JP4655644B2 - Periodic pattern unevenness inspection system - Google Patents

Description

  The present invention relates to an inspection apparatus for inspecting pattern unevenness in a product having a periodic pattern, and is formed periodically on a substrate such as an aperture grill, a photomask, or a color filter used for a cathode ray tube of a color television. The present invention relates to a periodic pattern unevenness inspection apparatus that can accurately detect streak-like unevenness in a pattern that is present.

  In the conventional periodic pattern unevenness inspection, a transmittance image is captured using coaxial transmission 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 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, the improvement in contrast between the uneven portion and the normal portion cannot be expected, and there is an intensity difference. Even if the above process 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 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 electronic components with fine display and bright screen, the periodic pattern tends to be miniaturized or to increase the aperture ratio. In the future, there will be a need for an inspection method and apparatus for periodic pattern irregularity inspection for a black matrix having a finer shape and a larger opening. That is, the conventional output with only the intensity (brightness) of the light intensity (brightness) based on the amplitude of the light is a limit, and unevenness cannot be clearly detected.
JP 2002-148210 A JP 2002-350361 A

  The present invention has been made to solve the above-described problems, and provides a periodic pattern unevenness inspection apparatus capable of imaging and detecting periodic patterns such as black matrix unevenness stably and with high accuracy. The purpose is to do.

A periodic pattern unevenness inspection apparatus according to the present invention is a periodic pattern unevenness inspection apparatus for inspecting streaky unevenness that occurs in a periodic pattern on a rectangular substrate, and the substrate is substantially horizontal. An XY stage (21) having a moving mechanism for holding and moving the substrate in the X-axis direction and the Y-axis direction within a two-dimensional planar field of view, and oblique transmission with respect to the periodic pattern of the substrate on the XY stage The four light sources (11A-11D) that individually illuminate the light and the diffracted light in the periodic pattern that is arranged on the opposite side of the light source with the XY stage sandwiched and illuminated obliquely by the light source Imaging means (31) for performing, two X guides (14) for guiding two of the four light sources in the X-axis direction with respect to the substrate on the XY stage,
Two Y guides (14) arranged so as to be orthogonal to the X guide and guiding the other two of the four light sources in the Y-axis direction with respect to the substrate on the XY stage,
First moving means (13) for individually moving each of the two light sources along each of the two X guides within a two-dimensional planar field of view;
Second moving means (13) for individually moving each of the other two light sources along each of the two Y guides in a two-dimensional planar field;
When each of the two light sources is moved in the X-axis direction by the first moving means, illumination of obliquely transmitted light from each of the two light sources is applied to the periodic pattern to be inspected. And first posture changing means (12) for changing the direction of each of the two light sources in conjunction with the first moving means,
When each of the other two light sources is moved in the Y-axis direction by the second moving means, oblique transmitted light is transmitted from each of the other two light sources with respect to the periodic pattern to be inspected. Second posture changing means (12) for changing the direction of each of the other two light sources in conjunction with the second moving means so as to be illuminated;
The first and second moving means and the first and second posture changing means so that the incident angles of the obliquely transmitted light by the four light sources change with respect to the periodic pattern to be inspected. And an optical condition 4-axis setting means (40a-40c) for setting each of the above operations .

  According to the first aspect of the present invention, the optical conditions of the four light sources (light wavelength, light intensity distribution, light incident angle, direction of light projection, area of the light projection illumination area, depth of focus) are set by the optical condition four-axis setting means. Etc.) individually. Specifically, it is necessary to grasp in advance through a verification test or the like how to operate the moving unit and the posture changing unit for each light source corresponding to the periodic pattern of the subject, and save this data as a recipe. deep. Then, when actually performing the examination, an optimum recipe is selected according to the periodic pattern of the subject, and the optical conditions of the four light sources are individually set according to the setting data selected and called. The shape of the periodic pattern is basically a rectangular shape, and unevenness of drawing often occurs periodically in the drawing horizontal direction and the drawing vertical direction (direction perpendicular to the drawing). Light is projected on the basis of four axes that are illuminated from opposite directions in the drawing vertical direction.

  When the inspection light is incident on the periodic pattern, the light is diffracted at the knife edge portion (displacement portion or inflection portion) and the stripe-shaped unevenness of the periodic pattern, and the diffracted light is detected to detect streak as a defect. Unevenness is detected.

  With respect to light diffraction, strong transmitted light is formed in a specific direction in the normal part of the periodic pattern. On the other hand, in the stripe-shaped uneven portion, diffracted light is generated in various directions in various directions according to the pattern shape and pitch interval without diffracted light being emitted only in a specific direction. Image processing and analysis are repeatedly performed based on optical detection data including these diffracted lights, and streaky irregularities are detected and displayed.

