Inspection equipment

Abstract

To provide an inspection device that can irradiate the object being inspected with more uniform light. [Solution] The inspection apparatus 1 comprises a light source 11, a first light guide 12, a homogenizer 14, a Fourier transform lens unit 13, an illumination optical system 17, a measurement stage, an imaging optical system 21, and an image sensor 25. The light source 11 emits light L1. The first light guide 12 has a first incident end 12a into which light L1 from the light source 11 enters, and a first exit end 12b. The Fourier transform lens unit 13 is provided between the first exit end 12b of the first light guide 12 and the homogenizer 14. The illumination optical system 17 is provided downstream of the homogenizer 14. The measurement stage is provided downstream of the illumination optical system 17, and the object to be inspected is placed on it. Light L1 from the object to be inspected enters the imaging optical system 21. The image sensor 25 receives the light L1 from the imaging optical system 21 and generates captured image data IM1.

Description

Technical Field

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[0001] The present disclosure relates to an inspection device.

Background Art

[0002] Conventionally, an inspection device for inspecting a photomask has been proposed (Patent Document 1). In Patent Document 1, the photomask inspection device includes an illumination unit, a detection unit, a holding unit, and a control unit. The holding unit holds the photomask. The illumination unit irradiates the photomask with light. The detection unit detects the light from the photomask. The control unit calculates the mask characteristics of the photomask based on the detection result by the detection unit, and inspects the photomask based on the mask characteristics.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When the uniformity of the light incident on the photomask decreases, the inspection accuracy decreases.

[0005] Therefore, an object of the present disclosure is to provide an inspection device that can irradiate a test object with more uniform light.

Means for Solving the Problems

[0006] The inspection apparatus comprises a light source that emits light, a first light guide having a first incident end into which the light from the light source is incident, and a first exit end, a homogenizer, a Fourier transform lens section provided between the first exit end of the first light guide and the homogenizer, an illumination optical system provided downstream of the homogenizer, a measurement stage provided downstream of the illumination optical system where the object to be inspected is placed, an imaging optical system into which the light from the object to be inspected is incident, and an image sensor that receives the light from the imaging optical system and generates image data. [Effects of the Invention]

[0007] This allows for more uniform illumination of the object being inspected. [Brief explanation of the drawing]

[0008] [Figure 1] This is a perspective view illustrating a schematic example of the configuration of an inspection device. [Figure 2] This diagram schematically shows an example of the optical configuration of an inspection device. [Figure 3] This diagram schematically shows an example of the configuration of an inspection device. [Figure 4] This graph schematically shows an example of the spatial distribution of light intensity at the first exit end of the first light guide. [Figure 5] This graph schematically shows an example of the spatial distribution of light intensity incident on the second incident end of the light guide member. [Figure 6] This graph schematically shows an example of the directional distribution of the intensity of each ray of light. [Figure 7] This diagram schematically shows an example of another configuration of the inspection device. [Modes for carrying out the invention]

[0009] The embodiments will be described in detail below with reference to the drawings. For the sake of clarity, the dimensions and number of parts in the drawings are exaggerated or simplified as needed. Parts with similar configurations and functions are denoted by the same reference numerals, and redundant explanations are omitted in the following description. The drawings also show XYZ Cartesian coordinates as appropriate to indicate the positional relationships of each component. For example, the Z-axis is aligned vertically, while the X and Y axes are aligned horizontally.

[0010] Furthermore, in the following explanations, similar components will be denoted by the same symbols, and their names and functions will also be the same. Therefore, detailed explanations of them may be omitted to avoid redundancy.

[0011] Furthermore, even if ordinal numbers such as "first" or "second" are used in the following descriptions, these terms are used for convenience to facilitate understanding of the embodiments and are not limited to the order that may result from these ordinal numbers.

[0012] When expressions indicating relative or absolute positional relationships are used (e.g., "in one direction," "along one direction," "parallel," "orthogonal," "center," "concentric," "coaxial," etc.), unless otherwise specified, such expressions shall not only strictly represent the positional relationship but also represent a state in which there is a relative displacement in terms of angle or distance within a tolerance or a range in which equivalent functionality is obtained. When expressions indicating equality are used (e.g., "identical," "equal," "homogeneous," etc.), unless otherwise specified, such expressions shall not only strictly represent a state in which there is a quantitatively exact equality but also represent a state in which there is a difference within a tolerance or a range in which equivalent functionality is obtained. When expressions indicating shape are used (e.g., "quadrilateral" or "cylindrical"), unless otherwise specified, such expressions shall not only strictly represent the geometrically exact shape but also represent a shape with features such as concavities or chamfers within a range in which equivalent effects are obtained. When expressions such as "possess," "equip," "include," or "have" a single component are used, such expressions are not exclusive expressions that exclude the existence of other components. When the expression "at least one of A, B, and C" is used, it includes A only, B only, C only, any two of A, B, and C, and all of A, B, and C.

[0013] <Inspection equipment> Figure 1 is a schematic perspective view showing an example of the configuration of inspection device 1, and Figure 2 is a schematic diagram showing an example of the optical configuration of inspection device 1. Inspection device 1 is a device that optically inspects a photomask 80, which is an example of an object to be inspected. When the object to be inspected is a photomask 80, inspection device 1 may also be called a photomask inspection device.

