JPH0643109A - Inspecting apparatus for extraneous substance - Google Patents

Abstract

PURPOSE:To facilitate detection of minute extraneous substances on a sample in separation from a circuit pattern by a method wherein the sample to be inspected which has the circuit pattern is illuminated obliquely by a light of a specific wavelength. CONSTITUTION:A reticle 6 is illuminated obliquely by an illuminating system (of which the wavelength of a laser light is about 550nm) 2 and a scattered light generated thereby is converged by an objective lens 41. A diffracted light (a) of a circuit pattern at the time when an angle theta defined by the positional relationship between the circuit pattern 80 on the reticle 6 and a projection image 60 of the illuminating system 2 on the surface of the reticle 6 is 0 deg. can run in the shape of a strip on a Fourier transform plane of the lens 41. Diffracted lights (b) and (c) from the pattern at the time when the angle theta is 45 deg. and 90 deg. do not enter the eye of the lens 41 and therefore they have no effect on detection. A scattered light from extraneous substances 70 on the reticle 6 has no directionality and therefore it is scattered on the whole of the Fourier transform plane. By intercepting the diffracted light (a) by disposing spatial filters 44 and 444 each having a strip-shaped light-intercepting part and a transmitting part outside the former part on the Fourier transform plane, the extraneous substances 70 can be detected in discrimination from the pattern 80.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foreign substance inspection apparatus for detecting foreign substances attached to a sample to be inspected having a circuit pattern such as a reticle, a photomask (hereinafter referred to as a reticle).

[0002]

2. Description of the Related Art In an exposure process of a reticle used for manufacturing an LSI or a printed circuit board, a reticle is inspected before printing a circuit pattern of the reticle on a wafer or the like. For example, even if microscopic foreign matter of micron order exists on the pattern, the circuit pattern is not normally transferred to the wafer due to the foreign matter, which causes a problem that all the LSI chips are defective. This problem has become more apparent with the recent high integration of LSIs, and the presence of finer foreign matter on the order of submicrons has become unacceptable.

In order to prevent such a transfer failure, it is indispensable to inspect the foreign matter before the exposure process, and various foreign matter inspection techniques have been conventionally provided for management of the reticle and the like.
For inspection of circuit patterns such as reticles, a device that obliquely irradiates a light source with good directivity such as laser light and detects scattered light generated from foreign matter is advantageous in terms of inspection speed and sensitivity, and is generally used. ing. However, in such a foreign matter inspection device, since diffracted light is generated also from the edge portion of the circuit pattern of the reticle or the like, it is necessary to devise a means for discriminating and detecting only the foreign matter from this diffracted light. Has been published.

The first is a foreign matter inspection apparatus having means for obliquely irradiating a linearly polarized laser beam at a specific incident angle and an oblique imaging optical system using a polarizing plate and a lens (for example, Japanese Patent Laid-Open No. 54-54). No. 101390 gazette). This device, when irradiated with linearly polarized light, utilizes the fact that the diffracted light from the circuit pattern and the scattered light from the foreign matter have different polarization directions, and detects only the foreign matter by shining it.

The second method is provided above the sample to be inspected so that the means for irradiating the sample to be inspected with a laser beam obliquely and scanning, and the irradiation point of the laser beam and the surface of the converging point are substantially coincident with each other.
A first lens that collects scattered light of the laser light, a light-shielding plate that is provided on the Fourier transform surface of the first lens and that shields the regularly diffracted light from the circuit pattern of the sample to be inspected, and a light-shielding plate. A second lens for performing an inverse Fourier transform on the scattered light from the foreign matter, a slit provided at the image forming point of the second lens for shielding scattered light from other than the laser light irradiation point on the sample to be inspected, and a slit. A foreign matter inspection device composed of a light receiver for receiving scattered light from a foreign matter that has passed (for example, Japanese Patent Laid-Open No. 59-65428 and Japanese Laid-Open Patent Publication No. 1-117).
No. 024, and Japanese Patent Laid-Open No. 1-153943). This device pays attention to the fact that the circuit pattern is generally formed in the same direction or a combination of a few directions in the visual field, and diffracted light by the edge portion of the circuit pattern in this direction is reflected on the Fourier transform plane. By removing it with the installed spatial filter, only scattered light from a foreign matter is emphasized and detected.

The third point is that although the diffracted light generated at the edge portion of the circuit pattern has directivity, the scattered light due to the foreign matter does not have directivity. A structure for discriminating foreign matter by taking a logical product of respective detection outputs (for example, Japanese Patent Laid-Open No. 59-186324).
Issue gazette).

Fourth, the phenomenon that the diffracted light from the edge portion of the circuit pattern concentrates only in a specific direction, while the diffracted light from the foreign matter scatters in all directions is utilized. However, a plurality of detectors are arranged to discriminate foreign matter (for example, Japanese Patent Laid-Open Nos. 60-154634 and 60-154635). .

As a method and an apparatus related to the inspection of minute foreign matter, a technique relating to a schlieren method, a phase-contrast microscope, a diffraction image of a light source of a finite size, for example, is written by Hiro Kubota, Applied Optics (Iwanami Zensho) 129- Pp. 136.

Further, when an array-shaped detector such as a one-dimensional solid-state image pickup device is used, when a foreign substance is detected across pixels forming the array, the output from the foreign substance is dispersed to a plurality of pixels. Detected, and as a result, the output from the detector becomes small by the amount of the dispersion, and there is a possibility that foreign matter may be missed, but as an invention to avoid this,
Japanese Unexamined Patent Publication No. 61-104242 discloses a method of inclining the arrangement of detectors in an array with respect to the scanning direction of a sample stage, and further, Japanese Unexamined Patent Publication Nos. 61-104244 and 61.
No. 104659 describes a method of using an array detector having a special shape and arrangement.

Further, although the unevenness and fluctuation of the illumination affect the reproducibility and accuracy of the detection, JP-A-60-38827 discloses an invention in which the intensity of scattered light is automatically calibrated using a standard sample. Is listed.

Further, Japanese Unexamined Patent Publication No. 56-132549 discloses an invention for preventing a large amount of scattered light generated from a large foreign substance from being mistaken for scattered light from a large number of small foreign substances.

[0012]

As described above, as the size of the foreign matter to be detected becomes smaller, the problem of overlooking the foreign matter that affects the LSI manufacturing has become a problem.

In the inventions of Japanese Patent Laid-Open No. 54-101390 and the like, the difference between the polarization direction of scattered light from a minute foreign substance and the polarization direction of diffracted light from the edge portion of the circuit pattern becomes small, so that Discrimination cannot be detected.

Next, in the invention disclosed in Japanese Patent Laid-Open No. 59-65428, the scattered light from the foreign matter is separated from the diffracted light from the circuit pattern by the light shielding plate, and only the scattered light from the foreign matter is detected by the slit. However, the detection mechanism is simple because foreign matter is detected by a simple binarization method. However, the diffracted light from the corner of the circuit pattern has a specific position like the diffracted light from the edge of the circuit pattern. There is little tendency to be biased to, and it is not possible to completely block the diffracted light from the corner portion of the circuit pattern by the spatial filter, and it is generated from the circuit pattern having the microstructure pattern of the micron order accompanying the recent high integration of LSI. The behavior of diffracted light is similar to that of scattered light from foreign matter,
Since the above tendency is stronger, it is practically difficult to separate and detect the foreign matter from the circuit pattern by a simple binarization method.

Further, in the inventions such as JP-A-59-186324 and JP-A-60-154634, it is difficult to adopt an optical system having a sufficient light-collecting ability due to the construction of the device. Therefore, it is practically difficult to detect the weak scattered light generated from a minute foreign substance.

Further, in the inventions of Japanese Patent Laid-Open No. 61-104242 and the like, it is necessary to specially manufacture a special detector due to its constitution, and it is necessary to form a special optical system, which is practically manufactured. The cost is high.

Further, the inventions of Japanese Patent Laid-Open No. 60-38827 and the like have drawbacks in that they are compatible with array-like detectors suitable for high-speed detection and in terms of configuration accuracy for detecting minute foreign matter. .

Further, in the inventions of JP-A-56-132549 and the like, since only one point of the large foreign matter is represented, there is a problem that the shape of the long and thin foreign matter cannot be accurately recognized.

The present invention has been made to solve the above problems, and an object thereof is to provide a foreign matter inspection apparatus capable of easily separating and detecting a minute foreign matter from a circuit pattern.

