Mirror-based relay device for optical inspection system

Abstract

An optical inspection system for inspecting a mask or a wafer, the system comprising: an objective lens for collecting light from an object to be inspected; the optical inspection system comprises an objective lens, an imaging assembly, a relay assembly placed on an optical path between the objective lens and the imaging assembly, for collecting light from the objective lens and relaying the collected light to the imaging assembly, in which the optical inspection system further comprises a mirror placed on an optical path between the objective lens and the relay module, and a relay assembly for changing the direction of the optical path at an angle away from the optical axis of the objective lens and into the optical axis of the relay assembly, the relay assembly comprising a reflective surface arranged such that the collected light passes back and forth within the relay assembly three times. Related apparatus and methods are also described.

Description

Technical Field

[0001] In some embodiments of the present disclosure, the present disclosure relates to relay modules for optical inspection systems, and more specifically but not exclusively to mirror-based catadioptric relay modules for optical inspection systems.

[0002] The present disclosure generally relates to systems and methods for detecting defects and anomalies in surfaces, and to systems and methods for detecting defects and anomalies in silicon wafers and / or masks used in the production of semiconductor devices. Background Art

[0003] In simple bright-field-based systems and / or methods for detecting defects and anomalies in surfaces, an illumination system illuminates a sample from above, and a collection optical system located above or below the sample detects light reflected or scattered from the sample. The term bright field as used herein refers to the light thus collected.

[0004] In typical dark-field-based techniques, either the sample is illuminated from above and light reflected from the sample is collected from the side, or the sample is illuminated from the side and light reflected from the sample is collected from above. The terms dark field and / or grey field as used herein refer to the light thus collected. Brief Description of the Drawings

[0005] Some embodiments of the present disclosure are described herein by way of example only with reference to the drawings. Referring now specifically to the drawings in detail, it should be emphasized that the details shown are by way of example and for purposes of illustrative discussion of embodiments of the present disclosure. In this regard, the description in conjunction with the drawings makes it apparent to those skilled in the art how the embodiments of the present disclosure may be practiced.

[0006] In the drawings:

[0007] FIG. 1 is a simplified illustration of components and an optical path in a prior art optical inspection system;

[0008] Figure 2A is a simplified illustration of components and an optical path in an example embodiment;

[0009] Figure 2B is a simplified illustration of components and an optical path in an example embodiment;

[0010] Figure 2C is a simplified illustration of components and an optical path in an example embodiment;

[0011] Figure 3 is Figure 2A a simplified isometric illustration of components and an optical path in an example embodiment of

[0012] Figure 4It is a simplified illustration of components and optical paths in an exemplary embodiment. Detailed implementation

[0013] In some embodiments of the present disclosure, the present disclosure relates to a relay module for an optical inspection system, and more particularly but not exclusively to a mirror-based catadioptric relay module for an optical inspection system.

[0014] To better understand some embodiments of the present disclosure, as shown in the accompanying drawings Figures 2A - 2C 、 Figure 3 and Figure 4 shown, first refer to the construction and operation of components and optical paths in a prior art optical inspection system as shown in FIG. 1, which is a simplified illustration of components and optical paths in a prior art optical inspection system.

[0015] FIG. 1 shows a cross-sectional view of components and optical paths of a prior art optical inspection system, which includes an objective lens assembly 104, a refractive relay assembly 108, a mirror 112, an optical focusing assembly 116, and an imaging assembly 118.

[0016] FIG. 1 demonstrates the optical light path through the components of the optical inspection system of FIG. 1. FIG. 1 shows illumination 120, which bypasses the mirror 112, passes through the lens 110 of the refractive relay assembly 108, passes through the objective lens assembly 104, and reaches the object to be inspected 102. By way of some non-limiting examples, the object to be inspected 102 can be a mask 102 or a wafer 102. The light reflected from the object to be inspected 102 is collected by the objective lens assembly 104, transmitted through the refractive relay assembly 108 to the mirror 112. The mirror changes the optical axis direction of the light path vertically to the side. The light from the mirror 112 passes through the focusing optical assembly 116 and reaches the imaging assembly 118.

