JP2010008336A - Sample wafer for calibration of image inspection device, and calibration method of image inspection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sample wafer for calibration that is used for calibration of an image inspection device performed for keeping the inspection accuracy of pinhole inspection and efficiently performs the calibration by providing a hard laser mark on a surface. <P>SOLUTION: This sample wafer for calibration is used for calibration of the image inspection device for inspecting a pinhole defect of a silicon wafer by image processing. The hard laser mark is provided on the surface of the sample wafer for calibration. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a sample wafer for calibration of an image inspection apparatus used in a method for inspecting crystal defects of a semiconductor silicon wafer, and a calibration method of an image inspection apparatus.

  In general, a semiconductor wafer is manufactured by growing a cylindrical semiconductor single crystal ingot by the Czochralski method (hereinafter referred to as “CZ method”) or a floating zone method, and then forming the grown semiconductor single crystal ingot into a thin plate shape. After the wafer was cut into pieces, the resulting wafer was subjected to a lapping process for adjusting the thickness and flatness of the wafer, an etching process for etching the wafer to remove wafer processing distortion, and an etching process. A polishing process or the like for further improving the surface roughness and flatness of the wafer to provide a mirror surface is performed, and a semiconductor wafer as a final product is manufactured. A device is subsequently formed on the semiconductor wafer to be a product manufactured in this manner, whereby a memory, a CPU, and the like are manufactured.

  In recent years, with the miniaturization of elements accompanying the high integration of semiconductor circuits such as DRAMs, a high-purity, low-defect, high-quality semiconductor wafer is required as the substrate. However, a semiconductor silicon wafer has a pinhole as one of crystal defects. Therefore, for example, when a silicon single crystal is manufactured by the CZ method, after the seed crystal is brought into contact with the silicon melt in the quartz crucible, the step of applying vibration to the crucible shaft that supports the quartz crucible is performed. Although a method of reducing the pinhole defect rate by reducing bubbles adhering to the surface of the inner wall of the crucible has been disclosed (see, for example, Patent Document 1), the generation of pinholes has been completely prevented. Not in.

  When a silicon single crystal is grown by the CZ method, a pinhole, which is a crystal defect that becomes a hole when bubbles contained in a melt obtained by melting a polycrystal in a quartz crucible is taken into the crystal, has a diameter of several μm. The larger one has a diameter of about 3 mm and penetrates the wafer. Among wafers manufactured from silicon crystals containing such pinholes through a slicing process, lapping process, etching process, mirror polishing process, etc., silicon containing this pinhole on the front surface, back surface, or inside thereof A wafer exists, and the silicon wafer including the pinhole is removed as a defective wafer in the inspection process. This pinhole inspection is performed by an image inspection apparatus using an infrared transmission image processing apparatus, and is performed by the inspection procedure shown in FIG.

First, as a procedure (a), a silicon wafer to be inspected is stored in a box and set in a device. Next, in step (b), the amount of emitted infrared light is set according to the resistivity of the wafer. Then, an infrared transmission image is captured from the camera by scanning the wafer in the procedure (c), and the image captured in the procedure (d) is binarized with a predetermined threshold value. Thereafter, in the procedure (e), the inspection area calculation for excluding the outer circumference of 1 mm, the wafer support portion and the like from the inspection area is performed. Then, the presence / absence of a pinhole is determined from the image data binarized in step (f), the wafer determined to have a pinhole is removed from the process, and the inspection is terminated in step (g).
Note that the image inspection apparatus needs to periodically calibrate the apparatus in order to maintain the inspection accuracy.

  Here, FIG. 7 is a flowchart showing the calibration procedure of the image inspection apparatus used for the conventional pinhole inspection. First, as a procedure (a), a calibration sample wafer is mounted on a box and set in an apparatus. Here, a wafer having a pinhole is used as a calibration sample wafer. This calibration sample wafer is a collection of wafers where pinholes were actually generated, and the pinhole diameter was confirmed with a microscope, and about 10 wafers with pinholes with different diameters of 50 μm to 700 μm were selected. is there. FIG. 8 schematically shows a sample wafer in which pinholes are generated.

  Next, as step (b), the amount of emitted infrared light is set based on the resistivity of the wafer. Then, an infrared transmission image is captured from the camera by scanning the wafer in the procedure (c), and the average luminance value profile of the image is confirmed in the procedure (d). Furthermore, a process of binarizing the image captured in the procedure (e) with a predetermined threshold value is performed. Then, in step (f), it is determined whether or not the process has been completed for the back side. If not, the wafer is inverted in step (g), and then steps (c) to (e) are repeated. At this time, the pinhole on the back surface is a pinhole that has been brought to the back surface by inverting the wafer, and the pinhole itself is the same. Here, FIG. 9 shows an example of an average luminance profile and a binarized image of images having different pinhole sizes.

