JP5119602B2 - Periodic pattern defect inspection method and defect inspection apparatus - Google Patents

Description

  The present invention relates to a defect inspection apparatus and a defect inspection method for inspecting a pattern-like uneven defect in a product such as a photomask for a memory having a periodic pattern. The present invention relates to a defect inspection method and a defect inspection apparatus for a periodic pattern capable of detecting a stripe-shaped unevenness generated in a formed pattern with high accuracy.

  The periodic pattern refers to a collection of line and space patterns having a constant interval (hereinafter referred to as a pitch). For example, a periodic pattern of stripes in which one pattern is arranged at a predetermined pitch, or A matrix-like periodic pattern in which patterns of openings are arranged at a predetermined pitch.

  In a conventional defect inspection of a periodic pattern, a transmittance image is captured using coaxial transmission illumination or planar illumination (see, for example, Patent Documents 1 and 2), and light intensity (brightness and luminance) in each image is captured. ) To visually recognize the streaky unevenness defect and the normal part. Therefore, in an image with a low so-called contrast with a small light intensity difference between the mura defect portion and the normal portion, the mura defect portion is extracted by expanding the intensity difference. That is, in the conventional method, the intensity distribution of diffracted light is measured, and an inspection is performed where the peak of the diffracted light appears.

However, in the conventional method, when inspecting the periodic pattern of the photomask for memory with a small pitch, even if the processing of the intensity difference is devised, the improvement in the contrast between the mura defect portion and the normal portion cannot be expected, There may be a case where a slight difference in the intensity of light generated in the uneven defect portion cannot be determined.
JP 2002-148210 A JP 2002-350361 A

  SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and a periodic pattern defect inspection method and defect inspection capable of inspecting a periodic pattern with a fine pitch such as a photomask for a memory with high accuracy. An object is to provide an apparatus.

In the defect inspection method for a periodic pattern according to the present invention, the periodic pattern drawn on the XY plane of the substrate at a predetermined pitch in the X-axis direction is irradiated with light having a center wavelength λ1 (= 500 nm) from four inspection light sources. In the periodic pattern defect inspection method for inspecting streaky unevenness defects occurring in the periodic pattern, (i) a central wavelength λ1 (= 500 nm) of the inspection light source from another light source different from the four inspection light sources Irradiating the periodic pattern with light having a single wavelength of a diffraction angle calculation wavelength λ2 (= 633 nm) that deviates from the direction opposite to each other in the drawing horizontal direction and the drawing vertical direction of the periodic pattern. The incident angle A at which the peak appears on the vertical axis of the diffractive surface is measured, and the first order diffracted light appears from the relationship of θ1 = (90−A) π / 180 using the measured incident angle A. The angle .theta.1 determined, or calculated pitch dimension d from the relationship d = 1 × used central wavelength .lambda.1 of the incident angle .theta.1 obtained the inspection light source λ1 / sin (θ1), or, the drawing information of the periodic pattern To obtain the pitch dimension of the periodic pattern from
(Ii) Diffracted light intensity of the normal portion and the uneven portion of the periodic pattern from the relationship of θtarget = sin ⁻¹ (1 × λ2 / d) using the obtained pitch dimension d and the diffraction angle calculation wavelength λ2. obtains the incident angle Shitatarget suitable for measurement so that the contrast can be taken of, calculating the incident angle B from the relationship between the incident angle Shitatarget using B = {90- (θtarget × 180 )} / π obtained, (iii) the Relatively align each of the four inspection light sources and the substrate so that light is incident on the periodic pattern from the four inspection light sources at an incident angle B , and (iv) center from each of the four inspection light sources Inspection is performed by irradiating the periodic pattern with light having a wavelength λ1 (= 500 nm) .

