Abstract
A catoptric (mirror-based) optical system uses Scheimpflug optics and non-concentric optics to generate unobscured highly magnified images (e.g., >100) in EUV reticle inspection tools. The Scheimpflug optics collect light beams from an object plane and directs the light beams along a first optical axis to generate an intermediate image at an intermediate image plane that is oblique to the object plane. The non-concentric optics redirect the light beams from the first optical axis to a second optical axis that is perpendicular to the intermediate image plane and generates a magnified image on a final image plane that is parallel to the intermediate image plane. The Scheimpflug optics may include a first mirror positioned to collect light beams reflected normal to the object plane and a second mirror positioned adjacent to the normal direction and configured to redirect the light beams onto the first optical axis.
Claims
1. A catoptric system for generating a magnified image using patterned light beams sourced from an imaged area, the imaged area being located on an object plane and the magnified image being generated on a final image plane, the catoptric system comprising: a first plurality of mirrors configured and arranged in accordance with the Scheimpflug condition to collect the patterned light beams from the imaged area and to redirect the patterned light beams along a first optical axis such that the redirected light beams form an intermediate image at an intermediate image plane, wherein both the first optical axis and the intermediate image plane are oblique to the object plane; and a second plurality of mirrors configured to redirect the light beams from the first optical axis to a second optical axis that is perpendicular to the intermediate image plane such that the redirected light beams form the magnified image at the final image plane.
2. The catoptric system of claim 1, wherein each mirror of the first plurality of mirrors and the second plurality of mirrors comprises a multilayer mirror stack configured to reflect extreme ultraviolet (EUV) light.
3. The catoptric system of claim 1, wherein a first magnification of the first plurality of mirrors is in the range of 5 to 30, wherein a second magnification of the second plurality of mirrors is in the range of 10 to 50, and wherein a combined magnification of the first plurality of mirrors and the second plurality of mirrors is in the range of 50 to 1000.
4. The catoptric system of claim 1, wherein the first plurality of mirrors are configured such that the first optical axis extends at a first oblique angle relative to the normal direction of object plane, said first oblique angle being in the range of 0.5 and 10.
5. The catoptric system of claim 1, wherein the first plurality of mirrors comprises: a first concave mirror positioned over object plane and configured/oriented to collect and reflect first light beams sourced from the imaged area such that the reflected light beams to converge along a first optical path; and a second concave mirror positioned over the object plane and adjacent to the imaged area, the second concave mirror being configured/oriented redirect the reflected light beams from the first optical path such that the redirected light beams converge along the first optical axis between the second concave mirror and the intermediate image plane.
6. The catoptric system of claim 5, wherein at least a portion of the first concave mirror is positioned to receive and reflect a normal light beam portion of the first light beams that are directed perpendicular to the object plane.
7. The catoptric system of claim 6, wherein the first concave mirror is configured and positioned such that a focal point of the first concave mirror is located between the first concave mirror and the second concave mirror, whereby the reflected light beams reflected from the first concave mirror invert before arriving at the second concave mirror.
8. The catoptric system of claim 6, wherein the second concave mirror is offset from the imaged area such that the normal light beam portion is unimpeded by the second concave mirror.
9. The catoptric system of claim 5, wherein the first and second concave mirrors comprise spherical mirrors respectively having first and second centers of curvature, and wherein the first and second concave mirrors are positioned and arranged such that both the first and second centers of curvature coincide with the first optical axis.
10. The catoptric system of claim 5, wherein the first and second concave mirrors comprise aspherical mirrors respectively having first and second symmetric axes, and wherein the first and second concave mirrors are positioned and arranged such that both the first and second symmetric axes coincide with the first optical axis.
11. The catoptric system of claim 1, wherein the second plurality of mirrors comprises: a third mirror positioned and configured to reflect the light beams passing along the first optical axis such that the reflected light beams are directed in parallel along a second optical path that extends at a fourth oblique angle relative to the first optical axis; and a fourth mirror positioned and configured to redirect the reflected light beams directed along the second optical path such that the redirected light beams are directed along the second optical axis.
12. The catoptric system of claim 11, wherein the third mirror comprises a convex mirror that is located between the intermediate image plane and the second convex mirror.
