WO2020130108A1

WO2020130108A1 - Laser machining method, and semiconductor device manufacturing method

Info

Publication number: WO2020130108A1
Application number: PCT/JP2019/049955
Authority: WO
Inventors: 大祐河口; 陽太郎和仁; 泰則伊ケ崎
Original assignee: 浜松ホトニクス株式会社
Priority date: 2018-12-21
Filing date: 2019-12-19
Publication date: 2020-06-25
Also published as: TW202108275A; JP2020102521A; JP7330695B2

Abstract

A laser machining method for cutting a semiconductor wafer along a virtual plane that is inside the semiconductor wafer and faces the surface of the semiconductor wafer, said method comprising: a first step for forming a plurality of modified spots along the virtual plane inside the semiconductor wafer by radiating laser light into the semiconductor wafer from the surface thereof; and a second step for forming by epitaxial growth, on the semiconductor wafer after the first step, a semiconductor layer for a semiconductor device.

Description

Laser processing method and semiconductor device manufacturing method

The present disclosure 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, so that the semiconductor object is a semiconductor such as a semiconductor wafer. A processing method for cutting out a member is known (see, for example, Patent Documents 1 and 2).

JP, 2017-183600, A JP, 2017-057103, A

By the way, there is a demand for thinning the semiconductor member by advancing cracks extending from the modified region and peeling (cutting) unnecessary portions from the semiconductor member. The semiconductor member to be thinned may include an epitaxial growth layer for a semiconductor device to be cut out later. In this case, when laser light is irradiated to form the modified region inside the semiconductor member, the leaked light may damage the epitaxial growth layer, resulting in deterioration of the quality of the semiconductor device.

The present disclosure aims 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 disclosure is a laser processing method for cutting a semiconductor wafer along a virtual surface facing the surface of the semiconductor wafer inside the semiconductor wafer. A first step of forming a plurality of modified spots along an imaginary plane by irradiating light, and after the first step, a semiconductor layer for a semiconductor device is formed by epitaxial growth on a semiconductor wafer. A second step.

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

In the laser processing method according to the present disclosure, after the second step, the semiconductor is changed from a surface different from the surface on which the semiconductor layer is formed in the semiconductor wafer so that the converging point does not overlap the modified spot when viewed from the direction intersecting the surface. A third step of forming a crack across the virtual surface by irradiating the inside of the wafer with laser light may be provided. As described above, the irradiation of the laser light may form a crack along the virtual surface that is the origin of the peeling. Even in this case, since the modified spot is formed prior to the formation of the semiconductor layer, the damage to the semiconductor layer is less likely to occur as compared with the case where all the laser processing is performed after the formation of the semiconductor layer. Suppressed.

Here, the present inventor found the following problems in the course of diligent studies to solve the above problems. That is, as described above, a modified spot is formed along the virtual surface inside the semiconductor wafer by irradiation with laser light, and a crack extending from the modified spot is developed to cut out a semiconductor device from the semiconductor wafer (peeling). In order to reduce the unevenness of the peeled surface and obtain a more suitable semiconductor device, it is effective to reduce the energy of the laser light on the virtual surface. If the energy on the virtual surface is too low, modified spots and cracks cannot be generated.

The present inventor has obtained the following knowledge by paying attention to such a problem and proceeding with further studies. That is, first, by irradiating a semiconductor wafer containing gallium with a laser beam, a plurality of modified spots and a deposition region containing gallium deposited in the plurality of modified spots are provided along the virtual surface. Form. Then, when the laser light is irradiated again in a later step, the modification spots formed in advance do not overlap the condensing point of the laser light, and the energy of the laser light on the virtual surface is set to the processing threshold of the semiconductor wafer. The region containing pre-formed gallium can be expanded even if the amount is lowered below the range. As a result, when the semiconductor wafer is peeled off by forming a crack across the virtual surface, the unevenness of the peeled surface can be reduced. The following invention was made based on such knowledge.

That is, in the laser processing method according to the present disclosure, the semiconductor wafer contains gallium, and in the first step, a plurality of modified spots and a plurality of modified spots are formed by irradiating the inside of the semiconductor wafer with laser light from the surface. Forming a plurality of deposition regions containing gallium deposited in the modified spots, and in the third step, irradiating the inside of the semiconductor wafer with laser light so that the energy on the virtual surface falls below the processing threshold of the semiconductor wafer. By this, the precipitation region may be enlarged and a crack may be formed across the virtual surface.

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 surface facing the surface that is the incident surface of laser light. Forming a plurality of deposition regions including. Then, in a later step, the inside of the semiconductor wafer is irradiated with laser light so that the condensing point does not overlap with the modified spot and the energy on the virtual surface falls below the processing threshold of the semiconductor wafer. Expand the area and create a crack across the virtual plane. As a result, as described above, it becomes possible to obtain a suitable semiconductor device in which unevenness is reduced due to peeling at the boundary of the crack across the virtual surface.

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

In the laser processing method according to the present disclosure, in the first step, the semiconductor wafer may be provided with a peripheral region that prevents the development of a plurality of cracks extending from the plurality of modified spots. In this case, during the epitaxial growth in the second step, unintentional formation of cracks across the imaginary plane and peeling are suppressed.

The laser processing method according to the present disclosure includes a fourth step between the first step and the second step, which measures the transmittance of the semiconductor wafer, and a fourth step between the fourth step and the second step. A fifth step of determining whether or not the measured transmittance is higher than a reference value, and if the result of the determination in the fifth step is that the transmittance is higher than the reference value, the first step May be carried out again. In this case, the modified spots can be sufficiently formed inside the semiconductor wafer prior to the second step of forming the semiconductor layer.

In the laser processing method according to the present disclosure, in the first step, a plurality of modified spots may be formed so that the plurality of cracks extending from the plurality of modified spots are not connected to each other. In this case, at the time of subsequent irradiation with laser light, the focus point of the laser light can be prevented from overlapping not only with the modified spot but also with the crack extending from the modified spot. As a result, it becomes possible to avoid formation of a new modified spot, a crack, or a region in which gallium is deposited at an unintended position during subsequent laser light irradiation. That is, a more suitable semiconductor member can be obtained.

In the laser processing method according to the present disclosure, 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 light along the virtual surface. In the third step, the condensing point of the pulsed laser light may be moved along the virtual plane between the rows of the reforming spots of a plurality of rows. In this case, it is possible to reliably prevent the converging points of the laser light in the third step from overlapping the plurality of modified spots.

In the laser processing method according to the present disclosure, 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 a crack over the virtual surface.

A semiconductor device manufacturing method according to the present disclosure includes a step of performing any one of the above laser processing methods, and a step of acquiring a plurality of semiconductor devices from a semiconductor wafer with a crack across a virtual surface as a boundary. This method implements the laser processing method described above. Therefore, a suitable semiconductor device can be obtained for the same reason.

In the semiconductor device manufacturing method according to the present disclosure, a plurality of virtual planes may be set so as to be aligned in the direction along the surface. In this case, a plurality of semiconductor devices can be acquired from one semiconductor wafer.

According to the present disclosure, it is possible to provide a laser processing method capable of obtaining a suitable semiconductor device and a semiconductor device manufacturing method.