  Next, a brief description will be given of a case where the diffracted light generated by the stripe-shaped unevenness is subjected to image processing and analysis. For example, two-dimensional image data of only the periodic pattern area 52 is cut out from the subject substrate 50 as shown in FIG. 10, and integrated data 61 is calculated for the cut-out two-dimensional image data as shown in FIG. Next, integrated moving average data 62 for the target point is calculated from the integrated data 61. Here, the moving average calculation possible range 64 can be changed. However, since this integrated moving average data 62 calculates a moving average centered on the point of interest, it cannot be calculated at both end portions 63 thereof. Therefore, for both end portions 63 that cannot be calculated, the moving average calculation range 64 by the least square method at the extreme end is calculated by the least square method based on the data at both ends of the moving average calculation range 64.

  Next, the difference between the integrated data 61 and the integrated moving average data 62 is calculated, and differential data 71 is obtained as shown in FIG. A threshold value 72 is provided in the difference data 71, and data exceeding the threshold value 72 is determined to be streak-like unevenness.

  However, since the both end portions 63 obtained by calculating the moving average by the least square method are predicted values by the least square method, it is expected that an error will occur. In order to cope with this, it is possible to set a value 73 different from the threshold 72 of the moving average calculation possible range 64 by the least square method. In this way, by using an inspection method specialized for streak-like unevenness, it becomes possible to detect streak-like unevenness with high accuracy.

In the invention of claim 2, the four light sources, the first and second moving means, and the first and second attitude changes are further made according to at least one of the periodic pattern to be inspected and the customer specifications. Each unit is individually set, and an axis-specific individual setting / storing function for saving the optical conditions set individually is added. By adding the individual setting and saving function for each axis, the optical system conditions can be set for each light source according to the sample and the customer's request, and detailed inspections according to the customer's request can be performed. It becomes possible. Also, by setting the optical conditions individually using this function, it is possible to reduce the level of pseudo defects (effect of reducing the level of pseudo defects), or to use for discrimination and separation.

  Since the inspection apparatus according to the present invention is a device that captures the diffraction phenomenon of light in a macro manner, the portion depending on the light projection angle (light incident angle) and the light wavelength that greatly affects the diffraction phenomenon is large. However, the periodic patterns of photomasks are very diverse, and it is difficult to set the optical conditions to a fixed condition because the patterns are various and the degree of streak-like unevenness varies greatly depending on the sample. It is. For this reason, it is necessary to set the conditions of the optical system according to the sample. Therefore, by using the individual axis setting / saving function for each axis and setting the optical conditions according to the sample and the customer's request for each axis, it is possible to provide a detailed inspection.

The invention of claim 3 further sets a reference condition for detecting basic stripe-like unevenness, and sets a plurality of reference conditions for detecting stripe-like unevenness that cannot be detected only by the reference condition, A reference condition / reference condition setting function for switching from the reference condition to the reference condition in accordance with the state of streaky irregularities generated in the periodic pattern is added. By adding the standard condition / reference condition setting function, not only fine inspections according to customer requirements are possible, but also streaky irregularities that could not be detected only with the standard conditions. Is possible.

  It is difficult to set the optical conditions to a fixed condition because the periodic patterns of photomasks are very diverse, and the patterns vary, and the degree of streak-like unevenness varies greatly from sample to sample. . For this reason, it is necessary to set the conditions of the optical system according to the sample. However, it is impossible to set conditions in a state where the pattern and defect level are unknown.

  Therefore, if a reference condition that can detect basic unevenness is set, all samples are measured using this reference condition, and the numerical condition is used when performing the quantification, the standard for quantification can be obtained. There is no shift. However, streaky irregularities that cannot be detected only with the reference conditions are inspected using a plurality of measurement conditions (reference conditions). That is, as shown in FIG. 9, a plurality of measurement conditions can be prepared in advance, and the inspection can be executed using all these conditions selectively. By doing so, it is possible to perform a detailed inspection according to the customer's request, and it is also possible to detect streaky irregularities that could not be detected only by the reference conditions.

  The invention of claim 4 further includes an illumination center position adjustment function for causing the imaging means to take an image when the luminance peak of the illumination light is shifted by a predetermined distance from the optical axis of the imaging means. This illumination center position adjustment function is one of the setting items of the optical system in which individual conditions can be set among the individual setting / saving functions for each axis. In the inspection apparatus of the present invention, a linear light source using a telecentric lens is used, but this type of light source may be affected by a captured image because of uneven brightness and illuminance. For example, if the illumination light is strong and the peak value is too high, white spots may appear on the screen and defects may not be identified. Therefore, as shown in FIG. 13, the peak 81 of the illumination light is intentionally shifted from the position of the center line 58 of the imaging area 56, and an inspection is performed using a gentle skirt portion with a luminance change. By adding this function, illuminance unevenness and luminance unevenness of the light source can be removed, and an image with good contrast can be displayed.

