JP5514754B2 - Inspection apparatus and inspection method - Google Patents

Description

  The present invention relates to an inspection apparatus and an inspection method, and more particularly to an inspection apparatus and an inspection method used for detecting a defect of a pattern formed on an inspection object such as a mask.

  In recent years, the circuit line width required for a semiconductor element has become increasingly narrower as the large scale integrated circuit (LSI) is highly integrated and has a large capacity. The semiconductor element uses an original pattern pattern (a mask or a reticle, which will be collectively referred to as a mask hereinafter) on which a circuit pattern is formed. Manufactured by forming. For manufacturing a mask for transferring such a fine circuit pattern onto a wafer, an electron beam drawing apparatus capable of drawing the fine pattern is used. Attempts have also been made to develop a laser beam drawing apparatus for drawing using a laser beam. The electron beam drawing apparatus is also used when drawing a circuit pattern directly on a wafer.

  Yield improvement is indispensable for the manufacture of LSIs that require a large amount of manufacturing costs. On the other hand, recent typical logic devices are required to form patterns with a line width of several tens of nanometers. Here, as a major factor for reducing the yield, there are mask pattern defects and variations in process conditions during exposure transfer. Until now, with the miniaturization of the LSI pattern dimension formed on a semiconductor wafer, it has been performed to absorb the variation margin of process conditions by increasing the dimensional accuracy of the mask. For this reason, in mask inspection, the dimensions that must be detected as pattern defects are miniaturized, and it is necessary to detect position errors of extremely small patterns. For this reason, high inspection accuracy is required for inspection apparatuses that detect defects in transfer masks used in LSI manufacturing.

  Defect detection methods include a die-to-die inspection method and a die-to-database inspection method. The die-to-die inspection method compares the same patterns of chips with different masks when a plurality of chips having the same pattern configuration are arranged in a part or the whole of the same mask. Inspection method. According to this method, since the mask patterns are directly compared, highly accurate inspection can be performed with a relatively simple apparatus configuration. However, it is impossible to detect a defect that exists in common in both patterns to be compared. On the other hand, the die-to-database inspection method is an inspection method in which reference data generated from design pattern data used for mask manufacture is compared with an actual pattern on the mask. Since a mechanism for generating a reference image is required, the apparatus becomes large, but a strict comparison with design pattern data can be performed. This method can be used only when there is only one chip transfer area in one mask.

  In die-to-database inspection, light emitted from a light source is irradiated onto a mask to be inspected via an optical system. The mask is placed on a table, and light irradiated as the table moves scans the mask. The light transmitted or reflected through the mask forms an image on the image sensor via the lens, and the optical image captured by the image sensor is sent to the comparison unit as measurement data. In the comparison unit, the measurement data and the reference data are compared according to an appropriate algorithm. If these data do not match, it is determined that there is a defect (see, for example, Patent Document 1).

  In a conventional inspection apparatus, it is determined whether a mask pattern image obtained by capturing an optical image with an image sensor is correct. However, it is difficult to distinguish the difference between a pattern shape defect and a pattern shape error that exists potentially in recent masks that have been miniaturized. In addition, because the required accuracy for the line width of the mask pattern and the gap distance with the adjacent pattern is increased, it is not necessary to compare the reference data generated based on the design pattern data with the pattern image taken by the inspection device. It is difficult to determine whether or not.

  Therefore, a method for determining a defect from the shape when the mask pattern is transferred to the wafer has been proposed. For example, Non-Patent Document 1 discloses a method for obtaining a wafer space image with a low-resolution optical system along with a method for collecting an inspection mask image with a CCD using a high-resolution optical system (see FIG. 1). ). In the former method, a wafer transfer image is estimated through the process of FIG. 2 from each mask image of a pattern to be inspected and a reference pattern collected by a high-resolution optical system, and then defect determination is performed by comparing the wafer transfer images with each other. To do. On the other hand, in the latter method, an optical system that simulates the optical system of the wafer transfer apparatus is provided, and a wafer transfer image is directly collected. In any of these methods, an image transferred on a wafer is predicted, and a defect is determined based on the predicted image. The latter method is also described in Non-Patent Document 2 (see the lower part of FIG. 3 and page 3).

JP 2008-112178 A Japanese Patent No. 3824542

Carl Hess et al., (KLA-Tencor Corporation), “A Novel Approach: High Resolution Inspection with Wafer Plane Detection Detection”, Proc. Of SPIE Vol. 7028, 70281F. Dan Rost et al., (MP-Mask Technology Center), “Qualification of Aerial Image 193 nm Inspection Tool for All Masks and All Process Steps”, Proc.