[0020]

To achieve this object, in the present invention, in a foreign matter inspection apparatus for detecting foreign matter adhered on an inspected sample having a circuit pattern, the inspected sample has a wavelength of 500 to 500 nm. Diffracted light from the linear portion of the circuit pattern by an illumination system that obliquely irradiates with 600 nm light and a spatial filter that collects scattered light and diffracted light generated from the sample to be inspected and is provided on the Fourier transform surface. A detection optical system that forms an image on the detector by blocking the light and a binarization circuit that sets the threshold value of the output of the detector, and binarizes the foreign matter data on the sample to be inspected. And a signal processing system.

In this case, the wavelength of the light is 550 nm, 5
It may be 43.5 nm, 514.5 nm, 532 nm.

Further, the illumination system is 500 to 600 n
A device that irradiates light having a wavelength band within the range of m may be used.

Further, the illumination system is 500 to 600 n
One that irradiates light of a single wavelength or a plurality of wavelengths within the range of m may be used.

Further, when the minimum diameter of the foreign matter to be detected by the illumination system is d and the numerical aperture of the detection optical system is NA, a wavelength of NA · d / 0.35 to NA · d / 0.24 is obtained. You may use what irradiates light.

[0025]

In this foreign matter inspection apparatus, scattered light from a minute foreign matter and diffracted light from the corner portion of the circuit pattern can be distinguished.

[0026]

[Example] Wolf, "Optical Principle (Principl
es of Optics) ”pp. 647-664, and the like, when minute particles have the same size as the wavelength of the illumination light, the scattered light from the foreign matter does not become uniform but has a sharp distribution. To have.

In the present invention, attention was paid to the fact that the above-mentioned overlooking of foreign matters has increased because the scattered light from these fine particles has a distribution.

This is not only related to the numerical aperture NA of the conventional detection optical system, but it is possible to detect a foreign substance even if the detection optical system cannot resolve the foreign substance. This is because it was thought to exist. However, as shown in the above-mentioned document, since scattered light from a minute foreign substance has an irregular directivity, it may not be detected by a detection optical system having a small numerical aperture NA. Occur.

That is, according to the idea of the present invention, it is clear that the detection optical system having the resolution of the prior art "may detect a minute foreign substance" but not "stablely detect". Became. It has been found that a resolution sufficient to resolve the size of the foreign matter to be detected is necessary to achieve the target of "detection of the foreign matter". The examination process is described below.

The physics of light scattering are quite complex in nature. The simplest problem, such as the case of a plane wave hitting a single sphere suspended in space, was first analyzed by Gustav Mie in 1908. A solution known as Mie's theory is a quadratic series of mathematical functions called spherical harmonics, but it is not mentioned here as it is outside the subject of this invention. However, the interpretation of the results is relatively easy.

Particles such as latex spheres reflect, refract,
A combination of processes such as absorption and diffraction scatter the light in the incident beam. The intensity of scattered light from spherical foreign matter (particles) is shown in FIG. FIG. 2 is a modification of the logical value of Mie's scattering in the case of particles deposited on a substrate as in the application of the present invention. The horizontal axis is a dimensionless number obtained by dividing the product of the diameter d of the detected foreign matter and π by the wavelength λ of the detection light (for example, 550 nm).

Here, a region where πd / λ is generally smaller than 4 (a foreign substance smaller than d = 0.7 μm when λ = 550 nm) is particularly called a Rayleigh scattering region, and scattered light from the foreign substance has a diameter d. It decreases sharply in inverse proportion to the sixth power. Therefore, in detecting the foreign matter in this region, it is necessary to pay sufficient attention to the sensitivity of the detector.

On the other hand, in a region where πd / λ is generally larger than 4, the scattered light is scattered with directionality according to the theory of diffraction.

The situation is as shown in FIG. In order to detect the foreign matter in this region, the scattered light from the foreign matter has a distribution, so it is necessary to determine the numerical aperture NA of the detector while paying attention to the distribution.

FIG. 4 shows the directions of diffracted light when the foreign material 70 on the reticle 6 is irradiated with the laser light 2221.
The diffracted light is the 0th-order diffracted light 2222, the one-dimensional diffracted light 2223,
Two-dimensional diffracted light continues at an angle θ.

The 0th-order diffracted light 2222 is a laser illumination 2221.
Detecting the scattered light of the foreign matter, which is the specularly reflected light, means detecting the diffracted light of the first order or higher.

The angle θ is obtained from the following equation of diffracted light.

D ₀ · sin θ = λ (1) Here, various definitions such as diameter, width, length or average value of diameter can be considered for d ₀ with respect to an irregular foreign substance.
However, since the following discussion holds regardless of the value of d ₀ ,
None of the above definitions have any effect on the result.
Therefore, here, d ₀ = d, that is, d ₀ is the diameter d of the foreign matter.
Suppose

The required numerical aperture NA of the detection optical system will be determined for the most severe condition of πd / λ = 4. First,
From the formula (1), the angle θ is 52 °. This means that the gap of the diffracted light will be up to 52 °, thus 52
If a detection optical system having an opening of not less than ° is used, at least only the first-order diffracted light can be detected, and foreign substances will not be missed.

In FIG. 5, the numerical aperture NA of the detection system objective lens 41 is obtained by the following equation.

NA = nsin (θ / 2) (2) where n is the refractive index of the optical path, and in air, n≈1,
NA becomes 0.44. Therefore, it is possible to detect the scattered light from the foreign matter without overlooking with the detection system having the numerical aperture NA larger than about 0.44.

In this case, the larger the numerical aperture NA, the more room for detection, and the more convenient the detection of foreign matter in the Rayleigh region. On the contrary, even when NA ≧ 0.44 is not satisfied,
When NA is about 0.4, the diffracted light has a certain width, so that it is possible to detect foreign matter in practical use.

On the contrary, when the numerical aperture NA is larger than 0.5, scattered light from the circuit pattern is incident on the detection system for the reason described later, which impedes the requirement to detect only scattered light from foreign matter. Therefore, the merit of intentionally increasing the numerical aperture NA is reduced. For this reason, approximately 0.
A numerical aperture NA of 4 to 0.6 is a practically appropriate numerical aperture NA.

Next, the detection of foreign matter in the Rayleigh area will be described.

As described above, in the detection optical system having the resolution of the prior art, "sometimes a minute foreign substance can be detected", not "stable detection". In order to achieve the target of "detection of foreign matter", it is necessary to have a resolution that can resolve the size of the foreign matter to be detected.

In the foreign matter inspection apparatus according to the present invention,
It has a detection optical system having a numerical aperture NA to the extent that a foreign matter to be detected is resolved. Specifically, it is calculated by the following equation.

D = 0.6 (λ / NA) (3) An optical system having a value approximately close to this numerical aperture NA is desirable. If the numerical aperture NA of the detection system cannot be set so as to satisfy the expression (3), it is necessary to shorten the wavelength λ of the illumination system and satisfy the expression (3).

That is, in the detection optical system for inspecting a foreign substance, it has not been conventionally considered necessary to have a resolving power for resolving a foreign substance, but in the present invention, detection for resolving a foreign substance as expressed by the equation (3) is performed. It is based on the new idea that an optical system is necessary.

However, the coefficient of the equation (3) does not need to be as large as the value for calculating the general resolution of 0.6, and according to the experiment conducted by the inventor of the present invention,
In the range of 0.24 to 0.6, the required foreign matter detection performance is exhibited. The reason will be described below.

FIG. 6 is a graph showing the relationship between the particle diameter d and the scattering cross section. This scattering cross section is proportional to the scattered light generated from a foreign substance, and is obtained from the theory of Mie scattering. The interpretation means that when the generated scattered light is observed, it is observed as if it is the scattered light generated from a foreign substance shown by the solid line in the figure. In the figure, the cross-sectional area is also shown geometrically along the dotted line. From this, it is understood that when observed with scattered light, it is observed larger than the actual size of the foreign matter. (This is exactly the reason why the foreign matter inspection is performed by scattered light.) And the ratio is about 3 to 6 times in area ratio from FIG.
3 to √6 times.

In this case, the equation (3) becomes the following equation, and the above experimental results can be explained.

