JP2792517B2 - Sample inspection method - Google Patents

Description

The present invention relates to a shadow mask used for a cathode ray tube for a color television, a color separation filter for a color imaging device, a color filter for a liquid crystal display panel, and a mesh electrode used for an electron tube. , VDT filters, mesh filters for filtration devices, rotary encoders, linear encoders, photomasks for ICs, Fresnel lenses, lenticular lenses, etc. Scratches of industrial products that are regularly and repeatedly arranged in the dimensional direction, or industrial products in which unit patterns are repeatedly arranged while the optical properties, shapes, and arrangement pitches in the one-dimensional and two-dimensional directions are gradually changed. With defects, irregularities, transmittance, and patterns such as pinholes, black spots, The present invention relates to a sample inspection method for automatically inspecting glass, colored films, and the like.

[Conventional technology]

Conventionally, defect inspection of industrial products in which unit patterns are periodically and repeatedly arranged is usually performed by visual or microscopic observation, but in such a method, in order to inspect a large number of products, Various inspection methods have been proposed because they require a great deal of labor and lack sensor accuracy and reliability due to sensory tests.

For example, in the case of industrial products having a periodic pattern with an equal pitch arrangement, pattern recognition is performed by examining video signals obtained by a microscope imaging device that sufficiently resolves the arrangement unit and the shape of the defect. Defects are detected by means such as comparing a signal obtained by similarly photographing a pattern without a defect.

For products with periodic apertures, such as mesh-shaped electrodes for electron tubes, defects are detected by optical Fourier transform spatial filtering using the light diffraction phenomenon due to the periodic pattern when irradiating coherent light. I have.

Next, with reference to FIG. 6, a method conventionally proposed for efficiently inspecting a periodic pattern with high accuracy will be described.

In order to detect an abnormality in the opening area of a pattern having a periodic opening as a unit pattern 51 as shown in FIG. 7, a transmission illuminating unit composed of an incandescent lamp 48 turned on by a DC power supply 49 and a diffusion plate 47 is used. The pattern 46 to be inspected is illuminated, and the inspection area is photographed by the TV camera 41. The image processing device 42 A / D converts the output signal of the TV camera into digital image data,
Various image processing including addition and subtraction of screens is performed at high speed by the frame memory and the arithmetic unit. The control device 43 controls the image processing device 42 and the pattern moving mechanism including the XY stage 50 and the driving mechanism 45 to move the pattern. In FIG. 7, 52 and 53 are unit patterns having defects.

In FIG. 6, shooting conditions under which the change due to the unit aperture of the video signal by the TV camera 41 is negligible, for example, so that about ten unit openings 11 are included in the pattern area corresponding to one pixel, and the direction in which the pattern is moved and changed is a The case where the displacement distance of the pattern is an integral multiple of the pixel pitch in the scanning line direction 41 will be described with reference to FIG.

The light transmittance distribution on a straight line passing through a place where the pattern has a defect is, for example, as shown in FIG.
A defect 54 having an opening area larger than that of the normal pattern 51, that is, a change 54 in light transmittance due to a white defect, as shown in FIG.
As shown by 52, a defect having a smaller opening area than the normal pattern 51, that is, a change 55 in light transmittance due to a black defect is detected. FIG. 8 (b) shows a video signal scanned on the same line as in FIG. 8 (a), which shows a gradual signal change (shading) due to uneven illumination of the pattern, uneven sensitivity of the imaging surface, and the like. ) And random noise generated in the video signal processing device, and local changes 56 of the signal due to dust or the like attached to the optical system.

By adding a plurality of frames to such a video signal, when the number of additions is N, the ratio of the random noise component is (FIG. 8 (c)). next,
When the same screen addition processing is performed by displacing the pattern,
As shown in FIG. 8 (d), the signal due to a defect on the pattern is also moving along with the movement of the pattern, but the position of the signal 56 due to shading of the imaging system, dust of the optical system, etc. has not changed. Therefore, when the data shown in FIG. 8D is subtracted from the data shown in FIG. 8C, the signal 56 due to shading or dust contained in both data is erased, and the signal 56 due to the change in the light transmittance of the pattern is removed. Only the reduced random noise component remains, and as a result, the signal due to the defect appears at the position separated by the number of pixels according to the amount of movement of the pattern and the value difference from the average value in the vicinity is almost the same, and the sign is inverted. The order of inversion is reversed depending on the type of defect (white defect, black defect).

