JP2008016629A - Manufacturing method of group iii nitride light emitting diode element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent an in-plane uniformity of light emission of a light emitting layer from deteriorating, in a flip-chip nitride LED where a p-type ohmic electrode and a high-reflectivity film are separated from each other by a light transmitting insulating film. <P>SOLUTION: The method of manufacturing a group III nitride light emitting diode element comprises a processes of: forming a p-type ohmic electrode 3 equipped with an opening pattern on the upper surface of a group III nitride compound semiconductor layer 2 on a transparent substrate 1, which is equipped with a light emitting element structure formed of a laminate composed of an n-type layer and a p-type layer, with a light emitting layer interposed between the n-type layer and p-type layer, and contains a p-type contact layer as the uppermost layer; forming a high-reflectivity film 5 which has higher reflectivity for light of certain wavelength emitted from the light emitting layer than the p-type ohmic electrode 3 in the position where the p-type ohmic electrode 3 is interposed between the film 5 itself and the group III nitride compound semiconductor layer 2; and forming a light-transmitting insulating film 4 that separates the p-type ohmic electrode 3 from the high-reflectivity film 5. The light-transmitting insulation film 4 is formed through an electron beam evaporation method. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a group III nitride light-emitting diode element formed using a group III nitride compound semiconductor, and in particular, a reflection structure for efficiently extracting light generated in a light emitting layer to the outside of the element. The present invention relates to a method for manufacturing a group III nitride light-emitting diode device comprising:

Group III nitride compound semiconductors represented by the general formula Al _a In _b Ga _1-ab N (0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ a + b ≦ 1) (hereinafter referred to as “nitride semiconductor”) Is also known). The nitride semiconductor includes GaN, InGaN, AlGaN, AlInGaN, AlN, InN, and the like. In the above chemical formula, a part of the group 3 element is substituted with boron (B), thallium (Tl), etc., and a part of N (nitrogen) is phosphorus (P), arsenic (As), antimony (Sb) Those substituted with bismuth (Bi) or the like are also included in the nitride semiconductor.

  A group 3 nitride-based light-emitting diode element (hereinafter also referred to as “nitride LED”) having a light-emitting element structure in which p-type and n-type nitride semiconductor layers are stacked with a light-emitting layer made of a nitride semiconductor interposed therebetween. Is known. A typical nitride LED is formed on a sapphire substrate using a vapor phase growth method such as a metal organic compound vapor phase growth (MOVPE) method, a hydride vapor phase growth (HVPE) method, or a molecular beam epitaxy (MBE) method. After laminating a n-type GaN contact layer, an InGaN light emitting layer, a p-type AlGaN cladding layer, and a p-type GaN contact layer in this order, a negative electrode is formed on the surface of the n-type GaN contact layer exposed by etching, and a p-type GaN contact is formed. Constructed by forming a positive electrode on the top surface of the layer.

  A nitride LED formed by laminating a nitride semiconductor layer on a transparent substrate such as a sapphire substrate has a “flip chip type” configuration suitable for extracting light generated in the light emitting layer to the outside of the device through the transparent substrate. be able to. In the flip-chip nitride LED, light extraction efficiency can be increased by efficiently reflecting light traveling in the direction opposite to the transparent substrate out of the light generated in the light emitting layer to the transparent substrate side. For this purpose, flip-chip nitride LEDs having various reflecting structures have been proposed (Patent Document 1).

  In the flip chip type nitride LED newly proposed in Patent Document 1, a nitride semiconductor layer having a p-type GaN contact layer as an uppermost layer is formed on a sapphire substrate, and a mesh made of Rh (rhodium) is formed on the upper surface thereof. A p-type ohmic electrode, a translucent insulating film made of silicon oxide, an Al (aluminum) film, and an Au (gold) film are sequentially stacked. This nitride LED is provided as a highly reflective film made of Al having a higher reflectivity in the ultraviolet to visible range than Rh, separately from the p-type ohmic electrode, and the light generated in the light emitting layer by this highly reflective film is a sapphire substrate It is said to show high light extraction efficiency because it is reflected to the side. In addition, since the p-type ohmic electrode and the Al film are separated by the translucent insulating film, alloying of Al and Rh is prevented, and excellent effects in terms of overall electrical, optical, and reliability It is supposed to demonstrate. In the present specification, hereinafter, a flip-chip nitride LED having a configuration in which a p-type ohmic electrode and a high-reflection film are separated by a light-transmitting insulating film will be referred to as an “electrode / high-reflection film-separated LED”. I will call it.

