JP2011038947A - Defect inspection device and image display method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a defect inspection device and an image display method capable of performing optimum color display corresponding to the purpose of the defect device, defect characteristics, or the like. <P>SOLUTION: The defect inspection device includes a signal processing device for imaging an image of a photomask in various illumination conditions, detecting a defect of the photomask by using an output signal from an A/D converter, and outputting a color image of the photomask including the detected defect. The signal processing device includes a conversion table generation means 23 with respect to luminance/color, and a luminance/color conversion means 24 of the photomask. The conversion table generation means 23 generates a conversion table, based on first and second two gradation values assigned, respectively to two kinds of mask patterns, and the number of colors of RGB assigned into a luminance gradation between the first gradation value and the second gradation value, or a parameter allocated to a gradation span. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a defect inspection apparatus for a photomask, and more particularly to a defect inspection apparatus that displays a detected defect as a framed color image.
The present invention also relates to an image display method for displaying a defect detected by a defect inspection apparatus on a monitor as a color image.

  Many photomasks are used in the LSI manufacturing process. If there is a defect in the photomask, an image of the defect is transferred onto the wafer, which causes a problem of reducing the yield in manufacturing the LSI. Therefore, defect inspection of a photomask is extremely important for increasing the yield in manufacturing the photomask. As a photomask defect inspection method, illumination light is projected toward the photomask, transmitted light or reflected light emitted from the photomask is detected by a light detection means, and die-to-die inspection method or die-to-database inspection method Defect inspection is performed. In these defect inspection methods, when the image signal output from the imaging device is compared with the reference signal, pseudo defects are generated due to error detection such as positional deviation or signal noise, and normal photo Even if it is a mask, there exists a possibility that it may determine with a defect inspection apparatus having a defect. Therefore, once the defect inspection is performed, the defect detected in the review process is displayed on the monitor, the inspection by the operator's visual inspection is performed, and it is determined whether or not the detected defect is a pseudo defect. ing.

  As a defect formed in the photomask, there is a defect caused by adhesion of a growing foreign substance called “Haze”. The luminance image of the defect due to the adhesion of the growing foreign matter is taken as a luminance image in which the luminance difference is small and the luminance changes smoothly as compared with the luminance of the surrounding normal part. Such a defect having a small luminance difference and a gradual change in luminance from the surrounding image is likely to be confused with a pseudo defect, and it is necessary to accurately determine whether or not it is a defect in the review process after the inspection is completed. . However, when a defect having a small luminance difference is displayed on a monitor as a monochrome image (grayscale image), there is a problem that it is difficult to distinguish it from surrounding images, and it is difficult to accurately grasp the size and shape of the defect.

A technique for displaying an image captured by a microscope as a color image is known (see, for example, Patent Document 1). In this color image display method, a luminance image captured by a microscope is converted into a digital image signal via an A / D device, and a fixed luminance conversion table is used, and R is used according to the luminance gradation of the captured image. , G, B colors are assigned and supplied to the monitor as color image signals.
JP 2002-23062 A

  The pseudo color image display method described above has an advantage that the defect image is displayed on the monitor as a color image different from the surrounding image, so that it is relatively easy to determine whether or not the defect is a defect in the review process. However, there are many defects in the photomask that have a small difference in luminance from the surrounding image and that gradually change in luminance, as represented by a growth foreign matter adhesion defect. When a defect having such characteristics is displayed by the conventional pseudo color display method, it is displayed as an image of the same color including a slight shade difference, and it is still difficult to determine whether or not it is a defect. In addition, since the periphery of the detected defect is difficult to be clearly displayed, there is a defect that it is difficult to clearly see the size and shape of the defect.

  Furthermore, since the photomask defect inspection device is inspected under different inspection conditions depending on the purpose of defect inspection and the characteristics of the detected defect, etc., it is optimal for the characteristics of the detected defect and the purpose of the defect inspection. Display method is necessary.

An object of the present invention is to realize a defect inspection apparatus and an image display method that can be clearly recognized even if a detected defect is a defect having a small luminance difference from the surrounding image or a defect whose luminance changes slowly. There is to do.
Another object of the present invention is to provide a defect inspection apparatus and an image display method capable of performing optimum color display of detected defects according to the purpose of defect inspection, the characteristics of the inspection object, and the like. It is in.

