JP2007288002A - Nitride semiconductor light emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve such a problem that an operating voltage is raised by forming insulation protective films in a nitride semiconductor light emitting device in which there are formed the consecutive insulation protective films from an upper part of a nitride semiconductor layer to an upper part of a positive electrode. <P>SOLUTION: A nitride semiconductor light emitting device 100 is equipped with a p-type nitride semiconductor layer 14 formed on an n-type nitride semiconductor layer 12 through an active layer 13, wherein a metallic positive electrode 16 is formed in a region excluding an edge part of a top face of the p-type nitride semiconductor layer 14 and furthermore by removing an aperture 22 there are formed consecutive insulating protective films 17 from a region which is not covered with the positive electrode 16 on the p-type nitride semiconductor layer 14 to an upper part of the positive electrode 16. The insulation protective films 17 include a portion formed by an electron beam evaporation method above the positive electrode 16. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a nitride semiconductor light emitting device, and more particularly to a nitride semiconductor light emitting device in which a continuous insulating protective film is formed from a nitride semiconductor layer to a positive electrode.

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

A nitride semiconductor light emitting device is formed by, for example, stacking an n-type nitride semiconductor layer, an active layer made of a nitride semiconductor, and a p-type nitride semiconductor layer in this order on a sapphire substrate, and p-type nitride semiconductor layer The negative electrode is formed on the upper surface of the n-type nitride semiconductor layer exposed by removing a part of the active layer, and the positive electrode is formed on the upper surface of the p-type nitride semiconductor layer. An insulating protective film made of an inorganic material such as silicon oxide or silicon nitride is formed on the upper surface of the nitride semiconductor layer excluding the region where the positive electrode and the negative electrode are formed, whereby the positive and negative electrodes and the external electrodes ( A short circuit between the nitride semiconductor and a conductive bonding material such as solder used for connection with a lead frame, a circuit board, an electrode provided on the side of the submount, etc., to which the light emitting element chip is fixed at the time of mounting is prevented. The In order to prevent this short circuit more effectively, the insulating protective film is a continuous film from the p-type nitride semiconductor layer to the positive electrode (Patent Document 1).

Here, in the conventional nitride semiconductor light emitting device, the insulating protective film is formed by a plasma CVD method or a sputtering method (Patent Document 2).

JP-A-6-177434 JP-A-11-150301

The inventors of the present invention examined the forward voltage (Vf) before and after the formation of the insulating protective film for the light emitting diode element corresponding to the conventional nitride semiconductor light emitting element. It has been found that there is a problem that Vf is remarkably increased later. An increase in Vf itself means a decrease in light emission efficiency, and a light emitting element having a high Vf generates a large amount of heat during operation. Becomes faster, the life is shortened, and the reliability is also lowered.

The present invention has been made in view of the above circumstances, and has solved the problem of an increase in operating voltage due to the formation of an insulating protective film, which has been found in conventional nitride semiconductor light-emitting devices, thereby achieving good light emission. An object of the present invention is to provide a nitride semiconductor light emitting device having efficiency and improved lifetime and reliability.

The present invention has been completed by diligently examining the configuration of the insulating protective film in the nitride semiconductor light emitting device in which a continuous insulating protective film is formed from the p-type nitride semiconductor to the positive electrode. The present invention has the following features.

