JP2008180578A - Periodic pattern unevenness inspection system - Google Patents

Abstract

There is provided a periodic pattern unevenness inspection apparatus capable of imaging and detecting periodic pattern unevenness stably and with high accuracy.
A non-uniformity pattern inspection apparatus for a substrate to be inspected, a moving mechanism for placing the substrate to be inspected and moving the substrate in the X-axis direction and the Y-axis direction, and the amount of movement and detection of the current position. An XY stage having a mechanism, a plurality of light sources that individually illuminate the periodic pattern of the inspection target substrate with substantially parallel light and obliquely transmitted light, and a two-dimensional plane parallel to the inspection target substrate. From light source moving means for moving each individually, light source angle adjusting means for individually changing the direction of each light source, and a periodic pattern that is disposed on the opposite side of the light source across the XY stage and illuminated with obliquely transmitted light Control of the imaging means using a line sensor camera that images the diffracted light, the XY stage, the light source, the light source moving means, the light source angle adjusting means, the imaging means, and the image processing on the inspection image It comprises a processing unit.
[Selection] Figure 1

Description

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

  In the unevenness inspection of the periodic pattern (hereinafter referred to as PM pattern) of a photomask, a transmittance image is captured using coaxial transmission illumination or planar illumination, and the intensity (brightness) of each image is compared. Thus, the uneven part and the normal part are visually recognized. For this reason, in the PM pattern, the difference in light intensity between the uneven portion and the normal portion is originally small, that is, by devising an intensity difference processing method for images with low contrast, the difference is expanded and the uneven portion is extracted. , Have been inspected.

  However, in the above prior art, in the imaging of the black matrix unevenness of the lattice-like periodic pattern, particularly the black matrix unevenness having a large opening, it is not possible to improve the contrast between the uneven portion and the normal portion. Even if the processing is devised, there is a problem that the inspection in the case of an image having 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 arranged at a constant period (hereinafter also referred to as a pitch). For example, a pattern of elongated slits is one-dimensional at a predetermined interval. Stripe-shaped periodic pattern arranged in a row, or a matrix-like (lattice-shaped) periodic pattern in which slit patterns are two-dimensionally arranged at predetermined intervals, such as black matrix openings. Etc.

  On the other hand, due to the increase in electronic components with fine display and bright screen, the PM pattern tends to be miniaturized or increase the aperture ratio. In the future, there will be a need for a method and apparatus for inspecting the periodic pattern unevenness for a black matrix having a finer shape and a larger opening. 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.

  Therefore, for the purpose of providing a periodic pattern unevenness inspection apparatus capable of stably and accurately imaging and detecting a pattern having a periodicity, for example, black matrix unevenness, illumination light is irradiated onto an object to be inspected. For example, an inspection apparatus as disclosed in Patent Document 1 that inspects transmitted diffracted light generated by the structure is proposed.

  However, in such an inspection method using diffracted light, when a surface imaging method is used as the imaging means, it is caused by a two-dimensional color distribution within an illumination range caused by a diffraction phenomenon or an illumination unit. An intensity distribution occurs in the inspection image and affects the inspection.

The two-dimensional color distribution caused by the diffraction phenomenon is generated in the inspection image, for example, obliquely from the illumination side parallel optical system 11 on the inspection substrate 50 having the inspection target pattern 51 as shown in FIG. When a two-dimensional image pickup device such as an area sensor camera is used as the image pickup device 31 when the illumination is performed, it is obtained due to the influence of the non-parallel component remaining in the parallel optical system and the illumination illuminance distribution. The inspection image to be obtained becomes an image having a color change distribution of two or more colors (or an intensity change distribution when the obtained image is monochrome) in one image like the image 52 in FIG. is there.

  In addition, as described above, since the PM pattern has a tendency toward miniaturization, a sufficiently fine resolution is required in the imaging means. An enormous cost is required to obtain an imaging area.

The known literature is described below.
JP 2006-208084 A

  In view of the above-described problems of the prior art, the present invention can capture and detect a black pattern unevenness of a periodic pattern, for example, a PM pattern stably and with high accuracy, and can detect at a higher speed. An object of the present invention is to provide a characteristic pattern unevenness inspection apparatus.

