KR20230137824A - Photomask inspection apparatus - Google Patents

Abstract

(Project) To provide a highly reliable photomask inspection device that can detect photomasks with higher detection accuracy.
(Solution) The photomask inspection device 1 includes a holding portion, a first light source 12a, a second light source 12b, a mixing portion 14, an illumination optical system 17, and an imaging optical system ( 21) It is provided with an image sensor 25 and an arithmetic processing unit 50. The holding portion holds the 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 section 14 mixes the first light L1a and the second light L1b. The illumination optical system 17 guides light L2 to the photomask 80. The image sensor 25 receives the light L2 incident through the imaging optical system 21 and generates a captured image IM1. The arithmetic processing unit 50 inspects the photomask 80 based on the captured image IM1.

Description

Photomask inspection device {PHOTOMASK INSPECTION APPARATUS}

This disclosure relates to a photomask inspection device.

Conventionally, inspection devices for inspecting photomasks (reticles) have been proposed (Patent Documents 1 and 2).

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

In Patent Document 2, a plurality of illumination sources are formed, and each illumination source includes a plurality of laser diode arrays. Beams output from a plurality of illumination sources are combined by beam combining optics, and the beams are incident on the sample with a random illumination profile. The beam reflected from the sample enters the detector and is detected by the detector. The inspection device determines sample parameters, such as the critical dimension of the sample, based on the signal output from the detector.

Japanese Patent Publication No. 2008-256671 Japanese Patent Publication No. 2020-064063

However, in Patent Document 1, the captured image along the g-line, the captured image along the h-line, and the i-line are captured at different timings. For this reason, positional deviation due to mechanical vibration of the inspection device occurs with respect to the captured image. Therefore, there is a problem that the composite image contains errors resulting from this positional deviation, which reduces inspection accuracy.

In Patent Document 2, a laser diode array is used as a light source. Since a plurality of light-emitting elements are formed in each laser diode array, a deviation occurs among the plurality of elements in at least one of the wavelength and phase of the light emitted from each illumination source. For this reason, the coherence of light emitted from each illumination source decreases.

Therefore, even if the illumination profile is close to that of the light source in the exposure apparatus, the diffraction phenomenon occurring in the sample in the inspection apparatus is significantly different from the diffraction phenomenon in the exposure apparatus. For this reason, there is a problem that the image detected by the detector is different from the image in the exposure device, and inspection precision is lowered. Additionally, if a problem occurs in any one of the plurality of elements, the entire device needs to be replaced, which reduces reliability.

Therefore, the present disclosure aims to provide a highly reliable photomask inspection device that can detect a photomask with higher detection accuracy.

A first aspect is a photomask inspection device, comprising: a holding portion for holding a photomask; a first light source including a single first semiconductor light emitting device that emits first light having a first peak wavelength; and a second light source including a single second semiconductor light emitting device emitting second light having a second peak wavelength different from the peak wavelength, the first light from the first light source and the second light from the second light source; It includes a mixing unit that mixes second light, an illumination optical system that guides the light mixed with the first light and the second light by the mixing unit to the photomask, and an objective lens, and emits light from the photomask. an imaging optical system into which the light is incident, 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. do.

The second aspect is a photomask inspection device related to the first aspect, wherein sigma, which is a ratio of the numerical aperture of the illumination optical system to the numerical aperture of the imaging optical system, is the same as the sigma in an exposure apparatus in which the photomask is used. do.

A third aspect is a photomask inspection device related to the first or second aspect, wherein the numerical aperture of the objective lens is greater than or equal to the numerical aperture of the objective lens in an exposure apparatus in which the photomask is used.

According to the photomask inspection device, the mixing unit mixes first light and second light having different peak wavelengths. Then, the mixed light passes through the photomask and is incident on the light-receiving surface of the image sensor through the imaging optical system. Therefore, the captured image includes a projected image of the photomask by light having the first peak wavelength and the second peak wavelength. In short, a captured image including a projection image by light having a plurality of peak wavelengths can be obtained through a single imaging operation.

For this reason, there is no need to synthesize a plurality of captured images obtained by sequentially irradiating light with different peak wavelengths, as in Patent Document 1. Therefore, unlike Patent Document 1, positional deviation for each peak wavelength does not occur in principle in the captured image. Accordingly, the calculation processing unit can inspect the photomask based on the captured image with higher inspection precision.

Moreover, according to the photomask inspection device, the first light source and the second light source include a single semiconductor light emitting device. For this reason, in principle, no deviation in wavelength or phase occurs in the diode array as in Patent Document 2, so the first light source can emit more coherent first light, and the second light source can emit more coherent first light. A balanced second light can be emitted. Accordingly, a diffraction phenomenon equivalent to the diffraction phenomenon in the exposure apparatus can be generated in the light passing through the photomask. Accordingly, the calculation processing unit can inspect the photomask with higher inspection precision. Moreover, the reliability of the first light source and the second light source is also high.

