JP5787261B2 - Inspection apparatus and inspection method - Google Patents

Description

  The present invention relates to an inspection apparatus and an inspection method.

  With regard to lithography technology for miniaturization of semiconductors, ArF lithography using an ArF excimer laser with an exposure wavelength of 193 nm as an exposure light source is currently being mass-produced. In addition, an immersion technique (called ArF immersion lithography) that fills the space between the objective lens of the exposure apparatus and the wafer with water to increase the resolution has begun to be used for mass production. In order to realize further miniaturization, various technical developments have been carried out for practical application of EUV lithography (Extremely Ultraviolet Lithography) with an exposure wavelength of 13.5 nm.

  The minimum size and depth of defects that are unacceptable in EUV masks, especially in substrates and blanks, are much smaller than in conventional ArF masks. This makes it difficult to detect defects in the EUV mask. In view of this, it is said that a minute irregularity defect having a wavelength of about 1/10 can be detected by inspecting the inspection light source with EUV light, that is, illumination light having the same wavelength as exposure light having a wavelength of 13.5 nm. In the actinic inspection in which the inspection is performed at the same wavelength as the exposure light, defects transferred by exposure can be detected. Therefore, the actinic inspection is particularly important in the EUV mask.

  Patent Documents 1 and 2 disclose an EUV mask inspection apparatus. In the inspection apparatuses disclosed in Patent Literatures 1 and 2, a Schwarzschild optical system is used. The Schwarzschild optical system is an optical system generally composed of two spherical mirrors, a concave mirror and a convex mirror, and is used for enlarging or reducing a planar image. As an illumination method, dark field illumination is used to detect weak scattered light with high sensitivity.

JP 2012-118304 A JP2012-154902A

  FIG. 11 shows the configuration of an inspection apparatus using a Schwarzschild optical system. The Schwarzschild optical system 10 includes a concave mirror 13 with a hole and a convex mirror 12. Further, the Schwarzschild optical system 10 is provided with a drop mirror 11 for guiding the illumination light L1 to the mask 21. The illumination light L 1 reflected by the drop mirror 11 enters the mask 21. If the mask 21 is defective, the illumination light L1 is scattered. The scattered light scattered by the defect of the mask 21 is reflected by the concave mirror 13 with holes and the convex mirror 12 and detected by the detector 14. In this way, the drop mirror 11 is disposed immediately below the convex mirror 12.

  By performing bright field illumination, it is possible to detect phase defects and the like with high sensitivity. However, since the Schwarzschild optical system 10 has a central light shielding region, it is difficult to realize bright field illumination. That is, since the reflected light regularly reflected by the mask 21 is blocked by the concave mirror 13 with a hole or the like, it is difficult to realize bright field observation. Detailed inspection becomes difficult because bright field observation is not possible.

  The present invention has been made in view of the above-described problems, and an object thereof is to provide an inspection apparatus and an inspection method that can be inspected in more detail.

  An inspection apparatus according to a first aspect of the present invention is an inspection apparatus that inspects an inspection object used for an EUV mask, and includes a Schwarzschild optical system having a convex mirror and a concave mirror, and reflected light reflected by the inspection object. A detector for detecting via the Schwarzschild optical system, and a drop mirror disposed on the inspection object side of the convex mirror and reflecting illumination light in the direction of the inspection object for performing dark field illumination. And means for changing an incident angle of the illumination light with respect to the inspection object so that at least a part of the illumination light becomes bright-field illumination light. In this structure, since it can illuminate with bright field illumination light, it can test | inspect in more detail.

  In the inspection apparatus, the means may include a drive mechanism that changes the angle of the reflecting surface of the drop mirror. Thereby, illumination with bright-field illumination light can be performed easily.

  In the above inspection apparatus, the means may be a transfer mirror that is detachably provided in a stage preceding the drop mirror. Thereby, illumination with bright-field illumination light can be performed easily.

  The inspection apparatus may further include an illumination optical system that guides the illumination light in the direction of the drop mirror, and the illumination optical system may include a light shielding member that spatially restricts the passage of the illumination light. Good. Thereby, illumination light can be appropriately incident on the inspection object.

  In the inspection apparatus, an opening for allowing the illumination light to pass through is formed in the light shielding member on the optical axis of the illumination optical system, and the light shielding member is disposed so as to be movable along the optical axis of the illumination optical system. May be. Thereby, since the solid angle of illumination light can be controlled, the dark field illumination component can be effectively removed.

  In the above inspection apparatus, the light shielding member may be disposed at a position conjugate with the convex mirror, and allow illumination light on the optical axis of the illumination optical system to pass therethrough. Thereby, the component of dark field illumination can be removed effectively.

  In the inspection apparatus, the light shielding member may be inserted partway through the illumination light spot on a surface that is disposed in the vicinity of the concave mirror included in the illumination optical system and is perpendicular to the optical axis of the illumination optical system. . Thereby, illumination light can be incident on the inspection object from a desired direction.

  In the inspection apparatus, the insertion position of the light shielding member may be changed on a plane perpendicular to the optical axis of the illumination optical system. Thereby, the incident direction of the illumination light with respect to the test object can be controlled.

