Optical device, mask inspection device, and inspection method for reflection-type mask

Abstract

An optical device (10) includes: an illumination optical system (12) that illuminates a surface of an object (20) with illumination light (L1) from a light source (11); and an image forming optical system (13) that forms light from the surface illuminated by the illumination optical system (12) into an image. The image forming optical system (13) includes a concave reflection mirror (PM1) that has formed therein an opening (15) which allows therethrough illumination light from a final optical member (IOF), which is disposed closest to the object (20) side among optical members constituting the illumination optical system (12) in an illumination optical path of the illumination optical system (12), and that condenses light (L2) from the surface. A reflection surface (16) of the concave reflection mirror (PM1) is formed around the opening (15).

Description

Optical device, mask inspection device, and inspection method for reflective mask

[0001] The present invention relates to an optical device, a mask inspection device using the same, and an inspection method for a reflective mask.

[0002] In recent years, with the progress of miniaturization of semiconductor integrated circuit elements, in order to improve the resolution of an optical system limited by the diffraction limit of light, a reduction projection lithography technique using soft X-rays with a shorter wavelength instead of conventional ultraviolet rays has been developed. Since there is no transparent substance in this wavelength range, a reflective mask is used instead of a conventional transmissive mask, and a reflective optical system is also used for the optical system. Patent Document 1 describes a reflective optical device using extreme ultraviolet (EUV) light, which is a type of soft X-ray, as a light source. In such an inspection of defects in a reflective mask, it is desired to capture as much light as possible from the reflective mask to be inspected and improve the detection accuracy of the inspection device.

[0003] U.S. Patent No. 7,679,731

[0004] The first optical device includes an illumination optical system that illuminates the surface of an object with illumination light from a light source, and an imaging optical system that forms an image of light from the surface illuminated by the illumination optical system. The imaging optical system includes an aperture that allows illumination light from the final optical member disposed closest to the object side in the illumination optical path of the illumination optical system among the optical members constituting the illumination optical system to pass through, and a concave mirror that condenses light from the surface. The reflecting surface of the concave mirror is formed around the aperture.

[0005] The second optical device comprises an illumination optical system that illuminates the surface of an object with illumination light from a light source, and an imaging optical system that forms an image of the light from the surface illuminated by the illumination optical system, wherein the imaging optical system has an opening formed therein that allows illumination light from the final optical member, which is located on the surface side in the illumination light path of the illumination optical system, to pass through, and includes a concave reflector that focuses the light from the surface, the exit pupil of the illumination optical system is located at the entrance pupil of the imaging optical system, and the illumination light passage range through which the illumination light from the illumination optical system passes is located inside the entrance pupil of the imaging optical system.

[0006] The third mask inspection device is an inspection device for inspecting a reflective mask, and comprises the optical device described above for inspecting the reflective mask as the object.

[0007] A fourth inspection method for inspecting a reflective mask includes placing the reflective mask on the object surface of the optical device described above, illuminating a part of the reflective mask with illumination light from the illumination optical system of the optical device, causing the light from the illuminated reflective mask to enter the imaging optical system of the optical device, and detecting the light from the reflective mask via the imaging optical system.

[0008] This is a schematic diagram showing the configuration of the mask inspection apparatus according to this embodiment. This is a schematic cross-sectional view of a reflective mask used in the optical apparatus according to this embodiment. This is a schematic cross-sectional view of the reflective mask used in the optical apparatus according to this embodiment during exposure. This is a schematic cross-sectional view of the reflective mask used in the optical apparatus according to this embodiment during inspection. This is a schematic diagram showing the configuration of the optical apparatus according to the first embodiment. This is a schematic diagram showing a part of the configuration of the optical apparatus according to this embodiment. This is a plan view of the concave reflector according to this embodiment. This is a schematic diagram showing the configuration of the optical apparatus according to the second embodiment. This is a schematic diagram showing the configuration of the optical apparatus according to the third embodiment. This is a flowchart showing the inspection method for a reflective mask.

[0009] Preferred embodiments of the present invention will be described below. First, the mask inspection apparatus 100 according to this embodiment will be described with reference to Figure 1. The mask inspection apparatus 100 is an apparatus for inspecting reflective masks used in exposure apparatuses, and detects defects in reflective masks by bright-field illumination using a reflective optical system. The mask inspection apparatus 100 consists of a light source 11 that generates illumination light including EUV light, an illumination optical system 12, an imaging optical system 13, a detector 14, and a stage 41. A reflective mask, which is the object to be inspected 20, is held on the stage 41. In the following description, the reflective mask, which is the object to be inspected 20, will be referred to as the reflective mask 20 as needed.

[0010] Light L1 emitted from the light source 11 illuminates the reflective mask 20 with the illumination optical system 12. Light L2 from the illuminated reflective mask 20 is imaged onto the detection surface 14a of the detector 14 by the imaging optical system 13. The detection surface 14a is, for example, a sensor. The detector 14 may be connected to an analysis device (not shown) and configured to detect defects in the reflective mask 20 by analyzing phase shifts caused by defects using the analysis device. In the mask inspection device 100, the illumination optical system 12 and the imaging optical system 13, which are included in the area enclosed by the dashed line in Figure 1, constitute the optical device 10 according to this embodiment.