  In addition, the database function that saves the optical condition set values together with the inspection result data and inspection surface image data in the database as a recipe, selects and calls the stored data, and collates the inspection result and inspection surface image with the data called A re-inspection function is added. By adding a database function and a re-inspection function, the various functions described above (1. Optical condition 4-axis setting function, 2. Individual axis setting / saving function, 3. Reference condition / reference condition setting function, 4. Lighting center) The set values of the optical conditions set by the position adjustment function) are stored as a recipe, and the inspection results and inspection images are stored in the database together with the recipe. For example, various kinds of data are stored in a database using an input / display panel screen as shown in FIG. Further, by performing a necessary input operation using the screen shown in FIG. 14, it is possible to select arbitrary data from the stored history data and easily check the already-proven inspection images and inspection results. In addition, if the re-inspection is executed after recalling the history data, the same optical conditions and judgment conditions are recalled from the saved recipe, and the inspection area is recalled and the inspection method that has been proven in the past is used. It becomes possible to inspect. In this way, inspection with high reproducibility can be performed.

The invention according to claim 5 enables the four light sources to individually switch on and off. This function is one of the specific functions included in the axis-specific individual setting / saving function. The light source is moved with respect to the substrate, the projection angle is changed variously, only the light source necessary for detecting streak-like unevenness is turned on, and the unnecessary light source is turned off. By doing so, extra light from the surroundings does not enter the imaging area, and only light necessary for detecting the defect is projected onto the imaging area, thereby improving inspection accuracy.

In the invention according to claim 6 , the four light sources have detachable optical filters that transmit light of a desired wavelength, respectively, and illumination light that is one of the optical conditions according to customer specifications and inspection recipes. Various wavelengths can be changed. This function is one of the specific functions included in the optical condition 4-axis setting function. A desired light wavelength is set based on customer specifications, etc., and an optical filter that matches the set wavelength is attached to the light source for inspection. After that, when inspecting according to another customer specification, etc., set another wavelength light based on the other customer specification, remove the optical filter used for the previous inspection from the light source, and match the other set wavelength Replace with another optical filter for inspection.

According to the present invention, since the optical condition is individually set for each light source by the optical condition four-axis setting function, streaky irregularities can be imaged and detected stably and with high accuracy. In addition, by adding the individual setting and saving function for each axis, the optical system conditions can be set for each light source according to the sample and the customer's request, and a detailed inspection is performed according to the customer's request. In addition, it is possible to reduce the level of pseudo defects (effect of reducing the level of pseudo defects) and to use it for discrimination and separation. In addition, by adding the standard condition / reference condition setting function, even if the pattern and defect level are not known, not only detailed inspection according to the customer's request is possible, but also only with the standard condition It is possible to detect streaky irregularities that could not be detected. In addition, by adding the illumination center position adjustment function, it is possible to remove unevenness in illuminance and brightness of the light source and display an image with good contrast .

  The best mode for carrying out the present invention will be described below with reference to the accompanying drawings.

  As shown in FIG. 1, the periodic pattern unevenness inspection apparatus according to the present invention includes an oblique transmission illumination unit 10, an XY stage unit 20 that moves and supports a subject substrate 50 that is transmitted and illuminated, and an imaging unit for imaging. 30 and a processing unit 40 having a function of emphasizing the captured image, determining whether or not the image is uneven, and displaying unevenness so that the operator can easily recognize the emphasized image. Yes.

  The oblique transmission illumination unit 10 includes four light sources 11A to 11D. Each of the light sources 11A to 11D is movably supported on a linear guide 14 by a swing mechanism 12 as a posture changing unit and a linear slider 13 as a moving unit. The linear guide 14 is composed of two X guides and Y guides which are arranged so as to be orthogonal to each other within a plane field of view. One of the two X guides is provided with the first light source 11A so as to be able to slide in the X direction, and the other is provided with the second light source 11B so as to be capable of sliding in the X direction. Also, one of the two Y guides is provided with a third light source 11C that can slide in the Y direction, and the other has a fourth light source 11D that can slide in the Y direction. The linear slider 13 is drivably engaged with the linear guide 14 and supports the light sources 11 </ b> A to 11 </ b> D via the swing mechanism 12. Further, each of the light sources 11A to 11D is provided with means for switching on and off (changing the point light source) so that the distance from the inspection target substrate, the incident angle of illumination light, and the direction can be switched. .

  The head swing mechanism 12 includes an ultra-small motor, a horizontal shaft connected to the motor rotation drive shaft, and a holder that rotates around the horizontal axis together with the light sources 11A to 11D. Each of the light sources 11A to 11D swings as shown in FIG. As a result, the light projection angle θ of the light from the light sources 11A to 11D changes variously, and illumination from various angles and directions is possible. Each of the light sources 11A to 11D can be detachably mounted with an optical filter that transmits light of a desired wavelength. The optical filter is prepared in one-to-one correspondence with the wavelength of light, and is changed to a desired optical filter in accordance with changes in customer specifications and inspection recipes.

