Optically based verification of internal facet orientation

Abstract

To provide a measurement technique which can be simply and easily mounted in response to demand for mass production.SOLUTION: A light guiding configuration generates a first incident light beam to be oriented to an outer surface vertically to the outer surface configured so as to be turned around into a sample or upward and a second incident light beam parallel to the first incident light beam and oriented to the light guiding configuration so as to make light to be made incident on itself vertically to the outer surface of the sample collide with an internal facet of the sample normally vertically, acquires a first return light beam by reflection from the outer surface of the first incident light beam, acquires a second return light beam by turning around into the sample or above the sample by a light guiding configuration of the second incident light beam, reflection from an internal facet of the second incident light beam, and reverse turning around by the light guiding configuration, measures an angle deviation between the return light beams, and estimates an actual angle of inclination of the internal facet to the outer surface from measured angle deviation.SELECTED DRAWING: Figure 5A

Description

[Technical Field]

[0001] The present disclosure generally relates to methods and systems for metrology of samples that include internal facets. [Background technology]

[0002] Some transparent optical elements, such as prismatic glass and waveguides, may contain reflective internal facets. To verify the orientation of such facets with high precision relative to one or more external surfaces of the optical element, the current state-of-the-art requires the implementation of high-end optics and complex alignment and calibration procedures. Thus, there is an unmet need in the art for a simple, easily implemented metrology technique that avoids the use of high-end optics, thereby meeting the demands of mass production. Summary of the Invention

[0003] Aspects of the present disclosure, according to some embodiments thereof, relate to methods and systems for metrology of samples that include one or more internal facets. More particularly, but not by way of limitation, according to some embodiments of the present disclosure, aspects of the present disclosure relate to optically-based methods and systems for metrology of samples that include one or more internal facets.

[0004] Advantageously, the present application discloses a fast, simple, and accurate method and system for verifying the tilt of an internal facet of a sample, or of multiple nominally parallel internal facets of a sample, relative to one or more external flat surfaces of the sample.

[0005] Thus, according to an aspect of some embodiments, there is provided an optically based method for verifying the orientation of one or more internal facets of a sample relative to an external flat surface of the sample, the method comprising: - Providing a sample that includes an external flat first surface and an internal facet that is nominally inclined (intended to be inclined by design and fabrication) at a nominal inclination angle μ relative to the first surface. - Providing a light guiding arrangement (LGA) configured to redirect light incident on the LGA in a direction perpendicular to the first surface into or onto the sample, so that light transmitted thereby into the sample impinges on the internal facet nominally perpendicular to the internal facet. - generating a first incident light beam (LB) directed at the first surface perpendicular to the first surface, and a second incident LB parallel to the first incident LB and directed at the LGA; Obtaining a first return LB by reflection of the first incident LB from a first surface. - Obtaining a second return LB by redirecting the second incident LB into or onto the sample by the LGA, reflecting the second incident LB from an internal facet, and redirecting it back by the LGA. - Measuring a first angular deviation of the second return LB relative to the first return LB. - estimating an actual inclination angle μ′ of the internal facet relative to the first external surface based on the measured first angular deviation.

[0006] According to some embodiments of the method, the sample includes a first portion and a second portion, with an internal facet extending between the first portion and the second portion, the first portion being positioned between a second surface external to the sample and the internal facet, and the transmitted LB, which constitutes a portion of the second incident LB, is transmitted directly or indirectly into the sample and enters the sample via the second surface.

[0007] According to some embodiments of the method, the LGA comprises at least a light bending component (LFC) nominally configured to bend light when projected in a direction perpendicular to the first surface at a light bending angle equal to a nominal tilt angle.

[0008] According to some embodiments of the method, the LFC is or includes a prism, one or more mirrors, and / or a diffraction grating.

[0009] According to some embodiments of the method, the light bending angle is insensitive to variations in the pitch of the LFC.

[0010] According to some embodiments of the method, the LFC is or includes a pentaprism or a prism with similar functionality, or a pair of mirrors placed at an angle to each other, or a mirror arrangement with similar functionality.

[0011] According to some embodiments of the method, the LGA further includes a coupling infrastructure configured to guide light bent by the LFC onto or into the sample so that light transmitted thereby into the sample impinges nominally perpendicularly on the internal facet.

[0012] According to some embodiments of the method, the coupling infrastructure includes a coupling prism (CP). The CP includes an external flat CP first surface, an external flat CP second surface nominally inclined at a nominal angle relative to the CP first surface, and an external CP third surface opposite the CP second surface. The CP has a refractive index that is the same as or close to the refractive index of the first portion of the sample (e.g., within 0.001%, 0.01%, or even 0.1%, each option corresponding to a separate embodiment). The CP is positioned such that the CP first surface is parallel to the first surface of the sample and is further oriented such that light bent by the LFC impinges nominally perpendicularly on the CP second surface.

[0013] According to some embodiments of the method, the coupling infrastructure further comprises a conformal interface disposed between the CP third surface and the sample and configured to adopt a shape such that the CP first surface is parallel to the sample first surface.

[0014] According to some embodiments of the method, the conformal interface has a refractive index that is the same as or close to the refractive index of the first portion of the sample (e.g., within 0.001%, 0.01%, or even 0.1%, each option corresponding to a separate embodiment).

[0015] According to some embodiments of the method, the conformal interface is or includes a liquid and / or a gel.

[0016] According to some embodiments of the method, the sample may be a prism, a waveguide, or a beam splitter.

[0017] According to some embodiments of the method, the first incident light LB and the second incident light LB constitute complementary portions of a single collimated light beam or are prepared by blocking one or more portions of a single collimated light beam.

[0018] According to some embodiments of the method, the first incident light LB and the second incident light LB are prepared by blocking one or more portions of a single collimated light LB.

[0019] According to some embodiments of the method, the single collimated LB is polychromatic.

[0020] According to some embodiments of the method, the single collimated LB is a laser beam.

[0021] According to some embodiments of the method in which the coupling infrastructure includes a CP, the method further includes an initial calibration stage in which a standard sample is utilized to calibrate the LFC, the CP, and / or the orientation of the sample.

[0022] According to some embodiments of the method in which the coupling infrastructure includes a CP, the method further includes generating an additional incident LB, where the additional incident LB is directed toward a first surface of the CP and is parallel to the first incident LB. The orientation of the CP is (a) calibrated and / or (b) tested for correct orientation during the measurement of the first angular deviation by measuring an additional angular deviation of the additional return LB relative to the first return LB. The additional return LB is obtained by reflection of the additional incident LB from the first CP surface.

[0023] According to some embodiments, the first angular deviation is obtained from measured coordinates of the first and second spots formed by the first and second returns LB, respectively, on the photosensitive surface of the optical sensor.

[0024] According to some embodiments of the method, the first angular deviation is measured using an autocollimator.

[0025] According to some embodiments of the method, the measured first angular deviation is Δu / f, where Δu is the difference between the coordinates of the first spot on the photosensitive surface of the autocollimator and the coordinates of the corresponding second spot, and f is the focal length of the collimator lens of the autocollimator. The first spot is formed by the first return beam LB, and the second spot is formed by the second return beam LB.

[0026] According to some embodiments of the method in which the coupling infrastructure includes a CP, the actual tilt angle of the internal facet relative to the first surface is obtained from the measured first angular deviation, as well as the value of the actual tilt angle of the CP second surface relative to the CP first surface, the value of the refractive index of the first portion of the sample, and optionally the value of the actual light bending angle of the LFC.

[0027] According to some embodiments of the method, the method further comprises measuring the actual light bending angle of the LFC.

[0028] According to some embodiments of the method in which the coupling infrastructure includes a CP, the method further includes measuring an actual tilt angle of the CP second surface relative to the CP first surface.

[0029] According to some embodiments of the method, the nominal tilt angle is an obtuse angle.

[0030] According to some embodiments of the method, the nominal tilt angle is an acute angle.

[0031] According to some embodiments of the method, the nominal tilt angle is 90° and the sample includes an external third surface that is flat and parallel to the first surface of the sample. The method further includes, after measuring the first angular deviation, performing: - Inverting the sample so that the first and third surfaces are reversed. generating a third incident LB oriented perpendicular to the third surface and a fourth incident LB parallel to the third incident LB and oriented towards the LGA; Obtaining a third return LB by reflection from the second surface of the third incident LB. - Obtaining a fourth return LB by redirecting the second incident LB into or onto the sample by the LGA, reflecting the second incident LB from an internal facet, and redirecting it back by the LGA. - Measuring the second angular deviation of the fourth return LB relative to the third return LB. - estimating an actual tilt angle between the first exterior surface and the interior facet based on the measured first angular deviation and the measured second angular deviation.

[0032] According to some embodiments of the method, wherein the coupling infrastructure comprises a CP, the CP further comprises a CP fourth surface opposite and parallel to the CP first surface, and inverting the sample involves inverting the CP such that the CP first surface and the CP fourth surface are reversed while maintaining a nominal orientation of the CP second surface relative to the sample.

[0033] According to some embodiments of the method, the uncertainty in the parallelism of the first surface of the sample and the third surface of the sample is smaller, or in some cases significantly smaller (e.g., by an order of magnitude or more), than the required measurement accuracy of the actual tilt angle.

[0034] According to some embodiments of the method in which the coupling infrastructure includes a CP, the actual tilt angle of the internal facet relative to the first surface is obtained from the measured first angular deviation, as well as the value of the actual tilt angle of the CP second surface relative to the CP first surface, and the value of the refractive index of the first portion of the sample.

[0035] According to some embodiments of the method, in which the coupling infrastructure includes a CP, the actual tilt angle is equal to or approximately equal to 90° + (δ1 - δ2) / (4n) + Δμ''' · (n-1) / n (e.g., the estimated actual tilt angle is between 90° + 0.95 · [(δ1 - δ2) / (4n) + Δμ''' · (n-1) / n] and 90° + 1.05 · [(δ1 - δ2) / (4n) + Δμ''' · (n-1) / n], 9 0°+0.9·[(δ1−δ2) / (4n)+Δμ′′·(n−1) / n)] to 90°+1.1·[(δ1−δ2) / (4n)+Δμ′′·(n−1) / n)], or 90°+0.8·[(δ1−δ2) / (4n)+Δμ′′·(n−1) / n)] to 90°+1.2·[(δ1−δ2) / (4n)+Δμ′′·(n−1) / n)], each alternative corresponding to a separate embodiment. δ1 and δ2 are the measured first and second angular deviations, respectively, and n is the refractive index of the first portion of the sample. Δμ′′ is the deviation of the inclination of the CP second surface relative to the CP first surface from 90°. Advantageously, according to some such embodiments, knowledge or measurement of the deviation of the actual light bending angle of the LFC from the nominal tilt angle is not required.

[0036] According to some embodiments of the method, the internal facet extends to a first surface of the sample.

[0037] According to some embodiments of the method, the sample includes k≧1 additional internal facets nominally parallel to the internal facet. In acquiring the second return LBs, k additional return LBs are acquired by reflecting the k LBs from each of the k additional internal facets, respectively. The k LBs constitute portions of the second incident LB that transmit into the sample and through the internal facet. In measuring the first angular deviations, k additional angular deviations of the k additional return LBs relative to the first return LB are measured. In estimating the actual tilt angle μ′ of the internal facet, (i) k additional actual tilt angles for each of the k additional internal facets are estimated, and / or (ii) an actual average tilt angle is estimated that is equal to or approximately equal to the average of the actual tilt angles of the internal facet and the k additional internal facets. The actual average tilt angle indicates the actual tilt angle μ′ of the internal facet.

[0038] According to some embodiments of the method, k≧2. A first one of the additional internal facets is positioned between the internal facet and a second one of the additional internal facets. For each m such that 2≦m≦k−1, the mth one of the k additional internal facets is positioned between the (m−1)th and (m+1)th one of the k additional internal facets. According to some such embodiments, each of the k+1 spots formed on the photosensor surface of the light or image sensor by the second return LB and the k additional return LBs may be attributed to (i.e., identified as being formed by) a respective return LB based on the brightness of the spot. The brightest one of the k+1 spots may be attributed to the second return LB, and for each j such that 2≦j≦k+1, the jth brightest spot may be attributed to the return LB resulting from reflection from the (j−1)th one of the k additional internal facets.

[0039] According to some embodiments of the method, the internal facet and each of the k additional internal facets are configured to reflect light of a respective spectrum, each spectrum being different from the others so as to make it possible to distinguish between the second return LB and the k additional returns LB.

[0040] According to an aspect of some embodiments, there is provided an optically based system for verifying the orientation of an internal facet of a sample relative to an external flat surface of the sample, the system including: - A light guiding arrangement (LGA) configured to redirect light that enters the LGA in a direction perpendicular to an external flat first surface of the sample into or onto the sample, whereby light transmitted into the sample impinges on an internal facet of the sample nominally perpendicular to the internal facet. an illumination and collection arrangement (ICA), ■A light generating assembly configured to (a) project a first incident light beam (LB) onto a first surface to generate a first return LB by reflection from the first surface, and (b) project a second incident LB onto the LGA parallel to the first incident LB to generate a second incident LB by redirecting the second incident LB into or onto the sample by the LGA, reflecting the second incident LB from an internal facet, and redirecting it back by the LGA; ■An ICA including at least one sensor configured to measure a first angular deviation of the second return LB relative to the first return LB, and / or an eyepiece assembly configured to enable manual measurement of the first angular deviation.

[0041] The measured first angular deviation indicates the actual tilt angle of the internal facet relative to the first surface.

[0042] According to some embodiments of the system, the light generation assembly includes a light source and an optical instrument.

[0043] According to some embodiments of the system, the at least one sensor includes one or more optical sensors and / or one or more image sensors (eg, one or more cameras).

[0044] According to some embodiments of the system, the sample includes a first portion and a second portion, with an internal facet extending between the portions, the first portion is positioned between an external second surface of the sample and the internal facet, and the LGA is configured to redirect the LGA into or onto the first portion via the second surface.

[0045] According to some embodiments of the system, the LGA includes at least a light bending component (LFC) nominally configured to bend light when projected in a direction perpendicular to the first surface at a light bending angle equal to the nominal tilt angle.

[0046] According to some embodiments of the system, the LFC is or includes a prism, one or more mirrors, and / or a diffraction grating.

[0047] According to some embodiments of the system, the light bending angle of the LFC is not affected by variations in the pitch of the LFC.

[0048] According to some embodiments of the system, the LFC is or includes a pentaprism or a prism with similar functionality, or a pair of mirrors placed at an angle to each other, or a mirror arrangement with similar functionality.

[0049] According to some embodiments of the system, the LGA further includes a coupling infrastructure configured to direct light bent by the LFC onto or into the sample so that light transmitted thereby into the sample impinges nominally perpendicularly on the internal facet.

[0050] According to some embodiments of the system, the coupling infrastructure includes a coupling prism (CP), the CP including an external flat CP first surface, an external flat CP second surface nominally tilted at a nominal angle relative to the CP first surface, and an external CP third surface (which may or may not be flat) opposite the CP second surface. The CP has a refractive index that is the same as or close to the refractive index of the first portion of the sample (e.g., within 0.001%, 0.01%, or even 0.1%, each option corresponding to a separate embodiment). The CP is positioned such that the CP first surface is parallel to the first surface of the sample and is further oriented such that light bent by the LFC impinges nominally perpendicularly on the CP second surface.

