METHOD OF PROCESSING WAFER

A method of processing a wafer having a plurality of devices formed in respective areas on a face side of the wafer, the areas being demarcated by a plurality of intersecting projected dicing lines, includes a resin applying step of coating the face side of the wafer with a liquid resin to cover an area of the wafer where the plurality of devices are present, a resin curing step of curing the liquid resin into a protective film, and a planarizing step of planarizing the protective film.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a method of processing a wafer having a plurality of devices formed in respective areas on a face side of the wafer, the areas being demarcated by a plurality of intersecting projected dicing lines established thereon.

Description of the Related Art

Wafers with a plurality of devices such as integrated circuits (ICs) or large-scale integrated (LSI) circuits formed in respective areas on a face side of the wafer, the areas being demarcated by a plurality of intersecting projected dicing lines established thereon, are divided by a dicing apparatus into individual device chips. The divided device chips are used in electric appliances such as mobile phones and personal computers.

There has been proposed in the art a technology for applying a laser beam whose wavelength is transmittable through a wafer to the wafer while positioning the focused spot of the laser beam within the wafer at positions aligned with projected dicing lines on a face side of the wafer, thereby forming modified layers in the wafer, thereafter grinding a reverse side of the wafer to thin down the wafer to a desired thickness, and then dividing the wafer into individual device chips at the modified layers along the projected dicing lines (see, for example, JP 2014-078569A).

There has also been proposed in the art a technology for applying a laser beam whose wavelength is absorbable by a wafer to the wafer while positioning the focused spot of the laser beam at projected dicing lines on the wafer, thereby forming grooves in the wafer by way of laser ablation, and then dividing the wafer into individual device chips at the grooves along the projected dicing lines (see, for example, JP 2004-188475A).

SUMMARY OF THE INVENTION

Some wafers have devices formed thereon that include surface irregularities on face sides thereof, i.e., protrusive electrodes, called “bumps,” for example. If such a wafer is processed according to the technology disclosed in JP 2014-078569A, then the wafer may be broken due to the bumps.

It is assumed that the technology disclosed in JP 2004-188475A is applied to a wafer with bumps as described above and the face side of the wafer is coated with a protective film of liquid resin. Since the protective film has thickness irregularities, when the wafer is processed by laser ablation with a laser beam having a wavelength that is absorbable by the wafer while the focused spot of the laser beam is positioned on the face side of the wafer along the projected dicing lines, grooves having different depths tend to be formed in the wafer along the projected dicing lines. When the wafer is then to be divided into individual device chips at the grooves, the grooves with the different depths make it difficult to divide the wafer properly into individual device chips without causing damage to the wafer.

It is therefore an object of the present invention to provide a method of processing a wafer that has protrusions on a face side thereof to divide the wafer into individual device chips without breaking or damaging the wafer.

In accordance with an aspect of the present invention, there is provided a method of processing a wafer having a plurality of devices formed in respective areas on a face side of the wafer, the areas being demarcated by a plurality of intersecting projected dicing lines. The method includes a resin applying step of coating the face side of the wafer with a liquid resin to cover an area of the wafer where the plurality of devices are present, a resin curing step of curing the liquid resin into a protective film, and a planarizing step of planarizing the protective film.

Preferably, the planarizing step includes the steps of holding a reverse side of the wafer on a chuck table, exposing the face side of the wafer, and cutting the protective film to planarize the protective film with a cutting unit having a single-point cutting tool.

Preferably, the method further includes a modified layer forming step of forming modified layers in the wafer along the respective projected dicing lines by applying a laser beam having a wavelength transmittable through the wafer to the wafer from the reverse side of the wafer along the projected dicing lines while positioning a focused spot of the laser beam within the wafer, and a dividing step of grinding the reverse side of the wafer with grindstones to finish the wafer to a predetermined thickness and dividing the wafer into individual device chips along the modified layers. Preferably, the method further includes a grinding step of grinding the reverse side of the wafer with grindstones to finish the wafer to a predetermined thickness, a modified layer forming step of forming modified layers in the wafer along the respective projected dicing lines by applying a laser beam having a wavelength transmittable through the wafer to the wafer from the reverse side of the wafer along the projected dicing lines while positioning a focused spot of the laser beam within the wafer, and a dividing step of dividing the wafer into individual device chips by exerting external forces to the wafer.

Preferably, the method further includes a laser ablation step of performing laser ablation on the wafer along the projected dicing lines by positioning a focused spot of a laser beam having a wavelength absorbable by the wafer on the face side of the wafer along the projected dicing lines and applying the laser beam to the wafer. Preferably, the method further includes a groove forming step of, before the resin applying step, forming grooves in the wafer along the respective projected dicing lines on the face side of the wafer. The resin applying step, the resin curing step, and the planarizing step are carried out after the groove forming step. A dividing step of grinding the reverse side of the wafer with grindstones to finish the wafer to a predetermined thickness and dividing the wafer into individual device chips by exposing the grooves is carried out after the planarizing step.