D = (0.6 / (√3 to √6)) · (λ / NA) = (0.24 to 0.35) · (λ / NA) (4) Also, on the reticle In the foreign matter inspection, the foreign matter diameter d to be detected
Is about 1/4 of the minimum size of the reticle, so the minimum size on the reticle is 2.5 μm (0.5 μm on the wafer for 5: 1 reduction transfer, which is 16 MDRAM phase). 0.6 μm, minimum size on reticle 1.5
In the case of μm (64MDRAM phase etc.), it is 0.4 μm.

Therefore, in order to detect a foreign matter of 0.4 μm by the detection optical system of NA = 0.4 obtained from the previous examination, λ = 660 to 46 is obtained from the following equation obtained by modifying the equation (4).
It can be seen that a light source having a wavelength shorter than 0 nm is required.

Λ = d · NA / (0.35-0.24) (5) Next, in this wavelength range, it is suitable for foreign matter inspection on a sample to be inspected such as a reticle on which a circuit pattern is formed. The selection of a different wavelength will be examined, but the principle of optically detecting a foreign substance, which is the premise of the selection, will be described.

The present invention has been made by paying attention to the fact that the circuit pattern of the reticle or the like is composed of vertical, horizontal, and diagonal straight lines and the intersections of the straight lines, that is, the corners of the circuit pattern. When the circuit pattern is irradiated with a laser beam or the like having good directivity at an incident angle i (i <90 °) from an oblique direction, the Fourier transform image of scattered light from the straight line portion of the circuit pattern is a circuit pattern in the illumination field. It is known that, regardless of the position, the light is condensed in a thin straight line at a specific position on the Fourier transform image plane, while the scattered light from the foreign matter is not biased to the specific position on the Fourier transform image plane. Therefore, as described above, a linear light-shielding plate, that is, a spatial filter is arranged at a specific position on the Fourier transform image plane to shield the scattered light from the linear portion of the circuit pattern and detect only the scattered light from the foreign matter. However, since scattered light from the corner portion of the circuit pattern and the fine structure portion in which the corner portion is continuous cannot be shielded, it is necessary to conduct an examination paying attention to the detection output of these scattered light. It will be described below in relation to the wavelength.

FIG. 7 is a graph showing the relationship between the light source wavelength and the scattered light intensity when the particle diameter d is 0.5 μm. From this graph, it is understood that if the detection light from the foreign matter is increased in order to facilitate the detection of the foreign matter, the detection should be performed by a light source with a short wavelength.

In this case, it should be noted that
The shorter wavelength also increases the scattered light from the circuit pattern. Even if the scattered light from foreign matter increases,
If the scattered light from the circuit pattern increases more, the improvement in the foreign matter detection performance cannot be expected. Therefore, in order to shorten the wavelength of foreign matter inspection on a sample with a circuit pattern, pay attention to the scattered light from the circuit pattern, and (discrimination ratio) = (output of detector that detected scattered light from foreign matter / circuit) It is necessary to make a study based on the discrimination ratio defined by the output of the detector that detects the scattered light from the pattern).

Therefore, experimental results by the inventor of measuring scattered light from various corners of the circuit pattern and scattered light from polystyrene standard particles as a model foreign substance at various wavelengths will be shown. FIG. 8 shows the measurement results when the wavelength is 830 nm, FIG. 9 shows the wavelength at 633 nm, FIG. 10 shows the wavelength at 544 nm, FIG. 11 shows the wavelength at 515 nm, and FIG. 12 shows the measurement result when the wavelength is 488 nm. The curve in the figure shows the change in detection output with respect to the standard particle size, and the scattered light detection output from each corner of the circuit pattern is plotted as ◯, and the shape of that corner is shown in the vicinity of ◯ (plan view). Indicated by. Further, the figure in which the corner portions are continuous shows the above-mentioned fine structure portion.

The scattered light detection output from the corner portion of the circuit pattern varies in accordance with each wavelength, but the detection performance at that wavelength is limited by the circuit pattern having the shape that produces the largest scattered light at that wavelength. It is a corner. Therefore, in each figure, among the scattered light from the corners of the circuit patterns of various shapes, standard particles that generate scattered light larger than the largest scattered light, that is, standard particles with a discrimination ratio of greater than 1, can be detected. It is shown as.

Since it is difficult to grasp the change in the detection performance depending on the wavelength as it is, the value of the corner portion of the circuit pattern that emitted the largest scattered light at each wavelength and the 0.5 μm standard particle having the smallest diameter in this measurement are used. FIG. 13 shows the relationship between the scattered light and the wavelength of the detection light source. In the wavelength range where the scattered light output from the 0.5 μm particles is larger than the scattered light from the circuit pattern, that is, in the wavelength range where the discrimination ratio is larger than 1, a simple device configuration is used only for comparing the scattered light detection outputs (binarization). It is possible to detect 0.5 μm particles. As is clear from FIG. 13, a wavelength of about 500 nm is measured at a wavelength of 500 nm.
There is a detectable region of 0.5 μm particles in the vicinity of nm.

Theoretically, if the discrimination ratio is larger than 1, foreign matter can be detected, but in an actual device, the influence of electrical and optical noise, vibration of the mechanical section, and even sensitivity variation of the detection system. Due to various factors, a margin is required between the level of scattered light from a foreign substance and the level of scattered light from a circuit pattern portion. The larger the margin, that is, the larger the discrimination ratio, the more stable the detection becomes. Therefore, FIG. 1 shows how the discrimination ratio changes depending on the wavelength of the detection light. As is clear from FIG. 1, 550n
The optimum wavelength exists near m.

As a light source in the vicinity of this, there is a green helium-neon laser (wavelength 543.5 nm) by 5s ₂ -2p ₁₀ transition of helium-neon gas. However, the green helium-neon laser currently has a low output (1 m
It is difficult to secure a sufficient amount of light because only the product of (W) is commercially available. Therefore, it is possible to use the green light (wavelength 514.5 nm) of the argon ion laser. At this wavelength, the effect as high as that of the green helium-neon laser light cannot be expected, but the red helium-neon laser light (wavelength 632.
It is clear from FIG. 1 that a discrimination ratio higher than 8 nm) is obtained and stable detection is possible. Further, with the green light of the argon ion laser, it is easy to obtain a light source with a large output. Its output is several tens of mW even with air cooling (several W with water cooling), and a large detection output can be obtained even when compared with the red helium-neon laser light.

Further, recently, a yag laser (wavelength 1064n) has been provided by a harmonic laser using a non-linear optical element.
m) large output as a second harmonic (several mW to several tens of m)
W) green light (wavelength 532 nm) can be obtained. Since the second harmonic of the YAG laser is close to the above-mentioned optimum wavelength (about 550 nm), it is considered to be most suitable for detecting a foreign substance.

As described above, according to the present invention, the wavelength of about 55 is used.
Oblique illumination with a 0 nm light source makes it possible to detect only foreign matter on a sample to be inspected on which a circuit pattern is formed, separately from the circuit pattern.

FIG. 14 is a diagram showing the structure of a foreign matter inspection apparatus according to the present invention. In the figure, 1 is an inspection stage unit, and the inspection stage unit 1 is a reticle 6 having a pellicle 7.
Is fixed to the upper surface by the fixing means 8 and is movable in the Z direction, and the reticle 6 is moved to the X stage via the Z stage 9.
X stage 10 to move in the same direction, and reticle 6 as well
Stage 11 for moving each stage of the Z stage 9, the X stage 10, and the Y stage 11, and a control system for detecting a focus position for detecting the Z direction position of the reticle 6. 13 and each of the stages 9 to 11 is controlled so that focusing can always be performed with a required accuracy during the inspection of the reticle 6.

The X stage 10 and the Y stage 11 are driven, and the reticle 6 is scanned with the laser light as shown in FIG. The scanning speed of the laser light can be set arbitrarily, but for example, the X stage 10 has a uniform acceleration time of about 0.2 seconds, a constant velocity motion of 4.0 seconds, and a uniform deceleration time of 0.2 seconds. And the stop time of about 0.2 seconds is formed so that the maximum speed is about 25 mm / second and the amplitude is 105 mm in a cycle of 1/2 cycle, and the Y stage 11 is equal to the acceleration time of the X stage 10 and the like. The reticle 6 is moved to 0.
If it is configured to move in steps of 5 mm in the Y direction, if 200 times are transferred during one inspection time, it is possible to transfer 100 mm in about 960 seconds.
A 100 mm square area can be scanned in about 960 seconds.

