JP5317138B2 - Inspection apparatus and defect inspection method - Google Patents

Description

  The present invention relates to an inspection apparatus for detecting defects existing in a photomask, and more particularly to an inspection apparatus in which the influence of optical distortion generated when a photomask is held on a stage is reduced.

  With the miniaturization of semiconductor devices, it is required that fine defects can be detected even in photomask inspection. As a mask inspection device that optically detects fine defects, a composite image of a transmission image and a reflection image of a photomask and a transmission image are simultaneously captured, and the defect is detected based on the captured composite image and the transmission image. A defect inspection apparatus is known (see, for example, Patent Document 1). In this defect inspection apparatus, a laser light source that emits linearly polarized laser light is used as an illumination light source, illumination light for transmission inspection is projected from the back side of the photomask, and illumination light for reflection inspection is emitted from the pattern forming surface side. Is projected. Illumination light for reflection inspection is coupled to the optical path of the objective lens via a polarization beam splitter. The transmitted light that has passed through the photomask is collected by the objective lens, passes through the polarization beam splitter, and enters the photodetector, and a transmitted image of the photomask is captured.

The defect inspection apparatus described above has an advantage that a defect formed near the edge of a pattern can be detected with high accuracy because a composite image obtained by combining a reflection image and a transmission image of a photomask is captured. In addition, since the illumination light for reflection inspection emitted from the laser light source using the polarization beam splitter is separated from the reflected light and transmitted light emitted from the photomask, an advantage that the illumination light can be used effectively is also achieved. Yes.
JP 2008-190938 A

  By performing defect inspection using transmitted light emitted from the photomask, it is possible to detect defects existing in parts other than the pattern of the photomask, which is extremely important in defect inspection of the photomask. On the other hand, the photomask is composed of a quartz substrate and a light shielding pattern such as a chromium film formed on the surface thereof. Therefore, when the illumination light for transmission inspection passes through the mask substrate of the photomask, when a local birefringence change occurs in the quartz substrate (mask substrate), when the illumination light passes through the mask substrate, The polarization state changes. When the polarization state of the transmitted light changes, when passing through the polarization beam splitter, a part of the transmitted light is cut by the polarization beam splitter, and transmitted light having a light amount smaller than a predetermined light amount value enters the photodetector. Become. As a result, the luminance value of the image signal output from the photodetector changes, which causes a problem that the defect detection sensitivity decreases. That is, for example, when a defect is detected by die-to-die comparison inspection, the luminance values of corresponding portions of two dies are compared, a difference is formed, and if the difference value exceeds a threshold value, it is determined as a defect. Therefore, when the amount of transmitted light emitted from the photomask is locally reduced, a luminance difference is formed between corresponding portions, and a pseudo defect is generated. On the other hand, in order to suppress the occurrence of pseudo defects, it is necessary to set a high threshold value. However, if the threshold value is set high, there is a problem that fine defects are not detected.

An object of the present invention is to realize an inspection apparatus and a defect inspection method in which an influence due to a change in birefringence existing in a mask substrate is reduced.
Furthermore, an object of the present invention is to realize an inspection apparatus capable of eliminating defects caused by changes in birefringence formed on a mask substrate and increasing the sensitivity of defect detection.

An inspection apparatus according to the present invention includes a light source device that generates illumination light, a first illumination optical system that projects illumination light emitted from the light source device as illumination light for transmission inspection toward a photomask to be inspected, Receiving a stage holding the photomask, an objective lens for condensing the transmitted light transmitted through the photomask, a light detecting means for receiving the transmitted light emitted from the objective lens, and a luminance signal output from the light detecting means; A signal processing device for detecting defects present in the photomask;
The signal processing device includes a memory that stores data of luminance distribution of a luminance signal output from the light detection unit by scanning a mask substrate before a mask pattern is formed with illumination light for transmission inspection. ,
The first illumination optical system includes correction means for correcting the intensity of illumination light emitted from the light source device,
During inspection of a photomask, the intensity of illumination light emitted from the light source device is corrected using luminance distribution data stored in the memory .

