JP5758518B2 - Manufacturing method of semiconductor light emitting device - Google Patents

Description

  The present invention relates to a method for manufacturing a semiconductor light emitting device.

  Nitride semiconductor light-emitting diode (hereinafter also referred to as LED (Light Emitting Device)) for application to white illumination. Improvement of luminous efficiency by studying crystal and device structure in order to achieve high efficiency and high output. Improvements in light extraction efficiency are being promoted.

  When growing an InGaN-based crystal, a sapphire substrate that is inexpensive, stable at high temperature, and capable of high crystal growth with a low-temperature buffer is often used. The sapphire substrate is an insulator and has no electrical conductivity and low thermal conductivity. For this reason, it is necessary to form both the p-electrode and the n-electrode on the nitride semiconductor side without producing an electrode on the back surface side of the sapphire substrate, the series resistance is likely to increase, and the heat dissipation when operating at high output is This is a problem when considering higher efficiency and higher output.

  A thin film type InGaN-based LED is known as one of LED structures that solve this problem and improve luminous efficiency and output (see, for example, Patent Document 1). In this thin-film type InGaN-based LED, an LED structure crystal grown on a sapphire substrate is transferred to another support substrate such as a Si substrate, copper, or gold. By forming a device after transfer onto a support substrate having electrical conductivity and high thermal conductivity, the spread of current increases due to vertical energization, the electrical conductivity characteristics are improved, and the heat dissipation is further improved.

  Also, if the structure is such that light is extracted from the n-layer side with the n-layer as the upper surface during transfer, the n-layer, which has a smaller resistance than the p-layer, eliminates the need for a transparent electrode for diffusing current, and the transparent electrode does not absorb. This improves the light extraction efficiency. This transfer process includes a process of bonding a crystal (epitaxial crystal) formed by epitaxial growth to a support substrate, and a lift-off process of peeling the epitaxial crystal and the sapphire substrate. The bonding process includes a plating technique and a joining technique using weight and heat, and the lift process includes laser lift-off and chemical lift-off using thermal decomposition of the interface by a laser.

  In such a thin film LED structure, the difference in refractive index between the surface of the GaN substrate and the external air is as large as about 2.5 times when the laser is lifted off, and the reflection of light at this boundary surface reduces the extraction efficiency. .

  Therefore, a technique for producing irregularities on the surface of the chip has been proposed (see, for example, Patent Document 2). The irregularities are formed by regrowth, polishing, and etching of the n-type nitride semiconductor layer. As a method that can be easily formed, irregularities are formed by roughening the surface of the n layer on the upper surface of the GaN substrate on the support substrate by alkali etching, thereby improving the light extraction efficiency.

  However, in the conventional alkali etching method, the size of the concavo-convex shape often does not increase even when the film thickness is reduced overall by increasing the etching time. There is a need for an etching control method capable of obtaining a concavo-convex shape that increases the light extraction efficiency on the surface of the GaN layer.

JP 2008-235362 A JP 2007-300069 A

  The present invention has been made in view of the above circumstances, and provides a method for manufacturing a semiconductor light emitting device capable of improving light extraction efficiency.

  According to an aspect of the present invention, there is provided a method for manufacturing a semiconductor light emitting device, comprising: forming an n-type nitride semiconductor layer, an active layer having a multi-quantum well structure of a nitride semiconductor, and a p-type nitride semiconductor layer on a first substrate; Providing a first laminated film laminated in order, forming a contact electrode on an upper surface of the p-type nitride semiconductor layer, attaching the first substrate and the second substrate, and Removing the first substrate, transferring the first laminated film onto the second substrate, and providing a second laminated film laminated on the second substrate in the reverse order of the first laminated film; Forming a concavo-convex region in the n-type nitride semiconductor layer by wet-etching the n-type nitride semiconductor layer using an alkaline solution, forming an n-electrode, and the second stacked film, The area of the film surface from the upper surface to the lower surface Increasing cross section includes a step of patterning so as tapered, the.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the semiconductor light-emitting device which can improve light extraction efficiency can be provided.

