WO2011070386A1

WO2011070386A1 - Monitoring device for the wire of a wire saw device and method for operating the same

Info

Publication number: WO2011070386A1
Application number: PCT/IB2009/007813
Authority: WO
Inventors: Jean-Marc Rosset; Rémy SCHULER
Original assignee: Applied Materials Inc
Current assignee: Applied Materials Inc
Priority date: 2009-12-11
Filing date: 2009-12-11
Publication date: 2011-06-16
Anticipated expiration: 2012-06-11
Also published as: TW201134629A

Abstract

A wire monitoring device for a wire saw device, a wire saw device and a method of monitoring a wire saw device are described. The wire monitoring device includes at least two sensors, adapted to provide a change of a sensor output signal in dependence of the presence of a wire adjacent to a sensor, wherein the sensors are adapted to be each provided adjacent to a wire of the wire saw device.

Description

MONITORING DEVICE FOR THE WIRE OF A WIRE SAW DEVICE AND

METHOD FOR OPERATING THE SAME

FIELD OF THE INVENTION

[0001] Embodiments of the present invention relate to a device for the monitoring of a wire of a wire saw device, a method for operating such a device, and a wire saw device including such a device. More particularly, the invention relates to a device for detecting defects or breakage of a wire of a wire saw device for cutting or sawing hard materials such as blocks of silicon or quartz, e.g., for cutting silicon wafers, for a squarer, for a cropper or the like.

BACKGROUND OF THE INVENTION

[0002] Wire saw devices exist for cutting blocks or bricks, 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 both guided and tensioned by wire guide cylinders. The wire that is used for sawing is generally provided with an abrasive material. As one option, the abrasive material can be provided as slurry. This may be done shortly before the wire touches the material to be cut. Thereby, the abrasive is carried to the cutting position by the wire for cutting the material. As another option, the abrasive can be provided on the wire with a coating, e.g., as a diamond wire. For example, diamond particles can be provided on a metal wire with a coating, wherein the diamond particles are imbedded in the coating of the wire. Thereby, the abrasive is firmly connected with the wire.

[0003] The wire is both guided and tensioned by wire guides. These wire guides are generally covered with a layer of synthetic resin and are scored with grooves having very precise geometry and size. The wire wound around the wire guides forms a web or wire web. During the sawing process, the wire is moved with considerable speed. The web generates a force perpendicular to the advance of a support beam or support holding the piece to be sawed. During sawing, the piece to be sawed is 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, e.g., within an hour. [0004] Generally, there is a tendency to use thinner wires in order to reduce the thickness of the cut and, thereby, to decrease the material wasted. There is also a desire to use diamond wires. These thinner wires and diamond wires are generally more susceptible to damage and, under high strain, the wires may break more easily. Further, there is a desire to increase the cutting speed for improving the throughput of wire saw devices. The maximum speed for moving the piece through the web, and also the maximum effective cutting area within a given amount of time is limited by several factors including wire speed, hardness of the material to be sawed, disturbing influences, desired precision, and the like. When the speed is increased, the strain on the wire is generally increased as well. Hence, the above-mentioned problems of avoiding damage or breakage of the wire are even more critical at higher sawing speeds.

[0005] The advantages of diamond wire, such as a higher achievable sawing speed, are accompanied by aspects such as a lower resistance to breaking and a higher price per length. When employing diamond wire, measures can be taken to assure that the higher tendency to breaking does not lead to loss in production due to downtimes.

[0006] If the wire breaks during the sawing process, it is of utter importance to detect the breaking as soon as possible after it has occurred and to stop the wire movement immediately. At the same time, it is desirable to detect if the wire develops a tendency to break at one or more positions along its length during the sawing process. If a break occurs, unwanted consequences may arise. The loose ends of the wire may move around in the machine in an uncontrollable manner, which might harm the wire guide system or other parts of the machine. Further, if the wire breaks and moves on, it will be torn out of the object to be sawed.

[0007] Conventionally, the above mentioned problems are taken care of by applying an electrical voltage to the wire. In the case of breaking, a loose wire end may then get in contact with the housing of the machine or other parts, and the resulting voltage on the housing can be detected. Further, the voltage applied to the wire at one end of the wire leading into the sawed object may be detected at another portion of the wire at a portion leading out of the object. In this manner, the wire break is detected if the voltage applied at one portion of the wire is no longer detected at another portion. [0008] However, conventional methods do not provide information about the location of the break and about potential breaking points, as the acquired information is limited to the possible statuses "intact" and "breakage" of the wire, regardless of the position of the break.

SUMMARY

[0009] In view of the above, a wire monitoring device according to independent claim 1, a wire saw device according to claim 14, and a method of monitoring a wire saw device according to independent claim 18 are provided. Further advantages, features, aspects and details are apparent from the dependent claims, the description and the drawings.

