KR101885614B1 - Wafer inspection method and wafer inspection apparatus - Google Patents

Abstract

A wafer inspection method capable of checking the presence or absence of a dot trace on a wafer surface is provided.
The wafer inspection method of the present invention is a method for inspecting a defect of a point shape at the periphery of the surface of the wafer 1 (D (1)) by using the first optical system 10 including the ring fiber illumination 11 and the first light receiving portion 12 A second optical system 20 having a laser light source 21 and a second light receiving unit 22 and having a lower detection sensitivity to the defect D than the first optical system 10, (S20) for detecting a defect (D) in the periphery of the surface of the wafer (1) by using the first step (S10) and the second step (S20) And extracting the point trace (D1) from the exclusive logical sum of the points (D).

Description

Technical Field [0001] The present invention relates to a wafer inspection method and a wafer inspection apparatus,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wafer inspection method and a wafer inspection apparatus for inspecting the presence or absence of defects that may occur on a wafer surface and more particularly to a wafer inspection method capable of inspecting presence or absence of a watermark on the periphery of a wafer surface ≪ / RTI >

BACKGROUND ART [0002] In order to improve product yield and reliability in the manufacturing process of semiconductor devices, defect inspection techniques for the surface of wafers that become substrates of semiconductor devices have become very important. Defects present on the surface of the wafer include various defects such as pits, COP and the like, polishing unevenness as a processing unit, scratches, and particles that are foreign particles attached to the wafer surface. Note that, in this specification, the substrate of the "wafer surface" refers to both the main surface of the wafer and the main surface on the side of the wafer, and is described separately from the case of indicating only the surface on one side.

Among defects on the surface of the wafer, defects of a kind that does not cause any problems exist from the viewpoints of device characteristics and product yield of device manufacture. On the other hand, defects of a kind that are not allowed to exist as a product exist. Thus, the surface of the wafer is inspected based on a predetermined determination criterion, and determination of good or defective product is made.

Conventionally, a surface of a wafer after a mirror surface polishing of a finished surface is scanned with laser light by using an LPD (Light Point Defect) inspection apparatus (laser surface inspection apparatus), and the surface of the wafer caused by particles, A wafer inspection for detecting scattered light is performed. The laser of the laser surface inspection instrument uses an optical system having a short wavelength and a small spot diameter in order to make it possible to measure minute LPD of a submicron order. In addition, in the LPD inspection apparatus, in order to determine the presence or absence of defects which are difficult to discriminate, visual inspection for judging the wafer surface by the naked eye is also used. Since the visual inspection is a sensory test, deviation of the judgment by the inspector is inevitable, and on the other hand, it takes time for the examiner to learn, and therefore, it is required to establish an objective inspection method and an automatic inspection method.

Here, as one of the wafer inspection methods, the present applicants propose a method of appropriately evaluating a wafer without relying on the appearance inspection, particularly regarding defects on the back surface side of the wafer, in Patent Document 1. That is, a map processing step of sequentially photographing the part image of the back side of the wafer along the circumferential direction of the wafer and synthesizing the photographed parts image to create a whole image of the back side of the wafer, And a differential processing step for creating a differential processing image on the back side of the wafer, wherein polishing unevenness, traces, scratches and particles are detected and evaluated based on the whole image or the differential processing image.

An optical system for creating the entire image of the wafer surface will be described with reference to Figs. 1A and 1B. 1B is a view showing a main portion extracted from FIG. 1A in order to show irradiated light L ₁ and reflected light (scattered light) L ₂ emitted by the ring-shaped fiber light 11. The first optical system 10 includes a ring fiber illumination 11 and a first light receiving section 12. The first light receiving section 12 includes a telecentric lens 13 and a light receiving section 14). In addition, the ring fiber illumination 11 is composed of an ultra-high-pressure mercury lamp. The irradiation light L ₁ irradiated by the ring fiber illumination 11 is incident on the wafer 1 at an angle of 20 ° with respect to the wafer surface and is irradiated with a defect D , It becomes a scattered light (L ₂ ). The first light receiving section 12 receives and captures the vertical scattered light among the scattered light L ₂ and measures the position information and luminance information of the first optical system 10.

