Patent ID: 12211732

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A method of transferring a wafer according to an embodiment of the present invention will be described hereinbelow with reference to the accompanying drawings. The method of transferring a wafer according to the present embodiment to be described below is performed after a tape has been affixed to a face side of a wafer and held on a chuck table and then a laser beam having a wavelength transmittable through the wafer has been applied to a reverse side of the wafer while a focused spot of the laser beam is being positioned within the wafer along projected dicing lines thereof, thereby forming modified layers in the wafer along the projected dicing lines. After the modified layers have been formed in the wafer, the method of transferring a wafer is carried out, and the face side of the wafer is exposed upwardly. Thereafter, external forces are exerted on the wafer to divide the wafer into individual device chips along the modified layers that function as division initiating points, and then a pick-up step is carried out to pick up the device chips.

FIG.1illustrates in perspective a semiconductor wafer10as a workpiece to be transferred in the method of transferring a wafer. The wafer10has a face side10aas one surface where a plurality of areas are demarcated by a plurality of intersecting projected dicing lines14and a plurality of devices12are formed in the respective areas.

As illustrated in an upper section ofFIG.1, an annular first frame F1having an opening F1ain which the wafer10can be positioned and a first tape T1having a sticky layer on its face side are prepared for use in combination with the wafer10. The wafer10is positioned centrally in the opening F1awith the face side10afacing downwardly and a reverse side10bthereof as another surface facing upwardly. The wafer10and the first frame F1are pressure-bonded to the first tape T1, so that the wafer10is held on the first frame F1by the tape T1as illustrated in a lower section ofFIG.1.

The wafer10held on the first frame F1by the tape T1is then delivered to a laser processing apparatus20illustrated inFIG.2A. Only part of the laser processing apparatus20is illustrated inFIG.2A. The laser processing apparatus20includes a chuck table, not illustrated, for holding the wafer10under suction thereon and a laser beam applying unit having a beam condenser22that applies a laser beam LB having a wavelength transmittable through the wafer10to the wafer10held on the chuck table. The laser processing apparatus20also includes an X-axis feeding mechanism, not illustrated, for processing-feeding the chuck table and the beam condenser22relatively to each other in X-axis directions, a Y-axis feeding mechanism, not illustrated, for indexing-feeding the chuck table and the beam condenser22relatively to each other in Y-axis directions perpendicular to the X-axis directions, and a rotating mechanism, not illustrated, for rotating the chuck table about its vertical central axis.

The wafer10that has been delivered to the laser processing apparatus20is placed and held under suction on the chuck table of the laser processing apparatus20with the reverse side10bfacing upwardly. An alignment step is then performed on the wafer10held on the chuck table, by alignment means, not illustrated, that includes an infrared image capturing device capable of applying infrared rays to the wafer10and capturing an image of reflected rays from the infrared rays transmitted from the reverse side10bof the wafer10. In the alignment step, the position of one of the projected dicing lines14on the face side10aof the wafer10is detected, and the chuck table is rotated by the rotating mechanism to align the detected projected dicing line14with the X-axis directions on the basis of the captured image. Information regarding the detected position of the projected dicing line14is stored in control means, not illustrated, of the laser processing apparatus20.

On the basis of the information regarding the detected position of the projected dicing line14obtained in the alignment step, the beam condenser22of the laser beam applying unit is positioned at a processing start position on the projected dicing line14that extends in a first direction. The beam condenser22emits and applies the laser beam LB to the wafer10while positioning the focused spot of the laser beam LB within the wafer10along the projected dicing line14, and the X-axis feeding mechanism processing-feeds the chuck table and hence the wafer10thereon in one of the X-axis directions, thereby forming a modified layer100in the wafer10along the projected dicing line14extending in the first direction. After the modified layer100has been formed in the wafer10along the projected dicing line14, the Y-axis feeding mechanism indexing-feeds the chuck table and hence the wafer10thereon in one of the Y-axis directions by a distance commensurate with the interval between adjacent projected dicing lines14to position a next projected dicing line14extending in the first direction directly below the beam condenser22. Then, the beam condenser22emits and applies the laser beam LB to the wafer10while positioning the focused spot of the laser beam LB within the wafer10along the next projected dicing line14, and the X-axis feeding mechanism processing-feeds the chuck table and hence the wafer10thereon in one of the X-axis directions, thereby forming a modified layer100in the wafer10along the next projected dicing line14extending in the first direction. The above process is repeated to form modified layers100in the wafer10along all the projected dicing lines14that extend in the first direction. The modified layers100are formed in the wafer10along the projected dicing lines14and cannot actually be seen from outside of the wafer10. InFIGS.2A,2Band some other figures, the modified layers100are indicated by the broken lines for illustrative purposes.

