Standard sample for pinhole measurement device, method for manufacturing standard sample for pinhole measurement device, and method for measuring pinhole

Abstract

To provide a standard sample in a proper size with respect to a pinhole defect existing in a silicon single crystal wafer.SOLUTION: There is provided a standard sample for pinhole measurement device in which a pinhole in a prescribed size is formed at a prescribed position in a silicon single crystal wafer. The standard sample is the bonded wafer obtained by bonding the two silicon single crystal wafers. A recess in a prescribed size is formed at a prescribed position on a surface of at least one silicon single crystal wafer. The other silicon single crystal wafer is bonded to the surface where the recess is formed, and the pinhole is formed on a bonding interface.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a standard sample for determining the size of pinholes in measuring pinholes present in silicon single crystal wafers, and a method for producing the same. [Background technology]

[0002] Silicon single crystal wafers (hereinafter sometimes simply referred to as wafers) are thought to be made of silicon with a purity of ten-nine (99.99999999%) or more, but in reality they contain dopants, oxygen, carbon, etc. They also contain void defects formed by a high concentration of vacancies, which are point defects.

[0003] Among these defects, there are particularly large cavities, or defects called pinholes. These defects are thought to be caused by bubbles generated in the melt being incorporated into the silicon single crystal during the pulling process. Pinholes are larger than other defects present in silicon single crystals, and some are 10 μm to 100 μm or larger in size.

[0004] The occurrence frequency of such pinhole defects is extremely low, and they can be found by inspecting all wafers. Inspection methods often involve transmitting infrared (IR) light through the wafer and detecting pinholes based on the difference in transmittance. For example, Patent Document 1 describes a method of identifying the position of a pinhole based on the difference in the amount of transmission. At this time, the transmittance changes where the pinhole is located. This difference in transmittance is converted into pinhole size, but there is no suitable standard sample for this purpose. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2012-2648 A Summary of the Invention [Problem to be solved by the invention]

[0006] There are several methods for relating the signal strength of a pinhole to the size of the pinhole, and the methods and problems involved are as follows:

[0007] One method is to measure the difference in transmittance at the pinhole area, and then measure the actual pinhole size using a cross-sectional TEM or similar. However, the pinhole size is too large to be measured using a cross-sectional TEM, and even if the cross-sectional shape is determined by cleavage as shown in Figure 2, it is difficult to determine the accurate pinhole size because only the cross-sectional area of ​​the pinhole is known and the three-dimensional shape cannot be determined. Since the pinhole shape is not controlled, the entire shape cannot be determined by detecting only a part of the cross-section. Also, unlike the above, even if the pinhole is spherical, the size still changes depending on the cleavage location as shown in Figure 3, so the accurate size cannot be determined.

[0008] There is a method of creating a controlled dent (laser mark) on the wafer surface and using this as a standard sample as a pinhole. In this case, since the dent is on the wafer surface, the size and depth of the dent can be measured, making it easy to calculate the IR transmittance, but when the pinhole is on the surface, unlike when it is inside the wafer, the reflected light does not undergo multiple reflections inside the cavity but instead goes outside the wafer, and the same phenomenon does not occur between the dent and the cavity inside the wafer. Therefore, this method cannot determine the size of the pinhole with sufficient accuracy.

[0009] The present invention has been made to solve the above problems, and has an object to provide a standard sample of an appropriate size for pinhole defects present in silicon single crystal wafers. [Means for solving the problem]

[0010] In order to solve the above problems, the present invention provides A standard sample for a pinhole measurement device in which a pinhole of a predetermined size is formed at a predetermined position inside a silicon single crystal wafer, The standard sample is a bonded wafer formed by bonding two silicon single crystal wafers together, in which a recess of a predetermined size is formed at a predetermined position on the surface of at least one of the silicon single crystal wafers, and the other silicon single crystal wafer is bonded to the surface on which the recess is formed, so that the pinhole is formed at the bonded interface.

[0011] The present invention can provide an appropriate size standard sample for pinhole defects present in a silicon single crystal wafer.

[0012] Moreover, the recess is preferably semi-spherical.

[0013] Such a recess shape can provide a more accurate standard sample.