JP 2006-100529 A

  The present inventors made a prototype of the electrode / high reflection film separation type LED proposed in Patent Document 1 and evaluated its characteristics. As a result, a conventional typical flip chip type in which a p-type ohmic electrode also serves as a reflection film. It was found that the in-plane uniformity of light emission in the light emitting layer tends to be lower than that of the nitride LED.

  This invention is made | formed in view of this situation, and it aims at providing the method of improving the said problem in electrode / high reflective film separated type LED.

  As a result of studies by the present inventors, it has been found that in the electrode / high reflection film separated type LED, the in-plane uniformity of light emission in the light emitting layer varies depending on the method of forming the translucent insulating film. Specifically, in-plane uniformity is reduced when a light-transmitting insulating film is formed by a plasma CVD method, whereas in-plane uniformity is reduced when a low-temperature film is formed by a method such as an electron beam evaporation method or a sputtering method. It has been found to be improved. Further, when the light-transmitting insulating film is formed by sputtering, the in-plane uniformity of light emission in the light-emitting layer is improved, while the forward voltage tends to increase, whereas it is formed by electron beam evaporation. It has also been found that such a tendency does not occur. The present inventors have completed the present invention based on these findings.

The manufacturing method of the present invention has the following characteristics.
(1) A Group 3 nitride compound comprising a light-emitting element structure formed on a transparent substrate and having an n-type layer and a p-type layer laminated with a light-emitting layer sandwiched therebetween, and a p-type contact layer as an uppermost layer Forming a p-type ohmic electrode in a pattern having an opening on the upper surface of the semiconductor layer; and a position sandwiching the p-type ohmic electrode between the group III nitride compound semiconductor layer and Forming a highly reflective film having a higher reflectivity than the p-type ohmic electrode at the wavelength of light generated in the light-emitting layer; and a translucent insulation separating the p-type ohmic electrode and the highly reflective film A method of manufacturing a group III nitride light-emitting diode device, comprising: forming a light-transmitting insulating film; and forming the light-transmitting insulating film using an electron beam evaporation method.
(2) The manufacturing method according to (1), wherein the translucent insulating film is formed to a thickness of 0.3 μm or more.
(3) The manufacturing method according to (1) or (2), wherein the translucent insulating film includes a dielectric multilayer film type reflective film.
(4) The manufacturing method according to any one of (1) to (3), wherein the p-type ohmic electrode is formed by an electron beam evaporation method.
(5) Further, after the highly reflective film forming step, the method includes a step of forming an insulating protective film for protecting the surface of the group III nitride compound semiconductor layer using a plasma CVD method or a sputtering method. (1) The manufacturing method in any one of (4).

According to the manufacturing method of the present invention, it is possible to obtain an electrode / high reflection film separation type LED having good in-plane uniformity of light emission in the light emitting layer. When the in-plane uniformity of light emission in the light emitting layer of the LED element is good, the deviation from the design value of the orientation characteristics of the lighting device or display device configured using the light emitting layer can be reduced. In addition, in an LED having high in-plane light emission uniformity in the light emitting layer, since current flows uniformly through the light emitting layer, heat is generated uniformly. Therefore, the progress of deterioration of the element becomes slow.
In addition, according to the manufacturing method of the present invention, it is possible to obtain a pole / high reflection film separated type LED having good in-plane uniformity of light emission in the light emitting layer without increasing the forward voltage. The lower the forward voltage of the LED, the higher the light emission efficiency and the less the amount of heat generated during driving, thereby improving the durability and reliability.

