JP2503919B2 - Foreign matter inspection device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foreign matter inspection apparatus for inspecting foreign matter attached to a photomask such as a reticle of an exposure apparatus used in a photolithography process for transferring a pattern onto a semiconductor substrate.

[0002]

2. Description of the Related Art Usually, a pattern of a photomask used in a photolithography process to be transferred to a semiconductor substrate is formed of chromium oxide or chromium. Then, in order to accurately transfer the pattern to the semiconductor substrate, it is necessary to inspect whether or not foreign matter such as dust adheres to the surface of the photomask in advance. Various proposals have been made as a device for detecting foreign matter attached to the photomask. As an example, for example, JP-A-62-1170
It is disclosed in Japanese Patent No. 963.

FIG. 4 is a perspective view showing an example of a conventional foreign matter inspection apparatus, and FIGS. 5 (a) and 5 (b) are views showing a detection segment and a filter segment on the pupil entrance plane of the photodetector in FIG. This foreign matter inspection apparatus, as shown in FIG. 4, has a photomask 24 in which a pattern is formed on a transparent substrate.
Further, a laser oscillator that scans with the scan mirror 20 and irradiates laser light, and a photodetector 23 that receives scattered light reflected from the photomask 24 through the detection optical system 22 are provided.

When inspecting whether or not foreign matter is attached to the photomask 24 with this foreign matter inspection apparatus, first, while moving the stage 9 on which the photomask 24 is mounted in the direction shown by the arrow, laser light is applied. Scan in the direction orthogonal to the moving direction. The photodetector 23 captures the scattered light of the laser light that is reflected by the laser light when it irradiates a pattern or a foreign object, and forms the scattered light pattern depending on the reflective object obtained on the pupil plane of the photodetector 23. By recognizing, it is inspected whether it is a foreign matter or a pattern.

For example, scattered light from a pattern is always detected as a diffracted light on the pupil plane with respect to the 0th order light, and scattered light from a foreign substance is 0 due to its three-dimensional structure. The next scattered light is asymmetric with respect to the optical axis. Therefore, when a plurality of photodetectors whose pupil entrance planes are divided into segments are used as shown in FIG. 5A, it is possible to discriminate between a pattern and a foreign substance by comparing the outputs of the symmetrical segments with respect to the center. You can That is, if there is scattered light 4 from the pattern, there is no output difference between the segments, and if there is scattered light 4 from a foreign substance, there is an output difference.

Further, since the scattered light from the pattern has a higher directivity and a larger output than the scattered light from the foreign matter, for example, the light is shielded by the segment on the pupil entrance plane as shown in FIG. 5B. By installing a filter and blocking the scattered light from the expected pattern with a blocking segment, the weak scattered light incident from the pupil plane without a filter is detected, and the presence of foreign matter is recognized and detected. The method of improving the S / N of was also adopted.

Further, the above-mentioned photodetectors are installed on the upper and lower surfaces of a reticle, which is a photomask, and a laser beam is projected onto the reticle to detect foreign matter by the presence or absence of output signals from both reflected light and transmitted light. I was doing double check.

[0008]

However, there are various shapes of the pattern formed on the photomask, and the direction of reflected scattered light changes depending on the pattern shape. Further, the scattered foreign matters have various positions, shapes, and sizes, and the directions of scattered light reflected from the foreign matters also change in various ways. In such a situation in which the directions of the reflected light from the foreign matter and the pattern change in various ways, the above-described conventional foreign matter inspection apparatus can judge the distinction between the pattern and the foreign matter in a certain direction, but the scattered light to be captured is detected by the detector. It is difficult to detect scattered light that is limited by the aperture diameter and reflected in various directions, and it is difficult to detect all the foreign substances attached to the photomask surface. In addition, in the case of a detector provided with a filter for increasing the S / N ratio, not only this problem is included, but also a problem that a light absorption rate is high and reflected light is weak depending on a foreign substance, which cannot be detected. Further, since the direction of scattered light changes depending on the formed pattern, there is a disadvantage in use that the filter must be replaced every time the shape of the pattern changes.

Therefore, an object of the present invention is to provide a foreign matter inspection apparatus capable of surely distinguishing a foreign matter from a pattern and detecting the presence or absence of the foreign matter even if the direction and shape of the pattern formed on the photomask are changed. That is.

