JP2001232550A - Cutting method using wire saw and wire saw - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure high machining precision while suppressing the wear of guide rollers and wire breaking when cutting is done by a wire saw. SOLUTION: A cutting method using the wire saw and the wire saw are provided to cut a workpiece 28 by feeding it for many wires W stretched over between guide rollers 24A and 24B. A wire tension of a part cutting the workpiece 28 is reduced after it is cut in a predetermined amount after the cutting of the workpiece 28 is started.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cutting a semiconductor ingot or the like using a wire saw and a wire saw.

[0002]

2. Description of the Related Art In recent years, a wire saw has been known as a means for cutting a wafer from a semiconductor ingot. In this wire saw, a cutting wire pulled out from a wire feeding member is wound around a plurality of guide rollers and then collected by a wire winding member. The rotation of both bobbins and the guide rollers causes the cutting wire to extend in its longitudinal direction. In the state of being driven at a high speed in the direction, a work made of the semiconductor ingot or the like is cut and fed in a direction substantially orthogonal to the plurality of wires arranged between the guide rollers, so that a large number of The slices are cut out at the same time.

[0003] In such a wire saw, it is necessary to adjust the wire tension to an appropriate value in order to perform good cutting of the work. Therefore, conventionally, during the cutting operation of the workpiece,
Tension control is performed to keep the wire tension constant. For example, Japanese Patent Application Laid-Open No. H4-152061 discloses a tension detecting means for detecting a wire tension in each region in a region from a wire feeding member to a guide roller and in a region from a guide roller to a wire winding member. And adjusting the rotational speed of the bobbin so that the tension detected by the tension detecting means is maintained at an appropriate tension.

[0004]

As described above, the apparatus which performs control so as to keep the wire tension constant all the time has a drawback that it is very difficult to set a target value of the wire tension. That is, when the target value of the wire tension is set low, when the work 28 is pressed against a large number of the arranged wires W as shown in FIG. 8 (that is, when the cutting operation of the work 28 is started), each wire W Immediately before biting into the work 28, each wire W is slightly displaced in the width direction (the direction of the arrow A1 or the arrow A2 in the figure) so that the wire W loses the resistance received from the circumferential surface of the work 28 and slides on the circumferential surface of the work 28. This causes a disadvantage that the cutting position is shifted. Conversely, when the target value of the wire tension is set high, the wear of the guide rollers and pulleys is promoted, and the risk of wire breakage increases.

SUMMARY OF THE INVENTION In view of such circumstances, an object of the present invention is to provide a cutting method using a wire saw and a wire saw that can ensure high processing accuracy while suppressing abrasion of a guide roller and the like and wire breakage.

[0006]

As a means for solving the above-mentioned problems, the present invention provides a wire winding member in which a cutting wire fed from a wire feeding member is wound around a plurality of guide rollers. Using a wire saw to be wound, a cutting method using a wire saw that cuts the work by cutting and feeding the work to these wires while driving a plurality of wires arranged between the guide rollers in the axial direction, This is a method of starting the cutting of the work by the wire and lowering the wire tension from a point when the work is cut by a predetermined amount.The cutting wire fed from the wire feeding member is wound around a plurality of guide rollers. While the wire is wound around the wire take-up member and a plurality of wires arranged between the guide rollers are driven in the axial direction, In a wire saw in which the work is cut by being cut and fed to the wires, a tension adjusting means for changing the tension of the wire in the portion for cutting the work, and Tension control means for operating the tension adjusting means so as to lower the tension from a point when the wire cuts the work by a predetermined amount.

According to these methods and the wire saw, at the beginning of the cutting of the work by each wire, the wire tension is maintained high, so that each wire loses the cutting resistance received from the peripheral surface of the work before cutting into the work. Thus, it can be prevented from being displaced in the width direction, so that an accurate cutting position can be secured. Then, by cutting the work to some extent and determining the cutting position by each wire and then lowering the wire tension, wear of the guide roller and the like and wire breakage can be suppressed.

The timing for lowering the wire tension may be set as appropriate. Specifically, the timing at which the cutting proceeds to such an extent that there is no risk of displacement of the wire in the width direction even if the tension of each wire is reduced is set. What is necessary is just to set it as a reference of the said timing.

