JP7330695B2 - LASER PROCESSING METHOD AND SEMICONDUCTOR DEVICE MANUFACTURING METHOD - Google Patents

Description

The present invention relates to a laser processing method and a semiconductor device manufacturing method.

By irradiating a semiconductor object such as a semiconductor ingot with a laser beam, a modified region is formed inside the semiconductor object, and a crack extending from the modified region is propagated, whereby a semiconductor such as a semiconductor wafer is removed from the semiconductor object. A processing method for cutting out a member is known (see Patent Documents 1 and 2, for example).

Japanese Patent Application Laid-Open No. 2017-183600 JP 2017-057103 A

By the way, there is a demand for thinning a semiconductor member by growing a crack extending from a modified region and peeling off (cutting out) an unnecessary portion from the semiconductor member. The semiconductor member to be thinned may include epitaxially grown layers for subsequent dicing of semiconductor devices. In this case, when laser light is irradiated to form a modified region inside the semiconductor member, the leaked light may damage the epitaxially grown layer, resulting in deterioration of the quality of the semiconductor device.

SUMMARY OF THE INVENTION An object of the present invention is to provide a laser processing method and a semiconductor device manufacturing method that enable acquisition of a suitable semiconductor device.

A laser processing method according to the present invention is a laser processing method for cutting a semiconductor wafer along a virtual plane facing the surface of the semiconductor wafer inside the semiconductor wafer, wherein a laser beam is projected from the surface to the inside of the semiconductor wafer. A first step of forming a plurality of modified spots along a virtual plane by irradiating with light, and after the first step, forming a semiconductor layer for a semiconductor device by epitaxial growth on the semiconductor wafer. and a second step.

In this method, prior to forming a semiconductor layer for a semiconductor device by epitaxial growth, a modified spot is formed inside the semiconductor wafer by irradiation with laser light. Therefore, the semiconductor layer cannot be damaged when the modified spots are formed. Therefore, by allowing the crack extending from the modified spot to grow and cutting (for example, peeling) the semiconductor wafer along the imaginary plane, it is possible to obtain a suitable semiconductor device in which damage is suppressed.

In the laser processing method according to the present invention, after the second step, the semiconductor is processed from a surface of the semiconductor wafer different from the surface on which the semiconductor layer is formed so that the focal point does not overlap the modified spot when viewed in a direction intersecting the surface. A third step of forming a crack across the virtual surface by irradiating the inside of the wafer with a laser beam may be provided. In this manner, a crack may be formed along a virtual plane, which is the starting point of delamination, by irradiating laser light. Even in this case, since the modified spots are formed prior to the formation of the semiconductor layer, damage to the semiconductor layer is less than in the case where all the laser processing is performed after the formation of the semiconductor layer. Suppressed.

Here, the inventor of the present invention has found the following problems while proceeding with intensive studies in order to solve the above problems. That is, as described above, a modified spot is formed along a virtual plane inside the semiconductor wafer by irradiating a laser beam, and a crack extending from the modified spot is developed to cut out a semiconductor device from the semiconductor wafer (separation). ), it is effective to reduce the energy of the laser beam on the virtual plane in order to reduce the unevenness of the peeled surface and obtain a more suitable semiconductor device. If the energy at the imaginary plane is too low, modification spots and cracks cannot be produced.

The inventor of the present invention focused on such problems and made further studies to obtain the following findings. That is, first, by irradiating a semiconductor wafer containing gallium with a laser beam, a plurality of modified spots and a precipitated region containing gallium deposited at the plurality of modified spots are formed along a virtual plane. Form. Then, when laser light is re-irradiated in a later process, the condensing point of the laser light is prevented from overlapping the previously formed modified spots, and the energy of the laser light on the virtual plane is set to the processing threshold of the semiconductor wafer. , the preformed gallium-containing region can be enlarged. As a result, when the semiconductor wafer is separated by forming a crack across the imaginary surface, the unevenness of the separated surface can be reduced. The following inventions have been made based on such findings.

That is, in the laser processing method according to the present invention, the semiconductor wafer contains gallium, and in the first step, by irradiating the inside of the semiconductor wafer with a laser beam from the surface, a plurality of modified spots and a plurality of forming a plurality of precipitation regions containing gallium precipitated in the modified spots of the above, and in the third step, irradiating the inside of the semiconductor wafer with a laser beam so that the energy in the virtual plane is below the processing threshold of the semiconductor wafer. may enlarge the precipitation area and form a crack across the imaginary plane.

In this case, first, by irradiating the inside of a semiconductor wafer containing gallium with laser light, a plurality of modified spots and deposited gallium are formed along a virtual plane facing the surface that is the incident plane of the laser light. forming a plurality of deposition regions including Then, in a subsequent step, the inside of the semiconductor wafer is irradiated with a laser beam so that the focal point does not overlap the modified spot and the energy in the virtual plane is below the processing threshold of the semiconductor wafer, thereby precipitating. Expand the area and create a crack that spans the imaginary plane. As a result, as described above, it is possible to obtain a suitable semiconductor device with reduced unevenness by peeling along the boundary of the crack extending across the virtual plane.

In the laser processing method according to the present invention, in the second step, by heating the semiconductor wafer for epitaxial growth, a plurality of cracks extending from each of the plurality of modified spots are propagated, thereby forming cracks across a virtual plane. You may In this case, the formation of the semiconductor layer and the formation of the crack across the imaginary plane can be performed at the same time.

In the laser processing method according to the present invention, in the first step, the semiconductor wafer may be provided with a peripheral edge region that prevents propagation of a plurality of cracks extending from the plurality of modified spots. In this case, during the epitaxial growth in the second step, it is possible to suppress the unintentional formation of cracks across the imaginary plane and the occurrence of peeling.

In the laser processing method according to the present invention, between the first step and the second step, a fourth step of measuring the transmittance of the semiconductor wafer, and between the fourth step and the second step, in the fourth step A fifth step of determining whether the measured transmittance is higher than the reference value, and if the transmittance is higher than the reference value as a result of the determination in the fifth step, the first step may be performed again. In this case, it is possible to sufficiently form modified spots inside the semiconductor wafer prior to the second step of forming the semiconductor layer.

In the laser processing method according to the present invention, in the first step, the plurality of modified spots may be formed such that the plurality of cracks extending from the plurality of modified spots are not connected to each other. In this case, when the laser beam is irradiated later, the focus point of the laser beam can be prevented from overlapping not only the modified spot but also the crack extending from the modified spot. As a result, it is possible to avoid the formation of new modified spots, cracks, and gallium-precipitated regions at unintended positions during subsequent laser light irradiation. That is, it becomes possible to obtain a more suitable semiconductor member.

In the laser processing method according to the present invention, in the first step, a plurality of rows of modified spots are formed as a plurality of modified spots by moving the focal point of the pulsed laser beam along the virtual plane. In the third step, the condensing point of the pulsed laser light may be moved along the virtual plane between the rows of modified spots. In this case, it is possible to reliably prevent the condensing points of the laser beams in the third step from overlapping the plurality of modified spots.

In the laser processing method according to the present invention, the semiconductor wafer may contain gallium nitride. In this case, the pressure (internal pressure) of the nitrogen gas generated along with the deposition of gallium can be used to easily form the crack across the imaginary plane.

A semiconductor device manufacturing method according to the present invention includes the steps of performing any one of the laser processing methods described above, and obtaining a plurality of semiconductor devices from a semiconductor wafer with a crack extending across a virtual plane as a boundary. This method implements the laser processing method described above. Therefore, for the same reason, it is possible to obtain a suitable semiconductor device.

In the semiconductor device manufacturing method according to the present invention, a plurality of virtual planes may be set so as to line up in the direction along the surface. In this case, it is possible to obtain a plurality of semiconductor devices from one semiconductor wafer.

ADVANTAGE OF THE INVENTION According to this invention, the laser processing method and semiconductor device manufacturing method which can acquire a suitable semiconductor device can be provided.

