Photomask cartridge with coated sensing region

Abstract

The invention relates to a photomask cartridge with a coated sensing region. A sensing region is created on an inner cartridge of a reticle container using a dry coating method. The sensing region is a discrete region having a specific spectral reflectance. The sensing region is positioned such that it is readable by a tool to determine a distance of a portion of the cartridge. The use of discrete zones and dry coating methods for applying the discrete zones overcomes the problems of inconsistency and difficulty in cleaning or maintaining the reflectance ratio of the inner box of the reticle container compared to inner boxes fully plated with materials or other wet coating applied materials.

Description

[0001] This application is a divisional application of the patent application for invention titled "Reticle Cassette with Coated Sensing Regions" with the application date of April 16, 2021, application number 202180032956.8.

[0002] Cross - Reference to Related Applications

[0003] This application claims the benefit and priority of U.S. Provisional Application No. 63 / 011,581, filed on April 17, 2020, the entire content of which is incorporated herein by reference for all purposes. Technical Field

[0004] This disclosure relates to reticle cassettes, and in particular, to the formation of sensing regions on a reticle cassette (such as an extreme ultraviolet (EUV) reticle cassette). Background Art

[0005] Reticle cassettes are used to hold lithography masks used during semiconductor processing (such as during extreme ultraviolet (EUV) processing). A reticle cassette may include a metal inner cassette that is handled and manipulated by one or more tools during processing. Some tools may use reflectance to determine the distance between the inner cassette and one or more sensors within the tool. Deionized (DI) water is commonly used to clean the reticle cassette, which can cause oxidation of some materials.

[0006] The inner cassette of a reticle cassette can be wet-coated with chromium to improve reflectance and appearance and to resist reflectance loss due to oxidation caused by cleaning with DI water. However, the shape of the reticle cassette causes difficulties in wet-coating. Summary of the Invention

[0007] This disclosure relates to reticle cassettes, and in particular, to the formation of sensing regions on a reticle cassette (such as an extreme ultraviolet (EUV) reticle cassette).

[0008] By selectively applying a reflective coating to discrete sensing regions on the reticle cassette using a dry coating process, a reflective material can be provided to interface with sensors on the processing tool without wet-coating the entire reticle cassette. Additionally, the reflective coating can be provided to have a desired thickness and strength.

[0009] In an embodiment, a cassette includes a bottom plate having a bottom plate surface. The bottom plate surface includes a bottom plate surface material and a reflective material. The reflective material of the bottom plate surface is disposed in one or more discrete bottom plate sensing regions. The cassette further includes a cover having a cover surface. The cover surface includes a cover surface material and the reflective material. The reflective material of the cover surface is disposed in one or more cover sensing regions.

[0010] In an embodiment, the cassette is an EUV photomask cassette. In an embodiment, the cassette further includes an outer cassette dome and an outer cassette door, and the cassette dome and the cassette door are configured to accommodate the bottom plate and the cover within the cassette dome when the door is attached to the cassette dome.

[0011] In an embodiment, the reflective material has a spectral reflectance between about 50% and about 70% at a wavelength of 880 nm. In an embodiment, the reflective material includes chromium. In an embodiment, only the reflective material includes the chromium.

[0012] In an embodiment, the one or more bottom plate sensing regions and the one or more cover sensing regions are positioned such that the distance between the cassette and the detector can be determined from reading the one or more bottom plate sensing regions and the one or more cover sensing regions.

[0013] In an embodiment, the bottom plate surface includes one of aluminum or nickel and the cover surface is one of aluminum or nickel.

[0014] In an embodiment, a method of manufacturing a photomask cassette includes: applying a reflective material to each of one or more discrete bottom plate sensing regions of a bottom plate of the photomask cassette using a dry coating process; and applying the reflective material to each of one or more discrete cover sensing regions of a cover of the photomask cassette using the dry coating process.

