White light coherence spectroscopy inspection using tilted reference beam and spatial filtering

Abstract

A system and method for characterizing a sample using white light interferometry are disclosed. The system and method may include an optical subsystem. The optical subsystem may include a reference element configured to tilt the optical axis of a reference beam with respect to the optical axis of a measurement beam, and a sample positioning stage configured to adjust the sample position of the sample along the Z direction of the sample. The system and method may include receiving an image of the sample. The system and method may include demodulating the interference pattern of the image using a filter. The system and method may include determining the position of the interference pattern on the image and instructing focusing based on the position of the interference pattern.

Description

Technical Field

[0001] The present disclosure generally relates to white light interferometric spectroscopy, and more particularly to white light interferometric spectroscopy using a reference beam inclined with respect to a measurement beam.

Background Art

[0002] Inspection systems are used to inspect samples such as printed circuit boards (PCBs), wafers, etc. Inspecting the sample can generate data such as three-dimensional (3D) data, surface height topology, and / or an image of the sample for various purposes. For example, the height of the sample or the distance from the imaging system can be determined to properly focus on the sample or to unwrap an abstract phase map of the sample. There are various conventional methods for generating such data.

[0003] Conventional methods have limitations such as low throughput, the presence of speckle, occlusion, and / or fixed sensitivity, but the limitations are not limited to these.

[0004] In a conventional method based on white light interferometric spectroscopy (WLI), a wide spectral band of white light is used to scan the z-axis, and 3D measurements with nanometer accuracy are performed. The interferometer is often arranged inside the objective lens in a Mirau or Michelson configuration, and only a small part of the light is retroreflected from the reference mirror surface. Features of the sample within the focal plane of the objective lens reflect or scatter the light that interferes with the reflected light from the reference mirror on the sensor. As the feature is scanned in the z-direction, the sample is focused or unfocused in various regions. This often corresponds to the coherence plane, and interference with the reference occurs. Therefore, the sensitivity is deeply related to the coherence of the illumination source. Generally, since a white light source emits light including a wide spectrum, the coherence is low and the z-resolution is high. As a problem of conventional WLI, it can be mentioned that when the sample is scanned along the z-direction to obtain the focal position, the throughput of the system is limited.

[0005] In laser triangulation, a laser beam is shone onto the sample at a certain angle and reflected off the sensor at the opposite angle. Depending on the angle, reflections from different heights illuminate the sensor at multiple different coordinates. The difference between the measured coordinate and the nominal coordinate is measured, and the focus is dynamically corrected according to the calculated difference. However, laser triangulation can produce speckle due to the inherent high coherence and low dynamic range associated with monochromatic light, and is susceptible to the spectral response of the sample. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] U.S. Patent Application Publication No. 2010 / 277746 [Patent Document 2] U.S. Patent No. 7330574 [Patent Document 3] U.S. Patent No. 5122648 [Overview of the project] [Problems that the invention aims to solve]

[0007] Therefore, it is advantageous to provide systems and methods that overcome the above challenges. [Means for solving the problem]

[0008] A characterization system is disclosed according to one or more exemplary embodiments of the present disclosure. In one exemplary embodiment, the system comprises an optical subsystem and a controller. In another exemplary embodiment, the optical subsystem comprises a detector, an illumination source, a beam splitter, a reference element, and a sample positioning stage. In another exemplary embodiment, the controller is communicatively coupled to the detector and the sample positioning stage. In another exemplary embodiment, the controller comprises one or more processors configured to receive an image of a sample, demodulate interference patterns in the image using filters, determine the location of the interference patterns on the image, and instruct focusing based on the location of the interference patterns.

[0009] Methods are disclosed according to one or more exemplary embodiments of the present disclosure. In one exemplary embodiment, the method includes providing an optical subsystem configured for characterizing a sample using white light interferometry. In another exemplary embodiment, the optical subsystem includes a reference element configured to tilt the optical axis of a reference beam with respect to the optical axis of a measurement beam, and a sample positioning stage configured to adjust the sample position of the sample along the z-direction of the sample. In another exemplary embodiment, the method includes receiving an image of the sample, demodulating an interference pattern in the image using a filter, determining the location of the interference pattern on the image, and instructing a focus adjustment based on the location of the interference pattern.

[0010] The general description above and the detailed description below are for illustrative and illustrative purposes only and should be understood as not necessarily limiting the invention described in the claims. The accompanying drawings are incorporated herein and constitute part thereof, illustrating embodiments of the invention and, together with the general description, contribute to illustrating the principles of the invention. [Brief explanation of the drawing]

[0011] Many of the advantages of this disclosure will be better understood by those skilled in the art by referring to the attached figures. [Figure 1A] This is a simplified block diagram of a characterization system according to one or more embodiments of the present disclosure. [Figure 1B] This is a simplified schematic diagram of an optical subsystem according to one or more embodiments of the present disclosure. [Figure 2A] This is a conceptual diagram of the coherence region between a reference beam and a measurement beam in a sample, according to one or more embodiments of the present disclosure. [Figure 2B] This is a conceptual diagram of the coherence region between a reference beam and a measurement beam in a sample including raised features, according to one or more embodiments of the present disclosure. [Figure 2C] This is a conceptual diagram of the coherence region between a reference beam and a measurement beam in a sample including a translucent layer, according to one or more embodiments of the present disclosure. [Figure 2D] This is a conceptual diagram of a coherence plane between a reference beam and a measurement beam for illustrating resolution and sensitivity according to one or more embodiments of the present disclosure. [Figure 3A] An image of a target step, including a calibrated focal position, according to one or more embodiments of the present disclosure. [Figure 3B] This is an amplitude image obtained from an image of the target step in Figure 3A, according to one or more embodiments of the present disclosure. [Figure 4] This is a simplified schematic diagram of an optical subsystem comprising an external Mach-Zehnder interferometer configuration according to one or more embodiments of the present disclosure. [Figure 5] This is a simplified schematic diagram of an optical subsystem comprising an interferometer configuration according to one or more embodiments of the present disclosure. [Figure 6] This is a flowchart illustrating steps performed by a method according to one or more embodiments of the present disclosure. [Figure 7] This is a flowchart illustrating steps performed by a method according to one or more embodiments of the present disclosure. [Figure 8] This is a flowchart illustrating steps performed by a method according to one or more embodiments of the present disclosure. [Figure 9] A flowchart showing steps performed by a method using a bandpass filter according to one or more embodiments of the present disclosure. [Figure 10] A simplified diagram of an image of a bump feature during horizontal scanning that can be used in an unwrapping process of a phase map according to one or more embodiments of the present disclosure. [Figure 11A] A demodulated image of a periodic feature and an interference pattern according to one or more embodiments of the present disclosure. [Figure 11B] A filter image of the same field of view as FIG. 11A after applying a spatial filter having a narrower bandpass window to demodulate an interference pattern according to one or more embodiments of the present disclosure. **DETAILED DESCRIPTION OF THE INVENTION**