13. The catoptric system of claim 11, wherein the third mirror comprises a concave mirror located between the intermediate image plane and the final image plane.
14. The catoptric system of claim 12, wherein the fourth mirror comprises a concave mirror configured to magnify the redirected light beams directed along the second optical axis such that the magnified image is formed on the final image plane, and wherein the intermediate image plane is located between the fourth mirror and the final image plane.
15. An inspection tool including: a first stage configured to support an object in an object plane; an illumination unit including an illumination source and illumination optics that are cooperatively configured to direct homogenous incident light onto the object; a second stage configured to support an image sensor in a final image plane, and a catoptric system configured to generate a magnified image on the image sensor using patterned light beams reflected from the object, the catoptric system comprising: a first plurality of mirrors configured and arranged in accordance with the Scheimpflug condition to collect the patterned light beams reflected from the object and to redirect the patterned light beams along a first optical axis such that the redirected light beams form an intermediate image at an intermediate image plane, wherein both the first optical axis and the intermediate image plane are oblique to the object plane; and a second plurality of mirrors configured to redirect the light beams from the first optical axis to a second optical axis that is perpendicular to the intermediate image plane such that the redirected light beams form the magnified image on the image sensor.
16. A method for inspecting an object disposed in an object plane, the method comprising: directing homogenous incident light onto the object; utilizing a first plurality of mirrors to collect light beams reflected from the object and to redirect the light beams along a first optical axis such that the redirected light beams form an intermediate image at an intermediate image plane, wherein both the first optical axis and the intermediate image plane are oblique to the object plane; utilizing a second plurality of mirrors to redirect the light beams from the first optical axis to a second optical axis that is perpendicular to the intermediate image plane such that the redirected light beams form the magnified image at a final image plane that is parallel to the intermediate image plane; and utilizing an image sensor disposed in the final image plane to capture the magnified image.
Description
BRIEF DESCRIPTION OF FIGURES
[0023] FIG. 1 is a side view depicting a catotropic optical system according to an embodiment.
[0024] FIGS. 2A and 2B are side views depicting a portion of the reflective optical system including Scheimpflug optics configured in accordance with alternative exemplary embodiments.
[0025] FIGS. 3A and 3B are side views illustrating problems associated with the use of Scheimpflug optics (alone) to generate high magnification images.
[0026] FIG. 4 is a side view depicting a reflective optical system according to another embodiment.
[0027] FIG. 5 is a ray tracing diagram depicting high magnification characteristics achieved by the catotropic optical system of FIG. 1 according to an exemplary embodiment.
[0028] FIG. 6 is a side view depicting a simplified inspection tool including the catotropic optical system of FIG. 1 according to another embodiment.
[0029] FIG. 7 is a partial perspective view showing a conventional EUVL system.
[0030] FIGS. 8A and 8B are side views depicting a reticle and a substrate, respectively, during operation of the EUVL system of FIG. 7.
[0031] FIGS. 9A and 9B are side views depicting a reticle and a substrate, respectively, and depict consequences of increasing the numerical aperture of imaging/projection optics used by the EUVL system of FIG. 7 according to a first example.
[0032] FIGS. 10A and 10B are side views depicting a reticle and a substrate, respectively, and depict consequences of increasing the numerical aperture of imaging/projection optics used by the EUVL system of FIG. 7 according to a second example.
[0033] FIG. 11 is a side view showing a partial conventional EUV inspection tool.
[0034] FIG. 12 is a top view depicting a profile of light captured by the conventional EUV inspection tool of FIG. 11.
DETAILED DESCRIPTION OF THE DRAWINGS
[0035] The following description is presented to enable one of ordinary skill in the art to make and use the methods and systems described herein as provided in the context of exemplary embodiments. Various additional simplifications and modifications, which will be apparent to those with skill in the art, are utilized for brevity and clarity. Therefore, the methods and systems described herein are not intended to be limited to the particular embodiments shown and described but are to be accorded the widest scope consistent with the principles and novel features herein disclosed.