  As the light sources 11A to 11D, linear light sources having a parallel optical system including a telecentric lens are used. This type of light source has uneven brightness and uneven illuminance, and if the illumination intensity is high, the captured image may be affected. In the inspection apparatus of the present embodiment, an illumination center position adjustment function is added as a measure for preventing luminance unevenness and illuminance unevenness.

  In the XY stage unit 20, a mask 50 as an inspection target substrate is placed and held at a predetermined position on the XY stage 21. The XY stage unit 20 has a measurement function, recognizes the position, and superimposes the optical axis of the apparatus on the inspection start position of the mask 50. The XY stage 21 is supported by an X drive mechanism 22 and a Y drive mechanism so as to be movable in the X direction and the Y direction in a horizontal plane.

  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, for example, a camera with a CCD, image data conversion, data storage and transmission. The imaging side parallel optical system 31 includes a projection optical system so that the inspection target pattern 51 can be projected and imaged at a desired magnification (including enlargement or reduction, and equal magnification).

  The processing unit 40 comprehensively manages the imaging unit 30, the XY stage unit 20, and the transmitted illumination unit 10, and also comprehensively manages means for sequentially processing the inspection process of the periodic pattern unevenness. Further, the processing unit 40 receives the image data captured from the imaging unit 30, extracts and compares the characteristics of the image according to a predetermined data processing procedure, calculates the difference, and determines pass / fail. A flow chart for sequentially processing the periodic pattern unevenness inspection process will be described later with reference to FIG.

  Next, the outline of the control system of the inspection apparatus will be described with reference to FIG.

  The inspection apparatus of the present invention is constituted by five subsystems 40a to 40e. The data input unit 40a includes a sensor unit 411, an illumination unit 412, a position fixing unit 413, and a position control unit 414. The sensor unit 411 includes a plurality of sensors such as a position sensor for position detection, a distance sensor for detecting a moving distance (including an encoder and a counter), and a light detection sensor for detecting luminance. The data processing unit 40b includes an image processing unit 415 that processes imaging data input from the sensor unit 411 of the data input unit 40a, and a data management unit 416 that manages the processed data. Detection signals are sent to the image processing unit 415 from each sensor of the sensor unit 411 as needed. The image processing unit 415 may be a part of the function of the personal computer 41 of the processing unit 40 or may be a processing unit independent of the personal computer 41.

  The illumination unit 412 controls the light sources 11A to 11D.

  The position fixing unit 413 controls the XY stage unit 20.

  The position control unit 414 individually controls the swing mechanism 12 and the linear slider 13 of the light sources 11A to 11D.

  The machine interface unit 40c includes a machine interlocking unit 417 that transmits / receives data to / from an external device such as a transport mechanism (not shown) that transports the mask 50 to be inspected, and an automatic supply / discharge unit that transfers the mask. 418.

  The human interface unit 40e includes an information display unit 42 that displays a processed image processed by the data processing unit 40b, and an interpersonal operation unit 43 that exchanges information with an operator.

  The system bus 40d is an interface between the human interface unit 40e and the other subsystems 40a to 40c for data transmission / reception.

  Next, the procedure for inspecting the periodic pattern unevenness will be schematically described with reference to FIG.

  The main switch is turned on to activate the apparatus, and inspection is started (step S1). Predetermined initial conditions are set, and the setting operation is terminated when all the initial conditions are obtained (step S2).

The X drive mechanism 22 and the Y drive mechanism 23 are driven, and the XY stage 21 is moved from the home position to the use position (step S3). The mask 50 is placed on the XY stage 21 (step S4). Next, the mask 50 is moved to the inspection start position together with the XY stage 21, and the periodic pattern 51 to be inspected is positioned in the imaging area 56 (step S5).

  The imaging conditions of the imaging unit 30 are set (step S6). The magnification of the camera 31 is set (step S7). Illumination conditions for the oblique transmission illumination unit 10 are set (step S8). When these settings are completed, the light sources 11A to 11D are slid, moved to swing, aligned with the imaging area 56, projected and illuminated on the pattern 51, and imaged (step S9). The first captured image is taken into the personal computer 41 of the processing unit 40 (step S10). It is determined whether or not there is a next imaging area (inspection target pattern) (step S11).

  If it is determined that there is a next imaging area (inspection target pattern), the mask 50 is moved by the XY stage 21, the next imaging area is positioned in the camera imaging area 56, and this is imaged (step S12). The pattern image of the next imaging area is taken into the personal computer 41 of the processing unit 40 (step S13). It is determined whether or not it is the last imaging area (step S14). If it is determined that it is the last imaging area, the process proceeds to step S16.

