JP4899306B2 - Periodic pattern unevenness inspection device - Google Patents

Description

  The present invention relates to an unevenness inspection apparatus for products having a periodic pattern.

  In a conventional periodic pattern unevenness inspection, a transmitted light image is captured using coaxial transmitted illumination or planar illumination (see, for example, Patent Documents 1 and 2), and the intensity (brightness) of light in each image is determined. This is a method of visually recognizing the uneven portion and the normal portion. For this reason, the difference in light intensity between the uneven part and the normal part is originally small, that is, by devising an intensity difference processing method for images with low contrast, the difference is expanded and the uneven part is extracted and inspected. ing.

  However, in the above-described prior art, in the imaging of the black matrix unevenness of the grid-like periodic pattern, particularly the black matrix unevenness having a large opening, the contrast between the uneven portion and the normal portion cannot be improved, and the intensity difference Even if the processing is devised, there is a problem that the inspection in the case of an image with a low contrast of the original image can only achieve a lower inspection ability than the visual sensory inspection method. The periodic pattern refers to an aggregate of slit patterns having a constant interval (hereinafter referred to as a pitch). For example, a striped periodic pattern in which one pattern is arranged at a predetermined pitch, or an opening. These patterns are a matrix-like periodic pattern in which these patterns are arranged at a predetermined pitch.

  On the other hand, due to the increase in fine display and electronic components with a bright screen, the periodic pattern tends to be miniaturized or the aperture ratio is increased. In the future, there will be a need for a method and apparatus for inspecting unevenness of a periodic pattern for an ultrafine black matrix having a higher aperture ratio and a larger aperture ratio. That is, there is a limit in the conventional output with only the intensity (brightness) of the light depending on the amplitude of the light.

  On the other hand, visual inspection is conventionally performed on periodic pattern portions of photomasks used for manufacturing color filters for imaging and display, such as CCD, CMOS, and LCD. Such an appearance inspection by a human needs skill, but is widely implemented because it can find a very fine defect.

  This makes use of the fact that human vision is sensitive to contrast fluctuations, but this contrast fluctuation is also difficult to detect with a single defect, and is very sensitive when it occurs continuously within a certain range. It uses the characteristics of the human eye's cone that it can recognize.

  And, by observing a microscopic size defect that can never be seen by human eyes by illuminating parallel light from an angle, the defect is emphasized from phenomena such as diffraction (scattering). It is learned and implemented empirically what can be confirmed.

  At this time, as described above, it is difficult to find a single point defect at the micro level, but a single point defect (for example, a defect having a side of about several nanometers to several tens of nanometers) does not necessarily become a defective product. Inspection at the micro level is separately performed with a microscope, and it is determined that there is no problem unless a threshold value determined as a defective product is exceeded by this inspection. However, even if the product is not judged as defective by the inspection using such a microscope, humans can perceive the continuous failure as described above with high sensitivity. Therefore, the point that should be judged in the visual inspection is different from increasing the detection power at the micro level.

  However, such visual inspection by humans has a problem that there are oversights and individual differences, and the determination criteria for non-defective products are not clear.

  In addition, when inspecting products such as photomasks, it is necessary to perform inspections in a clean space. However, in reality, not all environments are suitable for inspection. On the contrary, there is a problem of increasing the cause of defects.

  Even when a product is inspected in a clean room, contamination of the work is inevitable unless the cleanness of the clean room satisfies the conditions.

  There is also a problem in sealing the inspection apparatus with a box-shaped wall. Impurities generated at the stage of manufacturing the device cannot escape from the sealed space, and the work is still contaminated. Even if an inspection device is assembled with an extremely clean work environment and components, the inside of this inspection device is contaminated when a contaminated workpiece is introduced, and the workpiece to be inspected next is also contaminated. There is.

The known literature is described below.
JP 2002-148210 A JP 2002-350361 A

  In view of the above-described problems of the prior art, the present invention can stably and accurately image and detect periodic patterns, for example, black matrix unevenness, and further contaminate the workpiece with impurities. It is an object of the present invention to provide a periodic pattern unevenness inspection apparatus that does not occur.

