JP2009032795A - Method of manufacturing nitride semiconductor light emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a nitride semiconductor light emitting element whose chip shape can be stabilized and which has superior light emission efficiency. <P>SOLUTION: A group III nitride semiconductor layer 3 having a light emission portion is grown on a sapphire wafer 20 which is a transparent substrate. Laser light of 500 to 700 nm in wavelength is converged into the group III nitride semiconductor layer 3 to form a processed region 35 in the group III nitride semiconductor layer 3. A crack is made originating from the processed region 35 to divide the group III nitride semiconductor layer 3 and the transparent substrate 35 in every discrete element 21, thereby obtaining a plurality of LED chips 1. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a method for manufacturing a nitride semiconductor light emitting device using a group III nitride semiconductor. A group III nitride semiconductor is a semiconductor using nitrogen as a group V element in a group III-V semiconductor, and typical examples thereof are aluminum nitride (AlN), gallium nitride (GaN), and indium nitride (InN). . In general, it can be expressed as Al _x In _y Ga _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1).

  A semiconductor light emitting device having a structure in which a group III nitride semiconductor layer is grown on a sapphire substrate is known. Typical examples are blue light emitting diodes and semiconductor lasers. The group III nitride semiconductor layer has, for example, a stacked structure in which an n-type GaN layer, an active layer (light emitting layer), and a p-type GaN layer are stacked from the sapphire substrate side. With this configuration, electrons and holes are recombined in the active layer and light is emitted.

In the flip-chip type light emitting device, an n-side electrode and a p-side electrode are provided on the group III nitride semiconductor layer side, and these are flip-chip bonded to a circuit board. In this case, the light generated from the light emitting layer is observed through the sapphire substrate.
In the manufacturing process, a group III nitride semiconductor layer is grown on a sapphire wafer, and then the wafer is divided into individual elements. Sapphire and III-nitride semiconductors have different cleavage directions due to lattice mismatch. For this reason, in the technique of making a break with scribe flaws, the chip shape is not stable because the sapphire wafer and the group III nitride semiconductor layer have different fragility.
Japanese Patent Laid-Open No. 11-177137 JP 2004-268309 A

  In order to solve the above problem, it is conceivable to divide the sapphire wafer by applying laser processing using a YAG laser having a wavelength of 355 nm (for example, Patent Document 1). However, if a deep disassembly guide groove is to be formed by laser processing for good division, the heat generated by the absorption of the laser beam may adversely affect the device characteristics. Further, when grooves are formed on the surface of the sapphire wafer, the substrate material is heated and scattered as debris (dust) around the periphery, so that the surface of the substrate is contaminated. Furthermore, discoloration occurs in the portion that has absorbed the laser light. Due to these problems, there is a problem that the light emission efficiency of the light emitting element is deteriorated when the substrate dividing method using laser processing using a YAG laser or the like is employed.

  On the other hand, in the prior art of Patent Document 2, a split guide groove is not formed on the surface of the sapphire wafer, but a processing region by multiphoton absorption is formed inside the sapphire wafer, and the sapphire wafer is split starting from this processing region. is doing. However, even in this case, a decrease in light emission efficiency (light extraction efficiency) due to discoloration of the processed region is inevitable. In addition, when processing with a laser having a wavelength capable of processing sapphire, absorption occurs at the interface of the sapphire / Group III nitride semiconductor (for example, GaN), leading to a decrease in luminous efficiency.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing a nitride semiconductor light emitting device that can stabilize the chip shape and is excellent in luminous efficiency.

  The invention according to claim 1 for achieving the above object comprises a step of growing a group III nitride semiconductor layer having a light emitting part on a transparent substrate transparent to the emission wavelength of the light emitting part, A step of condensing a laser beam having a wavelength of 700 nm inside the group III nitride semiconductor layer to form a processing region inside the group III nitride semiconductor layer, and generating a crack from the processing region, A method of manufacturing a nitride semiconductor light-emitting device, including a step of dividing a group III nitride semiconductor layer and a transparent substrate.

