JPH0365862B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a foreign matter inspection apparatus suitable for inspecting foreign matter on a surface on which a pattern is formed, such as a patterned wafer or a photomask.

[Prior Art] Wafers and the like used in the manufacture of semiconductor devices are extremely susceptible to foreign matter adhesion, so a foreign matter inspection device is used to inspect the surface of wafers for foreign matter.

Such a wafer foreign matter inspection device is designed to spirally scan the wafer surface by irradiating an S-polarized beam onto the wafer surface while rotating and moving the wafer, and then pass the reflected light from the wafer surface into a lens system. A known method is to collect light from the reflected light, extract a P-polarized light component from the reflected light using a polarizing plate, make it incident on a photoelectric conversion element, and detect foreign matter on the wafer surface based on the level of this photoelectric conversion signal.

Even if a pattern exists within the irradiation spot of the S-polarized beam, the surface of the pattern is microscopically smooth, so that the reflected light is almost exclusively the S-polarized component. On the other hand, since the surface of a foreign object generally has minute irregularities, if a foreign object exists within the irradiation spot, the irradiated S-polarized beam will be scattered and the plane of polarization will be disturbed.
The reflected light will contain a considerable amount of P-polarized light component. Therefore, by comparing the level of the photoelectric conversion signal of the P-polarized light component with a certain threshold value, and determining that it is a foreign object when the photoelectric conversion signal exceeds the threshold value, the foreign object can be detected by distinguishing it from the pattern.

[Problems to be Solved] However, when such a conventional foreign matter inspection device attempts to detect minute foreign matter, there are cases in which patterns are periodically erroneously detected.

[Object of the Invention] An object of the present invention is to provide a foreign matter inspection device that prevents such erroneous detection of patterns.

[Means for Solving the Problem] According to the inventor's research, patterns are erroneously detected in conventional foreign object inspection equipment because the irradiation direction of the S-polarized beam is within a certain range with respect to the normal direction of the pattern. This often occurs when the angle is angled. In the case of a conventional scanning method in which the ratio inspection plane is rotated, a pattern satisfying such conditions appears periodically at a certain angle.

When a certain pattern meets such an angle condition, the level of the P-polarized light component ratio in the reflected light from that pattern is the same as the P-polarized light component included in the reflected light from a relatively small-diameter foreign object. level. For this reason, when the threshold value for comparison with the photoelectric conversion signal of the P-polarized light component is selected to detect a foreign object with a relatively small diameter, the pattern and the foreign object cannot be discriminated, and the pattern is erroneously detected.

Focusing on these points, the foreign matter inspection apparatus according to the present invention includes a means for XY scanning a surface to be inspected with an S-polarized beam, and a means for photoelectrically converting the P-polarized component of the reflected light of the S-polarized beam from the surface to be inspected. and means for determining the presence or absence of a foreign object on the surface to be inspected based on the output signal of the photoelectric conversion element, and the means for performing the XY scan includes at least a means for main scanning of the XY scan. The S-polarized beam is waved linearly in the main scanning direction, and the P of the reflected light is
The means for making the polarized light component enter the photoelectric conversion element includes a moving slit in which a transparent part moves to follow the S-polarized beam, and the P-polarized light component that enters the photoelectric conversion element passes through the transparent part. Constructed to be forced.

[Function] Most wafer patterns are oriented in the orthogonal axis direction with respect to the orientation flat. Naturally, the same applies to photomasks and reticles.

Therefore, if the main and sub-scanning directions of the XY scan are selected so that the main pattern and the irradiation beam do not have an unfavorable angular relationship as described above, the erroneous detection of patterns as in the conventional method can be almost eliminated. This will no longer occur, and foreign objects can be reliably distinguished from the pattern and detected.

Further, the output signal of the photoelectric conversion element includes not only signal components related to foreign objects but also background noise determined by the state of the surface to be inspected. In order to increase the signal-to-noise ratio of the signal and increase the detection sensitivity of minute foreign objects, it is necessary to narrow down the observation field sufficiently. However, in the case of the method of main scanning by swinging the S-polarized beam as in the present invention, such a field diaphragm cannot be performed with a fixed slit as in the conventional apparatus.