In order to solve the above-described problems in the present invention, first, the invention of claim 1 is an inspection apparatus for inspecting the periodic pattern unevenness of the substrate to be inspected,
An XY stage having a mechanism for mounting the substrate to be inspected and moving the substrate in the X-axis direction and the Y-axis direction, respectively, and a mechanism for detecting the movement amount and the current position;
A plurality of light sources that individually illuminate substantially parallel light and obliquely transmitted light with respect to the periodic pattern of the inspection target substrate on the XY stage;
A light source moving means for individually moving each of the light sources in a two-dimensional plane parallel to the inspection target substrate on the XY stage;
A light source angle adjusting means capable of individually changing the orientation of each of the light sources;
An imaging means using a line sensor camera that images the diffracted light in the periodic pattern that is disposed on the opposite side of the light source across the XY stage and illuminated obliquely by the light source;
A periodic pattern provided with processing means for performing management and control of operations of the XY stage, light source, light source moving means, light source angle adjusting means, and imaging means, and performing image processing on an inspection image obtained by the imaging means. This is a non-uniformity inspection apparatus.

  According to a second aspect of the present invention, there is provided the periodic pattern unevenness inspection apparatus according to the first aspect, wherein the imaging means comprises means for rotating about the optical axis.

  According to a third aspect of the present invention, there is provided means for limiting the range illuminated by the light source to only the imaging range at the time of line scanning for one column by the imaging means using the line sensor camera. This periodic pattern non-uniformity inspection apparatus is.

  In the present invention, a line sensor camera is used as an imaging unit, and a predetermined one-dimensional region of the inspection target substrate is continuously imaged while driving a stage on which the inspection target substrate is mounted. A two-dimensional inspection image is obtained by connecting two-dimensional images. Furthermore, a highly accurate inspection image can be obtained by arranging the imaging system in a form that eliminates the two-dimensional color distribution and intensity distribution and limiting the illumination range.

  Therefore, in the unevenness inspection apparatus according to the present invention, the two-dimensional color distribution and intensity distribution that occur when a diffracted light image is imaged can be eliminated by using a line sensor camera, and unevenness detection can be performed with high accuracy. . In general, a line sensor camera has a very large number of pixels arranged in one direction as compared to an area sensor camera, and therefore conditions such as resolution and imaging area necessary and sufficient for inspection can be easily realized.

  The first embodiment of the present invention will be described below.

  FIG. 1 is a schematic configuration diagram of a periodic pattern unevenness inspection apparatus of the present embodiment. 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 an image of the substrate to be inspected 50, and the captured image are enhanced. The processing unit 40 has a function of determining an uneven portion and displaying an enhanced image so that the operator can easily recognize the uneven portion. It is desirable that this apparatus be operated in a dark environment in which external light and stray light are reduced as much as possible and in a clean environment that prevents foreign matter from adhering to the substrate to be inspected.

  In the oblique transmission illumination unit 10, an up / down / left / right rotation drive unit 12 is disposed on a linear slider 13 on a linear guide 14, and illumination of the illumination side parallel optical system 11 is provided at the tip of the drive unit. Thereby, transmitted illumination from various angles and directions is possible with respect to the substrate 50 to be inspected on the XY stage unit 20.

  Further, a plurality of the lights (11A to 11D) are arranged, and for each of the lights, switching between turning on and off, adjusting the distance from the inspection target substrate 50 and the incident direction of the illumination light are individually possible. . It is also possible to add an optical system member such as a wavelength selection filter for improving the defect detection capability.

  In the XY stage unit 20, the inspection target substrate 50 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 a line sensor camera 31 as a means for capturing an image and an imaging side parallel optical system 32 parallel to the optical axis. As for the performance of the line sensor camera 31, it is desirable to select an optimum one according to the purpose. Further, by providing a plurality of line sensors having different performances and a sensor switching mechanism, an optimal sensor may be selected for each inspection by switching the used sensor.
The imaging-side parallel optical system 32 may have functions such as a magnification adjustment function and an automatic aperture adjustment function.

