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EP-4248171-B1 - OPTICAL-BASED VALIDATION OF ORIENTATIONS OF SURFACES

EP4248171B1EP 4248171 B1EP4248171 B1EP 4248171B1EP-4248171-B1

Inventors

  • EISENBERG, Ido

Dates

Publication Date
20260506
Application Date
20211118

Claims (15)

  1. An optical-based system for validating angles between external, flat surfaces of samples (10, 20), the system (100, 200, 300) comprising: a light folding component (102, 202, 302), LFC, nominally configured to fold light incident thereon at a nominal inclination angle defined by an external, flat first surface and an external, flat second surface of a sample, wherein a light folding angle of the LFC is insensitive to variations in a pitch thereof; and an illumination and collection arrangement (104, 204, 304), ICA, comprising: a light generation assembly configured to (a) project a first incident light beam, LB, on the first surface, so as to generate a first returned LB by reflection off the first surface, and (b) project a second incident LB on the LFC, in parallel to the first incident LB, so as to generate a second returned LB, by folding by the LFC, reflection off the second surface, and repassage via the LFC, wherein the first incident LB and the second incident LB are complementary portions of a collimated LB; and at least one sensor (114), configured to measure a first angular deviation of the second returned LB relative to the first returned LB, and/or an eyepiece assembly configured to enable manually measuring the first angular deviation; and wherein the measured first angular deviation is indicative of an actual inclination angle of the second surface relative to the first surface.
  2. The optical-based system of claim 1, wherein the system further comprises orienting infrastructure (120, 220, 320) configured to orient the sample such that the first incident LB normally impinges on the first surface, and a folded LB, obtained by folding of the second incident LB by the LFC, nominally normally impinges on the second surface.
  3. The optical-based system of claim 1 or claim 2, comprising the at least one sensor, and further comprising a computational module (130, 230, 330) configured to compute the actual inclination angle of the second surface relative to the first surface, based at least on the measured first angular deviation.
  4. The optical-based system of any one of claims 1 to 3, wherein the ICA further comprises a pair of blocking elements (246a, 246b) configured to allow selectively blocking each of the first incident LB and the second incident LB, wherein wherein the ICA is or comprises an autocollimator, the autocollimator comprising the light source and the at least one sensor, wherein the system further comprises orienting infrastructure (120, 220, 320) configured to orient the sample such that the first incident LB normally impinges on the first surface, and/or a folded LB, obtained by folding of the second incident LB by the LFC, nominally normally impinges on the second surface, and wherein the system further comprises a computational module (130, 230, 330) configured to compute the actual inclination angle of the second surface relative to the first surface, based at least on the measured first angular deviation.
  5. The optical-based system of any one of claims 1 to 4, wherein the LFC comprises a prism, wherein the prism is a pentaprism or a like-function prism.
  6. The optical-based system of any one of claims 1 to 5, wherein the system comprises the at least one sensor, wherein the light generation assembly comprises a light source (112) and optical equipment (118), wherein the light source is configured to generate a single LB, wherein the optical equipment is configured to collimate the single LB, thereby obtaining the collimated LB.
  7. The optical-based system of claim 6, the ICA is or comprises an autocollimator (240), the autocollimator comprising the light source and the at least one sensor, wherein the system further comprises orienting infrastructure (120, 220, 320) configured to orient the sample such that the first incident LB normally impinges on the first surface, and/or a folded LB, obtained by folding of the second incident LB by the LFC, nominally normally impinges on the second surface, and wherein the system further comprises a computational module (130, 230, 330) configured to compute the actual inclination angle of the second surface relative to the first surface, based at least on the measured first angular deviation.
  8. The optical-based system of any one of claims 3 to 7, comprising the at least one sensor and the computational module, wherein the nominal inclination angle is 90° and the sample further comprises an external, flat third surface, which is parallel to the first surface, and wherein the computational module is configured to compute the actual inclination angle additionally taking into account a measured second angular deviation of a fourth returned LB relative to a third returned LB, obtained by, with the sample flipped, such that the first surface and the third surface are inverted, ( a' ) projecting a third incident LB on the third surface of the sample, so as to generate the third returned LB by reflection off the third surface, and ( b' ) projecting a fourth incident LB on the LFC, in parallel to the third incident LB, so as to generate the fourth returned LB by folding thereof by the LFC, reflection off the second surface, and repassage via the LFC.
  9. The optical-based system of claim 8, wherein the computational module is further configured to compute an uncertainty in the computed value of the actual inclination angle taking into account at least manufacturing tolerances and imperfections of the LFC and the ICA.
  10. The optical-based system of claim 9, further comprising the orienting infrastructure, wherein the computational module is configured to compute the uncertainty in the computed value of the actual inclination angle additionally taking into account manufacturing tolerances and imperfections of the orienting infrastructure.
  11. An optical-based method for validating angles between external, flat surfaces of samples (10, 20), the method comprising: providing a sample comprising an external, flat first surface and an external, flat second surface nominally inclined at a nominal inclination angle relative to the first surface; generating a first incident light beam, LB, directed at the first surface, and a second incident LB parallel to the first incident LB; obtaining a first returned LB by reflection of the first incident LB off the first surface; obtaining a second returned LB by folding by a light folding component (102, 202, 302), LFC, the second incident LB at a light folding angle nominally equal to the nominal inclination angle, reflecting the folded LB off the second surface, and folding the reflected LB at the light folding angle by repassage via the LFC; measuring a first angular deviation of the second returned LB relative to the first returned LB; and deducing an actual inclination angle of the second surface relative to the first surface, based at least on the measured first angular deviation; wherein the first incident LB and the second incident LB are complementary portions of a single collimated LB; and wherein the light folding angle is insensitive to variations in a pitch of the LFC.
  12. The optical-based method of claim 11, wherein the first incident LB is directed at the first surface perpendicularly thereto.
  13. The optical-based method of claim 11 or claim 12, wherein the folding is implemented utilizing the LFC, wherein the LFC is or comprises a pentaprism or a like-function prism.
  14. The optical-based method of any one of claims 11 to 13, wherein the first angular deviation is measured using an autocollimator, wherein the measured first angular deviation between the returned LBs is equal to, or about equal to, Δu / f, wherein Δ u is a difference between a coordinate of a first spot and a corresponding coordinate of a second spot on a photosensitive surface of the autocollimator, f is the focal length of a collimating lens of the autocollimator, and wherein the first spot is formed by the first returned LB and the second spot is formed by the second returned LB.
  15. The optical-based method of any one of claims 11 to 14, wherein the nominal inclination angle is 90° and the sample comprises an external, flat third surface parallel to the first surface, wherein the first incident LB is directed at the first surface perpendicularly thereto, and wherein the method further comprises, following the measuring of the first angular deviation: flipping the sample, so as to invert the first and third surfaces while maintaining a nominal orientation of the second surface relative to the LFC; preparing a third incident LB, directed at the third surface, normally thereto, and a fourth incident LB parallel to the third incident LB; obtaining a third returned LB by reflection of the third incident LB off the third surface; obtaining a fourth returned LB by folding the fourth incident LB at a light folding angle nominally equal to the nominal inclination angle, reflection thereof off the second surface, and folding thereof at the light folding angle; measuring a second angular deviation of the fourth returned LB relative to the third returned LB; and wherein, in the deducing of the actual inclination angle, the actual inclination angle is deduced additionally taking into account the measured second angular deviation.

