WAFER PROCESSING PROCESS

Abstract

Wafer processing method for dividing a wafer (1) along multiple division lines (3) to obtain multiple individual component chips (1c), wherein the division lines (3) are formed on the front face (1a) of the wafer (1) such that they define multiple separate areas in which multiple components (5) are individually formed, wherein the wafer processing method comprises: a ring frame preparation step of preparing a ring frame (7) which has an inner opening (7a) for receiving the wafer (1); a polyester film provisioning step of positioning the wafer in the inner opening (7a) of the ring frame (7) and providing a polyester film (9) on a rear side (1b) of the wafer (1) and on a rear side (7c) of the ring frame (7), wherein no adhesive layer is arranged between the polyester film (9) and the wafer (1); a joining step of heating the polyester film (9) during the application of a pressure to the polyester film (9) after performing the polyester film provisioning step, whereby the wafer (1) and the ring frame (7) are joined by thermocompression joining over the polyester film (9) so that they form a frame unit (11) in a state in which the front (1a) of the wafer (1) and the front (7b) of the ring frame (7) are exposed; a division step of cutting the wafer (1) along each division line (3) using a cutting device (12) having a rotatable cutting blade (18), after performing the joining step, thereby dividing the wafer (1) into the individual component chips (1c); and a pickup step of blowing air out from the side of the polyester film (9) so that each component chip (1c) is pushed up, and picking up the component chip (1c) from the polyester film (9) after performing the division step.

Description

BACKGROUND OF THE INVENTIONTechnical FieldThe present invention relates to a wafer processing method for dividing a wafer along a plurality of division lines to obtain a plurality of individual device chips, the division lines being formed on the front side of the wafer, thereby defining a plurality of separate regions in which a plurality of devices are individually formed.DESCRIPTION OF THE RELATED ARTIn a manufacturing process for device chips to be used in electronic equipment such as mobile phones and PCs, first, a plurality of intersecting division lines (streets) are arranged on the front side of a wafer formed of, for example, a semiconductor, to thereby define a plurality of separate regions on the front side of the wafer. Next, in each divided region, a device such as an integrated circuit (IC), a large scale integration (LSI), and a light emitting diode (LED) is formed. Thereafter, a ring frame having an inner opening is prepared by previously attaching an adhesive tape called a division tape to the ring frame (the back side of the ring frame) at its outer portion so as to close the inner opening of the ring frame. Thereafter, a central portion of the adhesive tape is attached to the back surface of the wafer so that the wafer is accommodated in the inner opening of the ring frame. In this way, the wafer, the adhesive tape, and the ring frame are bonded to each other to form a frame unit. Thereafter, the wafer contained in this frame unit is processed to be divided along each division line, thereby obtaining a plurality of individual device chips including the respective devices.For example, a dicing apparatus is used to divide the wafer. The cutting apparatus includes a chuck table for holding the wafer via the adhesive tape and a cutting unit for cutting the wafer. The cutting unit includes a cutting blade for cutting the wafer and a spindle for rotating the cutting blade. The cutting blade has a central through hole, and the spindle is fitted into this central through hole of the cutting blade, so that the cutting blade and the spindle are rotated as a unit. An annular abrasive portion is provided around the outer periphery of the cutting blade to cut the wafer. In cutting the wafer using this cutting apparatus, the frame unit is placed on the chuck table, and the wafer is held on the upper surface of the chuck table via the adhesive tape. In this state, the spindle is rotated to thereby rotate the cutting blade, and the cutting unit is next lowered to a predetermined height. Thereafter, the chuck table and the cutting unit are relatively moved in a direction parallel to the upper surface of the chuck table. Accordingly, the wafer is cut along each division line by the cutting blade being rotated, so that the wafer is divided.Thereafter, the frame unit is transferred from the cutting device to another device for applying ultraviolet light to the adhesive tape, thereby reducing the adhesion of the adhesive tape. Thereafter, each device chip is picked up by the adhesive tape. As a processing apparatus capable of manufacturing the device chips with high efficiency, there is a cutting apparatus capable of continuously performing the process of dividing the wafer and the process of applying ultraviolet light to the adhesive tape (see, for example, Japanese Patent No. 3076179). Each device chip picked up by the adhesive tape is next attached to a predetermined wiring substrate or the like.Further prior art helpful to understand the present invention can be found in the following documents:WO 2014 / 157471 A1 relates to a wafer processing tape that has uniform extensibility and a property that enables device chips to be picked up.US 2014 / 0 295 646 A1 relates to a division film having a protective layer forming layer which has a substrate layer, an adhesive layer and a protective layer forming layer.US 2004 / 0 089 515 A1 relates to a method and an apparatus for receiving a semiconductor chip, a method and an apparatus for removing a semiconductor chip from a dividing band and a method for forming a perforated dividing band.US 2016 / 0 007 479 A1 relates to an apparatus for maintaining a chip spacing, in which the spacing between adjacent component chips is maintained.JP 2003-152056 A relates to a semiconductor element holder and a method for manufacturing the same.SUMMARY OF THE INVENTIONThe adhesive tape includes a base layer and an adhesive layer formed on the base layer. In cutting the wafer using the cutting apparatus, the cutting unit is positioned at a predetermined height such that the lower end of the cutting blade reaches a