JP2012146771A - Laser lift-off method and laser lift-off device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser lift-off method and a device thereof capable of preventing cracking as much as possible on a material layer after being peeled from a substrate.SOLUTION: A work 3 in which a material layer is formed on a substrate is irradiated with pulse laser light through the substrate under such condition as irradiation region is changed as time passes. The laser light is formed in such square shape as contains two sides extending in the direction parallel to the moving direction of the work 3. Irradiation is made such that the irradiation regions adjoining each other overlap each other. In a peeling region, with peeling being made sequentially from a substrate 1, irradiation is made to the work so that the peeling sides of the material layer to be peeled for the first time from the substrate are two sides, and an angle (angle θ1 when viewed from a non-resolution region side) formed with a peeling side A extending in the direction across the moving direction of the work and a side B' extending in the direction parallel to the moving direction of the work in the region in which peeling is completed comes to be an obtuse angle. Consequently, a material layer 2 can be peeled from the substrate 1 without causing a crack on the material layer 2.

Description

  In the manufacturing process of a semiconductor light emitting device formed of a compound semiconductor, the present invention decomposes the material layer by irradiating the material layer formed on the substrate with a laser beam, and peels the material layer from the substrate (hereinafter referred to as the following). The present invention relates to a laser lift-off method and a laser lift-off apparatus.

Laser for peeling a GaN-based compound material layer formed on a sapphire substrate by irradiating a laser beam from the back surface of the sapphire substrate in a manufacturing process of a semiconductor light-emitting device formed of a GaN (gallium nitride) -based compound semiconductor Lift-off technology is known. Hereinafter, the process of peeling the material layer from the substrate by irradiating the material layer formed on the substrate with laser light is referred to as laser lift-off.
For example, in Patent Document 1, a GaN layer is formed on a sapphire substrate, and laser light is irradiated from the back surface of the sapphire substrate, whereby GaN forming the GaN layer is decomposed, and the GaN layer is separated from the sapphire substrate. A laser lift-off method for peeling is described. Hereinafter, a substrate in which a material layer is formed is called a workpiece.
Patent Document 2 describes that a workpiece is irradiated with a line-shaped laser beam through a sapphire substrate while the workpiece is conveyed. Specifically, in this document, as shown in FIG. 12, the laser beam 124 is shaped so that the irradiation region 123 to the interface between the sapphire substrate 121 and the material layer 122 of the GaN-based compound is in a line shape, and the sapphire substrate 121 A laser lift-off method is disclosed in which the laser beam 124 is irradiated from the back surface of the sapphire substrate 121 while moving the laser beam 124 in a direction perpendicular to the longitudinal direction of the laser beam 124.
In Patent Document 3, for example, a rectangular beam spot is formed using a laser, and the material layer is laser lifted off from the substrate by sequentially irradiating the irradiated object while moving the beam spot relatively. It is described to do. FIG. 17 of Patent Document 3 shows that the beam spot 132 is moved concentrically with respect to a circular workpiece (wafer 131) and laser lift-off is performed as shown in FIG.

JP-T-2001-501778 JP 2003-168820 A Special table 2007-534164 gazette

As described above, when the GaN-based compound material layer formed on the sapphire substrate is peeled off by irradiating the laser beam from the back surface of the sapphire substrate, the GaN is decomposed when irradiated with the laser beam. The N ₂ gas that is applied causes shear stress to the GaN layer, which may cause cracks at the boundary of the laser light irradiation region.
In laser lift-off, it is important to prevent such cracks from occurring in the material layer after peeling.
As a laser light irradiation method, for example, as described in Patent Document 2, the laser light is shaped so that the irradiation region to the interface of the material layer is in a line shape, and the substrate is formed in a direction perpendicular to the longitudinal direction of the laser light. A method of irradiating a laser beam while scanning it, or scanning a rectangular beam spot concentrically with respect to a circular wafer as described in Patent Document 3, and irradiating while changing the irradiation area every time has been proposed. ing.
The method described in Patent Document 2 is to form an irradiation region in a line shape and irradiate while moving the irradiation region in the direction perpendicular to the longitudinal direction of the laser beam, and the laser beam corresponds to the width of the substrate. Although it is required to be shaped into a long shape, it is difficult to obtain a laser beam having such a shape with a large irradiation illuminance and cannot be realized easily.
Further, as described in FIG. 17 of Patent Document 3, in order to scan the beam spot, a mechanism for moving the square beam spot relatively concentrically on the work is necessary, and overlapping is required. The area of the irradiated region increases, and it is considered that a long time is required to irradiate the entire area of the workpiece with laser light, which is not efficient.

In addition, the inventors previously changed the position of the irradiation area of the laser beam having a small area formed in a square shape, while the end of each irradiation area overlaps the end of the adjacent irradiation area. The laser lift-off method is proposed. In this way, as shown in Patent Document 2, the laser beam is efficiently and cracked without forming a long and narrow shape and using a special mechanism for scanning the beam spot concentrically. The laser lift-off can be realized without causing it.
However, even when the laser light having a small area formed into a quadrangular shape as described above is irradiated while changing the irradiation region, cracks may occur in the material layer after peeling from the substrate.
The present invention solves the above-described problems, and an object of the present invention is to provide a laser lift-off method and apparatus capable of preventing the occurrence of cracks in a material layer after peeling from a substrate as much as possible.

