JP2001083452A - Method and device for performing scanning with laser beam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and a device for high-efficiently performing scanning with a laser beam at a high speed at an area from an ultraviolet area to a far ultraviolet area. SOLUTION: Plural polygon mirrors 108 and 109 are superposed and rotated while the phase of each mirror constituting the mirrors 108 and 109 is deviated by one-numberth the of object, so that the radiation of the incident laser beam 104 to the upper and lower polygon mirrors can be switched so as to perform the radiation of the laser beam within the effective scanning time of each polygon mirror surface by an A/O modulator 105. And also the same effect can be obtained by using a resonance operating type mirror for performing scanning.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of scanning an ultraviolet laser beam, particularly a far ultraviolet laser beam, at high speed and with high efficiency to irradiate an object to be inspected, for example, with an image signal from the object to be inspected. The present invention relates to a laser beam scanning method and apparatus capable of inspecting for defects such as minute foreign matter and pattern defects based on the method.

[0002]

2. Description of the Related Art A laser beam has excellent characteristics as a light source.
In the case of illuminating a certain area, it is common to scan by some scanning means before use. The scanning includes scanning by changing the reflection direction by mechanically driving a mirror, and scanning by changing the diffraction direction or refraction direction by giving an electric signal to the optical crystal. The former includes a galvanometer mirror and a polygon mirror (polyhedral mirror), and the latter includes an A / O deflector and an E / O deflector.

[0003] Japanese Patent Application Laid-Open No. 7-2017703 discloses that a laser is scanned using a polygon mirror and a galvanometer mirror,
An apparatus for drawing a pattern with a finely focused laser spot is described. Also, Japanese Patent Application Laid-Open No. 8-15630 describes an apparatus that scans a laser using a polygon mirror and an A / O deflector and draws a pattern with a finely focused laser spot. Also, Japanese Patent Application Laid-Open
Japanese Patent Application Laid-Open No. 142538 discloses a technique in which two polygon mirrors are scanned in synchronization with a half-period phase difference, and by switching between the two, the efficiency of the polygon mirror is improved. An apparatus for drawing a pattern with a finely focused laser spot is described. Japanese Patent Application Laid-Open No. 7-1970011 discloses that polygon mirrors are superposed in two stages by giving a half-period phase difference,
It is disclosed that the semiconductor laser is modulated in synchronization with the rotation. Japanese Patent Application Laid-Open No. 5-34621 discloses that a beam is two-dimensionally scanned by changing the reflection angle of a polyhedral mirror for each surface.

[0004]

Since the scanning by the polygon mirror (polyhedral mirror) is performed by continuous rotation, the beam scanning becomes invalid at the joint between the mirror surfaces, and the effective scanning time is reduced. As a result, the efficiency is reduced. There is a problem that it leads to a decrease. In addition, when scanning at a high speed, a plurality of polygon mirrors cannot be rotated synchronously due to continuous rotation, and a two-dimensional area can be scanned by combining polygon mirrors. Kaihei 10-1
As disclosed in JP-A-42538, scanning is performed by synchronizing two polygon mirrors and applying a half-period phase difference to each other, and switching between them to use them while improving the efficiency of the polygon mirrors. However, it was difficult in a high-speed area. Also, as disclosed in Japanese Patent Application Laid-Open No. H7-197011, even when the polygon mirrors are overlapped in two stages with a half-period phase difference, the laser is directly modulated.
Gas lasers and solid-state lasers that are unsuitable, or one laser is expensive, so multiple lasers can be arranged side by side for ON / OF
It is not suitable for use in the deep ultraviolet wavelength range where it is difficult to make the F wavelength.

Further, since the polygon mirror is continuously rotated, the scanning range cannot be changed. Therefore, the scanning shape of the polygon mirror is limited to a rectangle, and is not suitable for scanning a circular area. Was. Further, in a region using a light source of a far ultraviolet wavelength, scattered light is generated due to the surface roughness of the polygon mirror, and there is a problem that beam quality and reflection efficiency are reduced. The scanning by the galvanomirror can be performed only at a low speed of several hundred hertz at most with a general galvanomirror, and a high-speed galvanomirror called a resonant type capable of scanning several kilohertz or more has a drive signal. Is limited to a sine wave, the scanning angle changes sinusoidally, and the beam scanning speed is not constant. For this reason, especially when a detection signal is obtained by illumination by laser scanning using an accumulation type sensor, a signal from a region scanned slowly is relatively large, and a signal from a region scanned quickly is relatively large. There is a problem that it becomes smaller.

The E / O deflector has no crystal that can be used in the ultraviolet to far ultraviolet wavelength range, and can respond to the demand for a high-resolution optical system with a shorter wavelength light source in the future. Absent.

