JPH04127152A - Foreign matter inspecting device - Google Patents

Abstract

PURPOSE:To easily separate and detect a foreign matter of a submicron order on a circuit pattern by an easy constitution by binarizing scattered light and diffracted light which are generated on the same position on the circuit pattern by the irradiation of plural illuminating system through a space filter, calculating and displaying. CONSTITUTION:The circuit pattern of a substrate placed on an inspection stage part 1 is irradiated from respective oblique directions with two independent illuminating systems 23 arranged opposite to each other, and the beams of the scattered light and the diffracted light are respectively separated into the irradiating directions. The diffracted light from the linear part of the circuit pattern is shielded and eliminated by the space filters 44 and 444 arranged on each Fourier transform surface after separating, thereafter, a reverse Fourier transform image is formed and each image formed on each of detecting devices 51 and 531 separately used for the illuminating systems 2 and 3 are binarized by 1st and 2nd binarization circuits 52 and 552, and then, calculated by an AND circuit 53 so as to be displayed by a display means 55. Thus, the foreign matter of the submicron order on the circuit pattern can be separated from the circuit pattern.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a foreign matter inspection device for detecting foreign matter attached to a circuit pattern of a reticle, photomask, etc. The present invention relates to a reticle inspection method and apparatus for detecting foreign matter on the reticle and mask, which is performed with a simple configuration before transferring fine foreign matter onto a wafer.

[Conventional technology]

In the exposure process for reticles used to manufacture LSIs or printed circuit boards, the circuit patterns on the reticle are inspected before being printed and transferred onto the wafer. Even if there is a
There is a problem that all the chips become defective. This problem has become more obvious with the recent increase in the integration of LSIs, and the presence of even smaller foreign substances on the submicron order is no longer tolerated.

In order to prevent the above-mentioned transfer defects, foreign matter inspection before the exposure process is essential, and various foreign matter inspection techniques have been provided for the management of reticles etc., but inspection of circuit patterns on reticles etc. The method of irradiating the object obliquely with a light source with good directivity and detecting the scattered light generated from the foreign object is advantageous in terms of inspection speed and sensitivity and is commonly used.

However, in the above inspection method, diffracted light is also generated from the edges of the circuit pattern of the reticle, etc., so it is necessary to devise a way to distinguish and detect only foreign objects from this diffracted light, and the technology for this has not been made public. There is.

The first is a foreign matter inspection device (for example, Japanese Patent Application Laid-open No. 1982-101390), when linearly polarized light is irradiated, the diffracted light from the circuit pattern and the scattered light from the foreign object have different polarization directions, and this is used to detect only the foreign object by making it shine. .

Second, there is a means for irradiating and scanning a sample to be inspected from an oblique angle, and a means provided above the sample to be inspected so that the irradiation point of the laser beam and the condensing point surface almost coincide, and the laser beam a first lens for condensing scattered light; a light-shielding plate provided on the Fourier transform surface of the first lens for blocking regularly diffracted light from the circuit pattern of the test sample; and foreign matter obtained through the light-shielding plate. The second inverse Fourier transform of the scattered light from
a slit provided at the imaging point of the second lens to block scattered light from other than the laser beam irradiation point on the sample to be inspected, and a light receiver for receiving scattered light from a foreign object that has passed through the slit. A foreign matter inspection device is disclosed (for example, Japanese Patent Application Laid-Open No. 1983-65428). This device focuses on the fact that circuit patterns are generally configured in the same direction or a combination of two or three directions within the field of view, and uses a space installed on a Fourier transform surface to capture the diffracted light from the circuit pattern in this direction. By removing with a filter,
This method attempts to emphasize and detect only the scattered light from foreign objects.

Part 3 focuses on the fact that the diffracted light generated at the edge of the circuit pattern has directionality, but the light scattered by foreign objects does not, and the detection output of each of the multiple detectors installed diagonally It is configured to discriminate foreign substances by taking the logical product of
.

The fourth method utilizes the phenomenon that diffracted light from circuit pattern edges concentrates only in a specific direction, whereas light from foreign objects scatters in all directions, and multiple detectors are arranged. This is used to identify foreign substances. (for example,
JP-A-60-154634 and JP-A-60-1
54635).

In addition, as methods and devices related to micro foreign object inspection,
Techniques related to the Schlieren method, a phase contrast microscope, a diffraction image of a light source with a finite size, etc. are described, for example, in Kou Kubo 1), Applied Optics (Iwanami Zensho), pages 129 to 136.

[Problems to be Solved by the Invention] As described above, as foreign objects to be detected become smaller, the problem of overlooked foreign objects has become more and more problematic.

Said prior art No. 1 (for example, Japanese Patent Laid-Open No. 10139/1983)
0), the polarization direction of the scattered light from the minute foreign matter,
Since the difference in polarization direction of the diffracted light from the circuit pattern edge becomes small, there is a problem in that it is not possible to discriminately detect foreign objects.

Next, the second prior art (for example, Japanese Unexamined Patent Publication No. 59-65
No. 428) uses a light-shielding plate to separate the scattered light from the foreign object from the diffracted light from the circuit pattern, and uses a slit to detect only the scattered light from the foreign object. Foreign objects are detected using a simple binarization method. However, unlike the diffracted light from a straight line, the diffracted light from the intersection of the circuit pattern has a small tendency to be biased toward a specific position, and the spatial filter allows the detection mechanism to be simplified. It is not possible to completely block the diffracted light from the intersection,
In addition, the behavior of diffracted light generated from circuit patterns having micron-order microstructure patterns accompanying the recent trend toward high integration of LSIs has become similar to that of scattered light from foreign objects, so the above-mentioned tendency is even stronger. It has been practically difficult and problematic to separate and detect foreign substances from circuit patterns using the chemical method.