[0015] In an embodiment, the reflective material has a spectral reflectance between about 50% and about 70% at a wavelength of 880 nm.

[0016] In an embodiment, the dry coating process is selected from the group consisting of physical vapor deposition, sputter deposition, chemical vapor deposition, and plasma enhanced chemical vapor deposition.

[0017] In an embodiment, the one or more bottom plate sensing regions and the one or more cover sensing regions are positioned such that the distance between the cassette and the detector can be determined from reading the one or more bottom plate sensing regions and the one or more cover sensing regions. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present disclosure can be fully understood in conjunction with the following description of various illustrative embodiments considered in view of the accompanying drawings.

[0019] Figure 1A A bottom plan view of a bottom plate of a photomask cassette according to an embodiment is shown.

[0020] Figure 1B A bottom plan view of a cover of a photomask cassette according to an embodiment is shown.

[0021] Figure 1C Shown Figure 1BSide view of the lid of the mask box shown in the figure.

[0022] Figure 2 Flowchart showing a method of manufacturing a mask box according to an embodiment.

[0023] Figure 3 Mask box including an outer box and an inner box according to an embodiment.

[0024] Figure 4 Schematic diagram of a mask box in an extreme ultraviolet (EUV) tool according to an embodiment.

[0025] Although the present disclosure is susceptible to various modifications and alternative forms, specific illustrative embodiments have been shown by way of example in the drawings and will be described in detail herein. It should be understood, however, that the aspects of the present disclosure are not intended to be limited to the particular illustrative embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure. Detailed Description

[0026] The present disclosure relates to mask boxes, and more particularly, to the formation of sensing regions on mask boxes (e.g., extreme ultraviolet (EUV) mask boxes).

[0027] Figure 1A Plan view of the bottom of the bottom plate of a mask box according to an embodiment. The bottom plate 100 forms part of the inner box of the mask box. The bottom plate 100 includes one or more sensing regions 102.

[0028] The bottom plate 100 includes a bottom plate surface material that forms the surface of the bottom plate 100. The bottom plate surface material can be a material used to form the bottom plate, such as aluminum or any other suitable material for the bottom plate 100 of the mask box. Specifically, the bottom plate 100 can further include features for manipulating the mask box or the bottom plate 100. The bottom plate surface material can be a coating applied to the bottom plate 100 to form the surface of the bottom plate 100, such as a nickel coating.

[0029] In one or more embodiments, at least one sensing region 102 may be disposed on the surface of the base plate 100. The sensing region 102 is a discrete region made of a reflective material. The sensing region 102 is a defined region of the reflective material formed on a segment of the surface of the base plate 100. The one or more sensing regions 102 cover an area that is less than the entire surface of the base plate 100. The sensing region 102 may have any suitable shape for presenting the reflective material to be read by one or more sensors (e.g., sensors included in a tool for handling a mask cassette that includes the base plate 100). The sensing region 102 may include a sensing region material, which may be a material different from the surrounding base plate material on the surface of the base plate 100. For example, the base plate 100 may be made of aluminum, where the sensing region material is applied over the exposed aluminum material or nickel coating on the base plate 100 to form the discrete sensing region 102. In an embodiment, the sensing region material may be placed and in contact with a coating applied to the surface material of the base plate 100 to form the discrete sensing region 102. In an embodiment, the sensing region 102 may be applied to a coating made of a material different from the sensing region material used in the sensing region 102. In an embodiment, the sensing region 102 may be applied to a coating that includes at least some of the same materials as the sensing region 102 but is provided by a method different from dry coating. For example, a chromium coating may be applied to the chromium surface material used for the base plate 100, where the sensing region 102 is formed by applying additional chromium using a dry coating method to provide a different density, thickness, and uniformity of chromium within the sensing region 102 compared to the base plate surface material that is a wet-coated chromium on nickel.

