JP2842307B2 - Method for cutting III-V compound semiconductor crystal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cutting a single crystal ingot of a III-V compound semiconductor into a wafer using a wire saw. In particular, the present invention relates to an improvement capable of preventing a deviation of a wire of a wire saw when cutting a {100} plane wafer. Here, the group III-V compound semiconductor refers to a group III-V semiconductor such as GaAs, InP, and GaSb. The ingot is a rod-shaped single crystal grown by the LEC method or the HB method. The wafer is obtained by cutting an ingot by a parallel plane into thin pieces. A wire saw is a device in which a single wire is formed into a multi-layered triangular coil and brought into contact with the side surface of the ingot at equal intervals, and the wire is reciprocated to cut the ingot at a plurality of locations at once. .

[0002]

2. Description of the Related Art A III-V compound semiconductor single crystal ingot is manufactured by a pulling method (LEC method) or the like. The ingot in the lifting method has a circular cross section. This is cut along a plane perpendicular to the axis to obtain a wafer. Conventionally, an inner peripheral blade slicer has been used for cutting into wafers. In this method, an annular blade having an inner peripheral edge (inner peripheral blade) is rotated, and the ingot is cut one by one by the inner peripheral blade.

[0003] The inner peripheral blade is 0.1 mm to 0.12 mm.
This is a blade in which diamond particles having a particle size of about 0.05 mm are electrodeposited on an inner circumferential surface of an annular stainless steel plate having a thickness of mm. The inner blade is rotated at a high speed while applying tension to the vicinity of the breaking point, and is applied to the side surface of the ingot to cut the ingot into thin wafers. The blade itself has a considerable thickness. Even if the margin is the lowest,
It is about 0.3 mm. There are many cutting margins, and some materials are wasted. This is one drawback. Further, since the cutting is performed by diamond, the processing strain is large. After forming the wafer, the processing distortion must be removed by etching or the like. In addition, there is a disadvantage that it takes time since each piece is cut out.

[0004] However, the inner peripheral blade has a considerable rigidity itself and supports the outer periphery with a harder member, so that it is unlikely to bend in the circumferential and radial directions. An ideal plane can always be maintained. The blade surface does not swing left and right. The cut surface is always constant. For this reason, the inner peripheral blade slicer was an excellent cutting device capable of cutting a GaAs ingot into wafers with high accuracy. Until now, almost all GaAs and InP single crystals have been cut by an inner peripheral edge slicer.

The relationship between the cutting direction and the crystal orientation will be described. Compound semiconductor single crystals such as GaAs have a thickness of $ 01
The 1｝ direction is the cleavage plane. Therefore, when a device of {100} plane is cut out and a device is fabricated thereon, the device can be cut vertically and horizontally along the cleavage plane because two orthogonal directions are perpendicular to the plane. For this reason, GaAs wafers,
InP wafers are often cut at right angles to <100> grown ingots as axes to make {100} plane wafers.

Generally, the (0-1-1) and (0-11) planes, which are cleavage planes, are ground into planes, which are used as marks for the orientation of the ingot. Here, -1 should be drawn above 1 but cannot be described in the specification, so-is added before it. The same applies hereinafter. The plane of the (0-1-1) plane is O
The plane F (orientation flat) and the plane (0-11) are called IF (index flat). Since the lengths are different, the two can be distinguished. It is necessary to specify the direction of the wafer by two directions. This is GaAs, In
Since P and the like are two-element systems, (0-1-1) and (0-1
1) The planes are not equivalent.

When the ingot is cut out by the inner peripheral blade slicer, a carbon rod is bonded to the OF surface and the ingot is supported by the carbon rod. From the opposite surface, the inner peripheral blade is cut toward the carbon rod. The carbon rod is also slightly cut. Since the end of the wafer is bonded to the carbon rod, the wafer remains on the carbon rod and does not fall apart. After the cutting of the wafer is completed, the wafer is removed from the carbon rod. The cutting by the inner peripheral blade slicer is described in, for example, JP-A-60-11897.

[0008] As described above, the GaAs by the inner peripheral blade slicer is used.
Cutting of ingots has a proven track record and overcomes various problems. Excellent cutting accuracy and eliminates the need for loose abrasives. Even now, single crystals of GaAs or InP are cut by an inner peripheral slicer.