[0051] According to some embodiments of the system, the coupling infrastructure further includes a conformal interface disposed between the CP third surface and the sample such that the CP first surface is parallel to the sample first surface, the conformal interface having a refractive index that is the same as or close to the refractive index of the sample first portion (e.g., within 0.001%, 0.01%, or even 0.1%, each option corresponding to a separate embodiment).

[0052] According to some embodiments of the system, the conformal interface is or includes a liquid and / or a gel.

[0053] According to some embodiments of the system, the sample may be a prism, a waveguide, or a beam splitter.

[0054] According to some embodiments of the system in which the LGA includes at least one sensor, the system further includes a calculation module configured to calculate an actual tilt angle based on at least the measured first angular deviation.

[0055] According to some embodiments of the system, the calculation module is further configured to calculate the uncertainty in the calculated actual tilt angle, taking into account at least manufacturing tolerances and imperfections of the LGA and ICA.

[0056] According to some embodiments of a system including a CP, the system further includes an orientation infrastructure configured to orient the sample such that a first incident LB impinges perpendicularly on a first surface and / or such that a bent LB resulting from bending of a second incident LB by the LFC impinges nominally perpendicularly on a second surface of the CP.

[0057] According to some embodiments of the system, the system further includes an autocollimator, which includes a light source, at least one sensor, and a collimator lens or collimator lens assembly.

[0058] According to some embodiments of the system, the ICA further includes at least two shutters configured to selectively block each of the incident LBs and / or one or more spectral filters configured to at least facilitate differentiation of the returning LBs.

[0059] According to some embodiments of the system in which the sample includes a first portion and a second portion, the nominal tilt angle is 90° and the sample further includes an external flat third surface that is parallel to the first surface.

[0060] According to some embodiments of the system, the system is configured to facilitate sample inversion.

[0061] According to some embodiments of the system including at least one sensor and a computing module, the computing module is configured to calculate the actual tilt angle by additionally taking into account the measured second angular deviation of the fourth return LB relative to the third return LB. With the sample inverted such that the first and third surfaces are reversed: (a') the third return LB is obtained by projecting a third incident light beam onto the third surface of the sample to generate the third return LB by reflection from the third surface, and (b') the fourth return LB is obtained by projecting the fourth incident LB onto the LFC parallel to the third incident LB by redirecting the fourth incident LB into or onto the sample by the LGA, reflecting the fourth incident LB from an internal facet, and redirecting it back by the LGA to generate the fourth incident LB.

[0062] According to some embodiments of a system including a CP, the CP further includes an external, flat CP fourth surface that is parallel to the CP first surface, and the CP is mechanically reversible such that the CP first and CP fourth surfaces can be reversed while maintaining the nominal orientation of the CP second surface relative to the sample.

[0063] According to some embodiments of the system, the measured second angular deviation is obtained with the CP inverted such that the CP first surface and the CP fourth surface are inverted and the nominal orientation of the CP second surface relative to the sample is maintained.

[0064] According to some embodiments of the system in which the system includes an orientation infrastructure, the calculation module is configured to calculate the uncertainty in the calculated value of the actual tilt angle by additionally taking into account manufacturing tolerances and imperfections of the orientation infrastructure.

[0065] According to some embodiments of a system in which the light generation assembly includes a light source and an optical device, the light source is configured to generate a single LB and the optical device is configured to collimate the single LB.

[0066] According to some embodiments of the system, the first incident light LB and the second incident light LB are complementary portions of a collimated light LB.

[0067] According to some embodiments of the system, the light source is a polychromatic light source.

[0068] According to some embodiments of the system, the light source is configured to generate a laser beam.

[0069] Particular embodiments of the present disclosure may include some, all, or none of the above advantages. One or more other technical advantages may be readily apparent to those skilled in the art from the drawings, specification, and claims included in this application. Furthermore, while specific advantages are listed above, various embodiments may include all, some, or none of the listed advantages.

[0070] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. In case of conflict, the present patent specification, including definitions, will control. As used herein, the indefinite articles "a" and "an" mean "at least one" or "one or more," unless the context clearly dictates otherwise.

[0071] Unless otherwise specified, it will be understood from this disclosure that, according to some embodiments, terms such as "processing," "calculating," "operating," "determining," "estimating," "evaluating," or "measuring" may refer to acts and / or processes of a computer or computing system, or similar electronic computing device, that manipulate and / or transform data represented as physical (e.g., electronic) quantities in the registers and / or memory of the computing system into other data that is similarly represented as physical quantities in the memory, registers, or other such information storage, transmission, or display device of the computing system.

[0072] Embodiments of the present disclosure may include apparatuses for performing the operations herein. The apparatus may be specially constructed for the desired purposes, or may comprise a general-purpose computer that is selectively differentiated or reconfigured by a computer program stored in the computer. Such a computer program may be stored on a computer-readable storage medium, such as, but not limited to, a floppy disk, an optical disk, a CD-ROM, a magneto-optical disk, a read-only memory (ROM), a random access memory (RAM), an electrically programmable read-only memory (EPROM), an electrically erasable programmable read-only memory (EEPROM), a magnetic or optical card, or any other type of medium suitable for storing electronic instructions and capable of being coupled to a computer system bus.

[0073] The processes and displays presented herein are not inherently related to any particular computer or other apparatus. Various general-purpose systems may be used with programs in accordance with the teachings herein, or it may be convenient to construct more specialized apparatus to perform the desired method. The desired structure for a variety of these systems will appear from the following description. Additionally, descriptions of embodiments of the present disclosure do not refer to any particular programming language. It will be understood that a variety of programming languages may be used to implement the teachings of the present disclosure as described herein.

[0074] Aspects of the disclosure may be described in the general context of computer-executable instructions, such as program modules, being executed by a computer. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. The disclosed embodiments may also be practiced in distributed computing environments where tasks are performed by remote processing devices that are linked through a communications network. In a distributed computing environment, program modules may be located in both local and remote computer storage media, including memory storage devices. [Brief explanation of the drawings]

[0075] Some embodiments of the present disclosure will be described with reference to the accompanying drawings. The description, together with the drawings, will make apparent to those skilled in the art how some embodiments may be implemented. The drawings are for illustrative purposes and do not attempt to show structural details of the embodiments in more detail than is necessary for a fundamental understanding of the present disclosure. For clarity, some objects depicted in the drawings have not been drawn to scale. Furthermore, two different objects in the same drawing may be drawn to different scales. In particular, the scale of some objects may be greatly exaggerated compared to other objects in the same drawing. In the figure,

[0076] [Figure 1A] 1A and 1B schematically depict an optically based system for internal facet metrology of a sample during inspection of the sample, according to some embodiments. [Figure 1B] 10A-10C schematically depict the trajectory of a light beam within a light-guiding arrangement of a system and a sample, according to some embodiments. [Figure 1C] 1B schematically depicts spots on a photosensitive surface of a sensor of the system of FIG. 1A, according to some embodiments. [Figure 2]1B schematically depicts an optically-based system for internal facet metrology of a sample during inspection of the sample, the system corresponding to a specific embodiment of the system of FIG. 1A; [Figure 3] 1B schematically depicts an optically-based system for internal facet metrology of a sample during inspection of the sample, the system corresponding to a specific embodiment of the system of FIG. 1A; [Figure 4A] 1A-1C present non-limiting examples of samples that may be subjected to internal facet metrology by the system of FIG. 1A, according to some embodiments. [Figure 4B] 1A-1C present non-limiting examples of samples that may be subjected to internal facet metrology by the system of FIG. 1A, according to some embodiments. [Figure 4C] 1A-1C present non-limiting examples of samples that may be subjected to internal facet metrology by the system of FIG. 1A, according to some embodiments. [Figure 4D] 1A-1C present non-limiting examples of samples that may be subjected to internal facet metrology by the system of FIG. 1A, according to some embodiments. [Figure 5A] 1A schematically depicts an optically-based system for verifying perpendicularity of an internal facet of a sample relative to two parallel external flat surfaces of the sample during inspection of the sample, the system corresponding to a specific embodiment of the system of FIG. 1A. [Figure 5B] 1A schematically depicts an optically-based system for verifying perpendicularity of an internal facet of a sample relative to two parallel external flat surfaces of the sample during inspection of the sample, the system corresponding to a specific embodiment of the system of FIG. 1A. [Figure 5C] 5C is a schematic depiction of a spot on a photosensitive surface of a sensor of the system of FIGS. 5A and 5B, according to some embodiments; [Figure 5D] 5C is a schematic depiction of a spot on a photosensitive surface of a sensor of the system of FIGS. 5A and 5B, according to some embodiments; [Figure 6A]1B schematically depicts the inspection of a sample including a pair of nominally parallel internal facets, the inspection being performed using a system corresponding to a specific embodiment of the system of FIG. 1A. [Figure 6B] 6B is a schematic depiction of a spot on a photosensitive surface of a sensor of a system utilized to inspect the sample of FIG. 6A, according to some embodiments. [Figure 7] 1 presents a flowchart of an optically based method for internal facet metrology of a sample, according to some embodiments. [Figure 8A] 1 presents a flowchart of an optically based method for verifying the perpendicularity of an internal facet of a sample relative to two parallel external flat surfaces of the sample, according to some embodiments. [Figure 8B] 1 presents a flowchart of an optically based method for verifying the perpendicularity of an internal facet of a sample relative to two parallel external flat surfaces of the sample, according to some embodiments. [Figure 9] 1A and 1B schematically depict an optically based system for internal facet metrology of a sample during inspection of the sample, according to some embodiments. [Figure 10] 1A and 1B schematically depict an optically based system for internal facet metrology of a sample during inspection of the sample, according to some embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0077] The principles, uses, and implementations of the teachings disclosed in the present application may be better understood by reference to the accompanying specification and drawings. Those skilled in the art, having reviewed the specification and drawings of the present application, will be able to practice the teachings herein without undue effort or experimentation. In the drawings, like reference numerals refer to like parts throughout.

[0078] In the specification and claims of this application, the words "comprise" and "have" and their forms are not limited to the elements in a list with which they may be associated.

[0079] As used in this application, the term "about" may be used to specify the value of a quantity or parameter (e.g., the length of an element) within a continuous range of values near (and including) a given (recited) value. According to some embodiments, "about" may specify the value of the parameter to be between 80% and 120% of the given value. For example, stating that "the length of the element is equal to about 1 meter" is equivalent to stating that "the length of the element is between 0.8 meters and 1.2 meters." According to some embodiments, "about" may specify the value of the parameter to be between 90% and 110% of the given value. According to some embodiments, "about" may specify the value of the parameter to be between 95% and 105% of the given value.

[0080] As used herein, according to some embodiments, the terms "substantially" and "about" may be synonymous.

[0081] For ease of illustration, a three-dimensional Cartesian coordinate system is introduced in some of the drawings. Note that the orientation of the coordinate system relative to the depicted object may vary from one illustration to another. Also, the symbols

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[0082] In the figures, optional elements and optional steps (in the flow charts) are depicted with dashed lines.

[0083] Throughout the specification, an internal flat surface of a three-dimensional element (such as a flat boundary between two parts of a three-dimensional element or an internal flat layer of material embedded within a three-dimensional element) is referred to as an "internal facet."

[0084] system According to an aspect of some embodiments, an optically-based system for internal facet metrology of a sample is provided. FIG. 1A schematically depicts such a system, optically-based system 100, according to some embodiments. Optically-based system 100 is configured to verify the angle between an internal facet of a sample and an external flat surface of the sample. FIG. 1A presents a cross-sectional side view of system 100 and sample 10, according to some embodiments. (It should be understood that sample 10 does not form part of system 100.) Sample 10 is shown as being inspected by system 100.

[0085] Sample 10 includes an exterior first surface 12a (i.e., first exterior surface), an exterior second surface 12b (i.e., second exterior surface), and an interior facet 14. First surface 12a is flat. The remaining exterior surfaces of sample 10 may have any shape, such as, for example, curved, so long as the shape does not interfere with the positioning and orientation of sample 10, as described in more detail below. As a non-limiting example, second surface 12b is depicted as convex, but it should be understood that second surface 12b may be flat, concave, or even wavy or rough (e.g., unpolished), or may include multiple non-parallel flat surfaces. According to some embodiments not depicted in FIG. 1A , sample 10 may be shaped as a polyhedron.

[0086] The sample 10 is comprised of at least a first portion 16a and a second portion 16b. According to some embodiments, the first portion 16a and the second portion 16b are flat and share a common boundary defined by the internal facet 14. In such embodiments, the first portion 16a and the second portion 16b are each characterized by a different refractive index (i.e., the refractive index of the first portion 16a is different from the refractive index of the second portion 16b). As a non-limiting example, according to some such embodiments, the sample may be an element comprised of two glass portions, each characterized by two different refractive indices. Alternatively, according to some embodiments, the first portion 16a and the second portion 16b may be separated by a thin, flat layer of one or more materials formed by the internal facet 14. The layer is characterized by a refractive index different from at least one of the first portion 16a and the second portion 16b (the refractive indices of the two portions may or may not be the same). According to some such embodiments, the first portion 16a and the second portion 16b may be made of the same material, for example in embodiments in which the sample 10 is a prism or a waveguide and a flat layer / stratum of material having a refractive index different from that of the first portion 16a and / or the second portion 16b is incorporated within the sample 10 between the first portion 16a and the second portion 16b.

[0087] Sample 10 is fabricated to exhibit a (nominal) tilt angle α (shown in FIG. 1B) between first surface 12a and internal facet 14. However, due to imperfections in fabrication, the actual tilt angle α' between first surface 12a and internal facet 14 generally differs from the nominal tilt angle α. A straight (first) dashed line L shown in FIG. 1A intersects internal facet 14 and is tilted at a nominal tilt angle α relative to first surface 12a. Dashed line L indicates the intended tilt of internal facet 14. The nominal tilt angle α can be acute (i.e., α<90°), obtuse (i.e., α>90°), or even 90°. The supplementary angle to the actual tilt angle α' (i.e., β'=180°~α'), labeled β', is shown in FIG. 1B.

[0088] The orientation of the internal facets 14 is essentially unlimited, other than being inclined at a nominal inclination angle α relative to at least one external flat surface of the sample 10. Several different orientations of internal facets within samples having the same common geometry are described below in the description of Figures 4A-4D. The (actual) inclination angles of the internal facets can be measured using the system 100.

[0089] According to some embodiments, the first portion 16a is made of a transparent or translucent material, while the second portion 16b can be made of a transparent or translucent material, or in some cases an opaque material. According to some embodiments, the first portion 16a can be made of glass or crystal (or a transparent or translucent polymer or metal), and the second portion 16b can, in principle, be made of any material (including an opaque material). According to some embodiments in which the first portion 16a and the second portion 16b share a common boundary, the first portion 16a and the second portion 16b can be glued and / or welded (e.g., laser welded) to each other along the common boundary.

[0090] According to some embodiments, system 100 includes a light-guiding arrangement (LGA) 102 and an illumination and collection arrangement (or assembly, ICA) 104. System 100 may further include a controller 108 operatively associated with ICA 104 and configured to control its operation. According to some embodiments, as depicted in FIG. 1A , ICA 104 includes a light source 112 (or multiple light sources) and a sensor 114 (or multiple sensors). According to some alternative embodiments not depicted in FIG. 1A , ICA 104 includes an eyepiece assembly in place of sensor 114, thereby configuring for visual determination (i.e., by eye) of the actual tilt angle.

[0091] As described in more detail below, the ICA 104 is configured to output at least two parallel light beams (LB), including a first LB 105a (also referred to as the "first incident LB" and shown in FIG. 1A by a pair of parallel light rays) and a second LB 105b (also referred to as the "second incident LB" and shown in FIG. 1A by a pair of parallel light rays).