[0010] According to one embodiment, a wire monitoring device for a wire saw device is provided. The wire monitoring device includes at least two sensors, adapted to provide a change of a sensor output signal in dependence of the presence of a wire adjacent to a sensor, wherein the sensors are adapted to be each provided adjacent to a wire of the wire saw device.

[0011] According to a further embodiment, a wire saw device having a wire monitoring device is provided. Thereby, the wire monitoring device includes at least two sensors, adapted to provide a change of a sensor output signal in dependence of the presence of a wire adjacent to a sensor, wherein the sensors are adapted to be each provided adjacent to a wire of the wire saw device.

[0012] According to a yet further embodiment, a method for monitoring a wire saw device is provided. The method includes providing a wire monitoring device adapted to provide a change of a sensor output signal in dependence of the presence of a wire adjacent to a sensor and supervising via the monitoring unit if there is a change in the physical condition of a wire.

[0013] Embodiments are also directed at apparatuses for carrying out the disclosed methods and include apparatus parts for performing each described method step. These method steps may be performed by way of hardware components, a computer programmed by appropriate software, by any combination of the two or in any other manner. Furthermore, embodiments according to the invention are also directed at methods by which the described apparatus operates. It includes method steps for carrying out every function of the apparatus. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments. The accompanying drawings relate to embodiments of the invention and are described in the following:

[0015] Fig. 1 shows a schematic perspective view of a wire saw device according to an embodiment

[0016] Fig. 2 shows a schematic perspective top view of a wire saw device according to an embodiment.

[0017] Fig. 3 shows a schematic perspective front view of a monitoring device according to an embodiment.

[0018] Fig. 4 shows a schematic side view of a monitoring device according to the embodiment of Fig. 3.

[0019] Fig. 5 shows a schematic side view of a monitoring device according to another embodiment.

[0020] Fig. 6 shows a schematic front view of a monitoring device according to a further embodiment.

[0021] Fig. 7 shows a schematic front view of a monitoring device according to another embodiment.

[0022] Fig. 8 shows a schematic front view of a monitoring device according to yet another embodiment.

DETAILED DESCRIPTION OF THE INVENTION

[0023] Reference will now be made in detail to the various embodiments of the invention, 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, only the differences with respect to individual embodiments are described. Each example is provided by way of explanation of the invention and is not meant as a limitation of the invention. Further, features illustrated or described as part of one embodiment can be used on or in conjunction with other embodiments to yield yet a further embodiment. It is intended that the description includes such modifications and variations.

[0024] Furthermore, in the following description, a control unit may be understood as a device electronically controlling substantially all functions of a wire saw device, e.g., a cropper, a squarer, or a wafer cutting wire saw. Typically, the control unit is connected to sensors in order to monitor parameters of the machine operation and the sawing process. It is also connected to actuators and devices to steer the electric motors which move the wire. It also includes devices for interaction with an individual in order to receive commands and to report the status of the sawing process. A control unit may also be connected in some embodiments to a computer network to be controlled directly or remotely by an individual or an automated system such as a computer.

[0025] According to embodiments described herein, the methods of operating a wire saw device can be conducted by means of computer programs, software, computer software products and the interrelated controllers, which can typically have a CPU, a memory, a user interface, and input and output means being in communication with the corresponding components of the wire saw device. These components can be one or more of the components: motors, wire break detection units, wire tracking devices, and the like, which will be described in more detail below.

[0026] Furthermore, in the following description, a wire management unit will be understood as a device handling the supply of wire to a cutting area or working area of a wire saw device, such as a cropper, a squarer, or a wafer cutting wire saw. Typically, the wire saw includes a wire guide for transporting and guiding the wire in a wire moving direction while the wire management unit provides control of the wire tension. Furthermore, the wire provided by the wire management unit forms a wire web in the cutting area. Often, a wire web will be considered as the web formed by a single wire management unit. It should be understood that a wire web may contain more than one working area which is defined as an area in which a sawing process is performed. Thus, according to some embodiments described herein, a wire web can have multiple areas that are formed by a wire from different wire management units.

[0027] In an embodiment, which may be combined with other embodiments herein, a wire monitoring device for a wire saw device is provided. It includes at least two sensors, which are typically inductive sensors and are typically arranged in the form of an array on a support. The sensors are provided adjacent to wire portions of the wire saw device. The inductive sensors generate their own inductive field and detect any variation of the field induced by the presence/absence of a wire and the density of the wire in front of the sensor. If a wire breaks and the broken wire end passes the sensor, a change of the sensor output signal occurs. The sensor signals are constantly monitored by a control unit, which is typically the control unit of the wire saw device, which stops the operation of the wire saw device if a break is detected.

