JP2014096539A - Ultraviolet light-emitting element, and light-emitting structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultraviolet light-emitting element in which light extraction efficiency is improved, and deterioration of underfill agent can be suppressed when it is flip-chip mounted.SOLUTION: An ultraviolet light-emitting element includes a multilayer semiconductor layer having an n-type group III nitride semiconductor layer, a luminous layer, and a p-type group III nitride semiconductor layer, in which a translucent positive electrode is formed on the p-type group III nitride semiconductor layer, a negative electrode is formed on the n-type group III nitride semiconductor layer, and the emission wavelength is 300 nm or less. The ultraviolet light-emitting element further includes a translucent insulation layer formed on a surface including the side face of the multilayer semiconductor layer on the side where the positive and negative electrodes are formed, excepting the upper surface exposed part of the translucent positive electrode and the upper surface exposed part of the negative electrode, and a metallic reflective layer formed on the translucent insulation layer and the upper surface exposed part of the translucent positive electrode.

Description

  The present invention relates to a novel ultraviolet light-emitting element suitable for flip-chip mounting and a novel light-emitting structure including the flip-chip mounted ultraviolet light-emitting element.

  A light emitting element made of a nitride semiconductor can emit light in the visible region to the deep ultraviolet region, and has various applications such as illumination, inspection measurement, ultraviolet curing, and sterilization. Light emitting structures having these light emitting elements are strongly desired to have high output and high reliability, and it is necessary to increase the size (or increase integration) of the elements and to secure resistance against large input power (heat generation).

  A flip-chip structure is an effective structure for increasing the output (or integration) and efficiency of LEDs. In this structure, a predetermined semiconductor layer is grown on a translucent substrate, a positive electrode and a negative electrode for current injection are formed on the opposite side of the substrate, and the substrate side is used as a light extraction surface. In the LED of the flip chip structure, since the light from the light emitting part is emitted from the translucent substrate without being blocked, high light extraction efficiency can be realized. In addition, heat can be easily transferred from the back surface of the LED chip to the mounting substrate side, and the wiring length can be shortened, which is optimal for high output and high integration.

  From these viewpoints, flip-chip mounting is generally widely used, and various studies have been made to achieve higher light extraction efficiency (light output) (see, for example, Patent Documents 1 and 2).

  Patent Document 1 specifically proposes the following light-emitting element. The structure has a laminated semiconductor layer in which an n-type group III nitride semiconductor layer, a light emitting layer, and a p-type group III nitride semiconductor layer are formed in this order on a translucent support substrate. And a negative electrode and a positive electrode are formed in the laminated semiconductor layer side with respect to a translucent support substrate. Furthermore, on the p-type group III nitride semiconductor layer, which is the uppermost layer of the laminated semiconductor layer, a translucent positive electrode made of ITO (indium tin oxide) and Ag (silver) formed on the translucent positive electrode ), Al, Rh (rhodium) and the like. This light emitting element is used as a flip chip type light emitting structure for extracting light from the supporting substrate side.

  According to such a light-emitting element (light-emitting structure), part of the light emitted from the light-emitting layer and traveling toward the positive electrode passes through the light-transmitting positive electrode made of ITO and is reflected by the metal reflective layer. Since it is taken out from the conductive support substrate side, the light output is improved.

  Patent Document 2 specifically proposes the following light emitting element. The structure has a laminated semiconductor layer in which an n-type group III nitride semiconductor layer, a light emitting layer, and a p-type group III nitride semiconductor layer are formed in this order on a translucent support substrate. Then, the negative electrode and the positive electrode are formed on the laminated semiconductor layer side with respect to the translucent substrate. Furthermore, it has a protective film which coat | covered the semiconductor layer surface except the upper surface exposed part of the positive electrode and negative electrode surface. In this light emitting element, the protective film has at least a three-layer structure of a first layer made of an insulating film, a metal reflective layer on the first layer, and a second layer made of an insulating film on the metal layer. This light-emitting element is also used as a flip-chip structure that extracts light from the support substrate side.

  According to such a light emitting element (light emitting structure), part of the light emitted from the light emitting layer and directed to the side surface of the laminated semiconductor layer is transmitted through the first layer of the protective film, reflected by the metal reflective layer, and transmitted. Since it is taken out from the optical support substrate side, the light output is improved.

  Various light-emitting elements having the above-described structure have been proposed, but in recent years, semiconductor light-emitting elements (ultraviolet light-emitting elements) that emit ultraviolet light using aluminum gallium nitride (hereinafter referred to as AlGaN) -based semiconductor materials have been actively developed. Has been. These ultraviolet light-emitting elements have an emission wavelength of 300 nm or less and are attracting attention as low-power consumption and long-life ultraviolet light sources that replace mercury lamps. There is also a need for light-emitting elements and devices with high output and high reliability. It has been.

  In addition to the above reasons, it is considered that the ultraviolet light emitting element is advantageous to have a flip chip type structure from the following points. In an AlGaN-based light emitting device, a p-type gallium nitride (hereinafter referred to as GaN) layer is used as a p-type contact layer in order to improve the contact property between the p-type group III semiconductor layer and the positive electrode layer. GaN has a band gap energy of 3.4 eV and has an absorption edge at a light wavelength of 365 nm. Therefore, it almost absorbs ultraviolet light. Therefore, in the ultraviolet light emitting element, if a GaN layer is present in the light traveling path, the light emission output is reduced by absorption. For this reason, it is considered that a flip chip structure in which the positive electrode and the negative electrode are arranged in one direction and the light is extracted from the support substrate side is advantageous in the ultraviolet light emitting element.

JP 2004-179347 A JP 2004-08050 A

  For this reason, the inventors of the present invention produced a light emitting structure described in Patent Documents 1 and 2 using an ultraviolet light emitting element, and found that there was room for improvement in the following points.