  As a result of analysis of the birefringence of various photomasks by the present inventor, it has been found that the birefringence of the four corner areas of the photomask changes when the photomask is held on the stage. At the four corners of the photomask, there are gripping members for fixing to the stage, and it is understood that the birefringence of the mask substrate has changed due to the external stress. On the other hand, when the magnitude and direction of the local birefringence change on the mask substrate, when the polarized illumination light passes through the mask substrate, the polarization state of the transmitted light changes according to the magnitude and direction of the birefringence, A part of the transmitted light is cut when passing through the polarization beam splitter. Further, since the stress acting on the photomask acts locally, a change in birefringence also occurs locally. Therefore, the amount of light that passes through the photomask, passes through the polarizing beam splitter, and enters the photodetector locally changes, and the luminance value of the luminance signal output from the photodetector is in a non-uniform distribution state. End up. Therefore, in the present invention, prior to the defect inspection, a mask substrate (quartz substrate) in the same lot on which the mask pattern is not formed is mounted on the stage, scanned with illumination light in the same manner as in actual defect inspection, and transmitted. Light is detected by a photodetector. Then, luminance distribution data is created from the luminance value of the luminance signal output from the photodetector. In the actual defect inspection, the luminance value of the luminance signal output from the photodetector is corrected using the luminance distribution data. If the luminance value of the image signal is corrected based on the luminance distribution data in this way, the influence of the change in the birefringence formed on the mask substrate is reduced, the threshold value can be set low in the defect detection process, and the defect detection sensitivity. Can be increased. The birefringence or birefringence distribution existing on the mask substrate (quartz substrate) includes inherent birefringence, birefringence due to bending due to gravity, and birefringence due to external stress. . Of these, the birefringence distribution specific to the mask substrate has almost the same birefringence distribution in the same lot and the same type of mask substrate. It has also been found that the change in birefringence due to external stress and the change in birefringence due to gravity are almost the same in the same lot and the same type or size of mask substrate. Therefore, if luminance distribution data is acquired for one mask substrate of the same format or the same lot, it can be used for correction of another photomask of the same format.

In the present invention , correction can be performed on the illumination light source side. That is, for example, an optical modulator is disposed in the optical path between the illumination light source and the condenser lens, and the intensity of the illumination light is time-modulated in synchronization with scanning of the stage based on the luminance distribution data. Transmitted light having a uniform luminance value can be emitted.

  In the present invention, prior to the defect inspection, the mask substrate before the pattern is formed by the illumination light for transmission inspection is scanned, luminance distribution data is formed from the luminance signal output from the photodetector, and the luminance Since the luminance value of the image signal output from the photodetector or the intensity of the illumination light is corrected based on the distribution data, it is output from the photodetector even if a local stress is applied to the photomask. The problem that a non-uniform distribution is formed in luminance values is solved. As a result, since the threshold value in the defect detection process can be set low, it is possible to increase the defect detection sensitivity while suppressing the occurrence of pseudo defects.

It is a figure which shows an example of the mask inspection apparatus by this invention. It is a figure which shows the illumination area formed on a photomask. It is a figure which shows the measurement result of the incident light quantity distribution which injects into a photodetector. It is a figure which shows a series of processes of the defect inspection method by this invention. It is a figure which shows an example of the circuit structure of the test | inspection apparatus by this invention.

  FIG. 1 is a view showing an example of a mask inspection apparatus according to the present invention. In this example, a first illumination beam for transmission inspection and a second illumination beam for reflection inspection are projected onto a photomask to be inspected for defects, and a reflection / transmission composite image and a transmission image of the photomask are simultaneously captured. A mask inspection apparatus that detects defects using the captured composite image and transmission image will be described. As the illumination light source 1, a laser emitting a 213 nm laser beam is used. The generated laser beam is light linearly polarized in the first direction, for example, P-polarized light. A laser beam emitted from the laser is reflected by a total reflection mirror via a speckle pattern reduction device (not shown) and is incident on the first beam splitter 3. The first beam splitter 3 is a half prism that transmits a part of incident light and reflects a part thereof. The laser beam reflected by the first beam splitter becomes a first illumination beam for transmission inspection, and the transmitted laser beam forms a second illumination beam for reflection inspection.

