Monolithic optical retarder

Abstract

Coupled prisms have various problems, including interlayer delamination and contamination at the interface due to low-wavelength light interactions, and large beam deviations due to pyramidal effects from multiple components. [Solution] A monolithic optical retarder formed from a monolithic prism may include an input surface for receiving a light beam, an output surface that is aligned with the optical axis of the light beam before it enters the input surface, and three or more reflective surfaces. The three or more reflective surfaces may be oriented to provide an optical path for the light beam from the input surface to the output surface via reflection by the three or more reflective surfaces, and the monolithic optical retarder imparts a selected optical delay to the light beam based on total internal reflection at at least one of the reflective surfaces. The input surface, the output surface, and the three or more reflective surfaces may be oriented such that the optical axis of the light beam exiting the output surface is equal to the optical axis of the light beam incident on the input surface.

Description

Technical Field

[0001] Reference to Related Applications This application claims the benefit of U.S. Provisional Application No. 63 / 270,058 (filed on October 21, 2021, MONOLITHIC OPTICS FOR BROADBAND SPECTROSCOPY) under 35 U.S.C. § 119(e), the entire content of which is incorporated herein by reference.

[0002] The present disclosure generally relates to optical retarders, and more particularly to monolithic optical retarders. [[ID=I2]]

Background Art

[0003] Optical retarders such as wave plates are widely used in many applications including polarization analysis methods and reflectance measurement methods. Furthermore, broadband applications such as, but not limited to, spectroscopic polarization analysis methods or spectroscopic reflectance methods may require broadband optical retarders. For example, it may be desirable to provide a quarter-wave phase shift over a wide wavelength range. Existing broadband optical retarders are typically formed by two or more prisms coupled together. However, the coupled prisms can be plagued by various problems including, but not limited to, delamination and contamination of the interfaces due to low wavelength light interactions (e.g., interactions with deep ultraviolet (DUV) or vacuum ultraviolet (VUV) light), large beam deviations due to pyramid effects from multiple components, or mechanical rigidity limited by van der Waals forces.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] Therefore, it is necessary to develop systems and methods to solve the above-mentioned shortcomings. [Means for solving the problem]

[0006] A monolithic optical retarder is disclosed according to one or more exemplary embodiments of this disclosure. In one exemplary embodiment, the monolithic optical retarder is formed from a monolithic prism. In another exemplary embodiment, the monolithic prism includes an input surface for receiving a light beam, an output surface aligned with the optical axis of the light beam before it enters the input surface, and three or more reflective surfaces. In another exemplary embodiment, the three or more reflective surfaces are oriented to provide an optical path for the light beam from the input surface to the output surface via reflection by the three or more reflective surfaces, and the monolithic optical retarder imparts a selected optical delay to the light beam as it propagates along the optical path based on total internal reflection in at least one of the three or more reflective surfaces. In another exemplary embodiment, the input surface, the output surface, and the three or more reflective surfaces are oriented such that the optical axis of the light beam exiting the output surface is equal to the optical axis of the light beam entering the input surface. In this way, the light beam is not deflected by propagation along the optical path through the monolithic prism.

[0007] A measurement system is disclosed according to one or more exemplary embodiments of the present disclosure. In one exemplary embodiment, the system includes an illumination source for generating an illumination beam. In another exemplary embodiment, the system includes one or more illumination optics for directing the illumination beam onto a sample. In another exemplary embodiment, the system includes a detector. In another exemplary embodiment, the system includes one or more collection optics for collecting light from the sample as a collection beam and directing at least a portion of the collection beam onto the detector as detection light. In another exemplary embodiment, the system includes one or more monolithic optical retarders associated with at least one of one or more illumination optics or one or more focusing optics, wherein a particular monolithic optical retarder of one or more monolithic optical retarders is formed from a monolithic prism. In another exemplary embodiment, the monolithic prism includes an input surface for receiving a light beam, an output surface aligned with the optical axis of the light beam before it enters the input surface, and three or more reflective surfaces. In another exemplary embodiment, three or more reflective surfaces are oriented to provide an optical path for a light beam from an input surface to an output surface via reflection by the three or more reflective surfaces, and a monolithic optical retarder imparts a selected optical delay to the light beam as it propagates along the optical path, based on total internal reflection in at least one of the three or more reflective surfaces. In another exemplary embodiment, the input surface, the output surface, and the three or more reflective surfaces are oriented such that the optical axis of the light beam exiting the output surface is equal to the optical axis of the light beam entering the input surface. In this way, the light beam is not deflected by propagation along the optical path through the monolithic prism. In another exemplary embodiment, the system further includes a controller communicatively coupled to the detector, the controller including one or more processors configured to execute program instructions causing one or more processors to generate one or more measured values ​​of a sample based on the detected light.

[0008] A method is disclosed according to one or more exemplary embodiments of the present disclosure. In one exemplary embodiment, the method includes the step of generating an illumination beam. In another exemplary embodiment, the method includes the step of directing the illumination beam onto a sample. In another exemplary embodiment, the method includes the step of collecting light from the sample as a collection beam in response to the illumination beam. In another exemplary embodiment, the polarization of at least the illumination beam or the collection beam is controlled by at least one monolithic optical retarder formed from a monolithic prism. In another exemplary embodiment, the monolithic prism includes an input surface for receiving a light beam, an output surface aligned with the optical axis of the light beam before entering the input surface, and three or more reflective surfaces. In another exemplary embodiment, the three or more reflective surfaces are oriented to provide an optical path for the light beam from the input surface to the output surface via reflection by the three or more reflective surfaces, and the monolithic optical retarder imparts a selected optical delay to the light beam as it propagates along the optical path based on total internal reflection at at least one of the three or more reflective surfaces. In another exemplary embodiment, the input surface, output surface, and three or more reflective surfaces are oriented such that the optical axis of the light beam exiting the output surface is equal to the optical axis of the light beam entering the input surface. In this way, the light beam is not deflected by propagation along the optical path through the monolithic prism. In another exemplary embodiment, the method further includes the step of directing at least a portion of the collected beam to a detector as detection light. In another exemplary embodiment, the method further includes generating one or more measurement values ​​of the sample based on the detected light.

[0009] It should be understood that both the above summary and the following detailed description are illustrative and descriptive only and do not necessarily limit the claimed invention. The accompanying drawings incorporated into and constituting part of the specification illustrate embodiments of the invention and, together with the general description, help to illustrate the principles of the invention.

[0010] Many of the advantages of this disclosure can be better understood by those skilled in the art by referring to the accompanying drawings: [Brief explanation of the drawing]

[0011] [Figure 1] This is a conceptual block diagram of the components of a monolithic optical retarder according to one or more embodiments of the present disclosure. [Figure 2A] This is a schematic diagram of a monolithic optical retarder formed as a monolithic k-prism providing three reflective surfaces, according to one or more embodiments of the present disclosure. [Figure 2B] This is a schematic diagram of a monolithic optical retarder formed as a monolithic Fresnel rhombus providing four reflective surfaces, according to one or more embodiments of the present disclosure. [Figure 3A] This is a schematic diagram of a conventional multi-component k-prism formed of three prism components, according to one or more embodiments of the present disclosure. [Figure 3B] This is a schematic diagram of a conventional multi-component Fresnel rhombus providing two prism components according to one or more embodiments of the present disclosure. [Figure 4A] This is a block diagram of a measurement system including a monolithic optical retarder according to one or more embodiments of the present disclosure. [Figure 4B] This is a conceptual diagram of a measurement tool according to one or more embodiments of the present disclosure. [Figure 4C] This is a conceptual diagram of a measuring tool configured using a common objective lens according to one or more embodiments of the present disclosure. [Figure 5] This flowchart shows the steps performed in a measurement method using a monolithic optical retarder according to one or more embodiments of the present disclosure. [Modes for carrying out the invention]

[0012] Herein, we refer in detail to the disclosed subject matter shown in the accompanying drawings. This disclosure has been specifically shown and described with respect to particular embodiments and their particular features. The embodiments described herein are to be construed as illustrative rather than restrictive. It should be readily apparent to those skilled in the art that various changes and modifications in form and detail can be made without deviating from the spirit and scope of this disclosure.

[0013] Embodiments of this disclosure relate to systems and methods for providing broadband (e.g., achromatic) optical delay using monolithic optical elements without displacing an input beam. For the purposes of this disclosure, the term monolithic is used to indicate an element fabricated from a single block of a single material without any seams or interfaces between any components.

