JPH06201601A - Inspection device and system using it - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide an inspection apparatus capable of detecting a minute foreign substance or defect which has been difficult to detect in the past with a high S / N ratio. [Configuration] A laser beam 34 including two light components whose frequencies are different by Δω and whose polarization directions are the same is generated. This is branched by the half mirror 13, one of which is detected by the photoelectric detector 24 and is input to the synchronization detector 25 as reference light. The other is a polygon mirror 15 and an fθ lens 16
The scanning optical system consisting of 1 scans the inspection surface 18 as the laser beam 35. At the scanning spot position on the inspection surface 18, the laser beam 35 is intensity-modulated at the beat frequency Δω by optical heterodyne interference. Inspection surface 1
Scattered light 36 scattered by foreign matter and defects present in 8
Is detected by the photoelectric detector 22 and input to the synchronization detector 25. The synchronization detector 25 detects the scattered light signal in synchronization with the frequency Δω of the reference light.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the technical field of optically inspecting minute objects and defects existing on an inspection surface in, for example, semiconductor manufacturing.

[0002]

2. Description of the Related Art In a manufacturing process of a semiconductor device such as an IC or a liquid crystal display, an exposure circuit pattern formed on an original plate (reticle or photomask) is
It is manufactured by transferring onto a wafer surface coated with a resist by a semiconductor printing apparatus.

If foreign matter such as minute dust is present on the original plate surface during the transfer, the foreign matter is also transferred at the same time,
This causes a decrease in the yield of IC manufacturing. In particular, when a plurality of identical circuit patterns are arranged and printed on the wafer surface repeatedly by the step-and-repeat method, one foreign matter on the original plate is printed on the entire surface of the wafer, and one wafer becomes a defective product. Will cause a large decrease in the yield. Therefore, it is indispensable to detect the presence of foreign matter on the original plate in the IC manufacturing process, and various inspection methods have been conventionally proposed. For example, FIG. 11 is a configuration diagram of a conventional inspection apparatus that inspects the presence or absence of a foreign substance by detecting scattered light due to the foreign substance.

In FIG. 1, a laser beam from a laser light source 151 is made into an optimum laser beam for foreign matter inspection by a polarizer 152, a filter 153, a collimating system 154, etc., and a scanning mirror 157 such as a polygon is passed through a mirror 155. It is guided to the scanning optical system by the fθ lens 158. The scanning laser beam from the fθ lens 158 has a surface 16 to be inspected such as a reticle on which a circuit pattern is formed.
It is condensed as a scanning spot 159 on the surface of 0. The scanning stage system 166 relatively moves the scanning spot 159 and the surface to be inspected 160 perpendicularly to the scanning direction of the scanning spot 159, so that the entire surface of the surface to be inspected 160 can be two-dimensionally scanned.

A detection system composed of a lens system 161, a polarizer 162, an aperture 163, and a photoelectric detector 164 is arranged in the backward or side scattering direction with respect to the incident direction of the scanning laser beam. The arrangement direction of this detection system is set to a direction in which scattered light such as a circuit pattern on the surface to be inspected 160 has a specific diffraction direction, and avoids this and does not detect diffracted light.

In the apparatus having such a structure, the photoelectric detector 1 is used when no foreign matter is present in the scanning spot 159.
Although the scattered light is not detected at 64, if a foreign matter is present, the scattered light is isotropically generated from the minute foreign matter, so that the photoelectric detector 164 detects the scattered light. Therefore, by processing this detection signal by the signal processing system 165, the presence / absence of foreign matter can be inspected.

[0007]

However, in the above-mentioned conventional inspection apparatus, when the size of the foreign matter to be detected becomes extremely small (for example, 0.3 μm or less),
There is a problem in that the intensity of scattered light generated from a foreign substance becomes extremely weak, and it is difficult to distinguish scattered light due to the foreign substance from other stray light, which makes it difficult to detect the foreign substance.

The present invention has been made to solve the above problems, and an object thereof is to provide a detection device capable of detecting a minute foreign substance or defect which has been difficult to detect in the past with a high S / N ratio. Is. Another object of the present invention is to provide a system for manufacturing a highly integrated device by using the above inspection apparatus.