  The first illumination beam passes through the attenuator 4 and is converted to circularly polarized light through the quarter-wave plate 5. The illumination beam emitted from the quarter wavelength plate 5 is reflected by the total reflection mirror 6 and enters the condenser lens 7. Then, the light is collected by the condenser lens and incident on the back surface of the photomask 8 to form a first illumination area. The photomask 8 is disposed on the stage 9. The stage 9 is configured by an XY stage that can move in the X direction and the Y direction orthogonal to the X direction. The stage 9 moves zigzag in the X direction and the Y direction, and the photomask is scanned two-dimensionally with a circularly polarized illumination beam by the two-dimensional movement of the stage. A position sensor 10 for detecting the position of the stage in the X and Y directions is connected to the stage 9 to detect the position of the stage 9. The detected position information of the stage is supplied to a signal processing device described later. Incidentally, as a photomask to be inspected, a binary type photomask and a halftone type and a Levenson type phase shift mask are targeted.

  The transmitted light that has passed through the photomask is collected by the objective lens 11, passes through the quarter-wave plate 12, is converted into linearly polarized light (S-polarized light), and enters the polarizing beam splitter 13. Then, the light passes through the polarization beam splitter 13 and enters the total reflection mirror 14. The transmitted light reflected by the total reflection mirror 14 enters the field division mirror 16 through the imaging lens 15. The field dividing mirror functions to divide the field of the objective lens 10, passes light that has passed through one half of the field of the objective lens as it is, and reflects light emitted from the remaining half of the field. The light that has passed through the field dividing mirror 16 as it is enters the first photodetector 17, and the light reflected by the field dividing mirror enters the second photodetector 18. The first and second photodetectors can be composed of, for example, TDI sensors. Luminance signals (image signals) output from the TDI sensors 17 and 18 are supplied to the signal processing device 19.

  The second illumination beam for reflection inspection that has passed through the first beam splitter 3 is reflected by the total reflection mirror 19 and enters the ND filter 20 that acts as a field stop. This ND filter shields one half of the second illumination beam for reflection inspection, and emits only the remaining half of the beam. The second illumination beam emitted from the ND filter 21 is reflected by the polarization beam splitter 13 and travels on the optical path of the objective lens. Then, the light passes through the quarter-wave plate 12 and is converted into circularly polarized light. Further, the second illumination beam enters the photomask 8 through the objective lens 11 and forms a second illumination area with the circularly polarized illumination light.

  The area of the second illumination area is set to half of the area of the first illumination area formed by the first illumination beam for transmission inspection, and is formed so as to overlap the first illumination area. This state is shown in FIG. As shown in FIG. 2, the combined light of the transmitted light transmitted through the photomask and the reflected light reflected from the surface of the photomask is emitted from the second illumination area 30 formed on the surface of the photomask 8. . Further, transmitted light that has passed through the photomask is emitted from the third illumination area 31 that does not overlap the second illumination area of the first illumination area.

  The reflected light emitted from the second illumination area of the photomask is collected by the objective lens together with the transmitted light, converted into linearly polarized light (S-polarized light) by the quarter-wave plate 12, and enters the polarizing beam splitter 13. Further, the light passes through the polarization beam splitter 13 and enters the total reflection mirror 14. The reflected light and transmitted light emitted from the second illumination area are reflected by the total reflection mirror, pass through the imaging lens and the field division mirror as they are, and enter the first photodetector 17. Accordingly, the first photodetector receives the combined light of the transmitted light that has passed through the photomask and the reflected light that has been reflected, and forms a transmitted / reflected composite image in which the transmitted image and the reflected image of the photomask are combined. . Further, the transmitted light emitted from the third illumination area of the photomask is reflected by the field division mirror 16 and enters the second photodetector 18. Therefore, the second photodetector 18 forms a transmission image of the photomask. Image signals output from the first and second photodetectors 17 and 18 are supplied to a signal processing device 19. The signal processing device performs gain adjustment on the input image signal, and performs image processing such as filtering processing, binarization processing, and threshold comparison processing to detect defects.