[0010]

A feature of the present invention is that a laser beam irradiating means scans a photomask substrate which is moved in one direction with a laser beam having an amplitude of a predetermined length in a direction orthogonal to the one direction. And collects the reflected light from the photomask substrate, detects the light, and arranges it at an arbitrary central angle toward the midpoint of the scanning width of the laser light and tilts at the same inclination angle with respect to the photomask. A pair of photodetectors, an angle varying mechanism that changes the central angle of the pair of photodetectors, and an output photodetection signal of the pair of photodetectors is input while the central angle is changed by the angle varying mechanism. And a photodetection signal processing determination unit that determines the presence or absence of a foreign matter that has been processed and adhered to the photomask.

[0011]

The present invention will be described below with reference to the drawings.

FIG. 1 is a perspective view of a foreign matter inspection apparatus showing an embodiment of the present invention. As shown in FIG. 1, this foreign matter inspection apparatus includes a laser beam scanning unit 2 that scans a laser beam with an amplitude of a predetermined length in the direction of the arrow on a photomask 24 that is moved in the direction of the arrow. The reflected light from the photomask 24 is condensed and detected, and a pair of laser light is arranged at an arbitrary central angle θ toward the midpoint O of the scanning width of the laser light and tilted at the same inclination angle with respect to the photomask 24. The photodetectors 1a and 1b and one of the pair of photodetectors are fixed and the other is supported by the ring gear 6, and the central angle θ between the photodetectors 1a and 1b is changed by rotation of the pinion 8 of the motor 7. An angle varying mechanism and signal processing for determining the presence / absence of foreign matter adhering to the photomask 1 by inputting output light detection signals of the pair of photodetectors 1a and 1b while the central angle θ is changed by the angle varying mechanism. With the determination unit 4 There. Also,
The signal processing / determining unit 4 has a signal processing unit 12 that processes an output light detection signal, a determination function, and a stage 9
Is a computer for instructing a control unit 10 that controls the movement of the laser beam, the scanning of the laser beam, and the movement of the photodetector 1b.
It is composed of the PU 11.

Here, if the scanning width of the laser beam ideally matches the lateral length of the photomask 24, the inspection can be completed by moving the stage 9 once. It is necessary to increase the number of 1a and 1b or increase the field of view. However, this causes more scattered light reflected in various directions to be captured, making it difficult to determine whether the captured scattered light is from a pattern or a foreign substance. Therefore, in the present invention, the scanning width is set to the photomask 2
The width is made smaller than the width of 4 such as ⅕ or less, and the stage 9 is displaced in the width direction so that the inspection is performed by moving the stage 9 several times. The fields of view of the photodetectors 1a and 1b have a size including the length of the scanning width, and the scattered light that is expected to be reflected in all directions is limited to the scattered light that enters this field of view. There is. Instead, by changing the central angle θ formed by the photodetectors 1a and 1b, scattered light reflected in all directions can be captured. The central angle θ is preferably determined by the direction of scattered light reflected from the pattern. For example, if the pattern is a simple square, it may be set to 90 degrees so that only the reflected light is extracted as a signal. Also,
A condenser lens is provided on the front side of the light detection surfaces of the light detectors 1a and 1b so that even weak light from a foreign substance having a poor reflectance can be detected.

FIG. 2 is a flow chart for explaining the operation of the foreign matter inspection apparatus of FIG. 1, and FIG. 3 is a waveform diagram showing a signal due to scattered light from a foreign matter and a pattern. Next, the operation of the foreign matter inspection apparatus will be described with reference to FIGS. 1, 2 and 3.

First, as a preparation for inspection in advance, the central angle θ of the photodetectors 1a and 1b fixed to the same inclination degree
In order to arbitrarily set the photodetector 1 according to the pattern, the ring gear 6 is rotated by the motor 7 via the pinion 8.
The position of b is set, and it is set at a position where scattered light from the pattern of the photomask 24 is not received. For this position adjustment, it is necessary to confirm with an ammeter connected to the photodetectors 1a and 1b while irradiating the photomask 24 with laser light.