On the other hand, in this invention, the transparent part is S
Since it uses a moving slit that moves to follow the polarized beam, the observation field of view can be sufficiently narrowed down and the sensitivity for detecting minute foreign objects can be increased.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a perspective view showing a simplified structure of a foreign matter inspection apparatus to which the present invention is applied, and FIG. 2 is a schematic cross-sectional view showing a part thereof in an enlarged manner.

In FIG. 1, 10 is a movable table mechanism movable at least in the Y direction, and its driving means, encoder for position detection, etc. are omitted in the figure. This moving table mechanism 10 includes a wafer 1
A chuck 14 is attached to the chuck 14 for holding the parts 2 and the like by, for example, vacuum suction.

In this foreign matter inspection device, as an S-polarized beam,
An S-polarized laser light beam is used. To generate it, S-polarized laser oscillators 16, 18
is provided. The S-polarized laser oscillator 16 is
It is a device that generates an S-polarized laser beam of a certain wavelength λ ₁ , and is, for example, a semiconductor laser oscillator with a wavelength of about 8300 angstroms. S-polarized laser oscillator 1
8 generates an S-polarized laser beam of another wavelength λ ₂ , for example, a He--Ne laser oscillator with a wavelength of 6328 angstroms. Generating S-polarized laser beams with different wavelengths in this way is
This is to increase the irradiation density of the S-polarized laser beam on the surface to be inspected, and to avoid the influence when the pattern row on the surface to be inspected acts as a diffraction grating to enable detection of foreign objects.

After passing through the beam expander 20, the S-polarized laser beam having the wavelength λ ₁ is reflected by the half mirror 22 and enters the galvanometer mirror 24 for main scanning. The S-polarized laser beam of wavelength λ ₂ passes through the beam expander 26 and the half mirror 22 and enters the galvanometer mirror 24 .

Each beam is reflected by the galvanometer mirror 24, passes through the f-theta lens 30, and hits the surface of the wafer 12 (surface to be inspected) at an irradiation angle φ of approximately 2° (see Figure 2).
irradiated with. Here, the galvanometer mirror 24 is
Since the driving means (not shown) causes the S-polarized laser beam of each wavelength to rotate back and forth at high speed as shown by the arrow 28, the S-polarized laser beam of each wavelength is swung by a certain angle in the X direction (main scanning direction) and enters the f-theta lens 30. I am forced to do it. Therefore, the spot of the S-polarized laser beam on the wafer surface (surface to be inspected) is located at the galvanometer mirror 2.
It moves linearly at high speed in the X direction according to the rotation of 4.
In other words, main scanning is performed.

In synchronization with this main scanning, the moving table mechanism 10
The chuck 14 is moved in the Y direction by pitch feeding. By this movement in the Y direction, sub-scanning is performed by the S-polarized laser beam. In this way, the wafer surface (surface to be inspected) is scanned in the XY direction.

An elliptical mirror (semi-cylindrical lens) 34 is provided to collect reflected light in the Z direction from the wafer surface (surface to be inspected). On the lower surface of this elliptical mirror 34, there is an elongated opening 36 extending in the X direction as a light-transmitting window, facing the position corresponding to the main scanning line of the S-polarized laser beam on the wafer surface (detection surface). is formed. This opening has
A polarizing plate 38 is provided as an S-polarization cut filter.

