JPH0970747A - Wire saw - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent eccentric wear of a peripheral face of a wire and suppress waving of a face which is cut by providing a travelling base on a side where rotary central shafts of groove rollers on which a row of wires for cutting is stretched are positioned for the row of wires for cutting. SOLUTION: A travelling base 11 for material to be cut which fixes and moves a material to be cut 6 is provided on a side where rotary central shafts O2 , O3 of groove rollers 2, 3 on which a row of wire for cutting 5 is stretched are positioned for the row of wire 5. That is, the travelling base 11 for material to be cut which fixes and moves a workpiece 6 is provided inside a loop formed by winding and applying the groove rollers 1, 2, 3, and the material to be cut 6 is pressed against the row of wire 5 from the inner side of the loop. Consequently, since a side of a wire surface on which tensile residual stress is large is pressed against the material to be cut 6 and wears, the distribution of residual stress in the peripheral direction of wire becomes more symmetrical and the rotation of the wire 4 is likely to occur.

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 material such as a semiconductor material or ceramics into a large number of wafers with high precision by means of a wire and abrasive grains.

[0002]

2. Description of the Related Art A wire saw is constructed by winding a wire around a plurality of groove rollers at a predetermined pitch to stretch a wire row, running the wire, and pressing a material to be cut (hereinafter referred to as a work) against the wire row. This is an apparatus for cutting a work into a large number of wafers by the grinding action of the abrasive grains while pouring a working liquid containing the abrasive grains (hereinafter referred to as an abrasive liquid) between the wire row and the work.

FIG. 3 exemplifies the structure of a cutting processing part of a general wire saw. Three rotatable groove rollers 1, 2 and 3 are installed in parallel and three-dimensionally, and one wire 4 is engraved at a predetermined pitch on the resin outer peripheral surface of each groove roller. Further, the cutting wire row 5 (hereinafter simply referred to as a wire row) is formed by being wound around a large number of wire guide grooves. When the groove roller is rotated, the wire row 5 having a predetermined pitch runs. Abrasive liquid 7 is supplied from the abrasive liquid supply device 8 to the traveling wire array 5, and when the work 6 is pressed against the wire array 5 in this state, the cutting gradually progresses due to the grinding action of the abrasive grains in the abrasive liquid. Go. Work 6
Is fixed to a metal base 10 by a method such as adhesion via a dummy plate 9 made of glass or the like, and the metal base 10 is detachably attached to a work moving base 11 with screws 12. When this moving table 11 is moved in the direction of the wire row 5 and all the wires cut the work and proceed to cut to the dummy plate 9, the cutting is completed. After that, the work moving table 11 is lowered, the wire row 5 is extracted from the work 6, the work 6 is removed together with the metal base 10, the wafer is separated from the dummy plate 9, and the wafer is sampled. The cut wafer is finished into a product wafer through several polishing steps. Wafers used as electronic substrates such as silicon require extremely high flatness,
Even in the cutting process, a flatness with a height difference of 10 μm or less is required.

By the way, it is known that a wafer cut by a wire saw is mainly warped in the moving direction of the work.

FIG. 4 is a view showing a cross section of a wafer cut by a wire and its shape defect, and FIG. 4A is a view showing a wire traveling direction and a work moving direction in the wafer cutting cross section. (B) of the figure is an example of the shape of the wafer cut surface of the AA cross section shown in (a), and shows the magnification in the vertical direction of the wafer cut surface in an enlarged manner. In the cross section of the wafer cut by the wire, the wire traveling direction a-b is almost flat, but the work moving direction a'-b 'is likely to be warped as shown in FIG. 4B.

FIG. 5 is a diagram showing a typical shape generated on the wafer cut surface. The shape of the wafer cut surface shown in FIG. 4B is the gentle unevenness shown in FIG. 5A. It can be considered that (hereinafter referred to as undulations) and fine pitch irregularities (hereinafter referred to as waviness) shown in FIG. 5B are synthesized. The waviness in FIG. 5A is formed gradually during cutting for a long time, and the temperature of the resin on the groove roller surface changes during cutting, and the position of the wire guide groove may move little by little. It is considered to be the main cause. As a method for suppressing this, for example, in JP-A-62-251063, a groove roller shaft cooling method is used, and in JP-A-7-1442, a temperature-controlled abrasive liquid is supplied to the groove roller surface. Are disclosed respectively. On the other hand, it is said that the cause of the corrugations in FIG. 5B is poor roundness of the wire.

