HOLDING TABLE FOR HOLDING A WAFER THAT HAS A RECESSED SECTION

Abstract

holding table (16) holding a wafer (11) having a recessed section (19) and an annular outer circumferential section (21) surrounding the recessed section (19), wherein the holding table (16) has: a base (60);and a retaining section (62) projecting from an upper surface (60a) of the base (60) and configured to be inserted into the recessed section (19) of the wafer (11), the base (60) comprising: an annular groove (66) arranged in a region corresponding to the outer circumferential section (21) of the wafer (11), and a support element (68) arranged within the groove (66) and configured to be transformed from a softened state to a hardened state or from the hardened state to the softened state by the application of energy, wherein the recessed section (19) of the wafer (11) is held by the retaining section (62) and the outer circumferential section (21) of the wafer (11) is supported by the support element (68) in the hardened state.

Description

BACKGROUND OF THE INVENTIONField of the InventionThe present invention relates to a holding table for holding a wafer having a recessed portion.Description of the Prior ArtIn a method for manufacturing device chips, a wafer having a device region and a peripheral surplus region on a surface side thereof is used. The device region includes each device formed in each of a plurality of regions delimited by planned dividing lines (roads) arranged in a grid-like manner. The circumferential excess region surrounds the device region. A plurality of device chips each including a device are obtained by dividing the wafer along the planned dividing lines. The device chips are incorporated into various kinds of electronic devices such as mobile phones or personal computers.For dividing the wafer, a cutting device is used, for example. The cutting device includes a holding table that holds a workpiece, and a cutting unit having an annular blade that cuts the workpiece. The wafer is cut and divided by holding the wafer on the holding table, rotating the cutting blade, and causing the cutting blade to cut into the wafer. In addition, in recent years, with the miniaturization of electronic devices, a reduction in the thickness of the device chips has been desired. Accordingly, processing of thinning the wafer may be performed before division of the wafer. A grinding apparatus is used, for example, for thinning the wafer. The apparatus includes a holding table that holds the workpiece, and a grinding unit equipped with a grinding wheel having a plurality of grinding stones. The lower surface side of the wafer is ground by holding the wafer on the holding table and bringing the grinding stones into contact with the lower surface side of the wafer while rotating the holding table and the grinding wheel, respectively. The wafer is made so thin.When the wafer is ground to be made thin, the rigidity of the wafer decreases, and the wafer tends to be damaged in subsequent handling of the wafer (transportation, processing, cleaning of the wafer, and the like). Accordingly, a method has been proposed in which only a central portion of the lower surface side of the wafer that coincides with the device region is ground and made thin (see Japanese Patent Application Laid-Open JP 2007-19 379 A). When this method is used, an outer peripheral portion of the wafer remains in a thick state without being made thin. This prevents a decrease in the rigidity of the wafer, so that damage to the wafer is avoided.When only the central portion of the wafer is ground as described above, a wafer is obtained which has a recessed portion formed on the lower surface side and an annular outer peripheral portion surrounding the recessed portion. When the wafer is finally to be divided into a plurality of device chips, the outer peripheral portion of the wafer which is not made thin is first removed. For example, the outer peripheral portion is cut off from the wafer by holding the wafer on the holding table of the cutting device and annularly cutting a boundary region between the recessed portion and the outer peripheral portion of the wafer by the cutting blade (see Japanese Patent Application Laid-Open No. 2007-59 829 A).SUMMARY OF THE INVENTIONWhen the wafer having the recessed portion is to be processed by a processing apparatus such as the cutting apparatus, the wafer is held on the holding table. For example, the wafer is placed on the holding table such that the upper surface side (holding surface) of the holding table is inserted into the recessed portion of the wafer. The lower surface of the recessed portion of the wafer is thus held on the holding table. At this time, the outer peripheral portion of the wafer is disposed on the outside of the holding surface of the holding table and is not supported by the holding surface. Therefore, the wafer is insufficiently fixed to the holding table, and a processing error may occur. For example, when the wafer is cut by the cutting blade, vibration (fluctuation) may occur at the outer peripheral portion of the wafer, and chipping (chipping) or crack may occur in the wafer. Accordingly, a holding table having a cylindrical base and a portion protruding upward from the central portion of the base could be used for holding the wafer having the recessed portion. When this holding table is used, the recessed portion of the wafer is supported by the holding portion, and the outer peripheral portion of