  The processing unit 40 manages and controls operations of the imaging unit 30, the XY stage 20, and the transmitted illumination unit 10. Further, the processing unit 40 receives the image data from the imaging unit 30, performs predetermined data processing on the image data, digitizes the feature amount of the image data, and determines pass / fail. Examples of the data processing procedure include noise removal processing such as shading correction, feature enhancement by image filtering processing, feature extraction by a projection method, etc., and composite processing thereof. Further, examples of the feature amount of the image data include a luminance difference with the surrounding pixels of the target pixel, an area of a pixel group in which the luminance difference exceeds a set threshold, and the like.

  FIG. 2 shows a flow of processing in the periodic pattern unevenness inspection apparatus of this embodiment, and the processing of steps S1 to S16 is sequentially executed. The description of the processing contents in each step is shown below.

  The entire apparatus is started up such as turning on the power and turning on the light source (S1).

  Initial conditions are set before the inspection conditions are set (S2).

  The stage 21 is moved to the initial condition setting position set in S2 (S3).

  The substrate to be inspected 50 is placed at a predetermined position on the stage 21 (S4).

  The stage 21 is moved to the set inspection start position (S5).

  For the illuminations 11A to 11D of the oblique transmission illumination unit 10, the setting of the light amount, the vertical angle, the left and right angle, the setting of the light projection position on the substrate to be inspected (drive units 12 to 14), and other optical member conditions are set. (S6).

  The imaging magnification of the imaging unit 30 used at the time of inspection is set (S7).

  After the setting of the inspection conditions in steps S4 to S7 is completed, the image data is acquired by repeating the line scan imaging while moving the XY stage according to a predetermined operation. At this time, it goes without saying that the operation of the XY stage is moved perpendicularly to the arrangement direction of the light receiving pixels of the line sensor camera.

  If the stage needs to be reciprocated to obtain an image of the entire surface of the substrate to be inspected 50, the imaging may be performed when the stage is moved in both forward and reverse directions, or only when the stage is moved in the forward direction.

  Further, a plurality of inspection images may be acquired by repeating imaging in the same range a plurality of times. In the case of repeating the imaging a plurality of times, the setting of the oblique transmission illumination unit and the imaging unit may be changed to different settings for each imaging, and inspection images under a plurality of different inspection conditions may be acquired ( S8-S9).

  For the inspection image obtained as described above, the processing unit 40 performs various data processing such as noise removal processing such as shading correction, feature enhancement processing such as image filtering, and feature extraction processing such as a projection method. The characteristic amount of the inspection image is digitized, and the quality of the inspection substrate is determined and the result is output (S10 to 14).

  After the inspection of the substrate to be inspected is completed by these procedures, the substrate to be inspected is unloaded from the stage, the entire apparatus is lowered, and all the periodic pattern unevenness inspection processes of this apparatus are completed (S15 to S16). .

  The operations of the above steps are executed by an operation by the interpersonal operation device 43 or a program incorporated in advance, and the progress information and output results are displayed on the information display device 42.

  In the inspection apparatus for inspecting the periodic pattern unevenness provided with the above-described means, the periodic pattern unevenness inspection characterized in that it images diffracted light in the periodic pattern generated by illuminating obliquely transmitted light Device.

  In the periodic pattern unevenness inspection apparatus configured as described above, the light emitted from the oblique transmission illumination unit 10 is diffracted by the periodic pattern of the inspection target substrate 50 of the periodic pattern, and the diffracted light is used as an image. Captured by the imaging unit 30. The light diffracted from the opening has the effect of enhancing the difference in the shape and pitch of the slit (or opening), and the difference in the diffracted light is further emphasized by illumination that gradually changes the incident angle.

  The diffraction angle of the diffracted light diffracted by the inspection target substrate 50 changes when the black matrix width and gap width are subtly changed. Therefore, the image captured by the imaging unit 30 is changed in the black matrix. This results in an image in which uneven portions due to the above are 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 can be captured.

  In addition, by using a line sensor camera to capture the inspection image, in reality, a two-dimensional color distribution within the illumination range caused by non-parallel light components remaining in the parallel optical system of the illumination unit or the imaging unit In addition, it is possible to detect the unevenness with high accuracy by eliminating the intensity distribution caused by the illumination unit from the inspection image to be captured. Furthermore, an inspection image can be acquired at a high speed by continuous line scanning.

  In this manner, the unevenness image captured by the imaging unit 30 is subjected to unevenness portion extraction processing and determination processing by the processing unit 40. 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.