[0028] For modern wire saw devices like croppers, squarers, or wire saws, there is the desire to cut the hard material such as semiconductor material, for example, silicon, quartz, or the like, at high speed. The wire speed, that is the speed of the wire moving through the wire saw device, the wire management unit and the material to be sawed, respectively, can be, for example, 10 m/s or higher. Typically, the wire speed can be in a range , of 15 to 20 m/s. However, higher wire speeds of 25 m/s or 30 m/s can also be desirable and could be realized under certain conditions.

[0029] For unwinding the wire at the desired wire speed, the spool rotates with a rotation speed of up to several thousands rotations per minute. For example, 1000 to 2000 rpm can be provided for unwinding the wire.

[0030] In embodiments, which can be combined with other embodiments described herein, the wires may have different diameters depending on the type of device. In an embodiment pertaining to a squarer, the wire diameter may be from about 300 μιη to about 400 μηι, e.g., 310 μηι to 340 μηι. In an embodiment pertaining to a wafer cutting wire saw, the wire diameter may be from 60 μιη to 180 μιη, more typically from 80 μηι to 160 μηι. For all of the former, a twisting of the wire might increase the risk of breaking of the wire or of damaging the coating, so that a twist-free operation is advantageous. By using diamond wire, the throughput may be increased by a factor of 2 or even more. In comparison to conventional steel wire, the increasingly used diamond wire has some advantages such as higher achievable sawing speed. The speed with which the material to be sawed is moved relatively to the moving wire may be referred to as the material feed rate. The material feed rate in the embodiments described herein may be in the range of 2 μηι/s to 12 μιη/s, typically about 6 μιη/s to 10 μιη/s for a wafer cutting wire saw, respectively from 20 μηι/s to 40 μητ/s, typically from 28 μητ/s to 36 μηι/s for embodiments pertaining to a squarer. The respective data for other types of wire saw devices regarding wire speed, material feed rates, wire diameters and the like is well known to a skilled person and is not provided in greater detail. [0031] Fig. 1 shows a schematic front view of a wire saw device 100 including a wire monitoring device 1. The wire monitoring device 1 includes sensors 20 mounted to a support 30, which are provided adjacent to wire portions 210 of the wire web. The sensors are connected to a control unit 25, which may in some embodiments be the control unit of the wire saw device. The sensors 20 are shown for illustrative purposes only, their dimensions in the drawings do not necessarily reflect the dimensions of real sensors, which applies also to all other figures in this document. Wire saw device 100 has a wire guide device 110 including four wire guide cylinders 112, 114, 116, 118. A wire management unit 130 provides a wire to the wire guide cylinders 112, 114, 116, 118. The wire management unit 130 includes a supply coil 134 on which a wire reservoir, typically holding several hundred kilometers of wire, is provided. Fresh wire 230 is fed to wire guide device 110 from supply coil 134. Furthermore, wire management unit 130 includes a take-up spool 138 on which the used wire 240 is recoiled. In the embodiment shown in Fig. 1, the rotational axis of supply coil 134 and take-up spool 138 are parallel to the rotational axes of the wire guide cylinders 112, 114, 116, 118. Accordingly, no deflection pulley or similar device is required for feeding the wire to the wire guide 110. Due to the zero degree angle on the wire, the risk of wire breakage can be reduced. Typically, wire management unit 130 includes further devices such as low inertia pulleys (not shown) and tension arms (not shown) for wire tension regulation. In some embodiments, digital coders are provided on the tension arms.

[0032] Fig. 2 shows a schematic top view of wire saw device 100 including wire monitoring device 1 with support 30 and sensors 20. The device is connected via wires 15 to control unit 25, which is typically the control unit of the wire saw device 100. The wire 210 is spirally wound about the wire guide cylinders 112, 114 and forms between the two wire guide cylinders a layer 200 of parallel wires. This layer is typically referred to as a wire web 200. The different parallel wire portions (forming the wire web) of the wire 210 and the wire itself will in the following be both referred to under the numeral 210. Typically, wire guide cylinders 112, 114, 116, 118 are covered with a layer of synthetic resin and are scored with grooves having very precise geometry and size. The distance between the grooves, or the pitch of the grooves, determines the spacing Dl between two adjacent strings or lines of wire 210. This distance Dl also determines the maximum thickness of the slices cut by the wire saw device. However, for example, in the event a third media such as slurry is used, the slices may be about 10 μπι to 40 μηι thinner than the distance Dl. Typically, the wire thickness is between 120 μιη and 140 μπι, while distance Dl is from 120 μιη to 300 μηι, typically in the range of 200 μηι to 250 μιη. As an example, the grooves may have a pitch or distance of below 300 μη . Accordingly, the thickness of the wire is of the same order as the distance Dl . According to some embodiments, which can be combined with the other embodiments describe herein, the pitch or distance of the groove results in spacing between adjacent wires of about from 120 μπι to 200, typically of 160 μπι or smaller. In light of the above, embodiments described herein may provide a very large cutting area and a very high cutting rate

