Patent ID: 12194570

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The same or corresponding parts in the respective drawings are denoted with the same reference signs, and repetitive descriptions will be omitted.

[Configuration of Laser Processing Device]

As illustrated inFIG.1, a laser processing apparatus1includes a stage2, a light source3, a spatial light modulator4, a converging lens5, and a control unit6. The laser processing apparatus1is a device that forms a modified region12on an object11by irradiating the object11with laser light L. A first horizontal direction is referred to as an X direction below, and a second horizontal direction perpendicular to the first horizontal direction is referred to as a Y direction below. The vertical direction is referred to as a Z direction.

The stage2supports the object11by, for example, adsorbing a film attached to the object11. In the present embodiment, the stage2is movable along each of the X direction and the Y direction. The stage2is rotatable about an axis parallel to the Z direction.

The light source3outputs the laser light L having transparency to the object11, for example, by a pulse oscillation method. The spatial light modulator4modulates the laser light L output from the light source3. The spatial light modulator4is, for example, a spatial light modulator (SLM) of a reflective liquid crystal (LCOS: Liquid Crystal on Silicon). The converging lens5converges the laser light L modulated by the spatial light modulator4. In the present embodiment, the spatial light modulator4and the converging lens5are movable along the Z direction as a laser irradiation unit.

If the laser light L is converged in the object11supported by the stage2, the laser light L is particularly absorbed at a portion corresponding to a converging point C of the laser light L, and thus the modified region12is formed in the object11. The modified region12is a region in which the density, the refractive index, the mechanical strength, and other physical properties are different from those of the surrounding non-modified region. Examples of the modified region12include a melting treatment region, a fracture region, a dielectric breakdown region, and a refractive index change region.

As an example, if the stage2is moved along the X-direction and the converging point C is moved relative to the object11along the X-direction, a plurality of modified spots13are formed to be arranged in one row along the X-direction. One modified spot13is formed by irradiation with the laser light L of one pulse. The modified region12in one row is a set of a plurality of modified spots13arranged in one row. Adjacent modified spots13may be connected to each other or separated from each other, depending on the relative movement speed of the converging point C with respect to the object11and the repetition frequency of the laser light L.

The control unit6controls the stage2, the light source3, the spatial light modulator4, and the converging lens5. The control unit6is configured as a computer device including a processor, a memory, a storage, a communication device, and the like. In the control unit6, software (program) read into the memory or the like is executed by the processor, and thus reading and writing of data in the memory and the storage and communication by a communication device are controlled by the processor. Thus, the control unit6realizes various functions.

[Laser Processing Method and Semiconductor Member Manufacturing Method in First Embodiment]

As illustrated inFIGS.2and3, an object11of a laser processing method and a semiconductor member manufacturing method according to a first embodiment is a GaN ingot (semiconductor ingot, semiconductor object)20formed of gallium nitride (GaN) in, for example, a disc shape. As an example, the diameter of the GaN ingot20is 2 in and the thickness of the GaN ingot20is 2 mm. The laser processing method and the semiconductor member manufacturing method in the first embodiment are performed to cut out a plurality of GaN wafers (semiconductor wafer, semiconductor member)30from the GaN ingot20. As an example, the diameter of the GaN wafer30is 2 in and the thickness of the GaN wafer30is 100 μm.

Firstly, the laser processing apparatus1described above forms a plurality of modified spots13along each of a plurality of virtual planes15. Each of the plurality of virtual planes15is a plane facing the surface20aof the GaN ingot20in the GaN ingot20, and is set to be arranged in a direction facing the surface20a. In the present embodiment, each of the plurality of virtual planes15is a plane parallel to the surface20a, and has, for example, a circular shape. The plurality of virtual planes15are set to overlap each other when viewed from the surface20aside. In the GaN ingot20, a plurality of peripheral edge regions16are set to surround the plurality of virtual planes15, respectively. That is, each of the plurality of virtual planes15does not reach a side surface20bof the GaN ingot20. As an example, the distance between the adjacent virtual planes15is 100 μm, and the width (in the present embodiment, distance between the outer edge of the virtual plane15and the side surface20b) of the peripheral edge region16is equal to or more than 30 μm.

The plurality of modified spots13are sequentially formed for each virtual plane15from an opposite side of the surface20a, for example, by irradiation with laser light L having a wavelength of 532 nm. Since the plurality of modified spots13are formed in each of the plurality of virtual planes15in a similar manner, the formation of the plurality of modified spots13along the virtual plane15which is the closest to the surface20awill be described below in detail with reference toFIGS.4to11. InFIGS.5,7,9, and11, an arrow indicates the trajectory of the converging point C of the laser light L. In addition, modified spots13a,13b,13c, and13ddescribed later may be collectively referred to as the modified spot13, and fractures14a,14b,14c, and14ddescribed later may be collectively referred to as a fracture14.

Firstly, as illustrated inFIGS.4and5, the laser processing apparatus1forms a plurality of modified spots (first modified spots)13aalong the virtual plane15(for example, so as to be two-dimensionally arranged along all virtual planes15) by causing laser light L to enter into the GaN ingot20from the surface20a(first step). At this time, the laser processing apparatus1forms the plurality of modified spots13aso that the plurality of fractures14arespectively extending from the plurality of modified spots13aare not connected to each other. In addition, the laser processing apparatus1forms a plurality of rows of modified spots13aby moving the converging point C of the laser light L pulse-oscillated along the virtual plane15. InFIGS.4and5, the modified spot13ais indicated by a white outline (without hatching), and a range in which the fracture14aextends is indicated by a broken line (this is similarly applied toFIGS.6to11).

