JP2019216135A - Evaluation method of silicon wafer - Google Patents

Abstract

To provide an evaluation method of a silicon wafer, which can appropriately evaluate the quality of a silicon wafer.SOLUTION: A evaluation method of a silicon wafer includes a step of preparing a silicon single crystal in which a flat portion is formed along a crystal central axis on a part of the outer periphery of a straight body and the crystal orientation of the central axis is <111>, a step of cylindrically grinding the straight body of the silicon single crystal, and a step of cutting out a disk-shaped evaluation sample from the cylindrically ground straight body, a step of identifying an evaluation line passing through the center of the evaluation sample and orthogonal to the flat portion, and a step of evaluating the quality of the evaluation sample on the evaluation sample as the quality of the silicon wafer obtained from the straight body.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for evaluating a silicon wafer.

Conventionally, as shown in FIG. 4, when a silicon single crystal 1 having a central axis of a <111> crystal axis is manufactured, a part of the outer periphery of a straight body 11 (hereinafter, referred to as “a straight body 11 before grinding”) is formed. It is known that a flat portion 12 may be formed along the central axis (for example, see Patent Document 1).
The silicon single crystal 1 has a larger diameter than a target silicon wafer (hereinafter, referred to as “target diameter”) in consideration of quality requirements and the possibility that the diameter may fluctuate due to disturbance during pulling. Raised by a few percent larger diameter. As shown by a two-dot chain line in FIG. 5A, the straight body portion 21 after cylindrical grinding (hereinafter, referred to as “the straight body portion 21 after grinding”) with respect to the straight body portion 11 before grinding of the silicon single crystal 1. Is ground so as to have a cylindrical shape having a target diameter. For example, when cylindrical grinding is performed so that the straight body portion 11 before grinding with the diameter R1 becomes the straight body portion 21 after grinding with the target diameter R2, it is preferable to minimize material loss due to grinding. Taking such a viewpoint into consideration, as shown by the two-dot chain line, the center 21C after the grinding (hereinafter, referred to as the "center after the grinding") around the center of the inscribed circle of the one end surface 11A of the straight body portion 11 before the grinding. Preferably, the grinding is performed such that the center 21C is eccentric with respect to the center 11C before grinding (hereinafter, referred to as "center 11C before grinding").

JP 2017-210376 A

Generally, the quality evaluation of a silicon wafer obtained through cylindrical grinding as indicated by a two-dot chain line in FIG. 5A targets an area on an evaluation line extending from the center of the silicon wafer to the outer edge. .
However, in the evaluation results of silicon wafer manufacturers, the quality is within the allowable range, but for example, the quality of chips processed by the device manufacturer may not be within the allowable range.

  An object of the present invention is to provide a silicon wafer evaluation method capable of appropriately evaluating the quality of a silicon wafer.

  The inventor has obtained the following findings as a result of intensive studies. Here, the knowledge will be described by exemplifying an evaluation sample obtained from the straight body portion 21 after grinding and which is thicker than a silicon wafer subjected to mirror polishing or the like, but the same can be said for a silicon wafer. .

As shown in FIG. 5B, when the evaluation sample 3 is viewed from one surface side, an imaginary line passing through the pre-grinding center 11C and orthogonal to the flat portion 12 is represented by L11, and the arc portion 13 of the straight body portion 11 before grinding. Assuming that a virtual line passing through the arbitrary point 13A and the center before grinding 11C is L12, a grinding width H1 on the side opposite to the flat portion 12 side and a grinding width H2 on the flat portion 12 side on the virtual line L11 are: Is substantially the same, the grinding widths H1 and H2 on the imaginary line L11 are smaller than the grinding width H3 on the imaginary line L12.
The amount of change in quality in the radial direction (the amount of change in quality at a predetermined position based on the quality at the center in the radial direction) in the straight body portion 11 before grinding is small on the center side and large on the outer edge side. The tendency of the quality change amount is the same in the direction from the pre-grinding center 11C to the flat portion 12 and in the direction from the pre-grinding center 11C to the circular arc portion 13.