[0092] According to some embodiments, the optical device 118 may be configured to collimate the light generated by the light source 112, thereby generating (parallel) incident LBs 105a and 105b. According to some such embodiments, the optical device 118 may include a collimator lens or a collimator lens assembly (not shown). According to some embodiments, the incident LBs 105a and 105b may form complementary portions of a collimated light beam (focused by the collimator lens or collimator lens assembly). Alternatively, according to some embodiments, the incident LBs 105a and 105b may be spaced apart (and parallel). According to some such embodiments, the optical device 118 may further include one or more optical filters (e.g., light-absorbing filters or opaque plates) and / or one or more beam splitters, and optionally one or more mirrors (not shown) configured to prepare a pair of spaced-apart, parallel light beams from the collimated light beam.

[0093] According to some embodiments, the optical device 118 may further include a plurality of blocking elements (such as the blocking elements depicted in FIG. 2 ) configured to enable selective blocking of each incident LB 105, or at least to facilitate distinguishing between a first return LB 133 a caused by a first incident LB 105 and a second return LB 133 b caused by a second incident LB 105 b. As used herein, the term “blocking element” with respect to an optical element is broadly interpreted to encompass both an opaque element (such as a shutter) that can be controllably opened or closed and configured to block (when closed) an incident light beam, and a filtering element (such as a spectral filter) configured to completely or partially block one or more portions of the light spectrum (e.g., the visible spectrum).

[0094] According to some embodiments, light source 112 may be configured to generate or be capable of generating polychromatic light. According to some such embodiments, the spectrum of the light may be controllable. According to some embodiments, light source 112 may be configured to generate or be capable of generating monochromatic light.

[0095] According to some embodiments, the ICA 104 is or includes an autocollimator (i.e., some or all of the light source 112, the sensor 114, and the optics 118 constitute components of an autocollimator). According to some embodiments, the incident LB 105 constitutes adjacent partial beams of a single collimated wide-area LB produced by the autocollimator. According to such embodiments, the optics 118 may include an optical filter configured to transmit two partial beams of the collimated LB (such as the incident LB 105) prepared by the autocollimator and incident on the optical filter (the parallelism of the two partial beams is maintained upon exiting the optical filter).

[0096] According to some embodiments, as depicted in FIG. 1A , the LGA 102 includes an optical bending component 122 (LFC) and a coupling infrastructure 124 that can be disposed between the LFC 122 and the sample 10. The LFC 122 is configured to bend light projected onto it in a direction nominally perpendicular to the first surface 12 a at an optical bending angle α″ equal to the nominal tilt angle α. (That is, ideally, the optical bending angle α″ would be equal to the nominal tilt angle.) According to some embodiments, the LFC 122 can be or include a prism, one or more mirrors, or a diffraction grating. According to some embodiments, the LFC 122 can be a pentaprism (as depicted in FIG. 3 ) or a prism with similar functionality that is insensitive to pitch variations (in the sense that its optical bending angle remains unchanged when the pitch of the LFC 122 is slightly changed, i.e., when the LFC 122 is slightly rotated about the y-axis). According to some embodiments, the LFC 122 may be a pair of mirrors placed at an angle relative to each other, or a mirror configuration with similar functionality (ie, not susceptible to pitch variations).

[0097] In embodiments in which the internal facet 14 is (intentionally) not parallel to the second surface 12b, additional infrastructure may be required to maintain the propagation direction of light projected onto the second surface 12b (outside the sample 10) in a direction perpendicular to the internal facet 14 after it enters the sample 10. This may also be the case when the internal facet 14 and the second surface 12b are nominally parallel, because due to manufacturing tolerances, even if the second surface 12b is sufficiently smooth, the actual slope of the second surface 12b will generally differ slightly from the nominal slope. As described below, the coupling infrastructure 124 is configured for this purpose.

[0098] 1A, the coupling infrastructure 124 may include a coupling prism (CP) 132 and a conformal interface 134. The CP 132 includes an external planar (CP) first surface 138a, an external planar (CP) second surface 138b, and an external planar (CP) third surface 138c (which may or may not be planar). The CP second surface 138b is nominally inclined at a nominal inclination angle α relative to the CP first surface 138a, as indicated by a second dashed line L' that is parallel to the first dashed line L. The CP third surface 138c may be positioned opposite the CP first surface 138a.

[0099] According to some embodiments, the conformal interface 134 may be enclosed between and adjacent to the second surface 12b (of the sample 10) and the third surface 138c of the CP. The conformal interface 134 may be a liquid, gel, or paste characterized by surface tension and / or adhesive properties, such as maintaining its integrity and positioning when enclosed within a narrow space. According to some embodiments, the conformal interface 134 may be a malleable material. According to some embodiments, and as depicted in FIG. 1B , the refractive index of the CP 132 and the conformal interface 134 are each equal to or close to (e.g., within 0.001%, 0.01%, or 0.1%, each option corresponding to a separate embodiment) the refractive index of the sample 10. According to some embodiments, the values of the refractive index of the CP 132 and the conformal interface 134 are sufficiently small so that the overall uncertainty in the measurement of the actual tilt angle α′ does not exceed the required measurement precision. Thus, a light beam propagating through CP 132, conformal interface 134, and sample 10 maintains its direction of propagation as it transitions from CP 132 to conformal interface 134 and from conformal interface 134 to sample 10.

[0100] According to some embodiments, the system 100 may further include an orientation infrastructure 140 for orienting the sample 10 relative to the ICA 104. As a non-limiting example, the orientation infrastructure 140 may include an orientable (first) stage 142 (i.e., a first stage that can be oriented) configured for movement in six degrees of freedom. The stage 142 is configured to mount a sample, such as the sample 10, thereon. In particular, the orientation infrastructure 140 may be configured to orient the sample 10 such that the first incident LB 105a impinges perpendicularly on the first surface 12a. According to some embodiments, the orientation infrastructure 140 may be functionally associated with and configured to be controlled by the controller 108.

[0101] According to some embodiments, the orientation infrastructure 140 may be further configured to orient the CP 132 relative to the LGA 102, the ICA 104, and the sample 10. According to some such embodiments, the orientation infrastructure 140 may include an orientable second stage 144 configured to mount the CP 132 thereon and to rotate and, optionally, translate the CP 132 along each of three non-parallel axes.

[0102] As used herein, according to some embodiments, the terms "nominal" and "ideally" may be synonymous. When an object is intended, by design and fabrication, to exhibit (i.e., be characterized by) a certain intrinsic property (such as the tilt angle between the flat surfaces of a sample), the object may be said to "nominal" exhibit that property, but in reality, due to manufacturing tolerances, the object may actually exhibit that property imperfectly. This also applies to extrinsic properties of an object, such as the light propagation direction of a light beam. In this case, it should be understood that while the object was ideally prepared or otherwise manipulated to exhibit that property, in reality, the object may actually exhibit that property imperfectly due, for example, to inherent imperfections in the environment used for its preparation.

[0103] In operation, a first incident LB 105a is projected onto the sample 10 in a direction normal to the first surface 12a, and a second incident LB 105b is projected onto the LFC 122. The first incident LB 105a (or at least a portion thereof) is reflected from the first surface 12a and sensed by the sensor 114, as shown by the first return LB 133a.

[0104] The second incident LB105b is bent by the LFC 122 at an optical bending angle α'', as indicated by the bent LB 113b. The optical bending angle α'' is nominally equal to the nominal tilt angle α. However, in practice, due to manufacturing imperfections, the optical bending angle α'' of the LFC 122 may deviate slightly from the nominal tilt angle α. If the uncertainty in the optical bending angle of the LFC 122 (due to manufacturing tolerances) is lower or significantly lower than the accuracy with which the actual tilt angle of the internal facet 14 should be determined, the uncertainty in the optical bending angle can be ignored (i.e., it can be assumed that the LFC 122 bends the second incident LB105b exactly at the nominal tilt angle α). Otherwise, the uncertainty in the optical bending angle may contribute (non-negligibly) to the overall uncertainty in the measurement of the actual tilt angle.

[0105] To avoid cluttering the figures, typically only two rays of each light beam are shown. Also, it should be understood that the depiction of the light beams is schematic, and the depicted light beams may be wider or narrower than depicted. Thus, for example, according to some embodiments, a first incident LB 105a may impinge on the entire first surface 12a and / or a second incident LB 105b may impinge on the entire light-receiving surface of LFC 122.

[0106] 1B, the bent LB 113B travels to the CP 132. The transmitted LB 117b shows the portion of the bent LB 113b that transmits into the CP 132 via the CP second surface 138b (the portion of the bent LB 113b that is reflected at the CP second surface 138b is not shown, which may be negligible). The transmitted LB 117b propagates across the CP 132 from the CP second surface 138b to the CP third surface 138c, then across the conformal interface 134 from the CP third surface 138c to the second surface 12b of the sample 10, and finally propagates across the first portion 16a toward the internal facet 14.

[0107] Reflected LB121b shows the portion of transmitted LB117b reflected by internal facet 14 back to conformal interface 134 (the portion of transmitted LB117b, if any, that transmits from first portion 16a to second portion 16b is not shown). Reflected LB121b propagates across first portion 16a toward second surface 12b, then across conformal interface 134 from second surface 12b to CP third surface 138c, and finally across CP 132 from CP third surface 138c to CP second surface 138b. Outgoing LB125b shows the portion of reflected LB121b that exits CP 132 via CP second surface 138b (the portion of reflected LB121b that is internally reflected by CP second surface 138b is not shown). As indicated by the second return LB 133b, the output LB 125b moves towards the LFC 122 and is thereby bent by the light bending angle α''. More precisely, the output LB 125b is redirected by the LFC 122 (as indicated by the second return LB 133b) towards the ICA 104. The second return LB 133b is sensed by the sensor 114.

[0108] The transmitted LB 117b strikes the internal facet 14 at an incident angle θ. The angles are measured clockwise relative to the viewer's point of view. Angular values greater than 180° are made negative by subtracting 360°. Thus, as a non-limiting example intended to facilitate explanation by being more specific, in FIG. 1B, the incident angle θ is negative and the return angle θ is negative. R (i.e., the angle of reflection) is positive. More precisely, the angle of incidence θ is shown extending counterclockwise from the dotted line B, which represents the normal to the second surface 12b, to ray 117b1 (one of the two rays representing the transmitted LB 117b). The tilt angles α and α' are measured clockwise from the first surface 12a (as a non-limiting example intended for ease of illustration, in FIG. 1A , α' is shown as being greater than α). The nominal tilt angle α extends clockwise from the first surface 12a to the dashed line L, and the actual tilt angle α' extends clockwise from the first surface 12a to the internal facet 14.

[0109] The incident angle θ depends on the deviation Δα' = α - α' (i.e., the deviation of the tilt of the internal facet 14 from the nominal tilt), Δα'' = α - α'' (i.e., the deviation of the (actual) light bending angle of the LFC 122 from α), and Δα''' = α - α''' (i.e., the deviation of the tilt of the CP second surface 138b from the nominal tilt). If the system 100 were free of any imperfections (i.e., α''' = α'' = α) and the CP first surface 138a were oriented parallel to the first surface 12a, the incident angle θ would be equal to Δα'. In other words, whether the incident angle θ exactly equals Δα' depends on the uncertainties in the light bending angle α'' and the actual tilt angle α''', as well as any other related uncertainties in the parameters of the LGA 102, the ICA 104, and the alignment infrastructure 140 (i.e., the accuracy of their orientation). In particular, system 100 is nominally configured so that when Δα′=0, transmitted LB 117b impinges perpendicularly on internal facet 14. The normal to internal facet 14 is shown in FIG. 1B by (straight) dotted line B.

[0110] Typically, due to manufacturing imperfections in both the sample 10 and the LGA 102, the second return LB 133b is not parallel to the first return LB 133a. The angle δ (also referred to as the “angular deviation”) between the first return LB 133a and the second return LB 133b depends on the deviations Δα′, Δα″, and Δα′″ and the refractive index n of the first portion 16a (which is equal to or close to the refractive index of the CP 132 and the conformal interface 134). The angle δ is shown extending clockwise from ray 105b1 (one of the two rays representing the second incident LB 105b) to ray 133b1 (the one of the two rays representing the second return LB 133b) and is therefore positive in FIG. 1A .

[0111] The angle δ can be related to Δα′ using the laws of geometric optics, in particular Snell's law (and taking into account the actual light bending angle of the LFC 122, the actual tilt angle of the CP second surface 138b relative to the CP first surface 138a, and the refractive index n). In other words, Δα′ depends on Δα″, Δα′″, the measurement of the angle δ, and the refractive index n.

[0112] 1C, which schematically illustrates the first and second spots 147a and 147b formed by the first and second return beams 133a and 133b, respectively, on the photosensitive surface 148 of the sensor 114, according to some embodiments. u1 and u2 are the horizontal coordinates (i.e., as measured along the x-axis) of the first and second spots 147a and 147b, respectively. (The coordinate system illustrated in FIG. 1C is assumed to coincide with the coordinate system illustrated in FIG. 1A, up to a possible translation of the origin. Thus, the x-axis in FIG. 1C extends parallel to the first surface 12a, from the second incident beam 105b to the first incident beam 105a.) The angle δ can be directly inferred from the difference Δu=u2-u1. As a non-limiting example, if the measurement is based on an autocollimator (ie, in embodiments where the ICA 104 is or includes an autocollimator), then δ=Δu / f.

[0113] According to some embodiments, the controller 108 may be communicatively associated with the calculation module 130. The calculation module 130 may include a processor and volatile and / or non-volatile memory components. The processor may be configured to receive data (i.e., values of u1 and u2) from the controller 108 sensors 114 and calculate Δα′ based thereon. Optionally, according to some embodiments, the processor may be further configured to calculate the uncertainty in (the calculated value of) Δα′, taking into account manufacturing tolerances and calibration limits of the LGA 102 (including the uncertainty in the actual light bending angle), the ICA 104, and the alignment infrastructure 140. According to some embodiments, the calculation module 130 may be included in the system 100.

[0114] According to some embodiments, the light source 112 may be configured to generate a collimated (first) laser beam. According to some such embodiments, the optical device 118 may include a beam expander (not shown) configured to increase the diameter of the laser beam so that the expanded laser beam can simultaneously impinge on both the sample 10 and the LFC 122. In such embodiments, the first incident LB 105a and the second incident LB 105b may constitute complementary portions of the laser beam. Alternatively, the optical device 118 may include a beam splitter and optical elements configured to split the laser beam into a pair of parallel (spaced) partial beams, i.e., a first partial beam and a second partial beam, constituting the first incident LB 105a and the second incident LB 105b, respectively. According to some such embodiments, the optical device 118 may be configured to recombine the returning partial beams (i.e., the first returning LB 133a and the second returning LB 133b) and redirect the partial beams onto a single optical sensor (i.e., the sensor 114 according to some embodiments thereof). Ideally, when the second partial beam (after being redirected by the LFC 122 and transmitting to the sample 10) strikes the internal facet 14 perpendicularly, the recombined partial beams form a collimated (second) laser beam, and the two spots formed by the recombined partial beams on the optical sensor overlap each other. According to some other embodiments, two optical sensors may be used, the distance between them and their relative orientations being known. In such embodiments, each of the returning partial beams may be directed to a different one of the two optical sensors.