  In the inspection apparatus, the growth direction of the phase defect in the multilayer reflective film formed on the inspection object may be determined according to the size of the detected defect. Thereby, the growth direction of the phase defect can be easily determined.

  In the inspection apparatus described above, defect unevenness determination may be performed according to the direction of asymmetry of the image acquired by the detector. Thereby, the unevenness | corrugation of a defect can be discriminate | determined easily.

  The inspection method according to the present embodiment is an inspection method for inspecting an inspection object used for an EUV mask using a Schwarzschild optical system having a convex mirror and a concave mirror, and performs dark field illumination. A step of reflecting illumination light in the direction of the inspection object by a drop mirror arranged on the inspection object side, a step of detecting scattered light scattered by the inspection object via the Schwarzschild optical system, and the illumination Changing the incident angle of the illumination light with respect to the inspection object so that at least part of the light becomes bright-field illumination light. According to this method, since it can be illuminated with bright-field illumination light, it is possible to inspect in more detail.

  In the above inspection method, the incident angle may be changed by changing the angle of the reflecting surface of the drop mirror. Thereby, illumination with bright-field illumination light can be performed easily.

  In the above inspection method, the incident angle may be changed by inserting a transfer mirror in front of the drop mirror. Thereby, illumination with bright-field illumination light can be performed easily.

  In the inspection method described above, a light shielding member may be disposed in the illumination optical system that guides the illumination light in the direction of the drop mirror, and the light shielding member spatially restricts passage of the illumination light. . Thereby, illumination light can be appropriately incident on the inspection object.

  In the inspection method, an opening for allowing the illumination light to pass through is formed in the light shielding member on the optical axis of the illumination optical system, and the light shielding member is moved along the optical axis of the illumination optical system. May be. Thereby, since the solid angle of illumination light can be controlled, the dark field illumination component can be effectively removed.

  In the above inspection method, the light shielding member may be arranged at a position conjugate with the convex mirror so that illumination light on the optical axis of the illumination optical system passes therethrough. Thereby, the component of dark field illumination can be removed effectively.

  In the inspection method described above, the light shielding member may be inserted in the middle of the illumination light spot on a surface that is disposed in the vicinity of the concave mirror included in the illumination optical system and is perpendicular to the optical axis of the illumination optical system. . Thereby, illumination light can be incident on the inspection object from a desired direction.

  In the above inspection method, the insertion position of the light shielding member may be changed on a plane perpendicular to the optical axis of the illumination optical system. Thereby, the incident direction of the illumination light with respect to the test object can be controlled.

  In the above inspection method, the growth direction of the phase defect in the multilayer reflective film formed on the inspection object may be determined according to the size of the detected defect. Thereby, the growth direction of the phase defect can be easily determined.

  In the above inspection method, the unevenness of the defect may be determined according to the direction of asymmetry of the image acquired by the detector. It is possible to easily determine the unevenness of the defect.

  ADVANTAGE OF THE INVENTION According to this invention, the inspection apparatus and inspection method which can be test | inspected in detail can be provided.

It is a figure which shows the structure of the test | inspection apparatus concerning this Embodiment 1. FIG. It is a perspective view which shows the structural example of the movable mechanism of a drop mirror. It is a perspective view which shows the structural example of the movable mechanism of a drop mirror. It is a figure which shows the structure of the test | inspection apparatus concerning this Embodiment 2. FIG. It is a figure which shows the structure of the test | inspection apparatus concerning this Embodiment 3. FIG. It is a figure which shows the structure of the test | inspection apparatus concerning this Embodiment 4. It is a figure for demonstrating a mode that a convex defect is detected. It is a figure for demonstrating a mode that a concave defect is detected. It is a figure for demonstrating a mode that a phase defect is detected. It is a figure for demonstrating a mode that a phase defect is detected. It is a figure which shows the structure of the test | inspection apparatus using a Schwarzschild optical system.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following description shows preferred embodiments of the present invention, and the scope of the present invention is not limited to the following embodiments. In the following description, the same reference numerals indicate substantially the same contents.

  Hereinafter, an inspection apparatus and an inspection method according to embodiments of the present invention will be described with reference to the drawings. The inspection target may be a substrate used for an EUV mask (referred to as a substrate), a blank having a multilayer film or a resist on the substrate, or a patterned EUV mask. . In this specification, since it is intended for all inspection apparatuses of a mask substrate, a blank, and a patterned EUV mask, they are simply referred to as an EUV mask or a mask unless they are particularly distinguished.

Embodiment 1 FIG.
An inspection apparatus according to Embodiment 1 of the present invention will be described with reference to FIG. FIG. 1 is a diagram showing the overall configuration of an EUV mask inspection apparatus 100 whose main purpose is to detect blank defects. The inspection apparatus 100 includes a Schwarzschild optical system 10, a drop mirror 11, and a detector 14. The Schwarzschild optical system 10 includes a convex mirror 12 and a concave mirror 13 with a hole.

