TECHNICAL FIELD

[0001] Embodiments described herein relate to wires adapted for sawing hard and brittle materials, methods for refurbishing wires and wire saw devices. In particular, the present disclosure relates to a method for refurbishing a partially used diamond wire, specifically a small-diameter diamond wire. Diamond wires of the present embodiments are particularly adapted for cutting or sawing hard or brittle materials such as blocks of silicon or quartz, e.g., for cutting silicon wafers, silicon ingots or the like.

BACKGROUND

[0002] Wire saws are used for cutting blocks, bricks or thin slices, e.g., semiconductor wafers, from a piece of hard material such as silicon. In such devices, a wire is fed from a spool and is guided and tensioned by wire guide cylinders, herein also called wire guides. The wire that is used for sawing may be provided with an abrasive material. The abrasive material can be provided as slurry for example. The wire may be provided with the abrasive material shortly before the wire touches the material to be cut. The abrasive is carried to the cutting position by the wire for cutting the material.

[0003] Alternatively, the abrasive can be provided on the wire with a coating, e.g. as a diamond wire. In this case, diamond particles can be provided on a metal wire with a coating, wherein the diamond particles are imbedded in the coating of the wire and the abrasive is firmly connected to the wire. During the sawing process the diamond wire may be cooled. Cooling can be done with a water based liquid including, for example, using coolant additives. [0004] At present, in the field of silicon shaping such as brick squaring and wafer slicing, the wire used may be of a high-resistance, high-carbon content steel. The diameter of the wire determines the amount of lost material during a cut. With a wafer thickness in the order of, for instance, 80- 200 μιη, and a wire core diameter in the range of, for instance, 50-180 μιη, the amount of lost material generated in the slicing channel can sum up to, for instance, 60-170 μιη. As a result, almost 50% of the initial amount of hard and brittle materials loaded in the wire saw may be lost. As a result of raw material for wafering being cost intensive, there is a desire to reduce the amount of lost material (so-called "kerf loss").

[0005] In view of the foregoing, there is a tendency to use wires having a reduced diameter in order to reduce the thickness of the cut and to decrease the material wasted. Furthermore, when using diamond wires, after several cuts the diamond particles might pull out of the coating of the wire due to wire wear. In the case of diamond pull out, unwanted consequences may arise, such as loss of the abrasive material. In cases where diamond wires are used, the abrasive material is in the form of diamond grits. As a result of the loss of diamond grits, the diamond wire's cutting efficiency and lifetime is decreased and the wire has to be replaced more often. Moreover a damaged wire can deteriorate the surface quality of the sawn piece and the geometry of the wafer.

[0006] Embodiments of the present disclosure provide an increased diamond wire lifetime in sawing processes, particularly when using small-diameter diamond wires.

SUMMARY

[0007] In light of the above, a method for refurbishing a partially used wire, a wire for sawing hard and brittle materials, a wire saw device and a method for operating the wire saw are provided. Further aspects, advantages, and features of the embodiments of the present disclosure are apparent from the dependent claims, the description and the accompanying drawings.

[0008] According to one aspect, a method for refurbishing a partially used wire is provided. The method includes depositing a binder on the partially used wire. The partially used wire having abrasive grits. [0009] According to another aspect, a wire for sawing hard and brittle materials is provided. The wire includes a core wire and a coating including abrasive grits and a binder material. The binder material includes an initial binder and a subsequent binder.

[0010] According to another aspect, a wire saw device for sawing hard and brittle materials is provided. The wire saw device includes a wire and a wire usage stage determination system.

[0011] According to another aspect, a method for operating a wire saw is provided. The method includes sawing hard and brittle materials with a wire, determining the wire usage stage, refurbishing the partially used wire and sawing hard and brittle materials with the refurbished wire.

[0012] According to embodiments of the present disclosure, the wire is particularly a diamond wire.

