JPH07134104A - Foreign matter inspecting apparatus - Google Patents

Abstract

PURPOSE:To detect granular foreign matters at high precision and detect phase substances, which are stains, etc., as foreign matters by combining a light projecting and receiving system which receives back scattering light by making the incidence angle large with a light projecting and receiving system which receives weak scattering light by making the incidence angle small. CONSTITUTION:After laser beam from a light source 1 is expanded by expanders 2, 3, reflected by oscillation mirror 4, ad led to impinge on the surface of a reticle 9 at wide incident angle Q; 45 deg.<=Q<90 deg.; through a scanning lens 5. The scanning spot is scanned in X-direction and the back scattering light of scattering light due to foreign matters on the reticle 9 is received by a two-dimensional image sensor 15 through reflecting mirror 11 to detect granular foreign matters. Meanwhile, laser beam from a light source 21 is expanded by expanders 22, 23, reflected by oscillation mirror 24, and led to impinge on the surface of the reticle 9 at narrow incidence angle Q; 2 deg.<Q2<45 deg.; and scanning is carried out in X-direction. Weak diffraction light attributed to the foreign matters is received by the two-dimensional image sensor 35 to detect stains, such as spots, etc.

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 for detecting foreign matter other than a circuit pattern attached to a substrate such as a photomask, a reticle or a semiconductor wafer used in a semiconductor element manufacturing process.

[0002]

2. Description of the Related Art Generally, a semiconductor element manufacturing process includes a process of transferring a circuit pattern formed on a substrate such as a reticle or a photomask onto a semiconductor wafer by an exposure device. At this time, if foreign matter such as dust adheres to the substrate, the foreign matter image is also transferred together with the circuit pattern and appears as a defect in the circuit pattern, which causes a reduction in the yield of semiconductor device manufacturing.

Therefore, at present, a step of inspecting the presence or absence of foreign matter on the substrate before the transfer is indispensable. For such a foreign matter inspection, a foreign matter inspection apparatus of a system in which a laser beam is focused on a reticle and scanned to detect scattered light due to the foreign matter is used.

FIG. 4 shows an example of a conventional foreign matter inspection apparatus.
This is because the laser beam emitted from the light source 101 is
The beam expanders 102 and 103 make the beams have a predetermined beam diameter, and then the vibrating mirror 104 and the scanning lens 105.
Is obliquely incident on the surface to be inspected 109, and the scanning spot is moved in a predetermined direction on the surface to be inspected (the locus 107 of the scanning spot
Scan).

If foreign matter adheres to the surface to be inspected, scattered light is generated from the foreign matter. Of these, the backscattered light is received by the light receiving lens 112, the filter 113, and the lens 14 through the light receiving system. The presence or absence of foreign matter is detected by receiving light through the light receiving surface 115 formed of the end faces of the fibers A to F arranged in a slit shape on the pupil plane of the 112 system.

Generally, diffracted light from regularly arranged circuit patterns is discretely generated, and scattered light from a foreign substance is spatially continuous and generated with substantially uniform intensity. ~ If the intensity obtained on the pupil plane through F exceeds a predetermined value set in advance, it is judged as scattered light from a foreign substance, and if there is a variation in intensity for each fiber, it is determined as diffracted light from the pattern. Was.

[0007]

In the conventional foreign matter inspection apparatus as described above, the incident angle of the laser beam on the surface to be inspected is made as large as possible, and the backscattered light generated in almost the same direction as the incident light is detected. Is set. This is because if the intensity difference between the diffracted light from the pattern and the scattered light from the foreign matter is too large, the signal level of the scattered light from the foreign matter, which has a weak intensity, becomes almost 0 and is buried in noise and cannot be detected. Considering the intensity distribution of the diffracted light from
Since the intensity becomes weaker as it goes away from the direction of the 0th-order diffracted light, the accuracy of foreign matter detection is improved by receiving the backscattered light in which the intensity of the pattern diffracted light is sufficiently weak for detecting the foreign matter.