[0033] According to different embodiments, which can be combined with other embodiments described herein, the pitch, i.e., the distance between grooves, can be in a range of 225 μηι to 400 μηι, for example 300 μηι or below; the distance between adjacent wires 210 can be in a range of 120 μπι to 300μηι, for example, 200 μπι to 250 μπι or even 220 μπι or less; and/or the resulting wafer thickness can be in a range of 100 μιη to 250 μπι, for example, 180 μη to 220μιη or even 200 μηι or below. Thereby, it should be noted that the groove pitch and the groove geometry is typically adapted to a wire thickness and wire type and is adapted to the wafer thickness. Accordingly, a wire saw device having wire guiding cylinders with grooves is generally adapted for specific wafer thicknesses and wire diameters by the groove pitch and the groove geometry. The values for the groove pitch, the wire thicknesses and/or the wafer thicknesses can be insofar predetermined by the configuration of the wire saw device.

[0034] Furthermore, each wire guide cylinder 112, 114, 116, 118 is connected to a motor 122, 124, 126, 128 (shown in broken lines in Fig. 1). In the embodiment shown in Figs. 1 and 2, wire guide cylinders 112, 114, 116, 118 are directly driven by motors 122, 124, 126, 128. As shown in Fig. 2, each wire guide cylinder 1 12, 114 may be directly mounted to the motor shaft 123, 125 of the corresponding motor 122, 124. In some embodiments one or more of the motors are water-cooled.

[0035] During operation, e.g., during the sawing process, the motors 122, 124, 126, 128 drive the wire guide cylinders 112, 114, 116, 118 so that the wire guide cylinders rotate about their longitudinal axis. Thus, the wire in wire web 200 is transported into a wire transport direction 215, 225. In some embodiments, the transport speed of the wire is relatively high for example as much as 20 m/s. In one embodiment, one of the motors, e.g., motor 122, serves as a master motor whereas the remaining motors 124, 126, 128 serve as slave motors. In other words, master motor 122 controls the operation of slave motors 124, 126, 128 so that slave motors 124, 126, 128 follow master motor 112. Thus, synchronicity of operation of motors 122, 124, 126, 128 is improved and can be maintained during the sawing process. [0036] According to some embodiments, which can be combined with other embodiments described herein, two or more spools, are provided for forming at least one wire web. For example, two, three or even four spools can be used to provide the wire. Thereby, according to different embodiments, a method of sawing thinner wafers, e.g., in a range of 100 μηι to 170 μπι can be provided. Typically, the thinner wafers can also be sawed at higher speed, such as having a material feed rate is in the range of 2 μηι/s to 12 μη /s, typically about 5 μηι/s to 7 μτη/s.

[0037] Compared to a single wire system, the load on each wire can be reduced by having two or more spools and, thus, two or more wires. Generally, for a single wire web, the load is increased as compared to a dual wire web due to the increase of the wafer surface are to wire surface area. The increased load can result in lower cutting speeds. Accordingly, using two or more wires can increase the cutting speed, e.g., such that an effective cutting area or a cutting area rate of 12 m²/h or more can be provided.

[0038] Further, according to yet further embodiments, which can be combined with other embodiments, thinner wires can be used, for example, wires having a thickness of 80 μηι to 120 μηι, while the cutting area is increased. Typically, the wire thickness reduces during usage of the wire. Thus, if a single wire is used for a larger cutting area, the wire may be thinned until breakage of the wire results. Accordingly, the use of two wires to build a wire web, for example, a continuous wire web, on the one hand reduces the load on the wire and thereby allows for higher cutting speeds and, on the other hand, allows for thinner wires, which allows for smaller wire distance and thereby increased cutting area.

[0039] Fig. 3 shows a front view of an embodiment of a wire monitoring device 1 for a wire saw device. The device includes at least two sensors 20, which are typically connected to a control unit 25, which may be the control unit of the wire saw device. The sensors 20 are adapted to be provided adjacent to portions of a wire 210 of the wire saw device. For illustration purposes, in Fig. 3, wire portions in front of the device are shown (as dotted lines). The monitoring unit 25 is adapted to detect a change in the physical condition of a wire by analyzing the sensor signals. If a break of a wire 210 occurs and the broken end passes a sensor, the control unit detects the change of the sensor signal and typically stops the operation of the wire saw device. "Physical condition" pertains in this respect primarily to the question if the wire is intact, i.e., not broken. Further, also a change in the structure of the wire is regarded to be a change in the physical structure, e.g., if the wire has any type of defects, small cracks, ruptures, changes in its molecular structure, or the like. [0040] The sensors are typically connected via wires 15 to a control unit 25, which is typically the control unit of the wire saw device and which is adapted to be able to analyze the sensor signals, which will be further described below.

