JP4095621B2 - Optical image acquisition apparatus, optical image acquisition method, and mask inspection apparatus - Google Patents

Optical image acquisition apparatus, optical image acquisition method, and mask inspection apparatus Download PDF

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JP4095621B2
JP4095621B2 JP2005091972A JP2005091972A JP4095621B2 JP 4095621 B2 JP4095621 B2 JP 4095621B2 JP 2005091972 A JP2005091972 A JP 2005091972A JP 2005091972 A JP2005091972 A JP 2005091972A JP 4095621 B2 JP4095621 B2 JP 4095621B2
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pattern
film thickness
phase shift
light shielding
optical image
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JP2006276214A (en
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英雄 土屋
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アドバンスド・マスク・インスペクション・テクノロジー株式会社
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  The present invention relates to an optical image acquisition apparatus, an optical image acquisition method, or a mask inspection apparatus. For example, the present invention relates to a mask inspection apparatus used in semiconductor manufacturing and a technique for acquiring an optical image used in the mask inspection apparatus.

  In recent years, in the manufacturing process of large scale integrated circuits (LSIs), circuit line widths required for semiconductor elements have become increasingly narrower as LSIs become more highly integrated and have larger capacities. These semiconductor elements use an original pattern (also referred to as a photomask or reticle; hereinafter collectively referred to as a mask) on which a circuit pattern magnified 4 to 5 times is used, and so-called stepper light reduction for circuit pattern transfer. It is manufactured by exposing and transferring a pattern onto a wafer with an exposure apparatus to form a circuit. Therefore, a pattern drawing apparatus capable of drawing a fine circuit pattern is used for manufacturing a mask for transferring such a fine circuit pattern onto a wafer. A pattern circuit may be directly drawn on a wafer using such a pattern drawing apparatus. The electron beam drawing apparatus is also described in the literature (see, for example, Patent Document 1). Alternatively, development of a laser beam drawing apparatus for drawing using a laser beam in addition to an electron beam has been attempted and disclosed in the literature (for example, see Patent Document 2).

  However, as represented by a 1 gigabit class DRAM (Random Access Memory), a pattern constituting a large scale integrated circuit (LSI) is going to be on the order of submicron to nanometer. And the demand for completeness (pattern accuracy, defect-free, etc.) to the mask is increasing year by year. In recent years, pattern transfer has been performed near the limit resolution of steppers due to ultra-miniaturization and high integration, and high-precision photomasks have become the key to device manufacturing. That is, one of the major causes of the yield reduction in the manufacture of LSI is a defect of a mask used when an ultrafine pattern is exposed and transferred onto a semiconductor wafer by a photolithography technique. In particular, with the miniaturization of the pattern dimensions of LSIs formed on semiconductor wafers, the dimensions that must be detected as pattern defects have become extremely small. Therefore, a mask defect inspection apparatus that detects defects in ultrafine patterns is necessary, and improving the performance of the mask defect inspection apparatus is essential for the short-term development and improvement of manufacturing yield of advanced semiconductor devices.

  On the other hand, with the development of multimedia, LCDs (Liquid Crystal Display) are increasing in size of the liquid crystal substrate to 500 mm × 600 mm or more, and TFT (Thin Film Transistor) formed on the liquid crystal substrate. : Thin film transistors) and the like are being miniaturized. Therefore, it is required to inspect a very small pattern defect over a wide range. For this reason, it has become urgent to develop a mask defect inspection apparatus for inspecting defects of a photomask used for manufacturing such a large area LCD pattern and a large area LCD with high accuracy.

  Here, as a mask defect inspection method, “die to die (die-to-die) inspection” that compares the same pattern at different locations on the same mask, or CAD data (design data) used when drawing the mask pattern is compared. There is “die to database inspection”. In the inspection method in such an inspection apparatus, inspection is performed by dividing the strip into thin strip-like stripes and scanning the stripes continuously (actually, the table moves continuously).

For example, first, a mask is placed on an XYθ table, and a pattern formed on the mask is illuminated with an appropriate light source. The light transmitted through the mask enters the photodiode array through the magnifying optical system. Therefore, an optical image of the pattern is formed on the photodiode array. Then, the optical image is compared with the reference image according to an appropriate algorithm, and if they do not match, it is determined that there is a defect. Defect detection is performed by such a method (see, for example, Patent Document 3).
Here, in the case of die to die (die-to-die) inspection, the reference image is an optical image corresponding to a die other than the die area to be inspected, and in the case of die to database (die-to-database) inspection. Is the expected value of the optical image obtained from the design data of the area to be inspected.

  By the way, recently, the appearance of LSI with higher integration degree is desired, and accordingly, it is desired to further improve the resolution of the optical transfer apparatus. As means for realizing this demand, it has been proposed to provide a photomask with a phase shift pattern that utilizes interference of light. That is, it is necessary to form a phase shift pattern in a portion of the pattern formed on the photomask, particularly where a fine pattern is required. For example, although the halftone method is widely used at present, the light shielding film of the mask has various transmittances, and a light shielding film having a high transmittance is used as a halftone light shielding film in anticipation of a high phase shift effect. There is also. In this case, in order to shield a relatively large area, a method using a chromium film may be used. That portion exists on the glass substrate with a halftone light shielding film and a chromium light shielding film overlapping.

  Here, the pattern defect inspection apparatus is required to have a function capable of accurately detecting a pattern defect including a phase shift pattern. However, since the behavior of the detection signal due to the signal amplitude when the chrome pattern is imaged and the defect generated on the chrome pattern is different from the behavior of the detection signal due to the signal amplitude of the phase shift pattern portion and the defect, both are determined by the same defect determination method. It is difficult to detect a defect with the defect determination threshold.

Further, in the mask defect inspection apparatus, it is necessary to equip the mask with an autofocus mechanism in order to absorb the deflection of the mask and the change in the Z direction of the stage. In order to cope with recent fine patterns, as the lens numerical aperture of the optical system is increased, the depth of focus becomes extremely shallow, and a highly accurate autofocus mechanism is required. However, with conventional devices, fine patterns oscillate with a combination of the response characteristics of the autofocus mechanism and a specific period of the pattern, or cause interference to cause an offset at the in-focus position, resulting in an unclear image. End up. Therefore, in the conventional apparatus, the response speed of the autofocus mechanism is lowered so that the response characteristic of the autofocus mechanism and the cycle of the pattern do not interfere with each other, but this delays the follow-up to the pattern. That is, it is fixed at a certain focal height and cannot move. As a result, the image becomes unclear. Similarly, with the conventional apparatus, even in the case of a photomask in which a chrome pattern and a phase shift pattern are mixed, an in-focus position is not determined by an optical system having a shallow focal depth, resulting in an unclear image. Therefore, the conventional apparatus cannot detect defects with sufficient sensitivity.
Japanese Patent Laid-Open No. 2002-237445 US Pat. No. 5,386,221 Japanese Patent No. 3154802

  As described above, in the conventional mask defect inspection apparatus, the signal amplitude when the light shielding pattern is imaged, the behavior of the detection signal due to the defect generated on the light shielding pattern, the signal amplitude of the phase shift pattern portion, and the behavior of the detection signal due to the defect Therefore, there is a problem that it is difficult to detect defects with the same defect determination method and defect determination threshold.

