Heterodyne light source for metrology systems

Abstract

A metrology system including a heterodyne light source is provided. The heterodyne light source includes a first light source, an acousto-optic modulator, and source optics. The acousto-optic modulator receives at least one wavelength laser beam from the first light source and generates at least one corresponding frequency-shifted laser beam (e.g., having orthogonal polarization). The source optics include a receiving optical element portion and a birefringent optical element portion. The receiving optical element portion receives the wavelength laser beam and the corresponding frequency-shifted laser beam and directs the beams along an optical path toward the birefringent optical element portion. The birefringent optical element portion combines the beams to output a combined beam (e.g., which can be used as part of a measurement process to determine at least one measured distance to at least one surface point on a workpiece, etc.).

Description

Technical Field

[0001] This disclosure relates to precision metrology, and more specifically to apparatus and systems for measuring the surface of precision workpieces. Background Technology

[0002] Quality control of objects (e.g., workpieces) with specific surface profiles (e.g., produced through molding and / or machining) is increasingly demanding in terms of throughput, measurement resolution, and accuracy. Such workpieces may include, but are not limited to, optical components, electronic components, micromechanical components, etc. Ideally, these workpieces should be measured / inspected to ensure proper dimensions, functionality, etc. However, sub-micron or even sub-nanometer measurement tolerances may be required to confirm that the workpiece surface possesses certain application-desired characteristics.

[0003] Various precision metrology systems can be used for measuring and inspecting workpiece surfaces. For example, in some cases, metrology systems performing such operations may utilize digital holography (e.g., a camera may be used to acquire a processed hologram to determine measurements, etc.). An important component of such systems and / or other comparable measurement systems is the light source used to illuminate the workpiece being measured (e.g., inaccurate or inconsistent light sources can lead to inaccurate measurements, etc.). The signal-to-noise ratio of such systems is also an important factor (e.g., a lower ratio can result in less accurate measurements). It would be desirable to improve or otherwise enhance the configuration of such metrology systems (e.g., for measuring and inspecting workpiece surfaces, etc.). Summary of the Invention

[0004] The summary is provided to introduce, in a simplified form, the selection of concepts further described in the detailed embodiments below. This summary is not intended to identify key features of the claimed subject matter, nor is it intended to help determine the scope of the claimed subject matter.

[0005] This invention provides a metrology system including a heterodyne light source. The heterodyne light source includes a first light source, an acousto-optic modulator, and a source optics device. The first light source provides a first wavelength laser beam at least at a first frequency. The acousto-optic modulator is configured to receive the first wavelength laser beam and generate a corresponding first frequency-shifted laser beam with a polarization rotation (e.g., orthogonal) relative to the first wavelength laser beam. The source optics device receives and combines the first wavelength laser beam and the first frequency-shifted laser beam from the acousto-optic modulator, and outputs a corresponding first combined beam. The source optics device includes a receiving optical element portion and a birefringent optical element portion. The receiving optical element portion is configured to receive the first wavelength laser beam and the first frequency-shifted laser beam and guide the beams along an optical path to the birefringent optical element portion. The birefringent optical element portion is configured to receive the first wavelength laser beam and the first frequency-shifted laser beam and combine the beams to output a corresponding first combined beam.

[0006] In various embodiments, the metrology system further includes a processing section, wherein the first combined light beam is used as part of the measurement process, the processing section determining at least one measurement distance to at least one surface point on the workpiece. In various embodiments, the metrology system further includes measuring optics and a sensor device. The measuring optics are configured to receive the first combined light beam and utilize the first combined light beam to provide an optical output related to the distance to at least one surface point on the workpiece. The sensor device is configured to receive the optical output and generate a corresponding sensor output. The processing section receives the sensor output and utilizes the sensor output as part of the measurement process to determine at least one measurement distance to at least one surface point on the workpiece.

[0007] In various embodiments, the source optics, including a receiving optics section and a birefringent optics section, are arranged as an inline optics device. According to the inline optics device, a first wavelength laser beam and a first frequency-shifted laser beam (e.g., orthogonally polarized) each pass through the same set of components in a heterodyne source. For example, the same set of components in the inline optics device may include the same receiving optics in the receiving optics section and the same birefringent optics in the birefringent optics section, the birefringent optics combining the orthogonally polarized first wavelength laser beam and the first frequency-shifted laser beam into a first combined beam.

[0008] In various embodiments, the receiving optical element portion includes an imaging lens. In various embodiments, the imaging lens images the object plane in the acousto-optic modulator onto the birefringent optical element portion at a magnification that matches the separation angle between the acousto-optic modulator and the birefringent optical element portion.

[0009] In various embodiments, the first light source is a multi-wavelength light source (e.g., a multi-wavelength laser source) that provides at least a second wavelength laser beam at a second frequency. In such embodiments, an acousto-optic modulator may be configured to receive the second wavelength laser beam and generate a corresponding second frequency-shifted laser beam with a polarization rotation (e.g., orthogonal) relative to the second wavelength laser beam. A source optics device may receive and combine the second wavelength laser beam and the second frequency-shifted laser beam from the acousto-optic modulator, and may output a corresponding second combined beam. A receiving optics portion may be configured to receive the second wavelength laser beam and the second frequency-shifted laser beam, and guide the beams along an optical path toward a birefringent optics portion. The birefringent optics portion may be configured to receive the second wavelength laser beam and the second frequency-shifted laser beam, and combine the beams to output a corresponding second combined beam and a first combined beam (e.g., the first and second combined beams may co-propagate and / or be part of a total combined beam provided by a heterodyne source). In various embodiments, the receiving optical element portion includes a plurality of imaging lenses forming a chromaticity imaging system, wherein the object plane in the acousto-optic modulator is imaged onto the birefringent optical element portion with respect to the first and second wavelengths of the first and second wavelength laser beams at a magnification that matches the separation angle of both the acousto-optic modulator and the birefringent optical element portion.

[0010] In various embodiments, the receiving optical element portion includes a prism. In various embodiments, the birefringent optical element portion includes at least one of a birefringent beam shifter, a Wollaston prism, or a Rochon prism.

[0011] A method is provided for operating a metrology system including a heterodyne light source. The method includes operating a first light source of the heterodyne light source, an acousto-optic modulator of the heterodyne light source, and determining at least one measurement distance to at least one surface point on a workpiece. The first light source is operated to provide a first wavelength laser beam at least a first frequency. The acousto-optic modulator is operated to receive the first wavelength laser beam and generate a corresponding first frequency-shifted laser beam with a polarization rotation relative to the first wavelength laser beam. A source optics device receives and combines the first wavelength laser beam and the first frequency-shifted laser beam from the acousto-optic modulator, and outputs a corresponding first combined beam. The source optics device includes a receiving optical element portion and a birefringent optical element portion. The receiving optical element portion receives the first wavelength laser beam and the first frequency-shifted laser beam and guides the beams along an optical path toward the birefringent optical element portion. The birefringent optical element portion receives the first wavelength laser beam and the first frequency-shifted laser beam and combines the beams to output a corresponding first combined beam. Based on the measurement process utilizing the first combined beam, at least one measurement distance to at least one surface point on the workpiece is determined.

[0012] In various embodiments, the method further includes operating a sensor device configured to receive optical device output and generate a corresponding sensor device output. The optical device output is provided by a measuring optics device configured to receive a first combined light beam and utilize the first combined light beam to provide an optical device output relating to a distance to at least one surface point on the workpiece. The determination of at least one measured distance to at least one surface point is at least partially based on the sensor device output.

[0013] In various embodiments, the method further includes operating a first light source (e.g., a multi-wavelength laser source) to provide a second wavelength laser beam at least at a second frequency. In such embodiments, an acousto-optic modulator is operable to receive the second wavelength laser beam and generate a corresponding second frequency-shifted laser beam with a polarization rotation relative to the second wavelength laser beam. A receiving optical element portion may receive the second wavelength laser beam and the second frequency-shifted laser beam and may guide the beams along an optical path toward a birefringent optical element portion. The birefringent optical element portion may receive the second wavelength laser beam and the second frequency-shifted laser beam and combine the beams to output a corresponding second combined beam (e.g., the first and second combined beams may co-propagate and / or be a portion of a total combined beam provided by a heterodyne source). The determination of at least one measured distance to at least one surface point on the workpiece may be based on a measurement process utilizing both the first combined beam and the second combined beam. Attached Figure Description

[0014] Figure 1 This is a block diagram showing the various components of a metrology system including a heterodyne light source;

[0015] Figure 2 It includes similar to Figure 1 Block diagram of a digital holographic metrology system with a heterodyne light source;

[0016] Figures 3A to 3C Example of drawing Figure 2 A schematic diagram illustrating some of the operating principles of a digital holographic metrology system;

[0017] Figure 4 This is a schematic diagram of a lookup table for phase expansion used as part of the operation of a digital holographic metrology system;

[0018] Figure 5 The illustration comes from Figure 4 A diagram illustrating some values ​​in a lookup table;

[0019] Figure 6A and 6B It is a schematic diagram illustrating different operating modes of a digital holographic measurement system;

[0020] Figure 7This is a schematic diagram of a heterodyne light source that includes an imaging system with a single imaging lens and a Wollaston prism.

[0021] Figure 8 This is a schematic diagram of a heterodyne light source that includes an imaging system with two imaging lenses and a Wollaston prism.

[0022] Figure 9 This is a schematic diagram of a heterodyne light source including a receiving lens and a birefringent beam shifter;

[0023] Figure 10 This is a schematic diagram of a heterodyne light source including a receiving prism and a birefringent beam shifter;

[0024] Figure 11 It is a schematic diagram of a heterodyne light source including spatial filtering configuration and collimating lens;

[0025] Figure 12 It is a flowchart illustrating an exemplary implementation of a routine for operating a heterodyne light source; and

[0026] Figure 13 This is a flowchart illustrating an exemplary implementation of a routine for operating a digital holographic metrology system that includes a heterodyne light source. Detailed Implementation

[0027] Figure 1 This is a block diagram illustrating the various components of an embodiment of the metering system 100. For example... Figure 1 As shown, the measurement system 100 includes a heterodyne light source 110, an optical device 120, a sensor device 130, a timer 140, and a processing unit 150. In various embodiments, the heterodyne light source 110 may include a light source, an acousto-optic modulator, and source optics (e.g., as will be discussed below regarding...). Figures 7 to 11 (Examples described in more detail). In short, an acousto-optic modulator can be configured to receive one or more input wavelength laser beams from a light source and generate one or more corresponding frequency-shifted laser beams (e.g., which may be orthogonally polarized). Source optics can receive and combine the orthogonally polarized laser beams from the acousto-optic modulator and output the corresponding combined laser beam.

[0028] Optical device 120 (e.g., it may be a measuring optics device) receives a combined output beam from heterodyne light source 110. Optical device 120 utilizes (e.g., guides) the combined beam as part of a measurement process (e.g., as part of a process for measuring / determining at least one measurement distance to at least one surface point on workpiece surface 192, by guiding one or more beams to surface 192 of workpiece 190). As an example, in some embodiments (e.g., as will be discussed below)... Figure 2(As described in more detail), the measuring optical device 120 may be an interferometric optical device that receives a combined beam from the heterodyne light source 110 and uses the combined beam to provide an output for imaging the workpiece surface 192 (e.g., imaging onto an image plane) as part of the measurement process.

