CN116794928A

CN116794928A - Photomask inspection apparatus

Info

Publication number: CN116794928A
Application number: CN202310205204.8A
Authority: CN
Inventors: 岸本良
Original assignee: Screen Holdings Co Ltd
Current assignee: Screen Holdings Co Ltd
Priority date: 2022-03-22
Filing date: 2023-03-06
Publication date: 2023-09-22
Also published as: JP2023139436A; KR20230137824A; TW202338297A

Abstract

The invention provides a photomask inspection device with high reliability, which can detect a photomask with higher detection precision. The photomask inspection apparatus includes: the image processing device includes a holding unit, a first light source, a second light source, a mixing unit, an illumination optical system, an imaging optical system, an image sensor, and an arithmetic processing unit. The holding portion holds the photomask. The first light source includes a single first semiconductor light emitting element emitting first light. The second light source includes a single second semiconductor light emitting element that emits second light. The mixing section mixes the first light and the second light. The illumination optical system directs light to the photomask. The image sensor receives light incident through the imaging optical system and generates a photographed image. The arithmetic processing unit performs inspection of the photomask based on the captured image.

Description

Photomask inspection apparatus

Technical Field

The present disclosure relates to a photomask inspection apparatus.

Background

Inspection devices for inspecting a photomask (reticle) have been proposed from the past (patent document 1 and patent document 2).

Patent document 1 discloses a light source that outputs light including g-rays, h-rays, and i-rays. Light from the light source is irradiated to the photomask through the wavelength selective filter, and light transmitted through the photomask is incident on the photographing surface of the photographing member. The wavelength selective filter includes: a first filter that transmits only g-rays, a second filter that transmits only h-rays, and a third filter that transmits only i-rays. The light selectively passes through these first, second and third filters. When light passes through the first filter, only g-rays pass through the photomask and are incident on the photographing part, and thus the photographing part generates a photographed image under the g-rays. The imaging means generates an imaging image in the h-ray when the light passes through the second filter, and generates an imaging image in the i-ray when the light passes through the third filter. In patent document 1, these three captured images are synthesized by wavelength calculation, a synthesized image including g-rays, h-rays, and i-rays is generated, and inspection of a photomask is performed based on the synthesized image.

In patent document 2, a plurality of illumination sources are provided, and each illumination source includes a plurality of laser diode arrays. The light beams outputted from the plurality of illumination sources are coupled by the light beam coupling optical element, and the light beams are made incident on the sample with an arbitrary illumination distribution. The light beam reflected from the sample is incident on and detected by a detector. The inspection device obtains a sample parameter such as a limit size of the sample based on the signal output from the detector.

[ Prior Art literature ]

[ patent literature ]

Patent document 1 Japanese patent laid-open No. 2008-256671

[ patent document 2] Japanese patent laid-open No. 2020-064063

Disclosure of Invention

[ problem to be solved by the invention ]

However, in patent document 1, an image taken under g-rays, an image taken under h-rays, and an image taken under i-rays are taken at different times. Therefore, positional deviation caused by mechanical vibration of the inspection device occurs in the photographed image. Therefore, the resultant image includes an error due to the positional deviation, and there is a problem in that the inspection accuracy is lowered.

In patent document 2, a laser diode array is used as a light source. Since a plurality of light emitting elements are provided in each laser diode array, a deviation between the plurality of elements occurs in at least any one of the wavelength and the phase of light emitted from each illumination source. Therefore, the coherence of the light emitted from each illumination source is reduced.

Therefore, even if the illumination distribution is made close to the illumination distribution of the light source in the exposure apparatus, the diffraction phenomenon generated by the sample in the inspection apparatus is greatly different from the diffraction phenomenon in the exposure apparatus. Therefore, the image detected by the detector is different from the image in the exposure apparatus, and there is a problem in that the inspection accuracy is lowered. In addition, if any one of the plurality of elements is abnormal, the entire element needs to be replaced, and the reliability is poor.

Accordingly, an object of the present disclosure is to provide a photomask inspection apparatus with high reliability that can detect a photomask with higher detection accuracy.

[ means of solving the problems ]

A first embodiment is a photomask inspection apparatus, comprising: a holding portion for holding the photomask; a first light source including a single first semiconductor light emitting element emitting 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 configured to mix the first light from the first light source and the second light from the second light source; an illumination optical system that guides the light obtained by mixing the first light and the second light by the mixing section to the photomask; an imaging optical system including an objective lens and for inputting the light from the photomask; an image sensor that receives the light incident through the imaging optical system and generates a photographed image; and an arithmetic processing unit that performs inspection of the photomask based on the captured image.

A second embodiment is the photomask inspection apparatus according to the first embodiment, wherein a ratio of a numerical aperture of the illumination optical system to a numerical aperture of the imaging optical system, that is, sigma (sigma), is the same as the sigma in an exposure apparatus using the photomask.

A third embodiment is the photomask inspection apparatus according to the first or second embodiment, wherein the numerical aperture of the objective lens is equal to or larger than the numerical aperture of the objective lens in the exposure apparatus using the photomask.

