JPH0694630A - Inspecting apparatus for extraneous substance - Google Patents

Abstract

PURPOSE:To obtain an inspecting apparatus for an extraneous substance which can discriminate the extraneous substance from a circuit pattern with high precision irrespective of the pattern on a surface to be inspected. CONSTITUTION:A laser beam emitted from a laser light source 1 forms a beam spot on a surface 4 to be inspected, from an oblique direction, advancing via a vibrating mirror 2 and an f-theta lens 3 for scanning. A pattern diffracted light and an extraneous substance scattered light generated from the surface 4 by the application of the laser beam are sensed in virtually the same direction as the direction of incidence of the laser beam. An image on the eye plane of a light-sensing lens 6 is formed on a two-dimensional image sensor 9 by a relay lens 8 and the presence or absence of an extraneous substance is inspected on the basis of image information obtained from the image sensor 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foreign matter inspection apparatus, and more particularly to detecting foreign matter and circuit pattern defects other than a circuit pattern adhered on a substrate such as a reticle or photomask used in the manufacture of semiconductor elements. The present invention relates to a foreign matter inspection device that is preferably used when performing.

[0002]

2. Description of the Related Art Generally, a semiconductor element such as an IC is manufactured by transferring a circuit pattern formed on a substrate such as a reticle or a photomask onto a wafer coated with a resist by an exposure device. At this time, if foreign matter such as dust is present on the substrate, the foreign matter is transferred together with the circuit pattern, which causes a reduction in the yield of semiconductor device manufacturing.

Therefore, it is indispensable to inspect the presence or absence of foreign matter on the substrate in the process of manufacturing a semiconductor element, and various foreign matter inspection apparatuses have been proposed conventionally. An example of a conventional device of this type is, for example, one disclosed in Japanese Patent Laid-Open No. 1-158308. In this apparatus, the surface to be inspected is illuminated with coherent light to form a Fourier transform pattern of the illuminated area. At this time, the pupil plane of the Fourier transform lens (Fourier transform surface)
A spatial filter is placed on the surface to block the diffracted light from the pattern, and only the scattered light from the pattern defect or foreign matter is passed to form an image on the surface conjugate with the surface to be inspected. This makes it possible to remove the diffraction image of the pattern and detect only the defect (foreign matter) image, and it is possible to inspect the presence or absence of the foreign matter or defect on the surface to be inspected.

Another example of the conventional foreign matter inspection apparatus is disclosed in Japanese Patent Laid-Open No. 3-42556.
In this device, the light emitted from the surface to be inspected by irradiating with an energy beam (laser beam) is detected using a number of spatially arranged optical fibers, and the space of the light generated from the surface to be inspected is detected. The difference in the angular energy distribution distinguishes the pattern diffracted light and the foreign substance scattered light. That is, the energy distribution of the pattern diffracted light has peaks at a certain interval, whereas the energy distribution of the foreign substance scattered light is continuous, and this difference distinguishes the pattern from foreign substances or defects (hereinafter simply referred to as foreign substances). It

[0005]

However, in the conventional foreign matter inspection apparatus as described above, the light-shielding pattern of the spatial filter and the spatial arrangement of the optical fibers cannot be arbitrarily changed. In some cases, it is difficult to distinguish the diffracted light from the pattern and the scattered light from the foreign matter, and there is a problem in that erroneous detection is likely to occur.

That is, since the distribution of the pattern diffracted light is determined according to the arrangement direction and the pitch of the circuit pattern formed on the surface to be inspected, if the arrangement direction and the pitch of the circuit pattern change, the distribution of the diffracted light will naturally occur. Also changes. However, in the conventional device, the light-shielding pattern of the spatial filter and the arrangement of the optical fibers are set assuming a specific circuit pattern, so when inspecting a substrate on which different types of patterns are formed, The inconvenience arises in that pattern diffracted light that should not be received is detected. For this reason, in the conventional device, the pattern is erroneously detected as a foreign matter depending on the type of the circuit pattern, and the highly accurate inspection cannot be performed.

