JP3202591B2 - How to cut wire saws and cylindrical workpieces - Google Patents

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 cylindrical work of a brittle material such as a semiconductor ingot typified by silicon or gallium arsenide to form a wafer and a method for cutting the same.

[0002]

2. Description of the Related Art A wire saw is spirally wound between a plurality of rollers, and is wound on a wire which is parallel to a workpiece and is arranged in a row at a constant pitch. The wire saw is a cylindrical workpiece such as a semiconductor ingot or a synthetic quartz ingot. While pressing a rectangular work such as a workpiece, and supplying a processing liquid (hereinafter, referred to as slurry) containing abrasive grains between the work and the wire, the wire is moved in a linear direction to cut the work into a wafer shape. The apparatus is capable of cutting a large number (for example, several hundreds) of wafers having a constant thickness at the same time.

[0003]

However, the cutting of a cylindrical work such as a semiconductor ingot by the wire saw is different from the cutting of a square work such as the synthetic quartz ingot at the beginning of cutting the cylindrical work. There is a problem that the thickness of the obtained wafer is different between when cutting the central portion of the workpiece and when cutting is completed.

That is, as shown in FIG. 1A, the thickness of the wafer becomes relatively thin at the start and end of cutting, while the thickness of the wafer becomes relatively thick at the center of the work. I will. That is, in a single wafer, the middle of the cut surface becomes convex, causing a thickness variation, and this phenomenon occurs in almost all wafers obtained by one cut. The occurrence of this thickness variation is a problem inherent in cutting a cylindrical work by a wire saw, and the thickness variation tends to increase with an increase in the diameter of the cut cylindrical work. Especially, uniformity of thickness is required, and device integration will increase more and more in the future.
This is particularly problematic in the cutting of semiconductor silicon single crystal wafers having diameters as large as 300 mm or more.

The present invention has been made in view of the above-mentioned problems, and when a cylindrical work is cut by a wire saw, a cylindrical work can be obtained, in particular, a wafer having a small thickness variation can be obtained. It is an object to provide a method and an apparatus.

[0006]

According to a first aspect of the present invention, there is provided a method for cutting a cylindrical work using a wire saw, the method comprising: changing a cutting length of the cylindrical work. Alternatively, the viscosity of the cutting slurry supplied to the work is changed by changing the angle between the wire and the outer periphery of the work. In this way, by changing the viscosity of the cutting slurry supplied to the work, the work amount for the work is adjusted to be constant,
The thickness of the wafer to be cut can be made uniform.

According to a second aspect of the present invention, there is provided a method for cutting a cylindrical work according to the first aspect, wherein the viscosity of the slurry is increased as the cutting length of the cylindrical work is increased. And then reducing the viscosity of the slurry with decreasing cutting length. As described above, by increasing or decreasing the viscosity of the slurry according to the cutting length of the cylindrical work, the cylindrical work can be cut out with a uniform thickness distribution.

Further, according to a third aspect of the present invention, there is provided a method for cutting a cylindrical workpiece according to any one of the first and second aspects, wherein the change rate of the viscosity of the slurry is changed. Is characterized in that, compared with the rate of increase in slurry viscosity from the start of cutting to the cutting of the center of the cylindrical work, the rate of decrease in slurry viscosity from the cutting of the center of the cylindrical work to the end of cutting is reduced. . Thus, by changing the rate of increase or decrease in the viscosity of the slurry between the start of cutting the cylindrical work and the center part and the time of cutting the center part of the cylindrical work and the end of cutting, the thickness distribution can be increased. Can be made uniform.

According to a fourth aspect of the present invention, there is provided a method for cutting a cylindrical workpiece according to any one of the first to third aspects, wherein the change in viscosity of the slurry is not changed. And by adding a viscosity modifier to the slurry tank. Water can be used as the viscosity modifier of the slurry (Claim 5), and the coolant component of the slurry is desirably water-soluble (Claim 6). Thus, the change in viscosity can be easily adjusted by adding the viscosity modifier to the slurry tank.In that case, if the viscosity modifier is water and the coolant component of the slurry is water-soluble, The viscosity of the slurry can be adjusted and controlled reliably and at low cost.

The wire saw for cutting a cylindrical work according to the present invention includes means for changing the viscosity of the cutting slurry supplied to the work by changing the cutting length of the cylindrical work or changing the angle between the wire and the outer periphery of the work. It is characterized by comprising (claim 7). For the first time, the method according to claims 1 to 6 can be performed with a wire saw having such characteristics, and a wafer having a uniform thickness can be cut out.

