WAFER MANUFACTURING METHOD AND PROCESSING APPARATUS

In a flattening step included in a series of steps for manufacturing wafers from an ingot, the ingot is ground until the ingot has a thickness smaller than a thickness of the ingot as of the point in time when the series of steps is to be started, by a thickness obtained by adding up a finishing thickness of the wafer, an assumed thickness of a separation layer, and a distributed thickness obtained by dividing a surplus thickness of the ingot by a number obtained by subtracting one from a maximum number of wafers that can be manufactured from the ingot.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a wafer manufacturing method for manufacturing three or more wafers from an ingot and a processing apparatus therefor.

Description of the Related Art

Semiconductor device chips are typically manufactured with use of a wafer including a single crystal of silicon (Si), silicon carbide (SiC), gallium nitride (GaN), lithium tantalate (LiTaO3: LT), or lithium niobate (LiNbO3: LN), for example. This wafer is, for example, manufactured by being cut out from the ingot by a wire saw.

The cutting allowance for cutting out the wafer from the ingot by a wire saw is approximately 300 μm, which is relatively large. Moreover, minute surface irregularities are formed on a surface of the wafer which has been cut out as described above, and this wafer would be curved in whole (warp would occur in the wafer). Hence, when this wafer is to be used to manufacture chips, the surface of the wafer needs to be flattened by lapping, etching, and/or polishing being applied thereto.

In this case, the final amount of material used as the wafer is approximately two-thirds of the total amount of ingot. Stated differently, approximately one-third of the total amount of ingot is discarded when the wafer is cut out from the ingot and subsequently flattened on the surface thereof. Hence, manufacturing the wafer by a wire saw in the manner described above tends to lower productivity.

In light of this situation, there has been proposed a wafer manufacturing method for manufacturing a wafer from an ingot with use of a laser beam having a wavelength transmittable through the material of the ingot (see, for example, Japanese Patent Laid-open No. 2019-12765). Specifically, in this method, first, while a laser beam is applied to an ingot in such a manner that a focal point at which the laser beam is focused is positioned inside the ingot, the focal point and the ingot are moved relative to each other.

This leads to formation of a separation layer including modified portions and cracks extending from the modified portions inside the ingot. Further, in this method, external force is applied to the ingot such that the cracks further extend. Consequently, the ingot is separated at the separation layer, and a wafer is manufactured.

Further, when the wafer is manufactured from the ingot in this way, a separation layer (an ingot-side remaining separation layer and a wafer-side remaining separation layer) remains in each of the ingot and the wafer. Hence, in the wafer manufacturing method described above, each of the ingot and the wafer is ground, so that the ingot-side remaining separation layer and the wafer-side remaining separation layer are each removed, and each of the ingot and the wafer is flattened.

SUMMARY OF THE INVENTION

When the abovementioned wafer manufacturing method is repeated, an ingot having a thickness slightly smaller than the thickness necessary for manufacturing two wafers is sometimes left. In this case, the last wafer is manufactured by the ingot being ground over a long period of time until a finishing thickness of the wafer is obtained.

Yet, when a maximum number of wafers are to be manufactured from each ingot while a plurality of ingots are simultaneously processed, grinding each ingot over a long period of time for manufacturing the last wafer might become a bottleneck. In other words, in this case, when the last wafer is to be manufactured by grinding a specific ingot, processing of other ingots may be suspended over a long period of time.

In view of such a problem, an object of the present invention is to provide a wafer manufacturing method that is capable of reducing the length of time necessary for manufacturing the maximum number of wafers from each ingot while a plurality of ingots are processed simultaneously and a processing apparatus to be used for the wafer manufacturing method.

In accordance with an aspect of the present invention, there is provided a wafer manufacturing method for manufacturing three or more wafers from an ingot by repeating a series of steps including a separation layer forming step of forming a separation layer inside the ingot, a separating step of manufacturing each of the wafers by separating the ingot at the separation layer, after the separation layer forming step, and a flattening step of flattening each of the ingot and the wafer by removing each of an ingot-side remaining separation layer remaining in the ingot and a wafer-side remaining separation layer remaining in the wafer, after the separating step, the wafer manufacturing method including a calculating step of calculating a maximum number of the wafers manufacturable from the ingot and a surplus thickness of the ingot by referring to an initial thickness of the ingot, a finishing thickness of the wafer, and an assumed thickness of the separation layer, prior to manufacturing three or more of the wafers from the ingot. In the separation layer forming step, the separation layer is formed by moving, relative to each other, the ingot and a focal point where a laser beam having a wavelength transmittable through a material of the ingot is focused, while the laser beam is applied to the ingot such that the focal point is positioned to a predetermined depth from a face side of the ingot, and, in the flattening step, the ingot is ground until the ingot has a thickness smaller than a thickness of the ingot as of the point in time when the series of steps is to be started, by a thickness obtained by adding up the finishing thickness, the assumed thickness, and a distributed thickness obtained by dividing the surplus thickness by a number obtained by subtracting one from the maximum number, and the wafer is ground until the wafer has the finishing thickness.

Preferably, the predetermined depth is a depth corresponding to a first thickness obtained by adding up the finishing thickness and a thickness of the wafer-side remaining separation layer. Alternatively, the predetermined depth is preferably a depth corresponding to a second thickness obtained by adding up the finishing thickness, a thickness of the wafer-side remaining separation layer, and the distributed thickness. Still alternatively, the predetermined depth is preferably a depth greater than a first thickness obtained by adding up the finishing thickness and a thickness of the wafer-side remaining separation layer but smaller than a second thickness obtained by adding up the first thickness and the distributed thickness.