[0036] FIG. 1 shows a catoptric (mirror-based/reflective optical) system 100 according to an exemplary embodiment. Catoptric system 100 includes Scheimpflug optics 120 and non-concentric optics 130 that collectively project and magnify patterned light sourced from an imaged area IA residing in an object plane OB to generate a focused, highly magnified image MI of imaged area IA at a final image plane FIP. In some embodiments, both Scheimpflug optics 120 and non-concentric optics 130 comprise multilayered mirrors of the type utilized in EUVL systems and EUV reticle inspection tools (i.e., configured to reflect extreme ultraviolet light having a nominal wavelength of 13.5 nm). In alternative embodiments, Scheimpflug optics 120 and non-concentric optics 130 are configured as described below such that a size (e.g., width WMI) of highly magnified image MI is in the range of 50 (fifty times) to 1000 the size (width) of imaged area IM.
[0037] Scheimpflug optics 120 include a first concave mirror M1 and a second concave mirror M2 that are collectively configured and arranged in accordance with the Scheimpflug condition to collect the patterned light beams 92-1 from an imaged area IA residing in an object plane OB, and to redirect patterned light beams 92-3 along a first optical axis OA1 in a way that forms an intermediate image IIM in an intermediate image plane IIP. Arranging mirrors M1 and M2 such that they satisfy the Scheimpflug condition facilitates orienting first optical axis OA1 at an oblique angle relative to the object plane OP (such that first optical axis OA1 extends at a first oblique angle relative to the normal direction N of object plane OP. Satisfying the Scheimpflug condition also causes intermediate image plane IIP to form a second oblique angle with object plane OP (e.g., as indicated at the upper right portion of FIG. 1, where object plane OP is parallel to object plane OP).
[0038] First mirror M1 is positioned over object plane OP and configured/oriented to collect and reflect (redirect) light beams 92-1 sourced from imaged area IA such that the reflected (redirected) light beams 92-2 converge along a first optical path P1. At least a portion of mirror M1 is located directly over imaged area IA such that normal light beams 92-1N (i.e., a portion of light beams 92-1 directed in normal direction N from imaged area IA) are collected and redirected along first optical path P1. First mirror M1 is further configured and positioned such that its focal plane point FP-M1 is located between first mirror M1 and second mirror M2, whereby the light beams 92-2 passing along first optical path P1 is inverted before arriving at second mirror M2 (as set forth below with reference to FIGS. 2A and 2B, the inversion of light beams 92-2 is important to the arrangement of mirrors M1 and M2 such that they satisfy the Scheimpflug condition).
[0039] Second mirror M2 is positioned and oriented over object plane OP and adjacent to imaged area M2 to receive and redirect inverted light beams 92-2 directed by first mirror M1 along first optical path P1 such that redirected light beams 92-3 are redirected along first optical axis OA1. Second mirror M2 is configured (shaped) such that light beams 92-3 converge as they pass along first optical axis OA1 from second mirror M2 and focus to form intermediate image AI when they arrive at intermediate image plane IP1. To avoid the obscuration issue, the position of second mirror M2 is adjacent to but offset from the region immediately above imaged area IA (i.e., such that normal light beams 92-1N passing from imaged area IA to first mirror M1 are not impeded by any portion of mirror M2). To facilitate the placement (location) of second mirror M2 with a suitable offset, first oblique angle must be greater than a non-zero amount (e.g., greater than) 0.5 but should be less than or equal to 10 to avoid significant aberrations. It is possible to avoid obscuration using a first oblique angle of at least 0.5, but undesirable aberrations (e.g., COMA and astigmatism) are caused at larger tilt angles (e.g., when Scheimpflug optics 120 are configured and arranged such that first oblique angle is greater than) 10. In practical embodiments, obscuration may be avoided using Scheimpflug optics 120 configured/arranged such that first oblique angle is in the range of 0.5 to 2.5, and more preferably approximately 2.
[0040] FIGS. 2A and 2B respectively depict Scheimpflug optics 120A and 120B according to alternative specific embodiments. Both Scheimpflug optics 120A (FIG. 2A) and Scheimpflug optics 120B (FIG. 2B) include two concave mirrors that are arranged and configured as described above to direct patterned light from object plane OP along first optical axis OA1. For clarity and brevity, it is assumed that Scheimpflug optics 120A and Scheimpflug optics 120B share the same first optical axis OA1 and both form an intermediate image the same intermediate image plane IIP (i.e., in both examples first optical axis OA1 forms first oblique angle with normal direction N and forms a third oblique angle with intermediate image plane IIP), although in practical applications these planes/axes may differ from each other.