Hereinafter, the present invention will be specifically described with reference to the drawings.
FIG. 1 is a cross-sectional view showing an example of the structure of an electrode / high reflection film separation type LED obtained by the manufacturing method of the present invention. Reference numeral 1 denotes a transparent substrate, on which a nitride semiconductor layer 2 including a light emitting element structure formed by laminating an n-type layer and a p-type layer with a light emitting layer interposed therebetween is laminated. Nitride semiconductor layer 2 includes an n-type contact layer as an n-type layer, and also includes a p-type contact layer as an uppermost layer. Reference numeral 3 denotes a p-type ohmic electrode formed in a mesh pattern on the upper surface of the nitride semiconductor layer 2. A translucent insulating film 4 is formed so that the p-type ohmic electrode 3 is sandwiched between the nitride semiconductor layers 2, and a highly reflective film 5 is formed thereon. Since the translucent insulating film 4 separates the p-type ohmic electrode 3 and the highly reflective film 5, alloying of the p-type ohmic electrode 3 and the highly reflective film 5 is prevented. The translucent insulating film 4 is provided with an opening 4A so that a part of the p-type ohmic electrode 3 is exposed, and is electrically connected to the p-type ohmic electrode 3 through the opening 4A. A p-side bonding electrode 6 is formed. The p-side bonding electrode 6 is a positive-side contact electrode, and when a device is mounted, a metal wire or conductive adhesive (solder, conductive paste, etc.) used for connection to an external electrode is bonded to the surface. Is done. Reference numeral 7 denotes an n-type ohmic electrode, which is formed on the surface 2S of the n-type contact layer exposed by removing a part of the nitride semiconductor layer 2 by etching. The n-type ohmic electrode 7 also serves as a negative contact electrode.

A method of manufacturing the GaN-based LED shown in FIG. 1 will be described with reference to FIGS.
First, a transparent substrate 1 such as a sapphire substrate is prepared, and a nitride semiconductor layer 2 is formed thereon using a MOVPE method or the like. FIG. 2A is a top view of the wafer that has been subjected to the process of forming the nitride semiconductor layer 2 on the transparent substrate 1 as viewed from the nitride semiconductor layer 2 side. For convenience, only the region corresponding to one element is displayed, but the actual process is performed in units of wafers. The same applies to FIGS. 2B and 2C and FIGS. 3D to 3F.

  Next, as shown in FIG. 2B, a p-type ohmic electrode 3 is formed in a mesh pattern on the upper surface of the wafer on which the formation of the nitride semiconductor layer 2 has been completed (the upper surface of the nitride semiconductor layer 2). There is no limitation on the method of forming the electrode film, but the electron beam evaporation method is preferable because it causes little damage to the p-type contact layer. The patterning of the electrode film can be performed using a lift-off method. The patterned electrode film is subjected to heat treatment for reducing the contact resistance with the p-type contact layer.

  Next, a part of the nitride semiconductor layer 2 is removed by a reactive ion etching method using chlorine gas to expose the surface 2S of the n-type contact layer as shown in FIG. Then, an n-type ohmic electrode 7 is formed on the exposed surface. If necessary, heat treatment is performed to reduce the contact resistance between the n-type ohmic electrode and the n-type contact layer. This heat treatment and the heat treatment of the p-type ohmic electrode can be performed simultaneously.

  Next, as shown in FIG. 3D, a translucent insulating film 4 made of an inorganic material such as silicon oxide is formed. The translucent insulating film 4 is formed using an electron beam evaporation method. 4A is an opening that penetrates the translucent insulating film 4 and is provided for electrical connection between the p-side bonding electrode 6 and the p-type ohmic electrode 3 to be formed later.

  Next, as shown in FIG. 3E, a highly reflective film 5 is formed on the surface of the translucent insulating film 4. The material and configuration of the highly reflective film 5 are determined so that the reflectance at the wavelength of light generated in the light emitting layer is higher than that of the p-type ohmic electrode 3.

  Next, as shown in FIG. 3F, the p-side bonding electrode 6 is formed. The p-type ohmic electrode 3 and the p-side bonding electrode 6 come into contact with each other through the opening 4A provided in the light-transmitting insulating film 4, thereby achieving electrical connection therebetween.

  After the p-side bonding electrode 6 is formed, the LED chip is cut out from the wafer by using a well-known method in this field, such as scribing, dicing, or laser cutting.