[0011] The mask inspection device 100 may be configured to be housed in a housing 101 as shown in Figure 1. The housing 101 consists of a light source unit 30, an optical system chamber 40, and a connecting passage 50, with the light source unit 30 and the optical system chamber 40 connected via the connecting passage 50. Figure 1 is an example, in which the illumination optical system 12 is configured to extend from the light source unit 30 through the connecting passage 50 to a part of the optical system chamber 40. The imaging optical system 13, the stage 41 on which the reflective mask 20 is placed, and the detector 14 are housed within the optical system chamber 40. Note that the detailed configurations of the illumination optical system 12 and the imaging optical system 13 are omitted in Figure 1. Also, the configurations of the illumination optical system 12 and the imaging optical system 13 shown in Figure 1 are illustrative diagrams and do not represent the exact configuration of the optical systems. These detailed configurations will be described later along with the description of the optical device 10.

[0012] The stage 41 on which the reflective mask 20 is placed is connected to a drive device (not shown) and is configured to be movable up, down, left, and right. This allows for illumination of any position on the reflective mask 20 for inspection.

[0013] The light from the light source 11 uses light with wavelengths of 10 nm to 15 nm, such as soft X-rays, and EUV light with a wavelength of 13.5 nm, which are the same as or near the wavelengths used for exposing circuit patterns onto wafers. Since soft X-rays are absorbed by the atmosphere, the inside of the light source unit 30 and the optical system chamber 40 must be kept under vacuum. For this reason, the light source unit 30 and the optical system chamber 40 are connected to a vacuum pump (not shown). In addition, the connecting passage 50 that connects the light source unit 30 and the optical system chamber 40 is made of vacuum piping. With this configuration, the light from the light source 11 propagates from the light source unit 30, which is kept under vacuum, through the connecting passage 50 to the optical system chamber 40. The light source 11 may be an LPP (Laser Produced Plasma) type light source disclosed in US2024 / 0074022A1, or a DPP (Discharge Produced Plasma) type light source or an LDP (Laser-assisted Discharge Plasma) type light source may be used.

[0014] The object to be inspected 20 is a reflective mask used in the semiconductor lithography process. The reflective mask 20 will be explained with reference to Figures 2, 3A, and 3B.

[0015] Figure 2 shows a schematic cross-sectional view of the reflective mask 20. The reflective mask 20 is formed by depositing a reflective film 22 that reflects light of a predetermined wavelength (for the purposes of this explanation, let's assume it's soft X-rays) on a mask substrate 21 having sufficient strength and surface smoothness, and then forming a predetermined circuit pattern shape on top of that with an absorber 23 made of a material that absorbs soft X-rays. The reflective film 22 is formed, for example, by an alternating layered multilayer film of Mo (molybdenum) and Si (silicon). By irradiating such a reflective mask 20 with exposure illumination light, the circuit pattern formed on the reflective mask 20 is imaged onto a wafer coated with photoresist and transferred to the photoresist. Figure 3A is a side view of the reflective mask 20 in a coordinate system based on the reflective mask 20. In Figure 3A, for example, the exposure illumination light La is irradiated at an angle r1 tilted with respect to the normal h to the surface (pattern formation surface) of the reflective mask 20. By illuminating the reflective mask from an oblique angle in this way, the optical paths of the light incident on the reflective mask and the light reflected by the reflective mask can be separated.

[0016] The mask inspection device 100 is a device for inspecting defects in a reflective mask 20 used in such an exposure device. When irradiating the reflective mask 20 during inspection, it is desirable to use light with the same wavelength or a nearby wavelength as the exposure illumination light La. This creates conditions similar to those during circuit pattern exposure, allowing for accurate detection of defects in the reflective mask 20. Figure 3B is a side view of the reflective mask in a coordinate system based on the reflective mask 20. The incidence angle r2 of the inspection illumination light Lb shown in Figure 3B onto the reflective mask 20 may be the same as the exposure angle r1, or it may be slightly different. This incidence angle r2 will be described in more detail in the description of the optical device 10.

[0017] In Figures 3A and 3B, for explanatory purposes, the coordinate system is shown with the reflective mask 20 as the reference point, with the width direction as the Ym direction, the thickness direction perpendicular to the Ym direction as the Zm direction, and the depth direction perpendicular to both the Xm and Ym directions as the Xm direction.

[0018] Next, the configuration of the optical device 10 of this embodiment used in such a mask inspection device 100 will be described. Note that the same combination of reference numerals and numbers is used for each component of each embodiment that has the same role, but this does not mean that they have the same configuration.

[0019] <First Embodiment> Figure 4 shows the configuration of the optical device 10(1) according to the first embodiment. The optical device 10(1) includes an illumination optical system 12 that irradiates the object to be inspected 20 with light L1 from a light source 11, and an imaging optical system 13 that forms an image of the light L2 irradiated onto the object to be inspected 20 and reflected by the object to be inspected 20 on the detection surface 14a of the detector 14.

[0020] In the optical device 10, the light source 11 is soft X-rays such as EUV light, and the optical system is composed of a reflective system. Therefore, in order to reflect soft X-rays of a predetermined wavelength, a multilayer reflective film is formed on the reflective surfaces of the optical components that make up the optical system. Examples of reflective films used include alternating multilayer films of Mo (molybdenum) and Si (silicon), alternating multilayer films of Mo and SiC (silicon carbide), and alternating multilayer films of Ru (ruthenium) and Si.

[0021] In the following explanation, the direction parallel to the normal h to the surface of the object under inspection 20 is defined as the Z direction, the direction whose main component is the direction from the light source 11 toward the final optical component IOF and which is perpendicular to the Z direction is defined as the Y(+) direction, and the depth direction which is perpendicular to both the Y and Z directions is defined as the X direction. Note that the direction from the surface of the object under inspection 20 in Figure 4 toward the Z(+) direction will be used for explanation. The direction of light propagation will be explained by indicating the approximate direction using these X, Y, and Z directions.

