JP2017138250A - Pattern line width measurement device and pattern line width measurement method - Google Patents

Abstract

PURPOSE: To provide a measurement device that can perform a highly accurate CD measurement even when a pattern of a measurement object is smaller than a measurement frame size and a pattern of the measurement object other than the pattern thereof mixes in the measurement frame.CONSTITUTION: A pattern line width measurement device comprises: a slit 172 that is arranged between a light source and a stage, or between the stage and a TDI sensor 105 to block incidence of light upon an area on either side in an electric charge transfer direction of an area where a measurement object area is shot of an area allowing the TDI sensor to shoot; and a CD measurement unit 56 that measures a line width of a graphic pattern in the measurement object area, using a pattern image of the measurement object area shot by the TDI sensor. In a state where the incidence of light upon the area on either side in the electric charge transfer direction of the area where the measurement object area is shot is blocked by the slit, and a movement of the stage is restricted so as not to move with respect to the electric charge transfer direction, the area including the measurement object area is shot by the TDI sensor as transferring the electric charge.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a pattern line width measuring apparatus and a pattern line width measuring method. For example, the present invention relates to a pattern line width measurement method performed by an inspection apparatus that acquires an optical image of a pattern and inspects the pattern.

  In recent years, the circuit line width required for a semiconductor element has been increasingly narrowed as a large scale integrated circuit (LSI) is highly integrated and has a large capacity. These semiconductor elements use an original pattern pattern (also referred to as a mask or a reticle, hereinafter 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. Therefore, a pattern drawing apparatus using an electron beam capable of drawing a fine circuit pattern is used for manufacturing a mask for transferring such a fine circuit pattern onto a wafer. A pattern circuit may be directly drawn on a wafer using such a pattern drawing apparatus. Alternatively, development of a laser beam drawing apparatus for drawing using a laser beam in addition to an electron beam has been attempted.

  In addition, improvement in yield is indispensable for manufacturing an LSI that requires a large amount of manufacturing cost. However, as represented by a 1 gigabit class DRAM (Random Access Memory), the pattern constituting the LSI is about to be in the order of submicron to nanometer. One of the major factors that reduce the yield is a pattern defect of a mask used when an ultrafine pattern is exposed and transferred onto a semiconductor wafer by a photolithography technique. In recent years, with the miniaturization of LSI pattern dimensions formed on semiconductor wafers, the dimensions that must be detected as pattern defects have become extremely small. Therefore, it is necessary to improve the accuracy of a pattern inspection apparatus that inspects defects in a transfer mask used in LSI manufacturing.

  As an inspection method, an optical image obtained by imaging a pattern formed on a sample such as a lithography mask using a magnifying optical system at a predetermined magnification is compared with an optical image obtained by imaging design data or the same pattern on the sample. A method of performing an inspection by doing this is known. For example, as a pattern inspection method, “die to die inspection” in which optical image data obtained by imaging the same pattern at different locations on the same mask is compared, or a pattern is formed using CAD data with a pattern design as a mask. Drawing data (design pattern data) converted into a device input format for the drawing device to input at the time of drawing is input to the inspection device, design image data (reference image) is generated based on this, and the pattern and the pattern are generated. There is a “die to database (die-database) inspection” that compares an optical image that is captured measurement data. In the inspection method in such an inspection apparatus, the sample is placed on the stage, and the stage is moved so that the light beam scans on the sample and the inspection is performed. The sample is irradiated with a light beam by a light source and an illumination optical system. The light transmitted or reflected by the sample is imaged on the sensor via the optical system. The image picked up by the sensor is sent to the comparison circuit as measurement data. The comparison circuit compares the measured data and the reference data according to an appropriate algorithm after the images are aligned, and determines that there is a pattern defect if they do not match.

  In the pattern inspection, in addition to the pattern defect (shape defect) inspection, measurement of the line width (CD) deviation of the pattern on the sample surface is also required. Conventionally, the measurement of the line width (CD) of a pattern has used a dedicated measuring device. However, if these can be measured at the same time during pattern defect inspection, there are significant advantages in terms of cost and inspection time. Therefore, the request | requirement which ask | requires this measuring function is increasing in the inspection apparatus (for example, refer patent document 1).

  In order to realize CD measurement with an inspection apparatus, it is necessary to measure the line width (CD) of a pattern in an image from an optical image. In order to measure the line width (CD) of a pattern with high accuracy, it is desirable to provide a large number of measurement points and average the obtained results. Therefore, it has been studied to divide the sample surface area into a plurality of frame areas and average the line width (CD) of the patterns in the frame area image. Here, when only line and space patterns having the same pitch are arranged on the entire surface in the same frame region, the effect of averaging the line width (CD) of the pattern to be measured is maximized, and the CD measurement accuracy is best. Conversely, when patterns with different pitches or patterns other than line-and-space patterns are mixed in the same frame region, the number of measurement points for the same pattern is reduced, so the CD measurement accuracy is poor. turn into. For example, in a layout in which a plurality of patterns are mixed in a narrow area such as a logic circuit pattern, it is difficult to obtain highly accurate CD measurement.

JP 2014-181966 A

  Therefore, one embodiment of the present invention provides a measuring apparatus and method capable of performing CD measurement with high accuracy even when a measurement target pattern is smaller than the measurement frame size and when a pattern other than the measurement target pattern is mixed in the measurement frame. provide.

An apparatus for measuring a line width of a pattern according to an aspect of the present invention includes:
A stage on which a substrate on which a plurality of graphic patterns are formed is arranged;
It has a plurality of light receiving elements arranged in a two-dimensional form, and accumulates electric charges generated by photoelectrically converting the light received by each light receiving element in a predetermined direction while sequentially transferring between the light receiving elements at a predetermined cycle. A TDI (Time Delay Integration) sensor that captures a pattern image,
A light source and a stage that shields light from entering the regions on both sides in the charge transfer direction of the region where the measurement target region is imaged among the imageable regions of the TDI sensor when imaging the measurement target region on the substrate; Or a slit disposed between the stage and the TDI sensor,
A measurement unit that measures the line width of the graphic pattern in the measurement target region using the pattern image of the measurement target region imaged by the TDI sensor;
With
The imaging positions on the substrate of the plurality of light receiving elements in a state where light is blocked by the slits on both sides in the charge transfer direction of the region where the measurement target region is imaged among the imageable regions of the TDI sensor The region including the measurement target region is imaged by the TDI sensor while transferring the charge in a state in which the movement of the stage is restricted so that it does not move in the charge transfer direction of the TDI sensor.

