JP7283886B2 - Slicing method and slicing apparatus - Google Patents

Description

The present invention relates to a slicing method and a slicing apparatus.

For example, as one method of manufacturing a substrate (wafer) from hard and brittle materials such as silicon (Si), gallium nitride (GaN), silicon carbide (SiC), sapphire, and diamond, a laser is used to modify the interior of the hard and brittle materials. There is a method of forming a modified layer and separating into wafers using the modified layer as a boundary.

For example, in Patent Document 1, in the process of slicing a silicon wafer, a condensing point of a laser beam is aligned with the inside of a workpiece with a condenser lens, and the workpiece is relatively scanned with the laser beam to form a planar shape. is formed, and expansion/contraction due to heat generated inside the workpiece is used to separate a part of the workpiece as a substrate with the machining area as a boundary.

Japanese Patent Application Laid-Open No. 2011-60860

However, in the conventional method described above, if a hard and brittle material is used as the workpiece, chipping may occur in the vicinity of the portion where the wedge-shaped press-fitting material is press-fitted, or a moment may act in the direction in which the wafer warps. The wafer itself may crack.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a slicing method and a slicing apparatus capable of suppressing problems that occur when a modified layer is formed inside the workpiece and then the workpiece is separated using the modified layer as a boundary.

In a slicing method according to an aspect of the present invention, a laser beam emitted from a laser oscillator in the Z direction is scanned in the X direction and the Y direction while condensing the inside of the wafer to form a plurality of modified portions inside the wafer. a modified layer forming step of forming modified layers continuous in the X direction and the Y direction; and heating the modified layer with a heat source to a temperature lower than the melting point of the wafer and equal to or higher than the melting point of the modified layer. a modified layer melting step of melting the modified layer to form a liquid layer; and a separating step of separating the wafer with the liquid layer as a boundary, wherein the modified layer is formed from the plurality of Each of the modified portions has an uneven shape due to variations in length and position in the Z direction, and the thickness in the Z direction of each of the modified portions constituting the modified layer is In the unmodified layer of the wafer, the height difference between the highest position and the lowest position in the Z direction of the uneven shape formed corresponding to the difference in length and position of the modified portion in the Z direction is larger.

A slicing apparatus according to an aspect of the present invention emits a laser beam in the Z direction and scans in the X direction and the Y direction while concentrating the laser beam inside the wafer to form a plurality of modified portions inside the wafer in the X direction. and a laser oscillator for forming a modified layer continuous in the Y direction; a heat source for forming a liquid layer; and a separating section for separating the wafer with the liquid layer as a boundary, wherein the modified layer has a plurality of modified sections each having a different length in the Z direction. The thickness in the Z direction of each of the modified portions constituting the modified layer has an uneven shape due to variations in thickness and position, and the thickness in the Z direction is the same as that of the modified portion in the unmodified layer of the wafer. It is larger than the height difference between the highest position and the lowest position in the Z direction of the uneven shape formed corresponding to the difference in length and position in the Z direction.

ADVANTAGE OF THE INVENTION According to this invention, after forming a modified layer in the inside of a to-be-processed material, the trouble which arises when separating a to-be-processed material using a modified layer as a boundary can be suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS The schematic diagram which shows an example of the laser processing apparatus which concerns on embodiment of this invention. Schematic diagram showing an example of the moving direction of the workpiece during the modified layer forming operation according to the embodiment of the present invention. Schematic diagram showing an example of the moving direction of the workpiece during the modified layer forming operation according to the embodiment of the present invention. FIG. 4 is a diagram showing an example of laser irradiation pulse intervals according to an embodiment of the present invention; Schematic diagram showing a cross section of a work material during a modified layer forming operation according to an embodiment of the present invention. Schematic diagram showing a cross section of a work material during a modified layer forming operation according to an embodiment of the present invention. Schematic diagram showing a cross section of a work material during a modified layer forming operation according to an embodiment of the present invention. Schematic diagram showing a cross section of a workpiece after formation of a modified layer according to an embodiment of the present invention. Schematic diagram showing a cross section of a workpiece after formation of a modified layer according to an embodiment of the present invention. Schematic diagram of a separation device according to an embodiment of the present invention Schematic diagram showing a cross section of a workpiece during the workpiece separation operation according to the embodiment of the present invention. Schematic diagram showing a cross section of a workpiece during the workpiece separation operation according to the embodiment of the present invention. Schematic diagram showing an example of the thickness of the modified layer according to the embodiment of the present invention Schematic diagram showing a cross section of a work material on which a plurality of modified layers are formed according to an embodiment of the present invention. 1 is a perspective view showing a workpiece having a modified layer formed thereon according to an embodiment of the present invention; FIG. FIG. 2 is a schematic diagram showing a state in which the upper and lower parts of the workpiece according to the embodiment of the present invention are rotated horizontally, as seen from directly above; Schematic diagram showing a state before rotation of an end face in an XZ plane of a workpiece according to an embodiment of the present invention. Schematic diagram showing a state after the end face shown in FIG. 10B is rotated Schematic diagram showing a state in which the upper and lower parts of the workpiece according to the embodiment of the present invention are tilted in the Z direction. Schematic diagram showing a state before the end surface of the workpiece in the YZ plane is inclined according to the embodiment of the present invention. The schematic diagram which shows the state after the end surface shown in FIG. 11B inclines.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, in each figure, the same code|symbol is attached|subjected about a common component, and description is abbreviate|omitted suitably about those components.