BRIEF DESCRIPTION OF THE DRAWINGS [0013] So that the manner in which the above recited features of embodiments of the disclosure can be understood in detail, a more particular description of the embodiments, briefly summarized above, may be had by reference to embodiments described herein. The accompanying drawings relate to embodiments of the present disclosure and are described in the following: Fig. 1 shows a schematic sectional view of an embodiment of a partially used diamond wire, according to embodiments described herein;

Fig. 2 shows a box illustrating a method for refurbishing a partially used diamond wire, according to embodiments described herein;

Fig. 3 shows a schematic sectional view of an embodiment of a diamond wire that has been at least partially refurbished, according to embodiments described herein; Fig. 4 shows a schematic sectional view of a diamond wire, according to embodiments described herein;

Fig. 5 shows a schematic sectional view of an embodiment of a diamond wire after a dressing process, according to embodiments described herein;

Fig. 6A shows a process flow diagram illustrating a method of cleaning, refurbishing and dressing a partially used diamond wire, according to embodiments described herein;

Fig. 6B shows a schematic view of an apparatus set-up with a cleaning device, a deposition device and a dressing device, according to embodiments described herein; and

Fig. 7 shows a schematic sectional view of a diamond wire saw device with a wire usage stage determination system, according to embodiments described herein; and

DETAILED DESCRIPTION OF EMBODIMENTS

[0014] Reference will now be made in detail to the various embodiments of the present disclosure, one or more examples of which are illustrated in the figures. Within the following description of the drawings, the same reference numbers refer to same components. Generally, the differences with respect to individual embodiments are described. Each example is provided by way of explanation of embodiments of the disclosure and is not meant as a limitation of the embodiments. Further, features illustrated or described as part of one embodiment can be used on or in conjunction with other embodiments to yield a further embodiment. It is intended that the description includes such modifications and variations.

[0015] A wire as described herein may be understood as a wire for sawing hard and brittle materials, e.g., pv, semiconductor, display, and other wafers or ingots or bricks, from a piece of hard or brittle material such as silicon, sapphire, quartz, glass, silicon carbide, and other similar types of hard and brittle materials. In particular, a wire for use in a cropper, a squarer, or a wafer cutting wire saw. A wire saw as described herein may be understood as a wire saw wherein a wire of considerable length, such as at least 1 m, particularly at least 1 km, or even at least 50 km, is moved through the wire saw performing a multitude of slicing actions. The term "wire length" refers to the overall length of the wire and not only to the wire that is, at a given time, used for sawing. As used herein, the term "cutting" is used synonymously with "slicing" or "sawing".

[0016] According to embodiments herein, a wire may be understood as a wire including an abrasive material used for sawing hard and brittle materials. In particular, the abrasive material may be in the form of abrasive grits and in particular in the form of diamond grits. Consequently, as described herein, a diamond wire may be used which is understood as a wire including diamond as the abrasive material used for sawing, in particular, the abrasive material may be in the form of diamond grits.

[0017] Alternatively, a diamond wire may include silicon carbide (SiC) as the abrasive material used for sawing, in particular, the abrasive material may be in the form of silicon carbide grits. A diamond wire saw device may be understood as a wire saw wherein the diamond wire is wound around the wire guides and forms a web or wire web. During sawing, the piece to be sawed may be moved through the wire web wherein the speed of this movement determines the cutting speed and/or the effective cutting area that can be sawed within a given amount of time. According to further embodiments, which can be combined with embodiments described herein, during sawing the piece to be sawed may be static while the wire web may be moved through the piece to be sawed.

[0018] The diamond grits can be provided on a metal wire, referred to as core wire, with a coating to form a diamond wire. In particular, the diamond grits can be imbedded in the coating of the diamond wire. After sawing, wear of the diamond wire increases owing to the contact forces between the wire and the hard and brittle materials, and the coating thickness is reduced. As a result, the abrasive material might pull out of the coating of the wire causing loss of the diamond grits. Accordingly, the wire sawing efficiency is reduced, the diamond wire lifetime is decreased and the wire has to be replaced more often.

[0019] In view of the foregoing, there is a desire to increase the wire lifetime by fixing firmly the diamond grits in order to avoid diamond pull out. Various techniques are known to the inventor to maximize the diamond wire lifetime. For instance, the method of sharpening is known for macroscopic tools (e.g., insert or cutter for machining). This method is not applicable to small grits. Alternatively, for abrasive grits inserted into a binder, such as for a grinding wheel, the method of deepen is currently used for maximizing the wire lifetime. This method is applicable to high diameter diamond wires composed of several layers, e.g., for rock sawing, and needs several layers of abrasive grits.