[0007] In the A / O deflector, quartz is the only crystal that can be used in the ultraviolet to far ultraviolet region. However, quartz has a high sound speed. Although this does not hinder the use of the A / O element as a modulator, a problem arises when the A / O element is used as a deflector. When a diffraction grating is formed on quartz using an acoustic element, the change in the spacing between the diffraction gratings with respect to the change in the signal frequency applied to the acoustic element is small due to the magnitude of the sound speed. This means that the angle that can be polarized by the deflector becomes smaller. The sound speed of quartz is about 600
Since the upper limit of the frequency of the signal applied to the acoustic element that can be used at 0 m / s is about 150 MHz, even if the frequency change range is ± 100 MHz, it can be deflected by only 0.23 degrees. Therefore, in order to obtain a sufficient scanning range, it is necessary to provide a very long optical path length (1 m or more). When a long optical path is provided, there is a problem that the beam position and beam quality deteriorate due to environmental changes such as fluctuations of air in the optical path.

[0008] An object of the present invention is to solve the above problems.
Provided is a laser beam scanning method and apparatus capable of scanning an object at high speed and with high efficiency even with a short wavelength (ultraviolet to far ultraviolet) laser beam essential for high resolution. It is in. Another object of the present invention is to enable a laser beam having a short wavelength (from ultraviolet to far ultraviolet) to be scanned at high speed and with high efficiency on an object to be inspected having a circular shape such as a semiconductor wafer. To provide a laser beam scanning method and apparatus therefor. Further, another object of the present invention is to scan and irradiate a short-wavelength (ultraviolet to far-ultraviolet) laser beam onto an object to be inspected such as a semiconductor wafer at high speed and with high efficiency, and to irradiate the laser beam on the object to be inspected. It is an object of the present invention to provide a defect inspection apparatus capable of detecting an optical image at a high resolution and inspecting a defect such as a minute foreign matter or a pattern defect.

[0009]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention is to rotate a polygon mirror formed by superposing a plurality of mirrors whose mirror surfaces are shifted from each other in phase, and to apply an A / O modulator to the laser beam. A laser beam scanning method and apparatus for performing modulation by synchronizing with rotation of the polygon mirror and switching to irradiate and scan each of the rotating polygon mirrors. Also, the present invention
By rotating a polygon mirror composed of a plurality of mirrors with different numbers of mirror surfaces and overlapping with a fixed diameter so that the time per swing angle is almost the same, the laser beam is moved to the position of the object to be scanned. A laser beam scanning method and apparatus for switching and irradiating and scanning the desired rotating polygon mirror by an A / O modulator in accordance with the method.

Further, according to the present invention, a polygon mirror formed by changing the circumferential length of a mirror surface is rotated, and a laser beam is irradiated on each mirror surface of the rotating polygon mirror to change a scanning angle. And a laser beam scanning method characterized in that scanning is performed by using a laser beam. Also,
According to the present invention, scattered light reflected on each mirror surface by irradiating a laser beam on each mirror surface of the rotating polygon mirror by rotating a polygon mirror formed with a surface roughness of each mirror surface of approximately 50 Å or less RMS. And a device for scanning the laser beam, wherein the scanning is performed while light is shielded by a scattered light trap. Further, according to the present invention, in the method and the apparatus for scanning a laser beam, a distance between the scattered light trap and a mirror surface of the polygon mirror is 1 m or more.

Further, the present invention provides a resonance operation type mirror scanner which resonates, irradiates a laser beam on the mirror scanner which is resonatingly operated to scan, and at least one of a laser beam incident on the mirror or reflected by the mirror. A laser beam scanning method and apparatus for performing modulation control on both or both of them in accordance with the laser beam scanning position. Further, according to the present invention, in the method and the apparatus for scanning a laser beam, modulation control is performed based on an output of an encoder that detects a scanning position of a scanner. Further, according to the present invention, in the laser beam scanning method and the laser beam scanning apparatus, modulation control is performed based on a signal obtained by subtracting a predetermined phase difference amount from a drive signal for driving the scanner. Further, the present invention provides a resonance operation type mirror scanner that performs resonance operation, irradiates a laser beam onto the mirror scanner that is operated in resonance, scans the mirror scanner, reflects the mirror, and then moves the laser beam away from the optical axis center by an optical element. A laser beam scanning method and apparatus for deflecting the laser beam in accordance with the laser beam.

The present invention also provides a resonance operation type mirror scanner that performs a resonance operation, an irradiation optical system that irradiates a laser beam to the mirror scanner, and at least one of a laser beam incident on the mirror scanner or reflected by the mirror scanner. Or both of them, comprising modulation control means for performing modulation control in accordance with the scanning position of the laser beam, wherein the laser beam is scanned by the resonance operation of the mirror scanner, It is a scanning device. The present invention also provides a resonance operation type mirror scanner that performs a resonance operation, an irradiation optical system that irradiates a laser beam to the mirror scanner, and at least one of a laser beam incident on the mirror scanner or reflected by the mirror scanner, or both. A modulating means for performing modulation, a recognizing means for recognizing a scanning position of a laser beam,
A control signal generating means for generating a control signal for the modulation means based on the scanning position of the laser beam recognized by the recognition means.