1 is a configuration diagram of a laser processing apparatus; FIG. 1 is a side view of a GaN ingot that is an object of a laser processing method and a semiconductor member manufacturing method of a first example; FIG. 3 is a plan view of the GaN ingot shown in FIG. 2; FIG. 1 is a longitudinal sectional view of a part of a GaN ingot in one step of the laser processing method and the semiconductor member manufacturing method of the first example; FIG. 1 is a cross-sectional view of a portion of a GaN ingot in one step of the laser processing method and semiconductor member manufacturing method of the first example; FIG. 1 is a longitudinal sectional view of a part of a GaN ingot in one step of the laser processing method and the semiconductor member manufacturing method of the first example; FIG. 1 is a cross-sectional view of a portion of a GaN ingot in one step of the laser processing method and semiconductor member manufacturing method of the first example; FIG. 1 is a longitudinal sectional view of a part of a GaN ingot in one step of the laser processing method and the semiconductor member manufacturing method of the first example; FIG. 1 is a cross-sectional view of a portion of a GaN ingot in one step of the laser processing method and semiconductor member manufacturing method of the first example; FIG. 1 is a longitudinal sectional view of a part of a GaN ingot in one step of the laser processing method and the semiconductor member manufacturing method of the first example; FIG. 1 is a cross-sectional view of a portion of a GaN ingot in one step of the laser processing method and semiconductor member manufacturing method of the first example; FIG. FIG. 4 is a side view of a GaN ingot in one step of the laser processing method and the semiconductor member manufacturing method of the first example; FIG. 2 is a side view of a GaN wafer in one step of the laser processing method and the semiconductor member manufacturing method of the first example; 1 is an image of a peeled surface of a GaN wafer formed by an example laser processing method and semiconductor member manufacturing method. 15 is a height profile of the release surface shown in FIG. 14; 4 is an image of a peeled surface of a GaN wafer formed by a laser processing method and a semiconductor member manufacturing method of another example. 17 is a height profile of the release surface shown in FIG. 16; It is a schematic diagram for demonstrating the formation principle of the peeling surface by the laser processing method of an example, and a semiconductor member manufacturing method. It is a schematic diagram for demonstrating the formation principle of the peeling surface by the laser processing method of another example, and a semiconductor member manufacturing method. 4 is an image of a crack formed during an example laser processing method and semiconductor member manufacturing method. 10 is an image of a crack formed during another laser processing method and semiconductor member manufacturing method; It is an image of a modified spot and a crack formed by a laser processing method and a semiconductor member manufacturing method of a comparative example. 4 is an image of modified spots and cracks formed by the laser processing method and the semiconductor member manufacturing method of Example 1. FIG. FIG. 10 is an image of modified spots and cracks formed by the laser processing method and the semiconductor member manufacturing method of the second and third examples. FIG. FIG. 10 is a plan view of a GaN wafer, which is an object of the laser processing method and the semiconductor member manufacturing method of the second example; It is a side view of a portion of the GaN wafer in one step of the laser processing method and semiconductor member manufacturing method of the second example. It is a side view of a portion of the GaN wafer in one step of the laser processing method and semiconductor member manufacturing method of the second example. It is a side view of the semiconductor device in one step of the laser processing method and the semiconductor member manufacturing method of the second example. It is an image of the crack of the SiC wafer formed by the laser processing method and semiconductor member manufacturing method of a comparative example. 4 is an image of cracks in a SiC wafer formed by the laser processing method and the semiconductor member manufacturing method of the example. 4 is an image of a peeled surface of a SiC wafer formed by a laser processing method and a semiconductor member manufacturing method of Examples. 32 is a height profile of the release surface shown in FIG. 31; FIG. 10 is a plan view of a GaN ingot in one step of the laser processing method and the semiconductor member manufacturing method of the modified example; FIG. 10 is a plan view of a GaN ingot in one step of the laser processing method and the semiconductor member manufacturing method of the modified example; 1 is a configuration diagram of a laser processing apparatus; FIG. 1 is a longitudinal sectional view of a portion of a GaN wafer in one step of the laser processing method and semiconductor device manufacturing method of the embodiment; FIG. 1 is a cross-sectional view of a portion of a GaN wafer in one step of the laser processing method and semiconductor device manufacturing method of the embodiment; FIG. 1 is a longitudinal sectional view of a portion of a GaN wafer in one step of the laser processing method and semiconductor device manufacturing method of the embodiment; FIG. 1 is a cross-sectional view of a portion of a GaN wafer in one step of the laser processing method and semiconductor device manufacturing method of the embodiment; FIG.

A detailed description is provided below with reference to the drawings. In each figure, the same or corresponding parts are denoted by the same reference numerals, and redundant explanations are omitted.
[Configuration of laser processing device]

As shown in FIG. 1, the laser processing apparatus 1 includes a stage 2, a light source 3, a spatial light modulator 4, a condenser lens 5, and a controller 6. The laser processing apparatus 1 is an apparatus that forms a modified region 12 on an object 11 by irradiating the object 11 with a laser beam L. As shown in FIG. Hereinafter, the first horizontal direction will be referred to as the X direction, and the second horizontal direction perpendicular to the first horizontal direction will be referred to as the Y direction. Also, the vertical direction is referred to as the Z direction.

The stage 2 supports the object 11 by sucking a film attached to the object 11, for example. In this embodiment, the stage 2 is movable along each of the X direction and the Y direction. Also, the stage 2 is rotatable about an axis parallel to the Z direction.

The light source 3 outputs laser light L having transparency to the object 11 by, for example, a pulse oscillation method. The spatial light modulator 4 modulates the laser light L output from the light source 3 . The spatial light modulator 4 is, for example, a reflective liquid crystal (LCOS: Liquid Crystal on Silicon) spatial light modulator (SLM: Spatial Light Modulator). A condenser lens 5 collects the laser light L modulated by the spatial light modulator 4 . In this embodiment, the spatial light modulator 4 and the condenser lens 5 are movable along the Z direction as a laser irradiation unit.

When the laser beam L is condensed inside the object 11 supported by the stage 2, the laser beam L is particularly absorbed in a portion corresponding to the converging point C of the laser beam L, and the inside of the object 11 is reformed. A textured region 12 is formed. Modified region 12 is a region that differs in density, refractive index, mechanical strength, and other physical properties from surrounding unmodified regions. The modified region 12 includes, for example, a melting process region, a crack region, a dielectric breakdown region, a refractive index change region, and the like.

As an example, when the stage 2 is moved along the X direction and the focal point C is moved relative to the object 11 along the X direction, a plurality of modified spots 13 are arranged along the X direction. formed in rows. One modified spot 13 is formed by irradiation with one pulse of laser light L. FIG. A row of modified regions 12 is a set of a plurality of modified spots 13 arranged in a row. Adjacent modified spots 13 may be connected to each other or separated from each other depending on the relative moving speed of the focal point C with respect to the object 11 and the repetition frequency of the laser light L.

A control unit 6 controls the stage 2 , light source 3 , spatial light modulator 4 and condenser lens 5 . The control unit 6 is configured as a computer device including a processor, memory, storage, communication device, and the like. In the control unit 6, the software (program) loaded into the memory or the like is executed by the processor, and the reading and writing of data in the memory and storage and the communication by the communication device are controlled by the processor. Thereby, the control part 6 implement|achieves various functions.
[Laser processing method and semiconductor member manufacturing method according to the first example]

2 and 3, the object 11 is a GaN ingot (semiconductor ingot, semiconductor object) 20 made of gallium nitride (GaN), for example, formed into a disc shape. As an example, the diameter of GaN ingot 20 is 2 inches and the thickness of GaN ingot 20 is 2 mm. The laser processing method and semiconductor member manufacturing method of the first embodiment are performed to cut out a plurality of GaN wafers (semiconductor wafers, semiconductor members) 30 from a GaN ingot 20 . As an example, the diameter of GaN wafer 30 is 2 inches and the thickness of GaN wafer 30 is 100 μm.

First, the laser processing apparatus 1 described above forms a plurality of modified spots 13 along each of the plurality of virtual surfaces 15 . Each of the virtual surfaces 15 is a surface inside the GaN ingot 20 facing the surface 20a of the GaN ingot 20, and is set to be aligned in a direction facing the surface 20a. Here, each of the plurality of virtual surfaces 15 is a surface parallel to the surface 20a and has, for example, a circular shape. Each of the plurality of virtual planes 15 is set so as to overlap each other when viewed from the surface 20a side. GaN ingot 20 is provided with a plurality of peripheral regions 16 so as to surround each of the plurality of virtual planes 15 . In other words, each of the multiple virtual surfaces 15 does not reach the side surface 20 b of the GaN ingot 20 . As an example, the distance between adjacent virtual surfaces 15 is 100 μm, and the width of the peripheral region 16 (in this embodiment, the distance between the outer edge of the virtual surface 15 and the side surface 20b) is 30 μm or more.

The formation of the plurality of modified spots 13 is sequentially performed for each virtual surface 15 from the side opposite to the surface 20a by irradiation with laser light L having a wavelength of 532 nm, for example. Since the formation of the plurality of modified spots 13 is the same on each of the plurality of virtual surfaces 15, the formation of the plurality of modified spots 13 along the virtual surface 15 closest to the surface 20a will be described below with reference to FIGS. 11 for a detailed description. 5, 7, 9 and 11, arrows indicate the trajectory of the converging point C of the laser beam L. As shown in FIG. Further, the modified spots 13a, 13b, 13c, and 13d, which will be described later, are collectively referred to as the modified spots 13, and the cracks 14a, 14b, 14c, and 14d, which will be described later, are collectively referred to as the cracks 14 in some cases.

First, as shown in FIGS. 4 and 5, the laser processing apparatus 1 irradiates the GaN ingot 20 with a laser beam L incident from the surface 20a along a virtual plane 15 (for example, a virtual A plurality of modified spots 13a (first modified spots) are formed two-dimensionally along the entire surface 15 (step S1). At this time, the laser processing apparatus 1 forms the plurality of modified spots 13a so that the plurality of cracks 14a extending from the plurality of modified spots 13a are not connected to each other. Further, the laser processing apparatus 1 moves the focal point C of the pulse-oscillated laser beam L along the virtual plane 15 to form a plurality of rows of modified spots 13a. In FIGS. 4 and 5, the modified spots 13a are indicated by white (no hatching), and the range where the cracks 14a extend is indicated by broken lines (the same applies to FIGS. 6 to 11). Further, at this time, the gallium precipitated in each of the modified spots 13a spreads so as to enter the cracks 14a, thereby forming a precipitation region R containing the precipitated gallium around the modified spots 13a. .

