Base plate for supporting a reticle, and related systems and methods.

Abstract

A baseplate device used to support, transport, and process a reticle is described, including supporting the reticle during a step to detect particle contamination on the surface of the reticle before using the reticle in an extreme ultraviolet (EUV) lithography process. The baseplate device may be designed, for example, by the edge structure of the baseplate, to prevent or reduce the amount of light used in the reticle back-side inspection system, which is reflected from the baseplate and directed towards the camera of the reticle back-side inspection system.

Description

Technical Field

[0001] The present specification relates to a base plate device used for supporting, transporting and processing a reticle, including supporting the reticle during the step of detecting particle contamination on the surface of the reticle before using the reticle in an extreme ultraviolet (EUV) lithography process.

Background Art

[0002] One of the process steps commonly used in the fabrication of integrated circuits and other microelectronic and semiconductor devices is photolithography. In general, photolithography involves using a patterned template to selectively expose a specially prepared surface to a radiation source to create an etched surface layer. According to a particular method, the patterned template is a reticle, which is an extremely flat glass plate containing a pattern to be reproduced on a surface.

[0003] A photolithography step can be used multiple times when preparing microelectronic devices on a semiconductor wafer substrate. Useful photolithography techniques can use light of various wavelengths, including light in the ultraviolet range, light in the deep ultraviolet range, and light in the extreme ultraviolet range.

[0004] In some exemplary processes, the semiconductor wafer surface may be prepared by first depositing silicon nitride onto the surface, followed by a coating of a photosensitive liquid polymer or photoresist. Ultraviolet (UV) light, such as extreme ultraviolet light ("EUV"), is then transmitted through or reflected from the surface of a mask or reticle to project a desired pattern onto the photoresist-covered wafer. The portions of the photoresist exposed to the light are chemically modified and remain unaffected when the wafer is subsequently exposed to a chemical medium that removes the unexposed photoresist, leaving the modified photoresist on the wafer in the shape of the pattern on the mask. The wafer is then subjected to an etching process that removes the exposed portions of the nitride layer, leaving the nitride pattern on the wafer in the precise design of the mask.

[0005] When photolithography is performed using EUV light, the patterned light is applied to the photoresist by being reflected from the patterned reticle, as opposed to being transmitted through the patterned mask. To achieve the highest level of reflection of light from the reticle (also known as the "reflective photomask") onto the photoresist, the surface of the reticle receiving the EUV light for reflection should be free from defects, contamination, and damage as much as possible. Particle contamination on the surface of the reticle can be detrimental to the performance of the reticle during EUV photolithography. Particle contamination on the surface of the reticle can have an effect that interferes with the reflected light and can also affect the shape or positioning of the reticle, either of which will alter the direction and quality of the reflected light. [Overview of the project]

[0006] To reduce or avoid the presence of particle contamination on the reticle surface during a photolithography step, specialized devices and systems are used to detect particle contamination on the reticle surface before use in the photolithography step. These systems may be called “reticle backside inspection” (RBI) devices or modules and may be included as separate modules in larger EUV photolithography systems. During inspection, the reticle is supported by the flat surface of a base plate, which may be referred to herein as the “EUV base plate” or “base plate.” The base plate is useful for supporting, transporting, and transferring the reticle during the different steps of preparing and performing the EUV photolithography step in which the reticle is used.

[0007] The back-side inspection system operates to detect particles present on the back (unpatterned) surface of the reticle by shining light onto the back surface while the patterned (opposite) surface of the reticle is horizontally supported by a base plate. See Figure 1 and the related text in this specification. Light is directed at the back surface of the reticle at a shallow angle. If the light is not obstructed by particle contamination on the surface, the light will be reflected from the surface at the same shallow angle ("reflection angle").

[0008] However, if particles are present on the surface, light directed at the surface at a shallow angle can be redirected (bent, reflected, scattered, etc.) away from the reticle surface in various directions other than shallow reflection angles. The reticle back inspection system detector includes a camera positioned above the reticle, facing downward toward the reticle back surface. A portion of the light that has been scattered and redirected away from the reticle surface by particles on the surface is received by the camera. The camera associates this redirected light with the presence of particle contamination on the surface.

[0009] In addition to light being reflected from particle contamination, light directed at the reticle surface may also be deflected by the baseplate used to support the reticle during the inspection step. Light used to inspect the back surface may pass through the transparent portion of the reticle and reach the baseplate. The edges on the outer periphery of an EUV reticle are often transparent, and light used to detect particles on the reticle surface may pass through the reticle at the transparent edges and reach the baseplate below. Often, light may be reflected from the baseplate in a direction that does not reach the camera. However, some structures present on the baseplate have the potential to change the direction of light (reflect or deflect it) towards the camera. If light is redirected from the baseplate towards the camera, the camera will associate that light with the presence of particle contamination on the back surface of the reticle, meaning the system will produce a "false positive" reading by the detector, indicating the presence of particles on the surface when no particles are present.

[0010] In these reticle back-side inspection systems, it is necessary to reduce or avoid the occurrence of false positive readings caused by light being reflected from the EUV baseplate and towards the camera, and the camera associating that light with particle contamination.

[0011] According to this specification, EUV baseplates and baseplate structures, such as reticle supports, may be designed to prevent or reduce the amount of light used in a reticle back-side inspection system that is reflected from the baseplate and directed towards the camera of the reticle back-side inspection system, for example, by the edge structure of the baseplate. The baseplate may include features that reduce the amount of light deflected or reflected from the edge surface of the baseplate in a direction that would cause deflected light to reach the system's camera and register false positive readings. These features include "low-reflecting surfaces" applied to or formed on the edge structure.