[0014] An optical retarder introduces an optical delay (e.g., phase delay) corresponding to a phase shift or phase delay between orthogonal polarizations, which typically has the effect of correcting the polarization state of the input light. For example, a quarter-wave optical retarder can introduce a quarter-wavelength phase shift between orthogonal polarization components, which can have the effect of converting linearly polarized light to circularly polarized light, and vice versa. As another example, a half-wave optical retarder can introduce a quarter-wavelength phase shift between orthogonal polarization components, which can have the effect of rotating linearly polarized light by a selected angle.

[0015] In many applications, it is desirable to provide broadband optical delay without deflecting the optical path of the input light (e.g., introducing deviations in the position or angle of the optical path of the input light). In particular, the broadband optical delay can provide equivalent optical delay for multiple wavelengths, which can enable polarization correction of broadband input light or stable narrowband polarization correction over a range of possible input wavelengths. Further, by providing an optical delay with an undeviated optical path, an optical retarder can be inserted, removed, or rotated as needed while minimizing the impact on the optical path of the beam in a larger system. However, it is contemplated herein that providing an optical delay having both an undeviated optical path and broadband capabilities remains an important challenge, particularly for high-power beams or wavelengths extending into and below the ultraviolet (UV) spectral range.

[0016] Optical delay may be induced using a variety of techniques, including but not limited to propagation through a birefringent material or total internal reflection. For example, a waveplate typically utilizes a birefringent material with a direction-dependent refractive index to induce a direction-dependent phase delay on an input beam. A waveplate also does not deflect the optical path of the input beam when aligned at normal incidence. However, this technique is highly wavelength-dependent, as the refractive index of the birefringent material varies as a function of wavelength, and is thus typically limited to narrowband applications. As another example, broadband optical delay can be achieved using total internal reflection (TIR) from the inner surface of a prism. However, existing prism-based optical retarders, such as Fresnel rhombs or k-prisms, either require multiple prisms joined together, either to deflect the input beam or to achieve an undeviated optical path. The use of such joined prisms can introduce various limitations for demanding applications, including but not limited to potential delamination and contamination of interfaces when used with or exposed to deep ultraviolet (DUV) or vacuum ultraviolet (VUV) radiation, unacceptable large beam deviations due to the pyramid effect of multiple components, or mechanical rigidity limited by van der Waals forces.

[0017] Embodiments of the present disclosure relate to a monolithic optical retarder formed from a monolithic prism, the monolithic prism providing a broadband optical retarder and further providing an undeviated optical path for an output beam with respect to an input beam. In some embodiments, the monolithic prism includes an input surface for receiving an optical beam, an output surface aligned with the input surface, and three or more reflective surfaces. In particular, the input surface, the output surface, and the three or more reflective surfaces may be oriented to provide an optical path for the optical beam from the input surface to the output surface via total internal reflection by the three or more reflective surfaces. Further, at least one of the reflective surfaces may be oriented to impart an optical delay by total internal reflection (e.g., the angle of incidence is greater than the critical angle associated with TIR at a particular wavelength of the optical beam). For the purposes of the present disclosure, a reflective surface that imparts an optical delay to an optical beam via TIR is referred to as a delay surface. In this way, the total optical delay induced by the monolithic prism may correspond to the cumulative optical delay imparted by the delay surface along the optical path through the monolithic prism.

[0018] In some embodiments, the monolithic optical retarder includes one or more non-delay surfaces. For example, the non-delay surface may be oriented at an angle smaller than the critical angle associated with TIR and thus may reflect light without imparting an optical delay. The non-delay surface is considered suitable for controlling the optical path of light through the monolithic prism (e.g., ensuring an undeviated optical path for the output beam with respect to the input beam). Further, it is contemplated herein that the mixing of delay surfaces and non-delay surfaces may enable substantial flexibility in the design of the monolithic prism while achieving both selected optical delays without deflecting the optical beam.

[0019] Furthermore, any surface, including but not limited to non-delay surfaces, may include optical coatings to further modify or control the properties of the light beam. For example, a non-delay surface may include a coating to provide high reflectivity at angles above the critical angle. For example, the coating may include, but is not limited to, a metallic coating (e.g., a bare aluminum coating).

[0020] The monolithic optical retarders disclosed herein may have any number of retarding or non-retarding surfaces suitable for providing any selected optical retardation and an undeflected optical path for the output beam relative to the input beam. In some embodiments, the monolithic optical retarder is formed as a monolithic Fresnel k prism. In some embodiments, the monolithic optical retarder is formed as a monolithic Fresnel rhombus.

[0021] Monolithic optical retarders formed from monolithic prisms may offer numerous advantages over conventional prism designs, including, but not limited to, the ability to transmit UV / VUV / DUV light with high mechanical rigidity and high fluence, without any problems involving delamination or interfacial degradation that lead to scattering and / or loss of spectral fidelity. More generally, the monolithic optical retarders disclosed herein may operate over a wide range of wavelengths, including, but not limited to, 120–20,000 nm, depending on the materials used to form the monolithic prism.

[0022] Further embodiments of this disclosure relate to systems and methods for measurement using at least one monolithic optical retarder disclosed herein. In some embodiments, the measurement system including the monolithic optical retarder disclosed herein includes, but is not limited to, an ellipsometer (polarization analyzer) or a reflectometer.

[0023] Referring here to Figure 1-2B, a monolithic optical delay is described in more detail according to one or more embodiments of the present disclosure.

[0024] It is recognized herein that light undergoing total internal reflection at an interface may also be phase-shifted at the interface. For all polarization directions, this phase shift ranges from 0 degrees at the critical angle where TIR begins to 180 degrees at an incident angle of 90 degrees (this is merely a matter of convention and does not limit the disclosure). However, the phase shifts for p-polarized light (e.g., light with polarization parallel to the plane of incidence) and s-polarized light (e.g., light with polarization perpendicular to the plane of incidence) differ at intermediate angles, resulting in a phase difference (e.g., optical delay) between p-polarized and s-polarized light that depends on both the incident angle and refractive index of the material through which the light propagates. The exact phase difference can be characterized by the well-known Fresnel reflectance coefficient.

[0025] As a result, any optical delay or relative phase difference between the orthogonal p-polarized and s-polarized portions of a light beam can be achieved by continuous total internal reflection at a selected angle. It should be noted that the TIR-induced phase shift also depends slightly on the wavelength of light, as the refractive index of the material changes with wavelength. However, this wavelength-dependent effect is relatively weak, and therefore, broadband performance can typically be achieved within acceptable limits for many applications. In contrast, optical retarders based on birefringence (e.g., waveplates) are typically highly sensitive to wavelength and are typically limited to narrowband applications.

[0026] As previously stated herein, existing optical delay devices based on TIR-induced phase shift are intended to either deflect incident light, thereby making alignment and tuning difficult in larger systems, or reduce mechanical stability, requiring the bonding of multi-component prisms that limit output and / or wavelength range due to delamination or thermal problems.

[0027] Embodiments of this disclosure relate to monolithic optical delay devices that utilize TIR-induced phase shift.

[0028] Figure 1 is a conceptual block diagram of the components of a monolithic optical retarder 100 according to one or more embodiments of the present disclosure.

[0029] In some embodiments, the monolithic optical retarder 100 is formed as a monolithic prism 102 having an input surface 104, a plurality of reflective surfaces 106, and an output surface 108, where at least one of the reflective surfaces 106 acts as a delay surface that imparts optical delay to the light beam 110 through TIR (for example, the angle of incidence of the light beam 110 on the delay surface along the optical path is greater than the critical angle of TIR). Thus, the light beam 110 can undergo optical delay and associated polarization correction by entering the monolithic prism 102 through the input surface 104, propagating along the optical path including reflections from three or more reflective surfaces 106, and exiting the output surface 108, and the total optical delay imparted to the light beam 110 corresponds to the cumulative optical delay imparted by the delay surfaces along the optical path.

[0030] The monolithic prism 102 can include any number of non-delayed surfaces along the optical path, where the non-delayed surfaces correspond to reflective surfaces 106 oriented such that the incident angle of the light beam 110 is lower than the critical angle of TIR, and therefore no optical delay is imparted to the light beam 110. Thus, the reflective surfaces 106 along the optical path through the monolithic prism 102 can be divided into any combination of delayed and non-delayed surfaces, each containing at least one delayed surface.

[0031] The monolithic prism 102 may include an optical coating on any of the reflective surfaces 106 (e.g., any outer surface of the reflective surface 106). The coating may include, but is not limited to, any type of coating known in the art, including metallic or dielectric coatings. The coating may further have any number of layers. In some embodiments, the coating is a reflective coating, such as a metallic coating, and may generally be operable for any wavelength or wavelength range of the light beam 110. For example, the metallic coating may include, but is not limited to, a bare aluminum coating.

