JP7702880B2 - Measurement system and light diffraction method - Google Patents

Description

[0001] Embodiments of the present disclosure relate to apparatus and methods, and more particularly to measurement systems and methods that diffract light.

[0002] Virtual reality generally refers to a computer-generated simulated environment in which the user feels as if they are actually present. Virtual reality experiences are generated in 3D and viewed through a head-mounted display (HMD) such as glasses or other wearable display devices with near-eye display panels as lenses to display the virtual reality environment in place of the real environment.

[0003] Augmented reality, however, allows a user to view the environment around them through the display lenses of glasses or other HMD devices while viewing the environment and viewing images of virtual objects generated for display as part of the environment. Augmented reality can include any type of input, such as voice or haptic input, as well as virtual images, graphics, video, etc. that enhance or extend the environment experienced by the user. To achieve the augmented reality experience, the virtual images must be overlaid on the surrounding environment, and this overlay is achieved by optical devices.

[0004] One drawback in the art is that the fabricated optical devices tend to have non-uniform properties, such as grating pitch and grating orientation. Also, the deposited optical devices may inherit non-uniformities in their substrates, such as localized warping or deformation of the substrate. Also, if deposition is performed on a substrate that is placed on an uneven support surface, such as one that has defects or particles in the support surface, the substrate may tilt and the deposited optical devices may inherit that distortion.

[0005] Therefore, what is needed in the art is an apparatus and method for detecting non-uniformity in an optical device.

[0006] In one embodiment, a measurement system is provided that includes a stage, an optical arm coupled to an arm actuator configured to scan the optical arm and rotate the optical arm about an axis, and a detector arm. The stage has a substrate support surface. The stage is coupled to a stage actuator configured to move the stage in a scan path and rotate the stage about an axis. The optical arm includes a laser positioned adjacent to a beam splitter positioned in an optical path adjacent to a photodetector, the laser operable to project a deflected light beam at a beam angle θ along the optical path to the stage onto the beam splitter. The detector arm includes a detector actuator configured to scan the detector arm and rotate the detector arm about an axis, a first focusing lens, and a detector.

[0007] In another embodiment, a measurement system is provided that includes a stage, an optical arm coupled to an arm actuator configured to scan the optical arm and rotate the optical arm about an axis, a first detector arm, and a second detector arm. The stage has a substrate support surface. The stage is coupled to a stage actuator configured to move the stage in a scan path and rotate the stage about an axis. The optical arm includes a laser positioned adjacent to a beam splitter positioned in an optical path adjacent to a photodetector, the laser operable to project a deflected light beam at a beam angle θ along the optical path to the stage onto the beam splitter. Each detector arm includes a detector actuator configured to scan the detector arm, a first focusing lens, and a detector.

[0008] In yet another embodiment, there is provided a method for diffracting light, comprising projecting a beam of light having a wavelength λ _laser onto a first zone of a first substrate at a fixed beam angle θ ₀ and a maximum orientation angle φ _max , obtaining a displacement angle Δθ, determining a target maximum beam angle θ t- _max , where θ _t-max = θ ₀ + Δθ, and determining a test grating pitch P t _{- grating} by a modified grating pitch equation P _t-grating = λ _laser /(sin θ t _-max + sin θ ₀ ).

[0009] Measurement systems and methods measure local non-uniformity, such as grating pitch and grating orientation, in areas of an optical device. The local non-uniformity values are useful for evaluating the performance of the optical device.

[0010] In order that the features of the present disclosure as described above may be understood in detail, the present disclosure summarized above will now be more particularly described with reference to embodiments, some of which are illustrated in the accompanying drawings. It should be noted, however, that the accompanying drawings merely illustrate exemplary embodiments and therefore should not be considered as limiting the scope of the embodiments, as other equally effective embodiments may be permissible.