[0012] One type of low-reflective surface is a surface that is shaped or angled in such a way that light reflected from the low-reflective surface is not redirected toward the camera. Examples of this type of low-reflective surface include edge structures with a low radius of curvature and edge structures with a flat beveled surface that directs light that strikes the surface away from the camera.

[0013] Low-reflectivity surfaces can be made from or coated with materials designed to have low reflectivity, such as low spectral reflectance to light of wavelengths emitted by an illuminator, either as an addition or as an alternative. Low-reflectivity surfaces may be surfaces treated by processes such as chemical etching, laser ablation, laser texturing, or mechanical polishing to form a rough surface that exhibits relatively low reflectivity compared to the surface before treatment, for example, causing light to scatter over a range of directions away from the surface. Low-reflectivity surfaces can also be coated materials applied to a surface, which have low spectral reflectance to light of wavelengths emitted by an illuminator.

[0014] As an addition or alternative, the baseplate may include features (e.g., a "mask" or "screen") that, while the reticle is supported by the baseplate, block the light emitted by the illuminator before it reaches the reticle, preventing the light from passing through the transparent portion of the reticle, such as at a transparent edge, reaching the baseplate in the area of ​​the edge structure, and potentially being redirected towards the camera by the edge structure.

[0015] In one embodiment, the present invention relates to a base plate for supporting a reticle. The base plate includes a horizontal upper base plate surface and one or more edge structures. An example of an edge structure is the edge of an opening positioned vertically through the plate, the opening comprising an opening edge structure formed between the vertical opening sidewall and the upper base plate surface. Another example of an edge structure is the edge structure of a reticle support positioned within an opening. The reticle support may include a reticle support body that engages with the opening sidewall, an upper reticle support surface positioned above the upper base plate surface and adapted to support a reticle above the upper base plate surface, and a reticle support edge structure formed between the reticle support body and the upper reticle support surface. These or base plates including edge structures may include low-reflectivity surfaces in the edge structures. For example, an opening edge structure may include a low-reflectivity surface in the form of a bevel, a radius of curvature smaller than 0.3 millimeters, a surface having a spectral reflectance at least 10 percent lower than the spectral reflectance of the upper base plate surface, or a combination thereof. The reticle support edge structure may include a low-reflectivity surface in the form of a bevel, a radius of curvature smaller than 0.3 mm, a surface having a spectral reflectance at least 10 percent lower than the spectral reflectance of the upper baseplate surface, or a combination thereof.

[0016] In another aspect, the present invention relates to a reticle backside inspection device comprising: a vacuum chamber having an interior; a base plate as described herein and in the claims, located inside the chamber; an illuminator capable of directing light onto the surface of a reticle supported on the upper surface of the base plate; and a camera adapted to detect light redirected by particles on the surface of the reticle.

[0017] In another aspect, the present invention relates to a method of using the reticle backside inspection system described herein in a reticle backside particle inspection system for detecting particles on the backside surface of a reticle. The method includes using a reticle backside inspection system comprising: a vacuum chamber having an interior; a base plate described herein and in the claims, located inside the chamber; an illuminator capable of directing light onto the upper surface of the base plate; a reticle supported on the base plate; and a camera adapted to detect light redirected by particles on the upper surface of the base plate for detecting particles on the backside of the reticle. The method further includes directing light from the illuminator onto the backside surface of the reticle and the upper surface of the base plate, and using the camera to detect light reflected by particles on the upper surface of the base plate. The method may further include using the light detected by the camera to determine the amount of particles present on the upper surface of the base plate. [Brief explanation of the drawing]

[0018] [Figure 1] This is a side cross-section of an exemplary reticle back inspection system being described. [Figure 2] Figures A and B are side perspective views of the exemplary base plate described. [Figure 3] This is a side perspective view of an exemplary base plate being described. [Figure 4A] This is a side fracture view of an exemplary base plate described, including the edge structure. [Figure 4B] This is a side fracture view of an exemplary base plate described, including the edge structure. [Figure 4C] This is a side fracture view of an exemplary base plate described, including the edge structure. [Figure 4D] This is a side fracture view of an exemplary base plate described, including the edge structure. [Figure 5] This is a side cross-section of an exemplary reticle back inspection system being described. [Figure 6]It is a cutaway view of another embodiment of the optical screen described. [Figure 7] It is a cutaway view of an additional embodiment described. [Figure 8] It is a cutaway view of another embodiment of light blocked by an aperture edge structure and by a reticle support edge structure.

Mode for Carrying Out the Invention

[0019] All drawings are schematic and not to scale.

[0020] Figure 1 shows an example of a reticle backside inspection system that can be used to detect unwanted particle contamination in the form of extremely small particles (e.g., particles having dimensions on the micron scale) at low levels on the backside surface of a reticle. Particles on a reticle surface may be dust particles, surface debris carried by different surfaces and transferred to the reticle surface via air, or surface debris generated by peeling from different surfaces and transferred to the reticle surface via air.

[0021] These particles are fine and small (e.g., having dimensions on the micron scale) and may be present in extremely low quantities on the reticle backside surface. Systems and methods for detecting these particles, even when they are of extremely small size (based on volume, mass, or both) and even when present in extremely low quantities on the reticle backside surface, are important for semiconductor manufacturing, because these small particles present at low levels on the reticle backside surface can have a material impact on the performance of the reticle during photolithography steps.

