JPH068234A - Wire saw and cutting method therewith - Google Patents

Abstract

PURPOSE:To reduce undulation of a wafer formed by being cut off, by a method wherein a speed moving linearly a work in the direction pressing the work against a wire is changed periodically. CONSTITUTION:A work 40 is pressed against a row of wires which are in parallel with each other and a processing liquid containing an abrasive grain is supplied between the work 40 and wire 12 while feeding the wire in its wire direction. With this construction, the work 40 is cut off by a lapping action. Hereupon, a speed moving the work 40 linearly in the direction pressing the work 40 against the wire 12, that is, a cutting speed is changed periodically. Therefore, a wire saw is provided with linear moving devices 42-56 moving linealy the work 40 in the direction pressing the work 40 against a motor 54 and the wire 12 and control devices 56, 58 changing periodically a turning speed of the motor 54 based on an established pattern.

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 cutting a workpiece such as a semiconductor ingot to form a wafer, and a method for cutting the wire saw.

[0002]

2. Description of the Related Art A wire saw presses a work piece such as a semiconductor ingot against a row of wires having a constant pitch parallel to each other, and feeds the wire in the direction of the wire while including abrasive grains between the work piece 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 simultaneously obtained. The time required for one cutting is, for example, a diameter of 5
Inch silicon semiconductor ingot for 6 hours. 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 waviness occurs on the surface of the wafer. In today's circuit miniaturization, waviness on the surface of a wafer greatly reduces the yield of semiconductor devices.

In view of such problems, an object of the present invention is to provide a wire saw capable of reducing the waviness of a wafer formed by cutting and a method for cutting the same.

[0005]

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

In this wire saw cutting method, for example, as shown in FIGS. 1 and 4, the workpiece 40 is pressed against the parallel rows of the wires 12, and the wire 12 is fed in the direction of the workpiece 40, while the workpiece 40 is cut. By supplying a working liquid containing abrasive grains to the wire 12, the work 40 is cut by a lapping action, and the work 40 is pressed in the direction of pressing the work 40 against the wire 12. The linear moving speed, that is, the cutting speed is periodically changed as shown in FIG. 2, FIG. 5 or FIG.

The wire saw for carrying out this method is
The motor 54, the linear movement devices 42 to 52 that linearly move the workpiece 40 in the direction of pressing the workpiece 40 against the wire 12 by the rotation of the motor 54, and the rotation speed of the motor 54 based on the set pattern. And control devices 56 and 58 for changing the period periodically.

Even if the cutting speed is constant as in the conventional case, the cutting time is long, for example, 6 hours, so that the cutting conditions such as temperature change and the waviness occurs on the surface of the cut wafer. On the other hand, when the cutting speed is changed in a cycle of, for example, 1 hour as in the present invention, as shown in FIG.
The undulation occurs on the surface S of the cut wafer 40a in this cycle. The amplitude of this waviness is smaller than in the past. This can be considered that the undulation that occurs 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 basic pattern as shown in FIG. 2 or 5, for example.

With this configuration, it becomes easy to set the pattern.

In the second aspect of the present invention, the set pattern is such that the motor rotation speed becomes slower as the length of the wire 12 in contact with the workpiece 40 becomes longer with respect to the repetition of the same basic pattern. It is a modified version.

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

In the third aspect of the present invention, the number of repetitions is 4-8.

If the number of repetitions is too small, the effect of the present invention becomes small, and if the number of repetitions is too large, the average cutting speed becomes small and the time required for cutting becomes long. The preferable 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. 3 shows a schematic structure of a wire saw.

Rolling devices 10A having the same structure as each other,
10B and 10C are arranged with their axes parallel to each other,
The wire 12 is wound around ring-shaped grooves 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 side of the wire 12 has a tension adjusting mechanism 20.
It is wound around the wire winding drum 22 via.
The wire winding drum 22 is rotationally driven by a torque motor 24. Tension adjusting mechanism 20 and wire winding drum 22
The tension of the wire 12 between the tension adjusting mechanism 20 and the rolling device 10C 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 by the tension adjusting mechanism 20.

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

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

At one end of the work holder 42, one end of a shaft 44A is fixed perpendicularly to the upper surface of the work holder 42. The shaft 44A penetrates a guide cylinder 46A that is fixed with the axial direction vertical and is guided in the vertical direction.
Similarly, one end of a shaft 44B is fixed to the other end of the work holder 42 perpendicularly to the upper surface of the work holder 42. The shaft 44B penetrates a guide cylinder 46B that is fixed with the axial direction 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 vertically to the upper surface of the work holder 42. The feed screw 48 is screwed into a screw hole of a gear 50 axially supported on the fixed side. The gear 50 is connected to the motor 5 via the speed reducer 52.
It is rotationally driven at 4.

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 constructed as described above will be described.