  The photomask has a quartz substrate, and various light shielding patterns are formed on the surface of the quartz substrate. On the other hand, when the photomask 8 is held by the stage 9, stress acts on the quartz substrate. This stress causes optical distortion inside the quartz substrate, and optical anisotropy is formed inside the substrate. In this case, since the stress acting on the quartz substrate acts locally rather than uniformly on the entire surface of the substrate, the optical anisotropy formed on the quartz substrate is locally generated. For this reason, when polarized illumination light for transmission inspection enters the photomask, the polarization state of the transmitted light emitted from the photomask changes depending on where the optical anisotropy of the quartz substrate occurs, and is arranged in the subsequent stage. The amount of transmitted light changes when the light passes through a polarizing element such as a polarizing beam splitter. In other words, since the polarization beam splitter passes only the polarization component that vibrates along a predetermined direction, when the polarization state changes due to the optical anisotropy generated inside the substrate, the polarization beam splitter transmits the substrate according to the applied stress. The amount of transmitted light that is transmitted changes, and as a result, a light amount distribution occurs in the incident light that enters the photodetector.

  In FIG. 3A, a quartz substrate (mask substrate) 32 before a pattern is formed is arranged on the stage of the inspection apparatus shown in FIG. 1, and transmitted from the back side of the quartz substrate 32 in the same manner as in actual defect inspection. The measurement result of the incident light amount distribution of the transmitted light amount that is scanned by the illumination light for inspection, is emitted from the quartz substrate, and is detected by the photodetector 16, that is, the luminance distribution of the luminance signal output from the photodetector. A region not hatched or the like shows average luminance. On the other hand, areas 1 and 2 indicated by reference numerals 33 and 34 indicate regions having the lowest luminance value (incident light amount). Areas 3 and 4 indicated by reference numerals 35 and 36 indicate the second lowest luminance values. On the other hand, areas indicated by reference numerals 37 and 38 indicate areas having the highest luminance values. Furthermore, the areas indicated by reference numerals 39 and 40 are areas having the second highest luminance value.

  As shown in FIG. 3 (A), according to the experiment result by the present inventor, the incident light amount incident on the photodetector from the two corners 33 and 34 diagonally located among the four corners of the quartz substrate ( (Luminance value) is the smallest, and the amount of incident light at the two corners 37 and 38 located at different diagonals is the largest. The amount of incident light gradually increases or decreases from the corner toward the center of the substrate. On the other hand, when the photomask is held on the stage, the four corners of the photomask are fixed to the fixing device, so that the stress for fixing acts on the four corners. Therefore, according to the above experimental results, the optical anisotropy is locally generated inside the quartz substrate due to the stress acting on the substrate when the quartz substrate is held on the stage, and the stress acting on the substrate. It is considered that the polarization state is changed according to the change, and the amount of light transmitted through the polarization beam splitter 12 is changed.

  FIG. 3B shows a chip area to be formed on the quartz substrate having the luminance distribution of the luminance signal output from the photodetector shown in FIG. In this example, it is assumed that 9 chips of 3 × 3 are formed. A chip area (die) in which nine square areas denoted by reference numerals 41a to 41i are to be formed is shown. The first chip area 41a includes an area having a low luminance value. Therefore, in the mask inspection, the luminance value of the luminance signal output from the photodetector when scanning the first chip area is locally low. On the other hand, the adjacent second chip area 41b has an average luminance value throughout. Therefore, when the mask pattern is inspected, the luminance value of the luminance signal during the scanning of the second chip area 41b is relatively high. For this reason, when a defect is detected by the die-to-die comparison inspection between two adjacent chip areas 41a and 41b, a difference is formed in the luminance level of the image signal of these two chip areas. There is a problem that sensitivity decreases. That is, when a defect is detected by die-to-die comparison inspection, a luminance difference between corresponding portions of the two chips to be compared is detected, and if the detected luminance difference exceeds a predetermined threshold, it is determined that a defect exists. Is done. Therefore, when one of the chips to be compared has a uniform luminance distribution instead of a uniform luminance distribution, a luminance difference is generated by image comparison even for an image signal of a normal part. Therefore, the threshold value for determining a defect must be set larger than the necessity of avoiding the detection of the pseudo defect, and as a result, the defect detection sensitivity is lowered. In other words, since it is necessary to set a high threshold when performing defect determination, the brightness difference between two images is small when there is a fine defect, so it is determined that the brightness difference is equal to or less than the threshold and not a defect. become. On the other hand, if the threshold value is set low and the defect detection sensitivity is set high, there is a luminance difference between chips, so there is a luminance difference even for normal parts, and a pseudo defect that determines that the normal part is defective This causes a malfunction that increases. Such a problem occurs not only when a defect is detected by die-to-die comparison inspection but also when a defect is detected by die-to-database comparison inspection. Therefore, in order to improve the defect detection sensitivity in the photomask inspection, it is necessary to eliminate the stress distortion generated in the quartz substrate.

