Method for cutting a plurality of slices from a workpiece by means of a wire saw during a series of cutting operations

Abstract

The invention relates to a method for cutting a plurality of slices from a workpiece (4) by means of a wire saw, wherein a wire array (2) is tensioned in the plane between two wire guide rollers (1), wherein each of the two wire guide rollers (1) is mounted between a fixed bearing (5) and a floating bearing (6). The method comprises the delivery of the workpiece (4) via the wire array (2) by controlling the temperature of the workpiece (4) by wetting the workpiece (4) with a cooling medium, while at the same time moving the floating bearing (6) axially by controlling the temperature of the fixed bearing (5) with a cooling fluid according to a specification of a first temperature profile, and while at the same time moving the workpiece (4) along the workpiece axis by means of a control element (15) according to a specification of a second correction profile.

Description

TECHNICAL FIELD

[0001] The invention relates to a method for cutting a plurality of slices from a workpiece during a series of parting (dicing) operations by means of a wire saw, wherein the wire saw comprises a wire array consisting of moving wire sections of a sawing wire and an actuating device, and the wire array is tensioned in a plane between two wire guide rollers, and wherein each of the two wire guide rollers is supported between a fixed bearing and a floating bearing. During each of the parting operations, a respective workpiece is fed through the wire array by means of the actuating device along a feed direction perpendicular to the workpiece axis and perpendicular to the plane of the wire array, in the presence of a hard material and a working fluid which act abrasively on the workpiece. BACKGROUND

[0002] This method for cutting a plurality of slices can be implemented by means of a kiss-cutting slice or a grinding slice.

[0003] In the case of a kiss-cutting slice, a working fluid in the form of a slurry consisting of a hard material in a liquid carrier medium is fed to a working space formed between the wire surface and the workpiece. In the case of a kiss-cutting slice, material is removed by means of a three-body interaction involving a tool carrier (sawing wire), a tool (abrasive) and the workpiece.

[0004] In the case of a grinding slice, a sawing wire with a hard material firmly bonded in its surface is used, and a working fluid is supplied, which itself contains no grinding material and serves as a cooling lubricant. In the case of a grinding slice, material is removed by means of a two-body interaction involving a diamond-coated sawing wire as a tool and the workpiece.

[0005] In the case of a conventional wire saw, each of the wire guide rollers is provided near each of its end faces with a bearing which is connected in a fixed manner to the machine frame and is referred to as a fixed bearing, and near the opposite end face with a bearing which is movable relative to the machine frame in the axial direction of the wire guide roller and is referred to as a floating bearing.

[0006] There are known measures which aim to counteract changes in the arrangement of the wire array and the workpiece relative to one another during the parting operations in order to improve the planar parallelism of the main surfaces of the slices to be cut out.

[0007] US 5 377 568 discloses a method in which the position of a reference surface located on the outside of the wire guide rollers relative to the machine frame is measured, and a thermal length increase or length reduction of the wire guide rollers is achieved by adjusting the temperature inside the wire guide rollers until the measured change in the position of the reference surface has been compensated for again.

[0008] WO 2013 / 079683 A1 discloses a method in which firstly the shape of the slice obtained at different temperatures of the online guiding roller bearing is measured and each of these shapes is stored together with the corresponding associated bearing temperature, and then in a subsequent cut, the bearing temperature is selected which best matches the intended target shape.

[0009] US 5 875 770 discloses a method in which the shape of the slice from the cut is measured, a correction curve relating to the cutting depth is calculated by forming a difference with respect to a desired ideal shape of the slice, and in a subsequent cut, the workpiece is moved in axial direction with respect to the wire array during the cutting operation in accordance with the correction curve.

[0010] US 2002 / 0 174 861 A1 describes a method which envisages controlling the temperature of the workpiece in order to limit the warping of the slice cut off.

[0011] Despite these measures, there is still a need for improvement, on the one hand because these measures only have a limited effect and on the other hand because the requirements for flatness and planar parallelism of the slices are increasing, in particular in the semiconductor industry. SUMMARY

[0012] It is an object of the present invention to manufacture usable slices whose shape matches the target shape as closely as possible.