In the image data processed as described above, the brightness of only the defective portion is locally changed, so that it can be easily recognized as a defect when observed on a monitor. The types of defects can be identified in this order.

In addition, in the case of a shadow mask, not only the shape of the opening on the horizontal projection plane, but also abnormalities in the cross-sectional shape of the opening and scratches on surfaces other than the opening are targets for defect detection. It is required that foreign matter such as dust adhering to the surface should be detected separately from other defects.
This will be described with reference to FIG. 10 and FIG.

In FIGS. 9 and 10, if transmitted light illumination (transmitted bright field illumination) is used, a defect opening having a large opening area is regarded as a white defect, a defect opening having a small opening area, and a foreign substance at a position which blocks the opening. 61 can be detected as black defects respectively,
Further, if the reflected illumination light (reflective dark field illumination) is used, the flaw 62 and the foreign substance 61 on the shadow mask surface can be detected, and the foreign substance blocking the opening can be detected as a white defect. Defect detection is performed using these different illumination methods, and the position and type of the detected defect (white defect, black defect)
By examining data such as the signal level and the signal level, the type of defect can be identified more finely.

Further, as shown in FIG. 11, if the photographing method is set to be oblique photographing, it becomes possible to detect a sectional shape defect of the opening that cannot be detected by photographing from the vertical direction. Defect detection is performed a plurality of times sequentially from at least two or more directions as a rotation axis. If no defect is detected in any of these cases, the defect as shown in FIG. It can be determined that there was no 63.

 Next, a method of moving a pattern will be described.

As shown in FIG. 12, there is the object to be inspected located P ₀ to P _8, the movement of the aforementioned corresponding to P ₀ and P ₁ in FIG. In this case, when processing is performed only on image data obtained from two locations, a defect caused by a change in the aperture ratio in the H direction in the figure is detected, but a change in another direction, for example, the V direction is detected. There is a defect that the detection sensitivity is anisotropic that a defect that is large and has a small change in the H direction is not detected. For example, P ₀ in FIG.
Based on the image data obtained by imaging at P ₁ , P ₂ , P ₃ , and P ₄ , P ₀
And P _1, P ₀ and P _2, P ₀ and P _3, it is possible to eliminate the anisotropy by performing predetermined processing for each of a combination of P ₀ and P _4. Further, even if the detected based on the image data sum of the image data at each position which are arranged on the circumference is obtained by subtracting the image data of the center position P ₀ as P ₈ from P ₁ in FIG. Similarly, anisotropy can be avoided, and a value approximating the curvature of the brightness distribution that is easily visually responsive is obtained, and the inspection result is close to a visual inspection. The image data obtained by imaging at each position includes the above-described random noise component, shading component, and fixed noise component. The random noise component is obtained by adding a plurality of frames at each moving position. Can be suppressed by
Further, the shading component and the fixed noise component can be eliminated by performing the operation of the image data so that the total number of frames of the image data becomes “0”. For example, 32 frames at a position P ₀ of Figure 12, performs addition of 8 frames in P _1, is subtracted image data in P ₀ image data from the quadruple image data at P ₁ both The sum of image data is "0"
And the shading component and the fixed noise component are eliminated. Further, at each position P ₈ from P _1, when performing the screen addition of each four frames, since the addition result of the image data P ₈ from P ₁ corresponds to the sum of the image data of 32 frames P _By subtracting from the result of adding the image data for 32 frames at the position of ₀ , the shading component and the fixed noise component are similarly eliminated, and the brightness distribution
A dimensional derivative is obtained. Furthermore, when smoothing is applied to the image data in which the shading component and the fixed noise component are reduced by the above processing, the random noise component is further reduced, and it becomes possible to detect an extremely slight uneven component. It is also possible to suppress a change in image data due to a minute defect or short-period irregularity.

A method has also been proposed for automatically determining whether a product is good or bad based on image data that has been subjected to image processing as described above.