FIG. 1A to FIG. 1C are cross-sectional views showing a manufacturing process of a semiconductor light emitting device according to one embodiment. 2A to 2B are cross-sectional views illustrating a manufacturing process of a semiconductor light emitting device according to an embodiment. FIG. 3A to FIG. 3C are cross-sectional views illustrating a manufacturing process of a semiconductor light emitting device according to one embodiment. FIGS. 4A and 4B are electron micrographs of cross sections near the surface on which irregularities of the semiconductor light emitting device according to the embodiment and the comparative example are formed, respectively. 5A and 5B are electron micrographs of the surface when the etching time of the semiconductor light emitting device according to the embodiment is changed. The top view of the support substrate before isolate | separating into an individual element. Sectional drawing which shows the semiconductor light-emitting device by one Embodiment. The figure which shows the etching time dependence of the emitted light intensity of the semiconductor light-emitting device by one Embodiment and a comparative example.

  In the manufacturing method of the present invention, when forming an optical semiconductor element, an n-electrode is formed on the upper surface of the n-type nitride semiconductor layer for each element, and then the upper surface of the n-type nitride semiconductor layer is formed using an alkaline solution. Unevenness is formed by wet etching.

  The semiconductor light emitting device of the present invention comprises an uneven region formed on the surface of a region other than the region where the n electrode of the n-type nitride semiconductor layer is provided, and the uneven region has a height difference of 1 μm to 3 μm. 1st unevenness | corrugation and 2nd unevenness | corrugation smaller than the said 1st unevenness | corrugation whose height difference is 300 nm or less are mixed.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  A method for manufacturing a semiconductor light emitting device according to an embodiment of the present invention will be described with reference to FIGS. The manufacturing process of the semiconductor light emitting device according to the first embodiment is shown in FIGS.

First, a nitride semiconductor layer is sequentially grown on a substrate (wafer) on which a nitride semiconductor crystal is grown, for example, a sapphire substrate 10 by using, for example, a metal organic chemical vapor deposition (MOCVD) method.
That is, a GaN layer 12 serving as a buffer layer, an n-type GaN layer 14, an active layer 16 having a multiple quantum well structure made of InGaN, and a p-type GaN layer 18 are sequentially grown in this order on the sapphire substrate 10 (FIG. 1 (a)).

  Subsequently, a p-electrode (reflective contact electrode) 20 is formed on the p-type GaN layer 18 from a laminated film of Ni and Ag (FIG. 1B). The p electrode 20 is formed corresponding to each semiconductor light emitting element. Thereafter, an adhesive metal 22 in which Ti, Pt, and Au serving as adhesive metals are laminated in this order on the nitride semiconductor crystal films 12, 14, 16, and 18 so as to cover the p-electrode 20 (FIG. 1 (b)). Thereby, the portion of the adhesive metal 22 in the region where the p-electrode 20 is formed becomes a convex portion, and the portion of the adhesive metal 22 in the region where the p-electrode 20 is not formed becomes a concave portion (FIG. 1B). Subsequently, the bonding metal 22 is patterned using a known lithography technique. Thereafter, a laminated film (nitride semiconductor crystal film) having the p-type GaN layer 18, the active layer 16, the n-type GaN layer 14, and the GaN layer 12 is further patterned (FIG. 1C).

  By this patterning, the nitride semiconductor crystal film on the wafer becomes a mesa having a tapered cross section in which the area of the film surface increases from the p-type GaN layer 18 toward the GaN layer 12. Here, the “film surface” means the upper surface of each layer. When patterning the laminated film, the patterned adhesive metal may be used as a mask. Alternatively, the laminated film may be patterned before forming the adhesive metal 22, and then the adhesive metal 22 may be formed.