[0022] As shown in Figure 1, the system 100 includes a vacuum housing 110 that defines a vacuum chamber 108 internally. A reticle baseplate (also known as the "EIP baseplate" or "EUV inner pod baseplate") 112 is supported within the vacuum chamber 108 by a kinematic mount 114. The reticle 130 is supported by the baseplate 112 on its lower (patterned) surface 134, with its upper surface (the "back side" of the reticle) 132 facing upward toward the vacuum chamber 108 and the camera 140. An illuminator 116 produces light 122 at wavelengths that pass through the window 118. The light 122 is directed toward the surface 132 to inspect for any particles that may be present on the surface 132.

[0023] Light 122 is directed toward surface 132 at a shallow angle of incidence, which causes light 122 from illuminator 116 to be reflected from surface 132 at the same shallow angle (reflection angle), so that light 122 is not reflected in a direction that would allow the reflected light to be detected by camera 140. In the illustrated example, system 100 includes camera 140 positioned above reticle 130 and at an angle perpendicular to the horizontal surface of reticle 130. Light reflected directly from surface 132 at a shallow angle of reflection will not be received by camera 140. If there are no particles on surface 132 that would change the direction of light 122 from a shallow angle of reflection on surface 132, then at most a very low and predictable amount of light will be directed toward camera 140 and detected by camera 140.

[0024] However, if particulate contamination is present on surface 132, the light 122 from the illuminator 116 will be deflected or reflected by the particles and scattered as deflected light 122A over a range of directions within the vacuum chamber 108, including towards camera 140. The deflected light 122 received by camera 140 will be associated with the presence of particulate contamination on surface 132. In this configuration, camera 140 receives and detects the light 122A deflected by particulate contaminants present on surface 132 and registers the deflected light as being caused by particulate contamination on surface 132.

[0025] However, in addition to the particles present on surface 132, structural features of baseplate 112 may also cause light 122 from illuminator 116 to be reflected or deflected towards camera 140 as deflected light 122A. When this occurs, camera 140 detects the deflected light 122A and associates it with light caused by particle contamination on surface 132. The result is a "false positive" reading indicating the presence of particle contamination on the surface when no signal was generated by particle contamination.

[0026] The base plate 112 may have a different structure, which may cause the light 122 to be deflected in a direction that causes the deflected light 122A to be received by the camera 140, resulting in a false positive reading result. The base plate may be of a type useful for supporting, transporting, or otherwise supporting the reticle during the EUV photolithography step. Examples of useful base plates may be of a type that is a component of a “reticle pod,” as described, for example, in U.S. Patent Publications No. 9,745,119 and 9,919,863, and U.S. Patent Publication No. 2021 / 0057248, which are incorporated herein by reference in their entirety. These documents describe a reticle pod that includes a base plate for supporting the reticle during transport and a cover that may be placed on the base plate and the reticle to protect the reticle during movement.

[0027] Figures 2A and 2B show an example of a base plate 112 and a reticle 130 useful in an exemplary reticle back inspection system 100. The base plate 112 includes a location on its upper surface 150 that approximates the size and shape of the reticle. The patterned surface 134 of the reticle 130 may be positioned in a "downward" direction toward the upper surface 150 of the base plate 112. The upper surface 150 may be given a reflective metallic finish, such as reflective chromium or nickel.

[0028] Lateral containment pins 160 are attached to the base plate 112 on the upper surface 150. Multiple containment pins 160 are fixedly attached to the base plate 112 in locations near the outer perimeter of the space for positioning the reticle 130 above the surface 150, and are effective in guiding the positioning of the reticle 130 at desired locations above the surface 150. In some examples, the containment pins 160 have a tapered inclined surface shape to facilitate the positioning of the reticle 130 between the containment pins 160, and are configured in a regular pattern on the surface 150, and are dimensionally and positioned to cause the reticle 130 to be positioned at desired locations above the surface 150 between the containment pins. The containment pins 160 may be constructed from metal, such as steel or aluminum, or from other rigid materials including polymers.

[0029] In addition to the housing pins 160, the exemplary base plate 112 also includes a plurality of openings through the base plate and reticle supports 162 positioned within those openings. Each reticle support 162 is positioned within an opening or “opening” extending vertically through the base plate 112, and each reticle support 162 includes an upper surface positioned a height less than the upper surface 150 of the base plate 112. Each upper surface of the reticle support 162 is individually positioned a small distance above the surface 150, allowing the upper surface of the reticle support to contact the lower (patterned) surface 134 of the reticle 130, and positioning the lower surface 134 a small distance above the surface 150. Each upper surface of the reticle support 162 is positioned a certain distance above the upper surface 150 in order to separate the lower surface 134 from the upper surface 150 and to create a horizontally extending gap between their surfaces. The gap can be any useful size within the range of, for example, 0.001 to 0.010 inches.

[0030] As shown in Figures 2A and 2B, the base plate 112 includes a plurality of reticle supports 162 near pairs of receptacle pins 160 at the corners of the base plate 112 on the diagonals of the surface 150, so as to contact the surface of the reticle, which is positioned near each of the four corners of the reticle. Alternatively, one or more reticle supports 162 may be positioned as needed at any other useful location on the surface 150, which may be effective in providing support for the reticle 130 above the surface 150, preferably in a location that avoids contact with the patterned or otherwise sensitive areas of the patterned surface 134.

