JP2019086481A - Pattern inspection device and pattern inspection method - Google Patents

Abstract

To obtain the same measurement result with an external image acquisition device as a standard device from an exposure transfer simulation image obtained by simulating a transfer pattern image transferred by an exposure device.SOLUTION: An inspection device 100 comprises: a comparison processing part which determines whether a first optical image has a defect; an optical image acquisition mechanism 150 which acquires a second optical image as an exposure transfer simulation image obtained by simulating a transfer pattern image formed on a sample during exposure transfer with respect to a determined defective place; a storage device which stores a correction table having a correction threshold for a measurement threshold for measuring a size of a pattern in the second optical image defined based upon data obtained by an external image acquisition device acquiring the exposure transfer simulation image; and a size variation rate computation part which computes a size variable rate using a measurement pattern size of a pattern of a defect place measured from the second optical image using the correction threshold and a reference pattern size of a pattern corresponding to the defect place obtained from a second reference image corresponding to the second optical image.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a pattern inspection apparatus and a pattern inspection method. For example, the present invention relates to an apparatus and method for acquiring an exposure image of a mask substrate for exposure used in semiconductor manufacturing, and an apparatus and method for inspecting a pattern defect of the mask substrate for exposure.

  2. Description of the Related Art In recent years, with the high integration and large capacity of large scale integrated circuits (LSI), the line width of a circuit required for a semiconductor device is becoming narrower and narrower. These semiconductor devices use an original pattern (also referred to as a mask or a reticle; hereinafter collectively referred to as a mask) on which a circuit pattern is formed, and expose and transfer the pattern onto a wafer with a reduction projection exposure apparatus called a so-called stepper. It is manufactured by circuit formation. Therefore, in order to manufacture a mask for transferring such a fine circuit pattern to a wafer, a pattern drawing apparatus using an electron beam capable of drawing a fine circuit pattern is used. Pattern circuits may be drawn directly on a wafer using such a pattern drawing apparatus. Alternatively, development of a laser beam drawing apparatus for drawing using a laser beam other than the electron beam has been attempted.

  In addition, it is essential to improve the yield for the manufacture of LSI which requires a great deal of manufacturing cost. However, as typified by 1 gigabit grade DRAM (random access memory), the pattern which constitutes LSI is in the order of submicron to nanometer. One of the major factors to reduce the yield is a pattern defect of a mask used when exposing and transferring an ultrafine pattern on a semiconductor wafer by photolithography. In recent years, along with the miniaturization of the dimensions of LSI patterns formed on semiconductor wafers, the dimensions that must be detected as pattern defects have become extremely small. Therefore, there is a need to improve the accuracy of a pattern inspection apparatus for inspecting a defect of a transfer mask used in LSI manufacturing.

  As an inspection method, an optical image obtained by imaging at a predetermined magnification a pattern formed on a sample such as a lithography mask using a magnifying optical system, and a design data or an optical image obtained by imaging the same pattern on the sample It is known how to do the inspection by doing. For example, as a pattern inspection method, “die to die (die-to-die) inspection” in which optical image data obtained by imaging the same pattern at different places on the same mask are compared, The drawing data (design pattern data) converted to the device input format for drawing by drawing device at the time of drawing is input to the inspection device, a design image (reference image) is generated based on this, and the pattern is imaged There is a "die to database (die-database) inspection" that compares the measured optical data with the measured data. In an inspection method in such an inspection apparatus, a sample is placed on a stage, and movement of the stage causes a light flux to scan over the sample to perform an inspection. The sample is illuminated by a light source and illumination optics. The light transmitted or reflected by the sample is imaged on the sensor through an optical system. The image captured by the sensor is sent to the comparison circuit as measurement data. The comparison circuit compares the measurement data and the reference data according to an appropriate algorithm after alignment of the images, and determines that there is a pattern defect if they do not match.

  In semiconductor products having a short product cycle, shortening the production time is an important item. When a mask pattern having a defect is exposed and transferred onto a wafer, semiconductor devices made from the wafer become defective. Therefore, it is important to perform mask pattern defect inspection. Then, the defect found in the defect inspection is corrected by the defect correction device. However, if all the found defects are corrected, it will increase the manufacturing time and lead to a reduction in product value. Here, as the development of the inspection apparatus progresses, the inspection apparatus determines that there is a pattern defect even if a very small deviation occurs. However, when the mask pattern is transferred onto the wafer by an actual exposure apparatus, the circuit can be used as an integrated circuit as long as disconnection or / and short circuit of the circuit does not occur due to such a defect. Therefore, it is desirable to obtain an exposure image to be exposed on a wafer by an exposure apparatus. However, while the mask pattern is reduced and imaged on the wafer in the exposure apparatus, the mask pattern is enlarged and imaged on the sensor in the inspection apparatus. Therefore, the configuration of the optical system on the secondary side with respect to the mask substrate is originally different. Therefore, it is difficult for the inspection apparatus to reproduce the pattern image in the case of being transferred by the exposure apparatus as it is, even if the state of the illumination light is matched to the exposure apparatus.

  Therefore, on the side of the user who performs mask inspection with the inspection apparatus, for example, a dedicated machine manufactured by Carl Zeiss (for example, patent document) that generates and inspects an image as a spatial image as an exposure image transferred by exposure by the exposure apparatus. 1) is introduced to the production site as a standard device, and inspection with an exposure image is performed.

Japanese Patent Application Publication No. 2013-504774

  The standard device using the above-described spatial image takes time for measurement. Therefore, instead of creating an aerial image of the entire surface of the mask, an aerial image is created for a portion determined to be a defect by the inspection device, and inspection is performed on the exposed image. However, as described above, as the development of the inspection apparatus progresses, the inspection apparatus determines that there is a pattern defect even if a very small deviation occurs, and therefore, a large number of defective parts occur. If an aerial image is formed for all of these and exposure image inspection is performed, the throughput in mask manufacture will be very bad. Therefore, also in the inspection apparatus, it is required to reproduce the pattern image in the case of being transferred by the exposure apparatus, and to reduce the number of defective portions in advance in the inspection apparatus. Therefore, in the inspection apparatus, development of a system capable of capturing such an exposure image in addition to normal pattern defect inspection has been advanced.

  When inspection of pattern dimensions and the like is performed using the exposure image reproduced by the inspection apparatus developed as described above, the inspection result obtained may deviate from the inspection result by the above-described standard apparatus. . This is because the device configuration is originally different, and the obtained results are also different. However, it is difficult to determine which result is correct because each of them evaluates the pattern dimension in nanometer order. If this is the case, it is necessary for the user side to determine whether the inspection target mask substrate can be used for semiconductor manufacturing while wondering whether the result in any apparatus is correct. At present, it is desirable to inspect an exposure image using an aerial image as a standard, so it is desirable for the inspection apparatus to obtain the same result as the inspection result with such a standard apparatus.

  Therefore, according to one aspect of the present invention, it is possible to obtain, for example, measurement results similar to those of an external image acquisition apparatus serving as a standard apparatus from an exposure transfer simulation image simulating a transfer pattern image when transferred by an exposure apparatus. An inspection apparatus and its method are provided.

The pattern inspection apparatus according to one aspect of the present invention is
And a first optical image acquisition mechanism for acquiring a first optical image of a pattern by irradiating illumination light onto a mask substrate for exposure on which a pattern is formed and using transmitted light or reflected light obtained from the mask substrate ,
A comparison unit that determines the presence or absence of a defect in the first optical image by comparing the first reference image corresponding to the acquired first optical image with the first optical image;
A second optical image for obtaining a second optical image serving as an exposure transfer simulation image simulating a transfer pattern image formed on a sample when the pattern is exposed and transferred to a sample for a defect portion determined as a defect by inspection An image acquisition mechanism,
Measure the dimensions of the pattern in the second optical image based on data obtained by an external image acquisition device different from the second optical image acquisition mechanism that acquires an exposure transfer simulation image that simulates a transfer pattern image A storage device storing a correction table in which a correction threshold in which the measurement threshold is corrected is defined;
Corresponds to the measurement pattern dimension of the pattern of the defect portion measured from the second optical image using the correction threshold defined in the correction table and the defect portion obtained from the second reference image corresponding to the second optical image A dimensional change ratio calculation unit that calculates a dimensional change ratio using a reference pattern dimension of the target pattern;
It is characterized by having.

  Also, the correction table is set using an optical image obtained from the reference mask substrate serving as a reference using the second optical image acquisition mechanism and an optical image obtained from the reference mask substrate using the image acquisition device. Preferably, the corrected correction threshold is defined.

  In addition, it is preferable that, on the reference mask substrate, a plurality of types of pattern groups each formed of a plurality of patterns of the same type with different pattern sizes, arrangement pitches, defect types, and defect sizes be formed.

  In the correction table, the dimensional change rate of the pattern in the optical image obtained from the reference mask substrate using the second optical image acquisition mechanism is within the optical image obtained from the reference mask substrate using the image acquisition device. Preferably, a correction threshold is defined in which the measurement threshold is corrected to match the dimensional change rate of the pattern of.