[0014] It is also preferable that the surface of the one silicon single crystal wafer on which the recesses are formed has recesses of different sizes, at least 5 μm to 100 μm.

[0015] Such a standard sample would be more accurate and more practical.

[0016] In the present invention, A method for manufacturing a standard sample for a pinhole measurement device in which a pinhole of a predetermined size is formed at a predetermined position inside a silicon single crystal wafer, comprising: (1) preparing two silicon single crystal wafers; (2) forming a recess of a predetermined size at a predetermined position on a surface of at least one of the silicon single crystal wafers; (3) bonding another silicon single crystal wafer to the surface on which the recess is formed, thereby forming the pinhole at the bonding interface; and (4) adjusting the thickness of the bonded silicon single crystal wafer to a predetermined thickness to obtain the standard sample; The present invention provides a method for producing a standard sample for a pinhole measurement device, comprising:

[0017] According to the present invention, it is possible to produce a standard sample of an appropriate size for pinhole defects present in a silicon single crystal wafer.

[0018] In the step (2), the recessed portion having a hemispherical shape is preferably formed by a laser marker or a focused ion beam (FIB).

[0019] In this way, a more accurate standard sample can be easily produced.

[0020] In the step (2), it is preferable to form recesses having different sizes, at least between 5 μm and 100 μm, on the surface of the one of the silicon single crystal wafers.

[0021] In this way, a standard sample with higher accuracy and superior practicality can be easily manufactured.

[0022] In the step (4), it is preferable to perform one or more of surface grinding, etching, and surface polishing on both sides or one side of the bonded silicon single crystal wafer.

[0023] In this way, the thickness of the standard sample can be easily controlled to obtain a practical standard sample.

[0024] In the present invention, A method for measuring pinholes in a silicon single crystal wafer, comprising the steps of: (1) using a standard sample for the pinhole measurement device, measuring the size of at least one pinhole formed in the standard sample with the pinhole measurement device to obtain a measurement result; (2) calibrating the pinhole measurement device based on the measurement results; and (3) measuring pinholes in a silicon single crystal wafer to be measured using the calibrated pinhole measurement device; The present invention provides a method for measuring a pinhole, comprising:

[0025] By using an apparatus calibrated using the standard sample of the present invention, pinholes in silicon single crystal wafers can be measured with high accuracy. Effect of the Invention

[0026] Without a standard sample, each device would determine its own size, resulting in large differences between devices and making it difficult to perform highly accurate measurements. However, by calibrating the pinhole detector using a standard pinhole sample as in the present invention, pinhole sizes measured with different devices can be easily and accurately compared directly. [Brief description of the drawings]

[0027] [Figure 1] FIG. 2 is a schematic diagram showing an example of a standard sample of the present invention. [Diagram 2] FIG. 1 is an explanatory diagram for explaining a problem in determining the size of a pinhole by cross-sectional observation using a TEM. [Diagram 3] FIG. 13 is another explanatory diagram for explaining the problem in determining the size of a pinhole by cross-sectional observation using a TEM. [Figure 4] 4 is a diagram showing the positions and sizes of recesses formed on the surface of one of the wafers in Example 1. FIG. [Diagram 5] 1 shows the results of observing a recess (100 μm) formed on the surface of one of the wafers in Example 1 from above using a laser microscope. [Figure 6] 2 is a cross-sectional image of a recess (100 μm) formed on the surface of one of the wafers in Example 1, measured by a laser microscope. [Figure 7] 1 is a schematic diagram showing a procedure for producing a standard sample in Example 1. FIG. [Figure 8]FIG. 2 is a diagram showing the detected position and detected size of a pinhole when a pinhole in a standard sample is measured using a calibrated device in Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] As described above, there has been a need to develop a standard sample of an appropriate size for pinhole defects present in silicon single crystal wafers.

[0029] As a result of extensive investigation into the above-mentioned problems, the inventors have discovered that a pinhole standard sample can be prepared by forming a recess of a prescribed size on the surface of a wafer and then bonding the wafers together to create a pinhole of controlled shape and size inside the bonded wafer, thereby completing the present invention.