The periodic pattern defect inspection apparatus according to the present invention is a periodic pattern defect for inspecting streaky unevenness defects generated in a periodic pattern drawn at a predetermined pitch in the X-axis direction on the XY plane of a substrate. an inspection apparatus, an XY stage having a moving mechanism for moving each (a) said substrate substantially horizontally held, and in the X-axis and Y-axis directions the substrate in a two-dimensional plane field, ( b1) Four inspection light sources that emit light having a central wavelength λ1 (= 500 nm) and individually illuminate obliquely transmitted light with respect to the periodic pattern of the substrate on the XY stage, and (b2) A single wavelength light having a diffraction angle calculation wavelength λ2 (= 633 nm) that deviates from the center wavelength λ1 (= 500 nm) from the opposite direction in the drawing pattern horizontal direction and the drawing vertical direction. And other light sources for irradiating the period pattern, across the (c) the XY stage is arranged on the opposite side of the four inspection light source, the diffraction in the cyclic pattern that is illuminated obliquely transmitted light by the four inspection light source Imaging means for imaging light; (d) optical condition 4-axis setting means for individually setting the optical conditions of the four inspection light sources; and (e) optical conditions set by the optical condition 4-axis setting means. A moving means for individually moving each of the four inspection light sources in a two-dimensional plane visual field with respect to the substrate on the XY stage based on a condition; and (f) each of the four inspection light sources by the moving means. When moved, the obliquely transmitted light from each of the four inspection light sources with respect to the periodic pattern to be inspected based on the optical condition set by the optical condition four-axis setting means As lighting strikes, and posture changing means for creating changing each direction of the four inspection light source in conjunction with the mobile unit, the (g) wherein the diffraction from another source angles calculated for the wavelength λ2 (= 633nm) Irradiation with light of a single wavelength, the incident angle A at which the peak of the main diffracted light appears on the vertical axis of the diffraction surface is measured, and the relation θ1 = (90−A) π / 180 using the measured incident angle A Calculating the pitch angle d from the relationship of d = 1 × λ1 / sin (θ1) using the calculated incident angle θ1 and the center wavelength λ1 of the inspection light source , or Means for acquiring the pitch dimension of the periodic pattern from the drawing information of the periodic pattern; (h) a bandpass filter having a center wavelength λ1 (= 500 nm) attached to each of the four inspection light sources; ) said Using said diffraction angle calculation wavelength .lambda.2 a pitch dimension d which is ^{θtarget = sin -1 (1 × λ2} / d) of the relationship so that the contrast of the diffracted light intensity of the normal portion and the unevenness of the periodic pattern can be taken from An incident angle θtarget suitable for measurement is obtained, and an incident angle B is calculated from the relationship of B = {90− (θtarget × 180)} / π using the obtained incident angle θtarget, and the four inspections are performed at the incident angle B. Control means for controlling the operations of the moving means and the attitude changing means so that light enters the periodic pattern from a light source and relatively aligning each of the four inspection light sources with the substrate; It is characterized by comprising.

In the defect inspection method of the present invention, correlation data obtained by examining the relationship between the appearance of the defect image observed in the inspection visual field, the pitch of the periodic pattern, the wavelength of light, and the incident angle is obtained in advance, and the correlation Using the data, 633 nm can be selected as the diffraction angle calculation wavelength.

Here, the “diffraction angle calculation wavelength” is a convenient virtual value for obtaining the incident angle θtarget of light from the light source suitable for inspection when the periodic pattern is irradiated with light from the light source using the following equation. Say. The value (rad) of the diffraction angle calculation wavelength λ is determined based on the correlation data between the light source wavelength and the visibility of unevenness obtained in advance through a verification test based on the wavelength range of the irradiation light source.

θtarget = sin ⁻¹ (m * λ / d)
In the defect inspection apparatus of the present invention, a band-pass filter having a center wavelength of 500 nm is attached to each of the four inspection light sources, and light having a center wavelength of 500 nm emitted from each inspection light source is passed through the band-pass filter and centered on 500 nm. An image of a periodic pattern with good contrast in the wavelength band can be obtained. Further, the control means stores correlation data obtained by examining the relationship between the appearance of the defect image observed in the inspection field of view of the imaging means, the pitch of the periodic pattern, the wavelength of the light, and the incident angle, and the periodic pattern The correlation data can be recalled each time the test is performed. For example, periodic pattern information (pitch, etc.) and light source optical conditions (light wavelength, light intensity distribution, light incident angle, light projection direction, floodlight area, depth of focus, etc.) Set 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. When actually performing the inspection, an optimum recipe is selected according to the periodic pattern of the subject, and the optical conditions of the light source 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 (normal pattern displacement portion or inflection portion) and streaky unevenness (defect pattern displacement portion or inflection portion) of the periodic pattern. By detecting these diffracted lights, streaky irregularities as defects are detected.