[ Effect of the invention ]

According to the photomask inspection apparatus, the mixing portion mixes the first light and the second light having different peak wavelengths from each other. Further, the mixed light, i.e., light, is transmitted 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 formed by light having the first peak wavelength and the second peak wavelength. That is, by one shooting, a shot image including a projection image formed of light having a plurality of peak wavelengths can be obtained.

Therefore, as in patent document 1, it is not necessary to combine a plurality of captured images obtained by sequentially irradiating light having different peak wavelengths from each other. Therefore, unlike patent document 1, in the captured image, a positional deviation for each peak wavelength is not generated in principle. Therefore, the arithmetic processing unit can inspect the photomask based on the captured image with higher inspection accuracy.

Further, according to the photomask inspection apparatus, the first light source and the second light source include a single semiconductor light emitting element. Therefore, in principle, the wavelength and phase of the diode array as in patent document 2 are not shifted, and the first light source can emit the first light that is further coherent and the second light source can emit the second light that is further coherent. Therefore, the light transmitted through the photomask can be caused to have a diffraction phenomenon equivalent to that in the exposure apparatus. Therefore, the arithmetic processing unit can inspect the photomask with higher inspection accuracy. Moreover, the reliability of the first light source and the second light source is also high.

Drawings

Fig. 1 is a perspective view schematically showing an example of the structure of a photomask inspection apparatus.

Fig. 2 schematically shows an example of an optical structure of the photomask inspection apparatus.

Fig. 3 schematically shows an example of an optical configuration of the exposure apparatus.

Fig. 4 is a graph showing the transmittance and reflectance of the first dichroic mirror.

Fig. 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 flowchart showing an example of the operation of the photomask inspection apparatus.

Fig. 8 is a view showing the brightness distribution of the projection image on 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 projected image width.

Fig. 10 schematically shows an example of a captured image including 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 the defect brightness.

[ description of symbols ]

1: photomask inspection apparatus

10: lighting part

11: simulation light irradiation part

12. 12a to 12c: first light source, second light source (light source)

121: first semiconductor light-emitting element, second semiconductor light-emitting element (semiconductor light-emitting element)

13a, 13b, 13c: lens

14: mixing part

141: first dichroic mirror

142: second dichroic mirror

15: lens

16: light guide

17: illumination optical system

171: condensing lens

172: visual field diaphragm

173: condensing lens

174: aperture diaphragm

175: beam focusing lens

20: detection unit

21: imaging optical system

22: objective lens

23: aperture diaphragm

24: imaging lens

25: image sensor (optical sensor)

40: moving mechanism

50: arithmetic processing unit (control unit)

60: lifting mechanism

80: photomask and method for manufacturing the same

90: holding part

1000: exposure apparatus

1100: lighting part

1110: light source

1120: illumination optical system

1130: condensing lens

1140: visual field diaphragm

1150: condensing lens

1160: aperture diaphragm

1170: beam focusing lens

1200: image forming section

1210: objective lens

1220: aperture diaphragm

1230: imaging lens

A: wire (C)

D1: defects(s)

DL: defect brightness

DLmax: maximum value of defect brightness (maximum value)

DLmin: minimum value of defect brightness (minimum value)

Fmax: maximum value

G1, G2, G3: approximation of curve

L1, L1a, L1b, L1c, L2: light source

LD1: luminance distribution

LW: projection image width

LWmax: maximum value of projection image width (maximum value)

LWmin: minimum value of projection image width (minimum value)

IM1: shooting an image

P0: focal position

S1-S4: step (a)

W: substrate board

X, Y, Z: shaft

Δz: defocus amount

Detailed Description

Hereinafter, embodiments will be described in detail with reference to the drawings. In the drawings, the size and number of each portion are exaggerated or simplified for easy understanding. The same reference numerals are given to portions having the same structure and function, and overlapping description is omitted in the following description. In the drawings, XYZ orthogonal coordinates are appropriately shown to show the positional relationship of the respective structures. For example, the Z axis is arranged along the vertical direction, and the X axis and the Y axis 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 is true for the X-axis and the Y-axis.

In the following description, the same reference numerals are given to the same components, and the same names and functions are also used. Therefore, in order to avoid repetition, a detailed description thereof is sometimes omitted.

In the following description, even if a sequence number such as "first" or "second" is used, these terms are used for the convenience of understanding the content of the embodiments, and are not limited to the sequence in which these sequence numbers can be generated.

In the case where expressions showing a relative positional relationship or an absolute positional relationship (for example, "in one direction", "along one direction", "parallel", "orthogonal", "central", "concentric", "coaxial", etc.) are used, unless otherwise specified, the expressions mean not only the positional relationship but also a state in which angles or distances are relatively displaced within a range in which a tolerance or a function of the same degree can be obtained. When expressions (e.g., "identical", "equal", "homogeneous", etc.) indicating equal states are used, unless otherwise specified, the expressions are not only quantitatively and strictly indicative of equal states but also indicative of states having tolerances or differences in functions that can achieve the same degree. When an expression indicating a shape (for example, "quadrangular shape" or "cylindrical shape") is used, unless otherwise specified, the expression indicates not only the shape strictly geometrically but also a shape having, for example, irregularities or chamfers, within a range where the same degree of effect can be obtained. Where the expression "comprising," "including," "having," "containing," or "having" one component is used, the expression is not an exclusive expression of excluding the presence of other components. Where the expression of "at least any of A, B and C" is used, the expression includes any two of a only, B only, C, A, B only, and C, and all of A, B and C.

