JP3643468B2 - Method for determining the orientation flat orientation of single crystals - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for determining a processing position of an orientation flat (hereinafter abbreviated as an orientation flat) on an outer peripheral surface of a single crystal using an X-ray diffraction method.
[0002]
[Prior art]
First, the display of orientation index and plane index of silicon single crystal will be described. The crystal structure of silicon belongs to a cubic system. For example, for the [100] orientation of the crystal, there are six equivalent orientations including this. These equivalent orientation groups are indicated as <100>. For example, for the (100) plane of the crystal, there are six equivalent lattice planes including this. These equivalent plane groups are denoted as {100}. Speaking of the (110) plane of the crystal, there are 12 equivalent lattice planes including this, and these equivalent plane groups are denoted as {110}. In the following description, the crystal orientation and plane are displayed using such an equivalent orientation group and equivalent plane group.
[0003]
FIG. 9 is a perspective view of a silicon single crystal obtained by processing a silicon ingot produced by the Czochralski method (pulling from the melt) into a cylindrical shape. In the silicon single crystal body 10, the <100> orientation of the crystal coincides with the axis 12 of the cylindrical single crystal body 10. In performing orientation flat processing on the outer peripheral surface of this single crystal, it is considered that the orientation flat processing surface 14 is processed so as to be parallel to the {110} plane of the crystal. On the outer peripheral surface of the single crystal body, the outer peripheral surface and the {110} plane are parallel at four positions separated by 90 degrees along the circumferential direction. Therefore, X-ray diffraction is used to irradiate the outer peripheral surface of the single crystal body 10 and rotate the single crystal body about its axis, and from the {220} plane parallel to the {110} plane using the X-ray diffraction method. If a diffraction peak is searched (because it does not diffract in the {110} plane), four diffraction peaks should be found during one rotation of the single crystal. The orientation flat processing may be performed at any one of the four outer peripheral surface positions where the diffraction peaks are found. By the way, the four positions where the outer peripheral surface is parallel to the {110} plane are equivalent to each other. Therefore, it is not necessary to find the four diffraction peaks, and the orientation flat processing is performed at the position where the diffraction peak is first found. That's fine.
[0004]
FIG. 10 is a perspective view of a silicon single crystal in which the <100> orientation is inclined by an angle δ with respect to the axis 12a of the single crystal 10a. This inclination angle δ is called an off angle. This silicon single crystal 10a is pulled up so as to have a predetermined off-angle when manufactured by the Czochralski method. It is known that such an off-angle improves the characteristics when the wafer is cut out. Consider that the orientation flat processed surface 14a is formed so as to be parallel to the {110} plane on the outer peripheral surface of the silicon single crystal 10a. In this case, on the outer peripheral surface of the silicon single crystal body 10a, the outer peripheral surface becomes “substantially parallel” to the {110} plane at four positions A, B, C, and D separated by 90 degrees along the circumferential direction. Since the <100> orientation is inclined from the axis 12a of the single crystal body 10a, the {110} plane is not always exactly parallel to the outer peripheral surface at the four positions A to D on the outer peripheral surface.
[0005]
By the way, considering the relative positional relationship with the <100> orientation, the above-mentioned four positions A, B, C, and D where the outer peripheral surface is substantially parallel to the {110} plane are no longer equivalent to each other. Then, as the optimal position for forming the orientation flat processing, there is a case where the processing surface is specified such that only the position A, for example, is in a specific positional relationship with the inclined <100> orientation. On the other hand, only by observing the presence or absence of a diffraction peak on the {220} plane parallel to the {110} plane, the positions A, B, C, and D cannot be distinguished, and a specific position cannot be determined.
[0006]
Therefore, conventionally, the orientation flat processing position is predicted to some extent by optically detecting the crystal habit line at the stage of the silicon ingot, and then the orientation flat processing position is determined strictly by X-ray diffraction measurement (special feature). (Kaihei 4-264241). Since it is known that the position of the crystal habit line of the silicon ingot and the position where the orientation flat processing is to be formed are in a specific positional relationship, such a method can be adopted.