  With respect to light diffraction, strong transmitted light is formed in a specific direction in the normal part of the periodic pattern. Even in the stripe-shaped uneven part, diffracted light may be emitted only in a specific direction, but since the periodicity of the pattern (pattern shape and pitch interval) is different from the normal part, it is different from the normal part depending on the pattern shape and pitch interval. Diffracted light is generated in a different direction. Image processing and analysis are repeatedly performed based on optical detection data including these diffracted lights, and streaky irregularities are detected and displayed.

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 individually set the optical system conditions according to the corresponding sample. Therefore, in the present invention, the optical wavelength λ (diffraction angle calculation wavelength 633 nm) and the incident angle θ at that time are set as optical conditions that make it easy to find defects (striped irregularities) in the periodic pattern. Even if it is an inspection object of a simple pattern, it becomes possible to inspect with high accuracy without oversight.

  The set values of the optical conditions set as described above are stored as a recipe, and the inspection result and the inspection image are stored in the database together with the recipe. That is, by performing a necessary input operation using the panel screen, 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.

  According to the present invention, it is possible to detect streaky irregularities that could not be detected by the conventional method, and to inspect even a periodic pattern with a fine pitch such as a photomask for a memory with high accuracy. become.

  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 defect inspection apparatus for a periodic pattern 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 that has a function of emphasizing the captured image, determining whether the image is a streak-like unevenness defect, and displaying the streak-like unevenness defect so that the operator can easily recognize the emphasized image 40.

  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 tilting mechanism 12 as posture changing means and a linear slider 13 as moving means. 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 tilt 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 tilting 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 is tilted 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 (wavelength conversion means) (not shown) that transmits light of a desired wavelength. The optical filter functions as a wavelength converting means, and a plurality of types of optical filters are prepared corresponding to various periodic patterns, and each time a customer specification or inspection recipe is changed, a desired optical filter is correspondingly changed. Can be replaced.

  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 operates various functions such as an optical condition 4-axis setting function, individual axis setting / storing function, reference condition / reference condition setting function, illumination center position adjustment function, database function / re-inspection function, etc. The 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 tilt 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.

  The database function / re-inspection function is a function that stores optical condition setting values and the like as a recipe, and also stores inspection results and inspection screens in the database. By adding the database function / re-inspection function, the optical condition setting values set by the various functions described above are stored as recipes, and the inspection results and inspection images are also stored in the database.

  For example, the operator can input and change necessary recipes such as the conditions of the lamps 1 to 4 and the imaging conditions of the camera while viewing the image displayed on the screen using the input / display panel. Further, by performing a necessary input operation using the screen, 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 a periodic pattern defect inspection procedure will be 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 and tilted, aligned with the imaging area 56, illuminated by 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 and the driving of the XY stage 21 is stopped (step S15), and finally the image processing and determination processing in steps S16 to S21 are performed. The apparatus is 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, a case where a fine pattern formed on a memory photomask is inspected as a periodic pattern to be inspected will be described with reference to FIG.

First, the periodic pattern of the memory photomask to be inspected is irradiated with laser light while changing the incident angle, and the incident angle A at which the main diffracted light peak appears on the vertical axis of the diffraction surface is measured (step S31). ). The incident angle A obtained here is an angle using an axis parallel to the diffraction surface as a reference (0 degree) based on the apparatus specification of the present invention. In order to adjust the angle perpendicular to the diffractive surface as a reference (0 degree) and to match the format of a general theoretical formula for calculating the angle in radians, the incident angle A is changed to the incident angle θ ₁ by the following equation (1). Convert.

θ ₁ = (90−A) π / 180 (1)
The relationship of the following formula (2) is established between the incident angle θ _{M at} which m-th order diffracted light appears, the wavelength λ of the light irradiated on the pattern, and the pitch d of the periodic pattern.

θ _M = sin ⁻¹ (mλ / d) (2)
Based on the above equation (2), the pitch angle d of the periodic pattern is obtained from the following equation (3) using the incident angle θ ₁ and the laser light wavelength λ ₁ (step S32).

d = 1 × λ ₁ / sin (θ ₁ ) (3)
An incident angle θ target suitable for measurement is obtained from the following equation (4) using the obtained pitch dimension d and the diffraction angle calculation wavelength λ ₂ corresponding to the light source wavelength used for the inspection (step S33).

θtarget = sin ⁻¹ (1 × λ ₂ / d) (4)
The obtained incident angle θtarget is converted into an angle B conforming to the apparatus specifications of the present invention using the following equation (5).

