Method for cutting multiple slices from a workpiece with a wire saw during a series of cutting operations

Abstract

A method for cutting a plurality of slices from a workpiece with a wire saw during a series of cutting operations, the cutting operations being divided into initial cuts and subsequent cuts, the wire saw comprising a wire array of movable wire sections of a saw wire and a drive unit, the wire array being tensioned in a plane between two wire guide rollers, each of the two wire guide rollers being supported between a fixed bearing and a floating bearing, the method comprising the steps of: feeding each of the workpieces during each cutting operation past the wire array by the drive unit along a feed direction in the presence of a working fluid and a hard material that acts abrasively on the workpiece, the feed direction being perpendicular to a workpiece axis and perpendicular to the plane of the wire array; feeding the workpieces during each cutting operation past the wire array while controlling the temperature of the workpiece by wetting the workpiece with a cooling medium; and adjusting the temperature of the fixed bearing using the cooling fluid during each cutting operation in accordance with a first temperature profile that specifies a temperature of the cooling fluid depending on the cutting depth. and feeding the workpiece through the wire array simultaneously with axial movement of the floating bearing by driving a drive element in accordance with specifications of a second correction profile specifying movement of the workpiece, the first temperature profile being correlated with a first correction profile specifying movement of the floating bearing depending on the depth of cut, the feeding step further comprising feeding the workpiece through the wire array simultaneously with moving the workpiece along the workpiece axis by a drive element in accordance with specifications of a second correction profile specifying movement of the workpiece, the first and second correction profiles being different from a shape deviation, and the method further comprising determining the shape deviation during and / or before each cutting operation.

Description

[Technical field]

[0001] The invention relates to a method for cutting a number of slices from a workpiece by means of a wire saw during a series of cutting operations, the wire saw comprising a wire array of movable wire sections of a saw wire, a drive, the wire array being tensioned in a plane between two wire guide rollers, each of which is supported between a fixed bearing and a floating bearing, and during each said cutting operation, the respective workpiece is fed by the drive through the wire array along a feed direction, the feed direction being perpendicular to the workpiece axis and perpendicular to the plane of the wire array, in the presence of a working fluid and of a hard material acting abrasively on the workpiece. [Background technology]

[0002] Prior art / issue Such a method of cutting multiple slices can be achieved by lap slicing or grinding slicing.

[0003] In lap slicing, a working fluid in the form of a slurry of hard material in a liquid carrier is pumped into the working space formed between the wire surface and the workpiece. In lap slicing, material is removed by a three-body interaction involving the tool carrier (saw wire), the tool (abrasive) and the workpiece.

[0004] In abrasive slicing, a saw wire with a hard material firmly attached to its surface is used and is supplied with a working fluid, which itself does not contain any abrasive material and acts as a cooling lubricant. In abrasive slicing, material is removed by a two-body interaction involving the diamond-coated saw wire as the tool and the workpiece.

[0005] In conventional wire saws, each of the wire guide rollers has a bearing, called a fixed bearing, near each of its end faces, which is fixedly connected to the machine frame, and a bearing, called a floating bearing, near the opposite end face, which is movable in the axial direction of the wire guide roller relative to the machine frame.

[0006] There are known measures aimed at reducing the changes in the positioning of the wire array and the workpiece relative to one another during the cutting operation in order to improve the planar parallelism of the main surfaces of the slices to be cut.

[0007] US5377568 discloses a method in which the position of a reference surface located on the outside of the wire guide roller relative to the machine frame is measured and an increase or decrease in thermal length in the wire guide roller is induced by adjusting the temperature inside the wire guide roller until the measured change in position of the reference surface is again compensated for.

[0008] WO2013 / 079683A1 discloses a method in which first the slice shapes obtained at different temperatures of the wire guide roller bearing are measured, each of these shapes is stored with its associated bearing temperature, and then, during subsequent cuts, the bearing temperature that best matches the desired target shape is selected.

[0009] US5875770 discloses a method in which the shapes of slices from a cut are measured, a correction curve dependent on the depth of cut is calculated by making the difference of these slices to a desired ideal shape, and during subsequent cuts the workpiece is moved axially relative to the wire array during the cutting operation according to this correction curve.