[0014] <Photomask> First, a photomask 80, which is an example of a test object, will be described. The photomask 80 is a photomask used in an exposure apparatus (not shown). By performing an exposure process on a substrate using the photomask 80, the pattern of the photomask 80 can be transferred onto the substrate. The substrate is, for example, a substrate for a flat panel display. Note that various substrates such as a semiconductor substrate and a substrate for a solar cell can also be applied to the substrate.

[0015] The photomask 80 has a plate-like shape and, in a plan view, has, for example, a rectangular shape. The length of one side of the photomask 80 is set to be, for example, several tens of cm or more and several m or less. As a more specific example, the length of each side of the photomask 80 is 1.8 m and 2.0 m, respectively, and the thickness of the photomask 80 is, for example, 21 mm. A light-shielding film (not shown) is formed in a predetermined pattern on one main surface of the photomask 80. That is, the photomask 80 has a transmission portion that transmits light and a blocking portion that blocks light formed thereon. Note that the photomask 80 may be a phase shift mask provided with a phase shift film that transmits light at a lower transmittance than the transmission portion.

[0016] <Overview of the inspection apparatus> As illustrated in FIG. 2, the inspection apparatus 1 includes an image sensor (optical sensor) 25 that receives light from the photomask 80. The image sensor 25 has a light-receiving surface and detects light on the light-receiving surface. The inspection apparatus 1 inspects the photomask 80 based on the detection result of the image sensor 25.

[0017] The inspection apparatus 1 includes an illumination unit 10, a detection unit 20, a control unit 50, and a measurement stage 90. Hereinafter, first, an overview of each component of the inspection apparatus 1 will be described, and then an example of each component will be described in detail.

[0018] The measurement stage 90 is a member that supports or holds the test object (here, the photomask 80). The measurement stage 90 supports or holds the photomask 80 such that the thickness direction of the photomask 80 is along the Z-axis direction. In the example of FIG. 1, the measurement stage 90 supports only the peripheral portion of the photomask 80. However, the measurement stage 90 may entirely support the lower surface of the photomask 80 with a light-transmissive member.

[0019] The illumination unit 10 irradiates the light L1 onto the photomask 80 disposed on the measurement stage 90. The detection unit 20 detects the light L1 from the photomask 80. In the examples of FIGS. 1 and 2, the detection unit 20 is provided on the side opposite to the illumination unit 10 with respect to the measurement stage 90. That is, in FIGS. 1 and 2, the illumination method of the inspection apparatus 1 is transmission illumination. The illumination method is not limited to transmission illumination and may be epi-illumination (for example, coaxial epi-illumination). In the examples of FIGS. 1 and 2, since the illumination method is transmission illumination, the detection unit 20 detects the light L1 that has passed through the photomask 80 disposed on the measurement stage 90. The control unit 50 has a function of controlling each component of the inspection apparatus 1 and a function of inspecting the photomask 80 based on the detection result of the detection unit 20.

[0020] <Illumination unit> As shown in FIG. 2, the illumination unit 10 includes a light source 11, a first light guide 12, a Fourier transform lens unit 13, and an illumination optical system 17.

[0021] The light source 11 emits the light L1. The light L1 may include, for example, ultraviolet light. The light source 11 may be, for example, a lamp or a semiconductor light-emitting device. The lamp is, for example, a high-pressure mercury lamp. The semiconductor light-emitting device is, for example, an LED (Light Emitting Diode).

[0022] The first light guide 12 has a first incident end 12a and a first exit end 12b. Light L1 from the light source 11 is incident on the first incident end 12a of the first light guide 12. In the example in Figure 2, a lens 111 is provided between the first incident end 12a of the first light guide 12 and the light source 11. Light L1 from the light source 11 spreads out as it travels towards the lens 111 and is incident on the lens 111. The light L1 is focused on the first incident end 12a of the first light guide 12 by the bending action of the lens 111. The light L1 enters the interior of the first light guide 12 from the first incident end 12a.

[0023] The first light guide 12 also has a first reflective side surface 12c. The first reflective side surface 12c is a surface that forms the side of the internal optical path of the first light guide 12. Each ray of light L1 travels through the inside of the first light guide 12 from the first incident end 12a to the first exit end 12b, while being repeatedly reflected by the first reflective side surface 12c. Each ray of light L1 can undergo total internal reflection at the first reflective side surface 12c.

[0024] The first light guide 12 may be flexible. In other words, the first light guide 12 may be bendable or pliable.

[0025] The first light guide 12 may be a liquid light guide. The liquid light guide includes a cylindrical tube, a light guide liquid filled inside the tube, and translucent sealing parts that seal both longitudinal ends of the tube. The light guide liquid may be, for example, pure water. The refractive index of the inner surface of the tube is lower than that of the light guide liquid. The tube may be formed of, for example, a flexible synthetic resin. A film having a refractive index lower than that of the light guide liquid may be formed on the inner surface of the synthetic resin. The first reflective side surface 12c corresponds to the interface between the inner surface of the tube and the light guide liquid. The sealing parts are formed of, for example, glass such as quartz glass or multi-component glass. Multi-component glass contains multiple oxides (for example, boron oxide and aluminum oxide). The first incident end 12a corresponds to the surface of one sealing part, and the first exit end 12b corresponds to the surface of the other sealing part.

