JP4797276B2 - Cutting method of single crystal ingot - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for cutting a single crystal ingot, and more particularly to an improvement in a method for cutting a wafer from a columnar single crystal ingot such as a semiconductor or a dielectric.
[0002]
[Prior art]
When a wafer is cut out from a cylindrical or prismatic single crystal ingot, an inner peripheral slicer, an outer peripheral slicer, a wire saw, or the like is generally used.
[0003]
By the way, a wafer such as a semiconductor or dielectric used for an electronic component is often required to have a specific crystallographic orientation on its main surface. For example, when each of a plurality of wafers cut out from one columnar single crystal ingot should have a specific main surface orientation A, first, a reference cross section having the surface orientation A with high accuracy at one end of the columnar ingot. Is formed.
[0004]
When forming such a reference cross section, generally, the crystal orientation of the ingot is obtained by X-ray diffraction, and the first cross section is formed by a slicer so as to produce a plane orientation A at the end of the columnar ingot. Then, in order to confirm whether the first cross section correctly matches the plane orientation A, it is measured again by X-ray diffraction. If the first cross section is deviated from the plane orientation A by an angle amount greater than a predetermined allowable amount. If so, the second cross section is formed again by the slicer so as to correct the deviation angle. Such an operation is repeated until the end surface of the columnar ingot has a reference cross section that matches the surface orientation A with a predetermined high accuracy.
[0005]
After the reference cross section having the surface orientation A with high accuracy is formed at the end of the columnar ingot in this way, a plurality of wafers having the main surface of the surface orientation A are formed by, for example, a multi-wire saw as shown in FIG. It can be cut out at the same time.
[0006]
In the multi-wire saw shown in the schematic perspective view of FIG. 6, a columnar single crystal ingot 1 having a reference cross section 1 a having a plane orientation A is fixed to a fixing jig 3 via a carbon jig 2. The carbon jig 2 is used to prevent and hold the wafer cut out from the ingot 1 from falling. The fixing jig 3 is installed on the turning stage 11. A plurality of wires 13 are wound around the head roller 12. These wires 13 are moved along the longitudinal direction of the wires themselves by the rotation of the head roller 12. For example, a piano wire can be used as the wire 13. In the state as shown in FIG. 6, the periphery of the reference cross section 1 a of the columnar ingot 1 is observed by the tool scope 14. The tool scope 14 has a magnification of about 40 times, for example.
[0007]
FIG. 7 shows a state in which the reference cross section 1a of the columnar ingot 1 is viewed from the front. The tool scope 14 can be moved parallel to the wire 13, and the upper periphery of the circular or elliptical reference section 1a is observed at a distance indicated by a broken line 14a. Then, the turning stage 11 is adjusted and turned so that the horizontal direction x in the reference cross section 1a and the longitudinal direction of the wire 13 are parallel to each other. Thereafter, the ingot 1 is slowly raised along the upward direction y in the reference cross section 1a together with the fixed turning stage 11, and a plurality of wires 13 moving in the x direction are used to move the ingot 1 The wafer is cut out.
[0008]
Note that cutting oil mixed with abrasive grains such as silicon carbide or diamond is applied to the surface of the wire 13. Further, the parallelism between the upward direction y in the reference cross section 1a and the rising direction of the ingot 1 is confirmed by applying a dial gauge to the upper and lower parts of the reference cross section 1a. It is corrected using.
[0009]
[Problems to be solved by the invention]
In FIG. 7, when the upper periphery of the cross section 1a is observed by the tool scope 14 in order to set the x direction in the reference cross section 1a in parallel with the direction of the wire 13, as the distance from the uppermost point of the periphery increases in the left-right direction. The height decreases, that is, the observation distance 14a changes. Therefore, if the focus of the tool scope 14 is focused on the uppermost point of the reference cross section 1a, the focus shifts as the distance from the left and right directions increases, and the peripheral image of the cross section 1a appears blurred. For this reason, it is not easy to set the x direction in the cross section 1a parallel to the direction of the wire 13 with high accuracy while directly observing the periphery of the reference cross section 1a using the tool scope 14.