[0031] In relation to this specification, the reticle 130 includes a functional (reflective) patterned surface on most of the area of ​​the patterned surface 134, but may not be patterned in areas adjacent to the outer edge of the reticle. The outer edge of the reticle ("outer edge") may not be patterned and may be transparent, thereby allowing light 122 to pass through the reticle at locations of the outer edge. Light 122 passing through the reticle 130 at the outer edge may reach the upper surface 150 of the base plate 112. If the location where the light strikes the upper surface 150 is reflective and includes structures other than horizontally flat surfaces, for example, if the upper surface 150 includes rounded or cornered edges or other non-horizontal structures ("edge structures"), then light 122 passing through the reticle 130 at the transparent outer edge may strike the edge structures and be reflected or deflected towards the camera 140 as deflected light 122A. The deflected light 122A is received by the camera 140, which could cause the system 100 to mistakenly associate the deflected light 122A with particle contamination present on the surface 132, i.e., produce a false positive reading.

[0032] As described herein, the applicant has identified structures (e.g., “low-reflectivity surfaces” on edge structures) and methods for reducing the occurrence of light 122 being deflected or reflected as light 122A from the edge structures of the base plate, for example from the edge structures associated with the upper surface 150, and more specifically from the edge structures at the outer peripheral edge of the base plate 112, and being redirected towards the camera 140 to produce false positive reading results.

[0033] Figure 3 is an upper perspective view of an exemplary base plate 112 with additional details. The base plate 112 includes a horizontal upper surface 150 having openings or “openings” 170 and 172. Opening 170 is fitted to accommodate a reticle support 162 (not shown), and openings 172 are each fitted to accommodate a receptacle pin 160 (not shown). Each opening defines a circular edge (“edge structure”) between the vertical side wall of the opening and the horizontal upper surface 150.

[0034] Figure 4A shows a cross-section of a base plate 112, an opening 170 extending vertically through the base plate 112, a reticle support 162 housed within the opening 170, a housing pin 160, and a reticle 130. The reticle 130 is supported by the upper surface of the reticle support 162, which keeps the reticle 130 slightly above the surface 150, and the patterned surface 134 of the reticle 130 is separated from the surface 150 by a gap 180. The reticle support 162 contacts the patterned surface 134 at the outer edge of the reticle, for example, in locations that are not patterned and are transparent to light produced by the illuminator of the reticle back inspection system.

[0035] The opening 170 includes a circular edge structure 174 on its outer periphery. In a cross-section (as shown in Figure 4A), the edge structure 174 has a rounded surface formed between the horizontal surface 150 and the vertical side wall of the opening 170. The edge structure 174 has a radius of curvature specified by a circle with radius r1.

[0036] Furthermore, in Figure 4A, the reticle support 162 includes a circular edge structure 176 on the outer circumference of the reticle support 162 and adjacent to the horizontal upper surface of the reticle support 162. In a cross-section (as shown in Figure 4A), the edge structure 176 has a rounded surface formed between the horizontal upper surface of the reticle support 162 and the vertically extending outer cylindrical sidewall of the reticle support 162. The edge structure 176 has a radius of curvature specified by a circle having a radius of curvature r2.

[0037] The reticle support may be of any design and may be designed to provide a support structure for the reticle supporting the reticle as described, slightly above the upper surface 150 of the base plate, while reducing the presence of edge structures on the reticle support that may reflect or deflect light from the illuminator of the reticle back inspection system toward the camera of the reticle back inspection system.

[0038] In the example shown in Figure 4A, the reticle support 162 is a polymer structure having a substantially cylindrical upper body with a relatively flat (horizontal) upper surface 166 and an edge structure 176 extending around the outer circumference of the upper reticle surface 166. The opening 170 has an inner diameter slightly smaller than the outer diameter of the polymer reticle support 162. The reticle support 162 is mounted within the opening 170 at a position that causes the upper reticle surface 166 of the reticle support 162 to protrude slightly above the surface 150 in order to establish the height of the gap 180. The reticle support 162 may be held in place by fasteners (e.g., set screws) that allow the height of the upper surface of the reticle support to extend above the surface 150 and also allow for fine adjustment of the height of the upper surface above the surface 150.

[0039] According to this specification, EUV baseplates and baseplate structures, such as reticle supports, may be designed to prevent or reduce the amount of light used in a reticle back-side inspection system that is reflected from the baseplate and redirected toward the inspection system's camera. The baseplate may include features that reduce the amount of light deflected or reflected from the edge surface of the baseplate in a direction that would cause deflected light to reach the system's camera and register false positive readings, and these features include “low-reflectivity surfaces” applied to or formed on the edge structure. Additionally or alternatively, the baseplate may include features that reduce the amount of light that could pass through the transparent portion of the reticle, reach the baseplate and potentially redirect toward the camera, for example, at the outer edge of the reticle, while the reticle is supported by the baseplate.

[0040] The exemplary baseplate includes a non-horizontal edge structure. In a reticle supported by the baseplate, and in unpatterned areas of the reticle, such as at the outer edge of the reticle, light directed onto the back of the reticle to inspect particles can pass through the reticle and reach the baseplate. The light that reaches the baseplate can be directed away from the baseplate's edge structure and redirected towards the system's camera. The exemplary baseplate, as described, may be designed to reduce the amount of light thus deflected from the baseplate's edge structure towards the camera.