position lower than the lower surface (the back surface) of the wafer, so as to reliably divide the wafer. Accordingly, the adhesive layer of the adhesive tape attached to the back side of the wafer is also cut by the cutting blade at the time when the wafer is cut by the cutting blade. As a result, in slicing the wafer, cutting dust discharged from the wafer is generated, and cutting dust discharged from the adhesive layer is also generated. In cutting the wafer, cutting water is supplied to the wafer and the cutting blade. The cutting dust generated when the wafer is cut is taken into the cutting water and then distributed on the front side of the wafer. However, the cutting dust discharged from the adhesive layer may adhere to the front surface of each component again. Moreover, it is not easy to remove this cutting dust adhering to each device in a cleaning step to be performed after cutting the wafer. Accordingly, when the cutting dust discharged from the adhesive layer adheres to each device formed on the front side of the wafer, there arises a problem in that the quality of each device chip can be lowered.The present invention has been made in view of the above problem, and it is therefore an object of the present invention to provide a wafer processing method that prevents adhesion of cutting dust to the front side of each device when cutting the wafer, and thereby suppresses a decrease in the quality of each device chip.According to an aspect of the present invention, there is provided a wafer processing method for dividing a wafer along a plurality of division lines to obtain a plurality of individual device chips, the division lines being formed on a front side of the wafer so as to define a plurality of separate regions in which a plurality of devices are individually formed. The wafer processing method includes a ring frame preparation step of preparing a ring frame having an inner opening for accommodating the wafer; a polyester film provision step of positioning the wafer in the inner opening of the ring frame and providing a polyester film on a back side of the wafer and on a back side of the ring frame, with no adhesive layer interposed between the polyester film and the wafer; a bonding step of heating the polyester film while applying a pressure to the polyester film after performing the polyester film provision step, thereby bonding the wafer and the ring frame via the polyester film by thermo-compression bonding so as to form a frame unit in a state where the front side of the wafer and the front side of the ring frame are exposed; a dividing step of cutting the wafer along each division line using a cutting device having a rotatable cutting blade after performing the connecting step, thereby dividing the wafer into the individual device chips; and a receiving step of blowing air from the polyester film side so that each device chip is pushed up and receiving the device chip from the polyester film after performing the dividing step.Preferably, the bonding step includes a step of applying infrared light to the polyester film, thereby performing the the thermoplastically bonding.Preferably, the polyester film is larger than the ring frame, and the bonding step includes an additional step of cutting the polyester film after heating the polyester film, thereby removing a part of the polyester film outside the outer periphery of the ring frame.Preferably, the receiving step includes a step of widening the polyester film, thereby enlarging a distance between all the adjacent constituent elements.Preferably, the polyester film is formed of a material selected from the group consisting of polyethylene terephthalate and polyethylene naphthalate.In the case where the polyester film is formed of polyethylene terephthalate, the polyester film in the bonding step is preferably heated in the range of 250° C. to 270° C. In the case where the polyester film is formed of polyethylene naphthalate, the polyester film in the bonding step is preferably heated in the range from 160° C. to 180° C.Preferably, the wafer is formed of a material selected from the group consisting of silicon, gallium nitride, gallium arsenide, and glass.In the wafer processing method according to a preferred embodiment of the present invention, the wafer and the ring frame are bonded using the polyester film having no adhesive layer instead of an adhesive tape having an adhesive layer, and thereby form the frame unit consisting of the wafer, the ring frame and the polyester film bonded together. The bonding step of bonding the wafer and the ring frame via the polyester film is realized by thermoplastically bonding. After performing the bonding step, the wafer is cut using the cutting blade to be divided into the individual device chips. Thereafter, each device chip is received by the polyester film by blowing air from the polyester film side so that each device chip is pushed up. Each packaged device chip is next mounted on a predetermined wiring substrate or the like. When the target device chip is pushed up by blowing the air from the polyester film side when the device chip is picked up, a load applied to the device chip when the device chip is peeled from the polyester film can be reduced.When cutting the wafer using the cutting blade, the polyester film provided below the wafer is also cut by the cutting blade. That is, the wafer and the polyester film bonded to the back surface of the wafer are cut by the cutting blade together in a state where the front surface of the wafer is oriented upward. Accordingly, cutting dust discharged from the polyester film is generated. This cutting dust is taken up in cutting water supplied when the wafer is cut and then distributed on the front side of the wafer. However, since the polyester film does not have an adhesive layer, the cutting dust does not adhere to the wafer, so that the cutting dust can be more reliably removed in a cleaning step to be performed later. In this way, the frame unit according to the preferred embodiment of the present invention can be formed by thermoplastically bonding using the polyester film having no adhesive layer. Accordingly, when the wafer is cut, cutting dust discharged from an adhesive layer is not generated, so that it is possible to suppress degradation in quality of each device chip due to such cutting dust having adhesion.Thus, the wafer processing method according to the preferred embodiment of the present invention can exhibit the effect that cutting dust does not adhere to the front side of each device during cutting of the wafer, and a decrease in the quality of each device chip divided from the wafer can be suppressed.The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and the appended claims with reference to the appended drawings showing a preferred embodiment of the invention.BRIEF DESCRIPTION OF THE FIGURESFIG. 