JP6587822B2 - Appearance inspection device - Google Patents

Description

  The present invention relates to an appearance inspection apparatus, and more particularly to an appearance inspection apparatus for inspecting a medium-large photomask used in a manufacturing process of a flat panel display such as a liquid crystal or an organic EL.

  With the increase in definition of displays, the demand for inspection accuracy for medium-large photomasks that are the originals of the displays is increasing. Various techniques for inspecting defects of these photomasks have been proposed.

JP-A-8-137093

  As disclosed in Patent Document 1, in order to inspect defects in a photomask, a transmissive inspection that transmits light to the photomask and a reflective inspection that reflects light by the photomask are effective. . However, since the inspection for the transmission system and the inspection for the reflection system require separate imaging processes, the inspection takes time and a plurality of imaging devices are required.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a technique for speeding up inspection of a photomask.

  In order to solve the above problems, an appearance inspection apparatus according to an aspect of the present invention irradiates a transmission illumination light source that emits light that is transmitted through a photomask and light that is reflected by the photomask during irradiation of the transmission illumination light source. A reflected illumination light source, an objective lens that converts the transmitted light that has passed through the photomask and the reflected light that has been reflected by the photomask into parallel light, and a spectroscope that separates the parallel light converted by the objective lens into transmitted light and reflected light An imaging lens for transmitted light that forms an image of the transmitted light separated by the spectroscopic unit, an imaging lens for reflected light that images the reflected light separated by the spectroscopic unit, and an imaging lens for the transmitted light And an imaging unit that images the reflected light formed by the reflected light imaging lens.

  The imaging unit may cause the transmitted light imaged by the transmitted light imaging lens and the reflected light imaged by the reflected light imaging lens to be captured in different regions of the same imaging device.

  You may further provide the light-shielding member which suppresses the crosstalk of the transmitted light which the imaging lens for transmitted light imaged, and the reflected light which the imaging lens for reflected light imaged.

  The objective lens may include a plurality of lenses having different magnifications. The appearance inspection apparatus may further include an objective lens switching unit that switches a plurality of lenses. The transmitted light imaging lens and the reflected light imaging lens may each have a focus adjustment function for adjusting the focal position in conjunction with the lens switching by the objective lens switching unit.

  Each of the reflected light imaging lens and the transmitted light imaging lens may have a color magnification adjustment function for adjusting the color magnification in conjunction with the switching by the lens switching unit.

  The optical characteristic of the optical system consisting of the objective lens and the imaging lens for reflected light and the optical characteristic of the optical system consisting of the objective lens and the imaging lens for transmitted light are based on the wavelength λ of the passing light as the first axis and the focal position. In the graph with the shift s as the second axis, the wavelength of transmitted light is λg, the wavelength of reflected light is λe, d is a differential operator, and T is a predetermined threshold, (ds / dλ) λg <T and (ds / dλ) λe <T may be satisfied.

  According to the present invention, it is possible to provide a technique for speeding up the inspection of a photomask.

It is a figure which shows typically the internal structure of the external appearance inspection apparatus which concerns on embodiment. FIGS. 2A and 2B are diagrams schematically illustrating a photomask image captured by the appearance inspection apparatus according to the embodiment. It is a figure which shows the appearance of the defect in a photomask in the table | surface format in the image imaged with the external appearance inspection apparatus which concerns on embodiment. It is a figure which shows typically the internal structure of the imaging lens which concerns on embodiment. It is a figure which shows typically the optical characteristic of the system which combined the objective lens and imaging lens which concern on embodiment. It is a figure which shows the kind of objective lens which concerns on embodiment, the focal distance of each lens, and an expansion ratio in a table | surface form. It is a figure which shows typically the internal structure of the external appearance inspection apparatus which concerns on the 1st modification of embodiment. It is a figure which shows typically the cross section of the spectroscopy part which concerns on a 2nd modification. It is a figure which shows typically the optical characteristic of the imaging lens which concerns on a 3rd modification.

  An outline of an appearance inspection apparatus according to an embodiment of the present invention will be described. The appearance inspection apparatus according to the embodiment is preferably used for defect inspection of a photomask used in a manufacturing process of a flat panel display such as a liquid crystal or an organic EL, particularly for inspection of a medium-large photomask. An appearance inspection apparatus according to an embodiment simultaneously emits transmitted light for transmitting through a photomask and reflected light for reflecting by the photomask to the photomask, and transmits the transmitted light and reflected light of the photomask. Are simultaneously imaged in different regions of the same image sensor. This makes it easy to inspect defects that are difficult to image with the transmitted light of the photomask, or defects that are difficult to determine whether the image is imaged with the transmitted light of the photomask, from the image captured with the reflected light. . In particular, the appearance inspection apparatus according to the embodiment can image the transmitted light and reflected light of the photomask with a single imaging, which contributes to speeding up the appearance inspection of the photomask.