[0029] Sensor device 130 receives output from measuring optics device 120 and includes one or more sensors for sensing the output and providing corresponding output signals. Timer 140 provides timing signals (e.g., clock signals) for controlling the timing of both the acousto-optic modulator of heterodyne light source 110 and the sensors of sensor device 130. Processing unit 150 (e.g., including one or more processors 152) receives output from sensor device 130 and uses the output (e.g., to determine the measurement distance to a surface point on surface 192 of workpiece 190).

[0030] Those skilled in the art will understand that processing portion 150 (e.g., included or implemented in a computing system, etc.) and / or other processing or control systems described herein or that can be used with the elements and methods described herein can generally be implemented using any suitable computing system or apparatus, including distributed or networked computing environments, etc. Such systems or apparatuses may include one or more general-purpose or special-purpose processors (e.g., non-custom or custom devices) that execute software to perform the functions described herein. The software may be stored in memory, such as random access memory (RAM), read-only memory (ROM), flash memory, etc., or combinations of these components. The software may also be stored in one or more storage devices, such as optical-based disks, flash memory devices, or any other type of non-volatile storage medium for storing data. The software may include one or more program modules that include procedures, 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 program modules can be combined or distributed across multiple computing systems or apparatuses, and the functionality of program modules can be accessed via service calls in wired or wireless configurations.

[0031] Figure 2 This is a block diagram of a digital holographic metrology system 200 including a heterodyne light source 210, which in various embodiments can perform similar functions. Figure 1 Certain functions of the metering system. It should be understood that... Figure 2 Some numbered components 2XX may correspond to and / or have the same as Figure 1 The similarly numbered paired components 1XX operate in a similar manner and can be understood in a similar way, unless otherwise described below. This numbering scheme, indicating elements with similar design and / or function (i.e., unless otherwise stated and / or described), also applies to the rest of the figures herein. Figure 2As shown, the digital holographic metrology system 200 includes a heterodyne light source 210, an interferometric optics device 220, a sensor device 230, a timer 240, and a processing unit 250. In various embodiments, the digital holographic metrology system 200 can operate as a heterodyne imaging interferometer.

[0032] In various embodiments, the heterodyne light source 210 includes a coupling to an acousto-optic modulator (e.g., hereinafter referred to as...). Figures 7 to 11 (A more detailed description of certain examples) A ​​multi-wavelength laser source (e.g., a multi-wavelength laser source for providing laser beams of different wavelengths). In one embodiment, the multi-wavelength laser source can provide a first wavelength laser beam at a first frequency v1. An acousto-optic modulator receives the first wavelength laser beam and generates a corresponding first frequency-shifted laser beam at frequency v1 + Δv, which is combined with the first wavelength laser beam to form a first combined beam. Similarly, the multi-wavelength laser source can provide a second wavelength laser beam having a second frequency v2 different from the first frequency (i.e., having a corresponding second wavelength different from the first wavelength). An acousto-optic modulator receives the second wavelength laser beam and generates a corresponding second frequency-shifted laser beam at frequency v2 + Δv, which is combined with the second wavelength laser beam to form a second combined beam. Similarly, the multi-wavelength laser source can provide a third wavelength laser beam at a third frequency v3 different from the first and second frequencies (i.e., having a corresponding third wavelength different from the first and second wavelengths). An acousto-optic modulator receives the third wavelength laser beam and generates a corresponding third frequency-shifted laser beam at frequency v3 + Δv, which is combined with the third wavelength laser beam to form a third combined beam. In various embodiments, a multi-wavelength laser source can provide additional wavelength laser beams, wherein an acousto-optic modulator generates corresponding additional frequency-shifted laser beams. In various embodiments, different symbols are used interchangeably herein to denote / correspond to the frequencies of the laser beams (e.g., v, f, ω, etc.).

[0033] Timer 240 is coupled to heterodyne light source 210 (e.g., coupled to an acousto-optic modulator via a driver for the heterodyne light source) to provide a reference clock signal, upon which a modulation frequency Δv is generated. In various embodiments, the clock signal is provided at the modulation frequency Δv (e.g., in some embodiments, in the range of 40 MHz to 100 MHz). In various embodiments, the distributed clock signal may be equal to the acoustic frequency in the acousto-optic modulator and equal to the frequency shift Δv of the light beam (e.g., the photon frequency plus an acoustic phonon). In various alternative embodiments, the distributed clock signal may be any other frequency multiplied / divided to the desired target frequency using additional electronic components.

[0034] The interferometric optics 220 (e.g., it may also be referred to as a measurement optics device) includes a beam splitter 221, quarter-wave plates 223 and 226, a reference mirror 224 (e.g., it may also be referred to herein as a reference surface 224), an imaging lens portion 227 (e.g., an imaging lens including, for example, a camera lens), and a polarizer 228. In various embodiments, the interferometric optics 220 is formed and / or operates as a two-path interferometer. The imaging lens portion 227 (e.g., in some embodiments it may include multiple lenses and may be a telecentric device) is provided to image the surface 192 of the workpiece 190 (e.g., being measured and / or otherwise inspected, etc.) onto an image plane. In various embodiments, the image plane may be before, above, or after the sensors of the sensor device 230 (e.g., sensor TOF-1, sensor TOF-2, etc.) (e.g., in various embodiments, the sensors may be spatially arranged such that the optical path length from the imaging lens portion 227 to each sensor may be approximately the same). As will be described in more detail below, in various embodiments, each sensor TOF can detect the photomagnetic beat signal at a difference frequency Δv and demodulate it based on each pixel. In various embodiments, a depth frame may consist of four phase measurements. The recorded hologram can be digitally propagated to an image plane (e.g., after phase unwrapping) to extract the height map (e.g., measurements of surface points on a magnified workpiece surface 192 indicating workpiece 190).

[0035] Beam splitter 221 is optically aligned with reference mirror 224 along axis 222. Beam splitter 221 is also optically aligned with workpiece surface 192 along axis 225, which is substantially perpendicular to axis 222. Quarter-wave plate 226 is disposed between beam splitter 221 and workpiece surface 192, while quarter-wave plate 223 is disposed between beam splitter 221 and reference mirror 224. Imaging lens portion 227 and polarizer 228 are disposed along axis 225 between beam splitter 221 and sensor device 230. Imaging lens portion 227 and polarizer 228 are optically aligned between beam splitter 221 and sensor device 230.

[0036] The workpiece 190 to be inspected / measured is positioned relative to the digital holographic metrology system 200 such that the workpiece surface 192 is imaged by the imaging lens portion 227. In some embodiments, the workpiece surface 192 may be imaged onto the sensor of the sensor device 230 (e.g., sensor TOF-1, sensor TOF-2, etc.), but it should be understood that this is not a requirement in the digital holographic metrology system (e.g., in various embodiments, the workpiece surface 192 including corresponding surface points thereon may be imaged onto an image plane before or after the sensor TOF of the sensor device 230).

[0037] In, for example, the digital holographic metrology system disclosed herein, regardless of where the time-of-flight (TOF) sensor is located relative to the image plane, measurements of the laser beam by the TOF sensor can be digitally propagated to the image plane to determine the value appearing at the image plane, and this value can be used in the measurement process described herein. As an example of such numerical transfer, if the amplitude and phase of the laser beam are measured / determined at the measurement plane (e.g., at the TOF sensor), the corresponding values ​​can be numerically propagated (e.g., calculated) as occurs at the image plane, since the amplitude and phase of the laser beam vary with time and distance, (e.g., the relative position / distance of the image plane can be known based on the characteristics of the imaging lens, etc.). Such features may be particularly useful for measuring certain workpieces / workpiece characteristics (e.g., height variations on the workpiece surface may be large enough that the entire workpiece surface may not fit within the single measurement range of some systems, but, alternatively, the digital holographic metrology system disclosed herein can digitally propagate to the image plane to obtain / determine the desired values ​​for measurement, etc.).

[0038] exist Figure 2 In the example, each frequency-shifted laser beam is obtained by acousto-optic modulation of the corresponding wavelength laser beam (i.e., in the heterodyne source 210). However, it should be understood that in other embodiments, other techniques may be used to obtain each frequency-shifted laser beam. For example, for each wavelength / frequency-shifted laser beam pair, the laser may be a Zeeman laser having a laser medium provided in a strong axial magnetic field to generate two laser beams with different wavelengths / frequencies. According to the terminology used herein, laser beams with different wavelengths / frequencies may be referred to as separate laser beams in some cases, even if they share the same beam path. If the laser beams share a beam path and / or propagate together, such a combination of laser beams may be referred to as a combined beam in some cases.

[0039] In operation, timer 240 provides a clock or reference signal to the drivers of sensor device 230 and heterodyne light source 210. The acousto-optic modulator of heterodyne light source 210 is driven by the driver at a modulation frequency Δv. As described above, the multi-wavelength laser source of heterodyne light source 210 generates laser beams of different frequencies. For example, as mentioned above, the multi-wavelength laser source can provide a first wavelength laser beam with a first frequency v1. The acousto-optic modulator receives the input first wavelength laser beam and generates / generates a corresponding first frequency-shifted laser beam propagating along the first wavelength laser beam at a frequency of v1+Δv. As a result, the output of heterodyne light source 210 is a first combined beam relative to the first wavelength laser beam. As will be described in more detail below, the first combined beam can be detected by sensor device 230 using an envelope modulated with a difference frequency Δv.

[0040] Similarly, the multi-wavelength laser source of the heterodyne source 210 can provide a second-wavelength laser beam with a second frequency v2. The acousto-optic modulator receives the input second-wavelength laser beam and generates / generates a corresponding second-frequency-shifted laser beam with a frequency of v2 + Δv. This corresponding second-frequency-shifted laser beam propagates along the second-wavelength laser beam, and the corresponding output of the heterodyne source 210 is a second combined beam. Similarly, the multi-wavelength laser source can provide a third-wavelength laser beam with a third frequency v3. The acousto-optic modulator receives the input third-wavelength laser beam and generates / generates a corresponding third-frequency-shifted laser beam with a frequency of v3 + Δv. This corresponding third-frequency-shifted laser beam propagates along the third-wavelength laser beam, and the corresponding output of the heterodyne source 210 is a third combined beam. It should be understood that the total output of the heterodyne source 210 may therefore include a total combined beam (e.g., it may include first, second, and third combined beams, etc.). In various implementations, the multi-wavelength laser source of the heterodyne source 210 can provide additional wavelength laser beams and an acousto-optic modulator to generate corresponding additional frequency-shifted laser beams to form corresponding additional combined beams, which can also be included in the total combined beam as an output from the heterodyne source 210.

[0041] In various embodiments, the multi-wavelength laser source of the heterodyne source 210 may, in some cases, include individual laser sources for providing laser beams with different wavelengths. In various embodiments, it may be desirable for such individual laser sources (e.g., laser diodes) to have cryogenic sensitivity. In various embodiments utilizing individual laser sources (i.e., laser sources with corresponding wavelengths), the wavelength of each laser source may drift in the same direction due to temperature variations, etc., and the ratio between wavelengths can remain relatively stable, which can therefore lead to relatively stable measurement accuracy of the system. In various embodiments, the temperature sensitivity of each individual source can be configured to match the corresponding wavelength, which can reduce or eliminate any drift in the wavelength ratio due to temperature. When configuring, for example, the heterodyne source 210 disclosed herein, in various embodiments, individual laser sources (e.g., which may have different values ​​due to manufacturing tolerances, etc.) can be tested, and combinations of laser sources providing the desired ratio between wavelengths can be selected / utilized.