[0026] Alternatively, the first light guide 12 may contain multiple fibers. Each fiber includes a linear core and a cladding that has a lower refractive index than the core and covers the sides of the core. The interface between the core and the cladding corresponds to the first reflective surface 12c. The first incident end 12a corresponds to one end of each core in the longitudinal direction, and the first exit end 12b corresponds to the other end of each core in the longitudinal direction. Light L1 travels through the interior of each core, repeatedly reflecting off the first reflective surface 12c. The fibers are, for example, multimode fibers.

[0027] The first light guide 12 may include a cylindrical tube surrounding a bundle of fibers. The tube is formed of, for example, a flexible synthetic resin. The tube has, for example, a cylindrical shape.

[0028] The fibers may be formed from multi-component glass or quartz glass. When the fibers are formed from glass, the transmittance of the fibers for light L1 is relatively high. Therefore, the loss of light L1 in the first light guide 12 can be reduced. Each fiber may be coated with a flexible synthetic resin. This can improve the flexibility of the fiber. Alternatively, the fiber itself may be formed from a translucent synthetic resin. This synthetic resin can be at least one of, for example, silicone resin, acrylic resin, methacrylic resin, and fluororesin. When the fibers are formed from synthetic resin, the flexibility of the fiber itself is high. Therefore, the flexibility of the first light guide 12 can be improved.

[0029] The ratio of the longitudinal length (or optical path length) of the first light guide 12 to the cross-sectional length of the optical path of the first light guide 12 may be 10 or more. Here, the cross-sectional length is the diameter if the cross-section is circular, and if the cross-section is rectangular, for example, it is the length of the longest diagonal. If the first light guide 12 is a liquid light guide, the ratio of the longitudinal length of the tube to the inner diameter (diameter) of the tube may be 10 or more. If the first light guide 12 includes a fiber, the ratio of the longitudinal length of the fiber core to the cross-sectional diameter of the core may be 10 or more. This ratio may be 20 or more, or 50 or more. This allows the number of times the light L1 is reflected by the first reflective side surface 12c of the first light guide 12 to be increased. Such repeated reflections can further improve the uniformity of the light L1.

[0030] The Fourier transform lens section 13 is located downstream of the first light guide 12. The Fourier transform lens section 13 is positioned so that its front focal point is the first exit end 12b of the first light guide 12. A Fourier transform image of the image at the first exit end 12b is formed on the Fourier plane (a virtual plane including the rear focal point) of the Fourier transform lens section 13. In other words, light rays traveling in the same direction from each position of the first exit end 12b of the first light guide 12 are incident on the same position on the Fourier plane. The Fourier transform lens section 13 is formed by at least one lens 131. The Fourier transform lens section 13 may be formed by one lens 131 or by multiple lenses 131. In the example in Figure 2, the Fourier transform lens section 13 is formed by two lenses 131.

[0031] The homogenizer 14 is located downstream of the Fourier transform lens section 13. In other words, the Fourier transform lens section 13 is located between the first exit end 12b of the first light guide 12 and the homogenizer 14. The homogenizer 14 is located at the position where the light L1 of the Fourier plane of the Fourier transform lens section 13 is incident. The homogenizer 14 further homogenizes the incident light L1.

[0032] The homogenizer 14 includes, for example, a light guide member 15. The light guide member 15 has a second incident end 15a and a second exit end 15b. The second incident end 15a is located at the rear focal point of the Fourier transform lens section 13. That is, the second incident end 15a is provided on the Fourier plane. The light guide member 15 also has a second reflective side surface 15c. Light L1 travels through the inside of the light guide member 15 from the second incident end 15a to the second exit end 15b, while being repeatedly reflected by the second reflective side surface 15c. Each ray of light L1 can be totally reflected by the second reflective side surface 15c.

[0033] The light guide member 15 may be, for example, a second light guide. The second light guide may include a plurality of fibers. In this case, the core, cladding, and interface of each fiber correspond to the second reflective surface 15c. The second incident end 15a corresponds to one end in the longitudinal direction of each core, and the second exit end 15b corresponds to the other end in the longitudinal direction of each core. Light L1 travels through the interior of each core, reflecting off the second reflective surface 15c. The fibers may be formed from multi-component glass or quartz glass. If the fibers are formed from glass, each fiber may be coated with a synthetic resin. This can improve the flexibility of the fiber. Alternatively, the fiber itself may be formed from a flexible synthetic resin.

[0034] Alternatively, the second light guide may be a glass rod (also called a light pipe). The glass rod is made of, for example, quartz glass or multi-component glass. One end of the glass rod corresponds to the second incident end 15a, the other end corresponds to the second exit end 15b, and the side of the glass rod corresponds to the second reflective side 15c. Alternatively, the second light guide may be a liquid light guide.

[0035] The ratio of the length of the light guide member 15 along the optical path (optical path length) to the cross-sectional length of the optical path of the light guide member 15 may be 10 or more. For example, if the light guide member 15 includes a fiber, the ratio of the length of the fiber core in the longitudinal direction to the cross-sectional diameter of the core may be 10 or more. This allows the number of times the light L1 is reflected by the second reflective surface 15c of the light guide member 15 to be increased. Such repeated reflections can further improve the uniformity of the light L1.

