Search

EP-4737847-A1 - OPTICAL DEVICE AND INSPECTION METHOD

EP4737847A1EP 4737847 A1EP4737847 A1EP 4737847A1EP-4737847-A1

Abstract

An optical device for inspecting a to-be-inspected surface having a riblet structure in which projections each extending in a first direction are provided in a second direction intersecting the first direction is configured to include a condensing optical system that irradiates an irradiation region on the to-be-inspected surface with light from a light source and that condenses light reflected by the irradiation region, a photodetector that detects the light condensed by the condensing optical system, and an amount-of-light changing member capable of changing the ratio between the amounts of first reflected light reflected to the photodetector by a portion where the projections are not provided in the irradiation region and second reflected light reflected to the photodetector by the projections in the irradiation region.

Inventors

  • ARAI, MASANORI

Assignees

  • NIKON CORPORATION

Dates

Publication Date
20260506
Application Date
20230628

Claims (18)

  1. An optical device for inspecting a to-be-inspected surface having a riblet structure in which projections each extending in a first direction are provided in a second direction intersecting the first direction, the optical device comprising: a condensing optical system that irradiates an irradiation region on the to-be-inspected surface with light from a light source and that condenses light reflected by the irradiation region; a photodetector that detects the light condensed by the condensing optical system; and an amount-of-light changing member capable of changing the ratio between the amounts of first reflected light reflected to the photodetector by a portion where the projections are not provided in the irradiation region and second reflected light reflected to the photodetector by the projections in the irradiation region.
  2. The optical device according to claim 1, wherein the amount-of-light changing member changes the polarization state of the light directed to the irradiation region.
  3. The optical device according to claim 1 or 2, wherein the amount-of-light changing member reduces the amount of the first reflected light.
  4. The optical device according to claim 3, wherein the amount-of-light changing member does not reduce the amount of the second reflected light.
  5. The optical device according to any one of claims 1 to 4, wherein the amount-of-light changing member comprises: a first member that is disposed on the optical path of the first reflected light and that changes the polarization state of light from the light source to a first polarization state; and a second member that is disposed on the optical path of both the first reflected light and the second reflected light, and that changes light in the first polarization state emitted from the first member to a second polarization state different from the first polarization state.
  6. An optical device for inspecting a to-be-inspected surface having a riblet structure in which projections each extending in a first direction are provided in a second direction intersecting the first direction, the optical device comprising: a condensing optical system that irradiates an irradiation region on the to-be-inspected surface with light from a light source and that condenses light reflected by the irradiation region; a photodetector that detects the light condensed by the condensing optical system; a first member that is disposed on the optical path of first reflected light reflected to the photodetector by a portion where the projections are not provided in the irradiation region, and that changes the polarization state of light from the light source to a first polarization state; and a second member that is disposed on the optical path of both the first reflected light and second reflected light reflected to the photodetector by the projections in the irradiation region, and that changes light in the first polarization state emitted from the first member to a second polarization state different from the first polarization state.
  7. The optical device according to claim 5 or 6, wherein the first member is not disposed on the optical path of the second reflected light.
  8. The optical device according to any one of claims 5 to 7, wherein the first polarization state is linear polarization, and the first member transmits part of the first reflected light toward the photodetector, depending on the polarization state of the first reflected light emitted from the second member.
  9. The optical device according to claim 8, wherein the second polarization state is elliptical polarization.
  10. The optical device according to any one of claims 5 to 9, wherein the first member is a polarizing beam splitter, and the second member is a quarter-wave plate.
  11. The optical device according to any one of claims 5 to 10, wherein the second member is supported rotatably about an axis of rotation along the optical axis of the condensing optical system.
  12. The optical device according to any one of claims 5 to 11, wherein the condensing optical system comprises the first member and the second member.
  13. The optical device according to any one of claims 1 to 12, wherein the second reflected light is reflected to the photodetector by the projections in the irradiation region and the portion where the projections are not provided in the irradiation region.
  14. The optical device according to any one of claims 1 to 13, wherein the photodetector has a detection surface disposed on a plane different from a plane conjugate to the to-be-inspected surface with respect to the condensing optical system.
  15. The optical device according to any one of claims 1 to 14, further comprising an operation unit that inspects the riblet structure, based on the result of detection by the photodetector.
  16. An inspection method for inspecting a riblet structure, based on data indicating the result of detection by the optical device according to any one of claims 1 to 15.
  17. An inspection method for inspecting a to-be-inspected surface having a riblet structure in which projections each extending in a first direction are provided in a second direction intersecting the first direction, the inspection method comprising: irradiating an irradiation region on the to-be-inspected surface with light; condensing, with a condensing optical system, light reflected by the irradiation region in response to irradiation with the light; changing the ratio between the amounts of first reflected light reflected by a portion where the projections are not provided in the irradiation region and second reflected light reflected by the projections in the irradiation region; detecting the light condensed by the condensing optical system; and inspecting the riblet structure, based on the result of detection.
  18. An optical device for inspecting a to-be-inspected surface having a riblet structure in which projections each extending in a first direction are provided in a second direction intersecting the first direction, the optical device comprising: a condensing optical system that irradiates an irradiation region on the to-be-inspected surface with light from a light source and that condenses light reflected by the irradiation region; a photodetector that detects the light condensed by the condensing optical system; and an amount-of-light changing member that changes the polarization state of light linearly polarized in a predetermined direction and directed to the irradiation region of light from the light source and the polarization state of first reflected light reflected to the photodetector by a portion where the projections are not provided in the irradiation region, and that transmits part of the first reflected light, depending on the polarization state of the first reflected light.

