JP7447828B2 - How to cut the workpiece - Google Patents

Description

The present invention relates to a method for cutting a workpiece.

Conventionally, a wire saw has been known as a means for cutting out wafers from a workpiece such as a silicon ingot or a compound semiconductor ingot. In this wire saw, a wire row is formed by winding a large number of cutting wires (hereinafter simply referred to as wires) in a helical manner around a plurality of grooved rollers, and the cutting wires are axially wound. The workpiece is cut at each wire position simultaneously by being driven at high speed and feeding the workpiece into the wire array while appropriately supplying machining fluid (Patent Document 1).
In such a wire saw, for example, in a free abrasive type one, a slurry containing abrasive grains is used as the machining liquid. The abrasive grains are transported to the processing section by a wire driven at high speed, and the workpiece is ground by the abrasive action, thereby performing cutting.

Wires used in wire saws are generally straight wires, such as steel wires, as shown in Figure 3. A wire having a periodic wave shape as shown in Fig. 1 is also used. By trapping abrasive grains in its troughs, a wave-shaped wire can supply more abrasive grains to the processing section than a straight-shaped wire, and has excellent cutting efficiency. The wave height (amplitude) of a wire having a wave shape is mainly determined during wire manufacturing. In addition, in FIG. 2, the amplitude of the waveform is exaggerated with respect to the wire diameter (thickness of the line in FIG. 2) so that the waveform can be easily understood.

On the other hand, with wires that have a corrugated shape, it is difficult to select an amplitude suitable for the slurry used, and it is also difficult to manufacture a uniform amplitude in the longitudinal direction of the wire, so the amount of abrasive particles transported is unstable. Since the sharpness changes greatly during cutting, the shape accuracy of the cut wafer is inferior to that of a straight wire.

Japanese Patent Application Publication No. 2019-114690

The present invention has been made in view of the above-mentioned problems, and provides a method for cutting a workpiece using a wire having a corrugated shape, which has excellent cutting efficiency and excellent shape accuracy of the cut wafer. The purpose is to

In order to achieve the above object, the present invention forms a wire row by winding a wave-shaped wire around a plurality of grooved rollers, and while supplying slurry containing abrasive grains to the wire row, A method for cutting a workpiece using a wire saw, in which the workpiece is simultaneously cut at a plurality of locations lined up in the axial direction by applying tension to the wire and reciprocating it in the axial direction, and cutting and feeding the workpiece to the wire row. ,
The tension applied to the wire is in the range of 50% or more and 60% or less of the breaking strength of the wire, and
There is provided a method for cutting a workpiece, characterized in that the average amplitude of the waveform of the wire is in a range of 110% or more and 140% or less of the median diameter of the abrasive grains used for cutting.

In this way, by setting the tension applied to the wave-shaped wire (hereinafter simply referred to as tension) and the average amplitude of the wave shape within the above appropriate ranges, the sharpness is stabilized, resulting in excellent cutting efficiency and , it is possible to cut a workpiece with excellent shape accuracy of the cut wafer. Moreover, the risk of wire breakage can also be reduced.

At this time, the workpiece to be cut can be a silicon single crystal ingot.

In this way, a silicon single crystal wafer with good shape accuracy can be efficiently obtained.

As described above, with the workpiece cutting method of the present invention, it is possible to efficiently cut out high-quality wafers with excellent shape accuracy while suppressing the risk of wire breakage.

1 is a schematic diagram showing an example of a wire saw that can be used in the workpiece cutting method of the present invention. FIG. 2 is an explanatory diagram showing an example of a wire having a wave shape in a wire saw. FIG. 2 is an explanatory diagram showing an example of a linear wire in a wire saw.

Embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited thereto.
First, a wire saw that can be used in the workpiece cutting method of the present invention will be described with reference to FIG. As shown in FIG. 1, the wire saw 1 mainly includes a wire 2 for cutting a workpiece W, a plurality of grooved rollers 3 and 3' around which the wire 2 is wound, and grooved rollers 3 and 3' formed between the grooved rollers 3 and 3'. The wire row 11 that has been cut, the tension applying mechanisms 4 and 4' for applying tension to the wire 2, and the wire row 11 that can be cut and fed while holding the workpiece W to be cut, and that are opposite to the direction in which the cut is fed. It is equipped with a workpiece feeding means 5 that can also move the workpiece W relatively in the direction, and a machining fluid supply mechanism 6 having a nozzle 6a that supplies machining fluid (slurry containing abrasive grains) during cutting.