In the present embodiment, the laser light L pulse-oscillated is modulated by the spatial light modulator4so as to be converged at a plurality (for example, six) of converging points C arranged in the Y direction. The plurality of converging points C are relatively moved on the virtual plane15along the X direction. As an example, the distance between the converging points C adjacent to each other in the Y direction is 8 μm, and the pulse pitch (that is, value obtained by dividing the relative movement speed of the plurality of converging points C by the repetition frequency of the laser light L) of the laser light L is 10 μm. The pulse energy of the laser light L per converging point C (simply referred to as “pulse energy of the laser light L” below) is 0.33 μJ. In this case, the center-to-center distance between the modified spots13aadjacent to each other in the Y direction is 8 μm, and the center-to-center distance between the modified spots13aadjacent to each other in the X direction is 10 μm. The plurality of fractures14arespectively extending from the plurality of modified spots13aare not connected to each other.

As illustrated inFIGS.6and7, the laser processing apparatus1forms a plurality of modified spots (second modified spots)13balong the virtual plane15(for example, so as to be two-dimensionally arranged along all virtual planes15) by causing laser light L to enter into the GaN ingot20from the surface20a(second step). At this time, the laser processing apparatus1forms the plurality of modified spots13bso as not to overlap the plurality of modified spots13aand the plurality of fractures14a. In addition, the laser processing apparatus1forms a plurality of rows of modified spots13bby moving the converging point C of the laser light L pulse-oscillated along the virtual plane15between the rows of the plurality of rows of modified spots13a. In this step, a plurality of fractures14brespectively extending from the plurality of modified spots13bmay be connected to the plurality of fractures14a. InFIGS.6and7, the modified spot13bis indicated by dot hatching, and a range in which the fracture14bextends is indicated by a broken line (this is similarly applied toFIGS.8to11).

In the present embodiment, the laser light L pulse-oscillated is modulated by the spatial light modulator4so as to be converged at a plurality (for example, six) of converging points C arranged in the Y direction. The plurality of converging points C are relatively moved on the virtual plane15along the X direction at the center between the rows of the plurality of rows of modified spots13a. As an example, the distance between the converging points C adjacent to each other in the Y direction is 8 μm, and the pulse pitch of the laser light L is 10 μm. The pulse energy of the laser light L is 0.33 μJ. In this case, the center-to-center distance between the modified spots13badjacent to each other in the Y direction is 8 μm, and the center-to-center distance between the modified spots13badjacent to each other in the X direction is 10 μm.

As illustrated inFIGS.8and9, the laser processing apparatus1forms a plurality of modified spots (third modified spots)13calong the virtual plane15(for example, so as to be two-dimensionally arranged along all virtual planes15) by causing laser light L to enter into the GaN ingot20from the surface20a(second step). Furthermore, as illustrated inFIGS.10and11, the laser processing apparatus1forms a plurality of modified spots (third modified spots)13dalong the virtual plane15(for example, so as to be two-dimensionally arranged along all virtual planes15) by causing laser light L to enter into the GaN ingot20from the surface20a(second step). At this time, the laser processing apparatus1forms the plurality of modified spots13cand13dso as not to overlap the plurality of modified spots13aand13b. In addition, the laser processing apparatus1forms a plurality of rows of modified spots13cand13dby moving the converging point C of the laser light L pulse-oscillated along the virtual plane15between the rows of the plurality of rows of modified spots13aand13b. In this step, a plurality of fractures14cand14drespectively extending from the plurality of modified spots13cand13dmay be connected to the plurality of fractures14aand14b. InFIGS.8and9, the modified spot13cis indicated by solid-line hatching, and a range in which the fracture14cextends is indicated by a broken line (this is similarly applied toFIGS.10and11). InFIGS.10and11, the modified spot13dis indicated by solid-line hatching (solid-line hatching inclined opposite to the solid-line hatching of the modified spot13c), and a range in which the fracture14dextends is indicated by a broken line.

In the present embodiment, the laser light L pulse-oscillated is modulated by the spatial light modulator4so as to be converged at a plurality (for example, six) of converging points C arranged in the Y direction. The plurality of converging points C are relatively moved on the virtual plane15along the X direction at the center between the rows of the plurality of rows of modified spots13aand13b. As an example, the distance between the converging points C adjacent to each other in the Y direction is 8 μm, and the pulse pitch of the laser light L is 5 μm. The pulse energy of the laser light L is 0.33 μJ. In this case, the center-to-center distance between the modified spots13cadjacent to each other in the Y direction is 8 μm, and the center-to-center distance between the modified spots13cadjacent to each other in the X direction is 5 μm. In addition, the center-to-center distance between the modified spots13dadjacent to each other in the Y direction is 8 μm, and the center-to-center distance between the modified spots13dadjacent to each other in the X direction is 5 μm.

A heating device including a heater or the like heats the GaN ingot20, and thus the plurality of fractures14respectively extending from the plurality of modified spots13are connected to each other in each of the plurality of virtual planes15. In this manner, as illustrated inFIG.12, a fracture17crossing over the virtual plane15(simply referred to as a “fracture17” below) is formed in each of the plurality of virtual planes15. InFIG.12, the plurality of modified spots13and the plurality of fractures14, and a range in which the fracture17is formed are indicated by broken lines. A certain force may be caused to act on the GaN ingot20by a method other than heating, and thereby the plurality of fractures14may be connected to each other to form the fracture17. In addition, by forming the plurality of modified spots13along the virtual plane15, the plurality of fractures14may be connected to each other to form the fracture17.

Here, in the GaN ingot20, a nitrogen gas is generated in the plurality of fractures14respectively extending from the plurality of modified spots13. Therefore, by heating the GaN ingot20to expand the nitrogen gas, the fracture17can be formed by using the pressure (internal pressure) of the nitrogen gas. In addition, the peripheral edge region16prevents development of the plurality of fractures14to the outside (for example, side surface20bof the GaN ingot20) of the virtual plane15surrounded by the peripheral edge region16. Thus, it is possible to suppress escape of the nitrogen gas generated in the plurality of fractures14to the outside of the virtual plane15. That is, the peripheral edge region16is a non-modified region that does not include the modified spot13, and is a region that prevents development of the plurality of fractures14to the outside of the virtual plane15surrounded by the peripheral edge region16when the fracture17is formed in the virtual plane15surrounded by the peripheral edge region16. Therefore, the width of the peripheral edge region16is preferably equal to or more than 30 μm.