(1) A p-type nitride semiconductor layer formed on an n-type nitride semiconductor layer via an active layer is provided, and a positive electrode is formed in a region excluding the edge of the upper surface of the p-type nitride semiconductor layer. In addition, except for an opening provided on the positive electrode for connection to an external electrode, continuous from the region not covered by the positive electrode on the p-type nitride semiconductor layer to the positive electrode A nitride semiconductor light emitting device having an insulating protective film formed thereon, wherein the insulating protective film includes a portion formed by an electron beam evaporation method above the positive electrode element.
(2) The nitride semiconductor light emitting element according to (1), wherein the insulating protective film includes a portion formed by the electron beam evaporation method in contact with the positive electrode.
(3) The nitride semiconductor light-emitting element according to (2), wherein the insulating protective film includes only a portion formed by an electron beam evaporation method.
(4) The insulating protective film includes a laminated structure portion including at least a first layer formed by an electron beam evaporation method and a second layer formed by a plasma CVD method or a sputtering method. The nitride semiconductor light-emitting device according to 1.
(5) The nitride semiconductor light-emitting element according to (4), wherein the first layer is in contact with a positive electrode in the stacked structure portion.
(6) The nitride semiconductor light emitting element according to any one of (1) to (5), wherein the opening is formed in a rounded shape.
(7) The nitride semiconductor light emitting device according to any one of (1) to (6), wherein the positive electrode has a layer made of a platinum group element or Au at a portion in contact with the p-type nitride semiconductor layer. .
(8) The bonding reinforcing layer for increasing the adhesive strength between the positive electrode and the insulating protective film is formed between the positive electrode and the insulating protective film. The nitride semiconductor light emitting device according to any one of the above.

In the conventional nitride semiconductor light emitting device, the operating voltage rises with the formation of the insulating protective film because the thermal stress caused by the difference in thermal expansion coefficient between the insulating protective film and the positive electrode is the positive electrode. This is considered to be caused by a decrease in the adhesion between the positive electrode and the p-type nitride semiconductor layer, thereby increasing the contact resistance of the positive electrode. Therefore, in the nitride semiconductor light emitting device according to the present invention, the insulating protective film is configured to include a portion formed by the electron beam evaporation method above the positive electrode. According to the electron beam evaporation method, the insulating protective film is formed at a lower temperature than the plasma CVD method or the sputtering method, so that the thermal stress caused by the difference in thermal expansion coefficient between the insulating protective film and the positive electrode is reduced. . In addition, the inorganic thin film formed by the electron beam evaporation method has a lower density than the one formed by the plasma CVD method or the sputtering method and is easily deformed. The thermal stress resulting from the difference in expansion coefficient is alleviated by the deformation of the insulating protective film. Therefore, a decrease in adhesion between the positive electrode and the p-type nitride semiconductor layer due to the action of the thermal stress is prevented.

When the insulating protective film includes a portion formed by the electron beam evaporation method in contact with the positive electrode, it is considered that the thermal stress is mitigated more effectively due to the deformation of the portion. In that case, the entire insulating protective film may be formed by electron beam evaporation.

The insulating protective film includes a layer formed by an electron beam evaporation method and a plasma CVD method or a sputtering method so that at least a part formed by the electron beam evaporation method is included above the positive electrode. It is good also as a laminated film which laminated | stacked the formed layer. In order to simplify the manufacturing process, it is preferable that the entire insulating protective film is a laminated film. The layer formed by the plasma CVD method or the sputtering method is denser than the layer formed by the electron beam evaporation method, and becomes a layer having lower permeability such as water vapor harmful to the light emitting element. A decrease in the protective function of the insulating protective film due to the provision of the layer can be compensated. In this case as well, when the layer in contact with the positive electrode is a layer formed by electron beam evaporation, the thermal stress caused by the difference in thermal expansion coefficient between the insulating protective film and the positive electrode is more effectively generated. it is conceivable that.

The insulating protective film on the positive electrode is provided with an opening so that the positive electrode can be connected to the external electrode. By forming the opening into a rounded shape, the insulating protective film from the positive electrode is provided. Peeling is prevented. This delamination prevention effect is considered to be caused by the fact that the stress concentration on a specific part of the insulating protective film is eliminated, so that the deformation and destruction of the insulating protective film are suppressed. This means that, conversely, when the opening is formed in such a rounded shape, the thermal stress applied to the positive electrode tends to increase. Therefore, in this case, it is considered particularly effective to reduce the thermal stress received by the positive electrode by forming the portion of the insulating protective film located above the positive electrode by the electron beam evaporation method.