Further, the present invention is characterized in that the recognition means in the laser beam scanning device is constituted by an encoder for detecting a scanning position of a scanner. Further, the present invention is characterized in that the recognition means in the laser beam scanning device is constituted by a circuit for generating a signal obtained by subtracting a fixed phase difference from a drive signal for driving the scanner. The present invention also provides a resonance operation type mirror scanner that performs a resonance operation, an irradiation optical system that irradiates a laser beam to the mirror scanner, and deflects the laser beam according to the distance from the optical axis center after reflecting the mirror scanner. An optical element, wherein the laser beam is scanned by a resonance operation of the mirror scanner.

Further, the present invention is characterized in that the optical element in the laser beam scanning device is formed by a prism formed such that the curvature increases as the distance from the center of the optical axis increases. Also, the present invention is characterized in that the optical element in the laser beam scanning device is formed of a bundle fiber in which the direction of the fiber at the emission end is more greatly inclined as the distance from the optical axis increases. Further, the present invention is characterized in that the optical element in the laser beam scanning device is formed of a holographic plate or a diffraction grating formed such that the distance between the gratings becomes smaller as the distance from the optical axis increases.
The present invention also provides an A / O deflector that scans a laser beam, and has an optical path portion that is folded a plurality of times by a plurality of folding mirrors in an optical path after the laser beam is emitted from the A / O deflector. A laser beam scanning device characterized in that an optical path portion is sealed from the outside, and is thermally shielded from the outside by at least a heat insulating material or a heater for maintaining a temperature higher than the outside environment. Also, the present invention is a laser beam scanning device using an A / O deflector, which comprises a plurality of return mirror means in the optical path after emission of the A / O deflector, and the mirror means and an optical path section. It is characterized in that a sealing means for sealing the optical path portion from the outside and a heater means for maintaining at least a heat insulating means or a temperature higher than the external environment are provided.

As described above, according to the above configuration,
An object can be scanned at high speed and with high efficiency even by a laser beam of a short wavelength (from ultraviolet to far ultraviolet) which is essential for high resolution.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a laser beam scanning method and apparatus according to the present invention will be described with reference to the drawings. First, a first embodiment of the laser beam scanning device according to the present invention will be described with reference to FIG. That is, the first
In this embodiment, the plurality of polygon mirrors 108 and 109 are overlapped with the rotation phase shifted by 位相 of each mirror, and are configured to be rotated by the rotation motor 101. Polygon mirrors 108 and 1
Reference numerals 09 denote mirrors having the same shape, and their effective scanning time ratios (the time during which the laser beam impinges on the corners of each surface of the polygon mirror so that normal reflection cannot be performed is referred to as invalid time. The time during which the laser beam hits and can perform normal scanning is called effective scanning time (the effective scanning time ratio is indicated by the ratio of the effective operation time to the entire time). Also, they are
The rotation phase is shifted by １ ／ of each mirror constituting each polygon mirror and fixed to the spindle of the rotation motor 101.

On the other hand, a laser light source (not shown) is provided for each of these polygon mirrors 108 and 109.
Is irradiated through an A / O modulator 105. The A / O modulator 104 includes a rotating motor 101
Are controlled by the control signal generated by the rotational position-mirror switching signal converter 103 from the output 102 from the encoder attached to the
Switch to 7. When switching between two mirrors, the first-order diffracted light (for example, 107) of the A / O modulator 105
And the 0th order diffracted light (for example, 106), one A / O
Switching is performed by the modulator 105, which is convenient. of course,
Since it is sufficient to switch the optical path, other means may be used instead of the A / O modulator. That is, the polygon mirror 109
During the effective scanning time, the optical path is switched to 107, and during the invalid scanning time of the polygon mirror 109, the optical path is switched to. Therefore, the effective scanning time ratio of this polygon mirror system is approximately 100%.

Thus, even if a laser other than a semiconductor laser which is easy to modulate is used, and a polygon mirror having a high scanning speed and therefore a low effective scanning time ratio of about 50% is used, a high-speed laser can be efficiently used. The beam can be scanned. In this method, the effective scanning time ratio becomes 50% when the number of overlapping polygon mirrors is increased.
It will be possible to deal with shorter cases. in this case,
The mirrors constituting two or more polygon mirrors are overlapped with a phase shifted by one part.

