JP2962021B2 - Wire saw and its cutting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wire saw for forming a wafer by cutting a workpiece such as a semiconductor ingot and a method for cutting the same.

[0002]

2. Description of the Related Art In a wire saw, a workpiece such as a semiconductor ingot is pressed against a row of wires at a constant pitch parallel to each other, and while the wire is fed in the line direction, an abrasive grain is contained between the workpiece and the wire. By supplying the liquid, the workpiece is cut by the lapping action to form a wafer, and a large number of wafers having a constant thickness can be obtained at the same time. The time required for one cut is, for example, 5 mm in diameter.
6 hours for an inch silicon semiconductor ingot. During this time, it is necessary to increase the surface accuracy of the wafer by keeping the cutting conditions constant.

[0003]

However, it is not easy to keep the cutting conditions constant, and undulation occurs on the wafer surface. In today's finer circuit, undulations on the wafer surface greatly reduce the yield of semiconductor devices.

An object of the present invention is to provide a wire saw capable of reducing the undulation of a cut and formed wafer and a method of cutting the same in view of the above problems.

[0005]

The wire saw and the cutting method according to the present invention will be described with reference to the reference numerals of the corresponding components in the embodiment drawings.

In this wire saw cutting method, for example, as shown in FIGS. 1 and 4, a workpiece 40 is pressed against a row of wires 12 parallel to each other, and by supplying a working fluid containing abrasive grains between the wire 12, there forms a plurality of wafers simultaneously by cutting the workpiece 40 in the wrapping action, by the rotation of the motor 54, the wire 12 respect to linearly move the workpiece 40 in a direction of pressing the workpiece 40, the linear movement velocity, i.e. the cutting speed, for example 2, by periodically changing as shown in FIG. 5 or 6,
The linear movement speed pattern is a series of multiple convex patterns
To be in.

[0007] A wire saw for carrying out this method comprises:
A motor 54, by the rotation of the motor 54, the linear movement device 42 to 52 for linearly moving a workpiece 40 in a direction of pressing the workpiece 40 with respect to the wire 12, the speed of the based-out linear movement of the setting pattern Periodically change the speed
Pattern is a series of multiple convex patterns
And a control unit 56 and 58 you on.

[0008] Even if the cutting speed is kept constant as in the prior art, the cutting time is long, for example, 6 hours, so that cutting conditions such as temperature change and undulation occurs on the surface of the cut wafer. On the other hand, when the cutting speed is changed in a cycle of, for example, one hour as in the present invention, as shown in FIG.
An undulation is generated in this cycle on the cut surface S of the wafer 40a. The amplitude of this undulation is smaller than before. This can be considered that the swell generated when the cutting time is one cycle, for example, one hour, is repeated a plurality of times.

In the first aspect of the present invention, the set pattern is a repetition of the same convex basic pattern, for example, as shown in FIG. 2 or FIG.

In the case of this configuration, setting of the pattern is facilitated.

In the second aspect of the present invention, the setting pattern increases the contact length between the wire 12 and the workpiece 40.
As the maximum speed of the above-mentioned linear movement becomes slower,
It is a modified version of the pattern .

In this configuration, the pattern of the cutting resistance becomes substantially the same in each cycle, and the amplitude of the undulation formed on the surface of the cut wafer can be made substantially the same in each cycle. Can be smaller.

In a third aspect of the present invention, the speed of the linear movement is
By changing the degree periodically, one of the above workpieces can be cut
On the other hand, the convex linear movement speed pattern is repeated 4 to 8 times.

If the number of repetitions is too small, the effect of the present invention is reduced, and if the number of repetitions is too large, the average cutting speed is reduced and the time required for cutting is lengthened. A preferred range of the number of repetitions is about 4 to 8.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

First Embodiment FIG. 4 shows a schematic configuration of a wire saw.

The rolling devices 10A having the same configuration as each other,
10B and 10C are arranged with their axes parallel to each other,
A wire 12 is wound around a ring-shaped groove formed at a constant pitch on the surface of these rollers. The rolling devices 10A, 10B, and 10C are interlocked and rotated by a mechanism (not shown).

The starting end of the wire 12 is connected to a tension adjusting mechanism 20.
Is wound around the wire take-up drum 22.
The wire winding drum 22 is driven to rotate by a torque motor 24. Tension adjusting mechanism 20 and wire winding drum 22
Is adjusted by the voltage applied to the torque motor 24, and the tension of the wire 12 between the tension adjusting mechanism 20 and the rolling device 10C is adjusted to be constant by the tension adjusting mechanism 20.