  Laser light having a wavelength of 500 nm to 700 nm is not absorbed by a transparent substrate such as a sapphire substrate or a SiC substrate, and is not absorbed even by a group III nitride semiconductor. That is, this wavelength range is larger than the wavelength corresponding to the band gap of the transparent substrate and the group III nitride semiconductor. However, so-called multiphoton absorption occurs at the condensing point (focal position) where the laser light is condensed because the energy density of the laser light is high. That is, the material excited from the ground level to the virtual level by the incidence of the photon is excited to the excitation level by the incidence of another photon within a certain time constant, thereby absorbing the light. Occurs. Therefore, the laser beam can be absorbed only at a condensing point having a high energy density.

  In the method of the present invention, a laser beam having a wavelength of 500 nm to 700 nm is condensed inside the group III nitride semiconductor layer, and multiphoton absorption is generated at the condensing point, so that the inside of the group III nitride semiconductor layer is formed. A processing region (modified region) is formed. Absorption of laser light does not substantially occur except at the condensing point, so no discoloration occurs in the transparent substrate. Further, the dividing guide groove is not formed deeply from the substrate surface, but only the laser beam is absorbed at the condensing point inside the group III nitride semiconductor layer. For this reason, the entire substrate is not overheated, and debris due to alteration or scattering of the substrate material does not occur. Therefore, the characteristics of the group III nitride semiconductor layer are not significantly impaired by the processing with the laser light, and the light generated from the light emitting portion of the group III nitride semiconductor layer can be extracted outside with high efficiency. . In this way, a nitride semiconductor light emitting device with good luminous efficiency can be provided.

In addition, since the processing region is formed inside the group III nitride semiconductor layer, the substrate can be divided satisfactorily, and the divided pieces (similar to the case where the deep divided guide grooves are formed from the substrate surface) The shape of the chip) can be stabilized.
According to a second aspect of the present invention, before the dividing step, a dividing guide groove is formed by mechanical processing at a position corresponding to the processing region on the surface of the transparent substrate opposite to the group III nitride semiconductor layer. The method for manufacturing a nitride semiconductor light emitting device according to claim 1, further comprising a step of:

According to this method, the division guide groove is formed by mechanical processing on the surface of the transparent substrate, and then the substrate is divided. Thereby, the shape of the divided piece can be further stabilized.
The division guide groove may be formed before the processing region is formed by the laser beam or after the processing region is formed by the laser beam.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a schematic sectional view showing a mounting example of a flip chip type LED (light emitting diode) chip which is an example of a nitride semiconductor light emitting element. The LED chip 1 is obtained by forming a light emitting diode structure composed of a group III nitride semiconductor layer 3 on one main surface of a sapphire substrate 2 as a transparent substrate. A p-side electrode 4 and an n-side electrode 5 are formed on the surface of the group III nitride semiconductor layer 3. The p-side electrode 4 and the n-side electrode 5 are flip-chip bonded to the mounting substrate 6. That is, the electrodes 4 and 5 are bonded to a conductor pattern (not shown) formed on the mounting substrate 6 using a brazing material such as solder. Light generated from the group III nitride semiconductor layer 3 is transmitted to the outside through the sapphire substrate 2.

