JP3241403B2 - Foreign matter inspection apparatus and method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foreign matter inspection apparatus and a foreign matter inspection method for detecting foreign matter adhering to a substrate between circuit patterns of a reticle, a photomask or the like (hereinafter referred to as a reticle or the like), and more particularly, to a foreign matter inspection method. A foreign substance inspection apparatus, which is an inspection performed before transfer, and detects, with a simple configuration, fine foreign substances on the order of submicrons on a reticle having a phase shift film with an improved transfer resolution, such as the reticle. And its method.

[0002]

BACKGROUND ART LSI is had in the exposure step of a reticle or the like which is used to manufacture a printed circuit board, although the circuit pattern such as a reticle is inspected prior to baking transferred onto the wafer, the circuit pattern on the For example, even when a minute foreign matter of the order of microns exists, the circuit pattern is not normally transferred to the wafer due to the foreign matter, so that there is a problem that the total number of LSI chips becomes defective.
This problem has become more evident with the recent increase in the degree of integration of LSIs, and the presence of even smaller sub-micron-order foreign substances has become unacceptable.

In order to prevent the above-mentioned transfer failure, foreign substance inspection before the exposure step is indispensable, and various foreign substance inspection techniques have been conventionally provided for management of a reticle and the like. A method of irradiating obliquely with a light source having good directivity such as laser light and detecting scattered light generated from a foreign substance is advantageous and generally used in terms of inspection speed and sensitivity. However, in the above inspection method, since diffracted light is also generated from the edge portion of a circuit pattern such as a reticle, a device for discriminating and detecting only a foreign substance from the diffracted light is required. The technology for that is as follows. It is open to the public.

The first method is disclosed in, for example, JP-A-54-10139.
No. 0, a linearly polarized laser,
Means for irradiating the laser beam from the diagonal at a specific incident angle, in the foreign matter inspection apparatus characterized by comprising an oblique imaging optical system using a polarizing plate and lens, when irradiated with linearly polarized light, By utilizing the fact that the polarization direction of the light is different between the diffracted light from the circuit pattern and the scattered light from the foreign material, only the foreign material is shined and detected.

[0005] As two, a means for irradiating the sample to be inspected with laser light and scanning the same, and provided above the sample to be inspected so that the irradiation point of the laser light and the converging point surface substantially coincide with each other; A first lens that collects the scattered light of the laser light, and a light-shielding plate that is provided on the Fourier transform surface of the first lens and that shields regular diffracted light from the circuit pattern of the test sample,
A second lens for performing inverse Fourier transform of scattered light from a foreign substance obtained through the light shielding plate, and a light shielding unit provided at an image forming point of the second lens for shielding scattered light from a point other than the laser light irradiation point on the sample to be inspected. There has been disclosed a foreign matter inspection apparatus including a slit and a light receiver for receiving scattered light from a foreign matter passing through the slit (for example, Japanese Patent Application Laid-Open No. S59-65428).
Patent Publication, JP-A-1-117024 and JP-A-1-117024
153943). This device focuses on the fact that a circuit pattern is generally formed in the same direction within the field of view, or a combination of a few directions, and the diffracted light by the circuit pattern in this direction is set on the Fourier transform plane. This is intended to emphasize and detect only the scattered light from the foreign matter by removing the light with the spatial filter.

The third method is disclosed, for example, in Japanese Patent Application Laid-Open No. 57-8054.
As described in Japanese Patent Laid-Open Publication No. 6-62, attention is paid to the fact that diffracted light generated at the edge of a circuit pattern has directivity, but scattered light due to a foreign substance has no directivity. This is a configuration in which foreign objects are distinguished by taking the logical product of the respective detection outputs of the detector.

The fourth method uses a phenomenon that diffracted light from the edge of a circuit pattern concentrates only in a specific direction, but scatters from a foreign substance in all directions. A container is arranged to discriminate foreign substances (for example, JP-A-60-154634 and JP-A-60-154635).

The fifth problem is that when an array detector such as a one-dimensional solid-state image pickup device is used, foreign matter is detected across each pixel constituting the array, and a plurality of outputs from the foreign matter are detected. Are distributed and detected. As a result, the output from the detector will be small by the amount of dispersion and foreign objects may be missed. As an invention for avoiding this, Japanese Patent Application Laid-Open No. 61-104242 discloses a method in which the array of detectors is inclined with respect to the scanning direction of a sample table. Japanese Patent Application Laid-Open No. 61-104659 describes a method using an array detector having a special shape and arrangement.

As the sixth problem, unevenness and fluctuation of illumination affect reproducibility and accuracy of detection.
Japanese Patent Application No. 0-38827 describes an invention in which the intensity of scattered light is automatically calibrated using a standard sample which has been measured in advance.

Further, Japanese Patent Application Laid-Open No.
Japanese Patent Publication No. 2549 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. In addition, as a method and an apparatus related to the minute foreign matter inspection, a Schlieren method, a phase contrast microscope,
Techniques related to diffraction images of light sources of finite size are described in, for example, Hiroshi Kubota, Applied Optics (Iwanami Zensho), pp. 129-
It is described on page 136.

[0011]

As described above, as foreign matter to be detected becomes smaller, an increase in oversight of foreign matter affecting LSI manufacturing has become a problem. In the first prior art (for example, Japanese Patent Application Laid-Open No. 54-101390), the polarization direction of scattered light
Since the difference from the polarization direction of the diffracted light from the circuit pattern edge becomes small, there is a problem that foreign matter cannot be discriminated and detected.

The second prior art (for example, JP-A-59-65428, JP-A-1-117024 and JP-A-1-153943) discloses a circuit in which scattered light from a foreign substance is blocked by a light-shielding plate. It separates from the diffracted light from the pattern and detects only the scattered light from the foreign matter by the slit. It has a feature that the detecting mechanism is simplified because the foreign matter is detected by a simple binarization method. The diffracted light from the crossing portion has a small tendency to be deviated to a specific position like the diffracted light from the linear portion, and the spatial light cannot completely block the diffracted light from the crossing portion of the circuit pattern. In addition, since the diffracted light generated from the circuit pattern having the micron-order fine structure pattern accompanying the recent high integration of the LSI has a similar behavior to the scattered light from the foreign substance, the above tendency is further strengthened.
It is practically difficult to detect a foreign substance separately from a circuit pattern by a simple binarization method, which has been a problem.

The above-mentioned prior art 3 (for example,
80546) and the prior art 4 (for example, JP-A-60-154634 and JP-A-60-154).
154635), it is difficult to employ an optical system having a sufficient light-collecting ability due to the configuration of the device, and it is practically difficult to detect weak scattered light generated from minute foreign matter. Had a serious problem.

Further, in each device of the prior art No. 5 (for example, JP-A-61-104244 and JP-A-104242), a special detector is specially manufactured due to its configuration, However, there is a problem in that a complicated optical system needs to be configured, and the cost increases in practical use. Further, the aforementioned prior art 6 (for example, Japanese Patent Application Laid-Open No. 60-0388).
No. 27) has a drawback in that it is compatible with an array detector suitable for high-speed detection and has a configuration accuracy corresponding to detection of minute foreign matter. Further, in the device of the prior art 7 (for example, JP-A-56-132544), since only one point of a large foreign matter is represented, there is a problem that the shape of a particularly long and thin foreign matter cannot be accurately recognized.

Also, in order to improve the transfer resolution of a circuit pattern on a reticle formed of a metal thin film of chromium or the like, a transparent or translucent phase shift film or a phase shifter between circuit patterns on the reticle has recently been used. Reticles having a thin film (generally having a thickness of an odd multiple of half the wavelength of the exposure light source) have been developed. This film is transparent or translucent, but the circuit pattern (about 0.1μm thickness)
Diffraction light from the edge of the film is several times to several tens times larger than the diffraction light from the edge of the conventional circuit pattern. In addition, there is a problem that the detection sensitivity of foreign substances is significantly reduced.

An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a substrate sample (such as a reticle) having a circuit pattern formed on a transparent or translucent substrate, especially a phase shift film for improving the transfer resolution. Submicron-order fine foreign matter adhering between circuit patterns such as reticles having
An object of the present invention is to provide a foreign matter inspection apparatus and a method thereof, which can be easily and stably made highly sensitive with a simple optical configuration and can be separated and detected from the edge of a circuit pattern.

[0017]

In order to achieve the above-mentioned object, the present invention relates to a substrate sample having a circuit pattern formed on a transparent or translucent substrate, the foreign matter existing between the circuit patterns on the substrate. A foreign matter inspection device for detecting laser light, and irradiates the surface of the substrate sample on which a circuit pattern is formed, by condensing laser light from a direction inclined with respect to a vertical direction from the surface side. Front side
The oblique illumination optical system provided in the above, the laser light condensed and irradiated from the surface side by the oblique illumination optical system, generated from foreign matter existing between the circuit patterns on the substrate, Emitted to the back side through the substrate
An objective lens having an optical axis substantially perpendicular to foreign matter scattered light and resulting from the edge of the circuit pattern for condensing the edge scattered light is emitted to the back surface side passes through the substrate to be,
A spatial filter provided on a Fourier transform surface to block edge scattered light condensed by the objective lens, and an array type detector that receives foreign matter scattered light obtained through the spatial filter, converts the foreign matter scattered light into a detection signal, and outputs the detection signal. A detection optical system provided on the back surface side provided, and a circuit on the front surface of the substrate sample which is determined by a determination threshold value with respect to a detection signal output from an array type detector of the detection optical system. A foreign matter inspection apparatus and method including a signal processing circuit for detecting foreign matter attached between patterns.

