JP2008041866A - Nitride semiconductor element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nitride semiconductor element comprising a transparent electrode having an oxide surface and p- and n-electrodes being made of a common material. <P>SOLUTION: The nitride semiconductor element has an n-type nitride semiconductor layer (2) and a p-type semiconductor layer (4), an n-electrode (11) formed on the n-type nitride semiconductor layer (2), a transparent electrode (5) formed on the p-type semiconductor layer (4), and a p-type electrode (10) formed on a part of the transparent electrode (5). The n- and p-electrodes (11), (10) include a first and second metal layers (6), (7), the first metal layer (6) contains a platinum group metal and is formed like discrete islands, and the second metal layer (7) is made of a metal ohmic-contactable with the n-type nitride semiconductor layer (2), and contacts with this semiconductor layer (2) exposed between the islands of the first metal laminate (6) or the transparent electrode (5). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a nitride semiconductor device configured using a nitride semiconductor.

  Nitride semiconductors are used in light-emitting elements such as light-emitting diodes (LEDs) and laser diodes (LD), light-receiving elements such as solar cells and optical sensors, and electronic devices such as transistors and power devices. In particular, light emitting diodes using nitride semiconductors are widely used in various light sources used for backlights, illumination, traffic lights, large displays, and the like.

  A nitride semiconductor device using a nitride semiconductor basically has an n-type nitride semiconductor layer and a p-type nitride semiconductor layer stacked on a substrate, and is electrically connected to each of the n-type and p-type nitride semiconductor layers. In this structure, an electrode to be connected is formed. As an electrode electrically connected to the p-type nitride semiconductor layer, a structure is known in which a translucent electrode is formed on almost the entire surface of the p-type nitride semiconductor layer and a pad electrode made of metal is formed thereon. . This translucent electrode spreads the current injected from the pad electrode to the p-type nitride semiconductor layer and allows light from the nitride semiconductor light-emitting element to be transmitted and extracted outside. On the other hand, since an n-type nitride semiconductor generally has a low electric resistance, a pad electrode is formed directly on the n-type nitride semiconductor layer. (For example, see Patent Document 1)

Examples of such a translucent electrode on the p-type semiconductor layer include a gold / nickel oxide thin film (see Patent Document 2), indium tin oxide (hereinafter “ITO”), ZnO, In ₂ O ₃ , SnO. ₂ or the like is used (see Patent Document 2).

Japanese Patent Laid-Open No. 10-135515 JP 2003-124518 A

  In the conventional nitride semiconductor device described above, a pad electrode (hereinafter referred to as “p electrode”) formed on the translucent electrode on the p-type nitride semiconductor layer and a pad electrode (hereinafter referred to as “p-electrode”) formed on the n-type nitride semiconductor layer. , “N-electrode”) was usually made of different metals.

  For example, since the n-electrode is in good ohmic contact with the n-type nitride semiconductor layer, an ohmic contact layer such as Al, W, Cr, or Ti, a barrier layer such as Pt, and a bonding layer such as Au are laminated. It was common to form. On the other hand, it is necessary to use a material having good adhesion to the translucent electrode for the p-electrode. The translucent electrode is often a gold / nickel oxide thin film or ITO, and its surface is an oxide. Therefore, the p-electrode is generally formed by laminating a layer having a good adhesion layer with an oxide such as Rh and a bonding layer such as Au.

  However, if the p electrode and the n electrode can be made of a common material, the manufacturing process can be simplified and the manufacturing cost can be reduced. Therefore, an object of the present invention is to provide a nitride semiconductor device that includes a light-transmitting electrode whose surface is an oxide, and in which a p-electrode and an n-electrode are made of a common material.

In order to achieve the above object, a nitride semiconductor device of the present invention has an n-type nitride semiconductor layer and a p-type nitride semiconductor layer, and an n-electrode is provided on the n-type nitride semiconductor layer, and the p-type A nitride semiconductor device in which a light-transmitting electrode and a p-electrode are formed on a portion thereof on a nitride semiconductor layer,
The translucent electrode has at least a surface made of an oxide, and the n electrode and the p electrode have a first metal layer and a second metal layer in order from the side in contact with the n-type nitride semiconductor layer or the translucent electrode. The first metal layer includes a platinum group metal and is formed in a discrete island shape, and the second metal layer is formed of a metal capable of ohmic contact with the n-type nitride semiconductor layer. The n-type nitride semiconductor layer exposed from between the islands of the first metal layer or the translucent electrode is in contact.

  In this case, “translucent” means that the light emitted from the active layer can be transmitted from the outside so that visible light of all wavelengths need not be transmitted. In addition, in this case, the “metal layer” is not only a layer composed of pure metal elements but also an alloy of metal elements such as silicon and elements other than metal elements, and as a whole has good electrical conductivity similar to metals. The thing which shows is also included.

  According to the nitride semiconductor device of the present invention, it is possible to achieve both good adhesion to the translucent electrode and good ohmic contact to the n-type nitride semiconductor layer while configuring the p electrode and the n electrode with a common material, A nitride semiconductor device having excellent electrical characteristics and reliability can be provided. Therefore, the manufacturing process can be simplified and the manufacturing cost can be reduced as compared with the conventional nitride semiconductor element in which different materials are used for the p-electrode and the n-electrode.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. However, the embodiment described below exemplifies a nitride semiconductor device for embodying the technical idea of the present invention, and the present invention is not limited to the following embodiment.
Embodiment 1
FIG. 1 is a cross-sectional view showing a nitride semiconductor device 20 according to Embodiment 1 of the present invention, and FIG. 2 is a plan view thereof. As shown in FIGS. 1 and 2, the nitride semiconductor light emitting device of the first embodiment has an n-type nitride semiconductor layer on a substrate 1 optionally through a base layer (not shown) such as a buffer layer. 2, the active layer 3, and the p-type nitride semiconductor layer 4 are laminated in this order, and electrodes are connected to the n-type nitride semiconductor layer 2 and the p-type nitride semiconductor layer 4, respectively.