  FIG. 1 is a diagram schematically illustrating an internal configuration of an appearance inspection apparatus 100 according to an embodiment of the present invention, and more particularly, a schematic diagram illustrating an optical system of an imaging head unit. The appearance inspection apparatus 100 according to the embodiment includes a transmission illumination light source 10, a reflection illumination light source 12, a photomask 14, a first objective lens 16a, a second objective lens 16b, an objective lens switching unit 18, a spectroscopic unit 20, and a transmission. The imaging lens 26a for light, the imaging lens 26b for reflected light, the imaging part 28, the reflective illumination field stop 30, the collimator lens 32, the light shielding member 34, the quarter wavelength plate 36, and the optical member 38 are provided. The spectroscopic unit 20 includes a first dichroic mirror 22a, a second dichroic mirror 22b, and a reflecting unit 24.

  Although the details will be described later, the first objective lens 16a and the second objective lens 16b have the same function except for the magnification. Therefore, hereinafter, in the present specification, the first objective lens 16a and the second objective lens 16b are simply collectively referred to as “objective lens 16” unless otherwise specifically distinguished.

  The transmitted illumination light source 10 emits light for transmitting the photomask 14. The transmitted illumination light source 10 emits so-called g-rays, for example, light having a wavelength of 435.84 [nm]. The transmitted illumination light source 10 can be realized, for example, by wavelength-separating a light beam obtained from a known mercury lamp light source. Hereinafter, in this specification, the light emitted from the transmitted illumination light source 10 may be simply referred to as “g-line”. Therefore, in this specification, the transmitted light that has passed through the photomask is g-line.

  The reflected illumination light source 12 irradiates light for reflection on the photomask held by the photomask 14. The reflected illumination light source 12 irradiates so-called e-rays having a wavelength of 546.07 [nm], for example. Similarly to the transmissive illumination light source 10, the reflected illumination light source 12 can also be realized, for example, by wavelength-separating a light beam obtained from a known mercury lamp light source. Hereinafter, in this specification, the light emitted from the reflected illumination light source 12 may be simply referred to as “e-line”. Therefore, in this specification, the reflected light reflected by the photomask becomes e-line.

  The reflected illumination light source 12 emits e-rays while the transmissive illumination light source 10 emits g-rays. That is, the transmitted illumination light source 10 and the reflected illumination light source 12 irradiate g-line and e-line simultaneously, respectively.

  The objective lens 16 is disposed on the optical axis of the transmissive illumination light source 10 at a position facing the transmissive illumination light source 10 with the photomask 14 interposed therebetween. The objective lens 16 converts g-line transmitted through the photomask into parallel light. That is, the objective lens 16 is a lens constituting an infinite correction optical system.

  The objective lens 16 is also disposed between the photomask 14 and the reflected illumination light source 12 on the optical axis of the reflected illumination light source 12. The e-line irradiated from the reflected illumination light source 12 passes through the reflected illumination field stop 30 and the collimator lens 32, is converted into parallel light, and enters the first dichroic mirror 22a. An optical member 38 is arranged on the surface of the first dichroic mirror 22a opposite to the surface on which the e-line is incident. The first dichroic mirror 22a is arranged on the opposite side of the photomask 14 with the objective lens interposed therebetween. For this reason, the e-line that has passed through the first dichroic mirror 22 a and the optical member 38 enters the objective lens 16.

  The optical member 38 is a film having both functions of a polarizing beam splitter and a dichroic filter. More specifically, the optical member 38 functions as a polarization beam splitter that reflects 100% of the S-polarized component and transmits 100% of the P-polarized component of the e-rays emitted from the reflected illumination light source 12. The optical member 38 also functions as a dichroic filter that reflects 100% of the g-line. The e-line incident on the first dichroic mirror 22a transmits only the P-polarized component that is 50% of the total light amount by the action of the optical member 38. When the first dichroic mirror 22a and the optical member 38 are combined, a dichroic mirror having a polarization beam splitter characteristic at a specific wavelength is obtained.

  As shown in FIG. 1, in the appearance inspection apparatus 100 according to the embodiment, a ¼ wavelength plate 36 is disposed between the first dichroic mirror 22 a and the objective lens 16. For this reason, e-line (P-polarized light) transmitted through the first dichroic mirror 22 a and the optical member 38 is converted into circularly-polarized light by passing through the quarter-wave plate 36.

  The e-line (circularly polarized light) transmitted through the quarter-wave plate 36 passes through the objective lens 16 and is reflected by the photomask 14 held by the photomask 14 and returns to the objective lens 16 again. The e-line (circularly polarized light) reflected by the photomask 14 becomes parallel light by the objective lens 16 and is converted into linearly polarized light (S-polarized light) by passing through the quarter wavelength plate 36. This e-line (S-polarized light) is 100% reflected by the optical member 38 having a function as a polarization beam splitter.