In addition, the above-mentioned prior art No. 3 (for example, JP-A-59-18
6324) and the prior art No. 4 (for example,
JP-A-60-154634 and JP-A-60-1
54635), it is difficult to employ an optical system with sufficient light gathering ability due to the device configuration. Detecting weak scattered light generated from minute foreign matter has been practically difficult.

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, it is an object of the present invention to easily separate and detect submicron-order minute foreign matter attached to a circuit pattern such as a reticle from the circuit pattern using a simple configuration. An object of the present invention is to provide a foreign matter inspection device.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a foreign matter inspection device for detecting foreign matter attached to a substrate having a circuit pattern such as a photomask or reticle, in which the substrate is placed and
, Y, and Z directions, an illumination system having first and second independent light sources that diagonally face and illuminate the circuit pattern, and an illuminated inspection area. N imaged onto the detector.

A, an imaging optical system with a high numerical aperture of 0.4 or more.

In order to collect the scattered light and diffracted light generated at the same point on the circuit pattern by the irradiation of each illumination system and separate the light beams according to the irradiation direction, and to block the diffracted light from the straight portion of the circuit pattern. and a spatial filter provided on each Fourier transform surface after separation.

The apparatus is configured to include a signal processing system that calculates and displays foreign object data on the circuit pattern using a signal output from a binarization circuit in which a threshold value is set for the output of each of the detectors. .

[Effect]

Wolf, “Pr1nsple of 0pti
According to literature such as CS pp, 647-664, when minute particles have a size comparable to the wavelength of illumination light, the scattered light from the foreign matter is not uniform but has a sharp distribution.

In the present invention, we focused on the fact that the above-mentioned oversights have increased because the scattered light from these minute particles has a distribution.

Conventionally, not only was there no mention of the numerical aperture of the detection optical system, but it was also thought that when detecting a foreign object, it is possible to detect it even if the detection optical system cannot resolve the foreign object. This is because of this. However, as shown in the above literature, since the scattered light from microparticles has irregular directivity, it may not be detected by a detection optical system with a small numerical aperture, and as a result, the detection of foreign objects may be missed. happen.

In other words, according to the idea of the present invention, it has become clear that the detection optical system with the resolution of the prior art can "sometimes detect microscopic foreign objects," but not "can stably detect them." .

It has been found that in order to achieve the goal of "detecting foreign objects," it is necessary to have enough resolution to resolve the size of the foreign object to be detected.

The present invention includes a detection optical system having a numerical aperture (NA) large enough to resolve this foreign substance to be detected.

Specifically, it is calculated using the following formula (1).

An optical system having a value approximately close to NA is desirable.

Here, d is the size of the foreign object to be detected, λ is the wavelength of the illumination light, and NA is the numerical aperture.

If NA cannot be set to satisfy equation (1), it is necessary to shorten λ.

That is, in the present invention, it was not thought that resolving power was necessary in the detection optical system for foreign object inspection, but the formula (1
) is based on the novel idea that a detection optical system as shown in () is necessary.

However, the coefficient of equation (1) is 0.6, which is not necessarily a large value when calculating the general resolution, and according to experiments conducted for the present invention, it is 0.24 to 0. If it is within the range of 6, the required foreign object detection performance will be exhibited.

The reason for this will be explained below.

In FIG. 24, the horizontal axis represents the particle diameter and the vertical axis represents the scattering cross section. This scattering cross section is proportional to the scattered light generated from the foreign object, and is determined from the theory of Mie scattering. This interpretation means that when the generated scattered light is observed, it is observed as if it were generated by a foreign object of the size indicated by the solid line in the figure.

In the figure, the geometrical cross-sectional area is also indicated by a dotted line. From this, it can be seen that when observed with scattered light, the foreign object is observed to be larger than the actual size. (This is exactly why foreign object inspection is performed using scattered light.)
As shown in Figure 24, the ratio is approximately 3 to 6 times the area ratio.
Therefore, the diameter is σ~F times.

In this case, Equation (1) is as follows: 0.6 λ d=, τT-strike=0.35-0.24π00001.
(1)′, which explains the previous experimental results.

In addition, since the foreign object size d to be detected is set to about 174, which is the minimum dimension of the reticle, the minimum dimension on the reticle is 2.
．． 5 μm (0.5 μm on the wafer in case of 5:l reduction transfer)
.

This is 0.6 μm for a 16M DRAM phase, etc., and 0.6 μm for a minimum dimension of 1.5 μm (64M DRAM phase, etc.).
It is 4 μm.

Therefore, when detecting a foreign substance of 0.4 μm with λ=780nflI, an NA of about 0.4 or more is required.

The physics of light scattering is actually quite complex.

The simplest problem, when a plane wave is irradiated onto a single sphere suspended in space, was solved by Gustav in 1908.
First analyzed by Mie.

The solution known as Mie's theory is a hydrated series of mathematical functions called spherical harmonics, but it will not be mentioned as it is outside the scope of the present invention.