[0041] The sensors are typically inductive sensors, but embodiments also include optical sensors or any type of sensor suitable to be employed for the above purpose. Inductive sensors are typically used, as they are relatively inexpensive and as they provide their own field. Some types of defects are not necessarily visible, in contradiction to a break of the wire or a major rupture. It is thus desirable, but not necessary, to employ a sensor type which can also detect small or invisible defects, such as an inductive sensor principally can. In this manner, also small defects or changes of the wire condition may be detected via analysis of the sensor signal. In another embodiment, capacitive sensors are used. In some embodiments, it may be required to provide an external source for the electromagnetic or other fields which are to be detected by the sensors after being modified by wire portions 210.

[0042] The application of other types of sensors is also regarded as falling into the scope of the present invention. In an embodiment, radiation (as non-limiting examples: X-rays, alpha particle radiation, electron particle radiation, gamma rays, neutrons) is directed to the wire, and the measurement of the reflection or absorption of the radiation by the wire material is performed via a suitable sensor. In this particular example, special security measures would be necessary to avoid harmful effects of the radiation on individuals. In a further embodiment, ultrasonic sound is applied to the wire portions, and the reflection or absorption in the wire material is measured via the sensors. The sound generating mechanism may also be integrated into the sensors. In a further embodiment, optical sensors are used. These may be applied in the form of photo sensors or CCD-sensors (charged coupled devices), which may be adapted to provide an image of the wire portions to the monitoring unit.

[0043] The sensors are typically provided adjacent to a portion of the wire which shall be monitored or supervised. In a wire saw device employing a wire web as described above, the sensors are typically provided adjacent to portions of the wire which protrude parallel to each other as is depicted in Fig. 2. In an embodiment, the sensors 20 are mounted to a support 30, typically the surface of a board, solid body, or housing, which may be of plastic, metal, or any other suitable material. As metal might have an effect on the sensor characteristics of an inductive sensor, which would have to be taken into account, plastic is typically, but not necessarily chosen as a material. [0044] In the embodiment depicted in Fig. 3, four sensors 20 are substantially arranged in a row. If the distance between the parallel wire portions is small, as is typical for some wire saw devices for semiconductor processing, the physical dimensions of the sensors do not allow to arrange the sensors in a row having the same distances from each other as the parallel wire portions. In an embodiment described herein, the distance between the wires is from 120 μηι to 300 μηι. A typical inductive sensor, for example, has a diameter of 4 mm to 15 mm, e.g., 8 mm. As is obvious, several of these sensors cannot be placed in a row such that each sensor is adjacent to only one of the wires, because the distance of the wires from each other is much smaller than the diameter of one sensor. There is a plurality of possible measures proposed to overcome this limitation. Firstly, in the embodiment depicted in Fig. 3, each sensor is provided to monitor a plurality of adjacent wire portions 210, typically from 4 to 100 parallel wire portions, more typically from 20 to 50 wire portions. As a non-limiting example, if the parallel wire portions are arranged to have a distance of 0.2 mm from each other and the sensor has a diameter of 8 mm, each sensor is provided to supervise about 40 parallel wire portions. In the non-limiting exemplary embodiment of Fig. 3, each sensor 20 covers four wire portions 210. This relatively low number, compared to the 40 wires in the example above, is chosen to allow for better illustration. The distance between the centers of the sensors in one row may be, depending amongst other factors on the sensor diameter, from 2 mm to 30 mm, more typically from 5 mm to 20 mm.

[0045] Fig. 4 shows a perspective side view of the embodiment of Fig. 3. The sensing distance D2 between the sensors and the wire portions 210 is dependent on a plurality of factors, e.g., of the employed type of sensors, their technical specifications, the type and thickness of wire, etc. In an embodiment described herein employing inductive sensors, D2 is typically from 0.2 mm to 5 mm, more typically from 0.5 mm to 3 mm. Yet, depending especially on the type of sensor, significantly greater values may also be suitable.

[0046] Fig. 5 shows a further embodiment, in which a further distance sensor 35 is provided on support 30 in order to supervise the distance D2 between the sensors 20 and the wire portions 210. The signal of the distance sensor 35 is typically also monitored by the control unit 25. If the control unit is detecting a change of the distance D2, an actuator 45 mounted to a fixed part of the wire saw device and adapted to move the support 30 is activated in order to readjust the distance between the sensors 20 and the wire portions 210. The distance sensor 35 is typically also an inductive sensor, and the actuator 45 may be an electrical motor, e.g., a stepper motor, which is adapted to vary the distance D2 between sensors 20 and wires 210. In this manner, an optimized sensing distance D2 of the sensors 20. may be provided and controlled. The skilled person knows about the methods and suitable devices for implementing such a distance regulation mechanism.