A defect inspection apparatus according to the present invention includes an imaging apparatus that captures an image of an object to be inspected under various illumination conditions,
An A / D converter that converts a luminance image signal output from the imaging device into a gradation signal having a predetermined luminance gradation;
A signal processing device that detects a defect of the inspection object using an output signal from the A / D converter and outputs a color image of the inspection object including the detected defect, the signal processing device comprising: ,
A defect detection means for detecting a defect of the inspection object from an output signal output from the A / D converter;
A memory for storing luminance image information of the inspection object including the detected defect;
The imaging conditions of the imaging device, the first and second gradation values assigned to the two types of patterns formed on the object to be inspected under each imaging condition, and the first gradation value, An input means for inputting a parameter including the number of RGB colors or a gradation span assigned during a luminance gradation between the second gradation values;
Conversion table creating means for creating a luminance / color conversion table that defines the relationship between the gradation value and the color output based on the input parameters;
A luminance / color conversion unit that receives the conversion table created by the conversion table creation unit and the luminance image signal of the photomask stored in the memory and converts the luminance image signal into a color image signal; Features.

A defect inspection apparatus according to the present invention includes an imaging device that captures an image of a photomask under various illumination conditions,
An A / D converter that converts a luminance image signal output from the imaging device into a gradation signal having a predetermined luminance gradation;
A signal processing device that detects a photomask defect using an output signal from the A / D converter and outputs a color image of the photomask including the detected defect, the signal processing device comprising:
Defect detection means for detecting a photomask defect from an output signal output from the A / D converter;
A memory that stores luminance image information of the photomask including the detected defect;
The type of the photomask to be inspected, the imaging conditions of the imaging device, the first and second gradation values respectively assigned to the two types of mask patterns formed on the photomask under each imaging condition, and Input means for inputting a parameter including the number of RGB colors or a gradation span assigned in a luminance gradation between the first gradation value and the second gradation value;
Conversion table creating means for creating a luminance / color conversion table that defines the relationship between the gradation value and the color output based on the input parameters;
A luminance / color conversion unit that receives the conversion table created by the conversion table creation unit and the luminance image signal of the photomask stored in the memory and converts the luminance image signal into a color image signal; Features.

  In the defect inspection apparatus according to the present invention, when a defect detected as luminance information is reviewed, a luminance / color conversion table is created using parameters such as imaging conditions and the number of colors to be displayed. It is possible to perform color display that is optimal for the characteristics of defects and defects. In particular, even a defect having a small luminance difference from the surrounding image is displayed as a color image with a peripheral edge bordered with another color, so that the size and shape of the detected defect can be accurately recognized.

  Many photomasks are composed of two types of mask patterns. That is, in the case of a binary type photomask, it is composed of two types of mask patterns: a light transmission pattern that transmits exposure light and a light shielding pattern that blocks exposure light. In the case of a halftone type photomask, a light transmission pattern that transmits exposure light. And a half-tone pattern that gives a phase difference to the exposure light. On the other hand, many defects present in the binary type photomask are detected as a luminance image having a gradation value between the light transmission pattern and the light shielding pattern. It is detected as an image having a slightly lowered gradation value. In addition, many of the defects formed in the halftone photomask are slightly different from the image of the gradation value between the gradation value of the halftone pattern and the gradation value of the light transmission pattern or the gradation value of the halftone pattern. It is detected as an image having a lowered gradation value. Therefore, when a photomask is an object to be inspected, it is only necessary to specify the gradation values of the two types of mask patterns formed on the photomask and the number of RGB colors allocated between these gradation values, thereby determining the defect characteristics. And a conversion table consistent with the purpose of the defect inspection is formed. As a result, even a defect detected as a luminance image with a small luminance difference from the surroundings can be displayed on the monitor as a color image bordered with one or more different colors.

An image display method according to the present invention is an image display method for displaying a photomask image captured as a luminance image by an imaging device on a monitor as a color image,
Converting an output signal from the imaging device into a gradation signal of a predetermined luminance gradation using an A / D device;
Storing a luminance image of a photomask in a memory using an output signal from the A / D converter;
The type of photomask to be inspected, the imaging conditions of the imaging device when capturing an image of the photomask, and the first and second masks respectively assigned to two types of mask patterns formed on the photomask for each imaging condition Inputting a gradation value and a parameter including a number of RGB colors or a gradation span assigned in a luminance gradation between the first gradation value and the second gradation value;
Creating a luminance / color conversion table that defines the relationship between the luminance gradation and the color output using the input parameters;
Converting the luminance image signal into a color image signal using the generated luminance / color conversion table and the luminance image of the photomask stored in the memory;
And supplying the converted color image signal to a monitor to display a color image of the photomask.

