Method for simultaneously cutting out plurality of slices from workpiece by means of wire saw

Abstract

The invention relates to a method for simultaneously cutting out a plurality of slices (34) from a workpiece (1) by means of a wire saw, comprising: a cutting and grinding process in which the workpiece (1) is moved perpendicularly to the longitudinal axis (26) of the workpiece towards a wire web (24) of a sawing wire (4) stretched between two wire guide rollers (5, 6), the sawing wire (4) being moved in the longitudinal direction of the sawing wire, wherein the wire mesh (24) is supplied with a cooling lubricant, and wherein between the wire sections of the wire mesh (24) a slice (34) is produced which is fixed to the bar (2) and between which there is a cutting gap (22), and wherein the bar (2) and the slice (34) are removed from the wire mesh (24), the cutting gap (22) is sprayed with a liquid (21) by means of a spraying device during the removal of the strip beam (2) and the cutting blade (34) until the wire section has exited the cutting gap (22), the liquid (21) being supplied at high pressure by means of a nozzle (14) fixed to a nozzle strip beam (16, 17), the nozzle strip being moved parallel to the longitudinal axis (26) of the workpiece (1) in a rocking manner, wherein the liquid (21) and entrained air (35) occasionally excite the slice (34) to vibrate.

Description

Technical Field

[0001] The object of the invention is a method for simultaneously cutting (slicing or slicing) a plurality of slices from a workpiece by means of a wire saw, the method comprising:

[0002] an abrasive cutting process in which a workpiece is fed perpendicularly to its longitudinal axis towards a wire web which straddles a sawing wire between two wire guide rollers, the sawing wire moving in the longitudinal direction of the sawing wire, wherein a cooling lubricant is supplied to the wire web and wherein slices are produced between wire segments of the wire web which are fixed to a beam (bar) and between which there are cutting gaps; and

[0003] The beam and the slice are removed from the wire mesh.

[0004] For many applications, uniform slices with few crystal and structural defects with good plane parallelism of their front and back sides are required. An example is the slices of structured single-crystalline semiconductor material for microelectronic components. Such slices are obtained, for example, by cutting from a cylindrical workpiece. Background Art

[0005] For example, a method and a device for wire sawing are known from DE 10 2016 211 883 A1. For wire sawing, the sawing wire is guided spirally around at least two wire guide rollers in the following manner: the two wire guide rollers span a wire web facing the workpiece, the wire web consisting of wire segments extending parallel to each other. The sides of the wire guide rollers are provided with a plurality of annular closed grooves, which extend in a plane perpendicular to the axis of the wire guide rollers and guide the sawing wire. Rotating the wire guide rollers in the same direction generates a relative movement between the wire segments and the workpiece. The wire saw also has a feed device, to which the workpiece is fixed via a beam (to which the workpiece is bonded), and which feeds the workpiece perpendicularly to the wire web. When contact occurs between the workpiece and the wire web, the relative movement and the presence of an abrasive cutting tool result in material being removed from the workpiece. With continued feeding, the wire segments form a cutting gap in the workpiece, and the wire web slowly works through the entire workpiece until the wire web is completely located within the saw beam. The workpiece is then completely cut into slices, which are suspended from the beam like the teeth of a comb and are held only by the adhesive joints.

[0006] Once the cutting process has ended, the workpiece which has been cut into slices has to be retrieved from the wire web by reversing the direction of movement of the feed device (ingot retrieval).

[0007] Wire sawing can be distinguished into wire cut grinding and wire cut grinding. In the case of wire cut grinding, the sawing wire has no abrasive and the cutting tool is supplied in the form of a slurry as freely movable particles dispersed in a carrier fluid. In the case of wire cut grinding, the abrasive cutting agent is anchored on the surface of the sawing wire and a cutting fluid is supplied which serves as a cooling lubricant and does not contain any abrasive substances.

[0008] The saw wire is usually composed (or constructed) of hypereutectoid pearlitic steel (piano wire). Straight (flat) saw wires are used as well as structured (curled / corrugated) saw wires.