  When the light-emitting element described in Patent Document 1 is an ultraviolet light-emitting element, the metal reflective layer covers only a part of the surface of the p-type group III nitride semiconductor layer and is not covered with the metal reflective layer. Part of the light (ultraviolet light) traveling toward the side surface of the semiconductor layer is emitted to the outside as it is. In the flip-chip type light emitting device, an underfill agent made of resin is filled in the gap between the mounting substrate and the light emitting device for reinforcement after mounting. For this reason, in the structure described in Patent Document 1, a part of the ultraviolet light directed to the side surface of the laminated semiconductor layer is directly emitted to the outside and absorbed by the underfill agent, so that it does not contribute to light extraction. In addition, the underfill agent has a problem that the underfill agent deteriorates due to absorption of ultraviolet light.

  The structure described in Patent Document 2 is a structure in which the surface of the laminated semiconductor layer is covered with a protective film, but the upper surface exposed portion of the positive electrode is not covered with the protective film. Furthermore, Patent Document 2 only describes the use of platinum as the positive electrode. When this light emitting structure is applied to an ultraviolet light emitting device, the positive electrode has a film thickness of 700 nm, so that no light is transmitted through the electrode, the upper surface exposed portion is not covered with a protective film, and the positive electrode is free from ultraviolet light. There is a problem that most of the light emitted from the light emitting layer and directed to the positive electrode is absorbed by the positive electrode and does not contribute to light extraction because platinum having a low reflectance is used.

  Accordingly, the object of the present invention is made in view of the above-mentioned problems of the prior art, and emits light (ultraviolet light) emitted from the light emitting layer and directed toward the positive electrode, which is the direction opposite to the light extraction direction. An object of the present invention is to provide a light-emitting element with a high light-emission output with improved light extraction efficiency, which has a structure that efficiently reflects light. In addition, after flip-chip mounting, even when a resin underfill agent is filled in the gap between the mounting substrate and the resin, ultraviolet light is not absorbed by the resin, and deterioration of the resin can be suppressed. It is in providing a light-emitting element.

  In order to solve the above problems, the present inventors have conducted intensive studies. As a result, it has been found that the above-mentioned problems can be solved by making the ultraviolet light emitting device have the following structure, and the present invention has been completed.

That is, the first aspect of the present invention is a translucent substrate, an n-type group III nitride semiconductor layer formed on the translucent substrate, and an n-type group III nitride semiconductor layer layer. A laminated semiconductor layer having a light emitting layer and a p-type group III nitride semiconductor layer formed on the light emitting layer;
A translucent positive electrode is formed on the p-type group III nitride semiconductor layer,
A negative electrode is formed on the n-type group III nitride semiconductor layer exposed by removing a part of the n-type group III nitride semiconductor layer, the light emitting layer, and the p-type group III nitride semiconductor layer. In an ultraviolet light emitting device having an emission wavelength of 300 nm or less,
The surface of the laminated semiconductor layer on the side where the positive electrode is formed from the surface on which the negative electrode is formed, and the laminated semiconductor layer excluding the upper surface exposed portion of the translucent positive electrode and the upper surface exposed portion of the negative electrode The light-emitting insulating layer has a light-transmitting insulating layer on its surface, and has a metal reflective layer on the light-transmitting insulating layer and on the exposed upper surface of the light-transmitting positive electrode.

  Further, the second aspect of the present invention comprises a mounting base material and the ultraviolet light emitting element, the ultraviolet light emitting element is flip-chip mounted on the upper surface of the mounting base material, and between the mounting base material and the ultraviolet light emitting element. It is a light emitting structure formed by filling a resin in the gap.

  The ultraviolet light emitting device of the present invention is not a metal reflective layer formed only on the upper surface exposed portion of the positive electrode, but the surface of the laminated semiconductor layer on the positive electrode side from the surface on which the negative electrode is formed. In addition, a light-transmitting insulating layer is formed in all regions except the exposed portion of the upper surface of the negative electrode, and a metal reflective layer is formed on the light-transmitting insulating layer. Ultraviolet light emitted from the light-emitting layer with such a structure toward the translucent positive electrode is reflected internally by the metal reflection layer and can be extracted from the substrate side, and light extraction efficiency is higher than that of known techniques. Can be increased.

  Further, by adjusting the refractive index of the light-transmitting insulating layer, part of the ultraviolet light traveling from the stacked semiconductor layer to the light-transmitting insulating layer is totally reflected at the interface between the stacked semiconductor layer and the light-transmitting insulating layer. Therefore, the ultraviolet light which goes to the substrate side increases. Thus, by covering the positive electrode and the negative electrode side with the metal reflection layer and the translucent insulating layer, leakage of light to the outside can be suppressed, and a high light emission output can be obtained. Further, in the above structure, ultraviolet light does not leak to the outside of the electrode side. Therefore, even if a resin underfill agent is filled between the substrate and the chip after flip chip mounting, the underfill agent is deteriorated. Can be prevented. As a result, it is possible to improve the heat dissipation and mechanical strength of the light emitting structure including the ultraviolet light emitting element, thereby extending the life.

It is a longitudinal cross-sectional view which shows the light emitting structure of the form in Example 1 of this invention. It is a longitudinal cross-sectional view which shows the light emitting element of the form in Example 1 of this invention. It is a longitudinal cross-sectional view which shows the reference light emitting element in the Example of this invention. It is a longitudinal cross-sectional view which shows the light emitting element of the form in the comparative example 1 of this invention. It is a longitudinal cross-sectional view which shows the light emitting element of the form in the comparative example 2 of this invention.

  Hereinafter, embodiments of the invention will be described with reference to the drawings as appropriate. However, the light emitting element described below is for embodying the technical idea of the present invention, and the present invention is not limited to the following. In particular, the dimensions, materials, shapes, relative arrangements, and the like of the components described below are not intended to limit the scope of the present invention only to specific examples unless otherwise specified. Only. Note that the size, positional relationship, and the like of the members shown in each drawing may be exaggerated for clarity of explanation. In addition, each element constituting the present invention may be configured such that a plurality of elements are constituted by the same member and the plurality of elements are shared by one member, and conversely, the function of one member is constituted by a plurality of members. It can also be realized by sharing. Furthermore, each embodiment described below can also be applied by appropriately combining the components and the like unless otherwise specified.

