JP2010167509A - Fixed-abrasive grain saw wire and cutting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a saw wire quickly cutting a hard ingot and achieving satisfactory wafers having less surface roughness and waviness; and a cutting method. <P>SOLUTION: The wafer surface scratches due to fixed abrasive grains are reduced while achieving a cutting speed equivalent to that of a conventional fixed-abrasive grain method by using the fixed-abrasive grain saw wire in which a pair of flat parts confronting each other in a longitudinal direction of the wire, and the abrasive grains are fixedly attached only to a curved surface connecting both flat parts, and the amount of protrusion of the abrasive grains with respect to these flat parts is 10 μm or below. The wafers are further smoothed by generating a large number of rollings of free abrasive grains between the flat parts and the wafer surface by the cutting method which combines free abrasive grain method. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a saw wire that is a tool for cutting a hard material.

A saw machine is known as a machine for cutting a silicon ingot used for a solar cell or the like. FIG. 8 is a schematic view of a saw machine. The saw wire is prepared in the saw machine as follows. The wire wound around the supply reel 102 is supplied to the saw machine. The saw wire is guided to a plurality of guide rollers (not shown) and guided to the main roller 104. The saw wire is wound around the main roller 104 generally composed of two to four. Several tens to several hundreds of wire groups are stretched between the main rollers 104. Thereafter, the saw wire is guided to the plurality of guide rollers and wound around the discharge reel 106 in the same manner as in the supply.

Run the wire after the wire is set. In this state, the ingot 108 for processing the wire group stretched between the main rollers is pressed. Then, the ingot 108 is cut by the wire group, and a wafer having a thickness corresponding to the wire pitch is obtained.

There are two types of saw wires. 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 the loose abrasive type, slurry is sprayed on the part where the ingot and saw wire come into contact. Hard abrasive grains are used as the abrasive grains (free abrasive grains) contained in the slurry. For example, SiC or diamond is used. Such loose abrasive grains are often used as a slurry mixed with oil. The sprayed free abrasive grains adhere to the surface of the wire and are carried to the part in contact with the ingot. The ingot is cut and processed by rolling or wrapping between the wire and the ingot on which the loose abrasive grains that have been carried travel.

One of the problems in the free abrasive type is the cutting speed. The loose abrasive grains rolling between the wire and the ingot do not always contribute effectively to the cutting process. Furthermore, as another problem, if the slurry is not efficiently conveyed to the cutting portion, the wafer thickness is not stabilized and deteriorates.

The fixed abrasive type is a method for solving one problem of the free abrasive type. In many cases, the abrasive grains are uniformly fixed to the outer periphery of a wire having a round cross section. Patent Document 1 describes a typical fixed abrasive saw wire. Since the abrasive grains are fixed to the wire in advance, the rolling of the abrasive grains does not occur, and the ingot is cut by the abrasive grains continuing to effectively scratch the ingot as the wire travels. In the fixed abrasive type, a processing speed several times that of the free abrasive type is realized.

However, there is a problem with the fixed abrasive type. Cutting with the fixed abrasive grains applies a large processing stress to the ingot. Therefore, residual processing distortion occurs in the cut wafer, and the surface roughness and undulation, which are important quality items of the wafer, are deteriorated.

Therefore, for example, Patent Document 2 discloses a method in which a free abrasive grain type and a fixed abrasive grain type are combined. It is known that by performing both at the same time, cutting can be performed quickly and with little distortion.

JP 09-150314 A Japanese Patent No. 3314921

However, an optimal cutting process cannot be performed simply by simultaneously performing the fixed abrasive method using a wire with abrasive grains fixed to the outer periphery and the free abrasive method in which slurry is sprayed. In general fixed abrasive saw wires, abrasive grains are uniformly fixed on the outer periphery. Abrasive grains of 30 to 40 μm are widely used. Among them, about 60% is buried in the fixed layer of the wire. That is, about 12-16 micrometers of the fixed abrasive grain protrudes from the wire surface. When this saw wire is used, since the abrasive grains fixed to the wire are sharp, the cut wafer surface is roughened. This results in deep scratches on the wafer surface where extremely smooth quality is desired. The wafer obtained by the cutting process generally undergoes a step of polishing the surface. If deep flaws have occurred due to the cutting process, the wafer must be deeply polished. Then, material loss due to polishing increases and the yield deteriorates.