[0036] The illumination optical system 17 is located downstream of the homogenizer 14 (in this case, the light guide member 15). Light L1 from the homogenizer 14 is incident on the photomask 80 placed on the measurement stage 90 through the illumination optical system 17. The illumination optical system 17 may also focus the light L1 to cause a spot of light L1 to be incident on the photomask 80.

[0037] The illumination optical system 17 may be Köhler illumination or critical illumination. In the example in Figure 2, the illumination optical system 17 is Köhler illumination. In the example in Figure 2, the illumination optical system 17 includes a focusing lens 171, a field diaphragm 172, a relay lens 173, an aperture diaphragm 174, and a condenser lens 175. The focusing lens 171, field diaphragm 172, relay lens 173, aperture diaphragm 174, and condenser lens 175 are arranged in this order in the Z-axis direction, moving away from the exit end of the light guide 16.

[0038] Light L1 from the second exit end 15b of the light guide member 15 is focused by the focusing lens 171 and passes through the field diaphragm 172. The aperture diameter of the field diaphragm 172 is variable by the diaphragm mechanism, allowing adjustment of the illumination range (incident area) on the photomask 80. The light L1 that has passed through the field diaphragm 172 is focused by the relay lens 173 and passes through the aperture diaphragm 174. The light L1 that has passed through the aperture diaphragm 174 is focused onto the photomask 80 by the condenser lens 175. The aperture diameter of the aperture diaphragm 174 is variable by the diaphragm mechanism, allowing adjustment of the numerical aperture of the illumination optical system 17. The diaphragm mechanisms of the field diaphragm 172 and the aperture diaphragm 174 may be controlled by the control unit 50.

[0039] In this illumination optical system 17, the image of the second exit end 15b of the light guide member 15 is formed on the aperture diaphragm 174, and the image at the field diaphragm 172 is formed on the photomask 80 on the measurement stage 90.

[0040] <Detection Unit> Patterned light L1 from the photomask 80 placed on the measurement stage 90 is incident on the detection unit 20. In the example in Figure 2, the illumination method of the inspection device 1 is transmitted illumination, so the light L1 that has passed through the photomask 80 is incident on the detection unit 20. The detection unit 20 includes an imaging optical system 21 and an image sensor 25.

[0041] The imaging optical system 21 guides light L1 from the photomask 80 to the image sensor 25, causing an image of the photomask 80 to be formed on the light-receiving surface of the image sensor 25. In the example in Figure 2, the imaging optical system 21 includes an objective lens 22, an aperture diaphragm 23, and an imaging lens 24. The objective lens 22, aperture diaphragm 23, and imaging lens 24 are arranged in this order as they move away from the photomask 80 in the Z-axis direction. Light transmitted through the photomask 80 is magnified through the objective lens 22 and the imaging lens 24. The aperture diameter of the aperture diaphragm 23 is variable by an aperture mechanism, allowing the numerical aperture of the imaging optical system 21 to be adjusted. The aperture mechanism of the aperture diaphragm 23 may be controlled by a control unit 50.

[0042] Light L1 that has passed through the imaging lens 24 is incident on the light-receiving surface of the image sensor 25. The image sensor 25 is, for example, a CCD (Charge Coupled Device) image sensor or a CMOS (Complementary Metal Oxide Semiconductor) image sensor. The image sensor 25 generates captured image data IM1 based on the light L1 incident on its light-receiving surface and outputs the captured image data IM1 to the control unit 50. The control unit 50 inspects the photomask 80 based on this captured image data IM1.

[0043] <Lifting drive unit> As shown in Figure 2, the inspection device 1 may be provided with a lifting drive unit 60. The lifting drive unit 60 raises and lowers the measurement stage 90 in the Z-axis direction. This also raises and lowers the photomask 80 placed on the measurement stage 90. The lifting drive unit 60 has, for example, a ball screw mechanism and is controlled by the control unit 50. By raising and lowering the photomask 80 with the lifting drive unit 60, the photomask 80 can be moved to the focal point of the objective lens 22. Note that the lifting drive unit 60 only needs to have the function and structure to raise and lower the photomask 80 relative to the detection unit 20, and for example, it may raise and lower the detection unit 20.

[0044] <Mobile drive unit> As shown in Figure 2, the inspection device 1 may be provided with a moving drive unit 40. The moving drive unit 40 moves the movable illumination unit 19 and detection unit 20, which will be described below, relative to the photomask 80. The movable illumination unit 19 includes a first light guide 12, a Fourier transform lens unit 13, a homogenizer 14, and an illumination optical system 17. The moving drive unit 40 moves the movable illumination unit 19 and detection unit 20 together relative to the photomask 80, moving the incident region of light L1 on the photomask 80, while the detection unit 20 detects the light L1 from the incident region. In other words, the image sensor 25 generates captured image data IM1 of the incident region. For example, the moving drive unit 40 moves the movable illumination unit 19 and detection unit 20 along the X-axis and Y-axis directions, respectively. This allows the incident region of light L1 to be moved along the X-axis and Y-axis directions on the photomask 80, and the control unit 50 can inspect each incident region based on the captured image data IM1 including each incident region.

