JP2012002731A - Inspection apparatus and inspection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inspection apparatus and an inspection method capable of minimizing a measurement error and accurately measuring a stage position.SOLUTION: A measuring system 122 measures a position of an XYθ stage 102 with a laser interferometer 201 and a linear scale 202. A measured value measured by the laser interferometer 201 is converted to position component data on a position calculation part 203 and then passes through a low pass filter 204. A measured value measured by the linear scale 202 is converted to position component data on the position calculation part 203 and then passes through a high pass filter 205. The data passing through the low pass filter 204 and the data passing through the high pass filter 205 are added and combined on an adder 206.

Description

  The present invention relates to an inspection apparatus and an inspection method.

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

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

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

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

JP 2008-112178 A

  A laser interferometer is used to measure the stage position. In the laser interferometer, the wavelength of the laser beam to be used is a reference for distance measurement. The wavelength of the laser light varies depending on the refractive index of the medium through which it propagates. In the case of a laser interferometer used for measuring the stage position of an inspection apparatus, the medium through which the laser light propagates is air, and its refractive index changes due to changes in atmospheric pressure, changes in temperature, and the like. For this reason, for example, the atmospheric pressure sensor is used to monitor the atmospheric pressure change, and the measurement error due to the wavelength change due to the atmospheric pressure change is corrected.

  However, it is not possible to completely correct fluctuations in measured values due to local changes in atmospheric pressure or temperature in the optical path of the laser interferometer only by correcting measurement errors using an atmospheric pressure sensor or a temperature sensor. In addition, measurement errors due to air fluctuations in the optical path of the laser interferometer increase as the optical path length increases. Since the length of the optical path is required according to the movable stroke of the stage, the influence of the air fluctuation becomes more serious when the inspection target becomes large and the movable stroke of the stage is extended.

  Such a measurement error due to air fluctuation can be considered as an AC component of a measurement signal from the laser interferometer. Since the average value of the AC component is 0, it can be removed from the measurement signal by taking a sufficient time average. However, if the measurement value is passed through a low-pass filter (LPF) in order to obtain a time average, the position of the stage moving at high speed cannot be measured due to a time delay.

  On the other hand, a linear scale may be used for measuring the stage position. The linear scale includes a scale portion on which a scale is formed and a position sensor that reads the scale on the scale portion. By irradiating the scale fixed to the stage with light and measuring the amount of displacement with a position sensor, the position of the stage can be grasped. Since the linear scale is not affected by air fluctuation, the measurement error is small when viewed in a short time. However, if the temperature of the measurement environment changes during long-time measurement, the length changes depending on the thermal expansion coefficient of the material constituting the scale portion, and the true value is not displayed. Essentially this can be considered as an error due to the DC component.

  As described above, since each measuring device includes an error, such as an AC component error in a laser interferometer and a DC component error in a linear scale, it is unavoidable that any measurement method is used. The present invention has been made in view of these problems. That is, an object of the present invention is to provide an inspection apparatus and an inspection method capable of accurately measuring the stage position while minimizing measurement errors.

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

A first aspect of the present invention is an inspection apparatus that forms an image obtained by illuminating a sample with light on an image sensor through an optical system and determines the presence or absence of defects.
A stage on which the sample is placed;
First measuring means for measuring the position of the stage;
A second measuring means for measuring the position of the stage;
A first filter that attenuates the AC component of the measured value measured by the first measuring means and transmits the DC component;
A second filter that is complementary to the first filter and attenuates the DC component of the measured value measured by the second measuring means and transmits the AC component;
It has a composition part which synthesize | combines the output value of a 1st filter, and the output value of a 2nd filter, and outputs the obtained synthesized value.

In the first aspect of the present invention, the first filter is a low-pass filter,
The second filter is preferably a high pass filter.

In the first aspect of the present invention, the first measuring means is a laser interferometer,
The second measuring means is preferably a linear scale.

A second aspect of the present invention is an inspection method for forming an image obtained by illuminating a sample with light on an image sensor via an optical system and determining the presence or absence of a defect.
Measuring the position of the stage with the first measuring means;
Measuring the stage position with a second measuring means;
Inputting the measurement value measured by the first measurement means to a first filter that attenuates the AC component of the measurement value and transmits the DC component;
The measurement value measured by the second measurement means is complementary to the first filter, and is input to a second filter that attenuates the DC component of this measurement value and transmits the AC component. Process,
And a step of synthesizing the output value of the first filter and the output value of the second filter, and outputting the obtained synthesized value.