Further, the control system 13 for detecting the focal position may be one using an air micrometer or one for detecting the position by the laser interference method, or one having a structure for projecting a fringe pattern and detecting the contrast thereof. But it's okay. The coordinates X, Y, and Z are the directions shown in the figure.

2 is a first illumination system, 3 is a second illumination system,
Both are independent and consist of the same components. Reference numerals 21 and 31 denote laser light sources, the wavelength λ ₁ of the laser light source 21 is, for example, 514.5 nm, and the wavelength λ ₂ of the laser light source 31 is, for example, 532 nm, and the wavelengths λ ₁ and λ ₂ are different. Reference numerals 22 and 32 are condenser lenses, which condense the light beams emitted from the laser light sources 21 and 31, respectively, 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 larger than about 30 ° in order to avoid the objective lens 41 of the detection optical system 4 which will be described later, and in the case of the reticle 6 on which the pellicle 7 is mounted, the pellicle In order to avoid 7, the angle must be smaller than approximately 80 °, so approximately 30 ° <i
<80 °.

The light sources of the illumination systems 2 and 3 are approximately 550 nm.
Those having a wavelength of As a light source in the vicinity of this, there is a green helium-neon laser (wavelength 543.5 nm) by 5s ₂ -2p ₁₀ transition of helium-neon gas. However, since only green helium-neon laser products with a small output (about 1 mW) are currently on the market, it is difficult to secure a sufficient amount of light. Therefore,
Argon ion laser green light (wavelength 514.5 nm)
It is possible to use. At this wavelength, the effect of green helium-neon laser light cannot be expected, but
It is clear from FIG. 1 that a discrimination ratio higher than that of the conventionally used red helium-neon laser light (wavelength 632.8 nm) is obtained and stable detection is possible. Further, it is easy to obtain a light source having a large output with the green light of the argon ion laser. Its output is several tens of mW even with air cooling (several W with water cooling), and a large detection output can be obtained even when compared with the red helium-neon laser light.

Further, recently, a yag laser (wavelength 1064n) has been provided by a harmonic laser utilizing a non-linear optical element.
m) large output as a second harmonic (several mW to several tens of m)
W) green light (wavelength 532 nm) can be obtained. Since the second harmonic of the YAG laser is close to the above-mentioned optimum wavelength (about 550 nm), it is considered to be most suitable for detecting a foreign substance. As long as the light source has high brightness, a light source other than a laser such as a mercury lamp or a mercury xenon lamp can be used in the vicinity of 550 nm or 500 to 600 n.
A combination of filters for selecting the m wavelength range may be used.

FIG. 16 is a diagram showing a configuration example of the illumination system 2. In the figure, 21 is a laser light source. 223 is a concave lens, 224 is a cylindrical lens, 225 is a collimator lens, 226 is a condenser lens, and lenses 223 to
The condenser lens 22 is formed by 226. The laser light source 21 is arranged so as to have linearly polarized light having a magnetic field vector in the Y ′ direction (this state is called S-polarized light). For example, when the incident angle i is about 60 °, the reflectance on the glass substrate is about 5 times higher than that for P-polarized light (for example, Hiroshi Kubota, Applied Optics (Iwanami Zensho), page 144). ), It is possible to detect even smaller foreign matter. The illumination system 3 has the same configuration as the illumination system 2.

Then, in order to increase the illuminance of the illumination system 2, the numerical aperture NA of the focusing system is set to about 0.1 and the laser beam is set to about 10 μm.
Although the aperture has been narrowed down to m, the depth of focus is shortened to about 30 μm by this aperture, and it becomes impossible to focus on the entire inspection field 15 S (500 μm) shown in FIG. However, in this embodiment, as a countermeasure,
The cylindrical lens 224 can be tilted about the X ′ axis shown in FIG. 3 (FIG. 3 shows the already tilted state), and it becomes possible to focus on the entire area S of the inspection visual field 15 even if the incident angle i is 60 °, for example. When a one-dimensional solid-state image sensor is used for the detectors 51 and 551 of the signal processing system 5 described later, the inspection area of the inspection visual field 15 is the detectors 51 and 55.
Even if it becomes a straight line as in the case of 1, it becomes possible to illuminate the linear inspection region with a high illuminance and a uniform distribution.

Further, when the cylindrical lens 224 is tilted not only around the X ′ axis shown in FIG. 3 but also around the Y ′ axis, even when the incident angle i is 60 ° and the light is emitted from any direction, the inspection field of view is increased. High illuminance over the entire area S of 15
It is also possible to perform linear illumination with a uniform distribution.

Reference numeral 4 denotes a detection optical system. The detection optical system 4 is focused by an objective lens 41 facing the reticle 6, a viewing zone lens provided near the image forming position of the objective lens 41, that is, a field lens 43, and a field lens 43. Inspection field 1 of reticle 6 and mirror 42 for wavelength separation of the separated light flux
5, a spatial filter 44, 44 having a band-shaped light-shielding portion provided at the position of Fourier transform with respect to 5 and a transmitting portion outside thereof.
4, image forming lenses 45 and 445, and the inspection field 15 on the reticle 6 is detected by the detector 5 of the signal processing system 5 described later.
It is configured to form an image at 1,551. The field lens 43 has an upper focus position 46 on the objective lens 41.
Is imaged on the spatial filters 44, 444.

Reference numeral 5 is a signal processing system. The signal processing system 5 binarizes the outputs of the detectors 51 and 551 and the detectors 51 and 551, and first and second binarization circuits 52 and 552, and a logical product. It comprises a circuit 53, a microcomputer 54, and a display means 55.

The detectors 51 and 551 are formed by, for example, a charge transfer type one-dimensional solid-state image pickup device, and the X stage 1
The signal from the circuit pattern on the reticle 6 is detected while scanning 0, but in this case, if a foreign matter on the reticle 6 is present, the input signal level and the light intensity increase, so the detectors 51, 551. Is also formed to have a large output. As described above, the detectors 51, 551
The use of the one-dimensional solid-state image pickup device has an advantage that the detection visual field 15 can be widened while maintaining the resolution, but the present invention is not limited to this, and a two-dimensional one or a single device can be used. .

The binarization circuits 52 and 552 have preset threshold values for binarization, and the output values output from the detectors 51 and 551 are equal to or higher than the reflected light intensity corresponding to a foreign substance of a desired size. In the case of, the logic level "1" is output.

The AND circuit 53 is a binarization circuit 52, 552.
The signal from is taken in and the logical product of two signals is output. Further, the microcomputer 54 uses the AND circuit 53.
When it outputs a logic level "1", it is determined that "there is a foreign substance", and the position information of the X stage 10 and the Y stage 11 is calculated, and in the case of the detectors 51 and 551 which are not single elements, calculation is performed from the pixel position in that element. Information of foreign matter to be detected and detector 5
The detection output values of 1 and 551 are stored as foreign matter data, and the result is output to the display unit 55.

Next, the operation of the foreign substance inspection apparatus shown in FIG. 14 will be described with reference to FIGS.

FIG. 17 is a view showing the inspection situation of the reticle 6. In the figure, 70 is a foreign substance on the reticle 6, 81 is a linear portion of the circuit pattern 80, and 82 is a circuit pattern 80.
Is the corner section of.

When the illumination system 2 obliquely irradiates the reticle 6 and the generated scattered light is condensed by the objective lens 41, the circuit pattern 80 on the reticle 6 and the reticle 6 surface of the illumination system 2 shown in FIG. The angle pattern defined by the positional relationship with the projected image 60 on the
The diffracted light (a) of 0 ° pattern) appears as a band on the Fourier transform surface of the objective lens 41 as shown in FIG. Here, the type of the angle θ of the circuit pattern 80 is 0.
As shown in FIG. 17, the diffracted light (b) and (c) from the patterns with the angles θ of 45 ° and 90 ° are limited to the angle patterns of 45 °, 45 ° and 90 °. Since it does not enter the pupil, it does not affect the detection. On the other hand, since the scattered light from the foreign matter 70 has no directivity,
As shown in (e), it spreads over the entire Fourier transform surface.
Therefore, the spatial filters 44 and 444 having the band-shaped light-shielding portion and the light-transmitting portion outside the Fourier-transform surface are arranged to shield the diffracted light (a) from the 0 ° pattern shown in FIG. It is possible to detect the foreign matter 70 by discriminating it from the circuit pattern 80.

