JP2013115341A - Semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent leakage due to Ag migration.SOLUTION: A semiconductor device includes: a semiconductor stacked structure including a first semiconductor layer of a first conductivity type, an active layer formed on the first semiconductor layer, and a second semiconductor layer of a second conductivity type formed on the active layer; a wiring electrode layer formed in contact with one of the first semiconductor layer or the second semiconductor layer; a reflective electrode layer formed in contact with the other of the first semiconductor layer or the second semiconductor layer on which the wiring electrode layer is not formed, and containing Ag; a cap layer including at least two sets of stacks of a first cap layer formed to cover the reflective electrode layer and composed of a transparent conductive film and a second cap layer formed to cover the first cap layer and composed of metal, alloy, or metal nitride; and a supporting substrate bonded to the cap layer via an eutectic layer.

Description

  The present invention relates to a semiconductor element.

  In recent years, with the increase in output of semiconductor light emitting devices, devices having a structure in which a semiconductor film is attached and supported on a heat dissipation support substrate are used from the viewpoint of forming a light extraction structure. In order to realize a high output, a reflective electrode made of Ag or an Ag alloy is formed as an electrode having a high reflectivity between the semiconductor film and the support substrate.

  Although Ag has a high reflectivity, it is known that Ag ion migration is likely to occur, and migration is particularly likely to occur due to energization or temperature change. When Ag ion migration occurs, a phenomenon such as leakage that affects the characteristics and reliability of the device occurs.

  In order to prevent migration of Ag ions, it is widely performed to form a diffusion prevention layer made of a refractory metal such as Pt or a metal oxide such as ITO. For example, a metal oxide such as ITO is formed as a translucent electrode on the nitride semiconductor side, an Ag-based reflective electrode layer is formed thereon, and then a layer containing a refractory metal or metal nitride is used as a diffusion prevention layer. It is known to form (for example, refer to Patent Document 1).

JP 2008-192882 A

  When a metal film such as Pt is used as the diffusion prevention layer, it is subjected to high-temperature processing in the process such as stress during film formation and attachment to a heat dissipation support substrate, and thus the influence of thermal strain during the heat treatment is affected. In response, defects such as cracks in the diffusion prevention layer tend to occur.

  In addition, when an oxide film or the like is used as a diffusion prevention layer, although it is not easily affected by thermal distortion during heat treatment, a phenomenon occurs in which pinholes are generated during film formation and Ag moves therethrough, thereby preventing diffusion. Is inferior to metal films.

  An object of the present invention is to provide a semiconductor element capable of suppressing leakage due to Ag migration.

  According to one aspect of the present invention, a semiconductor element is formed on a first semiconductor layer of a first conductivity type, an active layer formed on the first semiconductor layer, and the active layer. A semiconductor stacked structure including a second conductivity type second semiconductor layer; a wiring electrode layer formed in contact with one of the first semiconductor layer or the second semiconductor layer; and the first semiconductor layer. Alternatively, a first cap comprising a reflective electrode layer containing Ag formed in contact with the other of the second semiconductor layers on which the wiring electrode layer is not formed, and a transparent conductive film formed to cover the reflective electrode layer A cap layer formed over the first cap layer and including at least two sets of a laminate of a second cap layer made of a metal, an alloy or a metal nitride, and the cap layer via a eutectic layer. And a supporting substrate to be bonded.

  ADVANTAGE OF THE INVENTION According to this invention, the semiconductor element which can suppress the leak by the migration of Ag can be provided.