[0041] Referring to FIG. 2A, Scheimpflug optics 120A are characterized in that both a first mirror MIA and a second mirror M1B are concave spherical mirrors. That is, the concave reflective surface of first mirror MIA conforms with a first spherical curvature CM1 (indicated by dash-dot line) having a corresponding center of curvature CCM1, and the concave reflective surface of second mirror M2A conforms with a second spherical curvature CM2 (indicated by dash-dot-dot line) having a corresponding center of curvature CCM2. According to the first embodiment, both first concave spherical mirror MIA and second concave spherical mirror M2A are positioned and arranged such that both center of curvature CCM1 and center of curvature CCM2 coincide with corresponding locations along first optical axis OA1 (i.e., both centers of curvature CCM1 and CCM2 define optical axis OA1, and optical axis OA1 is positioned.
[0042] Referring to FIG. 2B, Scheimpflug optics 120B are characterized in that both first mirror M1B and second mirror M2B are concave aspherical mirrors (e.g., even asphere of Zernike asphere) having corresponding symmetric axes. That is, the concave reflective surface of first mirror M1B conforms with a selected aspherical shape having a first symmetric axis AAM1, and the concave reflective surface of second mirror M2B conforms with a second aspherical shape having a corresponding second symmetric axis AAM2, where both axes AAM1 and AAM2 are indicated in FIG. 2B by corresponding thick dashed line segments. According to the second embodiment, both first concave aspheric mirror MIA and second concave aspheric mirror M2A are positioned and arranged such that both first symmetric axis AAM1 and second symmetric axis AAM2 coincide with corresponding locations along first optical axis OA1.
[0043] FIGS. 2A and 2B also illustrate how the mirrors of Scheimpflug optics 120A and 120B may be further configured to satisfy the Scheimpflug condition. Satisfying the Scheimpflug condition is relatively straight forward when the optics comprise a single thin lens having a single principal plane (referred to as a lens plane). In this simple case, the lens is oriented such that the lens plane, the object plane and the image plane all intersect at a single line (sometimes referred to as a Scheimpflug intersection). However, in the case of more complex optical arrangements (e.g., a thick lens, multiple lenses or, as in the case of Scheimpflug optics 120A and 120B, multiple mirrors), the Scheimpflug condition is satisfied when the two principle planes (principal surfaces) defined by the optical arrangement respectively intersect the object plane and the image plane along lines that can be joined by a plane (or line) that is parallel to the optical axis of the optical arrangement. Note that, as in the case of Scheimpflug optics 120A and 120B, the image plane must be flipped relative to the optical axis when the image is inverted (i.e., as discussed above with reference to FIG. 1, light beams 92-2 are inverted because focal point FP-M1 is located between mirrors M1 and M2, so the image passed along optical axis OA1 is inverted). Referring to FIG. 2A, exemplary principal planes P1A and P1B defined by mirrors MIA and M2A are indicated, along with a flipped intermediate image plane IIP-F, which is generated by flipping intermediate image plane IIP around first optical axis OA1 (i.e., such that both planes IIP and IIP-F diverge from first optical axis OA1 by third oblique angle ). In this example, Scheimpflug optics 120A satisfy the Scheimpflug condition because principal plane PIA intersects flipped intermediate image plane IIP-F at intersection line INT1, principal plane P2A intersects object plane OP at intersection line INT2, and intersection lines INT1 and INT2 can be connected by a line/plane OA1 that is parallel to first optical axis OA1. Similarly, as indicated in FIG. 2B, Scheimpflug optics 120B satisfy the Scheimpflug condition because principal planes P1B and P2B, which are defined by mirrors M1B and M2B, intersect with flipped intermediate image plane IIP-F and object plane OP at intersection lines INT1 and INT2 that can be connected by a line/plane OA1. The planes OP, IIP, IIP-F, PIA and P2A and the lines INT1 and INT2 are all orthogonal to the plane that the optical axis OA1 and the line N determine.
