JPH06324003A - Foreign object inspection apparatus and method - Google Patents

Abstract

(57) [Summary] (Correction) [Purpose] A manufacturing process that detects defects such as foreign particles that occur in a manufacturing process that forms a pattern on a substrate and manufactures an object, and analyzes them to take countermeasures. Foreign object inspection device and method for inspecting the foreign material occurrence state in [Structure] Illumination means 102, detection optical system 103, spatial filter unit 106, detector 107, operational amplifier 20
1. Detection head 10 composed of A / D converter 202
1, pitch detection means 212, operator processing system 203,
Foreign matter data memory 206, large foreign matter data memory 207,
Pattern memory 208, software processing system 201, parameter transmission means 209, foreign substance memory 211, coordinate data creation means 232, microcomputer 229, display means 2
It is composed of 30.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is a manufacturing process for manufacturing an object by forming a pattern on a substrate, such as a semiconductor manufacturing process, a liquid crystal display device manufacturing process, a printed circuit board manufacturing process,
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foreign matter inspection apparatus and method for detecting defects such as foreign matter that occur, analyzing them to take countermeasures, and inspecting the foreign matter occurrence state in a manufacturing process.

[0002]

2. Description of the Related Art In the conventional semiconductor manufacturing process, the presence of foreign matter on a semiconductor substrate (wafer) causes defects such as poor insulation of wiring and short circuits. Further, semiconductor elements are miniaturized and minute foreign matter remains in the semiconductor substrate. When present, the foreign matter also causes damage to the capacitor insulating film and gate oxide film. These foreign substances have various causes such as those generated from the operating part of the transfer device, those generated from the human body, those generated by reaction in the processing device by the process gas, and those mixed with chemicals or materials. Are mixed in various states.

Even in the same liquid crystal display element manufacturing process, if a foreign substance is mixed into the pattern or some kind of defect occurs, it cannot be used as a display element. The situation is the same in the manufacturing process of the printed circuit board, and the mixture of foreign matter causes a short circuit of the pattern and a defective connection.

As one of the conventional techniques for detecting a foreign substance on a semiconductor substrate of this type, as described in JP-A-62-89336, the semiconductor substrate is irradiated with a laser so that the semiconductor substrate is exposed. By detecting the scattered light from the foreign matter generated when the foreign matter adheres to the substrate and comparing it with the inspection result of the same type of semiconductor substrate that was inspected immediately before, false alarm due to the pattern is eliminated, and high sensitivity and high reliability are achieved. What enables foreign matter and defect inspection is also disclosed in Japanese Patent Laid-Open No. 63-1358.
As disclosed in Japanese Patent Laid-Open No. 48-48, the semiconductor substrate is irradiated with a laser to detect scattered light generated from a foreign substance adhering to the semiconductor substrate, and the detected foreign substance is laser-photographed. Some are analyzed by analytical techniques such as luminescence or secondary X-ray analysis (XMR).

Further, as a technique for inspecting the above-mentioned foreign matter, the wafer is irradiated with coherent light and the light emitted from the repetitive pattern on the wafer is removed by a spatial filter, and the foreign matter and defects having no repeatability are emphasized and detected. A method is disclosed.

[0006]

However, in the above-mentioned prior art, no consideration has been given to the point that high-performance foreign matter and large foreign matter can be discriminated and inspected.

In order to solve the above-mentioned problems of the prior art, an object of the present invention is to detect the detection signal logarithmically to reduce false information due to repetitive patterns, and to detect high-performance foreign objects and large foreign objects by inspecting them. An object is to provide an apparatus and a method thereof.

[0008]

In order to achieve the above object, the present invention provides an illumination system that linearly irradiates a plane wave light onto a substrate having a repeating pattern with different pitches, and an illumination system using the illumination system. An image forming optical system for forming an image of reflected light from the irradiated substrate, and a spatial filter installed in the middle of the image forming optical system so as to shield diffracted light from a repeating pattern having a small pitch on the substrate. A detector for detecting an optical image formed by the image forming optical system and obtained by the spatial filter; a logarithmic signal converting means for converting a signal detected by the detector into a logarithmic signal; and the logarithmic signal. The logarithmic signal level of one pixel on the detector converted by the converting means and the logarithm of the pixel at the corresponding position of the adjacent repeating pattern captured by the detector converted by the logarithmic signal converting means. Nos levels and are compared with the corresponding logarithmic signal levels of a plurality of pixels proximate to the location, 1 Some of the signal level of the corresponding point or close to point
When there is a pixel having a value equal to the signal level of one pixel, the signal detected by one pixel on the detector is determined to be a signal from a repeating pattern, the repeating pattern is erased, and the logarithmic signal conversion is performed. The logarithmic signal level of one pixel on the detector converted by the means and the logarithmic signal level of the corresponding pixel of the adjacent repeating pattern captured by the detector converted by the logarithmic signal converting means and the corresponding Foreign matter detection means for comparing the logarithmic signal levels of a plurality of pixels close to the point to obtain a difference or ratio signal, and comparing the difference or ratio signal with a plurality of threshold values to determine a plurality of types of foreign matter The foreign matter inspection device is characterized in that

Further, according to the present invention, a substrate having a repetitive pattern having a different pitch is linearly irradiated with plane wave light by an illumination system, and a reflected light image from the irradiated substrate is formed by an imaging optical system. An optical image formed by the imaging optical system obtained by passing through the spatial filter while forming an image and blocking diffracted light from a repetitive pattern having a small pitch on the substrate in the middle of the imaging optical system. Is detected by a detector, the detected signal is converted to a logarithmic signal by a logarithmic signal converting means, and the converted logarithmic signal level of one pixel on the detector and the detection converted by the logarithmic signal converting means. By comparing the logarithmic signal level of the pixel at the corresponding position of the adjacent repeating pattern captured by the device and the logarithmic signal level of the plurality of pixels close to the corresponding position, or 1 Some of the signal level of the portion in contact
When there is a pixel having a value equal to the signal level of one pixel, the signal detected by one pixel on the detector is judged to be a signal from a repeating pattern, the repeating pattern is erased, and further converted. The logarithmic signal level of one pixel on the detector and the logarithmic signal level of the pixel at the corresponding position of the adjacent repeating pattern taken in by the detector converted by the logarithmic signal converting means and a plurality of pixels close to the corresponding position. Of the pixels, the difference or ratio signal is obtained, and the difference or ratio signal is compared with a plurality of threshold values to perform a plurality of kinds of foreign matter determination.