It is a block diagram of a laser processing apparatus. It is a side view of a GaN ingot which is an object of the laser processing method and the semiconductor member manufacturing method of the first example. FIG. 3 is a plan view of the GaN ingot shown in FIG. 2. It is a longitudinal cross-sectional view of a part of the GaN ingot in one step of the laser processing method and the semiconductor member manufacturing method of the first example. It is a transverse cross section of a part of GaN ingot in one process of the laser processing method and semiconductor member manufacturing method of the 1st example. It is a longitudinal cross-sectional view of a part of the GaN ingot in one step of the laser processing method and the semiconductor member manufacturing method of the first example. It is a transverse cross section of a part of GaN ingot in one process of the laser processing method and semiconductor member manufacturing method of the 1st example. It is a longitudinal cross-sectional view of a part of the GaN ingot in one step of the laser processing method and the semiconductor member manufacturing method of the first example. It is a transverse cross section of a part of GaN ingot in one process of the laser processing method and semiconductor member manufacturing method of the 1st example. It is a longitudinal cross-sectional view of a part of the GaN ingot in one step of the laser processing method and the semiconductor member manufacturing method of the first example. It is a transverse cross section of a part of GaN ingot in one process of the laser processing method and semiconductor member manufacturing method of the 1st example. It 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. It is a side view of a GaN wafer in one process of a laser processing method and a semiconductor member manufacturing method of a 1st example. It is an image of the exfoliation surface of a GaN wafer formed by an example laser processing method and a semiconductor member manufacturing method. It is the height profile of the peeled surface shown in FIG. It is an image of the exfoliation surface of a GaN wafer formed by a laser processing method and a semiconductor member manufacturing method of other examples. It is the height profile of the peeling surface shown in FIG. It is a schematic diagram for demonstrating the formation principle of the peeling surface by a laser processing method and a semiconductor member manufacturing method of an example. It is a schematic diagram for demonstrating the formation principle of the peeling surface by the laser processing method and semiconductor member manufacturing method of another example. It is an image of a crack formed during the laser processing method and the semiconductor member manufacturing method of an example. It is an image of a crack formed in the middle of the laser processing method and the semiconductor member manufacturing method of another example. 5 is an image of modified spots and cracks formed by a laser processing method and a semiconductor member manufacturing method of a comparative example. 3 is an image of modified spots and cracks formed by the laser processing method and the semiconductor member manufacturing method of the first embodiment. 6 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 embodiments. It is a top view of a GaN wafer which is an object of a laser processing method and a semiconductor member manufacturing method of the 2nd example. It is a side view of a part of GaN wafer in one process of a laser processing method and a semiconductor member manufacturing method of a 2nd example. It is a side view of a part of GaN wafer in one process of a laser processing method and a semiconductor member manufacturing method of a 2nd example. It is a side view of a semiconductor device in one process of a laser processing method and a semiconductor member manufacturing method of a 2nd example. It is an image of a crack of a SiC wafer formed by a laser processing method and a semiconductor member manufacturing method of a comparative example. It is an image of a crack of a SiC wafer formed by a laser processing method and a semiconductor member manufacturing method of an example. It is an image of the peeled surface of the SiC wafer formed by the laser processing method and the semiconductor member manufacturing method of the example. It is the height profile of the peeled surface shown in FIG. It is a top view of a GaN ingot in one process of a laser processing method and a semiconductor member manufacturing method of a modification. It is a top view of a GaN ingot in one process of a laser processing method and a semiconductor member manufacturing method of a modification. It is a block diagram of a laser processing apparatus. It is a longitudinal cross-sectional view of a part of the GaN wafer in one step of the laser processing method and the semiconductor device manufacturing method of the embodiment. It is a cross-sectional view of a part of the GaN wafer in one step of the laser processing method and the semiconductor device manufacturing method of the embodiment. It is a longitudinal cross-sectional view of a part of the GaN wafer in one step of the laser processing method and the semiconductor device manufacturing method of the embodiment. It is a cross-sectional view of a part of the GaN wafer in one step of the laser processing method and the semiconductor device manufacturing method of the embodiment.

Hereinafter, a detailed description will be provided with reference to the drawings. In the drawings, the same or corresponding parts will be denoted by the same reference symbols and redundant description will be omitted.
[Configuration of laser processing equipment]

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 control unit 6. The laser processing apparatus 1 is an apparatus that forms a modified region 12 on the object 11 by irradiating the object 11 with a laser beam L. 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. The vertical direction is called the Z direction.

The stage 2 supports the target object 11 by, for example, adsorbing a film attached to the target object 11. In the present embodiment, the stage 2 is movable along each of the X direction and the Y direction. Further, the stage 2 can rotate about an axis parallel to the Z direction as a center line.

The light source 3 outputs a laser beam L that is transparent to the object 11 by using, 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). The condenser lens 5 condenses 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 as a laser irradiation unit along the Z direction.

When the laser light L is condensed inside the target object 11 supported by the stage 2, the laser light L is particularly absorbed at a portion corresponding to the condensing point C of the laser light L, and the inside of the target object 11 is modified. A quality region 12 is formed. The modified region 12 is a region in which density, refractive index, mechanical strength, and other physical properties are different from those of the surrounding unmodified region. The modified region 12 includes, for example, a melt-processed region, a crack region, a dielectric breakdown region, and a refractive index change region.

As an example, when the stage 2 is moved along the X direction and the condensing point C is moved relative to the target object 11 along the X direction, a plurality of modified spots 13 are moved along the X direction by 1. It is formed so as to line up in a row. One modified spot 13 is formed by irradiation with one pulse of laser light L. The one-row reforming region 12 is a set of a plurality of reforming spots 13 arranged in one row. The adjacent modified spots 13 may be connected to each other or may be separated from each other depending on the relative moving speed of the condensing point C with respect to the object 11 and the repetition frequency of the laser light L.

The control unit 6 controls the stage 2, the light source 3, the spatial light modulator 4, and the condenser lens 5. The control unit 6 is configured as a computer device including a processor, a memory, a storage, a communication device, and the like. In the control unit 6, the software (program) read into the memory or the like is executed by the processor, and the reading and writing of data in the memory and the storage and the communication by the communication device are controlled by the processor. Thereby, the control unit 6 realizes various functions.
[Laser Processing Method and Semiconductor Member Manufacturing Method According to First Example]

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

First, the laser processing apparatus 1 described above forms a plurality of modified spots 13 along each of a plurality of virtual surfaces 15. Each of the plurality of virtual surfaces 15 is a surface facing the surface 20a of the GaN ingot 20 inside 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 surfaces 15 is set so as to overlap each other when viewed from the front surface 20a side. A plurality of peripheral regions 16 are set in the GaN ingot 20 so as to surround each of the plurality of virtual surfaces 15. That is, each of the plurality of virtual surfaces 15 does not reach the side surface 20b of the GaN ingot 20. As an example, the distance between the adjacent virtual surfaces 15 is 100 μm, and the width of the peripheral region 16 (in the present 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 one virtual surface 15 from the side opposite to the surface 20a by the irradiation of the 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. This will be described in detail with reference to 11. In addition, in FIG. 5, FIG. 7, FIG. 9, and FIG. 11, the arrow indicates the locus of the condensing point C of the laser light L. Further, the modified

spots

13a, 13b, 13c, 13d described later may be collectively referred to as the modified spot 13, and the

cracks

14a, 14b, 14c, 14d described later may be collectively referred to as the crack 14.