[0044] Scheimpflug optics 120 generates intermediate image IIM and intermediate image plane IIP with characteristics (i.e., location, size, orientation) that are determined in part by the magnification of Scheimpflug optics 120. As is understood in the art, the magnification of Scheimpflug optics 120 may be changed (increased or decreased) by way of changing the curvature of mirrors M1 and/or M2. In the example depicted in FIG. 1, the location of intermediate image IIM relative to the object plane (i.e., a distance D1 along first optical axis OA1), the size (e.g., the width WIM) of intermediate image IIM and the slope/orientation of intermediate image plane IIP relative to object plane OP (i.e., second oblique angle ) are determined by the combined magnification mirrors M1 and M2. As discussed below with reference to FIGS. 3A and 3B, the location and size of intermediate image IIM and the orientation intermediate image plane IIP change in direct proportion to the combined magnification mirrors M1 and M2, and it not practical to capture/record intermediate image IIM using currently available image sensor technology, particularly when mirrors M1 and M2 are modified to generate intermediate image IIM at high magnification. That is, currently available image sensor technologies are configured to efficiently capture incident light that is directed substantially perpendicular (normal) to the image sensor's light receiving/detecting surface, but light received at sufficiently large oblique angles is often reflected (not captured), which greatly reduces the image sensor's efficiency.
[0045] FIGS. 3A and 3B respectively depict Scheimpflug optics 120C and 120D in which the combined magnification of the two mirrors (not shown for clarity) varies significantly. Referring to FIG. 3A, when the combined magnification of Scheimpflug optics 120C is relatively low, intermediate image IIMC is generated at a relatively short distance DIC along first optical axis OA1 and has a relatively small size/width WIMC relative to imaged area IA. In addition, third obtuse angle C between intermediate image plane IIPC and first optical axis OA1 is relatively large, meaning that pattern light beams 92-3 are directed at an incidence angle 1-C relative to normal direction NC1 (i.e., the direction perpendicular to intermediate image plane IIPC). FIG. 3A also depicts a hypothetical image sensor 88C arranged such that its light receiving surface is positioned and oriented (i.e., parallel to intermediate image plane IIPC) to capture intermediate image IIMC. Note that incidence angle 1-C relative to normal direction NC1 is relatively small, whereby it may be possible for image sensor 88C to capture at least some of patterned light beams that form intermediate image IIMC. Referring to FIG. 3B, when the combined magnification of Scheimpflug optics 120D is relatively high, intermediate image IIMD is generated at a relatively long distance DID from object plane OP and has a relatively large size/width WIMD. However, the increased magnification decreases third obtuse angle YD, whereby incidence angle 1-D is relatively large in relation to normal direction NC1 (i.e., the direction perpendicular to intermediate image plane IIPD), which makes it more difficult (or impossible) for a hypothetical image sensor 88D to capture intermediate image IIMD. Moreover, Scheimpflug optics is based on the theory of magnification in transverse and longitudinal directions; that is, achieving high magnification (100) in the transverse direction produces a longitudinal magnification of 10000, which requires an incidence angle 1-D (image plane tilt) of almost 90, making it impossible for image sensor 88D to capture any of patterned light beam 92-3.
[0046] Referring again to FIG. 1, catoptric system 100 utilizes non-concentric optics 130 to facilitate both high magnification and image capture of patterned light beams 92-3 exiting Scheimpflug optics 120. That is, non-concentric optics 130 includes a third mirror M3 and one or more fourth mirrors M4 that are collectively configured to redirect patterned light beams 92-3 from first optical axis OA1 to a non-concentric (different) second optical axis OA2 such that the redirected light beams become focused at a distance D2 along second optical axis OA2 to generate final magnified image MI on a final (second) image plane FIP. By configuring mirrors M3 and M4 such that non-concentric second optical axis OA2 is perpendicular to intermediate image plane IIP and such that final image plane FIP is parallel to intermediate image plane IP1, non-concentric optics 130 facilitates efficient image capture by positioning image sensor 88 on second optical axis OA2 and orienting the light receiving surface of image sensor 88 in final image plane FIP. In addition, non-concentric optics 130 facilitate generating the final magnified image MI at desired magnification (e.g., 100, 200, etc.) by way of modifying the curvature of mirror M4.
