White light interferometric inspection using tilted reference beam and spatial filtering

Abstract

Systems and methods for measuring characterization samples using white light interferometry are disclosed. Such systems and methods may include an optical subsystem. The optical subsystem may include a reference element configured to tilt an optical axis of a reference beam relative to an optical axis of a measurement beam, and a sample positioning stage configured to adjust a sample position of a sample along a Z-direction of the sample. Such systems and methods may include receiving an image of the sample. Such systems and methods may include demodulating an interference pattern of the image with a filter. Such systems and methods may include determining a location of the interference pattern on the image; and directing focus adjustment based on the position of the interference pattern.

Description

Technical Field

[0001] The present disclosure relates generally to white-light interferometry, and more particularly to white-light interferometry using a tilted reference beam relative to a measurement beam. Background Art

[0002] Inspection systems are used to inspect samples, such as printed circuit boards (PCBs), wafers, and the like. Samples can be inspected to generate data, such as three-dimensional (3D) data, surface height topology, and / or images of the sample for a variety of purposes. For example, the sample height or distance from the imaging system can be determined to properly focus on the sample or to unravel a blurred phase image of the sample. Various conventional methods exist for generating this data.

[0003] Conventional methods suffer from limitations such as, but not limited to, low throughput, presence of speckle, occlusions, and / or fixed sensitivity.

[0004] Conventional white light interferometry (WLI) methods use a broad spectral band of white light to scan the z-axis for nanometer-precision 3D measurements. The interferometer is typically positioned inside the objective in a Mirau or Michelson arrangement, where a small portion of the light is reflected back from the surface of a reference mirror. Features of the sample within the focal plane of the objective reflect or diffuse light, which interferes on the sensor with the light reflected from the reference mirror. As features are scanned in the z-direction, different areas of the sample are focused and out of focus (usually corresponding to the coherence plane) and interfere with the reference. Therefore, sensitivity is closely related to the coherence of the illumination source. In general, white light sources emit light that includes a broad spectrum, resulting in lower coherence and finer z-resolution. The challenge with conventional WLI is that scanning the sample along the z-direction to obtain the focus position limits the throughput of the system.

[0005] In laser triangulation, a laser line illuminates a sample from a certain angle and is reflected to a sensor at an opposite angle. Due to the angle, reflections from different heights will illuminate the sensor at different coordinates. The difference between the measured coordinates and the nominal coordinates is measured, and the focus is dynamically corrected based on the calculated difference. However, laser triangulation can suffer from speckle caused by the inherent high coherence and low dynamic range associated with monochromatic light, which is susceptible to the sample's spectral response.

[0006] Therefore, it would be advantageous to provide a system and method that overcomes the challenges described above. Summary of the Invention

[0007] According to one or more illustrative embodiments of the present disclosure, a characterization system is disclosed. In one illustrative embodiment, the system includes an optical subsystem and a controller. In another illustrative embodiment, the optical subsystem includes a detector, an illumination source, a beam splitter, a reference element, and a sample positioning stage. In another illustrative embodiment, the controller is communicatively coupled to the detector and the sample positioning stage. In another illustrative embodiment, the controller includes one or more processors configured to receive an image of the sample, demodulate an interference pattern of the image using a filter, determine a location of the interference pattern on the image, and guide focus adjustment based on the location of the interference pattern.

[0008] According to one or more illustrative embodiments of the present disclosure, a method is disclosed. In one illustrative embodiment, the method includes providing an optical subsystem configured for characterizing a sample using white light interferometry. In another illustrative embodiment, the optical subsystem includes a reference element configured to tilt an optical axis of a reference beam relative to an optical axis of a measurement beam, and a sample positioning stage configured to adjust a sample position of the sample along a z-direction of the sample. In another illustrative embodiment, the method includes receiving an image of the sample, demodulating an interference pattern of the image using a filter, determining a position of the interference pattern on the image, and guiding a focus adjustment based on the position of the interference pattern.

[0009] It should be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and do not necessarily limit the invention as claimed. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the general description, serve to explain the principles of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Those skilled in the art may better appreciate the numerous advantages of the present disclosure by referring to the accompanying drawings.

[0011] Figure 1A is a simplified block diagram of a characterization system according to one or more embodiments of the present disclosure.

[0012] Figure 1B is a simplified schematic diagram of an optical subsystem according to one or more embodiments of the present disclosure.

[0013] Figure 2A is a conceptual diagram of a coherence region between a reference beam and a measurement beam at a sample according to one or more embodiments of the present disclosure.

[0014] Figure 2B is a conceptual diagram of a coherence region between a reference beam and a measurement beam at a sample containing raised features, according to one or more embodiments of the present disclosure.

[0015] Figure 2C is a conceptual diagram of a coherence region between a reference beam and a measurement beam at a sample including a semi-transparent layer according to one or more embodiments of the present disclosure.

[0016] Figure 2D is a conceptual diagram of a coherence plane between a reference beam and a measurement beam to illustrate resolution and sensitivity according to one or more embodiments of the present disclosure.

[0017] Figure 3A is an image of a step target including a calibrated focus position according to one or more embodiments of the present disclosure.

[0018] Figure 3B According to one or more embodiments of the present disclosure Figure 3A Amplitude image derived from an image of a step-shaped target.

[0019] Figure 4 is a simplified schematic diagram of an optical subsystem including an external Mach-Zehnder interferometer configuration according to one or more embodiments of the present disclosure.

[0020] Figure 5 is a simplified schematic diagram of an optical subsystem including an interferometer-in-objective configuration according to one or more embodiments of the present disclosure.

[0021] Figure 6 is a flowchart illustrating steps performed in a method according to one or more embodiments of the present disclosure.