[0010]

In the present invention, the monitor of the mass production line does not need to monitor all points on the semiconductor substrate, and it suffices to monitor the semiconductor substrate at a certain ratio. We paid attention to the fact that the effect is great even if only the repeating portion of this memory is monitored.

In the repeating pattern, when coherent light is emitted, the light is emitted only in a specific direction. That is, in the case of the memory, the light emitted from the repeated portion in a specific direction can be blocked by the spatial filter, and the foreign matter that does not repeatedly occur can be detected with high sensitivity.

By the way, the yield at the time of semiconductor manufacturing is improved for the following reasons. Through a strict detection experiment on the number of foreign particles on a semiconductor substrate, it was newly found that the number of foreign particles does not increase or decrease gradually but increases or decreases suddenly. In the past, it was thought that the number of foreign substances would gradually increase or decrease, so as described above, one to one lot
Foreign substances and defects were inspected at a frequency of once a day. However, with this inspection frequency, a sudden increase in foreign matter may be overlooked or may be detected after a while while increasing, and a considerable number of defects will occur. That is, in a mass production line, it is necessary to quickly detect the occurrence of foreign matter and take countermeasures, and if time elapses from the generation of foreign matter to the detection of foreign matter generation, the number of defectives increases and the yield decreases. Therefore, it is possible to maintain a high yield by shortening the elapsed time from the generation of a foreign substance to the detection thereof. That is, it is possible to maximize the effect of the foreign matter inspection by shortening the sampling time of the monitor, ideally by sampling in real time.

On the other hand, the larger the number of pixels, the longer the inspection time. Therefore, it is necessary to increase the pixel size in order to realize high-speed inspection. Therefore, it is necessary to increase the pixel size and reduce the noise level. As a method for reducing this noise level, a method using polarization is analyzed in “Analysis of Reflected Light from LSI Wafer Pattern”, Proceedings of the Society of Instrument and Control Engineers, 17-2, 77/82 (1981). Has been done. According to this, the scattered light (noise) from the pattern is utilized by using the polarized light.
Can be attenuated. However, the attenuation rate of scattered light by this method depends on the direction of the detector, as analyzed in the above paper. Therefore, when condensing light emitted in various directions like using an imaging optical system, the attenuation rate is 0.1% to 0.01% when the respective attenuation rates are integrated.
It will be about.

On the other hand, in the method using the spatial filter of the present application, the attenuation rate is 0.001% to 0.0001.
Can be%. Light emitted from the repeating pattern is concentrated at a position corresponding to the pitch of the pattern. As an example of calculating the concentration ratio, the diffracted light intensity distribution in the case of a double slit is described in “Applied Optics” (Iwanami) by Hiroshi Kubota.
According to this, as the number of slits (in the present application, the number of repeating patterns that are simultaneously illuminated) increases, the concentration ratio increases. This ratio can also be calculated using the Fourier transform F []. The shape of the illuminated pattern is a (x,
y), the light intensity distribution at the position of the spatial filter is F
[A (x, y)]. Set the shape of the spatial filter to p
If (u, v), then p (u, v) * F [a (x,
y)] is the light passing through the spatial filter. If the shape of the figure complementary to the spatial filter is ￣p (u, v), then ￣p (u, v) * F [a (x, y)] is the light component shielded by the spatial filter. . The ratio of these two components becomes the previous attenuation rate. When the attenuation rate is calculated when the number of pattern repetitions is 3, it is about 0.001%. When the number of repetitions is 5, it becomes about 0.0001%, and if the number of repetitions is further increased, the attenuation rate decreases.
Therefore, the attenuation rate can be made lower than that using polarized light.

Furthermore, the present invention provides the operator processing
The detection signal is logarithmically converted to reduce false information due to repetitive patterns, and at the same time, it is possible to discriminate and inspect high performance foreign substances and large foreign substances.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of a specific embodiment of the online monitor of the present invention will be described below with reference to FIGS.

In this embodiment, as shown in FIG. 1, an illumination means 102, a detection optical system 103, a spatial filter unit 1 are provided.
06, detector 107, operational amplifier 201, A / D converter 202, detection head 101, pitch detection means 212, operator processing system 203, foreign matter data memory 206, large foreign matter data memory 207, pattern memory 2
08, software processing system 210, parameter transmission means 20
9, a foreign substance memory 211, coordinate data creation means 232, a microcomputer 229, and a display means 230.

Further, as shown in FIG. 2, the illumination means 102.
Is a beam expander including a semiconductor laser 112, a collimator lens 113, a concave lens 114, and a receiver lens 115, a cylindrical lens 116, and a mirror 11.
8 and the detection optical system is a Fourier transform lens 1
08, spatial filter unit 106, and Fourier transform lens 111.

Further, as shown in FIG. 3, the operator processing system 203 includes a 4-pixel adding means 214 and an octalizing means 21.
5. Cut-out means 2 including a plurality of line memories 216
04, buffer memory 217, determination pixel cutout unit 2
18, operator cutout means 219, 231, a comparison circuit group including a plurality of first comparison circuits 220, a first threshold setting circuit 221, a comparison circuit group including a plurality of second comparison circuits 223, a second threshold setting Circuit 222, OR circuit 22
4, 225 and AND circuits 226, 227, 228.