With the method of processing a wafer according to the present invention, since the protective film on the face side of the wafer is uniformized in thickness, the wafer is prevented from being broken even when a laser beam having a wavelength transmittable through the wafer is applied to the wafer along the projected dicing lines to form modified layers in the wafer, then the reverse side of the wafer is ground by grindstones to finish the wafer to a predetermined thickness, and the dividing step is carried out to divide the wafer into individual device chips along the modified layers. Further, even when the laser ablation step is carried out to perform laser ablation on the wafer along the projected dicing lines by positioning a focused spot of a laser beam having a wavelength absorbable by the wafer on the face side of the wafer along the projected dicing lines and the wafer is then divided into individual device chips, grooves formed in the wafer by way of laser ablation are uniform in depth because the protective film on the face side of the wafer is uniform in thickness, so that the wafer can appropriately be divided into individual device chips without being damaged.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A method of processing a wafer as a workpiece according to a preferred embodiment of the present invention will be described in detail hereinbelow with reference to the drawings.

FIG.1Aillustrates a wafer10to be processed by the method of processing a wafer according to the present embodiment and an apparatus20, partly illustrated, for coating the wafer10with a liquid resin. The wafer10is a silicon wafer, for example. The wafer10has a plurality of devices12formed in respective areas on a face side10aof the wafer10, the areas being demarcated by a plurality of intersecting projected dicing lines14. Each of the devices12has a plurality of bumps16on its face side, as illustrated at an enlarged scale in an upper inset in FIG. TA. The bumps16are protrusive electrodes for electric connection to outer circuits, and are made of an alloy of lead and tin as major components, for example.

In the method of processing a wafer according to the present embodiment, a resin applying step is initially carried out to coat the face side10aof the wafer10with a liquid resin L to be described below and cover an area of the wafer10where the devices12are present. Specifically, the wafer10is delivered to the apparatus20for coating the wafer10with the liquid resin L. The apparatus20includes at least a chuck table21and a support base23. The chuck table21has an upper holding surface22made of an air-permeable porous material. The chuck table21is connected to suction means, not illustrated, that, when actuated, generates and transmits a negative pressure to the holding surface22. The support base23houses therein an electric motor, not illustrated, for rotating a rotational shaft24about its central axis to rotate the chuck table21that is mounted on an upper end of the rotational shaft24.

The wafer10delivered to the apparatus20is placed on the chuck table21while the face side10aof the wafer10is facing upwardly and a reverse side10bthereof is facing downwardly, and then, the suction means connected to the chuck table21is actuated to hold the wafer10on the holding surface22under the negative pressure applied to the holding surface22.

When the wafer10has been held under suction on the chuck table21, as illustrated inFIG.1B, a liquid resin supply nozzle25is positioned immediately above the center of the wafer10, and the electric motor housed in the support base23is energized to rotate the rotational shaft24and the chuck table21about their central axis in the direction indicated by an arrow R1. Then, the liquid resin supply nozzle25supplies a predetermined amount of liquid resin L from an ejection port25ato the wafer10to coat the face side10aof the wafer10. The liquid resin L is, for example, an epoxy resin that is curable upon exposure to ultraviolet rays. The liquid resin supply nozzle25may supply the liquid resin L from the ejection port25ain a single spurt or a plurality of successive spurts. The amount of liquid resin L supplied from the ejection port25ato the wafer10is set to a level that should be enough for the liquid resin L applied to the face side10ato cover an area of the wafer10where the devices12are present. The resin applying step is now completed.

Then, a resin curing step is carried out to cure the liquid resin L applied to the wafer10. For carrying out the resin curing step, ultraviolet ray applying means26illustrated in a left section ofFIG.2is positioned immediately above the wafer10held by the apparatus20. Then, the ultraviolet ray applying means26applies ultraviolet rays UV to the liquid resin L that has coated the wafer10. When exposed to the applied ultraviolet rays UV, the liquid resin L is cured, forming a protective film L′ on the face side10aof the wafer10as illustrated in a right section ofFIG.2. The resin curing step is now completed. According to the present embodiment, a resin that is curable upon exposure to the ultraviolet rays UV is selected as the liquid resin L on the face side10aof the wafer10. However, the liquid resin L may be a resin that is curable over time, for example. If the liquid resin L is a resin that is curable over time, then the resin applying step is followed by a standby step, as the resin curing step, where the wafer10is left on the chuck table21until the liquid resin L applied to the wafer10is cured.

The protective film L′ has been formed to a thickness sufficiently large to embed the bumps16on the devices12. As a whole, the protective film L′ that contains the bumps16tends to have surface irregularities18because the protective film L′ has thickness irregularities due to surface irregularities on the face side10aof the wafer10and shrinkage caused when the liquid resin L is cured into the protective film L′. If a laser beam is applied to the face side10aof the wafer10to form dividing grooves in the wafer10along the projected dicing lines14by way of laser ablation, then the grooves are likely to have different depths that tend to cause a processing failure. Further, although an attempt may be made to hold the protective film L′ in position and grind the reverse side10bof the wafer10to thin down the wafer10, the wafer10may possibly be broken or damaged owing to the surface irregularities18. According to the present embodiment, a planarizing step is carried out to planarize the protective film L′.