the wafer is supported by the base. As a result, the wafer is securely fixed to the holding table, and a machining error cannot easily occur.However, when there is a difference between the depth of the recessed portion of the wafer and a protrusion amount (height) of the holding portion of the chuck table, the recessed portion and the outer peripheral portion of the wafer are not appropriately supported. The protrusion amount of the holding portion must therefore be accurately adjusted according to the depth of the recessed portion of the wafer. However, the depth of the recessed portion is different for each wafer. Therefore, the protrusion amount of the holding portion of the holding table needs to be changed each time the wafer to be processed is changed. This makes it difficult to work processing the holding table and thus reduces the efficiency of processing the wafer.The present invention has been made in view of such problems. It is an object of the present invention to provide a holding table that can easily and securely hold a wafer having a recessed portion.According to an aspect of the present invention, there is provided a holding table that holds a wafer having a recessed portion and an annular outer peripheral portion surrounding the recessed portion. The holding table includes a base and a holding portion protruding from an upper surface of the base and configured to be inserted into the recessed portion of the wafer. The base includes an annular groove disposed in a region corresponding to the outer peripheral portion of the wafer, and a support member disposed within the groove and configured to be changed from a softened state to a hardened state or from the hardened state to the softened state by application of energy. The recessed portion of the wafer is held by the holding portion, and the outer peripheral portion of the wafer is supported by the support member in the hardened state.Meanwhile, the support member is preferably a member that is rendered liquid when heated in a solidified state.The holding table according to an aspect of the present invention uses the support member whose hardness is changed by application of power as a member that supports the outer peripheral portion of the wafer. A plurality of kinds of wafers different in the depth of the recessed portion can be supported by deforming the support member according to the depth of the recessed portion of the wafer. The holding table that can easily hold the wafer having the recessed portion is thus realized. In addition, the holding table according to an aspect of the present invention holds the recessed portion of the wafer by the holding portion and supports the outer peripheral portion of the wafer by the support member. Thereby, the wafer is securely held on the holding table, and positional displacement or the like of the wafer does not easily occur.The above and other objects, features and advantages of the present invention and its mode of operation will be best understood by studying the following specification and appended claims with reference to the accompanying drawings which show a preferred embodiment of the invention, and the invention will be best understood thereby.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1 is a perspective view illustrating a cutting device; FIG. 2A is a perspective view illustrating the upper surface side of a wafer; FIG. 2B is a perspective view illustrating the lower surface side of the wafer; FIG. 3A is a perspective view illustrating the wafer supported by a frame; FIG. 3B is a sectional view illustrating the wafer supported by the frame; FIG. 4A is a perspective view illustrating a holding table; FIG. 4B is an enlarged sectional view illustrating a part of the holding table; FIG. 5 is a sectional view illustrating the holding table for holding the wafer; and FIG. 6 is an enlarged sectional view illustrating a part of the wafer held on the holding table.DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTAn embodiment according to an aspect of the present invention will be described below with reference to the accompanying drawings. First, an example of a configuration of a processing apparatus that may include a holding table according to the present embodiment will be described. FIG. 1 is a perspective view illustrating a cutting device 2 that performs cutting processing on a workpiece. Meanwhile, in FIG. 1, an X-axis direction (a machining feed direction, a first horizontal direction, or a front-rear direction) and a Y-axis direction (an index feed direction, a second horizontal direction, or a left-right direction) are directions perpendicular to each other. In addition, a Z-axis direction (a vertical direction, an up-down direction, or a height direction) is a direction perpendicular to the X-axis direction and the Y-axis direction.The cutting device 2 includes a base 4 that supports or houses components that form the cutting device 2. In a corner portion on the front side of the base 4, a rectangular opening 4 ais provided. A cartridge mounting base (cartridge elevator) 6 is provided in the opening 4a. To the cassette mounting base 6, a raising and lowering mechanism (not shown) is coupled. The raising-lowering mechanism raises and lowers the cartridge mounting base 6 along the Z-axis direction. On the upper surface of the cassette mounting base 6, a cassette 8 is mounted which accommodates a plurality of workpieces to be machined by the cutting device 2. In Fig. 1, the