[0009]

According to one embodiment of the present invention for solving the above-mentioned problems, a modulating means for modulating a light beam irradiated to an inspection position and a light scattered at the inspection position are synchronized with the modulation. The present invention is a system such as an inspection apparatus or an exposure apparatus using the inspection apparatus, which has a detecting means for detecting the same.

[0010]

[Embodiment] An apparatus for inspecting a surface to be inspected such as an exposure original plate (reticle or photomask) or a wafer, which is used in the field of manufacturing devices such as semiconductors, and more specifically, is attached to the surface to be inspected An embodiment in which the present invention is applied to an inspection apparatus for inspecting foreign matter such as dust or defects such as scratches on the surface to be inspected will be described. Needless to say, the applicable range of the present invention is not limited to the field of semiconductors and can be widely applied to surface inspection devices.

<First Embodiment> FIG. 1 is a diagram showing a first embodiment of the present invention. Further, FIG. 2 is a perspective view of a configuration centering on the scanning optical system and the detection optical system. In FIG. 1, 1 is a laser light source for generating a linearly polarized laser beam, 2 is a collimator optical system for converting the laser beam into an appropriate beam diameter, 3 is a filter system, 4, 8, 9, 14 are mirrors,
Reference numeral 5 is a demultiplexer (polarizing beam splitter), 6a and 6b are acousto-optic elements for modulating laser light at an appropriate shift frequency, 7a and 7b are drivers for driving the acousto-optic elements, and 10 is a multiplexer ( (Polarizing beam splitter), 11 is a λ / 4 plate for converting linearly knitted light into circularly polarized light, and 12 is a polarizer, and the above-mentioned members constitute a light source unit. 1
3 is a half mirror. 15 is a polygon mirror, 16
Is a fθ lens system, and members 15 and 16 form a scanning optical system. Reference numeral 18 denotes an inspection surface, which is an original plate such as a reticle and a mask. Reference numeral 17 is a scanning spot on the inspection surface 18, and 19 is an original plate placed in a predetermined direction (in the direction of an arrow in the drawing).
It is a stage system for moving to. Reference numerals 20 and 23 are condenser lens systems, 21 is a filter system such as a polarizer that passes a specific polarization component, and 22 and 24 are photoelectric detectors. The condenser lens system 20 is arranged so as to satisfy the Scheimpflug relationship so that the entire scanning area is imaged on the detection surface of the photoelectric detector 22. Further, 25 is a sync detector for synchronously detecting the modulated signal, and 26 is a signal processing system.

The laser beam from the laser light source 1 is converted into an appropriate beam diameter by the collimator optical system 2, intensity is attenuated by the filter system 3 including an ND filter and a polarizer, and a laser beam 31 having the optimal intensity for inspection is obtained. To do. This laser beam 31 is converted into S by the demultiplexer 5 such as a polarization beam splitter.
It is divided into a polarized laser 32a and a P polarized laser 32b. Of these, the S-polarized laser 32a is shifted by the acousto-optic device 6a driven by the driver 7a by a shift frequency ω1.
Is modulated by. Similarly, the P-polarized laser 32b is modulated at the shift frequency ω2 by the acousto-optic element 6b driven by the driver 7b. The two linearly polarized laser beams thus modulated are combined into a laser beam 33 by a combiner 10 such as a polarization beam splitter. The laser beams 33 have polarization directions orthogonal to each other and have a frequency Δω relative to each other.
It consists of two linearly polarized lights that differ by (= | ω1-ω2 |).

Although two acousto-optic elements are used in this embodiment, only one acousto-optic element may be used to modulate one of the lasers 32a and 32b with the frequency Δω. Also, light having the same properties as the laser beam 33 can be obtained by using a dual frequency Zeeman laser or modulating the injection current of the semiconductor laser.

The laser beam 33 is converted from linearly polarized light into circularly polarized light by passing through the λ / 4 plate 11, and two circularly polarized lasers that rotate in opposite directions of frequencies ω1 and ω2 are combined. Become. Then, by further passing through the polarizer 12 whose azimuth axis is set to a predetermined direction (here, the S polarization direction), the polarization directions are aligned, and thus the lights of the frequencies ω1 and ω2 in which the polarization directions match each other are combined. A linearly polarized laser 34 is obtained.