[0030] The sensing region 102 may be disposed on any part of the base plate 100 where a sensor may attempt to detect the base plate 100. In an embodiment, the sensing region 102 is disposed on the bottom surface of the base plate 100, and when the base plate 100 is assembled with a lid (e.g., the lid 150 shown and described below), the sensing region 102 is visible from the bottom of the mask cassette. In an embodiment, there is one sensing region 102 on the base plate 100. In an embodiment, there are multiple sensing regions 102 on the base plate. In an embodiment, the sensing region 102 is positioned on the bottom surface of the base plate 100 such that when the mask cassette including the base plate 100 is assembled, the sensing region 102 is not obscured by a lid such as Figure 1B and Figure 1B and 1C the lid 150 shown in Figure 1A In the embodiment shown in

[0031] The reflective material used in the sensing region 102 has a known spectral reflectance selected for use in conjunction with a detection system of a tool that uses a cassette including the base plate 100. In some embodiments, the reflective material may have a reflectance different from that of the base plate surface material, such as greater than or less than the reflectance of the base plate surface material. The sensing region 102 may provide a spectral reflectance at one or more predetermined wavelengths within a known predetermined range such that the light reflected by the sensing region 102 is associated with a specific distance of the inner cassette base plate 100 from a reference of a tool that uses a photomask (e.g., an extreme ultraviolet (EUV) tool for processing wafers, for example). As a non-limiting example, for at least one of the one or more predetermined wavelengths, the spectral reflectance of each of the sensing regions 102 ranges between approximately 57% and approximately 63%. In an embodiment, each of the sensing regions 102 has a spectral reflectance between approximately 57% and approximately 63% at a wavelength of 880 nm. The sensing region may comprise any suitable reflective material having the desired spectral reflectance properties and capable of being applied by a dry coating method. The reflective material may be an inert material selected such that it does not react during processing by the tool. As a non-limiting example, the reflective material may comprise chromium. In an embodiment, only one or more of the sensing regions 102 and 152 included in the photomask cassette comprise chromium.

[0032] The reflective material may be provided in the sensing region 102 by a dry coating method, such as physical vapor deposition (PVD), sputter deposition, chemical vapor deposition (CVD), and plasma enhanced chemical vapor deposition (PE-CVD). Compared to a wet coating method, such as plating the entire base plate 100, the resulting sensing region 102 may have a more durable and uniform coating within the sensing region 102. The improved durability may in turn improve the appearance of the sensing region 102 and the maintenance of the appropriate reflectivity.

[0033] Figure 1B A plan view of the bottom surface of the cover 150 of a photomask cassette according to an embodiment is shown, and Figure 1C shown Figure 1B a side view of the cover 150 of the photomask cassette shown in. The cover 150 includes a sensing region 152.

[0034] The cover 150 is configured to be coupled to a base plate (e.g., Figure 1A the base plate 100 shown in) to form a photomask cassette configured to accommodate a photomask. The cover 150 may be configured such that the photomask receiving portion 158 is enclosed by the base plate 100. Specifically, the cover 150 may further include features for manipulating the photomask cassette or the cover 150. The cover 150 may be made of any suitable material, such as aluminum. The surface of the cover 150 is the cover surface material, which may be the material forming the body of the cover 150, or a coating (e.g., nickel formed on the material).