In accordance with another aspect of the present invention, there is provided a processing apparatus for manufacturing three or more wafers from an ingot, including a laser processing unit for forming a separation layer inside the ingot, a separating unit for manufacturing each of the wafers by separating the ingot at the separation layer, a flattening unit for flattening the ingot by removing an ingot-side remaining separation layer remaining in the ingot, and a controller that controls the laser processing unit, the separating unit, and the flattening unit such that a series of steps including forming of the separation layer, separating of the ingot, and flattening of the ingot is repeated the number of times obtained by subtracting one from a maximum number of the wafers manufacturable from the ingot, in which the controller includes a memory for storing an initial thickness of the ingot, a finishing thickness of the wafers, and an assumed thickness of the separation layer, and a processor for calculating the maximum number and a surplus thickness of the ingot by referring to the initial thickness, the finishing thickness, and the assumed thickness, and the processor controls the laser processing unit such that the separation layer is formed by moving, relative to each other, the ingot and a focal point where a laser beam having a wavelength transmittable through a material of the ingot is focused, while the laser beam is applied to the ingot in such a manner that the focal point is positioned to a predetermined depth from a face side of the ingot, and controls the flattening unit such that the ingot is ground until the ingot has a thickness smaller than a thickness of the ingot as of the point in time when the series of steps is to be started, by a thickness obtained by adding up the finishing thickness, the assumed thickness, and a distributed thickness obtained by dividing the surplus thickness by a number obtained by subtracting one from the maximum number.

In the flattening step (specifically, the flattening of the ingot) included in the series of steps for manufacturing wafers from an ingot according to the present invention, the ingot is ground until the ingot has a thickness that is smaller than the thickness of the ingot as of the point in time when the series of steps is to be started, by a thickness obtained by adding up the finishing thickness of the wafer, the assumed thickness of the separation layer, the distributed thickness obtained by dividing the surplus thickness of the ingot by a number obtained by subtracting one from the maximum number of wafers manufacturable from the ingot.

When this series of steps is repeated, an ingot having a thickness that is equal to or greater than a minimum thickness of the ingot necessary for manufacturing the last wafer (specifically, a thickness obtained by adding up the finishing thickness of the wafer and the thickness of the ingot-side remaining separation layer) but equal to or smaller than a thickness obtained by adding up the minimum thickness of the ingot necessary for manufacturing the last wafer and the distributed thickness is subjected to the final flattening step.

In this case, grinding the ingot until the finishing thickness of the wafer is reached reduces the length of time necessary for manufacturing the last wafer. Hence, applying the present invention as the method for manufacturing a maximum number of wafers from each ingot while a plurality of ingots are simultaneously processed makes it unlikely for grinding of the ingots for manufacturing the last wafer from the ingots to become a bottleneck, making it possible to reduce the length of time necessary for such grinding.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment of the present invention will be described with reference to the attached drawings.FIG.1Ais a perspective view schematically illustrating an example of an ingot, whileFIG.1Bis a side view schematically illustrating the ingot depicted inFIG.1A. The ingot denoted by11and depicted inFIGS.1A and1Bis, for example, a single crystal of SiC and has a cylindrical shape having a face side11aand a reverse side11bthat are substantially parallel to each other.

The ingot11is manufactured with use of epitaxial growth. Note that, in order to have fewer lattice defects inside the ingot11, the ingot11is manufactured in such a manner that a c-axis11cof SiC is slightly tilted with respect to a perpendicular line11dof the face side11aand the reverse side11b. For example, an angle (off angle) a formed between the c-axis11cand the perpendicular line11dis 1° to 6° (typically 4°).

Further, on a side surface of the ingot11, two flat portions, i.e., a first orientation flat13and a second orientation flat15, for indicating a crystal orientation of SiC are formed. The first orientation flat13is longer than the second orientation flat15. The second orientation flat15is formed in such a manner as to be parallel to a crossline where a plane parallel to a c-plane11eof SiC intersects with the face side11aor the reverse side11b.

Note that the ingot11may be formed with use of, as a material, a single crystal of a substance other than SiC (for example, Si, GaN, LT, LN, or the like). Further, on the side surface of the ingot11, one of or both the first orientation flat13and the second orientation flat15may not be provided. Moreover, in place of such orientation flats, a cutout (notch) for indicating the crystal orientation of the material constituting the ingot11may be formed.

FIG.2is a flowchart schematically illustrating an example of the wafer manufacturing method for manufacturing three or more wafers from the ingot11. Stated briefly, this method repeats a series of steps for separating and flattening the ingot (n−1) times which is a number obtained by subtracting one from n (n is a natural number of three or more) which is the maximum number of wafers that can be manufactured from the ingot11and thereby manufactures n wafers from the ingot11.

Further, in this method, instead of being performed all at once in the series of steps performed for manufacturing the last wafer, removal of the surplus thickness (that is, a thickness that is a surplus of the thickness necessary for manufacturing n wafers) from the ingot11is performed in stages in each series of steps performed (n−1) times.