  In FIG. 1, for the sake of clarity, the direction perpendicular to the inspection surface of the mask 21 is shown as the Z direction, and the direction parallel to the paper surface is shown as the Y direction on the surface parallel to the inspection surface of the mask 21. . The Z direction is parallel to the optical axis A1 of the Schwarzschild optical system 10. Of the planes parallel to the plane of the mask 21, the direction parallel to the direction perpendicular to the Y direction is taken as the X direction. In the following description, it is assumed that the inspection surface of the mask 21 faces upward, and the illumination light is irradiated on the mask 21 obliquely from above, but the illumination direction is relative depending on the orientation of the inspection surface of the mask 21. To change.

  The inspection apparatus according to the present embodiment can switch between inspection using dark field illumination light and simultaneous illumination of dark field illumination light and bright field illumination light. Therefore, the drop mirror 11 is a movable mirror. The inspection with dark field illumination light has the same configuration as that shown in FIG.

  First, inspection by dark field illumination will be described. The drop mirror 11 is disposed immediately above the inspection location of the mask 21. Illumination light L1 from an EUV light source (not shown) falls from the side and enters the mirror 11. The illumination light L1 hits the drop mirror 11 and is reflected downward. The drop mirror 11 reflects the illumination light L <b> 1 in the direction of the mask 21 in order to perform dark field illumination. The optical axis of the illumination light L1 reflected by the drop mirror 11 is substantially perpendicular to the inspection surface of the mask 21. That is, the illumination light L1 reflected by the drop mirror 11 propagates along the Z axis. Since the illumination light L1 propagates while being narrowed by a concave mirror (not shown) or the like, the illumination light L1 is focused on the inspection location of the mask 21. In addition, an actinic test | inspection can be performed by using the same 13.5 nm EUV light as an exposure wavelength as illumination light L1.

  When the illumination light L1 is incident on the defective portion of the mask 21, the illumination light L1 is scattered. Scattered light is scattered obliquely upward. Part of the scattered light scattered by the mask 21 passes through the outside of the drop mirror 11 and enters the concave mirror 13 with a hole. That is, the scattered light L2 scattered outside the drop mirror 11 and inside the outer diameter of the concave mirror 13 with a hole is incident on the concave mirror 13 with a hole. The concave mirror 13 with a hole reflects the scattered light L2 obliquely downward. That is, the concave mirror 13 with a hole reflects the scattered light L <b> 2 in the direction of the convex mirror 12. The convex mirror 12 is disposed directly above the drop mirror 11. In other words, the drop mirror 11 is disposed on the mask 21 side of the convex mirror 12, that is, immediately below the convex mirror 12.

  The convex mirror 12 reflects the scattered light from the concave mirror 13 with a hole in the direction of the detector 14. The scattered light L <b> 2 reflected by the convex mirror 12 passes through the hole of the concave mirror 13 with a hole and enters the detector 14. The convex mirror 12 and the concave mirror 13 with holes detect the scattered light L2, and the detector 14 is a two-dimensional array photodetector such as a CCD (Charged Coupled Device) camera or a CMOS (Complementary Metal Oxide Semiconductor) sensor. For example, a TDI (Time Delay Integration) sensor can be used as the detector. The Schwarzschild optical system 10 enlarges and projects the image of the illumination location of the mask 21 onto the light receiving surface of the detector 14. Therefore, the detector 14 captures an enlarged image of the mask 21.

  A defect is detected by comparing the intensity of the scattered light L2 detected by the detector 14 with a threshold value. The mask 21 is placed on a stage or the like (not shown). Then, any part of the mask 21 can be inspected by moving the stage with respect to the Schwarzschild optical system 10. As described above, the inspection apparatus 100 is in a mode for performing dark field illumination inspection. That is, the specularly reflected light that is specularly reflected at the normal location of the mask 21 is blocked by the dropping mirror 11 and the like, and is not incident on the detector 14. Thereby, S / N of a scattered light can be made high from the defect location of the mask 21. FIG. When an inspection is performed using only dark field illumination, the illumination light is symmetric with respect to the optical axis.

  Furthermore, in addition to the dark field illumination inspection, the inspection apparatus 100 can perform a simultaneous illumination inspection that simultaneously illuminates dark field illumination light and bright field illumination light. That is, the detector 14 can be configured to simultaneously detect the scattered light by the dark field illumination inspection and the regular reflection light by the bright field illumination inspection. For example, after performing defect detection by dark field illumination inspection, the drop mirror 11 is changed to change the incident angle of the illumination light L1 on the mask 21. And the simultaneous illumination test | inspection which illuminates dark field illumination light and bright field illumination light simultaneously is performed. Therefore, the drop mirror 11 is moved. That is, the angle of the reflecting surface of the drop mirror 11 is changed using the drop mirror 11 as a movable mirror. By doing so, the incident angle of the illumination light L1 on the mask 21 can be changed.