  Incidentally, mask defects are classified into random defects and system defects. Random defects are caused by defects in the manufacturing process such as variations in process conditions in the drawing process, the etching process, and the like, and adhesion of foreign matter. On the other hand, the system defect is a phenomenon commonly found in masks such as line width variation and pattern position shift due to interference with neighboring patterns.

  Conventional inspection equipment mainly aims to detect random defects focused on pattern shapes, and system defects can be detected by analyzing images collected by the inspection equipment with another device or equipped with an exposure optical system. This was done by analyzing the wafer transfer image collected by the inspection device. Further, while defect detection is performed based on the wafer transfer image estimated by the inspection apparatus, the line width of the pattern is measured by another apparatus, and defect detection may be performed by this.

  In general, system defects are distributed depending on the feature and density of the pattern shape, and abnormalities due to random defects are superimposed on the system defects, resulting in defects that affect the wafer beyond the allowable margin. However, in the conventional method, since the allowable margin for random defects and the allowable margin for system defects are set separately, there are cases in which even minor defects that originally do not need to be treated as defects are detected and corrected. .

  The present invention has been made in view of these points. That is, the present invention is to provide an inspection apparatus and an inspection method that can reduce unnecessary defect correction by suppressing excessive defect detection.

  Other objects and advantages of the present invention will become apparent from the following description.

A first aspect of the present invention is an inspection apparatus that illuminates a sample on which a pattern is formed, forms an image of the sample on an image sensor via an optical system, and determines the presence or absence of a defect.
An optical image acquisition unit for acquiring an optical image of the sample from the image sensor;
A dimension measuring unit for measuring a dimension of the pattern in the optical image and a dimension of the pattern in the reference image serving as a reference for determination, and obtaining a first error therefrom;
A transfer image estimation unit that estimates each transfer image with respect to the optical image and the reference image on the sample, measures a dimension of the pattern in the transfer image, and obtains a second error;
A comparison unit that compares the transferred images and determines a defect when the difference exceeds a threshold value;
And a correction unit that corrects the second error at the location determined as a defect by the comparison unit with the first error.

  The first aspect of the present invention preferably includes a storage unit that stores a map describing the first error.

A second aspect of the present invention is an inspection method for illuminating a sample on which a pattern is formed, forming an image of the sample on an image sensor via an optical system, and determining the presence or absence of a defect.
Obtaining an optical image of the sample from the image sensor;
Measuring the dimension of the pattern in the optical image and the dimension of the pattern in the reference image serving as a reference for determination, and obtaining a first error therefrom,
Estimating each transfer image for the optical image and the reference image on the sample, measuring the dimension of the pattern in these transfer images, and determining a second error;
Comparing each transferred image and determining a defect when the difference exceeds a threshold;
And a step of correcting the second error at a location determined as a defect with the first error.

  The second aspect of the present invention preferably includes a step of determining whether or not the defect needs to be corrected from the second error corrected by the first error.

  The second aspect of the present invention preferably includes a step of creating a map describing the first error.

  ADVANTAGE OF THE INVENTION According to this invention, the inspection apparatus and inspection method which can reduce an unnecessary defect correction by suppressing an excessive defect detection are provided.

It is a system configuration figure of the inspection device in this embodiment. It is a conceptual diagram which shows the flow of the data in this Embodiment. It is a figure explaining a filter process. It is a figure explaining the acquisition procedure of mask collection data. It is a map figure which shows the actual size error distribution of a pattern about the drawing area | region of a mask. (A) is a figure which shows the actual size error distribution of the cross section along the AA 'line of FIG. 5, (b) is a figure which shows the actual size error (W) calculated by the wafer transcription | transfer simulator, (c) is a figure which shows a mode that added the element of (a) to (b). It is an example of the schematic diagram of a design pattern. (A) is an optical image corresponding to FIG. 7, and (b) is a reference image generated from FIG. It is a figure which shows a mode that the optical image of Fig.8 (a) and the reference image of FIG.8 (b) were piled up. (A) is a wafer transfer image estimated from the optical image of FIG. 8A, and (b) is a wafer transfer image estimated from the reference image of FIG. 8B. It is a figure which shows a mode that the wafer transfer image of Fig.10 (a) and FIG.10 (b) was piled up. It is a figure which shows a mode that the wafer transcription | transfer image of FIG. 11 was correct | amended using the dimension distribution map of this Embodiment.

  FIG. 1 is a system configuration diagram of an inspection apparatus according to the present embodiment. In this embodiment mode, a mask used in a photolithography method or the like is an inspection target.

  As illustrated in FIG. 1, the inspection apparatus 100 includes an optical image acquisition unit A and a control unit B.