1 is a schematic perspective view of a wafer; FIG. 2 is a schematic perspective view illustrating a manner of positioning the wafer and a ring frame on a holding surface of a chuck table; FIG. 3 is a schematic perspective view illustrating a polyester film providing step; FIG. 4 is a schematic perspective view illustrating a joining step; FIG. 5 is a schematic perspective view illustrating a modification of the joining step; FIG. 6 is a schematic perspective view illustrating another modification of the joining step; FIG. 7A is a schematic perspective view illustrating a manner of cutting the polyester film after performing the joining step; FIG. 7B is a schematic perspective view of a frame unit formed by performing the step illustrated in FIG. 7A ; FIG. 8 is a schematic perspective view illustrating a dividing step; FIG. 9 is a schematic perspective view illustrating a manner of loading the frame unit into a receptacle after performing the dividing step; FIG. 10A is a schematic sectional view illustrating a standby state in which a frame unit is fixed to a frame support table disposed at an initial position in a capturing step using the capturing apparatus illustrated in FIG. 9 ; and FIG. 10B is a schematic sectional view illustrating a working state in which the frame support table holding the frame unit with the polyester film is lowered to expand the polyester film in the receiving step.DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTA preferred embodiment of the present invention will now be described with reference to the accompanying drawings. First, a wafer to be processed by a processing method according to this preferred embodiment will be described. FIG. 1 is a schematic perspective view of a wafer 1. the wafer 1 is a substantially disk-shaped substrate formed of a material such as silicon (Si), silicon carbide (SiC), gallium nitride (GaN), and gallium arsenide (GaAs). The wafer 1 may be formed of any other semiconductor material. Further, the wafer 1 may be formed of a material such as sapphire, glass, and quartz. The wafer 1 has a front side 1 aand a back side 1 b. A plurality of intersecting division lines 3 are formed on the front surface 1 aof the wafer 1 so as to define a plurality of separate regions in each of which a plurality of devices 5 such as ICs and LEDs are formed. The intersecting division lines 3 are composed of a plurality of parallel division lines 3 extending in a first direction and a plurality of parallel division lines 3 extending in a second direction perpendicular to the first direction. In the processing method for the wafer 1 according to this preferred embodiment, the wafer 1 is cut along the intersecting division lines 3 and thereby divided into a plurality of individual device chips each including the plurality of devices 5.The wafer 1 is cut using a cutter. Before loading the wafer 1 into the cutting apparatus, the wafer 1 is bonded with a polyester film 9 (see FIG. 3 ) and a ring frame 7 (see FIG. 3 ) to thereby form a frame unit. Thus, the wafer 1 in the form of such a frame unit is loaded into the cutting apparatus and then cut into the individual device chips in the cutting apparatus by holding each device chip on the polyester film 9. Thereafter, the polyester film 9 is expanded to thereby increase the spacing between all the adjacent device chips. Thereafter, each device chip is picked up using a pickup device. The ring frame 7 is formed of a rigid material such as metal and has a circular inner opening 7 athat has a diameter larger than that of the wafer 1. The ring frame 7 has a front side 7 band a rear side 7 c. In forming the frame unit, the wafer 1 is accommodated in the inner opening 7 aof the ring frame 7 and positioned in such a manner that the center of the wafer 1 substantially coincides with the center of the inner opening 7 a.The polyester film 9 is a flexible (expandable) plastic film and has a planar front side and a planar rear side. The polyester film 9 is a circular film having a diameter larger than the outer diameter of the ring frame 7. The polyester film 9 is a film of a polymer (polyester) synthesized by polymerizing a dicarboxylic acid (compound having two carboxyl groups) and a diol (compound having two hydroxyl groups) as a monomer. Examples of the polyester film 9 include a polyethylene terephthalate film and a polyethylene naphthalate film. The polyester film 9 is transparent or translucent to visible light. As a variation, the polyester film 9 may be opaque. Since the polyester film 9 has no adhesive property, it cannot be adhered to the wafer 1 and the ring frame 7 at room temperature. However, the polyester film 9 is a thermoplastic film, so that when the polyester film 9 is heated to a temperature near its melting point under a predetermined pressure in a state where the polyester film 9 is in contact with the wafer 1 and the ring frame 7, the polyester film 9 is melted and thereby bonded to the wafer 1 and the ring frame 7. That is, the polyester film 9 can be bonded to the wafer 1 and the ring frame 7 by applying heat and pressure in the state where the polyester film 9 is in contact with the wafer 1 and the ring frame 7 to the polyester film 9. Thus, in the processing method for the wafer 1 according to this preferred embodiment, both the wafer 1, the ring frame 7, and the polyester film 9 are joined by thermoplastically bonding as mentioned above, thereby forming the frame unit.The steps of the processing method for the wafer 1 according to this preferred embodiment will now be described. Before bonding the wafer 1, the polyester film 9 and the ring frame 7, a polyester film providing step is performed using a chuck table 2 having a holding surface 2 aillustrated in FIG. 2. FIG. 2 is a schematic perspective view illustrating a manner of positioning