Then, a grinding device grinds (polishes) a portion of the GaN ingot20, which corresponds to each of the plurality of peripheral edge regions16and the plurality of virtual planes15to acquire a plurality of GaN wafers30from the GaN ingot20by using each of the plurality of fractures17as a boundary, as illustrated inFIG.13(third step). In this manner, the GaN ingot20is cut along each of the plurality of virtual planes15. In this step, portions of the GaN ingot20, which correspond to the plurality of peripheral edge regions16may be removed by machining other than grinding, laser processing, or the like.

Among the above steps, steps up to the step of forming the plurality of modified spots13along each of the plurality of virtual planes15correspond to the laser processing method in the first embodiment. Among the above steps, steps up to the step of acquiring the plurality of GaN wafers30from the GaN ingot20by using each of the plurality of fractures17as a boundary correspond to the semiconductor member manufacturing method in the first embodiment.

As described above, in the laser processing method in the first embodiment, the plurality of modified spots13aare formed along each of the plurality of virtual planes15, and the plurality of modified spots13bare formed along each of the plurality of virtual planes15so as not to overlap the plurality of modified spots13aand the plurality of fractures14a. Further, in the laser processing method in the first embodiment, the plurality of modified spots13cand13dare formed along each of the plurality of virtual planes15so as not to overlap the plurality of modified spots13aand13b. Thus, it is possible to form the plurality of modified spots13along each of the plurality of virtual planes15with high precision. As a result, it is possible to form the fracture17along each of the plurality of virtual planes15with high precision. Therefore, according to the laser processing method in the first embodiment, it is possible to acquire a plurality of suitable GaN wafers30by acquiring a plurality of GaN wafers30from the GaN ingot20by using each of the plurality of fractures17as a boundary.

Similarly, according to the laser processing apparatus1that performs the laser processing method in the first embodiment, it is possible to form the fracture17along each of the plurality of virtual planes15with high precision. Thus, it is possible to acquire a plurality of suitable GaN wafers30.

In addition, in the laser processing method in the first embodiment, the plurality of modified spots13aare formed so that the plurality of fractures14arespectively extending from the plurality of modified spots13aare not connected to each other. Thus, it is possible to form the plurality of modified spots13balong the virtual plane15with higher precision.

In addition, in the laser processing method in the first embodiment, the plurality of rows of modified spots13aare formed by moving the converging point C of the laser light L pulse-oscillated along the virtual plane15. Then, the plurality of rows of modified spots13bare formed by moving the converging point C of the laser light L pulse-oscillated along the virtual plane15between the rows of the plurality of rows of modified spots13a. Thus, it is possible to reliably prevent overlapping of the plurality of modified spots13bwith the plurality of modified spots13aand the plurality of fractures14a, and to form the plurality of modified spots13balong the virtual plane15with higher precision.

In particular, in the laser processing method in the first embodiment, if gallium nitride contained in the material of the GaN ingot20is decomposed by irradiation with the laser light L, gallium is deposited on the plurality of fractures14arespectively extending from the plurality of modified spots13a, and the laser light L is easily absorbed by the gallium. Therefore, forming the plurality of modified spots13bso as not to overlap the fractures14ais effective in forming the plurality of modified spots13balong the virtual plane15with high precision.

In the laser processing method in the first embodiment, if gallium nitride contained in the material of the GaN ingot20is decomposed by irradiation with the laser light L, a nitrogen gas is generated in the plurality of fractures14. Therefore, it is possible to easily form the fracture17by using pressure of the nitrogen gas.

Further, according to the semiconductor member manufacturing method in the first embodiment, with the step included in the laser processing method in the first embodiment, it is possible to form the fracture17along each of the plurality of virtual planes15with high precision. Thus, it is possible to acquire a plurality of suitable GaN wafers30.

In addition, in the semiconductor member manufacturing method in the first embodiment, the plurality of virtual planes15are set to be arranged in a direction facing the surface20aof the GaN ingot20. This makes it possible to acquire a plurality of GaN wafers30from one GaN ingot20.

Here, experimental results showing that, in a GaN wafer30formed by the laser processing method and the semiconductor member manufacturing method in the first embodiment, the unevenness appearing on the peeling surface of the GaN wafer30is reduced will be described.

FIG.14shows an image of a peeling surface of a GaN wafer formed by a laser processing method and semiconductor member manufacturing method in an example. (a) and (b) ofFIG.15show height profiles of the peeling surface illustrated inFIG.14. In this example, a plurality of modified spots13were formed along a virtual plane15in a manner that laser light L having a wavelength of 532 nm entered into a GaN ingot20from a surface20aof the GaN ingot20, and one converging point C was relatively moved on the virtual plane15along the X direction. At this time, the distance between the converging points C adjacent to each other in the Y direction was set to 10 μm, the pulse pitch of the laser light L was set to 1 μm, and the pulse energy of the laser light L was set to 1 μJ. In this case, as illustrated in (a) and (b) ofFIG.15, the unevenness of about 25 μm appeared on the peeling surface (surface formed by the fracture17) of the GaN wafer30.