[0042] Therefore, in various embodiments, different laser sources may be included to provide a desired combination of wavelength ratios (e.g., in a particular example embodiment, wavelengths of, for example, 633 nm, 687 nm, and 767 nm). In one embodiment, a first laser source included in a multi-wavelength laser source can provide a first wavelength laser beam (e.g., in a particular example embodiment, a nominal wavelength of 633 nm). The heterodyne source 210 can correspondingly generate the first combined beam as described above, including a first wavelength with vertical polarization. A first wavelength laser beam (e.g., 633 nm) and a wavelength with horizontal polarization A first frequency-shifted laser beam (e.g., each with linear polarization). Timer 240 generates a clock signal (e.g., 40 MHz) that sets the drive frequency of the acousto-optic modulator of the heterodyne source 210. As a result, the first combined beams cause a detected beat frequency signal (e.g., 40 MHz).

[0043] Similarly, a second laser source included in the multi-wavelength laser source of the heterodyne source 210 can provide a second wavelength laser beam (e.g., nominally 687 nm in a particular example embodiment). The heterodyne source 210 can correspondingly generate a second combined beam as described above, including a second wavelength with vertical polarization. A second wavelength laser beam (e.g., 687nm) and a wavelength with horizontal polarization The second frequency-shifted laser beam. Similarly, a third laser source included in a multi-wavelength laser source can provide a third wavelength laser beam (e.g., with a nominal wavelength of 767 nm in a particular example embodiment). The heterodyne source 210 can correspondingly generate a third combined beam as described above, including a third wavelength with vertical polarization. A third-wavelength laser beam (e.g., 767nm) and a wavelength with horizontal polarization The third frequency-shifted laser beam. As mentioned above, timer 240 can generate a clock signal (e.g., 40 MHz) that sets the drive frequency of the acousto-optic modulator of the heterodyne light source 210. As a result, each of the second and third combined beams generates a detected beat frequency signal at a modulation frequency (e.g., 40 MHz).

[0044] As mentioned above, during the operation of the digital holographic metrology system 200, the heterodyne source 210 outputs a total combined beam, comprising a combination of beams, to the interferometric optics 220. As will be described in more detail below, the interferometric optics 220 utilizes the combined beam to provide an output for imaging the surface 192 of the workpiece 190 (e.g., imaging onto an image plane). For example, in one example embodiment using three wavelengths, as will be described in more detail below, the output of the interferometric optics 220 may include first, second, and third interferometric beams. In various embodiments, a first interferometric beam is generated based on a first combined beam from the heterodyne source, a second interferometric beam is generated based on a second combined beam from the heterodyne source, and a third interferometric beam is generated based on a third combined beam from the heterodyne source.

[0045] Further relating to the above example, when the first combined beam is incident on the beam splitter 221 (e.g., a polarization beam splitter) of the interferometric optics device 220, the first reference beam having a frequency v1 and vertical polarization propagates along axis 222 toward the reference mirror 224, while the first signal beam having a frequency v1+Δv and horizontal polarization propagates along axis 225 to illuminate a portion of the workpiece surface 192. The first reflected reference beam (i.e., from the reference mirror 224) and the first reflected signal beam (i.e., from the workpiece surface 192) are then combined by the beam splitter 221 to form a first reflected combined beam, which propagates via the imaging lens portion 227 along axis 222 toward the sensor device 230. A quarter-wave plate 226 is used to transform the polarization of the first incident beam with frequency v1+Δv from horizontal to circular and the polarization of the first reflected signal beam from circular to vertical. Similarly, a quarter-wave plate 223 is used to transform the polarization of the first incident beam with frequency v1 from vertical to circular and the polarization of the first reflected reference beam from circular to horizontal. As a result, the polarizations of the first reflected signal beam and the first reflected reference beam, which are located behind the first and second quarter-wave plates respectively, are orthogonal, thus preventing interference.

[0046] The workpiece surface 192 is imaged onto an image plane via an imaging lens portion 227, as will be described in more detail below. A polarizer 228 controls the polarization of the first two reflected beams, allowing them to form a first interference beam. A first dichroic assembly 231-1 (e.g., a dichroic filter for separating individual wavelengths) operates to reflect the first interference beam IB-1 to the sensor TOF-1 of the sensor device 230 (e.g., a time-of-flight sensor, which in various embodiments may be a time-of-flight camera, etc.). As will be described in more detail below, the first dichroic assembly 231-1 also operates to transmit / pass through other interference beams of different wavelengths to continue being reflected along axis 225 by other dichroic assemblies to other sensors of the sensor device 230. In various embodiments, the dichroic assemblies, as defined herein, may each comprise any optical component capable of splitting a beam into two beams of different wavelengths. As mentioned above, the workpiece surface 192 is imaged onto an image plane via the imaging lens portion 227 (e.g., the image plane may be before, above, or after the sensor TOF-1).

[0047] When the second combined beam is incident on beam splitter 221, the second reference beam, having a frequency of v2 and vertical polarization, propagates along axis 222 toward reference mirror 224, while the second signal beam, having a frequency of v2+Δv and horizontal polarization, propagates along axis 225 to illuminate a portion of the workpiece surface 192. The second reflected reference beam and the second reflected signal beam are then combined by beam splitter 221, thus forming a second reflected combined beam, which propagates along axis 225 toward sensor device 230 via imaging lens portion 227. Quarter-wave plate 226 is used to transform the polarization of the second incident beam with frequency v2+Δv from horizontal to circular, and the polarization of the second reflected signal beam from circular to vertical. Similarly, quarter-wave plate 223 is used to transform the polarization of the second incident beam with frequency v2 from vertical to circular, and the polarization of the second reflected reference beam from circular to horizontal. As a result, the polarizations of the second reflected signal beam and the second reflected reference beam, respectively, after the first and second quarter-wave plates, are orthogonal, thereby preventing interference.

[0048] The workpiece surface 192 is imaged onto the image plane via the imaging lens portion 227, as will be described in more detail below. A polarizer 228 controls the polarization of the second two reflected beams, allowing them to form a second interference beam. A second dichroic assembly 231-2 operates to reflect the second interference beam IB-2 toward the sensor TOF-2 of the sensor device 230. Similar to how the first dichroic assembly 231-1 reflects the first interference beam IB-1 when transmitting / passing through the second interference beam IB-2, the second dichroic assembly 231-2 also operates to transmit / pass through other interference beams of different wavelengths to continue being reflected along axis 225 by other dichroic assemblies toward other sensors of the sensor device 230. As mentioned above, the workpiece surface 192 is imaged onto the image plane via the imaging lens portion 227 (e.g., the image plane may be before, above, or after the sensor TOF-2).

[0049] It should be understood that a similar process may occur for additional combined beams of the system. For example, similar to the process described above, there may be a final combined beam (e.g., the Nth combined beam), which may have a frequency v. N The corresponding final reference beam with vertical polarization and frequency v NThe final signal beam is polarized with +Δv and horizontal polarization. The corresponding final reflected reference beam and the final reflected signal beam can form a final reflected combined beam, thereby forming the final interference beam. The workpiece surface 192 can be imaged onto the image plane via the imaging lens portion 227, as will be described in more detail below. The final dichroic component 231-N operates to reflect the final interference beam IB-N toward the sensor TOF-N. As mentioned above, the workpiece surface 192 is imaged onto the image plane via the imaging lens portion 227 (e.g., the image plane may be before, above, or after the sensor TOF-N).

[0050] It should be understood that in the N=3 implementation, the final combined beam can be a third combined beam, or in the implementation where N is greater than 3, a third combined beam of the system may also exist. In either case, a corresponding third reference beam with frequency v3 and vertical polarization and a third signal beam with frequency v3+Δv and horizontal polarization may exist. The corresponding third reflection reference beam and the third reflection signal beam can form a third reflection combined beam, thereby forming a third interference beam. The third dichroic component 231-3 is operable to reflect the third interference beam IB-3 toward the sensor TOF-3 (i.e., the sensor TOF-N when N=3). It should be understood that the use of the dichroic component enables the use of multi-wavelength laser beams in the heterodyne light source 210, which are combined in a common beam path and then separated by the dichroic component for reception by the sensor TOF (e.g., as part of a related measurement function, etc.).

[0051] More specifically, as mentioned above, the first dichroic component 231-1 is configured to separate the first interference beam IB-1 from the second and third interference beams IB-2 and IB-3. The first interference beam IB-1 is guided (e.g., through the first dichroic component 231-1) to be received by the first sensor TOF-1 (e.g., a time-of-flight sensor). The second dichroic component 231-2 is configured to separate the second interference beam IB-2 from the third interference beam IB-3. The second interference beam IB-2 is guided (e.g., through the second dichroic component 231-2) to be received by the second sensor TOF-2 (e.g., a time-of-flight sensor). The third interference beam IB-3 is guided (e.g., through the third dichroic component 231-3) to be received by the third sensor TOF-3 (e.g., a time-of-flight sensor).

[0052] As mentioned above, the total output of the heterodyne source 210 can be a total combined beam (e.g., it may include first, second, and third combined beams, for example, in the example above where N=3). According to the operation described above, when the total combined beam from the heterodyne source 210 is incident on the beam splitter 221, the combined reference beam, including first, second, and third reference beams having corresponding frequencies v1, v2, and v3 and vertical polarization, propagates along axis 222 toward reference mirror 224 (e.g., the beam combination at reference mirror 224 can be represented as ∑v). i In this example, it is shown that the combined reference beam includes reference beams having frequencies v1, v2, and v3. Furthermore, according to the operation described above, when the total combined beam from the heterodyne source 210 is incident on the beam splitter 221, the combined signal beam, including first, second, and third signal beams having corresponding frequencies v1+Δv, v2+Δv, and v3+Δv and horizontal polarization, propagates along axis 225 to illuminate a portion of the workpiece surface 192 (e.g., the beam combination at the workpiece surface 192 can be represented as ∑v). i +Δv, which in this example indicates that the combined signal beam includes signal beams having frequencies v1+Δv, v2+Δv and v3+Δv.

[0053] In various embodiments, axis 225 may correspond to / be defined as the measurement axis of the digital holographic metrology system 200, and the measurement distance may correspond to the distance from the digital holographic metrology system 200 (e.g., from a designated component or reference point of the digital holographic metrology system 200, such as near or located at the quarter-wave plate 226, or near or located at the end of the housing surrounding the interference optics device 220, etc.) to a surface point on the workpiece surface 192. In various embodiments, axis 225 may also correspond to / be defined as the z-axis of the digital holographic metrology system 200, and the measurement distance may be referred to as the z-distance or according to the z-height. In various embodiments, different z-heights of surface points on the workpiece surface 192 (e.g., as part of the overall surface profile or otherwise) may be relative to a reference point and / or to each other according to their relative z-heights, such as relative to a reference point on the workpiece surface, which may be designated as having a z-height of z = 0. In various embodiments, the z-height of each surface point may correspond to / be determined according to the corresponding measurement distance / z-distance from the digital holographic metrology system 200 to the surface point.