FIG. 13 shows an example of measurement under the same conditions as in FIG.
13 (a) to 13 (e) are the same as FIG. 8, where A is a portion where the aperture ratio changes gradually, B is a portion where the aperture ratio changes periodically, and C is a portion where the aperture ratio changes. A large and isolated portion, D, is a local change component (fixed noise component) of the video signal due to contamination of the optical system. FIG. 13 (e) shows that components due to the change in the aperture ratio of the test object are extracted. In this case, the moving amount of the test object differs depending on the state of the unevenness to be detected. However, the moving amount of the test object increases with an increase in the cycle of the change in the unevenness, and is converted into the number of pixels of the frame memory. From about 2 pixels to about 20 pixels. Next, subtracting the average value of the image data of a sufficiently large area from the image data of FIG. 13 (e) results in the result shown in FIG. 13 (f), and the image data of FIG. 13 (g) is obtained by differentiating a predetermined threshold value according to the nature of the unevenness to be detected.
Unevenness can be automatically detected by setting S ₁ and S ₂ . FIG. 13 (h) sets thresholds S ₁ and S ₂ for the image data of FIG. 13 (g), and shows “1” when the threshold value is exceeded and “0” when the threshold value is not exceeded. It is quantified data. Then, to detect the isolated unevenness as shown in C of FIG. 13 (a), the product if a defect, the threshold such as the S ₁ to the image data of FIG. 13 (f) or (g) Should be set. In the case of detecting a periodically changing unevenness as shown by B in FIG. 13 (a) to determine a product defect, the image data of FIG. 13 (f) or (g) is
Setting a threshold such as S _2, as shown in FIG. 13 (h) 2
After the conversion into the coded data, the neighboring pixels are added to convert the data into the number of unevenness in a predetermined area as shown in FIG. 13 (i), that is, the density data. _Three
By setting and comparing, it is possible to detect only the periodically changing unevenness, and determine the quality of the product from the result.

Further, in order to measure the light transmittance and distribution of light-transmitting articles and the aperture ratio and distribution of industrial products having periodic openings such as shadow masks, meshes, and cloths, as shown in FIG. Irradiation light was received by the light receiver 71, and the light transmittance was measured based on the output of the light receiver in the case where the sample was interposed and the case where the sample was not interposed, or in the light-shielded state.

[Problems to be solved by the invention]

However, in a method of examining a video signal obtained by a microscope imaging apparatus, mechanical accuracy is required according to the size of a defect to be detected, so that the apparatus becomes expensive, and microscopic imaging is performed. There is a problem that the size of a screen that can be processed at one time becomes small, and it takes a lot of time to inspect the entire pattern to be inspected.

In the optical Fourier transform spatial filtering method using the diffraction phenomenon of light due to a periodic pattern, although the inspection speed and the detection density are excellent, a spatial filter must be created for each pattern to be inspected, and the precision is high. However, there is a problem that the size of the defect opening can not be discriminated from the reference value of the defect opening, although the apparatus becomes expensive due to the necessity of a special optical system.

In addition, in the method shown in FIGS. 6 to 13, when there is a change in the transmittance, it is not known whether the change is due to a defect in the pattern or due to the adhesion of noise or dust of the imaging device. Since it is necessary to repeat the movement of the pattern and the integration of the frame, it takes a long time to measure, and only by watching the change in the transmittance, the magnitude of the transmittance itself,
Or the distribution could not be measured.

In the method shown in FIG. 14, for example, as shown in FIG. 15, when measuring the transmittance of a shadow mask used in a cathode ray tube, the transmittance is originally determined in the beam direction in the cathode ray tube. However, when trying to measure with a set of emitters and receivers, it is necessary to mount the emitters and receivers at an angle, as shown in Fig. 16, and the structure becomes complicated. there were.

In each method, individual items can be inspected, but not all items can be inspected from image data obtained by a single imaging.

SUMMARY OF THE INVENTION The present invention is directed to solving the above problems, and provides a sample inspection method capable of performing an inspection of various items in a short time by image processing from image data obtained by imaging once for each sample. The purpose is to do.

[Means for solving the problem]

For this purpose, the present invention relates to a step of forming an optical image of an illumination unit on a light receiving surface of an imaging device by an optical imaging unit to capture an image, and disposing a sample between the imaging device and the illumination unit and illuminating the sample with the illumination unit. Imaging the transmitted light image of the sample on the light receiving surface of the photographing device by the optical imaging means. The image data of the illuminating unit obtained by the imaging and the image data of the transmitted light image of the sample are processed by the arithmetic unit. Calculating the transmittance of the sample by using the obtained transmittance distribution data, and inspecting the transmittance and / or defect and / or unevenness of the sample based on the determined transmittance distribution data. As a means, a cooled CCD is used as a camera or the like, and image data obtained by imaging the illumination unit is stored and used for each sample. Detection is performed under imaging conditions where moiré does not occur between Further, a differentiation process or a smoothing process is performed on each image data, and an imaging condition is set so that the level of each image data is substantially equal. Inspect for defects, pattern irregularities, and / or transmittance.

