Monolithic Optical Retarder

Abstract

A monolithic optical retarder formed from a monolithic prism may include an input surface for receiving a light beam, an output surface aligned with an 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 retardation to the light beam based on total internal reflection at at least one of the reflective surfaces. The input surface, output surface, and three or more reflective surfaces may also 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 entering the input surface.

Description

[Technical field]

[0001] REFERENCE TO RELATED APPLICATIONS This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Application No. 63 / 270,058 (filed Oct. 21, 2021, entitled MONOLITHIC OPTICS FOR BROADBAND SPECTROSCOPY), which is incorporated herein by reference in its entirety.

[0002] The present disclosure relates generally to optical retarders, and more particularly to monolithic optical retarders. [Background technology]

[0003] Optical retarders, such as wave plates, are widely used in many applications, including ellipsometry and reflectometry. In addition, broadband applications, such as but not limited to spectroscopic ellipsometry or spectroscopic reflectometry, 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 bonded together. However, bonded prisms may suffer from a variety of problems, including but not limited to delamination and contamination of 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 stiffness limited by van der Waals forces. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] US Patent Application Publication No. 2009 / 0091758 [Patent Document 2] US Patent Application Publication No. 2016 / 0209755 Summary of the Invention [Problem to be solved by the invention]

[0005] Therefore, there is a need to develop a system and method to address the above-mentioned shortcomings. [Means for solving the problem]

[0006] According to one or more exemplary embodiments of the present disclosure, a monolithic optical retarder is disclosed. 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 an 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 upon propagation 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, 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 manner, the light beam is not deflected by propagation along the optical path through the monolithic prism.

[0007] A metrology system is disclosed in accordance with 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 to the 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 to the detector as detection light. In another exemplary embodiment, the system includes one or more monolithic optical retarders associated with at least one of the one or more illumination optics or the one or more collection optics, and a particular monolithic optical retarder of the 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 the 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 upon propagation 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, the output surface, and the three or more reflective surfaces are oriented such that an optical axis of the light beam exiting the output surface is equal to an optical axis of the light beam entering the input surface. In this manner, 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 that cause the one or more processors to generate one or more metrology measurements of the sample based on the detected light.

[0008] A method is disclosed in accordance with one or more exemplary embodiments of the present disclosure. In one exemplary embodiment, the method includes generating an illumination beam. In another exemplary embodiment, the method includes directing the illumination beam to a sample. In another exemplary embodiment, the method includes 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 the light beam, an output surface aligned with an 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 retardation to the light beam upon propagation 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, the output surface, and the three or more reflective surfaces are oriented such that an optical axis of the light beam exiting the output surface is equal to an optical axis of the light beam entering the input surface. In this manner, the light beam is not deflected by propagation along the optical path through the monolithic prism. In another exemplary embodiment, the method further includes directing at least a portion of the collected beam as detection light to a detector. In another exemplary embodiment, the method further includes generating one or more metrology measurements of the sample based on the detected light.

[0009] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not necessarily restrictive of the invention as claimed. The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the general description, serve to explain the principles of the invention.

[0010] The numerous advantages of the present disclosure may be better understood by those skilled in the art by reference to the accompanying drawings: [Brief description of the drawings]

[0011] [Figure 1] FIG. 2 is a conceptual block diagram of components of a monolithic optical retarder in accordance with one or more embodiments of the present disclosure. [Figure 2A] FIG. 2 is a schematic diagram of a monolithic optical retarder formed as a monolithic k-prism providing three reflective surfaces in accordance with one or more embodiments of the present disclosure. [Figure 2B] FIG. 2 is a schematic diagram of a monolithic optical retarder formed as a monolithic Fresnel rhombus providing four reflective surfaces in accordance with one or more embodiments of the present disclosure. [Figure 3A] FIG. 1 is a schematic diagram of a conventional multi-component k-prism formed of three prism components in accordance with one or more embodiments of the present disclosure. [Figure 3B] FIG. 2 is a schematic diagram of a conventional multi-component Fresnel rhombus providing two prism components, in accordance with one or more embodiments of the present disclosure. [Figure 4A] FIG. 1 is a block diagram of a metrology system including a monolithic optical retarder in accordance with one or more embodiments of the present disclosure. [Figure 4B] FIG. 1 is a conceptual diagram of a metrology tool in accordance with one or more embodiments of the present disclosure. [Figure 4C] FIG. 1 is a conceptual diagram of a metrology tool configured with a common objective lens in accordance with one or more embodiments of the present disclosure. [Diagram 5] 1 is a flowchart illustrating steps performed in a metrology method using a monolithic optical retarder in accordance with one or more embodiments of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Reference will now be made in detail to the disclosed subject matter, which is illustrated in the accompanying drawings. The present disclosure has been specifically shown and described with respect to certain embodiments and certain features thereof. The embodiments described herein are to be construed as illustrative and not restrictive. It will be readily apparent to those skilled in the art that various changes and modifications in form and detail may be made therein without departing from the spirit and scope of the present disclosure.

[0013] Embodiments of the present disclosure are directed to systems and methods for providing broadband (e.g., achromatic) optical delay using monolithic optical elements without displacing the input beam. For purposes of this disclosure, the term monolithic is used to denote an element that is fabricated from a single block of a single material, with no seams or interfaces between any of the components.

[0014] An optical retarder introduces an optical retardation (e.g., phase retardation) that corresponds to a phase shift or phase retardation between light having orthogonal polarizations, which typically has the effect of modifying the polarization state of the input light. For example, a quarter-wave optical retarder can introduce a quarter-wave 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-wave 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 deviating 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, broadband optical delay can provide equivalent optical delay for multiple wavelengths, which can enable broadband input light polarization correction or stable narrowband polarization correction over a range of possible input wavelengths. Furthermore, by providing an optical delay with an unbiased optical path, optical retarders can be inserted, removed, or rotated as needed with minimal impact on the optical path of the beam in a larger system. However, it is contemplated herein that providing an optical delay with both an unbiased optical path and broadband capability remains a significant challenge, especially for high power beams or wavelengths that span the ultraviolet (UV) spectral range and below.