A wire saw is a relatively new ingot cutting device. For example, Japanese Patent Application Laid-Open No. HEI 3-20955
No. 5, JP-A-5-104432, etc., describe a wire saw. A wire saw is formed by winding a single wire around a multi-groove roller group arranged in a polygon such as a triangle or a quadrangle to form a multi-parallel wire group, and reciprocatingly rotating the multi-groove roller. , The wire is reciprocated. The distance P between the parallel wires is set to a distance (P = W−Y) obtained by subtracting the margin Y from the desired wafer thickness W. Appropriate tension is applied to the wire. The parallel wire group is brought into contact with the side surface of the ingot to reciprocate the wire. Then, a polishing liquid containing abrasive grains is supplied to the ingot from above. As the wire and abrasive rub against the outer surface of the ingot, the ingot is cut along the wire line.

[0010] The wire saw has the advantage of high throughput because many wafers can be cut at the same time. There is also an advantage that the cutting allowance is small. However, the wire saw has a low accuracy of wafer cutting. It is used to cut ceramics, which are powder materials, and polycrystalline materials. However, it is not yet widely used for cutting semiconductor single crystals that require high precision. This is because the unevenness of the wire causes a projection or a recess on the cut surface. It is only used to cut polycrystalline Si.

It has not yet been used for cutting a GaAs single crystal or an InP single crystal of a compound semiconductor. 4 to 7 show micrographs of the (100) plane when the GaAs ingot is cut so as to be parallel to (100) by a wire saw. Single-crystal wafers often have electronic devices on them, so they must be free of distortion and irregularities. The reliability of the wire saw is still poor, and the cutting performance is far from that of the inner peripheral edge slicer.

[0012]

However, the inner peripheral slicer is cut one by one from above the throughput.
A wire saw that can cut a large number of sheets at the same time is more advantageous. Also, since the wire is thinner than the inner peripheral blade, the cutting margin should be smaller than that of the inner peripheral slicer. If the cutting margin is small, a larger number of wafers can be cut out. This would also be advantageous.

[0013] GaAs or In depending on the wire source somehow.
I want to cut a P ingot into wafers. However, the wire saw has a smaller cross-sectional area than the inner peripheral blade slicer. It is natural that the cross-sectional area is small because it is a thin wire. The value obtained by dividing the total tension by the cross-sectional area is the stress per unit area. If the stress is too large, the wire will break. To avoid this, the wire cannot be tensioned too much.

Since it is not possible to apply sufficient tension,
When a GaAs ingot is cut by the current wire saw, the wire gradually shifts to the left or right and the cut surface is bent. That is, the wire source has a disadvantage that the single crystal of the compound semiconductor cannot be cut into a straight plane. When the cut surface of the wafer actually cut with a wire saw is observed with a microscope, the cut surface is distorted, and considerably large convex portions and concave portions are formed.

In the case of a 3-inch diameter ingot, the variation in surface height (WARP) reaches as much as 10 μm. If the height of the surface is different as described above, the surface is polished and the distortion remains even when etched. Therefore, a flat and smooth wafer cannot be produced. For this reason, it is still not possible to cut a compound semiconductor with a wire saw.

It is a first object of the present invention to provide a method for cutting a compound semiconductor ingot with a wire saw. Because of that, when cutting, we prevent the bias of the wire,
It is a second object of the present invention to provide a method for cutting a compound semiconductor ingot along a plane. Wire saw
It is a third object of the present invention to enable cutting by wire sawing and to realize the advantages of cutting by wire saw.

[0017]

SUMMARY OF THE INVENTION The present invention relates to a method for controlling the axial direction of an object in which <1.
00> from the compound semiconductor ingot {100} ±
When a wafer having a plane orientation within 15 ° is cut by a wire saw, the direction in which the wire reciprocates is 22.5 ° to 67.5 ° away from the cleavage direction of the ingot single crystal. Features. In particular, the direction should be 35 ° to 55 ° away from the cleavage direction. The azimuth is defined by the running direction of the wire. Since the ingot is sent at right angles to the running direction of the wire, the direction of sending the ingot is also determined by this.

The direction of ingot feed is 2 from the cleavage direction.
The direction is 2.5 ° to 67.5 °. The support position of the ingot is at the bottom of the ingot at an angle of 90 degrees from the running direction of the wire. Therefore, the support position is 2
2.5 ° to 67.5 °. More preferably, the ingot feed and the support position are in the direction of 35 ° to 55 ° from the cleavage plane.

There are four cleavage directions <011>, and there are also four directions <010> and <001> that are 45 ° apart from the cleavage direction. When displayed by individual directions, the spindle [10
[0-11], [0111], [01-
1], [011], and [0-1-1]. The directions perpendicular to the main axis [100] and at 45 ° to the cleavage direction are [00-1], [001], [010], and [0].
-10].