The pattern inspection method according to one aspect of the present invention is
Illumination light is irradiated to a mask substrate for exposure on which a pattern is formed by the pattern inspection apparatus, and a first optical image of the pattern is acquired using transmitted light or reflected light obtained from the mask substrate;
Determining the presence or absence of a defect in the first optical image by comparing the first reference image corresponding to the acquired first optical image with the first optical image in the pattern inspection apparatus;
In the pattern inspection apparatus, when a pattern is exposed and transferred onto a sample, a second optical image serving as an exposure transfer simulation image simulating a transfer pattern image formed on the sample when a pattern is exposed and transferred onto a sample The process to acquire,
A measurement threshold is used to measure the dimensions of the pattern in the second optical image based on data obtained by an external image acquisition device different from the pattern inspection device that acquires an exposure transfer simulation image that simulates a transfer pattern image. Creating a correction table in which a corrected correction threshold is defined;
Corresponds to the measurement pattern dimension of the pattern of the defect portion measured from the second optical image using the correction threshold defined in the correction table and the defect portion obtained from the second reference image corresponding to the second optical image Calculating and outputting a dimensional change rate using a reference pattern dimension of the target pattern;
It is characterized by having.

  According to one aspect of the present invention, it is possible to obtain, for example, measurement results similar to those of an external image acquisition apparatus serving as a standard apparatus from an exposure transfer simulation image simulating a transfer pattern image when transferred by an exposure apparatus. Therefore, in the inspection apparatus, when exposure and transfer is performed from among a plurality of defects determined, it is possible to remove usable portions as integrated circuits.

FIG. 1 is a configuration diagram showing a configuration of a pattern inspection apparatus in Embodiment 1. FIG. 7 is a conceptual view showing a part of an optical system of an exposure apparatus which is a comparative example in the first embodiment. FIG. 2 is a conceptual view showing a part of an optical system of the inspection apparatus in the first embodiment. FIG. 7 is a flowchart showing the main steps of the pattern inspection method in the first embodiment. FIG. 7 is a diagram showing an example of an evaluation pattern formed on a reference mask substrate in the first embodiment. FIG. 7 is a diagram showing an example of pattern types constituting an evaluation pattern in Embodiment 1; FIG. 7 is a view showing another example of pattern types constituting the evaluation pattern in the first embodiment. FIG. 7 is a diagram showing an example of defect types and defect sizes of evaluation patterns in Embodiment 1. FIG. 7 is a view showing another example of the defect type and the defect size of the evaluation pattern in the first embodiment. FIG. 7 is a view showing another example of the defect type and the defect size of the evaluation pattern in the first embodiment. FIG. 7 is a view showing another example of the defect type and the defect size of the evaluation pattern in the first embodiment. FIG. 7 is a view showing another example of the defect type and the defect size of the evaluation pattern in the first embodiment. FIG. 5 is a diagram showing an internal configuration of a correction table generation circuit in Embodiment 1. FIG. 5 is a diagram for explaining a method of measuring the line width dimension in the first embodiment. FIG. 7 is a diagram showing an example of a format of a correction table according to Embodiment 1. FIG. 3 is a view showing an example of the configuration of a normal inspection optical system and an example of the configuration of an exposure image inspection optical system in Embodiment 1. FIG. 2 is a conceptual diagram for explaining an inspection area in the first embodiment. FIG. 5 is a diagram showing an example of an internal configuration of a comparison circuit in the first embodiment. It is a figure for demonstrating the flow of the pattern test of Embodiment 1 and a comparative example.

Embodiment 1
FIG. 1 is a block diagram showing the configuration of a pattern inspection apparatus according to the first embodiment. In FIG. 1, an inspection apparatus 100 for inspecting a defect of a pattern formed on a mask substrate 101 includes an optical image acquisition mechanism 150 and a control system circuit 160 (control unit).

  The optical image acquisition mechanism 150 includes a light source 103, a transmission inspection illumination optical system 170 (transmission illumination optical system), a reflection inspection illumination optical system 175 (reflection illumination optical system), a movable XYθ table 102, an aperture 173, and an enlargement. An optical system 104, a photodiode array 105 (an example of a sensor), a sensor circuit 106, a stripe pattern memory 123, and a laser length measuring system 122 are included. The substrate 101 is placed on the XYθ table 102. The substrate 101 includes, for example, an exposure photomask (exposure mask substrate) for transferring a pattern onto a semiconductor substrate such as a wafer. Further, on the photomask, a pattern formed of a plurality of graphic patterns to be inspected is formed. The substrate 101 is disposed, for example, on the XYθ table 102 with the pattern formation surface facing downward.

  The transmission inspection illumination optical system 170 has a projection lens 180, an illumination shape switching mechanism 181, and an imaging lens 182. The transmission inspection illumination optical system 170 may have other lenses, mirrors, and / or optical elements. The reflective inspection illumination optical system 175 has at least one lens for illuminating the reflective inspection illumination light separated from the transmission inspection illumination light from the light source 103. The reflection inspection illumination optical system 175 may have other lenses, mirrors, and / or optical elements.

  The magnifying optical system 104 includes an objective lens 171, a projection lens 172, and an imaging lens 176. The objective lens 171, the projection lens 172, and the imaging lens 176 are each configured by at least one lens. In addition, other lenses and / or mirrors may be provided between the objective lens 171 and the projection lens 172 and / or between the projection lens 172 and the imaging lens 176.

  It is preferable to use, for example, a TDI (time delay integration) sensor as the photodiode array 105. The photodiode array 105 (image sensor) captures an optical image corresponding to the pattern formed on the substrate 101 while the XYθ table 102 on which the substrate 101 is mounted is moving.

  In the control system circuit 160, the control computer 110 that controls the entire inspection apparatus 100 controls the position circuit 107, the comparison circuit 108, the reference image creation circuit 112, the autoloader control circuit 113, the table control circuit 114, and the mode switching via the bus 120. Connected to control circuit 140, exposure simulation reference image creation circuit 142, correction table creation circuit 144, magnetic disk drive 109, magnetic tape drive 115, flexible disk drive (FD) 116, CRT 117, pattern monitor 118, and printer 119. . Also, the sensor circuit 106 is connected to the stripe pattern memory 123, and the stripe pattern memory 123 is connected to the comparison circuit 108. In addition, the XYθ table 102 is driven by an X axis motor, a Y axis motor, and a θ axis motor.

  In the first embodiment, a high-magnification pattern image is taken, and an inspection (normal inspection mode (1)) for inspecting the pattern image and an exposure image are obtained, and an inspection using the exposure image (exposure image inspection The mode (2) is configured to be switchable. In the normal inspection mode (1), in the optical image acquisition mechanism 150 of the inspection apparatus 100, the light source 103, the transmission inspection illumination optical system 170, the reflection inspection illumination optical system 175, the XYθ table 102, the magnification optical system 104, the photodiode array 105, The sensor circuit 106 forms a high-magnification normal inspection optical system (inspection optical image acquisition mechanism: first optical image acquisition mechanism). For example, an inspection optical system having a magnification of 400 to 500 times is configured. In the exposure image inspection mode (2), in the optical image acquisition mechanism 150 of the inspection apparatus 100, the light source 103, the transmission inspection illumination optical system 170, the XYθ table 102, the diaphragm 173, the magnification optical system 104, the photodiode array 105, and the sensor circuit An exposure image inspection optical system (optical image acquisition mechanism for exposure image: second optical image acquisition mechanism) is configured by the numeral 106. The ordinary inspection optical system and the exposure image inspection optical system are configured to share most of the optical devices. In other words, part of the configuration is configured by diverting the same optical device. This can suppress an increase in the number of parts.

  Further, the XYθ table 102 is driven by the table control circuit 114 under the control of the control computer 110. It can be moved by a drive system such as a three-axis (X-Y-θ) motor that drives in the X direction, the Y direction, and the θ direction. As these X motor, Y motor and θ motor, for example, linear motors can be used. The XYθ table 102 is movable in the horizontal direction and the rotational direction by the motor of each axis of XYθ. Then, the position of the objective lens 171 is fixed, and the XYθ table 102 is dynamically moved in the optical axis direction (Z-axis direction) by an autofocus (AF) control circuit (not shown) under the control of the control computer 110. The focal position of the objective lens 171 is adjusted to the pattern formation surface of the mask substrate 101. In such a case, the focal position is adjusted by moving the XYθ table 102 in the optical axis direction (Z-axis direction) by, for example, a piezoelectric element (not shown). Alternatively, the focus position (optical axis direction: Z-axis direction) of the objective lens 171 is dynamically adjusted on the pattern formation surface of the mask substrate 101 by an autofocus (AF) control circuit (not shown) under the control of the control computer 110. It is also preferable to In such a case, the focal position is adjusted by moving the objective lens 171 in the optical axis direction (Z-axis direction) by, for example, a piezoelectric element (not shown). The movement position of the mask substrate 101 disposed on the XYθ table 102 is measured by the laser measurement system 122 and supplied to the position circuit 107. The position circuit 107 calculates the irradiation position of the inspection light relatively from the position of the XYθ table 102 to be measured.