1 is a perspective view schematically showing an example of the configuration of a photomask inspection device.
FIG. 2 is a diagram schematically showing an example of the optical configuration of a photomask inspection device.
FIG. 3 is a diagram schematically showing an example of the optical configuration of an exposure apparatus.
Figure 4 is a graph showing the transmittance and reflectance of the first dichroic mirror.
Figure 5 is a graph showing the transmittance and reflectance of the second dichroic mirror.
Fig. 6 is a diagram schematically showing an example of a captured image.
Fig. 7 is a flow chart showing an example of the operation of the photomask inspection device.
Fig. 8 is a diagram showing the luminance distribution of the projection image in the line of each captured image.
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 projection image width.
Fig. 10 is a diagram schematically showing an example of a captured image containing a defect.
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 defect luminance.

Hereinafter, embodiments will be described in detail with reference to the drawings. Additionally, in the drawings, for the purpose of ease of understanding, the dimensions and numbers of each part are exaggerated or simplified as necessary. In addition, parts having the same structure and function are given the same reference numerals, and duplicate descriptions are omitted in the following description. Additionally, in the drawings, XYZ orthogonal coordinates are appropriately shown to indicate the positional relationship of each component. For example, the Z axis is located along a vertical direction, and the X and Y axes are located along a horizontal direction. In addition, in the description below, one side of the Z axis direction is also called the +Z side, and the other side is also called the -Z side. The same goes for the X and Y axes.

In addition, in the description shown below, like symbols are given to like components, and their names and functions are also assumed to be the same. Therefore, detailed descriptions of them may be omitted to avoid duplication.

In addition, in the description described below, although ordinal numbers such as “first” or “second” may be used, these terms are used for convenience to facilitate understanding of the content of the embodiment, There is no limitation to the order that can occur by these ordinal numbers.

When expressions expressing relative or absolute positional relationships (e.g., “in one direction,” “along one direction,” “parallel,” “orthogonal,” “center,” “concentric,” “coaxial,” etc.) are used, the expressions are not specifically mentioned. Unless otherwise specified, it not only strictly represents the positional relationship, but also represents a relatively displaced state in terms of angle or distance within the range where tolerance or the same degree of function is obtained. When expressions that indicate an equivalent state (e.g., “same,” “equal,” “homogeneous,” etc.) are used, the expression not only expresses a state of exact equality quantitatively, unless specifically stated, but also indicates a state of tolerance or It shall also indicate a state in which a car exists that achieves the same degree of function. When an expression representing a shape (e.g., “rectangular” or “cylindrical”) is used, unless otherwise specified, the expression not only strictly represents the shape geometrically, but also has the same degree of effect. In the range where , for example, shapes having irregularities, chamfers, etc. are also shown. When the expressions “to have,” “to provide,” “to be provided,” “to include,” or “to have” are used to describe one component, the expression is not an exclusive expression that excludes the presence of other components. When the expression “at least one of A, B, and C” is used, the expression means A only, B only, C only, any two of A, B, and C, and A, B, and C. includes everything.

＜Photomask inspection device＞

FIG. 1 is a perspective view schematically showing an example of the configuration of the photomask inspection device 1, and FIG. 2 is a diagram schematically showing an example of the optical configuration of the photomask inspection device 1. The photomask inspection device 1 is a device that inspects the photomask 80.

＜Photomask＞

First, the photomask 80, which is an inspection target, will be described. The photomask 80 is a photomask used in the exposure apparatus 1000. FIG. 3 is a diagram schematically showing an example of the optical configuration of the exposure apparatus 1000. The exposure apparatus 1000 can transfer the pattern of the photomask 80 to the substrate W by performing exposure processing on the substrate W using the photomask 80 . The substrate W is, for example, a substrate for a flat panel display. In addition, it is also possible to apply various substrates such as a semiconductor substrate and a solar cell substrate to the substrate W.

The photomask 80 has a plate-shaped shape, for example, a rectangular shape when viewed from the top. The length of one side of the photomask 80 is set to several meters, for example. 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, 2.1 mm. On one main surface of the photomask 80, a light-shielding film (not shown) is formed in a predetermined pattern. In short, the photomask 80 is formed with a transmitting portion that transmits light and a blocking portion that blocks the light. Additionally, the photomask 80 may be a phase shift mask formed with a phase shift film that transmits light with a lower transmittance than the transmission portion.

The photomask 80 is held in the exposure apparatus 1000 by a mask holding portion (not shown). The mask holding portion holds the photomask 80 in an attitude whose thickness direction follows the Z-axis direction. The mask holding portion supports only the peripheral portion of the photomask 80, for example.

As shown in FIG. 3 , exposure apparatus 1000 includes an illumination unit 1100 and an imaging unit 1200. The lighting unit 1100 and the imaging unit 1200 are formed on opposite sides of the photomask 80. In the example of FIG. 3 , the illumination portion 1100 is formed on the +Z side with respect to the photomask 80, and the imaging portion 1200 is formed on the −Z side with respect to the photomask 80.

The lighting unit 1100 includes a light source 1110 and an illumination optical system 1120. The light source 1110 emits light for exposure toward the illumination optical system 1120. The light for exposure is, for example, ultraviolet rays, and the light source 1110 is, for example, an ultraviolet irradiator such as a mercury lamp (eg, a high-pressure mercury lamp). Light from the light source 1110 is irradiated to the photomask 80 through the illumination optical system 1120.