[0020] The above techniques are applicable to wires with large abrasive grits and large wire diameter. Using wires having big abrasive grits and high wire diameter for cutting has the disadvantage of losing considerable amounts of raw material during a cut. The loss of raw material involves higher costs.

[0021] According to embodiments described herein, a method for refurbishing a partially used diamond wire is provided. The method includes depositing a binder on the partially used diamond wire. Depositing a binder firmly fixes the diamond grits to the wire and avoids pull out of the diamond grits from the coating of the wire. Accordingly, the lifetime of the diamond wire can be increased. Furthermore, replacement of the wire can be reduced if refurbishment takes place without taking the wire out of the wire saw. By reducing how often the wire is replaced, the operation of the wire saw does not need to be halted so often, therefore the time consumed and the high stand-still costs implied are minimized.

[0022] According to further embodiments, which can be combined with other embodiments herein, replacement of the wire may be done at the same time as other sawing pieces of the wire saw are being replaced. Accordingly, the wire saw does not need to be halted so often therefore the time consumed and the high stand-still costs implied are minimized.

[0023] As used herein, the term "partially used wire" refers to a wire having already been used for sawing, in particular, having already been used for sawing hard and brittle materials. According to embodiments herein, the partially used diamond wire may be a partially used diamond wire. Due to the sawing process, the coating thickness of a partially used diamond wire is smaller than the coating thickness of the diamond wire before sawing, in particular, after having been used for sawing hard and brittle materials. Accordingly, the binder thickness of a partially used diamond wire is smaller than the initial binder thickness. As used herein, the binder thickness is the thickness of the binder measured at the abrasive grits. The initial binder thickness corresponds to the initial thickness of the binder deposited on the unused diamond wire, i.e., the binder thickness of the wire before being used. In a partially used diamond wire, 30 % or more of the initial binder thickness may be lost, particularly 50 % or more of the initial binder thickness may be lost, more particularly 70 % of the initial binder thickness may be lost. In particular, each abrasive grit may have an emerged height (E), which can be measured, and a mean diameter (D) which can be given by the wire provider. The emerged height corresponds to the surface of the abrasive grit which is not covered by the binder. Accordingly, the emerged height may be of 0 μιη or more. The emerged height may be equal to the mean diameter. The emerged height may not be larger than the mean diameter. During the sawing process the thickness of the binder which is not at the abrasive grits may remain constant.

[0024] FIG. 1 shows an example of a partially used diamond wire 100 used for sawing in particular hard and brittle materials. The wire 100 has a core wire 150 and a coating material around the core wire. The core wire 150 may be of a high -resistance, high-carbon content steel. The coating includes an abrasive material, such as abrasive grits, and an initial binder 120 for connecting the abrasive material to the wire. According to embodiments herein, the abrasive grits 180 may be diamond grits. According to further embodiments, which can be combined with embodiments described herein, the abrasive grits 180 may be silicon carbide (SiC) grits.

[0025] As a result of the sawing process, the initial binder 120 thickness may be reduced, therefore decreasing the adhesion of the abrasive grits to the core wire 150. Reduction of the binder thickness may form regions 160 adjacent to the abrasive grits 180. The regions 160 may be regions of reduced binder thickness. According to some embodiments described herein, the regions 160 may be concave. The binder thickness in the middle of the concave regions may be smaller than the binder thickness on the sides of the concave regions. According to alternative embodiments described herein, regions 160 may be flat. Flat regions may have a constant binder thickness along the longitudinal direction of the wire. According to further embodiments described herein, the regions 160 may be a combination of concave and flat.

[0026] Currently, reduction of the binder thickness cannot be controlled, such that at a certain point a "threshold thickness" is reached at which point adhesion of the diamond grits to the wire can no longer be guaranteed and the diamond grits begin to pull out of the coating of the wire. At this threshold thickness, a domino effect may be triggered which results in the loss of the diamond grits.

