JP7215411B2 - Silicon wafer defect inspection method - Google Patents

Description

The present invention relates to a defect inspection method for silicon wafers.

Conventionally, slip dislocations occurring in silicon wafers have been inspected. A slip dislocation is a shallow step at the level of a silicon atom that is manifested by movement of a dislocation, and is characterized by having a length in a direction according to the crystal orientation.

For example, Patent Literature 1 discloses a defect inspection method for silicon wafers using laser light. This method detects defects formed on the surface of the silicon wafer by irradiating the surface of the silicon wafer with laser light from a laser light source and detecting the reflected light with a photodiode.

JP 2017-174933 A

However, with the method of Patent Document 1, sufficient detection sensitivity may not be obtained, for example, the scattering of laser light may become strong at the outer peripheral portion of the silicon wafer where slip dislocations mainly occur.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a silicon wafer defect inspection method capable of detecting slip dislocations occurring on the surface of a silicon wafer with high sensitivity.

The gist and configuration of the present invention are as follows.
(1) a light irradiation step of irradiating the surface of the silicon wafer with light from a light source;
a light detection step of detecting light reflected from the surface with a photodetector;
A defect inspection method for a silicon wafer, inspecting defects on the surface while rotating the silicon wafer relative to the light source and the photodetector,
The silicon wafer has an off-angle in which the normal direction of the main surface is inclined with respect to the crystal axis,
When the x-axis direction and the y-axis direction are orthogonal to the crystal axis and mutually orthogonal, the magnitude of the tilt angle of the off-angle with respect to the x-axis is different from the magnitude of the tilt angle of the off-angle with respect to the y-axis. ,
When the angle formed by the detection optical axis of the photodetector with respect to the surface in the side view of the silicon wafer is θ,
A defect inspection method for a silicon wafer, wherein the angle θ is adjusted in accordance with a position to be inspected on the circumference of the relatively rotating silicon wafer.

(2) In the above (1), it is preferable to adjust the angle θ by switching the magnitude from a predetermined reference angle according to the position to be inspected on the circumference of the relatively rotating silicon wafer.

(3) In (2) above, the angle θ is switched between the predetermined reference angle each time the silicon wafer is rotated 90° relative to the light source and the photodetector. is preferred.

(4) In (2) or (3) above, when the angle θ is increased from the predetermined reference angle, it is switched to be 1 to 3° greater than the predetermined reference angle, and
When decreasing the angle θ from the predetermined reference angle, it is preferable to switch the angle θ to be 1 to 3° smaller than the predetermined reference angle.

According to the present invention, it is possible to provide a silicon wafer defect inspection method capable of detecting slip dislocations occurring on the surface of a silicon wafer with high sensitivity.

It is a perspective view which shows some silicon ingots with a cut surface. FIG. 2 is a plan view of a silicon wafer schematically showing slip; 1 is a side view showing an example of an optical system that can be used in a silicon wafer defect inspection method according to an embodiment of the present invention; FIG. It is a top view of a silicon wafer for explaining the inspection method of one embodiment of the present invention.

Embodiments of the present invention will be exemplified in detail below with reference to the drawings.

A silicon wafer defect inspection method according to an embodiment of the present invention will be described.
First, a silicon wafer to be inspected will be described.

FIG. 1 is a perspective view showing a portion of a silicon ingot together with a cut surface. For example, in view of the optical properties and shrinkage of the obtained silicon wafer, when cutting the silicon wafer W from the silicon ingot, the normal direction of the main surface of the cut silicon wafer W is intentionally set to the crystal axis of the silicon ingot. An off-angle may be given so as to incline with respect to (growth axis).

In the example shown in FIG. 1, the crystal orientation of the crystal axis of the silicon ingot is <100>, and the directions orthogonal to the crystal axis are the x-axis direction and the y-axis direction (in this example, the notch is formed). position in the negative direction of the y-axis), in this example, the magnitude of the off-angle tilt angle with respect to the x-axis is different from the magnitude of the off-angle tilt angle with respect to the y-axis (the signs are different and the absolute If the values are equal, they are assumed to have the same magnitude). Only one of the inclination angle of the off-angle with respect to the x-axis and the inclination angle of the off-angle with respect to the y-axis may be set to 0°. Although not particularly limited, the off-angle tilt angle with respect to the x-axis can be −1 to 1°, and the off-angle tilt angle with respect to the y-axis can be −1 to 1°. For example, the off-angle inclination angle with respect to the x-axis can be set to 0.5°, and the off-angle inclination angle with respect to the y-axis can be set to 0.2°. A silicon ingot whose crystal orientation is <110> can also be used.

In a silicon wafer W having an off-angle, different crystal orientations appear every 45° on the circumference (as shown in the state of the silicon ingot in FIG. 1). In the illustrated example, the crystal orientation is <011> at the position of the notch, and <011> and <001> appear alternately on the circumference at intervals of 45°. In FIG. 1, the same notation is used for the crystal orientation in the positive direction and the negative direction.