[0022] Figure 7 is a flowchart illustrating steps performed in a method according to one or more embodiments of the present disclosure.

[0023] Figure 8 is a flowchart illustrating steps performed in a method according to one or more embodiments of the present disclosure.

[0024] Figure 9 is a flow chart illustrating steps performed in a method of utilizing a bandpass filter according to one or more embodiments of the present disclosure.

[0025] Figure 10 is a simplified diagram of an image of a bump feature during a lateral scan as may be utilized in a phase map unwrapping process, according to one or more embodiments of the present disclosure.

[0026] Figure 11A is a demodulated image of periodic features and interference patterns according to one or more embodiments of the present disclosure.

[0027] Figure 11Bis a method for demodulating the interference pattern after applying a spatial filter with a narrower bandpass window according to one or more embodiments of the present disclosure. Figure 11A Filtered image of the same field of view in . DETAILED DESCRIPTION

[0028] The present disclosure has been particularly shown and described with respect to certain embodiments and specific features thereof. The embodiments described herein are to be considered illustrative rather than restrictive. Those skilled in the art will readily appreciate that various changes and modifications in form and details may be made without departing from the spirit and scope of the present disclosure. Reference will now be made in detail to the disclosed subject matter as illustrated in the accompanying drawings.

[0029] Embodiments of the present disclosure relate to characterizing a sample using interference patterns, wherein the interference pattern is generated using a tilted optical axis of a reference beam in a white-light interferometry configuration and filtered using a spatial filter to demodulate the interference pattern. For example, the interference pattern can be used to generate height, surface height topology, vertical scan data, and / or the like. For example, tilting the reference beam causes the interference pattern to change position along the x-axis as the sample moves along the z-axis. In this regard, a specific position of the interference pattern in an image of the sample directly corresponds to a specific height of the sample and / or a specific distance between the sample and the characterization system. Thus, determining the interference pattern position can enable operations such as, but not limited to, autofocusing during a lateral scan of the sample by comparing the interference pattern position with a (known) calibrated focus position of the characterization system.

[0030] In an embodiment of the present disclosure, the optical axis of the reference beam is tilted at an angle relative to the optical axis of the measuring beam at and / or near the sample (i.e., the beams are non-parallel relative to each other). In this regard, a coherence region is generated between the (tilted) reference beam and the measuring beam. The positions of the coherence regions of the measuring beam and the reference beam correspond to an interference pattern at the detector. In an embodiment, conceptually, the coherence region may be the region where the coherence plane of the (tilted) reference beam intersects the coherence plane of the measuring beam. For a flat sample, the coherence region varies laterally (i.e., in the x-direction and / or y-direction) depending on the height (i.e., z-direction position) of the sample as the sample moves in the z-direction (e.g., vertically). The coherence region may correspond to an interference pattern on an image of the sample. In this regard, a single image can be used to determine the height / distance of at least a portion of the sample.

[0031] Conventional methods for focusing a sample can present challenges. For example, focusing may require stopping the lateral movement of the sample to obtain multiple focused images scanned along the z-direction (e.g., depth direction) to determine the optimal focus of the sample. Alternatively, tilting the interferometer can be used to focus the sample, as disclosed in U.S. Patent No. 6,449,048, issued September 10, 2002, which is incorporated herein by reference in its entirety. Tilting the entire interferometer can (theoretically) reduce the need to scan in the z-direction. However, three-dimensional features of the sample viewed at an angle may cause occlusions. In addition, fringe projection techniques can use relatively large angles to increase sensitivity, which can cause large occlusions in the presence of tall features.

[0032] However, it should be noted that in embodiments of the present disclosure, the reference beam is tilted for imaging purposes, while the measurement beam is generally not tilted, allowing for unobstructed lateral scanning. In this regard, the sample can be scanned laterally while simultaneously and continuously adjusting its focus, without stopping to focus using multiple images along the z-direction, and without obstruction of three-dimensional features caused by viewing at an oblique angle. It should be noted that focusing during lateral scanning is merely an example of an operation that can be provided by embodiments of the present disclosure, and many other operations are provided.

[0033] Embodiments may utilize filters (eg, spatial filters). Utilizing spatial filters may more efficiently and / or effectively determine the location of the interference pattern.

[0034] For purposes of this disclosure, language of "the location of the interference pattern" and the like includes determining the location, such as, but not necessarily limited to, determining the center / peak of the interference pattern, mapping a fit function to the interference function, and / or the like.

[0035] Figure 1A A simplified block diagram illustrating a characterization system 100 in accordance with one or more embodiments of the present disclosure.

[0036] The characterization system 100 includes an optical subsystem 102 configured to acquire one or more images from a sample 104 and a controller 108 communicatively coupled to the optical subsystem 102 .

[0037] In this regard, the one or more processors 110 of the controller 108 may perform any of the various process steps described throughout this disclosure. For example, the one or more processors 110 of the controller 108 may determine the location of the interference pattern on the image and focus the optical subsystem based on the location of the interference pattern. For example, focusing (i.e., directing focus adjustment) may include adjusting at least one of the sample positioning stage 106, the group of optical elements, or the entire optical subsystem 102 used to adjust the position of the sample 104. Figure 3AAn example of an interference pattern 302 is shown in . The group of optical elements may be, but is not necessarily required to be or limited to, a lens (such as an objective lens and / or the like), a beam splitter, and a reference element.

[0038] Figure 1B A simplified schematic diagram illustrating optical subsystem 102 in accordance with one or more embodiments of the present disclosure.

[0039] In an embodiment, Figure 1B An example white light interferometer configuration of optical subsystem 102 is illustrated, including a measurement arm 146 associated with sample 104 and a reference arm 148 associated with reference element 144 .