The laser beam reflected by each of the polygon mirrors 108 and 109 is placed on an object (in the case of inspecting a defect such as a minute foreign matter or a minute pattern defect on a circuit pattern, the object becomes the object to be inspected). An optical system (for example, a lens system) 110 having a function of a lens system 112 that can irradiate the same scanning line and a function of an F-θ lens 111 that can scan at the same scanning speed is provided.

Next, a second embodiment of the laser beam scanning apparatus according to the present invention will be described with reference to FIG. In the second embodiment, as shown in FIG. 2A, a polygon mirror 201 and a polygon mirror 202 having different numbers of faces are superposed. Therefore, the scanning angles of the polygon mirror (the angles at which the reflected laser beams are swung), which are inversely proportional to the number of surfaces, are different from each other. However, so that both times per swing angle are the same,
The diameter of the polygon mirror 201 and the diameter of the polygon mirror 202 are determined. With this configuration, as shown in FIG. 2B, for example, when a circular object 204 such as a semiconductor wafer is moved in the direction of arrow 205 in the figure and scanned by a polygon mirror in a direction orthogonal to the direction, a polygon mirror is used. In the region 208 where the scanning angle is small, the A / O modulator 105 switches to, for example, the 0th-order diffracted light 206 and performs scanning with the polygon mirror 202. In the region 209 where the scanning angle of the polygon mirror needs to be large, the A / O modulation is performed. Vessel 10
In 5, the light is switched to, for example, the first-order diffracted light 207, and scanning is performed by the polygon mirror 201. According to the second embodiment, it is possible to reduce the time required to scan the entire surface of the object 204 as compared with the case where the entire surface of the object 204 is scanned at the same scanning angle as that of the region 209.

Although the embodiment using two types of mirrors has been described here, it goes without saying that finer and more efficient illumination can be achieved by using more types of mirrors. Further, since the switching timing of each mirror is not so delicate, it is not necessary to detect the angle from the encoder attached to the rotary motor 101, and it is not necessary to rotate the mirror in synchronization. The motor 202 may be rotated by a separate motor. Also in the second embodiment, the laser beam reflected by each of the polygon mirrors 201 and 202 is used to inspect the object (for inspecting a defect such as a minute foreign matter or a minute pattern defect on a circuit pattern, the object to be inspected). An optical system (for example, a lens system) 110 having the function of the lens system 112 that can irradiate the same scanning line and the function of the F-θ lens 111 that can scan at the same scanning speed is provided.

Next, a third embodiment of the laser beam scanning device according to the present invention will be described with reference to FIGS. By the way, as the scanning object 204 of the laser beam,
In the case of a circular shape such as a semiconductor wafer, if the laser beam 210 is simply scanned in a rectangular shape circumscribing the scan target 204, the scan also goes outside the target area, and the irradiation efficiency of the laser beam is reduced. Therefore, in the third embodiment, as shown in FIG. 3A, a polygon mirror 300a (FIG. 3A is a polygon mirror 300a
Is shown from above. ), The angles with respect to the mirror surfaces 307a to 301a, 301a to 307a (that is, the lengths of the mirror surfaces in the circumferential direction) θ7 to θ1, θ1 to
By changing θ7, the irradiated laser beam 104 (106, 107; 206, 207) is reflected and the scanning range (scanning length) L7 to L1,
L1 to L7 can be changed. Note that FIG.
As shown in (b), for example, when a circular or circular object 204 such as a semiconductor wafer is scanned with a slit-shaped or spot-shaped laser beam 210 as indicated by L7 to L1 and L1 to L7, usually y For example, even if the stage (not shown) on which the object 204 is placed is intermittently moved in the y direction, the polygon mirror 300a is rotated at least one turn. The angle of each mirror surface may be determined so that the entire surface of the circular object 204 can be scanned. If the laser beam 210 has a slit shape, a linear image sensor including a CCD image sensor, a TDI image sensor, or the like can be used as a detector.

Further, as shown in FIG.
By forming the polygon mirrors 300b in which the inclination angles α7 to α1 and −α1 to −α7 are sequentially changed from the rotation axes of 7b to 301b and 301b to 307b, as shown in FIG. The spot-shaped laser beam 210 can be two-dimensionally scanned on the circular object 204. Note that FIG.
In (b), L1 to L7 are mirror surfaces 301b to 307b.
2 shows the scanning by. Therefore, the polygon mirror 30
In the case of 0b, it is not necessary to move the stage on which the circular object 204 is mounted in the y direction. However, when the object 204 is irradiated with the laser beam 210, positioning is required. Further, the third embodiment can be applied to each of the first and second embodiments.