The present invention also relates to a foreign substance inspection apparatus for detecting a foreign substance existing between the circuit patterns on the substrate in a substrate sample having a circuit pattern formed on a transparent or translucent substrate. With respect to the surface of the sample on which the circuit pattern is formed, from the back side of the surface,
An oblique illumination optical system provided on the back side for converging laser light from the direction inclined with respect to the vertical direction and transmitting and irradiating the substrate with the oblique illumination optical system, and the oblique illumination optical system The foreign matter scattered light emitted from the foreign matter existing between the circuit patterns on the substrate and emitted to the front side and the circuit pattern are emitted by the laser light condensed from the rear surface side and transmitted through the substrate. From the edge of the surface
Substantially perpendicular to the objective lens having an optical axis, resulting provided on the Fourier transform plane through the spatial filter and spatial filter for blocking edge scattered light is condensed by the objective lens for condensing the emitted are edge scattered light A detection optical system provided on the front side, which is provided with an array type detector for receiving the foreign matter scattered light to be converted into a detection signal and outputting the detection signal, and output from the array type detector of the detection optical system. A signal processing circuit for detecting a foreign substance attached between circuit patterns on the surface of the substrate sample by determining the detection signal with a determination threshold value .
And its method .

Further, the present invention provides the above foreign matter inspection apparatus and
In this method , the substrate sample is a reticle with a phase shift film.

The detection optical system has a numerical aperture (NA) of 0.4 to 0.6. Further, the signal processing system includes a circuit for correcting the detection value of the detector in accordance with the uneven illumination, a circuit for obtaining the sum of the detection values of the 2 × 2 pixels, and a shift of one pixel in four directions around the detector pixel. The circuit includes a circuit for obtaining the maximum value of the four added values, and a circuit for storing the detection result in a memory obtained by dividing the sample into blocks of several hundred pixels.

[0021]

[Action] Wolf, "Principles of
According to documents such as Optics “pp. 647-664”, when fine particles become as large as the wavelength of illumination light, scattered light from foreign matter has a sharp distribution without being uniform. In the present invention, attention has been paid to the fact that the above-mentioned oversight of foreign substances has increased due to the distribution of scattered light from these fine particles, which is conventionally caused by the numerical aperture (NA) of a detection optical system. Not only was not mentioned, but it was considered that detection of foreign matter was possible even when the detection optical system could not resolve the foreign matter. As shown, the scattered light from the minute foreign matter has an irregular directivity, and may not be detected by the detection optical system with a small numerical aperture.
As a result, it is considered that the detection of the foreign matter is overlooked.

That is, according to the concept of the present invention, it is clear that the detection optical system having the resolution of the prior art "can detect minute foreign matter in some cases" and not "can stably detect it." Became. In order to achieve the goal of “detection of foreign matter”, it has been found that a resolution sufficient to resolve the size of the foreign matter to be detected is necessary. The process of the study is described below.

The physics of light scattering is actually quite complex. The simplest problem, when a single sphere floating in space was irradiated with a plane wave, was the Gus in 1908.
Analyzed for the first time by tav Mie. The solution known as Mie's theory is a summation series of mathematical functions called spherical harmonics, but they are not mentioned because they depart from the subject 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 processes such as reflection, refraction, absorption, and diffraction. FIG. 19 shows the intensity of scattered light from a spherical foreign substance (particle).

FIG . 19 shows the theoretical value of the intensity of the scattered light from the foreign matter as a dimensionless number πD based on the wavelength λ of the laser beam and the particle diameter D of the foreign matter.
FIG. 7 is a diagram illustrating / λ, in which the logical value of Mie scattering is modified in the case of particles adhered to a substrate as in the application example of the present invention. The horizontal axis is the wavelength λ of the detection light (for example, 550 nm), and d is a dimensionless number using the diameter of the detected foreign matter. Here, a region where πd / λ is generally smaller than 4 (λ = 5
Foreign matter smaller than d = 0.7 μm at 50 nm) is particularly called a Rayleigh scattering region, and the scattered light from the foreign matter rapidly decreases in inverse proportion to the sixth power of the diameter. Therefore,
In detecting foreign matter in this region, it is necessary to pay sufficient attention to the sensitivity of the detector. In a region where πd / λ is approximately greater than 4, the scattered light is scattered in a directional manner according to the theory of diffraction.

The situation is as shown in FIG.
FIG. 12 is a diagram in which scattered light from a foreign substance is detected using the high NA optical system according to the present invention. In order to detect a foreign substance in this area, the scattered light from the foreign substance has a distribution, Must be determined by paying attention to the distribution. FIG.
FIG. 4 is an explanatory diagram showing directions of diffracted light from a foreign substance. FIG. 20 shows directions of diffracted light when laser illumination 2221 is performed on foreign matter 70 on reticle 6. The diffracted lights continue as 0-order diffracted light 2222, one-dimensional diffracted light 2223, and two-dimensional diffracted light separated by an angle θ.

The zero-order diffracted light 2222 is applied to a laser illumination 222.
Detecting the scattered light of the foreign matter, which is the first regular reflected light, means detecting the first or higher order diffracted light. Here, θ is obtained from the equation of the diffracted light as d ₀ · sin θ = λ. As for d ₀ , various definitions such as a diameter, a width, a length, or an average value of diameters can be considered for amorphous foreign matter.
However, since the following discussion holds regardless of the value of d ₀ ,
Neither of the above definitions affects the results.
Therefore, it is assumed here that d ₀ = d, that is, d ₀ is the particle diameter.

The required NA of the detection optical system is determined for the most severe case of πd / λ = 4.

[0028]

(Equation 1) Becomes This means that the gap of the diffracted light is at most 52 °. Therefore, if a detection optical system having an opening of 52 ° or more is used, at least only the first-order diffracted light can be detected, and the foreign matter is not overlooked.

FIG . 21 is an explanatory diagram showing the definition of the NA of the optical system. In FIG. 21 , NA = sin (θ / 2)
(N: refractive index of optical path, n ≒ 1 in air), the NA of the detection system objective lens 41 is obtained, and NA = 1 · sin (52 °)
/2)=0.44. Therefore, the scattered light from the foreign matter can be detected without missing by the detection system having the NA larger than about 0.44. In this case, the larger the NA, the more room for detection, and the better the detection of foreign matter in the Rayleigh region. Conversely, even when NA ≧ 0.44 is not satisfied, NA =
If it is about 0.4, the diffracted light has a certain width,
In practice, foreign matter can be detected. Conversely, NA is set to 0.5
If it is larger, the scattered light from the circuit pattern will enter the detection system for the reason described later, which impedes the requirement to detect only the scattered light from the foreign matter, and reduces the merit of increasing the NA. For this reason, NAs of about 0.4 to 0.6 rank are practically appropriate NAs.

Next, detection of foreign matter in the Rayleigh region will be described. As described above, the detection optical system having the resolution of the related art "may detect a minute foreign substance."
It is not "stable detection."
In order to achieve the goal of “detection of foreign matter”, a resolution that can resolve the size of the foreign matter to be detected is required. The present invention has a detection optical system having a numerical aperture (NA) enough to resolve the foreign matter to be detected. Specifically, it is calculated by the following equation (1). d = 0.6 (λ / NA) (1) An optical system having a value substantially close to this NA is desirable. Here, d is the size of the foreign matter to be detected, λ is the wavelength of the illumination light, N
A is the numerical aperture. If the NA of the detection system cannot be set to satisfy Expression (1), it is necessary to shorten Expression λ of the illumination system and satisfy Expression (1).

That is, in the detection optical system for inspecting foreign matter, it has not conventionally been considered that a resolving power for resolving foreign matter is necessary. He stands on a new idea that an optical system is necessary. However, the coefficient of equation (1) does not need to be as large as a value for calculating a general resolution of 0.6, and according to an experiment performed by the inventor of the present invention,
In the range of 0.24 to 0.6, the required foreign substance detection performance is exhibited.

