METHOD OF MANUFACTURING CHIPS

A method of manufacturing a plurality of chips by dividing a workpiece having a substrate harder than a monocrystalline Si substrate includes a cut groove forming step of, while holding the workpiece on a holding table with a surface of the workpiece being exposed, cutting the workpiece along each of projected dicing lines with a first cutting blade as it is vibrating at a frequency in the ultrasonic band, to form a cut groove in the workpiece such that the cut groove extends from the surface of the workpiece and terminates short of another surface of the workpiece, and a dividing step of, while holding the workpiece on the holding table with the other surface of the workpiece being exposed, cutting off an uncut residual portion from the workpiece along each of the lines with a second cutting blade to divide the workpiece into a plurality of chips.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a method of manufacturing a plurality of chips, e.g., device chips, from a workpiece having a substrate harder than a monocrystalline silicon (Si) substrate, by dividing the workpiece along a grid of projected dicing lines established on the workpiece.

Description of the Related Art

To cut workpieces such as semiconductor wafers having monocrystalline Si substrates or the like, it has been known in the art to use a cutting blade to cut a workpiece along a grid of projected dicing lines or streets established on a face side of the workpiece (see, for example, Japanese Patent Laid-open No. Hei 11-74228).

For example, while the face side of the workpiece is being exposed and a reverse side thereof is being held under suction on a holding table, the cutting blade as it is rotating at a high speed has its lower end placed in a position lower than the reverse side of the workpiece, and then, the holding table is processing-fed with cutting water such as pure water being supplied to the cutting blade. The cutting blade now cuts the workpiece along the direction in which the holding table is moved, forming a cut groove that extends in the workpiece from the face side to the reverse side thereof.

When the cutting blade cuts the workpiece in this way, chippings may occur in regions near the cut plane at the face side of the workpiece and regions near the cut plane at the reverse side of the workpiece. A cutting blade including abrasive grains having a relatively small average particle diameter may be used in order to reduce the size and number of those chippings. Since swarf is easier to remove from the face side of the workpiece by the action of the cutting water supplied thereto, the cutting blade including the abrasive grains having the relatively small average particle diameter is effective to reduce the size and number of the chippings on the face side of the workpiece.

However, as less cutting water is supplied to the reverse side of the workpiece than to the face side thereof, making the swarf harder to remove from the reverse side of the workpiece, the cutting blade including the abrasive grains having the relatively small average particle diameter tends to be clogged and loaded soon on the reverse side of the workpiece, and to become less efficient in cutting the workpiece on the reveres side. As a result, the workpiece is likely to have more and larger chippings at the reverse side.

There has been proposed, as a solution to the above difficulties, a method of cutting a workpiece with a cutting blade by, instead of cutting the workpiece fully thereacross all the way from the face side to the reverse side of the workpiece with the cutting blade, forming a first cut groove, i.e., a half-cut groove, in the workpiece that has a predetermined depth from the face side of the workpiece and that is short of the reverse side thereof, overturning the workpiece, and forming a second cut groove in the workpiece that extends from the reverse side of the workpiece to the bottom of the first cut groove (see, for example, Japanese Patent Laid-open No. 2013-58653).

Monocrystalline substrates made of silicon carbide (SiC), sapphire, or the like are harder than monocrystalline substrates of Si. It is comparatively difficult, though not completely impossible, to cut such high-hardness substrates with a cutting blade including abrasive grains having a relatively small average particle diameter.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above problems. It is an object of the present invention to provide a method of manufacturing chips by dividing a workpiece including a substrate harder than a monocrystalline Si substrate into a plurality of chips while reducing the number and size of chippings that occur in face and reverse sides of the workpiece when it is divided.

In accordance with an aspect of the present invention, there is provided a method of manufacturing chips by dividing a workpiece having a substrate harder than a monocrystalline Si substrate along a grid of projected dicing lines. The method includes a cut groove forming step of, while holding the workpiece on a holding table such that a surface of the workpiece is exposed, cutting the workpiece along each of the projected dicing lines with a first cutting blade as it is vibrating at a frequency in an ultrasonic band, to form a cut groove in the workpiece such that the cut groove extends from the surface of the workpiece and terminates short of another surface of the workpiece that is positioned opposite the surface thereof, and a dividing step of, after the cut groove forming step, while holding the workpiece on the holding table such that the other surface of the workpiece is exposed, cutting off an uncut residual portion from the workpiece along each of the projected dicing lines with a second cutting blade different from the first cutting blade to divide the workpiece into a plurality of chips.

In accordance with another aspect of the present invention, there is provided a method of manufacturing chips by dividing a workpiece having a substrate harder than a monocrystalline Si substrate along a grid of projected dicing lines. The method includes a cut groove forming step of, while holding the workpiece on a holding table such that a surface of the workpiece is exposed, cutting the workpiece along each of the projected dicing lines with a first cutting blade as it is vibrating at a frequency in an ultrasonic band, to form a cut groove in the workpiece such that the cut groove extends from the surface of the workpiece and terminates short of another surface of the workpiece that is positioned opposite the surface thereof, and a dividing step of, after the cut groove forming step, while holding the workpiece on the holding table such that the surface of the workpiece is exposed, cutting off an uncut residual portion from the workpiece along each of the projected dicing lines with a second cutting blade different from the first cutting blade to divide the workpiece into a plurality of chips.

Preferably, the substrate includes a substrate of SiC.

Preferably, the other surface of the workpiece is a face side of the workpiece, the projected dicing lines are established on the face side and demarcate a plurality of rectangular areas on the face side, with devices provided in the respective rectangular areas, the surface of the workpiece is a reverse side of the workpiece, the workpiece has a metal layer disposed on the reverse side thereof, the cut groove forming step includes cutting the substrate and the metal layer to form the cut groove that extends from the reverse side of the workpiece, and the dividing step includes cutting off the uncut residual portion from the face side of the workpiece.

Preferably, the second cutting blade has an edge thickness larger than an edge thickness of the first cutting blade, and the dividing step includes cutting the workpiece in order to increase a width of the cut groove.

Preferably, the second cutting blade has abrasive grains whose average particle diameter is smaller than an average particle diameter of abrasive grains of the first cutting blade.

Preferably, the cut groove forming step includes a cutting position detecting step of capturing an image of the other surface of the workpiece with an infrared camera from the surface of the workpiece and detecting at least one of the projected dicing lines on the basis of the captured image.

Preferably, the holding table used in the cut groove forming step has a holder including at least a portion that is transparent to visible light from a face side to a reverse side thereof, and the cut groove forming step includes a cutting position detecting step of capturing an image of the other surface of the workpiece through the holder with a visible light camera and detecting at least one of the projected dicing lines on the basis of the captured image.

With the methods of manufacturing chips according to the aspect and the other aspect of the present invention, since the first cutting blade as it is vibrating at a frequency in the ultrasonic band cuts the workpiece along each of the projected dicing lines in the cut groove forming step, the first cutting blade can cut the workpiece even though it has abrasive grains having a relatively small average particle diameter. In the dividing step after the cut groove forming step, the second cutting blade cuts off the uncut residual portion left to form another cut groove that extends to the bottom of the cut groove along each of the projected dicing lines, dividing the workpiece into a plurality of chips.

The uncut residual portions formed in the cut groove forming step contain cracks developed due to vibrations produced at the frequency in the ultrasonic band, and hence the workpiece can be cut with the second cutting blade including abrasive grains having a relatively small average particle diameter. Consequently, even though the second cutting blade has abrasive grains having the relatively small average particle diameter, it can divide the workpiece that includes the substrate harder than a monocrystalline Si substrate, into a plurality of chips. Further, the number and size of chippings near the surface and the other surface of the workpiece are reduced compared with a situation where the workpiece is cut fully thereacross all the way and a situation where the cutting blade is not vibrated at a frequency in the ultrasonic band when the cutting blade forms half-cut grooves in the workpiece.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

A first embodiment of the present invention will be described below with reference to the accompanying drawings.FIG.1is a flowchart of a method of manufacturing a plurality of device chips, i.e., chips,33(seeFIG.10B) according to the first embodiment. According to the first embodiment, a disk-shaped workpiece11(seeFIG.2A) is divided into the device chips33by the method as it performs a cut groove forming step S10, a workpiece overturning step S20, and a dividing step S30successively. First, the workpiece11will be described below with reference toFIGS.2A and2B.