[0017] It should be noted that the exit pupil of the light reflected from the object to be inspected 102 by the objective lens 104 is imaged at the pupil 114, such that there is a correspondence 140 between the exit pupil of the light reflected from the object to be inspected 102 by the objective lens assembly 104 and the pupil 114.

[0018] Now describe the light reflected and / or scattered from various gas-to-glass interfaces in the optical inspection system of FIG. 1.

[0019] A first instance of reflected and / or scattered light 132 shows reflection and / or scattering of the illumination light from the gas-to-glass interface of the lens surface in the objective lens assembly 104. The reflected and / or scattered light 132 enters the relay assembly 108, and at least some of the reflected and / or scattered light 132 may ultimately reach the imaging assembly 118 and degrade the image of the object 102 being inspected. The relay assembly 108 is close to the source of the reflected and / or scattered light 132 and potentially collects most of the reflected and / or scattered light 132 because the inlet to the relay assembly 108 occupies most of the solid angle seen from the gas-to-glass interface of the lens surface in the objective lens assembly 104.

[0020] A second instance of reflected and / or scattered light 134 shows reflection and / or scattering of the illumination light from the gas-to-glass interface of the lens surface in the refractive relay assembly 108. At least some of the reflected and / or scattered light 134 reaches the mirror 112, enters the focusing optical assembly 116, reaches the imaging assembly 118, and degrades the image of the object 102 being inspected. The relay assembly 108 is close to the mirror 112 and potentially collects most of the reflected and / or scattered light 134.

[0021] A third instance of reflected and / or scattered light 136 shows reflection and / or scattering of light from the glass-to-gas interface of the lens surface in the focusing assembly 116. At least some of the reflected and / or scattered light 136 reaches the imaging assembly 118 and degrades the quality of the image of the object 102 being inspected.

[0022] Overview

[0023] In an optical inspection system, replacing an existing refractive relay assembly with a reflective relay assembly potentially provides one or more of the benefits listed below. Optionally placing the relay assembly off the optical axis of the objective lens assembly may also provide one or more of the benefits listed below.

[0024] Potential benefits:

[0025] Reducing unwanted light reflections

[0026] In a reflective relay assembly, there are fewer air-to-glass or glass-to-air interfaces. The lenses in a refractive relay assembly provide two such interfaces, where each interface potentially reflects a certain small percentage of the light passing through, while the mirror in a reflective relay assembly provides only one surface and no unwanted reflections.

[0027] A relay assembly that is off the optical axis of the objective lens assembly can potentially reduce the capture of unwanted light reflections and / or unwanted stray light by the relay assembly.

[0028] Note that in the case of dark-field operation, most of the inspection image is dark, and in this case, unwanted light reflections can generate significant and more visible noise in the image, and even reduce the signal-to-noise ratio of the inspected image more than in the case of bright-field inspection.

[0029] Note that the switching between bright-field inspection and dark-field inspection can be performed before the illumination light enters the objective lens, or before the illumination light passes through the relay system and enters through the objective lens. When bright-field illumination is desired, an illumination beam is generated, the cross-section of which perpendicular to the illumination axis is a circle, and the illumination passing through the circle includes the center of the circle. When dark-field illumination is desired, an illumination beam is generated, the cross-section of which perpendicular to the illumination axis is a ring, and the center of the ring is not illuminated.

[0030] Reflection - refraction configuration

[0031] In some embodiments, the relay assembly is designed to use three mirrors in a reflective-refractive configuration.

[0032] In some embodiments, the relay assembly is designed to use only two mirrors in a reflective-refractive configuration.

[0033] Simplified configuration of an autofocus coupled to an inspection system

[0034] In some embodiments, an autofocus system is coupled to an inspection system that uses a relay assembly as described herein.

[0035] In some embodiments, the autofocus system is coupled to the inspection system through an optical element having a dichroic coating (see the non-limiting example reference numeral 212 in Figure 2A or the reference numeral 412 in Figure 4 ), such that the light going to and coming from the autofocus system passes through the optical element, while the light going to and coming from the relay assembly is reflected by the optical element.