[0032] As an example, it is recognized herein that an uncoated non-critical interface where the light beam 110 has an incident angle lower than the critical angle of TIR can typically transmit the first portion of the light beam 110 along the optical path, in addition to the second portion of the light beam 110. However, a coating on a non-delay surface can provide a high reflectivity of the light beam 110 along the optical path, and thus reduce or eliminate losses due to reflection at the non-delay surface.

[0033] The monolithic prism 102 can provide an undefended optical path for the light beam 110 so that the monolithic prism 102 can be inserted, removed, and / or rotated (e.g., along the optical axis of the light beam 110) without affecting the position or angle of the light beam 110. For example, the input surface 104 and output surface 108 can be aligned along the optical axis of the light beam 110 outside the monolithic prism 102. In this way, any modification to the optical path of the light beam 110 is limited to its location within the monolithic prism 102. Furthermore, it should be understood that in some embodiments, the output surface 108 and input surface 104 are parallel, but this is not a requirement.

[0034] The monolithic prism 102 may be formed as a seamless monolithic solid of any single material suitable for transmitting the light beam 110, such as glass or crystal, but is not limited to this. For example, the monolithic prism 102 may be formed from materials such as silica glass (e.g., UV-grade fused silica, BK7, etc.), fluoride glass (e.g., calcium fluoride (CaF2), magnesium fluoride (MgF2), etc.), zinc selenide, zinc sulfide, quartz, sapphire, etc., but is not limited to this. In a general sense, it is recognized herein that different materials have different optical properties and transmission bands and may therefore be suitable for different applications or wavelength ranges. For example, but is not limited to this, UV-grade materials such as fused silica or sapphire may be suitable for applications utilizing UV wavelengths, but is not limited to this. As another example, CaF2 may provide operation in the wavelength range of 120 to 7000 nm or any combination of wavelengths within that range, but is not limited to this. As another example, fused silica can provide operation in the wavelength range of 170–2500 nm or any combination of wavelengths within that range, though not limited to these. As yet another example, but not limited to, IR-transmitting materials such as ZnS or ZnSe may be suitable for applications utilizing IR wavelengths, but not limited to these. However, it should be understood that the monolithic prism 102 can generally be designed to operate with any wavelength or wavelength range of light beam 110, including but not limited to the range of 120 nm–20,000 nm.

[0035] Furthermore, the monolithic prism 102 may be formed from an isotropic material that provides a direction-independent refractive index, but this is not required. An isotropic material with a directionally independent refractive index may provide optical delay only by TIR-induced phase shift at the reflective surface 106, which is intended herein to facilitate broadband performance. However, it should be understood that this is not a requirement.

[0036] The monolithic prism 102 may include any number of reflective surfaces 106 arranged in any orientation to provide any desired amount of optical delay between the orthogonal polarization directions of the light beam 110. In particular, each reflective surface 106 acting as a delay surface may be arranged to provide any selected phase shift based on the angle of incidence of the light beam 110 and the refractive index of the material forming the monolithic prism 102. In this way, the monolithic prism 102 may provide a total phase shift based on the cumulative phase shift introduced by each of the reflective surfaces 106, and the phase shifts of the various reflective surfaces 106 do not need to be the same. As an example, it is recognized herein that a total phase shift in the range of 60 to 120 degrees is useful in many applications. Thus, in some embodiments, the monolithic prism 102 may include at least one reflective surface 106 that provides a phase shift in the range of 20 to 80 degrees. However, it should be understood that the above description is not limiting and any reflective surface 106 will generally provide any selected phase shift.

[0037] It is further intended herein that the relative phase shift (e.g., optical delay) between the orthogonal polarization components of the light beam 110 may generally have an elastic modulus of 360 degrees (or 2π radians). Thus, the cumulative relative phase shift from the reflective surface 106 of the monolithic prism 102 can exceed 360 degrees any number of times to provide any equivalent effective phase shift between 0 and 360 degrees. Furthermore, it may be advantageous to consider positive or negative relative phase shifts. For example, the phase shift between the orthogonal polarization components of the light beam 110 may be considered to be in the range of -180 degrees to +180 degrees. Therefore, it should be understood that the present disclosure or any embodiments provided are not limited to any particular convention for describing the relative phase difference between the orthogonal polarization components of the light beam 110.

[0038] Figures 2A and 2B show two non-limiting examples of a monolithic optical retarder 100 formed from a monolithic prism 102 providing three and four reflective surfaces 106, respectively, according to one or more embodiments of the present disclosure. Figures 3A and 3B show contrasting multi-component prism designs.

[0039] Figure 2A is a schematic diagram of a monolithic optical retarder 100 formed as a monolithic k-prism providing three reflective surfaces 106, according to one or more embodiments of the present disclosure. For example, Figure 2A shows the optical path 202 of a light beam 110 that passes through the input surface 104, reflects from a first reflective surface 106a having a first incident angle 204a, reflects from a second reflective surface 106b having a second incident angle 204b, reflects from a third reflective surface 106c having a third incident angle 204c, and passes through the output surface 108. In particular, Figure 2A shows a configuration in which the second reflective surface 106b is orthogonal to both the input surface 104 and the output surface 108, and the first reflective surface 106a and the third reflective surface 106c are symmetrically oriented such that the first incident angle 204a and the third incident angle 204c are equal.

[0040] Figure 2B is a schematic diagram of a monolithic optical retarder 100 formed as a monolithic Fresnel rhombus providing four reflective surfaces 106, according to one or more embodiments of the present disclosure. For example, Figure 2B shows the optical path 202 of an optical beam 110 passing through the input surface 104, which is reflected from a first reflective surface 106d having a first incident angle 204d, from a second reflective surface 106e having a second incident angle 204e, from a third reflective surface 106f having a third incident angle 204f, and from a fourth reflective surface 106g having a fourth incident angle 204g. It then passes through the output surface 108. In particular, Figure 2(B) shows a configuration in which the reflective surfaces 106d and e are parallel, the reflective surfaces 106f and g are parallel, and the reflective surfaces 106f and g are arranged to be reflectively symmetric with respect to the reflective surfaces 106d and e around vertex 206.

[0041] In this specification, however limited, it is considered that the design of the monolithic optical retarder 100, such as that illustrated in Figures 2A and 2B, may be adapted to provide a wide range of optical retardation values. In particular, the amount of TIR-induced optical retardation between orthogonal polarizations induced by any particular reflective surface 106 depends on the angle of incidence and refractive index of the monolithic prism 102, as previously stated herein. The refractive index can be adjusted by the selection of the material used to manufacture the monolithic prism 102. The angles of incidence to various reflective surfaces 106 can be adjusted based on the physical dimensions of the monolithic prism 102. Considering the design illustrated in Figure 2A as an example, the first angle of incidence 204a and the third angle of incidence 204c may be adjusted based on the angles of the first and third reflective surfaces 106a,c with respect to the input surface 104 and the output surface 108, and the second angle of incidence 204b may be adjusted based on the following dimensions, however limited: the lengths of the first and third reflective surfaces 106a,c or the prism height 208. Similarly, the incident angles 204d to g in the design shown in Figure 2B can be adjusted based on the prism thickness 210, or based on the angles and / or lengths of the reflective surfaces 106d to g.

[0042] Furthermore, the reflective surfaces 106a-c in Figure 2A or 106d-g in Figure 2B may generally include any combination of delayed and non-delayed surfaces, including at least one delayed surface. For example, the non-limiting designs illustrated in Figures 2A and 2B may be adapted to provide an incident angle above the critical angle for TIR, providing TIR-based optical delay, or to provide an incident angle below the critical angle, providing reflection without optical delay.

[0043] Furthermore, the design of the monolithic optical retarder 100 shown in Figures 2A and 2B provides a common incident plane to all reflective surfaces 106, which are in the plane of the figure. As a result, further adjustment of the incident angle 204 can be achieved by rotating the monolithic prism 102 in the plane of the figure. However, it should be understood that the monolithic optical retarder 100 disclosed herein does not necessarily need to provide reflective surfaces 106 having a common incident plane. Rather, the reflective surfaces 106 may generally be oriented in any preferred three-dimensional configuration.