Next, a fourth embodiment of the laser beam scanning apparatus according to the present invention will be described with reference to FIGS. The polygon mirror 601 shown in FIG. 6 is made by cutting a block of aluminum or its alloy or beryllium. When the mirror surface of the polygon mirror 601 thus formed is irradiated with a short wavelength of ultraviolet light or less as the laser beam 602, the surface accuracy (roughness) may be insufficient. FIG. 5 schematically shows a state in which the reflected beam in this case is projected on a screen. As shown in FIG. 5, when the surface accuracy of the mirror surface is insufficient, scattered light 502 is generated around the mirror surface in addition to the regular reflection light beam 501. According to an experiment conducted by the inventor, when the surface roughness of the mirror surface is generally set to 50 angstrom RMS or less, the amount of scattered light 502 can be reduced to 5% or less of the total reflected light amount.

Since these scattered lights 502 cause deterioration of beam quality, it is desirable to remove them as much as possible. Therefore, in the fourth embodiment, the scattered light 502 is removed by providing a scattered light trap 603 (for example, a plate with a hole through which the regular reflected beam 501 passes). By providing the scattered light trap 603 in this way, the mirror surface can have a surface roughness of not less than 50 Å RMS and a surface roughness of 50
Even if it is less than Angstrom RMS, scattered light 502
Can be removed to improve the quality of the scanning laser beam. By the way, the trapping performance of the scattered light 502 is improved when the separation distance between the polygon mirror surface and the scattered light trap 603 is increased. However, according to the experiment by the inventor, the trapping performance which is almost satisfactory can be obtained at the separation of about 1 m. know. The fourth embodiment described above can be applied to each of the first to third embodiments.

Next, a fifth embodiment of the laser beam scanning apparatus according to the present invention will be described with reference to FIGS.
The fifth embodiment is basically configured using a galvanomirror. A general galvanomirror can only scan at a low scanning frequency of several hundred hertz at most.
However, a resonance type galvanometer mirror called a resonance type is capable of scanning over several kilohertz, but the drive signal is limited to a sine wave. Therefore, the scanning angle changes sinusoidally, and the beam scanning speed is not constant. The object 204 placed on the stage 130 is scanned and irradiated with the laser beam 104 using a resonance type galvano mirror called a resonance type, and the object 2 is scanned.
In the case where an optical image obtained from the optical image 04 is obtained using an accumulation type sensor 801 such as a TDI image sensor, the scanning speed of the laser beam is not constant.
The intensity of the image signal from the slowly scanned area is relatively large, and the intensity of the image signal from the quickly scanned area is relatively small.

Therefore, as a fifth embodiment, as shown in FIG. 7, a scanner mirror 702 is connected to a sine wave signal source 70.
In the configuration of the resonance type galvano mirror (resonant operation type mirror scan) called a resonance type driven by the actuator 701 based on the sine wave drive signal 711 obtained from the arithmetic unit 3, the arithmetic unit 705 sends the mirror from the encoder 704 attached to the actuator to the mirror. Is read, and the scanning speed at that point is obtained from the read scanning angle to generate a control signal. The arithmetic unit 705 controls the A / O modulator 706 based on the control signal 710 indicating the scanning speed, and if the scanning is slow, the transmittance is reduced accordingly. The laser beam 7 that is incident on the scanner mirror 702
07 is changed. As a result, even if the scanning speed of the laser beam 140 applied to the object 204 fluctuates, the laser beam 140 having an intensity corresponding to the scanning speed is applied to the object 204 mounted on the stage 130. Therefore, the intensity of the light image obtained from the object 204 becomes constant, and the value of the detection signal (image signal) becomes constant even when the detector 801 shown in FIG. . In addition, 121 is a half mirror, 122
Indicates an objective lens.

In the fifth embodiment, the control using the A / O modulator 706 is not limited to the incident side and may be performed after reflection. However, after reflection, the laser beam is scanned. As a fifth embodiment, as shown in FIG. 8, even if the scanning speed of the laser beam 140 applied to the object 204 fluctuates, a detection signal (image signal) detected from the detector 801 is obtained. To the amplifier 8 based on the control signal 710 indicating the scanning speed output from the arithmetic unit 705.
A detection signal (image signal) 803 having a constant intensity can be obtained even when the amplification factor is changed.

Further, even if the A / O modulator 706 is not used, even if the scanning speed of the laser beam applied to the object 204 fluctuates, the intensity of the laser beam can be controlled in accordance with the scanning speed. Modulation means may be used. further,
Since the direction of the mirror 702 changes with a constant phase delay with respect to the sine wave drive signal 711 from the drive signal source 703, the control signal 710 used for controlling the transmittance and the amplification factor is used.
Is not an output from the encoder 704 as shown in FIG. 7 and FIG. 8, but a control signal from an arithmetic unit 901 which performs an operation to give a phase difference to the drive signal 711 itself as shown in FIG. Is also good. The fifth embodiment described above is a method in which the detection output is electrically constant, and
They in principle create losses and reduce efficiency. For this reason, it is desirable to realize optically constant speed scanning.