[0016] Optical retardation may be induced using a variety of techniques, such as, but not limited to, propagation through a birefringent material or total internal reflection. For example, waveplates typically utilize a birefringent material with a directionally dependent refractive index to induce a directionally dependent phase retardation on an input beam. Waveplates also do not deflect the optical path of an input beam when aligned at normal incidence. However, this technique is highly wavelength dependent and is typically limited to narrowband applications since the refractive index of birefringent materials varies as a function of wavelength. As another example, broadband optical retardation can be achieved using total internal reflection (TIR) ​​from the inner surface of a prism. However, existing prism-based optical retarders, such as Fresnel rhombuses or k-prisms, either deflect the input beam or require multiple prisms cemented together to achieve an undeflected optical path. The use of such cemented prisms may 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, unacceptably large beam deviations due to pyramiding effects of multiple components, or mechanical stiffness limited by van der Waals forces.

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

[0018] In some embodiments, the monolithic optical retarder includes one or more non-retardation surfaces. For example, the non-retardation surfaces may be oriented at angles smaller than the critical angle associated with TIR, and thus may reflect light without imparting optical retardation. It is believed that the non-retardation surfaces are suitable for controlling the optical path of light through the monolithic prism (e.g., ensuring an unbiased optical path for the output beam relative to the input beam). Furthermore, it is contemplated herein that a mixture of retardation and non-retardation surfaces may allow substantial flexibility in the design of the monolithic prism, while achieving both a selected optical retardation without deflecting the light beam.

[0019] Additionally, any surface, including but not limited to a non-retardant surface, may include an optical coating to further modify or control the characteristics of the light beam. For example, a non-retardant 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 metal coating, such as 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 unbiased 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 rhomboid.

[0021] It is contemplated herein that monolithic optical retarders formed from monolithic prisms may offer numerous benefits over conventional prism designs, including, but not limited to, high mechanical stiffness and the ability to transmit high fluences of UV / VUV / DUV light without any issues with 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 prisms.

[0022] Further embodiments of the present disclosure are directed to systems and methods for metrology using at least one monolithic optical retarder disclosed herein. In some embodiments, metrology systems including the monolithic optical retarders disclosed herein include, but are not limited to, ellipsometers or reflectometers.

[0023] 1-2B, a monolithic optical retarder is described in greater detail in accordance with one or more embodiments of the present disclosure.

[0024] It is recognized herein that light that is totally internally reflected at an interface may also undergo a phase shift 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 a 90 degree angle of incidence (this is merely a matter of convention and does not limit the present disclosure). However, the phase shift 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) is different at intermediate angles, which gives rise to a phase difference (e.g., optical retardation) between p-polarized light and s-polarized light that depends on both the angle of incidence and the refractive index of the material through which the light is propagating. The exact phase difference can be characterized by the well-known Fresnel reflection coefficient.

[0025] As a result, any optical retardation or relative phase difference between the orthogonal p-polarized and s-polarized portions of a light beam can be achieved by successive total internal reflections at selected angles. Note that the TIR-induced phase shift also depends slightly on the wavelength of the light, since the refractive index of materials varies with wavelength. However, this wavelength-dependent effect is relatively weak, and thus broadband performance can typically be achieved within acceptable tolerances for many applications. In contrast, optical retarders based on birefringence (e.g., wave plates) are typically highly sensitive to wavelength and are typically limited to narrowband applications.

[0026] As previously described herein, it is contemplated that existing optical delay devices based on TIR-induced phase shifts either deflect the incoming light, making alignment and tuning within a larger system difficult, or require bonding together multi-component prisms that reduce mechanical stability and limit output and / or wavelength range due to delamination or thermal issues.

[0027] SUMMARY OF THE DISCLOSURE Embodiments of the present disclosure are directed to a monolithic optical delay device that utilizes TIR-induced phase shifting.

[0028] FIG. 1 is a conceptual block diagram of components of a monolithic optical retarder 100 in accordance with 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 face 104, multiple reflective faces 106, and an output face 108, where at least one of the reflective faces 106 operates as a delay face that imparts optical delay to the light beam 110 through TIR (e.g., the angle of incidence of the light beam 110 on the delay face along the optical path is greater than the critical angle for TIR). Thus, the light beam 110 may undergo optical delay and associated polarization modification by entering the monolithic prism 102 through the input face 104, propagating along an optical path that includes reflections from three or more reflective faces 106, and exiting the output face 108, where the total optical delay imparted to the light beam 110 corresponds to the cumulative optical delay imparted by the delay faces along the optical path.

[0030] Monolithic prism 102 may include any number of non-retardant surfaces along the optical path, where the non-retardant surfaces correspond to reflective surfaces 106 that are oriented such that the angle of incidence of light beam 110 is below the critical angle for TIR, and thus no optical retardation is imparted to light beam 110. In this manner, the reflective surfaces 106 along the optical path through monolithic prism 102 may be divided into any combination of retardant and non-retardant surfaces, including at least one retardant surface.

[0031] The monolithic prism 102 may include an optical coating on any of the reflective surfaces 106 (e.g., any exterior surface of the reflective surface 106). The coating may include any type of coating known in the art, including but not limited to, a metallic or dielectric coating. The coating may further include any number of layers. In some embodiments, the coating is a reflective coating, such as but not limited to, a metallic coating, and generally may be operable for any wavelength or range of wavelengths 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 surface where light beam 110 has an angle of incidence less than the critical angle for TIR may typically transmit a first portion of light beam 110 along the optical path in addition to a second portion of light beam 110. However, a coating on the non-retardant surface may provide a high reflectivity of light beam 110 along the optical path, thus reducing or eliminating losses due to reflection at the non-retardant surface.