Further, as shown in FIG. 4, the pitch detecting means 212 comprises an FFT circuit 242, an operator pitch calculating means 241, a filter pitch calculating means 244 and a spatial filter control system 243.

(Relationship) The substrate 1 is illuminated by the illuminating means 102, and scattered light or diffracted light from foreign matter, defects or patterns on the surface is taken in, and the spatial filter unit 1
An optical filtering process is performed at 06, and the light is detected by the detector 107 in the detection optical system 103. The detected signal is amplified by the operational amplifier 201 in the detection head 101 into a signal having a large impedance and less susceptible to noise,
It is converted into a digital signal by the A / D converter 202 and transmitted to the operator processing system 203. Also, the detection optical system is 1
Since 03 has a sufficiently large depth of focus, if the substrate 1 is transported by a transport system (not shown) with mechanical accuracy, automatic focusing is basically unnecessary. Specifically, about 8
With a wavelength of 00 nm and a numerical aperture of 0.08, the depth of focus is about ± 100 microns. Of course, there is no problem with having an autofocus mechanism.

The pitch detecting means 212 measures the pattern repeat pitch and the chip pitch on the substrate 1 from the detection signals. In the operator processing system 203, the pattern information is removed by utilizing the repeatability of the chip pitch based on the information such as the chip repeat pitch transmitted by the parameter transmitting means 209. The result is stored in the foreign matter data memory 206, the large foreign matter data memory 207, and the pattern memory 208 shown in FIG. 1, and further based on the information such as the repeating pitch of the position coordinate chip of the test element group transmitted by the parameter transmitting means 209. To
Pattern information such as a test element group having no repeatability between chips is removed by the soft processing system 210 and stored in the foreign substance memory 211. Here, the coordinate data creating means 232 creates the coordinate data and stores it at the same time as the foreign substance information as needed. The above processing is managed by the microcomputer 229, and the display unit 2
It is displayed from 30.

Further, as shown in FIG. 2, the illumination means 102.
Then, the light from the semiconductor laser 112 is collimated as a plane wave by the collimator lens 113, the concave lens 114, and the receiver lens 115, and illuminates the substrate 1 through the cylindrical lens 116 and the mirror 118. Here, as shown in the figure, the illumination is collimated only in the x direction by the cylindrical lens 116, and is condensed on the substrate in the y direction. In the detection optical system 103, the light beam Fourier-transformed by the Fourier transform lens 110 is optically filtered by the spatial filter unit 106, and an image on the substrate is formed on the detector 107 by the Fourier transform lens 111. It

Further, the operator processing system 203 shown in FIG.
Then, the pixels 2 × 2 around the detection signal A / D converted by the A / D converter 202 are added and averaged by the 4-pixel adding means 214. The purpose of this process is to perform stable detection by averaging, but the detection performance (detection sensitivity) itself falls slightly, so a bypass means is installed so that it can be bypassed as necessary. The added signal is used as the octalizing means 21.
It is octal-coded by 5 and is stored in the buffer memory 217 as two-dimensional image data through the clipping means 204 composed of a plurality of line memories 216. After being stored
The determination pixel cutout unit 218 and the operator cutout units 219 and 231 cut out necessary data from the two-dimensional image data and send it to the comparison circuit 219. Here, the detector 107 uses a one-dimensional linear sensor so that high-speed detection can be performed by high-speed stage scanning. The line memory 216 and the buffer memory 217 convert the data from the detector 107 into a two-dimensional image.
Thus, every time the signal from the detector 107 is sent pixel by pixel, the entire image moves pixel by pixel in the x direction. This is so-called pipeline processing. A plurality of first comparison circuits 22
0 comparison circuit group, first threshold value setting circuit 221, a plurality of second comparison circuit 223 comparison circuit group, second threshold value setting circuit 222, OR circuits 224, 225, AND
The circuits 226, 227, and 228 extract the large foreign matter signal, the high-performance foreign matter signal, and the pattern signal by the logic described later.

Further, in the pitch detecting means 212 shown in FIG. 4, the FFT circuit 242 subjects the detected image to the Fourier transform processing, and from this result, the operator pitch calculating means 24
1, the operator pitch is calculated by the filter pitch calculation means 244, and the spatial filter pitch is calculated by the filter pitch calculation means 244.
It is sent to 19, 231.

(Principle) The principle of the parameter compression spatial filter (PRES (Parameter Reduction Spatial) filter) of the present invention will be described.

Conventionally, there has been disclosed a technique for detecting foreign matters or defects having non-repeatability by using the repeatability of the pattern on the wafer surface. However, even though the pattern has repeatability, the shape of the diffraction pattern differs depending on the repetition period and the shape of the basic pattern. Therefore, the shape of the spatial filter, which is the light shielding plate, must be changed according to the shape of the target repeating pattern. As a method for changing the spatial filter, a method using a photographic plate has been disclosed. With these methods, it took a long time to create a spatial filter suitable for the target, and a large-scale device was required.

Specifically, when illuminated with coherent light, that is, a plane wave from an oblique direction as shown in FIG. 5A, a diffraction pattern as shown in FIGS. 5B and 5C is obtained at the Fourier transform position. Suppose it was observed. In this case, when the pitch of the pattern on the substrate changes, not only the pitches px and py of the diffraction pattern but also the entire phase φ changes. Further, when the basic shape of the pattern on the substrate changes, the arrangement of the dot patterns forming the diffraction pattern also changes. That is, it is difficult to deal with the pattern shape because there are many parameters that describe the Fourier transform plane diffraction pattern.