The means for changing the viscosity of the cutting slurry includes at least a slurry viscosity detector and a flow controller for a viscosity modifier, detects the slurry viscosity in the slurry tank, and adjusts the viscosity in accordance with the value. The flow rate of the adjusting agent supplied to the slurry tank is controlled (claim 8). Here, the detection of the viscosity of the slurry in the slurry tank is desirably performed by a mass flow meter or a measurement of electric conductivity (Claim 9). Can be used (claim 10), and water can be used as a viscosity modifier of the slurry (claim 11). In this case, it is desirable to provide a means for stirring the slurry in the slurry tank to make the viscosity of the slurry in the slurry tank uniform.

Hereinafter, the present invention will be described in more detail. The inventor of the present invention has investigated and examined the causes of thickness variations when cutting the cylindrical work, and as a result, when cutting a cylindrical work such as a semiconductor ingot, when cutting the cylindrical work was started. When the wire and the workpiece were cut, and when the cutting was completed, the contact length between the wire and the workpiece, that is, the cutting length, was different, so the work amount of the wire and slurry on the workpiece would be different. . That is, since the cutting length is short at the start and end of cutting, the work amount of the wire and slurry on the work becomes relatively large, and as a result, the cutting allowance at the time of cutting increases,
The thickness of the wafer becomes thin. On the other hand, it is considered that the work length for the work becomes relatively small because the cutting length is long at the center of the work, and as a result the cutting allowance at the time of cutting is reduced, and the thickness of the wafer is considered to be large. Can be

The angle between the wire and the outer periphery of the work is acute from the start of cutting to the center of the work, and is obtuse from the center of the work to the end of cutting. In particular, at the start of cutting, the angle between the wire and the outer periphery of the work is sharp and has a wedge shape, so that the slurry is easily drawn into the cutting portion. On the other hand, since the angle between the wire and the outer periphery of the work becomes obtuse from the center of the work to the end of the cutting, the drawing of the slurry into the cutting portion tends to be deteriorated. For this reason, at the start of cutting, the work amount of the wire and the slurry on the work becomes particularly large, and as a result, the cutting amount at the start of cutting becomes particularly large. It is considered that the wafer becomes thin and a wafer having a shape as shown in FIG. 1A is cut out.

The inventor of the present invention has conceived of suppressing the variation in the thickness of the wafer by keeping the work amount constant for the cylindrical work regardless of the length of the cutting length or the change in the angle between the wire and the outer periphery of the work. In order to make the amount of work applied to the work constant, it was confirmed that it was effective to change the viscosity of the slurry in accordance with the change in the cutting length of the work or the angle between the wire and the outer periphery of the work. Completed.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited to these embodiments. Here, FIG. 1 is a conceptual diagram showing a cross-sectional shape of a wafer cut by a wire saw. FIG. 1A shows a wafer cut by a conventional apparatus and method, and FIG.
Shows a wafer cut by the apparatus and method of the present invention. FIG. 2 is a schematic diagram of a wire saw. FIG. 3 is a schematic view showing a cross section of the wire saw according to the embodiment of the present invention. FIG. 4 is a schematic view showing a cross section including the circulation system of the slurry of the wire saw of the present invention.

FIG. 2 is a schematic diagram showing a schematic configuration of a wire saw. In this wire saw, a wire 12 wound around two wire winding drums 22 and 32 driven by torque motors 24 and 34, respectively, is spirally wound between three rollers 10A, 10B and 10C. The wire 12 is parallel to each other at a constant pitch between the two rollers 10A and 10B,
The work is cut at this part. Further, for example, the wire 12 can be moved at a predetermined speed by rotating the roller 10C by a drive motor 7 connected to the lower roller 10C. When the wire 12 is wound from the wire winding drum 22 to the other wire winding drum 32 or in the opposite direction at a predetermined linear speed via the tension adjusting mechanisms 20 and 30, a cutting slurry (not shown) By pressing the columnar work 40 held by the work holder 42 onto the work cutting portion between the two rollers 10A and 10B while supplying the slurry from the supply device to the work cutting portion via the wire 12, The work 40 is cut.