B = {90− (θtarget × 180)} / π (5)
The light sources 11A to 11D of the inspection apparatus are respectively aligned with the mask 50 so that light is incident on the mask 50 at the incident angle obtained as described above (step S34).

  In each of the light sources 11A to 11D, the wavelength of the light source light is converted into a desired inspection designated wavelength by using an optical filter having a predetermined bandwidth, and the inspection area of the mask 50 is illuminated with the wavelength converted light (step S35). An imaging area is imaged by the imaging unit 30, and the imaging data is sent to the processing unit 40 for image processing. By observing / analyzing the image processing data, it is determined / evaluated whether the periodic pattern on the mask 50 has a streaky unevenness defect.

  When the inspection of a certain area is completed, the inspection target mask 50 is stepped by a predetermined distance by the XY stage unit 20, the next inspection target area is positioned within the measurement visual field of the imaging unit 30, and the next inspection is performed as described above. The area is inspected by irradiating light with a specified wavelength (step S36). In this way, illumination, imaging, observation, analysis, and evaluation are repeated one after another for the small area, and the entire area of the mask 50 is inspected.

Next, the outline of the digitization process for analyzing the stripe-like unevenness defect will be described with reference to FIGS.
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. 6, 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 to obtain differential data 71 as shown in FIG. A threshold value 72 is provided in the difference data 71, and a data exceeding the threshold value 72 is determined to be a streak-like unevenness defect.

  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. By using an inspection method specialized for streaky unevenness defects in this way, it becomes possible to detect streaky unevenness defects with high accuracy.

  The imaging of the periodic pattern and the defect detection will be further described.

  In the normal part of the periodic pattern 51, 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 defective part, the slit part (or opening part). ) Is unstable, and diffracted light is generated in various directions with various intensities in accordance with 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. If 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. The difference in the brightness of the diffracted light is caused by illumination that gradually changes the irradiation angle. Is further emphasized.

  The diffracted light diffracted by the mask 50 changes the diffraction angle due to subtle variations in the black matrix, so that the image captured by the imaging unit 30 is an image that emphasizes the defective portion caused by the variation in the black matrix. . 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 defects having various directions.

  In this manner, the defect image captured by the imaging unit 30 is subjected to defect portion extraction processing and determination processing by the processing unit 40. By displaying the determined position and level of the defect on the processing unit 40 simultaneously with the defect image, the use for defect monitoring is also effective.

  As shown in FIG. 5, 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, θ2, θ3, and 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 in the range of 30 ° to 70 ° because of limitations on the apparatus configuration.

Next, various embodiments of the present invention will be described with reference to FIGS.
Example 1
Illuminate the periodic pattern with 633 nm laser light and measure the diffraction angle of the main diffracted light peak, and calculate the pitch dimension d of the periodic pattern from the measured diffraction angle, or drawing information of the periodic pattern ( The pitch dimension d of the periodic pattern was obtained from the data.

  Next, the optimum inspection angle (incident angle) θtarget (= 54 °) was determined based on the diffraction angle calculation wavelength 633 nm corresponding to the center wavelength 500 nm of the illumination light used for the subsequent inspection and the pitch dimension d.

  When a band pass filter with a center wavelength of 500 nm is attached to an illumination light source (metal halide lamp) and a periodic pattern is illuminated at an incident angle of 54 °, an image with good contrast can be obtained as shown in FIG. The streaky unevenness defect 54 existing in the pattern 51 was clearly captured.

  By the way, illumination is performed at an incident angle calculated using the center wavelength of 500 nm of the illumination used for the inspection as a wavelength for calculating the diffraction angle, that is, at an incident angle at which the main diffracted light peak of the diffracted light intensity appears as in the conventional technique, It was investigated whether or not the defect could be captured as an image of visible light within the inspection visual field. As a result, in any case, the streaky unevenness defect could not be clearly captured as a visible light image.

  Next, a theoretical background in which a streaky unevenness defect cannot be captured in an inspection at an incident angle at which a main diffraction peak of diffracted light intensity appears, which is a conventional technique, will be described with reference to FIG.

  FIG. 9A shows the periodic pattern when the light incident through the band pass of the band centering on 500 nm is illuminated with the incident angle of the illumination light on the horizontal axis and the light intensity on the vertical axis. It is a characteristic diagram which shows typically the light intensity distribution of a normal part and a nonuniformity defect part, respectively. In the figure, the characteristic line E1 (solid line) indicates the light intensity distribution of the normal part, and the characteristic line F1 (broken line) indicates the light intensity distribution of the uneven defect part. The average pitch of the periodic pattern 51 was 1080 nm.