[0030] That is, the present invention provides a standard sample for a pinhole measurement device in which a pinhole of a predetermined size is formed at a predetermined position inside a silicon single crystal wafer, and the standard sample is a bonded wafer formed by bonding two silicon single crystal wafers together, in which a recess of a predetermined size is formed at a predetermined position on the surface of at least one of the silicon single crystal wafers, and the other silicon single crystal wafer is bonded to the surface on which the recess is formed, so that the pinhole is formed at the bonded interface.

[0031] The present invention will be described in detail below, but the present invention is not limited thereto.

[0032] [Standard sample for pinhole measurement device] FIG. 1 shows an example of a schematic diagram of a standard sample for the pinhole measurement device of the present invention. The standard sample 10 of the present invention is a silicon single crystal wafer in which a pinhole of a predetermined size is formed at a predetermined position inside the silicon single crystal wafer, and is a bonded wafer in which two silicon single crystal wafers are bonded together. One of the silicon single crystal wafers, silicon single crystal wafer 1, has a recess 3 of a predetermined size formed at a predetermined position on the surface. The other silicon single crystal wafer 2 is bonded to the surface on which this recess 3 is formed. The recess 3 located at the bonded interface becomes a pinhole of a predetermined size formed at a predetermined position inside the silicon single crystal wafer.

[0033] The silicon single crystal wafer is not particularly limited, and may be any silicon single crystal wafer available on the market. Of course, there is no limit to the size of the wafer, and any size of wafer available on the market may be used. In addition, a native oxide film may be formed on the wafer.

[0034] The shape of the recesses 3 is not particularly limited, but is preferably a hemispherical shape, and more preferably a hemispherical shape with a size (diameter) of 5 μm or more and 100 μm or less. As shown in Fig. 1, a plurality of recesses 3 may be formed, and the plurality of recesses may be of different sizes. In particular, it is preferable that recesses 3 of different sizes, at least 5 μm or more and 100 μm or less, are formed on the surface of one silicon single crystal wafer 1.

[0035] The standard sample of the present invention is not limited to one having recesses 3 formed only on the surface of one silicon single crystal wafer 1, but may be one having recesses 3 also formed on the surface of the other silicon single crystal wafer 2, and the surfaces having recesses are bonded together.

[0036] The standard sample of the present invention includes not only a bonded wafer obtained by simply bonding two silicon single crystal wafers together, but also a wafer in which one or both sides of the bonded wafer are ground, etched, or polished to reduce the thickness. The thickness of the standard sample of the present invention is not particularly limited, but from the viewpoint of practicality, it is preferable to have the thickness of one original silicon single crystal wafer before bonding. Desirably, the thickness is within ±50 μm, more preferably within ±30 μm, of the thickness of the standard silicon single crystal wafer determined by the diameter.

[0037] [Method of manufacturing standard samples for pinhole measurement devices] The present invention also provides a method for manufacturing a standard sample for a pinhole measurement device, in which a pinhole of a predetermined size is formed at a predetermined position inside a silicon single crystal wafer, the method including the steps of: (1) preparing two silicon single crystal wafers; (2) forming a recess of a predetermined size at a predetermined position on a surface of at least one of the silicon single crystal wafers; (3) bonding the other silicon single crystal wafer to the surface on which the recess is formed, to form the pinhole at the bonding interface; and (4) adjusting the thickness of the bonded silicon single crystal wafer to a predetermined thickness to obtain the standard sample.

[0038] The method for producing a standard sample of the present invention will be described in detail below. In the method for producing a standard sample of the present invention, it is preferable to carry out steps (2') and (2'') described below between the above steps (2) and (3).

[0039] <Step (1) Preparation of silicon single crystal wafer> Step (1) is a step of preparing two silicon single crystal wafers.

[0040] The silicon single crystal wafer to be prepared is not particularly limited, and may be any silicon single crystal wafer available on the market. Of course, there is no limit to the size of the wafer, and any size wafer available on the market may be used. For example, the diameter may be 50 mm to 300 mm, or more.

[0041] <Step (2) Formation of recesses> Step (2) is a step of forming recesses of a predetermined size at predetermined positions on the surface of at least one of the silicon single crystal wafers.