In order to achieve the above object, an invention according to claim 1 of the present invention is an inspection apparatus for inspecting unevenness of a periodic pattern of a substrate to be inspected,
An XY stage having a means for mounting the substrate to be inspected, recognizing the position, and means for driving in the X-axis direction and the Y-axis direction parallel to the plane of the substrate to be inspected;
An imaging unit including an imaging axis parallel optical system parallel to the optical axis of the inspection apparatus, and an axis perpendicular to the XY stage and the inspection target substrate;
A Z-axis drive unit disposed on the inspection target substrate and holding the imaging unit and driving in a Z-axis direction perpendicular to the plane of the inspection target substrate;
A plurality of light sources having an illumination side parallel optical system and capable of individually lighting by illuminating obliquely transmitted light on the inspection target substrate,
A plurality of vertical and horizontal rotation driving units capable of rotating each of the light sources individually in the vertical direction of the optical axis of the inspection apparatus and in the horizontal direction of the XY stage;
A processing unit that manages the imaging unit, the XY stage, the plurality of light sources, and the plurality of up / down / left / right rotation driving units, and that sequentially processes a process for inspecting the periodic pattern unevenness;
A drive unit cover arranged to cover the imaging unit and the Z-axis drive unit;
An overall apparatus cover having a clean unit and arranged to cover the entire inspection apparatus,
When imaging the diffracted light in the periodic pattern of the substrate to be inspected, which is generated by illuminating the oblique transmitted light, the incident angle and direction of the oblique transmitted light illumination are adjusted, and the difference in the diffracted light is determined. It is a periodic pattern nonuniformity inspection apparatus characterized by emphasizing .

  According to the inspection apparatus of the present invention as described above, it is possible to detect only the irregularity of the periodic pattern black matrix stably and with high accuracy.

  Furthermore, since the original image itself is an image in which unevenness is emphasized, the use as an unevenness monitoring device is also effective.

In addition, since a clean environment is always maintained inside the inspection machine, defects caused by the inspection machine are eliminated, and the reliability of inspection data is improved.

  By using the appearance inspection apparatus of the present invention, the inspection time is shortened and the inspection efficiency is improved.

  An appearance inspection apparatus according to the present invention will be described below based on an embodiment.

  FIG. 1 is a conceptual diagram showing a functional configuration of a periodic pattern unevenness inspection apparatus according to the present invention. As shown in FIG. 1, the oblique transmission illumination unit 10, the XY stage unit 20 capable of transmission illumination, the imaging unit 30 for imaging, the captured image is enhanced, the unevenness portion is determined, and further enhancement is performed. The processing unit 40 has a function of displaying the displayed image so that a person can easily recognize unevenness.

  In the oblique transmission illumination unit 10, an up / down / left / right rotation drive unit 12 that freely changes the height direction in the vertical direction and the left / right direction is arranged, and illumination of the illumination side parallel optical system 11 fixed to the tip of the drive unit is performed. It is provided and illumination from various angles and directions is possible. That is, the oblique transmission illumination unit 10 can set the transmission illumination of the parallel optical system 11 from various angles and directions. Furthermore, a plurality of the illuminations are arranged, and switching of lighting of the illuminations (change of the point light source), a distance from the inspection target substrate, or an incident angle and direction of illumination light can be switched.

  In the XY stage unit 20, the inspection target substrate is placed at a predetermined position of the XY stage unit. The XY stage unit has a measurement function, recognizes the position, and superimposes the optical axis of the apparatus on the inspection start position of the inspection target substrate. Using the means for driving in the X-axis and Y-axis directions, the XY stage is driven in the X-axis and Y-axis directions according to a preset operation procedure.

  The imaging unit 30 includes an imaging-side parallel optical system 31 parallel to the optical axis, and shares functions such as a means for capturing an image, such as a CCD camera, image data conversion, data storage and transmission.

  In the inspection apparatus for inspecting the periodic pattern unevenness having the above-described means, the periodic pattern can be imaged, and the feature can be extracted from the image data. The first feature extraction is a method of irradiating the inspection target substrate with transmitted illumination light that is parallel to the illumination optical axis and having an incident angle, and is diffracted by a periodic pattern caused by illuminating oblique transmitted light. It is a periodic pattern nonuniformity inspection apparatus characterized by imaging light. In the normal part of the periodic pattern, the shape and pitch of the slit part (or opening part) are constant, so that they interfere with each other, and strong diffracted light is generated in a certain direction. In the uneven part, the slit part (or opening part). Since the shape / pitch becomes unstable, diffracted light is generated with various intensities in various directions according to the shape / pitch. In the periodic pattern unevenness inspection apparatus configured as described above, the light emitted from the oblique transmission illumination unit 10 is diffracted at the opening of the inspection target substrate 50 of the black matrix of the periodic pattern, and the diffracted light. Is captured by the imaging unit 30 as an image. Next, the second feature extraction is a method of changing the incident angle. When the incident angle is smaller than 90 °, the observation environment is changed, and the difference in the shape and pitch of the slit (or opening) is emphasized. The difference in the diffracted light is further emphasized by illumination that changes the phase little by little.