The present invention has been made in view of the above point, and is a foreign substance capable of highly accurately discriminating between a foreign substance and a pattern, regardless of the arrangement direction and pitch of the circuit patterns formed on the surface to be inspected. The purpose is to provide an inspection device.

[0008]

According to a first aspect of the present invention, there is provided a foreign matter inspection apparatus, which comprises an irradiation optical system for obliquely entering a focused light beam onto a surface to be inspected having a pattern formed thereon, and the surface to be inspected. Means for scanning the surface to be inspected with the beam spot by relatively moving the light beam and the spot of the light beam, and light receiving optics for receiving light generated from the surface to be inspected by the irradiation of the light beam. In a foreign matter inspection apparatus having a system, the light receiving optical system is arranged to receive light generated in the same direction as the incident direction of the light beam among the light generated from the surface to be inspected, A substantially pupil plane or a substantially pupil conjugate plane of the light receiving optical system (hereinafter simply referred to as a pupil plane)
Is provided with image pickup means capable of outputting an image of the pupil plane as image information, and inspects the presence or absence of a foreign substance on the surface to be inspected based on the image information output from the image pickup means.

According to a second aspect of the present invention, there is provided a foreign matter inspection device including image processing means for extracting diffracted light information corresponding to diffracted light from a pattern formed on the surface to be inspected from the image information. The presence or absence of the foreign matter is inspected based on image information other than the information.

The numerical aperture of the irradiation optical system in the foreign matter inspection apparatus according to claim 3 can be changed according to the pattern formed on the surface to be inspected.

[0011]

The present invention has been made by paying attention to the fact that when a plurality of circuit patterns are present in the beam spot irradiated from the irradiation optical system, the diffracted light from the patterns is discretely generated. That is, when a plurality of patterns are present in the beam spot, if the light beam generated from the surface to be inspected is received by the light receiving optical system having an opening angle larger than the opening angle of the light beam irradiated to the surface to be inspected. In the pupil plane of the light receiving optical system, there are a portion where the diffracted light from the pattern is incident and a portion where the diffracted light is not incident.

On the other hand, when foreign matter such as dust exists in the beam spot, scattered light from the foreign matter is spatially continuously generated. That is, when foreign matter is present in the beam spot, the foreign matter scattered light is uniformly incident on the entire pupil plane of the light receiving optical system.

Therefore, in the present invention, an image pickup means is provided on the pupil plane of the light receiving optical system to detect the image on the pupil plane as image information,
Based on this image information, the foreign matter and the circuit pattern are discriminated. Specifically, the image information (2
It is possible to extract the signal component of the part where the diffracted light does not exist from the 3D image signal) and inspect for the presence of foreign matter by whether the signal level of the part where the diffracted light does not exist exceeds a threshold value set appropriately. Is.

In the present invention, as described above, the image of the pupil plane of the light receiving optical system is detected as image information, and the presence or absence of foreign matter is inspected based on this image information.
It is not necessary to prevent the pattern diffracted light from entering the light receiving optical system by the arrangement of the spatial filter and the light receiving element, and it is possible to accurately discriminate the pattern and the foreign matter regardless of the formed pattern.

At this time, in order to further improve the accuracy of discrimination between the foreign matter and the circuit pattern, it is preferable to adjust the aperture angle of the irradiation optical system according to the pattern on the surface to be inspected. That is,
When the pitch of the circuit pattern on the surface to be inspected is large, the diffraction angle of the pattern diffracted light becomes small, so the pitch of the diffraction pattern on the pupil plane of the light receiving optical system becomes narrow, and the signal component of the portion where no diffracted light exists Although it is difficult to extract, the diffraction pattern itself can be reduced by reducing the aperture angle of the irradiation optical system. The smaller the size of the diffraction pattern, the more the area where the diffracted light does not exist, that is, the area where only the scattered light of the foreign matter is detected increases. Therefore, even in the case of a relatively rough pattern, the accuracy of distinguishing the foreign matter from the pattern can be improved. It is possible.

Now, in the present invention, among the light generated from the surface to be inspected, the light generated in the substantially same direction as the incident light from the irradiation optical system, that is, the so-called backscattered light is received. Explain why.