  As apparent from FIG. 9A, the entire screen is bright at the incident angle α1 (= 62 °) corresponding to the first-order diffracted light peak, but the luminance difference between the characteristic lines E1 and F1 is small. The contrast becomes poor, and the image of the mura defect becomes unclear or does not appear. On the other hand, the entire screen becomes dark at an incident angle β1 (= 52 °) deviating from the peak of the first-order diffracted light, but the contrast as a whole is increased because the luminance difference between the characteristic lines E1 and F1 becomes large. As a result, the image of the mura defect was clearly captured.

  FIG. 9B is a diagram schematically showing the luminance levels of the normal part and the uneven defect part in the CCD dynamic range. As described above, in the present invention, since the inspection is carried out at a point outside the peak of the luminance level of the main diffracted light, the entire screen becomes dark. Therefore, the screen can be brightened by adjusting the gray level to the brightness of the normal portion of the camera sensitivity 0 to 255 in the CCD dynamic range.

(Example 2)
A periodic pattern different from that of the first embodiment is illuminated with a laser beam of 633 nm and the diffraction angle of the main diffracted light peak is measured, and the pitch dimension d of the periodic pattern is calculated from the measured diffraction angle, or the periodicity is calculated. The pitch dimension d of the periodic pattern was obtained from the pattern drawing information (data).

  Next, the optimum inspection angle (incident angle) θtarget (= 41.8 °) was obtained based on the diffraction angle calculation wavelength 633 nm corresponding to the center wavelength 500 nm of the illumination light used for the subsequent inspection and the pitch dimension d.

  When a bandpass filter with a central wavelength of 500 nm is attached to the illumination light source (metal halide lamp) and the periodic pattern is illuminated at an incident angle of 41.8 °, an image with good contrast can be obtained as shown in FIG. The streaky unevenness defect 54 existing in the periodic pattern 51 was clearly captured. The average pitch of the periodic pattern 51 was 864 nm.

  By the way, illumination is performed at an incident angle calculated using the center wavelength of 500 nm of the illumination used for the inspection as a wavelength for calculating the diffraction angle, that is, at an incident angle at which the main diffracted light peak of the diffracted light intensity appears as in the conventional technique, It was investigated whether or not the defect could be captured as an image of visible light within the inspection visual field. As a result, streaky unevenness defects could not be clearly captured as a visible light image.

  Since most of the shape of the periodic pattern 51 is rectangular as shown in FIG. 10, the stripe-like unevenness (drawing unevenness) is in the horizontal direction (X direction) and vertical direction (Y direction). In many cases, the incident angle is periodically generated. Therefore, there are several incident angles at which defects are easily found according to the pattern shape. For example, in a T-shaped pattern, for example, when θ1 and θ2 are incident angles at which defects are easy to find, it is grasped in advance by a verification test, and when a photomask including a T-shaped pattern is inspected, θ1, If θ2 is set, streak-like unevenness 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 incident angle θ itself is not directly detected, if the height level difference L between the light source / pattern is known, the light projection angle can be determined by detecting the distance between the light source / pattern. Can be sought.

  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, in advance by a verification test or the like, how to operate the moving means and the posture changing means for each light source corresponding to the periodic pattern 51 of the subject is stored, and this data is stored as a recipe. Keep it. 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 54 as a defect is detected by detecting the diffracted light respectively. Is done.

  Regarding light diffraction, in the normal portion of the periodic pattern 51, strong transmitted light is formed in a specific direction. On the other hand, in the streaky uneven portion 54, diffracted light is not emitted only in a specific direction, but diffracted light is generated with various intensities in various directions according to the pattern shape and pitch interval. Image processing and analysis are repeatedly performed based on optical detection data including these diffracted lights, and streaky irregularities are detected and displayed.

  Next, what kind of light is suitable for the illumination light will be described with reference to FIGS.

