KR100888026B1 - Saw wire - Google Patents

Abstract

A saw wire is provided to deal with a thickness deviation of a wafer due to the reduction of the diameter and supply defect of an abrasive by limiting the longitudinal residual stress to 400~1000MPa in the region of 5~10micro meter depth from the surface. In a saw wire for cutting hard material like a silicon block, diameter(D0) of the saw wire ranges from 0.08~0.03mmPhi. The longitudinal residual stress of the saw wire ranges from 400~1000MPa in the region of the depth of 5~10micron meters apart from the surface.

Description

Saw wire

The present invention relates to a saw wire, and more particularly to a saw wire excellent in workability.

In general, saw wire is used for cutting hard materials such as magnetic head chips or single crystal ingots for semiconductor wafers. The saw wire cut | disconnects a to-be-processed object by running, contacting to a to-be-adjusted object with the grinding liquid which mixed grinding particles, such as a silicon carbide powder and a diamond powder, and a lubricant, such as an oil.

The saw wire is made of high carbon steel wire having a high strength of 3300MPa to 4500MPa and a diameter of 0.08mmΦ to 0.3mmΦ to withstand the high tension received during grinding.

Furthermore, it is widely practiced to plate a copper, tin or brass that is softer than a high carbon steel wire material in order to meet the precise dimensional tolerances for use purposes and to ensure freshness. In particular, because brass is rich in ductility, there are many advantages when plating it on saw wires. That is, when brass is plated on the saw wire, the plated brass not only carries a lubricant between the saw wire and the drawing die, but also gives a lubricating function, so that the brass plated saw wire is relatively high precision. It is possible to suppress the disconnection even at very fast drawing speed while maintaining the wire diameter tolerance and roundness of the wire, thereby producing the saw wire at low production cost.

A method of forming a semiconductor wafer by cutting a hard material such as a silicon block using a saw wire is as follows. A series of saw wire rows are wound around a plurality of rollers having a plurality of grooves at a predetermined pitch, and then the series of saw wire rows are run. The silicon block to be cut is pressed with a predetermined force in this series of saw wire rows. At the same time, a polishing liquid is flowed between the saw wire row and the silicon block to cut the silicon block by the grinding action of the abrasive grains, thereby producing a wafer.

When using a saw wire to cut a hard material such as a silicon block to produce a product such as a semiconductor wafer, the efficiency of the cutting process and the quality of the cut wafer thickness are determined by the characteristics of the silicon block being cut and the running speed of the saw wire. It depends on many of the same factors. Among these various factors, how uniform the thickness of the saw wire and how much the saw wire can accompany the abrasive is important.

The series of saw wire rows used to cut hard materials, such as silicon blocks, are typically wound about 300 to 1000 times on a roller. The individual saw wires constituting this row of saw wires move along the grooves of the rollers during cutting of hard materials such as silicon blocks, where the saw wires are abrasives contained in the abrasive liquid injected between the silicon blocks and the saw wires. There is a problem in that the thickness of the wear is affected by the grinding action of the.

In addition, in the case where a soft plating layer is formed on the surface of the saw wire, in the initial stage of cutting the silicon block by the saw wire, the abrasive may be entrained by the soft plated layer on the surface of the saw wire, but as the cutting of the silicon block progresses the saw The soft plating layer on the surface of the wire is gradually removed to expose the base layer, thereby degrading the ability to accompany the abrasive. Accordingly, not only the efficiency of the cutting process of the hard material such as the silicon block is lowered, but also the thickness of the manufactured semiconductor wafer is not uniform and the flatness of the surface of the semiconductor wafer is deteriorated.

As a solution to this problem, saw wires having improved ability to accompany abrasives are disclosed in WO 90/12670. The saw wire disclosed in WO 90/12670 improves the ability to accompany abrasives by modifying its outer surface. That is, the ability to accompany the abrasive is improved by forming micro-cavities on the surface of the saw wire or by providing a plurality of circumferential grooves to have various diameters. However, this prior art has a problem that it is not easy to deform the outer surface of the saw wire.

In the present invention, even when the saw wire is worn and the diameter is reduced when cutting the hard material, the saw wire is significantly improved in the abrasive accommodating ability, thereby improving the efficiency of the cutting process, improving the uniformity of the thickness of the wafer, and the surface flatness. It is aimed at improving its.

In the saw wire used for cutting a hard material such as a silicon block, the present invention has a wire diameter of 0.08 mm? 0.30 mm?, And a depth from the surface of the saw wire is 5 µm to 10 µm. Disclosed is a sawing wire having a residual stress in the longitudinal direction of the sawing wire in a range of 400 MPa to 1000 MPa.