[0041] To reduce the amount of light deflected from the edge structure, an exemplary base plate may include an edge structure having a low-reflectivity surface, which may include, for example, an edge structure shape that reduces the amount of light reflected toward the camera, and a low-reflectivity surface on the edge structure formed by treating the edge structure surface to reflect less or absorb more light used in the back inspection system. Additionally or alternatively, the base plate or system may include a structure (e.g., a “screen” or “mask”) placed within the system, for example at the edge of the base plate, to selectively block light from the inspection system from reaching the edge structure of the base plate.

[0042] In various exemplary baseplates, the low-reflection edge structure may have a shape that allows a reduced, low, or minimal amount of light from the illuminator of the reticle back-to-back inspection system to be reflected by the edge structure toward the camera. The edge structure may include an aperture or a non-horizontal surface of the reticle support (e.g., a corner or edge) (e.g., 174, 176). To reduce the amount of light deflected from the edge structure, i.e., for the edge structure to function as a low-reflection edge structure, the area of ​​the non-horizontal surface of the edge structure may be reduced or minimized, or angled to prevent the light from being redirected toward the camera of the reticle back-to-back inspection system by the non-horizontal surface. For example, a corner may be formed to have a low radius of curvature. Alternatively, the edge structure may be formed as a beveled (or "chamfered") surface oriented at an angle that does not cause light to be reflected from the illuminator toward the camera, for example, at an angle that causes light reaching the bevel surface to be directed away from the camera at a shallow angle.

[0043] As shown in Figure 4B, the edge structure 174 of the opening 170 may be prepared to have a radius of curvature r1 smaller than 0.5 millimeters (500 microns), for example, 0.4, 0.3, 0.2, or 0.1 millimeters (100 microns). A low radius of curvature edge structure results in a smaller curved surface area where light (122) can be reflected and reoriented as deflected light (122A) towards the camera of the reticle back inspection system. The opening 170 and the edge structure 174 in the base plate 112 may be produced in the metal base plate by conventional machining techniques.

[0044] Similarly, as also shown in Figure 4B, the edge structure 176 of the reticle support 162 may be prepared to have a radius of curvature r2 smaller than 0.5 millimeters (500 microns), for example, 0.4, 0.3, 0.2, or 0.1 millimeters (100 microns). The low radius of curvature edge structure of the reticle support results in a smaller surface area over which light (122) can be reflected and reoriented as deflected light (122A) towards the camera of the reticle back inspection system. The reticle support 162 and the edge structure 176 may be produced in the polymer reticle support by standard polymer molding or forming techniques.

[0045] According to an alternative embodiment as shown in Figure 4C, the edge structure 174 of the aperture 170 may be prepared to have a bevel shape angled with respect to the direction of light received from the illuminator 116 of the reticle back inspection system 100, so as not to cause reflected light to be directed toward the camera 140. The edge structure 174 may be defined as a transition from the vertical sidewall of the aperture 170 to the bevel surface 182. The bevel surface 182 of the edge structure 174 is angled so as to cause light (122) from the back inspection system to be reflected at a shallow angle that does not cause deflected light (122A) to be directed toward the camera of the reticle back inspection system. The angle a1 can be any angle such that the light is deflected by the bevel surface 182 in a direction that does not cause the light to be received by the camera 140. Examples of useful values ​​for the angle a1 between the bevel surface 182 and the surface 150 can be less than 15 degrees or greater than 75 degrees, as shown. The opening 170 in the base plate 112 and the edge structure 174 with a beveled surface 182 can be created in a metal base plate by conventional machining techniques.

[0046] According to a similar embodiment also shown in Figure 4C, the edge structure 176 of the reticle support 162 may be prepared to have a bevel shape angled with respect to the direction of light received from the illuminator 116 of the reticle back inspection system 100, so as not to cause reflected light to be directed toward the camera 140. The bevel surface 184 of the edge structure 176 is angled so as to cause the light (122) from the back inspection system to be reflected at a shallow angle that does not cause deflected light (122A) to be directed toward the camera of the reticle back inspection system. The angle a2 can be any angle that directs the deflected light in a direction that does not cause the light to be received by the camera 140. Examples of useful values ​​for the angle a2 between the bevel surface 184 and the surface 150 can be less than 15 degrees or greater than 75 degrees, as shown. The reticle support 162 and the edge structure 176 may be produced in the polymer reticle support by standard polymer molding and forming techniques.

[0047] According to the alternative base plate shown in Figure 4D, the edge structure 174 of the opening 170 may be prepared to include a low-reflectivity surface 190 that has reduced ability to reflect light 122 from the illuminator 116 of the back inspection system (i.e., has low spectral reflectance) or absorbs light 122 from the illuminator 116 of the back inspection system, based on composition or texture (roughness vs. smoothness), but not necessarily on shape (e.g., low radius of curvature corner or bevel shape). The shape of the edge structure may be rounded, beveled, or otherwise, but the composition or texture of the edge structure surface will cause the edge structure surface to function as a low-reflectivity surface.

[0048] The low-reflectivity surface 190 may be any surface having a composition (e.g., due to an applied coating or treatment applied to the surface) or texture that exhibits lower reflectivity compared to the aperture 170 or other surfaces of the base plate 112, for example, lower reflectivity compared to the reflectivity of the surface 150 of the base plate 112 as measured by spectral reflectance to light having wavelengths emitted by the illuminator of the reticle back inspection system. The low-reflectivity surface 190 of the edge structure 174 of the metal base plate may have reflectivity to light emitted by the illuminator of the reticle back inspection system that is at least 10, 20, 30, 40, or 50 percent lower compared to the reflectivity of the surface 150 of the base plate 112 as measured by spectral reflectance to light emitted by the illuminator of the reticle back inspection system. The wavelength of the light may be a single wavelength or a range of wavelengths of light produced by the illuminator of the reticle back inspection system and directed toward the reticle surface to detect particle contamination on the surface.