  FIG. 2 is a schematic cross-sectional view for explaining a more detailed configuration of the LED chip 1. The group III nitride semiconductor layer 3 is formed by epitaxially growing a group III nitride semiconductor on one main surface of the sapphire substrate 2. The group III nitride semiconductor layer 3 includes, for example, an n-type GaN buffer layer 11 (for example, 4 μm), an n-type GaN contact layer 12 (for example, 1 μm to 10 μm), a light emitting layer 13 (active layer), and the like in order from the sapphire substrate 2 side. A p-type GaN contact layer 14 (for example, 0.2 μm to 1 μm) is laminated. A p-side electrode 4 is formed on the surface of the p-type GaN contact layer 14. Further, a part of the group III nitride semiconductor layer 3 is etched until the n-type GaN contact layer 12 is exposed to form a recess 15. An n-side electrode 5 is formed so as to be joined to the exposed portion of the n-type GaN contact layer 12. The light emitting layer 13 is, for example, a multiple quantum in which a quantum well layer composed of an InGaN layer (for example, 1 nm to 3 nm) and a barrier layer composed of a non-doped GaN layer (for example, 10 nm to 20 nm) are alternately and repeatedly formed (for example, 3 to 8 periods). It may have a well structure (MQW: multiple-quantum well. For example, a total thickness of 0.05 μm to 0.3 μm).

With such a configuration, when a forward voltage is applied between the p-side electrode 4 and the n-side electrode 5, electrons and holes are recombined in the light-emitting layer 13 to emit light.
The light emitting layer 13 generates light having a wavelength in the visible light region such as blue. The sapphire substrate 2 is a substrate that is transparent to the emission wavelength of the light emitting layer 13 (for example, the wavelength in the visible light region). Therefore, the light generated in the light emitting layer 13 can be observed through the sapphire substrate 2.

  FIG. 3 is a schematic perspective view of a sapphire wafer used in the manufacturing process of the LED chip 1. A plurality of individual elements 21 corresponding to individual LED chips 1 are collectively formed on a sapphire wafer 20 that is a base of the sapphire substrate 2. That is, the group III nitride semiconductor layer 3 is epitaxially grown on the surface of the sapphire wafer 20. Then, a recess 15 for exposing the n-type contact layer 14 is formed in the region of each individual element 21. Thereafter, a p-side electrode 4 joined to the p-type contact layer 14 and an n-side electrode 5 joined to the n-type contact layer 12 are formed. A plurality of individual elements 21 are thus formed on the sapphire wafer 20.

Next, a dividing step for dividing the sapphire wafer 20 along the scheduled cutting line 25 that is a boundary line between the individual elements 21 is performed.
FIG. 4 is an illustrative view for explaining the dividing step. A laser processing step (FIG. 4A) for processing with laser light along the planned cutting line 25 and a step for breaking the sapphire wafer 20 carrying the group III nitride semiconductor layer 3 by applying an external force (FIG. b)).

In the laser processing step shown in FIG. 4A, laser light is irradiated by a laser processing machine toward the sapphire wafer 20 on which the group III nitride semiconductor layer 3 is formed.
Although the detailed configuration is not shown, the laser processing machine includes a laser light generation unit, a condensing lens 30 for condensing the laser light from the laser light generation unit in the group III nitride semiconductor layer 3, and sapphire. And an XY stage mechanism for supporting the wafer 20. The laser light generation unit includes, for example, a laser light source such as a YAG laser or an excimer laser, and an optical system that converts the laser light emitted from the laser light source into parallel light.

  The condensing lens 30 condenses the parallel laser light from the laser light generating unit. The relationship between the condensing lens 30 and the sapphire wafer 20 is such that the focal position (condensing point) of the condensing lens 30 is the layer in the group III nitride semiconductor layer 3, more preferably the layer closest to the sapphire wafer 20. It is adjusted so as to be located in the mold buffer layer 11. This adjustment may be performed by adjusting the focal length of the condenser lens 30 or by adjusting the distance between the condenser lens 30 and the sapphire wafer 20. The distance between the condenser lens 30 and the sapphire wafer 20 may be adjusted by moving the condenser lens 30 closer to or away from the stage of the XY stage mechanism, or the stage of the XY stage mechanism may be adjusted to the condenser lens 30. You may carry out by approaching / separating with respect to it.