  The optical image acquisition unit A includes a light source 103, an XYθ table 102 that can move in the horizontal direction (X direction, Y direction) and the rotation direction (θ direction), an illumination optical system 170 that constitutes a transmissive illumination system, and magnification optics. A system 104, a photodiode array 105, a sensor circuit 106, a laser length measurement system 122, and an autoloader 130 are included.

  In the control unit B, the control computer 110 that controls the entire inspection apparatus 100 receives the position circuit 107, the first comparison circuit 108, the reference circuit 112, the development circuit 111, and the dimension measurement via the bus 120 serving as a data transmission path. Circuit (dimension measurement unit) 131, second comparison circuit 132, wafer transfer simulator (transfer image estimation unit) 400, transfer defect calculation circuit (correction unit) 134, autoloader control circuit 113, table control circuit 114, storage device (memory) Are connected to a magnetic disk device 109, a magnetic tape device 115, a flexible disk device 116, a CRT 117, a pattern monitor 118, and a printer 119. The XYθ table 102 is driven by an X-axis motor, a Y-axis motor, and a θ-axis motor controlled by the table control circuit 114. As these motors, for example, step motors can be used.

  Design pattern data serving as database-based reference data is stored in the magnetic disk device 109, read out as the inspection progresses, and sent to the development circuit 111. In the development circuit 111, the design pattern data is converted into image data (bit pattern data). Thereafter, this image data is sent to the reference circuit 112 to be used for generating reference data.

  In FIG. 1, constituent components necessary for the present embodiment are illustrated, but other known components necessary for inspecting the mask may be included.

  FIG. 2 is a conceptual diagram showing the flow of data in the present embodiment.

  As shown in FIG. 2, CAD data 201 created by a designer (user) is converted into design intermediate data 202 in a hierarchical format such as OASIS. The design intermediate data 202 stores design pattern data created for each layer and formed on each mask. Here, in general, the inspection apparatus is not configured to directly read OASIS data. That is, unique format data is used for each manufacturer of the inspection apparatus. For this reason, the OASIS data is converted into format data 203 unique to each inspection apparatus for each layer, and then input to the inspection apparatus 100 of FIG. 1, for example. In this case, the format data 203 can be data unique to the inspection apparatus 100, but can also be data compatible with the drawing apparatus.

  The format data 203 is input to the magnetic disk device 109 of FIG. That is, the design pattern data used when forming the pattern of the mask 101 is stored in the magnetic disk device 109.

  The figure included in the design pattern is a basic figure of a rectangle or a triangle. The magnetic disk device 109 includes information such as coordinates (x, y) at the reference position of the figure, side lengths, figure codes serving as identifiers for distinguishing figure types such as rectangles and triangles, and each pattern figure. Graphic data defining the shape, size, position, etc.

  Furthermore, a set of figures existing in a range of about several tens of μm is generally called a cluster or a cell, and data is hierarchized using this. In the cluster or cell, arrangement coordinates and repeated description when various figures are arranged alone or repeatedly at a certain interval are also defined. The cluster or cell data is further arranged in a strip-like region called a frame or stripe having a width of several hundred μm and a length of about 100 mm corresponding to the entire length in the X direction or Y direction of the mask.

  The input design pattern data is read from the magnetic disk device 109 by the development circuit 111 through the control computer 110.

  The expansion circuit 111 expands the design pattern to data for each graphic, and interprets a graphic code, a graphic dimension, and the like indicating the graphic shape of the graphic data. Then, binary or multivalued design image data is developed as a pattern arranged in a grid having a grid with a predetermined quantization size as a unit. The developed design image data calculates the occupancy ratio of the figure in the design pattern for each area (square) corresponding to the sensor pixel. And the figure occupation rate in each pixel becomes a pixel value.

  The design pattern data converted into binary or multi-value image data (design image data) as described above is then sent to the reference circuit 112. In the reference circuit 112, an appropriate filter process is performed on the design image data that is the image data of the received graphic.

  FIG. 3 is a diagram for explaining the filter processing.

  The mask sampling data 204 as an optical image obtained from the sensor circuit 106, which will be described later, is in a state in which the blur is caused by the resolution characteristics of the magnifying optical system 104, the aperture effect of the photodiode array 105, or the like, in other words, a spatial low pass The filter is active. Therefore, by applying the filtering process to the design image data that is the image data on the design side in which the image intensity (shading value) is a digital value, it can be matched with the mask collection data 204. In this way, a reference image to be compared with the mask collection data 204 is created.

  Next, a method for acquiring the mask collection data 204 will be described with reference to FIGS. 1 and 4.