  The diffracted light diffracted by the substrate to be inspected 50 causes a change in the diffraction angle due to subtle fluctuations in the black matrix, so that the image captured by the imaging unit 30 has uneven portions due to fluctuations in the black matrix. The image is emphasized. Furthermore, by using a parallel optical system for the oblique transmission illumination unit 10 and the imaging unit 30, an image in which the fluctuation of the diffracted light is more accurately emphasized is captured.

  The third feature extraction is a method of changing the position of the illumination light. Various features can be obtained by sequentially lighting a plurality of installed lights or changing the distance between the illumination light and the inspection target substrate 50. An optimum image can be acquired for unevenness having directionality.

  The processing unit 40 manages the imaging unit 30, the XY stage 20, and the transmitted illumination unit 10, and comprehensively manages means for sequentially processing the periodic pattern unevenness inspection process. Further, the processing unit 40 receives image data from the imaging unit 30, extracts image features from the data according to a predetermined data processing procedure (hereinafter referred to as feature extraction), and stores normal (non-defective) images registered in advance. Compare with the characteristics of the data, calculate the difference, and determine pass / fail. The means (flow diagram) for sequentially processing the inspection process for periodic pattern unevenness is shown in FIG. The flowchart is sequentially processed from the start to the end (in order from 1 to 23).

  Next, a feature extraction and collation analysis method of the processing unit 40 will be described. As described above, in the present invention, the diffraction phenomenon or contrast ratio of the captured images obtained by empirically acquired diffraction or change in illuminance of the transmission illumination light source, change in the point light source, change in the irradiation angle, etc. It is a method that has become. First, a feature of a normal (non-defective) image, for example, black matrix data is analyzed, the feature is extracted in detail, and a feature of the normal image is registered. Next, the characteristics of the experienced abnormal image are extracted for each imaging condition, for example, diffraction or illuminance change of the transmitted illumination light source, point light source change, irradiation angle change, etc. Register features. Thus, the feature extraction database of the present invention is completed. Next, using the ultra-low magnification lens of the imaging unit 30, the periodic pattern unevenness inspection process is sequentially processed, and the regions are divided into continuous regions that do not overlap based on the uniformity of the characteristics of normal images. Split processing. That is, for each imaging area, features are extracted, compared with the features of the normal image, and only the matching areas are registered as normal. The registration omission area, that is, the abnormal image area is classified according to certain attributes, for example, features of the abnormal image, and the captured image, position coordinates, defect name, etc. are assigned and temporarily registered. It is desirable that the characteristics of the normal image or the abnormal image are constantly updated to optimize the database with higher accuracy. Note that in the analysis method of feature extraction and collation comparison, the area of one imaging area is a major condition, and it is important to optimize the magnification of the extremely low magnification lens as appropriate.

  In the flowchart shown in FIG. 2, the means for sequentially processing the inspection process for periodic pattern unevenness has b6 imaging condition setting, that is, b7 magnification setting to b8 illumination condition setting as initial conditions. In addition, it is possible to change the image automatically for each image pickup area, for example, sequentially change from the first to the third irradiation condition. Furthermore, the comparison between the captured image data and the feature extraction database includes a processing system that can also perform parallel processing.

  The processing unit 40 determines whether the image data from the imaging unit 30 is good or bad by comparing the feature extraction of the image with a feature of normal image data registered in advance by a predetermined data processing procedure.

  By displaying the determined position and level of the uneven portion at the same time as the uneven image on the processing unit 40, the use for unevenness monitoring is also effective.