[0013] The object of the present invention is achieved by a method for cutting a plurality of slices from a workpiece by means of a wire saw during a series of cutting operations divided into an initial cut and a subsequent cut, wherein the wire saw comprises a wire array consisting of moving line sections of a saw wire and an actuating device, and the wire array is tensioned in a plane between two wire guiding rollers, wherein each of the two wire guiding rollers is supported between a fixed bearing and a floating bearing, wherein the method comprises

[0014] During each of the cutting operations, in the presence of a hard material and a working fluid which act abrasively on the workpiece, the respective workpiece is fed through the wire array by means of the actuating device along a feed direction perpendicular to the workpiece axis and perpendicular to the plane of the wire array, which comprises

[0015] During each of the cutting operations, the temperature of the workpiece is controlled by wetting the workpiece with a cooling medium while the workpiece is fed through the wire array;

[0016] During each of the severing operations, the workpiece is fed through the wire array while the floating bearing is simultaneously moved axially by regulating the temperature of the fixed bearing with a cooling fluid according to a specification of a first temperature profile, the first temperature profile specifying a temperature of the cooling fluid as a function of cutting depth and being related to a first correction profile, the first correction profile specifying a travel of the floating bearing as a function of cutting depth; and

[0017] During each of the severing operations, the workpiece is simultaneously moved along the workpiece axis by means of an actuating element according to a specification of a second correction profile while the workpiece is fed through the wire array, the second correction profile specifying a travel of the workpiece, wherein the first correction profile and the second correction profile counteract (suppress) a shape deviation; and

[0018] The shape deviation is determined during and / or before each of the severing operations.

[0019] The method can be configured to lap slices or ground slices. The cutting depth (doc) denotes the length in the direction of feed opposite to the area in which the workpiece is entered into the cutting of the workpiece to the area in which the workpiece is exited from the cutting.

[0020] Regulating the temperature of the fixed bearing (hereinafter referred to as wire guide temperature control, WGTC) causes a contraction or expansion of the fixed bearing and thus of its components along the axial direction of the wire guide roller, resulting in an axial movement of the floating bearing and thus of the wire guide roller relative to the workpiece. Regulating the temperature of the fixed bearing thus has the same effect in terms of quality (qualitatively) as moving the workpiece along the workpiece axis by means of an actuating element (hereinafter referred to as ingot positioning control, IPC). The actuating element is preferably a piezoelectric actuator. The variable that results in the respective travel is thus the temperature of the cooling fluid in the case of WGTC and a signal for driving the actuating element in the case of IPC.

[0021] According to the application, both measures are envisaged to minimize any possible shape deviation. There are specific advantages associated with this approach. If these measures are used in combination, a larger amplitude of movement (stroke) of the wire guide roller relative to the workpiece can be obtained than when only one of these measures is used. The range of movement of the floating bearing and the workpiece in which the variable causing the movement is linearly dependent is wider than the corresponding range that can be obtained when only one of the measures is used. The response time taken from changing the variable causing the movement to the actual occurrence of this movement is significantly more in the case of the WGTC than in the case of the IPC, in particular if the actuating element is a piezoelectric actuator. As a result, the two measures have different control bandwidths. It is therefore advantageous to suppress (counteract) shape deviations of relatively high frequency, i.e. shape deviations that change with a relatively large gradient depending on the cutting depth, by means of the IPC and to suppress shape deviations of relatively low frequency by means of the WGTC. Due to the different response times, the control by means of the IPC can be used to dampen the overshoot of the control by means of the WGTC. Furthermore, the combined control bandwidth of the IPC and the WGTC is greater than the control bandwidth of the IPC or the control bandwidth of the WGTC. The combination of the two measures makes it possible to obtain a greater stroke per unit of time, since the movement of the floating bearing and the workpiece is carried out by two independent actuators.

[0022] If the shape deviation is determined before the cutting operation, the term shape deviation refers to the deviation of the shape curve of the cut or the average shape curve of the cuts from the reference shape curve.