  The dropping mirror 11 rotates around the position of the point O in FIG. That is, the drop mirror 11 rotates with the X axis passing through the point O and perpendicular to the paper surface as the rotation axis. Thereby, illumination with bright-field illumination light can be performed easily. For example, the drop mirror 11 rotates along the two-dot chain line in FIG. The drop mirror 11 drives the movable mechanism to move in the YZ plane. Then, the drop mirror 11 is displaced and the angle of the reflection surface of the drop mirror 11 is changed according to the rotation angle of the movable mechanism. For example, when the X axis passing through the point O is rotated by 1 ° about the rotation axis, the reflecting surface of the drop mirror 11 is also rotated by 1 °. Then, the incident direction of the illumination light L1 with respect to the mask 21 changes twice.

  Here, even if the dropping mirror 11 is rotated, the incident position of the illumination light L1 on the mask 21 is not changed. That is, the position of the point O serving as the rotation axis is determined under the condition that the incident position of the illumination light L1 on the mask 21 does not change. The distance from the drop mirror 11 to the point O is about twice the distance from the mask 21 to the drop mirror 11.

  By doing in this way, at least a part of the illumination light L1 becomes bright-field illumination light. That is, a part of the specularly reflected light regularly reflected from the normal portion (non-defect portion) of the mask 21 passes through the outside of the drop mirror 11 and enters the concave mirror 13 with a hole. A part of the illumination light L1 becomes illumination light for dark field illumination, and the rest becomes illumination light for bright field illumination.

  When performing defect inspection, a dark field optical system with excellent throughput can be used. Then, when the defect is observed after the inspection, the drop mirror 11 is moved. In this way, an optical system that adds a bright field component to dark field illumination can be used. Simultaneous illumination is performed by dark field illumination light and bright field illumination light. Thereby, in addition to a dark field illumination test | inspection, the test | inspection by simultaneous illumination can be performed. More detailed inspection is possible.

  In the EUV light plane mirror, the angle of the reflecting surface at which an effective reflectance can be obtained is limited. In the case of the reference incident angle, the reflectance (usually about 65%) is the highest, and the reflectance decreases as the reference incident angle deviates. For example, if the incident angle deviates by more than ± 2 degrees from the reference angle, the reflectivity of the drop mirror 11 decreases. In this case, even if the direction of the reflecting surface of the drop mirror 11 is changed, the angle range in which a sufficient reflectance can be obtained is 4 degrees from +2 degrees to -2 degrees. If the tilt of the drop mirror 11 is changed by 3 degrees, the incident angle can be shifted by 6 °. The central optical axis of the illumination light L1 is inclined 6 degrees with respect to the Z axis. Illumination light L <b> 1 tilted in the range of 2 to 10 degrees (6 degrees ± 4 degrees) with respect to the Z axis is incident on the mask 21. Therefore, dark field illumination and 6 degree bright field illumination can coexist.

  Specifically, the reference incident angle is a state in which the reflecting surface of the drop mirror 11 is inclined by 44 degrees with respect to the incident direction of light. That is, the dropping mirror 11 is prepared so that the reflectance is maximized when the incident angle is 44 degrees. In this case, the reflectivity of the drop mirror 11 increases in the range of 44 degrees ± 2 degrees, that is, 42 to 46 degrees. Then, inspection with dark field illumination is performed in a state where the reflecting surface is inclined 45 degrees. When simultaneous illumination is performed with dark field illumination light and bright field illumination light, the reflecting surface of the drop mirror 11 is inclined by 42 degrees with respect to the incident direction of the light. Thereby, the incident angle of the illumination light L1 with respect to the mask 21 can be set to 6 degrees. Furthermore, 42 degrees and 45 degrees are included in a range of 44 degrees ± 2 degrees where the reflectivity of the drop mirror 11 is sufficiently high. Therefore, the drop mirror 11 can be arranged in a state where the reflectivity of the drop mirror 11 is sufficiently high. Or it is good also considering the incident angle used as the reference | standard of the dropping mirror 11 as 46 degree | times. In this case, when using dark field illumination light, the drop mirror 11 is set to 45 degrees, and when performing simultaneous illumination, the drop mirror 11 is set to 48 degrees.

  An advantage of performing bright field illumination (typically 6 degrees) similar to that of the exposure machine using the mask 21 will be described. When observing defects with a conventional dark field inspection apparatus, the illumination angle of the exposure machine is different from 6 degrees because it is dark field illumination. For this reason, the transfer characteristics of the observed defect are greatly different. As in the inspection apparatus 100 of the present embodiment, the real transfer characteristics are closer to each other by adding a bright field component. Conventionally, a change in transferability is generally evaluated by an apparatus having an optical system equivalent to that of an exposure machine. On the other hand, by applying the above optical system, it is possible to evaluate the transfer characteristics simultaneously with the inspection.

  The Schwarzschild optical system 10 for dark field inspection needs a central light shielding region of about 5 degrees by the convex mirror 12 in order to obtain a practical EUV light quantity. When a bright field optical system having an incident angle of 6 degrees used for EUV exposure is added to the Schwarzschild optical system 10, a region where EUV light is blocked by the convex mirror 12 in dark field illumination appears, and the bright field and dark field coexist. Lighting. By appropriately mixing the ratio of the illumination intensity of the bright field and the dark field, it is possible to enhance the scattered light from the edge due to the dark field while observing the bright field.