  Design pattern data (drawing data) serving as a basis for pattern formation of the mask substrate 101 may be input from the outside of the inspection apparatus 100 and stored in the magnetic disk drive 109.

  Here, FIG. 1 describes the components necessary to describe the first embodiment. It goes without saying that the inspection apparatus 100 may normally include other necessary components.

  FIG. 2 is a conceptual view showing a part of an optical system of an exposure apparatus as a comparative example in the first embodiment. 15 shows a part of an optical system of an exposure apparatus such as a stepper which exposes and transfers a pattern formed on a mask substrate 300 onto a semiconductor substrate. In the exposure apparatus, illumination light (not shown) is illuminated on the mask substrate 300, transmitted light 301 from the mask substrate 300 is incident on the objective lens 302, and light 305 passing through the objective lens 302 is a semiconductor substrate 304 (wafer: exposed) Image on the substrate). Although FIG. 2 shows one objective lens 302 (reduction optical system), it is needless to say that a combination of a plurality of lenses may be used. Here, in the present exposure apparatus, the pattern formed on the mask substrate 300 is reduced to, for example, 1⁄4 and exposed and transferred onto the semiconductor substrate 304. The numerical aperture NAi (the numerical aperture on the image i side) with respect to the semiconductor substrate 304 of the exposure apparatus at that time is set to, for example, NAi = 1.4. In other words, the numerical aperture NAi (the numerical aperture on the image i side) of the objective lens 302 which can pass through the objective lens 302 is set to, for example, NAi = 1.4. In the exposure apparatus, since the transmitted light image from the mask substrate 300 is reduced to 1⁄4, the sensitivity of the objective lens 302 to the mask substrate 300 is 1⁄4. In other words, the numerical aperture NAo (numerical aperture on the object o side) of the objective lens 302 capable of incidence when transmitted light is incident from the mask substrate 300 to the objective lens 302 is 1⁄4 of NAi, and NAo = 0.35 It becomes. Therefore, in the exposure apparatus, the transmitted light image from the mask substrate 300 of the light flux with the numerical aperture NAo = 0.35 is exposed and transferred onto the semiconductor substrate 304 as an image of the light flux with a very wide numerical aperture NAi = 1.4. become.

  FIG. 3 is a conceptual view showing a part of the optical system of the inspection apparatus in the first embodiment. Here, the numerical aperture of the inspection apparatus according to the first embodiment is compared with the numerical aperture of the exposure apparatus shown in FIG. In inspection apparatus 100 in the first embodiment, as shown in FIG. 3, illumination light (not shown) is illuminated on mask substrate 101, and transmitted light 11 from mask substrate 101 is incident on magnifying optical system 104 including an objective lens. The light 12 that has passed through the magnifying optical system 104 forms an image on a photodiode array 105 (image sensor). At that time, the numerical aperture NAo (the numerical aperture on the object o side) of the objective lens capable of being incident when the transmitted light 11 is incident on the magnifying optical system 104 from the mask substrate 101 is set to NAo = 0.9, for example. In the inspection apparatus 100, the transmitted light image from the mask substrate 300 is magnified by 200 to 500 times in order to be comparable in inspection, so the sensitivity of the magnifying optical system 104 to the mask substrate 101 is 200 to 500. Accordingly, the numerical aperture NAi (the numerical aperture on the image i side) of the magnifying optical system 104 with respect to the photodiode array 105 is 1/500 to 1/200 of NAo, and for example, the numerical aperture NAi is 0.004.

  Thus, the information amount of light obtained by the objective lens 302 of the exposure apparatus with NAo = 0.35 and the information amount of light obtained with the objective lens of the inspection apparatus 100 with NAo = 0.9, for example It is different. Therefore, the image on the semiconductor substrate 304 is different from the image on the light receiving surface of the photodiode array 105 in the number of luminous fluxes, so it is difficult to obtain the same image. Therefore, in order to equalize the objective lens 302 of the exposure apparatus, the NAo of the objective lens of the inspection apparatus 100 is set, for example, to NAo = 0.35 by narrowing the light flux with the diaphragm 173. Thereby, the number of luminous fluxes can be matched. Although only the magnifying optical system 104 is described in FIG. 3, a plurality of lenses are disposed in the magnifying optical system 104. In the magnifying optical system 104, as described above, at least the objective lens 171, the projection lens 172, and the imaging lens 176 are provided.

  Therefore, when the mask substrate 101 is disposed in the exposure apparatus, the objective lens 171 causes the transmitted light from the mask substrate 101 to be incident on the semiconductor substrate 304 and the objective lens 302 of the exposure apparatus transmits the light from the mask substrate 101. The illumination light imaged on the mask substrate 101 has the same numerical aperture NAo (NAo = 0.35) as the light 301 enters, and the transmitted light 11 transmitted through the mask substrate 101 enters. The imaging lens 176 focuses the light passing through the magnifying optical system 104 with a numerical aperture NAi (NAi = 0.001) sufficiently smaller than the objective lens 302 of the exposure apparatus, but the mask substrate The amount of information of light passing through 101 and reaching the photodiode array 105 can be matched to the exposure apparatus.

  FIG. 4 is a flowchart showing main steps of the pattern inspection method according to the first embodiment. In FIG. 4, the pattern inspection method according to the first embodiment includes the reference mask measurement step (S90), the correction threshold search step (S92), the correction table creation step (S94), the mode selection step (S102), and the like. Release step (S104), inspection illumination optical system arrangement step (S106), scan step (S108), reference image creation step (S110), frame division step (S112), comparison step (S114), A step of squeezing (S204), a step of arranging an illumination optical system for exposure (S206), a step of inputting defect candidate information (S208), a step of scanning (S210), a step of creating a reference image (S212) S214), CD measurement step (S216), CD measurement step (S218), dimensional change rate calculation step (S220), determination step (S222) When, performing the steps of.

  Here, when inspection of pattern dimensions and the like using the exposure image reproduced by the inspection apparatus 100 is performed, the inspection result obtained may be deviated from the inspection result of the external standard device. This is because the device configuration is originally different, and the obtained results are also different. However, it is difficult to determine which result is correct because each of them evaluates the pattern dimension in nanometer order. Therefore, in the first embodiment, the measurement threshold is corrected by the inspection apparatus 100 so as to obtain the same result as the inspection result of the standard apparatus. In order to obtain the corrected correction threshold value, first, the same reference mask substrate is measured by the inspection apparatus 100 and an external standard apparatus not shown, and the measurement result in the inspection apparatus 100 and the external standard apparatus not shown Compare with the measurement results of

  In the reference mask measurement step (S90), using the inspection apparatus 100, the figure pattern formed on the reference mask substrate serving as a reference is imaged, and the line width dimension CD of the figure pattern is measured. The line width dimension CD of the figure pattern separately formed on the reference mask substrate is also measured by an external standard device (for example, a dedicated machine manufactured by Carl Zeiss) not shown.

  Here, the inspection apparatus 100 captures an image of the reference mask substrate as an exposure image. Therefore, an inspection optical system by the light source 103, the transmission inspection illumination optical system 170, the XYθ table 102, the diaphragm 173, the magnifying optical system 104, the photodiode array 105, and the sensor circuit 106 (optical image acquisition mechanism for exposure image: second optical Image acquisition mechanism). Specifically, as described later, the diameter of the aperture of the diaphragm 173 is narrowed to make NAo of the objective lens 171 equal to that of the objective lens 302 of the exposure apparatus. For example, NAo of the objective lens of the inspection apparatus 100 is set to, for example, NAo = 0.35. Furthermore, the illumination shape switching mechanism 181 switches the optical element including the lens, the mirror, and the like so that the shape of the illumination light (inspection light) for transmission inspection becomes the same as the illumination shape used in the exposure apparatus.

  FIG. 5 is a diagram showing an example of an evaluation pattern formed on the reference mask substrate in the first embodiment. In FIG. 5, on the reference mask substrate 300, a plurality of types of pattern groups each formed of a plurality of patterns of the same type with different pattern sizes, arrangement pitches, defect types, and defect sizes are formed. As a plurality of types of patterns, for example, a hole pattern (A), a pillar pattern (B) in which the hole pattern (A) is reversed to black and white, a line and space (L / S) pattern (C) aligned in the x direction, and / or A line and space (L / S) pattern (D) aligned in the y direction can be mentioned.

  FIG. 6 is a diagram showing an example of pattern types constituting the evaluation pattern in the first embodiment. FIG. 6A shows an example of a hole pattern (A) in which rectangular patterns of x-direction width size dx and y-direction width size dy are arranged at a pitch Px in the x direction and a pitch Py in the y direction. There is. FIG. 6B shows an example of a pillar pattern (B) in which rectangular space patterns of x-direction width size dx and y-direction width size dy are arranged at a pitch Px in the x direction and a pitch Py in the y direction. ing.

