JPH0646182B2 - Apparatus and method for inspecting foreign matter on mask - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a method for exposing a mask on a mask before transferring a circuit pattern formed on the mask in an exposure process using a mask such as a reticle in LSI manufacturing. The present invention relates to an apparatus and method for inspecting foreign matter on a mask for simultaneously inspecting both lumpy foreign matter and thin-film foreign matter present in the above.

[Conventional technology]

A conventional device for detecting foreign matter on a mask such as a reticle is
JP-A-59-65428 and JP-A-54-1013.
No. 90. Japanese Unexamined Patent Publication No. 59-65428 discloses a foreign matter inspection device characterized by a linearly polarized laser, means for injecting the laser light at a specific incident angle, and an image forming optical system using a polarizing plate and a lens. . In this device, when linearly polarized light is irradiated, only the foreign matter is detected by shining it by utilizing the fact that the circuit pattern existing on the substrate and the foreign matter have different polarization directions of the reflected light.

Further, Japanese Patent Laid-Open No. 54-101390 discloses a laser light source,
A foreign matter inspection apparatus is disclosed which is characterized by means for obliquely irradiating the laser beam, a Fourier transform optical system using a lens, a spatial filter installed on the Fourier transform surface, and an imaging optical system. This device pays attention to the fact that the circuit pattern is generally formed in the same direction or a combination of a few directions in the field of view, and the diffracted light by the circuit pattern in this direction is placed in the Fourier transform plane. By removing with a filter, only the reflected light from the foreign matter is emphasized and detected.

Incidentally, as for the related matter as the foreign matter inspection, for example, Hiro Kubota, Applied Optics (Iwanami Zensho), pages 129 to 136.
There is a page.

[Problems to be solved by the invention]

As the LSI becomes highly integrated and the wiring pattern becomes finer, smaller foreign matter becomes a problem. In addition, foreign matter on the flat thin film also poses a problem, such as resist residue during reticle production, etching residue of chromium or chromium oxide for circuit pattern formation, and impurities that were dissolved in the reticle cleaning solution that aggregated during cleaning and drying. There is.

In the technique disclosed in Japanese Patent Laid-Open No. 54-101390, the reflected light from the minute lump foreign matter and the thin film foreign matter becomes weak, and these minute foreign matter and thin film foreign matter cannot be detected separately from the pattern. . Further, fine foreign matter can be emphasized by the technique of Japanese Patent Laid-Open No. 59-65428, but the circuit patterns that can be erased by scanning the irradiation laser are limited, and the same spatial filter is used for all circuits. It was impossible to erase the pattern.

An object of the present invention is to solve the above-mentioned problems of the prior art by emphasizing a lump foreign substance and a thin-film foreign substance present on a mask on which a circuit pattern is formed, simultaneously without erroneously detecting the circuit pattern, thereby achieving high reliability. An object is to provide an apparatus and method for inspecting foreign matter on a mask that can be inspected by.

[Means for solving problems]

