Apparatus and method for rotating an optical objective

Abstract

A dark-field optical system can include a rotating objective assembly having a dark-field objective that collects light from a sample within a collection numerical aperture, where the dark-field objective includes an entrance aperture and an exit aperture at symmetric relative azimuthal angles with respect to an optical axis, a rotation bearing that allows at least a portion of the dark-field objective including the entrance aperture and the exit aperture to rotate about the optical axis, and a rotation driver that controls a rotation angle of the entrance aperture. The system can also include a multi-angle illumination subsystem that illuminates the sample using an illumination beam that passes through the entrance aperture at two or more illumination azimuthal angles, where the azimuthal angle of the illumination beam on the sample can be selected by rotating the objective to any of the two or more illumination azimuthal angles.

Description

[0001] Cross-reference of related applications

[0002] This application claims the right to U.S. Provisional Application No. 63 / 025,192, filed May 15, 2020, entitled Apparatus and Method to Rotate an Optical Objective, entitled Apparatus and Method to Rotate an Optical Objective, with Anatoly Romanovsky, Jenn-Kuen Leong, Daniel Kavaldjiev, Chunhai Wang, Bret Whiteside, and Steve Xu as inventors, pursuant to 35 U.S. SC §119(e), the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure generally relates to optical measurement and, more specifically, to optical measurement using rotating optical objectives. Background Technology

[0004] Dark-field optical inspection or metrology systems used in the semiconductor industry typically generate measurements based on light collected from a sample (which excludes specular reflections of the illumination beam), where the specular illumination is located outside the collecting numerical aperture (NA) or blocked before reaching the detector. Furthermore, many optical inspection or metrology techniques utilize measurements based on illumination of the sample using different azimuth angles.

[0005] In such systems, it is generally desirable to utilize objectives with high focusing apertures (NAs) to collect light from the sample effectively over a wide range of angles. However, increasing the NA of the objective typically results in a progressively smaller gap between the sample and the objective, which limits the ability to illuminate the sample at angles of incidence beyond the focusing NA. Furthermore, dark-field measurements generated by blocking specular reflection illumination can suffer from unwanted scattering of specularly reflected light through blocking elements. Therefore, it is desirable to provide systems and methods for dark-field illumination using high NA objectives. Summary of the Invention

[0006] According to one or more illustrative embodiments of this disclosure, a dark-field optical system is disclosed. In one illustrative embodiment, the system includes an illumination source. In another illustrative embodiment, the system includes a rotating objective lens assembly. In another illustrative embodiment, the rotating objective lens assembly includes a dark-field objective lens for collecting measurement light from a sample within a light-gathering numerical aperture, wherein the dark-field objective lens includes an inlet aperture and an outlet aperture at symmetrical relative to the optical axis of the dark-field objective lens. In another illustrative embodiment, the rotating objective lens assembly includes a rotary bearing for allowing at least a portion of the dark-field objective lens, including the inlet aperture and the outlet aperture, to rotate about the optical axis. In another illustrative embodiment, the rotating objective lens assembly includes a rotary actuator for controlling the rotation angle of the inlet aperture. In another illustrative embodiment, the system includes a multi-angle illumination subsystem for illuminating the sample using illumination beams passing through the entrance aperture at two or more illumination azimuth angles, wherein a portion of the illumination beams is reflected by the sample and exits the objective lens through the exit aperture as a reflected illumination beam, and wherein the azimuth angle of the illumination beams on the sample can be selected by rotating the objective lens to any of the two or more illumination azimuth angles using the rotating objective lens assembly. In another illustrative embodiment, the system includes a light-gathering subsystem configured to guide at least a portion of the measurement light from the dark-field objective lens to one or more detectors.

[0007] According to one or more illustrative embodiments of this disclosure, a rotating objective assembly is disclosed. In one illustrative embodiment, the rotating objective assembly includes a dark-field objective for collecting measurement light from a sample within a light-gathering numerical aperture, wherein the objective includes an inlet aperture and an outlet aperture with symmetrical relative azimuth angles to the optical axis of the dark-field objective, and wherein the objective is configured to receive an illumination beam passing through the inlet aperture, wherein a portion of the illumination beam reflected by the sample exits the objective through the outlet aperture as a reflected illumination beam. In another illustrative embodiment, the rotating objective assembly includes a rotary bearing for allowing at least a portion of the dark-field objective, including the inlet aperture and the outlet aperture, to rotate about the optical axis. In another illustrative embodiment, the rotating objective assembly includes a rotary driver for controlling the rotation angle of the inlet aperture, wherein the azimuth angle of the illumination beam on the sample can be selected by rotating the objective to a selected rotation angle using the rotating objective assembly.

[0008] According to one or more illustrative embodiments of this disclosure, a dark-field measurement method is disclosed. In one illustrative embodiment, the method includes aligning a sample into the field of view of a dark-field objective, wherein the dark-field objective includes an inlet aperture and an outlet aperture at symmetrical relative azimuth angles with respect to the optical axis of the dark-field objective. In another illustrative embodiment, the method includes rotating the objective to align the inlet aperture along a selected azimuth angle for measurement. In another illustrative embodiment, the method includes illuminating the sample using an illumination beam passing through the inlet aperture at the selected azimuth angle, wherein a portion of the illumination beam reflected by the sample exits the dark-field objective through the outlet aperture as a reflected illumination beam. In another illustrative embodiment, the method includes collecting measurement light from the sample within a light-collecting numerical aperture of the dark-field objective. In another illustrative embodiment, the method includes generating one or more measurements associated with the sample based on the measurement light.

[0009] It should be understood that the foregoing general description and the following detailed description are merely exemplary and illustrative and do not necessarily limit the invention as claimed. The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments of the invention and, together with the general description, serve to explain the principles of the invention. Attached Figure Description

[0010] Those skilled in the art will better understand the many advantages of this disclosure by referring to the accompanying drawings, among which:

[0011] Figure 1A This is a conceptual block diagram illustrating a dark-field optical system according to one or more embodiments of the present disclosure.

[0012] Figure 1B This is a conceptual outline view of a dark field objective lens according to one or more embodiments of the present disclosure, illustrating the illumination and light-gathering path for dark field measurements.

[0013] Figure 1C This is a conceptual outline view of a dark-field objective lens formed as a hole in a housing according to one or more embodiments of the present disclosure.

[0014] Figure 1D This is a conceptual outline view of a dark-field objective lens formed as a notch in a housing according to one or more embodiments of the present disclosure.

[0015] Figure 1E This is a cross-sectional view of a lens element comprising two dark field apertures to provide a dark field illumination path within a light-collecting NA, according to one or more embodiments of the present disclosure.