However, interpretation of the results is relatively easy.

Particles, such as latex spheres, scatter light in an incident beam through a combination of reflection, refraction, absorption, and diffraction processes.

FIG. 21 shows the intensity of scattered light from spherical foreign objects (particles).

The diagram in FIG. 21 is a modification of the theoretical value of Mie scattering in the case of particles attached to a substrate as in the application of the present invention.

The horizontal axis is the wavelength λ (for example, 830 nm) of the detection light, and d is a dimensionless number using the diameter of the detected foreign object.

Here, πd/λ is approximately smaller than 4 (λ=83
Foreign particles (smaller than d=1.1 μm when 0 nm) are particularly called the Rayleigh scattering region, and the scattered light from the particles rapidly decreases in inverse proportion to the sixth power of the diameter. Therefore, in order to detect foreign matter in this region, it is necessary to pay sufficient attention to the sensitivity of the detector.

However, since the scattered light in this region is not scattered in a specific direction, there is no need to be very careful about the NA of the detector in the region described below.

In a region where πd/λ is approximately larger than 4, the scattered light is directionally scattered according to the theory of diffraction.

The situation is as shown in FIG. In order to detect foreign matter in this region, the NA of the detector must be determined with sufficient care because the scattered light from the foreign matter has a distribution.

FIG. 22 shows the direction of diffracted light when laser illumination 2221 is applied to the foreign object 70 on the reticle 6.

The diffracted lights include 0th-order diffracted light 2222, 1st-order diffracted light 2223,
The 0th-order diffracted light 2222, which is followed by the second-order diffracted light by an angle θ, is the specularly reflected light of the laser illumination 2221. Detecting the scattered light of the foreign object means that the first-order or higher-order diffracted light is detected. It will be detected.

Here, θ is from the diffraction equation It is determined by dsinθ=λ.

The necessary NA of the detection optical system is set to πd/λ, which is the most stringent condition.
Find the case where =4.

π・d/λ=4 d/λ=1.27 λ/d=0.79 From sinθ=λ/d θ=sin’(0,79) =52°.

This means that the interval between the diffracted lights becomes 52° at maximum, and therefore, if a detection optical system with an aperture of 52° or more is used, only the first-order diffracted light can be detected, and foreign particles can be detected. cannot be overlooked.

The detection t and the NA of the objective lens 41 are determined by (n: refractive index of the optical path, n#1 in air).Therefore, a detection system with a NA larger than approximately 0.44 will detect scattered light from foreign objects without missing it. can.

In this case, the larger the NA, the more margin there is for detection, and the more convenient it is for detecting foreign objects in the Rayleigh region.

Conversely, even if NA≧0.44 is not dropped, NA=0.4
However, since the diffracted light has a certain range, it is practically possible to detect the foreign matter.

Therefore, in the present invention, N and A are determined for the first time by particles.

It becomes possible to detect foreign objects using a detection optical system with a high numerical aperture of 0.4 or more, and it is possible to reduce the number of missed detections.

The present invention focuses on the fact that a circuit pattern such as a reticle is composed of straight lines in three directions (vertical, horizontal, and diagonal) and intersections of the straight lines. The circuit pattern is obliquely illuminated by a laser beam with good directivity at an angle of incidence i (i<90'
), the Fourier transform image of the diffracted light from the straight line portion of the circuit pattern is focused in a thin straight line at a specific position on the Fourier transform image plane, regardless of the position of the circuit pattern within the illumination field of view. On the other hand, it is known that scattered light from foreign objects is not biased toward a specific position on the Fourier transform image plane. However, changes in the intensity of diffracted light from the intersections and microstructures of the circuit pattern have not been clarified, and the present inventors have investigated all possible intersections and microstructures of the circuit pattern. Measurements of the shape have shown that even when the intersections and microstructures of circuit patterns of the same shape are illuminated by a light source with the same incident angle, the intensity of the diffracted light from the circuit pattern varies significantly depending on the direction in which the light source illuminates the circuit pattern. It was revealed that things are changing.

Based on the above measurement results, the circuit pattern of the board placed on the inspection stage section is illuminated obliquely by first and second illumination systems each having independent light sources placed at opposing positions and shifted in direction by 180 degrees. When irradiated with an incident angle i,
Scattered light and diffracted light generated at the same position on the circuit pattern by the irradiation are collected by the detection optical system and separated into beams according to the direction of irradiation. The diffracted light from the straight line portion is blocked and removed, an inverse Fourier transform image is created, and the image is formed on each detector for each illumination system and detected. The output of each detector is binarized by the first and second binarization circuits in the signal processing system in which thresholds are set, and the AND of the binarized outputs is taken by the AND circuit. . By calculating this logical product, submicron-order foreign matter on the circuit pattern can be detected separately from the circuit pattern, making it possible to detect only the foreign matter.

〔Example〕

The configuration of an embodiment of the present invention will be described below with reference to FIG. In the figure, reference numeral 1 denotes an inspection stage section, and the inspection stage section 1 includes a Z stage 9 which fixes a reticle 6 having a pellicle 7 on its upper surface by a fixing means 8 and is movable in the Z direction, and a Z stage 9 that is capable of moving the reticle 6 in the Z direction. an X stage 10 that moves the reticle in the X direction, a Y stage 11 that also moves the reticle in the Y direction, a Z stage 9, and an x stage 10.
．． It is composed of a stage drive system 12 that drives each stage of the Y stage 11, and a control system 13 for detecting the focus position that detects the position of the reticle 6 in the Z direction. Focusing can be controlled with high precision.