FIG.16shows an image of a peeling surface of a GaN wafer formed by a laser processing method and semiconductor member manufacturing method in another example. (a) and (b) ofFIG.17show height profiles of the peeling surface illustrated inFIG.16. In this example, a plurality of modified spots13were formed along a virtual plane15in a similar manner to the first step and the second step of the laser processing method and the semiconductor member manufacturing method in the first embodiment, in which laser light L having a wavelength of 532 nm entered into a GaN ingot20from a surface20aof the GaN ingot20. When the plurality of modified spots13awere formed, the distance between the converging points C adjacent to each other in the Y direction was set to 6 μm, the pulse pitch of the laser light L was set to 10 μm, and the pulse energy of the laser light L was set to 0.33 μJ. When the plurality of modified spots13bwere formed, the distance between the converging points C adjacent to each other in the Y direction was set to 6 μm, the pulse pitch of the laser light L was set to 10 μm, and the pulse energy of the laser light L was set to 0.33 μJ. When the plurality of modified spots13cwere formed, the distance between the converging points C adjacent to each other in the Y direction was set to 6 μm, the pulse pitch of the laser light L was set to 5 μm, and the pulse energy of the laser light L was set to 0.33 μJ. When the plurality of modified spots13dwere formed, the distance between the converging points C adjacent to each other in the Y direction was set to 6 μm, the pulse pitch of the laser light L was set to 5 μm, and the pulse energy of the laser light L was set to 0.33 μJ. In this case, as illustrated in (a) and (b) ofFIG.17, the unevenness of about 5 μm appeared on the peeling surface of the GaN wafer30.

From the above experimental results, it has been understood that, in the GaN wafer formed by the laser processing method and the semiconductor member manufacturing method in the first embodiment, the unevenness appearing on the peeling surface of the GaN wafer30is reduced, that is, the fracture17is formed along the virtual plane15with high precision. If the unevenness appearing on the peeling surface of GaN wafer30is reduced, the amount of grinding for planarizing the peeling surface is reduced. Thus, reducing the unevenness appearing on the peeling surface of GaN wafer30is advantageous in terms of material use efficiency and production efficiency.

Next, a principle of the unevenness appearing on the peeling surface of the GaN wafer30will be described.

For example, as illustrated inFIG.18, a plurality of modified spots13aare formed along the virtual plane15, and a plurality of modified spots13bare formed along the virtual plane15so that the modified spot13boverlaps a fracture14aextending from the modified spot13aon one side thereof. In this case, since laser light L is easily absorbed by gallium deposited on a plurality of fractures14a, it is easy to form the modified spot13bon the incident side of the laser light L with respect to the modified spot13aeven though the converging point C is located on the virtual plane15. Then, a plurality of modified spots13care formed along the virtual plane15so that the modified spot13coverlaps a fracture14bextending from the modified spot13bon one side thereof. Also in this case, since laser light L is easily absorbed by gallium deposited on a plurality of fractures14b, it is easy to form the modified spot13con the incident side of the laser light L with respect to the modified spot13beven though the converging point C is located on the virtual plane15. As described above, in this example, the plurality of modified spots13bare easily formed on the incident side of the laser light L with respect to the plurality of modified spots13a, and the plurality of modified spots13care easily formed on the incident side of the laser light L with respect to the plurality of modified spots13b.

On the other hand, for example, as illustrated inFIG.19, a plurality of modified spots13aare formed along the virtual plane15, and a plurality of modified spots13bare formed along the virtual plane15so that the modified spots13bdo not overlap the fractures14aextending from the modified spots13aon both sides thereof. In this case, although the laser light L is easily absorbed by gallium deposited on the plurality of fractures14a, the modified spots13bare also formed on the virtual plane15similarly to the modified spots13a, because the modified spots13bdo not overlap the fractures14a. Then, a plurality of modified spots13care formed along the virtual plane15so that the modified spots13coverlap the fractures14aand14brespectively extending from the modified spots13aand13bon both sides thereof. Further, a plurality of modified spots13dare formed along the virtual plane15so that the modified spots13doverlap the fractures14aand14brespectively extending from the modified spots13aand13bon both sides thereof. In these cases, since laser light L is easily absorbed by gallium deposited on the plurality of fractures14aand14b, it is easy to form the modified spots13cand13don the incident side of the laser light L with respect to the modified spots13aand13beven though the converging point C is located on the virtual plane15. As described above, in this example, the plurality of modified spots13cand13dare only easily formed on the incident side of the laser light L with respect to the plurality of modified spots13aand13b.

From the above principle, it can be understood that, in the laser processing method and the semiconductor member manufacturing method in the first embodiment, it is very important to form the plurality of modified spots13bso as not to overlap the plurality of modified spots13aand the plurality of fractures14arespectively extending from the plurality of modified spots13a, in order to reduce the unevenness appearing on the peeling surface of the GaN wafer30.

Next, experimental results showing that, in the laser processing method and the semiconductor member manufacturing method in the first embodiment, the fracture17is developed along the virtual plane15with high precision will be described.

(a) and (b) ofFIG.20show images of a fracture formed in the middle of a laser processing method and a semiconductor member manufacturing method in an example. (b) ofFIG.20shows an enlarged image in a rectangular frame in (a) ofFIG.20. In this example, a plurality of modified spots13were formed along a virtual plane15in a manner that laser light L having a wavelength of 532 nm entered into a GaN ingot20from a surface20aof the GaN ingot20, and six converging points C arranged in the Y direction were relatively moved on the virtual plane15along the X direction. At this time, the distance between the converging points C adjacent to each other in the Y direction was set to 6 μm, the pulse pitch of the laser light L was set to 1 μm, and the pulse energy of the laser light L was set to 1.33 μJ. Laser processing was stopped in the middle of the virtual plane15. In this case, as illustrated in (a) and (b) ofFIG.20, the fracture developed from a processed region to an unprocessed region was greatly deviated from the virtual plane15in the unprocessed region.