Here, the pulse-oscillated laser light L is modulated by the spatial light modulator 4 so as to be condensed at a plurality of (for example, six) condensing points C arranged in the Y direction. Then, the plurality of condensing points C are relatively moved on the virtual plane 15 along the X direction. As an example, the distance between adjacent condensing points C in the Y direction is 8 μm, and the pulse pitch of the laser light L (that is, the relative moving speed of the plurality of condensing points C is determined by the repetition frequency of the laser light L). value) is 10 μm. Further, the pulse energy of the laser light L per one condensing point C (hereinafter simply referred to as "pulse energy of the laser light L") is 0.33 μJ. In this case, the center-to-center distance between the modified spots 13a adjacent in the Y direction is 8 μm, and the center-to-center distance between the modified spots 13a adjacent in the X direction is 10 μm. Moreover, the plurality of cracks 14a respectively extending from the plurality of modified spots 13a are not connected to each other.

Subsequently, as shown in FIGS. 6 and 7, the laser processing apparatus 1 irradiates the inside of the GaN ingot 20 with the laser beam L from the surface 20a, thereby irradiating the GaN ingot 20 along the virtual plane 15 (for example, A plurality of modified spots (second modified spots) 13b are formed two-dimensionally along the entire imaginary surface 15 (step S2). At this time, the laser processing apparatus 1 forms the plurality of modified spots 13b so as not to overlap the plurality of modified spots 13a and the plurality of cracks 14a. In addition, the laser processing apparatus 1 moves the focal point C of the pulse-oscillated laser beam L along the virtual plane 15 between the rows of the modified spots 13a, so that the rows of the modified spots 13b are arranged. to form In this step, multiple cracks 14b extending from multiple modified spots 13b may connect to multiple cracks 14a. 6 and 7, the modified spot 13b is indicated by dot hatching, and the range where the crack 14b extends is indicated by broken lines (the same applies to FIGS. 8 to 11). Further, at this time, the gallium precipitated in each of the modified spots 13b spreads so as to enter the cracks 14b, thereby forming a precipitation region R containing the precipitated gallium around the modified spots 13b. .

Here, the pulse-oscillated laser light L is modulated by the spatial light modulator 4 so as to be condensed at a plurality of (for example, six) condensing points C arranged in the Y direction. Then, a plurality of condensing points C are relatively moved on the virtual plane 15 along the X direction at the center between the rows of the plurality of modified spots 13a. As an example, the distance between condensing points C adjacent in the Y direction is 8 μm, and the pulse pitch of the laser light L is 10 μm. Also, the pulse energy of the laser light L is 0.33 μJ. In this case, the center-to-center distance between the modified spots 13b adjacent in the Y direction is 8 μm, and the center-to-center distance between the modified spots 13b adjacent in the X direction is 10 μm.

Subsequently, as shown in FIGS. 8 and 9, the laser processing apparatus 1 irradiates the GaN ingot 20 with a laser beam L incident from the surface 20a along the virtual plane 15 (for example, A plurality of modified spots (third modified spots) 13c are formed two-dimensionally along the entire imaginary surface 15 (step S3). Furthermore, as shown in FIGS. 10 and 11, the laser processing apparatus 1 irradiates the GaN ingot 20 with a laser beam L incident on the inside of the GaN ingot 20 from the surface 20a along a virtual plane 15 (for example, a virtual A plurality of modified spots (third modified spots) 13d are formed two-dimensionally along the entire surface 15 (step S4). At this time, the laser processing apparatus 1 forms the plurality of modified spots 13c and 13d so as not to overlap the plurality of modified spots 13a and 13b.

In addition, the laser processing apparatus 1 moves the focal point C of the pulse-oscillated laser beam L along the virtual plane 15 between the rows of the plurality of modified spots 13a and 13b, so that the plurality of rows of modified spots 13a and 13b can be modified. Spots 13c and 13d are formed. In this step, a plurality of cracks 14c and 14d respectively extending from a plurality of modified spots 13c and 13d may connect to a plurality of cracks 14a and 14b. In FIGS. 8 and 9, the modified spot 13c is indicated by hatching with solid lines, and the range where the crack 14c extends is indicated by broken lines (the same applies to FIGS. 10 and 11). In FIGS. 10 and 11, the modified spot 13d is indicated by solid line hatching (the solid line hatching is inclined opposite to the solid line hatching of the modified spot 13c), and the range where the crack 14d extends is indicated by the broken line. there is Further, at this time, the gallium precipitated in each of the modified spots 13c and 13d expands so as to enter the cracks 14c and 14d. A region R is formed.

Here, the pulse-oscillated laser light L is modulated by the spatial light modulator 4 so as to be condensed at a plurality of (for example, six) condensing points C arranged in the Y direction. A plurality of condensing points C are relatively moved on the virtual plane 15 along the X direction at the center between the rows of the modified spots 13a and 13b. As an example, the distance between condensing points C adjacent in the Y direction is 8 μm, and the pulse pitch of the laser light L is 5 μm. Also, the pulse energy of the laser light L is 0.33 μJ. In this case, the center-to-center distance between the modified spots 13c adjacent in the Y direction is 8 μm, and the center-to-center distance between the modified spots 13c adjacent in the X direction is 5 μm. The center-to-center distance between the modified spots 13d adjacent in the Y direction is 8 μm, and the center-to-center distance between the modified spots 13d adjacent in the X direction is 5 μm.

Subsequently, a heating device including a heater or the like heats the GaN ingot 20 to join together the plurality of cracks 14 extending from the plurality of modification spots 13 on each of the plurality of imaginary planes 15, thereby forming the cracks 14 shown in FIG. In each of the plurality of virtual planes 15, a crack 17 (hereinafter simply referred to as "crack 17") extending across the virtual plane 15 is formed. In FIG. 12, the range where the multiple modified spots 13, the multiple cracks 14, and the cracks 17 are formed is indicated by broken lines. By applying some force to the GaN ingot 20 by a method other than heating, the plurality of cracks 14 may be interconnected to form the cracks 17 . Also, by forming a plurality of modified spots 13 along the imaginary plane 15 , a plurality of cracks 14 may be connected to each other to form a crack 17 .

Here, in GaN ingot 20 , nitrogen gas is generated in multiple cracks 14 extending from multiple modified spots 13 . Therefore, by heating the GaN ingot 20 to expand the nitrogen gas, the pressure (internal pressure) of the nitrogen gas can be used to form the cracks 17 . Moreover, since the peripheral region 16 prevents the plurality of cracks 14 from propagating to the outside of the virtual plane 15 surrounded by the peripheral region 16 (for example, the side surface 20b of the GaN ingot 20), the nitrogen generated in the plurality of cracks 14 Gas can be suppressed from escaping to the outside of the virtual surface 15 . That is, the peripheral region 16 is a non-modified region that does not include the modified spot 13, and when the crack 17 is formed in the virtual surface 15 surrounded by the peripheral region 16, the virtual surface 15 surrounded by the peripheral region 16 This is a region that prevents the development of a plurality of cracks 14 to the outside of the . Therefore, it is preferable to set the width of the peripheral region 16 to 30 μm or more.

Subsequently, a grinding device grinds (polishs) portions of the GaN ingot 20 corresponding to the plurality of peripheral regions 16 and the plurality of virtual surfaces 15, thereby forming a plurality of cracks 17 as shown in FIG. , a plurality of GaN wafers 30 are obtained from the GaN ingot 20 with each of them as a boundary (step S5). Thus, the GaN ingot 20 is cut along each of the virtual planes 15 . In this step, portions of the GaN ingot 20 corresponding to the plurality of peripheral regions 16 may be removed by mechanical processing other than grinding, laser processing, or the like.

Among the above steps, the steps up to the step of forming a plurality of modified spots 13 along each of the plurality of virtual surfaces 15 are the laser processing method of the first example. Further, among the above steps, the steps up to the step of obtaining a plurality of GaN wafers 30 from the GaN ingot 20 with each of the plurality of cracks 17 as boundaries constitute the semiconductor member manufacturing method of the first example.

As described above, in the laser processing method of the first example, the plurality of modified spots 13a are formed along each of the plurality of virtual surfaces 15, and the plurality of modified spots 13a and the plurality of cracks 14a are formed so as not to overlap each other. Then, a plurality of modified spots 13b are formed along each of the plurality of virtual planes 15. As shown in FIG. Furthermore, in the laser processing method of the first example, a plurality of modified spots 13c and 13d are formed along each of the plurality of virtual surfaces 15 so as not to overlap the plurality of modified spots 13a and 13b. Thereby, the plurality of modified spots 13 can be formed with high accuracy along each of the plurality of virtual surfaces 15, and as a result, the cracks 17 can be formed with high accuracy along each of the plurality of virtual surfaces 15. It becomes possible. Therefore, according to the laser processing method of the first example, it is possible to obtain a plurality of suitable GaN wafers 30 by obtaining a plurality of GaN wafers 30 from the GaN ingot 20 with each of the plurality of cracks 17 as boundaries. .