[0049] A typical surface 150 of the base plate 112 is a metallic (e.g., chromium, nickel, etc.) surface that highly reflects light across the visible wavelength range. Generally, edge surfaces 174 and apertures 170 include the same reflective metallic surfaces, for example, applied as a coating on a metallic (e.g., aluminum) base plate structure. The metallic surface of the edge structure may reflect light received from the illuminator of the reticle base plate inspection system, redirecting that light towards the system's camera and potentially causing false positive readings. The metallic (e.g., chromium) surface of the base plate can have a spectral reflectance of more than 60 percent of the wavelengths emitted by the illuminator of the reticle backside inspection system. For example, a metallic surface (150) or edge structure (174) made of chromium can have a spectral reflectance of more than 60 percent of the light with wavelengths emitted by the illuminator, for example, about 63 percent.

[0050] Examples of low-reflectivity surfaces 190 can have spectral reflectances of the same wavelength of light emitted by an illuminator, below 63 percent, below 60 percent, or below 55, 50, 45, 40, 30, or 20 percent. Examples of low-reflectivity surfaces may be made from oxides of metal surfaces with edge structures, such as chromium oxide or nickel oxide.

[0051] According to the exemplary base plate, the highly reflective metallic surface of the edge structure 174 of the opening 170 can be modified to reduce the reflectivity of the surface (measured as spectral reflectance) and create a low-reflectivity surface 190. For example, a highly reflective metallic coating on the surface of the edge structure (e.g., 174) can be treated by chemical etching, laser texturing, laser ablation, or mechanical polishing, or a combination thereof, to reduce the reflectivity of the surface and create a low-reflectivity surface 190.

[0052] The treatment may affect the chemical composition of the metal, the texture of the metal surface, or both. The low-reflectivity surface 190 obtained from the treatment may have a reflectivity to light emitted by an illuminator of a reticle back inspection system (such as measured by spectral reflectance) that is at least 10, 20, 30, 40, or 50 percent lower compared to the reflectivity of the surface 150 of the base plate 112, or compared to the reflectivity of the untreated surface of the edge structure 174, or both. For example, the low-reflectivity surface may have a spectral reflectance to light of wavelengths emitted by an illuminator that is below 63 percent, below 60 percent, or below 55, 50, 45, 40, 30, or 20 percent.

[0053] Alternatively or as an addition, the reflective metallic coating on the surface of the edge structure 174 of the metal base plate may be made of a material different from the material of the surface 150 and which has lower reflectivity to the light 122 emitted by the illuminator 116 or absorbs the light 122 emitted by the illuminator 116, in order to create a low-reflectivity surface 190. The low-reflectivity surface 190 created by the coating (optionally combined with chemical treatment, laser treatment, mechanical polishing, etc.) may have at least 10, 20, 30, 40, or 50 percent lower reflectivity to the light emitted by the illuminator of the reticle back-side inspection system (such as measured by spectral reflectance) compared to the reflectivity of the surface 150 of the base plate 112 and compared to the reflectivity of the untreated (uncoated) surface of the edge structure 174.

[0054] A coating that may be useful for creating a low-reflectivity surface 190 is any coating that can be applied to the surface of an edge structure and has reflectivity as measured by spectral reflectance, such as below 63 percent, below 60 percent, or below 55, 50, 45, 40, 30, or 20 percent for wavelengths of light emitted by an illuminator.

[0055] As also shown in Figure 4D, the edge structure 176 of the reticle support 162 may be prepared to have a low-reflectivity surface 192 that has reduced ability to reflect or absorb the light 122 from the illuminator 116 of the back inspection system, in order to prevent the light 122 from being reflected from the edge structure surface toward the camera 140.

[0056] The low-reflectivity surface 192 may be any surface having a chemical composition or texture that preferably produces low reflectivity, including, but not necessarily, lower reflectivity compared to other surfaces of the reticle support 162, as measured by the spectral reflectance to light of wavelengths emitted by the illuminator of the reticle back inspection system.

[0057] In the exemplary baseplates of this specification, the edge structure 176 of the reticle support 162 may include a texture that exhibits preferably low reflectivity on the edge structure surface, thereby creating a low-reflectivity surface 192. For example, the polymer surface of the edge structure (e.g., 176) may be treated to roughen the surface by chemical etching, laser texturing, laser ablation, or mechanical polishing, or a combination thereof, in order to reduce the reflectivity of the surface and create a low-reflectivity surface 192. The surface may also be created to have a non-smooth, for example, rough low-reflectivity surface during the molding of the reticle support 162. The low-reflectivity surface 192 formed by treating the surface to form a low-reflectivity surface (textured, rough surface) polymer surface by chemical etching, laser texturing, laser ablation, or mechanical polishing may have a surface that is at least 10, 20, 30, 40, or 50 percent lower reflectivity to light emitted by an illuminator of a reticle back-side inspection system (such as measured by spectral reflectance) compared to the reflectivity of the polymer surface before treatment.