(a) and (b) ofFIG.21show images of a fracture formed in the middle of a laser processing method and a semiconductor member manufacturing method in another example. (b) ofFIG.21shows an enlarged image in a rectangular frame in (a) ofFIG.21. In this example, a plurality of modified spots13were formed along a virtual plane15in a manner that laser light L having a wavelength of 532 nm entered into a GaN ingot20from a surface20aof the GaN ingot20, and six converging points C arranged in the Y direction were relatively moved on the virtual plane15along the X direction. Specifically, firstly, a plurality of rows of modified spots13were formed in Processed region1and Processed region2in a state where the distance between the converging points C adjacent to each other in the Y direction was set to 6 μm, the pulse pitch of the laser light L was set to 10 μm, and the pulse energy of the laser light L was set to 0.33 μJ. Then, a plurality of rows of modified spots13were formed in Processed region1and Processed region2in a state where the distance between the converging points C adjacent to each other in the Y direction was set to 6 μm, the pulse pitch of the laser light L was set to 10 μm, and the pulse energy of the laser light L was set to 0.33 μJ, so that each of the above rows is located between the rows of the plurality of rows of modified spots13already formed. Then, a plurality of rows of modified spots13were formed only in Processed region1in a state where the distance between the converging points C adjacent to each other in the Y direction was set to 6 μm, the pulse pitch of the laser light L was set to 5 μm, and the pulse energy of the laser light L was set to 0.33 μJ, so that each of the above rows is located between the rows of the plurality of rows of modified spots13already formed. In this case, as illustrated in (a) and (b) ofFIG.21, the fracture developed from Processed region1to Processed region2was not greatly deviated from the virtual plane15in Processed region2.

From the above experimental results, it has been understood that, in the laser processing method and the semiconductor member manufacturing method in the first embodiment, the fracture17is developed along the virtual plane15with high precision. The reason is assumed as follows: the plurality of modified spots13previously formed in Processed region2function as guides when the fracture is developed.

Next, experimental results showing that, in the laser processing method and the semiconductor member manufacturing method in the first embodiment, the extension amount of the fracture14extending from the modified spot13to the incident side of the laser light L and the opposite side thereof is suppressed will be described.

FIG.22shows an image (image in a side view) of a modified spot and a fracture formed by a laser processing method and a semiconductor member manufacturing method in a comparative example. In the comparative example, a plurality of modified spots13were formed along a virtual plane15in a manner that laser light L having a wavelength of 532 nm entered into a GaN ingot20from a surface20aof the GaN ingot20, and one converging point C was relatively moved on the virtual plane15along the X direction. Specifically, the plurality of modified spots13were formed along the virtual plane15in a state where the distance between the converging points C adjacent to each other in the Y direction was set to 2 μm, the pulse pitch of the laser light L was set to 5 μm, and the pulse energy of the laser light L was set to 0.3 μJ. In this case, as illustrated inFIG.22, the extension amount of the fracture14extending from the modified spot13to the incident side of the laser light L and the opposite side thereof was about 100 μm.

FIG.23shows images of a modified spot and a fracture formed by a laser processing method and a semiconductor member manufacturing method in a first example. (a) ofFIG.23shows an image in plan view, and (b) ofFIG.23shows an image in a side view. In the first example, a plurality of modified spots13were formed along a virtual plane15in a manner that laser light L having a wavelength of 532 nm entered into a GaN ingot20from a surface20aof the GaN ingot20, and six converging points C arranged in the Y direction were relatively moved on the virtual plane15along the X direction. Specifically, firstly, a plurality of modified spots13awere formed along the virtual plane15in a state where the distance between the converging points C adjacent to each other in the Y direction was set to 8 μm, the pulse pitch of the laser light L was set to 10 μm, and the pulse energy of the laser light L was set to 0.3 μJ. Then, a plurality of modified spots13bwere formed along the virtual plane15in a state where the distance between the converging points C adjacent to each other in the Y direction was set to 8 μm, the pulse pitch of the laser light L was set to 10 μm, and the pulse energy of the laser light L was set to 0.3 μJ in a state where the six converging points C arranged in the Y direction are shifted from the previous state in the Y direction by +4 μm. Then, a plurality of modified spots13were formed along the virtual plane15in a state where the distance between the converging points C adjacent to each other in the Y direction was set to 8 μm, the pulse pitch of the laser light L was set to 5 μm, and the pulse energy of the laser light L was set to 0.3 μJ in a state where the six converging points C arranged in the Y direction are shifted from the previous state in the Y direction by −4 μm. Then, a plurality of modified spots13were formed along the virtual plane15in a state where the distance between the converging points C adjacent to each other in the Y direction was set to 8 μm, the pulse pitch of the laser light L was set to 5 μm, and the pulse energy of the laser light L was set to 0.3 μm in a state where the six converging points C arranged in the Y direction are shifted from the previous state in the Y direction by +4 μm. Thus, it is assumed that the modified spot13aformed at the first time overlaps the modified spot13formed at the third time, and the modified spot13bformed at the second time overlaps the modified spot13formed at the fourth time. In this case, as illustrated in (b) ofFIG.23, the extension amount of the fracture14extending from the modified spot13to the incident side of the laser light L and the opposite side thereof was about 70 μm.