As a result of various studies by the present inventors, as described above, the end of each irradiation region overlaps with the end of the adjacent irradiation region while changing the irradiation region of the laser beam formed into a square shape as described above. It was found that the material layer can be peeled from the substrate while preventing the generation of cracks by irradiating the substrate.
However, it has been found that even with the laser lift-off method, cracks may occur in the material layer after peeling from the substrate, depending on the method of irradiating the workpiece with laser light. This will be described below.
FIG. 9 shows that the material layer is formed by irradiating the workpiece with laser light so that the edge portions of the irradiation region of the laser beam are sequentially superimposed in accordance with the conveyance direction of the workpiece while changing the irradiation region with respect to the workpiece. Shows a method of laser lift-off from the substrate.
This figure shows the case where the irradiation area of the laser beam on the workpiece is square (square). The black area in the figure is the irradiation area irradiated with the laser beam, and the shaded area is the laser beam. The irradiated area (exfoliated area), the white part is the area not irradiated with laser light (GaN undecomposed area), and the irradiated area sequentially moves in the direction indicated by the arrow in FIG. The laser beam is irradiated while changing every moment.
Moreover, in the same figure, when the peeling side of the material layer peeled for the first time from the substrate is two sides in the rectangular peeling region of the material layer peeled from the substrate (two-side peeling in FIG. 1A). , And the case of three sides (three-side peeling in FIG. 1B) and the case of one side (one-side peeling in FIG. 1C) are shown.

FIG. 10 is an image showing the state of the material layer peeled off by the laser lift-off method shown in FIG. 9, and after peeling from the substrate when laser lift-off is performed as shown in FIGS. 9 (a) to 9 (c). It shows the presence or absence of occurrence of cracks in the material layer.
10 shows a case where the GaN-based compound material layer formed on the sapphire substrate is peeled off by irradiating the rectangular laser beam shown in FIG. 9 from the back surface of the sapphire substrate. (A) shows the case where the peeling side of the material layer peeled from the substrate for the first time is two sides (FIG. 9 (a)), and FIG. 10 (b) shows the case where there are three sides (FIG. 9 (b)). FIG. 10C shows the case of one side (FIG. 9C).

As shown in FIG. 9 (a), when there are two sides peeled for the first time from the undecomposed region of the material layer, cracks did not occur as shown in FIG. 10 (a). As shown in FIG. 10, when the side peeled for the first time from the undecomposed region of the material layer was three sides, cracks occurred in the peeled material layer as shown in FIG.
The reason is considered as follows.
GaN, which is a material layer, is decomposed into Ga and N ₂ when irradiated with laser light. As shown in FIGS. 9 (a) and 9 (b), the N ₂ gas generated during the decomposition of GaN is not discharged from the side in contact with the undecomposed region of GaN in a rectangular separation region that is sequentially separated from the substrate. Since it is possible, it is discharged from the side already peeled off from the substrate.
As shown in FIG. 9 (a), in the GaN square peel region, when there are two sides peeled for the first time from the substrate, there are two sides already peeled from the substrate, and the N ₂ gas escape path Since these are the two sides and the N ₂ gas escapes from these two sides, no large gas pressure is applied to the region irradiated with light.
On the other hand, as shown in FIG. 9B, in the GaN square-shaped peeling region, when there are three sides peeled for the first time from the substrate, there is only one side already peeled from the substrate, There is only one side of N ₂ gas escape. For this reason, N ₂ gas cannot be sufficiently discharged, and stress generated by the pressure of N ₂ gas accumulates on three sides in contact with the undecomposed region of GaN in the material layer peeled from the substrate, It is considered that cracks occur in the GaN after peeling from the substrate.

As shown in FIG. 9C, even when the side peeled for the first time from the undecomposed region of the material layer is one side, as shown in FIG. Cracks occurred.
In this case, as shown in FIG. 9C, there are three sides already peeled from the substrate, so there is no problem with the discharge of N ₂ gas. However, since the stress generated when GaN is decomposed by laser light irradiation is concentrated only on one side in contact with the undecomposed region of GaN, when the strength of the material layer is not sufficient, It is thought that cracks occur.
As shown in FIG. 9 (c), the upper and lower regions are already peeled regions, and an undecomposed region remains between them. It is a special case to irradiate this undecomposed region with laser light. Although this does not occur when laser light is irradiated in order from one end of the work to the other end, such a case may occur depending on the method of irradiating the work with laser light. FIG. It is desirable to avoid the “one-side peeling” shown in FIG.

  As described above, the irradiation region of the laser beam on the workpiece has a quadrangular shape having one side extending in a direction parallel to the movement direction of the workpiece, and the material layer peeled from the substrate by irradiating the workpiece with the laser beam. As shown in FIGS. 9 (b) and 9 (c), the sides peeled off from the substrate for the first time in the rectangular peeled area are two sides as shown in FIG. 9 (a). Compared with the case where the peeling side of the material layer peeled off from the substrate for the first time is three sides or one side, as shown in FIG. 10A, it is possible to prevent cracks in the material layer after peeling from the substrate.

  However, as a result of various studies by the inventor, even if the workpiece is irradiated with laser light so that there are two sides of the material layer that is peeled off from the substrate for the first time, the moving direction of the workpiece that is peeled off from the substrate for the first time An angle formed by a peeling side extending in the intersecting direction and a side extending in a direction parallel to the moving direction of the workpiece in the peeled area (an angle viewed from the undecomposed area side, in FIG. 9A, side A and side B ′ May be cracked in the material layer after peeling from the substrate by concentrating on the acute angle part where the stress generated during laser light irradiation is applied. found.