[0040] In an embodiment, the reference element 144 is any element known in the art for guiding the optical axis of a light beam. For example, the reference element may include, but is not limited to, a reflective element (e.g., a mirror, a beam splitter, and the like), or another modulating element (e.g., an optical lens, a grating, and the like). For example, Figure 1B As shown in , reference element 144 can be a reflective reference element (eg, a mirror) positioned at an angle (α) to cause a tilt of the optical axis of reference beam 150 relative to the optical axis of measurement beam 140 .

[0041] In an embodiment, optical subsystem 102 includes an illumination source 114 configured to generate an illumination beam 116. In an embodiment, characterization system 100 includes an illumination path 118 including one or more components (eg, illumination lens 126) to direct illumination beam 116 to sample 104.

[0042] In one embodiment, the optical subsystem 102 includes a light collection path 120 that includes one or more components (e.g., a collection lens 130, a spatial filter 132, and / or the like) to collect light from the sample 104. It should be noted that as used throughout this disclosure, "illumination," "light," "light beam," "illumination beam," and the like may be interchangeable.

[0043] 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 light collection path 120. For example, the detector 124 can receive an image having an interference pattern thereon. As used herein, the detectable light 122 includes a portion of the illumination directed to the detector 124 and includes illumination emitted from the sample 104.

[0044] In one embodiment, the detector 124 is a multi-pixel detector (e.g., a camera, a 2D detector, and the like). For example, the detector 124 may include, but is not limited to, a photodiode array (PDA), a charge-coupled device (CCD), a complementary metal oxide semiconductor (CMOS) device, a time delay integration (TDI) detector, a line scan detector, a photomultiplier tube (PMT), an avalanche photodiode (APD), or the like.

[0045] In an embodiment, the optical subsystem 102 includes a sample positioning stage 106 configured to adjust the focus relative to the sample 104. For example, the focus can be adjusted by adjusting the position of the sample. Figure 1B A sample positioning stage 106 is described for adjusting the position of the sample 104 along any dimension (e.g., but not limited to, lateral position in the x-direction and / or y-direction, axially along the z-direction, tilt, tilt, or the like). In embodiments, the optical subsystem may alternatively and / or additionally be configured to adjust the focus of the measurement beam 140 and the reference beam 150 by adjusting them via optical elements (e.g., objective lens 134 or the like).

[0046] For lateral scanning, although not shown, the optical subsystem 102 may include one or more scanning optical elements suitable for scanning the beams 140, 150 across the sample 104. However, it should be noted that lateral scanning may also and / or alternatively be performed by moving the sample 104 with the sample positioning stage 106.

[0047] In embodiments, the optical subsystem 102 may be configured to selectively block the reference beam 150 to receive a secondary image without the interference pattern 302. For example, the optical subsystem 102 may include a shutter (not shown) or a beam deflector (e.g., an actuable mirror, an actuable lens) to selectively block (e.g., absorb, deflect, and the like) the reference beam 150 in the reference arm 148 from reaching the detector 124 during measurement / imaging. In this regard, the interference pattern 302 caused by the reference beam 150 may be repeatedly removed / added for dual-purpose imaging. For example, when the interference pattern 302 is blocked, the secondary image may have improved clarity, and when added / unblocked, the interference pattern 302 of the image may 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 to focus the sample 104 during a transverse scan. In this configuration, the detector 124 used to capture the secondary image can be the same detector used for focusing (e.g., using an image with the interference pattern 302), and vice versa. In embodiments, the selective blocking of the reference beam 150 can be considered "fast switching." This selective blocking can enable even faster operation, such as relatively fast autofocus and lateral scanning.

[0048] In an embodiment, focus adjustment (ie, focusing) of the guide sample 104 may be performed continuously, for example, during a lateral scan.

[0049] In an embodiment, the optical subsystem 102 includes a beam splitter 136 configured to split the illumination beam 116 into a measuring beam 140 and a reference beam 150 .

[0050] In one embodiment, the optical subsystem 102 includes a reference objective 142 configured to receive a reference beam 150 and direct it toward a reference element 144, and to receive light reflected from the reference element 144. In this regard, the reference objective 142 (although not necessarily required) and the reference element 144 can define a reference arm 148 of the optical subsystem 102. Similarly, the measurement beam 140 and the objective 134 (e.g., which can include a measurement objective) can define a measurement arm 146. As shown, the measurement arm 146 and the reference arm 148 at least partially overlap.

[0051] Figures 2A to 2C is a series of conceptual diagrams depicting scanning coherence gating in accordance with one or more embodiments of the present disclosure.

[0052] It should be noted that for the purposes of this disclosure, determining the “height” of the sample 104 may also refer to determining the distance between the sample 104 and the optical subsystem 102 .

[0053] Figure 2A A conceptual diagram illustrating a coherence region 210 defined at a sample 104 by planes 212 , 220 of mutual coherence of a reference beam 202 and a measuring beam 204 in accordance with one or more embodiments of the present disclosure.

[0054] The effective interference area (L) 206 on the sensor is determined by the coherence length (l c )208. Coherence length (l c )206 varies according to the wavelength (λ) and the spectral width (Δλ).

[0055] Coherence length (l c )208 is provided by Equation 1:

[0056]

[0057] The effective interference area (L) 206 on the sensor is given by Equation 2:

[0058]

[0059] For low coherence light, the coherence length (l c ) 208 is relatively short, resulting in a relatively narrow effective interference area (L) 206 on the sensor.

[0060] For a flat sample 104, the effective interference area (L) 206 on the sensor corresponding to the interference pattern on the sensor moves along the x-axis as the sample 104 moves in the z-axis.