  FIG. 7 is a view showing another example of pattern types constituting the evaluation pattern in the first embodiment. FIG. 7A shows an example of a line and space (L / S) pattern (C) in which line patterns of x-direction width size dx are arranged in the x-direction at a pitch Px and arranged in the x-direction. FIG. 7B shows an example of a line-and-space (L / S) pattern (D) arranged in the y direction in which line patterns are arranged in the y direction at a pitch Py with a y direction width size dy.

  FIG. 8 is a diagram showing an example of the defect type and the defect size of the evaluation pattern in the first embodiment. FIG. 8A shows a defect type (1) in which both ends of the pattern, for example, in the x direction are reduced by the defect size Δx. FIG. 8B shows a defect type (2) in which the right end of the pattern, for example, in the x direction, becomes smaller by the defect size Δx. FIG. 8C shows a defect type (3) in which the left end of the pattern in the x direction, for example, becomes smaller by the defect size Δx. Although the x-direction end is shown here, the same defect type may exist for the y-direction end.

  FIG. 9 is a diagram showing another example of the defect type and defect size of the evaluation pattern in the first embodiment. FIG. 9A shows a defect type (4) in which both ends of the pattern, for example, in the x direction are increased by the defect size Δx. FIG. 9B shows a defect type (5) in which the right end of the pattern, for example, in the x direction, is increased by the defect size Δx. FIG. 9C shows a defect type (6) in which the left end of the pattern, for example, in the x direction, is increased by the defect size Δx. Although the x-direction end is shown here, the same defect type may exist for the y-direction end.

  FIG. 10 is a diagram showing another example of the defect type and defect size of the evaluation pattern in the first embodiment. In FIG. 10A, a defect type (7) in which a recess (notch) having a defect size Δx in the x direction and a defect size Δy in the y direction is generated in part of the left end of the pattern in the x direction, for example Is shown. In FIG. 10B, a defect type (8) in which a convex portion (protrusion) of a defect size Δx in the x direction and a defect size Δy in the y direction is generated in part of the left end of the pattern in the x direction Is shown. Although the x-direction end is shown here, the same defect type may exist for the y-direction end. Also, although one end of the two ends is shown, the same type of defect may be present for the other end.

  FIG. 11 is a diagram showing another example of the defect type and the defect size of the evaluation pattern in the first embodiment. FIG. 11A shows a defect type (9) in which a rectangular pattern having a defect size Δx in the x direction and a defect size Δy in the y direction is connected to, for example, an upper corner of the pattern in the x direction. FIG. 11B shows a defect type (10) in which a recess (notch) having a defect size Δx in the x direction and a defect size Δy in the y direction is generated at the upper corner of the pattern, for example, in the x direction. Here, although one corner of the four corners of the pattern is shown, similar defect types may be present for the remaining other corners.

  FIG. 12 is a diagram showing another example of the defect type and the defect size of the evaluation pattern in the first embodiment. FIG. 12A shows a defect type (11) in which a recess (cutout) of a defect size Δx in the x direction and a defect size Δy in the y direction is generated in, for example, the central part of the pattern. FIG. 12B shows a defect type (12) in which a rectangular pattern of a defect size Δx in the x direction and a defect size Δy in the y direction is arranged with a gap in the vicinity of the periphery of the pattern.

  A pattern group of each pattern type in which the pattern size, the arrangement pitch, the defect type, and the defect size as described above are variable is formed on the reference mask substrate 300. In the example of FIG. 5, for example, for the hole pattern (A), a plurality of hole pattern groups in which the defect type is sequentially changed in the x direction and the defect size is sequentially increased in the y direction are The arrangement pitch is sequentially increased toward the y direction, and the pattern sizes are sequentially increased toward the y direction. Similarly, for the pillar pattern (B), a plurality of pillar pattern groups in which the defect type is sequentially changed in the x direction and the defect size is sequentially increased in the y direction are further arranged in the x direction. The sizes are sequentially increased, and the pattern sizes are sequentially increased in the y direction. Similarly, for line and space (L / S) patterns (C) aligned in the x direction, a plurality of L / S patterns in which defect types are sequentially changed in the x direction and defect sizes are sequentially increased in the y direction The groups are further arranged such that the arrangement pitch is sequentially increased in the x direction, and the pattern size is sequentially increased in the y direction. Similarly, for L / S patterns (D) aligned in the y direction, a plurality of L / S pattern groups in which defect types are sequentially changed in the x direction and defect sizes are sequentially increased in the y direction are further The arrangement pitch is sequentially increased in the x direction, and the pattern size is sequentially increased in the y direction.

  With respect to the evaluation pattern formed on the reference mask substrate 300 as described above, an optical image is captured by the optical image acquisition mechanism 150 set in the exposure image inspection mode (2) in the inspection apparatus 100. Further, pattern data of a design evaluation pattern which is a basis for forming the evaluation pattern on the reference mask substrate 300 is input from the outside of the inspection apparatus 100 and stored in the storage device 109. Then, the reference image generation circuit 112 generates a reference image of the evaluation pattern.

  On the other hand, on the side of a standard apparatus (not shown) to be compared with the inspection apparatus 100, the width dimension CD of each of the evaluation patterns is measured, and the dimensional change rate is calculated for each of the evaluation patterns. The dimensional change rate is defined, for example, as a difference obtained by subtracting the design CD size from the CD size of the measured image (space image) divided by the design CD size (or a% value obtained by multiplying the value by 100). Ru. When calculating the dimensional change rate at the inspection apparatus 100 side, for example, a difference obtained by subtracting the CD size of the reference image from the CD size of the optical image divided by the CD size of the reference image (or such value is 100 It can be defined by multiplied by%).

  FIG. 13 is a diagram showing an internal configuration of the correction table creating circuit in the first embodiment. In FIG. 13, storage devices 40, 42, 44 such as a magnetic disk drive, a correction threshold value search unit 46, and a correction table generation unit 48 are disposed in the correction table generation circuit 144 in the first embodiment. Each “to unit” such as the correction threshold value search unit 46 and the correction table creation unit 48 has a processing circuit. Such processing circuits include, for example, an electric circuit, a computer, a processor, a circuit board, a quantum circuit, or a semiconductor device. Each “-unit” may use a common processing circuit (the same processing circuit) or may use different processing circuits (separate processing circuits). Information input to and output from the correction threshold value search unit 46 and the correction table generation unit 48 and information under calculation are stored in a memory (not shown) each time.

  FIG. 14 is a diagram for explaining a method of measuring the line width dimension in the first embodiment. In FIG. 14, since the obtained optical image is obtained as the gradation value (pixel value: image intensity) for each pixel, as shown in FIG. 14, the ordinate value represents the gradation value (pixel value: image intensity), horizontal It is acquired as gradation profile data indicating the position on the axis. In the gradation value profile of the pattern in the reference image, the inter-AB dimension is measured from the gradation value profile of the pattern in the optical image with the measurement threshold Th at which the inter-EF dimension in FIG. , CD of the pattern in the optical image can be obtained.

  As described above, in the standard apparatus and the inspection apparatus 100 in the first embodiment, although the same pattern is measured, the obtained dimensional change rates may not match. Therefore, in the first embodiment, in the gradation value profile of the pattern in the reference image, each pattern of the evaluation pattern is not the preset measurement threshold Th in which the inter-EF dimension in FIG. 14 becomes the desired design width dimension. Then, a measurement threshold value Th ′ is obtained in which a dimensional change rate matching the dimensional change rate obtained by the standard device is obtained.

  Therefore, first, the data of the optical image of each pattern of the evaluation pattern acquired by the optical image acquisition mechanism 150 set to the exposure image inspection mode (2) is output to the correction table generation circuit 144, and the position circuit 107 Together with the position information calculated by The data of the reference image of each of the created evaluation patterns is output to the correction table generation circuit 144 and stored in the storage device 42 together with the position information on the design data. Further, data of the dimensional change rate of each pattern of the evaluation pattern obtained by the standard device is input from the outside of the inspection apparatus 100 and stored in the storage device 44.

  In the correction threshold value search step (S92), the correction threshold value search unit 46 first performs, for each pattern of the evaluation pattern, the data of the optical image, the data of the reference image, and the data of dimensional change rate obtained by the standard device. Read out from the corresponding storage device, and search for the measurement threshold Th ′ which becomes the CD size of the optical image and the CD size of the reference image from which a dimensional change rate matching the dimensional change rate obtained by the standard device can be obtained.

  In the correction table generation step (S94), the correction table generation unit 48 generates a correction table 32 in which a correction threshold value in which the measurement threshold value Th for measuring the dimension of the pattern is corrected is defined.