[0007]
[Problems to be solved by the invention]
In the conventional orientation flat processing position determination method described above, there is a problem that an optical detection device is required in addition to the X-ray detection device in order to determine the orientation flat processing position of a cylindrical single crystal with an off angle. is there.
[0008]
The present invention has been made to solve the above-described problems, and its object is to select a cylindrical single crystal having an off-angle from a plurality of outer peripheral surface positions where diffracted X-rays can be detected. Another object of the present invention is to provide an orientation flat machining position determination method capable of searching only an outer peripheral surface position having a specific positional relationship with an off-angle inclination direction. Another object of the present invention is to perform orientation flat processing of a single crystal having an off-angle by using only one X-ray detection device without requiring other detection means such as an optical detection device. It is to provide a method by which the position can be determined.
[0009]
[Means for Solving the Problems]
The orientation flat processing method of the present invention has a single crystal body in which a specific crystal orientation of a cylindrical single crystal body is inclined in a specific direction with respect to the axis of the single crystal body, that is, with an off-angle. It is applied to such a single crystal. Then, X-rays are irradiated to the outer peripheral surface of the single crystal body, and the orientation flat is detected by detecting diffraction X-rays from a predetermined crystal lattice plane (processing the orientation flat surface so as to be parallel to the crystal lattice plane). In using the method of determining the machining position, an outer peripheral surface position having a specific positional relationship with the off-angle inclination direction is found from a plurality of outer peripheral surface positions from which diffracted X-rays can be detected. If the single crystal has an off-angle, when there are multiple outer peripheral surface positions that are parallel to a predetermined crystal lattice plane, the positional relationship between these outer peripheral surface positions and the off-angle inclination direction is equivalent. In addition, these outer peripheral surface positions are not necessarily exactly parallel to a specific crystal lattice plane. Therefore, the direction of the diffracted X-rays from the plurality of outer peripheral surface positions tends to deviate from the diffraction plane when it is assumed that there is no off-angle. Therefore, for example, assuming that the above-described diffraction plane is horizontal, in the present invention, X-rays can be observed separately when the diffracted X-rays deviate upward from the diffraction plane described above and deviate downward. An X-ray absorber that partially covers the detection surface of the detector is provided. In this way, when diffracted X-rays can be detected at a plurality of outer peripheral surface positions, the X-ray intensity is attenuated when the diffracted X-rays from a certain outer peripheral surface strikes the X-ray absorber and passes therethrough. Diffracted X-rays from the position of the outer peripheral surface enter the X-ray detector as they are without hitting the X-ray absorber, resulting in a difference in detection intensity. Based on the magnitude relationship of the detected intensity and the appearance order thereof, the outer peripheral surface position having a specific positional relationship with respect to the off-angle inclination direction can be determined.
[0010]
In summary, the present invention includes the following steps (a) to (d). (A) An X-ray source is arranged so that the outer peripheral surface of the cylindrical single crystal can be irradiated with an X-ray beam, and X-ray diffracted by a predetermined crystal lattice plane on the outer peripheral surface can be detected. An X-ray source is arranged so that a diffraction plane including the X-ray source, the X-ray irradiation point on the outer peripheral surface, and the X-ray detector is perpendicular to the axis of the single crystal body. And placing an X-ray detector. (B) An X-ray absorber capable of partially covering the detection surface of the X-ray detector is disposed between the X-ray irradiation point and the X-ray detector, and the X-ray absorber is not transmitted without passing through the X-ray absorber. The diffracted X-rays that reach the detection surface enter a region on one side of the detection surface in a direction perpendicular to the diffraction plane, pass through the X-ray absorber, and then reach the detection surface. Positioning the X-ray absorber so that a line is incident on a region on the other side of the detection surface in a direction perpendicular to the diffraction plane. (C) rotating the single crystal around its axis and detecting the intensity of a plurality of diffraction peaks caused by the predetermined crystal lattice plane with the X-ray detector; (D) determining the orientation flat processing position based on the relative magnitude relationship of the intensities of the plurality of diffraction peaks and the order of their appearance;
[0011]
The X-ray transmittance of the X-ray absorber (the ratio of the X-ray intensity after transmission to the X-ray intensity before passing through the X-ray absorber) is suitably in the range of 30 to 80%, and is close to 50%. It is best to do. If the X-ray transmittance is too small, it will be difficult to observe as a diffraction peak, and if the X-ray transmittance is too large, the diffraction X-ray when passing through the X-ray absorber and attenuated will not hit the X-ray absorber. When entering the X-ray detector, the difference in intensity from the diffracted X-ray becomes small, making it difficult to distinguish both.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a perspective view showing an embodiment of the present invention. The cylindrical silicon single crystal body 16 has an upper portion (shown as Top) at the time of crystal pulling arranged on the upper side, and a lower portion at the time of crystal pulling (shown as Bottom) is arranged on the lower side. is there. The silicon single crystal body 16 is formed such that the <100> orientation of the crystal is inclined by an off angle δ with respect to the axis 18 of the cylindrical single crystal body 16. In this embodiment, δ = 4 degrees.