  According to the present invention, since the luminance / color conversion table is created based on the parameters including the imaging conditions, the number of colors assigned to the luminance gradation, etc., it is optimal for the purpose of defect inspection and the characteristics of the defect. Color display can be performed. In particular, even a defect image with a small luminance difference from the surrounding image is displayed as a color image with a fringed edge, so the size and shape of the detected defect can be clearly understood, and the occurrence of pseudo defects is suppressed. And the best treatment for defects.

It is a figure which shows an example of the defect inspection apparatus by this invention. It is a figure which shows an example of a signal processing apparatus. It is a figure which shows an example of a conversion table. It is a figure which shows the image which carried out the color display of the defect by growth foreign material adhesion by this invention. It is the photograph which displayed the actual haze defect detected by the mask inspection apparatus as a monochrome image. The actual photo will be submitted in the property submission form. It is the photograph which displayed the actual haze defect detected by the mask inspection apparatus as a color image by the conventional pseudo color display method. The actual photo will be submitted in the property submission form. 3 is a photograph showing an actual haze defect detected by a mask inspection apparatus as a color image by the color image display method according to the present invention. The actual photo will be submitted in the property submission form.

  FIG. 1 shows an example of a defect inspection apparatus according to the present invention. The defect inspection apparatus of this example captures three types of images: a transmission image of a photomask, a reflection image, and a simultaneous transmission / reflection illumination image (transmission / reflection composite image) according to the illumination conditions. For example, the transmitted illumination light is emitted from the first illumination light source 1 constituted by a mercury lamp. From the transmitted illumination light emitted from the first illumination light source 1, 248 nm illumination light is extracted through a filter (not shown). The illumination light is condensed by the condensing optical system 2, and the total reflection mirror 3. And enters the back surface of the photomask 5 through the condenser lens 4 as a convergent beam. The photomask 5 is mounted on the mask stage 6, and the entire surface is scanned by moving the mask stage in the X direction and in the Y direction perpendicular thereto.

  As a photomask to be inspected for defects, a binary type photomask in which two types of mask patterns are formed: a light shielding pattern formed of a chromium film that shields exposure light and a light transmission pattern that transmits exposure light. Or a phase shift mask on which two types of mask patterns, a halftone pattern formed of a halftone film formed on a glass substrate and functioning as a phase shifter, and a light transmission pattern that transmits exposure light are formed Are subject to inspection.

  The transmitted light emitted from the photomask 5 is collected by the objective lens 7 and enters the image sensor 10 through the half mirror 8 and the imaging lens 9. For example, a TDI sensor is used as the imaging element, and a transmission image of the photomask is captured.

  A second illumination light source 11 for capturing a reflected image of the photomask is disposed. As the second illumination light source, a light source that emits light having a wavelength different from that of the first illumination light source can be used. Alternatively, light having the same wavelength emitted from the mercury lamp used as the first illumination light source can be used as an optical fiber. A light source that emits through can be used. The illumination light emitted from the second illumination light source 11 is reflected by the half mirror 8 and enters the surface of the photomask 5 through the objective lens 9 as a focused beam. The reflected light reflected from the surface of the photomask is collected by the objective lens 7 and enters the image sensor 10 through the half mirror 8 and the imaging lens 9. Then, a reflected image of the photomask is captured by the image sensor 10.

  Next, the transmission / reflection simultaneous illumination image will be described. Both the 1st illumination light source 1 and the 2nd illumination light source 11 are operated, the illumination light for transmission is projected from the back surface side of the photomask 5, and the illumination light for reflection is projected simultaneously from the surface side. The transmitted light emitted from the photomask 5 enters the image sensor 10 through the objective lens, the half mirror, and the imaging lens. Further, the reflected light reflected by the surface of the photomask also enters the image sensor 11 via the objective lens, the half mirror, and the imaging lens. Therefore, on the image sensor, a reflection image and a transmission image of the same part of the photomask are formed so as to overlap each other, and a composite image obtained by combining the transmission image and the reflection image is captured.