[0047] In the embodiment depicted in FIG. 1, non-concentric optics 130 includes a (third) mirror M3 and at least one (fourth) mirror M4. Non-concentric optics 130 function to normalize the image plane by configuring mirror M3 such that patterned light beams 92-4, which are by redirected mirror M3 from first optical axis OA1 to a second optical path P2, remain substantially parallel between mirror M3 and mirror M4, and such that second optical path P2 forms a (fourth) oblique angle relative to first optical axis OA1. That is, mirrors M3 and M4 collectively form an optical subsystem having an optical axis (i.e., second optical axis OA2) that differs from first optical axis of Scheimpflug optics 120. Note also that non-concentric optics 130 is configured such that intermediate image plane IIP forms an object plane for the optical subsystem formed by mirrors M3 and M4. Configuring mirrors M3 and M4 in manner set forth below facilitates producing non-concentric optics 130 with the desired image plane normalization and magnification in the range of 10 to 50.
[0048] In alternative embodiments, (third) mirror M3 may be implemented using a convex spherical mirror or a concave spherical mirror. In the embodiment shown in FIG. 1, mirror M3 comprises a convex spherical mirror that is located between intermediate image plane IIP and second mirror M2. In an alternative embodiment shown in FIG. 4, optical system 100E includes Scheimpflug optics 120 configured as described above and non-concentric optics 130E including a (third) mirror M3E that is positioned between second mirror M2 and intermediate image plane IIP and is configured and oriented to reflect light beams 92-3 such that reflected light beams 92-4 are redirected in parallel along a second optical path P2E toward (fourth) mirror M4E. However, since second mirror M2 is a concave mirror, it may be advantageous to use convex mirror M3 (FIG. 1) to reduce the petzval field curvature.
[0049] Mirror M4 is configured and oriented to reflect patterned light beams 92-4 such that reflected light beams 92-5 are redirected along second optical axis OA2 to final image plane FIP. In some embodiments mirror M4 comprises a concave mirror configured to magnify parallel light beams 92-4 received from mirror M3 such that diverging light beams 92-5 directed along second optical axis OA2 focuses to generate magnified final image MI at final image plane FIP. In presently preferred embodiments mirror M4 is configured such that intermediate image plane IIP is located between mirror M4 and final image plane FIP (e.g., as depicted in FIG. 2). In other embodiments (not shown), mirror M4 may be configured such that final image plane FIP is located in front of or coplanar with intermediate image plane IIP.
[0050] FIG. 5 shows a ray tracing diagram for a catotropic optical system 100F configured to generate a magnified image MIF at final image plane FIP with a six-hundred-times (600) magnification. In this embodiment Scheimpflug optics 120F include mirror M1F and M2F configured to generate an intermediate image (i.e., at intermediate image plane IIP) with a magnification of 20, and non-concentric optics 130F including mirrors M3F and M4F configured magnified image MIF with the desired 600 magnification by magnifying the intermediate image by an additional 30. In other embodiments, Scheimpflug optics 120F may be configured to generate an intermediate image with a magnification in the range of 5 to 30, and non-concentric optics 130F may be configured to magnify the intermediate image by an additional amount in the range of 10 to 50. In some embodiments, the combined magnification of Scheimpflug optics 120F and non-concentric optics 130F is in the range of 50 to 1000.