[0036] Coupling the autofocus system to the inspection system (as described above and below with reference to FIGS. 2 and Figure 4 ) potentially provides benefits by simplifying the design of the inspection system.

[0037] Large FOV

[0038] A reflective-refractive optical design or a quasi-reflective-refractive optical design can provide a larger field of view (FOV) than a refractive optical design having a similar diameter and / or focal length.

[0039] In some embodiments, the relay assembly described herein is designed to have a large FOV.

[0040] Large numerical aperture (NA)

[0041] A reflective refractive optical design or a design similar to a reflective refractive optical design can provide a larger numerical aperture (NA) than a refractive optical design with a similar diameter and / or focal length.

[0042] In some embodiments, the relay assemblies described herein are designed to have a large NA.

[0043] Reducing unwanted light absorption

[0044] In a reflective relay assembly, there is less or no light passing through glass, while in a refractive relay assembly, light passes through a lens. A small amount of light can be absorbed by the lens. The greater the power of the light passing through the lens, the more likely the lens is to heat up and warp, potentially reducing the accuracy of optical inspection. A reflective surface or mirror absorbs little or no power. The benefit of increasing the illumination light power is that it increases the contrast of the inspected image and / or the imaging and the speed of passing through the inspected object can be increased by using higher power illumination. The reduction of the above-mentioned unwanted light absorption enables the inspected object to be optionally illuminated with a greater illumination power, thereby potentially achieving faster image acquisition and potentially achieving a faster inspection throughput, such as covering a larger area in a shorter time.

[0045] Now refer to Figure 2A , Figure 2A which is a simplified illustration of the components and the optical path in an exemplary embodiment.

[0046] Figure 2A A cross-sectional view of the components and the optical path of an optical inspection system is shown, and the optical inspection system includes an objective lens assembly 204, a mirror 212, and a reflective relay assembly 206.

[0047] Figure 2A Also demonstrated is Figure 2A the optical light path of the components of the optical inspection system through

[0048] Figure 2A The collected light 234 collected from an inspected object (such as a wafer or a mask) is shown, and the collected light 234 leaves the objective lens assembly 204 as light 232.

[0049] The light 232 is reflected by the first mirror 212, continues as light 230, and enters the reflective relay assembly 206.

[0050] In the relay assembly 206, the light 230 is reflected by the second mirror 214, continues as light 228, is reflected by the third mirror 216, continues as light 226, is reflected by the fourth mirror 218, and leaves the reflective relay assembly 206 and continues as light 224.

[0051] In some embodiments, light 224 may pass through one or more optional focusing components 220 and emerge as light 222, ultimately striking imaging array 246 or detector 246 or sensor 246.

[0052] In some embodiments, the illumination light for illuminating the object under inspection passes back through some, most, or all of the optical paths in the above optical path in reverse order.

[0053] It should also be noted that in some embodiments, the first mirror 212 may optionally be used to allow light 252 from an optional illumination system as described in Figure 2B and / or from an optional autofocus system 270 as described in Figure 2C to pass through.

[0054] It should be noted that, compared to the distance between the exit pupil of the light reflected from the object under inspection 102 through the objective lens assembly 104 and the pupil 114 (as shown in FIG. 1), the exit pupil 244 of the light reflected from the object under inspection through the reflection relay assembly 206 may optionally be located farther away from the objective lens assembly 204.

[0055] It should be noted that using reflective components in the relay assembly 206 reduces the number of glass-to-air and air-to-glass interfaces in the relay assembly 206, which are potential locations for reflecting and / or scattering light that may potentially degrade the image captured by the components of the exemplary embodiment shown in Figure 2A .

[0056] It should be noted that the optical design of the relay assembly 206 is similar to that of a catadioptric telescope.

[0057] It should be noted that placing the relay assembly 206 off the optical axis of the objective lens assembly 204 can reduce the reception of unwanted stray light from the objective lens assembly 204.

[0058] In some embodiments, the fourth mirror 218 and the second mirror 214 may be at the same distance from the third mirror 216 (which is not shown in Figure 2A ).

[0059] In some embodiments, the fourth mirror 218 and the second mirror 214 may be parts of the same mirror (which is not shown in Figure 2A ).