1 is a schematic sectional view showing an element structure of a nitride semiconductor light emitting element (LED element) 101 according to an embodiment of the present invention. It is a schematic sectional drawing for demonstrating the manufacturing method of the nitride semiconductor light-emitting device (LED element) 101 by the Example of this invention. It is a schematic sectional drawing for demonstrating the manufacturing method of the nitride semiconductor light-emitting device (LED element) 101 by the Example of this invention. It is a schematic sectional drawing for demonstrating the manufacturing method of the nitride semiconductor light-emitting device (LED element) 101 by the Example of this invention. It is a schematic sectional drawing for demonstrating the manufacturing method of the nitride semiconductor light-emitting device (LED element) 101 by the Example of this invention. It is a schematic sectional drawing for demonstrating the manufacturing method of the nitride semiconductor light-emitting device (LED element) 101 by the Example of this invention. It is a schematic sectional drawing for demonstrating the manufacturing method of the nitride semiconductor light-emitting device (LED element) 101 by the Example of this invention. It is a schematic sectional drawing for demonstrating the manufacturing method of the nitride semiconductor light-emitting device (LED element) 101 by the Example of this invention. It is a schematic sectional drawing for demonstrating the manufacturing method of the nitride semiconductor light-emitting device (LED element) 101 by the Example of this invention. It is a schematic sectional drawing showing the structure of the cap layer 53 by the comparative example 1 used for crack generation | occurrence | production evaluation experiment. It is a schematic sectional drawing showing the structure of the cap layer 55 by the comparative example 2 used for crack generation | occurrence | production evaluation experiment. It is a schematic sectional drawing showing the element structure of the flip chip type nitride semiconductor light emitting element (LED element) to which the Example of this invention is applied. It is a schematic sectional drawing showing the element structure of the nitride semiconductor light emitting element (LED element) of the junction down type to which the Example of this invention is applied.

  FIG. 1 is a schematic cross-sectional view showing an element structure of a nitride semiconductor light emitting element (LED element) 101 according to an embodiment of the present invention.

  The nitride semiconductor light emitting device (LED device) 101 includes, for example, an undoped GaN layer 21, an n-type GaN layer 22 doped with Si or the like, a strain relaxation layer 23 containing GaN / InGaN, and a multi-quantum made of a GaN / InGaN multilayer film. One of the GaN-based semiconductor layer (light-emitting portion) 2 and the GaN-based semiconductor layer (light-emitting portion) 2 including the active layer 24 having a well structure, the p-type AlGaN layer (cladding layer) 25 and the p-type GaN layer (contact layer) 26 The reflective electrode layer 4 composed of the Ni layer 41 and the Ag layer 42 formed on the main surface of the metal layer, covers the reflective electrode layer 4, and transparent oxide conductive layer (first cap layer) 51 as a diffusion preventing layer of Ag and metal A cap layer 5 composed of a stack of layers (second cap layers) 52, an n-side electrode (wiring electrode) 16 formed on the other main surface of the GaN-based semiconductor layer (light-emitting portion) 2, for example, Pt / Ti / A eutectic alloy layer of a eutectic layer 7 containing an eutectic material composed of i / Au / Pt / AuSn and an Au layer 6, and a silicon (Si) support substrate 10 bonded to the cap layer 5 through the eutectic alloy layer. It is comprised including.

  As shown in FIG. 1, in the embodiment of the present invention, the reflective electrode layer 4 including the Ag layer 42 is covered with a cap layer 5 to prevent Ag diffusion. In this embodiment, the cap layer 5 is configured by forming a stack of the oxide transparent conductive layer (first cap layer) 51 and the metal layer (second cap layer) 52 as one set, and forming two or more sets thereof. Yes.

  The oxide transparent conductive layer 51 is made of, for example, a transparent conductive film such as ITO, and is a microcrystalline or amorphous (low crystallinity) film with a small crystallite size to reduce thermal strain. It is preferable from the viewpoint. In this specification, “crystallite” means the largest group that can be regarded as a single crystal, and “crystallite having a small crystallite size” means that the crystallite size is X-ray diffraction. When measured by the method (Scherrer method), it refers to a crystal that is 500 Å or less.

  For example, in the case of ITO, the orientation direction of the crystal is easily oriented to <100> or <111>, and further, the orientation in those directions becomes stronger as the film thickness increases. Further, the orientation direction is conspicuous in the <100> direction in the sputtered film, and the <111> direction is conspicuous in the EB film. When the film thickness is between 100 and 1000 mm, these directions are not clear (not showing a sharp peak by X-ray diffraction) and are considered to be suitable for relaxation of thermal strain.

  The growth temperature of the oxide transparent conductive layer 51 is preferably set to 200 ° C. or less at which the crystallite size is small or amorphous (low crystallinity). For example, in the case of a sputtered film formed at a temperature of 200 ° C. or less, the size of the ITO crystallite is approximately 500 mm, and there is a tendency that the size is further reduced when the film is formed at a lower temperature.