  The light emitting device of the present invention emits ultraviolet light having a wavelength of 300 nm or less. Since the present invention is an ultraviolet light emitting device having an emission wavelength of 300 nm or less, it exhibits excellent effects. In other words, ultraviolet light alters and degrades organic polymer materials such as resins, but according to the light emitting structure of the present invention, it is the main component of the underfill agent while improving the light extraction efficiency. It is possible to prevent the resin from being exposed to ultraviolet light, and to suppress deterioration thereof. Therefore, the present invention can be suitably applied to a light emitting element having an emission wavelength of 300 nm or less. The lower limit of the emission wavelength is not particularly limited, but is 100 nm, and particularly 200 nm when a gallium aluminum nitride-based material is used.

  In the present invention, the refractive index, the transmittance, and the reflectance of each layer, film, and translucent positive electrode forming the ultraviolet light emitting element are based on a wavelength of 265 nm. This is because DNA has a maximum absorption around a wavelength of 265 nm, and this wavelength is most suitable for sterilization and has high industrial utility value. Hereinafter, when the refractive index, the transmittance, and the reflectance are simply used, the values for light with a wavelength of 265 nm are indicated.

  Next, each layer and film of the ultraviolet light emitting device of the present invention will be described.

<Translucent substrate>
The substrate used in the present invention is not particularly limited as long as the group III nitride semiconductor crystal can be epitaxially grown on the surface and transmits ultraviolet light. For example, sapphire, SiC (silicon carbide), AlN (aluminum nitride), Si (silicon) and the like can be mentioned. Among them, it is desirable to use an AlN single crystal substrate having a c-plane as a main surface.

  The translucent substrate is a translucent substrate that transmits light having a wavelength of 265 nm. Therefore, the transmittance of the light-transmitting substrate with respect to light having a wavelength of 265 nm is preferably as high as possible, but is preferably 50% or more, and more preferably 60% or more. The upper limit of the transmittance of the translucent substrate is most preferably 100%, but 80% is the upper limit in consideration of industrial production. Note that the translucency of the translucent substrate can be adjusted by the material, the thickness of the substrate, the crystallinity, and the impurity content.

  Moreover, the thickness of this translucent board | substrate is although it does not restrict | limit in particular, The thickness of a translucent board | substrate is 30-150 micrometers, Preferably it is 50-100 micrometers. When the thickness of the translucent substrate is 30 to 150 μm, the transmittance can be improved and the productivity can be improved. In addition, the thickness of this translucent substrate may satisfy the said range before the laminated semiconductor layer is grown. Moreover, after manufacturing an ultraviolet light emitting element, you may make it satisfy the thickness of the said range by grind | polishing last. This translucent substrate is the translucent substrate 1 in FIG. This will be described below with reference to FIG.

<Laminated semiconductor layer>
The laminated semiconductor layer (the laminated semiconductor 7 in FIG. 2) is made of a group III nitride semiconductor, and is formed on the translucent substrate 1 as shown in FIG. The light emitting layer 3 and the p-type group III nitride semiconductor layer 6 (a layer comprising the p-type cladding layer 4 and the p-type contact layer 5) are laminated in this order. Each layer will be described.

<N-type group III nitride semiconductor layer>
The n-type group III nitride semiconductor layer 2 is AlxInyGazN (x, y, z are rational numbers satisfying 0.05 <x ≦ 1.0, 0 ≦ y ≦ 0.95, 0 ≦ z <0.95, x + y + z = 1.0), and preferably contains an n-type impurity.

Although it does not specifically limit as an impurity, SI, Ge, Sn, etc. are mentioned, Preferably SI, Ge is mentioned. The concentration of the n-type impurity is 1.0 × 10 ¹⁷ / cm ³ or more and 1.0 × 10 ²⁰ / cm ³ or less, and preferably from 1.0 × 10 ¹⁸ / cm ³ or more from the viewpoints of crystallinity and contact characteristics. It is 1.0 × 10 ¹⁹ cm ³ or less. Such an n-type group III nitride semiconductor layer 2 can be manufactured by MOCVD.

  The refractive index of the n-type group III nitride semiconductor layer 2 is not particularly limited, but is preferably higher than the refractive index of the translucent insulating layer Ins described in detail below. The difference between the refractive index of the n-type group III nitride semiconductor layer 2 and the refractive index of the translucent insulating layer Ins is not particularly limited, but is preferably 0.5 to 2.0. The absolute value of the refractive index is not particularly limited, but is 1.5 to 3.0. This refractive index may be adjusted by the composition of the n-type group III nitride semiconductor layer 2 or the like.

  The thickness of the n-type group III nitride semiconductor layer 2 is not less than 100 nm and not more than 10,000 nm. From both viewpoints of crystallinity and conductivity of the n-type group III nitride semiconductor layer 2, the thickness is preferably 500 nm or more and 3000 nm or less.

  Although not shown in FIG. 2, a group III nitride forming AlN or an n-type group III nitride semiconductor layer 2 between the substrate 1 and the n-type group III nitride semiconductor layer 2 is used. And may have a buffer layer of the same composition.

<Light emitting layer>
The light emitting layer 3 has a multiple quantum well structure. AlxInyGazN (x, y, z are rational numbers satisfying 0.05 <x ≦ 1.0, 0 ≦ y ≦ 0.95, 0 ≦ z <0.95, and x + y + z = 1.0). Well layer and AlxInyGazN (x, y, z are 0.05 <x ≦ 1.0, 0 ≦ y ≦ 0.95, 0 ≦ z <0.95) having a larger band gap energy than the well layer. It is made up of a laminated structure of barrier layers composed of a rational number that satisfies x + y + z = 1.0).