Photomask inspection apparatus

Fig. 1 is a perspective view schematically showing an example of the structure of the photomask inspection apparatus 1, and fig. 2 is a view schematically showing an example of the optical structure of the photomask inspection apparatus 1. The photomask inspection apparatus 1 is an apparatus for inspecting the photomask 80.

< photomask >)

First, a photomask 80 to be inspected will be described. The photomask 80 is a photomask used in the exposure apparatus 1000. Fig. 3 schematically shows an example of an optical configuration of the exposure apparatus 1000. The exposure apparatus 1000 is capable of transferring a pattern of the photomask 80 to 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. The substrate W may be a semiconductor substrate, a solar cell substrate, or the like.

The photomask 80 has a plate-like shape, and has a rectangular shape in plan view, for example. The length of one side of the photomask 80 is set to, for example, about several m (meters). More specifically, the length of each side of the photomask 80 is 1.8m and 2.0m, respectively, and the thickness of the photomask 80 is 2.1mm, for example. A light shielding film (not shown) is formed in a predetermined pattern on one main surface of the photomask 80. That is, a transmission portion that transmits light and a blocking portion that blocks light are formed in the photomask 80. The photomask 80 may be a phase-shifting mask (phase-shifting mask) provided with a phase-shifting film that transmits light at a lower transmittance than the transmission portion.

The photomask 80 is held by a mask holding portion, not shown, in the exposure apparatus 1000. The mask holding portion holds the photomask 80 in a posture in which the thickness direction thereof is along the Z-axis direction. The mask holding portion supports, for example, only the peripheral edge portion of the photomask 80.

As shown in fig. 3, the 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, illumination unit 1100 is provided on the +z side with respect to photomask 80, and imaging unit 1200 is provided on the-Z side with respect to photomask 80.

The illumination section 1100 includes a light source 1110 and an illumination optical system 1120. The light source 1110 emits exposure light to the illumination optical system 1120. The exposure light is, for example, ultraviolet light, and the light source 1110 is, for example, an ultraviolet light irradiator such as a mercury lamp (e.g., a high-pressure mercury lamp). Light from light source 1110 passes through illumination optics 1120 and impinges on photomask 80.

In the example of fig. 3, illumination optics 1120 includes: a condenser lens 1130, a field stop 1140, a condenser lens 1150, an aperture stop 1160, and a condenser lens 1170. The condenser lens 1130, the field stop 1140, the condenser lens 1150, the aperture stop 1160, and the condenser lens 1170 are disposed in this order as they are away from the light source 1110 in the Z-axis direction. That is, the condensing lens 1130 is disposed at a position closest to the light source 1110. Light from the light source 1110 is condensed by a condenser lens 1130 and passes through a field stop 1140. The aperture 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 condensing lens 1150 and passes through an aperture stop 1160. Light passing through the aperture stop 1160 is focused by the beam focusing lens 1170 onto the photomask 80. The aperture of the aperture stop 1160 is variable, and the numerical aperture of the illumination optical system 1120 can be adjusted.

Further, a filter that transmits only light in a predetermined wavelength region among the light from the light source 1110 may be provided in the illumination optical system 1120.

The exposure light from the illumination section 1100 is transmitted through the transmission section of the photomask 80. The patterned light transmitted through the transmission portion of the photomask 80 enters the imaging portion 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, aperture stop 1220 and imaging lens 1230 are disposed in this order in the Z-axis direction as they are away from the photomask 80. The light transmitted through the transmission portion of the photomask 80 is amplified through the objective lens 1210 and the imaging lens 1230. The aperture 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, the numerical aperture of the imaging section 1200 is set to be small, for example, about 0.1 in the exposure apparatus 1000.

The substrate W is disposed on the opposite side of the imaging section 1200 from the photomask 80. In the example of fig. 3, the substrate W is disposed on the-Z side of the imaging section 1200. The substrate W is held in a horizontal posture by a substrate holding unit, not shown. The horizontal posture referred to herein means a posture 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 to the main surface on the +z side of the substrate W. Thus, the resist formed on the main surface of the substrate W is exposed to light in a pattern. That is, the pattern of the transmission portion of the photomask 80 is transferred to the main surface of the substrate W.

If the photomask 80 is defective, the pattern transferred to the substrate W is not preferable because it deviates from the design pattern. Accordingly, the photomask inspection apparatus 1 inspects the photomask 80.

Summary of photomask inspection apparatus

As illustrated in fig. 2, the photomask inspection apparatus 1 includes an image sensor (optical sensor) 25 that receives light transmitted through a photomask 80. As will be described in detail later, the photomask inspection apparatus 1 causes the pattern-shaped light irradiated onto the substrate W when the photomask 80 to be inspected is used in the exposure apparatus 1000 to be reproduced on the light receiving surface (imaging surface) of the image sensor 25 in a simulated manner. 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 inspect the photomask 80 based on the light on the substrate W in the exposure apparatus 1000 in a simulated manner.

