Photomask inspection equipment

Abstract

To provide a highly reliable photomask inspection apparatus that can detect a photomask at higher detection accuracy.SOLUTION: A photomask inspection apparatus 1 comprises a holding part, a first light source 12a, a second light source 12b, a mixing part 14, an illumination optical system 17, an image forming optical system 21, an image sensor 25, and an arithmetic processing part 50. A holding part holds a photomask 80. The first light source 12a includes a single first semiconductor light-emitting element 121 that emits first light L1a. The second light source 12b includes a single second semiconductor light-emitting element 121 that emits second light L1b. The mixing part 14 mixes the first light L1a and the second light L1b. The illumination optical system 17 leads light L2 to the photomask 80. The image sensor 25 receives light L2 that is made incident through the image forming optical system 21 to generate a captured image IM1. The arithmetic processing part 50 inspects the photomask 80 on the basis of the captured image IM1.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a photomask inspection apparatus. [Background technology]

[0002] BACKGROUND ART Inspection devices for inspecting photomasks (reticles) have been proposed (Patent Documents 1 and 2).

[0003] In Patent Document 1, a light source is provided that outputs light including g-line, h-line, and i-line. The light from the light source is irradiated onto a photomask through a wavelength-selective filter, and the light that passes through the photomask is incident on the imaging surface of an imaging means. The wavelength-selective filter includes a first filter that transmits only g-line, a second filter that transmits only h-line, and a third filter that transmits only i-line. Light selectively passes through these first, second, and third filters. When light passes through the first filter, only g-line is incident on the imaging means through the photomask, and the imaging means generates an image captured using the g-line. When light passes through the second filter, the imaging means generates an image captured using the h-line, and when light passes through the third filter, it generates an image captured using the i-line. In Patent Document 1, these three captured images are wavelength-combined to generate a composite image using light including g-line, h-line, and i-line, and the photomask is inspected based on the composite image.

[0004] In Patent Document 2, multiple illumination sources are provided, each of which includes multiple laser diode arrays. Beams output from the multiple illumination sources are combined by beam combining optics, causing the beams to be incident on a sample with a desired illumination profile. The beams reflected from the sample are incident on a detector and detected by the detector. The inspection device determines sample parameters, such as critical dimensions, based on the signals output from the detector. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-256671 [Patent Document 2] Japanese Patent Publication No. 2020-064063 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in Patent Document 1, an image captured with g-line, an image captured with h-line, and an image captured with i-line are captured at different times. As a result, positional variations occur in the captured images due to mechanical vibrations of the inspection device. Therefore, errors caused by this positional variations are included in the composite image, resulting in a problem of reduced inspection accuracy.

[0007] In Patent Document 2, a laser diode array is used as the light source. Each laser diode array is provided with multiple light-emitting elements, which causes variations in at least one of the wavelength and phase of the light emitted from each illumination source among the multiple elements. This reduces the coherence of the light emitted from each illumination source.

[0008] Therefore, even if the illumination profile is made closer to the illumination profile of the light source in the exposure tool, the diffraction phenomenon occurring at the sample in the inspection tool will be significantly different from the diffraction phenomenon in the exposure tool. As a result, the image detected by the detector will differ from the image in the exposure tool, resulting in a problem of reduced inspection accuracy. Furthermore, if an abnormality occurs in any one of the multiple elements, the entire system must be replaced, which reduces reliability.

[0009] Therefore, an object of the present disclosure is to provide a highly reliable photomask inspection apparatus that can detect photomasks with higher detection accuracy. [Means for solving the problem]

[0012] No. 1The embodiment is a photomask inspection device including: a holder for holding a photomask; a first light source including a single first semiconductor light emitting element that emits first light having a first peak wavelength; a second light source including a single second semiconductor light emitting element that emits second light having a second peak wavelength different from the first peak wavelength; a mixer that mixes the first light from the first light source and the second light from the second light source; an illumination optical system that guides the light obtained by mixing the first light and the second light by the mixer to the photomask; a movement driver that changes the relative position of the photomask and the illumination optical system in an optical axis direction; and an objective lens, wherein the light from the photomask is incident on an imaging light. an optical system, an image sensor that receives the light incident through the imaging optical system and generates a captured image, and an arithmetic processing unit that inspects the photomask based on the captured image, wherein the arithmetic processing unit obtains a focus evaluation value for each of the multiple captured images generated by the image sensor while changing the distance between the photomask and the illumination optical system, calculates mask characteristics based on each of the multiple captured images, and judges the quality of the photomask based on the mask characteristics that correspond to a range of a predetermined focus deviation amount in an exposure apparatus in which the photomask is used from the relative position at which the focus evaluation value is maximum among the multiple captured images. No. 2 The embodiment is 1 The photomask inspection device according to the embodiment includes a light guide through which the light mixed with the first light and the second light by the mixing section enters at an incident end, travels inside, and exits at an exit end, and an illumination optical system that guides the light exiting from the light guide to the photomask. [Effects of the Invention]

[0013] According to the photomask inspection device, the mixing unit mixes first and second light beams having different peak wavelengths. The mixed light beam then passes through the photomask and enters the light receiving surface of the image sensor via the imaging optical system. Therefore, the captured image includes a projected image of the photomask formed by the light beams having the first and second peak wavelengths. In other words, a single image capture can obtain a captured image including projected images formed by the light beams having multiple peak wavelengths.

[0014] Therefore, there is no need to combine multiple captured images obtained by sequentially irradiating light having different peak wavelengths, as in Patent Document 1. Therefore, unlike Patent Document 1, positional variations for each peak wavelength do not occur in principle in the captured images. Therefore, the arithmetic processing unit can inspect the photomask based on the captured images with higher inspection accuracy.