Next, the reason will be described. FIG.
FIG. 3 is a diagram showing a scattering cross-sectional area proportional to the intensity of scattered light from a foreign substance with respect to the diameter of the foreign substance. In FIG. 22 , the abscissa indicates the particle diameter, and the ordinate indicates the scattering cross section. This scattering cross section is proportional to the scattered light generated from the foreign matter, and is obtained from Mie's theory of scattering. This interpretation means that when the generated scattered light is observed, the scattered light is observed as if it were scattered light generated from the foreign matter indicated by the solid line in the figure. In the figure, the broken line also shows the geometrical cross-sectional area. Thus, it can be seen that when observed with scattered light, the size is observed larger than the actual foreign matter size. (This is exactly the reason why the foreign substance inspection is performed with scattered light.) And the ratio is about 3 to 6 times in area ratio from FIG. . In this case, the equation (1) is as follows: d = (0.6 / (√3 to √6)) · (λ / NA) = (0.24 to 0.35) · (λ / NA) (1) ', Which explains the results of the previous experiment.

In the inspection of foreign matter on the reticle, the size d of the foreign matter to be detected is set to about 1/4 of the minimum dimension of the reticle. Therefore, the minimum dimension 2.5 μm (5: 1) on the reticle.
0.5 μm on the wafer for reduced transfer, this is 16M
The size is 0.6 μm for a DRAM ( equivalent to a DRAM) and 0.4 μm for a minimum dimension on a reticle of 1.5 μm ( equivalent to a 64M DRAM). Therefore, in order to detect a 0.4 μm foreign substance with the detection optical system having the NA of 0.4 obtained from the above study, the equation (1) ′ is modified. Λ = d · NA / (0.35 ０．２0.24) (2) requires a light source having a shorter wavelength than λ = 660 nm to 460 nm.

Next, a study will be made to select a wavelength suitable for foreign substance inspection on a sample such as a reticle on which a circuit pattern is formed within this wavelength range. The principle of separation and detection will be described. The present invention focuses on the fact that a circuit pattern such as a reticle is composed of straight lines in three directions of vertical, horizontal and oblique directions and intersections of the straight lines (hereinafter, circuit pattern corners). When the circuit pattern is irradiated at an incident angle i (i <90 °) from an oblique direction with a laser beam or the like having a high directivity, a Fourier transform image of scattered light from a linear portion of the circuit pattern is formed within the illumination visual field. Regardless of the position of the circuit pattern, it is known that light is condensed in a thin linear shape at a specific position on the Fourier transform image plane, while scattered light from a foreign substance is not biased to a specific position on the Fourier transform image plane. ing.

Therefore, according to the present invention, a linear light-shielding plate (referred to as a spatial filter) is arranged at a specific position on the Fourier transform image plane to shield scattered light from a linear portion of a circuit pattern, and to scatter light from a foreign substance. It is based on the principle that can only detect. However, the scattered light from the circuit pattern corner portion and the fine structure portion where the corner portion is continuous cannot be completely shielded. For this reason, when detection is performed with a 10 × 20 μm ² detection pixel as shown in the related art (shown in FIG. 4B), scattered light from a plurality of pattern corners enters the pixel, and only foreign matter is detected. Cannot be detected. Therefore, in the present invention, the resolution of the pixels of the detector is increased to 2 × 2 μm ² (shown in FIG. 4C), and the influence from the circuit pattern is eliminated as much as possible, and the detection of a 0.5 μm foreign substance is enabled. In this case, the pixel of the detector is set to 2 × 2 μm ^2. The reason for this is described below, and the pixel is not necessarily 2 × 2 μm ^2.
Need not be.

The pixel size in this case may be smaller than the pattern size L on the reticle. Therefore,
In the case of a reticle in which a 0.8 μm process LSI is exposed by a stepper having a reduction ratio of 1/5, approximately 0.8 × 5 =
0.5 μm for 4 μm and 0.5 μm process LSI
What is necessary is just to detect with the pixel smaller than * 5 = 2.5 micrometers.
Actually, the value may be larger or smaller as long as the influence from the pattern corner can be sufficiently reduced. Specifically, it is desirable to have a minimum pattern size on the reticle to be inspected. If the order of magnitude of the minimum pattern size, even by only a corner of less than two to one pixel of the detector shown in it Figure 8 to enter the experiment is sufficient at this value. More specifically, the minimum dimension is 1.5 μm
In a reticle for a 64M DRAM, a pixel size of about 1 to 2 μm is desirable.

[0037]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a block diagram showing a configuration of a foreign matter inspection apparatus according to one embodiment of the present invention, and FIG.
FIG. 3 is a plan view showing a reticle inspection state in the apparatus shown in FIG.
FIG. 2 is an explanatory diagram illustrating a configuration example of an irradiation system in the apparatus in FIG. 1. In FIG. 1, reference numeral 1 denotes an inspection stage unit. The inspection stage unit 1 has a reticle 6 having a pellicle 7 fixed to an upper surface thereof by a fixing unit 8 and can be moved in the Z direction. An X stage 10 that moves the reticle 6 in the X direction, a Y stage 11 that also moves the reticle 6 in the Y direction, a stage drive system 12 that drives each of the Z stage 9, the X stage 10, and the Y stage 11, A focus position detection control system 13 for detecting the Z-direction position of the reticle 6, and each stage is controlled so as to be always in focus with required accuracy during the inspection of the reticle 6. .

The X stage 10 and the Y stage 11
Scanning is performed as shown by a dashed arrow in FIG. 2, and the scanning speed can be set arbitrarily. For example, X stage 10
Are set to a constant acceleration time of about 0.2 seconds, a constant velocity movement of 4.0 seconds, and a constant deceleration time of 0.2 seconds, and a stop time of about 0.2 seconds is set to a half cycle. Maximum speed about 25mm / sec, amplitude 1
Formed so as to make a periodic motion of 05 mm, and Y stage 1
If the reticle 6 is transported in the Y direction stepwise by 0.5 mm in steps of 0.5 mm in synchronization with the equal acceleration time and equal deceleration time of the X stage 10, 2
If the transfer is performed 100 times, it is possible to transfer 100 mm in about 960 seconds.
Scanning can be performed in 60 seconds. Further, the control system 13 for detecting the focal position may use an air micrometer, may detect the position by a laser interference method, or may have a configuration in which a stripe pattern is projected and its contrast is detected. . Note that the coordinates X,
Y and Z are directions shown in the figure.

In FIG. 1, reference numeral 2 denotes a first illumination system, and reference numeral 3 denotes a second illumination system, both of which are independent and made up of the same components. 21 and 31 in the laser light source, the wavelength of both the wavelength lambda ₁ of the laser light source 21, for example in the present example 5
When the wavelength λ ₂ of the laser light source 31 is 14.5 nm, for example, 53
Although it is different from 2 nm, generally the same wavelength may be used.
Reference numerals 22 and 32 denote condensing lenses, which converge light beams emitted from the laser light sources 21 and 31, respectively, and irradiate the light onto the circuit pattern of the reticle 6. In this case, the angle of incidence i of the two 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 described later, and when the subject is the reticle 6 on which the pellicle 7 is mounted, the pellicle Since it must be less than approximately 80 ° to avoid the number 7, approximately 30 ° <i <80 °.

The first illumination system 2 and the second illumination system 3
A detailed configuration example will be described with reference to FIG. FIG. 3 is a diagram showing a configuration example of the first illumination system 2 (in this case, the second illumination system 3 side is omitted because it has the same configuration). In the figure,
1 are the same as those in FIG. In FIG.
223 is a concave lens, 224 is a cylindrical lens, 2
Reference numeral 25 denotes a collimator lens, and reference numeral 226 denotes a condensing lens. The laser light source 21 is linearly polarized light having a magnetic field vector in the Y ′ direction (this state is called S-polarized light).
It is arranged so that it may have. For example, when the incident angle i is about 60 °, the reflectance on the glass substrate is about five times higher than that of the P-polarized light (for example, the S-polarized light is used).
This is because it is possible to detect even smaller foreign matter from the article by Hiroshi Kubota, Applied Optics (Iwanami Zensho, p. 144).

In order to increase the illuminance of the first illumination system 2 and the second illumination system 3, the numerical aperture (NA) of the condensing system is set to about 0.1.
Although the laser beam is narrowed down to about 10 μm, the depth of focus is shortened to about 30 μm by this narrowing, and it is impossible to focus on the entire inspection field 15 S (500 μm) shown in FIG. However, in the present embodiment, as a countermeasure against this, the cylindrical lens 224 is used.
Is tilted around the X ′ axis shown in FIG. 3 (FIG. 3 shows a tilted state). For example, even when the incident angle i is 60 °, it is possible to focus on the entire area S of the inspection visual field 15. When a one-dimensional solid-state imaging device is used for the detectors 51 and 551 of the signal processing system 5 to be described later, even if the inspection area of the inspection visual field 15 is linear as in the case of the detectors 51 and 551, the linear shape is not changed. The inspection area can be illuminated with high illuminance and uniform distribution.