The photomask inspection apparatus 1 includes: the illumination unit 10, the detection unit 20, the movement mechanism 40, the control unit 50, the lifting mechanism 60, and the holding unit 90. Hereinafter, first, an outline of the structure of the photomask inspection apparatus 1 will be described, and then, an example of each structure will be described in detail.

The holding portion 90 is a member for holding the photomask 80. The holding portion 90 holds the photomask 80 such that the thickness direction of the photomask 80 is along the Z-axis direction. In the example of fig. 1, the holding portion 90 supports only the peripheral edge portion of the photomask 80. The holding portion 90 may entirely support the lower surface of the photomask 80 by a light-transmitting member.

The illumination unit 10 and the detection unit 20 are disposed on opposite sides of the photomask 80 in the Z-axis direction. In the example of fig. 1 and 2, the illumination unit 10 is provided on the-Z side with respect to the photomask 80, and the detection unit 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 unit 10 includes: a simulation light irradiation unit 11, and an illumination optical system 17. The analog light irradiation section 11 emits light L2, the light L2 having a spectrum similar to that of light for exposure in the wavelength range of light irradiated by the light source 1110 of the exposure apparatus 1000. That is, the light L2 is light that mimics the light used for exposing the substrate W in the exposure apparatus 1000. The 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 section 10 to the photomask 80. The patterned light L2 transmitted through the transmission portion of the photomask 80 enters the detection portion 20.

The detection unit 20 includes: imaging optical system 21 and image sensor 25. The imaging optical system 21 images the light L2 transmitted through the photomask 80 on the light receiving surface of the image sensor 25. The sigma (=n1/N2) which is the ratio of the numerical aperture N1 of the illumination optical system 17 to the numerical aperture N2 of the imaging optical system 21 is set to the same value as the sigma (=n10/N20) which is the ratio of the numerical aperture N10 of the illumination optical system 1120 to the numerical aperture N20 of the imaging section 1200 of the exposure apparatus 1000. Thus, the luminance distribution of the light L2 incident on the light receiving surface of the image sensor 25 becomes a distribution that mimics the luminance distribution of the pattern-like light irradiated on the substrate W. That is, when the photomask 80 is used in the exposure apparatus 1000, the luminance distribution of the light irradiated onto the substrate W is reproduced in a simulated manner on the light receiving surface of the image sensor 25.

< illumination portion >)

As illustrated in fig. 2, the simulation 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 peak wavelengths different from each other. In the example of fig. 2, three light sources 12a to 12c are provided as the plurality of light sources 12. Each light source 12 includes a single semiconductor light emitting element 121. The semiconductor light emitting element 121 includes, for example, a light emitting diode element or a laser element. Such a single semiconductor light emitting element 121 includes, for example, a single semiconductor 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 365nm (the wavelength of so-called i-rays), for example. 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, 405nm (the wavelength of the so-called h-ray). 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, 436nm (the wavelength of the so-called g-ray). In the light-splitting distribution (spectrum) of the light L1 emitted from each light source 12, the peak wavelength may be only one. That is, the light L1 may be light of a single wavelength. Specifically, the spectrum of the light emitted from each light source 12 may have a steep mountain shape in which the intensity at the peak wavelength is set to the maximum intensity. When the semiconductor light emitting element 121 is a light emitting diode element, light L1 having a mountain-shaped spectrum with a slightly wider width is emitted, and when the semiconductor light emitting element 121 is a laser element, light L1 having a mountain-shaped spectrum with a relatively narrower width is emitted.

Power is supplied to each semiconductor light emitting element 121 individually from a power supply unit not shown. Each semiconductor light emitting element 121 emits light L1 at a luminance corresponding to the electric power from the power supply unit. The power supply unit is a current source, and includes a switching power supply circuit, for example. In this case, the power supply section controls the luminance of the light L1 by controlling the current supplied to the semiconductor light emitting element 121. Since the respective power supply units are individually controlled by the control unit 50, the brightness of the light L1 from the respective light sources 12 is individually controlled by the control unit 50.

A sensor (not shown) for measuring the intensity (or illuminance or light quantity) of the light L1 from the semiconductor light emitting element 121 may be provided for each light source 12. The sensor outputs a signal indicating the detected value to the control unit 50. The control section 50 controls the power supply section based on the detection value, and controls the current supplied from the power supply section to the semiconductor light emitting element 121. Thus, the control unit 50 can control the intensity of the light L1 emitted from the light source 12 with higher accuracy.

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

The mixing section 14 mixes the plurality of lights L1 respectively incident from the plurality of light sources 12. The mixing of light as described herein means making the optical paths of the plurality of lights L1 substantially uniform. 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 are incident on the first dichroic mirror 141. In the example of fig. 2, the light source 12a is disposed on the-X side of the first dichroic mirror 141, and irradiates the +x side with light L1a along the X-axis direction. The light source 12b is provided on the +z side with respect to 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 disposed in a posture in which the thickness direction thereof is along a direction from +x side and +z side toward-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 reflection direction of the light L1a. Fig. 4 is a graph showing the transmittance and reflectance of the first dichroic mirror 141. For the light L1a of the first peak wavelength (365 nm here), the transmittance of the first dichroic mirror 141 is low and the reflectance is high. 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).