[0047] In a further embodiment, exemplarily depicted in Fig. 6, the sensors 20 are provided in at least two substantially parallel rows. These rows are displaced with respect to each other, so that one sensor 20 of a first row is provided for first wire portions 210, and a second sensor of a second row is provided for wire portions 210 adjacent to the first wire portions. The distance between the parallel rows, measured between the centers of the sensors, may be from 3 mm to 40 mm, more typically from 6 mm to 20 mm. The displacement or offset between neighbored parallel rows may be from 2 mm to 15 mm, more typically from 3 to 8 mm. In this manner, also a plurality of wire portions having small distances from each other may be supervised by the monitoring device, almost regardless of the physical dimensions of the individual sensors. In Fig. 6, it can be seen that the sensors of the lower row would not fit into the spaces between the sensors of the upper row and thus, that the same number of sensors could not been placed in just one row. The arrangement of the sensors may also be described as an array or to have the appearance of a tilted matrix. In an embodiment described herein, the number of parallel rows may be from 2 to 8, more specifically from 3 to 5. Each parallel row may comprise from 3 to 30 sensors, more typically from 4 to 8 sensors. The connection wires 15 to connect the sensors with the control unit (not shown) are typically combined to a cable harness leading to the control unit, but also other variations are possible, i.e., by using a bus-type connection using industry standard equipment.

[0048] Further, as can be seen in the embodiment depicted in Fig. 6, one wire portion is monitored by two or more sensors, due to the overlap of the areas (indicated as D3) covered by the sensors of the different rows in a horizontal direction. In Fig. 6, this is, e.g., the case for the third and fourth wire portion (dotted lines) from the left, which are both adjacent to the left-most sensors 20 in the upper row and in the lower row of sensors. A defect in one of these wire portions will thus cause a change of the sensor signal in both of the sensors. By providing a suitable algorithm respectively a computer program for the control unit, which is a standard task for a skilled person, the control unit is enabled to locate the defect wire portion by taking into account and/or compare the changes of the signals in both sensors.

[0049] Fig. 7 shows a further exemplary embodiment, in which the overlap region D3 is smaller than in Fig. 6. In this case, e.g., the fourth wire is both in the range of a sensor of the upper row and the lower row. [0050] In some embodiments, as shown exemplarily in Fig. 8, dependent on the type of wire saw device and other factors, it can be desirable to have a very small number of wire portions covered by each sensor, e.g., only one wire portion. However, this may require a high number of sensors leading to the above mentioned problems with the spacing of the sensors due to the narrow distance between wire portions. This may be overcome by the above described arrangement of the sensors in a plurality of parallel rows offset to each other. Yet, a high number of sensors is also a cost factor, thus a compromise between location detection accuracy and number of sensors may be desirable. In Fig. 8, the connection wires 15 and the control unit 25 are not shown for reasons of clearness.

[0051] The signals of the sensors 20 are lead via the connecting wires 15 to a control unit. For economic reasons, this is typically the control unit of the wire saw device, but may also be a separate device. The control unit is adapted to monitor and analyze the signals of the plurality of sensors during operation of the wire saw device. Suitable algorithms for this purpose and how to implement them are well known to a skilled person. If a wire breaks and thus causes a change in the signal of one or more of the sensors, the control unit detects the change and triggers a reaction.

[0052] In an embodiment, the control unit immediately stops the operation of the wire saw device in case of a detected wire defect in order to prevent undesirable consequences which may result from a further operation with a wire defect, which were described above. In another embodiment, the control unit may additionally signal an alarm in case of a detected change of a sensor signal during the monitoring process. The alarm signal is typically signaled acoustically, e.g., by means of a beeper, a horn, or a loudspeaker, and may also be signaled optically by means of a light emitting device. The unit may also send a signal to an external device via a computer network or the like. Embodiments described herein relate to wire saw devices selected from the group consisting of a wire saw, a multiple wire saw, a squarer, and a cropper.

[0053] In order to provide fast and comfortable viewing of the location of the wire break by an individual, the control unit may be adapted in an embodiment to display on a display device the location of the break. The display device may be a control screen of the wire saw device, but also any other screen or display, e.g., on a remote computer. Also arrangements of light emitting diodes or the like are possible as display devices. Typically, the location of the break, as calculated by the control unit from the sensor data, is displayed graphically via a graphical representation of the wire web including the plurality of wire portions. As the location of the break is, in many cases, not exactly identified, but limited to a certain number of wire portions which may be affected; in an embodiment, the respective number of wire portions are highlighted or marked on the screen.

[0054] In another embodiment, the described method employing sensors is combined with another break detection method. This other method may include applying a voltage to a first part of the wire and monitoring via a sensor connected to a control unit whether this voltage is present at another part of the wire. If the wire is broken somewhere between the first part and the second part, the voltage will not be measurable at the second part and the control unit may stop the operation of the wire saw device. It may also, or alternatively be monitored if the voltage applied to the wire is present at a part of the machine other than the wire. In this case, it may be assumed that the wire is broken and is in contact with a part of the machine, and the control unit will also stop the operation.