the wafer 1 and the ring frame 7 on the holding surface 2 aof the chuck table 2. That is, the polyester film providing step is performed on the holding surface 2 aof the chuck table 2 as illustrated in FIG. 2. The chuck table 2 has a circular porous member having a diameter larger than the outer diameter of the ring frame 7. the porous member forms a central upper portion of the chuck table 2. the porous member has an upper surface serving as the holding surface 2 aof the chuck table 2. A suction pipe (not shown) is formed in the chuck table 2, and one end of the suction pipe is connected to the porous member. Further, a vacuum source 2 b(see FIG. 3 ) is connected to the other end of the suction pipe. The intake passage is provided with a selector switch 2 c(see FIG. 3 ) for switching between an ON state and an OFF state. When the ON state is established by the selector switch 2c, a vacuum generated by the vacuum source 2b is applied to a workpiece placed on the holding surface 2a of the chuck table 2, thereby holding the workpiece on the holding table 2 under suction.In the polyester film providing step, first, the wafer 1 and the ring frame 7 are placed on the holding surface 2 aof the chuck table 2 as illustrated in FIG. 2. At this time, the front side 1 aof the wafer 1 is oriented downward, and the front side 7 bof the ring frame 7 is also oriented downward. In this state, the wafer is positioned in the inner opening 7a of the ring frame 7. Thereafter, as shown in FIG. 3, the polyester film 9 is provided on the back surface 1 b(upper surface) of the wafer 1 and the back surface 7 c(upper surface) of the ring frame 7. FIG. 3 is a schematic perspective view illustrating a manner of providing the polyester film 9 to the wafer 1 and the ring frame 7. That is, as shown in FIG. 3, the polyester film 9 is provided so as to completely cover the wafer 1 and the ring frame 7. In the polyester film providing step, the diameter of the polyester film 9 is set larger than the diameter of the holding surface 2 aof the chuck table 2, If the diameter of the polyester film 9 is not larger than the diameter of the holding surface 2 a, such a problem may occur that, when the vacuum from the vacuum source 2 bis applied to the holding surface 2 aof the chuck table 2 in a bonding step to be performed later, the vacuum may be lost from any gap between the polyester film 9 and the holding surface 2 abecause the holding surface 2 ais not completely covered with the polyester film 9, so that a pressure cannot be appropriately applied to the polyester film 9.Next, in the processing method for the wafer 1 according to this preferred embodiment, a bonding step is performed in such a manner that the polyester film 9 is heated to bond the wafer 1 and the ring frame 7 by thermoplastically bonding via the polyester film 9. FIG. 4 is a schematic perspective view illustrating the joining step according to this preferred embodiment. As shown in FIG. 4, the transparent or visible light translucent polyester film 9 is provided so as to completely cover the wafer 1, the ring frame 7, and the holding surface 2 aof the chuck table 2, all of which are shown by broken lines in FIG. 4. In the joining step, the selector switch 2 cis operated to establish the ON state in which the vacuum source 2 bis in communication with the porous member of the chuck table 2, i.e., the holding surface 2 aof the chuck table 2, so that a vacuum generated by the vacuum source 2 bis applied to the polyester film 9 provided on the chuck table 2. Accordingly, the polyester film 9 is brought into close contact with the wafer 1 and the ring frame 7 by the atmospheric pressure applied to the upper surface of the polyester film 9.Thereafter, the polyester film 9 is heated in a state where the polyester film 9 is sucked from the vacuum source 2 b, and thereby performs thermoplastically joining. In this preferred embodiment shown in Fig. 4, the heating of the polyester film 9 is effected, for example, by a heat gun 4 provided above the chuck table 2. The heat gun 4 includes a heating means such as a heating wire and an air blowing mechanism such as a fan. Accordingly, the heat gun 9 can heat ambient air and blow the heated air. In a state where the vacuum is applied from the vacuum source 2 bto the polyester film 9, the heat gun 4 is operated to supply hot air 4 ato the upper surface of the polyester film 9. Accordingly, when the polyester film 9 is heated to a predetermined temperature, the polyester film 9 is bonded to the wafer 1 and the ring frame 7 by thermo-compression bonding.Another method for heating the polyester film 9 may be used. For example, each member on the polyester film 9 heated to a predetermined temperature may be pressed against the wafer 1 and the ring frame 7. FIG. 5 is a schematic perspective view illustrating such a modification of the joining step. As shown in FIG. 5, the transparent or visible light translucent polyester film 9 is provided so as to completely cover the wafer 1, the ring frame 7, and the holding surface 2 aof the chuck table 2, all of which are shown by broken lines in FIG. 5. In this modification shown in Fig. 5, a heat roller 6 having a heat source is used. Specifically, first, the vacuum generated by the vacuum source 2 bis applied to the polyester film 9, so that the polyester film 9 is brought into close contact with the wafer 1 and the ring frame 7 by the atmospheric pressure applied to the upper surface of the polyester film 9.Thereafter, the heat roller 6 is heated to a predetermined temperature and next placed at an end located on the outer periphery of the holding surface 2 a, as shown in FIG. 5, on the holding surface 2 aof the chuck table 2. Thereafter, the heat roller 6 is rotated about its axis to roll on the chuck table 2 via the polyester film 9 from the above one end to another end diametrically opposite to the above one end. As a result, the polyester film 9 is bonded to the wafer 1 and the ring frame 7 by thermo-compression bonding. In the case where a force for pressing the polyester film 9 is applied from the heat roller 6, the thermoplastically bonding is effected at a pressure higher than the atmospheric pressure. Preferably, the cylindrical surface of the heat roller 6 is coated with a fluoroplastic. Further, the heat roller 6 may be replaced with an iron-like