JP2023139436A - Photomask inspection apparatus - Google Patents

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

The present disclosure relates to a photomask inspection apparatus.

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

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

In US Pat. No. 5,300,300, multiple illumination sources are provided, each illumination source including a plurality of laser diode arrays. Beams output from multiple illumination sources are combined by beam combining optics to make the beams incident on the sample with an arbitrary illumination profile. The beam reflected from the sample is incident on a detector and detected by the detector. The inspection device determines sample parameters such as critical dimensions of the sample based on signals output from the detector.

JP2008-256671A JP2020-064063A

However, in Patent Document 1, a g-line image, an h-line image, and an i-line image are captured at different timings. Therefore, positional variations due to mechanical vibration of the inspection device occur in the captured image. Therefore, there is a problem in that the composite image contains errors caused by this positional variation, resulting in a decrease in inspection accuracy.

In Patent Document 2, a laser diode array is used as a light source. Since each laser diode array is provided with a plurality of light emitting elements, variations occur among the plurality of elements in at least one of the wavelength and phase of light emitted from each illumination source. Therefore, the coherence of the light emitted from each illumination source decreases.

Therefore, even if the illumination profile is made close to the illumination profile of the light source in the exposure device, the diffraction phenomenon occurring in the sample in the inspection device will be significantly different from the diffraction phenomenon in the exposure device. For this reason, there is a problem in that the image detected by the detector is different from the image in the exposure device, resulting in a decrease in inspection accuracy. Furthermore, if any one of the plurality of elements becomes abnormal, the entire element must be replaced, resulting in poor reliability.

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

A first aspect is a photomask inspection apparatus, which includes: a holding part that holds a photomask; a first light source that includes 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; and the first light from the first light source and the second light source. a mixing unit that mixes the second light from the mixing unit; 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; and an objective lens; an imaging optical system into which the light is incident, an image sensor which receives the light incident through the imaging optical system and generates a captured image, and inspects the photomask based on the captured image. and an arithmetic processing section.

A second aspect is the photomask inspection apparatus according to the first aspect, wherein sigma, which is a ratio of the illumination optical system to the numerical aperture of the imaging optical system, is the Same as Sigma.

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

According to the photomask inspection apparatus, the mixing section mixes the first light and the second light having mutually different peak wavelengths. Then, the mixed light passes through the photomask and enters 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 other words, a captured image including projection images of light having a plurality of peak wavelengths can be obtained by capturing an image once.

Therefore, unlike Patent Document 1, there is no need to combine a plurality of 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 the captured image in principle. Therefore, the arithmetic processing unit can inspect the photomask based on the captured image with higher inspection accuracy.

Moreover, according to the photomask inspection apparatus, the first light source and the second light source include a single semiconductor light emitting element. Therefore, variations in wavelength or phase in the diode array as in Patent Document 2 do not occur in principle, the first light source can emit more coherent first light, and the second light source can emit more coherent first light. It can emit two lights. Therefore, a diffraction phenomenon equivalent to the diffraction phenomenon in an exposure device can be caused in the light passing through the photomask. Therefore, the arithmetic processing section can inspect the photomask with higher inspection accuracy. Moreover, the reliability of the first light source and the second light source is also high.

FIG. 1 is a perspective view schematically showing an example of the configuration of a photomask inspection device. 1 is a diagram schematically showing an example of an optical configuration of a photomask inspection device. 1 is a diagram schematically showing an example of an optical configuration of an exposure apparatus. It is a graph showing transmittance and reflectance of a first dichroic mirror. It is a graph showing the transmittance and reflectance of a second dichroic mirror. FIG. 2 is a diagram schematically showing an example of a captured image. 3 is a flowchart illustrating an example of the operation of the photomask inspection apparatus. FIG. 3 is a diagram showing the brightness distribution of a projected image in a line of each captured image. 7 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. FIG. 2 is a diagram schematically showing an example of a captured image including a defect. It 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 brightness.

Hereinafter, embodiments will be described in detail with reference to the drawings. In the drawings, the dimensions and numbers of each part are exaggerated or simplified as necessary for the purpose of easy understanding. Also, parts having similar configurations and functions are designated by the same reference numerals, and redundant explanation will be omitted in the following description. Further, in the drawings, XYZ orthogonal coordinates are appropriately shown to indicate the positional relationship of each component. 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 in the Z-axis direction is also referred to as the +Z side, and the other side is also referred to as the -Z side. The same applies to the X-axis and Y-axis.