FIG. 6 is a diagram showing a state of waviness caused by a wire having a poor roundness. According to the report on 745 pages of the Seiki Society Spring Conference Academic Lectures in 1980,
When the wire 4 having an elliptical cross section enters the workpiece cutting groove 21 as shown in FIG. 6 (a), the groove bottom 21 'in the major axis cc direction of the wire cross section is further ground and cut. It is assumed that the groove 21 is inclined in the direction of arrow A. By the way, as the cutting groove 21 shifts from the vertical plane as shown in FIG. 6B, the tension of the wire between the groove rollers 2 and 3 shown in FIG. 3 increases, so that the wire shown in FIG. The restoring force indicated by the arrow B'in FIG. This restoring force advances the grinding of the groove bottom 21 'in the direction of the short diameter c'c' of the wire cross section. That is, the bending of the cutting groove in the direction A due to the poor circularity of the wire and the bending of the cutting groove in the direction B due to the restoring force of the wire are alternately generated, so that the corrugation shown in FIG. 5B is formed. To be done.

FIG. 7 is a diagram for explaining the cutting action of the wire and the abrasive grains in the cutting groove of the work.

Since the wire used in the wire saw is drawn by using a die having a very high roundness, the roundness of the wire cross section is very good in a new state. However, as shown in the figure, in the cutting process, it is approximately half of the wire surface that contacts the bottom portion 21 'of the work cutting groove 21 via the abrasive grain 20, and this portion is much harder than the wire. Sliding with 20 causes slight wear.

FIG. 8 is a view showing a state of the wire passing through a large number of cutting grooves formed in the work 6. The running wire 4 passes through the cutting groove 21-1 on the end side shown in the same drawing and goes around the plurality of groove rollers once, and then the next cutting groove 21-
2 and then pass through the adjacent cutting grooves one after another, and finally pass through the last end cutting groove 21-n and go out of the cutting area of the work. When a specific portion of the wire surface is rubbed intensively, the roundness gradually deteriorates. In cutting with a wire saw, wear of the wire is essentially unavoidable. Therefore, in order to keep the roundness of the wire, it is necessary to wear the entire circumference of the wire as evenly as possible. In FIG.
The condition is that the wire rotates in the circumferential direction before passing through n.

An apparatus for rotating a wire in the circumferential direction is disclosed in, for example, Japanese Utility Model Laid-Open No. 59-14136.

FIG. 9 is a view showing an apparatus for forcibly rotating a wire in the circumferential direction disclosed in the publication. As shown in the figure, a pair of wire rotating rollers 22 and 23 sandwiching a wire row are provided between the groove rollers 1 and 2, and wires 24 supporting the respective rollers are opposite to each other as indicated by arrows 25 and 26. In this method, the wire is rotated in the circumferential direction by moving the wire in the direction. However, this method can be applied when the traveling speed of the wire is a low speed of about 100 m / min. 400 per minute recently
For a wire saw whose cutting efficiency has been improved by running at a high speed of m or more, it is necessary to frequently and rapidly move the wire rotating rollers 22 and 23 in the axial direction, which causes disconnection due to instability of the wire row tension. There is a fear. Further, when the tension of the wire is large, there is a fatal defect that it is difficult to impart circumferential rotation to the wire with such a rotating roller.

[0013]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances and allows a wire to rotate in the circumferential direction during cutting without using an additional device such as the wire rotating roller. An object of the present invention is to provide a wire saw capable of suppressing the waviness of the wafer cut surface by causing the entire circumference of the wire to be evenly worn.