Similarly, according to the laser processing apparatus 1 that carries out the laser processing method of the first example, since it is possible to form the cracks 17 with high accuracy along each of the plurality of virtual planes 15, a plurality of suitable GaN Wafer 30 can now be obtained.

Further, in the laser processing method of the first example, the plurality of modified spots 13a are formed so that the plurality of cracks 14a extending from the plurality of modified spots 13a are not connected to each other. Thereby, the plurality of modified spots 13b can be formed along the virtual plane 15 with higher accuracy.

Further, in the laser processing method of the first example, by moving the focal point C of the pulse-oscillated laser beam L along the virtual plane 15, a plurality of rows of modified spots 13a are formed, and pulse-oscillated spots 13a are formed. A plurality of rows of modified spots 13b are formed by moving the focal point C of the laser beam L along the virtual plane 15 between the rows of the modified spots 13a. This reliably prevents the plurality of modified spots 13b from overlapping the plurality of modified spots 13a and the plurality of cracks 14a, thereby forming the plurality of modified spots 13b along the virtual plane 15 with higher accuracy. can be done.

In particular, in the laser processing method of the first example, when gallium nitride contained in the material of the GaN ingot 20 is decomposed by irradiation with the laser light L, gallium precipitates in the plurality of cracks 14a extending from the plurality of modified spots 13a. (the precipitation region R is formed), and the laser light L is easily absorbed by the gallium. Therefore, forming the plurality of modified spots 13b so as not to overlap the crack 14a is effective in forming the plurality of modified spots 13b along the virtual plane 15 with high accuracy.

Further, in the laser processing method of the first example, when gallium nitride contained in the material of the GaN ingot 20 is decomposed by the irradiation of the laser light L, nitrogen gas is produced in the plurality of cracks 14 . Therefore, it is possible to easily form the crack 17 by using the pressure of the nitrogen gas.

Further, according to the semiconductor member manufacturing method of the first example, the cracks 17 can be formed with high accuracy along each of the plurality of virtual surfaces 15 by the steps included in the laser processing method of the first example. , a plurality of suitable GaN wafers 30 can be obtained.

Further, in the semiconductor member manufacturing method of the first example, the plurality of virtual planes 15 are set so as to line up in the direction facing the surface 20 a of the GaN ingot 20 . Thereby, it becomes possible to obtain a plurality of GaN wafers 30 from one GaN ingot 20 .

Experimental results showing that the GaN wafers 30 formed by the laser processing method and the semiconductor member manufacturing method of the first example have less unevenness appearing on the peeled surface of the GaN wafers 30 will now be described.

FIG. 14 is an image of a peeled surface of a GaN wafer formed by an example laser processing method and semiconductor member manufacturing method, and FIGS. Profile. In this example, a laser beam L having a wavelength of 532 nm is made incident inside the GaN ingot 20 from the surface 20a of the GaN ingot 20, and one focal point C aligned in the Y direction is projected onto the virtual plane 15 along the X direction. A plurality of modified spots 13 were formed along the imaginary plane 15 by relatively moving the . At this time, the distance between the condensing points C adjacent 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 shown in FIGS. 15(a) and 15(b), unevenness of about 25 μm appeared on the peeled surface of the GaN wafer 30 (surface formed by cracks 17).

FIG. 16 is an image of a peeled surface of a GaN wafer formed by a laser processing method and a semiconductor member manufacturing method according to another example, and FIGS. 17(a) and 17(b) are shown in FIG. Height profile of the release surface. In this example, a laser beam L having a wavelength of 532 nm is made incident inside the GaN ingot 20 from the surface 20a of the GaN ingot 20, and the first and second steps of the laser processing method and semiconductor member manufacturing method of the first embodiment are performed. A plurality of modified spots 13 were formed along the imaginary plane 15 in the same manner as in . When forming the plurality of modified spots 13a, the distance between the condensing points C adjacent in the Y direction was set to 6 μm, the pulse pitch of the laser light L was set to 10 μk, and the pulse energy of the laser light L was set to 0.33 μJ. When forming the plurality of modified spots 13b, the distance between the condensing points C adjacent 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 forming the plurality of modified spots 13c, the distance between the condensing points C adjacent 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 forming the plurality of modified spots 13d, the distance between the condensing points C adjacent 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 shown in FIGS. 17(a) and 17(b), unevenness of about 5 μm appeared on the peeled surface of the GaN wafer 30 .

From the above experimental results, in the GaN wafer formed by the laser processing method and the semiconductor member manufacturing method of the first example, the unevenness appearing on the peeled surface of the GaN wafer 30 is reduced. was found to be formed with good accuracy. It should be noted that if the unevenness appearing on the peeled surface of the GaN wafer 30 is reduced, the amount of grinding required for flattening the peeled surface can be reduced. Therefore, reducing the irregularities appearing on the peeled surface of the GaN wafer 30 is advantageous in terms of material utilization efficiency and production efficiency.

Next, the principle by which unevenness appears on the peeled surface of the GaN wafer 30 will be described.

For example, as shown in FIG. 18, a plurality of modified spots 13a are formed along the imaginary plane 15, and the modified spot 13b overlaps the crack 14a extending from the modified spot 13a on one side thereof. A plurality of modified spots 13 b are formed along the surface 15 . In this case, the laser beam L is likely to be absorbed by the gallium deposited in the plurality of cracks 14a. The modified spot 13b is likely to be formed on the light L incident side. Subsequently, a plurality of modified spots 13c are formed along the imaginary plane 15 so that each modified spot 13c overlaps the crack 14b extending from the modified spot 13b on one side thereof. In this case also, the laser beam L is likely to be absorbed by the gallium deposited in the plurality of cracks 14b. The modified spot 13c is likely to be formed on the light L incident side. Thus, in this example, the plurality of modified spots 13b are formed on the incident side of the laser beam L with respect to the plurality of modified spots 13a, and the plurality of modified spots 13c are formed on the plurality of modified spots 13b. On the other hand, it is likely to be formed on the incident side of the laser light L.

On the other hand, for example, as shown in FIG. 19, a plurality of modified spots 13a are formed along the imaginary surface 15 so that the modified spots 13b do not overlap the cracks 14a extending from the modified spots 13a on both sides thereof. , to form a plurality of modified spots 13b along the imaginary plane 15. FIG. In this case, the laser beam L is easily absorbed by the gallium deposited in the plurality of cracks 14a, but since the modified spots 13b do not overlap the cracks 14a, the modified spots 13b are similar to the modified spots 13a. is formed on the virtual surface 15 at . Subsequently, a plurality of modified spots 13c are formed along the imaginary plane 15 so that the modified spot 13c overlaps the cracks 14a and 14b extending from the modified spots 13a and 13b on both sides thereof. Furthermore, a plurality of modified spots 13d are formed along the imaginary plane 15 so that the modified spot 13d overlaps the cracks 14a and 14b extending from the modified spots 13a and 13b on both sides thereof. In these cases, gallium precipitated in the plurality of cracks 14a and 14b easily absorbs the laser beam L, so even if the condensing point C is located on the virtual plane 15, the modified spots 13a and 14b are The modified spots 13c and 13d are easily formed on the incident side of the laser beam L with respect to 13b. Thus, in this example, the plurality of modified spots 13c and 13d are only likely to be formed on the incident side of the laser light L with respect to the plurality of modified spots 13a and 13b.

From the above principle, in the laser processing method and the semiconductor member manufacturing method of the first example, the plurality of modified spots 13a and the plurality of cracks 14a extending from the plurality of modified spots 13a are not overlapped. It can be seen that the formation of the spots 13b is extremely important for reducing unevenness appearing on the peeled surface of the GaN wafer 30. FIG.

Next, experimental results showing that the crack 17 propagates along the virtual plane 15 with high precision in the laser processing method and the semiconductor member manufacturing method of the first example will be described.

20(a) and 20(b) are images of cracks formed during an example of the laser processing method and the semiconductor member manufacturing method, and FIG. It is an enlarged image within the frame. In this example, a laser beam L having a wavelength of 532 nm is made incident inside the GaN ingot 20 from the surface 20a of the GaN ingot 20, and six focal points C arranged in the Y direction are projected onto the virtual plane 15 along the X direction. A plurality of modified spots 13 were formed along the imaginary plane 15 by relatively moving the . At this time, the distance between the condensing points C adjacent 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. Then, the laser processing was stopped in the middle of the virtual surface 15 . In this case, as shown in FIGS. 20(a) and 20(b), the crack that propagated from the machined area to the unmachined area largely deviated from the virtual plane 15 in the unmachined area.