[0044] Subsequently, the total optical delay induced by the monolithic prism 102 can be determined as the cumulative delay induced by various reflective surfaces 106 (for example, the reflective surfaces 106 function as delay surfaces). Thus, based on the selection of materials, design, and physical dimensions of the monolithic prism 102, any desired optical delay between orthogonal polarizations can be induced. For example, a monolithic optical retarder 100, such as those illustrated in Figures 2A and 2B, may be adapted to provide a π / 2 retarder to act as a quarter-wavelength retarder, a π retarder to act as a half-wavelength retarder, or any other selected value. Furthermore, it should be understood that while the monolithic optical retarder 100 may simply provide an optical delay between p-polarization and s-polarization at any particular reflective surface 106, the specific effect on the polarization state of the light beam 110 may depend on the input polarization of the light beam 110. For example, a monolithic optical retarder 100 that provides a π / 2 delay can convert linearly polarized light to circularly polarized light when oriented at a specific angle (for example, an angle of 45 degrees provides equal amounts of p-polarized and s-polarized light at the reflective surface 106), but can generate elliptically polarized light for other input orientations.

[0045] Furthermore, the design of the monolithic optical retarder 100 shown in Figures 2A and 2B does not induce any misalignment of the optical axis of the light beam 110 when the light beam 110 is aligned to enter the input surface 104 at a perpendicular incidence angle. For example, the light beam 110 can follow a straight (e.g., unmisaligned) optical axis 212 into and extending from the monolithic prism 102, regardless of the optical path within the monolithic prism 102, in which case all misalignment of the light beam 110 occurs within the monolithic prism 102. In this way, the monolithic optical retarder 100 can be inserted, removed, and / or rotated (e.g., along the optical axis 212 of the light beam 110) without altering the optical axis 212 of the light beam 110.

[0046] Referring here to Figures 3A and 3B, contrasting multi-component retarder designs are shown to further highlight the unique aspects of the monolithic optical retarder 100 disclosed herein. Figure 3A is a schematic diagram of a conventional multi-component k-prism 302 formed of three prism components 304, according to one or more embodiments of the present disclosure. Figure 3A can be considered a conventional multi-prism variation of the monolithic prism 102 shown in Figure 2A. Figure 3B is a schematic diagram of a conventional multi-component Fresnel rhombus 306 providing two prism components 304, according to one or more embodiments of the present disclosure. In a general sense, it should be recognized that the conventional multi-component variations of Figures 3A and 3B may include any number of prism components 304 joined by any number of optical interfaces 308.

[0047] The monolithic optical retarder 100 formed from the monolithic prism 102 may offer numerous advantages over conventional multi-component retarders, including, but not limited to, the ability to transmit high mechanical rigidity and high fluence UV / VUV / DUV light without any problems related to delamination or interface degradation that would lead to scattering and / or loss of spectral fidelity, as is discussed herein.

[0048] For example, it is recognized herein that a conventional multi-component retarder formed from bonded prism components 304 may require an optically polished optical surface on each prism component at the optical interface 308 between the prism components 304. However, the polishing compound may become trapped in surface cracks, which can lead to hot spots at the interface, at least in part due to the difference in the coefficient of thermal expansion (CTE) between the trapped polishing compound and the substrate prism material. As a result, a monolithic optical retarder 100 that does not beneficially include such an optical interface 308 may offer superior high-power performance.

[0049] As another example, the monolithic optical retarder 100 disclosed herein is not subject to the risk of delamination. In contrast, the difference in the coefficient of thermal expansion (CTE) between the captured abrasive compound and the substrate prism material of a conventional multi-component prism can lead to delamination at the optical interface 308. Furthermore, conventional multi-component prisms generally have a limited temperature operating range due to the risk of delamination.

[0050] As another example, the monolithic optical retarder 100 disclosed herein provides an uninterrupted optical path through the monolithic prism 102, and therefore provides high beam uniformity with minimal or no scattering. In contrast, contact lines in the beam path of conventional multi-component prisms can be a source of scattering and spatial inhomogeneity.

[0051] As another example, a monolithic optical retarder 100, as disclosed herein, due to its monolithic design, results in minimal or no beam deviation and excellent parallelism. Generally, axial beam deviation is associated with the stacking of geometric tolerances of the k-prism and increases cumulatively with increasing number of prism components 304.

[0052] As another example, the monolithic optical retarder 100 disclosed herein provides high material uniformity throughout the monolithic prism 102, promoting high spatial (e.g., refractive index) uniformity and high polarization uniformity. Generally, providing consistent spatial and polarization uniformity in a single substrate material is easier than joining multiple prism components 304 together.

[0053] As another example, the monolithic optical retarder 100 disclosed herein provides high mechanical rigidity, high thermal stability, and high inter-component hardware matching, which generally promotes low cost and high manufacturing yield of components.

[0054] Referring here to Figure 4A-5, a system and method for measurement using a monolithic optical retarder 100 will be described in more detail according to one or more embodiments of this disclosure. It is intended herein that the monolithic optical retarder 100 may be incorporated into any type of measurement system known in the art that requires polarization control of a light beam 110.

[0055] Figure 4A is a block diagram of a measurement system 400 including a monolithic optical retarder 100 according to one or more embodiments of the present disclosure.

[0056] In some embodiments, the measurement system 400 includes a measurement tool 402 for generating measurement data associated with one or more samples. The measurement tool 402 may include any type of measurement tool known in the art that is suitable for providing scattering measurement signals at one or more wavelengths. For example, the measurement tool 402 may include, but is not limited to, a spectrometer, a spectro-ellipsometer with one or more illumination angles, a spectro-ellipsometer for measuring Müller matrix elements (e.g., using a rotational compensator), a spectrophotometer, a scatterometer, or a polarimeter. Furthermore, the measurement tool 402 can operate in imaging or non-imaging configurations.

[0057] Furthermore, the measurement tool 402 may include a single measurement tool or multiple measurement tools. For example, a measurement tool including multiple hardware configurations is generally described in U.S. Patent No. 7,933,026, which is incorporated herein by reference in its entirety. A measurement system incorporating multiple measurement tools is generally described in U.S. Patent No. 7,478,019, which is incorporated herein by reference in its entirety. Focused beam ellipsometry based primarily on reflective optics is generally described in U.S. Patent No. 5,608,526, which is incorporated herein by reference in its entirety. The use of an apodizer to mitigate the effects of light diffraction causing illumination spot spreading beyond the size defined by geometrical optics is generally described in U.S. Patent No. 5,859,424, which is incorporated herein by reference in its entirety. The use of a high numerical aperture tool with simultaneous illumination at multiple incident angles is generally described in U.S. Patent No. 6,429,943, which is incorporated herein by reference in its entirety.

[0058] The measurement tool 402 can generate measurement data associated with any location on the sample. In some embodiments, the measurement tool 402 generates measurement data of device features on the sample. In this regard, the measurement tool 402 can directly characterize features of interest. In some embodiments, the measurement tool 402 generates measurement data of one or more measurement targets (e.g., targets) that include fabrication features designed to represent device features on the sample. In this regard, measurements of one or more measurement targets distributed across the sample can be attributed to device features. For example, the size, shape, or distribution of sample features may not be suitable for accurate measurement. In contrast, the measurement targets can include features on one or more sample layers having size, shape, and distribution that are adjusted so that the measurement data of the targets is highly sensitive to one or more selected physical or optical attributes of the features. The measurement data of the targets can then be associated (e.g., through a model) with specific values ​​of the selected attributes.

[0059] Measurement targets can be sensitive to a wide variety of physical or optical attributes, including but not limited to CD, overlay, sidewall angle, film thickness, film composition, or process-related parameters (e.g., focal point, dose, etc.), and can therefore be designed to facilitate their measurement. For this purpose, measurement targets may include any combination of periodic structures (e.g., one, two, or three-dimensional periodic structures) or isolated aperiodic features. The use of measurement tools to characterize aperiodic features is generally described in U.S. Patent No. 9,291,554, granted March 22, 2016, which is incorporated herein by reference in its entirety. Furthermore, measurement targets can generally be characterized by having one or more spatial frequencies (e.g., one or more pitches) that can be attributed to a pattern or distribution of features. The use of symmetric target designs in scattering measurement overlay measurements is generally described in U.S. Patent Application Publication No. 2015 / 0204664, published July 23, 2015, which is incorporated herein by reference in its entirety.

[0060] The measurement targets may be located at multiple points on the sample. For example, the targets may be located within the scribe line (e.g., between dies) and / or on the die itself. Multiple targets can be measured simultaneously or sequentially by the same or more measuring tools, as described in U.S. Patent No. 7,478,019. This entire description is incorporated herein by reference.