Next, a sixth embodiment of the laser beam scanning apparatus according to the present invention will be described with reference to FIGS. In the sixth embodiment, in FIG.
4 is used. The beam reflected by the resonance type scanner (resonant operation type mirror scan) 701 has a slow scanning speed at a large deflection angle (a small amount of change per unit time of the deflection angle) and a scanning speed at a small deflection angle. Is fast (the change amount of the deflection angle per time is large). Therefore, where the deflection angle is large, the curved surface of the surface of the prism 704 is formed such that the curvature increases as the distance from the center increases so that the deflection angle further increases in accordance with the angle. In the sixth embodiment, FIG. 11 shows a case where the reflection direction is changed by the bundle fiber 1101 instead of the prism 704 to change the direction. In this bundle fiber 1101, the direction of the fiber on the output side is inclined in the direction in which the deflection angle increases toward the periphery. In the sixth embodiment,
FIG. 12 shows a case where the reflection direction is changed by a holographic plate (or a defractive element) 1201 instead of the prism 704 to change the direction. The holographic plate 1201 is formed so that the interval between the diffraction gratings is narrowed so that the beam on the emission side is inclined in a direction in which the deflection angle becomes larger as it goes to the periphery.

Although the above has described the embodiments of the resonant type galvanometer mirror, these facts apply to all other resonance operation type mirrors. As described above, although the A / O deflector can hardly take a scanning angle, its high-speed scanning property and easy control are still attractive. When using such an A / O deflector, it is necessary to secure a long optical path after emission in order to obtain a required scanning range at a small scanning angle. However, when a long optical path is provided, the beam position and beam quality may deteriorate due to environmental changes such as fluctuations of air in the optical path. Therefore,
As shown in FIG. 13, after the light is emitted from the A / O deflector 1301, a plurality of optical paths are formed by the return mirrors 1302 and 1303 in a compact space, and a plurality of optical paths are formed. This unit
The optical path that can stably obtain the required scanning range by preventing thermal fluctuations of the air and the optical components by thermally shielding from the outside by thermal insulation and heaters that maintain the temperature higher than the external environment Will have a length. As described above, according to the present invention, high-speed and high-efficiency laser beam scanning can be performed even in the far ultraviolet region.

Next, an embodiment of a defect inspection apparatus provided with the above-described laser beam scanning device will be described with reference to FIG. In this embodiment, the illumination optical system is configured by epi-illumination. Of course, the illumination optical system may be constituted by oblique illumination. As the illumination light source 1, for example, a DUV (far ultraviolet ray) laser (eg, an excimer laser KrF = 248n)
m, excimer laser ArF = 198 nm, etc.).
As described above, since the DUV (far ultraviolet) laser has a short wavelength, it has a high resolution, and an optical image based on scattered light or diffracted light from a defect such as an extremely small foreign substance of 0.1 μm or less can be obtained. Become. Therefore, the illumination optical system 2 includes an illumination light source 1 such as a DUV laser, a polarization control optical system 3 for setting the polarization of the illumination light 104, and the first optical system that scans the pupil 17 of the objective lens 122 with a laser beam. Pupil scanning illumination optical system 4 configured in the fifth to fifth embodiments, and half mirror (1) 1
21. The basic configuration of the detection optical system 10 includes an objective lens 122, an imaging lens 12, an enlargement optical system 13, a polarization detection optical system 14 for setting the polarization of detection light before the image sensor, and a UUV quantum efficiency. Is 10
% Or more of the image sensor 15 (801). The polarization detection optical system 1 in the detection optical system 10
Reference numeral 4 denotes a member for shielding specularly reflected light (zero-order diffracted light) from the object (sample) 204, and may be constituted by a spatial filter. In this case, it is necessary to use, for example, an annular illumination optical system instead of the polarization control optical system 3 in the illumination optical system 2.

Further, a half mirror (2) 21 is provided in the middle of the detection optical path, and the surface of the sample 204 is
An auto focus system 22 for focusing on the focus 22 is arranged. Further, a half mirror (3) 31 is provided so that the pupil position of the objective lens 122 can be observed by the lens (1) 32 and the pupil observation optical system 33. Further, a half mirror (4) 41 is provided so that the pattern on the sample 204 can be observed and aligned by the lens (2) 42 and the alignment optical system 43. Therefore, the DUV laser beam emitted from the illumination light source 1 is, for example, converted into linearly polarized light by the polarization control optical system 3 and is scanned two-dimensionally on the pupil 17 of the objective lens 122 by the pupil scanning illumination optical system 4 for irradiation. Will be done. The reflected light from the sample 204 passes through the half mirror (1) 5 through the pupil 17 of the objective lens 122, and converts the light image of the sample 122 into the imaging lens 1
The image sensor 15 (8
01) The image is enlarged and formed on the top. In addition, for example, the specular reflection light (0
By blocking the linearly polarized light component, which is the (second order diffracted light) component, the image sensor 15 (801) can receive a light image formed by the scattered light or the diffracted light component obtained from the surface of the sample 204. Become.