  As a material for the oxide transparent conductive layer 51, an oxide transparent conductive film such as ZnO, AZO, or IZO can be used in addition to ITO. Since the temperature and film forming conditions for microcrystalline to amorphous differ depending on the material of the oxide transparent conductive film, it is necessary to set the crystallite to be small crystallite or amorphous.

  The oxide transparent conductive layer 51 preferably has a thickness of 100 mm or more per layer, and more preferably in the range of 100 to 1000 mm. If the film thickness is less than 100 mm, it is too thin to reduce the thermal strain of the metal layer 52. Moreover, when the film thickness is thicker than 1000 mm, the crystallinity of the oxide transparent conductive layer 51 is increased, and the force for relaxing the thermal strain is weakened. Furthermore, defects such as pinholes, which are defects of the transparent conductive film, are likely to occur. The transparent conductive film is randomly oriented at the time of initial nucleation, and tends to become crystal grains with uniform orientation as the film thickness increases. In this embodiment, the oxide transparent conductive layer 51 is made amorphous or microcrystalline with a low crystallinity of 100 to 1000 （(crystallite is 500 Å or less) so that thermal strain is easily relaxed.

  As described above, the oxide transparent conductive layer 51 has a function of relieving thermal strain generated by heat treatment, but may have a pinhole, and Ag migration may occur through the pinhole. It is done. Therefore, in this embodiment, the metal layer (second cap layer) 52 is formed so as to cover the oxide transparent conductive layer 51 to improve the diffusion preventing function.

  As a material for the metal layer 52, it is possible to use a metal such as Ti, Pt, TiN, an alloy, or a metal nitride in addition to TiW. The film thickness of the metal layer 52 is preferably equal to or greater than the film thickness of the oxide transparent conductive layer 51. It is considered that the upper limit of the film thickness is sufficient if it is about twice the thickness of the oxide transparent conductive layer 51. This is because the oxide transparent conductive layer 51 having low crystallinity is not high in surface flatness, and it is sufficient if the flatness can be relaxed.

  Sputtering, EB vapor deposition, etc. can be used as the method for forming the oxide transparent conductive layer 51 and the metal layer 52. When the film is formed by sputtering, film adhesion and coverage performance are higher, and Ag diffusion is performed. Excellent prevention function.

  For example, three sets of the oxide transparent conductive layer (first cap layer) 51 and the metal layer (second cap layer) 52 are formed as shown in FIG. The total thickness of the cap layer 5 is preferably larger than the thickness of the reflective electrode layer 4, and more preferably 1.5 times or more. The number of stacked layers may be one or more because the total thickness of the cap layer 5 is thicker than the thickness of the reflective electrode layer 4, but two or more sets are preferably formed.

  Even if a pinhole is generated in the oxide transparent conductive layer (first cap layer) 51, the two or more layers of the oxide transparent conductive layer 51 are overlapped so that the positions of the pinholes are hardly overlapped. This is because it is considered that the migration of Ag through the pinhole is prevented.

  The cap layer 5 is preferably configured so that the oxide transparent conductive layer 51 is always in contact with the reflective electrode layer 4. This is because the end face of the reflective electrode layer 4 is most likely to be strained. Therefore, an oxide transparent conductive layer 51 that works to alleviate thermal strain is disposed on the bottom surface so as to be in contact with the reflective electrode layer 4. This is to increase the effect.

  Further, by setting the oxide transparent conductive layer 51 as the first layer close to the reflective surface of the reflective electrode layer 4, a portion having a higher contact resistance than the reflective electrode layer 4 is formed around the reflective electrode layer 4, It is possible to form a region that does not flow electricity when energized but can serve as an energization path when a high voltage is applied. Thereby, the reliability (electrostatic withstand voltage) at the time of instantaneous high voltage application can be improved.

  In addition, when the present inventors actually measured the electrostatic withstand voltage of the LED element 101 according to the present example by a human body model (HBM) experimental method, 75 having an electrostatic withstand voltage of 1 kV or more. % Obtained. On the other hand, in the case of a TiW-only cap layer structure, no one having an electrostatic withstand voltage of 1 kV or more was obtained.