  Here, the g-line irradiated to the transmitted illumination light source 10 and transmitted through the photomask 14 and converted into parallel light by the objective lens 16 is light having both P-polarized light component and S-polarized light component. However, since the optical member 38 also has a function as a dichroic filter, it reflects the g-line 100%.

  As described above, since the transmitted illumination light source 10 and the reflected illumination light source 12 simultaneously irradiate g-line and e-line, respectively, the light transmitted through the objective lens 16 becomes light in which the g-line and e-line are mixed. Yes. Therefore, the light transmitted through the objective lens 16 and reflected by the optical member 38 is also mixed with g-line and e-line.

  The second dichroic mirror 22b is disposed on the optical axis of the light that is 100% reflected by the optical member 38. The second dichroic mirror 22b reflects g-line 100% and transmits e-line 100%. For this reason, the light transmitted through the objective lens 16 and reflected by the optical member 38 is separated by the second dichroic mirror 22b into a g-line as transmitted light and an e-line as reflected light. That is, the second dichroic mirror 22b separates the parallel light converted by the objective lens 16 into transmitted light and reflected light.

  The reflector 24 is disposed on the optical axis of the e line that has passed through the second dichroic mirror 22b. The reflection unit 24 is, for example, a normal mirror and reflects 100% of the e-line that has passed through the second dichroic mirror 22b.

  The transmitted light imaging lens 26a is disposed on the optical axis of the g line reflected by the second dichroic mirror 22b. The transmitted light imaging lens 26a collects g-line that is parallel light separated by the second dichroic mirror 22b, and forms an image of the transmitted light of the photomask 14 on the image sensor provided in the imaging unit 28. The reflected light imaging lens 26b is disposed on the optical axis of the e-line reflected by the reflecting unit 24. The reflected light imaging lens 26b collects the e-line, which is parallel light separated by the second dichroic mirror 22b, and forms an image of the reflected light of the photomask 14 on the imaging device included in the imaging unit 28. Although the details will be described later, the transmitted light imaging lens 26a and the reflected light imaging lens 26b have the same lens configuration, and the focal position and the color magnification can be adjusted. Hereinafter, in the present specification, when there is no particular distinction between the imaging lens for transmitted light 26a and the imaging lens for reflected light 26b, they are simply referred to as “imaging lens 26”.

  The imaging unit 28 images the transmitted light imaged by the transmitted light imaging lens 26a and the reflected light imaged by the reflected light imaging lens 26b. As described above, the appearance inspection apparatus 100 according to the embodiment can simultaneously image the transmitted light and the reflected light of the photomask 14. Thereby, the time required for the defect inspection of the photomask 14 can be shortened.

  FIGS. 2A and 2B are diagrams schematically illustrating an image of the photomask 14 captured by the appearance inspection apparatus 100 according to the embodiment. More specifically, FIG. 2A is a schematic diagram showing a transmission image of the photomask 14, and FIG. 2B is a schematic diagram showing a reflection image of the photomask 14.

  The images shown in FIGS. 2A to 2B illustrate the chrome pattern 202 formed on the glass substrate 200. 2 (a)-(b) is a region showing a so-called halftone mask 204.

  There are various types of defects on the photomask 14, and “chrome defects”, “pinholes”, “foreign substances”, and “watermarks” will be described as typical defects.

  “Chromium defects” indicate a state where chromium is attached to a place where it should not be. For this reason, the chromium defect is a defect generated on the glass substrate 200 or on the halftone. In FIGS. 2A and 2B, a region denoted by reference numeral 206a is a chromium defect on the glass, and a region denoted by reference numeral 206b is a chromium defect on the halftone. Since chromium is a metal, it reflects light while preventing transmission of light. For this reason, as shown in FIG. 2A, the chromium defect is picked up black in the transmission image. On the other hand, as shown in FIG. 2B, the chrome defect is picked up white in the reflected image.

  “Pinhole” indicates a state in which chrome or halftone is missing in a minute region. A pinhole defect is a state where there is no chrome or halftone in the place where it should be, and it is a small hole. In FIGS. 2A and 2B, the area indicated by reference numeral 206c is a pinhole generated on the chrome, and the area indicated by reference numeral 206d is a pinhole generated on the halftone. Since the pinhole transmits light, there is no k at which light is reflected in the pinhole. For this reason, as shown to Fig.2 (a), a pinhole is imaged white in a transmitted image. On the other hand, as shown in FIG. 2B, the pinhole is captured black in the reflected image.