  The XY stage mechanism includes a stage that carries the sapphire wafer 20 at a position facing the condenser lens 30, and a stage moving mechanism that moves the stage two-dimensionally along the X direction and the Y direction perpendicular thereto. . The X direction and the Y direction are, for example, directions along the horizontal plane. The XY stage mechanism may further include a mechanism for moving the stage along the Z direction (for example, the vertical direction) that is a direction approaching / separating from the condenser lens 30 as necessary.

  The laser light generation unit generates laser light having a wavelength of 500 nm to 700 nm (more specifically, 532 nm, second harmonic YAG). Further, the laser light generating unit is a laser beam having such intensity that no laser light is absorbed except in the vicinity of the focal position of the condenser lens 30 in the group III nitride semiconductor layer 3 or the sapphire wafer 20, and multiphoton absorption occurs at the focal position. Generate light.

More specifically, the laser beam has an energy density of 5.0 × 10 ⁹ W / cm ^{2 to} 2.0 × 10 ¹⁰ W / cm ² at the focal position of the condenser lens 30. The output of the generating unit may be adjusted. Thereby, multiphoton absorption can be reliably generated at the focal position.
Further, it is preferable to adjust the output of the laser light generating unit so that the energy density in the surface of the group III nitride semiconductor layer 3 or in the sapphire wafer 20 is 1.0 × 10 ⁷ W / cm ² or less. As a result, absorption of laser light other than at the focal position can be avoided, and the surface of the group III nitride semiconductor layer 3 is processed, or the sapphire wafer 20 is discolored due to laser processing. Can be avoided.

  While the laser beam is irradiated onto the wafer 20 from the laser processing machine, the wafer 20 is moved relative to the laser beam irradiation position so that the irradiation position of the laser beam moves along the scheduled cutting line 25. That is, the wafer 20 is moved in the direction along the scheduled cutting line 25 by the XY stage mechanism. As a result, the laser beam scans the wafer 20 along the planned cutting line 25. As a result, in the group III nitride semiconductor layer 3, the focal position (condensing point of the laser beam) of the condenser lens 30 moves along the planned cutting line 25, and a processing region 35 corresponding to the locus of the focal position. Will be formed.

  During the scanning process, the laser beam may be constantly applied to the wafer 20, or the laser beam generation unit may be turned on / off to intermittently apply the laser beam. If the laser beam is always irradiated at the time of scanning, the processing region 35 has a continuous shape. If the laser beam is irradiated intermittently at the time of scanning, a plurality of processes divided into perforations at a predetermined interval in the scanning direction. The region 35 is formed along the planned cutting line 25.

  After the laser processing step, a break step shown in FIG. 4B is performed. That is, an external force in a direction perpendicular to the main surface is applied to the sapphire wafer 20 along the planned cutting line 25. Thereby, the sapphire wafer 20 is cracked with the processing region 35 as a starting point, and the sapphire wafer 20 and the group III nitride semiconductor layer 3 are cracked along the crack. In this way, the sapphire wafer 20 and the group III nitride semiconductor layer 3 are divided for each individual element 21 along the planned cutting line 25, and as a result, a plurality of LED chips 1 are obtained.

  Before the break process, a thinning process for thinning the sapphire wafer 20 by grinding or polishing (for example, chemical mechanical polishing) may be performed as necessary. For example, the initial thickness of the sapphire wafer 20 is about 350 μm, and the thickness is reduced to about 80 μm. This thinning step may be performed between the laser processing step and the break step, or may be performed before the laser processing step. However, in order to facilitate handling of the sapphire wafer 20 in the laser processing step, it is preferable that a thinning step is performed after the laser processing step.

  In the laser processing step, the processing region 35 is formed by multiphoton absorption inside the group III nitride semiconductor layer 3, but the surface region of the group III nitride semiconductor layer 3 and the absorption of the laser light in the sapphire wafer 20. Is avoided. Therefore, debris caused by laser processing does not occur, and undesired discoloration (coloring) does not occur in the sapphire wafer 20. In addition, laser processing is not performed from the surface of the substrate to a deep position, but only a limited region in the group III nitride semiconductor layer 3 (near the focal position of the condenser lens 30) is processed by multiphoton absorption. Absent. Therefore, the group III nitride semiconductor layer 3 is not overheated in the laser processing step. Therefore, the LED chip 1 can have good light emission efficiency.