  As described above, the transparent conductive film 51 reduces the thermal strain applied to the metal layer 52 by forming the cap layer 5 in the laminated structure of the oxide transparent conductive layer 51 and the metal layer 52 made of metal, alloy or metal nitride. By carrying out, it becomes difficult to enter defects, such as a crack of the cap layer 5, and the migration of Ag is suppressed. Therefore, the characteristics and reliability of the element are improved.

  Hereinafter, a method for manufacturing a nitride semiconductor light emitting device (LED device) 101 according to an embodiment of the present invention will be described with reference to FIGS.

  First, as shown in FIG. 2, a sapphire substrate (growth substrate) 1 is prepared, thermal cleaning is performed, and the GaN buffer layer 20 is grown at a low temperature, for example, at 500 ° C. by MOCVD, and then the substrate temperature is raised to 1000 ° C. Allow to crystallize. Thereafter, the GaN-based semiconductor layer 2 is grown on the GaN buffer layer 20. For example, after putting the sapphire substrate 1 into the MOCVD apparatus and growing the buffer layer 20, an undoped GaN layer 21 and an n-type GaN layer 22 doped with Si or the like are grown at a growth temperature of 1000 ° C. Thereafter, the strain relaxation layer 23 containing GaN / InGaN is grown at a growth temperature of 730 ° C. Subsequently, as the active layer 24, for example, a multiple quantum well structure made of a GaN / InGaN multilayer film is grown at a growth temperature of 700.degree. Further, a p-type AlGaN layer (cladding layer) 25 and a p-type GaN layer (contact layer) 26 are sequentially grown on the active layer 24. The film thickness of the buffer layer 20 and the GaN-based semiconductor layer 2 is, for example, about 6 μm. The growth substrate is not limited to sapphire, but may be a GaN or SiC substrate.

  Subsequently, as shown in FIG. 3, a reflective electrode layer 4 is formed. For example, the Ni layer 41 is deposited by electron beam (EB) deposition in the order of about 5 mm and the Ag layer 42 in order of about 3000 mm. Next, a resist mask is formed in the size of the light emission pattern, and the reflective electrode is etched at 25 ° C. for 20 seconds with an etchant adjusted at a ratio of {nitric acid: water: acetic acid: phosphoric acid} = {1: 1: 8: 10}. Layer 4 is etched to the state shown in FIG. Thereafter, heat treatment is performed at 400 ° C. for 2 minutes in an atmosphere of a gas containing oxygen. The Ni layer 41 improves the adhesion of the Ag layer 42 to the p-type GaN layer 26 and has a function of a transparent electrode, and the Ag layer 42 has a function as a reflective electrode.

  Next, as illustrated in FIG. 5, the oxide transparent conductive layer (first cap layer) 51 and the metal layer (second cap layer) 52 covering the oxide transparent conductive layer (first cap layer) 51 are stacked. A cap layer 5 is formed so as to cover the reflective electrode layer 4.

The oxide transparent conductive layer (first cap layer) 51 is made of, for example, a transparent conductive film such as ITO, and is formed to cover the reflective electrode layer 4 with a sputtering apparatus at room temperature. The oxygen partial pressure is 2.5 × 10 ⁻² Pa and the power is 100 W. The film thickness is about 1000 mm. The oxide transparent conductive layer (ITO) 51 is a microcrystalline or amorphous (low crystallinity) film having a small crystallite size.

  The metal layer (second cap layer) 52 is made of, for example, a metal film such as TiW, and is formed to cover the oxide transparent conductive layer (first cap layer) 51 with a sputtering apparatus at room temperature. The argon partial pressure is 1 Pa and the power is 300 W. The film thickness is about 1000 mm.

  Subsequently, as shown in FIG. 6, the oxide transparent conductive layer (first cap layer) 51 and the metal layer (second cap layer) 52 are stacked in one set, and the stack is further repeated two sets, A cap layer 5 composed of a total of three sets of layers is formed. The total thickness of the cap layer 5 is about 6000 mm. A eutectic (Au) layer 6 made of Au having a thickness of about 2000 mm is formed so as to cover the laminated layer of the cap layer 5.

  Next, a Si substrate 10 having a eutectic layer 7 containing a eutectic material composed of Pt / Ti / Ni / Au / Pt / AuSn on its surface is prepared, and as shown in FIG. The crystal layer 7 is laminated and thermocompression-bonded (eutectic) at a pressure of 6 kN and a temperature of 330 to 350 ° C. in vacuum.