  The “foreign matter” is a substance other than glass, chromium, or halftone that is a constituent material of the photomask 14, and is, for example, fine dust attached to the photomask 14. In FIGS. 2A to 2B, the region denoted by reference numeral 206e is a foreign matter on the glass. On the other hand, the region denoted by reference numeral 206f in FIG. Foreign substances have the property of scattering light. For this reason, as shown in FIG. 2A, the foreign matter on the glass is captured black in the transmission image. Further, as shown in FIG. 2B, the foreign matter on the glass is picked up black in the reflected image. Note that since chrome blocks light, foreign matter on the chrome is not captured in the transmission image. On the other hand, as shown in FIG. 2B, the foreign matter on the chrome is captured black in the reflected image.

  The “watermark” indicates a state in which an inorganic substance or an organic substance dissolved in the liquid is deposited on the photomask 14 when the liquid used for cleaning the photomask 14 is dried. The watermark can be present on glass, chrome, and halftone. On the other hand, the liquid used for cleaning often agglomerates on a narrow area on the photomask 14, for example, on a halftone, and as a result, the watermark often protrudes on the halftone and partly on chrome.

  Like a foreign object, a watermark present on chrome is not captured in a transmission image, but appears only in a reflection image. Further, the watermark on the halftone may be difficult to observe even in the reflected image. On the other hand, the watermark on chrome is captured black in the reflected image. Therefore, by observing the watermark present on the chrome, the operator can infer that the watermark exists on the halftone.

  FIG. 3 is a diagram showing the appearance of defects in the photomask 14 in a table format in an image captured by the appearance inspection apparatus 100 according to the embodiment, and is described above with reference to FIGS. 2 (a) to 2 (b). It is the figure on which the appearance of each made defect was put together. In FIG. 3, (white) or (black) indicates that the image is captured in white or black depending on the shooting conditions. Therefore, when the shooting conditions are changed, the image is often not captured, or even if the image is captured, it is difficult for the operator to visually recognize the image.

As shown in FIG. 3, for example, both a chromium defect on glass and a foreign substance on glass are captured black in a transmission image. Therefore, the operator cannot distinguish between the chromium defect on the glass and the foreign material on the glass only by observing the reflection image. On the other hand, in the reflection image, the chromium defect on the glass is imaged white, while the foreign matter on the glass is imaged black. Thus, by comparing the transmitted image and the reflection image, the operator can determine the foreign matter on the glass and chrome defects on glass.

  Further, for example, foreign matters on chrome and watermarks on chrome are not captured in the transmission image. Therefore, the operator cannot even visually recognize the foreign matter on the chrome or the watermark on the chrome simply by observing the transmission image. On the other hand, foreign matters on chrome and watermarks on chrome are imaged black on the reflected image. For this reason, after performing the automatic inspection with the transmission image and the reflection image, the operator can visually recognize the foreign matter on the chromium and the watermark on the chromium for the first time by observing the reflection image.

  The appearance inspection apparatus 100 according to the embodiment simultaneously captures a reflected image and a transmitted image. For this reason, according to the appearance inspection apparatus 100 according to the embodiment, it is possible to omit the trouble of taking a reflected image again and to provide image information for defect inspection with higher accuracy.

  Returning to the description of FIG. The imaging unit 28 is realized by, for example, a known TDI sensor (Time Delay Integration sensor). The imaging unit 28 according to the embodiment includes a 6k pixel (6000 pixel) TDI sensor as an imaging device. Now, if the size of one pixel in the TDI sensor is 10.4 [μm], the size of the image pickup device itself of the TDI sensor is 10.4 [μm] × 6000 = 62.4 [mm]. Including the power supply and cooling mechanism of the imaging device, the width of the imaging unit 28, that is, the length in the major axis direction of the TDI sensor is about 90 mm.

  Here, a mode in which the transmitted light imaged by the transmitted light imaging lens 26a and the reflected light imaged by the reflected light imaging lens 26b are respectively imaged by different TDI sensors is also conceivable. If the transmitted light and the reflected light are imaged by two imaging units each having a 2k pixel (2048 pixel) TDI sensor, the two imaging units need to be arranged side by side in the long axis direction of the TDI sensor.

  Even in a 2k pixel TDI sensor, if the size of one pixel is 10.4 [μm], the size of the image sensor itself of the TDI sensor is 10.4 [μm] × 2048 = 21.3 [mm]. For this reason, including the cooling mechanism of the image sensor and the like, the width of the image pickup unit including the 2k sensor, that is, the length of the TDI sensor in the long axis direction is about 60 mm. As a result, if two image pickup units are arranged side by side in the long axis direction of the TDI sensor, a space of about 120 [mm] is required.

  Therefore, the imaging unit 28 according to the embodiment uses the transmitted light imaged by the transmitted light imaging lens 26a and the reflected light imaged by the reflected light imaging lens 26b in different regions of the same imaging device. Take an image. Thereby, compared with the case where the transmitted light and reflected light are imaged by different imaging units, the space for arranging the imaging unit 28 can be reduced. As a result, space saving, power saving, and weight reduction of the appearance inspection apparatus 100 can be realized.