[0009] In the case of wire cut grinding, the cutting agent is usually composed of silicon carbide (SiC), and the carrier fluid is usually made of oil or ethylene glycol. In the case of wire cut grinding, the cutting agent is usually composed of water (possibly with wetting agents and anti-foaming additives), and the abrasive anchored in the saw wire is usually diamond.

[0010] For wire sawing, the sawing wire is led from a first stock (usually in the form of a first reel) on which the sawing wire is wound and after use is fed into a second stock, which is also usually in the form of a second reel. The first reel is referred to as the new wire reel and the second reel is referred to as the used wire reel (old wire reel). Wire sawing may involve a unidirectional or bidirectional wire movement. In the case of unidirectional wire sawing, the sawing wire moves from the new wire reel to the used wire reel in the longitudinal wire direction during the entire cutting process. In the case of wire sawing with bidirectional wire movement, the sawing wire moves during the cutting process by means of at least one pair of direction reversals, wherein a pair of direction reversals comprises a first movement of the sawing wire in a first wire longitudinal direction with a first length and a second movement of the sawing wire in a second direction diametrically opposite to the first direction with a second length. In particular, wire sawing with bidirectional wire movement may comprise a plurality of such pairs of wire direction reversals, wherein the first length is selected to be greater than the second length, such that the entire wire stock moves from the new wire reel to the used wire reel during the cutting process. The above method is called pilgrim mode cutting or wire reciprocating cutting.

[0011] Wire saws are also known in the art, in which the workpiece can be pivoted about an axis parallel to the longitudinal axis of the workpiece during the cutting process. In particular, this rotational movement can be realized in the form of a continuous sequence consisting of a plurality of pairs of rotational changes, wherein a pair of rotational changes comprises a clockwise rotation at a first angular velocity through a first angle, and a subsequent counterclockwise rotation at a second angular velocity through a second angle. In this case, the first and second angular velocities as well as the first and second angles can also vary during the course of the cutting process, for example depending on the cutting depth or on the instantaneous (transient) length of the sawing line in the workpiece. This repetitive oscillating movement of the workpiece is also referred to as swaying of the workpiece. For example, US2022 / 0134600 A1 describes a device suitable for this purpose.

[0012] During the cutting process, material is removed primarily along the contact surface along which the saw line is in material-removing contact with the workpiece and which extends opposite to the direction in which the workpiece is fed. This contact surface is referred to as the primary cutting surface. The contact surface between the saw line and the workpiece that is presented perpendicularly to this direction (that is to say in the direction of the workpiece axis) is referred to as the secondary cutting surface, where no forces act as a result of the workpiece feed and therefore no material removal takes place. During the entire cutting process, the sum of all instantaneous secondary cutting surfaces of the cutting gap forms the front and rear sides of adjacent slice pairs.

[0013] During wire sawing without wobbling, the main cutting surface extends along the entire arc length from the entry of the sawing wire into the cutting gap to the exit of the sawing wire from the cutting gap. During wire sawing with wobbling, the main cutting surface at any time consists only of the short arc segment with which the sawing wire comes into contact with the cutting wire bent due to the wobbling between the workpiece and the cutting gap. The wobbling improves the supply of cooling lubricant or slurry to the cutting gap, even in the case of workpieces with large diameters.

[0014] For cut-off grinding, the material removal rate is proportional to the pressure on the major cutting faces. For cut-off grinding, the material removal rate increases disproportionately with the pressure on the major cutting faces. Therefore, with the aid of rocking, cut-off grinding (but not cut-off grinding) can be performed faster than without rocking.