Next, the signal processing system will be described with reference to FIG. That is, the signal processing system has a UUV quantum efficiency of 1
It is indicated by the gray value accumulated for each column pixel obtained from the image sensor 15 (801) composed of, for example, a TDI image sensor of about 0% or more in synchronization with the movement of the inspection object 204 in the y-axis direction. An AD conversion circuit 402 that performs AD conversion of an image signal and a digital image signal output from the AD conversion circuit are shifted by, for example, one chip (or a plurality of pitches) of a circuit pattern repeated in the y-axis direction. A delay memory 403 that delays by an amount, a digital detection image signal 408 obtained from the AD conversion circuit 402, and 1 for example obtained from the delay memory 403.
For example, a difference image signal is extracted by comparing with the digital reference image signal 409 delayed by the pitch, and the extracted difference image signal is binarized by a predetermined threshold to detect a defect candidate such as a foreign substance or a defect of a circuit pattern. A comparison circuit 404 for forming a binarized image signal shown, and a binarized image signal indicating a defect candidate such as a foreign substance obtained from the comparison circuit 404, the area, position coordinates, and maximum length ( For example, a defect candidate feature amount extraction circuit 405 for extracting feature amounts such as projection lengths in the x-axis direction and the y-axis direction) and moments, and a defect candidate feature extracted by the defect candidate feature amount extraction circuit 405. A defect determination circuit 406 that determines the defect when the amount exceeds a predetermined determination criterion. In addition, as a feature amount, a three-dimensional feature amount may be extracted by adding a grayscale value based on a digital detection image signal obtained from the AD conversion circuit 402 at a point specified as a defect candidate.

In particular, in order to detect a defect such as an extremely small foreign matter of about 0.1 μm or less, erroneous detection is performed by excluding fine irregularities on the surface of the object to be inspected 204 and noise components based on a base pattern. Need to be prevented. For this purpose, a difference image signal that exceeds a predetermined threshold is once extracted as a defect candidate, and from the feature amount of each extracted defect candidate, whether a defect such as a foreign substance or the like is genuine, such as fine irregularities on the surface or a base pattern. By discriminating whether the information is a false report based on the information, it is possible to find a defect such as a genuine very small foreign matter.

[0036]

According to the present invention, it is possible to perform high-speed and high-efficiency laser beam scanning even with a short-wavelength (ultraviolet to far-ultraviolet) laser light source essential for high resolution.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of a laser beam scanning device according to the present invention.

FIG. 2 is a configuration diagram showing a second embodiment of the laser beam scanning device according to the present invention.

FIG. 3 is a configuration diagram showing a third embodiment of the laser beam scanning device according to the present invention.

FIG. 4 is a diagram illustrating the structure of an irregular polygon mirror applied to a third embodiment.

FIG. 5 is a diagram illustrating a state of light reflected by a polygon mirror.

FIG. 6 is a configuration diagram showing a fourth embodiment of the laser beam scanning device according to the present invention.

FIG. 7 is a configuration diagram showing a fifth embodiment of the laser beam scanning device according to the present invention.

FIG. 8 is a configuration diagram showing a modified example of the fifth embodiment of the laser beam scanning device according to the present invention.

FIG. 9 is a configuration diagram showing still another modified example of the fifth embodiment of the laser beam scanning device according to the present invention.

FIG. 10 is a configuration diagram showing a sixth embodiment of the laser beam scanning device according to the present invention.

FIG. 11 is a configuration diagram showing a modified example of the sixth embodiment of the laser beam scanning device according to the present invention.

FIG. 12 is a configuration diagram showing still another modified example of the sixth embodiment of the laser beam scanning device according to the present invention.

FIG. 13 is a configuration diagram showing another embodiment of the laser beam scanning device according to the present invention.

FIG. 14 is a configuration diagram showing one embodiment of a defect inspection apparatus provided with a laser beam scanning device according to the present invention.

15 is a configuration diagram showing a signal processing system in the defect inspection device shown in FIG.