[0035] In addition to or instead of the sensing area 102 disposed on the bottom plate 100, one or more sensing areas 152 may also be disposed on the cover 150. The one or more sensing areas 152 are discrete areas containing reflective material. The one or more sensing areas 152 cover an area less than the entire surface of the cover 150. The reflective material can be applied by a dry coating process. The sensing area 152 can have any suitable shape for presenting the reflective material to be read by one or more sensors (such as sensors included in a tool for handling a photomask cassette containing the cover 150). The sensing area 152 can use the same or different reflective materials as the sensing area on the bottom plate to be used in conjunction with the cover 150, such as Figure 1A the reflective material of the sensing area 102 on the bottom plate 100 shown in. One or more sensing areas can be disposed on the cover 150 such that when the cover 150 is combined with a bottom plate (such as the bottom plate 100) to form the inner cassette of a photomask cassette, the one or more sensing areas can be read by a tool. In an embodiment, the sensing area 152 is positioned such that when the photomask cassette including the bottom plate and the cover 150 is assembled, the sensing area 152 is not blocked by the bottom plate of the bottom plate 100 such as Figure 1A shown in. In Figure 1B and 1C In the embodiment shown in, four sensing areas 152 are provided, where two sensing areas 152 are on the bottom surface of the extension 154 from the side 156 of the cover (as visible in Figure 1B ), and two sensing areas are on the outward-facing side surface of the cover 150 (as visible in Figure 1C ).

[0036] The reflective material used in the sensing area 152 has a known spectral reflectance ratio selected for use in conjunction with the detection system of a tool for handling a cassette containing the cover 150. The reflective material can be selected to be an inert material that does not react during processing by the tool. The sensing area 152 can provide a spectral reflectance ratio at one or more predetermined wavelengths within a known predetermined range such that the light reflected by the sensing area 152 is associated with a specific distance of the inner cassette cover 150 from a reference of the tool (such as an extreme ultraviolet (EUV) tool for processing wafers using a photomask). As a non-limiting example, for at least one of the one or more predetermined wavelengths, the spectral reflectance ratio of each of the sensing areas 152 ranges between approximately 57% and approximately 63%. In an embodiment, each of the sensing areas 152 has a spectral reflectance ratio between approximately 57% and approximately 63% at a wavelength of 880 nm. The sensing area 152 can include any suitable reflective material having the desired spectral reflectance properties and capable of being applied by a dry coating method. The reflective material can be selected to be an inert material that does not react during processing by the tool. As a non-limiting example, the reflective material can include chromium. In an embodiment, only one or more of the sensing areas 102 and 152 included in the photomask cassette contain chromium.

[0037] The reflective material can be provided in the sensing area 152 by a dry coating method, such as physical vapor deposition (PVD), sputter deposition, chemical vapor deposition (CVD), and plasma enhanced chemical vapor deposition (PE-CVD). Compared with a wet coating method, such as coating the entire cover 150, the resulting sensing area 152 can have a more durable and uniform coating within the sensing area 152. Subsequently, the improved durability can improve the appearance of the sensing area 152 and the maintenance of the appropriate reflectivity.

[0038] The cover 150 can include further features for the function of the photomask cassette contained therein. For example, the cover 150 can include a photomask receiving portion 154 that forms a part of the internal space configured to receive a photomask, such as a lithography mask.

[0039] Figure 2 A flowchart showing a method of manufacturing a photomask cassette according to an embodiment. The method 200 includes: providing a bottom plate 202; optionally coating the bottom plate 204; applying a reflective material to one or more sensing areas 206 on the bottom plate using a dry coating method; providing a cover 208; optionally coating the cover 210; and applying a reflective material to one or more sensing areas 212 on the cover using a dry coating method. Some embodiments of the method may also include a polishing step, where one or more sensing areas are polished to achieve a desired spectral reflectivity.

[0040] At 202, a bottom plate can be provided. The bottom plate is a formed bottom plate for use in a photomask cassette. The bottom plate can be any suitable material for the bottom plate of a photomask cassette, as a non-limiting example, such as aluminum. The bottom plate provided at 202 can include all the features of the completed bottom plate, such as walls defining a photomask receiving portion, photomask supports, features for engaging with the cover, features for engaging with automation within a tool for using or manipulating a photomask, and the like, when the bottom plate is provided at 202.