[0023] If the shape deviation is determined during the cutting operation, the term shape deviation refers to the deviation of the position of a line through the centers of the observed kerf (sawing seam) from the position of the reference trace, or the deviation of the position of an average line representing a plurality of such lines from the position of the reference trace. If the cutting operation is completely fault-free, i.e. without an unintended axial movement of the wire guide roller and / or an unintended axial movement of the workpiece, this line and the reference trace would have the same position relative to a common reference point. The common reference point is a position in space that remains stationary, for example a position on the machine frame. If a plurality of kerfs are observed, the positions of the lines through the centers of these kerfs are averaged to give the position of an average line. The point(s) at the same height of this line or average line and the reference trace represent a certain cutting depth. The distance of such a point on this line or average line from the corresponding point on the reference trace thus indicates the shape deviation at the cutting depth represented by these points.

[0024] The observation of the kerf or kerfs is preferably carried out by irradiation with optical radiation, IR radiation, X-rays or gamma rays. Furthermore, it is also conceivable to mechanically scan the kerf or to inductively or capacitively measure the kerf.

[0025] The shape deviation is determined during and / or before each of the cutting-off operations.

[0026] According to one embodiment, the determination of the shape deviation is based on observing one or more kerfs during the cutting-off operation, and two closed control loops are established. A first control loop responds by means of the WGTC to a control error, i.e. to the determined shape deviation, and a second control loop responds by means of the IPC, wherein the movements of the float bearing and the workpiece to be performed to correct the shape deviation are implemented with work allocated between the loops. The float bearing is moved by means of the WGTC according to a first correction curve, which determines the travel of the float bearing depending on the cutting depth. The first temperature curve, which specifies the temperature of the cooling fluid depending on the cutting depth, is associated with the first correction curve. The temperature change of the cooling fluid required to produce the specified travel of the float bearing of the respective wire guide roller is determined beforehand by experiment. The first correction curve determines the proportion of the travel of the float bearing to be performed to reduce the shape deviation depending on (in terms of) the cutting depth. The workpiece is moved by means of the IPC according to a second correction curve. The second correction curve determines the proportion of the travel of the workpiece to be performed to reduce the shape deviation depending on the cutting depth. The sum of the two proportions corresponds to the travel required to reduce the determined shape deviation. The proportions of the travel can be divided equally or differently. Where applicable, a further proportion of the relative movement between the workpiece and the wire section of the wire array in the form of a third correction curve is taken into account, which specifies a length change of the workpiece depending on the cutting depth. The length change is produced by wetting the workpiece with a cooling medium (ingot cooling, IC).

[0027] According to another embodiment, the determination of the shape deviation is based on a comparison of the average shape curve of the cut slices with a reference shape curve, which provides a total correction curve that determines the travel required to avoid the shape deviation (in terms of the comparison) that would be expected without the use of countermeasures, depending on (as a function of) the cutting depth, even before the cutting-off operation. The total correction curve is divided into a first correction curve and a second correction curve, and, where applicable, a third correction curve, and this determines the proportions of the travel to be performed by means of the WGTC and the IPC, and, where applicable, the length change of the workpiece to be performed by means of the IC. In this case, too, the proportions of the travel and the length change of the workpiece can be divided equally or in some other ratio.

[0028] According to another embodiment, the WGTC and the IPC are employed to suppress (counteract) the shape deviation, the determination of which is performed during each of the cutting-off operations, and the IC is employed to suppress the shape deviation determined before each of the cutting-off operations, or vice versa.

[0029] According to another embodiment, WGTC and IC are employed to suppress shape deviations, the determination of which is performed during each of the cutting-off operations, and IPC is employed to suppress shape deviations determined prior to each of the cutting-off operations, or vice versa.

[0030] According to another embodiment, IPC and IC are employed to suppress shape deviations, the determination of which is performed during each of the cutting-off operations, and WGTC is employed to suppress shape deviations determined prior to each of the cutting-off operations, or vice versa.