[Explanation of symbols]

101: rotary motor, 108, 109, 201, 20
2, 300, 300a, 300b, 601: polygon mirror, 105, 706: A / O modulator, 204: scanning object (object to be inspected), 301a to 307a,
301b to 307b: mirror surface, 701: actuator, 702: resonance operation type galvanometer mirror (scanner mirror), 1301: A / O deflector, 1302, 1303 ...
Folding mirror.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Minoru Yoshida 292, Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside Production Research Laboratory, Hitachi, Ltd. (72) Yukio Utsu 292, Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside Hitachi, Ltd. Production Technology Research Laboratory (72) Inventor Shunji Maeda 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture F-term in Hitachi, Ltd. Production Technology Research Laboratory F-term (reference) LL57 LL62 MM16 QQ03 QQ11 QQ25 2H045 AA03 AA04 AB24 AB38 BA13 BA43 CB35 DA02 DA12 5C072 AA03 CA06 DA21 DA23 HA02 HA12 HB06 HB13

Claims (13)

[Claims] 1. A polygon mirror comprising a plurality of superimposed mirrors whose phases are shifted from each other are rotated, and a laser beam is modulated by an A / O modulator in synchronization with the rotation of the polygon mirror to rotate. A scanning method of a laser beam, characterized in that each polygon mirror is switched to be irradiated and scanned. 2. A polygon mirror comprising a plurality of mirrors having different numbers of mirror surfaces and having a diameter determined so that the time per swing angle is substantially equal to each other, is rotated, and a laser beam is emitted. A / depending on the position of the scanned object
A method for scanning a laser beam, wherein the rotating desired polygon mirror is switched by an O modulator and irradiated for scanning. 3. A polygon mirror, which is formed by changing a circumferential length of a mirror surface, is rotated, and a laser beam is irradiated on each mirror surface of the rotating polygon mirror to perform scanning while changing a scanning angle. A method for scanning a laser beam, characterized in that: 4. A polygon mirror having a surface roughness of not more than 50 angstrom RMS is rotated, and a laser beam is irradiated on each mirror surface of the rotating polygon mirror to reflect the laser beam on each mirror surface. A scanning method of a laser beam, wherein light is scanned with light being shielded by a scattered light trap. 5. A resonating mirror scanner is operated to resonate, and a laser beam is irradiated to the resonating mirror scanner for scanning, and at least one or both of the laser beam incident on the mirror or reflected by the mirror is applied. On the other hand, a laser beam scanning method characterized in that modulation control is performed in accordance with the scanning position of the laser beam. 6. A resonance operation type mirror scanner is operated to resonate, a laser beam is irradiated to the mirror scanner which is operated to resonate, and scanning is performed. After the mirror is reflected, the laser beam is separated by an optical element from the center of the optical axis. And a laser beam scanning method. 7. A polygon mirror constituted by superposing a plurality of mirrors whose phases on the mirror surfaces are shifted from each other, driving means for rotating and driving the polygon mirror, and modulating a laser beam in synchronization with the rotation of the polygon mirror. A for irradiating by switching to each polygon mirror
And a / O modulator, wherein the laser beam is scanned by a polygon mirror rotated and driven by the driving means. 8. A polygon mirror comprising a plurality of mirrors having different numbers of mirror surfaces and having a diameter determined so that the time per swing angle is substantially the same, and rotating the polygon mirror. And an A / O modulator for switching and irradiating a laser beam to the desired polygon mirror in accordance with the position of the object to be scanned, and the laser beam is rotationally driven by the driving means. A scanning device for a laser beam, wherein a scanning is performed on the object to be scanned by a polygon mirror. 9. A polygon mirror constituted by changing a circumferential length of a mirror surface, a driving means for rotating and driving the polygon mirror, and an irradiation optical system for irradiating a laser beam to the polygon mirror. A laser beam scanning device, wherein the laser beam is scanned by changing the scanning angle by each mirror surface of a polygon mirror rotated and driven by the driving means. 10. A polygon mirror having a surface roughness of about 50 angstrom RMS or less on each mirror surface, driving means for rotating the polygon mirror, and a laser beam applied to each mirror surface of the polygon mirror. An irradiating optical system; and a scattered light trap for shielding scattered light reflected on each mirror surface of the polygon mirror, wherein the laser beam is regularly reflected by each mirror surface of the polygon mirror rotated and driven by the driving unit. A laser beam scanning apparatus, wherein scanning of reflected light is obtained through a scattered light trap. 11. A resonating mirror scanner that resonates, an irradiating optical system that irradiates a laser beam to the mirror scanner, and at least one or both of a laser beam incident on the mirror scanner or reflected by the mirror scanner. A laser beam scanning device, comprising: a modulation control unit that performs modulation control according to a scanning position of a laser beam, wherein the laser beam is scanned by a resonance operation of the mirror scanner. 12. A mirror scanner for resonating operation, an irradiating optical system for irradiating a laser beam to the mirror scanner, and an optical system for reflecting the mirror scanner to deflect the laser beam in accordance with the distance from the center of the optical axis. And a device for scanning the laser beam by a resonance operation of the mirror scanner. 13. An A / O deflector for scanning a laser beam, wherein the A / O deflector has, in an optical path after the laser beam is emitted, an optical path portion which is folded a plurality of times by a plurality of folding mirrors. A laser beam scanning device characterized in that a portion is sealed from the outside and is thermally shielded from the outside by at least a heat insulating material or a heater for maintaining a temperature higher than the outside environment.