  The dark field scattered light component from the defect can be arbitrarily added to the bright field image, which is the exposure image, so that the transferability of the defect can be changed depending on the component ratio of the bright field to the dark field. It is an effective means for evaluating sex. Thereby, it can test | inspect in detail.

(About drive mechanism)
The drive mechanism that drives the drop mirror 11 serves as means for changing the incident angle of the illumination light with respect to the mask 21 so that part of the illumination light L1 becomes bright-field illumination light. Here, FIG. 2 shows a configuration example of a drive mechanism for moving the drop mirror 11. FIG. 2 is a perspective view schematically showing the configuration of the drive mechanism 50. Here, the drive mechanism 50 includes a 3-axis + 1-axis translation actuator. The angle of the drop mirror 11 is adjusted by the three extendable actuators 52, and the position is given only one degree of freedom by the actuator 57.

  The drop mirror 11 is connected to an annular frame 56 via an arm 55. Further, the arm 55 is provided with an actuator 57 for moving the drop mirror 11 in translation. The actuator 57 expands and contracts in the XY plane. By driving the actuator 57, the drop mirror 11 translates in the XY plane.

  The frame 56 is attached by three actuators 52. The actuator 52 extends in the Z direction. That is, the actuator 52 serves as a support and supports the frame 56. The actuator 52 expands and contracts in the Z direction. The actuator 52 connects the frame 56 and the base plate 51. Therefore, if the three actuators 52 are driven independently, the frame 56 is inclined from the XY plane. As a result, three-axis operation is possible, and the angle of the reflecting surface can be changed.

  By setting it as such a structure, the drop mirror 11 can be made into an appropriate position and reflection angle. For example, the drop mirror 11 can be moved in an orbit close to an arc. For the actuator 52 and the actuator 57, a cylinder, a piezoelectric element, or the like can be used. The expansion / contraction length of the actuator 52 or the actuator 57 is controlled.

  FIG. 3 shows another configuration example of the drive mechanism 50. FIG. 3 is a perspective view showing a drive mechanism 50 using a six-axis actuator 52. Six degrees of freedom of the position and angle of the drop mirror 11 are controlled by the six extendable actuators 52. The drop mirror 11 is connected to an annular frame 56 via an arm 55. The frame 56 is attached by six actuators 52. The actuator 52 serves as a support and supports the frame 56. The actuator 52 extends in an oblique direction inclined from the Z direction. The actuator 52 expands and contracts in an oblique direction inclined from Z. The actuator 52 connects the frame 56 and the base plate 51. Therefore, if the six actuators 52 are driven independently, the frame 56 can be tilted from the XY plane and can be translated. As a result, six-axis operation becomes possible.

  By setting it as such a structure, the dropping mirror 11 can be made into arbitrary positions and reflection angles. For example, the drop mirror 11 can be moved along a trajectory along an arc. A 6-axis actuator having the actuator 52 as a cylinder can be used for the drive mechanism 50.

  In the case of the structure as shown in FIGS. 2 and 3, the drop mirror 11 is held by a frame 56, which is a movable structure, via a thin arm 55. Therefore, the actuator 52 and the actuator 57 can be arranged at a position off the optical axis of the Schwarzschild optical system 10. Thus, a structure that does not block the effective NA range of the imaging optical system is possible. Further, the drop mirror 11 has an advantage that it can be used in common in the case of only the dark field and in the case of the bright field and the dark field. In addition, a method of realizing a structure that moves in the circumferential direction with respect to the rotation shown in FIG. Alternatively, the drop mirror 11 may be moved using a link mechanism or the like.

Embodiment 2. FIG.
An inspection apparatus 100 according to the present embodiment will be described with reference to FIG. In the present embodiment, a transfer mirror 15 is provided instead of the drive mechanism of the first embodiment. Note that the basic configuration of the Schwarzschild optical system 10 and the like is the same as that of the first embodiment, and thus description thereof is omitted.

  The transfer mirror 15 is detachably provided in the optical path of the illumination light L1. The transfer mirror 15 is detachably provided at the front stage of the drop mirror 11. For example, the transfer mirror 15 can be inserted into the optical path by moving the transfer mirror 15 along the X direction. Thereby, illumination with bright-field illumination light can be performed easily.

  When performing dark field illumination, the transfer mirror 15 is removed from the optical path. Accordingly, the illumination light L1 is reflected by the drop mirror 11 to illuminate the mask 21. On the other hand, when performing simultaneous illumination, the transfer mirror 15 is inserted in an optical path. Therefore, the illumination light L 1 is reflected by the transfer mirror 15 and illuminates the mask 21. That is, by inserting the transfer mirror 15 in front of the drop mirror 11, the illumination light L 1 is reflected by the transfer mirror 15 without entering the drop mirror 11.