[0054] In configurations utilizing dichroic components, such as those disclosed herein, it may be desirable, in various embodiments, that the wavelengths of the light beams be sufficiently separated so that the beams can be effectively separated by dichroism. Conversely, some existing systems have utilized beams with very close wavelengths (e.g., with intervals less than 1 nm, for example, to achieve combined wavelengths for a long absolute measurement range, etc.). Alternatively, in configurations disclosed herein, it is advantageous to utilize combinations of wavelengths with relatively large intervals (e.g., at least 2% or 5% of the shortest wavelength value, or at least 10 nm or 20 nm), such that wavelength-based dichroism can effectively separate the beams. A specific example combination of wavelengths satisfying such a requirement is λ1 = 633 nm, λ2 = 687 nm, and λ3 = 767 nm (e.g., 2% of the shortest wavelength is less than 13 nm, and 5% is less than 32 nm, each less than the interval between the shortest and longest wavelengths, or the interval between any wavelengths in this example, such as an interval of 10 nm or 20 nm).

[0055] For each Time-of-Flight (TOF) sensor in sensor device 230 (e.g., TOF-1, TOF-2…TOF-N), in various embodiments, it may be a time-of-flight sensor configured to determine the phase relationship between the modulated signal received at each pixel and the interfering beam. The sensor TOF outputs a signal that compares the phase of the modulation intensity of the light signal falling on each pixel with an electrical reference signal of the modulation frequency derived from a signal from timer 240 (e.g., which may be used as a common clock source). In various embodiments, the sensor TOF may output a quadrature signal (IQ) for calculating the phase. In various embodiments, such calculations may be performed on the sensor itself (e.g., on a chip / processor on the sensor TOF) or on an associated processor / chip (e.g., provided in sensor electronics 255 of processing section 250 or host computer 258, etc.). Typically, processing section 250 receives the output from the sensor TOF (e.g., TOF-1, TOF-2…TOF-N) of sensor device 230 and uses the output (e.g., to determine the measured distance to a surface point on surface 192 of workpiece 190).

[0056] In various embodiments, timer 240 may be part of or receive timing signals from at least one of the sensor TOFs (e.g., sensor TOF-1). In such embodiments, the phase and frequency of the acousto-optic modulator of the heterodyne light source 210 may be effectively controlled by the sensor TOF (i.e., by a timer of the sensor TOF). In various embodiments, each sensor TOF may perform four phase measurements with a 90-degree offset within a depth frame to measure amplitude and phase. Each pixel on each sensor TOF may be a photonic mixer device for combined detection and demodulation. In various embodiments, the sensor TOF may be sensitive only to the difference frequency from the measurement signal and the reference arm (i.e., including reference mirror 224). The sum-frequency term may be averaged and removed along with the DC term by associated double sampling.

[0057] In various embodiments, the digital holographic metrology system 200 operates as a phase-shifting holographic system that measures the phase difference between a workpiece wave and a reference wave (e.g., from corresponding reflected signal beams and reflected reference beams) based on each pixel. Some existing systems require computational steps to calculate a hologram from at least three interferograms, while, according to the principles disclosed herein, computation can be performed at least in near real-time (e.g., on a Time-of-Flight sensor or in a processing section, etc.). In various embodiments, the measured hologram is digitally propagated to an image plane, where a phase unrolling routine is used to combine phase information from all wavelengths to reconstruct the surface profile over a relatively long, unambiguous range (e.g., an absolute measurement range).

[0058] Regarding Time-of-Flight (TOF) sensors, it should be understood that in various implementations, such as time-of-flight sensors in time-of-flight cameras, the phase resolution can be used to achieve a large unambiguous range (NAR) for system measurements (e.g., for determining the absolute measurement distance to a surface point on a workpiece). Generally, the better the resolution of the TOF sensor, the longer the achievable unambiguous range (e.g., as a decodeable path). As defined herein, a time-of-flight sensor is any sensor or configuration configured to sense values ​​indicating the amplitude and phase of a laser beam. The ratio of wavelengths used is another important factor regarding the achievable unambiguous range. Therefore, in various implementations, for a given system, it is desirable to determine / utilize a wavelength ratio that results in the signal being unpacked / decoded in a manner capable of achieving a large unambiguous range.

[0059] Figures 3A to 3C It is a drawing similar to Figure 2 A schematic diagram illustrating some operating principles of the digital holographic metrology system 200 and the digital holographic metrology system 300. Figures 3A to 3C Only certain parts of the digital holographic measurement system 300 are shown in the illustration to simplify the description of its operating principles. It should be understood that... Figures 3A to 3C Some numbered components 3XX may correspond to and / or have the same as Figure 1 Similar numbered paired components 1XX or Figure 2 The operation is similar to that of the numbered pairing components 2XX, and can be understood in a similar manner, unless otherwise described below. Figure 3A As illustrated, the output of the heterodyne light source 310 is received by the interferometric optics device 320. Correspondingly, the output of the interferometric optics device 320 is received by the sensor device 330.

[0060] Similar to the above about Figure 2 In the described operation, the heterodyne light source 330 can provide an output consisting of a collimated beam having multiple fundamental frequencies in one polarization and all frequency-shifting components in orthogonal polarization states (e.g., provided as a total combined collimated beam including a first combined beam, a second combined beam, a third combined beam, etc.). When the first combined beam is incident on the beam splitter 321 (e.g., a polarization beam splitter) of the interferometric optics 320, the first signal beam having a frequency f1 propagates to illuminate a portion of the workpiece surface 192, while the first reference beam having orthogonal polarization and a frequency f1+Δf propagates toward the reference surface 324 (e.g., a reference mirror). It should be understood that in this example, the beams used for the signal beam and the reference beam are relative to those described above regarding... Figure 2 The beam used in the described example is switched, and any configuration can be used in various implementations. The first reflected signal beam and the first reflected reference beam are then combined by beam splitter 321 to form a first reflected combined beam propagating toward sensor device 330.

[0061] When the second combined beam is incident on beam splitter 321, the second signal beam with frequency f2 propagates to illuminate a portion of the workpiece surface 192, while the second reference beam with orthogonal polarization and frequency f2+Δf propagates toward the reference surface 324. The second reflected signal beam and the second reflected reference beam are then combined by beam splitter 321, thus forming a second reflected combined beam propagating toward sensor device 330. A similar process occurs when the third combined beam is incident on beam splitter 321, etc. In various embodiments, this type of process can be performed to measure a reference point RP on the workpiece surface 192 (e.g., which may be specified as z=0 or other z-heights) and subsequently to measure other surface points SP on the workpiece surface, as will be discussed below. Figure 3B A more detailed description.

[0062] Similar to the process described above, the total output of the heterodyne light source 310 can be a total combined beam (e.g., in the example of N=3, it can include first, second, and third combined beams). According to the operation described above, when the total combined beam from the heterodyne light source 310 is incident on the beam splitter 321, the combined signal beam, including first, second, and third signal beams having corresponding frequencies f1, f2, and f3 and vertical polarization, propagates along the axis to illuminate a portion of the workpiece surface 192 (e.g., the beam combination at the workpiece surface 192 can be represented as ∑f i In this example, it indicates that the combined signal beam includes signal beams having frequencies f1, f2, and f3. Furthermore, according to the operation described above, when the total combined beam from the heterodyne source 310 is incident on the beam splitter 321, the combined reference beam, including first, second, and third reference beams having corresponding frequencies f1+Δf, f2+Δf, and f3+Δf and horizontal polarization, propagates along an axis toward the reference surface 324 (e.g., the beam combination at the reference surface 324 can be represented as ∑f). i +Δf, in this example, indicates that the combined reference beam includes reference beams having frequencies f1+Δf, f2+Δf, and f3+Δf.

[0063] Figure 3B Various example signals related to the above process are illustrated, including a first set of example signals 380-1 and a second set of example signals 380-2. The first set of example signals 380-1 includes a first reference beam signal RB1 (e.g., having a frequency f1+Δf), a first signal beam signal SB1 (e.g., having a frequency f1), a first combined beam signal CB1 (e.g., modulated with a beat frequency Δf), and a first combined beam phase shift signal CBPS1 (e.g., modulated with a beat frequency Δf, having an additional phase shift caused by the path length difference 2Δz). In various embodiments, the first combined beam signal CB1 may be generated by measuring a reference point on the workpiece surface (e.g., ...). Figure 3A The first combined beam phase shift signal CBPS1 is generated by subsequently measuring different surface points on the workpiece surface (e.g., reference point RP). Figure 3A Surface points (SP) are generated. For example... Figure 3B As indicated, the difference between signals CB1 and BCPS1 corresponds to the first phase shift. Where c corresponds to the speed of light.

[0064] The second set of example signals 380-2 includes a second reference beam signal RB2 (e.g., having a frequency f2+Δf), a second signal beam signal SB2 (e.g., having a frequency f2), a second combined beam signal CB2 (e.g., modulated with a beat frequency Δf), and a second combined beam phase shift signal CBPS2 (e.g., modulated with a beat frequency Δf, having an additional phase shift caused by the path length difference 2Δz). In various embodiments, the second combined beam signal CB2 may be generated by a reference point on the surface of the workpiece (e.g., ...). Figure 3A The reference point RP in the reference beam is used. The second combined beam phase shift signal CBPS2 can be obtained by subsequently measuring surface points on the workpiece surface (e.g., reference point RP). Figure 3A This is caused by surface points (SP) in the middle. For example... Figure 3B As shown, the difference between signals CB2 and BCPS2 corresponds to the second phase shift. Where c corresponds to the speed of light. It should be understood that the speed of light can be used to determine the third phase shift. A third combination of beams is used to perform a similar process.

[0065] Figure 3C The illustration shows the relationship with Figure 3B Some components of the digital holographic metrology system 300 related to phase shift processing are shown. For example... Figure 3C As shown, the sensor device 330 includes sensors TOF-1, TOF-2, and TOF-3, each sensor including corresponding pixel arrays 335-1, 335-2, and 335-3. In each pixel array, corresponding pixels 336-1, 336-2, and 336-3 are designated for measuring specific surface points on the workpiece surface 192 (e.g., as shown in the image). Figure 3A The surface point SP is shown. In various embodiments, the processing section 350 can receive (e.g., at the sensor electronics 355) information about the phase shift. Data such as (e.g., as described above). Then processing section 350 (e.g., using computer 358) can perform phase expansion (e.g., based on phase shift). (The value of Δz is determined by...). In various embodiments, determining the value of Δz corresponds to determining the measured distance to a surface point (e.g., surface point SP) on surface 192 of workpiece 190. The following is about... Figure 4 and 5 A simplified example of using a lookup table to perform phase expansion (e.g., to determine Δz) is described in more detail.

[0066] Figure 4 This is a schematic diagram of a lookup table 400 used for phase unrolling as part of the operation of a digital holographic metrology system. Figure 4In the example, the first column corresponds to a first sensor TOF-1, which receives a signal corresponding to a laser beam with a first wavelength λ1 (e.g., where λ1 = 500 nm). The first column includes signals corresponding to different possible phases. The value (for example, Figure 4 phase This corresponds to the above regarding Figures 3A to 3C The phase shift mentioned above). Figure 4 In the diagram, the second column corresponds to the second sensor TOF-2, which receives signals corresponding to a laser beam with a second wavelength λ2 (e.g., where λ2 = 800 nm). The second column includes signals corresponding to different possible phases. The third column corresponds to the third sensor TOF-3, which receives signals corresponding to a third wavelength laser beam having a third wavelength λ3 (e.g., where λ3 = 1000 nm). The third column includes values ​​corresponding to different possible phases. The value. As a concrete instance of using lookup table 400, if the phase With values ​​corresponding to 216 degrees, 90 degrees, and 288 degrees respectively, it can be seen that these values ​​correspond to the surface height Δz of the measurement surface point SP at Δz = 0.9 micrometers (e.g., relative to...). Figure 3A The height of the reference point RP on the workpiece surface is shown. The values ​​in the fourth column of Table 400 are shown extending in 0.1-micron steps over the range from surface height Δz = 0 to Δz = 2.0 microns (for a total unambiguous range of 2.0 microns). Such relationships are... Figure 5 This is further illustrated below, which will be described in more detail.