A configuration of a laser processing apparatus (modified layer forming apparatus) 100 according to an embodiment of the present invention will be described. FIG. 1 is a schematic diagram of a slicing apparatus 100 according to this embodiment.

A laser processing apparatus 100 has a fixed table 2 , a driving stage 3 , a laser oscillator 4 , a mirror 6 and a lens 7 .

The workpiece 1 is made of, for example, gallium nitride (an example of a hard brittle material, hereinafter also referred to as GaN), and is a member to be processed in which a modified layer 8 to be described later is formed. The work material 1 preferably has a diameter of 2 inches and a thickness of 400 μm, for example, but the diameter and thickness are not limited to the above values, and an ingot material thicker than 400 μm may be used. Ingot material with a diameter greater than 2 inches may also be used.

The fixed table 2 fixes the workpiece 1 by vacuum suction, for example. As the fixed table 2, a table is used which does not cause displacement of the workpiece 1 due to driving of the driving stage 3, which will be described later.

The drive stage 3 can be driven in the X-axis, Y-axis, and Z-axis directions, and can rotate in the θ direction. Further, the drive stage 3 can control the relative position of the laser beam 5 with respect to the workpiece 1 .

A laser oscillator 4 emits linearly polarized laser light 5 having a diameter of about 4 mm, for example, to the workpiece 1 . For example, the laser light 5 has a wavelength with a transmittance of 50% or more (e.g., a wavelength of 532 nm), a pulse width of 0.2 picoseconds or more and 100 picoseconds or less (e.g., 15 picoseconds), and a maximum It is a picosecond laser with an output of 50W. Also, the maximum repetition frequency of the laser light 5 is 1 MHz.

In addition, the laser oscillator 4 can control ON/OFF of the laser beam 5 by exchanging a control signal (double arrow of broken line shown in FIG. 1) with the drive stage 3 .

For the transmittance measurement, for example, a spectrophotometer with an integrating sphere (V7100 manufactured by JASCO Corporation; not shown) is used. The transmittance is the ratio of the amount of light transmitted through the workpiece 1 (the amount of light received by the photometer) to the total amount of light emitted from the laser oscillator 4 .

The mirror 6 can reflect 90% or more of the laser beam 5 emitted from the laser oscillator 4 and send it to the lens 7 . As the mirror 6, for example, a dielectric multilayer mirror that reflects the laser light 5 with a wavelength of 532 nm with high reflectance can be used.

The lens 7 is a lens capable of correcting the aberration that occurs when the laser beam 5 is condensed (when the laser beam 5 passes through the workpiece 1) to an optimum amount of aberration according to the depth of machining. .

A focal point A (tip of the laser beam 5a) of the laser beam 5a transmitted through the lens 7 is located inside the workpiece 1 at a distance B from the surface of the workpiece 1 (upper surface in the figure). adjusted.

As the lens 7, for example, a lens with an aberration correction ring for a microscope that transmits the laser light 5 with a wavelength of 532 nm, a numerical aperture (NA) of 0.7, and a focal length of 4 mm is used. be able to.

At least the surface of the lens 7 on which the laser beam 5 is incident is mirror-finished so that the laser beam 5 has a transmittance of at least 50% or more with respect to the workpiece 1 .