[0041] At 204, the bottom plate can be optionally coated. The coating can be any suitable coating to be applied to the bottom plate, such as a coating for improving appearance, providing abrasion resistance, providing an inert surface compatible with use in a processing tool, or any other desired function of such a coating. The coating applied at 204 can be by a wet coating process, such as plating or any other coating method, including immersing the bottom plate in a liquid. At 204, one or more such coatings can be applied to the bottom plate. One of the coatings applied to the bottom plate at 204 can be nickel.

[0042] In some embodiments, at 206, a dry coating method may be used to apply a reflective material to one or more discrete locations on the bottom plate to form a sensing area. The dry coating method may be any method that does not involve applying a liquid to the bottom plate during coating. As a non-limiting example, the dry coating method may be physical vapor deposition (PVD), sputter deposition, chemical vapor deposition (CVD), and plasma-enhanced chemical vapor deposition (PE-CVD). The one or more sensing areas to which the reflective material is applied at 206 are discrete areas, and these discrete areas constitute less than the entire surface of the bottom plate. The one or more sensing areas may be defined, for example, by a mask applied by a dry coating method during deposition, where the mask only allows deposition on the one or more sensing areas.

[0043] The reflective material applied to the bottom plate at 206 has a known spectral reflectance selected for use in conjunction with a detection system of a tool that includes the bottom plate. The reflective material may be an inert material selected such that it does not react during use of the reticle cassette within the tool. As a non-limiting example, the reflective material may include chromium. The reflective material may be applied to the sensing area such that the sensing area provides a spectral reflectance at one or more predetermined wavelengths within a known predetermined range, such that the light reflected by the sensing area is associated with a specific distance of the inner cassette bottom plate from a reference in the tool (e.g., an extreme ultraviolet (EUV) tool used for processing with a reticle). As a non-limiting example, for at least one of the one or more predetermined wavelengths, the spectral reflectance of each of the sensing areas ranges between approximately 50% and approximately 70%. In an embodiment, each of the sensing areas has a spectral reflectance between approximately 50% and approximately 70% at a wavelength of 880 nm.

[0044] At 208, a cover is provided. The cover is a formed cover for the reticle cassette. The cover may be any suitable material for the reticle cassette cover, as a non-limiting example, such as aluminum. The cover provided at 208 may include all the features of the completed cover, such as walls that define the reticle containment portion, features for engaging with the bottom plate, features for engaging with automation within the tool that uses the reticle, and the like, when the cover is provided at 208.

[0045] Optionally, a cover is coated at 210. The coating can be any suitable coating to be applied to the cover, such as a coating for improving appearance, providing abrasion resistance, providing an inert surface compatible with the use of a photomask for processing, or any other desired function of this coating. The coating applied at 210 can be by a wet coating process, such as plating or any other coating method, including immersing the cover in a liquid. At 210, one or more such coatings can be applied to the cover. The one or more coatings applied at 210 to the cover can be the same coatings as those applied to the bottom plate at 204. The one or more coatings applied at 210 to the cover can include one or more coatings different from the one or more coatings applied to the bottom plate at 204. One of the coatings applied at 210 can be nickel.

[0046] In some embodiments, at 212, a dry coating method can be used to apply a reflective material to one or more discrete locations on the cover to form a sensing region. A dry coating method can be any method that does not include applying a liquid to the cover during coating. As a non-limiting example, a dry coating method can be physical vapor deposition (PVD), sputter deposition, chemical vapor deposition (CVD), and plasma-enhanced chemical vapor deposition (PE-CVD). The one or more sensing regions to which the reflective material is applied at 212 are discrete regions, and these discrete regions make up less than the entire surface of the cover. The one or more sensing regions can be defined by a mask, for example, applied by a dry coating method during deposition, where the mask only allows deposition on the one or more sensing regions.