In order to achieve the above object, the present invention provides a table scanning means for placing a mask on which a circuit pattern is formed and scanning it two-dimensionally, and a vertical surface on the surface of the mask scanned by the table scanning means. A diagonally illuminating means for obliquely collecting linearly polarized laser light for collecting and statically illuminating vertically polarized laser light from a direction inclined at a predetermined angle with respect to a direction by a focusing optical system,
An annular illumination laser light concentric with a vertical optical axis that passes through an irradiation point where the linearly polarized laser light is obliquely focused and illuminated by the static illumination static illumination means and has a shorter wavelength than the linearly polarized laser light is collected by a focusing optical system. Converging and transmitting illumination means for converging and illuminating the ring-shaped illumination laser light for static transmission illumination from the back side of the mask, and the straight line arranged on the surface side of the mask so as to have an optical axis on the vertical optical axis. Objective that collects the reflected and scattered light from the surface of the mask by the obliquely converging static illumination means of the polarized laser light and the transmitted light obtained by passing through the mask by the converging stationary transmission illumination means of the annular illumination laser light. With a lens
A branching optical system for branching the reflected and scattered light and the transmitted light collected by the objective lens, a wavelength separating means for separating the lights obtained by the branching optical system by different wavelengths, and the branching optical system. A relay lens that refocuses the Fourier-transformed image on the mask obtained by the objective lens on the conjugate plane for each of the reflected and scattered light and the transmitted light that are split by the branching optical system. Reflected scattered light from the circuit pattern that is incident on the objective lens among the reflected scattered light that is arranged on the conjugate Fourier transform surface that is re-imaged by the relay lens in the branched optical path and that is separated by the wavelength separation means. A first spatial filter for shielding the light, and a first spatial filter that receives reflected scattered light from the lumpy foreign matter existing on the mask obtained through the first spatial filter. The first one-dimensional solid-state image sensor for converting into an elementary signal and the first Fourier transform plane which is re-imaged by the relay lens in the optical path branched by the branch optical system are arranged and separated by the wavelength separation means. A phase difference plate or a second spatial filter that reduces the transmitted light other than the thin-film foreign matter incident on the objective lens in the transmitted light
A second one-dimensional solid-state imaging device for receiving diffracted light from a thin-film foreign substance obtained through the phase difference plate or the second spatial filter and converting it into a second pixel signal; and the first one-dimensional solid-state imaging device. A first pixel signal converted from an element and the second pixel signal;
An inspecting apparatus for foreign matter on a mask, comprising: an inspecting unit for inspecting lumpy foreign matter and thin-film foreign matter existing on the mask by a second pixel signal converted from the one-dimensional solid-state image pickup device. . Further, the present invention is characterized in that, in the foreign matter inspection device on the mask, the wavelength separating means is installed in each optical path branched by the branching optical system. Further, the present invention is characterized in that, in the foreign matter inspection device on the mask, the branching optical system is composed of a wavelength separating mirror and the wavelength separating means is also integrated. Further, according to the present invention, in the foreign matter inspection device on the mask, a polarization filter is further installed in the optical path of the reflected scattered light separated by the branch optical system. Further, the present invention is characterized in that, in the foreign matter inspection device on the mask, the relay lens is installed between the objective lens and the branch optical system. Further, the present invention is characterized in that, in the foreign matter inspection device on the mask, the inclination angle of the linearly polarized laser light emitted by the obliquely focused static illumination means can be adjusted. Further, according to the present invention, in the foreign matter inspection device on the mask, as the inspection means, there is provided a logical sum circuit for performing a logical sum of the first pixel signal and the second pixel signal. Further, according to the present invention, a mask on which a circuit pattern is formed is two-dimensionally scanned, and linearly polarized laser light is condensed on the surface of the scanned mask from a direction inclined by a predetermined angle with respect to the vertical direction. The system condenses the light for static illumination, and condenses the annular illumination laser light, which is concentric with the vertical optical axis passing through the irradiation point to be condensed and irradiated and has a shorter wavelength than the linearly polarized laser light, by the condensing optical system. Then, static transmission illumination is performed from the back side of the mask, and the objective lens is arranged so as to have an optical axis on the vertical optical axis. An optical system that collects scattered light and the transmitted light obtained by passing through the mask by converging static transmission illumination of the annular illumination laser light and splits the reflected scattered light and the transmitted light collected by the objective lens. Branched by and different from each other Reflection from the circuit pattern that is separated according to wavelength and is incident on the objective lens by a spatial filter arranged on a conjugate plane of a Fourier transform image on a mask obtained by the objective lens with respect to the separated reflected scattered light. The first-dimensional one-dimensional solid-state imaging device receives the scattered light reflected from the lumped foreign substance existing on the mask by shielding the scattered light, converts the scattered light into the first pixel signal, and the separated transmitted light is the objective lens. Diffraction from the thin-film foreign matter by reducing the transmitted light other than the thin-film foreign matter entering the objective lens by the phase difference plate or the spatial filter arranged on the conjugate plane of the Fourier transform image on the mask obtained by the relay lens. The light is received by the second one-dimensional solid-state image sensor, converted into a second pixel signal, and converted from the first one-dimensional solid-state image sensor. On the mask, the lump-like foreign matter and the thin-film foreign matter existing on the mask are inspected by the first pixel signal and the second pixel signal converted from the second one-dimensional solid-state imaging device. It is a foreign matter inspection method.

[Action]

With the above-described configuration, the reflected and scattered light from the edges of the circuit pattern formed on the mask is highly sensitive, that is, emphasized, to the reflected and scattered light generated from the edge of the circuit pattern, and the reflected and scattered light from the lumped foreign matter existing on the mask is The first one-dimensional solid-state imaging device detects the first pixel signal and the transmitted diffracted light from the thin film foreign substance of metal or dielectric having a different refractive index from the glass substrate existing on the mask is used as the second one-dimensional solid-state imaging device. The element can detect it as the second pixel signal, and as a result, it is possible to simultaneously inspect the lump-like foreign matter and the thin-film-like foreign matter existing on the mask with high reliability.

〔Example〕

A specific embodiment of the present invention will be described below with reference to FIGS. 1 to 18.

(1) Structure The present invention is, as shown in FIG. 1, a sample stage part 4 composed of an XY stage 1, a stage drive system 2 and a clamp 3.
A minute foreign matter illuminating section 12 including an He-Ne laser 8, a beam expander 9, a condenser lens 10, and an incident light angle setting means 11, an objective lens 13, and a half mirror 15 that reflects an optical path and branches. A relay lens 14 forming a Fourier transform plane conjugate with the Fourier transform plane of the objective lens 13, and a Fourier transform plane conjugate with the Fourier transform plane of the objective lens 13 reflected and branched by the half mirror 15. Spatial filter 16, polarizing plate 17, interference filter 18 that allows reflected and diffracted light from the He-Ne laser light to pass through, and one-dimensional solid-state image sensor 1 that outputs a pixel signal.
A thin foreign matter illuminating unit 3 including a minute foreign matter detecting unit 20 configured by 9 and a He-Cd laser 31 and a lens 32, an annular plate 33, a coupling lens, and a condenser lens 34.
5, a half mirror 15 that passes through the optical path from the objective lens 13 and branches, a relay lens 14 that forms a Fourier transform surface conjugate with the Fourier transform surface of the objective lens 13, and a branch that passes through the half mirror 15 A spatial filter 21 arranged on a Fourier transform plane conjugate with the Fourier transform plane of the objective lens 13, a color filter 22 that passes the transmitted diffracted light by the He-Cd laser light, and a one-dimensional solid-state image sensor 23 that outputs a pixel signal. A thin-film foreign matter detection unit 24, binarization circuits 114 and 115, and an OR circuit 2
5, a stage control system 26, a CRT display 28, a printer 29, and a control unit 30 including a microcomputer 27. The reticle 5 is placed on the XY stage 1 and fixed in a two-dimensional direction by the minute foreign matter illuminating section 12, the minute foreign matter detecting section 20, and the thin film foreign matter illuminating section 35.
And the thin-film foreign matter detection unit 24 is two-dimensionally scanned.