contour of the cassette 8 is shown by a double-dotted line. In the cassette 8, for example, disc-shaped wafers 11 are accommodated as the workpieces.FIG. 2A is a perspective view illustrating the upper surface side of a wafer 11. FIG. 2B is a perspective view illustrating the lower surface side of the wafer 11. The wafer 11 is, for example, a disk-shaped substrate formed of a semiconductor such as silicon. The wafer 11 has an upper surface (first surface) 11 aand a lower surface (second surface) 11 bwhich are substantially parallel to each other. The wafer 11 is divided into a plurality of rectangular regions by a plurality of planned dividing lines (streets) 13 arranged in a lattice-like manner so as to intersect each other. In each of the plurality of regions delimited by the planned dividing lines 13, a device 15 such as an integrated circuit (IC), a large scale integration (LSI), a light emitting diode (LED), or a microelectromechanical system (MEMS) is formed.The wafer 11 has, on the upper surface 11 a, a substantially circular device region 17 ain which a plurality of devices 15 are formed, and an annular peripheral surplus region 17 bsurrounding the device region 17 a. The circumferential surplus portion 17 bcorresponds to an annular portion having a predetermined width (for example, about 2 mm) including the outer circumferential edge of the upper surface 11 a.In FIG. 2A, a boundary between the device region 17 aand the peripheral surplus region 17 bis indicated by a double-dashed line.Note that the material, shape, configuration, size, and the like of the wafer 11 are not limited to specific configurations. For example, the wafer 11 may be a substrate formed of a semiconductor other than silicon (GaAs, InP, GaN, SiC, or the like), glass, a ceramic, a plastic, a metal, or the like. In addition, the type, number, shape, structure, size, arrangement, and the like of the constituent elements 15 are not limited to specific configurations.A plurality of device chips each including the device 15 are manufactured by lattice-dividing the wafer 11 along the planned dividing lines 13. In addition, device chips of thin configuration are obtained when the wafer 11 is divided after the wafer 11 is subjected to processing for thinning.For thinning the wafer 11, for example, a grinding apparatus is used. The grinding apparatus includes a holding table (chuck table) that holds the wafer 11 and a grinding unit equipped with a grinding wheel including a plurality of grinding stones. The bottom surface 11 bside of the wafer 11 is ground by holding the wafer 11 on the holding table and bringing the grinding stones into contact with the bottom surface 11 bside of the wafer 11 while rotating the holding table and the grinding wheel, respectively. The wafer 11 is thus made thin.When the entire side of the bottom surface 11 bof the wafer 11 is ground, since the entire wafer 11 is made thin, the rigidity of the wafer 11 decreases, and the wafer 11 tends to be damaged in subsequent handling of the wafer 11 (transportation, processing, cleaning, and the like of the wafer 11). Therefore, preferably, only a central portion of the lower surface 11 bside of the wafer 11 is subjected to thinning processing (grinding processing).When only the central portion of the wafer 11 is thinned out, as shown in FIG. 2B, a circular recessed portion 19 is formed in the central portion of the lower surface 11 bof the wafer 11. Meanwhile, the recessed portion 19 is provided at a position corresponding to the device region 17 a. For example, the diameter of the recessed portion 19 is set substantially identical to the diameter of the device region 17 a, and the recessed portion 19 is formed at a position corresponding to the device region 17 a. The recessed portion 19 has a circular bottom surface 19 athat is substantially parallel to the top surface 11 aand the bottom surface 11 bof the wafer 11, and an annular side surface (inner wall) 19 bthat is substantially perpendicular to the bottom surface 19 aand is connected to the bottom surface 11 band the bottom surface 19 a. In addition, at the periphery of the recessed portion 19, an outer peripheral portion 21 of the wafer 11 which is not subjected to thinning processing (grinding processing) remains. The outer peripheral portion 21 surrounds the recessed portion 19. when only the central portion of the wafer 11 is made thin as described above, a decrease in the rigidity of the wafer 11 is avoided because the outer peripheral portion 21 of the wafer 11 is maintained in a thick state, so that damage to the wafer 11 is not easily possible. That is, the non-thin outer peripheral portion 21 of the wafer 11 functions as a reinforcing portion (reinforcing region) that reinforces the wafer 11.The wafer 11 in which the recessed portion 19 is formed is cut along the planned dividing lines 13 by the cutting device 2 (see FIG. 1 ), and thus is divided into a plurality of device chips. When the wafer 11 is to be processed by the cutting apparatus 2, the wafer 11 is first supported by an annular frame.FIG. 3A is a perspective view illustrating the wafer 11 supported by a frame 25. FIG. 3B is a sectional view illustrating the wafer 11 supported by the frame 25. A tape 23 having a size to cover the entire side of the bottom surface 11 bof the wafer 11 is attached to the side of the bottom surface 11 bof the wafer 11. For example, the circular band 23 whose diameter is larger than that of the wafer 11 is attached so