  In addition, it is preferable that an area including the measurement target area is imaged by the TDI sensor while the substrate is shifted in a direction orthogonal to the charge transfer direction of the TDI sensor.

In addition, the line width of the graphic pattern is measured at a plurality of measurement points in the frame area where the graphic pattern is arranged among a plurality of frame areas obtained by dividing the inspection area of the substrate by a size not larger than the imageable width of the TDI sensor. Defined by multiple line width statistics,
The measurement target area is smaller than the frame area.

Moreover, the determination which determines whether the said measurement object area | region corresponds to a defect position about the several measurement object area | region on a board | substrate is input about the defect position information determined as the defect among the several graphic patterns formed in the board | substrate. Further comprising
When the measurement target region corresponds to a defect position, the measurement target region is excluded from the region for measuring the line width of the pattern,
With respect to the remaining measurement target areas that were not excluded, the movement of the stage was restricted so that the imaging positions of the plurality of light receiving elements on the substrate did not move with respect to the charge transfer direction of the TDI sensor, and by the slits The TDI sensor is used to transfer the charge to the measurement target area while transferring the charges in a state where light is incident on both sides in the charge transfer direction of the area in which the measurement target area is imaged among the imageable areas of the TDI sensor. It is preferable that the area to be captured is imaged.

The method for measuring the line width of a pattern according to an aspect of the present invention includes:
It has a plurality of light receiving elements arranged in a two-dimensional form, and accumulates electric charges generated by photoelectrically converting the light received by each light receiving element in a predetermined direction while sequentially transferring between the light receiving elements at a predetermined cycle. By using a TDI (time delay integration) sensor that captures a pattern image, measurement is performed on a substrate on which a plurality of graphic patterns are formed on the stage in the imageable area of the TDI sensor. In a state where light incident on both sides in the charge transfer direction of the region where the target region is imaged is shielded by a slit disposed between the light source and the stage or between the stage and the TDI sensor, and In a state where the movement of the stage is limited so that the imaging position of the light receiving element on the substrate does not move with respect to the charge transfer direction of the TDI sensor, A step of imaging a region including the measurement area by the TDI sensor while feeding,
Measuring the line width of the graphic pattern in the measurement target region using the pattern image of the measurement target region imaged by the TDI sensor;
It is provided with.

  According to one aspect of the present invention, high-precision CD measurement can be performed even when the measurement target pattern is smaller than the measurement frame size and when a pattern other than the measurement target pattern is mixed in the measurement frame.

1 is a configuration diagram illustrating a configuration of a pattern inspection apparatus according to a first embodiment. 6 is a diagram illustrating an example of a light receiving surface and a charge accumulation direction of a TDI sensor according to Embodiment 1. FIG. 6 is a diagram for describing an imaging operation by a TDI sensor in Embodiment 1. FIG. FIG. 3 is a conceptual diagram for explaining an inspection region in the first embodiment. 6 is a diagram showing an example of a pattern layout in a frame area in the first embodiment. FIG. 6 is a diagram illustrating an example of a frame image serving as a comparative example of Embodiment 1. FIG. FIG. 4 is a flowchart showing main steps of the pattern inspection method in the first embodiment. 6 is a diagram for describing filter processing according to Embodiment 1. FIG. 2 is a diagram illustrating an internal configuration of a CD measurement circuit according to Embodiment 1. FIG. FIG. 5 is a diagram showing an example of a pattern layout in a frame area where slits are arranged in the first embodiment. 6 is a diagram for explaining measurement points in the first embodiment. FIG. 6 is a diagram for explaining CD measurement in Embodiment 1. FIG. 6 is a diagram illustrating an example of a pattern, a pixel value, and an example of a profile according to Embodiment 1. FIG. 6 is a diagram illustrating an example of a measurement image in Embodiment 1. FIG. FIG. 10 is a diagram showing another example of a measurement image in the first embodiment. It is a figure which shows another example of the pattern layout in the frame area | region in which the slit in Embodiment 1 is arrange | positioned.

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

  The optical image acquisition unit 150 includes a light source 103, an illumination optical system 170, a movable XYθ table 102, a magnifying optical system 104, a slit 172, a slit driving mechanism 174, a TDI (time delay integration) sensor 105, and a sensor. A circuit 106, a stripe pattern memory 123, and a laser length measurement system 122 are included. A substrate 101 is arranged on the XYθ table 102. Examples of the substrate 101 include a photomask for exposure that transfers a pattern to a wafer. In addition, a plurality of graphic patterns to be inspected are formed on this photomask. For example, the substrate 101 is arranged on the XYθ table 102 with the pattern formation surface facing downward.

  In the control system circuit 160, a control computer 110 serving as a computer is connected via a bus 120 to a position circuit 107, a comparison circuit 108, a development circuit 111, a reference circuit 112, an autoloader control circuit 113, a table control circuit 114, and a slit position control circuit. 140, a CD measurement circuit 142, a mode selection circuit 144, a magnetic disk device 109, a magnetic tape device 115, a flexible disk device (FD) 116, a CRT 117, a pattern monitor 118, and a printer 119. 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. The XYθ table 102 is driven by an X-axis motor, a Y-axis motor, and a θ-axis motor. The XYθ table 102 is an example of a stage.