[0067] Figure 5 The illustration comes from Figure 4 A diagram illustrating some values ​​of the lookup table. Figure 5 This includes three graphs, 500A, 500B, and 500C, each indicating the period of the phase value on the Y-axis and plotted relative to the surface height scale included along the X-axis at the top of graph 500A (and also indicating the phase value corresponding to each indicated surface height for each 0.1-micron step on the bottom X-axis of each graph). Figure 5 As shown, graph 500A plots the first phase corresponding to a laser beam having a first wavelength λ1 (i.e., where λ1 = 500 nm). The value is shown as a cycle through 8 periods. Graph 500B plots the second phase corresponding to a laser beam having a second wavelength λ2 (i.e., where λ2 = 800 nm). The value is given, and this value is shown as a cycle through 5 periods. Graph 500C plots the third phase corresponding to a laser beam with a third wavelength λ3 (i.e., where λ3 = 1000 nm). The value is given, and the value is shown as a cycle through 4 periods.

[0068] like Figure 5 As shown, the surface height Δz value depends not only on each phase value, but also on the period during which each phase value falls. As an example, for a surface height Δz = 0.9 micrometers as mentioned above, the phase... The degree falls within the fourth period of the corresponding waveform, and the phase... The degree falls within the third period of the corresponding waveform, and the phase... The degree falls within the second period of the corresponding waveform. Therefore, the phase unrolling process determines the unique surface height Δz corresponding to the unique combination of phase values ​​(i.e., and it is based on...). Figure 5 The graphical representation is used to indicate each period that falls within the phase value.

[0069] exist Figure 4 and Figure 5 In the example, wavelengths λ1 = 500 nm, λ2 = 800 nm, and λ3 = 1000 nm were chosen to simplify the explanation of the operating principle described above, and in this example, result in an unambiguous range of 2.0 micrometers. Based on the principles disclosed herein, other wavelength combinations can be selected and utilized (e.g., which can result in a longer unambiguous range). For example, a combination of wavelengths λ1 = 633 nm, λ2 = 687 nm, and λ3 = 767 nm, which can be implemented using certain commercially available laser sources, can result in an unambiguous range of approximately 8.82 mm in some embodiments. In various embodiments, the corresponding Δz step size can be selected / utilized based on the accuracy of the phase measurement (e.g., according to the signal-to-noise ratio, etc.).

[0070] In various implementations, various types of phase unrolling routines can be utilized (e.g., for determining the surface height Δz value based on a unique combination of phase values). For example, as mentioned above... Figure 4 and 5 An alternative or supplement to the described lookup table is to use machine learning processes for phase unrolling. As an example of such phase unrolling utilizing machine learning, a K-nearest neighbor (KNN) regressor can be trained on data used for machine learning. The effectiveness of such processing has been determined by training a KNN regressor on clean data without any noise and then using it to demonstrate phase unrolling performed relative to relatively noisy data. Such tests have confirmed that these processes (e.g., involving the use of machine learning for phase unrolling, such as utilizing a KNN model) result in high accuracy for determining measurements.

[0071] It should be understood that, for example, the digital holographic metrology system disclosed herein (e.g., with heterodyne detection using a time-of-flight camera as a sensor) can have various advantages over certain existing metrology systems. The utilized heterodyne detection enables a high signal-to-noise ratio in holography, which is used to increase the unambiguous range (NAR) and the accuracy of the performed measurements. Furthermore, a long unambiguous range (e.g., absolute measurement range) is achieved using a phase unwinding routine independent of the synthesized wavelength. Wavelength multiplexing is performed (e.g., by utilizing dichroism, which is commercially available at a relatively low cost and can be used to separate signal beams with individual wavelengths). Wavelength multiplexing can be used with multiple TOF cameras to capture all phases of all wavelengths relatively simultaneously within a depth frame to improve environmental robustness.

[0072] This rapid acquisition of measurement data helps ensure minimal or no movement between the workpiece and the system while the measurement data is being captured (e.g., unlike existing systems where images and / or data are captured individually or otherwise sequentially, thus taking more time and potentially allowing workpiece movement relative to the system, such as due to vibration, accidental movement, normal workpiece travel, etc.). Compared to existing systems, direct phase measurement reduces computational workload without requiring phase retrieval routines. The configurations disclosed herein, in some embodiments, can utilize three different wavelengths to achieve similar performance to existing multi-wavelength systems utilizing six different wavelengths, and thus can result in similar performance at a lower cost. In various embodiments, configurations such as those disclosed herein can be used for applications such as high-throughput inline metrology sampling / measurement.

[0073] Figure 6A and 6B This is a schematic diagram illustrating different operating modes of the digital holographic metrology system 600 disclosed herein. The digital holographic metrology system 600 is similar to... Figure 2 and 3A Digital holographic metering systems 200 and 300 for 3C, unless otherwise described below. Figure 6A and 6B Only certain parts of the digital holographic measurement system 600 are shown in the illustration. For simplicity, the descriptions of the operating principles of different modes are simplified. Figure 6A and 6B As shown, the digital holographic metrology system 600 includes a heterodyne light source 610, an interferometric optics device 620, a sensor device 630, a timer 640, and a processing unit 650. The heterodyne light source 610 includes a multi-wavelength laser light source 611 and an acousto-optic modulator (AOM) 612 (e.g., similar components are described as including...). Figure 2 (in the heterodyne light source 210). Figure 2One difference between the digital holographic metrology system 200 and the digital holographic metrology system 600 is that the digital holographic metrology system 600 includes a switch 619 for switching between different modes (e.g., included in the heterodyne light source 610 or others), as will be described in more detail below.

[0074] Figure 6A The illustration depicts a digital holographic metering system 600 operating in amplitude modulated continuous wave (AMCW) mode 601A, while Figure 6B A digital holographic metrology system 600 operating in digital holographic mode 601B is illustrated (e.g., switch 619 is used as part of the mode switching). As will be described in more detail below, AMCW mode 601A can be characterized as providing relatively coarse scale measurements (e.g., using one or more sensors (TOF) to perform certain time-of-flight measurement operations), while digital holographic mode 601B (e.g., it can be as described above regarding...) Figure 2 and 3A The operation described in 3C can be characterized as providing relatively fine scale measurements. For this purpose, measurements of two modes can be combined to provide high-precision measurements over a relatively large unambiguous range.

[0075] like Figure 6A As shown, for AMCW mode 601A, switch 619 connects timer 640 (e.g., which provides a clock signal) to multi-wavelength laser source 611 (e.g., a current source connected to multi-wavelength laser source 611) to modulate the intensity of the light. Acousto-optic modulator 612 does not receive a clock signal from timer 640 and remains off in various embodiments. Light from multi-wavelength laser source 611 thus passes through acousto-optic modulator 612 (e.g., as zero-order light). It should be understood that, according to the operation in this example, no reference beam is guided by beam splitter 621 to reference mirror 624. Instead, the zero-order light passing through acousto-optic modulator 612 passes through beam splitter 621 and illuminates surface 192 of workpiece 190, which is imaged by optical device 620 based on reflected light (e.g., guided towards sensor device 630 as by beam splitter 621). Sensor device 630 has one or more sensors with TOF (e.g., see...). Figure 2 The distance / height of a surface point on the workpiece surface 192 is measured via zero-difference detection. Based on this operation of one or more TOF sensors, a relatively coarse measurement range can be achieved (e.g., in a particular example implementation, a non-ambiguous range of approximately 1.5 meters with a potential distance error of approximately 0.5% at such distances corresponding to approximately 7.5 mm).

[0076] Therefore, this type of operation of the AMCW mode 601A effectively provides coarse-scale measurements, which can be utilized Figure 6B The digital holographic mode 601B is used to provide fine-scale measurements, which can solve... Figure 6A The potential distance error in coarse-scale measurements, for example, having an unambiguous range greater than the potential distance error (e.g., greater than 7.5 mm in this example). For digital holographic mode 601B, switch 619 connects timer 640 to acousto-optic modulator 612, which is turned on, and digital holographic metrology system 600 as described above. Figure 2 and 3A It operates as described in 3C. In various implementations, the digital holographic metrology system 600 can alternate between modes 601A and 601B on a frame-by-frame basis to achieve the desired measurement.

[0077] As mentioned above, in Figure 2 In a specific instance implementation of the configuration (i.e., Figure 6B Operating similarly to the configuration, using a combination of wavelengths λ1 = 633 nm, λ2 = 687 nm, and λ3 = 767 nm (which can be achieved using certain commercially available laser sources), in some implementations, can result in an unambiguous range of approximately 8.82 mm. Note that this is greater than the 7.5 mm potential error in the coarse-scale measurement used for AMCW mode 601A in the examples described above. Therefore, measurements from both modes in these examples can be combined to achieve a total unambiguous range of approximately 1.5 meters with sub-micron accuracy. It should be understood that using both modes 601A and 601B allows the total unambiguous range to be extended (e.g., extended to 1.5 meters) without the need for additional laser sources. In a specific example, to achieve a similar increase in unambiguous range using only the digital holographic mode, such as mode 601B, additional laser sources might be required (e.g., adding three additional laser sources, for example, a total of six laser sources for wavelengths λ1, λ2, λ3, λ4, λ5, and λ6). Compared to such alternative configurations, such as... Figure 6A and 6B The use of the two modes 601A and 601B shown can result in less complex and lower-cost systems (e.g., utilizing and implementing measurements from only three laser sources / wavelengths λ1, λ2, λ3 instead of six, etc.).

[0078] In various implementations, different techniques can be used to combine measurements of AMCW mode 601A and digital holographic mode 601B. As mentioned above, in various implementations, AMCW mode 601A provides surface height data at a coarser scale and can be primarily used in some cases to resolve ambiguity where the unfolding extends beyond the original holographic range. In a specific example implementation, α = the unambiguous range of the measurement in digital holographic mode 601B, while z_AMCW = the surface height measurement of AMCW mode 601A, and z_Holo = the holographic z-height measurement of digital holographic mode 601B. Term I = floor(_z_AMCW / α) provides an integer multiple of the digital holographic unambiguous range of digital holographic mode 601B (e.g., the measured height is expected to be within the unambiguous range of AMCW mode 601A). As mentioned above, in a specific implementation, a modulation frequency of 100 MHz may correspond to an AMCW unambiguous range of 1.5 meters, and the digital holographic unambiguous range may be greater than the potential distance error (e.g., greater than 7.5 mm in this example). The final z-height can be determined by Δz = I·α + z_Holo. According to this equation, in one example of determining the combined measurement distance to a first surface point on the workpiece, the first AMCW mode measurement distance provides an integer multiple of the digital holographic unambiguous range, which is combined with the first digital holographic mode measurement distance to determine the combined measurement distance to the first surface point on the workpiece.