Therefore, the grinding amount of the portion having a large change in quality on the virtual line L11 is smaller than that on the virtual line L12.
That is, among the intersections between the outer edge 3A of the evaluation sample 3 and the virtual line L11, the intersection on the side opposite to the flat portion 12 side is P1, and the intersection on the point 13A side between the intersection between the outer edge 3A and the virtual line L12 is P3. , The area on the evaluation line M1 extending from the center 3C of the evaluation sample 3 (hereinafter referred to as “sample center 3C”) to the intersection P1 is compared with the area on the evaluation line M3 extending from the sample center 3C to the intersection P3. Therefore, there are many parts where the amount of change in quality is large.
When the intersection between the outer edge 3A of the evaluation sample 3 and the imaginary line L11 is P2, the area on the evaluation line M2 extending from the sample center 3C to the intersection P2 is also an evaluation line. As compared with the region on M3, there are many portions where the amount of change in quality is large.
From these facts, the quality evaluation on the evaluation lines M1 and M2 passing through the center of the inscribed circle on the one end surface 11A of the straight body portion 11 before grinding and orthogonal to the flat portion 12 is performed on the other portions. This is considered to be a severe condition compared to. That is, if the quality on the evaluation lines M1 and M2 is within the allowable range, the quality on the evaluation line M3 is also within the allowable range. It is considered that the quality on the lines M1 and M2 may not be within the allowable range.
The present inventors have completed the present invention based on the above findings.

  The silicon wafer evaluation method of the present invention is obtained from a silicon single crystal in which a flat portion is formed along the crystal central axis on a part of the outer periphery of the straight body portion and the crystal orientation of the central axis is <111>. A method for evaluating a silicon wafer, wherein the step of preparing the silicon single crystal, the step of cylindrically grinding the straight body portion of the silicon single crystal, and cutting out a disk-shaped evaluation sample from the straightened cylindrical body portion A step of specifying an evaluation line passing through the center of the evaluation sample and orthogonal to the flat portion, and a step of evaluating the quality of the evaluation sample on the evaluation line as the quality of a silicon wafer obtained from the straight body portion And is carried out.

According to the present invention, in a disk-shaped evaluation sample cut out from a cylindrical body subjected to cylindrical grinding, an evaluation line passing through the center of the evaluation sample and orthogonal to the flat portion is specified, and the quality on the evaluation line in the evaluation sample is determined. Is evaluated as the quality of a silicon wafer obtained from the straight body after the cylindrical grinding (the straight body after the grinding). As described above, since the evaluation on the evaluation line is a stricter condition than the quality evaluation performed on other parts, by shipping only silicon wafers satisfying the stricter condition, the silicon wafer manufacturer Although the evaluation result indicates that the quality is within the allowable range, the defect that the quality of the chip processed by the device maker is not within the allowable range can be suppressed, and the quality of the silicon wafer can be appropriately evaluated.
The specifications of the evaluation sample of the present invention, for example, the thickness, polishing conditions, etching conditions, and the like may be the same as or different from the silicon wafer to be shipped as a product.
Further, in the present invention, the evaluation line does not have to be a line strictly passing through the center of the disk-shaped evaluation sample and orthogonal to the flat portion, but may be a line shifted within an allowable range. A line passing through the center of the tangent circle and orthogonal to the flat portion may be a line rotated by 5 ° or less about the center of the sample (the center of the inscribed circle).

  In the silicon wafer evaluation method of the present invention, before the step of cutting out the evaluation sample from the straight body, performing a step of performing a marking process on the straight body, the step of specifying the evaluation line is the marking It is preferable to specify the position of the evaluation line based on the processed position.

  ADVANTAGE OF THE INVENTION According to this invention, an evaluation line can be easily specified based on the position where the marking process of the evaluation sample was performed.

  In the silicon wafer evaluation method of the present invention, the step of specifying the evaluation line is a line connecting the center of the evaluation sample and the position where the marking process is performed on the outer peripheral portion of the evaluation sample, and the center of the evaluation sample. It is preferable that the evaluation line be specified by rotating at a predetermined angle as a rotation center.

  According to the present invention, an evaluation line can be specified by a simple method of simply rotating a line connecting the center of the evaluation sample and the position where the marking process is performed at a predetermined angle.

  In the method for evaluating a silicon wafer according to the present invention, the step of evaluating includes, among the evaluation lines, the quality of a portion extending from the center of the evaluation sample to the flat portion side, and the flat portion side from the center of the evaluation sample. It is preferable to evaluate at least one of the quality of the portion extending on the opposite side to the above.

  According to the present invention, the in-plane distribution of the quality of a silicon wafer obtained from a straight body having a flat portion can be appropriately evaluated without overlooking a defect.

  In the method for evaluating a silicon wafer according to the present invention, it is preferable that in the evaluating step, at least one of resistivity, oxygen concentration, and defect density is evaluated.