FIG. 11 is a diagram showing a simulation result of a stress distribution generated at the time of laser beam irradiation on the peeling side of the material layer peeled off from the substrate for the first time. This figure shows “isostress lines” connecting points with equal stress, and the numbers in the figure show the stress values at each isostress line.
FIG. 11B shows an acute angle formed between a peeling side extending in a direction intersecting with a moving direction of a workpiece to be peeled for the first time from the substrate and a side extending in a direction parallel to the moving direction of the workpiece in the peeled area (this example) FIG. 9 is a diagram showing a simulation result showing a portion where stress generated at the time of laser beam irradiation concentrates when the angle is 90 °.
As shown in the figure, an angle formed by a peeling side A extending in a direction intersecting with the moving direction of the work and a side B ′ extending in a direction parallel to the moving direction of the work in the peeled area (viewed from the undecomposed area side) When the angle is 90 °, the stress generated during laser beam irradiation is concentrated in the vicinity of the side A where the sides A and B ′ intersect at 90 °, and the maximum stress value is 11.0 GPa. ing.
In order to avoid cracks in the material layer after peeling from the substrate, it is necessary to reduce the area of the laser light irradiation area on the work or to reduce the energy of the laser light applied to the work. .

When the area of the laser light irradiation region on the workpiece is reduced, there is a problem that the time required for the laser lift-off process becomes longer and the throughput is lowered.
On the other hand, in the laser lift-off, for example, GaN (gallium nitride) constituting the material layer needs to be irradiated with laser light having an energy exceeding the decomposition threshold of GaN, and the laser is set to fall below the decomposition threshold of GaN. The energy of light cannot be set. Therefore, the energy of the laser beam is set to exceed the decomposition threshold of GaN, and is set to be 1.15 VE or less when the decomposition threshold of GaN is VE.
By the way, since the energy of the laser beam varies slightly with time due to various factors, it is preferable that the energy of the laser beam is set to have a slight margin with respect to the decomposition threshold of GaN. In other words, reducing the energy of the laser beam applied to the workpiece makes it impossible to secure a margin for the GaN decomposition threshold VE, and the laser beam energy reduces the GaN decomposition threshold due to slight fluctuations in the laser energy. This is likely to cause a problem of undecomposition of GaN.

In the present invention, the laser beam irradiation area on the workpiece is increased accordingly, and the laser beam energy is set to ensure a certain margin with respect to the decomposition threshold of GaN. In order to prevent cracks in the material layer after peeling, the following solution was adopted.
That is, as shown in FIG. 1 (a), the laser beam is always separated from the substrate in the rectangular separation region of the material layer, and the material layer peeled off from the substrate for the first time has two separation sides (same as the same). The angle formed by the peeling side A (side A, side B) extending in the direction intersecting the workpiece movement direction and the side B ′ extending in the direction parallel to the workpiece movement direction in the peeled area (not shown) The workpiece 3 is irradiated so that the angle θ1) viewed from the decomposition region side becomes an obtuse angle (greater than 90 °). In addition, when the shape of the irradiation region is a parallelogram, as shown in the figure, the peeling side A extending in the direction intersecting the moving direction of the workpiece, and the direction parallel to the moving direction of the workpiece in the peeled region The angle θ1 formed by the side B ′ extending in the direction is equal to the angle θ2 formed by the two peeled sides that are peeled for the first time.

FIG. 11A shows a separation side A extending in a direction intersecting with the movement direction of the workpiece, and the movement direction of the workpiece in the peeled area, in which the separation layer of the material layer peeled off from the substrate for the first time is two sides. FIG. 6 is a diagram showing simulation data representing a portion where stress generated at the time of laser beam irradiation is concentrated when an angle formed by a side B ′ extending in a direction parallel to the angle is an obtuse angle.
As shown in the figure, when the angle formed by the peeling side A extending in the direction intersecting the workpiece moving direction and the side B ′ extending in the direction parallel to the workpiece moving direction in the peeled area is an obtuse angle, the laser The stress generated at the time of light irradiation is not concentrated on the corner as shown in FIG. 11 (b), but dispersed and applied to the peeling edge A extending in the direction intersecting the moving direction of the workpiece peeled for the first time from the substrate, It can be seen that the stress is locally concentrated in one place. The maximum stress value in this case is 9.1 GPa, which is relaxed compared to FIG.
In FIG. 1A, the two sides A and B of the peeling side are straight lines, and the peeling side A extends in a direction intersecting the moving direction of the workpiece, and in the direction parallel to the moving direction of the workpiece in the peeled area. Although the angle formed by the extending side B ′ is an obtuse angle, as shown in FIG. 1B, the peeling side A extending in the direction intersecting the moving direction of the workpiece peeled for the first time from the substrate, and the peeled side The angle formed by the side B ′ extending in the direction parallel to the moving direction of the workpiece in the region may be an obtuse angle, and the two sides may be connected by a convex curve C on the decomposition region side.

