pattern portions, the second plurality of pattern portions do not appear repeatedly on the pattern at regular intervals, and wherein the second plurality of pattern portions are different from the first plurality of pattern portions at least partially due to different filtering by the first cutoff frequency and the second cutoff frequency; acquiring, with the camera, a second image stack comprising a second plurality of images of the workpiece surface having the second projection image, wherein each image of the second image stack corresponds to a different Z height; determining second focus curve data based at least in part on an analysis of the images of the second image stack; as well as The three-dimensional positions of a plurality of surface points on the surface of the workpiece are determined using the second focus curve data.

20. A pattern projection portion for use with a metrology system, The metering system comprises: an objective lens section including an objective lens selected from a group of objective lenses, wherein each of the objective lenses in the group has a different magnification and a cutoff frequency, and a magnification state of the metering system is configured to be changed by changing the objective lenses included in the objective lens section; light source; as well as a camera configured to receive image light transmitted along an imaging light path and provide an image of a workpiece surface including the projected pattern; The pattern projection part comprises: A pattern component having a pattern, wherein at least a majority of the area of ​​the pattern comprises a plurality of pattern portions, the plurality of pattern portions not repeating at regular intervals on the pattern, wherein the pattern portions comprise darker pattern portions and lighter pattern portions, wherein the pattern portions comprise pattern portions having different sizes, wherein the pattern portions of different sizes comprise at least a pattern portion of a first size, a pattern portion of a second size, a pattern portion of a third size, and a pattern portion of a fourth size, wherein the length of each of the pattern portion of the second size, the pattern portion of the third size, and the pattern portion of the fourth size is at least two, three, or four times the corresponding length of the pattern portion of the first size, respectively; as well as a pattern positioning portion configured to position the pattern component in an optical path between the light source and the objective lens; wherein after the pattern component is positioned in the optical path, light from the light source is configured to be transmitted toward the pattern to form pattern light, the pattern light is transmitted through the objective lens to form a projection pattern on the workpiece surface, and wherein the objective lens is configured to input image light including the projection pattern generated from the workpiece surface and transmit the image light along the imaging optical path, and wherein the camera is configured to receive the image light transmitted along the imaging optical path and capture an image stack including a plurality of images of the workpiece surface having the projection pattern, wherein each image of the image stack corresponds to a different Z height, and wherein the images are configured to be analyzed to determine focus curve data indicating the three-dimensional positions of a plurality of surface points on the workpiece surface.

21. The pattern projection portion of claim 20, wherein the plurality of pattern portions of the pattern correspond to spatial frequencies below a highest cutoff frequency of the objective lens in the set of objective lenses.

22. The pattern projection portion according to claim 20, wherein the pattern portions of different sizes further include at least a pattern portion of a fifth size, a pattern portion of a sixth size, a pattern portion of a seventh size, and a pattern portion of an eighth size, wherein the lengths of the pattern portion of the fifth size, the pattern portion of the sixth size, the pattern portion of the seventh size, and the pattern portion of the eighth size are respectively at least five times, six times, seven times, or eight times the corresponding lengths of the pattern portion of the first size.

23. The pattern projection portion of claim 20, wherein the pattern portion of the first size is a smallest pattern portion among the plurality of pattern portions.

24. The pattern projection portion according to claim 23, wherein the pattern portion of the first size has an area of ​​at least 2 micrometers x 2 micrometers and at most 20 micrometers x 20 micrometers.

Images