  In FIG. 1, the optical image acquisition unit A acquires an optical image of the mask 101, that is, mask collection data 204. Here, the mask collection data 204 is an image of a mask on which a figure based on the figure data included in the design pattern is drawn. A specific method for acquiring the mask collection data 204 is as follows, for example.

  The mask 101 to be inspected is placed on an XYθ table 102 provided so as to be movable in the horizontal direction and the rotation direction by motors of XYθ axes. Then, light is emitted from the light source 103 disposed above the XYθ table 102 to the pattern formed on the mask 101. More specifically, the light beam emitted from the light source 103 is applied to the mask 101 via the illumination optical system 170. Below the mask 101, an enlargement optical system 104, a photodiode array 105, and a sensor circuit 106 are arranged. The light that has passed through the mask 101 forms an optical image on the photodiode array 105 via the magnifying optical system 104. Here, the magnifying optical system 104 may be configured such that the focus is automatically adjusted by an automatic focusing mechanism (not shown). Further, although not shown, the inspection apparatus 100 irradiates light from below the mask 101, guides the reflected light to the second photodiode array through the magnifying optical system, and collects the transmitted light and the reflected light simultaneously. It may be configured.

  FIG. 4 is a diagram for explaining a procedure for acquiring the mask collection data 204 as an optical image.

  As shown in FIG. 4, the inspection area is virtually divided into a plurality of strip-like inspection stripes 20 having a scan width W in the Y direction, and each of the divided inspection stripes 20 is continuously scanned. Thus, the operation of the XYθ table 102 is controlled, and an optical image is acquired while moving in the X direction. An image having a scan width W as shown in FIG. 4 is continuously input to the photodiode array 105. When an image in the first inspection stripe 20 is acquired, an image having a scan width W is continuously input to the second inspection stripe 20 in the same manner while the XYθ table 102 is moved in the opposite direction. The third inspection stripe 20 is acquired while moving in the direction opposite to the direction in which the image in the second inspection stripe 20 is acquired, that is, in the direction in which the image in the first inspection stripe 20 is acquired. In this way, it is possible to shorten a useless processing time by continuously acquiring images.

  The pattern image formed on the photodiode array 105 in FIG. 1 is photoelectrically converted by the photodiode array 105 and further A / D (analog-digital) converted by the sensor circuit 106. Sensors are arranged in the photodiode array 105. An example of this sensor is a TDI (Time Delay Integration) sensor. While the XYθ table 102 continuously moves in the X-axis direction, the pattern of the mask 101 is imaged by the TDI sensor. Here, the light source 103, the magnifying optical system 104, the photodiode array 105, and the sensor circuit 106 constitute a high-magnification inspection optical system.

  The XYθ table 102 is driven by a table control circuit 114 under the control of the control computer 110, and can be moved by a drive system such as a three-axis (XY-θ) motor that drives in the X, Y, and θ directions. It has become. As these X-axis motor, Y-axis motor, and θ-axis motor, for example, step motors can be used. The movement position of the XYθ table 102 is measured by the laser length measurement system 122 and sent to the position circuit 107. The mask 101 on the XYθ table 102 is automatically conveyed from the autoloader 130 driven by the autoloader control circuit 113, and is automatically discharged after the inspection is completed.

  The mask collection data 204 output from the sensor circuit 106 is sent to the first comparison circuit 108 (first comparison unit) together with data indicating the position of the mask 101 on the XYθ table 102 output from the position circuit 107. It is done. The mask collection data 204 is, for example, 8-bit unsigned data and represents the brightness gradation of each pixel. Further, the reference image described above is also sent to the first comparison circuit 108.

  In the first comparison circuit 108, the mask collection data 204 sent from the sensor circuit 106 and the reference image generated by the reference circuit 112 are compared using an appropriate comparison determination algorithm. The comparison is performed using only a transmission image, only a reflection image, or an algorithm that combines transmission and reflection. As a result of the comparison, when the difference between the two exceeds a predetermined threshold (first threshold), the location is determined as a defect. If it is determined as a defect, the coordinates, the mask collection data 204 and the reference image that are the basis for the defect determination are stored in the magnetic disk device 109 as a mask inspection result 205.

  In the present embodiment, the mask collection data 204 is also sent to the dimension measurement circuit 131. In the dimension measuring circuit 131, the dimension of the mask collection data 204, for example, the line width of the line pattern is measured. A reference image is also sent from the reference circuit 112 to the dimension measuring circuit 131. Then, the dimension of the reference image (the dimension of the line pattern according to the above example) is measured. In the dimension measuring circuit 131, the actual dimension error or error ratio of the line width as the first error is obtained from these values. Specifically, for example, the method of Patent Document 2 (Japanese Patent No. 3824542) is applicable. Instead of the line width, the distance between the lines may be measured, and the actual size error or the error ratio of the distance between the lines may be obtained from this value.