The wire 2 is unwound from one wire reel 7, passes through a traverser 8, passes through a tension applying mechanism 4 including a powder clutch (constant torque motor 9), and enters the grooved roller 3. The wire row 11 is formed by winding the wire 2 around the grooved rollers 3 and 3' about 400 to 500 times. The wire 2 is wound onto a wire reel 7' via a traverser 8' via another tension applying mechanism 4' consisting of a powder clutch (constant torque motor 9') or the like. Note that the wire 2 has a wave shape as shown in FIG. 2, and its relationship with the abrasive grains in the slurry satisfies certain conditions. This condition will be described later.

In such a wire saw 1, the workpiece W is cut and fed to the wire row 11 by the workpiece feeding means 5 while the wire 2 is reciprocated in the axial direction, thereby cutting the workpiece W at a plurality of locations lined up in the axial direction. Can be cut at the same time. Note that the reciprocating movement of the wire 2 is such that the wire 2 wound between the plurality of grooved rollers 3 and 3' is advanced by a predetermined length in one direction, and then moved in the opposite direction by a length smaller than the above-mentioned amount of advance. The wire 2 can be sent out in one direction by retracting the wire 2 and repeating this cycle as one feeding cycle. The grooved roller 3' is equipped with a drive motor 10, and the wire 2 wound around the grooved roller 3' can be driven in a reciprocating direction at a predetermined period.

Next, a method of cutting a workpiece according to the present invention using a wire saw 1 as shown in FIG. 1 will be described. Here, a case will be explained in which the work W to be cut is a silicon single crystal ingot and a silicon single crystal wafer is obtained, but the present invention is not limited to this, and other ingots such as compound semiconductor ingots can also be cut. It is also applicable to cases where

First, the wire saw 1 is prepared, and at this time, the relationship between the wire 2 and the abrasive grains satisfies certain conditions as described above by combining the wire 2 and the abrasive grains in the slurry used for cutting. The wire 2 may be prepared according to the abrasive grain to be used, or the abrasive grain may be prepared according to the wire 2 to be used. Specifically, the average value (average amplitude) of the height of the waveform of the wire 2 having a waveform is set to be in a range of 110% or more and 140% or less of the median diameter of the abrasive grains used for cutting. In this way, by setting the average amplitude of the wave shape of the wire 2 to 140% or less of the median diameter of the abrasive grains, the maximum diameter of the abrasive grains captured in the valleys of the wire and transported to the processing section is stabilized. Since the sharpness is stable, the shape precision of the wafer cut out from the workpiece W is improved. In addition, by setting the average amplitude of the wave shape of wire 2 to 110% or more of the median diameter of the abrasive grains, the abrasive grains with the median diameter that are expected to contribute the most to machining can be applied to the troughs of the wave shape of wire 2. The cutting efficiency is superior to that of a straight wire as shown in FIG. 3 because the wire is easily captured by the wire and transported to the processing section.
It is sufficient that the average value of the amplitudes satisfies the above conditions, but it is preferable to have a uniform amplitude because the above effects can be more reliably obtained. Further, when cutting, tension is applied to the wire 2, and the average amplitude here refers to a value before applying the tension.

Note that the combination of the wire 2 and abrasive grains having a wave shape that satisfies the above conditions is sufficient, and the types of the wire 2 and the abrasive grains themselves are not particularly limited.
For example, as the wire 2, a steel wire having a wire diameter of about 100 to 180 μm and an average wave amplitude of about 5.7 to 16.6 μm can be prepared, and the abrasive grains include silicon carbide abrasive grains, etc. Diamond abrasive grains are commonly used. It is possible to prepare abrasive grains with a grain count of #800 to #3000 and a median diameter of about 5.7±0.5 to 18±1 μm.
Note that the abrasive grain size can be measured by, for example, a laser diffraction/scattering method.