[0022] The illumination optical system 12 consists of an aperture S, a first illumination system optical element IO1, a second illumination system optical element IO2, and a final optical element IOF, all arranged along the illumination path of light L1 from the light source 11. The aperture S is positioned at position IF1, which is optically conjugate to the light emission point of the light source 11. Position IF1 can be considered as the position where the image of the light emission point of the light source 11 is formed. Light traveling in a convergent state toward the position of aperture S diverges after passing through aperture S and travels in a direction with the Y(+) component as the main component, is reflected by the first illumination system optical element IO1, and the reflected light travels in a direction with the Y(+) component as the main component. The first illumination system optical element IO1 is composed of an ellipsoidal mirror and is configured such that the reflected light is focused at position IF2, which is optically conjugate to the light emission point of the light source 11, and then diverges again. Here, position IF1 is positioned at or near the first focal point of the elliptical mirror of the first illumination system optical component IO1, and position IF2 is positioned at or near the second focal point.

[0023] Light reflected by the first illumination system optical component IO1 is reflected by the second illumination system optical component IO2, which is composed of an ellipsoidal mirror, and the reflected light travels in a direction with the Y(+) component as the main component. The illumination optical system 12 may also be configured without the first illumination system optical component IO1. Here, position IF2 is positioned at or near the first focal point of the ellipse of the ellipsoidal mirror of the second illumination system optical component IO1, and the surface of the object to be inspected 20 is positioned at or near the second focal point. By using ellipsoidal mirrors in the first illumination system optical component IO1 and the second illumination system optical component IO2, light can be efficiently focused and the illumination light path can be controlled with high precision.

[0024] The light reflected by the second illumination system optical component IO2 is reflected by the final optical component IOF, whose reflective surface is a plane mirror, and bent in a direction where a certain Z(-) component of the object to be inspected is the main component. The final optical component IOF is positioned such that the angle of incidence of the illumination light on the object to be inspected 20 is oblique. This angle of incidence is the same as the angle of the exposure illumination light when the reflective mask 20, which is the object to be inspected, is used in an exposure apparatus. The light reflected by the final optical component IOF is irradiated onto the object to be inspected 20 through an opening 15 formed in the concave reflecting mirror PM1 of the imaging optical system 13. The final optical component IOF is not limited to a plane mirror; it may also be a concave mirror, a convex mirror, or an aspherical mirror.

[0025] When using the optical device 10 in the mask inspection device 100, it is conceivable to configure the light source 11, aperture S, and first illumination system optical component IO1 within the light source unit 30, and the second illumination system optical component IO2 and final optical component IOF within the optical system chamber 40.

[0026] The arrangement of the final optical element IOF and the angle of incidence to the object under inspection 20 will be further explained. Figure 5 shows an enlarged configuration diagram of a part of the optical device 10. It is preferable that the value of the sine of the half-angle θ of the opening angle 2θ, which indicates the range of the illumination beam of the illumination light directed from the final optical element IOF (not shown in Figure 5) toward the surface of the object under inspection 20, be set to less than 0.35. It is also preferable that the final optical element IOF of the illumination optical system 12 be arranged such that the angular range of the illumination beam irradiated onto the surface of the object under inspection 20 with respect to the normal h of the surface of the object under inspection 20 is between 0° and 20°. As mentioned above, the reflective mask that reflects the EUV light of the object under inspection 20 is assumed to be a film structure formed by an alternating layered multilayer film of Mo (molybdenum) and Si (silicon), and this film structure is typically designed so that the reflectivity is high in the angular range to which the exposure light is incident when used in an exposure device. By using the angle range described above, the reflective mask of the above film type can be illuminated with illumination light in an angle range where the reflectivity is high, making it possible to increase the amount of light L2 from the object to be inspected 20. Consequently, the detection accuracy of the mask inspection device 100 can be improved. The optical device 10 may further include a holding device (not shown) that can adjust the angle of the final optical member IOF. With such a configuration, it is possible to adjust the incident angle on the object to be inspected 20 and adjust the position of the illumination field by the illumination optical system 12.

[0027] Returning to Figure 4, the imaging optical system 13 will be described. The image of the object to be inspected 20, illuminated by the illumination optical system 12, is formed on the detection surface 14a of the detector 14 via the imaging optical system 13. The imaging optical system 13 comprises a concave reflecting mirror PM1, a second imaging system optical element PM2, an imaging system optical element PM3, and an imaging system optical element PM4. In the example shown in Figure 4, the imaging optical system 13 comprises four optical elements PM1, PM2, PM3, and PM4, but the number of optical elements in the imaging optical system 13 is not limited to four; for example, it may have two, three, five, six, or more.

[0028] Light L2 reflected by the object under inspection 20 in the direction with the Z(+) component as the main component is reflected by the concave mirror PM1 and propagates in the direction with the Z(-) component as the main component. In the following explanation, the "object surface" of the imaging optical system 13 refers to the surface on which an object placed in the imaging optical system 13 can be imaged through the imaging optical system 13, and refers to the surface of the object under inspection 20 that is placed (or will be placed) on the stage.

[0029] The concave reflector PM1 is positioned between the object to be inspected 20 and the final optical element IOF in the Z direction. By positioning the concave reflector PM1 between the object surface of the imaging optical system 13 and the final optical element IOF, a configuration can be achieved in which the imaging light beam is not interposed around the final optical element IOF. This prevents so-called "vignetting," where a portion of the imaging light beam is blocked by the final optical element IOF or the holding mechanism that holds the final optical element IOF.