[0012] The present disclosure is particularly illustrated and described in certain embodiments and with respect to certain features thereof. The embodiments described herein are considered to be illustrative rather than limiting. It will be readily apparent to those skilled in the art that various changes and modifications in form and detail can be made without departing from the spirit and scope of the present disclosure. The disclosed subject matter illustrated in the accompanying drawings will be described in detail below.

[0013] Embodiments of this disclosure relate to characterizing a sample using an interference pattern, which is generated using the tilted optical axis of a reference beam in a white light interferometry configuration, filtered using a spatial filter, and demodulated. For example, height, surface height topology, and / or longitudinal scanning data may be generated using the interference pattern. For example, the tilted reference beam changes the position of the interference pattern along the x-axis as the sample moves in the z-axis. Thus, a specific position of the interference pattern in the image of the sample directly corresponds to a specific height of the sample and / or a specific distance from the sample to the characterization system. Therefore, once the position of the interference pattern is determined, operations such as autofocus during lateral scanning of the sample may be possible, non-limitingly, by comparing the position of the interference pattern with the position of a (known) calibrated focal point in the characterization system.

[0014] In embodiments of this disclosure, in and / or near the sample, the optical axis of the reference beam is tilted at an angle with respect to the optical axis of the measurement beam (i.e., the beams are not parallel). Therefore, a coherence region is generated between the (tilted) reference beam and the measurement beam. The location of the coherence region between the measurement beam and the reference beam corresponds to the interference pattern in the detector. In embodiments, conceptually, the coherence region may be the region where the coherence plane of the (tilted) reference beam intersects with the coherence plane of the measurement beam. For a flat sample, as the sample moves in the z direction (e.g., vertical direction), the coherence region changes laterally (i.e., in the x and / or y directions) based on the height of the sample (i.e., position in the z direction). The coherence region may correspond to the interference pattern on an image of the sample. Therefore, the height / distance of at least a portion of the sample can be determined using a single image.

[0015] Conventional methods for focusing samples may present challenges. For example, during focusing, it may be necessary to stop the lateral movement of the sample to obtain multiple focused images scanned along the z-direction (e.g., the depth direction) in order to determine the optimal focus for the sample. Alternatively, focusing of the sample may be achieved by tilting the interferometer, as disclosed in U.S. Patent No. 6,449,048, issued September 10, 2002, which is entirely incorporated herein by reference. Tilting the entire interferometer may (theoretically) reduce the need for z-direction scanning. However, 3D features of the sample viewed at certain angles may be occluded. Furthermore, fringe projection techniques may use relatively large angles to increase sensitivity, which can result in significant occlusion when high features are present.

[0016] However, in embodiments of this disclosure, the measurement beam is generally not tilted for imaging purposes, and tilting the reference beam enables occlusion-free lateral scanning. Therefore, because multiple images are used for focusing, there is no need to stop along the z-direction, and the sample can be laterally scanned while simultaneously and continuously adjusting the focal length of the sample without occlusion of 3D features caused by viewing at a tilted angle. Focusing during lateral scanning is just one example of the operations that embodiments of this disclosure may provide, and many other operations are also provided.

[0017] Embodiments may utilize filters such as spatial filters. Using spatial filters allows for more efficient and / or effective determination of the interference pattern's location.

[0018] For the purposes of this disclosure, expressions such as “location of interference pattern” include, but are not limited to, determining the location of the center / peak of the interference pattern and / or mapping the fitting function to the interference function.

[0019] Figure 1A shows a simplified block diagram of a characterization system 100 according to one or more embodiments of the present disclosure.

[0020] The characterization system 100 includes an optical subsystem 102 configured to acquire one or more images from a sample 104, and a controller 108 that is communicatively coupled to the optical subsystem 102.

[0021] Therefore, one or more processors 110 of the controller 108 may perform any of the various process steps described throughout this disclosure. For example, one or more processors 110 of the controller 108 may determine the location of an interference pattern on an image and focus on an optical subsystem based on the location of the interference pattern. For example, focusing (i.e., instructing to focus) may include adjusting at least one of the sample positioning stage 106 that adjusts the position of the sample 104, a group of optical elements, or the entire optical subsystem 102. An example of an interference pattern 302 is shown in Figure 3A. The group of optical elements may, but are not limited to, lenses such as objective lenses, beam splitters, and reference elements.

[0022] Figure 1B shows a simplified schematic diagram of an optical subsystem 102 according to one or more embodiments of the present disclosure.

[0023] In one embodiment, Figure 1B shows an exemplary white light interferometer configuration of an optical subsystem 102, comprising a measuring arm 146 associated with a sample 104 and a reference arm 148 associated with a reference element 144.