Description

TECHNICAL FIELD The present disclosure relates generally to methods and systems for surface-metrology of samples. BACKGROUND Optical elements, such as glass prisms, are increasingly required to exhibit higher angular tolerances between surfaces thereof. To meet the required angular tolerances, high-precision metrology for validating the angles between surfaces is necessitated, which, in turn, necessitates use of high-end optical components, and complex alignment and calibration procedures. There is thus an unmet need in the art for simple and easily implementable metrology techniques, which avoid the use of high-end optical components, thereby addressing mass production demands. US4056323A discloses an interferometer optical system for general use to measure optical parallelism or relative rotational or joint translational positions of the two spaced subject mirrors uses coherent light split into two beams which are directed, one normal to one of the two mirrors and the other normal to the other of the two mirrors. JP2003065739A discloses a device for measuring angle of polygon mirror that includes a laser light source, a half mirror which splits a laser beam in order to make laser beams enter two adjoining surfaces of the polygon mirror at the same time, and a CCD camera which simultaneously detects reflecting light from the polygon mirror, and reduces the measurement time by simultaneously detecting angles of the two surfaces when measuring the angular accuracy of a polygon mirror and the deviation of pyramid. JPH09304036A discloses an angle measuring apparatus sheds collimated light emitted from first laser optic systems and second laser optic systems respectively to both two faces including a reference prism whose angle of interest has been measured and a prism to be measured located at a position with the reference prism placed. A publication "Measuring the angles and pyramidal error of high-precision prisms" by Jaramillo-Nunez A et al. (in Oprical Engineering, Soc. of Photo-Optical Instrumentation Engineers, Bellingham, vol. 36 no. 10, pages 2868-2871) discloses use of a Twyman-Green interferometer to measure the wedge angles and pyramidal errors of high-precision optical prisms. SUMMARY Aspects of the disclosure, according to some embodiments thereof, relate to methods and systems for surface-metrology of samples. More specifically, but not exclusively, aspects of the disclosure, according to some embodiments thereof, relate to optical-based methods and systems for metrology of external surfaces of samples. However, the claims define optical-based systems and methods. The present application discloses fast, simple, and precise methods and systems for measuring the inclination of an external, flat surface of a sample relative to one or more other external, flat surfaces thereof. To achieve this, two parallel-prepared light beams (LBs) may be employed: The first LB is impinged on an external, flat first surface of the sample. The second LB is redirected so as to nominally impinge on an external, flat second surface of the sample - whose inclination angle relative to the first surface is to be validated - at the same incidence angle as the first LB. The angular deviation between the reflected LBs, after the second reflected LB has been redirected again, is then measured. Advantageously, according to some embodiments of the disclosed technology, a collimated light source, a light sensor (or image sensor), a light folding component to redirect the second LB, and orienting infrastructure to orient the sample suffice in order to validate inclinations of external, flat surfaces. Thus there is provided an optical-based method for validating angles between external, flat surfaces of samples. The method includes: Providing a sample including an external, flat first surface and an external, flat second surface nominally inclined (intended by design and fabrication to be inclined) at a nominal inclination angle relative to the first surface.Generating a first incident light beam (LB), directed at the first surface, and a second incident LB parallel to the first incident LB.Obtaining a first returned LB by reflection of the first incident LB off the first surface.Obtaining a second returned LB by folding the second incident LB at a light folding angle nominally equal to the nominal inclination angle, reflecting the folded LB off the second surface, and folding the reflected LB at the light folding angle.Measuring a first angular deviation of the second returned LB relative to the first returned LB.Deducing an actual inclination angle of the second surface relative to the first surface, based at least on the measured first angular deviation. According to some embodiments of the method, the deduced actual inclination angle equals α + δ/2, or about equals α + δ/2 (e.g. the deduced actual inclination angle is between α + 0.475 · δ and α + 0.525 · δ, between α + 0.45 · δ and α + 0.55 · δ, or even between α + 0.4 · δ an