  If it is determined that it is not the last imaging area, the process returns to step S11, the next imaging area is imaged (step S12), the captured image is captured (step S13), and it is determined again whether or not it is the last imaging area. Determine (step S14).

  If it is determined in step S11 that there is no next imaging area, the imaging is terminated, the drive of the XY stage 21 is stopped (step S15), and the apparatus is finally stopped (step S22).

  If it is determined in step S14 that it is the last imaging area, the imaging data is transferred to the processing unit 40 (step S16), and the personal computer 41 performs image processing (step S17). Then, the image processing result data is output (step S18), and the output result is evaluated (step S19). When the evaluation determination is completed, the inspection process is terminated (process S20). The mask 50 is lifted from the stage 21, transferred to the transfer arm, and unloaded from the chamber (step S21). The apparatus is stopped and the inspection is finished (step S22).

  Next, an outline of periodic pattern imaging and unevenness detection will be described.

  In the normal part of the periodic pattern 51, the shape and pitch of the slit part (or opening) are constant, so that they interfere with each other, and strong chamfered light is generated in a certain direction. In the uneven part, the slit part (or opening part). ) Becomes unstable, and diffracted light is generated in various directions with various intensities according to the shape and pitch.

  In the inspection apparatus, the light emitted from the oblique transmission illumination unit 10 is diffracted at the opening of the black matrix mask 50 of the periodic pattern 51, and the diffracted light is captured by the imaging unit 30 as an image. When the incident angle θ is smaller than 90 °, the observation environment is changed, and the difference in the shape and pitch of the slit (or opening) is emphasized, and the difference in the diffracted light is further increased by the illumination that changes the position little by little. To be emphasized.

  The diffracted light diffracted by the mask 50 changes the diffraction angle due to subtle variations in the black matrix. Therefore, the image captured by the imaging unit 30 is an image in which uneven portions due to the black matrix variation are emphasized. Become. 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.

In addition, by sequentially lighting a plurality of installed lights, it is possible to obtain an optimal image for unevenness having various directions.

  The unevenness image thus 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 unevenness position and level on the processing unit 40 at the same time as the unevenness image, the use for unevenness monitoring is also effective.

  As shown in FIG. 4, when setting the optical condition of each light source based on the optical condition four-axis setting function, the distance between the light sources / masks is variously changed and light is projected from the light sources 11A to 11D to the pattern 51. Various angles of light θ1 to θ4 can be changed. Thereby, it becomes possible to project the optimal inspection light onto the pattern according to the shape and type of the pattern 51. Note that the projection angles θ1 to θ4 are preferably in the range of 30 to 70 °. In addition, the distance L from the mask, which is the subject substrate, to the orbit of the light source varies depending on the size of the subject substrate. For example, when the subject substrate is a large color filter, the distance L is preferably about 1 m. When the subject substrate is a photomask for manufacturing a semiconductor device, the distance L is used as the objective lens performance. Accordingly, it is desirable that the thickness is about several mm to several hundred mm.

1) Optical condition 4-axis setting function
The optical condition 4-axis setting function is used to project light from two light sources to the photomask in the horizontal direction (X direction) and also when projecting from another two light sources in the vertical direction (Y direction). This is a function for setting the projection angle θ of the four light sources or the distance from each light source to the inspection target pattern to a desired value. Since most of the shape of the periodic pattern 51 is a rectangle as shown in FIG. 6, streaky irregularities (rendering irregularities) are periodically generated in the horizontal direction (X direction) and vertical direction (Y direction) of drawing. Therefore, there are some projection angles at which defects are easily found according to the pattern shape. For example, in a T-shaped pattern, θ1 and θ2 are projection angles at which it is easy to find defects in advance through a verification test, and when a photomask including a T-shaped pattern is inspected, θ1 is set as the projection angle of the recipe condition. , Θ2 is set, streaky irregularities can be detected reliably and efficiently. The reason why the number of light sources is set to four is that, in order to eliminate the luminance deficiency, in addition to considering the complementation of luminance, switching is performed using only two light sources in the X direction or only two light sources in the Y direction. Measurement is made possible.

  The four light sources 11 </ b> A to 11 </ b> D can appropriately change the projection angle according to the distance from the pattern to be inspected to the light source. Even when the light projection angle θ itself is not directly detected, if the height level difference L between the light source / pattern is known, the light projection angle is detected by detecting the distance between the light source / pattern. Can be requested.