[0042] For example, a recess of a specified size is formed at a specified position on the surface of a mirror-polished wafer (PW: Polished Wafer). At this time, the recess can be formed using a laser marker or FIB (Focused Ion Beam). At this time, it is desirable to form the recess at a fixed position (e.g., 2 cm mesh) so that it can be distinguished from defects other than pinholes detected by a pinhole detector. The shape of the recess is not particularly limited and may be a cone, a square pyramid, a thin recess, etc., but a hemisphere is desirable.

[0043] <Step (2') Repolishing and cleaning> If the recesses are formed using a laser marker or FIB in step (2), silicon may be scattered around the recesses or the recesses may bulge, making subsequent bonding impossible. For this reason, it is preferable to perform repolishing and cleaning after forming the recesses.

[0044] <Step (2'') Measuring the size of the recess> Before lamination, the size of the recess is measured in advance using an optical or tactile shape measuring device. At this time, it is preferable to measure the size of the recess (diameter, depth, shape).

[0045] <Step (3) Lamination> Step (3) is a step of bonding another silicon single crystal wafer to the surface on which the recesses are formed, thereby forming the pinholes at the bonding interface.

[0046] For example, a PW having the same resistivity as the PW with the recess is prepared and bonded. At this time, it is preferable that a natural oxide film is formed on at least one of the bonding surfaces. The formation of a natural oxide film on the bonding surfaces increases the bonding strength after bonding. Then, a heat treatment (for example, 1000°C) is performed to bond the two wafers.

[0047] <Step (4) Adjustment of wafer thickness> The step (4) is a step of adjusting the thickness of the bonded silicon single crystal wafer to a predetermined thickness to obtain the standard sample.

[0048] The wafer made by bonding two wafers together cannot be inserted into equipment designed for normal 300mm wafer thickness as is, so it needs to be thinned. One or both sides are surface ground, etched, and polished to create a standard sample of the specified thickness so that the recesses are not exposed on the surface. For example, the ideal finished thickness is 775μm, which is the normal thickness of PW, for a diameter of 300mm, but this is not always the case.

[0049] [Method of measuring pinholes] The present invention also provides a method for measuring pinholes in a silicon single crystal wafer, comprising the steps of: (1) using a standard sample for the above-mentioned pinhole measurement device, measuring the size of at least one pinhole formed in the standard sample with the pinhole measurement device to obtain measurement results; (2) calibrating the pinhole measurement device based on the measurement results; and (3) using the calibrated pinhole measurement device to measure pinholes in the silicon single crystal wafer to be measured.

[0050] The bonded wafer obtained above is used as a standard sample, and the size of the pinholes in this standard sample is measured using a pinhole measuring device to detect the size of the pinholes. Next, the pinhole measuring device is calibrated so that the detected size is the size of the recess actually formed in the standard sample. Using the pinhole measuring device calibrated in this way, pinholes in the silicon single crystal wafer to be measured are detected. This makes it possible to grasp the lower detection limit of the measuring device, and therefore to select a measuring device with high detection sensitivity for measurement.

[0051] Although an example in which a recess is formed only on one of the wafers has been described above, the present invention is not limited to this. Recesses may be formed on both wafers and the wafers may be bonded together to form a standard sample. EXAMPLES

[0052] The present invention will be specifically described below using examples and comparative examples, but the present invention is not limited to these.

[0053] Example 1 A standard sample was prepared according to the procedure shown in FIG.

[0054] First, as shown in Figure 4, a laser marker was used to form regularly spaced hemispherical recesses on a 300 mm wafer (Figure 7 (1)). The diameters (apertures) of the recess surface were 100 μm, 50 μm, 40 μm, 30 μm, 20 μm, 10 μm, 8 μm, and 5 μm, starting from the leftmost row. Figure 5 shows the results of observing the 100 μm diameter laser mark marks (recesses) from above with a laser microscope, and Figure 6 shows a cross-sectional image of the recesses measured with a laser microscope. As can be seen from Figure 6, the depth of the hemispherical recesses was 55 μm.

[0055] The wafer was then repolished to remove any irregularities around the laser marks and then cleaned.