  FIG. 5 is an illustrative view for illustrating a manufacturing method according to another embodiment of the present invention. In FIG. 5, parts corresponding to the parts shown in FIG. 4 are given the same reference numerals as those in FIG. In this embodiment, after the laser processing step (FIG. 5A, the same step as FIG. 4A), the sapphire wafer 20 is thinned as necessary, and then shown in FIG. 5B. As described above, the division guide groove 36 is formed on the main surface of the sapphire wafer 20 opposite to the group III nitride semiconductor layer 3 along the planned cutting line 25 (see FIG. 3). The division guide groove 36 is formed not by laser processing, but by mechanical processing such as ruled writing processing by the diamond cutter 37 or groove forming processing by a dicing saw.

  The division guide groove 36 formed by mechanical processing cannot be formed deeply, and has a depth of about 2 μm to 3 μm, for example. However, since the laser processing region 35 is formed in the group III nitride semiconductor layer 3, the division of the wafer 20 in the break process (FIG. 5C, the same process as FIG. 4B) becomes poor. There is nothing. Then, by forming the division guide groove 36 in addition to the laser processing region 35, the LED chip 1 having a more stable shape can be obtained.

  As mentioned above, although two embodiment of this invention was described, this invention can also be implemented with another form. For example, in the above-described embodiment, the laser beam is irradiated from the surface on the group III nitride semiconductor layer 3 side, but the laser beam is transmitted through the sapphire wafer 20 from the side opposite to the group III nitride semiconductor layer 3. The light may be condensed inside the group III nitride semiconductor layer 3.

In the above-described embodiment, the LED chip 1 having the configuration in which the group III nitride semiconductor layer 3 is formed on the sapphire substrate 2 has been described. However, as the substrate, a SiC substrate or other transparent substrate can be used.
In the above-described embodiment, the example in which the present invention is applied to the manufacture of LED chips has been described. However, the present invention can be similarly applied to semiconductor laser chips and other light emitting elements.

  In addition, various design changes can be made within the scope of matters described in the claims.

It is an illustration sectional view showing the example of mounting of the flip chip type LED chip which is an example of the nitride semiconductor light emitting element. It is an illustration sectional view for explaining the detailed composition of a LED chip. It is a schematic perspective view of a sapphire wafer used in the LED chip manufacturing process. It is an illustration figure for demonstrating the division | segmentation process which concerns on 1st Embodiment. It is an illustration figure for demonstrating the division | segmentation process which concerns on 2nd Embodiment.

Explanation of symbols

1 LED chip 2 Sapphire substrate 3 Group III nitride semiconductor layer 4 P-side electrode 5 N-side electrode 6 Mounting substrate 11 n-type GaN buffer layer 12 n-type GaN contact layer 13 Light-emitting layer (light-emitting portion)
14 p-type GaN contact layer 15 recess 20 sapphire wafer 21 individual element 25 line to be cut 30 condensing lens 35 processing area 36 divided guide groove 37 diamond cutter

Claims (2)

Growing a group III nitride semiconductor layer having a light emitting part on a transparent substrate transparent to the light emission wavelength of the light emitting part;
A step of condensing a laser beam having a wavelength of 500 nm to 700 nm inside the group III nitride semiconductor layer to form a processing region inside the group III nitride semiconductor layer;
A method for producing a nitride semiconductor light emitting device, comprising: generating a crack from the processing region to divide the group III nitride semiconductor layer and the transparent substrate.   The method further includes forming a split guide groove by mechanical processing at a position corresponding to the processing region on a surface of the transparent substrate opposite to the group III nitride semiconductor layer before the splitting step. 2. A method for producing a nitride semiconductor light emitting device according to 1.

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