By such a first dichroic mirror 141, the light L1a is reflected and reflected toward the-Z side along the Z-axis direction, and the light L1b passes through the first dichroic mirror 141 and advances toward the-Z side. Thus, the optical paths of the light L1a and the light L1b desirably coincide. That is, the light L1a and the light L1b are mixed.

The mixed light L1c is incident on the second dichroic mirror 142. In the example of fig. 2, the second dichroic mirror 142 is disposed on the-Z side than the first dichroic mirror 141. The light source 12c is disposed on the-X side of the second dichroic mirror 142, and irradiates the +x side with light L1c along the X axis direction. The second dichroic mirror 142 has a plate-like shape, and is disposed in a posture in which the thickness direction thereof is along a direction from +x side and +z side toward-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 reflection direction of the mixed light. Fig. 5 is a graph showing the transmittance and reflectance of the second dichroic mirror 142. The second dichroic mirror 142 has a low transmittance and a high reflectance for the light L1a and the light L1 b. On the other hand, the second dichroic mirror 142 has a high transmittance and a low reflectance for the light L1c.

By such a second dichroic mirror 142, the mixed light including the light L1a and the light L1b is reflected and reflected toward the +x side in the X-axis direction, and the light L1c passes through the second dichroic mirror 142 and advances toward the +x side. Thus, the optical paths of the light L1a, the light L1b, and the light L1c are desirably uniform. That is, the light L1a, the light L1b, and the light L1c are mixed. The mixed light including the light L1a, the light L1b, and the light L1c corresponds to the light L2.

In the example of fig. 2, the light L2 is condensed to the incident end of the light guide 16 by the lens 15. The light L2 advances inside the light guide 16 and exits from the exit 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 together. In the example of fig. 2, the emission end of the light guide 16 corresponds to the emission end of the pseudo light irradiation section 11.

The plurality of light sources 12 are controlled in such a manner that the spectrum of the light L2 emitted from the simulation light irradiation section 11 is similar to the spectrum of the light used for exposure in the exposure apparatus 1000. As a specific example, in the exposure apparatus 1000, a case will be described in which the light emitted from the illumination unit 1100 includes i-rays, h-rays, and g-rays. In this case, the light sources 12a, 12b, and 12c are controlled so that the peak values of the intensities of the i-ray, h-ray, and g-ray included in the light correspond to the peak values of the intensities of the light L1a, the light L1b, and the light L1c, respectively. Thus, the simulation light irradiation unit 11 can emit light L2 that mimics the light in the exposure apparatus 1000.

The target value related to the peak value of the 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 peak value of the intensity of each light L1 using an input device (e.g., a keyboard or a mouse) not shown. The control unit 50 controls the light source 12 based on the detection value of the sensor included in the light source 12 and the target value. This makes it possible to bring the spectrum of the light L2 including the light L1a, the light L1b, and the light L1c closer to the spectrum of the light in the exposure apparatus 1000 with higher accuracy.

In the example of fig. 2, the exit end of the light guide 16 is disposed on the-Z side than 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 condenser lens 171, a field stop 172, a condenser 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 disposed in this order as they are away from the exit end of the light guide 16 in the Z-axis direction.

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

< detection portion >)

The patterned light L2 transmitted through the transmission portion of the photomask 80 enters the detection portion 20. The detection unit 20 includes: an imaging optical system 21, and an image sensor 25.

The imaging optical system 21 images the patterned light L2 transmitted 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 disposed in this order as being away from the photomask 80 in the Z-axis direction. The numerical aperture of the objective lens 22 is equal to or larger than the numerical aperture of the objective lens 1210 in the exposure apparatus 1000. The light transmitted through the photomask 80 is amplified through the objective lens 22 and the imaging lens 24. The aperture of the aperture stop 23 is variable by a stop mechanism, and the numerical aperture of the imaging optical system 21 can be adjusted. The diaphragm mechanism of the aperture diaphragm 23 can 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 charge coupled device (Charge Coupled Device, CCD) image sensor or a complementary metal oxide semiconductor (Complementary Metal Oxide Semiconductor, CMOS) 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 checks the photomask 80 based on the captured image IM 1.

< moving mechanism >)

The moving mechanism 40 moves the holding portion 90 in the XY plane. Thereby, the photomask 80 held by the holding portion 90 also moves in the XY plane. The moving mechanism 40 has, for example, a ball screw (Ballscrew) mechanism, and is controlled by the control unit 50. The photomask 80 can be scanned by moving the photomask 80 in the XY plane, thereby enabling the illumination unit 10 and the detection unit 20 to scan the photomask 80. Therefore, the illumination unit 10 can irradiate each measurement region of the photomask 80 with the light L2, and the image sensor 25 can generate the captured image IM1 in each measurement region of the photomask 80. Therefore, the control unit 50 can perform inspection for a plurality of measurement areas of the photomask 80. The moving mechanism 40 may have a function and a structure for moving the photomask 80 relative to the illumination unit 10 and the detection unit 20, and may, for example, integrally move the illumination unit 10 and the detection unit 20.