First, considering the intensity distribution of the diffracted light generated from the pattern, the intensity in the direction in which the 0th-order diffracted light (regular reflection light) is generated is the maximum, and the intensity becomes weaker as the distance from the 0th-order diffracted light increases. Become. Even if the intensity of the pattern diffracted light is high, discrimination based on the discreteness of the pattern diffracted light and the continuity of the foreign substance scattered light is basically possible, but if the intensity of the pattern diffracted light is too high, there are the following inconveniences. . That is,
When detecting the foreign substance scattered light and the pattern diffracted light by the same image pickup means, if the intensity difference between the two is too large, the signal level of the foreign substance scattered light with weak intensity becomes almost 0, and the signal level is buried in noise. It is possible that the threshold is not exceeded. In such a case, even if the foreign matter is actually present, the foreign matter cannot be detected and an accurate inspection cannot be performed.

Therefore, in the present invention, the light beam is obliquely incident on the surface to be inspected to receive the backscattered light which makes the intensity of the pattern diffracted light sufficiently weak, thereby improving the detection accuracy of the foreign matter. is there. At this time, it may be possible to collectively irradiate a region having a certain area without condensing the light beam on the surface to be inspected, but in this case, the light receiving optical system has a so-called “orientation” configuration, The optical system becomes very complicated. Therefore, in the present invention, the light beam is condensed on the surface to be inspected and the surface to be inspected is scanned with the beam spot.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view of a main part of the foreign matter inspection apparatus according to this embodiment. In the figure, a laser beam emitted from a laser light source 1 enters a scanning f-θ lens 3 through a vibrating mirror 2, is reflected by a mirror 15, and forms a beam spot on a surface 4 to be inspected from an oblique direction. To do. Then, the beam spot on the surface 4 to be inspected is moved along the scanning locus 5 by rotating the vibrating mirror 2 in the direction of the arrow. At this time, the surface to be inspected 4 is transported in a direction orthogonal to the scanning locus 5 by a transport mechanism (not shown), so that the entire surface to be inspected 4 is scanned by the beam spot.

In the present embodiment, the laser light source 1, the vibrating mirror 2, the scanning f-θ lens 3 and the mirror 15 constitute an irradiation optical system. The aperture angle of this irradiation optical system is 4
It can be adjusted according to the pitch of the circuit pattern (not shown) formed above, the wavelength of the laser beam, the expected type of foreign matter, and the like.

On the other hand, the pattern diffracted light and the foreign substance scattered light generated from the surface to be inspected 4 by the scanning with the beam spot are reflected by the mirror 16 and enter the light receiving lens 6. The image of the pupil plane of the light receiving lens 6 is formed on the two-dimensional image sensor 9 by the relay lens 8. That is,
The pupil surface of the light receiving lens 6 and the light receiving surface of the two-dimensional image sensor 9 are conjugate. The slit 7 is arranged at a position conjugate with the surface 4 to be inspected, shields stray light, and scans the trajectory 5.
It plays the role of improving the detection sensitivity by passing only the light from.

In this embodiment, the mirror 16, the light receiving lens 6, the slit 7, the relay lens 8 and the two-dimensional image sensor 9 constitute a light receiving optical system. This light receiving optical system corresponds to the above-mentioned irradiation optical system. It is arranged so as to receive light from the surface to be inspected 4 in a direction substantially coincident with the incident direction of the laser beam. In this way, the backscattered light from the surface to be inspected 4 is received, because the diffraction order of the pattern diffracted light increases and the intensity of the diffracted light decreases in this direction, so it is weaker than the pattern diffracted light. This is because it is suitable for detecting such foreign matter scattered light.

Further, in this embodiment, as shown in the figure, two light receiving optical systems having the same structure are arranged so as to be substantially symmetrical with respect to the optical axis of the irradiation optical system. Two light-receiving optical systems are provided in this embodiment for the following reason.