  In order to solve the above-described problems, in the present invention, prior to defect inspection, the quartz substrate before the pattern is formed is mounted on the inspection apparatus, and the entire inspection area is scanned using illumination light for transmission inspection, The luminance distribution of the luminance signal output from the photodetector is measured. Subsequently, the correction factor is calculated so that the luminance of the image signal output from the photodetector is uniform over the entire quartz substrate. In actual defect inspection, the luminance signal output from the photodetector is corrected by multiplying it by a correction factor, and the defect detection processing is performed using the corrected luminance signal. In this way, if a correction factor is created using a quartz substrate before the pattern is formed and correction processing is performed on the output signal from the photodetector, the luminance distribution due to optical distortion generated in the substrate is almost equal. Since the extinguished image signal is obtained, it is possible to set a small threshold value in the defect detection determination. As a result, the generation of pseudo defects is reduced, and the defect detection sensitivity can be further increased.

  FIG. 4 is a flowchart showing an example of the defect inspection method according to the present invention. In the present invention, prior to the defect inspection, the quartz substrate alone before the mask pattern is formed is scanned with illumination light for transmission inspection, and the luminance distribution detected by the photodetector is measured. In step 1, the quartz substrate before the mask pattern constituting the photomask is formed is placed on the stage of the inspection apparatus and fixed to the stage.

  Subsequently, by using illumination light for transmission inspection used in actual defect inspection, almost the entire surface of the quartz substrate is two-dimensionally scanned in the same manner as in actual defect inspection. And the transmitted light which permeate | transmits a quartz substrate, and injects into a photon detection means through a polarization separation means is detected, and the luminance distribution of the luminance signal output from a photodetector is measured (step 2). The luminance signal output from the light detection means is A / D converted and sequentially stored in the memory.

  Subsequently, a correction value is calculated using the incident light amount distribution stored in the memory (step 3). That is, the correction value is calculated so that the luminance value of the luminance signal output from the light detection means becomes a constant value over the entire quartz substrate. The calculated correction factor is stored in the memory. It is also possible to generate a correction value by directly supplying the luminance signal output from the A / D converter to the correction value calculation means.

  When the measurement of the incident light quantity distribution on the quartz substrate is completed, the quartz substrate is removed from the stage, a photomask to be defect-inspected is placed on the stage, and actual defect inspection is started (step 4).

  During the inspection, the luminance signal output from the light detection means is corrected using the correction value stored in the memory (step 5).

  Subsequently, using the corrected luminance signal, a die-to-die comparison inspection or a die-to-database comparison inspection is performed to detect defects present in the photomask. If a defect is detected, the address is stored in the defect memory.

  FIG. 5 is a diagram showing an example of a signal processing apparatus of the inspection apparatus according to the present invention. The inspection apparatus according to the present invention has two operation modes: a luminance distribution measurement mode for measuring the luminance distribution due to optical distortion of the photomask, and a defect inspection mode for detecting defects present in the photomask. Further, in this example, the correction for correcting the luminance distribution caused by the optical distortion formed on the photomask using the luminance value of the image signal output from the second photodetector 18 that captures the transmission image of the photomask. Form a value.

  The image signal output from the second photodetector 18 is input to the A / D converter 40 through an amplifier (not shown) and converted into a digital signal. The image signal output from the A / D converter 40 is input to the common terminal of the switching means 41. The switching means 41 has two output terminals, the first output terminal is connected to the luminance distribution correction means 42 operating in the defect inspection mode, and the second output terminal is a luminance distribution memory 43 operating in the luminance cloth measurement mode. Connect to.