[0024] In embodiments, the reference element 144 is any element known in the art for aligning the optical axis of a beam. For example, the reference element includes, but is not limited to, a reflective element (e.g., a mirror, a beam splitter, etc.) or another modulation element (e.g., an optical lens, an optical grating, etc.). For example, as shown in Figure 1B, the reference element 144 may be a reflective reference element (e.g., a mirror) positioned at an angle (α) and tilting the optical axis of the reference beam 150 with respect to the optical axis of the measurement beam 140.

[0025] In one embodiment, the optical subsystem 102 includes an illumination source 114 configured to generate an illumination beam 116. In another embodiment, the characterization system 100 includes an illumination path 118 which includes one or more components (e.g., an illumination lens 126) for oriented the illumination beam 116 toward the sample 104.

[0026] In one embodiment, the optical subsystem 102 comprises a focusing path 120 including one or more components (e.g., a focusing lens 130 and / or a spatial filter 132) for collecting light from the sample 104. Note that terms such as "illumination," "light," "beam," and "illumination beam" are used interchangeably throughout this disclosure.

[0027] In one embodiment, the optical subsystem 102 includes at least one detector 124 configured to capture at least a portion of the detectable light 122 from the focusing path 120. For example, the detector 124 may receive an image including interference patterns. The detectable light 122 as used herein includes a portion of the illumination directed towards the detector 124, and also includes illumination emitted from the sample 104.

[0028] In embodiments, the detector 124 is a multi-pixel detector (e.g., a camera, a 2D detector, etc.). For example, the detector 124 includes, but is not limited to, a photodiode array (PDA), a charge-coupled device (CCD), a complementary metal-oxide-semiconductor (CMOS) device, a time-delay integral (TDI) detector, a line scanning detector, a photomultiplier tube (PMT), an avalanche photodiode (APD), and the like.

[0029] In an embodiment, the optical subsystem 102 includes a sample positioning stage 106 configured to adjust the focal length relative to the sample 104. For example, the focal length may be adjusted by adjusting the position of the sample. For example, Figure 1B shows the sample positioning stage 106 for adjusting the position of the sample 104 along any dimension, such as, but not limited to, the lateral position in the x and / or y directions, the axial position along the z direction, tip, and inclination. Furthermore / or, in an embodiment, the optical subsystem may be configured to adjust the focal length by adjusting the measurement beam 140 and the reference beam 150 via optical elements (e.g., an objective lens 134).

[0030] Although not shown, in the case of transverse scanning, the optical subsystem 102 may include one or more scanning optical elements suitable for scanning beams 140, 150 across the entire sample 104. However, it should be noted that transverse scanning can also be performed additionally / alternatively by moving the sample 104 on the sample positioning stage 106.

[0031] In embodiments, the optical subsystem 102 may be configured to perform selective shielding of the reference beam 150 in order to receive a secondary image without interference patterns 302. For example, the optical subsystem 102 may include a shutter (not shown) or beam deflector (e.g., a movable mirror, a movable lens) for selectively blocking (e.g., absorbing, deflecting, etc.) the reference beam 150 in the reference arm 148 from reaching the detector 124 during measurement / imaging. Thus, interference patterns 302 from the reference beam 150 can be repeatedly removed and added for dual-use imaging. For example, when interference patterns 302 are blocked, the clarity of the secondary image may be improved, and when added / unblocked, the interference patterns 302 in the image can be used for focusing purposes. For example, the reference beam 150 may be configured to be unblocked once per image / frame cycle and / or once every few images / frames for focusing the sample 104 during lateral scanning. In such a configuration, the detector 124 used for capturing the secondary image may be the same as the detector used for focusing (e.g., using an image with interference pattern 302), and vice versa. In the embodiment, selective blocking of the reference beam 150 may be considered a "fast switch." Such selective blocking may enable even faster operations, such as relatively fast autofocus or lateral scanning.

[0032] In this embodiment, instructions for focusing (i.e., adjusting the focus) of the sample 104 can be continuously performed during lateral scanning or the like.

[0033] In one embodiment, the optical subsystem 102 includes a beam splitter 136 configured to split the illumination beam 116 into a measurement beam 140 and a reference beam 150.

[0034] In one embodiment, the optical subsystem 102 includes a reference objective lens 142 configured to receive a reference beam 150 and direct it toward a reference element 144, and to receive reflected light from the reference element 144. Thus, the reference objective lens 142 (optional) and the reference element 144 may form a reference arm 148 of the optical subsystem 102. Similarly, the measuring beam 140 and the objective lens 134 (which may include, for example, a measuring objective lens) may form a measuring arm 146. As shown in the figure, the measuring arm 146 and the reference arm 148 overlap at least partially.

[0035] Figures 2A to 2C are a series of conceptual diagrams illustrating scanning coherence gating according to one or more embodiments of the present disclosure.

[0036] For the purposes of this disclosure, it should be noted that determining the "height" of sample 104 may also be referred to as determining the distance between sample 104 and the optical subsystem 102.

[0037] Figure 2A shows a conceptual diagram of a coherence region 210 determined by mutually coherent surfaces 212, 220 of the reference beam 202 and the measurement beam 204 in a sample 104, according to one or more embodiments of the present disclosure.

[0038] The effective interference region on sensor (L)206 is defined by the coherence length (l c Based on 208. Coherence length (l c )206 is based on wavelength (λ) and spectral width (Δλ).

[0039] Coherence length (l c )208 can be found using Equation 1.

number

[0040] The effective interference region on sensor (L)206 is calculated using Equation 2.

number

[0041] In the case of low-coherence light, the coherence length (l c )208 is relatively short, resulting in a relatively narrow effective interference region on sensor (L)206.

[0042] In the case of a flat sample 104, the effective interference region on sensor (L) 206 corresponding to the interference pattern on the sensor moves in the x-axis direction based on the sample 104 moving in the z-axis direction.

[0043] Figure 2B shows a conceptual diagram of a coherence region 210 and a second coherence region 216 between a reference beam 202 and a measurement beam 204 in a sample 104 including a raised feature, according to one or more embodiments of the present disclosure.