The present inventors consider the reason why an electrode / high reflection film separation type LED with good in-plane uniformity of light emission in the light emitting layer can be obtained by the manufacturing method of the present invention as follows.
In the conventional manufacturing method, the light-transmitting insulating film is formed by a CVD method such as a plasma CVD method. However, the CVD method requires a relatively high wafer temperature during film formation. The thermal stress generated due to the difference in thermal expansion coefficient between the light insulating film and the p-type ohmic electrode was relatively large. The contact state between the p-type ohmic electrode and the p-type contact layer is partially changed by the action of the thermal stress, and a region having a high contact resistance between the two is locally formed. Current injection from the electrode to the nitride semiconductor layer does not occur uniformly, and as a result, the non-uniformity of the emission intensity in the plane of the light emitting layer is high.
On the other hand, in the manufacturing method of the present invention, since the insulating protective film is formed by the electron beam evaporation method, the wafer temperature at the time of forming the insulating protective film can be lowered as compared with the CVD method. For this reason, the thermal stress generated by the difference in thermal expansion coefficient between the insulating protective film and the p-type ohmic electrode is reduced, so that the above-described problem that occurs when the CVD method is used is alleviated. In addition, the inorganic thin film formed by the electron beam evaporation method is less dense than the CVD method and easily deforms, so that the thermal stress is relaxed due to the deformation on the insulating protective film side. Therefore, it is considered that the thermal stress acting on the p-type ohmic electrode is reduced.

  Note that as a method for forming the light-transmitting insulating film at a relatively low wafer temperature, a sputtering method can be given in addition to the electron beam evaporation method. As described above, the sputtering method is used for forming the light-transmitting insulating film. Then, the forward voltage of the LED becomes higher than when the electron beam evaporation method is used. Although the details of the cause are unknown, it is likely that molecular or cluster thin film materials collide at high speed in a region where the surface of the p-type contact layer is not covered with the p-type ohmic electrode during film formation by sputtering. As a result, nitrogen is desorbed from the nitride semiconductor crystal and a donor defect is generated. For this reason, the p-type carrier density in the vicinity of the surface of the p-type contact layer is lowered and the contact resistance with the electrode is increased. It seems that there is not.

Next, a preferred embodiment of the present invention will be described.
As a substrate that can be used when forming a nitride semiconductor layer by vapor phase epitaxial growth, sapphire, SiC, GaN, AlGaN, AlN, Si, GaAs, GaP, spinel, ZnO, at least on the surface layer portion including the crystal growth surface, Examples include a substrate having a single crystal layer made of NGO (NdGaO ₃ ), LGO (LiGaO ₂ ), LAO (LaAlO ₃ ), ZrB ₂ , TiB ₂ or the like. When this substrate is a transparent substrate (a substrate having such a high transmittance that there is no practical problem at the emission wavelength of the LED), it is used as a structure in the LED element after being used for forming a nitride semiconductor layer. Can leave. On the other hand, if this substrate is not a transparent substrate, it can be used for forming a nitride semiconductor layer, and then removed by a method such as polishing, laser lift-off, or etching, and replaced with a separately prepared transparent substrate. Such substitution of the substrate can be arbitrarily performed according to the purpose even when the substrate used when forming the nitride semiconductor layer is a transparent substrate.

  The nitride semiconductor layer includes an n-type layer and a light-emitting layer so that the electron carriers injected into the n-type layer and the hole carriers injected into the p-type layer recombine in the light-emitting layer to generate light. A light-emitting element structure in which p-type layers are stacked may be included, and conventionally known techniques can be referred to as appropriate for the detailed configuration. Preferably, the light emitting element structure is a double hetero type, and the light emitting layer is a multiple quantum well (MQW) structure.

  For the configuration of the p-type ohmic electrode, conventionally known techniques can be referred to as appropriate. Preferably, the portion of the p-type ohmic electrode that is in contact with the p-type contact layer is formed of a simple substance or an alloy of a platinum group element such as Rh, Pt (platinum), or Pd (palladium). This is because platinum group elements have high light reflectance in the ultraviolet to visible short wavelength region.