Further, as shown in FIG. 2, a fixed light shielding plate 60 is fixed to the lower side of the polarizing plate 38, and a rotating light shielding plate 62 is provided below the fixed light shielding plate 60. These constitute a moving slit, the details of which are shown and explained in FIG. 3. The fixed light-shielding plate 60 is formed by, for example, covering one surface of a rectangular transparent plate such as transparent glass with a light-shielding thin film, leaving a narrow light-transmitting area 60A in the main scanning direction. The rotating light-shielding plate 62 is formed by, for example, covering one surface of a circular transparent plate such as transparent glass with a light-shielding thin film, leaving a substantially elliptical light-transmitting region 62A. The rotating light shielding plate 62 is fixed to a rotating shaft 63 at the center, and this rotating shaft 63 is driven by a rotation drive mechanism (not shown) to rotate the galvano mirror 2.
It is rotationally driven in synchronization with the drive of 4. the result,
The overlapping portion of the transparent regions 60A and 62A, that is, the transparent portion 64 of the moving slit moves in the main scanning direction following the movement of the S-polarized laser beam.

However, almost Z from the wafer surface (surface to be inspected)
The reflected light in the direction enters the polarizing plate 38 through the light transmitting portion 64 of the moving slit, and only the P polarized light component enters the elliptical mirror 34. Here, it is clear that the observation field on the wafer surface is determined by the transparent portion 64 of the moving slit. The spot of the S-polarized laser light beam may be significantly larger than the observation field of view.

Referring again to FIGS. 1 and 2, an integrating sphere 40 is provided on one side of the elliptical mirror 34. As shown in FIG.
An elongated opening 42 extending in the X direction is formed on the coupling surface of the integrating sphere 40 and the elliptical mirror 34.
The two are optically coupled via this opening 42. Therefore, the light P focused on the elliptical mirror 34
The polarized laser beam enters the integrating sphere 40 through the aperture 42 and is scattered within the sphere.

Photomultipliers 44 and 46 as photoelectric elements are provided above the integrating sphere 40. Second
As shown in the figure, each photomultiplier 44,4
The light receiving end of 6 faces the inside of the integrating sphere 40, and in front of the light receiving end there is a dichroic filter 48,
50 is attached.

Of the light incident on the integrating sphere 40, only the P-polarized laser beam with the wavelength λ ₁ passes through the dichroic filter 48 and enters the photomultiplier 44, and only the P-polarized laser beam with the wavelength λ ₂ passes through the dichroic filter 48.
6 and enters the photomultiplier 46.

In this way, using the elliptical mirror 34 and the integrating sphere 40, the P-polarized component of the reflected light is transferred to the photomultiplier 4.
4 and 46, main scanning can be performed over a relatively wide range. Lens systems have problems such as defocusing, and the main scanning range has to be limited to a fairly narrow range, making them impractical and likely to be expensive.

Here, even if a pattern exists within the irradiation spot of the S-polarized laser beam, the surface of the pattern is microscopically smooth, so that the reflected light is almost only the S-polarized component. On the other hand, since the surface of a foreign object generally has minute irregularities, if a foreign object exists within the irradiation spot, the irradiated S-polarized beam will be scattered and the polarization plane will be disturbed, and the reflected light will have a P-polarized component. It will include quite a lot. The level of the P-polarized light component is approximately proportional to the size of the foreign object. The levels of the output signals of the photomultipliers 44 and 46 are proportional to the respective amounts of incident light. Therefore, the output signal levels of the photomultipliers 44 and 46 reflect the presence or absence of foreign matter at the scanning point and the size of the foreign matter.

FIG. 4 is a block diagram of the signal processing section of this foreign matter inspection device. In this figure, the output signals of the photomultipliers 44 and 46 are transmitted to the summing amplifier 5.
4 and is added and amplified and input to the comparator circuit 56. This comparison circuit 56 compares the level of the input signal with a threshold set by a data processing system (not shown), and outputs a logic "1" level signal when a signal with a level equal to or higher than the threshold is input. do. This output signal is input to a data processing system. Note that the output signal of the position encoder of the moving table mechanism 14 is input to the data processing system. The moving table mechanism 14, the galvanometer mirror 24, and the S-polarized laser oscillators 16 and 18
The driving of is controlled by a data processing system.

