JP3336392B2 - 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 for detecting foreign matter other than a circuit pattern adhered to a substrate such as a photomask, a reticle, or a semiconductor wafer used in a semiconductor device manufacturing process.

[0002]

2. Description of the Related Art Generally, a semiconductor device 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 apparatus. 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, appears as a defect in the circuit pattern, and causes a reduction in the yield of semiconductor device production.

Therefore, at present, a step of inspecting the substrate for the presence or absence of foreign matter before transfer is indispensable. For such a foreign substance inspection, a foreign substance inspection apparatus of a type in which a laser beam is condensed and scanned on a reticle to detect scattered light due to the foreign substance 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
After having a predetermined beam diameter by the beam expanders 102 and 103, the vibration mirror 104 and the scanning lens 105
The scanning spot is condensed at an oblique incidence on the surface 109 to be inspected, and the scanning spot moves in a predetermined direction
Scanning).

If foreign matter adheres to the surface to be inspected, scattered light is generated from the foreign matter. Among them, the backward scattered light is transmitted through a light receiving system consisting of a light receiving lens 112, a filter 113 and a lens 14. The presence / absence of a foreign substance is detected by receiving light through a light receiving surface 115 composed of end faces of fibers A to F arranged in a slit shape on the pupil plane of the 112 system.

Generally, diffracted light from a regularly arranged circuit pattern is discretely generated, and scattered light from a foreign substance is spatially continuously generated at substantially uniform intensity. When the intensity obtained on the pupil plane via F exceeds a predetermined value, it is determined as scattered light from a foreign substance, and when there is a variation in intensity for each fiber, it is determined as diffracted light from the pattern. Was.

[0007]

In the above-described conventional foreign matter inspection apparatus, the angle of incidence of the laser beam on the surface to be inspected is made as large as possible, and the backscattered light generated in substantially the same direction as the incident light is detected. It is set as follows. 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 with the weak foreign matter is almost close to 0 and cannot be detected because it is buried in noise and cannot be detected. Considering the intensity distribution of the diffracted light from
Since the intensity becomes weaker as the distance from the direction of the 0th-order diffracted light increases, the accuracy of foreign matter detection is improved by receiving the backscattered light whose pattern diffracted light intensity is sufficiently weak for detecting foreign matter.

However, in the foreign substance inspection apparatus having such a configuration, particulate foreign substances are accurately detected. However, if a phase substance such as an oil film or stains adheres to the substrate, the phase substance is detected as a foreign substance. It was very difficult to do. Since the phase object is a thin object having no height unlike the granular foreign material, scattered light hardly occurs when the incident angle is large.
Therefore, in the conventional foreign matter inspection apparatus, the light corresponding to the diffracted light from the phase object has too low intensity to be detected.

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 particulate foreign matter with high accuracy but also phase objects such as spots as foreign matter.

[0010]

In order to achieve the above object, in the foreign matter inspection apparatus according to the first aspect of the present invention, a first light source and a light beam from the light source are irradiated on a surface of an object to be inspected at a predetermined incident angle. A first oblique incidence optical system comprising first condensing means for converging light thereon, and a first optical system comprising at least one set of light receiving optical systems for receiving first scattered light from the surface of the inspection object. A foreign matter inspection device for detecting the presence or absence of foreign matter on the surface of the inspection object based on an output signal from the light receiving means, wherein a second light source and a light beam from the light source are reflected by the first oblique light source. A second oblique incidence optical system including a second light condensing means for condensing light on the surface of the inspection object at an incident angle different from that of the incident optical system, and receiving a second scattered light from the inspection object surface At least one
A second light receiving means comprising at least one set of light receiving optical systems, wherein the incident angle with respect to the inspection object surface by the first oblique incidence optical system is θ ₁ , and the incident angle by the second oblique incidence optical system is when the corner is theta _2, and with the following condition is satisfied. 45 ° ≦ θ ₁ <90 °, 0 <θ ₂ <45 °

According to a second aspect of the present invention, there is provided a foreign matter inspection apparatus according to the first aspect.
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 a second scattered light from the second oblique incidence optical system. It has means for receiving only light. Also, billing
In the foreign matter inspection method according to the invention according to claim 3, claim 1 or
The foreign matter inspection device according to claim 2 is used to inspect the surface to be inspected.
It inspects things.