[0055] In a further embodiment, the control unit is switchable to a teach-in mode, either manually via a switch, or automatically via the control unit of the wire saw device or remotely via a computer network. In the teach-in mode, the control unit detects the sensor signals and if, for example, due to a specifically prepared sawing operation with a smaller wire web, i.e. having a smaller number of parallel wire portions, at one or more of the sensors no wire is present, the control unit automatically adjusts its operation such that sensors without a wire present are internally marked to be in extra state, meaning that there is no wire present adjacent to the respective sensor. The control unit stores the information about the presence of a wire adjacent to each of the sensors until it is switched off, reset, or until the teach-in mode is activated again. Typically, the control unit has a reset switch or function which, when activated, puts the unit into a predefined state.

[0056] The terms supervising or monitoring are to be understood as follows. During operation, the electronic control unit constantly analyzes the signals of each of the plurality of sensors. Ways to implement such a control unit for the intended purpose are well known to a skilled person. During a sawing process, the wire is moving with considerable speed adjacent to the sensors. If, as an example, the sensors are inductive sensors, an electrical field induced in the wire portion adjacent to the sensor is modified by the metallic material of the wire. As long as the wire is intact and has a homogeneous structure, this modification of the electric field is constant over time, and hence the output signal of the sensor is also constant. As soon as a portion of a wire having a structural defect passes along a sensor, the modification of the electrical field changes. The amount of the change is dependent on the size of the defect, i.e., the larger the defect, the larger the change of the sensor signal is. The biggest change of the sensor signal results from the fact that the wire is suddenly not present any more, i.e. if the wire has just broken and the loose end has passed a sensor. Thus, by analyzing the sensor signals over time, the control unit can detect a change of a sensor signal and can thus analyze that the respective wire portion which just passes the respective sensor must exhibit some kind of defect. During typical operation of a wire saw device, this defect is in most cases a complete break of the wire, leaving two loose ends. As was described above, typically one sensor is supervising a plurality of wire portions, as is depicted, e.g., in Figs. 2, 3, 6, 7, and 8. Thus, a defect or break of one of the wire portions 210 leads to a modification of the signal of the sensor. As a defect of any one of the plurality of wire portions adjacent to one sensor (e.g., four wire portions for each sensor in Fig. 3) will lead to a change in the signal of the respective sensor, the control unit cannot detect which of the wire portions has caused the change of the signal, and thus it is not possible to exactly identify the defect wire. However, this is typically not a problem, as the exact location of a defect may also be investigated optically by an individual after a subsequent stop of the machine.

[0057] In an embodiment, the control unit is designed to be able to distinguish between different grades of defects. This means a slight change of a sensor signal, which is not caused by a break, but a minor damage of the wire, e.g., a small crack, is analyzed by the control unit and identified as such. It may then be signaled to the control unit as an anomaly. The control unit of the device is, in this embodiment, adapted to decide if the change of the sensor signal is severe enough to halt the operation, or if it suffices to just signal an alarm to an individual controlling the operation or to perform similar actions. The ability of the system to detect small defects in the wire is strongly dependent from the type of the supervised machine, the wire employed and particularly the type of sensor. It is noted that in wire saw devices with very fast moving wire (10 to 20 m/s), such as some wire saw devices for semiconductor processing described herein, the effectiveness of the sensor system may be too low to detect small defects. In this case, a reliable detection may only be possible for complete wire breaks. However, this question is strongly dependent on the individual system, the wire used, the type of sensor employed and the properties of the algorithm applied on the control unit.

[0058] As described above a plurality of embodiments are provided. According to one embodiment, a wire monitoring device for a wire saw device is provided. The wire monitoring device includes at least two sensors, adapted to provide a change of a sensor output signal in dependence of the presence of a wire adjacent to a sensor, wherein the T IB2009/007813 sensors are adapted to be each provided adjacent to a wire of the wire saw device. According to typical embodiments, the sensors can be selected from the group consisting of: inductive sensors and capacitive sensors. According to yet further embodiments, which can be combined with other embodiments described herein, the sensors are provided in a manner such that each sensor is adjacent to a plurality of different portions of the wire, whereby the portions protrude substantially parallel to each other. Typically, according to yet further optional additional or alternative modifications the sensors can be mounted to a support in one row or in at least two rows. Thereby, as a yet further optional implementation, the distance between the centre of neighbored sensors in a row can be from 2 mm to 30 mm; the rows can be substantially parallel; and/or the parallel rows can be displaced with respect to each other and the distance between the rows can be from 3 mm to 40 mm.

[0059] According to yet further embodiments, which can be combined with other embodiments described herein, the wire monitoring device can further include: a distance sensor provided on support, and an actuator mounted to a fixed part of the wire saw device and adapted to change a distance between sensors and wire; and/or a control unit (25), which is adapted to perform a teach-in modus, comprising a check to examine if a wire is present adjacent to each sensor. Thereby, as a yet further typical additional implantation the control unit can be adapted to store inforaiation about the presence of a wire adjacent to each sensor and /or to signal an alarm in case of a detected change of a sensor signal during monitoring.