[0060] In some embodiments, the fourth mirror 218 may optionally extend as 218B, as shown in FIG. 2, where the extension 218B may optionally be transparent.

[0061] In some embodiments, the second mirror 214 may optionally extend as 214B, as shown in Figure 2A .

[0062] Note that, compared to a reflective relay assembly 206 as shown in Figure 2A , a refractive relay assembly such as refractive relay assembly 108 shown in FIG. 1 includes more glass-to-air and air-to-glass interfaces that produce unwanted reflections. The reflective relay assembly 206 produces zero or at least far fewer such unwanted reflections.

[0063] Note that, as Figure 2A and as shown in other figures showing example embodiments, the reflective relay assembly moves the exit pupil 244 of the relay assembly away from the lens of the objective assembly, thereby reducing the light passing through the reflective relay assembly 206 that is produced by reflections from the glass-to-air and air-to-glass interfaces in the objective assembly.

[0064] Note that the imaging assembly 246 is typically used in the Figure 2A optical inspection system shown in

[0065] Now referring to Figure 2B , Figure 2B is a simplified illustration of the components and optical path in an example embodiment.

[0066] Figure 2B Shows the Figure 2A components and (one or more) optical paths (represented by the same reference numerals) shown in

[0067] plus additional (one or more) optional autofocus components 260.

[0068] In some embodiments, the first mirror 212 is used to allow light 262 to pass through the optional autofocus system 260.

[0069] Now referring to Figure 2C , Figure 2C is a simplified illustration of the components and optical path in an example embodiment.

[0070] Figure 2C Shows the Figure 2A components and (one or more) optical paths (represented by the same reference numerals) shown in

[0071] In some embodiments, the first mirror 212 is used to allow light to pass through the optional illumination system 270.

[0072] An optional illumination system 270 can optionally provide illumination 272 to impinge on the first mirror 212, pass through the first mirror 212 and through the objective lens assembly 204 to illuminate an object to be inspected, such as a wafer or a mask.

[0073] In some embodiments, the optional illumination system 270 can optionally provide annular illumination 274 that bypasses the mirror 212, passes through the objective lens assembly 204, passes through the objective lens assembly 104, and reaches the object to be inspected. Such an illumination scheme can provide illumination for using dark-field-based techniques.

[0074] Now referring Figure 3 , Figure 3 is Figure 2A a simplified isometric view of the components and optical paths in an exemplary embodiment of

[0075] Figure 3 An isometric view of the components and optical paths of an optical inspection system is shown, the optical inspection system including an objective lens assembly 304, a mirror 312, and a reflective relay assembly 306.

[0076] Figure 3 Demonstrates the optical light path through the components of the Figure 3 optical inspection system of

[0077] Figure 3 Collected light 334 collected from an object to be inspected (such as a wafer or a mask) is shown, and the collected light 334 exits the objective lens assembly 304.

[0078] The light 334 is reflected by the first mirror 312, continues as light 332, and enters the reflective relay assembly 306 as light 330.

[0079] In the relay assembly 306, the light 330 is reflected by the second mirror 314, continues as light 328, is reflected by the third mirror 316, continues as light 324, is reflected by the fourth mirror 318, and exits the reflective relay assembly 306 and continues as light 324.

[0080] In some embodiments, the light 324 can optionally pass through one or more optional focusing components 322, emerge as light 320, and ultimately impinge on an imaging array (not shown) or a detector (not shown) or a sensor (not shown).

[0081] In some embodiments, the illumination light for illuminating the object to be inspected passes back through some, most, or all of the optical paths in the above optical path in the reverse order.

[0082] Figure 3 The light passing through the components of the optical inspection system is shown.

[0083] Note that, compared with the distance between the exit pupil of the light reflected from the object 102 through the objective lens assembly 104 and the pupil 114 (as shown in FIG. 1), the exit pupil 344 of the light reflected from the object through the reflection relay assembly 306 can optionally be located at a position farther from the objective lens assembly 304.

[0084] Now refer to Figure 4 , Figure 4 which is a simplified illustration of the components and optical paths in an exemplary embodiment.