[0115] According to some alternative embodiments, the ICA 104 may be configured for interferometry. That is, the light source 112, some or all of the optical device 118, and the sensor 114 may constitute components of an interferometry environment, as described below. In such embodiments, the light source 112 may be configured to generate a coherent and planar wavefront. The optical device 118 may be configured to split the generated wavefront into two wavefronts: a first (coherent and planar) incident wavefront and a second (coherent and planar) incident wavefront, constituting the first incident LB 105a and the second incident LB 105b, respectively. In such embodiments, the angle δ may be inferred from the interference pattern formed by the first returning LB 133a and the second returning LB 133b. More specifically, in such an embodiment, the first return LB 133a constitutes a first return wavefront resulting from reflection of the first incident wavefront from the first surface 12a, and the second return LB 133b constitutes a second return wavefront resulting from bending of the second incident wavefront by the LFC 122, reflection off the internal facet 14, and bending again by the LFC 122. The returning wavefronts are recombined, and their interference pattern is measured by the sensor 114. If the first and second wavefronts impinge perpendicularly on their respective surfaces (i.e., first surface 12a or internal facet 14, respectively), the recombined wavefront forms a uniform pattern on the sensor 114. If the second surface 12b deviates from the nominal tilt, the recombined wavefront forms a periodic pattern on the sensor 114. The deviation Δα′ can be inferred from the periodicity of the pattern.

[0116] According to some embodiments, the system 100 may further include two shutters configured to enable selective blocking of each of the first return LB 133a and the second return LB 133b, so that each return LB 133 can be sensed separately (thereby facilitating attributing each spot to the return LB that caused it).

[0117] According to some embodiments, first surface 12a may be coated or temporarily coated with a reflective coating, such that light incident on first surface 12a is maximally reflected or at least increases reflection from first surface 12a. According to some embodiments, CP second surface 138b may be coated with an anti-reflective coating, such that external light incident on second surface 138b is maximally transmitted to CP 132 and internal light incident on second surface 138b is maximally transmitted from CP 132. According to some embodiments in which light source 112 is configured to generate polychromatic light, first surface 12a may be coated with a first coating configured to reflect light within a first spectrum, and CP second surface 138b (or LFC 122 or internal facet 14) may be coated with a second coating configured to reflect light within a second spectrum, where the second spectrum does not overlap or substantially does not overlap with the first spectrum. In such an embodiment, the selective blocking of the first return LB133a and the second return LB133b may be implemented using a spectral filter or spectral filter arrangement (optionally instead of a shutter) positioned to receive each return LB133 and configured to enable selective blocking or at least partial blocking of light of the second spectrum and the first spectrum, respectively.

[0118] According to some alternative embodiments, a first (passive) spectral filter may be used to filter the first incident LB 105a into a first spectrum, and a second (passive) spectral filter may be used to filter the second incident LB 105b into a second spectrum. In such embodiments, to enable separate sensing of each return LB 133, an additional spectral filter may be used, positioned between the spectral filter and the sensor 114 and configured to enable selective filtering of light into the first spectrum or the second spectrum.

[0119] It should be noted that a spectral filter or spectral filter arrangement may be used to reduce the signal associated with stray light arriving at the sensor 114 associated with any one of the incident LBs 105 .

[0120] 1A, internal facet 14 is shown as sectioning (i.e., dividing) sample 10, and particularly as extending to first surface 12a, but it should be understood that the scope of the present disclosure is not limited to measuring samples of such shapes. Any sample that includes a flat exterior surface and an internal facet that is inclined relative to the flat exterior surface but does not extend to the flat exterior surface may undergo internal facet measurement using system 100, as described above.

[0121] FIG. 2 schematically depicts an optical-based system 200 for verifying the angle between an internal facet of a sample and a flat external surface of the sample, according to some embodiments. System 200 corresponds to a specific embodiment of system 100. More specifically, FIG. 2 provides a side view of system 200 and sample 10 inspected by system 200, according to some embodiments. System 200 includes an LGA 202 and an ICA 204, which correspond to specific embodiments of LGA 102 and ICA 104. According to some embodiments, as depicted in FIG. 2, system 200 may further include an orientation infrastructure 240, a controller 208, and optionally, a computing module 230. Orientation infrastructure 240, controller 208, and computing module 230 correspond to specific embodiments of orientation infrastructure 140, controller 108, and computing module 130, respectively. Orientation infrastructure 240 may include a first stage 242 and a second stage 244 that correspond to specific embodiments of first stage 142 and second stage 144, respectively.

[0122] According to some embodiments, the ICA 204 includes an autocollimator 250. The autocollimator 250 can be configured to generate a collimated broad LB 201 in a direction perpendicular to the first surface 12a of the sample 10. The first incident LB 205a and the second incident LB 205b respectively constitute a first partial beam and a second partial beam of LB 201. The first incident LB 205a and the second incident LB 205b correspond to specific embodiments of the first incident LB 105a and the second incident LB 105b, respectively. Also shown are bent LB 213b and output LB 225b, which correspond to specific embodiments of the bent LB 113b and output LB 225b, respectively.

[0123] LGA 202 includes an LFC 222 and a bonding infrastructure 224 that correspond to specific embodiments of LFC 122 and bonding infrastructure 124, respectively. According to some embodiments, as depicted in Figure 2, bonding infrastructure 224 includes a CP 232 and a conformal interface 234 that correspond to specific embodiments of CP 132 and conformal interface 134, respectively. CP 232 includes a CP first surface 238a, a CP second surface 238b, and a CP third surface 238c that correspond to specific embodiments of CP first surface 138a, CP second surface 138b, and CP third surface 138c, respectively, of CP 132.

[0124] The additional incident LBs 205s can be used to orient the CP second surface 238b (nominally) parallel to the internal facet 14. More specifically, the additional incident LBs 205s can be used to ensure parallelism between the CP first surface 238a of the CP 232 and the first surface 12a of the sample 10 (where the first incident LB 205a impinges perpendicularly). This is because when the CP first surface 238a is oriented parallel to the first surface 12a, the additional incident LBs 205s impinge perpendicularly on the CP first surface 238a. Therefore, by measuring the angular deviation of the additional return LBs 233a, obtained by reflection of the additional incident LBs 205s from the CP first surface 238a, relative to the first return LBs 233a, the orientation of the CP first surface 238a can be adjusted (by rotating the second stage 244 and / or the first stage 242) until parallelism with respect to the first surface 12a is achieved. When the CP first surface 238a is positioned parallel to the first surface 12a, (nominal) parallelism of the CP second surface 238b and the internal facet 14 can be achieved by rotating the CP 232 around an axis parallel to the z-axis.

[0125] 2, the optics of the ICA 204 may include a pair of blocking elements 256a and 256b that enable selective blocking of each of the first incident LB 205a and the second incident LB 205b, or that facilitate distinguishing at least between the first return LB 233a and the second return LB 233b. According to some such embodiments, the ICA 204 is further configured to generate additional incident LBs 205s, and the optics may further include a third blocking element 256s configured to enable selective blocking of the additional incident LB 205s, or that facilitate distinguishing at least between the first return LB 233a and the second return LB 233b.

[0126] According to some embodiments, each blocking element 256a and 256b, and blocking element 256s (if included), may be a shutter.

[0127] According to some embodiments, first surface 12a may be coated or temporarily coated with a reflective coating, which maximizes reflection of light incident on first surface 12a or at least increases reflection from first surface 12a. According to some embodiments, CP second surface 238b may be coated with an anti-reflective coating, which maximizes transmission of light incident on second surface 238b into CP 232 or at least increases transmission to CP 232. According to some embodiments, CP first surface 238a may be coated with a reflective coating, which maximizes reflection of light incident on CP first surface 238a or at least increases reflection from CP first surface 238a.

[0128] According to some embodiments (in which the autocollimator 250 is configured to generate polychromatic light), to facilitate distinguishing between the first return LB 233a and the second return LB 233b, the first surface 12a may be coated with a first coating configured to reflect light in a first spectrum, the CP second surface 238b may be coated with a coating configured to transmit light in a second spectrum different from the first spectrum into the CP 232, and / or the internal facet 14 may be configured to reflect light of the second spectrum (and at least partially transmit light in the first spectrum). According to some such embodiments, a spectral filter or spectral filter arrangement (e.g., included in the autocollimator 250) configured to enable controllable filtering of light in the first spectrum or the second spectrum may be used to facilitate separate sensing of each return LB 233.

[0129] According to some embodiments in which the ICA 204 is further configured to generate additional incident LBs 205s, the CP first surface 238a may be coated with a third coating configured to reflect light in a third spectrum different from each of the first and second spectra, thereby facilitating the distinction of the additional return LBs 233s from each of the first and second return LBs 233a and 233b. In such embodiments, the spectral filter or spectral filter arrangement (e.g., included in the autocollimator 250) may be further configured to enable controllable filtering of light in the third spectrum.

[0130] According to some embodiments, blocking elements 256a and 256b may be (passive) spectral filters (e.g., dichroic filters) configured to filter light in the first and second spectra, respectively. In such embodiments, to enable separate sensing of each return LB 233, an additional spectral filter may be used, positioned between blocking element 256 and autocollimator 250 or included within autocollimator 250, and configured to enable selective filtering of light in the first or second spectrum.

[0131] FIG. 3 schematically depicts an optical-based system 300 for verifying the angle between an internal facet of a sample and a flat external surface of the sample, according to some embodiments. System 300 corresponds to a specific embodiment of system 100 in which the LFC is or includes a prism. More specifically, FIG. 3 provides a side view of system 300 and sample 10 inspected by system 300. System 300 includes an LGA 302 and an ICA 304 (components not shown), which correspond to specific embodiments of LGA 102 and ICA 104. According to some embodiments, as depicted in FIG. 3 , system 300 may further include a controller 308, an orientation infrastructure 340, and, optionally, a computing module 330. Orientation infrastructure 340, controller 308, and computing module 330 correspond to specific embodiments of orientation infrastructure 140, controller 108, and computing module 130, respectively.

[0132] LGA 302 includes prism 322 and bonding infrastructure 324, which includes CP 332 and conformal interface 334. Prism 322 corresponds to a specific embodiment of LFC 122. CP 332 and conformal interface 334 correspond to a specific embodiment of CP 332 and conformal interface 134.

[0133] According to some embodiments, prism 322 may be insensitive to pitch variations, i.e., rotation about the y-axis, over at least a continuous range of pitch angles. According to some such embodiments, as depicted in FIG. 3, prism 322 may be a pentaprism or a prism with similar functionality, such as a prism including an even number of internally reflective surfaces. According to some alternative embodiments not depicted in FIG. 3, instead of prism 322, LGA 302 may include two mirrors nominally mounted with respect to each other at the same angle as the mounting angles of the two surfaces of prism 322 (pentaprism first surface 328a and pentaprism second surface 328b). First surface 328a and second surface 328b internally reflect a transmitted portion of second incident LB 305b.

[0134] 3 shows first incident LB 305a, first return LB 333a, second incident LB 305b, bent LB 313b, transmitted LB 317b, reflected LB 321b, output LB 325b, and second return LB 333b, which correspond to specific embodiments of first incident LB 105a, first return LB 133a, second incident LB 105b, bent LB 113b, transmitted LB 117b, reflected LB 121b, output LB 125b, and second return LB 133b, respectively. Also shown in FIG. 3 are the trajectories of second incident LB 305b and output LB 325b within prism 322 after entering prism 322. The through portions of second incoming LB 305b after transmission into prism 322, reflection within prism 322, and two reflections within prism 322 are numbered 309b1, 309b2, and 309b3, respectively. The through portions of second outgoing LB 325b after refraction into prism 322, reflection within prism 322, and two reflections within prism 322 are numbered 329b1, 329b2, and 329b3, respectively.

[0135] 4A-4D provide examples of the orientation of internal facets within a sample according to some embodiments. The depicted samples are non-limiting and are intended to illustrate, using specific examples, that the capabilities of system 100 are not limited in principle, so long as the sample includes: (i) a flat external (first) surface; (ii) an internal facet positioned at an angle relative to the first surface; and (iii) a first portion located between the sample's external second surface and the internal facet, characterized by a uniform refractive index, that allows a light beam transmitted into the sample through the second surface to impinge perpendicularly on the internal facet through a continuous, linear path.

[0136] Referring to FIG. 4A, a sample 40 according to some embodiments is depicted. The sample 40 includes an external, flat first surface 42a, an external, second surface 42b, and an internal facet 44. The second surface 42b is positioned opposite the internal facet 44. A first portion 46a of the sample 40 is characterized by a uniform refractive index and is partially bounded by the second surface 42b and the internal facet 44. The internal facet 44 is nominally inclined at 90° relative to the first surface 42a. According to some embodiments, as depicted in FIG. 4A, the second surface 42b may be flat and nominally oriented parallel to the internal facet 44. The sample 40 further includes an external, third surface 42c positioned opposite the first surface 42a.

[0137] Also shown is a system CP432 for internal facet metrology of a sample (only CP432 of the system is shown), which corresponds to a specific embodiment of system 100. In particular, CP432 corresponds to a specific embodiment of CP132. CP432 includes an external planar CP first surface 438a, an external planar CP second surface 438b, and an external CP third surface (not numbered). CP second surface 438b is nominally inclined at a nominal inclination angle relative to CP first surface 438a. CP432 is oriented such that CP first surface 438a is parallel to first surface 42a and CP second surface 438b is nominally parallel to internal facet 44. A conformal interface (not shown) may be disposed between CP third surface 438a and second surface 42b.

[0138] When the sample 40 is inspected, according to the teachings disclosed herein, the incident LB is refracted by the LFC so that it strikes the CP second surface 438b nominally perpendicularly, as described in the description of the system 100.

[0139] According to some embodiments, as depicted in Figure 4A, the third surface 42c is flat and parallel to the first surface 42a, and the uncertainty in the parallelism between the third surface 42c and the first surface 42a is less than the required measurement accuracy of the tilt angle. The systems depicted in Figures 5A and 5B can be used to measure the (actual) tilt angle.

[0140] Referring to FIG. 4B, a sample 40′ according to some embodiments is depicted. Sample 40′ includes an external flat first surface 42a′, an external second surface 42b′, and an internal facet 44′. A first portion 46a′ of sample 40′ is characterized by a uniform refractive index and is partially bounded by second surface 42b′ and internal facet 44′. Sample 40′ has the same geometrical configuration as sample 40, but differs in the tilt angle (relative to first surface 42a′) of internal facet 44′, which is obtuse. More specifically, the tilt of internal facet 44′ differs from the tilt of internal facet 44′ by a rotation about an axis parallel to the y-axis.

[0141] Also shown is a system CP432' for measuring the internal facets of a sample (only CP432' is shown), which corresponds to a specific embodiment of system 100. In particular, CP432' corresponds to a specific embodiment of CP132. CP432' includes an external planar CP first surface 438a', an external planar CP second surface 438b', and an external CP third surface (not numbered). CP second surface 438b' is nominally inclined at a nominal inclination angle relative to CP first surface 438a'. CP432' is oriented such that CP first surface 438a' is parallel to first surface 42a' and CP second surface 438b' is nominally parallel to internal facet 44'. A conformal interface (not shown) may be disposed between CP third surface 438a', second surface 42b', and the first surface 42b'.

[0142] When the sample 40' is inspected, according to the teachings disclosed herein, the incident LB is refracted by the LFC so that it strikes the CP second surface 438b' nominally perpendicularly, as described in the description of the system 100.