  The imaging unit 28 uses 2048 pixels from one end of the TDI sensor as an imaging device for transmitted light, and uses 2048 pixels from the other end as an imaging device for reflected light. When the transmitted light and the reflected light are imaged in different areas of the same imaging device in this way, there is a possibility that a light beam crosstalk that is not an imaging target may occur in each area. Therefore, the appearance inspection apparatus 100 according to the embodiment is a light shielding member for suppressing crosstalk between the transmitted light imaged by the transmitted light imaging lens 26a and the reflected light imaged by the reflected light imaging lens 26b. 34 is provided.

  The light shielding member 34 is disposed between the TDI sensor and the imaging lens for transmitted light 26a and the imaging lens for reflected light 26b in the central portion of the TDI sensor included in the imaging unit. The light blocking member 34 is disposed so as to block the reflected light toward the image sensor for transmitted light and reflect the transmitted light toward the image sensor for reflected light. As a result, the 2048 pixels arranged in the center of the TDI sensor included in the imaging unit 28 cannot contribute to imaging. However, by arranging the light blocking member 34, crosstalk between the transmitted light imaged by the transmitted light imaging lens 26a and the reflected light imaged by the reflected light imaging lens 26b is suppressed, so that the imaging unit 28 can The image to be captured can be made clear.

  As described above, the objective lens 16 according to the embodiment includes the first objective lens 16a and the second objective lens 16b having different magnifications. Although not limited, as an example, the magnification of the first objective lens 16a is 20.8 [times], and the magnification of the second objective lens 16b is 10.4 [times]. The objective lens switching unit 18 is realized by, for example, a known revolver, and can switch between the first objective lens 16a and the second objective lens 16b.

  Generally, when the magnification of the objective lens 16 is changed, the longitudinal chromatic aberration characteristic is also changed. For this reason, for example, when an operator who is a user of the appearance inspection apparatus 100 switches the objective lens 16, the axial chromatic aberration characteristic is changed. Therefore, each of the transmitted light imaging lens 26a and the reflected light imaging lens 26b has a focus adjustment function for adjusting the focal position in conjunction with the switching of the objective lens by the objective lens switching unit 18.

  FIG. 4 is a diagram schematically illustrating an internal configuration of the imaging lens 26 according to the embodiment. As shown in FIG. 4, the imaging lens 26 according to the embodiment includes a first lens 40 and a second lens 42. The first lens 40 is, for example, a convex lens for imaging the parallel light converted by the objective lens 16. The second lens 42 is an achromatic lens for realizing achromaticity, for example. As shown in FIG. 4, the imaging lens 26 is arranged in the order of the first lens 40 and the second lens 42 from the light incident side.

  In FIG. 4, when the distance L1 from the light incident side of the imaging lens 26 to the second lens 42 is changed, the focal position of the imaging lens 26 is also changed. Therefore, the imaging lens 26 changes the distance L1 according to the magnification of the objective lens 16 so that the light passing through the imaging lens 26 is imaged by the imaging unit 28. The distance L1 to be adjusted by the imaging lens 26 may be determined in advance by experiments. The imaging lens 26 can realize a focus adjustment function by using an elastic member or a stopper (not shown) so that the first lens 40 moves in conjunction with the rotation of the revolver that is the objective lens switching unit 18, for example.

  Here, both the transmitted light imaging lens 26a and the reflected light imaging lens 26b include the same first lens 40 and second lens 42. In general, the imaging lens 26 is known to have a phenomenon called lateral chromatic aberration in which the magnification varies depending on the wavelength of light passing therethrough. Specifically, e-line is less refracted by the lens than g-line. For this reason, even when capturing the same subject, an image captured using the g line is captured smaller than an image captured using the e line.

  Thus, the reflected light imaging lens 26b and the transmitted light imaging lens 26a according to the embodiment each have a color magnification adjustment function for adjusting the color magnification in conjunction with the switching by the objective lens switching unit 18. In FIG. 4, when the distance L2 between the first lens 40 and the second lens 42 is changed, the magnification of the imaging lens 26 is also changed. Therefore, the imaging lens 26 changes the distance L2 between the first lens 40 and the second lens 42 so that the image captured using the transmitted light and the image captured using the reflected light have the same magnification. To do. The distance L2 to be adjusted by the imaging lens 26 may be determined in advance by experiments. For example, the imaging lens 26 adjusts the color magnification by using an elastic member or a stopper (not shown) so that the first lens 40 and the second lens 42 move in conjunction with the rotation of the revolver that is the objective lens switching unit 18. Functions can be realized.