[0031] The surface of the slice consists of a main surface and an edge surface. The main surface comprises the front side and the back side of the slice. As is common in the case of warp measurements, the slice can be measured by being arranged between a pair of sensors. Each of the sensors measures the distance of the slice facing the main surface at a measurement point. The measurement points can be distributed over the main surface, or can be positioned along the diameter of the slice deviating no more than ±20° with respect to the feeding direction. The measurement points are preferably located at positions i along the diameter of the slice, in particular opposite the feeding direction, and are thus each associated with a specific cutting depth. The density of the measurement points is preferably not less than 1 per cm, and the distance between one measurement point and the nearest adjacent point is preferably the same for all measurement points.

[0032] The shape curve of the slice is the line connecting the measurement points si, which are calculated at positions i according to the rule si = D - (FDi - BDi), wherein D is the distance between the sensors, FDi is the distance between the upper sensor and the respective measurement point on the front side of the slice, and BDi is the distance between the lower sensor and the respective measurement point on the back side of the slice. It should be noted that the present invention can also be implemented using an alternative definition of the shape curve, as long as this alternative definition encodes the shape of the slice in dependence on the slice depth (i.e. makes it a function of the cutting depth).

[0033] The average shape curve of the slices is a shape curve obtained by averaging the shape curves of a plurality of slices. The reference shape curve is a desired (ideal) shape curve, preferably the shape curve of a slice having completely flat and mutually parallel main surfaces. The average shape curve is determined for the slices resulting from preferably at least 1 to 5 (times) of cutting-off operations with the aid of the same wire saw, wherein these cutting-off operations are (already) performed immediately prior to the cutting-off operation to be carried out by the wire saw. The selection of the slices for the creation of the average shape curve can be based on the slices or on the cuts, or can comprise both. In case of a selection based on the slices, certain slices from a cutting-off operation are used to determine the respective average shape curve by averaging, while other slices are excluded. For example, only those slices having a certain position in the workpiece are considered in the averaging process, for example only every 15th to 25th slice along the workpiece axis. Another possibility of a selection based on the slices is to exclude the slices having the largest and smallest shape curve deviation from the average shape curve of all slices in the cutting-off operation (so-called trimmed mean). Alternatively, slices can be excluded from the averaging slices whose shape curve deviates from the average shape curve of all slices in the cutting-off operation by more than 1 to 2 sigma (sigma). In a selection based on the cuts, all slices from at least one cutting-off operation are used to determine the average shape curve, and all slices from at least one other cutting-off operation are excluded therefrom.

[0034] The average shape curve of the slices in a cutting-off operation changes over the course of a series of cutting-off operations. The changes are preferably used to assess the performance of the wire saw. They can indicate wear of the sawing wire and / or of the face layer of the wire guide rollers or of any other component of the wire saw that is subject to wear. Therefore, preferably, a threshold value of the shape deviation is defined, when this threshold value is reached or exceeded, a maintenance activity (predictive maintenance activity) is initiated instead of another cutting-off operation. Even before such a threshold value is reached, such changes can be used as a reason to take adjustment measures to counteract the deterioration of the work results due to wear. For example, such adjustment measures can be a change of the composition and / or temperature of the working fluid and / or a change of the sawing wire speed and / or other process-specific parameters.

[0035] The cutting-off operations performed after a change in the sawing system represent a special case. Such a change in the sawing system occurs, for example, when there is a change in the wire guide rollers, a mechanical adjustment of the wire saw, or a change in the physical or chemical properties of the working fluid. The first or initial cutting-off operations after a change in the sawing system, i.e. the so-called initial cuts, preferably consist of 1 to 5 cutting-off operations. For the initial cuts, the shape deviation is preferably determined by comparing the average shape curve of the slices with the reference shape curve, wherein the average shape curve of the slices resulting from the same wire saw in the course of one or more initial cuts performed prior to the change in the sawing system is used.