[Action]

The present invention obtains a transmittance distribution from image data obtained by capturing a light source in advance and image data obtained when the sample is illuminated, and detects a defect, pattern unevenness, transmittance, or the like in a single measurement from an abnormality in the transmittance distribution. Inspection is performed.By using a cooled CCD camera, dark current and noise can be greatly reduced to a negligible level, and the absolute value of transmittance can be measured, eliminating noise components as before. It is not necessary to move the sample to take the difference, thereby greatly reducing the inspection time and performing image processing such as differentiation processing and smoothing processing on the obtained image data.
Inspections for all items can be performed in a single measurement.

〔Example〕

 Hereinafter, embodiments will be described with reference to the drawings.

FIG. 1 is a diagram showing one embodiment of the present invention using a cooled CCD camera as an imaging device, wherein 1 is a cooled CCD camera, 2 is an image processing device, 3 is a lens, 4 is a shutter,
Reference numeral 5 denotes a shutter driving device, 6 denotes a sample, 7 denotes an illumination device, and 8 denotes a power supply.

The cooled CCD camera 1 is a CCD camera that can be cooled by an electronic cooling method or the like to greatly reduce dark current and noise to a negligible level and perform long-time exposure in a dark area. It is characterized by good image quality and can clearly show dark areas with high image quality that could not be projected with a conventional high-sensitivity television camera.
Pixels can detect up to several photons per second. If a cooled CCD camera having such excellent performance is used as a photographing device, highly accurate measurement can be performed as compared with a case where a normal CCD camera is used.

Using such a CCD camera 1, a sample 6 is illuminated by an illumination device 7 driven by a power supply 8, and the transmitted light is imaged through a lens 3. In this case, conditions such that moire does not occur between the periodic pattern and the pixels of the imaging device, for example, the focus is blurred by the lens 3,
A plurality of unit patterns are included in a pattern area corresponding to a pixel.

At this time, if the image data taken without the sample is I ₁ , the image data taken with the sample in is I, and the image data taken with the shutter 4 closed is I ₀ , the transmittance T of a point on the sample is Can be calculated as Here, I, I ₀ , and I ₁ are the image data at the corresponding positions. If the image data when the shutter is closed (light amount = 0) can be ignored, the transmittance can be obtained as T = I / I ₁ . This calculation can be performed by an inter-screen calculation after each image data is stored in the frame memory by the image processing device 2. If the number of pixels of the cooled CCD camera is 512 × 512, about 250,000 transmittance data can be obtained by this calculation. Since the image data thus obtained does not include components such as shading and dust of the imaging system, the image data is subjected to image processing according to each inspection item as described above, so that the image data can be measured in one measurement. An inspection can be performed. The light source can be stably keep the image data I ₁ is stored in the memory if, which it is not necessary to perform measurement for each sample when to use, to shorten the measurement time.

With a normal solid-state image sensor or image pickup tube, the linearity of the light amount and the video signal is not sufficient, and the effect of thermoelectrons is large, making high-precision measurement difficult. Is the spatial resolution, linearity, S / N
Is good, but there is a problem that the imaging time is long (about 1 ms per pixel, about 4 minutes as 250,000 pixels)
In the present invention, by using the cooled CCD camera 1, an image can be captured in about several seconds and the linearity is improved.

Defect detection is performed by differentiating the image data to obtain image data equivalent to the result of conventional imaging (frame integration) → sample movement → imaging (frame integration) without moving the sample. After that, if the same image processing is performed, the defect can be detected. In this case, for example, feature extraction may be performed by using a spatial filter for differential processing as shown in FIGS. 2 (a), 2 (b) and 2 (c). One-dimensional edge extraction can be performed by using the spatial filter shown in FIGS. 2A and 2B, and two-dimensional edge enhancement can be performed by using the spatial filter shown in FIG. 2C. it can. And the variation of the image data,
The spatial filter may be selected in accordance with the resolution characteristics, the nature of the defect to be detected, and the like. The white / black defect is identified by using the spatial filter shown in FIG. , Can be identified by the size of the pixel of interest with respect to surrounding pixels.