[0016] Figure 1FThis is a contour view of a dark field objective lens with a dark field aperture according to one or more embodiments of the present disclosure, the dark field aperture being formed as a hole through a portion of the housing to provide a dark field illumination path outside the light-collecting NA of the dark field aperture.

[0017] Figure 1G This is a conceptual schematic view of a dark field optical system according to one or more embodiments of the present disclosure, illustrating a single illumination source providing illumination at a single azimuth angle.

[0018] Figure 2A This is a conceptual top view of a dark field optical system comprising two illumination channels providing illumination beams at two azimuth angles separated by 90 degrees, according to one or more embodiments of the present disclosure.

[0019] Figure 2B This is a schematic outline view of a multi-angle lighting subsystem including a rotatable lighting channel according to one or more embodiments of the present disclosure.

[0020] Figure 3 This is a flowchart illustrating the steps performed in a dark field measurement method according to one or more embodiments of the present disclosure. Detailed Implementation

[0021] The disclosed subject matter will now be described in detail with reference to the accompanying drawings. This disclosure has been particularly shown and described with respect to certain embodiments and their specific features. The embodiments set forth herein are to be regarded as illustrative rather than restrictive. It will be readily apparent to those skilled in the art that various changes and modifications in form and detail can be made without departing from the spirit and scope of this disclosure.

[0022] Embodiments of this disclosure relate to systems and methods for rotating objective assemblies suitable for dark-field optical measurements using selectable azimuth angles of incidence.

[0023] Dark-field optical measurements are typically performed by illuminating the sample with an illumination beam that often has a limited angular range and generating measurements based on the light emitted from the sample at an angle that excludes specular reflections of the illumination beam. Therefore, the measurements are sensitive to scattered and / or diffracted light. For example, a dark-field image may typically contain no signal (or “dark” signal) when the sample is smooth, but may exhibit a significant signal in the presence of scattering or diffraction. Therefore, dark-field optical measurements are commonly used, but not limited to, the inspection and / or metrology of semiconductor devices at various stages of manufacturing.

[0024] In a general sense, a dark field configuration can be achieved by not collecting specularly reflected illumination beams or by inserting one or more elements into the light-collecting arm to block, redirect, or otherwise prevent specularly reflected illumination beams from reaching the detector. For example, specularly reflected light can be avoided by illuminating the sample outside the collecting numerical aperture (NA) of the system (e.g., the objective lens used to collect light from the sample), such that the specularly reflected portion of the illumination beam remains outside the collecting NA. As another example, specularly reflected illumination collected by the system can be blocked or redirected by an aperture or mirror typically placed at the pupil plane.

[0025] In this paper, it is carefully considered that for certain applications requiring high sensitivity (e.g., (but not limited to) defect inspection on smooth, unpatterned wafers using high-intensity illumination to provide measurable signals from small defects), avoiding the collection of specularly reflected light may be preferred. However, for example, blocking or redirecting high-intensity specular reflections can produce unwanted scattering that can reduce the sensitivity of the measurement. This noise source is absent when specular illumination is simply not collected.

[0026] However, a configuration where both illumination and specular reflection illumination are entirely outside the system's focusing NA can limit the available focusing NA. For example, as the focusing NA of the objective lens decreases, the gap between the objective lens and the sample typically decreases. As the NA approaches 1 in air, illuminating the sample at an angle outside the focusing NA becomes increasingly difficult and sometimes impractical.

[0027] Embodiments of this disclosure relate to a dark-field objective lens (e.g., a dark-field objective) having at least one pair of dark-field apertures symmetrically opposite to each other about a central optical axis. This dark-field objective collects light from a sample within a collecting numerical aperture (NA) and may further include dark-field apertures for providing a path for the illumination beam to reach the sample and for the specularly reflected portion of the illumination beam to exit the dark-field objective. In this way, specularly reflected light from the sample is not collected by the dark-field objective, achieving dark-field operation without blocking reflected illumination, thus eliminating noise from beam blockers in the system causing false reflections of the reflected illumination beam. For example, the pair of dark-field apertures may include an inlet aperture and an outlet aperture symmetrically opposite to each other. The inlet aperture and outlet aperture may have (but do not need to have) the same polar angle (e.g., measured relative to the optical axis) or elevation angle (e.g., measured relative to a plane normal to the optical axis). For example, inlet apertures and outlet apertures having a common polar angle are suitable for use with flat and leveled samples. However, it is desirable to have outlet pores with different polar angles or different shapes (e.g., elongated shapes) to accommodate specular reflections from non-flat or unleveled samples.

[0028] In some embodiments, the dark field aperture is arranged such that the paths of the illumination beam and the specular reflection beam are outside the light-collecting NA. For example, the dark field aperture can provide a path through a portion of the housing that would otherwise be inaccessible. In some embodiments, the dark field aperture is arranged such that the paths of the illumination beam and the specular reflection beam are within the light-collecting NA. In this configuration, the light-collecting NA is slightly reduced at the azimuth angle associated with the dark field aperture. However, this configuration allows for an increased (e.g., maximized) light-collecting NA at other azimuth angles to improve overall sensitivity. This configuration can also collect scattered light at angles close to the specular reflection angle and therefore is highly sensitive to many small defects that only cause small deviations in illumination.

[0029] Further consideration here suggests that this dark-field objective can be used to provide dark-field measurements at multiple azimuth angles. For example, when inspecting surfaces other than bare semiconductor wafers, surface roughness can become a dominant noise source, causing laser illumination to induce speckle patterns (e.g., at the detector plane) that can reduce contrast and limit measurement sensitivity. However, this contrast reduction caused by speckle can be overcome by averaging multiple measurements (with associated speckle patterns) generated using illumination at different azimuth angles. Multidirectional illumination is substantially described, for example, in U.S. Patent No. 9,176,072, issued November 3, 2015, and U.S. Patent No. 10,739,275, issued August 11, 2020, the entire contents of which are incorporated herein by reference.

[0030] In a general sense, a dark-field objective can have any number of dark-field apertures to provide illumination at multiple azimuth or polar angles. However, increasing the number of dark-field apertures can increase cost, manufacturing complexity, reduce the light-gathering anode (NA), and increase the possibility of unwanted scattering. In some embodiments, a dark-field measurement system includes a rotary bearing for providing rotation of the dark-field objective to align the dark-field aperture (e.g., the inlet aperture) to a selected azimuth angle to achieve a measurement at that selected azimuth angle. In this way, multiple measurements using illumination from multiple azimuth angles can be achieved using a dark-field objective with a single pair of symmetrically opposite dark-field apertures. Furthermore, this system is suitable for highly sensitive measurements on a wide range of samples with varying surface smoothness.