[0047] The reflective material applied to the cover at 212 has a known spectral reflectance selected for use in conjunction with a detection system of a tool that includes the cover. The reflective material can be an inert material selected such that it does not react when the photomask is being used. As a non-limiting example, the reflective material can include chromium. The reflective material can be applied to the sensing regions such that the sensing regions provide a spectral reflectance at one or more predetermined wavelengths within a known predetermined range to allow the light reflected by the sensing regions to be correlated with a specific distance of the inner box bottom plate from a reference of a tool (such as an extreme ultraviolet (EUV) tool used for processing with a photomask). As a non-limiting example, for at least one of the one or more predetermined wavelengths, the spectral reflectance of each of the sensing regions ranges between approximately 50% and approximately 70%. In an embodiment, each of the sensing regions has a spectral reflectance between approximately 50% and approximately 70% at a wavelength of 880 nm. In some cases, the sensing regions can be polished to achieve the desired spectral reflectivity.

[0048] The bottom plate and the cover processed during method 200 can be used as an inner box of a photomask cassette for containing a photomask, for example, for containing a lithography mask to be used in the extreme ultraviolet (EUV) processing of a wafer.

[0049] Figure 3Disclosed is a photomask cassette including an outer case and an inner case according to an embodiment. The photomask cassette 300 includes an inner case 302, and the inner case 302 includes a lid 304 and a bottom plate 306. The photomask cassette 300 further includes an outer case 308, and the outer case 308 includes an outer case dome 310 and an outer case door 312. The photomask cassette 300 can be used to enclose a photomask 316. The photomask 316 can be any suitable photomask, such as, by way of non-limiting example, a photolithography mask used when processing wafers using extreme ultraviolet (EUV).

[0050] The inner case 302 includes a lid 304 and a bottom plate 306. The lid 304 and the bottom plate 306 are configured to be connected together. The lid 304 and the bottom plate 306 together define an internal space that is sized and shaped to accommodate a photomask, such as a photolithography mask to be used in the extreme ultraviolet (EUV) processing of wafers. In some embodiments, at least one of the lid 304 and the bottom plate 306 may each include one or more sensing regions 314, and the one or more sensing regions 314 are discrete regions including a reflective material. In some embodiments, both the lid 304 and the bottom plate 306 each include one or more of the sensing regions 314. The sensing regions 314 can be the sensing regions 102 and 152 as described above. In the view shown in Figure 3 when viewed from the perspective of Figure 3 the sensing regions 314 along the side surface of the lid 304 are visible, while other sensing regions are hidden by other components. The other sensing regions 304 can be provided, for example, on side or bottom surfaces that are not visible in the perspective view of Figure 3 such as in the positions of the sensing regions 102 and 152 shown in Figure 1A and 1B . The reflective material can be applied to the sensing regions of the lid 304 and the bottom plate 306 by a dry coating process. The lid 304 can be, for example, the lid 150 described above and shown in Figure 1B . The bottom plate 306 can be, for example, the bottom plate 100 described above and shown in Figure 1A .

[0051] The outer case 308 is configured to accommodate the inner case 302 within an internal space defined by the outer case dome 310 and the outer case door 312. For example, during transportation and handling of the photomask cassette 300, the outer case dome can be fastened to the outer case door 312 to enclose the internal space and house the inner case 302. The outer case dome 310 and the outer case door 312 can each include one or more polymer materials or be made entirely of one or more polymer materials.

[0052] Figure 4 A schematic diagram of a photomask cassette in an extreme ultraviolet (EUV) tool according to an embodiment is shown. In the embodiment shown in Figure 4 the inner case 400 is placed into the tool 402.

[0053] The inner case 400 can be any suitable inner case of a photomask case, such as inner case 302, or an inner case including the bottom plate 100 and the cover 150. The inner case 400 includes a plurality of sensing regions 404.