In the second aspect of the present invention, the first measuring means is a laser interferometer,
The second measuring means is a linear scale,
The first filter is a low pass filter,
The second filter is preferably a high pass filter.

  According to the first aspect of the present invention, an inspection apparatus capable of accurately measuring the stage position while minimizing the measurement error is provided.

  According to the second aspect of the present invention, there is provided an inspection method capable of accurately measuring the stage position while minimizing a measurement error.

It is a block diagram of the inspection apparatus in this Embodiment. It is a figure explaining the acquisition procedure of mask measurement data. It is a block diagram of the length measurement system in this Embodiment. It is a figure showing the input value of the unit response of a coordinate measurement value. It is a figure which shows the output value of a low-pass filter with respect to the input value of FIG. It is a figure which shows the output value of a filter complementary to the filter of FIG. It is a figure which shows the output value obtained by adding the filter function of FIG. 5 and the filter function of FIG. It is a figure which shows the relationship between an input value in case noise is contained in the input value of a low-pass filter, and an output value. It is a figure which shows the output value obtained by adding the output value from the high-pass filter of the coordinate measurement value by a linear scale to the filter function of FIG. It is a top view which shows the structure of the stage vicinity of this Embodiment. It is an example of the figure explaining the external appearance of the stage by this Embodiment. It is a conceptual diagram which shows the flow of the data in this Embodiment.

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

  As illustrated in FIG. 1, the inspection apparatus 100 includes an optical image acquisition unit A and a control unit B. In FIG. 1, constituent components that are essential parts are described, but other known components necessary for inspecting the mask may be included. In this embodiment, a die-to-database inspection method is taken as an example, but a die-to-die inspection method may be used. In this case, one optical image of the same pattern in a different area in the mask is handled as a reference image.

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

  In the control unit B, a control computer 110 that controls the entire inspection apparatus 100 is provided with a position circuit 107, a comparison circuit 108, a reference circuit 112, a development circuit 111, and an autoloader control circuit 113 via a bus 120 serving as a data transmission path. Are connected to a stage control circuit 114, a magnetic disk device 109 as an example of a storage device, a magnetic tape device 115, a flexible disk device 116, a CRT 117, a pattern monitor 118, and a printer 119. The XYθ stage 102 is driven by an X-axis motor, a Y-axis motor, and a θ-axis motor controlled by a stage control circuit 114. As these motors, for example, step motors are used.

  In the inspection apparatus 100, the optical image acquisition unit A acquires an optical image of the photomask 101, that is, mask measurement data. Here, the mask measurement data is an image of a mask on which a graphic based on the graphic data included in the design pattern is drawn. A specific method for acquiring the mask measurement data is, for example, as follows.

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

  FIG. 2 is a diagram for explaining a procedure for acquiring mask measurement data.

  As shown in FIG. 2, the inspection area is virtually divided into a plurality of strip-shaped inspection stripes 20 having a scan width W in the Y direction, and each of the divided inspection stripes 20 is continuously scanned. Thus, the operation of the XYθ stage 102 is controlled, and an optical image is acquired while moving in the X direction. An image having a scan width W as shown in FIG. 4 is continuously input to the photodiode array 105. When the image in the first inspection stripe 20 is acquired, the image of the scan width W is continuously input to the second inspection stripe 20 in the same manner while the XYθ stage 102 moves in the opposite direction. The third inspection stripe 20 is acquired while moving in the direction opposite to the direction in which the image in the second inspection stripe 20 is acquired, that is, in the direction in which the image in the first inspection stripe 20 is acquired. In this way, it is possible to shorten a useless processing time by continuously acquiring images.

  The pattern image formed on the photodiode array 105 is photoelectrically converted and then A / D (analog-digital) converted by the sensor circuit 106. The photodiode array 105 is provided with an image sensor. An example of the image sensor is a TDI (Time Delay Integration) sensor. For example, the pattern of the photomask 101 is imaged by the TDI sensor while the XYθ stage 102 continuously moves in the X-axis direction.