(Comparative Example 1)
FIG. 11 is a characteristic diagram showing the light intensity distribution of illumination light (band light) having a bandwidth at the center of the blue spectrum with respect to the normal part and the mura defect part. The periodic pattern was illuminated with illumination light having a bandwidth at the center of the blue spectrum using a filter having an optimum bandwidth for observing mura defects. In the figure, the characteristic line E3 (solid line) indicates the light intensity distribution of the normal part, and the characteristic line F3 (broken line) indicates the light intensity distribution of the uneven defect part. As is apparent from the figure, the entire screen is bright at the incident angle α3 (= 62 °) corresponding to the first-order diffracted light peak, but the contrast is poor because the luminance difference between the characteristic lines E3 and F3 is small. And the image of the mura defect becomes unclear or does not appear. On the other hand, the entire screen becomes dark at an incident angle β3 (= 54 °) that deviates from the peak of the first-order diffracted light, but the contrast as a whole is increased because the luminance difference between the characteristic lines E3 and F3 becomes large. As a result, the image of the mura defect was clearly captured.

(Comparative Example 2)
FIG. 12 is a characteristic diagram showing the light intensity distribution of the blue spectrum illumination light (spectrum light) related to the normal part and the uneven defect part. The illumination light of the blue spectrum was illuminated to the periodic pattern using a filter. In the figure, the characteristic line E4 (solid line) indicates the light intensity distribution of the normal part, and the characteristic line F4 (broken line) indicates the light intensity distribution of the uneven defect part. Although there is a tradeoff with the sensitivity of the line sensor built in the CCD camera 31, even at an incident angle α4 (= 62 °) corresponding to the first-order diffracted light peak, an incident angle β4 ( = 60 °), in any case, the contrast was poor, the image of the mura defect became unclear, and the image of the mura defect could be seen, but it was found difficult to observe.

(Comparative Example 3)
FIG. 13 is a characteristic diagram showing the light intensity distribution of the white illumination light with respect to the normal part and the uneven defect part. In the figure, the characteristic line E5 (solid line) indicates the light intensity distribution in the normal part, and the characteristic line F5 (broken line) indicates the light intensity distribution in the uneven defect part. Although there is a tradeoff with the sensitivity of the line sensor built in the CCD camera 31, even at an incident angle α5 (= 62 °) corresponding to the first-order diffracted light peak, an incident angle β5 ( = 40 °), the contrast was poor in any case, and an image of uneven defects did not appear.

  According to the present invention, streak-like unevenness generated in a pattern periodically formed on a substrate such as a photomask or a wafer can be detected with high accuracy.

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 the general defect inspection method. The flowchart which shows the procedure which test | inspects the defect of the periodic pattern of the memory photomask. The figure which shows the positional relationship of a test object and a light source seeing a test | inspection apparatus from the side. The top view which shows typically the mask as a subject. The wave form diagram for demonstrating the calculation procedure when test | inspecting a periodic pattern. FIG. 6 is another waveform diagram for explaining a calculation procedure when inspecting a periodic pattern. (A) is a characteristic diagram which shows the light intensity distribution of a normal part and a nonuniformity defect part, respectively, (b) is a figure which shows typically the luminance level of a normal part and a nonuniformity defect part in a CCD dynamic range. The plane schematic diagram which shows an example of the periodic pattern which has a nonuniformity defect part. The characteristic diagram which shows the light intensity distribution of the illumination light of the bandwidth of the blue spectrum center regarding a normal part and a nonuniformity defect part. The characteristic diagram which shows the light intensity distribution of the blue spectrum illumination light regarding a normal part and a nonuniformity defect part. The characteristic diagram which shows the light intensity distribution of the white illumination light regarding a normal part and a nonuniformity defect part.

Explanation of symbols

10: Obliquely transmitted illumination part, 11A-11D ... Light source,
12 ... posture changing means (tilting mechanism),
13 ... Moving means (linear slider), 14 ... Guide path (linear guide),
20 ... XY stage part, 22 ... X drive mechanism, 23 ... Y drive mechanism,
30 ... Imaging unit, 31 ... Imaging side parallel optical system (imaging means, CCD camera), 32 ... Camera optical axis (center line),
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 (2)