FIG. 3 is a schematic sectional view showing the embodiment of the present invention when the wire saw of FIG. 2 is viewed from the direction A. The cutting slurry consists of two rollers 10A and 10B
The slurry supply nozzles 50A, 5A,
0B. When cutting the cylindrical work, when the wire 12 is sent from the roller 10A to the roller 10B, the slurry is supplied from the supply nozzle 50A, and when the wire 12 is sent in the opposite direction, the slurry is supplied from the supply nozzle 50B. You. The slurry supply nozzles 50A and 50B are connected to the rollers 10A or 10A.
A number of nozzles are arranged in the longitudinal direction of B, and the flow of the slurry has a curtain shape.

Next, FIG. 4 is a schematic sectional view of the wire saw including the circulation system of the slurry. In this apparatus, at the time of cutting a cylindrical work, the pressure of the cutting slurry 62 stored in the slurry tank 60 is increased by a pump 66 and supplied to the wire 12 from the slurry supply nozzle 50A or 50B through a slurry supply pipe 64, and the work is cut. Forty cuts. Slurry scattered from the cut portion of the work 40 and the wire 12 is collected at the bottom of the wire saw cover 70, collected in the slurry tank 60 by the slurry collection pipe 72, and again passed through the slurry supply pipe 64 to cut the slurry of the work 40. To form a circulatory system that is fed to

The slurry tank 60 is provided with a slurry viscosity detector 61. The viscosity adjusting agent is supplied from the viscosity adjusting agent tank 80 to the slurry tank 60 through a viscosity adjusting agent supply pipe 82. The pipe 82 is provided with an electromagnetic valve 84, and the electromagnetic valve 84 is connected to the slurry viscosity detector 61. By controlling the opening / closing degree in accordance with the slurry viscosity detected by the method and the cutting length of the work or the angle between the wire and the outer periphery of the work, the slurry viscosity in the slurry tank can be adjusted. .
The adjustment of the slurry viscosity is performed by processing the viscosity signal and the output of the encoder for confirming the movement position of the cutting length by a converter,
This can be performed by opening and closing the electromagnetic valve 84. As the viscosity detector 61, a generally used viscometer may be used, and it is preferable that the viscosity is obtained by measuring a mass flow meter or electric conductivity. This is because according to these methods, so-called on-line viscosity measurement becomes possible, and control and management of slurry viscosity can be performed accurately and easily.

It is preferable to provide a slurry agitator 63 in the slurry tank 60 in order to mix the supplied viscosity modifier and the slurry and to make the slurry viscosity in the slurry tank 60 uniform. The stirring means may be in accordance with a generally used technique, for example, a rotating mechanism in which a stirring rod is immersed in the slurry 62 and rotated by a motor, a swing mechanism, a vibration mechanism, or the like. Further, the cutting length can be detected from the positional relationship of the work 40 with respect to the wire 12, and for example, can be easily determined from the distance of pressing the work holder 42 against the wire 12 and the diameter of the work.

The cutting slurry is usually circulated and used as shown in FIG. 4, but the heat generated during cutting of the work evaporates the water in the slurry, and the slurry collected in the slurry tank 60 has a viscosity. It is very expensive.
Here, of the components contained in the slurry, almost all of the abrasive grains and the coolant component are recovered because the former is solid, and almost the entire amount is recovered because the latter is nonvolatile. Therefore, only the water serving as the medium is lost during cutting among the components of the slurry.

Therefore, when water is used as the viscosity modifier, the viscosity of the slurry can be adjusted by adjusting the amount of water in the slurry. That is, by controlling the amount of water as the viscosity adjusting agent fed from the viscosity adjusting agent tank 80, the viscosity of the slurry in the slurry tank 60 can be freely adjusted and controlled. And
When water is used as the viscosity modifier, the coolant component of the slurry is preferably water-soluble so as to be uniformly mixed with water.

When the viscosity of the slurry increases, the slurry is easily wound around the wire, and the slurry is easily drawn into the work cutting section. As a result, a large amount of slurry is supplied to the work cutting section, and the Work load will increase. On the other hand, if the viscosity of the slurry decreases, the opposite effect will be achieved.

In the present invention, the viscosity of the slurry is adjusted according to the change in the cutting length of the work and the angle between the wire and the outer periphery of the work, thereby reducing the thickness variation of the cut wafer. That is, FIG. 5 shows a pattern example of the change in the slurry viscosity. When the cutting of the work 40 is started, the viscosity of the slurry is minimized, and the viscosity of the slurry is increased with an increase in the cutting length. So that the viscosity of the slurry is the highest,
Next, the viscosity of the slurry is reduced as the cutting length is reduced.