Here, instead of the plane wave as shown in FIGS. 6A and 6B, x as shown in FIGS. 6D and 6C is used.
Suppose that the direction is narrowed down on the sample 1, and the y direction is coherent, that is, a plane wave is illuminated. In this case, the Fourier transform plane does not form an image in the u-axis direction but has a compressed shape in the u-axis direction. As a result, the spatial filter 106 is compressed into a one-dimensional parameter only in the v-axis direction. Here, the pitch p in the v-axis direction of the compressed diffraction pattern is a pitch corresponding to the pitch in the y-axis direction of the region illuminated on the substrate surface. Also, one one
The thickness w of the diffraction pattern on the line of the book is determined by the numerical aperture sin β on the Fourier transform surface of the front Fourier transform lens 110. Specifically, it is determined by the exit side numerical aperture of the illumination system 102 and the numerical aperture of the front Fourier transform lens 110. Therefore, the illumination system 102 and the Fourier transform lens 11
It is determined if 0 is determined, and is not affected by the pattern on the substrate 1 to be inspected. However,
In some cases, such as when changing the numerical aperture of illumination, it may be better to make the width of the linear spatial filter 106 variable.

In practice, a one-dimensional image sensor capable of continuously scanning a stage (not shown) is suitable as the detector 107 in order to realize high-speed inspection. When this one-dimensional image sensor is used, the one-dimensional sensor shape, that is, the linear illumination on the surface of the sample 1 is suitable for improving the illumination efficiency. In order to realize such illumination, it is necessary to narrow down at least one direction. That is, the one-way coherent illumination has a great effect on improving the efficiency of illumination intensity.

As described above, the shapes of the patterns on the substrate are different in the related art, and the spatial filter corresponding to each pattern is required to cope with the various patterns. . However, according to the invention,
From a different point of view, it is possible to think of these various spatial filters as functions of only the pitch p, and the spatial filter having multidimensional parameters is compressed into one dimension. By compressing the dimension of the parameter of the spatial filter in this manner, it is possible to simplify the spatial filter that has a difficulty in responding to the shape change due to the complicated shape, and make it possible to deal with all repetitive patterns.

The above structure is applicable not only to detecting foreign matters or defects on a wafer or a liquid crystal display element, but also to any inspection object for detecting non-repetitive portions from a repetitive pattern. is there. Specifically, it can be applied to a semiconductor mask, a reticle, a micromachining component using a semiconductor process, other micromachining components, a printed circuit board, and the like. The present invention, when inspecting these objects, realizes high-speed inspection by realizing illumination with high illuminance while applying spatial filtering technology without exchanging spatial filters for each object. .

(Spatial Filter Control, Operator Pitch Control) Based on FIGS. 7A and 7B, (A) the pattern erasing method by the spatial filter 106 and (B) the pattern erasing by the shot comparison operator in the operator pitch processing system 203. Method and software processing system 210 (206-
The TEG pattern erasing method will be described with reference to (C) software in 211) and the like. In the present invention, the repeatability of cells having a pitch of several hundreds of microns or less is erased by using the spatial filter 106, and the operator processing system 203 (21
(B) Shot comparison by (B) shot comparison operator is repeated by several hundreds of micron pitch or more, and the pattern is erased by using the repeatability between adjacent chips (in some cases, between shots meaning one exposure), and further repeatability The chip without TEG pattern (TEG pattern) is software processing system 210
In (206 to 211), the data is erased so as not to be inspected by using the coordinate / matrix data. Here, there are parameters required for each erasing. Spatial filter pitch is required for erasing by the spatial filter 106, chip pitch is required for erasing by repeating between chips, and chip position information is required for erasing a chip (TEG pattern) having no repeat. . Therefore, the detection head 10 of the present invention
It is desirable that 1 can detect at least two chips at the same time.
That is, the visual field size of the detection optical system 103 of the detection head 101 needs to be at least 2 chips or more. Of course, this visual field size is only desirable, and the positional relationship of the plurality of detection heads 101 to be installed is accurately known, and this positional relationship is stored in the parameter transmission means 209, and the operator processing system When this comparison processing is performed between a plurality of detection heads 101 such as 203, the field size does not have to be two chips or more. However, considering the required accuracy of the optical system (detection head) 101 and the complexity of the circuit system for data processing in the operator processing system 203 and the software processing system 210, the field of view size is 2 chips or more. Is desirable. Further, although the description has been made with two or more chips here, when two or more chips are written on the reticle used as a mask when the pattern is transferred onto the wafer 1 by the stepper, between the chips. In many cases, a pattern called a test element group (TEG) is written, and in order to erase these patterns as well, when erasing using the above-mentioned repetition pitch, the pitch between chips is used instead of using the pitch between chips. The pitch between the pattern printed on one exposure and the pattern on the reticle) (stored in the parameter transmission means 209).
Need to be used. Of course, this method is not always necessary, and TE formed in these one shots
There is no problem even if the G pattern is erased in a later process.

These pieces of information are measured in advance corresponding to the substrate 1 and stored in the parameter transmitting means 209.
From the stored information, the parameter corresponding to the substrate is selected and fed back to the particle defect inspection apparatus of the present invention (the operator processing system 203 via the software processing system 210 and the parameter transmission means 209). Therefore, it is necessary to identify the substrate when using this method. For the purpose of this identification, a number or a symbol corresponding to the substrate is written on the substrate. Read this symbol prior to inspection, and from the number to the board, product version number, lot number,
Knowing the product type, knowing the process from the data of the place where the foreign substance inspection device of the present invention is installed, the parameter transmission means 209
The pitch of the spatial filter 106 and the threshold value may be set by setting the pitch detection means 212 via the.

In implementing the foreign matter defect method of the present invention, it is not always necessary to obtain the parameters as described above and send them to the apparatus of the present invention as described above. Rather, as described below, it may be desirable for the device to be uniquely acquired by the present invention. With the above method, it is necessary to know the value of the parameter to be input in advance, but if it is acquired independently, such a trouble is not required. Of course, it is not necessary to read the number printed on the board.