The scanning speed of the X stage 10 and the Y stage 11 can be set arbitrarily, but for example, the X stage 10 is set to a uniform acceleration time of about 0.2 seconds, a uniform motion of 4°0 seconds,
A constant deceleration time of 0.2 seconds is set, a stopping time of approximately 0.2 seconds is set at 1/2 cycle, a maximum speed of approximately 25 mm/second, and an amplitude of 105.
The Y stage 11 is formed to perform periodic motion of 0.0 mm, and the reticle 6 is moved in synchronization with the uniform acceleration time and uniform deceleration time of the X stage 1o. If it is configured to move in the Y direction in steps of 5 mm, 20
If we decide to transfer 0 times, it will be possible to transfer 1°0mm in about 960 seconds, and the area of 100 squares will be transferred about 96 times.
This means that scanning can be done in 0 seconds.

The control system 13 for detecting the focal position may be one that uses an air micrometer, one that detects the position by laser interferometry, or one that projects a striped pattern and detects its contrast. good. In addition,
The coordinates x, y, z are the directions shown in the figure.

2 is a first illumination system, and 3 is a second illumination system, both of which are independent and composed of the same components. 21,3
Reference numeral 1 denotes a laser light source, and the wavelengths of both laser light sources are such that the wavelength λ1 of the laser light source 21 is, for example, 830 nm, and the wavelength λ of the laser light source 31 is 830 nm.
2 is different from 780 nm, for example. Reference numerals 22 and 32 denote condenser lenses that condense the light beams emitted from the laser light sources 21 and 31 and irradiate them onto the circuit pattern of the reticle 6.

In this case, the incident angle i of both with respect to the circuit pattern is approximately 3 to avoid the objective lens 41 of the detection optical system 4 described later.
If the object to be examined is a reticle 6 equipped with a pellicle 7, it must be made smaller than approximately 80' to avoid the pellicle 7, so it is set to approximately 30° by 80'. Ru.

A detailed configuration example of the first illumination system 2 and the second illumination system 3 will be explained with reference to FIGS. 2 and 3. FIG. 2 is a diagram showing an example of the configuration of the first illumination system 2 (in this case, the second illumination system 3 side is omitted because the configuration is the same), and FIG. 3 is a diagram showing the luminous flux emitted from the laser light source 21. at any Z position
It is a perspective view showing a cross-sectional state parallel to the −Y plane. In the figure, the same reference numerals as in FIG. 1 indicate the same things. 21 is a laser light source using a semiconductor laser. 221 is a collimator lens, 222 is a 1/2 wavelength plate, 223 is a concave lens, 224 is a cylindrical lens, 225 is a collimator lens, and 226 is a condensing lens, and the condensing lens 22 is formed by reference numerals 221 to 226. The laser light source 21 has a rectangular firing point 211 with a width (X direction) of approximately 1 μm or less and a length (Y direction) of several μm to several tens of μm.
The laser beam emitted from the ignition point 211 is diffracted at a wide angle laterally (in the X direction) due to the diffraction phenomenon at the ignition point 211, forming an elliptical beam 212 as shown in FIG. uses a semiconductor laser, so
Normally, it has linearly polarized light with a magnetic field vector in the Y direction, and in order to narrow the laser beam to the inspection field of view 15, it needs to be emitted to the collimator lens 221 at a wider angle than the laser light source 21. For this reason, a cylindrical lens 224 is used to form a laser beam whose longitudinal direction is in the Y' direction shown in FIG. 2, and a 1/2 wavelength plate 222 is provided in the optical path to rotate the P-polarized laser beam by 90° to make it S-polarized.

For example, when the incident angle i is about 60°, the reflectance on the glass substrate is about 5 times higher than that of P-polarized light (for example, Kubo 1), published by Hiroko, Applied Optics (Iwanami). Complete book) No. 144), it becomes possible to detect even smaller foreign objects.

In order to increase the illuminance of the first illumination system 2, the numerical aperture (NA) of the condensing system is set to approximately 0. 1 and the laser beam to about 10
The depth of focus is reduced to approximately 30 μm, and the inspection field of view 15 shown in Figure 2 is narrowed down to approximately 30 μm.
It becomes impossible to focus on the entire area S (approximately 500 μm). However, in this embodiment, as a countermeasure to this, the cylindrical lens 224 is tilted around the X' axis shown in FIG. 2 (FIG. 2 shows a state in which it has already been tilted).
For example, even if the incident angle i is 60°, it is possible to focus on the entire area S of the inspection field of view 15. , the inspection area of the inspection field of view 15 is the detector 51
, 551, it is possible to illuminate the linear inspection area with high illuminance and uniform distribution.

Furthermore, the cylindrical lens 224 is
By tilting around the Y' axis as well as around the Y' axis, for example, even if the incident angle i is 60° and the irradiation is from any direction, the whole area S of the inspection field of view 15 can be illuminated with high illuminance and uniformly. It is possible to provide linear illumination with a distribution.