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

  FIG. 3 is a configuration diagram of the length measurement system 122 in the present embodiment. In the present embodiment, the position of the XYθ stage 102 is measured using a laser interferometer 201 (first measurement means) and a linear scale 202 (second measurement means). A measurement value measured by the laser interferometer 201 is converted into position component data by the position calculation unit 203 and then passes through a low-pass filter (LPF; first filter) 204 set to a predetermined cutoff frequency. . On the other hand, the measurement value measured by the linear scale 202 is converted into position component data by the position calculation unit 203 and then passes through a high-pass filter (HPF; second filter) 205 set to a predetermined cutoff frequency. To do. The data that has passed through the low-pass filter 204 and the data that has passed through the high-pass filter 205 are added and synthesized by an adder 206 as an example of a synthesis unit. The obtained composite value is input to the position circuit 107 in FIG.

  Generally, the filtering process to time series data is expressed by a function by Z conversion. That is, both input data and output data are expressed by Z conversion, and the filter function is expressed by a ratio of Z conversion of input data to Z conversion of output data.

  When a certain low-pass filter (LPF) is expressed as F (Z), a high-pass filter (HPF) that is a complementary filter of this filter is expressed as 1-F (Z). A value obtained by adding the output values of the pair of filters is expressed by the added filter function, and F (Z) + {1−F (Z)} = 1.

For example, the relative position coordinate between the mask and the objective lens constituting the magnifying optical system is (x, y). Filter processing by the low-pass filter and the high-pass filter performed for the coordinate x is expressed by the following equations, respectively. Note that ε _AC is an error due to an AC component, and ε _DC is an error due to a DC component.

LPF (x + ε _AC ) = LPF (x) + LPF (ε _AC ) (1)
HPF (x + ε _DC ) = HPF (x) + HPF (ε _DC ) (2)

Here, since LPF (ε _AC ) and HPF (ε _DC ) are sufficiently smaller than LPF (x) and HPF (x), respectively, LPF (ε _AC ) ≈0 and HPF (ε _DC ) ≈0. Can think. Therefore, the value obtained by adding the right sides of the expressions (1) and (2) is as shown in the expression (3).

LPF (x) + HPF (x) + LPF (ε _AC ) + HPF (ε _DC )
= LPF (x) + HPF (x) (3)

Since the low-pass filter and the high-pass filter are linear filters, equation (3) can be transformed into equation (4).

LPF (x) + HPF (x) = (LPF + HPF) (x) (4)

Here, since the low-pass filter and the high-pass filter are in a complementary relationship, the relationship LPF + HPF = 1 is established. Therefore, Equation (4) becomes Equation (5).

(LPF + HPF) (x) = x (5)

  As described above, the error is reduced from the measurement value by performing the filtering process on the measurement value (x + ε) (ε: measurement error) of the coordinate x using the low-pass filter and the complementary high-pass filter. can do. The same applies to the coordinate y.

  As an example, a fifth-order Butterworth filter (Butterworth Filter) is considered as an analog filter.

  FIG. 4 shows input values of unit responses. The horizontal axis represents time expressed in arbitrary units, and the vertical axis represents coordinate measurement values by a laser interferometer. The output value of the low-pass filter with respect to this input value is shown in FIG. FIG. 6 shows a step response of a high-pass filter complementary to the low-pass filter shown in FIG. When the filter function of FIG. 5 and the filter function of FIG. 6 are added, the same input value as shown in FIG. 4 is obtained. This relationship is shown in FIG.

  Based on the above assumptions, consider the case where noise is included only in the input value to the low-pass filter. At this time, the relationship between the input value to the low-pass filter and the output value is as shown in FIG. As can be seen from FIG. 8, although the noise component is attenuated by taking the time average, the time delay is caused by passing through the low-pass filter, the response is delayed, and the final error is large.

  FIG. 9 is a graph in which a coordinate measurement value by a linear scale is input to a high-pass filter, and an output value thereof is added to the filter function of FIG. In FIG. 8, the slow-response component is complemented by the output value of the high-pass filter, so that the accuracy of the finally obtained value is high.

  As described above, by performing the filtering process on the measurement values of the laser interferometer 201 and the linear scale 202, respective errors can be reduced. Therefore, measurement accuracy can be maintained even if the temperature and pressure of the measurement environment vary. In the present embodiment, the sampling interval of measured values, the frequency characteristics of each filter, and the like are optimized as appropriate for each inspection apparatus.

  FIG. 10 is an example of a plan view showing a configuration in the vicinity of the XYθ stage 102 of FIG.