Specifically, in each series of steps in the method, the thickness of the ingot11is reduced by a thickness obtained by adding up the minimum thickness (specifically, a thickness obtained by adding up a finishing thickness of the wafer and an assumed thickness of the separation layer that are described later) of the ingot11that decreases in association with the manufacturing of the wafer and a distributed thickness (specifically, a thickness obtained by dividing the surplus thickness by (n−1)).

In the wafer manufacturing method illustrated inFIG.2, first, the parameters identified beforehand are referred to, and then, n, which is the maximum number of wafers that can be manufactured from the ingot11, and the surplus thickness of the ingot11are calculated (calculating step S1).FIG.3is a side view schematically illustrating the parameters to be referred to in the calculating step S1.

In the calculating step S1, reference is made to an initial thickness T0of the ingot11, a finishing thickness (that is, a thickness of the wafer that has been flattened in a non-final flattening step S5and a final flattening step S6that are described later) T1of the wafer, and an assumed thickness (that is, a thickness which the separation layer formed inside the ingot11in the separation layer forming step S2described later is assumed to have) T2of the separation layer.

Specifically, in this method, the ingot11is separated (n−1) times which is a number obtained by subtracting one from n which is the maximum number of wafers that can be manufactured from the ingot11. Hence, the initial thickness T0of the ingot11has a value that satisfies the following inequations (1) and (2).

Further, when the inequations (1) and (2) above are modified, n which is the maximum number of wafers that can be manufactured from the ingot11can be recognized to be a natural number that satisfies the following inequation (3).

Further, if n, which is the maximum number of wafers that can be manufactured from the ingot11, can be calculated, the surplus thickness T3of the ingot11that is represented by the following equation (4) can also be calculated.

Moreover, if n, which is the maximum number of wafers that can be manufactured from the ingot11, and the surplus thickness T3of the ingot11are calculated, a distributed thickness ΔT of the ingot11that is represented by the following equation (5) can also be calculated.

For example, when the initial thickness T0of the ingot11is 20 mm (20,000 μm), the finishing thickness T1of the wafer is 350 μm, and the assumed thickness T2of the separation layer is 80 μm, n which is the maximum number of wafers that can be manufactured from the ingot11is 46, and the surplus thickness T3of the ingot11is 300 μm. Further, in this case, the distributed thickness ΔT of the ingot11is 6.67 μm.

After the calculating step S1, a separation layer is formed inside the ingot11(separation layer forming step S2).FIG.4is a perspective view schematically illustrating the manner of the separation layer forming step S2. Note that an X-axis direction and a Y-axis direction that are illustrated inFIG.4are directions perpendicular to each other in a horizontal plane, and a Z-axis direction is a direction (vertical direction) perpendicular to the X-axis direction and the Y-axis direction.

The separation layer forming step S2is performed in a laser processing apparatus2. The laser processing apparatus2has a chuck table4including a circular holding surface that is substantially parallel to a horizontal plane and that can hold the ingot11thereon.

The chuck table4is coupled to a suction mechanism (not illustrated). This suction mechanism has, for example, an ejector or the like. When the suction mechanism is operated, suction force acts in a space near the holding surface of the chuck table4. Hence, when the suction mechanism is operated in a state in which the ingot11is placed on the holding surface, the ingot11is held on the holding surface of the chuck table4.

Further, the chuck table4is coupled to a rotation mechanism (not illustrated). This rotation mechanism has, for example, a pulley, a motor, and the like. When the rotation mechanism is operated, the chuck table4rotates about a straight line passing through the center of the holding surface and extending along the Z-axis direction, as a rotational axis.

Above the chuck table4, a head8of a laser beam application unit6is provided. The head8is provided on a distal end portion of a cylindrical housing10extending along the Y-axis direction. Note that, the head8houses an optical system such as a condensing lens and a mirror, while the housing10houses an optical system such as a mirror and/or a lens.

A proximal end portion of the housing10is coupled to a moving mechanism. This moving mechanism has, for example, a ball screw, a motor, and the like. When the moving mechanism is operated, the head8and the housing10move along the X-axis direction, the Y-axis direction, and/or the Z-axis direction.

The laser beam application unit6includes a laser oscillator (not illustrated) that generates a laser beam having a wavelength (for example, 1,064 nm) that is transmittable through the material of the ingot11. This laser oscillator includes, for example, a laser medium such as neodymium-doped yttrium aluminum garnet (Nd:YAG). When a laser beam is generated by the laser oscillator, the laser beam is emitted toward the holding surface side of the chuck table4through the optical systems housed in the housing10and the head8.

Further, provided on a side portion of the housing10is an imaging unit12that is capable of capturing an image of the holding surface side of the chuck table4. The imaging unit12includes, for example, a light source such as a light emitting diode (LED), an objective lens, and an imaging element such as a charge coupled device (CCD) image sensor or a complementary metal oxide semiconductor (CMOS) image sensor.

When the separation layer forming step S2is to be performed in the laser processing apparatus2, first, the ingot11is placed on the holding surface of the chuck table4such that the face side11afaces upward. Next, the suction mechanism is operated such that the ingot11is held on the chuck table4. Subsequently, in reference to the image of the face side11aof the ingot11which has been captured by the imaging unit12and the like, the rotation mechanism rotates the chuck table4such that the second orientation flat15becomes parallel to the X-axis direction.

Then, the moving mechanism moves the head8and the housing10along the X-axis direction and/or the Y-axis direction such that a region in the ingot11that is slightly on the inner side from the second orientation flat15is positioned in the X-axis direction as viewed from the head8in plan view. Next, the moving mechanism moves the head8and the housing10along the Z-axis direction such that a focal point where the laser beam emitted from the head8is focused is positioned to a predetermined depth from the face side11aof the ingot11.