FIG.3illustrates in perspective a cutting apparatus30, partly illustrated, that is suitable for carrying out the planarizing step. As illustrated inFIG.3, the cutting apparatus30includes a cutting unit31mounted on an apparatus body for vertical movement. The cutting unit31includes a movable base32movable vertically by a cutting feed mechanism, not illustrated, and a spindle unit33mounted on the movable base32. The spindle unit33is supported on the movable base32by a support member32amounted on a front surface of the movable base32.

The spindle unit33includes a spindle housing33amounted on the support member32a, a rotatable spindle33brotatably disposed in the spindle housing33a, and a servomotor33cas a rotary actuator for rotating the rotatable spindle33babout its vertical central axis. The rotatable spindle33bhas a lower end portion protruding downwardly beyond a lower end of the spindle housing33a. A single-point cutting tool mount33dshaped as a circular plate is mounted on a lower end of the rotatable spindle33b.

The single-point cutting tool mount33dhas a tool mount hole33edefined therein that extends vertically through the single-point cutting tool mount33din an outer circumferential portion thereof that is spaced radially outwardly from the central axis of the rotatable spindle33b. A single-point cutting tool34is inserted in the tool mount hole33eand fastened in position by a fastening bolt35that is threaded in an internally threaded hole, not illustrated, defined laterally in the single-point cutting tool mount33dand that has a tip end pressed against the single-point cutting tool34. According to the present embodiment, the single-point cutting tool34is formed as a bar-shaped cutting tool of tool steel such as a cemented carbide alloy. The single-point cutting tool34has, on its lower distal end, a cutting edge made of diamond or the like. The single-point cutting tool34mounted on the single-point cutting tool mount33dis rotatable in unison with the single-point cutting tool mount33dwhen the rotatable spindle33bis rotated by the servomotor33c.

The cutting apparatus30includes a chuck table mechanism36. The chuck table mechanism36includes a rotatable chuck table36ashaped as a circular plate. The chuck table36ahas an upper holding surface made of an air-permeable porous material and connected to a suction source, not illustrated. The chuck table mechanism36includes a moving mechanism, not illustrated, housed in the apparatus body of the cutting apparatus30. The moving mechanism moves the chuck table36atogether with a cover member36bin the direction indicated by an arrow R3. In the cutting apparatus30illustrated inFIG.3, the chuck table36aholds the wafer10delivered from the apparatus20under suction on the holding surface thereof.

The cutting apparatus30illustrated inFIG.3is generally constructed as described above. The planarizing step according to the present embodiment that is carried out using the cutting apparatus30will be described below.

The wafer10is held under suction on the chuck table36aof the cutting apparatus30while the protective film L′ on the face side10ais facing upwardly. The servomotor33cis then energized to rotate the single-point cutting tool mount33dabout its central axis in the direction indicated by an arrow R2, and the cutting feed mechanism, not illustrated, is actuated to lower the single-point cutting tool mount33dto a predetermined height where the cutting edge of the single-point cutting tool34mounted on the single-point cutting tool mount33dcan remove the surface irregularities18of the protective film L′ on the wafer10. The moving mechanism, not illustrated, is actuated to move the chuck table mechanism36in the direction indicated by the arrow R3, causing the chuck table36awith the wafer10held thereon to pass through a processing area beneath the single-point cutting tool mount33d. When the chuck table36awith the wafer10held thereon passes through the processing area, the surface irregularities18are removed from the protective film L′ on the wafer10by the single-point cutting tool34, as illustrated in a lower inset inFIG.3. The planarizing step is now completed.

According to the present invention, the planarizing step may not necessarily be performed by the cutting apparatus30and may be carried out using a polishing apparatus or the like, for example.

The method of processing a wafer according to the present embodiment, which includes the resin applying step, the resin curing step, and the planarizing step described above, makes it possible to favourably perform any of various types of division for dividing the wafer10into individual device chips as described below. First division among the various types of division will be described below with reference toFIGS.4A through4C,5A,5B,13A, and13B.

FIG.4Aillustrates in perspective the wafer10with the planarized protective film L′ formed according to the above method of processing a wafer, and a laser processing apparatus40suitable for performing the first division. As illustrated inFIG.4A, the laser processing apparatus40includes, on a base table40a, a laser applying unit41for applying a laser beam to the wafer10as a workpiece, i.e., a target to be processed, a holding unit42for holding the wafer10, an image capturing unit43for capturing an image of the wafer10held by the holding unit42, a feed mechanism assembly44for processing-feeding and indexing-feeding the laser applying unit41and the holding unit42relatively to each other and moving the image capturing unit43and the holding unit42relatively to each other, and a frame45including a vertical wall45aerected from the base table40abehind the feed mechanism assembly44and a horizontal wall45bextending horizontally from an upper end portion of the vertical wall45a.