[0143] Referring to FIG. 4C, a sample 40″ is depicted according to some embodiments. Sample 40″ includes an external flat first surface 42a″, an external second surface 42b″, an external third surface 42c″, an external fourth surface 42d″, and an internal facet 44″ nominally inclined at 90° relative to the first surface 42a. A first portion 46a″ of sample 40″ is characterized by a uniform refractive index and is partially bounded by the second surface 42b″ and the internal facet 44″. The third surface 42c″ is positioned opposite the first surface 42a″. The fourth surface 42d″ extends between the first surface 42a and the second surface 42b″ and shares a common side with the second surface 42b″. According to some embodiments, as depicted in FIG. 4C, the fourth surface 42d′ is flat. Sample 40″ has the same geometrical outline as sample 40, but the orientation of the internal facet 44″ is different. More specifically, the orientation of internal facet 44'' differs from the orientation of internal facet 44 by a rotation about an axis parallel to the z-axis.

[0144] Also shown is a system CP432'' for internal facet metrology of a sample (only CP432'' of the system is shown), which corresponds to a specific embodiment of system 100. In particular, CP432'' corresponds to a specific embodiment of CP132. CP432'' includes an external planar CP first surface 438a'', an external planar CP second surface 438b'', and an external CP third surface (not numbered). CP second surface 438b'' is nominally inclined at a nominal inclination angle relative to CP first surface 438a''. CP432'' is oriented such that CP first surface 438a'' is parallel to first surface 42a'' and CP second surface 438b'' is nominally parallel to internal facet 44''. A conformal interface (not shown) may be disposed between the CP third surface and second surface 42b''.

[0145] When sample 40'' is inspected, according to the teachings disclosed herein, as described in the description of system 100, incident LB is refracted by LFC so that it strikes CP second surface 438b'' nominally perpendicularly.

[0146] According to some embodiments, as depicted in Figure 4C, the third surface 42c" is flat and parallel to the first surface 42a, and the uncertainty in the parallelism between the third surface 42c" and the first surface 42a" is less than the required measurement accuracy of the tilt angle. The systems depicted in Figures 5A and 5B can be used to measure the (actual) tilt angle.

[0147] Referring to FIG. 4D, a sample 40'' according to some embodiments is depicted. Sample 40'' includes an external flat first surface 42a'''', an external second surface 42b'''', and an internal facet 44''. A first portion 46a'' of sample 40'' is characterized by a uniform refractive index and is partially bounded by second surface 42b''' and internal facet 44'''. Sample 40'' has the same geometric configuration as sample 40, but differs in the obtuse tilt angle γ (relative to first surface 42a'') of internal facet 44''' and its orientation relative to second surface 42b'''. More specifically, the tilt of internal facet 44''' differs from the tilt of internal facet 44 by a rotation about a first axis parallel to axis s (shown in FIG. 4C). Axis s is located in the yz plane, approximately midway between the positive y-axis and the positive z-axis.

[0148] The top edge 48a''' of the internal facet 44''' extends along the first surface 42a'''. Also shown are: (i) a dashed first line T1, a straight line extending along the internal facet 44''' and perpendicular to the top edge 48a''', (ii) a dashed second line T2, a straight line perpendicular to the first surface 42a''' and intersecting the first line T1 at the top edge 48a''', and (iii) a dashed third line T3, a straight line extending from the first line T1 to the second line T2 parallel to the first surface 42a''' (and thus perpendicular to the second line T2). Finally, the tilt angle γ is shown.

[0149] Also shown is CP 432''' of a system for internal facet metrology of a sample (only CP 432''' of the system is shown), which corresponds to a specific embodiment of system 100. In particular, CP 432''' corresponds to a specific embodiment of CP 132. CP 432''' includes an external planar CP first surface 438a''', an external planar CP second surface 438b''', and an external CP third surface (not numbered). CP second surface 438b''' is nominally inclined at a nominal inclination angle relative to CP first surface 438a'''. CP 432''' is oriented such that CP first surface 438a''' is parallel to first surface 42a''', and CP second surface 438b''' is nominally parallel to internal facet 44'''. A conformal interface (not shown) may be disposed between the CP third surface and second surface 42b'''.

[0150] When the sample 40''' is inspected, according to the teachings disclosed herein, as described in the description of the system 100, the incident LB is refracted by the LFC so that it strikes the CP second surface 438b''' nominally perpendicularly.

[0151] 5A and 5B schematically depict an optical-based system 500 for verifying the perpendicularity of an internal facet of a sample relative to at least two other external, flat surfaces of the sample that are parallel to one another, according to some embodiments. System 500 corresponds to a specific embodiment of system 100. More specifically, FIGS. 5A and 5B present cross-sectional side views of system 500 and sample 50 inspected by system 500, respectively, according to some embodiments.

[0152] Sample 50 includes an external flat first surface 52a, an external flat second surface 52b, an external flat third surface 52c, and an internal facet 54. Similar to internal facet 14 (which forms the boundary between, or a thin flat layer disposed between, first and second portions 16a and 16b of sample 10), internal facet 54 forms the boundary between, or a thin flat layer disposed between, first and second portions 56a and 56b of sample 50. First surface 52a and third surface 52c are parallel by design. Furthermore, sample 50 is fabricated to exhibit a (nominal) tilt angle of internal facet 54 of 90° relative to first surface 52a (and third surface 52c). However, due to fabrication imperfections, the actual tilt angle of internal facet 52b relative to first surface 52a, labeled χ' in FIGS. 5A and 5B, typically differs from 90°.

[0153] It should be noted that, using state-of-the-art manufacturing techniques, the (manufacturing) tolerance of the actual angle between external flat surfaces that are fabricated to be parallel is significantly smaller than the tolerance of the actual angle between an internal facet and an external flat surface. Therefore, because first surface 52a and third surface 52c are fabricated to be parallel, their deviation from parallelism is expected to be negligible compared to the deviation of the actual tilt angle χ' from 90°. Therefore, the actual angle ψ' between internal facet 54 and first surface 52a (also referred to as the "actual supplementary angle") can be considered to be equal to 180° ~ χ', i.e., the supplementary angle to the actual tilt angle χ'. (The nominal value of the actual supplementary angle is 90°.)

[0154] System 500 includes an LGA 502 and an ICA 504. LGA 502 corresponds to a specific embodiment of LGA 102 and includes an LFC 522 and a bonding infrastructure 524 corresponding to specific embodiments of LFC 122 and bonding infrastructure 124, respectively. LFC 522 is nominally configured to refract light incident on it by 90° in a direction perpendicular to the nominal slope of internal facet 54. According to some embodiments, LFC 522 may be a prism, one or more mirrors, or a diffraction grating. According to some embodiments, LFC 522 may be a pentaprism or a similarly functional prism configured to refract light incident on it by 90° (i.e., not sensitive to pitch variations). According to some embodiments, LFC 522 may be a pair of angled mirrors or a similarly functional mirror configuration (i.e., not sensitive to pitch variations) configured to refract light incident on it by 90°.

[0155] According to some embodiments, as depicted in FIGS. 5A and 5B, bonding infrastructure 524 may include CP 532 and conformal interface 534, which correspond to specific embodiments of CP 132 and conformal interface 134, respectively. CP 532 includes CP first surface 538a, CP second surface 538b, and CP third surface 538c, which correspond to specific embodiments of CP first surface 138a, CP second surface 138b, and CP third surface 138c, respectively. CP second surface 538b is nominally perpendicular to CP first surface 538a. CP 532 further includes CP fourth surface 538d positioned opposite CP first surface 538a. According to some embodiments, as depicted in FIGS. 5A and 5B, CP fourth surface 538d may be parallel to CP first surface 538a.

[0156] According to some embodiments, system 500 may further include an orienting infrastructure 540 that corresponds to a specific embodiment of orienting infrastructure 140. Orienting infrastructure 540 includes an orientable first stage 542 and an orientable second stage 544, which are configured for depositing and orienting sample 50 and CP 532, respectively, essentially as described with respect to first stage 142 and second stage 144 in the description of system 100.

[0157] According to some embodiments, as depicted in Figures 5A and 5B, the system 500 may further include a controller 508 and, optionally, a computing module 530, which correspond to specific embodiments of the controller 108 and the computing module 130, respectively.

[0158] ICA 504 corresponds to a specific embodiment of ICA 104 and includes a light source 512, a sensor 514, and optionally an optical device 518, which correspond to specific embodiments of light source 112, sensor 114, and optical device 118, respectively. According to some embodiments, light source 512 and sensor 514, and some or all of optical device 518, may constitute components of an autocollimator, which may be similar to autocollimator 250. According to some embodiments, optical device 518 may include a blocking element (not shown), which may be similar to blocking element 256.

[0159] The ICA 504 is configured to emit a first incident light LB 505a directed toward the sample 50 and a second incident light LB 505b directed toward the LFC 522. The ICA 204 and the sample 50 are positioned and oriented such that the first incident light LB 505a is perpendicularly incident on the first surface 52a. In operation, the first incident light LB 505a (or at least a portion thereof) is reflected from the first surface 52a, as shown by the first return light LB 533a. The first return light LB 533a is sensed by the sensor 514.

[0160] The LFC 522 is configured to nominally bend the second incident LB 505b by 90°. More precisely, the LFC 522 is configured and oriented to bend the second incident LB 505b such that the (first) bent LB 513b (resulting from the bending of the second incident LB 505b) is nominally oriented at 90° relative to the second incident LB 505b and nominally perpendicular to the CP second surface 538b. In practice, due to manufacturing imperfections (and, in embodiments where the LFC 522 is susceptible to pitch variations, due to alignment imprecision), the actual light bending angle χ'' of the LFC 522 may deviate slightly from 90°. As described in more detail below, the effects of manufacturing imperfections in LFC 522 can be offset or substantially offset by inverting sample 50 so that first surface 52a and third surface 52c are inverted, inverting CP 532 so that first surface 538a and CP fourth surface 538d are inverted, and then repeating the measurements described in the next two paragraphs.

[0161] In operation, the bent LB 513b, or at least a portion thereof, transmits into the CP 532 via the CP second surface 538b, as indicated by the (first) transmitted LB 517b. The transmitted LB 517 propagates across the CP 532, the conformal interface 534, and the first portion 56a, and impinges on the internal facet 54 at a (first) angle of incidence η1, essentially as described above for the transmitted LB 117b in the description of FIG. 1B. The angle of incidence η1 depends on Δχ′=90°−χ′ (i.e., the deviation from 90° in the tilt of the internal facet 54 relative to the first surface 52a), Δχ″=90°−χ″ (i.e., the deviation from 90° in the (actual) light bending angle of the LFC 522), and Δχ′″=90°−χ′″ (i.e., the deviation from 90° in the tilt of the CP second surface 538b relative to the CP first surface 538a). In particular, system 500 is nominally configured so that when Δχ′=0, transmitted LB 517b impinges perpendicularly on internal facet 54. The normal to internal facet 54 is indicated in FIG. 5A by (straight) dashed line C1.

[0162] As shown by (first) reflected light LB521b, transmitted light LB517b (or at least a portion thereof) is specularly reflected by internal facet 54 (i.e., reflected at a return angle ζ1 equal to the negative of first incident angle η1). Reflected light LB521b returns to LFC 522 via first portion 56a, conformal interface 534, and CP 532. (First) exiting light LB525b is refracted out of CP 532 via CP second surface 538b (unless it is exactly perpendicularly incident on CP second surface 538b, in which case the first portion maintains its propagation direction, and a second portion of reflected light LB521b that is specularly reflected by CP second surface 538b within CP 532 is not shown). The outgoing LB 525b is bent by the LFC 522 at a light bending angle χ'', as indicated by the second returning LB 533b. The second returning LB 533b is sensed by the sensor 514.

[0163] The angle δ1 between the second return LB 533b and the first return LB 533a (also referred to as the "first angular deviation") depends on the deviations Δχ', Δχ'', and Δχ''' and the refractive index n' of the first portion 56a (which is equal to or close to the refractive index of the CP 532 and the conformal interface 534). FIG. 5C schematically depicts the first spot 547a and the second spot 547b formed by the first return LB 533a and the second return LB 533b, respectively, on the photosensitive surface 548 of the sensor 514, according to some embodiments. w1 and w2 are the horizontal coordinates (i.e., as measured along the x-axis) of the first spot 547a and the second spot 547b, respectively. The angle δ1 can be directly inferred from the difference Δw=w2-w1.

[0164] Referring to Figure 5B, compared to Figure 5A, sample 50 has been inverted so that first surface 52a and third surface 52c are reversed (while maintaining the nominal orientation of internal facet 54 relative to LGA 502), and CP 532 has been inverted so that CP first surface 538a and CP fourth surface 538d are reversed (while maintaining the nominal orientation of CP second surface 538b relative to sample 50).

[0165] In operation, a third incident LB 505a' is directed at the sample 50 perpendicular to the sample 50, and a fourth incident LB 505b' is directed at the LFC 522. The third incident LB 505a' (or at least a portion thereof) is reflected from the third surface 52c, as shown by a third return LB 533a'. The third return LB 533a' is sensed by the sensor 514.

[0166] The fourth incident LB 505b' strikes the LFC 522, resulting in a second bent LB 513b'. The second bent LB 513b' strikes the CP second surface 538b, resulting in a second transmitted LB 517b'. The second transmitted LB 517b' traverses the CP 532, traverses the conformal interface 534, and propagates into the first portion 56a of the sample 50. The second transmitted LB 517b' strikes the internal facet 54 at a second incident angle η. The second angle of incidence η2 depends on the deviations Δψ'=90°-ψ' (i.e., the deviation from 90° in the inclination of the internal facet 54 relative to the third surface 52c), Δχ''=90°-χ'', and Δχ'''=90°-χ''' (implicitly assuming that the uncertainty in the parallelism of the CP first surface 538a and the CP fourth surface 538d is smaller than the required measurement accuracy of the actual inclination angle χ'). The normal to the internal facet 54 is indicated in FIG. 5B by the (straight) dashed line C2.

[0167] As shown by the second reflection LB521b', the second transmitted light LB517b' (or at least a portion thereof) is specularly reflected by the internal facet 54 (i.e., reflected at a return angle ζ2 equal to the negative of the second incident angle η2). The second reflection LB521b' returns to the LFC 522 via the first portion 56a, the conformal interface 534, and the CP 532. The second output light LB525b' indicates a portion of the second reflection LB521b' that exits the CP 532 via the CP second surface 538b (the portion of the second reflection LB521b' that is internally reflected by the CP second surface 538b is not shown). The second output light LB525b' is bent by the LFC 522 at an optical bending angle χ'', as shown by the fourth return light LB533b'. The fourth return light LB533b' is sensed by the sensor 514.

[0168] The angle δ2 between the fourth return LB 533b' and the third return LB 533a' (also referred to as the "second angle deviation") depends on the deviations Δχ', Δχ'', and Δχ''' and the refractive index n'. More specifically, the angle δ2 exhibits the same dependence on the deviations Δχ', Δχ'', and Δχ''' and the refractive index n', respectively, as the angle δ1 exhibits: Δχ'=180°-Δχ', Δχ'', and Δψ'''=180°-Δχ''' and the refractive index n'. FIG. 5D schematically depicts the third spot 547a' and the fourth spot 547b' formed by the third return LB 533a' and the fourth return LB 533b', respectively, on the photosensitive surface 548 according to some embodiments. w1 and w2 are the horizontal coordinates of the third spot 547a' and the fourth spot 547b', respectively. The angle δ2 can be directly inferred from the difference Δw′=w2′−w1′.

[0169] Although Figures 5C and 5D show Δw and Δw' as both negative (and therefore δ1 and δ2 are both negative), it should be understood that in general, Δw and Δw' can have opposite signs (and therefore δ1 and δ2 have opposite signs) or both can be positive (and therefore δ1 and δ2 are both positive).