First, as shown in FIGS. 4 and 5, the laser processing apparatus 1 causes the laser light L to enter the GaN ingot 20 from the surface 20 a and irradiate the laser light L along the virtual plane 15 (for example, a virtual plane). A plurality of modified spots 13a (first modified spots) are formed (two-dimensionally arranged 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 forms the modified spots 13a in a plurality of rows by moving the condensing point C of the pulsed laser light L along the virtual surface 15. 4 and 5, the modified spot 13a is shown in white (no hatching), and the range in which the crack 14a extends is shown by broken lines (the same applies to FIGS. 6 to 11). Further, at this time, the gallium deposited in each of the modified spots 13a spreads so as to enter the crack 14a, so that a deposition region R containing the deposited gallium is formed around the modified spot 13a. ..

Here, the pulsed 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 surface 15 along the X direction. As an example, the distance between the condensing points C adjacent to each other 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). The divided value) is 10 μm. 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 adjacent modified spots 13a in the Y direction is 8 μm, and the center-to-center distance between adjacent modified spots 13a in the X direction is 10 μm. Further, the cracks 14a extending from the modified spots 13a are not connected to each other.

Subsequently, as shown in FIGS. 6 and 7, the laser processing apparatus 1 causes the laser light L to enter the GaN ingot 20 from the surface 20 a and irradiates the laser light L along the virtual surface 15 (for example, A plurality of modified spots (second modified spots) 13b are formed so as to be arranged two-dimensionally along the entire virtual 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. Moreover, the laser processing apparatus 1 moves the condensing point C of the pulsed laser light L along the virtual plane 15 between the rows of the reforming spots 13a of the plurality of rows to thereby form the reforming spots 13b of the plurality of rows. To form. In this step, the cracks 14b extending from the modified spots 13b may be connected to the cracks 14a. 6 and 7, the modified spot 13b is shown by dot hatching, and the range in which the crack 14b extends is shown by broken lines (the same applies to FIGS. 8 to 11). Further, at this time, the gallium deposited in each of the modified spots 13b spreads so as to enter the crack 14b, so that a deposition region R containing the deposited gallium is formed around the modified spot 13b. ..

Here, the pulsed 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 surface 15 along the X direction at the centers between the rows of the reformed spots 13a. As an example, the distance between the condensing 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 adjacent modified spots 13b in the Y direction is 8 μm, and the center-to-center distance between adjacent modified spots 13b in the X direction is 10 μm.

Then, as shown in FIGS. 8 and 9, the laser processing apparatus 1 causes the laser light L to enter the GaN ingot 20 from the surface 20 a and irradiate the laser light L along the virtual surface 15 (for example, A plurality of modified spots (third modified spots) 13c are formed so as to be two-dimensionally arranged along the entire virtual surface 15 (step S3). Further, as shown in FIGS. 10 and 11, the laser processing apparatus 1 causes the laser light L to enter the GaN ingot 20 from the front surface 20 a and irradiate the laser light L along the virtual surface 15 (for example, a virtual surface). A plurality of modified spots (third modified spots) 13d are formed so as to be two-dimensionally arranged 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.

Further, the laser processing apparatus 1 moves the condensing point C of the pulsed laser light L along the virtual plane 15 between the rows of the reforming

spots

13a and 13b of the plurality of rows, thereby reforming the plurality of rows. The

spots

13c and 13d are formed. In this step, the

cracks

14c and 14d extending from the modified

spots

13c and 13d may be connected to the cracks 14a and 14b. 8 and 9, the modified spot 13c is shown by solid line hatching, and the range in which the crack 14c extends is shown by broken lines (also in FIGS. 10 and 11). 10 and 11, the modified spot 13d is shown by solid line hatching (solid line hatching that is the reverse of the solid line hatching of the modified spot 13c), and the range in which the crack 14d extends is shown by broken lines. There is. Further, at this time, the gallium deposited in each of the reformed

spots

13c and 13d spreads so as to enter the

cracks

14c and 14d, so that the deposited gallium is deposited around the reformed

spots

13c and 13d. Region R is formed.

Here, the pulsed 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 converging points C are relatively moved on the virtual surface 15 along the X direction at the center between the rows of the reformed

spots

13a and 13b of the plurality of rows. As an example, the distance between the condensing 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 adjacent modified spots 13c in the Y direction is 8 μm, and the center-to-center distance between adjacent modified spots 13c in the X direction is 5 μm. Further, the center-to-center distance between the modified spots 13d adjacent to each other in the Y direction is 8 μm, and the center-to-center distance between the modified spots 13d adjacent to each other in the X-direction is 5 μm.

Subsequently, a heating device including a heater or the like heats the GaN ingot 20 to connect the plurality of cracks 14 extending from the plurality of modified spots 13 to each other on each of the plurality of virtual planes 15, thereby being shown in FIG. As described above, a crack 17 (hereinafter, simply referred to as “crack 17”) that extends over the virtual surface 15 is formed in each of the plurality of virtual surfaces 15. In FIG. 12, a range in which the plurality of modified spots 13, the plurality of cracks 14, and the crack 17 are formed is shown by a broken line. The cracks 17 may be formed by connecting the plurality of cracks 14 to each other by applying some force to the GaN ingot 20 by a method other than heating. Further, by forming the plurality of modified spots 13 along the virtual surface 15, the plurality of cracks 14 may be connected to each other to form the crack 17.

Here, in the GaN ingot 20, nitrogen gas is generated in a plurality of cracks 14 extending from the plurality of modified spots 13, respectively. Therefore, by heating the GaN ingot 20 and expanding the nitrogen gas, the crack 17 can be formed by utilizing the pressure (internal pressure) of the nitrogen gas. Moreover, since the peripheral region 16 prevents the cracks 14 from propagating to the outside of the virtual surface 15 surrounded by the peripheral region 16 (for example, the side surface 20b of the GaN ingot 20), nitrogen generated in the cracks 14 is prevented. It is possible to prevent the gas from escaping to the outside of the virtual surface 15. That is, the peripheral area 16 is a non-modified area that does not include the modified spot 13, and when the crack 17 is formed on the virtual surface 15 surrounded by the peripheral area 16, the virtual surface 15 surrounded by the peripheral area 16 is formed. It is a region that prevents the plurality of cracks 14 from propagating to the outside. Therefore, the width of the peripheral region 16 can be set to 30 μm or more.

Then, the grinding device grinds (polishs) the portions of the GaN ingot 20 corresponding to the plurality of peripheral regions 16 and the plurality of virtual surfaces 15, respectively, so that a plurality of cracks 17 are formed 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). In this way, the GaN ingot 20 is cut along each of the virtual surfaces 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 laser processing method of the first example includes up to the step of forming the plurality of modified spots 13 along each of the plurality of virtual surfaces 15. Further, among the above steps, the steps up to the step of obtaining the plurality of GaN wafers 30 from the GaN ingot 20 with each of the plurality of cracks 17 as the boundary are 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 so as not to overlap the plurality of modified spots 13a and the plurality of cracks 14a. Then, a plurality of modified spots 13b are formed along each of the plurality of virtual surfaces 15. 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 accurately formed along each of the plurality of virtual surfaces 15, and as a result, the crack 17 can be formed accurately along each of the plurality of virtual surfaces 15. It will be 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 a boundary. ..