[0010]
Under such circumstances, an ingot cutting method as illustrated in FIGS. 8 and 9 has been attempted. FIG. 8 is similar to FIG. 7, but in FIG. 8, the cutter knife blade 4 is joined at the top of the reference section 1a. FIG. 9 shows a state where the ingot 1 in FIG. 8 is viewed from the right side. As can be seen more clearly in this figure, the blade 4 of the cutter knife is joined to the upper part of the reference cross section 1a by a double-sided joining tape 5.
[0011]
Thus, in the wafer cutting method using the blade 4 of the cutter knife, as shown in FIG. 8, the height of the blade edge of the blade 4 does not change even if it is separated from the center in the left-right direction, and the observation distance 14a is It does not change. That is, even if the tool scope 14 is focused on the center of the blade edge of the blade 4, the focus does not deviate greatly as the distance from the tool scope 14 increases. Therefore, as compared with the case of directly observing the periphery of the reference cross section 1a through the tool scope 14, the wafer cutting method using the cutter knife blade 4 can obtain a wafer having a principal surface closer to the plane orientation A. it can.
[0012]
However, the blade 4 of the cutter knife is made by rolling from a rolled steel sheet, and its side surface joined to the reference cross section 1a is not necessarily a perfect plane. Further, since the double-sided bonding tape 5 is made of a soft polymer tape and an adhesive, if the pressing force when the blade 4 of the cutter knife is bonded is not uniform, the parallelism between the blade edge and the reference cross section 1a. May shift. Furthermore, when the cutting edge of the blade 4 is observed by magnifying it 40 times through the tool scope 14, the cutting edge is often seen in a fairly wide width with a halation. In such a case, it is not easy to accurately adjust the turning stage 11 so that the longitudinal direction of the blade edge of the blade 4 is parallel to the wire 13. Furthermore, after the setting in the x direction in the reference cross section 1a is completed, there is a risk of injury from the cutting edge when the cutter knife blade 4 and the double-sided bonding tape 5 are peeled off from the cross-section 1a. It is often difficult to remove 5 as well.
[0013]
In view of the situation in the prior art as described above, the present invention provides a method for easily cutting a wafer having a main surface parallel to a reference cross section formed at an end of a columnar single crystal ingot with high accuracy. The purpose is to do.
[0014]
[Means for Solving the Problems]
According to the present invention, in a method of simply cutting a wafer having a principal surface parallel to a reference cross section previously formed at least at one end of a columnar single crystal ingot with high accuracy, the reference cross section is crystallographic. A first surface that is cut with high precision in advance so as to have a predetermined plane orientation, and that a predetermined cleaved piece is bonded to the vicinity of the periphery of the reference cross section by the surface tension of the liquid , and the cleaved piece is bonded to the reference cross section. Having a completely flat cleavage surface and a completely flat second cleavage surface intersecting with the first cleavage surface, and a ridge where the first and second cleavage surfaces intersect is formed by a slicer or a wire saw. It is characterized by being set to be parallel to the cut surface.
[0015]
In addition, it is preferable that the liquid which joins a cleavage piece on a reference | standard cross section is oil.
[0016]
As the cleaved piece, a compound semiconductor can be preferably used. The first and second cleavage planes preferably intersect each other at a solid angle in the range of 45 to 135 degrees, and more preferably intersect each other at a solid angle in the range of 85 to 95 degrees.
[0017]
The ingot is fixed to the turning means via a predetermined jig, and a ridge where the first and second cleavage planes intersect is observed with a microscope that can be moved parallel to the cutting blade or saw wire. The turning axis of the turning means is the microscope. It is preferable that they are disposed within the movable range of the visual field.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
In the schematic perspective view of FIG. 1, an embodiment of a method for cutting a single crystal ingot according to the present invention is shown. The multi-wire saw shown in FIG. 1 is the same as that of FIG. 6, but in FIG. 1, a thin rectangular parallelepiped cleaved piece 6 is joined to the reference cross section 1a of the single crystal InP ingot 1 by the surface tension of the oil. Yes. The cleavage piece 6 is made of InP, which is the same material as the ingot 1. In general, many compound semiconductors such as GaAs and InP have good cleavage properties, and can be preferably used as the material of the cleavage piece 6.