FIGS. 21(a) and 21(b) are images of cracks formed during the laser processing method and the semiconductor member manufacturing method of another example, and FIG. It is an enlarged image in the rectangular frame in (a). In this example, a laser beam L having a wavelength of 532 nm is made incident inside the GaN ingot 20 from the surface 20a of the GaN ingot 20, and six focal points C arranged in the Y direction are projected onto the virtual plane 15 along the X direction. A plurality of modified spots 13 were formed along the imaginary plane 15 by relatively moving the . Specifically, first, the distance between the condensing points C adjacent in the Y direction is 6 μm, the pulse pitch of the laser light L is 10 μm, and the pulse energy of the laser light L is 0.33 μJ. A plurality of rows of modified spots 13 were formed in the . Subsequently, the distance between adjacent condensing points C in the Y direction is 6 μm, the pulse pitch of the laser light L is 10 μm, and the pulse energy of the laser light L is 0.33 μJ. A plurality of rows of modified spots 13 were formed so that each row was positioned at the center between the rows of modified spots 13 formed. Subsequently, the distance between the condensing points C adjacent in the Y direction is set to 6 μm, the pulse pitch of the laser light L is set to 5 μm, and the pulse energy of the laser light L is set to 0.33 μJ. A plurality of rows of modified spots 13 were formed such that each row was positioned at the center between rows of modified spots 13 in rows. In this case, as shown in FIGS. 21(a) and 21(b), the crack that propagated from the machining region 1 to the machining region 2 did not deviate greatly from the virtual plane 15 in the machining region 2. FIG.

From the above experimental results, it was found that the crack 17 propagates along the virtual plane 15 with high precision in the laser processing method and the semiconductor member manufacturing method of the first example. It is assumed that this is because the plurality of modified spots 13 previously formed in the processing region 2 acted as a guide when the crack propagated.

Next, in the laser processing method and the semiconductor member manufacturing method of the first example, experimental results showing that the amount of extension of the crack 14 extending from the modified spot 13 to the incident side of the laser beam L and the opposite side is suppressed. explain.

FIG. 22 is an image (side view image) of modified spots and cracks formed by the laser processing method and the semiconductor member manufacturing method of the comparative example. In this comparative example, a laser beam L having a wavelength of 532 nm is incident on the inside of the GaN ingot 20 from the surface 20a of the GaN ingot 20, and one condensing point C is directed relative to the virtual plane 15 along the X direction. A plurality of modified spots 13 were formed along the imaginary plane 15 by moving to . Specifically, the distance between the condensing points C adjacent in the Y direction is 2 μm, the pulse pitch of the laser light L is 5 μm, and the pulse energy of the laser light L is 0.3 μJ. A quality spot 13 was formed. In this case, as shown in FIG. 22, the extension amount of the crack 14 extending from the modified spot 13 to the incident side of the laser beam L and the opposite side was about 100 μm.

23A and 23B are images of modified spots and cracks formed by the laser processing method and the semiconductor member manufacturing method of the first embodiment, FIG. is an image viewed from the side. In this first embodiment, a laser beam L having a wavelength of 532 nm is made incident inside the GaN ingot 20 from the surface 20a of the GaN ingot 20, and six focal points C arranged in the Y direction are projected along the X direction. A plurality of modified spots 13 were formed along the imaginary plane 15 by relatively moving on the plane 15 . Specifically, first, the distance between the condensing points C adjacent in the Y direction is 8 μm, the pulse pitch of the laser light L is 10 μm, and the pulse energy of the laser light L is 0.3 μJ. to form a modified spot 13a. Next, with the six condensing points C aligned in the Y direction shifted +4 μm in the Y direction from the previous state, the distance between adjacent condensing points C in the Y direction was 8 μm, and the pulse pitch of the laser light L was 10 μm. , the pulse energy of the laser light L was set to 0.3 μJ, and a plurality of modified spots 13 b were formed along the imaginary surface 15 . Next, with the six condensing points C aligned in the Y direction shifted from the previous state by -4 μm in the Y direction, the distance between adjacent condensing points C in the Y direction was 8 μm, and the pulse pitch of the laser light L was changed. A plurality of modified spots 13 were formed along the imaginary surface 15 by setting the laser beam L to 5 μm and the pulse energy of the laser beam L to 0.3 μJ. Next, with the six condensing points C aligned in the Y direction shifted +4 μm in the Y direction from the previous state, the distance between adjacent condensing points C in the Y direction was 8 μm, and the pulse pitch of the laser light L was 5 μm. , the pulse energy of the laser beam L was set to 0.3 μJ, and a plurality of modified spots 13 were formed along the imaginary surface 15 . As a result, the first modified spot 13a and the third modified spot 13 overlap each other, and the second modified spot 13b and the fourth modified spot 13 overlap each other. It is assumed that In this case, as shown in FIG. 23(b), the extension amount of the crack 14 extending from the modified spot 13 to the incident side of the laser beam L and the opposite side was about 70 μm.

24(a) and 24(b) are images of modified spots and cracks formed by the laser processing method and semiconductor member manufacturing method of the second example, and FIG. 24(a) is a plan view. , and FIG. 24B is an image viewed from the side. In this second embodiment, a laser beam L having a wavelength of 532 nm is made incident inside the GaN ingot 20 from the surface 20a of the GaN ingot 20, and the first step and the first step of the laser processing method and semiconductor member manufacturing method of the first example are performed. A plurality of modified spots 13 were formed along the imaginary plane 15 in the same manner as in the second step. When forming the plurality of modified spots 13a, the distance between the condensing points C adjacent 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 forming the plurality of modified spots 13b, the distance between the condensing points C adjacent 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 forming the plurality of modified spots 13c, the distance between the condensing points C adjacent 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 forming the plurality of modified spots 13d, the distance between the condensing points C adjacent 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 shown in FIG. 23(b), the extension amount of the crack 14 extending from the modified spot 13 to the incident side of the laser beam L and the opposite side was about 50 μm.

(c) and (d) of FIG. 24 are images of modified spots and cracks formed by the laser processing method and the semiconductor member manufacturing method of the third embodiment, and (c) of FIG. An image, (d) of FIG. 24 is an image in a side view. In this example, a plurality of modified spots 13 were further formed along the virtual surface 15 in the state shown in FIG. . Specifically, first, the distance between the condensing points C adjacent in the Y direction is 8 μm, the pulse pitch of the laser light L is 5 μm, and the pulse energy of the laser light L is 0.1 μJ. A plurality of rows of modified spots 13 were formed such that each row was positioned in the center between the rows of modified spots 13 . In this case, as shown in (d) of FIG. 24, the extension amount of the crack 14 extending from the modified spot 13 to the incident side of the laser beam L and the opposite side was about 60 μm.

From the above experimental results, if a plurality of modified spots 13b are formed along the virtual surface 15 so as not to overlap the plurality of modified spots 13a and the plurality of cracks 14a already formed along the virtual surface 15 ( 1st, 2nd and 3rd embodiments), it was found that the extension of the crack 14 extending from the modified spot 13 to the incident side of the laser beam L and the opposite side was suppressed. When forming a plurality of modified spots 13 along the virtual surface 15, along the virtual surface 15, so as not to overlap the plurality of modified spots 13a and 13b already formed along the virtual surface 15. If a plurality of modified spots 13 are provided (second and third embodiments), the amount of extension of the cracks 14 extending from the modified spots 13 to the incident side of the laser beam L and the opposite side can be further suppressed. Do you get it.
[Laser processing method and semiconductor member manufacturing method of the second example]

As shown in FIG. 25, the object 11 of the laser processing method and the semiconductor member manufacturing method of the second example is a GaN wafer (semiconductor wafer, semiconductor object) 30 made of GaN, for example, in the shape of a disk. As an example, the diameter of GaN wafer 30 is 2 inches and the thickness of GaN wafer 30 is 100 μm. The laser processing method and semiconductor member manufacturing method of the second example are performed to cut out a plurality of semiconductor devices (semiconductor members) 40 from the GaN wafer 30 . As an example, the outer shape of the GaN substrate portion of the semiconductor device 40 is 1 mm×1 mm, and the thickness of the GaN substrate portion of the semiconductor device 40 is several tens of μm.

First, the laser processing apparatus 1 described above forms a plurality of modified spots 13 along each of the plurality of virtual surfaces 15 . Each of the plurality of virtual surfaces 15 is a surface facing the surface 30a of the GaN wafer 30 inside the GaN wafer 30, and is set to be aligned in the direction in which the surface 30a extends. In this embodiment, each of the plurality of virtual planes 15 is a plane parallel to the surface 30a and has, for example, a rectangular shape. Each of the plurality of virtual planes 15 is set to be two-dimensionally arranged in a direction parallel to and perpendicular to the orientation flat 31 of the GaN wafer 30 . A plurality of peripheral regions 16 are set on the GaN wafer 30 so as to surround each of the plurality of virtual planes 15 . In other words, each of the multiple virtual surfaces 15 does not reach the side surface 30b of the GaN wafer 30 . As an example, the width of the peripheral region 16 corresponding to each of the plurality of virtual surfaces 15 (half the distance between adjacent virtual surfaces 15 in the second example) is 30 μm or more.