The modified layer 8 is formed of modified components of gallium nitride in the vicinity of the focal point A, and is mainly composed of gallium (Ga), gallium dimers, and Ga _x N _y clusters generated by decomposition of GaN. It is formed. In forming the modified layer 8, the thickness of the modified layer 8 is adjusted to 20 μm or less. The layer 8 has an uneven shape.

Next, operations of the laser processing apparatus 100 shown in FIG. 1 will be described with reference to FIGS. 2A, 2B, 3A, 3B, and 3C. 2A, 2B, 3A, 3B, and 3C are schematic diagrams for explaining the modified layer forming operation by the laser processing apparatus 100. FIG.

Since the laser beam 5a has a transmittance of 50% or more with respect to the workpiece 1, as described above, the laser beam 5a is condensed in the vicinity of the condensing point A with small attenuation. Here, as an example, the distance B between the focal point A and the surface of the workpiece 1 is set to 1/2 of the thickness of the workpiece 1, 400 μm, ie, 200 μm.

Since the aberration correction ring of the lens 7 is adjusted according to the thickness of the workpiece 1, the laser beam 5a is condensed at the focal point A most. As described above, since the laser beam 5 is a picosecond laser, multiphoton absorption processing mainly causes the reaction represented by the following formula (1) at the condensing point A to form the modified layer 8 .
2GaN→2Ga+N ₂ (1)

According to the material analysis results, it is known that Ga is mainly generated in the modified layer 8, and Ga dimers and Ga _x N _y clusters are formed in addition to Ga. Ga is called a liquid metal with a melting point Tm of 29.8°C.

A workpiece 1 fixed to a fixed table 2 is driven by a drive stage 3 to move relative to a laser beam 5a. Thereby, a planar modified layer 8 is formed.

FIGS. 2A and 2B each show an example of the moving direction of the workpiece 1 (which may also be called the scanning direction of the laser beam 5a) in the modified layer forming operation. Arrows E1 and E2 indicate scanning directions while irradiating laser pulses, and are actually as shown in FIG. 2C.

As indicated by each arrow E1 in FIG. 2A, the workpiece 1 is alternately moved in a predetermined direction and in the opposite direction in the Y-axis direction while being shifted by the line spacing D1 in the X-axis direction. You may form the modified layer 8 by repeating.

Alternatively, as shown by arrows E2 in FIG. 2B, the material to be processed 1 is moved in the same direction in the Y-axis direction while being shifted by the line spacing D1 in the X-axis direction. 8 may be formed.

A laser irradiation pulse interval D2 in the Y-axis direction indicates an interval between adjacent laser pulses in the scanning direction shown in FIG. For example, the laser irradiation pulse interval D2 is a value calculated by the following formula (2).
D2=V/F (2)

For example, when the repetition frequency is 1000 kHz and the scanning speed is 1000 mm/s, the modified layer 8 is formed near the condensing point A every 1 μm. Both the line interval D1 and the laser irradiation pulse interval D2 are preferably equal to or less than the focused spot diameter of the laser beam 5 (for example, 1 μm or less). is not limited to

3A to 3C each show a cross section of the workpiece 1 during the modified layer forming operation.

FIG. 3A shows the formation state of the modified layer 8 at the end of the workpiece 1. FIG. 9x indicates the energy density profile in the X direction and 9z indicates the energy density profile in the Z (depth) direction.

In both the X direction and the Z direction, a phenomenon called multiphoton absorption occurs due to the sudden increase in energy density in the vicinity of the focal point of the laser beam 5a. Therefore, the laser beam 5a is transmitted through areas other than the condensing point, whereas the laser beam is absorbed only at the condensing point where the energy density is high. be. The modified portion 8a is formed linearly by scanning the laser beam 5a in the Y-axis direction.

After forming the modified portion 8a shown in FIG. 3A, as shown in FIG. 3B, by scanning the laser beam 5a a plurality of times in the Y-axis direction at positions shifted by the line interval D1 in the X-axis direction, continuous A reformed portion 8b is formed. Finally, as shown in FIG. 3C, a planar modified layer 8 is formed over the entire surface of the workpiece 1 .

The modified layer 8 formed in this manner is affected by the driving accuracy of the driving stage 3 and the surface accuracy of the fixed table 2 (workpiece 1). shape.