  In the inspection apparatus 100, the light source 103, the XYθ table 102, the illumination optical system 170, the magnifying optical system 104, the TDI sensor 105, and the sensor circuit 106 constitute a high-magnification inspection optical system. The XYθ table 102 is driven by the table control circuit 114 under the control of the control computer 110. It can be moved by a drive system such as a three-axis (XY-θ) motor that drives in the X, Y, and θ directions. For example, step motors can be used as these X motor, Y motor, and θ motor. The XYθ table 102 can be moved in the horizontal direction and the rotation direction by a motor of each axis of XYθ. The movement position of the XYθ table 102 is measured by the laser length measurement system 122 and supplied to the position circuit 107. The focal position (focus position) of the magnifying optical system 104 on the pattern forming surface of the substrate 101 is set to a height position in the optical axis direction of the magnifying optical system 104 by a piezo element (not shown) controlled by an AF control circuit (not shown). It is adjusted by controlling.

  Here, FIG. 1 shows components necessary for explaining the first embodiment. It goes without saying that the inspection apparatus 100 may normally include other necessary configurations.

  FIG. 2 is a diagram showing an example of the light receiving surface and the charge accumulation direction of the TDI sensor in the first embodiment. In FIG. 2, the TDI sensor 105 has a plurality of light receiving elements 11 arranged two-dimensionally. The TDI sensor 105 accumulates charges generated by photoelectric conversion of the light received by each light receiving element 11 in a predetermined direction (charge accumulation direction) while sequentially transferring between the light receiving elements 11 at a predetermined cycle. . In the example of FIG. 2, charges are accumulated in the x direction. Then, the charge accumulated (accumulated) up to the final light receiving element 11 in the x direction is output as pixel intensity data of one pixel.

  FIG. 3 is a diagram for explaining an imaging operation by the TDI sensor in the first embodiment. FIG. 3A shows an example in which, for example, the right end image (transmission image or reflection image) of the substrate 101 is formed on the left end region of the TDI sensor 105 by the magnifying optical system at the imaging start time. In the TDI sensor 105, the charges imaged by the respective light receiving elements 11 are transferred in the charge accumulation direction. Therefore, in order to continue imaging at the same position, the charges are synchronized with the timing cycle in which the charges are transferred in the charge accumulation direction. 3 (b), FIG. 3 (c), and FIG. 3 (d), the position of the substrate 101 is set so that the light receiving element 11 to which the charge is transferred captures the same position of the substrate 101. Move sequentially. By such an operation, the results of imaging the same position of the substrate 101 by the plurality of light receiving elements 11 are cumulatively added while being delayed in time, so that an image signal with sufficient strength can be obtained and a highly accurate image by the averaging effect can be obtained. A signal can be obtained.

  In the example of FIGS. 3A to 3D, the light of the pattern image on the surface of the substrate 101 is focused on the TDI sensor 105 by the magnifying optical system 104 at a position symmetrical to the optical axis. Although the charge accumulation direction of the TDI sensor 105 and the movement direction of the substrate 101 are shown in the opposite directions, the present invention is not limited to this. Even if the magnifying optical system 104 is configured such that the charge receiving destination light receiving element 11 images the same position of the substrate 101 when the charge accumulation direction of the TDI sensor 105 and the movement direction of the substrate 101 are the same. Good.

  FIG. 4 is a conceptual diagram for explaining an inspection region in the first embodiment. As shown in FIG. 4, the inspection area 10 (the entire inspection area) of the substrate 101 has a plurality of strip-shaped inspection stripes 20 having a scan width W (capable of image pickup by the TDI sensor 105) in the Y direction, for example. Virtually divided. Then, the inspection apparatus 100 acquires an image (stripe region image) for each inspection stripe 20. For each of the inspection stripes 20, an image of a graphic pattern arranged in the stripe region is taken in the longitudinal direction (X direction) of the stripe region using laser light. The optical image is acquired while the TDI sensor 105 continuously moves in the X direction relatively by the movement of the XYθ table 102. The TDI sensor 105 continuously captures optical images having a scan width W as shown in FIG. In other words, the TDI sensor 105 captures an optical image of a pattern formed on the mask substrate 101 using inspection light while moving relative to the XYθ table 102 (stage). In the first embodiment, after taking an optical image in one inspection stripe 20, the optical image having the scan width W is similarly moved while moving in the Y direction to the position of the next inspection stripe 20 and moving in the opposite direction. Take images continuously. That is, imaging is repeated in a forward (FWD) -backforward (BWD) direction in the opposite direction on the forward path and the backward path.

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

  Here, the image of the inspection stripe 20 (stripe region image) is 1 / m in size (an integer of m ≧ 1) of the width of the inspection stripe 20 (y direction) in the x and y directions, in other words, in the Y direction. The image is divided into a plurality of frame images with a size equal to or smaller than the scan width W (capable of image capturing by the TDI sensor 105). Therefore, the inspection area 10 is virtually divided into a plurality of frame areas 32 having such a frame image size. In the example of FIG. 4, each inspection stripe 20 is virtually divided into a plurality of frame regions 32 in the x and y directions, for example, with a size that is ¼ the width of the inspection stripe 20 (y direction). For example, the image is divided into 512 × 512 pixel frame images. Alternatively, in the example of FIG. 4, each inspection stripe 20 may be divided into a plurality of frame images in the x direction with a width similar to the width of the inspection stripe 20, for example, the scan width W. In such a case, the inspection area 10 is virtually divided into a plurality of frame areas 30 having such a frame image size. In other words, the inspection area 10 of the photomask is virtually divided into a plurality of strip-shaped inspection stripes 20 with one size (y-direction size) of the frame area 30, and each inspection stripe 20 is divided into another size (x (Direction size) is virtually divided into a plurality of frame regions 30.

  FIG. 5 is a diagram showing an example of a pattern layout in the frame area in the first embodiment. The example of FIG. 5 shows a case where a plurality of different patterns 40, 42, 44, 46 are arranged in the frame region 32 (or frame region 30). For example, a case where a logic pattern is arranged on the substrate 101 serving as a photomask is applicable. Many pattern types are arranged in the logic pattern and the like, and the periodic pattern is difficult to arrange. The plurality of patterns 40, 42, 44, 46 are small patterns each having a small size. Therefore, even if the frame image of the frame region 32 (or the frame region 30) is imaged as described above using the TDI sensor 105, the line pattern portion (black pattern portion) and the space pattern portion (white pattern portion) in each pattern. The measurement points of the degree necessary for measuring the line width CD with the portion) with high accuracy cannot be obtained. Therefore, it is difficult to obtain meaningful data even if a CD is measured from an inspection image captured by the inspection apparatus 100.