Next, as shown in FIG. 1, wire rows 11 are formed by winding the wires 2 prepared as described above around a plurality of grooved rollers 3, 3'.
Then, the tension applied to the wire 2 is adjusted by the tension applying mechanisms 4, 4'. At this time, the tension applied to the wire 2 having a wave shape is set in a range of 50% or more and 60% or less of the breaking strength of the wire 2. In this way, by setting the tension of the wire 2 to 50% or more of the breaking strength, it is possible to suppress wobbling of the wire 2 during cutting, thereby stabilizing the cutting trajectory and improving the shape accuracy of the cut wafer. Further, by setting the tension of the wire 2 to 60% or less of the breaking strength, it is possible to suppress the risk of the wire 2 breaking during cutting.
Note that the breaking strength of the wire can be defined as the force (N/cm ² ) at which the wire breaks in a tensile test of the wire, based on, for example, the tensile test for metal materials (JIS Z 2241).

Subsequently, the wire 2 is caused to reciprocate in the axial direction of the wire 2 by the driving motor 10 under tension. In addition, supply of slurry containing abrasive grains from the machining fluid supply mechanism 6 is also started. This abrasive grain has a median diameter that satisfies the above-mentioned relationship with the average amplitude of the waveform of the wire 2.
Then, by cutting and feeding the workpiece W to the wire row 11 by the workpiece feeding means 5, the workpiece W is simultaneously cut at a plurality of locations lined up in the axial direction.
After the cutting is completed, the cut work W is pulled out from the wire row 11 by relatively moving the work W in a direction opposite to the direction in which the cut was fed.

Through the steps described above, a plurality of wafers (silicon single crystal wafers) can be obtained from the workpiece W at the same time. Moreover, since the relationship between the average amplitude of the wave shape of the wire 2 and the median diameter of the abrasive grains in the slurry, and the relationship between the tension applied to the wire 2 and the breaking strength, satisfy the relationships described above, the wire It is possible to effectively reduce the risk of disconnection of wires 2, and it is possible to cut out wafers with excellent shape accuracy (for example, wafers with a warp of 5 μm or less) with high cutting efficiency. Thereby, it is possible to improve the yield and productivity of wafer manufacturing.

EXAMPLES Hereinafter, the present invention will be explained in more detail by showing Examples and Comparative Examples of the present invention, but the present invention is not limited thereto.
(Example, comparative example)
Using the wire saw 1 shown in FIG. 1, the workpiece was cut under the conditions shown in Table 1 regarding the workpiece to be cut, the wire, and the processing fluid (slurry containing abrasive grains).
Specifically, a cylindrical silicon single crystal ingot with a diameter of approximately 300 mm was used as the work to be cut.
Further, as the processing liquid, a slurry containing abrasive grains (material: SiC) having a median diameter of 8 μm was used.
The cutting wire (steel wire) was a linear wire with a wire diameter of 130 μm, a wire with a wire diameter of 130 μm, and an average wave amplitude of 8.0 μm, 8.8 μm, 11.2 μm, Wires with four types of periodic waveforms of 12 μm were used. As mentioned above, since the median diameter of the abrasive grains is 8 μm, the ratios (ratio A) of the average amplitude of the waveform of the wire to the median diameter were 100%, 110%, 140%, and 150%.
The tension of the wire during cutting was varied in four steps: 23 N/cm ² , 25 N/cm ² , 30 N/cm ² , and 33 N/cm ² . That is, the ratios (ratio B) of applied tension to the breaking strength of the wire (approximately 50 N/cm ² ) were 45%, 50%, 60%, and 65%.
In addition, when using a wire having a wave shape, the ratio of the average amplitude of the wave shape of the wire to the median diameter of the abrasive grains is either 110% or 140%, and the ratio of the applied tension to the breaking strength of the wire is 50%. The case of either 60% is an example using the cutting method of the present invention. The case under other conditions is a comparative example.
The workpiece was cut under the above conditions, the warp of the plurality of cut wafers was measured, and the average warp value was calculated for each cutting condition. The wires are shown in Table 3.

First, as can be seen from Table 2 (all comparative examples), the linear wire has a workpiece feed rate of 0.18 mm/min or less and a wire tension of 25 N/cm ² (ratio B: 50%) or less. Within this range, a good Warp of 5 μm or less was obtained. However, since a straight wire has a lower abrasive carrying capacity than a wave-shaped wire, the load applied to the wire during cutting increases, and when the workpiece feed rate is 0.18 mm/min, Cutting with a tension greater than 25 N/cm ² (Ratio B: 50%) increased the risk of the wire breaking during cutting. Further, when the workpiece feed rate was 0.20 mm/min, when cutting was performed with a tension greater than 23 N/cm ² (ratio B: 45%), the risk of wire breakage during cutting increased.