As an example in FIG. 3C, the modified layer 8 is illustrated as a shape in which elliptical modified portions 8a and 8b are connected. It becomes flatter than the exit side of the laser beam 5a. This is because the shape of the incident side of the laser beam 5a is determined by the position of the focal point with little vertical movement, while on the outgoing side of the laser beam 5a, the leakage light not used for processing at the focal point is the processing threshold value. This is because it is difficult to define the modification range because the modification progresses in a range exceeding .

4A and 4B are schematic diagrams showing cross sections of the workpiece 1 on which the modified layer 8 is formed. FIG. 4A shows a cross section in a sub-scanning direction (for example, X-axis direction) perpendicular to the laser scanning direction (which may also be called a main scanning direction; for example, Y-axis direction). FIG. 4B shows a cross section in the Y-axis direction parallel to the laser scanning direction.

Since the modified layer 8 is formed by connecting linear modified portions 8a and 8b (see FIGS. 3A and 3B), as shown in FIG. 4A, in the X-axis direction perpendicular to the laser scanning direction, Z Regardless of the presence or absence and degree of variation in direction, a shape with large irregularities can be obtained. In addition, as shown in FIG. 4B, in the Y-axis direction parallel to the laser scanning direction, a shape with small unevenness is obtained, which is dominated by the accuracy of the drive stage 3 and the surface accuracy of the fixed table 2 .

Next, a separating apparatus 200 (an example of the slicing apparatus of the present invention) for separating the workpiece 1 on which the modified layer 8 is formed will be described with reference to FIG. FIG. 5 is a schematic diagram of the separation device 200 according to this embodiment.

The separation device 200 has a separation jig 11 (an example of a separation section) and a heating device 12 (an example of a heating section).

The adhesive sheet 10 has adhesive strength on both sides. This adhesive strength is lost when heated above 120° C. (thermal peeling temperature To). As the adhesive sheet 10, for example, a dicing tape can be used.

The separation jig 11 can move horizontally in the X-axis direction, the Y-axis direction, and the Z-axis direction, and can rotate in the θ direction (see FIG. 1). Moreover, the separation jig 11 has a temperature measurement function, and can feed back the measured temperature to the heating device 12, which will be described later.

The heating device 12 is a contact-type heat source (such as a hot plate) that heats the workpiece 1 . The heating device 12 controls the heating temperature based on the temperature measured by the separation jig 11 so as to be equal to or higher than the melting point Tn of the modified layer 8 and lower than the thermal peeling temperature To of the adhesive sheet 10 . Since the main component of the modified layer 8 is gallium (Ga), the melting point Tn of the modified layer 8 can be regarded as the melting point Tm of Ga.

Next, the operation of the separation device shown in FIG. 5 will be described with reference to FIGS. 6A and 6B. 6A and 6B are schematic diagrams for explaining the separation operation of the workpiece by the separation device.

When the modified layer 8 is heated to the melting point Tn or higher by the heating device 12, the modified layer 8 melts. At this time, using the separation jig 11, a load is applied in a direction substantially parallel to the XY plane on which the modified layer 8 is formed, and the upper wafer (hereinafter referred to as the upper wafer) of the workpiece 1 with the modified layer 8 as a boundary , simply referred to as the upper portion) 1a and the lower wafer (hereinafter simply referred to as the lower portion) 1b of the workpiece 1 are shifted in a direction substantially parallel to the XY plane. As a result, the workpiece 1 is separated into an upper portion 1a and a lower portion 1b.

Moreover, the adhesive force of the adhesive sheet 10 is lost by being heated to the thermal peeling temperature To or higher by the heating device 12 . Thereby, the upper part 1 a and the lower part 1 b after separation can be separated from the separation jig 11 .

FIG. 6A shows the case where the upper portion 1a and the lower portion 1b are shifted in the C1 direction (X-axis direction perpendicular to the laser scanning direction). As described above, the modified layer 8 is melted by the heating of the heating device 12, but the unmodified portion (which may be referred to as the GaN portion) around the modified layer 8 has a direction perpendicular to the C1 direction ( Z direction) remains uneven. Therefore, as shown in FIG. 6A, when the upper portion 1a and the lower portion 1b are shifted in the C1 direction, the uneven portion of the upper portion 1a and the uneven portion of the lower portion 1b interfere with each other. Therefore, the upper portion 1a and the lower portion 1b cannot be sufficiently displaced, and the workpiece 1 cannot be separated into the upper portion 1a and the lower portion 1a.