4 is a detection optical system, and the detection optical system 4 includes an objective lens 41 facing the reticle 6, and a viewing area lens (hereinafter referred to as a field lens) provided near the imaging position of the objective lens 41.
43, a mirror 42 for wavelength separation of the light beam condensed by the field lens 43, a spatial filter 44 having a band-shaped light-shielding portion provided at the Fourier transform position with respect to the inspection field 15 of the reticle 6 and a transmitting portion outside the band-shaped light-shielding portion; 444, and imaging lenses 45, 445, and are configured to image the inspection field 15 on the reticle 6 onto detectors 51, 551 of the signal processing system 5, which will be described later. The field lens 43 forms an image of the upper focal point 46 on the objective lens 41 onto a spatial filter 44.444.

5 is a signal processing system, and the signal processing system 5 includes the detector 51,
551, first and second binarization circuits 52 and 552 for binarizing the outputs of the detectors 51 and 551, an AND circuit 53, a microcomputer 54, and a display means 5.
It consists of 5.

The detectors 51 and 551 are formed of, for example, a charge transfer type one-dimensional solid-state image sensor, and detect signals from the circuit pattern on the reticle 6 while scanning the X stage 10. If a foreign object is present,
Since the input signal level and light intensity are increased, the outputs of the detectors 51 and 551 are also increased.

As mentioned above, if a one-dimensional solid-state image sensor is used for the detectors 51 and 551, there is an advantage that the detection field of view can be widened while maintaining the resolution. Alternatively, a single element can also be used.

The binarization circuits 52 and 552 have thresholds for binarization set in advance, and an output value that is equal to or higher than the reflected light intensity corresponding to the foreign object of the size to be detected output from the detectors 51 and 551 is input. The circuit is configured to output a logic level "1" when the signal is detected.

The AND circuit 53 takes in the signals from the binarization circuits 52 and 552, and outputs the AND of the two signals. Further, the microcomputer 54 determines that there is a foreign object when the AND circuit 53 outputs a logic level "1", and the microcomputer 54 determines that there is a foreign object, and provides position information of the X stage 1o and the Y stage 11, and the detector 51.551 which is not a single element. In this case, the foreign object position information calculated from the pixel position in the element and the detectors 51, 5
The detection output value of 51 is stored as foreign object data, and the result is output to display means 55.

Next, the operation of the inspection device will be explained with reference to FIGS. 4 to 10. In the figure, the same reference numerals as in FIG. 1 indicate the same things. FIG. 4 is a diagram showing the inspection status of the reticle 6, FIG. 5 is a plan view explaining the angle pattern of the circuit pattern, FIG. 6 is a diagram showing the distribution of scattered light and diffracted light on the Fourier transform surface, and FIG. Figure 7 (A) is a diagram showing the corners of the circuit pattern, and Figure 7 (B) is a diagram showing the corners of the circuit pattern.
Figure 8 is a detailed diagram of part A. Figure 8 is an explanatory diagram of the relationship between the detected output value of scattered light from a foreign object and the detected output value from the circuit pattern. Figure 9
The figure shows a circuit pattern with a fine structure pattern,
FIG. 10 is a diagram showing the output value level of a detection signal detected from a foreign object and a part of a corner of a circuit pattern.

In FIG. 4(A), 70 is a foreign object on the reticle 6 fixed on the Z stage 9 by the fixing means 8, 81 is a straight line portion of the circuit pattern 80, and 82 is a part of a corner of the circuit pattern 8o.

The reticle 6 is illuminated obliquely by the first illumination system 2 or the second illumination thread 3, and the generated scattered light is transmitted to the objective lens 4.
1, when the angle θ defined by the positional relationship between the circuit pattern 80 on the reticle 6 and the projected image 60 of the illumination system 2 or 3 on the reticle 6 surface as shown in FIG. The diffracted light of the angle pattern (hereinafter referred to as O° pattern) is
On the Fourier transform surface of the objective lens 41, it appears in a band shape as shown in FIG. 6(a). Here, the circuit pattern 80
The types of angle θ are limited to O', 45°, and 90° angle patterns, and as shown in Figure 4 (A), the diffracted light from the 45° and 90° patterns (b), c) does not enter the pupil of the objective lens 41, so it does not affect detection. On the other hand, since the scattered light from the foreign object 70 has no directionality, it spreads over the entire surface of the Fourier transform surface as shown in FIG. 6(e). Therefore, by arranging a spatial filter 44,444 having a band-shaped light shielding part on the Fourier transform surface and a transmitting part outside the band-shaped light shielding part, the diffracted light (a) from the O degree pattern shown in FIG. By blocking light, it becomes possible to distinguish the foreign object 70 from the circuit pattern 80 and detect it.

This configuration makes it possible to realize a high NA detection optical system for the first time.
Af! :0.5, the opening area is low NA
It can be made about 20 times as powerful as the detection optical system.

However, the scattered light from a portion of the circuit pattern corner (shown in FIG. 4(D)) cannot be sufficiently blocked by the linear spatial filter. Therefore, the conventional 10×20 μm
! When detection is performed using the detection pixels (as shown in FIG. 4(B)), scattered light from a portion of a plurality of pattern corners enters the pixel, making it impossible to detect only the foreign object.

Therefore, in the present invention, the resolution of the pixels of the detector is increased to 2.times.2 .mu.m' as shown in FIG. 4(C). ), eliminate the influence from circuit patterns as much as possible, 0. It is possible to detect foreign matter of 5 μm. Furthermore, here, the pixel of the detector is set to 2×2 μm′, but this value is not necessarily 2×2 μm′, as will be described below.