[0033] The monolithic prism 102 may provide an undeflected optical path for the light beam 110 such that the monolithic prism 102 may 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 face 104 and the output face 108 may be aligned along the optical axis of the light beam 110 outside of the monolithic prism 102. In this manner, any modifications to the optical path of the light beam 110 are limited to locations within the monolithic prism 102. Additionally, while in some embodiments the output face 108 and the input face 104 are parallel, it should be understood that this is not a requirement.

[0034] The monolithic prism 102 may be formed as a solid, seamless, monolithic piece of any single material suitable for transmitting the light beam 110, such as, but not limited to, glass or crystal. For example, the monolithic prism 102 may be formed from materials such as, but not limited to, 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. In a general sense, it is recognized herein that different materials have different optical properties and transmission bands and thus may be suitable for different applications or wavelength ranges. By way of example, but not limited to, a UV grade material such as, but not limited to, fused silica or sapphire may be suitable for applications utilizing UV wavelengths. As another example, CaF2 may provide operation in, but not limited to, a wavelength range of 120-7000 nm or any combination of wavelengths therein. As another example, fused silica may provide operation at a wavelength range of 170-2500 nm or any combination of wavelengths therein, without limitation. As another example, without limitation, IR-transmissive materials such as ZnS or ZnSe may be suitable for applications utilizing IR wavelengths, without limitation. However, it should be understood that the monolithic prism 102 may generally be designed to operate with light beams 110 having any wavelength or range of wavelengths, including, but not limited to, the range of 120 nm to 20,000 nm.

[0035] Additionally, the monolithic prism 102 may, but need not, be formed from an isotropic material that provides a directionally independent index of refraction. It is contemplated herein that an isotropic material with a directionally independent index of refraction may provide optical retardation solely through TIR-induced phase shifts at the reflective surface 106, which may 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 retardation between orthogonal polarization directions of the light beam 110. In particular, each reflective surface 106 acting as a retardation 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 manner, 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 need not be the same. By way of example, it is recognized herein that a total phase shift in the range of 60 degrees 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 non-limiting and that any reflective surface 106 generally provides any selected phase shift.

[0037] It is further contemplated herein that the relative phase shift (e.g., optical retardation) between the orthogonal polarization components of the light beam 110 may generally have a modulus of 360 degrees (or 2π radians). In this manner, the cumulative relative phase shift from the reflective surface 106 of the monolithic prism 102 may exceed 360 degrees any number of times to provide any equivalent effective phase shift between 0 degrees and 360 degrees. Furthermore, it may be convenient 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 range from -180 degrees to +180 degrees. It should therefore be understood that the present disclosure or any of the 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 monolithic optical retarders 100 formed from monolithic prisms 102 that provide three and four reflective surfaces 106, respectively, in accordance with one or more embodiments of the present disclosure. Figures 3A and 3B show contrasting multi-component prism designs.

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

[0040] FIG. 2B is a schematic diagram of a monolithic optical retarder 100 formed as a monolithic Fresnel rhombus providing four reflective surfaces 106, in accordance with one or more embodiments of the present disclosure. For example, FIG. 2B shows a light path 202 of a light beam 110 through the input face 104, reflecting off a first reflective surface 106d with a first angle of incidence 204d, reflecting off a second reflective surface 106e with a second angle of incidence 204e, reflecting off a third reflective surface 106f with a third angle of incidence 204f, reflecting off a fourth reflective surface 106g with a fourth angle of incidence 204g, and passing through the output face 108. In particular, FIG. 2B shows a configuration in which the reflective surfaces 106d,e are parallel, the reflective surfaces 106f,g are parallel, and the reflective surfaces 106f,g are arranged with reflection symmetry about the vertex 206 with respect to the reflective surfaces 106d,e.

[0041] It is contemplated herein that the design of the monolithic optical retarder 100, such as, but not limited to, those 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 reflecting surface 106 depends on the angle of incidence and the refractive index of the monolithic prism 102 as previously described herein. The refractive index can be adjusted by the selection of the material used to fabricate the monolithic prism 102. The angles of incidence on the various reflecting 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 reflecting surfaces 106a,c relative to the input surface 104 and the output surface 108, and the second angle of incidence 204b may be adjusted based on, but not limited to, the dimensions: the length or prism height 208 of the first and third reflecting surfaces 106a,c. Similarly, the angles of incidence 204d-g in the design shown in FIG. 2B can be adjusted based on the prism thickness 210, or based on the angles and / or lengths of the reflective surfaces 106d-g.

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

[0043] 2A and 2B provides a common plane of incidence for all reflective surfaces 106, which is the plane of the figure. As a result, further adjustment of the angle of incidence 204 may be achieved by rotating the monolithic prism 102 within the plane of the figure. However, it should be understood that the monolithic optical retarders 100 disclosed herein need not provide reflective surfaces 106 with a common plane of incidence. Rather, the reflective surfaces 106 may generally be oriented in any suitable three-dimensional configuration.

[0044] The total optical retardation induced by the monolithic prism 102 may then be determined as the cumulative retardation induced by the various reflective surfaces 106 (e.g., the reflective surfaces 106 function as retardation surfaces). Thus, based on the selection of materials, design, and physical dimensions of the monolithic prism 102, any desired optical retardation between orthogonal polarizations can be induced. For example, but not limited to, a monolithic optical retarder 100, such as that illustrated in FIGS. 2A and 2B, may be adapted to provide a π / 2 retarder to operate as a quarter-wave retarder, a π retarder to operate as a half-wave retarder, or any other selected value. Furthermore, it should be understood that while the monolithic optical retarder 100 may simply provide an optical retardation between p-polarized and s-polarized light at any particular reflective surface 106, the particular 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 providing a π / 2 retardation may convert linearly polarized light to circularly polarized light when oriented at a particular angle (e.g., a 45 degree angle provides equal amounts of p-polarized and s-polarized light at the reflective surface 106), but may produce elliptically polarized light for other input orientations.