FIG. 1 is a schematic diagram illustrating a configuration of a measurement system according to some embodiments. FIG. 1 is a schematic diagram illustrating a configuration of a measurement system according to some embodiments. FIG. 1 is a schematic diagram illustrating a configuration of a measurement system according to some embodiments. 1A-C are schematic diagrams illustrating a beam position detector according to some embodiments. FIG. 2 is a schematic cross-sectional view showing a first zone according to an embodiment. FIG. 1 is a schematic diagram illustrating a measurement system including one or more detector arms according to some embodiments. FIG. 1 is a schematic diagram illustrating a measurement system including one or more detector arms according to some embodiments. FIG. 1 is a schematic diagram illustrating a measurement system including one or more detector arms according to some embodiments. FIG. 1 is a schematic diagram illustrating a measurement system including one or more detector arms according to some embodiments. FIG. 2 is a flow diagram of a method for diffracting light according to an embodiment.

[0016] To facilitate understanding, wherever possible, the same reference numbers have been used to designate identical elements common to the figures. It is believed that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.

[0017] Embodiments of the present disclosure relate to a measurement system and method for measuring local non-uniformity of an optical device. The measurement system includes a stage, an optical arm, and one or more detector arms including one or more focusing lenses. Light projected from the optical arm reflects off a substrate disposed on the stage, and the reflected light from the substrate surface is incident on a detector. The deflection of the focusing lens from its optical center is used to determine the local non-uniformity of the optical device. A light diffraction method includes measuring a scattered light beam from the substrate surface, and the local distortion is obtained from the measurements. The embodiments disclosed herein may be particularly useful, but are not limited to, for measuring the local uniformity of an optical system.

[0018] As used herein, the term "about" refers to a +/- 10% variation from the nominal value. It is understood that such variation may be included in any value presented herein.

[0019] FIG. 1A is a schematic diagram illustrating a first configuration 100A of a measurement system 101 according to one embodiment. As shown, the measurement system 101 includes a stage 102, an optical arm 104A, and one or more detector arms 150. The measurement system 101 is configured to diffract light generated by the optical arm 104. The light generated by the optical arm 104 is directed toward a substrate disposed on the stage 102, and the diffracted light is incident on one or more detector arms 150.

[0020] As shown, the stage 102 includes a support surface 106 and a stage actuator 108. The stage 102 is configured to hold a substrate 103 on the support surface 106. The stage 102 is coupled to the stage actuator 108. The stage actuator 108 is configured to move the stage 102 in a scan path 110 along the X and Y directions and to rotate the stage 102 about the Z axis. The stage 102 is configured to move and rotate the substrate 103 such that light from the optical arm 104A is incident on different portions or regions of the substrate 103 during operation of the measurement system 101.

[0021] The substrate 103 includes one or more optical devices 105 having one or more regions 107 of gratings 109. Each region 107 has a grating 109 with an orientation angle φ and a pitch P, where P is defined as the distance between adjacent points, such as adjacent first edges 301 or the centers of mass of adjacent gratings 109 (FIG. 3). The pitch P and orientation angle φ of the grating 109 in the first region 111 may be different from the pitch P and orientation angle φ of the grating 109 in the second region 113 of the one or more regions 107. Also, local warping or other deformations of the substrate 103 may result in a variation in the local pitch P' and a variation in the local orientation angle φ'. The measurement system 101 may be used to measure the pitch P and orientation angle φ of the grating 109 for each of the regions 107 of each optical device 105. The substrate 103 may be a single crystal wafer of any size, such as having a radius of about 150 mm to about 450 mm. As shown, light beam 126A from optical arm 104A scatters from region 107 to become initial R ₀ beam 450, which is described in more detail below.

[0022] The optical arm 104, the detector arm 150, and the stage 102 are coupled to a controller 130. The controller 130 facilitates control and automation of the method of measuring the pitch P and orientation angle φ of the grating 109 described herein. The controller may include a central processing unit (CPU) (not shown), memory (not shown), and support circuits (or I/O) (not shown). The CPU may be one of any form of computer processor used in industry to control various processes and hardware (e.g., motors and other hardware) and to monitor processes (e.g., transport device position and scan time, etc.). The memory (not shown) is connected to the CPU and may be a readily available memory such as a random access memory (RAM). Software instructions and data may be encoded and stored in the memory to instruct the CPU. Also connected to the CPU are support circuits (not shown) for supporting the processor in a conventional manner. The support circuits may include conventional caches, power supplies, clock circuits, input/output circuits, subsystems, etc. The programs (or computer instructions) readable by the controller determine the tasks that can be performed on the substrate 103. The program may be software readable by the controller and may include, for example, code for monitoring and controlling the position of the substrate, the position of the optical arm, etc.