In the present invention, the height of the wave shape after the use of the saw wire is H _W , the pitch of the wave shape after the use of the saw wire is P _W , the wire diameter before the use of the saw wire is D ₀ , and the wire diameter after the use of the saw wire is In the case of D ₁ , it is preferable to satisfy H _W = 0.5 (D ₀ -D ₁ ) to 1.5 (D ₀ -D ₁ ) and P _W = 30D ₀ to 50D ₀ .

In the process of manufacturing a wafer by cutting a silicon block using a saw wire, the present inventors have investigated the characteristics of the saw wire that affects the efficiency of the cutting process and the quality of the cut wafer. Could confirm.

First, as the process of manufacturing the wafer by cutting the silicon block using the saw wire, the diameter of the saw wire is reduced. The diameter of the saw wire is reduced depending on the conditions of the working process, but the diameter of the saw wire is usually reduced from 10 μm to 20 μm after the work.

Second, after use, the shape of the saw wire may occur when the circles of the saw wire are changed and when the wave shape is generated.

Third, the efficiency of the cutting process may be higher in cases where the residual wave form appears on the saw wire after use than in the other cases.

Fourth, the quality of the wafers produced, as is generally known, may be better when the wave form appears on the saw wire after use than otherwise.

The present inventors have obtained the following conclusions after studying the above facts.

In the process of manufacturing a wafer by cutting a hard material such as a silicon block using a saw wire, there is a section in which the residual wave shape generated in the saw wire during use increases the efficiency of the cutting process and the wafer quality. The section shall satisfy the following relation for the wire diameter of the saw wire before and after use.

H _W = 0.5 (D ₀ -D ₁ ) to 1.5 (D ₀ -D ₁ ),

P _W = 30D ₀ ~ 50D ₀

Here, H _W is the wave-like height after the use of the saw wire, P _W is the wave-like pitch after the use of the saw wire, D ₀ is the wire diameter before the use of the saw wire, and D ₁ is the wire diameter after the use of the saw wire ( 1 and 2).

In addition, the saw wire that satisfies the above conditions should have the residual stress (tensile residual stress) in the longitudinal direction of the saw wire in the range of 400 MPa to 1000 MPa in the region where the depth from the surface thereof is in the range of 5 μm to 10 μm. .

The reason for setting the above conditions in the present invention is as follows.

The reason for limiting the wave height after the use of the saw wire to 0.5 to 1.5 times the amount of change in the diameter before and after the use of the saw wire is a wave that can compensate for the change in the thickness of the wafer accompanying the decrease in the saw wire diameter during use. It is because it confirmed that the height of a phase is 0.5 to 1.5 times with respect to the diameter change amount before and behind use of a saw wire.

In addition, the reason why the wave-like pitch before the use of the saw wire is limited to 30 to 50 times the diameter before the use of the saw wire is that the wave-like pitch before the use of the saw wire is smaller than 30 times the diameter before the use of the saw wire. In this case, when the wave phase occurs, the tension of the saw wire becomes excessive when the wave phase occurs, which increases the possibility that the saw wire is disconnected, and the pitch of the wave before the saw wire is 50 times the diameter of the saw wire before use. This is because when it becomes larger than twice, it is difficult to achieve the object of the present invention, which is an increase in the amount of abrasive supplied due to the generation of waves.

The reason for limiting the residual stress in the longitudinal direction of the saw wire to the region having a depth of 5 μm to 10 μm from the surface of the saw wire is that when the depth is less than 5 μm from the surface of the saw wire, Even if the residual stress of is large, the depth is too small compared to the entire wire to produce the desired wave shape. If the depth is greater than 10 μm from the surface of the saw wire, the wave shape is already formed. Because it does not have a big impact.

Further, the reason for limiting the residual stress in the longitudinal direction of the saw wire in the range of 400 MPa to 1000 MPa is that at a lower value, the desired wave shape cannot be formed, and at higher values, the wave shape height is used to achieve the object of the present invention. This is because it becomes larger than 0.5 (D ₀ -D ₁ ) to 1.5 (D ₀ -D ₁ ) to deteriorate the quality of the wafer.

More preferably, the residual stress in the longitudinal direction of the saw wire is preferably limited to the range of 450 MPa to 950 MPa. The reason is that as the wafer is manufactured by cutting the silicon block using the saw wire, the ratio of the depth of wear of the saw wire and the wave height formed at this time is 0.7 (D ₀ -D ₁ ) to 1.3 (D ₀ -D ₁ ). This is because a small variation in the log results in a wafer having a uniform thickness with little difference between the thickness of the first wafer and the last wafer when the silicon block is cut.