  Further, in the conventional mask defect inspection apparatus, in the fine pattern, on the other hand, the response characteristic of the autofocus mechanism and the pattern period oscillate or oscillate, or an offset occurs in the in-focus position, resulting in an image. There was a problem that it became unclear. Further, the conventional apparatus has a problem that, in the fine pattern, by controlling the autofocus mechanism at a low frequency, the follow-up to the pattern is delayed, resulting in an unclear image. Similarly, in the case of a conventional apparatus, even in the case of a photomask in which a chrome pattern and a phase shift pattern are mixed, there is a problem that an in-focus position is not determined by an optical system having a shallow focal depth, resulting in an unclear image. was there.

  An object of the present invention is to provide an inspection method capable of overcoming the above-described problems and capable of inspecting a defect even with a mask having a plurality of films having different signal amplitudes and behaviors of detection signals due to defects. Another object of the present invention is to provide a technique for acquiring an optical image without improving the focus offset due to the above-mentioned interference while improving the followability to the pattern.

An optical image acquisition device according to an aspect of the present invention includes:
The design shape data of the pattern on the glass mask and the film thickness information of the pattern are input, and for each region obtained by subdividing a predetermined region based on the design shape data of the pattern and the film thickness information of the pattern, A first calculation unit that calculates a value obtained by multiplying an area ratio occupied by the pattern by a film thickness of the pattern on the pattern surface;
A second calculation unit that calculates a value obtained by dividing the total value calculated for each area obtained by subdividing the predetermined area by the number of areas in each area;
Have
An average film thickness calculator that uses the value calculated by the second calculator as the average film thickness;
When acquiring an optical image of a mask pattern region corresponding to the predetermined region using a mask pattern created based on the design shape data of the pattern and the film thickness information of the pattern, the average film thickness An optical image acquisition unit that acquires an optical image by adjusting the in-focus position to
It is provided with.

An optical image acquisition device according to another aspect of the present invention is provided.
The design shape data of the phase shift pattern on the glass mask, the film thickness information of the phase shift pattern, the design shape data of the light shielding pattern on the glass mask and the film thickness information of the light shielding pattern are input, and a predetermined area is A first bit pattern for the phase shift pattern for each region subdivided by an arbitrary first quantization size, film thickness information of the phase shift pattern, and the predetermined region as the first quantization size. An average film thickness of the predetermined region is obtained by using the second bit pattern for the light shielding pattern for each region subdivided by a second quantization dimension that is an integral multiple of and the film thickness information of the light shielding pattern. An average film thickness calculation unit to be calculated;
When acquiring an optical image of a mask pattern created based on the design shape data of the phase shift pattern, the film thickness information of the phase shift pattern, the design shape data of the light shielding pattern, and the film thickness information of the light shielding pattern An optical image acquisition unit that acquires an optical image of an area of a mask pattern corresponding to the predetermined area by aligning the focus position with the average film thickness;
It is provided with.

And the optical image acquisition method of one aspect of the present invention includes:
The design shape data of the phase shift pattern on the glass mask, the film thickness information of the phase shift pattern, the design shape data of the light shielding pattern on the glass mask and the film thickness information of the light shielding pattern are input, and a predetermined area is A first bit pattern for the phase shift pattern for each region subdivided by an arbitrary first quantization size, film thickness information of the phase shift pattern, and the predetermined region as the first quantization size. An average film thickness of the predetermined region is obtained by using the second bit pattern for the light shielding pattern for each region subdivided by a second quantization dimension that is an integral multiple of and the film thickness information of the light shielding pattern. An average film thickness calculation step to be calculated;
The predetermined region using a mask pattern created based on the design shape data of the phase shift pattern, the film thickness information of the phase shift pattern, the design shape data of the light shielding pattern, and the film thickness information of the light shielding pattern When acquiring an optical image of the area of the mask pattern corresponding to the optical image acquisition step of acquiring the optical image by adjusting the focus position to the average film thickness,
It is provided with.

In addition, the mask inspection apparatus of one embodiment of the present invention includes:
An optical image acquisition unit for acquiring an optical image of a mask pattern created based on the design shape data of the first and second patterns;
A comparison unit that compares the optical image of the mask pattern with a reference image using any of the changeable comparison determination threshold values;
Determining which of the changeable comparison determination thresholds is to be used based on the design shape data of the first and second patterns, and outputting the determined result to the comparison unit And
It is provided with.

  According to one aspect of the present invention, the focus position can be adjusted to the average film thickness, and when an optical image of a predetermined area is acquired, the optical image is acquired without causing a focus offset due to oscillation or interference. Can do. As a result, the autofocus mechanism can be controlled with higher responsiveness than before, and the followability to the pattern can be improved. According to another aspect of the present invention, the film type of the acquired image can be known in advance based on the design shape data of the first and second patterns. A plurality of comparison determination thresholds can be used properly depending on the determination target (film type). As a result, a defect inspection can be performed even with a mask having a plurality of films in which the behavior of detection signals due to signal amplitude and defects is different.

Embodiment 1 FIG.
FIG. 1 is a conceptual diagram showing the configuration of the mask inspection apparatus in the first embodiment.
In FIG. 1, a mask inspection apparatus 100 for inspecting a mask defect, which is an example of an optical image acquisition apparatus, includes an optical image acquisition unit and a control system circuit. The optical image acquisition unit includes an XYθ table 102, a light source 103, a magnifying optical system 104, a photodiode array 105, a sensor circuit 106, a laser length measurement system 122, an autoloader 130, and a piezo element 142. In the control system circuit, a control computer 110 serving as a computer is connected via a bus 120 to a position circuit 107, a comparison circuit 108, a development circuit 111, a reference circuit 112, an autoloader control circuit 113, a table control circuit 114, a magnetic disk device 109, It is connected to a magnetic tape device 115, a flexible disk device (FD) 116, a CRT 117, a pattern monitor 118, a printer 119, and an autofocus control circuit 140. The XYθ table 102 is driven by an X-axis motor, a Y-axis motor, and a θ-axis motor.