In the present invention, these directions ([00-1] [0
01], [010], and [0-10]). The direction of ingot feed is a direction orthogonal to both the main shaft direction and the traveling direction. The support of the ingot is on the opposite side in the feed direction.

For example, if the traveling direction of the wire is [00-1], the cutting starts from the (0-10) plane, the traveling direction (ingot feeding direction) becomes [010], and the supporting member moves in the direction of the (010) plane. Fixed to

Further, ± 2 before and after these optimum four directions.
It is assumed that a range of 2.5 ° is assumed, and the traveling direction of the wire may be in this range. That is, the traveling direction of the wire is [00-1] ± 22.5 °, [001] ± 2
2.5 °, [010] ± 22.5 °, [0-10] ± 2
The range may be 2.5 °. 2 from the above cleavage plane
The expression 2.5 to 67.5 ° is equivalent to this.

In particular, deviations from these four directions are ± 1.
That is, it is better to be within 0 °. The traveling direction of the wire is [00-1] ± 10 ° [001] ± 10 °,
It can be represented by a simple notation of [010] ± 10 ° and [0-10] ± 10 °. 3 from the cleavage plane
The expression 5 ° to 55 ° states the same thing.

The extent of deviation from 45 ° to be allowed depends on the requirement for flatness of the wafer surface. If it is desired to obtain a flatter surface, it is better to match the running direction of the wire to the direction at 45 ° from the cleavage. However, if the flatness requirement is not so severe, the angle may deviate further from the direction at 45 ° from the cleavage.

The present invention cuts a compound semiconductor ingot by reciprocating a fine wire while giving free abrasive grains to the ingot. This reduces the cutting margin to 0.18 mm. For inner peripheral slicer, 0.
It could not be reduced to 3 mm or less.

The present invention can reduce the cutting margin by as much as 0.12 mm. The traveling speed of the wire is slow, and a large force is not applied to the crystal because loose grains are used. In a conventional inner peripheral blade slicer, a 3-inch GaAs ingot is set to 0.3
It could not be cut to a thickness of 8 mm. That is, 0.3
The yield for cutting out an 8 mm wafer was 0%. According to the present invention, 3-inch GaAs can be cut into wafers having a thickness of 0.38 mm, and the yield is 80% or more. This is an amazing achievement.

Since the wire is made to travel in a direction to cancel the intrinsic anisotropy of the crystal, lateral displacement of the wire is prevented. Thin wires have a small cross-sectional area and cannot be tensioned much. However, since the displacement of the wire is eliminated, the ingot can be cut with a small tension without bending the surface.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The principles of the present invention are somewhat difficult to understand. Therefore, it will be described in detail below. FIG. 1 shows a schematic principle diagram of a wire saw. Since the wire saw itself is well known, its detailed structure is not shown. Three multi-groove rollers-1, 2, and 3 are provided in parallel. The multi-groove roller is obtained by engraving a large number of grooves at equal intervals on a cylindrical long roller. The rollers can rotate about their respective central axes.

A multi-groove row is driven by a driving device (not shown).
La-1, 2, and 3 can be rotated left and right at the same linear velocity. These are arranged in a triangular shape. The multi-groove roller has a large number of grooves 11, 12, 1 and 2, respectively.
3 is engraved. To pass through the groove to the multi-groove roller,
The wire 4 is wound. Although it is one continuous wire, it is repeatedly wound around a multi-groove roller.

A vertically movable ingot table 5 is provided at a portion corresponding to the base of the triangle. A supporting jig 6 (carbon rod) is adhered to the GaAs ingot 7. A jig 6 is fixed on the ingot table 5. The ingot is a single crystal having <100> in the axial direction. The purpose is to cut this into wafers having a plane orientation within {100} ± 15 °.

After attaching the ingot to the ingot table 5, the wire is reciprocated, and while the abrasive grains are flowing,
Raise the ingot table to bring the wire into contact with the top surface of the ingot. The wire 4 simultaneously strikes the top surface of the ingot at a plurality of locations. Grooves 8, 8, ... are cut out at equal intervals on the upper surface of the ingot. Ingot tea
Instead of raising the cable, it is also possible to cut by lowering the wire saw itself.

The direction of the cut is of primary importance to the present invention. Conventionally, the wire saw travels in the direction of the cleavage (0 ± 1 ± 1) and proceeds. The traveling direction and traveling direction of the wire are different. The running direction of the wire is the direction of the wire itself. The direction of travel implies a slow relative movement of the wire with respect to the ingot. If the ingot table moves, the direction is exactly opposite to the movement of the ingot table.