[0014]

An extremely thin wire having a diameter of 0.2 mm or less used for a wire saw has poor rigidity and can be easily twisted. In FIG. 3, the wire is spirally wound around the wire guide groove of the groove roller while being shifted by one pitch of the wire row between at least one of the groove rollers 1 and 3, and the groove rollers 1 and 2. The wire is twisted every time it changes. As a result, the wire having poor rigidity runs while rotating little by little in the circumferential direction. This will be referred to as rotation of the wire in the circumferential direction. The present inventors repeated experiments and studies under the consideration that rotation of the wire is hindered by some cause to cause poor roundness of the wire, and as a result, the following findings were obtained. .

1) When the wire is wound around a groove roller, the outer peripheral surface of the wire which is in contact with the work when cutting the work is
In the conventional wire saw, the surface having a small residual stress is in contact with the work due to the influence of the magnitude of the residual stress during the manufacture of the wire.

2) Therefore, the outer peripheral surface of the wire having a small residual stress is worn, the residual stress of the surface becomes smaller, and the outer peripheral surface of the wire having a smaller residual stress tends to contact the work piece.

3) In order to evenly wear the wire in the circumferential direction, it is necessary to rotate the wire during running. For that purpose, when the wire is wound around a groove roller, the outer circumference of the wire is large in residual stress. The work must be pressed against the wire so that it contacts the surface.

The present invention has been made on the basis of such knowledge, and its gist is to "wind a wire around a plurality of rollers having wire guide grooves of a predetermined pitch on the outer circumference and cut the wires between the rollers. A plurality of groove rollers for tensioning the row, a work moving base for pressing the work on the wire row, and a machining liquid containing abrasive grains between the work and the wire row In a wire saw including a polishing liquid supply device, a moving table is installed on a side where a rotation center axis of a groove roller stretching the cutting wire row is located with respect to the cutting wire row. The wire saw is characterized by

Since the groove rollers are necessary for forming the wire row, the number of groove rollers may be at least two and is not particularly limited. It is preferably three or four.

Since the rotation of the wire during the cutting of the wire is greatly affected by the stress distribution remaining during the manufacture of the wire, this point will be described first. In a wire saw,
The wire is used under high tension to improve the cutting efficiency and the cutting accuracy. Therefore, in order to prevent wire breakage, the tensile strength of the wire is required to be extremely high, around 3000 MPa. Therefore, the carbon content is 0.8%
The front and rear high carbon steels are used, and the strength is increased by utilizing the work hardening by cold die wire drawing.

FIG. 10 is a diagram showing the radial distribution of residual stress in the longitudinal section of the wire. As shown in the figure, a large tensile residual stress σt is formed in the vicinity of the surface of the wire, and a compressive residual stress σc is formed in the core, which balances with the tensile residual stress σt.

This residual stress distribution rarely becomes symmetrical with respect to the axis as shown in FIG.

FIG. 11 is a diagram showing an example in which the residual stress of the wire is distributed asymmetrically in the radial direction.

Usually, as shown in FIG. 3A, the tensile residual stress σt on one surface Y is equal to the tensile residual stress σt on the opposite surface X.
is greater than t. When such a wire is cut into short pieces, it bends in the longitudinal direction of the wire as shown in FIG. 11B, and the surface X side comes to the outside of the bend. The radius of curvature ρ becomes smaller as the residual stress distribution becomes less symmetrical. Even if the residual stress distribution of a new wire is completely symmetrical with respect to the axis, it is possible to prevent the wire from bending in the longitudinal direction because the symmetry is broken due to uneven wear during cutting. Is considered impossible in reality.

By the way, when the wire which is going to bend in the longitudinal direction is wound around the groove roller, it is wound around the groove roller so as to coincide with the bending direction of the wire itself.

FIG. 12 is a diagram showing the positional relationship between the wire peripheral surface and the roller when the wire is wound around the groove roller. As shown in the figure, the surface X having a small tensile residual stress σt comes to the outside at the winding portion around each groove roller. This is because the bending energy required for winding is minimized, and this state is the most stable, and the wire surface X is always located outside the loop of the wire that surrounds the groove roller. When the work 6 is cut in the state of FIG. 12, the wire surface X side is rubbed by the abrasive grains to run, and the surface X side is worn. As described above, as a result of the abrasion of the surface layer portion (X side) of the wire having a small tensile residual stress, the tensile residual stress σt on the surface X side becomes small, and the wire 4 has a smaller ρ.
I'm about to turn. That is, the tendency to maintain the positional relationship between the surfaces Y and X in FIG. 12 becomes stronger,
The aforementioned wire rotation cannot be expected.

As described above, in the cutting by the conventional wire saw shown in FIG. 3, the rotation of the wire is hindered by the asymmetry of the residual stress of the wire, which becomes more remarkable by the cutting process. . This is due to the structure in which the work 6 is pressed from the side opposite to the side where the rotation centers O ₂ and O _{3 of the} groove rollers 2 and 3 on which the wire row 5 is stretched are located, as shown in FIG. is there. Therefore, conversely, the work is pressed against the wire row 5 from the side where the rotation centers O ₂ and O _{3 of the} groove rollers ₂ and ₃ are located to cut the work, so that the circumference of the wire having large tensile residual stress is cut. Since the surface (Y side) is worn and the difference in residual stress in the wire circumferential direction is reduced, the rotation of the wire can be maintained.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing one embodiment of the present invention.

In this example, three groove rollers 1, 2, and 3 are used, and the outer surface of each roller is made of resin. The pitch of the wire guide groove is about 0.4 to 3 mm and is determined by the application of the wafer. A thin wire 4 having a diameter of 0.2 mm or less is wound around the roller so as to run at a speed of about 100 to 1000 m / min. The cutting material moving table 11 for fixing and moving the cutting material 6 includes a rotation center axis O ₂ of the groove rollers 2 and 3 which stretches the cutting wire row 5 with respect to the cutting wire row 5,
It is installed on the side where O ₃ is located. That is, in the case of the same figure, it is inside the wire loop.

The difference from the conventional wire saw shown in FIG.
The material moving base 11 for fixing and moving the work 6 is installed inside the loop formed by winding the groove rollers 1, 2, and 3. The work is a wire from the inside of the loop. Pressed against row 5.

With this structure, in FIG. 12, the wire surface Y side having a large tensile residual stress σt is pressed against the work and is worn, so that the distribution of the residual stress in the wire circumferential direction becomes more symmetrical, and the wire A situation in which rotation easily occurs.

FIG. 2 is another example of the embodiment of the present invention. The difference from the wire saw is that auxiliary rollers 2'and 3'are added to the groove rollers 2 and 3, respectively. With such a configuration in which the auxiliary roller is provided, the side on which the rotation center axis of the groove roller that stretches the wire row with respect to the wire row 5 is located is the outside of the wire loop, and the workpiece moving base 1
1 can be placed outside the wire loop in the same way as a conventional wire saw.

It is not always necessary to provide wire guide grooves in the auxiliary rollers 2'and 3 '. Even in this case, the wire surface on the side where the tensile residual stress σt is large comes into contact with the work 6 and is worn away, so that there is an effect that the residual stress distribution of the wire is corrected so as to be symmetrical in the circumferential direction.

In addition to the wire saw having the above structure, a workpiece moving base is provided on the side on which the center of rotation of the groove roller in which the cutting wire row is arranged with respect to the wire row is located, and the work is pressed against the wire row. Other configurations may be used as long as they satisfy the conditions. Further, it goes without saying that the present invention can be applied regardless of a traveling method for a work such as a reciprocating type and a one-way type.

[0035]

EXAMPLE Five silicon ingots were cut using the same wire under the following conditions with the wire saw having the structure shown in FIG. After cutting, cut off 50 cm of the used wire by 10 cm to obtain a radius of curvature ρ of the wire (Fig. 11 (b)).
And the roundness α (minimum diameter / maximum diameter) of the wire cross section. Further, the waving height W of the cut wafer was measured.

Material to be cut Material: Silicon (Ingot) Diameter: 200 mm Length: 200 mm Wire saw Wire diameter: 0.16 mm Wire running speed: 600 m / min Groove roller diameter: 150 mm Auxiliary roller diameter: 80 mm Cutting speed: 0.4 mm / Separation Abrasive: SiC abrasive grains (average particle size 25 μm) and lapping oil were mixed and cut, and the thickness of the cut wafer was 0.9 mm, and 190 wafers per ingot. This cutting was repeated 5 times.