The work piece 40 is lowered, the work piece 40 is brought into contact with the wire 12, and the grooved roller tension adjusting mechanism 20 is provided.
Is rotated so that the wire 12 travels in the line direction, and a working liquid containing abrasive grains is applied to 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. The motor speed pattern corresponding to this pattern is set in the program setting unit 58. In this example, the cutting speed is 0 μ / m to 600 in a cycle of 1 hour.
After increasing to μ / m, this speed is maintained for a certain time,
It decreases from 600 μ / m to 0 μ / m. Such a basic pattern is repeated 6 times for cutting one workpiece 40.

Even if the cutting speed is constant as in the conventional case, since the cutting time is long, the cutting conditions such as the temperature are changed and the undulation occurs on the surface of the cut wafer. In contrast,
When the cutting speed is changed in a cycle of 1 hour as described above,
As shown in FIG. 3A, the undulation occurs on the surface S of the cut wafer 40a in a cycle of 1 hour. The amplitude of this waviness is smaller than in the past. It can be considered that the swell generated when the cutting time is 1 hour is repeated 6 times.

Wafer 40a is formed by using loose abrasive grains in the next step.
When lapping is applied to the surface of the wafer 40a, the surface S
The bumps are hit to remove this portion, 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 wafer cut by the conventional method and the wafer cut by this embodiment were subjected to the lap treatment and the etching treatment under the same conditions, the final undulation size was 40 to 60 μm. The reason was 20 μm or less. However, the size of the waviness is defined by measuring the surface height curve from one end to the other end of the diameter line of the wafer, taking the straight line connecting the one end and the other end as the base line, and projecting the surface height curve to the base line. Side maximum height a and concave side maximum height b (a> 0,
Let b + 0) be the sum a + b. For measuring swell, Perthe
Pertometer model S6P from n company was used.

In FIG. 2, the basic pattern is repeated 6 times, but if the number of repetitions is too small, the effect of the present invention becomes small, and if the number of repetitions is too large, the average cutting speed becomes small and the time required for cutting becomes long. . It was found that the preferable range of the number of repetitions is about 4 to 8.

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

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 the cutting in the third embodiment.
In this example, the maximum cutting speed in each cycle is defined as the cutting diameter d
By making the length (the length d at which the wire 12 is in contact with the workpiece 40 at the same time) longer, the cutting resistance pattern becomes substantially the same in each cycle.

In this way, since the amplitude of the undulations formed on the surface S of the wafer 40a can be made substantially the same in each cycle, the undulations can be made smaller than in the first and second embodiments. it can.

The other points are the same as those of the first embodiment.

The period T where f (t) = f (t + T)
Pattern f (t) g (d), which is obtained by multiplying the pattern No. by a function g (d) whose value becomes smaller as the cutting diameter d becomes longer,
Program setter 58 as a pattern of motor rotation speed
It may be set to.

[0036]

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

In the first aspect of the present invention, since the set pattern is the repetition of the same basic pattern, there is an effect that it is easy to set the pattern.

In the second aspect of the present invention, the set pattern is modified such that the motor rotation speed becomes slower as the length of the wire simultaneously contacting the workpiece becomes longer with respect to the repetition of the same basic pattern. Since the pattern of cutting resistance is almost the same in each cycle, the amplitude of the waviness formed on the surface of the cut wafer can be made almost the same in each cycle, and the waviness can be made smaller. It has the effect of being able to.

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

[Brief description of drawings]

FIG. 1 is a configuration diagram of a workpiece lifting device for a wire saw according to an embodiment of the present invention.

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

FIG. 3 is a cross-sectional view showing a wafer surface shape after cutting and after 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 cutting speed with respect to time after the start of cutting in the second embodiment of the present invention.

FIG. 6 is a diagram showing a pattern of cutting speed with respect to time after the start of cutting according to the 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 Speed reducer 54 Motor 56 Speed controller 58 Program setting device

Claims (5)

[Claims] 1. A work piece (40) is pressed against rows of wires (12) parallel to each other, and while the wire is fed in its linear direction, an abrasive grain is included between the work piece and the wire. In a wire saw cutting method of cutting a workpiece by lapping action by supplying a working liquid, a speed at which the workpiece is linearly moved in a direction of pressing the workpiece against the wire is periodically changed. A wire saw cutting method characterized by the above. 2. A work piece (40) is pressed against rows of wires (12) parallel to each other, and while the wire is fed in the direction of the wire, an abrasive grain is included between the work piece and the wire. A wire saw that cuts a workpiece by a lapping action by supplying a working liquid, a motor (54), and the rotation of the motor that moves the workpiece in a direction in which the workpiece is pressed against the wire. A wire saw comprising: a linear moving device (42 to 52) for linearly moving; and a control device (56, 58) for periodically changing the rotation speed of the motor based on a set pattern. 3. The wire saw according to claim 2, wherein the set pattern is a repetition of the same basic pattern. 4. The rotation speed of the motor (54) becomes slower as the length of the wire (12) in contact with the workpiece (40) becomes longer with respect to the repetition of the same basic pattern. The wire saw according to claim 2, wherein the wire saw is modified as follows. 5. The wire saw according to claim 3, wherein the number of repetitions is 4 to 8.