  Thus, the means for changing the incident angle of the illumination light L1 with respect to the mask 21 is the transfer mirror 15 that is detachably provided. The positions of the transfer mirror 15 and the drop mirror 11 are different. Furthermore, the angle of the reflective surface of the transfer mirror 15 and the reflective surface of the drop mirror 11 are different. Therefore, the same effect as in the first embodiment can be obtained.

Embodiment 3 FIG.
An inspection apparatus 100 according to the present embodiment will be described with reference to FIG. FIG. 5 is a diagram illustrating the overall configuration of the inspection apparatus 100. In the present embodiment, a configuration of the illumination optical system 30 is provided in addition to the configuration of FIG. Since the configuration other than the illumination optical system 30 is the same as that of the first embodiment, the description thereof is omitted. In Embodiment 3, the illumination solid angle is controlled by providing a pinhole 32 in the illumination optical system 30.

  The illumination optical system 30 includes a light source 35, a concave mirror 31, a pinhole 32, and a concave mirror 33. The concave mirror 31 and the concave mirror 33 are, for example, elliptical mirrors. The light source 35 emits EUV light as illumination light L1. The light source 35 may be provided with a homogenizer that makes the illumination light L1 uniform. The illumination light L1 from the light source 35 is reflected by the concave mirror 31. The illumination light L1 reflected by the concave mirror 31 enters the pinhole 32. The pinhole 32 is a light blocking member that spatially blocks the illumination light L1.

  The opening of the pinhole 32 is disposed around the optical axis of the illumination optical system 30. The pinhole 32 blocks part of the illumination light L1 reflected by the concave mirror 31. The illumination light L1 that has passed through the pinhole 32 enters the concave mirror 33. The concave mirror 33 drops the illumination light L1 and reflects it toward the mirror 11. And the pinhole 32 is arrange | positioned so that a movement along the optical axis direction (arrow direction) of the illumination optical system 30 is carried out. Thereby, an illumination solid angle can be controlled.

  Further, the pinhole 32 may be arranged at a position conjugate with the position of the convex mirror 12. In this way, contrast is not obtained as much as the focal position, but an image of the pinhole 32 is formed in the vicinity of the convex mirror 12. The position of the convex mirror 12 is the position of the convex mirror 12 while the scattered light L2 is reflected by the mask 21 and travels toward the concave mirror 13 with a hole.

  When only bright-field illumination is desired, light blocked by the concave mirror 13 with a hole can be efficiently removed. That is, by making the opening diameter of the pinhole 32 sufficiently small, the passage of illumination light is spatially restricted, and the beam diameter is reduced. As a result, the specularly reflected light from the mask 21 passes through the outside of the convex mirror 12. The dark field component scattered by the mask 21 can be efficiently removed. The component ratio of the specularly reflected light component and the scattered light can be easily adjusted. Further, the pinhole 32 can be an aperture having a large opening diameter. Alternatively, the pinhole 32 can be a diaphragm having a variable opening. By doing so, the component ratio of the specularly reflected light component and the scattered light can be easily adjusted.

Embodiment 4 FIG.
An inspection apparatus 100 according to the present embodiment will be described with reference to FIG. FIG. 6 is a diagram illustrating the overall configuration of the inspection apparatus 100. In the fourth embodiment, a light shielding plate 34 is used in place of the pinhole 32 of the third embodiment. Note that the description of the same configuration as in the first and third embodiments is omitted.

  In the inspection apparatus 100 according to the present embodiment, the light shielding plate 34 is disposed in the vicinity of the concave mirror 33. The light shielding plate 34 is a light shielding member that spatially shields the illumination light L1. For example, the light shielding plate 34 is inserted in one half of the optical path in the cross section of the illumination light L1. By doing so, the distribution of the angular components of the illumination light L1 irradiated on the mask 21 can be changed. On the surface perpendicular to the optical axis of the illumination optical system 30, the light shielding plate 34 is disposed partway along the spot of the illumination light L 1. On the surface perpendicular to the optical axis of the illumination optical system 30, the half-side illumination light L 1 is shielded, and the other-side half illumination light L 1 illuminates the mask 21. The light shielding plate 34 controls the angular distribution of the scattered light L2.

  A structure capable of adjusting the angle distribution of scattered light from the dark field illumination can be realized, and a structure in which the ratio between the bright field and the dark field is changed is also possible. By changing the insertion position of the light shielding plate 34 in the direction perpendicular to the optical axis, the ratio of the bright field to the dark field can be changed. By doing in this way, it becomes possible to change the ratio of illumination light with a simple structure. As described above, the light shielding plate 34 serves as a stop for limiting the angle components of the regular reflection light and the scattered light. For this reason, it is preferable to arrange the light shielding plate 34 in the vicinity of the concave mirror 33, that is, in a position close to the pupil plane.

  For example, when the direction inclined by 6 degrees from the Z axis is used as the optical axis of the illumination light L1, if the light shielding plate 34 is inserted up to half of the optical path of the illumination optical system 30, illumination is performed in an illumination angle range of 6 degrees to 10 degrees. Can do. Therefore, the illumination angle range can be easily controlled. As described above, according to the third and fourth embodiments, the illumination light can be incident on the mask 21 at a desired angle. Further, instead of the light shielding plate 34, a pinhole, an aperture, or the like may be arranged. Pinholes and aperture openings are arranged at positions shifted from the optical axis of the illumination optical system 30. Even if it does in this way, the same effect can be acquired.