In the example of FIG. 3 , the illumination optical system 1120 includes a condenser lens 1130, a field stop 1140, a convergence lens 1150, an aperture stop 1160, and a condenser lens 1170. The condenser lens 1130, field stop 1140, condenser lens 1150, aperture stop 1160, and condenser lens 1170 are formed in this order as they move away from the light source 1110 in the Z-axis direction. In short, the converging lens 1130 is formed at the position closest to the light source 1110. Light from the light source 1110 is collected by the condenser lens 1130 and passes through the field stop 1140. The aperture diameter of the field stop 1140 is variable, and the illumination range can be adjusted. The light that has passed 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.

Additionally, an optical filter that transmits only light within a predetermined wavelength range among the light from the light source 1110 may be formed in the illumination optical system 1120.

Light for exposure from the illumination unit 1100 passes through the transmission part of the photomask 80. The patterned light passing through the transmission portion of the photomask 80 is incident on the imaging portion 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 formed in this order as they move away from the photomask 80 in the Z-axis direction. The light passing through the transmission part of the photomask 80 is expanded through the objective lens 1210 and the imaging lens 1230. The aperture diameter of the aperture stop 1220 is variable, and the numerical aperture of the imaging unit 1200 can be adjusted. When the substrate W is a substrate for a flat panel display, in the exposure apparatus 1000, the numerical aperture of the imaging portion 1200 is set small, for example, about 0.1.

The substrate W is formed on the side opposite to the photomask 80 with respect to the imaging portion 1200. In the example of FIG. 3 , the substrate W is formed on the -Z side of the imaging portion 1200. The substrate W is held in a horizontal position by a substrate holding portion not shown. The horizontal posture referred to here is an posture in which the thickness direction of the substrate W follows the Z-axis direction.

The patterned light from the imaging unit 1200 is irradiated to the main surface on the +Z side of the substrate W. Thereby, the resist formed on the main surface of the substrate W is exposed in a pattern. In short, the pattern of the transparent portion of the photomask 80 is transferred to the main surface of the substrate W.

If the photomask 80 is a defective product, the pattern transferred to the substrate W deviates from the designed pattern, which is not preferable. So, the photomask inspection device 1 inspects the photomask 80.

＜Overview of photomask inspection equipment＞

As illustrated in FIG. 2 , the photomask inspection device 1 includes an image sensor (optical sensor) 25 that receives light that has transmitted through the photomask 80 . As will be described in detail later, the photomask inspection device 1 uses this image sensor to transmit patterned light irradiated onto the substrate W when the photomask 80, which is an inspection target, is used in the exposure device 1000. It is simulated and reproduced on the light-receiving surface (imaging surface) of (25). The image sensor 25 detects light on the light-receiving surface, and the photomask inspection device 1 inspects the photomask 80 based on the detection result. In short, the photomask inspection device 1 can simulate the photomask 80 based on the light on the substrate W in the exposure device 1000.

The photomask inspection device 1 includes an illumination unit 10, a detection unit 20, a moving mechanism 40, a control unit 50, a lifting mechanism 60, and a holding unit 90. Below, an outline of the configuration of the photomask inspection device 1 will first be described, and then an example of each configuration will be described in detail.

The holding portion 90 is a member that holds the photomask 80. This holding portion 90 holds the photomask 80 so that the thickness direction of the photomask 80 follows the Z-axis direction. In the example of FIG. 1, the holding portion 90 supports only the peripheral portion of the photomask 80. However, the holding portion 90 may support the entire lower surface of the photomask 80 by being a light-transmitting member.

The illumination unit 10 and the detection unit 20 are formed on opposite sides of the photomask 80 in the Z-axis direction. In the examples of FIGS. 1 and 2 , the illumination portion 10 is formed on the -Z side with respect to the photomask 80, and the detection portion 20 is formed on the +Z side with respect to the photomask 80.

The lighting unit 10 irradiates light L2 toward the photomask 80. In the example of FIG. 2 , the illumination unit 10 includes a pseudo-light irradiation unit 11 and an illumination optical system 17. The pseudo-light irradiation unit 11 emits light L2 having a spectrum similar to the spectrum of the light used for exposure in the wavelength range of light irradiated by the light source 1110 of the exposure apparatus 1000. In short, the light L2 is light that imitates the light used to expose 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 patterned light L2 passing through the transmission part of the photomask 80 is incident on the detection part 20.

The detection unit 20 includes an imaging optical system 21 and an image sensor 25. The imaging optical system 21 forms an image of the light L2 that has 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 the illumination optical system relative to the numerical aperture N20 of the imaging portion 1200 of the exposure apparatus 1000. It is set to the same value as sigma (=N10/N20), which is the ratio of the numerical aperture N10 of (1120). As a result, the luminance distribution of the light L2 incident on the light-receiving surface of the image sensor 25 mimics the luminance distribution of the patterned light irradiated on the substrate W. In short, when the photomask 80 is used in the exposure apparatus 1000, the luminance distribution of light irradiated onto the substrate W is simulated on the light-receiving surface of the image sensor 25.

＜Lighting Department＞

As illustrated in FIG. 2 , the pseudo-light irradiation unit 11 includes a plurality of light sources 12 and a mixing unit 14.