  The optical conditions of the four light sources (light wavelength, light intensity distribution, light incident angle, direction of light projection, area of the floodlight illumination area, depth of focus, etc.) are individually set by the optical condition 4-axis setting means. To do. Specifically, it is necessary to grasp in advance through a verification test or the like how to operate the moving unit and the posture changing unit for each light source corresponding to the periodic pattern of the subject, and save this data as a recipe. deep. Then, when actually performing the examination, an optimum recipe is selected according to the periodic pattern of the subject, and the optical conditions of the four light sources are individually set according to the setting data selected and called. The shape of the periodic pattern is basically a rectangular shape, and unevenness of drawing often occurs periodically in the drawing horizontal direction and the drawing vertical direction (direction perpendicular to the drawing). Light is projected on the basis of four axes that are illuminated from opposite directions in the drawing vertical direction. When the inspection light is incident on the periodic pattern, the light is diffracted at the displacement portion or the inflection portion of the periodic pattern and the streak-like unevenness, and the streaky unevenness as a defect is detected by detecting each of the diffracted lights. The With respect to light diffraction, strong transmitted light is formed in a specific direction in the normal part of the periodic pattern. On the other hand, in the stripe-shaped uneven portion, diffracted light is generated in various directions in various directions according to the pattern shape and pitch interval without diffracted light being emitted only in a specific direction. Image processing and analysis are repeatedly performed based on optical detection data including these diffracted lights, and streaky irregularities are detected and displayed.

  With this function, it is possible to detect with high sensitivity streaky irregularities that appear periodically in the horizontal and vertical directions of drawing.

2) Individual setting and saving function for each axis
The axis-specific individual setting / storing function is a function for individually setting the optical system conditions according to the sample state and customer specifications (request items) and storing the setting conditions as individual recipes.

  By providing this function, it is possible to cope with various photomask patterns and defect levels.

  Since the periodic pattern of the photomask is various and the inspection device is a device that captures the light diffraction phenomenon macroscopically, the projection angle is an angle (emphasis angle) that cannot be canceled by the diffraction phenomenon. Or an angle (weak angle) at which the pseudo defect is not recognized as a defect on the screen. This is because the detection of streak-like unevenness has a large part depending on the light projection angle and wavelength that greatly affects the diffraction phenomenon.

  However, it is very difficult to make the optical conditions constant because there are various patterns and the degree of stripe-like unevenness greatly varies depending on the sample.

  Therefore, by individually setting the optical system conditions according to the sample, it is possible to individually prepare the optical conditions suitable for the sample state and customer's request, and it becomes possible to perform a finer inspection. .

  For example, in the conventional inspection apparatus, as shown in FIG. 7A, when the lamp A is turned on, the edge on the A side short side clearly appears as a pseudo defect on the screen. Even when the lamp B is turned on, the edge on the short side of the B side appears clearly on the screen as a pseudo defect.

  On the other hand, in the inspection apparatus of the present invention, since the conditions of the optical system are individually set, the lamps A and B are turned on at the same time, and as shown in FIG. The image of the pseudo-defect is so thin that it is not recognized. When there is no defect (streaky unevenness) or pseudo defect at all, a gray screen is displayed.

  FIG. 8 is a schematic diagram for explaining the principle of generation of a shadow (ghost) due to multiple reflection (bottom reflection) light. When the inspection light 2 is incident on the mask 50 and illuminates the pattern 51, a real image 34 of the pattern is formed on the image plane 33 of the imaging unit 30. On the other hand, the bottom surface reflected light from the pattern 51 is reflected again (multiple reflection) by the bottom surface of the mask 50, and this multiple reflection image is formed on the image surface 33 to become a shadow (ghost) 35. If this shadow (ghost) 35 appears on the image surface 33 as an image of a pseudo defect, it causes a decrease in the accuracy of the pass / fail judgment of the real image 34. However, in this embodiment, since the pseudo defect image is displayed so as to be thinned by the axis-specific individual setting / saving function, the inspection accuracy is improved.

  By providing this function, it can be used for discrimination and separation of pseudo defects and is effective in reducing the level of pseudo defects.

3) Standard condition / reference condition setting function
The reference condition / reference condition setting function is a function for setting a plurality of reference conditions in order to set a common reference condition for all patterns and detect defects that cannot be detected only by the standard reference condition.

  Since the periodic pattern of the photomask is various, it is necessary to set optical conditions suitable for the inspection target pattern. When creating an inspection recipe, it is desirable to set conditions individually for each pattern, but it is impossible to set conditions in a state where the pattern and the defect level are unknown. Therefore, if a reference condition that can detect basic unevenness is set, all samples are measured using this reference condition, and the numerical condition is used when performing the quantification, the standard for quantification can be obtained. There is no shift. However, streaky irregularities that cannot be detected only with the reference conditions are inspected using a plurality of measurement conditions (reference conditions).

  As shown in FIG. 9, for streak-like unevenness that cannot be detected only by the reference condition or is insufficiently detected, an optimum condition is selected from the plurality of reference conditions 1 to 3, and the selected reference condition is set. It is possible to detect defects with high accuracy.