[0085] Figure 4 FIG. shows a cross-sectional view of the components and optical paths of an optical inspection system, which includes an objective lens assembly 404, a mirror 412, and a reflection relay assembly 406.

[0086] Figure 4 Also demonstrated is the optical path of the components of the optical inspection system through Figure 4 .

[0087] Figure 4 FIG. shows the light 432 collected by the objective lens assembly 404 from the object to be inspected. By way of some non-limiting examples, the object to be inspected can be a mask or a wafer. The light 432 leaves the objective lens assembly 404 as light 434 and is reflected from the first mirror 412 as light 430, and the first mirror 412 guides the light 430 into the reflection relay assembly 406.

[0088] The light 430 enters the reflection relay assembly 406, passes through the refractive element 420, is reflected from the second mirror 414 as light 428, is reflected from the third mirror 420 as light 426, is reflected from the fourth mirror 418 as light 424, and passes through the refractive element 420 as light 422.

[0089] In some embodiments, the illumination light for illuminating the object to be inspected can pass back along the above optical path in the reverse order.

[0090] In some embodiments, the first mirror 412 is used to allow light from an autofocus system ( Figure 4 not shown in Figure 2A ), similar to the first mirror 212 described with reference to

[0091] It should be noted that, compared to the distance between the exit pupil of the light reflected from the object 102 through the objective lens assembly 104 and the pupil 114 (as shown in FIG. 1), the exit pupil 444 of the light reflected from the object through the reflective relay assembly 406 can optionally be located further away from the objective lens assembly 404 along the optical path.

[0092] It should be noted that using reflective components in the relay assembly 406 reduces the number of glass-to-air and air-to-glass interfaces in the relay assembly 406, which are potential locations for reflecting and / or scattering light that may potentially degrade the image captured by the components of the exemplary embodiment shown in Figure 4 the example embodiment shown.

[0093] It should be noted that the optical design of the relay assembly 406 is similar to that of a catadioptric telescope.

[0094] In some embodiments, the fourth mirror 418 and the second mirror 414 can be at the same distance from the third mirror 416 (which is not shown in Figure 4 the figure).

[0095] In some embodiments, the fourth mirror 418 and the second mirror 414 can be part of the same mirror (which is not shown in Figure 4 the figure).

[0096] It should be noted that, compared to the reflective relay assembly 406 as shown in Figure 4 and other figures showing the exemplary embodiment, refractive relay assemblies such as the refractive relay assembly 108 shown in FIG. 1 include more glass-to-air and air-to-glass interfaces that generate unwanted reflections. The reflective relay assembly 408 generates far fewer such unwanted reflections.

[0097] It should be noted that, as shown in Figure 4 and other figures showing the exemplary embodiment, the reflective relay assembly moves the exit pupil 444 of the relay assembly away from the lens of the objective lens assembly, thereby reducing the light generated by reflections from the glass-to-air and air-to-glass interfaces in the objective lens assembly passing through the reflective relay assembly 408.

[0098] It should be noted that the imaging assembly 448 is typically used in the Figure 4 optical inspection system shown in Figure 2A and is similar to the imaging assembly 246 shown in

[0099] Examples of the reflected and / or scattered light 446 illustrate reflection and / or scattering of the illumination light from the gas-to-glass interface of the lens surface in the objective lens assembly 404. The reflected and / or scattered light 446 enters the relay assembly 406, and at least some of the reflected and / or scattered light 446 may ultimately reach the imaging assembly (not shown) and degrade the image of the object under inspection. However, compared with the reflected and / or scattered light shown in FIG. 1, the relay assembly 406 is not as close to the source of the reflected and / or scattered light 446, and collects a smaller portion of the reflected and / or scattered light 446 relative to the portion collected by the configuration shown in FIG. 1. SUMMARY OF THE INVENTION

[0100] Example 1:

[0101] An optical inspection system for inspecting a mask or a wafer, the system comprising: an objective lens for collecting light from an object under inspection; a relay assembly placed on an optical path between the objective lens and an imaging assembly for collecting light from the objective lens and relaying the collected light to the imaging assembly; wherein the optical inspection system further comprises a mirror placed on the optical path between the objective lens and the relay module for changing a direction of the optical path at an angle away from an optical axis of the objective lens and into an optical axis of the relay assembly; the relay assembly comprising: a first optical element along the optical axis of the relay assembly is a reflective surface, a second optical element along the optical axis of the relay assembly is a reflective surface for receiving light reflected from the first optical element, and a third optical element along the optical axis of the relay assembly is a reflective surface for receiving light reflected from the second optical element, such that the collected light passes back and forth three times within the relay assembly.