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

The light source 12a emits light L1a having a first peak wavelength. The first peak wavelength is for example 365 nm (the so-called i-line wavelength). 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 that is different from both the first peak wavelength and the second peak wavelength. The third peak wavelength is for example 436 nm (the so-called g-line wavelength). In the optical spectral distribution (spectrum) of the light L1 emitted from each light source 12, there may be only one peak wavelength. In short, the light L1 may be light of a single wavelength. Specifically, the spectrum of light emitted from each light source 12 may have a steep mountain shape with the intensity at the peak wavelength being the maximum intensity. When the semiconductor light-emitting device 121 is a light-emitting diode device, light L1 having a slightly wide acid-phase spectrum is emitted, and when the semiconductor light-emitting device 121 is a laser device, light L1 is emitted with a relatively narrow acid-phase spectrum. Light (L1) with

Power is individually supplied to each semiconductor light emitting device 121 from a power supply unit (not shown). Each semiconductor light emitting element 121 emits light L1 with luminance according to the power from its power supply unit. The power supply 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 light L1 by controlling the current supplied to the semiconductor light emitting device 121. Since each power supply unit is individually controlled by the control unit 50, the luminance of light L1 from each light source 12 is individually controlled by the control unit 50.

A sensor (not shown) that measures the intensity (or illuminance, light quantity) of the light L1 from the semiconductor light-emitting device 121 may be formed in each light source 12. The sensor outputs a signal representing the detection value to the control unit 50. The control unit 50 controls the power supply unit based on the detected value, and controls the current supplied from the power supply unit to the semiconductor light emitting device 121. Thereby, the control unit 50 can control the intensity of light L1 emitted from the light source 12 with higher precision.

Light L1a emitted from the light source 12a enters the mixing section 14 through the lens 13a, and light L1b emitted from the light source 12b enters the mixing section 14 through the lens 13b. The light L1c emitted from the light source 12c is incident on the mixing section 14 through the lens 13c.

The mixing unit 14 mixes the plurality of lights L1 incident from the plurality of light sources 12, respectively. Mixing of light as used herein refers to substantially matching the optical paths of a plurality of lights L1. In the example of FIG. 2, the mixing section 14 includes a first dichroic mirror 141 and a second dichroic mirror 142.

Light L1a and light L1b are incident on the first dichroic mirror 141. In the example of FIG. 2, the light source 12a is formed on the -X side of the first dichroic mirror 141, and radiates light L1a toward the +X side along the X-axis direction. The light source 12b is formed on the +Z side of the first dichroic mirror 141, and irradiates the light L1b toward the -Z side along the Z-axis direction. The first dichroic mirror 141 has a plate-like shape, and is arranged in an attitude whose thickness direction is from the +X side and +Z side to the -X side and -Z side. 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 transmittance of the first dichroic mirror 141 for light L1a of the first peak wavelength (here 365 nm) is low, and the reflectance is high. On the other hand, the transmittance of the first dichroic mirror 141 for the light L1b of the second peak wavelength (here 405 nm) and the light L1c of the third peak wavelength (here 436 nm) is high and the reflectance is low. .

By this first dichroic mirror 141, the light L1a is reflected and reflected toward the -Z side along the Z axis, and the light L1b passes through the first dichroic mirror 141 to -Z. Proceed to the Z side. As a result, the optical paths of light L1a and light L1b ideally coincide. In short, light (L1a) and light (L1b) are mixed.

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 formed on the -Z side of the first dichroic mirror 141. The light source 12c is formed on the -X side of the second dichroic mirror 142, and irradiates the light L1c toward the +X side along the The second dichroic mirror 142 has a plate-like shape, and is arranged in an attitude whose thickness direction is from the +X side and +Z side to the -X side and -Z side. The second dichroic mirror 142 reflects the mixed light and transmits light L1c in the same direction as the reflection direction of the mixed light. FIG. 5 is a graph showing the transmittance and reflectance of the second dichroic mirror 142. The transmittance of the second dichroic mirror 142 for light L1a and light L1b is low, and the reflectance is high. On the other hand, the transmittance of the second dichroic mirror 142 for light L1c is high and the reflectance is low.

By this second dichroic mirror 142, the mixed light including the light L1a and the light L1b is reflected to the +X side along the It passes through the wing mirror 142 and proceeds to the +X side. As a result, the optical paths of light L1a, light L1b, and light L1c ideally coincide. In short, light (L1a), light (L1b) and light (L1c) are mixed. A mixed light containing light (L1a), light (L1b), and light (L1c) corresponds to light (L2).

In the example of FIG. 2 , light L2 is focused by lens 15 at the entrance end of light guide 16. Light L2 travels inside the light guide 16 and is emitted from the emission end of the light guide 16. The 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 a plurality of optical fibers are bundled. In the example of FIG. 2, the emission end of the light guide 16 corresponds to the emission end of the pseudo-light irradiation unit 11.