[0023] As shown, the optical arm 104A includes a white light source 114A, a first beam splitter 116A, a second beam splitter 118A, a laser 120, a detector 122, and a spectrometer 124. The white light source 114 may be a fiber-coupled light source. The first beam splitter 116A is positioned in an optical path 126A adjacent to the white light source 114. The white light source 114 is operable to project white light at a beam angle θ along the optical path 126A to the substrate 103, according to one embodiment. The laser 120 may be a fiber-coupled light source. The laser 120 is positioned adjacent to the first beam splitter 116A. The laser 120 is operable to project a light beam having a wavelength to the first beam splitter 116A such that the light beam is deflected at a beam angle θ along the optical path 126A to the substrate 103. The second beam splitter 118A is disposed in the optical path 126A adjacent to the first beam splitter 116A. The second beam splitter 118A is operable to deflect the light beam reflected by the substrate 103 to the detector 122. The spectrometer 124 is coupled to the detector 122 and determines the wavelength of the light beam deflected to the detector 122. The light beam described herein may be a laser beam. The optical arm 104 transmits the light beam along the optical path 126 so that the light is deflected by the substrate 103 and measured by one or more detector arms 150.

[0024] Figure IB is a schematic diagram illustrating a second configuration 100B of the measurement system 101 according to one embodiment. As shown, the optical arm 104B includes a laser 120, a beam splitter 128, and a beam position detector 132. The beam position detector 132 may include an image sensor, such as a CCD or CMOS sensor. The beam splitter 128 is positioned in the optical path 126B adjacent to the beam position detector 132. The laser 120 is positioned adjacent to the beam splitter 128. The laser 120 is operable to project a light beam having a wavelength onto the beam splitter 128 such that the light beam is deflected at a beam angle θ along the optical path 126B to the substrate 103. The optical arm 104B includes a polarizer 156, such as a half wave plate, and a quarter wave plate 158 according to one embodiment. The polarizer 156 is between the laser 120 and the beam splitter 128. The polarizer 156 maximizes the efficiency of the light beam deflected by the beam splitter 128 at the beam angle θ. The quarter wave plate 158 is in the optical path 126B and is positioned adjacent to the beam splitter 128. The quarter wave plate 158 maximizes the efficiency with which the light beam reflected from the substrate 103 reaches the beam position detector 132 and reduces the light beam reflected back to the laser 120.

1C is a schematic diagram illustrating a third configuration 100C of the measurement system 101 according to one embodiment. The optical arm 104C includes lasers 134a, 134b, ... 134n (collectively referred to as "lasers 134") and beam splitters 136a, 136b, ... 136n (collectively referred to as "beam splitters 136"). The beam splitters 136 are positioned adjacent to each other in the optical path 126C adjacent to the beam position detector 132. The laser 134a is configured to project a light beam having a first wavelength onto the beam splitter 136a such that the light beam of the first wavelength is deflected at a beam angle θ along the optical path 126c to the substrate 103. Laser 134b is configured to project a light beam having a second wavelength onto beam splitter 136b such that the light beam at the second wavelength is deflected at beam angle θ along optical path 126c to substrate 103. Laser 134n is configured to project a light beam having a third wavelength onto beam splitter 136n such that the light beam at the third wavelength is deflected at beam angle θ along optical path 126c to substrate 103.

[0026] The optical arm 104C may include polarizers 156a, 156b, ... 156n (collectively referred to as "polarizers 156C") and a quarter wave plate 158. The polarizers 156C are between the lasers 134 and the beam splitters 136. The polarizers 156C maximize the efficiency of the light beams deflected by the beam splitters 136 at the beam angle θ. The quarter wave plate 158 is in the optical path 126C and is positioned adjacent to the beam splitter 136n. The quarter wave plate 158 maximizes the efficiency with which the light beams reflected from the substrate 103 reach the beam position detector 132. The quarter wave plate 158 is interchangeable for a desired wavelength.

[0027] In any of the above configurations 100A, 100B, 100C, the optical arm 104A, 104B, 104C may include an arm actuator 112 configured to rotate the optical arm 104 about the z-axis and scan the optical arm in the z-direction. The optical arm 104 may be fixed while measurements are being taken.