[0015] Moreover, in the photomask inspection device, the first light source and the second light source each include a single semiconductor light-emitting element. Therefore, wavelength or phase variations, such as those in the diode arrays described in Patent Document 2, do not occur in principle, and the first light source can emit a more coherent first light, and the second light source can emit a more coherent second light. Therefore, a diffraction phenomenon equivalent to that in an exposure device can be generated in the light passing through the photomask. Therefore, the processing unit can inspect the photomask with higher inspection accuracy. Furthermore, the reliability of the first light source and the second light source is also high. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a perspective view schematically illustrating an example of the configuration of a photomask inspection apparatus. [Figure 2] FIG. 1 is a diagram schematically illustrating an example of an optical configuration of a photomask inspection apparatus. [Figure 3] FIG. 1 is a diagram schematically illustrating an example of the optical configuration of an exposure apparatus. [Figure 4] 4 is a graph showing the transmittance and reflectance of a first dichroic mirror. [Figure 5] 10 is a graph showing the transmittance and reflectance of the second dichroic mirror. [Figure 6] FIG. 2 is a diagram schematically illustrating an example of a captured image. [Figure 7] 10 is a flowchart showing an example of the operation of the photomask inspection apparatus. [Figure 8] 10A and 10B are diagrams illustrating the luminance distribution of a projected image on a line of each captured image. [Figure 9] 10 is a graph showing the relationship between the Z-axis position and the focus evaluation value, and the relationship between the Z-axis position and the width of the projected image. [Figure 10] FIG. 10 is a diagram schematically illustrating an example of a captured image including a defect. [Figure 11] 10 is a graph showing the relationship between the Z-axis position and the focus evaluation value, and the relationship between the Z-axis position and the defect brightness. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments will be described in detail with reference to the drawings. Note that in the drawings, the dimensions and number of each part are exaggerated or simplified as necessary for ease of understanding. Parts having similar configurations and functions are given the same reference numerals, and duplicate explanations will be omitted in the following description. In addition, in the drawings, XYZ Cartesian coordinates are appropriately shown to show the positional relationship of each part. For example, the Z axis is arranged along the vertical direction, and the X and Y axes are arranged along the horizontal direction. In the following description, one side of the Z axis direction will be referred to as the +Z side, and the other side will be referred to as the -Z side. The same applies to the X and Y axes.

[0018] In the following description, the same components are denoted by the same reference numerals, and their names and functions are also the same. Therefore, detailed descriptions of them may be omitted to avoid duplication.

[0019] Furthermore, in the following description, even if ordinal numbers such as "first" or "second" are used, these terms are used for convenience to facilitate understanding of the contents of the embodiments, and are not limited to the ordering that may result from these ordinal numbers.

[0020] When expressions indicating relative or absolute positional relationships (e.g., "in one direction," "along one direction," "parallel," "orthogonal," "center," "concentric," "coaxial," etc.) are used, unless otherwise specified, the expressions 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 range in which tolerance or equivalent functionality is obtained. When expressions indicating an equal state (e.g., "identical," "equal," "homogeneous," etc.) are used, the expressions not only represent a state in which there is strict quantitative equality but also represent a state in which there is a difference in which tolerance or equivalent functionality is obtained, unless otherwise specified. When expressions indicating a shape (e.g., "rectangular shape" or "cylindrical shape," etc.) are used, the expressions not only represent a geometrically strict shape but also represent a shape with, for example, irregularities or chamfers within a range in which equivalent effects are obtained, unless otherwise specified. When the expressions "comprise," "include," "have," "includes," "includes," or "have" are used to describe one component, the expressions are not exclusive expressions that exclude the presence of other components. When the phrase "at least one of A, B, and C" is used, the phrase includes A only, B only, C only, any two of A, B, and C, and all of A, B, and C.

[0021] <Photomask inspection equipment> Fig. 1 is a perspective view that schematically shows an example of the configuration of a photomask inspection apparatus 1, and Fig. 2 is a diagram that schematically shows an example of the optical configuration of the photomask inspection apparatus 1. The photomask inspection apparatus 1 is an apparatus that inspects a photomask 80.

[0022] <Photomask> First, the photomask 80 to be inspected will be described. The photomask 80 is a photomask used in the exposure tool 1000. FIG. 3 is a diagram schematically showing an example of the optical configuration of the exposure tool 1000. The exposure tool 1000 performs an exposure process on the substrate W using the photomask 80, thereby transferring the pattern of the photomask 80 onto the substrate W. The substrate W 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 used as the substrate W.

[0023] The photomask 80 has a plate-like shape, e.g., a rectangular shape in a plan view. The length of one side of the photomask 80 is set to, e.g., about several meters. As a more specific example, the lengths of the sides of the photomask 80 are 1.8 m and 2.0 m, respectively, and the thickness of the photomask 80 is, e.g., 2.1 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 is formed with a transmitting portion that transmits light and a blocking portion that blocks light. The photomask 80 may also be a phase shift mask provided with a phase shift film that transmits light with a transmittance lower than that of the transmitting portion.

[0024] Photomask 80 is held by a mask holder (not shown) in exposure tool 1000. The mask holder holds photomask 80 in a position where its thickness direction is along the Z-axis direction. The mask holder supports only the peripheral edge of photomask 80, for example.

[0025] As shown in Fig. 3, exposure apparatus 1000 includes an illumination unit 1100 and an imaging unit 1200. Illumination unit 1100 and imaging unit 1200 are provided on opposite sides of photomask 80. In the example of Fig. 3, illumination unit 1100 is provided on the +Z side of photomask 80, and imaging unit 1200 is provided on the -Z side of photomask 80.

[0026] The illumination unit 1100 includes a light source 1110 and an illumination optical system 1120. The light source 1110 emits exposure light toward the illumination optical system 1120. The exposure light is, for example, ultraviolet light, and the light source 1110 is, for example, an ultraviolet irradiator such as a mercury lamp (e.g., a high-pressure mercury lamp). The light from the light source 1110 is irradiated onto the photomask 80 through the illumination optical system 1120.