In the present invention, as described above, in order to detect the foreign matter or defect by distinguishing the foreign matter or defect adhering to the substrate having the complicated background pattern from the background pattern, pattern removal in three steps is performed. It has a function. With this pattern removal function, a portion which is actually determined to be a pattern is discarded without being an inspection target.
Specifically, the spatial filter 106 erases repetitions of a pitch of several hundreds of microns or less, and the parameter transmission means 209.
Based on the parameter given via the parameter, the operator processing system 203 erases the repetitions of several hundreds of micron pitch or more using the repeatability between chips, and the chip having no repeatability is the coordinates stored in the parameter transmission means 209. The data is erased based on the matrix data so as not to be inspected by the software processing system 210 or the like.

The reason why the area in which the pattern is formed is excluded from the inspection object is as follows.
Even if a pattern is formed, adjacent chips have patterns having the same shape and emitting the same amount of light in the same emission direction. Therefore, if the detected light intensities of the light from these two patterns are compared, the spatial filter 106
It should be possible to inspect for foreign matters or defects even in a region where a pattern having a shape that cannot be erased is formed. However, in the case of detecting scattered light, the intensity of the detected light is likely to be unstable in these patterns, and if the above-described pattern removal by comparison is performed, a false alarm (pattern information that is not a foreign matter will be detected as a foreign matter). )
However, it will increase. Therefore, it may be more effective to remove the area where the pattern is formed from the inspection object. That is, in consideration of stability, when detecting scattered light in particular, by removing the region in which a complicated pattern is formed from the inspection target, or by comparing the detected light intensities of light from adjacent chip patterns. It should be decided whether to inspect for foreign material.

(Log Scale Threshold) FIG. 8 shows a comparison test in which an optical processing method such as a spatial filter is used as a pre-process, and a comparison test is performed only with an electric signal without using such a process. The state of the detection signal at this time is schematically shown in FIG. The method using the spatial filter 106 can remove only the pattern information without losing the information on the defect in the pattern portion, but the method using the chip comparison detects the foreign substance and defect information and the pattern information in a superimposed form, and Therefore, the particle defect signal can be detected only within the dynamic range during photoelectric conversion. That is, when the pattern signal is extremely large and the foreign matter defect signal is extremely small, the foreign matter defect signal is missed in the pattern signal, and it is difficult to distinguish and detect the foreign matter defect signal from the pattern signal.

In FIG. 8, the horizontal axis shows the detection position and the vertical axis shows the detection signal intensity. The left side shows the signal 18 containing the foreign matter or foreign matter defect information 4, and the right side shows the signal 19 not containing the foreign matter defect information to be compared. Here, when the pixel size detected as one signal is detected as 13, the detection light corresponding to the areas 16 and 17 hatched is detected. In this case, since the foreign matter defect information 4 is small with respect to the total area, the two detection signals 16 and 17 cannot be stably compared. Specifically, it is buried in noise. In this case, even if the light intensity of the illumination is increased, the foreign matter defect information 4
In order to be able to detect, a detector with a large dynamic range is required. Here, when the pixel size is changed from 13 to 14, the detection signals become 7 and 8, and the foreign matter defect information 4 can be detected by comparison. Reducing the pixel size produces such an effect. On the contrary, if the detection signals 18 and 19 can be stably eliminated (by an essential comparison without changing to electric signals or the like), specifically, the detection signals can be detected at, for example, 10 positions or more. If possible, the detection signals become 5 and 6, which are at a level at which comparison inspection can be performed. In this case, since the pixel size remains the same as the previous 13, the high-speed detection with large pixels becomes possible. If the light intensity of the illumination is increased, the defect information 4 such as foreign matter can be detected even with a detector having a small dynamic range. The method using the spatial filter 106 of the present invention is to detect the minute foreign substance defect information 4 while using the pixel 13 as described above.

As described above, even if the pattern signal in the portion between the adjacent chips to be compared can be made extremely stable by devising the optical system or the like, the light intensity is 1: 100 or 1: 1.
The limit is detection with a dynamic range of about 000. Therefore, if the foreign matter defect signal is small or the pattern signal is large so that a dynamic range larger than this is required, the foreign matter defect signal is included in some of the signals by comparing the signal intensities between the adjacent chips. It is not possible to determine whether it is included or not included. The presence / absence of foreign matter can be inspected by comparison only when the ratio of the foreign matter defect signal to the pattern signal is sufficiently large. If this ratio is small, foreign objects will be overlooked or false alarms will increase if the threshold value is reduced to inspect foreign particles.

Therefore, it is difficult to inspect foreign matters existing on these patterns without false alarms, and there is no choice but to eliminate false alarms or reduce the foreign matter detection sensitivity to detect only large foreign matters. The purpose of eliminating the false alarm described above is to use the embodiment in which the region in which the pattern is formed is excluded from the inspection object in the present invention.

In order to reduce the foreign matter detection sensitivity so that only large foreign matter can be detected, a log scale comparison inspection as described below is required. Certainly, even if adjacent chips are formed with patterns that have the same shape and emit the same amount of light in the same emission direction, the detection light from these two patterns is not completely the same. Therefore,
The detected light intensities of the light from these two patterns are likely to fluctuate and comparison is difficult. Therefore, at the time of comparison, a cut out by the operators 219 and 231 and p cut out by the operator 218 are assigned to the plurality of first comparison circuits 22.
When 0 and a plurality of second comparison circuits 223 are used for comparison, it can be determined that the two signals are different and that a foreign substance is present if Expression (1) is satisfied.

[0043]

## EQU00001 ## (a-p)>. Delta. (Equation 1) However, in this method, when there is a variation that varies in the ratio to the absolute amount when the absolute level of the signal is large, there is no foreign matter but there is a foreign matter. The possibility of so-called false information to judge increases. Therefore, when the ratio of the two signals satisfies the equation (2), it is determined as a foreign matter.

[0044]

## EQU00002 ## (a / p)>. Delta. (Equation 2) However, in practice, the division of two signals increases the scale of the arithmetic circuit. Therefore, in practice, the threshold value is set logarithmically,
When the equation (3) is satisfied, it is determined that a foreign substance is present.

