JP3099451B2 - 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 an apparatus for detecting foreign matter on an object to be inspected on which a pattern is mainly formed, such as a photomask, a semiconductor wafer, and a liquid crystal panel used in a semiconductor manufacturing apparatus.
It relates.

[0002]

2. Description of the Related Art In recent years, in a semiconductor manufacturing process, improvement of product reliability and yield have been important issues. Most of the failures in the initial steps of the manufacture of highly integrated semiconductors are caused by foreign substances in the process. Therefore, in order to solve these problems, it is essential to develop a device capable of inspecting foreign substances at high speed and with high reliability.

Conventionally, most foreign particle inspection devices basically detect laser scattered light, and a device for a mirror-surface inspection object can detect a foreign particle of about 0.2 μm. On the other hand, in an apparatus for an object to be inspected with a pattern, it is necessary to make various efforts to distinguish the pattern formed on the object to be inspected from the adhered foreign matter and detect the foreign matter of the object to be inspected. Is possible,
It is possible to detect a foreign substance of about 0.5 μm.

Hereinafter, with reference to FIG. 6, as an example of a conventional apparatus for inspecting a test object with a pattern, scattered light at a pattern edge when a deflection laser is irradiated,
A description will be given of a patterned wafer foreign matter inspection apparatus that performs detection by utilizing the difference in deflection characteristics of scattered light caused by foreign matter. In each figure, (a) shows that reflected light from a vertical pattern is quenched by an analyzer with respect to S-polarized laser illumination light, and (b) shows reflected light from an angled pattern. FIG. 4C shows that only the scattered light from the foreign matter reaches the follower, 1 shows S-deflection laser illumination, 2 shows reflected light from the pattern, and 3 shows detection. Reference numeral 4 denotes an analyzer, 5 denotes an objective lens, and 6 denotes a foreign substance.

In FIG. 6A, an S-deflection laser beam is irradiated horizontally on a wafer. At this time, the reflected light from the pattern perpendicular to the illumination light on the wafer does not change its deflection, and proceeds to the objective lens with S deflection. Since the analyzer has an analysis axis perpendicular to the deflection of the reflected light, the reflected light is extinguished and does not reach the detector. Further, as shown in FIG. 3B, reflected light from a pattern having an angle α with respect to the illumination light does not enter the objective lens and is not detected. In FIG. 3C, when the illumination light is applied to the foreign matter, the deflection of the reflected light from the foreign matter changes, and P deflection occurs. Since these pass through the analyzer, foreign substances can be detected.

[0006]

With the conventional configuration, it is impossible to reliably and reliably inspect foreign substances with required accuracy. The reason is as follows. Generally, when a test object such as a patterned wafer or a photomask is irradiated with a laser beam, scattered light is omnidirectionally generated from a foreign substance adhering to the test object and is formed on the test object. Scattered light having directivity is generated from an edge of a pattern, that is, a so-called circuit pattern (an edge of a light shielding portion such as chrome). Therefore, in consideration of the scattered light generated by the edge of the pattern, the detection is performed using a means such as deflection. However, in such an apparatus for detecting foreign matter, when laser light is incident on a photomask, the laser light is reflected on the incident surface, and the laser light is transmitted through a light transmitting portion other than the circuit pattern. The reflected or transmitted laser light is further reflected or scattered inside the device and reaches the above-mentioned photoelectric means, and generates a photoelectric signal as if scattered light was received from the foreign matter, even though there is no foreign matter. Would.

[0007]

According to the present invention, the surface of an object to be inspected is irradiated with light from a plurality of different directions simultaneously or sequentially , and the optical information formed by each is taken into an image sensor.
A foreign matter inspection apparatus for detecting foreign matter in an object to be inspected by comparing a plurality of obtained images and distinguishing a pattern formed on the object to be inspected from foreign matter adhering thereto ,
The smallest value among the gray values of the corresponding pixels of several images
Output to detect foreign matter in the test object.
Features.

[0008]

According to this configuration, the apparatus can be easily configured, and foreign substances can be detected with high accuracy and high reliability. This is because the method of irradiating light was devised and the method of processing the obtained image was simplified.