Further, the saw wire having the abrasive grains fixed on the outer periphery also has the abrasive grains fixed to a plane perpendicular to the surface through which the ingot is dug (hereinafter referred to as a cut surface). Therefore, the thickness of the kerf removed by cutting is approximated to a value obtained by adding twice the size of the abrasive grains to the diameter of the wire. That is, the material loss is increased as compared with the free abrasive type saw wire. The same applies to the case where the free abrasive grain method is carried out simultaneously.

In the case of a saw wire having uniform abrasive grains fixed on the outer periphery, the guide roller and the main roller that guide from the supply reel to the discharge reel are easily damaged by the fixed abrasive grains. For this reason, it is necessary to take measures such as making each roller hard so as not to be scratched, and the burden of capital investment has increased.

As described above, it is an object of the present invention to provide a fixed abrasive saw wire and a cutting method that suppress the deterioration of the surface roughness, thickness, and undulation of the wafer surface, reduce material loss, and reduce equipment damage. To do.

As means for solving the above-mentioned problems, the wire cross section has a shape having two straight flat portions facing each other in the longitudinal direction, and abrasive grains are fixed to at least one surface side connecting both flat surfaces. In the fixed abrasive saw wire, the fixed abrasive saw wire has a protruding amount of the fixed abrasive grains of 0 to 10 μm or less with respect to a flat surface with respect to the flat portion facing the wire.

It is preferable that the two flat portions facing each other as the wire cross-sectional shape are parallel. Furthermore, the wire cross-sectional shape is more preferably a track shape.

Furthermore, the wire cross-section has a shape having two straight flat portions facing each other in the longitudinal direction, and while moving a fixed abrasive saw wire with abrasive grains fixed to at least one side connecting both flat surfaces, A fixed-abrasive saw wire, which is performed while spraying a slurry containing abrasive grains, and the protruding amount of the abrasive grains fixed to a plane based on the plane portion facing the wire is equal to or less than the grain size of the free abrasive grains. By using the cutting method used, the ability of the wire can be maximized.

The slurry contains free abrasive grains. The loose abrasive is preferably SiC or diamond fine particles.

By using the saw wire of the present invention, a fixed abrasive type cutting speed is achieved. Further, the obtained wafer has a smooth surface and a stable thickness. In addition, since the wire thickness can be designed thin, cutting can be performed with little material loss.

Furthermore, the capability which the saw wire of this invention has can be exhibited to the maximum by using the saw wire of this invention and combining a loose abrasive type.

Typical sectional view of the saw wire of the present invention Other embodiments of the saw wire of the present invention Conventional fixed abrasive saw wire Sectional view in the cutting method of the present invention and the conventional example Schematic of loose abrasive rolling when using the wire of the present invention and loose abrasive together Cross section of cutting process of the present invention and the conventional example Sectional drawing of the state where the saw wire of the present invention is wound around the main roller Schematic diagram of a typical saw machine

The point of the present invention is that “abrasive grains are not fixed to a wire side surface (hereinafter simply referred to as a wire side surface) that is not a cut surface” and “the wire has a flat portion on the wire side surface”. is there. The operation at these two points will be described in detail below.

There is the following reason that “the abrasive grains are not fixed to the side surface of the wire”. One is based on the knowledge that, in the conventional fixed abrasive type, only a specific surface of the abrasive grains fixed to the wire is worn violently. The wire is wound around a plurality of main rollers. Under this circumstance, the twist of the wire is small, and the wire and the ingot are in contact with each other on substantially the same surface. That is, the abrasive grains fixed other than the surface in contact with the ingot hardly contribute to the cutting process.

The other is based on the knowledge that the abrasive grains fixed to the side surfaces of the wires are roughening the wafer surface as described above. The wafer is scratched by the fixed abrasive grains and suffers deep scratches. Generally, the size of abrasive grains to be fixed is several tens of μm. That is, the wafer is scratched by a maximum of several tens of micrometers.