The predetermined depth is set with reference to the parameters identified beforehand. Specifically, the predetermined depth is set to be equal to or greater than a thickness (first thickness) obtained by adding up the finishing thickness T1of the wafer and a thickness of the separation layer (wafer-side remaining separation layer) that remains in the wafer after the wafer has been separated from the ingot11but equal to or smaller than a thickness (second thickness) that is obtained by adding up the first thickness and the distributed thickness ΔT of the ingot11. Further, in brief, the thickness of the wafer-side remaining separation layer is a thickness corresponding to a thickness obtained by subtracting the thickness of the separation layer (ingot-side remaining separation layer) that remains in the ingot11after the wafer has been separated from the ingot11from the assumed thickness T2of the separation layer.

Next, while a laser beam is emitted from the head8, the moving mechanism moves the head8and the housing10along the X-axis direction such that the focal point where the laser beam is focused passes through the ingot11from one end to the other end thereof in the X-axis direction. That is, while a laser beam is applied to the ingot11, the ingot11and the focal point where the laser beam is focused are moved relative to each other along a crossline where a plane parallel to the c-plane11eof the material (here, SiC) of the ingot11intersects with the face side11a.

Subsequently, the moving mechanism moves the head8and the housing10along the Y-axis direction such that the head8is positioned in the X-axis direction as viewed from a region slightly farther from the second orientation flat15than the region to which the laser beam has already been applied, in plan view. Then, a laser beam is applied again to the ingot11as described above.

Further, until the completion of laser beam application to the region in the ingot11that is farthest from the second orientation flat15, the movement of the head8and the housing10along the Y-axis direction and the application of the laser beam to the ingot11are repeated. This completes the separation layer forming step S2.

FIG.5Ais a cross sectional view schematically illustrating, in an enlarged form, part of the ingot11that has undergone the separation layer forming step S2, whileFIG.5Bis a plan view schematically illustrating the ingot11that has undergone the separation layer forming step S2. In the separation layer forming step S2, the modified portions17in which the crystal structure of the material (here, SiC) of the ingot11is disordered are formed inside the ingot11with the focal point where the laser beam is focused as the center.

Further, when the modified portions17are formed inside the ingot11, the volume of the ingot11expands, and internal stress is generated in the ingot11. This internal stress is mitigated by cracks19extending from the modified portions17. Note that the cracks19mainly extend along the c-plane11e. As a result, a separation layer21that includes a plurality of modified portions17and the cracks19extending from the plurality of modified portions17is formed inside the ingot11.

After the separation layer forming step S2, a wafer is manufactured by the ingot11being separated at the separation layer21(separating step3).FIGS.6A and6Bare each a side view schematically illustrating the manner of the separating step S3. The separating step S3is performed in a separating apparatus14. The separating apparatus14includes a chuck table16having the same structure as the chuck table4illustrated inFIG.4.

The chuck table16is coupled to a table-side suction mechanism (not illustrated). The table-side suction mechanism has, for example, a vacuum pump or the like. When this table-side suction mechanism is operated, suction force acts in a space near a holding surface of the chuck table16. Hence, when the table-side suction mechanism is operated in a state in which the ingot11is placed on the holding surface, the ingot11is held on the holding surface of the chuck table16.

Above the chuck table16, there is provided a separating unit18. The separating unit18has a suction plate20which has, on its lower surface, a plurality of suction ports. The plurality of suction ports are in communication with a separating unit-side suction mechanism such as a vacuum pump via suction channels formed inside the suction plate20. When the separating unit-side suction mechanism is operated, suction force acts in a space near the lower surface of the suction plate20.

Further, an upper portion of the suction plate20is coupled to a vertical direction moving mechanism22. The vertical direction moving mechanism22has, for example, an air cylinder or the like. When the vertical direction moving mechanism22is operated, the suction plate20moves along the vertical direction.

When the separating step S3is to be performed in the separating apparatus14, first, the ingot11in which the separation layer21is formed in the inside thereof is placed on the holding surface of the chuck table16such that the face side11afaces upward, in a state in which the chuck table16and the suction plate20are sufficiently spaced from each other. Next, the table-side suction mechanism is operated such that the ingot11is held on the chuck table16.

Subsequently, the vertical direction moving mechanism22lowers the suction plate20such that the lower surface of the suction plate20comes into contact with the face side11aof the ingot11(seeFIG.6A). Then, the separating unit-side moving mechanism is operated such that the face side11aof the ingot11is sucked toward the upper side.

Next, the vertical direction moving mechanism22lifts the suction plate20such that the suction plate20is spaced from the chuck table16(seeFIG.6B). At this time, tensile stress acts on the ingot11, and the cracks19included in the separation layer21further extend.

As a result, the ingot11is separated at the separation layer21, and an ingot11in which the face side11aincludes the ingot-side remaining separation layer and a wafer23in which one side includes the wafer-side remaining separation layer are manufactured. Note that each of the face side11aof the ingot11and the one side of the wafer23has a recessed and protruding shape reflecting the distribution of the modified portions17and the cracks19in the separation layer21. This completes the separating step S3.