The horizontal wall45bof the frame45houses therein an optical system, not illustrated, of the laser applying unit41. The laser applying unit41includes a beam condenser41adisposed on the lower surface of a distal end portion of the horizontal wall45b. The beam condenser41ais movable in Z-axis directions, i.e., vertical directions, indicated by an arrow Z. According to the present embodiment, the laser applying unit41is capable of selectively emitting a laser beam having a wavelength transmittable through the wafer10and a laser beam having a wavelength absorbable by the wafer10. The image capturing unit43is disposed on the lower surface of the distal end portion of the horizontal wall45bat a position adjacent to the beam condenser41ain X-axis directions, i.e., horizontal directions, indicated by an arrow X. The image capturing unit43includes an ordinary visible-light image capturing device such as a charge-coupled device (CCD) for capturing images based on a visible light beam, infrared ray applying means for applying infrared rays to a workpiece, an optical system for capturing infrared rays emitted from the infrared ray applying means, and an image capturing device such as an infrared CCD for outputting an electric signal representing the infrared rays captured by the optical system.

As illustrated inFIG.4A, the holding unit42includes a rectangular X-axis movable plate42amovably mounted on the base table40afor movement in the X-axis directions, a rectangular Y-axis movable plate42bmovably mounted on the X-axis movable plate42afor movement in Y-axis directions, i.e., horizontal directions, that are perpendicular to the X-axis directions, a hollow cylindrical support post42cfixedly mounted on an upper surface of the Y-axis movable plate42b, and a rectangular cover plate42dfixedly mounted on an upper end of the support post42c. The cover plate42dhas an oblong hole defined therein that accommodates therein a chuck table42eextending upwardly. The chuck table42eis rotatable about its vertical central axis by rotary actuating means, not illustrated, housed in the support post42c. The chuck table42eincludes a suction chuck42fin the shape of a circular plate that is made of an air-permeable porous material and that is lying essentially horizontally. The suction chuck42fis fluidly connected to suction means, not illustrated, by a fluid channel extending through the support post42c.

The feed mechanism assembly44includes an X-axis feed mechanism46and a Y-axis feed mechanism47. The X-axis feed mechanism46converts rotary motion of an electric motor46ainto linear motion with a ball screw46band transmits the linear motion to the X-axis movable plate42a, thereby processing-feeding the X-axis movable plate42ain one of the X-axis directions or the other along a pair of guide rails40bthat are disposed on the base table40aand that extend in the X-axis directions. The Y-axis feed mechanism47converts rotary motion of an electric motor47ainto linear motion with a ball screw47band transmits the linear motion to the Y-axis movable plate42b, thereby indexing-feeding the Y-axis movable plate42bin one of the Y-axis directions or the other along a pair of guide rails42gthat are disposed on the X-axis movable plate42aand that extend in the Y-axis directions.

The laser processing apparatus40illustrated inFIG.4Ais generally constructed as described above. A modified layer forming step of the first division, which is carried out using the laser processing apparatus40, will be described in detail below.

First, as illustrated inFIG.4A, the wafer10is placed and held under suction on the suction chuck42fof the chuck table42ewhile the protective film L′ formed on the face side10ais facing downwardly and the reverse side10bis facing upwardly.

The feed mechanism assembly44is actuated to move the wafer10held on the chuck table42eto a position directly below the image capturing unit43. When the wafer10reaches the position directly below the image capturing unit43, the image capturing unit43captures an image of the wafer10. Specifically, the image capturing unit43is electrically connected to a control unit and a display unit, not illustrated. The image capturing unit43applies infrared rays to the reverse side10bof the wafer10on the chuck table42eand captures an image of the wafer10. The control unit then detects, from the captured image, one of the projected dicing lines14to which a laser beam is to be applied on the face side10awith the protective film L′ formed thereon. The control unit then stores the X and Y coordinates representing the positional information of the detected projected dicing line14, and performs alignment processing for turning the chuck table42eto bring the detected projected dicing line14into alignment with the X-axis directions.