[0051] FIG. 6 shows an inspection system 200 that utilizes catoptric system 100 to generate a magnified image MI on an image sensor 88 using patterned light beams reflected from a reticle (object) 80. Inspection system 200 includes an illumination unit 210, a first stage (e.g., X-Y table) 220 configured to support and move (scan) reticle 80 and a second stage 230 configured to support and move (scan) image sensor 88 in synchronization with first stage 220. Inspection system 200 also includes a controller (not shown) that controls the operation of illumination source 210, first stage 220 and second stage 230 during high magnification inspection of reticle 80. Illumination unit 210 includes an illumination source 211 and illumination optics 214 that are cooperatively configured to direct homogenous incident light 212 onto an upper surface of reticle 80. Illumination unit 210 is depicted in greatly simplified form for clarity and brevity, and is constructed and operated in a manner known to those skilled in the art. In one embodiment illumination unit 210 generates and directs homogenous EUV light 212 having a nominal wavelength of 13.5 nm onto reticle 80 in a manner similar to that described with reference to FIG. 7. In other embodiments, illumination unit 210 may be configured to generate light (electromagnetic radiation) 212 at other wavelengths that may benefit from the use of catoptric systems (e.g., other EUV light in the range of 10 to 121 nm, or X-ray radiation with a wavelength below 10 nm). In one embodiment, illumination source 210 is controlled to generate and direct homogenous EUV light 212 onto reticle 80 as a series of pulses, where each EUV light pulse includes corresponding light beams that are directed through a first pupil (not shown) onto a corresponding elongated portion of reticle 80. Each light beam of each incident light pulse is either reflected from one of reticle's micro-mirrors 81 or is absorbed by (i.e., not reflected from) absorber 82. The reflected light beams form patterned light that is directed away (e.g., upward) from reticle 80 and projected by way of catoptric system 100 to image sensor 88. In one embodiment, the patterned light beams produced in response to each pulse are directed onto a corresponding elongated portion of the image sensor 88 by way of a second pupil (not shown), whereby the partial image (pattern of reflected EUV light) is captured and stored. After each pulse, first stage 220 incrementally shifts reticle 80 and second stage 230 incrementally shifts image sensor 88, and a next pulse is directed onto a second elongated portion of reticle 80, light reflected from the second portion is transmitted by the optical system 100 onto a corresponding second elongated portion of the image sensor 88, and a second partial image is captured and stored. This process is repeated until image data is generated for a desired scan region of reticle 80 has been collected.
[0052] As implemented by inspection system 200, catoptric system 100 is arranged relative to stages 220 and 230 such that an upper surface of reticle 80 forms object plane OP and such that a light receiving surface of image sensor 88 forms final image plane FIP. Scheimpflug optics 120 utilize mirror M1 to collect the patterned light beams reflected from the object 80 and to redirect the patterned light beams along first optical path P1 toward mirror M2. Mirror M2 redirects the patterned light beams along first optical axis OA1 such that the redirected light beams 92-3 form an intermediate image at intermediate image plane IIP. Both first optical axis OA1 and intermediate image plane IIP are oblique to object plane OP (e.g., first optical axis OA1 forms an acute angle relative to normal direction N). Non-concentric optics 130 include mirror M3 configured to redirect parallel patterned light beams from first optical axis OA1 along second optical path P2 toward mirror M4, and mirror M4 is configured to redirect these patterned light beams along second optical axis OA2 such that the redirected light beams 92-5 are focused to form magnified image MI at the light receiving surface of image sensor 88. Both intermediate image plane IIP and final image plane FIP are perpendicular to second optical axis OA2.
[0053] In some embodiments inspection system 200 includes an image processing system (not shown) that is configured to process the captured/stored image data (e.g., to stitch together the image data captured during each incremental pulse/exposure), thereby providing image data corresponding to a two-dimensional image of the scanned region of the reticle 80 in order to detect reticle defects (e.g., by comparing the two-dimensional image with known-good image data and identifying anomalies). In some embodiments the inspection system 200 also includes a repair system (not shown) that utilizes the two-dimensional image data to repair all identified reticle defects using known techniques. Image processing systems and repair systems are known in the art and may be utilized in conjunction with the image data processing the captured/stored image data.
[0054] The various embodiments of the structures and methods of this invention that are described above are illustrative only of the principles of this invention and are not intended to limit the scope of the invention to the embodiments described. For example, although the invention is described with specific reference to catoptric (mirror-based/reflective optical) systems used in high energy (e.g., EUV) systems and tools, the combined use of Scheimpflug optics and non-concentric optics may be beneficially utilized in dioptric (lens-based/transmissive) and catadioptric (both mirror-based/reflective and lens-based/transmissive) systems. Moreover, although described with specific reference to high magnification catadioptric systems, the combined use of Scheimpflug optics and non-concentric optics may be beneficially utilized in some low magnification catadioptric systems, such as in EUV manufacturing systems of the type described with reference to FIG. 7. Thus, the invention is limited only by the following claims and their equivalents.