Formation of the plurality of modified spots 13 along each of the plurality of virtual surfaces 15 is performed in the same manner as steps S1 to S4 of the laser processing method and the semiconductor member manufacturing method of the first example. Thereby, in the GaN wafer 30, as shown in FIG. of cracks 14 (ie, cracks 14a, 14b, 14c, 14d) are formed. In FIG. 26, the range where multiple modified spots 13 and multiple cracks 14 are formed is indicated by dashed lines.

Subsequently, the semiconductor manufacturing equipment forms a plurality of functional elements 32 on the surface 30a of the GaN wafer 30, as shown in FIG. Each of the plurality of functional elements 32 is formed such that one functional element 32 is included in one virtual plane 15 when viewed from the thickness direction of the GaN wafer 30 . The functional element 32 is, 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 second example, the semiconductor manufacturing apparatus functions as a heating device when forming the plurality of functional elements 32 on the surface 30a. That is, when forming the plurality of functional elements 32 on the surface 30 a , the semiconductor manufacturing apparatus heats the GaN wafer 30 to form the plurality of cracks 14 extending from the plurality of modified spots 13 on each of the plurality of virtual surfaces 15 . are connected to each other, a crack 17 is formed in each of the plurality of virtual planes 15 (that is, a crack 17 across the virtual planes 15). In FIG. 27, the range where the multiple modified spots 13, the multiple cracks 14, and the crack 17 are formed is indicated by broken lines. Note that a heating device different from the semiconductor manufacturing device may be used. Further, by applying some force to the GaN wafer 30 by a method other than heating, the plurality of cracks 14 may be connected to each other to form the cracks 17 . Also, by forming a plurality of modified spots 13 along the imaginary plane 15 , a plurality of cracks 14 may be connected to each other to form a crack 17 .

Here, in the GaN wafer 30 , nitrogen gas is generated within a plurality of cracks 14 respectively extending from a plurality of modified spots 13 . Therefore, by heating the GaN ingot 20 to expand the nitrogen gas, the pressure of the nitrogen gas can be used to form the cracks 17 . Moreover, since the peripheral edge region 16 prevents the plurality of cracks 14 from propagating to the outside of the virtual surface 15 surrounded by the peripheral edge region 16 (for example, the adjacent virtual surface 15, the side surface 30b of the GaN wafer 30), the plurality of cracks Nitrogen gas generated in 14 can be suppressed from escaping to the outside of imaginary surface 15 . That is, the peripheral region 16 is a non-modified region that does not include the modified spot 13, and when the crack 17 is formed in the virtual surface 15 surrounded by the peripheral region 16, the virtual surface 15 surrounded by the peripheral region 16 This is a region that prevents the development of a plurality of cracks 14 to the outside of the . Therefore, it is preferable to set the width of the peripheral region 16 to 30 μm or more.

Subsequently, the laser processing device cuts the GaN wafer 30 into individual functional elements 32, and the grinding device grinds the portions corresponding to the plurality of virtual surfaces 15, as shown in FIG. A plurality of semiconductor devices 40 are obtained from the GaN wafer 30 with each of the plurality of cracks 17 as boundaries (step S6). Thus, the GaN wafer 30 is cut along each of the virtual planes 15 . In this step, the GaN wafer 30 may be cut into individual functional elements 32 by mechanical processing (for example, blade dicing) other than laser processing.

Among the above steps, the steps up to the step of forming a plurality of modified spots 13 along each of the plurality of virtual surfaces 15 are the laser processing method of the second example. Further, among the above steps, the steps up to the step of obtaining a plurality of semiconductor devices 40 from the GaN wafer 30 with each of the plurality of cracks 17 as boundaries constitute the semiconductor member manufacturing method of the second example.

As described above, according to the laser processing method of the second example, similarly to the laser processing method of the first example, it is possible to form a plurality of modified spots 13 along each of the plurality of virtual surfaces 15 with high accuracy. As a result, the cracks 17 can be accurately formed along each of the plurality of virtual planes 15 . Therefore, according to the laser processing method of the second example, it is possible to obtain a plurality of suitable semiconductor devices 40 by obtaining a plurality of semiconductor devices 40 from the GaN wafer 30 with each of the plurality of cracks 17 as boundaries. . It is also possible to reuse the GaN wafer 30 from which a plurality of semiconductor devices 40 have been cut.

Similarly, according to the laser processing apparatus 1 that implements the laser processing method of the second example, since it is possible to form the cracks 17 with high accuracy along each of the plurality of virtual surfaces 15, a plurality of suitable semiconductors Acquisition of the device 40 becomes possible.

Moreover, in the laser processing method of the second example, the plurality of modified spots 13a are formed so that the plurality of cracks 14a extending from the plurality of modified spots 13a are not connected to each other. Thereby, the plurality of modified spots 13b can be formed along the virtual plane 15 with higher accuracy.

Further, in the laser processing method of the second example, by moving the focal point C of the pulse-oscillated laser beam L along the virtual plane 15, a plurality of rows of modified spots 13a are formed, and pulse-oscillated spots 13a are formed. A plurality of rows of modified spots 13b are formed by moving the focal point C of the laser beam L along the virtual plane 15 between the rows of the modified spots 13a. This reliably prevents the plurality of modified spots 13b from overlapping the plurality of modified spots 13a and the plurality of cracks 14a, thereby forming the plurality of modified spots 13b along the virtual plane 15 with higher accuracy. can be done.

In particular, in the laser processing method of the second example, when gallium nitride contained in the material of the GaN wafer 30 is decomposed by the irradiation of the laser light L, gallium precipitates in the plurality of cracks 14a extending from the plurality of modified spots 13a. Then, the laser light L is easily absorbed by the gallium. Therefore, forming the plurality of modified spots 13b so as not to overlap the crack 14a is effective in forming the plurality of modified spots 13b along the virtual plane 15 with high accuracy.

Further, in the laser processing method of the second example, when gallium nitride contained in the material of the GaN wafer 30 is decomposed by the irradiation of the laser light L, nitrogen gas is generated in the plurality of cracks 14 . Therefore, it is possible to easily form the crack 17 by using the pressure of the nitrogen gas.

Further, according to the semiconductor member manufacturing method of the second example, the cracks 17 can be formed with high accuracy along each of the plurality of virtual surfaces 15 by the steps included in the laser processing method of the second embodiment. Therefore, it is possible to obtain a plurality of suitable semiconductor devices 40 .

Further, in the semiconductor member manufacturing method of the second example, the plurality of virtual planes 15 are set to be aligned in the direction in which the surface 30a of the GaN wafer 30 extends. Thereby, it becomes possible to obtain a plurality of semiconductor devices 40 from one GaN wafer 30 .
[Modification]

The above example can be modified arbitrarily. For example, various numerical values regarding the laser light L are not limited to those described above. However, in order to suppress the crack 14 from extending from the modified spot 13 to the incident side of the laser light L and the opposite side, the pulse energy of the laser light L is 0.1 μJ to 1 μJ and the pulse of the laser light L The width is preferably between 200 fs and 1 ns.

Moreover, the semiconductor object processed by the laser processing method and the semiconductor member manufacturing method is not limited to the GaN ingot 20 of the first example and the GaN wafer 30 of the second example. The semiconductor member manufactured by the semiconductor member manufacturing method is not limited to the GaN wafer 30 of the first example and the semiconductor device 40 of the second example. One virtual plane may be set for one semiconductor object.

As an example, the material of the semiconductor object may be SiC. Even in that case, according to the laser processing method and the semiconductor member manufacturing method, as described below, it is possible to accurately form a crack extending along the virtual plane.

(a) and (b) of FIG. 29 are images (side view images) of cracks in SiC wafers formed by the laser processing method and the semiconductor member manufacturing method of the comparative example, and (b) of FIG. 30 is an enlarged image within the rectangular frame in FIG. 29(a). In this comparative example, a laser beam having a wavelength of 532 nm is incident from the surface of the SiC wafer into the interior of the SiC wafer, and six focal points aligned in the Y direction are moved relatively along the X direction on a virtual plane. A plurality of modified spots were formed along the imaginary plane. At this time, the distance between the condensing points C adjacent 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 shown in FIGS. 29(a) and 29(b), a crack extending in a direction inclined by 4° to 5° with respect to the virtual plane was generated.

(a) and (b) of FIG. 30 are images (side view images) of cracks in SiC wafers formed by the laser processing method and the semiconductor member manufacturing method of the example, and (b) of FIG. 31 is an enlarged image within the rectangular frame in FIG. 30(a). In this example, a laser beam having a wavelength of 532 nm was made incident on the inside of the SiC wafer from the surface of the SiC wafer, and similarly to the first and second steps of the laser processing method and the semiconductor member manufacturing method of the first embodiment, , formed multiple modified spots along the imaginary plane. When forming a plurality of modified spots corresponding respectively to the plurality of modified spots 13a, 13b, 13c, and 13d, the distance between adjacent condensing points C in the Y direction is 8 μm, and the pulse pitch of the laser beam L is 8 μm. is 15 μm, and the pulse energy of the laser light L is 4 μJ. In this case, as shown in FIGS. 30(a) and 30(b), the occurrence of cracks extending in a direction inclined by 4° to 5° with respect to the virtual plane was suppressed. FIG. 31 is an image of the peeled surface of the SiC wafer formed by the laser processing method and semiconductor member manufacturing method of the example, and FIGS. profile. In this case, the unevenness appearing on the peeled surface of the SiC wafer was suppressed to about 2 μm.