The entire image of the wafer surface can be obtained by scanning the entire surface of the wafer using the first optical system 10 and performing image processing. Further, in order to shorten the scanning time, it is general to arrange a plurality of first optical systems 10 on the front and back surfaces of the wafer. 2A is an example of an entire image on one side of the wafer obtained by the first optical system 10 and FIG. 2B is an example of an entire image of the wafer obtained by the LPD inspection (manufactured by KLA-Tencor Corporation) It is a map. As shown in Figs. 2A and 2B, defects such as scratches and particles can be detected by any device. In the case of the laser surface inspection apparatus, "trace" and "haze" are detected as an aggregate of LPD of small size. However, when the first optical system 10 is used, unlike the laser surface inspection apparatus (LPD inspection apparatus) Quot; traces " or " haze " can be identified and detected. However, since the shape of such a defect has a specific spread and is not a point shape, it is excluded from the defect of " point shape " in this specification.

Japanese Patent Application Laid-Open No. 2010-103275

As described above, by using the wafer inspection apparatus, it has become possible to detect various defects without depending on visual inspection by the naked eye. However, defects have point-like defects having a diameter of about 5 to 3000 占 퐉 called "point marks", and such point marks can not be detected unless they have been visually inspected by hitherto. Hereinafter, with reference to Figs. 3A to 3C, a point trace and its generation mechanism will be described.

The dot trace is formed, for example, as follows. After the wafer 1 is polished, the wafer 1 is immersed and cleaned in a cleaning agent solution, and then spin drying is performed in order to remove the cleaning agent solution. The cleaning solution component 2 in a mist state is biased to the periphery of the wafer 1 due to the centrifugal force acting on the wafer 1 during spin drying. Silicon (Si), for example, a wafer material is melted out and oxygen (O ₂ ) in the outside air is also blown in the cleaning chemical liquid component 2 as a residue (FIG. Then, when the cleaning liquid agent component 2 evaporates, the portion where the cleaning liquid agent component 2 is adhered is a circular concave portion (it may be said that the wafer 1 is partly etched). In the recess the edge of the circular metasilicate and the precipitate (2 ') is formed due to (H ₂ SiO ₃₎ and potassium silicate (K ₂ SiO _3), that the trail (D1) of the crater (crater) shape is formed . Once the point marks D1 are formed, the polishing marks remain in the wafer 1 (Fig. 3C), since the polishing allowances are almost uniform in the surface even if further polishing is carried out. The diameter of the point trace is approximately 5 to 3000 占 퐉, as described above. The width of the edge of the circular concave portion (so-called outer ring-shaped ring) is approximately 0.2 to 30 占 퐉. , And about 0.1 to 30 nm. As described above, the height of the edge of the point trace D1 is very small in comparison with the diameter and the width of the edge.

Since the shape and size of the point trace D1 are the same as described above, the scattered light pattern due to the point trace D1 is detected only at the periphery of the edge of the crater shape and not at the inside of the edge of the crater shape. This is because, on the inner side of the edge portion of the crater shape, there is almost no irregularity and a scattered light pattern becomes the same as a flat surface without defect. As described above, the dot marks D1 are detected as an aggregate of minute LPDs in the conventional inspection apparatus. In addition, when the width of the edge of the concave portion of the point trace is relatively large (for example, 2 탆 or more), it is difficult to distinguish from the small size LPD because the size of the defect is the same as that of the scattered light pattern. Since wafers with dot marks are normally determined to be defective in terms of quality control, they have been accompanied by visually inspected wafers that have no dot marks on the wafers. However, as described above, since the appearance inspection requires the determination by the inspector, it is required to establish an objective inspection method and an automatic inspection method.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a wafer inspection method and a wafer inspection apparatus capable of checking whether or not a point trace exists on a wafer surface, taking the above problems into consideration.

In order to achieve the above object, the inventors of the present invention have intensively studied and conceived to detect defects on the wafer surface by an optical system in which the above-described light source of the first optical system 10 is replaced with a laser light source. Therefore, when the inventors tried to inspect wafers by such a light source, when the light source is a laser light source and the detection sensitivity is lower than that of the first optical system 10, a point defect (D1) , And it was confirmed that only the particle was detected. As described above, in the first optical system 10, the defect D determined as the particle also includes the point trace D1. Therefore, the inventors of the present invention found that only the dot traces D1 can be extracted from the exclusive OR of the defects D detected by both optical systems, thereby completing the present invention. The present invention is based on the above findings and examination, and the main points of the present invention are as follows.