However, in the foreign matter inspection apparatus having such a configuration, although the granular foreign matter is detected with high accuracy, when a phase object such as an oil film or stain is attached on the substrate, the phase object is detected as the foreign matter. It was very difficult to do. Since the phase object is thin and has no height unlike the granular foreign matter, scattered light is hardly generated when the incident angle is large.
Therefore, the conventional foreign matter inspection apparatus cannot detect the light corresponding to the diffracted light from the phase object because its intensity is too weak.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and to provide a foreign matter inspection apparatus which can detect not only granular foreign matter with high accuracy but also phase objects such as stains as foreign matter.

[0010]

In order to achieve the above object, in the foreign matter inspection apparatus according to the invention as defined in claim 1, the first light source and the light flux from the light source are incident on the surface of the object to be inspected at a predetermined incident angle. A first oblique-incidence optical system including a first light-collecting unit that collects light on the upper side, and at least one set of light-receiving optical systems that receives the first scattered light from the surface of the object to be inspected. And a light beam from the light source in the foreign matter inspecting device for detecting the presence or absence of a foreign matter on the surface of the object to be inspected based on an output signal from the light receiving means. A second oblique incidence optical system including a second condensing unit that condenses on the surface of the inspection object at an incident angle different from that of the incident optical system, and receives second scattered light from the surface of the inspection object. At least 1
A second light receiving means composed of at least a pair of light receiving optical systems, and an incident angle of θ ₁ by the first oblique incidence optical system with respect to the surface of the object to be inspected is incident by the second oblique incidence optical system. When the angle is θ ₂ , the following condition is satisfied. 45 ° ≦ θ ₁ <90 °, 0 <θ ₂ <45 °

Further, in the foreign matter inspection apparatus according to the invention described in claim 2, in the foreign matter inspection apparatus according to claim 1,
The first light receiving optical system receives only the first scattered light from the first oblique incidence optical system, and the second light receiving optical system receives the second scattering light from the second oblique incidence optical system. It has means for receiving only light.

[0012]

The present invention has the first aspect in the first oblique-incidence optical system.
The light beam from the light source is condensed by the first condensing means on the surface of the object to be inspected at a predetermined incident angle, and the first scattered light from the surface of the object to be inspected is composed of at least one set of light receiving optical systems. While being received by the first light receiving means, the second scattered light is received by the second light receiving means composed of at least one set of light receiving optical systems, and on the surface of the object to be inspected based on the output signal from the light receiving means. The foreign matter inspection device detects the presence or absence of foreign matter.

Here, it is assumed that the incident angle θ ₁ by the first oblique incidence optical system satisfies the condition of 45 ° ≦ θ ₁ <90 °. Therefore, the incident angle with respect to the surface of the object to be inspected is set to be large, and the backscattered light is received at a position away from the direction of the 0th order diffracted light where the intensity of the diffracted light from the pattern is weak, and high detection accuracy for particulate foreign matter Is obtained. If the incident angle θ ₁ is smaller than the lower limit of the above condition, the detection sensitivity is lowered, which is not practical.

On the other hand, according to the present invention, in the second oblique incidence optical system, the light beam from the second light source is incident on the surface of the object to be inspected by the second condensing means at an incident angle different from that of the first oblique incidence optical system. The second scattered light from the surface of the object to be inspected is received by the second light receiving means including at least one light receiving optical system, and the object to be inspected is based on the output signal from the light receiving means. The presence or absence of foreign matter on the surface is detected, and the incident angle θ ₂ by the second oblique incidence optical system satisfies the condition of 0 <θ ₂ <45 °.

Therefore, the light beam from the second grazing incidence optical system has a small incident angle with respect to the surface of the object to be inspected, and scattered light from a weak phase object which cannot be received by an ordinary foreign matter inspection apparatus can be detected. . The backscattered light obtained at such a small incident angle setting also mixes diffracted light from a pattern whose intensity is not weakened,
With respect to the foreign matter as the phase object, it is not necessary to detect even a minute matter, and it is sufficient if a matter having a certain size can be roughly detected, and the influence of the diffracted light from the pattern does not pose a problem as much as the first light receiving optical system. In addition, regarding the spot size on the surface of the object to be inspected by the second condensing means,
It does not have to be as small as that by the light condensing means. In addition,
When the incident angle θ ₂ exceeds the upper limit of the above condition, the intensity of scattered light from the phase object becomes too weak and detection is difficult.