Similarly, the terminal end of the wire 12 is wound around a wire winding drum 32 via a tension adjusting mechanism 30. The wire winding drum 32 includes a torque motor 34.
Is driven to rotate. The tension of the wire 12 between the rolling device 10C and the tension adjusting mechanism 30 is adjusted to be constant by the tension adjusting mechanism 30, and the tension of the wire 12 between the tension adjusting mechanism 30 and the wire winding drum 32 is reduced by a torque motor 34. Is adjusted by the voltage applied to.

The workpiece 40 is, for example, a semiconductor ingot, and its orientation flat surface is adhered to the work holder 12. The work holder 12 is shown in FIG.
Is driven up and down by the device shown in FIG.

At one end of the work holder 42, one end of a shaft 44A is fixed vertically to the upper surface of the work holder 42. The shaft 44A penetrates a fixedly mounted guide cylinder 46A with the axial direction being vertical, and is guided in the vertical direction.
Similarly, one end of a shaft 44 </ b> B is fixed to the other end of the work holder 42 perpendicular to the upper surface of the work holder 42. The shaft 44B penetrates a fixedly mounted guide cylinder 46B with the axial direction being vertical, and is guided in the vertical direction. At the center of the work holder 42, one end of a feed screw 48 is fixed perpendicular to the upper surface of the work holder 42. The feed screw 48 is screwed into a screw hole of a gear 50 that is supported on the fixed side. The gear 50 is connected to the motor 5 via a speed reducer 52.
4 is driven to rotate.

The speed controller 56 controls the rotation speed of the motor 54 according to the rotation speed pattern set in the program setting device 58.

Next, the operation of the wire saw configured as described above will be described.

The workpiece 40 is lowered, the workpiece 40 is brought into contact with the wire 12, Wa tire 12 is traveling in the line direction, against which working fluid containing abrasive grains flow in the wire 12. When the workpiece 40 is lowered in this state, the workpiece 40 is cut by the lapping action, and a large number of wafers are simultaneously formed.

FIG. 2 shows a pattern of the cutting speed with respect to the time t after the start of cutting, that is, the processing speed of the workpiece 40. In the program setting unit 58, a motor rotation speed pattern corresponding to this pattern is set. In this example, the cutting speed is increased from 0 μm / min to 600 μm / min in a one-hour cycle, and then the speed is maintained for a certain period of time and decreases from 600 μm / min to 0 μm / min . Such a basic pattern is repeated six times for cutting one workpiece 40.

Even if the cutting speed is kept constant as in the prior art, the cutting time is long, so that cutting conditions such as temperature change, and the surface of the cut wafer undulates. In contrast,
When the cutting speed is changed in a cycle of one hour as described above,
As shown in FIG. 3A, undulations occur on the cut surface S of the wafer 40a in a cycle of one hour. The amplitude of this undulation is smaller than before. This can be considered that the swell generated when the cutting time is one hour is repeated six times.

In the next step, the wafer 40a is formed using free abrasive grains.
When the lapping process is performed on the surface plate, the surface S of the wafer 40a is
3B, and this portion is removed, and as shown in FIG. 3B, a wafer 40b having a flat surface is obtained. Next, when the wafer 40b is immersed in an etching solution such as a mixed acid solution for a predetermined time, the work strain layer near the surface of the wafer 40b is removed.

When the lapping process and the etching process are performed on the wafer cut by the conventional method and the wafer cut by the present embodiment under the same conditions, the final waviness is 40 to 60 μm. However, it became 20 μm or less. However, the size of the undulation is defined by measuring a surface height curve from one end to the other end of the diameter line of the wafer, using a straight line connecting the one end and the other end as a base line, and projecting the surface height curve from the base line. Side maximum height a and concave side maximum height b (a> 0,
b> 0) is assumed to be a + b. For measuring swell, use Perthe
A Pertometer model S6P from n companies was used.

In FIG. 2, the basic pattern is repeated six times. If the number of repetitions is too small, the effect of the present invention is reduced, and if the number of repetitions is too large, the average cutting speed is reduced and the time required for cutting is increased. . It was found that the preferable range of the number of repetitions was about 4 to 8.

[Second Embodiment] FIG. 5 shows a pattern of the cutting speed with respect to time t after the start of cutting in the second embodiment.
In this example, the cutting speed is changed periodically in the range of 200 to 540 μm / min, and the average cutting speed is higher than in the first embodiment.

The other points are the same as in the first embodiment.

[Third Embodiment] FIG. 6 shows a pattern of the cutting speed with respect to the time t after the start of cutting in the third embodiment.
In this example, the maximum cutting speed in each cycle is determined by the cutting diameter d.
As the length (the length d during which the wire 12 is simultaneously in contact with the workpiece 40) becomes longer, the cutting resistance pattern is made substantially the same in each cycle.

By doing so, the amplitude of the undulation formed on the surface S of the wafer 40a can be made substantially the same in each cycle, so that the undulation can be made smaller than in the first and second embodiments. it can.

The other points are the same as the first embodiment.

Note that a period T where f (t) = f (t + T) is satisfied.
A pattern f (t) g (d) obtained by multiplying the above pattern by a function g (d) whose value decreases as the cutting diameter d increases,
The program setting unit 58 is used as a motor rotation speed pattern.
May be set.

[0036]

As described above, in the wire saw and the cutting method according to the present invention, the speed of linearly moving the workpiece in the direction in which the workpiece is pressed against the wire is periodically changed. The undulation is formed on the surface of the wafer thus formed at this cycle, which has an effect that the amplitude of the undulation can be reduced as compared with the conventional case, and greatly contributes to the improvement in the yield of the semiconductor device.

In the first aspect of the present invention, since the set pattern is a repetition of the same basic pattern, there is an effect that the pattern can be easily set.

In the second aspect of the present invention, the setting pattern is such that the longer the contact length between the wire and the workpiece is, the more the straight line becomes.
Since the convex basic pattern is modified so that the maximum speed of movement is reduced , the pattern of the cutting resistance becomes substantially the same in each cycle, and the undulation formed on the surface of the cut wafer. Can be made almost the same in each cycle,
This has the effect that the swell can be reduced.

In the third aspect of the present invention, since the number of repetitions is 4 to 8, the effects of the present invention are sufficiently obtained, and the average cutting speed is reduced and the time required for cutting becomes too long. This has the effect that it can be avoided.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an apparatus for elevating and lowering a workpiece of a wire saw according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a change in a cutting speed with respect to a time after the start of cutting according to the first embodiment of the present invention.

FIG. 3 is a cross-sectional view showing a wafer surface shape after cutting and lapping.

FIG. 4 is a schematic configuration diagram of a wire saw according to an embodiment of the present invention.

FIG. 5 is a diagram showing a pattern of a cutting speed with respect to a time after the start of cutting according to a second embodiment of the present invention.

FIG. 6 is a diagram showing a pattern of a cutting speed with respect to a time after the start of cutting according to a third embodiment of the present invention.

[Explanation of symbols]

 10, 10A, 10B, 10C Rolling device 10 Wire 20, 30 Tension adjusting mechanism 22, 32 Wire winding drum 24, 34 Torque motor 40 Workpiece 40a, 40b Wafer 42 Work holder 44A, 44B Shaft 46A, 46B Guide cylinder 48 Feed screw 50 Gear 52 Reducer 54 Motor 56 Speed controller 58 Program setting device

Claims (5)

(57) [Claims] 1. A workpiece (40) is pressed against a row of mutually parallel wires (12) and contains abrasive grains between the workpiece and the wire while feeding the wire in the direction of the wire. In a wire saw cutting method for cutting a workpiece by a lapping action to form a plurality of wafers at the same time by supplying a working fluid, the rotation of a motor causes the workpiece to be wound on the wire. by linearly moving the workpiece into the press against direction, by periodically changing the linear movement <br/> speed, the linear moving speed pattern double
A wire saw cutting method, characterized in that a number of convex patterns are connected . 2. A workpiece (40) is pressed against a row of mutually parallel wires (12) and contains abrasive grains between the workpiece and the wire while feeding the wire in its linear direction. In a wire source for cutting a workpiece by a lapping action to form a plurality of wafers at the same time by supplying a working fluid, a motor (54) and the rotation of the motor cause the wire to be connected to the wire. a linear movement device (42 to 52) for linearly moving the workpiece in a direction of pressing the against the workpiece, by periodically changing the speed of the based-out straight line moves to the setting pattern, the velocity The pattern is a series of multiple convex patterns
Wire saw, characterized in that it comprises a be that the control device so that the form and (56, 58), the. 3. The wire saw according to claim 2, wherein the setting pattern is a repetition of the same convex basic pattern. 4. The method according to claim 1, wherein the setting pattern includes the wire (1).
2) the longer the contact length between the workpiece (40) and
The convex basic pattern is designed to reduce the maximum speed of the linear movement.
3. The method according to claim 2, wherein the turn is modified.
The described wire saw. 5. The method according to claim 5, wherein the speed of the linear movement is periodically changed.
, The convex linear movement speed for cutting one of the workpieces
The degree pattern is repeated 4 to 8 times.
The method of claim 1.