The method of lowering the tension can be set as appropriate, and the target value for adjusting the wire tension may be gradually lowered from the time when a predetermined amount of cut is made, or when the cutting of the work is started. The wire target tension may be set as a first target tension, and the wire target tension may be switched to a second target tension lower than the first target tension from a point in time when the work is cut by a predetermined amount. In the latter case, the control content is simplified.

The tension adjusting means may be, for example, a means for adjusting the relative relationship between the wire feeding speed and the winding speed. However, the tension adjusting means may include a region extending from the wire feeding member to the guide roller and the wire winding speed from the guide roller. Tension detecting means for detecting the tension of the wire in a region reaching the member,
Tension operating means for operating the wire tension in the area so that the tension detected in each area is closer to the target tension set by the target tension setting means, the wire with higher responsiveness Precise adjustment of tension is possible.

Specifically, the tension operating means includes a pair of fixed pulleys on which the wire is hooked in a region from the wire feeding member to the guide roller and a region from the guide roller to the wire winding member; It is preferable that the apparatus includes a movable pulley disposed between the movable pulley and a pulley position operating unit that changes the position of the movable pulley by driving the movable pulley. In this case, the tension control unit may include a wire length adjustment unit that operates the pulley position operation unit so that the tension detected by the tension detection unit approaches the target tension set by the target tension setting unit. do it.

Further, the tension adjusting means is connected to at least one of the plurality of guide rollers, and a roller driving means for rotating and driving the guide rollers, and a roller driving means other than the guide rollers to which the roller driving means is connected. Rotational resistance applying means for increasing the tension of a wire portion for cutting the work by applying rotational resistance to any one of the guide rollers may be provided. In this case, by applying a rotational resistance to a specific guide roller, the tension of the wire portion for cutting the work can be increased by that much, and the rotational resistance is applied from the point when the work is cut by a predetermined amount. The wire tension can be reduced by reducing the rotational resistance provided by the means.

Here, the "rotational resistance" given to a specific guide roller may be any resistance to rotation for following the guide roller driven by the roller driving means (ie, relative rotational resistance). The rotation resistance imparting means may rotate the guide roller in the same direction as the driving direction of the roller driving means.

For example, a first drive motor is connected to at least one of the plurality of guide rollers, and a second drive motor is connected to any guide roller other than the guide roller to which the first drive motor is connected. However, even if different torque command values are given to the first drive motor and the second drive motor, the tension of the wire portion for cutting the work can be increased by the torque difference. In this configuration, of the first drive motor and the second drive motor, the motor for which a high torque is set serves as the roller driving unit, and the motor on which the low torque is set is the rotational resistance applying unit, This is a means for giving resistance to the rotation for the other guide roller to follow the guide roller which is driven to rotate by the driving means. That is, the difference between the torques commanded by both motors corresponds to the relative rotational resistance.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described with reference to FIGS.

The wire saw shown in FIG. 1 includes a pair of wire feeding / winding devices 10A, 10B and four guide rollers 24A, 24B, 26A, 26B disposed therebetween. Of these guide rollers, the guide rollers 24A and 24B are arranged at the same height position, and the guide rollers 26A and 26B are
A, 24B are disposed below.

A fixed pulley 12A, 14A, 16A and a wire length operating device 18 are arranged between the wire feeding and winding device 10A and the guide rollers 24A, 24B, 26A, 26B in order from the side near the wire feeding device 10A.
A, a movable pulley 20A, and a fixed pulley 22A are provided. Similarly, the wire feeding and winding device 10
B and the guide rollers 24A, 24B, 26A, 26B, the fixed pulleys 12B, 14B, 16B, and the wire length operating device 1 in order from the side closer to the wire winding device 10B.
8B, a movable pulley 20B, and a fixed pulley 22B.

Each wire feeding and winding device 10A, 10
B is a bobbin 9A, 9B around which a cutting wire W is wound.
And bobbin drive motors 11A and 11
B. One wire feeding and winding device 1
The wire W paid out from the 0A bobbin 9A is fixed to pulleys 12A, 14A, 16A and a wire length operating device 18A.
Of the movable pulley 20A and the fixed pulley 22A, and the guide rollers 24A, 24B, 26B, 2
After being wound many times outside 6A, the fixed pulley 22B,
The movable pulley 20B and the fixed pulleys 16B, 14B and 12B of the wire length operating device 18B are wound in this order, wound around the bobbin 9B of the other wire feeding / winding device 10B, and the wire is operated by the two wire length operating devices 18A and 18B. An appropriate tension is applied to W. Further, the guide rollers 24A, 24B, 26B, 26
A roller drive motor 25 for rotating this rotation shaft is connected to the rotation shaft of a specific guide roller of A (the guide roller 26A in the illustrated example).