Next, the average luminance profile of the front surface and the back surface is compared in the procedure (h), the number of pixels of the binarized image data on the front surface and the back surface is compared, and the value is different between the front surface and the back surface in the procedure (i). If the values are the same on the front and back surfaces, determine the number of sample wafers in step (j). If there is still a sample wafer, use the next sample wafer. Perform calibration. If it is the last sample wafer, calibration is completed in step (k).
Since a single wafer basically has only one pinhole, when scanning with multiple cameras, the pinhole position is changed by rotating the wafer to change the pinhole position. Need to scan.

  In this calibration, a wafer in which pinholes are actually generated is used as a calibration sample wafer. Therefore, it is extremely difficult to manufacture a sample wafer having a pinhole having an arbitrary diameter, depth, or the same size. Further, it is necessary to confirm the focal points of the front and back cameras at the time of calibration, but it is difficult to obtain a wafer having pinholes on the front and back surfaces. For this reason, there is a problem that the front and back surfaces of the sample wafer in which pinholes are generated only on one side are reversed and the front and back sides are virtually reproduced.

JP 2007-210803 A

  The present invention has been made in view of the above problems, and can be efficiently calibrated in a calibration sample wafer used for calibration of an image inspection apparatus for maintaining the inspection accuracy of pinhole inspection. An object of the present invention is to provide a calibration sample wafer and a calibration method for an image inspection apparatus.

  In order to solve the above problems, the present invention provides a calibration sample wafer used for calibration of an image inspection apparatus for inspecting a pinhole defect of a silicon wafer by image processing, and a hard laser mark is provided on the surface of the calibration sample wafer. Provided is a sample wafer for calibration of an image inspection apparatus characterized by being applied.

  As described above, since the hard laser mark is provided on the surface of the calibration sample wafer, a hole having a desired diameter and depth can be freely formed by the hard laser mark. By using it as a substitute for a hole, a sample wafer can be manufactured very easily. Therefore, it is possible to obtain a sample wafer that can be calibrated with high accuracy and that the time required for calibration can be greatly shortened and calibrated efficiently.

In the calibration sample wafer of the present invention, it is preferable that the hard laser mark is provided with two or more types of hard laser marks having different diameters and / or depths of the hard laser mark. 2).
As described above, since there are two or more types of hard laser marks having different diameters and depths, the number of sample wafers can be reduced. In addition, when there are multiple cameras, if the same kind of pinhole is formed in each area scanned by each camera, the sample wafer can be made one, and the wafer can be changed to change the pinhole position. There is no need to rotate. Therefore, the calibration procedure which has been conventionally performed can be omitted, the time required for calibration can be greatly shortened, and the sample wafer can be calibrated efficiently.

In the calibration sample wafer of the present invention, the hard laser mark is provided on both surfaces of the calibration sample wafer, and the diameter and depth of the corresponding hard laser mark on both surfaces of the calibration sample wafer. Are preferably the same (claim 3).
By having the same hard laser mark on both sides of the sample wafer, it is possible to make the sample wafer unnecessary to invert the wafer. Therefore, the procedure for reversing the wafer can be omitted in the conventional calibration procedure, and the time required for calibration can be greatly shortened. Also, since it is not necessary to invert the wafer and virtually reproduce the front and back, the sample wafer can be calibrated with high accuracy without causing reproducibility problems.

  Furthermore, a calibration method for an image inspection apparatus is provided, wherein the image inspection apparatus is calibrated using the sample wafer for calibration of the image inspection apparatus of the present invention. (Claim 4).

  As described above, since the sample wafer can be easily manufactured by calibrating the image inspection apparatus using the calibration sample wafer of the image inspection apparatus of the present invention, the sample wafer can be prepared in a short time. it can. In addition, calibration can be performed with one sample wafer, and since it is not necessary to reverse the front and back, the time required for calibration of the image inspection apparatus can be greatly shortened. Further, since it is not necessary to invert and calibrate the wafer, it is not necessary to consider the reproducibility of the front and back of the wafer, and the calibration accuracy can be improved.