On the other hand, FIG. 6B shows the case where the upper portion 1a and the lower portion 1b are shifted in the C2 direction (Y-axis direction parallel to the laser scanning direction). There are few uneven portions in the laser scanning direction. Therefore, as shown in FIG. 6B, when the upper portion 1a and the lower portion 1b are shifted in the C2 direction, interference between the uneven portions of the upper portion 1a and the uneven portions of the lower portion 1b is less likely to occur. Thus, the workpiece 1 can be separated into an upper portion 1a and a lower portion 1b.

Further, as shown in FIG. 7, Rza is the surface roughness (length in the Z direction) of the unmodified layer of the upper portion 1a, and Rzb is the surface roughness (length in the Z direction) of the unmodified layer of the lower portion 1b. , where F is the thickness (length in the Z direction) of the modified layer 8, the modified layer 8 is formed so as to satisfy F>Rza and F>Rzb. Furthermore, it is preferable to form the modified layer 8 having a thickness F that is 10% or more larger than the surface roughnesses Rza and Rzb. As a result, it is possible to reduce the influence of the interference due to the uneven portions described above, and to realize more stable separation.

For example, when the thickness F is approximately 10 μm and the surface roughnesses Rza and Rzb are each approximately 20 μm, it becomes difficult to separate the upper portion 1a and the lower portion 1b. Therefore, in that case, it is preferable to form the modified layer 8 so that the thickness F is larger than 20 μm. In order to obtain such a thickness F, it is necessary to widen the region where the energy density exceeds the processing threshold in the vicinity of the focal point. Therefore, it is sufficient to increase the power of the laser light 5a or use a lens with a slightly smaller NA (numerical aperture).

Next, the inclination at the time of separation will be explained.

FIG. 9 shows a perspective view of the workpiece 1 on which the modified layer is formed. In the modified layer thickness F, the thickness of the portion where adjacent laser scans are connected on the XZ plane is Gx, and the thickness of the portion where adjacent laser scans are connected on the YZ plane is Gy. The size of the work piece 1 in the X direction is W1, and the size of the work piece 1 in the Y direction is W2.

FIG. 10A is a schematic diagram showing a state in which the upper portion 1a and the lower portion 1b of the workpiece 1 are rotated in the horizontal direction, viewed from directly above. FIG. 10B is a schematic diagram showing the state before the end face of the workpiece 1 on the XZ plane rotates. FIG. 10C is a schematic diagram showing a state after the end surface shown in FIG. 10B has been rotated.

As shown in FIG. 10C, the displacement of the lower portion 1b with respect to the upper portion 1a by a distance H causes the upper portion 1a and the lower portion 1b to rotate by an angle θ1 as shown in FIG. 10A. As a result, a collision point 15 shown in FIG. 10C occurs, and no further rotation is possible. The angle θ1 can be expressed by Equation (3) below.
θ1=tan ⁻¹ (H/W2)≈H/W2 [rad] (3)

FIG. 11A is a schematic diagram showing a state in which the upper portion 1a and the lower portion 1b are tilted in the Z direction. FIG. 11B is a schematic diagram showing a state before the end surface of the workpiece 1 on the YZ plane is inclined. FIG. 11C is a schematic diagram showing a state after the end surface shown in FIG. 11B is tilted.

As shown in FIG. 11A, the lower portion 1b is inclined with respect to the upper portion 1a by an angle .theta.2 shown in FIG. 11C. The angle θ2 can be expressed by Equation (4) below.
θ2=tan ⁻¹ (Gy/W2)≈Gy/W2 [rad] (4)

For example, when thickness Gx=Gy=5 μm, H=10 μm, W1=W2=50 mm, θ1=H/W2=10/(50×1000)=0.2 mrad
θ2=Gy/W2=5/(50×1000)=0.1 mrad
becomes.

10B and 10C, or between the state shown in FIG. 11B and the state shown in FIG. 11C, the relative positions of the upper portion 1a and the lower portion 1b Modifications are possible and the wafers can be separated. Therefore, this state can be defined as substantially parallel.

In the above description, the case where there is one modified layer 8 is described as an example, but there may be a plurality of modified layers 8 . This case will be described below with reference to FIG. FIG. 8 is a schematic diagram showing a cross section of the workpiece 1 on which a plurality of modified layers 8 are formed.

In FIG. 8, the pressing portion 13 can be adjusted to any height of the wafers 1c, 1d, 1e, 1f, and 1g after slicing the workpiece 1, and has a strength that can withstand the separation load in the C direction. .