  The p-type ohmic electrode preferably has a film thickness of 0.06 μm or more and 0.1 μm or more so that the reflectivity to light generated in the light emitting layer is sufficiently high and the sheet resistance is not increased. It is more preferable. If the film thickness of the p-type ohmic electrode is smaller than 30 nm, light is transmitted through the electrode film, and loss due to absorption at that time is increased, which is not preferable. There is no particular upper limit to the thickness of the p-type ohmic electrode, but if the film thickness is too large, the material is wasted. Therefore, the thickness of the p-type ohmic electrode is preferably 1 μm or less, preferably 0.5 μm or less. It is more preferable that the thickness be 0.3 μm or less.

  The p-type ohmic electrode is formed in a pattern having an opening. The patterns having openings include various patterns such as a mesh shape, a branched shape, a comb shape, a radial shape, a spiral shape, and a meander shape. An example of a pattern having an opening is shown in FIG. 4A shows an example of a mesh pattern having a square opening, FIG. 4B shows an example of a mesh pattern having a circular opening, and FIG. 4C shows a multi-ring pattern and a radial pattern. FIG. 4D shows an example of a meander pattern, FIG. 4E shows an example of a comb pattern, and FIG. 4F shows an example of a branch pattern. The opening here is not limited to the hole-like portion penetrating the electrode film, but includes a notch that is continuous with the outer periphery of the electrode film. In a pattern having an opening, the band width when the shape of the electrode film or the opening is a band, or the maximum width of the opening when the shape of the opening is a dot (width in the direction in which the width is maximum) ) Is preferably 1 μm to 50 μm, more preferably 2 μm to 25 μm, and particularly preferably 2 μm to 15 μm. Further, the area ratio of the opening to the p-type ohmic electrode (the area ratio of the opening to the total area of the electrode film portion and the opening) is preferably in the range of 50% to 80%.

  Preferable materials for the light-transmitting insulating film include various metal oxides, metal nitrides, and metal oxynitrides. Preferred examples of the metal oxide are silicon oxide, titanium oxide, zirconium oxide, tantalum oxide, hafnium oxide, yttrium oxide, magnesium oxide, aluminum oxide, and niobium oxide. Preferred examples of the metal nitride are silicon nitride and aluminum nitride. In addition to these, magnesium fluoride can also be suitably used. The translucent insulating film may be a multilayer film, and may include, for example, a configuration of a dielectric multilayer film type reflection film formed by laminating thin films having different refractive indexes. The film thickness of the translucent insulating film may be any film thickness that can substantially prevent alloying of the p-type ohmic electrode and the highly reflective film, preferably 0.1 μm or more, more preferably 0.2 μm or more, and particularly Preferably it is 0.3 micrometer or more. Increasing the thickness of the light-transmitting insulating film has an advantage that reflection due to a difference in refractive index is likely to occur at the interface between the nitride semiconductor layer and the light-transmitting insulating film. The loss caused by reflection caused by the difference in refractive index between the nitride semiconductor layer and the light-transmitting insulating film is smaller than the loss caused by reflection by the metal high reflection film. If the film thickness of the translucent insulating film exceeds 3 μm, it becomes difficult to perform patterning using a simple lift-off method.

  The entire light-transmitting insulating film is preferably formed by electron beam evaporation, but a layer formed by electron beam evaporation and a layer formed by methods other than electron beam evaporation such as CVD and sputtering. It is good also as a structure which piled up. In that case, the layer formed by the electron beam evaporation method occupies 80% or more of the film thickness.

  The translucent insulating film may be any material that can substantially prevent the p-type ohmic electrode 3 and the highly reflective film 5 from being alloyed. For example, the electrode / highly reflective film separated LED shown in FIG. In addition, the shape of the translucent insulating film 4 can be set so that the highly reflective film 5 is in contact with the nitride semiconductor layer 2 in the opening of the p-type ohmic electrode 3.

  Preferred materials for the highly reflective film are Ag (silver), Al, Rh, Pt, etc., which have a high reflectivity in the near ultraviolet to visible wavelength range, and in particular, Ag and Al. Platinum group elements (Ir, Pd, Ru, Os) other than Rh and Pt can also be suitably used. Ag alloys and Al alloys in which thermal stability and chemical stability are improved by adding other elements to Ag and Al within a range that does not significantly impair the light reflectivity can also be suitably used.