[0019]
Since cleavage occurs along specific atomic planes that are regularly arranged in the crystal, the cleaved fracture surface can be flat in atomic order. Along with this, the ridge formed by the intersection of the two cleavage planes has high accuracy linearity.
[0020]
FIG. 2 schematically shows a state in which the cleaved piece 6 is observed through the tool scope 14 in the state of FIG. A horizontal line in the cross-line frame 14 b shown enlarged in the tool scope 14 is set parallel to the longitudinal direction of the wire 13. Then, the angle is adjusted by the turning stage 11 so that the ridge where the surface in contact with the reference cross section 1a and the narrow upper surface of the surface of the cleavage piece 6 are parallel to the cross horizontal line. As a result, the horizontal x-axis direction in the reference cross section 1 a is accurately parallel to the longitudinal direction of the wire 13.
[0021]
The top view of FIG. 3 and the corresponding side view of FIG. 4 illustrate the process of such an angle adjustment. Referring to these drawings, first, the tool scope 14 is disposed at an arbitrary first position 14I close to one end of the cleavage piece 6. Here, the focus of the tool scope 14 is made to coincide with the upper surface F1 of the wire 13. And the horizontal line in the crosshair frame 14b and the side surface of the wire 13 are made to correspond within the microscope visual field. Next, the tool scope 14 is moved in parallel with the wire 13 to an arbitrary second position 14 II close to the other end of the cleavage piece 6. Then, at the second position 14II, the tool scope 14 is turned so that the horizontal line in the crosshair frame 14b and the side surface of the wire 13 exactly coincide. As a result, the horizontal line in the crosshair frame 14b in the tool scope 14 and the wire 13 are set accurately in parallel.
[0022]
Thereafter, the focus of the tool scope 14 is made to coincide with the upper surface F2 of the cleavage piece 6. Then, by moving the tool scope 14 back and forth, the long side of the upper surface of the cleavage piece 6 and the horizontal line in the cross-line frame 14b are made to coincide. Next, the tool scope 14 is returned in parallel with the wire 13 in the vicinity of the first position 14I described above. Then, the turning stage 11 on which the ingot 1 is installed is turned so that the long side of the upper surface of the aforementioned cleaved piece 6 and the horizontal line in the cross-hair frame 14b exactly coincide with each other. As a result, the horizontal x direction in the reference cross section 1a of the ingot 1 and the longitudinal direction of the wire 13 are accurately set in parallel.
[0023]
In such an angle adjustment, in the InP cleaved piece 6, the surface in contact with the reference cross section 1 a and the narrow upper surface are orthogonal to each other and the upper surface becomes a horizontal surface, and the ridge where these surfaces intersect is the tool scope 14. Makes it easier to observe clearly. As a result, the accuracy of the cutting plane orientation can be further improved. In general, the solid angle formed by the surface in contact with the reference cross section 1a and the narrow upper surface in the surface of the cleaved piece 6 is preferably in the range of 45 to 135 degrees, and is preferably 85 to 95 degrees. More preferably, it is within the range. Further, since the cleaved pieces 6 are joined by the surface tension of oil, joining and peeling of the cleaved pieces 6 with respect to the reference cross section 1a can be performed very easily.
[0024]
According to the embodiment as described above, a wafer was actually cut out from 14 columnar InP single crystal ingot samples in different lots. FIG. 5 shows a deviation angle in the x direction between the main surface orientation of the wafer cut out in this case and the surface orientation of the reference cross section 1a.