From the above experimental results, even when the material of the semiconductor object is SiC, according to the laser processing method and the semiconductor member manufacturing method, it is found that a crack extending along the virtual plane is formed with high accuracy along the virtual plane. Ta. The SiC wafers used in the comparative examples and examples described above are 4H-SiC wafers having an off angle of 4±0.5°, and the direction in which the focal point of the laser beam is moved is the m-axis direction. is.

Moreover, the method of forming the plurality of modified spots 13a, 13b, 13c, and 13d is not limited to the one described above. A plurality of modified spots 13a may be formed such that a plurality of cracks 14a respectively extending from the plurality of modified spots 13a are connected to each other. Also, the plurality of modified spots 13b may be formed so as not to overlap the plurality of modified spots 13a. Even if a plurality of modified spots 13b overlap with a plurality of cracks 14a respectively extending from a plurality of modified spots 13a, if the plurality of modified spots 13b do not overlap with the plurality of modified spots 13a, the plurality of modified spots 13b 13a and 13b are formed along the virtual plane 15 with high accuracy. Moreover, the method of forming the plurality of modified spots 13c and 13d is arbitrary, and the plurality of modified spots 13c and 13d may not be formed. Further, as shown in FIG. 33, for example, by rotating the GaN ingot 20, a plurality of condensing points arranged in the radial direction are relatively rotated (a dashed-dotted line arrow) to form a plurality of rows of modified spots. 13, and further, as shown in FIG. 34, a plurality of condensing points are arranged in the radial direction with each of the plurality of condensing points positioned between the rows of the plurality of rows of modified spots 13. may be relatively rotated (dash-dotted arrows) to form multiple rows of modified spots 13 .

Further, in the laser processing method and the semiconductor member manufacturing method of the first example, the formation of the plurality of modified spots 13 may be sequentially performed for each of the plurality of virtual surfaces 15 from the side opposite to the surface 20a. Further, in the laser processing method and the semiconductor member manufacturing method of the first example, the formation of a plurality of modified spots 13 is performed along one or more virtual planes 15 on the side of the surface 20a, and one or more GaN wafers are formed. After cutting 30, surface 20a of GaN ingot 20 may be ground, and again, formation of multiple modification spots 13 may be performed along one or more imaginary planes 15 on surface 20a side.

Moreover, in the laser processing method and the semiconductor member manufacturing method of the first and second examples, the peripheral region 16 may not be formed. In the laser processing method and the semiconductor member manufacturing method of the first example, when the peripheral region 16 is not formed, after forming the plurality of modified spots 13 along each of the plurality of virtual planes 15, for example, the GaN ingot 20 It is also possible to obtain a plurality of GaN wafers 30 by etching the substrate.

In addition, each configuration in the above example is not limited to the materials and shapes described above, and various materials and shapes can be applied. In addition, each configuration in one example or modified example described above can be arbitrarily applied to each configuration in another example or modified example.

Moreover, the laser processing apparatus 1 is not limited to the one having the configuration described above. For example, the laser processing device 1 does not have to include the spatial light modulator 4 .
[Laser processing method and semiconductor device manufacturing method according to the embodiment]

FIG. 35 is a diagram showing a laser processing apparatus. As shown in FIG. 35, the laser processing apparatus 1A is different from the laser processing apparatus 1 shown in FIG. , is different from the laser processing apparatus 1 . In the laser processing apparatus 1A, the light source 3, the spatial light modulator 4, and the condenser lens 5 constitute an irradiation section 45. As shown in FIG. That is, the laser processing apparatus 1A includes a stage 2A that supports the GaN wafer 30, an irradiation unit 45 that irradiates the GaN wafer 30 supported by the stage 2A with a laser beam L, and a measurement unit that measures the transmittance of the GaN wafer 30. 50 , and a control unit 6 that controls the irradiation unit 45 and the measurement unit 50 .

Stage 2A includes a transmission portion 2T that transmits measurement light IL used for measurement. The measurement unit 50 includes a light source 51 that irradiates the measurement light IL toward the GaN wafer 30 supported on the stage 2A, and a photodetector 52 that detects the measurement light IL transmitted through the GaN wafer 30 and the transmission unit 2T. and measures the transmittance of the GaN wafer 30 based on the detection result of the photodetector 52 .

In the method according to this embodiment, first, steps S1 to S3 are performed in the same manner as in the first example. That is, as shown in FIG. 36, by irradiating the inside of the GaN wafer 30 with the laser light L from the surface 30a of the GaN wafer 30 (instead of the GaN ingot 20), the surface 30a is opposed to the inside of the GaN wafer 30. A plurality of modified spots 13 (modified spots 13a to 13c) and a plurality of precipitation regions R containing gallium deposited in the plurality of modified spots 13 are formed along the virtual plane 15 ( first step). In this first step, the energy of the laser beam L on the virtual plane 15 is naturally above the processing threshold of the GaN wafer 30 .

The irradiation conditions of the laser light L when forming the modified spots 13a to 13c can be defined as follows, for example. First, as the pulse energy of the laser beam L increases, the precipitation region R formed around the modified spot 13 tends to increase. Therefore, when the distance between the converging points C of the laser light L (for example, in the Y direction) is relatively increased (the modified spots 13 and the precipitation regions R are formed relatively roughly), the subsequent laser It is desirable to increase the pulse energy of the laser light L from the viewpoint of enlarging the deposition region R by light irradiation. On the other hand, when the distance between the focal points C of the laser beam L (for example, in the Y direction) is relatively small (the modified spots 13 and the precipitation regions R are formed relatively densely), the laser beam Even if the pulse energy of is reduced, the deposition region R can be enlarged by laser light irradiation in a later step. As an example, if the pulse pitch of the laser light L is constant at 10 μm, and the distance between the condensing points C adjacent in the Y direction is 8 μm, the pulse energy of the laser light L is set to about 2 μJ, The deposition region R can be enlarged by laser light irradiation in a later step. Further, when the distance between adjacent condensing points C in the Y direction is set to 4 μm, the pulse energy of the laser beam L is set to about 0.67 μJ, so that the laser beam irradiation in the subsequent process will cause the precipitated region to grow. R can be expanded. Furthermore, when the distance between adjacent condensing points C in the Y direction is set to 2 μm, the pulse energy of the laser beam L is set to about 0.33 μJ, so that the laser beam irradiation in the subsequent process will cause the deposition region to R can be expanded.

Subsequently, the transmittance of the GaN wafer 30 is measured (fourth step). Subsequently, it is determined whether or not the transmittance measured in the fourth step is higher than the reference value (fifth step). A reference value for the transmittance of the GaN wafer 30 can be set to, for example, 0.5 (50%). Then, if the result of determination in the fifth step is that the transmittance is higher than the reference value, the formation of the modified spots 13 is deemed insufficient, and the first step is performed again. On the other hand, if the transmittance is equal to or less than the reference value as a result of determination in the fifth step, the process proceeds to the subsequent step.

That is, in the subsequent step, as shown in FIG. 37, the GaN wafer 30 is placed in the chamber H of the semiconductor manufacturing equipment. Then, a semiconductor layer (epitaxial growth layer) 70 for a semiconductor device is formed on the GaN wafer 30 by epitaxial growth. Here, the semiconductor layer 70 is formed on the surface 30a of the GaN wafer 30. As shown in FIG. Any method can be used for the epitaxial growth here, but the GaN wafer 30 can be heated to about 1030° C., for example.

Subsequently, the GaN wafer 30 provided with the semiconductor layer 70 is taken out from the chamber H. Then, as shown in FIGS. 38 and 39, the focal point C of the laser beam L is arranged so as not to overlap the modified spot 13 when viewed from the direction (Z direction) intersecting the surface 30a of the GaN wafer 30. . Here, each of the plurality of condensing points C is arranged between the modified spots 13a and 13b adjacent to each other in the Y direction. Further, here, as an example, the condensing point C can be arranged so as not to overlap the crack 14 and the precipitation region R in addition to the modified spot 13 . In addition, the energy on the virtual plane 15 is set below the processing threshold of the GaN wafer 30 . In this state, the inside of the GaN wafer 30 is irradiated with a laser beam L from a rear surface 30r opposite to the front surface 30a (the surface of the GaN wafer 30 different from the surface on which the semiconductor layer 70 is formed).