The traveling direction is perpendicular to the traveling direction. The present invention can cut an off-angle wafer (up to 15 degrees), but here, for simplicity, $ 10
Description will be made assuming that a wafer of 0 ° is cut out. The axis of the ingot is defined as the X axis. The traveling direction of the wire is defined as the Y-axis direction. The traveling direction of the wire saw is defined as the Z-axis direction. Hereinafter, description will be made using such coordinates in common.

That is, in FIG. 1, X is defined toward the front, Y is defined to the left, and the Z axis is defined downward. ｛...｝ indicates the collective index of the surface, but here, the individual surface is expressed (1
00) will be used to designate the faces individually. Collectively, directions are represented by <...>. Individual line direction is […]
Represented by

Conventionally, the wire travels parallel to the cleavage plane and the wire travels parallel to the other cleavage plane. That is, Y = [01
-1], and the traveling direction Y, such as Z = [011],
The traveling direction Z was determined. Of course, there are four cases. When Y = [011] and Z = [0-11],
When Y = [0-11] and Z = [0-1-1], there are cases where Y = [0-1-1] and Z = [01-1].
The above arrangement shall represent the other three equivalent cases.

Since the cleavage plane is a plane where the crystal is easily broken, it seems natural to determine the traveling direction parallel to the cleavage plane and the traveling direction parallel to the cleavage plane. The wire cuts the crystal in the direction of travel. The cleavage plane is a plane that can be easily cut.
If so, the running direction of the wire should match the cleavage plane, and it is natural to think so.

However, there is a problem here. If the Y-axis is selected as the cleavage direction and the Z-axis is also selected as the cleavage direction, the cut surface is distorted in an arc shape. FIG. 8 is a central longitudinal sectional view of the ingot when the wire is cut by running the wire in the cleavage direction. A number of curves show the cutting line trajectory by the wire. The wire first deviates to the left. Deflection is greatest at the center (the part with the largest cutting width). Why does this inconvenience occur when cutting in the direction that should be optimal?

This is considered to be related to the anisotropy peculiar to the compound semiconductor. Since compound semiconductors are binary systems, there is room for complicated anisotropy. FIG. 2, FIG.
FIG. 3 is a plan view and a perspective view showing a plane orientation of a crystal. The upper surface is shown as a (100) plane. Ingot (10
0) Since the wafer is cut, the wafer surface becomes parallel to the upper surface. The direction in which the wire cuts is perpendicular to this (0
± 1 ± 1), (00 ± 1), (0 ± 10), etc.
Here, an object having an off-angle of 15 degrees at the maximum is also considered, but is initially limited to a simple (100) plane.

In order to indicate the direction of the wafer, OF (0-
1-1) and IF (0-11) are attached. Both are cleavage planes. Conventionally, either OF or IF is determined in the traveling direction and traveling direction of the wire.

However, two cleavage directions (0-1-1),
(0-11) do not seem to be equivalent. FIG. 11 shows a depression formed when a Vickers indenter of a quadrangular pyramid is pressed against (100). The direction of the diagonal of the pyramid is the cleavage direction [0
-1-1] and [0-11]. Small grooves are formed in these directions. Larger grooves are obliquely generated in these directions. These are [01
0] and [001], but do not completely match. Rather, the direction in which the four oblique grooves enter makes an angle of about 35 ° with one of the cleavage directions [0-11]. About 55 ° to the other cleavage direction [0-1-1]
With an angle of

This is an anisotropy generated by embedding a completely symmetrical quadrangular pyramid in four directions. [0-1]
1] The direction is assumed to be the A direction. The [0-1-1] direction in which grooves are difficult to enter will be referred to as the B direction. All of them are cleavage directions, but there is anisotropy in the way of grooves when a pyramid is driven.

When the (100) plane is cut using a wire saw, cracks are formed in parallel from the wire saw, and the cracks become larger and the cuts become deeper. Then, when the wire saw moves in the direction A, cracks should easily occur. B
When moving in the direction, it is considered that cracks are less likely to occur and multiply.

Then, according to the above definition, it can be considered that a groove is not easily formed in the OF direction and a groove is easily formed in the IF direction. But it is not. The back surface of a wafer having a (100) plane is a (-100) plane. On the back side, the way of entering the groove is reversed. When the pyramid is pressed against the back surface, it is difficult to form a groove in the [0-11] direction. [0-
1-1] It is easy to form a groove in the direction. In other words, the direction in which the groove easily enters and the direction in which the groove does not easily enter the front and back sides of the wafer are rotated by 90 degrees.