[0045]

## EQU00003 ## log (a / p) = loga-logp> .delta. (Equation 3) As described above, by using the equation (3), if the threshold of quantization is set using the logarithmic axis, An operation that originally needs to be divided can be processed by subtraction in the first comparison circuit 220 and the second comparison circuit 223.
The circuit configuration shown in FIG. 3 realizes the logic described above. For the logarithmic processing as described above, the threshold value of the octalization processing system 215 shown in FIG. 3 may be set logarithmically.

Further, FIG. 3 shows the subtraction processing in the first comparison circuit 220 and the second comparison circuit 223 using the logarithmic octalization processing in the octalization processing system 215 described above. However, this method is not necessarily used, and the method of the above division processing as it is or the multi-value quantization other than octalization may be used. In this case, if the ternarization is used, all the foreign matters on the pattern are discarded without being detected, and if the large multi-value quantization is used and the optical system is stable, detection of smaller foreign matters on the pattern is performed. Will be possible.

Here, the above-mentioned δ is set in the first threshold value setting circuit 221, and in the plurality of first comparison circuits 220, the comparison based on the above-mentioned (Equation 1) or (Equation 2) or (Equation 3) is performed. And the difference between the operator (pixel) 218 and the operator (pixel) 219 and 231 is equal to or larger than the threshold value δ is ORed by the OR circuit 224, and all the first
The comparison circuit 220 outputs a “0” to erase the repeated pattern between chips (shots), and any one of the first comparison circuits 220 outputs a value equal to or larger than the threshold value δ as “1”, and the AND circuit 227. When the large foreign matter signal “1” is not output, the AND circuit 228 is ANDed, the high performance foreign matter signal is output, and stored in the foreign matter data memory 206. Further, in the plurality of first comparison circuits 220, comparison is performed based on the above (Formula 1), (Formula 2) or (Formula 3), and the operator (pixel) 218 and the operators (pixels) 219 and 231 are compared. When all the differences are equal to or less than the threshold value δ, “0” is output from all the first comparison circuits 220, AND is taken in the AND circuit 226, it is detected as a repeated pattern between chips (shots), and stored in the pattern memory 208. To be done. In addition, the second threshold setting circuit 222 basically sets the minimum threshold of large foreign matter to be detected. Therefore, a plurality of second comparison circuits 223
In the case where the difference between the operator (pixel) 218 and the operators (pixels) 219 and 231 is equal to or larger than the minimum threshold value of large foreign matter, the OR circuit 225 performs an OR, and all the first comparison circuits 223 output “0”. The repeated pattern between chips (shots) is erased, and either
Comparing circuit 223 outputs a value larger than the minimum threshold value of large foreign matter as “1”, and naturally OR circuit 224 also outputs “1”, AND circuit 227 outputs AND, and a large foreign matter signal is output. Foreign object data memory 20
Stored in 7. That is, this case corresponds to the case where a pattern larger than the minimum threshold value of the large foreign matter is detected in the operator 218 and the operators 219 and 231, and is detected as the large foreign matter. Here, more importantly, in the present invention, at least one threshold smaller than the threshold used for so-called foreign matter detection is set. It goes without saying that this is necessary when using the above equation (3).

FIG. 9 shows the state of quantization by the above logarithmic threshold. The horizontal axis represents the detection position and the vertical axis represents the detection signal. Logarithmic threshold values 50, 51, 52, 53, and 54 are set, and signals in portions separated by the pitch p are compared.
Here, by making a multi-value and betting the allowable range that is determined to be the same at the time of comparison, for example, by betting, not only the pattern signals 55 and 58 quantized to the same value, but also quantized to one different value. Pattern signals 56, 59, and 5
No. 7 and 60 are judged as patterns and are not false information. That is, by increasing the ratio of the logarithmic threshold value at the time of quantization, the allowable range is increased and the false alarm can be reduced, but only larger foreign matter can be detected on the pattern. Further, both the foreign matter signals 61 and 62 can be detected. Further, by widening the operator 231 in the plane direction, the quantization error in the plane direction can be allowed.

As described above, in the pattern erasing by the spatial filter 106 and the pattern erasing by the chip comparison,
There is an essential difference. That is, the method using the spatial filter can detect defects by emphasizing the defects in the pattern portion, but the method using the chip comparison uses photoelectric conversion of the foreign matter defect information in the pattern portion as it is and compares the detected information, and then the comparison is performed. That's what you need. The method using the spatial filter is just like emphasizing only defects by cell comparison using interference.

(Quantization Error in Plane Direction and Quantization Error in Depth Direction) Here, the method using repetition between chips used is basically a comparative inspection, but a short wavelength, point light source. The following configuration is used in order to stably realize such a comparison inspection by detecting scattered light using the laser light source.
An operator that realizes a pattern removal method using repetition between chips is formed by a plurality of pixels in the x direction and the y direction in the plane direction. Further, the comparison of whether the signals should be judged to have the same level or to be judged to have different signal levels due to the presence of a defect or a foreign substance on one side is given by (Equation 1), (Equation 2), The equation (3) is used. The foreign matter and the pattern can be stably distinguished from each other by the sampling enlargement processing in the plane direction and the light intensity direction of the comparative numerical values in these comparisons.

(Filter Size) The design concept of the spatial filter 106 will be described below. In the foreign matter and defect inspection apparatus of the present invention, the pattern information having a large pitch is erased by repeating the chips by the operator. Therefore, the "spatial frequency that can be eliminated by the operator" must be larger than the "spatial frequency that can be eliminated by the operator." The reason will be described below.

Consider a case where patterns of pattern pitches L1 and L2 (L1 <L2) are formed on the substrate 1 as shown in FIG. The illumination light is θ
The light is diffracted in the directions of 1 and θ2 and forms a diffraction pattern of pitches pf1 and pf2 (pf1> pf2) on the spatial filter 106. Therefore, the following formula is established.