[0025]
That is, in the graph of FIG. 5, the horizontal axis represents the deviation angle (degree) in the x direction, and the vertical axis represents the number of ingot samples. When statistical calculation was performed on the numerical value of the deviation angle from which the graph was based, the arithmetic mean error e was 0.009 degrees and the standard deviation σ was 0.005 degrees. Therefore, if the displacement angle in the x direction is managed by 3σ, the cutting method of the present invention has the ability to suppress the error in the error range of e + 3σ = 0.024 degrees with respect to the x direction.
[0026]
For comparison, the above-described cutting method using the cutter knife blade was performed for the same number of samples. As a result, the arithmetic average error e was 0.025 degrees and the standard deviation σ was 0.009 degrees. Therefore, if 3σ is managed in the cutting method of this comparative example, the cutting method has an ability to suppress within an error range of e + 3σ = 0.052 degrees with respect to the x direction. As is apparent from the comparison between the comparative example and the above-described embodiment, it can be seen that the accuracy of the plane orientation of the wafer cut by the cutting method of the present invention can be remarkably improved.
[0027]
In the above embodiment, the surface tension of oil is used to join the cleaved piece 6 to the reference cross section 1a. However, it goes without saying that the surface tension of water may be used if desired.
[Brief description of the drawings]
FIG. 1 is a schematic perspective view showing a method of cutting a single crystal ingot according to an embodiment of the present invention.
FIG. 2 is a top view showing a field of view of the tool scope in FIG.
FIG. 3 is a top view illustrating a method of setting the parallelism between the horizontal direction of the reference cross section of the ingot and the saw wire.
4 is a side view corresponding to FIG. 3. FIG.
FIG. 5 is a graph showing angular accuracy in a method for cutting a single crystal ingot according to an embodiment of the present invention.
FIG. 6 is a schematic perspective view showing a conventional method for cutting a single crystal ingot.
7 is a diagram illustrating a state in which a reference cross section of the ingot in FIG. 6 is viewed from the front.
FIG. 8 is a front view showing a cutting method attempted in the prior art.
FIG. 9 is a diagram illustrating a state in which the ingot in FIG. 8 is viewed from the right side surface.
[Explanation of symbols]
1 Columnar single crystal ingot, 1a Reference cross section, 2 Carbon jig, 3 Fixing jig, 4 Cutter knife blade, 5 Double-sided adhesive tape, 6 Cleaved piece, 11 Rotating stage, 12 Head roller, 13 Wire, 14 Tool scope, 14a Line of sight through tool scope, 14b Tool scope field of view, 14I tool scope first position, 14II tool scope second position, F1 tool scope first focal plane, F2 tool scope second focus surface.

Claims (6)

A method of simply cutting out a wafer having a principal surface parallel to a reference cross section previously formed at least at one end of a columnar single crystal ingot with high accuracy,
The reference cross section has been cut with high accuracy in advance so as to have a predetermined crystal orientation crystallographically,
A predetermined cleavage piece is bonded to the vicinity of the periphery of the reference cross section by the surface tension of the liquid ;
The cleaved piece has a completely flat cleaved surface as a first surface joined to the reference cross section, and a completely flat second cleaved surface intersecting the first cleaved surface,
A method for cutting a single crystal ingot, characterized in that a ridge where the first and second cleavage planes intersect is set to be parallel to a cutting surface by a slicer or a wire saw. The method for cutting a single crystal ingot according to claim 1 , wherein the liquid is oil. The method for cutting a single crystal ingot according to claim 1 or 2, wherein the cleaving piece is characterized by comprising a compound semiconductor. The method for cutting a single crystal ingot according to any one of claims 1 to 3 , wherein the first and second cleavage planes intersect each other at a solid angle within a range of 45 to 135 degrees. . The method for cutting a single crystal ingot according to claim 4 , wherein the first and second cleavage planes intersect each other at a solid angle within a range of 85 to 95 degrees. The ingot is fixed to the turning means via a predetermined jig, and a ridge where the first and second cleavage surfaces intersect is observed by a microscope capable of moving in parallel with a cutting blade or saw wire, and the turning axis of the turning means The method for cutting a single crystal ingot according to any one of claims 1 to 5 , wherein is disposed within a movable range of the field of view of the microscope.

Images