[0028] The beam position detector 132 of the second configuration 100B and the third configuration 100C is operable to determine the beam position of the light beam reflected from the substrate 103 to the beam position detector 132. FIG. 2A illustrates one embodiment of a position sensitive detector 201A, i.e., the beam position detector 132 as a lateral sensor. FIG. 2B illustrates one embodiment of the beam position detector 132 as a four-quadrant sensor 201B. FIG. 2C illustrates some embodiments of the beam position detector 132 as an image sensor array 201C, such as a charge-coupled device (CCD) array or a complementary metal-oxide semiconductor (CMOS) array.

[0029] Figure 4A is a schematic diagram illustrating a detector arm 150 according to one embodiment. As shown, the detector arm 150 includes a detector 410, a detector arm actuator 152, and a first focusing lens 401. The detector arm actuator 152 is configured to rotate the detector arm 150 about the z-axis to scan the detector arm 150 in the z-direction. In Figures 4A-4D, light from the light path 126 reflects off of the region 107 of the substrate 103. The light is reflected into an initial R ₀ beam 450 and focused by the first focusing lens 401 into a first R ₀ beam 411. The first R ₀ beam 411 is incident on the detector 410. The detector 410 is any optical device used in the art to detect light, such as a CCD array or a CMOS array.

[0030] Prior to measuring region 107, the measurement system 101 may be calibrated with a known substrate 103 and the detector arm 150 may be positioned such that the first _R0 beam 411 is incident on the optical center 401c of the first focusing lens 401. Any of the measurement systems 101 described above and below may be calibrated with a known substrate 103 as described herein. Due to local distortions in region 107, the initial _R0 beam 450 in the reference region 107 is no longer incident on the optical center 401c of the focusing lens 401. For example, there may be a local bow of the substrate 103 in region 107 or a global wafer tilt, wedge, warp, bow, etc. The presence of particles on the support surface may cause the substrate 103 to tilt on the support surface 106, and particles disposed between the substrate 103 and the support surface may cause local and/or global distortions such as an increase in the height of the region 107, a tilt of the region relative to the support surface (shown in Figures 4A-4D as a tilted substrate 103t). In these cases with a tilted substrate 103t, the initial R ₀ beam 450t is incident on the first focusing lens 401 at a first angle Δθ ₁ , according to one embodiment, and the first R ₀ beam 411t is focused on a portion of the detector 410 that is about a first delta distance Δ ₁ away from the focused first R ₀ beam 411 of the known substrate 103. The first delta distance Δ ₁ is determined by Δ ₁ = f ₁ ^* tan(Δθ ₁ ), where f ₁ is the focal length of the focusing lens 401. In this manner, the first delta distance Δ ₁ and the first angle Δθ ₁ can be used to obtain local distortion information, as described in more detail below. According to one embodiment, the resolution of the detector 410 is less than about Δ ₁ .

[0031] Figure 4B is a schematic diagram illustrating a detector arm 150 according to one embodiment. As shown, the detector arm 150 further includes a second focusing lens 402 and a third focusing lens 403. The initial _R0 beam 450t is incident on the first focusing lens 401 at an angle of Δθ ₁ , which focuses the initial _R0 beam into a first _R0 beam 411t. The first _R0 beam 411t is incident on the second focusing lens 402, which focuses the first _R0 beam into a second _R0 beam 412t. The second R ₀ beam 412 is incident on a second incident spot on the third focusing lens 403, which focuses the second R ₀ beam into a third R 0 beam 413t to a portion of the detector 410 that is about a second delta distance Δ ₂ away from the focused third R ₀ beam of the _known substrate, where Δ ₂ = Δ ₁ ^* f ₃ /f ₂ , where f ₂ is the focal length of the second focusing lens and f ₃ is the focal length of the third focusing lens. Furthermore, Δ ₂ = f ₃ ^* f ₁ ^* tan(Δθ ₁ )/f _2. The second delta distance Δ ₂ can thus be used to obtain local distortion information through the first angle Δθ ₁ , as described in more detail below. In some embodiments, the second delta distance Δ ₂ is greater than the first delta distance Δ ₁ , which allows the use of a detector 410 having a lower resolution since the detector is limited only by the magnitude of the second delta distance Δ _2. According to one embodiment, the resolution of the detector 410 is less than about Δ ₂ .