  On the other hand, for example, in the case of a logic pattern or the like, when a CD measurement pattern is intentionally created at a plurality of substantially evenly distributed positions on the mask surface in order to confirm the CD accuracy of the pattern formed on the mask surface. There is. Conventionally, for such a micropattern (CD measurement pattern), for example, a CD has to be measured using a CD-SEM (Critical Dimension-Scanning Electron Microscope). However, it is desired to perform CD measurement of such a minute pattern with the inspection apparatus 100. For example, as shown in the pattern 40, a line and space pattern extending in the x direction is created as a CD measurement pattern. Therefore, in the first embodiment, CD measurement of such a minute pattern is performed as follows.

  FIG. 6 is a diagram illustrating an example of a frame image that is a comparative example of the first embodiment. FIG. 6 shows a case where the pattern 40 is the CD measurement target among the plurality of patterns 40, 42, 44, 46 arranged in the frame region 32 (or the frame region 30) shown in FIG. In the comparative example of the first embodiment, as shown in FIGS. 3A to 3D, the position of the substrate 101 is moved by moving the XYθ table 102 in synchronization with the timing period transferred in the charge accumulation direction. The position of the substrate 101 is fixed in the x direction without moving the XYθ table 102 in the x direction, and an image is taken by the TDI sensor 105. As a result, as shown in FIG. 6, an image having a shape in which the pattern 40 extends in the x direction that is the charge accumulation direction can be captured. Here, the case where the remaining patterns 42, 44, 46 among the plurality of patterns 40, 42, 44, 46 are different from the line and space pattern extending in the x direction is shown. For example, a pattern including a line pattern extending in the y direction may be used. The TDI sensor 105 sequentially transfers charges generated by photoelectric conversion of the light received by each light receiving element 11 between the light receiving elements 11 in a predetermined cycle toward the x direction (constant direction) as a charge accumulation direction. The pattern image is captured by accumulating. Therefore, if the position of the substrate 101 is fixed in the x direction, information on each position in the x direction within the frame region 32 (or the frame region 30) is integrated. Therefore, except for the case where only black patterns or only white patterns are arranged in the x direction, the obtained image has an intermediate gradation in which the black pattern and the white pattern are mixed as shown in FIG. It will be out of focus. Therefore, the S / N ratio cannot be obtained between the line pattern (black pattern) and the space pattern (white pattern). Therefore, in such a state, CD measurement of the line pattern (black pattern) and the space pattern (white pattern) becomes difficult. Therefore, in the first embodiment, the S / N ratio is improved by devising as described later.

  FIG. 7 is a flowchart showing main steps of the pattern inspection method according to the first embodiment. 7, the pattern inspection method according to the first embodiment includes a shape defect inspection mode selection step (S102), an optical image acquisition step (S104), a frame division step (S106), and a reference image creation step (S108). A comparison step (S110), a micro-pattern CD inspection mode selection step (S202), a coordinate setting step (S204), a determination step (S206), a stage moving step (S208), and a slit placement step (S210). A series of steps of an optical image acquisition step (S212), a line width CD measurement step (S214), an average line width CDave calculation step (S216), and a determination step (S218) are performed.

  The pattern line width measurement method according to the first embodiment includes a micro pattern CD inspection mode selection step (S202), a coordinate setting step (S204), a determination step (S206), and a stage movement. Step (S208), Slit placement step (S210), Optical image acquisition step (S212), Line width CD measurement step (S214), Average line width CDave calculation step (S216), Determination step (S218) This is a series of processes.

  First, the substrate 101 on which a plurality of graphic patterns are formed is transported and placed on the XYθ table 102.

  As the shape defect inspection mode selection step (S102), the mode selection circuit 144 selects a shape defect inspection mode. With this selection, the slit position control circuit 140 controls the slit driving mechanism 174 to move the slit 172 to a position that is off the optical path. For example, a cylinder mechanism or the like is preferably used as the slit driving mechanism 174.

  As an optical image acquisition step (S104), the optical image acquisition unit 150 acquires optical images of a plurality of patterns formed on the substrate 101 using the TDI sensor 105 for each stripe region. Specifically, it operates as follows.

  A plurality of graphic patterns formed on the substrate 101 are irradiated from a suitable light source 103 with laser light (for example, DUV light) having a wavelength equal to or lower than the ultraviolet region, which serves as inspection light, via the illumination optical system 170. The light transmitted through the substrate 101 is formed as an optical image on the TDI sensor 105 (an example of a sensor) through the magnifying optical system 104 and is incident thereon.

  The pattern image formed on the TDI sensor 105 is photoelectrically converted by each light receiving element 11 of the TDI sensor 105, and further A / D (analog / digital) converted by the sensor circuit 106. Then, pixel data is stored in the stripe pattern memory 123 for each inspection stripe 20. When capturing such pixel data (stripe region image), the dynamic range of the TDI sensor 105 is, for example, a dynamic range having a maximum gradation when the amount of illumination light is 60% incident. Thereafter, the stripe region image is sent to the comparison circuit 108 together with data indicating the position of the substrate 101 on the XYθ table 102 output from the position circuit 107. The measurement data (pixel data) is, for example, 8-bit unsigned data, and represents the brightness gradation (light quantity) of each pixel. The stripe area image input into the comparison circuit 108 is stored in a memory (not shown).

  As the frame dividing step (S106), as described above, the comparison circuit 108 divides each captured stripe area image into the frame areas 32 (or frame areas 30) to obtain the frame areas 32 (or frame areas 30). Create a frame image for each.

  As the reference image creation step (S108), the reference image creation unit such as the development circuit 111 and the reference circuit 112 uses the frame image based on the design data (drawing data) to form a plurality of graphic patterns on the substrate 101. A reference image of an area corresponding to (optical image) is created. Here, a plurality of reference images (design images) corresponding to the plurality of frame regions 32 (or frame regions 30) are created. Specifically, it operates as follows. First, the development circuit 111 reads design data from the magnetic disk device 109 through the control computer 110, and converts each graphic pattern of each frame area defined in the read design data into binary or multivalued image data. The image data is sent to the reference circuit 112.