[0030] The concave mirror PM1 is positioned at an angle so that the light reflected from its reflective surface travels more in the Y(+) direction. This positioning will be explained using a partially enlarged view of the optical device 10 in Figure 5. As shown in Figure 5, let O be the center of the sphere when the reflective surface 16 is fitted to the sphere. Let G be the centroid of the region on the concave mirror PM1 where the reflective surface 16 is formed, or the effective reflective region used for reflecting light L2 from the surface of the object to be inspected 20 on the reflective surface 16. If the line connecting the center of the sphere O and the centroid G is taken as the reference axis I of the concave mirror PM1, then the concave mirror PM1 is positioned such that, in the Y direction, the reference axis I is tilted toward the light source 11 side of the concave mirror PM1 side of the reference axis I toward the center of the sphere O. In other words, the center of the sphere O is located toward the second imaging system optical member PM2 side toward the centroid G. This configuration allows for a larger angular range of light from the object being inspected 20 that is reflected from the concave reflector PM1 toward the second imaging system optical element PM2.

[0031] The opening 15 formed in the concave reflector PM1 to allow illumination light from the final optical component IOF of the illumination optical system 12 to pass through will be described.

[0032] Figure 6 shows a plan view of the concave reflector PM1 as seen from the side of the object to be inspected 20. The concave reflector PM1 has an opening 15 that allows illumination light from the final optical member IOF to pass through, and a reflective surface 16 (the part shown by the shaded area in Figure 6) is formed around it to collect light L2 from the surface of the object to be inspected 20. The reflective surface 16 may be formed on all surfaces of the concave reflector PM1 that face the object surface other than the opening 15, or it may be formed on only a part of it.

[0033] As shown in Figure 6, when reflective surfaces 16 are formed on surfaces other than the opening 15, the space S1 occupied by the illumination beam incident from the final optical member IOF to the illumination area on the surface of the object to be inspected 20 via the opening 15 of the concave reflector PM1, as shown in Figure 5, is surrounded by the space S2 occupied by the imaging beam incident on the reflective surfaces 16 formed around the opening 15. By forming reflective surfaces 16 on all surfaces facing the object surface other than the opening 15, light including diffracted and scattered light from the surface of the object to be inspected 20 can be captured over a wide angular range without adding any new reflective members.

[0034] Let's return to Figure 4 for further explanation. As shown in Figure 4, the light reflected by the reflective surface 16 of the concave mirror PM1 is reflected by the second imaging system optical member PM2 in directions having Y(+) and Z(+) components. Due to the focusing action of the reflective surface 16 of the concave mirror PM1, this reflected light becomes a converged beam and is directed toward the second imaging system optical member PM2. The second imaging system optical member PM2 is positioned away from the light source 11 relative to the concave mirror PM1. More specifically, it is positioned outside the space S2 occupied by the imaging beam in Figure 5 that is reflected by the object plane of the imaging optical system 13 and incident on the reflective surface 16 of the concave mirror PM1, and on the opposite side from the light source 11. This configuration allows the imaging optical path of the imaging optical system 13 to be moved away from the illumination optical path. This also ensures space for the final optical member IOF of the illumination optical system 12. In this configuration, the optical path of the light reflected from the second imaging optical element PM2 is configured to pass through the Y(+) side of the final optical element IOF. This configuration allows the illumination optical path to be set up while avoiding the space occupied by the imaging optical path.

[0035] It is preferable that the maximum incident angle of light incident on the second imaging system optical member PM2 be less than 45°. As mentioned above, the reflective surface of the second imaging system optical member PM2 uses a reflective film formed by, for example, an alternating multilayer film of Mo (molybdenum) and Si (silicon). When the incident angle of light incident on such a periodic multilayer film structure becomes large, the reflectivity of soft X-rays decreases. In addition, the reflectivity of P-polarized light, which is parallel to the direction of light propagation, decreases significantly compared to the reflectivity of S-polarized light, and the pupil transmittance distribution of the optical system becomes non-uniform. By configuring the maximum incident angle to be less than 45°, it is possible to prevent a decrease in the reflectivity of P-polarized light and suppress the occurrence of "apodization," in which the pupil transmittance distribution of the optical system changes from a uniform distribution to a non-uniform distribution.

[0036] The second imaging system optical component PM2 may be a concave mirror, a convex mirror, or a combination of a plane mirror and an aspherical element. When the second imaging system optical component PM2 is composed of a convex reflecting mirror, an optical component with a convex surface is positioned next to the concave reflecting mirror PM1 in the optical path of the imaging optical system 13, making it easier to correct aberrations generated in the imaging optical system.

[0037] Light reflected by the second imaging system optical member PM2 is reflected by the third imaging system optical member PM3 in directions having Y(-) and Z(-) components. Light reflected by the third imaging system optical member PM3 is reflected in the Z(+) direction by the fourth imaging system optical member PM4 and focused onto the detection surface 14a of the detector 14, which is positioned optically conjugate to the object surface. As a result, the detector 14 can observe an image of the object to be inspected 20. The third imaging system optical member PM3 and the fourth imaging system optical member PM4 may be concave mirrors, convex mirrors, or plane mirrors combined with aspherical elements.