  On the other hand, an Au—Sn layer 32 serving as an adhesive metal is formed on the Si substrate 30 serving as a support substrate (FIG. 2A). Then, the adhesive metal 22 on the sapphire substrate and the adhesive metal 32 on the Si substrate 30 are arranged so as to face each other, and a pressure is applied for a predetermined time at a high temperature of 250 ° C. or higher. Then, the adhesive metal 32 on the Si substrate 30 is bonded together. In this bonding, since the melting point temperature of the contact electrode 20 is considerably higher than the melting point temperature of the adhesive metal 32, the bonding is performed in a state of being bitten into the adhesive metal 32 (FIG. 2A).

Next, as shown in FIG. 2B, a UV (Ultra-Violet) laser, for example, a laser with a wavelength of 248 nm of KrF is pulsed from the sapphire substrate 10 side, and nitride semiconductor crystal films 12, 14, 16, The sapphire substrate 10 is peeled from 18. At this time, the exposed surface of the GaN layer 12 is a surface to be wet etched.
Subsequently, the nitride semiconductor crystal films 12, 14, 16, and 18 are patterned using a known lithography technique and separated for each semiconductor light emitting element. At this time, the adhesive metal 22 is not patterned, and the adhesive metal 22 is exposed between the nitride semiconductor crystal films separated for each semiconductor light emitting element. Further, the patterned nitride semiconductor crystal film becomes a mesa having a tapered cross section in which the area of the film surface continuously increases from the GaN layer 12 toward the p-type GaN layer 18.

Next, for example, a SiO ₂ film 40 is formed as a protective layer so as to cover the tapered nitride semiconductor crystal film and the exposed surfaces of the adhesive metals 22 and 32 (FIG. 3B). The nitride semiconductor crystal film has a mesa shape, the minimum diameter of the lower surface of the nitride semiconductor crystal film in contact with the adhesive metal 22 is smaller than the minimum diameter of the upper surface of the adhesive metal 22, and the adhesive metal of the adhesive metal 22 Since the minimum diameter of the lower surface in contact with 32 is smaller than the minimum diameter of the upper surface of the adhesive metal 32, the adhesive metal 22 and the lower peripheral edge region of the mesa-shaped nitride semiconductor crystal film are in close contact with each other, and the protection It is possible to form the protective layer 40 without step breakage without being hollow between the layer 40 and the adhesive metals 22 and 32.

Next, the protective layer 40 covering the upper surface of each semiconductor light emitting element is removed. However, the protective layer 40 in the outer peripheral region on the upper surface of each semiconductor light emitting element (the upper surface of the GaN layer 12) is left. Thereby, the upper surface is exposed except for the outer peripheral region of the upper surface of each semiconductor light emitting element (FIG. 3C). At this time, the surface roughness of the upper surface of the GaN layer 12 is about 100 nm to 3000 nm.

  Subsequently, an n-electrode 44 is formed at the central portion of the upper surface of the exposed GaN layer 12 (FIG. 3C). The n-electrode 44 is not limited to the central portion, and may be formed anywhere on the exposed upper surface of the GaN layer 12. Moreover, it is preferable to use an alkali-resistant electrode material as the material for the n-electrode. In particular, it is preferable to use a material containing any one metal of Pt, Au, Ni, and Ti. By using this material, the size of unevenness (high and low) formed on the upper surface of the GaN layer 12 by alkali etching described later. Difference) can be made large. Since the n-electrode 44 is formed on the flat GaN layer 12, it can be formed with good adhesion.