  In the method for evaluating a silicon wafer according to the present invention, the evaluating step evaluates a quality on a line obtained by rotating the evaluation line by 5 ° or less around a center of the evaluation sample as a rotation center, as a quality on the evaluation line. Is preferred.

4 is a flowchart illustrating a method for evaluating a silicon wafer according to an embodiment of the present invention. It is explanatory drawing of the evaluation method of the said silicon wafer, (A) shows the straight body part before cylindrical grinding, (B) shows an evaluation sample. 4 is a graph showing measurement results of oxygen concentration in the example of the present invention. FIG. 3 is a perspective view of a silicon single crystal whose central axis is a <111> crystal axis. It is explanatory drawing of the subject of this invention, (A) shows the straight body part before cylindrical grinding, (B) shows an evaluation sample.

[Embodiment]
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 1, the central axis as shown in FIG. 4 is a silicon single crystal 1 having a <111> crystal axis, and a flat portion 12 is formed on a part of the outer periphery of the straight body portion 11 before grinding. The silicon single crystal 1 is manufactured (Step S1).
At this time, the silicon single crystal 1 may be manufactured so that the target diameter of the straight body portion 21 after grinding becomes 200 mm, 300 mm, 450 mm, or another size, but is preferably 300 mm or less. From the viewpoint of minimizing material loss, the silicon single crystal 1 has a size such that when the target diameter is 200 mm, the grinding widths H1 and H2 shown in FIG. When the target diameter is 300 mm, it is preferable that the grinding widths H1 and H2 are set to be not less than 4 mm and not more than 24 mm. The method for producing the silicon single crystal 1 is not particularly limited, and may be an MCZ (Magnetic field applied Czochralski) method in which a magnetic field is applied to the silicon melt, or a CZ (Czochralski) method in which a magnetic field is not applied. Good.

  Next, when the silicon single crystal 1 has a shoulder portion, a straight body portion and a tail portion, the shoulder portion and the tail portion are cut, and when the silicon single crystal 1 has no tail portion, the shoulder portion is cut. Is acquired (step S2). At this time, it is preferable to cut the shoulder and the tail in a direction perpendicular to the central axis of the silicon single crystal 1. The process of step S3 may be performed without performing the process of step S2 (without cutting at least one of the shoulder and the tail).

  Thereafter, as shown in FIG. 2A, an evaluation line M passing through the center of the inscribed circle of the one end surface 11A and orthogonal to the flat portion 12 is specified on one end surface 11A of the straight body portion 11 before grinding. An evaluation line mark 4A and a notch mark 4B for specifying a position where the marking process has been performed, for example, a formation position of the notch 22 are provided (step S3). It is preferable that the position where the evaluation line mark 4A and the notch mark 4B are provided is a position that is not ground by cylindrical grinding. The position where the evaluation line mark 4A is provided is preferably on the evaluation line M, and the position where the notch mark 4B is provided is preferably on a notch specifying virtual line L1 described later. When at least one of the shoulder portion and the tail portion is not cut, the evaluation line mark 4A and the notch mark 4B may be given to the uncut portion. The shape and size of the evaluation line mark 4A and the notch mark 4B are not particularly limited, but preferably have a specification that can be easily recognized by an operator or an inspection device. The evaluation line mark 4A and the notch mark 4B may be provided by using a pen, scribing, or laser.

Next, the positional relationship between the evaluation line M and the formation position of the notch 22 when viewed from the one end face 11A side is grasped (step S4). Specifically, first, the center of the inscribed circle of the one end face 11A is specified as the center 21C after grinding, and the outer shape of the straight body portion 21 after grinding after performing cylindrical grinding around the center 21C after grinding is specified. I do.
Then, after setting a notch specifying virtual line L1 extending from the post-grinding center 21C to the formation position of the notch 22 specified based on the notch mark 4B, the evaluation line M extends from the post-grinding center 21C to the flat portion 12 side. And the notch specifying virtual line L1 are grasped as the positional relationship between the evaluation line M and the position where the notch 22 is formed.

Thereafter, cylindrical grinding is performed around the center 21C after the grinding (step S5) to obtain the straight body 21 after the grinding, and as shown in FIG. 2 (B), on the outer periphery of the straight body 21 after the grinding. Is formed in a part of (step S6).
The disk-shaped evaluation sample 3 is obtained from the straight body portion 21 after the notch 22 is formed (step S7). The evaluation sample 3 obtained at this time may be cut out from the longitudinal end of the straight body 21 after grinding, or may be cut into a plurality of cylindrical blocks after grinding. , May be cut out from the end of the block. In order to evaluate the quality, the evaluation sample 3 is subjected to processing such as polishing and etching.

