Optical property evaluation device

Abstract

The present invention provides an optical properties evaluation apparatus for evaluating the optical properties of light-transmitting materials. [Solution] The optical properties evaluation device consists of a light source 10, a photodetector 20, a focusing optical system 30, and an evaluation unit 40. The light source 10 is capable of emitting divergent light. The photodetector 20 is capable of detecting the light intensity distribution of light incident on the detection surface. The focusing optical system 30 causes the light beam from the light source 10 to be incident on the light-transmitting member 1 at a predetermined incident angle to form an illumination spot having a predetermined shape and size on the light-transmitting member 1, and causes the reflected light from the light-transmitting member 1 to be incident on the detection surface of the photodetector 20 to form an image of the light source. The evaluation unit 40 evaluates the reflected light and scattered light from the light-transmitting member 1 based on the light intensity distribution detected by the photodetector 20.

Description

Technical Field

[0003]

[0001] The present invention relates to an optical property evaluation apparatus, and particularly to an optical property evaluation apparatus for evaluating the optical properties of a light transmissive member.

Background Art

[0002] Conventionally, in semiconductor lithography, a pellicle made of a resin thin film has been used as a dust cover for a photomask. When exposing a semiconductor wafer, since the pellicle has a high transmittance with respect to excimer laser ultraviolet light from a light source, the laser passes through the pellicle and the pattern of the photomask is transferred to the semiconductor wafer. Then, the photomask and the pellicle are arranged at separate positions and are out of the depth of focus of the projection optical system, so the image of foreign matter attached to the pellicle is blurred and not transferred to the semiconductor wafer. Thus, the pellicle is useful for preventing manufacturing defects of semiconductor wafers due to foreign matter.

[0003] In recent years, the miniaturization of semiconductor circuit patterns has been progressing in response to the high functionality and high speed of communication systems. For forming fine circuits, an EUV (Extreme Ultraviolet) light source is used. Different from the case of visible light, in the case of EUV light, since the wavelength is extremely short, it is absorbed by the resin thin film, so the resin thin film cannot be used as a pellicle. Therefore, it is necessary to use a material excellent in EUV transmittance. In addition, an EUV light source generates a high-temperature plasma of, for example, 300,000 Kelvin instantaneously by irradiating laser light onto xenon or tin. Such an EUV light source requires an improvement in the numerical aperture (NA) in order to progress the miniaturization of semiconductor circuit patterns. Specifically, an EUV light source with an NA of 0.25 and an EUV light source with an even higher NA of 0.33 are also known. And further progress in increasing the NA has occurred, and an EUV light source with an NA of 0.55 has also emerged. Development of a new material pellicle that can withstand the exposure environment of such an EUV light source and has excellent EUV transmittance has been underway.

[0004] As an apparatus for inspecting pellicles, for example, Patent Document 1 is known. The pellicle inspection apparatus of Patent Document 1 includes an illumination optical system that focuses a solid-state laser light source, which generates a laser beam with a wavelength of 355 nm, which is the third harmonic of a YAG laser, onto the pellicle, and an objective lens having an optical axis perpendicular to the pellicle. It also has a focusing optical system that focuses scattered light emitted from foreign matter present on the pellicle, and a detection system that detects the scattered light focused by the focusing optical system. By providing a photodetector that receives specularly reflected light from the pellicle, contamination formed on the pellicle can also be detected.

[0005] Furthermore, there are also known devices for inspecting photomasks that are irradiated with EUV light from an EUV light source, such as Patent Document 2. In the device for inspecting photomasks described in Patent Document 2, the photomask is irradiated with EUV light from an EUV light source, and the EUV light reflected from the photomask is guided through a projection lens to the image sensor of an EUV camera so that the photomask forms an image on the image sensor. The EUV light then passes through a pellicle placed between the projection lens and the image sensor. That is, the pellicle is placed after the imaging optical system to prevent contaminants from inside the EUV camera from reaching the image sensor. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2015-204339 [Patent Document 2] Japanese Patent Publication No. 2024-125210 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] When evaluating the optical properties of light-transmitting materials such as pellicles, it is important to incident light on the material and evaluate its optical properties, including reflected light, scattered light, and transmitted light relative to the incident light. Scattered light is light that diffuses and spreads around the specularly reflected light. In the case of pellicles used in EUV lithography systems, a problem arises when scattered light from the material spreads and falls within the range of the photomask-side aperture of the projection optical system. Therefore, when evaluating the optical properties of light-transmitting materials, it is necessary to be able to evaluate scattered light within an angular range corresponding to the range of the photomask-side aperture of the projection optical system, but conventionally, there has been no device that can appropriately evaluate such scattered light.

[0008] For example, the apparatus described in Patent Document 1 could detect scattered light emitted from foreign matter present on the pellicle, but it could not evaluate the optical properties of the pellicle itself, such as scattered or reflected light. Furthermore, because it did not use an EUV light source, it could not evaluate the optical properties of the pellicle under EUV light.