  In the case of defect inspection using a transmission image, defects mainly due to foreign matter or growth foreign matter adhering to the light transmission pattern and the halftone pattern are detected. In the case of defect inspection using a reflection image, A defect due to repair unevenness is detected. In the case of defect inspection by simultaneous transmission and reflection illumination, both the foreign matter adhering on the light shielding pattern and the defect due to the adhering foreign matter and the growing foreign matter on the halftone pattern are detected. Therefore, the illumination conditions are determined according to the purpose of the defect inspection.

  The analog image signal output from the image sensor 10 is converted by the A / D converter 12 into a gradation signal having a predetermined luminance gradation (digital luminance signal). In this example, the A / D converter 12 converts an analog luminance image signal output from the imaging apparatus into, for example, an 8-bit (256 gradation) gradation signal. The 256 gradation signals output from the A / D converter are input to the signal processing device 13. The signal processing device 13 detects defects in the input gradation signal (digital luminance signal) by a die-to-die inspection method or a die-to-database inspection method. When a defect is detected, the image including the defect is stored in the defect memory together with the defect address information. Then, after the scanning of the entire surface of the photomask is completed, the image of the photomask including the defect is converted into a color image and displayed on the monitor 14 to review the defect.

  FIG. 2 is a diagram illustrating an example of a signal processing apparatus. The 256 gradation luminance image signal output from the A / D converter 12 is supplied to the defect inspection means 20. The defect inspection means 20 detects defects by, for example, a die-to-die inspection method or a die-to-database inspection method. When a defect is detected, a photomask image including the detected defect is stored in the defect memory 21 together with address information. That is, in the defect memory, the identification number of the detected defect, the address information, the defect and the surrounding luminance image are stored for each defect.

In reviewing the detected defect, the operator inputs parameters for creating a luminance / color conversion table via the input means 22 such as a keyboard. Input the following parameters as input parameters.
a. Photomask type Enter the type of photomask inspected, such as a binary photomask or a halftone photomask. Note that the type of photomask is not essential, and is input as necessary.
b. Imaging conditions Illumination conditions are used as imaging conditions when the photomask is imaged by the imaging device, in this example. That is, any one of reflected illumination, transmitted illumination, and transmitted / reflected simultaneous illumination is input.
c. The gradation value of the mask pattern The gradation value of 256 gradations for the mask pattern (light transmission pattern, halftone pattern, light shielding pattern) formed on the photomask is input. In the case of a binary type photomask, there are two types of mask patterns, a light shielding pattern that blocks exposure light and a light transmission pattern that transmits exposure light. In the case of a halftone type photomask, a light transmission pattern that transmits exposure light; It has two types of mask patterns, a halftone pattern that functions as a phase shifter. Therefore, gradation values for these two types of mask patterns are assigned. In this example, the gradation value of the light transmission pattern is the first gradation value, and the gradation value of the halftone pattern or the light shielding pattern is the second gradation value. For the first and second gradation values, the luminance value of illumination light emitted from each mask pattern is measured in advance for each illumination condition for various photomasks, and converted into gradation values via an A / D converter. Then, the obtained gradation value can be used. As an example, in this example, the following gradation values are assigned to various mask patterns.
(Halftone photomask)
Illumination condition First gradation value (light transmission part) Second gradation value (halftone part)
Transmitted light illumination 200 100
Reflected light illumination 10 200
Simultaneous reflection and transmission illumination 100 200
(Binary type photomask)
Illumination condition First gradation value (light transmission part) Second gradation value (light shielding pattern part)
Transmitted light illumination 200 10
Reflected light illumination 10 200
Simultaneous reflection and transmission illumination 200 100
d. Number of colors assigned to the luminance gradation between the first gradation value and the second gradation value For example, when a transmitted illumination light inspection is performed on a halftone photomask, the number of colors is one or more Enter. In the case of a binary type photomask, two or more colors are input. At this time, the number of border colors formed around the detected defect changes in accordance with the number of input colors. Therefore, when reviewing an image having a small luminance difference from the surrounding image of the defect, such as a defect caused by growth foreign matter adhesion, it is preferable to set a large number of colors to be assigned.