Next, an evaluation line M1 for evaluating the quality of the evaluation sample 3 is specified (step S8). Specifically, the evaluation sample 3 is placed on a table (not shown) of the inspection apparatus, and as shown in FIG. 2B, when the evaluation sample 3 is viewed from the same side as FIG. A line extending from the sample center 3C of the evaluation sample 3 that coincides with the rear center 21C to the notch 22 is regarded as the notch specifying virtual line L1, and the notch specifying virtual line L1 is rotated clockwise by θ1 (= 180 ° −θ). The line thus specified is specified as the evaluation line M1. This evaluation line M1 is located on the evaluation line M.
Thereafter, the quality on the evaluation line M1 of the evaluation sample 3 placed on the table, for example, at least one of the resistivity, the oxygen concentration, and the defect density of the silicon wafer obtained from the straight body 21 after grinding is determined. The quality is evaluated (step S9). The quality evaluation may be performed on the entire area on the evaluation line M1, or may be performed on a plurality of measurement points on the evaluation line M1.

[Operation and Effect of Embodiment]
According to the above embodiment, the evaluation line M passing through the center of the inscribed circle at the one end surface 11A in the axial direction of the straight body portion 11 before grinding and orthogonal to the flat portion 12, that is, the evaluation line with the least amount of grinding during cylindrical grinding. In order to evaluate the quality on M as the quality of the silicon wafer, if the quality on the evaluation line M falls within the allowable range, a line rotated by a predetermined angle in the circumferential direction of the evaluation sample with respect to the evaluation line M, for example, The quality on the evaluation line M3 shown in FIG. 5B also falls within the allowable range. Therefore, it is possible to suppress the defect that the quality of the chips processed by the device maker is not within the allowable range, but the quality of the silicon wafer maker is within the allowable range according to the evaluation result of the silicon wafer maker. Can be evaluated.

  Since the formation positions of the evaluation line M and the notch 22 can be confirmed based on the evaluation line mark 4A and the notch mark 4B provided on the one end surface 11A of the straight body portion 11 before grinding, the evaluation line M1 can be easily specified.

[Modification]
It should be noted that the present invention is not limited only to the above embodiment, and various improvements and design changes can be made without departing from the spirit of the present invention.

As shown in FIG. 2B, a line obtained by rotating the notch specifying virtual line L1 counterclockwise by θ is set as an evaluation line M2 included in the evaluation line M, and the quality on the evaluation line M2 is evaluated. Alternatively, the quality on both the evaluation line M1 and the evaluation line M2, that is, the quality of the entire evaluation line M may be evaluated.
The positions of the evaluation line mark 4A and the notch mark 4B need not be on the evaluation line M and the notch specifying virtual line L1 as long as the position of the evaluation line M and the formation position of the notch 22 can be specified.
A silicon wafer to be shipped as a product may be regarded as an evaluation sample of the present invention, and the processing of steps S8 to S9 may be performed on the silicon wafer.
The silicon wafer evaluation method of the present invention may be applied to the evaluation sample 3 in which the notch 22 is not formed. In this case, the evaluation line mark 4A may be provided so that the evaluation line mark 4A remains on the evaluation sample 3 even after processing such as cylindrical grinding, polishing for quality evaluation, and etching.
The quality on the line obtained by rotating the evaluation line M by 5 ° or less to the right or left in FIG. 2B with the sample center 3C of the evaluation sample 3 as the rotation center was evaluated as the quality on the evaluation line M. You may.

  Next, examples of the present invention will be described. The present invention is not limited to the embodiments.

First, a silicon single crystal 1 having a target diameter of 300 mm and having a flat portion 12 was manufactured by using the CZ method. The size of the silicon single crystal 1 was set so that the grinding widths H1 and H2 shown in FIG. 5B became 4 mm.
Next, the evaluation line mark 4A and the notch mark 4B are given to the straight body portion 11 before grinding obtained from the silicon single crystal 1, and the positional relationship between the evaluation line M and the formation position of the notch 22 is grasped. By performing the grinding, a straight body portion 21 having a target diameter after grinding was obtained.