The plurality of light sources 12 are controlled so that the spectrum of the light L2 emitted from the pseudo-light irradiation unit 11 is similar to the spectrum of the light used for exposure in the exposure apparatus 1000. As a specific example, a case where, in the exposure apparatus 1000, the light emitted from the lighting unit 1100 includes the i-line, h-line, and g-line will be described. In this case, the light source 12a is installed so that the intensity peaks of the i-line, h-line, and g-line included in the light coincide with the intensity peaks of the light L1a, light L1b, and light L1c, respectively. Light source 12b and light source 12c are controlled. As a result, the pseudo-light irradiation unit 11 can emit light L2 that imitates the light in the exposure apparatus 1000.

Additionally, the target value regarding the peak intensity of light L1 from each light source 12 may be set in advance, for example, and recorded in a non-transitory storage unit (for example, memory or hard disk), not shown. Alternatively, the user may input the peak intensity of each light L1 using an input device (eg, keyboard or 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 spectrum of light L2 including light L1a, light L1b, and light L1c can be made closer to the spectrum of light in the exposure apparatus 1000 with higher precision.

In the example of FIG. 2 , the emission end of the light guide 16 is formed on the -Z side of the illumination optical system 17, and emits light L2 toward the illumination optical system 17. In the example of FIG. 2 , the illumination optical system 17 includes a converging lens 171, a field stop 172, a converging lens 173, an aperture stop 174, and a condenser lens 175. The condenser lens 171, the field stop 172, the condenser lens 173, the aperture stop 174, and the condenser lens 175 are arranged in this order as they move away from the exit end of the light guide 16 in the Z-axis direction. It is formed by

Light L2 from the exit end of the light guide 16 is condensed by the converging lens 171 and passes through the field stop 172. The aperture diameter of the field stop 172 is variable by the stop mechanism, and the illumination range can be adjusted. Light L2 that has passed through the field stop 172 is condensed by the condenser lens 173 and passes through the aperture stop 174. Light L2 that has passed through the aperture stop 174 is condensed onto the photomask 80 by the condenser lens 175. The aperture diameter of the aperture stop 174 is variable by the aperture mechanism, and the numerical aperture N1 of the illumination optical system 17 can be adjusted. The aperture mechanisms of the field stop 172 and the aperture stop 174 may be controlled by the control unit 50 .

＜Detection unit＞

The patterned light L2 passing through the transmission part of the photomask 80 is incident on the detection part 20. The detection unit 20 includes an imaging optical system 21 and an image sensor 25.

The imaging optical system 21 forms an image of the patterned light L2 that has passed through the transmission portion 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 formed in this order as they move away 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 passing through the photomask 80 is expanded through the objective lens 22 and the imaging lens 24. The aperture diameter of the aperture stop 23 is variable by the aperture mechanism, and the numerical aperture of the imaging optical system 21 can be adjusted. The diaphragm mechanism of the aperture stop 23 may be controlled by the control unit 50.

Light L2 that passes 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 a captured image IM1 based on light incident on its light-receiving surface, and outputs the captured image IM1 to the control unit 50 . The control unit 50 inspects the photomask 80 based on this captured image IM1.

＜Movement equipment＞

The moving mechanism 40 moves the holding portion 90 within the XY plane. Thereby, the photomask 80 held on the holding portion 90 also moves within the XY plane. The moving mechanism 40 has a ball screw mechanism, for example, and is controlled by the control unit 50. By moving the photomask 80 within the XY plane, the illumination unit 10 and the detection unit 20 can be scanned with respect to the photomask 80. For this reason, the lighting unit 10 irradiates light L2 to each measurement area of the photomask 80, and the image sensor 25 captures the captured image IM1 in each measurement area of the photomask 80. can be created. Accordingly, the control unit 50 can inspect a plurality of measurement areas of the photomask 80. Additionally, the moving mechanism 40 may have a function and structure to move the photomask 80 relative to the lighting unit 10 and the detection unit 20, for example, the lighting unit 10 and the detection unit 20. ) can be moved integrally.

＜Elevating mechanism＞

The lifting mechanism 60 raises and lowers the holding portion 90 in the Z-axis direction. As a result, the photomask 80 held by the holding portion 90 is also raised and lowered. The lifting mechanism 60 has a ball screw mechanism, for example, and is controlled by the control unit 50. By the lifting mechanism 60 lifting the photomask 80, the photomask 80 can be moved to the focus of the objective lens 22. In addition, the lifting mechanism 60 may have a function and structure to raise and lower the photomask 80 relative to the detection unit 20, and may, for example, raise and lower the detection unit 20.

＜Control section＞

The control unit 50 can control the photomask inspection device 1 as a whole. For example, the control unit 50 controls the lighting unit 10, the moving mechanism 40, and the lifting mechanism 60, as described above. Additionally, 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. Mask characteristics include, for example, the line width of the pattern formed on the photomask 80, the spacing between patterns, or various defects. The method for obtaining mask characteristics will be described in detail later.

The control unit 50 is an electronic circuit device and may have, for example, an arithmetic processing unit and a storage unit. For example, the arithmetic processing unit may be an arithmetic processing unit such as a CPU (Central Processor Unit). The storage unit may have a non-transitory storage unit (for example, ROM (Read Only Memory) or a hard disk) and a temporary storage unit (for example, RAM (Random Access Memory)). In the non-transitory storage unit, for example, a program that specifies the processing to be executed by the control unit 50 may be stored. When the processing device executes this program, the control unit 50 can execute the processing specified in the program. Of course, part or all of the processing executed by the control unit 50 may be executed by hardware.