Next, in step A of FIG. 2, the laser light is scanned on the photomask 24, and at the same time, the stage 9 moves in the direction shown in the figure in synchronization with the movement of the laser light. Next, when the photodetectors 1a and 1b simultaneously detect scattered light while the stage 9 is moving, in step C, the stage 9 is temporarily stopped and the photodetector 1b is moved by the motor 7 in either direction. Then, in step D, as shown in FIG. 3A, if scattered light is always detected regardless of the moved position, it is determined in step F that there is a foreign substance. Then, in step J, the photodetector 1b is returned to the initial position and the inspection is started from step A. Further, as shown in FIG. 3B, when there is a position where scattered light is not detected in the process of moving the position of the photodetector 1b, it is determined that the signal detected first is from the pattern. It is determined that there is no foreign matter in step E. Then, in step J, the position of the photodetector 1b is returned to the first position where scattered light was not detected, and the process returns to step A to continue the inspection.

2 shown in the signal waveform diagram of FIG. 3 (b).
The dotted line represents the threshold value for separating the noise component and the scattered light. After that, the position of the photomask 24 is shifted and the same operation is repeated, and after the steps G and H, the inspection of the entire surface of the photomask 24 is completed. In the method of this embodiment, if a large amount of foreign matter is attached to the photomask 24, it is feared that the inspection time will take time. It is used for the purpose of final cleanliness check such as before processing, and the photodetector with a large field of view like this device only needs to automatically scan the photomask several times. It doesn't matter. Further, by storing the movement position, the central angle, and the like of the photodetector in accordance with the type of photomask, it is possible to shorten the inspection time when performing the inspection again.

In the embodiment described above, only one of the two photodetectors is movable and the other is fixed, but the same effect can be obtained by moving the two photodetectors. Is obtained.

[0019]

As described above, according to the present invention, the laser beam scanning region is formed at an arbitrary center angle and the same inclination angle with respect to the center of the laser beam scanning region on the photomask having various patterns. A pair of photodetectors having a field of view including a center angle variable mechanism for changing the center angle is provided, the center angle is set according to the shape of the pattern, and the photomask is moved while scanning the laser beam. Sometimes the pattern and the directivity of the reflected light from the foreign matter are recognized by the pair of photodetectors, and the presence or absence of the foreign matter is determined by the waveform of the output signal of the photodetectors. There is an effect that the presence or absence of the foreign matter can be determined by surely distinguishing the foreign matter and the pattern regardless of the direction and shape of the foreign matter.

[Brief description of drawings]

FIG. 1 is a perspective view of a foreign matter inspection apparatus showing an embodiment of the present invention.

FIG. 2 is a flow chart for explaining the operation of the foreign matter inspection device of FIG.

FIG. 3 is a waveform diagram showing a signal due to scattered light from a foreign matter and a pattern.

FIG. 4 is a perspective view showing an example of a conventional foreign matter inspection apparatus.

5 is a diagram showing a detection segment and a filter segment on a pupil plane of the photodetector in FIG.

[Explanation of symbols]

 1a, 1b Photodetector 2 Laser beam scanning unit 4 Signal processing / determination unit 6 Ring gear 7 Motor 8 Pinion 9 Stage 10 Control unit 11 CPU 12 Signal processing unit 20 Scan mirror 22 Detection optical system 23 Photodetector 24 Photomask

Claims (3)

(57) [Claims] 1. A laser light irradiation means for scanning a laser beam on a photomask substrate which is moved in one direction with an amplitude of a predetermined length in a direction orthogonal to the one direction, and reflected light from the photomask substrate. A pair of photodetectors which are arranged at an arbitrary central angle facing the midpoint of the scanning width of the laser light and tilted at the same inclination angle with respect to the photomask, An angle varying mechanism for changing the central angle of the photodetector, and a foreign matter adhering to the photomask by input processing output photodetection signals of the pair of photodetectors while the central angle is changed by the angle varying mechanism. A foreign matter inspection apparatus, comprising: a light detection signal processing determination means for determining the presence or absence. 2. The foreign matter inspection apparatus according to claim 1, wherein the central angle is set according to a shape of a pattern formed on the photomask. 3. The foreign matter inspection apparatus according to claim 1, wherein the field of view of the photodetector has a size including the length of the scanning width.