[0045] 2A and 2B does not induce any shifting of the optical axis of the light beam 110 when the light beam 110 is aligned to enter the input face 104 at a normal incidence angle. As an example, the light beam 110 may follow a straight (e.g., non-shifted) optical axis 212 extending to and from the monolithic prism 102, regardless of its optical path within the monolithic prism 102, in which case all shifting of the light beam 110 occurs within the monolithic prism 102. In this manner, the monolithic optical retarder 100 may be inserted, removed, and / or rotated (e.g., along the optical axis 212 of the light beam 110) without changing the optical axis 212 of the light beam 110.

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

[0047] It is contemplated herein that a monolithic optical retarder 100 formed from a monolithic prism 102 may offer numerous benefits over conventional multi-component retarders, including, but not limited to, high mechanical stiffness and the ability to transmit high fluences of UV / VUV / DUV light without any issues with delamination or interfacial degradation that lead to scattering and / or loss of spectral fidelity.

[0048] For example, it is recognized herein that a conventional multi-component retarder formed from bonded prism components 304 may require optically polished optical surfaces on each prism component at the optical interfaces 308 between the prism components 304. However, the polishing compound may become trapped in surface cracks, which may lead to hot spots at the interface due at least in part to differences 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 beneficially does not include such optical interfaces 308 may provide superior high power performance.

[0049] As another example, the monolithic optical retarder 100 disclosed herein does not suffer from the risk of delamination. In contrast, differences in the coefficient of thermal expansion (CTE) between the trapped polishing compound and the substrate prism material of a conventional multi-component prism may lead to delamination at the optical interface 308. Furthermore, conventional multi-component prisms may 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, thus providing high beam uniformity with minimal or no scattering. In contrast, contact lines in the beam path of a conventional multi-component prism can be a source of scattering and spatial non-uniformity.

[0051] As another example, the monolithic optical retarder 100 as disclosed herein provides minimal or no beam deviation and excellent parallelism due to the monolithic design. In general, the axial beam deviation is associated with the geometric tolerance stack-up of the k-prisms and increases cumulatively with an increase in the number of prism components 304.

[0052] As another example, the monolithic optical retarder 100 disclosed herein provides high material uniformity across the monolithic prism 102, facilitating high spatial (e.g., refractive index) uniformity and high polarization uniformity. In general, it is easier to provide consistent spatial and polarization uniformity with a single substrate material than with multiple prism components 304 bonded together.

[0053] As another example, the monolithic optical retarder 100 disclosed herein provides high mechanical stiffness, high thermal stability, high component-to-component hardware matching, and generally facilitates high manufacturing yields at low component costs.

[0054] 4A-5, systems and methods for metrology using the monolithic optical retarder 100 are described in more detail in accordance with one or more embodiments of the present disclosure. It is contemplated herein that the monolithic optical retarder 100 may be incorporated into any type of metrology system known in the art that requires polarization control of the light beam 110.

[0055] FIG. 4A is a block diagram of a metrology system 400 including a monolithic optical retarder 100 in accordance with one or more embodiments of the present disclosure.

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

[0057] Further, the metrology tool 402 may include a single metrology tool or multiple metrology tools. For example, metrology tools including multiple hardware configurations are generally described in U.S. Patent No. 7,933,026, which is incorporated herein by reference in its entirety. A metrology system incorporating multiple metrology tools is generally described in U.S. Patent No. 7,478,019, which is incorporated herein by reference in its entirety. Focused beam ellipsometry, which is primarily based 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 apodizers to mitigate the effects of optical diffraction, which causes the spread of an illumination spot beyond a size defined by geometric optics, is generally described in U.S. Patent No. 5,859,424, which is incorporated herein by reference in its entirety. The use of high numerical aperture tools with simultaneous multiple incidence angle illumination is generally described in U.S. Patent No. 6,429,943, which is incorporated herein by reference in its entirety.

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

[0059] Metrology targets may be designed to be sensitive to, and therefore facilitate the measurement of, 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., focus, dose, etc.). To this end, metrology targets may include any combination of periodic structures (e.g., one-, two-, or three-dimensional periodic structures) or isolated non-periodic features. The use of metrology tools to characterize non-periodic features is generally described in U.S. Patent No. 9,291,554, issued March 22, 2016, which is incorporated herein by reference in its entirety. Additionally, metrology targets may generally be characterized as 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 scatterometry overlay metrology 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] Metrology targets may be located at multiple sites on the sample. For example, targets may be located within the scribe lines (e.g., between the dies) and / or on the dies themselves. Multiple targets may be measured simultaneously or sequentially by the same or multiple metrology tools, as described in U.S. Patent No. 7,478,019, which is incorporated herein by reference in its entirety.

[0061] In some embodiments, the metrology 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., a memory). In this regard, the one or more processors 406 of the controller 404 may perform any of the various process steps described throughout this disclosure. Additionally, the memory medium 408 may store any type of data used by any component of the metrology system 400. For example, the memory medium 408 may store a recipe for the metrology tool 402, metrology data generated by the metrology tool 402, or the like.

[0062] The one or more processors 406 of the controller 404 may include any processing element known in the art. In this sense, the one or more processors 406 may include any microprocessor-type device configured to execute algorithms and / or instructions. In some embodiments, the one or more processors 406 may comprise 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 programs configured to operate the metrology system 400 as described throughout this disclosure. Furthermore, it should be appreciated that the term "processor" may be broadly defined to encompass any device having one or more processing elements that executes program instructions from a non-transitory memory medium 408.

[0063] The memory medium 408 may include any storage medium known in the art suitable for storing program instructions executable by the associated one or more processors 406. For example, the storage medium 408 may include a non-transitory storage medium. As another example, the memory medium 408 may include, but is not limited to, a read-only memory, a random access memory, a magnetic or optical memory device (e.g., disk), a magnetic tape, a solid-state drive, and the like. Furthermore, it is noted that the memory medium 408 may be housed in a common controller housing along with the one or more processors 406. In some embodiments, the memory medium 408 may be located remotely relative to the physical location of the one or more processors 406 and the controller 404. For example, the one or more processors 406 of the controller 404 may access a remote memory (e.g., a server) accessible via a network (e.g., the Internet, an intranet, etc.). Thus, the above description should not be construed as limiting the present invention, but merely as illustrative.