[0061] Figure 2B A conceptual diagram illustrating a coherence region 210 and a second coherence region 216 between a reference beam 202 and a measurement beam 204 at a sample 104 including raised features, in accordance with one or more embodiments of the present disclosure.

[0062] In an embodiment, a raised feature (e.g., a bump) 214 of the sample 104 may cause a second effective coherence region (L) 214 on the sensor. The raised feature results in a second coherence region 216 that is higher in the z-direction. Depending on the various height differences of the sample 104, there may be other coherence regions that interfere.

[0063] Figure 2C A conceptual diagram illustrating a coherence region 218 between a reference beam 202 and a measurement beam 204 at a sample 104 including a semi-transparent layer, according to one or more embodiments of the present disclosure.

[0064] For example, one or more semi-transparent layers (e.g., a deposited substrate layer or any other layer or coating) can cause coherent regions 218 with corresponding interference patterns on the image. These coherent regions 218 can depend on the layer thickness. It should be noted that for the purposes of this disclosure, a semi-transparent layer includes a layer that is at least partially transparent, as well as a layer that is completely transparent or nearly completely transparent.

[0065] In this regard, various corresponding interference patterns 302 generated from such coherent regions (eg, coherent region 218) may be used to identify one or more layers.

[0066] Figure 2D A conceptual diagram illustrating a coherence plane 220 to illustrate resolution and sensitivity according to one or more embodiments of the present disclosure.

[0067] The resolution can be characterized by the above process 1 and equation 2 to determine the effective interference area (L) 206 on the sensor and the coherence length (l c )208.

[0068] The sensitivity is determined based on the tilt angle (α) of the reference beam 202:

[0069] Δz = Δxtan(α) (Equation 3)

[0070] Consider the example case where each pixel is 1.15 microns and α is 2 degrees.

[0071] In this case:

[0072]

[0073] In this way, a height change (Δz) of 10 microns causes a measurable shift (Δx) in the interference pattern of 250 pixels in the received image. Furthermore, the calculation can be reversed to determine the height change (Δz) of the sample 104 based on the measurable shift Δx. An example of a measurable shift Δx is given by Figure 3B A measurable offset Δx 308 between the interference pattern 302a and the interference pattern 302b is shown.

[0074] Figure 3A An image 300 of a step target including a calibrated focus position 306 in accordance with one or more embodiments of the present disclosure is illustrated. Note that the image 300 of the step target includes two interference patterns 302, each corresponding to a different region of the sample 104 having a unique height.

[0075] The step target exhibits an 8 micron height step variation corresponding to an approximately 200 pixel position difference in the interference patterns 302a, 302b as originally received in the image 300. This difference results in an approximately 0.04 micron per pixel correlation between sample height and pixel position of the interference patterns 302a, 302b.

[0076] In embodiments, the sample height can be dynamically actuated to a calibrated focal plane (i.e., focus position) of the optical subsystem 102 by calibrating the focus position. For example, multiple images along the z-axis can be acquired for a reference sample (e.g., a flat sample) until the sample is in focus. Furthermore, the position of the interference pattern 302 on the detector 124 (e.g., a sensor) at the focal length can correspond to the calibrated focus position 306.

[0077] For example, Figure 6 . This method may include various steps, such as receiving a calibrated focus position 306; and determining a difference 304 between the calibrated focus position 306 and the position of the interference pattern 302 on the image. For example, the difference may be, include, correspond to, or be derived from the previously described Δx.

[0078] Figure 3B Describe one or more embodiments of the present disclosure Figure 3A 302a, 302b.

[0079] Figure 4A simplified schematic diagram illustrating an optical subsystem 102 including an external Mach-Zehnder interferometer configuration in accordance with one or more embodiments of the present disclosure.

[0080] In one embodiment, the optical subsystem 102, configured as an external Mach-Zehnder interferometer, includes a delay line 404. The delay line may include one or more (e.g., four) reflective surfaces (e.g., mirrors, beam splitters, and the like). Although the reference element 144 is shown as directing a substantially perpendicular reference beam for simplicity of illustration, in one embodiment, the reference element 144 directs the reference beam such that it is tilted relative to the measurement beam (e.g., at an angle α) at the sample.

[0081] In an embodiment, the optical subsystem 102 in an external Mach-Zehnder interferometer configuration includes an additional beam splitter 136 and / or a tube lens 402. The tube lens 402 may collimate the reference beam.

[0082] Figure 5 A simplified schematic diagram illustrating an optical subsystem 102 including an interferometer-in-objective configuration in accordance with one or more embodiments of the present disclosure.

[0083] In an embodiment, the optical subsystem 102 is an intra-objective interferometer configuration that includes a reference element that tilts the reference beam at, near, and / or after the objective 134 .

[0084] In an embodiment, the optical subsystem 102 is an intra-objective interferometer configuration including a tube lens 402 .

[0085] In an embodiment, the optical subsystem 102 is an intra-objective interferometer configuration that includes a beam splitter positioned after the objective 134 along the propagation direction of the illumination beam 116 .

[0086] Figure 6 A flow chart illustrating steps performed in method 600 is illustrated in accordance with one or more embodiments of the present disclosure.

[0087] In step 602 , the position of the interference pattern 302 (eg, fringe pattern) is compared to a nominal position of known height (eg, calibrated focus position 306 ).

[0088] In step 604 , the position of the interference pattern 302 is converted to a height based on the comparison with the nominal position in step 602 .