After the alignment processing, the X-axis feed mechanism46is actuated to move the chuck table42ein one of the X-axis directions and position the detected projected dicing line14of the wafer10directly below the beam condenser41aof the laser applying unit41, as illustrated inFIG.4B. Then, at the same time that the X-axis feed mechanism46is actuated to processing-feed the chuck table42ein the X-axis direction, the beam condenser41ais moved in one of the Z-axis directions to position a focused spot P1of a laser beam LB1whose wavelength is transmittable through the wafer10within the wafer10, and the laser applying unit41emits and applies the laser beam LB1to the reverse side10bof the wafer10, thereby forming a modified layer100in the wafer10along the detected projected dicing line14, as illustrated inFIG.4C. After the modified layer100has been formed in the wafer10along the projected dicing line14, the Y-axis feed mechanism47is actuated to indexing-feed the chuck table42ein one of the Y-axis directions by a distance equal to the interval between adjacent projected dicing lines14and to position, directly below the beam condenser41aof the laser applying unit41, a next projected dicing line14where no modified layer100has been formed. Then, at the same time that the X-axis feed mechanism46is actuated to processing-feed the chuck table42ein one of the X-axis directions, the beam condenser41ais moved in one of the Z-axis directions if necessary to position the focused spot P1of the laser beam LB1within the wafer10, and the laser applying unit41emits and applies the laser beam LB1to the reverse side10bof the wafer10, thereby forming a modified layer100in the wafer10along the next projected dicing line14.

The above laser processing sequence is repeated to processing-feed the wafer10in one of the X-axis directions and indexing-feed the wafer10in one of the Y-axis directions, and to apply the laser beam LB1to the wafer10while the wafer10is being processing-fed in the X-axis direction, thereby forming modified layers100in the wafer10along all the projected dicing lines14that extend in a first direction. Then, the wafer10is turned 90 degrees to align, with the X-axis directions, all the projected dicing lines14that extend in a second direction perpendicular to the first direction and that have not undergone the processing. Thereafter, the above laser processing sequence is repeated to form modified layers100in the wafer10along all the projected dicing lines14that extend in the second direction. In this manner, the modified layers100are formed in the wafer10along all the projected dicing lines14established on the face side10aof the wafer10. The modified layer forming step is now completed.

After the modified layer forming step, the wafer10is delivered to a grinding apparatus50(partly illustrated) illustrated inFIG.5Ato perform a dividing step. As illustrated inFIG.5A, the grinding apparatus50includes a chuck table51that is rotatable about its central axis by rotary actuating means, not illustrated, and a grinding unit52. The grinding unit52includes a rotatable spindle52athat is rotatable by rotary actuating means, not illustrated, a wheel mount52bmounted on a lower end of the rotatable spindle52a, and a grinding wheel52cattached to a lower surface of the wheel mount52b. A plurality of grindstones52dare mounted in an annular array on a lower surface of the grinding wheel52c.

As illustrated inFIG.5A, the wafer10delivered to the grinding apparatus50is held under suction on the chuck table51while the protective film L′ formed on the face side10ais facing downwardly and the reverse side10bis facing upwardly. Then, the rotatable spindle52aof the grinding unit52is rotated about its central axis in the direction indicated by an arrow R4at a speed of 6000 rpm, for example, and the chuck table51is rotated about its central axis in the direction indicated by an arrow R5at a speed of 300 rpm, for example. Then, a grinding feed mechanism, not illustrated, coupled to the grinding unit52is actuated to lower the grinding unit52in the direction indicated by an arrow R6, bringing the grindstones52dinto abrasive contact with the reverse side10bof the wafer10. After the grindstones52dhave been brought into abrasive contact with the reverse side10bof the wafer10, the grinding feed mechanism grinding-feeds, i.e., lowers, the grinding unit52at a grinding feed speed of 1 μm/second, for example. The wafer10is ground by the grindstones52dwhile the thickness thereof is being measured by a contact-type thickness measuring gage, not illustrated, so that the wafer10can be ground to a predetermined finish thickness. Then, external forces are exerted on the ground wafer10to divide the wafer10into individual device chips12′ along the modified layers100formed in the wafer10along the projected dicing lines14, as illustrated inFIG.5B. At this point, the dividing step comes to an end. The first division is now completed.

After the wafer10has been divided into individual device chips12′ in the first division as described above, the wafer10is then sent to a picking-up step, not illustrated, when required. In the picking-up step, as illustrated inFIG.13A, an annular frame F having an opening Fa capable of accommodating the wafer10therein is prepared, and the wafer10is turned upside down to orient the protective film L′ formed on the face side10aupwardly and to orient the reverse side10bdownwardly and is positioned centrally in the opening Fa. The wafer10is held by the annular frame F through an adhesive tape T applied to both of them and interposed therebetween. Then, as illustrated inFIG.13B, the protective film L′ is removed from the wafer10, exposing the face side10aof the wafer10that has been divided into the individual device chips12′, so that the individual device chips12′ can readily be picked up.

Prior to the first division, the resin applying step, the resin curing step, and the planarizing step had already been carried out, and the thickness of the protective film L′ had been uniformized. Therefore, even when the reverse side10bof the wafer10is ground by the grindstones52dand the wafer10is divided into individual device chips12′ in the dividing step after the modified layer forming step, the wafer10is prevented from being broken.

The various types of division referred to above include second division that can be carried out in combination with the method of processing a wafer that includes the resin applying step, the resin curing step, and the planarizing step. The second division will be described below with reference toFIGS.6through9.