[0013]
FIG. 2 is a plan view of the silicon single crystal body 16 as viewed from above. Positions A, B, C, and D at which the outer peripheral surface of the single crystal body 16 is substantially parallel to the {110} plane of the crystal are at four positions separated by 90 degrees along the outer peripheral surface. In this single crystal, the inclination direction 38 of the off angle δ is set in a direction that bisects the positions A and B.
[0014]
Returning to FIG. 1, an X-ray source 22 and an X-ray detector 24 are arranged in a plane 20 perpendicular to the axis 18 of the single crystal body 16. The X-ray beam 26 emitted from the X-ray source passes through the incident slit 28 and then enters the X-ray irradiation point 30 on the outer peripheral surface of the single crystal body 16. X-rays 32 diffracted at the X-ray irradiation point 30 are detected by the X-ray detector 24.
[0015]
Here, the deviation of the direction of the diffracted X-ray will be described. In this single crystal, since there is an off-angle δ, a phenomenon occurs in which the diffracted X-rays deviate from the plane 20 (horizontal plane) perpendicular to the axis of the single crystal. FIG. 3A is a front view showing the direction of diffracted X-rays when the position A reaches the X-ray irradiation point 30. Since the position A is close to the inclination direction of the off angle δ, the {110} plane is slightly downward from the vertical state. Therefore, even if the incident X-ray beam 26 is incident horizontally, the direction of the diffracted X-rays 32 is slightly lower than the horizontal plane. Similarly, when the position B comes to the X-ray irradiation point, it becomes a slightly downward diffracted X-ray.
[0016]
On the other hand, FIG. 3B shows the direction of the diffracted X-ray when the position C comes to the X-ray irradiation point. Since the position C is far from the inclination direction of the off angle δ, the {110} plane is slightly upward from the vertical state. Therefore, even if the incident X-ray beam 26 is incident horizontally, the direction of the diffracted X-ray 32 is slightly upward from the horizontal plane. Similarly, when the position D comes to the X-ray irradiation point, it becomes a slightly upward diffracted X-ray.
[0017]
Here, the degree of deviation of the diffracted X-ray will be described. When the off angle δ is 4 degrees and the tilt direction is as shown in FIG. 2, assuming that the distance from the X-ray irradiation point 30 in FIG. 1 to the detection window of the X-ray detector 24 is 70 mm, the position at the detection window is The diffracted X-rays from A and B deviate about 3 mm from the horizontal plane, and the diffracted X-rays from positions C and D deviate about 3 mm from the horizontal plane.