[0027] According to embodiments described herein, in order to compensate for these effects a method for refurbishing a partially used diamond wire is disclosed. FIG. 2 shows a box illustrating the disclosed method. Refurbishing a partially used diamond wire may include depositing 202 a binder on the partially used diamond wire.

[0028] As exemplarily shown in FIG. 3, a subsequent binder 320 may be deposited to at least partially fill the regions 160, formed after wire 100 has been used for sawing. Deposition of the subsequent binder 320 allows for firmly reinforcing the abrasive grits 180 to the wire and avoiding that the abrasive grits pull out of the coating of the wire. Accordingly, the diamond wire can be used for further cutting processes and thus, the wire lifetime can be increased.

[0029] According to some embodiments described herein, the binder may be deposited in an amount related to the reduction of the initial binder thickness. More particularly, the binder may be deposited on a partially used diamond wire in an amount equal to the amount of binder removed during use of the wire. For instance, a sufficient amount of the binder may be provided, i.e., an amount which ensures the diamond grits are firmly fixed to the wire and the regions 160 are not overfilled or underfilled.

[0030] As used herein, the deposited binder thickness may correspond to the thickness of the subsequent binder. For instance, the deposited binder thickness may be 30 % or more of the removed binder thickness, particularly the deposited binder thickness may be 50 % or more of the removed binder thickness, more particularly the deposited binder thickness may be 70 % or more of the removed binder thickness. [0031] According to embodiments herein, the deposition of the binder may cover at least 70% of the surface of the abrasive grits, particularly at least 85% of the surface of the abrasive grits, more particularly 100% of the surface of the abrasive grits. When the binder covers 100% of the surface of the abrasive grits, the emerged height (E) may be of 0 μιη. When the binder covers 0% of the surface of the abrasive grits, the emerged height may be equal to the mean diameter (D). According to further embodiments, which can be combined with other embodiments described herein, the binder may be deposited before 20% of the abrasive grits are pulled out, preferably before 15% of the abrasive grits are pulled out, more preferably before 10% of the abrasive grits are pulled out. According to different embodiments, the binder may be deposited when the partially used diamond wire has a binder thickness of from 20 μιη to 0 μιη. According to further embodiments, the binder may be deposited when the ratio E/D is in the range 1 to 0.1, particularly in the range 0.5 to 0.1, more particularly 0.2.

[0032] Accordingly, the diamond wire may be thick enough to increase the diamond grits adhesion to the wire, thin enough to avoid taking up the available volume for kerf extraction, and thin enough to keep a wire as thin as possible. As used herein, the term "thin wire" is used synonymously with "small-diameter wire". By using small-diameter wires the thickness of the cut may be reduced. As a result, the raw material wasted, i.e., hard and brittle materials, may be decreased. [0033] FIG. 4 shows a refurbished diamond wire 400 with a core wire 150, abrasive grits 180 and a binder 420 with a planar surface, according to embodiments of the present disclosure. The binder can be provided in an amount related to the reduction of the initial binder thickness such that the regions 160 are filled to provide a planar binder surface, as shown in FIG. 4. [0034] Instances of diamond wire usage are multiple and complex, e.g., breakage, scratching, pull out, etc. In order to avoid or at least reduce these instances, it is beneficial to refurbish a partially used diamond wire before irreversible degradation cases take place. Regarding pull out of the diamond grits from the coating of the wire, irreversible degradation cases take place when a certain binder thickness, as described herein "threshold thickness", is reached at which point adhesion of the diamond grits to the wire can no longer be guaranteed and the diamond grits begin to pull out in an uncontrolled manner.

[0035] According to embodiments, which can be combined with other embodiments described herein, the subsequent binder 320 may be deposited when the partially used diamond wire has a binder thickness of from 20 μιη to 0 μιη, particularly when the partially used diamond wire has a binder thickness of from 10 μιη to 0 μιη, more particularly when the partially used diamond wire has a binder thickness of from 4 μιη to 0 μιη. As a result, loss of the diamond grits can be avoided and the diamond wire lifetime can be increased. [0036] According to further embodiments, which can be combined with other embodiments described herein, the method for refurbishing a partially used diamond wire may further include determining the wire usage stage. The wire usage stage can be determined by direct measurement, for instance, by using an optical control to measure the amount of binder removed during use of the wire. An optical control can also be used for analyzing the wire quality and detecting a malfunction on the wire, such as a crack or the like. Further examples of direct measurement may include the use of a camera, a capacitor sensor or an inductive sensor.