Further, when the cylindrical lens 224 is tilted about the Y ′ axis in addition to the X ′ axis shown in FIG. 3, for example, even when the incident angle i is 60 ° and the light is emitted from an arbitrary direction, the inspection field of view can be improved. It is possible to perform linear illumination with high illuminance and uniform distribution over the entire 15 areas S.
In FIG. 1, reference numeral 4 denotes a detection optical system. The detection optical system 4 includes an objective lens 41 facing the reticle 6, a viewing zone lens (hereinafter referred to as a field lens) 43 provided near an image forming position of the objective lens 41, and a field lens. A mirror (not shown) for wavelength separation of the light beam condensed by 43, a band-shaped light shielding portion provided at the position of the Fourier transform with respect to the inspection visual field 15 of the reticle 6, and a spatial filter 44 having a transmission portion outside thereof; 444, and imaging lenses 45 and 445, and are configured to form an image of the inspection field 15 on the reticle 6 on detectors 51 and 551 of the signal processing system 5 described later. The field lens 43 converts the upper focal position 46 on the objective lens 41 into spatial filters 44,44.
4 is formed.

In FIG. 1, reference numeral 5 denotes a signal processing system. The signal processing system 5 includes the detectors 51 and 551 and the detectors 51 and 551.
It comprises first and second binarization circuits 52 and 552 for binarizing the output of 551, an AND circuit 53, a microcomputer 54, and display means 55. The detectors 51 and 551 are formed of, for example, a charge-transfer type one-dimensional solid-state imaging device, and detect signals from a circuit pattern on the reticle 6 while scanning the X stage 10.
In this case, if a foreign substance is present on the reticle 6, the input signal level and the light intensity increase, so that the outputs of the detectors 51 and 551 are also increased. If one-dimensional solid-state imaging devices are used for the detectors 51 and 551 as described above, there is an advantage that the detection visual field can be widened while maintaining the resolution. However, the present invention is not limited to this. Alternatively, a single element can be used.

The binarization circuits 52 and 552 have threshold values for binarization set in advance, and output the reflected light intensity equal to or higher than the reflected light intensity corresponding to the foreign matter having the size to be detected, which is output from the detectors 51 and 551. It is configured to output a logic level “1” when a value is input. Shading correction circuits 113 and 123 and 4-pixel addition processing circuits 114 and 1
24 will be described later. The block processing circuit 112
This circuit takes in signals from the binarization circuits 52 and 552 and prevents double counting of two signals. This will also be described later. The microcomputer 54
When the block processing circuit 112 outputs the processing level “1”, it is determined that “there is a foreign substance”, and when the position information of the X stage 10 and the Y stage 11 is detected and the detectors 51 and 551 are not single elements, The position information of the foreign matter calculated from the pixel position in the element and the detection output values of the detectors 51 and 551 are stored as foreign matter data, and the result is displayed on the display means 5.
5 is output.

Next, the operation of the inspection apparatus will be described with reference to FIGS . 4 to 8 and FIG . FIG. 4 is an explanatory view showing a reticle inspection situation according to the present invention, FIG. 5 is a plan view illustrating an angle pattern of a circuit pattern according to the present invention, and FIG. 6 is a scattering on a Fourier transform plane according to the present invention. FIG . 7 is an explanatory view showing a distribution state of light and diffracted light, and FIG . 7 is an enlarged view showing a circuit pattern having a fine structure pattern .
FIG. 8 is a diagram showing the output value level of a detection signal detected from a foreign substance and a circuit pattern corner. In the figure, FIG.
The same reference numerals indicate the same components.

In FIG. 4A, reference numeral 70 denotes a foreign matter on the reticle 6 fixed on the Z stage 9 by the fixing means 8, 81 denotes a linear portion of the circuit pattern 80, and 82 denotes a corner of the circuit pattern 80. Department. The reticle 6 relating to the substrate sample is illuminated obliquely by the first illumination system 2 or the second illumination system 3, and scattered light generated is emitted from the objective lens 41.
When the light is focused, the circuit pattern 80 on the reticle 6 shown in FIG. 5 and the projected image 6 of the illumination system 2 or 3 on the reticle 6 surface
When the angle θ defined by the positional relationship with 0 is 0 °, the diffracted light of the angle pattern (hereinafter referred to as 0 ° pattern) is in a band shape on the Fourier transform plane of the objective lens 41 as shown in FIG. Appears in. Here, the type of the angle θ of the circuit pattern 80 is limited to the angle patterns of 0 °, 45 °, and 90 °, and diffracted light (b) from the 45 ° and 90 ° patterns as shown in FIG. , (C) show the objective lens 41
Does not affect the detection.

On the other hand, the scattered light from the foreign substance 70 has no directionality and spreads over the entire surface of the Fourier transform surface as shown in FIG. For this reason, the spatial filters 44, which have a band-shaped light shielding portion on the Fourier transform surface and a transmission portion outside thereof,
By disposing the 444 and blocking the diffracted light (a) from the 0 ° pattern shown in FIG. 4A, it is possible to detect the foreign matter 70 by distinguishing it from the circuit pattern 80. With this configuration, a high NA detection optical system can be realized for the first time.
Is set to 0.5, the aperture area can be about 20 times that of the low NA detection optical system. However, the scattered light from the corner portion of the circuit pattern (see FIG. 4D) cannot be sufficiently shielded by the linear spatial filter. For this reason, when detection is performed using a conventional detection pixel of 10 × 20 μm ² (see FIG. 4B), scattered light from a plurality of pattern corners enters four pixels, and only foreign matter is detected. Not detectable.

Therefore, in the present invention, the pixels of the detector are 2 × 2
The resolution was increased to μm ² (see FIG. 4 (C)), and the influence from the circuit pattern was eliminated as much as possible, enabling the detection of a 0.5 μm foreign substance. Here, the pixel of the detector is 2 × 2 μm
^It was set to ² for the following reason.
It is not always necessary to be 2 × 2 μm ² . The pixel size in this case may be smaller than the pattern size L on the reticle. Therefore, when a 0.8 μm process LSI is exposed with a stepper having a reduction ratio of 1/5, a reticle is approximately 0.8 × 5 = 4 μm, 0.5 μm process LSI.
In the case of I, it is sufficient to detect with a pixel smaller than about 0.5 × 5 = 2.5 μm.

In practice, the value may be larger or smaller as long as the influence from the pattern corner can be sufficiently reduced. Specifically, it is desirable to have a minimum pattern size on the reticle to be inspected. If the order of magnitude of the minimum pattern size is sufficient in this value by the experiment shown in it Figure 8 that only the corner of less than two enters one pixel of the detector. More specifically, for a 64 MDRAM reticle having a minimum dimension of about 1.5 μm,
A pixel size of about 1-2 μm is desirable.

The above contents will be described again. Circuitry corner portion 82 can be at the intersection of the pattern 80 is, because it is composed and Looking at the portion microscopically a continuous angle of the corner 820, the diffracted light from the corner portion 82 (d)
6 tends to spread on the Fourier transform plane, and cannot be completely shielded by the spatial filters 44 and 444.
As shown in FIG. For this reason, one detector 51
Alternatively, when diffracted light from the plurality of corners 82 enters the 551, the output V of the detector 51 or 551 increases, and the detection from the foreign matter 70 cannot be performed.

That is, the detected output values 822 from the plurality of corners 82 are equal to the detected output values 8 from the single corner 82.
Becomes a higher value than the 21, than was binarized at the level of point line 90, is not able to detect a detection output value 701 from the foreign matter 70 is separated. As a countermeasure against this inconsistency, in the present invention, the inspection field 15 on the reticle 6 is formed on the detectors 51 and 551 via the objective lens 41 and the imaging lenses 45 and 445. By selecting the dimensions of the detectors 51 and 551 and the imaging magnification, the detection visual field 15 on the reticle 6 surface is set to an arbitrary size (for example, 2 μm × 2 μm). Are not simultaneously incident on the detectors 51 and 551.

However, even if it is possible to detect foreign matter having the conventional dimensions, in the case of detecting foreign matter on the order of submicrons, separation detection from some corner portions 82 is insufficient depending on the shape of the circuit pattern 80. Further, due to the high integration of the LSI, diffracted light generated from a circuit pattern having a micron-order dimension 84 as shown in FIG. Since the behavior is more similar to that of the scattered light from 70, it is more difficult to detect the foreign matter 70 separately from the circuit pattern.

The present invention is applicable to a circuit pattern having a micron-order dimension 84 as shown in FIG.
The following measures are taken to detect foreign matter. FIG. 8 is an explanatory view of the above.
Reference numeral 702 denotes a detection output value of scattered light from the minute foreign matter 70 on the order of submicron, and 864, 874, 865, 875,
866, 876, 867, 877 are 0 °, 45 °, 9
Detection output values 861, 871, 86 of diffracted light from all corners 82 formed by each circuit pattern of 0 °
Reference numerals 2,872, 863, and 873 indicate detection output values of diffracted light from a microstructured circuit pattern having a dimension 84 on the order of microns. Of these, 701, 861,
862, 863, 864, 865, 866, 867 are:
The output values detected by the first illumination system 2 are also represented by 702, 8
71,872,873,874,875,876,87
7 indicates a detection output value by the second illumination system 3.