[0089] In step 606, a focus adjustment is conducted by adjusting at least one of the sample position or an optical element. The focus adjustment is based on the shift in the interference pattern 302 in step 604. For example, the sample positioning stage 106 can be used to adjust the sample position in the z-direction based on the position of the interference pattern 302. For example, the sample position can be adjusted during a lateral scan of the sample 104 to maintain focus (e.g., autofocus). By way of another example, an optical element, such as an objective lens, can be adjusted (e.g., moved, twisted, and the like) such that the focal length of the optical subsystem 102 shifts along the z-direction.

[0090] In step 608, the next image is captured. For example, another image of the sample 104 may be received and the above steps repeated.

[0091] In an embodiment, focusing may include determining a maximum height difference from a calibrated focus position that may have been measured (determined by the number of sensor pixels and the reference beam tilt), and limiting the movement of the z stage to no more than the measured distance.

[0092] Figure 7 A flow chart illustrating steps performed in method 700 is illustrated in accordance with one or more embodiments of the present disclosure.

[0093] In step 702, fringe analysis is performed on the sample 104. For example, the optical subsystem 102 may be configured to characterize the sample 104 using white light interferometry to generate data (e.g., surface height topology) of the sample 104 based on the interference pattern 302 received during the lateral scan (e.g., including the "fringe" pattern to be analyzed).

[0094] In step 704, features are identified that correspond to the interference pattern 302. For example, features may include, but are not limited to, variations in surface height of the sample, such as bumps, defects, steps, solderable components, other electrical components, and / or any other features.

[0095] In step 706, the height of the feature is determined.

[0096] A scan distance is determined based on the interference width in step 708. For example, the feature can be scanned along the z-axis, the y-axis, and / or the x-axis.

[0097] In step 710, the next image is captured. For example, another image of the sample 104 may be received.

[0098] Figure 8 A flow chart illustrating steps performed in method 800 is illustrated in accordance with one or more embodiments of the present disclosure.

[0099] In step 802, an image is received. For example, scanning microscopy blurred (ie, unwrapped) phase data may be received, such as from a different imaging method.

[0100] In step 804 , an off-axis white light interferometry (WLI) image is received, for example, via the optical subsystem 102 .

[0101] In step 806, fringe analysis is performed on the image received in step 804. For example, fringe analysis may be performed on fringe bands of the interference pattern 302 corresponding to one-third (and / or greater than one-third) of the holographic unambiguous range. For example, the holographic unambiguous range may be based on (and / or equal to) the wavelength used when acquiring the image in step 802. In this regard, the fringe bands most likely to cause errors in the phase unwrapping process may be analyzed and used to improve the unwrapping process.

[0102] In step 808, features are identified.

[0103] In step 810, the next image is captured. It should be noted that steps 804-810 may be performed repeatedly and continuously, for example, during a lateral scan configured to map the surface height topology of the sample 104. In this regard, the entire sample 104 or a portion thereof may be examined.

[0104] In step 812 , a height (eg, a coarse height) is determined across the full field of view (FOV). For example, the height may be determined across the full FOV of the sample 104 .

[0105] In step 814, the holographic blur data is unfolded. For example, a scanning microscope phase map can be unfolded based on the surface height topology.

[0106] Figure 9 A flow chart illustrating steps performed in a method 900 utilizing a bandpass filter 904 is illustrated in accordance with one or more embodiments of the present disclosure.

[0107] In embodiments, an image (eg, image 300 ) may be adjusted (eg, filtered, etc.) to improve analysis of interference pattern 302 .

[0108] In a first step, an image 902 of the sample 104 is received. The image may be configured to be captured by the detector 124, for example.

[0109] In a second step, a bandpass filter is utilized to generate the envelope of the interference pattern 302 as shown in image 908. The location of the interference pattern 302 can be considered as the center / peak of the interference pattern envelope. Alternatively and / or in addition, a fit function (for example, any fit function such as a Gaussian fit function) that fits the envelope around the peak can be used to determine the location of the interference pattern 302. The bandpass filter 904 can conceptually filter the portion 906 of the power spectrum as shown.

[0110] For example, physical and / or digital bandpass filters can be used to filter the image 902 received in the first step. The bandpass filter can be configured to filter out noise, other undesirable frequencies, and / or features from the image. The physical bandpass filter can be a physical device (e.g., a filter wheel) placed in front of the detector 124 of the optical subsystem 102, and the digital bandpass filter can be based on an image processing algorithm known in the art that is configured to filter the image.

[0111] Using a bandpass filter as a filter can be a useful tool for analyzing interference patterns, allowing for more accurate analysis of the interference pattern. By filtering out noise, the interference pattern can be more easily identified and analyzed. Additionally, the bandpass filter can be used to identify one or more layers in the image, such as one or more semi-transparent layers. This can be useful for analyzing the structure of a sample, such as identifying defects or other features. The filtered interference pattern can be generated using an inverse Fourier transform (IFT), a mathematical operation that converts a frequency-domain representation of a signal into a spatial-domain representation. The filtered interference pattern can then be used to generate image 908, which can be used for further analysis.

[0112] Figure 10 The following describes one or more embodiments of the present disclosure as may be used in a phase diagram unwrapping process (e.g., see Figure 8 Simplified diagrams of images 1000, 1002 of bump features 1004 during a lateral scan utilized in and / or 9). In an embodiment, features located in a region of interest (ROI) are tracked during a lateral scan.

[0113] The first image 1000 illustrates a bump feature 1004 during a lateral scan in the x-direction. The first image 1000 can be generated by using an off-axis configuration of the optical subsystem 102. The image 1000 can include an interference pattern 302e generated by interference of the reference beam 150 and the measurement beam 140.