Similarly, according to the laser processing apparatus 1 that implements the laser processing method of the first example, it is possible to accurately form the crack 17 along each of the plurality of virtual surfaces 15, and thus a plurality of suitable GaN layers can be formed. The wafer 30 can be acquired.

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 more accurately along the virtual surface 15.

Further, in the laser processing method of the first example, the condensing point C of the pulsed laser light L is moved along the virtual surface 15 to form the modified spots 13a in a plurality of rows and pulsed. By moving the condensing point C of the laser light L along the virtual surface 15 between the rows of the plurality of rows of modified spots 13a, the plurality of rows of modified spots 13b are formed. Thereby, it is possible to reliably prevent the plurality of reformed spots 13b from overlapping the plurality of reformed spots 13a and the plurality of cracks 14a, and to form the plurality of reformed spots 13b along the virtual surface 15 with higher accuracy. You can

Particularly, 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 beam L, gallium is deposited in the cracks 14a extending from the modified spots 13a. Then, the deposition 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 accurately forming the plurality of modified spots 13b along the virtual surface 15.

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 generated in the plurality of cracks 14. Therefore, the crack 17 can be easily formed by utilizing the pressure of the nitrogen gas.

Further, according to the semiconductor member manufacturing method of the first example, the cracks 17 can be accurately formed along each of the virtual surfaces 15 by the steps included in the laser processing method of the first example. Thus, it is possible to obtain a plurality of suitable GaN wafers 30.

In addition, in the semiconductor member manufacturing method of the first example, the plurality of virtual surfaces 15 are set to be aligned in the direction facing the surface 20 a of the GaN ingot 20. This makes it possible to obtain a plurality of GaN wafers 30 from one GaN ingot 20.

Here, an explanation will be given of the experimental results showing that the GaN wafer 30 formed by the laser processing method and the semiconductor member manufacturing method of the first example has smaller irregularities on the separated surface of the GaN wafer 30.

FIG. 14 is an image of a peeled surface of a GaN wafer formed by the laser processing method and the semiconductor member manufacturing method of an example, and FIGS. 15A and 15B show the height of the peeled surface shown in FIG. It is a profile. In this example, laser light L having a wavelength of 532 nm is made incident on the inside of the GaN ingot 20 from the surface 20a of the GaN ingot 20, and one condensing point C arranged in the Y direction is placed on the virtual surface 15 along the X direction. Were relatively moved to form a plurality of modified spots 13 along the virtual surface 15. At this time, the distance between adjacent condensing points C in the Y direction was 10 μm, the pulse pitch of the laser light L was 1 μm, and the pulse energy of the laser light L was 1 μJ. In this case, as shown in (a) and (b) of FIG. 15, irregularities of about 25 μm appeared on the separated surface (surface formed by the crack 17) of the GaN wafer 30.

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 of another example, and FIGS. 17(a) and 17(b) are shown in FIG. It is a height profile of a peeling surface. In this example, laser light L having a wavelength of 532 nm is made to enter the inside of 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 the semiconductor member manufacturing method of the first embodiment. Similarly, the plurality of modified spots 13 were formed along the virtual surface 15. When forming the plurality of modified spots 13a, the distance between the condensing points C adjacent to each other in the Y direction was 6 μm, the pulse pitch of the laser light L was 10 μk, and the pulse energy of the laser light L was 0.33 μJ. When forming the plurality of modified spots 13b, the distance between the condensing points C adjacent to each other in the Y direction was 6 μm, the pulse pitch of the laser light L was 10 μm, and the pulse energy of the laser light L was 0.33 μJ. When forming the plurality of modified spots 13c, the distance between the condensing points C adjacent to each other in the Y direction was 6 μm, the pulse pitch of the laser light L was 5 μm, and the pulse energy of the laser light L was 0.33 μJ. When forming the plurality of modified spots 13d, the distance between the condensing points C adjacent to each other in the Y direction was 6 μm, the pulse pitch of the laser light L was 5 μm, and the pulse energy of the laser light L was 0.33 μJ. In this case, as shown in FIGS. 17A and 17B, unevenness of about 5 μm appeared on the separated 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 irregularities appearing on the separated surface of the GaN wafer 30 are small, that is, the cracks 17 along the virtual surface 15. Was found to be formed with high precision. It should be noted that if the irregularities appearing on the peeled surface of the GaN wafer 30 become small, the amount of grinding for flattening the peeled surface will be small. Therefore, it is advantageous in terms of material utilization efficiency and production efficiency that the irregularities appearing on the separated surface of the GaN wafer 30 become small.

Next, the principle that 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 a virtual surface 15, and the modified spots 13b are virtual so that the modified spots 13b overlap the cracks 14a extending from the modified spots 13a on one side. A plurality of modified spots 13b are formed along the surface 15. In this case, since the laser light L is easily absorbed by the gallium deposited in the plurality of cracks 14a, even if the condensing point C is located on the virtual surface 15, the laser is not applied to the modified spot 13a. The modified spot 13b is easily formed on the incident side of the light L. Then, a plurality of modified spots 13c are formed along the virtual surface 15 so that the modified spots 13c overlap the cracks 14b extending from the modified spots 13b on one side. Also in this case, since the laser light L is easily absorbed by the gallium deposited in the plurality of cracks 14b, even if the condensing point C is located on the virtual surface 15, the laser is not applied to the modified spot 13b. The modified spot 13c is easily formed on the incident side of the light L. As described above, in this example, the plurality of modified spots 13b are formed on the incident side of the laser light L with respect to the plurality of modified spots 13a, and further, the plurality of modified spots 13c are formed into the plurality of modified spots 13b. On the other hand, it tends 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 virtual surface 15 so that the modified spots 13b do not overlap the cracks 14a extending from the modified spots 13a on both sides thereof. , A plurality of modified spots 13b are formed along the virtual surface 15. In this case, although the laser light L is easily absorbed by the gallium deposited in the plurality of cracks 14a, the modified spot 13b does not overlap the crack 14a, so the modified spot 13b is similar to the modified spot 13a. Are formed on the virtual surface 15. Subsequently, a plurality of modified spots 13c are formed along the virtual surface 15 so that the modified spots 13c overlap the

cracks

14a and 14b extending from the modified

spots

13a and 13b on both sides thereof. Further, a plurality of modified spots 13d are formed along the virtual surface 15 so that the modified spots 13d overlap the

cracks

14a and 14b extending from the modified

spots

13a and 13b on both sides thereof. In these cases, since the laser light L is easily absorbed by the gallium deposited on the plurality of

cracks

14a and 14b, even if the condensing point C is located on the virtual surface 15, the modified spots 13a, The modified

spots

13c and 13d are easily formed on the incident side of the laser light L with respect to 13b. As described above, in this example, the modified

spots

13c and 13d are easily formed on the incident side of the laser light L with respect to the modified

spots

13a and 13b.