[0056] After bonding a wafer of the same thickness as the wafer with the recess formed therein as described above, they were bonded by heat treatment (temperature: 1000°C, 1 hour) to produce a bonded wafer (Figure 7 (2)). This bonded wafer was thinned to a thickness of 800 μm by double-sided grinding, and then etched and double-sided polished to a thickness of 775 μm, the same as the thickness of one wafer, to produce a standard sample with a recess formed at a specified position inside the wafer (Figure 7 (3)).

[0057] The pinholes of the prepared standard sample were measured with a pinhole measuring device. In Example 1, an IR (infrared) pinhole measuring device from device manufacturer A was used. At this time, after calibration so that the size of a recess with a diameter of 100 μm was 100 μm when detected, the size of each recess of the standard sample was measured. As a result, defects were detected at the positions shown in FIG. 8. Here, by comparing FIG. 4 with FIG. 8, it means that those not shown in FIG. 8 could not be detected as pinholes. That is, all large pinholes with diameters of 10 to 100 μm were detected at almost the size of the recess formed, but pinholes with a diameter of 8 μm were sometimes detected and sometimes not, and pinholes with a diameter of 5 μm could not be detected. Therefore, it can be estimated that the detection limit of this device is equivalent to 8 μm (hemisphere).

[0058] Example 2 Using an IR (infrared) pinhole measuring device from device manufacturer B, which is different from the device from device manufacturer A used in Example 1, the pinholes of the standard sample prepared in Example 1 were measured in the same manner as in Example 1. Even in this case, after calibration with a recess of 100 μm diameter on the standard sample, recesses of 50, 40, and 30 μm were similarly detected as equivalent to their sizes. The lower detection limit of the device from device manufacturer B at this time was 20 μm.

[0059] (Comparative Example) When a 100 μm hemispherical pinhole in the above standard sample was detected using pinhole measuring devices from equipment manufacturers A and B before the calibration in Examples 1 and 2, the size was 85 μm with the device from equipment manufacturer A and 75 μm with the device from equipment manufacturer B. The cause of these differences is thought to be that the standard samples made by each manufacturer were not appropriate when determining the pinhole size on which the calculations were based.

[0060] Thus, it has become clear that the standard sample of the present invention is an appropriate standard sample for pinhole defects present in silicon single crystal wafers. In particular, in the above embodiment, the pinhole is a hemisphere close to a sphere, and is not a perfect sphere, but can show a value closer to the size calculated from a pinhole of an indefinite shape. This makes it possible to quantitatively grasp the lower detection limit of the device, and to compare the measurement accuracy between pinhole measurement devices. In addition, although it is a conversion of the hemisphere diameter, it has become possible to determine the difference between the actual size and the displayed size of the measurement device. As a result, by performing calibration using the standard sample of the present invention, the displayed size of the measurement device can be regarded as the actual pinhole size even when measured with a different measurement device.