[0027] In the example of FIG. 3 , the illumination optical system 1120 includes a condenser lens 1130, a field stop 1140, a condenser lens 1150, an aperture stop 1160, and a condenser lens 1170. The condenser lens 1130, the field stop 1140, the condenser lens 1150, the aperture stop 1160, and the condenser lens 1170 are arranged in this order, increasing in distance from the light source 1110 in the Z-axis direction. That is, the condenser lens 1130 is arranged closest to the light source 1110. Light from the light source 1110 is condensed by the condenser lens 1130 and passes through the field stop 1140. The aperture diameter of the field stop 1140 is variable, allowing the illumination range to be adjusted. Light passing through the field stop 1140 is condensed by the condenser lens 1150 and passes through the aperture stop 1160. Light passing through the aperture stop 1160 is condensed onto the photomask 80 by the condenser lens 1170. The aperture diameter of the aperture stop 1160 is variable, and the numerical aperture of the illumination optical system 1120 can be adjusted.

[0028] The illumination optical system 1120 may be provided with an optical filter that transmits only light within a predetermined wavelength range from the light source 1110 .

[0029] The exposure light from the illumination unit 1100 passes through the transparent portions of the photomask 80. The patterned light that has passed through the transparent portions of the photomask 80 enters the imaging unit 1200 (imaging optical system). The imaging unit 1200 includes an objective lens 1210, an aperture stop 1220, and an imaging lens 1230. The objective lens 1210, the aperture stop 1220, and the imaging lens 1230 are arranged in this order with increasing distance from the photomask 80 in the Z-axis direction. The light that has passed through the transparent portions of the photomask 80 is enlarged via the objective lens 1210 and the imaging lens 1230. The aperture diameter of the aperture stop 1220 is variable, allowing the numerical aperture of the imaging unit 1200 to be adjusted. When the substrate W is a substrate for a flat panel display, the numerical aperture of the imaging unit 1200 in the exposure apparatus 1000 is set small, for example, to approximately 0.1.

[0030] The substrate W is provided on the opposite side of the photomask 80 with respect to the imaging unit 1200. In the example of Fig. 3, the substrate W is provided on the -Z side of the imaging unit 1200. The substrate W is held in a horizontal position by a substrate holder (not shown). The horizontal position here means that the thickness direction of the substrate W is aligned with the Z-axis direction.

[0031] The patterned light from the imaging unit 1200 is irradiated onto the main surface on the +Z side of the substrate W. This exposes the resist formed on the main surface of the substrate W in a patterned manner. In other words, the pattern of the transparent portion of the photomask 80 is transferred onto the main surface of the substrate W.

[0032] If the photomask 80 is defective, the pattern transferred onto the substrate W will deviate from the designed pattern, which is undesirable. Therefore, the photomask inspection apparatus 1 inspects the photomask 80.

[0033] <Photomask inspection system overview> 2, the photomask inspection apparatus 1 includes an image sensor (optical sensor) 25 that receives light transmitted through the photomask 80. As will be described in detail later, the photomask inspection apparatus 1 artificially reproduces, on the light receiving surface (imaging surface) of the image sensor 25, the pattern of light that is irradiated onto the substrate W when the photomask 80 to be inspected is used in the exposure apparatus 1000. The image sensor 25 detects the light on the light receiving surface, and the photomask inspection apparatus 1 inspects the photomask 80 based on the detection results. In other words, the photomask inspection apparatus 1 can artificially inspect the photomask 80 based on the light on the substrate W in the exposure apparatus 1000.

[0034] The photomask inspection device 1 includes an illumination unit 10, a detection unit 20, a movement mechanism 40, a control unit 50, a lifting mechanism 60, and a holding unit 90. Below, we will first provide an overview of the configuration of the photomask inspection device 1, and then provide a detailed description of an example of each component.

[0035] The holding part 90 is a member that holds the photomask 80. The holding part 90 holds the photomask 80 so that the thickness direction of the photomask 80 is along the Z-axis direction. In the example of FIG. 1, the holding part 90 supports only the peripheral edge part of the photomask 80. However, the holding part 90 may support the entire lower surface of the photomask 80 using a light-transmitting member.

[0036] The illumination unit 10 and the detection unit 20 are provided on opposite sides of the photomask 80 in the Z-axis direction. In the example of Figures 1 and 2, the illumination unit 10 is provided on the -Z side of the photomask 80, and the detection unit 20 is provided on the +Z side of the photomask 80.

[0037] The illumination unit 10 irradiates light L2 toward the photomask 80. In the example of FIG. 2, the illumination unit 10 includes a simulated light irradiation unit 11 and an illumination optical system 17. The simulated light irradiation unit 11 emits light L2 having a spectrum similar to the spectrum of light used for exposure within the wavelength range of light irradiated by the light source 1110 of the exposure apparatus 1000. In other words, the light L2 is light that simulates the light used for exposing the substrate W in the exposure apparatus 1000. This light L2 is incident on the photomask 80 from the -Z side through the illumination optical system 17. In other words, the illumination optical system 17 guides the light L2 from the illumination unit 10 to the photomask 80. The pattern-shaped light L2 that has passed through the transmission portion of the photomask 80 is incident on the detection unit 20.

[0038] The detection unit 20 includes an imaging optical system 21 and an image sensor 25. The imaging optical system 21 forms an image of light L2 transmitted through the photomask 80 on the light receiving surface of the image sensor 25. Sigma (=N1 / N2), which is the ratio of the numerical aperture N1 of the illumination optical system 17 to the numerical aperture N2 of the imaging optical system 21, is set to the same value as Sigma (=N10 / N20), which is the ratio of the numerical aperture N10 of the illumination optical system 1120 to the numerical aperture N20 of the imaging unit 1200 of the exposure apparatus 1000. As a result, the luminance distribution of light L2 incident on the light receiving surface of the image sensor 25 mimics the luminance distribution of the pattern-like light irradiated onto the substrate W. In other words, the luminance distribution of light irradiated onto the substrate W when the photomask 80 is used in the exposure apparatus 1000 is reproduced in a pseudo manner on the light receiving surface of the image sensor 25.

[0039] <Lighting Department> As illustrated in FIG. 2, the simulated light irradiation unit 11 includes a plurality of light sources 12 and a mixer 14.

[0040] The plurality of light sources 12 emit light L1 having different peak wavelengths from one another. In the example of FIG. 2, three light sources 12a to 12c are provided as the plurality of light sources 12. Each light source 12 includes a single semiconductor light emitting element 121. The semiconductor light emitting element 121 includes, for example, a light emitting diode element or a laser element. Such a single semiconductor light emitting element 121 includes, for example, a single semiconductor laminate structure having a single p-type semiconductor layer and a single n-type semiconductor layer.

[0041] The light source 12a emits light L1a having a first peak wavelength. The first peak wavelength is, for example, 365 nm (the wavelength of the so-called i-line). The light source 12b emits light L1b having a second peak wavelength different from the first peak wavelength. The second peak wavelength is, for example, 405 nm (the wavelength of the so-called h-line). The light source 12c emits light L1c having a third peak wavelength different from both the first peak wavelength and the second peak wavelength. The third peak wavelength is, for example, 436 nm (the wavelength of the so-called g-line). The optical spectral distribution (spectrum) of the light L1 emitted by each light source 12 may have only one peak wavelength. In other words, the light L1 may be light of a single wavelength. Specifically, the spectrum of the light emitted by each light source 12 may have a steep mountain-like shape with the intensity at the peak wavelength being the maximum intensity. When the semiconductor light emitting element 121 is a light emitting diode element, it emits light L1 having a spectrum with a slightly broad peak, and when the semiconductor light emitting element 121 is a laser element, it emits light L1 having a spectrum with a relatively narrow peak.

[0042] Each semiconductor light emitting element 121 is individually supplied with power from a power supply unit (not shown). Each semiconductor light emitting element 121 emits light L1 at a luminance corresponding to the power from the power supply unit. The power supply unit is, for example, a current source and includes, for example, a switching power supply circuit. In this case, the power supply unit controls the luminance of the light L1 by controlling the current supplied to the semiconductor light emitting element 121. Since each power supply unit is individually controlled by the control unit 50, the luminance of the light L1 from each light source 12 is individually controlled by the control unit 50.

[0043] Each light source 12 may be provided with a sensor (not shown) that measures the intensity (or illuminance, light amount) of light L1 from the semiconductor light emitting element 121. The sensor outputs a signal indicating the detected value to the control unit 50. The control unit 50 controls the power supply unit based on the detected value to control the current supplied from the power supply unit to the semiconductor light emitting element 121. This allows the control unit 50 to control the intensity of light L1 emitted from the light source 12 with higher precision.

[0044] Light L1a emitted from light source 12a enters mixing section 14 through lens 13a, light L1b emitted from light source 12b enters mixing section 14 through lens 13b, and light L1c emitted from light source 12c enters mixing section 14 through lens 13c.

[0045] The mixer 14 mixes the multiple light beams L1 incident from the multiple light sources 12. Here, mixing of light beams means substantially matching the optical paths of the multiple light beams L1. In the example of FIG. 2, the mixer 14 includes a first dichroic mirror 141 and a second dichroic mirror 142.

[0046] Light L1a and light L1b are incident on the first dichroic mirror 141. In the example of FIG. 2, light source 12a is located on the −X side of the first dichroic mirror 141 and irradiates light L1a toward the +X side along the X-axis direction. Light source 12b is located on the +Z side of the first dichroic mirror 141 and irradiates light L1b toward the −Z side along the Z-axis direction. The first dichroic mirror 141 has a plate-like shape and is disposed with its thickness direction aligned from the +X and +Z sides toward the −X and −Z sides. The first dichroic mirror 141 reflects light L1a and transmits light L1b in the same direction as the reflection direction of light L1a. FIG. 4 is a graph showing the transmittance and reflectance of the first dichroic mirror 141. The first dichroic mirror 141 has low transmittance and high reflectance for light L1a of a first peak wavelength (365 nm in this case). On the other hand, the first dichroic mirror 141 has high transmittance and low reflectance for the light L1b of the second peak wavelength (here, 405 nm) and the light L1c of the third peak wavelength (here, 436 nm).

[0047] Light L1a is reflected by the first dichroic mirror 141 along the Z axis toward the -Z side, and light L1b passes through the first dichroic mirror 141 and travels toward the -Z side. This ideally causes the optical paths of light L1a and light L1b to coincide. In other words, light L1a and light L1b are mixed.

[0048] This mixed light and light L1c are incident on the second dichroic mirror 142. In the example of FIG. 2, the second dichroic mirror 142 is located on the -Z side of the first dichroic mirror 141. The light source 12c is located on the -X side of the second dichroic mirror 142 and irradiates light L1c to the +X side along the X-axis direction. The second dichroic mirror 142 has a plate-like shape and is disposed with its thickness direction aligned from the +X and +Z sides toward the -X and -Z sides. The second dichroic mirror 142 reflects the mixed light and transmits light L1c in the same direction as the reflection of the mixed light. FIG. 5 is a graph showing the transmittance and reflectance of the second dichroic mirror 142. The second dichroic mirror 142 has low transmittance and high reflectance for light L1a and light L1b. On the other hand, the second dichroic mirror 142 has a high transmittance and a low reflectance for the light L1c.

[0049] By this second dichroic mirror 142, the mixed light containing light L1a and light L1b is reflected toward the +X side along the X-axis direction, and light L1c passes through the second dichroic mirror 142 and travels toward the +X side. As a result, the optical paths of light L1a, light L1b, and light L1c ideally coincide. In other words, light L1a, light L1b, and light L1c are mixed. The mixed light containing light L1a, light L1b, and light L1c corresponds to light L2.

[0050] In the example of FIG. 2, light L2 is focused by lens 15 onto the incident end of light guide 16. Light L2 travels inside light guide 16 and exits from the exit end of light guide 16. Light guide 16 may be, for example, a liquid light guide including a tube filled with a liquid that transmits light, or may be a fiber light guide in which multiple optical fibers are bundled. In the example of FIG. 2, the exit end of light guide 16 corresponds to the exit end of pseudo-light irradiator 11.

[0051] The multiple light sources 12 are controlled so that the spectrum of light L2 emitted by this simulative light irradiation unit 11 resembles the spectrum of the light used for exposure in the exposure apparatus 1000. As a specific example, a case will be described in which the light emitted by the illumination unit 1100 in the exposure apparatus 1000 includes i-rays, h-rays, and g-rays. In this case, light sources 12a, 12b, and 12c are controlled so that the intensity peaks of the i-rays, h-rays, and g-rays included in the light coincide with the intensity peaks of light L1a, light L1b, and light L1c, respectively. This allows the simulative light irradiation unit 11 to emit light L2 that mimics the light in the exposure apparatus 1000.

[0052] Note that a target value for the peak intensity of the light L1 from each light source 12 may be set in advance and recorded in a non-temporary storage unit (e.g., a memory or a hard disk) not shown. Alternatively, a user may input the peak intensity of each light L1 using an input device (e.g., a keyboard or a mouse) not shown. The control unit 50 controls the light source 12 based on the detection value of the sensor included in the light source 12 and the target value. As a result, the light L1a, the light L1b, and the light L1c The spectrum of light L2 containing these can be made closer to the spectrum of light in exposure apparatus 1000 with higher accuracy.

[0053] 2, the exit end of light guide 16 is located on the -Z side of illumination optical system 17, and emits light L2 toward illumination optical system 17. In the example of Fig. 2, illumination optical system 17 includes a condenser lens 171, a field stop 172, a condenser lens 173, an aperture stop 174, and a condenser lens 175. Collector lens 171, field stop 172, condenser lens 173, aperture stop 174, and condenser lens 175 are arranged in this order with increasing distance from the exit end of light guide 16 in the Z-axis direction.

[0054] Light L2 from the output end of light guide 16 is collected by condenser lens 171 and passes through field stop 172. The aperture diameter of field stop 172 is variable by an aperture mechanism, making it possible to adjust the illumination range. Light L2 that has passed through field stop 172 is collected by condenser lens 173 and passes through aperture stop 174. Light L2 that has passed through aperture stop 174 is collected onto photomask 80 by condenser lens 175. The aperture diameter of aperture stop 174 is variable by an aperture mechanism, making it possible to adjust the numerical aperture N1 of illumination optical system 17. The aperture mechanisms of field stop 172 and aperture stop 174 may be controlled by control unit 50.

[0055] <Detection section> The pattern-shaped light L2 transmitted through the transmitting portion of the photomask 80 is incident on the detecting unit 20. The detecting unit 20 includes an imaging optical system 21 and an image sensor 25.

[0056] The imaging optical system 21 forms an image of the pattern-shaped light L2 that has passed through the transmitting portions of the photomask 80 on the light-receiving surface of the image sensor 25. In the example of FIG. 2, the imaging optical system 21 includes an objective lens 22, an aperture stop 23, and an imaging lens 24. The objective lens 22, the aperture stop 23, and the imaging lens 24 are arranged in this order with increasing distance from the photomask 80 in the Z-axis direction. The numerical aperture of the objective lens 22 is equal to or greater than the numerical aperture of the objective lens 1210 in the exposure apparatus 1000. The light that has passed through the photomask 80 is enlarged via the objective lens 22 and the imaging lens 24. The aperture diameter of the aperture stop 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 stop 23 may be controlled by the control unit 50.

[0057] Light L2 transmitted through imaging lens 24 is incident on the light receiving surface of image sensor 25. Image sensor 25 is, for example, a CCD (Charge Coupled Device) image sensor or a CMOS (Complementary Metal Oxide Semiconductor) image sensor. Image sensor 25 generates a captured image IM1 based on the light incident on its light receiving surface and outputs the captured image IM1 to control unit 50. Control unit 50 inspects photomask 80 based on this captured image IM1.

[0058] <Movement mechanism> The moving mechanism 40 moves the holder 90 within the XY plane. This causes the photomask 80 held by the holder 90 to move within the XY plane. The moving mechanism 40 has, for example, a ball screw mechanism and is controlled by the control unit 50. The movement of the photomask 80 within the XY plane allows the illumination unit 10 and the detection unit 20 to scan the photomask 80. As a result, the illumination unit 10 irradiates each measurement area on the photomask 80 with light L2, and the image sensor 25 generates a captured image IM1 of each measurement area on the photomask 80. This allows the control unit 50 to inspect multiple measurement areas on the photomask 80. Note that the moving mechanism 40 only needs to have the function and structure to move the photomask 80 relative to the illumination unit 10 and the detection unit 20. For example, the illumination unit 10 and the detection unit 20 may be moved integrally.

[0059] <Lifting mechanism> The lifting mechanism 60 raises and lowers the holder 90 in the Z-axis direction. As a result, the photomask 80 held by the holder 90 also raises and lowers. The lifting mechanism 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 mechanism 60, the photomask 80 can be moved to the focal point of the objective lens 22. Note that the lifting mechanism 60 only needs to have the function and structure to raise and lower the photomask 80 relative to the detection unit 20, and may raise and lower the detection unit 20, for example.

[0060] <Control unit> The control unit 50 can control the entire photomask inspection apparatus 1. For example, the control unit 50 controls the illumination unit 10, the moving mechanism 40, and the lifting mechanism 60, as described above. The control unit 50 also functions as an arithmetic processing unit that determines the mask characteristics of the photomask 80 based on the captured image IM1 generated by the image sensor 25. The mask characteristics include, for example, the line width of the pattern formed on the photomask 80, the spacing between patterns, or various defects. How to determine the mask characteristics will be described in detail later.

[0061] The control unit 50 is an electronic circuit device and may have, for example, an arithmetic processing unit and a memory unit. The arithmetic processing unit may be, for example, an arithmetic processing unit such as a CPU (Central Processor Unit). The memory unit may have a non-transitory memory unit (for example, a ROM (Read Only Memory) or a hard disk) and a temporary memory unit (for example, a RAM (Random Access Memory)). The non-transitory memory unit may store, for example, a program that defines the processing to be performed by the control unit 50. The processing unit executes this program, allowing the control unit 50 to 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.

[0062] <Mask characteristic calculation method> Next, an example of a method for calculating the mask characteristics of the photomask 80 based on the captured image IM1 captured by the image sensor 25 will be described.

[0063] 6 is a diagram schematically illustrating an example of a captured image IM1. The captured image IM1 contains a pattern of light L2. The luminance distribution of this light L2 corresponds to a projected image of the transparent portion of the photomask 80. In the example of FIG. 6, the projected image contains a vertical portion extending vertically and a horizontal portion extending rightward from the middle of the vertical portion.

[0064] 6 also shows an example of the luminance distribution on line A extending in the width direction of the vertical portion. In the luminance distribution, control unit 50 determines the position of the rising edge where the luminance value rises from zero and the position of the falling edge where the luminance value falls to zero, and calculates the width of the vertical portion (projected image width) based on both positions.

[0065] However, if the position of the objective lens 22 relative to the photomask 80 deviates from the focal position in the Z-axis direction, the projected image in the captured image IM1 may vary. In other words, if the lifting mechanism 60 stops the holder 90 at a position deviated from the focal position, the projected image may differ from the image projected at the focal position.

[0066] When substrate W is a substrate for a flat panel display, the numerical aperture of imaging unit 1200 in exposure apparatus 1000 is small, about 0.1, and therefore the depth of focus of imaging unit 1200 is large. However, as will be described in detail later, even a slight deviation of about 10 μm from the focal position will cause the width of the projected image in captured image IM1 to fluctuate.

[0067] Therefore, here, the position of the holder 90 in the Z-axis direction relative to the objective lens 22 (hereinafter referred to as the Z-axis position) is sequentially changed, and each time, the image sensor 25 generates a captured image IM1, and the control unit 50 performs inspection based on these multiple captured images IM1. An example of the inspection method will be specifically described below.

[0068] 7 is a flowchart showing an example of the operation of the photomask inspection apparatus 1. Here, the moving mechanism 40 moves the holder 90 to a predetermined measurement position. The control unit 50 causes the multiple light sources 12 to irradiate light L1 (step S1). As a result, light L2 simulating the light in the exposure tool 1000 passes through a transparent portion in a predetermined measurement region of the photomask 80, and the pattern-like light L2 passes through the imaging optical system 21 and is incident on the light-receiving surface of the image sensor 25.

[0069] Next, the control unit 50 controls the lifting mechanism 60 and the image sensor 25 to generate captured images IM1 at each Z-axis position (step S2). For example, the lifting mechanism 60 moves the holding unit 90 within a predetermined lifting range (focus range) including the focal position, while the image sensor 25 sequentially generates captured images IM1. Note that the lifting mechanism 60 may stop the holding unit 90 at the image capturing timing. This allows multiple captured images IM1 corresponding to multiple Z-axis positions to be obtained.

[0070] Next, the control unit 50 calculates mask characteristics based on the multiple captured images IM1 (step S3). Here, the projected image width is calculated as the mask characteristic. FIG. 8 shows the luminance distribution of the projected image on line A of each captured image IM1. More specifically, FIG. 8 shows the luminance distribution LD1 at the focal position and the luminance distribution at Z-axis positions 10 μm away from the focal position on the +Z side and the -Z side. As can be seen from FIG. 8, when defocus occurs, the luminance distribution fluctuates according to the amount of defocus. Therefore, the projected image widths calculated based on each luminance distribution differ from each other.

[0071] Therefore, the control unit 50 calculates a focus evaluation value for each of the multiple captured images IM1. The focus evaluation value is an index that indicates the degree of focus, and the higher the focus evaluation value, the better the focus. The focus evaluation value may be, for example, an index indicated by the high-frequency components among the frequency components obtained by Fourier transforming the luminance distribution of the captured image IM1. The higher the high-frequency components, the more abruptly the luminance distribution changes, and therefore the clearer the contours of the projected image and the better the focus. Alternatively, various indices such as the contrast and sharpness of the captured image IM1 may be used as the focus evaluation value.

[0072] Since the multiple captured images IM1 correspond to multiple Z-axis positions, the focus evaluation value calculated based on the luminance distribution of each captured image IM1 also corresponds to the Z-axis position. Similarly, the projected image width calculated based on the luminance distribution of line A in each captured image IM1 also corresponds to the Z-axis position. FIG. 9 is a graph showing the relationship between the Z-axis position and the focus evaluation value, and the relationship between the Z-axis position and the projected image width. The example of FIG. 9 also shows approximate curves G1 and G2. Approximate curve G1 is calculated based on plot points showing the relationship between the Z-axis position and the focus evaluation value, and approximate curve G2 is calculated based on plot points showing the relationship between the Z-axis position and the projected image width.