(a) and (b) ofFIG.24show images of a modified spot and a fracture formed by a laser processing method and a semiconductor member manufacturing method in a second example. (a) ofFIG.24shows an image in plan view, and (b) ofFIG.24shows an image in a side view. In the second example, a plurality of modified spots13were formed along a virtual plane15in a similar manner to the first step and the second step of the laser processing method and the semiconductor member manufacturing method in the first embodiment, in which laser light L having a wavelength of 532 nm entered into a GaN ingot20from a surface20aof the GaN ingot20. When the plurality of modified spots13awere formed, the distance between the converging points C adjacent to each other in the Y direction was set to 8 μm, the pulse pitch of the laser light L was set to 10 μm, and the pulse energy of the laser light L was set to 0.3 μJ. When the plurality of modified spots13bwere formed, the distance between the converging points C adjacent to each other in the Y direction was set to 8 μm, the pulse pitch of the laser light L was set to 10 μm, and the pulse energy of the laser light L was set to 0.3 μJ. When the plurality of modified spots13cwere formed, the distance between the converging points C adjacent to each other in the Y direction was set to 8 μm, the pulse pitch of the laser light L was set to 5 μm, and the pulse energy of the laser light L was set to 0.3 μJ. When the plurality of modified spots13dwere formed, the distance between the converging points C adjacent to each other in the Y direction was set to 8 μm, the pulse pitch of the laser light L was set to 5 μm, and the pulse energy of the laser light L was set to 0.3 μJ. In this case, as illustrated in (b) ofFIG.24, the extension amount of the fracture14extending from the modified spot13to the incident side of the laser light L and the opposite side thereof was about 50 μm.

(c) and (d) ofFIG.24show images of a modified spot and a fracture formed by a laser processing method and a semiconductor member manufacturing method in a third example. (c) ofFIG.24shows an image in plan view, and (d) ofFIG.24shows an image in a side view. In the third example, a plurality of modified spots13were further formed along the virtual plane15in the state illustrated in (a) and (b) ofFIG.24(that is, virtual plane15on which the plurality of rows of modified spots13were already formed). Specifically, firstly, a plurality of rows of modified spots13were formed in a state where the distance between the converging points C adjacent to each other in the Y direction was set to 8 μm, the pulse pitch of the laser light L was set to 5 μm, and the pulse energy of the laser light L was set to 0.1 μJ, so that each of the above rows is located between the rows of the plurality of rows of modified spots13already formed. In this case, as illustrated in (d) ofFIG.24, the extension amount of the fracture14extending from the modified spot13to the incident side of the laser light L and the opposite side thereof was about 60 μm.

From the above experimental results, it has been understood that, if the plurality of modified spots13bare formed along the virtual plane15so as not to overlap the plurality of modified spots13aalready formed along the virtual plane15and the plurality of fractures14a(first example, second example, and third example), the extension amount of the fracture14extending from the modified spot13to the incident side of the laser light L and the opposite side thereof is suppressed. When the plurality of modified spots13are further formed along the virtual plane15, if the plurality of modified spots13are formed along the virtual plane15so as not to overlap the plurality of modified spots13aand13balready formed along the virtual plane15(second example and third example), it is easy to form a fracture crossing over the virtual plane15.

[Laser Processing Method and Semiconductor Member Manufacturing Method in Second Embodiment]

As illustrated inFIG.25, an object11of a laser processing method and a semiconductor member manufacturing method according to a second embodiment is a GaN wafer (semiconductor wafer, semiconductor object)30formed of GaN in, for example, a disc shape. As an example, the diameter of the GaN wafer30is 2 in and the thickness of the GaN wafer30is 100 μm. The laser processing method and the semiconductor member manufacturing method in the second embodiment are performed to cut out a plurality of semiconductor devices (semiconductor members)40from the GaN wafer30. As an example, the outer shape of the GaN substrate portion of the semiconductor device40is 1 mm×1 mm, and the thickness of the GaN substrate portion of the semiconductor device40is several tens of μm.

Firstly, the laser processing apparatus1described above forms a plurality of modified spots13along each of a plurality of virtual planes15. Each of the plurality of virtual planes15is a plane facing a surface30aof the GaN wafer30in the GaN wafer30, and is set to be arranged in a direction in which the surface30aextends. In the present embodiment, each of the plurality of virtual planes15is a plane parallel to the surface30a, and has, for example, a rectangular shape. The plurality of virtual planes15are set to be two-dimensionally arranged in a direction parallel to an orientation flat31of the GaN wafer30and a direction perpendicular to the orientation flat31. In the GaN wafer30, a plurality of peripheral edge regions16are set to surround the plurality of virtual planes15, respectively. That is, each of the plurality of virtual planes15does not reach a side surface30bof the GaN wafer30. As an example, the width (in the present embodiment, half of the distance between the adjacent virtual planes15) of the peripheral edge region16corresponding to each of the plurality of virtual planes15is equal to or more than 30 μm.

The plurality of modified spots13are formed along each of the plurality of virtual planes15in a similar manner to the first step and the second step of the laser processing method and the semiconductor member manufacturing method in the first embodiment. Thus, in the GaN wafer30, as illustrated inFIG.26, a plurality of modified spots13(that is, modified spots13a,13b,13c, and13d) and a plurality of fractures14(that is, fractures14a,14b,14c, and14d) are formed along each of the plurality of virtual planes15. InFIG.26, a range in which the plurality of modified spots13and the plurality of fractures14are formed is indicated by a broken line.

Then, as illustrated inFIG.27, a semiconductor manufacturing device forms a plurality of functional elements32on the surface30aof the GaN wafer30. Each of the plurality of functional elements32is formed so that one functional element32is included in one virtual plane15when viewed from a thickness direction of the GaN wafer30. The functional element32is, for example, a light receiving element such as a photodiode, a light emitting element such as a laser diode, a circuit element such as a memory, or the like.

In the present embodiment, when the plurality of functional elements32are formed on the surface30a, the semiconductor manufacturing device functions as a heating device. That is, when the plurality of functional elements32are formed on the surface30a, the semiconductor manufacturing device heats the GaN wafer30, and thus the plurality of fractures14respectively extending from the plurality of modified spots13are connected to each other in each of the plurality of virtual planes15. In this manner, a fracture17(that is, fracture17crossing over the virtual plane15) is formed in each of the plurality of virtual planes15. InFIG.27, the plurality of modified spots13and the plurality of fractures14, and a range in which the fracture17is formed are indicated by broken lines. A heating device different from the semiconductor manufacturing device may be used. In addition, a certain force may be caused to act on the GaN wafer30by a method other than heating, and thereby the plurality of fractures14may be connected to each other to form the fracture17. In addition, by forming the plurality of modified spots13along the virtual plane15, the plurality of fractures14may be connected to each other to form the fracture17.