FIG.2Aillustrates the workpiece11in perspective. The workpiece11has a monocrystalline SiC substrate, i.e., an SiC substrate,13(seeFIG.8A) that is harder than a monocrystalline Si substrate. The hardness of the workpiece11is assessed by the Mohs scale of hardness, for example. The Mohs hardness of a monocrystalline Si substrate is indicated by7, whereas the Mohs hardness of a monocrystalline SiC substrate is indicated by9. As illustrated inFIG.2A, the workpiece11, i.e., the monocrystalline SiC substrate13, has a notch defined in an outer circumferential portion thereof to represent the crystal orientation thereof. The workpiece11may alternatively have an orientation flat instead of the notch.

The substrate of the workpiece11is not limited to the SiC substrate13. The workpiece11may instead have another substrate that is harder than the monocrystalline Si substrate, such as a sapphire substrate whose Mohs hardness is indicated by9or a monocrystalline gallium nitride (GaN) substrate, i.e., a GaN substrate, whose Mohs hardness is indicated by9. As illustrated inFIG.8A, the SiC substrate13has an Si-surface13a, i.e., an silicon-terminated surface, and a C-surface13b, i.e., a carbon-terminated surface, that is opposite to the Si-surface13a. The Si-surface13alies on a face side (another surface)11aof the workpiece11. The workpiece11also includes a circuit layer15disposed on the face side11ain contact with the Si-surface13a. The circuit layer15includes a metal interconnect layer and a low-dielectric-constant insulating layer (also referred to as a low-k material layer) that are alternately disposed on the face side11a. The workpiece11is free of a circuit layer15, etc., on the C-surface13b. The C-surface13bcorresponds to a reverse side (a surface)11bof the workpiece11.

As illustrated inFIG.2A, a plurality of projected dicing lines, i.e., streets,17are established in a grid pattern on the face side11a. The projected dicing lines17demarcate a plurality of rectangular areas on the face side11awhere respective devices19such as metal-oxide-semiconductor field-effect transistors (MOSFETs) or insulated gate bipolar transistors (IGBTs) are disposed. The devices19are not limited to any particular kinds, quantities, shapes, structures, sizes, layouts, etc. A predetermined key pattern, not illustrated, to be used in specifying the positions of the projected dicing lines17is disposed on the face side11a. The thickness of the workpiece11, i.e., the distance from the face side11ato the reverse side11bon the projected dicing lines17, is in the range of 100 μm to 350 μm, for example. However, the thickness of the workpiece11is not limited to the specific range indicated.

As illustrated inFIG.2B, when the workpiece11is processed, the workpiece11is handled in the form of a workpiece unit27where the workpiece11is integrally combined with an annular frame25of metal by a circular tape, i.e., a dicing tape,23made of a resin material or the like.FIG.2Billustrates the workpiece unit27in perspective. The annular frame25has an inner circumferential edge that defines a circular opening that is larger in diameter than the workpiece11.

In the workpiece unit27illustrated inFIG.2B, the workpiece11is positioned in the circular opening of the annular frame25with the reverse side11bexposed upwardly. The tape23is affixed to the face side11aof the workpiece11and one surface, which faces downwardly inFIG.2B, of the annular frame25. The tape23has a diameter larger than that of the circular opening of the annular frame25. The tape23is a film of resin including a base layer of resin and a glue layer, i.e., an adhesive layer, laminated on the base layer. The film is substantially transparent to and is transmissive of visible light and ultraviolet (UV) radiation.

The base layer is made of such a resin as polyolefin (PO), polyvinyl chloride (PVC), or polyethylene terephthalate (PET). The adhesive layer is made of an acryl-based resin, an epoxy-based resin, or the like that is UV-curable. The adhesive layer is disposed coextensively on one surface of the base layer. The UV-curable resin has relatively strong adhesive power before it is irradiated with UV rays. However, the adhesive power of the UV-curable resin is lowered once irradiated with UV rays. The tape23may be free of the adhesive layer at least in its area held in contact with the workpiece11. In this case, the workpiece11is affixed to the tape23by way of thermocompression bonding, instead of adhesive bonding. After the workpiece unit27has been delivered to a cutting apparatus2(seeFIG.3), the workpiece11is cut along the projected dicing lines17by the cutting apparatus2.

FIG.3illustrates the cutting apparatus2in perspective. InFIG.3, the cutting apparatus2is illustrated in reference to a three-dimensional XYZ coordinate system having an X-axis extending in horizontal directions, i.e., processing feed directions, a Y-axis extending in horizontal directions, i.e., indexing feed directions, and a Z-axis extending in vertical or upward and downward directions, i.e., incising feed directions. The X-axis and the Y-axis extend perpendicularly to each other and extend perpendicularly to the Z-axis. The cutting apparatus2includes a base4supporting thereon various components of the cutting apparatus2. The cutting apparatus2also includes a ball-screw-type X-axis moving unit6mounted on an upper surface of the base4. The X-axis moving unit6has a pair of guide rails8extending substantially parallel to the X-axis.

A movable table10is slidably disposed on the guide rails8for sliding movement along the guide rails8. A nut, not illustrated, that is fixedly disposed on a reverse side, i.e., a lower surface, of the movable table10is operatively threaded over a screw shaft12extending substantially parallel to the X-axis and lying between the guide rails8. The screw shaft12has an end coupled to a drive source14such as a stepping motor. When the drive source14is energized, it rotates the screw shaft12about its central axis, causing the nut to move the movable table10along the X-axis along the guide rails8. A cylindrical support post10ais mounted substantially centrally on an upper surface of the movable table10.

A rectangular table cover10bis supported on the movable table10and lies above the support post10a. A disk-shaped chuck table, i.e., a holding table,16is disposed on an upper surface of the table cover10b. The support post10ahouses therein a drive source, not illustrated, such as an electric motor that is coupled to the chuck table16. When the drive source is energized, it rotates the chuck table16about its central axis that extends substantially parallel to the Z-axis. The chuck table16has a disk-shaped frame made of a metal material such as stainless steel. The frame has a disk-shaped cavity defined in an upper portion thereof. The cavity is smaller in diameter than the frame.

A disk-shaped porous plate made of porous ceramic is fixedly disposed in the cavity in the frame. The porous plate is fluidly connected to a suction source, not illustrated, such as a vacuum pump through a predetermined fluid channel, not illustrated, defined in the frame. When the suction source is actuated, it generates and transmits a negative pressure through the fluid channel to the porous plate. The frame and the porous plate have respective upper surfaces that lie flush with each other, jointly making up a substantially flat holding surface16aof the chuck table16. The holding surface16alies substantially parallel to an XY plane defined along the X-axis and the Y-axis.

When the workpiece unit27is placed on the chuck table16, the workpiece11is held under suction on the holding surface16awith the tape23interposed therebetween by the negative pressure from the suction source that is applied to the porous plate. A plurality of, four inFIG.3, clamp units18are disposed circumferentially around the chuck table16at substantially equal intervals. Each of the clamp units18clamps and secures in position the frame25of the workpiece unit27placed on the chuck table16.

A ball-screw-type Y-axis moving unit20that is different from the X-axis moving unit6is mounted on the upper surface of the base4. The Y-axis moving unit20has a pair of guide rails22extending substantially parallel to the Y-axis. A movable block24is slidably disposed on the guide rails22for sliding movement along the guide rails22. The movable block24has a horizontal plate24aon the guide rails22. A nut, not illustrated, is fixedly disposed on a lower surface of the horizontal plate24a.