Based on the above, in the present invention, the above-described problem is solved as follows.
(1) A workpiece having a material layer formed on a substrate is irradiated with a laser beam from a laser source through the substrate, and the material layer is decomposed at the interface between the substrate and the material layer. In the laser lift-off method for peeling, the laser beam is irradiated to the workpiece while changing the irradiation region for the workpiece, and the edge portion of the irradiation region is unidirectionally relative to the laser source. The images are sequentially superimposed as they move to.
The irradiation region of the laser beam on the workpiece has a first edge portion extending in a direction crossing the moving direction of the workpiece, and a second edge portion extending in a direction parallel to the moving direction of the workpiece, A peeling region of the material layer that is sequentially peeled off from the substrate by laser light includes a first edge (side A) extending in a direction intersecting with a moving direction of the workpiece corresponding to the first edge portion, and the first And two edges that are peeled off from the substrate for the first time, consisting of a second edge (side B) extending in a direction parallel to the moving direction of the workpiece corresponding to the two edge portions.
The laser beam is parallel to the movement direction of the workpiece in the first edge (side A) peeled off from the substrate for the first time in the peeling region and the peeled region peeled off by the laser light. The workpiece is irradiated so that the angle formed by the second edge (side B ′) extending in the direction becomes an obtuse angle on the undecomposed region side of the material layer.
(2) In (1), the laser beam is formed such that each irradiation region group including irradiation regions overlapping in the one direction is sequentially arranged from one end to the other end of the workpiece. The irradiation region group formed first and the irradiation region group formed last are formed so as to extend from one edge portion and the other edge portion of the workpiece.
(3) In a laser lift-off device that irradiates a workpiece having a material layer formed on a substrate with laser light through the substrate and peels the material layer from the substrate at the interface between the substrate and the material layer. A laser source that generates laser light in a wavelength region that passes through the substrate, a transport mechanism that relatively transports the work and the laser source, and the laser light changes the irradiation area of the work every moment, The workpiece is irradiated so that each irradiation region is sequentially arranged from one end to the other end of the workpiece, and the edge of the irradiation region moves in one direction relative to the laser source. As a result, a laser beam emitted from the laser source and a control unit for controlling the irradiation interval of the laser beam and the transfer operation of the workpiece by the transfer mechanism so as to be sequentially superimposed. Laser optics for forming the first edge portion extending in a direction crossing the moving direction of the workpiece and a second edge portion extending in a direction parallel to the moving direction of the workpiece and irradiating the workpiece The control unit extends in a direction in which a peeling region of the material layer, which is sequentially peeled from the substrate by the laser beam, intersects a moving direction of the workpiece corresponding to the first edge portion. Two edges that are peeled off from the substrate for the first time are composed of a first edge (side A) and a second edge (side B) extending in a direction parallel to the moving direction of the workpiece corresponding to the second edge portion. And in the peeling region, the first edge (side A) peeled off from the substrate for the first time and the peeled region peeled off by the laser beam extend in a direction parallel to the moving direction of the workpiece. Angle out with 2'nd edge (edge B') that is, as an obtuse angle in the undecomposed region side of the material layer, irradiating the laser beam on the workpiece.
(4) In the above (3), the control unit is configured such that an irradiation region group composed of irradiation regions overlapped in the one direction formed first in the workpiece and an irradiation region group formed last are one of the workpieces. The workpiece is irradiated with laser light so as to extend from the edge portion and the other edge portion.

In the present invention, the following effects can be obtained.
(1) Since the material layer peeled from the substrate for the first time in the square peeled region of the material layer peeled sequentially from the substrate has two peeled sides, N generated by the decomposition of GaN ₂ gas is discharged from the two sides already peeled from the substrate, and a sufficient escape path for the N ₂ gas can be secured, and the stress generated when GaN decomposes is the two sides in contact with the undecomposed region of GaN. Applied in a dispersed manner.
Furthermore, an angle formed by the first edge peeled off from the substrate for the first time and a second ′ edge extending in a direction parallel to the moving direction of the workpiece in the peeled area peeled off by the laser beam is the material. Since the obtuse angle is formed on the undecomposed region side of the layer, it is avoided that the stress generated at the time of laser light irradiation is locally concentrated near the corner where the first edge and the second 'edge intersect. Is done.
For this reason, generation | occurrence | production of the crack in the material layer after peeling from a board | substrate can be prevented as much as possible.
(2) By irradiating the workpiece with laser light so that the first irradiation region group and the last irradiation region group formed on the workpiece extend from one edge portion and the other edge portion of the workpiece. Also, in the irradiation region group formed at the beginning and the end of the workpiece, the sides to be peeled are two sides, and the sides to be peeled can be always two sides in the entire area of the workpiece.
(3) By moving the irradiation area of the laser beam linearly on the workpiece, the laser lift-off process can be performed on the entire area of the workpiece, and it is not necessary to use a special mechanism for scanning the laser beam. The configuration can be simplified.

It is a figure explaining the laser lift-off method in this invention. It is a conceptual diagram explaining the outline | summary of the laser lift-off process of the Example of this invention. It is a figure which shows a mode that a laser beam is irradiated to a workpiece | work. A laser lift-off method of irradiating a laser beam so that an angle formed by a peeling side A extending in a direction intersecting with the moving direction of the workpiece and a side B ′ extending in a direction parallel to the moving direction of the workpiece in the peeled region becomes an obtuse angle. FIG. It is a figure which shows the other example of the irradiation area | region of the laser beam to a workpiece | work. In the Example of this invention, it is a figure which shows the light intensity distribution of the laser beam irradiated on the area | region S1, S2 which mutually adjoins a workpiece | work. It is a conceptual diagram of the laser lift-off apparatus of the Example of this invention. It is a figure explaining the manufacturing method of the semiconductor light-emitting device which can apply a laser lift-off process. It is a figure explaining the case where a laser beam is irradiated so that a GaN undecomposed area | region may become 2 sides, 3 sides, and 1 side. It is the figure which showed typically the surface state of the material layer after peeling at the time of irradiating a laser beam so that a GaN undecomposed area | region may become 2 sides, 3 sides, and 1 side. It is a figure which shows the simulation result of the stress distribution which generate | occur | produces at the time of the laser beam irradiation in the peeling edge of the material layer peeled from the board | substrate for the first time. It is a figure which shows the prior art example irradiated while moving a line-shaped laser beam to the orthogonal | vertical direction with the longitudinal direction of a laser beam. It is a figure which shows the prior art example irradiated while moving a square-shaped beam spot concentrically.