[0012]

According to the present invention, there is provided a first obliquely incident light optical system, comprising:
A light beam from the light source is condensed on the surface of the inspection object at a predetermined incident angle by the first light condensing means, and the first scattered light from the inspection object surface is composed of at least one or more light receiving optical systems. While receiving the light by the first light receiving means, the second scattered light is received by the second light receiving means comprising at least one or more sets of light receiving optical systems, and on the surface of the inspection object based on an output signal from the light receiving means. This is a foreign matter inspection device that 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 test object is set large, and the backscattered light is received at a position distant from the direction of the 0th-order diffracted light, at which the intensity of the diffracted light from the pattern becomes weak. Is obtained. Note that the incident angle theta ₁ is smaller than the lower limit of the above condition is not practical fall detection sensitivity.

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 inspection object at an incident angle different from that of the first oblique incidence optical system by the second focusing means. And a second scattered light from the surface of the object to be inspected is received by a second light receiving means comprising at least one set of light receiving optical systems, and the object to be inspected is received based on an output signal from the light receiving means. This is to detect the presence or absence of foreign matter on the surface, and the incident angle θ ₂ by the second oblique incidence optical system satisfies the condition of 0 <θ ₂ <45 °.

Therefore, the luminous flux of the second oblique incidence optical system has a small incident angle with respect to the surface of the test object, and can detect scattered light from a phase object having a low intensity that cannot be received by a normal foreign matter inspection device. . Note that the backscattered light obtained at such a small incident angle setting also includes diffracted light from a pattern whose intensity is not so weak.
Regarding foreign matter as a phase object, it is not necessary to detect even a very small one, and it is sufficient that an object having a certain size can be roughly detected, and the effect of diffracted light from the pattern is less problematic than in the first light receiving optical system. In addition, the spot size on the surface of the test object by the second light condensing means is also equal to the first size.
It is not necessary to make the size smaller than that by the light collecting means. In addition,
When the incident angle theta ₂ exceeds the upper limit of the condition, the scattered light from the phase objects is difficult to detect the strength is too weak.

As described above, according to the foreign matter inspection apparatus of the present invention, it is possible to detect not only particulate foreign matter with high accuracy but also foreign matter as a phase object.

Further, in the present invention, the first light receiving optical system receives only the first scattered light by 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 by 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 in which laser light sources having different wavelengths are used for the first light source and the second light source, and a wavelength selective filter such as an interference filter is provided in each light receiving optical system. . At this time, since the intensity of the scattered light increases as the wavelength of the irradiation light becomes shorter, the wavelength of the first light source of the first oblique incidence optical system for the particulate foreign matter requiring higher precision detection sensitivity is increased. It is desirable to use the shorter one.

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

[0020]

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 (for example, argon) is used as the first light source 1, and a laser having a longer wavelength (for example, helium neon) is used as the second light source 2.

As shown in FIG. 1, first, in a first oblique incidence optical system, a laser beam emitted from a first light source 1 is expanded to a predetermined beam diameter by beam expanders 2 and 3. The light is reflected by the oscillating mirror 4 and condensed 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 trajectory 7 by the vibration of the vibrating mirror 4, and the table (not shown) on which the reticle 9 is mounted is driven in the y direction to move the entire surface of the reticle 9. Is scanned. If (granular) foreign matter adheres to the surface of the reticle 9, scattered light is generated, and of the scattered light, backward scattered light is incident on 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 is reflected by the light receiving lens 12,
After passing through the slit 13 and the lens 14, the light reaches the detection unit and is detected. In this embodiment, a two-dimensional image sensor arranged so that its light receiving surface is conjugate with the pupil plane of the light receiving lens 12 is used as the detection unit. Here, to receive the backscattered light generated in the same direction as the large incident angle,
Granular foreign matter can be detected with high accuracy.