Next, the conversion table creation process in the conversion table creation means 23 will be described. In this example, a case will be described in which the inspection result of the transmitted light inspection is reviewed for the halftone photomask. FIG. 3 is a diagram showing an example of the conversion table created by the conversion table creating means 23, which will be described with reference to FIG.
The operator inputs a halftone photomask as the type of photomask inspected, and inputs transmitted light illumination as an illumination condition. In addition, as the gradation value (luminance value) of the mask pattern, 200 (256 gradation gradation values) is input as the first gradation value and 100 is input as the second gradation value. Further, three colors are input as the number of RGB colors assigned to the luminance gradation between the first gradation value and the second gradation value. Note that, for example, red and blue colors are assigned in advance to the gradation region of the gradation value corresponding to the light transmission pattern and the halftone pattern formed on the photomask.

The conversion table creating means 23 uses the luminance gradation between the first gradation value and the second gradation value and the number of assigned RGB colors to assign a gradation span to one color. Is calculated. The calculation formula is shown below.
(First gradation value−second gradation value) ÷ (number of colors + 1) × 2 = 50
As derived from the above formula, when three colors are assigned to the gradation area between the gradation value corresponding to the light transmission portion and the gradation value corresponding to the halftone portion, 50 gradations are assigned to each color. Tone spans are assigned. If the gradation span does not become an integer, the remainder of the division can be included in the center color, for example. Subsequently, a conversion curve defining the relationship between the luminance gradation and the color output is created for each color. As shown in FIG. 3, the conversion curve can be defined by a straight line connecting the gradation values at both ends of the gradation span and the peak value of the color output, or can be defined by various curves and straight lines such as a sine curve. be able to. When setting the conversion curve, it is preferable that the gradation values at both ends of each color are set so that the gradation value of the peak of the color output of the adjacent color becomes zero output or in the vicinity thereof. By defining the conversion curve in this way, it becomes possible to trim the outline of the detected defect with the primary color.

  Subsequently, the conversion table creation unit 23 assigns a color to each assigned color. When assigning colors, the colors are assigned so that adjacent colors are not the same.

  Further, the conversion table creation means assigns a color to a gradation area lower than the gradation value corresponding to the luminance value of the halftone portion. In this color assignment, as an example, the same color and gradation span assigned between the first gradation value and the second gradation value are sequentially set. In this way, the conversion table shown in FIG. 3 is completed.

  The generated conversion table is supplied to the luminance / color conversion means 24. The luminance / color conversion unit 24 converts the luminance image signal of the photomask received from the defect memory 21 into a color image signal using the conversion table, and outputs the color image signal to the monitor 14.

  FIG. 4 schematically shows an example in which an image including a defect (haze defect) caused by adhesion of a growth foreign substance formed in the light transmission part is converted into a color image using the conversion table shown in FIG. FIG. 4A shows a state in which a luminance image including a defect with a small luminance difference is displayed on the monitor, and FIG. 4B shows a gradation value shown along the II line for the detected defect. The defect due to the growth foreign matter has a characteristic that the brightness difference from the surrounding image is small and the brightness gradually changes from the periphery toward the inside. Therefore, it is difficult to clearly grasp the entire defect.

  A case where a luminance image is converted into a color image using the conversion table according to the present invention will be described. The gradation value of the light transmission part around the detected defect is 200, and is displayed in red. On the other hand, the gradation value of the defect image gradually decreases from the periphery of the defect toward the inside, and the gradation value decreases to about 150 inside the defect. At this time, as indicated by an arrow a in FIG. 3, the color output gradually changes from red to blue as the gradation value decreases from 200, and further changes to green through the blue primary color region. Therefore, the edge portion of the defect in which the gradation value gradually decreases is displayed mainly as a border image of blue color. Therefore, when an image with a small luminance difference from the surroundings is displayed as a luminance image on the monitor, such as a defect caused by growth foreign matter adhesion, it is displayed as a green image with a bordered blue area in the red surrounding image. Is done.

  Next, a description will be given of photographic data in which a haze defect actually formed on a photomask using the image display method according to the present invention is actually displayed on a monitor. FIG. 5 shows an actual photograph in which a haze defect detected using a defect inspection apparatus is actually displayed on a monitor. The defect inspection apparatus used was a photomask defect inspection apparatus “MATRICS series” manufactured by Lasertec. As an inspection condition, detection was performed by simultaneous illumination in which transmitted light illumination and reflected light illumination were simultaneously performed. FIG. 5A is a photograph displaying the detected haze defect as a monochrome image, and FIG. 5B is a photograph displaying the same image data by a conventional pseudo color display method. Is a photograph displayed using the image display method according to the present invention. In FIG. 5C, since the border around the defect is difficult to see on the drawing, the periphery of the defect image is overwritten with a black line. The original photographs in Figs. 5 (A) to 5 (C) were submitted separately as property submissions. For actual monochrome and color photographs corresponding to Fig. 5, please refer to the property submission.