Furthermore, in Table 3, the four Warp values surrounded by bold frames are the results of the example, and the others are the results of the comparative example. Since the wave-shaped wire has a higher ability to carry abrasive grains than the straight-shaped wire, the load applied to the wire is reduced, and the risk of the wire breaking during cutting can be suppressed. A straight wire was broken at 25 N/cm ² (Ratio B: 50%).Even when the feed speed of the workpiece was 0.20 mm/min, the wire tension was 30 N/cm ² (Ratio B: 60%). ), this prevents wire breakage. However, if it exceeds 30 N/cm ² to 33 N/cm ² (ratio B: 65%), the risk of wire breakage increases. Although there are cases where sliced wafers with good shape accuracy of 4.6 μm were obtained using 33 N/cm ² , considering the risk of wire breakage, cutting should be performed at 30 N/cm ² (ratio B: 60%) or less. Conceivable. On the other hand, at 23 N/cm ² (ratio B: 45%), the warp exceeded 5 μm, possibly due to wire wobbling due to insufficient tension, and good shape accuracy could not be obtained.
In addition, when the average amplitude of the waveform is 8.0 μm (ratio A: 100%), the cutting efficiency is poor, probably because it is difficult to transport the abrasive grains with the median diameter, which is said to contribute most to the cutting process. It took a long time to do this, and the shape accuracy was also poor. In addition, in the case of 12.0 μm (ratio A: 150%), the shape accuracy was not good, probably because the wave shape of the wire was large and the maximum diameter of the abrasive grains captured and transported by the troughs was not stable.

From the above, the tension applied to the wave-shaped wire should be in the range of 50% to 60% of the breaking strength, and the average amplitude of the wave should be in the range of 110% to 140% of the median diameter of the abrasive grains used for cutting. By using a wire within this range, a sliced wafer with excellent shape accuracy and a warp of 5 μm or less could be obtained in a shorter time than when using a straight wire. When using a straight wire, taking into consideration the Warp value, the average feed speed of the workpiece had to be at most 0.18 mm/min as shown in Table 2, but when the present invention is implemented, it can be reduced to 0.20 mm/min. It was possible to obtain sliced wafers with sufficiently high shape accuracy even at the minimum processing time, and the process time could be shortened.
By the way, the effectiveness of the present invention is not limited to cases where the workpiece feed rate is 0.20 mm/min or less; when cutting was also attempted at a faster workpiece feed rate, similarly high-quality sliced wafers were obtained. was able to obtain.

Note that the present invention is not limited to the above embodiments. The above-mentioned embodiments are illustrative, and any embodiment that has substantially the same configuration as the technical idea stated in the claims of the present invention and has similar effects is the present invention. within the technical scope of the invention.

1...wire saw, 2...wire, 3, 3'...grooved roller,
4, 4'...Tension applying mechanism, 5...Workpiece feeding means, 6...Machining fluid supply mechanism,
6a... Nozzle, 7, 7'... Wire reel, 8, 8'... Traverser,
9, 9'... Constant torque motor, 10... Drive motor, 11... Wire row,
W...Work.

Claims (2)

A wire array is formed by winding a wire having a wave shape around a plurality of grooved rollers, and while supplying slurry containing abrasive grains to the wire array, tension is applied to the wire and the wire is caused to reciprocate in the axial direction. , a method for cutting a workpiece using a wire saw, in which the workpiece is simultaneously cut at a plurality of locations aligned in the axial direction by cutting and feeding the workpiece to the wire row,
The tension applied to the wire is in the range of 50% or more and 60% or less of the breaking strength of the wire, and
The average amplitude of the wave shape of the wire is in the range of 110% or more and 140% or less of the median diameter of the abrasive grains used for cutting ,
A method for cutting a workpiece, characterized in that the feed rate of the workpiece is 0.20 mm/min or less . 2. The method for cutting a workpiece according to claim 1, wherein the workpiece to be cut is a silicon single crystal ingot.

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