(2) Relationship between constituent elements The relationship between the constituent elements in each constituent part will be described below.

In the sample stage 4, the reticle 5 is fixed on the XY stage 1 by the mechanical clamp 3.

The X stage 1 has a uniform acceleration time of approximately 0.1 seconds, a constant velocity motion of 0.1 seconds, and a constant deceleration time of 0.1 seconds as a half cycle, and a maximum speed of 1 m / second and an amplitude of 200 mm. exercise.

The Y stage is cycled in equal acceleration time and equal deceleration time of the X stage 1, and is fed in 0.15 mm stepwise in one direction.
If you send 670 times in one inspection time, it will be 100 in about 130 seconds.
mm can be sent.

With this configuration, a 100 mm square area can be scanned in about 130 seconds.

In this embodiment, scanning is performed by the XY stage, but scanning may be performed by the Xθ stage shown in FIG.

The Xθ stage includes an X stage 33, an X stage drive system 2, a θ stage 94, a θ stage gear 32, a θ stage drive system 31, a mask 95, and a clamp 3.

The θ stage 94 rotates at a constant speed of 4 times / second.

The X stage 33 is fed at a constant speed of about 70 mm at 0.6 mm / sec.

Therefore, a 100 mm square area can be scanned in about 120 seconds.

At this time, the mask 95 fixed to the θ stage shields light except the inspection region.

In the minute foreign matter illuminating section 12, the He—Ne laser 8 and the condenser lens 10 are fixed by the incident angle setting means 11. This He-Ne laser emits linearly polarized light. H
The light emitted from the e-Ne laser 8 is incident on the reticle 5 at a constant incident angle i through the beam expander 9 and the condenser lens 10. The light reflected and diffracted by the reticle 5 passes through the objective lens 13 and the relay lens 14, and is reflected on the half mirror 15 and is branched on the spatial filter 16 arranged on the Fourier transform plane conjugate with the Fourier transform plane of the objective lens 13. Designed to collect light. That is, a real image of the light source of the He—Ne laser 8 is formed on the spatial filter 16 through the beam expander 9, the condenser lens 10, the objective lens 13, and the relay lens 14. With this configuration, the Fraunhofer diffraction image of the pattern 7 on the reticle can be formed in the plane including the spatial filter 16.

The polarization direction of the light beam 55 is perpendicular (P-polarized light or parallel (S-polarized light)) to the incident surface (the surface including the light beam 55 and the optical axis 96).

However, in terms of device design, the configuration described above may be approximated to the following configuration. That is, the diameter dp of the light beam incident on the condenser lens 10 is set to about 0.5 to 2 mm,
The distance Lp from the condenser lens 10 to the reticle 5 is 30 to
The image of the light source is formed on the reticle 5 with a length of about 100 mm. Further, the spatial filter 16 is installed on the Fourier transform plane when only the objective lens 13 and the relay lens 14 are considered. With this configuration, since the light beam emitted onto the reticle 5 is close to a parallel light beam, the objective lens 13 is practically used.
And it is approximately considered to be Fourier-transformed by only the relay lens 14. Further, in this case, the illumination section 97 on the reticle 5 becomes an ellipse, and its minor axis length α _i is determined by the following equation.

α _i = 1.22. λ. Lp / dp (1) where λ is the wavelength of the irradiation light. This α _i should be determined by the light intensity required for detection and the size of the object to be illuminated. In this embodiment, dp = 1 mm, Lp = 50
mm and α _i = 40 μm.

Also, the illumination is not from the oblique direction, but as shown in FIG.
Although it may be performed from above through the half mirror 35, the specularly reflected light from the circuit pattern 7 is reflected on the objective lens 13, and this reflected light needs to be completely shielded, which is not preferable.

Such illumination from above is effective in the inspection of a reticle provided with a foreign matter adhesion preventive tool composed of a thin film 36, frames 37, and h as shown in FIG. (This foreign matter adhesion preventive tool is installed for the purpose of preventing foreign matter from coming close to the reticle 5.
-65428 and the like. That is, when illuminating from an oblique direction, the beam 37 blocks the light beam 38 and forms an area 39 that cannot be illuminated, whereas the light beam 4 from above
If illuminated with 0, this area 39 will be very small. As described above, the illumination from above has the effect of reducing the universal detection area.

Furthermore, the He-Ne laser 8 (wavelength 633 nm) is
A laser having another wavelength such as an e-Cd laser or an Ar laser may be used, and a quinocene lamp or a halogen lamp other than the laser may be used. However, in any of these light sources, linearly polarized light is desirable, and in the case of a light source that is not linearly polarized light, it is necessary to install a polarizing filter immediately after the light source.

In the minute foreign matter detecting section, the pattern 7 and the foreign matter 6 on the reticle 5 are imaged on the one-dimensional solid-state imaging device 19 by the objective lens 13 and the relay lens 14.

Here, the spatial filter 16 is installed on the image forming planes of the beam expander 9, the condenser lens 10, the relay lens 14, and the objective lens 13 of the light source of the He—Ne laser 8.
The polarization filter 17 is also installed at this position.

The polarization filter 17 is oriented so that the light flux of the He—Ne laser 8 is blocked. Specifically, when S-polarized light is incident, the polarization axis is perpendicular to the incident surface, and when P-polarized light is incident, it is installed in parallel.

Here, the polarization filter 17 may be installed at any position between the reticle 5 and the one-dimensional solid-state imaging device 19, instead of the above position.