[0044] In one embodiment, a raised feature (e.g., a bump) 214 of the sample 104 may create a second effective coherence region on the sensor (L) 214. The raised feature causes the second coherence region 216 to rise in the z direction. Other coherence regions of interference may exist depending on the varying heights of the sample 104.

[0045] Figure 2C shows a conceptual diagram of a coherence region 218 between a reference beam 202 and a measurement beam 204 in a sample 104 including a translucent layer, according to one or more embodiments of the present disclosure.

[0046] For example, one or more translucent layers (e.g., a deposited substrate layer, or another layer or coating) may produce coherence regions 218 with corresponding interference patterns on the image. These coherence regions 218 may depend on the thickness of the layer. For the purposes of this disclosure, it should be noted that translucent layers include not only layers that are completely transparent or nearly completely transparent, but also layers that are at least partially transparent.

[0047] Therefore, one or more layers can be identified using various corresponding interference patterns 302 generated from the coherence region (e.g., coherence region 218).

[0048] Figure 2D shows a conceptual diagram of a coherence surface 220 for illustrating resolution and sensitivity according to one or more embodiments of the present disclosure.

[0049] Resolution is determined by the effective interference region on sensor (L)206 and the coherence length (l c )208 can be characterized by the above equations 1 and 2 for determining 208.

[0050] The sensitivity is determined based on the inclination angle (α) of the reference beam 202.

number

[0051] Let's consider the case where each pixel is 1.15 microns in size and α is 2 degrees.

[0052] In this case, the following holds true:

number

[0053] Thus, a change in height (Δz) of 10 microns results in a measurable shift (Δx) of 250 pixels in the interference pattern of the received image. Furthermore, by reverse calculation, the change in height (Δz) of sample 104 can also be determined based on the measurable shift Δx. An example of the measurable shift Δx is shown as the measurable shift Δx308 between interference pattern 302a and interference pattern 302b in Figure 3B.

[0054] Figure 3A shows an image 300 of a target step including a calibrated focal position 306 according to one or more embodiments of the present disclosure. Note that the image 300 of the target step includes two interference patterns 302, each of which corresponds to a different region of the sample 104 having its own unique height.

[0055] The target step difference represents an 8-micron change in height, corresponding to a difference of approximately 200 pixels between the positions of interference patterns 302a and 302b in the initially received image 300. This difference creates a correlation of approximately 0.04 microns per pixel between the height of the sample and the pixel positions of interference patterns 302a and 302b.

[0056] In one embodiment, the sample height may be dynamically changed with respect to the calibrated focal plane (i.e., focal position) of the optical subsystem 102 by calibrating the focal position. For example, multiple images along the z-axis of a reference sample (e.g., a planar sample) may be acquired until the sample is in focus. Furthermore, the position of the interference pattern 302 on the detector 124 (e.g., a sensor) at that focal length may correspond to the calibrated focal position 306.

[0057] An example of a focusing method is shown in Figure 6. Such a method may include various steps, such as receiving a calibrated focal position 306 and determining the difference 304 between the calibrated focal position 306 and the interference pattern 302 on the image. For example, this difference may be the aforementioned Δx, which is included in, corresponds to, or derived from it.

[0058] Figure 3B shows an amplitude image 310 derived from image 300 of the interference pattern 302 of the target step in Figure 3A, according to one or more embodiments of the present disclosure. For example, image 310 may be a filtered or processed version of image 300 configured to enable tracking of interference patterns 302a, 302b.

[0059] Figure 4 shows a simplified schematic diagram of an optical subsystem 102 comprising an external Mach-Zehnder interferometer configuration according to one or more embodiments of the present disclosure.

[0060] In an embodiment, the optical subsystem 102 within the external Mach-Zehnder interferometer configuration includes a delay line 404. The delay line may comprise one or more (e.g., four) reflective surfaces (e.g., mirrors, beam splitters, etc.). For illustrative purposes, the reference element 144 is shown with the reference beam oriented substantially perpendicularly; however, in an embodiment, the reference element 144 aligns the reference beam so that it is tilted (e.g., at an angle α) relative to the measurement beam in the sample.

[0061] In one embodiment, the optical subsystem 102 within the external Mach-Zehnder interferometer configuration comprises an additional beam splitter 136 and / or a tube lens 402. The tube lens 402 can collimate the reference beam.

[0062] Figure 5 shows a simplified schematic diagram of an optical subsystem 102 comprising an interferometer configuration within an object according to one or more embodiments of the present disclosure.

[0063] In one embodiment, the optical subsystem 102 is an interferometer configuration in the objective lens 134, comprising a reference element that tilts the reference beam near and / or behind the objective lens 134.

[0064] In one embodiment, the optical subsystem 102 is an interferometer configuration comprising a tube lens 402.

[0065] In one embodiment, the optical subsystem 102 is an intra-objective interferometer configuration comprising a beam splitter positioned after the objective lens 134 along the propagation direction of the illumination beam 116.

[0066] Figure 6 shows a flowchart illustrating the steps performed in Method 600 according to one or more embodiments of the present disclosure.

[0067] In step 602, the position of the interference pattern 302 (e.g., fringe pattern) is compared to a nominal position at a known height (e.g., calibrated focal position 306).

[0068] In step 604, the position of the interference pattern 302 is converted to a height based on a comparison with the nominal position in step 602.

[0069] In step 606, focusing is indicated by adjustment of at least one of the sample position or optical elements. Focusing is based on the transformation of the interference pattern 302 in step 604. For example, the sample position in the z direction may be adjusted using the sample positioning stage 106 based on the position of the interference pattern 302. For example, the sample position may be adjusted during lateral scanning of the sample 104 to maintain focus (e.g., autofocus). As another example, optical elements such as the objective lens may be adjusted (e.g., moved, distorted, etc.) so that the focal length of the optical subsystem 102 moves along the z direction.

[0070] In step 608, the next image is captured. For example, another image of sample 104 may be received, and the above steps may be repeated.