[0009]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of a foreign matter inspection apparatus according to the present invention, which uses a laser beam as illumination for a semiconductor photomask.

Hereinafter, a basic apparatus configuration and a processing method of an embodiment using the first invention of the present invention will be described first. FIG. 1 shows a basic device configuration. Reference numeral 11 denotes a sample table, 12 denotes a photomask, 13 denotes a laser oscillation source which is provided horizontally with respect to the X axis and can irradiate an object to be inspected at a predetermined incident angle, 1
4 is a laser oscillation source similar to 13 installed at 45 degrees to the X axis, 15 is a laser oscillation source similar to 13 installed perpendicular to the X axis, and 16 is installed at 135 degrees to the X axis. A laser oscillation source similar to 13; 17 a condenser lens;
Denotes an image sensor, 19 denotes an image sensor controller, 20 denotes an image processing device, 21 denotes an image memory, and 22 denotes a region to be inspected. Here, it is assumed that the photomask 12 has a pattern in the same direction with respect to the X and Y axes, and is installed on the sample stage 11. It is assumed that the laser oscillation sources 13 to 16 can instantaneously oscillate and stop. Further, it is assumed that the laser oscillation sources 13 to 16 are oscillating at a spot diameter capable of irradiating the entire inspection area of the photomask 13 imaged by the imaging element 18.

First, an area to be inspected is illuminated by a laser oscillation source 13 and an image is captured using an image pickup device 18 (hereinafter referred to as an image).
This is called image 1). Next, the laser oscillation sources 14-1
6, the same processing is performed to capture images (hereinafter, these are referred to as images 2 to 4). FIG. 2 shows a region to be inspected.
25 is a pattern and 26 is a foreign substance. FIG.
4 is shown. It can be seen from the figure that the image 1 has a pattern in the Y direction and the image 3 has a pattern in the X direction. On the other hand, it can be seen that the foreign substance shines through the images 1 to 4.

Next, a method for processing the four captured images will be described. As shown in FIG. 4, the corresponding pixels of the images 1 to 4 are compared, and the smallest value among those gray values is output. However, there is a case where a smoothing process and a comparison with a pixel around the target pixel are required in order to accurately determine the correspondence between the pixels of each image from the difference in the illumination direction.
For simplicity, FIG. 5 shows an example in which the pixels at the same position are compared with each other in a case of comparing the gradation values of 64 gradations in a 3 × 3 area.
Such processing is performed for each region to be inspected, and a pixel having a shading value equal to or higher than a certain threshold value is regarded as a position where a foreign substance exists. As shown in FIG. 5, it can be seen that only foreign matter appears in the output image by this processing. This focuses on the fact that foreign matter is output through the images 1 to 4, while only the pattern perpendicular to the laser incident direction is output.

An embodiment using the second invention of the present invention will be described below. In the apparatus according to the first aspect, the laser incident direction is limited to the most necessary three directions, and the laser light of the wavelength corresponding to the three colors of the color-capable image sensor is simultaneously irradiated,
Take in the color-capable image sensor. This makes it possible to efficiently input optical information.

An embodiment using the third invention of the present invention will be described below. In the apparatus according to the first aspect of the present invention, the laser incident direction is limited to the most necessary three directions, a plurality of laser beams having different wavelengths are simultaneously irradiated, and an image is formed by a three-panel camera or a two-panel camera using a corresponding filter. Capture. This makes it possible to efficiently input optical information.

According to the second and third aspects of the present invention, it is possible to simultaneously capture the images 1 to 3, and the third aspect of the present invention.
By combining the two inventions, it is possible to construct a high-speed, high-accuracy, and high-reliability foreign matter inspection apparatus.