  The film thickness of the well layer is 1 nm or more, preferably 2 nm or more, and the upper limit is 100 nm.

The thickness of the barrier layer is 1 nm or more, preferably 2 nm or more, and the upper limit is 1 μm. The light emitting layer may have a multiple quantum well structure or a single quantum well structure.
Such a light emitting layer 3 can be manufactured by the MOCVD method.

<P-type group III nitride semiconductor layer>
The p-type group III nitride semiconductor layer 6 includes a p-type cladding layer 4 and a p-type contact layer 5.

  The p-type cladding layer 4 is AlxInyGazN (x, y, z are rational numbers satisfying 0.05 <x ≦ 1.0, 0 ≦ y ≦ 0.95, 0 ≦ z <0.95, and x + y + z = 1. 0).

As an impurity of the p-type cladding layer 4, Mg is preferably exemplified. The doping concentration of Mg is 1.0 × 10 ¹⁷ cm ⁻³ or more, preferably 1.0 × 10 ¹⁷ cm ⁻³ or more. The film thickness of the p-type cladding layer 4 is 5 nm to 1000 nm, preferably 10 nm to 50 nm.

The p-type contact layer 5 is AlxInyGazN (x, y, z are rational numbers satisfying 0 <x ≦ 1.0, 0 ≦ y ≦ 0.1, 0 ≦ z <1.0, and x + y + z = 1.0) Is). As the impurity of the p-type contact layer 5, Mg is preferably mentioned as in the p-type cladding layer 4. The doping concentration of Mg is 1.0 × 10 ¹⁷ cm ⁻³ or more. The film thickness of the p-type contact layer 5 is 1 nm or more and 50 nm or less, preferably 5 nm or more and 30 nm or less from the viewpoint of ultraviolet light transmittance and p-type contact characteristics.

From the viewpoint of contact characteristics, the composition of the p-type contact layer 5 is preferably GaN. Hereinafter, the case where the p-type contact layer 5 is a GaN layer will be described. Since the GaN layer has an absorption edge at a wavelength of 365 nm, light with a wavelength of 265 nm hardly transmits when the film thickness of the GaN layer is large. The relationship between the film thickness and the transmittance is expressed by T = exp (−αt), where T is the transmittance, α is the absorption coefficient (cm ⁻³ ), and t is the film thickness (cm). Rate is obtained. In GaN, α = 1.8 × 10 ⁵ (cm ⁻¹ ) at 265 nm. However, if the thickness of the GaN layer is too small, the current does not spread sufficiently, and the electrical characteristics of the light emitting element may be deteriorated.

  In order to improve the light extraction efficiency of the p-type group III nitride semiconductor layer 6, it is preferable that the transmittance of the p-type group III nitride semiconductor layer 6 with respect to light having a wavelength of 265 nm is 50% or more. More preferably, the transmittance is 60% or more. The upper limit of the transmittance is not particularly limited, but it is 95% in consideration of production stability.

  The transmittance of the p-type group III nitride semiconductor layer 6 is mostly determined by the p-GaN layer (p-type contact layer 5). Therefore, the thickness of the p-GaN layer (p-type contact layer 5) is preferably 1 nm or more and 39 nm or less, and more preferably 1 nm or more and 29 nm or less.

  Such a p-type group III nitride semiconductor layer can be manufactured by MOCVD.

<Negative electrode>
The negative electrode P <b> 1 is formed on the exposed surface of the n-type group III nitride semiconductor layer 2. The exposed surface of the n-type group III nitride semiconductor layer 2 is formed by means such as etching. As an etching method, dry etching such as reactive ion etching and inductively coupled plasma etching is preferably used. After the exposed surface of the n-type group III semiconductor layer 2 is formed, it is preferable to perform a surface treatment with an acid or alkali solution in order to remove etching damage. Thereafter, an ohmic negative electrode is formed on the exposed surface of the n-type group III nitride semiconductor layer 2.

  Electrode patterning can be performed using a lift-off method. In the lift-off method, a photoresist is applied to the surface on which an electrode is to be formed, and then irradiated with ultraviolet rays using a UV exposure machine equipped with a photomask, and then immersed in a developing solution to dissolve the exposed photoresist to form a desired pattern. The electrode metal is deposited on the patterned photoresist, the photoresist is dissolved with a stripping solution, and a pattern of the electrode metal is formed. Other patterning methods include the following methods. An electrode metal film is formed on the electrode formation surface, and after applying a photoresist, the photoresist is patterned through an exposure and development process. Thereafter, the electrode metal is patterned by dry etching or wet etching using the photoresist as a mask, and the photoresist is dissolved by a stripping solution. The lift-off method is preferably used because the process is simpler than the patterning method.

  Examples of the method for depositing the negative electrode metal include vacuum vapor deposition, sputtering, and chemical vapor deposition, but vacuum vapor deposition is preferable in order to eliminate impurities in the electrode metal. Various materials can be used for the negative electrode, but a known material can be selected. For example, Ti, Al, Rh, Cr, In, Ni, Pt, Au, etc. can be used. Among these, Ti, Al, Rh, Cr, Ni, and Au are preferably used. These negative electrodes may be a single layer having a layer containing an alloy or an oxide of these metals, or a multilayer structure, and a preferable combination from the viewpoint of ohmic properties and reflectivity is Ti, Al, and Au.

  The thickness is not particularly limited, but is preferably 2 nm or more in consideration of production stability, and the upper limit is 2 μm. After depositing the negative electrode metal, heat treatment is preferably performed at a temperature of 300 ° C. to 1100 ° C. for 30 seconds to 3 minutes in order to improve contact with the n-type semiconductor layer. About the temperature and time of heat processing, what is necessary is just to implement on optimal conditions suitably according to the metal seed | species and film thickness of a negative electrode.