Next, the laser beam 34 is split into two by the half mirror 13. One laser beam reflected by the half mirror 13 is condensed on the photoelectric conversion surface of the photoelectric detector 24 by the condenser lens 23. Since the focused laser generates an optical beat due to optical heterodyne interference at the focusing position, the photoelectric detector detects the frequency Δ
The beat signal of ω is detected. This signal is the sync detector 2
5 is used as a reference signal in synchronization detection.

On the other hand, the other laser beam that has passed through the half mirror 13 has a polygon mirror 15 and an fθ lens system 1.
6 is introduced into the scanning optical system. Then, the laser beam 35 deflected by this scanning optical system is
8 to form a scanning spot 17. As the polygon mirror 15 rotates, the scanning spot 17 moves in a direction perpendicular to the paper surface of FIG. 1 to optically scan the surface of the inspection surface 18. At the same time, the stage 19 moves the inspection surface 18 in a direction orthogonal to the optical scanning direction, so that the inspection surface is two-dimensionally scanned. FIG. 2 is a perspective view showing the state of the two-dimensional scanning in an easy-to-understand manner.

Here, the state near the scanning spot 17 is shown in FIG.
Will be described in detail. In the figure, 52 is the focal depth determined by the fθ lens system 16, 53 is the scanning direction,
Reference numeral 54 is an interference region where the intensity is modulated. fθ lens system 1
The lasers 35 emitted from the
This is a combination of two linearly polarized lasers having 1 and ω2 and having the same polarization direction. The laser 35 is designed so as to converge on the inspection surface to form the scanning spot 17, and the linearly polarized lasers cause optical heterodyne interference at the scanning spot position. The region 54 in which the optical heterodyne interference occurs depends on the depth of focus 52 of the fθ lens system, and has a length on the order of several tens of μm in this embodiment. In this interference region 54, as a result of optical heterodyne interference occurring under the one-color condition, the intensity of the scanning spot 17 is modulated at the beat frequency Δω, and as shown in FIG. 4, a sinusoidal (period Δt = 1 / Δω) bright and dark is produced. It will be repeated. That is, the scanning spot 17 has a frequency Δ
It can be considered that the intensity is modulated by ω. As described above, the region in which the intensity of the laser 35 is modulated by the optical heterodyne interference is only the minute region 54, and the intensity is not substantially modulated in the section from the laser light source 1 to the region 54 before this region. Therefore, even if stray light is generated from an optical component or the like in the section where the intensity is not modulated, the stray light does not have the frequency component of Δω because the intensity is not modulated, and the noise of the stray light is detected by the synchronous detection of Δω described later. Can be eliminated.

FIG. 5 is an enlarged view of a case where a foreign matter or defect exists on the inspection surface on which the scanning spot is formed. 62 is a foreign substance, 63 is a scattered light from the foreign substance, 64 is a scattered light from an edge portion of a circuit pattern or the like, and 65 is a detection system. The laser light 35 from the scanning optical system is incident on the inspection surface 18 at an angle φ and converges on the inspection surface to form a scanning spot.
On the other hand, the detection system 65 is arranged so as to detect in the directions of angles β and θ with respect to the incident direction of the laser light 35 as illustrated. For this detection direction, an angle at which scattered light from other than the foreign substance 62 (for example, diffracted scattered light from the circuit pattern) becomes as small as possible is selected. In this embodiment, as shown in FIG. 2, the detection system is arranged laterally with respect to the direction of incident light on the inspection surface. Here, the detection system satisfies the Scheimpflug relationship such that the scanning area on the inspection surface 18 is formed as an image on the detection surface of the photoelectric detector 22 by the condenser lens system 20.