In addition, in the following description, similar components are shown with the same reference numerals, and their names and functions are also the same. Therefore, detailed descriptions thereof may be omitted to avoid duplication.

In addition, in the description below, even if ordinal numbers such as "first" or "second" are used, these terms are used to make it easier to understand the content of the embodiments. These ordinal numbers are used for convenience and are not limited to the order that can occur based on these ordinal numbers.

When expressions indicating relative or absolute positional relationships are used (e.g., "in one direction," "along one direction," "parallel," "orthogonal," "centered," "concentric," "coaxial," etc.), the expressions , unless otherwise specified, not only strictly represents the positional relationship, but also represents a state in which they are relatively displaced in terms of angle or distance within a range where tolerance or the same level of function can be obtained. When expressions indicating equal conditions are used (e.g., "same," "equal," "homogeneous," etc.), unless otherwise specified, the expressions do not only express quantitatively strictly equal conditions, but also include tolerances or It also represents a state in which there is a difference in which the same level of functionality can be obtained. When an expression indicating a shape (for example, "square shape" or "cylindrical shape") is used, unless otherwise specified, the expression does not only represent the shape strictly geometrically, but also has the same effect. Shapes with unevenness, chamfering, etc., for example, are also expressed as long as the shape can be obtained. When the expressions "comprising," "comprising," "comprising," "containing," or "having" one component are used, the expressions are not exclusive expressions that exclude the presence of other components. When the expression "at least one of A, B, and C" is used, the expression includes only A, only B, only C, any two of A, B, and C, and A, B and C.

<Photomask inspection equipment>
FIG. 1 is a perspective view schematically showing an example of the configuration of the photomask inspection apparatus 1, and FIG. 2 is a diagram schematically showing 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.

<Photomask>
First, the photomask 80 to be inspected will be described. Photomask 80 is a photomask used in exposure apparatus 1000. FIG. 3 is a diagram schematically showing an example of the optical configuration of exposure apparatus 1000. The exposure apparatus 1000 can transfer the pattern of the photomask 80 onto the substrate W by performing an exposure process on the substrate W using the photomask 80. The substrate W is, for example, a substrate for a flat panel display. Note that various substrates such as a semiconductor substrate and a solar cell substrate can be applied to the substrate W.

The photomask 80 has a plate-like shape, and has, for example, a rectangular shape when viewed from above. The length of one side of the photomask 80 is set to, for example, about several meters. As a more specific example, the lengths of each side of the photomask 80 are 1.8 m and 2.0 m, respectively, and the thickness of the photomask 80 is, for example, 2.1 mm. A light shielding film (not shown) is formed on one main surface of the photomask 80 in a predetermined pattern. That is, the photomask 80 is formed with a transmitting part that transmits light and a blocking part that blocks light. Note that the photomask 80 may be a phase shift mask provided with a phase shift film that transmits light with lower transmittance than the transmitting portion.

Photomask 80 is held in exposure apparatus 1000 by a mask holding section (not shown). The mask holding section holds the photomask 80 in a posture such that its thickness direction is along the Z-axis direction. For example, the mask holding section supports only the peripheral portion of the photomask 80.

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

Illumination section 1100 includes a light source 1110 and an illumination optical system 1120. A light source 1110 emits exposure light toward an 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 (for example, a high-pressure mercury lamp). Light from the light source 1110 is irradiated onto the photomask 80 through the illumination optical system 1120.

In the example of FIG. 3, 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 diaphragm 1140, the condenser lens 1150, the aperture diaphragm 1160, and the condenser lens 1170 are provided in this order as they move away from the light source 1110 in the Z-axis direction. That is, the condenser lens 1130 is provided at the position closest to the light source 1110. Light from the light source 1110 is focused by a condenser lens 1130 and passes through a field stop 1140. The aperture diameter of the field stop 1140 is variable, and the illumination range can be adjusted. The light passing through the field stop 1140 is condensed by a condenser lens 1150 and passes through an aperture stop 1160. The light passing through the aperture stop 1160 is focused onto the photomask 80 by a 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.