  First, the luminance distribution measurement mode will be described. A quartz substrate is placed on a stage, and the back surface of the quartz substrate is two-dimensionally scanned with illumination light for transmission inspection by two-dimensional movement of the stage. The luminance value of the image signal output from the photodetector 18 is sequentially A / D converted and stored in the luminance distribution memory 43 via the switching means 41. The luminance distribution data stored in the luminance distribution memory is supplied to the correction value calculation means 44, and the correction value is calculated so that the luminance value of the luminance signal output from the photodetector 18 becomes a constant value over the entire quartz substrate. . The calculated correction value is stored in the correction value memory 45. The correction values stored in the correction value memory 45 are sequentially supplied to the light quantity distribution correction means 42 in the actual inspection of the photomask. The correction value for the entire quartz substrate is calculated, and the light quantity distribution measurement mode ends.

  Subsequently, inspection of the photomask to be inspected for defects starts. At this time, the switching means 41 is switched so that the A / D converter 40 and the light quantity distribution correction means 42 are connected. The quartz substrate is removed from the stage and a photomask to be inspected is mounted. The photomask is scanned with illumination light for transmission inspection and illumination light for reflection inspection by two-dimensional movement of the stage. The image signal output from the photodetector 18 is sequentially supplied to the luminance distribution correction unit 42 via the A / D converter 40 and the switching unit 41. The luminance distribution correcting unit 42 corrects the luminance value of the sequentially input image signal using the correction value and the stage position signal supplied from the correction memory 45, and the corrected image signal is converted into the subsequent two-dimensional image forming unit 46. To supply.

  In this example, a defect is detected by die-to-die comparison inspection. The previously formed two-dimensional image of the first die is stored in the delay memory 47. Subsequently, the image signal of the second die formed next is sequentially supplied to the image comparison means 48 and also supplied to the delay memory 47 sequentially. The two-dimensional image of the first die stored in the delay memory is supplied to the image comparison unit 48 in synchronization with the image signal of the second die output from the two-dimensional image forming unit 46. The image comparison means 48 compares the two input image signals and outputs the difference value. The formed difference value is supplied to the threshold value comparison means 49. The threshold value comparison means 49 compares the input difference value with a set threshold value, and determines that the defect is a defect if the difference value exceeds the threshold value. The determination output is supplied to the defective address determination means 50. The address determination unit 50 specifies the address of the part determined to be defective using the output signal from the threshold comparison unit 49 and the stage position signal, and supplies the result to the defect address memory 51.

  In the present invention, the influence of optical distortion that occurs when the photomask is held on the stage is removed or reduced, so that the threshold value set in the threshold value comparison means 49 can be set low, so that the defect detection sensitivity is further increased. Get higher.

  The present invention is not limited to the above-described embodiments, and various modifications and changes can be made. For example, in the above-described embodiment, the light amount distribution of incident light incident on the photodetector is corrected by software, but it can also be corrected by hardware. In this case, for example, in a shading correction circuit that performs shading correction, it is also possible to perform luminance distribution correction using correction data.

  Furthermore, in the above-described embodiment, the luminance value of the image signal output from the photodetector is corrected. However, it is also possible to correct the intensity (light quantity) of illumination light on the illumination side. For example, it is possible to arrange an optical modulator such as an E / O modulator in the optical path between the light source device and the condenser lens and temporally modulate the intensity of the illumination light using the correction data. is there. In this case, the intensity of illumination light can be easily corrected by controlling the applied voltage applied to the E / O modulator based on the correction data.

  Furthermore, the present invention can be applied not only to a photomask on which a pattern is formed as an inspection target, but also to inspection of mask blanks before the pattern is formed.

DESCRIPTION OF SYMBOLS 1 Illumination light source 2,6,20 Total reflection mirror 3 1st beam splitter 4 Attenuator 5,12 1/4 wavelength plate
7 condenser lens 8 photomask 9 stage 10 position sensor 11 objective lens 13 polarizing beam splitter 15 imaging lens 16 field dividing mirror 17 first photodetector 18 second photodetector 19 signal processing device 40 A / D converter 41 Switching means 42 Brightness distribution correcting means 43 Brightness distribution data memory 44 Correction value calculating means 45 Correction value memory 46 Two-dimensional image forming means 47 Delay memory 48 Image comparing means 49 Threshold comparing means 50 Defective address determining means 51 Defective address memory

Claims (10)