The fact that grooves are easily formed is from the viewpoint of a crystal. From the viewpoint of the wire, the cutting resistance is small. The fact that grooves are difficult to enter means that the cutting resistance is large.

On the surface of the (100) wafer, IF
The direction is a small cutting resistance (A direction), and the OF direction is a large cutting resistance (B direction) (FIG. 9). On the back surface, the IF direction has a large cutting resistance (B direction) and the OF direction has a small cutting resistance (A direction) (FIG. 10). When cut into wafers, there is a difference between the front and back of the wafer.

However, when cutting an ingot with a wire saw, there is a difference on both sides of the wire. Although a new surface is created by being cut by the wire, the two opposing surfaces have different orientations of cutting resistance. This is shown in FIG. The case where the direction of the wire is parallel to the cleavage direction is shown. Since it is cut by the wire, surfaces C and D are created on both sides thereof. On the surface C, the lateral direction is the direction in which the cutting resistance is small (A direction). On the surface D, the lateral direction is the direction in which the cutting resistance is large. The directions of the grooves generated by the quadrangular pyramids on the plane C and the plane D are illustrated.

Since the wire reciprocates in the lateral direction, the surface C has a small cutting resistance. Surface D has a large cutting resistance. This is the same when the wire advances in the Y direction and when the wire retreats in the -Y direction. It is not compensated by reciprocating motion. For this reason, the wire gradually increases the cutting resistance D
It is presumed that it moves away from the surface and approaches the C surface where the cutting resistance is small.

This direction is defined as -X. The traveling direction of the wire is Y, and the traveling direction is Z. Now, it is assumed that the origin is the center of the cut surface and the coordinate is X where the axial direction of the ingot is X. In this coordinate system, the direction of the small cutting resistance is the Y direction on the C plane and the Z direction on the D plane. The bending amount of the wire is determined by the difference T between the wire tension T and the cutting resistance. The magnitude of the cutting resistance depends on the length L of the wire in contact with the surface of the ingot.

At the beginning of cutting, the contact length between the wire and the surface is short. Therefore, the difference in cutting resistance is small and the deflection is small. However, as the cutting progresses, the contact area between the wire and the surface increases. The radius of the ingot is R, and the cutting depth is Q. The Z coordinate of the wire and the cutting depth Q have a relationship of Z = QR. That is, Z is (Q = 0) -R at first, passes through 0, and increases to + R (Q = 2R). This is the end of cutting. The contact length L of the wire with the ingot is

L = 2 (2RQ−Q ² ) ^1/2 (1) L = 2 (R ² −Z ² ) ^1/2 (2)

Is as follows. Cutting resistance continues to increase until the wire reaches the center of the ingot, and their difference continues to increase.
However, when the wire cut more than half and passed the center,
The contact length L starts to decrease. So the difference in cutting force also starts to decrease. That is, in the process from the beginning to the end of cutting, the ratio S / T of the cutting resistance difference S and the tension T increases at first,
Decrease later. The tension is constant. The cutting resistance difference S is proportional to the contact length L. The wire first shifts to the left and then shifts to the right. The leftward displacement is proportional to the above L. Therefore, the deviation Δx of the leftward wire is

Δx = −K (R ² −Z ² ) ^1/2 (3)

Is as follows. The reason why-is attached is that the direction of high cutting resistance and low cutting resistance is assumed as shown in FIG.
K is a proportionality constant and is K = 2σ / T (σ is a difference in cutting resistance per unit length). Then, the cross section of the cut ingot is as shown in FIG. This explains why the cross section becomes convex right. Equation (3) expresses this convex distortion.

The present invention solves this difficulty as follows. If the cutting resistance is always the same on the left and right, such lateral displacement of the wire should be prevented. To do so, both surfaces created by the wire must have a large cutting force (B) in a direction at 45 degrees to the direction of the wire.
Direction) and a small cutting resistance (A direction). This is shown in FIG. The wire cuts the ingot, creating an E-plane and an F-plane. On the E surface, the direction (A direction) where the cutting resistance is small extends in the -YZ direction. On the F-plane, the direction of the small cutting resistance extends in the YZ directions. In any of the surfaces E and F, the wire travels in a direction in which the cutting resistance takes an intermediate value. Therefore, a difference in cutting resistance does not occur between the E surface and the F surface.

This will be described more microscopically. In FIG. 13, when the wire moves forward (Y direction), the cutting resistance is small on the surface E and large on the surface F. On the other hand, when moving backward (−Y direction), the cutting resistance is large on the surface E and small on the surface F. The wire reciprocates. Therefore, by the reciprocating operation, the surface E,
The difference in cutting force at F is averaged.