pressing member having a flat base plate and a heat source. In this case, the pressing member is heated to a predetermined temperature to thereby provide a hot plate which is next pressed onto the polyester film 9 held on the chuck table 2.Another method for heating the polyester film 9 may be used in the following manner. FIG. 6 is a schematic perspective view illustrating such another modification of the joining step. As shown in FIG. 6, the transparent or visible light translucent polyester film 9 is provided so as to completely cover the wafer 1, the ring frame 7, and the holding surface 2 aof the chuck table 2, all of which are shown by broken lines in FIG. 6. In this modification shown in Fig. 6, an infrared lamp 8 is provided above the chuck table 2 to heat the polyester film 9. The infrared lamp 8 can apply infrared light 8a having an absorption wavelength at least for the material of the polyester film 9. In the modification shown in FIG. 6, the vacuum generated by the vacuum source 2 bis also applied to the polyester film 9 first, so that the polyester film 9 is brought into close contact with the wafer 1 and the ring frame 7 by the atmospheric pressure applied to the upper surface of the polyester film 9. Thereafter, the infrared lamp 8 is operated to apply the infrared light 8a to the polyester film 9, thereby heating the polyester film 9.When the polyester film 9 is heated to a temperature near its melting point by performing any of the above methods, the polyester film 9 is bonded to the wafer 1 and the ring frame 7 by thermoplastically bonding. After bonding the polyester film 9, the selector switch 2c is operated to establish the OFF state in which the connection between the porous member of the chuck table 2 and the vacuum source 2b is completed. Accordingly, the suction holding by the chuck table 2 is finished.Thereafter, the polyester film 9 is circularly cut along the outer periphery of the ring frame 7 to remove an undesirable peripheral portion of the polyester film 9. FIG. 7A is a schematic perspective view illustrating a manner of cutting the polyester film 9. As shown in Fig. 7A, a disk-shaped (ring-shaped) cutter 10 is used to cut the polyester film 9. The cutter 10 has a central through hole 10a into which a rotating shaft 10b is fitted. Accordingly, the cutter 10 is rotatable about the axis of the rotating shaft 10b. First, the cutter 10 is positioned above the ring frame 7. At this time, the rotating shaft 10 bis arranged to extend in the radial direction of the chuck table 2. Thereafter, the cutter 10 is lowered until the outer periphery (cutting edge) of the cutter 10 comes into contact with the polyester film 9 placed on the ring frame 7. That is, the polyester film 9 is caught between the cutter 10 and the ring frame 7, so that the polyester film 9 is cut by the cutter 10 to form a cut trace 9a. Further, the cutter 10 is rotatably guided on the polyester film 9 along a circular line disposed between the inner periphery of the ring frame 7 (i.e., outside of the inner opening 7 aof the ring frame 7) and the outer periphery of the ring frame 7, and thereby forms the cut track 9 acircularly along the above circular line. As a result, a predetermined central portion of the polyester film 9 is surrounded by the circular cut trace 9a. Thereafter, a remaining outer portion of the polyester film 9 outside the circular cut trace 9a is removed. That is, an undesired outer portion of the polyester film 9 including an outermost outer portion outside the outer periphery of the ring frame 7 can be removed.The cutter 10 may be replaced with an ultrasonic cutter for cutting the polyester film 9. Further, a vibration source for vibrating the cutter 10 at a frequency in an ultrasonic band may be connected to the cutter 10. Further, when the polyester film 9 is cut, the polyester film 9 may be cooled to be cured to facilitate the cutting operation. By cutting the polyester film 9 as mentioned above, a frame unit 11 shown in FIG. 7B is formed, in which the frame unit 11 is composed of the wafer 1, the ring frame 7, and the polyester film 9 bonded together. That is, the wafer and the ring frame 7 are bonded to each other via the polyester film 9 to form the frame unit 11 as shown in FIG. 7B. FIG. 7B is a schematic perspective view of the frame unit 11 in a state where the front side 1 aof the wafer and the front side 7 bof the ring frame 7 are exposed upward.In performing the the thermoplastically bonding as mentioned above, the polyester film 9 is preferably heated to a temperature equal to or below the melting point of the polyester film 9. When the heating temperature is higher than the melting point of the polyester film 9, there is a possibility that the polyester film 9 is melted to such an extent that the shape of the polyester film 9 cannot be maintained. Further, the polyester film 9 is preferably heated to a temperature equal to or higher than the softening point of the polyester film 9. When the heating temperature is lower than the softening point of the polyester film 9, the thermoplastically bonding cannot be carried out properly. Accordingly, the polyester film 9 is preferably heated to a temperature equal to or higher than the softening point of the polyester film 9 and equal to or lower than the melting point of the polyester film 9. Further, there is a case where the softening point of the polyester film 9 may be unknown. In order to deal with such a case, when the thermoplastically bonding is performed, the polyester film 9 is preferably heated to a temperature equal to or higher than a predetermined temperature and equal to or lower than the melting point of the polyester film 9, the predetermined temperature being lower than the melting point of the polyester film 9 by 20° C.In the case where the polyester film 9 is, for example, a polyethylene terephthalate film, the heating temperature in the bonding step is preferably set in the range of 250° C. to 270° C. Further, in the case where the polyester film 9 is a polyethylene naphthalate film, the heating temperature in the bonding step is preferably set in the range of 160° C. to 180° C.The heating temperature is defined herein as the temperature of the polyester film 9 to be heated in performing the bonding step. As the heat sources including the heat gun 4, the heat roller 6, and