[0058] Alternatively or as an addition, the polymer surface of the edge structure 176 may be coated with a material different from the polymer material of the edge structure 176 and which preferably has low reflectivity to or absorbs light 122 emitted by the illuminator 116, in order to create a low-reflectivity surface 192. The low-reflectivity surface 192 of the coating (optionally combined with chemical treatment, laser treatment, mechanical polishing, etc.) may have at least 10, 20, 30, 40, or 50 percent lower reflectivity to light emitted by the illuminator of the reticle back-side inspection system (such as measured by spectral reflectance) compared to the reflectivity of the uncoated polymer surface of the edge structure 176 or compared to the reflectivity of the surface 150 of the base plate 112.

[0059] A coating that may be useful for creating a low-reflectivity surface 192 can be applied to the polymer surface of the edge structure 176 and may be any coating having reflectivity, as measured by spectral reflectance, that is at least lower than the reflectivity of the uncoated surface of the edge structure 176.

[0060] In other exemplary systems, the base plate used in a reticle back inspection system may include a structure such as a light screen ("screen" or "mask") that reduces the amount of light or prevents light from being directed towards the reticle in the transparent areas of the reticle, such as at the outer edge of the reticle, thereby preventing light from passing through the transparent areas of the reticle, reaching the base plate supporting the reticle, and reaching the edge structure of the base plate, thereby potentially preventing the direction of light from changing towards the inspection system's camera.

[0061] Figure 5 shows an exemplary reticle back-side inspection system 100, which includes the features of system 100 of Figure 1, and includes a vacuum housing 110, a vacuum chamber 108, a reticle base plate 112, a kinematic 114, and a reticle 130 having a lower (patterned) surface 134 supported by the base plate 112 and an upper surface (reticle "back side") 132 facing upward toward the vacuum chamber 108 and camera 140. An illuminator 116 produces light 122 at wavelengths passing through the window 118. The light 122 is directed toward surface 132 to inspect for any particles that may be present on surface 132.

[0062] The base plate 112 is shown as including an edge structure that, as described, is capable of deflecting light from the illuminator 116 toward the camera 140 when light passes through the reticle 130 and reaches the aperture 170 and the edge structure which may be the structure 174, 176, or both of the reticle support 162.

[0063] The system 100 in Figure 5 further includes a light screen 186 supported by a base plate 112. The light screen (or "screen") 186 may be any structure that can be positioned at the edge of the base plate 112 in a location between the illuminator 116 and the reticle 130, particularly in a location between the illuminator 116 and the edge structure of the base plate 112, as exemplified by structures 174, 176. In this embodiment, the light screen 186 is positioned vertically. The light screen 186 does not transmit light 122, preventing the light 122 from reaching the reticle 130, or prevents the light 122 from reaching the edge structures 174, 176, thereby preventing the direction of the light 122 from changing towards the camera 140.

[0064] The screen 186 can be positioned at any useful location on the base plate to prevent light from reaching the base reticle 130 or edge structures (e.g., 174, 176). Figures 2A and 2B show useful locations for the screen 186, positioned near the outer edge of the base plate 112, as well as near the edge structure of the reticle support 162 and associated openings (not shown). Furthermore, Figure 6 shows another embodiment in which the base plate 112 acts as a light screen for the reticle support body 162, preventing light from striking the reticle support edge 176. In this embodiment, the reticle support edge is positioned below the upper surface of the base plate 112. The edge structure of the reticle 130 is the transition from the receiving pin 160 to the bevel edge structure. Furthermore, Figure 8 shows another embodiment in which the reticle support edge structure blocks light from the opening edge structure.

[0065] The reticle support positioned on the baseplate may also reflect light either by the surface of the reticle support or by the fasteners used to hold the reticle support on the baseplate. Accidental reflection of light can also be a problem and may produce false positive readings. In another embodiment shown in Figure 7, a baseplate 112 for supporting a reticle (not shown) includes a horizontal baseplate surface 115 and a reticle support 162 positioned on the horizontal baseplate surface 115. The reticle support 162 includes a base 194 and at least one reticle contact feature 196 extending from the base 194. At least one reticle contact feature on the distal end of the support structure 162. The base 194 may include one or more fasteners 198 for holding the base on the horizontal baseplate surface. One or more fasteners 198 are embedded in a counterbore 200 to conceal the edges from light at a shallow angle. In another embodiment, the fastener 198 or edge structure 202 includes (i) a bevel, (ii) a radius of curvature smaller than 0.3 millimeters, (iii) a surface having a spectral reflectance at least 10 percent lower than the spectral reflectance of the upper base plate surface, or (iv) a low-reflectance surface created from a combination thereof.

Claims

1. A base plate for supporting a reticle, wherein the base plate is The surface of the horizontal base plate and An opening arranged vertically through the plate, wherein the opening comprises an opening edge structure formed between the vertical opening side wall and the surface of the base plate, A reticle support disposed within the opening, wherein the reticle support is Reticle support body that engages with the opening side wall, An upper reticle support surface, positioned above the horizontal plate surface and adapted to support the reticle above the base plate surface, and Reticle support edge structure formed between the reticle support body and the surface of the reticle support A reticle support equipped with Equipped with, The opening edge structure comprises a low-reflectance surface, including a bevel, a radius of curvature smaller than 0.3 mm, a surface having a spectral reflectance at least 10 percent lower than the spectral reflectance of the upper base plate surface, or a combination thereof. The reticle support edge structure comprises a low-reflectance surface, including a bevel, a radius of curvature smaller than 0.3 mm, a surface having a spectral reflectance at least 10 percent lower than the spectral reflectance of the upper base plate surface, or a combination thereof. At least one light screen positioned on the surface of the base plate, wherein the at least one light screen does not transmit light and prevents light from reaching the aperture edge structure or the reticle support edge structure. A base plate equipped with the following features.