  A photomask 101 (an example of a glass mask) to be inspected is placed on an XYθ table 102 provided so as to be movable in a horizontal direction and a rotation direction by motors of XYθ axes, and is formed on the photomask 101. The pattern is illuminated by a suitable light source 103. The light that has passed through the photomask 101 forms an optical image on the photodiode array 105 via the magnifying optical system 104 and is incident thereon. In order to absorb the deflection of the photomask 101 and the change in the Z direction of the XYθ table 102, focusing on the photomask 101 is performed using the piezo element 142 controlled by the autofocus control circuit 140.

FIG. 2 is a block diagram showing the internal configuration of the development circuit.
In FIG. 2, an expansion circuit 111 includes an I / F (interface) 212 connected to the bus, a data memory 222, a graphic interpretation circuit 232, a pattern generation circuit 242, an I / F 214, a data memory 224, a graphic interpretation circuit 234, a pattern. A generation circuit 244, an average film thickness calculation circuit 250, and a pattern synthesis circuit 260 are provided. The average film thickness calculation circuit 250 includes a weighting calculation circuit 252, an averaging calculation circuit 254, and a pattern overlap state determination circuit 256. An output from the average film thickness calculation circuit 250 is transmitted to the comparison circuit 108 and the autofocus control circuit 140. An output from the pattern synthesis circuit 260 is transmitted to the reference circuit 112. Further, optical image data is transmitted from the optical image acquisition unit 150 to the comparison circuit 108. As described above, the optical image acquisition unit 150 includes the XYθ table 102, the light source 103, the magnifying optical system 104, the photodiode array 105, the sensor circuit 106, the laser length measurement system 122, the autoloader 130, and the piezo element 142. . In FIG. 2, the XYθ table 102, the light source 103, the magnifying optical system 104, the photodiode array 105, and the sensor circuit 106 are shown, and the remaining configuration is omitted.

FIG. 3 is a diagram illustrating an example of a photomask.
The pattern formed on the photomask 101 is divided into, for example, a peripheral pattern 21 and a circuit pattern 22. The circuit pattern 22 is further divided into a logic controller unit 23 and a memory unit 24. The resolution of the optical transfer apparatus can be further improved by forming a phase shift pattern using light interference at a portion of the circuit pattern 22 where a fine pattern is required.

FIG. 4 is a diagram illustrating an example of a phase shift structure.
Various schemes have been considered for the phase shift structure. The Levenson scheme shown in FIG. 4A, the auxiliary pattern scheme shown in FIG. 4B, the edge enhancement scheme shown in FIG. 4C, and FIG. There are a chromeless method shown in d) and a halftone method shown in FIG. The photomask 101 is formed on the glass substrate 25 using the light shielding pattern 26 and the phase shift pattern 27. For example, the light shielding pattern 26 is a pattern in which a chromium layer having a light shielding function is provided on the surface of the glass substrate 25 in a predetermined shape (hereinafter referred to as a chromium pattern). The phase shift pattern 27 is made of a translucent material such as SiO 2 or MoSi.

FIG. 5 is a diagram illustrating an example of pattern design data.
The pattern design data uses a rectangle or triangle as a basic figure, and is described, for example, by combining the figure X dimension L1, Y height L2, and figure arrangement coordinates (x, y) as shown in FIG. . In the data file, the X dimension L1 and Y height L2 of the figure, the arrangement coordinates (x, y) of the figure, a film type code that becomes an identifier for distinguishing the light shielding pattern from the phase shift pattern, a rectangle or a triangle A graphic code serving as an identifier for distinguishing between and a setting condition at the time of drawing and inspection are included. Here, one data file is created for each film type code. Therefore, two data files of the light shielding pattern (chrome pattern) design data and the phase shift pattern design data are used.

FIG. 6 is a diagram illustrating an example of a photomask formed of a halftone film and a chromium film.
In FIG. 6, in the photomask, a pattern of a halftone film is formed on a glass substrate, and a chromium film is formed on the halftone film in order to shield a relatively large area. By forming a chromium film on the halftone film, sufficient light shielding can be performed over a relatively large area.

FIG. 7 is a diagram for explaining an optical image acquisition procedure.
As shown in FIG. 7, the region to be inspected is virtually divided into a plurality of thin strip-like inspection stripes with a scan width W of about 200 μm in the Y direction, and each of the divided inspections is further divided. The operation of the XYθ table 102 is controlled so that the stripe is continuously scanned, and an optical image is acquired while moving in the X direction. In the photodiode array 105, images having a scan width W as shown in FIG. 7 are continuously input. Then, after acquiring the image of the first inspection stripe, the image of the scan width W is continuously input in the same manner while moving the image of the second inspection stripe in the opposite direction. When an image in the third inspection stripe is acquired, the image moves while moving in the direction opposite to the direction in which the image in the second inspection stripe is acquired, that is, in the direction in which the image in the first inspection stripe is acquired. To get. 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 is photoelectrically converted by the photodiode array 105 and further A / D (analog-digital) converted by the sensor circuit 106. These light source 103, magnifying optical system 104, photodiode array 105, and sensor circuit 106 constitute a high-magnification inspection optical system.

  The XYθ table 102 is driven by the table control circuit 114 under the control of the control computer 110. The movement position of the XYθ table 102 is measured by the laser length measurement system 122 and supplied to the position circuit 107. The photomask 101 on the XYθ table 102 is transported from an autoloader 130 driven by an autoloader control circuit 113.

  The measurement pattern data output from the sensor circuit 106 is sent to the comparison circuit 108 together with data indicating the position of the photomask 101 on the XYθ table 102 output from the position circuit 107.

  On the other hand, the magnetic disk device 109 stores drawing data of a phase shift pattern used when forming a pattern on the photomask 101 serving as a mask to be inspected and drawing data of a chromium light shielding film. These are used for inspection. The XYθ table 102 on which the photomask 101 is placed scans the entire surface of the mask by operations in the continuous movement direction (X) and step movement direction (Y). These data are, for example, a single stage continuous movement (X direction). The phase shift pattern drawing data and the chrome light shielding film drawing data are taken into the control computer 110 and the inspection reference data is created with the amount required for the inspection as a unit (inspection stripe). In other words, the design data used at the time of pattern formation of the photomask 101 is read out from the magnetic disk 109 which is an example of a storage device to the development circuit 111 through the control computer 110 as a unit of strip-shaped area called an inspection stripe shown in FIG. It is. Here, the design data of the light shielding pattern (chrome pattern) and the phase shift pattern (halftone pattern) are read out.