Here, in the GaN wafer30, a nitrogen gas is generated in the plurality of fractures14respectively extending from the plurality of modified spots13. Therefore, by heating the GaN ingot20to expand the nitrogen gas, the fracture17can be formed by using the pressure of the nitrogen gas. In addition, the peripheral edge region16prevents development of the plurality of fractures14to the outside (for example, adjacent virtual plane15, side surface30bof the GaN wafer30) of the virtual plane15surrounded by the peripheral edge region16. Thus, it is possible to suppress escape of the nitrogen gas generated in the plurality of fractures14to the outside of the virtual plane15. That is, the peripheral edge region16is a non-modified region that does not include the modified spot13, and is a region that prevents development of the plurality of fractures14to the outside of the virtual plane15surrounded by the peripheral edge region16when the fracture17is formed in the virtual plane15surrounded by the peripheral edge region16. Therefore, the width of the peripheral edge region16is preferably equal to or more than 30 μm.

Then, the laser processing apparatus cuts the GaN wafer30for each functional element32, and the grinding device grinds a portion corresponding to each of the plurality of virtual planes15. In this manner, as illustrated inFIG.28, a plurality of semiconductor devices40are acquired from the GaN wafer30by using each of the plurality of fractures17as a boundary (third step). In this manner, the GaN wafer30is cut along each of the plurality of virtual planes15. In this step, the GaN wafer30may be cut for each functional element32by machining (for example, blade dicing) other than laser processing.

Among the above steps, steps up to the step of forming the plurality of modified spots13along each of the plurality of virtual planes15correspond to the laser processing method in the second embodiment. Among the above steps, steps up to the step of acquiring the plurality of semiconductor devices40from the GaN wafer30by using each of the plurality of fractures17as a boundary correspond to the semiconductor member manufacturing method in the second embodiment.

As described above, according to the laser processing method in the second embodiment, similarly to the laser processing method in the first embodiment, it is possible to form the plurality of modified spots13along each of the plurality of virtual planes15with high precision. As a result, it is possible to form the fracture17along each of the plurality of virtual planes15with high precision. Therefore, according to the laser processing method in the second embodiment, it is possible to acquire a plurality of suitable semiconductor devices40by acquiring a plurality of semiconductor devices40from the GaN wafer30by using each of the plurality of fractures17as a boundary. Further, it is possible to reuse the GaN wafer30after the plurality of semiconductor devices40are cut out.

Similarly, according to the laser processing apparatus1that performs the laser processing method in the second embodiment, it is possible to form the fracture17along each of the plurality of virtual planes15with high precision. Thus, it is possible to acquire a plurality of suitable semiconductor devices40.

In addition, in the laser processing method in the second embodiment, the plurality of modified spots13aare formed so that the plurality of fractures14arespectively extending from the plurality of modified spots13aare not connected to each other. Thus, it is possible to form the plurality of modified spots13balong the virtual plane15with higher precision.

In addition, in the laser processing method in the second embodiment, the plurality of rows of modified spots13aare formed by moving the converging point C of the laser light L pulse-oscillated along the virtual plane15. Then, the plurality of rows of modified spots13bare formed by moving the converging point C of the laser light L pulse-oscillated along the virtual plane15between the rows of the plurality of rows of modified spots13a. Thus, it is possible to reliably prevent overlapping of the plurality of modified spots13bwith the plurality of modified spots13aand the plurality of fractures14a, and to form the plurality of modified spots13balong the virtual plane15with higher precision.

In particular, in the laser processing method in the second embodiment, if gallium nitride contained in the material of the GaN wafer30is decomposed by irradiation with the laser light L, gallium is deposited on the plurality of fractures14arespectively extending from the plurality of modified spots13a, and the laser light L is easily absorbed by the gallium. Therefore, forming the plurality of modified spots13bso as not to overlap the fractures14ais effective in forming the plurality of modified spots13balong the virtual plane15with high precision.

In the laser processing method in the second embodiment, if gallium nitride contained in the material of the GaN wafer30is decomposed by irradiation with the laser light L, a nitrogen gas is generated in the plurality of fractures14. Therefore, it is possible to easily form the fracture17by using pressure of the nitrogen gas.

Further, according to the semiconductor member manufacturing method in the second embodiment, with the step included in the laser processing method in the second embodiment, it is possible to form the fracture17along each of the plurality of virtual planes15with high precision. Thus, it is possible to acquire a plurality of suitable semiconductor devices40.

In addition, in the semiconductor member manufacturing method in the second embodiment, the plurality of virtual planes15are set to be arranged in a direction in which the surface30aof the GaN wafer30extends. Accordingly, it is possible to acquire a plurality of semiconductor devices40from one GaN wafer30.

[Modification Examples]

The present disclosure is not limited to the above embodiments. For example, various numerical values related to the laser light L are not limited to those described above. In order to suppress extension of the fracture14from the modified spot13to the incident side and the opposite side of the laser light L, it is preferable that the pulse energy of the laser light L be 0.1 μJ to 1 μJ and the pulse width of the laser light L be 200 fs to 1 ns.

In addition, the semiconductor object to be processed by the laser processing method and the semiconductor member manufacturing method according to one aspect of the present disclosure is not limited to the GaN ingot20in the first embodiment and the GaN wafer30in the second embodiment. The semiconductor member manufactured by the semiconductor member manufacturing method according to one aspect of the present disclosure is not limited to the GaN wafer30in the first embodiment and the semiconductor device40in the second embodiment. One virtual plane may be set for one semiconductor object.