  The actual size error of the line width is obtained by the equation (1). Further, the actual size error of the distance between lines can be obtained from the equation (2). However, the line width of the defective portion in the mask sampling data 204 is Lerr, and the distance between the lines is Serr. Further, in the reference image, the line width serving as a comparison standard is Lref, and the distance between the lines is Sref.

  The error ratio of the line width is obtained by the equation (3). Further, the error ratio of the line-to-line distance can be obtained by Expression (4). However, the line width of the defective portion in the mask sampling data 204 is Lerr, and the distance between the lines is Serr. Further, in the reference image, the line width serving as a comparison standard is Lref, and the distance between the lines is Sref.

  When the error ratio of the line width and the error ratio of the distance between the lines are compared and the error ratio of the line width is larger, the error ratio of the line width is obtained and used for the defect determination in the subsequent process. It can be said that it is practical. Therefore, in the present embodiment, it is preferable to use the larger one of the error ratio calculated for the line width of the pattern and the error ratio calculated for the inter-line distance of the pattern for defect determination. However, since it may be difficult to find an edge pair depending on the size of the pattern, it is more preferable to make a determination using both the error ratio and the actual size error.

  When the pattern to be formed is not a stripe pattern but a hole pattern, an actual size error or an error ratio with respect to the horizontal width or vertical width of the hole diameter is calculated.

The actual size error of the lateral width is obtained by Expression (5). Further, the actual size error of the vertical width is obtained from the equation (6). However, the horizontal width that is the comparison standard in the reference image is set as Hole _H ref, and the vertical width is set as Hole _V ref. In addition, for the mask sampling data 204 having a defective portion, the horizontal width is set to “Hole _H err” and the vertical width is set to “Hole _V err”.

The error ratio of the lateral width is obtained by Expression (7). Further, the vertical width error ratio is obtained by the equation (8). However, the horizontal width that is the comparison standard in the reference image is set as Hole _H ref, and the vertical width is set as Hole _V ref. In addition, for the mask sampling data 204 having a defective portion, the horizontal width is set to “Hole _H err” and the vertical width is set to “Hole _V err”.

  In the dimension measuring circuit 131, the calculated actual size error or error ratio data is further mapped. A map of actual size error or error ratio in the mask plane is stored in the magnetic disk device 109 as a size distribution map 135. However, the mapping may be performed outside the inspection apparatus. Furthermore, it is also possible to perform correction processing in a transfer defect calculation circuit 134 (described later) using the calculated actual size error or error ratio data without mapping.

  By the way, as a defect generated in a fine pattern, not only a shape defect represented by unevenness (edge roughness) of a pattern edge but also a gap between adjacent patterns due to an abnormal line width of the pattern or a positional deviation of the pattern is not appropriate. The phenomenon has become important. For this reason, the request | requirement with respect to pattern precision has become very high, and the difficulty in mask manufacture is also increasing increasingly. Therefore, the yield of masks that meet the standards is reduced, leading to an increase in mask manufacturing costs. For these reasons, a method of using a wafer transfer simulator (also referred to as a lithography simulator or a process simulator) as a defect determination method has been proposed. In this method, an exposure image transferred from the mask to the wafer by the exposure apparatus is estimated, and the quality of the pattern is determined on the exposure image. The wafer transfer simulator is a transfer image estimation unit in the present invention.

  The mask inspection result 205 and the size distribution map 135 are read from the magnetic disk 109 by the control computer 110 and sent to the wafer transfer simulator 400. At this time, instead of the reference image in the mask inspection result 205, an image obtained by simulating a mask manufacturing process from pattern data before adding a RET pattern for mask design may be used.

  In wafer transfer simulator 400, a wafer transfer image is estimated by simulation. Specifically, the wafer transfer image is estimated from the reference image serving as a model, and the wafer transfer image is also estimated from the mask collection data 204.

  Further, the wafer transfer simulator 400 uses the mask collection data 204 and each wafer transfer image of the reference image to calculate an actual size error or error ratio of the pattern size as the second error. For example, the actual size error or error ratio of the line width in the line pattern is calculated. Instead of the line width, an actual size error or an error ratio of the distance between the lines may be calculated. In the case of a hole pattern, an actual size error or error ratio is calculated for the horizontal or vertical width of the hole diameter. These calculation methods and the like are the same as in the case where the dimension measurement circuit 131 calculates from the mask collection data 204 and the reference image.

  Data calculated by the wafer transfer simulator 400 is sent to the second comparison circuit 132 together with the size distribution map 135.