as to cover the lower surface 11 bside of the wafer 11. As the tape 23, a flexible sheet including a circular base material and an adhesive layer (adhesive layer) provided on the base material may be used. For example, the base material is formed of a plastic such as polyolefin, polyvinyl chloride, or polyethylene terephthalate, and the adhesive layer is formed of an epoxy-based, acrylic-based, rubber-based adhesive, or the like. In addition, a curable resin cured by irradiation with ultraviolet rays can be used as the adhesive layer.The tape 23 is bonded along the contour of the lower surface 11 bside of the wafer 11. That is, as illustrated in FIG. 3B, the tape 23 is fixed along the lower surface 19 aand the side surface 19 bof the recessed portion 19 and a lower surface of the outer peripheral portion 21. Meanwhile, while FIG. 3B illustrates an example in which a small gap is present between the wafer 11 and the tape 23 at an outer peripheral portion of the lower surface 19 aof the recessed portion 19, the tape 23 may also be attached so as to be in close contact with the entire area of the lower surface 19 aand the side surface 19 b.The annular frame 25 formed of a metal such as stainless steel (SUS) is attached to an outer peripheral portion of the band 23. A circular opening 25 athat can accommodate the wafer 11 is provided in a central portion of the frame 25. The wafer 11 is fixed to the central portion of the tape 23 exposed inside the opening 25a. The wafer 11 is thus supported by the frame 25 via the belt 23. The wafer 11 is accommodated in the cassette 8 (see FIG. 1 ) in a state of being supported by the frame 25.A rectangular opening 4 b, the longitudinal direction of which is along the X-axis direction, is provided in a region located at one side of the opening 4 aof the base 4. A ball screw type moving unit (moving mechanism) 10 is provided inside the opening 4 b. An upper portion of the moving unit 10 is covered by a dust-proof and drip-proof cover 12 in the form of bellows and a moving table 14 in the form of plate.On the moving table 14, a holding table (chuck table) 16 that holds the wafer 11 is provided. The upper surface of the holding table 16 forms a holding surface 16 athat holds the wafer 11. Meanwhile, details of the configuration of the holding table 16 will be described later (see FIG. 4A ). In addition, a plurality of clamps 18 are provided on the periphery of the holding table 16 to grip and fix the frame 25 supporting the wafer 11.The moving unit 10 moves the holding table 16 along the X-axis direction together with the moving table 14. The rotational drive source rotates the holding table 16 about a rotational axis substantially parallel to the Z-axis direction.In a region adjacent to the opening 4 bof the base 4, a support structure 20 is provided. An upper portion of the support structure 20 is disposed along the Y-axis direction so as to overlap the opening 4 b. In addition, on the front side of the upper portion of the support structure 20, a ball screw type moving unit (moving mechanism) 22 is provided.The moving unit 22 has a pair of guide rails 24 fixed to the front side of the support structure 20. The pair of guide rails 24 are arranged parallel to each other along the Y-axis direction. Further, the pair of guide rails 24 are provided with a moving plate 26 in the form of a flat plate in a state of being slidable in the Y-axis direction along the guide rails 24. The lower surface side (rear surface side) of the moving plate 26 is provided with a nut portion (not illustrated). A ball screw 28 disposed substantially parallel to the guide rails 24 is screwed into the nut portion. In addition, a pulse motor (not illustrated) is coupled to an end portion of the ball screw 28. When the pulse motor rotates the ball screw 28, the moving plate 26 moves in the Y-axis direction along the guide rails 24.A pair of guide rails 30 arranged parallel to each other along the Z-axis direction are fixed to the upper surface side (front side) of the moving plate 26. Further, the pair of guide rails 30 is provided with a moving plate 32 in the form of a flat plate that is slidable in the Z-axis direction along the guide rails 30. The lower surface side (rear surface side) of the moving plate 32 is provided with a nut portion (not illustrated). Screwed into the nut portion is a ball screw 34 disposed substantially parallel to the guide rails 30. In addition, a pulse motor 36 is coupled to an end portion of the ball screw 34. When the pulse motor 36 rotates the ball screw 34, the moving plate 32 moves in the Z-axis direction along the guide rails 30.A processing unit (cutting unit) 38 that subjects the wafer 11 to cutting processing is attached to a lower portion of the moving plate 32. The machining unit 38 has a tubular housing 40. The housing 40 houses a cylindrical spindle (not shown) disposed along the Y-axis direction. A distal end portion (one end side) of the spindle is exposed to the outside of the housing 40. A rotational drive source (not illustrated), such as a motor that rotates the spindle, is coupled to a proximal end portion (the other end side) of the spindle.The distal end portion of the spindle is provided with an annular cutting blade 42. The cutting blade 42 is a processing tool that cuts the wafer 11 by cutting into the wafer 11. The cutting blade 42 is formed by fixing abrasive grains of diamond, cubic boron nitride (cB), or the like using a bonding material. Meanwhile, the