[0015] By reversing the workpiece feed, after the wire sawing, the removal of the workpiece cut into slices from the wire web occurs. In this case, the sawing wire is moved slowly in the longitudinal direction of the wire and a cutting fluid is added so that the cutting fluid is sucked into the cutting gap as a lubricant and prevents the friction of the sawing wire in the cutting gap and the jamming of the individual wire segments between the secondary cutting surfaces of the cutting gap that are located opposite to each other. For the ingot retrieval after the wire sawing grinding, before the sawing wire enters the cutting gap, due to the slow wire movement, most of the slurry drips from the sawing wire, so that the thickness of the slurry film surrounding the sawing wire in the cutting gap is substantially less than the thickness of the slurry film during the previous cutting process. Therefore, during the ingot retrieval after the wire sawing grinding, there is play on the sawing wire in the cutting gap and the sawing wire does not get stuck. This facilitates the wire web to slide evenly through the cutting gap and eventually slide out of the gap without the sawing wire getting stuck between the secondary cutting surfaces of the gap or causing material removal from the secondary cutting surfaces.

[0016] In the case of wire cut grinding, there is no cutting tool slurry surrounding the saw wire. Therefore, the width of the cutting gap is the same as the wire diameter (including the diamonds incorporated in the saw wire). Therefore, during ingot retrieval, there is no play on the saw wire within the cutting gap, which means that it often gets stuck at different cutting depths. Therefore, the slow wire longitudinal movement means that additional material removal occurs immediately and cuts are formed in the walls of the cutting gap. Since the walls of the cutting gap form the front side of one slice and the back side of the immediately adjacent slice, cuts are formed in the respectively obtained wafers. Slices with cuts in the surface are not suitable for demanding applications.

[0017] The feed device is further reset when the sawing wire remains stuck at a cutting depth during the ingot retrieval after wire cutting grinding. As a result, the sawing wire is deflected in the transverse direction of the wire and elastically stretched in the longitudinal direction of the wire. The sawing wire is thus subjected to increasingly greater restoring forces. When the restoring forces have grown sufficiently, the sawing wire jumps out of the cutting depth at which it was stuck during the retrieval to a smaller cutting depth at which it is stuck again, and so on (stuck and sliding movement of the sawing wire). Taking into account the longitudinal extension of the wire due to the lateral deflection of the sawing wire, if the pulling force exceeds the material strength of the sawing wire, the sawing wire breaks during the ingot retrieval. In this case, the workpiece must be completely removed from the damaged wire web, the wire residues must be manually removed from the cutting gap, and the wire web must be repaired again before the next cutting process. This is both time-consuming and expensive.

[0018] The sawing wire occasionally breaks during the cutting process due to overloading of the sawing wire or material defects. The partially cut workpiece must then be removed from the damaged wire web by resetting the feed device, removing the remaining wire from the cutting gap, repairing the wire web, threading the wire section back into the existing cutting gap and feeding the workpiece again to the cutting depth where the wire break occurred, so that the cutting process can be completed. In the case of wire cutting grinding, since the sawing wire has sufficient play in the cutting gap due to the surrounding slurry film, the threading and feeding of the workpiece into the wire web occurs effortlessly without the sawing wire getting stuck at a given cutting depth. In the case of wire cutting grinding, in which the sawing wire has no freedom of movement, the sawing wire gets stuck during the feeding of the workpiece and a cut is produced.

[0019] Even if the diamond-coated sawing wire gets stuck in an unforeseeable manner during the workpiece feed after the wire has broken or when resetting the feed from the wire web during ingot retrieval, the lack of freedom of movement leads in any case to additional material removal from the side walls delimiting the gap and thus damages the front and rear sides of the slice concerned. This damage causes material stresses on the damaged surface, which lead to elastic deformation of the slice if the stresses on the front and rear sides of the slice cannot balance each other (which is usually not the case). This elastic deformation caused by surface damage is superimposed on the plastic deformation, and the plastic deformation cannot be determined individually by measuring the slice shape after the wire sawing and therefore cannot be removed selectively by appropriate measures. The latter is necessary because the elastic deformation disappears when the damaged layer is removed in the subsequent material removal process, while the plastic deformation remains if it is not removed by selective material removal.