[0032] Although three focusing lenses 401, 402, 403 are included in detector arm 150 as described above, it is contemplated that any number of focusing lenses may be used, and the lenses may be configured similarly as described above to result in even larger delta distances being measured by detector 410.

[0033] Figure 4C is a schematic diagram illustrating a measurement system 101 with a first detector arm 150 and a second detector arm 150' according to one embodiment. The first detector arm 150 is substantially similar to the detector arm described above in Figure 4A. As shown, the second detector arm 150' includes a first focusing lens 401', a detector 410', and a detector actuator 152'. In this embodiment, light following the optical path 126 is backscattered to generate a reflected _R1 beam 450t'. The second detector arm 150t' is located after the optical arm 104, according to one embodiment, and the optical arm is at least partially transparent to the reflected _R1 beam 450t'.

[0034] The reflected _R1 beam 450t' is incident on a third focused spot on the first focusing lens 401' at a third delta distance Δ ₃ from the optical center 401c' of the first focusing lens, according to one embodiment, which focuses the reflected _R1 beam into the first _R1 beam 411t'. The third delta distance Δ ₃ is determined by Δ ₃ = f ₁ ' ^* tan(Δθ ₂ ), where f ₁ ' is the focal length of the focusing lens 401'. In this manner, the third delta distance Δ ₃ and the second angle Δθ ₂ can be used to obtain local distortion information, as described in more detail below. The resolution of the detector 410' is less than about Δ ₃ , according to one embodiment. The displacement angle Δθ is determined by Δθ=Δθ ₂ −Δθ ₁ , where the displacement angle Δθ provides the local distortion of the pitch of the grating P _t-grating , as will be described in more detail below.

[0035] Figure 4D is a schematic diagram illustrating a measurement system 101 with a first detector arm 150 and a second detector arm 150' according to one embodiment. The first detector arm 150 is substantially similar to the detector arm described above in Figure 4B. As shown, the second detector arm 150' includes a first focusing lens 401', a second focusing lens 402', a third focusing lens 403', a detector 410', and a detector actuator 152'. In this embodiment, light following the optical path 126 is backscattered to generate a reflected _R1 beam 450t'. The second detector arm 150' is located behind the optical arm 104 according to one embodiment, which is at least partially transparent to the reflected _R1 beam 450'.

[0036] The reflected _R1 beam 450t' is incident on a third focused spot of the first focusing lens 401' at a third delta distance Δ ₃ from the optical center 401c' of the first focusing lens, according to one embodiment, which focuses the reflected _R1 beam into a first _R1 beam 411t'. The first _R1 beam 411t' is incident on the second focusing lens 402', which focuses the first _R1 beam into a second _R1 beam 412t'. The second _R1 beam 412t' is incident on a fourth focused spot a fourth delta distance _Δ4 from the optical center 403c' of the third focusing lens 403', which focuses the second R1 beam to a third _R1 beam 413t' for a portion of the detector 410' that is about the fourth delta distance _Δ4 away from the focused third _R1 beam _of the known substrate. In this manner, the fourth delta distance _Δ4 can be used to obtain localized distortion information, similar to the second delta distance _Δ2 .

[0037] In some embodiments, the fourth delta distance _Δ4 is greater than the third delta distance _Δ3 , which allows for the use of a detector 410' with a lower resolution since the detector is only limited by the magnitude of the fourth delta distance _Δ4 . The two delta distances _Δ2 , _Δ4 allow for a more detailed measurement of the local distortion of the region 107. According to one embodiment, the third delta distance _Δ3 is greater than the first delta distance _Δ3 . The resolution of the detector 410' is less than about _Δ4 , according to one embodiment. According to one embodiment, the focal length of the first focusing lens 401 of the first detector arm 150 is different from the focal length of the second focusing lens 402 of the first detector arm, which in turn is different from the focal length of the third focusing lens 403 of the first detector arm.