materials of the abrasive grains and the joining material, and the particle diameter of the abrasive grains are not limited to specific materials and particle diameters, and are appropriately selected according to the material of the wafer 11, the type of cutting, and the like. As the cutting blade 42, for example, a hub-type cutting blade (hub blade) is used. The hub blade is formed by connecting an annular base made of metal or the like to an annular cutting edge formed along the outer peripheral edge of the base. As the cutting edge of the hub blade, an electro-formed grinding stone formed by fixing abrasive grains using a joining agent such as nickel plating is used. On the other hand, as the cutting blade 42, a disk type blade (disk blade) may also be used.The disk blade is an annular cutting edge formed by fixing abrasive grains using a joining material of metal, ceramic, plastic, or the like.The cutting blade 42 mounted on the processing unit 38 is moved by the moving unit 22. The position of the cutting blade 42 in the Y-axis direction and a depth of cutting the cutting blade 42 into the wafer 11 are thus adjusted.An imaging unit (camera) 44 that images the wafer 11 held on the holding table 16 is provided at a position adjacent to the processing unit 38. An image obtained by imaging the wafer 11 held on the holding table 16 by the imaging unit 44 is used for alignment between the wafer 11 and the processing unit 38, for example.At a side of the opening 4b opposite to the opening 4a, an opening 4c defining a cylindrical cleaning space (cleaning chamber) is provided. Inside the opening 4c, a cleaning unit 46 for cleaning the wafer 11 is provided. The cleaning unit 46 includes a holding table (turntable) 48 that holds the wafer 11. A rotational drive source (not shown) such as a motor that rotates the holding table 48 about a rotational axis substantially parallel to the Z-axis direction is coupled to the holding table 48. In addition, a plurality of clamps 50 are provided on the periphery of the holding table 48 to grip and fix the frame 25 supporting the wafer 11. Above the holding table 48, a nozzle 52 is disposed that supplies a cleaning fluid (for example, a mixed fluid in which water and air are mixed with each other) to the wafer 11 held on the holding table 48. The wafer 11 is cleaned by supplying the fluid from the nozzle 52 to the wafer 11 while rotating the holding table 48 holding the wafer 11.When the wafer 11 is to be processed by the cutting apparatus 2, the wafer 11 accommodated in the cassette 8 is first transported to the holding table 16 by a transport mechanism (not shown), and the wafer 11 is held on the holding table 16. In addition, the frame 25 is fixed by the plurality of clamps 18. Then, the cutting blade 42 mounted on the processing unit 38 is rotated and caused to cut into the wafer 11 while supplying a liquid (cutting liquid) such as pure water to the wafer 11. The wafer 11 is thus cut. The processed wafer 11 is transported to the cleaning unit 46 by the transport mechanism (not shown) and then cleaned by the cleaning unit 46. Thereafter, the wafer 11 is transported by the transport mechanism (not shown) and accommodated in the cassette 8.Next, an example of a configuration of the holding table 16 in the cutting apparatus 2 will be described. FIG. 4A is a perspective view illustrating the holding table 16. The holding table 16 is a holding table capable of holding the wafer 11 having the recessed portion 19 (see FIGS. 2B and 3B ).The holding table 16 includes a disk-shaped base (a base or a frame body) 60 formed of glass, a ceramic, a metal, a plastic, or the like. A central portion of the base 60 is provided with a cylindrical holding portion 62 projecting upward from an upper surface 60 aof the base 60. Meanwhile, the holding portion 62 may be connected to the base 60 or may be formed independently of the base 60 and then fixed to the upper surface 60 aof the base 60.A central portion on an upper surface 62 aof the holding portion 62 is provided with a cylindrical recessed portion (groove) 62 b. A disk-shaped holding member 64 is fitted into the recessed portion 62 b. The holding member 64 is a member formed of a porous material such as a porous ceramic. The holding member 64 has air holes (suction pipes) inside that lead from an upper surface to a lower surface of the holding member 64. The holding member 64 is connected to an intake source 70 (see FIG. 5 ) such as an ejector via a flow line 60 b(see FIG. 5 ), a valve (not illustrated), and the like provided in the base 60. An upper surface 64 aof the holding member 64 forms a circular suction surface that sucks the wafer 11. In addition, the upper surface 62 aof the holding portion 62 and the upper surface 64 aof the holding member 64 are disposed substantially in the same plane, and form the holding surface 16 aof the holding table 16.On the outside of the holding portion 62, an annular groove 66 is provided in a region of the upper surface 60 aside of the base 60. For example, the groove 66 having a predetermined width is formed along the outer peripheral edge of the holding portion 62 so as to be disposed adjacent to the holding portion 62 and surround the holding portion 62.FIG. 4B is an enlarged sectional view illustrating a part of the holding table 16. The groove 66 has an annular side surface (inner wall) 66 adisposed on the inner side in the radial direction of the base 60, and an annular side surface (inner wall) 66 