[0053]

[Formula 4] Df / (2 · N.A.) = Pf1 / sin θ1 (Formula 4)

[0054]

## EQU00005 ## sin .theta.1 = .lamda. / L1 (Equation 5) Here, Df is the diameter of the optical systems 110 and 111 on the pupil plane, and N. A. (Numerical Apartment) is the numerical aperture of the optical system 110.

Of the diffraction patterns, the diffraction pattern with the pitch pf1 is shielded by the spatial filter 106, but the diffraction pattern with the pitch pf2 has a too small pitch.
It is assumed that the spatial filter 106 cannot block light. That is,
The pattern on the substrate with the pattern pitch L1 is erased by the spatial filter and does not form an image on the detector 107, but the pattern with the pattern pitch L2 is imaged on the detector 107 without being shielded by the spatial filter and is not erased. (Hereinafter, "the pattern is erased" means that "the light emitted from the pattern, that is, the light having the pattern information is shielded by the spatial filter 106, so that the detector 1
07 does not reach the light and does not form an image of the pattern on the detector. " ) Therefore,
From the equations (4) and (5), the following equation (6) is established.

[0056]

[Equation 6] L1 = (Df · λ) / (2 · pf1 · NA) (Equation 6) Here, the spatial filter 106 has a certain size as a manufacturing precision due to the limitation of the numerical aperture of the illumination 102 and the like. You will need more. Therefore, from the equation (6), if pf1 is kept large, the pitch of the pattern that can be erased by the spatial filter 106 becomes small.

Here, as shown in FIG. 11, a plurality of chips are formed on the substrate 1 at a pitch Lt. The information of the pattern having the pattern pitch L2 is erased by using the repetition between the chips. Specifically, the signal repeatedly detected at the chip pitch Lt is the pattern pitch L2.
The detection signal itself is deleted by determining that the signal is from the pattern. (In this case, “erasing the pattern information” literally means “deleting or discarding the signal”.) Here, in order to avoid the quantization error in the plane direction, which will be described later, Operators 219, 231
Has a size of nx pixels in the x direction and ny pixels in the y direction,
If a pattern exists in this operator, the judgment pixel is judged to be a pattern. Therefore, the rate α of the detection area depending on the size of the operators 219 and 231 is expressed by the following equation (Equation 7).

[0058]

[Formula 7] α = 1− (w · nx / L2) (Formula 7) On the contrary, from the formula (7),

[0059]

## EQU00008 ## L2 = 1- (w.nx / .alpha.) (Equation 8) Therefore, if the detection area ratio .alpha. Is kept large, the pitch of the erasable pattern becomes large.

Here, in order to erase the patterns of all pitches on the substrate, as shown in FIG. 13, the pattern pitch L1 that can be erased by the above spatial filter should be larger than the pattern pitch L2 that can be erased by the operator. . That is, as shown in FIG. 13, it is necessary that the erasure by the spatial filter and the erasure by the operator overlap. As a result, even if a repetitive pattern of a certain pitch appears on the substrate, the pattern can be erased by the spatial filter 106 or the operator, and as a result, only minute foreign matter can be detected.

Here, as shown in FIG. 12, the variable pitch PRES filter 106 has a minimum pitch pf1 = 1 m.
It is formed so that the pitch can be continuously changed from m to the maximum pitch of 2 · pf1 = 2 mm. Further, in order to prevent or suppress the interference phenomenon on the detector 107 due to the spatial filter 106, it is necessary to limit the number of filters, pitch, and filter width. That is, the above-mentioned minimum spatial filter pitch is limited not only in production but also in order to suppress the interference phenomenon. At this time, the above relational expression among the number of filters, the field size, and the operator size becomes important.

Whether or not the pattern can be erased by the spatial filter 106 does not depend on the pitch of the pattern to be erased, but on the number of linear spatial filters, as described below. The size of the spatial filter surface is D,
Let pfs be the minimum spatial filter pitch, nf be the number of linear spatial filters, and Lm be the maximum pattern pitch that can be shielded by the spatial filter of pfs. It is assumed that the field of view of the detector is X, the pixel size is w, and the number of pixels is N. Let the operator size be no when the operator compares two chips.

[0063]

[Formula 9] pfs / D = λ / (N.A. · Lm) (Formula 9) To make the detection area ratio α sufficiently large,

[0064]

[Formula 10] k · no · w = Lm (k >> 1) (Formula 10)

[0065]

[Equation 11] D / pfs = nf (Equation 11) is required.

If the pixel size is set near the resolution of the optical system, it is necessary and sufficient from the inspection time and the detection performance.

[0067]

[Expression 12] w = k0 · λ / N.A. (Expression 12) From Expression (10), Expression (11), and Expression (12),

[0068]

[Formula 13] pfs = D / (k · k0 · no) (Formula 13)

[0069]

Α = 1- (1 / k) = 1-((no · k0) / nf) (Equation 14), and the detection area ratio α is determined only by the operator size and the number of linear filters. If k0 is about 1 and the operator size no is 3, it is sufficient to have 15 or more linear spatial filters to set the detection area ratio to 80% or more. The above examination results show that regardless of the pitch of the pattern to be detected,
This means that if the pixel size is made equal to the detector size and approximately 15 linear spatial filters or more are used, patterns of all pitches can be dealt with.

It is obvious that the present invention can be applied to a substrate such as a TFT substrate.

The present invention is also disclosed in JP-A-04-56245.
It is obvious that the invention can be applied to the foreign matter monitor in the mass production line and the mass production start of the semiconductor manufacturing process described in the publication.

[0072]

According to the present invention, as a foreign matter monitor in a mass production start-up and a mass production line in a semiconductor manufacturing process, detection signals are logarithmically converted to reduce false alarms due to repetitive patterns, and high performance foreign matter and large foreign matter are detected. It has the effect that it can be inspected separately.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing a specific configuration of the detection head shown in FIG.