The position of the spatial filter 16 may be a position between the reticle 5 and the objective lens 13 and immediately before the objective lens 13. This is because the luminous flux 55 by the He-Ne laser 8 is approximately parallel light and the pattern (hereinafter referred to as pattern) 7 is fine, so that a Fraunhofer diffraction image can be obtained without using the objective lens 13 or the like. This is because
However, when detecting thin-film foreign matter, it is desirable not to enter the thin-film foreign matter detector.

The relay lens 14 may not be used, but in reality, a collective lens is often used as the objective lens 13, and the beam expander 9, the condenser lens 10, and the objective lens 13 are used.
The image forming position of the light source of the He—Ne laser 8 may be inside the objective lens 13. In this case, a spatial filter should be installed at the imaging position after passing through the relay lens 14. Furthermore, as the relay lens 14,
A Fourier transform lens can also be used. At this time, since the Fourier transform image of the pattern becomes sharp, the spatial filter can effectively shield the light from the pattern.

The interference filter 18 can block the illumination light from the thin-film foreign matter illumination unit 35, and can detect only the light from the He—Ne laser 8.

Here, as the one-dimensional solid-state image pickup device 19, as shown in FIG. 5, an array of 50 pin silicon photodiodes having a parallelogrammatic detector opening 42 is arranged vertically in the direction of the X stage. is doing. Further, the magnification of the optical system and the size of the element are designed so that an area of about 3 μm square on the reticle 5 is imaged with respect to one element.

As a result, light from other than the foreign matter does not enter the detector, which makes it possible to detect foreign matter that scatters weaker light, that is, minute foreign matter. Moreover, by arranging the elements, many areas can be detected at one time, and the inspection speed is improved. Since the pin silicon photodiode has high sensitivity and fast response speed, it is possible to detect weak light at high speed.

By the way, the reason why the opening of the pin silicon diode is formed into a parallelogram is to prevent the image of the foreign matter 6 from entering the dead zone between the openings 42 and becoming undetectable due to the scanning of the XY stage 1. .

However, in order to achieve the object of the present invention of detecting minute foreign matter, a charge transfer type solid-state element may be used instead of the pin silicon photodiode.
The structure using a pinhole and a photomultiplier shown in No. 28 may be used.

In the thin film foreign matter illuminating section 35, a He-Cd laser (wavelength 4
(42 nm) passes through the lens 32 and illuminates the annular plate 33 having an annular opening. The light emitted from the annular plate 33 passes through the coupling lens 34 to illuminate the reticle 5 from the back side, passes through the objective lens 13, the half mirror 14, and the relay lens 14, and forms an image on the spatial filter 21.

Here, when the laser light source has a sufficient intensity, the lens 32
May or may not be a beam expander. Further, the ring plate 33 may have a pinhole as an opening. This is also the case when the light source has sufficient intensity.

Further, since the laser light source such as the He-Cd laser 31 emits spatially coherent light, the reticle 5 may be directly illuminated without using the ring plate 33 and the coupling lens 34. Also in this case, the spatial filter 21 is installed at the position of the Fourier transform plane by the relay lens 14 where the image of the light source of the He-Cd laser 31 can be formed. Further, in order to obtain a sufficient light intensity, the lens 32 may be left and the light may be condensed on the reticle 5. Similar to the minute foreign matter illuminating section, the position of the spatial filter 21 may be designed by approximation.

Further, the He-Cd laser 31 is a He-Ne laser, H
Other laser light sources such as e-Cd laser (325 nm) and Ar laser may be used, and other light sources such as mercury lamp, quinocene lamp, and halogen lamp may be used.

Further, when the thin-film foreign matter has a low transmittance for a specific wavelength, phase contrast microscopy may not be used. However, in this case, in order to distinguish from the pattern 7, a configuration for processing the detection signal on a computer is used.

Here, when the He-Cd laser is used, there is an effect that the minute foreign matter and the thin-film foreign matter are distinguished and detected by the difference in the wavelength of the illumination light. Further, as the phase contrast microscope, it is possible to detect a thinner film by using a light source having a shorter wavelength. Further, the wavelength of the He-Cd laser light is the reticle 5 by the exposure.
Since the wavelength is close to that when transferring the pattern from,
There is an effect that a foreign matter that is actually a problem can be detected under the same conditions.

In the thin-film foreign matter detection unit 24, the phase difference microscope is formed by the spatial filter 21 having the same shape as the ring plate 33.
Since the phase contrast microscope is described in many documents, its description is omitted here. (Example: Kubota, Applied Optics, Iwanami Zensho, pages 129 to 136) The color filter 22 blocks the light from the minute foreign matter illuminating section 12 and detects only the thin-film foreign matter.

Further, when a laser is used as a light source, when the annular plate is used as a pinhole or when the annular plate is not used, it is necessary to separately design the shape of the spatial filter. That is, since the real images of these light sources become points, the spatial filter also reduces the light intensity at one point in the center and delays the phase by 1/2 wavelength.

Further, since it is possible to detect by thinning the edge portion of the thin-film foreign matter, a spatial filter that shields light instead of delaying the phase by 1/2 wavelength may be used. This is the Schlieren method and is a well-known method.

The one-dimensional solid-state image pickup device may be a charge transfer type device or one in which pin silicon photodiodes are arranged in parallel one-dimensionally, similarly to the minute foreign matter detection unit. In addition, JP-A-5
A configuration in which a pinhole and a detector such as a photomultiplier tube are combined as described in 9-65428 may be used.