From the above, it can be said that “the abrasive grains are not fixed to the side surface of the wire” is good.

However, it goes without saying that there is no problem even if the abrasive grains are fixed to the surface that does not contact the ingot. The effect that cutting | disconnection waste is easy to be discharged | emitted by the abrasive grain being fixed to the surface which does not contact an ingot, or the unevenness | corrugation is provided to the wire surface is expectable.

Moreover, since the abrasive grains are fixed only to a part, it is difficult to damage each part of the saw machine. In the saw wire cross section, since there are few portions to which the abrasive grains are fixed, it can be performed on the surface where the abrasive grains are not fixed when being applied to each roller. In that case, the groove of the roller for guiding the saw wire is preferably substantially U-shaped. The wire can be stably run while receiving the side without the abrasive grains with the groove.

Next, “the wire has a flat portion on the side surface of the wire” has the following reason. The conventional loose abrasive type generally uses a wire having a round cross section. Therefore, except for the condition of the presence or absence of loose abrasive grains in the slurry, the wafer surface and the wire are in line contact or point contact. As a result, it has been found that the surface roughness of the wafer is deteriorated. In contrast, because the wire side surface of the present invention is flat, the wafer surface and the wire are in surface contact.

Or, when the loose abrasive type is used in combination, loose abrasive grains often exist between the wafer surface and the flat portion of the wire. FIG. 4 shows a schematic view using the saw wire of the present invention and the free abrasive type. As in the present invention of FIG. 4, the flat portion of the wire is a condition that more loose abrasive grains are likely to receive the same pressure. In contrast, in the conventional method using both the fixed abrasive grain type and the loose abrasive grain type, the loose abrasive grains 20a do not effectively act on cutting or smoothing the wafer surface.

FIG. 5 shows the effect of loose abrasive grains present between the wafer surface and the flat portion of the wire. As shown in FIG. 5, more free abrasive grains cause equivalent rolling while the wafer surface and the wire plane move relative to each other. A lot of loose abrasive rolling successively destroys the fine protrusions present on the wafer surface. Thus, the wafer surface is finished more smoothly.

Furthermore, the position of the wire is stabilized by having a flat portion on the side surface of the wire. FIG. 6 shows a sectional view of the cutting process. Since the conventional wire has a circular cross-section, the cutting direction is not straight due to a slight change in tension (hereinafter referred to as “position misalignment”). Wafering of the wafer occurs due to this misalignment. On the other hand, the flat portion of the wire of the present invention and the wafer surface are substantially parallel, and the wire is sandwiched between the wafer surfaces during processing. Therefore, the position where the wire travels is stable, and the occurrence of undulation is prevented.

From the above, it can be said that “the wire has a flat portion on the side surface of the wire” is good.

In addition, it is preferable that the plane part to oppose is parallel. In that case, both planar portions are positioned in parallel with the wafer surface obtained by the cutting process. At this time, rolling of free abrasive grains occurs uniformly. However, the present invention is not limited to the case where both plane portions are parallel.

Moreover, since the effect which finishes a wafer smoothly will be acquired if it has a plane part, the restriction | limiting is not necessary for the magnitude | size of the area. The larger the area, the larger the number of loose abrasive grains that are rolled equivalently, and the greater the effect of finishing the wafer surface smoothly.

However, if the flat portion of the wire is made larger, the cross-sectional shape of the wire becomes flatter. FIG. 1 shows a cross-sectional view of the saw wire of the present invention. In the cross section of the wire, the distance between a pair of substantially flat portions is referred to as a minor axis b, and the other is referred to as a major axis a. When set in a general saw machine, for example, the main roller is wound around the major axis a as shown in FIG. The side in contact with the main roller in the major axis a direction is the inner peripheral side 28 of the wire and the other is the outer peripheral side 26 of the wire. At this time, if the cross-sectional shape of the wire becomes too flat, the stress difference between the inner peripheral side 28 and the outer peripheral side 26 of the wire increases. Particularly on the outer peripheral side, the tensile stress is large and the abrasive fixed layer is liable to break, and the occurrence of abrasive drop increases. Therefore, it is better to limit the flatness so that the stress difference between the inner peripheral side and the outer peripheral side does not increase. For example, the value a / b obtained by dividing the major axis a by the minor axis b is preferably the following numerical value.
1.0 <a / b <1.5
However, it should correspond to a desired cross-sectional shape depending on the form of the saw machine, and is not limited to the above range.