In this case, the size of the pixel need only be smaller than the minimum pattern size on the reticle.

Therefore, a reticle for exposing 0.8 μm processes I and SI using a stepper with a reduction ratio of 115 is approximately 0.8 μm.
8×5=4 μm, in a 0.5 μm process LSI, it is sufficient to detect pixels smaller than approximately 0.5×5=2.5 μm.

In fact, the value may be larger or smaller as long as the pattern corner can be made sufficiently small.

Specifically, the minimum pattern size on the reticle to be inspected is desirable. If the size is about this minimum pattern size, less than two corners will fit into one pixel of the detector, and this value is sufficient according to the experiment shown in FIG. 10.

More specifically, 64MD with a minimum dimension of about 1.5 μm
For a RAM reticle, a pixel size of about 1 to 2 μm is desirable.

The NA of the high NA detection optical system adopted this time is 0. 5. This is about 20 times the area ratio compared to the conventional device.

In addition, the pixels of the detector, which were conventionally 10 x 20 μI, have been changed to 2 x
The resolution has been increased to 2 μm', making it possible to detect foreign matter of 0.5 μm.

With this invention, we can inspect the circuit pattern surface of the reticle in 15 minutes and output the results.

However, the corner part 82 formed at the intersection of the circuit pattern 80 shown in FIG. 7(A) is a continuous angular corner 820 as shown in FIG. 7(B) microscopically looking at the core.
, the diffracted light from the corner part 82 (
d) also tends to spread on the Fourier transform plane, and the spatial filters 44 and 444 cannot completely block the light, resulting in a situation as shown in FIG. 6(d). Therefore, when diffracted light from a plurality of corner portions 82 is incident on one detector 51 or 551, the output (2) of the detector 51 or 551 increases, making it impossible to detect the foreign object 70 differently.

Figure 8 shows this state, where some corners 8
The detection output value 822 from the foreign object 70 is higher than the detection output value 821 from the single corner part 82, and the detection output value from the foreign object 70 is higher than the detection output value 821 from the single corner part 82. This indicates that the value 701 cannot be detected separately.

As a countermeasure for the problem explained in FIG. By selecting the dimensions and imaging magnification of the detectors 51 and 551, the detection field of view 15 on the 6 surfaces of the reticle can be set to any size (for example, 2 μm x 2 μm), and even though the detection optical system 4 is simple, it can be The diffracted light from the corner portion 82 is prevented from entering the detectors 51 and 551 at the same time. However, even if it is possible to detect a foreign object of the conventional size, depending on the shape of the circuit pattern 80, separation of the foreign object from some corners 82 is insufficient for detecting a submicron-order foreign object. , due to the high integration of LSIs, diffracted light generated from a circuit pattern having a dimension 84 on the micron order as shown in FIG. Since the behavior of the foreign object 7o is becoming more similar to that of the scattered light from the circuit pattern, it is becoming more difficult to separate and detect the foreign object 7o from the circuit pattern.

The present invention has the measures described below to enable foreign matter to be detected even for a circuit pattern having dimensions 84 on the micron order as shown in FIG. 9 above. FIG. 8 is an explanatory diagram thereof. In the figure, 701, 702 are scattered light detection output values from a minute foreign object 70 on the submicron order, 864, 874, 865, 875, 866, .
876°867.877 is O', 45', 90'
All corner portions 82 formed by each circuit pattern of
Detection output value of diffracted light from 861, 871, 862.
872, 863, 873 have dimensions of micron order 8
4 shows the detected output values of diffracted light from a fine structure circuit pattern having a pattern of 4. Of these, 701,861,86
2,863,864°865.866.867 is the first
The detection output value by the illumination system 2 is also 702,871
, 872° 873.874, 875, 876.877 indicate the detection output value by the second illumination system 3, for example 86
1←→871 is the detection output value for each illumination system at the same position of the circuit pattern, where 861 indicates the value by the first illumination system 2, and 871 indicates the value by the second illumination system 3. Further, as can be seen from the figure, the foreign matter 70 has a smaller variation in the detected output value of scattered light depending on the irradiation direction than the circuit pattern. Note that a dotted line 91 in the figure indicates a threshold value of the detected output value.

From FIG. 8 above, it is clear that even with the same circuit pattern, the output of the diffracted light differs greatly depending on the direction in which it is irradiated.Moreover, the reticle 6 surface is illuminated from two diagonal directions that are 180 degrees apart and opposite to each other. In this case, it can be seen that the output value of the diffracted light on either side is always smaller than the output value from the submicron-order foreign matter, as shown by the mark ◎ in the figure.

Therefore, in the present invention, the above-mentioned output values from the same position on the six surfaces of the reticle are detected separately by the detectors 51 and 551, and the smaller detected output value of the values indicated by the ◎ mark is adopted. , after being binarized by the binarization circuits 52 and 552,
By calculating the logical product in the logical product circuit 53, it is possible to separate and detect only the submicron-order foreign matter 70 from the circuit pattern 80.