When the ingot11has not yet been separated (n−1) times (step S4: NO), the ingot11is ground until the ingot11has a predetermined thickness, so that the ingot-side remaining separation layer is removed, and the ingot11is flattened, and the wafer23is ground until the wafer23has the finishing thickness T1, so that the wafer-side remaining separation layer is removed, and the wafer23is flattened (non-final flattening step S5).

Note that the predetermined thickness is a thickness that is smaller than the thickness of the ingot11as of the point in time of start of the series of steps including the separation layer forming step S2, the separating step S3, and the non-final flattening step S5(that is, the point in time of start of the separation layer forming step S2), by a thickness obtained by adding up the finishing thickness T1of the wafer23, the assumed thickness T2of the separation layer21, and the distributed thickness ΔT of the ingot11.

FIG.7is a perspective view schematically illustrating the manner of the non-final flattening step S5. The non-final flattening step S5is performed in a grinding apparatus24. The grinding apparatus24includes a chuck table26having a holding surface that has a shape corresponding to a conical side surface in which the center is slightly protruding than the outer edge and that can hold the wafer23thereon.

The chuck table26is coupled to a suction mechanism. This suction mechanism has an ejector or the like. When the suction mechanism is operated, suction force acts in a space near the holding surface of the chuck table26. Hence, when the suction mechanism is operated in a state in which the ingot11or the wafer23is placed on the holding surface, the ingot11or the wafer23is held on the holding surface of the chuck table26.

Further, the chuck table26is coupled to a horizontal direction moving mechanism. The horizontal direction moving mechanism has, for example, a ball screw, a motor, and the like. When the horizontal direction moving mechanism is operated, the chuck table26moves along the horizontal direction.

Further, the chuck table26is coupled to a rotation mechanism (not illustrated). The rotation mechanism has, for example, a pulley, a motor, and the like. When the rotation mechanism is operated, the chuck table26rotates about a straight line passing through the center of the holding surface, as the rotational axis.

Provided near the chuck table26is a measuring unit (not illustrated). The measuring unit has, for example, a contact-type or non-contact-type thickness measuring instrument or the like. The measuring unit can measure the thickness of the ingot11or the wafer23that is held on the holding surface of the chuck table26.

Above the chuck table26, a grinding unit28is provided. The grinding unit28has a spindle30whose upper end portion is coupled to a motor. A lower end portion of the spindle30is provided with a disk-shaped mount32, and a grinding wheel34is mounted on the mount32.

The grinding wheel34includes an annular base36and a plurality of grindstones38disposed in a spaced manner along a circumferential direction of the base36. Lower surfaces of the plurality of grindstones38are disposed at substantially the same height, and serve as the grinding surfaces for grinding the ingot11and the wafer23.

The spindle30is coupled to a vertical direction moving mechanism. The vertical direction moving mechanism has, for example, a ball screw, a motor, and the like. When the vertical direction moving mechanism is operated, the spindle30, the mount32, and the grinding wheel34move along the vertical direction.

When the non-final flattening step S5is to be performed in the grinding apparatus24, for example, the wafer23is ground to the finishing thickness T1after the ingot11has been ground to the predetermined thickness described above. In this case, first, in a state in which the chuck table26and the grinding wheel34are sufficiently spaced from each other in each of the horizontal direction and the vertical direction, the ingot11is placed on the holding surface of the chuck table26in such a manner that the face side11afaces upward.

Next, the suction mechanism is operated such that the ingot11is held on the chuck table26. Subsequently, the horizontal direction moving mechanism moves the chuck table26such that the center of the holding surface of the chuck table26and the trajectory followed by the plurality of grindstones38when the grinding wheel34is rotated together with the spindle30overlap in the vertical direction.

Then, the rotation mechanism is operated to rotate the chuck table26, and the motor coupled to the upper end portion of the spindle30is operated to rotate the grinding wheel34. Next, the spindle30, the mount32, and the grinding wheel34are lowered by the vertical direction moving mechanism such that the grinding surface of any of the plurality of grindstones38comes into contact with the face side11aof the ingot11.

This starts grinding of the ingot11. This grinding, i.e., lowering the grinding wheel34while both the chuck table26and the grinding wheel34are rotated, is continued until the thickness of the ingot11measured by the measuring unit reaches the abovementioned predetermined thickness.

When the grinding of the ingot11is completed, the horizontal direction moving mechanism and the vertical direction moving mechanism are operated such that rotation of both the chuck table26and the grinding wheel34is stopped and the chuck table26and the grinding wheel34are sufficiently spaced from each other in each of the horizontal direction and the vertical direction.

Next, the wafer23is ground to the finishing thickness T1by a procedure similar to the one described above. This completes the non-final flattening step S5. Note that, in the non-final flattening step S5, one of the grinding of the ingot11or the grinding of the wafer23may be performed in a grinding apparatus different from the grinding apparatus24. In this case, grinding of the ingot11can be performed in tandem with grinding of the wafer23.

Further, the thickness of the ingot11and the thickness of the wafer23each of which is to be removed in the non-final flattening step S5change depending on the abovementioned predetermined depth (that is, the distance between the focal point of the laser beam to be applied to the ingot11in the separation layer forming step S2and the face side11aof the ingot11).

Specifically, in a case where the predetermined depth corresponds to the abovementioned first thickness (that is, the thickness obtained by adding up the finishing thickness T1of the wafer23and the thickness of the wafer-side remaining separation layer), the thickness of the ingot11to be removed in the non-final flattening step S5corresponds to a thickness obtained by adding up the thickness of the ingot-side remaining separation layer and the distributed thickness ΔT of the ingot11, while the thickness of the wafer23to be removed in the non-final flattening step S5corresponds to the thickness of the wafer-side remaining separation layer.