[0020] US2009 / 0223539 A1 describes a method for cleaning wafers for solar applications, for example, which are immersed in a cleaning bath after the cutting process is completed and removed from the wire saw, still suspended by its adhesive joint on the saw beam (sacrificial beam). The cutting gap (cut) is exposed to a flushing fluid from a plurality of independent jet nozzles. At the point where the flushing fluid is sprayed in, the cutting gap is widened in the water bath, so that the cleaning action is increased. By moving the nozzle relative to the workpiece, all cutting gaps can be widened one after another and thus cleaned successively. The method described does not help to avoid the consequences of jamming and sliding movements of the sawing wire during ingot retrieval.

[0021] JP 2006-66793 A describes a similar method, in which a cut piece is sprayed with a jet of fluid after the cutting process has been completed and removed from the wire saw, in order to clean the side surfaces by means of a spray nozzle.

[0022] US 2011 / 0168212 describes a similar method for cleaning thin, fragile solar wafers after sawing and removal of the cut workpiece from the wire saw.

[0023] JP2004-106360 describes a method in which, after wire-cut grinding of the workpiece and ingot retrieval, flushing fluid is fed through channels present in the beam to clean the cutting gap. Summary of the invention

[0024] The object of the invention is to avoid jamming and sliding movements of the saw wire and their adverse consequences.

[0025] The object of the present invention is achieved by a method for simultaneously cutting a plurality of slices from a workpiece by means of a wire saw, the method comprising:

[0026] A cut-off grinding process in which a workpiece is moved perpendicularly to the longitudinal axis of the workpiece towards a wire web of a sawing wire stretched between two wire guide rollers, the sawing wire being moved in the longitudinal direction of the sawing wire, wherein a cooling lubricant is supplied to the wire web, and wherein cut-offs are produced between the wire sections of the wire web, which are fixed to a beam and have a cutting gap in between, and

[0027] removing the beam and the slice from the wire mesh,

[0028] Characterized in that during the removal of the beam and the slice, the cutting gap is sprayed with a fluid by means of a spray device until the wire segment has left the cutting gap, wherein the fluid is supplied with high pressure (high pressure) through a nozzle fixed to a nozzle holder, and the nozzle holder moves in a rocking manner parallel to the longitudinal axis of the workpiece, wherein the fluid and the entrained air occasionally (infrequently) excite vibrations of the slice.

[0029] During the removal, the nozzle sprays the fluid onto the cutting gap. During this period, the surrounding air swirls and causes the slice to vibrate by means of the Bernoulli effect. The nozzle holder performs a rocking stroke motion parallel to the workpiece axis, which is why the fluid from at least one nozzle in the plane of the corresponding cutting gap occasionally encounters each cutting gap. In this way, the fluid penetrates deep into the cutting gap, and the change in the spray pressure caused by the rocking motion gradually leads to a continuous periodic fanning of all the cutting gaps during the removal of the beam and the slice from the cutting gap.

[0030] The pressure at which the fluid is supplied through the nozzle is preferably selected in such a way that the exit velocity of the flushing agent corresponds to the velocity of the wire movement relative to the workpiece.

[0031] Preferably, the nozzles are a constituent part of a spraying device which comprises in each case at least one nozzle holder which is arranged laterally of the wire guide rollers of the wire web between the respective wire guide roller and the workpiece. The nozzle holder can perform a stroke movement parallel to the workpiece axis and is preferably arranged parallel to the axis of rotation of the wire guide rollers.

[0032] Particularly preferably, exactly two nozzle holders are provided, with respect to which, viewed in the direction of the workpiece axis, new wires are arranged on the inlet side of the workpiece and used wires are arranged on the outlet side of the workpiece. The nozzles are preferably oriented in such a way that each nozzle generates a partial fluid flow which is oriented tangentially to the wire web and in one of the planes in which the cutting gaps extend. The amplitude of the rocking movement of the respective nozzle holder parallel to the longitudinal axis of the workpiece is preferably at least half the gap between two adjacent nozzles. The total stroke corresponding to the double amplitude is therefore at least the gap between two nozzles. In this way, it is ensured that after a period of rocking movement, each nozzle has covered all cutting gaps located between it and the adjacent nozzles.