  As shown in FIG. 10, the laser interferometer as the first measuring means in this embodiment includes a first laser interferometer 300a that measures the position of the XYθ stage 102 in the Y direction, and the X direction of the XYθ stage 102. And a second laser interferometer 300b for measuring the position of. These laser interferometers can be, for example, heterodyne interferometers.

  In the first laser interferometer 300 a, the laser light emitted from the laser head 107 a is bent by the mirror 402 and enters the beam splitter 403. The laser light is separated into reference light and measurement light by the beam splitter 403 and then enters the interferometers 404 and 406, respectively. The interferometers 404 and 406 have a semi-transparent mirror inside, and divide the light incident by the semi-transparent mirror into two different optical paths. Here, one of the reference lights is incident on the reference mirror 405, and one of the measurement lights is incident on the mirror 3a attached to the XYθ stage 102. The reflected light reflected by these mirrors is observed.

  The second laser interferometer 300b is similar to the first laser interferometer 300a, and the laser light emitted from the laser head 107b is bent by the mirror 408 and enters the beam splitter 409. The laser light is split into reference light and measurement light by the beam splitter 409 and then enters the interferometers 410 and 412, respectively. The interferometer 410 causes reference light to enter the reference mirror 411, and the interferometer 412 causes measurement light to enter the mirror 3 a attached to the XYθ stage 102. An interference image is created on the light receiving element by the reflected light reflected by these mirrors.

The inspection apparatus 100 of FIG. 1 includes a linear scale that measures the positions of the XYθ stage 102 in the X direction and the Y direction as a second measuring unit. The linear scale includes a linear scale 16a that measures the X position on the XYθ stage 102 and a linear scale 16b that measures the Y position. The linear scale 16a is composed of a scale (scale) 16a _{1 serving as} a ruler and a detector 16a ₂ that acquires position information from the scale 16a ₁ . Similarly, the linear scale 16b is also formed in the scale 16b ₁ and the detector 16b _2. As the linear scale, for example, a photoelectric scale that converts an optical signal into a digital electric signal can be used. Specifically, the light from the light emitting element is divided into a plurality of scanning windows, and a sine according to the change in the amount of light transmitted (or reflected) through the lattice scale by the light receiving element (photodiode) corresponding to each window. A wave signal is generated. The phase of the sine wave signal generated from each window is shifted by 90 degrees, and the amount of movement is calculated from a plurality of sine wave signals having this phase difference.

  FIG. 11 is an example of a diagram illustrating the appearance of the stage according to the present embodiment. As shown in this figure, the stage 701 is configured to be movable in the X direction on a base 702. The base 702 is fixed on the base 704, and the stage 701 is movable in the Y direction because the base 704 is configured to be movable on the rail 703. Reference numerals 705a and 705b denote mirrors, and reference numerals 706a and 706b denote laser interferometers, which measure the position of the stage 701 as described with reference to FIG. That is, the position of the stage 701 in the X direction is measured by the mirror 705a and the laser interferometer 706a, and the position of the stage 701 in the Y direction is measured by the mirror 705b and the laser interferometer 706b. On the other hand, reference numerals 707a and 707b are scales constituting a linear scale, and reference numerals 708a and 708b are detectors. The position in the X direction of the stage 701 is measured by the scale 707a and the detector 708a, and the position in the Y direction of the stage 701 is measured by the scale 707b and the detector 708b.

  In the inspection apparatus according to the present embodiment, design pattern data serving as database-type reference data is stored in the magnetic disk device 109 of FIG. 1, read as the inspection proceeds, and sent to the development circuit 111. . In the development circuit 111, the design pattern data is converted into image data (bit pattern data). Thereafter, this image data is sent to the reference circuit 112 and used to generate a reference image to be a standard image.

  FIG. 12 is a conceptual diagram showing the flow of data in the present embodiment.

  As shown in FIG. 12, CAD data 501 created by a designer (user) is converted into design intermediate data 502 in a hierarchical format such as OASIS. The design intermediate data 502 stores design pattern data created for each layer and formed on each mask. Here, in general, the inspection apparatus 100 is not configured to directly read OASIS data. That is, unique format data is used for each manufacturer of the inspection apparatus 100. For this reason, the OASIS data is input to the inspection apparatus 100 after being converted into format data 503 unique to each inspection apparatus for each layer. The format data 503 can be data unique to the inspection apparatus 100, but may be data compatible with the drawing apparatus.