FIG. 2 is a conceptual diagram for explaining the outline of the laser lift-off process according to the embodiment of the present invention.
As shown in the figure, in the present embodiment, the laser lift-off process is performed as follows.
A work 3 in which a material layer 2 is formed on a substrate 1 that transmits laser light is placed on a work stage 31 with the material layer 2 facing down. The work stage 31 on which the work 3 is placed is placed on a transport mechanism 32 such as a conveyor, and is transported by the transport mechanism 32 at a predetermined speed. The workpiece 3 is irradiated with a pulse laser beam L emitted from a pulse laser source (not shown) through the substrate 1 while being conveyed in the arrow AB direction in the figure together with the workpiece stage 31.
The workpiece 3 is formed by forming a material layer 2 of a GaN (gallium nitride) compound on the surface of a substrate 1 made of sapphire. The substrate 1 may be any material that can satisfactorily form a GaN-based compound material layer and transmits laser light having a wavelength necessary for decomposing the GaN-based compound material layer. A GaN-based compound can be used for the material layer 2 in order to efficiently output high-output blue light with low input energy. As the material layer 2, a group III compound can be used, such as the GaN compound, indium gallium nitride (InGaN) compound, aluminum gallium nitride (AlGaN) compound, or the like.

The laser beam should be appropriately selected according to the substrate 1 and the substance constituting the material layer peeled from the substrate 1. When the GaN-based compound material layer 2 is peeled from the sapphire substrate 1, for example, a KrF (krypton fluorine) excimer laser that emits a wavelength of 248 nm can be used. The light energy (5 eV) with a laser wavelength of 248 nm is between the band gap of GaN (3.4 eV) and the band gap of sapphire (9.9 eV). Therefore, a laser beam having a wavelength of 248 nm is desirable for peeling the material layer of the GaN-based compound from the sapphire substrate.

When the material layer 2 is irradiated with pulsed laser light, GaN in the material layer 2 is decomposed into Ga and N ₂ . When GaN decomposes, a phenomenon as if it has exploded occurs, and the edge of the irradiation region of the pulse laser beam on the material layer 2 is damaged to some extent.
In the laser lift-off process of the present invention, since the material layer that is peeled off from the substrate for the first time is made to have two sides, the laser lift-off process is performed without damaging the material layer as described above. It can be carried out.

In the present invention, the shape of the irradiation region of the pulse laser beam irradiated on the workpiece needs to be a quadrangle having an edge portion on one side extending in parallel with the moving direction of the workpiece at the time of pulse laser beam irradiation.
In view of the structure of the laser device, when the aspect ratio of the irradiation region is 1: X, X is preferably 20 or less, and the area of the irradiation region is preferably 30 mm ² or less.

FIG. 3 below shows a pulse formed so that the irradiation area on the workpiece becomes a quadrangle (parallelogram in this example) having an edge portion on one side extending in parallel with the moving direction of the workpiece during pulse laser beam irradiation. 1 shows a laser lift-off method of the present invention in which laser light is irradiated while conveying a workpiece in one direction with respect to a laser source. FIG. 3A shows an irradiation region formed on the workpiece, and FIG. 3B is an enlarged view of a portion X in FIG. Although FIG. 2 shows the case where the workpiece is rectangular, FIG. 3 shows the case where the workpiece 3 is circular.
In this laser lift-off method, by adjusting the irradiation interval of the pulse laser beam and the conveyance speed of the workpiece 3, as shown in FIG. 3B, the workpiece 3 in the irradiation region of the parallelogram shaped pulse laser beam is obtained. To the workpiece 3 so that both the edge portion extending in the direction parallel to the moving direction (directions of arrows HA and HC in FIG. 3) and the edge portion extending obliquely with respect to the moving direction of the workpiece 3 overlap. Irradiate pulsed laser light.

Further, in the laser lift-off method of FIG. 3, pulse laser light is sequentially irradiated so that each irradiation region is arranged in a line toward the direction of HA on the paper surface so as to exceed the edge portion above the paper surface of the work 3, Pulsed laser light irradiation areas S1 to S4 are formed. Then, after the workpiece is moved in the HB direction below the paper surface by the amount obtained by subtracting the laser superimposed region ST from the size of the pulse laser irradiation region, the pulse laser beam is directed toward the HC direction (the same direction as HA) on the paper surface. Are sequentially irradiated so that the irradiation regions are arranged in a line, thereby forming pulsed laser beam irradiation regions S5 to S10.
Edge portions (first edge portions) extending in a direction oblique to the moving direction of the workpieces of the irradiation regions S1 to S10 adjacent in the moving direction of the workpiece 3 overlap each other. Further, edge portions (second edges) extending in the direction parallel to the moving direction of the workpiece 3 in the irradiation areas S1 and S6, S2 and S7, S3 and S8, and S4 and S9 that are adjacent in the direction orthogonal to the moving direction of the workpiece 3. Part) overlap each other.