[0170] Each of the measured angles δ1 and δ2 can be used to provide a respective estimate of the deviation angle Δχ′. If the system 500 were perfect, η2 would be equal to −η1 and δ1 would be equal to −δ2. However, in reality, the two estimates will generally differ because the actual light bending angle deviates from 90° and the actual tilt angle of the CP second surface 538b deviates from 90°. Because the dependence of δ1 and δ2 on the deviation Δχ″ is the same (if the LFC is not affected by pitch variations) or substantially the same (i.e., both δ1 and δ2 increase as χ″ increases and decrease as χ″ decreases), by averaging the two estimates of the deviation angle Δχ′, the deviation of the (actual) light bending angle from 90° can be canceled or substantially canceled. If the estimated value of the actual tilt of the internal facets 54 averaged in this way is denoted by <χ'> and the average estimated deviation of the actual tilt angle from 90° is denoted by <Δχ'> (i.e., <χ'>=90°-<Δχ'>), then it can be shown that <χ'>=90°+(δ1-δ2) / (4n')+Δχ'''·(n'-1) / n'. More generally, <χ'> can be 90°+0.95·[(δ1-δ2) / (4n)+Δχ'''·(n-1) / n)] to 90°+1.05·[(δ1-δ2) / (4n)+Δχ'''·(n-1) / n)], 90°+0.9·[(δ1-δ2) / (4n)+Δχ'''·(n-1) / n)] to 90°+1.1·[(δ1-δ2) / (4n)+Δχ'''·(n-1) / n)], or possibly 90°+0.8·[(δ1-δ2) / (4n)+Δχ'''·(n-1) / n)]=90°+1.2·[(δ1-δ2) / (4n)+Δχ'''·(n-1) / n)]. Each alternative corresponds to a separate embodiment. In particular, in embodiments in which ICA 504 is or includes an autocollimator, <χ'> can be shown to be equal to or approximately equal to 90°+(Δw-Δw') / (2·f0·n')+Δχ'''·(n'-1) / n', where f0 is the focal length of the collimator lens of the autocollimator.

[0171] 5A and 5B, the light source 512 and optics 518 may be configured to generate an expanded (collimated) laser beam or a pair of parallel, spaced apart (collimated) laser beams, essentially as described above in the description of system 100. According to still other embodiments, the ICA 504 may be or include an interferometry environment, as described above in the description of system 100.

[0172] 1A, 1B, 2, 3, 5A, and 5B, the samples are shown as including a single internal facet (e.g., internal facet 14 in sample 10 and internal facet 54 in sample 50), the disclosed system may be utilized to obtain information about multiple nominally parallel internal facets. According to some embodiments, the information may be aggregate information, and may identify the average or mean of the actual tilt angles of the internal facets, or a weighted average of the actual tilt angles, as described below.

[0173] Referring to FIG. 6A, FIG. 6A depicts such a sample, sample 60, according to some embodiments. For ease of explanation by being more specific, sample 60 is shown as including two nominally parallel internal facets; however, those skilled in the art will readily understand that the teachings of FIGS. 6A and 6B can be readily applied to samples including three or more nominally parallel internal facets. Sample 60 includes an external, flat first surface 62a, an external, second surface 62b, a first internal facet 64a, and a second internal facet 64b. Second surface 62b is disposed at an angle relative to first surface 62a (which may or may not be flat). First internal facet 64a is flat and nominally inclined at a nominal inclination angle (not shown) relative to first surface 62a. Second internal facet 64b is flat and nominally parallel to first internal facet 64a. The first internal facet 64a is positioned between the second surface 62b and the second internal facet 64b. The first portion 66a of the sample 60 is partially bounded by the second surface 62b and the first internal facet 64a. The second portion 66b of the sample 60 is partially bounded by the first internal facet 64a and the second internal facet 64b. The second internal facet 64b extends between the second portion 66b and the third portion 66c of the sample 60. The first portion 66a and the second portion 66b have the same refractive index (or similar refractive indexes). The first internal facet 64a constitutes a thin layer of material characterized by a refractive index different from that of the first portion 66a and the second portion 66b.

[0174] Using any one of systems 100, 200, or 300, information regarding the actual tilt angles of first internal facet 64a and second internal facet 64b relative to first surface 62a can be obtained essentially as described above in the corresponding descriptions, with additions / adjustments as described below. In embodiments where the nominal tilt angle is 90° and sample 60 includes an external flat third surface 62c that is parallel to first surface 62a, system 500 can be used to obtain information regarding the actual tilt angles essentially as described above in the corresponding descriptions, with additions / adjustments as described below.

[0175] For ease of explanation and to make the discussion more concrete, assume that a system (not shown in FIG. 6A ) corresponding to a specific embodiment of system 100 is utilized to inspect sample 60. A first incident LB 605a (of which only a single ray is shown) is shown projected normally onto first surface 62a. A first return LB 633a is obtained from reflection of first incident LB 605a from first surface 62a. Also shown is a transmitted LB 617b (of which only a single ray is shown), which can be obtained by nominally bending a second incident LB at a nominal tilt angle (using an LFC of a system (not shown) used to perform the inspection). The transmitted LB 617b then transmits into the CP of the system. The CP is oriented such that the bent LB is nominally normal incident on an external flat surface of the CP that is nominally parallel to internal facet 64. The transmitted LB 617b exits the CP and enters a conformal interface positioned between the CP and sample 60. The CP and conformal interface are each characterized by a refractive index that is equal to or at least close to the refractive index of the first and second portions 66 a and 66 b of the sample 60 .

[0176] Transmitted LB 617b enters sample 60 through second surface 62b. Transmitted LB 617b strikes first internal facet 64a nominally perpendicularly. Reflected LB 621b corresponds to the portion of transmitted LB 617b that is specularly reflected off first internal facet 64a. (First) transmitted portion 637b corresponds to the portion of transmitted LB 617b that is transmitted into second portion 66b. Transmitted portion 637b strikes second internal facet 64b nominally perpendicularly. Reflected portion 641b corresponds to the portion of transmitted portion 637b that is specularly reflected off second facet 64b. Second transmitted portion 645b represents the portion of reflected portion 641b that is reflected back to first portion 66a via first internal facet 64a.

[0177] 6B schematically depicts a first spot 647a and a pair of spots 647b (including a second spot 647b1 and a third spot 647b2) on a photosensitive surface 648 of a sensor 614 of a system used to inspect a sample 60, according to some embodiments. The first spot 647a is formed by a first return LB 633a. The second spot 647b1 and the third spot 647b2 are formed by returns LB caused by the reflected LB 621b and the second transmitted portion 645b (i.e., caused by reflections from the first internal facet 64a and the second internal facet 64b, respectively). By utilizing blocking elements and blocking / filtering techniques, the first return LB 633a can be distinguished from returns LB (not shown) caused by the reflected LB 621b and the second transmitted portion 645b. If the second spot 647b1 (and the third spot 647b2) cannot be attributed to one of the two returns LB caused by the reflected LB 621b and the second transmitted portion 645b, only aggregate information (e.g., the average actual tilt) about the first internal facet 64a and the second internal facet 64b can be extracted from the positions of the second spot 647b1 and the third spot 647b2 (from the average deviation angle of the returns LB associated with the reflected LB 621b and the second transmitted portion 645b relative to the first return LB 633a).

[0178] According to some embodiments, the intensity of the return LB associated with the reflection LB 621b may be significantly greater than the intensity of the return LB associated with the second transmitted portion 645b. Thus, depending on whether the brightness of the first spot 647b1 is higher or lower than the brightness of the second spot 647b2, the first spot 647b1 may be attributed to the reflection LB 621b or the second transmitted portion 645b, respectively (and vice versa for the second spot 647b2).

[0179] According to some embodiments, the first internal facet 64a is configured to reflect light of a first spectrum, and the second internal facet 64b is configured to reflect light of a second spectrum. The second spectrum differs from the first spectrum sufficiently to allow for a distinction between the return LB resulting from reflection from the first internal facet 64a and the return LB resulting from reflection from the second internal facet 64b. The distinction can be made using a spectral filter configured to selectively filter light of either the first or second spectrum, as described above in the description of Figures 1A and 2. A distinction can be made similarly between the first return LB 633a and the return LB resulting from reflection from the internal facets 64a.

[0180] According to some embodiments in which the sample 60 includes a third surface 62c opposite the first surface 62a, additional aggregate or individual information regarding the actual tilt angles of the internal facets 64 can be obtained by inverting the sample 60 so that the first surface 62a and the third surface 62c are reversed while maintaining the orientation of the second surface 62b relative to the LGA used to perform the measurements, and repeating the measurements essentially as described above in the description of the system 500 and later in the description of the method of Figures 8A and 8B.

[0181] method According to aspects of some embodiments, an optically-based method for metrology of internal facets of a sample is provided. The method may be used to verify the orientation of one or more internal facets of a sample relative to an external flat surface of the sample. Figure 7 presents a flowchart of such a method, optically-based method 700, according to some embodiments. Method 700 may include the following stages: An optional step 705 in which the system used to implement the method (eg, system 100) is calibrated. A sample to be tested (e.g., sample 10) is provided, step 710. The sample includes an external flat first surface (a flat first external surface, e.g., first surface 12a) and an internal facet (e.g., internal facet 14) that is nominally inclined at a nominal inclination angle (e.g., nominal inclination angle α) relative to the first surface. A pair of parallel light beams (LB) are generated (e.g., by the light source 112 and the optical device 118, or by the autocollimator 250) in step 720: a first incident LB (e.g., first incident LB 105a) is projected perpendicularly onto a first surface of the sample, and a second incident LB (e.g., second incident LB 105b) is projected parallel to the first incident LB onto a light-guiding arrangement (LGA, e.g., LGA 102). A stage 730 in which a first return LB (for example, first return LB 133a) is obtained from reflection of the first incident LB from a first surface of the sample. - Stage 740 in which a second return LB (e.g., second return LB 133b) is obtained by redirecting the second incident LB into or onto the sample by the LGA, reflecting the second incident LB from the internal facet after impinging nominally perpendicularly on the internal facet, and redirecting it back by the LGA. A stage 750 in which the angular deviation of the second return LB relative to the first return LB is measured by sensing the first and second return LB (for example by the sensor 114 or the autocollimator 250). A stage 760 in which the actual tilt angle of the internal facet relative to the first surface (eg, actual tilt angle α′) is estimated based at least on the measured angular deviation f.

[0182] As used herein, the term "obtaining" may be used in both an active and passive sense. Thus, for example, obtaining a first return LB in step 730 may result from the generation of a first incident LB in step 720, rather than from an action implemented in step 730. In general, a step may represent an active action performed by a user or by a system used to implement the method, and / or the result or effect of one or more actions performed in one or more previous steps.

[0183] Method 700 may be implemented using an optically-based system, such as any one of optically-based systems 100, 200, and 300 described above in their respective descriptions, or a similar optically-based system. In particular, according to some embodiments, method 700 may be autocollimator-based, laser beam distance measurement-based, or interferometry-based, as detailed in the descriptions of various embodiments of system 100. In step 730, the second incident LB may be nominally bent at a nominal tilt angle using one of LFC 122, LFC 222, and prism 322, or an LFC with similar functionality. Similarly, the second return LB may be obtained using one of LFC 122, LFC 222, and prism 322, or an LFC with similar functionality.

[0184] According to some embodiments, the internal facet may define a flat boundary between a first portion (e.g., first portion 16a) and a second portion (e.g., second portion 16b) of the sample having different refractive indices. Alternatively, according to some embodiments, the internal facet may constitute a thin, flat layer between the first and second portions of the sample, having a different refractive index from each of the first and second portions (which may have the same or different refractive indices). The first portion may extend between the internal facet and an external, flat second surface (e.g., second surface 12b) of the sample. In step 740, a transmitted LB (e.g., transmitted LB 117b) constituting the portion of the second incident LB transmitted into the sample may be incident through the second surface.

[0185] According to some embodiments, in step 720, a collimated light beam, such as LB 201, may be generated, of which a first partial beam and a second partial beam constitute the first incident light beam LB and the second incident light beam LB, respectively. According to some embodiments, the first incident light beam LB and the second incident light beam LB may be adjacent. According to some embodiments, the first incident light beam LB and the second incident light beam LB may form complementary portions of the collimated light beam. Alternatively, according to some embodiments, a portion of the collimated light beam located between the first incident light beam LB and the second incident light beam LB may be removed (e.g., blocked using a light-absorbing filter or an opaque plate) to separate them. According to some embodiments, the collimated light beam may be generated using an autocollimator, such as autocollimator 250.

[0186] According to some embodiments, the LFC may be configured such that its light bending angle is independent of the pitch angle at which the LFC is placed (thus the second incident LB nominally bends at a nominal tilt angle α regardless of the pitch angle). According to some such embodiments, the LFC may be a pentaprism or a prism with similar functionality, or a pair of plane mirrors placed at an angle relative to each other, or a mirror configuration with similar functionality, as described above in the description of systems 100 and 300 under the "System" subsection.

[0187] According to some embodiments, in addition to the LFC, the LGA may include a coupling infrastructure, such as coupling infrastructure 124. The coupling infrastructure is configured to direct light nominally bent by the LFC at a nominal tilt angle (e.g., bent LB 113b) into or onto the sample such that transmitted light (e.g., transmitted LB 117b) impinges nominally perpendicularly on the internal facet.

[0188] According to some embodiments, the coupling infrastructure may include a coupling prism (CP), such as CP 132, and a conformal interface, such as conformal interface 134. The CP and conformal interface are each characterized by a refractive index equal to or approximately equal to the refractive index of the sample, or, in embodiments in which the first and second portions of the sample do not have the same refractive index, by a refractive index equal to or approximately equal to the refractive index of at least a first portion of the sample. The CP includes an external flat first surface (referred to as the "CP first surface"), an external flat second surface (referred to as the "CP second surface"), and an external third surface (referred to as the "CP third surface"), e.g., CP first surface 138a, CP second surface 138b, and CP third surface 138c, respectively. In particular, the CP second surface is nominally inclined at a nominal inclination angle α relative to the CP first surface.

[0189] The conformal interfaces are disposed adjacent each other between the CP and the first portion of the sample to define a continuum of materials having the same or nearly the same refractive index. More specifically, the conformal interfaces are disposed between the third surface of the CP and the second surface of the sample, and the CP and sample are aligned with one another such that the second surface of the CP and an internal facet of the sample are nominally parallel.

[0190] Forming a continuum of materials with the same or similar refractive indices helps ensure, in step 740, that (i) the propagation direction of the light beam transmitted into the CP (e.g., transmitted LB 117b) is maintained when traversing from the CP into the conformal interface and then from the conformal interface into the first portion of the sample, and (ii) the propagation direction of the light beam reflected from the internal facet (e.g., reflected LB 121b) is maintained when traversing from the first portion of the sample into the conformal interface and then from the conformal interface into the CP. Advantageously, this helps ensure that the transmitted portion (e.g., transmitted LB 117b) of the light beam (e.g., bent LB 113b) incident normally on the CP second surface nominally strikes the internal facet of the sample nominally normal.

[0191] Thus, in an embodiment including both a CP and a conformal interface, a bent LB (e.g., bent LB 113b) obtained by bending the second incident LB by the LFC strikes the second surface of the CP nominally perpendicularly and is transmitted (at least partially) into the CP. The transmitted LB (e.g., transmitted LB 117b) traverses the CP, the conformal interface, and the first portion of the sample in succession. The transmitted LB strikes the internal facet nominally perpendicularly and is reflected (at least partially) from the internal facet. The reflected LB (e.g., reflected LB 121b) traverses the first portion, the conformal interface, and the CP back. At least a portion of the reflected LB (e.g., outgoing LB 125b) exits the CP in the direction of the LFC. The LFC nominally bends the outgoing LB at a nominal tilt angle, thereby obtaining a second returning LB.