[0071] In the embodiment, focusing may include determining the maximum height difference from a measurable calibrated focal position (determined by the number of pixels in the sensor and the inclination angle of the reference beam) and limiting the movement of the z-stage so as not to exceed the measurement range.

[0072] Figure 7 shows a flowchart illustrating the steps performed in Method 700 according to one or more embodiments of the present disclosure.

[0073] In step 702, fringe analysis is performed on sample 104. For example, the optical subsystem 102 may be configured to generate data for sample 104 (e.g., surface height topology) using white light interferometry based on interference patterns 302 received during lateral scanning (e.g., including the “fringe” pattern of the object to be analyzed) and to characterize sample 104.

[0074] In step 704, features corresponding to the interference pattern 302 are identified. For example, features may include, but are not limited to, variations in the surface height of the sample such as bumps, defects, steps, solderable components, other electrical components, and / or other features.

[0075] In step 706, the height of the feature is determined.

[0076] In step 708, the scanning distance is determined based on the interference width. For example, a feature may be scanned along the z, y, and / or x axes.

[0077] In step 710, the following image is acquired. For example, another image of sample 104 may be received.

[0078] Figure 8 shows a flowchart illustrating the steps performed in Method 800 according to one or more embodiments of the present disclosure.

[0079] In step 802, the image is received. For example, ambiguous (i.e., unwrapped) phase data from a scanning microscope may be received due to different imaging methods.

[0080] In step 804, an off-axis white light interferometry (WLI) image is received, for example, via the optical subsystem 102.

[0081] In step 806, a fringe analysis is performed on the image received in step 804. For example, a fringe analysis may be performed on the fringe band of interference pattern 302 that corresponds to 1 / 3 (and / or more than 1 / 3) of the clear range of the holography. For example, the clear range of the holography may be based on (and / or equal to) the wavelength used when acquiring the image in step 802. Therefore, the unwrapping process may be improved by analyzing and using the fringe band that is most likely to cause errors in the phase unwrapping process.

[0082] In step 808, the feature is identified.

[0083] In step 810, the following image is captured. Note that steps 804 to 810 can be performed repeatedly and continuously, such as during a lateral scan configured to map the surface height topology of sample 104. Thus, all or part of sample 104 may be inspected.

[0084] In step 812, the height (e.g., rough height) can be determined across the entire field of view (FOV). For example, the height can be determined across the entire FOV of sample 104.

[0085] In step 814, ambiguous holographic data is unwrapped. For example, a scanning microscope phase map may be unwrapped based on surface height topology.

[0086] Figure 9 shows a flowchart illustrating the steps performed in Method 900 using a bandpass filter 904 according to one or more embodiments of the present disclosure.

[0087] In the embodiment, the image (e.g., image 300) may be adjusted (e.g., filtered) to improve the analysis of the interference pattern 302.

[0088] In the first step, an image 902 of sample 104 is received. For example, the image may be configured to be captured by a detector 124.

[0089] In the second step, a bandpass filter is used to generate an envelope for the interference pattern 302, as shown in Figure 908. The location of the interference pattern 302 is considered to be the center / vertex of the interference pattern envelope. Alternatively, and / or in addition to this, the location of the interference pattern 302 may be determined using a fitting function (e.g., any fitting function such as a Gaussian fitting function) that fits the envelope near the vertex. Conceptually, the bandpass filter 904 may filter the portion of the power spectrum 906 shown in the figure.

[0090] For example, a physical bandpass filter and / or a digital bandpass filter may be used to filter the image 902 received in the first step. The bandpass filter may be configured to remove noise, other unwanted frequencies, and / or features from the image. The physical bandpass filter may be a physical device such as a filter wheel placed in front of the detector 124 of the optical subsystem 102, and the digital bandpass filter may be based on an image processing algorithm known in the art for filtering images.

[0091] Using a bandpass filter as a filter provides a useful tool for analyzing interference patterns, enabling more accurate analysis of these patterns. Removing noise makes it easier to identify and analyze interference patterns. Furthermore, bandpass filters can be used to identify one or more layers within an image, such as one or more translucent layers. This can contribute to structural analysis of a sample, including the identification of defects and other features. The filtered interference pattern can be generated using the inverse Fourier transform (IFT), a mathematical operation that transforms the frequency-domain representation of a signal into its spatial-domain representation. Image 908 can be generated using the filtered interference pattern, which is available for further analysis.

[0092] Figure 10 shows simplified images 1000, 1002 of a bump feature 1004 during a lateral scan according to one or more embodiments of the present disclosure, which may be used in a phase map unwrapping process (see, for example, Figures 8 and / or 9). In the embodiment, features within a region of interest (ROI) are tracked during the lateral scan.

[0093] Image 1000 shows a bump feature 1004 during transverse scanning in the x-direction. Image 1000 may be generated by the optical subsystem 102 using an off-axis configuration. Image 1000 may include an interference pattern 302e generated by the interference of the reference beam 150 and the measurement beam 140.

[0094] The second image 1002 shows the same bump feature 1006 at different locations during a lateral scan. In the embodiment, feature detection may occur when a feature enters an ROI. As shown in the figure, the bump feature generates an interference pattern 302f. If an interference pattern 302f occurs in a specific region of the image (e.g., an ROI), as in image 1002, feature registration may be determined. The registration is stored in memory 112 and used to map features of the sample 104. For example, the region of interest may be defined as a distance (e.g., pixel distance) (e.g., 1 / 3 of the wavelength) corresponding to a change in height equal to (and / or greater than) 1 / 3 of the ambiguous unwrapped range.

[0095] Figures 11A and 11B show an analysis of multi-noise spatial frequency images that can be generated by periodic features 1102 (e.g., bumps).

[0096] In the embodiment, the image is filtered to narrow the size of the spatial filter window (which may be defined, for example, by the area of ​​the spatial spectrum (2D FFT)). For example, the spatial filter image may be generated from an image of sample 104 (e.g., 300). An example of the location of a physical spatial filter component is shown as the focusing component 132 in Figure 1B, which may include a spatial filter.