  As described above, the p-side bonding electrode is a positive contact electrode. When the portion including the outermost surface is made of Au, the p-side bonding electrode can easily bond a metal wire or solder to the surface. In addition, when the portion including the outermost surface is formed of Au, Au alloy, Sn, or Sn alloy, the p-side bonding electrode can easily bond solder containing Au or Sn (tin) as a component to the surface. .

  In the electrode / high reflection film separation type LED illustrated in FIGS. 1 and 5, the p-side bonding electrode 6 is laminated on the high reflection film 5, but between the high reflection film 5 and the p-side bonding electrode 6. When alloying occurs, the reflectivity of the highly reflective film 5 decreases, and the problem arises that the bonding property between the p-side bonding electrode 6 and the metal wire or solder is deteriorated. In order to prevent this, it is preferable to interpose a barrier layer between the highly reflective film 5 and the p-side bonding layer 6. The barrier layer is, for example, a so-called refractory metal such as W (tungsten), Mo (molybdenum), Ta (tantalum), Nb (niobium), V (vanadium), or Zr (zirconium), a platinum group element, or Ti (titanium). , Ni (nickel) or the like, or an alloy thereof. Further, it can be formed of an inorganic material such as a metal oxide, a metal nitride, or a metal oxynitride. In order to prevent alloying of the high reflection film 5 and the p-side bonding electrode 6, the p-side bonding electrode 6 is placed on the high reflection film 5 as in the electrode / high reflection film separation type LED illustrated in FIG. You may form so that it may not laminate | stack. In this case, it is preferable to protect the surface of the highly reflective film 5 by covering it with an insulating protective film.

  For the configuration of the n-type ohmic electrode, conventionally known techniques can be referred to as appropriate. In a preferred n-type ohmic electrode, the portion in contact with the n-type contact layer is formed of a single substance such as Al, Ti, W, Ni, Cr, V, or an alloy thereof. In the electrode / high reflection film separation type LED shown in FIG. 1, FIG. 5, FIG. 6, and FIG. 7, the n-type ohmic electrode also serves as the contact electrode, but the negative side connected to the n-type ohmic electrode These contact electrodes can also be provided separately. The n-side contact electrode also has a good bondability with a metal wire if the portion including the outermost surface is made of Au, and if it is made of Au, Au alloy, Sn, Sn alloy, etc., solder and The bondability is improved.

  When using a transparent substrate having n-type conductivity, for example, an SiC substrate, GaN substrate, ZnO substrate or the like imparted with n-type conductivity, an n-type ohmic electrode is formed on the surface of the transparent substrate, and the substrate passes through the substrate. Thus, it is possible to employ a configuration in which current is supplied to the n-type layer included in the nitride semiconductor layer.

  An insulating protective film for protecting the surface of the nitride semiconductor including the end face of the light emitting layer is formed separately from the translucent insulating film for preventing alloying of the p-type contact layer and the highly reflective film. It is desirable. FIG. 7 shows an example of an electrode / high reflection film separation type LED provided with an insulating protective film 8. In the example of this figure, the insulating protective film 8 covers the entire upper surface of the element except for a part of the upper surfaces of the p-side bonding electrode 6 and the n-type ohmic electrode 7, and the element is damaged or in the environment. Protects against moisture. The insulating protective film 8 can be formed of various metal oxides, metal nitrides, and metal oxynitrides. Preferred examples of the metal oxide include silicon oxide, titanium oxide, zirconium oxide, tantalum oxide, and hafnium oxide. , Yttrium oxide, magnesium oxide, aluminum oxide, and niobium oxide. Preferred examples of the metal nitride include silicon nitride and aluminum nitride. In addition to these, magnesium fluoride can also be suitably used. The thickness of the insulating protective film 8 is preferably 0.2 μm to 1 μm. The insulating protective film 8 is preferably formed by a plasma CVD method or a sputtering method, which can form a denser film than the electron beam evaporation method.