[0061] In some embodiments, the measurement system 400 includes a controller 404. In some embodiments, the controller 404 includes one or more processors 406 configured to execute program instructions maintained on a memory medium 408 (e.g., memory). In this regard, one or more processors 406 of the controller 404 can perform any of the various process steps described throughout this disclosure. Furthermore, the memory medium 408 can store any type of data used by any component of the measurement system 400. For example, the memory medium 408 may store recipes for a measurement tool 402, measurement data generated by the measurement tool 402, or the like.

[0062] One or more processors 406 of the controller 404 may include any processing elements known in the art. In this sense, one or more processors 406 may include any microprocessor type device configured to execute algorithms and / or instructions. In some embodiments, one or more processors 406 may consist of a desktop computer, a mainframe computer system, a workstation, an image computer, a parallel processor, or any other computer system (e.g., a networked computer) configured to execute a program configured to operate the measurement system 400, as described throughout this disclosure. Furthermore, it should be recognized that the term “processor” can be broadly defined to include any device having one or more processing elements that execute program instructions from a non-temporary memory medium 408.

[0063] The memory medium 408 may include any storage medium known in the art that is suitable for storing program instructions executable by one or more associated processors 406. For example, the storage medium 408 may include non-temporary storage media. Another example of the memory medium 408 may include, but is not limited to, read-only memory, random-access memory, magnetic or optical memory devices (e.g., disks), magnetic tapes, solid-state drives, etc. Furthermore, it should be noted that the memory medium 408 may be housed in a common controller housing together with one or more processors 406. In some embodiments, the memory medium 408 may be located remotely from the physical locations of one or more processors 406 and the controller 404. For example, one or more processors 406 of the controller 404 may have access to remote memory (e.g., a server) accessible via a network (e.g., the internet, an intranet, etc.). Therefore, the above description should not be construed as limiting the invention, but merely as an example.

[0064] Furthermore, the controller 404 and any associated components (e.g., processor 406, storage medium 408, etc.) may include one or more controllers housed in a common housing or multiple housings. In addition, the controller 404 may be integrated with and / or perform the functions of any component in the measurement system 400.

[0065] The controller 404 can further perform any number of processing or analysis steps. For example, the measurement target may be modeled (parameterized) using any technique known in the art, including, but not limited to, a geometric engine, a process modeling engine, or a combination thereof. The use of process modeling is generally described in U.S. Patent Application Publication 2014 / 0172394, which is incorporated herein by reference in its entirety. A geometric engine may, but is not required to be, implemented by AcuShape software, a product provided by KLA Corp. Furthermore, the EM solver may utilize any method known in the art, including, but not limited to, exact coupled wave analysis (RCWA), finite element method analysis, moment analysis methods, surface integration techniques, volume integration techniques, or finite difference time-domain analysis.

[0066] Controller 404 may further analyze the data collected from the measurement tool 402 and apply the collected data to a model using any data fitting and optimization technique known in the art, including but not limited to libraries, fast degree reduction models, machine learning algorithms such as regression and neural networks, support vector machines (SVMs), and dimensionality reduction algorithms (e.g., principal component analysis (PCA), independent component analysis (ICA), local linear embeddings (LLE), etc.). This may include sparse representations of the data (e.g., Fourier transform or wavelet transform, Kalman filters, algorithms that facilitate matching from the same or different tool types, etc.). For example, data collection and / or fitting may, but are not required to be, performed by Signal Response Metrology (SRM), a product provided by KLA Corp.

[0067] In some embodiments, the controller 404 analyzes the raw data generated by the instrumentation tool 402 using an algorithm that does not involve modeling, optimization, and / or fitting (e.g., phase characteristic evaluation). It should be noted herein that the computational algorithms performed by the controller may, but are not required, be adapted for instrumentation applications through parallelization, distributed computing, load balancing, multi-service support, design and implementation of computing hardware, or the use of dynamic load optimization. Furthermore, various implementations of the algorithms may, but are not required, be performed by the controller 404 (e.g., firmware, software, or a field-programmable gate array (FPGA)) or by one or more programmable optical elements associated with the instrumentation tool 402.

[0068] Figure 4B is a conceptual diagram of a measurement tool 402 according to one or more embodiments of the present disclosure.

[0069] In some embodiments, the measurement tool 402 includes an illumination source 410 for generating an illumination beam 412. The illumination beam 412 may include, but is not limited to, light of one or more selected wavelengths, including ultraviolet (UV) radiation, visible light, or infrared (IR) radiation. For example, the measurement tool 402 may include an illumination source 410 suitable for generating an illumination beam 412 with wavelengths ranging from 120 to 20,000 nm, or any subset or combination of wavelengths within that range.

[0070] The measurement system 400 may include any number or type of illumination sources 410 known in the art. In some embodiments, the illumination source 410 includes, but is not limited to, one or more narrowband laser sources, one or more broadband laser sources, one or more supercontinuum laser sources, one or more white light laser sources, one or more quantum cascade lasers (QCLs), and other laser sources. In some embodiments, the illumination source 410 includes one or more light-emitting diodes (LEDs). In some embodiments, the illumination source 410 includes, but is not limited to, an arc lamp, a discharge lamp, an electrodeless lamp, and other lamp sources. For example, the lamp source may include, but is not limited to, a Xe lamp source, a deuterium (D2) lamp source, or a halogen lamp source. In some embodiments, the illumination source 410 includes a broadband plasma (BBP) illumination source. In some embodiments, the illumination source 410 provides a tunable illumination beam 412. For example, the illumination source 410 may include a tunable illumination source (e.g., one or more tunable lasers, etc.). As another example, the illumination source 410 may include a broadband illumination source coupled to a tunable filter. The illumination source 410 can further provide an illumination beam 412 having any time profile. For example, the illumination beam 412 may have a continuous time profile, a modulation time profile, a pulsed time profile, and so on.

[0071] In some embodiments, the illumination source 410 directs an illumination beam 412 onto the sample 414 via an illumination path 416 and collects the light emitted from the sample as a collection beam 418 (e.g., collection beam) via a collection path 420. The collection beam 418 may include, but is not limited to, any combination of light from the sample 414 generated in response to the incident illumination beam 412, such as reflected light, scattered light, diffracted light, or luminescence from the sample 414. In some embodiments, the sample 414 is placed on a sample stage 422, which may include, but is not limited to, a linear translation stage, a rotation stage, or any combination of tip / inclined stages.

[0072] In some embodiments, the illumination path 416 may include an illumination focusing element 424 for focusing the illumination beam 412 onto the sample 414. The illumination path 416 may include one or more illumination beam adjustment components 426 suitable for modifying and / or adjusting the illumination beam 412. For example, one or more illumination beam adjustment components 426 may include, but are not limited to, one or more polarizers, one or more filters, one or more beam splitters, one or more apodizers, one or more beam shapers, one or more diffusers, one or more homogenizers, or one or more lenses. In some embodiments, one or more illumination beam adjustment components 426 in the illumination path 416 may include at least one monolithic optical retarder 100 to provide polarization control of the illumination beam 412, which may act as the light beam 110 illustrated in Figures 1-3B.

[0073] In some embodiments, the collection path 420 may include a collection and focusing element 428 for capturing the beam 418 collected from the sample 414. In some embodiments, the measurement system 400 includes a detector 430 configured to detect at least a portion of the collected beam 418 emanating from the sample 414 through the collection path 420. The detector 430 may include any type of photodetector known in the art that is suitable for measuring the illumination received from the sample 414. For example, the detector 430 may include, but is not limited to, a CCD detector, a CMOS detector, a TDI detector, a photomultiplier tube (PMT), an avalanche photodiode (APD), and the like. In some embodiments, the detector 430 may include a spectroscopic detector that is suitable for identifying the wavelength of radiation emanating from the sample 414.

[0074] The focusing path 420 may further include any number of focusing beam adjustment elements 432 for directing and / or correcting the illumination focused by the focusing element 428, including, but not limited to, one or more lenses, one or more filters, one or more polarizers, or one or more phase plates. In some embodiments, one or more collecting beam adjustment elements 432 in the collecting path 420 include at least one monolithic optical retarder 100 to provide polarization control of the collecting beam 418, which may act as the light beam 110 illustrated in Figures 1-3B.

[0075] In some embodiments, the measuring tool 402 depicted in Figure 4B may facilitate multi-angle illumination of the sample 414 and / or multiple illumination sources 410 (e.g., coupled to one or more additional detectors 430). In this regard, the measuring tool 402 shown in Figure 4B can perform multiple measuring measurements. In some embodiments, the measuring tool 402 may include multiple detectors 430 to facilitate multiple measuring measurements by the measuring tool 402 (e.g., multiple measuring tools).