[0018]
Next, an X-ray absorber that plays an important role in the present invention will be described. FIG. 4A is a perspective view showing the arrangement of the X-ray absorber, and FIG. 4B is a front view thereof. The X-ray detector 24 is a nominal 2 inch scintillation counter. The detection window 34 has a vertically elongated rectangular shape, and the detection surface is exposed to the detection window 34. In this embodiment, the height of the detection window 34 is 50 mm and the width is 10 mm. The X-ray absorber 36 can select and cover either the upper half or the lower half of the detection window 34. The X-ray absorber 36 can attenuate the characteristic X-ray intensity used in the X-ray diffractometer to about half. When using Kα rays of a Cu target, if a Ni foil having a thickness of about 10 to 15 μm is used as an X-ray absorber, the X-ray transmittance becomes around 50%. Specifically, when one Ni foil having a thickness of 5 μm is used as an X-ray absorber, the X-ray transmittance is 78%. When two Ni foils are used in an overlapping manner, the X-ray transmittance is 59%. %, 46% when 3 sheets are stacked, and 34% when 4 sheets are stacked.
[0019]
Next, a procedure for determining the orientation flat machining position will be described. First, assume the following. The orientation flat surface is processed so as to be parallel to the {110} plane on the outer peripheral surface of the silicon single crystal body, and the relative positional relationship with the inclination direction of the off angle δ is at the position A in FIG. It is assumed that the orientation flat surface is processed at a position closest to the inclination direction 38 of the off-angle when viewed from the right. First, in FIG. 1, the X-ray source 22 and the X-ray detector 24 are arranged in an angular relationship such that diffracted X-rays from the {220} plane (parallel to the {110} plane) of silicon can be detected. The X-ray absorber 36 in FIG. 4 is positioned so as to cover the lower half of the detection window 34 of the X-ray detector 24.
[0020]
When the X-ray optical system is arranged as described above, the intensity of the diffracted X-ray 32 is detected by the X-ray detector 24 while rotating the silicon single crystal body 16 about its axis. When the rotation angle positions A, B, C, and D (positions at which the outer peripheral surface is substantially parallel to {110} of the crystal) on the outer peripheral surface of the silicon single crystal 16 come to the X-ray irradiation point 30, the diffracted X-rays 32 will be detected. Since the <100> orientation has an off-angle, the diffracted X-rays from A, B, C, and D are slightly shifted up or down from the horizontal plane 20 including the X-ray source 22 and the X-ray irradiation point 30. However, even if it is slightly shifted up and down in this way, the height of the detection window of the X-ray detector 24 is 50 mm, so that the diffracted X-ray 32 can be detected.
[0021]
FIG. 5 is a graph of the output pattern of the X-ray detector. The horizontal axis represents the rotational angle position around the axis of the silicon single crystal, and the vertical axis represents the detection intensity of the X-ray detector. Note that the rotation direction of the silicon single crystal is determined to rotate counterclockwise when viewed from the upper portion (Top side) when the crystal is pulled. This graph shows a pattern when the silicon single crystal is rotated about two times from an arbitrary angular position. That is, starting from the angular position E point, it is rotated once and returned to the point E, and is further rotated one more time. While the silicon single crystal is rotated once, four diffraction peaks from the {220} plane can be observed. The same symbols A, B, C, and D are attached to the respective diffraction peaks from positions A, B, C, and D. Since the diffracted X-rays from the positions A and B are shifted downward from the horizontal plane as shown in FIG. 3A, the X-ray absorber hits the X-ray absorber 36 of FIG. The X-ray detector 24 is entered. At that time, the incident position of the diffracted X-rays to the X-ray detector is as shown in a region 40 of FIG. On the other hand, the diffracted X-rays from the positions C and D shift upward from the horizontal plane as shown in FIG. 3B, and therefore enter the X-ray detector 24 as they are without hitting the X-ray absorber 36 in FIG. The incident position of the diffracted X-ray at that time is as shown in a region 42 in FIG. Therefore, the detection intensity of the diffraction peaks at the positions A and B is about half of the detection intensity at the positions C and D.