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

Exposure light from the illumination section 1100 is transmitted through the transmission section of the photomask 80. The patterned light that has passed through the transmitting portion of the photomask 80 is incident on the imaging section 1200 (imaging optical system). The imaging section 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 provided in this order as they move away from the photomask 80 in the Z-axis direction. The light transmitted through the transparent portion of the photomask 80 is magnified via 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 section 1200 can be adjusted. When the substrate W is a substrate for a flat panel display, the numerical aperture of the imaging section 1200 in the exposure apparatus 1000 is set to be small, for example, about 0.1.

The substrate W is provided on the opposite side of the photomask 80 with respect to the imaging section 1200. In the example of FIG. 3, the substrate W is provided on the -Z side with respect to the imaging section 1200. The substrate W is held in a horizontal position by a substrate holder (not shown). The horizontal position here is a position in which the thickness direction of the substrate W is along the Z-axis direction.

The patterned light from the imaging section 1200 is irradiated onto the main surface of the substrate W on the +Z side. As a result, the resist formed on the main surface of the substrate W is exposed in a pattern. That is, the pattern of the transparent portion of the photomask 80 is transferred onto the main surface of the substrate W.

If the photomask 80 is defective, the pattern transferred to the substrate W will deviate from the designed pattern, which is not preferable. Therefore, the photomask inspection apparatus 1 inspects the photomask 80.

<Overview of photomask inspection equipment>
As illustrated in FIG. 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 uses the light-receiving surface of the image sensor 25 ( (imaging surface). The image sensor 25 detects light on the light receiving surface, and the photomask inspection apparatus 1 inspects the photomask 80 based on the detection result. That is, the photomask inspection apparatus 1 can pseudo-inspect the photomask 80 based on the light on the substrate W in the exposure apparatus 1000.

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

The holding section 90 is a member that holds the photomask 80. This 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 section 90 supports only the peripheral portion of the photomask 80. However, the holding section 90 may support the entire lower surface of the photomask 80 with a light-transmitting member.

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

The illumination unit 10 irradiates the photomask 80 with light L2. In the example of FIG. 2, the illumination section 10 includes a pseudo light irradiation section 11 and an illumination optical system 17. The pseudo 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. That is, the light L2 is light imitating the light used to expose the substrate W in the exposure apparatus 1000. This light L2 enters 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 section 10 to the photomask 80. The patterned light L2 transmitted through the transmitting portion of the photomask 80 is incident on the detecting portion 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 passed 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 aperture of the illumination optical system 1120 to the numerical aperture N20 of the imaging section 1200 of the exposure apparatus 1000. It is set to the same value as sigma (=N10/N20), which is the ratio of the number N10. Thereby, the brightness distribution of the light L2 incident on the light-receiving surface of the image sensor 25 imitates the brightness distribution of the patterned light irradiated onto the substrate W. That is, the luminance distribution of light irradiated onto the substrate W when the photomask 80 is used in the exposure apparatus 1000 is simulated on the light receiving surface of the image sensor 25.

<Lighting section>
As illustrated in FIG. 2, the pseudo light irradiation section 11 includes a plurality of light sources 12 and a mixing section 14.

The plurality of light sources 12 emit light L1 having mutually different peak wavelengths. 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 device 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 (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 (so-called H-line wavelength). 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 (so-called g-line wavelength). In the optical spectral distribution (spectrum) of the light L1 emitted by each light source 12, there may be only one peak wavelength. In other words, the light L1 may have a single wavelength. Specifically, the spectrum of the light emitted by each light source 12 may have a steep mountain-like shape with the maximum intensity at the peak wavelength. When the semiconductor light emitting element 121 is a light emitting diode element, it emits light L1 having a somewhat wide mountain-like spectrum, and when the semiconductor light emitting element 121 is a laser element, it emits light L1 having a relatively narrow mountain-like spectrum. Emit light L1.

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

Each light source 12 may be provided with a sensor (not shown) that measures the intensity (or illuminance or amount of light) of the light L1 from the semiconductor light emitting element 121. The sensor outputs a signal indicating the detected value to the control section 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 the light L1 emitted from the light source 12 with higher accuracy.