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

[0065] The controller 404 may further perform any number of processing or analysis steps. For example, the metrology 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 No. 2014 / 0172394, which is incorporated herein by reference in its entirety. The geometric engine may, but need not, be implemented by AcuShape software, a product offered by KLA Corp. Additionally, the EM solver may utilize any method known in the art, including, but not limited to, rigorous coupled wave analysis (RCWA), finite element analysis, method of moment analysis, surface integration techniques, volume integration techniques, or finite difference time domain analysis.

[0066] The controller 404 may further analyze the data collected from the metrology tool 402 using any data fitting and optimization technique known in the art, including, but not limited to, libraries, fast reduced order models, machine learning algorithms such as regression, neural networks, support vector machines (SVM), dimensionality reduction algorithms (e.g., principal component analysis (PCA), independent component analysis (ICA), locally linear embedding (LLE), etc.), and apply the collected data to a model, a sparse representation of the data (e.g., Fourier or wavelet transforms, Kalman filters, algorithms that facilitate matching from the same or different tool types, etc.). For example, the data collection and / or fitting may be, but need not be, performed by Signal Response Metrology (SRM), a product offered by KLA Corp.

[0067] In some embodiments, the controller 404 analyzes the raw data generated by the metrology tool 402 using algorithms that do not involve modeling, optimization, and / or fitting (e.g., phase characterization, etc.). It is noted herein that the computational algorithms executed by the controller may, but need not, be tuned for the metrology application through the use of parallelization, distributed computing, load balancing, multi-service support, computing hardware design and implementation, or dynamic load optimization. Additionally, various implementations of the algorithms may, but need not, be executed by the controller 404 (e.g., firmware, software, or field programmable gate array (FPGA), etc.) or one or more programmable optical elements associated with the metrology tool 402.

[0068] FIG. 4B is a conceptual diagram of a metrology tool 402 in accordance with one or more embodiments of the present disclosure.

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

[0070] The metrology system 400 may include any number or type of illumination sources 410 known in the art. In some embodiments, the illumination source 410 includes a laser source, such as, but 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). In some embodiments, the illumination source 410 includes one or more light emitting diodes (LEDs). In some embodiments, the illumination source 410 includes a lamp source, such as, but not limited to, an arc lamp, a discharge lamp, an electrodeless lamp, etc. 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 an adjustable illumination beam 412. For example, the illumination source 410 may include an adjustable illumination source (e.g., one or more tunable lasers, etc.). As another example, the illumination source 410 can include a broadband illumination source coupled to a tunable filter. The illumination source 410 can further provide an illumination beam 412 having any temporal profile. For example, the illumination beam 412 can have a continuous temporal profile, a modulated temporal profile, a pulsed temporal profile, etc.

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

[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 conditioning components 426 suitable for modifying and / or conditioning the illumination beam 412. For example, the one or more illumination beam conditioning 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, the one or more illumination beam conditioning components 426 in the illumination path 416 include at least one monolithic optical retarder 100 to provide polarization control of the illumination beam 412, which may operate as the light beam 110 illustrated in FIGS. 1-3B.

[0073] In some embodiments, the collection path 420 may include a collection focusing element 428 for capturing the collected beam 418 from the sample 414. In some embodiments, the metrology 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 optical detector known in the art suitable for measuring 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 suitable for identifying wavelengths of radiation emanating from the sample 414.

[0074] The collection path 420 may further include any number of collection beam conditioning elements 432 for directing and / or modifying the illumination collected by the collection 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, the one or more collection beam conditioning elements 432 in the collection path 420 include at least one monolithic optical retarder 100 to provide polarization control of the collected beam 418, which may operate as the light beam 110 illustrated in FIGS. 1-3B.

[0075] In some embodiments, the metrology 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 metrology tool 402 shown in Figure 4B can perform multiple metrology measurements. In some embodiments, the metrology tool 402 can include multiple detectors 430 to facilitate multiple metrology measurements by the metrology tool 402 (e.g., multiple metrology tools).

[0076] Additionally, the metrology tool 402 can facilitate multi-angle illumination of the sample 414 and / or multiple illumination sources 410. In this regard, the metrology tool 402 can perform multiple metrology measurements. In some embodiments, one or more optical components may be mounted on a rotatable arm (not shown) that pivots about the sample 414 such that the angle of incidence 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. FIG. 4G is a conceptual diagram of a metrology tool 402 configured with a common objective lens, in accordance with one or more embodiments of the present disclosure. In some embodiments, the metrology tool 402 includes a beam splitter 434 oriented such that the objective lens 436 can simultaneously direct the illumination beam 412 to 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 in conjunction with the illumination focusing element 424 and / or collection focusing element 428 of FIG. 4B.

[0078] 4A-4C , it is contemplated herein that a metrology tool 402 may include any number of monolithic optical retarders 100 in any configuration. For example, the metrology tool 402 may include one or more monolithic optical retarders 100 in the illumination path 416 and / or collection path 420. The monolithic optical retarders 100 in either position may be located in finite or infinite conjugate space. For example, but not limited to, the monolithic optical retarders may be located in a field plane or a pupil plane of the metrology tool 402.

[0079] Further, 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 need not be, rotatable within the metrology tool 402. In this manner, the effect of the monolithic optical retarder 100 on the polarization of light passing through it may be dynamically controlled by the rotation angle of the monolithic optical polarizer 100. In some embodiments, the metrology tool 402 includes at least one rotatable monolithic optical retarder 100. In some embodiments, the metrology 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 metrology tool 402 includes at least one fixed (e.g., non-rotating) 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 limiting.

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

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

[0082] 5 is a flow chart illustrating steps performed in a method 500 for metrology using a monolithic optical retarder, in accordance with one or more embodiments of the present disclosure. Applicant notes that the embodiments and enabling techniques previously described herein in the context of metrology system 400 should be construed as extending to method 500. However, it is further noted that method 500 is not limited to the architecture of metrology system 400.