Further, when the positive electrode has a layer made of a platinum group element or Au (gold) which is a chemically stable element in a portion in contact with the p-type nitride semiconductor layer, the positive electrode and the p-type semiconductor layer There is a tendency for adhesion to be low. The platinum group elements are Rh (rhodium), Pd (palladium), Pt (platinum), Ir (iridium), Ru (ruthenium), and Os (osmium). Therefore, in this case, it is considered to be particularly effective to reduce the thermal stress received by the positive electrode by forming the portion of the insulating protective film located above the positive electrode by the electron beam evaporation method.

In addition, if an adhesion strengthening layer is formed between the positive electrode and the insulating protective film to increase the adhesive strength between the positive electrode and the insulating protective film, the stability of the insulating protective film is improved, while the positive electrode and the insulating protective film are insulated. Thermal stress relaxation due to deformation / destruction of the protective film interface is less likely to occur. Therefore, in this case, it is considered to be particularly effective to reduce the thermal stress received by the positive electrode by forming the portion of the insulating protective film located above the positive electrode by the electron beam evaporation method.

According to the present invention, in the nitride semiconductor light emitting device in which a continuous insulating protective film is formed from the p-type nitride semiconductor to the positive electrode, it is possible to prevent the operating voltage from increasing with the formation of the insulating protective film. Therefore, the nitride semiconductor light emitting device according to the present invention has better light emission efficiency and improved lifetime and reliability compared to a conventional nitride semiconductor light emitting device having an insulating protective film formed in the same manner. It will be.

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

FIG. 1 is a cross-sectional view schematically showing the structure of a light-emitting diode element that is a nitride semiconductor light-emitting element according to an embodiment of the present invention. In FIG. 1, 100 is a nitride semiconductor light emitting device, 11 is a substrate, 12 is an n-type nitride semiconductor layer, 13 is an active layer, 14 is a p-type nitride semiconductor layer, 15 Is a negative electrode, 16 is a positive electrode, and 17 is an insulating protective film. The negative electrode 15 is formed on the surface of the n-type nitride semiconductor layer 12 exposed by removing a part of the p-type nitride semiconductor layer 14 and the active layer 13 by etching. The positive electrode 16 is formed on the upper surface of the p-type nitride semiconductor layer 14. The upper surface of the p-type nitride semiconductor layer 14 is covered with the positive electrode 16 except for its edge. The insulating protective film 17 is formed by an electron beam vapor deposition method, and the upper surface side of the element 100 except for the opening 21 provided on the negative electrode 15 and the opening 22 provided on the positive electrode 16. Covers the whole. FIG. 2 shows the shapes of the openings 21 and 22 when the element 100 shown in FIG. 1 is viewed from the upper surface side. Both openings are rounded at the intersection of the straight lines that define the contour shape. That is, both openings are formed in a rounded shape. These openings may be circular or elliptical. Circular and elliptical shapes are also rounded.

The light emitting diode element shown in FIG. 1 can be manufactured as follows.
First, an n-type nitride semiconductor layer is formed on a substrate 11 using a vapor phase epitaxial growth method such as a MOVPE (organometallic compound vapor phase growth) method, an HVPE (hydride vapor phase growth) method, or an MBE (molecular beam epitaxy) method. 12, the active layer 13 and the p-type nitride semiconductor layer 14 are sequentially grown and stacked. A buffer layer may be interposed between the substrate 11 and the n-type nitride semiconductor layer 12. An annealing process and an electron beam irradiation process for activating the p-type impurity added to the p-type nitride semiconductor layer 14 can be appropriately performed.

Next, the positive electrode 16 is formed on the surface of the p-type nitride semiconductor layer 14 using a method such as vapor deposition or sputtering. The positive electrode 16 is subjected to heat treatment for reducing the contact resistance with the p-type nitride semiconductor layer 14 as necessary. Next, the n-type nitride semiconductor layer is etched by a depth reaching the n-type nitride semiconductor layer 12 from the surface side of the p-type nitride semiconductor layer 14 by a reactive ion etching method using chlorine gas. 12 is partially exposed. Next, the negative electrode 15 is formed on the exposed surface of the n-type nitride semiconductor layer 12 using a method such as vapor deposition or sputtering. The negative electrode 15 is subjected to heat treatment for reducing the contact resistance with the n-type nitride semiconductor layer 12 as necessary.