Description

FIELD The present disclosure relates to an optical device and an inspection method used for inspecting an object surface having a riblet structure. BACKGROUND Configurations of an inspection device for inspecting the quality of a fine structure have been proposed (see, e.g., Patent Literature 1). CITATION LIST PATENT LITERATURE Patent Literature 1: U.S. patent No. 8842271 SUMMARY An optical device according to the present disclosure is an optical device for inspecting a to-be-inspected surface having a riblet structure in which projections each extending in a first direction are provided in a second direction intersecting the first direction. The optical device includes a condensing optical system that irradiates an irradiation region on the to-be-inspected surface with light from a light source and that condenses light reflected by the irradiation region; a photodetector that detects the light condensed by the condensing optical system; and an amount-of-light changing member capable of changing the ratio between the amounts of first reflected light reflected to the photodetector by a portion where the projections are not provided in the irradiation region and second reflected light reflected to the photodetector by the projections in the irradiation region. An inspection method according to the present disclosure is an inspection method for inspecting a to-be-inspected surface having a riblet structure in which projections each extending in a first direction are provided in a second direction intersecting the first direction. The inspection method includes irradiating an irradiation region on the to-be-inspected surface with light; condensing, with a condensing optical system, light reflected by the irradiation region in response to irradiation with the light; changing the ratio between the amounts of first reflected light reflected by a portion where the projections are not provided in the irradiation region and second reflected light reflected by the projections in the irradiation region; detecting the light condensed by the condensing optical system; and inspecting the riblet structure, based on the BRIEF DESCRIPTION OF DRAWINGS FIG. 1 schematically illustrates irradiation of an object surface having a riblet structure with light.FIG. 2 illustrates a riblet structure.FIG. 3 illustrates reflection of light on an object surface having a riblet structure.FIG. 4 schematically illustrates the configuration of an optical device.FIG. 5 schematically illustrates condensation of light by an optical member disposed closest to an object surface in a condensing optical system.FIG. 6 illustrates a relationship of projection in the condensing optical system.FIG. 7 schematically illustrates first received-light data.FIG. 8 schematically illustrates the configuration of a computer.FIG. 9 is a functional block diagram of a processor included in the computer.FIG. 10 illustrates the ratio between the amounts of first reflected light and second reflected light in the first received-light data.FIG. 11 schematically illustrates second received-light data.FIG. 12 is a flowchart of a process for inspecting a riblet structure.FIG. 13 is a flowchart of a process for measuring a riblet structure.FIG. 14 schematically illustrates the configuration of an optical device according to a modified example. DESCRIPTION OF EMBODIMENTS An optical device and an inspection method of the present application will now be described in detail with reference to the attached drawings. FIG. 1 schematically illustrates irradiation of an object surface having a riblet structure with light, and FIG. 2 illustrates a riblet structure. In the present embodiment, an optical device 1 is a predetermined distance away from an object surface OS having a riblet structure formed thereon, and inspects the object surface OS by irradiating an irradiation region IR on the object surface OS with light. For convenience of description, the following describes a case in which the optical device 1 is used for inspecting a riblet structure (object surface OS), but the optical device 1 can also be applied to measurement of a riblet structure (object surface OS). For illustrative purposes, FIG. 1 shows the optical device 1 disposed farther from the object surface OS than a predetermined position. The object surface OS may be an envelope including ridgelines of riblet or a surface of an object on which a riblet structure will be formed. The object surface OS may be referred to as a surface of a workpiece. Formation of a riblet structure on an object surface OS enables reduction in frictional resistance between the object surface OS and a fluid contacting the object surface OS. However, a change in the shape of the riblet structure may reduce the effect of reduction in frictional resistance between the object surface OS and a fluid. Thus, an optical device for inspecting the shape of a riblet structure on an object surface OS conveniently is desired. It may be said that at le