  Here, the focal length of the imaging lens 26 also varies depending on the wavelength of light. FIG. 5 is a diagram schematically illustrating optical characteristics of a system in which the objective lens 16 and the imaging lens 26 according to the embodiment are combined, and is a graph illustrating the wavelength dependence of the focal length. In FIG. 5, the horizontal axis represents the focal position shift s in the system including the objective lens 16 and the imaging lens 26, and the vertical axis represents the wavelength λ of light passing through the system including the objective lens 16 and the imaging lens 26. Indicates. In FIG. 5, the wavelength of the g-line (approximately 436 [nm]) is denoted by λg, and the wavelength of the e-line (approximately 546 [nm]) is denoted by λe.

  In FIG. 5, when the focus position shift s is 0, the focus of the system including the objective lens 16 and the imaging lens 26 is the position of the image sensor provided in the imaging unit 28. When the focal position shift s becomes larger than 0, it indicates that the focal point of the system including the objective lens 16 and the imaging lens 26 is connected beyond the imaging element included in the imaging unit 28. On the other hand, when the focal position shift s is less than 0, it indicates that the focal point of the system including the objective lens 16 and the imaging lens 26 is focused in front of the image sensor included in the imaging unit 28.

  As shown in FIG. 5, the focal position of the g line is different from the focal position of the e line. More specifically, the focal position of the e line is beyond the focal position of the g line. Therefore, the distance L1 of the reflected light imaging lens 26b and the transmitted light imaging lens 26a according to the embodiment is adjusted so that the light passing therethrough is imaged by the imaging unit 28. .

  FIG. 6 is a table showing the types of the objective lens 16 according to the embodiment and the focal lengths and magnifications of the respective lenses in a tabular format. As shown in FIG. 6, when the focal length of the 10.4 [times] objective lens 16 is a [mm] and the focal length of the imaging lens 26 is A [mm], the g line. The enlargement ratio is A / a [times]. Here, b is the focal length of the g-line of the objective lens 16 of 20.8 [times], and b is different from the focal length of the g-line of the objective lens 16 of 10.4 [times]. For this reason, when the focal length of the g-line of the imaging lens 26 is A [mm], the magnification of the g-line is A / b [times]. Since a and b are different values, A / a and A / b are also different values.

  Therefore, the distance L2 in FIG. 4 is changed, and the focal length of the g-line of the imaging lens 26 is changed to A ′ = A × b / a. As a result, A / a and A '/ b have the same magnification. The same applies to the e line. Thus, by designing the appearance inspection apparatus 100 by previously determining the components shown in the table of FIG. 6 by experiment, the optical characteristics resulting from the change in the magnification of the objective lens 16 and the difference in the wavelength of light used for image formation It is possible to provide an image that is easy to perform defect inspection.

  As described above, according to the appearance inspection apparatus 100 according to the embodiment, the inspection of the photomask 14 can be speeded up. In particular, since the transmission image and reflection image of the photomask 14 can be provided to the operator at the same time, the accuracy of defect inspection of the photomask 14 can be improved. Furthermore, by capturing the transmission image and the reflection image of the photomask 14 with the same image sensor, the imaging head unit of the appearance inspection apparatus 100 can be reduced in size and weight.

  The present invention has been described based on the embodiments. The embodiments are exemplifications, and it will be understood by those skilled in the art that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are within the scope of the present invention. . Such modifications will be described below.

(First modification)
FIG. 7 is a schematic diagram showing an internal configuration of the appearance inspection apparatus 102 according to the first modification of the embodiment, and particularly a schematic diagram showing an optical system of the imaging head unit. The appearance inspection apparatus 100 according to the first modification includes a transmitted illumination light source 10, a reflected illumination light source 12, a photomask 14, a first objective lens 16a, a second objective lens 16b, an objective lens switching unit 18, and a spectroscopic unit 20. , A transmitted light imaging lens 26 a, a reflected light imaging lens 26 b, an imaging unit 28, a reflected illumination field stop 30, and a collimator lens 32. The spectroscopic unit 20 includes a first dichroic mirror 22a, a second dichroic mirror 22b, and a reflecting unit 24. Hereinafter, in the appearance inspection apparatus 102 according to the first modified example, a portion overlapping with the appearance inspection apparatus 00 according to the embodiment. The description is omitted or simplified as appropriate.

  Unlike the appearance inspection apparatus 100 according to the embodiment, the appearance inspection apparatus 102 according to the first modification does not include the quarter wavelength plate 36 and the optical member 38. Instead, the first dichroic mirror 22a according to the first modification reflects 100% of the g line and reflects 50% / 50% of the e line. The second dichroic mirror 22b and the reflection unit 24 are the same as the second dichroic mirror 22b and the reflection unit 24 according to the embodiment, respectively.

  For this reason, the e-line irradiated from the reflected illumination light source 12 is transmitted 50% through the first dichroic mirror 22a, passes through the objective lens 16, and is reflected by the photomask 14. The e-line reflected by the photomask 14 passes through the objective lens 16 again and reaches the first dichroic mirror 22a. The e-line that has reached the first dichroic mirror 22a is further reflected by 50% by the first dichroic mirror 22a and travels toward the second dichroic mirror 22b.