bdisposed on the outer side in the radial direction of the base 60. The side surface 66 ais formed, for example, in substantially the same plane as the side surface of the holding portion 62. Specifically, the side surface 66 bis formed in an upwardly protruding shape so that the inclination of the side surface 66 bsgradually decreases from the bottom of the groove 66 to the upper surface 60 aof the base 60.A support member 68 that supports the outer peripheral portion 21 (see FIG. 5 ) of the wafer 11 is provided inside the groove 66. The support member 68 is a member whose hardness is changed by the application of energy. Meanwhile, details of the support member 68 will be described later.FIG. 5 is a sectional view illustrating the holding table 16 for holding the wafer 11. The holding portion 62 of the holding table 16 is formed in such a size that it can be inserted into the recessed portion 19 of the wafer 11. For example, the diameter of the holding portion 62 is set smaller than the diameter of the recessed portion 19 of the wafer 11. For example, the outer diameter of the groove 66 (diameter of an upper end of the side surface 66 b) is set to be equal to or larger than the diameter of the wafer 11, and the width of the groove 66 is set to be equal to or larger than the width of the outer peripheral portion 21 of the wafer 11. In addition, the position of the groove 66 is set such that the outer peripheral portion 21 of the wafer 11 and the groove 66 overlap each other when the wafer 11 is disposed above the holding table 16.The wafer 11 is disposed on the holding table 16 so that the lower surface 11 bside is directed toward the holding surface 16 a. At this time, the wafer 11 is arranged such that the upper surface 62 aside of the holding portion 62 is inserted and fitted into the recessed portion 19. The lower surface 19 aof the recessed portion 19 of the wafer 11 is thus supported by the holding surface 16 avia the belt 23. Then, when a negative pressure of the suction source 70 is caused to act on the upper surface 64 aof the holding member 64, the lower surface 19 aof the recessed portion 19 of the wafer 11 is held by the holding portion 62 via the belt 23 under suction. In addition, the lower surface side of the outer peripheral portion 21 of the wafer 11 is inserted into the groove 66 provided on the base 60. Thereby, the tape 23 attached to the lower surface side of the outer peripheral portion 21 of the wafer 11 comes into contact with the support member 68 filled in the groove 66.FIG. 6 is an enlarged sectional view illustrating a part of the wafer 11 held on the holding table 16. Here, the support member 68 is a member that is hardened by application of a predetermined energy, and thus transitions from a softened state (uncured state) to a hardened state. For example, the support member 68 is formed of a material that has a flowable and freely deformable state before the application of the energy and that is solidified and fixed in its shape when the predetermined energy is applied. Specifically, the support member 68 is formed of a material hardened by the application of an electromagnetic wave (visible rays, infrared rays, ultraviolet rays, microwaves, or the like). For example, an ultraviolet curable resin cured by the application of ultraviolet rays, a visible light curable resin cured by the application of visible light, a thermosetting resin cured by heating, or the like may be used as the support member 68. In addition, a material (anti-Pd 2 L 2 or the like) hardened by the application of an ultrasonic wave could be used as the supporting member 68.When the wafer 11 is placed on the holding table 16, the support member 68 is held in an uncured state (an uncured state or a softened state), i.e., in a state of being deformable by the application of an external force. Then, when the outer peripheral portion 21 of the wafer 11 is inserted into the groove 66, the support member 68 is deformed according to the position (height) of the outer peripheral portion 21 of the wafer 11. The tape 23 attached to the outer peripheral portion 21 of the wafer 11 is thus embedded in the support member 68. Meanwhile, as illustrated in FIG. 6, when the wafer 11 is held on the holding table 16, a part of the belt 23 is in contact with the side surface 66 bof the groove 66. Thereby, it is possible to prevent a local force from being applied to the tape 23, so that the tape 23 is less likely to be damaged.Next, the support member 68 is hardened by applying the predetermined energy to the support member 68. For example, below the holding table 16, an energy application unit 72 is provided which applies the predetermined energy to the support member 68. When the energy is applied to the support member 68 by the energy application unit 72, the support member 68 is hardened and solidified in a state of being in contact with the tape 23.The type of energy applied from the energy applying unit 72 to the support member 68 is determined according to a property of the support member 68. For example, in a case where the support member 68 is an ultraviolet curable resin, a light source (lamp) that applies ultraviolet rays is used as the energy application unit 72, and the support member 68 is irradiated with ultraviolet rays from the energy application unit 72 via the base 60. Further, in a case where the support member 68 is a visible light curable resin, a light source (lamp) that applies visible light is used as the power