[0031] Additional embodiments of this disclosure relate to a dark-field measurement system comprising a rotating objective lens assembly and a multi-angle illumination subsystem for illuminating a sample at a selected azimuth angle. In one embodiment, the multi-angle measurement subsystem includes a static illumination assembly arranged at a fixed azimuth angle. In this manner, measurements at a fixed azimuth angle can be provided by rotating the dark-field objective lens to align the dark-field aperture to the fixed azimuth angle. In another embodiment, the multi-angle illumination subsystem includes a rotatable illumination assembly. For example, the multi-angle illumination subsystem may include one or more beam delivery components (e.g., optical fibers, free-space components, or the like) that maintain alignment with the entrance aperture when the dark-field objective lens is rotated. In this manner, measurements can be performed at any selected azimuth angle.

[0032] Additional embodiments of this disclosure relate to a sample leveling subsystem for leveling a sample relative to a pair of dark-field apertures. The leveling subsystem can adjust the position and / or tilt of the sample to ensure accurate alignment of the illumination beam through the specular reflection of the inlet aperture with the outlet aperture, mitigating potential noise from scattering attributable to reflections of the illumination beam on a portion of the objective lens when misaligned. For example, the leveling subsystem may include a leveling sensor for monitoring the reflection of the illumination beam and an adjustable sample stage for adjusting the sample as needed, at least by flipping or tilting.

[0033] For reference Figures 1A to 3 The present disclosure provides a more detailed description of a system and method for measuring a selected azimuth angle using a rotatable objective lens, according to one or more embodiments.

[0034] Figure 1A This is a conceptual block diagram illustrating a dark field optical system 100 according to one or more embodiments of the present disclosure.

[0035] In one embodiment, the dark-field optical system 100 includes a multi-angle illumination subsystem 102 that provides illumination at two or more azimuth angles, a rotating objective assembly 104 for rotating a dark-field objective lens 106 having at least a pair of symmetrically opposed dark-field apertures 108 to align with the multi-angle illumination subsystem 102, and a detector 110 for capturing light collected in the light-collecting NA of the dark-field objective lens 106 from the sample 112. For example, the pair of symmetrically opposed dark-field apertures 108 may include an entrance aperture providing an unobstructed path for illumination from the multi-angle illumination subsystem 102 to the sample 112 and an exit aperture providing an unobstructed path for a portion of the illumination reflected by the sample 112.

[0036] Dark-field measurements can be performed using illumination from any azimuth angle addressable by the multi-angle illumination subsystem 102, by rotating the dark-field objective 106 using the rotating objective assembly 104 to align the dark-field aperture 108, which operates as the entrance aperture of the dark-field objective 106, to the selected azimuth angle and collect the associated measurement light. For example, the rotating objective assembly 104 may include a rotary bearing 114 and an associated rotary actuator 116 to drive or otherwise control the rotation of the dark-field objective 106.

[0037] For reference Figures 1B to 1F Various non-limiting configurations and designs of the dark field objective 106 are described according to one or more embodiments of the present disclosure. Figure 1B This is a conceptual outline view of a dark field objective 106 according to one or more embodiments of the present disclosure, illustrating the illumination and light-gathering path for dark field measurements. Figures 1C to 1D yes Figure 1B A conceptual profile view of the dark field objective 106 rotated 90 degrees about its optical axis 118 is provided to illustrate various non-limiting designs of the dark field aperture 108.

[0038] In one embodiment, the dark field aperture 108 is formed as a void in the housing 120 of the dark field objective 106, thereby providing an unobstructed dark field illumination path 122 to or from the sample 112 at a selected polar angle 124. For example, as Figure 1B As explained, the dark field aperture 108 can extend from the outer diameter of the housing 120 to the measuring end 126 of the housing 120 near the sample 112. Figure 1B Further explanation is provided of a pair of symmetrically positioned dark-field apertures 108 (here distributed along the X-axis) for providing a dark-field illumination path 122 for both the illumination beam 128 and the reflected illumination beam 130 (e.g., a portion of the illumination beam 128 reflected by the sample 112). In this configuration, the dark-field illumination path 122 may intersect the optical axis 118 at the working distance of the dark-field objective 106 (e.g., the location where the sample 112 is placed). After illuminating the sample 112 with the illumination beam 128, the measurement light 132 (e.g., scattered and / or diffracted light) may be collected within the light-collecting NA 134 of the dark-field objective 106.

[0039] The dark field aperture 108 may have any shape, configuration, or design suitable for providing an unobstructed dark field illumination path 122 through at least a portion of the housing 120 of the dark field objective lens 106, such as (but not limited to) a hole, notch, or indentation. Figure 1CThis is a conceptual outline view of a dark-field objective lens 106 formed as an aperture in a housing 120 according to one or more embodiments of the present disclosure. This aperture can be formed by fabrication (e.g., but not limited to, drilling). Furthermore, this aperture can have any selected diameter or varying diameter along the dark-field illumination path 122. For example, the dark-field aperture 108 may have (but does not need to have) a varying diameter that increases with radial position to approximate the focused illumination beam 128 or the divergent reflected illumination beam 130. Although illustrated as a circular aperture, the dark-field aperture 108 can generally have any shape. Figure 1D This is a conceptual outline view of a dark-field objective lens 106 formed as a notch in a housing 120 according to one or more embodiments of the present disclosure. Additionally, a dark-field aperture 108 configured to serve as an inlet aperture may have the same or different size and / or shape as a dark-field aperture 108 configured to serve as an outlet aperture. In this way, the size and / or shape can be customized for a specific purpose or desired distribution of light. For example, the size and / or shape of the dark-field aperture 108 can be customized according to a desired distribution of scattered light from sample 112 (e.g., the distribution of measurement light 132 from a desired defect type, or the like).

[0040] Dark field aperture 108 may be configured to provide a dark field illumination path 122 at any selected polar angle 124 relative to optical axis 118. In one embodiment, polar angle 124 is configured within light-collecting NA 134 of dark field aperture 108. For example, dark field aperture 108 may include a gap through housing 120 and one or more lens elements of dark field aperture 108. Figure 1E This is a cross-sectional view of a lens element 136 comprising two dark field apertures 108 to provide a dark field illumination path 122 within a light-collecting NA 134, according to one or more embodiments of the present disclosure. It is carefully considered herein that a dark field illumination path 122 having a polar angle 124 within the light-collecting NA 134 can facilitate the collection of measurement light 132 at an angle close to the illumination beam 128 and / or the reflected illumination beam 130. As a non-limiting example, when used for defect inspection, certain defects (e.g., but not limited to, shallow bumps, pits, or scratches) can scatter light close to the reflected illumination beam 130. Therefore, a dark field aperture 108 providing a dark field illumination path 122 having a polar angle 124 within the light-collecting NA 134 can facilitate the collection of measurement light 132 associated with such defects, and thus provide sensitive detection of such defects. However, it should be understood that... Figure 1D The illustration of lens element 136 is provided for illustrative purposes only and should not be construed as limiting. For example, dark field objective 106 may generally have any suitable design for collecting light within a selected light-collecting NA 134. Thus, dark field aperture 108 may pass through any number of lens elements 136 or their sub-elements.