  In the present embodiment, the electrode formed on the p-type nitride semiconductor layer 4 is formed by laminating a p-electrode 10 as a pad electrode on a part of a translucent electrode 5 made of a conductive oxide such as ITO. Composed. The translucent electrode 5 is formed on almost the entire surface of the p-type nitride semiconductor layer 4 in order to spread the current to the p-type nitride semiconductor layer 4 having a relatively high resistance. In addition, an extension 61 extending linearly from the p-electrode 10 is formed, thereby further improving the current distribution. On the other hand, an n-electrode 11 that is a pad electrode is connected to the n-type nitride semiconductor layer 2. As shown in FIGS. 1 and 2, when the substrate 1 is an insulating substrate such as sapphire, both p and n electrodes are formed on the semiconductor layer side. That is, a part of the p-type nitride semiconductor layer 4, the active layer 3, and the n-type nitride semiconductor layer 2 is removed from the semiconductor layer side to expose the n-type nitride semiconductor layer 2, and the n electrode 11 is exposed on the exposed surface. Form.

  The p electrode 10 and the n electrode 11 are electrodes formed for connection to an external circuit. When face-up mounting is performed (when the semiconductor layer side is a main light extraction surface), the p electrode 10 and the n electrode 11 are used. Is connected to an external circuit by wire bonding or the like. When flip-chip mounting is used, that is, when the substrate side is the main light extraction surface, the pad electrode is connected to an external circuit via a eutectic layer (bump: Ag, Au, Sn, In, Bi, Cu, Zn, etc.). Connected to the electrode. The semiconductor layer side of the nitride semiconductor element 20 is covered with an insulating protective film 12 made of an oxide such as Si, Ti, Ta, etc., except for part of the p-electrode 10 and the n-electrode 11. For this reason, the p-electrode 10 and the n-electrode 11 are connected to the outside through the through holes 12 a and 12 b formed in the insulating protective film 12.

  The p electrode 10 and the n electrode 11 (hereinafter collectively referred to as “the present pad electrode”) in the present embodiment have the same configuration and are in contact with the translucent electrode 5 or the n-type nitride semiconductor layer 2. The first metal layer 6, the second metal layer 7, the barrier layer 8 such as Pt, and the bonding layer 9 such as Au are sequentially provided. The composition of the barrier layer 8 and the bonding layer 9 can be appropriately selected according to the method of external connection, and can be omitted.

  FIG. 3 is an enlarged cross-sectional view schematically showing the vicinity of the interface between the pad electrode and the base (translucent electrode 5 or n-type nitride semiconductor layer 2). The first metal layer 6 includes a platinum group (Ru, Rh, Pd, Os, Ir, Pt) as a main component, and is formed in a discrete island shape. Since the platinum group has high adhesion to not only metals but also oxides, it has a strong adhesion to the translucent electrode 5 made of a conductive oxide such as ITO. On the other hand, the second metal layer 7 is made of a material capable of making ohmic contact with the n-type nitride semiconductor layer 2 and is formed on the entire surface covering the first metal layer 6. As a result, the p-electrode 10 and the n-electrode 11 can be made of a common material, and both the adhesion to the translucent electrode 5 and the good ohmic contact to the n-type nitride semiconductor layer 2 can be achieved. A nitride semiconductor device having excellent properties can be provided. Therefore, the manufacturing process can be simplified and the manufacturing cost can be reduced as compared with the conventional nitride semiconductor element in which different materials are used for the p-electrode and the n-electrode.

  That is, conventionally, in order to ensure the adhesion of the p-electrode to the translucent electrode 5, which is a conductive oxide, the first layer of the p-electrode 10 has good adhesion to the oxide Rh or Pt. The platinum group was used. However, in the platinum group such as Rh and Pt, good ohmic contact cannot be obtained with respect to the n-type nitride semiconductor layer 2. Therefore, it is necessary to use a metal material other than the platinum group for the first layer of the n electrode 11. there were. Therefore, it is difficult to form the p-electrode 10 and the n-electrode 11 from the same material. This leads to an increase in lead time due to an increase in the process and increases the manufacturing cost.

  On the other hand, according to the present pad electrode, the p electrode 10 and the n electrode 11 can be made of the same material, and the adhesion to the translucent electrode 5 and the good ohmic contact to the n-type nitride semiconductor layer 2 are achieved. Can be compatible. First, the adhesion to the translucent electrode 5 is good because the first metal layer 6 is made of a platinum group. That is, the first metal layer 6 made of a platinum group has good adhesion to the translucent electrode 5 that is an oxide, and also exhibits good adhesion to the second metal layer 7 that is a metal. In addition, the island-shaped first metal layer 6 serves as an anchor for the second metal layer 7 because the periphery thereof is embedded in the second metal layer 7. Therefore, the present pad electrode shows strong adhesion to the translucent electrode 5.

  On the other hand, the ohmic contact with the n-type nitride semiconductor layer is improved when the first metal layer 6 has an island shape and the second metal layer 7 is a material capable of ohmic contact. That is, the first metal layer 6 made of a platinum group exhibits high contact resistance with respect to the n-type nitride semiconductor layer 2, but the island of the first metal layer 6 is formed by forming the first metal layer 6 in an island shape. The n-type nitride semiconductor layer 2 exposed from between them can be brought into contact with the next second metal layer 7. Therefore, by configuring the second metal layer 7 with a material that can be in ohmic contact with the n-type nitride semiconductor layer 2, good ohmic contact between the pad electrode and the n-type nitride semiconductor layer 2 can be ensured.