  As shown in FIG. 5A, when the haze defect detected by the defect inspection apparatus is displayed as a monochrome image, the haze defect is displayed as a thin gray image with respect to the surrounding normal part. Therefore, it is an image that is difficult to see with the naked eye when displayed on a monitor. As shown in FIG. 5B, when the image is displayed using the conventional pseudo color display method, it is a color image of the same color as the surrounding image (yellow color image) and is a light gray image of the same color, that is, It is displayed as a yellow shade image. The haze defect is an image that is difficult to visually recognize with the naked eye because it is displayed as a grayscale image of the same color as the surroundings. As shown in FIG. 5C, when the image is displayed using the image display method according to the present invention, the normal part is displayed as purple (mixed color of red and blue), and the central portion of the haze defect is displayed as a green image. Displayed, a dark red border is formed around the green image. Accordingly, the haze defect is displayed as a color image in which the periphery of the center portion displayed in green is bordered with a red image.

  In the conventional pseudo color display method for displaying in three colors of RGB, since the peripheral portion of the defect image with a small luminance difference from the surroundings is displayed with the same color shading difference, the peripheral edge of the defect is similar to the luminance display image. It was difficult to clearly identify the defect, and it was difficult to identify the size and shape of the defect. On the other hand, in the image display method according to the present invention, the inside and the periphery of the detected defect and the periphery of the defect are displayed in different colors, and the defect periphery is displayed as an edged image. The size and shape can be clearly seen.

  Next, a modification of the conversion table creation unit will be described. In the embodiment described above, the type of photomask, the illumination conditions, the gradation values assigned to the mask pattern, and the number of RGB colors are used as parameters for creating the conversion table. However, since the gradation value of the mask pattern is almost common in many photomasks, the gradation value of the mask pattern (the gradation value of the light transmission portion, the gradation value of the halftone portion, and the gradation value of the light shielding pattern). (Tone value) can be stored in advance in the conversion table creation means, and can be calculated using the stored tone value of the mask pattern.

  Further, instead of the number of RGB colors allocated between the first gradation value and the second gradation value, it is also possible to input the gradation span of each allocated color. In this case, by inputting the gradation span, the conversion table creating means defines the conversion curve based on the inputted gradation span and calculates the assigned RGB gradation number. Therefore, either the number of colors or the gradation span can be used as the input parameter, or both the number of colors and the gradation span can be input.

DESCRIPTION OF SYMBOLS 1 1st illumination light source 2 Condensing lens system 3 Total reflection mirror 4 Condensing lens 5 Photomask 6 Mask stage 7 Objective lens 8 Half mirror 9 Imaging lens 10 Imaging element 11 2nd illumination light source 12 A / D converter 13 Signal Processing Device 14 Monitor 20 Defect Inspection Unit 21 Defect Memory 22 Input Unit 23 Conversion Table Creation Unit 24 Luminance / Color Conversion Unit

Claims (9)