The change pattern of the viscosity of the slurry is different from the rate of increase in the viscosity of the slurry from the start of cutting to the cutting of the center of the cylindrical work. The viscosity reduction rate is reduced. As shown in FIG. 1 (a), this is because the wire and slurry during the cutting from the center of the cylindrical work to the end of the cutting are smaller than the time from the start of cutting to when the center of the cylindrical work is cut. This corresponds to the relative decrease in the workload for the work.

[0026]

EXAMPLES Examples of the present invention and comparative examples will be described below. (Example) A wire saw of the present invention has a diameter of about 20.
A 0 mm semiconductor silicon single crystal ingot was cut. The slurry viscosity pattern as shown in FIG. 5 was used.
Pa · s, the slurry viscosity is increased as the work cutting length is increased, the slurry viscosity is 100 mPa · s when cutting the center of the ingot, and then the slurry viscosity is reduced as the cutting length is reduced, and 60 mP at the end of cutting.
a · s. Under these conditions, 10 ingots were cut, and about 2500 wafers were cut out. As shown in FIG. 6, the thickness of the obtained wafer was a total of 5 points at the center of the wafer and at the periphery (3 mm from the periphery in each direction).
Measurement was made at points, and the difference TV5 between the maximum value and the minimum value was determined.

Comparative Example 1 A semiconductor having a diameter of about 200 mm was prepared in the same manner as in Example except that the slurry viscosity was adjusted to 60 mPa · s at the start of cutting, but the slurry viscosity was not adjusted at all after the start of cutting. A silicon single crystal ingot was cut. Five ingots were cut, and about 1000 wafers were cut out. As shown in FIG. 6, the thickness of the obtained wafer is measured at a total of five points, that is, at the center of the wafer and at the periphery (3 mm from the periphery in each direction), as shown in FIG. 6, and the difference TV5 between the maximum value and the minimum value is obtained. Was.

Comparative Example 2 A slurry having a diameter of about 200 mm was prepared in the same manner as in Example except that the slurry viscosity was adjusted to 80 mPa · s at the start of cutting, and the slurry viscosity was maintained at 80 mPa · s from the start to the end of cutting. Of the semiconductor silicon single crystal ingot was cut. Five ingots were cut, and about 1000 wafers were cut out.
As shown in FIG. 6, the thickness of the obtained wafer is
The measurement was performed at a total of five points, that is, four points at the center of the wafer and at the periphery (3 mm from the periphery in each direction), and the difference TV5 between the maximum value and the minimum value was determined.

The results obtained in the examples, comparative examples 1 and 2 are summarized in Table 1.

[Table 1]

The cross-sectional shape of the wafer cut by the method and apparatus of the present invention is as shown in FIG. 1 (b). A remarkable improvement was observed as compared with (a). As can be seen from Table 1, according to the present invention, TV5, which is an index of thickness variation in the wafer surface, is greatly reduced as compared with the comparative example. Furthermore, FIG.
Since the cut surface was uniform and smooth as shown in (b), the crack generation rate of the wafer was greatly improved. Therefore, according to the present invention, it is possible to improve not only the variation in thickness but also the cutting yield and productivity.

The present invention is not limited to the above embodiment. The above embodiment is an exemplification, and has substantially the same configuration as the technical idea described in the scope of the claims of the present invention. It is included in the technical scope of the invention.

For example, the “cylindrical work” in the present invention does not mean only a columnar work whose cut surface is completely circular, but has a cut surface of an ellipse or a circle, but a part thereof. This includes the case where there is a notch (so-called orientation flat). If the cutting of the work changes the cutting length or the angle between the wire and the periphery of the work as the cutting progresses, the slurry may be appropriately adjusted according to the form. The viscosity pattern can be changed and applied in the same manner as described above.

In the above embodiment, the case where water is used as the viscosity modifier has been described by way of example. However, the present invention is not limited to this, and other solvents, such as various organic solvents, may be used. You can also.

Further, in the above embodiment, the case where the solenoid valve is used to adjust the feed amount of the viscosity modifier has been described by way of example. However, the present invention is not limited to this. If it is possible to adjust and control the feed amount of
Various other commonly used valves or various flow meters can also be used.