  In the second comparison circuit 132, the wafer transfer image estimated from the reference image and the wafer transfer image estimated from the mask collection data 204 are compared using an appropriate comparison determination algorithm. As a result of the comparison, when the difference between the two exceeds a predetermined threshold (second threshold), the location is determined as a defect. If it is determined as a defect, the coordinates and the wafer transfer image that is the basis for the defect determination are sent to the transfer defect calculation circuit 134 together with the second error and the size distribution map 135.

  In the transfer defect calculation circuit 134, the second error (W) calculated by the wafer transfer simulator 400 and the first error (from the size distribution map 135) calculated for the portion determined as a defect by the second comparison circuit. M), the value (E) of equation (9) is calculated. Here, E is a value obtained by correcting the second error with the first error. In this specification, E is referred to as “corrected transfer image error”. In equation (9), k represents the error (dimensions and line width error rate) in the actual mask while the first error (M) represents the error (dimension and line width error rate), while the second error (W) represents the reduced transfer exposure. Since this represents an error (dimension or line width error rate) in the transferred wafer image, it is a coefficient for adjusting these differences.

  The relationship between the above values (W, M, E) will be described with reference to FIGS.

  FIG. 5 is a map showing the actual size error distribution of the pattern calculated based on the collected mask image for the drawing region 1002 of the mask 1001. Each curve in the drawing area 1002 is connected to a portion where the actual size distribution error is equal. For example, in the region surrounded by the curve 1003, the finished line width of the pattern formed on the mask becomes thicker than the ideal line width based on the design data as it goes inward, but the region surrounded by the curve 1004 Then, as it goes inward, the finished line width of the pattern formed on the mask becomes narrower than the ideal line width based on the design data.

  FIG. 6A shows an actual size error distribution of a cross section along the line A-A ′ of FIG. 5. The horizontal axis represents the position in the X direction, and the vertical axis represents the actual size error (M) calculated by the dimension measuring circuit 131.

  FIG. 6B is a plot of the actual size error (W) calculated by the wafer transfer simulator 400 for the coordinates estimated as defects by the second comparison circuit 132.

  FIG. 6C is a plot of the value (E) obtained from Equation (9) for the coordinates estimated to be defective by the second comparison circuit 132. In this figure, the element of FIG. 6A is added to FIG. 6B, that is, the actual size error calculated from the wafer transfer image is corrected by the actual size error of the pattern on the mask.

  In the conventional method, defect determination is performed based on FIG. 6B, and correction processing is performed on five locations with large actual size errors. However, by correcting the data shown in FIG. 6B with the data shown in FIG. That is, in FIG. 6C, the portion denoted by reference numeral 1005 is in the region where the line width is narrow according to FIG. Nevertheless, the fact that the actual size error is positive in FIG. 6B is presumed that the degree of abnormality is high as shown in FIG. 6C. Therefore, the pattern actually formed on the wafer is considered to be extremely thick compared to the peripheral pattern, and it can be said that the defect needs to be corrected. On the other hand, in FIG. 6B, the four places other than the reference numeral 1005 are presumed that the degree of abnormality is not high according to FIG. 6C, and it can be determined that the defect correction is not particularly necessary.

  Thus, in the present embodiment, the corrected transfer image error (E) is calculated from the second error (W) calculated by the wafer transfer simulator and the first error (M) obtained from the dimension distribution map. ) Is calculated. And defect determination is performed based on this value (E).

  On the other hand, in the conventional method, the defect determination is performed based on whether or not the error (W) obtained from the wafer transfer estimated image exceeds a predetermined allowable margin. Further, the line width of the pattern is measured with another apparatus, and the defect is determined based on an allowable margin different from the above.

  According to the method of the present embodiment, the following effects can be obtained over the conventional method. That is, according to the conventional method, the allowable margin for random defects and the allowable margin for system defects are set separately, so that even minor defects that do not need to be handled as defects may be detected and corrected. However, according to the present embodiment, the influence of the system defect and the random defect can be determined in an overlapping manner, so that the defect determination can be performed in a state close to an actual wafer transfer image. Therefore, excessive defect detection in the conventional method is suppressed, and unnecessary defect correction can be reduced. Thereby, the manufacturing yield of the mask can be improved, the time required for inspection and correction can be shortened, and the time required for mask manufacturing can be shortened.

  FIG. 7 is a schematic diagram of a design pattern. FIG. 8A shows an actual mask pattern corresponding to FIG. 7, which is an optical image obtained by the optical image acquisition unit A of FIG. FIG. 8B is a mask reference image generated from the design pattern of FIG. FIG. 9 is an overlay of the optical image of FIG. 8A and the reference image of FIG. 8B for comparison. From FIG. 9, it can be seen that the line width of the optical image indicated by the solid arrow is narrower than the line width of the reference image indicated by the dotted arrow. Further, a portion indicated by reference numeral 1006 is a defective portion where the optical image becomes convex, and a portion indicated by reference numeral 1007 is a defective portion where the optical image becomes concave.