The saw wire of the present invention is proportional to the reduction of its diameter during use of the saw wire by limiting the residual stress in the longitudinal direction in the range from 400 MPa to 1000 MPa in the region from 5 μm to 10 μm in depth from its surface. By forming the residual wave shape, thereby compensating the wafer thickness variation due to the decrease in diameter and the supply instability of the abrasive, significantly improving the cutting speed and significantly improving the quality of the wafer. Accordingly, the saw wire of the present invention can be used not only for wafers requiring ultra-precise surfaces, such as magnetic heads such as VTR and ATR, and semiconductor chips, but also for manufacturing solar wafers for solar power generation requiring high productivity.

The invention is explained in more detail by the following examples in conjunction with the accompanying drawings.

A saw wire according to a preferred embodiment of the present invention will be described. The saw wire has a diameter from 0.08 mm to 0.30 mm, and the residual stress in the longitudinal direction of the saw wire is from 400 MPa to 1000 MPa in the region from 5 μm to 10 μm in depth from the surface.

Seven saw wires having a diameter of 0.14 mm and different residual stresses in the longitudinal direction were produced. Using these seven saw wires, three silicon blocks having a cross section of 156 mm x 156 mm were simultaneously cut to compare the roughness of the wafers. The working conditions used at this time were 470 mm in length of a silicon block, 47 micrometers in pitch of a saw wire, 12.5 m / sec of a feed rate of a saw wire, and 360 micrometer / min of cutting speed of a silicon block. In addition, in order to compare the cutting performance, the maximum cutting speed at which the saw wire passing through the silicon block was not warped was also measured. The measured results are shown in Table 1 below.

TABLE 1

Tensile strength (MPa) Residual stress (MPa) Wire form after use Wafer Defect Rate (%) Cutting speed (㎛ / min) Diameter change (㎛) Hw (μm) Pw (μm) damage TTV thickness Sawing Marks Example 1 3,787 487 13 9 5,086 1.9 0.5 0.3 5.6 680 Example 2 3,839 695 14 13 5,495 1.3 0.0 0.0 1.2 745 Example 3 3,820 812 14 15 4,902 1.6 0.0 0.0 1.8 765 Example 4 3,852 916 15 17 6,538 2.2 0.7 0.6 3.7 740 Comparative Example 1 3,846 247 12 0 ∞ 5.4 5.8 4.3 33.1 440 Comparative Example 2 3,794 1,130 17 42 5,966 7.7 4.2 5.3 25.7 575 Comparative Example 3 3,835 1,185 19 23 7,538 6.9 4.9 5.1 28.6 523

As shown in Table 1 above, it can be seen that Examples 1 to 4 of the present invention significantly reduce the defect occurrence rate of the wafer at the time of cutting the silicon block compared to Comparative Examples 1 to 3. In addition, it can be seen that the maximum cutting speed of Examples 1 to 4 of the present invention is about 1.5 times faster than the maximum cutting speed of Comparative Examples 1 to 3.

As can be seen in the above embodiment, the present invention limits the residual stress in the longitudinal direction of the saw wire from 400 MPa to 1000 MPa in the region from 5 μm to 10 μm deep from the surface, thereby providing a maximum cutting speed and wafer quality. It can be seen that it shows an improvement effect that significantly improves.

The present invention relates to a saw wire used in a wire saw machine, and can be used for cutting and slicing hard materials such as semiconductors, ceramics, cemented carbides, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the height and pitch with respect to the wave image before use of the saw wire which concerns on one Example of this invention.

2 is a view showing the height and pitch of the wave image after the use of the saw wire in one embodiment of the present invention.

Brief description of symbols for the main parts of the drawings

D ₀ : Diameter before use of saw wire D ₁ : Diameter after use of saw wire

H _W : Height of wave after use of saw wire

P _W : Pitch on wave after use of saw wire

Claims (3)

In the saw wire used for cutting hard materials such as silicon blocks, The wire diameter of the saw wire is in the range of 0.08 mmΦ to 0.30 mmΦ, A saw wire having a residual stress in the longitudinal direction of the saw wire in a range of 400 MPa to 1000 MPa in a region where a depth from the surface of the saw wire is in a range of 5 μm to 10 μm. The method of claim 1, When the height of the wave shape after the use of the saw wire is H _W , the pitch of the wave shape after the use of the saw wire is P _W , the wire diameter before the use of the saw wire is D ₀ , and the wire diameter after the use of the saw wire is D ₁ . , H _W = 0.5 (D ₀ -D ₁ ) to 1.5 (D ₀ -D ₁ ), P _W = 30D ₀ ~ 50D ₀ Saw wire to satisfy. The method according to claim 1 or 2, A saw wire having a residual stress in the longitudinal direction of the saw wire in a range of 450 MPa to 950 MPa in a region in which a depth from the surface of the saw wire is in a range of 5 μm to 10 μm.

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