[0037] Alternatively, the wire usage stage can be determined by indirect measurement. Indirect measurement may be done in situ and/or ex situ. In situ measurement may be based on a deflection or bow of the wire due to application of a known force. Further, in situ measurements may include applying a voltage to the wire and measuring the voltage, for instance, at the terminals of the wires. By applying a voltage, wire defects related to the wire usage can be detected. In particular, an alternating voltage (AC) may be applied for diamond wires. Ex situ measurements may be based on the wafer geometry and the wafer quality, such as the total thickness variation (TTV), saw marks, etc. Further examples of ex situ measurements may be based on wafer property measurements, such as resonant frequency measurement techniques on cantilever beam test structures, direct tensile stress measurement techniques, capacitance/voltage measurement techniques on fixed- fixed beam bridge structures, load/deflection techniques on suspended thin-film membranes under tensile stress and known pressure load, and an electrostatic pull-in approach using tethered rigid parallel-plate structures. [0038] Another embodiment of the present disclosure provides determining the wire usage stage based on calibration data. Accordingly, the removed binder thickness after a single cut may be measured. The measurement of the removed binder thickness may be repeated for several cuts. In particular, the removed binder thickness may be measured in the regions at the abrasive grits.

[0039] A table showing the removed binder thickness for several single cuts may be made. The table may be a cumulative table, i.e., the table shows the removed binder thickness of the corresponding cut added to the removed binder thickness of the preceding cuts. Based on this table, one can determine the wire usage stage by controlling the number of cuts made by the diamond wire. This table may provide calibration data which could, for example, describe the wire usage stage as a function of the wire exposure or the surface swan per wire portion.

[0040] After determining the wire usage stage, a binder may be provided to the partially used diamond wire in relation to the wire usage stage. Accordingly, the wire may be refurbished by filling the coating material with a binder until the diamond grits are firmly fixed to the wire. More particularly, the binder may be deposited as a function of the wire usage stage. Accordingly, the binder may be provided in a sufficient amount, i.e., where diamond grits are firmly fixed to the wire and where the regions 160 are not overfilled or underfilled. [0041] Generally, molecular layers of oil on the surface of the diamond wire can prevent adhesion of the diamond grits to the core wire. Furthermore, the presence of dust and impurities on the surface of the diamond wire may jeopardize the refurbishing process. Accordingly, in embodiments herein, the partially used diamond wire may be cleaned before refurbishing, i.e., the partially used diamond wire may be cleaned before depositing a binder on the partially used diamond wire.

[0042] According to embodiments herein, the method for refurbishing a partially used diamond wire may further include cleaning the partially used diamond wire before depositing the binder, in order to improve the adhesion of the diamond grits to the core wire and to improve the refurbishing process. There is a clear distinction between cleaning before refurbishing and conventional cleaning done before sawing. Cleaning the wire before sawing may improve the quality of the cutting surface and may reduce the number of spark faults. Cleaning before sawing is normally not adapted to improve the adhesion of the diamond grits to the core wire and to improve the refurbishing process.

[0043] Cleaning before refurbishing may include processes such as solvent cleaning, hot alkaline detergent cleaning, electro-cleaning and acid treatment, and systems such as ultrasonic systems, aqueous systems, primary wire wipe (PWW), air wipes and spiral brushes with metal and synthetic filaments. These cleaning processes and systems may be designed to remove dust, impurities and possible excessive oil/lubricant from the wire.

[0044] According to embodiments of the present disclosure, the deposition of a binder on the partially used diamond wire may be done by electroplating. After electroplating, the diamond wire may be partly covered due to electroplating. As such, the surface of the diamond wire may be irregular and exhibit plating protrusions that may extend massively.