[0036] According to the application, it is proposed to additionally provide a control of the temperature of the workpiece during each of the severing operations, more particularly by wetting the workpiece with a cooling medium (ingot cooling, IC). According to one embodiment, the control is performed by means of a closed control loop, wherein the temperature of the workpiece forms the controlled variable and the temperature of the cooling medium forms the manipulated variable of the control loop. The reference variable of the control loop is preferably a constant temperature. The cooling medium is preferably a fluid or a working fluid used in the lapping or grinding slice. By controlling the temperature of the workpiece, it is possible to limit the shape deviations of the slice caused by thermal expansion of the workpiece. The control loop can be implemented, for example, as described in US 2002 / 0 174 861 Al.

[0037] According to a preferred embodiment, the temperature of the workpiece is controlled according to a second temperature profile, which specifies the temperature of the cooling medium as a function of the cutting depth. The second temperature profile is related to a third correction profile, which is inverse to the shape deviation. The temperature of the cooling medium influences the elongation of the workpiece and thus the relative position of the workpiece and the wire segments of the wire array. The length change of the workpiece is deliberately produced by controlling the temperature of the workpiece in order to reduce the shape deviation together with the movement of the floating bearing and the workpiece.

[0038] The wire saw used according to the application comprises two or more wire guide rollers. The temperature regulation of the fixed bearings of the wire guide rollers can be limited to the two wire guide rollers between which the wire array is tensioned, by means of which the workpiece is fed (fed in).

[0039] The workpiece is preferably composed of a semiconductor material, such as silicon, in polycrystalline or monocrystalline state. The periphery of the cross section of the workpiece is square, rectangular or circular. In the case of a cylindrical workpiece, the workpiece axis extends through the center of the cylinder. The method according to the application is particularly suitable for producing circular semiconductor wafers composed of monocrystalline silicon, which have a diameter of at least 200 mm, in particular at least 300 mm.

[0040] The details of the application are described below with reference to the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 Features of the wire saw that play a role in the use of the application are shown schematically.

[0042] Figure 2 Further details of the wire saw are shown.

[0043] Figure 3 The trajectory of the cut through the workpiece is shown, as well as an imagined trajectory represented by a reference line.

[0044] Figure 4 The arrangement of the kerf between the two sensors used to determine the shape deviation of the kerf before the cut-off operation is shown.

[0045] Figure 5 The advantages obtained when increasing the amplitude of the WGTC and the IPC are shown.

[0046] Figure 6 The range in which the amplitude of the movement A is linearly related to the variable that causes it is shown.

[0047] Figure 7 The advantageous division of the total correction curve between the WGTC and the IPC is shown.

[0048] Figure 8 The greater stroke that can be obtained in a unit of time by combining the WGTC with the IPC is shown.

[0049] Figure 9 How the advantageous division of the total correction curve between the WGTC and the IPC attenuates the overshoot of the amplitude that would be observed in the case of using the WGTC as the only measure is shown.

[0050] List of used reference signs

[0051] 1 wire guide roller

[0052] 2 wire array

[0053] 3 saw wire

[0054] 4 workpiece

[0055] 5 fixed bearing

[0056] 6 floating bearing

[0057] 7 machine frame

[0058] 8 face layer portion

[0059] 9 passage

[0060] 10 directional arrow

[0061] 11 directional arrow

[0062] 12 actuating device

[0063] 13 kerf probe

[0064] 14 data processing unit

[0065] 15 actuating element

[0066] 16 control unit

[0067] 17 kerf

[0068] 18 reference trace

[0069] 19 upper sensor

[0070] 20 lower sensor

[0071] 21 slice

[0072] 22 device for adjusting the temperature of the workpiece DETAILED DESCRIPTION