  The format data 503 is input to the magnetic disk device 109 of FIG. That is, the design pattern data used when forming the pattern of the photomask 101 is stored in the magnetic disk device 109.

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

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

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

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

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

  Next, filter processing in the reference circuit 112 will be described.

  The mask measurement data 504 as an optical image obtained from the sensor circuit 106, which will be described later, is blurred due to the resolution characteristics of the optical system and the aperture effect of the photodiode array, in other words, a spatial low-pass filter is applied. Is in a state. Therefore, it is possible to match the mask measurement data 504 by filtering the bit pattern data, which is the image data on the design side, in which the image intensity (shading value) is a digital value. In this way, a reference image to be compared with the mask measurement data 504 is created.

  As described above, in this embodiment, the position of the XYθ stage 102 is measured using the laser interferometer 201 and the linear scale 202. A measurement value measured by the laser interferometer 201 is converted into position component data by the position calculation unit 203 in FIG. 3 and then passes through the low-pass filter 204. On the other hand, the measurement value measured by the linear scale 202 is converted into position component data by the position calculation unit 203 and then passes through the high-pass filter 205. The data that has passed through the low-pass filter 204 and the data that has passed through the high-pass filter 205 are added and synthesized by the adder 206, and the resultant synthesized value is input to the position circuit 107.

  Data indicating the position of the photomask 101 on the XYθ stage 102 output from the position circuit 107 is sent to the comparison circuit 108 together with mask measurement data 504 (hereinafter also simply referred to as an optical image) output from the sensor circuit 106. Sent. The mask measurement data 504 is, for example, 8-bit unsigned data, and represents the brightness gradation of each pixel. Further, the reference image described above is also sent to the comparison circuit 108.

  In the comparison circuit 108, before the optical image and the reference image are compared, pattern alignment in these images is performed. Thereafter, the defect detection unit 108b performs a defect detection process for the pattern after comparing these images.

  In the defect detection unit 108b, the mask measurement data 504 sent from the sensor circuit 106 and the reference image generated by the reference circuit 112 are compared using an appropriate comparison determination algorithm. The comparison is performed using only a transmission image, only a reflection image, or an algorithm that combines transmission and reflection. A plurality of algorithms are selected according to the nature of the defect. A threshold value is set for each algorithm, and an algorithm having a reaction value exceeding the threshold value is detected as a defect. In this case, first, a temporary threshold is set for the algorithm, and a defect inspection result performed based on this threshold is reviewed in a review process described later. When this process is repeated and it is determined that sufficient defect detection sensitivity is obtained, the provisional threshold is determined as the algorithm threshold.

  If the difference between the mask measurement data 504 and the reference image exceeds the threshold value as a result of the comparison, the location is determined as a defect. If the defect is determined, the coordinates, the mask measurement data 504 and the reference image that are the basis for the defect determination are stored in the magnetic disk device 109 as a mask inspection result 505.

  The mask inspection result 505 is sent to the review device 500 that is an external device of the inspection device 100. The review is an operation in which the operator determines whether the detected defect is a problem. The review device 500 displays an image of a defective portion of the mask while moving the stage on which the mask is placed so that the defect coordinates of each defect can be observed. At the same time, these are displayed side by side on the screen so that the determination conditions for defect determination and the optical image and reference image that are the basis for determination can be confirmed. By displaying the defect on the mask and the ripple state on the wafer transfer image side by side in the review process, it becomes easy to determine whether or not the mask pattern should be corrected. In general, a reduction projection of about 1/4 is performed from the mask to the wafer, so this scale is also taken into consideration when displaying them side by side.

  All the defects detected by the inspection apparatus 100 are determined by the review apparatus 500. The determined defect information is returned to the inspection apparatus 100 and stored in the magnetic disk device 109. When at least one defect to be corrected is confirmed by the review apparatus 500, the mask is sent to the correction apparatus 600 that is an external apparatus of the inspection apparatus 100 together with the defect information list 506. In the case of a pattern defect, the correction method differs depending on whether the defect type is a convex defect or a concave defect. Therefore, the defect information list 506 is attached with the defect type including the irregularities and the defect coordinates. For example, it is attached whether the shading film is to be cut or compensated, and cut out pattern data for recognizing the pattern of the portion to be corrected by the correction device. Here, the above-described mask measurement data 504 can be used as the pattern data.