  As described above, according to the first embodiment of the present invention, only unevenness of the periodic pattern black matrix can be detected stably, with high accuracy, and at high speed.

  Next, a second embodiment of the present invention will be described.

  The outline of the periodic pattern unevenness inspection apparatus of the present embodiment is almost the same as that of the first embodiment shown in FIG. 1, but the imaging unit 30 includes a rotation mechanism having the optical axis as a rotation center. The point is different.

  Also, the flow of processing in the periodic pattern unevenness inspection apparatus of this embodiment is almost the same as that of the first embodiment, but in the imaging condition setting in step S7 of FIG. Is different.

  In the present embodiment, the light emitted from the oblique transmission illumination unit 10 is diffracted at the opening of the periodic pattern of the inspection target substrate 50, and the diffracted light is captured by the imaging unit 30 as an image. At this time, the line sensor camera is arranged such that the arrangement direction of the light receiving pixels of the line sensor camera is perpendicular to the direction in which the color change or the intensity change is strong within the illumination range by the rotation mechanism. The direction in which the color change or the intensity change is strong within the illumination range is specifically the illumination light projection direction.

  The relationship between the arrangement direction of the light receiving pixels of the line sensor camera and the direction in which the color change or the intensity change is strong within the illumination range will be described with reference to FIG. In FIG. 3A, the light beam 15 irradiated from the illumination side parallel optical system 11 is diffracted by the periodic structure of the inspection target pattern 51, and the diffracted light in a specific direction is collected by the imaging side parallel optical system 32. An image is formed by the imaging means 31.

  At this time, when a two-dimensional image pickup device such as an area sensor camera is used as the image pickup device 31, two or more colors of inspection images are obtained in one image as shown in the image 52 in FIG. The image has the above color change distribution (intensity change distribution when the obtained image is monochrome).

  The color distribution in the image 52 obtained by the two-dimensional imaging means varies depending on the periodicity of the pattern 51 and the optical conditions and settings of the imaging unit 30 and the oblique transmission illumination unit 10, but generally the principle of diffraction. Accordingly, the distribution is strongly distributed along an axis having an angle larger than 0 degrees with respect to the vertical direction of the periodic pattern, that is, the light projecting direction (X-axis direction in FIG. 3). In the following description, the image 52 will be described with reference to a drawing in which there are two color distributions of the color 53 on the long wavelength side and the color 54 on the short wavelength side.

  When a one-dimensional imaging means such as a line sensor camera is used as the imaging means 31, it is possible to eliminate a unidirectional distribution out of the in-plane distribution. However, as shown in FIG. 4A, when the sensor elements are arranged using the rotation mechanism so that the scan range 34 is parallel to the direction in which the color distribution changes strongly, the obtained inspection image 55 has a color distribution. The image will be left.

  On the other hand, as shown in FIG. 4B, when the sensor elements are arranged so that the scan range 34 is perpendicular to the direction in which the color distribution changes strongly, the obtained image 55 is an image with a reduced color distribution. It becomes. However, the present invention is not limited to the example described above, and when the in-plane distribution change is stronger in the direction other than the light projecting direction, it is desirable to arrange the sensor elements so as to be perpendicular to the strong direction.

  In this way, the arrangement direction of the light receiving pixels of the line sensor camera is arranged perpendicularly to the direction in which the color change or the intensity change is strong, and an image is picked up. It is possible to obtain an inspection image that eliminates the image more strongly.

  As described above, according to the second embodiment of the present invention, an inspection image in which the two-dimensional color distribution and intensity distribution are more powerfully eliminated can be obtained, and high-speed inspection can be performed.

  Next, a third embodiment of the present invention will be described.

  In the periodic pattern unevenness inspection apparatus of this embodiment, the imaging unit 30 includes a rotation mechanism having the optical axis as a rotation center, as in the second embodiment. Further, the illumination side parallel optical system 11 in the oblique transmission illumination unit 10 is provided with a mechanism that limits the illumination range to only the scan range during one line scan.

  The processing flow in the periodic pattern unevenness inspection apparatus of this embodiment is also the same as that of the second embodiment.