[0038] In the Z direction, a concave mirror PM1 is positioned between the detector 14 and the object to be inspected 20. This configuration reduces the area in which the imaging light beam is blocked by the optical components constituting the illumination optical system 12 and the holding mechanism that holds the optical components. Furthermore, the detector 14 is positioned on the Y(+) side with respect to the concave mirror PM1. More specifically, the detector 14 is positioned outside the space S2 (see Figure 5) occupied by the imaging light beam reflected from the object surface of the imaging optical system 13 and incident on the reflective surface 16 of the concave mirror PM1, and on the side opposite to the side where the light source 11 is located. This configuration reduces the area in which the imaging light beam is blocked by the optical components constituting the illumination optical system 12 and the holding mechanism that holds the optical components.

[0039] The detection surface 14a of the detector 14 is positioned so as to be non-parallel to the object plane of the imaging optical system 13. If the object plane of the imaging optical system 13 and the detection surface 14a are positioned approximately parallel, the imaging optical path extends in the height direction (Z direction) of the optical device 10, making it more susceptible to height restrictions at the installation location. By bending the imaging optical path and configuring the imaging optical system 13 so that the detection surface 14a of the detector 14 is non-parallel to the object plane of the imaging optical system 13, it is possible to prevent the overall height of the optical device 10 in the Z direction from becoming too high relative to the optical path length required to construct this optical system, thereby making it less susceptible to height restrictions at the installation location.

[0040] In the optical device 10 according to this embodiment, the size of the final optical element IOF in the illumination optical system 12 is smaller than the size of the concave reflector PM1. This configuration makes it possible to secure the imaging optical path of the imaging optical system 13 without having to route the optical path in an unreasonable way.

[0041] In the optical device 10 according to the present embodiment, the exit pupil of the illumination optical system 12 is located at the entrance pupil of the imaging optical system 13, and a illumination light passage range through which illumination light from the illumination optical system 12 passes is located inside the entrance pupil of the imaging optical system 13. By adopting such a configuration, light including diffracted light and scattered light from defects and foreign matters on the reflective mask can be captured in a wide angular range, and the detection sensitivity of defects and foreign matters can be improved. The illumination light passage range may refer to a two-dimensional area through which the illumination light passes or an area occupied by the illumination light within a plane when a predetermined plane is assumed. In the above, the two-dimensional area through which the illumination light passes or the area occupied by the illumination light within the virtual plane where the entrance pupil is located can be used as the illumination light passage range in the virtual plane where the entrance pupil is located.

[0042] The optical device 10(1) irradiates the reflective mask 20, which is the inspection object, with illumination light through the opening 15 formed in the concave mirror PM1, so that the illumination angle when the reflective mask 20 is used and the illumination angle of the illumination light by the optical device 10(1) can be made substantially the same. At the same time, light (diffracted light and scattered light) from defects and foreign matters on the reflective mask 20 can be captured from a wide angular range. As a result, a bright and high-contrast image can be obtained, so that the accuracy of defect detection can be improved.

[0043] <Second Embodiment> Fig. 7 is a schematic diagram showing the configuration of an optical device 10(2) according to the second embodiment. The optical device 10(2) according to the second embodiment is the same as the first embodiment except that the positions of the third imaging system optical member PM3, the fourth imaging system optical member PM4, and the detector 14 are different from those in the configuration of the optical device 10(1) according to the first embodiment, and accordingly the imaging optical path is different, and redundant descriptions are omitted.

[0044] The optical device 10(②) includes an illumination optical system 12 that irradiates the inspection object 20 with light L1 from the light source 11, and an imaging optical system 13 that forms an image of the light L2 irradiated to the inspection object 20 and reflected by the inspection object 20 on the detector 14.

[0045] The illumination optical system 12, like the first embodiment, is composed of an aperture S, a first illumination system optical component IO1, a second illumination system optical component IO2, and a final optical component IOF, all arranged along the illumination optical path of the light L1 from the light source 11. The arrangement is the same as in the first embodiment and will not be described further.

[0046] The image of the object to be inspected 20 illuminated by the illumination optical system 12 is formed on the detection surface 14a of the detector 14 by the imaging optical system 13. The imaging optical system 13 comprises a concave reflecting mirror PM1, a second imaging system optical member PM2, an imaging system optical member PM3, and an imaging system optical member PM4. Light L2 reflected from the object to be inspected 20 in a direction with a Z(+) component as the main component is reflected by the concave reflecting mirror PM1 in a direction with a Z(-) component as the main component. Similar to the first embodiment, the reflective surface of the concave reflecting mirror PM1 is tilted toward the Y(+) direction, and is configured so that the reflected light is reflected more toward the Y(+) direction. That is, the point of focus of the reflected light by the concave reflecting mirror PM1 is tilted toward the Y(+) side of the field of view on the object to be inspected 20. In the second embodiment shown in Figure 7 and in other embodiments, the second imaging system optical member PM2 is positioned in front of the focal point of the reflected light from the concave mirror PM1 (the image formation position of the object to be inspected 20), so this focal point becomes a virtual point. In other words, the concave mirror PM1 is tilted and positioned such that the position where the virtual image of the object to be inspected 20 is formed by the concave mirror PM1 is located on the Y(+) side of the field of view.