[0061] This specification includes the following inventions. [1]: A standard sample for a pinhole measurement device in which a pinhole of a predetermined size is formed at a predetermined position inside a silicon single crystal wafer, the standard sample being a bonded wafer in which two silicon single crystal wafers are bonded together, in which a recess of a predetermined size is formed at a predetermined position on the surface of at least one of the silicon single crystal wafers, and the other silicon single crystal wafer is bonded to the surface with the recess formed therein, so that the pinhole is formed at the bonded interface. [2]: The standard sample for a pinhole measurement device according to the above [1], wherein the recess has a hemispherical shape. [3]: A standard sample for a pinhole measurement device according to the above [1] or [2], characterized in that on the surface of the one of the silicon single crystal wafers on which the recesses are formed, recesses of at least 5 μm or more and 100 μm or less in different sizes are formed. [4]: A method for manufacturing a standard sample for a pinhole measurement device, in which a pinhole of a predetermined size is formed at a predetermined position inside a silicon single crystal wafer, comprising the steps of: (1) preparing two silicon single crystal wafers; (2) forming a recess of a predetermined size at a predetermined position on a surface of at least one of the silicon single crystal wafers; (3) bonding the other silicon single crystal wafer to the surface on which the recess is formed, to form the pinhole at the bonding interface; and (4) adjusting the thickness of the bonded silicon single crystal wafer to a predetermined thickness, to obtain the standard sample. [5]: A method for manufacturing a standard sample for a pinhole measurement device according to the above [4], characterized in that in the step (2), the hemispherical recess is formed by a laser marker or a focused ion beam (FIB). [6]: A method for producing a standard sample for a pinhole measurement device according to the above [4] or [5], characterized in that in the step (2), recesses having different sizes of at least 5 μm to 100 μm are formed on the surface of the one of the silicon single crystal wafers. [7]: A method for producing a standard sample for a pinhole measurement device according to the above [4], [5] or [6], characterized in that in the step (4), one or both sides of the bonded silicon single crystal wafer are subjected to one or more of surface grinding, etching and surface polishing. [8]: A method for measuring pinholes in a silicon single crystal wafer, comprising: (1) a step of using a standard sample for the pinhole measurement device described in [1], [2], or [3] above, and measuring the size of at least one pinhole formed in the standard sample with the pinhole measurement device to obtain a measurement result; (2) a step of calibrating the pinhole measurement device based on the measurement result; and (3) a step of measuring pinholes in a silicon single crystal wafer to be measured using the calibrated pinhole measurement device.

[0062] The present invention is not limited to the above-described embodiment. The above-described embodiment is merely an example, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits similar effects is included in the technical scope of the present invention. [Explanation of symbols]

[0063] 1...one silicon single crystal wafer; 2...the other silicon single crystal wafer; 3...recess, 10...standard sample.

Claims

1. A standard sample for a pinhole measurement device in which a pinhole of a predetermined size is formed at a predetermined position inside a silicon single crystal wafer, The standard sample is a bonded wafer formed by bonding two silicon single crystal wafers together, in which a recess of a predetermined size is formed at a predetermined position on the surface of at least one of the silicon single crystal wafers, and the other silicon single crystal wafer is bonded to the surface on which the recess is formed, so that the pinhole is formed at the bonded interface.

2. 2. The standard sample for a pinhole measuring device according to claim 1, wherein the recess has a hemispherical shape.

3. 2. The standard sample for a pinhole measurement device according to claim 1, characterized in that recesses of at least 5 μm to 100 μm in size are formed on the surface of the one silicon single crystal wafer on which the recesses are formed.

4. A method for manufacturing a standard sample for a pinhole measurement device in which a pinhole of a predetermined size is formed at a predetermined position inside a silicon single crystal wafer, comprising: (1) preparing two silicon single crystal wafers; (2) forming a recess of a predetermined size at a predetermined position on the surface of at least one of the silicon single crystal wafers; (3) a step of bonding another silicon single crystal wafer to the surface on which the recess is formed, thereby forming the pinhole at the bonding interface; and (4) adjusting the thickness of the bonded silicon single crystal wafer to a predetermined thickness to obtain the standard sample; A method for producing a standard sample for a pinhole measurement device, comprising:

5. 5. The method for producing a standard sample for a pinhole measurement device according to claim 4, wherein in the step (2), the recess having a hemispherical shape is formed by a laser marker or a focused ion beam (FIB).

6. 5. The method for manufacturing a standard sample for a pinhole measurement device according to claim 4, wherein in the step (2), recesses having different sizes of at least 5 μm to 100 μm are formed on the surface of the one of the silicon single crystal wafers.

7. 7. The method for manufacturing a standard sample for a pinhole measurement device according to claim 4, wherein in the step (4), one or more of surface grinding, etching, and surface polishing are performed on both sides or one side of the bonded silicon single crystal wafer.

8. A method for measuring pinholes in a silicon single crystal wafer, comprising the steps of: (1) a step of using a standard sample for the pinhole measurement device according to any one of claims 1 to 3, measuring the size of at least one pinhole formed in the standard sample with the pinhole measurement device to obtain a measurement result; (2) calibrating the pinhole measurement device based on the measurement results; and (3) measuring pinholes in a silicon single crystal wafer to be measured using the calibrated pinhole measurement device; A method for measuring a pinhole, comprising:

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