Then, the rotating mechanism rotates the chuck table and hence the wafer10thereon through 90 degrees to align one of the projected dicing lines14that extend in a second direction perpendicular to the first direction with the X-axis directions. The beam condenser22emits and applies the laser beam LB to the wafer10while positioning the focused spot of the laser beam LB within the wafer10along the projected dicing line14extending in the second direction, and the X-axis feeding mechanism processing-feeds the chuck table and hence the wafer10thereon in one of the X-axis directions, thereby forming a modified layer100in the wafer10along the projected dicing line14extending in the second direction. The wafer10is then indexing-fed to position a next projected dicing line14extending in the second direction directly below the beam condenser22. Then, the beam condenser22emits and applies the laser beam LB to the wafer10while positioning the focused spot of the laser beam LB within the wafer10along the next projected dicing line14, and the X-axis feeding mechanism processing-feeds the chuck table and hence the wafer10thereon in one of the X-axis directions, thereby forming a modified layer100in the wafer10along the next projected dicing line14extending in the second direction. The above process is repeated to form modified layers100in the wafer10along all the projected dicing lines14that extend in the second direction, as illustrated inFIG.2B. In this manner, the modified layers100are formed in the wafer10along all the projected dicing lines14on the face side10aof the wafer10. After the laser processing apparatus20has processed the wafer10with the laser beam LB, the method of transferring a wafer according to the present embodiment is carried out in order to make the wafer10ready for the pick-up step following the division of the wafer10into individual device chips.

The process that is to be applied to the wafer10for making the wafer10suitable for method of transferring a wafer according to the present invention is not limited to the laser processing process described above, and may be a cutting process that can be performed by a dicing apparatus30illustrated inFIG.3, for example. The cutting process will be described below with reference toFIG.3.

The wafer10held on the first frame F1by the tape T1as described above with reference toFIG.1is delivered to the dicing apparatus30illustrated inFIG.3. Only part of the dicing apparatus30is illustrated inFIG.3.

The dicing apparatus30includes a chuck table, not illustrated, for holding the wafer10under suction and a cutting unit31for cutting the wafer10held under suction on the chuck table. The chuck table is rotatable about its central axis by a rotating mechanism. The dicing apparatus30also includes an X-axis moving mechanism, not illustrated, for processing-feeding the chuck table in X-axis directions indicated by an arrow X. The cutting unit31includes a spindle33rotatably supported in a spindle housing32axially extending in Y-axis directions indicated by an arrow Y, an annular cutting blade34mounted on a distal end of the spindle33, a cutting fluid nozzle35for supplying a cutting fluid to a region where the wafer10is cut by the cutting blade34, and a blade cover36covering the cutting blade34. The dicing apparatus30also includes a Y-axis moving mechanism, not illustrated, for indexing-feeding the cutting blade34in the Y-axis directions. The cutting blade34on the distal end of the spindle33is rotatable about its central axis by a spindle motor, not illustrated, in the direction indicated by an arrow R1.

Prior to a dividing step of dividing the wafer10into individual device chips with the cutting blade34, the wafer10is placed and held under suction on the chuck table of the dicing apparatus30with the reverse side10bfacing upwardly. An alignment step, which is similar to the alignment step described above, is then performed on the wafer10, aligning one of the projected dicing lines14extending in a first direction with the X-axis directions and the cutting blade34. Then, the cutting blade34that is being rotated at a high speed is forced to cut into the wafer10from the reverse side10balong the projected dicing line14aligned with the X-axis directions, and the chuck table is processing-fed by the X-axis moving mechanism to form a dividing groove110in the wafer10along the projected dicing line14. Then, the chuck table is indexing-fed by the Y-axis moving mechanism to align a next projected dicing line14extending in the first direction with the X-axis directions and the cutting blade34. Then, the cutting blade34forms a dividing groove110in the wafer10along the next projected dicing line14in the same manner as described above. The above process is repeated to form dividing grooves110in the wafer10along all the projected dicing lines14that extend in the first direction.