The protrusions can result in a high resistance at the respective positions when the wire is moved through the hard and brittle material's ingot at high speed. Consequently, in such a case, the wire at these positions is exposed to a high load and tends to break earlier at these positions. According to further embodiments, after electroplating, the diamond wire may be totally covered due to electroplating.

[0045] According to embodiments, which can be combined with other embodiments described herein, the method for refurbishing a partially used diamond wire may further include dressing the diamond wire after depositing the binder. FIG. 5 shows a refurbished diamond wire after dressing 500. The wire 500 has a core wire 150, a coating material around the core wire and a protective material 520 provided on the coating. The coating includes an abrasive material, such as abrasive grits 180, and a binder for connecting the abrasive material to the wire. [0046] In one aspect, the protective material 520 may be Si0 ₂ material or A1 ₂ 0 ₃ material. According to further embodiments, the protective material 520 may be applied as a lubricant containing water or oil, in order to avoid or reduce dust and impurities accumulating on the diamond wire surface. The protective material 520 may form a protective layer which is highly adhesive to the core wire, very hard and has a good surface planarity. As a result, irregularities and plating protrusions on the surface of the diamond wire may be reduced and a diamond wire capable of sawing hard and brittle materials, with high planarity and highly accurately, may be provided. Dressing processes further provide wire protection against wear during wire use. Accordingly, the diamond wire lifetime may be increased by applying a dressing process. [0047] FIG. 6A shows a process flow diagram illustrating a method for refurbishing a partially used diamond wire according to embodiments described herein. The method may include determining 630 the wire usage stage, cleaning 632 the partially used diamond wire before depositing a binder, depositing 634 a binder on the partially used diamond wire and dressing 636 the diamond wire after depositing the binder. [0048] As shown in FIG. 6B, cleaning 632 the partially used diamond wire before depositing a binder can be done in a cleaning device 602, depositing 634 a binder on the partially used diamond wire can be done in a deposition device 604 and dressing 636 the partially used diamond wire after depositing the binder can be done in a dressing device 606. After dressing, the diamond wire may be mounted to the diamond wire saw 700 for further use of the diamond wire in cutting processes. A diamond wire usage stage determination system may be included in the diamond wire saw 700 for determining the wire usage stage. Transport systems 610 may be used for carrying the wire from one device to another. An example of a transport system may be a guidance rail.

[0049] According to embodiments herein, the cleaning 632, depositing 634 and dressing 636 might be done in the wire saw. These processes may not be done during the sawing process where the wire saw is cutting at high speed (~20m/s). For having a sufficient subsequent binder anchoring, the deposition of the binder on the partially used diamond wire may be done at a wire velocity below 100 m/min, particularly below 50 m/min, more particularly below 30 m/min. Accordingly, deposition inside a wire saw could be realized at reduce wire speed, for example, when loading/unloading the cutting pieces between two consecutive cuts.

[0050] According to embodiments described herein, the method for refurbishing a partially used diamond wire may be applied to small-diameter diamond wires. Small- diameter diamond wires may be understood as wires having a core wire with a diameter of 350 μηι to 10 μηι, particularly a diameter of 150 μιη to 10 μιη, more particularly a diameter of 50 μιη to 10 μιη.

[0051] As described herein, the term "core wire diameter" refers to the diameter of the core wire without the coating material. Accordingly, the diameter of the core wire may be smaller than the diameter of the diamond wire. The diamond wire may include the core wire and the coating material.

[0052] According to embodiments, which can be combined with other embodiments described herein, the core wire may be made of steel and may be coated with diamond grits bound to the core wire by electroplating. Alternatively, the diamond grits may be bound to the core wire using resin technology.

[0053] Electroplating may be primarily used to change the surface properties of an object, e.g. abrasion and wear resistance, corrosion protection, lubricity, aesthetic qualities, etc. Electroplating is a process that uses electrical current to cover a surface, in particular is a process of depositing a metal on a conductive surface. In electroplating, the part to be plated is the cathode of the circuit, which may in embodiments be the partially used diamond wire.