[0083] In some embodiments, the method 500 includes a step 502 of generating an illumination beam 412. For example, the illumination beam 412 can be, but need not be, generated by an illumination source 410, as described with respect to FIGS. 4A-4C. In some embodiments, the method 500 includes a step 504 of directing the illumination beam 412 to a sample 414. In some embodiments, the method 500 includes a step 506 of collecting light from the sample 414 in response to the illumination beam (e.g., a collection beam 418) as a collection beam, where the polarization of at least the illumination beam or the collection beam is controlled by at least one monolithic optical retarder 100 disclosed herein. In this manner, the monolithic optical retarder 100 can operate on a light beam 110 including the illumination beam 412 for a monolithic optical retarder 100 located in the illumination path 416 and / or the collection beam 418 for a 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 the light beam 110 (e.g., the illumination beam 412 or the collected 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. In this manner, 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 imparts a selected optical retardation to the light beam 110 upon propagation 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, the method 500 includes directing 508 at least a portion of the collected beam to a detector as detected light. In some embodiments, the method 500 includes generating 510 one or more metrology measurements of the sample 414 based on the detected light. For example, the metrology measurements may include, but are not limited to, spectroscopic measurements, ellipsometric measurements, or polarimetric measurements. Additionally, the metrology measurements may characterize any aspect of the sample 414, including, but not limited to, material properties of one or more films thereon, dimensional measurements of a fabricated structure, position measurements of a fabricated structure, or identification of defects on the sample 414.

[0086] Those skilled in the art will recognize that the component operations, devices, objects, and their accompanying discussion described herein are used as examples for conceptual clarity, and that various configuration modifications are contemplated. Thus, as used herein, the specific examples described and the accompanying discussion are intended to be representative of their more general classes. In general, the use of any specific example is intended to represent its class, and non-inclusion of specific components, operations, devices, and objects should not be construed as limiting.

[0087] As used herein, directional terms such as "top", "bottom", "up", "down", "up", "upper", "lower", "lower" and the like are intended to provide relative positions for purposes of description and are not intended to indicate an absolute frame of reference. Various modifications to the described embodiments will be apparent to those skilled in the art and the general principles defined herein may be applied to other embodiments.

[0088] With respect to the use of virtually any plural and / or singular term herein, those of skill in the art can convert from plural to singular and / or from singular to plural as appropriate to the context and / or application. The various singular / plural permutations are not expressly set forth herein for ease of understanding.

[0089] The subject matter described herein illustrates different components that are sometimes included within or connected to other components. It should be understood that such depicted architectures are merely exemplary, and that in fact many other architectures that achieve the same functionality may be implemented. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively "associated" such that the desired functionality is achieved. Thus, any two components herein that are combined to achieve a particular functionality can be considered to be "associated" with each other such that the desired functionality is achieved, regardless of the architecture or intermediate components. Similarly, any two components so associated can also be considered to be "connected" or "coupled" with each other to achieve the desired functionality, and any two components capable of being so associated can also be considered to be "couplable" with each other to achieve the desired functionality. Specific examples of what can be coupled include, but are not limited to, physically coupleable and / or physically interacting components and / or wirelessly interactable and / or wirelessly interacting components and / or logically interacting and / or logically interacting components.

[0090] It should further be understood that the present invention is defined by the appended claims. In general, those skilled in the art will understand that the terms used in this specification and in particular in the appended claims (e.g., the body of the appended claims) are generally intended as "open" terms (e.g., the term "including" should be interpreted as "including but not limited to", the term "having" should be interpreted as "having at least", the term "includes" should be interpreted as "includes but not limited to", etc.). Those skilled in the art will further understand that if a specific number of claim recitations introduced are intended, such intention will be expressly recited in the claim, and in the absence of such recitation, no such intention exists. For example, as an aid to understanding, the following appended claims may include the use of the introductory phrases "at least one" and "one or more" to introduce the claim recitation. However, the use of such phrases should not be interpreted as meaning that the introduction of a claim recitation with the indefinite article "a" or "an" limits any particular claim that includes such an introduced claim recitation to an invention that includes only one such recitation. The same applies to the use of clear articles used to introduce claim recitations, even when the same claim includes the introductory phrase "one or more" or "at least one" and an indefinite article such as "a" or "an" (e.g., "a" and / or "an" should typically be interpreted to mean "at least one" or "one or more"). Also, those skilled in the art will recognize that even when a specific number of introduced claim recitations is explicitly recited, such recitation should typically be interpreted to mean at least the recited number (e.g., a bare recitation of "two recitations" without other modifiers typically means at least two recitations, or two or more recitations).Furthermore, in instances where a conventional expression similar to "such as at least one of A, B, and C" is used, such a configuration is generally intended in the sense that one of ordinary skill in the art would understand the conventional expression (e.g., "a system having at least one of A, B, and C" includes, but is not limited to, systems having only A, only B, only C, A and B together, A and C together, B and C together, and / or A, B, and C together). In instances where a conventional expression similar to "such as at least one of A, B, or C" is used, such a configuration is generally intended in the sense that one of ordinary skill in the art would understand the conventional expression (e.g., "a system having at least one of A, B, or C" includes, but is not limited to, systems having only A, only B, only C, A and B together, A and C together, B and C together, and / or A, B, and C together). Those skilled in the art will further appreciate that virtually any disjunctive word and / or phrase presenting two or more alternative terms, wherever in the description, claims, or drawings, should be understood to contemplate 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] It is believed that the present disclosure and many of its attendant advantages will be understood from the foregoing description, and it will be apparent that various changes can be made in the form, construction and arrangement of the elements without departing from the disclosed subject matter or sacrificing all of its material advantages. The forms described are merely illustrative, and it is the intent of the following claims to embrace and include such modifications. Moreover, it is to be understood that the invention is defined by the appended claims.