Returning to FIG. 1, when scattered light is generated by a foreign substance or defect in the scanning spot 17, the intensity of this scattered light is modulated in synchronization with the intensity modulation frequency Δω of the scanning spot. The intensity-modulated scattered light 36 is taken in by the condenser lens 20 arranged in the optimum detection direction as described above, and passed through the filter system 21 such as a polarizer through the polarization direction component of the specific direction to the photoelectric detector. Two
Detected in 2. This filter system 21 excludes scattered light from the circuit pattern (having a polarization plane in a specific direction depending on the polarization direction of the incident laser light), and scatters light from foreign matters or defects (various polarization planes due to depolarization). Part of the signal) is selectively passed, and the influence of the circuit pattern is reduced to contribute to the improvement of the S / N ratio. The detection signal of the scattered light detected by the photoelectric detector 22 is input to the synchronization detector 25. As described above, the reference signal of the frequency Δω from the photoelectric detector 24 is also input to the synchronization detector 25,
Only the component of the frequency Δω of the scattered light detection signal is detected in synchronization with this reference signal. Then, based on the signal obtained by the synchronization detector 25, the signal processing system 26 determines the presence / absence of foreign matter or defect, and stores / displays data.

The synchronization detector 25 is, for example, a lock-in amplifier and detects only the signal having the component of frequency Δω from the scattered light detection signal in synchronization with the reference signal of frequency Δω. The synchronization detector 25 can also be configured by combining a frequency filter having a high frequency selectivity and a detection circuit, and in this case, it is not necessary to input the reference signal.

FIG. 6 shows an example of a scattered light detection signal obtained by the photoelectric detector 22, and shows a signal waveform when a foreign substance or a defect is present. Reference numeral 71 is a curve representing signal strength, 72 is an envelope, and 73 is a noise level. Scanning spot 17
Is intensity-modulated by the frequency Δω, the scattered light intensity is accordingly modulated by Δω (= 1 / Δt) as shown by the curve 71. Sync detector 25 and signal processing system 2
In 6, the noise level 7 is obtained by obtaining the signal like the envelope 72.
The foreign matter and the defect are recognized in consideration of 3. Here, as shown in FIG. 7, the time width ΔT in which the scattered light due to the foreign matter or the defect is generated is the size of the scanning spot 17 and the spot 1
7 depends on the speed of scanning over the inspection surface 18. That is, in FIG. 7, the time from when the edge of the scanning spot 17 is caught by the foreign matter 62 to when the scanning spot 17 moves to the position of the spot 17 ′ after moving at the scanning speed v is the signal time width ΔT in FIG.

It should be noted that the intensity modulation period Δt needs to be smaller than the time ΔT in which scattered light due to a foreign substance or a defect occurs. For example, the scanning speed v is set so that Δt <ΔT / 5.
And the frequency Δω is preferably selected. That is, when the optical scanning frequency is ω _scan , the shift frequency of the laser and the rotation speed of the polygon mirror are selected so that Δω> 5ω _scan .

In the above embodiments, the scattered light is detected in order to discriminate the foreign matter or the defect, but the foreign matter or the defect is also inspected by detecting the fluorescence scattered from the light irradiation position. The present invention can be applied to a system. That is, since the intensity of the generated fluorescence depends on the intensity of the irradiation light, foreign matter and defects can be inspected with a high S / N ratio by detecting the fluorescence in synchronization with the intensity modulation of the irradiation light.

According to this embodiment described above, the following effects can be obtained. (1) Since the intensity of stray light from areas other than the scanning spot is not modulated, noise can be greatly reduced by synchronous detection. (2) By synchronously detecting the modulation signal, adverse effects on the measurement signal due to 1 / f noise such as shot noise of the photoelectric detector are eliminated, and scattered light from a weak foreign matter is detected with a high S / N ratio. be able to. (3) Since the scanning light is intensity-modulated by optical heterodyne interference, a high modulation frequency (for example, several tens Mz) can be easily obtained, and a high scanning speed can be supported. That is, the surface inspection can be performed at high speed.