[0041] In another embodiment, the polar angle 124 is configured outside the light-collecting NA 134 of the dark field aperture 108. In this way, the presence of the dark field aperture 108 does not restrict the light-collecting NA 134. Figure 1F This is a contour view of a dark-field objective lens 106 having a dark-field aperture 108 according to one or more embodiments of the present disclosure, the dark-field aperture 108 being formed through a hole in a portion of the housing 120 to provide a dark-field illumination path 122 outside the light-collecting NA 134 of the dark-field aperture 108. However, it should be understood that... Figure 1F The illustration of dark-field objective 106 is provided for illustrative purposes only and should not be construed as limiting. Similar to... Figure 1B and 1C The dark field aperture 108, which is formed through the housing 120 to provide a dark field illumination path 122 outside the light-collecting NA 134, can have any suitable size or shape (including (but not limited to) holes or notches).

[0042] Again, for general reference Figures 1A to 1F The rotating objective lens assembly 104 is described in more detail according to one or more embodiments of the present disclosure.

[0043] In a general sense, a dark-field objective 106 may have any number of dark-field apertures 108 or be symmetrically opposite each other at any number of azimuth or polar angles. However, with due consideration herein, it is desirable to simultaneously provide measurements using illumination with freely selectable azimuth angles or multiple measurements using illumination with two or more selected azimuth angles, while also limiting the number of dark-field apertures 108 in the dark-field objective 106. For example, it may be possible that increasing the number of dark-field apertures 108 could also increase the cost and / or complexity of manufacturing the dark-field objective 106. As another example, the dark-field apertures 108 within the light-collecting NA 134 (e.g., as per [reference to...]) Figure 1E (Description) The collection of measurement light 132 may have to be limited for at least the associated azimuth angle. In this way, increasing the number of dark field apertures 108 can be attributed to a reduction in signal and thus a decrease in measurement sensitivity. As another example, dark field apertures 108 may scatter light 132 themselves or otherwise distort measurement light 132, which can introduce noise into the measurement.

[0044] Therefore, the rotary bearing 114 in the rotating objective assembly 104 can rotate the dark field objective 106 to align the dark field aperture 108 to a selected azimuth angle for illuminating the sample 112. The rotary bearing 114 may contain any component or any number of components suitable for rotating the dark field objective 106 about the central optical axis 118.

[0045] The rotary bearing 114 may comprise any type of bearing suitable for providing rotation of at least a portion of the dark field objective 106, such as (but not limited to) mechanical bearings (e.g., mechanical ball bearings or the like) or non-contact bearings (e.g., air bearings, magnetic bearings or the like). In one embodiment, the rotary bearing 114 includes a fixed portion 138 and a rotatable portion 140, wherein the rotatable portion is mounted to or integrated with the dark field objective 106, and the fixed portion is adapted to secure the dark field objective 106 within the dark field optical system 100.

[0046] In one embodiment, the rotary bearing 114 is provided as a dedicated component separate from the dark field objective 106. For example, the rotary bearing 114 may include or be formed as a rotating objective base, wherein a rotatable portion is configured to receive and secure the dark field objective 106, such that the entire dark field objective 106 is rotatable. Furthermore, the rotary bearing 114 or its various components may have any design suitable for securing or connecting to the dark field objective 106. For example, Figure 1B A non-limiting configuration is described, wherein the rotatable portion 140 includes an inner ring 142 having a diameter equal to or greater than the diameter of the dark field objective 106 and at least one lip 144 extending from the inner ring 142. In this configuration, the dark field objective 106 may include a lower body 146 having a diameter equal to or less than the diameter of the inner ring 142 of the rotary bearing 114 and a mounting extension 148 extending from the lower body 146 such that the mounting extension 148 of the dark field objective 106 can rest on the lip 144. Figure 1B The inner ring 142 described herein further includes two lips 144 at opposite ends of the inner ring 142. In this manner, the retaining portion 138 may extend at least partially into the gap between the two lips 144 to provide mechanical stability. The dark field objective 106 may be secured to the rotatable portion 140 (e.g., the inner ring 142) using any technique known in the art (including, but not limited to, one or more retaining screws or compression rings).

[0047] In another embodiment, at least a portion of the rotary bearing 114 is integrated with the dark field objective 106. For example, a housing 120 of the dark field objective 106, or a portion thereof, may be attached to or otherwise form the rotatable portion 140 of the rotary bearing 114. Additional portions of the housing 120 may then be attached to or otherwise form the fixed portion 138. In this configuration, various drive components may also be integrated within, coupled to, the dark field objective 106, or a combination thereof.

[0048] In another embodiment, the rotating objective assembly 104 includes a rotating actuator 116 for driving the rotating bearing 114. For example, the rotating actuator 116 may include (but is not limited to) one or more gears for driving a mechanical bearing, a magnetic actuator for rotating a magnetic bearing, or the like. The rotating actuator 116 may further include one or more actuators, drivers, and / or control circuitry for controlling the movement and position of the dark field objective 106. In a general sense, any means of rotating at least a portion of the dark field objective 106 to align the dark field aperture 108 (e.g., the entrance aperture) to a selected azimuth angle for measurement is permitted within the spirit and scope of this disclosure.

[0049] For reference Figure 2A and 2B The multi-angle illumination subsystem 102 is described in more detail according to one or more embodiments of the present disclosure.

[0050] In one embodiment, the multi-angle lighting subsystem 102 includes two or more fixed-angle lighting channels 202 oriented to provide an illumination beam 128 at one or more fixed azimuth angles (e.g., but not limited to, 45 degrees, 90 degrees, or 180 degrees). Figure 2A This is a conceptual top view of a dark-field optical system 100 comprising two illumination channels 202 providing illumination beams 128 at two azimuth angles separated by 90 degrees, according to one or more embodiments of the present disclosure. In this configuration, dark-field measurements based on illumination along the X and Y directions can be efficiently generated using a dark-field objective 106 comprising a single pair of dark-field apertures 108 (e.g., inlet and outlet apertures) by sequentially rotating the dark-field objective 106 to the two azimuth angles and collecting measurement light 132 at each angle for measurement.

[0051] In another embodiment, the multi-angle lighting subsystem 102 includes at least one lighting source 204 for generating the lighting beam 128. In one embodiment, each lighting channel 202 includes a separate lighting source 204. In another embodiment, the lighting source 204 provides the lighting beam 128 to two or more lighting channels 202.