In this case, even if the cracks19inadvertently extend longer toward the reverse side11bof the ingot11in the separation layer forming step S2and the separating step S3, it is highly likely that the ingot11can be flattened without the cracks19remaining in the ingot11.

Further, in a case where the predetermined depth corresponds to the second thickness mentioned above (that is, the thickness obtained by adding up the first thickness and the distributed thickness ΔT of the ingot11), the thickness of the ingot11to be removed in the non-final flattening step S5corresponds to the thickness of the ingot-side remaining separation layer, while the thickness of the wafer23to be removed in the non-final flattening step S5corresponds to the thickness obtained by adding up the thickness of the wafer-side remaining separation layer and the distributed thickness ΔT of the ingot11.

In this case, even if the cracks19inadvertently extend longer toward the face side11aof the ingot11in the separation layer forming step S2and the separating step S3, it is highly likely that the wafer23can be flattened without the cracks19remaining in the wafer23.

Further, in a case where the predetermined depth is greater than the first thickness but smaller than the second thickness, the thickness of the ingot11to be removed in the non-final flattening step S5corresponds to a thickness obtained by adding up the thickness of the ingot-side remaining separation layer and a thickness obtained by multiplying the distributed thickness ΔT of the ingot11by (k/k+1) (k is a positive real number), while the thickness of the wafer23to be removed in the non-final flattening step S5corresponds to a thickness obtained by adding up the thickness of the wafer-side remaining separation layer and a thickness obtained by multiplying the distributed thickness ΔT of the ingot11by (1/k+1).

In this case, even if the cracks19inadvertently extend to some extent toward the face side11aand the reverse side11bof the ingot11in the separation layer forming step S2and the separating step S3, it is highly likely that both the ingot11and the wafer23can be flattened without the cracks19remaining in both the ingot11and the wafer23.

After the non-final flattening step S5, the separation layer forming step S2and the separating step S3are performed again. Further, until the ingot11is separated (n−1) times, the non-final flattening step S5, the separation layer forming step S2, and the separating step S3are repeated in turn.

When the ingot11is separated (n−1) times (step S4: YES), each of the ingot11and the wafer23is ground to the finishing thickness T1, so that the separation layers remaining in the ingot11and the wafer23(that is, the ingot-side remaining separation layer and the wafer-side remaining separation layer) are removed, and the ingot11and the wafer23(two wafers) are flattened (final flattening step S6).

Note that the thickness of the ingot11as of the point in time when the series of steps including the separation layer forming step S2, the separating step S3, and the final flattening step S6is to be started (that is, the point in time when the separation layer forming step S2that is to be performed for the last time is to be started) corresponds to a thickness obtained by adding up a thickness obtained by doubling the finishing thickness T1of the wafer23, the assumed thickness T2of the separation layer21, and the distributed thickness ΔT of the ingot11.

Further, the thickness of the ingot11as of the point in time when the final flattening step S6is to be started is equal to or greater than the minimum thickness of the ingot11necessary for manufacturing the last wafer23(specifically, a thickness obtained by adding up the finishing thickness T1of the wafer23and the thickness of the ingot-side remaining separation layer) but equal to or smaller than a thickness obtained by adding up the minimum thickness of the ingot11necessary for manufacturing the last wafer23and the distributed thickness ΔT of the ingot11.

The final flattening step S6is performed in a manner similar to that of the non-final flattening step S5described above. Hence, detailed description of the final flattening step S6is omitted here. Upon completion of the final flattening step S6, manufacturing n wafers23from the ingot11is completed. In other words, the wafer manufacturing method illustrated inFIG.2is completed.

In the non-final flattening step S5included in the series of steps for manufacturing the wafers23from the ingot11in the wafer manufacturing method illustrated inFIG.2, the ingot11is ground until the ingot11has a thickness that is smaller than the thickness of the ingot11as of the point in time when the series of steps is to be started, by the thickness obtained by adding up the finishing thickness T1of the wafer23, the assumed thickness T2of the separation layer21, and the distributed thickness ΔT of the ingot11obtained by dividing the surplus thickness T3of the ingot11by (n−1) which is a number obtained by subtracting one from n which is the maximum number of wafers23that can be manufactured from the ingot11.

When the series of steps is repeated, an ingot11having a thickness that is equal to or greater than the minimum thickness of the ingot11necessary for manufacturing the last wafer23(specifically, the thickness obtained by adding up the finishing thickness T1of the wafer23and the thickness of the ingot-side remaining separation layer) but is equal to or smaller than the thickness obtained by adding up the minimum thickness of the ingot11necessary for manufacturing the last wafer23and the distributed thickness ΔT of the ingot11is subjected to the final flattening step S6.

In this case, grinding the ingot11until the finishing thickness T1of the wafer23is obtained reduces the length of time necessary for manufacturing the last wafer23. Hence, applying the wafer manufacturing method illustrated inFIG.2as the method for manufacturing the maximum n wafers23from each ingot11while simultaneously processing a plurality of ingots11makes it unlikely for the grinding of the ingot11for manufacturing the last wafer23from each ingot11to become a bottleneck, making it possible to reduce the length of time necessary for manufacturing the last wafer23.