As shown in FIG. 6 to be described later, the irradiation regions of the respective pulsed laser beams are superimposed on regions exceeding the decomposition threshold VE of GaN that is the material layer. In this way, as shown in FIG. 3, a plurality of irradiation region groups G1 to G6 are formed in which irradiation regions of a plurality of pulsed laser beams formed in sequence are arranged in a line in one direction.
In the laser lift-off method of the present invention, the irradiation of the pulse laser beam is started from the one end 3a of the workpiece 3, and the pulse laser beam is finally irradiated to the other end 3b of the workpiece. That is, as shown in FIG. 3, each irradiation region group is formed so that each irradiation region group G1 to G6 is sequentially arranged from one end 3a to the other end 3b of the workpiece in the order in which the laser beams are irradiated. To do. In the irradiation region group G1 formed first in the workpiece 3, the irradiation regions S1 to S4 are irradiated with pulsed laser light so as to extend from one edge portion (one end 3a) of the workpiece 3. In the irradiation region group G6 formed last in the workpiece 3, the pulse laser beam is irradiated so that each irradiation region extends from the other edge portion (the other end 3b) of the workpiece 3. In this way, in the parallelogram-shaped exfoliation region of GaN that is sequentially exfoliated from the substrate, the edge part that is exfoliated for the first time from the substrate is always two sides.
For example, in the irradiation region S1, since the sides other than the two edge portions that are peeled off from the substrate for the first time are in contact with the outer edge portion of the work 3 and are not undecomposed regions, N ₂ gas generated during GaN decomposition is discharged from the outer edge portion. Is done. Similarly, also in the irradiation region S2, sides other than the two edge portions that are peeled off from the substrate for the first time are in contact with the outer edge portion of the work 3 and the irradiation region S1, and the N ₂ gas generated during GaN decomposition is released from the outer edge portion. Discharged.

FIG. 4 shows a peeling side A (first edge portion) extending in a direction crossing the moving direction of the workpiece 3 and a direction parallel to the moving direction of the workpiece in the peeled area in the material layer peeled from the substrate. It is a figure explaining the laser lift-off method which irradiates a laser beam with respect to a workpiece | work so that the angle | corner which side B '(2' edge part) makes becomes an obtuse angle.
As shown in the figure, in the laser lift-off method of the present invention, in the peeling region S8 of the material layer peeled from the substrate, a peeling edge A extending in a direction intersecting with the moving direction of the workpiece 3 peeled from the substrate for the first time; The laser beam is irradiated to the workpiece 3 so that the angle formed by the side B ′ extending in the direction parallel to the moving direction of the workpiece in the peeled area becomes an obtuse angle.
When the shape of the region irradiated with the laser beam to the workpiece 3 is a parallelogram, as shown in FIG. 4, the material is composed of two sides: a side A that is peeled off from the substrate for the first time and a side B ′ of the peeled region. It is necessary to appropriately set the scanning direction of the laser light so that the angle formed on the undecomposed region side of the layer becomes an obtuse angle. Specifically, it is necessary to scan the laser beam so that the acute angle portion of the parallelogram is the head in the scanning direction.

FIG. 5 is a diagram illustrating another example of the irradiation region of the laser beam on the workpiece.
In FIG. 5A, the shape of the peeling region SN is a parallelogram, and the angle formed by the two sides of the side A that is peeled off from the substrate for the first time and the side B ′ of the peeled region is on the undecomposed region side. The obtuse angle is such that the two sides of the side A and the side B ′ are connected by a convex curve C on the decomposition region side.
Further, FIG. 4B shows that the shape of the peeling region SN2 is a square shape, and two sides of the side A that is peeled off for the first time from the substrate and the side B ′ of the peeled region are convex to the decomposition region side. The shape is connected by a curved line, and the angle formed by the tangent of side A and side B ′ is an obtuse angle on the undecomposed region side.
FIG. 4C shows a shape close to a trapezoid, and the angle formed by the two sides of the side A peeled off from the substrate for the first time and the side B ′ of the peeled region is an obtuse angle on the undecomposed region side. .
As in this example, the shape of the irradiation region of the laser beam to the workpiece may be a shape that is not strictly rectangular, and in this case, the side A that is peeled off from the substrate for the first time and the side B that has been peeled off are used. The angle formed by the two sides of ′ is set to be an obtuse angle on the undecomposed region side.

FIG. 6 is a diagram showing the light intensity distribution of the laser light irradiated on the workpiece so as to overlap the regions S1 and S2 adjacent to each other of the workpiece 3 shown in FIG. 3, and aa ′ in FIG. It is line sectional drawing.
In the figure, the vertical axis indicates the intensity (energy value) of the laser beam irradiated to each irradiation area of the workpiece, and the horizontal axis indicates the conveyance direction of the workpiece. L1 and L2 indicate the profiles of the laser beams irradiated to the workpiece irradiation areas S1 and S2, respectively. The laser beams L1 and L2 are not irradiated at the same time, but the laser beam L2 is irradiated after one pulse interval from the irradiation of the laser beam L1.
In this example, as shown in FIG. 6, the cross sections of the laser beams L1 and L2 are formed in a substantially trapezoidal shape having a flat surface on the top (peak energy PE) following the edge portion LE that gently spreads in the circumferential direction. Yes. The laser beams L1 and L2 are superimposed in an energy region exceeding a decomposition threshold VE necessary for decomposing and peeling the material layer of the GaN-based compound from the sapphire substrate, as indicated by broken lines in FIG.
That is, in the light intensity distribution of each laser beam, the intensity (energy value) CE of the laser beam at the intersection position C between the laser beams L1 and L2 is set to a value exceeding the decomposition threshold value VE.

This is because, as described above, when the irradiation region is shifted from S1 to S2 after the irradiation region S1 of FIG. 3 is irradiated with the laser light, the temperature of the region S1 is already lowered to the room temperature level. This is because even if the irradiation region S2 is irradiated with the laser light in a state where the temperature of the region S1 is lowered to the room temperature level, the irradiation amount of the pulse laser light irradiated to each of the irradiation regions S1 and S2 is not integrated.
The intensity CE of the laser beam at the crossing position C between the laser beams L1 and L2, that is, the intensity of each pulsed laser beam in the region irradiated with the laser beam superimposed, becomes a value exceeding the decomposition threshold VE. By setting to, sufficient laser energy can be applied to peel the material layer from the substrate, and the material layer is surely peeled from the substrate without causing cracks in the material layer formed on the substrate. be able to.