FIG. 3 is a diagram showing a specific configuration of an operator processing unit shown in FIG.

FIG. 4 is a diagram showing a specific configuration of a parameter detection system shown in FIG.

FIG. 5 is a diagram showing a conventional technique according to the present invention.

FIG. 6 is a diagram showing a basic concept of the present invention.

FIG. 7 is a diagram showing a repeated pattern removing method according to the present invention.

FIG. 8 is a schematic diagram showing an effect of a comparative inspection by the optical filter ring according to the present invention.

FIG. 9 is a diagram showing the relationship between the detection signal intensity of a pattern and a foreign matter according to the present invention.

FIG. 10 is a perspective view showing a state when light is shielded by the spatial filter according to the present invention.

FIG. 11 is a schematic diagram illustrating an operator process according to the present invention.

FIG. 12 is a schematic diagram for explaining the shape of the spatial filter according to the present invention.

FIG. 13 is a schematic diagram for explaining conditions of pattern erasing according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Substrate, 101 ... Detection head, 102 ... Illumination means, 103 ... Detection optical system, 106 ... Spatial filter (unit), 107 ... Detector, 202 ... A / D converter,
203 ... Operator processing system, 204 ... Cutting means,
206 ... Foreign matter data memory, 207 ... Large foreign matter data memory, 208 ... Pattern memory, 209 ... Parameter transmission means, 210 ... Software processing system, 211 ... Foreign matter memory, 212 ... Pitch detection means, 214 ... Four pixel addition means, 215 ... Octalization means, 216 ... Plural line memories, 217 ... Buffer memory, 218 ... Judgment pixel cutout means, 219, 231 ... Operator cutout means, 220 ... First comparison circuit, 221 ... First threshold value setting circuit, 222 ... second threshold value setting circuit, 223 ... second
Comparing circuits, 224, 225 ... OR circuits, 226, 2
27, 228 ... AND circuit, 229 ... Microcomputer, 230 ... Display means, 232 ... Coordinate data creating means, 241 ... Operator pitch calculating means, 242 ...
FFT circuit, 243 ... Spatial filter control system, 244
... Filter pitch calculation means

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshimasa Oshima 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa, Ltd.Hitachi, Ltd., Institute of Industrial Science (72) Inventor Yukio Mibo 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Stock Company Hitachi Production Engineering Laboratory (72) Inventor Hidetoshi Nishiyama 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Ltd. Production Engineering Laboratory Hitachi, Ltd. (72) Inventor Kazuhiko Matsuoka 111 Nishiyote-cho, Takasaki-shi Gunma Company Hiritsu Plant Takasaki Plant (72) Inventor Executive Officer Yoshiharu 111 Nishiyokote-cho, Takasaki City, Gunma Prefecture Hiritsu Plant Takasaki Plant (72) Inventor Norihiro Minatani 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Hitachi Image Information System Co., Ltd.

Claims (2)

[Claims] 1. An illumination system that linearly irradiates a plane wave light onto a substrate having a repetitive pattern with different pitches, and imaging optics that forms a reflected light image from the substrate illuminated by the illumination system. System, a spatial filter installed in the middle of the imaging optical system so as to block diffracted light from a repetitive pattern with a small pitch on the substrate, and an image obtained by the imaging optical system obtained through the spatial filter. Detector for detecting the reflected light image, logarithmic signal conversion means for converting the signal detected by the detector into a logarithmic signal, and logarithmic signal of one pixel on the detector converted by the logarithmic signal conversion means The level and the logarithmic signal level of the pixel at the corresponding position of the adjacent repeating pattern captured by the detector converted by the logarithmic signal converting means and the plurality of pixels close to the corresponding position. When a pixel having a value equivalent to the signal level of one pixel exists in the signal levels of the corresponding portion or the adjacent portion by comparing with several signal levels, it is detected by one pixel on the detector. The signal is judged to be a signal from a repeating pattern, the repeating pattern is erased, and the logarithmic signal level of one pixel on the detector converted by the logarithmic signal converting means and the logarithmic signal converting means are converted. Comparing the logarithmic signal level of the pixel at the corresponding position of the adjacent repeating pattern captured by the detector and the logarithmic signal level of the plurality of pixels close to the corresponding position to obtain a difference or ratio signal, and the difference or ratio signal A foreign matter inspection device, comprising: foreign matter detecting means for comparing a ratio signal with a plurality of threshold values to determine a plurality of types of foreign matter. 2. A substrate having repetitive patterns with different pitches is irradiated with a plane wave light linearly by an illumination system, and a reflected light image from the irradiated substrate is formed by an imaging optical system. Diffracted light from a repetitive pattern having a small pitch on the substrate is shielded by a spatial filter in the middle of the imaging optical system, and the optical image obtained by the spatial filter and formed by the imaging optical system is detected by a detector. The detected signal is converted into a logarithmic signal by the logarithmic signal conversion means, and the logarithmic signal level of one pixel on the converted detector and the detector converted by the logarithmic signal conversion means are captured. And comparing the logarithmic signal level of the pixel at the corresponding position of the adjacent repeating pattern and the logarithmic signal level of the plurality of pixels near the corresponding position, and comparing the signal at the corresponding position or the adjacent position. When there is a pixel having a value equivalent to the signal level of one pixel in the level, it is determined that the signal detected by one pixel on the detector is a signal from a repeating pattern, and the repeating pattern is erased, Further, the logarithmic signal level of one pixel on the converted detector and the logarithmic signal level of the corresponding pixel of the adjacent repeating pattern captured by the detector converted by the logarithmic signal converting means and the corresponding logarithmic signal level. A foreign substance characterized by obtaining a difference or ratio signal by comparing logarithmic signal levels of a plurality of pixels close to a point and comparing the difference or ratio signal with a plurality of threshold values to make a plurality of kinds of foreign substance determinations. Inspection method.