Prior to the second division, the resin applying step, the resin curing step, and the planarizing step has already been carried out. No modified layer forming step has been carried out on the wafer10, and the wafer10with the protective film L′ formed on the face side10athereof is delivered to the grinding apparatus50described above with reference toFIGS.5A and5Bto perform a grinding step. As illustrated inFIG.6, the wafer10delivered to the grinding apparatus50is held under suction on the chuck table51while the protective film L′ formed on the face side10ais facing downwardly and the reverse side10bis facing upwardly. Then, the rotatable spindle52aof the grinding unit52is rotated about its central axis in the direction indicated by the arrow R4at a speed of 6000 rpm, for example, and the chuck table51is rotated about its central axis in the direction indicated by the arrow R5at a speed of 300 rpm, for example. Then, the grinding feed mechanism, not illustrated, coupled to the grinding unit52is actuated to lower the grinding unit52in the direction indicated by the arrow R6, bringing the grindstones52dinto abrasive contact with the reverse side10bof the wafer10. After the grindstones52dhave been brought into abrasive contact with the reverse side10bof the wafer10, the grinding feed mechanism grinding-feeds, i.e., lowers, the grinding unit52at a grinding feed speed of 1 μm/second, for example. The wafer10is ground by the grindstones52dwhile the thickness thereof is being measured by a contact-type thickness measuring gage, not illustrated, so that the wafer10can be ground to a predetermined finish thickness. At this point, the grinding step is ended.

After the wafer10has been ground to a predetermined finish thickness in the grinding step, the wafer10is delivered to the laser processing apparatus40described above with reference toFIGS.4A through4Cto perform the modified layer forming step. The wafer10is placed and held under suction on the suction chuck42fof the chuck table42ewhile the protective film L′ formed on the face side10ais facing downwardly and the reverse side10bis facing upwardly. The alignment processing described above is performed on the wafer10, and then, the X-axis feed mechanism46is actuated to move the chuck table42ein one of the X-axis directions and position one of the projected dicing lines14of the wafer10directly below the beam condenser41aof the laser applying unit41, as illustrated inFIG.7A. Then, at the same time that the X-axis feed mechanism46is actuated to processing-feed the chuck table42ein the X-axis direction, the beam condenser41ais moved in one of the Z-axis directions to position a focused spot P2of a laser beam LB2whose wavelength is transmittable through the wafer10within the wafer10, and the laser applying unit41emits and applies the laser beam LB2to the reverse side10bof the wafer10, thereby forming a modified layer110in the wafer10along the projected dicing line14that extends in a first direction, as illustrated inFIG.7B. After the modified layer110has been formed in the wafer10along the projected dicing line14, the Y-axis feed mechanism47is actuated to indexing-feed the chuck table42ein one of the Y-axis directions by a distance equal to the interval between adjacent projected dicing lines14and to position, directly below the beam condenser41aof the laser applying unit41, a next projected dicing line14where no modified layer110has been formed. Then, at the same time that the X-axis feed mechanism46is actuated to processing-feed the chuck table42ein one of the X-axis directions, the beam condenser41ais moved in one of the Z-axis directions if necessary to position the focused spot P2of the laser beam LB2within the wafer10, and the laser applying unit41emits and applies the laser beam LB2to the reverse side10bof the wafer10, thereby forming a modified layer110in the wafer10along the next projected dicing line14.

The above laser processing sequence is repeated to processing-feed the wafer10in one of the X-axis directions and indexing-feed the wafer10in one of the Y-axis directions, and to apply the laser beam LB2to the wafer10while the wafer10is being processing-fed in the X-axis direction, thereby forming modified layers100in the wafer10along all the projected dicing lines14that extend in the first direction. Then, the wafer10is turned 90 degrees to align, with the X-axis directions, all the projected dicing lines14that extend in a second direction perpendicular to the first direction and that have not undergone the processing. Thereafter, the above laser processing sequence is repeated to form modified layers110in the wafer10along all the projected dicing lines14that extend in the second direction. In this manner, the modified layers100are formed in the wafer10along all the projected dicing lines14established on the face side10aof the wafer10. The modified layer forming step is now completed.

Laser processing conditions in the modified layer forming step of the second division are set as follows, for example.

Average output power: 1.0 W

After the modified layer forming step, the wafer10is delivered from the laser processing apparatus40. Then, as illustrated inFIG.8, an annular frame F having an opening Fa capable of accommodating the wafer10therein is prepared for performing a dividing step, and the wafer10is held by the annular frame F through an adhesive tape T applied to both of them and interposed therebetween while the protective film L′ formed on the face side10ais facing upwardly and the reverse side10bis facing downwardly. Then, as illustrated inFIG.9, the protective film L′ is removed from the wafer10. After the protective film L′ has been removed from the wafer10, external forces G are exerted radially outwardly on the wafer10to pull the adhesive tape T in radially outward directions, dividing the wafer10into individual device chips12′. At this point, the dividing step is ended. The second division is now completed.