[0060] According to a further embodiment, a wire saw device having a wire monitoring device according to any of the embodiments described herein is provided. Typically, the wire saw device can be an element selected from the group consisting of: a wire saw, a multiple wire saw, a squarer, and a cropper. Further, typically a distance between a sensor and a wire portion can be from 0.2 mm to 5 mm; and/or the sensors can be connected to the control unit of the wire saw device.

[0061] According to a yet further embodiment, a method for monitoring a wire saw device is provided. The method includes monitoring a change of a sensor output signal in dependence of the presence of a wire adjacent or the structure of the wire; and supervising via the monitoring unit if there is a change in the physical condition of a wire. Typically, this can include: supervising a change in the physical condition comprises a change of the density of the wire adjacent to a sensor, e.g., wherein supervising comprises analyzing a sensor signal. According to yet further embodiments, which can be combined with other embodiments described herein, the method can be combined with another break detection method, wherein a voltage is applied to a first part of the wire and it is monitored whether the voltage is present at another part of the wire, and/or it is monitored whether the voltage is present at a part of the wire saw device other than the wire. Typical further alternative or additional implementations can further include performing a teach-in, wherein the control unit checks for each connected sensor whether a wire is present adjacent to the sensor.

[0062] While the foregoing is directed to embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

WHAT IS CLAIMED IS:

1. A wire monitoring device (1) for a wire saw device, comprising at least two sensors (20) being adapted to provide a change of a sensor output signal in dependence of the presence of a wire (210) adjacent to the respective sensor, wherein the sensors (20) are adapted to be each provided adjacent to a wire (210) of the wire saw device.

2. The wire monitoring device of claim 1, wherein the sensors (20) are inductive sensors.

3. The wire monitoring device of claim 1, wherein the sensors (20) are capacitive sensors.

4. The wire monitoring device of any preceding claim, wherein the sensors (20) are provided in a manner such that each sensor is adjacent to a plurality of different portions of the wire (210), whereby the portions protrude substantially parallel to each other.

5. The wire monitoring device of any preceding claim, wherein the sensors (20) are mounted to a support (30) in one row.

6. The wire monitoring device of claims 1 to 4, wherein the sensors (20) are mounted to a support (30) in at least two rows.

7. The wire monitoring device of claims 4 or 6, wherein the distance between the centre of neighbored sensors (20) in a row is from 2 mm to 30 mm.

8. The wire monitoring device of claims 6 or 7, wherein the rows are substantially parallel.

9. The wire monitoring device of claim 6 to 8, wherein the parallel rows are displaced with respect to each other and the distance between the rows is from 3 mm to 40 mm.

10. The wire monitoring device of any preceding claim, further comprising a distance sensor (35) provided on support (30), and an actuator (45) mounted to a fixed part of the wire saw device and adapted to change a distance between sensors (20) and wire (210).

11. The wire monitoring device of any preceding claim, further comprising a control unit (25), which is adapted to perform a teach-in modus, comprising a check to examine if a wire is present adjacent to each sensor.

12. The wire monitoring device of claim 11, wherein the control unit (25) is adapted to store information about the presence of a wire adjacent to each sensor.

13. The wire monitoring device of any preceding claim, wherein the control unit (25) is adapted to signal an alarm in case of a detected change of a sensor signal during monitoring.

14. A wire saw device, comprising a wire monitoring device according to any of claims 1 to 13.

15. The wire saw device according to claim 14, wherein the wire saw device is an element selected from the group consisting of: a wire saw, a multiple wire saw, a squarer, and a cropper.

16. The wire saw device according to claims 14 or 15, wherein a distance between a sensor (20) and a wire portion is from 0.2 mm to 5 mm.

17. The wire saw device of claims 14 to 16, wherein the sensors (20) are connected to the control unit (25) of the wire saw device.

18. A method for monitoring a wire saw device, comprising

- providing a wire monitoring device (1) according to any one of claims 1 to 12,

- supervising via the monitoring unit if there is a change in the physical condition of a wire (210).

19. The method of claim 18, wherein supervising a change in the physical condition comprises a change of the density of the wire (210) adjacent to a sensor (20).

20. The method of claim 19, wherein supervising comprises analyzing a sensor signal.

21. The method of claims 18 to 20, wherein the method is combined with another break detection method, wherein a voltage is applied to a first part of the wire (210) and it is monitored whether the voltage is present at another part of the wire (210), and/or it is monitored whether the voltage is present at a part of the wire saw device other than the wire.

22. The method of claims 18 to 21, further comprising performing a teach-in, wherein the control unit checks for each connected sensor (20) whether a wire (210) is present adjacent to the sensor.