Note that the details described above are one mode of the present invention, the present invention is not limited to the details described above. For example, in the present invention, before the calculating step S1, a measuring step of measuring the initial thickness T0of the ingot11may be performed.

Further, in the present invention, after the separation layer forming step S2but before the separating step S3, an ultrasonic wave applying step of applying ultrasonic waves to the face side11aof the ingot11may be performed. In this case, the cracks19included in the separation layer21extend in the ultrasonic wave applying step, and the ingot11is easily separated in the separating step S3.

Further, the present invention may relate to a processing apparatus for manufacturing three or more wafers23from the ingot11.FIG.8is a block diagram schematically illustrating an example of such a processing apparatus. The processing apparatus denoted by40and illustrated inFIG.8includes a laser processing unit42, a separating unit44, a flattening unit46, and a controller48.

The laser processing unit42has, for example, a structure similar to that of the laser processing apparatus2illustrated inFIG.4. Hence, in the laser processing unit42, the separation layer21can be formed inside the ingot11in the manner described above.

The separating unit44has, for example, a structure similar to that of the separating apparatus14illustrated inFIGS.6A and6B. Hence, in the separating unit44, the ingot11can be separated at the separation layer21, and the wafer23can be manufactured, in the manner described above.

The flattening unit46has, for example, a structure similar to that of the grinding apparatus24illustrated inFIG.7. Hence, in the flattening unit46, the ingot-side remaining separation layer remaining in the ingot11and the wafer-side remaining separation layer remaining in the wafer23can each be removed, and each of the ingot11and the wafer23can be flattened, in the manner described above.

Note that, in the flattening unit46, only the flattening of the ingot11may be performed. In this case, a flattening unit different from the flattening unit46may be provided in the processing apparatus40, and perform flattening of the wafer23. Alternatively, in this case, flattening of the wafer23may be performed in an apparatus (for example, a grinding apparatus) different from the processing apparatus40.

The controller48includes a processor50and a memory52. The processor50includes, for example, a central processing unit (CPU) and the like. Further, the memory52includes, for example, a volatile memory such as a dynamic random access memory (DRAM) or a static random access memory (SRAM) and a non-volatile memory such as a solid state drive (SSD) (a Not AND (NAND) flash memory) or a hard disk drive (HDD) (a magnetic storage device).

The memory52stores data, programs, and the like used in the processor50. Examples of the data include, for example, the initial thickness T0of the ingot11, the finishing thickness T1of the wafer23, the assumed thickness T2of the separation layer21, the thickness of the ingot-side remaining separation layer, and the thickness of the wafer-side remaining separation layer. Further, examples of the programs include programs used for performing the wafer manufacturing method illustrated inFIG.2in the processing apparatus40.

The processor50reads out and executes the programs stored in the memory52while using the data stored in the memory52. For example, the processor50refers to the initial thickness T0of the ingot11and other relevant data items stored in the memory52and reads out from the memory52the program for performing the wafer manufacturing method illustrated inFIG.2, to execute the program.

Specifically, when the wafer manufacturing method illustrated inFIG.2is to be performed in the processing apparatus40, first, the processor50refers to the initial thickness T0of the ingot11, the finishing thickness T1of the wafer23, and the assumed thickness T2of the separation layer21that are stored in the memory52, and calculates n, which is the maximum number of wafers23that can be manufactured from the ingot11, and the surplus thickness T3of the ingot11(calculating step S1).

Further, the processor50causes the memory52to store n, i.e., the maximum number of wafers23that can be manufactured from the ingot11, and the surplus thickness T3of the ingot11. Further, the processor50may calculate the distributed thickness ΔT of the ingot11by referring to n, i.e., the maximum number of wafers23that can be manufactured from the ingot11, and the surplus thickness T3of the ingot11, and may cause the memory52to store the calculated distributed thickness ΔT.

When the calculating step S1is completed, the processor50controls the laser processing unit42, the separating unit44, and the flattening unit46such that the series of steps including the forming of the separation layer21(the separation layer forming step S2), the separating of the ingot11(the separating step S3), and the flattening of the ingot11(the non-final flattening step S5or the final flattening step S6) is repeated (n−1) times, which is a number obtained by subtracting one from n, i.e., the maximum number of wafers23that can be manufactured from the ingot11.

Further, in the processing apparatus according to the present invention, instead of all the processing units (specifically, the laser processing unit, the separating unit, and the flattening unit) being controlled by one controller, each processing unit may be provided with one controller and controlled by a different controller.FIG.9is a block diagram schematically illustrating an example of a processing apparatus in which a controller is provided for each processing unit.

The processing apparatus denoted by54and illustrated inFIG.9includes a laser processing unit56having a sub-controller56a, a separating unit58having a sub-controller58a, a flattening unit60having a sub-controller60a, and a main controller62. In other words, the processing apparatus54has a structure similar to that of the processing apparatus40illustrated inFIG.8, except that the controller48is divided into the sub-controllers56a,58a, and60aand the main controller62.

The laser processing unit56has, for example, the sub-controller56aincluding a processor and a memory, in addition to the constituent elements similar to those of the laser processing apparatus2illustrated inFIG.4. This memory stores, for example, data, programs, and the like necessary for performing the forming of the separation layer21(the separation layer forming step S2) in the laser processing unit56.

The separating unit58has, for example, the sub-controller58aincluding a processor and a memory, in addition to the constituent elements similar to those of the separating apparatus14illustrated inFIGS.6A and6B. This memory stores, for example, data, programs, and the like necessary for performing the separating of the ingot11(the separating step S3) in the separating unit58.