The thin-film foreign matter that can be detected by this detection system has a phase difference of about 10 nm or more, as long as it has a phase difference. Further, even when the particle is thick, it is possible to detect the phase difference due to the nonuniformity of the thickness of the foreign matter. Therefore, in fact, it is possible to detect a foreign substance having an arbitrary thickness of 10 nm to several μm.

In the control unit, the microcomputer 27 controls the stage control system 26 to drive the XY stage. At the same time, the pixel signals from the one-dimensional solid-state image pickup devices 19 and 23 are binarized by the binarization circuits 114 and 115 and taken into the microcomputer 27 connected by the logical sum generation circuit 25.

The result is displayed on the printer 29 and the CRT display 28.

In this embodiment, after the pixel signals from the one-dimensional solid-state image pickup devices 23 and 19 are processed by the logical sum generation circuit 25,
It is incorporated in the microcomputer 27. But,
The OR circuit 25 is omitted and the binarization circuits 114 and 1
The 15 signals may be directly taken into the microcomputer 27. In this case, the two types of foreign matter can be detected separately.

Further, the same function as that of the logical sum generation circuit 25 can be provided to the microcomputer 27 to detect two kinds of foreign matters without distinguishing them.

Further, the control unit 30 may be configured by an analog addition circuit 116 and a binarization circuit 117, as shown in FIG.

(3) Design of Shape of Spatial Filter Here, the shape of the spatial filter used for detecting the minute foreign matter will be described with reference to FIGS. 6 to 18. This shape should be designed optimally according to the illumination method and the polarization method of the illumination light.

First, the behavior of illumination light will be described.

FIG. 6 is an enlarged view of the reticle. A pattern 7 having an edge 47 parallel to the direction 48 is formed on the reticle substrate 46. Pattern 7 is chrome oxide, substrate 46 is SiO
It is formed by ₂ .

FIG. 7 is a sketch showing the relationship between the illumination light 55, the diffracted light 59, 60 by the pattern 7 in the direction 48, and the aperture 64 of the objective lens 13 when the reticle is illuminated. The polarization directions are indicated by arrows 58, 62 and 63. Also, the spherical surface 65 that is in contact with the aperture 64 of the objective lens 13 is considered, and the diffracted light 5
9 and 60, the spherical surface 65, and the revolutions 61 and 98, the polarizations 62 and 63 of the diffracted light are shown. The curve Y including these intersections 61 and 98 becomes a circle 66.

FIG. 8 is a plan view of FIG. A circle including the intersection of the diffraction destination and the spherical surface 65 when the pattern direction 48 is changed is shown by straight lines 99 to 102.

The intersections of the incident light 56 and the emitted light 57 and the spherical surface 65 are indicated by points 105 and 57, respectively.

Here, the polarization direction of the linearly polarized reflected light incident on the substance having the refractive index n at an arbitrary incident angle i is obtained by the following formula.
(From “Analysis of reflected light of LSI wafer pattern”) (Rs, Rp) = (S (i) Es, P (i) Ep) ...
(2) Here, Es and Ep are the intensities of the incident light and Rs and Rp are the intensities of the S-polarized component and the P-polarized component of the reflected light, respectively. Also,
S (φ) and P (φ) are calculated by the following equations.

Using this equation, the intersection point 6 of the diffracted light 59 when P-polarized light (linearly polarized light having an electric field vector parallel to the incident surface) is incident
The polarization 62 at 1 is calculated. At this time, the edge 47 of the pattern 7 is considered to be a set of planes 49, 50 and 51 having normal vectors 52, 53 and 54, and reflection on each plane is considered. That is, the planes 49 to 51
The direction of the reflected light and the polarization direction of the light incident on the
It is calculated in (2), and this is the direction of the diffracted light 59 and the polarized light 62.

The results are shown in FIG. 8 by the arrows of the polarization directions 62, 63 and the like.

Hereinafter, blocking of diffracted light from the pattern will be described. The blocking of the diffracted light from the pattern is performed by the incident angle i of the incident light 55,
The three elements of the spatial filter 16 and the polarization filter 17 are used to effectively block the light.

According to FIG. 8, the light diffracted in the range 67 does not enter the lens opening 64. That is, these diffracted lights are blocked by setting the incident angle of the illumination light. When the incident angle i is large, the exit point 57 is separated from the lens opening 64 and becomes the exit point 74, so that the range 67 of diffracted light that can be blocked becomes the range 106, and a wider range of diffracted light can be blocked.

By setting this incident angle i, it is possible to block the diffracted light from the pattern of the direction 48 perpendicular to the circle 66 showing the diffracted light, that is, the pattern having the direction of the range 71 shown in FIG.

It can then be seen that the polarization within range 68 is approximately parallel to the plane of incidence. On the other hand, the polarization directions in the ranges 69 and 70 are not parallel.

Therefore, the diffracted light that enters the range 68 is not reflected by the polarization filter 1
Shut off by 7. Further, the spatial filter 16 blocks the diffracted light entering the ranges 69 and 70. The shape of the spatial filter 16 is shown in FIG. It is formed by the light shielding portion 75 and the transmission portion 76. Here, the edge 108 of the spatial filter 16 is a curve because the lens aperture 64 is a plane and the set of points where the diffracted light 59 intersects the lens aperture 64 is a curve. Since the lens opening 64 is a Fourier transform surface, the shape here may be considered. That is, the spatial filter 16 may be designed in a similar shape in consideration of the polarization state on the lens aperture 64. However, the opening 64
Note that is a plane.

The incident on the range 68 is the diffracted light from the pattern having the direction of the range 72, and the incident on the ranges 69 and 70 is the diffracted light from the pattern having the directions of the ranges 73 and 74.