In the above embodiment of the first invention of the present invention, four laser oscillation sources are provided. However, a single laser oscillation source may be separated from a single laser oscillation source and irradiated using a half mirror or the like. Also, the method of oscillating and stopping the laser light is not specified. Further, the incident direction and the number of laser oscillation sources are not specified as long as the pattern can be canceled by image processing. Further, the wavelength of the laser beam is not specified as long as the wavelength of the reflected light from the object to be inspected responds to the image sensor. Also, the spot diameter is not specified as long as it can irradiate an area of one or more visual field of the image sensor. Further, the incident angle of the laser beam is not specified as long as it is an angle at which a minute foreign substance can be captured and an image capable of canceling a pattern by image processing can be obtained. Also, the gradation and threshold value of the image processing are not specified as long as the foreign matter can be recognized. In addition, although the method of replacing the image with the minimum value of the corresponding pixel of the image obtained by the image processing method has been described, any processing method that can cancel a pattern, noise, and the like is not specified.

In the above embodiment of the second aspect of the present invention, the wavelength of the laser used is not specified as long as the wavelength of the reflected light corresponds to the three colors of the color image sensor.

In the above embodiment of the third aspect of the present invention, the laser light of each wavelength to be irradiated does not interfere,
If the reflected light from the inspection object has a wavelength that responds to each image sensor, no specification is made.

[0019]

As described above, according to the present invention, an apparatus can be simply constructed, and foreign objects can be detected with high accuracy and high reliability. According to experiments of the apparatus and the processing method used in the present invention, it has been found that the area assigned to one pixel of the image sensor can be about 4 to 9 times larger than the actual size of the foreign matter. This is because the scattered light of the foreign matter spreads more than the size of the foreign matter because the intense laser light that is the coherent light is applied to the object to be inspected, and the image pickup element reacts to the size of the actual foreign matter or more. Thus, by combining an efficient laser irradiation method and a high-speed image processing method, a minimum of 0.5 × 100 × 100 mm photomask can be achieved.
In the case of detecting a foreign matter of μm as an example, it is known that the processing can be performed in about 4 minutes. Further, the processing speed can be further improved by devising a plurality of device configurations. Further, by changing the magnification of the condenser lens in accordance with the size of the foreign matter to be detected, the apparatus can be easily changed. Also, unlike the conventional method, since the image sensor is used for the detector, it is possible to easily recognize the shape and content of the foreign matter.

In the semiconductor manufacturing process, the influence of foreign matter is great, and there has been a great demand for a device capable of inspecting foreign matter at high speed and with high reliability. For this reason,
The effect of the present invention seems to be very large.

[Brief description of the drawings]

FIG. 1 is a diagram showing a basic configuration.

FIG. 2 is a diagram showing a region to be inspected;

FIG. 3 is a diagram showing an input image.

FIG. 4 is a diagram showing an image processing method.

FIG. 5 is a diagram showing a result of image processing;

FIG. 6 is a diagram showing a conventional foreign matter inspection device.

[Explanation of symbols]

 13 Laser Oscillation Source 14 Laser Oscillation Source 15 Laser Oscillation Source 16 Laser Oscillation Source 17 Condensing Lens 18 Image Sensor 19 Image Sensor Controller 20 Image Processor 21 Image Memory 22 Inspection Area Learning Update

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-60-253222 (JP, A) JP-A 1-1117024 (JP, A) JP-A 1-263539 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) G01N 21/956 G06T 7/00 H01L 21/66

Claims (3)

(57) [Claims] 1. A surface of an object to be inspected is irradiated simultaneously or sequentially with light from a plurality of different directions, light information formed by each is taken into an image pickup device, and a plurality of obtained images are compared and formed on the object to be inspected. Foreign matter that detects foreign matter in the inspected object by distinguishing the pattern that is
In the inspection device, the shade of a corresponding pixel of the plurality of images is
By outputting the smallest value among the values,
A foreign matter inspection device for detecting foreign matter on a body. 2. The apparatus according to claim 1, wherein light of wavelengths corresponding to three colors of the color-capable image sensor is simultaneously irradiated, taken into the color-capable image sensor, and input of optical information is efficiently performed. The foreign matter inspection device according to claim 1. 3. The apparatus according to claim 1, wherein a plurality of light beams having different wavelengths are radiated at the same time, taken into a plurality of image pickup devices through respective filters, and optical information is input efficiently. The foreign matter inspection device described in the above.