[0022]
If the intensity of the diffracted X-ray is detected by rotating the silicon single crystal around its axis from an arbitrary rotational position and detecting the intensity of two diffraction peaks (hereinafter referred to as a large peak) and a small intensity. It should be possible to observe two diffraction peaks (hereinafter referred to as small peaks). Of these diffraction peaks, assuming that orientation flat processing is performed at a position A having a positional relationship as shown in FIG. 2 with respect to the off-angle δ, the magnitude relationship of the diffraction peaks and the order of their appearance are based on the relationship. Thus, the position A can be determined as follows. That is, it is only necessary to find a small peak that appears next to the large peak, and it can be determined that this small peak is a diffraction peak from position A. When the rotation of the silicon single crystal is started, it is completely unknown where the X-ray irradiation point 30 on the outer peripheral surface is in relation to the positions A to D. The small peak next to the large peak can be found at about half a turn. Even in the worst case, the next small peak after the large peak can always be found by only one rotation plus one quarter rotation.
[0023]
If the position A can be determined as described above, orientation flat processing may be performed at the position A. Specifically, an orientation flat processing apparatus is provided on the opposite side of the X-ray diffraction optical system with the silicon single crystal interposed therebetween, and after the position A is determined, orientation flat processing can be performed with this orientation flat processing apparatus.
[0024]
Even when orientation flat processing is performed on the position B (or C or D) instead of the position A, the position can be determined in the same manner as described above. For example, position B is the second small peak when two small peaks follow the large peak, position C is the next large peak after the small peak, and position D is the next small peak. This is the second largest peak when two large peaks follow.
[0025]
Next, the case where the inclination direction of the off angle δ is different from the case of FIG. 2 will be described. FIG. 6 is a drawing similar to FIG. 2, but the inclination direction of the off angle is different. This silicon single crystal has an <100> orientation off-angle inclination direction 38a at any one of the four positions A1, B1, C1, and D1 whose outer peripheral surface is parallel to the {110} plane. (For example, it corresponds to the direction of A1). In this case, a diffraction pattern as shown in FIG. 7A can be obtained by rotating the silicon single crystal. That is, since the diffracted X-ray from the position A1 is shifted downward from the horizontal plane, it reaches the region 44 as shown in FIG. 8A and hits the X-ray absorber 36, where the X-ray intensity is reduced to about half. Attenuates. On the other hand, since the diffracted X-ray from the position C1 is shifted upward from the horizontal plane, it reaches the region 48 and enters the detection window 34 of the X-ray detector 24 without hitting the X-ray absorber 36. Further, since the diffracted X-rays from the positions B1 and D1 come out horizontally (the {110} plane is kept vertical at the positions B1 and D1), only the lower half of the diffracted X-rays comes to the region 46. Is attenuated by the X-ray absorber 36 and enters the detection window 34. Therefore, as shown in FIG. 7A, the position A1 is a small peak, the positions B1 and D1 are medium peaks, and the position C1 is a large peak. Accordingly, the positions A1 to D1 can be determined based on the magnitude relationship of the diffraction peak intensity and the order of appearance.
[0026]
FIG. 7B shows a diffraction pattern when the position of the X-ray absorber 36 is shifted with respect to the silicon single crystal as shown in FIG. As shown in FIG. 8B, the upper end of the X-ray absorber 36 is shifted below the center line in the vertical direction of the detection window 34, and the detection window 34 is covered with the X-ray absorber 36. It is only about 1/3 below. The diffracted X-ray from the position A1 comes to the region 44 and hits the X-ray absorber 36, where the X-ray intensity is attenuated to about half. On the other hand, the diffracted X-ray from the position C1 comes to the region 48 and does not hit the X-ray absorber 36 and enters the detection window 34 of the X-ray detector 24 as it is. Then, the diffracted X-rays from the positions B1 and D1 come to the region 46 and enter the detection window 34 of the X-ray detector 24 without hitting the X-ray absorber 36. Therefore, as shown in FIG. 7B, the position A1 is a small peak, and the positions B1, C1, and D1 are large peaks. Accordingly, the positions A1 to D1 can be determined based on the magnitude relationship of the diffraction peak intensity and the order of appearance.
[0027]
Incidentally, since the off-angle inclination direction is set to a desired direction at the stage of manufacturing the silicon single crystal by the pulling method, can the diffraction pattern as shown in FIG. 5 be obtained from this silicon single crystal? Whether such a pattern can be obtained is already known before diffraction measurement.