An imaging device that captures an image of an object to be inspected under various illumination conditions;
An A / D converter that converts a luminance image signal output from the imaging device into a gradation signal having a predetermined luminance gradation;
A signal processing device that detects a defect of the inspection object using an output signal from the A / D converter and outputs a color image of the inspection object including the detected defect, the signal processing device comprising: ,
A defect detection means for detecting a defect of the inspection object from an output signal output from the A / D converter;
A memory for storing luminance image information of the inspection object including the detected defect;
The imaging conditions of the imaging device, the first and second gradation values assigned to the two types of patterns formed on the object to be inspected under each imaging condition, and the first gradation value, An input means for inputting a parameter including the number of RGB colors or a gradation span assigned during a luminance gradation between the second gradation values;
Conversion table creating means for creating a luminance / color conversion table that defines the relationship between the gradation value and the color output based on the input parameters;
A luminance / color conversion unit that receives the conversion table created by the conversion table creation unit and the luminance image signal of the photomask stored in the memory and converts the luminance image signal into a color image signal; A feature defect inspection device. An imaging device that captures an image of a photomask under various illumination conditions;
An A / D converter that converts a luminance image signal output from the imaging device into a gradation signal having a predetermined luminance gradation;
A signal processing device that detects a photomask defect using an output signal from the A / D converter and outputs a color image of the photomask including the detected defect, the signal processing device comprising:
Defect detection means for detecting a photomask defect from an output signal output from the A / D converter;
A memory that stores luminance image information of the photomask including the detected defect;
The imaging conditions of the imaging device, the first and second gradation values respectively assigned to two types of mask patterns formed on the photomask in each imaging condition, and the first gradation value and the first gradation value Input means for inputting parameters including the number of RGB colors or gradation span assigned during luminance gradation between two gradation values;
Conversion table creating means for creating a luminance / color conversion table that defines the relationship between the gradation value and the color output based on the input parameters;
A luminance / color conversion unit that receives the conversion table created by the conversion table creation unit and the luminance image signal of the photomask stored in the memory and converts the luminance image signal into a color image signal; A feature defect inspection device. 3. The defect inspection apparatus according to claim 2, wherein the photomask to be inspected is a halftone photomask in which two types of mask patterns of a light transmission pattern and a halftone pattern functioning as a phase shifter are formed. Or, using a binary photomask in which two types of mask patterns of a light transmission pattern and a light shielding pattern are formed,
When displaying the image of the halftone photomask, the gradation value assigned to the light transmission pattern is used as the first gradation value, and the gradation value assigned to the halftone pattern is used as the second gradation value. Use
When displaying the binary photomask image, the gradation value assigned to the light transmission pattern is used as the first gradation value, and the gradation value assigned to the light shielding pattern is used as the second gradation value. A defect inspection apparatus characterized by being used.   4. The defect inspection apparatus according to claim 2, wherein illumination conditions of the imaging device are used as the imaging conditions, the imaging device projects reflected illumination light toward a photomask to be inspected, and reflected illumination light. A defect inspection apparatus characterized by selectively imaging a transmission image or a reflection image of a photomask.   5. The defect inspection apparatus according to claim 4, wherein the imaging device simultaneously projects transmitted illumination light and reflected illumination light toward a photomask to be inspected, and can capture a transmitted and reflected simultaneous illumination image of the photomask, and illumination conditions. A defect inspection apparatus that selectively captures a transmission image, a reflection image, or a transmission / reflection simultaneous illumination image of a photomask by changing   The defect inspection apparatus according to any one of claims 1 to 5, wherein the luminance / color conversion table includes a conversion curve that defines a relationship between a luminance gradation range and a color output for each color, A defect inspection apparatus, wherein a color output of an adjacent conversion curve is zero at a luminance value that is a peak of the color output of each color conversion curve. An image display method for displaying an image of an inspection object imaged as a luminance image by an imaging device on a monitor as a color image,
Converting an output signal output from the imaging device into a gradation signal having a predetermined luminance gradation using an A / D converter;
Storing a luminance image of the object to be inspected in a memory using an output signal from the A / D converter;
Imaging conditions of the imaging device when capturing an image of the inspection object, first and second gradation values respectively assigned to two types of patterns formed on the inspection object for each imaging condition; And inputting a parameter including the number of RGB colors or a gradation span assigned in a luminance gradation between the first gradation value and the second gradation value;
Creating a luminance / color conversion table that defines the relationship between the luminance gradation and the color output using the input parameters;
Converting the luminance image signal into a color image signal using the generated luminance / color conversion table and the luminance image of the photomask stored in the memory;
And supplying the converted color image signal to a monitor to display a color image of the object to be inspected. The defect image display method according to claim 7, wherein the inspection object is a halftone photomask in which two types of mask patterns of a light transmission pattern and a halftone pattern functioning as a phase shifter are formed. Or, using a binary photomask in which two types of mask patterns of a light transmission pattern and a light shielding pattern are formed,
When displaying the image of the halftone photomask, the gradation value assigned to the light transmission pattern is used as the first gradation value, and the gradation value assigned to the halftone pattern is used as the second gradation value. Use
When displaying the binary photomask image, the gradation value assigned to the light transmission pattern is used as the first gradation value, and the gradation value assigned to the light shielding pattern is used as the second gradation value. An image display method characterized by being used.   The image display method according to claim 8, wherein an illumination condition of an imaging device is used as an imaging condition when imaging the image of the photomask, and a transmission image, a reflected image of the photomask is used as a luminance image of the inspection object, Alternatively, an image display method using any one of the transmission / reflection simultaneous illumination images.