  After the n-electrode 44 is formed, an alkaline solution is supplied, and the upper surface of the exposed GaN layer 12 is wet-etched to roughen the upper surface of the exposed GaN layer 12, that is, the GaN layer 12 is exposed. Thus, the GaN layer 12a having irregularities formed on the upper surface is obtained (FIG. 3C). By performing wet etching after the n-electrode 44 is formed, the etching effect is enhanced and the unevenness is deepened. This is presumably because electrons or holes move between the surface of the GaN layer 12 and the n-electrode 44, and an electrochemical reaction occurs on each surface and etching proceeds. An n-electrode 44 is formed for each optical semiconductor element. Accordingly, the unevenness is increased as compared with the case where one electrode is provided per wafer, and the etching state is uniform in each element in the wafer surface.

  In this embodiment, potassium hydroxide having a concentration of 1 mol / l and a temperature of 70 ° C. was used as the alkaline solution, and etching was performed for 15 minutes. When sufficient etching proceeds, the surface becomes clouded. The unevenness can be further increased by irradiating with UV in a state immersed in potassium hydroxide. The size of the unevenness is about several hundred nm to several μm. The unevenness can also be increased by performing etching while applying an intermittent voltage of 3 V to 10 V between the n electrode 44 and the GaN layer 12.

  FIG. 4A shows an electron micrograph of the cross section of the surface of the GaN layer 12 with the irregularities formed in this way. As can be seen from FIG. 4A, various irregularities are formed. When the surface and cross-sectional image of the height (difference in height) of the unevenness formed on the GaN layer 12 according to this embodiment are observed with an electron microscope image, large unevenness of several μm (1 μm to 3 μm) and several hundred nm (300 nm or less) ) Of small irregularities of the order. Thereby, reflection at the interface between the GaN layer 12 and air is reduced, and the light extraction efficiency can be increased.

  On the other hand, a semiconductor light emitting device as a comparative example of the present embodiment is formed in the same manner as the present embodiment except that the upper surface of the GaN layer 12 is etched without forming the n electrode 44. FIG. 4B shows an electron micrograph of a cross section of the surface of the GaN layer 12 where the irregularities are formed in the semiconductor light emitting device of this comparative example. As can be seen from FIGS. 4A and 4B, the unevenness formed in the semiconductor light emitting device of this embodiment is larger than the unevenness formed in the semiconductor light emitting device of the comparative example. When the height of the unevenness formed on the GaN layer 12 was measured according to this comparative example, only a small unevenness of about 200 nm was present, and unlike the present embodiment, there was no large unevenness on the order of 1 μm.

Moreover, in the manufacturing method of this embodiment, the electron micrograph of the surface of the GaN layer 12 in which the unevenness | corrugation was formed when etching time is performed for 5 minutes and when performing for 15 minutes is shown in FIGS. Each is shown in b). As can be seen from FIGS. 5 (a) and 5 (b), when etching is performed for 15 minutes as in this embodiment, large unevenness and small unevenness are mixed. Only formed.
Next, FIG. 6 shows a plan view seen from the n-electrode 44 side after such irregularities are formed. As can be seen from FIG. 6, a plurality of non-isolated elements are arranged on the Si substrate 30. Thereafter, as shown in FIG. 3C, a p-electrode 46 is formed on the surface of the silicon substrate 30 opposite to the side on which the n-electrode 44 is formed.

  Next, after the process shown in FIG. 3C is completed, the protective layer 40, the adhesive metals 22, 32, and the Si substrate 30 are diced and separated into the respective semiconductor light emitting elements, whereby the semiconductor light emitting shown in FIG. Complete the device. The semiconductor light emitting device of the comparative example is also separated into each semiconductor light emitting device by dicing.

  As shown in FIG. 8, the semiconductor light emitting device of the present embodiment thus obtained has a light extraction efficiency 1.2 times greater than that of the semiconductor light emitting device of the comparative example. FIG. 8 is a diagram showing a change in light emission intensity of the semiconductor light emitting devices of the present embodiment and the comparative example when the etching time is changed.

  As described above, according to the present embodiment, it is possible to provide a method for manufacturing a semiconductor light emitting device with high light extraction efficiency.