[0052] The illumination source 204 may comprise any type of illumination source suitable for providing at least one illumination beam 128. The illumination beam 128 may comprise one or more selected wavelengths of light, including (but not limited to) vacuum ultraviolet (VUV), deep ultraviolet (DUV), ultraviolet (UV) radiation, visible radiation, or infrared (IR) radiation. The illumination source 204 may further generate an illumination beam 128 comprising any selected wavelength range. In another embodiment, the illumination source 204 may comprise a spectrally tunable illumination source for generating an illumination beam 128 having a tunable spectrum.

[0053] In one embodiment, the illumination source 204 is a laser source. For example, the illumination source 204 may include (but is not limited to) one or more narrowband laser sources, broadband laser sources, supercontinuum laser sources, white light laser sources, or the like. In this respect, the illumination source 204 can provide an illumination beam 128 with high coherence (e.g., high spatial coherence and / or temporal coherence). In another embodiment, the illumination source 204 includes a laser-continuous plasma (LSP) source. For example, the illumination source 204 may include (but is not limited to) an LSP lamp, LSP bulb, or LSP chamber suitable for housing one or more elements that can emit broadband illumination when excited into a plasma state by a laser source. In another embodiment, the illumination source 204 includes a lamp source. For example, the illumination source 204 may include (but is not limited to) an arc lamp, discharge lamp, electrodeless lamp, or the like. In this respect, the illumination source 204 can provide an illumination beam 128 with low coherence (e.g., low spatial coherence and / or temporal coherence).

[0054] The illumination source 204 may further generate an illumination beam 128 having any time profile. For example, the illumination source 204 may generate a continuous illumination beam 128, a pulsed illumination beam 128, or a modulated illumination beam 128. In addition, the illumination beam 128 may be delivered from the illumination source 204 via free space propagation or guided light (e.g., optical fiber, optical tube, or the like).

[0055] Figure 2B This is a schematic outline view of a multi-angle illumination subsystem 102 including a rotatable illumination channel 202 according to one or more embodiments of the present disclosure. In one embodiment, the rotatable illumination channel 202 includes one or more rotatable beam delivery optics 206 aligned to guide an illumination beam 128 through a dark field aperture 108 (e.g., an entrance aperture) regardless of the azimuth of the dark field objective 106. For example, the rotatable beam delivery optics 206 or a portion thereof may be (e.g., using a base 208) fixed to a rotating portion of the dark field objective 106. In this configuration, dark field measurements can be performed at any selected azimuth by: rotating the dark field objective 106 and the rotatable beam delivery optics 206 to the selected azimuth; guiding the illumination beam 128 to a sample 112 at the selected azimuth; and collecting the measurement light 132 within the light-collecting NA 134 of the dark field objective 106.

[0056] The rotatable beam delivery optics 206 may comprise any optical element known in the art suitable for guiding the illumination beam 128 through the dark field aperture 108 at any selected azimuth angle. Furthermore, the rotatable beam delivery optics 206 may include or receive the illumination beam 128 from an illumination source 204, which may be fixed relative to the dark field objective 106 or rotatable together with the dark field objective 106. For example, Figure 2BThis describes a non-limiting configuration of a rotatable beam delivery optics 206, which includes an optical fiber 210 that accepts an illumination beam 128 from an illumination source 204 and guides the illumination beam 128 through a dark field aperture 108, and an output focuser 212.

[0057] However, it should be understood that Figure 2A and 2B Provided for illustrative purposes only and not to be construed as limiting. For example, the dark-field optical system 100 may include any number of dedicated illumination channels 202 or any number of fixed-angle illumination channels 202. Furthermore, although... Figure 2B Only the illumination beam 128 is described, but it should be understood that... Figure 2B The dark field objective 106 may include a reflected illumination beam 130 that can propagate through it (e.g., as shown in the image). Figure 1B Additional dark field porosity 108 (as described in the text).

[0058] Refer again Figures 1A to 1B Various additional components of the dark field optical system 100 are described in more detail according to one or more embodiments of the present disclosure.

[0059] In one embodiment, the leveling subsystem 152 includes a sample stage 150 adapted to at least adjust the angular position (e.g., tilt and tilt) of the sample 112. In this way, the angular position of the sample 112 can be adjusted prior to measurement to ensure that the reflected illumination beam 130 exits the dark field objective 106 through the dark field aperture 108 (e.g., exit aperture). For example, the top surface of the sample 112 may be bent (intentionally or unintentionally), patterned, or otherwise deviated from its nominal state, such that the sample 112 may require precise alignment prior to measurement to ensure that the reflected illumination beam 130 exits the dark field objective 106 through the dark field aperture 108.

[0060] In one embodiment, the dark-field optical system 100 includes a leveling subsystem 152 for monitoring and controlling the angular position of the sample 112 using an automated process to determine the exit of the reflected illumination beam 130 through the dark-field aperture 108 from the dark-field objective lens 106. For example, the leveling subsystem 152 may include a leveling sensor 154 for monitoring the sample 112 and / or the reflected illumination beam 130.

[0061] In one embodiment, such as Figure 1BThe description indicates that the leveling sensor 154 includes one or more optical detectors positioned to receive the reflected illumination beam 130 passing through the dark field aperture 108. For example, the leveling sensor 154 may include a power monitoring sensor for monitoring the power of the reflected illumination beam 130 propagating through the dark field aperture 108. In this way, the sample 112 can be aligned to provide the relative maximum power passing through the dark field aperture 108. As another example, the leveling sensor 154 may include a position-sensitive optical detector. In this way, the position of the reflected illumination beam 130 can be monitored and the sample 112 can be aligned by specifying that the reflected illumination beam 130 is positioned appropriately.

[0062] In another embodiment, such as in Figure 1B The description further clarifies that the leveling sensor 154 may include one or more sample position sensors, such as (but not limited to) proximity or height sensors. In this way, the leveling sensor 154 can provide a measurement of the physical orientation of the sample 112 and can be aligned by orienting the sample 112 to a horizontal position.

[0063] It should be further understood that the dark field optical system 100 may include any number or type of leveling sensors 154, and the examples above are provided for illustrative purposes only and should not be construed as limiting.

[0064] In another embodiment, the dark-field optical system 100 includes a controller 156 communicatively coupled to one or more components of the dark-field optical system 100. In another embodiment, the controller 156 includes one or more processors 158. For example, the one or more processors 158 may be configured to execute a set of program instructions maintained in a memory device 160 or memory. The one or more processors 158 of the controller 156 may include any processing element known in the art. In this sense, the one or more processors 158 may include any microprocessor-type device configured to execute algorithms and / or instructions.