With this configuration, a detection optical system having a high numerical aperture NA can be realized for the first time, and when the numerical aperture NA is selected to be 0.5, the aperture area is about 20 times as large as that of the detection optical system having a low numerical aperture NA. You can also

However, the circuit pattern 8 shown in FIG.
The scattered light from the corner portion 82 of 0 cannot be sufficiently shielded by the linear spatial filters 44 and 444. For this reason, when detection is performed with a detection pixel of 10 × 20 μm ² as in the conventional method shown in FIG. 20B, scattered light from a plurality of corners 82 enters the pixel, and only foreign matter is detected. Can not be detected. Therefore, in this embodiment, FIG.
As shown in (c), the resolution of the pixels of the detector is increased to 2 × 2 μm ² , and the influence from the circuit pattern is eliminated as much as possible.
The foreign matter of 0.5 μm can be detected. Further, here, the pixel of the detector is set to 2 × 2 μm ² , but the reason for this is described below, and it is not necessarily required to be 2 × 2 μm ² .

In this case, the pixel size has only to be smaller than the pattern size L on the reticle 6. Therefore,
In the case of exposing a 0.8 μm process LSI with a stepper with a reduction ratio of 1/5, it is about 0.8 × 5 = 4 μ for a reticle.
m, 0.5 μm Process LSI: 0.5 × 5 =
It suffices to detect with a pixel smaller than 2.5 μm.

Further, in actuality, it may be further increased or decreased as long as it is a value capable of sufficiently reducing the influence from the corner portion 82.

Specifically, the minimum pattern size on the reticle 6 to be inspected is desirable. If the size is about the minimum pattern size, less than two corners 82 will be included in one pixel of the detectors 51 and 551, and this value is also obtained by the experiment (described later) shown in FIG. It is enough.

Further, specifically, the minimum dimension is 1.5 μm.
For a 64 MDRAM reticle, the pixel size of about 1 to 2 μm is desirable.

The above contents will be described again with reference to FIG.
When the corner portion 82 formed at the intersection of the circuit pattern 80 shown in FIG. 21A is viewed microscopically, it is composed of the corners 820 having continuous angles as shown in FIG. As shown in FIG. 19D, the diffracted light (d) from the corner 82 also tends to spread on the Fourier transform plane, and cannot be completely shielded by the spatial filters 44 and 444. Therefore, when the diffracted light from the plurality of corners 82 is incident on one of the detectors 51, 551, for example, the detector 51, the output V of the detector 51 increases and the detection of the foreign matter 70 cannot be performed. FIG. 22 shows this state, in which the detection output value 822 from the plurality of corner portions 82 becomes higher than the detection output value 821 from the single corner portion 82, and the dotted line 90 shown in FIG. It is shown that binarizing the level cannot detect the detection output value 701 from the foreign matter 70 separately.

As a measure against the inconvenience described with reference to FIG. 22, in this embodiment, the inspection visual field 15 on the reticle 6 is imaged on the detectors 51, 551 via the objective lens 41, the imaging lenses 45, 445 and the like. The detector 51,
By selecting the size of 551 and the imaging magnification, the detection visual field 15 on the surface of the reticle 6 is set to an arbitrary size (for example, 2 μm × 2 μm), and the simple detection optical system 4 allows the plurality of corners 82 to be used. The diffracted light of the detector 51,
551 and 551 are not simultaneously incident. However, even if the foreign matter of the conventional size can be detected, in the detection of the foreign matter of the submicron order, the separation detection from a part of the corner portion 82 is insufficient depending on the shape of the circuit pattern 80, and the LSI 23, the pattern 8 having a dimension on the order of micron, which is finer than the dimension 83 of the normal structural portion of the circuit pattern 80, is obtained by the high integration.
Since the diffracted light generated from No. 4 becomes more similar in behavior to the scattered light from the foreign matter 70, it becomes more difficult to detect the foreign matter 70 separately from the circuit pattern 80.

In this embodiment, foreign matter can be detected even with respect to the pattern 84 having a dimension on the order of micron as shown in FIG. 23 by taking the measures described below. FIG. 24 is an explanatory diagram thereof. In the figure, reference numerals 701 and 702 denote scattered light detection output values from the minute foreign matter 70 on the order of submicron, and 864, 874, and 8 respectively.
65, 875, 866, 876, 867, 877 is 0
Detection output values of the diffracted light from all the corners 82 formed by the respective circuit patterns of °, 45 °, and 90 °, 861,
Reference numerals 871, 862, 872, 863, and 873 denote detection output values of the diffracted light from the pattern 84 having dimensions on the order of microns, respectively. Of these, the detected output value 701,
861, 862, 863, 864, 865, 866, 8
67 indicates a detection output value by the illumination system 2, and detection output values 702, 871, 872, 873, 874, 875,
Reference numerals 876 and 877 indicate detection output values by the illumination system 3, for example, detection output values 861 and 871 are detection output values at the same position of the circuit pattern 80, and the detection output value 861 is a value by the illumination system 2. 871 is a value by the illumination system 3. Further, as can be seen from the figure, the foreign matter 70
Compared with the circuit pattern 80, the fluctuation of the detection output value of scattered light depending on the irradiation direction is smaller. The dotted line 91 indicates the threshold value of the detection output value.

As is clear from FIG. 24, the output of the diffracted light varies greatly depending on the irradiation direction even with the same circuit pattern, and the reticle 6 is shifted from the oblique direction in two opposite directions with a 180 ° shift. When illuminated, the output value of the diffracted light on either side is as shown by the ● mark in the figure.
It can be seen that it is always smaller than the output value from a submicron-order foreign material. Therefore, in this embodiment, the detection output values 861 and 871 from the same position on the surface of the reticle 6 are detected.
Etc. are separately detected by the detector 51 and the detector 551,
After adopting the smaller detection output value indicated by the mark ● and binarizing it by the binarizing circuit 52 and the binarizing circuit 552,
The logical product is obtained by the logical product circuit 53 so that only the foreign matter 70 of submicron order can be separated from the circuit pattern 80 and detected.

As shown in FIG. 24, the binarization circuits 52, 5
When the threshold value 91 is set to 52, the detection output values 701 and 702 of the foreign material 70 and the detection output values 861, 863, 874 and 875 of the circuit pattern are the values of the threshold value 91 or more. Since the binarization output is the output from only one of the binarization circuit 52 and the binarization circuit 552, it is not output from the AND circuit 53, and therefore only the foreign matter 70 is detected separately from the circuit pattern. be able to. Then, in addition to the position information of the X stage 10 and the Y stage 11 at the time of detection, when the detectors 51 and 551 are not single elements, the position information of the foreign matter 70 calculated from the pixel position in the element and the detector 51. , 551 detection output values are used as foreign object data by the microcomputer 5
4 is stored in the memory managed by the computer 4, and the stored contents are arithmetically processed and displayed on the display means 55 such as a CRT.

Next, an example of a missed foreign material in the prior art is shown in FIG. These foreign substances are the foreign substances whose dimensions should be detected. In this embodiment, a mechanism for overlooking according to these conventional techniques is examined, and a foreign matter inspection device having a novel structure is proposed.

The problem of the conventional device will be described with reference to FIG. In a foreign matter inspection apparatus that detects foreign matter on a reticle, a method of removing diffracted light from a circuit pattern formed on the reticle and detecting only scattered light from the foreign matter is an important point of the technology. Therefore, methods such as a method of analyzing the polarization state of scattered light and a method of comparing the outputs of a plurality of detectors have been developed and put into practical use. However, in order to avoid the influence of scattered light generated from the circuit pattern in any of them, a detection optical system with a small numerical aperture NA of about 0.1 is diagonally arranged to avoid scattered light from the circuit pattern. There is. In such a configuration, for the reason described later,
This causes a problem that it is easy to overlook an irregularly shaped foreign substance. Another problem is the pattern removal technology that has been used as an auxiliary in various inspection technologies in response to the miniaturization of circuit patterns. Many of these adopt a method of automatically lowering the detection sensitivity of the foreign matter detector when a circuit pattern is found during inspection. In such a method, there is a problem that foreign substances near the pattern edge are missed while reducing erroneous detection of the circuit pattern. However, as described below, this embodiment solves these two problems.