The foreign matter inspection operation of the foreign matter inspection apparatus having the above configuration will be explained. First, under the control of the data processing system, XY scanning of the wafer surface (surface to be inspected) begins. Normally, both the S-polarized laser oscillators 16 and 18 are operated, and a threshold value is set in the comparator circuit 56 according to the conditions.

The P-polarized light component of the reflected laser light from the scanning point at each time is incident on the elliptical mirror 34 via the polarizing plate 38, and further incident on the integrating sphere 40. Then, a signal proportional to the wavelength λ ₁ component of the P-polarized laser light is output from the photomultiplier 44, and a signal proportional to the wavelength λ ₂ component is output from the photomultiplier 46. The summation amplification signal of each signal is obtained by the comparator circuit 56
and is compared with a threshold.

If a foreign object larger than a certain size is present at the scanning point, the level of the addition amplified signal becomes equal to or higher than the threshold value, and a logic "1" signal is output from the comparator circuit 56. When the data processing system receives the "1" signal, it determines that a foreign object has been detected at that scanning point, and the scanning position information at that time (known from the encoder output of the moving table mechanism and the angle of the galvano mirror 24), Stored in foreign object table on internal memory.

If the wafer 30 is set at a certain angle between the direction of the main patterns on the wafer surface and the X and Y directions, very few patterns will have the above-mentioned angular relationship with the irradiation direction of the S-polarized laser beam. Therefore, erroneous detection of patterns as in the conventional case hardly occurs. Furthermore, since the observation field of view can be narrowed down sufficiently by the movable slit, minute foreign objects can be detected with high sensitivity.

Normally, both S-polarized laser beams are irradiated as described above to increase the irradiation density, but on wafer surfaces and photomasks, minute patterns are arranged at minute intervals, so only one wavelength is used. The pattern row may act as a diffraction grating, making normal foreign matter inspection impossible.

In this case, foreign matter inspection can be performed by changing the threshold value of the comparator circuit 56 to approximately half the value by using only one wavelength where no diffraction phenomenon occurs. For example, when only the wavelength λ ₁ is used, only the S-polarized laser oscillator 16 is operated on the data processing system side, and the threshold value of the comparator circuit 56 is set to about half the value in the case of both wavelengths. Then, a similar foreign object inspection is performed.

Note that instead of selectively operating the S-polarized laser oscillator, a switch circuit is inserted between the photomultipliers 44, 46 and the summing amplifier 54, and only one of the photomultipliers corresponding to the wavelength to be used is switched to the summing amplifier. 56, foreign matter inspection may be performed using only one wavelength.

Alternatively, one of λ ₁ and λ ₂ , for example λ ₂ , is mainly inspected, and λ ₁ is used for determining the diffraction pattern portion.

Although one embodiment of the present invention has been described above in detail, the present invention can be implemented with various modifications.

For example, the output signal of the photomultiplier may be digitized and input to a data processing system, and level comparison may be performed through software processing.

The photomultiplier can also be replaced by other photoelectric conversion elements.

The light-transmitting area of the rotating light-shielding plate of the moving slit is
It can also be formed in a spiral shape with ends. It is also possible to apply a light-shielding thin film to one surface of the polarizing plate, leaving a light-transmitting area similar to that of the fixed light-shielding plate, thereby omitting the fixed light-shielding plate. A light-shielding film having a minute light-transmitting portion formed thereon may be run below or above the polarizing plate, thereby forming a moving slit. However, the movable slit of the above embodiment has a structure that can easily follow high-speed scanning and is easily dust-proof.

It is also possible to arrange the moving slit in the condensing part of the elliptical mirror.

In the embodiment described above, sub-scanning is performed by moving the surface to be inspected, but sub-scanning can also be performed by moving the S-polarized beam. In that case, it is necessary to move the light-transmitting portion of the moving slit also in the sub-scanning direction.

Further, the present invention is also applicable to a similar foreign matter inspection device that uses a light beam other than a laser beam.

Furthermore, the present invention can be applied to objects to be inspected other than wafers,
For example, it can be applied to devices that inspect foreign substances on the surfaces of masks, reticles, pellicle membranes, and the like.