＜Calculation method of mask characteristics＞

Next, an example of a method for calculating mask characteristics of the photomask 80 based on the captured image IM1 captured by the image sensor 25 will be described.

FIG. 6 is a diagram schematically showing an example of the captured image IM1. The captured image IM1 contains pattern-shaped light L2. The luminance distribution of this light L2 corresponds to the projected image of the transparent portion of the photomask 80. In the example of Fig. 6, the projection image includes a vertical portion extending vertically and a horizontal portion extending to the right from the middle of the vertical portion.

In the example of Fig. 6, an example of the luminance distribution in the line A extending in the width direction of the vertical portion is also schematically shown. In the luminance distribution, the 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 determines the width (projection) of the vertical portion based on both positions. Find the image width).

However, if the position of the objective lens 22 with respect to the photomask 80 deviates from the focus position in the Z-axis direction, the projected image in the captured image IM1 may change. In short, if the lifting mechanism 60 stops the holding portion 90 at a position offset from the focus position, the projected image may be different from the projected image at the focus position.

When the substrate W is a substrate for a flat panel display, the numerical aperture of the imaging portion 1200 in the exposure apparatus 1000 is as small as about 0.1, so the depth of focus of the imaging portion 1200 is large. However, as will be described in detail later, even if there is a slight deviation of about 10 μm from the focus position, the width of the projection image in the captured image IM1 changes.

So, here, the position of the holding portion 90 in the Z-axis direction (hereinafter referred to as the Z-axis position) with respect to the objective lens 22 is sequentially changed, and the image sensor 25 captures the captured image IM1 each time. generates, and the control unit 50 performs inspection based on these plurality of captured images IM1. Below, an example of an inspection method is described in detail.

FIG. 7 is a flow chart showing an example of the operation of the photomask inspection device 1. Here, the moving mechanism 40 moves the holding portion 90 to a predetermined measurement position. The control unit 50 irradiates light L1 to the plurality of light sources 12 (step S1). As a result, the light L2 imitating the light in the exposure apparatus 1000 passes through the transmission portion in the predetermined measurement area of the photomask 80, and the patterned light L2 passes through the imaging optical system 21 to produce an image. It is incident on the light-receiving surface of the sensor 25.

Next, the control unit 50 controls the lifting mechanism 60 and the image sensor 25 to generate the captured image IM1 at each Z-axis position in the image sensor 25 (step S2). For example, the lifting mechanism 60 moves the holding portion 90 within a predetermined lifting range (focus range) including the focus position, while the image sensor 25 sequentially generates the captured image IM1. do. Additionally, the lifting mechanism 60 may stop the holding unit 90 at the imaging timing. In this way, a plurality of captured images IM1 corresponding to a plurality of Z-axis positions can be obtained.

Next, the control unit 50 determines mask characteristics based on the plurality of captured images IM1 (step S3). Here, the projection image width is obtained as a mask characteristic. FIG. 8 shows the luminance distribution of the projection image on line A of each captured image IM1. More specifically, FIG. 8 shows the luminance distribution (LD1) at the focus position and the luminance distribution at the Z-axis positions 10 μm away from the focus position on the +Z side and -Z side. As can be understood from Fig. 8, when defocus occurs, the luminance distribution changes depending on the amount of defocus. For this reason, the projection image widths obtained based on each luminance distribution are different from each other.

Therefore, the control unit 50 calculates focus evaluation values for each of the plurality of captured images IM1. The focus evaluation value is an indicator of the extent to which focus is achieved, and the higher the focus evaluation value, the more focus is achieved. For example, the focus evaluation value may be an index representing a high-frequency component among the frequency components obtained by Fourier transforming the luminance distribution of the captured image IM1. The higher the high-frequency component, the more rapidly the luminance distribution changes, so the outline of the projected image becomes clearer and more focused. Alternatively, various indices such as contrast and sharpness of the captured image IM1 may be employed as focus evaluation values.

Since the plurality of captured images IM1 correspond to a plurality of 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 projection image width calculated based on the luminance distribution in line A of 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 projection image width. In the example of Fig. 9, an approximate curve (G1) and an approximate curve (G2) are also shown. The approximation curve G1 is calculated based on plot points indicating the relationship between the Z-axis position and the focus evaluation value, and the approximation curve G2 is calculated based on the plot points indicating the relationship between the Z-axis position and the projection image width. do.

The focus evaluation value takes the maximum value when the Z-axis position becomes the focus position (P0). So, first, the control unit 50 finds the Z-axis position (in short, the focus position (P0)) at which the focus evaluation value becomes the maximum. For example, the control unit 50 calculates the approximation curve G1 by an approximation method such as the least squares method, based on a plurality of focus evaluation values each corresponding to a plurality of Z-axis positions. Then, the control unit 50 calculates the Z-axis position when the focus evaluation value reaches the maximum value (Fmax) in the approximation curve G1 as the focus position P0.