The mask inspection apparatus 100 reads this data, and in the case of only the light shielding pattern (chrome pattern) design data, the case of only the phase shift pattern design data, or the case where both are mixed, each circuit required for the inspection Set the operation mode. Here, the case where both are mixed is demonstrated.
In the development circuit 111, when design data of a light shielding pattern (chrome pattern) is input to the I / F 212, the design data is temporarily stored in the data memory 222 serving as a memory unit. Then, the sent graphic data is sent from the data memory 222 to the graphic interpretation circuit 232, and interprets the graphic code indicating the graphic shape of the graphic data as shown in FIG. Then, the pattern generation circuit 242 develops binary or multi-value graphic pattern data as a grid pattern having a predetermined quantization dimension. Similarly, when design data of a phase shift pattern (halftone pattern) is input to the I / F 214, the design data is temporarily stored in the data memory 224 serving as a memory unit. Then, the sent graphic data is sent from the data memory 224 to the graphic interpretation circuit 234, and interprets the graphic code indicating the graphic shape of the graphic data as shown in FIG. Then, the pattern generation circuit 244 develops binary or multi-value graphic pattern data as a grid pattern having a predetermined quantization dimension. The developed pattern data of each grid is temporarily stored in a large-capacity stripe pattern memory (not shown) provided in the pattern generation circuits 242 and 244. The capacity is desirably large enough to store the pattern data of the grid for one inspection stripe. Alternatively, the data may be stored in the data memories 222 and 224 or the magnetic disk device 109.

  Here, it is assumed that the design data of the light shielding pattern and the phase shift pattern is identified by the computer 110. Therefore, the development circuit 111 prepares two sets from the data memory to the pattern generation circuit, and generates pattern data for each of the light shielding pattern and the phase shift pattern.

  The pattern synthesizing circuit 260 handles the halftone graphic pattern data and the chrome graphic pattern data as developed predetermined grid patterns, and synthesizes them by superimposing patterns at the same position. At this time, the generated pattern data is a signal amplitude that considers the transmittance through the glass surface, the transmittance at the light source wavelength used for the inspection of the halftone shading film, and the transmittance of the shading pattern (chrome pattern). Is sent to the reference circuit 112 for generating reference data. For example, when irradiating light to a mask to be inspected and receiving light that is transmitted by a sensor for inspection, the transmittance at the inspection light wavelength of the light shielding pattern (chrome pattern) film becomes almost zero, and the phase shift pattern The transmittance of the (halftone) film at the inspection light wavelength is several percent to several tens percent. And about each grid of a grid pattern, the area ratio which a glass surface (Qz) occupies x the transmittance | permeability which permeate | transmits a glass surface (for example, "1"), and the area ratio which a halftone film (HT) occupies x halftone film The sum of the transmittance (for example, “15-20”), the area ratio occupied by the Cr film, and the transmittance (for example, “0”) for transmitting the Cr film, Multi-value data. When each cell is one pixel, the multi-value data is used as the gradation value of the pixel.

  In FIG. 1, since the inspection is performed using the transmission image, the generated pattern data includes the transmittance that transmits the glass surface, the transmittance at the light source wavelength used for the inspection of the halftone light shielding film, and the light shielding pattern (chrome). The composition processing such as weighted addition of the signal amplitude in consideration of the transmittance of the pattern) is performed, but of course, it may be configured to perform the inspection using the reflected image. In such a case, the generated pattern data is a signal amplitude weighting considering the reflectance on the glass surface, the reflectance at the light source wavelength used for the inspection of the halftone light shielding film, and the reflectance of the light shielding pattern (chrome pattern). A synthesis process such as addition may be performed. When inspecting using reflected light, the glass pattern region is photographed dark because it hardly reflects light, and the light shielding pattern (chrome pattern) is photographed brightly because it reflects well. The phase shift pattern (halftone) film is in the middle. For each grid of the grid pattern, the area ratio occupied by the glass surface (Qz) × the reflectance reflecting the glass surface (for example, “0”) and the area ratio occupied by the halftone film (HT) × halftone film The sum of the reflectance (for example, “80 to 85”), the area ratio occupied by the Cr film, and the reflectance (for example, “1”) for reflecting the Cr film is obtained, and the obtained value is calculated as the square. Multi-value data. When each cell is one pixel, the multi-value data is used as the gradation value of the pixel.

  The reference circuit 112 performs an appropriate filter process on the sent graphic image data to generate a reference image.

FIG. 8 is a diagram for explaining the filter processing.
The measurement pattern data obtained from the sensor circuit 106 is in a state in which blurring occurs due to the resolution characteristics of the magnifying optical system 104, the aperture effect of the photodiode array 105, interference between adjacent pixels, that is, a state in which a filter is applied, in other words. For example, since the image is in a continuously changing analog state, the image data on the design side where the image intensity (light / dark value) is a digital value is also filtered to match the measurement pattern data.

  Then, the comparison circuit 108 cuts out the measurement pattern data to be a real image and the reference image as an image of a predetermined area (area). Then, the measurement pattern data and the reference image are aligned (area alignment), and the area-aligned measurement pattern data and the reference image are compared. For example, if the difference is equal to or greater than a set threshold value, it is determined as a defect. To do. Various means can be considered as a method of detecting a defect by the comparison circuit 108. For example, there are various means such as a level comparison method that compares the signal level of the captured pattern image with the signal level of the reference pattern, and a method that compares the differential values of both. Further, it is conceivable to use a reflection image in addition to a transmission image.

  Here, when inspecting a photomask in which a line-and-space fine pattern is formed on a glass substrate with a predetermined period by a halftone film, an optical system that automatically captures a mask image during continuous movement inspection scanning is used. In the focus mechanism, the piezo element 142 is servo-controlled by the autofocus control circuit 140 so that the film surface is focused. That is, servo control is performed so that the glass surface is focused on the glass surface, and in the region where the halftone film is formed, servo control is performed so that the upper surface of the halftone film is focused. However, as described above, if the response characteristic of the servo and a specific period of the pattern interfere with each other and oscillate, it will react more excessively than the original control amount. If the drive and servo response characteristics of the piezo element 142 are sufficiently lower than the frequency at which oscillation occurs (for example, 20 Hz) so as not to cause such a phenomenon, a follow-up delay occurs in the fine pattern, and the fixed pattern height is fixed and moved. It will disappear. Therefore, in this embodiment, an average film thickness distribution is obtained for each predetermined region, and the focus offset is corrected according to the pattern.

  That is, as an average film thickness calculation step, the average film thickness calculation circuit 250, which is an example of an average film thickness calculation unit, inputs pattern design shape data and the pattern film thickness information, and the pattern design shape data Based on the film thickness information of the pattern, the average film thickness of a predetermined region is calculated. For example, the predetermined area is an area of 200 μm × 200 μm.

FIG. 9 is a diagram for explaining a method of calculating the average film thickness.
FIG. 9A shows a region where a line-and-space fine pattern is formed on the glass substrate 202 at a predetermined cycle by the halftone film 204 having a film thickness t1 as the predetermined region. An average film thickness is calculated for each grid pattern subdivided with the above-described predetermined quantization size in the region, and an average film thickness as the predetermined region is calculated. As a grid pattern having a predetermined quantization size, for example, it is preferable to divide into a pixel unit. FIG. 9A shows the pixel X1 in the predetermined area.

  As shown in FIG. 9B, when the pixel X1 is viewed from above, the region of the pixel X1 is a region where the region (HT) of the halftone film 204 and the region (Qz) of the glass surface are mixed. In the average film thickness calculation circuit 250, the weighting calculation circuit 252 which is an example of a calculation unit, for each pixel which is each region obtained by subdividing the predetermined region, the pattern occupies the area ratio occupied by the pattern on the pattern surface. A value obtained by multiplying the film thickness by a multiplier is calculated. In other words, among the regions of the pixel X1, the area ratio of the region (HT) is a1, the area ratio of the region (Cr) of the Cr film 206 is b1, and the area ratio of the region (Qz) is c1 (where a1 + b1 + c1 = 1). Then, since b1 = 0, the average film thickness T1 at the pixel X1 is T1 = a1 · t1.

  And the average film thickness in the whole predetermined area | region in which the line and space pattern of the halftone film | membrane 204 containing the pixel X1 and a glass surface was formed is calculated. An averaging calculation circuit 254, which is an example of a calculation unit, calculates a value obtained by dividing the total value calculated for each pixel, which is each area obtained by subdividing the predetermined area, by the number of areas in each area. The value calculated by the averaging calculation circuit 254 is set as the average film thickness in the predetermined region.

FIG. 10 is a diagram showing a state where a predetermined area is subdivided.
As shown in FIG. 10, when such a predetermined area including the pixel X1 is an area X of 200 μm × 200 μm, the average film thickness T in the area X is the average film thickness Tn of each pixel of the number n of pixels in the area X. Is the value divided by the number of pixels n.

  As the optical image acquisition step, the average film thickness T of the area X calculated by the average film thickness calculation circuit 250 is output to the autofocus control circuit 140. The autofocus control circuit 140 is configured so that the optical image acquisition unit 150 has the pattern described above. When an optical image of a mask pattern region corresponding to area X is acquired using a photomask 101 on which a mask pattern created based on the design shape data of the pattern and the film thickness information of the pattern is formed, The element 142 is controlled. Then, the optical image acquisition unit 150 acquires an optical image by adjusting the in-focus position to the average film thickness T.

  As described above, when acquiring an optical image of a region in which a fine pattern of line and space of a predetermined cycle is formed by offsetting the focus position to the average film thickness, the servo response characteristics and the pattern cycle Can be prevented from oscillating due to interference. Therefore, the response frequency can be increased from 20 Hz to 100 Hz, for example, and the followability to the pattern when scanning other regions that do not hit the oscillation frequency can be improved.

  Similarly, FIG. 9A shows a photomask 101 in which a halftone film 204 having a film thickness t1 is formed over a large area, and a chromium (Cr) film 206 serving as a light shielding film is formed thereon. Yes. Here, the total film thickness of the halftone film 204 and the Cr film 206 is indicated by t2. When the Cr film 206 is further mixed in the predetermined region, the average film thickness is calculated as follows.

  As an average film thickness calculation step, the average film thickness calculation circuit 250 includes a design shape data of the halftone film 204 pattern, film thickness information of the halftone film 204, a design shape data of the pattern of the Cr film 206, and the Cr film 206. The film thickness information is input, and the average film thickness of a predetermined region is calculated based on the design shape data and the film thickness information.

  For example, when the pixel X2 is included in a predetermined region, as shown in FIG. 9B, when the pixel X2 is viewed from the top, the region of the pixel X2 is the region (HT) of the halftone film 204 and the Cr film. The region 206 (Cr) and the glass surface region (Qz) are mixed. In the average film thickness arithmetic circuit 250, the weighting arithmetic circuit 252 which is an example of the arithmetic unit has an area ratio that the halftone film 204 occupies the entire surface of the pattern surface for each pixel that is a subdivision of a predetermined region. Multiplied by the film thickness of the halftone film 204 and a value obtained by multiplying the area ratio of the Cr film 206 over the entire pattern surface by the sum t2 of the film thicknesses of the halftone film 204 and the Cr film 206. Calculate the total value. In other words, if the area ratio of the region (HT) is a2, the area ratio of the region (Cr) is b2, and the area ratio of the region (Qz) is c2 (where a2 + b2 + c2 = 1) in the region of the pixel X2. The average film thickness T2 at X2 can be expressed by T2 = a1 · t1 + b1 · t2.

  And the average film thickness in the whole predetermined area | region containing the pixel X2 is calculated. An averaging calculation circuit 254, which is an example of a calculation unit, calculates a value obtained by dividing the sum of the total values calculated for each pixel as each area obtained by subdividing the predetermined area by the number of areas in each area. The value calculated by the averaging calculation circuit 254 is set as the average film thickness in the predetermined region.

  The average film thickness T of the predetermined region calculated by the average film thickness calculation circuit 250 is output to the autofocus control circuit 140. As an optical image acquisition process, the autofocus control circuit 140 includes the optical image acquisition unit 150 configured to A mask pattern created based on the design shape data of the pattern of the tone film 204, the film thickness information of the halftone film 204, the design shape data of the pattern of the Cr film 206, and the film thickness information of the Cr film 206 was formed. When an optical image of a mask pattern region corresponding to a predetermined region is acquired using the photomask 101, the piezo element 142 is controlled. Then, the optical image acquisition unit 150 acquires an optical image by adjusting the in-focus position to the average film thickness T.

  As described above, the focus offset can be corrected according to the pattern by obtaining the average film thickness distribution for each predetermined region.

FIG. 11 is a diagram for explaining comparison with the prior art in focus control.
In an actual inspection apparatus, the mask placed on the stage with the optical system fixed is continuously and stepped, but in this figure, the mask is fixed and displayed as the lens moves. In the conventional autofocus control, as described above, there is a problem that a follow-up delay occurs, and there is a section where the focus is not achieved in a changing portion from glass to halftone. In the section (1), since the pattern is fine, the pattern changes at any height between the glass and the halftone film thickness. Further, as shown in the section (2), in the conventional focus control, there may be a phenomenon in which the response characteristic of the servo interferes with the pattern period and reacts more excessively than the original control amount. According to the present embodiment, the pattern information of the destination where the stage travels can be calculated in advance and controlled to the in-focus position, so that it can be stably controlled to an intermediate height between the glass and the halftone film thickness. become. Further, not only the section (1) in the example of FIG. 11 but also the section (2) can be similarly calculated for averaging the film thickness of the pattern. For this reason, it is possible to stably control to an appropriate height between the glass and the halftone film thickness even in the section (2). Furthermore, since the response frequency can be increased, the followability to the pattern can also be improved.

  As described above, in the average film thickness calculation circuit 250 of the present embodiment, the film data on the mask to be inspected is weighted by adding the weight corresponding to the film thickness to each pattern data of the light shielding pattern and the phase shift pattern. A thickness distribution can be obtained. The obtained film thickness distribution map is transmitted to the autofocus control circuit 140. As described above, the calculation method of the film thickness distribution is that the film thickness data of the light shielding pattern and the phase shift pattern are input in advance, and the pattern map has a pattern on the basis of the location where the pattern does not exist. The areas are weighted corresponding to each film thickness and added. The obtained film thickness distribution map is desirably transmitted to the autofocus control circuit 140 for a predetermined space area so that the autofocus circuit does not react erroneously by a minute pattern change.

  In the above description, an example in which the grid pattern is divided into pixel units has been described. However, the grid pattern may be divided into binary bit patterns. In such a case, in each cell of the light shielding pattern, a value obtained by multiplying each cell by a logic 1 and a logic 0 by no pattern, and by multiplying each cell by the thickness t3 (here, t3) of the light shielding pattern is a predetermined region. Within. Similarly, in each cell of the phase shift pattern, the value obtained by multiplying each cell by the film thickness t1 of the phase shift pattern is summed within a predetermined region, with the logic “1” indicating the presence of the pattern and the logic “0”. A value obtained by dividing the sum of the total value in the light shielding pattern and the total value in the phase shift pattern by the number of cells in the predetermined area may be used as the average film thickness in the predetermined area. That is, the weighting calculation circuit 252 calculates a value obtained by multiplying each cell by the film thickness t3 of the light shielding pattern, and sums the calculated values within a predetermined region. Similarly, the weighting calculation circuit 252 calculates a value obtained by multiplying each square by the film thickness t1 of the phase shift pattern, and totals the values within a predetermined region. Then, the averaging calculation circuit 254 may calculate a value obtained by dividing the sum of the total value in the light shielding pattern and the total value in the phase shift pattern by the number of cells in a predetermined area.

  Next, the phase shift pattern (halftone pattern) is often used for a main pattern portion where a fine pattern is to be formed even within one mask, as shown in FIGS. On the other hand, a light shielding pattern (chrome pattern) may be used as a supplementary pattern for a wide pattern. By making the defect judgment of the light-shielding pattern (chrome pattern) used as a supplement to the defect detection sensitivity required for the phase shift pattern (halftone pattern), it is possible to falsely detect defects that do not need to be considered originally. You can do it.

  That is, as an optical image acquisition step, the optical image acquisition unit 150 acquires an optical image of the photomask 101 on which a mask pattern created based on the design shape data of the halftone pattern and the design shape data of the chrome pattern is formed. In this case, as a determination step, the pattern overlap state determination circuit 256, which is an example of a determination unit, can select one of the comparison determination thresholds that can be changed based on the design shape data of the halftone pattern and the design shape data of the chrome pattern. The comparison determination threshold is used, and the determination result (threshold correction signal) is output to the comparison circuit 108. Then, as a comparison process, the comparison circuit 108 compares the optical image of the mask pattern with the reference image using any of the changeable comparison determination thresholds according to the input determination result of the pattern overlap state determination circuit 256. . Then, as a determination step, the pattern overlap state determination circuit 256 is configured such that when the chrome pattern is formed on the halftone pattern, the comparison circuit 108 determines that the optical image and the reference image of the mask pattern in which the chrome pattern exists. Is compared with a comparative determination threshold value with relatively low sensitivity. Since the chrome pattern is a light-shielding pattern that is used supplementarily over a wide area, a comparatively low sensitivity comparison judgment threshold is sufficient. As a result, it is possible to avoid erroneously detecting defects that do not need to be considered.

  As described above, in the present embodiment, the pattern overlap state determination circuit 256 identifies the phase shift pattern (halftone pattern) region and the light-shielding pattern (chrome pattern) region and inspects them as a determination threshold correction signal. Information on the inside region may be transmitted to the comparison circuit 108. Therefore, the comparison circuit 108 can dynamically change the determination threshold for comparison determination.

  Here, in the pattern overlap state determination circuit 256, the pattern generation circuit 244 includes even a little chrome pattern in each square of the graphic pattern data developed in binary or multivalue as a grid pattern of a predetermined quantization dimension. If so, it is desirable to make a determination so as to use a comparative determination threshold with relatively low sensitivity. For example, in the case where each cell is a pixel unit as shown in FIG. 9, if there is even a small area ratio b of the region (Cr), it is determined to use a comparatively weak comparison determination threshold value. The chrome pattern is originally used as a loose pattern with a wide area and dimensional accuracy. Therefore, the comparison determination threshold value may be loose.

Here, the grid pattern having a predetermined quantization dimension may be a binary bit pattern.
FIG. 12 is a diagram illustrating an example of a binary bit pattern.
FIG. 12A shows a part of the chromium pattern as the pattern A. FIG. 12B shows a part of the halftone pattern as the pattern B. Then, the halftone pattern and the chrome pattern are each handled as a bit pattern of a predetermined grid, and the patterns at the same position are superimposed and synthesized. As a synthesis method, a method of taking a logical product as shown in FIG. 12 (c) by regarding each pattern as a logic 1 and no pattern as a logic 0 can be considered. Then, the pattern overlap state determination circuit 256 determines that the bit region that has become logic 1 after synthesis is used with a comparatively low sensitivity comparison determination threshold value. If the grids do not match and differ, they may be synthesized by resampling the other in accordance with one.

  Here, in order to relax the defect judgment threshold only in the area of the shading pattern (chrome pattern), a bit map of the chrome pattern is obtained, and the comparison is made so that the logic 1 area is treated as sensitivity reduction and the logic 0 area is treated as normal sensitivity. What is necessary is just to notify a circuit.

  Further, the same consideration is effective at the pattern boundary between the phase shift pattern (halftone pattern) and the light shielding pattern (chrome pattern). Therefore, it is conceivable that a boundary region having a predetermined width is defined from the edge position of the chrome pattern, and that region relaxes the defect determination threshold. In such a case, the pattern overlap state determination circuit 256 determines that the bit area that has become logic 1 after the synthesis uses a comparatively low sensitivity comparison determination threshold value, and also performs logic 1 in the bit area that has become logic 0. It may be determined to use a comparative determination threshold value having a relatively low sensitivity for a predetermined number of bits from the bit region. As such a boundary region, it is preferable that the width within 1/20 of the width of only the phase shift pattern from the pattern boundary position of the phase shift pattern (halftone pattern) and the light-shielding pattern (chrome pattern) is set as the relaxation region. is there. For example, when the width of only the phase shift pattern is 10 μm, the relaxation region may be within 0.5 μm from the boundary.

  As described above, by determining a region where the comparison determination threshold value is relaxed and notifying the comparison circuit 108, it is possible to avoid erroneously detecting a defect that should not be considered originally.

Embodiment 2. FIG.
In the first embodiment, the case where the grid pattern is represented by a bit pattern of “1” or “0” has been described, but instead of such “1” or “0”, a phase shift pattern (halftone) film inspection is performed. The transmittance or reflectance at the light wavelength and the transmittance or reflectance at the inspection light wavelength of the light shielding pattern (chrome pattern) film may be used. In other words, transmittance or reflectance may be used as an identifier. Since other configurations may be the same as those in the first or second embodiment, description thereof is omitted.

  When the average film thickness calculation is performed, in each cell of the light shielding pattern, the presence of a pattern is set as a transmittance value (for example, “0”) or the reflectance value (for example, “1”), and the value without pattern is set to other values. Within the region, a value obtained by adding the film thickness t3 of the light shielding pattern by the number of cells having a pattern among the cells is calculated. Similarly, in each cell of the phase shift pattern, a pattern is set as a transmittance value (for example, “15 to 20”) or a reflectance value (for example, “80 to 85”), and no pattern is set as another value. Within the region, a value obtained by adding the film thickness t1 of the phase shift pattern by the number of cells having a pattern among the cells is calculated. Then, a value obtained by dividing the sum of the added total value in the light shielding pattern and the added total value in the phase shift pattern by the number of cells in the predetermined area may be used as the average film thickness in the predetermined area. That is, the weighting calculation circuit 252 calculates a value obtained by adding the film thickness t3 of the light shielding pattern by the number of cells having the pattern. Similarly, the weighting calculation circuit 252 calculates a value obtained by adding the film thickness t1 of the phase shift pattern by the number of cells having the pattern. Then, the averaging calculation circuit 254 may calculate a value obtained by dividing the sum of the total value in the light shielding pattern and the total value in the phase shift pattern by the number of cells in a predetermined area.

  When pattern overlap state determination is performed, the pattern overlap state determination circuit 256 indicates that there is a pattern in each cell of the light shielding pattern, and that there is a transmittance value (for example, “0”) or a reflectance value (for example, “1”), and there is no pattern. As other values, the determination threshold value may be relaxed at the positions of the cells having a pattern among the cells in a predetermined region.

  As described above, even when the transmittance or reflectance is used as an identifier, the same effect as in the first embodiment can be obtained.

Embodiment 3 FIG.
In each of the above-described embodiments, the halftone graphic pattern data and the chrome graphic pattern data generated by the pattern generation circuits 242 and 244 are each handled as a predetermined grid pattern, and the patterns at the same position are superimposed and combined. Explained. In the third embodiment, the quantization dimension for developing the halftone graphic pattern data is set to a relatively fine dimension to express a fine pattern, and the quantization dimension for developing the chrome graphic pattern data is set to a relatively large quantization dimension. A case where a combination is used will be described. Since other configurations may be the same as those in the first or second embodiment, description thereof is omitted.

FIG. 13 is a diagram illustrating an example of grid patterns having different developed quantization dimensions.
In FIG. 13, part of the halftone (HT) graphic pattern data is shown in FIG. 13A, and part of the chrome (Cr) graphic pattern data is shown in FIG. 13B. Here, the halftone (HT) pattern is developed with a quantization dimension of 1/2 (1/4 in area) of the chromium (Cr) pattern. If the grids are different, resample the other to match one. In such a case, it is preferable to match the quantization dimension of the halftone (HT) pattern to the quantization dimension of the chromium (Cr) pattern. This is because when the pattern overlap state determination is performed, it is desirable to relax the determination threshold in a region where there is even a small amount of the chrome region.
The pattern generation circuit 244 resamples the halftone figure pattern data with a four times quantization size. When resampling is performed, the logical presence of the original bit pattern is regarded as logic 1, and the non-pattern is regarded as logic 0, and the logical sum of the original four cells located within the cell of the quadruple quantization size is calculated. Thus, the result may be a square value having a quantization size of 4 times for re-sampling. By making a region having a halftone region even a little, it is possible to avoid an erroneous determination that the region is a Cr region but not an HT region when combined. Then, the two patterns may be synthesized when the grids match.

Here, depending on the quantization dimension to be developed, a quantization error occurs during synthesis.
FIG. 14 is a diagram illustrating another example of grid patterns having different developed quantization dimensions.
For example, when a certain predetermined area is viewed, the bit pattern of the halftone (HT) pattern shown in FIG. 14A and the bit pattern of the chrome (Cr) pattern shown in FIG. 14B are developed. In such a case, if these two are combined, the grid positions will not match as shown in FIG. Further, since the quantization error is also generated when converting the original pattern design data to the bit pattern data, the error is accumulated when the other is resampled in accordance with one, for example, halftone and chrome. There is a risk that the edge position will deviate from the correct position.

  Therefore, the pattern generation circuits 242 and 244 match the quantization dimension of the light shielding pattern (chrome pattern) and the grid position with the quantization dimension of the phase shift pattern (halftone) and the grid position, or quantize both. By making the dimension (grid size) an integer multiple, it is possible to avoid quantization errors associated with synthesis when calculating the average film thickness and determining the pattern overlap state in the average film thickness calculation circuit 250.

FIG. 15 is a diagram illustrating another example of grid patterns having different developed quantization dimensions.
For example, when a certain predetermined area is viewed, the bit pattern of the halftone (HT) pattern shown in FIG. 15A and the bit pattern of the chrome (Cr) pattern shown in FIG. 15B are developed. 15B, the quantization dimension of the bit pattern of the chrome (Cr) pattern shown in FIG. 15B is an integral multiple of the quantization dimension of the bit pattern of the halftone (HT) pattern shown in FIG. When the two are combined, the grid positions coincide as shown in FIG. 15C, and a quantization error can be avoided.

  For example, the size of one grid may be adjusted to a predetermined reference dimension called a design rule on the design data side such as 100 nm or 10 nm. It is also preferable to align the pixel dimensions.

Embodiment 4 FIG.
In each of the above-described embodiments, the example in which the light shielding pattern (chrome pattern) design data and the phase shift pattern design data are identified by the control computer 110 has been described, but in the fourth embodiment, the control computer 110 does not identify the light shielding pattern (chrome pattern) design data and phase shift pattern design data. A case where processing is performed by the expansion circuit 111 will be described.

  In each of the embodiments described above, in the data file shown in FIG. 5, since the data file is stored in the magnetic disk device 109 for each film type, the control computer 110 identifies each film type, 111. Therefore, as shown in FIG. 2, the development circuit 111 also includes one set of the I / F 212, the data memory 222, the graphic interpretation circuit 232, and the pattern generation circuit 242, the I / F 214, the data memory 224, and the graphic for each film type. And an interpretation circuit 234 and a set of pattern generation circuit 244.