  Further, as an accompanying effect of the 6 degree illumination, when combining bright field and dark field illumination, the central axis of the illumination light is shifted from the central axis (Z axis) of the Schwarzschild optical system 10, resulting in asymmetric illumination. Therefore, it is possible to determine the unevenness of the defect by examining the direction of asymmetry of the luminance distribution of the image. Hereinafter, a method for determining an uneven defect will be described. FIG. 7 is a diagram illustrating a state in which the convex defect 22 protruding from the surface of the mask 21 is detected. FIG. 8 is a diagram illustrating a state in which the concave defect 23 that is recessed from the surface of the mask 21 is detected. FIG. 7A and FIG. 8A are YZ cross-sectional views showing a defect portion. FIG. 7B and FIG. 8B are XY plan views showing defect portions. FIG. 7C and FIG. 8C show Y direction profiles of the detected light intensity detected by the detector 14.

  The illumination light L1 is asymmetric with respect to the Z axis. Therefore, the profile of the detected light intensity in the Y direction changes between the convex defect 22 and the concave defect 23. For example, in FIGS. 7 and 8, the illumination light L1 is incident on the mask 21 from obliquely upper left. Therefore, since the illumination is asymmetric, the intensity of the specularly reflected light changes depending on whether the convex defect 22 or the concave defect 23 is used.

  For example, the detection light intensity is low in the left half of the convex defect 22, and the detection light intensity is high in the right half. On the contrary, the detection light intensity is low in the left half of the concave defect 23 and the detection light intensity is high in the right half. The convex defect 22 and the concave defect 23 have different surface inclination angles, so that a change occurs in the profile in the Y direction. It is possible to determine whether the defect is a concave defect or a convex defect depending on the order of the profile irregularities. Therefore, it is possible to easily determine the unevenness of the defect according to the asymmetry direction of the image acquired by the detector 14.

  Furthermore, when there is an asymmetry in the internal structure of the phase defect, the growth direction inside the defect can be determined. A method for determining the growth direction of defects will be described with reference to FIGS. FIG. 9 shows a configuration in which defects grow along the incident direction of the illumination light L1, and FIG. 9 shows a configuration in which the phase defect 26 grows inclined from the incident direction of the illumination light L1. FIGS. 9A and 10A are cross-sectional views showing a phase defect portion of the mask 21. FIG. In FIG. 9A and FIG. 10A, the phase defect 26 having the same size exists. FIGS. 9B and 10B are diagrams showing defect sizes detected by the phase defect 26 having the same size.

  When there is a defect on quartz serving as a mask substrate, a phase defect grows when the multilayer reflective film 24 that reflects EUV light is formed thereon. A phase defect grows asymmetrically with respect to a direction perpendicular to the inspection surface of the mask 21. The growth direction of the anisotropic phase defect 26 can be determined based on the defect size.

  The direction of specularly reflected light that is regularly reflected by the mask 21 changes depending on the growth direction of the phase defect 26. For example, when the growth direction of the phase defect 26 is close to the incident direction of the illumination light L1, the defect size becomes small. When the growth direction of the phase defect 26 is greatly deviated from the incident direction of the illumination light L1, the defect size becomes large. Therefore, the illumination direction can be changed by tilting the drop mirror 11 or rotating the mask 21. By changing the illumination direction, the defect size of the phase defect 26 is changed. The direction in which the defect size becomes the smallest can be the growth direction of the phase defect 26. Since the shape of the defect varies depending on the change in the direction of illumination, the growth direction inside the defect can be determined. Thus, an optical system sensitive to the detection of the phase defect 26 and the unevenness determination can be realized. Dark field asymmetric illumination is also useful information for classifying characteristics such as defect depth and internal structure. Such detection processing of the concavo-convex defect and the phase defect 26 can be performed by a processing device that captures detection data from the detector 14.

  Further, Embodiments 1 to 4 may be combined as appropriate. For example, the configurations of the third and fourth embodiments may be applied to the configuration of the second embodiment. Furthermore, the configurations of Embodiments 3 and 4 may be applied simultaneously.

  The inspection object can be used for an EUV mask. For example, a mask substrate used for an EUV mask, a blank (mask blank) in which a multilayer film or a resist is provided on the mask substrate, or a patterned EUV mask with a pattern formed can be an inspection object. By using a mask sub slate or a blank determined to be a non-defective product by inspection with the above inspection apparatus, a patterned EUV mask can be manufactured with high productivity. Further, the resist on the wafer is exposed using this EUV mask or a patterned EUV mask determined to be non-defective by inspection. Then, the resist can be developed and an etching process can be performed to form a pattern on the wafer. By doing in this way, a wafer with a pattern can be manufactured with high productivity. Of course, the inspection object is not limited to an EUV mask for EUV exposure, a mask substrate, a mask blank, a mask with a pattern, or the like.