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

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

20A and 20B are images of cracks formed during the laser processing method and the semiconductor member manufacturing method of an example, and FIG. 20B is a rectangle in FIG. 20A. It is an enlarged image in the frame. In this example, laser light L having a wavelength of 532 nm is made to enter the inside of the GaN ingot 20 from the surface 20a of the GaN ingot 20, and the six condensing points C arranged in the Y direction are arranged on the virtual surface 15 along the X direction. Were relatively moved to form a plurality of modified spots 13 along the virtual surface 15. At this time, the distance between the condensing points C adjacent to each other in the Y direction was 6 μm, the pulse pitch of the laser light L was 1 μm, and the pulse energy of the laser light L was 1.33 μJ. Then, the laser processing was stopped in the middle of the virtual surface 15. In this case, as shown in (a) and (b) of FIG. 20, the crack that propagated from the processed region to the unprocessed region largely deviated from the virtual surface 15 in the unprocessed region.

21(a) and 21(b) are images of cracks formed during the laser processing method and the semiconductor member manufacturing method of another example of the embodiment, and FIG. 21(b) is an image of FIG. It is an enlarged image in a rectangular frame in (a). In this example, laser light L having a wavelength of 532 nm is made to enter the inside of the GaN ingot 20 from the surface 20a of the GaN ingot 20, and the six condensing points C arranged in the Y direction are arranged on the virtual surface 15 along the X direction. Were relatively moved to form a plurality of modified spots 13 along the virtual surface 15. Specifically, first, the processing area 1 and the processing area 2 are set such that the distance between the condensing points C adjacent to each other 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 on the surface. Then, the distance between the condensing points C adjacent to each other 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 such that each row was positioned in the center between the plurality of rows of modified spots 13. Then, the distance between the condensing points C adjacent to each other in the Y direction is 6 μm, the pulse pitch of the laser light L is 5 μm, and the pulse energy of the laser light L is 0.33 μJ. A plurality of rows of reforming spots 13 were formed such that each row was positioned at the center between the rows of reforming spots 13. In this case, as shown in (a) and (b) of FIG. 21, the crack propagated from the processing region 1 to the processing region 2 was not largely deviated from the virtual surface 15 in the processing region 2.

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

Next, in the laser processing method and the semiconductor member manufacturing method of the first example, the experimental results showing that the extension amount of the crack 14 extending from the modified spot 13 to the incident side of the laser light L and the opposite side thereof 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 made incident on the inside of the GaN ingot 20 from the surface 20a of the GaN ingot 20, and one condensing point C is relatively moved on the virtual plane 15 along the X direction. The plurality of modified spots 13 were formed along the imaginary plane 15 by moving the modified spots 13 to. Specifically, the distance between the condensing points C adjacent to each other 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. 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 laser light L incident side 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. 23A is an image in plan view, and FIG. Is an image in side view. In the first embodiment, laser light L having a wavelength of 532 nm is made incident on the inside of the GaN ingot 20 from the surface 20a of the GaN ingot 20, and the six condensing points C arranged in the Y direction are virtual along the X direction. By relatively moving on the surface 15, a plurality of modified spots 13 were formed along the virtual surface 15. Specifically, first, the distance between the condensing points C adjacent to each other 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. The modified spot 13a of No. 1 was formed. Then, 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 the converging points C adjacent in the Y direction is 8 μm, and the pulse pitch of the laser light L is 10 μm. A plurality of modified spots 13b were formed along the virtual surface 15 by setting the pulse energy of the laser light L to 0.3 μJ. Then, with the six converging points C arranged in the Y direction shifted from the previous state by -4 μm in the Y direction, 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 changed. A plurality of modified spots 13 were formed along the virtual surface 15 with the pulse energy of the laser beam L being 5 μm and 0.3 μJ. Subsequently, with the six condensing points C arranged in the Y direction shifted from the previous state by +4 μm in the Y direction, the distance between the converging points C adjacent in the Y direction is 8 μm, and the pulse pitch of the laser light L is 5 μm. A plurality of modified spots 13 were formed along the virtual surface 15 with the pulse energy of the laser light L set to 0.3 μJ. 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 (b) of FIG. 23, the extension amount of the crack 14 extending from the modified spot 13 to the incident side of the laser light L and the opposite side thereof was about 70 μm.

24A and 24B are images of modified spots and cracks formed by the laser processing method and the semiconductor member manufacturing method of the second example, and FIG. 24A is a plan view. 24B is an image in a side view. In the second embodiment, laser light L having a wavelength of 532 nm is made incident on the inside of 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 the semiconductor member manufacturing method of the first example. Similar to the two steps, a plurality of modified spots 13 were formed along the virtual surface 15. When forming the plurality of modified spots 13a, the distance between the condensing points C adjacent to each other in the Y direction was 8 μm, the pulse pitch of the laser light L was 10 μm, and the pulse energy of the laser light L was 0.3 μJ. When forming the plurality of modified spots 13b, the distance between the condensing points C adjacent to each other in the Y direction was 8 μm, the pulse pitch of the laser light L was 10 μm, and the pulse energy of the laser light L was 0.3 μJ. When forming the plurality of modified spots 13c, the distance between the condensing points C adjacent to each other in the Y direction was 8 μm, the pulse pitch of the laser light L was 5 μm, and the pulse energy of the laser light L was 0.3 μJ. When forming the plurality of modified spots 13d, the distance between the condensing points C adjacent to each other in the Y direction was 8 μm, the pulse pitch of the laser light L was 5 μm, and the pulse energy of the laser light L was 0.3 μJ. In this case, as shown in (b) of FIG. 23, the extension amount of the crack 14 extending from the modified spot 13 to the incident side of the laser light L and the opposite side thereof was about 50 μm.

24C and 24D are images of modified spots and cracks formed by the laser processing method and the semiconductor member manufacturing method of the third embodiment, and FIG. 24C is a plan view. An image, (d) of FIG. 24, is an image in a side view. In this embodiment, a plurality of modified spots 13 are further formed along the virtual surface 15 in the state shown in FIG. 23 (that is, the virtual surface 15 on which a plurality of rows of modified spots 13 have already been formed). .. Specifically, first, the distance between adjacent condensing points C 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 reforming spots 13 were formed such that each row was positioned at the center between the rows of reforming spots 13. In this case, as shown in FIG. 24D, 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 thereof was about 60 μm.

From the above experimental results, if the modified spots 13b are formed along the virtual surface 15 so as not to overlap the modified spots 13a and the cracks 14a already formed along the virtual surface 15 (( 1st Example, 2nd Example, and 3rd Example), it turned out that the extension amount of the crack 14 extended from the modification spot 13 to the incident side of the laser beam L and the opposite side is suppressed. When further 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. With a plurality of modified spots 13 (second and third embodiments), the extension amount of the crack 14 extending from the modified spot 13 to the laser light L incident side and the opposite side can be further suppressed. Do you get it.
[Laser Processing Method and Semiconductor Member Manufacturing Method of Second Example]

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 formed of GaN in a disk shape, for example, as shown in FIG. As an example, the GaN wafer 30 has a diameter of 2 inches and the GaN wafer 30 has a thickness of 100 μm. The laser processing method and the 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 μm.