The bobbin driving motors 11A, 11A
B, the rotational drive direction of the bobbins 9A and 9B and the rotational drive direction of the guide roller 26A by the roller drive motor 25 are switched between forward and reverse, so that the wire W
A state in which it is fed out from A and wound on a bobbin 9B,
The state in which the wire W is unreeled from the bobbin 9B and wound around the bobbin 9A is switched.

That is, in this wire saw, a large number of wires W are reciprocated in the longitudinal direction while being stretched in parallel with each other between the guide rollers 24A and 24B.

Above the wire W stretched between the guide rollers 24A and 24B, there is provided a work feeder 30 for moving a cylindrical work (for example, a semiconductor ingot) 28. The work feed device 30 includes a work holding unit 32 and a work feed motor 34. The work holding unit 32 holds the work 28 in a direction in which a target crystal orientation can be obtained based on the crystal axis. The work feed motor 34 is provided with the work holding unit 32 in combination with a ball screw (not shown). 32 and the work 28 are integrally moved up and down (that is, cut and fed). In this embodiment, the work feed motor 34 is constituted by a servomotor, and also serves as a feed position detecting means for detecting a cutting feed position of the work 28.

Above the wire W stretched between the guide rollers 24A and 24B, slurry supply devices 36A and 36B are provided at positions on both left and right sides of the work 28. These slurry supply devices 36A and 36B simultaneously supply a processing liquid (slurry) in which abrasive grains are mixed to each of the wires W driven at a high speed, and cause the wires W to adhere to the surface of the wires W.

Therefore, in this wire saw, a large number of wires W stretched between the guide rollers 24A and 24B are simultaneously driven at a high speed in the longitudinal direction, and the working fluid is supplied to these wires W from the slurry supply devices 36A and 36B. While being supplied, the work W is cut and sent downward with respect to these wires W, whereby a large number of wafers are simultaneously cut out from the work W at one time.

Next, the wire length operating devices 18A, 18
The structure of B will be described with reference to FIGS. Since the configurations of the two wire length operation devices 18A and 18B are the same, the description will be made by taking the wire length operation device 18A as an example.

The movable pulley 20A includes a fixed pulley 16
A, 22A, and the wire length changes due to the vertical movement of the movable pulley 20A (specifically, the wire length increases when the movable pulley 20A descends, and the movable pulley 2
0A rises, the wire length decreases).
A, 20A and 22A are provided.

The supporting member 38 of the fixed pulley 22A has a tension detector (tension detecting means) such as a load cell.
The tension detector 40 detects the load applied to the support member 38 and detects the tension of the wire W.

The movable pulley 20A is attached to the tip of a lever 44 so as to be rotatable about a rotation shaft 42. A rotation center shaft 46 is fixed to the base end of the lever 44, and the rotation center shaft 46 is connected to a swing cylinder (pulley position operation means) 50 fixed to a fixed side plate 48. The operation of the moving cylinder 50 causes the lever 44 and the movable pulley 20A to rotate around the rotation center axis 46. Further, an encoder 52 is connected to the rotation center shaft 46.
2, the rotation angle position of the rotation center shaft 46, in other words, the position of the movable pulley 20A can be detected.

The wire saw is provided with a controller 60 as shown in FIG. This controller 6
0 has a wire length adjusting means 62, a speed adjusting means 64, and a target tension setting means 66.

The wire length adjusting means 62 includes a tension detector 40 on each of the wire feeding side and the wire winding side.
In order to keep the wire tension detected at the target tension T set by the target tension setting means 66, the swing cylinder 5
An electric signal is output to a pneumatic servo circuit 54 for driving the movable pulleys 20A and 20B to adjust the positions of the movable pulleys 20A and 20B. Specifically, for example, when the detected tension on the wire feeding / winding device 10A side is higher than the target tension T, the lever 44 connected to the swing cylinder 50 is rotated clockwise in FIG. By moving the movable pulley 20A closer to the fixed pulleys 16A and 22A, the wire length is reduced. Conversely, when the detected tension is lower than the target tension T, the lever 44 connected to the swing cylinder 50 is moved to the position shown in FIG.
Is controlled to increase the wire length by turning the movable pulley 20A away from the fixed pulleys 16A and 22A by rotating the movable pulley 20A counterclockwise.