[0192] According to some embodiments, an additional incident LB (e.g., additional incident LB 205s) may be projected nominally normal to the CP first surface in step 705. The additional incident LB may be used to verify alignment of the CP first surface and the sample first surface, for example, by measuring the angular deviation between the first return LB and the additional return LB (e.g., additional return LB 233s) obtained from reflection of the additional incident LB away from the CP first surface.

[0193] According to some embodiments, in step 705, a “gold standard” (GS) sample may be used as part of the calibration of the system used to implement method 700. More specifically, for a given test sample, a corresponding GS sample (i.e., a sample known to exhibit the required geometry with high accuracy and have the same refractive index as the test sample) may be used in the system calibration. The GS sample may be used to calibrate the alignment infrastructure (e.g., alignment infrastructure 140, alignment infrastructure 240) and the LGA such that (i) the first incident light impinges perpendicularly on a first surface (similar to first surface 12 a) of the GS sample, and (ii) the transmitted LB impinges perpendicularly on an internal facet (similar to internal facet 14) of the GS sample (i.e., with the accuracy allowed by the GS sample and the LGA).

[0194] According to some embodiments, an orientable stage (e.g., stage 142) on which the sample can be mounted may be used to orient the GS sample relative to the LGA (as a whole or each of its single components (e.g., CP) and the ICA. Additionally or alternatively, a second orientable stage (e.g., second stage 144) may be used to orient the CP relative to the GS sample and LFC. An autocollimator may be used to verify the perpendicularity of the transmitted LB, regardless of whether the autocollimator is part of the ICA (in embodiments in which the system includes an autocollimator) or is not included in the system.

[0195] According to some embodiments, once the sample under test is provided, e.g., placed on an orientable stage, calibration or additional calibration may be performed after step 710. The additional calibration may include, for example, orienting or reorienting the orientable stage on which the sample under test is mounted so that the first incident LB strikes a first surface of the sample under test perpendicularly. According to some embodiments, in step 750, an autocollimator (e.g., autocollimator 250, or more generally, the same autocollimator in embodiments in which an autocollimator is used to adjust the incident LB) may be used to sense the first and second return LBs (e.g., positions where the return LBs strike the photosensitive surface of the autocollimator's sensor) and thereby measure the angular deviation. According to some embodiments, a blocking element, such as a shutter and / or a spectral filter, may be used to selectively block (or at least partially block) each return LB, essentially as described above in the description of systems 100 and 200. In addition to making it easier to attribute each of a pair of spots (spots on the photosensitive surface of an optical or image sensor (e.g., sensor 114) used to sense the return LB) to the return LB that formed the spot, blocking one return LB can serve to increase measurement accuracy by attenuating the signal associated with stray light while sensing the other return LB.

[0196] According to some embodiments, particularly those in which steps 710, 720, and 730 are implemented using an autocollimator, such as autocollimator 250, step 740 determines the angular deviation of the second return LB relative to the first return LB.

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[0197] In step 750, the actual tilt angle

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[0198] According to some embodiments in which a sample (e.g., sample 60) includes multiple internal facets (e.g., internal facet 64) nominally perpendicular to the first surface, and the sample is further characterized by a uniform or nearly uniform refractive index except for the internal facets, in step 740, multiple return LBs are obtained by redirecting the second incident LB into or onto the sample by the LGA, reflecting the second incident LB from each internal facet, and redirecting it back by the LGA, essentially as described in the description of Figures 6A and 6B. In step 750, multiple angular deviations of each return LB relative to the first return LB are measured by sensing the first return LB and each of the multiple return LBs. According to some such embodiments, in step 760, an actual tilt angle of each of the multiple internal facets relative to the first surface can be estimated based at least on the multiple measured angular deviations. According to some embodiments, each of the spots formed by the multiple return LBs on the photosensor surface of a sensor (e.g., sensor 614) can be attributed to each of the multiple return LBs based on the relative brightness of the spots and / or, in embodiments where each internal facet is configured to reflect a respective different spectrum of light, using a spectral filter. Additionally or alternatively, according to some embodiments, aggregate information regarding the actual tilt angle (such as an average of the actual tilt angles) is estimated based at least on the multiple measured angular deviations.

[0199] 8A and 8B present a flowchart of an optically-based method 800 for metrology of internal facets of a sample, according to some embodiments. Method 800 corresponds to a specific embodiment of method 700 and can be used to verify the perpendicularity of one or more internal facets of a sample relative to at least two external flat surfaces of the sample that are parallel to one another. Method 800 can include the following steps: A sample to be tested (e.g., sample 50) is provided, step 805. The sample includes an external flat first surface (i.e., a first outer surface that is flat, e.g., first surface 52a), an external second surface (i.e., a second outer surface that may or may not be flat, e.g., second surface 52b), an external flat third surface parallel to the first surface (i.e., a third outer surface that is flat, e.g., third surface 52c), and an internal facet that is nominally inclined at 90° to the first surface. A first pair of parallel LBs is generated (e.g., by the light source 512 and, optionally, the optics 518) in step 810: a first incident LB (e.g., first incident LB 505a) is projected perpendicularly onto a first surface of the sample, and a second incident LB (e.g., second incident LB 505b) is projected onto the LGA (parallel to the first incident LB). A stage 815 in which a first return LB (eg first return LB 533a) is obtained from reflection of the first incident LB from the first surface. - Stage 820 in which a second return LB (e.g., second return LB 533b) is obtained by redirecting the second incident LB into or onto the sample by the LGA, reflecting the second incident LB from the internal facet after impinging nominally perpendicularly on the internal facet, and redirecting it back by the LGA. A stage 825 in which the (first) angular deviation of the second return LB relative to the first return LB is measured by sensing the first and second return LB (for example by the sensor 514). - Step 830 in which the sample is flipped so as to reverse the first and third surfaces (while maintaining the nominal orientation of the internal facets relative to the LGA). A second pair of parallel LBs is generated (e.g., by the light source 512 and optionally the optics 518) in step 835: a third incident LB (e.g., third incident LB 505a') is projected perpendicularly onto the third surface of the sample, and a fourth incident LB (e.g., fourth incident LB 505b') is projected onto the LGA (parallel to the third incident LB). A stage 840 in which a third return LB (for example a third return LB 533a') is obtained from reflection of the third incident LB from a third surface. - Stage 845 in which a fourth return LB (e.g., fourth return LB 533b') is obtained by redirecting the fourth incident LB into or onto the sample by the LGA, reflecting the fourth incident LB from the internal facet after impinging nominally perpendicularly on the internal facet, and redirecting it back by the LGA. A stage 850 in which the (second) angular deviation of the fourth return LB relative to the third return LB is measured by sensing the third and fourth return LB (for example by the sensor 514). - A stage 855 in which the actual tilt angle of the internal facet relative to the first surface is estimated based on the measured angular deviation.

[0200] Method 800 may be implemented using an optically-based system, such as optically-based system 500 or a similar optically-based system, as described above in the description of FIGS. 5A-5D . In particular, according to some embodiments, method 800 may be autocollimator-based, based on measuring the distance between laser beams, or based on interferometry. In step 820, a first bent LB and a second returned LB may be obtained from the second incident LB and the first reflected LB, respectively, using an LFC configured to refract light incident on it by nominally 90°, such as LFC 522 or an LFC with similar functionality. According to some embodiments, the LFC may be or include a prism (e.g., a pentaprism) configured to refract light by 90°, or one or more mirrors configured (together) to refract light by 90°. Similarly, in step 845, a second bent LB and a fourth returned LB may be obtained from the fourth incident LB and the second reflected LB, respectively, using the LFC 522 or an LFC of similar functionality.

[0201] According to some embodiments, in addition to the LFC, the LGA may include a coupling infrastructure, such as coupling infrastructure 524. The coupling infrastructure is configured to direct light bent by the LFC (e.g., bent LB 513b) into or onto the sample such that transmitted light (e.g., transmitted LB 517b) strikes the internal facet nominally normal.

[0202] According to some embodiments, the coupling infrastructure may include a coupling prism (CP), such as CP 532, and a conformal interface, such as conformal interface 534. The CP and conformal interface are each characterized by a respective refractive index equal to or close to that of the sample, or, in embodiments in which the first and second portions of the sample do not have the same refractive index, equal to or close to that of at least a first portion of the sample. The CP includes an external flat first surface (referred to as the “CP first surface”), an external flat second surface (referred to as the “CP second surface”), and an external third surface (referred to as the “CP third surface”), e.g., CP first surface 538a, CP second surface 538b, and CP third surface 538c, respectively. Notably, the CP second surface is nominally inclined perpendicular to the CP first surface. The CP and conformal interface may be utilized essentially as described above in the description of method 700, or, optionally, additionally, as described below.

[0203] According to some embodiments, the CP includes an external, flat fourth surface (referred to as "CP fourth surface"), such as CP fourth surface 538d. The CP fourth surface is opposite and parallel to the CP first surface. In such embodiments, in step 830, the CP may also be inverted, like the CP first surface and the CP fourth surface, while maintaining the nominal orientation of the CP second surface (the surface through which light bent by the LFC enters the CP) relative to the internal facet.

[0204] According to some embodiments, an autocollimator (e.g., an autocollimator) may be used to generate multiple pairs of parallel incident LBs in steps 810 and 835. According to some embodiments, an autocollimator (e.g., an autocollimator used in preparing the incident LBs) may be used to sense the return LBs in steps 815, 820, 840, and 845. According to some embodiments, a shutter and / or a spectral filter may be used to selectively block (or at least partially block) one of the second and first return LBs and one of the fourth and third return LBs, essentially as described above in the description of Figures 5A and 5B.

[0205] According to some embodiments, method 800 may include an optional calibration step (not shown in FIGS. 8A and 8B ) similar to step 705 of method 700, which is repeated (in part) after flipping the sample in step 830 (and performed before steps 835-855). More specifically, in step 830, after flipping the sample, the orientation of the sample may be reoriented so that light transmitted into the sample is nominally normal to the incident light on the internal facets. In embodiments in which the CP is also flipped, the CP may also be reoriented so that light bent by the LFC (e.g., second bent LB 513b′) impinges on the second surface of the CP nominally normal.

[0206] According to some embodiments, particularly in embodiments in which steps 810, 815, 820, 835, 840, and 845 are implemented using an autocollimator (e.g., autocollimator 250), step 825 determines a first angular deviation of the second return LB relative to the first return LB.

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[0207] In step 855, the actual tilt angle

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[0208] According to some embodiments in which the sample (e.g., sample 60) includes multiple internal facets (e.g., internal facet 64) nominally perpendicular to the first surface and the sample is further characterized by a uniform or nearly uniform refractive index except for the internal facets, in step 820, a first plurality of return LBs are obtained by redirecting a second incident LB into or onto the sample by the LGA, reflecting the second incident LB from each internal facet, and redirecting it back by the LGA, essentially as described in the description of Figures 6A and 6B. In step 825, a first plurality of angular deviations of each of the first plurality of return LBs relative to the first return LB are measured by sensing the first return LB and each of the first plurality of return LBs. Similarly, in step 845, a second plurality of return LBs are obtained by redirecting a fourth incident LB into or onto the sample by the LGA, reflecting the fourth incident LB from each internal facet, and redirecting it back by the LGA. In step 850, a second plurality of angular deviations of each second return LB relative to the third return LB are measured by sensing the third return LB and each of the second plurality of return LBs. According to some such embodiments, in step 855, an actual tilt angle of each of the plurality of internal facets relative to the first surface may be estimated based at least on the first plurality of measured angular deviations and the second plurality of measured angular deviations. According to some embodiments, each of the spots formed by the plurality of return LBs may be attributed to each of the plurality of return LBs based on the relative brightness of the spots and / or using a spectral filter in embodiments in which each internal facet is configured to reflect a respective different spectrum of light. Additionally or alternatively, according to some embodiments, aggregate information regarding the actual tilt angle (e.g., an average of the actual tilt angles) is estimated based at least on the first and second plurality of measured angular deviations.

[0209] According to some embodiments in which when the sample is flipped, the first and third surfaces of the sample are inverted while maintaining the orientation of the internal facets relative to the LGA, and the internal facets remain nominally parallel to the CP second surface (when the CP is not flipped), method 800 may include four additional measurements: a first measurement in which both the sample and CP are not flipped, a second measurement in which the sample is not flipped and the CP is flipped, a third measurement in which both the sample and CP are flipped, and a fourth measurement in which the sample is flipped and the CP is not flipped. The four measurements are:

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[0210] Additional Systems FIG. 9 schematically depicts an optical-based system 900 for internal facet metrology of a sample, according to some embodiments. System 900 is similar to system 100, but unlike some embodiments of system 100, does not include a bonding infrastructure (e.g., bonding infrastructure 124). System 900 is configured for use with a sample that includes at least two external flat surfaces and an internal facet that is nominally inclined at a nominal tilt angle relative to a first of these two surfaces. Such a sample, sample 90, according to some embodiments, is depicted in FIG. 9. Sample 90 includes an external flat first surface 92a, an external flat second surface 92b, and an internal facet 94. Internal facet 94 is nominally inclined at a nominal tilt angle ω relative to first surface 92a. Sample 90 is shown as being inspected by system 900.

[0211] System 900 includes an ICA 904 and an LFC 922, which may correspond to specific embodiments of ICA 104 and LFC 122, respectively. ICA 904 may include a light source, at least one sensor, and optionally, an optical instrument (all not shown), which may correspond to specific embodiments of light source 112, at least one sensor 114, and optical instrument 118. System 900 may further include a controller, an orientable stage, and a computing module (all not shown), which may correspond to specific embodiments of controller 108, first stage 142, and computing module 130. The controller may be functionally associated with the ICA 904 components, stages, and computing module, respectively, similar to the functional association of controller 108 with ICA 104 components, first stage 142, and computing module 130.

[0212] During operation, the ICA 904 generates a pair of incident light beams LB, i.e., a first incident light beam LB 905a and a second incident light beam LB 905b that is parallel to the first incident light beam LB 905a. The first incident light beam LB 905a is projected nominally perpendicular to the first surface 92a. A first return light beam LB 933a is obtained by reflection of the first incident light beam LB 905a from the first surface 92a and sensed by a sensor (not shown) of the ICA 904.

[0213] The second incident LB 905b is bent by LFC 922, as shown by bent LB 913b. The bent LB 913b strikes the second surface 92b. The transmitted LB 917b represents the portion of the bent LB 913b that penetrates into the sample 90. The transmitted LB 917b strikes the internal facet 94 nominally normal. That is, the nominal bend angle of the LFC 922 and the orientation of the sample 90 relative to the LFC 922 are selected so that the transmitted LB 917b strikes the internal facet 94 nominally normal.

[0214] Reflected light LB921b indicates the portion of transmitted light LB917b that is specularly reflected off internal facet 94. Exit light LB925b indicates the portion of reflected light LB921b that leaves sample 90 by refraction through second surface 92b. Second returned light LB933b is obtained by bending of exit light LB925b by LFC 922. Second returned light LB933b is sensed by a sensor in ICA 904.