At this time, the imaging optical system does not necessarily select a lens, a high-resolution camera, or a super-sensitive camera that can detect the contrast difference of diffracted light of a single point defect (for example, a defect having a side of several nanometers to several tens of nanometers) at the micro level. There is no need. It is possible to select optical components capable of detecting continuous defects to the last, and it is possible to take a wide inspection area at a low cost and once. For example, in order to inspect a photomask having a side of 150 mm, If an optical system capable of imaging a 30 mm square is selected for the inspection area, the entire imaging can be performed with the smallest number of imaging times of 25. Even if it takes 2 seconds for each imaging, the inspection time for one surface is as follows. Less than 1 minute. (It is possible to further increase the speed by improving the inspection stage capability and calculation processing capability.)
Again, a single-point defect at the micro level (for example, a defect with a side of several nanometers to several tens of nanometers) does not necessarily become a defective product. The design made it possible to inspect at such a high speed. Further, the measurement accuracy is a high-precision inspection apparatus capable of detecting extremely minute pattern dimension defects of 10 nm level at the continuous defect detection level.

  Next, FIG. 3 is a conceptual diagram showing a functional configuration for preventing workpiece contamination according to the present invention. As shown in FIG. 3, an inspection apparatus that places an inspection target substrate 50 on the stage 2, scans the camera with the Z-axis drive unit 4 under the imaging conditions irradiated from the illumination unit 1, and captures the image data. It is. The entire device cover 6 prevents impurities from entering the inside of the device. Furthermore, the drive part cover 9 is equipped in the drive part which is easy to generate | occur | produce dust on the workpiece | work upper part. A transparent glass 7 is attached to the lower surface of the drive unit cover to capture transmitted light, or only the lens unit of the camera 3 is exposed from the drive unit cover, and other parts are covered to generate dust from the drive unit. To prevent contamination.

  At this time, since there is no function to remove newly introduced impurities simply by covering the entire apparatus, the clean unit 5 is attached to the ceiling of the apparatus main body frame 60, and clean air is constantly supplied to discharge impurities. . The inside of the device is positive with respect to the outside, and the air from the outside is supplied with clean air through the HEPA filter, ULPA filter, etc. of the clean unit, exhausted from the opening 8 to the floor of the device body frame 60, and impurities are introduced into the device Remove from inside.

  Further, by providing the handling space 61, it is possible to prevent contamination during work such as opening the sample case.

It is a conceptual diagram which shows the function structure of the periodic pattern nonuniformity inspection apparatus of this invention. It is a flowchart which processes sequentially the process of the test | inspection of the periodic pattern nonuniformity of this invention. It is a conceptual diagram which shows the functional mechanic which prevents the contamination with the impurity of the test | inspection apparatus of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Illumination part 2 ... Stage 3 ... Camera 4 ... Z-axis drive part 5 ... Clean unit 6 ... Whole apparatus cover 8 ... Opening part 7 ... Transparent glass 9 ... Drive part cover 10 ... Oblique transmission illumination part 11 ... Illumination side parallel optics System 12: Up / down / left / right rotation operation unit 20: XY stage unit 30 ... Imaging unit 31 ... Imaging side parallel optical system 40 ... Processing unit 50 ... Inspection target substrate 60 ... Apparatus body frame 61 ... Handling space

Claims (1)

An inspection apparatus for inspecting unevenness of a periodic pattern of an inspection target substrate,
An XY stage having a means for mounting the substrate to be inspected, recognizing the position, and means for driving in the X-axis direction and the Y-axis direction parallel to the plane of the substrate to be inspected;
An imaging unit including an imaging axis parallel optical system parallel to the optical axis of the inspection apparatus, and an axis perpendicular to the XY stage and the inspection target substrate;
A Z-axis drive unit disposed on the inspection target substrate and holding the imaging unit and driving in a Z-axis direction perpendicular to the plane of the inspection target substrate;
A plurality of light sources having an illumination side parallel optical system and capable of individually lighting by illuminating obliquely transmitted light on the inspection target substrate,
A plurality of vertical and horizontal rotation driving units capable of rotating each of the light sources individually in the vertical direction of the optical axis of the inspection apparatus and in the horizontal direction of the XY stage;
A processing unit that manages the imaging unit, the XY stage, the plurality of light sources, and the plurality of up / down / left / right rotation driving units, and that sequentially processes a process for inspecting the periodic pattern unevenness;
A drive unit cover arranged to cover the imaging unit and the Z-axis drive unit;
An overall apparatus cover having a clean unit and arranged to cover the entire inspection apparatus,
When imaging the diffracted light in the periodic pattern of the substrate to be inspected, which is generated by illuminating the oblique transmitted light, the incident angle and direction of the oblique transmitted light illumination are adjusted, and the difference in the diffracted light is determined. A periodic pattern unevenness inspection apparatus characterized by emphasizing .

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