A light source device that generates illumination light; a first illumination optical system that projects illumination light emitted from the light source device toward a photomask to be inspected as illumination light for transmission inspection; and a stage that holds the photomask. An objective lens that collects the transmitted light that has passed through the photomask, a light detection means that receives the transmitted light emitted from the objective lens, and a luminance signal output from the light detection means to receive defects present in the photomask. A signal processing device to detect,
The signal processing device includes a memory that stores data of luminance distribution of a luminance signal output from the light detection unit by scanning a mask substrate before a mask pattern is formed with illumination light for transmission inspection. ,
The first illumination optical system includes correction means for correcting the intensity of illumination light emitted from the light source device,
An inspection apparatus that corrects the intensity of illumination light emitted from the light source device using luminance distribution data stored in the memory during inspection of a photomask . The inspection apparatus according to claim 1 , wherein the luminance distribution is generated due to a local change in birefringence formed on the mask substrate,
The inspection device according to claim 1, wherein the light detection means receives the transmitted light emitted from the objective lens through the polarization separation means. 3. The inspection apparatus according to claim 1 , wherein the correction means uses the luminance distribution data stored in the memory so that the luminance value of the luminance signal output from the photodetector is substantially the entire surface of the mask substrate. An inspection apparatus comprising means for calculating a correction value for correction so as to be uniform over the entire area, and correcting the intensity of illumination light emitted from the light source device using the correction value. In the testing apparatus according to claim 1, 2, or 3, as the polarization separator, the inspection apparatus comprising a 1/4-wave plate and the polarization beam splitter. 5. The inspection apparatus according to claim 4 , wherein the light source device generates linearly polarized illumination light that vibrates in a specific direction, and the illumination light is converted into circularly polarized light and incident on the photomask. The inspection apparatus is characterized in that after being transmitted, the light is converted into linearly polarized light by the ¼ wavelength plate, and the linearly polarized transmitted light passes through the polarizing beam splitter and enters the light detecting means. The inspection apparatus according to claim 1, 2, 3, 4, or 5, the inspection apparatus further reflection inspection through the objective lens toward the pattern-formed surface on which a pattern of the photomask is formed An inspection apparatus comprising: a second illumination optical system for projecting illumination light for illumination, wherein the illumination light for reflection inspection is incident on the objective lens through the polarizing beam splitter. 2. The inspection apparatus according to claim 1 , wherein the correction means for correcting the intensity of illumination light emitted from the light source device includes a light modulator disposed in an optical path between the light source device and the photomask. An inspection apparatus for controlling the control voltage of the tester based on the luminance distribution data or the correction value. 7. The inspection apparatus according to claim 6, wherein the illumination light for transmission inspection emitted from the first illumination optical system forms a first illumination area on the back surface of the photomask and is emitted from the second illumination optical system. The reflected inspection illumination light forms a second illumination area on the surface of the photomask,
2. The inspection apparatus according to claim 1, wherein the second illumination area is formed so as to overlap the first illumination area, and the area is set to half of the first illumination area. A light source that generates illumination light; a stage that supports a photomask to be inspected; means for projecting illumination light for transmission inspection emitted from the light source toward the photomask disposed on the stage; and a photomask Present in the photomask using an inspection device having a light detection means for receiving the transmitted light transmitted through the light detection device and a signal processing device for detecting defects present in the photomask based on the luminance signal output from the light detection means A defect inspection method for detecting defects to be performed,
Placing the mask substrate before the mask pattern is formed on the stage of the inspection apparatus;
Scanning the mask substrate with illumination light for transmission inspection, receiving transmitted light emitted from the mask substrate by a light detection means, and forming data of a luminance distribution of a luminance signal output from the light detection means;
Storing the formed luminance distribution data in a memory;
Removing the mask substrate from the stage and placing a photomask to be inspected for defects on the stage;
Correcting the intensity of illumination light emitted from the light source using the luminance distribution data;
Scanning the photomask with the corrected illumination light for transmission inspection;
Receiving the transmitted light transmitted through the photomask by the light detection means;
And a step of detecting a defect present in the photomask based on a luminance signal output from the light detection means. The defect inspection method according to claim 9, wherein the luminance distribution is generated due to a local change in birefringence formed on the mask substrate,
The defect detection method , wherein the light detection means receives the transmitted light emitted from the objective lens through the polarization separation means.

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