[0047] Similar to the first embodiment, the concave mirror PM1 is formed with an aperture 15 for allowing the illumination light from the final optical member IOF to pass therethrough. The light reflected by the reflecting surface 16 of the concave mirror PM1 is reflected by the second imaging system optical member PM2 disposed outside the space S2 occupied by the imaging light beam incident on the reflecting surface 16 of the concave mirror PM1 and on the side opposite to the light source 11 side in the directions having Y(+) component and Z(+) component. Different from the first embodiment, the light reflected by the second imaging system optical member PM2 is reflected by the third imaging system optical member PM3 in the directions having Y(+) component and Z(−) so as to move away from the illumination optical path and the concave mirror PM1. The light reflected by the third imaging system optical member PM3 is reflected by the fourth imaging system optical member PM4 in the directions having Y(+) component and Z(+) component so as to move away from the illumination optical path and the concave mirror PM1, and is condensed on the detection surface <14a> of the detector 14 disposed at a position optically conjugate to the object surface. In other words, in the imaging optical system 13 of the optical apparatus 10(2) of the second embodiment, the optical members PM1 to PM4 are arranged such that the traveling direction of the imaging light from the visual field region of the imaging optical system 13 is away from the visual field region in the direction including the Y(+) component. Specifically, on the side in the direction including the Y(+) component of the optical path of the imaging light beam from the visual field region toward the concave mirror PM1, the imaging light beam from the second imaging system optical member PM2 toward the third imaging system optical member PM3 is located, and on the side in the direction including the Y(+) component of the optical path of the imaging light beam from the second imaging system optical member toward the third imaging system optical member PM3, the imaging light beam from the fourth imaging system optical member PM2 toward the detector 14 is located.

[0048] With the above-described configuration, the imaging optical path extends in the Y(+) side direction, and the detection surface <14a> of the detector 14 is arranged on the Y(+) side with respect to the concave mirror PM1.With such a configuration, it is possible to reduce the area where the imaging light beam is blocked by the optical members constituting the illumination optical system 12 and the holding mechanism that holds the optical members.

[0049] Furthermore, the optical device 10(2) of the second embodiment, like the optical device 10(1) of the first embodiment, has the effect of being able to adjust the illumination direction to the object to be inspected 20 to approximately the illumination angle when the reflective mask 20 is used, and to capture light (diffracted light and scattered light) from defects or foreign matter in the reflective mask 20 from a wide range of angles.

[0050] <Third Embodiment> Figure 8 is a schematic diagram showing the configuration of the optical device 10(3) according to the third embodiment. The optical device 10(3) according to the third embodiment is configured such that the imaging optical path extends horizontally rather than vertically in the optical device 10(2) according to the second embodiment, with the third imaging optical member PM3, the fourth imaging optical member PM4, and the detector 14 arranged accordingly. In this case, the length of the optical device 10(3) in the horizontal direction, i.e., the Y direction in Figure 1, is longer due to the optical path length required for imaging, but the height can be reduced compared to the first embodiment, making it less susceptible to height restrictions at the installation location. With this configuration, the area in which the imaging light beam is obstructed by the optical members constituting the illumination optical system 12 and the holding mechanism that holds the optical members can be reduced. The other configurations of the optical device 10(3) are the same as in the second embodiment, and their explanation is omitted.

[0051] With the above configuration, it is possible to provide an optical device that can capture as much light as possible from the reflective mask 20 to be inspected and improve detection sensitivity, as well as a mask inspection device using such an optical device.

[0052] Next, a method for inspecting a reflective mask using the optical device according to this embodiment will be described with reference to Figure 9. Figure 9 is a flowchart illustrating a method for inspecting a reflective mask. In Figure 9, first, the reflective mask 20 is placed on the object surface of the optical device 10 (step S11). Next, a part of the reflective mask 20 is illuminated with illumination light from the illumination optical system 12 of the optical device 10 (step S12). Then, the light from the illuminated reflective mask 20 is incident on the imaging optical system 13 of the optical device 10 (step S13). The light from the reflective mask 20 via the imaging optical system 13 is detected (step S14). With such a mask inspection method, it is possible to capture as much light as possible from the reflective mask 20 and improve the defect detection sensitivity of the reflective mask. In the above description, the mask inspection device 100 detected defects in the reflective mask using bright-field illumination, but defects in the reflective mask may also be detected using dark-field illumination or a combination of bright-field illumination and dark-field illumination.