[0010] US 2002 / 0174861 A1 describes a method which envisages controlling the temperature of the workpiece to limit bowing of the cut slices. Summary of the Invention [Problem to be solved by the invention]

[0011] Despite these measures, there is still a need for improvements, on the one hand because they have only limited effectiveness and on the other hand because the requirements in terms of flatness and plane parallelism of the slices are becoming ever more stringent, especially in the semiconductor industry.

[0012] The aim of the invention is to have available slices whose shape matches the target shape as closely as possible. [Means for solving the problem]

[0013] The object of the invention is a method for cutting a number of slices from a workpiece by means of a wire saw during a series of cutting operations divided into initial and subsequent cuts, the wire saw comprising a wire array of a movable wire section of a saw wire and a drive, the wire array being tensioned in a plane between two wire guide rollers, each of which is supported between a fixed bearing and a floating bearing, the method comprising the steps of feeding, during each of the cutting operations, the respective workpiece by the drive through the wire array along a feed direction in the presence of a working fluid and of a hard material acting abrasively on the workpiece, the feed direction being perpendicular to the workpiece axis and perpendicular to the plane of the wire array, the feeding step comprising the steps of feeding the wire array while controlling the temperature of the workpiece by wetting it with a cooling medium during each of the cutting operations, the step of feeding comprising the steps of feeding the wire array while controlling the temperature of the workpiece by wetting it with a cooling medium during each of the cutting operations, the step of feeding comprising the steps of feeding the respective workpiece by means of the drive through the wire array along a feed direction in the presence of a working fluid and of a hard material acting abrasively on the workpiece, the step of feeding comprising the steps of feeding the respective workpiece by means of the drive through the wire array while controlling the temperature of the workpiece by wetting it with a cooling medium during each of the cutting operations ... and during each cutting operation, feeding the workpiece through the wire array simultaneously with axial movement of the floating bearing by adjusting a temperature of the fixed bearing with the cooling fluid according to specification of a first temperature profile specifying a temperature of the cooling fluid depending on the depth of cut, the first temperature profile being correlated with a first compensation profile specifying a movement of the floating bearing depending on the depth of cut, the feeding step further comprising feeding the workpiece through the wire array simultaneously with moving the workpiece along the workpiece axis by a drive element according to specification of a second compensation profile specifying a movement of the workpiece, the first and second compensation profiles being different from a shape deviation, and the method further comprising determining the shape deviation during and / or before each cutting operation.

[0014] The method may be configured as lap slicing or grinding slicing. Depth of cut (doc) refers to the length of the area from the entry cut into the workpiece to the exit cut from the workpiece, opposite the feed direction.

[0015] Regulating the temperature of the fixed bearings (hereinafter referred to as Wire Guide Temperature Control (WGTC)) causes a contraction or expansion of the fixed bearings and thus their parts in the axial direction of the wire guide rollers, resulting in an axial movement of the floating bearings relative to the workpiece and thus of the wire guide rollers. Regulating the temperature of the fixed bearings therefore has the same effect in nature as moving the workpiece along its axis by means of a drive element (hereinafter referred to as Ingot Positioning Control (IPC)). The drive element is preferably a piezoelectric actuator. The variable causing the respective movement is therefore the temperature of the cooling fluid in the case of WGTC and the signal used to drive the drive element in the case of IPC.

[0016] According to the invention, both strategies are envisaged to minimise any possible shape deviations. There are particular advantages associated with this approach. When these strategies are used in combination, it is possible to realise a larger amplitude (amount of movement) of the movement of the wire guide roller relative to the workpiece than would be possible if only one of these strategies were used. The range in which the floating bearing and the movement of the workpiece depend linearly on the variables causing the movement is larger than the corresponding range available if only one of these strategies is used. The response time between changing the variables causing the movement and the movement actually occurring is significantly more for WGTC than for IPC, especially if the driving element is a piezoelectric actuator. These two strategies therefore have different control bandwidths. It is therefore advantageous to address relatively high frequency shape deviations by IPC, i.e. shape deviations that vary with a relatively large gradient depending on the cutting depth, and relatively low frequency shape deviations by WGTC. Due to the different response times, the control by IPC can be used to suppress the overshoot of the control by WGTC. Also, the control bandwidth of the combination of IPC and WGTC is larger than the control bandwidth of IPC or the control bandwidth of WGTC. The combination of both strategies makes it possible to achieve a larger movement per unit of time, since the floating bearing and the movement of the workpiece are performed by two independent actuators.