[0009] Furthermore, in the apparatus described in Patent Document 2, the pellicle is positioned after the imaging optical system and the photomask is imaged on the image sensor, so it was not possible to evaluate optical properties such as scattered light and reflected light from the pellicle.

[0010] Therefore, there was a need for the development of a device capable of evaluating the optical properties of pellicles used in semiconductor lithography using EUV light sources, which are essential for the formation of microcircuits.

[0011] In view of these circumstances, the present invention aims to provide an optical property evaluation device for evaluating the optical properties of a light-transmitting member. [Means for solving the problem]

[0012] To achieve the above-described objectives of the present invention, the optical property evaluation apparatus according to the present invention may include a light source capable of emitting divergent light, a photodetector capable of detecting the light intensity distribution of light incident on a detection surface, a focusing optical system that causes a light beam from the light source to be incident on a light-transmitting member at a predetermined incident angle to form an irradiation spot having a predetermined shape and size on the light-transmitting member, and causes reflected light from the light-transmitting member to be incident on the detection surface of the photodetector to form an image of the light source, and an evaluation unit that evaluates the reflected and scattered light from the light-transmitting member based on the light intensity distribution detected by the photodetector.

[0013] Here, the focusing optical system consists of a focusing mirror that focuses divergent light from a light source onto the detection surface of a photodetector, and the focusing mirror only needs to be capable of causing the light beam, which is in the process of converging from the focusing mirror, to be incident on a light-transmitting member at a predetermined incident angle, thereby forming an illumination spot on the light-transmitting member.

[0014] Furthermore, the focusing optical system may consist of a first focusing mirror that focuses divergent light from a light source to a predetermined intermediate focusing point and a second focusing mirror that focuses divergent light diverging from the intermediate focusing point onto the detection surface of a photodetector. The first focusing mirror may cause the luminous beam in the process of converging before the intermediate focusing point or the luminous beam in the process of diverging after the intermediate focusing point to be incident on a light-transmitting member at a predetermined incident angle to form an illumination spot on the light-transmitting member, and the second focusing mirror may cause the reflected light from the light-transmitting member to be incident on the detection surface of the photodetector to form an image of the light source.

[0015] Furthermore, the evaluation unit only needs to calculate the reflected light intensity and scattered light intensity, or the reflectance and scattering rate of the light-transmitting member, by separating the reflected light and scattered light within a predetermined range based on the light intensity distribution detected by the photodetector, and integrating the separated light intensity distributions within the predetermined range, respectively.

[0016] Furthermore, the focusing optical system includes an angle-stopping aperture having an aperture that cuts out divergent light from a light source within a predetermined range, and the angle-stopping aperture only needs to be able to change the angle of incidence of the light beam incident on the light-transmitting member by changing the position of its aperture.

[0017] In addition, the light condensing optical system includes an aperture for angular aperture that has an aperture for cutting out the divergent light from the light source within a predetermined range. The aperture for angular aperture can change the size of the irradiation spot formed on the light transmission member by changing the size of its aperture, or can change the shape of the irradiation spot formed on the light transmission member by changing the shape of its aperture.

[0018] Furthermore, it includes a transmitted light detector capable of detecting the light intensity of the transmitted light from the light transmission member that is incident on the detection surface. The evaluation unit may evaluate the transmitted light intensity or transmittance of the light transmission member based on the light intensity of the transmitted light detected by the transmitted light detector.

[0019] Also, the light source is a plasma light source capable of irradiating divergent light with an extreme ultraviolet wavelength, and the light transmission member may be a pellicle used for extreme ultraviolet lithography.

Advantages of the Invention

[0020] In the optical property evaluation apparatus of the present invention, by using a light condensing optical system capable of spatially separating the reflected light and scattered light from the light transmission member, there is an advantage that optical properties such as the reflected light and scattered light of the light transmission member can be appropriately evaluated using the divergent light from the light source. Also, by using the aperture for angular aperture, the incident angle to the light transmission member can be easily changed, so there is an advantage that the optical properties of the light transmission member for different incident angles corresponding to differences in the numerical aperture of the light source can also be easily evaluated.