FIG. 7 is a conceptual diagram showing the configuration of the optical system of the laser lift-off device according to the embodiment of the present invention. In the figure, a laser lift-off device 10 includes a laser source 20 that generates pulsed laser light, a laser optical system 40 for shaping the laser light into a predetermined shape, a work stage 31 on which the work 3 is placed, A transport mechanism 32 that transports the work stage 31 and a controller 33 that controls the irradiation interval of the laser light generated by the laser source 20 and the operation of the transport mechanism 32 are provided.
The laser optical system 40 includes cylindrical lenses 41 and 42, a mirror 43 that reflects the laser light in the direction of the workpiece, a mask 44 for shaping the laser light into a predetermined shape, and the laser light L that has passed through the mask 44. And a projection lens 45 for projecting an image onto the work 3. The area and shape of the irradiation region of the pulse laser beam on the work 3 can be appropriately set by the laser optical system 40.
A workpiece 3 is disposed at the tip of the laser optical system 40. The work 3 is placed on the work stage 31. The work stage 31 is placed on the transport mechanism 32 and is transported by the transport mechanism 32. Thereby, the workpiece | work 3 is conveyed sequentially in the direction of the arrows A and B shown in FIG. 2, and the irradiation area of the laser beam in the workpiece | work 3 changes every moment. The control unit 33 controls the pulse interval of the pulsed laser light generated by the laser source 20 so that the degree of superimposition of each laser light irradiated on the irradiation region adjacent to the workpiece 3 becomes a desired value.

The laser light L generated from the laser source 20 is, for example, a KrF excimer laser that generates ultraviolet light having a wavelength of 248 nm. An ArF laser or a YAG laser may be used as the laser source. Here, the light incident surface 3 </ b> A of the work 3 is disposed farther in the optical axis direction of the laser light than the focal point F of the projection lens 45. On the contrary, the light incident surface 3A of the workpiece 3 may be disposed closer to the projection lens 45 than the focal point F of the projection lens 45 in the optical axis direction of the laser light. Thus, by arranging the light incident surface 3A of the workpiece 3 so as not to coincide with the focal point F of the projection lens 45, laser light having a trapezoidal light intensity distribution as shown in FIG. 6 is obtained.
The pulsed laser light L generated by the laser source 20 passes through the cylindrical lenses 41 and 42, the mirror 43, and the mask 44, and is then projected onto the work 3 by the projection lens 45. The pulse laser beam L is irradiated to the interface between the substrate 1 and the material layer 2 through the substrate 1 as shown in FIG. By irradiating the pulse laser beam L at the interface between the substrate 1 and the material layer 2, GaN near the interface between the material layer 2 and the substrate 1 is decomposed. In this way, the material layer 2 is peeled from the substrate 1.

Next, a method for manufacturing a semiconductor light emitting device that can use the laser lift-off method described above will be described. Below, the manufacturing method of the semiconductor light-emitting device formed of a GaN-based compound material layer will be described with reference to FIG.
As the substrate for crystal growth, a sapphire substrate capable of crystal growth of a gallium nitride (GaN) compound semiconductor that transmits laser light and forms a material layer is used. As shown in FIG. 8A, a GaN layer 102 made of a GaN-based compound semiconductor is rapidly formed on the sapphire substrate 101 by using, for example, a metal organic chemical vapor deposition method (MOCVD method).
Subsequently, as illustrated in FIG. 8B, an n-type semiconductor layer 103 and a p-type semiconductor layer 104 that are light emitting layers are stacked on the surface of the GaN layer 102. For example, GaN doped with silicon is used as the n-type semiconductor, and GaN doped with magnesium is used as the p-type semiconductor.
Subsequently, as shown in FIG. 8C, solder 105 is applied on the p-type semiconductor layer 104. Subsequently, as shown in FIG. 8D, the support substrate 106 is attached on the solder 105. The support substrate 106 is made of, for example, an alloy of copper and tungsten.
Then, as shown in FIG. 8E, the laser beam 107 is irradiated from the back surface side of the sapphire substrate 101 toward the interface between the sapphire substrate 101 and the GaN layer 102. The laser beam 107 is shaped so that the irradiation region is a square having an area of 0.25 mm ² or less and the light intensity distribution is substantially trapezoidal as shown in FIG.
By irradiating the interface between the sapphire substrate 101 and the GaN layer 102 with the laser beam 107 and decomposing the GaN layer 102, the GaN layer 102 is peeled from the sapphire substrate 101. ITO 108 which is a transparent electrode is formed on the surface of the GaN layer 102 after peeling by vapor deposition, and the electrode 109 is attached to the surface of the ITO 108.

According to the laser lift-off method of the present invention, as described above, in the GaN separation region that is sequentially separated from the substrate, the edge portion that is separated from the substrate for the first time is always two sides. Generation of cracks in GaN can be prevented or suppressed.
Moreover, when the shape of the irradiation region of the pulse laser beam is a parallelogram having two sides extending in the moving direction of the workpiece, the irradiation regions are easily overlapped.
In addition, when GaN decomposes by irradiating pulse laser light, the present inventors damage the edge portion of the irradiation region. The magnitude of damage due to this decomposition is large in the laser light irradiation area. The larger the irradiation area S, the greater the force applied to the boundary (edge part) of the pulse laser beam irradiation area, but the edge length (peripheral length of the irradiation area) L can be increased. For example, it was found that the force applied per unit length of the edge portion is small, and the damage is small even if the irradiation area is the same.
That is, it is considered that the damage can be reduced by reducing the value of [irradiation area S] / [peripheral length L]. Specifically, by setting the value of S / L to 0.125 or less, It has been found that the laser lift-off process can be performed without causing damage.