First, the arrangement of the light receiving optical system is such that the light from the surface to be detected 4 is received at a position slightly shifted in the direction of the scanning locus 5 with respect to the laser beam incident direction (in the case of FIG. 1).
In addition, an arrangement is conceivable in which the light from the surface to be inspected 4 is received at a position slightly shifted upward or downward with respect to the laser beam incident direction. However, the light receiving lens 6 of the light receiving optical system is actually quite large, and disposing the light receiving optical system on the upper side or the lower side of the irradiation optical system has many difficulties in assembling the apparatus.

Therefore, in this embodiment, as shown in FIG. 1, the light receiving optical system is arranged at a position slightly displaced from the irradiation optical system in the direction of the scanning locus 5, but in principle, It is possible to detect foreign matter with a single light receiving optical system. However, if only the light-receiving optical system on the front side of the drawing is provided, the scattered light of the foreign matter is likely to be received when the foreign matter is on the front side of the scanning locus 5, and the foreign matter is located on the back side of the scanning locus 5. It is conceivable that scattered light is difficult to be received. Therefore, in the present invention, the two light receiving optical systems are arranged symmetrically with respect to the incident direction of the laser beam so that the detection sensitivity does not differ depending on the position of the foreign matter.

Now, the light intensity distribution on the pupil plane of the light receiving lens 6 will be described. FIG. 2 shows an image of the pupil plane of the light receiving lens 6 formed on the two-dimensional image sensor 9, and the diffracted light by the pattern formed on the surface to be inspected 4 is shown by a diffraction pattern 11 in the figure. The scattered light due to the foreign matter attached on the surface 4 is indicated by scattered light 12. Further, FIG. 3 shows an image signal of one scanning line obtained from the two-dimensional image sensor 9.

First, FIG. 2A shows a case in which the beam spot is sufficiently large with respect to the pitch of the circuit pattern (periodic pattern) and a plurality of patterns are present in the beam spot, and a foreign substance is also present in the beam spot. The distribution is shown. As shown in the figure, the pattern diffracted light 11 is discretely distributed at a predetermined pitch (inversely proportional to the pitch of the pattern on the surface 4 to be inspected), whereas the foreign particle scattered light 12 is uniform. It is distributed.

As shown in FIG. 3A, the image signal in this case has a high peak at the position corresponding to the pattern diffracted light 11, and the portion 12 of only the scattered light from the foreign matter has a certain level of uniformity. It becomes the background.

FIG. 2B shows a case where only the circuit pattern is present in the beam spot and there is no foreign matter. In this case, the image signal is other than the pattern diffracted light 11 as shown in FIG. 3B. The light intensity of the portion becomes almost zero.

Further, FIG. 2C shows a case where only a foreign substance exists in the beam spot, and the image signal in this case has a uniform light intensity of a certain level as shown in FIG. 3C. Become.

Next, an example of the foreign matter inspection method in this embodiment will be described with reference to FIGS. First, FIG. 4A corresponds to FIG. 3A described above and shows an image of the pupil plane of the light receiving lens 6 formed on the two-dimensional image sensor 9. Similar to FIG. 3, the pattern diffracted light is shown by the diffraction pattern 11 in the figure, and the scattered light by the foreign matter adhering to the surface to be inspected 4 is shown by the scattered light 12.

When the foreign matter on the surface 4 to be inspected is irradiated with the laser beam from the irradiation optical system, the laser beam is spatially and uniformly scattered by the foreign matter as described above. That is, in the region of the scattered light 12 on the pupil plane, the light intensity is almost averaged. The light intensity changes according to the size of the foreign matter.

Next, FIG. 5 is a flow chart showing an example of the foreign matter inspection method in this embodiment. Hereinafter, each step will be described step by step. [Step 100] In step 100, the reading of the image signal by the two-dimensional image sensor 9 of FIG. 1 is started. At this time, the image of the pupil plane of the light receiving lens 6 detected by the two-dimensional image sensor 9 is as shown in FIG. 4A, and the control unit (not shown) displays the image of the pupil plane along the scanning line 10. To detect. Then, the process proceeds to step 101.