  Here, the figure defined in the design data is, for example, a rectangle or triangle as a basic figure. For example, coordinates (x, y) at the reference position of the figure, side length, figure type such as rectangle or triangle, etc. The graphic data defining the shape, size, position, etc. of each pattern graphic is stored with information such as a graphic code serving as an identifier for distinguishing between them.

When the design pattern information as the graphic data is input to the expansion circuit 111, the data is expanded to data for each graphic, and a graphic code indicating the graphic shape of the graphic data, a graphic dimension, and the like are interpreted. Then, binary or multivalued design image data is developed and output as a pattern arranged in a grid having a grid with a predetermined quantization dimension as a unit. In other words, the design data is read, the occupancy ratio of the figure in the design pattern is calculated for each grid formed by virtually dividing the inspection area as a grid with a predetermined size as a unit, and the n-bit occupancy data is calculated. Output. For example, it is preferable to set one square as one pixel. If a resolution of 1/2 ⁸ (= 1/256) is given to one pixel, 1/256 small areas are allocated by the figure area arranged in the pixel, and the occupation ratio in the pixel is set. Calculate. Then, it is output to the reference circuit 112 as 8-bit occupation ratio data.

  Next, the reference circuit 112 performs an appropriate filter process on the design image data that is the image data of the received graphic.

  FIG. 8 is a diagram for explaining the filter processing in the first embodiment. The measurement data as an optical image obtained from the sensor circuit 106 is in a state in which the filter is activated by the resolution characteristic of the magnifying optical system 104, the aperture effect of the TDI sensor 105, or the like, in other words, in an analog state that continuously changes. By applying the filtering process to the design image data, which is the image data on the design side whose intensity (shading value) is a digital value, it can be matched with the measurement data. In this way, a design image (reference image) to be compared with the frame image (optical image) is created. The created reference image is output to the comparison circuit 108, and the reference image output in the comparison circuit 108 is stored in a memory (not shown).

  As described above, a plurality of reference images corresponding to a plurality of frame regions 32 (or frame regions 30) based on design data in which patterns are respectively defined in a plurality of frame regions 32 (or frame regions 30) having different positions. Create Thereby, a plurality of reference images corresponding to a plurality of frame images of each inspection stripe 20 imaged from the substrate 101 are created.

  As a comparison step (S110), the comparison circuit 108 first reads out a frame image (optical image) of the frame region 32 (or frame region 30), which is a measurement image to be compared, from a storage device (not shown) in the comparison circuit 108. Similarly, a reference image to be compared is read from a storage device (not shown) in the comparison circuit 108. Then, alignment is performed using a predetermined algorithm. For example, alignment is performed using a least square method.

  Next, the comparison circuit 108 compares the frame image with the reference image for each pixel. The comparison circuit 108 compares the two for each pixel according to a predetermined determination condition, and determines the presence or absence of a defect such as a shape defect. For example, if the gradation value difference for each pixel is larger than the determination threshold, it is determined as a defect. Then, the comparison result is output. The comparison result may be output from the magnetic disk device 109, the magnetic tape device 115, the flexible disk device (FD) 116, the CRT 117, the pattern monitor 118, or the printer 119. Further, defect information as a comparison result is output to the CD measurement circuit 142.

  Next, the process proceeds to the line width CD measurement of the minute pattern to be measured.

  FIG. 9 is a diagram illustrating an internal configuration of the CD measurement circuit according to the first embodiment. In FIG. 9, storage devices 50 and 52 such as a magnetic disk device, a coordinate setting unit 53, a determination unit 54, a line width CD measurement unit 56, an average line width CDave calculation unit 58, and a determination unit are included in the CD measurement circuit 142. 59 is arranged. Each “˜ unit” such as the coordinate setting unit 53, the determination unit 54, the line width CD measurement unit 56, the average line width CDave calculation unit 58, and the determination unit 59 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 / output to / from the coordinate setting unit 53, determination unit 54, line width CD measurement unit 56, average line width CDave calculation unit 58, and determination unit 59 and information being calculated are stored in a memory (not shown) each time. Further, the defect information as a comparison result is stored in the storage device 50.

  As the minute pattern CD inspection mode selection step (S202), the mode selection circuit 144 selects a minute pattern CD inspection mode.

  As the coordinate setting step (S204), the coordinate setting unit 53 sets the coordinates of the measurement target region. The coordinates of the measurement target area are prepared in advance. Alternatively, an area in which a minute pattern smaller than the size of the frame area 32 (or frame area 30) is formed may be read from design data stored in the magnetic disk device 109. In the first embodiment, the measurement target region is a region smaller than the frame region 32 (or the frame region 30). When the frame region 32 is, for example, 30 μm square, the measurement target region may be, for example, a size of 10 μm square or less. In the first embodiment, a line-and-space pattern extending in the same x direction as the charge accumulation direction (charge transfer direction) of the TDI sensor 105 is selected as a minute pattern to be measured. In particular, a 1: 1 line and space pattern extending in the x direction is desirable. However, the present invention is not limited to this. A line-and-space pattern extending in the x direction other than 1: 1 may be used. Alternatively, an array pattern constituted by a plurality of rectangular patterns arranged in an array arranged in the x direction may be used. For example, the coordinates of the measurement target region are preferably the center position or one of the four corners of the measurement target region defined by a rectangle, for example, the lower left position.

  If the micropattern to be measured is a line and space pattern extending in the y direction orthogonal to the same x direction as the charge accumulation direction (charge transfer direction) of the TDI sensor 105, the orientation of the substrate 101 is set to 90. Rotate degrees. Specifically, the substrate 101 placed on the XYθ table 102 is lifted by an arm or the like of a transfer robot (not shown), and the arrangement angle is rotated 90 degrees by another alignment chamber or the like. Thereafter, the substrate 101 may be placed on the XYθ table 102 again by the arm of the transfer robot. Thereby, the arrangement can be changed to a line and space pattern extending in the same x direction as the charge accumulation direction (charge transfer direction) of the TDI sensor 105.