On the other hand, in the second oblique incidence optical system,
The laser beam emitted from the light source 21 is expanded to a predetermined beam diameter by the beam expanders 22 and 23, then reflected by the vibrating mirror 24, and passed through the scanning lens 25 onto the surface of the reticle 9 to form a first oblique beam. The light is condensed at an incident angle smaller than that in the case 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 reticle 9 mounting table in the y direction. If foreign matter (phase object) adheres to the surface of the reticle 9,
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 is reflected by the light receiving lens 32,
After passing through the slit 33 and the lens 34, the light reaches the two-dimensional image sensor 35 arranged so that the light receiving surface thereof is 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 a stain such as a stain, which is a phase object having no height.

In the two light receiving optical systems, the slit 1
3. Since the slits 33 are each conjugate with the spot scanning locus and are constituted by an interference filter, the light from the other oblique incidence optical system cannot reach the sensor and there is no signal mixing. . In addition, these slits
The filter is not limited to the interference filter and may be any filter that has a filter effect on the other light.

Here, a method of processing 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 test surface is discretely generated, the image on the pupil plane is shown in FIG.
As shown in FIG. 2 (b), the image signal of one scanning line is as shown in FIG. 2 (b). In addition, since the scattered light due to the foreign matter is continuously generated spatially, 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 FIG. 2C, and the image signal of one scanning line is shown in FIG.
As shown in FIG.

Therefore, in the case where the pattern diffracted light and the foreign matter scattered light are mixed, in order to detect only the signal due to the foreign matter scattered light, the signal intensities B ₁ , B ₁ of the parts other than the lattice portion of the pattern diffracted light are required. _2, B ₃ can determine the presence or absence of a foreign object by detecting whether 0 or more or a predetermined value or more. In addition, when the pattern period is constant over the entire surface to be inspected, the position of the pattern diffracted light is also constant, so that it is sufficient to extract an image signal of a portion where the diffracted light does not come.

In the above-described embodiment, two types of laser beams 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 a configuration using laser light of the same wavelength is used, it suffices if there is means for distinguishing two types of optical systems.

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

[0030]

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

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a foreign matter inspection apparatus according to one 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 matter inspection device in FIG. 1;

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 device.

[Explanation of symbols]

 1, 21, 101: light source 4, 24, 104: vibrating mirror 5, 25, 105: scanning lens 7, 107, 67A, 67B: scanning spot locus 9, 109: reticle 11, 111: reflecting mirror 12, 32, 112 : Light receiving lens 13, 33: slit (interference filter) 113: slit 35: two-dimensional image sensor

Claims (3)

(57) [Claims] A first oblique incidence optical system comprising: a first light source; and a first light condensing means for condensing a light beam from the light source on a surface of the inspection object at a predetermined incident angle; First from the inspection object side
A first light receiving means comprising at least one set of light receiving optical systems for receiving scattered light, and a foreign matter inspection apparatus for detecting presence or absence of foreign matter on the surface of the inspection object based on an output signal from the light receiving means A second oblique incidence comprising: a second light source; and a second condensing means for condensing a light beam from the light source on the surface of the inspection object at an incident angle different from that of the first oblique incidence optical system. An 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 inspection object. A foreign matter inspection apparatus characterized by satisfying the following conditions when the incident angle by the oblique incidence optical system is θ ₁ and the incident angle by the second oblique incidence 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 by the first oblique incidence optical system, and the second light receiving optical system is the second oblique incidence optical system. By the second
2. The foreign matter inspection apparatus according to claim 1, further comprising means for receiving only the scattered light. (3) Foreign matter inspection according to claim 1 or claim 2.
Inspecting foreign matter on the surface to be inspected using the device
Foreign matter inspection method.