As described above, according to the foreign matter inspection apparatus of the present invention, not only the particulate foreign matter can be detected accurately, but also the foreign matter as the phase object can be detected.

According to the present invention, the first light receiving optical system receives only the first scattered light from the first oblique incidence optical system,
Further, since the second light receiving optical system is provided with means for receiving only the second scattered light from the second oblique incidence optical system, each light receiving optical system has a signal from a different optical system. Can be avoided.

As such means, for example, there is a method of using laser light sources having different wavelengths for the first light source and the second light source, and providing a wavelength selective filter such as an interference filter in each light receiving optical system. . At this time, the shorter the wavelength of the irradiation light is, the higher the intensity of the scattered light becomes. Therefore, the wavelength of the first light source of the first oblique incidence optical system for the granular foreign matter, which requires a more accurate detection sensitivity, is set. It is desirable to use the shorter one.

In addition to using two light sources having different wavelengths, the first and second light sources having the same wavelength are used, and the first and second scattered lights are shifted by spatially or temporally shifting. It is also possible to distinguish each corresponding light receiving optical system.

[0020]

EXAMPLES The present invention will be described below with reference to examples. FIG. 1 shows a foreign matter inspection apparatus when inspecting the surface of the reticle 9 using light sources having different wavelengths in the first oblique incidence optical system and the second oblique incidence optical system. Here, a laser having a relatively short wavelength (eg, argon) was used as the first light source 1, and a laser having a longer wavelength (eg, helium neon) was used as the second light source 2.

As shown in FIG. 1, first, in the first grazing incidence optical system, the laser beam emitted from the first light source 1 is expanded to a predetermined beam diameter by the beam expanders 2 and 3. , Is reflected by the vibrating mirror 4 and is focused on the surface of the reticle 9 via the scanning lens 5 at a relatively large incident angle to form a scanning spot. The scanning spot scans the surface of the reticle 9 in the x direction as a locus 7 by the vibration of the vibrating mirror 4, and drives a table (not shown) on which the reticle 9 is placed in the y direction to cover the entire surface of the reticle 9. Are scanned. If (granular) foreign matter adheres to the surface of the reticle 9, scattered light is generated, and of this scattered light, backscattered light enters the first light receiving optical system.

In the first light receiving optical system, the scattered light from the foreign matter is reflected by the reflecting mirror 11, and the light receiving lens 12,
After passing through the slit 13 and the lens 14, it reaches the detection unit and is detected. In this embodiment, a two-dimensional image sensor is used as the detection unit, the light receiving surface of which is arranged at a position conjugate with the pupil plane of the light receiving lens 12. Here, since the backscattered light generated in the same direction as the large incident angle is received,
Granular foreign matter can be detected with high accuracy.

On the other hand, in the second oblique incidence optical system, the second
The laser beam emitted from the light source 21 is expanded by the beam expanders 22 and 23 to have a predetermined beam diameter, is then reflected by the vibrating mirror 24, and is reflected on the surface of the reticle 9 via the scanning lens 25. The light is condensed at an incident angle smaller than that of the incident optical system to form a scanning spot. The scanning spot scans the surface of the reticle 9 in the x direction by the vibration of the vibrating mirror 24, and the entire surface of the reticle 9 is scanned by driving the mounting table of the reticle 9 in the y direction. If foreign matter (phase object) is attached on the surface of the reticle 9,
The backscattered light from the foreign matter enters the second light receiving optical system.

In the second light receiving optical system, the scattered light from the foreign matter is reflected by the reflecting mirror 31, and the light receiving lens 32,
After passing through the slit 33 and the lens 34, the light receiving surface thereof reaches a two-dimensional image sensor 35 arranged so as to come to a position conjugate with the pupil plane of the light receiving lens 32 and is detected. Here, since the backscattered light generated in the same direction as the small incident angle is detected, it is possible to detect stains such as stains which are phase objects having no height.

In both light receiving optical systems, the slit 1
3. Since the slit 33 and the slit 33 are respectively conjugate with the spot scanning locus and are composed of interference filters, the light from the other oblique incidence optical system cannot reach the sensor and there is no mixing of signals. . These slits are
Not limited to the interference filter, any filter may be used as long as it has a filter effect on the other light.