[0079] Figures 7 to 11 The diagram illustrates a heterodyne light source (e.g., which can be used as...). Figure 1 Heterodyne light source 110 and / or Figure 2 Various implementation schemes of heterodyne light sources 210, etc. In various implementation schemes, Figures 7 to 10 Each of these configurations can be characterized as an inline optics device for co-propagating and cross-polarized beams (e.g., from an acousto-optic modulator for heterodyne interference, etc.). More specifically, each of these embodiments can be characterized as an inline optics device for combining orthogonally polarized output beams (e.g., from an acousto-optic modulator) into a single beam for use as the output of a heterodyne source. In the inline optics devices disclosed herein, orthogonally polarized beams are noted to each pass through the same set of components of the source optics device, wherein birefringent optical element portions (i.e., including birefringent optical elements) combine orthogonally polarized output beams into a single beam path as part of a single combined beam.

[0080] It should be understood that the embodiments described below may have advantages over certain alternative embodiments. For example, in one alternative embodiment, an optical fiber connection may be utilized (e.g., the output of the acousto-optic modulator may be focused by a lens into an optical fiber (e.g., a polarization-maintaining fiber)). However, such a configuration may have high connection losses due to a combination of: beam shift in the clipped focal plane; beam size / mode field diameter mismatch; and / or limited fiber input numerical aperture (NA). In another alternative embodiment, two polarization beams and reflectors may be utilized, whereby a first beam from the acousto-optic modulator may be directed upward by a first beamsplitter to be reflected by a first reflector to a second reflector, which reflects the first beam downward back to a second beamsplitter, which directs the first beam forward, and a second beam from the acousto-optic modulator passes straight through the first and second beamsplitters to propagate out of the configuration together with the first beam. However, such a configuration may have mismatched beam parameters due to unequal path lengths (i.e., the first and second beams) and a lack of a common beam path (i.e., through different optical elements), which may result in a lack of robustness. It should be understood that the following description regarding... Figures 7 to 11 The described implementation scheme has certain advantages over this configuration.

[0081] Figure 7 This is a schematic diagram of a heterodyne light source 710, which includes a laser light source 711, an acousto-optic modulator 712, a driver 713, and a source optics 718 (i.e., it includes a receiving optics portion 714p and a birefringent optics portion 715p). The receiving optics portion 714p includes an imaging system with a single imaging lens 714. The birefringent optics portion 715p includes a Wollaston prism 715.

[0082] In operation, a timer (e.g., timer 140, timer 240, etc.) can provide a timing signal (e.g., a clock / reference signal) to the driver 713. The driver 713 then drives the acousto-optic modulator 712 at a modulation frequency Δω. A laser source 711 can provide a first wavelength laser beam at a first frequency ω1 (i.e., having a corresponding first wavelength). The acousto-optic modulator 712 (e.g., a sheared wave AOM) receives the input first wavelength laser beam and generates / generates a corresponding first frequency-shifted laser beam at a frequency ω1+Δω, which is orthogonally polarized relative to the input first wavelength laser beam. The object plane in the acousto-optic modulator 712 is imaged into the Wollaston prism 715 by the imaging lens 714 at a magnification M that matches both the separation angle α of the acousto-optic modulator 712 and the separation angle β of the Wollaston prism 715, where M = tan(α) / tan(β). According to the operating characteristics of the Wollaston prism 715, the output is a first combined beam, which includes a combined first wavelength laser beam with a first frequency ω1 and a first frequency-shifted laser beam with orthogonal polarization at a frequency ω1+Δω.

[0083] The components of the heterodyne source 710 (e.g., including the imaging lens 714 and the Wollaston prism 715) can therefore be characterized as inline optics for co-propagating and cross-polarized beams. More specifically, these components can be characterized as inline optics for combining orthogonally polarized output beams into a single beam from the heterodyne source output. Figure 7 As indicated, the output of the heterodyne light source 710 may be provided to or received by a measuring optical device MOA (e.g., measuring optical devices 120, 220, etc.) for, for example, for measurement operations (e.g., for determining at least one measurement distance to at least one surface point on the workpiece based on a measurement process utilizing a first combined beam).

[0084] Figure 8 This is a schematic diagram of a heterodyne light source 810, which includes a laser light source 811, an acousto-optic modulator 812, a driver 813, and a source optics device 818 (i.e., it includes a receiving optics section 814p and a birefringent optics section 815p). The receiving optics section 814p includes an imaging system with two imaging lenses 814A and 814B. The birefringent optics section 815p includes a Wollaston prism 815. The heterodyne light source 810 and... Figure 9 , 10 The heterodyne light sources 910, 1010, and 1110 will be understood as being related to 11. Figure 7 The heterodyne light source 710 operates similarly, unless otherwise described below. Regarding imaging systems with a single imaging lens 714... Figure 7 Heterodyne light source 710, Figure 8 The main difference of the heterodyne light source 810 is that it includes an imaging system with multiple lenses 814A and 814B, which can provide certain desired operating characteristics for certain applications, as will be described in more detail below.

[0085] In an embodiment where the laser source 811 can be a multi-wavelength laser source, the diffraction angle α of the acousto-optic modulator 812 can depend on the wavelength, for example... Figure 7In some implementations, light beams with different wavelengths may therefore not propagate together (e.g., this could lead to beam clipping later in the configuration). To address this problem, the imaging system (i.e., including lenses 814A and 814B) can be configured as a chromatic imaging system, where the magnification can be wavelength-dependent and can be matched to the diffraction angle α of the acousto-optic modulator 812 (i.e., for each wavelength) (e.g., such that laser beams of different wavelengths will propagate together and / or otherwise not experience beam clipping later in the configuration). More specifically, according to this configuration, the object plane in the acousto-optic modulator 812 is imaged by the chromatic imaging system (i.e., including imaging lenses 814A and 814B) into the Wollaston prism 815 at a magnification M that varies with each wavelength and is matched to the separation angle α(ω) of the acousto-optic modulator 812 and the separation angle β(ω) of the Wollaston prism 815 for each wavelength, where M = tan(α(ω)) / tan(β(ω)).

[0086] Figure 9 This is a schematic diagram of a heterodyne light source 910, which includes a laser light source 911, an acousto-optic modulator 912, a driver 913, and a source optics 918 (i.e., it includes a receiving optical element portion 914p and a birefringent optical element portion 915p). The receiving optical element portion 914p includes a receiving lens 914. The birefringent optical element portion 915p includes a birefringent beam shifter 915.

[0087] Similar to the above about Figure 7 In this operation, the acousto-optic modulator 912 (e.g., a sheared-wave AOM) receives the input first-wavelength laser beam and generates / generates a corresponding first-frequency-shifted laser beam, which is orthogonally polarized relative to the input first-wavelength laser beam. An input lens 914 focuses (e.g., at focal length f) onto the acousto-optic modulator 912 and images to infinity (i.e., the individual beams are collimated). According to the operating characteristics of the birefringent beam shifter 915, the first-wavelength laser beam passes through, while the first-frequency-shifted laser beam (i.e., orthogonally polarized) is effectively shifted to be output together with the first-wavelength laser beam. Therefore, the output of the birefringent beam shifter 915 is a first combined beam, which includes the combined first-wavelength laser beam and the orthogonally polarized first-frequency-shifted laser beam.

[0088] The components of the heterodyne source 910 (e.g., including the imaging lens 914 and the birefringent beam shifter 915) can therefore be characterized as inline optics for co-propagating and cross-polarized beams. More specifically, these components can be characterized as inline optics for combining orthogonally polarized output beams into a single beam from the heterodyne source output. Figure 9As indicated, the output of the heterodyne light source 910 may be provided to or received by a measuring optical device MOA (e.g., measuring optical devices 120, 220, etc.) for, for example, for measurement operations (e.g., for determining at least one measurement distance to at least one surface point on the workpiece based on a measurement process utilizing a first combined beam).

[0089] Figure 10 This is a schematic diagram of a heterodyne light source 1010, which includes a laser source 1011, an acousto-optic modulator 1012, a driver 1013, and a source optics device 1018 (i.e., it includes a receiving optical element portion 1014p and a birefringent optical element portion 1015p). The receiving optical element portion 1014p includes a receiving prism 1014. The birefringent optical element portion 1015p includes a birefringent beam shifter 1015. The heterodyne light source 1010 will be understood as... Figure 9 The heterodyne light source 910 operates similarly, unless otherwise described below. Regarding the one with receiving lens 914... Figure 9 Heterodyne light source 910, Figure 10 The main difference of the heterodyne light source 1010 is that it alternatively includes a receiving prism 1014, which can be correspondingly combined without imaging. In various embodiments, for the receiving prism 1014, the prism apex angle (e.g., and in some embodiments, the number of vertices) can be matched with the separation angle between the acousto-optic modulator 1012 and the input wavelength laser beam.

[0090] As mentioned above, Figures 7 to 10 The embodiments share certain similar operational characteristics. In each configuration, a source optics device (e.g., source optics 718, 818, 918, or 1018) receives and combines at least a first wavelength laser beam and a first frequency-shifted laser beam from an acousto-optic modulator, and outputs a corresponding first combined beam. In each configuration, the source optics device includes a receiving optical element portion (e.g., including at least one receiving optical element, such as corresponding lenses 714, 814A and 814B, 914, and prism 1014) and a birefringent optical element portion (e.g., including at least one birefringent optical element, such as corresponding Wollaston prisms 715 and 815, and corresponding birefringent beam shifters 915 and 1015). It should be understood that alternative birefringent optical elements (e.g., Rochon prisms, etc.) may be utilized in other embodiments. In each configuration, the receiving optical element portion is configured to receive the first wavelength laser beam and the first frequency-shifted laser beam and guide the beam along the optical path to the birefringent optical element portion. The birefringent optical element is configured to receive a first wavelength laser beam and a first frequency-shifted laser beam, and combine the beams to output a corresponding first combined beam.

[0091] It should be understood that Figures 7 to 10Each configuration of the birefringent optical element (e.g., including the corresponding Wollaston prisms 715 and 815 and the corresponding birefringent beam shifters 915 and 1015) can be characterized in various embodiments for use in a reverse / rearward direction relative to certain other uses of such components. More specifically, such birefringent optical elements are more typically used to receive beams and / or co-propagating beams along an optical path on one side, and then split the beams to provide them as an output. Compared to such existing uses, according to Figures 7 to 10 The configuration involves corresponding birefringent optical elements that receive different beams and then combine the beams to be output into a single combined beam (e.g., including portions of co-propagating beams). As mentioned above, Figures 7 to 10 The implementation schemes are therefore all configured as inline optics for combining orthogonally polarized output beams into a single beam from a heterodyne source. For example... Figures 7 to 10 As indicated, the output of each heterodyne light source may be provided to or received by a measuring optics MOA (e.g., measuring optics 120, 220, etc.) for, for example, for measurement operations (e.g., for determining at least one measurement distance to at least one surface point on the workpiece based on a measurement process utilizing a combined beam).

[0092] Figure 11 This is a schematic diagram of a heterodyne light source 1110, which includes a laser source 1111, an acousto-optic modulator 1112, a driver 1113, and a source optics 1118 (i.e., which includes a spatial filter configuration 1116 and a collimating lens 1117). In various embodiments, the laser source 1111 may be a multi-wavelength laser source (e.g., providing first, second, third, etc. wavelength laser beams), and the acousto-optic modulator 1112 may correspondingly generate a combined beam, as described herein. In various embodiments, the combined beam from the acousto-optic modulator 1112 (e.g., containing first, second, third, etc. combined beams) may pass through the spatial filter configuration 1116 and the collimating lens 1117 in the path to the measurement optics MOA. According to the principle of conservation of momentum, different wavelengths can be diffracted at different angles by the operation of the acousto-optic modulator 1112. In one embodiment, the spatial filtering configuration 1116 may include a microscope objective lens 1116A and a pinhole filter element 1116B. The combined beam from the acousto-optic modulator 1112 can be imaged by the objective lens 1116A onto the pinhole filter element 1116B (e.g., containing a 10 μm pinhole), such that diffracted and non-diffracted beams of different wavelengths overlap, and the light exiting the pinhole filter element 1116B is effectively used as a point source (e.g., having a 10 μm pinhole) to provide a beam to the collimating lens 1117. Figure 11The indicated available overlap area UA). After the combined beam (e.g., including first, second, third, etc. combined beams) passes through the spatial filter configuration 1116, the collimating lens 1117 operates to collimate the combined beam.