  When the second metal layer 7 is a metal that easily oxidizes, such as Al, Ti, W, etc., the first metal layer 6 also contributes to adhesion with the n-type nitride semiconductor layer 2. That is, when a part of the surface of the second metal layer 7 is oxidized during the growth of the second metal layer 7, the nitride semiconductor and the oxide have poor adhesion. It becomes easy to peel between the semiconductor layers 2. However, when the first metal layer 6 including the platinum group is formed between the second metal layer 7 and the n-type nitride semiconductor layer 2, the platinum group has high adhesion to the oxide, and thus the second metal layer Even if a portion of 7 is oxidized, good adhesion to the first metal layer 6 is maintained. Therefore, when the second metal layer 7 is a metal that is easily oxidized, the pad electrode has the first metal layer 6, thereby improving the adhesion with the n-type nitride semiconductor layer 2.

  The first metal layer 6 is not particularly limited as long as it contains a platinum group (Ru, Rh, Pd, Os, Ir, Pt) as a main component and exhibits good adhesion to an oxide. Pt, Pd, Ir, or an alloy selected from these alloys is preferably contained as a main component. More preferably, it consists of these metals or alloys. These metals have high adhesion to oxides such as ITO among the platinum group.

  Further, the shape of the first metal layer 6 is not particularly limited as long as it is a discrete island shape in which the base can be exposed. For example, each island may have various shapes such as a circle, a rectangle, and a polygon in plan view. Further, the diameter of each island is not particularly limited, but is preferably 0.5 to 3 nm. As a result, the adhesion between the second metal layer 7 and the n-type nitride semiconductor layer 2 is improved, and an ohmic contact is easily obtained. The coverage of the first metal layer 6 is preferably 15 to 90%. If the coverage is within this range, the balance between adhesion and ohmic contact will be good. The coverage of the first metal layer 6 is a region in which the cross section is observed with a transmission electron microscope (TEM) or the like, the length of the measured cross section in the interface direction is L, and the first metal layer 6 is in contact with the underlayer. Is defined as 1 / L, where l is the length of.

  Moreover, it is preferable that the film thickness of the 1st metal layer 6 is a 0.1-40 nm thin film, and the 2nd metal layer 7 can contact a base | substrate favorably by this. Further, by setting the film thickness of the first metal layer 6 to 0.1 to 3 nm, it becomes possible to form the first metal layer in an island shape with a fine diameter by sputtering described later.

The first metal layer 6 can be formed in an island shape by patterning using photolithography, but it is preferable to grow in an island shape using sputtering. That is, in sputtering, island-shaped nuclei are generated as clusters in the early stage of growth, and when the growth is continued, the island-shaped clusters are connected to grow into a uniform film. Therefore, by stopping sputtering before growing into a uniform film, it is possible to form the first metal layer 7 in the form of discrete islands having a fine diameter. If the substrate is cooled during sputtering, the island-like clusters are less likely to be connected, and the island-like first metal layer 6 can be made thicker.

  The second metal layer 7 is not particularly limited as long as it is a material that can make ohmic contact with the n-type nitride semiconductor layer 2. For example, it is composed of a metal selected from Al, Ti, V, Cr, Mn, Co, Zn, Ge, Zr, Nb, Mo, Ru, Hf, Ta, W, Re, or an alloy containing a metal selected from these metals. it can. Especially, it is preferable that it is 1 type selected from the alloy containing the metal selected from Al, Ti, W, V, or the metal selected from these. These materials have particularly good ohmic contact with the n-type nitride semiconductor layer 2. The second metal layer 7 is preferably made of a metal having a higher reflectance than the first metal layer 6. For example, Al has a high reflectance with respect to a typical emission wavelength (350 to 800 nm) of the active layer 3 and also has a low absorption. For this reason, when the second metal layer 7 of the p electrode 10 and the n electrode 11 is made of Al, the absorption loss of light emission inside the nitride semiconductor element is reduced, and the light emission efficiency of the nitride semiconductor element 20 is improved.

  If the thickness of the second metal layer 7 is too thin, the contact resistance with the n-type nitride semiconductor layer 2 tends to increase. Moreover, when the film thickness of the second metal layer 7 is too thick, it is not preferable because the film formation time becomes long. Therefore, the thickness of the second metal layer 7 is preferably 50 to 200 nm. The second metal layer 7 can be formed by a normal thin film growth method such as vacuum deposition or sputtering.

  The barrier layer 8 is a metal selected from the group consisting of Ti, Zr, Hf, Ta, W, Re, Os, Ir, Pt, Fe, Co, Ni, Ru, Rh, and Pd, or an alloy containing these metals. It is desirable. In particular, Ti, Ta, W, and Pt are desirable. The thickness of the barrier layer is preferably 10 nm or more because it is not a uniform single film if it is too thin, and is preferably 500 nm or less from the viewpoint of productivity. More preferably, it is 50-300 nm.

  The bonding layer 9 is preferably a metal selected from the group consisting of Au, Al, Ni, and Cu, or an alloy containing these, because of good adhesion to bumps and wires. The thickness of the bonding layer 9 is preferably 100 to 1000 nm because of excellent productivity. More preferably, it is 200-800 nm, Most preferably, it is 200-500 nm.