[0033] The number of nozzles per nozzle holder is preferably 10 to 50. A number of nozzles as large as possible is particularly preferred. The upper limit of the number is determined only by the size of the nozzles. As a result, the stroke required for the oscillating movement of the nozzle holder is smaller and the covering of the cutting gap occurs at shorter intervals.

[0034] During the cut-off grinding process, the workpiece is fed by means of a feed device. The wire guide rollers rotate in the same direction so that the wire sections describe a relative movement with the workpiece and during engagement with the workpiece as a result of the feed movement, material removal occurs.

[0035] At the end of the cut-off grinding process, the workpiece is completely sliced ​​and a plurality of cutting gaps extending parallel to one another are formed between the slices, which are held by the beams.

[0036] Removing the beam and the cut piece from the cutting gap includes resetting the feed device while the wire segment is moved in the longitudinal direction of the wire in the presence of cooling lubricant.

[0037] The workpiece is preferably a cylindrical rod consisting of (composed of) a single-crystalline semiconductor material.

[0038] The method preferably further comprises: during the cut-off grinding process, the workpiece pivots about an axis parallel to the longitudinal axis of the workpiece, wherein the workpiece performs a plurality of pairs of pivoting movements, and a pair of pivoting movements comprises a first pivoting movement at a first angular velocity and a first angle, and a second pivoting movement at a second angular velocity and a second angle. The first angular velocity and the second angular velocity and the first angle and the second angle of two pairs of pivoting movements in the consecutive pairs of pivoting movements are preferably different.

[0039] The sawing wire is preferably a hypereutectoid pearlitic steel wire (piano wire) having a cutting tool fixed on its surface. The cutting tool is preferably diamond.

[0040] During the cut-off grinding process, the movement of the sawing wire in the longitudinal direction can occur with or without a reversal of direction. With a reversal of direction, during the movement of the sawing wire in the longitudinal direction, the sawing wire is moved by means of a plurality of pilgrim steps, wherein each pilgrim step comprises a first movement of the sawing wire in a first longitudinal direction by a first length and a second movement of the sawing wire in a second longitudinal direction diametrically opposite to the first wire longitudinal direction by a second length, and the first length is greater than the second length.

[0041] The cooling lubricant and the fluid are preferably made of water (which may contain liquid additives). The two can have the same composition or different compositions. The liquid additive is preferably a wetting agent, a corrosion inhibitor, a viscosity improving (influencing) agent (such as ethylene glycol and / or methylcellulose), a defoaming agent or any mixture of these agents.

[0042] The procedure according to the invention is preferably also used to react appropriately to interruptions in the cutting process, in particular interruptions as a result of the breakage of the sawing wire. It prevents the wire segments from getting stuck and grooves or elastic deformations from adversely affecting the quality of the cut during the removal of the workpiece after the wire has broken and during the reverse movement of the workpiece back to the position before the wire breakage.

[0043] The interruption of the cut-off grinding process occurs while the movement of the sawing line in the longitudinal direction continues and includes the removal of the workpiece from the cutting gap, the return of the workpiece into the cutting gap, and the continuation of the cut-off grinding process. During the return of the workpiece, the fluid is sprayed into the cutting gap through the nozzle, and the nozzle holder moves parallel to the longitudinal axis of the workpiece.

[0044] During the cutoff grinding process, the movement of the sawing wire in the longitudinal direction preferably takes place at a speed which is at least ten times faster than the speed at which the sawing wire moves in the longitudinal direction during removal and return of the workpiece when the cutoff grinding process is interrupted.

[0045] The present invention is presented below in preferred exemplary embodiments of a wire saw with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 Features of the wire saw and workpiece are shown which aid in understanding the present invention.

[0047] Figure 2 (A) and (B) show details of an injection device suitable for carrying out the method according to the invention.