DESCRIPTION OF SYMBOLS 10 Schwarzschild optical system 11 Drop mirror 12 Convex mirror 13 Concave mirror with a hole 14 Detector 15 Transfer mirror 21 Mask 22 Convex defect 23 Concave defect 26 Phase defect 30 Illumination optical system 31 Concave mirror 32 Pinhole 33 Concave mirror 34 Shading plate 50 Drive mechanism 51 Base plate 52 Actuator 55 Arm 56 Frame 57 Actuator L1 Illumination light L2 Scattered light

Claims (20)

An inspection apparatus for inspecting an inspection object used for an EUV mask,
A Schwarzschild optical system having a convex mirror and a concave mirror;
A detector that detects the reflected light reflected by the inspection object via the Schwarzschild optical system;
A drop mirror that is disposed on the inspection object side of the convex mirror and performs dark field illumination, and includes a drop mirror that reflects illumination light in the direction of the inspection object;
Means for changing an incident angle of the illumination light with respect to the inspection object so that a part of the illumination light becomes bright-field illumination light,
The inspection object is imaged in a state where the dark field illumination light and the bright field illumination light are simultaneously illuminated, and a defect is detected based on the captured image.
An inspection apparatus in which a ratio of the dark field illumination light and the bright field illumination light in the case of simultaneous illumination is set according to the defect to be detected .   The inspection apparatus according to claim 1, wherein the means includes a drive mechanism that changes an angle of a reflection surface of the drop mirror.   The inspection apparatus according to claim 1, wherein the means is a transfer mirror that is detachably provided at a stage preceding the drop mirror. An illumination optical system for guiding the illumination light in the direction of the drop mirror;
The inspection apparatus according to claim 1, wherein the illumination optical system includes a light shielding member that spatially restricts passage of the illumination light. An opening for allowing the illumination light to pass through is formed in the light shielding member on the optical axis of the illumination optical system,
The inspection apparatus according to claim 4, wherein the light shielding member is arranged to be movable along an optical axis of the illumination optical system.   The inspection apparatus according to claim 4, wherein the light shielding member is disposed at a position conjugate with the convex mirror and allows illumination light on an optical axis of the illumination optical system to pass therethrough.   The light shielding member is disposed in the vicinity of a concave mirror included in the illumination optical system, and the light shielding member is inserted partway through a spot of illumination light on a surface perpendicular to the optical axis of the illumination optical system. The inspection apparatus according to item 1.   The inspection apparatus according to claim 7, wherein the insertion position of the light shielding member can be changed on a plane perpendicular to the optical axis of the illumination optical system.   The inspection apparatus according to claim 1, wherein a growth direction of a phase defect in the multilayer reflective film formed on the inspection target is determined according to the size of the detected defect.   The inspection apparatus according to claim 1, wherein the unevenness of the defect is determined according to a direction of asymmetry of the image acquired by the detector. An inspection method for inspecting an inspection object used for an EUV mask using a Schwarzschild optical system having a convex mirror and a concave mirror,
Reflecting illumination light in the direction of the inspection object by a drop mirror disposed on the inspection object side of the convex mirror to perform dark field illumination;
Detecting scattered light scattered by the inspection object via the Schwarzschild optical system;
Changing the incident angle of the illumination light with respect to the inspection object so that a part of the illumination light becomes bright-field illumination light;
Imaging the inspection object in a state of simultaneously illuminating the dark field illumination light and the bright field illumination light, and detecting defects based on the captured image,
An inspection method in which a ratio between the dark field illumination light and the bright field illumination light in the case of simultaneous illumination is set according to the defect to be detected .   The inspection method according to claim 11, wherein the incident angle is changed by changing an angle of a reflecting surface of the drop mirror.   The inspection method according to claim 11, wherein the incident angle is changed by inserting a transfer mirror in front of the drop mirror. In the illumination optical system that guides the illumination light in the direction of the drop mirror, a light shielding member is disposed,
The inspection method according to claim 11, wherein the light shielding member spatially restricts the passage of the illumination light. An opening for allowing the illumination light to pass through is formed in the light shielding member on the optical axis of the illumination optical system,
The inspection method according to claim 14, wherein the light shielding member is moved along an optical axis of the illumination optical system.   The inspection method according to claim 14, wherein the light shielding member is disposed at a position conjugate with the convex mirror and allows illumination light on an optical axis of the illumination optical system to pass therethrough.   17. The light-shielding member is disposed in the vicinity of a concave mirror included in the illumination optical system, and the light shielding member is inserted partway through a spot of illumination light on a surface perpendicular to the optical axis of the illumination optical system. The inspection method according to item 1.   The inspection method according to claim 17, wherein the insertion position of the light shielding member is changed on a plane perpendicular to the optical axis of the illumination optical system.   19. The inspection method according to claim 11, wherein the growth direction of the phase defect in the multilayer reflective film formed on the inspection target is determined according to the size of the detected defect.   The inspection method according to any one of claims 11 to 19, wherein the unevenness of the defect is determined according to the asymmetry direction of the acquired image to be inspected.

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