<Translucent positive electrode>
The translucent positive electrode P2a is formed on the p-type contact layer 5. This positive electrode P2a must be transparent to light having a wavelength of 265 nm. Specifically, the transmittance is 60% or more, preferably 70% or more, with respect to 265 nm light. Although not particularly limited, the upper limit is preferably 100%, and industrially preferably 90% or more.

  As for the patterning of the positive electrode P2a, it is preferable to use a lift-off method similarly to the patterning of the negative electrode P1. The metal material used for the positive electrode can be selected from known materials, although various examples are available. For example, Ni, Cr, Au, Mg, Zn, and Pd can be used. The translucent positive electrode may be a single layer having a layer containing an alloy or oxide of these metals, or a multilayer structure. A preferable combination is Ni / Au.

  Since the positive electrode P2a must have translucency, the smaller the film thickness, the better. Specifically, it is 10 nm or less, more preferably 5 nm or less, and the lower limit is 0.5 nm.

  The method for depositing the metal of the positive electrode P2a includes vacuum deposition, sputtering, chemical vapor deposition and the like, as with the formation of the negative electrode P1, but vacuum deposition is preferred in order to eliminate impurities in the electrode metal. After depositing the positive electrode metal, heat treatment is preferably performed at a temperature of 200 ° C. to 800 ° C. for 30 seconds to 3 minutes in order to improve the contact property with the p-type contact layer 5. About the temperature and time of heat processing, what is necessary is just to implement on suitable conditions suitably according to the metal seed | species and film thickness of positive electrode P2a.

<Translucent insulating layer>
As shown in FIG. 2, the translucent insulating layer Ins is a surface of the laminated semiconductor layer 7 on the side where the translucent positive electrode P2a is formed from the surface on which the negative electrode P1 is formed, and the translucent positive electrode It is formed at least on the surface of the laminated semiconductor layer 7 excluding the upper surface exposed portion of P2a and the upper surface exposed portion of the negative electrode P1. That is, as shown in FIG. 2, the translucency is obtained from the upper surface of the n-type semiconductor layer 2, the upper surface of the p-type contact layer 5, the side surface of the p-type semiconductor layer 6, the side surface of the light emitting layer 3, and the surface on which the negative electrode P1 is formed. At least the translucent insulating layer Ins is formed on the side surface of the n-type semiconductor layer 2 on the side where the positive electrode P2a is formed (however, the upper surface exposed portion of the translucent positive electrode P2a and the upper surface exposed portion of the negative electrode P1) Except). Therefore, although not shown, the light-transmitting insulating layer may be formed on the side surface of the n-type group III nitride semiconductor layer on the light-transmitting substrate side and / or on the side surface of the light-transmitting substrate.

  The translucent insulating layer Ins needs to transmit light having a wavelength of 265 nm, and the transmittance is preferably 70% or more. The upper limit of the transmittance is 100%. This transmittance can be adjusted by the material and thickness of the translucent insulating layer Ins.

  The patterning of the light-transmitting insulating layer Ins is preferably performed by a lift-off method, similarly to the patterning of the negative electrode P1 and the light-transmitting positive electrode P2a.

The material of the translucent insulating layer Ins is not particularly limited as long as it is a material having translucency with respect to ultraviolet light (wavelength: 250 nm to 350 nm). Specific examples include alkali metal or alkaline earth metal fluorides, silicon dioxide (SiO ₂ ), and aluminum oxide. Among them, it is preferable to use an alkali metal or alkaline earth metal fluoride because the refractive index in the ultraviolet region is small, and it is particularly preferable to use calcium fluoride (CaF) or magnesium fluoride (MgF). preferable.

  Examples of the method for depositing the light-transmitting insulating layer Ins include vacuum vapor deposition, sputtering, chemical vapor deposition, and the like. A suitable method may be used as appropriate depending on the material to be deposited.

  The film thickness of the translucent insulating layer Ins is 30 nm to 500 nm, preferably 50 nm to 200 nm. When the film thickness is 30 to 500 nm, it is possible to prevent deterioration of the coverage at the step portion and increase the transmittance of ultraviolet light.

  The refractive index of the translucent insulating layer Ins is preferably lower than the refractive index of the n-type group III nitride semiconductor layer 2. Since the refractive index of the translucent insulating layer Ins is lower than the refractive index of the n-type group III nitride semiconductor layer 2, all of the light traveling from the n-type group III nitride semiconductor layer 2 toward the translucent insulating layer Ins is obtained. Reflection can occur. As described above, the difference in refractive index is preferably 0.5 to 2.0. The absolute value of the refractive index of the translucent insulating Ins film is not particularly limited, but is preferably 1.7 or less, and particularly preferably 1.5 or less. This refractive index can be adjusted by the material of the translucent insulating layer Ins.

<Metal reflective layer>
As shown in FIG. 2, the metal reflection layer R is disposed so as to cover the entire surface of the translucent insulating layer Ins except for the exposed portion of the upper surface of the negative electrode. However, it is necessary to arrange so as not to contact the upper surface exposed portion of the negative electrode P1.

  The metal reflection layer R also serves as a bonding electrode for the translucent positive electrode P2a. The patterning of the metal reflective layer R is preferably performed by a lift-off method, similarly to the patterning of the negative electrode P1, the light transmissive positive electrode P2a, and the light transmissive insulating layer Ins.

  For the metal reflective layer, it is desirable to use a material having a high reflectivity of ultraviolet light, and examples thereof include Al, Rh, Si, Ge, Cr, etc. Among them, it is preferable to use Al having the highest reflectivity in the ultraviolet light wavelength region. More preferred. In order to improve the adhesion, an active metal such as TI or V may be used for the first layer to form a multilayer film.

  The metal reflection layer R can be deposited by vacuum evaporation, sputtering, chemical vapor deposition, etc., as with the negative electrode P1, the translucent positive electrode P2a, and the translucent insulating layer Ins, depending on the material to be deposited. A suitable method may be used as appropriate.