For example, 861 ← → 871 is a detection output value for each illumination system at the same position of the circuit pattern, where 861 indicates a value obtained by the first illumination system 2 and 871 indicates a value obtained by the second illumination system 3. Further, as can be seen from the drawing, the foreign matter 70 has a smaller variation in the scattered light detection output value depending on the irradiation direction than the circuit pattern. Note that a broken line 91 in the figure indicates a threshold value of the detection output value. From FIG. 8 , it was found that even with the same circuit pattern, the output of the diffracted light greatly differs depending on the irradiation direction.
When light is illuminated from two oblique directions facing each other, the output value of the diffracted light on either side is smaller than the output value from a submicron-order foreign substance, as indicated by the ● mark in the figure. You can see that it is always small.

FIG . 34 is a block diagram showing the structure of a foreign matter inspection apparatus according to still another embodiment of the present invention. In the figure,
1 are the same as those in FIG. 1, and the description thereof is omitted. In the apparatus shown in FIG. 34, the output values from the same position on the surface of the reticle 6 are separately detected by the wavelength separation filter 47 into the detectors 51 and 651, and the smaller one of the values indicated by ● is used. , Binarized by the binarization circuits 52 and 652, and the logical product is taken by the logical product circuit 53, and the foreign matter 70 of submicron order is obtained.
Only the circuit pattern 80 can be separated and detected.

As shown in FIG . 8 , the binarization circuits 52 and 65
When the threshold value 91 is set to 2, the values equal to or larger than the threshold value 91 become the detection output values 701 and 702 of the foreign matter 70 and the detection output values 861, 863, 874 and 875 of the circuit patterns. Is output from only one of the binarization circuits 52 and 552, and is not output from the AND circuit 53. Therefore, only the foreign matter 70 is separated from the circuit pattern and detected. can do. Then, in addition to the positional information of the X stage 10 and the Y stage 11 at the time of detection, detectors 51 and 65 are provided.
If 1 is not a single element, the position information of the foreign substance 70 calculated from the pixel position in that element and the detectors 51 and 65
The detected output value of 1 is stored as foreign matter data in a memory managed by the microcomputer 54, and the stored content is processed and displayed on a display means 55 such as a CRT.

FIG . 9 is an explanatory view showing an embodiment of a foreign matter which was missed in the prior art, FIG. 10 is a view for explaining the problem of the prior art, and FIG. 11 is a view for explaining the problem of the prior art. It is. These foreign substances shown in FIGS. 9A to 9C are foreign substances having dimensions that should be detected in terms of dimensions. The present invention examines the mechanism of oversight in these conventional techniques and proposes a foreign substance inspection method with a novel configuration.

FIG . 10 shows a problem with the conventional apparatus . In the apparatus for inspecting 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 used. , Will be an important point of technology. Therefore, the method of analyzing the polarization state of scattered light,
A method of comparing the outputs of a plurality of detectors has been developed and put into practical use. However, in each case, in order to avoid the influence of scattered light generated from the circuit pattern, an optical system having a small aperture of about 0.1 NA is disposed obliquely to avoid scattered light from the circuit pattern. In such a configuration, there is a problem that an irregularly shaped foreign matter is easily missed for a reason described later. The NA used here is a numerical value expressing the characteristics of the lens, which is determined by the aperture diameter of the lens and the distance to the target object . Specifically, using the θ in the diagram shown on the right side of FIG. It is a numerical value obtained by sin θ.

Another problem is a pattern removal technique which has been used in various inspection techniques to cope with miniaturization of circuit patterns. Many of these methods employ a method of automatically lowering the detection sensitivity of a foreign object detector when a circuit pattern is found during inspection. Such a method has a problem in that erroneous detection of a circuit pattern is reduced while foreign matter near the pattern edge is missed.

The following describes solutions to these two problems according to the present invention. FIG. 12 is an explanatory view of detecting scattered light from foreign matter using the high NA optical system according to the present invention, FIG. 13 is a configuration diagram showing a main part of the apparatus shown in FIG. 1, and FIG. for each histogram shown for the detection foreign material number of articles present the bright and the prior art, FIG. 15 is a histogram showing the results of classifying the detected foreign matter 14 by deposition position of the foreign matter. Images 1004 and 1005 in FIG. 12 are obtained by observing scattered light generated when a foreign object is irradiated with a laser from above. What should be noted in this image is that the scattered light (e) from the foreign matter is distributed with a direction. For this reason, in the conventional low NA detector 1001 shown by a broken line, unless the detector is installed at an appropriate position, the scattered light (e) generated from the foreign matter is not necessarily incident on the low NA optical system properly. Oversight occurs. Moreover, since the degree of distribution of the scattered light differs depending on the size and shape of the foreign matter, it is practically impossible to properly arrange the low NA optical system for all the foreign matter.

FIG. 11 shows the result of experimentally measuring this .
Shown in The scattered light distribution when the foreign matter is illuminated with a laser beam having an incident angle of 60 ° is obtained by changing the detection angle of the foreign matter with the detection optical systems 1001 and 1002 having a low NA (NA ≒ 0.1). Measured and shown. This figure shows the point A
1001 indicates that the detection level exceeds the detection threshold value, whereas point B1002 indicates that the detection cannot be performed without exceeding the detection threshold value. Since the scattered light distribution of the actual foreign matter is not constant, it indicates that the detection performance is not stable with the low numerical aperture detection methods such as A and B.

Therefore, in the present invention, it has been developed that the high NA detecting optical system 41 having a large aperture effectively condenses scattered light from foreign substances having various scattering distributions. As shown in FIG. 13 , a laser 21, a condenser lens 22, an objective lens 41,
A reticle 6 is formed by an apparatus including a field lens 43, a spatial filter 44, an imaging lens 45, and a detector 51.
FIG. 14 shows the effect of the present invention in detecting the foreign matter 70 above. In FIG. 14 , the vertical axis represents the total number of foreign substances detected by five reticles, and the horizontal axis represents the dimensions of the detected foreign substances. Further, among the foreign substances, the foreign substances detected in the related art are shown in different colors.

The detection capability of the prior art was set to 0.8 μm. For this reason, it can be understood that there is a difference between the present invention and the detection ability in the area of the foreign matter smaller than 1 μm. However, even in the area of a foreign substance larger than 1 μm, the present invention has seen a significant improvement in the number of detections. The detection rate is about 10 times as high as the number of detections in the prior art. This is presumably because the high-NA detection optical system employed in the present invention responds well to irregularly shaped foreign matter and stably detects scattered light from the foreign matter.

Next, a description will be given of a situation of detecting foreign matter adhering to a circuit pattern edge. FIG . 15 shows the result of classifying the detected foreign matter in FIG. 14 according to the position where the foreign matter is attached.
The adhering position is such that the circuit pattern surface of the reticle includes a glass portion (transmissive portion), a chrome portion (a light-shielding portion, the light-shielding portion is often formed of a thin metal film such as chrome), and an edge portion which is a boundary between the two. 3 regions. Of these, the edge portion is most affected by the adhesion of foreign matter, and the foreign matter in the chrome portion does not affect the transfer as long as it stays on the chrome portion. It is clear from FIG. 15 that the detection performance for the foreign matter at the edge portion which has the most influence on the transfer, that is, the need for detection is improved.

If the idea described above that the foreign matter on the chrome portion is not taken into consideration is used, the configuration as shown in FIG. 16 can be realized. FIG. 16 is a main part configuration diagram of a foreign substance inspection apparatus according to another embodiment of the present invention. In the example of FIG. 16 , the arrangement of the illumination system including the laser 21 and the condenser lens 22 is the same as that of the example of FIG. 13 , but the detection optics including the objective lens 41, the field lens 43, the spatial filter 44, and the imaging lens 45. The system and the detector 51 are connected to the circuit pattern 8 of the reticle 6.
0 is provided on the back side of the surface on which 0 is formed. In this case, foreign matter on the chrome portion cannot be detected, but scattered light from the foreign matter on the glass portion and the edge portion, which affects transfer failure, can be detected through the reticle 6 which is a transparent base material.

As an advantage of this configuration, there is a correspondence to a reticle having a cross section as shown in FIG . FIG.
Scattered light from a reticle with a phase shifter film according to the present invention,
FIG . 18 is an explanatory diagram showing diffracted light, and FIG . 18 is a configuration diagram of a main part of a foreign matter inspection device according to still another embodiment of the present invention. In the reticle in FIG. 17 , a pattern (shifter pattern) 1003 of a phase shifter film for improving transfer resolution is provided between chrome portions. This film is transparent,
Since it has a structure several times as large as the chrome portion (about 0.1 μm thick), the diffracted light from the edge portion 1006 is larger than the diffracted light from the edge portion of the chrome portion. Becomes

However, in the configuration in which the detection optical system is provided below as shown in FIG. 16 , the diffracted light generated from the shifter pattern 1003 is shielded by the chrome portion of the reticle itself, and does not enter the detection optical system. Does not affect the detection of Also, here, the reticle, the illumination system 2 and the objective lens 41 are arranged as shown in the figure, but the purpose of the present invention is to make the phase shifter film arranged on the chrome portion the edge of the pattern 1003 from the edge 1006. This can be achieved by shielding the scattered light using the chrome portion. Therefore, since the illumination system 2 and the objective lens 41 only need to be on the opposite sides of the reticle 6, respectively, the configuration shown in FIG . However, since the shifter pattern 1003 have a thickness, for oblique illumination, in the configuration of FIG. 18, since the portion 1007 which can not be illuminated occurs, it is preferable in the configuration of FIG. 16.