Also, by using the spatial filter of FIG. 2 (c) for the detection and determination of unevenness, the same result as that of performing a series of imaging operations as described in FIG. 13 is obtained. Similarly to the above, detection and determination can be performed by performing screen addition processing and threshold setting.

By the way, in the transmittance measurement method shown in FIG. 1, since a variation in data for each pixel directly affects the data, image data of a small area around the measurement point, for example, 5 It is necessary to calculate an average value such as × 5pix to 10 × 10pix. When the number of measurement points is limited, the processing time by the CPU requires less time.However, when the number of measurement points is large, the processing time by the CPU requires a lot of time. After performing a smoothing filter process, which is one type of image processing, on a given frame memory and reading out predetermined image data, the speed can be increased.

As described above, the cooling type CCD is characterized by the linearity of the video signal to the integrated light quantity is good, when measuring low transmittance sample image data I ₁ captured without sample Even if the value is set to a value close to max, the value of the image data I captured with the sample put in becomes small, and a slight error in linearity, a dark current, and the like affect the transmittance value.

For this reason, when imaging I and I ₁ , it is more accurate to image the two image data levels so that the two image data levels are almost equal and have a sufficient size. , A correction operation is required.

As one method for that, the exposure time at the time of I ₁ imaging,
By operating the shutter so as to be 1 / T of I, I and I ₁ can be made substantially the same value.

However, the mechanical shutter has a variation in operation time, and therefore has a disadvantage that an error increases when the shutter opening time is short, and when this error cannot be ignored,
It is sufficient to measure the shutter open time and correct the data based on the measured value.

FIG. 3 is a view showing another embodiment of the present invention for realizing this, and the same numbers as those in FIG. 1 indicate the same contents. In the figure, 9 is a half mirror, 10 is an optical sensor, 11
Is a measuring device.

In the present embodiment, the exposure time is obtained by detecting a part of the light at the time of imaging by the half mirror 9 with the sensor 10 and measuring the time during which the detection signal is obtained by the measuring device 11. Correcting the data by way exposure time obtained, it is possible to substantially equalize the two image data level of I and I _1.

Further, by changing the accumulation time of the cooled CCD, for example, it may be equal to the level of the I and I ₁ by lengthening towards the image data I captured put sample. In this case, the time can be set with sufficient accuracy. However, when the light transmittance is low, since the time for imaging I ₁ is I / T times that of I, for example, the transmittance is 0.1.
In the case of about%, it takes 1000 times as long.

Also it can be changed brightness of the light source at the time of imaging of the I and I ₁ obtain similar results.

In the method using the conventional light emitting and receiving device shown in FIG. 14 and FIG. 16, since the measurement points are limited, in order to obtain transmittance data at a predetermined position of a sample of a predetermined shape such as a shadow mask, Had to be measured after positioning the sample with respect to the measurement system. On the other hand, in the method of the present invention, since the transmittance data is obtained as high-resolution image data, this image data is processed to automatically recognize the position and rotation of the sample and obtain data at a predetermined position. Automatic measurement can be easily performed. Also, the change of the measurement symmetrical type can be dealt with simply by changing the program without mechanical adjustment.

FIG. 4 is a diagram showing a measuring method in a case where a change in a measured value such as variation, variation, drift, or the like of illumination light poses a problem.

In this embodiment, the field of view of the sample 6 by the illumination device 7
21 is enlarged as shown in the figure, and a reference plate 22 having a constant transmittance is arranged in the imaging region so that there is a portion not blocked by the sample, and image data of the reference plate is read for each image data. In this way, for example, if the intensity of the illumination light fluctuates, the exposure amount of the portion of the reference plate 22 also fluctuates in the same manner, so that correction is performed using the data here to eliminate the influence of the fluctuation of the illumination light. And reproducibility can be improved.

The transmittance measurement of the shadow mask must be performed in the beam direction inside the cathode ray tube as described above,
The measuring method in this case will be described with reference to FIG.

FIG. 5 is a view showing another embodiment of the present invention, in which 31 is a light source, 32 is a Fresnel lens, and 33 is a shadow mask.

In the figure, a shadow mask is illuminated and exposed with light from a light source 31. At this time, by selecting a photographing angle in relation to a distance to a sample and a photographing area of a cooled CCD camera, a beam direction in the cathode ray tube with respect to the shadow mask is changed. It can be measured at an approximate angle θ.