[0054] The tool 402 can be any suitable tool for handling or operating on the inner case 400. As a non-limiting example, the tool 402 can be an extreme ultraviolet (EUV) tool that uses a photomask (such as a lithography mask). The tool 402 can be in a vacuum chamber, where the inner case 400 is removed from an outer case (not shown) and placed into the tool 402 within the vacuum chamber. During use of the photomask in the tool 402, the cover can be removed from the bottom plate of the inner case 400 to expose the photomask contained within the inner case 400. The tool 402 includes a light source 406 and a detector 408. The light source 406 and the detector 408 are positioned such that light provided by the light source 406 can be reflected through the sensing region 404 towards the detector 408, and the light detected at the detector 408 can determine the distance from the inner case 400. The light source can provide light of one or more predetermined wavelengths (as non-limiting examples, including 880 nm). The sensing regions 404 of the inner case 400 can provide a spectral reflectance at one or more predetermined wavelengths within a known predetermined range to allow the light detected at the detector 408 to be correlated with a specific distance from the inner case 400. As a non-limiting example, for at least one of the one or more predetermined wavelengths, the spectral reflectance of each of the sensing regions 404 ranges between approximately 50% and approximately 70%. In an embodiment, each of the sensing regions 404 has a spectral reflectance between approximately 50% and approximately 70% at 880 nm.

[0055] Aspect:

[0056] It should be understood that any one of aspects 1 to 9 can be combined with any one of aspects 10 to 16.

[0057] Aspect 1. A case, comprising:

[0058] A bottom plate having a bottom plate surface, the bottom plate surface including a bottom plate surface material;

[0059] A cover having a cover surface, the cover surface including a cover surface material; and

[0060] One or more discrete sensing regions, each of the sensing regions including a reflective material, the one or more discrete sensing regions being disposed on one or both of the bottom plate surface and the cover surface.

[0061] Aspect 2. The case according to aspect 1, wherein the case is an EUV photomask case.

[0062] Aspect 3. The cassette according to aspect 2, further comprising an outer cassette dome and an outer cassette door, the cassette dome and the cassette door being configured to accommodate the bottom plate and the cover within the cassette dome when the door is attached to the cassette dome.

[0063] Aspect 4. The cassette according to any one of aspects 1 to 3, wherein the reflective material has a spectral reflectance between approximately 50% and approximately 70% at a wavelength of 880 nm.

[0064] Aspect 5. The cassette according to any one of aspects 1 to 4, wherein the reflective material has a reflectance different from the reflectance of the bottom plate surface material.

[0065] Aspect 6. The cassette according to any one of aspects 1 to 5, wherein the reflective material comprises chromium.

[0066] Aspect 7. The cassette according to aspect 6, wherein only the reflective material comprises the chromium.

[0067] Aspect 8. The cassette according to any one of aspects 1 to 7, wherein the one or more sensing regions are positioned such that the distance between the cassette and the detector can be determined from reading the one or more sensing regions.

[0068] Aspect 9. The cassette according to any one of aspects 1 to 8, wherein the bottom plate surface comprises one of aluminum or nickel and the cover surface is one of aluminum or nickel.

[0069] Aspect 10. The cassette according to any one of aspects 1 to 9, wherein each of the bottom plate surface and the cover surface comprises one or more of the discrete sensing regions.

[0070] Aspect 11. A method of manufacturing a photomask cassette, comprising:

[0071] Applying a reflective material to each of one or more discrete sensing regions on either the bottom plate of the photomask cassette or the cover of the photomask cassette using a dry coating process.

[0072] Aspect 12. The method according to aspect 11, wherein the reflective material has a spectral reflectance different from the spectral reflectance of the bottom plate and the spectral reflectance of the cover.

[0073] Aspect 13. The method according to any one of aspects 11 to 12, wherein the reflective material has a spectral reflectance between approximately 50% and approximately 70% at a wavelength of 880 nm.

[0074] Aspect 14. The cassette according to any one of aspects 11 to 13, wherein one of the bottom plate or the lid comprises a surface material, and the reflective material has a reflectivity different from that of the surface material.

[0075] Aspect 15. The method according to any one of aspects 11 to 14, further comprising applying a coating to one of the bottom plate and the lid.