< lifting mechanism >)

The lifting mechanism 60 lifts and lowers the holding portion 90 in the Z-axis direction. Thereby, the photomask 80 held by the holding portion 90 is also lifted and lowered. The lifting mechanism 60 has, for example, a ball screw mechanism, and is controlled by the control unit 50. The photomask 80 can be moved to the focal point of the objective lens 22 by lifting and lowering the photomask 80 by the lifting and lowering mechanism 60. The elevating mechanism 60 may have a function and a structure for elevating the photomask 80 relative to the detecting unit 20, and may elevate the detecting unit 20, for example.

< control part >)

The control unit 50 can integrally integrate the photomask inspection apparatus 1. For example, as described above, the control unit 50 controls the illumination unit 10, the moving mechanism 40, and the lifting mechanism 60. 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, line widths of patterns formed on the photomask 80, intervals between patterns, and 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 device and a storage unit. The arithmetic processing device may be, for example, an arithmetic processing device such as a central processing unit (Central Processor Unit, CPU). The storage section may have a non-temporary storage section (e.g., read Only Memory (ROM) or a hard disk) and a temporary storage section (e.g., random access Memory (Random Access Memory, RAM)). The non-temporary storage unit may store, for example, a program for defining the processing executed by the control unit 50. By executing the program by the processing device, the control unit 50 can execute the processing specified by the program. Of course, part or all of the processing performed by the control unit 50 may be performed by hardware.

Method for calculating mask characteristics

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

Fig. 6 schematically shows an example of the captured image IM 1. The captured image IM1 includes the patterned light L2. The luminance distribution of the light L2 corresponds to a projection image of the transmission portion of the photomask 80. In the example of fig. 6, the projection image includes a vertical portion extending in the longitudinal direction and a horizontal portion extending rightward from halfway of the vertical portion.

In the example of fig. 6, an example of the luminance distribution on the line a extending in the width direction of the vertical portion is also schematically shown. The control unit 50 obtains 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 in the luminance distribution, and obtains the width (projected image width) of the vertical portion based on the two positions.

However, when the position of the objective lens 22 with respect to the photomask 80 is deviated from the focal position in the Z-axis direction, the projection image may vary in the captured image IM 1. That is, when the lifting mechanism 60 stops the holding portion 90 at a position deviated from the focal position, the projected image may be different from that at the focal position.

When the substrate W is a substrate for a flat panel display, the numerical aperture of the imaging unit 1200 in the exposure apparatus 1000 is as small as about 0.1, and thus the focal depth of the imaging unit 1200 is large. However, as will be described in detail later, even if the focal position is slightly deviated by about 10 μm, the width of the projection image in the captured image IM1 varies.

Therefore, here, the position of the holding portion 90 in the Z-axis direction (hereinafter, referred to as Z-axis position) with respect to the objective lens 22 is sequentially changed, the captured image IM1 is generated each time by the image sensor 25, and the control portion 50 performs inspection based on these plurality of captured images IM1. An example of the inspection method is 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 moves the holding portion 90 to a predetermined measurement position. The control unit 50 irradiates the light L1 to the plurality of light sources 12 (step S1). Thus, the light L2 imitating the light in the exposure apparatus 1000 passes through the transmission portion in the predetermined measurement region of the photomask 80, and the patterned light L2 passes through the imaging optical system 21 and enters the light receiving surface of the image sensor 25.

Next, the control unit 50 controls the lifting mechanism 60 and the image sensor 25 so that the image sensor 25 generates a captured image IM1 at each Z-axis position (step S2). For example, the elevation mechanism 60 moves the holding portion 90 within a predetermined elevation range (focus range) including the focus position, and the image sensor 25 sequentially generates the captured image IM1. The lifting mechanism 60 may stop the holding unit 90 at the time of shooting. Thus, a plurality of photographed images IM1 corresponding to a plurality of Z-axis positions can be obtained.

Next, the control unit 50 obtains mask characteristics based on the plurality of captured images IM1 (step S3). Here, the projected image width is obtained as a mask characteristic. Fig. 8 shows the luminance distribution of the projection image on the line a of each captured image IM 1. More specifically, fig. 8 shows the luminance distribution LD1 at the focal position and the luminance distribution at the Z-axis position which is 10 μm away from the focal position to the +z side and the-Z side, respectively. As can be understood from fig. 8, when defocus occurs, the luminance distribution fluctuates according to the defocus amount. Therefore, the projected image widths obtained based on the respective luminance distributions are different from each other.

Therefore, the control unit 50 calculates the focus evaluation value of each of the plurality of captured images IM 1. The focus evaluation value is an index indicating how well the focus is aligned, and the higher the focus evaluation value is, the more the focus is aligned. The focus evaluation value may be an index represented by a high frequency component among frequency components obtained by fourier transforming the luminance distribution of the captured image IM1, for example. The higher the high frequency component, the steeper the brightness distribution change, so the outline of the shadowgraph image is clear and in focus. Alternatively, various indexes such as contrast and sharpness of the captured image IM1 may be used 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 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 on the line a of each captured image IM1 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 approximation curve G1 and an approximation curve G2 are also shown. The approximate curve G1 is calculated based on a drawing point indicating a relationship between the Z-axis position and the focus evaluation value, and the approximate curve G2 is calculated based on a drawing point indicating a relationship between the Z-axis position and the projected image width.