[0114] Second image 1002 illustrates the same bump feature 1006 in a different position during a lateral scan. In embodiments, feature detection may occur when the feature enters an ROI. As shown, the bump feature causes an interference pattern 302f to be generated. When interference pattern 302f is generated in a particular region of the image (e.g., the ROI), as shown by image 1002, the registration of the feature may be determined. The registration may be stored in memory 112 and used to map features of sample 104. For example, a region of interest may be defined as a distance (e.g., a pixel distance) corresponding to a height variation equal to (and / or greater than) one-third of the blur spread distance (e.g., one-third of a wavelength).

[0115] Figure 11A and 11B Analysis of a noisy spatial frequency image, such as may be caused by periodic features 1102 (eg, bumps and the like), may be illustrated.

[0116] In an embodiment, the image is filtered to reduce the size of the spatial filter window (e.g., as may be defined by the area of the spatial spectrum (two-dimensional FFT)). For example, a spatially filtered image may be generated from an image of sample 104 (e.g., 300). An example of the location of the physical spatial filter components is given by Figure 1B The light collecting component 132 in FIG. 1 is shown as including a spatial filter.

[0117] Figure 11A A demodulated image 1100 illustrating periodic features 1102 and interference pattern 302 in accordance with one or more embodiments of the present disclosure may be generated, for example, by demodulating an initially captured image by applying a bandpass filter.

[0118] Figure 11B The invention provides a method for applying a narrower bandpass filter (with Figure 11A ) to demodulate the filtered image 1110 after the interference pattern 302. In this regard, Figure 11B The interference pattern 302 in (which is a demodulated fringe pattern) can be more easily distinguished from periodic features.

[0119] In an embodiment, by transversely scanning the sample 104 and sequential image acquisition (at an appropriate frame rate), the height profile can in principle be reconstructed, provided that the contrast of the interference signal is high enough and can be well separated from the spatial frequency of the periodic features on the sample.

[0120] In one embodiment, the controller 108 may be configured to generate vertical scanning data (eg, effective vertical scanning data). For example, the vertical scanning data may be three-dimensional data.

[0121] In embodiments, analysis of an image for the purpose of determining interference pattern 302 may be limited to one or more regions. In this regard, analysis may be computationally less expensive, thereby further accelerating operations such as focusing and lateral scanning of sample 104. For example, determination of the location of interference pattern 302 may be limited to a selected portion of the image. The selected portion may be any portion, such as, but not necessarily limited to, a cropped portion of the image using a preselected crop, or the portion may include the location of an expected interference pattern based on the likely location of interference pattern 302. For example, the preselected crop may be 10% or less (or the like), such that the outermost 10% of the image on each side is not analyzed.

[0122] Reference again Figure 1A and 1B , describing embodiments of various components in additional detail.

[0123] In an embodiment, the illumination path 118 includes one or more illumination lenses 126 to direct the illumination beam 116 from the illumination source 114 to the sample 104. In addition, the illumination lenses 126 may be arranged to relay one or more field planes or pupil planes to a location within the illumination path 118. The illumination path 118 may further include one or more illumination adjustment components 128 adapted to modify and / or adjust the illumination beam 116. The illumination adjustment components 128 may, but are not required to, be positioned at the field planes and / or pupil planes in the illumination path 118. For example, the one or more illumination adjustment components 128 may include, but are not limited to, an illumination aperture stop, an illumination field stop, 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.

[0124] In one embodiment, the light collection path 120 includes one or more collection lenses 130 for directing the detectable light 122 from the sample 104 to the detector 124. In another embodiment, the light collection path 120 includes one or more collection light conditioning components 132 adapted to modify and / or condition the detectable light 122. For example, the one or more collection light conditioning 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.

[0125] It should be noted herein that one or more components of the characterization system 100 can be communicatively coupled to various other components of the characterization system 100 in any manner known in the art. For example, the one or more processors 110 can be communicatively coupled to each other and to other components via a wired (e.g., copper wire, fiber optic cable, and the like) or wireless connection (e.g., RF coupling, IR coupling, WiMax, Bluetooth, 3G, 4G, 4G LTE, 5G, and the like). By way of another example, the controller 108 can be communicatively coupled to one or more components of the characterization system 100 via any wired or wireless connection known in the art.

[0126] In one embodiment, the one or more processors 110 may include any one or more processing elements known in the art. In this sense, the one or more processors 110 may include any microprocessor-type device configured to execute software algorithms and / or instructions. In one embodiment, the one or more processors 110 may be composed of: a desktop computer, a mainframe computer system, a workstation, an image computer, a parallel processor, or other computer systems (e.g., networked computers) configured to execute programs configured to operate the representation system 100, as described throughout this disclosure. It should be recognized that the steps described throughout this disclosure may be implemented by a single computer system or alternatively multiple computer systems. In addition, it should be recognized that the steps described throughout this disclosure may be implemented on any one or more of the one or more processors 110. In general, the term "processor" may be broadly defined to encompass any device having one or more processing elements that execute program instructions from memory 112. Furthermore, the various subsystems of the characterization system 100 (e.g., the optical subsystem 102, the interferometer, the controller 108, the user interface, and the like) may include processors or logic elements adapted to perform at least some of the steps described throughout this disclosure. Therefore, the above description should not be construed as limiting the present disclosure, but is merely illustrative.

[0127] The memory 112 may include any storage medium known in the art suitable for storing program instructions executable by the associated one or more processors 110 and data received from the characterization system 100. For example, the memory 112 may include non-transitory storage media. For example, the memory 112 may include, but is not limited to, ROM, RAM, magnetic or optical storage (e.g., disk), tape, solid-state drive, and the like. It should be further noted that the memory 112 may be housed in a common controller housing with the one or more processors 110. In alternative embodiments, the memory 112 may be remotely located relative to the physical location of the processors 110, controller 108, and the like. In another embodiment, the memory 112 maintains program instructions for causing the one or more processors 110 to perform the various steps described throughout this disclosure.