Next, an insulating protective film 17 is formed by electron beam evaporation so as to cover the entire surface on the upper surface side of the element. Thereafter, a part of the insulating protective film 17 is removed by etching, an opening 21 is formed on the negative electrode 15, and an opening 22 is formed on the positive electrode 16. The negative electrode 15 and the positive electrode 15 are formed in each opening. The electrode 16 is exposed. Note that the lift-off method can be used to form the insulating protective film 17 into a shape having the openings 21 and 22 from the beginning. Finally, the substrate is cut using a known method in this field such as dicing, scribing, laser fusing, etc., to obtain a chip-like light emitting diode element.

In the light emitting diode element shown in FIG. 1, the substrate 11 includes a sapphire substrate, a SiC substrate, a GaN substrate, an AlGaN substrate, an AlN substrate, a Si substrate, a GaAs substrate, a GaP substrate, a spinel substrate, a ZnO substrate, an NGO (NdGaO3) substrate, Any known substrate applicable to the epitaxial growth of a nitride semiconductor, such as an LGO (LiGaO2) substrate, an LAO (LaAlO3) substrate, a ZrB2 substrate, or a TiB2 substrate, can be used arbitrarily. If the substrate is conductive, a negative electrode can be formed on the substrate. It is not essential to leave the substrate used for crystal growth of the nitride semiconductor in the light-emitting element that is the final product, and part or all of the substrate may be removed by methods such as polishing, etching, and laser lift-off. After the removal, a support substrate prepared separately may be replaced.

The band gap and film thickness of n-type nitride semiconductor layer 12, active layer 13 and p-type nitride semiconductor layer 14, types of impurities added to each layer, impurity concentration distribution in the thickness direction in each layer, etc. are well known. It can be set by referring to the technology as appropriate. These nitride semiconductor layers may have a certain crystal composition, may be a laminate composed of layers having different crystal compositions, or may include a portion where the crystal composition is inclined. . In order to increase the light emission efficiency, it is preferable to form a double heterostructure, and the active layer preferably has a quantum well structure, particularly a multiple quantum well structure.

In the n-type nitride semiconductor layer 12, it is preferable that the portion in contact with the negative electrode has a sufficiently high electron concentration in order to reduce the contact resistance with the negative electrode. On the other hand, a p-type impurity such as Mg (magnesium) is added to a portion of the p-type nitride semiconductor layer 14 in contact with the positive electrode (a portion including the upper surface) at a concentration higher than the concentration at which the hole concentration becomes maximum. It is preferable to reduce the contact resistance with the positive electrode.

The negative electrode 15 has a portion in contact with the n-type nitride semiconductor layer 12 as a simple substance such as Al (aluminum), Ti (titanium), W (tungsten), Ni (nickel), Cr (chromium), V (vanadium), Or it is preferable to form with the alloy containing 1 or more types of metals chosen from these. Further, the negative electrode 16 is preferably provided with a surface layer made of Au or a platinum group element, which has good resistance to oxidation and corrosion.

In order to reduce the contact resistance with the p-type nitride semiconductor layer 14, the positive electrode 16 has a portion in contact with the p-type nitride semiconductor layer 14 as a simple substance such as a platinum group element, Au, Ni, Co (cobalt), Or it is preferable to form with the alloy containing 1 or more types of metals chosen from these. For the purpose of reducing light absorption by the positive electrode and preventing a decrease in light emission efficiency, the portion is preferably formed of a platinum group element having good light reflectivity, and particularly preferably formed of Rh. Further, the positive electrode 16 is preferably provided with a surface layer made of Au or a platinum group element that has good resistance to oxidation and corrosion. Further, a bonding pad can be added to the positive electrode.