[0017] If the shape deviation is determined before the cutting operation, the term shape deviation refers to the deviation of a shape profile of a slice or an average shape profile of a slice from a reference shape profile.

[0018] If the shape deviation is determined during a cutting operation, the term shape deviation refers to the deviation of the position of a line passing through the center of an observed kerf or the deviation of the position of an average line representing a number of such lines from the position of a reference trajectory. This line and the reference trajectory will have the same position relative to a common reference if the cutting operation is completely problem-free, i.e. if there are no accidental axial movements of the wire guide rollers and / or of the workpiece. This common reference is a position in space that remains stationary, for example a position on the machine frame. If multiple kerfs are observed, the positions of the line passing through the centers of these kerfs are averaged to provide the position of the average line. Points of the line or the average line and the reference trajectory at the same height represent a particular cutting depth. The distance of such points on the line or the average line from the corresponding points on the reference trajectory thus indicates the shape deviation at the cutting depth represented by these points.

[0019] Observation of the incision or incisions is preferably carried out by irradiation with optical, infrared, X-ray or gamma radiation, although mechanical scanning of these incisions or induction or volumetric measurements of these incisions may also be considered.

[0020] The shape deviation is determined during and / or before each cutting operation. According to one embodiment, the determination of the shape deviation is based on observing one or more kerfs during the cutting operation, and two closed control loops are established. The first control loop corresponds to the control error, i.e. the determined shape deviation, by the WGTC, and the second control loop corresponds by the IPC, and the work is divided between these loops, so that the movements of the floating bearing and the workpiece, which are carried out to correct the shape deviation, are carried out. The floating bearing is moved by the WGTC according to a first correction profile, which determines the movement of the floating bearing depending on the cutting depth. The first temperature profile, which specifies the temperature of the coolant depending on the cutting depth, is correlated with the first correction profile. It is determined beforehand by experiments what temperature change of the cooling fluid is necessary to produce a given movement of the floating bearing of the respective wire guide roller. The first correction profile determines the proportion of the movement carried out by the floating bearing in dependence on the cutting depth to reduce the shape deviation. The workpiece is moved by the IPC according to the second correction profile. The second compensation profile determines the ratio of the movement that the workpiece performs to reduce the shape deviation in dependence on the cutting depth. The sum of both ratios corresponds to the movement required to reduce the determined shape deviation. These ratios of movements may be equally divided or may be divided differently. If applicable, a further percentage of the relative movement between the workpiece and the wire sections of the wire array is taken into account in the form of a third compensation profile that specifies the change in the length of the workpiece in dependence on the cutting depth. The change in length is brought about by wetting the workpiece with a cooling medium (ingot cooling, IC).

[0021] According to a further embodiment, the determination of the shape deviation is based on a comparison of the average shape profile of the slices already cut with a reference shape profile, which provides an overall correction profile that determines, even before the cutting operation, what movements are necessary depending on the cutting depth to avoid the expected shape deviation if no action is taken in light of the comparison. The overall correction profile is divided into a first correction profile and a second correction profile, and, if applicable, a third correction profile, which determines what proportion of movements should be made by the WGTC and IPC, and what proportion of workpiece length change should be made by the IC, if applicable. Again, the proportions of workpiece movement and length change can be divided equally or in some other ratio.

[0022] According to a further embodiment, the WGTC and IPC are adopted to be different from the shape deviation, the determination of which is made during each cutting operation, and the IC is adopted to be different from the shape deviation determined before each cutting operation, or vice versa.

[0023] According to a further embodiment, the WGTC and IC are employed to be different from the shape deviation, the determination of which is made during each cutting operation, and the IPC is employed to be different from the shape deviation determined before each cutting operation, or vice versa.

[0024] According to a further embodiment, IPC and IC are employed to differ from the shape deviation, the determination of which is made during each cutting operation, and WGTC is employed to differ from the shape deviation determined before each cutting operation, or vice versa.