[0053] Regarding the embodiments described above, the following additional notes are provided. [Addendum 1] An optical device comprising an illumination optical system for illuminating the surface of an object with illumination light from a light source, and an imaging optical system for imaging the light from the surface illuminated by the illumination optical system, wherein the imaging optical system comprises a concave mirror that has an opening for allowing illumination light from the final optical member, which is positioned closest to the object in the illumination light path of the illumination optical system, to pass through, and which collects the light from the surface, and the reflective surface of the concave mirror is formed around the opening. [Addendum 2] The optical device according to Addendum 1, wherein the space occupied by the illumination light beam incident on the illumination region on the surface through the opening is surrounded by the space occupied by the imaging light beam caused by the light from the surface incident on the reflective surface formed around the opening from the illumination region. [Addendum 3] The optical device according to Addendum 1 or 2, wherein the imaging optical system comprises an imaging optical member that reflects the light from the surface reflected by the reflective surface formed around the opening of the concave mirror. [Note 4] The optical apparatus according to any one of Notes 1 to 3, wherein the imaging optical system comprises an imaging optical member that reflects light reflected by the concave mirror, and the imaging optical member is located on a second side opposite to the first side where the light source is located, outside the space occupied by the imaging light beam reflected by the object surface of the imaging optical system and incident on the reflective surface of the concave mirror. [Note 5] The optical apparatus according to Note 4, wherein when the reflective surface of the concave mirror is fitted with a spherical surface, the concave mirror is positioned such that the reference axis of the concave mirror is such that the concave mirror is tilted toward the first side with respect to the spherical surface, when the line connecting the center of the sphere of the spherical surface and the centroid of the region where the reflective surface is formed or the effective reflection region that reflects light from the surface on the reflective surface is defined as the reference axis of the concave mirror. [Note 6] The optical apparatus according to Note 4 or 5, wherein the light from the concave mirror reflected by the imaging optical element passes to the second side of the concave mirror. [Note 7] The optical apparatus according to Note 6, wherein the optical path of the light from the concave mirror reflected by the imaging optical element is located to the second side of the final optical element of the illumination optical system.[Note 8] The optical device according to any one of Notes 1 to 7, wherein the imaging optical system comprises an imaging optical element that reflects light reflected by the concave mirror, and the center of the sphere when the reflective surface of the concave mirror is fitted with a sphere is located on the side of the imaging optical element that is greater than the center of gravity of the region where the reflective surface is formed or the effective reflection region that reflects light from the surface on the reflective surface. [Note 9] The optical device according to any one of Notes 1 to 8, wherein the imaging optical element has a convex mirror on the reflective surface that reflects light from the concave mirror. [Note 10] The optical device according to any one of Notes 1 to 9, wherein the concave mirror is positioned between the object surface and the final optical element of the illumination optical system in the direction of the normal to the object surface of the imaging optical system. [Note 11] The optical device according to any one of Notes 1 to 10, further comprising a detector formed by the imaging optical system, which has a detection surface positioned at an optically conjugate position with the surface of the object. [Note 12] The optical apparatus according to Note 11, wherein the detection surface is located outside the space occupied by the imaging light beam reflected from the object surface of the imaging optical system and incident on the reflective surface of the concave mirror, and is located on a second side opposite to the first side where the light source is located. [Note 13] The optical apparatus according to Note 11 or 12, wherein the concave mirror is located between the detector and the object surface in the direction of the normal to the object surface of the imaging optical system. [Note 14] The optical apparatus according to any one of Notes 11 to 13, wherein the object surface of the imaging optical system and the detection surface are non-parallel. [Note 15] The optical apparatus according to any one of Notes 1 to 14, wherein the sine of the half-angle of the opening angle of the illumination light from the final optical member toward the surface is less than 0.35. [Note 16] The optical apparatus according to any one of Notes 1 to 15, wherein the angular range of the illumination beam irradiated from the final optical member of the illumination optical system onto the surface of the object with respect to the normal of the surface is between 0° and 20°. [Note 17] The optical apparatus according to any one of Notes 1 to 16, wherein the size of the final optical member is smaller than the size of the concave reflector.[Note 18] The optical apparatus according to any one of Notes 1 to 17, wherein the imaging optical system comprises an imaging optical element that reflects light from the surface reflected by the concave mirror, and the maximum incident angle of the light incident on the imaging optical element is less than 45°. [Note 19] The optical apparatus according to any one of Notes 1 to 18, further comprising a holding device that can adjust the angle of the final optical element. [Note 20] The optical apparatus according to any one of Notes 1 to 19, wherein the exit pupil of the illumination optical system is located at the entrance pupil of the imaging optical system, and the illumination light passage range through which the illumination light from the illumination optical system passes is located inside the range of the entrance pupil of the imaging optical system. [Note 21] An optical device comprising an illumination optical system for illuminating the surface of an object with illumination light from a light source, and an imaging optical system for imaging the light from the surface illuminated by the illumination optical system, wherein the imaging optical system comprises a concave reflecting mirror having an opening that allows illumination light from the final optical member, which is located on the surface side in the illumination light path of the illumination optical system, to pass through, and which collects the light from the surface, the exit pupil of the illumination optical system is located at the entrance pupil of the imaging optical system, and the illumination light passage range through which the illumination light from the illumination optical system passes is located inside the entrance pupil of the imaging optical system. [Note 22] An inspection device for inspecting a reflective mask, comprising the optical device described in any one of Notes 1 to 21 for inspecting the reflective mask as the object. [Appendix 23] An inspection method for inspecting a reflective mask, comprising: placing the reflective mask on the object surface of an optical device described in any one of Appendix 1 to 21; illuminating a part of the reflective mask with illumination light from the illumination optical system of the optical device; causing the light from the illuminated reflective mask to enter the imaging optical system of the optical device; and detecting the light from the reflective mask via the imaging optical system.

[0054] At least some of the constituent elements of each embodiment described above can be appropriately combined with at least some other constituent elements of each embodiment described above. Some of the constituent elements of each embodiment described above may not be used.

[0055] The present invention is not limited to the embodiments described above, and can be modified as appropriate without contradicting the gist or idea of ​​the invention as can be read from the claims and the specification as a whole. Optical devices, mask inspection devices, and mask inspection methods involving such modifications are also included in the technical scope of the present invention.

[0056] 100 Mask inspection device 10 Optical device 11 Light source 12 Illumination optical system 13 Imaging optical system 14 Detector 15 Aperture 16 Reflecting surface IO1 First illumination system optical component IO2 Second illumination system optical component IOF Final optical component PM1 Concave mirror PM2 Second imaging system optical component PM3 Third imaging system optical component PM4 Fourth imaging system optical component 20 Object to be inspected, reflective mask 30 Light source unit 40 Optical system chamber 50 Connection passage

Claims

1. An optical device comprising: an illumination optical system for illuminating the surface of an object with illumination light from a light source; and an imaging optical system for imaging the light from the surface illuminated by the illumination optical system, wherein the imaging optical system has an opening formed therein that allows illumination light from the final optical member, which is positioned furthest toward the object in the illumination light path of the illumination optical system, to pass through, and a concave reflecting mirror that collects the light from the surface, and the reflective surface of the concave reflecting mirror is formed around the opening.