<Embodiment 2> FIG. 8 is a block diagram of the second embodiment of the present invention. In the figure, the same reference numerals as those in FIG. 1 represent the same members. This embodiment has the same basic principle as the embodiments of FIGS. 1 and 2, but the structure of the light source unit is changed. 40 is a half mirror which is a demultiplexer, 41 is a half mirror which is a multiplexer, and 42 is a filter system for setting the intensity. In this embodiment, when the laser is divided and modulated with different shift frequencies, the half mirror 40 is used, and thus the divided light has the same polarization direction. The modulated lights are combined by the half mirror 41. The combined light is a linearly polarized laser having frequencies ω ₁ and ω ₂ and a uniform polarization direction, as in the laser 34 of FIG. One of the two divided by the half mirror 41 is detected as reference light by the photoelectric detector 24, and the other is guided to the scanning optical system via the filter system 42. Since the half mirror is used in this embodiment, the λ / 4 plate and the polarizer as in the previous embodiment are not required.

In both the first and second embodiments described above,
Since the intensity of the laser light irradiated on the inspection surface is modulated by optical heterodyne interference, a high modulation frequency of, for example, several tens of MHz can be easily obtained, but to further simplify the configuration, an acousto-optical element or A modulation element such as a chopper may be arranged in the optical path for intensity modulation, or the light source itself may be controlled to modulate the emission intensity.

<Embodiment 3> FIG. 9 is a view showing an embodiment of a manufacturing system for manufacturing a semiconductor device by printing a circuit pattern of an original plate such as a reticle or a photomask on a semiconductor wafer. The system roughly includes an exposure device, an original storage device, an original inspection device, and a controller, which are arranged in a clean room.

Numeral 901 is a far-ultraviolet light source such as an excimer laser, numeral 902 is an illumination system unit, and the exposure position E.I. P. It has the function of illuminating the original set in the above at the same time (batch) from above with a predetermined NA (numerical aperture). Reference numeral 909 denotes an ultra-high resolution lens system (or mirror system) for transferring the circuit pattern formed on the original plate onto a wafer 910 such as a silicon substrate. During printing, the wafer is moved step by step according to a moving stage 911 for each shot. Repeat exposure while shifting. Reference numeral 900 denotes an alignment optical system for aligning the original and the wafer prior to the exposure operation, and has at least one original observation microscope system. An exposure apparatus is configured by the above members.

On the other hand, reference numeral 914 denotes an original storage device which stores a plurality of originals inside. Reference numeral 913 is an original inspection device, which includes the configuration of the previous embodiment. The original inspection device 913 detects that the selected original is pulled out from the original storage device 914 and the exposure position E.E. P. The foreign matter inspection on the original plate is carried out before being set to 1. The principle and operation of the foreign matter inspection are the same as those in the above-mentioned embodiment. Controller 91
Reference numeral 8 is for controlling the sequence of the entire system, and controls the operation commands of the original storage device 914 and the original inspection device 913, as well as the basic operations of the exposure apparatus, such as alignment, exposure, and step feed of the wafer. .

The manufacturing process of a semiconductor device using the system of this embodiment will be described below. First, the original storage device 914
The original to be used is taken out and set in the original inspection device 913. Next, the original inspection device 914 inspects the foreign matter on the original. As a result of the inspection, when it is confirmed that there is no foreign matter, this original plate is exposed at the exposure position E. P. Set to.
Next, the semiconductor wafer 910 which is the exposure target is set on the moving stage 911. Then, according to the step feed of the moving stage 911 by the step & repeat method, the original pattern is reduced and projected on each region of the semiconductor wafer while shifting each shot, and the exposure is repeated. After the exposure on one semiconductor wafer is completed, the semiconductor wafer is accommodated and a new semiconductor wafer is supplied, and similarly, the exposure of the original pattern is repeated by the step & repeat method.

The exposed semiconductor wafer that has been exposed is subjected to processing such as development and etching by an apparatus provided separately from this system. After this, a semiconductor device is manufactured through an assembly process such as dicing, wire bonding, and packaging. According to this embodiment, it is possible to manufacture a highly integrated semiconductor device having a very fine circuit pattern, which has been difficult to manufacture in the past.

<Embodiment 4> FIG. 10 is a diagram showing an embodiment of an original plate cleaning inspection system for manufacturing a semiconductor device. The system roughly has an original plate storage device, a cleaning device, a drying device, an inspection device, and a controller, which are arranged in a clean chamber.