[0076] Furthermore, the measuring tool 402 can facilitate multi-angle illumination of the sample 414 and / or multiple illumination sources 410. In this regard, the measuring tool 402 can perform multiple measurement operations. In some embodiments, one or more optical components may be mounted on a rotatable arm (not shown) that pivots around the sample 414, such that the incident angle of the illumination beam 412 on the sample 414 can be controlled by the position of the rotatable arm.

[0077] In some embodiments, one or more components are common to both the illumination path 416 and the collection path 420. Figure 4G is a conceptual diagram of a measuring tool 402 configured with a common objective lens according to one or more embodiments of the present disclosure. In some embodiments, the measuring tool 402 includes a beam splitter 434 oriented so that the objective lens 436 can simultaneously direct the illumination beam 412 towards the sample 414 and capture the collection beam 418 emanating from the sample 414. In this regard, the objective lens 436 may operate in place of, or together with, the illumination focusing element 424 and / or the light focusing element 428 in Figure 4B.

[0078] Generally referring to Figures 4A to 4C, it is intended herein that the measuring tool 402 may include any number of monolithic optical retarders 100 in any configuration. For example, the measuring tool 402 may include one or more monolithic optical retarders 100 in the illumination path 416 and / or the focusing path 420. The monolithic optical retarders 100 at either location may be positioned in a finite or infinite conjugate space. For example, the monolithic optical retarders may be located in the field of view plane or pupil plane of the measuring tool 402, but are not limited to these.

[0079] Furthermore, the monolithic optical retarder 100 may be used in conjunction with additional components, including but not limited to additional polarization control components. In addition, since the monolithic optical retarder 100 provides an unpolarized optical path for light passing through it, the monolithic optical retarder 100 may, but does not need to be, rotatable within the measuring tool 402. In this way, the effect of the monolithic optical retarder 100 on the polarization of light passing through it can be dynamically controlled by the rotation angle of the monolithic optical polarizer 100. In some embodiments, the measuring tool 402 includes at least one rotatable monolithic optical retarder 100. In some embodiments, the measuring tool 402 includes at least one rotatable monolithic optical retarder 100 and at least one polarizer, which may be fixed or rotatable. In some embodiments, the measuring tool 402 includes at least one fixed (e.g., non-rotatable) monolithic optical retarder 100 and at least one rotatable polarizer. However, it should be understood that the above examples are provided for illustrative purposes only and should not be construed as limitations.

[0080] In some embodiments, the measuring tool 402 includes at least one monolithic optical retarder 100 in a fixed (e.g., non-rotating) configuration and a rotating polarizer.

[0081] In some embodiments, the controller 404 may be communicatively coupled to any component of the measurement system 400. In some embodiments, the controller 404 is communicatively coupled to the illumination source 410 to provide one or more selected wavelengths of illumination for scattering measurement. In some embodiments, the controller 404 is coupled to one or more elements of the illumination path 416 to direct adjustments to the angle of incidence between the illumination beam 412 and the sample 414.

[0082] Figure 5 is a flowchart showing the steps performed in Method 500 for measurement using a monolithic optical retarder, according to one or more embodiments of the present disclosure. The applicant notes that the embodiments and enabling techniques described herein in the context of the measurement system 400 should be construed as extending to Method 500. However, it should be further noted that Method 500 is not limited to the architecture of the measurement system 400.

[0083] In some embodiments, Method 500 includes a step 502 of generating an illumination beam 412. For example, the illumination beam 412 can be generated by an illumination source 410, as described with respect to Figures 4A-4C, but is not required. In some embodiments, Method 500 includes a step 504 of directing the illumination beam 412 towards a sample 414. In some embodiments, Method 500 includes a step 506 of collecting light from the sample 414 (e.g., a collection beam 418) as a collection beam in response to the illumination beam, wherein the polarization of at least the illumination beam or the collection beam is controlled by at least one monolithic optical retarder 100 disclosed herein. Thus, the monolithic optical retarder 100 can operate on a light beam 110 including the illumination beam 412 for the monolithic optical retarder 100 located in the illumination path 416 and / or the collection beam 418 for the monolithic optical retarder 100 located in the collection path 420.

[0084] For example, the monolithic optical retarder 100 may include an input surface 104 for receiving a light beam 110 (e.g., an illumination beam 412 or a focusing beam 418), an output surface 108 aligned with the optical axis 212 of the light beam 110 before it enters the input surface 104, and three or more reflective surfaces 106. Thus, the three or more reflective surfaces 106 may be oriented to provide an optical path for the light beam 110 from the input surface 104 to the output surface 108 via reflection by the three or more reflective surfaces 106. Furthermore, the input surface 104, the output surface 108, and the three or more reflective surfaces 106 may be oriented such that the optical axis 212 of the light beam exiting the output surface 108 is equal to the optical axis 212 of the light beam entering the input surface 104. Here, the monolithic prism 102 provides a selected optical delay to the light beam 110 as it propagates along the optical path, based on total internal reflection at at least one of the three or more reflective surfaces 106.

[0085] In some embodiments, Method 500 includes step 508 of directing at least a portion of the collected beam to a detector as detection light. In some embodiments, Method 500 includes step 510 of generating one or more measurement values ​​of the sample 414 based on the detected light. For example, the measurement values ​​may include, but are not limited to, spectroscopic measurements, polarization analysis measurements, or polarization measurements. Furthermore, the measurement values ​​may characterize any aspect of the sample 414, including, but are not limited to, material properties of one or more films thereon, dimensional measurements of a fabricated structure, positional measurements of a fabricated structure, or identification of defects on the sample 414.

[0086] Those skilled in the art will recognize that the constituent actions, devices, objects, and associated discussions described herein are used as examples for conceptual clarity, and that various configuration modifications are considered. Therefore, as used herein, the specific examples and associated discussions described are intended to be representative of their more general class. In general, the use of any particular example is intended to represent its class, and the exclusion of specific constituent actions, devices, and objects should not be interpreted as limitation.

[0087] When used herein, terms indicating direction, such as “up,” “down,” “up,” “down,” “up,” “upward,” “downward,” and “downward,” are intended to provide relative positions for illustrative purposes and not to indicate an absolute reference frame. Various modifications to the embodiments described will be apparent to those skilled in the art, and the general principles defined herein may be applicable to other embodiments.

[0088] With regard to the use of substantially any plural and / or singular terms herein, those skilled in the art can convert from plural to singular and / or singular to plural as appropriate to the context and / or use. Various singular / plural substitutions are not explicitly stated herein for the sake of clarity.

[0089] The subject matter described herein illustrates different components that, in some cases, are contained within or connected to other components. It should be understood that such depicted architectures are merely illustrative, and in practice, many other architectures can be implemented to achieve the same functionality. Conceptually, any arrangement of components to achieve the same function is effectively “associated” in such a way that the desired function is achieved. Thus, any two components in this specification combined to achieve a particular function, whether in architecture or as intermediate components, can be considered “associated” with each other in such a way that the desired function is achieved. Similarly, any two such associated components can also be considered “connected” or “joined” with each other in such a way that the desired functionality is achieved, and any two components that can be associated in such a way can also be considered “joinable” with each other in such a way that the desired functionality is achieved. Specific examples of joinable components include, but are not limited to, physically joinable and / or physically interacting components and / or wirelessly interactable and / or wirelessly interacting components and / or logically interacting and / or logically interactable components.

[0090] Furthermore, it should be understood that the present invention is defined by the appended claims. Generally, it will be understood by those skilled in the art that the terms used herein and in particular in the appended claims (e.g., the body of the appended claims) are generally intended to be “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “at least having,” and the term “includes” should be interpreted as “includes but not limited to,” etc.). It will further be understood by those skilled in the art that if a specific number of claims to be introduced is intended, such intention will be explicitly stated in that claim, and if such statement is not made, such intention does not exist. For example, for the sake of understanding, the following appended claims may include introducing the claims using the introductory phrases “at least one” and “one or more.” However, the use of such phrases should not be interpreted as meaning that the introduction of a claim description with the indefinite article "a" or "an" limits any particular claim containing such introduced description to an invention containing only one such description. The same applies to the use of clear articles used to introduce a claim description, even if the same claim contains an introductory phrase such as "one or more" or "at least one" and an indefinite article such as "a" or "an" (for example, "a" and / or "an" should typically be interpreted as meaning "at least one" or "one or more"). Furthermore, even if a specific number of claims being introduced is explicitly listed, it will be recognized that such descriptions should typically be interpreted as meaning at least the number listed (for example, a bare list of "two lists" without other modifying factors typically means at least two lists, or two or more lists).Furthermore, in cases where a conventional expression similar to "at least one of A, B, and C" is used, such a configuration is generally intended to be understood by a person skilled in the art as including, but not limited to, a system having only A, only B, only C, both A and B, both A and C, both B and C, and / or a system having both A, B, and C. It will be further understood by those skilled in the art that virtually any separate word and / or phrase presenting two or more alternative terms, wherever it may appear in a description, claim, or drawing, should be understood as construing the possibility of including one of the terms, either of the terms, or both terms. For example, the phrase "A or B" will be understood to include the possibilities of "A" or "B" or "A and B".