  FIG. 10A is a wafer transfer image estimated from the optical image of FIG. FIG. 10B is a wafer transfer image estimated from the reference image of FIG. FIG. 11 is an overlay of the wafer transfer images shown in FIGS. 10A and 10B for comparison. From FIG. 11, at the location indicated by reference numeral 1008, the line width of the wafer transfer image estimated from the optical image (indicated by the solid arrow) is the line of the wafer transfer image estimated from the reference image (indicated by the dotted arrow). It can be seen that it is thicker than the width. On the other hand, at the location indicated by reference numeral 1009, it can be seen that the line width of the wafer transfer image estimated from the optical image is narrower than the line width of the wafer transfer image estimated from the reference image.

  FIG. 12 is a diagram illustrating a state in which the wafer transfer image of FIG. 11 is corrected using the dimension distribution map in the present embodiment. As shown in FIG. 9, it is known from the comparison between the optical image and the reference image that the line width of the pattern in this region is narrower than the design value, and this tendency is added to FIG. As shown, it is possible to determine a defect in a state close to an actual transfer image. That is, it is estimated from FIG. 11 that the portion indicated by reference numeral 1010 is thick in the wafer transfer image, but considering the tendency of FIG. 9, the line width at this portion is considered to be further thickened. Therefore, it is determined that this defect has a serious effect, and is sent to the defect correction process. On the other hand, although it is estimated from FIG. 11 that the wafer transfer image is thinned at the position indicated by reference numeral 1011, it is offset by the thin pattern on the mask, and the dimensional error is considered to be small. Therefore, it can be determined that this defect does not need to be corrected.

  The result calculated by the transfer defect calculation circuit 134 is stored in the magnetic disk device 109 as a transfer image inspection result 206.

  The mask inspection result 205 and the transfer image inspection result 206 are sent to the review device 500. The review is an operation in which the operator determines whether the detected defect is a problem. In the present embodiment, with reference to the transfer image inspection result 206, defects that are determined not to be corrected can be excluded from the review target.

  In the review process, the operator determines whether correction is necessary based on the mask inspection result 205 and the transfer image inspection result 206. Specifically, the operator compares and reviews the reference image that is the basis for the defect determination and the optical image including the defect. If the pattern shape formed on the mask is relatively simple, the operator predicts the defective portion on the wafer from the defective portion of the mask without starting the wafer transfer simulator 400, and determines whether correction is necessary. Judgment can be made. On the other hand, if the pattern formed on the mask is fine and it is difficult to determine whether correction is necessary without estimating the wafer transfer image, the transfer image inspection result obtained according to the above-described method is used as the basis. To review.

  The review apparatus 500 displays an image of a defective portion of the mask using the observation optical system of the inspection apparatus 100 while moving the table on which the mask is placed so that the defect coordinates of each defect can be observed. . At the same time, these are displayed side by side on the screen so that the determination conditions for defect determination and the optical image and reference image that are the basis for determination can be confirmed. As the screen, a screen of the control computer 110 or a computer screen separately prepared is used. By displaying the defects on the mask and the ripples on the wafer transfer image side by side in the review process, it becomes easy to determine whether or not the mask pattern should be corrected. In general, a reduction projection of about 1/4 is performed from the mask to the wafer, so this scale is also taken into consideration when displaying them side by side.

  In the review process, it is not always necessary to move the table, and the defect image can be obtained by browsing the images that are the basis for determining each defect stored in the mask inspection result 205 and the transfer image inspection result 206 side by side. It is also possible to review whether or not correction is necessary.

  If it is determined that there is a defect in the inspection apparatus through the above steps, the mask collection data that is the basis and the reference image corresponding thereto are stored in the inspection apparatus together with these coordinates. When the inspection for one mask is completed, the operator visually confirms the pattern of the defect portion using the observation optical system in the inspection apparatus. Then, after determining the necessity for correction and whether or not correction is possible, the defect to be corrected is discriminated, and this mask is sent to the correction device together with information necessary for correction. Here, the information necessary for correction includes, for example, coordinates in the mask, whether the defect is convex or concave, that is, whether the shading film is to be shaved or compensated, and the pattern of the portion to be corrected by the correction device Pattern data for recognizing. As the pattern data, the above-described mask collection data can be used.