The above three elements (incident angle i, polarization filter 17, spatial filter 16) block diffracted light from patterns having all directions.

On the other hand, the polarization direction of the scattered light from the foreign matter is not aligned in one direction like the above-mentioned diffracted light, so that the polarized light other than the direction 109 is also incident on the range 68, so that it is blocked by these filters. There is no such thing. The analysis of the polarization direction of scattered light from foreign matter is described by Born & Wolf, Principles of
Optics, pages 652-656.

Similarly, FIG. 10 shows the polarization direction of the diffracted light when S-polarized light (linearly polarized light having an electric field vector perpendicular to the incident surface) is incident.

In this case, with the same spatial filter as shown in FIG.
The diffracted light that enters the ranges 78 and 110 is blocked, and the diffracted light that enters the range 77 is blocked by the polarization filter installed by rotating the polarization filter shown in FIG. 9 by 90 °.

Further, FIG. 11 shows a polarization direction 111 of incident light and a polarization direction 112 of diffracted light when vertically incident. In this case, the diffracted light that enters the ranges 79, 80, 81, 82 and 87 is blocked by the spatial filter 16, and the ranges 85, 8
The diffracted light incident on 6, 87 and 88 may be blocked by the polarization filter 17.

Further, it was found by experiments that when the incident angle of the luminous flux of the He-Ne laser 8 was set to about 60 °, the reflected light from the pattern having the pattern angle β of about 23 ° was strong. Therefore, the thirteenth
It is preferable to use a spatial filter having a shape as shown in the figure. This filter effectively shields the diffracted light from the above 23 ° pattern and can take in more scattered light from foreign matter.

Further, it was found from experiments that the larger the incident angle, the larger the scattered light from the foreign matter.

The reticle 5 may use a foreign matter adhesion preventive tool composed of the frame 37 and the thin film 36 as shown in FIG. In this case, when the incident angle is large, there is a region 39 which is blocked by the frame 37 and cannot be illuminated. Here, with the configuration in which the minute foreign matter illuminating section 120 having the same configuration as the minute foreign matter illuminating section 12 is also used as illumination from the side rotated by 180 °, this area is illuminated and inspection is enabled. In this case, as shown in FIG. 14, the light flux is divided by the half mirror 88, and the configuration including the spatial filter 89, the polarization filter 90, the interference filter 91, and the one-dimensional solid-state imaging device 92 is added, and each is shown in FIG. When the spatial filter 16 is used as 16 and 89 rotated by 180.degree. With respect to each other, when the region 39 is inspected, it is inspected by the detector 92 only by illumination with the light beam 41. This allows
There are no uninspectable areas.

Of course, this non-inspectable region can also be inspected by rotating the reticle 5 by 180 °.

Further, the light sources of the minute foreign matter illuminating section 12 and the minute foreign matter illuminating section 120 are changed so that the wavelengths of the light beams 55 and 119 are λ ₁ , respectively.
and lambda _2, lambda ₁ using a wavelength separation mirror in place of the half mirror _88, may be configured to separate the lambda _2. According to this method, it is not necessary to switch the light source.

Moreover, these two-way illumination has another effect. As shown in FIG. 6, the actual minute foreign matter is not symmetrical. With the illumination by the light flux 55 and the illumination by the light flux 119,
The intensity and polarization of scattered light differ depending on the size and shape of the anti-slopes 121 and 122. In such a case, erroneous detection may occur in the case of only one, whereas in the case of bidirectional irradiation, there is a high possibility of detection in either one, and the reliability of detection is improved.

Further, the minute foreign matter detection unit 20 can also be detected by one optical system by using the spatial filter shown in FIG.

Further, by using this calculation result, the reflected light from the pattern 7 can be effectively shielded by partially changing the direction of the polarization filter as shown in FIG. Further, when the polarization direction extremely changes in a minute area, it cannot be approximated, and thus it may be used together with the light shielding plate.

In this case, since the distribution of polarized light differs depending on the material forming the pattern 7 and the material of the substrate 46, the combination of the polarized light 113 may be redesigned by calculation using Expression (2).

Further, although the illuminating means has been described by using S-polarized light or P-polarized light, linearly polarized light of arbitrary polarization is calculated by calculating the polarization of reflected light for linearly polarized light having a polarization direction other than S-polarized light or P-polarized light. On the other hand, it is possible to design a polarization filter that effectively shields the reflected light from the pattern.

The pattern 7 of the actual reticle 5 may be a combination of only the patterns of β = 0 ° and 90 ° as shown in FIG. In this case, a filter for blocking the diffracted light from the β = 0 ° pattern by the light blocking unit 75 may be installed by the spatial filter as shown in FIG. It has already been described that the diffracted light from the β = 90 ° pattern due to the oblique illumination does not enter the objective lens 13. The scattered light from the end portion 123 of the pattern has a negligible intensity.

Further, FIG. 19 shows a spatial filter in the case of using the apparatus for vertical incidence shown in FIG. 3 for inspecting such a pattern.

The spatial filter 16 shown in FIGS. 18 and 19 can completely block the diffracted light from the pattern 7. Therefore, when it is known in advance that the pattern is as shown in FIG. 17, these spatial filters are effective. Therefore, the spatial filter 16 has a mechanism that can be exchanged, and is used in place of the spatial filter 16 shown in FIG. 18 or FIG. 19 when the pattern shown in FIG. 17 is known.

The three cases have been described above. The polarization direction of the incident light,
The incident angle, the shape of the spatial filter, and the orientation of the polarization filter should be designed according to the above concept.