[0091] Many of the present disclosure and its associated advantages will be understood from the foregoing description, and it will become clear that various modifications can be made to the form, structure, and arrangement of the components without deviating from the disclosed subject matter or sacrificing all of its material advantages. The described forms are for illustrative purposes only, and it is the intent of the following claims to encompass and include such modifications. Furthermore, it should be understood that the present invention is defined by the appended claims.

Claims

1. It is a monolithic optical retarder, It comprises a monolithic prism, and the monolithic prism is Formed from a single block of a single material, and made from an isotropic material that provides a direction-independent refractive index, An input surface for receiving the light beam, Before entering the input surface, the output surface is aligned with the optical axis of the light beam, Three or more reflective surfaces, which are oriented to provide an optical path for the light beam from the input surface to the output surface via reflection by the three or more reflective surfaces, The monolithic optical retarder provides a total optical delay to the light beam as it propagates along the optical path based on the total internal reflection in at least one of the three or more reflective surfaces, and the input surface, the output surface, and the three or more reflective surfaces are oriented such that the optical axis of the light beam exiting the output surface aligns with the optical axis of the light beam entering the input surface. A monolithic optical retarder wherein the three or more reflective surfaces include one or more delay surfaces and one or more non-delay surfaces, the angle of incidence of the light beam to the one or more delay surfaces is greater than the critical angle of total internal reflection, the total optical delay on the light beam during propagation along the optical path corresponds to the cumulative optical delay on the light beam provided by the one or more delay surfaces, the one or more non-delay surfaces control the optical path of the light passing through the monolithic prism so that the optical axis of the light beam exiting the output surface is aligned with the optical axis of the light beam entering the input surface, and the one or more non-delay surfaces are provided with a metallic or dielectric coating.

2. The monolithic optical retarder according to claim 1, characterized in that the angle of incidence of the light beam to one or more delay surfaces is greater than the critical angle of total internal reflection for at least one wavelength in the ultraviolet spectral region, the vacuum ultraviolet spectral region, or the deep ultraviolet spectral region.

3. The monolithic optical retarder according to claim 1, characterized in that the angle of incidence of the light beam to one or more delay surfaces is greater than the critical angle of total internal reflection for wavelengths including the visible spectral region.

4. The monolithic optical retarder according to claim 1, characterized in that the angle of incidence of the light beam to one or more delay surfaces is greater than the critical angle of total internal reflection for wavelengths including the infrared spectral region.

5. The monolithic optical retarder according to claim 1, characterized in that the angle of incidence of the light beam to one or more delay surfaces is greater than the critical angle of total internal reflection for wavelengths in the range of 120 nanometers to 20,000 nanometers.

6. The monolithic optical retarder according to claim 1, characterized in that the angle of incidence of the light beam to one or more delay surfaces is greater than the critical angle of total internal reflection for wavelengths in the range of 120 nanometers to 7000 nanometers.

7. The monolithic optical retarder according to claim 1, characterized in that the angle of incidence of the light beam to one or more delay surfaces is greater than the critical angle of total internal reflection for wavelengths in the range of 170 nanometers to 2500 nanometers.

8. The monolithic optical retarder according to claim 1, characterized in that at least one of the one or more delay planes has an optical delay in the range of 20 degrees to 80 degrees.

9. The monolithic optical retarder according to claim 1, characterized in that the total optical delay is in the range of 60 degrees to 120 degrees.

10. The monolithic optical retarder according to claim 1, characterized in that the total optical delay is 90 degrees.

11. The monolithic optical retarder according to claim 1, characterized in that the total optical delay is 180 degrees.

12. The three or more reflective surfaces are A first reflective surface oriented to receive light from the input surface and oriented at a selected angle with respect to the input surface, A second reflective surface is oriented to receive light from the first reflective surface and is perpendicular to the input surface, A third reflective surface is oriented to receive light from the second reflective surface and is oriented at a selected angle with respect to the output surface, The monolithic optical retarder according to claim 1, characterized by including the following:

13. The monolithic optical retarder according to claim 12, characterized in that the selected angle is greater than the critical angle of total internal reflection.

14. The three or more reflective surfaces are A first reflective surface oriented to receive light from the input surface, A second reflective surface is oriented to receive light from the first reflective surface and is parallel to the first reflective surface, A third reflective surface oriented to receive light from the second reflective surface and A fourth reflective surface is oriented to receive light from the third reflective surface and is parallel to the third reflective surface, The monolithic optical retarder according to claim 1, characterized by including the following:

15. The monolithic optical retarder according to claim 1, characterized in that the monolithic prism is a monolithic k-prism.

16. The monolithic optical retarder according to claim 1, characterized in that the monolithic prism has a shape that is a monolithic Fresnel rhombic retarder formed by combining Fresnel rhombuses.

17. The monolithic optical retarder according to claim 1, characterized in that the monolithic prism is made of glass.

18. The monolithic optical retarder according to claim 1, characterized in that the monolithic prism is at least one of fused silica, quartz, sapphire, calcium fluoride, magnesium fluoride, BK7, zinc sulfide, or zinc selenide.

19. The monolithic optical retarder according to claim 1, characterized in that the input surface, the output surface, and the three or more reflective surfaces are polished surfaces.

20. The monolithic optical retarder according to claim 1, characterized in that the monolithic prism rotates around the optical axis of the light beam incident on the input surface and provides polarization adjustment to the light beam by the angle of rotation.

21. It is a measurement system, A light source for generating an illumination beam, One or more illumination optics that direct the illumination beam onto the sample, Detector and One or more collection optical systems collect light from the sample as a collected beam and direct at least a portion of the collected beam to the detector as detection light, One or more monolithic optical retarders associated with at least one of the one or more illumination optical systems or the one or more collection optical systems, wherein a particular monolithic optical retarder of the one or more monolithic optical retarders is It is a monolithic prism, Formed from a single block of a single material, and made from an isotropic material that provides a direction-independent refractive index, An input surface for receiving the light beam, Before entering the input surface, the output surface is aligned with the optical axis of the light beam, The monolithic optical retarder comprises three or more reflective surfaces, which are oriented to provide an optical path for the light beam from the input surface to the output surface via total internal reflection by the three or more reflective surfaces, wherein the monolithic optical retarder imparts a selected optical delay to the light beam as it propagates along the optical path based on the total internal reflection by the three or more reflective surfaces, and the input surface, the output surface, and the three or more reflective surfaces are oriented such that the optical axis of the light beam exiting the output surface is equal to the optical axis of the light beam entering the input surface, and there is one or more of the three or more reflective surfaces. A monolithic prism comprising a delay surface and one or more non-delay surfaces, wherein the angle of incidence of the light beam to the one or more delay surfaces is greater than the critical angle of total internal reflection, the total optical delay on the light beam during propagation along the optical path corresponds to the cumulative optical delay on the light beam imparted by the one or more delay surfaces, the one or more non-delay surfaces control the optical path of the light passing through the monolithic prism so that the optical axis of the light beam exiting the output surface is aligned with the optical axis of the light beam entering the input surface, and the one or more non-delay surfaces are provided with a metallic or dielectric coating. A controller communicatively coupled to the detector, comprising one or more processors configured to execute program instructions causing one or more processors to generate one or more measured values ​​of the sample based on detected light, A measurement system equipped with the following features.

22. The measurement system according to claim 21, characterized in that at least one of the one or more monolithic optical retarders rotates along the optical axis of each light beam and provides polarization adjustment to the light beam by the angle of rotation.

23. The measurement system according to claim 21, wherein at least one of the one or more monolithic optical retarders is one of the one or more illumination optical systems, and at least one of the one or more monolithic optical retarders receives the illumination beam as a light beam.

24. The measurement system according to claim 21, wherein at least one of the one or more monolithic optical retarders is one of the one or more focusing optical systems, and at least one of the one or more monolithic optical retarders receives the focused beam as an optical beam.

25. The measurement system according to claim 21, characterized in that it includes a broadband measurement tool with wavelengths in the range of 120 nanometers to 20,000 nanometers.