Further, the adhered abrasive grains are preferably trued. In general, the abrasive grains fixed to the wire are entirely covered with a fixing layer. In contrast, the state where the abrasive grains are trued is a state where the fixing layer at the tip of the abrasive grains covered with the fixing layer is removed. By doing so, it becomes a state where sharper abrasive grains are stripped off, and the initial cutting performance is particularly good.

The method of producing the wire of the present invention is as follows. First, a wire having a desired size and a round cross section is obtained by wire drawing or the like. By rolling the wire, a desired deformed wire having a round cross section and a flat surface on the side surface of the wire is obtained.

In addition, when finishing an irregular cross section, it is preferable that the cross section is symmetrical with respect to the center line in the major axis direction. In general use, the cutting direction coincides with the major axis direction. At this time, if left-right asymmetry, the axis is shifted with respect to the cutting direction, and cutting cannot be performed properly. However, it should correspond to a desired cross-sectional shape depending on the form of the saw machine, and is not limited to a symmetrical wire.

A conventional method may be used to fix the abrasive grains to the wire. Generally, after the wire is immersed in a molten metal or resin layer or plated, or at the same time, the abrasive grains are dispersed and temporarily fixed. Since the surface to be fixed is specified, there is no particular limitation as long as it is a method for fixing to the portion. Thereafter, a treatment is performed to make the fixation more reliable.

In the case of the method in which the abrasive grains are temporarily fixed all around, it is necessary to remove the abrasive grains temporarily fixed to the side surface of the wire. The method for removing the abrasive grains can be easily removed by bringing them into physical contact with, for example, a roller. Since it can be easily removed as long as it is temporarily fixed, it is not particularly limited to this method.

In addition, the process of obtaining the wire of the irregular cross section which has a plane part may be after fixing an abrasive grain. When the flat portion is formed by rolling, for example, after temporary fixing, the abrasive grains are aligned so as not to exceed the extension line of the wire flat portion. Therefore, a flatter wire side surface is formed.

It is very important that the “abrasive grains are aligned so that they do not exceed the extended surface of the wire plane portion”. This is because the wafer surface is roughened when the fixed abrasive grains have a larger amount of protrusion than the extended surface of the wire plane portion. That is, it means that the same form as that when the abrasive grains are fixed to the wire plane portion is obtained. Therefore, it is desirable that the fixed abrasive grains be aligned so as not to exceed the extended surface of the wire plane portion as much as possible.

However, in particular, in the case of a cutting process using free abrasive grains, the extension of the wire plane part may be slightly exceeded. That is, there is no problem as long as the protruding amount is equal to or less than the grain size of the free abrasive grains. This is because, in this case, loose abrasive grains larger than the protruding abrasive grains contact the wafer surface. Since rolling or lapping with free abrasive grains precedes, scratches due to fixed abrasive grains are extremely small. Since generally used abrasive grains are # 1000 to 1500 (particle diameter is about 10 to 15 μm), there is no problem if the protruding amount of the abrasive grains is 10 μm or less.

Table 1 shows the results of actual cutting with the saw wire of the present invention. Table 1 shows the results of evaluating the surface roughness and undulation of the wafer when a 2-inch silicon ingot was cut. As a conventional example, a free abrasive grain type and a fixed abrasive grain type, as an example of the present invention, only the saw wire of the present invention and the saw wire of the present invention are combined with the free abrasive grain type, and the wafers obtained are compared. It was. The surface roughness and undulation of the wafer was measured using a contact type surface roughness meter.