FIG. 27 is a diagram showing a state in which scattered light generated when a foreign substance is irradiated with laser light is observed from above, and FIG. 27 (a) shows a case of scattered light from a foreign substance having a diameter d of 1 μm. 27 (b) shows the case of scattered light from a foreign substance having a diameter d of 2 μm. As is clear from this figure, the scattered light from the foreign matter is directionally distributed. For this reason, in the conventional foreign matter inspection device with a low numerical aperture NA, if the detector is installed at an incorrect position, the scattered light generated from the foreign matter may enter the detection optical system with a low numerical aperture NA properly. Not to mention, oversight occurs. Moreover, the distribution of the scattered light differs depending on the size and shape of the foreign matter,
It is practically impossible to properly arrange the detection optical system having a low numerical aperture NA for all the foreign matters.

FIG. 28 shows a result of experimentally measuring this.
Shown in. The numerical aperture NA of the scattered light distribution when the foreign matter 70 is illuminated with a laser beam having an incident angle of 60 ° is low (NA≈0.1).
While changing the detection angle with the detection optical systems 1001 and 1002,
The level of scattered light from the foreign material 70 was measured and shown by a solid line.
As is apparent from this figure, at point A, the detection level exceeds the detection threshold value, whereas at point B, it does not exceed the detection threshold value and detection cannot be performed. Since the scattered light distribution of the foreign matter 70 is not constant, the detection optical system 1001,
The detection performance is not stable in a detection method using a detection optical system having a low numerical aperture NA such as 1002.

Therefore, in this embodiment, the detection light system 41 having a large aperture and a high numerical aperture NA effectively collects the scattered light from the foreign matter having various scattering distributions.

As shown in FIG. 29, the laser light source 21, the condenser lens 22, the objective lens 41, and the field lens 4 are used.
FIG. 30 shows the result of detecting the number of foreign particles 70 on the reticle 6 by the device including the spatial filter 44, the spatial filter 44, the imaging lens 45, and the detector 51. In FIG. 30, the vertical axis indicates the total amount of foreign matter detected by the five reticles, and the horizontal axis indicates the size of the detected foreign matter. Further, among the foreign substances, the foreign substances detected by the conventional technique are also shown.

Since the detection capability of the prior art was 0.8 μm, it can be understood that the detection capability of this embodiment is superior to the conventional detection capability in the region where the diameter d of the foreign matter is smaller than 1 μm. However, even in the region where the diameter d of the foreign matter is larger than 1 μm, the number of detected particles is significantly improved in this embodiment. The detection rate is about 10 times as high as that of the detection number in the conventional technique.

It is considered that this is because the detection optical system having a high numerical aperture NA used in this embodiment responds well to irregularly shaped foreign matter and stably detects scattered light from the foreign matter.

Next, the state of detection of foreign matter attached to the edge portion of the circuit pattern will be described. Figure 31
Shows the result of classifying the detected number shown in FIG. 30 according to the foreign matter adhesion position. The adhesion positions were classified into three regions, that is, the glass part (transmissive part), the chrome part (light-shielding part) of the reticle 6, and the edge part which is the boundary part between the two. Of these, the edge portion is most affected by foreign matter adhesion, and the foreign matter in the chrome portion does not affect the transfer as long as it remains on the chrome portion. Then, as is apparent from FIG. 31, the detection performance for the foreign matter at the edge portion, which most needs to be detected because it most affects the transfer, is improved.

By using the idea that the foreign matter on the chrome portion does not pose a problem, the configuration as shown in FIG. 32 is also possible. In this case, it is not possible to detect foreign matter on the chrome portion, but the glass portion that affects the transfer failure,
The scattered light from the foreign matter at the edge portion can be transmitted through the reticle 6 which is a transparent base material.

An advantage of this structure is that it can be applied to a reticle having a cross section as shown in FIG. In the reticle shown in FIG. 33, the phase shifter film 10 for improving the transfer resolution is provided between the circuit patterns 80 made of chromium.
03 is provided. Although the phase shifter film 1003 is transparent, it has a thickness several times that of the circuit pattern 80 (thickness of about 0.1 μm). Therefore, the diffracted light from the edge portion 1006 of the phase shifter film 1003 has the thickness of the circuit pattern 80. It becomes larger than the diffracted light from the edge part.

However, in the structure in which the detection system is provided below as shown in FIG. 32, the diffracted light generated from the phase shifter film 1003 is shielded by the circuit pattern 80 of the reticle 6 itself and does not enter the detection system. , Does not affect the detection of foreign matter.

Further, the purpose of this embodiment is to provide an edge portion 1006 of the phase shifter film 1003 arranged on the chromium portion.
This can be achieved by using the circuit pattern 80 to block the scattered light from the. Therefore, the illumination system 21 and the objective lens 41 need only be on the opposite sides of the reticle 6, and the configuration shown in FIG. 34 may be used.

However, since the phase shifter film 1003 is thick, in the case of oblique illumination, a portion 1007 that cannot be illuminated with the configuration of FIG. 34 is produced, and therefore the configuration shown in FIG. 32 is preferable.

In particular, in the array type detector,
If the detection / judgment of foreign matter is performed in pixel units, the following inconveniences occur. That is, in the case where the foreign matter is detected / determined with the pixel size of the detector of 2 × 2 μm ² , the foreign matter is detected over a plurality of (2-4) pixels as shown in FIG. Under the condition, the scattered light from the foreign matter is also dispersed to a plurality of pixels, and as a result, the detection output of one pixel is 1/2 to 1/4 (actually, due to the influence of crosstalk between detector pixels. It decreases to about 1/3), and the foreign matter detection rate decreases. Further, the positional relationship between the pixels of the detector and the minute foreign matter is very delicate due to its size, and changes with each inspection. In this case, even if the same sample is used, the results differ from test to test, and the reproducibility of detection decreases.

[0108] Therefore, as shown in FIG. 36 performs by reducing the detection pixels in 1 × 1 [mu] m ^2, electrically adding detection outputs of the four 1 × 1 [mu] m ² pixels adjacent each pixel, 2 ×
Simulate the detection output by 2 μm ² pixels. This is obtained by overlapping by 1 μm (a, b, c, d in the figure),
The maximum value (a in the figure) is used as a representative output of 2 × 2 μm ² pixels to detect the foreign matter (4 pixel addition processing). As a result, the fluctuation of the detection output from the same foreign matter is actually suppressed to ± 10%, and the detection reproducibility of 80% or more can be secured for all the foreign matter. Note that FIG. 30 shows the result when the 4-pixel addition process is performed (detection reproducibility of 80% or more).
Is. FIG. 37 shows an example of the detection reproducibility in the case where the 4-pixel addition process is not performed, but it is clear that the detection reproducibility cannot be sufficiently secured without the 4-pixel addition process.

FIG. 38 shows a block diagram of a specific example of the 4-pixel addition processing circuit. This is a one-dimensional image sensor in which 512 pixels when reduced to 1 μm are arranged. An output 2503 from an odd-numbered pixel and an output 2502 of an even-numbered pixel of the one-dimensional image sensor are separately output. This is an example of a (general) one-dimensional image sensor. 256-stage shift register 2501, 1-stage shift register 2504, and 1 pixel (1 μm reduced by adders 2505 to 2508).
4 pixels (2 × 2 pixels) shifted in 4 directions by m) are added, and the average value of each average value is obtained by the dividers 2509 to 2512. Then, the maximum value determination circuit 2513 calculates the maximum value in the four directions, and the detected value 25
It outputs as 14.

In this method, only foreign matter is made bright and visible by optical processing and detection is performed. Therefore, when the detected signal is larger than the set threshold value, "there is foreign matter".
It is possible to detect foreign matter by making a determination (binarization). However, the detection signal has variations in sensitivity characteristics (about ± 15%) for each pixel of the one-dimensional image sensor, and sensitivity unevenness (shading) due to the illuminance distribution of the illumination light source. As a result, as shown in FIG. 39, the size of the detection signal varies depending on the pixel (position in the Y direction) that detects even the same foreign matter, and it is impossible to stably detect the foreign matter by binarizing with the threshold value. is there.

For this reason, as shown in FIG.
In the standard sample 111 shown in FIG. 4, the shading caused by the above variation and the illuminance distribution of the illumination light source was measured in advance, and as shown in FIG. 40 (b), shading correction data obtained by calculating the reciprocal of this measurement data was obtained. Find, Fig. 40 (c)
As a result, the amplifier gain of the detector detection signal is changed for each pixel by this, the influence of shading is eliminated, and the foreign matter is detected. The standard sample 111 is placed on the inspection stage of FIG. 1 or installed in the vicinity of the inspection stage, but it is also possible to place it on the sample stage instead of the reticle only during shading measurement.