[0054] According to embodiments described herein, the anode may be made of the metal to be plated on the partially used diamond wire. The cathode and the anode may be immersed in an electrolyte solution containing one or more dissolved metal salts as well as other ions that permit the flow of electricity. A power supply may supply a direct current to the anode, which oxidizes the metal atoms comprised in the anode and allows them to dissolve in the solution. At the cathode, the dissolved metal ions in the electrolyte solution may be reduced at the interface between the solution and the cathode, such that they plate out onto the cathode. The rate at which the anode is dissolved may be equal to the rate at which the cathode is plated. The rate at which the cathode is plated may depend on the current flowing through the circuit. In this manner, the ions in the electrolyte bath may be continuously replenished by the anode. For the present embodiments, the metal to be plated on the partially used diamond wire may be nickel. Alternatively, the metal to be plated on the partially used diamond wire may be copper, silver, or tin. [0055] According to alternative embodiments, resin technology may be used to bound diamond grits to a core wire to form a diamond wire. The resins used may include water based coating resins, powder coating resins or UV-curing coating resins.

[0056] According to further embodiments, which can be combined with other embodiments described herein, the deposited binder is a metallic binder. For instance, the binder may be made from a material comprising nickel, copper, silver and/or tin.

[0057] According to embodiments, a diamond wire is provided for sawing hard and brittle materials. The diamond wire may include a core wire 150 and a coating covering the outer surface of the core wire. The coating may include abrasive grits 180 and a binder, such that the abrasive grits may be provided on the core wire with a binder. The binder may be configured to provide adhesion of the abrasive grits to the core wire. The binder may include an initial binder 120, deposited on the unused diamond wire, and a subsequent binder deposited on the partially used diamond wire.

[0058] According to further embodiments, which can be combined with other embodiments described herein, the core wire 150 may have a diameter of 350 μιη to 10 μιη, particularly a diameter of 150 μιη to 10 μιη, more particularly a diameter of 50 μιη to 10 μιη.

[0059] According to embodiments, which can be combined with other embodiments described herein, where the diamond wire may have a diameter of 350 μιη to 10 μιη, the diamond grits may have a mean diameter of 50 μιη to 1 μιη, particularly a mean diameter of 20 μιη to 1 μιη, more particularly of 5 μιη to 1 μιη.

[0060] According to embodiments described herein, the diamond wire cross-section is circular. According to further embodiments described herein, the wire cross-section is non- circular. In particular, the wire cross section may be rectangular, possibly with rounded corners. Furthermore, according to embodiments, the wire's cross section is non-square, in particular, the wire's cross-section may be non-square rectangular.

[0061] According to some embodiments, which can be combined with other embodiments described herein, the diamond wire may be used in a wire saw for sawing hard and brittle materials. [0062] According to further embodiments described herein, a diamond wire saw for sawing hard and brittle materials is provided. The diamond wire saw as disclosed herein may include a diamond wire and a diamond wire usage stage determination system. In embodiments described herein, the diamond wire saw may not be adapted to operate with an uncoated wire such as a steel wire. The sawing process with an uncoated wire further involves the use of slurry. For instance, the diamond wire saw of the present application may differ from conventional slurry based steel wire saws by the form and shape of the used nozzles; by the tank for the coolant; by the shape, form and arrangement of pulleys for guiding the wire. [0063] FIG. 7 shows a schematic sectional view of a diamond wire saw 700 including a diamond wire 730 and a diamond wire usage stage determination system 760. The diamond wire usage stage determination system 760 may determine the wire usage stage by any of a direct measurement, an indirect measurement or based on calibration data.

[0064] For instance, the wire usage stage determination system 760 may determine the amount of binder removed during use of the wire by a direct measurement. Examples of direct measurements may include the use of an optical control, a camera, a capacitor sensor or an inductive sensor. An optical control can also be used for analyzing the wire quality and detecting a malfunction such as a crack or the like.

[0065] Alternatively, the wire usage stage determination system 760 may determine the amount of binder removed during use of the wire by indirect measurement. Indirect measurement may be done in situ and/or ex situ. In situ measurements may be done at the diamond wire usage stage determination system 760. In situ measurements may be based on a deflection or bow of the wire at a known wire tension. In situ measurements may alternatively be based on the acting force between the wire and the ingot or brick, preferably the vertical force or the friction force. Further, in situ measurements may include applying a voltage to the wire and measuring the voltage, for instance, at the terminals of the wires.