[0102] Example 2:

[0103] The optical inspection system according to Example 1, wherein the relay assembly comprises two or more mirrors in a reflective-refractive configuration.

[0104] Example 3:

[0105] The optical inspection system according to any one of Examples 1-2, wherein the relay assembly comprises three mirrors in a reflective-refractive configuration.

[0106] Example 4:

[0107] The optical inspection system according to any one of Examples 1-3, wherein the optical inspection system is configured to provide illumination light for illuminating the object under inspection through the relay assembly in an opposite direction on the optical path for collecting light from the objective lens.

[0108] Example 5:

[0109] The optical inspection system according to any one of Examples 1-4, wherein the optical inspection system is configured to transfer from a light field operation to a dark field operation.

[0110] Example 6:

[0111] The optical system according to any one of Examples 1-5, wherein the angle is in the range between 75 degrees and 105 degrees.

[0112] Example 7:

[0113] The optical inspection system according to any one of Examples 1-6, wherein the first optical element in the relay assembly in the direction along the optical path of the collected light is configured to receive light on substantially half of the area of the first optical element; and the third optical element in the relay assembly in the direction along the optical path of the collected light is configured to receive light on substantially half of the area of the third optical element.

[0114] Example 8:

[0115] The optical inspection system according to any one of Examples 1-7, wherein the relay module images the exit pupil of the objective lens outside the relay module.

[0116] Example 9:

[0117] A method for improving the signal-to-noise ratio in an image generated by an optical mask or wafer inspection system, the system comprising: an objective lens for collecting light from an object to be inspected; a relay assembly for relaying the collected light; a mirror placed on the optical path between the objective lens and the relay module for changing the direction of the optical path at an angle away from the optical axis of the objective lens and into the optical axis of the relay assembly; and an imaging assembly for receiving the collected light from the relay module and generating an image based on the collected light; the method comprising reducing the number of gas-to-glass interfaces in the relay assembly by using at least one mirror in the relay assembly.

[0118] Example 10:

[0119] The method according to Example 9, comprising reducing the number of gas-to-glass interfaces in the relay assembly by using at least two mirrors in the relay assembly.

[0120] Example 11:

[0121] The method according to Example 9, comprising reducing the number of gas-to-glass interfaces in the relay assembly by using at least three reflective surfaces.

[0122] Example 12:

[0123] The method according to any one of Examples 9 - 11, including using a refractive - reflective design for the relay assembly.

[0124] Example 13:

[0125] An optical inspection system for inspecting a mask or a wafer, the system comprising: an objective lens for illuminating an object to be inspected and collecting light from the object to be inspected; a relay assembly placed on an optical path between the objective lens and an imaging assembly for relaying the illumination light to the objective lens, collecting light from the objective lens, and relaying the collected light to the imaging assembly; wherein: the optical inspection system further comprises a mirror placed on the optical path between the objective lens and the relay module for changing the direction of the optical path at an angle away from the optical axis of the objective lens and into the optical axis of the relay assembly; the relay assembly comprises: a first optical element along the optical axis of the relay assembly is a refractive element; a second optical element along the optical axis of the relay assembly is a reflective surface; a third optical element along the optical axis of the relay assembly is a reflective surface deposited on the surface of the first optical element; a fourth optical element along the optical axis of the relay assembly is a reflective surface; a fifth optical element along the optical axis of the relay assembly is the first optical element; such that the collected light passes back and forth three times within the relay assembly; and the relay module images the exit pupil of the objective lens outside the relay assembly.

[0126] Example 14:

[0127] The optical inspection system according to Example 13, wherein the second optical element and the fourth optical element are reflective surfaces on a single mirror.