A notch 22 was formed in the straight body 21 after the grinding, and one evaluation sample 3 was obtained from the longitudinal end of the straight body 21 after the grinding. Next, the evaluation sample 3 was subjected to a pretreatment necessary for oxygen concentration measurement, for example, etching, polishing, and the like, and then the evaluation sample 3 was set in an inspection device. Thereafter, an evaluation line M1 included in the evaluation line M was set on the inspection surface of the evaluation sample 3, and the oxygen concentration on the evaluation line M1 was measured at intervals of 5 mm (Example 1). The oxygen concentration was measured based on ASTM F121-1979 using FTIR (Fourier Transform Infrared Spectroscopy).
On the surface to be inspected of the same evaluation sample 3, the oxygen concentration on the evaluation line M1 and an arbitrary line that does not overlap with the extension of the evaluation line M1 was measured at the same interval as in Example 1 (Comparative Example 1). The measurement was performed between the sample center 3C and a position 145 mm away from the sample center 3C in the radial direction.
FIG. 3 shows the measurement results of the oxygen concentration in Example 1 and Comparative Example 1.
Further, based on the measurement results of Example 1 and Comparative Example 1, ROG (Radial Oxygen Gradient: oxygen concentration gradient) represented by the following equation (1) was calculated. Table 1 shows the results.
ROG (%) = {(maximum oxygen concentration−minimum oxygen concentration) / minimum oxygen concentration} × 100) (1)

As shown in FIG. 3, the oxygen concentration from the center 3C of the sample to the position of 125 mm was substantially the same in Example 1 and Comparative Example 1, but the oxygen concentration of Example 1 outside the position of 130 mm was And smaller than Comparative Example 1, and decreased toward the outer edge of Evaluation Sample 3. Further, as shown in Table 1, the ROG of Example 1 was larger than the ROG of Comparative Example 1.
From the above, the quality evaluation of Example 1 is a stricter condition than the quality evaluation of Comparative Example 1. By performing the quality evaluation under the strict conditions, the shipment of silicon wafers whose quality is not within the allowable range is suppressed. I was able to confirm that I can do it.

  1 ... silicon single crystal, 3 ... evaluation sample, 11 ... straight body (before cylindrical grinding), 12 ... flat part, 21 ... straight body (cylindrical ground), M, M1, M2 ... evaluation line.

Claims (6)

A method for evaluating a silicon wafer obtained from a silicon single crystal in which a flat portion is formed along a crystal central axis on a part of an outer periphery of a straight body portion and a crystal orientation of a central axis is <111>,
Preparing the silicon single crystal,
A step of cylindrically grinding the straight body of the silicon single crystal,
A step of cutting out a disc-shaped evaluation sample from the cylindrical body subjected to cylindrical grinding,
A step of identifying an evaluation line passing through the center of the evaluation sample and orthogonal to the flat portion,
Evaluating the quality of the evaluation sample on the evaluation line as the quality of a silicon wafer obtained from the straight body portion. In the method for evaluating a silicon wafer according to claim 1,
Prior to the step of cutting out the evaluation sample from the straight body, performing a step of performing a marking process on the straight body,
The method of evaluating a silicon wafer, wherein the step of specifying the evaluation line specifies a position of the evaluation line based on a position where the marking process is performed. In the method for evaluating a silicon wafer according to claim 2,
The step of specifying the evaluation line rotates a line connecting a center of the evaluation sample and a position where the outer peripheral portion of the evaluation sample is subjected to the marking process at a predetermined angle around the center of the evaluation sample as a rotation center. A method for evaluating a silicon wafer, wherein the evaluation line is specified. In the method for evaluating a silicon wafer according to any one of claims 1 to 3,
The step of evaluating the quality of a portion of the evaluation line extending from the center of the evaluation sample to the flat portion side, and the quality of a portion extending from the center of the evaluation sample to the opposite side to the flat portion side. A method for evaluating a silicon wafer, wherein at least one of the methods is evaluated. In the method for evaluating a silicon wafer according to any one of claims 1 to 4,
The method for evaluating a silicon wafer, wherein the evaluating includes evaluating at least one of resistivity, oxygen concentration, and defect density. In the method for evaluating a silicon wafer according to any one of claims 1 to 5,
The evaluating step is a method of evaluating a silicon wafer, wherein the quality on a line obtained by rotating the evaluation line by 5 ° or less about the center of the evaluation sample as a rotation center is regarded as the quality on the evaluation line. .

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