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

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

The light L1a and the light L1b enter the first dichroic mirror 141. In the example of FIG. 2, the light source 12a is provided on the −X side of the first dichroic mirror 141, and emits light L1a on the +X side along the X-axis direction. The light source 12b is provided on the +Z side of the first dichroic mirror 141, and emits light L1b on the -Z side along the Z-axis direction. The first dichroic mirror 141 has a plate-like shape, and is arranged with its thickness direction along the direction from the +X side and +Z side to the -X side and -Z side. The first dichroic mirror 141 reflects the light L1a and transmits the light L1b in the same direction as the direction in which the light L1a is reflected. FIG. 4 is a graph showing the transmittance and reflectance of the first dichroic mirror 141. The first dichroic mirror 141 has a low transmittance and a high reflectance for the light L1a having the first peak wavelength (here, 365 nm). On the other hand, the first dichroic mirror 141 has a high transmittance and a low reflectance for the light L1b having the second peak wavelength (405 nm here) and the light L1c having the third peak wavelength (436 nm here).

The light L1a is reflected by the first dichroic mirror 141 to the -Z side along the Z-axis direction, and the light L1b passes through the first dichroic mirror 141 and proceeds to the -Z side. As a result, the optical paths of the light L1a and the light L1b ideally match. In other words, the light L1a and the light L1b are mixed.

This mixed light and light L1c enter the second dichroic mirror 142. In the example of FIG. 2, the second dichroic mirror 142 is provided on the −Z side with respect to the first dichroic mirror 141. The light source 12c is provided on the −X side of the second dichroic mirror 142, and emits light L1c on the +X side along the X-axis direction. The second dichroic mirror 142 has a plate-like shape, and is arranged with its thickness direction along the direction 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 the light L1c in the same direction as the direction in which the mixed light is reflected. FIG. 5 is a graph showing the transmittance and reflectance of the second dichroic mirror 142. The second dichroic mirror 142 has a low transmittance and a high reflectance for the light L1a and the light L1b. On the other hand, the second dichroic mirror 142 has a high transmittance and a low reflectance with respect to the light L1c.

The second dichroic mirror 142 reflects the mixed light including the light L1a and the light L1b to the +X side along the X-axis direction, and the light L1c passes through the second dichroic mirror 142 to the +X side. move on. As a result, the optical paths of the light L1a, the light L1b, and the light L1c ideally match. That is, the light L1a, the light L1b, and the light L1c are mixed. Mixed light including light L1a, light L1b, and light L1c corresponds to light L2.

In the example of FIG. 2, the light L2 is focused by the lens 15 onto the incident end of the light guide 16. The light L2 travels inside the light guide 16 and exits from the output 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 output end of the light guide 16 corresponds to the output end of the pseudo light irradiation section 11.

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

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

In the example of FIG. 2, the output end of the light guide 16 is provided on the -Z side relative to the illumination optical system 17, and emits the light L2 toward the illumination optical system 17. In the example of FIG. 2, the 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. The condensing lens 171, the field diaphragm 172, the condensing lens 173, the aperture diaphragm 174, and the condenser lens 175 are provided in this order as they move away from the output end of the light guide 16 in the Z-axis direction.

Light L2 from the output end of the light guide 16 is condensed by a condenser lens 171 and passes through a field stop 172. The aperture diameter of the field diaphragm 172 is variable by a diaphragm mechanism, and the illumination range can be adjusted. The light L2 that has passed through the field stop 172 is condensed by a condenser lens 173 and passes through an aperture stop 174. The light L2 that has passed through the aperture stop 174 is focused 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 diaphragm mechanisms of the field diaphragm 172 and the aperture diaphragm 174 may be controlled by the control unit 50.

<Detection part>
The patterned light L2 transmitted through the transmitting portion of the photomask 80 is incident on the detecting portion 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 transmitting 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 provided 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 greater than or equal to the numerical aperture of the objective lens 1210 in the exposure apparatus 1000. The light transmitted through the photomask 80 is magnified via the objective lens 22 and the imaging lens 24. The aperture diameter of the aperture stop 23 is variable by a diaphragm mechanism, and the numerical aperture of the imaging optical system 21 can be adjusted. The diaphragm mechanism of the aperture diaphragm 23 may be controlled by the control section 50.