[Effects of the Invention] As detailed above, according to the present invention, the foreign matter inspection device inspects the surface to be inspected in the XY direction using the S-polarized beam.
scanning means; means for causing the P-polarized component of the reflected light of the S-polarized beam from the surface to be inspected to enter a photoelectric conversion element; and determining the presence or absence of foreign matter on the surface to be inspected based on the output signal of the photoelectric conversion element. , and the means for performing the XY scan linearly swings the S-polarized beam in the main scanning direction for at least the XY scan, and sends the P-polarized component of the reflected light to the photoelectric conversion element. The means for making the light incident on the photoelectric conversion element includes a moving slit in which a light-transmitting part moves to follow the S-polarized light beam, and the P-polarized light beam incident on the photoelectric conversion element is
Since the polarized light component is configured to pass through the transparent part, false detection of the pattern almost never occurs, and foreign objects can be reliably distinguished from the pattern and detected.The observation field is sufficiently narrowed down by the movable slit to detect minute foreign objects. The detection sensitivity can be increased.

[Brief explanation of drawings]

FIG. 1 is a schematic perspective view showing a part of the foreign matter inspection device according to the present invention, with a part cut away. FIG. 2 is a schematic cross-sectional view showing an enlarged part of the same foreign matter inspection device. FIG. FIG. 4 is a block diagram of the signal processing section. 10...Moving table, 14...Chick, 1
2... Wafer, 16, 18... S-polarized laser oscillator, 22... Half mirror, 24... Galvano mirror, 30... f-theta lens, 34... Elliptical mirror, 36... Aperture (transparent window) , 38...Polarizing plate (S polarization cut filter means), 40... Integrating sphere,
44,46...Photomultiplier, 48,50
. . . dichroic filter, 54 . . . summing amplifier, 56 . . . comparator circuit, 60 .

Claims (1)

[Scope of Claims] 1: means for XY scanning a surface to be inspected with an S-polarized beam; means for causing a P-polarized component of reflected light of the S-polarized beam from the surface to be inspected to enter a photoelectric conversion element; means for determining the presence or absence of foreign matter on the surface to be inspected based on the output signal of the conversion element, and the means for performing the XY scanning includes at least
The means for linearly swinging the S-polarized beam in the main scanning direction for main scanning and making the P-polarized component of the reflected light enter the photoelectric conversion element includes a light-transmitting section that follows the S-polarized beam. What is claimed is: 1. A foreign matter inspection device comprising a moving slit through which a moving slit is moved, and a P-polarized light component incident on the photoelectric conversion element is made to pass through the light-transmitting section. 2 The means for performing the XY scan moves the surface to be inspected linearly in the sub-scanning direction.
2. The foreign matter inspection apparatus according to claim 1, wherein sub-scanning of XY scanning is performed, and the light-transmitting portion of the moving slit moves in the main scanning direction following the S-polarized beam. 3. The means for causing the P-polarized light component of the reflected light to enter the photoelectric conversion element includes: an elliptical mirror having a transparent window facing the surface to be inspected; an integrating sphere that receives light from the elliptical mirror; an S-polarized light cut filter; and a moving slit, the S-polarization cut filter and the moving slit are provided in or facing the transparent window, and the photoelectric conversion element is optically coupled to the inside of the integrating sphere. A foreign matter inspection device according to claim 2, characterized in that: 4. The means for causing the P-polarized light component of the reflected light to enter the photoelectric conversion element includes: an elliptical mirror having a transparent window facing the surface to be inspected; an integrating sphere that receives light from the elliptical mirror; an S-polarized light cut filter; The S-polarization cut filter is provided at or facing the transparent window, the moving slit is provided at the condensing portion of the elliptical mirror, and the photoelectric conversion element is located inside the integrating sphere. 3. The foreign matter inspection device according to claim 2, wherein the foreign matter inspection device is optically coupled to a foreign matter inspection device.