The second division offers the same advantages as with the first division because the resin applying step, the resin curing step, and the planarizing step have already been carried out. Accordingly, the wafer10can well be divided into individual device chips12′ in the second division.

The various types of division referred to above include third division for dividing the wafer10into individual device chips. The third division can be carried out in combination with the method of processing a wafer that includes the resin applying step, the resin curing step, and the planarizing step. The third division will be described below with reference toFIGS.10A through10C.

After the resin applying step, the resin curing step, and the planarizing step, in the third division, as illustrated inFIG.10A, an annular frame F having an opening Fa capable of accommodating the wafer10therein is prepared, and the wafer10with the protective film L′ formed on the face side10athereof is positioned centrally in the opening Fa with the protective film L′ facing upwardly. The wafer10is held by the annular frame F through an adhesive tape T applied to both of them and interposed therebetween. Since the protective film L′ is formed on the face side10aof the wafer10, the wafer10is held on the adhesive tape T with the face side10afacing upwardly inFIG.10A.

The wafer10is then delivered to the laser processing apparatus40described above with reference toFIGS.4A through4Cto perform a laser ablation step. The wafer10is placed and held under suction on the suction chuck42fof the chuck table42ewhile the protective film L′ formed on the face side10ais facing upwardly. Then, the alignment processing described above is performed on the wafer10held on the chuck table42eon the basis of an image of the wafer10captured by the image capturing unit43of the laser processing apparatus40. Specifically, the control unit detects one of the projected dicing lines14formed on the face side10a, from the captured image. The rotary actuating means, not illustrated, coupled to the chuck table42eis actuated to turn the wafer10to bring the projected dicing line14into alignment with the X-axis directions. The control unit, not illustrated, stores the positional information of the detected projected dicing line14.

Then, on the basis of the positional information of the detected projected dicing line14, the beam condenser41aof the laser applying unit41is positioned in alignment with the projected dicing line14that extends in a first direction, as illustrated inFIG.10A. At the same time that the X-axis feed mechanism46is actuated to processing-feed the chuck table42ein one of the X-axis directions, the beam condenser41ais moved in one of the Z-axis directions to position a focused spot of a laser beam LB3whose wavelength is absorbable by the wafer10on the face side10aalong the projected dicing line14, and the laser applying unit41emits and applies the laser beam LB3to the wafer10, thereby forming a dividing groove120in the protective film L′ and the wafer10along the projected dicing line14extending in the first direction by way of laser ablation. The protective film L′ and the wafer10are ruptured along the dividing groove120. After the dividing groove120has been formed in the protective film L′ and the wafer10along the projected dicing line14, the Y-axis feed mechanism47is actuated to indexing-feed the chuck table42eand hence the wafer10in one of the Y-axis directions by a distance equal to the interval between adjacent projected dicing lines14and to position, directly below the beam condenser41aof the laser applying unit41, a next projected dicing line14where no dividing groove120has been formed extending in the first direction. Then, at the same time that the X-axis feed mechanism46is actuated to processing-feed the chuck table42ein one of the X-axis directions, the beam condenser41ais moved in one of the Z-axis directions if necessary to position the focused spot of the laser beam LB3on the face side10aalong the next projected dicing line14, and the laser applying unit41emits and applies the laser beam LB3to the wafer10, thereby forming a dividing groove120in the protective film L′ and the wafer10along the next projected dicing line14. Similarly, dividing grooves120are formed in the protective film L′ and the wafer10along all the projected dicing lines14that extend in the first direction. Then, the wafer10is turned 90 degrees to align, with the X-axis directions, all the projected dicing lines14that extend in a second direction perpendicular to the first direction and that have not undergone the processing. Thereafter, the above laser processing sequence is repeated to form dividing grooves120in the protective film L′ and the wafer10along all the projected dicing lines14that extend in the second direction. In this manner, the dividing grooves120are formed in the protective film L′ and the wafer10along all the projected dicing lines14established on the face side10aof the wafer10, as illustrated inFIG.10B. The laser ablation step is now completed.

Laser processing conditions in the laser ablation step of the third division are set as follows, for example.

Average output power: 3.0 W

As illustrated inFIG.10B, since the protective film L′ and the wafer10are ruptured along the dividing grooves120, the wafer10is divided into individual device chips12′. The protective film L′ is removed as required to expose the face side10aof the wafer10, as illustrated inFIG.10C, making the device chips12′ readily available for pickup. The protective film L′ may be removed by any of various types of processing. For example, a solvent for dissolving the protective film L′ may be applied to the surface thereof, or an adhesive tape having appropriate adhesive power may be affixed to the surface of the protective film L′ and pulled to peel off the protective film L′.

The various types of division referred to above include fourth division for dividing the wafer10into individual device chips. The fourth division can be carried out in combination with the method of processing a wafer that includes the resin applying step, the resin curing step, and the planarizing step. The fourth division will be described below with reference toFIGS.11A through13B.