[0215] According to some embodiments, the angular deviation of the second return LB 933b relative to the first return LB 933a can be obtained from the horizontal distance between the second spot and the first spot formed by the second return LB 933b and the first return LB 933a, respectively, on the photosensitive surface of the sensor, as described above in the description of system 100 and method 700. From the measurement of the angular deviation, the deviation of the (actual) tilt of the internal facet 94 from the nominal tilt can be derived, essentially as described in the description of system 100 and method 700.

[0216] FIG. 10 schematically depicts an optical-based system 1100 for internal facet metrology of a sample, according to some embodiments. System 1100 is configured for use with a sample that includes an external flat surface and an internal facet that is nominally inclined relative to the surface at a nominal tilt angle. Such a sample, sample 1010, according to some embodiments, is depicted in FIG. 10. Sample 1010 includes an external flat (first) surface 1012a and an internal facet 1014. Internal facet 1014 is nominally inclined relative to first surface 1012a at a nominal tilt angle ω′. Sample 1010 is shown as it is being inspected by system 1100.

[0217] System 1100 includes an ICA 1104 and an LFC 1122, which may be similar to ICA 104 and LFC 122, respectively, but differ therefrom as described below. ICA 1104 may include a light source, at least one sensor, and optionally, optics (all not shown), which may be similar to light source 112, at least one sensor 114, and optics 118, respectively. System 1100 may further include a controller and a computing module (all not shown), which may correspond to specific embodiments of controller 108 and computing module 130. The controller may be functionally associated with ICA 1104 components and computing module 130, respectively, similar to the functional association of controller 108 with ICA 104 components and computing module 130. System 1100 may further include an orientable stage (not shown), which may be similar to first stage 142 and controlled by the controller.

[0218] During operation, the ICA 1104 generates a pair of incident light beams LB, i.e., a first incident light beam LB 1105a and a second incident light beam LB 1105b that is parallel to the first incident light beam LB 1105a. The first incident light beam LB 1105a is projected nominally perpendicular to the first surface 1012a. A first return light beam LB 1133a is obtained by reflection of the first incident light beam LB 1105a from the first surface 1012a and sensed by a sensor (not shown) of the ICA 1104.

[0219] The second incident LB 1105b is bent by the LFC 1122, as shown by bent LB 1113b. The bent LB 1113b strikes the first surface 1012a. The transmitted LB 1117b represents the portion of the bent LB 1113b that is refracted within the sample 1000. The transmitted LB 1117b strikes the internal facet 1014 nominally normal. That is, the nominal bend angle of the LFC 1122 and the orientation of the sample 1000 relative to the LFC 1122 are selected such that the transmitted LB 1117b strikes the internal facet 1014 nominally normal.

[0220] Reflected LB 1121b indicates the portion of transmitted LB 1117b that is specularly reflected by internal facet 1014. Outgoing LB 1125b indicates the portion of reflected LB 1121b that leaves sample 1000 by refraction through first surface 1012a. Second returning LB 1133b is obtained by bending outgoing LB 1125b by LFC 1122. Second returning LB 1133b is sensed by a sensor in ICA 1104.

[0221] According to some embodiments, the angular deviation of the second return LB 1133b relative to the first return LB 1133a can be obtained from the horizontal distance between the second spot and the first spot formed by the second return LB 1133b and the first return LB 1133a, respectively, on the photosensitive surface of the sensor, as described above in the description of system 100 and method 700. From the measurement of the angular deviation, the deviation of the (actual) tilt of the internal facet 1014 from the nominal tilt can be derived, similar to the derivation of the actual tilt angle α' from the angular deviation δ (described in the description of system 100 and method 700).

[0222] According to some embodiments, the nominal bend angle of the LFC 1122 may be selected to maximize the strength of the second return LB 1133b.

[0223] It should be understood that certain features of the present disclosure, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the present disclosure, which are, for brevity, described in the context of a single embodiment, may also be provided separately, in any suitable subcombination, or in any manner suitable with any other described embodiment of the present disclosure. Features described in the context of an embodiment should not be considered essential features of that embodiment, unless expressly stated otherwise.

[0224] Although steps of methods according to some embodiments may be described in a particular sequence, the methods of the present disclosure may include some or all of the described steps being performed and / or occurring in a different sequence. The methods of the present disclosure may include some of the described steps or all of the described steps. No particular step of a disclosed method should be considered essential to the method unless specifically stated.

[0225] While the present disclosure has been described in conjunction with specific embodiments thereof, it is evident that numerous alternatives, modifications, and variations apparent to those skilled in the art may exist. Accordingly, the present disclosure embraces all such alternatives, modifications, and variations that fall within the scope of the appended claims. It is to be understood that the present disclosure is not necessarily limited in its application to the details of construction and arrangement of components and / or methods described herein. Other embodiments may be implemented and the embodiments may be carried out in various ways.

[0226] The phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. Citation or identification of any reference in this application should not be construed as an admission that such reference is available as prior art to the present disclosure. The section headings used herein are for ease of understanding the specification and should not be construed as necessarily limiting.

Claims

1. 1. An optically-based method for verifying the orientation of one or more internal facets of a sample relative to an external flat surface of the sample, the method comprising: providing a sample including an external flat first surface and an internal facet nominally inclined at a nominal inclination angle μ relative to said first surface; providing a light guiding arrangement (LGA) configured to redirect light incident on the LGA in a direction normal to the first surface into or onto the sample so that light transmitted into the sample impinges on the internal facet nominally normal to the internal facet; generating a first incident light beam (LB) directed at the first surface perpendicular to the first surface and a second incident LB parallel to the first incident LB and directed at the LGA; Obtaining a first return beam LB by reflection of the first incident beam LB from the first surface; Obtaining a second return LB by redirecting the second incident LB into or onto the sample by the LGA, reflecting the second incident LB from the internal facet, and redirecting it back by the LGA; Measuring a first angular deviation of the second return LB relative to the first return LB; and estimating an actual tilt angle μ′ of the internal facet relative to the first surface based at least on the measured first angular deviation.

2. 2. The optical-based method of claim 1, wherein the sample includes a first portion and a second portion, the internal facet extending between the first portion and the second portion, the first portion being positioned between a second surface external to the sample and the internal facet, and wherein transmitted LB, constituting a portion of the second incident LB transmitted directly or indirectly into the sample, enters the sample via the second surface.

3. 3. The optical-based method of claim 2, wherein the LGA comprises at least a light bending component (LFC) nominally configured to bend light when projected in a direction normal to the first surface at a light bending angle equal to the nominal tilt angle.

4. The optics-based method of claim 3 , wherein the LFC is or comprises a prism, one or more mirrors, and / or a diffraction grating.

5. The optical-based method of claim 4 , wherein the light bending angle is insensitive to variations in the pitch of the LFC.

6. 6. The optically-based method of claim 5, wherein the LFC is or comprises a pentaprism or a prism with similar functionality, or a pair of mirrors placed at an angle to each other, or a mirror arrangement with similar functionality.

7. 4. The optically-based method of claim 3, wherein the LGA further comprises a coupling infrastructure configured to guide the light bent by the LFC onto or into the sample, so that light transmitted thereby into the sample impinges nominally perpendicularly on the internal facet.

8. the coupling infrastructure comprises a coupling prism (CP), the CP comprising an external flat CP first surface, an external flat CP second surface nominally inclined at the nominal inclination angle relative to the CP first surface, and an external CP third surface opposite the CP second surface; the CP has a refractive index that is the same as or close to the refractive index of the first portion of the sample; 8. The optically-based method of claim 7, wherein the CP is positioned such that a first surface of the CP is parallel to the first surface of the sample and is further oriented such that the light bent by the LFC impinges on a second surface of the CP nominally perpendicularly.

9. 9. The optical-based method of claim 8, wherein the coupling infrastructure further comprises a conformal interface disposed between the CP third surface and the sample and configured to adopt a shape such that the CP first surface is parallel to the first surface of the sample.

10. 10. The optics-based method of claim 9, wherein the conformal interface has a refractive index that is the same as or close to the refractive index of the first portion of the sample.

11. The optical-based method of claim 9 , wherein the conformal interface is or comprises a liquid and / or a gel.

12. The optics-based method of claim 2 , wherein the sample is a prism, a waveguide, or a beam splitter.

13. 2. The optically-based method of claim 1, wherein the first incident light LB and the second incident light LB constitute complementary portions of a single collimated light beam or are prepared by blocking one or more portions of a single collimated light beam.

14. The optics-based method of claim 13 , wherein the single collimated LB is polychromatic or the single collimated LB is a laser beam.

15. The optically-based method of claim 8 , further comprising an initial calibration stage, in which a standard sample is utilized to calibrate the LFC, the CP, and / or the orientation of the sample.

16. 9. The optically-based method of claim 8, further comprising generating an additional incident LB directed at the CP first surface and parallel to the first incident LB, wherein the orientation of the CP is (a) calibrated and / or (b) tested for correct orientation during the measurement of the first angular deviation by measuring an additional angular deviation of the additional return LB relative to the first return LB, the additional return LB being obtained by reflection of the additional incident LB from the CP first surface.

17. 2. The optically-based method of claim 1, wherein the first angular deviation is obtained from measured coordinates of a first spot and a second spot formed by the first return LB and the second return LB, respectively, on a photosensitive surface of a light or image sensor.

18. The optics-based method of claim 1 , wherein the first angular deviation is measured using an autocollimator.

19. 20. The optics-based method of claim 18, wherein the measured first angular deviation is equal to Δu / f, where Δu is the difference between coordinates of a first spot and corresponding coordinates of a second spot on the photosensitive surface of the autocollimator, f is the focal length of a collimator lens of the autocollimator, and the first spot is formed by the first return LB and the second spot is formed by the second return LB.

20. 9. The optics-based method of claim 8, comprising the CP, wherein the actual tilt angle of the internal facet relative to the first surface is obtained from the measured first angular deviation taking into account a value of the actual tilt angle of the CP second surface relative to the CP first surface and a value of the refractive index of the first portion of the sample.

21. the sample comprises the first portion and the second portion, the nominal tilt angle is 90°, the sample comprises an external third surface that is flat and parallel to the first surface of the sample, and the method further comprises, following the measurement of the first angular deviation: inverting the sample to invert the first and third surfaces while maintaining the nominal orientation of the internal facets relative to the LGA; generating a third incident LB directed normal to the third surface and a fourth incident LB parallel to the third incident LB and directed toward the LGA; Obtaining a third return beam LB by reflection of the third incident beam LB from the second surface; Obtaining a fourth return LB by redirecting the second incident LB into or onto the sample by the LGA, reflecting the second incident LB from the internal facet, and redirecting it back by the LGA; Measuring a second angular deviation of the fourth return LB relative to the third return LB; 13. The optics-based method of claim 2, further comprising: estimating an actual tilt angle between the first surface and the internal facet based on the measured first angular deviation and the measured second angular deviation.

22. The method according to claim 22, wherein the sample comprises the first portion and the second portion, the nominal tilt angle is 90°, the sample comprises an external third surface that is flat and parallel to the first surface of the sample, and wherein, following the measurement of the first angular deviation, inverting the sample to invert the first and third surfaces while maintaining the nominal orientation of the internal facets relative to the LGA; generating a third incident LB directed normal to the third surface and a fourth incident LB parallel to the third incident LB and directed toward the LGA; Obtaining a third return beam LB by reflection of the third incident beam LB from the second surface; Obtaining a fourth return LB by redirecting the second incident LB into or onto the sample by the LGA, reflecting the second incident LB from the internal facet, and redirecting it back by the LGA; Measuring a second angular deviation of the fourth return LB relative to the third return LB; and estimating an actual tilt angle between the first surface and the internal facet based on the measured first angular deviation and the measured second angular deviation; 9. The optical-based method of claim 8, wherein the optical-based method comprises the CP, the CP further comprising a CP fourth surface opposite and parallel to the CP first surface, and wherein the inversion of the sample involves inverting the CP such that the CP first surface and the CP fourth surface are reversed while maintaining a nominal orientation of the CP second surface relative to the sample.

23. 22. The optics-based method of claim 21, wherein the uncertainty in the parallelism of the first surface of the sample and the third surface of the sample is significantly smaller than the required measurement accuracy of the actual tilt angle.

24. The method according to claim 24, wherein the sample comprises the first portion and the second portion, the nominal tilt angle is 90°, the sample comprises an external third surface that is flat and parallel to the first surface of the sample, and wherein, following the measurement of the first angular deviation, inverting the sample to invert the first and third surfaces while maintaining the nominal orientation of the internal facets relative to the LGA; generating a third incident LB directed normal to the third surface and a fourth incident LB parallel to the third incident LB and directed toward the LGA; Obtaining a third return beam LB by reflection of the third incident beam LB from the second surface; Obtaining a fourth return LB by redirecting the second incident LB into or onto the sample by the LGA, reflecting the second incident LB from the internal facet, and redirecting it back by the LGA; Measuring a second angular deviation of the fourth return LB relative to the third return LB; and estimating an actual tilt angle between the first surface and the internal facet based on the measured first angular deviation and the measured second angular deviation; 9. The optics-based method of claim 8, wherein the optics-based method includes the CP, and the actual tilt angle of the internal facet relative to the first surface is obtained from the measured first angular deviation, a value of the actual tilt angle of the CP second surface relative to the CP first surface, and a value of the refractive index of the first portion of the sample.

25. The method according to claim 25, wherein the sample comprises the first portion and the second portion, the nominal tilt angle is 90°, the sample comprises an external third surface that is flat and parallel to the first surface of the sample, and wherein, following the measurement of the first angular deviation, inverting the sample to invert the first and third surfaces while maintaining the nominal orientation of the internal facets relative to the LGA; generating a third incident LB directed normal to the third surface and a fourth incident LB parallel to the third incident LB and directed toward the LGA; Obtaining a third return beam LB by reflection of the third incident beam LB from the second surface; Obtaining a fourth return LB by redirecting the second incident LB into or onto the sample by the LGA, reflecting the second incident LB from the internal facet, and redirecting it back by the LGA; Measuring a second angular deviation of the fourth return LB relative to the third return LB; and estimating an actual tilt angle between the first surface and the internal facet based on the measured first angular deviation and the measured second angular deviation; The optical-based method of claim 8 , further comprising measuring an actual tilt angle of the CP second surface relative to the CP first surface.

26. the sample includes k≧1 additional internal facets nominally parallel to the internal facet; In the acquisition of the second return beams, k additional return beams are acquired by reflecting k beams from each of the k additional internal facets, and the k beams collectively constitute a portion of the second incident beam that is transmitted into the sample and further transmitted through the internal facets; In the measurement of the first angular deviation, k additional angular deviations of the k additional return LBs relative to the first return LB are measured; 16. The optics-based method of claim 1, wherein when estimating the actual tilt angle μ′ of the internal facet, (i) k additional actual tilt angles of each of the k additional internal facets are estimated, and / or (ii) an actual average tilt angle is estimated that is equal to or approximately equal to an average of the actual tilt angles of the internal facet and the k additional internal facets, wherein the actual average tilt angle indicates the actual tilt angle μ′ of the internal facet.

27. 27. The optics-based method of claim 26, wherein k≧2, a first one of the additional internal facets is positioned between the internal facet and a second one of the additional internal facets, and wherein, for each m such that 2≦m≦k−1, an m one of the k additional internal facets is positioned between the (m−1) and (m+1) one of the k additional internal facets.

28. 27. The optically-based method of claim 26, wherein the internal facet and each of the k additional internal facets are configured to reflect light of a respective spectrum, each spectrum being distinct from the other spectra so as to allow differentiation between the second return LB and each of the k additional return LBs.

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