The standard sample 111 is required to have a uniform unevenness characteristic with a fine uneven surface, and a glass substrate having a fine processing mark formed by polishing a glass substrate or a thin film having fine unevenness (for example, aluminum is sputtered to form a substrate). The one with the film formed on it) is used. However, it is practically difficult to uniformly process the minute irregularities on the standard sample 111 with respect to pixels 1 × 1 μm ² . Therefore, the correction data is obtained from an average value obtained by repeating the shading measurement many times (for example, 1000 times).

Further, since scattered light from minute unevenness has unevenness of strength and intensity, a simple average value (for example, data obtained by repeating 1000 times divided by 1000) is too small to calculate. The accuracy of may decrease.
Under such conditions, divide the value by a fraction of the number of iterations.
(For example, it is 200 after 1000 times of repetition). Shading before correction shown in FIG.
Comparing with the correction data shown in (b), 50
It can be seen that the shading, which was present in about%, is corrected to 5% or less.

If the correction data is remeasured / updated for each inspection, the optical fluctuation component can be removed even if the illumination / detection system and the like are temporally unstable.

FIG. 41 shows a block diagram of a concrete example of the shading correction circuit. A / D the detected value of the one-dimensional image sensor
3212 converted value (here, 256 gradations, 8 bits)
To a subtraction circuit 3209 for subtracting the value of the dark current portion of the one-dimensional image pickup device from the memory 3206 controlled by the synchronization circuit 3205 for each pixel, and the shading correction magnification for each pixel controlled by the synchronization circuit 3205. A multiplication circuit 3210 that multiplies by the data from the memory 3207 and the detected value of the one-dimensional image sensor A /
A value 321 obtained by D conversion (here, 256 gradations and 8 bits)
The intermediate bit output circuit 3211 is configured to return the multiplication result, which is twice the number of bits (here, 16 bits) to the original number of bits (here, 8 bits). Note that this embodiment is an example in which correction is performed by a digital circuit.
Similar results can be obtained even if analog correction is performed before D conversion.

When the foreign matter determination is performed in pixel units of 2 × 2 μm ² , for example, when there is a foreign matter having a size of 2 μm or more, the number of pixels detecting the foreign matter is different from the actual number of foreign matter. Become. If one foreign matter of 10 μm exists, it will be detected with the number of pixels of (10 μm / 2 μm) ² = 25, and if you try to observe the detected foreign matter as it is, all 25 detection results will be obtained. It is necessary to check, which causes inconvenience.

Conventionally, the grouping processing function for checking the connection relation between the pixels in which the foreign matter is detected by software and judging that "one foreign matter is detected" when the pixels are adjacent to each other is I was avoiding the inconvenience. But,
Since this method requires software-like processing, a large amount of time is required for processing when there are a large number of detection signals (for example, about 10 minutes for 1000 detection signals), which causes a new inconvenience.

Therefore, in this embodiment, the entire inspection area is set to 1
Field of view that can be observed every time (for example, 32 × 32μ
m ² ) blocks, and all detection signals in the same block are determined as the same foreign matter (block processing). As a result, even a large foreign matter can be observed and confirmed within a visual field range at one time regardless of its shape.

The block process is a simple grouping process in terms of function, but has a feature that it can be easily implemented as hardware. In this embodiment, the block processing is implemented in hardware so that the processing is performed in real time, and the throughput of the apparatus including the inspection time is significantly increased (detection signal 100
In the case of 0, it can be improved to 2/3 or less as compared with the conventional one.

FIG. 42 shows a block diagram of a concrete example of the block processing circuit. In the figure, 2901 to 2904 are latch circuits, 2905 is a comparison circuit, 2906 is a counter, 2
Reference numeral 907 is a comparison circuit, 2908 to 2911 are comparison circuits, 2
912 to 2914 are counters, 2915 is a latch circuit,
2916 to 2918 are addition circuits, 2919 is a comparison circuit,
Reference numeral 2920 is a selection circuit, 2921 to 2924 are shift registers, 2925 and 2926 are counters, and 2927 is a memory. In the case of the example of FIG. 42, not only the determination of the same foreign matter but also the number of detection signals that are the basis of the determination can be classified and counted according to a preset large / medium / small threshold value. The maximum value of the detection signal in the block can also be known. From these data, it is devised so that it is possible to estimate the approximate size of a foreign substance and the situation in which a plurality of foreign substances are contained in the same block. A circuit for outputting an inspection stop signal when the number of signals for detecting foreign matter reaches a preset number is also incorporated.

FIG. 43 shows an example of the relationship between the shading correction circuit, the 4-pixel addition processing circuit, and the block processing circuit. In the figure, 301 is a detector signal, 302 is an A / D converter, 303 is a shading correction circuit, 304 is a 4-pixel addition processing circuit, 305 is a block processing circuit, and 306 is a particle inspection result.

[0122]

As described above, in the foreign matter inspection apparatus according to the present invention, the scattered light from a minute foreign matter and the diffracted light from the corner portion of the circuit pattern can be easily distinguished from each other. The foreign matter can be detected separately from the circuit pattern. As described above, the effect of the present invention is remarkable.

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between a light source wavelength and a discrimination ratio.

FIG. 2 is a graph showing the relationship between πd / λ and scattered light intensity.

FIG. 3 is a perspective view showing a state in which scattered light from a foreign matter is detected by using a detection optical system having a high numerical aperture NA.

FIG. 4 is a diagram showing directions of diffracted light from a foreign substance.

FIG. 5 is a diagram showing a definition of a numerical aperture NA of an optical system.

FIG. 6 is a graph showing the relationship between the particle diameter d and the scattered light cross-sectional area.

FIG. 7 is a graph showing a relationship between a light source wavelength and a scattered light cross section.

FIG. 8 is a graph showing an output of a detector that detects scattered light from a corner portion of a standard particle and a circuit pattern when a light source wavelength is 830 nm.

FIG. 9 is a graph showing the output of the detector that detected the scattered light from the corners of the standard particles and the circuit pattern when the light source wavelength was 633 nm.

FIG. 10 is a graph showing an output of a detector that detects scattered light from a corner portion of a standard particle and a circuit pattern when a light source wavelength is 544 nm.

FIG. 11 is a graph showing an output of a detector that detects scattered light from a corner portion of a standard particle and a circuit pattern when a light source wavelength is 515 nm.

FIG. 12 is a graph showing an output of a detector that detects scattered light from a corner portion of a standard particle and a circuit pattern when a light source wavelength is 488 nm.

FIG. 13 is a graph showing an output of a detector that detects scattered light from 0.5 μm standard particles and a corner portion of a circuit pattern, with respect to a light source wavelength.

FIG. 14 is a diagram showing a foreign matter inspection device according to the present invention.

15 is a diagram showing a reticle to be inspected by the foreign substance inspection apparatus shown in FIG.

16 is a diagram showing a part of the foreign matter inspection device shown in FIG.

17 is a perspective view showing an inspection state of a reticle by the foreign substance inspection apparatus shown in FIG.

18 is a plan view illustrating an angle pattern of a circuit pattern of a reticle to be inspected by the foreign substance inspection device shown in FIG.

FIG. 19 is a diagram showing a distribution state of scattered light and diffracted light on a Fourier transform surface.

20 is a diagram for explaining a method of processing foreign matter data of the foreign matter inspection apparatus shown in FIG.

21A is a diagram showing a corner portion of a circuit pattern of a reticle to be inspected by the foreign substance inspection apparatus shown in FIG. 14, and FIG. 21B is a detailed view of portion A of FIG.

FIG. 22 is a graph illustrating the relationship between the detection output value of scattered light from a foreign substance and the detection output value of scattered light from a circuit pattern.

FIG. 23 is a diagram showing a circuit pattern having a fine structure pattern.

FIG. 24 is a graph showing an output value level of a detection signal detected from a foreign matter and a corner portion of a circuit pattern.

FIG. 25 is a diagram showing an example of a foreign substance missed by the conventional technique.

FIG. 26 is a diagram for explaining a problem of the conventional technique.

FIG. 27 is a diagram showing a distribution state of scattered light on a Fourier transform surface.

FIG. 28 is a diagram for explaining a problem of the conventional technique.