[0073] The focus evaluation value is maximized when the Z-axis position is the focus position P0. Therefore, first, the control unit 50 determines the Z-axis position (i.e., the focus position P0) at which the focus evaluation value is maximized. For example, the control unit 50 calculates an approximation curve G1 using an approximation method such as the least squares method based on a plurality of focus evaluation values ​​corresponding to a plurality of Z-axis positions. Then, the control unit 50 calculates the Z-axis position on the approximation curve G1 at which the focus evaluation value is maximized Fmax as the focus position P0.

[0074] Next, the control unit 50 calculates the projected image width LW at the focal position P0. First, the control unit 50 calculates the projected image width for each captured image IM1. This makes it possible to obtain multiple projected image widths corresponding to multiple Z-axis positions. Next, the control unit 50 calculates an approximation curve G2 using an approximation method such as the least squares method based on the multiple Z-axis positions and the multiple projected image widths. Then, the control unit 50 calculates the projected image width LW at the focal position P0 based on the approximation curve G2 and the focal position P0.

[0075] Next, the control unit 50 judges whether the photomask 80 is good or bad based on the mask characteristics (here, the projected image width LW) (step S4). For example, the control unit 50 judges whether the difference between the projected image width LW and the target width is equal to or less than a predetermined width tolerance, and if the difference is greater than the width tolerance, the control unit 50 judges the photomask 80 to be defective. The width tolerance is, for example, set in advance and stored in the storage unit.

[0076] <Effects of the embodiment> As described above, according to the photomask inspection apparatus 1, the illumination unit 10 emits light L2 that imitates the light of the exposure apparatus 1000, and the sigma of the photomask inspection apparatus 1 is set to be the same as the sigma of the exposure apparatus 1000. This allows the light (projected image) on the substrate W in the exposure apparatus 1000 to be reproduced in a pseudo manner on the light receiving surface of the image sensor 25. Therefore, the photomask inspection apparatus 1 can determine whether the photomask 80 is good or bad based on the projected image on the substrate W.

[0077] Moreover, according to the photomask inspection apparatus 1, the mixer 14 mixes multiple light beams L1 having different peak wavelengths. The illumination unit 10 then irradiates the photomask 80 with light beam L2, which is the mixed light, and the light beam L2 that has passed through the photomask 80 is incident on the light receiving surface of the image sensor 25. Therefore, the captured image IM1 includes a projected image of the photomask 80 formed by the light beams L2 having multiple peak wavelengths. In other words, a single image capture can obtain the captured image IM1 including the projected image formed by the light beams L2 having multiple peak wavelengths.

[0078] Therefore, unlike Patent Document 1, there is no need to combine multiple captured images obtained by sequentially irradiating light having different peak wavelengths. Therefore, unlike Patent Document 1, positional variations for each peak wavelength do not occur in principle in the captured image IM1. Therefore, the control unit 50 can calculate the projected image width with high accuracy, and the photomask 80 can be inspected with higher inspection accuracy.

[0079] Moreover, according to the photomask inspection apparatus 1, each light source 12 includes a single semiconductor light-emitting element 121. Therefore, the wavelength or phase variations that occur in a diode array as in Patent Document 2 do not occur in principle, and each light source 12 can emit more coherent light L1. Therefore, a diffraction phenomenon equivalent to the diffraction phenomenon in the exposure apparatus 1000 can be caused in the light L2 that passes through the photomask 80. Therefore, the control unit 50 can inspect the photomask 80 with higher inspection accuracy.

[0080] Furthermore, since the light source 12 including a single semiconductor light emitting element 121 does not, in principle, have any variation in the emission direction, it is possible to suppress variation in the light incident on the light guide 16. This also allows the control unit 50 to inspect the photomask 80 with higher inspection accuracy. Moreover, the reliability of the light source 12 is also high.

[0081] <Mask characteristics: defect brightness> In the above example, the inspection method was described using the projected image width as the mask characteristic. However, the defect brightness may also be used as the mask characteristic. FIG. 10 is a diagram schematically illustrating an example of a captured image IM1 including a defect D1. In FIG. 10, the defect D1 is a defect in the light-shielding film formed on the photomask 80. Specifically, the defect D1 is a defect in which the light-shielding film is not properly formed and light L2 passes through, and is also called a white defect.

[0082] Here, the brightness value of defect D1 is calculated. Hereinafter, the brightness value of defect D1 is also referred to as defect brightness. This defect brightness also varies depending on the position of holder 90 in the Z-axis direction, so control unit 50 may calculate the defect brightness based on multiple captured images IM1, similar to the projected image width.

[0083] Specifically, in step S3, the control unit 50 first calculates the defect brightness and focus evaluation value for each captured image IM1. This allows for obtaining a plurality of defect brightnesses corresponding to a plurality of Z-axis positions, and a plurality of focus evaluation values ​​corresponding to a plurality of Z-axis positions. FIG. 11 is a graph showing the relationship between the Z-axis position and the focus evaluation value, and the relationship between the Z-axis position and the defect brightness. The example in FIG. 11 also shows approximation curves G1 and G3. Approximation curve G3 is calculated based on plot points of the Z-axis position and the defect brightness.

[0084] As described above, the control unit 50 determines the focal position P0 at which the focus evaluation value reaches the maximum value Fmax based on the approximate curve G1. Next, the control unit 50 calculates the approximate curve G3 based on multiple Z-axis positions and multiple defect intensities using an approximation method such as the least squares method. Then, the control unit 50 calculates the defect intensity DL at the focal position P0 based on the approximate curve G3 and the focal position P0.

[0085] Next, in step S4, the control unit 50 determines whether the photomask 80 is good or bad based on the mask characteristics (here, the defect luminance DL). For example, the control unit 50 determines whether the defect luminance DL is equal to or less than a predetermined defect tolerance, and determines that the photomask 80 is defective when the defect luminance DL is greater than the defect tolerance.

[0086] As described above, the photomask inspection apparatus 1 can determine the quality of the photomask 80 based on the brightness value of the defect D1. Note that, although the above example has been described using a white defect as the defect D1, various other defects such as a black defect can also be used as the defect D1.