Then, the rotating mechanism rotates the chuck table and hence the wafer10thereon through 90 degrees to align one of the projected dicing lines14that extend in a second direction perpendicular to the first direction with the X-axis directions and the cutting blade34. The cutting process described above is performed on the wafer10along all the projected dicing lines14extending in the second direction, thereby forming dividing grooves110in the wafer10along all the projected dicing lines14extending in the second direction. After the dicing apparatus30has formed the dividing grooves110in the wafer10with the cutting blade34, dividing the wafer10into individual device chips including the respective devices12, the method of transferring a wafer according to the present embodiment is carried out. The method of transferring a wafer according to the present embodiment will be described below. According to the present embodiment, it is assumed that the laser processing apparatus20has processed the wafer10with the laser beam LB before the method of transferring a wafer is carried out.

The wafer10processed by the laser beam LB is delivered to a table40for removing a frame illustrated inFIG.4A, and positioned above the table40. The table40is a substantially circular table having an annular tapered surface42as an upper surface and a circular flat suction chuck43that is disposed centrally on the annular tapered surface42and that is similar in dimension to the wafer10. The suction chuck43is made of an air-permeable porous material and fluidly connected to suction means, not illustrated. As illustrated inFIG.4B, the annular tapered surface42includes a slanted surface that is progressively lower toward an outer circumferential edge thereof. The table40has a plurality of suction holes44defined therethrough that are open in the annular tapered surface42at spaced intervals along a circular array surrounding the suction chuck43. The suction holes44are also fluidly connected to the suction means. When the suction means is actuated, it generates a negative pressure Vm that is transmitted to the suction chuck43and hence an upper surface thereof and also to the suction holes44.

After the wafer10held on the first frame F1by the first tape T1has been positioned above the table40, the suction means is actuated, and the first frame F1is fixed in position by fixing means, not illustrated. Then, as illustrated inFIG.4B, pressing forces P for pressing the first tape T1downwardly are applied to an annular region of the first tape T1that lies between the first frame F1and the wafer10, detaching the first tape T1downwardly from the first frame F1(first-frame removing step). As illustrated inFIG.4C, the wafer10is drawn under the negative pressure Vm to the suction chuck43, and an outer circumferential region of the first tape T1is drawn under the negative pressure Vm to the annular tapered surface42of the table40.

After the first-frame removing step has been carried out, as illustrated inFIG.5A, a second frame F2with a circular second tape T2pressure-bonded thereto is prepared. The second frame F2has an opening F2ain which the wafer10can be positioned. The second frame F2with the circular second tape T2pressure-bonded thereto has a reverse side facing upwardly. According to the present embodiment, the second frame F2and the first frame F1are made of the same structure and material, whereas the second tape T2and the first tape T1are made of the same structure and material.

Then, the second tape T2that is pressure-bonded to the second frame F2and has the sticky layer facing downwardly is pressure-bonded to the upwardly facing reverse side10bof the wafer10held under suction on the table40. The second tape T2is pressure-bonded to the reverse side10bof the wafer10with use of a pressure-bonding roller50illustrated inFIG.5B, for example. Specifically, the pressure-bonding roller50is rotated about its central axis in the direction indicated by an arrow R2while pressing the second tape T2against the wafer10and moved in the direction indicated by an arrow R3, thereby progressively pressure-bonding the second tape T2to the reverse side10bof the wafer10(second-tape pressure-bonding step).FIG.5Cillustrates in side elevation the manner in which the second-tape pressure-bonding step is carried out, with only the second tape T2and the second frame F2being illustrated in cross section. As illustrated inFIG.5C, the second tape T2is inclined to the reverse side10bof the wafer10, and the pressure-bonding roller50is pressed downwardly against the second tape T2while being rotated in the direction indicated by the arrow R2and moved in the direction indicated by the arrow R3, progressively pressure-bonding the second tape T2to the reverse side10bof the wafer10in a manner to progressively flatten the slanted second tape T2against the wafer10. Therefore, air is prevented from being trapped between the second tape T2and the reverse side10bof the wafer10. According to the present embodiment, since the table40has the annular tapered surface42as its upper surface as described above, the outer circumferential region of the first tape T1is not pressure-bonded to the second tape T2.