FIG. 8 shows, as an example, the case where the holding portion 13 is adjusted to the height of the wafer 1d in order to separate the wafer 1c. When the load is applied in the C direction, by suppressing the displacement of the wafers 1d to 1g below the wafer 1, the load in the C direction acts on the separation of the modified layer between the wafer 1c and the wafer 1d. Therefore, only the wafer 1c can be separated.

After separating the wafer 1c, the surface of the wafer 1d is polished. After that, the remaining work piece 1 is fixed by the adhesive sheet 10 again, and the position of the pressing portion 13 is changed to the height of the wafer 1e. Thereby, the wafer 1d can be separated.

By repeating the above operation for the wafers 1e to 1g, the wafers 1e to 1g can be separated. The separated wafers 1c to 1g are polished in a post-process to remove the modified layer 8. FIG. As a result, it can be used as a GaN wafer.

As described above, according to the present embodiment, the modified layer 8 of the material to be processed 1 formed by condensing the laser beam 5a is heated to a temperature lower than the melting point of the material to be processed 1 and equal to or higher than the melting point of the modified layer 8. By heating at , the modified layer 8 is melted, and the workpiece 1 is separated with the melted modified layer 8 as a boundary.

As a result, in the present embodiment, after the modified layer is formed inside the work material, problems (for example, chipping, cracking, cracking, etc.) that occur when the work material is separated with the modified layer as a boundary are eliminated. can be suppressed. Therefore, the yield at the time of separation can be improved. In addition, since the polishing amount can be reduced in the post-process, reduction of material loss can be expected.

The present invention is not limited to the description of the above embodiments, and various modifications are possible without departing from the spirit of the present invention. Each modification will be described below.

[Modification 1]
Although linear scanning in the Y-axis direction has been described as an example in the embodiments, the present invention is not limited to this. For example, linear scanning in the X-axis direction, rotational scanning around the .theta.-axis, arc scanning in which the workpiece 1 is placed at a position eccentric from the rotation center of the .theta.-axis, or the like may be used. When X-axis scanning is used, the work piece 1 can be separated in the same manner as in the above-described embodiment. Alternatively, it is necessary to apply a separation load in the arc direction.

[Modification 2]
In the embodiment, the case where a contact heat source is used as the heating device 12 is described as an example, but the heating device 12 may be a non-contact heat source. For example, as a non-contact heat source, a light source that emits light that has a transmittance of 80% or more with respect to the material to be processed 1 and that the modified layer 8 exhibits an absorption of 50% or more (for example, IR heater, halogen lamps, etc.) may be used. Also in this case, as in the embodiment, it is possible to separate Ga deposited in the reformed portion while heating.

[Modification 3]
In the embodiment, the case where the heating temperature of the heating device 12 is equal to or higher than the melting point Tn of the modified layer 8 and lower than the thermal peeling temperature To of the adhesive sheet 10 has been described as an example, but the present invention is not limited to this. For example, when the adhesive sheet 10 is not used (for example, when fixed on a support substrate and not peeled off, or when fixed by vacuum adsorption, etc.), the heating temperature is set to the melting point Tn or higher of the modified layer 8, and , may be set below the melting point of the workpiece 1 (GaN substrate).

[Modification 4]
In the embodiment, a case where a material having a diameter of 2 inches, a thickness of 400 μm, and a material made of gallium nitride is used as the workpiece 1 has been described as an example. , but not limited to. The material of the workpiece 1 is, for example, a silicon substrate, a sapphire substrate, a substrate obtained by epitaxially growing a GaN layer on a sapphire substrate, a gallium arsenide (GaAs) substrate, an indium phosphide (InP) substrate, or an aluminum gallium nitride (AlGaN). A /GaN substrate, a SiC substrate, a substrate obtained by epitaxially growing a GaN layer on a SiC substrate, diamond, or the like may be used. That is, any material can be used as long as it allows laser light to pass therethrough and can form a modified layer. However, a material with a low melting point (for example, GaN) is suitable for the modified layer.

[Modification 5]
In the embodiment, the case where the wavelength of the laser light 5 emitted from the laser oscillator 4 is 532 nm has been described as an example, but the wavelength of the laser light 5 is not limited to this. Any wavelength can be used as long as the wavelength has a transmittance. However, shorter wavelengths are preferable because the dimensions in the thickness direction and horizontal direction of the condensing point A inside the workpiece 1 are smaller, and workability is improved.