The nut on the horizontal plate24ais operatively threaded over a screw shaft26extending substantially parallel to the Y-axis and lying between the guide rails22. The screw shaft26has an end coupled to a drive source28such as a stepping motor. When the drive source28is energized, it rotates the screw shaft26about its central axis, causing the nut to move the movable block24along the Y-axis along the guide rails22. The movable block24also has a vertical plate24bextending upwardly from the horizontal plate24a. A Z-axis moving unit30is mounted on a side surface of the vertical plate24bthat extends substantially parallel to a YZ plane defined along the Y-axis and the Z-axis. The Z-axis moving unit30has a pair of guide rails30a, one illustrated inFIG.3, extending substantially parallel to the Z-axis.

A holder32is slidably disposed on the guide rails30afor sliding movement along the guide rails30a. A nut, not illustrated, that is fixedly disposed on a reverse side of the holder32is operatively threaded over a screw shaft, not illustrated, extending substantially parallel to the Z-axis and lying between the guide rails30a. The screw shaft has an end coupled to a drive source30bsuch as a stepping motor. When the drive source30bis energized, it rotates the screw shaft about its central axis, causing the nut to move the holder32along the Z-axis along the guide rails30a. A hollow cylindrical spindle housing34that has a longitudinal axis extending substantially parallel to the Y-axis is fixedly supported by the holder32.

An infrared camera36for capturing an image of the workpiece11on the chuck table16with infrared rays is mounted on a side of the spindle housing34. The infrared camera36has one or more lenses, not illustrated, a light source, not illustrated, such as a light emitting diode (LED) for emitting infrared rays, and a solid-state image capturing device, i.e., a solid-state image sensor, not illustrated, for photoelectrically converting infrared rays into electric signals. The infrared camera36functions as a microscopic camera. A cylindrical spindle38(seeFIG.4) that has a longitudinal axis extending substantially parallel to the Y-axis has a portion rotatably supported in the spindle housing34. The spindle38has a proximal end portion, not illustrated, where a drive source, not illustrated, such as an electric motor is provided.

The spindle38has a distal end portion projecting axially from the spindle housing34. A first cutting blade40is mounted on the distal end portion of the spindle38. According to the first embodiment, the first cutting blade40is a hubless, i.e., washer-type, blade having an annular cutting edge. As illustrated inFIG.4, the first cutting blade40has a first surface40aand a second surface40bthat are opposite each other and that lie substantially parallel to each other. The first cutting blade40has a circular through opening40cdefined diametrically centrally therein by an inner circumferential edge of the first cutting blade40. The first cutting blade40is made of abrasive grains of diamond, cubic boron nitride (cBN), or the like that are bound together by a binder of metal, ceramic, resin, or the like.

FIG.4illustrates, in perspective, a cutting unit42including the first cutting blade40.FIG.5illustrates the cutting unit42in side elevation and partly in cross section. As illustrated inFIG.4, the distal end portion of the spindle38has external threads38aon its outer circumferential surface. A disk-shaped mount44made mainly of metal has a central through hole44adefined therein. The mount44is fixedly mounted on the spindle38as follows. When the mount44is fitted over the distal end portion of the spindle38, the distal end portion of the spindle38is inserted in the central through hole44a. At this time, the external threads38aon the distal end portion of the spindle38protrude from the mount44. Thereafter, an annular mounting nut44bthat is internally threaded is threaded over the external threads38aon the distal end portion of the spindle38. The annular mounting nut44bis then tightened to fasten the mount44to the spindle38.

The mount44has a disk-shaped flange46that has an annular ridge46apositioned on an outer circumferential portion of the flange46. The annular ridge46aprotrudes in a thicknesswise direction of the flange46that is perpendicular to the radial directions of the flange46. As illustrated inFIG.5, a resin layer46bmade of a synthetic resin is disposed on an annular surface of a distal end of the ridge46a. The mount44also includes a first tubular boss48protruding in the thicknesswise direction of the flange46beyond the ridge46a. The first tubular boss48is smaller in diameter than the flange46. The first cutting blade40and other parts are disposed on an outer circumferential side surface of the first tubular boss48.

The first tubular boss48has external threads48aon the outer circumferential side surface of a distal end portion thereof. The mount44also includes a second tubular boss50protruding in an opposite thicknesswise direction of the flange46. The second tubular boss50is smaller in diameter than the flange46but larger in diameter than the first tubular boss48. The central through hole44ain the mount44extends axially through the flange46, the first tubular boss48, and the second tubular boss50and includes a portion complementarily fitted over a frustoconical portion of the spindle38that is positioned closer to the proximal end portion thereof than the external threads38a.

A disk-shaped presser flange52made mainly of metal is mounted on the first tubular boss48. The presser flange52has an annular ridge52aprotruding in a thicknesswise direction of the presser flange52that is perpendicular to the radial directions of the presser flange52. The annular ridge52ais substantially equal in inside diameter and outside diameter to the annular ridge46aof the flange46. As illustrated inFIG.5, a resin layer52bmade of a synthetic resin is disposed on an annular surface of a distal end of the annular ridge52a. The presser flange52has a radially central opening52cthat extends axially therethrough and that is defined diametrically centrally therein by an inner circumferential edge of the presser flange52.

The first cutting blade40is assembled on the mount44as follows. The mount44has already been fastened to the spindle38by the annular mounting nut44b, as described above. The inner circumferential edge of the first cutting blade40that defines the circular through opening40cin the first cutting blade40and the inner circumferential edge of the presser flange52that defines radially central opening52cin the presser flange52are fitted over the first tubular boss48such that the first cutting blade40is sandwiched between the resin layer46bon the ridge46aof the flange46of the mount44and the resin layer52bon the annular ridge52aof the presser flange52. With the first cutting blade40and the presser flange52being disposed on the outer circumferential side surface of the first tubular boss48, an annular mounting nut54that is internally threaded is threaded over the external threads48aon the distal end portion of the first tubular boss48. The first cutting blade40as sandwiched between the flange46and the presser flange52is now fixedly mounted on the distal end portion of the spindle38.

The first cutting blade40can be vibrated at a frequency in the ultrasonic band in the range of 20 kHz to 500 kHz, for example. In order to make the first cutting blade40thus vibratable, an annular ultrasonic vibrator60ais disposed radially inwardly of the annular ridge46aof the flange46of the mount44. According to the present embodiment, the annular ultrasonic vibrator60ais of the electrostrictive type and has an annular piezoelectric body62a.

The annular piezoelectric body62ais made of piezoelectric ceramic such as barium titanate or lead zirconate titanate, for example. The annular piezoelectric body62ahas a pair of opposite annular side surfaces on which a pair of electrodes64a1and64a2are disposed in sandwiching relation to the annular piezoelectric body62a. An insulating film66ais disposed between the electrodes64a1and64a2and also between the electrodes64a1and64a2and the flange46to prevent the electrodes64a1and64a2from electrically contacting each other and also to prevent the electrodes64a1and64a2and the flange46from electrically contacting each other.

Another annular ultrasonic vibrator60bis disposed radially inwardly of the annular ridge52aof the presser flange52. The annular ultrasonic vibrator60bsimilarly includes an annular piezoelectric body62b, a pair of electrodes64b1and64b2, and an insulating film66b. A pair of electric interconnects68aand68bare embedded in the first tubular boss48of the mount44. Each of the electric interconnects68aand68bhas a pair of bifurcated end portions extending radially outwardly to the outer circumferential side surface of the first tubular boss48.

One of the bifurcated end portions of the electric interconnect68ain the mount44is electrically connected through a lead70ato the electrode64a1of the ultrasonic vibrator60a, whereas the other bifurcated end portion of the electric interconnect68ain the mount44is electrically connected through a lead70bto the electrode64b1of the ultrasonic vibrator60b. Similarly, one of the bifurcated end portions of the electric interconnect68bin the mount44is electrically connected through a lead70cto the electrode64a2of the ultrasonic vibrator60a, whereas the other bifurcated end portion of the electric interconnect68bin the mount44is electrically connected through a lead70dto the electrode64b2of the ultrasonic vibrator60b.