the infrared lamp 8 mentioned above, some kinds of heat sources capable of setting an output temperature have been put into practical use. However, even if such a heat source is used to heat the polyester film 9, the temperature of the polyester film 9 does not reach the above-set discharge temperature in some cases. In order to deal with such a case, the output temperature of the heat source may be set to a temperature higher than the melting point of the polyester film 9 to heat the polyester film 9 to a predetermined temperature.After performing the above-mentioned joining step, a dividing step is performed in such a manner that the wafer 1 in the state of the frame unit 11 is cut by a cutting blade to obtain individual device chips. The dividing step is performed using a cutter 12 shown in FIG. 8 in this preferred embodiment. FIG. 8 is a schematic perspective view illustrating the dividing step. As illustrated in FIG. 8, the cutting apparatus 12 includes a cutting unit 14 for cutting a workpiece and a chuck table (not illustrated) for holding the workpiece. The cutting unit 14 includes a cutting blade 18 having an annular abrasive portion (cutting edge) for cutting the workpiece, and a spindle (not illustrated) for supporting the cutting blade 18 so as to rotate the cutting blade 18. The cutting blade 18 has a central through hole for mounting the front end of the spindle. The cutting blade 18 is composed of an annular base (terminal) having the above-mentioned central through hole and an annular abrasive portion provided along the outer periphery of the annular base. The spindle is rotatably supported in a spindle housing 16, and the base end of the spindle is connected to a spindle motor (not shown) accommodated in the spindle housing 16. Accordingly, the cutting blade 18 can be rotated by operating the spindle motor. The chuck table has an upper surface as a holding surface for holding the wafer 1.When the workpiece is cut by the cutting blade 18, heat is generated by the friction between the cutting blade 18 and the workpiece. Further, when the workpiece is cut by the cutting blade 18, cutting dust is generated from the workpiece. In order to remove such heat and cutting dust discharged from cutting the workpiece, cutting water such as clean water is supplied to the cutting blade 18 and the workpiece during cutting of the workpiece. Accordingly, the cutting unit 14 includes a pair of cutting water nozzles 20 for supplying cutting water to the cutting blade 18 and the workpiece, the pair of cutting water nozzles 20 being disposed so as to face both sides of the cutting blade 18. In FIG. 8, only one of the two cutting water nozzles 20 is shown.In cutting the wafer 1, the frame unit 11 is placed on the chuck table in the state where the front surface 1 aof the wafer 1 is exposed upward. Accordingly, the wafer 1 is held on the chuck table via the polyester film 9. Thereafter, the chuck table is rotated to cause the division lines 3 on the front side 1 aof the wafer 1 extending in the first direction to be parallel to a feeding direction in the cutting apparatus 12.Further, the chuck table and the cutting unit 14 are relatively moved in a direction perpendicular to the feeding direction in a horizontal plane, to thereby position the cutting blade 18 directly above an extension of a predetermined one of the division lines 3 extending in the first direction.Thereafter, the spindle is rotated to thereby rotate the cutting blade 18. Thereafter, the cutting unit 14 is lowered to a predetermined height, and the chuck table and the cutting unit 14 are relatively moved in the feeding direction parallel to the upper surface of the chuck table. Accordingly, the abrasive portion of the cutting blade 18 that is rotated comes into contact with the wafer 1, thereby cutting the wafer 1 along the predetermined division line 3 in the feeding direction. As a result, a cut trace 3a (groove) is formed along the predetermined division line 3 so as to completely cut the wafer 1 and the polyester film 9. After cutting the wafer 1 and the polyester film 9 along the predetermined division line 3, the chuck table and the cutting unit 14 are relatively moved in an index direction perpendicular to the feeding direction by the pitch of the division lines 3. Thereafter, the above cutting operation along the next division line adjacent to the above predetermined division line 3 is similarly performed. After similarly performing the cutting operation along all the other division lines 3 extending in the first direction, the chuck table is rotated 90 degrees about its axis perpendicular to the holding surface, so that the other division lines 3 extending in the second direction perpendicular to the first direction become parallel to the feeding direction. Thereafter, the above cutting operation is similarly performed along all the other division lines 3 extending in the second direction. After performing the cutting operation along all the other division lines 3 extending in the second direction, the dividing step is finished.The cutting device 12 may include a cleaning unit (not shown) provided in the vicinity of the cutting unit 14. That is, the wafer 1 cut by the cutting unit 14 can be transferred to the cleaning unit and then cleaned by the cleaning unit. For example, the cleaning unit includes a cleaning table having a holding surface for holding the frame unit 11 and a cleaning water nozzle configured to be horizontally moved in opposite directions above the frame unit 11 held on the holding surface of the cleaning table. The cleaning water nozzle acts to supply cleaning water such as clean water to the wafer 1. The cleaning table is rotatable about its axis perpendicular to the holding surface. In operation, the cleaning table is rotated about its axis and at the same time the cleaning water is supplied from the cleaning water nozzle to the wafer 1. During this supply of the cleaning water, the cleaning water nozzle is horizontally moved in opposite directions along a path passing through the position just above the center of the holding surface of the cleaning table. Accordingly, the entire surface of the front surface 1 aof the wafer 1 can be cleaned by the cleaning water.By performing the dividing step as mentioned above, the wafer 1 is divided into the individual device chips