The same effect can be obtained even in the configuration shown in FIG. 32 in which the illumination system and the optical detection system are respectively arranged on the back side of the circuit pattern surface. FIG. 32 is a main part configuration diagram of a foreign substance inspection device according to still another embodiment of the present invention. As mentioned earlier, the inspection target does not include a chrome part.
When the scattered light on the front surface and the back surface is detected by the two systems of optical detection systems in such a configuration as described above, the whole surface including the chromium portion can be inspected with a certain performance.

FIG . 33 is a diagram showing the output of a detector according to the present invention which has detected standard particles and scattered light from a circuit pattern corner. That is, in FIG. 33 , the standard particles, which are model foreign matter, and the circuit pattern (edge portion of the chrome portion) and the shifter pattern from the front surface detection system (4 in FIG. 1) and the back surface detection system (40 in FIG. 1) are used. The scattered light detection output is shown. In FIG. 33 , the horizontal axis indicates the particle diameter, the vertical axis indicates the scattered light detection output, and the particles that exceed the level of the scattered light detection output from the circuit pattern and the phase shifter film indicated by the horizontal line in the figure are detectable particles. is there. From the figure, it can be seen that the scattered light from the standard particles on the chrome part has several times the output of the standard particles on the glass part, and especially that of 0.8 μm or more is larger than the level of the scattered light from the phase shifter film. It turns out that it becomes.

That is, even a foreign substance on the chromium portion affected by the phase shifter can detect particles of 0.8 μm or more. Therefore, in the present invention, as shown in FIG. 1, the rear surface detection system handles the foreign matter on the glass portion, and the front surface detection system handles the foreign material on the chrome portion.
It is also possible to detect foreign substances that may move from the chrome part to other parts. In addition, the need for foreign matter detection on a chrome portion may be as follows. The concept of permitting foreign matter on the chrome portion described above mainly holds at the time of exposure. However, in the manufacturing process of the reticle with the phase shift film, foreign matter on the chrome portion may cause a problem.

A reticle with a phase shift film is generally
After the formation of the chromium portion (the process up to this point is the same as for a reticle without a shifter film), a shifter film material is applied or sputtered on the entire surface, and a pattern (shifter pattern) using a shifter film is formed by an etching process. It is. Therefore, if foreign matter is present on the chromium portion before film formation, the film formation is adversely affected, and defects such as bubbles and chips may be generated in the shifter film. Therefore, in addition to the foreign substance inspection after the shifter pattern is formed as described above, the foreign substance inspection of the entire surface including the chromium portion before and after the film formation (in the method of the present invention, defects such as bubbles and chips are similar to foreign substances). Can be detected). However, in this case, since the shifter pattern is not formed, and no scattered light is generated from the shifter pattern, the entire surface can be detected with high sensitivity by providing a surface detection system as shown in FIG. 1 of the present invention. .

Further, in the case of detecting and judging foreign matter in a pixel unit, particularly in an array type detector, the following inconvenience occurs. FIG. 23 is an explanatory diagram and a diagram when a foreign substance is detected at 2 × 2 μm ² pixels without performing the 4-pixel addition process .
24 is an explanatory view showing the detection of foreign matter at 1 × 1 μm ² pixels by the four-pixel addition processing. FIG. 25 is a columnar shape showing an example of the foreign matter detection reproducibility of the present invention when the four-pixel addition processing is not applied. FIG. 26 is a block diagram showing an example of a four-pixel addition processing circuit. Assuming that a foreign object is detected and determined using a pixel size of 2 × 2 μm ² as an example,
As shown in FIG. 23 , under the condition that foreign matter is detected over a plurality of (two to four) pixels, scattered light from the foreign matter is also dispersed into a plurality of pixels, and as a result, the detection output of one pixel Is reduced to 1/2 to 1/4 (actually, about 1/3 due to the influence of crosstalk between detector pixels), and the detection rate of foreign matter is reduced.

The positional relationship between the pixel 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 result is different for each test, and the reproducibility of detection is reduced. Therefore, this time, as shown in FIG. 24 , the detection pixels are reduced to 1 × 1 μm ² ,
The detection outputs of four 1 × 1 μm ² pixels adjacent to each pixel are electrically added to simulate the detection outputs of 2 × 2 μm ² pixels. This is obtained by overlapping each 1 μm (a, b, c, d in the figure), and the maximum value (a in the figure) is 2 × 2 μm
The detection of foreign matter is determined as a representative output of ^two pixels. As a result, the variation of the detection output from the same foreign substance is within ± 10% in actual results, and the detection reproducibility of 80% or more can be secured for all the foreign substances.

FIG . 14 shows a result (detection reproducibility of 80% or more) when the four-pixel addition processing circuit is applied. An example of the detection reproducibility before application is shown in FIG. 25 , but it is clear that the detection reproducibility is not sufficiently ensured unless the four-pixel addition processing is performed. FIG. 26 shows a block diagram of a specific example of the four-pixel addition processing circuit. This means that the number of pixels when reduced to 1 μm is 5
In a one-dimensional imaging device in which 12 pixels are arranged, an output 2503 from an odd-numbered pixel and an output 2502 from an even-numbered pixel of the one-dimensional imaging device are separately output (general) one-dimensional imaging device. This is an example. One pixel (1 μm) reduced by 256-stage shift register 2501, one-stage shift register 2504, and adders 2505 to 2508
Four pixels (2 × 2 pixels) shifted in four directions are added one by one, and the average values of the respective average values are obtained by the dividers 2509 to 2512. The maximum value determination circuit 2513 outputs 4
The maximum value in the directions is obtained and output as a detection value 2514 from a foreign substance.

In this method, only foreign matter is made bright and visible by optical processing, and detection is performed. Therefore, when a signal detected from a set threshold value is large, it is determined that “foreign matter is present” (binarization). As a result, foreign matter can be detected. However, the detection signal has variations in sensitivity characteristics (approximately ± 15%) for each pixel of the one-dimensional image sensor detector and sensitivity unevenness (shading) due to the illuminance distribution of the illumination light source.
FIG. 27 is a diagram showing the influence of shading on foreign object detection, FIG. 28 is a diagram showing the principle of shading, and FIG. 29 is a block diagram of an example of a shading correction circuit. Due to the presence of shading, as shown in FIG. 27 , the magnitude of the detection signal varies depending on the pixel (position in the Y direction) in which the same foreign matter is detected, and it is impossible to stably detect the foreign matter by binarization using a threshold. It is.

In the present invention, as shown in FIG. 28 , shading including the above is measured (a) on the standard sample 111 of FIG. 1 in advance, and shading correction data (b) calculated by calculating the reciprocal of this measurement data is obtained. ) Is obtained, and the amplifier gain of the detector detection signal is changed for each pixel, thereby eliminating the influence of shading and (c) detecting foreign matter. The standard sample 111 is placed on the inspection stage in FIG. 1 or placed near the inspection stage. However, a configuration in which the standard sample 111 is placed on the sample stage instead of the reticle only during shading measurement is also possible. The standard sample 111 is required to have a uniform scattering characteristic on the surface of the fine unevenness, and to have a fine grinding mark by polishing a glass substrate or a thin film capable of forming fine unevenness (for example, aluminum is sputtered on the substrate by sputtering). Film-formed one) is used. However, it is practically difficult to uniformly process the fine irregularities on the standard sample 111 for the pixels of 1 × 1 μm ² . Therefore, correction data was obtained from an average value obtained by repeating the shading measurement many times (for example, 1000 times).

Further, since the scattered light from the minute unevenness has a strong and weak unevenness, a simple average value (for example, a value obtained by dividing 1000 times of repeated data by 1000) becomes too small, and the value of the calculation becomes too small. Accuracy may decrease. Under such conditions, the value to be divided may be set to a fraction of the number of repetitions (for example, 200 for 1000 repetitions). FIG.
As shown in FIG. 8 , comparing the shading (a) before correction and the (b) after correction, it can be seen that the shading that existed about 50% before correction is corrected to 5% or less. If the correction data is re-measured and updated for each inspection, the optical fluctuation component can be removed even if the illumination, the optical detection system, and the like are temporally unstable.

FIG . 29 is a block diagram showing a specific example of the shading correction circuit. A / D detection value of one-dimensional image sensor
Converted value (here, 256 gradations, 8 bits) 3212
A subtraction circuit 3209 for subtracting the value of the dark current portion of the one-dimensional image sensor from data from the memory 3206 controlled by the synchronization circuit 3205 for each pixel, and a shading correction magnification by the synchronization circuit 3205 for each pixel. A multiplying circuit 3210 for multiplying by the data from the controlled memory 3207, and a value 3 obtained by A / D conversion (in this case, 256 gradations, 8 bits) of the detection value of the one-dimensional image sensor
A medium-bit output circuit 3211 is provided to return the result of multiplication that has become twice as many as 212 bits (here, 16 bits) to the original number of bits (here, 8 bits). As can be seen from the figure, this example is an example in which correction is performed by a digital circuit, but the same result can be obtained by performing analog correction before A / D conversion.