The electric interconnects68aand68bin the mount44are supplied with electric power from an alternating current (AC) power supply78such as a high-speed bipolar power supply through a rotary transformer70. The rotary transformer70includes a power receiving unit72disposed in the second tubular boss50of the mount44and a power supplying unit74disposed in a distal end portion of the spindle housing34. The power receiving unit72includes an annular core and a coil wound around the annular core. The coil has an end electrically connected to the electric interconnect68aand the other end electrically connected to the electric interconnect68b.

Likewise, the power supplying unit74also includes an annular core and a coil wound around the annular core. The coil of the power supplying unit74has opposite ends electrically connected through respective leads76aand76bto the AC power supply78. The AC power supply78is electrically connected to a signal generator80that controls the frequency of an AC voltage to be supplied from the AC power supply78to the rotary transformer70.

When the AC power supply78supplies electric power through the rotary transformer70to the electrodes64a1and64a2, the annular piezoelectric body62avibrates, i.e., contracts and expands, in the radial directions of the mount44and the presser flange52. Similarly, when the AC power supply78supplies electric power through the rotary transformer70to the electrodes64b1and64b2, the annular piezoelectric body62bvibrates, i.e., contracts and expands, in the radial directions of the mount44and the presser flange52.

InFIG.5, clearances are illustrated as being present between the ultrasonic vibrators60aand60band the first cutting blade40. Actually, however, the ultrasonic vibrators60aand60band the first cutting blade40are held against each other with some members, not illustrated, interposed therebetween. When the piezoelectric bodies62aand62bvibrate, the mount44, the presser flange52, and the first cutting blade40are vibrated together. According to the present embodiment, the piezoelectric bodies62aand62bvibrate in the radial directions of the first cutting blade40, instead of in the thicknesswise directions of the first cutting blade40. The first cutting blade40is vibrated to an amplitude of 5.0 μm, for example.

The cutting apparatus2includes a controller or a control unit, not illustrated, for controlling operations of the X-axis moving unit6, the chuck table16, the Y-axis moving unit20, the Z-axis moving unit30, the cutting unit42, the infrared camera36, the AC power supply78, the signal generator80, etc. The controller is a computer including a processor, i.e., a processing device, such as a central processing unit (CPU), and a memory, i.e., a storage device.

The memory includes a main storage device such as a dynamic random access memory (DRAM), a static random access memory (SRAM), or a read only memory (ROM), and an auxiliary storage device such as a flash memory, a hard disk drive, or a solid state drive. The auxiliary storage device stores software including predetermined programs. The controller has its functions performed by operating the processor, etc., according to the programs.

The steps illustrated inFIG.1will be described below with reference toFIGS.6through10B. First, as illustrated inFIG.6, the workpiece unit27is placed on the chuck table16. Then, the workpiece11is held under suction on the holding surface16awith the tape23interposed therebetween, and the frame25is clamped and secured in position by the clamp units18. At this time, the reverse side11bof the workpiece11is exposed upwardly. Then, the infrared camera36captures an infrared image of the face side11aof the workpiece11with infrared rays transmitted through the workpiece11from the reverse side11b, thereby acquiring the image of the face side11a.

The key pattern on the face side11ais spaced from the projected dicing lines17by predetermined distances. Then, the controller detects the position, on the XY plane, of at least one of the projected dicing lines17on the basis of the coordinates of the key pattern that is included in the image of the face side11aand the distances by which the key pattern is spaced from the projected dicing lines17(cutting position detecting step).

FIG.6illustrates, in side elevation and partly in cross section, the position detecting step of the method according to the first embodiment. After the cutting position detecting step, the chuck table16is turned about its central axis to make the one of the projected dicing lines17substantially parallel to the X-axis, thereby adjusting the orientation of the workpiece11. While the workpiece11is being held under suction on the holding surface16a, the first cutting blade40cuts the workpiece11along the projected dicing line17, forming a cut groove11c(seeFIG.8B) that terminates short of the face side11a, in the workpiece11along the projected dicing line17(cut groove forming step S10).

FIG.7illustrates, in side elevation and partly in cross section, the cut groove forming step S10of the method according to the first embodiment. In the cut groove forming step S10, the spindle38is rotated at a predetermined speed, and the first cutting blade40is vibrated at the frequency in the ultrasonic band. The first cutting blade40as it is rotating and vibrating is vertically moved to have its lower end placed in a vertical position between the reverse side11band the face side11aof the workpiece11. While the first cutting blade40is being supplied with cutting water such as pure water, the first cutting blade40is placed on an extension of the projected dicing line17. Then, the chuck table16is moved along the X-axis to cause the first cutting blade40to cut the workpiece11along the projected dicing line17.

FIG.8Aalso illustrates the cut groove forming step S10in enlarged fragmentary side elevation and partly in cross section. As illustrated inFIG.8A, the first cutting blade40has an edge thickness40d. When the first cutting blade40cuts the workpiece11along the projected dicing line17, it forms a cut groove11c(seeFIG.8B) in the workpiece11along the projected dicing line17. The cut groove11chas a width11dthat is essentially the same as the edge thickness40dof the first cutting blade40, that is, the thickness of the first cutting blade40between the first surface40aand the second surface40bthereof. According to the first embodiment, the abrasive grains of the first cutting blade40have an average particle diameter of 3.0 μm, and the edge thickness40dis 30 μm.

If the size of a particle is represented by a certain particle diameter, i.e., length, then the average particle diameter referred to above is specified on the basis of a frequency distribution of particle diameters of a particle group. A particle diameter is represented by any of various known diameters including geographic diameters, equivalent diameters, etc. The geographic diameters include a Feret diameter, a directed maximum diameter, i.e., a Krummbein diameter, a Martin diameter, a sieve diameter, etc., whereas the equivalent diameters include a projected area circle equivalent diameter, i.e., a Heywood diameter, an isosurface area sphere equivalent diameter, an isovolumetric sphere equivalent diameter, a Stokes' diameter, a light scattering diameter, etc. When a frequency distribution of particle diameters of a particle group is plotted as a graph having a horizontal axis representing particle diameters (p) and a vertical axis representing frequencies, the average diameter of a weight-based distribution or a volume-based distribution represents an average particle diameter, for example.

The portion of the workpiece11that is left between the bottom of the cut groove11cand the face side11ais referred to as an uncut residual portion11e(seeFIG.8B). The uncut residual portion11eshould preferably have a thickness in the range of 20 μm to 50 μm. If the thickness of the uncut residual portion11eexceeds 50 μm, then it may tend to load a second cutting blade84to be described later, lowering the quality of the reverse side11band the side surfaces of the cut groove11cthat are to be cut by the second cutting blade84. If the thickness of the uncut residual portion11eis less than 20 μm, then the workpiece11may crack from the cut groove11cin the subsequent workpiece overturning step S20. If the workpiece11cracks, device chips33to be fabricated from the workpiece11may positionally be shifted in the subsequent dividing step S30, lowering the quality of the device chips33.

After the cut groove11chas been formed in the workpiece11along the projected dicing line17from one end to the other, the cutting unit42is indexing-fed along the Y-axis to bring the first cutting blade40into alignment with another projected dicing line17adjacent to the projected dicing line17along which the cut groove11chas been formed. Then, the first cutting blade40forms a cut groove11cin the workpiece11along the other projected dicing line17. After cut grooves11chave been formed in the workpiece11along all the projected dicing lines17that extend along a direction, the chuck table16is turned approximately 90 degrees about its central axis. Then, cut grooves11care formed in the workpiece11along all the projected dicing lines17that extend along another direction that extends perpendicularly to the direction described above. When the cut grooves11chave been formed in the workpiece11along all the projected dicing lines17on the workpiece11, the uncut residual portions11eare left in the workpiece11along all the projected dicing lines17. An example of processing conditions in the cut groove forming step S10, i.e., first processing conditions, is illustrated below.Spindle rotational speed: 30000 rpmProcessing feed speed: 20 mm/sCutting mode: Downward cuttingCutting water flow rate: 1.0 L/minFirst cutting blade amplitude: 5.0 μm

FIG.8Billustrates the workpiece unit27that has undergone the cut groove forming step S10, in enlarged fragmentary side elevation and partly in cross section. After the cut groove forming step S10, the workpiece11is overturned (Workpiece overturning step S20).