(4) Operation The reticle 5 is placed, the He-Ne laser 8 and the He
-Light is emitted from the Cd laser 31.

The light from the He-Ne laser 8 emits the pattern 7 and the foreign matter 6
The light from the pattern 7 is reflected or scattered by the spatial filter 16 and the polarization filter 17, and only the scattered light from the foreign matter 6 is reflected by the objective lens 13 and the relay lens 14 on the one-dimensional solid-state image sensor 19. Is imaged.

With respect to the light from the He-Cd laser 31, only the transmitted light from the thin-film foreign matter is emphasized by the phase contrast microscope composed of the objective lens 13, the annular plate 33 and the spatial filter 21, and the light on the one-dimensional solid-state imaging device 23. Is imaged.

Here, the XY stage 1 is driven, and the signals from the one-dimensional solid-state image pickup devices 19 and 23 are binarized.
5 and the logical sum generation circuit 25 to be incorporated into the microcomputer 27. At the same time, since the microcomputer 27 controls the stage control system 26, the position of the XY stage 1 when a foreign substance is detected is stored in the memory inside the microcomputer 27.

When detecting a foreign substance, a certain threshold value is determined, and if a signal larger than that value is input, it is determined as a foreign substance.

The signal processing when the sample shown in FIG. 21 is detected will be described below with reference to FIGS. 22 to 28.

The minute foreign matter 6 and the thin film foreign matter 118 are placed on the reticle 5 on which the pattern 7 is formed.

The reticle 5 is placed on the XY stage 1, and the X stage scans in the direction 124. In this case, a signal from one element in the one-dimensional solid-state image pickup element 19 is shown in FIG. The scattered light from the minute foreign matter 6 is detected as a peak 125.

A signal from one element in the one-dimensional solid-state image pickup element 23 is shown in FIG. The signal from the thin-film foreign matter 118 is detected as a peak 126.

The 22nd detection signal obtained by ordinary transmitted light illumination is shown. In the present embodiment, this signal is 7 in the one-dimensional solid-state image pickup device 23 when the thin film foreign matter illuminating unit is a xenon lamp and the spatial filter 21 and the color filter 22 are removed.
This is the signal detected by the element.

This signal distinguishes between the pattern 7 and the substrate 46,
The minute foreign matter 6 and the thin-film foreign matter 118 are not detected.
The effect of the present invention is shown in FIGS. 22, 23 and 24.
It is clear when comparing the figures.

The signals shown in FIGS. 23 and 28 are binarized 114.
And the thresholds 127 and 12 set in 115
8 is binarized to obtain the signals and peaks 129 and 130 shown in FIGS. 25 and 26, respectively. The signal shown in FIG. 28 is generated by the logical sum generation circuit 25 and is incorporated in the microcomputer 27.

Here, depending on the type of the foreign matter 118 and the shape of the spatial filter 21, the edge of the foreign matter 118 may be emphasized and become a signal 133. In this case, the binarized signal is the second
The peaks 134 and 135 in FIG. 6 are counted, and are counted as two foreign matters, but it does not matter in the sense that the original purpose of foreign matter detection is achieved.

In the microcomputer 27, the positions 131 and 132 of these two peaks 129 and 130 are calculated from the signal when controlling the stage control system 26.

Here, according to the circuit configuration shown in FIG. 20, the analog addition circuit 116 obtains the signal shown in FIG. 27, and the binarization circuit 117 outputs the binarized signal shown in FIG. 28. can get. This signal is sent to the microcomputer 27
, Positions 131 and 132 are calculated.

The present invention has been described above with reference to the embodiments. In this embodiment, the half mirror 15, the interference filter 18, and the color filter 22 are used to detect minute foreign matter and thin-film foreign matter by another detection system. This has the effect of distinguishing the two types of foreign matter.

〔The invention's effect〕

According to the present invention, the reflected and scattered light from the block-like foreign substance existing on the mask is highly sensitive, that is, emphasized to the reflected and scattered light and the transmitted diffracted light generated from the edge of the circuit pattern formed on the mask. Is detected as a first pixel signal by the first one-dimensional solid-state image sensor, and transmitted diffracted light from a thin film foreign substance of a metal or a dielectric having a different refractive index from the glass substrate existing on the mask The solid-state image sensor can detect the second image signal, and as a result, the lump foreign substance and the thin film foreign substance existing on the mask can be inspected at the same time with high reliability.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a sectional view of a stage, FIG. 3 is a block diagram of an illumination unit, FIG. 4 is a side view of a reticle, and FIG. 5 is one-dimensional solid-state imaging. FIG. 6 is a perspective view of the device, FIG. 6 is an enlarged view of the reticle, FIG. 7 is a perspective view showing the polarization direction of the emitted light, and FIGS. 8, 10 and 11 are plan views of FIG. Figure 9, Figure 12, Figure 13, Figure 1
5, FIG. 18 and FIG. 19 are plan views of the spatial filter, FIG. 14 is a block diagram of the detector, FIG. 16 is a plan view of the polarization filter, FIG. 17 is a plan view of the pattern, and FIG. Fig. 21 is a block diagram of the control unit. Fig. 21 is a sectional view of the reticle.
22 to 28 are diagrams showing signals. 1 ... XY stage, 5 ... reticle, 8 ... He-N
e laser, 31 ... He-Cd laser, 13 ... Objective lens, 16 ... Spatial filter, 17 ... Polarization filter,
21 ... Spatial filter, 19, 23 ... One-dimensional solid-state imaging device, 27 ... Microcomputer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yukio Utsu 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Inside the Institute of Industrial Science, Hitachi, Ltd. (56) Reference JP-A-61-65107 (JP, A) Kai 59-65428 (JP, A)