The focus evaluation value takes the maximum value when the Z-axis position is the focus position P0. Therefore, first, the control unit 50 obtains the Z-axis position (i.e., the focal position P0) at which the focal point evaluation value is the maximum value. For example, the control unit 50 calculates the approximation curve G1 by an approximation method such as the least square method (Least squares method) based on a plurality of focus evaluation values corresponding to a plurality of Z-axis positions, respectively. Then, the control unit 50 calculates the Z-axis position when the focus evaluation value is the maximum value Fmax in the approximation curve G1 as the focus position P0.

Next, the control unit 50 obtains the projection image width LW at the focal position P0. First, the control unit 50 obtains a projection image width for each captured image IM 1. Thus, a plurality of projection image widths corresponding to the plurality of Z-axis positions can be obtained. Next, the control unit 50 calculates an approximation curve G2 based on the plurality of Z-axis positions and the plurality of projection image widths by an approximation method such as a least square method. Then, the control unit 50 calculates the projected image width LW at the focal position P0 based on the approximation curve G2 and the focal position P0.

Next, the control section 50 determines whether or not the photomask 80 is good based on the mask characteristics (here, the projected image width LW) (step S4). For example, the control unit 50 determines whether or not the difference between the projection image width LW and the target width is equal to or smaller than a predetermined width allowable value, and determines that the photomask 80 is defective when the difference is larger than the width allowable value. The width allowable value is set in advance, for example, and stored in the storage unit.

Effect of the embodiments >

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 set to be the same as the sigma of the exposure apparatus 1000. This allows the light (projection image) on the substrate W in the exposure apparatus 1000 to be reproduced on the light receiving surface of the image sensor 25 in a simulated manner. Therefore, the photomask inspection apparatus 1 can determine whether the photomask 80 is good or not based on the projection image on the substrate W.

Further, according to the photomask inspection apparatus 1, the mixing portion 14 mixes the plurality of lights L1 having different peak wavelengths from each other. Then, the illumination unit 10 irradiates the light L2, which is the mixed light, onto the photomask 80, 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 formed of the light L2 having a plurality of peak wavelengths. That is, by one shooting, a shot image IM1 including a projection image formed of light L2 having a plurality of peak wavelengths can be obtained.

Therefore, as in patent document 1, it is not necessary to combine a plurality of captured images obtained by sequentially irradiating light having different peak wavelengths from each other. Therefore, unlike patent document 1, in the captured image IM1, a positional deviation for each peak wavelength is not generated 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.

Further, according to the photomask inspection apparatus 1, each light source 12 includes a single semiconductor light-emitting element 121. Therefore, in principle, there is no wavelength or phase shift in the diode array as in patent document 2, and each light source 12 can emit light L1 that is further coherent. Therefore, the light L2 transmitted through the photomask 80 can be caused to have a diffraction phenomenon equivalent to that in the exposure apparatus 1000. Therefore, the control section 50 can inspect the photomask 80 with higher inspection accuracy.

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

Mask properties: defect brightness >, and method for producing the same

In the example, the inspection method is described using the projected image width as the mask characteristic. However, as mask characteristics, defect brightness may also be employed. Fig. 10 schematically shows an example of the captured image IM1 including the defect D1. In fig. 10, a defect D1 is a defect of a light shielding film formed on the photomask 80. Specifically, the defect D1 is a defect that transmits the light L2 without forming a light shielding film properly, and is also called a white defect.

Here, the luminance value of the defect D1 is obtained. Hereinafter, the luminance value of the defect D1 is also referred to as defect luminance. Since the defect luminance also varies depending on the position of the holding unit 90 in the Z-axis direction, the control unit 50 can determine the defect luminance based on the plurality of captured images IM1, similarly to the projection image width.

Specifically, in step S3, first, the control unit 50 obtains the defect brightness and the focus evaluation value for each captured image IM 1. Thus, a plurality of defect brightnesses corresponding to the plurality of Z-axis positions and a plurality of focus evaluation values corresponding to the plurality of Z-axis positions can be obtained. Fig. 11 is a graph showing the relationship between the Z-axis position and the focus evaluation value and the relationship between the Z-axis position and the defect brightness. In the example of fig. 11, an approximation curve G1 and an approximation curve G3 are also shown. The approximate curve G3 is calculated based on the Z-axis position and the plotted point of the defect brightness.

As described above, the control unit 50 obtains the focal position P0 at which the focal point evaluation value is the maximum value Fmax based on the approximation curve G1. Next, the control unit 50 calculates an approximation curve G3 by an approximation method such as a least square method based on the plurality of Z-axis positions and the plurality of defect luminances. Then, the control unit 50 calculates the defect luminance DL at the focal position P0 based on the approximation curve G3 and the focal position P0.

Next, in step S4, the control unit 50 determines whether or not the photomask 80 is good based on the mask characteristics (here, defect luminance DL). For example, the control unit 50 determines whether or not the defect luminance DL is equal to or less than a predetermined defect allowable value, and determines that the photomask 80 is defective when the defect luminance DL is greater than the defect allowable value.