[0025] The surface of the slice is composed of a main surface and an edge surface. The main surface comprises the front side and the back side of the slice. The slice can be measured by being placed between a pair of sensors, as is customary for measuring the warpage. Each sensor measures the distance of the opposite main surface of the slice at a measurement point. The measurement points may be distributed over the main surface or may be located along the diameter of the slice offset by no more than ±20° from the feed direction. The measurement points are preferably located at positions i along the diameter of the slice, specifically opposite to the feed direction, so that each measurement point is associated with a specific cutting depth. The density of the measurement points is preferably as high as one per cm, and the distance between one measurement point and the nearest neighbor is preferably the same for all measurement points.

[0026] The shape profile of a slice is the line connecting the measurement points si, which are calculated at position i according to the rule si=D-(FDi-BDi), where D is the distance between the sensors, FDi is the distance between the top sensor and the respective measurement point on the front side of the slice, and BDi is the distance between the bottom sensor and the respective measurement point on the back side of the slice. Note that alternative definitions of the shape profile can also be used to implement the invention, insofar as they encode the shape of the slice depending on the cutting depth.

[0027] The average shape profile of a slice is a shape profile obtained by averaging the shape profiles of a number of slices. The reference shape profile is a shape profile of a slice with a desired shape profile, preferably with perfectly flat and mutually parallel main faces. The average shape profile is determined for slices resulting from at least 1-5 cutting operations, preferably with the same wire saw, which cutting operations immediately precede the cutting operation performed by this wire saw. The selection of slices for creating the average shape profile may be slice-based or cut-based or may include both. In the case of slice-based selection, certain slices from the cutting operations are used to determine the respective average shape profile by averaging, while other slices are excluded. For example, only slices having a certain position in the workpiece are taken into account, for example every 15th-25th slice along the workpiece axis. Another possibility for slice-based selection is to exclude slices with maximum and minimum deviations of the shape profile from the average shape profile of all slices in the cutting operation (so-called trimmed average). Alternatively, it is possible to exclude slices whose shape profile deviates from the average shape profile of all slices in the cutting operation by more than 1-2 sigma from the averaging. In cut-based selection, all slices from at least one cutting operation are used to determine the average shape profile, and all slices from at least one other cutting operation are excluded therefrom.

[0028] The average shape profile of the slices in the cutting operation changes during the sequence of cutting operations. The changes are preferably used to evaluate the performance of the wire saw. They may indicate wear of the saw wire and / or the sheathing of the wire guide roller or other parts of the wire saw exposed to wear. Thus, preferably, a threshold of shape deviations is defined, which, when reached or exceeded, triggers a maintenance operation (predictive maintenance operation) instead of a further cutting operation. Even before such a threshold is reached, such changes can be used as an opportunity to take corrective measures to limit the deterioration of the work result due to wear. Such corrective measures can be, for example, a change in the composition and / or temperature of the working fluid and / or a change in the wire speed and / or other parameters specific to the process.

[0029] Cutting operations performed after a change of the saw system represent a special case. Such a change of the saw system occurs, for example, when there is a change of the wire guide rollers, a mechanical adjustment to the wire saw or a change of the physical or chemical properties of the working fluid. The first cutting operation after the change of the saw system, the so-called initial cut, preferably consists of one to five cutting operations. In the initial cut, the shape deviation is preferably determined by comparing the average shape profile of the slices with a reference shape profile, where the average shape profile of the slices produced by the same wire saw during one or more initial cuts performed before the saw system is changed is used.

[0030] According to the invention, it is proposed to additionally provide control of the temperature of the workpiece during each cutting operation, more specifically by wetting the workpiece with a cooling medium (ingot cooling, IC). According to an embodiment, the control is performed by a closed control loop, the temperature of the workpiece forming the controlled variable and the temperature of the cooling medium forming 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 lap slicing or abrasive slicing. By controlling the temperature of the workpiece, shape deviations of the slices due to the thermal expansion of the workpiece can be suppressed. The control loop may be implemented, for example, as described in US 2002 / 0174861 A1.