Actually, when the ingot was fixed at the azimuth rotated by 45 degrees and cut by the wire saw, the wire did not bend to the left or right. That is, the cut surface was perpendicular to the axis. FIG. 14 shows the cutting line. The cutting line is a clean straight line. This is a direction in which the ingot makes an angle of 45 degrees with respect to the Z direction (the traveling direction of the wire: the feeding direction).

That is, the Z direction is [00-1] and the Y direction is [010], or the Z direction is [0-10] and the Y direction is “001”. Since the resistance is balanced, the deflection of the wire is eliminated, that is, the traveling direction and the traveling direction of the wire may be [00 ± 1] and [0 ± 10].

This is one of the optimum conditions. Actually, there may be a case where the angle may deviate from this by 22.5 °. How much surface distortion does the deviation from optimal conditions allow? It depends on the condition. In the example described below, the wire is run in the cleavage direction as before, and the surface is deformed (WARP).
Is 12 μm, the wire is run in the 45-degree direction and the distortion is 4 μm. If the allowable distortion value is 8 μm, a deviation of 22.5 degrees is permitted. The deviation from the cleavage direction is 22.5 degrees to 67.5 degrees.

If the conditions are further severe, the deviation from 45 degrees is suppressed to about 10 degrees. That is, the deviation from the cleavage direction is 35 degrees to 55 degrees. The angle between the cleavage direction and the traveling direction (Y) of the wire is defined as Φ. The resistance on the surface E is C + σcosΦ, and the resistance on the surface F is C + σsinΦ
Becomes Then the difference between left and right cutting forces is 2 ^1/2 σ sin
(Φ−π / 2). In other words, the leftward shift of the wire

Δx = −2 ^3/2 σ (R ² −Z ² ) ^1/2 sin (Φ−π / 2) (4)

Is obtained. If Φ is 45 degrees or less, the cutting line is convex in the −X direction as shown in FIG. If Φ is 45 degrees or more, the cutting line is convex in the + X direction. The maximum deviation is Z = 0
And assign

Δxmax = −2 ^3/2 σRsin (Φ−π / 2) (5)

Is obtained. The upper limit of the angle Φ between the wire direction and the cleavage direction is determined by the conditions imposed on the wafer cutting shape. Here, Φ is primarily Φ = 22.5 to 67.
5 degrees

[0064]

[Example] <100> by the LEC method with a diameter of 76 mm
The ingot of the undoped GaAs crystal pulled in the direction is cut into (100) wafers. Using a wire saw device as shown in FIG. 1, the wafer is cut into many wafers at once. Processing was performed by two types of cutting methods A and B having different ingot mounting directions and running directions, and the results were compared. First, the common conditions are as follows.

Workpiece: LEC method AMP <100> GaAs single crystal Diameter 76 mm Abrasive: GC # 2000 Wrapping oil: PS-LP500 (12 kg /
10L) Cutting speed (feed) Vz: 4 mm / h Wire linear speed Vy: 100 m / min Wire diameter: φ0.12 mm

Method A (conventional method: comparative example) (011) Surface support. Wire traveling direction Z = <011>, wire traveling direction Y = <01-1> Method B (Invention: Example) (010) Surface support. Wire traveling direction Z = <010>, wire traveling direction Y = <0
01>

[Explanation of Comparative Example] In the case of the method A, the wire was bent in one direction in the middle, so that a wafer having good flatness could not be obtained. FIG. 15 is a plan view and a height profile diagram showing the distribution of the height of the surface of the wafer cut by the method A. One scale is 0.50 μm. Wire moves from top to bottom in plan view (Z direction)
doing. That is, the horizontal direction in the plan view is the traveling (reciprocating) direction Y of the wire. They are approximately the same height in the direction of travel of the wire.

However, the height greatly differs in the traveling direction (Z). It is high at the beginning (top) of cutting, low at the middle, and high again at the end of cutting. The anisotropy in the Z direction is large. In this cutting method, both the Y direction (running direction) and the Z direction (traveling direction) are cleavage directions. When viewed from the Y direction, it has a large concave shape. This is the beginning of the wire X
This indicates that the sheet is bent in the direction (perpendicular to the plane of the paper and the back direction), and returns to the −X direction after passing through the center.

Here, a parameter called WARP is used to evaluate the variation in the height of the non-planar surface. This is the difference between the height of the highest point and the height of the lowest point for this plane given an average plane. A parameter called BOW was also measured. This is the height of the central part from a plane including the peripheral part of the wafer. The sample of FIG.
1.4 μm, bow is 2.1 μm.