[0128] Therefore, those skilled in the art to which the present invention pertains can understand that although the present invention has been described according to preferred examples, the concepts on which the present disclosure is based can easily be used as a basis for other structures, systems, and processes designed to achieve several purposes of the present invention.

[0129] The various illustrative logical blocks, modules, and algorithmic steps described in connection with the examples disclosed herein can be implemented as electronic hardware, computer software, or a combination of both. To clearly illustrate this interchangeability of hardware and software, the various illustrative components, blocks, modules, and steps are described above in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. The described functionality can be implemented in different ways for each particular application, but such implementation decisions should not be interpreted as causing any deviation from the scope of the present disclosure.

[0130] It should also be understood that the systems according to the present disclosure can be implemented at least in part on a suitably programmed computer. Similarly, the present disclosure contemplates a computer program readable by a computer for performing the methods of the present invention. The present disclosure further contemplates a non-transitory computer-readable memory tangibly embodying a program of instructions executable by a computer for performing the methods of the present disclosure.

[0131] Moreover, it should be understood that the language and terminology used herein are for descriptive purposes and should not be regarded as limiting.

[0132] It should be noted that the words “comprising,” “including,” and “having” used throughout the appended claims should be construed to mean “including but not limited to.” Unless expressly stated to the contrary, the indefinite articles “a” or “an” used herein in the specification and claims should be understood to mean “at least one.” As used herein in the specification and claims, the phrase “and / or” should be understood to mean “either or both” of the elements so combined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases.

[0133] Therefore, it is important that the scope of the present invention not be construed as limited by the illustrative examples set forth herein. Other variations are possible within the scope of the present invention as defined by the appended claims. Other combinations and sub-combinations of features, functions, elements, and / or properties can be claimed by modifying the claims or by filing new claims in this application or a related application. These modified or new claims, whether they relate to different combinations or the same combination, and whether they are different in scope, broader, narrower, or equal compared to the original claims, are also considered to be included within the subject matter of this specification.

[0134] As used herein with respect to a quantity or value, the term “about” means “within ±25% of.”

[0135] The terms “comprising,” “including,” “having,” and their variations mean “including but not limited to.”

[0136] The term “consisting of” is intended to mean “including and limited to.”

[0137] The term “consisting essentially of” means that a composition, method, or structure may include additional ingredients, steps, and / or parts, but only if the additional ingredients, steps, and / or parts do not materially alter the basic and novel characteristics of the claimed composition, method, or structure.

[0138] As used herein, the singular forms "a", "an", and "the" include plural referents unless the context clearly dictates otherwise. For example, the term "a unit" or "at least one unit" can include multiple units, including combinations thereof.

[0139] The term "exemplary" is used herein to mean "serving as an example, instance, or illustration". Any embodiment described as exemplary is not necessarily to be construed as preferred or advantageous over other embodiments, and / or to exclude features from other embodiments.

[0140] The term "optionally" is used herein to mean "provided in some embodiments and not provided in other embodiments". Any particular embodiment of the present disclosure may include a plurality of "optional" features, unless such features conflict.

[0141] Unless otherwise indicated, the numbers and any numerical ranges based thereon used herein are approximations within the reasonable measurement accuracy and rounding error understood by those skilled in the art.

[0142] It will be appreciated that, for clarity, certain features of the present disclosure described in the context of separate embodiments may also be provided in combination in a single embodiment. Conversely, for brevity, the various features of the present disclosure described in the context of a single embodiment may also be provided separately, or in any suitable sub-combination, or appropriately in any other described embodiment of the present disclosure. Certain features described in the context of various embodiments are not considered to be essential features of those embodiments unless the embodiment is inoperative without those elements.

[0143] Although the present disclosure has been described in connection with specific embodiments thereof, many alternatives, modifications, and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications, and variations that fall within the spirit and broad scope of the appended claims.

[0144] The (multiple) applicant(s) intend that all publications, patents, and patent applications mentioned in this specification be incorporated herein by reference in their entirety, as if each individual publication, patent, or patent application were specifically and individually indicated to be incorporated herein by reference when cited. Additionally, the citation or identification of any reference in this application should not be construed as an admission that such reference is available as prior art to the present invention. To the extent that section headings are used, they should not be construed as necessarily limiting. Additionally, any (multiple) priority documents of this application are incorporated herein by reference in their entirety.