The insulating protective film 17 is made of an inorganic material. Preferred inorganic materials include 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. A preferred example of the metal nitride is silicon nitride. In addition to these, magnesium fluoride can also be suitably used. The insulating protective film may be a multilayer film in which layers made of different inorganic materials are stacked. Although the film thickness of the insulating protective film 17 can be set to 0.05 μm to 3 μm, for example, it is preferably 0.1 μm to 1 μm, and more preferably 0.2 μm to 0.5 μm.

In the nitride semiconductor light emitting device 100 illustrated in FIG. 1, the entire insulating protective film 17 is formed by an electron beam evaporation method. The insulating protective film includes a layer formed by an electron beam evaporation method and an electron beam evaporation method. It is good also as a structure which laminated | stacked the layer formed by methods other than. In that case, as in the light-emitting diode element 100 illustrated in FIG. 3, the entire insulating protective film 17 is composed of a layer 17a formed by an electron beam evaporation method and a layer 17b formed by a method other than the electron beam evaporation method. A structure may be used, or like the light emitting diode element 100 illustrated in FIG. 4, only a portion of the insulating protective film 17 formed on the positive electrode 16 may be formed by an electron beam evaporation method. Alternatively, a laminated structure including the layer 17b formed by a method other than the electron beam evaporation method may be used. Further, only a part of the portion formed on the positive electrode 17 may have such a laminated structure. Here, examples of the method for forming the insulating protective film other than the electron beam evaporation method include a plasma CVD method and a sputtering method. 3 and 4, the layer 17a formed by the electron beam evaporation method is in contact with the positive electrode 16. However, the layer 17b formed by a method other than the electron beam evaporation method is replaced with the positive electrode 16. You may make it contact. Further, the laminated structure may be an alternating laminated structure including two or more layers of any one or both of a layer formed by an electron beam vapor deposition method and a layer formed by a method other than the electron beam vapor deposition method.

Between the negative electrode 15 and the positive electrode 16 and the insulating protective film 17, an adhesion reinforcing layer for increasing the adhesive strength may be formed. In particular, in the case where a surface layer made of Au or a platinum group element is provided on the negative electrode 15 or the positive electrode 16, the adhesion between the surface layer and the insulating protective film is lowered. It is preferable to use a reinforcing layer. The adhesion strengthening layer is mainly composed of any metal selected from W, Ti, Cr, Ni, Cu and Al, or an oxide thereof, and is formed to a thickness of several nanometers to several tens of nanometers by a sputtering method.

As an example of the present invention, a light-emitting diode element (light emission wavelength: 405 nm) for flip-chip mounting whose cross-sectional structure is shown in FIG. 5 was produced. The element size was set so that the size after chip formation was 350 μm square.

First, using a well-known MOVPE method, an undoped GaN layer 121 having a thickness of 2 μm and Si-doped GaN are formed on a C-plane sapphire substrate 11 having a diameter of 2 inches via an AlGaN low-temperature growth buffer layer (not shown). An n-type contact layer 122 having a thickness of 3 μm, an active layer 13 having a multiple quantum well structure in which six GaN barrier layers and InGaN well layers are stacked, and a p-type cladding layer having a thickness of 0.05 μm made of Mg-doped AlGaN. 141, a 0.1 μm-thick p-type contact layer 142 made of Mg-doped GaN was grown and laminated in this order. After the lamination, in order to activate Mg doped in the p-type cladding layer and the p-type contact layer, heat treatment was performed at 900 ° C. for 1 minute in a nitrogen atmosphere using an RTA apparatus.

Next, on the surface of the p-type contact layer 142, using an electron beam evaporation method, an alternating layered film of an Au layer and a Pt layer is laminated on the 30-nm-thick Rh layer so that the uppermost layer is an Au layer. Then, a positive electrode 16 having a total film thickness of 0.6 μm was formed by further laminating a Ti layer having a thickness of 10 nm as an adhesion reinforcing layer thereon. After the formation, heat treatment was performed at 500 ° C. for 1 minute in a nitrogen atmosphere using an RTA apparatus.