[0035]

As described above, in the wire saw and the method for cutting a cylindrical work according to the present invention, the viscosity of the slurry supplied to the work is adjusted according to the cutting length of the cylindrical work or the angle between the wire and the outer periphery of the work. By changing the thickness, not only the thickness variation in the wafer plane is largely improved, but also as a secondary effect, the incidence of wafer cracking during cutting is reduced, and the cutting yield and productivity are improved. be able to. Therefore, the utility value of the present invention in the industry is extremely high.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a cross-sectional shape of a wafer cut by a wire saw, wherein (a) shows a wafer cut by a conventional apparatus and method, and (b) shows a wafer cut by an apparatus and method of the present invention. Is shown.

FIG. 2 is a schematic view of a wire saw.

FIG. 3 is a schematic view showing a cross section of the wire saw according to the embodiment of the present invention.

FIG. 4 is a schematic diagram showing a cross section including a circulation system of a slurry of the wire saw of the present invention.

FIG. 5, showing the embodiment of the present invention, is a diagram illustrating a change pattern of slurry viscosity when cutting a cylindrical workpiece.

FIG. 6 is a diagram showing a wafer thickness measurement position after cutting.

[Explanation of symbols]

 7: drive motor, 10A, 10B, 10C: roller, 12: wire, 20, 30: tension adjusting mechanism, 22, 32: wire winding drum, 24, 34: torque motor, 40: cylindrical work, 42: work Holder, 50A, 50B: slurry supply nozzle, 60: slurry tank, 61: slurry viscosity detector, 62: slurry for cutting, 63: slurry stirrer, 64: slurry supply pipe, 66: pump, 70: wire saw cover, 72: slurry collection pipe, 80: viscosity modifier tank, 82: viscosity modifier supply pipe, 84: solenoid valve.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Kohei Toyama Odakura Odaikura, Saigo-mura, Nishishirakawa-gun, Fukushima Prefecture 150 Shin-Etsu Semiconductor Co., Ltd. Shirakawa Plant (56) References JP-A-8-99261 (JP, A) JP JP-A-7-52149 (JP, A) JP-A-8-243920 (JP, A) JP-A-1-1633056 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) B28D 5 / 04 B24B 27/06 B24B 57/02

Claims (12)

(57) [Claims] 1. A method for cutting a cylindrical work using a wire saw, wherein the viscosity of the cutting slurry supplied to the work is changed by changing the cutting length of the cylindrical work or changing the angle between the wire and the outer periphery of the work. A method of cutting a cylindrical workpiece. 2. The cylindrical work according to claim 1, wherein the viscosity of the slurry increases as the cutting length of the cylindrical work increases, and then the viscosity of the slurry decreases as the cutting length decreases. How to cut. 3. The method according to claim 1, wherein the rate of change in the viscosity of the slurry is compared with a rate of increase in the viscosity of the slurry from the start of cutting to the cutting of the center of the cylindrical work. Reduce the slurry viscosity reduction rate,
The method for cutting a cylindrical workpiece according to claim 1, wherein the columnar workpiece is cut. 4. The cylindrical workpiece according to claim 1, wherein the viscosity of the slurry is changed by adding a viscosity modifier to a slurry tank. How to cut. 5. The viscosity modifier of the slurry is water,
5. The method for cutting a cylindrical workpiece according to claim 4, wherein: 6. The method for cutting a cylindrical workpiece according to claim 1, wherein a coolant component of the slurry is water-soluble. 7. A wire saw for cutting a cylindrical work, comprising means for changing the viscosity of the cutting slurry supplied to the work by changing the cutting length of the cylindrical work or changing the angle between the wire and the outer periphery of the work. A wire saw for cutting a cylindrical work. 8. The means for changing the viscosity of the cutting slurry includes at least a slurry viscosity detector and a flow controller for a viscosity modifier, detects the slurry viscosity in the slurry tank, and adjusts the viscosity in accordance with the value. The wire saw for cutting a cylindrical workpiece according to claim 7, wherein the wire saw controls a flow rate of the adjusting agent supplied to the slurry tank. 9. The wire saw for cutting a cylindrical work according to claim 8, wherein the detection of the viscosity of the slurry in the slurry tank is performed by a mass flow meter or a measurement of electric conductivity. 10. The wire saw for cutting a cylindrical workpiece according to claim 8, wherein the flow rate controller of the viscosity adjusting agent is an electromagnetic valve or a flow meter. 11. The wire saw for cutting a cylindrical workpiece according to claim 8, wherein the viscosity modifier of the slurry is water. 12. The wire saw for cutting a columnar workpiece according to claim 7, wherein a means for stirring the slurry is provided in the slurry tank.