The speed adjusting means 64 moves the positions of the movable pulleys 20A and 20B detected by the encoder 52 to a preset reference position (here, a position where the lever 44 is horizontal as shown by a solid line in FIG. 2). The control signals are respectively output to the bobbin drive motors 11A and 11B so that the rotational speeds of the bobbins 9A and 9B are adjusted so as to approach each other.
For example, in a state where the wire W is paid out from the bobbin 9A and is wound around the bobbin 9B, the movable pulley 20A on the payout side is used.
Is detected at a position lower than the reference position, the rotational speed of the bobbin 9A on the side serving as the wire feeding member is reduced in order to raise the movable pulley 20A. If it is detected that 20A is located above the reference position, the movable pulley 20A
In order to lower A, the rotational speed of the bobbin 9A on the side serving as the wire feeding member is increased. On the other hand, when it is detected that the movable pulley 20B on the wire winding side is at a position lower than the reference position, the bobbin 9B on the side serving as the wire winding member is moved to raise the movable pulley 20B. When the rotational speed is increased and, conversely, it is detected that the movable pulley 20B is at a position above the reference position, the bobbin 9B on the side serving as a wire winding member is moved to lower the movable pulley 20B. It is configured to reduce the rotation speed of.

In the above-described example, the description has been given of the state in which the wire is paid out from the bobbin 9A and wound on the bobbin 9B.
Conversely, the wire is fed from the bobbin 9B and
The speed adjusting means 64 performs the same control even in the state of being wound.

The target tension setting means 66 sets the target tension T of the wire W and inputs it to the wire length adjusting means 62 as described above. Instead, the target tension T is changed according to the feed position of the work 28. Specifically, based on a signal from a work feed motor 34 also serving as a means for detecting a cutting feed position of the work, the wire saw is started to start cutting the work 28 as shown in FIG. The first target tension T1 is set before cutting, and after cutting by the predetermined amount s, the target tension T is reduced to the second target tension T2 (<T1).

The predetermined amount s may be set to such a value that the cutting position by each wire W can be determined, and is generally preferably about 10 to 15 mm.

Next, the operation of this device will be described.

For example, when the wire W is unreeled from the bobbin 9A and wound on the bobbin 9B, the detection value of the tension detector 40 attached to the fixed pulley 22A (ie, the upstream side of the work processing position) Is detected by the wire length adjusting means 62.
The wire length adjusting means 62 compares the detected tension value with the target tension T set by the target tension setting means 66. If the former is higher than the latter, the movable pulley is adjusted by an amount corresponding to the difference. When the wire tension is reduced by lowering the wire length by raising 20A, the wire tension is increased by lowering the movable pulley 20A by an amount corresponding to the difference when the latter is higher than the former. Enhance. Therefore, even when the wire tension rises instantaneously due to the cutting resistance of the work 28 or the like, the movable pulley 20A is quickly driven up in response to this, so that an excessive rise in the wire tension is avoided. Is prevented from being broken due to the above.

On the other hand, the detection signal of the encoder 52 provided on the wire length operating device 18A (ie, the movable pulley 20)
The A position detection signal) is taken into the speed adjusting means 64. The speed adjusting means 64 compares the detection position of the movable pulley 20A with a preset reference position, and when the former is higher than the latter, the bobbin which is a wire feeding bobbin to lower the movable pulley 20A. Increase the rotation speed of 9A. Conversely, if the former is lower than the latter, the rotational speed of the bobbin 9A, which is a wire feeding bobbin, is reduced to raise the movable pulley 20A. By such control, in the steady state, the movable pulley 20A is held substantially at the reference position, and a margin for the movement is secured.

That is, in this apparatus, the movable pulley 20
The position of each movable pulley 20A, 20B is adjusted to the reference position by adjusting the rotation speed of the bobbins 9A, 9B, while the instantaneous increase and decrease of the wire tension can be dealt with by the vertical movement of A, 20B.