[0073] A wire saw suitable for carrying out the method according to the application comprises a wire array 2 consisting of moving line sections of a saw wire 3, which is tensioned in the plane between two wire guide rollers 1. During the cutting operation, the workpiece 4 is fed through the wire array 2 along a feed direction perpendicular to the workpiece axis and perpendicular to the plane of the wire array 2 by means of an actuating device 12. During this operation, the wire guide rollers 1 tensioning the wire array 2 and the workpiece 4 are moved in axial direction according to (corresponding to) the direction arrows 10, 11, respectively, in dependence on (according to) a first and a second correction curve. The first and the second correction curve counteract (suppress) a shape deviation determined before or during the cutting operation. In order to determine the shape deviation during the cutting operation, there is a cut detection 13 for observing the cut. Furthermore, there is a data processing unit 14 for creating the first correction curve, the second correction curve and, if applicable, a third correction curve. The data processing unit 14 transmits control signals to an actuating element 15, which causes the workpiece 4 to be moved according to the second correction curve in the direction along the workpiece axis as indicated by the direction arrow 11 in dependence on the cutting depth. Furthermore, there is a device 22 for adjusting the temperature of the workpiece 4. If the shape deviation is determined before each cutting operation, the data processing device 14 transmits a second temperature curve to the device 22, which causes a change of the workpiece length according to the third correction curve.

[0074] As Figure 2The wire guide roller 1 is shown mounted between a fixed bearing 5 and a floating bearing 6. The fixed bearing 5 and the floating bearing 6 are supported on a machine frame 7. The wire guide roller 1 has a facing 8 provided with a groove in which the saw wire 3 runs. The fixed bearing 5 comprises a channel 9 through which a cooling fluid for adjusting the temperature of the fixed bearing 5 passes. If the temperature of the fluid is increased, the thermal expansion of the fixed bearing 5 causes an axial movement of the wire guide roller 1 in the direction of the floating bearing 6 and the floating bearing 6 moves outwardly relative to the machine frame 7 in the direction of the axis of the wire guide roller 1 as indicated by the direction arrow 10. If the temperature of the cooling fluid is decreased, a movement of the wire guide roller 1 and the floating bearing 6 in the opposite direction is caused. The temperature of the cooling fluid is specified by a first temperature curve dependent on the first correction curve as a function of the cutting depth. A control unit 16 connected to a heat exchanger and a pump ensures that the fluid passing through the fixed bearing 5 has the temperature required by the respective first temperature curve when a certain cutting depth is reached. The data processing unit 14 transmits a second temperature curve to the control unit 16 which causes a movement of the floating bearing according to the first correction curve.

[0075] Figure 3 The trajectory of the cut 17 through the workpiece 4 and the intended trajectory represented by the reference trace 18 are shown. The respective deviation of the line through the center of the cut relative to the reference trace corresponds to the total correction curve which can be divided into the form of the first correction curve and the second correction curve and, if applicable, the third correction curve.

[0076] Figure 4 The arrangement of the cut piece between two sensors 19, 20 for determining the shape deviation of the cut piece before the cutting operation is shown. The sensors 19, 20 measure the distance FD1 of the sensor 19 from the front side of the cut piece 21 and the distance BD1 of the lower sensor 20 from the back side of the cut piece 21 at a certain position i along the diameter of the cut piece 21 in the feed direction according to a certain cutting depth. The shape curve of the cut piece is the line connecting the measured values si calculated according to the rule si = D - (FD1 - BD1), wherein D denotes the distance between the sensors. The shape deviation of the cut piece is obtained by comparing the shape curve of the cut piece with a reference shape curve. The deviation relative to the reference shape curve dependent on the cutting depth corresponds to the total correction curve which is divided between the WGTC and the IPC in the form of the first correction curve and the second correction curve.

[0077] Figure 5The advantages obtained when increasing the amplitudes of the WGTC and the IPC are shown. If the total correction curve requires a stroke of the order of magnitude A of the dashed line, it is not possible to achieve this stroke by means of the WGTC or the IPC alone, since the stroke that can be achieved with the respective individual measure is not sufficient. This is only possible in combination with the WGTC and the IPC.

[0078] Figure 6 It is shown that in the range B2 with the stationary position B1 the amplitude A of the movement is linearly dependent on the variable (input, I) that causes the movement. Outside this range, a deviation from the linear behavior occurs, resulting in an error Δ. By combining the WGTC and the IPC, the range B2 in which the entire system reacts linearly is increased.