[0093] Typically, multi-wavelength laser sources can be used in Figures 7 to 11 In various configurations of the implementation scheme (e.g., especially as mentioned above) Figure 8 and 11 As described, although it can also be used in other configurations. (Regarding...) Figure 11 The multi-wavelength laser source 1111 provides the following description of its operation; however, it should be understood that this description can also be applied when a multi-wavelength laser source is correspondingly used. Figures 7 to 10 Any configuration of the multi-wavelength laser source 1111. In one example embodiment, the multi-wavelength laser source 1111 can provide a first wavelength laser beam with a first frequency ω1 (i.e., having a corresponding first wavelength), and the acousto-optic modulator 1112 receives the first wavelength laser beam and generates a corresponding first frequency-shifted laser beam with a frequency of ω1+Δω. Similarly, the multi-wavelength laser source 1111 can provide a second wavelength laser beam with a second frequency ω2 (i.e., having a corresponding second wavelength), and the acousto-optic modulator 1112 receives the second wavelength laser beam and generates a corresponding second frequency-shifted laser beam with a frequency of ω2+Δω. Similarly, the multi-wavelength laser source 1111 can provide a third wavelength laser beam with a third frequency ω3 (i.e., having a corresponding third wavelength), and the acousto-optic modulator 1112 receives the third wavelength laser beam and generates a corresponding third frequency-shifted laser beam with a frequency of ω3+Δω. In various embodiments, the multi-wavelength laser source 1111 can provide additional or fewer wavelength laser beams (e.g., where the acousto-optic modulator 1112 generates corresponding additional or fewer frequency-shifted laser beams). For the operation of the acousto-optic modulator 1112, it should be understood that the phase shift Δω on the acoustic wave produces the same amount of optical phase shift Δω on all beams, regardless of wavelength. For such operation, in various embodiments, it may be desirable for the driver 1113 to be a phase-locked radio frequency (RF) driver.

[0094] As mentioned above, a timer is coupled to a driver 1113 of the acousto-optic modulator 1112 to provide a reference clock signal, based on which a modulation frequency Δω is generated in the driver 1113. In one embodiment, the clock signal is provided at a modulation frequency Δω (e.g., in the range of 40 MHz to 100 MHz). The distributed clock signal can be equal to the acoustic wave frequency in the acousto-optic modulator 1112 and equal to the frequency shift Δω of the light beam (e.g., the photon frequency plus an acoustic phonon). In various alternative embodiments, the distributed clock signal can be any other frequency, and then multiplied / divided to the desired target frequency using additional electronic components.

[0095] In this example, each frequency-shifted laser beam is obtained by acousto-optic modulation of a laser beam of corresponding wavelength. Some advantages of this configuration include the availability of multiple wavelengths, all with the same frequency shift, and the possibility of phase-locking; the overall configuration (e.g., relative to some existing configurations) can be relatively less complex and less costly. In various alternative configurations, other methods can be used to obtain each frequency-shifted laser beam. For example, for each source / frequency-shifted laser beam pair, the laser can be a Zeeman laser with a laser medium provided in a strong axial magnetic field to generate two beams with different frequencies. In various other alternative implementations, an electro-optic modulator can be used instead of an acousto-optic modulator, or a combination of multiple dual-wavelength sources (e.g., lasers operating simultaneously at two wavelengths) can be used.

[0096] In various embodiments, the multi-wavelength laser source 1111 may include, in some configurations, separate laser sources for providing laser beams with different wavelengths. For example, different laser sources may be included to provide a desired combination of wavelength ratios (e.g., in a particular example embodiment, wavelengths of, for example, 633 nm, 687 nm, and 767 nm). For example, in one embodiment, a first laser source included in the multi-wavelength laser source 1111 may provide a first wavelength laser beam (e.g., in a particular example embodiment, a nominal wavelength of 633 nm). The heterodyne source 1110 may correspondingly generate the first combined beam as described above, including a first wavelength with vertical polarization. A first wavelength laser beam (e.g., 633 nm) and a wavelength with horizontal polarization A first frequency-shifted laser beam (e.g., each with linear polarization) is generated. A timer generates a clock signal (e.g., 40 MHz) that sets the drive frequency of the acousto-optic modulator 1112 (e.g., driver 1113). As a result, the first combined beams result in a detected beat frequency signal (e.g., 40 MHz).

[0097] Similarly, a second laser source included in the multi-wavelength laser source 1111 can provide a second wavelength laser beam (e.g., nominally 687 nm in a particular example embodiment). The heterodyne source 1110 can correspondingly generate a second combined beam as described above, including a second wavelength with vertical polarization. A second wavelength laser beam (e.g., 687nm) and a wavelength with horizontal polarization (e.g., each with linear polarization) a second frequency-shifted laser beam. Similarly, a third laser source included in the multi-wavelength laser source 1111 can provide a third wavelength laser beam (e.g., nominally 767 nm in a particular example embodiment). The heterodyne source 1110 can correspondingly generate a third combined beam as described above, including a third wavelength with vertical polarization. A third-wavelength laser beam (e.g., 767nm) and a wavelength with horizontal polarization A third frequency-shifted laser beam (e.g., each with linear polarization). As mentioned above, a timer can generate a clock signal (e.g., 40 MHz) that sets the drive frequency of the acousto-optic modulator 1112 (e.g., driver 1113). As a result, each of the second and third combined beams generates a detected beat frequency signal at the modulation frequency (e.g., 40 MHz). In various embodiments, it may be desirable to use any single laser source with a narrow linewidth (e.g., for having a long coherence length).

[0098] Figure 12 This is a flowchart illustrating an exemplary embodiment of routine 1200 for operating a heterodyne light source. At block 1210, a first source of the heterodyne light source is operated to provide at least a first wavelength laser beam. At block 1220, an acousto-optic modulator operating the heterodyne light source is configured to receive the first wavelength laser beam and generate a corresponding first frequency-shifted laser beam (e.g., having a polarization orthogonal to the polarization of the first wavelength laser beam). In various embodiments, a source optics device receives and combines the first wavelength laser beam and the first frequency-shifted laser beam from the acousto-optic modulator and outputs a corresponding first combined beam. The source optics device includes a receiving optical element portion and a birefringent optical element portion. The receiving optical element portion is configured to receive the first wavelength laser beam and the first frequency-shifted laser beam and guide the beam along an optical path to the birefringent optical element portion. The birefringent optical element portion is configured to receive the first wavelength laser beam and the first frequency-shifted laser beam and combine the beams to output a corresponding first combined beam (e.g., to a measuring optics device). At block 1230, based on a measurement process utilizing the first combined beam, at least one measuring distance to at least one surface point on the workpiece is determined.

[0099] Figure 13 This is a flowchart illustrating an exemplary embodiment of routine 1300 for operating a digital holographic metrology system including a heterodyne light source. At block 1310, the heterodyne light source is operated as a multi-wavelength source (e.g., a multi-wavelength laser source) to provide at least a first wavelength laser beam and a second wavelength laser beam. At block 1320, an acousto-optic modulator of the heterodyne light source is operated to: receive the first wavelength laser beam and generate a corresponding first frequency-shifted laser beam, which is combined with the first wavelength laser beam to form a first combined beam; and receive the second wavelength laser beam and generate a corresponding second frequency-shifted laser beam, which is combined with the second wavelength laser beam to form a second combined beam. An interferometric optics device receives the combined beam from the heterodyne light source and uses the combined beam to provide an output for imaging a workpiece. The output includes at least: a first interference beam generated based on the first combined beam from the heterodyne light source; and a second interference beam generated based on the second combined beam from the heterodyne light source.

[0100] At block 1330, a sensor device is operated to receive output from an interferometric optical device. This sensor device includes at least first and second time-of-flight sensors and a first dichroic component. The first dichroic component is configured to separate a first interference beam from a second interference beam, the first interference beam being guided for reception by the first time-of-flight sensor and the second interference beam being guided for reception by the second time-of-flight sensor. At block 1340, output is received from the first and second time-of-flight sensors, and this output is used to determine at least one measurement distance to at least one surface point on the workpiece.

[0101] Although preferred embodiments of the present disclosure have been illustrated and described, many variations of the feature arrangements and sequences of operation shown and described will be apparent to those skilled in the art based on this disclosure. Various alternative forms can be used to implement the principles disclosed herein. Furthermore, the various embodiments described above can be combined to provide further embodiments. All U.S. patents referenced in this specification are incorporated herein by reference in their entirety. If it is necessary to employ concepts from various patents and applications to provide additional embodiments, aspects of the embodiments may be modified.

[0102] These and other changes can be made to the embodiments based on the above-described detailed description. Generally, the terminology used in the following claims should not be construed as limiting the claims to the specific embodiments disclosed in the specification and claims, but should be construed as encompassing all possible embodiments and the full scope of authorized equivalents of such claims.

Claims

1. A measurement system comprising: Heterodyne light source, the heterodyne light source comprising: A multi-wavelength laser source is used to provide at least a first wavelength laser beam at a first frequency, a second wavelength laser beam at a second frequency, and a third wavelength laser beam at a third frequency, wherein the second frequency is different from the first frequency and the third frequency is different from both the first and second frequencies. an acousto-optic modulator, the acousto-optic modulator being configured to: Receive the first wavelength laser beam and generate a corresponding first frequency-shifted laser beam with a polarization rotation relative to the first wavelength laser beam; Receive the second wavelength laser beam and generate a corresponding second frequency-shifted laser beam with a polarization rotation relative to the second wavelength laser beam; Receive the third wavelength laser beam and generate a corresponding third frequency-shifted laser beam with a polarization rotation relative to the third wavelength laser beam; and Source optical device, the source optical device being configured to: The source optical device receives and combines the first wavelength laser beam and the first frequency-shifted laser beam from the acousto-optic modulator, and outputs a corresponding first combined beam. The source optical device includes a receiving optical element portion and a birefringent optical element portion, wherein the receiving optical element portion is configured to receive the first wavelength laser beam and the first frequency-shifted laser beam, and guide the first wavelength laser beam and the first frequency-shifted laser beam along an optical path toward the birefringent optical element portion, and the birefringent optical element portion is configured to receive the first wavelength laser beam and the first frequency-shifted laser beam, and combine the first wavelength laser beam and the first frequency-shifted laser beam to output the corresponding first combined beam. The system receives and combines the second wavelength laser beam and the second frequency-shifted laser beam from the acousto-optic modulator, and outputs a corresponding second combined beam. The receiving optical element portion is configured to receive the second wavelength laser beam and the second frequency-shifted laser beam, and guide the second wavelength laser beam and the second frequency-shifted laser beam along an optical path toward the birefringent optical element portion. The birefringent optical element portion is configured to receive the second wavelength laser beam and the second frequency-shifted laser beam, and combine the second wavelength laser beam and the second frequency-shifted laser beam to output the corresponding second combined beam and the first combined beam. The system receives and combines the third wavelength laser beam and the third frequency-shifted laser beam from the acousto-optic modulator, and outputs a corresponding third combined beam. The receiving optical element is configured to receive the third wavelength laser beam and the third frequency-shifted laser beam, and guide the third wavelength laser beam and the third frequency-shifted laser beam along an optical path toward the birefringent optical element. The birefringent optical element is configured to receive the third wavelength laser beam and the third frequency-shifted laser beam, and combine the third wavelength laser beam and the third frequency-shifted laser beam to output the corresponding third combined beam, as well as the first combined beam and the second combined beam. The processing section is configured to determine the measurement distance to a surface point on the workpiece, wherein... The determination of the measurement distance to the surface point on the workpiece is based on the measurement process using the first combined beam, the second combined beam, and the third combined beam.