  As described above, in the appearance inspection apparatus 102 according to the first modified example, among the e rays irradiated from the reflected illumination light source 12, the e rays reaching the imaging unit 28 are 25%. In the case of the appearance inspection apparatus 100 according to the embodiment, the efficiency is reduced as compared with the case where the e-line reaching the imaging unit 28 is 50%. However, since the appearance inspection apparatus according to the first modification does not require the quarter-wave plate 36 and the optical member 38, the manufacturing cost can be reduced. In addition, since the imaging unit 28 has higher light receiving sensitivity than the e-line compared to the g-line, the dose reduction of the e-line reaching the imaging unit 28 can be compensated.

(Second modification)
In the above description, the case where the first dichroic mirror 22a, the second dichroic mirror 22b, and the reflection unit 24 exist separately in the spectroscopic unit 20 has been described. Alternatively, the spectroscopic unit 20 may be formed by integrating the first dichroic mirror 22a, the second dichroic mirror 22b, and the reflecting unit 24.

  FIG. 8 is a diagram schematically illustrating a cross section of the spectroscopic unit 21 according to the second modification. The spectroscopic unit 21 according to the second modification includes a triangular prism 44a, a first rhomboid prism 44b, a second rhomboid prism 44c, an optical member 38, and a dichroic filter 46. As shown in FIG. 8, the spectroscopic unit 21 according to the second modification has the optical member 38 fixed by a triangular prism 44a and a first rhomboid prism 44b, and the first rhomboid prism 44b and the second rhomboid prism 44b. A dichroic filter 46 is fixed to the rhomboid prism 44c. By integrally forming the constituent members in this way, it is possible to suppress the deviation of the optical axis of the spectroscopic unit 21 as compared with the case where the respective members are separated. In addition, since most of the region through which parallel light passes is filled with glass having a high refractive index, field curvature can be suppressed.

(Third Modification)
In the above description, the case where the wavelength dependency of the focal length of the imaging lens 26 is the graph shown in FIG. 5 has been described. In the graph shown in FIG. 5, the rate of change of the focal position shift s when the wavelength of transmitted light is λg, that is, (ds / dλ) _{λg is} almost zero. Similarly, the change rate of the focal position shift s at the wavelength λe of the reflected light, that is, (ds / dλ) _λe is almost zero. In this case, even if the wavelength of the light emitted by the transmitted illumination light source 10 has a slight fluctuation width around λg, it means that the focal length fg is not substantially changed. Similarly, even if the wavelength of the light emitted from the reflected illumination light source 12 has a slight fluctuation centering on λe, it means that the focal length fe does not change substantially.

  In general, the optical characteristics of a system composed of lens groups are determined by the refractive index and Abbe number of each lens constituting the system. Therefore, depending on the combination of the objective lens 16 and the imaging lens 26, it may be difficult to realize the optical characteristics as shown in FIG.

Therefore, in the visual inspection apparatus according to the third modification, the system of the objective lens 16 and the imaging lens 26 has the wavelength λ of light passing through the system as the first axis and the focal position shift s as the second axis. Oite in the graph,
( _Ds / dλ) _λg <T and (ds / dλ) _λe <T (1)
It has an optical characteristic that holds. Here, λg is the wavelength of transmitted light, λe is the wavelength of reflected light, d is a differential operator, and T is a predetermined threshold.

FIG. 8 is a diagram schematically illustrating optical characteristics of the imaging lens 26 according to the third modification. As shown in FIG. 9, the imaging lens 26 according to the third modification also has a rate of change of the focal length at λg, that is, (ds / s), similarly to the imaging lens 26 according to the embodiment. dλ) _{λg is} almost zero.

On the other hand, as shown in FIG. 9, the imaging lens 26 according to the third modification differs from the appearance inspection apparatus 100 according to the embodiment in the rate of change of the focal position shift s at λe of the wavelength of the reflected light. The absolute value has a value greater than zero. For this reason, if the wavelength of the light emitted from the reflected illumination light source 12 has a slight fluctuation width centering on λe, a slight error occurs in the position of the focal point fe depending on the wavelength. However, as shown in Expression (1), if (ds / dλ) _λe is less than the predetermined threshold T, the error of the focal point fe is in a negligible range.

  Therefore, the “predetermined threshold value T” is a reference threshold value for determining whether or not the error in the focal length f of the imaging lens 26 due to the width of the light source toward the wavelength band is within an allowable range. is there. The value of the threshold value T may be determined by experiment in consideration of the bandwidth of the transmitted illumination light source 10 or the reflected illumination light source 12, the size of the inspection object of the appearance inspection apparatus 100, and the like. According to the experiment of the inventor of the present application, in the visual inspection apparatus according to the third modification, the value of the threshold value T may be about 5000 to 8000, more preferably about 6000 to 7000, and further preferably about 6670. I understood.