[0097] Figure 11A shows a demodulated image 1100 of a periodic feature 1102 and an interference pattern 302 according to one or more embodiments of the present disclosure. For example, image 1100 may be generated by demodulating an initially captured image with a bandpass filter applied.

[0098] Figure 11B shows a filtered image 1110 after applying a narrower bandpass filter (compared to Figure 11A) to demodulate the interference pattern 302 according to one or more embodiments of the present disclosure. As a result, the interference pattern 302 in Figure 11B is a demodulated fringe pattern that can be more easily distinguished from periodic features.

[0099] In this embodiment, by scanning the sample 104 laterally and sequentially acquiring images (at an appropriate frame rate), it is possible in principle to reconstruct a height profile if the contrast of the interference signal is sufficiently high, and to sufficiently separate it from the spatial frequency of periodic features on the sample.

[0100] In one embodiment, the controller 108 may be configured to generate longitudinal scan data (e.g., effective longitudinal scan data). For example, the longitudinal scan data may be three-dimensional data.

[0101] In embodiments, the analysis of the image for the purpose of determining the interference pattern 302 may be limited to one or more regions. This can reduce the computational cost of the analysis, thereby further speeding up operations such as focusing and lateral scanning of the sample 104. For example, the determination of the location of the interference pattern 302 may be limited to a selected portion of the image. The selected portion may be, but is not limited to, any portion of the image, such as a cropped portion using a pre-selected crop, or a portion containing the expected location of the interference pattern based on the likely location of the interference pattern 302. For example, the pre-selected crop may be 10% or less (e.g.), so that the outermost 10% on each side of the image is not analyzed.

[0102] Refer again to Figures 1A and 1B to further describe the embodiments of the various components.

[0103] In an embodiment, the illumination path 118 includes one or more illumination lenses 126 for oriented the illumination beam 116 from the illumination source 114 to the sample 104. Furthermore, the illumination lenses 126 may be positioned to relay one or more field planes or pupil planes to a position within the illumination path 118. The illumination path 118 may further include one or more illumination adjustment components 128 suitable for modifying and / or adjusting the illumination beam 116. The illumination adjustment components 128 may, but are not required to be, positioned on the field planes and / or pupil planes within the illumination path 118. For example, one or more illumination adjustment components 128 may, but are not limited to, illumination aperture diaphragms, illumination field diaphragms, one or more polarizers, one or more compensators, one or more filters, one or more beam splitters, one or more diffusers, one or more homogenizers, one or more apodizers, one or more beam shapers, one or more mirrors, one or more lenses, and / or one or more masks.

[0104] In one embodiment, the focusing path 120 includes one or more focusing lenses 130 for directing detectable light 122 from the sample 104 to the detector 124. In another embodiment, the focusing path 120 includes one or more focusing adjustment components 132 suitable for correcting and / or adjusting the detectable light 122. For example, one or more focusing adjustment components 132 may include, but are not limited to, one or more polarizers, one or more filters, one or more beam splitters, one or more diffusers, one or more apodizers, or one or more beam shapers.

[0105] It should be noted that one or more components of the characterization system 100 may be communicatively coupled to various other components of the characterization system 100 in any manner known in the art. For example, one or more processors 110 may be communicatively coupled to each other and to other components via wired (e.g., copper wire, fiber optic cable, etc.) or wireless connections (e.g., RF coupling, IR coupling, WiMAX, Bluetooth, 3G, 4G, 4G LTE, 5G, etc.). As another example, a controller 108 may be communicatively coupled to one or more components of the characterization system 100 via any wired or wireless connection known in the art.

[0106] In one embodiment, one or more processors 110 may include any one or more processing elements known in the art. In this context, one or more processors 110 may include any microprocessor type device configured to execute software algorithms and / or instructions. In one embodiment, one or more processors 110 may consist of a desktop computer, a mainframe computer system, a workstation, an image computer, a parallel processor, or other computer system (e.g., a networked computer) configured to run a program configured to operate the characterization system 100, as described throughout this disclosure. It should be understood that the steps described throughout this disclosure may be performed by a single computer system or multiple computer systems. Furthermore, it should be understood that the steps described throughout this disclosure may be performed by any one or more of the one or more processors 110. In general, the term “processor” may be broadly defined to include any device having one or more processing elements that execute program instructions from memory 112. Furthermore, several different subsystems of the characterization system 100 (e.g., optical subsystem 102, interferometer, controller 108, user interface, etc.) may include processors or logic elements suitable for performing at least some of the steps described throughout this disclosure. Therefore, the above description should not be construed as an limitation to this disclosure, but merely as an example.

[0107] The memory 112 may include any storage medium known in the art that is suitable for storing program instructions executable by one or more associated processors 110 and data received from the characterization system 100. For example, the memory 112 may include a non-temporary memory medium. For example, the memory 112 may include, but is not limited to, ROM, RAM, magnetic or optical memory (e.g., disks), magnetic tape, solid-state drives, etc. Furthermore, it should be noted that the memory 112 may be housed in a controller housing common to one or more processors 110. In alternative embodiments, the memory 112 may be located remotely with respect to the physical location of the processors 110, controller 108, etc. In another embodiment, the memory 112 holds program instructions for causing one or more processors 110 to perform various steps described through this disclosure.

[0108] In one embodiment, the user interface is communicatively coupled to a controller 108. The user interface includes, but is not limited to, one or more desktops, tablets, smartphones, smartwatches, etc. In another embodiment, the user interface includes a display used to display data from the characterization system 100 to the user. The display of the user interface may include any display known in the art. For example, the display may include, but is not limited to, a liquid crystal display (LCD), an organic light-emitting diode (OLED) based display, or a CRT display. Those skilled in the art will recognize that any display device that can be integrated with the user interface is suitable for implementation of the disclosure. In another embodiment, the user may input selections and / or commands in response to data displayed to the user via a user input device of the user interface.