  In addition, when the bonding layer 9 is made of a material having poor adhesion to the insulating protective film 12 (Au or the like), the pad electrode of the present case is an annular adhesion layer made of Ni, Ti, Pt, Co or the like on the bonding layer 9. You may have. That is, when the bonding layer 9 is made of Au or the like, if the insulating protective film 12 is formed thereon, the adhesiveness of the insulating protective film 12 is low. Peeling may occur. Therefore, as shown in FIG. 4A, an adhesion layer 13 such as Ni is formed on the bonding layer 9, and an insulating protective film 12 is formed thereon. And after making the through-hole 12a (or 12b), as shown to FIG. 4B, the contact bonding layer 13 is etched by Ar sputtering etc., and the bonding layer 9 is exposed. Thereby, peeling of the insulating oxide 12 can be suppressed. The electrode thus formed has a structure in which an annular adhesion layer 13 is formed between the bonding layer 9 and the insulating protective film 12.

  As long as the first metal layer 6 and the second metal layer 7 are formed of a common material, the type and presence of the barrier layer 8 and the bonding layer 9 may be different between the p electrode 10 and the n electrode 11. Moreover, the film thicknesses of the p electrode 10 and the n electrode 11 may be different.

  The shape of the present pad electrode is not particularly limited, and may be various shapes such as a polygon such as a circle, a triangle, and a rectangle. The size of the present pad electrode is not particularly limited, but is set to such a size that a current can efficiently flow through the translucent electrode 5 and the n-type nitride semiconductor layer 2.

  If the p-electrode 10 and the n-electrode 11 are on the same surface as in the present embodiment, the p-electrode 10 and the n-electrode 11 are made of the same material. Can be formed in the same process. If the p-electrode 10 and the n-electrode 11 can be formed in the same manufacturing process as described above, the manufacturing process is simplified, and an inexpensive and highly reliable nitride semiconductor light emitting device can be obtained. As a method of forming the p-electrode 10 and the n-electrode 11 with the same material and in the same process, for example, a mask having a predetermined pattern is formed on the translucent electrode 5 and the n-type nitride semiconductor layer 2 with a resist. After that, for example, the first metal layer 6, the second metal layer 7, the barrier layer 8, and the bonding layer 9 may be sequentially laminated by a sputtering apparatus.

Hereinafter, other configurations of the nitride semiconductor device 20 of the present embodiment will be described in detail.
(Translucent electrode 5)
The translucent electrode 5 of the present embodiment is made of a conductive oxide. Since the conductive oxide is more translucent than a translucent electrode made of a metal thin film, a light emitting element with high luminous efficiency can be obtained. The conductive oxide is preferably an oxide containing at least one element selected from the group consisting of zinc (Zn), indium (In), tin (Sn), and magnesium (Mg). More specifically, ZnO, In ₂ O ₃ , SnO ₂ and ITO can be mentioned. Among them, ITO can be preferably used because it is a material having high light transmittance in visible light (visible region) and high conductivity.

  The translucent electrode 5 made of a conductive oxide preferably has a lower density than the upper surface side in the vicinity of the interface with the p-type nitride semiconductor layer 4. For example, it is preferable that the porous state is only in the vicinity of the interface with the semiconductor layer. The porous state is, for example, a state where a plurality of pores having a diameter of about 20 to 200 nm are present uniformly or non-uniformly. On the other hand, the upper surface side of the translucent electrode 5 made of a conductive oxide is preferably formed as a transparent film with good crystallinity. In the region where the density of the translucent electrode 5 on the semiconductor side is low, the film may be partially amorphous, but is formed as a transparent film or a substantially transparent film. It is preferable.

  It is preferable that this low density region is suppressed to a range of 10 to 50% of the total thickness of the conductive oxide film from the interface with the p-type nitride semiconductor layer 4. Thus, since the density is low only on the p-type nitride semiconductor layer 4 side, the light-transmitting property can be improved while reducing the contact resistance with the p-type nitride semiconductor layer 4. Further, since the density on the surface side of the translucent electrode 5 made of a conductive oxide is high, the adhesion between the translucent electrode 5 and the p-electrode 10 is further improved.

  In addition, although the total film thickness of the translucent electrode 5 which consists of an electroconductive oxide is not specifically limited, For example, it is preferable to set to about 100-1000 nm. Moreover, it is preferable to set the area | region where a density is low to about 10-500 nm. Further, the translucent electrode 5 made of a conductive oxide is not only visible light but also, for example, light generated from the active layer made of the above-described gallium nitride compound semiconductor, that is, a wavelength of about 360 nm to 650 nm, preferably 380 nm to 560 nm. More preferably, the light can be transmitted efficiently without absorbing light having a wavelength of 400 nm to 600 nm, for example, with a transmittance of 90% or more, or 85% or more, more preferably 80% or more. Thereby, it can utilize as an electrode of the nitride semiconductor light emitting element of the intended wavelength.

  The translucent electrode 5 made of a conductive oxide can be formed by a method known in the art. For example, sputtering method, reactive sputtering method, vacuum deposition method, ion beam assisted deposition method, ion plating method, laser ablation method, CVD method, spray method, spin coating method, dipping method, or a combination of these methods and heat treatment Various methods can be used.