The wafer inspection method of the present invention comprises a first step of detecting a point-like defect in the periphery of a wafer surface by using a first optical system including a ring fiber illumination and a first light receiving unit, A second step of detecting the defect on the periphery of the wafer surface by using a second optical system having a lower detection sensitivity to the defect than the first optical system; And a step of extracting a point trace from the exclusive OR of each defect detected by the two processes.

Here, it is preferable that the second optical system detects only the defect in the peripheral portion.

It is preferable that the defects detected in the first step comprise particles and the dot marks, and the defects detected in the second step comprise the particles.

In addition, it is preferable that the laser light source is a blue LED laser.

It is preferable that the peripheral portion is within a range of 3.5 mm from the outer edge of the wafer.

It is preferable that the lower limit of the detection sensitivity of the defect by the first optical system is 0.5 占 퐉 or less and the lower limit of the sensitivity of the defect detection by the second optical system is 1 占 퐉 or more.

A wafer inspection apparatus of the present invention comprises a second optical system having a first optical system including a ring fiber illumination and a first light receiving unit, a laser light source, and a second light receiving unit, the detection sensitivity of which is lower than that of the first optical system, A moving unit for moving at least one of the wafer, the first optical system, and the second optical system; and a control unit for controlling the first optical system, the second optical system,

Wherein the control unit controls the first optical system to detect a point-like defect in the periphery of the wafer surface and to control the second optical system to detect the defect in the periphery of the wafer surface And extracting a point trace from the exclusive OR of each defect detected by the first optical system and the second optical system.

According to the present invention, it is possible to provide a wafer inspection method and a wafer inspection apparatus capable of checking presence or absence of a dot trace on a wafer surface.

1A and 1B are schematic views illustrating a first optical system 10 used in an embodiment of the present invention. FIG. 1A is a schematic view showing the entire first optical system 10, (L ₁ ) and scattered light (L ₂ ) due to the incident light L ₁ .
2A and 2B show an entire image of a wafer defect detected by a conventional example. FIG. 2A shows an example of a whole image of a wafer defect obtained by the first optical system 10, FIG. 2B shows an example of a wafer defect detected by a commercially available LPD inspection apparatus Is an example of a whole image of a wafer defect obtained by the above method.
Figs. 3A to 3C are schematic views for explaining a generation mechanism of a point trace. Fig.
4 is a flowchart showing a wafer inspection method according to an embodiment of the present invention.
5 is a schematic view for explaining a second optical system 20 used in an embodiment of the present invention.
6 is a schematic plan view of a wafer inspection apparatus 100 according to an embodiment of the present invention.
Figs. 7A and 7B are diagrams showing a point trace previously confirmed in the embodiment, where 7a is an AFM image and 7b is a graph showing the height thereof.
8A to 8C are schematic diagrams showing the positions of the dot traces in the embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 4 is a flowchart of a wafer inspection method according to an embodiment of the present invention. The first optical system 10 already described in FIGS. 1A and 1B and the second optical system 20 described later with reference to FIG. 5 are used in combination The presence or absence of a point trace is determined. 6 is a schematic plan view of a wafer inspection apparatus 100 according to an embodiment of the present invention and the wafer inspection apparatus 100 has the first optical system 10 and the second optical system 20 .

(Wafer inspection method)

As shown in Figs. 4 and 1A, 1B, 5 and 6, a wafer inspection method according to an embodiment of the present invention includes a ring fiber illumination 11 and a first light receiving portion 12 having a first light receiving portion 12 (S10) for detecting a point-like defect (D) at the periphery of the surface of the wafer (1) by using the optical system (10) and a laser light source (21) and a second light- And a second step S20 of detecting the defect D at the periphery of the surface of the wafer 1 using the second optical system 20 having a lower detection sensitivity to the defect D than the first optical system 10 And a step (S30) of extracting a point trace from the exclusive OR of each defect (D) detected by the first process (S10) and the second process (S20). Hereinafter, the details of each step will be described in order.