[0109] All methods described herein may include storing the results of one or more steps of an embodiment of the method in memory. The results may include any results described herein and may be stored in any manner well known in the art. The memory may include any memory described herein or any other suitable storage medium well known in the art. After the results are stored, they may be accessed in memory, used by any embodiment of the method or system described herein, formatted for display to a user, and used by another software module, method, or system, etc. Furthermore, the results may be stored “permanently,” “semi-permanently,” “temporarily,” or for a certain period of time. For example, the memory may be RAM, and the results do not necessarily have to persist indefinitely in memory.

[0110] Each of the embodiments of the methods described above is further intended to include any other step(s) of any other method(s) described herein. In addition, each of the embodiments of the methods described above may be carried out by any of the systems described herein.

[0111] Those skilled in the art will recognize that the components, operations, devices, objects, and accompanying descriptions described herein are used as examples to clarify concepts, and that various configuration modifications are intended. Therefore, as used herein, the specific embodiments and accompanying discussions described are intended to represent their more general class. In general, the use of a particular embodiment is intended to represent that class and should not be considered as limiting the exclusion of specific components, operations, devices, and objects.

[0112] As used herein, directional terms such as “vertical,” “lateral,” “top,” “bottom,” “over,” “under,” “upper,” “upward,” “lower,” “down,” and “downward” are intended to provide relative positions for illustrative purposes and not to specify an absolute reference frame. Various modifications to the embodiments described will be apparent to those skilled in the art, and the general principles defined herein may apply to other embodiments.

[0113] With regard to the use of substantially any plural and / or singular terms herein, a person skilled in the art may interpret them from plural to singular and / or singular to plural as appropriate to the context and / or use. Various singular / plural permutations are not explicitly listed herein for clarity.

[0114] The subject matter described herein may include different components that are contained within or connected to other components. Such described architectures are merely illustrative, and it should be understood that many other architectures can be implemented to achieve the same function. Conceptually, any arrangement of components to achieve the same function is effectively “associated” to achieve the desired function. Thus, any two components in this specification combined to achieve a particular function can be considered “associated” with each other, and as a result, the desired function is achieved regardless of the architecture or intermediate components. Similarly, any two such associated components can also be considered “connected” or “joined” with each other to achieve the desired function, and any two components that may be so associated can be considered “joinable” with each other to achieve the desired function. Specific examples of joinable components include, but are not limited to, components that are physically joinable and / or physically interactable, and / or wirelessly interactable and / or wirelessly interacting, and / or logically interacting and / or logically interactable.

[0115] Furthermore, it should be understood that the present invention is defined by the appended claims. Generally, it will be understood by those skilled in the art that the terms used herein, and in particular in the appended claims (e.g., in the text of the appended claims), are generally intended to be “open” terms (for example, “including” should be interpreted as “including but not limited to,” “having” should be interpreted as “at least having,” and “includes” should be interpreted as “including but not limited to,” etc.). If a particular number of claim recitations are intended, such intent will be explicitly stated in the claims, and if there is no such statement, such intent will not exist, it will be understood by those skilled in the art. For example, to aid understanding, the following appended claims may include the use of the introductory phrases “at least one” and “one or more” to introduce the claim recitations. However, the use of such phrases should not be interpreted as meaning that the introduction of a claim description with the indefinite article "a" or "an" limits any particular claim containing the description thus introduced to an invention containing only one such description, even if the same claim contains the introductory phrase "one or more" or "at least one" and the indefinite article "a" or "an" (for example, "a" and / or "an" should generally be interpreted as meaning "at least one" or "one or more"). In addition, even if a specific number of descriptions in the introduced claim is explicitly stated, a person skilled in the art will recognize that such a description should generally be interpreted as meaning at least the number stated (for example, a description of only "two descriptions" without other modifiers usually means at least two descriptions or two or more descriptions).Furthermore, in examples where idiomatic expressions similar to "at least one of A, B, and C, etc." are used, such configurations are generally intended to be understood by those skilled in the art (for example, "a system having at least one of A, B, and C" is not limited to but includes systems having only A, only B, only C, A and B together, A and C together, B and C together, and / or systems having A, B, and C together, etc.). In examples where idiomatic expressions similar to "at least one of A, B, or C, etc." are used, such configurations are generally intended to be understood by those skilled in the art (for example, "a system having at least one of A, B, or C" is not limited to but includes systems having only A, only B, only C, A and B together, A and C together, B and C together, and / or systems having A, B, and C together, etc.). It will be further understood by those skilled in the art that substantially any separate word and / or phrase representing two or more alternative terms should be understood to take into account the possibility of including one of the terms, either of the terms, or both terms in the description, claims, or drawings. For example, the phrase "A or B" will be understood to include the possibilities of "A" or "B" or "A and B".

[0116] Many of the present disclosure and its associated advantages are to be understood from the foregoing description, and it will be clear that various modifications can be made to the form, structure, and arrangement of the components without departing from the disclosed subject matter or sacrificing all of its important advantages. The forms described are for illustrative purposes only, and the intent of the following claims is to encompass and include such modifications. Furthermore, it should be understood that the present invention is defined by the appended claims.

Claims

1. A characterization system that characterizes a sample using white light interferometry, An optical subsystem, A detector configured for multi-pixel imaging, A lighting source configured to generate an illumination beam, A beam splitter configured to split the illumination beam into a measurement beam and a reference beam, A reference element configured to tilt the optical axis of the reference beam with respect to the optical axis of the measurement beam, A sample positioning stage configured to adjust the sample position of the sample along the Z direction corresponding to the focal length of the optical subsystem, An optical subsystem comprising, A controller communicatively coupled to the detector and the sample positioning stage, wherein the controller comprises one or more processors, and the one or more processors are connected to the one or more processors The image of the aforementioned sample is received, The interference pattern of the aforementioned image is demodulated using a filter. Determine the position of the interference pattern on the aforementioned image. The system instructs the system to adjust the focus based on the position of the interference pattern. A controller configured to execute program instructions, wherein the focus adjustment includes adjusting at least one of the sample positioning stage or the optical elements of the optical subsystem, A characteristic evaluation system equipped with the following features.