As shown in FIG. 10, when a threshold value 91 is set in the binarization circuits 52 and 552, the values above the threshold value 91 are the detection output values 701 and 702 of the foreign object 70 and the detection output value 861 of the circuit pattern. ,863°874.875, but
The binarized output from these circuit patterns is sent to the binarized circuit 5.
Since the output is only from either one of the circuit patterns 2 and 552, it is not output from the AND circuit 53, and therefore only the foreign matter 7° can be detected separately from the circuit pattern. Then, the X stage 10 and Y stage 1 at the time of detection
In addition to the position information of 1, if the detector 51 551 is not a single element, the position information of the foreign object 70 calculated from the pixel position in the element and the detection output value of the detectors 51 and 551 are used as foreign object data. The data is stored in a memory managed by the microcomputer 54, and the stored contents are processed and displayed on a display means 55 such as a CRT.

FIG. 11 shows an example of a missed foreign object in the prior art.

These foreign objects have dimensions that should normally be detected.

In the present invention, we examine the mechanism by which these conventional techniques miss the detection, and propose a foreign object inspection method with a new configuration.

FIG. 12 shows problems with the conventional device.

A foreign matter inspection device on a reticle removes the diffracted light from the circuit pattern formed on the reticle, and removes the diffracted light from the foreign matter. The key point of the technology is a method that detects only light.

Therefore, methods for analyzing the polarization state of scattered light and methods for comparing the outputs of multiple detectors have been developed and put into practical use. However, in order to avoid the influence of scattered light generated from the circuit pattern, an optical system with a small aperture of approximately NA 0.1 is arranged diagonally to avoid the scattered light from the circuit pattern.

With such a configuration, a problem arises in that irregularly shaped foreign objects are easily overlooked for reasons described later.

The NA used here is determined by the aperture diameter of the lens and the distance to the target object. This is a numerical value that expresses the characteristics of the lens, and specifically, it is a numerical value determined by NA=Sinθ using θ in the figure shown on the right.

Another problem is that in response to the miniaturization of circuit patterns,
This is a pattern removal technique that has begun to be used as an auxiliary in various inspection techniques. Most of these systems automatically lower the detection sensitivity of the foreign object detector when a circuit pattern is found during inspection. Although such a method reduces erroneous detection of circuit patterns, it has the problem of overlooking foreign objects near the edges of the pattern.

Now, the solutions of the present invention to these two problems will be described below.

Photographs 1004 and 1005 in FIG. 14 are views of scattered light generated when a foreign object is irradiated with a laser from above. What should be noted in this photograph is that the scattered light (e) from the foreign object is distributed in a directional manner.

For this reason, with the conventional low NA detector 1.001, unless the detector is installed in an appropriate position, the scattered light (e) generated by the foreign object may not enter the low NA optical system properly. Otherwise, oversight will occur. Moreover, the distribution of these scattered lights varies depending on the size and shape of the foreign object.
It is virtually impossible to properly position a low NA optical system for all foreign objects.

The results of experimentally measuring this are shown in FIG.

A detection optical system 1001.1 with a low NA (0,1) detects the scattered light distribution when a foreign object is illuminated with a laser beam at an incident angle of 60'.
002, the level of scattered light from the foreign object was measured and shown while changing the detection angle. This figure shows that at point A1001 the detection level exceeds the detection threshold, while at point Bl
002 indicates that the detection threshold is not exceeded and detection is not possible.

A because the scattered light distribution of an actual foreign object is not constant.

This shows that detection performance is not stable in a detection method with a low numerical aperture like B.

Therefore, in the present invention, a high NA detection optical system 41 with a large aperture
We devised a method to effectively collect scattered light from foreign objects with various scattered light distributions.

Laser 21. Condensing lens 22. Objective lens 41° field lens 43. Spatial filter 44. Imaging lens 45.
With a device configured as shown in FIG. 15 with a detector 51,
The effect of the present invention in detecting foreign matter 70 on reticle 6 is shown in FIG.

The evaluation sample was a 0.5 μm LSI 16MDRAM.
Five reticles were used.

In the figure, the vertical axis represents the total of foreign objects detected by five reticles, and the horizontal axis represents the dimensions of the detected foreign objects. Also,
Among the detected foreign substances, foreign substances that were also detected by the conventional technique are shown in different colors.

The detection ability of the conventional technology is 0. It was supposed to be 8 μm. Therefore, it is understandable that there is a difference in detection ability with the present invention in the region of foreign particles smaller than 1 μm.

However, even in the area of foreign particles larger than 1 μm, the present invention shows a significant improvement in the number of foreign particles detected.

The detection rate is about 9 times higher than that of the conventional technology.

This is considered to be because the high NA detection optical system employed in the present invention responds well to irregularly shaped foreign objects and stably detects scattered light from foreign objects.

Next, a description will be given of the detection status of foreign matter attached to the edge of a circuit pattern. FIG. 17 shows the results of classifying the detected foreign objects shown in FIG. 16 according to the adhesion position of the foreign objects. Regarding the attachment positions, the circuit pattern surface of the reticle was classified into three areas: a glass part (transmissive part), a chrome part (light-shielding part), and an edge part which is the boundary between the two parts. Among these, the edge portion is most affected by foreign matter adhesion, and foreign matter on the chrome portion does not affect transfer as long as it remains on the chrome portion.

It is clear from FIG. 17 that the detection performance for foreign matter at the edge portion, which affects the transfer the most, that is, where detection is most necessary, is improved.

By using the idea described here that foreign matter on the chrome portion is not a problem, a configuration as shown in FIG. 18 is also possible.

In this case, foreign matter on the chrome portion cannot be detected, but scattered light from foreign matter on the glass portion and edge portion, which affects transfer defects, can be detected through the reticle, which is a transparent base material.