  Note that the inspection apparatus 100 itself may have a review function. In this case, the mask inspection result 505 is displayed on the CRT 117 of the inspection apparatus 100 or on the screen of a separately prepared computer together with incidental information for defect determination.

  In the review process, the defect is displayed on the monitor based on the data created from the inspection result, and the operator determines whether this is a really problematic defect and classifies the defect. Specifically, a comparison image is generated from an optical image that is measurement data and a reference image, and defects displayed on the comparison image are reviewed by an operator. Pixel data in these images is expressed by gradation values for each pixel. That is, each pixel is given any value from 0 gradation to 255 gradation from a color palette having 256 gradation values, thereby displaying a drawing pattern or a defect.

  As described above, in this embodiment, the position of the stage is measured using a laser interferometer and a linear scale. The measurement value measured by the laser interferometer passes through a low-pass filter after being converted into position component data. On the other hand, the measurement value measured on the linear scale is converted into position component data and then passes through the high-pass filter. By adding the output value from the low-pass filter to the output value from the high-pass filter, it is possible to reduce each of the error of the laser interferometer and the error of the linear scale. This makes it possible to accurately measure the stage position while minimizing measurement errors due to temperature and pressure fluctuations in the measurement environment.

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

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

3a, 402,408,705a, 705b mirror 16a, 16b, 202 linear scale _{16a 1, 16b 1, 707a,} 707b scales _{16a 2, 16b 2, 708a,} 708b detector 20 test stripe 100 inspection apparatus 101 photomask 102 XY.theta. Stage DESCRIPTION OF SYMBOLS 103 Light source 104 Magnifying optical system 105 Photodiode array 106 Sensor circuit 107 Position circuit 107a, 107b Laser head 108 Comparison circuit 108a Positioning part 108b Defect detection part 109 Magnetic disk apparatus 110 Control computer 111 Development circuit 112 Reference circuit 113 Autoloader control circuit 114 Stage control circuit 115 Magnetic tape device 116 Flexible disk device 117 CRT
118 Pattern Monitor 119 Printer 120 Bus 122 Measuring System 130 Autoloader 170 Illumination Optical System 201, 706a, 706b Laser Interferometer 203 Position Calculation Unit 204 Low Pass Filter 205 High Pass Filter 206 Adder 300a First Laser Interferometer 300b Second Laser Interferometer 403, 409 Beam splitter 404, 406, 410, 412 Interferometer 405, 411 Reference mirror 500 Review device 501 CAD data 502 Design intermediate data 503 Format data 504 Mask measurement data 505 Mask inspection result 506 Defect information list 600 Correction device 701 Stage 702, 704 Base 703 Rail

Claims (5)

In an inspection apparatus that images an image obtained by illuminating a sample on an image sensor through an optical system and determines the presence or absence of defects,
A stage on which the sample is placed;
First measuring means for measuring the position of the stage;
Second measuring means for measuring the position of the stage;
A first filter that attenuates the AC component of the measurement value measured by the first measurement means and transmits the DC component;
A second filter that is complementary to the first filter and attenuates the DC component of the measurement value measured by the second measurement means and transmits the AC component;
An inspection apparatus comprising: a combining unit that combines the output value of the first filter and the output value of the second filter and outputs the obtained combined value. The first filter is a low-pass filter;
The inspection apparatus according to claim 1, wherein the second filter is a high-pass filter. The first measuring means is a laser interferometer;
3. The inspection apparatus according to claim 1, wherein the second measuring unit is a linear scale. In an inspection method for determining the presence or absence of defects by forming an image obtained by illuminating a sample on an image sensor through an optical system,
Measuring the position of the stage with a first measuring means;
Measuring the position of the stage with a second measuring means;
Inputting the measurement value measured by the first measurement means to a first filter that attenuates an AC component of the measurement value and transmits a DC component;
A measurement value measured by the second measurement means is complementary to the first filter, and is a second filter that attenuates the DC component of the measurement value and transmits the AC component. Input process;
And a step of synthesizing the output value of the first filter and the output value of the second filter and outputting the obtained synthesized value. The first measuring means is a laser interferometer;
The second measuring means is a linear scale;
The first filter is a low-pass filter;
The inspection method according to claim 4, wherein the second filter is a high-pass filter.

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