[0031] According to a preferred embodiment, the temperature of the workpiece is controlled according to a second temperature profile that specifies the temperature of the cooling medium depending on the depth of cut. The second temperature profile is correlated with a third compensation profile that is different from the shape deviation. The temperature of the cooling medium affects the elongation of the workpiece and therefore the relative position of the workpiece and the wire sections of the wire array. The change in the length of the workpiece is carefully brought about by the control of the temperature of the workpiece in order to reduce the shape deviations associated with the floating bearing and the movement of the workpiece.

[0032] The wire saw used according to the invention comprises two or more wire guide rollers, the regulation of the temperature of the fixed bearings of which may be limited to the two wire guide rollers between which the wire array is tensioned and through which the workpiece is fed.

[0033] The workpiece is preferably made of a semiconductor material such as silicon in the polycrystalline or monocrystalline state. The cross-sectional circumference of the workpiece is square, rectangular or circular. In the case of cylindrical workpieces, the workpiece axis runs through the center of the cylinder. The method according to the invention is particularly suitable for the production of circular semiconductor wafers made of monocrystalline silicon with a diameter of at least 200 mm, in particular at least 300 mm.

[0034] The invention will now be described in detail with reference to the drawings. [Brief description of the drawings]

[0035] [Figure 1] FIG. 2 is a schematic diagram showing the features of a wire saw which play a role in the use of the present invention; [Diagram 2] FIG. 2 shows further details of the wire saw. [Diagram 3] FIG. 2 shows the course of a kerf through a workpiece and the expected course represented by a reference trajectory; [Figure 4] FIG. 13 shows the arrangement of a slice between two sensors for determining shape deviations before a cutting operation. [Diagram 5] FIG. 13 illustrates the advantage gained when WGTC and IPC amplitudes are added. [Figure 6] FIG. 1 shows the range over which the amplitude A of the movement depends linearly on the variable causing the movement. [Figure 7] FIG. 1 illustrates an advantageous division of the global correction profile between WGTC and IPC. [Figure 8] FIG. 13 illustrates how combining WGTC and IPC can produce larger movements per unit time. [Figure 9] FIG. 13 illustrates how the advantageous split of the global correction profile between WGTC and IPC reduces the amplitude overshoot observed when WGTC is used as the only strategy. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE PRESENT EMBODIMENT A wire saw suitable for carrying out the method according to the invention comprises a wire array 2 consisting of a movable wire section of a saw wire 3, which is tensioned in a plane between two wire guide rollers 1. During the cutting operation, the workpiece 4 is fed by a drive 12 through the wire array 2 along a feed direction, which is perpendicular to the workpiece axis and perpendicular to the plane of the wire array 2. During this operation, each of the wire guide rollers 1 tensioning the wire array 2 and the workpiece 4 are respectively moved axially according to the direction arrows 10 and 11 depending on a first and a second correction profile. The first and second correction profiles address shape deviations that are determined before or during the cutting operation. To determine the shape deviations during the cutting operation, there is a kerf detector 13 for observing the kerf. Furthermore, a data processing unit 14 is provided for creating the first, second and, if applicable, third correction profiles. The data processing unit 14 sends control signals to the drive element 15 which cause a movement of the workpiece 4 in a direction along the workpiece axis indicated by the directional arrow 11 depending on the cutting depth according to the second correction profile. Furthermore, a device 22 is provided for regulating the temperature of the workpiece 4. When the shape deviation is determined before each cutting operation, the data processing unit 14 sends to the device 22 a second temperature profile which results in a change in the length of the workpiece according to a third correction profile.

[0037] As shown in FIG. 2, the wire guide roller 1 is 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 an outer casing 8 with a groove, into which the saw wire 3 extends. The fixed bearing 5 is provided with a channel 9 through which a cooling fluid passes for adjusting the temperature of the fixed bearing 5. When the temperature of the fluid is raised, the thermal expansion of the fixed bearing 5 causes an axial movement of the wire guide roller 1 towards the floating bearing 6, which in turn moves outward in the direction indicated by the directional arrow 10 of the axis of the wire guide roller 1 relative to the machine frame 7. When the temperature of the cooling fluid is lowered, 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 in dependence on the cutting depth by a first temperature profile, which is correlated with the first compensation profile. A control unit 16 connected to the heat exchanger and the pump ensures that the fluid passing through the fixed bearing 5 has the temperature required by the respective first temperature profile when a particular cutting depth is reached. The data processing unit 14 transmits to the control unit 16 the first temperature profile which causes a movement of the floating bearing according to the first correction profile.