Reference numeral 920 denotes an original storage device which stores a plurality of originals and supplies the originals to be cleaned. A cleaning device 921 cleans the original plate with pure water. 92
A drying device 2 dries the washed original plate. 9
Reference numeral 23 denotes an original plate inspection device for inspecting foreign substances on the cleaned original plate including the configuration of the previous embodiment. A controller 924 controls the sequence of the entire system.

The operation will be described below. First, the original plate to be cleaned is taken out from the original plate storage device 920 and supplied to the cleaning device 921. The original plate cleaned by the cleaning device 921 is sent to the drying device 922 to be dried. After the drying, it is sent to the inspection device 923, and the inspection device 923 inspects the foreign matter on the original plate by using the method of the previous embodiment. If no foreign matter is found as a result of the inspection, the original is returned to the original storage device 920. Also, if foreign matter is confirmed,
The original plate is returned to the cleaning device 921, a cleaning / drying operation is performed, and then an inspection is performed again, and this is repeated until the foreign matter is completely removed. Then, the completely cleaned original plate is returned to the original plate storage device 920.

Thereafter, the cleaned original plate is set in an exposure apparatus, and a circuit pattern of the original plate is printed on a semiconductor wafer to manufacture a semiconductor device. As a result, it is possible to manufacture a highly integrated semiconductor device having a very fine circuit pattern, which has been difficult to manufacture in the past.

[0036]

According to the present invention, it is possible to detect minute foreign matters, defects, etc., which were difficult to detect in the past, with a high S / N ratio. Further, if the present invention is applied to device manufacturing,
It is possible to manufacture a highly integrated device which has been difficult to manufacture in the past.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a first embodiment of the present invention.

FIG. 2 is a perspective view of a configuration centering on a scanning optical system and a detection optical system.

FIG. 3 is an explanatory diagram of a state near a scanning spot portion.

FIG. 4 is a diagram showing a waveform of intensity modulation at a scanning spot.

FIG. 5 is an enlarged view around a scanning spot.

FIG. 6 is a diagram showing a scattered light signal detected.

FIG. 7 is an explanatory diagram of a time width for scanning a foreign substance.

FIG. 8 is a configuration diagram of a second embodiment of the present invention.

FIG. 9 is a configuration diagram of an embodiment of a semiconductor manufacturing system.

FIG. 10 is a configuration diagram of an embodiment of an original plate cleaning inspection system.

FIG. 11 is a configuration diagram of a conventional inspection device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 laser light source 2 collimator optical system 3 filter system 5 demultiplexer (polarizing beam splitter) 6a, 6b acousto-optical element 10 multiplexer (polarizing beam splitter) 11 λ / 4 plate 12 polarizer 15 polygon mirror 16 fθ lens system 20 , 23 Condensing lens system 21 Polarizer 22, 24 Photoelectric detector 25 Synchronous detector 26 Signal processing system

Front page continuation (72) Inventor Minoru Yoshii 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Tetsushi Nose 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (8)

[Claims] 1. An inspection apparatus comprising: a modulation unit that modulates a light beam applied to an inspection position; and a detection unit that detects light scattered at the inspection position in synchronization with the modulation. 2. The inspection apparatus according to claim 1, further comprising scanning means for scanning the inspection surface with the light beam. 3. The inspection apparatus according to claim 1, wherein the detection means detects light scattered laterally with respect to the incident direction of the light beam. 4. The inspection apparatus according to claim 1, wherein the modulation means performs intensity modulation by causing optical heterodyne interference between two light beams having different frequencies. 5. The inspection apparatus according to claim 1 or 2 for inspecting an original plate on which an exposure pattern is formed, and an exposure for exposing an exposure object to the exposure pattern of the original plate inspected by the inspection apparatus. An exposure system comprising: an apparatus. 6. A cleaning device for cleaning the original plate and an inspection of the original plate cleaned by the cleaning device.
The original plate cleaning inspection system, comprising: 7. The method according to claim 1, further comprising a step of inspecting an original plate on which a transfer pattern is formed by the inspection apparatus, and a step of exposing and transferring the circuit pattern of the inspected original plate onto a transfer target. Device manufacturing method. 8. A device manufactured by the manufacturing method according to claim 7.