As an example, the material of the semiconductor object may be SiC. Also in this case, according to the laser processing method and the semiconductor member manufacturing method in one aspect of the present disclosure, as described below, it is possible to form a fracture crossing over a virtual plane, along the virtual plane with high precision.

(a) and (b) ofFIG.29show images (images in side view) of a fracture of a SiC wafer formed by the laser processing method and the semiconductor member manufacturing method in a comparative example. (b) ofFIG.29shows an enlarged image in a rectangular frame in (a) ofFIG.29. In this comparative example, a plurality of modified spots are formed along a virtual plane in a manner that laser light having a wavelength of 532 nm enters into a SiC wafer from the surface of the SiC wafer, and six converging points arranged in the Y direction are relatively moved on the virtual plane along the X direction. At this time, the distance between the converging points C adjacent to each other in the Y direction was set to 2 μm, the pulse pitch of the laser light was set to 15 μm, and the pulse energy of the laser light was set to 4 μJ. In this case, as illustrated in (a) and (b) ofFIG.29, a fracture extending in a direction inclined from the virtual plane by 4° to 5° is formed.

(a) and (b) ofFIG.30show images (images in side view) of a fracture of a SiC wafer formed by the laser processing method and the semiconductor member manufacturing method in an example. (b) ofFIG.30shows an enlarged image in a rectangular frame in (a) ofFIG.30. In this example, a plurality of modified spots were formed along a virtual plane in a similar manner to the first step and the second step of the laser processing method and the semiconductor member manufacturing method in the first embodiment, in which laser light having a wavelength of 532 nm entered into a SiC wafer from the surface of the SiC wafer. When a plurality of modified spots respectively corresponding to the plurality of modified spots13a,13b,13c, and13dwere formed, the distance between the converging points C adjacent to each other in the Y direction was set to 8 μm, the pulse pitch of the laser light L was set to 15 μm, and the pulse energy of the laser light L was set to 4 μJ. In this case, as illustrated in (a) and (b) ofFIG.30, forming a fracture extending in a direction inclined from the virtual plane by 4° to 5° is suppressed.FIG.31shows an image of a peeling surface of a SiC wafer formed by a laser processing method and semiconductor member manufacturing method in an example. (a) and (b) ofFIG.32show height profiles of the peeling surface illustrated inFIG.31. In this case, the unevenness appearing on the peeling surface of the SiC wafer is suppressed up to about 2 μm.

From the above experimental results, it has been understood that, even when the material of the semiconductor object is SiC, according to the laser processing method and the semiconductor member manufacturing method in one aspect of the present disclosure, a fracture crossing over the virtual plane is formed along virtual plane with high precision. The SiC wafer used in the comparative example and the example described above is a 4H-SiC wafer having an off angle of 4±0.5°. A direction in which the converging point of the laser light is moved is an in-axis direction.

In addition, the method of forming the plurality of modified spots13a,13b,13c, and13dis not limited to the above description. The plurality of modified spots13amay be formed so that the plurality of fractures14arespectively extending from the plurality of modified spots13aare connected to each other. The plurality of modified spots13bmay be formed so as not to overlap the plurality of modified spots13a. Even though the plurality of modified spots13boverlap the plurality of fractures14arespectively extending from the plurality of modified spots13a, if the plurality of modified spots13bdo not overlap the plurality of modified spots13a, the plurality of modified spots13aand13bare formed along the virtual plane15with high precision. The plurality of modified spots13cand13dmay be formed in any method, and the plurality of modified spots13cand13dmay not be formed. As illustrated inFIG.33, for example, a plurality of rows of modified spots13are formed, for example, by rotating the GaN ingot20to relatively rotate a plurality of converging points arranged in a radial direction (arrow indicated by a dashed-dotted line). Further, as illustrated inFIG.34, in a state where each of the plurality of converging points is located between the rows of the plurality of rows of modified spots13, the plurality of rows of modified spots13may be formed by relatively rotating the plurality of converging points arranged in the radial direction (arrow indicated by a dashed-dotted line).

Further, in the laser processing method and the semiconductor member manufacturing method in the first embodiment, the plurality of modified spots13may be sequentially formed for each of the plurality of virtual planes15from the opposite side of the surface20a. In addition, in the laser processing method and the semiconductor member manufacturing method in the first embodiment, the plurality of modified spots13may be formed along one or the plurality of virtual planes15on the surface20aside. After one or a plurality of GaN wafers30are cut out, the surface20aof the GaN ingot20may be ground, and then the plurality of modified spots13may be formed again along one or the plurality of virtual planes15on the surface20aside.

In the laser processing method and the semiconductor member manufacturing method in the first embodiment and the second embodiment, the peripheral edge region16may not be formed. When the peripheral edge region16is not formed in the laser processing method and the semiconductor member manufacturing method in the first embodiment, it is possible to acquire a plurality of GaN wafers30by forming a plurality of modified spots13along each of the plurality of virtual planes15, and then etching the GaN ingot20, for example.

The laser processing apparatus1is not limited to a device having the above-described configuration. For example, the laser processing apparatus1may not include the spatial light modulator4.

Various materials and shapes can be applied to each configuration in the above-described embodiment without being limited to the above-described materials and shapes. Further, the configurations in the embodiment or the modification examples described above can be randomly applied to the configuration in another embodiment or modification examples.

REFERENCE SIGNS LIST

1laser processing apparatus2stage4spatial light modulator (laser irradiation unit)5converging lens (laser irradiation unit)13modified spot13amodified spot (first modified spot)13bmodified spot (second modified spot)13c,13dmodified spot (third modified spot)14,14a,14b,14c,14dfracture15virtual plane17fracture crossing over virtual plane20GaN ingot (semiconductor ingot, semiconductor object)20asurface30GaN wafer (semiconductor wafer, semiconductor member, semiconductor object)30asurface40semiconductor device (semiconductor member)L laser light