The surface roughness (Rz) was measured in the range of 2.5 mm for each of the three points of the cutting start portion, the central portion, and the cutting end portion of the obtained wafer with respect to the cutting direction. The maximum value among the three measured points was used as a comparative control. Similarly, the maximum height difference was evaluated for 40 mm from the cutting start part to the end part of the wafer with respect to the cutting direction. Furthermore, relative evaluation is performed by setting the processing speed, the maximum surface roughness and the undulation in the conventional loose abrasive type to 1.

In the saw wire of the present invention, a flat portion was formed at the time of temporary fixing of the abrasive grains, and the saw wires were aligned. Therefore, a saw wire in which the protruding amount of the fixed abrasive grains with respect to the flat portion was 0 to 1 μm was used. Further, as a comparative example, by another manufacturing method, cutting is performed by using a free abrasive grain in combination with a saw wire having a flat portion, fixing abrasive grains only in the cutting process direction, and a fixed abrasive grain protruding amount of 20 μm. went. In all runs, loose abrasive # 1500 was used.

From the results shown in Table 1, the present invention has improved surface roughness and undulation compared with the results of the conventional method. Even when no loose abrasive is used in combination, the reason why the effect is obtained as compared with the conventional fixed abrasive type is presumed as follows.

In the saw wire of the present invention, the same cutting process as in the conventional fixed abrasive type is performed. At this time, large cutting waste is generated. In the conventional saw wire, the cutting waste is easily taken in between the abrasive grains uniformly fixed to the outer periphery. However, in the saw wire of the present invention, the abrasive grains are fixed only on the cut surface. Accordingly, the amount of cutting waste not remaining between the abrasive grains and overflowing to the side surface of the wire increases. It is presumed that these cutting scraps work effectively between the flat portion of the wire and the wafer surface.

That is, it performs the same function as the abrasive grains in the slurry in the free abrasive type. The cutting waste is the same component as the wafer, and has sufficient hardness to polish the wafer surface. The cutting scraps roll or wrap between the wire plane portion and the wafer surface to destroy the convex portion of the wafer surface. By this destruction, the wafer surface is finished to a smooth surface.

When loose abrasive grains were used in combination with the saw wire of the present invention, a much smoother surface than the conventional loose abrasive type was achieved. Regardless of the combination of loose abrasive grains, the saw wire of the present invention achieved the same cutting speed as that of the conventional fixed abrasive grain type.

In addition, the processing speed is also high when the protruding amount of the abrasive grains implemented as a comparative example is large. However, the surface roughness of the wafer was poor and the undulation was also worsened. This is because the fixed abrasive grains easily scratch the wafer surface due to the large protrusion amount. In addition, the distance between the flat portion of the wire and the wafer surface increases, and the wire is not stable. As a result, the cutting direction was not stable and the wafer quality deteriorated.

In contrast, according to the present invention, the wire was not misaligned during the cutting process and was stable, so that a good wafer surface with small undulation was finished.

Although the present invention relates to a saw wire, it can be assumed that a blade saw used for cutting a hard material can also be diverted.

2 Saw wire 4 Core material 6 Abrasive grain fixing layer 8 Wire side face 10 Abrasive grain (adhesion)
12 Truing unit 20 Free abrasive grains 22 Wafer surface 24 Cutting scraps 102 Supply reel 104 Main roller 106 Discharge reel 108 Ingot

Claims (3)

In the fixed abrasive saw wire characterized in that the wire cross section has a shape having two straight flat portions facing each other in the longitudinal direction, and the abrasive grains are fixed to at least one surface side connecting both flat surfaces.
A fixed-abrasive saw wire in which the protruding amount of the fixed abrasive grains is 0 to 10 μm with respect to a plane based on the plane portion of the wire. 2. The fixed abrasive saw wire according to claim 1, wherein the cross-sectional shape of the wire is a track shape. While running a fixed-abrasive saw wire in which the wire cross-section has a shape having two straight flat portions facing each other in the longitudinal direction and the abrasive grains are fixed to at least one surface connecting both the flat surfaces, free abrasive grains The fixed abrasive type saw wire is used in which the amount of protrusion of abrasive grains fixed to a plane with reference to the plane portion facing the wire is equal to or less than the grain size of the free abrasive grains. Cutting method to be performed.