2. The metering system according to claim 1, further comprising: A measuring optical device configured to receive a first combined beam, a second combined beam, and a third combined beam, and to utilize the first combined beam, the second combined beam, and the third combined beam to provide an optical output related to the distance to the surface point on the workpiece; and A sensor device configured to receive the output of the optical device and generate a corresponding sensor device output. The processing section receives the output of the sensor device and uses the sensor device output as part of the measurement process to determine the measurement distance to the surface point on the workpiece.

3. The metrology system of claim 1, wherein the source optics of the receiving optical element portion and the birefringent optical element portion are arranged as an inline optics, the first wavelength laser beam and the first frequency-shifted laser beam are orthogonally polarized and each pass through the same receiving optical element of the receiving optical element portion and the same birefringent optical element of the birefringent optical element portion, the birefringent optical element combining the orthogonally polarized first wavelength laser beam and the first frequency-shifted laser beam into the first combined beam.

4. The metering system according to claim 3, wherein: The second wavelength laser beam and the second frequency-shifted laser beam are orthogonally polarized and each passes through the receiving optical element of the receiving optical element portion and the birefringent optical element of the birefringent optical element portion, and the birefringent optical element combines the orthogonally polarized second wavelength laser beam and the second frequency-shifted laser beam into the second combined beam; as well as The third wavelength laser beam and the third frequency-shifted laser beam are orthogonally polarized and each passes through the receiving optical element of the receiving optical element portion and the birefringent optical element of the birefringent optical element portion, and the birefringent optical element combines the orthogonally polarized third wavelength laser beam and the third frequency-shifted laser beam into the third combined beam.

5. The metrology system of claim 1, wherein the receiving optical element portion includes an imaging lens, and the object plane in the acousto-optic modulator is imaged onto the birefringent optical element portion at a magnification matching the separation angle of both the acousto-optic modulator and the birefringent optical element portion.

6. The metrology system of claim 1, wherein the receiving optical element portion comprises a plurality of imaging lenses forming a chromaticity imaging system, and the object plane in the acousto-optic modulator is imaged onto the birefringent optical element portion with respect to both the first and second wavelengths of the first and second wavelength laser beams at a magnification matching the separation angle of both the acousto-optic modulator and the birefringent optical element portion.

7. The metering system of claim 1, wherein the receiving optical element portion comprises a prism.

8. The metrology system of claim 1, wherein the birefringent optical element portion comprises at least one of a birefringent beam shifter, a Wollaston prism, or a Rochon prism.

9. A method for operating a metrology system including a heterodyne light source, the method comprising: The heterodyne light source is operated to provide a first wavelength laser beam at least at a first frequency; An acousto-optic modulator of the heterodyne light source is operated to receive the first wavelength laser beam and generate a corresponding first frequency-shifted laser beam with a polarization rotation relative to the first wavelength laser beam. A source optics device receives and combines the first wavelength laser beam and the first frequency-shifted laser beam from the acousto-optic modulator and outputs a corresponding first combined beam. The source optics device includes a receiving optical element portion and a birefringent optical element portion. The receiving optical element portion receives the first wavelength laser beam and the first frequency-shifted laser beam and guides them along an optical path toward the birefringent optical element portion. The birefringent optical element portion receives the first wavelength laser beam and the first frequency-shifted laser beam and combines them to output the corresponding first combined beam. Operate the multi-wavelength laser source to provide a second wavelength laser beam at a second frequency different from the first frequency; The acousto-optic modulator is operated to receive the second wavelength laser beam and generate a corresponding second frequency-shifted laser beam with a polarization rotation relative to the second wavelength laser beam. The source optics receive and combine the second wavelength laser beam and the second frequency-shifted laser beam from the acousto-optic modulator, and output a corresponding second combined beam. The receiving optics portion receives the second wavelength laser beam and the second frequency-shifted laser beam and guides them along the optical path toward the birefringent optics portion. The birefringent optics portion receives the second wavelength laser beam and the second frequency-shifted laser beam and combines them to output the corresponding second combined beam and the first combined beam. The multi-wavelength laser source is operated to provide a third wavelength laser beam at a third frequency that is different from the first frequency and the second frequency; The acousto-optic modulator is operated to receive the third wavelength laser beam and generate a corresponding third frequency-shifted laser beam with a polarization rotation relative to the third wavelength laser beam. The source optics receive and combine the third wavelength laser beam and the third frequency-shifted laser beam from the acousto-optic modulator, and output a corresponding third combined beam. The receiving optics portion receives the third wavelength laser beam and the third frequency-shifted laser beam and guides them along an optical path toward the birefringent optics portion. The birefringent optics portion receives the third wavelength laser beam and the third frequency-shifted laser beam and combines them to output the corresponding third combined beam and the first combined beam. The measurement distance to a surface point on the workpiece is determined based on the measurement process using the first combined beam, the second combined beam, and the third combined beam.

10. The method of claim 9, further comprising: An operating sensor device is configured to receive an optical device output and generate a corresponding sensor device output, wherein the optical device output is provided by a measuring optics device configured to receive the first combined light beam and utilize the first combined light beam to provide the optical device output related to the distance to the at least one surface point on the workpiece, wherein the determination of the at least one measured distance to the at least one surface point is at least partially based on the sensor device output.

11. The method of claim 9, wherein the receiving optical element portion includes an imaging lens, and the object plane in the acousto-optic modulator is imaged into the birefringent optical element portion at a magnification matching the separation angle of both the acousto-optic modulator and the birefringent optical element portion.

12. The method of claim 9, wherein the receiving optical element portion comprises a plurality of imaging lenses forming a chromaticity imaging system, and the object plane in the acousto-optic modulator is imaged onto the birefringent optical element portion with respect to both the first and second wavelengths of the first and second wavelength laser beams at a magnification matching the separation angle of both the acousto-optic modulator and the birefringent optical element portion.

13. The method of claim 9, wherein the birefringent optical element portion comprises at least one of a birefringent beam shifter, a Wollaston prism, or a Rochon prism.

14. A heterodyne light source for a metrology system for determining a measurement distance, the heterodyne light source comprising: A multi-wavelength laser source is used to provide at least a first wavelength laser beam at a first frequency, a second wavelength laser beam at a second frequency, and a third wavelength laser beam at a third frequency, wherein the second frequency is different from the first frequency and the third frequency is different from both the first and second frequencies. an acousto-optic modulator, the acousto-optic modulator being configured to: Receive the first wavelength laser beam and generate a corresponding first frequency-shifted laser beam with a polarization rotation relative to the first wavelength laser beam; Receive the second wavelength laser beam and generate a corresponding second frequency-shifted laser beam with a polarization rotation relative to the second wavelength laser beam; Receive the third wavelength laser beam and generate a corresponding third frequency-shifted laser beam with a polarization rotation relative to the third wavelength laser beam; and Source optical device, the source optical device being configured to: The source optical device receives and combines the first wavelength laser beam and the first frequency-shifted laser beam from the acousto-optic modulator, and outputs a corresponding first combined beam. The source optical device includes a receiving optical element portion and a birefringent optical element portion, wherein the receiving optical element portion is configured to receive the first wavelength laser beam and the first frequency-shifted laser beam, and guide the first wavelength laser beam and the first frequency-shifted laser beam along an optical path toward the birefringent optical element portion, and the birefringent optical element portion is configured to receive the first wavelength laser beam and the first frequency-shifted laser beam, and combine the first wavelength laser beam and the first frequency-shifted laser beam to output the corresponding first combined beam. The system receives and combines the second wavelength laser beam and the second frequency-shifted laser beam from the acousto-optic modulator, and outputs a corresponding second combined beam. The receiving optical element portion is configured to receive the second wavelength laser beam and the second frequency-shifted laser beam, and guide the second wavelength laser beam and the second frequency-shifted laser beam along an optical path toward the birefringent optical element portion. The birefringent optical element portion is configured to receive the second wavelength laser beam and the second frequency-shifted laser beam, and combine the second wavelength laser beam and the second frequency-shifted laser beam to output the corresponding second combined beam and the first combined beam. The system receives and combines the third-wavelength laser beam and the third-frequency-shifted laser beam from the acousto-optic modulator, and outputs a corresponding third combined beam. The receiving optical element is configured to receive the third-wavelength laser beam and the third-frequency-shifted laser beam, and guide them along the optical path toward the birefringent optical element. The birefringent optical element is configured to receive the third-wavelength laser beam and the third-frequency-shifted laser beam, and combine them to output the corresponding third combined beam and the first combined beam. The first combined beam, the second combined beam, and the third combined beam are configured to be used as part of the measurement process for determining the measurement distance to a surface point on the workpiece.

15. The heterodyne light source of claim 14, wherein the receiving optical element portion includes an imaging lens, and the object plane in the acousto-optic modulator is imaged into the birefringent optical element portion at a magnification matching the separation angle of both the acousto-optic modulator and the birefringent optical element portion.

16. The heterodyne light source of claim 14, wherein the receiving optical element portion comprises a plurality of imaging lenses forming a chromaticity imaging system, and the object plane in the acousto-optic modulator is imaged onto the birefringent optical element portion with respect to both the first and second wavelengths of the first and second wavelength laser beams at a magnification matching the separation angle of both the acousto-optic modulator and the birefringent optical element portion.

17. The heterodyne light source of claim 14, wherein the birefringent optical element portion comprises at least one of a birefringent beam shifter, a Wollaston prism, or a Rochon prism.

18. The heterodyne light source of claim 14, wherein the source optics of the receiving optical element portion and the birefringent optical element portion are arranged as an inline optics, the first wavelength laser beam and the first frequency-shifted laser beam are orthogonally polarized and each pass through the receiving optical element of the receiving optical element portion and the birefringent optical element of the birefringent optical element portion, the birefringent optical element combining the orthogonally polarized first wavelength laser beam and the first frequency-shifted laser beam into the first combined beam.

19. The heterodyne light source according to claim 18, wherein: The second wavelength laser beam and the second frequency-shifted laser beam are orthogonally polarized and each passes through the receiving optical element of the receiving optical element portion and the birefringent optical element of the birefringent optical element portion, and the birefringent optical element combines the orthogonally polarized second wavelength laser beam and the second frequency-shifted laser beam into the second combined beam; as well as The third wavelength laser beam and the third frequency-shifted laser beam are orthogonally polarized and each passes through the receiving optical element of the receiving optical element portion and the birefringent optical element of the birefringent optical element portion, and the birefringent optical element combines the orthogonally polarized third wavelength laser beam and the third frequency-shifted laser beam into the third combined beam.

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