[0128] In one embodiment, a user interface is communicatively coupled to the controller 108. The user interface may include, but is not limited to, one or more desktop computers, tablet computers, smartphones, smart watches, or the like. In another embodiment, the user interface includes a display for displaying data representing the 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 capable of being integrated with the user interface is suitable for implementation in the present disclosure. In another embodiment, the user may enter selections and / or instructions in response to data displayed to the user via a user input device of the user interface.

[0129] All methods described herein may include storing the results of one or more steps of the method embodiments in a memory. The result may include any result described herein and may be stored in any manner known in the art. The memory may include any memory described herein or any other suitable storage medium known in the art. After the result has been stored, the result may be accessed in the memory and used by anyone in the method or system embodiments described herein, formatted to display to the user, used by another software module, method or system, and the like. In addition, the result may be stored "permanently", "semi-permanently", "temporarily" or for a period of time. For example, the memory may be RAM, and the result may not necessarily remain in the memory indefinitely.

[0130] It is further contemplated that each of the embodiments of the method described above may include any other steps of any other method described herein. Additionally, each of the embodiments of the method described above may be performed by any of the systems described herein.

[0131] Those skilled in the art will recognize that, for the sake of conceptual clarity, the components, operations, devices, objects, and accompanying discussions described herein are used as examples, and various configuration modifications are contemplated. Therefore, as used herein, the specific examples set forth and the accompanying discussions are intended to represent their more general class. In general, the use of any specific example is intended to represent its class, and the omission of specific components, operations, devices, and objects should not be considered limiting.

[0132] As used herein, directional terms (such as "vertical," "lateral," "top," "bottom," "above," "below," "up," "upward," "down," "downwardly," and the like) are intended to provide relative positions for descriptive purposes and are not intended to specify an absolute reference frame. Various modifications to the described embodiments will be apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments.

[0133] Regarding the use of substantially any plural and / or singular terms herein, those skilled in the art can appropriately convert from the plural to the singular and / or from the singular to the plural depending on the context and / or application. For clarity, various singular / plural arrangements are not explicitly set forth herein.

[0134] The subject matter described herein sometimes illustrates different components that are contained within or connected to other components. It should be understood that such depicted architectures are merely exemplary, and in fact many other architectures that achieve the same functionality can be implemented. In a conceptual sense, any arrangement of components that achieve the same functionality is effectively "associated" so as to achieve the desired functionality. Therefore, any two components that are combined to achieve a specific functionality herein can be considered to be "associated" with each other so as to achieve the desired functionality, regardless of the architecture or intermediate components. Similarly, any two components that are so associated can also be considered to be "connected" or "coupled" to each other to achieve the desired functionality, and any two components that can be so associated can also be considered to be "coupleable" to each other to achieve the desired functionality. Specific examples of coupleable include, but are not limited to, physically compatible and / or physically interactive components, and / or wirelessly interactive and / or wirelessly interactive components, and / or logically interactive and / or logically interactive components.

[0135] In addition, it should be understood that the present invention is defined by the appended claims. Those skilled in the art will understand that, in general, the terms used herein and especially in the appended claims (e.g., the body of the appended claims) are generally intended to be "open" terms (e.g., the term "including" should be interpreted as "including but not limited to", the term "having" should be interpreted as "at least having", the term "includes" should be interpreted as "including but not limited to" and the like). Those skilled in the art will further understand that if a specific number of claim recitations is intended, such intention will be explicitly stated in the claims, and in the absence of such a statement, such intention does not exist. For example, to aid understanding, the claims below may contain the use of the introductory phrases "at least one" and "one or more" to introduce claim recitations. However, the use of such phrases should not be construed as implying that the introduction of a claim recitation by the indefinite article "a" or "an" limits any particular claim containing the introduced claim recitation to inventions containing only one such recitation, even when the same claim contains the introductory phrases "one or more" or "at least one" and an indefinite article (e.g., "a" or "an") (e.g., "a" and / or "an" should generally be construed to mean "at least one" or "one or more"); the same applies to the use of definite articles to introduce claim recitations. Furthermore, even if a specific number of introduced claim recitations is explicitly recited, those skilled in the art will recognize that such recitation should generally be construed to mean at least the recited number (e.g., the mere recitation of "two recitations" without other modifiers generally means at least two recitations, or two or more recitations). Furthermore, in those instances where conventional expressions similar to “at least one of A, B, and C, and the like” are used, such construction is generally contemplated in the sense that one skilled in the art would understand the conventional expressions (e.g., “a system having at least one of A, B, and C” would include, but is not limited to, systems having only A, only B, only C, both A and B, both A and C, both B and C, and / or both A, B, and C, and the like). In those instances where conventional expressions similar to “at least one of A, B, or C, and the like” are used, such construction is generally contemplated in the sense that one skilled in the art would understand the conventional expressions (e.g., “a system having at least one of A, B, or C” would include, but is not limited to, systems having only A, only B, only C, both A and B, both A and C, both B and C, and / or both A, B, and C, and the like). Those skilled in the art will further understand that virtually any transitional conjunction and / or phrase, whether in the description, claims, or drawings, presenting two or more alternatives should be understood to contemplate the possibility of including one, either, or both of the items.For example, the phrase "A or B" will be understood to include the possibilities of "A" or "B" or "A and B."

[0136] It is believed that from the foregoing description, the present disclosure and its many attendant advantages will be understood, and it will be apparent that various changes can be made in the form, construction, and arrangement of components without departing from the disclosed subject matter or sacrificing all of its material advantages. The forms described are illustrative only, and the appended claims are intended to cover and encompass such changes. Furthermore, it should be understood that the invention is defined by the appended claims.