  By doing so, it is possible to perform a detailed inspection according to the customer's request, and it is also possible to detect streaky irregularities that could not be detected only by the reference conditions.

4) Lighting center position adjustment function
The illumination center position adjusting function is a function of intentionally shifting the center position of the illumination from the camera optical axis and capturing an image at a gentle part where the luminance changes. This illumination center position adjustment function is one of the setting items of the optical system in which individual conditions can be set among the individual setting / saving functions for each axis. Since this function is an auxiliary function and may or may not be used, the operator can select by pressing the selection button on the recipe input screen.

  The inspection apparatus of the present invention is a linear light source using a telecentric lens. However, since these optical systems have uneven brightness and uneven illuminance, they may affect actual captured images. For example, this function is used when the peak brightness of the illumination light is too high and the contrast between light and dark is lost, and the defect is not identified due to white spots on the screen. Specifically, as shown in FIG. 13, the peak 81 of the luminance distribution 80 of the illumination light is intentionally shifted by a predetermined distance from the center line 58 of the imaging field 56 of the camera, and the gentle bottom portion 82 of the luminance change. Take an image with. By adding this function, illuminance unevenness and luminance unevenness of the light source can be removed, and an image with good contrast can be displayed.

5) Database function / re-examination function
The database function / re-inspection function is a function that saves the set values of the optical conditions set in the above 1) to 4) as a recipe, and also saves the inspection results and the inspection screen in the database. By adding a database function and a re-inspection function, the various functions described above (1. Optical condition 4-axis setting function, 2. Individual axis setting / saving function, 3. Reference condition / reference condition setting function, 4. Lighting center) The set values of the optical conditions set by the position adjustment function) are stored as a recipe, and the inspection results and inspection images are stored in the database together with the recipe.

  For example, as shown in FIG. 14, the operator inputs necessary recipes such as each condition of the lamps 1 to 4 and the imaging condition of the camera while viewing the image displayed on the screen using the input / display panel. Can be changed. Further, by performing a necessary input operation using the screen shown in FIG. 14, it is possible to select arbitrary data from the stored history data and easily check the already-proven inspection images and inspection results. In addition, if the re-inspection is executed after recalling the history data, the same optical conditions and judgment conditions are recalled from the saved recipe, and the inspection area is recalled and the inspection method that has been proven in the past is used. It becomes possible to inspect. In this way, inspection with high reproducibility can be performed.

  Next, an outline of the inspection of streaky unevenness in the periodic pattern will be described with reference to FIGS.

  Only the rectangular periodic pattern region of the mask to be inspected is cut out, and as shown in FIG. 11, integrated data 61 is obtained by calculation for the cut out two-dimensional image data. Here, only the integration in the vertical direction (Y-axis direction) in FIG. 10 will be described, but the integration data in the horizontal direction (X-axis direction) can be obtained in the same manner.

  Next, integrated moving average data 62 for the target point is calculated from the integrated data 61 shown in FIG. Here, the moving average calculation possible range 64 can be changed. However, since the moving average centered on the point of interest is calculated, it is impossible to calculate the integrated moving average data 62 at both end portions 63. Therefore, the end portions 63 that cannot be calculated are moved. The integrated moving average data is calculated using the least square method based on the data at both ends of the average calculable range 64.

  Next, a difference from the integrated moving average data 62 is obtained by the least square method. Thereby, the difference data 71 shown in FIG. 12 is obtained. A predetermined threshold value 72 determined from customer specifications and the like is set. Difference data 71 exceeding the threshold value 72 is determined to be unacceptable, and data not exceeding the threshold value 72 is determined to be acceptable. In this way, the pass / fail determination of the stripe-shaped uneven portion is performed.

  However, both end portions 63 for which the moving average is obtained by the least square method are predicted values by the least square method, and thus there is a risk of causing an error. As a countermeasure, it is possible to set a value 73 different from the threshold value 72 of the moving average calculation range 64 for both end portions 63.

  As described above, the stripe-shaped unevenness can be inspected with high accuracy by the inspection method specialized for the stripe-shaped unevenness.

  The apparatus of the present invention is used to detect streaky unevenness defects that occur in a pattern periodically formed on a substrate such as an aperture grill, a photomask, or a color filter used in a color television CRT.