[0079] Figure 7 The advantageous division of the total correction curve between the WGTC and the IPC is shown, which includes the compensation of low-frequency shape deviations by means of the WGTC and the first correction curve and the compensation of high-frequency shape deviations by means of the IPC and the second correction curve. For this purpose, a conversion (frequency splitting) technique is preferably used, which allocates the low-frequency part of the shape deviations to the correction by means of the WGTC and the high-frequency part of the shape deviations to the correction by means of the IPC by means of a low-pass filter (LP) and a high-pass filter (HP).

[0080] Figure 8 It is shown that by means of the combination of the WGTC and the IPC a greater total amplitude A2+A1 can be obtained in a unit of time Δ, since the movement of the workpiece and the floating bearing is carried out by two independent actuators. When using the WGTC or the IPC alone, only one of the amplitudes A1 and A2 can be obtained in this time unit, respectively.

[0081] Figure 9 It is shown how the advantageous division of the total correction curve between the WGTC and the IPC damps the overshoot of the amplitude A over time t (right-hand graph), which would be observed when using the WGTC as the only measure (left-hand graph).

[0082] The above description of illustrative embodiments is to be taken as exemplary. The disclosure made herein is, in one aspect, to enable persons skilled in the art to practice the application and its associated advantages, and in another aspect, to cover adaptations, modifications, and variations of the structures and methods described herein, which are within the scope of those skilled in the art to which it pertains.

Claims

1. A method for cutting out a plurality of slices from a workpiece by means of a wire saw during a series of dicing operations divided into an initial cut and subsequent cuts, wherein, The wire saw comprises a wire array consisting of moving wire segments of a sawing wire and an actuating device, and the wire array is tensioned in a plane between two wire guide rollers, wherein each of the two wire guide rollers is supported between a fixed bearing and a floating bearing, the method comprising During each of the cutting-off operations, with abrasive-hardly acting hard material and working fluid present on the workpiece, the respective workpiece is fed through the wire array along a feed direction perpendicular to a workpiece axis and perpendicular to the plane of the wire array by means of the actuating device, which comprises During each of the cutting-off operations, the temperature of the workpiece is controlled by wetting the workpiece with a cooling medium while feeding the workpiece through the wire array; During each of the cutting-off operations, the workpiece is fed through the wire array while simultaneously axially moving the floating bearing by regulating the temperature of the fixed bearing with a cooling fluid according to a specification of a first temperature profile, which specifies the temperature of the cooling fluid in dependence on the cutting depth and in correlation with a first correction profile, which specifies the travel of the floating bearing in dependence on the cutting depth; and While feeding the workpiece through the wire array, the workpiece is simultaneously moved along the workpiece axis according to a specification of a second correction profile by means of an actuating element, which specifies the travel of the workpiece, wherein the first correction profile and the second correction profile are inversely shaped; and The shape deviation is determined during each of the cutting-off operations by comparing the position of the wire passing through the center of at least one kerf with the position of a reference trace and / or before each of the cutting-off operations by comparing an average shape profile of the already cut slices with a reference shape profile.

2. The method of claim 1, wherein, The average shape profile is determined by averaging the shape profiles of selected slices, wherein the selection is based on the slices, based on the cuts, or based on the slices and based on the cuts.

3. The method of claim 1 or 2, wherein, The already cut slices are from at least 1 to 5 cutting-off operations immediately preceding the respective cutting-off operation.

4. The method of any of claims 1 to 2, wherein, The temperature of the workpiece is controlled by means of a closed control loop, wherein the temperature of the workpiece forms the controlled variable and the temperature of the cooling medium forms the manipulated variable of the control loop.

5. The method of any of claims 1 to 2, wherein, The temperature of the workpiece is controlled according to a second temperature profile, which specifies the temperature of the cooling medium in dependence on the cutting depth and in correlation with a third correction profile, wherein the third correction profile is inversely shaped to the shape deviation.

6. The method of any of claims 1 to 2, wherein, If the shape deviation determined before the respective cutting-off operation reaches or exceeds a given threshold value, a maintenance measure is initiated instead of the respective cutting-off operation.

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