  As described above, the imaging lens 26 according to the third modified example is effective in that the optical design is easy as compared with the imaging lens 26 according to the embodiment.

(Fourth modification)
The case where the color magnification adjustment function is realized by the lens configuration of the imaging lens 26 has been described above. Alternatively, the color magnification adjustment may be realized by image processing. This can be realized, for example, by providing an image processor (not shown) and enlarging / reducing an image captured by the imaging unit 28 based on information indicating the magnification of the objective lens 16 and the wavelength of light. The image may be enlarged / reduced using a known bilinear, bicubic, spline interpolation algorithm, or linear interpolation algorithm. As a result, the lens configuration of the imaging lens 26 can be simplified, and the robustness of the entire optical system can be improved.

  DESCRIPTION OF SYMBOLS 10 Transmission illumination light source, 12 Reflection illumination light source, 14 Photomask, 16 Objective lens, 16a 1st objective lens, 16b 2nd objective lens, 18 Objective lens switching part, 20, 21 Spectroscopy part, 22a 1st dichroic mirror, 22b Second dichroic mirror, 24 reflector, 26 imaging lens, 26a imaging lens for transmitted light, 26b imaging lens for reflected light, 28 imaging unit, 32 collimator lens, 34 light shielding member, 36 1/4 wavelength plate, 38 optical member, 40 first lens, 42 second lens, 44a triangular prism, 44b first rhomboid prism, 44c second rhomboid prism, 46 dichroic filter, 100, 102 visual inspection device, 200 glass substrate, 202 chrome pattern , 2 04 Halftone mask.

Claims (6)

A transmission illumination light source for irradiating light that passes through the photomask;
A reflected illumination light source for irradiating light reflected on the photomask during irradiation of the transmitted illumination light source;
An objective lens for converting the transmitted light transmitted through the photomask and the reflected light reflected by the photomask into parallel light;
A spectroscopic unit for separating the parallel light converted by the objective lens into transmitted light and reflected light;
An imaging lens for transmitted light that images the transmitted light separated by the spectroscopic unit;
A reflected light imaging lens that forms an image of the reflected light separated by the spectroscopic unit;
An imaging unit that images the transmitted light imaged by the transmitted light imaging lens and the reflected light imaged by the reflected light imaging lens;
The wavelength of the transmitted light and the wavelength of the reflected light are different from each other,
The spectroscopic unit includes a first dichroic mirror and a second dichroic mirror, and is opposite to a surface on which light to be reflected by the reflected illumination light source of the first dichroic mirror is incident. An optical member is arranged on the surface of
The optical member functions as a polarization beam splitter for the reflected light reflected by the photomask and the light reflected by the reflected illumination light source , and reflects the transmitted light by 100%. Function as a filter,
The optical member reflects the reflected light and reflects the transmitted light;
Separating the transmitted light reflected by the optical member by the second dichroic mirror and the reflected light reflected by the photomask ;
An appearance inspection apparatus in which a quarter-wave plate is disposed between the objective lens and the dichroic mirror of the spectroscopic unit.   2. The imaging unit according to claim 1, wherein the transmitted light imaged by the transmitted-light imaging lens and the reflected light imaged by the reflected-light imaging lens are each captured in different regions of the same imaging device. Appearance inspection apparatus as described.   The visual inspection apparatus according to claim 2, further comprising a light shielding member that suppresses crosstalk between the transmitted light formed by the transmitted light imaging lens and the reflected light formed by the reflected light imaging lens. The objective lens has a plurality of lenses with different magnifications,
The appearance inspection apparatus further includes an objective lens switching unit that switches the plurality of lenses,
4. The transmitted light imaging lens and the reflected light imaging lens each include a focus adjustment function for adjusting a focal position in conjunction with lens switching by the objective lens switching unit. An appearance inspection apparatus according to claim 1.   The visual inspection apparatus according to claim 4, wherein each of the reflected-light imaging lens and the transmitted-light imaging lens has a color magnification adjustment function that adjusts a color magnification in conjunction with switching by the lens switching unit. The optical characteristic of the optical system consisting of the objective lens and the reflected light imaging lens and the optical characteristic of the optical system consisting of the objective lens and the transmitted light imaging lens are obtained by setting the wavelength λ of the passing light to the first wavelength λ. In the graph with the axis and focal position shift s as the second axis, the wavelength of the transmitted light is λg, the wavelengths of the reflected light are λe and d are differential operators, and T is a predetermined threshold value.
( _Ds / dλ) _λg <T and (ds / dλ) _λe <T
The appearance inspection apparatus according to claim 1, wherein:

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