[0028]
By the way, if the position of the X-ray absorber is shifted upward in FIG. 4 so as to cover the upper half of the X-ray detector, the magnitude relationship of the diffraction peaks is reversed in the diffraction patterns of FIGS. In this case, the diffraction peak from the target position can be found by the same method as described above.
[0029]
In the above-described embodiment, the axis of the single crystal body is set up vertically and the X-ray source and the X-ray detector are arranged in the horizontal plane, but another arrangement may be adopted. That is, the X-ray source and the X-ray detector may be arranged in the vertical plane with the axis of the single crystal body being horizontal.
[0030]
【The invention's effect】
The orientation flat processing position determination method according to the present invention has a specific positional relationship with a tilt direction of an off angle from a plurality of outer peripheral surface positions where a diffraction X-ray can be detected for a cylindrical single crystal having an off angle. In order to find a certain outer peripheral surface position, the detection surface of the X-ray detector is partially covered with an X-ray absorber, and based on the relative magnitude relationship of the detection intensity of a plurality of diffraction peaks and the order of their appearance. The orientation flat machining position is determined. Thus, the orientation flat processing position of the single crystal can be determined by using only one X-ray detection device without requiring other detection means such as an optical detection device.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an embodiment of the present invention.
FIG. 2 is a plan view of a silicon single crystal viewed from above.
FIG. 3 is a front view showing the direction of diffracted X-rays when position A or C comes to the X-ray irradiation point.
FIG. 4 is a perspective view showing the arrangement of an X-ray absorber and a front view of a detector.
FIG. 5 is a graph of an output pattern of an X-ray detector.
FIG. 6 is a plan view similar to FIG. 2 in the case where the off-angle inclination directions are different.
7 is a graph of an output pattern similar to that of FIG. 5 for the silicon single crystal of FIG.
FIG. 8 is a front view of a detector showing the arrangement of X-ray absorbers.
FIG. 9 is a perspective view of a silicon single crystal body.
FIG. 10 is a perspective view of a silicon single crystal in which the <100> orientation is inclined by an angle δ with respect to the axis of the single crystal.
[Explanation of symbols]
16 Single crystal 18 Axis 20 Diffraction plane 22 X-ray source 24 X-ray detector 26 X-ray beam 28 Entrance slit 30 X-ray irradiation point 32 Diffraction X-ray 34 Detection window 36 X-ray absorber

Claims (2)

In a method for determining the orientation flat processing position on the outer peripheral surface of a single crystal in which a specific crystal orientation of the cylindrical single crystal is inclined in a specific direction with respect to the axis of the single crystal, A method for determining an orientation flat processing position of a single crystal comprising steps.
(A) An X-ray source is arranged so that the outer peripheral surface of the cylindrical single crystal can be irradiated with an X-ray beam, and X-ray diffracted by a predetermined crystal lattice plane on the outer peripheral surface can be detected. An X-ray source is arranged so that a diffraction plane including the X-ray source, the X-ray irradiation point on the outer peripheral surface, and the X-ray detector is perpendicular to the axis of the single crystal body. And placing an X-ray detector.
(B) An X-ray absorber capable of partially covering the detection surface of the X-ray detector is disposed between the X-ray irradiation point and the X-ray detector, and the X-ray absorber is not transmitted without passing through the X-ray absorber. The diffracted X-rays that reach the detection surface enter a region on one side of the detection surface in a direction perpendicular to the diffraction plane, pass through the X-ray absorber, and then reach the detection surface. Positioning the X-ray absorber so that a line is incident on a region on the other side of the detection surface in a direction perpendicular to the diffraction plane.
(C) rotating the single crystal around its axis and detecting the intensity of a plurality of diffraction peaks caused by the predetermined crystal lattice plane with the X-ray detector;
(D) determining the orientation flat processing position based on the relative magnitude relationship of the intensities of the plurality of diffraction peaks and the order of their appearance; 2. The orientation flat processing position determination method according to claim 1, wherein the X-ray absorber has an X-ray transmittance of 30 to 80% at a wavelength to be used.

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