Brief Description of the Drawings

[0021] [Figure 1] FIG. 1 is a schematic diagram for explaining the optical property evaluation apparatus of the present invention. [Figure 2] FIG. 2 is a schematic diagram for explaining the light incident on the detection surface of the light detector of the optical property evaluation apparatus of the present invention. [Figure 3] FIG. 3 is a graph for explaining the light intensity distribution detected by the light detector of the optical property evaluation apparatus of the present invention. [Figure 4]FIG. 4 is a schematic diagram for explaining the condensing optical system of the optical property evaluation apparatus of the present invention. [Figure 5] FIG. 5 is a schematic diagram for explaining an example in which an aperture for angular aperture is provided in the condensing optical system of the optical property evaluation apparatus of the present invention. [Figure 6] FIG. 6 is a schematic diagram for explaining the aperture of the aperture for angular aperture of the condensing optical system of the optical property evaluation apparatus of the present invention. [Figure 7] FIG. 7 is a schematic diagram for explaining the difference in the size of the irradiation spot with respect to the difference in the size of the aperture of the aperture for angular aperture of the condensing optical system of the optical property evaluation apparatus of the present invention. [Figure 8] FIG. 8 is a schematic diagram for explaining the angular range to be evaluated for the reflected light and scattered light detected by the photodetector of the optical property evaluation apparatus of the present invention. [Figure 9] FIG. 9 is a schematic diagram for explaining another example of the condensing optical system of the optical property evaluation apparatus of the present invention. [Figure 10] FIG. 10 is a schematic diagram for explaining the specific configuration of the optical property evaluation apparatus of the present invention.

Embodiments for Carrying Out the Invention

[0022] Hereinafter, embodiments for carrying out the present invention will be described together with illustrated examples. The optical property evaluation apparatus of the present invention is for evaluating the optical properties of a light transmissive member. FIG. 1 is a schematic diagram for explaining the optical property evaluation apparatus of the present invention. Here, the light transmissive member 1 may be, for example, a pellicle used in extreme ultraviolet lithography. Note that the light transmissive member 1 is not necessarily limited to a pellicle, and any optical filter or the like used for separating spaces having different degrees of vacuum, etc., as long as it is necessary to evaluate the reflected light and scattered light with respect to the incident light from a divergent light source. As shown in FIG. 1, the optical property evaluation apparatus of the present invention mainly includes a light source 10, a photodetector 20, a condensing optical system 30, and an evaluation unit 40.

[0023] The light source 10 is capable of emitting divergent light. Specifically, it could be, for example, a discharge plasma light source or a laser plasma light source. More specifically, it could be an EUV (Extreme Ultraviolet) light source capable of emitting divergent light at EUV wavelengths. Furthermore, the light source 10 may be a light-emitting point, or it may be a virtual light source that includes a light source aperture placed near the divergent light emission point and cuts out the divergent light within a predetermined range. In addition, it is also possible to use a light source that combines a light source with a small divergence angle, such as a high-harmonic light source or a synchrotron radiation light source, with a curved mirror or the like that converts it into divergent light.

[0024] The photodetector 20 is capable of detecting the light intensity distribution of light incident on the detection surface. The photodetector 20 can be, for example, a one-dimensional line sensor or a two-dimensional area sensor. For example, if the light source 10 is an EUV light source, the photodetector 20 can be a CCD camera or CMOS camera that supports EUV light.

[0025] The focusing optical system 30 is used to form an image of the light source 10 on the photodetector 20. Specifically, the focusing optical system 30 is an optical system that causes a light beam from the light source 10 to be incident on the light-transmitting member 1 at a predetermined incident angle to form an illumination spot of a predetermined shape and size on the light-transmitting member 1, and then causes the reflected light from the light-transmitting member 1 to be incident on the detection surface of the photodetector 20 to form an image of the light source. The focusing optical system 30 can be, for example, a focusing mirror. Specifically, it can be a toroidal mirror or a spheroidal mirror, etc. Alternatively, multiple focusing mirrors can be combined to ultimately form an image of the light source 10 on the photodetector 20.

[0026] Figure 2 will be used to explain in more detail the light incident on the detection surface of the photodetector 20. Figure 2 is a schematic diagram illustrating the light incident on the detection surface of the photodetector of the optical characteristic evaluation apparatus of the present invention. In the figure, parts with the same reference numerals as in Figure 1 represent the same objects. The light beam from the light source 10 is incident on the light-transmitting member 1 as focused light by the focusing optical system 30, and an irradiation spot S is formed on the light-transmitting member 1 as shown in the figure. In the light-transmitting member 1, the light is divided into transmitted light, reflected light, and scattered light. The reflected light from the light-transmitting member 1 is imaged on the detection surface of the photodetector 20. That is, the image of the light source 10 is imaged on the photodetector 20. On the other hand, the scattered light scattered by the light-transmitting member 1 reaches the photodetector 20 but does not form an image because the direction of the light ray changes. Therefore, the reflected light and scattered light are detected by the photodetector 20 as predetermined light intensity distributions.

[0027] Figure 3 is a graph illustrating the light intensity distribution detected by the photodetector of the optical property evaluation apparatus of the present invention. The graph in Figure 3 shows the light intensity as a function of position on the detection surface of the photodetector. When the image of the light source 10 is imaged onto the photodetector 20 using the focusing optical system 30, as shown in Figure 3, the reflected light has a narrow angular distribution and high intensity, while the scattered light has a wide angular distribution and low intensity. Therefore, the reflected light and scattered light can be spatially separated. However, if the light beam from the light source is imaged onto a light-transmitting member using the focusing optical system, the distribution of the reflected light on the detection surface of the photodetector 20 becomes wider and the intensity decreases, and the reflected light and scattered light can no longer be spatially separated.