Actually, 34 wafers are cut out from the same ingot by the method A. Several parameters were measured for these wafers. FIG. 1 shows a histogram of WARP for measuring the height of a surface.
FIG. The horizontal axis is the value of WARP. The vertical axis is the number of samples having that value. There are nine WARPs having a size of 10 μm and eight having a size of 11 μm. In addition, 8μ
It is widely distributed between m and 14 μm. The average value of WARP is 10.07 μm. The standard deviation σ was 1.44 μm.

[Explanation of Example] In the case of the method B, the wire was not bent in any direction, and a straight line could be maintained from the beginning to the end. FIG. 16 is a plan view and a height profile diagram showing the distribution of the height of the surface of the wafer cut by the method B. One scale is 0.50 as before
μm. In the plan view, the wire advances from the upper right to the lower left (Z direction). That is, the direction (45 degrees) of clockwise rotation from horizontal in the plan view is the traveling (reciprocating) direction Y of the wire.
Unlike the case where the cutting is performed by the method A, the surface height is substantially the same in both the traveling direction of the wire (Y direction) and the traveling direction of the wire (Z direction). Of course, contour lines appear in the plan view, but their density is sparser than in the previous example.

From the perspective view, it can be seen that the waves are waving at an angle of 45 °. Since the wire traveling direction is the Y direction, this wave is formed by the weak wire motion.

In the example shown in FIG. 16, WARP is 3.7.
μm. bow is 0.6 μm. Compared with the example of FIG. 15, the WARP is reduced to about 1/3.

WARP was measured for 25 wafers cut from the same ingot with a wire saw. FIG. 18 shows the histogram. The horizontal axis is the value of WARP (in 1 μm increments), and the vertical axis is the number of wafers taking values within that range. The average value was 3.34 μm. The standard deviation σ is 0.72 μm. WARP is also reduced to one third as compared with the case of the histogram shown in FIG. Further, the standard deviation has been reduced to almost half.
According to the present invention, the WARP is small, and the variation of the WARP is small.

[0075]

The cutting by the wire saw cannot be cut into a flat surface due to the temporal bending of the wire, and has not been applied to the cutting of compound semiconductor single crystal wafers. The present invention makes it possible for the first time to cut a single crystal ingot grown to <100> into a (100) ± 15 ° wafer by a wire saw.

In this method, the cutting direction is removed from two orthogonal cleavage planes, and the anisotropy of the orthogonal cleavage plane is averaged. Ideally, the running direction (Y direction) of the wire saw is at 45 degrees to the cleavage direction. That is, the traveling direction is set to [00 ± 1] or [0 ± 10]. These exist four around the <100> axis.

When projected on the YZ plane, there are four angles Φ formed with the Y axis in four directions of 0 °, 90 °, 180 °, and 270 °. The range may be ± 45 °. Since the single crystal ingot of the compound semiconductor can be cut by the wire saw, the following excellent effects are obtained.

Conventionally, Ga has been produced by an inner peripheral slicer.
The ingot of As and InP was cut, and this had a cutting margin of 300 μm. Too much cutting margin loss. Since the present invention enables cutting with a wire saw, the cutting margin can be suppressed to 200 μm or less. Material loss can be reduced to 2/3 or less. In the case of an expensive material such as GaAs, the effect of reducing such cut-off loss is significant.

Cutting with a wire saw causes less material damage than cutting with a conventional inner peripheral blade slicer. Therefore, a thinner wafer can be cut out. For example, it is very difficult to cut a 3-inch GaAs ingot to a thickness of 400 μm using an inner peripheral slicer.

However, according to the wire saw, 3 inch GaAs
s can be cut into wafers having a thickness of 400 μm.
Because thinner wafers can be cut, more wafers can be produced from ingots of the same length. Combined with the advantage of a small cutting margin, the manufacturing cost per wafer can be significantly reduced.

When cutting any kind of compound semiconductor crystal, the cutting time can be shortened with the wire saw compared with the inner peripheral slicer. Equipment productivity is improved. This is because the wafers are not cut one by one but cut in parallel at once.

In the case of a crystal having strong anisotropy, a long cutting time was required for the inner peripheral slicer. For example, in the case of a 3 inch ingot, a GaAs crystal to which a small amount of Si is added takes 15 minutes or more to cut with an inner peripheral slicer. If 100 pieces are cut, it is 1500 minutes (25 hours). If you can use a wire saw, 10
Since 0 sheets can be cut, the feed speed Vy is set to 1 mm /
h can be cut in about 8 hours. Cutting time can be greatly reduced. The more difficult the material is to cut, the longer it takes, so the effect of time reduction is great.