The light L2 transmitted 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 the light incident on its own 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 mechanism>
The moving mechanism 40 moves the holding part 90 within the XY plane. As a result, the photomask 80 held by the holding section 90 also moves within the XY plane. The moving mechanism 40 has, for example, a ball screw mechanism, and is controlled by a control section 50. By moving the photomask 80 within the XY plane, the illumination section 10 and the detection section 20 can be scanned with respect to the photomask 80. Therefore, the illumination unit 10 can irradiate each measurement area of the photomask 80 with the light L2, and the image sensor 25 can generate a captured image IM1 in each measurement area of the photomask 80. Therefore, the control unit 50 can inspect multiple measurement areas of the photomask 80. Note that the moving mechanism 40 only needs to have the function and structure of moving the photomask 80 relative to the illumination section 10 and the detection section 20. You may move it.

<Lifting mechanism>
The elevating mechanism 60 moves the holding section 90 up and down in the Z-axis direction. As a result, the photomask 80 held by the holding section 90 also moves up and down. The lifting mechanism 60 includes, for example, a ball screw mechanism, and is controlled by the control unit 50. By raising and lowering the photomask 80 by the lifting mechanism 60, the photomask 80 can be moved to the focal point of the objective lens 22. Note that the elevating mechanism 60 only needs to have the function and structure of elevating the photomask 80 relative to the detecting section 20, and may elevate the detecting section 20, for example.

<Control unit>
The control unit 50 can control the photomask inspection apparatus 1 as a whole. For example, the control unit 50 controls the illumination unit 10, the moving mechanism 40, and the elevating mechanism 60 as described above. The control unit 50 also functions as an arithmetic processing unit that obtains 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 patterns formed on the photomask 80, the spacing between the patterns, or various defects. The method for determining the mask characteristics will be described in detail later.

The control unit 50 is an electronic circuit device, and may include, for example, an arithmetic processing unit and a storage unit. The arithmetic processing device may be, for example, a CPU (Central Processor Unit). The storage unit may include a non-temporary storage unit (for example, a ROM (Read Only Memory) or a hard disk) and a temporary storage unit (for example, a RAM (Random Access Memory)). The non-temporary storage unit may store, for example, a program that defines the processing that the control unit 50 executes. 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.

<How to calculate mask characteristics>
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.

FIG. 6 is a diagram schematically showing an example of the captured image IM1. The captured image IM1 includes patterned light L2. The brightness 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 includes a vertical portion extending in the vertical direction and a horizontal portion extending rightward from the middle of the vertical portion.

In the example of FIG. 6, an example of the luminance distribution in a line A extending in the width direction of the vertical portion is also schematically shown. The control unit 50 determines the position of the rising edge where the brightness value rises from zero and the position of the falling edge where the brightness value falls to zero in the brightness distribution, and calculates the width of the vertical portion (projection image width) based on both positions. ).

By the way, if the position of the objective lens 22 with respect to the photomask 80 deviates from the focal position in the Z-axis direction, the projected image may vary in the captured image IM1. That is, if the elevating mechanism 60 stops the holding part 90 at a position shifted from the focal position, the projected image may be different from the projected image at the focal position.

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

Therefore, here, the position of the holding unit 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 each time, the image sensor 25 generates the captured image IM1, and the control unit 50 performs an inspection based on these plurality of captured images IM1. An example of the inspection method will be specifically described below.

FIG. 7 is a flowchart showing an example of the operation of the photomask inspection apparatus 1. Here, the moving mechanism 40 is moving the holding part 90 to a predetermined measurement position. The control unit 50 causes the plurality of light sources 12 to irradiate the light L1 (step S1). As a result, the light L2 imitating the light in the exposure apparatus 1000 is transmitted through the transmission part in the predetermined measurement area of the photomask 80, and the patterned light L2 is incident on the light receiving surface of the image sensor 25 through the imaging optical system 21. do.