[0045] In the example shown in Figure 2, the light source 11, lens 111, and the first incident end 12a of the first light guide 12 are not moved by the moving drive unit 40. Here, since the first light guide 12 is flexible, the first incident end 12a is fixed while the first exit end 12b is moved by the moving drive unit 40. In other words, the shape of the first light guide 12 changes according to the position of the first exit end 12b. The longitudinal length of the first light guide 12 is set so that the incident area of ​​light L1 in the photomask 80 can move to cover the entire surface of the photomask 80. The length of the first light guide 12 is set to, for example, several meters or more (for example, about 10 meters).

[0046] On the other hand, the relative positional relationships of the various components inside the movable lighting unit 19 remain constant and do not change due to the driving of the moving drive unit 40. For this reason, for example, the shape of the light guide member 15 remains constant.

[0047] <Department Head> The control unit 50 can control the inspection device 1 as a whole. For example, as described above, the control unit 50 controls the illumination unit 10, the movement drive unit 40, and the lifting drive unit 60. The control unit 50 also functions as a calculation processing unit that inspects the photomask 80 based on the captured image data IM1 generated by the image sensor 25.

[0048] The control unit 50 is an electronic circuit device and may include, for example, an arithmetic processing unit and a memory unit. The arithmetic processing unit may be, for example, a CPU (Central Processor Unit). The memory unit may include a non-temporary memory unit (e.g., ROM (Read Only Memory) or hard disk) and a temporary memory unit (e.g., RAM (Random Access Memory)). The non-temporary memory unit may store, for example, a program that defines the processing to be performed by the control unit 50. By executing this program, the processing unit 50 can perform the processing defined in the program. Of course, some or all of the processing performed by the control unit 50 may be performed by hardware.

[0049] <Effects and Effects> As described above, the moving drive unit 40 moves the movable illumination unit 19 and the detection unit 20. This movement changes the shape of the first light guide 12. Figure 3 is a schematic diagram showing an example of the configuration of the inspection device 1. In the example of Figure 3, the relative positions of the movable illumination unit 19 and the detection unit 20 with respect to the photomask 80 are different from the relative positions in Figure 2. Specifically, their positions in the X-axis direction are different. As shown in Figures 2 and 3, the shape of the first light guide 12 changes due to the movement by the moving drive unit 40. Therefore, the shape of the optical path (e.g., fiber or light guide liquid) within the first light guide 12 changes according to the position of the movable illumination unit 19 (i.e., the position of the incident region of light L1 in the photomask 80). As the shape of the optical path changes, the path of the light rays of light L1 traveling along that optical path also changes, so the spatial distribution of light L1 at the first exit end 12b of the first light guide 12 also changes. In other words, the spatial distribution of light L1 at the first emission end 12b changes according to the position of the movable illumination unit 19.

[0050] Figure 4 is a schematic graph showing an example of the spatial distribution (in other words, positional distribution) of the intensity of light L1 at the first exit end 12b of the first light guide 12. In Figure 4, the vertical axis represents the intensity of light L1, and the horizontal axis represents the position in the X-axis direction at the first exit end 12b. Figure 4 shows graphs G12A and G12B. Graph G12A shows the spatial distribution of the intensity of light L1 at the first exit end 12b at the position shown in Figure 2. Graph G12B shows the spatial distribution of the intensity of light L1 at the first exit end 12b at the position shown in Figure 3. In the example in Figure 4, in graph G12A, the intensity at one position in the X-axis direction is lower than the intensity at the other position in the X-axis direction, whereas in graph G12B, the intensity at one position in the X-axis direction is higher than the intensity at the other position in the X-axis direction. As can be seen from Figure 4, the spatial distribution of the light intensity L1 at the first exit end 12b changes according to the shape of the optical path within the first light guide 12.

[0051] Such changes in the spatial distribution of the intensity of light L1 can become larger as the range of movement of the movable illumination unit 19 by the moving drive unit 40 increases. In other words, the larger the photomask 80 becomes, the greater the changes in the spatial distribution of the intensity of light L1 can become.

[0052] Incidentally, the variation in the direction of propagation of light ray L1 within the first exit end 12b is relatively small. This is because, as light L1 travels through the first light guide 12 while repeatedly reflecting off the first reflective surface 12c, the direction of propagation of light L1 becomes more dispersed. In other words, the directional distribution (or angular distribution) of the intensity of light L1 at the first exit end 12b is less variable than the spatial distribution of the intensity of light L1 at the first exit end 12b.

[0053] The Fourier transform lens section 13 forms a Fourier transform image of the image at the first exit end 12b on the Fourier plane. In other words, light rays L1 traveling in the same direction at the first exit end 12b are incident at the same position on the Fourier plane. Therefore, the spatial distribution (positional distribution) of the intensity of light L1 on the Fourier plane ideally coincides with the directional distribution (angular distribution) of the intensity of light L1 at the first exit end 12b. Consequently, variations in the spatial distribution of the intensity of light L1 on the Fourier plane can be reduced. Since the incident surface of the homogenizer 14 (here, the second incident end 15a of the light guide member 15) is provided on the Fourier plane, light L1 with a more uniform spatial distribution of intensity can be incident on this incident surface.