FIG.9illustrates the workpiece overturning step S20in perspective. As illustrated inFIG.9, in the workpiece overturning step S20, a tape, i.e., a dicing tape,29is affixed to the reverse side11bof the workpiece11, and then, UV rays are applied to the face side11aof the workpiece11to reduce the bonding strength between the tape23and the workpiece11. Thereafter, the tape23is peeled off from the workpiece11. The tape29is a film of resin including a base layer of resin and a glue layer, i.e., an adhesive layer, laminated on the base layer, for example. The film is substantially transparent and is transmissive of visible light. When the tape29has been affixed and the tape23has been peeled off, the resultant assembly including the workpiece11integrally combined with the annular frame25by the tape29makes up a workpiece unit31where the face side11aof the workpiece11is exposed.

If the workpiece11is affixed to the tape23by way of thermocompression bonding instead of adhesive bonding, then the tape23can be peeled off from the workpiece11in the manner of a 180-degree peeling test. Specifically, an end of the tape23is gripped, and the tape23is folded back on itself through approximately 180 degrees, after which the gripped end is moved relatively to the workpiece11along the direction in which the tape23has been folded back. If the tape23is cooled, the tape23shrinks and can easily be peeled off. The tape23that is affixed to the workpiece11by way of thermocompression bonding instead of adhesive bonding is advantageous in that no adhesive is left on the workpiece11after the tape23has been peeled off.

After the workpiece overturning step S20, a cutting apparatus2a(seeFIG.10A) is used to cut the workpiece11to divide it into a plurality of device chips33(dividing step S30). The cutting apparatus2ais essentially the same as the cutting apparatus2described above, except as follows. The cutting apparatus2aincludes a visible light camera, not illustrated, instead of the infrared camera36. The visible light camera has one or more lenses, not illustrated, a light source, not illustrated, such as an LED for emitting visible light, and a solid-state image capturing device, i.e., an image sensor, for photoelectrically converting visible light into electric signals. The cutting apparatus2ahas a cutting unit42that is free of the ultrasonic vibrators60aand60bthat produce vibrations in the ultrasonic band. Further, the cutting unit42of the cutting apparatus2ahas a spindle38on which the second cutting blade84different from the first cutting blade40is mounted.

As illustrated inFIG.10A, the second cutting blade84has an edge thickness84dlarger than the edge thickness40dof the first cutting blade40. For example, the edge thickness84dof the second cutting blade84is 35 μm. The average particle diameter of the abrasive grains of the second cutting blade84is smaller than the average particle diameter of the abrasive grains of the first cutting blade40. For example, the average particle diameter of the abrasive grains of the second cutting blade84is 1.0 μm.

Although the cutting apparatus2ais different from the cutting apparatus2as regards the visible light camera, the second cutting blade84, etc., the other structural details of the cutting apparatus2aare essentially identical to those of the cutting apparatus2. Therefore, in the description of the cutting apparatus2a, those components of the cutting apparatus2athat are identical to those of the cutting apparatus2are denoted by identical reference characters. In the dividing step S30, while the workpiece unit31is being held under suction on the chuck table16with the face side11afacing upwardly, the visible light camera captures an image of the face side11aof the workpiece11, and the position, on the XY plane, of at least one of the projected dicing lines17is detected on the basis of the captured image (cutting position detecting step).

After the cutting position detecting step, one of the projected dicing lines17is made substantially parallel to the X-axis, thereby adjusting the orientation of the workpiece11. While the workpiece11is being held under suction on the holding surface16awith the tape29interposed therebetween, the second cutting blade84cuts the workpiece11to divide it into a plurality of device chips33(dividing step S30).

FIG.10Aillustrates the dividing step S30in enlarged fragmentary side elevation and partly in cross section. In the dividing step S30, the second cutting blade84is not vibrated at a frequency in the ultrasonic band, but the second cutting blade84as it is rotating is vertically moved to have its lower end placed in a vertical position between the holding surface16aand the reverse side11bof the workpiece11. While the second cutting blade84is being supplied with cutting water such as pure water, the second cutting blade84is placed on an extension of the projected dicing line17. Then, the chuck table16is moved along the X-axis to cause the second cutting blade84to cut the workpiece11along the projected dicing line17, removing the uncut residual portion11efrom the workpiece11and fully severing the workpiece11.

When the second cutting blade84is positioned in alignment with the projected dicing line17, the second cutting blade84has its center in its widthwise directions aligned with the center of the projected dicing line17in its widthwise directions. Since the edge thickness84dis larger than the edge thickness40d, the second cutting blade84cuts off both side surfaces of the cut groove11cas well as the uncut residual portion11ein the dividing step S30.

After the second cutting blade84has cut the workpiece11along the projected dicing line17from one end to the other, the cutting unit42including the second cutting blade84is indexing-fed along the Y-axis to bring the second cutting blade84into alignment with another projected dicing line17adjacent to the projected dicing line17along which the second cutting blade84has previously cut the workpiece11. Then, the second cutting blade84cuts the workpiece11along the other projected dicing line17. After the second cutting blade84has cut the workpiece11along all the projected dicing lines17that extend along a direction, the chuck table16is turned approximately 90 degrees about its central axis. Then, the second cutting blade84cuts the workpiece11along all the projected dicing lines17that extend along another direction that extends perpendicularly to the direction described above. In this fashion, the second cutting blade84cuts the workpiece11to divide it into a plurality of device chips33.

FIG.10Billustrates the workpiece unit31that has undergone the dividing step S30in enlarged fragmentary side elevation and partly in cross section. In the dividing step S30, the second cutting blade84forms dividing grooves11fin the workpiece11along the respective projected dicing lines17. Each of the dividing grooves11fhas a width11gthat is substantially the same as the edge thickness84dof the second cutting blade84. The dividing grooves11fextend all the way through the workpiece11to the tape29on the reverse side11b. An example of processing conditions in the dividing step S30, i.e., second processing conditions, is illustrated below.Spindle rotational speed: 55000 rpmProcessing feed speed: 10 mm/sCutting mode: Downward cuttingCutting water flow rate: 1.0 L/min

According to the present embodiment, in the cut groove forming step S10, the first cutting blade40as it vibrates at the frequency in the ultrasonic band cuts the workpiece11along the projected dicing lines17. Hence, the first cutting blade40can cut the workpiece11that includes the SiC substrate13, even though the first cutting blade40has abrasive grains having a relatively small average particle diameter. In the dividing step S30, the second cutting blade84cuts off the uncut residual portions11e, dividing the workpiece11into a plurality of device chips33. The uncut residual portions11econtain cracks developed due to vibrations produced at the frequency in the ultrasonic band, and hence resistance to the second cutting blade84is reduced. Consequently, even though the second cutting blade84has abrasive grains having a relatively small average particle diameter, it can cut the workpiece11that includes the SiC substrate13.

The first cutting blade40and the second cutting blade84, each having abrasive grains having a relatively small average particle diameter, are effective to divide the workpiece11that includes the SiC substrate13into a plurality of device chips33. The first cutting blade40and the second cutting blade84are able to reduce the number and size of chippings near the face and reverse sides11aand11bof the workpiece11, compared with a situation where the workpiece11is cut fully thereacross all the way and a situation where the cutting blade is not vibrated at a frequency in the ultrasonic band when the cutting blade forms half-cut grooves in the workpiece.

According to the present embodiment, the reverse side11b, i.e., the C-surface13b, of the workpiece11is not cut by the first cutting blade40cutting into the workpiece11through the face side11a, i.e., the Si-surface13a, but the reverse side11b, facing upwardly, of the workpiece11is cut by the first cutting blade40that cuts into the workpiece11through the reverse side11btoward the face side11afacing downwardly. The applicant has found that, when the SiC substrate13is cut, chippings are likely to occur at the C-surface13b. The method of manufacturing device chips33according to the first embodiment is effective to reduce chippings occurring at the C-surface13b, compared with a situation where the face side11a, facing upwardly, of the workpiece11is cut by the first cutting blade40that cuts into the workpiece11through the face side11atoward the reverse side11bfacing downwardly. According to the present embodiment, the relatively small average particle diameter referred to above is 6.0 μm or less. A cutting blade made of abrasive grains having an average particle diameter in excess of 6.0 μm is not preferable because, if it is used to cut the workpiece11, the number and size of chippings that occur at the face side11aand/or the reverse side11bare liable to increase.