29 is a diagram showing a part of the foreign matter inspection device shown in FIG.

FIG. 30 is a graph showing the relationship between the size of a detected foreign substance and the number of detected foreign substances.

FIG. 31 is a graph showing the relationship between the size of detected foreign matter and the number of detected foreign matter.

FIG. 32 is a diagram showing a part of another foreign matter inspection apparatus according to the present invention.

FIG. 33 is a diagram showing scattered light / diffracted light from a reticle with a phase shifter film.

FIG. 34 is a diagram showing a part of another foreign matter inspection apparatus according to the present invention.

FIG. 35 is a diagram showing a state in which a foreign substance is detected by 2 × 2 μm ² pixels.

FIG. 26 is a diagram showing a state in which foreign matter is detected by 1 × 1 μm ² pixels.

FIG. 37 is a graph showing the relationship between the size of detected foreign matter and the number of detected foreign matter.

FIG. 38 is a block diagram showing a 4-pixel addition processing circuit.

FIG. 39 is a graph for explaining the influence of shading on foreign matter detection.

FIG. 40 is a graph for explaining the principle of shading.

FIG. 41 is a block diagram showing a shading correction circuit.

FIG. 42 is a block diagram showing a block processing circuit.

FIG. 43 is a block diagram showing a relationship among a shading correction circuit, a 4-pixel addition processing circuit, and a block processing circuit.

[Explanation of symbols]

 2 ... First illumination system 3 ... Second illumination system 4 ... Detection optical system 5 ... Signal processing system 6 ... Reticle 44 ... Spatial filter 444 ... Spatial filter 51 ... Detector 551 ... Detector 52 ... First binary value Circuit 552 ... second binarization circuit 70 ... foreign matter 80 ... circuit pattern

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] July 29, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Change

[Correction content]

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between a light source wavelength and a discrimination ratio.

FIG. 2 is a graph showing the relationship between πd / λ and scattered light intensity.

FIG. 3 is a perspective view showing a state in which scattered light from a foreign matter is detected by using a detection optical system having a high numerical aperture NA.

FIG. 4 is a diagram showing directions of diffracted light from a foreign substance.

FIG. 5 is a diagram showing a definition of a numerical aperture NA of an optical system.

FIG. 6 is a graph showing the relationship between the particle diameter d and the scattered light cross-sectional area.

FIG. 7 is a graph showing a relationship between a light source wavelength and a scattered light cross section.

FIG. 8 is a graph showing an output of a detector that detects scattered light from a corner portion of a standard particle and a circuit pattern when a light source wavelength is 830 nm.

FIG. 9 is a graph showing the output of the detector that detected the scattered light from the corners of the standard particles and the circuit pattern when the light source wavelength was 633 nm.

FIG. 10 is a graph showing an output of a detector that detects scattered light from a corner portion of a standard particle and a circuit pattern when a light source wavelength is 544 nm.

FIG. 11 is a graph showing an output of a detector that detects scattered light from a corner portion of a standard particle and a circuit pattern when a light source wavelength is 515 nm.

FIG. 12 is a graph showing an output of a detector that detects scattered light from a corner portion of a standard particle and a circuit pattern when a light source wavelength is 488 nm.

FIG. 13 is a graph showing an output of a detector that detects scattered light from 0.5 μm standard particles and a corner portion of a circuit pattern, with respect to a light source wavelength.

FIG. 14 is a diagram showing a foreign matter inspection device according to the present invention.

15 is a diagram showing a reticle to be inspected by the foreign substance inspection apparatus shown in FIG.

16 is a diagram showing a part of the foreign matter inspection device shown in FIG.

17 is a perspective view showing an inspection state of a reticle by the foreign substance inspection apparatus shown in FIG.

18 is a plan view illustrating an angle pattern of a circuit pattern of a reticle to be inspected by the foreign substance inspection device shown in FIG.

FIG. 19 is a diagram showing a distribution state of scattered light and diffracted light on a Fourier transform surface.

20 is a diagram for explaining a method of processing foreign matter data of the foreign matter inspection apparatus shown in FIG.

21A is a diagram showing a corner portion of a circuit pattern of a reticle to be inspected by the foreign substance inspection apparatus shown in FIG. 14, and FIG. 21B is a detailed view of portion A of FIG.

FIG. 22 is a graph illustrating the relationship between the detection output value of scattered light from a foreign substance and the detection output value of scattered light from a circuit pattern.

FIG. 23 is a diagram showing a circuit pattern having a fine structure pattern.

FIG. 24 is a graph showing an output value level of a detection signal detected from a foreign matter and a corner portion of a circuit pattern.

FIG. 25 is a diagram showing an example of a foreign substance missed by the conventional technique.

FIG. 26 is a diagram for explaining a problem of the conventional technique.

FIG. 27 is a diagram showing a distribution state of scattered light on a Fourier transform surface.

FIG. 28 is a diagram for explaining a problem of the conventional technique.

29 is a diagram showing a part of the foreign matter inspection device shown in FIG.

FIG. 30 is a graph showing the relationship between the size of a detected foreign substance and the number of detected foreign substances.

FIG. 31 is a graph showing the relationship between the size of detected foreign matter and the number of detected foreign matter.

FIG. 32 is a diagram showing a part of another foreign matter inspection apparatus according to the present invention.

FIG. 33 is a diagram showing scattered light / diffracted light from a reticle with a phase shifter film.

FIG. 34 is a diagram showing a part of another foreign matter inspection apparatus according to the present invention.

FIG. 35 is a diagram showing a state in which a foreign substance is detected by 2 × 2 μm ² pixels.

FIG. 36 is a diagram showing a state in which foreign matter is detected in 1 × 1 μm ² pixels.

FIG. 37 is a graph showing the relationship between the size of detected foreign matter and the number of detected foreign matter.

FIG. 38 is a block diagram showing a 4-pixel addition processing circuit.

FIG. 39 is a graph for explaining the influence of shading on foreign matter detection.

FIG. 40 is a graph for explaining the principle of shading.

FIG. 41 is a block diagram showing a shading correction circuit.

FIG. 42 is a block diagram showing a block processing circuit.

FIG. 43 is a block diagram showing a relationship among a shading correction circuit, a 4-pixel addition processing circuit, and a block processing circuit.

[Description of Codes] 2 ... First illumination system 3 ... Second illumination system 4 ... Detection optical system 5 ... Signal processing system 6 ... Reticle 44 ... Spatial filter 444 ... Spatial filter 51 ... Detector 551 ... Detector 52 ... First binarization circuit 552 ... Second binarization circuit 70 ... Foreign matter 80 ... Circuit pattern

Front page continuation (51) Int.Cl. ⁵ Identification code Office reference number FI Technical display location G06F 15/64 C 9073-5L H01L 21/027 21/66 J 8406-4M

Claims (8)

[Claims] 1. A foreign matter inspection apparatus for detecting a foreign matter adhered on an inspected sample having a circuit pattern, and an illumination system for obliquely irradiating the inspected sample with light having a wavelength of 500 to 600 nm, and the inspected object. A detection optical system that collects scattered light and diffracted light generated from the sample and shields the diffracted light from the linear portion of the circuit pattern by a spatial filter provided on the Fourier transform surface, and forms an image on the detector. And a signal processing system for binarizing the output of the detector by a binarizing circuit having a threshold value set therein and computing and displaying the foreign particle data on the sample to be inspected. 2. The foreign matter inspection apparatus according to claim 1, wherein the wavelength of the light is 550 nm. 3. The foreign matter inspection apparatus according to claim 1, wherein the wavelength of the light is 543.5 nm. 4. The foreign matter inspection apparatus according to claim 1, wherein the wavelength of the light is 514.5 nm. 5. The foreign matter inspection apparatus according to claim 1, wherein the wavelength of the light is 532 nm. 6. The foreign matter inspection apparatus according to claim 1, wherein the illumination system emits light having a wavelength band within a range of 500 to 600 nm. 7. The foreign matter inspection apparatus according to claim 1, wherein the illumination system irradiates light of a single wavelength or a plurality of wavelengths within a range of 500 to 600 nm. 8. NA when the minimum diameter of the foreign matter to be detected by the illumination system is d and the numerical aperture of the detection optical system is NA.
The foreign matter inspection apparatus according to claim 1, wherein light having a wavelength of d / 0.35 to NA · d / 0.24 is irradiated.