[0028] Referring again to Figure 1, the evaluation unit 40 evaluates the reflected and scattered light from the light-transmitting member 1 based on the light intensity distribution detected by the photodetector 20 as described above. As shown in Figure 3, since the reflected and scattered light from the light-transmitting member 1 are spatially separated, it is possible to easily separate the reflected and scattered light on the detection surface of the photodetector 20. For example, it is possible to separate the angular range of light with a predetermined light intensity or higher as reflected light, and the angular range of light with a predetermined light intensity around that as scattered light. Therefore, the evaluation unit 40 can calculate the reflected light intensity and scattered light intensity of the light-transmitting member 1 by separating the reflected and scattered light in predetermined ranges based on the light intensity distribution and integrating the separated light intensity distributions, respectively. Alternatively, if the divergent light from the light source 10 is appropriately separated by a beam splitter or the like to obtain the incident light intensity, the evaluation unit 40 may determine the reflectance by dividing the reflected light intensity by the incident light intensity. Similarly, the scattering rate may be determined by dividing the scattered light intensity by the incident light intensity.

[0029] Thus, the optical property evaluation apparatus of the present invention uses a focusing optical system 30 that can form an image of the light source 10 on a photodetector 20 and spatially separate the reflected light and scattered light from the light-transmitting member 1. This makes it possible to appropriately evaluate the optical properties of the light-transmitting member 1, such as the reflected light and scattered light, using the divergent light from the light source 10.

[0030] The focusing optical system 30 of the optical property evaluation apparatus of the present invention will be described in more detail below using Figure 4. Figure 4 is a schematic diagram illustrating the focusing optical system of the optical property evaluation apparatus of the present invention. In the figure, components with the same reference numerals as in Figure 1 represent the same components. For explanatory purposes, the focusing mirror is replaced with a refractive lens having equivalent function. Also, to make the light incident on the photodetector 20 easier to understand, reflected light and scattered light are represented as transmitted light. As shown in the figure, divergent light from the light source 10 is cut out to a predetermined range by the light source aperture 11 and emitted. Of course, it is also possible to use a light source 10 that is cut out to a predetermined range in advance and emitted. The emitted divergent light is incident on the focusing mirror 31 that constitutes the focusing optical system 30. The focusing mirror 31 focuses the divergent light from the light source 10 onto the detection surface of the photodetector 20. As a result, the image of the light source 10 is imaged onto the photodetector 20. Therefore, it is possible to reduce the size of the spot of the image of the light source 10 that is imaged onto the detection surface of the photodetector 20. The focusing mirror 31 is configured to direct the light beam from the focusing mirror 31 onto the light-transmitting member 1 at a predetermined incident angle, thereby forming an illumination spot S on the light-transmitting member 1. In other words, the light-transmitting member 1 to be evaluated is positioned at a predetermined angle to the light beam in the process of convergence.

[0031] The light-transmitting member 1 should be arranged on a stage that is movable in one or two axes, and should be configured to allow for the evaluation of its optical properties by scanning it to sequentially form irradiation spots S across the entire area of ​​the light-transmitting member 1.

[0032] In semiconductor lithography using an EUV light source and an EUV projection optical system, the angle of incidence to the EUV photomask is determined by conditions such as the numerical aperture (NA) of the EUV projection optical system. Therefore, in the optical property evaluation apparatus of the present invention, the light-transmitting member 1 can be evaluated using the angle of incidence to the EUV photomask actually used. Here, the angle of incidence to the EUV photomask changes depending on the NA of the EUV projection optical system. Specifically, for example, when the NA is 0.33, the angle of incidence is set to 6 degrees, and when the NA is 0.55, the angle of incidence is set to 5.3 degrees. Therefore, in the optical property evaluation apparatus of the present invention, if the light-transmitting member 1 can be evaluated using the angle of incidence to the EUV photomask actually used depending on the EUV light source, it becomes possible to evaluate the optical properties appropriately in an environment similar to the actual usage environment of the light-transmitting member 1. That is, if the angle of incidence is configured to be changeable, it becomes possible to evaluate the optical properties appropriately according to the projection optical system of the exposure machine. For example, it is certainly possible to change the angle of the stage for positioning the light-transmitting member 1 in order to change the angle of incidence. However, changing the stage angle depends on mechanical precision and also requires changes to mechanisms such as the transport system that mounts the light-transmitting member 1 on the stage, making it not easy. Therefore, as described below, the present invention makes it possible to easily change the incident angle to the light-transmitting member 1 without changing the stage angle by using an angle aperture in the focusing optical system.