Next, the control unit 50 controls the lifting mechanism 60 and the image sensor 25 to cause the image sensor 25 to generate a captured image IM1 at each Z-axis position (step S2). For example, while the elevating mechanism 60 moves the holding part 90 within a predetermined elevating range (focus range) including the focal position, the image sensor 25 sequentially generates the captured images IM1. Note that the elevating mechanism 60 may stop the holding section 90 at the imaging timing. Thereby, 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 projected image width is determined as the mask characteristic. FIG. 8 shows the brightness 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 spaced 10 μm apart from the focal position on the +Z side and on the -Z side. As can be understood from FIG. 8, when defocus occurs, the brightness distribution changes depending on the amount of defocus. Therefore, the projected image widths determined based on each brightness distribution are different from each other.

Therefore, the control unit 50 calculates a focus evaluation value for each of the plurality of captured images IM1. The focus evaluation value is an index indicating the degree of focus, and the higher the focus evaluation value, the better the focus is. The focus evaluation value may be, for example, an index indicated by a high frequency component among frequency components obtained by Fourier transforming the brightness distribution of the captured image IM1. The higher the high frequency component is, the more steeply the brightness distribution changes, so the outline of the projected image is clearer and more focused. Alternatively, various indicators such as the contrast and sharpness of the captured image IM1 may be employed as the focus evaluation value.

Since the plurality of captured images IM1 correspond to the plurality of Z-axis positions, the focus evaluation value calculated based on the brightness distribution of each captured image IM1 also corresponds to the Z-axis position. Similarly, the projected 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 projected image width. In the example of FIG. 9, an approximate curve G1 and an approximate curve G2 are also shown. The approximate curve G1 is calculated based on the plot points showing the relationship between the Z-axis position and the focus evaluation value, and the approximate curve G2 is calculated based on the plot points showing the relationship between the Z-axis position and the projected image width. .

The focus evaluation value takes the maximum value when the Z-axis position becomes the focus position P0. Therefore, first, the control unit 50 determines the Z-axis position where the focus evaluation value becomes the maximum value (that is, the focus position P0). For example, the control unit 50 calculates the approximate 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 when the focus evaluation value reaches the maximum value Fmax in the approximate curve G1 as the focus position P0.

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

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

<Effects of the embodiment>
As described above, according to the photomask inspection apparatus 1, the illumination unit 10 emits the light L2 imitating the light of the exposure apparatus 1000, and the sigma of the photomask inspection apparatus 1 is the same as the sigma of the exposure apparatus 1000. is set the same as. Thereby, the light (projected image) on the substrate W in the exposure apparatus 1000 can 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.

Moreover, according to the photomask inspection apparatus 1, the mixing unit 14 mixes the plurality of lights L1 having mutually different peak wavelengths. Then, the illumination unit 10 irradiates the photomask 80 with light L2, which is the mixed light, and the light L2 transmitted 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 by the light L2 having a plurality of peak wavelengths. In other words, by one-time imaging, it is possible to obtain a captured image IM1 that includes projection images of the light L2 having a plurality of peak wavelengths.

Therefore, unlike Patent Document 1, there is no need to combine a plurality of 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 the captured image IM1 in principle. Therefore, the control unit 50 can calculate the projected image width with high accuracy, and can inspect the photomask 80 with higher inspection accuracy.

Moreover, according to the photomask inspection apparatus 1, each light source 12 includes a single semiconductor light emitting element 121. Therefore, variations in wavelength or phase in the 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 that in the exposure apparatus 1000 can be caused in the light L2 passing through the photomask 80. Therefore, the control unit 50 can inspect the photomask 80 with higher inspection accuracy.

Further, since the light source 12 including the single semiconductor light emitting element 121 does not have variations in the emission direction in principle, variations in the 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 accuracy. Moreover, the reliability of the light source 12 is also high.

<Mask characteristics: defect brightness>
In the above example, the inspection method was explained using the projected image width as the mask characteristic. However, defect brightness may be employed as the mask characteristic. FIG. 10 is a diagram schematically showing an example of a captured image IM1 including the 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 the light L2 is transmitted through the defect, and is also called a white defect.

Here, the brightness value of the defect D1 is determined. Hereinafter, the brightness value of the defect D1 will also be referred to as defect brightness. Since this defect brightness also varies depending on the position of the holding section 90 in the Z-axis direction, the control section 50 preferably calculates the defect brightness based on the plurality of captured images IM1, similarly to the projection image width.