[0066] Ex situ measurements may be done at the diamond wire usage stage determination system 760. Ex situ measurements may be based on the wafer geometry and the wafer quality, such as TTV, saw marks, etc. Further examples of ex situ measurements may be based on wafer property measurements such as, resonant frequency measurement techniques on cantilever beam test structures, direct tensile stress measurement techniques, capacitance/voltage measurement techniques on fixed-fixed beam bridge structures, load/deflection techniques on suspended thin-film membranes under tensile stress and known pressure load, and an electrostatic pull-in approach using tethered rigid parallel- plate structures.

[0067] According to further embodiments, the diamond wire usage stage determination system 760 may determine the wire usage stage based on calibration data. For the calibration, the thickness of binder removed at the abrasive grits after a single cut may be determined. An abacus may be made with the determined thickness as a function of the wire exposure.

[0068] Accordingly, after a single cut the removed binder thickness may be measured. This measurement may be repeated after several cuts and in particular, the removed binder thickness may be measured in the regions at the abrasive grits. A table showing the removed initial binder thickness for several single cuts may be made. The table may be a cumulative table, i.e., the table shows the removed binder thickness of the corresponding cut added to the removed binder thickness of the preceding cuts. Based on this table, one can determine the wire usage stage by controlling the number of cuts the wire has done.

[0069] During the cutting action, one or more ingots or bricks (with reference signs 702, 704, 706, 708) may be pushed through the wire web in order to slice them. This is indicted by the arrows sandwiched between ingots 702, 704, and 706, 708, respectively.

[0070] The diamond wire saw 700 may have a wire guide device including four wire guide cylinders 712, 714, 716, 718. The wire guide cylinders may be covered with a layer of synthetic resin, and are scored with grooves having very precise geometry and size. The wire guide cylinder 712, 714, 716, 718 may be connected to a motor or drive (with reference signs 722, 724, 726, 728, shown with dashed lines in FIG. 7). The motor or drive may be adapted for performing a back-and-forth movement of the wire. The back-and- forth movement of the wire is denoted with reference numbers 715, 725. In embodiments, as those shown in FIG. 7, wire guide cylinders 712, 714, 716, 718 are directly driven by motors 722, 724, 726, 728. The one or more motors may be controlled by the wire saw control. The wire feed spool 734, if still complete, may hold several hundred kilometers of diamond wire. The diamond wire 730 may be fed to the wire guide cylinders 712, 714, 716, 718 from the wire feed spool 734. The wire take-up spool 738 may be provided, upon which the used diamond wire 730 is recoiled. [0071] The diamond wire 730 may be spirally wound about the wire guide cylinders 712, 714, 716, 718 and may form a layer of parallel wires between the wire guide cylinders. This layer is referred to as a wire web. According to the embodiments illustrated, four wire webs 750, 751, 752, 753 may be provided.

[0072] According to further embodiments, which can be combined with other embodiments described herein, the diamond wire saw 700 may have a wire guide device including two wire guide cylinders 712, 714. The diamond wire 730 may be spirally wound about the wire guide cylinders 712, 714 and may form a layer of parallel wires between the two wire guide cylinders. Sawing may take place using at least one wire web, more preferably, using two wire webs 750, 752 at the same time. [0073] Sawing takes place using at least one wire web, more particularly, using two wire webs at the same time (as illustrated in FIG. 7). The number of parallel wire portions corresponds to the number of slicing processes. For instance, the wire may be wound up in such a way that the resulting wire web includes 100 wire portions arranged in parallel. An ingot or brick pushed through this web of 100 wires is sliced into 101 wafer pieces. The motors driving the wire may be motors having a small momentum in order to stop and accelerate within a short time period.

[0074] According to some embodiments, the movement of the diamond wire is unidirectional, i.e., in the forward direction. According to other embodiments, the movement may include a movement in the backward direction, in particular, the movement can be a back-and-forth movement of the wire in which the movement direction of the wire is amended repeatedly.

[0075] While the foregoing is directed to embodiments described herein, other and further embodiments may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.