Specifically, in order to form a conductive oxide, for example, ITO, a method of forming a film with a sputtering apparatus using a target for forming an ITO film may be used. Moreover, the method etc. which form into a film at room temperature or high temperature by vacuum evaporation are mentioned. In addition, after forming a conductive oxide film such as an ITO film, heat treatment may be performed. Examples of the heat treatment method include a lamp annealing process and an annealing process using a heating furnace. Laser ablation may be used as a process after the ITO film is formed. Furthermore, these methods may be arbitrarily combined.
Further, as a method of forming conductive oxide films having different densities in the film thickness direction, for example, when forming a conductive oxide film such as an ITO film by sputtering, the oxygen partial pressure is small as a sputtering gas. Alternatively, a method of switching from zero gas to a larger gas, or a method of gradually increasing the oxygen partial pressure and a method of forming a film by gradually or rapidly increasing the input power of the sputtering apparatus can be used. In addition, when a conductive oxide film such as an ITO film is formed by vacuum deposition, a method of rapidly or gradually increasing or decreasing the temperature of the semiconductor layer, a method of rapidly decreasing the film formation rate, an ion gun And a method of irradiating oxygen ions from the middle of the film formation.

  In addition, after forming a conductive oxide film, for example, an ITO film, for example, under a reducing gas atmosphere (specifically, carbon monoxide, hydrogen, argon, or a mixed gas of two or more thereof), 200 Examples include a method of annealing at a temperature of about 650 ° C. for a predetermined time according to the thickness of the conductive oxide film. Alternatively, a multi-step heat treatment may be used, such as forming a conductive oxide film, for example, an ITO film halfway, then heat-treating, and subsequently forming and heat-treating. Examples of the heat treatment method include a lamp annealing process and an annealing process using a heating furnace. Further, as a process after forming the ITO film, electron beam irradiation or laser ablation may be used. Furthermore, these methods may be arbitrarily combined.

(Substrate 1)
As the substrate 1 on which the nitride semiconductor light emitting element is formed, for example, a known insulating substrate or conductive substrate such as sapphire, spinel, SiC, nitride semiconductor (for example, GaN), GaAs, or the like can be used. The insulating substrate may be finally removed or may not be removed. When the insulating substrate is not finally removed, both the p electrode and the n electrode are usually formed on the same surface side of the semiconductor layer. When the insulating substrate is finally removed or a conductive substrate is used, both the p-electrode 10 and the n-electrode 11 may be formed on the same surface side of the nitride semiconductor layer, or on different surfaces. Each may be formed.

(N-type nitride semiconductor layer 2, active layer 3, p-type nitride semiconductor layer 4)
The n-type nitride semiconductor layer 2, the active layer 3, and the p-type nitride semiconductor layer 4 are not particularly limited. For example, In _X Al _Y Ga _1- XYN (0 ≦ X, Gallium nitride compound semiconductors such as 0 ≦ Y and X + Y ≦ 1) are preferably used. Each of these nitride semiconductor layers may have a single layer structure, but may have a laminated structure of layers having different compositions and film thicknesses, a superlattice structure, or the like. In particular, the active layer 3 preferably has a single quantum well or multiple quantum well structure in which thin films that produce quantum effects are stacked. The well layer is preferably a nitride semiconductor containing In.

  In general, such a nitride semiconductor layer may be configured as a homostructure, a heterostructure, a double heterostructure, or the like having a MIS junction, a PIN junction, or a PN junction. The nitride semiconductor layer can be formed by a known technique such as MOVPE, metal organic chemical vapor deposition (MOCVD), hydride vapor deposition (HVPE), molecular beam epitaxy (MBE), or the like. Further, the thickness of the nitride semiconductor layer is not particularly limited, and various thicknesses can be applied.

  The laminated structure of the nitride semiconductor layers includes, for example, a buffer layer made of AlGaN, an undoped GaN layer, an n-side contact layer made of Si-doped n-type GaN, and a superlattice in which GaN layers and InGaN layers are alternately laminated. Active layer having a multiple quantum well structure in which GaN layers and InGaN layers are alternately stacked, superlattice layer in which Mg-doped AlGaN layers and Mg-doped InGaN layers are alternately stacked, p-side contact made of Mg-doped GaN Layer, and the like.

Embodiment 2. FIG.
In the present embodiment, gold / nickel oxide is used as the translucent electrode 5 instead of the conductive oxide. Other points are the same as in the first embodiment. Here, the translucent electrode 5 made of gold / nickel oxide is formed by sequentially laminating a gold layer 5a and a nickel oxide layer 5b in order from the side in contact with the p-type nitride semiconductor layer 4, as shown in FIG. It refers to something that has a different structure.

  Gold / nickel oxide is widely used as the translucent electrode 5 of the nitride semiconductor element 1 because it is easier to manufacture than a conductive oxide such as ITO. That is, the gold / nickel oxide electrode is obtained by laminating a metal thin film of nickel and gold in this order from the side in contact with the p-type nitride semiconductor 4 and annealing in an oxidizing atmosphere such as air. The nickel layer and the gold layer are switched upside down by annealing, and the nickel layer is oxidized to become transparent nickel oxide, so that the entire electrode becomes translucent. The gold / nickel oxide electrode thus obtained has a structure in which a gold layer 5a and a nickel oxide layer 5b are sequentially laminated from the side in contact with the p-type nitride semiconductor layer 4.

  The nitride semiconductor element 20 including the translucent electrode 5 made of gold / nickel oxide can also be configured with the same material for the p-electrode 10 and the n-electrode 11 by applying the present invention. Can be simplified and the manufacturing cost can be reduced. That is, since the surface of the translucent electrode 5 made of gold / nickel oxide is also an oxide, a metal having good adhesion is limited to a part of metals such as a platinum group. However, a platinum group having good adhesion to the oxide cannot make good ohmic contact with the n-type nitride semiconductor layer 2. For this reason, the p electrode 10 formed on the translucent electrode 5 and the n electrode 11 formed on the n-type nitride semiconductor layer 2 are generally formed of different materials.