First, the laser processing apparatus 1 described above forms a plurality of modified spots 13 along each of a 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 so as to be aligned in the direction in which the surface 30a extends. In the present embodiment, each of the plurality of virtual surfaces 15 is a surface parallel to the surface 30a and has, for example, a rectangular shape. Each of the plurality of virtual planes 15 is set to be arranged two-dimensionally in a direction parallel to the orientation flat 31 of the GaN wafer 30 and a direction perpendicular to the orientation flat 31. In the GaN wafer 30, a plurality of peripheral regions 16 are set so as to surround each of the plurality of virtual surfaces 15. That is, each of the plurality of 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 the adjacent virtual surfaces 15 in the second example) is 30 μm or more.

The 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. As a result, in the GaN wafer 30, as shown in FIG. 26, a plurality of modified spots 13 (that is, modified

spots

13a, 13b, 13c, 13d) and a plurality of modified spots 13 are provided along each of the plurality of virtual planes 15. 14 (that is, the

cracks

14a, 14b, 14c, 14d) are formed. In FIG. 26, the range in which the plurality of modified spots 13 and the plurality of cracks 14 are formed is indicated by a broken line.

Subsequently, the semiconductor manufacturing apparatus 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 surface 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, and the plurality of cracks 14 extending from the plurality of modified spots 13 on each of the plurality of virtual surfaces 15 are formed. Are connected to each other, a crack 17 (that is, a crack 17 across the virtual surface 15) is formed in each of the plurality of virtual surfaces 15. In FIG. 27, the range in which the plurality of modified spots 13, the plurality of cracks 14, and the crack 17 are formed is indicated by broken lines. A heating device different from the semiconductor manufacturing device may be used. The cracks 17 may be formed by connecting the plurality of cracks 14 to each other by applying some force to the GaN wafer 30 by a method other than heating. Further, by forming the plurality of modified spots 13 along the virtual surface 15, the plurality of cracks 14 may be connected to each other to form the crack 17.

Here, in the GaN wafer 30, nitrogen gas is generated in the cracks 14 extending from the modified spots 13, respectively. Therefore, by heating the GaN ingot 20 and expanding the nitrogen gas, the crack 17 can be formed by utilizing the pressure of the nitrogen gas. Moreover, since the peripheral region 16 prevents the plurality of cracks 14 from propagating to the outside of the virtual surface 15 surrounded by the peripheral region 16 (for example, the adjacent virtual surface 15 and the side surface 30b of the GaN wafer 30), the plurality of cracks is prevented. It is possible to prevent the nitrogen gas generated in 14 from escaping to the outside of the virtual surface 15. That is, the peripheral area 16 is a non-modified area that does not include the modified spot 13, and when the crack 17 is formed on the virtual surface 15 surrounded by the peripheral area 16, the virtual surface 15 surrounded by the peripheral area 16 is formed. It is a region that prevents the plurality of cracks 14 from propagating to the outside. Therefore, the width of the peripheral region 16 can be set to 30 μm or more.

Then, the laser processing device cuts the GaN wafer 30 into each functional element 32, and the grinding device grinds the portions corresponding to each of the plurality of virtual planes 15, as shown in FIG. 28. A plurality of semiconductor devices 40 are obtained from the GaN wafer 30 with each of the plurality of cracks 17 as a boundary (step S6). In this way, the GaN wafer 30 is cut along each of the plurality of virtual planes 15. In this step, the GaN wafer 30 may be cut into each functional element 32 by mechanical processing (for example, blade dicing) other than laser processing.

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

As described above, according to the laser processing method of the second example, as in the laser processing method of the first example, it is possible to accurately form the plurality of modified spots 13 along each of the plurality of virtual surfaces 15. As a result, the crack 17 can be accurately formed along each of the plurality of virtual surfaces 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 a boundary. .. It is also possible to reuse the GaN wafer 30 after cutting out the plurality of semiconductor devices 40.

Similarly, according to the laser processing apparatus 1 that implements the laser processing method of the second example, it is possible to accurately form the crack 17 along each of the virtual surfaces 15, and thus a plurality of suitable semiconductors can be formed. The device 40 can be acquired.

Further, 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 more accurately along the virtual surface 15.

Moreover, in the laser processing method of the second example, the condensing point C of the pulsed laser light L is moved along the virtual plane 15 to form a plurality of rows of modified spots 13a and pulsed. By moving the condensing point C of the laser light L along the virtual surface 15 between the rows of the plurality of rows of modified spots 13a, the plurality of rows of modified spots 13b are formed. Thereby, it is possible to reliably prevent the plurality of reformed spots 13b from overlapping the plurality of reformed spots 13a and the plurality of cracks 14a, and to form the plurality of reformed spots 13b along the virtual surface 15 with higher accuracy. You can

Particularly, 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 is deposited in the cracks 14a extending from the 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 accurately forming the plurality of modified spots 13b along the virtual surface 15.

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 irradiation with the laser light L, nitrogen gas is generated in the plurality of cracks 14. Therefore, the crack 17 can be easily formed by utilizing the pressure of the nitrogen gas.

Further, according to the semiconductor member manufacturing method of the second example, the cracks 17 can be accurately formed along each of the 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 surfaces 15 are set to be aligned in the direction in which the surface 30a of the GaN wafer 30 extends. This makes it possible to obtain a plurality of semiconductor devices 40 from one GaN wafer 30.
[Modification]

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

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 surface 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 over the virtual surface along the virtual surface.

29A and 29B are images (images in side view) of the cracks of the SiC wafer formed by the laser processing method and the semiconductor member manufacturing method of the comparative example, and FIG. 29A is an enlarged image within a rectangular frame in FIG. In this comparative example, laser light having a wavelength of 532 nm is made incident on the inside of the SiC wafer from the surface of the SiC wafer, and the six converging points arranged in the Y direction are relatively moved on the virtual surface along the X direction. By doing so, a plurality of modified spots were formed along the virtual surface. At this time, the distance between the condensing points C adjacent to each other in the Y direction was 2 μm, the pulse pitch of the laser light was 15 μm, and the pulse energy of the laser light was 4 μJ. In this case, as shown in (a) and (b) of FIG. 29, a crack extending in a direction inclined by 4° to 5° with respect to the virtual plane occurred.

30A and 30B are images (images in side view) of the cracks of the SiC wafer formed by the laser processing method and the semiconductor member manufacturing method of the example, and FIG. 30 is an enlarged image in the rectangular frame in FIG. In this example, a laser beam having a wavelength of 532 nm is made to enter the inside of the SiC wafer from the surface of the SiC wafer, and the laser processing method and the semiconductor member manufacturing method according to the first embodiment have the same first and second steps. , A plurality of modified spots were formed along the virtual plane. When forming a plurality of modified spots corresponding to the respective modified

spots

13a, 13b, 13c, 13d, the distance between the condensing points C adjacent in the Y direction is 8 μm, and the pulse pitch of the laser light L is set. Was 15 μm, and the pulse energy of the laser beam L was 4 μJ. In this case, as shown in (a) and (b) of FIG. 30, the generation of cracks extending in the 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 the semiconductor member manufacturing method of the example, and FIGS. 32A and 32B show the height of the peeled surface shown in FIG. It is a 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, it is found that even when the material of the semiconductor object is SiC, according to the laser processing method and the semiconductor member manufacturing method, the cracks extending over the virtual surface are accurately formed along the virtual surface. It was The SiC wafers used in the above-described comparative examples and examples are 4H-SiC wafers having an off angle of 4±0.5°, and the direction in which the focusing point of the laser light is moved is the m-axis direction. Is.