In this case, when parallelism of the illumination light at each point in the measurement area is required, a large-area sample such as a shadow mask or an aperture grille can be formed by using the Fresnel lens 32 as a condenser lens as shown in the figure. It can be measured with a simple lighting device.

In addition, although the inspection method of the periodic pattern has been described above, an image having a uniform signal level can be obtained when an image is captured without a periodic pattern, such as a glass or a transparent film having a colored layer. If it is, the present invention can be applied.

〔The invention's effect〕

As described above, according to the present invention, a transmittance distribution is obtained from image data obtained by capturing a light source in advance and image data obtained when the sample is illuminated. The inspection of unevenness, transmittance, etc. is performed.By using a cooled CCD camera, dark current and noise can be greatly reduced to a negligible level, and the absolute value of transmittance can be measured. In this way, it is not necessary to move the sample to remove the noise component and take the difference, so that the inspection time can be greatly reduced, and image processing such as differentiation processing and smoothing processing can be performed on the obtained image data. By doing so, it is possible to inspect all items with one measurement. If the light source is stable, the stored image data can be used as the image data without the sample, and various inspections can be performed, thereby enabling high-speed automatic inspection. In the case of a shadow mask, the exchange of the sample and the detection determination process proceed in parallel in 1 second of imaging, so that an automatic inspection of several seconds cycle is possible. If it is necessary to improve the data accuracy for each screen, frame integration may be performed. When the method is applied to a shadow mask or an AG (Avercap grill), inspection can be performed efficiently, and the beam direction can be improved. There is an advantage that can be inspected. Further, in the inspection method of the present invention, the depth of focus does not matter because, for example, the focus is blurred, so that moire does not occur between the periodic pattern and the pixels of the imaging device. It is possible.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing a spatial filter, FIG. 3 is a diagram showing another embodiment of the present invention in which an exposure time is measured, and FIG. FIG. 5 is a view showing another embodiment of the present invention in which fluctuations in illumination light and changes in measured values are corrected, FIG. 5 is a view showing another embodiment of the present invention in which a photographing angle is set, and FIG. FIG. 7 is a diagram for explaining a conventional periodic pattern inspection method, FIG. 7 is a diagram for explaining a periodic pattern and its defect, FIG. 8 is a diagram for explaining a conventional detection method, and FIG. FIG. 10, FIG. 11 is a diagram for explaining an illumination method, FIG. 12 is a diagram for explaining a pattern moving method, FIG. 13 is a diagram for explaining a method for automating inspection, FIG. 14 is a diagram showing a conventional transmittance measuring method using a light emitting and receiving device, and FIG. 15 is a diagram showing an incident angle of a beam with respect to a shadow mask. FIG. 16 is a diagram showing a conventional example for setting at an angle the emitter and receiver to the sample. DESCRIPTION OF SYMBOLS 1 ... Cooled CCD camera, 2 ... Image processing apparatus, 3 ... Lens, 4 ... Shutter, 5 ... Shutter drive device, 6 ... Sample,
7 lighting device, 8 power supply, 9 half mirror, 10 optical sensor, 11 measuring device, 31 light source, 32 Fresnel lens,
33 ... Shadow mask.

Claims (7)

(57) [Claims] A step of forming an optical image of an illumination unit on a light-receiving surface of a photographing device by an optical imaging unit to capture an image; and disposing a sample between the photographing device and the illumination unit to collect a sample illuminated by the illumination unit. A step of imaging the transmitted light image on the light receiving surface of the photographing device by the optical imaging means and capturing the image, using an arithmetic unit to convert the image data of the illuminating unit obtained by the imaging and the image data of the transmitted light image of the sample using an arithmetic unit Calculating the transmittance of the sample, and determining the transmittance of the sample and / or the defect based on the determined transmittance distribution data.
Alternatively, a sample inspection method including a step of inspecting for unevenness. 2. The sample inspection method according to claim 1, wherein the imaging means is a cooled CCD. 3. The sample inspection method according to claim 1, wherein image data obtained by imaging the illumination unit is stored and used for each sample. 4. The detection according to claim 1, wherein the detection is performed under an imaging condition in which moire does not occur between the periodic pattern and pixels of the imaging device.
Inspection method of the described sample. 5. The sample inspection method according to claim 1, wherein each image data is subjected to a differentiation process or a smoothing process. 6. The sample inspection method according to claim 1, wherein the imaging conditions are set so that the levels of the respective image data become substantially equal. 7. The method according to claim 1, wherein the sample is a shadow mask.