  Next, as shown in FIG. 8, the excimer laser is irradiated from the back surface (sapphire substrate side) of the sapphire substrate 1, the buffer layer 20 is decomposed, and the sapphire substrate 1 and the GaN-based semiconductor layer 2 are separated. The state shown in FIG. Ga generated by laser lift-off is removed with hot water or the like, and then surface-treated with hydrochloric acid. Any surface treatment can be used as long as it can etch a nitride semiconductor, and an acid such as phosphoric acid, sulfuric acid, KOH, or NaOH, or a chemical such as alkali can be used. The surface treatment may be performed by dry etching using Ar plasma or chlorine plasma, polishing, or the like.

  Thereafter, the GaN-based semiconductor layer 2 is patterned by an existing photolithography technique. Specifically, a photoresist is applied to the surface of the GaN-based semiconductor layer 2, exposed and developed, and unnecessary portions (exposed portions) of the GaN-based semiconductor layer 2 are removed by dry etching, so that adjacent GaN-based semiconductors A street portion is formed between the layers 2. Thereafter, the photoresist is removed with a remover.

Next, Ti / Al / Ti / Pt / Au are sequentially formed as the n-side electrode (wiring electrode) 16 to obtain the state shown in FIG. The electrode configuration used for the n-side electrode 16 preferably has a contact resistance of 1 × 10 ⁻⁴ Ωcm ² or less, and other materials may be used as long as the electrode configuration is commensurate with it. For example, the n-side electrode 16 has a planar shape such as a stripe having an area of about 5 to 15% of the total area of the main surface of the GaN-based semiconductor layer 2.

  Thus, the nitride semiconductor light emitting device 101 is completed. When a plurality of elements are manufactured from a single substrate, the elements are separated by breaking after scribing.

  In order to whiten the blue GaN light emitting element, a yellow phosphor is put in a resin for sealing and filling the light emitting element.

  The inventors have evaluated the occurrence of cracks at the stage where the nitride semiconductor light emitting device 101 according to this example was actually manufactured to the state shown in FIG. Moreover, what was actually shown in FIG.10 and FIG.11 as the comparative example 1 and the comparative example 2 was produced, and generation | occurrence | production evaluation of a crack was performed.

  As shown in FIG. 6, the semiconductor device according to this example used for evaluating the occurrence of cracks has a GaN-based semiconductor layer (light emitting portion) 2 formed on a growth substrate 1 and a reflective electrode layer 4 formed thereon. The cap layer 5 (three sets of the oxide transparent conductive layer 51 and the metal layer 52 is laminated) and the eutectic (Au) layer 6 are formed so as to cover the reflective electrode layer 4. .

  As shown in FIG. 10, in the semiconductor device according to Comparative Example 1, instead of the cap layer 5 according to this example, a cap layer 53 made of a single TiW film having a thickness of 6000 mm is formed, and a eutectic ( The Au) layer 6 is formed, and the semiconductor element according to the comparative example 2 has a Pt film 54 with a thickness of 1000 mm instead of the cap layer 5 according to this embodiment, as shown in FIG. This is a stage in which a stack of 1000 Ｔｉ TiW film 52 is made into one set, a cap layer 55 made of three sets is formed, and a eutectic (Au) layer 6 is formed thereon. .

  Evaluation of the occurrence of cracks was carried out by leaving the cap layer for 1 minute in nitric acid and forming a film if there was Ag erosion (nitric acid entered from the crack, Ag was etched and the Ag line was retracted). This was done by judging that there was cracking due to the stress of time. In this evaluation method, in Comparative Example 1 and Comparative Example 2, the occurrence of erosion was observed in almost the entire periphery, but the Ag erosion was hardly observed in the semiconductor element according to this example. Therefore, although cracks occurred in Comparative Examples 1 and 2, it is considered that no cracks occurred in this example.

  Moreover, after bonding with the support substrate 10 (state shown in FIG. 7), the occurrence of cracks was determined by photographic observation. In this photographic observation, it was determined that a crack had occurred if Ag protruded from the original Ag line. Also in this case, in Comparative Example 1 and Comparative Example 2, as shown in FIGS. 10 and 11, cracks CR were observed at the edge portions of the cap layers 53 and 55, but the edge of the cap layer 5 according to the present example. No cracks were observed in the part.