26. The measurement system according to claim 21, characterized in that the measurement system includes at least one of a polarization analyzer, a reflectometer, a scatometer, or a polarimeter.

27. The three or more reflective surfaces are A first reflective surface oriented to receive light from the input surface and oriented at a selected angle with respect to the input surface, A second reflective surface is oriented to receive light from the first reflective surface and is perpendicular to the input surface, A third reflective surface is oriented to receive light from the second reflective surface and is oriented at a selected angle with respect to the output surface, The measurement system according to claim 21, characterized by including the following:

28. The three or more reflective surfaces are A first reflective surface oriented to receive light from the input surface, A second reflective surface is oriented to receive light from the first reflective surface and is parallel to the first reflective surface, A third reflective surface oriented to receive light from the second reflective surface, A fourth reflective surface is oriented to receive light from the third reflective surface and is parallel to the third reflective surface, The measurement system according to claim 21, characterized by including the following:

29. The measurement system according to claim 21, characterized in that the monolithic prism is a monolithic k-prism.

30. The measurement system according to claim 21, characterized in that the monolithic prism has a shape that is a monolithic Fresnel rhombic retarder formed by combining Fresnel rhombuses.

31. The measurement system according to claim 21, characterized in that the monolithic prism is made of glass.

32. A measurement method, The steps include generating an illumination beam and The steps include directing the illumination beam towards the sample, The step is to collect light from the sample as a collection beam in response to the illumination beam, wherein the polarization of at least the illumination beam or the collection beam is controlled by at least one monolithic optical retarder formed from a monolithic prism, and the monolithic prism is Formed from a single block of a single material, and made from an isotropic material that provides a direction-independent refractive index, An input surface for receiving the light beam, Before entering the input surface, the output surface is aligned with the optical axis of the light beam, The monolithic optical retarder comprises three or more reflective surfaces, which are oriented to provide an optical path for a light beam from the input surface to the output surface via reflection by the three or more reflective surfaces, and which impart a selected optical delay to the light beam as it propagates along the optical path based on total internal reflection in at least one of the three or more reflective surfaces, wherein the input surface, the output surface, and the three or more reflective surfaces are oriented such that the optical axis of the light beam exiting the output surface is equal to the optical axis of the light beam entering the input surface, and the three or more The reflective surface includes one or more delay surfaces and one or more non-delay surfaces, wherein the angle of incidence of the light beam to the one or more delay surfaces is greater than the critical angle of total internal reflection, the total optical delay on the light beam during propagation along the optical path corresponds to the cumulative optical delay on the light beam provided by the one or more delay surfaces, the one or more non-delay surfaces control the optical path of the light passing through the monolithic prism so that the optical axis of the light beam exiting the output surface is aligned with the optical axis of the light beam entering the input surface, and the one or more non-delay surfaces are provided with a metallic or dielectric coating. The steps include directing at least a portion of the collected beam towards a detector as detection light, A step of generating one or more measurement values ​​of the sample based on the detected light, Measurement methods including

33. The three or more reflective surfaces are A first reflective surface oriented to receive light from the input surface and oriented at a selected angle with respect to the input surface, A second reflective surface is oriented to receive light from the first reflective surface and is perpendicular to the input surface, A third reflective surface is oriented to receive light from the second reflective surface and is oriented at a selected angle with respect to the output surface, The measurement method according to claim 32, characterized by including the following:

34. The three or more reflective surfaces are A first reflective surface oriented to receive light from the input surface, A second reflective surface is oriented to receive light from the first reflective surface and is parallel to the first reflective surface, A third reflective surface oriented to receive light from the second reflective surface, A fourth reflective surface is oriented to receive light from the third reflective surface and is parallel to the third reflective surface, The measurement method according to claim 32, characterized by including the following:

35. The measurement method according to claim 32, characterized in that at least one of the one or more measurement values ​​includes at least one of polarization analysis measurement, reflectance measurement, scattering measurement, or polarization measurement.

36. It is a monolithic optical retarder, It comprises a monolithic prism, and the monolithic prism is Formed from a single block of a single material, and made from an isotropic material that provides a direction-independent refractive index, An input surface for receiving the light beam, Before entering the input surface, the output surface is aligned with the optical axis of the light beam, Three or more reflective surfaces, which are oriented to provide an optical path for the light beam from the input surface to the output surface via reflection by the three or more reflective surfaces, A monolithic optical retarder comprising: a monolithic optical retarder that imparts a total optical delay to the light beam as it propagates along the optical path based on total internal reflection at at least one of the three or more reflective surfaces; the input surface, the output surface, and the three or more reflective surfaces are oriented such that the optical axis of the light beam exiting the output surface aligns with the optical axis of the light beam entering the input surface; the three or more reflective surfaces include one or more delay surfaces and one or more non-delay surfaces; the angle of incidence of the light beam to the one or more non-delay surfaces is lower than the critical angle of total internal reflection; the one or more non-delay surfaces impart zero optical delay to the light beam; the one or more non-delay surfaces control the optical path of the light passing through the monolithic prism so that the optical axis of the light beam exiting the output surface aligns with the optical axis of the light beam entering the input surface; and the one or more non-delay surfaces are coated with a metal or dielectric material.

37. It is a measurement system, A light source for generating an illumination beam, One or more illumination optics that direct the illumination beam onto the sample, Detector and One or more collection optical systems collect light from the sample as a collected beam and direct at least a portion of the collected beam to the detector as detection light, One or more monolithic optical retarders associated with at least one of the one or more illumination optical systems or the one or more collection optical systems, wherein a particular monolithic optical retarder of the one or more monolithic optical retarders is It is a monolithic prism, Formed from a single block of a single material, and made from an isotropic material that provides a direction-independent refractive index, An input surface for receiving the light beam, Before entering the input surface, the output surface is aligned with the optical axis of the light beam, The monolithic optical retarder comprises three or more reflective surfaces, which are oriented to provide an optical path for the light beam from the input surface to the output surface via total internal reflection by the three or more reflective surfaces, wherein the monolithic optical retarder imparts a selected optical delay to the light beam as it propagates along the optical path based on the total internal reflection at the three or more reflective surfaces, and the input surface, the output surface, and the three or more reflective surfaces are oriented such that the optical axis of the light beam exiting the output surface is equal to the optical axis of the light beam entering the input surface. The three or more reflective surfaces include one or more delayed surfaces and one or more non-delayed surfaces, the angle of incidence of the light beam onto the one or more non-delayed surfaces is lower than the critical angle of total internal reflection, the one or more non-delayed surfaces impart zero optical delay to the light beam, the one or more non-delayed surfaces control the optical path of the light passing through the monolithic prism so that the optical axis of the light beam exiting the output surface is aligned with the optical axis of the light beam entering the input surface, and the one or more non-delayed surfaces are coated with metal or dielectric, the monolithic prism, A controller communicatively coupled to the detector, comprising one or more processors configured to execute program instructions causing one or more processors to generate one or more measured values ​​of the sample based on detected light, A measurement system equipped with the following features.

38. A measurement method, The steps include generating an illumination beam and The steps include directing the illumination beam towards the sample, The step is to collect light from the sample as a collection beam in response to the illumination beam, wherein the polarization of at least the illumination beam or the collection beam is controlled by at least one monolithic optical retarder formed from a monolithic prism, and the monolithic prism is Formed from a single block of a single material, and made from an isotropic material that provides a direction-independent refractive index, An input surface for receiving the light beam, Before entering the input surface, the output surface is aligned with the optical axis of the light beam, The monolithic optical retarder comprises three or more reflective surfaces, oriented to provide an optical path for a light beam from the input surface to the output surface via reflection by the three or more reflective surfaces, and the monolithic optical retarder imparts a selected optical delay to the light beam as it propagates along the optical path based on total internal reflection in at least one of the three or more reflective surfaces, wherein the input surface, the output surface, and the three or more reflective surfaces are oriented such that the optical axis of the light beam exiting the output surface is equal to the optical axis of the light beam entering the input surface, the three or more reflective surfaces include one or more delay surfaces and one or more non-delay surfaces, the angle of incidence of the light beam to the one or more non-delay surfaces is lower than the critical angle of total internal reflection, the one or more non-delay surfaces impart zero optical delay to the light beam, the one or more non-delay surfaces control the optical path of the light passing through the monolithic prism so that the optical axis of the light beam exiting the output surface is aligned with the optical axis of the light beam entering the input surface, and the one or more non-delay surfaces are provided with a metallic or dielectric coating. The steps include directing at least a portion of the collected beam towards a detector as detection light, A step of generating one or more measurement values ​​of the sample based on the detected light, Measurement methods, including those mentioned above.

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