  As described above, in the present invention, the calibration sample wafer used in the calibration of the image inspection apparatus for maintaining the inspection accuracy of the pinhole inspection has a surface provided with a desired hard laser mark. is there. As a result, calibration can be performed with high accuracy, a sample wafer can be easily produced, and the time required for calibration of the image inspection apparatus can be greatly shortened and calibration can be performed efficiently.

Hereinafter, the present invention will be described more specifically.
As described above, for inspection of pinholes, which are crystal defects of a semiconductor silicon wafer, an image inspection apparatus using an infrared transmission image processing apparatus is used. In order to maintain the inspection accuracy of the image inspection apparatus. It is necessary to calibrate the device periodically. However, the calibration sample wafer used for the calibration is manufactured by selecting from the wafers in which pinholes are actually generated. Therefore, there are a plurality of calibration sample wafers, and it is necessary to repeat the same procedure many times in the calibration of the image inspection apparatus, and the calibration cannot be performed efficiently. The cause was found to be a problem with the calibration sample wafer itself used for calibration.

Therefore, the present inventors tried to produce a calibration sample wafer for an image inspection apparatus having a hard laser mark on the surface instead of a pinhole.
As a result, it is possible to easily produce a sample wafer having a pinhole with a hard laser mark having a desired diameter and depth, and there is a pinhole with a hard laser mark having a different diameter and depth on one wafer. In addition, a sample wafer having pinholes of the same size corresponding to both the front and back surfaces could be produced.

  Then, it was found that by using the calibration sample wafer for calibration of the image inspection apparatus, high-accuracy calibration can be performed and calibration can be performed with one wafer, so that the time required for calibration can be greatly shortened. Further, it has been found that the calibration accuracy of the image inspection apparatus is improved because it is not necessary to invert the front and back of the calibration sample wafer.

The present invention has been completed based on the above findings, and the present invention will be described below in more detail with reference to the drawings. However, the present invention is not limited to these.
FIG. 1 schematically shows a calibration sample wafer of the image inspection apparatus of the present invention.
As shown in FIG. 1, a hard laser mark 2 is provided on the surface of the calibration sample wafer 1.

The hard laser mark 2 is a hole cut by a hard laser marker as an alternative to a pinhole, and there are a plurality of hard laser marks 2. The plurality of holes exist on both the front and back surfaces, and the left side of the row indicates the front side hole and the right side indicates the back side hole. Further, there are five types of diameters of 70 μm, 60 μm, 50 μm, 40 μm, and 30 μm in three areas in the radial direction of the surface of the wafer, and three types of depths of 40 μm, 30 μm, and 20 μm. There is a hole.
The reason why laser marking is performed on the three areas on the surface of the calibration sample wafer is that three cameras are arranged in parallel in the image inspection apparatus, and the number of cameras installed is one. If it is a stand, it is only necessary that one area is laser-marked. Further, the diameter, depth, number and type of the hard laser mark are not limited to this.

  The hard laser mark needs to be marked at a desired position on the wafer with an irradiation condition having a desired diameter and depth after investigating the irradiation condition of the laser to be used in advance. In order to change the hole diameter, the laser beam diameter may be changed. To change the depth, the laser output may be changed. Further, the front and back surfaces of the wafer are formed in this order so that the positions of the holes do not overlap on the front and back surfaces of the wafer.

  In this way, the surface of the calibration sample wafer is provided with a hard laser mark instead of a pinhole, so that a hole having a desired diameter and depth can be freely formed at a desired position on the wafer. can do. Therefore, the image inspection apparatus can be accurately calibrated using this. In addition, the sample wafer can be manufactured very easily, the time required for calibration of the image inspection apparatus can be greatly reduced, and a calibration sample wafer can be calibrated efficiently.

In this case, as shown in FIG. 1, it is preferable that the hard laser mark on the surface of the calibration sample wafer is provided with two or more types of hard laser marks having different diameters and / or depths.
As described above, since there are two or more types of hard laser marks having different diameters and depths, the number of sample wafers can be greatly reduced as compared with the conventional one. For example, as shown in FIG. Therefore, since the image inspection apparatus can be calibrated without performing a calibration procedure that has been repeatedly performed many times in the past, the time required for calibration can be greatly reduced. And it can be set as the sample wafer for calibration which can be calibrated efficiently.