In addition, according to the present embodiment, end faces that are cut by the second cutting blade84having the abrasive grains whose average particle diameter is smaller than the average particle diameter of the abrasive grains of the first cutting blade40serve as outer peripheral side surfaces, i.e., four side surfaces, of the device chips33. Accordingly, since surface irregularities of the side surfaces of the device chips33that are cut by the second cutting blade84are reduced compared with surface irregularities of the side surfaces of the device chips33that are cut by the first cutting blade40, the device chips33have increased mechanical strengths and better appearances. However, the present embodiment is not limited to the processing feed speed, the spindle rotational speed, the cutting water flow rate, and the average particle diameters of the abrasive grains of the first cutting blade40and the second cutting blade84as described above. These parameters may be adjusted depending on the cutting quality, the cutting time, etc.

Experimental results will be described below with reference toFIGS.11A through13B.FIGS.11A through11Fillustrate, in enlarged plan, an Si-surface13aof a first SiC substrate13-1that has been divided by the method according to the first embodiment (Experiment A). No devices19were present on the first SiC substrate13-1cut in Experiment A. In Experiment A, the first SiC substrate13-1had a diameter of 4 inches, i.e., approximately 100 mm, and a thickness of 100 μm, and the uncut residual portion11eleft in the cut groove forming step S10had a thickness of 25 μm.

The cut groove forming step S10, the workpiece overturning step S20, and the dividing step S30were carried out to form 96 dividing grooves, i.e., cut grooves,11falong a first direction A1and 96 dividing grooves11falong a second direction A2perpendicular to the first direction A1. Indexed distances in the first direction A1and the second direction A2across the dividing grooves11fwere 1.0 mm. The first direction A1is substantially perpendicular to the lengthwise directions of the orientation flat of the first SiC substrate13-1, and the second direction A2is substantially parallel to the lengthwise directions of the orientation flat. The other processing conditions were the same as those of the first embodiment.

FIGS.11A through11Fillustrates areas near the intersections of the dividing grooves11fin the Si-surface13aof the first SiC substrate13-1. The intersections illustrated inFIGS.11A through11Fare located at different positions on the first SiC substrate13-1.FIG.11Aillustrates the 20th dividing groove11famong those dividing grooves11fthat extend laterally, i.e., horizontally, inFIG.11A. Similarly,FIG.11Billustrates the 30th dividing groove11f,FIG.11Cillustrates the 40th dividing groove11f,FIG.11Dillustrates the 50th dividing groove11f,FIG.11Eillustrates the 60th dividing groove11f, andFIG.11Fillustrates the 70th dividing groove11f.

FIGS.12A through12Fillustrate, in enlarged plan, an Si-surface13aof a second SiC substrate13-2that has been divided by a method of manufacturing a plurality of device chips according to a comparative example (Experiment B). In the comparative example, the second SiC substrate13-2that was cut had a diameter of 4 inches and a thickness of 100 μm. In the comparative example, the first cutting blade40was not vibrated, and the first cutting blade40as it was rotating was vertically moved to have its lower end placed in a vertical position between the face side11aof the workpiece11and the holding surface16a. The first cutting blade40cut the workpiece11whose reverse side11bwas exposed, fully thereacross all the way in one stroke, forming a cut groove, i.e., a dividing groove, in the workpiece11.

In the comparative example, as a first cutting blade whose abrasive grains had an average particle diameter of 1.0 μm found it difficult to cut the workpiece11, the first cutting blade40that was used had abrasive grains having an average particle diameter of 3.0 μm. The spindle rotational speed was 30000 rpm, the processing feed speed was 20 mm/s, the cutting mode was downward cutting, and the cutting water flow rate was 1.0 L/min. The first cutting blade40somehow managed to cut the workpiece11by being frequently dressed.

FIGS.12A through12Fillustrates areas near the intersections of a plurality of dividing grooves in the C-surface13bof the second SiC substrate13-2. The intersections illustrated inFIGS.12A through12Fare located at different positions on the second SiC substrate13-2.FIG.12Aillustrates the 20th dividing groove among those dividing grooves that extend laterally, i.e., horizontally, inFIG.12A. Similarly,FIG.12Billustrates the 30th dividing groove,FIG.12Cillustrates the 40th dividing groove,FIG.12Dillustrates the 50th dividing groove,FIG.12Eillustrates the 60th dividing groove, andFIG.12Fillustrates the 70th dividing groove.

As illustrated inFIGS.12A through12F, the method according to the comparative example resulted in an increase in the number and size of chippings35compared with the method according to the first embodiment. InFIGS.12A through12F, representative chippings35are indicated by the arrows.

It is clear from a comparison between Experiments A and B that the number and size of chippings on the Si-surface13a, i.e., the face side11aof the workpiece11, can greatly be reduced by vibrating the first cutting blade40at a frequency in the ultrasonic band in the cut groove forming step S10. In Experiment A, the chippings had sizes in the range of 3.0 μm to approximately 6.0 μm. In Experiment B, the chippings had sizes in the range of 10 μm to approximately 25 μm. Although not illustrated, the number and size of chippings on the C-surface13b, i.e., the reverse side11bof the workpiece11, can also be reduced by applying the method according to the first embodiment.

FIG.13Aillustrates, in cross section, the SiC substrate13that has been divided by the method according to the first embodiment illustrated inFIGS.11A through11F, i.e., Experiment A described above, the view illustrating a cut surface37aof an SiC chip37.FIG.13Billustrates, in cross section, the SiC substrate13that has been divided by the method according to the comparative example illustrated inFIGS.12A through12F, i.e., Experiment B described above, the view illustrating a cut surface39aof an SiC chip39.

The cut surfaces37aand39aillustrated inFIGS.13A and13Bare illustrated as magnified 100 times by an optical microscope. Black lines that extend substantially longitudinally along the cut surfaces37aand39arepresent recesses, i.e., chippings, formed in the cut surfaces37aand39a. A comparison ofFIGS.13A and13Bmakes it clear that the vibrations of the first cutting blade40at a frequency in the ultrasonic band in the cut groove forming step S10and the cutting of the SiC substrate13with the second cutting blade84in the subsequent dividing step S30lead to a reduction in the number and size of chippings in the cut surfaces37aand39a, i.e., the side surfaces of the device chips33.

Modification of First Embodiment

A modification of the first embodiment will be described below with reference toFIGS.14A and14B. The modification is different from the first embodiment in that the tape23is affixed to the reverse side (another surface)11band a surface of the frame25such that the face side (a surface)11ais exposed, making up a workpiece unit41(seeFIG.14A), and the cut groove forming step S10is carried out on the workpiece unit41.

FIG.14Aillustrates, in enlarged fragmentary side elevation and partly in cross section, a cut groove forming step S10according to the modification of the first embodiment. The cut groove forming step S10according to the modification is carried out by using a cutting apparatus2bthat is different from the cutting apparatus2described above. The cutting apparatus2bhas the cutting unit42including the first cutting blade40and the ultrasonic vibrators60aand60band includes a visible light camera, not illustrated, instead of the infrared camera36.

After the cut groove forming step S10, in the workpiece overturning step S20, the tape29is affixed to the face side11aand a surface of the frame25, and the tape23affixed to the reverse side11bis peeled off, making up a workpiece unit43(seeFIG.14B). After the workpiece overturning step S20, the dividing step S30including the cutting position detecting step is carried out.

FIG.14Billustrates, in enlarged fragmentary side elevation and partly in cross section, a dividing step S30according to the modification of the first embodiment. The dividing step S30according to the modification is carried out by using a cutting apparatus2cthat is different from the cutting apparatus2adescribed above. The cutting apparatus2chas the second cutting blade84and includes the infrared camera36instead of a visible light camera.