In the case where foreign matter determination is performed in units of 2 × 2 μm ² pixels, for example, when foreign matter having a size of 2 μm or more is present, the number of pixels in which foreign matter is detected differs from the actual number of foreign matter. Become. If there is one foreign substance of 10 μm, it will be detected with (10 μm / 2 μm) ² = about 25 pixels, and if it is attempted to observe the detected foreign substance, all 25 detection results will be obtained. Must be checked, which causes inconvenience. Conventionally, this disadvantage is avoided by a software-based grouping processing function that examines the connection relationship between pixels in which a foreign object is detected and, when pixels are adjacent, determines that "one foreign object has been detected". I was However, this method requires software processing, so that when a large number of detection signals are used, the processing takes a long time (for example, about 10 minutes for 1000 detection signals), which causes a new inconvenience.

Therefore, in the present invention, the entire inspection area is divided into blocks of a visual field range (for example, 32 × 32 μm ² ) that can be observed at a time, and all the detection signals in the same block are determined as the same foreign matter (block processing). ).
Thus, even a large foreign object can be observed and confirmed within a field of view at one time regardless of its shape. The block processing is a simple grouping processing in terms of function, but has a feature that it can be easily implemented in hardware. In the present invention, the processing is performed in real time by the hardware of the block processing, and the throughput of the apparatus including the inspection time is greatly increased (in the case of 1000 detection signals, the throughput is 2
/ 3 or less).

FIG . 30 is a block diagram showing an example of the block processing circuit. In the case of the example of FIG. 30 , not only the determination of the same foreign substance but also the number of detection signals serving as the basis for 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, a device is devised so that the approximate size of the foreign matter, the situation where a plurality of foreign matters are included in the same block, and the like can be estimated. Also,
A circuit for outputting an inspection stop signal when the number of foreign object detection signals reaches a preset number is also incorporated.

FIG . 31 is a block diagram showing an example of the relationship among a shading correction circuit, a 4-pixel addition processing circuit, and a block processing circuit. That is, the detector signal 3301 is A
The shading correction circuit 3 via the / D converter 3302
After the respective processes of the 303 and 4-pixel addition processing circuit 3304 and the block processing circuit 3305 are performed, the foreign substance detection result 3
306 is output.

[0083]

As described above in detail, according to the present invention, a substrate sample having a circuit pattern formed on a transparent or translucent substrate, particularly a reticle having a phase shift film for improving transfer resolution, etc. In the above, fine foreign matter of sub-micron order adhering between circuit patterns can be easily and stably separated and detected from the edge of the circuit pattern easily and with high sensitivity mainly by a simple optical configuration. It works.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a foreign matter inspection apparatus according to one embodiment of the present invention.

FIG. 2 is a plan view showing a reticle inspection state in the apparatus of FIG. 1;

FIG. 3 is an explanatory diagram showing a configuration example of an irradiation system in the apparatus of FIG.

FIG. 4 is an explanatory diagram showing a reticle inspection state according to the present invention.

FIG. 5 is a plan view illustrating an angle pattern of a circuit pattern according to the present invention.

FIG. 6 is an explanatory diagram showing the distribution of scattered light and diffracted light on the Fourier transform surface according to the present invention.

FIG. 7 is an enlarged view showing a circuit pattern having a fine structure pattern.

FIG. 8 is a diagram showing output value levels of a detection signal detected from a foreign substance and a circuit pattern corner;

FIG. 9 is an explanatory view showing an embodiment of a foreign matter that was missed in the prior art.

FIG. 10 is an explanatory diagram for describing a problem of the related art.

FIG. 11 is an explanatory diagram for explaining a problem of the related art.

FIG. 12 is an explanatory diagram illustrating detection of scattered light from a foreign substance using the high NA optical system according to the present invention.

FIG. 13 is a configuration diagram showing a main part of the device shown in FIG. 1;

FIG. 14 is a columnar graph showing the number of detected foreign particles with respect to the size of detected foreign particles in each of the present invention and the prior art.

FIG. 15 is a column graph showing the result of classifying the detected foreign matter in FIG . 14 according to the position where the foreign matter is attached.

FIG. 16 is a main part configuration diagram of a foreign matter inspection apparatus according to another embodiment of the present invention.

FIG. 17 is an explanatory diagram showing scattered light and diffracted light from a reticle with a phase shifter film according to the present invention.

FIG. 18 is a main part configuration diagram of a foreign substance inspection apparatus according to still another embodiment of the present invention.

FIG. 19 is a diagram illustrating theoretical values of the intensity of scattered light from a foreign substance with respect to a dimensionless number πD / λ based on the wavelength λ of the laser beam and the particle diameter D of the foreign substance.

FIG. 20 is an explanatory diagram showing directions of diffracted light from a foreign substance.

FIG. 21 is an explanatory diagram showing the definition of NA of an optical system.

FIG. 22 is a diagram showing a scattered light cross-sectional area proportional to a scattered light intensity from a foreign substance with respect to a foreign substance diameter.

FIG. 23 is an explanatory diagram in a case where a foreign substance is detected by 2 × 2 μm ² pixels without performing the 4-pixel addition process.

FIG. 24 is an explanatory diagram in which a foreign substance is detected at 1 × 1 μm ² pixels by a 4-pixel addition process.

FIG. 25 is a columnar graph showing an example of foreign matter detection reproducibility of the present invention when the four-pixel addition processing is not applied.

FIG. 26 is a block diagram illustrating an example of a four-pixel addition processing circuit;

FIG. 27 is a diagram showing the influence of shading on foreign object detection.

FIG. 28 is a diagram showing the principle of shading.

FIG. 29 is a block diagram illustrating an example of a shading correction circuit.

FIG. 30 is a block diagram illustrating an example of a block processing circuit.

FIG. 31 is a block diagram illustrating an example of a relationship among a shading correction circuit, a four-pixel addition processing circuit, and a block processing circuit.

FIG. 32 is a main part configuration diagram of a foreign substance inspection apparatus according to still another embodiment of the present invention.

FIG. 33 is a diagram showing the output of a detector that detects scattered light from a standard particle and a circuit pattern corner according to the present invention.

FIG. 34 is a block diagram showing a configuration of a foreign matter inspection apparatus according to still another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Inspection stage part 2 ... 1st illumination system 3 ... 2nd 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, 551, 651 detector 52 first binary circuit 552 second binary circuit 53 AND circuit 70 foreign matter 80 circuit pattern 111 standard sample 112 Block processing circuit 113 First shading correction circuit 123 Second shading correction circuit 114 First four-pixel addition processing circuit 124 Second four-pixel addition processing circuit 223 Concave lens 224 Cylindrical lens 225 Collimator lens 226 ... Condensing lens

Claims (11)