In the wire saw, after the ingot and the wire are attached, the operation becomes completely automatic, so that no manual operation is required. Labor saving can increase productivity.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view of a wire saw.

FIG. 2 is a plan view showing a plane orientation of a plane of a group III-V compound semiconductor crystal.

FIG. 3 is a perspective view showing the orientation of each surface of a group III-V compound semiconductor crystal.

FIG. 4 shows a GaAs ingot (1)
An electron micrograph of the (100) plane when cut parallel to (00). The magnification is 100 times.

FIG. 5 shows a GaAs ingot (1)
An electron micrograph of the (100) plane when cut parallel to (00). Magnification is 200 times.

FIG. 6 shows a GaAs ingot (1)
An electron micrograph of the (100) plane when cut parallel to (00). The magnification is 1000 times.

FIG. 7 shows a GaAs ingot (1)
An electron micrograph of the (100) plane when cut parallel to (00). The magnification is 3000 times.

FIG. 8 is a central longitudinal section of the ingot for showing the bending of the cut surface when the ingot is cut by running the wire saw in a direction parallel to the cleavage plane and advancing the wire saw in a direction parallel to the other cleavage plane. FIG.

FIG. 9 is a plan view showing the direction in which cracks occur when a quadrangular pyramid indenter is pressed against the surface of a (100) wafer.

FIG. 10 is a plan view showing the direction in which cracks occur when a quadrangular pyramid indenter is pressed against the back surface of a (100) wafer.

FIG. 11 is a micrograph of a crack derived from a concave portion when a quadrangular pyramid indenter is pressed against a (100) wafer. The vertical direction is the <0-1-1> direction, and the horizontal direction is the <01-1> direction. The cracks do not make 45 ° to these directions. It extends at an angle of about 35 degrees with respect to the <01-1> direction.

FIG. 12 is a central longitudinal cross-sectional view of the ingot cut along a plane including the axis of the GaAs ingot when the wire runs parallel to the cleavage direction and advances in another cleavage direction. The direction in which cracks extend on both sides of the kerf is schematically illustrated.

FIG. 13 includes the axis of the GaAs ingot when the wire is run in a direction at 45 ° to the cleavage direction and the wire is advanced (feeded) in a direction at 45 ° to another cleavage direction. FIG. 3 is a central vertical cross-sectional view of the ingot cut along a plane. The direction in which cracks extend on both sides of the kerf is shown.

FIG. 14 shows a graph of 45 to cleavage plane according to the concept of the present invention.
Run the wire in the direction of
When sending the wire in the direction of the angle of
FIG. 3 is a central longitudinal sectional view of the ingot for showing a path along which the wire cuts the ingot.

FIG. 15 is a plan view and a perspective view showing a height distribution of a surface of a cut wafer in a case where a wire runs parallel to a cleavage direction and a wire advances parallel to another cleavage direction (conventional method). One line represents a height of 0.5 μm.

FIG. 16 shows a case where a wire runs parallel to a plane that forms an angle of 45 ° with respect to the cleavage direction, and the wire advances in a direction that forms an angle of 45 ° with another cleavage direction. The top view and perspective view which show the height distribution of the surface.

FIG. 17 is a histogram of WARP of 34 wafers cut out by a conventional method. The horizontal axis shows the value of WARP (in 1 μm increments), and the vertical axis shows the frequency.

FIG. 18 is a histogram of WARP of 25 wafers cut out according to the present invention. The horizontal axis shows the value of WARP (in 1 μm increments), and the vertical axis shows the frequency.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Multi-groove roller 2 Multi-groove roller 3 Multi-groove roller 4 Wire 5 Ingot table 6 Jig 7 Ingot 8 Groove 11 Groove 12 Groove 13 Groove

Claims (2)

(57) [Claims] When a wafer having a plane orientation within {100} ± 15 ° from a III-V compound semiconductor single crystal ingot is cut by a wire saw, the direction in which the wire reciprocates is from the cleavage direction of the ingot single crystal. 22.5 ° -6
It is characterized in that the direction is 7.5 ° away.
A method for cutting a group III-V compound semiconductor crystal. 2. The III-V compound semiconductor crystal according to claim 1, wherein the direction in which the wire reciprocates is a direction away from the cleavage direction of the ingot single crystal by 35 ° to 55 °. Cutting method.