(Example)
As an example of the present invention, an electrode / high reflection film separation type LED shown in FIG. 7 was produced as follows.
A C-plane sapphire substrate is used as the transparent substrate 1, and a low-temperature buffer layer made of AlGaN and Si (silicon) are doped at a concentration of 5 × 10 ¹⁸ cm ⁻³ by using the MOVPE method. Type GaN contact layer, GaN barrier layer having a thickness of 8 nm and InGaN well layer having a thickness of 2 nm (emission wavelength: 400 nm), a light emitting layer having an MQW (multiple quantum well) structure in which 10 layers are alternately stacked, Mg ( Magnesium) doped at a concentration of 5 × 10 ¹⁹ cm ⁻³ and a p-type Al _0.15 Ga _0.85 N cladding layer having a thickness of 0.03 μm, Mg doped at a concentration of 1 × 10 ²⁰ cm ⁻³ A p-type GaN layer contact layer having a thickness of 0.2 μm was laminated in this order. After the lamination, in order to activate Mg added to the p-type layer, a wafer annealing process was performed using a rapid thermal annealing (RTA) apparatus. Thus, the LED wafer in which the nitride semiconductor layer 2 including the light emitting element structure was formed on the transparent substrate 1 was obtained.

  A square shape in which p-type ohmic electrodes 3 are regularly arranged horizontally and vertically on the upper surface of the LED wafer obtained as described above (the upper surface of the p-type GaN contact layer included as the uppermost layer in the nitride semiconductor layer 2). A mesh pattern (lattice pattern) having openings was formed. One side of the opening was 8 μm, and the width of the strip-shaped electrode film part separating adjacent openings was 2 μm. The electrode film was formed by laminating a 0.05 μm thick Rh layer, a 0.1 μm thick Au layer, and a 0.01 μm thick Ni layer in this order using an electron beam evaporation method. . Here, the Ni thin film provided at the top is an adhesion reinforcing layer for strongly attaching the translucent insulating film 4 to be formed later to the p-type ohmic electrode 3. The patterning of the electrode film was performed by a normal lift-off method using a photolithography technique.

Next, the p-type GaN contact layer, the p-type Al _0.15 Ga _0.85 N cladding layer, and a part of the light emitting layer are removed by reactive ion etching to expose the surface 2S of the n-type GaN contact layer. I let you. After the exposure, on the surface 2S of the n-type GaN contact layer, an electron beam evaporation method is used to form a 0.03 μm thick Al layer, a 0.1 μm thick Pd layer, a 0.1 μm thick Au layer, An n-type ohmic electrode 7 was formed by laminating a Pt layer having a thickness of 0.1 μm and an Au layer having a thickness of 0.4 μm in this order. Thereafter, in order to lower the contact resistance between the p-type ohmic electrode 3 and the n-type ohmic electrode 7 and the nitride semiconductor layer 2, the wafer was heat-treated at 500 ° C. for 1 minute in a nitrogen stream.

Next, a translucent insulating film 4 made of silicon oxide and having a thickness of 0.3 μm was formed so as to cover the p-type ohmic electrode 3 by using an electron beam evaporation method. Granular SiO ₂ (size: 1 mm to 3 mm) manufactured by Canon Optron Co., Ltd. was used as the vapor deposition material. While the wafer was not heated or cooled during the deposition, the surface temperature of the wafer became about 100 ° C. to 150 ° C. due to radiation from the crucible. The atmosphere during vapor deposition was a vacuum atmosphere, and ion beam assist, plasma assist, etc. were not performed. The film formation rate was set to 30 nm / min.

Next, a highly reflective film 5 made of Al and having a thickness of 0.2 μm was formed on the translucent insulating film 4 by using an electron beam evaporation method.
Next, the p-side bonding electrode 6 that was electrically connected to the p-type ohmic electrode 3 through the opening 4A of the translucent insulating film 4 and was laminated on the highly reflective film 5 was formed. The p-side bonding electrode 6 was formed by laminating a 0.05 μm thick Ti layer, a 0.1 μm thick Pt layer, and a 0.4 μm thick Au layer in this order using an electron beam evaporation method. . The p-side bonding layer having this three-layer structure has good solderability because the surface layer is an Au layer. In addition, since the lower two layers (Ti layer and Pt layer) separate the Au layer as the surface layer from the highly reflective layer 5 made of Al, between this Au layer and the highly reflective layer 5, It is difficult for alloying to occur.