Further, as a feature of this wire saw, a first target tension T1 is set as a target tension T from the start of cutting the workpiece 28 to the start of cutting of a predetermined amount s, and the cutting of the same predetermined amount s is performed. Since the target tension T is later reduced to the second target tension T2, a high wire tension is maintained at the beginning of the cutting of the work 28, and the wire W loses the cutting resistance received from the work 28 and the arrow in FIG. A1
Or, when a minute displacement as shown by an arrow A2 is suppressed, thereby securing an appropriate cutting position to enhance the processing accuracy, while performing a cut of a predetermined amount s to eliminate the possibility of minute displacement of the wire W. Then, by reducing the wire tension, wear of each guide roller and pulley and wire breakage can be effectively suppressed.

In addition, the present invention can adopt the following embodiments in addition to the above.

(1) In the example shown in FIG. 5, the target tension T is changed to the first target tension T
Although the control is discontinuously switched from the first target tension T2 to the second target tension T2, the target tension T may be gradually (for example, continuously) decreased from the predetermined time point.

(2) In the example shown in FIG. 5, the target tension T is set to the first target tension T from the start of the wire saw. It is sufficient that a high wire tension can be maintained until the cutting is performed.For example, the target tension is set to be low for a predetermined period from the start of the wire saw to the actual start of cutting the work. Is also good.

(3) In the present invention, a specific means for adjusting the wire tension is not particularly limited. For example, if the movable range of the movable pulleys 20A and 20B can be sufficiently secured, the speed adjusting means 64 can be omitted, and conversely, the wire length operating device 1 that operates the movable pulleys 20A and 20B.
It is also possible to omit 8A and 18B and adjust the wire tension only by adjusting the speed of the speed adjusting means 64. However, by actively driving the movable pulleys 20A, 20B using the wire length operating devices 18A, 18B as described above, the wire tension can be accurately adjusted with higher responsiveness.

As means for temporarily increasing the wire tension (the tension of the wire portion contributing to the cutting of the work 28) at the beginning of cutting the work, for example, as shown in FIG. Motor 25
A and 25B are connected to each other, and at the beginning of cutting of the work 28, different torque commands are input to the main motors 25A and 25B from the main motor control means 68 of the controller 60 shown in FIG. The drive torque of 25B may have a difference.

That is, the movable pulleys 20A, 20B
In the tension adjustment by the driving of, the lower target tension Te is always set, and at least a predetermined amount s from the start of wire cutting.
In the period until cutting is performed, a difference is made between the driving torque applied to the guide roller 26A and the driving torque applied to the guide roller 26B, and the guide roller 24
The tension of each wire W between A and 24B (the tension of the wire portion that cuts the workpiece) is increased by ΔTe from the target tension Te, and the torque difference is reduced after the lapse of the period (to eliminate the torque difference). The main motor control means 66 may perform control to lower the tension of the wire portion that cuts the work.

For example, when the wire W is fed from the bobbin 9A and wound on the bobbin 9B, the main motor 25
When a high torque command is input to B and a low torque command is input to the main motor 25A, the guide roller 26A has a resistance to the rotation for the guide roller 26A to follow the rotation of the guide roller 26B by the torque difference. Is given, and the tension of the wire W can be locally increased in the region of the guide rollers 26B-24B-24A-26A due to the rotation resistance.

Alternatively, the drive force is applied only to the guide roller 26B of the two guide rollers 26A and 26B shown in FIG. It is possible to temporarily increase the tension initially.

(4) As described above, the wire length operating device 18
When the movable pulleys 20A and 18B are used, the movable pulleys 20A and 20B are not limited to be displaced by the rotation of the lever 44 as shown in FIG.
A and 20B may be moved linearly. In this case, as a means for changing the position, a feed screw mechanism, a rack and pinion mechanism, or the like may be used. Also, when the movable pulley is swung, the drive source thereof is not limited to the swing cylinder 50, and for example, a servo motor may be used. The specific configuration of the tension detector 40 is not particularly limited, and may be a combination of a differential transformer and a spring in addition to the load cell.

[0048]

As described above, according to the present invention, when cutting with a wire saw, the wire tension is reduced after a predetermined amount of incision has been made after the start of wire cutting. Initially, the wire tension is increased to secure an accurate cutting position and, consequently, a high processing accuracy, and thereafter, the wire tension is reduced, whereby there is an effect that wear of the guide roller and the like and wire breakage can be suppressed.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a wire saw according to an embodiment of the present invention.