[0054] Figure 5 is a schematic graph showing an example of the spatial distribution of the intensity of light L1 incident on the second incident end 15a of the light guide member 15. Figure 5 shows graphs G15A and G15B. Graph G15A shows the spatial distribution of the intensity of light L1 at the second incident end 15a at the position shown in Figure 2, and graph G15B shows the spatial distribution of the intensity of light L1 at the second incident end 15a at the position shown in Figure 3. As shown in Figure 5, the variation in the spatial distribution of the intensity of light L1 at the second incident end 15a is smaller than the variation in the spatial distribution of the intensity of light L1 at the first exit end 12b. In other words, the Fourier transform lens section 13 can reduce the variation in the spatial distribution of the intensity of light L1 at the second incident end 15a of the light guide member 15.

[0055] Light L1 travels through the inside of the light guide member 15 from the second input end 15a towards the second output end 15b. The shape of the optical path inside the light guide member 15 is hardly changed by the moving drive unit 40. In other words, the shape of the light guide member 15 is constant. Therefore, the spatial distribution of the intensity of light L1 at the second output end 15b of the light guide member 15 does not change much compared to the intensity distribution of light L1 at the first output end 12b of the first light guide 12. Consequently, the spatial distribution of the intensity of light L1 at the second output end 15b can be made more uniform. Conversely, the shape of the light guide member 15 is designed so as to maintain uniformity in the spatial distribution of the intensity of light L1 at the second output end 15b.

[0056] Furthermore, the light L1 travels through the inside of the light guide member 15 while being repeatedly reflected by the second reflective side surface 15c. As a result, the direction of propagation of each ray of light L1 is dispersed as it travels through the light guide member 15. In other words, the repeated reflection at the second reflective side surface 15c of the light guide member 15 makes the distribution of the direction of propagation of the light rays more uniform. Consequently, the directional distribution (angle distribution) of the intensity of light L1 at the second output end 15b is also made uniform.

[0057] Figure 6 is a schematic graph showing an example of the directional distribution of the intensity of each ray of light L1. In the example in Figure 6, the vertical axis represents the intensity of light L1, and the horizontal axis represents the direction of propagation of the ray in angle. The angle may be set based on, for example, the direction along the optical path (i.e., the normal direction of the cross section perpendicular to the optical path). Figure 6 shows graphs G15aA, G15aB, G15bA, and G15bB. Graph G15aA shows the directional distribution of light L1 intensity at the second incident end 15a at the position shown in Figure 2, graph G15aB shows the directional distribution of light L1 intensity at the second incident end 15a at the position shown in Figure 3, graph G15bA shows the directional distribution of light L1 intensity at the second exit end 15b at the position shown in Figure 2, and graph G15bB shows the directional distribution of light L1 intensity at the second exit end 15b at the position shown in Figure 3. As shown in Figure 6, the variability in the directional distribution of light L1 intensity at the second exit end 15b can be reduced (see graphs G15bA and G15bB).

[0058] As described above, the inspection device 1 can improve the uniformity of light L1 (spatial and directional distribution of intensity) at the second emission end 15b of the light guide member 15. Since the second emission end 15b functions as a pseudo-light source for the illumination optical system 17, more uniform light L1 can be incident on the illumination optical system 17. Consequently, the uniformity of light L1 in the incident region that is incident on the photomask 80 through the illumination optical system 17 can be improved. For example, even if the position of the movable illumination unit 19 changes, more uniform light L1 can be incident on the photomask 80. Therefore, the inspection device 1 can inspect the entire surface of the photomask 80 with higher accuracy and more uniformity.

[0059] More generally, the Fourier transform lens section 13 improves the uniformity of light L1 to some extent, and the subsequent homogenizer 14 further improves the uniformity of light L1. As a result, the inspection device 1 can inspect the photomask 80 with higher accuracy and uniformity.

[0060] Furthermore, the Fourier transform lens section 13 directs the rays of light L1 traveling in the same direction, emitted from the entire surface of the first output end 12b of the first light guide 12, to the same position on the second input end 15a of the light guide member 15. In other words, the intensity of light L1 at any position on the second input end 15a is formed by the rays of light L1 traveling in the same direction from all positions on the first output end 12b. Conversely, the light L1 at each position on the first output end 12b is dispersed across the entire surface of the second input end 15a according to the direction of propagation of the light ray. Therefore, variations in the spatial distribution of intensity at the first output end 12b can be absorbed more appropriately, and more uniform light L1 can be incident on the second input end 15a.

[0061] Here, for comparison, let's consider the case where a uniformization means such as a microarray lens is provided instead of the Fourier transform lens section 13. A microarray lens has multiple lenses, and the bending action of each lens disperses the light L1, thereby uniformizing the light L1. Therefore, if low-intensity light L1 is incident on some of the multiple lenses, the effect of this variation will inevitably occur at the second incident end 15a as well. To reduce this effect, if the light L1 is dispersed more widely by the lenses, the amount of light L1 that cannot be incident on the second incident end 15a of the light guide member 15 will increase, and the loss of light L1 will increase. In contrast, with the Fourier transform lens section 13, the amount of light L1 that does not occur on the second incident end 15a is small, so the loss of light L1 can be reduced. Also, as described above, light L1 with a more uniform spatial distribution of intensity can be incident on the second incident end 15a.