Claims

1. A characterization system for characterizing a sample using white light interferometry, comprising: An optical subsystem comprising: a detector configured for multi-pixel imaging; an illumination source configured to generate an illumination beam; a beam splitter configured to split the illumination beam into a measuring beam and a reference beam; a reference element configured to tilt the optical axis of the reference beam relative to the optical axis of the measuring beam; and a sample positioning stage configured to adjust a sample position of the sample along a Z direction associated with a focal length of the optical subsystem; and a controller communicatively coupled to the detector and the sample positioning stage, wherein the controller comprises one or more processors configured to execute program instructions causing the one or more processors to: receiving an image of the sample; demodulating the interference pattern of the image using a filter; determining a position of the interference pattern on the image; and A focus adjustment is directed based on the position of the interference pattern, wherein the focus adjustment includes adjusting at least one of the sample positioning stage or an optical element of the optical subsystem.

2. The characterization system of claim 1 , wherein the controller is further configured to cause the one or more processors to: Selective blocking of the reference beam is performed for receiving a secondary image without the interference pattern. 3 . The characterization system of claim 2 , wherein the selective blocking is configured to be repeatedly performed during a transverse scan for receiving a plurality of secondary images.

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

5. The characterization system of claim 1 , wherein guiding the focus adjustment based on the position of the interference pattern comprises: The focus adjustment is guided based on the position of the interference pattern during a lateral scan of the sample to maintain focus.

6. The characterization system of claim 1 , wherein the controller is further configured to cause the one or more processors to: Vertical scanning data is generated along the depth direction of the sample during the lateral scanning of the sample.

7. The characterization system of claim 1 , wherein guiding the focus adjustment based on the position of the interference pattern comprises: The focus adjustment is guided based on the position of the interference pattern to produce a surface height topology of the sample.

8. The characterization system of claim 7, wherein the controller is further configured to execute the program instructions to cause the one or more processors to: A phase map is unfolded based on the surface height topology. 9 . The characterization system of claim 8 , wherein unfolding the phase map based on the surface height topology comprises unfolding a scanning microscope phase map based on the surface height topology.

10. The characterization system of claim 1 , wherein the controller is further configured to execute the program instructions to cause the one or more processors to: receiving a calibrated focus position; and A difference between the calibrated focus position and the position of the interference pattern on the image is determined. 11 . The characterization system of claim 10 , wherein directing the focus adjustment based on the position of the interference pattern comprises directing the focus adjustment based on the difference.

12. The characterization system of claim 1 , wherein receiving the image of the sample comprises: The image of the sample is received during a lateral scan of the sample. 13 . The characterization system of claim 12 , wherein directing the focus adjustment comprises continuously directing the focus adjustment for each received image such that the sample is continuously maintained in focus during the lateral scan of the sample.

14. The characterization system of claim 1, wherein the optical subsystem comprises an external interferometer configuration.

15. The characterization system of claim 1, wherein the optical subsystem comprises an intra-objective interferometer configuration such that the beam splitter is positioned after the objective along a propagation direction of the illumination beam.

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

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

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

19. The characterization system of claim 1, wherein the one or more layers comprise one or more semi-transparent layers.

20. A method comprising: Providing an optical subsystem configured for characterizing a sample using white light interferometry, the optical subsystem comprising: a reference element configured to tilt an optical axis of a reference beam relative to an optical axis of a measurement beam, and a sample positioning stage configured to adjust a sample position of the sample along a Z direction of the sample; receiving an image of the sample; demodulating the interference pattern of the image using a filter; determining a position of the interference pattern on the image; and A focus adjustment is directed based on the position of the interference pattern, wherein the focus adjustment includes adjusting at least one of the sample positioning stage or an optical element of the optical subsystem.

21. The method of claim 20, further comprising performing selective blocking of the reference beam for receiving a secondary image without the interference pattern.

22. The method of claim 21, wherein the selective blocking is configured to be performed repeatedly during a transverse scan for receiving a plurality of secondary images.

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

24. The method of claim 20, wherein directing the focus adjustment based on the position of the interference pattern comprises: The focus adjustment is guided based on the position of the interference pattern during a lateral scan of the sample to maintain focus.

25. The method of claim 20, further comprising generating vertical scanning data along a depth direction of the sample during the lateral scanning of the sample.

26. The method of claim 20, wherein directing the focus adjustment based on the position of the interference pattern comprises: The focus adjustment is guided based on the position of the interference pattern to produce a surface height topology of the sample.

27. The method of claim 26, further comprising: A phase map is unfolded based on the surface height topology.

28. The method of claim 27, wherein unfolding the phase map based on the surface height topology comprises unfolding a scanning microscope phase map based on the surface height topology.

29. The method of claim 20, further comprising: receiving a calibrated focus position; and A difference between the calibrated focus position and the position of the interference pattern on the image is determined.

30. The method of claim 29, wherein directing the focus adjustment based on the position of the interference pattern comprises directing the focus adjustment based on the difference.

31. The method of claim 20, wherein the receiving the image of the sample comprises: The image of the sample is received during a lateral scan of the sample.

32. The method of claim 31 , wherein directing the focus adjustment comprises continuously directing the focus adjustment for each received image such that the sample continuously remains in focus during the lateral scan of the sample.

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

34. The method of claim 20, wherein the method is performed via an optical subsystem comprising an intra-objective interferometer configuration such that a beam splitter is positioned after the objective.

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

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

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

38. The method of claim 37, wherein the one or more layers comprise one or more translucent layers.

Images