[0033] Figure 5 is a schematic diagram illustrating an example in which an angle-stopping aperture is provided in the focusing optical system of the optical characteristic evaluation apparatus of the present invention. In the figure, parts with the same reference numerals as in Figure 4 represent the same components. Also, as in Figure 4, in Figure 5, for explanatory purposes, reflected light and scattered light are replaced with transmitted light to make the light incident on the photodetector 20 easier to understand. The angle-stopping aperture 32 is used to change the incident angle to the light-transmitting member 1. As shown in the figure, diverging light emitted from the light source 10 is incident on the focusing mirror 31 that constitutes the focusing optical system 30. In this illustrated example, the focusing optical system 30 further has an angle-stopping aperture 32. The angle-stopping aperture 32 has an opening that cuts out the diverging light from the light source 10 within a predetermined range. In the illustrated example, an example in which the angle-stopping aperture 32 is provided before the focusing mirror 31 is shown, but the present invention is not limited to this, and the angle-stopping aperture 32 may be provided after the focusing mirror 31.

[0034] The aperture of the angle diaphragm aperture will be explained using Figure 6. Figure 6 is a schematic diagram illustrating the aperture of the angle diaphragm aperture of the focusing optical system of the optical characteristic evaluation device of the present invention. The illustrated example shows the angle diaphragm aperture 32 as seen from the light source 10 side. As shown in Figure 6(a), the angle diaphragm aperture 32 has an opening 32a at a position offset from the center. By rotating the angle diaphragm aperture 32 having such an opening 32a 180 degrees up and down, it is possible to change the position of the opening 32a as shown in Figure 6(b). Referring again to Figure 5, it can be seen that the angle of incidence to the light transmitting member 1 differs depending on the position of the incident light beam. For example, it can be seen that the angle of incidence of the light beam incident to the light transmitting member 1 changes depending on whether the opening 32a of the angle diaphragm aperture 32 is on the upper side, i.e., configured as in Figure 6(a), or on the lower side, i.e., configured as in Figure 6(b). In other words, the angle of incidence to the light-transmitting member 1 can be changed by changing the position of the opening 32a of the angle-reducing aperture 32. Specifically, for example, the opening 32a can be configured such that the angle of incidence is 5.3 degrees when in the position shown in Figure 6(a), and 6 degrees when rotated 180 degrees vertically to the position shown in Figure 6(b).

[0035] Furthermore, as shown in Figures 6(c) and 6(d), the size of the aperture 32 for angle diaphragm use may be changed. That is, it may be a larger aperture 32b compared to the aperture 32a shown in Figures 6(a) and 6(b). This difference in aperture size manifests as a difference in the size of the illumination spot formed on the light-transmitting member 1. Figure 7 is a schematic diagram illustrating the difference in illumination spot size for different aperture sizes of the angle diaphragm aperture of the focusing optical system of the optical characteristic evaluation apparatus of the present invention. The illustrated example shows the illumination spot S on the light-transmitting member 1 as seen from the light source 10 side. When the angle diaphragm aperture 32 has an aperture 32a as shown in Figures 6(a) and 6(b), an illumination spot S corresponding to the size of the aperture 32a is formed on the light-transmitting member 1, as shown in Figures 7(a) and 7(b). On the other hand, if the angle diaphragm aperture 32 has a large opening 32b as shown in Figures 6(c) and 6(d), the size of the illumination spot S increases accordingly, as shown in Figures 7(c) and 7(d). Thus, the angle diaphragm aperture 32 makes it possible to change the size of the illumination spot S formed on the light-transmitting member 1 by changing the size of its opening. Therefore, for example, if it is desired to evaluate a part of the light-transmitting member 1 in detail, the size of the illumination spot S can be reduced to increase the detection resolution on the surface of the light-transmitting member 1. Alternatively, the size of the illumination spot S can be increased to reduce the detection resolution on the surface of the light-transmitting member 1, thereby completing the scanning of the entire area of ​​the light-transmitting member 1 in a short time. Note that, as shown in Figure 7, the position where the illumination spot S is formed also changes depending on the position of the opening of the angle diaphragm aperture 32, but position calibration can be performed as appropriate if it is desired to match the positions.

[0036] Similarly, the angle-stabilizing aperture 32 can also change the shape of the illumination spot S formed on the light-transmitting member 1 by changing the shape of its opening. For example, if the opening is square instead of circular, the shape of the illumination spot S will also be square. Therefore, by making the shape of the opening of the angle-stabilizing aperture 32 square, it becomes possible to arrange the illumination spots S in a grid pattern, for example, when scanning the entire area of ​​the light-transmitting member 1, enabling efficient scanning without gaps. Furthermore, if the shape of the opening is rectangular enough to cover the width of the light-transmitting member 1, it is possible to configure the system to complete scanning a wide area of ​​the light-transmitting member 1 in a single-axis scan.