  FIG. 15 is a diagram showing an example of the format of the correction table in the first embodiment. The correction table 32 is an optical image obtained from the reference mask substrate 300 serving as a reference using the exposure image inspection optical system (exposure image optical image acquisition mechanism: second optical image acquisition mechanism) of the inspection apparatus 100. A correction threshold value set using the standard image forming apparatus and an optical image obtained from the same reference mask substrate 300 using the standard apparatus serving as an external image acquiring apparatus is defined. Specifically, as shown in FIG. 15, the correction table creation unit 48 relates pattern type, pattern size, arrangement pitch, defect type, defect size, dimensional change rate obtained by the standard device, and correction threshold value. Thus, the correction table 32 is created. It should be noted that the correction threshold may be the searched measurement threshold Th ′ itself, or it may be searched from the measurement threshold Th in which the inter-EF dimension in FIG. 14 preset in the inspection apparatus 100 is the desired design width. It may be a change amount (for example, a difference value or an addition value) for becoming the measurement threshold value Th ′ or a change rate. In other words, the correction table 32 is in the optical image obtained from the reference mask substrate 300 using the exposure image inspection optical system of the inspection apparatus 100 (exposure image optical image acquisition mechanism: second optical image acquisition mechanism). Correction where the measurement threshold Th is corrected so that the dimensional change rate of the pattern matches the dimensional change rate of the pattern in the optical image obtained from the same reference mask substrate 300 using a standard device as an external image acquisition device A threshold is defined. Furthermore, in other words, the correction table 32 is obtained by a standard device which is an external image acquisition device different from the exposure image inspection optical system (optical image acquisition mechanism for exposure image: second optical image acquisition mechanism) of the inspection apparatus 100. The dimensions of the pattern in the exposure transfer simulation image (exposure image image: second optical image) acquired by the exposure image inspection optical system of the inspection apparatus 100 based on the acquired data are simulated. A correction threshold corrected with the measurement threshold Th is defined. The created correction table 32 is output to the comparison circuit 108.

  After the above-described pre-inspection process is completed, inspection is performed on the substrate 101 to be actually inspected.

  In the normal inspection mode (1), when the normal inspection mode (1) in which the pattern image of high magnification is picked up and the pattern image is inspected in the mode selection step (S102) is selected, Among them, the squeeze release step (S104), the inspection illumination optical system arrangement step (S106), the scan step (S108), the reference image creation step (S110), the frame division step (S112), and the comparison step (S114) And each step of.

  When the exposure image inspection mode (2) is selected in the mode selection step (S102), in the exposure image inspection mode (2), among the steps in FIG. 4, the aperture step (S204) and the illumination optical system for exposure Placement step (S206), defect candidate information input step (S208), scan step (S210), reference image creation step (S212), correction threshold calculation step (S214), and CD measurement step (S216) Each step of the CD measurement step (S218), the dimensional change rate calculation step (S220), and the determination step (S222) is performed.

  Therefore, first, in the mode selection step (S102), one of the normal inspection mode (1) and the exposure image inspection mode (2) is selected. For example, one of the inspection modes (1) and (2) may be selected from a keyboard, a mouse, a touch panel, etc. (not shown). Then, the information on the selected inspection mode is output to the mode switching control circuit 140 under the control of the control computer 110. The mode switching control circuit 140 switches the arrangement or the like of the inspection optical system in accordance with the input inspection mode information. In the first embodiment, first, the normal inspection mode (1) is selected.

  In the squeeze release step (S104), the mode switching control circuit 140 enlarges the diameter of the aperture of the diaphragm 173 and increases the passable light flux, thereby performing NAo of the objective lens 171 at the time of the normal high resolution inspection. Make it equal. For example, NAo of the objective lens of the inspection apparatus 100 is set to, for example, NAo = 0.9. Alternatively, the opening of the aperture 173 may be completely opened. If the diameter of the aperture of the aperture 173 is already large (or completely open), such a process may be omitted.

  In the inspection illumination optical system arrangement step (S106), the illumination shape switching mechanism 181 uses the shape of the illumination light (inspection light) for transmission inspection under normal control under the control of the mode switching control circuit 140. An optical element for illumination of the exposure apparatus is moved from the optical path to the outside of the optical path so as to have an illumination shape. Alternatively, the optical element including the lens, the mirror and the like is switched for normal inspection. Such a step may be omitted as long as the illumination shape is already in use for the normal inspection.

  FIG. 16 is a diagram showing an example of the configuration of a normal inspection optical system and an example of the configuration of an exposure image inspection optical system according to Embodiment 1. FIG. 16 shows a part of the configuration of FIG. The scale of the positions of the components in FIGS. 1 and 16 is not the same. FIG. 16A shows an example of the configuration of a normal inspection optical system. In the normal inspection optical system (inspection optical image acquisition mechanism: first optical image acquisition mechanism), the illumination shape of the transmission inspection illumination optical system 170 is controlled by the illumination shape switching mechanism 181 to the illumination shape used in the normal inspection. ing. Then, the restriction is released so that the numerical aperture NAo (the numerical aperture on the object o side) of the objective lens 171 capable of incidence when the transmitted light is incident from the substrate 101 to the magnifying optical system 104 becomes, for example, NAo = 0.9. ing. An example of the configuration of the exposure image inspection optical system shown in FIG. 16B will be described later.

  An optical image configured as a normal inspection optical system (inspection optical image acquisition mechanism: first optical image acquisition mechanism) by the steps of the above-described step of releasing the squeeze and arrangement of the inspection illumination optical system as the scanning step (S108) The acquisition mechanism 150 irradiates illumination light to the substrate 101 (exposure mask substrate) on which the pattern is formed, and uses transmitted light or reflected light obtained from the substrate 101 to form an optical image (first optical image of the pattern). Get). Specifically, it operates as follows.

  In FIG. 1 and FIG. 16A, laser light (for example, DUV light) having a wavelength equal to or lower than the ultraviolet range, which is inspection light, is generated from the light source 103. The generated light is illuminated to the illumination shape switching mechanism 181 by the projection lens 180, and the illumination light (first illumination light) that has become the illumination shape used at the time of regular inspection by the illumination shape switching mechanism 181 is the imaging lens As a result, an image is formed on the patterned surface of the substrate 101 from the back surface side opposite to the patterned surface of the substrate 101. The transmitted light (mask pattern image) transmitted through the substrate 101 is incident on the objective lens 171, and travels to the imaging lens 176 via the projection lens 172 by the objective lens 171. Then, the imaging lens 176 focuses transmitted light (mask pattern image) on the light receiving surface of the photodiode array 105. Then, the photodiode array 105 captures the formed image. During the scanning operation, the XYθ table 102 moves continuously.

  In addition, it may be reflection inspection instead of transmission inspection. For that purpose, the light generated from the light source 103 is divided into two light beams of different trajectories by a half mirror (not shown), and one light beam is incident on the reflection inspection illumination optical system 175 (reflection illumination optical system). The other light beam may be advanced to the transmission inspection illumination optical system 170 (transmission illumination optical system) described above. Alternatively, it may be shut off. The reflection inspection illumination optical system 175 (reflection illumination optical system) illuminates a light beam on a beam splitter (not shown), and the beam splitter reflects the light beam and enters the objective lens 171. The objective lens 171 focuses the incident light beam on the pattern formation surface of the substrate 101. Then, the reflected light (mask pattern image) reflected from the substrate 101 is incident on the objective lens 171, and proceeds to the imaging lens 176 via the projection lens 172 by the objective lens 171. Then, the imaging lens 176 focuses transmitted light (mask pattern image) on the light receiving surface of the photodiode array 105. Then, the photodiode array 105 captures the formed image. Alternatively, simultaneous inspection of transmission and reflection may be performed. In such a case, two photodiode arrays may be prepared, one of which receives transmitted light from the substrate 101 and the other of which receives reflected light from the substrate 101. The trajectories of the transmitted light and the reflected light may be shifted by slightly shifting the irradiation position on the substrate 101 between the transmission inspection light and the reflection inspection light. As a result, it is possible to simultaneously capture both the transmission image and the reflection image of the pattern.

  FIG. 17 is a conceptual diagram for explaining an inspection area in the first embodiment. The inspection area 10 (entire inspection area) of the substrate 101 is virtually divided into a plurality of strip-shaped inspection stripes 20 having a scan width W, for example, in the y direction, as shown in FIG. Then, the inspection apparatus 100 acquires an image (stripe area image) for each inspection stripe 20. For each of the inspection stripes 20, an image of a figure pattern arranged in the stripe region in the longitudinal direction (x direction) of the stripe region is captured using a laser beam. By the movement of the XYθ table 102, the substrate 101 is moved in the x direction, and as a result, an optical image is obtained while the photodiode array 105 is relatively continuously moved in the -x direction. The photodiode array 105 continuously captures an optical image of a scan width W as shown in FIG. In other words, the photodiode array 105, which is an example of a sensor, captures an optical image of a pattern formed on the substrate 101 using inspection light while moving relative to the XYθ table 102. In the first embodiment, after capturing an optical image in one inspection stripe 20, the optical image is moved to the position of the next inspection stripe 20 in the y direction, and while moving in the opposite direction this time, similarly the optical image of the scan width W is Capture images continuously. That is, imaging is repeated in the forward (FWD) -back forward (BWD) direction in the opposite direction on the forward path and the return path.

  Here, the direction of imaging is not limited to repetition of forward (FWD) -backforward (BWD). You may image from one direction. For example, FWD-FWD may be repeated. Alternatively, BWD-BWD may be repeated.