Here, a method of processing the pupil image information in the two-dimensional sensors 15 and 35 will be described. First, an image of the pupil plane of each light receiving lens is formed on each two-dimensional sensor. Since the diffracted light due to the pattern regularly formed on the surface to be inspected is discretely generated, the image on the pupil plane is shown in FIG.
2B, the image signal of one scanning line is as shown in FIG. 2B. Further, the scattered light due to the foreign matter is spatially continuously generated, so that the intensity distribution on the pupil plane is substantially uniform, and the image on the pupil plane where the diffracted light due to the pattern and the foreign matter scattered light are mixed is shown in the figure. 2 (c) has an intensity distribution, and the image signal of one scanning line is shown in FIG. 2 (d).
As shown in.

Therefore, when the pattern diffracted light and the foreign substance scattered light are mixed, in order to detect only the signal due to the foreign substance scattered light, the signal intensities B ₁ and B of the portions other than the grid portion of the pattern diffracted light are detected. The presence or absence of a foreign substance can be determined by detecting whether or not B ₂ and B ₃ are 0 or more or a predetermined value or more. Further, when the pattern period is constant over the entire surface to be inspected, the position of the pattern diffracted light is also constant, and therefore the image signal of the portion where the diffracted light does not come may be extracted.

In the above embodiment, two kinds of laser light having different wavelengths are used as means for avoiding mixing of signals from the other optical system into the first and second light receiving optical systems.
The present invention is not limited to this, and even if the laser light of the same wavelength is used, a means for distinguishing the two types of optical systems may be used.

For example, as shown in FIG. 3, a spot scanning position (67) by the first oblique incidence optical system is formed on the surface of the reticle 9.
A) and the spot scanning position (67) of the second oblique incidence optical system.
B) is spatially displaced from the detection method, and AOM
There is a method of temporally separating by using (ultrasonic modulator) or an optical chopper, the laser light of the same wavelength is alternately used for the first optical system and the second optical system.

[0030]

As described above, the present invention has an effect that not only can granular foreign matter be detected with high accuracy, but also foreign matter as a phase object can be detected.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a foreign matter inspection apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic diagram illustrating a method of processing pupil image information in a two-dimensional sensor of the foreign substance inspection apparatus in FIG.

FIG. 3 is a schematic diagram showing a spot scanning locus on a reticle in a modification of the embodiment of the present invention.

FIG. 4 is a schematic configuration diagram of a conventional foreign matter inspection apparatus.

[Explanation of symbols]

 1, 21, 101: Light source 4, 24, 104: Vibration mirror 5, 25, 105: Scanning lens 7, 107, 67A, 67B: Scanning spot locus 9, 109: Reticle 11, 111: Reflection mirror 12, 32, 112 : Light receiving lens 13, 33: Slit (interference filter) 113: Slit 35: Two-dimensional image sensor

Claims (2)

[Claims] 1. A first oblique-incidence optical system comprising a first light source and a first condensing means for condensing a light beam from the light source on a surface of an object to be inspected at a predetermined incident angle, and the object to be inspected. First from the inspection object side
Foreign matter inspecting device for detecting the presence or absence of foreign matter on the surface of the object to be inspected based on an output signal from the light receiving means. In the second oblique incidence, a second light source and a second condensing means for condensing a light beam from the light source onto the surface of the inspection object at an incident angle different from that of the first oblique incidence optical system. The optical system and a second light receiving unit including at least one set of light receiving optical systems for receiving the second scattered light from the surface of the object to be inspected are further provided, and the first light with respect to the surface of the object to be inspected. A foreign matter inspection apparatus satisfying the following conditions when the incident angle by the oblique incident optical system is θ ₁ and the incident angle by the second oblique incident optical system is θ ₂ . 45 ° ≦ θ ₁ <90 °, 0 <θ ₂ <45 ° 2. The first light-receiving optical system receives only the first scattered light from the first oblique-incidence optical system, and the second light-receiving optical system includes the second oblique-incidence optical system. By the second
The foreign matter inspection apparatus according to claim 1, further comprising means for receiving only the scattered light of.