2. The base plate according to claim 1, wherein the opening edge structure comprises a low-reflectivity coating having a spectral reflectance at least 50 percent lower than the spectral reflectance of the upper base plate surface.

3. The base plate according to claim 1, wherein the opening edge structure comprises a textured surface formed by a process selected from chemical etching, laser texturing, laser ablation, or mechanical polishing.

4. The base plate according to claim 1, wherein the reticle support edge structure comprises a low-reflectivity coating having a spectral reflectance at least 50 percent lower than the spectral reflectance of the upper base plate surface.

5. The base plate according to claim 1, wherein the reticle support edge structure comprises a textured surface formed by a process selected from chemical etching, laser texturing, laser ablation, or mechanical polishing.

6. The base plate according to claim 1, further comprising a reticle supported on the upper surface of the base plate.

7. The base plate according to claim 1, wherein the bevel of the opening edge structure is set to an angle outside the range of 15 to 75 degrees.

8. The base plate according to claim 1, wherein the bevel of the reticle edge structure is set to an angle outside the range of 15 to 75 degrees.

9. The base plate according to claim 1, wherein the lower edge of the bevel of the opening edge structure is positioned lower than the reticle support edge structure such that the reticle support edge structure shields the lower edge of the bevel of the opening edge structure from light.

10. The base plate according to claim 1, wherein the lower edge of the bevel of the reticle support edge structure is positioned lower than the base plate such that the base plate shields the lower edge of the bevel of the reticle support edge structure from light.

11. It is a reticle backside inspection device, A vacuum chamber with an interior, The base plate according to claim 1 located inside the above-mentioned interior, A lighting fixture capable of directing light toward the base plate, A camera adapted to detect light redirected by particles on the back surface of a reticle supported on the upper surface of a base plate, and A reticle back-side inspection device equipped with the following features.

12. A method using the reticle back side inspection device according to claim 11, wherein the method is The upper surface of the base plate supports the reticle, Directing the light from the illuminator towards the reticle, The camera is used to detect light reflected by particles on the surface of the reticle. Methods that include...

13. The method according to claim 12, further comprising using the light detected by the camera to determine the amount of particles on the reticle surface.

14. It is a reticle backside inspection device, A vacuum chamber with an interior, A base plate having an upper surface and an edge structure, A lighting fixture capable of directing light onto the upper surface of the base plate, Camera and Equipped with, The aforementioned base plate is Horizontal upper base plate surface, An opening that is vertically positioned through the plate, wherein the opening has an opening edge structure formed between the vertical opening side wall and the surface of the upper base plate, A reticle support disposed within the opening, wherein the reticle support is The reticle support body engages with the aforementioned opening side wall, An upper reticle support surface, positioned above the upper surface of the horizontal plate and adapted to support the reticle above the upper base plate surface, A reticle support edge structure formed between the reticle support body and the upper reticle support surface. A reticle support comprising, The aperture edge structure comprises a low-reflectance surface, including a bevel, a radius of curvature smaller than 0.3 mm, a surface having a spectral reflectance smaller than 60 percent at the wavelength of light emitted by the illuminator, or a combination thereof. The reticle support edge structure comprises a low-reflectance surface including a bevel, a radius of curvature smaller than 0.3 mm, a surface having a spectral reflectance smaller than 60 percent at the wavelength of light emitted by the illuminator, or a combination thereof. At least one light screen positioned on the surface of the base plate, wherein the at least one light screen does not transmit light and prevents light from reaching the aperture edge structure or the reticle support edge structure. A reticle back-side inspection device equipped with the following features.

15. The inspection device according to claim 14, wherein the aperture edge structure comprises a low-reflectivity coating having a spectral reflectance of less than 50 percent at the wavelength of light emitted by the illuminator.

16. The inspection device according to claim 14, wherein the opening edge structure comprises a textured surface formed by a process selected from chemical etching, laser texturing, laser ablation, or mechanical polishing.

17. The inspection device according to claim 14, wherein the reticle support edge structure comprises a low-reflectivity coating having a spectral reflectance of less than 50 percent at the wavelength of light emitted by the illuminator.

18. The inspection device according to claim 14, wherein the reticle support edge structure comprises a textured surface formed by a process selected from chemical etching, laser texturing, laser ablation, or mechanical polishing.

19. A base plate for supporting a reticle, wherein the base plate is (a) Horizontal base plate surface and (b) comprising a reticle support disposed on the surface of the horizontal base plate, wherein the reticle support is (i) Base and, (ii) A support structure extending from the base, wherein the support structure has an edge structure and at least one reticle contact feature on the distal end of the reticle support structure, and the base includes (1) a fastener for holding the base on the surface of the horizontal base plate, the fastener being embedded in a counterbore to conceal the edge from light at a shallow angle, or (2) the fastener or the edge structure having a low-reflectance surface including a bevel, a radius of curvature less than 0.3 millimeters, a surface having a spectral reflectance at least 10 percent lower than the spectral reflectance of the upper base plate surface, or a combination thereof. Base plate.

20. The base plate according to claim 19, wherein the edge structure comprises a textured surface formed by a process selected from chemical etching, laser texturing, laser ablation, or mechanical polishing.

Images