Claims

1. An optical inspection system for inspection of a mask or a wafer, the system comprising: an objective lens, which collects light from the object being inspected; a relay component, the relay component being placed on an optical path between the objective lens and the imaging component, and being used to collect light from the objective lens and relay the collected light to the imaging component; in: The optical inspection system further includes a mirror (212) disposed in the optical path between the objective lens and the relay module for changing the direction of the optical path at an angle away from the optical axis of the objective lens and into the optical axis of the relay module; The relay component comprises: A first optical element along the optical axis of the relay assembly is a reflective surface (214); a second optical element along the optical axis of the relay assembly being a reflective surface (216) for receiving light reflected from the first optical element; and a third optical element along the optical axis of the relay assembly being a reflective surface (218) for receiving light reflected from the second optical element, The collected light is made to pass back and forth three times in the relay component.

2. The optical inspection system according to claim 1, wherein: The relay assembly includes two or more mirrors in a catadioptric configuration.

3. The optical inspection system of claim 1, wherein: The relay assembly includes three mirrors in a catadioptric configuration.

4. The optical inspection system of claim 1, wherein: The optical inspection system is configured to provide illumination light for illuminating the inspected object through the relay assembly in an opposite direction on the optical path for collecting light from the objective lens.

5. The optical inspection system of claim 1 configured to transfer from light field operation to dark field operation.

6. The optical system according to claim 1, wherein: The angle is in the range between 75 and 105 degrees.

7. The optical inspection system of claim 1, wherein: the first optical element (214) in the relay assembly in the direction along the optical path for collecting light being configured to receive light over substantially half of an area of ​​the first optical element; and The third optical element (218) in the relay assembly in the direction along the optical path of the collected light is configured to receive light over substantially half of the area of ​​the third optical element.

8. The optical inspection system of claim 1, wherein: The relay module images the exit pupil of the objective lens outside the relay module.

9. A method for improving the signal-to-noise ratio in an image produced by an optical mask or wafer inspection system, The system comprises: an objective lens, which collects light from the object being inspected; a relay component for relaying the collected light; a mirror (212) placed in an optical path between the objective lens and the relay module for changing the direction of the optical path at an angle away from the optical axis of the objective lens and into the optical axis of the relay module; and an imaging assembly for receiving the collected light from the relay module and generating an image based on the collected light; The method includes reducing the number of gas-to-glass interfaces in the relay assembly by using at least one mirror in the relay assembly.

10. The method of claim 9, comprising reducing the number of gas-to-glass interfaces in the relay assembly by using at least two mirrors in the relay assembly.

11. The method of claim 9, comprising reducing the number of gas-to-glass interfaces in the relay assembly by using at least three reflective surfaces.

12. The method of claim 9, comprising using a catadioptric design for the relay assembly.

13. An optical inspection system for inspection of a mask or a wafer, the system comprising: an objective lens for illuminating an object to be inspected and collecting light from the object to be inspected; a relay assembly, the relay assembly being placed in an optical path between the objective lens and the imaging assembly, for relaying illumination light to the objective lens, collecting light from the objective lens, and relaying the collected light to the imaging assembly; in: The optical inspection system further includes a mirror positioned in the optical path between the objective lens and the relay module for changing the direction of the optical path at an angle away from the optical axis of the objective lens and into the optical axis of the relay module; The relay component comprises: A first optical element along the optical axis of the relay assembly is a refractive element (420); A second optical element along the optical axis of the relay assembly is a reflective surface (414); a third optical element along the optical axis of the relay assembly being a reflective surface (416) deposited on a surface of the first optical element; a fourth optical element along the optical axis of the relay assembly being a reflective surface (418); a fifth optical element along the optical axis of the relay assembly being the first optical element (420); Allowing the collected light to pass back and forth three times within the relay assembly; and The relay module images the exit pupil of the objective lens outside the relay assembly.

14. The optical inspection system of claim 13, wherein: The second optical element and the fourth optical element are reflective surfaces on a mirror.

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