[0037] Thus, in the optical property evaluation apparatus of the present invention, it is possible to easily adapt to conditions such as the angle of incidence and the range of reflected and scattered light to be evaluated for the optical properties of the light-transmitting member 1 by arbitrarily switching only the angle aperture 32. The angle aperture 32 can be switched by rotating the angle aperture 32, which has one opening, 180 degrees up and down as described above, or several types of apertures can be prepared. Furthermore, a single angle aperture 32 with several types of apertures can be configured to be rotatable, and the unnecessary apertures can be covered with a shutter film or the like while exposing only the necessary apertures, thereby allowing the switching of several types of apertures to be performed.

[0038] Figure 8 is a schematic diagram illustrating the angular range to be evaluated for reflected and scattered light detected by the photodetector of the optical property evaluation apparatus of the present invention. The illustrated example shows the reflected light on the detection surface of the photodetector 20 and the scattered light around it. In this example, the distance from the light-transmitting member 1 to the detection surface of the photodetector 20 is specifically set to 150 mm. As described above, in the optical property evaluation apparatus of the present invention, reflected light and scattered light can be spatially separated, and the range with high light intensity in a narrow angular distribution can be determined as reflected light. Therefore, as shown in Figure 8(a), the reflected light can specifically be in a range of, for example, φ0.3 mm. On the other hand, scattered light spreads around the reflected light, but the angular range of scattered light to be evaluated can be as long as it corresponds to the range of the photomask-side aperture of the projection optical system. Specifically, this range can be, for example, φ12.4 mm (the value obtained by multiplying the tangent of 4.73 degrees by the distance of 150 mm from the light-transmitting member 1 to the detection surface of the photodetector 20). In other words, depending on the angular range in which scattered light should be evaluated, a predetermined angular range can be extracted, and the light intensity distribution of that predetermined angular range can be extracted by the evaluation unit 40 to evaluate the scattered light. Furthermore, the angular range of the scattered light is not necessarily limited to a circle; as shown in Figure 8(b), the angular range can be changed for the x-axis and y-axis directions. That is, the light intensity distribution can be evaluated with an angular range of 3.94 degrees in the x-axis direction and 7.9 degrees in the y-axis direction. Thus, the angular range of the scattered light can be arbitrarily set on the evaluation unit 40 side.

[0039] Here, the illustrated examples described above, specifically those shown in Figures 4 and 5, describe a configuration in which the focusing optical system 30 is configured to cause the intermittent light beam from the focusing mirror 31 to be incident on the light-transmitting member 1 at a predetermined incident angle, thereby forming an illumination spot S on the light-transmitting member 1. However, the present invention is not limited to this. Figure 9 is a schematic diagram illustrating another example of the focusing optical system of the optical characteristic evaluation apparatus of the present invention. In the figure, components with the same reference numerals as in Figure 5 represent the same components. For illustrative purposes, the diagram is shown in which the focusing mirror is replaced with a refractive lens having equivalent function. Also, to make the light incident on the photodetector 20 easier to understand, reflected light and scattered light are represented as transmitted light. As shown in the figure, the divergent light emitted from the light source 10 is incident on the first focusing mirror 31a constituting the focusing optical system 30. The first focusing mirror 31a focuses the divergent light from the light source 10 to a predetermined intermediate focal point C. Furthermore, a second focusing mirror 31b is provided to focus the divergent light emitted from the intermediate focusing point C onto the detection surface of the photodetector 20. In the illustrated example, the first focusing mirror 31a is configured to cause the divergent light beam after the intermediate focusing point C to be incident on the light-transmitting member 1 at a predetermined incident angle, thereby forming an illumination spot S on the light-transmitting member 1. The second focusing mirror 31b is configured to cause the reflected light from the light-transmitting member 1 to be incident on the detection surface of the photodetector 20, thereby forming an image of the light source 10. As a result, the image of the light source 10 is formed on the photodetector 20. Thus, in the optical characteristic evaluation apparatus of the present invention, the light beam incident on the light-transmitting member 1 may be not only a divergent light beam but also a divergent light beam. In the illustrated example, an example is shown in which the divergent light beam after the intermediate focusing point C is incident on the light-transmitting member 1, but it may also be configured in which the divergent light beam before the intermediate focusing point C is incident on the light-transmitting member 1.

[0040] Next, the specific configuration of the optical property evaluation apparatus of the present invention will be described using Figure 10. Figure 10 is a schematic diagram illustrating the specific configuration of the optical property evaluation apparatus of the present invention. In the figure, parts with the same reference numerals as those in Figure 1 and Figure 5 represent the same components. In the illustrated example, a wavelength selection filter 12 is provided so that the wavelength of light from the light source 10 can be appropriately selected. The light-transmitting member 1 is shown to be placed on a stage 2 that can move in one or two axes. The condensing optical system 30 in the illustrated example is shown to bend the light beam using bending mirrors 33 and 34. Such bending mirrors 33 and 34 can be used as appropriate when the light beam cannot be bent due to limitations in the physical size of the photodetector 20 and the light-transmitting member 1. By bending the light beam with bending mirrors, it becomes possible to use the photodetector 20 even when the detection surface is small, thus making it possible to miniaturize the entire apparatus.

[0041] The illustrated example further includes a transmitted light detector 50. The transmitted light detector 50 is capable of detecting the light intensity of transmitted light from the light-transmitting member 1 incident on its detection surface. Specifically, the transmitted light detector 50 may be, for example, a photodiode. It may also be a CCD camera or a CMOS camera. The evaluation unit 40 should be configured to evaluate the transmitted light intensity or transmittance of the light-transmitting member 1 based on the light intensity of the transmitted light detected by the transmitted light detector 50. When evaluating transmittance, the transmitted light intensity should be divided by the incident light intensity. For example, the light intensity at the transmitted light detector 50 depending on the presence or absence of the light-transmitting member 1 may be used. However, the intensity of the light source 10 may fluctuate over time. Therefore, as shown in the illustrated example, the light beam from the light source 10 should be split by the beam splitter 35, and the incident light intensity should be constantly monitored by the beam monitor detector 36. This makes it possible to obtain a transmittance that compensates for time fluctuations. Furthermore, when determining the reflectance and scattering rate in the evaluation unit 40, if the reflectance and scattering rate are determined using the reflected light intensity and scattered light intensity detected by the photodetector 20 and the incident light intensity detected by the beam monitor detector 36, evaluation values ​​that compensate for time variations can be obtained.

[0042] The following describes the procedure for evaluating the optical properties of the light-transmitting member 1 using the optical property evaluation apparatus of the present invention. The evaluation procedure will be described using the apparatus configuration shown in Figure 10 as an example. First, the sensitivity of each detector—the photodetector 20, the transmitted light detector 50, and the beam monitor detector 36—is calibrated. This can be done, for example, by detecting EUV light from the light source 10 with each detector before installing the light-transmitting member 1, and then calibrating the photodetector 20 or the evaluation unit 40 that processes the signal from the photodetector 20 so that the same light intensity measurement value is obtained. Next, the light-transmitting member 1, such as a pellicle, to be evaluated for optical properties is placed on the stage 2. The stage 2 moves the light-transmitting member 1 to the measurement start position, and the angle aperture 32 irradiates the light-transmitting member 1 with EUV light from the light source 10 for a predetermined time at a predetermined incidence angle. Then, the light intensity of the light reaching the photodetector 20, the transmitted light detector 50, and the beam monitor detector 36 is detected. Specifically, the photodetector 20 detects the light intensity distribution of reflected and scattered light from the light-transmitting member 1 as shown in Figure 3. Furthermore, the transmitted light detector 50 detects the light intensity of the light transmitted from the light-transmitting member 1. The beam monitor detector 36 detects the light intensity of the EUV light from the light source 10. Using the detection results from each of these detectors, the evaluation unit 40 calculates the reflectance, transmittance, and scattering rate, respectively. After that, the stage 2 on which the light-transmitting member 1 is placed is moved to move the position where the irradiation spot is formed so as to scan the light-transmitting member 1. Then, the light-transmitting member 1 is irradiated with light from the light source 10 again for a predetermined time. These procedures are repeated to scan the entire area of ​​the light-transmitting member 1. Furthermore, in the optical property evaluation apparatus of the present invention, after scanning the entire area of ​​the light-transmitting member 1 is complete, the evaluation unit 40 can also calculate the reflectance distribution, scattering rate distribution, and transmittance distribution for the entire area. This makes it possible to evaluate the in-plane distribution, such as whether the reflectance, scattering rate, and transmittance are uniform across the entire area of ​​the light-transmitting member 1. Once these evaluations are complete, the light-transmitting member 1 is removed from the stage 2, and the evaluation procedure is terminated.

[0043] Furthermore, the optical property evaluation apparatus of the present invention can also evaluate the temporal changes in the optical properties of the light-transmitting member 1 when it is irradiated with EUV light from the light source 10 for a long period of time. Therefore, it is also possible to evaluate the durability of the light-transmitting member 1.

[0044] Here, we will explain the specific processing of the detected data for reflectance, scattering, and transmittance. First, as described above, we use a photodetector 20, a transmitted light detector 50, and a beam monitor detector 36 that have been calibrated to have the same sensitivity. When EUV light is irradiated from the light source 10 without the light-transmitting member 1, the output of the beam monitor detector 36 is defined as PD0, and the output of the transmitted light detector 50 is defined as A0. Next, when the light-transmitting member 1 is placed and EUV light from the light source 10 is irradiated onto the light-transmitting member 1 at a predetermined incident angle, the output of the beam monitor detector 36 is defined as PD1, the output of the transmitted light detector 50 is defined as A1, the central output of the photodetector 20 is defined as BR1, and the peripheral output is defined as BS1. That is, the central output BR1 corresponds to the reflected light intensity distribution, and the peripheral output BS1 corresponds to the scattered light intensity distribution. Using these outputs, the evaluation unit 40 can determine the reflectance, scattering, and transmittance using the following formulas. Reflectance=PD0 / PD1*BR1 / A0 Scattering rate=PD0 / PD1*BS1 / A0 Transmittance=PD0 / PD1*A1 / A0

[0045] It should be noted that the optical property evaluation apparatus of the present invention is not limited to the illustrated examples described above, and various modifications can be made without departing from the spirit of the present invention. [Explanation of Symbols]

[0046] 1 Light-transmitting member 2 stages 10 light source 11 Light source aperture 12 wavelength selective filters 20 Photodetectors 30 Focusing Optical System 31. Focusing mirror 31a First focusing mirror 31b Second focusing mirror 32a,32b opening 32-degree aperture for angle diaphragm 33,34 Folding mirror 35 Beam Splitter 36 Beam monitor detector 40 Evaluation Department 50 Transmitted light detector

Claims

1. An optical properties evaluation apparatus for evaluating the optical properties of a light-transmitting member, wherein the optical properties evaluation apparatus is A light source capable of emitting divergent light, A photodetector capable of detecting the light intensity distribution of light incident on the detection surface, A focusing optical system for causing a light beam from the light source to be incident on a light-transmitting member at a predetermined incident angle to form an illumination spot having a predetermined shape and size on the light-transmitting member, and causing the reflected light from the light-transmitting member to be incident on the detection surface of a photodetector to form an image of the light source, An evaluation unit that evaluates reflected and scattered light from a light-transmitting member based on the light intensity distribution detected by the photodetector, An optical properties evaluation apparatus characterized by comprising the following:

2. In the optical property evaluation apparatus according to claim 1, The aforementioned focusing optical system consists of a focusing mirror that focuses divergent light from a light source onto the detection surface of a photodetector. The aforementioned focusing mirror causes the light beam, which is in the process of converging from the focusing mirror, to be incident on a light-transmitting member at a predetermined incident angle, thereby forming an illumination spot on the light-transmitting member. An optical properties evaluation apparatus characterized by the following features.

3. In the optical property evaluation apparatus according to claim 1, The aforementioned focusing optical system comprises a first focusing mirror that focuses divergent light from a light source to a predetermined intermediate focusing point, and a second focusing mirror that focuses divergent light emitted from the intermediate focusing point onto the detection surface of a photodetector. The first focusing mirror causes the light beam, which is converging before the intermediate focusing point or diverging after the intermediate focusing point, to be incident on the light-transmitting member at a predetermined incident angle, thereby forming an illumination spot on the light-transmitting member. The second focusing mirror causes reflected light from the light-transmitting member to be incident on the detection surface of the photodetector to form an image of the light source. An optical properties evaluation apparatus characterized by the following features.

4. An optical property evaluation apparatus according to claim 1, wherein the evaluation unit separates reflected light and scattered light within a predetermined range based on the light intensity distribution detected by a photodetector, and calculates the reflected light intensity and scattered light intensity, or the reflectance and scattering rate of a light-transmitting member, by integrating the separated light intensity distributions within the predetermined range.

5. In the optical property evaluation apparatus according to claim 1, the focusing optical system comprises an angle aperture having an aperture that cuts out divergent light from a light source within a predetermined range, The angle-reducing aperture can change the incident angle of the light beam incident on the light-transmitting member by changing the position of its opening. An optical properties evaluation apparatus characterized by the following features.

6. In the optical property evaluation apparatus according to claim 1, the focusing optical system comprises an angle aperture having an aperture that cuts out divergent light from a light source within a predetermined range, The optical properties evaluation apparatus is characterized in that the angle aperture can change the size of the illumination spot formed on the light-transmitting member by changing the size of its opening, or the shape of the illumination spot formed on the light-transmitting member by changing the shape of its opening.

7. An optical property evaluation apparatus according to claim 1, further comprising a transmitted light detector capable of detecting the light intensity of transmitted light from a light-transmitting member incident on a detection surface, The evaluation unit evaluates the transmitted light intensity or transmittance of the light-transmitting member based on the light intensity of the transmitted light detected by the transmitted light detector. An optical properties evaluation apparatus characterized by the following features.

8. In the optical property evaluation apparatus according to any one of claims 1 to 7, The aforementioned light source is a plasma light source capable of emitting divergent light of extreme ultraviolet wavelengths. The light-transmitting material is a pellicle used in extreme ultraviolet lithography. An optical properties evaluation apparatus characterized by the following features.

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