application unit 72, and the support member 68 is irradiated with visible light from the power application unit 72 via the base 60. In addition, in a case where the support member 68 is a thermosetting resin, a heater such as an infrared lamp is used as the power application unit 72, and the support member 68 is heated by the power application unit 72. In addition, when the support member 68 is a member hardened by application of an ultrasonic wave, an ultrasonic vibrator emitting the ultrasonic wave is used as the energy application unit 72, and the ultrasonic wave is applied from the energy application unit 72 to the support member 68.When the support member 68 is solidified, the support member 68 supports the outer peripheral portion 21 of the wafer 11 from a lower side via the belt 23. thereby the recessed portion 19 of the wafer 11 is held by the holding portion 62, and the outer peripheral portion 21 of the wafer 11 is supported by the support member 68 in a hardened state. The entire wafer 11 is thus securely fixed to the holding table 16.Meanwhile, the position (height) of the outer peripheral portion 21 of the wafer 11 held on the holding table 16 differs according to the depth of the recessed portion 19 of the wafer 11. in particular, as the depth of the recessed portion 19 of the wafer 11 increases, the lower surface 19 aof the recessed portion 19 is disposed closer to the upper surface 11 aside of the wafer 11, and the lower surface 11 bof the wafer 11 (lower surface of the outer peripheral portion 21) is disposed further below. Therefore, a distance (height difference) between the lower surface of the outer peripheral portion 21 of the wafer 11 and the lower surface of the groove 66 differs according to the depth of the recessed portion 19. When the support member 68 is used as described above, the support member 68 is deformed in an uncured state according to the depth of the recessed portion 19 so that the wafer 11 is held in a planar (non-bent) state at a time when the wafer 11 is placed on the holding table 16. When the power is thereafter applied to the support member 68, the support member 68 is hardened in a state of being deformed according to the depth of the recessed portion 19 and supporting the outer peripheral portion 21 of the wafer 11. That is, the support member 68 functions as a support member whose thickness is variable according to the depth of the recessed portion 19 of the wafer 11. The holding table 16 can therefore hold a plurality of kinds of wafers 11 different in depth from the recessed portion 19. Consequently, it is not necessary to perform work of height adjustment (protrusion amount) of the holding portion 62 according to the depth of the recessed portion 19 of the wafer 11, so that the wafer 11 having the recessed portion 19 can be easily held.The wafer 11 held on the holding table 16 is cut by the cutting blade 42 mounted on the processing unit 38 (see FIG. 1 ). For example, the wafer 11 is divided along the planned dividing lines 13 (see FIG. 2A ) by the cutting blade 42. In this way, a plurality of device chips each including the device 15 are obtained.When the wafer 11 is to be divided, first, the annular outer peripheral portion 21 is removed from the wafer 11. Specifically, the positions of the holding table 16 and the cutting blade 42 are adjusted such that the cutting blade 42 is disposed directly above an outer peripheral portion of the recessed portion 19 of the wafer 11. Next, the cutting blade 42 is lowered while being rotated, and the cutting blade 42 is caused to cut into the outer peripheral portion of the recessed portion 19 of the wafer 11. An amount of lowering of the cutting blade 42 at this time is set so that a lower end of the cutting blade 42 reaches the tape 23. Then, the holding table 16 is rotated in a state where the cutting blade 42 has cut into the wafer 11 while the rotation of the cutting blade 42 is maintained. The wafer 11 is thus cut and cut annularly along the outer peripheral portion of the recessed portion 19. Consequently, the annular outer peripheral portion 21 is separated from the wafer 11. Then, the outer peripheral portion 21 separated from the wafer 11 is peeled off from the tape 23 and removed.Thereafter, the wafer 11 from which the outer peripheral portion 21 has been removed is cut along the planned dividing lines 13 (see FIG. 2A ). Consequently, the thinned central portion of the wafer 11 is divided into a plurality of device chips, and the thinned device chips are obtained.As described above, when the outer peripheral portion 21 of the wafer 11 is removed in advance before the wafer 11 is divided into the plurality of device chips, the cutting blade 42 can be prevented from coming into contact with the outer peripheral portion 21 of the wafer 11 at the time of cutting the wafer 11 along the scheduled division lines 13 in a subsequent step. The cutting of the wafer 11 can thus be performed smoothly.Meanwhile, the support member 68 is preferably a reversible member that is changed from a hardened state (non-softened state) to a softened state by performing predetermined processing. In this case, the support member 68 can be reused to support the next wafer by softening the support member 68 and thus returning the support member 68 to the state before hardening when the processed wafer 11 is transported from the holding table 16 or after the processed wafer 11 is transported from the holding table 16.As described above, the