  The image of the pattern formed on the photodiode array 105 is photoelectrically converted by each light receiving element of the photodiode array 105, and is further A / D (analog / digital) converted by the sensor circuit 106. Then, the pixel data of the inspection stripe 20 to be measured is stored in the stripe pattern memory 123. When imaging such pixel data (stripe area image), it is preferable that the dynamic range of the photodiode array 105 be, for example, a dynamic range in which the case where the light amount of the illumination light is 60% incident is the maximum gradation.

  Further, when acquiring an optical image of the inspection stripe 20, the laser length measuring system 122 measures the position of the XYθ table 102. The measured position information is output to the position circuit 107. The position circuit 107 (arithmetic unit) calculates the irradiation position of the illumination light of the substrate 101 using the measured position information.

  Thereafter, the stripe area image is sent to the comparison circuit 108 together with data indicating the position on the substrate 101 output from the position circuit 107. The measurement data (pixel data) is, for example, 8-bit unsigned data, and expresses the gradation (brightness) of the brightness of each pixel. The stripe area image output into the comparison circuit 108 is stored in a storage device described later.

  In the reference image forming step (S110), the reference image forming circuit 112 detects the inspection stripe 20, for example, based on pattern data defined in design data (drawing data) on which the pattern is formed on the substrate 101. A reference image is created for each frame area 30 of a plurality of frame areas 30 divided by the same width as the scan width W. Specifically, it operates as follows. First, pattern data defined in design data (drawing data) is read from the storage device 109 through the control computer 110, and each graphic pattern defined in the read design pattern data is converted into binary or multilevel image data. Do.

  Here, the figure defined in the design pattern data is, for example, a rectangle or triangle as a basic figure, and for example, the coordinates (x, y) at the reference position of the figure, the length of the side, the figure such as a rectangle or triangle Graphic data in which the shape, size, position, and the like of each pattern graphic are defined is stored as information such as a graphic code serving as an identifier for distinguishing species.

When design pattern data to be such graphic data is input to the reference image generation circuit 112, it is expanded to data for each graphic, and a graphic code, a graphic dimension, etc. indicating the graphic shape of the graphic data are interpreted. Then, it is developed as binary or multi-valued design pattern image data as a pattern arranged in a unit of grid having a predetermined quantization dimension and output. In other words, the design data is read, and the occupancy rate of the figure in the design pattern is calculated for each square obtained by virtually dividing the inspection area as a square in units of predetermined dimensions, and the n-bit occupancy rate data is calculated. Output. For example, it is preferable to set one square as one pixel. Then, assuming that one pixel has a resolution of 1/2 ⁸ (= 1/256), the small area of 1/256 is allocated by the area of the figure arranged in the pixel, and the occupancy rate in the pixel is calculated. Calculate Then, it is output to the reference circuit 112 as 8-bit occupancy rate data. Such squares (inspection pixels) may be aligned with the pixels of the measurement data.

  Next, the reference image generation circuit 112 appropriately filters the design image data of the design pattern, which is the image data of a figure. Optical image data as a measurement image is in a state in which a filter is applied by an optical system, in other words, in a continuously changing analog state, so design image data whose image intensity (grayscale value) is an image data on the design side is a digital value. The filter data can also be adjusted to the measured data. The image data of the created reference image is output to the comparison circuit 108 together with the position information on the design data, and stored in a memory (not shown).

  FIG. 18 is a diagram showing an example of the internal configuration of the comparison circuit in the first embodiment. In FIG. 18, in the comparison circuit 108, storage devices 50, 52, 56, 57, 60, 61, 62, 68 such as magnetic disk devices, a frame division unit 54, an alignment unit 58, a comparison processing unit 59, defects An information interpretation unit 64, a measurement threshold value calculation unit 66, CD measurement units 70 and 72, a dimensional change rate calculation unit 74, and a comparison processing unit 76 are arranged. The frame division unit 54, the alignment unit 58, the comparison processing unit 59, the defect information interpretation unit 64, the measurement threshold calculation unit 66, the CD measurement units 70 and 72, the dimensional change ratio calculation unit 74, and the comparison processing unit 76 The unit has a processing circuit. Such processing circuits include, for example, an electric circuit, a computer, a processor, a circuit board, a quantum circuit, or a semiconductor device. Each “-unit” may use a common processing circuit (the same processing circuit) or may use different processing circuits (separate processing circuits). The frame division unit 54, the alignment unit 58, the comparison processing unit 59, the defect information interpretation unit 64, the measurement threshold calculation unit 66, the CD measurement units 70 and 72, the dimensional change rate calculation unit 74, and the comparison processing unit 76 Information and information being calculated are stored in a memory (not shown) each time.

  The data of the reference image sent to the comparison circuit 108 is stored in the storage device 50. Also, the data of the stripe area image sent to the comparison circuit 108 is stored in the storage device 52. The correction table 32 sent to the comparison circuit 108 is stored in the storage device 68.

  In the frame division step (S112), the frame division unit 54 reads the stripe area image, and divides the stripe area image into a predetermined size (for example, the same width as the scan width W) in the x direction. For example, it is divided into frame images of 512 × 512 pixels. Thus, for the plurality of frame areas 30 in which the inspection stripe 20 is divided by, for example, the same width as the scan width W, frame images of the respective frame areas 30 can be obtained. The frame image is stored in the storage unit 56.

  In the comparison step (S114), the alignment unit 58 first performs a predetermined algorithm on the frame image (first optical image) to be compared and the reference image (first reference image) to be compared. Align. For example, alignment is performed using the method of least squares.

  The comparison processing unit 59 (comparison unit) compares the reference image (first reference image) corresponding to the acquired frame image (first optical image) with the frame image (first optical image). Thus, it is determined whether or not there is a defect in the frame image (first optical image). Specifically, the comparison processing unit 59 compares, for each pixel, the frame image (first optical image) aligned with the reference image (first reference image) to be compared. The two are compared for each pixel according to a predetermined determination condition using a predetermined determination threshold to determine the presence or absence of a defect such as a shape defect, for example. For example, if the tone value difference for each pixel is larger than a predetermined determination threshold, it is determined as a defect candidate. Then, the comparison result is output. The comparison result may be output to the storage device 57, the monitor 117, and the memory 118. Alternatively, it may be output from the printer 119.

  In the above-described example, the “die to database (die database) inspection” of comparing a reference image created from design data (drawing data) based on which a pattern is formed on the substrate 101 with an optical image has been described. It is not limited to this. You may perform "die to die (die-die) inspection" which compares the optical image data which imaged the same pattern of the different places on the same board | substrate 101. FIG.

  For example, the stripe area image described above may include images of two dies on which the same pattern is formed. Therefore, in the case of die-to-die inspection, a frame image of the frame area 30 of the die (2) corresponding to the frame image of the frame area 30 of the die (1) is similarly generated. Here, for example, the frame image of the frame area 30 of the die (2) becomes a reference image (first reference image) corresponding to the frame image of the frame area 30 of the die (1). Then, the alignment unit 58 performs alignment between the frame image of the die (1) and the frame image of the die (2). Then, the comparison processing unit 59 compares the frame image of the die (1) with the frame image of the die (2) for each pixel. The comparison result may be output to the storage device 57, the monitor 117, and the memory 118. Alternatively, it may be output from the printer 119.

  As described above, the inspection apparatus 100 inspects the presence or absence of a defect in the pattern formed on the substrate 101, and acquires a defect location. However, as described above, when the mask pattern is transferred onto the wafer by an actual exposure apparatus, the circuit may be used as an integrated circuit if disconnection or / and short circuit of the circuit does not occur due to such defects. It is. However, even in the case where disconnection or / and short circuit does not occur at the stage of the mask substrate, it is necessary to exclude the one having high possibility of disconnection or / and short circuit by using as a semiconductor device. Therefore, the dimensional change rate described above is used as a parameter in the determination. Therefore, in the inspection apparatus 100 according to the first embodiment, following the normal inspection in the normal inspection mode (1), the exposure image inspection in the exposure image inspection mode (2) is performed on the defective portion.

  Therefore, the process returns to the mode selection step (S102), and this time, the exposure image inspection mode (2) is selected. Information on the selected inspection mode is output to the mode switching control circuit 140 under the control of the control computer 110. The mode switching control circuit 140 switches the arrangement or the like of the inspection optical system in accordance with the input inspection mode information.

  In the squeezing process (S204), the mode switching control circuit 140 narrows the diameter of the aperture of the squeeze 173 and squeezes the passable light flux to make NAo of the objective lens 171 equal to the objective lens 302 of the exposure apparatus. For example, NAo of the objective lens of the inspection apparatus 100 is set to, for example, NAo = 0.35.

  In the illumination optical system arranging step (S206) for the exposure, under the control of the mode switching control circuit 140, the illumination shape switching mechanism 181 is an illumination shape that the shape of the illumination light (inspection light) for transmission inspection uses in the exposure apparatus. The optical element including the lens, the mirror and the like is switched to have the same illumination shape as in. Such an optical element may be arranged switchably in advance according to the illumination condition of the exposure apparatus.