FIG. 2 is a plan view of a silicon wafer, schematically showing slip. In FIG. 2, the length of the slip is exaggerated when schematically showing the slip. In the silicon wafer W as described above, regions in which relatively many slips occur in the vertical direction and regions in which relatively many slips occur in the lateral direction are alternately formed on the circumference at intervals of 90°.

Thus, first, the silicon wafer W to be subjected to the method of the present embodiment has an off-angle in which the normal direction of the main surface is inclined with respect to the crystal axis. Further, when the x-axis direction and the y-axis direction are orthogonal to the crystal axis and mutually orthogonal, the magnitude of the off-angle tilt angle with respect to the x-axis is different from the magnitude of the off-angle tilt angle with respect to the y-axis.
The conductivity type of the silicon wafer can be, for example, p-type, but can also be n-type. Although the diameter of the silicon wafer is not particularly limited, it can be, for example, 200 mm, 300 mm, or 450 mm.

Next, an optical system used for the method of this embodiment will be described.
FIG. 3 is a side view showing an example of an optical system that can be used in a silicon wafer defect inspection method according to an embodiment of the present invention. FIG. 3 shows a side view of the silicon wafer W. FIG.

As shown in FIG. 3, this optical system includes a silicon wafer W as an object of defect inspection, a light source 1 for irradiating light onto the surface of the silicon wafer W, and a photodetector for detecting light reflected from the surface. 2 and .

The light source 1 can be any known one used for inspecting the surface of a silicon wafer W for defects. The light source 1 is preferably a spot-type light guide capable of emitting quasi-parallel light, but may also be a condensing lamp such as a fluorescent lamp, or may be a laser light source. .

The photodetector 2 can be any known device capable of detecting defects in the surface of the silicon wafer W by detecting light reflected from the surface of the silicon wafer W. FIG. The photodetector 2 has a high-resolution lens (not particularly limited, but for example a tencentric lens, which can have a magnification of 0.5 to 1.5 times and a depth of focus of 50 to 80 mm). A high-resolution area camera (although not particularly limited, for example, the resolution can be 1.0 to 3.0 MPixel and the frame rate can be 50 to 200 fps) is preferable.

FIG. 4 is a plan view of a silicon wafer for explaining the inspection method of one embodiment of the present invention. As shown in FIG. 4, in this embodiment, the silicon wafer W is rotated relative to the light source 1 and the photodetector 2 (in this example, the position on the circumference of the light source 1 and the photodetector 2 is is fixed and the silicon wafer W is rotated), and the surface of the silicon wafer W is inspected for defects. As shown in FIG. 3, in this example, the light source 1 is placed above the outer peripheral portion of the silicon wafer W where slips are likely to occur (for example, the area can be up to 6 mm radially inward from the outer edge of the silicon wafer W). and photodetector 2 are located. In FIG. 4, the area to be inspected is indicated by a circular dashed line. Here, as shown in FIG. 3, in the side view of the silicon wafer W, the angle formed by the detection optical axis of the photodetector 2 with respect to the surface of the silicon wafer W is θ, and in the side view of the silicon wafer W, , the angle φ formed by the optical axis of the incident light with respect to the surface of the silicon wafer W.

In the inspection method of the present embodiment, the angle θ is adjusted according to the inspection target position on the circumference of the silicon wafer W that rotates relatively.
The effects of the silicon wafer defect inspection method of the present embodiment will be described below.

According to the defect inspection method for the silicon wafer W of the present embodiment, first, the silicon wafer W to be inspected has an off-angle in which the normal direction of the main surface is inclined with respect to the crystal axis. As a result, as shown in FIGS. 2 and 4, when the silicon wafer W is rotated relative to the light source 1 and the photodetector 2, a relatively large amount of vertical slip occurs. , and a region where relatively many slips occur in the lateral direction appear alternately with respect to the positions of the light source 1 and the photodetector 2 at every 90° on the circumference.
The longitudinal slip detection sensitivity depends on the tilt angle of the off-angle with respect to the x-axis (relatively larger than the tilt angle of the off-angle with respect to the y-axis), and the slip detection sensitivity in the lateral direction is It depends on the tilt angle of the off-angle with respect to the y-axis (relatively larger than the tilt angle of the off-angle with respect to the x-axis). The magnitude of the tilt angle is different from that of the off-angle. Therefore, the slip in the vertical direction and the slip in the lateral direction have different optical reflection intensities.
In contrast, in the present embodiment, the angle θ is adjusted according to the inspection target position on the circumference of the silicon wafer W that is relatively rotated. As a result, the position of the photodetector 2 can be adjusted so that the detection sensitivity is good for vertical slips and horizontal slips, which have different optical reflection intensities.
Therefore, according to the defect inspection method of the silicon wafer W of this embodiment, the slip dislocation generated on the surface of the silicon wafer can be detected with high sensitivity.