[0048] List of reference symbols used

[0049] 1 Workpiece

[0050] 2 beams

[0051] 3 Feed direction

[0052] 4 Sawing lines

[0053] 5Left line guide roller

[0054] 6Right line guide roller

[0055] 7 Rotation axis

[0056] 8 Rotation axis

[0057] 9. Direction of supply of wire

[0058] 10 Direction of line movement

[0059] 11 Direction of rotation of wire guide roller

[0060] 12 Bracket

[0061] 13 Bracket

[0062] 14 Nozzle

[0063] 15 Cooling lubricant

[0064] 16 Left nozzle bracket

[0065] 17 Right nozzle bracket

[0066] 18 Axis of left nozzle bracket

[0067] 19 Axis of right nozzle bracket

[0068] 20 Nozzle

[0069] 21 Fluid

[0070] 22 Cutting gap

[0071] 23 Grooves

[0072] 24-wire network

[0073] 25 Bonded joints

[0074] 26 Longitudinal axis of the workpiece

[0075] 27 Swinging

[0076] 28 Swinging

[0077] 29 Movement direction

[0078] 30Wider cutting gap

[0079] 31 Nozzles

[0080] 32 Nozzles

[0081] 33 Diamond

[0082] 34 slices

[0083] 35 Entrained Air DETAILED DESCRIPTION

[0084] like Figure 1 As shown, during wire sawing, the sawing wire 4 is guided spirally around at least two wire guide rollers in the following manner: Two wire guide rollers 5 and 6 span across a wire web 24 facing the workpiece 1, which consists of wire segments extending parallel to one another. The wire guide rollers have the shape of a right circular cylinder and have rotation axes 7 and 8 oriented parallel to one another and about which the wire guide rollers can rotate in direction 11. The wire guide rollers are provided with a plurality of annular closed grooves 23 on their sides extending in planes perpendicular to the rotation axes 7 and 8, which guide the sawing wire 4. Rotating the wire guide rollers in the same direction generates a relative movement between the wire segments and the workpiece. In this case, new sawing wire is drawn from a first wire stock, the so-called new wire reel (direction 9), and used sawing wire is fed into a second wire stock, the so-called used wire reel (direction 10). The wire saw also has a feed device to which the workpiece 1 is fixed by means of a beam 2 by means of an adhesive joint 25 and which feeds the workpiece perpendicularly to the wire web (direction 3). After contact between the workpiece and the wire web occurs, the relative movement and the presence of the abrasive cutting tool cause material to be removed from the workpiece. By continuous feeding, relative movement and the supply of cutting tools, each wire segment in the wire web 24 forms a cutting gap 22 by continuously removing material from the workpiece. The side walls of the cutting gap 22 each define a pair of adjacent slices in the wafer, the rear side and the front side of a second slice 34.

[0085] The cutting tool is a diamond 33, which is fixedly bonded into the surface of the wire 1. During the cut-off grinding process, a cooling lubricant 15 is supplied to the wire web 24 via two nozzle holders 12, 13, which are each provided with a nozzle 14, on the left and right side of the workpiece, which cooling lubricant itself does not contain abrasive cutting tools (hard substances). The cut-off grinding process ends when the entire wire web has been completely worked through the workpiece and remains in the beam 2. The slice 34 that has completely cut the workpiece is then suspended on the half-cut beam like the teeth of a comb, connected to the beam 2 only by the adhesive joint 25.

[0086] The wire saw shown is provided with a left nozzle holder 16 and a right nozzle holder 17. The nozzle holders 16, 17 carry a plurality of nozzles 20 which spray a fluid 21 onto a cutting gap 22 in a workpiece 1. The axes 18 and 19 of the nozzle holders are arranged parallel to each other and parallel to the axes of rotation 7 and 8 of the wire guide rollers 5 and 6 of the stretching wire web 24 and perpendicular to the cutting gap 22 of the workpiece 1 or parallel to the longitudinal axis 26 of the workpiece 1. The nozzle holders perform oscillating movements 27 and 28 in the direction of their axes 18 and 19. By means of this periodic displacement, the (fluid) stream of the fluid 21 leaving the individual nozzles 20 covers the cutting gap 22 of the workpiece 1 at periodic intervals.