  The occurrence of cracks in the subsequent steps can be determined by Ag migration from the cracks and when the leakage occurs, the PL emission intensity decreases or Ag precipitates at the pn junction.

  As mentioned above, according to the Example of this invention, the cap layer 5 which covers the reflective electrode layer 4 was made into the laminated structure of the metal transparent layer 51 and the metal layer 52 which consists of a metal, an alloy, or a metal nitride. Thereby, the transparent conductive film 51 can relieve the thermal strain applied to the metal layer 52. Therefore, defects such as cracks in the cap layer 5 are difficult to enter, Ag migration is suppressed, and the characteristics and reliability of the element can be improved.

  Furthermore, the oxide transparent conductive layer 51 is made amorphous or microcrystalline with a low crystallinity of 100 to 1000 Å (crystallite is 500 Å or less), so that thermal strain can be easily reduced.

  Further, according to the embodiment of the present invention, the oxide transparent conductive layer 51 is the first layer in contact with the reflective electrode layer 4 so that the contact resistance around the reflective electrode layer 4 is higher than that of the reflective electrode layer 4. A region is formed. Therefore, it is possible to form a region that does not flow electricity during normal energization, but can serve as an energization path when a high voltage is applied. Thereby, the reliability (electrostatic withstand voltage) at the time of instantaneous high voltage application can be improved.

  In the above-described embodiment, a sapphire substrate is used as the growth substrate 1, but a GaN substrate, an SiC substrate, or the like can be used as the growth substrate. The material of the semiconductor layer 2 is not limited to GaN, and may be AlGaInP, ZnO, or the like.

  As mentioned above, although this invention was demonstrated along the Example and the modification, this invention is not limited to these. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

  For example, in the embodiment of the present invention, if the Ag layer 42 is included in the reflective electrode layer 4, a flip-chip type that does not remove the growth substrate 1 shown in FIG. 12 or a transparent substrate such as GaN or SiC as the growth substrate 1 shown in FIG. The present invention is also applicable to a junction down type using a conductive substrate.

DESCRIPTION OF SYMBOLS 1 ... Sapphire substrate, 2 ... GaN-type semiconductor layer (light emission part), 4 ... Reflective electrode layer, 5 ... Cap layer, 6 ..., 7 ... 10 ... Silicon (Si) substrate, 16 ... N side electrode (wiring electrode) 20 ... buffer layer, 21 ... undoped GaN layer, 22 ... Si-doped n-type GaN layer, 23 ... strain relaxation layer, 24 ... active layer, 25 ... p-type AlGaN layer (cladding layer), 26 ... p-type GaN layer ( Contact layer), 41 ... Ni layer, 42 ... Ag layer, 51 ... Oxide transparent conductive layer (first cap layer), 52 ... Metal layer (second cap layer), 53, 55 ... Cap layer, 54 ... Pt layer , 101... Nitride semiconductor light emitting device (LED device)

Claims (4)

A first conductivity type first semiconductor layer; an active layer formed on the first semiconductor layer; and a second conductivity type second semiconductor layer formed on the active layer. A semiconductor laminated structure;
A wiring electrode layer formed in contact with one of the first semiconductor layer or the second semiconductor layer;
A reflective electrode layer containing Ag formed in contact with the other of the first semiconductor layer or the second semiconductor layer where the wiring electrode layer is not formed;
A stack of a first cap layer made of a transparent conductive film formed so as to cover the reflective electrode layer and a second cap layer formed so as to cover the first cap layer and made of metal, an alloy, or a metal nitride is at least A cap layer containing two or more sets;
A semiconductor device having a support substrate bonded to the cap layer through a eutectic layer.   2. The semiconductor device according to claim 1, wherein the first cap layer has a thickness greater than 100 mm and equal to or less than 1000 mm. 3.   The semiconductor element according to claim 1, wherein the transparent conductive film is amorphous or microcrystalline with a crystallite size of 500 μm or less.   The semiconductor element according to claim 1, wherein the metal layer is made of a metal, an alloy, or a metal nitride.

Images