Claims

1. 1. A monolithic optical retarder comprising: a monolithic prism, the monolithic prism comprising: an input surface for receiving a light beam; an output face aligned with the optical axis of the light beam before it enters the input face; three or more reflective surfaces 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 imparts a total optical retardation 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 face, the output face, and the three or more reflective surfaces being oriented such that an optical axis of the light beam exiting the output face is aligned with an optical axis of the light beam entering the input face; A monolithic optical retarder, wherein the three or more reflective surfaces include one or more retardation surfaces, an angle of incidence of the light beam on the one or more retardation surfaces is greater than a critical angle for total internal reflection, and a total optical delay on the light beam as it propagates along the optical path corresponds to a cumulative optical delay on the light beam imparted by the one or more retardation surfaces.

2. 10. The monolithic optical retarder of claim 1 , wherein an angle of incidence of the light beam on the one or more retardation surfaces is greater than a critical angle of total internal reflection for at least one wavelength in the ultraviolet, vacuum ultraviolet, or deep ultraviolet spectral regions.

3. 10. The monolithic optical retarder of claim 1, wherein an angle of incidence of the light beam on the one or more retardation surfaces is greater than a critical angle for total internal reflection for wavelengths including the visible spectral range.

4. 10. The monolithic optical retarder of claim 1, wherein an angle of incidence of the light beam on the one or more retardation surfaces is greater than a critical angle for total internal reflection for wavelengths that include the infrared spectral region.

5. 10. The monolithic optical retarder of claim 1, wherein an angle of incidence of the light beam on the one or more retardation surfaces is greater than a critical angle of total internal reflection for wavelengths in the range of 120 nanometers to 20,000 nanometers.

6. 10. The monolithic optical retarder of claim 1, wherein an angle of incidence of the light beam on the one or more retardation surfaces is greater than a critical angle of total internal reflection for wavelengths in the range of 120 nanometers to 7000 nanometers.

7. 10. The monolithic optical retarder of claim 1, wherein an angle of incidence of the light beam on the one or more retardation surfaces is greater than a critical angle of total internal reflection for wavelengths in the range of 170 nanometers to 2500 nanometers.

8. 10. The monolithic optical retarder of claim 1, wherein the optical retardation of at least one of said one or more retardation surfaces ranges from 20 degrees to 80 degrees.

9. 10. The monolithic optical retarder of claim 1, wherein the total optical retardation is in the range of 60 degrees to 120 degrees.

10. 2. The monolithic optical retarder of claim 1, wherein the total optical retardation is 90 degrees.

11. 2. The monolithic optical retarder of claim 1, wherein the total optical retardation is 180 degrees.

12. The three or more reflecting surfaces are a first reflective surface oriented to receive light from the input surface and oriented at a selected angle relative to the input surface; a second reflective surface oriented to receive light from the first reflective surface and perpendicular to the input surface; a third reflective surface oriented to receive light from the second reflective surface and oriented at a selected angle relative to the output surface; and 2. The monolithic optical retarder of claim 1, comprising:

13. 13. The monolithic optical retarder of claim 12, wherein the selected angle is greater than a critical angle for total internal reflection.

14. The three or more reflecting surfaces are a first reflective surface oriented to receive light from the input surface; a second reflective surface oriented to receive light from the first reflective surface and parallel to the first reflective surface; a third reflective surface oriented to receive light from the second reflective surface; and a fourth reflective surface oriented to receive light from the third reflective surface and parallel to the third reflective surface; and 2. The monolithic optical retarder of claim 1, comprising:

15. 2. The monolithic optical retarder of claim 1, wherein the monolithic prism is a monolithic k-prism.

16. 2. The monolithic optical retarder of claim 1, wherein said monolithic prism is a monolithic Fresnel rhombic retarder.

17. 10. The monolithic optical retarder of claim 1, wherein the monolithic prism is glass.

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

19. 10. The monolithic optical retarder of claim 1, wherein the input surface, the output surface and the three or more reflective surfaces are polished surfaces.

20. 2. The monolithic optical retarder of claim 1, wherein the monolithic prism is rotatable about an optical axis of the light beam incident on the input face to provide polarization adjustment to the light beam without deflecting the light beam.

21. 1. A measurement system comprising: an illumination source for generating an illumination beam; one or more illumination optics for directing the illumination beam onto a sample; A detector; one or more collection optics that collect light from the sample as a collected beam and direct at least a portion of the collected beam as detection light to the detector; one or more monolithic optical retarders associated with at least one of the one or more illumination optics or the one or more collection optics, a particular monolithic optical retarder of the one or more monolithic optical retarders comprising: A monolithic prism, an input surface for receiving a light beam; an output face aligned with the optical axis of the light beam before it enters the input face; a monolithic optical retarder comprising: three or more reflective surfaces 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, the monolithic optical retarder imparting a selected optical delay to the light beam as it propagates along the optical path based on total internal reflection at the three or more reflective surfaces, the input surface, the output surface, and the three or more reflective surfaces being oriented such that an optical axis of the light beam exiting the output surface is equal to an optical axis of the light beam entering the input surface, the three or more reflective surfaces including one or more delay surfaces, an angle of incidence of the light beam on the one or more delay surfaces being greater than a critical angle for total internal reflection, and a total optical delay on the light beam as it propagates along the optical path corresponds to a cumulative optical delay on the light beam imparted by the one or more delay surfaces; a controller communicatively coupled to the detector, the controller comprising one or more processors configured to execute program instructions that cause the one or more processors to generate one or more metrology measurements of the sample based on the detected light; A measurement system comprising:

22. 22. The metrology system of claim 21, wherein at least one of the one or more monolithic optical retarders is rotatable along an optical axis of a respective light beam to provide polarization adjustment to the light beam without deflecting the respective light beam.

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

24. 22. The metrology system of claim 21, wherein at least one of the one or more monolithic optical retarders is one of the one or more focusing optics, and wherein at least one of the one or more monolithic optical retarders receives a focused beam as a light beam.