  As a determination step (S206), the determination unit 54 inputs defect position information determined to be a defect among a plurality of graphic patterns formed on the substrate 101, and the measurement target region for the plurality of measurement target regions on the substrate 101 is input. Is determined as a defect position. Specifically, the determination unit 54 refers to the defect information stored in the storage device 50 and determines whether or not the defect position overlaps the measurement target region indicated by the set coordinates. If the defect position overlaps the measurement target area indicated by the set coordinates, the CD measurement at the coordinates is stopped and the process proceeds to the determination step (S218). If the defect position does not overlap the measurement target area indicated by the set coordinates, the process proceeds to the stage moving step (S208).

  As the stage moving step (S208), the table control circuit 114 moves the XYθ table 102 to a position where an optical image of the measurement target area indicated by the set coordinates can be taken. In other words, the XYθ table 102 is moved so that, for example, the center of the left end of the measurement target area indicated by the coordinates set on the optical axis of the illumination light is aligned.

  As the slit placement step (S210), the slit position control circuit 140 controls the slit driving mechanism 174 to move the slit 172 on the optical path. Specifically, among the imageable areas of the TDI sensor 105, an XYθ table is formed so as to shield light from entering the areas on both sides in the charge transfer direction of the area where the measurement target area indicated by the set coordinates is imaged. A slit 172 is arranged between the 102 and the TDI sensor 105.

  FIG. 10 is a diagram showing an example of a pattern layout in the frame region where the slits are arranged in the first embodiment. In the example of FIG. 10A, the pattern 40 to be measured among the plurality of patterns 40, 42, 44, 46 of different types arranged in the frame region 32 (or frame region 30) shown in FIG. The regions on both sides in the x-direction of the measurement target region where is disposed are covered with the slits 172 (the left slit 172a and the right slit 172b). Since the slit 172 is not in contact with the substrate 101, specifically, the slit 172 is disposed between the magnifying optical system 104 and the TDI sensor 105, and the measurement target region is imaged. The incidence of light to the regions on both sides in the x direction of the region is blocked. At this time, as shown in FIG. 10A, a partial area on both sides in the x direction of the measurement target area where the pattern 40 is arranged may overlap with the slit 172. Even when a positional deviation error occurs in the arrangement position of the slit 172 by overlapping a part, it is possible to reliably prevent light from entering a portion other than the pattern 40 in the x direction.

  As the optical image acquisition step (S212), the optical image acquisition unit 150 receives light from both sides in the charge transfer direction of the region where the measurement target region is imaged among the imageable regions of the TDI sensor 105 by the slit 172. Charges are transferred in a shielded state and with the movement of the XYθ table 102 restricted so that the imaging positions of the plurality of light receiving elements 11 on the substrate 101 do not move with respect to the charge transfer direction of the TDI sensor 105. The TDI sensor 105 captures an area including the measurement target area. In other words, the region to be measured is imaged with the XYθ table 102 fixed in the x direction. The pattern 40 in the measurement target region is irradiated with laser light (for example, DUV light) having a wavelength equal to or less than the ultraviolet region, which is inspection light, from the appropriate light source 103 via the illumination optical system 170. The light that has passed through the measurement target region of the substrate 101 is formed as an optical image on the TDI sensor 105 via the magnifying optical system 104 and is incident thereon.

  The pattern image formed on the TDI sensor 105 is photoelectrically converted by each light receiving element 11 of the TDI sensor 105, and further A / D (analog / digital) converted by the sensor circuit 106. Then, pixel data is stored in the stripe pattern memory 123 for each measurement target region. When capturing such pixel data (measurement target region image), the dynamic range of the TDI sensor 105 is, for example, a dynamic range having a maximum gradation when the amount of illumination light is 60% incident. Thereafter, the measurement target region image is sent to the CD measurement circuit 142 together with data indicating the position of the substrate 101 on the XYθ table 102 output from the position circuit 107. The measurement data (pixel data) is, for example, 8-bit unsigned data, and represents the brightness gradation (light quantity) of each pixel. The stripe area image input into the CD measurement circuit 142 is stored in the memory 52.

  FIG. 10B shows an example of a frame image according to the first embodiment. In the first embodiment, as shown in FIGS. 3A to 3D, the position of the substrate 101 is sequentially moved by moving the XYθ table 102 in synchronization with the timing period transferred in the charge accumulation direction. Instead, the position of the substrate 101 is fixed in the x direction without moving the XYθ table 102 in the x direction, and an image is taken by the TDI sensor 105. Thereby, images at the same position are continuously incident on the same light receiving element 11. The TDI sensor 105 sequentially transfers charges generated by photoelectric conversion of the light received by each light receiving element 11 between the light receiving elements 11 in a predetermined cycle toward the x direction (constant direction) as the charge accumulation direction. The pattern image is picked up by accumulating it. Therefore, when the position of the substrate 101 is fixed in the x direction, information on each position in the x direction in the frame region 32 (or the frame region 30) is integrated. As a result, as shown in FIG. 10B, an image having a shape in which the pattern 40 extends in the x direction, which is the charge accumulation direction, can be captured. In the first embodiment, the slits 172 cover both sides of the pattern 40 in the x direction, which is the charge accumulation direction, so that only the black pattern or only the white pattern is arranged in the x direction. Therefore, it is possible to suppress an intermediate gradation (blurred) in which the black pattern and the white pattern are mixed in the pattern image of the measurement target region. Therefore, the S / N ratio can be increased between the line pattern (black pattern) and the space pattern (white pattern). It should be noted that the region shifted in the y direction of the pattern 40 of the measurement target region has an intermediate gradation (blurred) in which the black pattern and the white pattern are mixed, but there is no need to measure the CD. .