[0038] 3 shows the course of a kerf 17 through a workpiece 4 and its expected course represented by a reference trajectory 18. Each deviation of a line through the centre of the kerf from the reference trajectory corresponds to an overall correction profile which may be divided in the form of a first and a second and, if applicable, a third correction profile.

[0039] FIG. 4 shows the arrangement of a slice between two sensors 19, 20 for determining the shape deviation before the cutting operation. The sensors 19, 20 measure the distance FDi of the upper sensor 19 from the front side of the slice 21 and the distance BDi of the lower sensor 20 from the back side of the slice 21 at a specific position i along the diameter of the slice 21 in the feed direction according to a specific cutting depth. The shape profile of the slice is the line connecting the measured values ​​si, which are calculated according to the rule si=D-(FDi-BDi), where D denotes the distance between the sensors. The shape deviation of the slice is obtained by comparing the shape profile of the slice with a reference shape profile. The deviation from the reference shape profile in dependence on the cutting depth corresponds to an overall correction profile, which is divided between the WGTC and the IPC in the form of a first and a second correction profile.

[0040] Figure 5 shows the advantage obtained when the amplitudes of WGTC and IPC are added. If the overall correction profile requires a movement of the amplitude A of the order of the dashed line, this movement would not be possible to achieve by WGTC or IPC individually, since the movement achievable by each individual measure would be insufficient. Only the combination of WGTC and IPC makes this possible.

[0041] Figure 6 shows that within a range B2 with a rest position B1, the amplitude A of the movement depends linearly on the variable causing the movement (input I). Outside this range, deviations from linear behavior occur, giving rise to Δ errors. By combining WGTC and IPC, the range B2 in which the whole system reacts linearly is increased.

[0042] 7 shows an advantageous division of the overall correction profile between WGTC and IPC, consisting of suppressing low-frequency shape deviations by WGTC and a first correction profile and suppressing high-frequency shape deviations by IPC and a second correction profile. For this purpose, a crossover is preferably used, which assigns the low-frequency part of the shape deviation to the correction by WGTC and the high-frequency part of the shape deviation to the correction by IPC by means of a low-pass filter (LP) and a high-pass filter (HP).

[0043] Figure 8 shows that the combination of WGTC and IPC allows a larger total amplitude A2+A1 to be achieved per unit time Δ, since the floating bearing and workpiece movements are performed by two independent actuators. If WGTC or IPC were used alone, only one amplitude, A1 and A2, respectively, would be possible in this time unit.

[0044] FIG. 9 shows (right panel) how the advantageous split of the global correction profile between WGTC and IPC reduces the overshoot in amplitude A over time t (left panel) observed when WGTC is used as the only strategy.

[0045] The above description of the exemplary embodiments should be understood as illustrative, the disclosure made thereby enabling, on the one hand, those skilled in the art to understand the present invention and its associated advantages, and, on the other hand, encompassing modifications and variations to the described structures and methods that are obvious within the understanding of those skilled in the art. [Explanation of symbols]

[0046] List of reference numbers used 1 Wire guide roller 2 Wire Array 3 Saw Wire 4 Workpiece 5 Fixed bearing 6 Floating bearing 7 machine frame 8 Exterior materials 9 Channels 10 Directional Arrows 11 Directional Arrows 12 Drive unit 13 Cutting edge detector 14 Data Processing Unit 15 Driving Elements 16 Control Unit 17 Cutting Edge 18 Reference trajectory 19 Upper Sensor 20 Lower Sensor 21 slices 22 Device for adjusting the temperature of the workpiece