[Step 101] In Step 101,
The control unit detects the intensity of this image signal based on the read image signal, and stores the intensity at the position along the scanning line in a memory unit (not shown). When detecting the image of the pupil plane shown in FIG. 4A, the intensity of the image signal along the scanning line 10 is as shown in FIG. 4B. Then, the process proceeds to step 102.

[Step 102] In Step 102,
The control unit causes the memory unit to store the intensity at the lowest intensity position (bottom position) based on the intensity of the image signal. In this case, the intensity of the image signal at the bottom position B ₁ is stored. Then, the process proceeds to step 103.

[Step 103] In step 103,
The control unit causes the memory unit to store the intensity at the maximum value position (peak position) based on the intensity of the image signal in step 101. In this example, the control unit controls the peak position P
The strength at ₁ is stored in the memory section. Then, the process proceeds to step 104.

[Step 104] In step 104,
The control unit determines whether the reading of the image signal along the scanning line 10 is completed. If the reading is not completed, the process proceeds to step 101, and if the reading is completed, the process proceeds to step 105. Now, scan line 1
Since the image signal accompanying 0 is being read, the control unit moves to step 101 again and continues to read the image signal. Then, steps 102 to 103 are sequentially executed to store the image signal intensities at the bottom positions B ₂ , B ₃ and the peak position P ₂ in the memory unit,
Go to step 104. At this time, in step 104, since the reading of the image signal for one scanning line has been completed, the process proceeds to step 105.

[Step 105] In step 105,
Regarding the intensities at the bottom positions B ₁ , B ₂ , B ₃ stored in the memory unit, these bottom positions B ₁ , B ₂ ,
The average value K of the intensities at B ₃ is calculated, and the process proceeds to step 106.

[Step 106] In step 106,
The control unit determines whether or not the average value K of the intensity at the bottom position is 0. If K = 0 here, the control unit determines that no foreign matter is present on the surface 4 to be inspected, and proceeds to step 108. Then, if K ≠ 0, the control unit determines that a foreign substance is present on the surface 4 to be inspected, and proceeds to step 107.

[Step 107] In step 107,
The control unit reads out the image signal read from the two-dimensional image sensor 9 from the memory unit and converts it into an image signal in which the intensity equal to or higher than a value (K + σ) obtained by adding a predetermined value σ to the average value K is set to 0. The converted image signal is stored in the memory unit as foreign object data. Then step 1
Move to 08.

It should be noted that the predetermined value σ is preferably a value that allows the light scattered by the foreign matter to contain the intensity distribution shown on the two-dimensional image sensor 9. In the present embodiment, this value σ is set.
Has been previously determined based on experimental data. In this example, the image signal read from the two-dimensional image sensor 9 is an image signal as shown in FIG. 4B, and if a portion showing an intensity of K + σ or more is converted into 0 in this image signal, The image signal shown in FIG. 4 (c), that is, the foreign substance data.

[Step 108] In step 108,
The control unit determines whether reading of all the scanning lines has been completed. Here, if the reading of all the scanning lines is completed, the process proceeds to step 110, and if the reading of all the scanning lines is not completed, the process proceeds to step 109.

In order to simplify the explanation, in the present embodiment, in the image of the pupil plane shown in FIG. 4 (a), only the scanning line 10 is shown as the scanning line to be read out. Image reading is performed so that scanning is performed sequentially from the edge of the image on the pupil plane.

[Step 109] In Step 109,
The control unit starts reading the next scanning line. afterwards,
Go to step 101. Then, from step 101 to step 109 until reading of all the scanning lines is completed.
Are sequentially executed.

[Step 110] In Step 110,
The control unit performs integration of the foreign substance data stored in the memory unit for each scanning line, adds integrated values corresponding to each scanning line, and proceeds to step 111, that is, FIG.
When the foreign substance data shown in (c) is integrated, the area becomes a shaded area, and this area is added for each scanning line.

[Step 111] In Step 111,
The control unit determines the size of the foreign matter adhering to the surface to be inspected 4 based on the added integrated value. At this time, it is preferable that the correspondence between the added integral value and the size of the foreign matter is stored in the memory unit in advance. Step 10 above
With 0 to 111, it becomes possible to detect the foreign matter deposited on the surface 4 to be inspected and to estimate the size of the foreign matter.