This step is based on the following findings. That is, first, by irradiating a semiconductor object containing gallium with a laser beam, along a virtual plane, a plurality of modified spots, a deposition region containing gallium deposited at the plurality of modified spots, and to form Then, when laser light is re-irradiated in a later process, the laser light energy on the imaginary plane is applied to the semiconductor object (while avoiding overlapping of the previously formed modification spots with the focal points of the laser light). Even lowering below the processing threshold can enlarge the pre-formed gallium-containing precipitation region. As a result, when the semiconductor member is cut out by forming a crack across the imaginary surface, the unevenness of the cut out surface can be reduced.

Here, the laser processing apparatus 1 moves the focal point C of the pulsed laser light L along the virtual plane 15 . Further, the pulse-oscillated laser beam L is modulated by the spatial light modulator 4 so as to be condensed at a plurality of (for example, six) condensing points C arranged in the Y direction. Then, the plurality of condensing points C are relatively moved on the virtual plane 15 along the X direction. As an example, the distance between condensing points C adjacent in the Y direction is 1 μm, and the pulse pitch of the laser light L is 10 μm. Also, the pulse energy of the laser light L is 0.33 μJ. According to this irradiation condition, although no modified spot is formed at the position corresponding to the focal point C of the laser beam L, the deposition region R is enlarged. Subsequent steps are the same as in the first example. Thereby, a semiconductor device including the semiconductor layer 70 is obtained from the GaN wafer 30 .

As described above, in the method according to the present embodiment, the modified spots 13 are formed inside the GaN wafer 30 by irradiating the laser light L prior to forming the semiconductor layer 70 for the semiconductor device by epitaxial growth. . Therefore, the semiconductor layer 70 cannot be damaged when the modified spots 13 are formed. Therefore, by exfoliating the GaN wafer 30 by allowing the crack extending from the modified spot 13 to grow, a suitable semiconductor device with less damage can be obtained.

Further, in the method according to the present embodiment, after the second step, the semiconductor layer 70 on the GaN wafer 30 is formed so that the condensing point C does not overlap the modified spot 13 when viewed from the direction intersecting the surface 30a. A third step is provided for forming a crack across the virtual surface 15 by irradiating the inside of the GaN wafer 30 with the laser light L from the rear surface 30r different from the surface. In this manner, the irradiation of the laser beam L may form a crack along the virtual plane 15 that is the starting point of separation. Note that even in this case, since the modified spots 13 are formed prior to the formation of the semiconductor layer 70, the semiconductor layer 70 is less processed than when all the laser processing is performed after the semiconductor layer 70 is formed. damage to is suppressed.

Further, in the method according to the present embodiment, in the first step, by irradiating the inside of the GaN wafer with the laser light L from the surface 30a, the plurality of modified spots 13 and at the plurality of modified spots 13 A plurality of deposition regions R containing deposited gallium are formed, and in the third step, the interior of the GaN wafer 30 is irradiated with laser light L such that the energy in the virtual plane 15 is below the processing threshold of the GaN wafer 30. , the precipitation region R is expanded and a crack extending over the virtual surface 15 is formed.

In this manner, first, by irradiating the inside of the GaN wafer 30 containing gallium with the laser beam L, a plurality of modified spots 13 are formed along the virtual surface 15 facing the surface 30a, which is the incident surface of the laser beam L. , and a plurality of deposition regions R containing deposited gallium. Then, in a later process, the laser beam L is introduced into the inside of the GaN wafer 30 so that the focal point C does not overlap the modified spot 13 and the energy on the imaginary plane 15 is below the processing threshold of the GaN wafer 30 . By irradiating with , the precipitation region R is expanded and a crack extending over the imaginary surface 15 is formed. As a result, as described above, it is possible to obtain a suitable semiconductor device with reduced unevenness by peeling along the boundary of the crack extending across the imaginary surface 15 .

The above embodiment describes an example of a laser processing method and a semiconductor device manufacturing method according to the present invention. Therefore, the laser processing method and the semiconductor device manufacturing method according to the present invention are not limited to the above embodiments, and various modifications can be applied.

For example, in the laser processing method, in the second step, by heating the GaN wafer 30 for epitaxial growth, a plurality of cracks extending from the plurality of modified spots 13 are propagated to form cracks extending over the virtual plane 15. You may In this case, the formation of the semiconductor layer 70 and the formation of the crack across the imaginary surface 15 can be performed simultaneously.

At this time, in the first step, the GaN wafer 30 may be provided with a peripheral edge region 16 that prevents the development of the plurality of cracks 14 extending from the plurality of modified spots 13 . In this case, during the epitaxial growth in the second step, it is possible to suppress the unintentional formation of cracks across the virtual surface 15 and the occurrence of peeling.

In the above method, the transmittance of the GaN wafer 30 is measured in the fourth step, and if the transmittance is determined to be higher than the reference value in the fifth step, the first step is performed again. The case where the modified spots 13 are sufficiently formed by the heat treatment is exemplified. In this case, the damage to the semiconductor layer 70 could be suppressed by reducing the energy of the laser processing after forming the semiconductor layer 70 or refraining from laser light irradiation.

On the other hand, in the first step, the semiconductor layer 70 is formed in the second step while maintaining a state in which the transmittance is higher than the reference value. of laser processing may be implemented. In this case, since the amount of the modified spots 13 formed in advance is reduced, it is possible to suppress warping of the semiconductor layer 70 during epitaxial growth in the second step. Even in this case, damage to the semiconductor layer 70 is suppressed as compared with the case where all the laser processing is performed after the semiconductor layer 70 is formed. Also, in this case, the measurement and determination of the transmittance of the GaN wafer 30 are not essential.

The above embodiment describes an example of a laser processing method and a semiconductor device manufacturing method according to the present invention. Therefore, the laser processing method and the semiconductor device manufacturing method according to the present invention are not limited to the above embodiments, and various modifications can be applied.

For example, the elements of the first example, the second example, and their modifications can be arbitrarily applied to the method according to the above embodiment. As an example, in the first step, the plurality of modified spots 13 can be formed so that the plurality of cracks 14 extending from the plurality of modified spots 13 are not connected to each other. Further, in the first step, by moving the focal point C of the pulse-oscillated laser beam L along the virtual plane 15, a plurality of rows of modified spots 13 are formed as the plurality of modified spots 13. In the third step, the focal point C of the pulse-oscillated laser beam L can be moved along the virtual plane 15 between the multiple rows of modified spots 13 .

Reference numerals 13: modification spot, 15: imaginary surface, 30: GaN wafer (semiconductor wafer), 30a: surface, 70: semiconductor layer, L: laser beam, R: precipitation region.

Claims (9)

A laser processing method for cutting the semiconductor wafer along a virtual plane facing the surface of the semiconductor wafer inside the semiconductor wafer,
a first step of forming a plurality of modified spots along the virtual plane inside the semiconductor wafer by irradiating the inside of the semiconductor wafer with a laser beam from the surface;
a second step of forming a semiconductor layer for a semiconductor device by epitaxial growth on the semiconductor wafer after the first step;
after the second step, the inside of the semiconductor wafer from a surface different from the surface on which the semiconductor layer is formed in the semiconductor wafer so that the focal point does not overlap the modified spot when viewed in a direction intersecting the surface; A third step of forming a crack across the virtual surface by irradiating a laser beam on the
A laser processing method comprising: the semiconductor wafer contains gallium;
In the first step, by irradiating the interior of the semiconductor wafer with a laser beam from the surface, the plurality of modified spots and the plurality of precipitation regions containing gallium deposited at the plurality of modified spots. to form
In the third step, by irradiating the interior of the semiconductor wafer with a laser beam such that the energy in the virtual plane is below the processing threshold of the semiconductor wafer, the precipitation region is expanded and a crack extending across the virtual plane is formed. to form
The laser processing method according to claim 1 . In the first step, the semiconductor wafer is provided with a peripheral region that inhibits propagation of a plurality of cracks extending from the plurality of modified spots, respectively.
The laser processing method according to claim 1 or 2 . a fourth step of measuring the transmittance of the semiconductor wafer between the first step and the second step;
A fifth step of determining whether the transmittance measured in the fourth step is higher than a reference value between the fourth step and the second step;
further comprising
As a result of the determination in the fifth step, if the transmittance is higher than the reference value, the first step is performed again.
The laser processing method according to any one of claims 1 to 3 . In the first step, the plurality of modified spots are formed so that the plurality of cracks extending from the plurality of modified spots are not connected to each other.
The laser processing method according to any one of claims 1 to 4 . In the first step, a plurality of rows of modified spots are formed as the plurality of modified spots by moving a focal point of pulsed laser light along the virtual plane;
In the third step, a focal point of the pulsed laser light is moved along the virtual plane between the plurality of rows of modified spots,
The laser processing method according to any one of claims 1 to 5 . wherein the semiconductor wafer comprises gallium nitride;
The laser processing method according to any one of claims 1 to 6 . a step of performing the laser processing method according to any one of claims 1 to 7 ;
a step of obtaining a plurality of semiconductor devices from the semiconductor wafer with the crack extending across the virtual plane as a boundary;
A semiconductor device manufacturing method comprising: A plurality of the virtual planes are set so as to line up in a direction along the surface,
9. The semiconductor device manufacturing method according to claim 8 .

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