Claims

1. 1. A method for cutting a plurality of slices from a workpiece by a wire saw during a series of cutting operations, the cutting operations being divided into initial and subsequent cuts, the wire saw comprising a wire array of a movable wire section of a saw wire and a drive, the wire array being tensioned in a plane between two wire guide rollers, each of the two wire guide rollers being supported between a fixed bearing and a floating bearing, the method comprising the steps of feeding a respective workpiece through the wire array by the drive along a feed direction in the presence of a working fluid and a hard material acting abrasively on the workpiece, the feed direction being perpendicular to a workpiece axis and perpendicular to the plane of the wire array, the feeding step comprising the steps of feeding the workpiece through the wire array while controlling a temperature of the workpiece by wetting the workpiece with a cooling medium during each cutting operation, and feeding the workpiece through the wire array while controlling a temperature of the workpiece by wetting the workpiece with a cooling medium during each cutting operation, the step of feeding the workpiece through the wire array according to a first temperature profile specification, the first temperature profile specifying a temperature of the cooling fluid in dependence on a depth of cut during each cutting operation. and feeding the workpiece through the wire array simultaneously with the axial movement of the floating bearing by adjusting a temperature of a bearing, the first temperature profile being correlated with a first compensation profile specifying a movement of the floating bearing depending on the depth of cut, the feeding step further comprising feeding the workpiece through the wire array simultaneously with moving the workpiece along the workpiece axis by a drive element according to specifications of a second compensation profile specifying a movement of the workpiece, the first compensation profile being a rate of movement of the floating bearing with the depth of cut and the second compensation profile being a rate of movement of the workpiece with the depth of cut, the first and second compensation profiles being different from a shape deviation of the slice such that a shape deviation of the slice can be reduced, the shape deviation being measured during each of the cutting operations by comparing a position of a line through the center of at least one kerf with a position of a reference trajectory, the method further comprising the step of determining the shape deviation during and / or before each of the cutting operations.method.,

2. A method for cutting a plurality of slices from a workpiece by means of a wire saw during a series of cutting operations, the cutting operations being divided into initial and subsequent cuts, the wire saw comprising a wire array of movable wire sections of a saw wire and a drive arrangement, the wire array being tensioned in a plane between two wire guide rollers, each of the two wire guide rollers being supported between a fixed bearing and a floating bearing, the method comprising the steps of feeding, during each of the cutting operations, a respective workpiece through the wire array by the drive arrangement along a feed direction in the presence of a working fluid and a hard material acting abrasively on the workpiece, the feed direction being perpendicular to a workpiece axis and perpendicular to the plane of the wire array, the feeding comprising the steps of feeding, during each of the cutting operations, the workpiece through the wire array while controlling a temperature of the workpiece by wetting the workpiece with a cooling medium, and selecting, during each of the cutting operations, a first temperature profile specifying a temperature of the cooling fluid in dependence on a cutting depth. and feeding the workpiece through the wire array simultaneously with axial movement of the floating bearing by adjusting a temperature of the fixed bearing with the cooling fluid according to a specification of a cutting rule, the first temperature profile being correlated with a first compensation profile specifying a movement of the floating bearing depending on the depth of cut, the feeding step further comprising feeding the workpiece through the wire array simultaneously with moving the workpiece along the workpiece axis by a drive element according to a specification of a second compensation profile specifying a movement of the workpiece, the first compensation profile being a rate of movement of the floating bearing with the depth of cut and the second compensation profile being a rate of movement of the workpiece with the depth of cut, the first and second compensation profiles being different from a shape deviation of the slice such that a shape deviation of the slice can be reduced, the shape deviation being determined before each cutting operation by comparing an average shape profile of already cut slices with a reference shape profile.

3. The method of claim 2 , wherein the average shape profile is determined by averaging shape profiles of selected slices, the selection being made on a slice-by-slice basis, a cut-by-cut basis, or a slice-by-cut basis.

4. The method according to claim 2 or 3, wherein the already cut slices result from at least one to five cutting operations immediately preceding the respective cutting operation.

5. A method according to any one of the preceding claims, wherein the temperature of the workpiece is controlled by a closed control loop, the temperature of the workpiece forming a controlled variable and the temperature of the cooling medium forming a manipulated variable of the control loop.

6. 5. The method according to claim 1, wherein the temperature of the workpiece is controlled according to a second temperature profile, the second temperature profile specifying a temperature of the cooling medium depending on the cutting depth and interrelated with a third correction profile, the third correction profile being different from the shape deviation.

7. The method according to any one of claims 1 to 4, wherein if the shape deviation determined before each cutting operation reaches or exceeds a defined threshold value, a maintenance action is initiated instead of the respective cutting operation.

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