Further, as shown in FIG. 1, the hard laser mark on the surface of the calibration sample wafer is applied to both surfaces of the wafer, and the diameter and depth of the corresponding hard laser mark on both surfaces of the wafer are the same. Preferably there is.
Thus, in the calibration of the image inspection apparatus, the sample wafer can be calibrated including the confirmation of the focus of the camera by the hard laser marks on the front surface and the back surface without inverting the wafer. Therefore, the procedure for reversing the wafer can be omitted in the conventional calibration procedure, and the time required for calibration can be greatly shortened. In addition, since it is not necessary to consider the influence on reproducibility of the calibration accuracy when the wafer is inverted, it is possible to provide a sample wafer that can accurately calibrate the image inspection apparatus.

Here, FIG. 2 is a diagram schematically showing a configuration of an image inspection apparatus using the infrared transmission image processing apparatus of the present invention.
The image inspection apparatus 9 is mainly composed of an infrared transmission image processing apparatus 8. The infrared transmission image processing apparatus 8 transmits the infrared ray 5 from the infrared light source 3 through the line fiber 4 to the silicon wafer 6 which is an inspection object, An image is captured by the line camera 7, and the image is captured and processed. Then, from the processed data, the image inspection device 9 determines the presence or absence of a pinhole and inspects the pinhole.

  Here, since the field of view of the line camera 7 is as narrow as about 1/6 of the diameter of the silicon wafer 6 that is the object to be inspected, three cameras are installed in parallel at an interval of about twice the width of the field of view. ing. For example, cameras with a visual field width of 50 mm are installed at 100 mm intervals on a wafer having a diameter of 300 mm. In this state, the entire surface of the wafer can be scanned by scanning the wafer from the front to the back, moving the wafer laterally by the width of the field of view, and scanning from the back to the front again.

Next, FIG. 3 is a flowchart showing the calibration procedure of the image inspection apparatus using the calibration sample wafer of the present invention.
First, as a procedure (a), a box in which a calibration sample wafer having a hard laser mark on the surface of the wafer of the present invention is mounted is set in an image inspection apparatus. Next, in step (b), the amount of emitted infrared light is set according to the resistivity of the wafer. Then, an infrared transmission image is captured from the camera by scanning the wafer in the procedure (c), the average luminance value profile of the image is confirmed in the procedure (d), and the captured image is detected with a predetermined threshold value in the procedure (e). Perform binarization. Here, FIG. 4 shows an example of an average luminance profile for each diameter and depth of the hard laser mark in the calibration sample wafer of the present invention. FIG. 5 shows an example of a binarized image according to the diameter and depth of the hard laser mark in the calibration sample wafer of the present invention.

  Next, in step (f), the average luminance profile of the front surface and the back surface is compared, and the number of pixels of the binarized image data on the front surface and the back surface is compared. h) The device is adjusted. If the values on the front and back surfaces are the same in step (f), the calibration is terminated in step (g).

  Thus, by calibrating the image inspection apparatus using the sample wafer for calibration of the image inspection apparatus of the present invention, a sample wafer can be easily produced by forming a hole by hard laser marking instead of a pinhole. . Further, since a plurality of hard laser marks can be formed on a single wafer with a desired diameter and depth, the number of sample wafers can be reduced to one. It is only necessary to perform (e) once, and the time required for calibration can be greatly reduced.

  Further, by calibrating the image inspection apparatus using the calibration sample wafer of the image inspection apparatus of the present invention, since the hard laser mark is applied to both the front and back surfaces of the wafer, the wafer is reversed. , It is not necessary to carry out steps (c) to (e). As a result, the time required for calibration of the image inspection apparatus can be further shortened.

  Further, since it is not necessary to invert and calibrate the wafer, it is not necessary to consider the calibration accuracy due to the reproducibility of the front and back of the wafer. Therefore, the image inspection apparatus can be calibrated with high accuracy.

Next, the present invention will be described more specifically with reference to Examples and Comparative Examples of the present invention, but the present invention is not limited to these.
(Example)
First, a thin disc-shaped wafer was prepared by slicing a P-type <100> single crystal silicon ingot pulled up by the CZ method. In order to prevent the wafer from cracking and chipping, the outer edge portion was chamfered, and then lapping, etching, and mirror polishing were performed to flatten the wafer.
After that, set the wafer on a hard laser marking device (excimer processing machine manufactured by Sumitomo Heavy Industries, Ltd., laser oscillator, INDEX 848 manufactured by Rumonics), adjust the laser output and laser beam diameter, and apply the hard laser mark as shown in Fig. 1. Thus, a calibration sample wafer was produced.
Next, the calibration sample wafer produced above is mounted in a storage box, set in the infrared transmission image processing apparatus (RXP-1200 manufactured by Raytex) shown in FIG. 2, and image inspection is performed according to the calibration procedure of FIG. The instrument was calibrated.