[0076] Aspect 16. The method according to any one of aspects 11 to 15, wherein the dry coating process is selected from the group consisting of physical vapor deposition, sputter deposition, chemical vapor deposition, and plasma enhanced chemical vapor deposition.

[0077] Aspect 17. The method according to any one of aspects 11 to 16, wherein one or more bottom plate sensing regions and one or more lid sensing regions are positioned such that the distance between the cassette and the detector can be determined from reading the one or more bottom plate sensing regions and the one or more lid sensing regions.

[0078] Aspect 18. The method according to any one of aspects 11 to 17, further comprising applying the reflective material to each of one or more discrete sensing regions on the bottom plate of the photomask cassette or the lid of the photomask cassette using the dry coating process.

[0079] The examples disclosed in this application are considered illustrative rather than restrictive in all respects. The scope of the present disclosure is indicated by the appended claims rather than by the foregoing description; and all changes within the meaning and scope of the equivalents of the claims are intended to be embraced therein.

Claims

1. A photomask cassette, comprising: A bottom plate having a bottom plate surface, the bottom plate surface including a bottom plate surface material; A cover having a cover surface, the cover surface including a cover surface material; And A plurality of sensing regions, each of the plurality of sensing regions including a reflective material, wherein the reflective material is applied using a dry coating process, the plurality of sensing regions being disposed on one or both of the bottom plate surface and the cover surface, wherein at least one of the plurality of sensing regions is disposed on the bottom surface of the bottom plate.

2. The photomask cassette according to claim 1, wherein the photomask cassette is an EUV photomask cassette.

3. The photomask cassette according to claim 2, wherein the photomask cassette further includes an outer box dome and an outer box door, the outer box dome and the outer box door being configured to accommodate the bottom plate and the cover within the outer box dome when the outer box door is attached to the outer box dome.

4. The photomask cassette according to claim 1, wherein the reflective material has a reflectivity different from the reflectivity of the bottom plate surface material.

5. The photomask cassette according to claim 1, wherein the reflective material includes chromium.

6. The photomask cassette according to claim 5, wherein only the reflective material includes the chromium.

7. The photomask cassette according to claim 1, wherein the plurality of sensing regions are positioned such that the distance between the photomask cassette and a detector can be determined from reading the plurality of sensing regions.

8. The photomask cassette according to claim 1, wherein the bottom plate surface includes one of aluminum or nickel and the cover surface is one of aluminum or nickel.

9. The photomask cassette according to claim 1, wherein each of the bottom plate surface and the cover surface includes one or more of the plurality of sensing regions.

10. A method of manufacturing a photomask cassette, comprising: Providing a bottom plate and a cover; And Applying a reflective material to each of the plurality of sensing regions on one of the bottom plate of the photomask cassette or the cover of the photomask cassette using a dry coating process, wherein at least one of the plurality of sensing regions is disposed on the bottom surface of the bottom plate.

11. The method according to claim 10, wherein the reflective material has a spectral reflectivity different from the spectral reflectivity of the bottom plate and the spectral reflectivity of the cover.

12. The method according to claim 10, wherein one of the bottom plate or the cover includes a surface material, and the reflective material has a reflectivity different from the reflectivity of the surface material.

13. The method according to claim 10, further comprising applying a coating to one of the bottom plate and the cover.

14. The method according to claim 10, wherein the dry coating process is selected from the group consisting of physical vapor deposition, sputter deposition, chemical vapor deposition, and plasma enhanced chemical vapor deposition.

15. The method according to claim 10, wherein the plurality of sensing regions are positioned such that the distance between the photomask cassette and a detector can be determined from reading one or more sensing regions of the bottom plate and one or more discrete sensing regions of the cover.

16. The method according to claim 10, further comprising polishing the reflective material to achieve a desired reflectivity in the plurality of sensing regions.

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