  In the example of FIGS. 1 and 2, the defect information determined through the review process is stored in the magnetic disk device 109 of FIG. When at least one defect to be corrected is confirmed by the review apparatus 500, the mask is sent to the correction apparatus 600 that is an external apparatus of the inspection apparatus 100 together with the defect information list 207. Since the correction method differs depending on whether the defect type is a convex defect or a concave defect, the defect information list 207 is attached with the defect type including the unevenness and the defect coordinates.

  As described above, according to the present embodiment, the corrected transfer is performed from the second error (W) calculated by the wafer transfer simulator and the first error (M) obtained from the dimension distribution map. An image error (E) is calculated. And defect determination is performed based on this value (E). According to this method, the influence of the system defect and the random defect can be judged in an overlapping manner, so that the defect can be judged in a state close to an actual wafer transfer image. Therefore, excessive defect detection is suppressed, and unnecessary defect correction can be reduced. Thereby, the manufacturing yield of the mask can be improved, the time required for inspection and correction can be shortened, and the time required for mask manufacturing can be shortened.

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

  For example, in the above-described embodiment, the die-to-database inspection method for comparing the reference data generated from the design pattern data used for mask manufacturing with the actual pattern on the mask has been described. However, the present embodiment compares the same patterns of chips with different masks when a plurality of chips having the same pattern configuration are arranged in a part or the whole of the same mask. It can also be applied to a die-to-die inspection method. According to the die-to-die inspection method, an image (simulated image) similar to that obtained by photographing an actual mask with an SEM microscope can be generated.

  Further, as a defect determination method, there is a method using a mask image estimated from an image photographed by a transmission optical system of an inspection apparatus and an image photographed by a reflection optical system of the inspection apparatus. This method is effective in guaranteeing the quality of the mask itself.

  Furthermore, in the above embodiment, description of parts that are not directly required for the description of the present invention, such as the device configuration and control method, has been omitted, but the required device configuration and control method can be appropriately selected and used. Needless to say, you can. In addition, all pattern inspection apparatuses or pattern inspection methods that include elements of the present invention and whose design can be changed as appropriate by those skilled in the art are included in the scope of the present invention.

DESCRIPTION OF SYMBOLS 100 Inspection apparatus 101 Mask 102 XY (theta) table 103 Light source 104 Magnification optical system 105 Photodiode array 106 Sensor circuit 107 Position circuit 108 First comparison circuit 109 Magnetic disk apparatus 110 Control computer 111 Expansion circuit 112 Reference circuit 113 Autoloader control circuit 114 Table control Circuit 115 Magnetic tape device 116 Flexible disk device 117 CRT
118 Pattern Monitor 119 Printer 120 Bus 122 Laser Measurement System 130 Autoloader 131 Dimension Measurement Circuit 132 Second Comparison Circuit 134 Transfer Defect Calculation Circuit 135 Dimension Distribution Map 170 Illumination Optical System 201 CAD Data 202 Design Intermediate Data 203 Format Data 204 Mask Acquisition Data 205 Mask inspection result 206 Transfer image inspection result 207 Defect information list 400 Wafer transfer simulator 500 Review device 600 Correction device

Claims (5)

In an inspection apparatus for illuminating a sample on which a pattern is formed, forming an image of the sample on an image sensor via an optical system, and determining the presence or absence of defects,
An optical image acquisition unit for acquiring an optical image of the sample from the image sensor;
A dimension measuring unit for measuring a dimension of the pattern in the optical image and a dimension of the pattern in a reference image serving as a reference for the determination, and obtaining a first error therefrom;
A transfer image estimator that estimates each transfer image for the optical image on the sample and the reference image, and measures a dimension of the pattern in these transfer images to obtain a second error;
A comparison unit that compares the transferred images and determines a defect when the difference exceeds a threshold;
An inspection apparatus comprising: a correction unit that corrects the second error at a location determined as a defect by the comparison unit using the first error.   The inspection apparatus according to claim 1, further comprising a storage unit that stores a map describing the first error. In an inspection method for illuminating a sample on which a pattern is formed, forming an image of the sample on an image sensor via an optical system, and determining the presence or absence of defects,
Obtaining an optical image of the sample from the image sensor;
Measuring the dimension of the pattern in the optical image and the dimension of the pattern in a reference image serving as a reference for the determination, and obtaining a first error therefrom,
Estimating each transfer image for the optical image on the sample and the reference image, measuring the dimensions of the pattern in these transfer images, and determining a second error;
Comparing each of the transferred images and determining a defect when the difference exceeds a threshold;
And a step of correcting the second error at the location determined as the defect by the first error.   The inspection method according to claim 3, further comprising a step of determining whether or not the defect needs to be corrected from the second error corrected by the first error. The inspection method according to claim 3, further comprising a step of creating a map describing the first error.