  On the other hand, as described in the first embodiment, in the case of the present pad electrode, the island-shaped first metal layer 6 ensures adhesion with the oxide, and the second metal layer 7 forms the n-type nitride. In order to ensure ohmic contact with the semiconductor layer 2, a nitride semiconductor device having excellent electrical characteristics and reliability while achieving both adhesion and ohmic contact while constituting the p electrode 10 and the n electrode 11 with the same material. Can provide. Thereby, compared with the case where the p electrode 10 and the n electrode 11 are formed with different materials, the process can be simplified and the manufacturing cost can be reduced.

  For the translucent electrode 5 made of gold / nickel oxide, the p electrode 10 and the n electrode 11 can be formed of the same material system if the p electrode 10 is formed before annealing. That is, since the surface of the translucent electrode 5 made of gold / nickel oxide is a gold layer before the nickel layer and the gold layer are turned upside down by annealing, various metals exhibit high adhesion. Therefore, if the p-electrode 10 is formed before the light-transmitting electrode 5 made of gold / nickel oxide is annealed, the same material as that of the n-electrode 11 can be obtained. However, in this case, the nickel layer / gold layer remains as it is on the translucent electrode 5 where the p-electrode 10 is formed even after annealing, and the translucent electrode 5 does not become translucent. Therefore, an absorption loss of light emission occurred at the portion of the p electrode 10. On the other hand, when the present invention is applied, the p-electrode 10 can be formed after the transparent electrode 5 is first annealed to change the entire surface into a gold / nickel oxide layer. Therefore, the entire surface of the translucent electrode 5 is translucent, the absorption loss generated in the p-electrode 10 is improved, and the light emission efficiency is improved.

  In the translucent electrode 5 made of gold / nickel oxide used in the present embodiment, the film thickness of the gold layer 5a is preferably 6 to 30 nm, thereby improving the balance between sheet resistance and translucency. . That is, if the gold layer is too thick, the translucency decreases, and if the gold layer 5a is too thin, the sheet resistance increases. Further, the thickness of the nickel oxide layer 5b is preferably 6 to 10 nm. As a result, ohmic contact is improved. Note that partially unoxidized nickel may remain in the nickel oxide.

Embodiment 3 FIG.
In this embodiment, the insulating protective film 12 made of an oxide is formed before the p electrode 10 and the n electrode 11 are formed. Other points are the same as in the first embodiment. That is, in Embodiment 1, the insulating protective film made of oxide is formed after the p-electrode 10 and the n-electrode 11 are formed on the translucent electrode 5 and the n-type nitride semiconductor layer 2. In the embodiment, the insulating protective film 12 is formed before forming the p electrode and the n electrode.

  FIG. 6 is an enlarged cross-sectional view schematically showing the vicinity of the n electrode 11 of the nitride semiconductor device 20 according to the present embodiment. The structure in the vicinity of the p electrode 10 is the same. In the present embodiment, an insulating protective film 12 is formed between the n electrode 11 and the n-type nitride semiconductor layer 2, and the n electrode 11 and the n-type nitride are passed through the through-hole 12 b formed in the insulating protective film 12. The physical semiconductor layer 2 is in contact. The n electrode 11 is formed in a slightly larger area than the through hole 12b of the insulating protective film in order to avoid the exposure of the n-type nitride semiconductor layer 2. For this reason, the n-electrode 11 and the insulating protective film 12 are in contact with each other at the annular portion surrounding the through hole 12 b of the insulating protective film 12. When a conventional n-electrode, for example, the first layer is Ti or Al, such a structure cannot be taken. This is because Ti and Al have poor adhesion to oxides, and peeling may occur between the n-electrode 11 and the insulating protective film 12. On the other hand, since the n-electrode 11 of the present embodiment has the island-shaped first metal layer 6 containing a platinum group, it exhibits high adhesion to the insulating protective film 12 made of oxide. . Therefore, even with the structure as shown in FIG. 6, a highly reliable nitride semiconductor device can be obtained.

  Further, with the structure as in the present embodiment, even when a material having poor adhesion to the insulating protective film 12 is selected for the bonding layer 9, the adhesion layer 13 as described in the first embodiment is formed. The process to do becomes unnecessary. Therefore, the manufacturing process of the electrode can be simplified and the manufacturing cost can be further reduced.

Embodiment 4 FIG.
FIG. 7 is a schematic cross-sectional view showing the nitride semiconductor device 20 according to the fourth embodiment. In the present embodiment, when the translucent electrode 5 made of a conductive oxide such as ITO is formed on the surface of the p-type nitride semiconductor layer 4, the exposed material of the n-type nitride semiconductor layer 2 is made of the same material. An n-side translucent electrode 5 ′ (= translucent material) is formed. And when forming the n electrode 11, it forms so that n side translucent electrode 5 'may be covered. Thus, by forming a translucent electrode on both the p-side and the n-side and covering the n-side translucent electrode 5 ′ with the n-electrode 11, the absorption loss of light emission by the n-electrode 11 is reduced and n The side translucent electrode 5 'can be prevented from peeling off. Other points are the same as in the first embodiment.

  FIG. 8 is an enlarged cross-sectional view showing the vicinity of the n-electrode 11 in FIG. An n-side translucent electrode 5 ′ is formed on the surface of the n-type nitride semiconductor layer 2 and is in ohmic contact with the n-type nitride semiconductor layer 2. An n electrode 11 is formed so as to cover the n-side translucent electrode 5 ′ and to be joined to the n-type nitride semiconductor layer 2. The electrode configured in this way can reduce the absorption loss of light emission by the n-electrode 11. That is, the n-electrode 11 is preferably made of a metal having a relatively high reflectance, but a certain amount of absorption loss always occurs when light is reflected on the lower surface of the n-electrode 11. If the n-side translucent electrode 5 ′ is formed on the main junction surface with the n-type nitride semiconductor layer 2 as in the present embodiment, the translucent electrode 5 ′ hardly absorbs light. Absorption loss when reflected by the electrode can be reduced.