2. The optical apparatus according to claim 1, wherein the space occupied by the illumination beam incident on the illumination region on the surface through the opening is surrounded by the space occupied by the imaging beam caused by light from the surface incident on the reflective surface formed around the opening from the illumination region.

3. The optical apparatus according to claim 1 or 2, wherein the imaging optical system comprises an imaging optical member that reflects light from the surface reflected by the reflective surface formed around the aperture of the concave reflecting mirror.

4. The optical apparatus according to any one of claims 1 to 3, wherein the imaging optical system comprises an imaging optical member that reflects light reflected by the concave mirror, and the imaging optical member is located on a second side opposite to the first side where the light source is located, outside the space occupied by the imaging light beam that is reflected by the object surface of the imaging optical system and incident on the reflective surface of the concave mirror.

5. The optical apparatus according to claim 4, wherein when the reflective surface of the concave reflector is fitted to a spherical surface, the concave reflector is positioned such that the concave reflector is tilted toward the first side with respect to the spherical surface, when the line connecting the center of the spherical surface when the reflective surface of the concave reflector is fitted to the spherical surface and the centroid of the region where the reflective surface is formed or the effective reflective region that reflects light from the surface on the reflective surface is defined as the reference axis of the concave reflector.

6. The optical apparatus according to claim 4 or 5, wherein the light from the concave mirror reflected by the imaging optical element passes to the second side of the concave mirror.

7. The optical apparatus according to claim 6, wherein the optical path of the light from the concave mirror reflected by the imaging optical element is located on the second side of the final optical element of the illumination optical system.

8. The optical apparatus according to any one of claims 1 to 7, wherein the imaging optical system comprises an imaging optical member that reflects light reflected by the concave mirror, and the center of the spherical surface when the reflective surface of the concave mirror is fitted with a spherical surface is located on the side of the imaging optical member than the center of gravity of the region where the reflective surface is formed or the center of gravity of the effective reflective region that reflects light from the surface on the reflective surface.

9. The optical apparatus according to any one of claims 1 to 8, wherein the imaging optical member has a convex reflector on the reflective surface that reflects light from the concave reflector.

10. The optical apparatus according to any one of claims 1 to 9, wherein the concave reflecting mirror is positioned between the object surface and the final optical member of the illumination optical system in the direction of the normal to the object surface of the imaging optical system.

11. The optical apparatus according to any one of claims 1 to 10, further comprising a detector having a detection surface formed by the imaging optical system and positioned at a location optically conjugate to the surface of the object.

12. The optical apparatus according to claim 11, wherein the detection surface is located outside the space occupied by the imaging light beam that is reflected from the object surface of the imaging optical system and incident on the reflective surface of the concave mirror, and is located on a second side opposite to the first side where the light source is located.

13. The optical apparatus according to claim 11 or 12, wherein the concave mirror is positioned between the detector and the object surface in the direction of the normal to the object surface of the imaging optical system.

14. The optical apparatus according to any one of claims 11 to 13, wherein the object plane of the imaging optical system and the detection plane are non-parallel.

15. The optical apparatus according to any one of claims 1 to 14, wherein the sine of the half-angle of the opening angle of the illumination light from the final optical member toward the surface is less than 0.

35.

16. The optical apparatus according to any one of claims 1 to 15, wherein the angular range of the illumination beam irradiated from the final optical member of the illumination optical system onto the surface of the object with respect to the normal of the surface is between 0° and 20°.

17. The optical apparatus according to any one of claims 1 to 16, wherein the size of the final optical member is smaller than the size of the concave reflector.

18. The optical apparatus according to any one of claims 1 to 17, wherein the imaging optical system comprises an imaging optical member that reflects light from the surface reflected by the concave mirror, and the maximum incident angle of the light incident on the imaging optical member is less than 45°.

19. The optical apparatus according to any one of claims 1 to 18, further comprising a holding device capable of adjusting the angle of the final optical member.

20. The optical apparatus according to any one of claims 1 to 19, wherein the exit pupil of the illumination optical system is located at the entrance pupil of the imaging optical system, and the illumination light passing range through which the illumination light from the illumination optical system passes is located inside the range of the entrance pupil of the imaging optical system.

21. An optical device comprising: an illumination optical system for illuminating the surface of an object with illumination light from a light source; and an imaging optical system for imaging the light from the surface illuminated by the illumination optical system, wherein the imaging optical system comprises a concave reflecting mirror having an opening that allows illumination light from the final optical member, which is located on the surface side in the illumination light path of the illumination optical system, to pass through, and which collects the light from the surface, the exit pupil of the illumination optical system being located at the entrance pupil of the imaging optical system, and the illumination light passage range through which the illumination light from the illumination optical system passes being located inside the entrance pupil of the imaging optical system.

22. An inspection apparatus for inspecting a reflective mask, comprising an optical device according to any one of claims 1 to 21 for inspecting the reflective mask as the object.

23. An inspection method for inspecting a reflective mask, comprising: placing the reflective mask on the object surface of an optical device described in any one of claims 1 to 21; illuminating a part of the reflective mask with illumination light from the illumination optical system of the optical device; causing the light from the illuminated reflective mask to enter the imaging optical system of the optical device; and detecting the light from the reflective mask via the imaging optical system.

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