  In FIG. 16B described above, an example of the configuration of the exposure image inspection optical system is shown. As shown in FIG. 16B, in the exposure image inspection optical system (exposure image optical image acquisition mechanism: second optical image acquisition mechanism), the illumination shape of the transmission inspection illumination optical system 170 is used in the exposure device. The optical element is controlled by the illumination shape switching mechanism 181 so as to have an illumination shape similar to the illumination shape. Then, the light beam is depressed such that the numerical aperture NAo (the numerical aperture on the object o side) of the objective lens 171 capable of incidence when the transmitted light is incident from the substrate 101 to the magnifying optical system 104 becomes, for example, NAo = 0.35. ing.

  In the defect candidate information input step (S208), the control computer 110 reads data of the inspection result of the normal defect inspection from the storage device 57, and inputs information of a defect (currently defect candidate) determined as a defect. The information on the defect portion includes the position (coordinates) of the defect portion, design data of the pattern of the defect portion, and data of a frame image including the defect portion. The information on the defective portion is output to the comparison circuit 108, the exposure simulation reference image generation circuit 142, and the table control circuit 114. For example, the information on the defective portion output to the comparison circuit 108 is stored in the storage device 61.

  Then, the table control circuit 114 causes the illumination position of the inspection light to be at the imaging start position of the area including the defect (for example, the frame area 30) or to be near the front of the defect in the imaging direction. The XYθ table 102 is moved. Alternatively, the table control circuit 114 moves the XYθ table 102 to the imaging start position of the inspection stripe 20 including the defect portion. Here, as an example, the XYθ table 102 is moved so that the illumination position of the inspection light is at the imaging start position of the frame area 30 including the defect portion.

  An optical system configured as an optical system for inspecting an exposure image (optical image acquisition mechanism for exposure image: second optical image acquisition mechanism) by each process of the above-described narrowing and arrangement of the illumination optical system for exposure as a scanning process (S210) The image acquisition mechanism 150 is an exposure transfer simulation image that simulates a transfer pattern image formed on a sample (for example, a semiconductor wafer) when the pattern is exposed and transferred to a defect portion determined as a defect by inspection. An optical image (second optical image) is acquired. Specifically, imaging is performed as follows.

  In FIG. 1 and FIG. 16B, laser light (for example, DUV light) having a wavelength equal to or less than the ultraviolet range serving as inspection light generated from the light source 103 is illuminated on the illumination shape switching mechanism 181 by the projection lens 180 and illuminated. The illumination light (second illumination light) whose illumination shape is the same as the illumination shape used in the exposure apparatus by the shape switching mechanism 181 passes from the back side opposite to the pattern formation surface of the substrate 101 by the imaging lens 182 An image is formed on the pattern formation surface of the substrate 101. The transmitted light (mask pattern image) transmitted through the substrate 101 is narrowed by the aperture 173 and then enters the objective lens 171, and the objective lens 171 travels to the imaging lens 176 via the projection lens 172. Then, the imaging lens 176 focuses transmitted light (exposure image) on the light receiving surface of the photodiode array 105. Then, the photodiode array 105 captures the formed image. During the scanning operation, the XYθ table 102 moves continuously.

  When acquiring an optical image (exposure image: second optical image) to be an exposure transfer simulation image of a defect area (for example, the frame area 30 or the inspection stripe 20) including the defect portion, the laser length measuring system 122 , The position of the XYθ table 102 is measured. The measured position information is output to the position circuit 107. The position circuit 107 calculates the irradiation position of the illumination light of the substrate 101 using the measured position information.

  Thereafter, an exposure image image (exposure transfer simulation image: second optical image) of the defect area including the defect portion is sent to the comparison circuit 108 together with data indicating the position on the substrate 101 output from the position circuit 107. The measurement data (pixel data) is, for example, 8-bit unsigned data, and expresses the gradation (brightness) of the brightness of each pixel. The exposure image image output into the comparison circuit 108 is stored in the storage device 62.

  In the reference image forming step (S212), the exposure simulation reference image forming circuit 142 can obtain the pattern of the defective portion by exposure based on the pattern data defined in the design data (drawing data). An assumed exposure simulated reference image (second reference image) is created. The exposure simulation reference image is created in the same size as the exposure image, for example, the size in accordance with the frame area 30. First, pattern data defined in design data (drawing data) is read from the storage device 109 through the control computer 110, and each graphic pattern defined in the read design pattern data is converted into binary or multilevel image data. Do. In such a case, it is preferable to set in advance a conversion function for generating an image by simulation or the like so as to obtain a shape obtained when exposure and transfer. The image data of the created exposure simulation reference image is output to the comparison circuit 108 together with the position information on the design data and stored in the memory 60.

  In the correction threshold value calculation step (S214), first, the defect information interpretation unit 64 reads the information (defect information) of the defect part from the storage device 61 and interprets the defect information. Here, the pattern type, the pattern size, the arrangement pitch, the defect type, and the defect size of the defect pattern are interpreted. For example, the pattern type of the pattern, the pattern size, and the arrangement pitch are interpreted from the design data of the pattern of the defect portion. Then, the defect type of the defect generated in the pattern and the defect size are interpreted from the data of the frame image including the defect portion.

  The measurement threshold calculator 66 reads the correction table 32 from the storage device 68, and the correction threshold corresponding to (or closest to) the pattern type, the pattern size, the arrangement pitch, the defect type, and the defect size interpreted from the information of the defect location. Calculate (or search for) If it corresponds between the two correction thresholds, it is preferable to calculate the correction threshold after linear interpolation. The obtained correction threshold is output to the CD measurement units 70 and 72.

  In the CD measurement step (S216), the CD measurement unit 70 measures the pattern size of the pattern of the defect from the optical image (exposure image: second optical image) to be an exposure transfer simulation image using the calculated correction threshold. Measure (CD dimensions of the optical image). When the correction threshold is defined as the measurement threshold Th ′ itself, the CD measurement unit 70 cuts off the A′B ′ cut at the measurement threshold Th ′ in the gradation profile of the optical image to be the exposure transfer simulation image shown in FIG. Measure the dimensions. When the correction threshold is defined as a variation (for example, a difference value or an addition value) from the measurement threshold Th preset in the inspection apparatus 100, the CD measurement unit 70 determines the measurement threshold preset in the inspection apparatus 100. The measurement threshold Th ′ obtained by adding the correction threshold to Th or subtracting it from the measurement threshold Th measures the dimension A′B ′ cut out in the gradation profile of the optical image to be the exposure transfer simulated image shown in FIG. If the correction threshold is defined as a rate of change from the measurement threshold Th preset in the inspection apparatus 100, the CD measurement unit 70 obtains the measurement threshold Th preset in the inspection apparatus 100 by the correction threshold. With the measurement threshold value Th ′, the dimension between A ′ and B ′ cut out in the gradation profile of the optical image to be the exposure transfer simulated image shown in FIG. 14 is measured.

  In the CD measurement step (S218), the CD measurement unit 72 uses the calculated correction threshold value to calculate the reference pattern dimension (CD dimension of the reference image) of the pattern corresponding to the defect from the exposure simulation reference image (second reference image). Measure). If the correction threshold is defined as the measurement threshold Th ′ itself, the CD measurement unit 72 measures the dimension between E′F ′ cut off at the measurement threshold Th ′ in the gradation profile of the exposure simulation reference image shown in FIG. . When the correction threshold is defined as the amount of change (for example, a difference value or an addition value) from the measurement threshold Th preset in the inspection apparatus 100, the CD measurement unit 72 determines the measurement threshold preset in the inspection apparatus 100. The size between E′F ′ cut out in the gradation profile of the exposure simulation reference image shown in FIG. 14 is measured with the measurement threshold Th ′ obtained by adding the correction threshold to Th or subtracting it from the measurement threshold Th. If the correction threshold is defined as a rate of change from the measurement threshold Th preset in the inspection apparatus 100, the CD measurement unit 70 obtains the measurement threshold Th preset in the inspection apparatus 100 by the correction threshold. With the measured threshold value Th ′, the dimension between E′F ′ cut out in the gradation profile of the exposure simulation reference image shown in FIG. 14 is measured.

  In the dimensional change rate calculation step (S220), the dimensional change rate calculation unit 74 uses the correction threshold value defined in the correction table 32 to generate an exposure transfer simulation image from an optical image (exposure image: second optical image) Using the measured pattern dimensions of the measured pattern of the defect portion and the reference pattern dimensions of the pattern corresponding to the defect portion obtained from the exposure simulation reference image (second reference image) corresponding to the exposure transfer simulation image Calculate the dimensional change rate. The dimensional change rate is a difference obtained by subtracting the reference pattern dimension (CD dimension) of the exposure simulated reference image from the measurement pattern dimension (CD dimension) of the exposure transfer simulated image divided by the reference pattern dimension (CD dimension) of the exposure simulated reference image It can be defined as a value (or a% value obtained by multiplying such value by 100). The calculated dimensional change rate is output to the comparison processing unit 76. Alternatively, it may be further output to the storage device 109, the monitor 117, and the memory 118. Alternatively, it may be output from the printer 119.