[0087] according to Figure 1 The preferred layout of FIG. 1 shows the nozzle holder 16 on the left side of the workpiece 1, in other words on the new wire entry side, and the nozzle holder 17 on the right side of the workpiece 1, in other words on the used wire exit side, and both are below the wire web 24 when viewed from the direction of the feed device. Deviating from this, the nozzle holder can also be arranged above the wire web 24.

[0088] As mentioned above, the method according to the invention can also be carried out using a wire saw in which the workpiece can be pivoted about an axis parallel to the longitudinal axis of the workpiece during the cutting and grinding process. During this oscillation, at any point in time, only the partial section of the entire wire section that runs within the cutting gap is in material removal contact with the workpiece. Viewed in the longitudinal direction of the wire, a gap is formed both before and after the instantaneous contact surface between the sawing wire and the workpiece extending in the feed direction of the workpiece. If the nozzle holder is arranged above the wire mesh, the fluid can reach particularly well between the sawing wire and the workpiece. If the nozzle holder is arranged below the wire mesh, then despite the oscillation, almost no fluid can enter between the sawing wire and the workpiece. On the other hand, in this case, the cut part of the workpiece (the subsequent wafer) that protrudes below the wire mesh is caused to vibrate particularly effectively by the Bernoulli effect of the fluid flow and thus leads to a periodic expansion and reduction of the cutting gap width.

[0089] Figure 2 (A) and (B) show details of the spraying device including the nozzle holders 16 and 17 in a plan view (seen from the direction of the feed device) with respect to the left nozzle holder 16 and a part of the workpiece 1 with the cutting gap 22 and the longitudinal axis 26 of the workpiece.

[0090] Figure 2(A) shows a nozzle holder 16 with an axis 18 parallel to the longitudinal axis 26 of the workpiece at the beginning of a rocking movement 27 parallel to the axis 18. There are nozzles 31 from which in each case a portion of the flow of the fluid 21 flows precisely in the plane of the cutting gap 22, with the result that the fluid 21 is forced deep into the cutting gap 22. During this process, a pair of adjacent slices 34 that divide the cutting gap 22 in the direction of movement 29 are elastically pressed away from the cutting gap, with the result that the cutting gap is elastically widened to a widened cutting gap 30. In addition, there are nozzles 32 from which no flow of the fluid 21 flows in the plane of the cutting gap 22, and therefore these nozzles 32 do not elastically widen the cutting gap. The flow of the fluid 21 entrains air 35 from the environment by means of momentum exchange.

[0091] When the left nozzle holder 16 has performed a rocking movement 27 in the direction of the axis 18, it reaches the other end of its rocking movement. Figure 2 (B) The nozzle 31 (some of the flow from the nozzle 31 presses the fluid into the cutting gap and thus widens the cutting gap) is in different positions and widens the other cutting gaps to the position according to Figure 2 (A) The magnitude of the amplitude of the rocking motion 27 corresponds at least to the value of the gap between two adjacent nozzles.

[0092] During the rocking motion 27, the flow of fluid 21 (fluid is incompressible) and the air 35 entrained by the flow (air / gas is compressible) diffuse outside the slice 34 and the cutting gap 22. Since they flow around the slice and the cutting gap in different planes during the rocking motion, the slice 34 is excited by the dynamic air pressure changes of the air entrained by the flow to produce vibrations (Bernoulli effect). In other words, it causes elastic deflection of the slice and a periodically widening and tapering cutting gap.