  In the present embodiment, a part of the upper surface and the side surface of the nitride semiconductor crystal film, and the junction between the side surface and the adhesive metal are covered with the protective layer 40 that is not cut off, so an alkaline solution is used. Even when the upper surface of the nitride semiconductor crystal film is roughened, the active layer and the reflective contact electrode 20 can be sufficiently protected. Thereby, the reflective contact electrode 20 having a large area can be formed, and the reflectance can be improved. Furthermore, since a large contact electrode can be formed, a reduction in operating voltage can be expected. In addition, since the protective layer 40 without any step is formed, it is possible to prevent device leakage or short circuit due to metal adhesion during the manufacturing process. Further, since the protective layer 40 without any step is formed, it can withstand the manufacturing process of the thin film type semiconductor light emitting device having a large impact such as bonding and laser lift-off, and the protective layer is not cracked. .

  As the support substrate, a silicon substrate, a silicon carbide substrate, a substrate in which germanium is bonded to the silicon substrate, or a substrate in which a metal such as copper is plated on the silicon substrate can be used. Further, as the silicon substrate, a substrate having any one of the (111), (110), and (100) orientations may be used, and a substrate having an off angle may be used.

  The protective layer is preferably made of a material containing any of silicon dioxide, silicon nitride, zirconium oxide, niobium oxide, and aluminum oxide.

In addition to potassium hydroxide, tetramethylammonium hydroxide can be used as a chemical solution in alkaline etching. A desirable concentration is 0.1 mol / l to 10 mol / l.

  Further, as the contact electrode 20, it is desirable to use aluminum or aluminum in addition to silver.

  The adhesive metal 22 preferably contains any of titanium, platinum, gold, and tungsten.

  Further, as the adhesive metal 32, in addition to Au—Sn, a low melting point metal that is a metal eutectic such as Au—Si, Ag—Sn—Cu, or Sn—Bi, or a non-solder material such as Au, Sn, or Cu. Can be used.

10 Nitride semiconductor crystal growth substrate (sapphire substrate)
12 GaN layer (buffer layer)
14 n-type GaN layer 16 active layer (InGaN layer) with multiple quantum well structure
18 p-type GaN layer 20 p-electrode (reflective contact electrode)
22 Adhesive metal 30 Support substrate 32 Adhesive metal 40 Protective layer 44 n-electrode 46 p-electrode

Claims (5)

Providing a first stacked film in which an n-type nitride semiconductor layer, an active layer having a multi-quantum well structure of nitride semiconductor, and a p-type nitride semiconductor layer are stacked in this order on a first substrate;
Forming a contact electrode on the upper surface of the p-type nitride semiconductor layer;
Bonding the first substrate and the second substrate;
Removing the first substrate, transferring the first laminated film onto the second substrate, and providing a second laminated film laminated on the second substrate in a reverse order to the first laminated film; When,
forming an n-electrode;
Forming an uneven region in the n-type nitride semiconductor layer by wet-etching the n-type nitride semiconductor layer with an alkaline solution after forming the n-electrode ;
The pre-Symbol second multilayer film, the area of the film surface increases toward the lower surface from the upper surface, a step of patterning so that the cross section is tapered,
A method for manufacturing a semiconductor light emitting device comprising:   2. The method of manufacturing a semiconductor light emitting element according to claim 1, wherein the uneven region includes a first unevenness having a height difference of 1 μm to 3 μm and a second unevenness smaller than the first unevenness having a height difference of 300 nm or less.   The method for manufacturing a semiconductor light-emitting element according to claim 1, wherein the alkaline solution contains potassium hydroxide or tetramethylammonium hydroxide.   4. The method of manufacturing a semiconductor light emitting element according to claim 1, wherein the removal of the first substrate is performed by irradiating a laser from the first substrate side to peel the first substrate from the second laminated film. 5.   The method of manufacturing a semiconductor light emitting element according to claim 4, wherein the laser is a UV laser.