The periodic pattern drawn on the XY plane of the substrate at a predetermined pitch in the X-axis direction is irradiated with light having a central wavelength λ1 (= 500 nm) from four inspection light sources, thereby causing streak-like uneven defects generated in the periodic pattern. In the defect inspection method of the periodic pattern to be inspected,
(I) Light having a single wavelength of a diffraction angle calculation wavelength λ2 (= 633 nm) that deviates from the central wavelength λ1 (= 500 nm) of the inspection light source from another light source different from the four inspection light sources . The periodic pattern is irradiated from opposite directions in the drawing horizontal direction and the drawing vertical direction, the incident angle A at which the peak of the main diffracted light appears on the vertical axis of the diffraction surface is measured, and the measured incident angle A is used. The incident angle θ1 at which the first-order diffracted light appears is determined from the relationship θ1 = (90−A) π / 180, and d = 1 × λ1 / sin (θ1) using the calculated incident angle θ1 and the center wavelength λ1 of the inspection light source. Calculating the pitch dimension d from the relationship , or obtaining the pitch dimension of the periodic pattern from the drawing information of the periodic pattern,
(Ii) Diffracted light intensity of the normal portion and the uneven portion of the periodic pattern from the relationship of θtarget = sin ⁻¹ (1 × λ2 / d) using the obtained pitch dimension d and the diffraction angle calculation wavelength λ2. An incident angle θtarget suitable for measurement so as to obtain a contrast of λ is obtained, and an incident angle B is calculated from the relationship of B = {90− (θtarget × 180)} / π using the obtained incident angle θtarget.
(Iii) Relatively aligning each of the four inspection light sources and the substrate so that light enters the periodic pattern from the four inspection light sources at the incident angle B ;
(Iv) A periodic pattern defect inspection method, wherein the periodic pattern is irradiated with light having a central wavelength λ1 (= 500 nm) from each of the four inspection light sources. A periodic pattern defect inspection apparatus for inspecting streaky uneven defects generated in a periodic pattern drawn at a predetermined pitch in the X-axis direction on the XY plane of a substrate ,
(A) an XY stage including a moving mechanism that holds the substrate substantially horizontally and moves the substrate in the X-axis direction and the Y-axis direction within a two-dimensional planar field of view;
(B1) Four inspection light sources that emit light having a central wavelength λ1 (= 500 nm) and individually illuminate obliquely transmitted light with respect to the periodic pattern of the substrate on the XY stage;
(B2) A direction in which light having a single wavelength of a diffraction angle calculation wavelength λ2 (= 633 nm) that deviates from the center wavelength λ1 (= 500 nm) of the inspection light source is opposed to each other in the drawing horizontal direction and drawing vertical direction of the periodic pattern. Other light sources that irradiate the periodic pattern from
(C) an imaging unit that is disposed on the opposite side of the four inspection light sources across the XY stage, and that images diffracted light in the periodic pattern illuminated obliquely by the four inspection light sources;
(D) optical condition 4-axis setting means for individually setting the optical conditions of the four inspection light sources;
(E) moving means for individually moving each of the four inspection light sources in a two-dimensional planar field of view with respect to the substrate on the XY stage based on the optical condition set by the optical condition four-axis setting means; ,
(F) When each of the four inspection light sources is moved by the moving means, the periodic pattern to be inspected based on the optical condition set by the optical condition four-axis setting means Posture changing means for changing the orientation of each of the four inspection light sources in conjunction with the moving means so that each of the four inspection light sources is illuminated with obliquely transmitted light;
(G) irradiating light of a single wavelength of the diffraction angle calculation wavelength λ2 (= 633 nm) from the other light source , and measuring an incident angle A at which the peak of the main diffracted light appears on the vertical axis of the diffraction surface; The incident angle θ1 at which the first-order diffracted light appears is determined from the relationship θ1 = (90−A) π / 180 using the measured incident angle A, and d = 1 using the calculated incident angle θ1 and the center wavelength λ1 of the inspection light source. Means for calculating the pitch dimension d from the relationship of xλ1 / sin (θ1) or obtaining the pitch dimension of the periodic pattern from the drawing information of the periodic pattern;
(H) a bandpass filter having a center wavelength λ1 (= 500 nm) attached to each of the four inspection light sources;
(I) Diffracted light intensity of the normal portion and the uneven portion of the periodic pattern from the relationship of θtarget = sin ⁻¹ (1 × λ2 / d) using the obtained pitch dimension d and the diffraction angle calculation wavelength λ2. The incident angle θ target suitable for the measurement is obtained so as to obtain the contrast , and the incident angle B is calculated from the relationship of B = {90− (θ target × 180)} / π using the obtained incident angle θ target. The relative positions of each of the four inspection light sources and the substrate are controlled by controlling the operations of the moving means and the posture changing means so that light enters the periodic pattern from the four inspection light sources. Control means;
A defect inspection apparatus for periodic patterns, comprising:

Images