  In the third embodiment, the light emitted from the oblique transmission illumination unit 10 is diffracted at the opening of the inspection target substrate 50 having a periodic pattern, and the diffracted light is captured by the imaging unit 30 as an image. At this time, the arrangement direction of the light receiving pixels of the line sensor camera is arranged so as to be perpendicular to the light projecting direction, and the light emitted from the oblique transmission illumination unit 10 illuminates only the scan range during the line scan. Irradiated as follows.

  The effect of illuminating only the scan range will be described with reference to FIG. When illumination is performed out of the scanning range, a pattern 56 that is not to be inspected is reflected due to multiple reflection as shown in FIG. 5A, resulting in a pseudo defect 57 that reduces the inspection accuracy. However, by illuminating only the scan range, this problem can be avoided as shown in FIG.

  In this manner, in the third embodiment of the present invention, the arrangement direction of the light receiving pixels of the line sensor camera is arranged perpendicular to the direction in which the color change or the intensity change is strong, and only the scan range is illuminated, thereby inspecting. It is possible to obtain an inspection image that strongly eliminates two-dimensional color distribution and intensity distribution from an image and eliminates false defects due to multiple reflection.

  As described above, according to the third embodiment of the present invention, it is possible to obtain an inspection image in which two-dimensional color distribution, intensity distribution, and pseudo defects due to multiple transfer are eliminated, and high-speed inspection is possible. It becomes.

According to the present invention, in a product having a periodic pattern such as a photomask, unevenness affecting the product can be detected stably, with high accuracy, and at high speed.

It is the schematic which shows the function structure of the periodic pattern nonuniformity inspection apparatus which concerns on this invention. It is a flowchart which shows the processing operation in the periodic pattern nonuniformity inspection which concerns on this invention. It is a schematic diagram which shows the outline of the color distribution in the periodic pattern imaging which concerns on this invention. It is the schematic which shows the relationship between the color distribution in the periodic pattern imaging which concerns on this invention, and the arrangement direction of a line sensor element. It is the schematic which shows the effect of limitation of the illumination range which concerns on the 3rd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Oblique transmission illumination part 11A-11D ... Illumination 12 ... Vertical / horizontal rotation operation part 13 ... Linear slider 14 ... Linear guide 15 ... Light beam 20 ... XY stage part 21 ... Stage 22 ... X drive mechanism 23 ... Y drive mechanism 30 ... Imaging Unit 31 ... Line sensor camera 32 ... Imaging side parallel optical system 33 ... Imaging side optical axis 34 ... Scanning range 40 ... Processing unit 41 ... Image processing device 42 ... Information display device 43 ... Personal operation device 50 ... Substrate 51 to be inspected ... Inspection Target pattern 52... Image captured by two-dimensional imaging means 53... Color distribution (long wavelength side)
54 ... Color distribution (short wavelength side)
55 ... Image captured by line sensor camera 56 ... Non-inspection pattern 57 ... Pseudo defect

Claims (3)

An inspection apparatus for inspecting unevenness of a periodic pattern of a substrate to be inspected,
An XY stage having a mechanism for mounting the substrate to be inspected and moving the substrate in the X-axis direction and the Y-axis direction, respectively, and a mechanism for detecting the movement amount and the current position;
A plurality of light sources that individually illuminate substantially parallel light and obliquely transmitted light with respect to the periodic pattern of the substrate to be inspected on the XY stage;
A light source moving means for individually moving each of the light sources in a two-dimensional plane parallel to the inspection target substrate on the XY stage;
A light source angle adjusting means capable of individually changing the direction of each of the light sources;
An imaging means using a line sensor camera that images the diffracted light in the periodic pattern that is disposed on the opposite side of the light source across the XY stage and illuminated obliquely by the light source;
A periodic pattern provided with processing means for performing management and control of operations of the XY stage, light source, light source moving means, light source angle adjusting means, and imaging means, and performing image processing on an inspection image obtained by the imaging means. Unevenness inspection device.   The periodic pattern unevenness inspection apparatus according to claim 1, wherein the imaging unit includes a unit that rotates about the optical axis of the imaging unit.   The periodic pattern unevenness inspection apparatus according to claim 2, further comprising a unit that limits a range illuminated by the light source to only an imaging range during a line scan for one column by an imaging unit using the line sensor camera. .

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