If only the presence of foreign matter is detected, the operation of storing the intensity value of the image signal in step 102 in the memory section, the conversion to foreign matter data in step 107, and steps 110 to 111. The operation of estimating the size of the foreign substance from the foreign substance data shown in FIG.

Further, since the intensity of the image on the pupil plane due to the scattered light from the foreign matter adhering to the surface 4 to be inspected is uniformly distributed over the entire area of this pupil plane, it is determined whether or not the foreign matter is detected in step 106. If it is determined that the average value K of the intensities at the bottom position is K = 0, the foreign matter inspection may be terminated because there is no foreign matter.

Further, in the above description, the detection of the foreign matter adhering to the surface to be inspected has been described. However, the apparatus according to the present invention has a defect in the pattern itself formed on the surface to be inspected (a chip or an unnecessary protrusion). It goes without saying that it can also be applied to the inspection of.

[0050]

As described above, according to the present invention, the image of the pupil plane of the light receiving means is detected as image information, and the foreign matter and the circuit pattern are discriminated based on this image information. The foreign matter inspection can be performed with high accuracy regardless of the arrangement pitch and the direction of the formed pattern. Also,
If you examine the relationship between the size of foreign matter and the intensity of scattered light in advance,
It is possible to estimate not only the presence or absence of foreign matter but also the size of foreign matter.

[Brief description of drawings]

FIG. 1 is a perspective view of essential parts of a foreign matter inspection apparatus according to an embodiment of the present invention.

FIG. 2 is a conceptual diagram showing an image of a pupil plane of a light receiving lens,
(A) shows the case where the pattern and the foreign matter exist in the beam spot, (b) shows the case where only the pattern exists in the beam spot, and (c) shows the case where only the foreign matter exists in the beam spot.

FIG. 3 is a diagram showing an intensity distribution of an image signal along a scanning line, and (a) to (c) correspond to the cases of (a) to (c) of FIG.

FIG. 4A is a conceptual diagram showing an image of a pupil plane of a light receiving lens, and FIGS. 4B and 4C are diagrams showing intensity distributions of image signals along scanning lines.

FIG. 5 is a flow chart for explaining an example of a foreign matter inspection method in the embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Laser light source, 2 ... Vibration mirror, 3 ... Scanning f-theta lens, 4 ... Test surface, 5 ... Scan locus, 6 ... Light receiving lens, 7
... slits, 8 ... relay lens, 9 ... two-dimensional image sensor, 10 ... scanning line, 11 ... pattern diffracted light, 12 ...
Foreign matter scattered light, 15, 16 ... Mirror.

Claims (3)

[Claims] 1. An irradiation optical system for obliquely entering a focused light beam onto a test surface having a pattern formed on the surface,
Scanning means for scanning the surface to be inspected with a beam spot by relatively moving the surface to be inspected and the spot of the light beam; and light generated from the surface to be inspected by irradiation of the light beam. In a foreign matter inspection apparatus having a light receiving optical system for receiving light, the light receiving optical system is arranged so as to receive light generated from the surface to be inspected, which light is generated in substantially the same direction as the incident direction of the light beam. At the same time, the substantially pupil plane or the substantially pupil conjugate plane of the light receiving optical system is provided with image pickup means capable of outputting an image of the pupil plane or the pupil conjugate plane as image information, and image information outputted from the image pickup means A foreign matter inspection device for inspecting the presence or absence of a foreign matter on the surface to be inspected based on the above. 2. An image processing means for extracting diffracted light information corresponding to diffracted light from a pattern formed on the surface to be inspected from the image information, based on image information other than the diffracted light information. The foreign matter inspection apparatus according to claim 1, wherein the presence or absence of the foreign matter is inspected. 3. The foreign matter inspection apparatus according to claim 1, wherein the numerical aperture of the irradiation optical system can be changed according to a pattern formed on the surface to be inspected.