According to the modification, the workpiece11including the SiC substrate13can be divided into a plurality of device chips33by using the first cutting blade40and the second cutting blade84, each having abrasive grains having a relatively small average particle diameter. In addition, the number and size of chippings near the face and reverse sides11aand11bof the workpiece11are reduced compared with a situation where the workpiece11is cut fully thereacross all the way and a situation where the cutting blade is not vibrated at a frequency in the ultrasonic band when the cutting blade forms half-cut grooves in the workpiece.

Second Embodiment

A second embodiment of the present invention will be described below with reference toFIGS.15through16B.FIG.15is a flowchart of a method of manufacturing a plurality of device chips33according to the second embodiment. According to the first embodiment, the workpiece11is cut stepwise by a bridge cutting step in which the dividing grooves11fare formed contiguously to the cut grooves11c. According the second embodiment, however, the workpiece11is cut stepwise by a stepwise cutting step performed on a workpiece unit43′ (seeFIGS.16A and16B) where the tape23is affixed to the face side (another surface)11aand a surface of the frame25such that the reverse side (a surface)11bis exposed.

FIG.16Aillustrates, in enlarged fragmentary side elevation and partly in cross section, a cut groove forming step S10according to the second embodiment. The cut groove forming step S10according to the second embodiment is carried out by using the cutting apparatus2(seeFIG.3) that has the cutting unit42including the first cutting blade40and the ultrasonic vibrators60aand60band the infrared camera36. According to the second embodiment, as illustrated inFIG.15, after the cut groove forming step S10, the dividing step S30is carried out, with the workpiece overturning step S20being omitted.

FIG.16Billustrates, in enlarged fragmentary side elevation and partly in cross section, a dividing step S30according to the second embodiment. The dividing step S30according to the second embodiment is carried out by using the cutting apparatus2c(seeFIG.14B) that is free of the ultrasonic vibrators60aand60bfor producing vibrations in the ultrasonic band but that includes the cutting unit42having the second cutting blade84mounted on the spindle38and the infrared camera36.

According to the second embodiment, the number and size of chippings can be reduced to a certain extent though not as much as the first embodiment. According to the second embodiment, particularly, as no workpiece overturning step S20is carried out, the workpiece11is prevented from cracking due to the workpiece overturning step S20. The reduced risk of cracking contributes to an increase in the yield of device chips33.

Modification of Second Embodiment

A modification of the second embodiment will be described below with reference toFIGS.17A and17B. The modification is different from the second embodiment in that the tape23is affixed to the reverse side (another surface)11band a surface of the frame25such that the face side (a surface)11ais exposed, making up a workpiece unit41′ (seeFIG.17A).

FIG.17Aillustrates, in enlarged fragmentary side elevation and partly in cross section, a cut groove forming step S10according to the modification of the second embodiment. The cut groove forming step S10according to the modification is carried out by using the cutting apparatus2b(seeFIG.14A) that has the cutting unit42including the first cutting blade40and the ultrasonic vibrators60aand60band the visible light camera, not illustrated. After the cut groove forming step S10, the dividing step S30is carried out, with the workpiece overturning step S20being omitted, as with the second embodiment.

FIG.17Billustrates, in enlarged fragmentary side elevation and partly in cross section, a dividing step S30according to the modification of the second embodiment. The dividing step S30according to the modification is carried out by using the cutting apparatus2a(seeFIG.10B) including the second cutting blade84and the visible light camera, not illustrated. Also according to the modification, the number and size of chippings can be reduced to a certain extent though not as much as the first embodiment, and, in addition, the workpiece11is prevented from cracking due to the workpiece overturning step S20.

Third Embodiment

A third embodiment will be described below with reference toFIGS.18through19B.FIG.18illustrates, in perspective, a cutting apparatus2dused in the third embodiment. InFIG.18, the cutting apparatus2dis illustrated in reference to a three-dimensional XYZ coordinate system similar to the three-dimensional XYZ coordinate system illustrated inFIG.3. The cutting apparatus2dhas a base86supporting various components thereon. An X-axis and Y-axis moving mechanism88is disposed on an upper surface of the base86. The X-axis and Y-axis moving mechanism88includes a pair of guide rails90extending substantially parallel to the X-axis. An X-axis movable table92is slidably mounted on the guide rails90.

A nut, not illustrated, that is fixedly disposed on a reverse side, i.e., a lower surface, of the X-axis movable table92is operatively threaded over a screw shaft94extending substantially parallel to the X-axis and lying between the guide rails90. The screw shaft94has an end coupled to a drive source96such as a stepping motor. A pair of guide rails98extending substantially parallel to the Y-axis are fixedly mounted on an upper surface of the X-axis movable table92. A Y-axis movable table100is slidably mounted on the guide rails98.

The Y-axis movable table100includes rectangular bottom and top plates that lie substantially parallel to the XY plane. The bottom and top plates have respective ends in a direction along the Y-axis that are connected to each other by a rectangular side plate that lies substantially parallel to an XZ plane defined along the X-axis and the Z-axis. The Y-axis movable table100is open at an end thereof in another direction along the Y-axis and at opposite sides in opposite directions along the X-axis. The bottom and top plates of the Y-axis movable table100define a space therebetween in which a lower visible light camera124to be described below can be inserted.

A nut, not illustrated, that is fixedly disposed on a lower surface of the bottom plate of the Y-axis movable table100is operatively threaded over a screw shaft102extending substantially parallel to the Y-axis and lying between the guide rails98. The screw shaft102has an end coupled to a drive source104such as a stepping motor. The top plate of the Y-axis movable table100has a circular opening defined therein, and a chuck table, i.e., a holding table,106is disposed in the circular opening in the top plate. The chuck table106is rotatably supported on the top plate of the Y-axis movable table100for rotation about a rotational axis extending substantially parallel to the Z-axis.

The chuck table106is rotated about the rotational axis by rotational power transmitted from a rotary drive source108including a pulley via an endless belt108atrained around an outer circumferential side surface of the chuck table106. The chuck table106includes an annular frame made of a metal material such as stainless steel. A disk-shaped holder106ais disposed in the opening of the annular frame. The holder106ais made of a material that is substantially transparent to visible light, such as soda glass, borosilicate glass, or quartz glass. The holder106ahas a face side acting as an upper holding surface that is of a circular shape and lies substantially flatwise, and a reverse side that is opposite to the face side and that is also of a circular shape and lies substantially flatwise.

The holder106ahas a plurality of suction channels, not illustrated, defined therein to transmit a negative pressure therethrough and hold the workpiece11under suction thereon. The holder106aalso has a plurality of openings positioned at ends, i.e., upper ends, of the suction channels in an outer circumferential portion of the face side of the holder106a. The openings are disposed at substantially equal spaced intervals circumferentially around the holder106a. The suction channels have other ends, i.e., lower ends, fluidly connected to a suction source, not illustrated, such as a vacuum pump via a fluid channel, not illustrated. At least a region of the holder106a, except the suction channels and the openings, extending from the face side to the reverse side of the holder106ais substantially transparent to visible light.

A wall-shaped support structure110is disposed on the base86near the end of the Y-axis movable table100in the other direction along the Y-axis. A Z-axis moving mechanism112is mounted on a side surface of the support structure110that faces in one of the directions along the X-axis. The Z-axis moving mechanism112includes a pair of guide rails114extending substantially parallel to the Z-axis. A spindle housing116shaped as a rectangular parallelepiped that has a longitudinal axis extending substantially parallel to the Y-axis is slidably mounted on the guide rails114for sliding movement along the Z-axis.

A nut, not illustrated, that is fixedly disposed on a side surface of the spindle housing116that faces the support structure110is operatively threaded over a screw shaft118extending substantially parallel to the Z-axis and lying between the guide rails114. The screw shaft118has an upper end coupled to a drive source120such as a stepping motor. The spindle38(seeFIG.4) whose longitudinal axis extends substantially parallel to the Y-axis has a portion rotatably supported in the spindle housing116. The spindle38has a distal end portion on which the first cutting blade40(seeFIG.5) is mounted by the mount44and the presser flange52.