Specifically, in step S3, the control unit 50 first obtains the defect brightness and focus evaluation value for each captured image IM1. Thereby, it is possible to obtain a plurality of defect brightnesses corresponding to a plurality of Z-axis positions, and a plurality of focus evaluation values respectively 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 defect brightness. 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 plot points of the Z-axis position and defect brightness.

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

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 brightness DL). For example, the control unit 50 determines whether the defect brightness DL is less than or equal to a predetermined defect tolerance value, and determines that the photomask 80 is a defective product when the defect brightness DL is greater than the defect tolerance value. .

As described above, the photomask inspection apparatus 1 can determine whether the photomask 80 is good or bad based on the brightness value of the defect D1. In addition, although the above-mentioned example adopted and explained the white defect as the defect D1, various defects, such as a black defect, can also be adopted as the defect D1.

<Variations in projected images in exposure apparatus 1000>
The photomask inspection apparatus 1 simulates the luminance distribution (projected image) of patterned light on the substrate W in the exposure apparatus 1000 on the light receiving surface of the image sensor 25. That is, the captured image IM1 when a 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 variations in the projected image on the substrate W due to defocus.

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

Since the amount of defocus ΔZ (maximum value) that may occur due to mechanical errors of the exposure apparatus 1000 can be determined in advance, the variation in the projected image width that occurs in the exposure apparatus 1000 can be determined based on the relationship shown in FIG. . For example, the amount of defocus ΔZ may be set in advance and stored in the storage unit, or the user may input the amount of defocus ΔZ using an input device (for example, a keyboard or mouse) not shown.

The control unit 50 determines the maximum width of the projected image in the range between a position shifted from the focal position P0 by a focal displacement amount ΔZ on the −Z side and a position shifted from the focal position P0 on the +Z side by a focal displacement amount ΔZ. A value LWmax and a minimum value LWmin are calculated based on the approximate curve G2. The range from the minimum value LWmin to the maximum value LWmax corresponds to variations in the projected image width that occur in the exposure apparatus 1000.

The control unit 50 may determine the quality of the photomask 80 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 greater than or equal to 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 less than or equal to the allowable upper limit. do. 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 when the maximum value LWmax is greater than the allowable upper limit.

Similarly, the control unit 50 may calculate the variation in defect brightness caused by the amount of defocus ΔZ. Specifically, the control unit 50 controls, in a range between a position shifted from the focus position P0 to the -Z side by the focus shift amount ΔZ and a position shifted from the focus position P0 to the +Z side by the focus shift amount ΔZ. The maximum value DLmax and minimum value DLmin of defect brightness are calculated based on the approximate 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.

The control unit 50 may determine whether the photomask 80 is good or bad based on the maximum value DLmax of defect brightness. 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 larger than the defect tolerance value.

Here, the terms in the column of means for solving the problem and the terms in the column of modes for carrying out the invention are associated. The first light source corresponds to one of the light sources 12a to 12c, and the second light source corresponds to one of the light sources 12a to 12c, which 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 by the first semiconductor light emitting element, and the second light corresponds to the light L1 emitted by the second semiconductor light emitting element.

As mentioned above, although the photomask inspection apparatus 1 has been explained in detail, the above explanation is an example in all aspects, and this disclosure is not limited thereto. Further, the various modifications described above can be applied in combination as long as they do not contradict each other. And it is understood that numerous variations not illustrated can be envisioned without departing from the scope of this disclosure.

1 Photomask inspection device 10 Illumination section 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 Illumination optical system 21 Imaging optical system 22 Objective lens 25 Image sensor 50 Arithmetic processing section (control section)
80 Photomask 90 Holding part

Claims (3)

a holding part that holds 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 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 obtained by mixing 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 apparatus, comprising: an arithmetic processing unit that inspects the photomask based on the captured image. The photomask inspection device according to claim 1,
A photomask inspection apparatus, wherein sigma, which is a ratio 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 photomask inspection apparatus according to claim 1 or 2,
A photomask inspection apparatus, wherein the numerical aperture of the objective lens is greater than or equal to the numerical aperture of an objective lens in an exposure apparatus in which the photomask is used.

Images