[0087] <Variations in Projected Images in Exposure Apparatus 1000> The photomask inspection apparatus 1 artificially reproduces the luminance distribution (projected image) of the patterned light on the substrate W in the exposure apparatus 1000 on the light receiving surface of the image sensor 25. In other words, the captured image IM1 when defocus occurs in the photomask inspection apparatus 1 corresponds to the projected image on the substrate W when a similar defocus occurs in the exposure apparatus 1000. Therefore, the photomask inspection apparatus 1 can also evaluate the variation in the projected image on the substrate W caused by defocus.

[0088] 9 can be regarded as the relationship between the Z-axis position and the projected image width in exposure apparatus 1000. In other words, in exposure apparatus 1000, the relationship between the position (Z-axis position) of photomask 80 relative to objective lens 1210 and the width of the projected image on substrate W corresponds to the relationship in FIG.

[0089] The defocus amount ΔZ (maximum value) that can occur due to mechanical errors of exposure apparatus 1000 or the like can be determined in advance, and therefore the variation in the width of the projected image that occurs in exposure apparatus 1000 can be determined based on the relationship in Fig. 9. The defocus amount ΔZ may be set in advance and stored in a memory unit, for example, or the user may input the defocus amount ΔZ using an input device (e.g., a keyboard or mouse) not shown.

[0090] Based on the approximation curve G2, the control unit 50 calculates the maximum value LWmax and minimum value LWmin of the projected image width in the range between a position shifted by the defocus amount ΔZ from the focal position P0 to the -Z side and a position shifted by the defocus amount ΔZ from the focal position P0 to the +Z side. The range from the minimum value LWmin to the maximum value LWmax corresponds to the variation in the projected image width that occurs in the exposure apparatus 1000.

[0091] The control unit 50 may determine whether the photomask 80 is defective based on the minimum value LWmin and maximum value LWmax of the projected image width. Specifically, the control unit 50 determines whether the minimum value LWmin is equal to or greater than the allowable lower limit of the variation in the width of the projected image on the substrate W, and whether the maximum value LWmax is equal to or less than the allowable upper limit. The control unit 50 determines that the photomask 80 is defective when the minimum value LWmin is less than the allowable lower limit and / or when the maximum value LWmax is greater than the allowable upper limit.

[0092] Similarly, the control unit 50 may calculate the variation in defect brightness caused by the defocus amount ΔZ. Specifically, the control unit 50 calculates the maximum value DLmax and minimum value DLmin of the defect brightness in the range between a position shifted by the defocus amount ΔZ from the focal position P0 to the -Z side and a position shifted by the defocus amount ΔZ from the focal position P0 to the +Z side, based on the approximation curve G3 (see also FIG. 11). The range from the minimum value DLmin to the maximum value DLmax corresponds to the variation in defect brightness that occurs in the exposure apparatus 1000.

[0093] The control unit 50 may determine whether the photomask 80 is good or bad based on the maximum defect brightness value DLmax. Specifically, the control unit 50 determines whether the maximum value DLmax is equal to or less than a defect tolerance. The control unit 50 may determine that the photomask 80 is defective when the maximum value DLmax is greater than the defect tolerance.

[0094] Here, the terms in the "Means for Solving the Problems" section correspond to the terms in the "Description of Embodiments" section. The first light source corresponds to any one of light sources 12a to 12c, and the second light source corresponds to one of light sources 12a to 12c that is different from the first light source. The first semiconductor light emitting element corresponds to semiconductor light emitting element 121 belonging to the first light source, and the second semiconductor light emitting element corresponds to semiconductor light emitting element 121 belonging to the second light source. The first light corresponds to light L1 emitted by the first semiconductor light emitting element, and the second light corresponds to light L1 emitted by the second semiconductor light emitting element.

[0095] As described above, the photomask inspection apparatus 1 has been described in detail, but the above description is merely an example in all respects, and this disclosure is not limited thereto. Furthermore, the various modifications described above can be combined and applied as long as they are not mutually contradictory. It is understood that many modifications not exemplified can be envisioned without departing from the scope of this disclosure. [Explanation of symbols]

[0096] 1. Photomask inspection equipment 10 Lighting Section 12,12a~12c 1st light source, 2nd light source (light source) 121 First semiconductor light emitting element, second semiconductor light emitting element 14 Mixing section 17 Illumination optical system 21 Imaging optical system 22 Objective Lens 25 Image Sensor 50 arithmetic processing unit (control unit) 80 Photomask 90 Holding part

Claims

1. a holder for holding a photomask; a first light source including a single first semiconductor light emitting element that emits first light having a first peak wavelength; a second light source including a single second semiconductor light emitting element that emits second light having a second peak wavelength different from the first peak wavelength; a mixer that mixes the first light from the first light source and the second light from the second light source; an illumination optical system that guides the light obtained by mixing the first light and the second light by the mixing unit to the photomask; a movement drive unit that changes the relative position between the photomask and the illumination optical system in the optical axis direction; an imaging optical system including an objective lens onto which the light from the photomask is incident; an image sensor that receives the light incident through the imaging optical system and generates a captured image; a processing unit that inspects the photomask based on the captured image; Equipped with the arithmetic processing unit determines a focus evaluation value for each of the plurality of captured images generated by the image sensor while changing the distance between the photomask and the illumination optical system, calculates mask characteristics based on each of the plurality of captured images, and determines the quality of the photomask based on the mask characteristics corresponding to a range shifted by a predetermined focus shift amount in an exposure apparatus in which the photomask is used from the relative position at which the focus evaluation value is maximum among the plurality of captured images.

2. 2. The photomask inspection apparatus according to claim 1, a light guide into which the light obtained by mixing the first light and the second light by the mixing section is incident from an incident end, travels inside, and is emitted from an exit end; an illumination optical system that guides the light emitted from the light guide to the photomask.

Images