still supported by the polyester film 9. In cutting the wafer 1, the cutting unit 14 is positioned at a predetermined height such that the lower end of the cutting blade 18 has a lower level than the back surface 1 bof the wafer 1 to reliably divide the wafer 1. Accordingly, when the wafer 1 is cut by the cutting blade 18, the polyester film 9 bonded to the back surface 1b of the wafer 1 is also cut by the cutting blade 18, so that cutting dust discharged from the polyester film 9 is generated. In the case where an adhesive tape having an adhesive layer is used in place of the polyester film 9 in the frame unit 11, cut dust of the adhesive tape discharged from the adhesive layer is generated. In this case, the cutting dust is taken into the cleaning water supplied from the cleaning water nozzles 20 and then distributed on the front side 1 aof the wafer 1. The cutting dust emanating from the adhesive layer can again adhere to the front side of each component 5. Moreover, it is not easy to remove the cutting dust adhering to the front side of each device 5 in a cleaning step of cleaning the wafer 1 after the dividing step. When the cutting dust discharged from the adhesive layer adheres to each device 5, there arises such a problem that the quality of each device chip divided from the wafer 1 is lowered.In contrast, the processing method for the wafer 1 according to this preferred embodiment has the following advantage. In this preferred embodiment, instead of an adhesive tape having an adhesive layer, the polyester film 9 having no adhesive layer is used in the frame unit 11. Even if the cutting dust discharged from the polyester film 9 is generated and then dispersed on the front surface 1a of the wafer 1 when it is taken into the cleaning water, this grinding dust does not adhere to the wafer 1, but is reliably removed in the following cleaning step. Accordingly, it is possible to suppress degradation of each device chip due to the cutting dust.After performing the dividing step or the cleaning step, a pickup step is performed to pick up each device chip from the polyester film 9. The capturing step is performed using a capturing device 22 illustrated in FIG. 9. FIG. 9 is a schematic perspective view illustrating a manner of loading the frame unit 11 into the receptacle device 22. As shown in FIG. 9, the take-up device 22 includes a cylindrical drum 24 and a frame holding unit 26 including a frame support table 30 provided around the cylindrical drum 24. The cylindrical barrel 24 has an inner diameter larger than the diameter of the wafer 1 and an outer diameter smaller than the inner diameter of the ring frame 7 (the diameter of the inner opening 7a). The frame support table 30 of the frame holding unit 26 is an annular table having a circular inner opening larger in diameter than the drum 24. that is, the frame support table 30 has an inner diameter larger than the outer diameter of the drum 24. further, the frame support table 30 has an outer diameter larger than the outer diameter of the ring frame 7. the inner diameter of the frame support table 30 is substantially equal to the inner diameter of the ring frame 7. the frame support table 30 has an upper surface as a support surface for supporting the ring frame 7 via the polyester film 9 thereon. First, the height of the upper surface of the frame support table 30 is set equal to the height of the upper end of the drum 24 (see FIG. 10A ). Further, the upper end portion of the drum 24 is surrounded by the inner periphery of the ring frame 7 in this initial step.A plurality of clamps 28 are provided on the outer periphery of the frame support table 30. Each clamp 28 acts to hold the ring frame 7 supported on the frame support table 30. That is, when the ring frame 7 of the frame unit 11 is placed on the frame support table 30 via the polyester film 9 and then held by each clamp 28, the frame unit 11 can be fixed to the frame support table 30. The frame support table 30 is supported by a plurality of rods 32 extending in a vertical direction. That is, each rod 32 is connected at its upper end to the lower surface of the frame support table 30. An air cylinder 34 for vertically moving each rod 32 is connected to the lower end of each rod 32. Specifically, the lower end of each rod 32 is connected to a piston (not shown) movably accommodated in the air cylinder 34. Each air cylinder 34 is supported on a disk-shaped base 36. That is, the lower end of each air cylinder 34 is connected to the upper surface of the disk-shaped base 36. Accordingly, when each air cylinder 34 is operated in the initial stage, the frame support table 30 is lowered with respect to the fixed-in-place drum 24.Further, a push-up mechanism 38 for pushing up each component chip carried on the polyester film 9 is provided inside the drum 24. The push-up mechanism 38 has a function of blowing air 38a upward. That is, each device chip is arranged to be pushed up by the polyester film 9 from the push-up mechanism 38 disposed below the polyester film 9. Further, a gripper 40 (see FIG. 10B ) capable of holding each device chip under suction is provided above the drums 24. Both the push-up mechanism 38 and the gripper 40 are movable in a horizontal direction parallel to the upper surface of the frame support table 30. The gripper 40 is connected to a vacuum source 40a (see Fig. 10B) via a selector switch 40b (see Fig. 10B).In the capturing step, first, each air cylinder 34 in the capturing device 22 is operated to adjust the height of the frame support table 30 so that the height of the upper end of the drum 24 corresponds to the height of the upper surface of the frame support table 30. Thereafter, the frame unit 11 transferred from the cutting device 12 is placed on the drum 24 and the frame support table 30 in the pick-up device 22 in a state where the front side 1 aof the wafer 1 of the frame unit 11 is oriented upward. Thereafter, each clamp 28 is operated to fix the ring frame 7 of the frame unit 11 to the upper surface of the frame support table 30. FIG. 10A is a schematic sectional view illustrating a standby state in which the frame unit 11 is attached to the frame support table 30 set at the initial position. At this time, the plurality of cut traces 3 ahave already been formed in the wafer 1 in the dividing step, so that the wafer 1 