After the second-tape pressure-bonding step has been carried out, the suction means fluidly connected to the table40is inactivated, releasing the first tape T1from the table40. As illustrated inFIG.6, a pressure-bonding force reducing step is carried out to reduce the pressure-bonding force of the first tape T1by imparting an external stimulus to the first tape T1. In the pressure-bonding force reducing step, specifically, ultraviolet ray applying means60is positioned above the first tape T1and applies ultraviolet rays L to the first tape T1. The first tape T1is an ultraviolet-curable tape that can be cured upon exposure to ultraviolet rays L. The ultraviolet rays L are applied as an external stimulus to the first tape T1, reducing the pressure-bonding force of the first tape T1by curing the sticky layer thereof (pressure-bonding force reducing step). InFIG.6, the ultraviolet ray applying means60is illustrated as being positioned above the first tape T1to apply ultraviolet rays L from above to the first tape T1. Actually, however, after the second-tape pressure-bonding step has been carried out as illustrated in FIGS.5A through5C, the first tape T1is turned over to face downwardly and the ultraviolet ray applying means60applies ultraviolet rays L from below to the first tape T1. The first tape T1is thus prevented from being bonded to the second tape T2. However, the present invention is not limited to the actual process in which the first tape T1faces downwardly and the ultraviolet ray applying means60applies ultraviolet rays L from below to the first tape T1. According to the present invention, the first tape T1may face upwardly and the ultraviolet ray applying means60may apply ultraviolet rays L from above to the first tape T1.

After the pressure-bonding force reducing step has been carried out, as illustrated in an upper section ofFIG.7, the first tape T1whose pressure-bonding force has been reduced is peeled off from the face side10aof the wafer10that is pressure-bonded to the second tape T2(peeling step). For carrying out the peeling step, a peeling tape T3is affixed to an outer circumferential portion of the first tape T1as illustrated in the upper section ofFIG.7, and then pulled horizontally to peel off the first tape T1from the face side10aof the wafer10as illustrated in a lower section ofFIG.7. The wafer10is thus transferred from the first tape T1to the second tape T2without the wafer10being damaged. The wafer10as transferred to the second tape T2has the face side10afacing upwardly in readiness for the pick-up step. The method of transferring a wafer according to the present embodiment now comes to an end.

After the wafer10has been transferred from the first tape T1to the second tape T2with the face side10abeing exposed, external forces are exerted on the wafer10to divide the face side10aalong the modified layers100that function as division initiating points into individual device chips. Then, the pick-up step is carried out to pick up the individual device chips.

According to the above embodiment, the pressure-bonding force reducing step is carried out after the first-frame removing step and the second-tape pressure-bonding step have been carried out. However, the present invention is not limited to such a sequence of steps. The pressure-bonding force reducing step may be carried out after the first-frame removing step has been carried out.

Further, according to the above embodiment, ultraviolet rays are imparted as an external stimulus to the first tape T1in the pressure-bonding force reducing step. However, the present invention is not limited to ultraviolet rays as an external stimulus. Another form of external stimulus such as heating or cooling may be imparted to the first tape T1to reduce the pressure-bonding force thereof. An external stimulus to be applied to the first tape T1is selected depending on the material of the first tape T1.

Moreover, according to the above embodiment, the first tape T1has a sticky layer on its face side and the second tape T2also has a sticky layer on its face side. However, the present invention is not limited to such a tape structure. The first tape T1and the second tape T2may each include a thermocompression bonding tape free of a sticky layer, which is made of polyolefin or polyester that develops sticky power when heated.

The present invention is not limited to the details of the above described preferred embodiment. The scope of the invention is defined by the appended claim and all changes and modifications as fall within the equivalence of the scope of the claim are therefore to be embraced by the invention.