  The thickness of the metal reflective layer R is 100 to 500 nm, preferably 200 nm to 400 nm. When the film thickness of the metal reflective layer R is 100 to 500 nm, it is possible to prevent light transmission and increase the reflectance, and to improve productivity.

  The reflectivity of the metal reflection layer R is preferably 70% or more with respect to the wavelength of light having a wavelength of 265 nm. The upper limit of the reflectance is not particularly limited, but is 100%, and particularly 95% in consideration of industrial production.

<About processing of light emitting element>
After manufacturing the ultraviolet light emitting element having the above-described configuration, the transmittance of the substrate 1 can be improved by grinding or polishing the lower surface of the substrate 1 to reduce the thickness of the substrate 1. Thereafter, element isolation is performed by appropriately using a known element isolation method such as scribing, dicing, or laser fusing.

  The light emitting device manufactured by the above method is used by flip-chip mounting on a mounting substrate. Next, the mounting substrate will be described.

<Base material for mounting>
As shown in FIG. 1, the mounting base M is disposed so as to face the surface having the electrodes of the ultraviolet light emitting element. The translucent positive electrode P2a and the negative electrode P1 of the ultraviolet light-emitting element are electrically connected to the positive electrode E1 and the negative electrode E2 of the mounting base M through an electrically independent solder B, respectively. The mounting base M is preferably made of a highly thermally conductive material such as AlN or SiC from the viewpoint of heat dissipation.

  Various aligners can be used for bonding the mounting substrate M and the ultraviolet light emitting element, and a general reflow process is suitable. The ultraviolet light emitting element is preferably provided with an overcoat layer with Au having a high affinity for solder as the outermost surface.

<Underfill agent>
The underfill agent U is filled in the gap between the ultraviolet light emitting element and the mounting substrate M as shown in FIG. In general, an epoxy resin and a filler are used. As an alternative to the epoxy resin, one made of a silicone resin, a phenol resin, a silicone resin, a polyimide resin, or the like may be used. For filling, a side fill method utilizing capillary action is suitable. For dropping, a dispenser and needle, or a micropipette may be used as appropriate. Although the amount of dripping differs depending on the chip size, when the underfill agent U covers the side surface of the ultraviolet light emitting element, the light output is expected to be reduced by the absorption of the ultraviolet light of the underfill agent U. It is desirable that the amount be the minimum necessary to fill the voids of the substrate M. In order to prevent generation of voids and formation of unfilled regions, those having a low viscosity before curing are preferred, specifically 10 Pa · s or less, preferably 5 Pa · s or less. In order to prevent peeling due to stress caused by the difference in thermal expansion coefficient between the mounting substrate M, the ultraviolet light emitting element, and the underfill agent U, those having a low thermal expansion are preferable, and the linear expansion coefficient is 30 ppm / ° C. or less (at the glass transition temperature or lower). Are preferred. In general, since the linear expansion coefficient increases above the glass transition temperature, those having a high glass transition temperature are preferred. The elastic modulus is generally 10 GPa or less, but a lower one is more suitable. Moreover, in order to promote the heat transfer from the light emitting element to the mounting substrate M, those having high thermal conductivity are preferable, and those containing an insulating filler such as AlN, MgO, alumina, silica and the like are preferable.

  Next, a more specific embodiment will be described. First, in order to clarify the effect of the present invention, a reference light emitting structure to be used as a reference was manufactured as follows.

(Reference light-emitting structure (I))
Reference light-emitting element (I) shown in FIG. 5 having no metal reflection layer R (p-GaN layer thickness (p-type contact layer thickness) 23 nm, transmittance 66.1%: (p-type III group semiconductor layer) Transmittance)) was prepared. In addition, this reference light emitting device (I) has a Ni / Au (20 nm / 50 nm) layer as a positive electrode P and a Ti / Al / Au (20 nm / 200 nm / 5 nm) layer as a negative electrode. . The n-type semiconductor nitride layer of the reference light emitting device (I) had a refractive index of 2.4. This reference light-emitting element (I) was bonded to a mounting substrate, and a reference light-emitting structure (I) in the case where the resin (underfill agent) was not filled was produced. The light output of this reference light emitting structure (I) was measured with an integrating sphere. Hereinafter, the value of the light output is set to 1.000 so that the value of the light output of the reference light emitting structure (I) becomes a reference. This reference light emitting structure (I) is not practical because it does not use an underfill agent.

(Reference light emitting structure (II))
Next, in the production of the reference light emitting structure (I), a reference light emitting structure (II) was produced by performing the same operation except that the underfill agent was filled. This underfill agent contains a resin component containing bisphenol A type liquid epoxy resin and bisphenol F type liquid epoxy resin, filler components such as silicon dioxide and carbon black (about 50% by mass), and a trace amount of additives. (The viscosity of this underfill agent was 10 Pa · s, and the glass transition point was 135 ° C.). In the reference light emitting structure (II) filled with the underfill agent, the light output was 0.400 (relative value: relative value to the light output of the reference light emitting structure (I)).

(Verification of reference optical structure (II))
The light output of the reference light emitting structure (II) was reduced to 40% of the light output of the reference light emitting structure (I). The light output decreased because the underfill agent covering the side surface of the ultraviolet light emitting element absorbed the light. This indicates that the proportion of light emitted from the light emitting layer that passes through the surface of the laminated semiconductor layer on the side where the positive electrode is formed from the surface where the negative electrode is formed is 60%. . In the reference light-emitting structure (II), the positive electrode (Ni / Au: 20 nm / 50 nm) has a reflectance of 43.4% (Ni reflectance (43.4%) is used) and a transmittance of 0%. Since the transmittance of the p-GaN layer (23 nm) is 66.1%, light passing through the light extraction surface (lower surface) from the light emitting layer toward the translucent substrate is measured. It can be estimated that the proportion is 84% (relative value is 0.40 × 84% = 0.336). This 84% is a value calculated as follows. First, when the light output from the light emitting layer toward the light transmissive substrate is t, the light output from the light emitting layer toward the positive electrode and reflected and extracted from the light transmissive substrate side is t × 0.661 × 0. 434 × 0.661. Since the light output of the reference light emitting structure (II) is 0.40,
0.400 = t + t × 0.661 × 0.434 × 0.661 can be considered. When t is obtained from this equation, 0.34 is obtained, and 0.336 / 0.400 = 84% can be obtained. On the other hand, the proportion of the light output from the light-emitting layer toward the positive electrode side and extracted from the translucent substrate side by reflection is 16% (relative value is 0.400 × 16% = 0.064) in the measured light output. It can be estimated that there is.