2. The controller provides one or more processors with The characterization system according to claim 1, further configured to perform selective shielding of the reference beam in order to receive a secondary image without the interference pattern.

3. The characterization system according to claim 2, wherein the selective light shielding is configured to be performed repeatedly during lateral scanning in order to receive multiple secondary images.

4. The characteristic evaluation system according to claim 1, wherein determining the position of the interference pattern is limited to the selected portion of the image.

5. To instruct the focus adjustment based on the position of the interference pattern is to The characterization system according to claim 1, comprising instructing the focus adjustment based on the position of the interference pattern during lateral scanning of the sample in order to maintain focus.

6. The controller provides one or more processors with The characteristic evaluation system according to claim 1, further configured to generate longitudinal scanning data along the depth direction of the sample during lateral scanning of the sample.

7. To instruct the focus adjustment based on the position of the interference pattern is to The characterization system according to claim 1, comprising instructing the focus adjustment based on the position of the interference pattern in order to generate the surface height topology of the sample.

8. The controller provides the one or more processors to The characteristic evaluation system according to claim 7, further configured to execute a program instruction that unwraps a phase map based on the surface height topology.

9. The characterization system according to claim 8, wherein unwrapping the phase map based on the surface height topology includes unwrapping the phase map of a scanning microscope based on the surface height topology.

10. The controller provides the one or more processors to Receive the calibrated focal position, The difference between the calibrated focal position and the position of the interference pattern on the image is determined. The characteristic evaluation system according to claim 1, further configured to execute the aforementioned program instructions.

11. The characteristic evaluation system according to claim 10, wherein instructing the focus adjustment based on the position of the interference pattern includes instructing the focus adjustment based on the difference.

12. Receiving the image of the sample means The characterization system according to claim 1, comprising receiving the image of the sample during lateral scanning of the sample.

13. The characterization system according to claim 12, wherein the instruction for focus adjustment includes continuously instructing the focus adjustment for each received image so that the focus of the sample is continuously maintained during the lateral scanning of the sample.

14. The characteristic evaluation system according to claim 1, wherein the optical subsystem comprises an external interferometer configuration.

15. The characterization system according to claim 1, wherein the optical subsystem comprises an interferometer configuration such that the beam splitter is positioned behind the objective lens along the propagation direction of the illumination beam.

16. The characterization system according to claim 1, wherein the filter comprises at least one of a spectral filter or a spatial filter for generating a filtered interference pattern.

17. The characterization system according to claim 16, wherein at least one of the spectral filter or the spatial filter is a bandpass filter.

18. The characterization system according to claim 1, wherein the controller is further configured to execute program instructions causing one or more processors to identify one or more layers based on the interference pattern, and the one or more layers are semi-transparent.

19. The characterization system according to claim 1, wherein the one or more layers include one or more translucent layers.

20. It is a method, To provide an optical subsystem configured for characterizing a sample using white light interferometry, comprising: a reference element configured to tilt the optical axis of a reference beam with respect to the optical axis of a measurement beam; and a sample positioning stage configured to adjust the sample position of the sample along the Z-direction of the sample. Receiving an image of the aforementioned sample, Demodulating the interference pattern of the aforementioned image using a filter, Determining the position of the interference pattern on the aforementioned image, To instruct focus adjustment based on the position of the interference pattern, The focus adjustment includes adjusting at least one of the optical elements of the sample positioning stage or the optical subsystem, method.

21. The method according to claim 20, further comprising performing selective shielding of the reference beam in order to receive a secondary image without the interference pattern.

22. The method according to claim 21, wherein the selective light shielding is configured to be performed repeatedly during lateral scanning in order to receive multiple secondary images.

23. The method according to claim 20, wherein determining the position of the interference pattern is limited to a selected portion of the image.

24. To instruct the focus adjustment based on the position of the interference pattern is to The method according to claim 20, comprising instructing the focus adjustment based on the position of the interference pattern during the lateral scanning of the sample in order to maintain focus. 。

25. The method according to claim 20, further comprising generating longitudinal scanning data along the depth direction of the sample during the transverse scanning of the sample.

26. To instruct the focus adjustment based on the position of the interference pattern is to The method according to claim 20, comprising instructing the focus adjustment based on the position of the interference pattern in order to generate the surface height topology of the sample.

27. The method according to claim 26, further comprising unwrapping a phase map based on the surface height topology.

28. The method according to claim 27, wherein unwrapping the phase map based on the surface height topology includes unwrapping the phase map of a scanning microscope based on the surface height topology.

29. Receiving the calibrated focal position, The difference between the calibrated focal position and the position of the interference pattern on the image is determined. The method according to claim 20, further comprising:

30. The method according to claim 29, wherein instructing the focus adjustment based on the position of the interference pattern includes instructing the focus adjustment based on the difference.

31. Receiving the image of the sample means The method according to claim 20, comprising receiving the image of the sample during a lateral scan of the sample.

32. The method according to claim 31, wherein the instruction to adjust focus includes continuously instructing the adjustment for each received image so that the focus of the sample is continuously maintained during the lateral scanning of the sample.

33. The method according to claim 20, wherein the optical subsystem comprises an external interferometer configuration.

34. The method according to claim 20, wherein the method is carried out via an optical subsystem comprising an interferometer configuration within an objective lens such that the beam splitter is positioned after the objective lens.

35. The method according to claim 20, wherein the filter comprises at least one of a spectral filter or a spatial filter for generating a filtered interference pattern.

36. The method according to claim 20, wherein at least one of the spectral filter or spatial filter comprises a bandpass filter.

37. The method according to claim 20, further comprising identifying one or more layers based on the interference pattern.

38. The method according to claim 37, wherein the one or more layers include one or more translucent layers.

Images