  However, since an oxide such as ITO does not necessarily have good adhesion to the n-type nitride semiconductor layer, peeling is likely to occur between the n-side translucent electrode 5 ′ and the n-type nitride semiconductor layer 2. Therefore, in the present embodiment, the n-side translucent electrode 5 ′ is covered with the n-electrode 11, and the n-electrode 11 is bonded to the n-type nitride semiconductor layer 2 exposed around the n-side translucent electrode 5 ′. Let The n electrode 11 thus formed exhibits strong adhesion with the translucent electrode 5 ′ by the first metal layer 6 and exhibits strong adhesion with the n-type nitride semiconductor layer 2 by the second metal layer 7. Therefore, by forming the n-electrode 11 so as to cover the n-side translucent electrode 5 ′, peeling of the n-side translucent electrode 5 ′ from the n-type nitride semiconductor layer 2 can be suppressed.

  A preferable material for the n-side translucent electrode 5 ′ in the present embodiment is the same as that described for the translucent electrode 5 in the first embodiment. The n-side translucent electrode 5 ′ is preferably formed simultaneously with the same material as the translucent electrode 5 formed on the p-type nitride semiconductor layer 4, but is not necessarily limited thereto. For example, the n-side translucent electrode 5 ′ may be formed of a translucent conductive oxide different from the p-side. In addition, since the n-electrode 11 can make ohmic contact with the n-type nitride semiconductor layer 2, the n-side translucent electrode 5 'may be a translucent material having no conductivity.

  In addition, the n electrode 11 in the present embodiment may be bonded to both the n-side translucent electrode 5 ′ and the n-type nitride semiconductor layer 2, and is not necessarily limited to the configuration shown in FIGS. . For example, as shown in FIG. 9, even though a through hole or a through groove 5 a is formed in a part of the n-side translucent electrode 5 ′ and the n electrode 11 is joined to the n-type nitride semiconductor layer 2 through them. good. Instead of covering the entire upper surface of the n-side translucent electrode 5 ′ with the n-electrode 11, only the side surface of the n-side translucent electrode 5 ′ and a part of the upper surface continuous with the side surface may be covered. (I think it's hard to imagine when thinking about wires, but I'll spread it just in case).

A nitride semiconductor device having the structure shown in FIG. 1 was fabricated as follows.
A buffer layer made of an AlN layer is formed on the sapphire substrate 1, and a contact layer made of n-type GaN doped with Si 7 × 10 ¹⁸ cm ⁻³ as an n-type nitride semiconductor layer 2 thereon, and Si A lower cladding layer made of n-type GaN doped with 5 × 10 ¹⁸ cm ⁻³ was formed. Next, a single quantum well structure having an In _0.95 Ga _0.05 N well layer is formed as the active layer 3, and Mg is doped 1 × 10 ¹⁸ cm ⁻³ as the p-type nitride semiconductor layer 4. An upper cladding layer made of p-type Al _0.25 Ga _0.75 N and a contact layer made of p-type GaN doped with 5 × 10 ¹⁹ cm ^{−3 of} Mg were formed.

  Next, a photoresist was formed on the p-type nitride semiconductor layer 4, and the photoresist was left only in the region that became the light emitting surface by lithography. Etching was performed until the n-type contact layer was exposed by reactive ion etching, and the photoresist was removed.

  Next, ITO was formed on the p-type GaN contact layer. First, after being immersed in buffered hydrofluoric acid (BHF) for 1 minute at room temperature, an ITO film was formed by a vacuum sputtering apparatus. Specifically, Ar was used as the sputtering gas, and discharge was performed under a pressure of 0.5 Pa to form 200 nm ITO. Etching was performed so that a predetermined region on the p-type GaN contact layer remained. In order to make ohmic contact between the ITO and the p-type GaN contact layer, heat treatment was performed at 550 ° C. in a nitrogen atmosphere.

Next, the p electrode 10 and the n electrode 11 were simultaneously formed as follows.
Using a sputtering apparatus, Rh / Al / Pt / Au was laminated so that the film thickness was 3 nm, 100 nm, 30 nm, and 50 nm at a pressure of 4 × 10 ⁻⁴ Pa or less. Here, Rh is the first metal layer 6, Al is the second metal layer 7, Pt is the barrier layer 8, and Au is the bonding layer 9. The sputtering conditions can be as follows. First, the substrate temperature is in the range of room temperature to 500 ° C., preferably room temperature. After exhausting the inside of the chamber to 10 ⁻⁴ to 10 ⁻⁷ Pa, a sputtering gas is introduced to bring the pressure to 0.1 to 10 Pa, and then discharge is performed. Preferably it sets to the range of 0.2-5Pa. As the sputtering gas, He, Ne, Ar, Kr, Xe, or the like can be used, but easily available Ar is preferable. It is preferable to supply electric power of 0.1 to 2 kW. The thickness of the layer to be formed can be adjusted by the discharge time and supply power. In the Rh / Al / Pt / Au layer formed in this way, Rh, which is the first metal layer 6, was island-shaped, and the other layers were continuous films. Thereafter, the metal film other than the predetermined electrode formation region was removed by a lift-off method.

  After the obtained nitride semiconductor device is wire-bonded at about 150 ° C. to accelerate deterioration, a shear test between the wire bonding portion and the p-electrode 10 is performed with a shear tester (BT-2400 manufactured by DAGE). And the presence / absence of peeling between the translucent electrode 5 and the p-electrode 10 was examined. The peeling occurrence rate was almost 0%. Moreover, when the current-voltage characteristic was measured, it became a graph shown with the code | symbol 22 in FIG. 10, and showed favorable ohmic contact property.