(Comparative example)
Similar to the embodiment, from a thin disk-shaped wafer sliced from a single crystal silicon ingot pulled up by the CZ method, one pinhole of the same diameter and depth (12 types) as in the embodiment is actually provided for each wafer. Twelve generated ones were selected and the same lapping process as in the example was performed. And the sample wafer for calibration was produced, without giving a hard laser mark on the wafer surface.
Next, the sample wafer for calibration prepared above was mounted in a storage box, set in an infrared transmission image processing apparatus (RXP-1200 manufactured by Raytex), and calibrated according to the calibration procedure of FIG.
However, since there are three cameras, steps (c) to (e) were repeated three times by changing the position of the pinhole by rotating the wafer.

  In the calibration of the image inspection apparatus of the example, the time required from the setting of the calibration sample wafer in the storage box in the procedure (a) in FIG. 3 to the completion of the calibration in the procedure (g) was about 2 hours. . In the calibration of the image inspection apparatus of the comparative example, it took about 4 hours from the time when the calibration sample wafer was set in the storage box in the procedure (a) in FIG. 7 to the end of the calibration in the procedure (k). .

  4, 5, and 9, the average luminance profile and the binarized image of the hard laser mark or pinhole of the example and the comparative example at a diameter of 70 μm and a depth of 20 μm are almost the same, and Even when the sample wafer for calibration is used, it can be seen that the calibration can be performed with the same accuracy as the conventional one. In addition, from FIGS. 1, 4, 5, and 9, the embodiment can freely produce a hard laser mark having a desired diameter and depth, but in the comparative example, there is a pinhole having a desired diameter. It can be seen that it is difficult to produce a sample wafer for calibration and that a plurality of wafers are necessary.

From the above, according to the sample wafer for calibration of the image inspection apparatus of the present invention, a hard laser mark having a desired diameter and depth can be easily applied, and a plurality of wafers can be provided on one wafer. Since the hard laser mark is applied to both the front and back surfaces, when used for calibration of an image inspection apparatus, the time required for calibration can be greatly shortened, and efficient calibration can be performed. Specifically, calibration can be completed in half of the conventional time.
In addition, since hard laser marks are provided on both surfaces of one wafer, the reproducibility due to reversal of the front and back of the wafer has no influence on the calibration, so that the calibration accuracy can be improved.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

It is a figure which shows typically the sample wafer for calibration of the image inspection apparatus of this invention. It is a figure which shows typically the structure of the image inspection apparatus using the infrared transmission image processing apparatus of this invention. It is the flowchart which showed the calibration procedure of the image inspection apparatus using the sample wafer for calibration of the image inspection apparatus of this invention. It is a figure which shows the example of the average brightness | luminance profile according to the diameter and the depth of a hard laser mark in the sample wafer for calibration of this invention. It is a figure which shows the example of the binarized image according to the diameter and depth of the hard laser mark in the sample wafer for calibration of this invention. It is the flowchart which showed the test | inspection procedure of the conventional pinhole. It is the flowchart which showed the calibration procedure of the image inspection apparatus used for the conventional pinhole inspection. It is a figure which shows typically the sample wafer in which the conventional pinhole has generate | occur | produced. It is a figure which shows the example of the average luminance profile and binarized image of the image from which the conventional pinhole size differs.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Sample wafer for calibration, 2 ... Hard laser mark, 3 ... Infrared light source, 4 ... Line fiber, 5 ... Infrared, 6 ... Silicon wafer, 7 ... Line camera, 8 ... Infrared transmission image processing apparatus, 9 ... Image inspection apparatus .

Claims (4)

  A calibration sample wafer used for calibration of an image inspection apparatus for inspecting pinhole defects of a silicon wafer by image processing, wherein a hard laser mark is provided on the surface of the calibration sample wafer. Sample wafer for calibration of image inspection equipment.   2. The calibration of an image inspection apparatus according to claim 1, wherein the hard laser mark is provided with two or more kinds of hard laser marks having different diameters and / or depths of the hard laser mark. Sample wafer.   The hard laser mark is provided on both surfaces of the calibration sample wafer, and the diameter and depth of the corresponding hard laser mark on both surfaces of the calibration sample wafer are the same. 3. A sample wafer for calibration of the image inspection apparatus according to 1 or 2.   A calibration method for an image inspection apparatus, wherein the image inspection apparatus is calibrated using the sample wafer for calibration of the image inspection apparatus according to any one of claims 1 to 3.

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