Next, a resist mask having a predetermined shape is formed on the p-type contact layer 142 on which the positive electrode 16 is formed, and n-type contact is performed by RIE (reactive ion etching) using chlorine gas, as shown in FIG. Layer 122 was exposed. After the exposure, on the surface of the n-type contact layer, an alternating layer film of Au layer and Pt layer was laminated on the TiW alloy layer with a film thickness of 100 nm using the RF sputtering method so that the uppermost layer was an Au layer. A negative electrode 15 having a total film thickness of 0.7 μm was formed. After the formation, heat treatment was performed at 500 ° C. for 1 minute in a nitrogen atmosphere using an RTA apparatus.

Subsequently, an insulating protective film 17 made of silicon oxide and having a thickness of 300 nm was formed so as to cover the entire surface of the element 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.

Subsequently, the insulating protective film 17 was partially removed by RIE using tetrafluoromethane, and a part of the upper surface of the positive electrode and the negative electrode were exposed as shown in FIG. Finally, light emitting diode elements were cut out from the wafer into chips by a method usually used in this field. In this manner, a chip-like light emitting diode element having a forward voltage (Vf) of 3.4 V or less at a current value of 20 mA could be obtained.

As a comparative example, a chip-like light emitting diode element was fabricated in the same manner as in the above example except that the insulating protective film was formed by the plasma CVD method. The insulating protective film was formed by plasma CVD using TEOS (tetraethylorthosilicate) as a raw material and the wafer was heated to 350 ° C. The chip light-emitting diode element of this comparative example had a forward voltage (Vf) of 3.9 V or more at a current value of 20 mA.

It is sectional drawing which shows typically the structure of the nitride semiconductor light-emitting device concerning one Embodiment of this invention. FIG. 2 is a diagram showing a shape of an opening when the nitride semiconductor light emitting element shown in FIG. 1 is viewed from the upper surface side. It is sectional drawing which shows typically the structure of the nitride semiconductor light-emitting device concerning one Embodiment of this invention. It is sectional drawing which shows typically the structure of the nitride semiconductor light-emitting device concerning one Embodiment of this invention. It is sectional drawing which shows typically the structure of the nitride semiconductor light-emitting device concerning one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Substrate 12 N-type nitride semiconductor layer 13 Active layer 14 P-type nitride semiconductor layer 15 Negative electrode 16 Positive electrode 17 Insulating protective films 21 and 22 Opening portion 100 Nitride semiconductor light emitting device

Claims (8)

a p-type nitride semiconductor layer formed on the n-type nitride semiconductor layer via an active layer, and a positive electrode is formed in a region excluding the edge of the upper surface of the p-type nitride semiconductor layer; Continuous insulation protection from the region not covered by the positive electrode on the p-type nitride semiconductor layer to the positive electrode except for the opening provided for connection to the external electrode on the positive electrode A nitride semiconductor light emitting device having a film formed thereon,
The nitride semiconductor light-emitting element, wherein the insulating protective film includes a portion formed by an electron beam evaporation method above the positive electrode. The nitride semiconductor light-emitting element according to claim 1, wherein the insulating protective film includes a portion formed by the electron beam evaporation method in contact with the positive electrode. The nitride semiconductor light-emitting element according to claim 2, wherein the insulating protective film includes only a portion formed by an electron beam evaporation method. 2. The nitridation according to claim 1, wherein the insulating protective film has a laminated structure portion including at least a first layer formed by an electron beam evaporation method and a second layer formed by a plasma CVD method or a sputtering method. Semiconductor light emitting device. The nitride semiconductor light-emitting element according to claim 4, wherein in the stacked structure portion, the first layer is in contact with a positive electrode. The nitride semiconductor light-emitting element according to claim 1, wherein the opening is formed in a rounded shape. The nitride semiconductor light-emitting device according to claim 1, wherein the positive electrode has a layer made of a platinum group element or Au at a portion in contact with the p-type nitride semiconductor layer. The nitriding according to any one of claims 1 to 7, wherein an adhesion reinforcing layer is formed between the positive electrode and the insulating protective film to increase an adhesive strength between the positive electrode and the insulating protective film. Semiconductor light emitting device.