FIG. 16 is a diagram illustrating an example of a data file.
FIG. 16 shows a case where design data of different film types is mixed in one data file. In the case where both are mixed as in this case, identification information indicating the film type is added to each graphic unit, a unit of a group in which a certain number of graphics are combined, or a unit in which a plurality of groups are combined. .

FIG. 17 is a block diagram showing an internal configuration of a development circuit according to the fourth embodiment.
In FIG. 17, an expansion circuit 111 includes an I / F (interface) 212 connected to a bus, a data memory 222, a graphic interpretation circuit 232, a pattern generation circuit 242, a pattern generation circuit 244, an average film thickness calculation circuit 250, a pattern synthesis. A circuit 260 is provided. The configuration shown in FIG. 2 eliminates the I / F 214, the data memory 224, and the graphic interpretation circuit 234. Others are the same as in FIG.

  In the fourth embodiment, the figure interpretation circuit 232 identifies the film type, and the pattern generation circuit 242 and the pattern generation circuit 244 generate patterns of the light shielding pattern (chrome pattern) and the phase shift pattern (halftone), respectively. Let it be done. Others may be the same as those of the above-described embodiments, and thus the description thereof is omitted.

  As described above, even when design data with different film types is mixed in the design data file, the same effects as those of the above-described embodiments can be obtained.

Embodiment 5. FIG.
In each of the above-described embodiments, the die-to-database inspection is assumed. However, even if the die-to-die inspection is performed, if the shading pattern (chrome pattern) design data and the phase shift pattern design data are available, Using the data, the position of the light shielding pattern can be determined to change the defect determination threshold value. Similarly, the average film thickness distribution can be calculated, and the focus position can be offset to correct the focus.

  As described above, when each of the above embodiments is applied, the defect detection sensitivity can be set according to the importance level of a single mask pattern, and the focus offset can be corrected according to the thickness of the light shielding film. The defect detection performance of the mask defect inspection apparatus can be improved with a simple configuration. As a result, the production yield of the exposure mask, the semiconductor element, and the LCD is improved, the rework of the product is reduced, and the total production cost can be reduced.

  In the above description, what is described as “˜circuit” or “˜process” can be configured by a computer-operable program. Or you may make it implement by not only the program used as software but the combination of hardware and software. Alternatively, a combination with firmware may be used. When configured by a program, the program is recorded on a recording medium such as a magnetic disk device, a magnetic tape device, an FD, or a ROM (Read Only Memory).

  The embodiments have been described above with reference to specific examples. However, the present invention is not limited to these specific examples.

  In addition, although descriptions are omitted for parts and the like that are not directly required for the description of the present invention, such as a device configuration and a control method, a required device configuration and a control method can be appropriately selected and used.

  In addition, all optical image acquisition apparatuses, optical image acquisition methods, mask inspection apparatuses, and mask inspection methods that include elements of the present invention and that can be appropriately modified by those skilled in the art are included in the scope of the present invention.

1 is a conceptual diagram showing a configuration of a mask inspection apparatus in a first embodiment. It is a block diagram which shows the internal structure of an expansion | deployment circuit. It is a figure which shows an example of a photomask. It is a figure which shows an example of the structure of a phase shift. It is a figure which shows an example of pattern design data. It is a figure which shows an example of the photomask formed with a halftone film and a chromium film. It is a figure for demonstrating the acquisition procedure of an optical image. It is a figure for demonstrating a filter process. It is a figure for demonstrating the method of calculating an average film thickness. It is a figure which shows the state which subdivided the predetermined area | region. It is a figure for demonstrating the comparison with the prior art in focus control. It is a figure which shows an example of a binary bit pattern. It is a figure which shows an example of the grid pattern from which an expansion | deployment quantization dimension differs. It is a figure which shows another example of the grid pattern from which an expansion | deployment quantization dimension differs. It is a figure which shows another example of the grid pattern from which an expansion | deployment quantization dimension differs. It is a figure which shows an example of a data file. FIG. 10 is a block diagram showing an internal configuration of a development circuit in a fourth embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Mask inspection apparatus 101 Photomask 102 XY (theta) table 103 Light source 104 Magnification optical system 105 Photodiode array 106 Sensor circuit 108 Comparison circuit 109 Magnetic disk apparatus 111 Expansion circuit 140 Autofocus control circuit 142 Piezo element 150 Optical image acquisition part 250 Average film thickness Arithmetic circuit 252 Weighting arithmetic circuit 254 Averaging arithmetic circuit 256 Pattern overlap situation determination circuit

Claims (2)

  1. The design shape data of the phase shift pattern on the glass mask, the film thickness information of the phase shift pattern, the design shape data of the light shielding pattern on the glass mask and the film thickness information of the light shielding pattern are input, and a predetermined area is A first bit pattern for the phase shift pattern for each region subdivided by an arbitrary first quantization size, film thickness information of the phase shift pattern, and the predetermined region as the first quantization size. An average film thickness of the predetermined region is obtained by using the second bit pattern for the light shielding pattern for each region subdivided by a second quantization dimension that is an integral multiple of and the film thickness information of the light shielding pattern. An average film thickness calculation unit to be calculated;
    When acquiring an optical image of a mask pattern created based on the design shape data of the phase shift pattern, the film thickness information of the phase shift pattern, the design shape data of the light shielding pattern, and the film thickness information of the light shielding pattern An optical image acquisition unit that acquires an optical image of an area of a mask pattern corresponding to the predetermined area by aligning the focus position with the average film thickness;
    An optical image acquisition apparatus comprising:
  2. The design shape data of the phase shift pattern on the glass mask, the film thickness information of the phase shift pattern, the design shape data of the light shielding pattern on the glass mask and the film thickness information of the light shielding pattern are input, and a predetermined area is A first bit pattern for the phase shift pattern for each region subdivided by an arbitrary first quantization size, film thickness information of the phase shift pattern, and the predetermined region as the first quantization size. An average film thickness of the predetermined region is obtained by using the second bit pattern for the light shielding pattern for each region subdivided by a second quantization dimension that is an integral multiple of and the film thickness information of the light shielding pattern. An average film thickness calculation step to be calculated;
    The predetermined region using a mask pattern created based on the design shape data of the phase shift pattern, the film thickness information of the phase shift pattern, the design shape data of the light shielding pattern, and the film thickness information of the light shielding pattern When acquiring an optical image of the area of the mask pattern corresponding to the optical image acquisition step of acquiring the optical image by adjusting the focus position to the average film thickness,
    An optical image acquisition method comprising:
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