  FIG. 11 is a diagram for explaining measurement points in the first embodiment. The line width CD of the line pattern 12 (black pattern) (or / and space pattern) extending in the x direction may be measured, for example, for each pixel arranged in the x direction, as shown in FIG. Therefore, as the length of the optical image in the x direction becomes longer, the number of measurement points can be increased. Here, the x-direction length of the obtained optical image depends on the imaging time. If the imaging time is lengthened, the length of the obtained optical image in the x direction can be lengthened accordingly. Therefore, by adjusting the imaging time, the necessary number of measurement points for measuring the line width CD of the line pattern (black pattern) and the line width CD of the space pattern can be secured.

  As described above, when the measurement target region corresponds to the defect position, the measurement target region is excluded from the region for measuring the line width CD of the pattern, and the remaining measurement target regions that are not excluded are respectively An area including the measurement target area is imaged.

As the line width CD measurement step (S214), the line width CD measurement unit 56 (measurement unit) uses the pattern image of the measurement target area captured by the TDI sensor 105 to display the line width CD of the graphic pattern in the measurement target area. Measure. In the pattern gradation value profiles in the optical image of the captured pattern 40 of the measurement target region of the substrate 101, the detection threshold value Th _0, between two points gradation value profile of the line pattern of the pattern 40 in the optical image intersect By measuring the dimension, the width dimension CD of the line pattern can be obtained. Similarly, the width CD of the space pattern can be obtained by measuring the size between two points where the gradation value profile of the space pattern of the pattern 40 in the optical image intersects with the detection threshold Th ₀ .

  FIG. 12 is a diagram for explaining CD measurement in the first embodiment. As shown in FIG. 12, each line width CD of the adjacent line pattern (black pattern) and space pattern (white pattern) is measured. Further, as shown in FIG. 11, the CD is measured at each of a plurality of measurement points.

  As the average line width CDave calculation step (S216), the average line width CDave calculation unit 58 calculates statistical values of a plurality of line widths CD measured at a plurality of measurement points in the frame region 32 (or frame region 30). To do. For example, the average value CDave is calculated. However, the statistical value is not limited to the average value, and for example, the maximum value, the minimum value, or the median value may be used. When the measurement target pattern 40 is not a 1: 1 line and space pattern, the statistical value of the line width CD obtained at a plurality of measurement points is calculated for each line pattern and each space pattern. Good. Such a statistical value is defined and output as the line width of the pattern of the measurement target region.

  As the determination step (S218), the determination unit 59 determines whether or not the CD measurement is completed for all the measurement target patterns determined in advance. When the CD measurement is completed for all the measurement target patterns, the line width CD measurement result of each measurement target pattern is output together with the position information of the measurement target pattern. The CD measurement result may be output from the magnetic disk device 109, the magnetic tape device 115, the flexible disk device (FD) 116, the CRT 117, the pattern monitor 118, or the printer 119. If CD measurement has not been completed for all the measurement target patterns, the process returns to the coordinate setting step (S204), and the material of the next measurement target region is set. Then, the steps from the coordinate setting step (S204) to the determination step (S218) are repeated until the CD measurement is completed for all the measurement target patterns.

  As described above, according to the first embodiment, high-precision CD measurement can be performed even when the measurement target pattern is smaller than the measurement frame size and when a pattern other than the measurement target pattern is mixed in the measurement frame.

FIG. 13 is a diagram illustrating an example of a pattern, a pixel value, and an example of a profile in the first embodiment. A line pattern or space pattern image is composed of pixel values (gradation values) captured by the TDI sensor 105. And as shown to Fig.13 (a), CD is measured using the pixel group 26 in the CD measurement point of a measurement object pattern among several pixels which comprise this image. By plotting the pixel group 26, as shown in FIG. 13B, a gradation value profile of the measurement target pattern is configured. The gradation value profile may be created by connecting adjacent pixel values with a straight line, or may be created by approximating with an approximate curve. Then, the width dimension CD of the pattern can be obtained by measuring the dimension between two points where the gradation value profile of the pattern intersects at the detection threshold Th ₀ . Here, due to the arrangement positional relationship between the measurement target pattern and the TDI sensor 105, the measurement target pattern and the position of the pixel to be measured are shifted. Therefore, the tone value profile of the same measurement target pattern may change as shown in FIG. When the gradation value profile changes, the measured CD value also shifts (an error occurs). Therefore, in the first embodiment, by taking the following means, the measurement accuracy is further improved by averaging such errors.

  In the optical image acquisition step (S212), the optical image acquisition unit 150 captures an area including the measurement target area by the TDI sensor 105 while shifting the substrate 101 in the y direction orthogonal to the charge transfer direction (x direction) of the TDI sensor 105. To do.

FIG. 14 is a diagram illustrating an example of a measurement image in the first embodiment.
FIG. 15 is a diagram illustrating another example of the measurement image in the first embodiment.
The example of FIG. 14 shows an example of an image captured by the TDI sensor 105 while moving the XYθ table 102 by a shift width of one pixel in the y direction at a predetermined cycle. The example of FIG. 15 shows an example of an image captured by the TDI sensor 105 while moving the XYθ table 102 with a shift width of several tens of pixels in the y direction at a predetermined cycle. The line width CD of the graphic pattern is defined by statistical values of a plurality of line widths measured at a plurality of measurement points in the frame region 32 (or the frame region 30). CD measurement is performed on the image portion, and a statistical value is calculated using the measurement result of each image portion whose position is shifted in the y direction, so that the CD error due to the relationship between the measurement target pattern and the position of the measured pixel Can be averaged. Therefore, CD error can be reduced. As shown in FIGS. 14 and 15, the shift amount in the y direction may be larger or smaller than the pixel size. More preferably, a shift amount of about 0.5 to 5 pixels is desirable.

  In the above-described example, the pattern line width measuring method in the first embodiment has been described in the case where it is performed after the part that is not the defect position is known in advance by the determination in the determination step (S206), but is not limited thereto.

  FIG. 16 is a diagram showing another example of the pattern layout in the frame area where the slits are arranged in the first embodiment. In the example of FIG. 16A, the case where the defect 41 exists on the pattern 40 to be measured in the pattern layout in the frame region shown in FIG.

  When the optical image acquisition step (S212) is performed in this state, an image in which the defect 41 is extended in the x direction is obtained with the width of the defect 41 in the y direction size, as shown in FIG. Therefore, even if a defect inspection is not performed in advance, the presence or absence of a defect can be inspected from such an image.