[0065] One or more processors 158 of controller 156 may comprise any processor or processing element known in the art. For the purposes of this disclosure, the terms “processor” or “processing element” may be broadly defined to cover any means having one or more processing or logic elements (e.g., one or more microprocessor devices, one or more application-specific integrated circuit (ASIC) devices, one or more field-programmable gate arrays (FPGAs), or one or more digital signal processors (DSPs)). In this sense, one or more processors 158 may comprise any means configured to execute algorithms and / or instructions (e.g., program instructions stored in memory). In one embodiment, one or more processors 158 may embody a desktop computer, host computer system, workstation, graphics computer, parallel processor, networked computer, or any other computer system configured to execute a program (the program being configured to operate or in conjunction with the dark field optical system 100) as described throughout this disclosure. Furthermore, different subsystems of the dark field optical system 100 may include processors or logic elements suitable for performing at least a portion of the steps described in this disclosure. Therefore, the above description should not be construed as limiting the embodiments of this disclosure but is merely illustrative. Furthermore, the steps described throughout this disclosure can be implemented by a single controller or alternatively by multiple controllers. Additionally, controller 156 may comprise one or more controllers housed within a common housing or multiple housings. In this manner, any controller or combination of controllers can be individually packaged as a module suitable for integration into the dark-field optical system 100.

[0066] Memory device 160 may comprise any storage medium known in the art suitable for storing program instructions executable by one or more associated processors 158. For example, memory device 160 may comprise a non-transitory memory medium. As another example, memory device 160 may comprise (but is not limited to) read-only memory (ROM), random access memory (RAM), magnetic or optical memory devices (e.g., magnetic disks), magnetic tape, solid-state drives, and the like. It should be further noted that memory device 160 may be housed together with one or more processors 158 in a common controller housing. In one embodiment, memory device 160 may be remotely located relative to the physical location of one or more processors 158 and controller 156. For example, one or more processors 158 of controller 156 may access remote memory (e.g., a server) accessible via a network (e.g., the Internet, intranet, and the like).

[0067] The controller 156 may (e.g., via control signals) guide or receive data from any component of the dark-field optical system 100. The controller 156 may be further configured to perform any of the various process steps described throughout this disclosure. For example, the controller 156 may guide the rotating objective assembly 104 to rotate the dark-field objective 106 to a selected azimuth angle, receive data from one or more leveling sensors 154, guide the sample stage 150 to orient the sample 112 such that the reflected illumination beam 130 exits the dark-field objective 106 through the dark-field aperture 108, receive measurement data from the detector 110, and / or generate metrological measurements based on the measurement data.

[0068] In one embodiment, the dark field optical system 100 includes a user interface 162 communicatively coupled to a controller 156. In one embodiment, the user interface 162 may include (but is not limited to) one or more desktop computers, laptop computers, tablet computers, and the like. In another embodiment, the user interface 162 includes a display for displaying data from the dark field optical system 100 to a user. The display of the user interface 162 may include any display known in the art. For example, the display may include (but is not limited to) a liquid crystal display (LCD), an organic light-emitting diode (OLED) based display, or a CRT display. Those skilled in the art will recognize that any display device capable of being integrated with the user interface 162 is suitable for embodiments of this disclosure. In another embodiment, a user may input selections and / or commands in response to data displayed to the user via a user input device of the user interface 162.

[0069] For reference Figure 1A and 1F In light of consideration herein, the dark field optical system 100 may comprise or be configured as any type of optical system known in the art. In one embodiment, the dark field optical system 100 is an inspection system suitable for identifying and / or characterizing defects on a sample 112 (e.g., but not limited to, a bare semiconductor wafer, a wafer comprising one or more films, or a patterned wafer). In another embodiment, the dark field optical system 100 is a metrology system suitable for generating one or more metrological measurements indicative of one or more aspects of the sample 112 (e.g., but not limited to, overlay error between features on one or more sample layers, film thickness, film composition, or critical dimension (CD) of one or more features).

[0070] Furthermore, the dark-field optical system 100 can operate in either imaging or non-imaging modes. For example, a dark-field optical system 100 operating in imaging mode may include at least one detector 110 suitable for capturing an image, which may be positioned at any suitable plane within the dark-field optical system 100. For example, a detector 110 positioned at the field of view plane may produce an image of one or more features on the sample 112. In another example, a detector 110 at the pupil plane may produce an image representing the angular distribution of the measurement light 132 from the sample 112. As another example, a dark-field optical system 100 operating in non-imaging mode may include one or more single-pixel detectors 110.

[0071] Figure 1G This is a conceptual schematic view of a dark field optical system 100 according to one or more embodiments of the present disclosure, illustrating a single illumination source 204 that provides illumination at a single azimuth angle.

[0072] In one embodiment, illumination source 204 directs illumination beam 128 to sample 112 via illumination path 164. Illumination path 164 may include one or more lenses 166 or additional illumination optics 168 suitable for modifying and / or adjusting illumination beam 128. For example, one or more illumination optics 168 may include (but are not limited to) one or more polarizers, one or more filters, one or more beam splitters, one or more diffusers, one or more homogenizers, one or more apodizers, one or more beam shapers, or one or more shutters (e.g., mechanical shutters, electro-optic shutters, acousto-optic shutters, or the like). As another example, one or more illumination optics 168 may include an aperture stop for controlling the illumination angle on sample 112 and / or a field stop for controlling the spatial range of illumination on sample 112. In one example, illumination path 164 includes an aperture stop positioned in a plane conjugate to the back focal plane of dark field objective 106 to provide telecentric illumination of sample 112.

[0073] In another embodiment, detector 110 is configured to capture measurement light 132 via light-collecting path 170. For example, light-collecting path 170 may include a dark-field objective 106 and, as appropriate, one or more additional light-collecting path lenses 172. In this respect, detector 110 may receive radiation reflected or scattered from sample 112 (e.g., via specular reflection, diffuse reflection, and the like) or generated by sample 112 (e.g., emission or the like associated with absorption of illumination beam 128).

[0074] The light-collecting path 170 may further include any number of light-collecting optics 174 for guiding and / or modifying the illumination collected by the dark-field objective 106, including (but not limited to) one or more light-collecting path lenses 172, one or more filters, one or more polarizers, or one or more beam stops. Additionally, the light-collecting path 170 may include a field stop for controlling the spatial extent of the sample 112 imaged onto the detector 110, or an aperture stop for controlling the angular extent of illumination from the sample used to generate an image on the detector 110. In another embodiment, the light-collecting path 170 includes an aperture stop positioned in a plane conjugate to the back focal plane of the optical element (dark-field objective 106) to provide telecentric imaging of the sample.

[0075] Detector 110 may comprise any type of optical detector known in the art for measuring illumination received from sample 112. For example, detector 110 may comprise a sensor suitable for generating one or more images of static sample 112 (e.g., in a static operating mode), such as (but not limited to) a charge-coupled device (CCD), complementary metal-oxide-semiconductor (CMOS) sensor, photomultiplier tube (PMT) array, or avalanche photodiode (APD) array. Furthermore, detector 110 may comprise a multi-tap sensor having two or more taps per pixel, including (but not limited to) a multi-tap CMOS sensor. In this respect, the charge in the multi-tap pixel can be directed to any selected tap based on one or more drive signals to the pixel during the exposure window. Thus, during a single readout phase, a multi-tap sensor comprising an array of multi-tap pixels can generate multiple images, each associated with a different tap of an associated pixel. Furthermore, for the purposes of this disclosure, the taps of the multi-tap sensor may refer to output taps connected to associated pixels. In this respect, reading out each tap of the multi-tap sensor (e.g., during the readout phase) can generate a separate image.

[0076] As another example, detector 110 may include a sensor suitable for generating one or more images of sample 112 in motion (e.g., in a scanning operation mode). For example, detector 110 may include a line sensor comprising a row of pixels. In this respect, dark-field optics 100 can generate continuous images (e.g., strip images) one row at a time by translating sample 112 in a scanning direction perpendicular to the pixel row, measuring the field of view, and continuously timing the line sensor during a continuous exposure window.

[0077] In another example, detector 110 may include a TDI sensor comprising multiple pixel rows and readout rows. The TDI sensor can operate in a similar manner to a line sensor, except that a clock signal continuously moves charge from one pixel row to the next until the charge reaches the readout row (where a line of image is generated). By synchronizing charge transfer (e.g., based on a clock signal) with the movement of the sample along the scan direction, charge can continue to accumulate across pixel rows to provide a relatively higher signal-to-noise ratio compared to a line sensor.

[0078] In another embodiment, detector 110 includes a spectral detector suitable for identifying wavelengths of radiation emitted from sample 112. In another embodiment, dark-field optical system 100 may include multiple detectors 110.

[0079] For reference Figure 3 , Figure 3 This is a flowchart illustrating the steps performed in a dark field measurement method 300 according to one or more embodiments of this disclosure. The applicant notes that the embodiments and implementation techniques previously described in the background description of the dark field optical system 100 should be interpreted as extending to method 300. However, it should be further noted that method 300 is not limited to the architecture of the dark field optical system 100.

[0080] In one embodiment, method 300 includes step 302 of aligning a sample with the optical axis of a dark-field objective, wherein the dark-field objective includes an inlet aperture and an outlet aperture at symmetrical relative azimuth angles with respect to the optical axis. For example, step 302 may include aligning the sample such that the top surface of the sample is located at a working distance of the dark-field objective and is normal to the optical axis. In another embodiment, method 300 includes step 304 of rotating the objective to align the inlet aperture along a selected azimuth angle for measurement. The dark-field objective can be rotated using any technique known in the art, such as (but not limited to) a rotary bearing 114 disclosed relative to the dark-field optical system 100. In another embodiment, method 300 includes step 306 of illuminating the sample using an illumination beam passing through the inlet aperture at a selected azimuth angle, wherein a portion of the illumination beam reflected by the sample exits the objective through the outlet aperture as a reflected illumination beam. In this manner, the reflected illumination beam can exit the dark-field objective without interacting with any components of the objective. In this document, it is carefully considered that this technique can eliminate or at least mitigate unwanted scattering of the reflected illumination beam, which can facilitate highly sensitive dark-field measurements. Furthermore, step 306 can be repeated to provide measurements at any number of selected azimuth angles. In another embodiment, method 300 includes step 308 of collecting measurement light from the sample within a light-gathering numerical aperture of an objective lens, which may (but does not need to) be centered on the optical axis. In another embodiment, method 300 includes step 310 of generating one or more measurements associated with the sample based on the measurement light. For example, the measurements may include (but are not limited to) defect inspection or metrological measurements.

[0081] The topics described herein sometimes indicate that other components contain or are connected to other components. It should be understood that such depicted architectures are merely exemplary, and many other architectures can in fact be implemented to achieve the same functionality. Conceptually, any arrangement of components used to achieve the same functionality is effectively “associated” to achieve the desired functionality. Therefore, any two components combined herein to achieve a particular functionality can be considered “associated” with each other to achieve the desired functionality, regardless of the architecture or intermediate components. Similarly, any two such associated components can also be considered “connected” or “coupled” to each other to achieve the desired functionality, and any two components that can be suchly associated can also be considered “coupleable” to each other to achieve the desired functionality. Specific instances of coupleability include (but are not limited to) components that can physically interact and / or physically interact with each other, and / or components that can wirelessly interact and / or wirelessly interact with each other, and / or components that can logically interact and / or logically interact with each other.

[0082] It is believed that this disclosure and its many accompanying advantages will be understood from the foregoing description, and it will be appreciated that various changes can be made to the form, construction, and arrangement of the components without departing from the disclosed subject matter or sacrificing all its material advantages. The forms described are merely illustrative, and the appended claims are intended to cover and encompass such changes. Furthermore, it should be understood that the invention is defined by the appended claims.

Claims

1. A dark-field optical system, comprising: Lighting source; Rotating objective lens assembly, comprising: A dark-field objective lens configured to collect measurement light from a sample within a light-collecting numerical aperture, wherein the dark-field objective lens includes an inlet aperture and an outlet aperture that are symmetrically oriented relative to the optical axis of the dark-field objective lens. A rotary bearing that allows at least a portion of the dark field objective lens, including the inlet aperture and the outlet aperture, to rotate about the optical axis; and A rotary actuator that controls the rotation angle of the inlet orifice; A multi-angle illumination subsystem configured to illuminate the sample using an illumination beam passing through the entrance aperture at any of two or more illumination azimuth angles, wherein a portion of the illumination beam reflected by the sample exits the dark-field objective as a reflected illumination beam through the exit aperture, wherein the azimuth angle of the illumination beam on the sample can be selected by rotating the dark-field objective to any of the two or more illumination azimuth angles using the rotating objective assembly; and A photon collection system configured to guide at least a portion of the measurement light from the dark-field objective to one or more detectors.

2. The dark-field optical system of claim 1, wherein the inlet aperture provides a dark-field illumination path to the sample at an polar angle within the light-collecting numerical aperture.

3. The dark field optical system of claim 2, wherein the inlet aperture extends through a portion of the housing of the dark field objective and at least one lens element of the dark field objective.

4. The dark-field optical system of claim 1, wherein the entrance aperture provides a dark-field illumination path to the sample at an polar angle outside the light-gathering numerical aperture.