(57) [Claims] 1. A foreign matter inspection apparatus for detecting foreign matter existing between circuit patterns on a substrate sample having a circuit pattern formed on a transparent or translucent substrate, comprising: From the surface side , the direction inclined from the surface side with respect to the vertical direction .
Ri, the oblique illumination optical system provided on the surface side to be irradiated by focusing a laser beam, the laser beam irradiated by focusing from the surface side by the oblique lateral illumination optical system, on the substrate Foreign matter scattered light generated from the foreign matter existing between the circuit patterns and transmitted through the substrate and emitted to the back side and generated from the edge of the circuit pattern and transmitted through the substrate to the back side.
Substantially perpendicular to the objective lens having an optical axis, resulting provided on the Fourier transform plane through the spatial filter and spatial filter for blocking edge scattered light is condensed by the objective lens for condensing the emitted are edge scattered light A detection optical system provided on the back surface side, which is provided with an array-type detector that receives the foreign matter scattered light received, converts it into a detection signal, and outputs the detection signal; and outputs the detection light from the array-type detector of the detection optical system. A signal processing circuit for detecting a foreign matter attached between circuit patterns on the surface of the substrate sample by determining the detection signal with a determination threshold value. 2. A foreign matter inspection apparatus for detecting foreign matter present between said circuit patterns on a substrate sample having a circuit pattern formed on a transparent or translucent substrate, comprising: to the surface of but formed, from the back side of the surface, than direction is inclined to the vertical, oblique, which is by focusing a laser beam is provided on the back side to be irradiated is transmitted through the substrate An illumination optical system, and the oblique illumination optical system collects light from the rear surface side and irradiates the laser light transmitted through the substrate, thereby generating a foreign substance existing between the circuit patterns on the substrate and generating a front surface. an objective lens having an optical axis edge scattered light is emitted to the surface side resulting from the edge of the foreign matter scattered light and the circuit pattern to be emitted to the side in a substantially vertical direction for focusing, Fourier variables A spatial filter provided on a surface for shielding edge scattered light condensed by the objective lens, and an array-type detector for receiving foreign matter scattered light obtained through the spatial filter, converting the foreign matter scattered light into a detection signal, and outputting the detection signal Between the detection optical system provided on the surface side to be configured and the circuit pattern on the surface of the substrate sample by judging the detection signal output from the array type detector of the detection optical system by a judgment threshold value And a signal processing circuit for detecting a foreign substance attached to the object. 3. A reticle having a phase shift film in which a circuit pattern is formed on a transparent or translucent substrate and a phase shifter film is formed between desired circuit patterns, wherein the circuit also includes a phase shifter film on the substrate. a foreign matter inspection apparatus for detecting a foreign substance existing between the patterns, the circuit pattern and the phase shifter film of the phase shift film with a reticle is formed surface from the surface side,
An oblique illumination optical system provided on the surface side for condensing and irradiating laser light from a direction inclined with respect to the vertical direction, and the laser beam is condensed and irradiated from the surface side by the oblique illumination optical system. The laser light is generated from foreign matter existing between the circuit patterns including also on the phase shifter film on the substrate, and is generated from foreign matter scattered light transmitted through the substrate and emitted to the back side, and from the edge of the circuit pattern. An objective lens having an optical axis in a substantially vertical direction for collecting edge scattered light that is transmitted through the substrate and emitted to the back side, and is provided on a Fourier transform surface to collect edge scattered light collected by the objective lens. backside configured with an array type detector converts the foreign substances scattered light obtained through the spatial filter and spatial filtering on the detected signal by receiving shielded
Between the detection optical system provided on the side and the circuit pattern on the surface of the reticle provided with the phase shift film by judging a detection signal outputted from the array type detector of the detection optical system by a judgment threshold value. A foreign matter inspection device, comprising: a signal processing circuit for detecting attached foreign matter. 4. A reticle having a phase shift film in which a circuit pattern is formed on a transparent or translucent substrate, and a phase shifter film is formed between desired circuit patterns, wherein the circuit also includes a phase shifter film on the substrate. What is claimed is: 1. A foreign matter inspection device for detecting foreign matter existing between patterns, comprising: a surface on which a circuit pattern and a phase shifter film of the reticle having a phase shift film are formed;
From more directions is inclined with respect to the vertical direction, by focusing the laser beam is provided on the back side to be irradiated is transmitted through the substrate
The oblique illumination optical system, and the circuit pattern including the phase shifter film on the substrate by the laser light condensed from the rear surface side by the oblique illumination optical system and transmitted through the substrate. Foreign matter scattered light generated from the foreign matter present between and emitted to the front side and the surface side generated from the edge of the circuit pattern
Objective lens having an optical axis in a substantially vertical direction for condensing edge scattered light emitted to the object, a spatial filter provided on a Fourier transform surface to shield edge scattered light condensed by the objective lens, and the spatial filter A detection optical system provided on the front surface side which is provided with an array type detector for receiving the obtained foreign matter scattered light, converting it into a detection signal, and outputting the signal, and an output from the array type detector of the detection optical system And a signal processing circuit for detecting a foreign substance attached between circuit patterns on the surface of the reticle with the phase shift film by determining a detection signal based on a determination threshold value. 5. A numerical aperture (N) of an objective lens of said detection optical system.
5. The foreign matter inspection apparatus according to claim 1, wherein A) is in a range of 0.4 to 0.6. 6. In the signal processing circuit, a pixel signal obtained from each pixel of the array type detector is cut out by shifting one pixel at a time from a reference position in four directions around the reference position in a 2 × 2 pixel group, and these cut outs are cut out. The maximum value of the four average pixel signals obtained from each of the obtained four 2 × 2 pixel groups as an average pixel signal of the 2 × 2 pixel group at the reference position,
The method according to any one of claims 1 to 4, wherein a foreign substance is detected by making a determination using a determination threshold based on an average pixel signal of a 2x2 pixel group at a reference position obtained from the circuit. Foreign matter inspection device. 7. The signal processing circuit according to claim 1, wherein the inspection area is divided into a plurality of blocks, and all of the detection signals in the same divided block are determined as the same foreign matter. A foreign matter inspection device described in any one of the above. 8. A foreign matter inspection method for detecting foreign matter present between said circuit patterns on said substrate, wherein said circuit pattern is formed on a transparent or translucent substrate, said method comprising the steps of: the relative surface on which a circuit pattern is formed in the substrate sample, from the surface side, from the direction tilted with respect to the vertical direction, an illumination step of irradiating by focusing the laser beam, by the illumination step The laser light condensed and irradiated from the front side is generated from a foreign substance existing between the circuit patterns on the substrate, and transmitted through the substrate to the back side.
Foreign matter scattered light emitted to the front side and generated from the edge of the circuit pattern are transmitted through the substrate and emitted to the back side.
That the edge scattered light condensed by the objective lens, the spatial filter provided on a Fourier transform plane to shield the edge scattered light is condensed by the objective lens, foreign matter scattered light array detector obtained through the spatial filter A detection step of receiving light from the detector and converting it into a detection signal, and outputting the detection signal; and a circuit on the surface of the substrate sample, wherein the detection signal output from the array type detector is determined by a determination threshold value in the detection step. A signal processing step of detecting foreign matter adhering between the patterns. 9. A foreign matter inspection method for detecting foreign matter existing between circuit patterns on a substrate sample having a circuit pattern formed on a transparent or translucent substrate, the method comprising the steps of: , relative to the surface on which a circuit pattern is formed in the substrate sample, from the back side of the surface, than direction is inclined relative to the vertical direction, illumination by focusing the laser beam is irradiated is transmitted through the substrate a step, by focusing from the back surface side by the laser beam emitted passes through the substrate by the illumination step, the table is generated from a particle that exists between the circuit pattern on the substrate
The foreign matter scattered light emitted to the surface side and the edge scattered light generated from the edge of the circuit pattern and emitted to the surface side are collected by the objective lens, and collected by the objective lens by the spatial filter provided on the Fourier transform surface. A detection step of shielding edge scattered light to be emitted, receiving foreign substance scattered light obtained through the spatial filter with an array-type detector, converting it into a detection signal and outputting the detection signal, and outputting the signal from the array-type detector in the detection step A signal processing step of detecting a foreign substance attached between circuit patterns on the surface of the substrate sample by determining the detected signal with a determination threshold value. 10. A reticle with a phase shift film in which a circuit pattern is formed on a transparent or translucent substrate and a phase shifter film is formed between desired circuit patterns, wherein the circuit also includes a phase shifter film on the substrate. a foreign matter inspection method for detecting a foreign substance existing between the patterns, the oblique illumination optical system, the circuit pattern and the phase shifter film formed surface of the phase shift film with reticle, from the surface side, An illumination step of condensing and irradiating laser light from a direction inclined with respect to the vertical direction; and a phase shifter film on the substrate by the laser light condensed and irradiated from the front side in the illumination step. d of the circuit pattern foreign matter scattered light and the circuit pattern to be emitted to the back surface side passes through the substrate is generated from a particle that exists between even including upper The edge scattered light is emitted to the back surface side passes through the substrate resulting from di condensed by the objective lens, the light shielding edge scattered light is condensed by the objective lens by the spatial filter provided on a Fourier transform plane A detecting step of receiving the foreign matter scattered light obtained through the spatial filter by the array type detector, converting the scattered light into a detection signal and outputting the detection signal, and determining the detection signal output from the array type detector in the detection step A signal processing step of detecting a foreign substance attached between circuit patterns on the surface of the reticle with a phase shift film by making a determination based on a threshold value. 11. A reticle having a phase shift film in which a circuit pattern is formed on a transparent or translucent substrate and a phase shifter film is formed between desired circuit patterns, wherein the circuit also includes the phase shifter film on the substrate. What is claimed is: 1. A foreign matter inspection method for detecting foreign matter existing between patterns, comprising: using an oblique illumination optical system, with respect to a surface on which the circuit pattern and the phase shifter film of the reticle having the phase shift film are formed, a back surface side of the front surface; From , an illumination step of condensing laser light from a direction inclined with respect to the vertical direction and transmitting and irradiating the substrate, and condensing the laser light from the back side by the illumination step and transmitting the laser light through the substrate. the emitted laser beam, the foreign matter scattered light Contact is emitted to the surface generated from a particle that exists between the circuit pattern including the phase shifter film on the substrate Injection of the surface side resulting from the fine the circuit pattern of the edge
The edge scattered light collected by the objective lens is collected by an objective lens, the edge scattered light collected by the objective lens is shielded by a spatial filter provided on the Fourier transform surface, and the foreign matter scattered light obtained through the spatial filter is detected in an array type. A detection step of receiving the light with a detector and converting it into a detection signal, and outputting the detection signal; and detecting the detection signal output from the array type detector by a determination threshold value in the detection step, and detecting the surface of the reticle with the phase shift film. A signal processing step of detecting foreign matter attached between the circuit patterns.