[0038] Although Figures 4C-4D show measurement system 101 having two detector arms 150, 150' with the same number of focusing lenses, it should be understood that any odd number of lenses can be used in each detector arm. For example, the first detector arm 150 can have one focusing lens and the second detector arm 150' can have three focusing lenses, or vice versa. In another example, the first detector arm 150 has five focusing lenses and the second detector arm 150' has three focusing lenses.

[0039] In all of the above and following embodiments, Δ ₁ , Δ ₂ , Δ ₃ , and Δ ₄ are in the range of about 10 um to about 1 mm, and Δθ ₁ , Δθ ₂ , Δθ ₃ , and Δθ ₄ are in the range of about 0.001° to about 1°, for example, in the range of about 0.001° to about 0.1°.

[0040] Figure 5 is a flow diagram of a method 500 for diffracting light in accordance with one embodiment. Although the method steps are described with reference to Figure 5, one of ordinary skill in the art will understand that any system configured to perform the method steps in any order falls within the scope of the embodiments described herein.

[0041] The method 500 begins at step 540 where a light beam having a wavelength λ is projected at a fixed beam angle θ ₀ and a maximum orientation angle φ _max onto a first region 107 of a first substrate 103. The method 500 may use any of the configurations 100A, 100B, 100C of Figures 1A-1C, 4A-4D of the measurement system 101 and any of the configurations of the detector arm 150. The white light source 114 projects white light at a fixed beam angle θ ₀ along an optical path 126A to a reference region 107, which has one or more gratings 109, where θ ₀ = arcsin(λ _laser /2P _grating ), where P _grating is the design/average pitch of the grating.

[0042] In step 550, a displacement angle Δθ is obtained. The displacement angle Δθ is equal to a first angle Δθ 1, where Δθ ₁ is determined by Δ ₁ =f ₁ ^* tan(Δθ ₁ ), according to some embodiments, and the measured displacement distance _{Δ 1 as} described above. In some embodiments, the displacement angle Δθ is determined by Δθ=Δθ ₂ -Δθ ₁ , where the second angle Δθ ₂ is determined by Δ ₂ =f ₁ ^* f ₃ ^* tan(Δθ ₂ )/f ₂ as described above.

[0043] In step 560, the stage 102 is rotated until an initial intensity maximum (initial I _max ) at a fixed beam angle θ ₀ is measured to obtain a maximum orientation angle φ _max . The maximum orientation angle φ _max corresponds to the orientation angle φ of the one or more gratings 109 in the reference area 107. A target maximum beam angle θ _t-max is calculated, where θ _t-max = θ ₀ + Δθ. The calculation of the target maximum beam angle θ _t-max using Δθ takes into account global distortions such as global tilt and bow of the substrate.

[0044] In step 570, a test grating pitch Pt _-grating is determined at the maximum orientation angle _φmax . Determining the initial pitch involves projecting white light at a fixed beam angle _θ0 and the maximum orientation angle _φmax , and solving the equation Pt _-grating = _Pgrating + ΔP = _λlaser / (sin _θt-max + sin _θ0 ). Furthermore, the change in measured pitch ΔP is found as follows:

［００４５］

[0045]

[0046] The measured change in pitch ΔP can be from about 1 pm to about 5 nm.

[0047] In one embodiment, steps 540, 550, 560, and 570 are repeated. In step 570, steps 540, 550, and 560 are repeated for subsequent zones of one or more regions 107 of one or more optical devices 105, or steps 540, 550, and 560 are repeated for subsequent regions, as the stage 102 is scanned along the scan path 110. Steps 540, 550, 560, and 570 can then be repeated after the entire substrate 103 has been rotated about 180° about the z-axis, allowing for a global measurement of the wafer wedge.

[0048] As discussed above, devices and methods are included that are configured to measure local non-uniformity of an optical device. Reflected laser light is detected by a detector arm. The detector arm includes one or more focusing lenses that focus the light onto a detector, such as a camera. Displacement of the reflected light relative to the test substrate is used to calculate the local non-uniformity present. The substrate can be scanned so that non-uniformity in different regions of the substrate can be measured.