An advantage of this configuration is that it can be used with a reticle having a cross section as shown in FIG.

In the reticle shown in FIG. 19, a phase shifter film is provided between the chrome patterns for the purpose of improving transfer resolution. This film is transparent but has a chrome pattern (thickness 0.
Because it has a structure several times the size of (about 1 μm),
The diffracted light from the edge portion 1006 of the film is larger than the diffracted light from the chrome pattern edge portion.

However, in a configuration in which the detection system is provided below as shown in Figure 18, the diffracted light generated from the phase shifter film is blocked by the chrome pattern of the reticle itself and does not enter the detection system, which affects the detection of foreign objects. does not affect

Although the reticle, illumination system 21, and objective lens 41 are arranged as shown in the figure, the purpose of the present invention is to reduce scattered light from the edge portion 1006 of the phase shifter 1003 placed on the chrome portion. This can be achieved by blocking light using a chrome pattern. Therefore, lighting system 2
1. The configuration shown in FIG. 20 may be used since the objective lens 41 only needs to be on the opposite side to the reticle 6.

However, since the phase shifter 1003 is thick, in the case of oblique illumination, the portion 10o that cannot be illuminated in the configuration of FIG.
7 occurs, so the configuration of FIG. 18 is better.

〔Effect of the invention〕

Since the present invention is configured as described above, fine foreign matter of submicron order adhering to a circuit pattern such as a reticle can be easily separated from the circuit pattern and detected using a simple optical configuration. It can produce remarkable effects.

[Brief explanation of drawings]

FIG. 1 is an overall schematic configuration diagram showing one embodiment of the present invention, and FIG.
The figure shows an example of the configuration of the illumination system in Figure 1 (in this case, the symmetrical side is omitted because it has the same configuration), and Figure 3 shows the luminous flux emitted from the laser light source in Figure 2 at any Z position. FIG. 4 is a diagram showing the state of inspection of the reticle according to the present invention, and FIG. 5 is a plan view illustrating the angle pattern of the circuit pattern according to the present invention. , 6th
The figure shows the distribution of scattered light and diffracted light on the Fourier transform surface according to the present invention, FIG. 7 (A) shows a part of the corner of the circuit pattern, and FIG. (A
), Figure 8 is an explanatory diagram of the relationship between the detected output value of scattered light from a foreign object and the detected output value from the circuit pattern, and Figure 9 shows a circuit pattern having a fine structure pattern. Figure 10 is a diagram showing the output value level of a detection signal detected from a foreign object and a part of a circuit pattern corner.
Figure 1 shows an example of a foreign object missed by conventional technology; Figure 12
The figure is a diagram for explaining the problems of the prior art, Figure 13 is a diagram for explaining the problems of the prior art, and Figure 14 is for detecting scattered light from foreign objects using the high NA optical system according to the present invention. FIG. 15 is a diagram showing the main components of the present invention shown in FIG. 1, and FIG. 16 is a diagram showing the number of detected foreign objects with respect to the detected foreign object size for the present invention, the prior art, and each case. , FIG. 17 is a diagram showing the foreign matter detected according to the present invention classified into the foreign matter adhesion position side, FIG. 18 is a schematic configuration diagram showing another embodiment of the present invention, and FIG. 19 is a diagram showing the foreign matter detected according to the present invention. Diagram 20 showing scattered light and diffracted light from such a reticle with a transfer shifter film.
The figure is a schematic configuration diagram showing another embodiment of the present invention, and FIG. 21 shows the theoretical value of the intensity of scattered light from a foreign object, which is determined by the wavelength λ of the laser beam and the dimensionless number πD/λ depending on the particle size of the foreign object. 22 is a diagram showing the direction of diffracted light from a foreign object,
Figure 23 is a diagram showing the definition of the NA of the optical system, and Figure 24 is a diagram showing the definition of the NA of the optical system, and Figure 24 shows the scattering cross section proportional to the intensity of scattered light from a foreign object.
FIG. 1... Inspection stage section, 2... First illumination system, 3.
. Second illumination system, 4...Detection optical system, 5...Signal processing system, 6...Reticle, 9...Z stage, 10...X
Stage, 11...Y stage, 21.31...Laser light source, 44.444...Spatial filter, 51,5
51...Detector, 52...First binarization circuit, 55
2... Second binarization circuit, 53... AND circuit, 70
... Foreign matter, 80 ... Circuit pattern, 221 ... Collimator lens, 222 ... 1/2 wavelength plate, 223.
... Concave lens, 224 ... Cylindrical lens, 2
25... Collimator lens, 226... Condensing lens.

Claims (1)

[Claims] 1. In a foreign matter inspection device that detects foreign matter attached to a substrate with a circuit pattern such as a photomask or reticle,
an inspection stage section consisting of a movable stage on which the circuit pattern is placed and its drive control system; an illumination system that illuminates the circuit pattern from an oblique direction; The generated scattered light and diffracted light are collected by an optical system with an NA of 0.4 or more, and a spatial filter provided on the Fourier transform surface blocks the diffracted light from the linear portion of the circuit pattern, and the light is focused on the detector. a detection optical system that generates an image, a signal processing system that binarizes the output of the detector using a binarization circuit with a threshold value set, and calculates and displays foreign object data on the circuit pattern based on the output value of the binarization circuit. A foreign matter inspection device characterized by comprising: