JP2011079074A - Wire-cut machining method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wire-cut machining method using a conventional wire for producing a wafer having a consequently good surface accuracy without causing the deflection of the wire independently of whether a special deflection suppressing mechanism exists or not. <P>SOLUTION: The wire-cut machining method is provided for cutting a workpiece pushed against a running wire, or using multiple wire saws for cutting the workpiece pushed against running wires in the state of being wound in multiple turns on the outer peripheries of two or more roller groups arranged at predetermined spaces. Herein, at least two wires being tensed while contacting each other at one cutting position run in the same direction. At this time, such a positional relationship is desirably established in the cross section perpendicular to a wire longitudinal direction that the wires are arranged longer in the cutting direction. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a wire cutting method using a multi-wire saw, which is used for cutting a workpiece using a wire, particularly for cutting a hard and brittle material.

A wire saw is known as a machine for cutting a hard and brittle material (hereinafter referred to as a workpiece) typified by silicon used in solar cells and the like. FIG. 1 is a schematic view of a multi-wire saw that performs a plurality of cutting processes with a single machine. The wire is prepared in a multi-wire saw as follows. The wire 2 wound around the supply reel 4 is supplied to the multi-wire saw. The wire 2 is guided to a main roller 6 by being guided by a plurality of guide rollers (not shown). The wire 2 is wound around a main roller 6 generally composed of 2 to 4 wires. Several tens to several hundreds of wire groups are stretched between the main rollers 6. Thereafter, the wire 2 is guided by a plurality of guide rollers and wound around the discharge reel 8 in the same manner as in the supply.

Run the wire after the wire is set on the multi-wire saw. In this state, a workpiece 10 made of silicon or the like to be processed is pressed against a group of wires stretched between the main rollers 6. Then, the workpiece 10 is cut by the wire group, and a thin plate (hereinafter referred to as a wafer) having a thickness corresponding to the wire pitch is obtained.

There are two types of saw wire cutting. One is a method of cutting while spraying slurry containing abrasive grains. The other is a method in which cutting is performed using a wire in which abrasive grains are fixed in advance. In general, the former is called a free abrasive type, and the latter is called a fixed abrasive type.

In any of the methods, there is the following problem when the workpiece is pressed against the wire for cutting. The wire is tensioned between main rollers (hereinafter referred to as tension). However, when the workpiece is strongly pressed against the wire, for example, in FIG. 1, the wire is pressed downward. Hereinafter, the movement of the wire traveling position by pressing the workpiece is referred to as “deflection”.

FIG. 2 is an explanatory view of the bending of the wire that occurs at the time of cutting, where (a) is before the start of cutting and (b) is being cut. The wire 2 originally wound around the main roller 6 as shown in (a) is stretched between the main rollers 6. However, when the workpiece 10 is pressed against the wire as shown in (b), the wire is bent. This bending occurs due to the wire being stretched or the like.

The influence of this bending is described in Patent Document 1, for example. Specifically, it describes the surface accuracy of the wafer due to changes in deflection. When bending occurs during cutting, the surface accuracy of the wafer, such as “roughness” and “underi”, decreases, and the degree of decrease in surface accuracy increases as the degree of change in the maximum amount of bending increases. Therefore, it is described that it is very important to reduce the degree of change in the maximum deflection amount during cutting in order to improve the surface accuracy of the wafer.

Therefore, in Patent Document 1, the workpiece is placed on the table so that the center position of the workpiece is shifted in the stretching direction with respect to the center position of the cutting wire, thereby reducing the amount of bending of the wire. It is going to be.

In addition, in Patent Document 2, for example, during cutting of a workpiece, the workpiece is cut while controlling the wire tension by a tension applying mechanism according to the amount of bending of the wire with respect to the feed direction of the workpiece. A method is described.

JP 2007-54909 A JP 2007-30117 A

However, in any case, it is a premise that the wire is bent, and an essential solution has not been reached. Alternatively, it is possible to provide a mechanism for absorbing some of the bending of the wire on the device side, but the device becomes large and the cost is high.

Further, in Patent Document 1, it is possible to expect a reduction in bending in the vicinity of both ends of the main roller, but the effect is reduced when the workpiece reaches near the center between the main rollers. Further, in Patent Document 2, there are tension applying mechanisms for eliminating the bending at both ends of the wire supply side and the wire take-up side, and therefore among the plurality of wires wound around the main roller, near the center of the main roller. Almost no effect on the wire stretched with can be expected. As a result, the tension difference is increased by the wire, that is, the amount of bending is increased, and the surface accuracy of the workpiece is lowered.

Therefore, the present invention provides a wire cutting method that uses a conventional wire, regardless of the presence or absence of a special bending suppression mechanism, and does not cause the wire to be bent, resulting in a wafer having good surface accuracy. .

The present invention is a cutting method for solving the above problems,
In a wire cutting processing method in which a workpiece is pressed against a traveling wire and cut, it is performed in a state where at least two wires are in contact with each other without being twisted at one cutting point and are traveling in the same direction while being stretched. It is characterized by that.

In particular, it is more effective in a wire cutting method using a multi-wire saw that presses and cuts a workpiece against a wire that is run in a state where the outer periphery of two or more roller groups arranged at predetermined intervals is wound around a plurality of times. Demonstrate.

When preparing a wire for the multi-wire saw,
More preferably, the number of wires at one cutting point is at least two, and the arrangement of the wires is long in the cutting direction in a cross section perpendicular to the wire longitudinal direction.

The wire used in the method of the present invention is particularly effective when the abrasive grains are fixed on the surface.

When the cutting process is performed by the method of the present invention, the bending generated in the wire is extremely reduced. As a result, it is possible to perform a cutting process for obtaining a wafer having good surface accuracy.

Schematic of multi-wire saw Explanatory drawing of wire bending that occurs during cutting Explanatory drawing of the action of force when pressing the workpiece in the conventional method Sectional view of wire and workpiece when cutting by conventional method Explanatory drawing of the action of force when pressing the work in the method of the present invention Sectional view of wire and workpiece during cutting by the method of the present invention Other examples in the cross section of the wire and workpiece when cutting by the method of the present invention

Conventionally, one point is cut with one wire, but the greatest feature of the present invention is that the same portion is cut with two or more wires. The operation will be described in detail below with reference to FIGS.

FIG. 3 is an explanatory diagram of the action of force when the workpiece is pressed in the conventional method, and FIG. 4 is a cross-sectional view of the wire and the workpiece during cutting by the conventional method. Usually, the wire is stretched with a tension T applied thereto. In this state, the workpiece 10 is pressed against the wire 2 from above with the pressing force F1. A reaction force F2 against the pressing force F1 acts on the wire 2 and is pushed down to a position where the balance of the force is maintained. At this time, the wire is stretched by applying a tension of the resultant force T1, that is, a load. From the above results, the wire is bent L1 with respect to the initially stretched position.

On the other hand, FIG. 5 is an explanatory view of the action of the force when the workpiece is pressed in the method of the present invention, and FIG. 6 is a cross-sectional view of the wire and the workpiece during cutting by the method of the present invention. In the present invention, the reaction force F2 is obtained by two wires. That is, about two half of F2, which is the reaction force f1 or f2, is distributed and loaded on each of the two wires. Therefore, the tension increased per wire is halved and the elongation of the wire is greatly reduced. As a result, the wire deflection L2 is extremely small.

In the present invention, it is extremely important that at least two wires are in contact with each other at one cutting point and are stretched in the same direction while being stretched, and the number of wires to be used is not particularly problematic.

For example, in the case of using a single wire, it can be achieved by winding at least two rounds around the same portion when the group of at least two rollers for stretching the wire is circulated. When the running groove of the wire is engraved on the roller surface, the wire may be wound around the same running groove twice. By doing so, it can be set as the state where two wires were stretched in the running groove in each roller which stretches a wire. In this state, the wire can be run to perform cutting with higher accuracy.

Similarly, in the case of a multi-wire saw, when winding around at least two main roller groups that stretch the wire, the wire is wound around the same running groove several times, and then cut. Move to the next running groove between the main rollers that are not used. Similarly, the wire is wound around the traveling groove that has moved in the same manner as before. By repeating this for all the running grooves, a plurality of wires can be stretched in all the running grooves.

Alternatively, as another form in the case of a multi-wire saw, the present invention may be applied only to cutting performed near the center of the main roller. In this case, in the vicinity of both ends of the main roller, the tension of the wire is controlled by using the conventional tension adjusting mechanism to reduce the bending, and in the vicinity of the center of the main roller, as in the present invention, with respect to the same running groove. By wrapping the wire a plurality of times, it is possible to perform good cutting with suppressed bending with respect to all cutting.

The same applies to the case of using a plurality of wires. A plurality of wires to be used are stretched, for example, guided to one place before the roller. When these wire groups are stretched between two rollers, all the wires are bundled so as to run in the same place, and are stretched on the apparatus as if they were one. When the running groove of the wire is engraved on the roller surface, all the wires may be placed in the running groove. In this state, cutting is performed by pressing the workpiece while controlling all the wires to travel at the same speed.

Here, “the wire travels in the same location” means that a plurality of wires travel in one cut location, but the magnitude of the effect of the present invention obtained by the positional relationship of the wires is determined. For example, FIG. 7 shows another example of a cross section of a wire and a workpiece when being cut by the method of the present invention. (C) is a case where two wires travel along one cutting point, and is a case where the two wires are arranged long in the cutting direction (hereinafter referred to as the vertical direction). On the other hand, (d) shows a case where two wires travel through one cutting point, and the two wires are arranged in a direction perpendicular to the cutting direction (hereinafter referred to as a lateral direction). Each of them has the effect of the present invention. Particularly, as shown in (c), when the arrangement of each wire is long in the cutting direction, the cutting width L3 can be reduced and the cutting is removed. The volume to be cut is small and cutting can be performed more quickly.

In order to arrange the wires long in the cutting direction as described above, for example, it is easy to fix the positional relationship of the wires by, for example, providing a travel groove carved in a roller for stretching the wires. However, the present invention is not limited to this method, and the positional relationship of the wires may be determined.

Or it cannot be overemphasized that the bending L at the time of a cutting | disconnection can be made small, so that there are many wires which run the one cutting | disconnection location. (E) of FIG. 7 is a case where three wires run through one cutting point. That is, when the purpose is to cut faster, the number of wires traveling through one cutting point may be increased, and the pressing force of the workpiece may be increased while arranging the wires in the vertical direction as much as possible. However, when the number of wires traveling through one cutting point increases, specifically, when the number is 5 or more, it is structurally difficult to maintain the vertical arrangement, and the wires spread laterally and become stable. That is, the cutting width L3 increases and the yield of the workpiece decreases. Therefore, in order to carry out the present invention more efficiently, 2 to 4 wires are desirable as the number of wires traveling through one cutting point.

Further, it is more preferable to use a wire having abrasive grains fixed on the wire surface. In this case, the frictional force is increased by the abrasive grains fixed to each other, and the relative speed between the plurality of wires traveling through one cutting point is decreased. Therefore, the plurality of wires are moved more integrally, and the friction between the wires is reduced. That is, wire damage is also reduced.

A wire was actually wound around a multi-wire saw, and the conventional and the present invention were compared. A wire in which about 20 μm of abrasive grains were fixed to a core material having a diameter of 0.12 mm was used and wound around a multi-wire saw in the conventional manner. The distance between the main rollers in the multi-wire saw is 500 mm, and the wire is stretched by the same distance. Further, as an example of the present invention, one wire is used to make two rounds around the main roller group for each running groove, and two wires are stretched in the same running groove.

Cutting experiments were performed in each of the conventional method and the method of the present invention. A 50 mm square cuboid Si workpiece was prepared and cut. The apparatus was stopped every time the workpiece was lowered by 5 mm, and the amount of bending of the wire was measured with a ruler. The bending amount was measured by measuring the descent distance of the wire from the reference position when the position of the wire before cutting was taken as the reference position. The results are shown in Table 1.

In the conventional method, a deflection of 4 to 6 mm occurs, whereas in the method of the present invention, the amount of deflection can be suppressed to 1 mm or less.

Further, undulation was measured on the wafer obtained by completing the cutting. A surface roughness meter was used to measure a range of 40 mm in the center in the wafer cutting direction with respect to the front and back of the wafer surface. As a result, the numerical value of the undulation generated on the wafer was reduced by half, and good surface quality could be obtained.

2 ... Wire 4 ... Supply reel 6 ... Main roller 8 ... Discharge reel 10 ... Workpiece

Claims (4)

In a wire cutting processing method in which a workpiece is pressed against a traveling wire and cut, it is performed in a state where at least two wires are in contact with each other without being twisted at one cutting point and are traveling in the same direction while being stretched. Wire cutting method. In a wire cutting method using a multi-wire saw in which a workpiece is pressed against a wire that has been run in a state where the outer periphery of two or more roller groups arranged at a predetermined interval is wound around a plurality of times, one cutting point The wire cutting method performed in a state where at least two wires are not twisted but are in contact with each other without being twisted and stretched in the same direction. The wire cutting method according to claim 1 or 2, wherein the number of wires at one cutting point is at least two, and the arrangement of each wire is long in the cutting direction in a cross section perpendicular to the longitudinal direction of the wire. The wire cutting method according to any one of claims 1 to 3, wherein a wire having abrasive grains fixed on a surface thereof is used in the method.