has already been divided into a plurality of individual device chips 1 c(see FIG. 10B ).Thereafter, each air cylinder 34 is operated to lower the frame supporting table 30 of the frame holding unit 26 with respect to the drum 24. As a result, the polyester film 9 fixed by each clamp 28 to the frame holding unit 26 is expanded radially outward as shown in Fig. 10B. FIG. 10B is a schematic sectional view illustrating a processing state in which the frame support table 30 holding the ring frame 7 with the polyester film 9 is lowered to expand the polyester film 9. When the polyester film 9 is expanded radially outward as mentioned above, the distance between adjacent device chips 1c carried on the polyester film 9 is increased as shown in Fig. 10B. Accordingly, contact between the adjacent device chips 1 cmay be suppressed, and each device chip 1 cmay be easily accommodated. Thereafter, a target device chip 1c is selected and the push-up mechanism 38 is next moved to a position directly below this target device chip 1c as shown in FIG. 10B. Moreover, as illustrated in FIG. 10B, the gripper 40 is also moved to a position directly above this target device chip 1 c. Thereafter, the push-up mechanism 38 is operated to push up the target device chip 1c through the polyester film 9 by blowing out the air 38a from the side of the polyester film 9. Further, the selector switch 40b is operated to cause the gripper 40 to communicate with the vacuum source 40a. As a result, the target device chip 1 cis held by the gripper 40 under suction and thereby picked up by the polyester film 9. Such a pick operation is similarly performed for all the other device chips 1c. Thereafter, each packaged device chip 1 cis attached to a predetermined wiring substrate or the like for actual use.When the target device chip is pushed up by blowing out the air 38a from the polyester film 9 side when the device chip is picked up, a load applied when the device chip is peeled from the polyester film 9 is reduced.In the wafer processing method according to this preferred embodiment mentioned above, the frame unit 11 containing the wafer 1 can be formed without using an adhesive tape having an adhesive layer. Accordingly, when the wafer 1 is cut, no cutting dust of the adhesive tape is generated from the adhesive layer, so that this cutting dust does not adhere to each device chip 1c. As a result, there is no possibility that the quality of each device chip 1 cis lowered.The present invention is not limited to the above preferred embodiment, but various modifications may be made within the scope of the present invention. For example, while in the above preferred embodiment, the polyester film 9 is selected from a polyethylene terephthalate film and a polyethylene naphthalate film, this is illustrative only. That is, the polyester film usable in the present invention may be formed of any other materials (polyesters) such as polytrimethylene terephthalate, polybutylene terephthalate or polybutylene naphthalate.

Claims

A wafer processing method for dividing a wafer (1) along a plurality of division lines (3) to obtain a plurality of individual device chips (1c), the division lines (3) being formed on the front side (1a) of the wafer (1) so as to define a plurality of separate regions in which a plurality of devices (5) are individually formed, the wafer processing method comprising: a ring frame preparing step of preparing a ring frame (7) having an inner opening (7a) for accommodating the wafer (1); a polyester film providing step of positioning the wafer in the inner opening (7a) of the ring frame (7) and providing a polyester film (9) on a back side (1b) of the wafer (1) and on a back side (7c) of the ring frame (7), wherein an adhesive layer is not interposed between the polyester film (9) and the wafer (1); a bonding step of heating the polyester film (9) while applying a pressure to the polyester film (9) after performing the polyester film providing step, thereby bonding the wafer (1) and the ring frame (7) by thermo-compression bonding via the polyester film (9) to form a frame unit (11) in a state where the front side (1a) of the wafer (1) and the front side (7b) of the ring frame (7) are exposed; a dividing step of cutting the wafer (1) along each division line (3) using a cutting device (12) having a rotatable cutting blade (18) after performing the connecting step, thereby dividing the wafer (1) into the individual device chips (1c); and a receiving step of blowing air from the polyester film (9) side so as to push up each device chip (1c), and receiving the device chip (1c) from the polyester film (9) after performing the dividing step.The wafer processing method according to claim 1, wherein the bonding step includes a step of applying infrared light to the polyester film (9), thereby performing the the thermoplastically bonding.The wafer processing method according to claim 1 or 2, wherein the polyester film (9) is larger than the ring frame (7), and wherein the bonding step includes an additional step of cutting the polyester film (9) after heating the polyester film (9), thereby removing a part of the polyester film (9) outside an outer periphery of the ring frame (7).The wafer processing method according to any one of the preceding claims, wherein the accommodating step includes a step of widening the polyester film (9) to thereby increase a distance between all the adjacent device chips (1c).The wafer processing method according to any one of the preceding claims, wherein the polyester film (9) is formed of a material selected from the group consisting of polyethylene terephthalate and polyethylene naphthalate.The wafer processing method according to claim 5, wherein the polyester film (9) is formed of polyethylene terephthalate, and the polyester film (9) is heated in the range of 250°C to 270°C in the bonding step.The wafer processing method according to claim 5, wherein the polyester film (9) is formed of polyethylene naphthalate, and the polyester film (9) is heated in the range of 160°C to 180°C in the bonding step.The wafer processing method according to any one of the preceding claims, wherein the wafer (1) is formed of a material selected from the group consisting of silicon, gallium nitride, gallium arsenide, and glass.

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