First, in step S10, a point-like defect (D) on the periphery of the surface of the wafer 1 is detected. This process can be performed in the same manner as the conventional technique for detecting defects across the wafer surface. That is, by using the first optical system 10 already described with reference to Figs. 1A and 1B, a predetermined position on the periphery of the surface of the wafer 1 is irradiated, and vertical scattered light (Luminance information) at the predetermined position (hereinafter, referred to as " defect information "). In order to detect the minute size LPD, the lower limit of the detection sensitivity of the first optical system is preferably 1.0 占 퐉 or less, more preferably 0.5 占 퐉 or less, and more preferably 0.1 占 퐉 or less. The lower limit of the detection sensitivity is preferably as small as possible, and is not intended to be limiting, but may be, for example, 0.01 mu m. As the light source of the ring fiber illumination 10, an ultra high-pressure mercury lamp or the like may be used as described above. Further, the diameter of the irradiation area by the ring fiber illumination 10 can be set to, for example, 5 to 40 mm. Among the obtained defect information, together with its position, the first optical system 10 acquires the defect (D) which has been determined to be the scattered light by the conventional particle.

Here, as described above, the defect (D) determined as a particle by the first optical system 10 also includes a point trace D1. Therefore, in the first step (S10) of using the first optical system 10, a point-like defect D consisting of the point trace D1 and the particle D2 is detected. In other words, it may be said that the defect D in the point shape detected in the first step (S10) consists of the particle D2 and the point trace D1.

3A to 3C, a point trace D1 is formed on the periphery of the surface of the wafer 1 as in the case of the prior art. Therefore, the detection by the present step S10 may be performed by scanning the first optical system in the entire in-plane direction of the wafer 1 to acquire the defect information and acquire all the information of the defect. In the case where only the periphery of the wafer 1, It is also possible to acquire defective information concerning the point-like defect (D). Further, in order to clearly determine the type of defect, the defect information may be subjected to differential processing, filter processing, and the like to extract a point-like defect (D) in the periphery of the wafer, if necessary.

Further, by providing a plurality of first optical systems 10 on both surfaces of the wafer surface, it is possible to acquire defect information quickly. The first optical system 10 may be provided above and below the central portion of the surface of the wafer 1 in addition to the peripheral portion in the case where the first optical system 10 is scanned across the entire surface of the wafer 1. [

5, the second optical system 20 including the laser light source 21 and the second light receiving section 22 is used to form a point-like shape at the periphery of the surface of the wafer 1. [ The defect D is detected together with its position. For example, the second optical system 20 is fixed to either or both of the upper and lower sides of the periphery of the wafer 1, the wafer 1 is placed on the rotary table 3, So that only the defect D in the periphery of the wafer may be detected. Further, as in the first optical system 10, the second optical system 20 may be scanned at the periphery of the wafer.

Here, it is assumed that the sensitivity of the point-like defect (D) detected by the second optical system (20) is less sensitive (worse) than that of the first optical system (10) so that the point trace can not be detected. In this case, it is preferable to set the lower limit of detection sensitivity to 1 mu m. Both of the point trace D1 and the particle D2 are detected and the point trace D1 is used in combination with the first optical system as described later on below if the detection sensitivity of the second optical system 20 becomes excessively good, Can not be extracted. Although not intended to be limiting, the spot diameter of the laser light having such a detection sensitivity can be exemplified by 70 mu m to 270 mu m. The wavelength of the laser beam is not particularly limited as long as it is in the range of visible light, and blue (about 450 to about 495 nm) is preferable.

The laser light source 21 irradiates a predetermined position on the periphery of the wafer 1 and receives the scattered light by the irradiation light L ₃ to the second light receiving section 22, If the scattered light intensity exceeding the value is obtained, it can be determined that the defect is attributable to the particle D2. This is because, unlike the first optical system 10, the second optical system 20 uses the laser light source 21 whose wavelength of the irradiation light source is in the range of, for example, white light (380 nm to 800 nm). Therefore, the detection sensitivity of the LPD is not less than 2 占 퐉 and the intensity of the scattered light from the point trace D1 is not so strong as to be judged to be defective. On the other hand, the intensity of the scattered light from the particle D2, It is possible to obtain a sufficient strength to judge a defect. As the laser light source 21, a blue LED laser can be used. However, a metal halide lamp, a mercury lamp, or the like may be used as long as it is a laser light source that can not detect the dot trace D1 but can be detected by the particle D2, and is not particularly limited. As the second light receiving section 22, for example, a CCD camera can be used.