The method of forming the plurality of modified

spots

13a, 13b, 13c, 13d is not limited to the above. The plurality of modified spots 13a may be formed such that the plurality of cracks 14a extending from the plurality of modified spots 13a are connected to each other. Further, the plurality of modified spots 13b may be formed so as not to overlap the plurality of modified spots 13a. Even if the plurality of reforming spots 13b overlap the plurality of cracks 14a extending from the plurality of reforming spots 13a, if the plurality of reforming spots 13b do not overlap the plurality of reforming spots 13a, the plurality of reforming spots 13b do not overlap. 13a and 13b are accurately formed along the virtual surface 15. Further, 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 (dashed-dotted arrows), and a plurality of rows of modified spots are formed. 34, and further, as shown in FIG. 34, a plurality of condensing points arranged in the radial direction with each of the plurality of condensing points positioned between the rows of the modified spots 13 in a plurality of rows. May be relatively rotated (arrows indicated by alternate long and short dash lines) to form a plurality of rows of modified spots 13.

In addition, 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 the plurality of modified spots 13 is performed along the one or more virtual surfaces 15 on the front surface 20a side, and the one or more GaN wafers. After the 30 is cut out, the surface 20a of the GaN ingot 20 may be ground, and again, the plurality of modified spots 13 may be formed along the one or more virtual surfaces 15 on the surface 20a side.

Further, 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 case where the peripheral region 16 is not formed in the laser processing method and the semiconductor member manufacturing method of the first example, after forming the plurality of modified spots 13 along each of the plurality of virtual surfaces 15, for example, the GaN ingot 20 is formed. It is also possible to obtain a plurality of GaN wafers 30 by performing etching on them.

Also, various materials and shapes can be applied to each configuration in the above-described examples without being limited to the above-described materials and shapes. Further, each configuration in the above-described one example or modified example can be arbitrarily applied to each configuration in another example or modified example.

Further, the laser processing device 1 is not limited to the one having the above-mentioned configuration. For example, the laser processing device 1 may not include the spatial light modulator 4.
[Laser Processing Method According to Embodiment and Semiconductor Device Manufacturing Method]

FIG. 35 is a diagram showing a laser processing device. As shown in FIG. 35, the laser processing apparatus 1A is different from the laser processing apparatus 1 shown in FIG. 1 in that the laser processing apparatus 1A further includes a measuring unit 50 and that the laser processing apparatus 1A includes a stage 2A instead of the stage 2. , The laser processing apparatus 1 is different. In the laser processing apparatus 1</b>A, the light source 3, the spatial light modulator 4, and the condenser lens 5 form an irradiation unit 45. That is, the laser processing apparatus 1A includes the stage 2A that supports the GaN wafer 30, the irradiation unit 45 that irradiates the GaN wafer 30 supported by the stage 2A with the laser light L, and the 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.

The stage 2A includes a transmission part 2T that transmits the measurement light IL used for measurement. The measurement unit 50 includes a light source 51 that irradiates the GaN wafer 30 supported by the stage 2A with the measurement light IL, and a photodetector 52 that detects the measurement light IL transmitted through the GaN wafer 30 and the transmission unit 2T. Then, the transmittance of the GaN wafer 30 is measured based on the detection result of the photodetector 52.

In the method according to the present embodiment, first, steps S1 to S3 are carried out in the same manner as the above-mentioned first example. That is, as shown in FIG. 36, by irradiating the laser light L from the surface 30 a of the GaN wafer 30 (in place of the GaN ingot 20) to the inside of the GaN wafer 30, the surface 30 a is opposed to the inside of the GaN wafer 30. A plurality of reforming spots 13 (reforming spots 13a to 13c) and a plurality of deposition regions R containing gallium deposited in the plurality of reforming spots 13 are formed along the virtual surface 15 ( First step). In the first step, of course, the energy of the laser light L on the virtual surface 15 exceeds 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 specified as follows, for example. First, as the pulse energy of the laser light L increases, the deposition region R formed around the modified spot 13 tends to increase. Therefore, when the distance between the condensing points C of the laser light L (for example, in the Y direction) is relatively increased (the modified spot 13 and the deposition region R are relatively coarsely formed), the subsequent laser is used. The pulse energy of the laser light L can be increased from the viewpoint of enlarging the deposition region R by irradiation with light. On the other hand, when the distance between the condensing points C of the laser light L (for example, in the Y direction) is relatively small (the modified spots 13 and the deposition regions R are relatively densely formed), the laser light is used. Even if the pulse energy of is reduced, the deposition region R can be enlarged by irradiation with laser light in a later step. As an example, when the pulse pitch of the laser light L is fixed to 10 μm, when 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 irradiation with laser light in a later step. Further, when the distance between the condensing points C adjacent to each other in the Y direction is 4 μm, the pulse energy of the laser light L is set to about 0.67 μJ, so that the deposition area is formed by the irradiation of the laser light in the subsequent step. R can be expanded. Further, when the distance between the condensing points C adjacent to each other in the Y direction is 2 μm, the pulse energy of the laser light L is set to about 0.33 μJ, so that the deposition region is formed by the irradiation of the laser light in a later step. R can be expanded.

Subsequently, the transmittance of the GaN wafer 30 is measured (fourth step). Then, it is determined whether the transmittance measured in the fourth step is higher than the reference value (fifth step). The reference value of the transmittance of the GaN wafer 30 can be set to 0.5 (50%), for example. Then, as a result of the determination in the fifth step, if the transmittance is higher than the reference value, the formation of the modified spots 13 is considered to be insufficient, and the first step is performed again. On the other hand, as a result of the determination in the fifth step, if the transmittance is equal to or less than the reference value, 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 apparatus. 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 30 a of the GaN wafer 30. Although any method can be used for the epitaxial growth here, the GaN wafer 30 can be heated to, for example, about 1030° C.

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 condensing point C of the laser light L is arranged so as not to overlap the modified spot 13 when viewed from the direction (Z direction) crossing the surface 30 a of the GaN wafer 30. .. Here, each of the plurality of condensing points C is arranged between the modified spot 13a and the modified spot 13b which are adjacent to each other in the Y direction. Further, here, as an example, the condensing point C may be arranged so as not to overlap the crack 14 and the deposition region R in addition to the modified spot 13. Then, the energy on the virtual surface 15 is set to be lower than the processing threshold of the GaN wafer 30. In that state, the laser light L is irradiated to the inside of the GaN wafer 30 from the back surface (the surface of the GaN wafer 30 different from the surface on which the semiconductor layer 70 is formed) 30r opposite to the front surface 30a.

-This process is based on the following findings. That is, first, by irradiating a semiconductor object containing gallium with laser light, along a virtual plane, a plurality of modified spots, and a deposition region containing gallium deposited in the plurality of modified spots, To form. Then, when the laser light is irradiated again in a later step, the energy of the laser light on the virtual plane is changed (while preventing the modified spots formed in advance from overlapping the focused spots of the laser light). Even if it is lowered below the processing threshold value, the deposition region containing gallium formed in advance can be expanded. As a result, when a semiconductor member is cut out by forming a crack across a virtual surface, it is possible to reduce the unevenness of the cut surface.