Next, an insulating protective film 8 made of silicon oxide and having a thickness of 0.5 μm is formed by plasma CVD so as to cover the entire upper surface of the wafer, and then a part of the upper surface of the p-side bonding electrode 6 is formed. In order to expose a part of the upper surface of the n-type ohmic electrode 7, an opening was formed in the insulating protective film 8 by dry etching.
Finally, the lower surface of the transparent substrate 1 was polished to reduce its thickness to 100 μm, and then an LED chip was cut out from the wafer using a scribing method. The size of the LED chip was 350 μm square.

  The obtained LED chip (bare chip) was flip-chip mounted, and the forward voltage at an energization current of 20 mA was measured. Further, when the light emission state of the LED chip when the energization current is gradually increased is observed from the lower surface side of the transparent substrate 1 as the light extraction surface using an optical microscope, the energization current is increased to 0.1 mA. Then, light emission was uniformly generated in the entire projection region of the p-type ohmic electrode 3.

(Comparative Example 1)
For comparison, an LED chip was produced in the same manner as in the example except that the light-transmitting insulating layer was formed by the plasma CVD method, and the forward voltage at an energization current of 20 mA was measured. It was 4V. On the other hand, when the energization current was gradually increased, the light emission state of the LED chip was observed from the lower surface side of the transparent substrate, which is the light extraction surface, using an optical microscope. The energization current was increased to 0.2 mA. However, in the projected region of the p-type ohmic electrode, there were sites that emitted light and sites that did not emit light at all.

(Comparative Example 2)
For comparison, an LED chip was produced in the same manner as in the example except that the light-transmitting insulating layer was formed by sputtering, and the forward voltage at an applied current of 20 mA was measured. Met.

It is sectional drawing which shows the structural example of the group III nitride light emitting diode element obtained by the manufacturing method of this invention. It is a figure for demonstrating the manufacturing process of the group 3 nitride-type light emitting diode element shown in FIG. It is a figure for demonstrating the manufacturing process of the group 3 nitride-type light emitting diode element shown in FIG. It is a figure which illustrates the pattern of a p-type ohmic electrode. It is sectional drawing which shows the structural example of the group III nitride light emitting diode element obtained by the manufacturing method of this invention. It is sectional drawing which shows the structural example of the group III nitride light emitting diode element obtained by the manufacturing method of this invention. It is sectional drawing which shows the structural example of the group III nitride light emitting diode element obtained by the manufacturing method of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Transparent substrate 2 Nitride semiconductor layer 3 P-type ohmic electrode 4 Translucent insulating film 5 High reflection film 6 P-side bonding electrode 7 N-type ohmic electrode 8 Insulating protective film

Claims (5)

A Group 3 nitride compound semiconductor layer comprising a light emitting device structure formed on a transparent substrate and having an n-type layer and a p-type layer stacked with a light-emitting layer sandwiched therebetween, and a p-type contact layer as an uppermost layer Forming a p-type ohmic electrode on the upper surface in a pattern having an opening;
A highly reflective film is formed at a position sandwiching the p-type ohmic electrode with the Group III nitride compound semiconductor layer and having a higher reflectance than the p-type ohmic electrode at the wavelength of light generated in the light emitting layer. A film forming step;
A translucent insulating film forming step of forming a translucent insulating film separating the p-type ohmic electrode and the highly reflective film;
An electron beam evaporation method is used to form the light-transmitting insulating film.   The manufacturing method of Claim 1 which forms the said translucent insulating film in the film thickness of 0.3 micrometer or more.   The manufacturing method according to claim 1, wherein the translucent insulating film includes a dielectric multilayer film type reflective film.   The manufacturing method according to claim 1, wherein the p-type ohmic electrode is formed by an electron beam evaporation method.   Furthermore, it has the process of forming the insulation protective film for protecting the surface of a group 3 nitride type compound semiconductor layer using a plasma CVD method or sputtering method after the said high reflective film formation process. 4. The production method according to any one of 4 above.