In the fourth division, prior to the resin applying step, a groove forming step is carried out to form grooves in the wafer10along the projected dicing lines14established on the face side10aof the wafer10. Specifically, the wafer10is delivered to a cutting apparatus60illustrated inFIG.11A. As illustrated inFIG.11A, the cutting apparatus60includes a chuck table, not illustrated, for holding the wafer10under suction thereon and a cutting unit62for cutting the wafer10held under suction on the chuck table. The chuck table is rotatable about its vertical central axis. The cutting apparatus60also includes X-axis moving means, not illustrated, for processing-feeding the chuck table and hence the wafer10held thereon in an X-axis direction indicated by an arrow X. The cutting unit62includes a spindle housing63, a spindle64rotatably supported in the spindle housing63for rotation about its horizontal central axis extending parallel to a Y-axis direction indicated by an arrow Y, an annular cutting blade65held on a distal end of the spindle64, and a blade cover66covering the cutting blade65. The cutting apparatus60further includes Y-axis moving means, not illustrated, for indexing-feeding the cutting blade65in the Y-axis direction. The spindle64is rotatable by a spindle motor, not illustrated.

For carrying out the groove forming step according to the present embodiment, the wafer10is placed and held under suction on the chuck table of the cutting apparatus60with the face side10afacing upwardly. One of the projected dicing lines14of the wafer10that extend in a first direction is aligned with the X-axis direction and positioned in alignment with the cutting blade65. The cutting blade65that is rotating at a high speed in the direction indicated by an arrow R7is positioned in alignment with the projected dicing line14aligned with the X-axis direction. Then, the cutting blade65is forced to cut into the wafer10from the face side10ato a depth terminating short of the reverse side10bbut reaching at least a finish thickness of the devices12, and at the same time, the chuck table is processing-fed in the X-axis direction, thereby forming a groove130in the wafer10along the projected dicing line14, as illustrated inFIG.11B. Thereafter, the cutting blade65of the cutting unit62is indexing-fed in the Y-axis direction into alignment with a next projected dicing line14where no groove130has been formed, the next projected dicing line14extending in the first direction and being disposed adjacent to the projected dicing line14where the groove130has just been formed. Then, the cutting blade65cuts into the wafer10, forming a groove130in the wafer10along the next projected dicing line14. The above cutting processing is repeated to form grooves130in the wafer10along all the projected dicing lines14that extend in the first direction. Then, the chuck table is turned 90 degrees to align, with the X-axis direction, one of the projected dicing lines14of the wafer10that extend in a second direction perpendicular to the first direction, and to position the projected dicing line14in alignment with the cutting blade65. The above cutting processing is repeated to form grooves130in the wafer10along all the projected dicing lines14that extend in the second direction. As illustrated inFIG.11C, grooves130are now formed in all the projected dicing lines14established on the face side10aof the wafer10. The groove forming step is now completed.

After the groove forming step, the resin applying step of coating the face side10aof the wafer10with the liquid resin L to cover an area of the wafer10where the devices12are present, the resin curing step of curing the liquid resin L into the protective film L′, and the planarizing step of planarizing the protective film L′ are carried out. After the planarizing step, the wafer10with the planarized protective film L′ is delivered to a grinding apparatus50illustrated inFIG.12to perform a dividing step. The grinding apparatus50illustrated inFIG.12is the same as the grinding apparatus50described above with reference toFIG.6, and will not be described in detail below. The protective film L′ of the wafer10is placed and held under suction on the chuck table51of the grinding apparatus50. As illustrated inFIG.12, the reverse side10bof the wafer10is ground by the grindstones52duntil the grooves130are exposed and the wafer10is finished to achieve a finish thickness of the devices12. As a result, as illustrated in an upper inset inFIG.13A, the wafer10is divided into individual device chips12′. The dividing step is now completed.

At the time that the wafer10is simply divided into the device chips12′, the wafer10still remains integral, retaining its shape, on account of the protective film L′ affixed to the face side10a. As illustrated inFIG.13A, an annular frame F having an opening Fa capable of accommodating the wafer10therein is prepared, and the wafer10is turned upside down to orient the protective film L′ formed on the face side10aupwardly and to orient the reverse side10bdownwardly and is positioned centrally in the opening Fa. The wafer10is held by the annular frame F through an adhesive tape T applied to both of them and interposed therebetween. Then, as illustrated inFIG.13B, the protective film L′ is removed from the wafer10, exposing the face side10aof the wafer10that has been divided into the individual device chips12′, so that the individual device chips12′ can readily be picked up. When the fourth division is carried out, the resin applying step, the resin curing step, and the planarizing step are also carried out in combination therewith. Since the protective film L′ has been uniformized in thickness, when the dividing step is carried out to grind the reverse side10bof the wafer10and divide the wafer10into individual device chips12′, the wafer10is prevented from being broken.