  However, in the above calculation, light absorption in the laminated semiconductor layer other than the p-GaN layer (p-type contact layer) is small and ignored, and reflection between each layer is not taken into consideration.

(Verification of comparative light emitting structure (I))
As shown in FIG. 4, a transparent insulating layer Ins (SiO ₂ : 400 μm, transmittance 90%, refractive index 1.50) is formed on the surface of the laminated semiconductor excluding the upper surface exposed portion of the positive electrode and the upper surface exposed portion of the negative electrode. The comparative light-emitting structure (I) composed of the comparative light-emitting element (I) on which the metal reflection layer R (Ti / Al / Au: 1 nm / 250 nm / 5 nm, reflectance 77.5%) was formed was verified. This comparative light-emitting element (I) is the same as the reference light-emitting element (I) except that a translucent insulating layer and a metal reflective layer are formed at the locations shown in FIG. This comparative light emitting element structure (I) is obtained by bonding the comparative light emitting element (I) to the same mounting substrate as that of the reference light emitting structure (II) and filling the same underfill agent.

  From the measurement results of the reference light emitting structures (I) and (II), 60% (relative value 0.6) of the light emitted from the light emitting layer passes through the interface between the semiconductor and the translucent insulating layer. From the transmittance of the light-transmitting insulating layer Ins and the reflectance of the metal reflecting layer R, 62.8% (90% × 77.5% × 90% = 62) of the light incident on the light-transmitting insulating layer from the semiconductor side. .8%) re-enters the semiconductor. If all the re-incident light is taken out, the comparative light emitting structure (I) is 0.377 (0.6 × 62.8% = 0.377) than the relative value of the reference light emitting structure (II). The light output of the comparative light emitting structure (I) can be estimated to be 0.777 (relative value 0.400 + 0.377).

  In the comparative light emitting structure (I), even when Pt (reflectance 39.6%) is used as the positive electrode, the light output does not change because the difference in reflectance from Ni (reflectance 43.4%) is small. it is conceivable that.

(Verification of comparative light emitting structure (II))
As shown in FIG. 5, the positive electrode is a translucent positive electrode P2a (Ni / Au: 2 nm / 2 nm, transmittance 85.1%), and the metal reflective layer R (Ti / Al / Au: 1 nm / 250 nm / 5 nm, reflectance 77.5%) The comparative light emitting structure (II) composed of the comparative light emitting element (II) was verified. This comparative light-emitting element (II) is the same as the reference light-emitting element (I) except that the translucent positive electrode P2a and the metal reflective layer R are provided only on the translucent positive electrode. This comparative light emitting element structure (II) is obtained by bonding the comparative light emitting element (II) to the same mounting substrate as that of the reference light emitting structure (II) and filling the same underfill agent.

  The reflectance of the positive electrode of the reference light emitting structure (II) is 43.4%, whereas the reflectance of the structure in which the transparent positive electrode P2a and the metal reflective layer R are stacked is 56.0%. (85.1% × 77.5% × 85.1% = 56.0%: However, for the sake of simplicity, the reflection at the transparent positive electrode P2a is not considered). Therefore, among the light emitted from the light emitting layer, the light emitted to the positive electrode side, reflected by the positive electrode and emitted to the light extraction side is a relative value of 0.064 to 0. 0 of the reference light emitting structure (II). 083 (0.064 × 56.0% / 43.4% = 0.083). Thereby, the light output of the comparative light emitting structure (II) can be estimated to be 0.419 (relative value 0.336 + 0.083).

(Verification of the implementation light-emitting structure (I))
The implementation light emitting structure (I) using the implementation light emitting element (I) which has the translucent positive electrode P2a, the translucent insulating layer Ins, and the metal reflective layer R as shown in FIG. 2 was verified. The light-emitting element (I) uses a translucent positive electrode P2a (Ni / Au: 2 nm / 2 nm, transmittance 85.1%), and a translucent insulating layer Ins (SiO ₂ : 400 μm, transmittance 90). %, Refractive index 1.50) Same as the reference light emitting element (I) except that a metal reflective layer R (Ti / Al / Au: 1 nm / 250 nm / 5 nm, reflectance 77.5%) is provided as shown in FIG. belongs to. This working optical element structure (I) is obtained by bonding the working light emitting element (I) to the same mounting substrate as that of the reference light emitting structure (II) and filling the same underfill agent.

  Similar to the comparative light emitting structure (I), 62.8% (relative value 0.377) of the light incident on the translucent insulating layer from the semiconductor side is obtained by the translucent insulating layer Ins and the metal reflecting layer R. It re-enters the semiconductor and is taken out from the substrate side. Similarly to the comparative light emitting structure (II), among the light emitted from the light emitting layer, the light emitted to the positive electrode side, reflected by the positive electrode and emitted to the light extraction side is the reference light emitting structure ( The relative value of II) is increased from 0.064 to 0.083 (0.064 × 56.0% / 43.4% = 0.083). The light passing from the light emitting layer toward the translucent substrate and passing through the light extraction surface (lower surface) is considered to be the same as the reference light emitting structures (I) and (II) and remains at a relative value of 0.336.