25. The measurement system of claim 21 , wherein the measurement system comprises a broadband measurement tool.

26. 22. The metrology system of claim 21, wherein the metrology system comprises at least one of an ellipsometer, a reflectometer, a scatterometer, or a polarimeter.

27. The three or more reflecting surfaces are a first reflective surface oriented to receive light from the input surface and oriented at a selected angle relative to the input surface; a second reflective surface oriented to receive light from the first reflective surface and perpendicular to the input surface; a third reflective surface oriented to receive light from the second reflective surface and oriented at a selected angle relative to the output surface; and 22. The measurement system of claim 21, further comprising:

28. The three or more reflecting surfaces are a first reflective surface oriented to receive light from the input surface; a second reflective surface oriented to receive light from the first reflective surface and parallel to the first reflective surface; a third reflective surface oriented to receive light from the second reflective surface; and a fourth reflective surface oriented to receive light from the third reflective surface and parallel to the third reflective surface; 22. The measurement system of claim 21, further comprising:

29. 22. The metrology system of claim 21, wherein the monolithic prism is a monolithic k-prism.

30. 22. The metrology system of claim 21, wherein the monolithic prism is a monolithic Fresnel diamond retarder.

31. 22. The metrology system of claim 21, wherein the monolithic prism is glass.

32. A measurement method comprising: generating an illumination beam; directing the illumination beam towards a sample; collecting light from the sample as a collection beam in response to the illumination beam, wherein 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 comprising: an input surface for receiving a light beam; an output face aligned with the optical axis of the light beam before it enters the input face; and 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, the monolithic optical retarder imparting 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, the input surface, the output surface, and the three or more reflective surfaces are oriented such that an optical axis of the light beam exiting the output surface is equal to an optical axis of the light beam entering the input surface, the three or more reflective surfaces include one or more delay surfaces, an angle of incidence of the light beam on the one or more delay surfaces is greater than a critical angle for total internal reflection, and a total optical delay on the light beam as it propagates along the optical path corresponds to a cumulative optical delay on the light beam imparted by the one or more delay surfaces, directing at least a portion of the collection beam as detection light to a detector; generating one or more metrology measurements of the sample based on the detected light; Measurement methods including.

33. The three or more reflecting surfaces are a first reflective surface oriented to receive light from the input surface and oriented at a selected angle relative to the input surface; a second reflective surface oriented to receive light from the first reflective surface and perpendicular to the input surface; a third reflective surface oriented to receive light from the second reflective surface and oriented at a selected angle relative to the output surface; and The method of claim 32, further comprising:

34. The three or more reflecting surfaces are a first reflective surface oriented to receive light from the input surface; a second reflective surface oriented to receive light from the first reflective surface and parallel to the first reflective surface; a third reflective surface oriented to receive light from the second reflective surface; and a fourth reflective surface oriented to receive light from the third reflective surface and parallel to the third reflective surface; The method of claim 32, further comprising:

35. 33. The metrology method of claim 32, wherein at least one of the one or more metrology measurements includes at least one of an ellipsometry measurement, a reflectance measurement, a scatterometry measurement, or a polarimetry measurement.

36. A monolithic optical retarder comprising: a monolithic prism, the monolithic prism comprising: an input surface for receiving a light beam; an output face aligned with the optical axis of the light beam before it enters the input face; three or more reflective surfaces 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 imparts a total optical retardation 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 face, the output face, and the three or more reflective surfaces are oriented such that an optical axis of the light beam exiting the output face is aligned with an optical axis of the light beam entering the input face, the three or more reflective surfaces include one or more non-retardation surfaces, an angle of incidence of the light beam on the one or more non-retardation surfaces is lower than a critical angle for total internal reflection, and the one or more non-retardation surfaces impart zero optical retardation to the light beam.

37. A measurement system comprising: an illumination source for generating an illumination beam; one or more illumination optics for directing the illumination beam onto a sample; A detector; one or more collection optics that collect light from the sample as a collected beam and direct at least a portion of the collected beam as detection light to the detector; one or more monolithic optical retarders associated with at least one of the one or more illumination optics or the one or more collection optics, a particular monolithic optical retarder of the one or more monolithic optical retarders comprising: A monolithic prism, an input surface for receiving a light beam; an output face aligned with the optical axis of the light beam before it enters the input face; a monolithic optical retarder comprising: three or more reflective surfaces 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, the monolithic optical retarder imparting a selected optical retardation to the light beam as it propagates along the optical path based on total internal reflection at the three or more reflective surfaces, the input surface, the output surface, and the three or more reflective surfaces being oriented such that an optical axis of the light beam exiting the output surface is equal to an optical axis of the light beam entering the input surface, the three or more reflective surfaces including one or more non-retardation surfaces, the angle of incidence of the light beam on the one or more non-retardation surfaces being lower than a critical angle for total internal reflection, the one or more non-retardation surfaces imparting zero optical retardation to the light beam; a controller communicatively coupled to the detector, the controller comprising one or more processors configured to execute program instructions that cause the one or more processors to generate one or more metrology measurements of the sample based on the detected light; A measurement system comprising:

38. A measurement method comprising: generating an illumination beam; directing the illumination beam towards a sample; collecting light from the sample as a collection beam in response to the illumination beam, wherein 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 comprising: an input surface for receiving a light beam; an output face aligned with the optical axis of the light beam before it enters the input face; 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, the monolithic optical retarder imparting a selected optical retardation to the light beam upon propagation 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 an optical axis of the light beam exiting the output surface is equal to an optical axis of the light beam entering the input surface, the three or more reflective surfaces include one or more non-retardation surfaces, an angle of incidence of the light beam on the one or more non-retardation surfaces is lower than a critical angle for total internal reflection, the one or more non-retardation surfaces impart zero optical retardation to the light beam, directing at least a portion of the collection beam as detection light to a detector; generating one or more metrology measurements of the sample based on the detected light; Measurement methods, including

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