[0062] For further comparison, we also consider a structure without the Fourier transform lens section 13. In this structure, the longitudinal length of the light guide member 15 needs to be sufficiently long in order to sufficiently homogenize the light L1. This would result in a larger and heavier illumination unit 10. In contrast, by providing the Fourier transform lens section 13, a smaller and lighter illumination unit 10 can be realized. Therefore, the load on the moving drive unit 40 can also be reduced.

[0063] In the example described above, a movable drive unit 40 is provided, but this is not necessarily the case. In cases where the object to be inspected is small, the movable drive unit 40 may not be provided. Even without this, the light L1 from the light source 11 can be made more uniform, and the uniformized light L1 can be irradiated onto the object to be inspected. Furthermore, even if the intensity distribution of the light L1 from the light source 11 fluctuates over time, the illumination unit 10 can absorb these fluctuations and irradiate the object to be inspected with more uniform light L1.

[0064] Furthermore, if the first light guide 12 includes plastic fibers or a liquid light guide, the flexibility of the first light guide 12 can be improved. This makes it easier for the moving drive unit 40 to move the movable lighting unit 19.

[0065] Furthermore, if the optical path of the first light guide 12 is formed by glass or a light-guiding liquid (e.g., pure water), the transmittance of the optical path is high, which reduces the loss of light L1 in the first light guide 12. As a result, the inspection device 1 can inspect the photomask 80 with higher efficiency. The same applies to the light-guiding member 15.

[0066] Furthermore, if the first light guide 12 is a liquid light guide, even if the shape of the first light guide 12 changes, no stress is generated in the light-guiding liquid that forms the light path. Therefore, the lifespan of the first light guide 12 can be extended.

[0067] <Shape of the light guide component> Since the size of the photomask 80 in plan view is large, a relatively large space is formed in the portion adjacent to the movable illumination unit 19 in the horizontal direction (X-axis direction or Y-axis direction). In order to make effective use of this space, the light guide member 15 may extend in an S-shape, as shown in Figure 2. That is, at least a part of the light guide member 15 may extend in a direction having a component parallel to the direction of movement of the moving drive unit 40. Hereinafter, this component will be referred to as the movement direction component. In other words, the extending direction of at least a part of the optical path of the light guide member 15 may have a movement direction component. Here, the extending direction may be, for example, the direction in which the central axis of the second reflective surface 15c, which is surrounded by the second reflective surface 15c, extends.

[0068] Here, for comparison, we consider a structure in which the light guide member 15 has a rod-like shape that extends linearly along the Z-axis. In this structure, the size of the movable illumination unit 19 in the Z-axis direction increases, leading to an increase in the size of the inspection device 1.

[0069] In contrast, if at least a portion of the light guide member 15 extends in a direction having a component in the direction of movement, although the size of the light guide member 15 in that direction of movement increases, the size of the photomask 80 in that direction of movement is larger than that of the light guide member 15, so the size of the inspection device 1 hardly increases. In other words, since there is a large space facing the photomask 80 in the Z-axis direction, even if the size of the light guide member 15 in the direction of movement is large, the light guide member 15 can be placed in this space. Furthermore, by increasing the length of the optical path of the light guide member 15, the light L1 can be made more uniform. As described above, if the extension direction of at least a portion of the light guide member 15 has a component in the direction of movement, the optical path of the light guide member 15 can be lengthened and the light L1 can be made more uniform while suppressing an increase in the size of the inspection device 1.

[0070] <Other examples of homogenizers> Figure 7 is a schematic diagram showing another example of the configuration of the inspection apparatus 1. The homogenizer 14 may be, for example, frosted glass. The frosted glass is provided on the Fourier plane. The frosted glass has, for example, a plate-like shape. Fine irregularities are formed on at least one main surface of the frosted glass. Light L1 from the Fourier transform lens section 13 is scattered by the irregularities on the main surface of the frosted glass and spreads more uniformly. As a result, the homogenizer 14 can emit more uniform light L1 to the illumination optical system 17.

[0071] Alternatively, the homogenizer 14 may be a microarray lens. A microarray lens has, for example, multiple lenses arranged in a matrix. The number of rows and columns is arbitrary, but may be, for example, five or more, or ten or more. The microlens array is provided in the Fourier plane. The light L1 incident on the microarray lens is dispersed by each lens, so that more uniform light L1 is incident on the illumination optical system 17.

[0072] Alternatively, the homogenizer 14 may be a fly array lens. The fly array lens is provided on the Fourier plane. Multiple lenses are formed on both principal surfaces of the fly array lens, and light L1 is homogenized by passing through both principal surfaces.

[0073] Even with this structure, the Fourier transform lens section 13 homogenizes the spatial distribution of the intensity of light L1. Furthermore, the homogenizer 14 disperses the light L1, thereby homogenizing its directional distribution as well. Consequently, the illumination optical system 17 can receive a uniform beam of light L1.

[0074] As described above, the inspection apparatus 1 has been explained in detail, but the above description is illustrative in all respects, and this disclosure is not limited thereto. Furthermore, the various modifications described above can be applied in combination as long as they do not contradict each other. And it is understood that a number of modifications not illustrated can be conceivable without falling outside the scope of this disclosure.