  Therefore, the light output of the practical light emitting structure (I) can be estimated as 0.796 (0.377 + 0.083 + 0.336 = 0.996).

  The light-emitting structure (I) has a light-emitting structure (comparative light-emitting structure (I)) provided with a translucent insulating layer / metal reflective layer only on the side surface, and a reflective metal layer only on the translucent positive electrode. The output is improved as compared with the light emitting structure having the comparative light emitting structure (II). And when a light emitting element discharge | releases ultraviolet light, if the structure of implementation light emission structure (I) is used, exposure to the ultraviolet light of an underfill agent can be prevented and degradation can be suppressed.

  Note that when a metal reflective layer is provided without a light-transmitting insulating layer, it cannot be used as a light emitting element because a short circuit occurs between the positive electrode and the negative electrode.

(Verification of the light emitting structure (II))
In the implementation light emitting structure (I), the light emitting structure (I) is the same as the implementation light emitting structure (I) except that the light-transmitting insulating layer Ins is changed to calcium fluoride (CaF: film thickness 400 nm, refractive index 1.46, transmittance 92%). The implementation light emitting structure (II) having a similar structure was verified. When using CaF, because of their small refractive index for light of 265nm as compared to SiO ₂ used in the embodiment luminous structure (I), and the semiconductor layer than the structure of the embodiment luminous structure (I) using SiO ₂ The reflectance at the interface with the translucent insulating layer is increased, and the light output is greater than that of the light emitting structure (I). The critical angle, which is the minimum incident angle at which total reflection occurs, is determined by the refractive index. According to Snell's law, when light enters the medium (B) from the medium (A), the critical angle is arcsin (medium ( The refractive index of A) / the refractive index of the medium (B). Specifically, the critical angle of light incident on the SiO ₂ insulating layer from the n-type nitride semiconductor layer (for example, AlGaN layer) is 38.7 degrees, whereas the n-type nitride semiconductor layer to the CaF insulating layer The critical angle of light incident on is 37.5 degrees. When CaF is used for the light-transmitting insulating layer, the critical angle becomes smaller, and as a result, the reflectance at the interface between the semiconductor layer and the light-transmitting insulating layer is increased.

(Verification of the light-emitting structure (III))
In the light emitting structure (I), the light emitting structure (I) is the same as the light emitting structure (I) except that the light-transmitting insulating layer Ins is changed to magnesium fluoride (CaF: film thickness 400 nm, refractive index 1.41, transmittance 92%). The implementation light emitting structure (II) having a similar structure was verified. The critical angle of light incident on the MgF insulating layer from the n-type nitride semiconductor layer is 36.0 degrees, which is smaller than those in the case of the light-emitting structure (I) and the light-emitting structure (II). Since the reflectance at the interface between the nitride semiconductor layer and the insulating layer is high, the light output is higher than those of the light emitting structure (I) and the light emitting structure (II).

  The above verification results are summarized in Table 1.

DESCRIPTION OF SYMBOLS 1 Translucent substrate 2 n-type group III nitride semiconductor layer 3 Light emitting layer 4 p-type cladding layer 5 p-type contact layer 6 p-type group III nitride semiconductor layer 7 Multilayer semiconductor layer P2a Translucent positive electrode
Ins Translucent insulating layer R Metal reflective layer P1 Negative electrode P2 Positive electrode M Mounting substrate E1 Mounting substrate side negative electrode E2 Mounting substrate side positive electrode U Underfill agent B Solder

Claims (5)

Translucent substrate, n-type group III nitride semiconductor layer formed on the translucent substrate, light-emitting layer formed on the n-type group III nitride semiconductor layer, and formed on the light-emitting layer A laminated semiconductor layer having a p-type group III nitride semiconductor layer formed,
A translucent positive electrode is formed on the p-type group III nitride semiconductor layer,
A negative electrode is formed on the n-type group III nitride semiconductor layer exposed by removing a part of the n-type group III nitride semiconductor layer, the light emitting layer, and the p-type group III nitride semiconductor layer. In an ultraviolet light emitting device having an emission wavelength of 300 nm or less,
The surface of the laminated semiconductor layer on the side where the light transmitting positive electrode is formed from the surface on which the negative electrode is formed, excluding the upper surface exposed portion of the light transmitting positive electrode and the upper surface exposed portion of the negative electrode. An ultraviolet light emitting device comprising: a light-transmitting insulating layer on a surface of a laminated semiconductor layer; and a metal reflective layer on the light-transmitting insulating layer and on an upper surface exposed portion of the light-transmitting positive electrode. . The refractive index of the translucent insulating layer with respect to light with a wavelength of 265 nm is lower than the refractive index of the n-type group III nitride semiconductor layer with respect to light with a wavelength of 265 nm,
The transmittance of the light-transmitting insulating layer with respect to light having a wavelength of 265 nm is 70% or more,
The transmittance of the translucent positive electrode with respect to light having a wavelength of 265 nm is 60% or more,
The reflectance of the metal reflection layer with respect to light having a wavelength of 265 nm is 70% or more
The ultraviolet light-emitting device according to claim 1, wherein a transmittance of the p-type III nitride semiconductor layer with respect to light having a wavelength of 265 nm is 50% or more.   2. The ultraviolet light emitting element according to claim 1, wherein the translucent insulating layer is made of a material selected from an alkali metal or alkaline earth metal fluoride, silicon dioxide, and aluminum oxide. The translucent positive electrode has a layer made of a metal selected from Ni, Cr, Au, Mg, Zn, and Pd, or a layer made of an oxide of the metal,
2. The semiconductor light emitting element according to claim 1, wherein the translucent positive electrode has a thickness of 10 nm or less.   A mounting base material and the ultraviolet light emitting element according to claim 1, wherein the ultraviolet light emitting element is flip-chip mounted on an upper surface of the mounting base material, and a resin is provided in a gap between the mounting base material and the ultraviolet light emitting element. A light emitting structure comprising:

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