Claims (8)

[Claims] 1. A table scanning means for placing a mask on which a circuit pattern is formed and scanning it two-dimensionally, and a predetermined angle with respect to the vertical direction on the surface of the mask scanned by the table scanning means. Obliquely converging static illumination means for linearly polarized laser light for concentrating vertically polarized laser light from a tilted direction by means of a condensing optical system and for static illumination, and converging and irradiating the linearly polarized laser light with oblique concentrating static illumination means. The annular illumination concentric with the vertical optical axis passing through the irradiation point and having a wavelength shorter than that of the linearly polarized laser light is condensed by a condensing optical system to perform static transmission illumination from the back side of the mask. From the surface of the mask by means of a stationary static illumination device for collecting laser light and an oblique focusing static illumination device for the linearly polarized laser light arranged on the surface side of the mask so as to have an optical axis on the vertical optical axis. The reflected scattered light And an objective lens for condensing the transmitted light obtained by passing through the mask by the condensing static transmission illumination means of the annular illumination laser light, and the reflected scattered light and the transmitted light condensed by the objective lens are branched. Branching optical system, wavelength separating means for separating light obtained by branching by the branching optical system into different wavelengths, and reflected scattered light and transmission that are branched by the branching optical system and are separated by the wavelength separating means. A relay lens for re-imaging the Fourier transform image on the mask obtained by the objective lens on each conjugate plane for each light, and a conjugate Fourier image re-formed by the relay lens in the optical path branched by the branching optical system. A first shield which is arranged on the conversion surface and shields the reflected and scattered light from the circuit pattern which is incident on the objective lens among the reflected and scattered light separated by the wavelength separating means. An inter-filter, a first one-dimensional solid-state image sensor that receives reflected scattered light from the lumpy foreign substance existing on the mask obtained through the first spatial filter, and converts the light into a first pixel signal; Of the transmitted light, which is arranged on the conjugate Fourier transform plane re-imaged by the relay lens in the optical path branched by the system and is separated by the wavelength separation means, the transmitted light other than the thin-film foreign matter incident on the objective lens Retardation plate or a second spatial filter for reducing light and a second primary for receiving diffracted light from a thin film foreign substance obtained through the retardation plate or the second spatial filter and converting the diffracted light into a second pixel signal. An original solid-state image sensor, a first pixel signal converted from the first one-dimensional solid-state image sensor and a second pixel signal converted from the second one-dimensional solid-state image sensor, and a block existing on the mask. An apparatus for inspecting foreign matter on a mask, comprising: an inspecting unit for inspecting the foreign matter and the thin-film foreign matter. 2. The foreign matter inspection device on a mask according to claim 1, wherein the wavelength separating means is installed in each optical path branched by the branching optical system. 3. An apparatus for inspecting foreign matter on a mask according to claim 1, wherein the branching optical system comprises a wavelength separating mirror and the wavelength separating means is also integrated. 4. The foreign matter inspection device on a mask according to claim 1, further comprising a polarizing filter provided in the optical path of the reflected and scattered light separated by the branch optical system. 5. The foreign matter inspection device on a mask according to claim 1, wherein the relay lens is installed between the objective lens and the branch optical system. 6. An apparatus for inspecting foreign matter on a mask according to claim 1, wherein the inclination angle of the linearly polarized laser light emitted by the obliquely converging static illumination means can be adjusted. 7. The mask according to claim 1, further comprising, as the inspection means, a logical sum circuit for calculating a logical sum of the first pixel signal and the second pixel signal. Foreign matter inspection device. 8. A optics for two-dimensionally scanning a mask having a circuit pattern formed thereon and collecting linearly polarized laser light on the surface of the scanned mask from a direction inclined at a predetermined angle with respect to the vertical direction. The system collects the static illumination with the system and collects the ring-shaped illumination laser light, which is concentric with the vertical optical axis passing through the irradiation point to be focused and irradiated and has a shorter wavelength than the linearly polarized laser light, by the focusing optical system Then, static transmission illumination is performed from the back side of the mask, and the objective lens is arranged so as to have an optical axis on the vertical optical axis. An optical system that collects scattered light and the transmitted light obtained by passing through the mask by converging static transmission illumination of the annular illumination laser light and splits the reflected scattered light and the transmitted light collected by the objective lens. Branched off due to different from each other Reflection from the circuit pattern that is separated by the length and is incident on the objective lens by the spatial filter arranged on the conjugate plane of the Fourier transform image on the mask obtained by the objective lens of the separated reflected scattered light by the relay lens. The first-dimensional one-dimensional solid-state imaging device receives the scattered light reflected from the lumped foreign substance existing on the mask by shielding the scattered light, converts the scattered light into the first pixel signal, and the separated transmitted light is the objective lens. Diffraction from the thin-film foreign matter by reducing the transmitted light other than the thin-film foreign matter entering the objective lens by the phase difference plate or the spatial filter arranged on the conjugate plane of the Fourier transform image on the mask obtained by the relay lens. The light is received by the second one-dimensional solid-state image sensor, converted into a second pixel signal, and converted from the first one-dimensional solid-state image sensor. The is converted from the first pixel signal second one-dimensional solid-state image pickup element 2
The method for inspecting foreign matter on a mask, which comprises inspecting lumpy foreign matter and thin-film foreign matter existing on the mask by the pixel signal of 1.