[Modification 6]
In the embodiment, the pulse width of the laser light 5 is 0.2 picoseconds or more and 100 picoseconds or less, and the maximum repetition frequency of the laser light 5 is 1 MHz. not. For example, the pulse width of the laser light 5 may be in the range of 1 femtosecond (fs) or more and 1 nanosecond (ns) or less, as long as it enables internal processing by multiphoton absorption. The repetition frequency of the laser beam 5 should be selected from the range of 10 MHz or less in which the laser oscillator 4 can oscillate, from the relationship between the workability resulting from the interaction between the workpiece 1 and the laser beam 5 and the productivity. good.

[Modification 7]
In the embodiment, the case where the numerical aperture of the lens 7 is 0.7 has been described as an example, but the numerical aperture is not limited to this, and may be 0.4 or more and 0.95 or less. However, in order to reduce the diameter of the condensing point A, it is preferable that the numerical aperture of the lens 7 is large. As the lens 7, it is desirable to use a lens with an aberration correction function because the energy density of the condensing point A can be increased. good too.

[Modification 8]
Further, the modified layer forming operation and the work material separation operation described in the embodiment are performed by simultaneously irradiating a plurality of portions of the work material 1 with the laser light 5 using, for example, a mirror, a diffractive optical element, or a phase modulation element. , can also be applied to machining the workpiece 1. In that case, the processing time can be shortened, so the productivity is further improved.

INDUSTRIAL APPLICABILITY The present invention can be applied to general techniques for forming a modified layer inside a hard and brittle material using a laser and separating the material into wafers with the modified layer as a boundary.

REFERENCE SIGNS LIST 1 workpiece 1a upper wafer 1b lower wafer of workpiece 1 1c, 1d, 1e, 1f, 1g wafer 2 fixed table 3 drive stage 4 laser oscillator 5, 5a laser light 6 mirror 7 lens 8 modification Quality layer 8a, 8b Modification unit 10 Adhesive sheet 11 Separation jig 12 Heating device 13 Pressing unit 15, 16 Collision point 100 Laser processing device 200 Separation device

Claims (5)

A laser beam emitted in the Z direction from a pulse laser oscillator is condensed and irradiated inside the wafer to generate a modified portion, and the laser beam is scanned in the X and Y directions to form a plurality of laser beams inside the wafer. a modified layer forming step of forming a modified layer in which modified portions are continuous in the X direction and the Y direction;
A modified layer melting step of heating the modified layer to a temperature lower than the melting point of the wafer and equal to or higher than the melting point of the modified layer by a heat source to melt the modified layer to form a liquid layer;
a separation step of separating the wafer with the liquid layer as a boundary;
The modified layer has an uneven shape in which each of the plurality of modified portions has different lengths and positional variations in the Z direction,
The thickness in the Z direction of each of the modified portions constituting the modified layer is formed corresponding to the difference in the length and position of the modified portion in the Z direction in the unmodified layer of the wafer. larger than the height difference between the highest position and the lowest position in the Z direction of the uneven shape
slicing method. In the separation step, the wafer is separated in a direction parallel to the scanning direction of the laser beam.
The slicing method according to claim 1. The pulse width of the laser light is 0.2 picoseconds or more and 100 picoseconds or less.
The slicing method according to claim 1 or 2. The laser light has a wavelength at which the transmittance of the wafer is 50% or more,
The slicing method according to any one of claims 1 to 3. A pulsed laser beam is emitted in the Z direction, and the inside of the wafer is focused and irradiated to generate a modified portion, and the laser beam is scanned in the X and Y directions to form a plurality of modified portions inside the wafer. a laser oscillator that forms a modified layer that is continuous in the X direction and the Y direction;
a heat source that melts the modified layer by heating the modified layer to a temperature lower than the melting point of the wafer and higher than or equal to the melting point of the modified layer to form a liquid layer;
a separating unit that separates the wafer with the liquid layer as a boundary;
The modified layer has an uneven shape in which each of the plurality of modified portions has different lengths and positional variations in the Z direction,
The thickness in the Z direction of each of the modified portions constituting the modified layer is formed corresponding to the difference in the length and position of the modified portion in the Z direction in the unmodified layer of the wafer. larger than the height difference between the highest position and the lowest position in the Z direction of the uneven shape
slicing device.

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