holding table 16 according to the present embodiment uses the support member 68 whose hardness is changed by the application of power as a member for supporting the outer peripheral portion 21 of the wafer 11. Multiple kinds of wafers 11 different in depth from the recessed portion 19 can be supported by deforming the support member 68 according to the depth from the recessed portion 19 of the wafer 11. Thus, the holding table 16 is realized, which can easily hold the wafer 11 having the recessed portion 19. In addition, the holding table 16 holds the recessed portion 19 of the wafer 11 by the holding portion 62 and supports the outer peripheral portion 21 of the wafer 11 by the support member 68.Meanwhile, in the above embodiment, a case where the support member 68 is a member that is changed from a softened state (uncured state) to a cured state by application of energy has been described. However, the support member 68 could be a member that is changed from a hardened state (uncured state) to a softened state by application of energy.In this case, the power application unit 72 heats and softens the support member 68 in a hardened state when the holding table 16 holds the wafer 11. Then, in a state where the tape 23 attached to the outer peripheral portion 21 of the wafer 11 is in contact with the support member 68, the heating of the support member 68 is stopped, and the support member 68 is cooled. As a result, the support member 68 is hardened in a softened state, and the outer peripheral portion 21 of the wafer 11 is supported by the support member 68 via the belt 23. For example, a thermoplastic resin such as polyethylene, polypropylene, polyvinyl chloride, polystyrene, acrylic, polyacetal or polytetrafluoroethylene or wax may be used as the supporting member 68. In this case, the support member 68 can be made to be in a liquid state by being heated in the solidified state. In addition, the support member 68 can be solidified by being cooled in a liquid state.Further, as the supporting member 68, an electrorheological fluid (ER fluid) whose viscosity is reversibly changed by application of a stress may also be used. The ER fluid is produced, for example, by dispersing particles formed of aluminosilicate or the like in an insulating oil such as a silicone oil.In addition, the apparatus including the holding table 16 is not limited to a specific apparatus. For example, the holding table 16 may be incorporated into a processing device (a grinding device, a polishing device, a laser processing device, or the like) other than a cutting device or a cleaning device.The grinding apparatus includes a processing apparatus (grinding unit) that grinds the wafer 11. The grinding unit has a spindle. An annular grinding wheel having a plurality of grinding stones is attached to a distal end portion of the spindle. The wafer 11 is ground by being held on the holding table 16 installed in the grinding apparatus, and then bringing the grinding stones into contact with the wafer 11 while the grinding stones are rotated.The polishing apparatus includes a processing apparatus (polishing unit) that polish the wafer 11. The polishing unit includes a spindle. A disc-shaped polishing pad is attached to a distal end portion of the spindle. The wafer 11 is polished by being held on the holding table 16 installed in the polishing apparatus, and then bringing the polishing pad into contact with the wafer 11 while the polishing pad is rotated.The laser processing apparatus includes a processing unit (laser irradiation unit) that applies a laser beam for processing the wafer 11. The laser irradiation unit includes, for example, a laser oscillator that pulse-oscillates a laser having a predetermined wavelength, and a condenser that concentrates the laser oscillated from the laser oscillator. The wafer 11 is subjected to laser processing by being held on the holding table 16 installed in the laser processing apparatus and then irradiated with a laser beam from the laser irradiation unit.The cleaning apparatus includes a nozzle or the like that supplies a fluid (clean water or the like) for cleaning the wafer 11. The wafer 11 is cleaned by being held on the holding table 16 installed in the cleaning apparatus, and then the fluid from the nozzle is supplied to the wafer 11 while the holding table 16 is rotated.

Claims

A holding table (16) holding a wafer (11) having a recessed portion (19) and an annular outer peripheral portion (21) surrounding the recessed portion (19), the holding table (16) comprising: a base (60); and a holding portion (62) protruding from an upper surface (60a) of the base (60) and configured to be inserted into the recessed portion (19) of the wafer (11), wherein the base (60) includes: an annular groove (66) disposed in a region corresponding to the outer peripheral portion (21) of the wafer (11); and a support member (68) disposed inside the groove (66) and configured to be changed from a softened state to a hardened state or from the hardened state to the softened state by application of energy, and wherein the recessed portion (19) of the wafer (11) is held by the holding portion (62) and the outer peripheral portion (21) of the wafer (11) is supported by the support member (68) in the hardened state.The holding table (16) according to claim 1, wherein the support member (68) is a member that is brought into a liquid state when heated in a solidified state.

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