  In the above description, a series of “˜circuits” includes 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). A program used in the case of comprising at least one computer and at least one processor is 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, the position circuit 107, the comparison circuit 108, the expansion circuit 111, the reference circuit 112, the autoloader control circuit 113, the table control circuit 114, the slit position control circuit 140, the CD measurement circuit 142, the mode selection circuit 144, etc. Or may be realized by at least one computer such as the control computer 110 and at least one processor.

  The embodiments have been described above with reference to specific examples. However, the present invention is not limited to these specific examples. For example, in the embodiment, a transmission illumination optical system using transmitted light is shown as the illumination optical system 170, but the present invention is not limited to this. For example, a reflective illumination optical system using reflected light may be used. Alternatively, the transmitted light and the reflected light may be used simultaneously by combining the transmitted illumination optical system and the reflected illumination optical system. Further, in the example of FIG. 1, the position of the slit 172 has been described as being disposed between the XYθ table 102 and the TDI sensor 105, but is not limited thereto. The position of the slit 172 may be between the light source 103 and the XYθ table 102.

  In addition, although descriptions are omitted for parts and the like that are not directly required for the description of the present invention, such as a device configuration and a control method, a required device configuration and a control method can be appropriately selected and used. For example, although the description of the configuration of the control unit that controls the inspection apparatus 100 is omitted, it goes without saying that the required control unit configuration is appropriately selected and used.

  In addition, all pattern inspection apparatuses, pattern inspection methods, pattern line width measurement apparatuses, and pattern line width measurement methods that include elements of the present invention and that can be appropriately modified by those skilled in the art are included in the scope of the present invention. The

DESCRIPTION OF SYMBOLS 10 Inspection area 12 Line pattern 20 Inspection stripe 30, 32 Frame area 50, 52 Memory | storage device 53 Coordinate setting part 54 Judgment part 56 CD measurement part 58 CDave operation part 59 Judgment part 100 Inspection apparatus 101 Board | substrate 102 XY (theta) table 103 Light source 104 Magnification optics System 105 TDI sensor 106 Sensor circuit 107 Position circuit 108 Comparison circuit 109 Magnetic disk device 110 Control computer 111 Expansion circuit 112 Reference 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 Measurement System 123 Stripe Pattern Memory 140 Slit Position Control Circuit 142 CD Measurement Circuit 144 Mode Selection Circuit 150 Optical Image Acquisition Unit 160 Control System Circuit 170 Illumination Optical System 172 Slit

Claims (5)

A stage on which a substrate on which a plurality of graphic patterns are formed is arranged;
It has a plurality of light receiving elements arranged in a two-dimensional form, and accumulates electric charges generated by photoelectrically converting the light received by each light receiving element in a predetermined direction while sequentially transferring between the light receiving elements at a predetermined cycle. A TDI (Time Delay Integration) sensor that captures a pattern image,
When imaging the measurement target region on the substrate, shielding of the incidence of light to the regions on both sides in the charge transfer direction of the region where the measurement target region is imaged among the imageable regions of the TDI sensor, A slit disposed between a light source and the stage or between the stage and the TDI sensor;
A measurement unit that measures a line width of a graphic pattern in the measurement target region using a pattern image of the measurement target region captured by the TDI sensor;
With
Of the plurality of light receiving elements, the slits shield light from entering the regions on both sides in the charge transfer direction of the region where the measurement target region is imaged among the imageable regions of the TDI sensor. The region including the measurement target region is imaged by the TDI sensor while transferring the charge while the movement of the stage is restricted so that the imaging position on the substrate does not move with respect to the charge transfer direction of the TDI sensor. An apparatus for measuring a line width of a pattern.   The pattern line width measuring apparatus according to claim 1, wherein the region including the measurement target region is imaged by the TDI sensor while shifting the substrate in a direction orthogonal to a charge transfer direction of the TDI sensor. The line width of the graphic pattern is measured at a plurality of measurement points in the frame area where the graphic pattern is arranged among a plurality of frame areas obtained by dividing the inspection area of the substrate by a size equal to or smaller than the imageable width size of the TDI sensor. Defined by multiple line width statistics measured,
3. The pattern line width measuring apparatus according to claim 1, wherein the measurement target area is smaller than the frame area. Input defect position information determined as a defect among a plurality of graphic patterns formed on the substrate, and determine whether the measurement target region corresponds to the defect position for a plurality of measurement target regions on the substrate. A determination unit;
When the measurement target region corresponds to the defect position, the measurement target region is excluded from the region for measuring the line width of the pattern,
With respect to the remaining measurement target areas that were not excluded, the movement of the stage was limited so that the imaging positions of the plurality of light receiving elements on the substrate did not move with respect to the charge transfer direction of the TDI sensor, In addition, while the slits block the incidence of light to the regions on both sides in the charge transfer direction of the region where the measurement target region is imaged among the imageable regions of the TDI sensor, The line width measuring apparatus for a pattern according to claim 1, wherein an area including the measurement target area is imaged by the TDI sensor. It has a plurality of light receiving elements arranged in a two-dimensional form, and accumulates electric charges generated by photoelectrically converting the light received by each light receiving element in a predetermined direction while sequentially transferring between the light receiving elements at a predetermined cycle. By using a TDI (Time Delay Integration) sensor that picks up a pattern image, a TDI sensor on a substrate on which a plurality of graphic patterns are formed, which are arranged on the stage in the imageable region of the TDI sensor. In a state in which light incident on both sides in the charge transfer direction of the region to be imaged is shielded by a slit disposed between the light source and the stage or between the stage and the TDI sensor In addition, the stays are set so that the imaging positions of the plurality of light receiving elements on the substrate do not move with respect to the charge transfer direction of the TDI sensor. Movement with restricted, and a step of imaging a region including the measurement area by the TDI sensor while transferring the charges,
Measuring a line width of a graphic pattern in the measurement target region using a pattern image of the measurement target region imaged by the TDI sensor;
A method for measuring the line width of a pattern.