Further, as a conventional example, cutting was carried out under the same conditions as above except that a wire saw having the structure shown in FIG. 3 was used.

FIG. 13 shows the measurement result of the example of the present invention.

FIG. 14 shows the measurement results of the conventional example.

The waviness height of the wafer is an average value of all the wafers. The roundness also shows an average value. In the conventional wire saw shown in FIG. 14, the radius of curvature ρ and the roundness α decrease as the number of times the wire is used increases, and the corrugation height W gradually increases. That is, selective wear of only the same side of the wire peripheral surface leads to deterioration of cutting accuracy. On the other hand, in the case of the example of the present invention, FIG.
It can be seen from 3 that the radius of curvature ρ increases as the number of times the wire is used increases, and the difference in residual stress on the wire peripheral surface decreases. The reason why the roundness is a little worse at the first time is that the wear of the wire is small at the initial stage of cutting, and the difference in residual stress on the wire peripheral surface does not become small. As the number of times of use increases, the roundness improves. Has become. Therefore,
The waviness also became smaller as the number of cuttings increased, which was completely opposite to the result of the conventional example.

[0041]

According to the wire saw of the present invention, the radial asymmetry of the residual stress inevitably possessed by a new wire is automatically corrected during the cutting process to effectively cause the rotation of the wire to effectively prevent the wire from rotating. Uneven wear can be prevented, and thereby waviness of the cut surface can be suppressed. Since the same wire can be repeatedly used without deteriorating the cutting accuracy, the running cost can be reduced. Further, there is also a ripple effect that the number of polishing steps in the subsequent process can be shortened by improving the cutting accuracy. The demand for electronic wafer materials represented by silicon is ever increasing, and the wire saw of the present invention exerts an extremely great effect industrially.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a cutting processing part of a wire saw according to the present invention.

FIG. 2 is a diagram showing another example of the cutting processing part of the wire saw of the present invention.

FIG. 3 is a perspective view showing a configuration of a typical processed portion of a conventional wire saw.

FIG. 4 is a diagram showing a cross section of a wafer cut by a wire saw and its shape defect.

FIG. 5 is a diagram showing a typical shape generated on a wafer cut surface.

FIG. 6 is an explanatory diagram of corrugation formation by a wire having a poor roundness.

FIG. 7 is a diagram illustrating a cutting action between a wire and abrasive grains in a cutting groove of a work.

FIG. 8 is a diagram showing a state of a wire passing through a large number of cutting grooves formed on a work.

FIG. 9 is an explanatory diagram of a method for forcibly imparting circumferential rotation to a wire.

FIG. 10 is a radial distribution diagram of residual stress of a wire.

FIG. 11 is an explanatory diagram of a wire having an asymmetric residual stress distribution.

FIG. 12 is a diagram showing a positional relationship between a wire peripheral surface and a groove roller when a wire having an asymmetric residual stress distribution is wound around the groove roller. It is.

FIG. 13 is a diagram showing a result of continuous cutting with the wire saw of the present invention.

FIG. 14 is a diagram showing a result of continuous cutting with a conventional wire saw.

[Explanation of symbols]

 1, 2, 3 Groove roller 2'3 'Auxiliary groove roller 4 Wire 5 Cutting wire row 6 Cutting material (workpiece) 7 Abrasive liquid 8 Abrasive liquid supply device 9 Dummy plate 10 Metal base 11 Moving material moving table 12 Fixed Screw 20 Abrasive grain 21 Work cutting groove 21 'Cutting groove bottom

Claims (1)

[Claims] 1. A plurality of groove rollers for winding a wire around a plurality of rollers having wire guide grooves engraved with a predetermined pitch on the outer periphery to stretch a cutting wire row between the rollers, and a wire row to be cut. In a wire saw having a material moving base for pressing a material and a grinding liquid supply device for supplying a working liquid containing abrasive grains between the material to be cut and a wire row, the moving base is used for the cutting. A wire saw, wherein the wire saw is installed on the side where the rotation center axis of the groove roller, which stretches the cutting wire array, is located with respect to the wire array.