[0049] The measurement system and method can measure non-uniform characteristics of an optical device on a substrate, such as grating pitch and grating orientation. Additionally, the measurement system and method can determine localized warping and deformation of the underlying substrate. Imperfections in the underlying support surface, such as grain imperfections, can also be located to determine whether the substrate or optical device has acceptable characteristics. Measurements can be performed on substrates or optical devices of various sizes and shapes.

[0050] While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the present disclosure may be devised without departing from the basic scope thereof, as determined by the following claims.

Claims (10)

a stage having a substrate support surface coupled to a stage actuator configured to move the stage in a scan path and rotate the stage about an axis perpendicular to the substrate support surface ;
an optical arm coupled to an arm actuator configured to scan the optical arm in a direction along which the axis extends and rotate the optical arm about the axis to cause the optical arm to project a light beam along an optical path at a beam angle θ onto a substrate disposed on the substrate support surface;
a laser positioned adjacent to a beam splitter positioned in the optical path adjacent a first detector, the laser operable to project a light beam deflected at the beam angle θ along the optical path to the stage onto the beam splitter; and an optical arm including the first detector disposed on the optical arm operable to detect a light beam reflected into the optical arm in the optical path through the beam splitter;
A detector arm,
a detector actuator configured to scan the detector arm in a direction along which the axis extends and to rotate the detector arm about the axis such that diffracted light of the light beam generated by the optical arm is incident on the detector arm;
A first focusing lens;
a second detector configured to obtain a first delta distance Δ ₁ that moves a first incident spot of the initial R ₀ beam projected onto the first focusing lens away from an optical center of the first focusing lens to determine local distortion information;
a detector arm including
A measurement system comprising: The optical arm further comprises:
a white light source operable to project white light along the light path to the stage at the beam angle θ;
a spectrometer coupled to the first detector for determining a wavelength of the light beam deflected onto the first detector;
The measurement system of claim 1 , comprising: The optical arm further comprises:
a polarizer positioned between the laser and the beam splitter;
a quarter wave plate positioned adjacent to the beam splitter in the optical path;
The measurement system of claim 1 , comprising: The measurement system of claim 1 , wherein the first detector has a resolution of less than about Δ ₁ . The measurement system of claim 1 further comprising a second focusing lens and a third focusing lens. 6. The measurement system of claim 5, wherein the initial _R0 beam is focused by the first focusing lens into a first _R0 beam, the first _R0 beam is focused by the second focusing lens into a second _R0 beam, and the second _R0 beam is focused by the third focusing lens into a third _R0 beam. the third _R0 beam is incident on the third focusing lens at a third entrance spot;
the third incident spot is a second delta distance _Δ2 away from the optical center of the third focusing lens ;
the second delta distance _Δ2 is greater than the first delta distance Δ1 _;
The measurement system of claim 6 . a stage having a substrate support surface coupled to a stage actuator configured to move the stage in a scan path and rotate the stage about an axis perpendicular to the substrate support surface ;
an optical arm coupled to an arm actuator configured to scan the optical arm in a direction along which the axis extends and rotate the optical arm about the axis to cause the optical arm to project a light beam along an optical path at a beam angle θ onto a substrate disposed on the substrate support surface;
a laser positioned adjacent to a beam splitter positioned in the optical path adjacent a first detector, the laser operable to project a light beam deflected at the beam angle θ along the optical path to the stage onto the beam splitter; and an optical arm including the first detector disposed on the optical arm operable to detect a light beam reflected into the optical arm in the optical path through the beam splitter;
a first detector arm and a second detector arm, each of which comprises:
a detector actuator configured to scan the first detector arm or the second detector arm;
A first focusing lens;
a second detector configured to obtain a first delta distance Δ ₁ that moves a first incident spot of the initial R ₀ beam projected onto the first focusing lens away from an optical center of the first focusing lens to determine local distortion information;
a first detector arm and a second detector arm including:
A measurement system comprising: The measurement system of claim 8 , wherein the second detector arm is positioned rearward of the optical arm. the light beam is reflected by a workpiece disposed on the stage to become a reflected _R1 beam, the reflected _R1 beam being incident on the first focusing lens of the second detector arm at a first incident spot on the second detector arm;
the first incident spot on the second detector arm is a third delta distance _Δ3 away from the optical center of the first focusing lens of the second detector arm;
The measurement system of claim 9 .

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