As described above, only the particle D2 is detected in the point-like defect D detected in the second step S20 using the second optical system 20, without the point trace D1. In other words, it may be said that the defect (D) in the point shape detected in the second step (S20) is composed of the particle D2. Further, the second optical system 20 can detect defects having a large size or traces having a high haze level in addition to the point-like defect (D).

In the flowchart of Fig. 4, the second step (S20) is performed after the first step (S10) is performed. However, this step may be changed, and any step may be performed first. Between the first step (S10) and the second step (S20), the wafer 1 may be carried by the moving part 30 (see FIG. 6). The moving section 30 referred to here may include the rotating table 3 described above or may include the scanning section of the first optical system 10. [

After the first step (S10) and the second step (S20), in step S30, an exclusive OR (EX-XOR) of each defect (D) detected by the first step (S10) OR). As described above, the defect D detected in the first step S10 is the point trace D1 and the particle D2, and the defect D detected in the second step S20 is the particle D2, , And the point trace D1 is not included. Therefore, when the exclusive OR of both is taken, only the point trace D1 is extracted.

The presence or absence of point marks on the peripheral surface of the wafer surface can be checked by the wafer inspection method that performs the first step (S10) to the third step (S30).

Further, the wafer 1 is preferably a mirror-finished silicon wafer. This is because, as described above, it is important to confirm that there are no dot marks on a mirror-finished silicon wafer. The peripheral edge for checking the presence or absence of a dot trace may be within a range of 3.5 mm or less from the outer edge of the wafer, and may be within a range of 3 mm or less. Since the dot marks exist only in the periphery of the wafer, specifically, within the range of 3.5 mm from the periphery of the wafer as in the case of the prior art, the inspection time can be shortened by narrowing it to this range. The range can be further shortened. It is also possible to shorten the inspection time by detecting the defect D only in the periphery of the wafer 1 in either the first step (S10) or the second step (S20).

(Wafer inspection apparatus)

A wafer inspection apparatus 100 according to an embodiment of the present invention includes a ring fiber illumination 11 and a first light receiving section 12 as shown in Figs. 6 and 1A, 1B, A second optical system 20 having a first optical system 10 and a laser light source 21 and a second light receiving unit 22 and having a detection sensitivity lower than that of the first optical system 10; A moving unit 30 for moving at least one of the optical system 10 and the second optical system 20 and a control unit 50 for controlling the first optical system 10, the second optical system 20, and the moving unit 30 ). Here, the control unit 50 controls the first optical system 10 to detect a point-like defect D at the periphery of the surface of the wafer 1, and also controls the second optical system 20 The defect D at the periphery of the surface of the wafer 1 is detected and a point trace is obtained from the exclusive OR of each defect D detected by the first optical system 10 and the second optical system 20 D1). In Fig. 6, the first optical system 10 and the second optical system 20 are shown one by one, but they may be provided on the opposite side of the wafer 1, or a plurality of them may be provided. It is preferable that the first optical system 10 and the second optical system 20 are provided perpendicular to the wafer 1 in order to receive the vertical scattered light of the defect D. [

The control unit 50 is realized by a suitable processor such as a CPU (central processing unit) or an MPU and can have a recording unit such as a memory and a hard disk. The transfer of the command and the operation of each part are controlled by executing a program for operating the aforementioned wafer inspection method stored in the control unit 50 in advance. The moving unit 30 may include a scanning unit that scans the first optical system 10 and the scanning unit includes an arm connected to the first light receiving unit 12 (camera, etc.) of the first optical system 10, A driving stepping motor for driving the arm, and a servo motor. The moving section 30 may include the same scanning section for scanning the second optical system 20 or may include a rotary table 3 for rotating the wafer 1. [ The unit in which the first optical system 10 is installed and the unit in which the second optical system 20 are provided may be partitioned independently of each other and the moving unit 30 may move the wafer 1 A load port may be provided.

[Example]

While the embodiments of the present invention have been described above, they are merely representative examples, and the present invention is not limited to these embodiments, and various modifications are possible within the scope of the gist of the invention. The following examples are not intended to limit the scope of the invention.

In order to confirm that the point trace can be detected by the wafer inspection method according to the embodiment of the present invention, the following experiment was conducted.