[0093] Studies on which the invention is based and which aim to avoid jamming and slipping of the sawing wire during the ingot retrieval and during the repositioning of the workpiece after an interruption in the cutting and grinding process have shown that it is necessary to excite the vibration of the slice in order to reduce the friction of the sawing wire in the narrow cutting gap. Widening the cutting gap by forcing in a fluid at the changing cutting gap and the associated cleaning action occur too slowly as a single measure. It is therefore not feasible to prevent the sawing wire from buckling or warping caused by strain during the ingot retrieval or during the repositioning of the workpiece after an interruption.

[0094] Only the excitation of the vibrations of the slices by means of a fluid flow with entrained air, obtained by means of the Bernoulli effect, has proven to be a suitable means for achieving this purpose.

Claims

1. A method for simultaneously cutting a plurality of slices from a workpiece by means of a wire saw, the method comprising: A cut-off grinding process, wherein the workpiece is moved perpendicularly to the longitudinal axis of the workpiece towards a wire web of a sawing wire stretched between two wire guide rollers, the sawing wire being moved in the longitudinal direction of the sawing wire, wherein a cooling lubricant is supplied to the wire web, and wherein cut-offs are produced between the wire sections of the wire web, which are fixed to a beam and have a cutting gap in between, and removing the beams and the slices from the wire web, The invention is characterized in that the cutting gap is sprayed with a fluid by means of a spray device during the removal of the beam and the slice until the wire section has left the cutting gap, wherein the fluid is supplied with high pressure through a nozzle fixed to a nozzle holder, and the nozzle holder moves in a wobbling manner parallel to the longitudinal axis of the workpiece, wherein the fluid and the entrained air occasionally excite vibrations of the slice.

2. The method according to claim 1, characterized in that The amplitude of the rocking motion is equal to or greater than the total gap between two adjacent nozzles.

3. The method according to claim 1 or 2, characterized in that: The cutting and grinding process is interrupted while the sawing wire continues to move in the longitudinal direction, comprising: removing the workpiece from the cutting gap; returning the workpiece into the cutting gap; and The cutoff grinding process is continued, wherein during the return of the workpiece, fluid is injected into the cutting gap through the nozzle and the nozzle holder is moved parallel to the longitudinal axis of the workpiece.

4. The method according to any one of claims 1 to 3, characterized in that During the cutting and grinding process, the workpiece pivots about an axis parallel to the longitudinal axis of the workpiece, wherein the workpiece performs multiple pairs of pivoting motions, and a pair of pivoting motions includes a first pivoting motion at a first angular velocity and a first angle, followed by a second pivoting motion at a second angular velocity and a second angle.

5. The method according to claim 4, characterized in that The first angular velocity and the second angular velocity and the first angle and the second angle of two pairs of consecutive pairs of pivoting movements are different.

6. The method according to any one of claims 1 to 5, characterized in that The cooling lubricant includes water and a first liquid additive, and the fluid includes water and a second liquid additive.

7. The method according to claim 6, characterized in that The first liquid additive is the same as the second liquid additive and comprises a wetting agent or a corrosion inhibitor or a viscosity influencer, a defoamer or a mixture thereof.

8. The method according to any one of claims 1 to 7, characterized in that The sawing wire consists of a hypereutectoid pearlitic steel wire with diamond fixed on the surface as a cutting tool.

9. The method according to any one of claims 1 to 8, characterized in that The workpiece is a cylindrical rod of single-crystalline semiconductor material.

10. The method according to claim 3, characterized in that During the cutoff grinding process the sawing wire moves in the longitudinal direction at a speed at least ten times faster than the speed at which the sawing wire moves in the longitudinal direction during removal and return of the workpiece.

11. The method according to any one of claims 1 to 10, characterized in that The sawing wire moves in the longitudinal direction without reversing direction.

12. The method according to any one of claims 1 to 10, characterized in that In case of a reversal of direction, the sawing wire moves in the longitudinal direction, wherein the sawing wire is moved by means of a plurality of pilgrim steps, each pilgrim step comprising a first movement of the sawing wire in the first longitudinal direction by a first length and a second movement of the sawing wire in a second longitudinal direction diametrically opposite to the first wire longitudinal direction by a second length, and the first length is greater than the second length.

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