As described above, the photomask inspection apparatus 1 can determine whether the photomask 80 is good or not based on the luminance value of the defect D1. In the above example, the white defect was described as the defect D1, but various defects such as a black defect may be used as the defect D1.

< deviation of projection image in Exposure apparatus 1000 >

The photomask inspection apparatus 1 reproduces the brightness distribution (projection image) of the pattern-like light on the substrate W in the exposure apparatus 1000 in a simulated manner on the light receiving surface of the image sensor 25. That is, the captured image IM1 generated by the photomask inspection apparatus 1 when defocus is generated corresponds to a projected image on the substrate W generated by the exposure apparatus 1000 when defocus is similarly generated. Therefore, the photomask inspection apparatus 1 can also evaluate the variation of the projection 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 the exposure apparatus 1000. That is, in the exposure apparatus 1000, the relationship between the position (Z-axis position) of the photomask 80 relative to the objective lens 1210 and the projected image width on the substrate W corresponds to the relationship in fig. 9.

Since the defocus amount Δz (maximum value) that can be generated due to a mechanical error of the exposure apparatus 1000 or the like can be obtained in advance, the deviation of the projection image width generated in the exposure apparatus 1000 can be obtained based on the relationship of fig. 9. The defocus amount Δz may be set in advance and stored in the storage unit, for example, or the user may input the defocus amount Δz using an input device (for example, a keyboard or a mouse) not shown.

The control unit 50 calculates the maximum LWmax and the minimum LWmin of the projection image width in the range between the position deviated from the focal position P0 to the-Z side by the defocus amount Δz and the position deviated from the focal position P0 to the +z side by the defocus amount Δz based on the approximation curve G2. The range from the minimum value LWmin to the maximum value LWmax corresponds to the deviation of the width of the projection image generated in the exposure apparatus 1000.

The control unit 50 can determine whether the photomask 80 is good or not based on the minimum value LWmin and the maximum value LWmax of the projection image width. Specifically, the control unit 50 determines whether or not the minimum value LWmin is equal to or greater than the allowable lower limit value of the variation in the projection image width on the substrate W, and determines whether or not the maximum value LWmax is equal to or less than the allowable upper limit value. When the minimum value LWmin is smaller than the allowable lower limit value and/or when the maximum value LWmax is larger than the allowable upper limit value, the control unit 50 determines that the photomask 80 is defective.

Similarly, the control unit 50 may calculate the deviation of the defective luminance due to the defocus amount Δz. Specifically, the control unit 50 calculates the maximum value DLmax and the minimum value DLmin of the defect luminance in the range between the position deviated from the focal position P0 to the-Z side by the defocus amount Δz and the position deviated from the focal position P0 to the +z side by the defocus amount Δz based on the approximation curve G3 (see also fig. 11). The range from the minimum value DLmin to the maximum value DLmax corresponds to the deviation of the defect luminance generated in the exposure apparatus 1000.

The control section 50 can determine whether the photomask 80 is good or not based on the maximum value DLmax of the defect luminance. Specifically, the control unit 50 determines whether or not the maximum value DLmax is equal to or less than the defect allowable value. When the maximum value DLmax is greater than the defect allowable value, the control unit 50 may determine that the photomask 80 is defective.

Here, the terms in the technical means column of the solution to the problem are associated with the terms in the column of the embodiment. The first light source corresponds to any one of the light sources 12a to 12c, and the second light source corresponds to a different one of the light sources 12a to 12c from the first light source. The first semiconductor light emitting element corresponds to the semiconductor light emitting element 121 belonging to the first light source, and the second semiconductor light emitting element corresponds to the semiconductor light emitting element 121 belonging to the second light source. The first light corresponds to the light L1 emitted from the first semiconductor light emitting element, and the second light corresponds to the light L1 emitted from the second semiconductor light emitting element.

As described above, the photomask inspection apparatus 1 is described in detail, but the description is illustrative in all aspects, and the present disclosure is not limited thereto. The above-described various modifications can be applied in combination as long as they do not contradict each other. Moreover, it will be appreciated that many variations not illustrated may be envisaged without departing from the scope of the disclosure.

Claims

1. A photomask inspection apparatus comprising:

a holding portion for holding the photomask;

a first light source including a single first semiconductor light emitting element emitting 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 configured to mix the first light from the first light source and the second light from the second light source;

an illumination optical system that guides the light obtained by mixing the first light and the second light by the mixing section to the photomask;

an imaging optical system including an objective lens and for inputting the light from the photomask;

an image sensor that receives the light incident through the imaging optical system and generates a photographed image; and

And an arithmetic processing unit that performs inspection of the photomask based on the captured image.

2. The photomask inspection apparatus according to claim 1, wherein,

the ratio of the numerical aperture of the illumination optical system to the numerical aperture of the imaging optical system, that is, sigma, is the same as the sigma in the exposure apparatus using the photomask.

3. The photomask inspection apparatus according to claim 1 or 2, wherein,

the numerical aperture of the objective lens is equal to or more than the numerical aperture of the objective lens in the exposure apparatus using the photomask.