Here, the laser processing apparatus 1 moves the focal point C of the pulsed laser light L along the virtual surface 15. Further, the pulsed 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 surface 15 along the X direction. As an example, the distance between the condensing points C adjacent to each other in the Y direction is 1 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. According to this irradiation condition, although the modified spot is not formed at the position corresponding to the condensing point C of the laser light L, the deposition region R is enlarged. The subsequent steps are the same as those in the above first example. As a result, 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 the irradiation of the laser light L before the formation of the semiconductor layer 70 for the semiconductor device by the epitaxial growth. .. Therefore, the semiconductor layer 70 cannot be damaged when the modified spot 13 is formed. Therefore, by advancing the crack extending from the modified spot 13 and peeling the GaN wafer 30, a suitable semiconductor device in which damage is suppressed can be obtained.

In the method according to the present embodiment, the semiconductor layer 70 in the GaN wafer 30 is formed after the second step 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 of forming a crack across the virtual surface 15 by irradiating the inside of the GaN wafer 30 with the laser light L from the back surface 30r different from the surface is provided. As described above, the irradiation of the laser beam L may form a crack along the virtual surface 15 that is the starting point of peeling. Even in this case, since the modified spot 13 is formed prior to the formation of the semiconductor layer 70, the semiconductor layer 70 is compared with the case where all the laser processing is performed after the formation of the semiconductor layer 70. Damage is suppressed.

Further, in the method according to the present embodiment, in the first step, the laser light L is irradiated from the surface 30a to the inside of the GaN wafer, so that the plurality of modified spots 13 and the plurality of modified spots 13 are formed. Forming a plurality of deposition regions R containing deposited gallium, and in the third step, irradiating the inside of the GaN wafer 30 with laser light L such that the energy on the virtual surface 15 falls below the processing threshold of the GaN wafer 30. Thereby, the deposition region R is enlarged and a crack is formed across the virtual surface 15.

As described above, first, by irradiating the inside of the GaN wafer 30 containing gallium with the laser light L, the plurality of modified spots 13 are formed along the virtual surface 15 facing the surface 30a that is the incident surface of the laser light L. , And a plurality of deposition regions R containing the deposited gallium. Then, in a later step, the laser light L is introduced inside the GaN wafer 30 so that the converging point C does not overlap the modified spot 13 and the energy on the virtual surface 15 falls below the processing threshold of the GaN wafer 30. Is irradiated to expand the precipitation region R and form a crack across the virtual surface 15. As a result, as described above, it becomes possible to obtain a suitable semiconductor device in which unevenness is reduced by peeling with the crack extending over the virtual surface 15 as a boundary.

The above embodiments describe one example of the laser processing method and the semiconductor device manufacturing method according to the present disclosure. Therefore, the laser processing method and the semiconductor device manufacturing method according to the present disclosure are not limited to the above embodiment, 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 respectively extending from the plurality of modified spots 13 are propagated to form a crack across the virtual surface 15. You may. In this case, the formation of the semiconductor layer 70 and the formation of the crack over the virtual surface 15 can be performed at the same time.

At this time, in the first step, the GaN wafer 30 may be provided with the peripheral region 16 that prevents the development of the plurality of cracks 14 extending from the plurality of modified spots 13, respectively. In this case, during the epitaxial growth in the second step, unintentional formation of cracks across the imaginary plane 15 and peeling are suppressed.

In addition, 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 in which the modified spots 13 are sufficiently formed by the above-described example has been described. In this case, damage to the semiconductor layer 70 could be suppressed by lowering the energy of laser processing after forming the semiconductor layer 70 or by refraining from irradiation with laser light.

On the other hand, in the first step, the semiconductor layer 70 is formed in the second step while maintaining the transmittance higher than the reference value, and then in the third step, with the energy exceeding the processing threshold of the GaN wafer 30. Laser processing may be performed. In this case, since the amount of the modified spots 13 formed in advance is small, it is possible to suppress the warp of the semiconductor layer 70 during the 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 laser processing is performed after the formation of the semiconductor layer 70. Moreover, in this case, the measurement and determination of the transmittance of the GaN wafer 30 are not essential.

For example, the elements of the first example, the second example, and the respective modified examples 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. In the first step, the condensing point C of the pulsed laser light L is moved along the virtual surface 15 to form a plurality of modified spots 13 as a plurality of modified spots 13. In the third step, the condensing point C of the pulsed laser light L can be moved along the virtual surface 15 between the rows of the reforming spots 13 in a plurality of rows.

Provided are a laser processing method capable of obtaining a suitable semiconductor device and a semiconductor device manufacturing method.

Reference numeral 13 is a modified spot, 15 is a virtual surface, 30 is a GaN wafer (semiconductor wafer), 30a is a surface, 70 is a semiconductor layer, L is a laser beam, R is a deposition region.

Claims

A laser processing method for cutting the semiconductor wafer along a virtual surface facing the surface of the semiconductor wafer inside the semiconductor wafer,
A first step of forming a plurality of modified spots along the virtual surface inside the semiconductor wafer by irradiating the inside of the semiconductor wafer with laser light from the surface,
A second step of forming a semiconductor layer for a semiconductor device on the semiconductor wafer by epitaxial growth after the first step;
A laser processing method comprising:
After the second step, the inside of the semiconductor wafer is viewed from a surface different from the surface on which the semiconductor layer is formed in the semiconductor wafer so that a converging point does not overlap the modified spot when viewed from a direction intersecting the surface. A third step of forming a crack across the virtual surface by irradiating a laser beam on
The laser processing method according to claim 1.
The semiconductor wafer contains gallium,
In the first step, by irradiating the inside of the semiconductor wafer with laser light from the surface, the plurality of modified spots and a plurality of deposition regions containing gallium deposited at the plurality of modified spots. To form
In the third step, by irradiating the inside of the semiconductor wafer with laser light so that the energy on the virtual surface falls below the processing threshold value of the semiconductor wafer, the deposition region is expanded, and cracks extend across the virtual surface. To form,
The laser processing method according to claim 2.
In the second step, by heating the semiconductor wafer for the epitaxial growth, a plurality of cracks respectively extending from the plurality of modified spots are propagated to form a crack across the virtual surface,
The laser processing method according to claim 1.
In the first step, the semiconductor wafer is provided with peripheral regions that prevent the development of a plurality of cracks extending from the plurality of modified spots, respectively.
The laser processing method according to any one of claims 1 to 4.
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 or not the transmittance measured in the fourth step is higher than a reference value between the fourth step and the second step,
Further equipped with,
As a result of the determination in the fifth step, when 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 5.
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 6.
In the first step, a plurality of rows of modified spots are formed as the plurality of modified spots by moving the focal point of the pulsed laser light along the virtual surface,
In the third step, the condensing point of the pulsed laser light is moved along the virtual plane between the rows of the reforming spots of the plurality of rows.
The laser processing method according to claim 2 or 3.
The semiconductor wafer includes gallium nitride,
The laser processing method according to any one of claims 1 to 8.
Carrying out the laser processing method according to any one of claims 1 to 9;
A step of obtaining a plurality of semiconductor devices from the semiconductor wafer with a crack across the virtual plane as a boundary;
A semiconductor device manufacturing method comprising:
A plurality of the virtual surfaces are set so as to be arranged in a direction along the surface,
The semiconductor device manufacturing method according to claim 10.