As described above, when the shape of the irradiation region of the pulse laser beam is a parallelogram, when the area S (mm ² ) of the irradiation region and the peripheral length L (mm), the area S of the irradiation region is Since the value of S / L can be reduced compared with other quadrangles such as an equal rectangle, the force applied per unit length of the edge portion of the irradiation region is reduced as described above, and the irradiation area S is the same. Even if it exists, the damage to the irradiation area | region of a pulse laser beam can be made small.

In the laser lift-off method of the present invention, if the angle formed between the side A that is peeled off for the first time from the substrate and the side B ′ of the peeled region is an obtuse angle on the undecomposed region side, In short, the shape of the irradiation region of the pulse laser beam may be a quadrangular shape having one side extending in a direction parallel to the moving direction of the workpiece.
Therefore, the shape of the irradiation region of the pulse laser beam may be a trapezoid. In particular, the irradiation region of the pulse laser beam is preferably a quadrangular shape having two sides extending in a direction parallel to the movement direction of the workpiece in order to easily overlap each irradiation region adjacent in the movement direction of the workpiece.
According to the laser lift-off method of the present invention described above, by making the angle formed by the two peeled sides separated from the substrate for the first time as an obtuse angle, as shown in the simulation result of FIG. The generated stress is dispersed over the entire length of the peeling side A extending in the direction intersecting the moving direction of the workpiece peeled off for the first time from the substrate, so that the stress is prevented from being concentrated locally in one place. For this reason, it can prevent reliably that a crack arises in the material layer after peeling from a board | substrate.

DESCRIPTION OF SYMBOLS 1 Substrate 2 Material layer 3 Work 10 Laser lift-off device 20 Laser source 31 Work stage 32 Transport mechanism 33 Control unit 40 Laser optical system 41, 42 Cylindrical lens 43 Mirror 44 Mask 45 Projection lens 101 Sapphire substrate 102 GaN layer 103 N-type semiconductor layer 104 p-type semiconductor layer 105 solder 106 support substrate 107 laser beam 108 transparent electrode (ITO)
109 Electrode L Laser light

Claims (4)

A laser that irradiates a workpiece in which a material layer is formed on a substrate with a laser beam from a laser source through the substrate, decomposes the material layer at an interface between the substrate and the material layer, and peels the workpiece from the substrate In the lift-off method,
The laser beam is irradiated onto the workpiece while changing the irradiation region on the workpiece, and the edge of the irradiation region is sequentially superimposed as the workpiece moves in one direction relative to the laser source. And
The irradiation region of the laser beam on the workpiece has a first edge portion extending in a direction intersecting with the moving direction of the workpiece, and a second edge portion extending in a direction parallel to the moving direction of the workpiece,
A peeling region of the material layer that is sequentially peeled from the substrate by the laser light includes a first edge extending in a direction intersecting with a moving direction of the workpiece corresponding to the first edge portion, and the second edge Having two edges that are peeled off from the substrate for the first time, comprising a second edge extending in a direction parallel to the moving direction of the workpiece corresponding to the part,
The laser beam extends in a direction parallel to the movement direction of the workpiece in the first edge that is peeled off from the substrate for the first time in the peeling region and the peeled region that is peeled off by the laser light. The laser lift-off method, wherein the workpiece is irradiated such that an angle formed with an edge becomes an obtuse angle on the undecomposed region side of the material layer.   Each irradiation region group consisting of irradiation regions overlapping in the one direction by the laser beam is formed so as to be sequentially arranged from one end to the other end of the workpiece, and the irradiation region group formed first in the workpiece 2. The laser lift-off method according to claim 1, wherein the last formed irradiation region group is formed so as to extend from one edge portion and the other edge portion of the workpiece. In a laser lift-off device that irradiates a workpiece having a material layer formed on a substrate with laser light through the substrate, decomposes the material layer at the interface between the substrate and the material layer, and peels the material layer from the substrate.
A laser source that generates laser light in a wavelength region that passes through the substrate;
A transport mechanism for relatively transporting the workpiece and the laser source;
The laser beam is irradiated onto the workpiece so that each irradiation region is sequentially arranged from one end to the other end of the workpiece while changing the irradiation region on the workpiece, and an edge portion of the irradiation region is A control unit that controls an irradiation interval of the laser light and a conveyance operation of the workpiece by the conveyance mechanism so that the workpieces are sequentially superimposed as the workpiece moves in one direction relative to the laser source; ,
The laser beam emitted from the laser source is shaped into a shape having a first edge portion extending in a direction intersecting the moving direction of the workpiece and a second edge portion extending in a direction parallel to the moving direction of the workpiece. A laser optical system for irradiating the workpiece,
The controller is
A first edge extending in a direction intersecting with a moving direction of the workpiece corresponding to the first edge portion, and a second edge, wherein a peeling region of the material layer sequentially peeled from the substrate by the laser light Having two edges that are peeled off for the first time from the substrate, comprising a second edge extending in a direction parallel to the moving direction of the workpiece corresponding to the part,
In the peeling region, the first edge that is peeled off from the substrate for the first time, and a second ′ edge that extends in a direction parallel to the moving direction of the workpiece in the peeled region that has been peeled off by the laser beam. The laser lift-off device, wherein the workpiece is irradiated with the laser beam such that an angle formed is an obtuse angle on the undecomposed region side of the material layer.   The control unit includes an irradiation region group consisting of irradiation regions overlapping in the one direction formed first in the workpiece and an irradiation region group formed last from one edge portion and the other edge portion of the workpiece. The laser lift-off device according to claim 3, wherein the workpiece is irradiated with laser light so as to extend.

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