The flattening unit60has, for example, the sub-controller60aincluding a processor and a memory, in addition to the constituent elements similar to those of the grinding apparatus24illustrated inFIG.7. This memory stores, for example, data, programs, and the like necessary for performing the flattening of the ingot11and the wafer23(the non-final flattening step S5and the final flattening step S6) in the flattening unit60.

Note that, in the flattening unit60, only the flattening of the ingot11may be performed. In this case, a flattening unit different from the flattening unit60may be provided in the processing apparatus54, and perform flattening of the wafer23. Alternatively, in this case, flattening of the wafer23may be performed in an apparatus (for example, a grinding apparatus) different from the processing apparatus54.

The main controller62includes a processor and a memory. This memory stores in advance, for example, the initial thickness T0of the ingot11, the finishing thickness T1of the wafer23, the assumed thickness T2of the separation layer21, the thickness of the ingot-side remaining separation layer, and the thickness of the wafer-side remaining separation layer. Further, the main controller62is connected to the sub-controllers56a,58a, and60avia a wired or wireless communication line.

In the processing apparatus54, the calculating step S1is carried out by the main controller62. Specifically, the processor of the main controller62calculates n, i.e., the maximum number of wafers23that can be manufactured from the ingot11, and the surplus thickness T3of the ingot11, by referring to the initial thickness T0of the ingot11, the finishing thickness T1of the wafer23, and the assumed thickness T2of the separation layer21that are stored in the memory of the main controller62.

Further, the processor of the main controller62transmits, to the sub-controller56a, data necessary for identifying the predetermined depth described above (that is, the distance between the focal point of the laser beam to be applied to the ingot11in the separation layer forming step S2and the face side11aof the ingot11). Note that this data includes, for example, the finishing thickness T1of the wafer23, the thickness of the wafer-side remaining separation layer, and data (specifically, n, i.e., the maximum number of wafers23that can be manufactured from the ingot11, and the surplus thickness T3of the ingot11) necessary for calculating the distributed thickness ΔT of the ingot11.

Further, the processor of the main controller62transmits, to the sub-controller60a, data necessary for identifying the predetermined thickness described above. Note that the data includes, for example, the finishing thickness T1of the wafer23, the assumed thickness T2of the separation layer21, and the data necessary for calculating the distributed thickness ΔT of the ingot11.

Note that the processor of the main controller62may calculate the distributed thickness ΔT of the ingot11in addition to n, i.e., the maximum number of wafers that can be manufactured from the ingot11, and the surplus thickness T3of the ingot11. In this case, the processor of the main controller62may transmit, to the sub-controllers56aand60a, the distributed thickness ΔT of the ingot11per se, in place of the data necessary for calculating the distributed thickness ΔT of the ingot11.

When the calculating step S1is completed in the main controller62, the main controller62transmits a signal instructing the sub-controller56ato perform the forming of the separation layer21(the separation layer forming step S2) in the laser processing unit56. Further, when the separation layer forming step S2is completed by the sub-controller56acontrolling the constituent elements similar to those of the laser processing apparatus2illustrated inFIG.4, a signal indicating the completion is transmitted from the sub-controller56ato the main controller62.

When the signal from the sub-controller56ais received by the main controller62, the main controller62transmits a signal instructing the sub-controller58ato perform the separating of the ingot11(the separating step S3) in the separating unit58. Further, when the separating step S3is completed by the sub-controller58acontrolling the constituent elements similar to those of the separating apparatus14illustrated inFIGS.6A and6B, a signal indicating the completion is transmitted from the sub-controller58ato the main controller62.

When the signal from the sub-controller58ais received by the main controller62, the main controller62transmits a signal instructing the sub-controller60ato perform flattening of the ingot11(the non-final flattening step S5) in the flattening unit60. Further, when the non-final flattening step S5is completed by the sub-controller60acontrolling the constituent elements similar to those of the grinding apparatus24illustrated inFIG.7, a signal indicating the completion is transmitted from the sub-controller60ato the main controller62.

Further, transmission and reception of signals between the sub-controllers56a,58a, and60aand the main controller62are repeated until the signal indicating the completion of the separating step S3is received from the sub-controller58aby the main controller62(n−1) times, which is a number obtained by subtracting one from n, i.e., the maximum number of wafers23that can be manufactured from the ingot11.

Further, when the signal from the sub-controller58ais received by the main controller62(n−1) times, the main controller62transmits a signal instructing the sub-controller60ato perform flattening of the ingot11(the final flattening step S6) in the flattening unit60. Further, when the final flattening step S6is completed by the sub-controller60acontrolling the constituent elements similar to those of the grinding apparatus24illustrated inFIG.7, a signal indicating the completion is transmitted from the sub-controller60ato the main controller62.

In addition, the processing apparatus40or54may include additional constituent elements. For example, the processing apparatus40or54may be provided with a measuring unit for measuring the initial thickness T0of the ingot11. Further, the processing apparatus40or54may be provided with a conveying unit for conveying the ingot11into any of the laser processing unit42or56, the separating unit44or58, and the flattening unit46or60or conveying out the ingot11from any of the abovementioned units.

Furthermore, the structures, methods, and other relevant matters related to the abovementioned embodiment can be modified and implemented as appropriate without departing the scope of object of the present invention.