Now, the details of the experiment conducted based on the above embodiment will be described below.
A silicon wafer having a diameter of 300 mm, p-type, and crystal plane (100) was prepared as an object to be inspected for surface defects. A spot-type light guide capable of emitting pseudo-parallel light was prepared as a light source, and a high-resolution area camera with a high-resolution lens was prepared as a photodetector.
In the peripheral area of the silicon wafer (the area up to 6 mm radially inward from the edge of the silicon wafer), the positions of the light source and the photodetector are fixed at the angle φ of 73° and the angle θ of 74 to 80. The surface defects were inspected while changing the temperature in °. In Table 1, the reference angle (77°) of the angle θ was obtained in advance as an angle at which the overall evaluation of the sensitivity at 360° is the best when the angle φ is 73° and the silicon wafer is rotated 360°. It is. 0° on the circumference is the position where the notch is formed.
The evaluation results are shown in Table 1 below. In Table 1, the evaluation "A+" indicates that the amount of light is sufficiently good within the range, the evaluation "A" indicates that the amount of light is sufficiently good, but the amount of light is good in some areas, and the evaluation "B" indicates that the amount of light is good. , the evaluation "C" indicates that the amount of light is slightly insufficient or excessive, and the evaluation "D" indicates that the amount of light is slightly insufficient or excessive. If the evaluation is "A+", "A", or "B", the amount of light is good, so slip dislocations generated on the surface of the silicon wafer can be detected with high sensitivity.

As shown in Table 1, when the position on the circumference is 0 to 45°, the evaluation is "A+" when the angle θ is 74 to 76°, and when the position on the circumference is 45 to 135° , the evaluation is "A+" when the angle θ is 78 to 80°, and when the position on the circumference is 135 to 225°, the evaluation is "A+" when the angle θ is 74 to 76°, If the position on the circumference is 225 to 315°, the evaluation is "A+" if the angle θ is 78 to 80°, and if the position on the circumference is 315 to 0°, the angle θ is 74 to 76. °, the evaluation was "A+".

For this reason, it is possible to adjust the angle θ by switching its magnitude from a predetermined reference angle (77° in the above example) according to the position to be inspected on the circumference of the relatively rotating silicon wafer. It was found to be more preferable for detecting slip dislocations generated on the surface of a silicon wafer with high sensitivity.
In the above experimental example, the predetermined reference angle was obtained in advance by comprehensive evaluation of 360°, but the present invention is not limited to this case. can be determined.

Further, from the results shown in Table 1, the angle θ can be switched between a predetermined reference angle each time the silicon wafer W is rotated by 90° relative to the light source 1 and the photodetector 2. was found to be preferable. This is because, as described above, there are regions with different optical reflection intensities, where there is a relatively large amount of slip in the longitudinal direction, and regions where there is a relatively large amount of slip in the lateral direction. , appear alternately with respect to the light source and the photodetector at every 90° on the circumference.

Furthermore, from Table 1, when the angle θ is increased from a predetermined reference angle, it is switched to be 1 to 3° greater than the predetermined reference angle, and the angle θ is decreased from the predetermined reference angle. It has also been found that it is preferable to switch the angle so that it is 1 to 3° smaller than the predetermined reference angle.

1: light source 2: photodetector W: silicon wafer

Claims (4)

a light irradiation step of irradiating the surface of the silicon wafer with light from a light source;
a light detection step of detecting light reflected from the surface with a photodetector;
A defect inspection method for a silicon wafer, inspecting defects on the surface while rotating the silicon wafer relative to the light source and the photodetector,
The silicon wafer has an off-angle in which the normal direction of the main surface is inclined with respect to the crystal axis,
When the x-axis direction and the y-axis direction are orthogonal to the crystal axis and mutually orthogonal, the magnitude of the tilt angle of the off-angle with respect to the x-axis is different from the magnitude of the tilt angle of the off-angle with respect to the y-axis. ,
When the angle formed by the detection optical axis of the photodetector with respect to the surface in the side view of the silicon wafer is θ,
A defect inspection method for a silicon wafer, wherein the angle θ is adjusted in accordance with a position to be inspected on the circumference of the relatively rotating silicon wafer. 2. The silicon wafer defect inspection method according to claim 1, wherein said angle .theta. 3. The angle θ of the silicon wafer according to claim 2, wherein each time the silicon wafer is rotated by 90° relative to the light source and the photodetector, the angle θ is changed from the predetermined reference angle. Defect inspection method. When the angle θ is increased from the predetermined reference angle, it is switched to be 1 to 3° greater than the predetermined reference angle, and
4. The defect inspection method for a silicon wafer according to claim 2, wherein when the angle θ is reduced from the predetermined reference angle, it is switched to be 1 to 3 degrees smaller than the predetermined reference angle.

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