Next, the control unit 50 determines the projection image width LW at the focus position P0. First, the control unit 50 determines the projection image width for each captured image IM1. Accordingly, a plurality of projection image widths corresponding to a plurality of Z-axis positions can be obtained. Next, the control unit 50 calculates the approximation curve G2 by an approximation method such as the least squares method, based on the plurality of Z-axis positions and the plurality of projection image widths. Then, the control unit 50 calculates the projection image width LW at the focus position P0 based on the approximation curve G2 and the focus position P0.

Next, the control unit 50 determines whether the photomask 80 is good or bad based on the mask characteristics (here, the projection image width (LW)) (step S4). For example, the control unit 50 determines whether the difference between the projection image width LW and the target width is less than or equal to a predetermined width tolerance value, and when the difference is greater than the width tolerance value, the photomask 80 is considered defective. It is determined that it is. The width tolerance value is set in advance, for example, and stored in the storage unit.

＜Effects in the embodiment＞

As described above, according to the photomask inspection device 1, the lighting unit 10 emits light L2 that imitates the light of the exposure device 1000, and also emits light L2 that imitates the light of the exposure device 1000. is set equal to the sigma of the exposure apparatus 1000. As a result, the light (projected image) on the substrate W in the exposure apparatus 1000 can be simulated on the light-receiving surface of the image sensor 25. For this reason, the photomask inspection device 1 can determine whether the photomask 80 is good or bad based on the projected image on the substrate W.

Furthermore, according to the photomask inspection device 1, the mixing section 14 mixes a plurality of lights L1 having different peak wavelengths. Then, the illumination unit 10 radiates light L2, which is the mixed light, to the photomask 80, and the light L2 transmitted through the photomask 80 is incident on the light-receiving surface of the image sensor 25. Accordingly, the captured image IM1 includes a projection image of the photomask 80 by light L2 having a plurality of peak wavelengths. In short, a captured image IM1 including a projection image by light L2 having a plurality of peak wavelengths can be obtained through one imaging operation.

For this reason, there is no need to synthesize a plurality of captured images obtained by sequentially irradiating light with different peak wavelengths, as in Patent Document 1. Therefore, unlike Patent Document 1, in principle, position deviation for each peak wavelength does not occur in the captured image IM1. Accordingly, the control unit 50 can calculate the projection image width with high precision and inspect the photomask 80 with higher inspection precision.

Moreover, according to the photomask inspection device 1, each light source 12 includes a single semiconductor light emitting element 121. For this reason, in principle, no deviation in wavelength or phase occurs in the diode array as in Patent Document 2, and each light source 12 can emit more coherent light L1. Accordingly, a diffraction phenomenon equivalent to the diffraction phenomenon in the exposure apparatus 1000 can be generated in the light L2 passing through the photomask 80. Accordingly, the control unit 50 can inspect the photomask 80 with higher inspection precision.

In addition, since deviation in the emission direction does not occur in principle in the light source 12 including a single semiconductor light-emitting element 121, deviation of light incident on the light guide 16 can also be suppressed. This also allows the control unit 50 to inspect the photomask 80 with higher inspection precision. Moreover, the reliability of the light source 12 is high.

＜Mask characteristics: defect luminance＞

In the example described above, the inspection method was explained by employing the projection image width as the mask characteristic. However, defect brightness may be adopted as the mask characteristic. FIG. 10 is a diagram schematically showing an example of a captured image IM1 including a defect D1. In FIG. 10, defect D1 is a defect in the light-shielding film formed on the photomask 80. Specifically, the defect (D1) is a defect through which the light (L2) transmitted without the light-shielding film being properly formed, and is also called a white defect.

Here, the luminance value of defect (D1) is obtained. Hereinafter, the luminance value of defect (D1) is also called defect luminance. Since this defect luminance also changes depending on the position of the holding unit 90 in the Z-axis direction, the control unit 50 may determine the defect luminance based on the plurality of captured images IM1, similar to the projection image width.

Specifically, in step S3, first, the control unit 50 obtains defect brightness and focus evaluation values for each captured image IM1. As a result, it is possible to obtain a plurality of defect luminances respectively corresponding to a plurality of Z-axis positions and a plurality of focus evaluation values respectively corresponding to the 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 defect luminance. In the example of Fig. 11, an approximate curve (G1) and an approximate curve (G3) are also shown. The approximate curve G3 is calculated based on the plot points of the Z-axis position and defect brightness.

As above, the control unit 50 determines the focus position P0 at which the focus evaluation value becomes the maximum value Fmax based on the approximation curve G1. Next, the control unit 50 calculates the approximate curve G3 by an approximation method such as the least squares method, based on the plurality of Z-axis positions and the plurality of defect brightnesses. Then, the control unit 50 calculates the defect luminance DL at the focus position P0 based on the approximation curve G3 and the focus position P0.

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

As described above, the photomask inspection device 1 can determine whether the photomask 80 is good or bad based on the luminance value of the defect D1. In addition, in the above-described example, white defects were used as the defect (D1), but various defects such as black defects, for example, can also be used as the defect (D1).