FIG. 2 is a front view of tension adjusting means provided on the wire saw.

FIG. 3 is a plan view of the tension adjusting means.

FIG. 4 is a block diagram showing a functional configuration of a controller provided in the wire saw.

FIG. 5 is a graph showing a relationship between a cutting feed position of a workpiece and a target tension set by the controller.

FIG. 6 is an overall configuration diagram of a wire saw according to another embodiment of the present invention.

FIG. 7 is a block diagram illustrating a functional configuration of a controller provided in the wire saw of FIG. 7;

FIG. 8 is a perspective view showing a small displacement of the wire when the wire starts to cut into the work.

[Explanation of symbols]

9A, 9B bobbin (wire feeding member and wire winding member) 11A, 11B bobbin driving motor 16A, 16B, 22A, 22B fixed pulley 18A, 18B wire length operating device 20A, 20B movable pulley 24A, 24B, 26A, 26B guide roller 25A, 25B Main motor (roller driving means and rotation resistance applying means) 28 Work 40 Tension detector 60 Controller 62 Wire length adjusting means 64 Speed adjusting means 66 Target tension setting means 68 Main motor control means (Tension controlling means) T Target tension T1 First target tension T2 Second target tension W Wire

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Claims (7)

[Claims] 1. A wire saw, in which a cutting wire fed from a wire feeding member is wound around a plurality of guide rollers and wound by a wire winding member, a plurality of cutting wires are arranged between the guide rollers. In a cutting method using a wire saw that cuts a work by cutting and feeding the work to these wires while driving the wire in the axial direction, after starting to cut the work by the wire, a predetermined amount of the work is cut. A cutting method using a wire saw, wherein the wire tension is reduced from a point in time. 2. The method for cutting a workpiece by a wire saw according to claim 1, wherein when the cutting of the workpiece is started, the wire tension is adjusted with the first target tension as a target, and the first target is cut from a point in time when the workpiece is cut by a predetermined amount. A cutting method using a wire saw, wherein the wire tension is adjusted to a second target tension lower than the tension. 3. A cutting wire fed from a wire feeding member is wound around a plurality of guide rollers and wound on a wire winding member, and a plurality of wires arranged between the guide rollers are arranged in an axial direction. In a wire saw in which the work is cut by being cut and sent to these wires in a state where the work is driven, tension adjusting means for changing the tension of the wire at a portion where the work is cut, and A wire saw, comprising: tension control means for operating the tension adjusting means so as to lower the tension of the wire at the cutting portion from the point when the wire cuts the work by a predetermined amount. 4. The wire saw according to claim 3, wherein the wire target tension is set to a first target tension at the start of cutting of the work, and the wire target tension is set to the first target tension from a point when the work is cut by a predetermined amount. Target tension setting means for switching to a lower second target tension, and the tension control means is configured to operate the tension adjusting means with the target tension set by the target tension setting means as a target. A wire saw characterized by the above-mentioned. 5. The wire saw according to claim 4, wherein tension detecting means for detecting a tension of the wire in a region from the wire feeding member to the guide roller and a region from the guide roller to the wire winding member, and the respective regions. Tension operation means for operating the wire tension in the tension control means so as to operate the tension operation means to bring the tension detected in each of the regions closer to the target tension set by the target tension setting means. A wire saw characterized by the following. 6. The wire saw according to claim 5, wherein the tension operation means includes a pair of fixed pulleys on which the wire is hooked in a region from the wire feeding member to the guide roller and a region from the guide roller to the wire winding member. And a movable pulley disposed between these fixed pulleys, and a pulley position operating means for changing the position of the movable pulley by driving the movable pulley, and the tension control means detects the tension detected by the tension detection means. A wire saw comprising wire length adjusting means for operating the pulley position operating means so that the tension approaches the target tension set by the target tension setting means. 7. A wire saw according to claim 3, wherein said tension adjusting means is connected to at least one of said plurality of guide rollers, and said roller driving means rotates said guide rollers, and said roller driving means. A rotational resistance applying means for increasing the tension of a wire portion for cutting the work by applying rotational resistance to any guide roller other than the connected guide roller, and the tension control means comprises a A wire saw, wherein the rotational resistance applied by the rotational resistance applying means is reduced from a point in time when the work is cut by a predetermined amount.