5. The dark-field optical system of claim 4, wherein the inlet aperture extends through a portion of the housing of the dark-field objective and at least one lens element of the dark-field objective.

6. The dark-field optical system of claim 1, wherein the measurement light comprises: At least one of the scattered or diffracted light from the sample.

7. The dark-field optical system of claim 1, wherein the multi-angle illumination subsystem comprises: Two or more illumination channels at two or more fixed azimuth angles relative to the optical axis, wherein the rotary driver is configured to selectively rotate the dark field objective to align the entrance aperture to any of the two or more fixed azimuth angles used for measurements using the two or more illumination channels.

8. The dark-field optical system of claim 1, wherein the multi-angle illumination subsystem comprises: One or more rotatable beam delivery optics aligned with the inlet aperture, wherein the one or more rotatable beam delivery optics rotate together with the dark field objective.

9. The dark-field optical system of claim 8, wherein the one or more rotatable beam delivery optics comprises: An optical fiber, which is aligned with the inlet aperture.

10. The dark-field optical system of claim 1, further comprising: A controller communicatively coupled to the one or more detectors, the controller comprising one or more processors configured to execute program instructions that cause the one or more processors to: Receive measurement data from one or more detectors; and One or more measurements associated with the sample are generated based on the measurement data.

11. The dark-field optical system of claim 1, further comprising: A sample stage for adjusting the angular position of the sample.

12. The dark-field optical system of claim 10, further comprising: A leveling sensor provides a measurement indicating the angular position of the sample relative to the optical axis, wherein the controller is configured to adjust the position of the sample stage during the measurement based on the measurement from the leveling sensor to specify the portion of the illumination beam reflected by the sample that exits the exit aperture.

13. The dark-field optical system of claim 12, wherein the leveling sensor comprises: A sample position sensor that provides a measurement of the angular position of the sample.

14. The dark-field optical system of claim 12, wherein the leveling sensor comprises: One or more optical detectors are positioned to receive the reflected illumination beam.

15. The dark-field optical system of claim 1, wherein the dark-field objective includes an additional entrance aperture and an additional exit aperture oriented in a symmetrical azimuth angle, wherein the multi-angle illumination subsystem is further configured to illuminate the sample through the additional entrance aperture.

16. The dark-field optical system of claim 1, wherein the rotating bearing comprises: At least one of ball bearings, air bearings, or magnetic bearings.

17. The dark-field optical system of claim 1, wherein the rotating bearing comprises: Rotatable parts and fixed parts.

18. The dark-field optical system of claim 17, wherein the dark-field objective is fixed to the rotatable portion.

19. The dark-field optical system of claim 17, wherein a first portion of the housing of the dark-field objective includes the rotatable portion, and a second portion of the housing of the dark-field objective includes the fixed portion.

20. The dark-field optical system of claim 1, wherein at least one of the inlet aperture or the outlet aperture comprises: hole.

21. The dark-field optical system of claim 1, wherein at least one of the inlet aperture or the outlet aperture comprises: A notch that extends to the end of the dark-field objective that faces the sample.

22. A rotating objective lens assembly, comprising: A dark-field objective configured to collect measurement light from a sample within a light-collecting numerical aperture, wherein the dark-field objective includes an inlet aperture and an outlet aperture symmetrically oriented relative to the optical axis of the dark-field objective, wherein the dark-field objective is configured to receive an illumination beam passing through the inlet aperture, wherein a portion of the illumination beam reflected by the sample exits the dark-field objective through the outlet aperture as a reflected illumination beam. A rotary bearing that allows at least a portion of the dark field objective lens, including the inlet aperture and the outlet aperture, to rotate about the optical axis; and A rotary actuator controls the rotation angle of the inlet aperture, wherein the azimuth angle of the illumination beam on the sample can be selected by rotating the dark field objective to a selected rotation angle using the rotating objective assembly.

23. The rotating objective assembly of claim 22, wherein the inlet aperture provides a dark-field illumination path to the sample at an polar angle within the light-gathering numerical aperture.

24. The rotating objective assembly of claim 23, wherein the inlet aperture extends through a portion of the housing of the dark field objective and at least one lens element of the dark field objective.

25. The rotating objective assembly of claim 22, wherein the inlet aperture provides a dark-field illumination path to the sample at an polar angle outside the light-gathering numerical aperture.

26. The rotating objective assembly of claim 25, wherein the inlet aperture extends through a portion of the housing of the dark field objective and at least one lens element of the dark field objective.

27. The rotating objective lens assembly of claim 22, wherein the measuring light comprises: At least one of the scattered or diffracted light from the sample.

28. The rotating objective assembly of claim 22, wherein the rotating driver is configured to rotate the dark field objective to any rotation angle.

29. The rotating objective lens assembly of claim 22, wherein the rotation angle ranges from 180 degrees.

30. The rotating objective lens assembly of claim 22, wherein the rotation angle ranges from 90 degrees.

31. The rotating objective lens assembly of claim 22, wherein the rotating bearing comprises: At least one of ball bearings, air bearings, or magnetic bearings.

32. The rotating objective lens assembly of claim 22, wherein the rotating bearing comprises: Rotatable parts and fixed parts.

33. The rotating objective assembly of claim 32, wherein the dark field objective is fixed to the rotatable portion.

34. The rotating objective assembly of claim 32, wherein a first portion of the housing of the dark field objective includes the rotatable portion, and a second portion of the housing of the dark field objective includes the fixed portion.

35. The rotating objective lens assembly of claim 22, wherein at least one of the inlet aperture or the outlet aperture comprises: hole.

36. The rotating objective lens assembly of claim 22, wherein at least one of the inlet orifice or the outlet orifice comprises: An opening extends to the end of the dark-field objective that faces the sample.

37. A dark field measurement method, comprising: Align the sample to the field of view of the dark field objective of the rotating objective assembly, wherein the dark field objective includes an inlet aperture and an outlet aperture that are symmetrical relative to the optical axis of the dark field objective. The dark field objective lens is rotated by a rotary bearing and a rotary driver to align with the inlet aperture along a selected azimuth angle used for measurement; The sample is illuminated by an illumination beam passing through the inlet aperture at the selected azimuth angle using a multi-angle illumination subsystem, wherein a portion of the illumination beam reflected by the sample exits the dark field objective through the outlet aperture as a reflected illumination beam; Measurement light is collected from the sample within the light-collecting numerical aperture of the dark-field objective; and One or more measurements associated with the sample are generated based on the measurement light.

38. The dark-field measurement method of claim 37, wherein aligning the sample with the optical axis of the dark-field objective comprises: The sample is leveled to direct the reflected illumination beam to exit the dark field objective through the exit aperture.

Images