<Deviation of projected image in exposure apparatus 1000>

The photomask inspection device 1 simulates the luminance distribution (projection image) of light on the pattern on the substrate W in the exposure device 1000 on the light-receiving surface of the image sensor 25. In short, the captured image IM1 when defocus occurs in the photomask inspection device 1 corresponds to the projected image on the substrate W when the same defocus occurs in the exposure device 1000. . For this reason, the deviation of the projected image on the substrate W resulting from defocus can also be evaluated by the photomask inspection device 1.

For example, the relationship between the Z-axis position and the projection image width in FIG. 9 can be regarded as the relationship between the Z-axis position and the projection image width in the exposure apparatus 1000. In short, in the exposure apparatus 1000, the relationship between the position of the photomask 80 (Z-axis position) with respect to the objective lens 1210 and the projected image width on the substrate W corresponds to the relationship in FIG. 9 .

Since the amount of defocus ΔZ (maximum value) that may occur due to mechanical errors in the exposure apparatus 1000, etc. can be obtained in advance, the deviation in the projection image width that occurs in the exposure apparatus 1000 can be calculated using the relationship in FIG. 9 It can be obtained based on . The amount of defocus (ΔZ) may, for example, be set in advance and stored in the memory, or the user may input the amount of defocus (ΔZ) using an input device (e.g., keyboard or mouse) not shown. do.

The control unit 50 operates in a range between a position deviated by the defocus amount ΔZ from the focus position P0 to the -Z side and a position deviated by the defocus amount ΔZ from the focus position P0 to the +Z side. The maximum value (LWmax) and minimum value (LWmin) of the projection image width are calculated based on the approximation curve (G2). The range from this minimum value (LWmin) to the maximum value (LWmax) corresponds to the deviation of the projection image width that occurs in the exposure apparatus 1000.

The control unit 50 may determine whether the photomask 80 is good or bad based on the minimum value (LWmin) and maximum value (LWmax) of the projection image width. Specifically, the control unit 50 determines whether the minimum value LWmin is greater than or equal to the allowable lower limit of the deviation of the projection image width on the substrate W, and whether the maximum value LWmax is less than or equal to the allowable upper limit. The control unit 50 determines that the photomask 80 is a defective product when the minimum value (LWmin) is less than the allowable lower limit and/or the maximum value (LWmax) is greater than the allowable upper limit.

Similarly, the control unit 50 may calculate the deviation in defect luminance resulting from the amount of defocus ΔZ. Specifically, the control unit 50 controls the range between a position that is shifted by the defocus amount (ΔZ) from the focus position (P0) to the -Z side and a position that is shifted by the defocus amount (ΔZ) to the +Z side from the focus position (P0). The maximum value (DLmax) and minimum value (DLmin) of defect luminance in are calculated based on the approximate curve G3 (see also FIG. 11). The range from this minimum value (DLmin) to the maximum value (DLmax) corresponds to the variation in defect luminance that occurs in the exposure apparatus 1000.

The control unit 50 may determine whether the photomask 80 is good or bad based on the maximum value (DLmax) of defect luminance. Specifically, the control unit 50 determines whether the maximum value DLmax is less than or equal to the defect tolerance value. The control unit 50 may determine that the photomask 80 is a defective product when the maximum value DLmax is greater than the defect tolerance value.

Here, the terms in the section on means for solving the problem and the terms in the section on forms for carrying out the invention are matched. The first light source corresponds to any one of the light sources 12a to 12c, and the second light source corresponds to one of the light sources 12a to 12c that is different from the first light source. The first semiconductor light-emitting device corresponds to the semiconductor light-emitting device 121 belonging to the first light source, and the second semiconductor light-emitting device corresponds to the semiconductor light-emitting device 121 belonging to the second light source. The first light corresponds to the light L1 emitted from the first semiconductor light-emitting device, and the second light corresponds to the light L1 emitted from the second semiconductor light-emitting device.

As described above, the photomask inspection device 1 has been described in detail, but the above description is illustrative in all aspects and the disclosure is not limited thereto. In addition, the various modifications described above can be applied in combination as long as they do not contradict each other. In addition, it is construed that many modifications not illustrated can be assumed without departing from the scope of this disclosure.

1: Photomask inspection device
10: lighting unit
12, 12a to 12c: first light source, second light source (light source)
121: first semiconductor light-emitting device, second semiconductor light-emitting device
14: mixing section
17: Lighting optical system
21: imaging optical system
22: objective lens
25: image sensor
50: Operation processing unit (control unit)
80: Photomask
90: maintenance part

Claims (3)

A holding part that holds the photomask,
a first light source including a single first semiconductor light emitting device that emits first light having a first peak wavelength;
a second light source including a single second semiconductor light emitting device that emits second light having a second peak wavelength different from the first peak wavelength;
a mixing unit 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 light mixed with the first light and the second light by the mixing unit to the photomask;
an imaging optical system including an objective lens and into 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 photomask inspection device comprising an arithmetic processing unit that inspects the photomask based on the captured image. According to claim 1,
A photomask inspection device wherein sigma, which is a ratio of the numerical aperture of the illumination optical system to the numerical aperture of the imaging optical system, is the same as the sigma in an exposure apparatus in which the photomask is used. The method of claim 1 or 2,
A photomask inspection device, wherein the numerical aperture of the objective lens is equal to or greater than the numerical aperture of the objective lens in an exposure apparatus in which the photomask is used.