1 is a structural block perspective view showing an outline of an inspection apparatus of the present invention. The block diagram which shows the control system of the test | inspection apparatus of this invention. The flowchart which shows the procedure of an inspection method. The figure which shows an inspection apparatus seeing from the side. (A) is a schematic plan view showing the positional relationship between the subject and the light source, and (b) is a schematic side view showing the positional relationship between the subject and the light source. The top view which shows an example of a periodic pattern. (A) is a figure which shows typically the imaging screen when test | inspected with the conventional apparatus, (b) is a figure which shows typically the imaging screen when test | inspected with this invention apparatus. The schematic diagram for demonstrating the generation | occurrence | production principle of the shadow (ghost) by multiple reflection (bottom surface reflection) light. The conceptual block diagram which shows the relationship between a reference condition and a reference condition in order to demonstrate a reference condition / reference condition setting function. The top view which shows typically the mask as a subject. The wave form diagram for demonstrating the calculation procedure when test | inspecting a stripe-shaped nonuniformity. FIG. 6 is another waveform diagram for explaining a calculation procedure when inspecting stripe-like unevenness. The schematic diagram for demonstrating an illumination center position adjustment function. The plane schematic diagram which shows collectively the layout of input screens, such as a recipe, and display screens, such as a camera image.

Explanation of symbols

10: Obliquely transmitted illumination part, 11A-11D ... Light source,
12 ... posture changing means (swing mechanism),
13 ... Moving means (linear slider), 14 ... Guide path (linear guide),
20 ... XY stage part, 22 ... X drive mechanism, 23 ... Y drive mechanism,
DESCRIPTION OF SYMBOLS 30 ... Imaging part, 31 ... Imaging side parallel optical system (imaging means, CCD camera), 32 ... Camera optical axis (center line), 33 ... Image plane, 34 ... Real image, 35 ... Shadow (ghost),
40 ... processing unit, 41 ... personal computer (image processing unit), 42 ... LCD (information display unit), 43 ... key board (personal operation unit),
DESCRIPTION OF SYMBOLS 50 ... Mask (subject board | substrate), 51 ... Pattern, 52 ... Stripe unevenness, 53 ... Periodic pattern area, 56 ... Imaging area (inspection area), 58 ... Center line (camera optical axis),
61 ... Integrated data, 62 ... Integrated moving average data, 63 ... Moving average calculation range by least square method, 64 ... Moving average calculation range, 71 ... Difference data, 72 ... Threshold of moving average calculation range, 73 ... Minimum 2 Multiplicative moving average calculation range threshold.

Claims (6)

A periodic pattern unevenness inspection apparatus for inspecting streaky unevenness generated in a periodic pattern on a rectangular substrate,
An XY stage comprising a moving mechanism for holding the substrate substantially horizontally and moving the substrate in the X-axis direction and the Y-axis direction within a two-dimensional planar field of view;
Four light sources that individually illuminate obliquely transmitted light with respect to the periodic pattern of the substrate on the XY stage;
An imaging unit that is disposed on the opposite side of the light source across the XY stage, and that images diffracted light in the periodic pattern illuminated obliquely by the light source;
Two X guides for guiding two of the four light sources in the X-axis direction with respect to the substrate on the XY stage,
Two Y guides arranged so as to be orthogonal to the X guide and guiding the other two of the four light sources in the Y-axis direction with respect to the substrate on the XY stage,
First moving means for individually moving each of the two light sources along each of the two X guides within a two-dimensional planar field of view;
Second moving means for individually moving each of the other two light sources along each of the two Y guides within a two-dimensional planar field of view;
When each of the two light sources is moved in the X-axis direction by the first moving means, illumination of obliquely transmitted light from each of the two light sources is applied to the periodic pattern to be inspected. First posture changing means for changing the orientation of each of the two light sources in conjunction with the first moving means;
When each of the other two light sources is moved in the Y-axis direction by the second moving means, oblique transmitted light is transmitted from each of the other two light sources with respect to the periodic pattern to be inspected. Second posture changing means for changing the direction of each of the other two light sources in conjunction with the second moving means so that illumination is applied;
The first and second moving means and the first and second posture changing means so that the incident angles of the obliquely transmitted light by the four light sources change with respect to the periodic pattern to be inspected. Optical condition 4-axis setting means for setting the operations of
A periodic pattern non-uniformity inspection apparatus comprising: Furthermore, the four light sources, the first and second moving means, and the first and second attitude changing means are individually set according to at least one of the periodic pattern to be inspected and the customer specification. The inspection apparatus according to claim 1, further comprising an axis-specific individual setting / storing function for storing the optical conditions set individually. Furthermore, a basic condition for detecting basic stripe-shaped unevenness is set, and a plurality of reference conditions for detecting a stripe-shaped unevenness that cannot be detected only by the reference condition are set, respectively, so that the stripes generated in the periodic pattern are detected. The inspection apparatus according to claim 1, further comprising a reference condition / reference condition setting function for switching from the reference condition to the reference condition according to a state of unevenness.   4. The illumination center position adjusting function of causing the imaging means to pick up an image when the luminance peak of the illumination light is shifted by a predetermined distance from the optical axis of the imaging means. The inspection device described. The inspection apparatus according to claim 1 , wherein the four light sources can be switched on and off individually. The inspection apparatus according to claim 1, wherein each of the four light sources has an optical filter that transmits light of a desired wavelength in a detachable manner.

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