First, a silicon wafer (so-called a policy wafer (also referred to as PW wafer)) having a diameter of 300 mm and a thickness of 775 탆 was prepared and subjected to visual inspection by a naked eye in advance on one side of the wafer, I confirmed that there was a trace.

This point trace was observed with an AFM, and as shown in Fig. 7A, a defect in a crater shape was confirmed. A graph of the height in the axial direction in Fig. 7A is shown in Fig. 7B. The diameter of the dot trace was 150 mu m, the width of the edge was 20 mu m, and the height of the edge was 18 nm.

A wafer inspection method according to the present invention was performed on a silicon wafer having this dot trace. The lower limit of the detection sensitivity of the defect by the first optical system is 0.16 mu m (that is, the defect of the point shape having a diameter of 0.16 mu m or more can be detected) and the lower limit of the sensitivity of the defect detection by the second optical system is 5.0 mu m Defects in a point shape of 탆 or more can be detected). First, as shown in Fig. 8 (a), when a defect (D) having a point shape in the periphery of the wafer on the one side is detected by the first step (S10) using the first optical system 10, Defects in shape were detected. In Fig. 8A, the code of each defect type is also shown, but it is not possible to confirm whether each defect is a point trace D1 or a particle D2 in this step.

Next, as shown in FIG. 8B, when the defect (D) having a point shape in the periphery of the wafer is detected by the second process (S20) using the second optical system 20, (D) was detected. Since the defect detected by this step is the particle D2, the symbol D2 is added in Fig. 8B. 8A and 8B, the wafer position is adjusted based on the notch position (not shown) of the wafer (as a result, the position of the defect D is also matched). 8B, the defect at the position not present in FIG. 8B is the dot trace D1, and the other defect is the defect of the particle D2. . The result of this judgment agrees with the result of the appearance inspection previously performed, and it was confirmed that the presence or absence of the dot trace can be reliably inspected by this inspection method.

[Industrial Availability]

According to the present invention, it is possible to provide a wafer inspection method and a wafer inspection apparatus capable of checking presence or absence of a dot trace on a wafer surface.

1: wafer
10: First optical system
11: Ring fiber light
12: First light receiving portion
20: Second optical system
21: Laser light source
22: Second light receiving portion
30:
50:
D: Defect (point shape)
D1: Point trace
D2: Particles

Claims (7)

A wafer inspection method capable of checking the presence or absence of a crater shaped watermark on the periphery of a wafer surface,
A first step of detecting a point-like defect in the periphery of the wafer surface by using a first optical system including a ring fiber illumination and a first light receiving unit,
A second step of detecting the defect in the periphery of the wafer surface using a second optical system having a laser light source and a second light receiving unit and having a lower detection sensitivity to the defect than the first optical system;
And extracting the point trace from the exclusive OR of each defect detected by the first process and the second process,
Wherein the defect corresponding to the point trace is a defect which is detected by the first optical system but is not detected by the second optical system. delete The method according to claim 1,
Wherein the defect detected in the first step comprises particles and the dot trace, and the defect detected in the second step comprises the particles. The method according to claim 1,
Wherein the laser light source is a blue LED laser. The method according to claim 1,
Wherein the peripheral portion is within a range of 3.5 mm from the outer edge of the wafer. The method according to claim 1,
Wherein a lower limit of detection sensitivity of said defect by said first optical system is 0.5 占 퐉 or less and a lower limit of detection sensitivity of said defect by said second optical system is 1 占 퐉 or more. A wafer inspection apparatus capable of checking the presence or absence of a crater-shaped point trace at the periphery of a wafer surface,
A first optical system having a ring fiber illumination and a first light receiving portion, for detecting a point-like defect in the periphery of the wafer surface,
A second optical system having a laser light source and a second light receiving unit, the second optical system having a lower detection sensitivity to the defect than the first optical system,
A moving unit that moves at least one of the wafer, the first optical system, and the second optical system;
And a control unit for controlling the first optical system, the second optical system, and the moving unit,
Wherein the control unit controls the first optical system to detect a point-like defect at the periphery of the wafer surface and controls the second optical system to detect the defect at the periphery of the wafer surface And extracting the point traces from the exclusive OR of each of the defects detected by the first optical system and the second optical system,
Wherein the defect corresponding to the point trace is a defect which is detected by the first optical system but is not detected by the second optical system.

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