[Comparative Example 1]
A nitride semiconductor device was fabricated in the same manner as in Example 1 except that Rh / Pt / Au was formed at a film thickness of 100 nm / 30 nm / 50 nm as the p electrode 10 and the n electrode 11.

  After the obtained nitride semiconductor device is wire-bonded at about 150 ° C. to accelerate deterioration, a shear test between the wire bonding portion and the p-electrode 10 is performed with a shear tester (BT-2400 manufactured by DAGE). Then, the presence or absence of peeling between the translucent electrode 5 and the p-electrode 10 was examined, and the occurrence rate of peeling was almost 0%. However, when the current-voltage characteristics were measured, a graph indicated by reference numeral 24 in FIG. 10 was obtained, which showed a very large contact resistance.

[Comparative Example 2]
A nitride semiconductor device was fabricated in the same manner as in Example 1 except that Al / Pt / Au was formed at a film thickness of 100 nm / 30 nm / 50 nm as the p electrode 10 and the n electrode 11.

  When the current-voltage characteristics of the obtained nitride semiconductor device were measured, a graph indicated by reference numeral 26 in FIG. 10 was obtained, and good ohmic contact was obtained. However, after the obtained nitride semiconductor device is wire-bonded at about 150 ° C. for accelerating deterioration, it is measured between the wire bonding portion and the p-electrode 10 by a shear tester (BT-2400 manufactured by DAGE). When a shear test was performed to examine the presence or absence of peeling between the translucent electrode 5 and the p-electrode 10, the occurrence rate of peeling was about 5%.

1 is a cross-sectional view schematically showing a nitride semiconductor device according to the first embodiment. FIG. 2 is a plan view of the nitride semiconductor device shown in FIG. FIG. 3 is a schematic cross-sectional view showing an example of an electrode in the present invention. FIG. 4A is a process diagram illustrating a manufacturing process of an electrode including an adhesion layer. FIG. 4B is a process diagram illustrating a process following the process illustrated in FIG. 4A. FIG. 5 is a partially enlarged view showing the vicinity of the electrode of the nitride semiconductor device according to the second embodiment. FIG. 6 is a partially enlarged view showing the vicinity of the electrode of the nitride semiconductor device according to the third embodiment. FIG. 7 is a cross-sectional view schematically showing a nitride semiconductor device according to the fourth embodiment. FIG. 8 is a partially enlarged view showing the vicinity of the electrode of the nitride semiconductor device shown in FIG. FIG. 9 is a partial enlarged cross-sectional view showing a modification of FIG. FIG. 10 is a graph showing current-voltage characteristics of Examples and Comparative Examples.

Explanation of symbols

1 substrate,
2 n-type nitride semiconductor layer,
3 active layer,
4 p-type nitride semiconductor layer,
5 translucent electrode,
6 first metal layer,
7 Second metal layer,
8 barrier layer,
9 Bonding layer,
10 p electrode 11 n electrode,
12 Insulating protective film

Claims (10)

an n-type nitride semiconductor layer and a p-type nitride semiconductor layer; an n-electrode on the n-type nitride semiconductor layer; a translucent electrode on the p-type nitride semiconductor layer; A nitride semiconductor device having an electrode formed thereon,
The translucent electrode has at least a surface made of an oxide,
The n electrode and the p electrode include a first metal layer and a second metal layer in order from the side in contact with the n-type nitride semiconductor layer or the translucent electrode,
The first metal layer includes a platinum group metal and is formed in discrete island shapes.
The second metal layer is made of a metal capable of being in ohmic contact with the n-type nitride semiconductor layer, and the n-type nitride semiconductor layer or the translucent electrode exposed from the islands of the first metal layer. A nitride semiconductor device that is in contact with each other.   The nitride semiconductor device according to claim 1, wherein the first metal layer has a thickness of 0.1 to 40 nm.   3. The nitride semiconductor light-emitting element according to claim 1, wherein the first metal layer contains, as a main component, one selected from Rh, Pt, Pd, Ir, or an alloy thereof.   The second metal layer is made of Al, Ti, V, Cr, Mn, Co, Zn, Ge, Zr, Nb, Mo, Ru, Hf, Ta, W, Re, or an alloy containing a metal selected from these. The nitride semiconductor device according to any one of claims 1 to 3, wherein the nitride semiconductor device is one selected from the group.   The nitride according to any one of claims 1 to 4, wherein the second metal layer is one selected from the group consisting of Al, Ti, W, V, or an alloy thereof. Semiconductor element.   6. The nitride semiconductor device according to claim 1, wherein the translucent electrode is made of a conductive oxide.   The nitride semiconductor device according to claim 6, wherein the conductive oxide is indium tin oxide.   6. The nitride semiconductor device according to claim 1, wherein the translucent electrode includes a gold layer and a nickel oxide layer from a side in contact with the p-type nitride semiconductor layer.   An insulating protective film is formed between the n-type nitride semiconductor layer and the n electrode, and the n electrode and the n-type nitride semiconductor layer are in contact with each other through a through hole formed in the insulating protective film. The nitride semiconductor device according to claim 1, wherein the nitride semiconductor device is characterized in that: A translucent material is formed on the surface of the n-type nitride semiconductor layer, and the n-electrode is formed so as to cover at least a part of the translucent material and to be bonded to the n-type nitride semiconductor layer. The nitride semiconductor device according to claim 1, wherein the nitride semiconductor device is formed.

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