[0075] This disclosure includes the following aspects:

[0076] The first embodiment is an inspection apparatus comprising a light source that emits light, a first light guide having a first incident end into which the light from the light source is incident, and a first exit end, a homogenizer, a Fourier transform lens section provided between the first exit end of the first light guide and the homogenizer, an illumination optical system provided downstream of the homogenizer, a measurement stage provided downstream of the illumination optical system on which an object to be inspected is placed, an imaging optical system into which the light from the object to be inspected is incident, and an image sensor that receives the light from the imaging optical system and generates image data.

[0077] A second embodiment is an inspection apparatus according to the first embodiment, further comprising a moving drive unit that moves the illumination optical system, the homogenizer, and the Fourier transform lens unit to move the incident region of the object to be inspected to which the light is incident, wherein the first light guide is flexible.

[0078] A third embodiment is an inspection apparatus according to the second embodiment, wherein the homogenizer has a second incident end and a second exit end, and includes a light guide member through which the light incident from the second incident end travels toward the second exit end with total internal reflection.

[0079] A fourth embodiment is an inspection apparatus according to the third embodiment, wherein at least a portion of the light guide member extends in a direction having a component parallel to the direction of movement of the moving drive unit.

[0080] A fifth aspect is an inspection apparatus according to the third or fourth aspect, wherein the light guide member includes a plurality of fibers.

[0081] The sixth aspect is an inspection apparatus according to any one of the second to fifth aspects, wherein the first light guide includes a liquid light guide.

[0082] The seventh aspect is an inspection apparatus according to any one of the first to sixth aspects, wherein the object to be inspected includes a photomask.

[0083] According to the first embodiment, the Fourier transform lens section is provided between the first exit end of the first light guide and the homogenizer. Therefore, the light obtained by Fourier transforming the light at the first exit end is incident on the homogenizer. Consequently, light with a more uniform spatial distribution of intensity is incident on the homogenizer. Furthermore, the light loss in the Fourier transform lens section is small. The homogenizer further homogenizes this light before it is incident on the illumination optical system. This further improves the uniformity of the light incident on the measurement stage.

[0084] According to the second embodiment, the shape of the first light guide changes flexibly in accordance with the movement of the illumination optical system, homogenizer, and Fourier transform lens section, so that they can be appropriately moved even if the position of the light source is fixed. As the shape of the first light guide changes, the shape of the optical path of the first light guide changes, so the spatial distribution of light at the first exit end of the first light guide changes in accordance with the change in the shape of the first light guide. However, even if the spatial distribution of light at the first exit end changes, the Fourier transform lens section and homogenizer can homogenize the light with low loss, and uniform light can be incident on the object under inspection. In other words, even if the position of the incident region on the object under inspection changes, uniform light can be incident on the incident region.

[0085] According to the third embodiment, light can be homogenized with lower loss.

[0086] According to the fourth embodiment, the optical path of the light guide member can be lengthened while suppressing an increase in the size of the inspection device. By lengthening the optical path of the light guide member, the light can be made more uniform.

[0087] According to the fifth embodiment, the fiber has a very large ratio of the length of the optical path to the cross-sectional diameter of the optical path, which allows for further homogenization of the light.

[0088] According to the sixth embodiment, even if the shape of the first light guide changes, no stress is generated in the light guide liquid that forms the optical path, thus extending the lifespan of the first light guide. Furthermore, light loss in the first light guide is also reduced.

[0089] According to the seventh aspect, the photomask can be properly inspected. [Explanation of symbols]

[0090] 1. Inspection device 11 Light source 12. First Light Guide 12a 1st entrance end 12b 1st output end 13. Fourier transform lens section 14 Homogenizer 15 Light guide member 15a 2nd entrance end 15b 2nd output end 17 Illumination optical system 21 Imaging Optical System 25 Image Sensors 80. Object under inspection (photomask) 90 measurement stages

Claims

1. A light source that emits light, A first light guide having a first incident end into which the light from the light source is incident, and a first exit end, Homogenizer and, A Fourier transform lens portion is provided between the first exit end of the first light guide and the homogenizer, An illumination optical system provided downstream of the homogenizer, A measurement stage is provided downstream of the aforementioned illumination optical system, on which the object to be inspected is placed, An imaging optical system into which the light from the object under inspection is incident, An image sensor that receives the light from the imaging optical system and generates captured image data, An inspection device equipped with the following features.

2. An inspection apparatus according to claim 1, The system further comprises a moving drive unit that moves the illumination optical system, the homogenizer, and the Fourier transform lens unit to move the incident region of the object under inspection to which the light is incident, The first light guide is a flexible inspection device.

3. The inspection apparatus according to claim 2, The homogenizer described above is An inspection apparatus including a light guide member having a second incident end and a second exit end, wherein light incident from the second incident end travels toward the second exit end with total internal reflection.

4. The inspection apparatus according to claim 3, An inspection device wherein at least a portion of the light guide member extends in a direction having a component parallel to the direction of movement of the moving drive unit.

5. An inspection apparatus according to claim 3 or claim 4, The light guide member is an inspection device that includes multiple fibers.

6. An inspection apparatus according to any one of claims 2 to 4, The inspection apparatus includes a liquid light guide as the first light guide.

7. An inspection apparatus according to any one of claims 1 to 4, The object to be inspected is an inspection device including a photomask.

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