The spindle38, the first cutting blade40, the ultrasonic vibrator60ain the mount44, the ultrasonic vibrator60bin the presser flange52, etc., jointly make up the cutting unit42described above. An upper visible light camera122that functions as a microscope camera is mounted on a side surface of the spindle housing116that faces in the one of the directions along the X-axis. The upper visible light camera122has one or more lenses, not illustrated, a light source, not illustrated, such as an LED for emitting visible light, and a solid-state image capturing device, i.e., a solid-state image sensor, not illustrated, for photoelectrically converting visible light into electric signals. The upper visible light camera122captures an image of the upper side of the workpiece11held under suction on the chuck table106.

The lower visible light camera124that functions as a microscope camera is disposed below the spindle housing116. The lower visible light camera124also has one or more lenses, not illustrated, a light source, not illustrated, such as an LED for emitting visible light, and a solid-state image capturing device, i.e., a solid-state image sensor, not illustrated, for photoelectrically converting visible light into electric signals. The lower visible light camera124is movable along the Z-axis by a ball-screw-type Z-axis moving mechanism126mounted on the base86. However, the lower visible light camera124is fixed in position against movement parallel to the XY plane.

The lower visible light camera124captures an image of the lower side of the workpiece11held under suction on the chuck table106. Specifically, while being inserted in the space in the Y-axis movable table100, the lower visible light camera124captures an image of the lower side of the workpiece11through the holder106athat is substantially transparent to visible light.

The cutting apparatus2dincludes a controller or a control unit, not illustrated, for controlling operations of the X-axis and Y-axis moving mechanism88, the chuck table106, the cutting unit42, the Z-axis moving mechanism112, the upper visible light camera122, the lower visible light camera124, and the Z-axis moving mechanism126, in addition to the above-mentioned AC power supply78, signal generator80, etc. Since the controller is similar to the controller of the cutting apparatus2, the controller will be omitted from detailed description.

As illustrated inFIG.19A, a workpiece51according to the third embodiment is different from the workpiece11described above in that a metal layer53is disposed in contact with the C-surface13bof the SiC substrate13all over a reverse side51bof the workpiece51. Other details of the workpiece51are identical to those of the workpiece11. The metal layer53functions, for example, as electrodes of the devices19and heat radiation plates of the device chips33. The metal layer53may be of a laminated structure including laminated layers of a plurality of metals or a single-layer structure including a single layer of a metal.

The workpiece51has a face side51athat corresponds to the face side11aof the workpiece11. The reverse side51bof the workpiece51corresponds to the reverse side11bof the workpiece11. When the workpiece51is cut, the workpiece51is handled in the form of a workpiece unit where the workpiece51is supported on the frame25by the tape23, as illustrated inFIG.2B. According to the third embodiment, the workpiece51is cut by the cutting unit42while the workpiece51is being held under suction on the chuck table106such that the face side51afaces the chuck table106and the metal layer53positioned over the reverse side51bis exposed upwardly.

According to the third embodiment, the workpiece51is divided into device chips33according to the flowchart illustrated inFIG.1, that is, by the bridge cutting step.FIG.19Aillustrates, in enlarged fragmentary side elevation and partly in cross section, a cut groove forming step S10according to the third embodiment. According to the third embodiment, the lower visible light camera124captures an image of the face side51aof the workpiece51through the holder106a. Then, the controller detects the position, on the XY plane, of at least one of the projected dicing lines17on the basis of the coordinates of the key pattern that is included in the image of the face side51aand the distances by which the key pattern is spaced from the projected dicing lines17(cutting position detecting step).

Thereafter, the chuck table16is turned about its central axis to make the one of the projected dicing lines17substantially parallel to the X-axis, thereby adjusting the orientation of the workpiece51. While the workpiece51is being held under suction on the holder106a, the first cutting blade40cuts the workpiece51along the projected dicing line17, forming a cut groove11cthat extends from the reverse side51band terminates short of the face side51ain the workpiece11along the projected dicing line17(cut groove forming step S10).

In the cut groove forming step S10, the first cutting blade40as it is rotating at a predetermined speed and vibrating at a frequency in the ultrasonic band is vertically moved to have its lower end placed in a vertical position between the reverse side51band the face side51aof the workpiece51. While the first cutting blade40is being supplied with cutting water such as pure water, the first cutting blade40is placed on an extension of the projected dicing line17. Then, the chuck table106is moved along the X-axis to cause the first cutting blade40to cut the SiC substrate13and the metal layer53along the projected dicing line17, forming a cut groove11cin the workpiece51that extends from the reverse side51b.

After the cut groove forming step S10, as illustrated inFIG.9, the tape29is affixed to the reverse side51b, and the tape23is peeled off from the face side51ain the workpiece overturning step S20. After the workpiece overturning step S20, the dividing step S30is carried out by using a cutting apparatus2e(seeFIG.19B). The cutting apparatus2eis essentially the same as the cutting apparatus2dexcept that the cutting unit42is free of the ultrasonic vibrators60aand60band the second cutting blade84is used in place of the first cutting blade40.

FIG.19Billustrates, in enlarged fragmentary side elevation and partly in cross section, a dividing step S30according to the third embodiment. In the dividing step S30, while the workpiece unit is being held under suction on the chuck table106, the upper visible light camera122captures an image of the face side51a, and the position, on the XY plane, of at least one of the projected dicing lines17is detected on the basis of the captured image (cutting position detecting step). After the cutting position detecting step, the chuck table106is turned about its central axis to make the one of the projected dicing lines17substantially parallel to the X-axis, thereby adjusting the orientation of the workpiece51. Then, the second cutting blade84cuts off the uncut residual portion11eor the like near the face side51a, dividing the workpiece51(dividing step S30).

Modification of Third Embodiment

A modification of the third embodiment will be described below with reference toFIGS.20A and20B. The modification is different from the third embodiment in that, in the cut groove forming step S10, the tape23is affixed to the reverse side (another surface)51band a surface of the frame25such that the face side (a surface)51ais exposed, making up a workpiece unit.

FIG.20Aillustrates, in enlarged fragmentary side elevation and partly in cross section, a cut groove forming step S10according to the modification of the third embodiment. The cut groove forming step S10according to the modification is carried out by using the cutting apparatus2dhaving the cutting unit42that includes the first cutting blade40and the ultrasonic vibrators60aand60b. After the cut groove forming step S10, the workpiece overturning step S20, and then, the dividing step S30are carried out.

FIG.20Billustrates, in enlarged fragmentary side elevation and partly in cross section, a dividing step S30according to the modification of the third embodiment. The dividing step S30according to the modification is carried out by using the cutting apparatus2eas with the third embodiment. In the cutting position detecting step, the lower visible light camera124is used. Also, according to the modification, the number and size of chippings can be reduced. According to the third embodiment and the modification thereof, the workpiece51is cut according to a sequence including the workpiece overturning step S20(seeFIG.1, i.e., the bridge cutting step). However, the workpiece51may be cut according to a sequence free of the workpiece overturning step S20(seeFIG.15, i.e., the stepwise cutting step).

The structures, methods, etc., according to the above embodiments and modifications may be changed or modified without departing from the scope of the present invention. The first cutting blade40and the second cutting blade84may be hub-type cutting blades instead of hubless cutting blades. A hub-type cutting blade includes an annular base made of a metal material such as aluminum alloy and an annular cutting edge extending along an outer circumferential edge portion of the annular base in integrally combination therewith. The cutting edge of the hub-type cutting blade is constructed as an electrodeposited grindstone made of abrasive grains bound together by a binder such as a nickel-plated layer, for example.

Instead of the ultrasonic vibrators60aand60bprovided in the mount44and the presser flange52that are positioned on the distal end portion of the spindle38, ultrasonic vibrators such as Langevin-type vibrators may be disposed in series longitudinally on the proximal end portion of the spindle38. Moreover, a dual dicer, not illustrated, having the spindle38with the first cutting blade40mounted thereon and another spindle with the second cutting blade84mounted thereon may be used instead of the different cutting apparatuses in the cut groove forming step S10and the dividing step S30.