  In the determination step (S222), the comparison processing unit 76 compares and determines whether the calculated dimensional change rate is larger than a predetermined determination threshold for each defective portion. Then, if the calculated dimensional change rate is larger than a predetermined determination threshold, such a defective portion is output to the storage device 109, the monitor 117, and the memory 118 as a real defective portion. Alternatively, it may be output from the printer 119. If the calculated dimensional change rate is not greater than a predetermined determination threshold, it is excluded as a pseudo defect from the defect group determined as a defect.

  FIG. 19 is a diagram for explaining the flow of pattern inspection in the first embodiment and the comparative example. FIG. 19A shows, as a comparative example, a flow of inspection in the case of using an inspection apparatus that performs defect inspection without performing exposure image inspection. FIG. 19B shows the flow of inspection in the case of performing exposure image inspection by the inspection apparatus 100 of the first embodiment. In FIG. 19A, a defect inspection is performed on a substrate 101 such as an exposure mask by a conventional inspection apparatus. In the inspection apparatus, even if a very small deviation occurs, it is determined that there is a pattern defect, so a large number of defect points occur. Information on defects of such a large number of mask patterns is output to an external standard device 400 that inspects an exposure image using an aerial image. Then, the dimensional change rate is calculated for each of the defective portions of these many mask patterns. As a result, when all the parts are OK, the mask pattern is exposed and transferred on the sample such as a wafer by the exposure apparatus 500. Conversely, if there is only one NG location, the mask will be repaired or discarded. A standard device using an aerial image takes time to measure. Therefore, if an aerial image is created for all defective portions of a large number of mask patterns and an exposure image inspection is performed, the throughput in mask production becomes very poor.

  On the other hand, as shown in FIG. 19B, in the first embodiment, in the inspection apparatus 100 as well, the defective part of the mask pattern determined as a defect in the normal defect inspection is transferred by the exposure apparatus 500. The pattern image in the case of image is reproduced, and the dimensional change rate is calculated respectively. As a result, in the inspection apparatus 100, the number of defective parts can be reduced in advance. Furthermore, in the first embodiment, the measurement threshold value used for dimension measurement in the case of calculating the dimensional change rate is corrected so as to match the dimensional change rate when measured by the external standard device 400. Therefore, under the same judgment condition as that of the external standard device 400, the number of defect points output to the external standard device 400 can be reduced. Therefore, the time required for the defect confirmation operation in the standard apparatus 400 can be significantly reduced, and the throughput in mask manufacturing can be improved. Alternatively, the defect confirmation operation in the standard device 400 may be omitted. Thereby, the throughput can be further improved.

  As described above, according to the first embodiment, for example, from the exposure transfer simulation image simulating the transfer pattern image when transferred by the exposure apparatus 500, the measurement result similar to that of the external image acquisition device serving as the standard device 400, for example. You can get Therefore, in the inspection apparatus 100, when the exposure transfer is performed from among a plurality of defects determined, it is possible to remove a usable portion as an integrated circuit.

  In the above description, each “circuit” has a processing circuit, and an electric circuit, a computer, a processor, a circuit board, a quantum circuit, a semiconductor device, or the like can be used as the processing circuit. Moreover, each "-circuit" may use a common processing circuit (the same processing circuit). Alternatively, different processing circuits (separate processing circuits) may be used. The program for executing the processor or the like may be recorded on a recording medium such as a magnetic disk device, a magnetic tape device, an FD, or a ROM (read only memory). For example, even if the position circuit 107, the comparison circuit 108, the reference image generation circuit 112, the mode switching control circuit 140, the exposure simulation reference image generation circuit 142, the correction table generation circuit 144, etc. are configured by at least one circuit described above. Good.

  The embodiments have been described above with reference to specific examples. However, the present invention is not limited to these specific examples. For example, as a pattern dimension for obtaining the dimensional change rate, it is preferable to measure the space dimension between pattern portions such as a plurality of rectangles in addition to the dimension of a pattern portion such as a rectangle. As a result, since the dimensional change rate of the distance between patterns can be obtained, a failure reserve group such as a short circuit can be obtained by inspection.

  Further, when capturing an exposure image, the transmitted light of the substrate 101 may be separated into a plurality of polarized waves and captured for each polarized wave, and then combined while being weighted by a predetermined model function.

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

  In addition, all polarization image acquisition devices, pattern inspection devices, and polarization image acquisition methods that include the elements of the present invention and whose design can be appropriately modified by those skilled in the art are included in the scope of the present invention.

Reference Signs List 10 inspection area 11 transmitted light 12 light 20 inspection stripe 30 frame area 32 correction table 40, 42, 44 storage device 46 correction threshold value search unit 48 correction table generation unit 50, 52, 56, 57, 60, 61, 62, 68 storage Device 54 Frame division unit 58 Alignment unit 59 Comparison processing unit 64 Defect information interpretation unit 66 Measurement threshold calculation unit 70, 72 CD measurement unit 74 Dimension change ratio calculation unit 76 Comparison processing unit 100 Inspection device 101 Substrate 102 XYθ table 103 Light source 104 Magnification optical system 105 Photodiode array 106 Sensor circuit 107 Position circuit 108 Comparison circuit 109 Magnetic disk drive 110 Control computer 112 Reference image creation circuit 113 Autoloader control circuit 114 Table control circuit 115 Magnetic tape device 116 FD
117 CRT
118 pattern monitor 119 printer 120 bus 122 laser length measurement system 123 stripe pattern memory 140 mode switching control circuit 142 exposure simulation reference image creation circuit 144 correction table creation circuit 150 optical image acquisition mechanism 160 control system circuit 170 transmission inspection illumination optical system 171 objective Lens 172 Projection lens 173 Aperture 175 Reflection inspection illumination optical system 176 Imaging lens 180 Projection lens 181 Illumination shape switching mechanism 182 Imaging lens 300 Mask substrate 301 Transmitted light 302 Objective lens 304 Semiconductor substrate 305 Light 400 Standard device 500 Exposure device

Claims (5)

Illumination light is irradiated to a mask substrate for exposure on which a pattern is formed, and a first optical image acquisition of the first optical image of the pattern is performed using transmitted light or reflected light obtained from the mask substrate. Mechanism,
A comparison unit that determines the presence or absence of a defect in the first optical image by comparing a first reference image corresponding to the acquired first optical image with the first optical image;
A second optical image is obtained which is an exposure transfer simulation image simulating a transfer pattern image formed on the sample when the pattern is exposed and transferred to a sample at a defect portion determined as a defect by the inspection. 2 optical image acquisition mechanism,
A pattern of the second optical image based on data obtained by an external image acquisition device different from the second optical image acquisition mechanism for acquiring an exposure transfer simulation image simulating the transfer pattern image A storage device for storing a correction table in which a correction threshold in which a measurement threshold for measuring a dimension is corrected is defined;
Obtained from the measurement pattern dimension of the pattern of the defect portion measured from the second optical image using the correction threshold defined in the correction table, and the second reference image corresponding to the second optical image A dimensional change rate calculation unit for calculating a dimensional change rate using a reference pattern dimension of a pattern corresponding to the defective portion to be selected;
A pattern inspection apparatus comprising:   The correction table uses an optical image obtained from a reference mask substrate serving as a reference using the second optical image acquisition mechanism and an optical image obtained from the reference mask substrate using the image acquisition device. The pattern inspection apparatus according to claim 1, wherein the correction threshold set is set.   3. The pattern according to claim 2, wherein a plurality of types of pattern groups each formed of a plurality of patterns of the same type with different pattern sizes, arrangement pitches, defect types and defect sizes are formed on the reference mask substrate. Inspection device.   In the correction table, a dimensional change rate of a pattern in the optical image obtained from the reference mask substrate using the second optical image acquisition mechanism is obtained from the reference mask substrate using the image acquisition device. 3. The pattern inspection apparatus according to claim 2, wherein the correction threshold value in which the measurement threshold value is corrected is defined so as to coincide with a dimensional change rate of a pattern in the optical image. A step of irradiating a mask substrate for exposure on which a pattern is formed by a pattern inspection apparatus, and acquiring a first optical image of the pattern using transmitted light or reflected light obtained from the mask substrate When,
The pattern inspection apparatus determines the presence or absence of a defect in the first optical image by comparing the first reference image corresponding to the acquired first optical image with the first optical image. The process to
In the pattern inspection apparatus, when the pattern is exposed and transferred onto a sample at a defective portion determined as a defect by the inspection, an exposure transfer simulation image simulating a transfer pattern image formed on the sample is formed. Obtaining an optical image of
The dimensions of the pattern in the second optical image are measured based on data obtained by an external image acquisition device different from the pattern inspection device, which acquires an exposure transfer simulation image simulating the transfer pattern image. Creating a correction table in which a correction threshold in which the measurement threshold is corrected is defined;
Obtained from the measurement pattern dimension of the pattern of the defect portion measured from the second optical image using the correction threshold defined in the correction table, and the second reference image corresponding to the second optical image Calculating and outputting a dimensional change rate using the reference pattern dimension of the pattern corresponding to the defective portion to be
A pattern inspection method comprising: