JP4325232B2 - Nitride semiconductor device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a nitride semiconductor (In) used in a light emitting element such as a light emitting diode element (LED) or a laser diode element (LD), a light receiving element such as a solar cell or an optical sensor, or an electronic device such as a transistor or a power device. _x Al _y Ga _1-xy N, 0 ≦ x, 0 ≦ y, x + y ≦ 1) For child Related.
[0002]
[Prior art]
Sapphire has been demonstrated to be desirable as a substrate for growing high-efficiency nitride semiconductor light-emitting devices because of the stability of the epitaxial growth process in a high-temperature ammonia atmosphere. Specifically, nitride semiconductor elements grown on sapphire substrates are used for high-intensity blue LEDs, pure green LEDs, and LDs (laser diodes), and are used for full-color displays, signal displays, image scanners, optical disks. A medium such as a DVD for storing a large amount of information such as a light source, a light source for communication, or a printing device. Furthermore, application to electronic devices such as field effect transistors (FETs) is also expected.
[0003]
Although nitride semiconductor is a promising semiconductor material, it is difficult to manufacture a bulk single crystal. Therefore, at present, a hetero epitaxy technique for growing GaN on a heterogeneous substrate such as sapphire or SiC by using metal organic chemical vapor deposition (MOCVD) is widely used. In particular, when a sapphire substrate is used, a method in which AlGaN is formed as a buffer layer on the sapphire substrate at a low temperature of about 600 ° C., and then a nitride semiconductor layer is grown thereon. Thereby, the crystallinity improvement of the nitride semiconductor layer was realized.
[0004]
However, sapphire is an insulator with poor thermal conductivity, which causes the device to have a limited structure. For example, in the case of a conductive substrate such as GaAs or GaP, one electrode can be provided on the upper surface of the semiconductor device, and another electrode can be provided on the bottom surface. Two electrodes are provided on the same surface. For this reason, when an insulating substrate such as sapphire is used, the effective light emitting area in the same substrate area is narrowed as compared with the conductive substrate. Furthermore, when an insulator substrate is used, the number of elements (chips) that can be taken from a wafer having the same diameter is small.
[0005]
Nitride semiconductor elements using insulator substrates such as sapphire are face-up and face-down types, but these have both electrodes on the same surface, so the current density increases locally and the element (chip). Generates heat. In addition, since a wire is required for each of the pn electrodes in the wire bonding process for the electrodes, the chip size is increased and the yield of the chip is reduced. Furthermore, sapphire has a high hardness and a hexagonal crystal structure. Therefore, when sapphire is used as a growth substrate, it is necessary to separate the sapphire substrate by scribing, and the number of manufacturing steps must be increased compared to other substrates.
[0006]
On the other hand, an element having a structure in which a p electrode and an n electrode are arranged to face each other has been proposed. For example, in Patent Document 2, an n-electrode made of Ti / Al is formed on the back surface of an n-type GaN substrate, and a p-electrode made of Ni / Au is formed on the surface of a p-type contact layer made of p-type GaN. A nitride semiconductor device to be formed is described. In Patent Document 3, in a nitride semiconductor crystal in which a gallium nitride layer is stacked on a sapphire substrate, the sapphire substrate and the GaN buffer layer are ground and removed, an n electrode is formed on the exposed n-type GaN, and a p-type is formed. A semiconductor light emitting device chip is described in which electrodes and n-type electrodes are formed on opposite end faces. By arranging the p electrode and the n electrode to face each other, it can be expected that the current distribution can be made uniform and the heat generation of the element can be suppressed.
[0007]
Patent Document 2 describes that a Ti / Al electrode is used as an n electrode of an element in which the p electrode and the n electrode are arranged to face each other. This Ti / Al electrode is made of, for example, an alloy of titanium and aluminum or laminated with titanium and aluminum as an electrode capable of obtaining ohmic contact with the n-type gallium nitride compound semiconductor layer in Patent Document 3. As described as an electrode composed of a multilayer film, it is a typical n electrode in an element in which a p electrode and an n electrode are formed on the same surface. Other typical n electrodes include W / Al electrodes.
[0008]
[Patent Document 1]
JP 7-45867 A
[Patent Document 2]
JP 2000-340892 A
[Patent Document 3]
JP-A-11-238913
[0009]
[Problems to be solved by the invention]
However, even if the Ti / Al electrode is used as the n electrode of an element having a structure in which the p electrode and the n electrode are arranged to face each other, the contact resistance is large and good ohmic characteristics cannot be obtained. There was a problem that the characteristics expected of the device could not be obtained sufficiently.
[0010]
Accordingly, the present invention solves the above-described problem, and has a structure in which a p-electrode and an n-electrode are arranged to face each other, and a nitride semiconductor device having an n-electrode that can obtain good ohmic characteristics. Child The purpose was to provide.
[0011]
[Means for Solving the Problems]
In order to solve the above problems, a nitride semiconductor device according to the present invention has a p-electrode formed on one main surface of a laminate made of a nitride semiconductor, an n-electrode formed on the other main surface, and both electrodes The nitride semiconductor device is configured to face each other, wherein the other main surface is the (000-1) plane of the n-type nitride semiconductor layer, and the n electrode is in contact with the (000-1) plane. It has an alloy layer containing an n-type impurity.
[0012]
According to the present invention, an n-electrode having an alloy layer containing an n-type impurity is formed so that the alloy layer is in contact with the (000-1) plane of the n-type nitride semiconductor layer. An n-electrode having good ohmic contact with the (000-1) plane, which was difficult with an electrode, can be obtained. The reason for this is not clear, but the following reasons are possible.
GaN having a wurtzite type crystal structure is asymmetric in the c-axis direction and has a Ga plane (0001) (hereinafter referred to as + c plane) and an N plane (000-1) (hereinafter referred to as -c plane). The N atoms are arranged on the surface of the -c plane. A conventional n-electrode, for example, a Ti / Al electrode is formed on the + c plane, whereas the n-electrode of the present invention is formed on the -c plane. The n-type impurities in the alloy layer are combined with dangling bonds of N atoms exposed on the −c plane and change to, for example, SiN. The n-type impurity is originally easily incorporated into the crystal lattice of the nitride semiconductor, and can react with N atoms on the surface to such an extent that the crystal lattice is not broken. Thereby, it is considered that the vicinity of the surface of the GaN layer (several atomic layers) has a higher carrier concentration than in the GaN layer, the contact resistance is reduced, and the ohmic characteristics are improved.
Since the element of the present invention can reduce the contact resistance in the element in which both electrodes are arranged to face each other, the electrode area can be reduced, thereby further reducing the size of the element. In addition, since the contact resistance is reduced, the current distribution is made uniform and the heat generation of the element can be suppressed. In the case of a light emitting element, the current flows through the entire light emitting layer, and the light emission is more uniform and high intensity. Can be made. Needless to say, since the electrodes are opposed to each other, a short circuit between the p electrode and the n electrode can be prevented.
[0013]
The element of the present invention is the above n-type impurity contained in n-type nitride semiconductor layer But The same as the n-type impurity contained in the alloy layer And the n-type impurity is Si or Ge. Thereby, a favorable ohmic contact can be obtained.
[0016]
The element of the present invention can be produced, for example, by the following production method. That is, a method of manufacturing a nitride semiconductor device in which a p-electrode, a laminate composed of a plurality of nitride semiconductor layers, and an n-electrode are laminated on one main surface of a conductive substrate having two opposing main surfaces And at least an n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer are grown on one main surface of an insulating growth substrate having two opposing main surfaces. A laminated body for bonding, and a first bonding layer made of one or more metal layers is provided on the p-type nitride semiconductor layer, and one or more layers are formed on one main surface of the conductive substrate. A second bonding layer made of a metal layer is provided, the first bonding layer and the second bonding layer are opposed to each other, the bonding laminate and the conductive substrate are bonded by heating and pressure bonding, and the bonding is performed. By removing the insulating growth substrate of the laminated body to expose the n-type nitride semiconductor layer, And forming an n-electrode having an alloy layer in contact with the n-type nitride semiconductor layer formed by the exposed include.
[0017]
In addition, this departure In the light The first bonding layer and the second bonding layer have a first eutectic forming layer and a second eutectic forming layer, respectively, and constitute the first and second eutectic forming layers at the time of bonding. The eutectic can be formed by diffusing the metals to be diffused together.
[0018]
In addition, this departure In the light Is in contact with one main surface of the insulating growth substrate and Ga _e Al _1-e An underlayer including a buffer layer made of N (0 <e ≦ 1) and a high-temperature growth layer made of either undoped GaN or GaN doped with n-type impurities can be provided.
[0019]
In particular, in a nitride semiconductor element in the ultraviolet region of 380 nm or less, Ga contacts with one main surface of the growth substrate. _e Al _1-e An underlayer including a buffer layer made of N (0 <e ≦ 1) and a high-temperature growth layer made of either undoped GaN or GaN doped with n-type impurities can be provided. The underlayer has the effect of improving the crystallinity of the nitride semiconductor grown thereon. Furthermore, a high-temperature growth layer made of either undoped GaN or GaN doped with n-type impurities can greatly improve the crystallinity of the nitride semiconductor layer grown thereon by growing this layer. . In order to obtain a nitride semiconductor device with good crystallinity, it is necessary to grow a GaN layer at a high temperature on the growth substrate and further on the buffer layer. Even if an active layer or the like is grown without growing this layer, the crystallinity is very poor, and in a nitride semiconductor light emitting device or the like, the light emission output is very weak, which is not practical.
[0020]
Thus, by providing a high-temperature growth layer made of GaN, a nitride semiconductor element with good crystallinity can be obtained. However, when GaN is included as an underlayer, the active layer is separated from the active layer by self-absorption of GaN in the ultraviolet region. A part of the light is absorbed by the GaN layer, and the light emission output decreases. In the present invention, after bonding the conductive substrates, the growth substrate and the underlying GaN are removed, so that self-absorption can be achieved while maintaining good crystallinity of the nitride semiconductor constituting the device. It becomes possible to suppress.
[0021]
In addition, this departure In the light After removing the insulating growth substrate, the buffer layer and the high temperature growth layer can be removed.
[0022]
In addition, this departure In the light In the removing step, the entire surface of the other main surface of the growth substrate can be irradiated with electromagnetic waves to remove the growth substrate and the underlayer.
[0023]
In addition, this departure Clearly Accordingly, the coating layer containing the fluorescent material can be formed on at least a part of the surface of the nitride semiconductor device. The light-emitting element of the present invention is formed by forming a coating layer containing a fluorescent material that absorbs light from the light-emitting element and emits light having a wavelength different from the light on at least a part of the surface of the light-emitting element. Can do.
[0024]
In the element of the present invention, in particular, the light emitting element, the nitride semiconductor element formed by bonding to the conductive substrate is applied to the active layer of Al _a In _b Ga _1-ab By forming a coating layer containing a fluorescent material that absorbs part or all of light from N (0 ≦ a ≦ 1, 0 ≦ b ≦ 1, a + b ≦ 1) and emits light of different wavelengths. Can emit light of various wavelengths. In particular, by containing YAG, white light can be emitted, and uses such as a light source for illumination are greatly expanded.
[0025]
In addition, regarding fluorescent substances that emit light of different wavelengths by absorbing part or all of the light, materials that absorb visible light and emit different light are limited, and there is a problem in material selectivity. However, there are a large number of materials that absorb ultraviolet light and emit different light, and the materials can be selected according to various applications. One of the factors from which the material can be selected is that the fluorescent material that absorbs ultraviolet light has a higher light conversion efficiency than the visible light conversion efficiency. Especially in white light, the possibilities are further expanded, such as obtaining white light with high color rendering properties. According to the present invention, a nitride semiconductor light emitting device with less self-absorption can be obtained in a nitride semiconductor device that emits light in the ultraviolet region, and a white light emitting device with very high conversion efficiency can be obtained by coating a fluorescent material. Can do.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic cross-sectional view showing an example of the structure of a nitride semiconductor device according to the present invention. The element is formed such that a bonding layer 7, a p-electrode 6, a laminate 2 made of a nitride semiconductor, and an n-electrode 9 are sequentially stacked on a conductive substrate 8, and the p-electrode 6 and the n-electrode 9 face each other. The p-side protective film 20 and the n-side protective film 21 are formed in addition to the exposed surfaces of the p-electrode 6 and the n-electrode 9, respectively. Here, the stacked body 2 has a structure in which the p-type nitride semiconductor layer 5, the active layer 4, and the n-type nitride semiconductor layer 3 having the dimple 331 on the exposed surface are sequentially stacked from the p-electrode 6 side. ing. Note that the bonding layer 7 plays a role of bonding the conductive substrate 8 and the stacked body 2, and the first bonding layer 71 and the second bonding layer 72 are integrally formed.
[0027]
More specifically, the surface of n-type nitride semiconductor layer 3 has an exposed -c plane, and n electrode 9 has an alloy layer (not shown) that contacts the -c plane and contains an n-type impurity. Yes. Here, as the n-type impurity, a known substance used for a nitride semiconductor can be used, and examples thereof include C, Si, Ge, Se, and S. Among these, using Si is preferable because a GaN layer having a high carrier concentration can be formed near the surface.
[0028]
The metal that forms the alloy layer is a metal that forms an alloy with the n-type impurity, and is at least selected from the group consisting of Al, Ag, Ti, Mo, Nb, Ta, Hf, Pt, and W, for example. One kind of metal can be used. The composition of a preferable alloy layer is W—Al—Si, W—Si, and more preferably W—Si. By using these, an alloy containing Si can be easily formed. In addition, W _x Si _1-x In this case, it is preferable that 0.3 ≦ x <1. This is because if n is smaller than 0.3, the n-electrode is easily peeled off.
[0029]
The n-electrode is preferably a multilayer film in which one or more metal layers are further laminated on the alloy layer. For example, the alloy layer further includes Pt / Au, W / Au, Ti / Au, Ni / Au, etc. It is preferable to form a metal multilayer film. When the alloy layer contains Al, Al easily diffuses. Therefore, a diffusion barrier layer such as Ti is included as a layer for preventing the diffusion of Al closest to the alloy layer of the metal multilayer film layer. Most preferably, the structure including the alloy layer is W-Si / Pt / Au. The n-electrode can be produced by forming one or more metal layers on the alloy layer or alloy forming layer by vapor deposition or sputtering to form a multilayer film, and then annealing. The thickness of the n electrode is preferably 0.1 to 1.5 μm.
[0030]
Hereinafter, a method for manufacturing a nitride semiconductor light emitting device according to the present invention will be described. 2 to 4 are schematic cross-sectional views showing an example of the manufacturing process of the nitride semiconductor light emitting device according to the present invention. On the surface of the growth substrate 1, a base layer 32 composed of a buffer layer 31a and a high temperature growth layer 31b is formed (FIG. 2A). Next, an n-type cladding layer 33 is stacked on the base layer 32 to form the n-type nitride semiconductor layer 3, and the p-type nitride including the active layer 4, the p-type cladding layer 51 and the p-type contact layer 52 is formed. The semiconductor layers 5 are sequentially stacked (FIG. 2A).
[0031]
Next, the p-electrode 6 is formed on the p-type contact layer 52 (FIG. 2B). Here, after forming the p-electrode 6 on the p-type contact layer 52, an annealing process for obtaining an ohmic contact is performed. Further, an insulating p-side protective film 20 is formed so as to cover other than the exposed surface of the p-electrode 6.
[0032]
Next, a first bonding layer 71 made of one or more metal layers is formed on the p-electrode 6 (FIG. 2C). On the other hand, a second bonding layer 72 made of one or more metal layers is formed on the surface of the conductive substrate 8 (FIG. 2C).
[0033]
Next, the conductive substrate 8 is laminated on the growth substrate 1 so that the first bonding layer 71 and the second bonding layer 72 are opposed to each other and bonded by heating and pressing (FIG. 3D). ). Here, the first bonding layer 71 and the second bonding layer 72 are integrated at the time of bonding to form the bonding layer 7.
[0034]
Next, the growth substrate 1 bonded to the conductive substrate 8 is placed in a polishing machine, the growth substrate 1 is lapped, the growth substrate 1 and the base layer 32 are removed, and the n-type cladding layer 33 is exposed. (FIG. 3E). Then, the surface of the n-type cladding layer 33 is wet-etched, for example, to expose the −c plane.
[0035]
Next, in order to improve the light extraction efficiency, the exposed surface of the n-type cladding layer 33 is masked with a resist having a predetermined pattern, and etched by RIE to form a dimple 331 having an uneven surface on the surface of the n-type cladding layer 33. (FIG. 4 (f)). This step can be omitted.
[0036]
Next, a predetermined pattern of SiO is formed on the exposed surface of the n-type cladding layer 33. ₂ A mask is formed, and an isolation groove 10 for element isolation is formed (FIG. 4G).
[0037]
Next, a multilayer film including an n-type impurity and a metal that forms an alloy with the n-type impurity is formed on the n-type cladding layer 33, annealed to form the n-electrode 9, and the n-electrode 9 exposed. An insulating n-side protective film 21 is formed so as to cover other than the surface (FIG. 4H). Then, the element is separated into chips by dicing (FIG. 4I).
[0038]
In the method of the present invention, the growth substrate is made of sapphire or spinel (MgAl) whose main surface is any one of the C-plane, R-plane, and A-plane. ₂ O ₄ And an oxide substrate lattice-matched with a nitride semiconductor, and sapphire and spinel are preferable. Further, it is preferable to use an off-angle substrate for growth. In this case, the crystallinity of the underlayer made of gallium nitride can be improved by using a step-off angle.
[0039]
The growth substrate used in the nitride semiconductor light emitting device of the present invention preferably has dimples having an uneven shape on the growth surface. It is preferable that a nitride semiconductor layer can be grown by facet growth of a nitride semiconductor with few crystal defects by growing on a growth substrate for dimples having an uneven shape. Specifically, the dimple is preferable because at least the step of the recess is 5 nm or more, and in particular, a flat surface exists in the recess and the protrusion, so that the active layer is easily smoothed. When the active layer has irregularities, the yield in light emission characteristics is deteriorated.
[0040]
When a nitride semiconductor layer is stacked on the growth substrate, a nitride semiconductor with improved crystallinity can be obtained by growing ELOG (Epitaxially Lateral Overgrowth) on the base layer. Specifically, a base layer is grown on the growth substrate, a plurality of stripe-shaped masks are formed on the base layer, and a nitride semiconductor is selectively grown from the opening of the mask, accompanied by lateral growth. A nitride semiconductor layer (lateral growth layer) formed by growth is formed. Since this laterally grown layer has reduced threading dislocations, the crystallinity of the nitride semiconductor formed on the laterally grown layer can be improved.
[0041]
As the growth substrate, it is preferable to use a substrate in which the main surface of the material to be the growth substrate is off-angled, and further a substrate that is off-angled stepwise. When an off-angle substrate is used, three-dimensional growth of the surface is not seen, step growth appears, and the surface tends to be flat. Further, when the direction along the step (step direction) of the sapphire substrate that is off-angled in a step shape is formed perpendicular to the A surface of the sapphire, the nitride semiconductor step surface is in the direction of the laser resonator It is preferable that the laser beam is less diffusely reflected by the surface roughness.
[0042]
The conductive substrate may be any substrate material having conductivity, for example, a semiconductor substrate made of a semiconductor such as Si or SiC, a single metal substrate, or two types having a small non-solid solution or a small solid solution limit. Although a metal substrate made of a composite of the above metals can be used, it is preferable to use a metal substrate. This is because the metal substrate has superior mechanical characteristics as compared with the semiconductor substrate, is easily elastically deformed, and further plastically deformed, and is difficult to break. Furthermore, the metal substrate has one or more metals selected from highly conductive metals such as Ag, Cu, Au, and Pt, and one type selected from metals having high hardness such as W, Mo, Cr, and Ni. What consists of the above metals can be used. Furthermore, it is preferable to use a Cu—W or Cu—Mo composite as the metal substrate. This is because Cu has high thermal conductivity and has excellent heat dissipation. Further, in the case of a Cu—W composite, the Cu content x is 0 <x ≦ 30 wt%, and in the case of a Cu—Mo composite, the Cu content x is 0 <x ≦ 50 wt%. Is preferred. Further, a composite of a metal such as Cu-diamond and ceramics can be used. The thickness of the conductive substrate is preferably 50 to 500 μm in order to improve heat dissipation.
[0043]
Further, it is preferable that the first bonding layer has at least an ohmic contact with the p-type nitride semiconductor layer and a p-electrode having a high reflectance in contact with the p-type nitride semiconductor layer. Any of Rh, Ag, Ni / Au, Ni / Au / Rh, and Rh / Ir, more preferably Rh / Ir, can be used for the p-electrode. Here, since the p-electrode is formed on the p-type nitride semiconductor layer having a higher resistivity than the n-type nitride semiconductor layer, the p-electrode is preferably formed on almost the entire surface of the p-type nitride semiconductor layer. The thickness of the p electrode is preferably 0.05 to 0.5 μm.
[0044]
In addition, it is preferable to form an insulating protective film on the exposed surface of the p-type nitride semiconductor layer on which the p-electrode of the first bonding layer is formed. This protective film material includes SiO ₂ , Al ₂ O ₃ , ZrO ₂ TiO ₂ , Ta ₂ O ₅ , Nb ₂ O ₅ , MgF ₂ , SiN, and the like, which are formed as a single layer or multiple layers. In the case of forming in multiple layers, it is preferable to repeat the formation from the nitride semiconductor layer side so that the refractive index is relatively (low refractive index / high refractive index). The thickness of these single layer film and multilayer film is adjusted and reflected. When the film thickness is not adjusted to reflect the light from the active layer, a highly reflective metal film such as Al, Ag, and Rh may be formed on the protective film. With these structures, light extraction efficiency can be improved.
[0045]
In addition, a first eutectic formation layer is provided on the p-electrode of the first bonding layer, and a second eutectic formation layer is provided on the main surface of the conductive substrate in the second bonding layer. Is preferred. The first and second eutectic forming layers are layers that diffuse together to form a eutectic during bonding, and are each made of a metal such as Au, Sn, Pd, or In. The combination of the first and second eutectic forming layers is preferably Au—Sn, Sn—Pd, or In—Pd. More preferably, the combination uses Sn for the first eutectic formation layer and Au for the second eutectic formation layer.
[0046]
In addition, it is preferable to provide an adhesion layer and a barrier layer from the p electrode side between the first eutectic formation layer of the first bonding layer and the p electrode. The adhesion layer is a layer that ensures high adhesion with the p-electrode, and any one of Ti, Ni, W, and Mo is preferable. The barrier layer is a layer that prevents the metal constituting the first eutectic forming layer from diffusing into the adhesion layer, and is preferably Pt or W. Further, in order to further prevent the metal of the first eutectic formation layer from diffusing into the adhesion layer, an Au film having a thickness of about 0.3 μm is provided between the barrier layer and the first eutectic formation layer. It may be formed. Note that the adhesion layer, the barrier layer, and the Au film are preferably provided between the second eutectic layer and the conductive substrate.
[0047]
In addition, the temperature at which the bonding laminate and the conductive substrate are heat-pressed is 150 ° C. or higher and 500 ° C. or lower, preferably 150 ° C. or higher and 350 ° C. or lower. By setting the temperature to 150 ° C. or higher, the diffusion of the metal in the eutectic formation layer is promoted to form a eutectic having a uniform density distribution, and the adhesion between the bonding laminate and the conductive substrate can be improved. When the temperature is higher than 500 ° C., the metal of the eutectic forming layer diffuses to the barrier layer and further to the adhesion layer, and good adhesion cannot be obtained.
[0048]
In order to remove the growth substrate after bonding the conductive substrates, polishing, etching, electromagnetic wave irradiation, or a combination of these methods can be used. The electromagnetic wave irradiation uses, for example, a laser for electromagnetic waves, and after bonding the conductive substrate, the entire surface of the growth substrate where the underlayer is not formed is irradiated with a laser to decompose the underlayer and the growth substrate. The underlayer can be removed. Further, after removing the growth substrate and the underlying layer, the exposed surface of the nitride semiconductor layer is subjected to CMP to expose a desired film. Thereby, removal of a damage layer and adjustment of the thickness and surface roughness of a nitride semiconductor layer can be performed.
[0049]
In addition, the following method can also be used for electromagnetic wave irradiation. That is, an underlying layer made of a nitride semiconductor is formed on a growth substrate, and then the underlying layer is partially etched to the growth substrate to form irregularities, and then ELOG growth is performed on the underlying layer having irregularities. To form a lateral growth layer. Next, after sequentially forming an n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer on the laterally grown layer, a conductive substrate is bonded onto the p-type nitride semiconductor layer. Next, the growth substrate and the underlayer can be removed by irradiating the entire surface of the growth substrate where the underlayer is not formed with laser to decompose the underlayer. According to this method, N generated by decomposition of the nitride semiconductor during electromagnetic wave irradiation. ₂ The gas spreads into the gap formed between the above unevenness and the lateral growth layer, prevents the growth substrate from cracking due to the gas pressure, and further prevents the underlayer from burring due to the crack. A nitride semiconductor substrate having good state and crystallinity can be obtained. In addition, since the working process can be simplified as compared with the polishing method, the yield can be improved.
[0050]
In addition, after removing the growth substrate, in order to improve the light extraction efficiency, the exposed surface of the n-type nitride semiconductor layer may be formed with irregularities (dimple processing) by RIE. The cross-sectional shape of the unevenness can be a mesa shape or an inverted mesa shape, and the planar shape can be an island shape, a lattice shape, a rectangular shape, a circular shape, or a polygonal shape.
[0051]
In addition, SiO is covered so as to cover the exposed surface other than the n-electrode. ₂ , Al ₂ O ₃ , ZrO ₂ TiO ₂ , Si ₃ N ₄ , MgF ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ An insulating protective film such as is formed. This layer is a single layer or a multilayer, and is a non-reflective coating (AR coating) film that does not reflect.
[0052]
The p electrode and the n electrode are not particularly limited in size and shape as long as the p electrode is formed on one main surface of the nitride semiconductor element and the n electrode is formed on the other main surface. Preferably, the size and the shape are not particularly limited as long as both electrodes are arranged to face each other so as not to overlap each other when viewed from the stacking direction of the nitride semiconductor layers. Thereby, in the case of a face-down structure, the emitted light can be efficiently extracted without being blocked by the n-electrode. For example, when the p-electrode is formed on almost the entire surface of the p-type nitride semiconductor layer, the n-electrode may be formed on two or four corners of the n-type nitride semiconductor layer, It may be formed, and furthermore, it may be formed in a lattice shape at the corner.
[0053]
Hereinafter, a specific configuration of the nitride semiconductor device according to the present embodiment will be described with reference to FIGS.
In the present invention, the n-type nitride semiconductor layer, the active layer, and the p-type nitride semiconductor layer are all made of a nitride semiconductor, preferably Al. _x In _y Ga _1-xy N (0 ≦ x, 0 ≦ y, x + y ≦ 1). All layers are made of Al _x In _y Ga _1-xy N (0 ≦ x, 0 ≦ y, x + y <1), that is, at least one nitride semiconductor containing Ga is included. The n-type nitride semiconductor layer and the p-type nitride semiconductor layer are composed of a plurality of layers and have at least a layer that functions as a cladding layer. In addition, the n-type nitride semiconductor layer has a buffer layer for epitaxially growing the nitride semiconductor layer on the substrate at the joint surface with the substrate. The active layer may have either a single quantum well structure or a multiple quantum well structure, and preferably has a multiple quantum well structure in which a well layer and a barrier layer are repeatedly stacked. When the nitride semiconductor light emitting device of the present invention is formed as a laser device, a light guide layer is also provided between the active layer and the cladding layer.
When a nitride semiconductor light emitting device that emits light at 380 nm or less is obtained, a light emitting device with high luminous efficiency can be obtained by forming the base layer to the p-type contact layer as follows.
[0054]
(Underlayer)
The underlayer 32 can be composed of at least one nitride semiconductor, but includes a buffer layer 31a grown at a low temperature on the growth substrate 1 and a high-temperature grown layer 31b grown at a high temperature on the buffer layer 31a. It is preferable to comprise.
[0055]
As the buffer layer 31a, Ga _i Al _1-i A nitride semiconductor composed of N (0 <i ≦ 1), preferably having a small proportion of Al, and more preferably using GaN, improves the crystallinity of the nitride semiconductor grown on the buffer layer. The film thickness of the buffer layer is preferably 0.002 to 0.5 μm, more preferably 0.005 to 0.2 μm, and still more preferably 0.01 to 0.02 μm. The growth temperature of the buffer layer is preferably 200 to 900 ° C, more preferably 400 to 800 ° C.
[0056]
As the high temperature growth layer 31b, preferably, undoped GaN or GaN doped with n-type impurities can be used. The film thickness of the high-temperature growth layer is 500 mm or more, more preferably 5 μm or more, and further preferably 10 μm or more. The growth temperature of the high-temperature growth layer is 900 to 1100 ° C., preferably 1050 ° C. or higher.
[0057]
(N-type cladding layer)
The n-type cladding layer 33 is not particularly limited as long as it has a composition larger than the band gap energy of the active layer 4 and can confine carriers in the active layer 4. _j Ga _1-j N (0 <j <0.3) is preferred. Here, more preferably, 0.1 <j <0.2. The thickness of the n-type cladding layer is not particularly limited, but is preferably 0.01 to 0.1 μm, more preferably 0.03 to 0.06 μm. The n-type impurity concentration of the n-type cladding layer is not particularly limited, but preferably 1 × 10. ¹⁷ ~ 1x10 ²⁰ / Cm ³ , More preferably 1 × 10 ¹⁸ ~ 1x10 ¹⁹ / Cm ³ It is. Further, in the present invention, after removing the growth substrate and the underlying layer and the high-temperature growth layer GaN after bonding the conductive substrates, a certain amount of film thickness is required, in which case 1 μm to 10 μm, Preferably, it is 1 μm to 5 μm.
[0058]
(Active layer)
The active layer 4 used in the present invention includes at least Al. _a In _b Ga _1-ab A well layer composed of N (0 ≦ a ≦ 1, 0 ≦ b ≦ 1, a + b ≦ 1), Al _c In _d Ga _1-cd And a barrier layer made of N (0 ≦ c ≦ 1, 0 ≦ d ≦ 1, c + d ≦ 1). More preferably, the well layer and the barrier layer are each made of Al. _a In _b Ga _1-ab N (0 <a ≦ 1, 0 <b ≦ 1, a + b <1) and Al _c In _d Ga _1-cd N (0 <c ≦ 1, 0 ≦ d ≦ 1, c + d <1). Further, the wavelength in the active layer is 380 nm or less, and specifically, the band gap energy of the well layer is a wavelength of 380 nm or less.
[0059]
The nitride semiconductor used for the active layer may be any of non-doped, n-type impurity doped, and p-type impurity doped. Preferably, a light-emitting element is formed by using a non-doped, undoped, or n-type impurity doped nitride semiconductor. High output can be achieved. More preferably, when the well layer is undoped and the barrier layer is n-type impurity doped, the output and the light emission efficiency of the light emitting element can be increased.
[0060]
(P-type cladding layer)
The p-type cladding layer 52 is not particularly limited as long as it has a composition larger than the band gap energy of the active layer 4 and can confine carriers in the active layer 4. _k Ga _1-k N (0 ≦ k <1) is used, especially Al _k Ga _1-k N (0 <k <0.4) is preferred. Here, more preferably, 0.15 <k <0.3. The film thickness of the p-type cladding layer is not particularly limited, but is preferably 0.01 to 0.15 μm, more preferably 0.04 to 0.08 μm. The p-type impurity concentration of the p-type cladding layer is 1 × 10 ¹⁸ ~ 1x10 ²¹ / Cm ³ 1 × 10 ¹⁹ ~ 5x10 ²⁰ cm ³ It is. When the p-type impurity concentration is in the above range, the bulk resistance can be reduced without reducing the crystallinity.
[0061]
(P-type contact layer)
The p-type contact layer 51 is made of Al. _f Ga _1-f N (0 ≦ f <1) is used, in particular Al _f Ga _1-f By configuring with N (0 <f <0.3), good ohmic contact with the ohmic electrode 6 becomes possible. The p-type impurity concentration is 1 × 10 ¹⁷ / Cm ³ The above is preferable.
[0062]
The p-type contact layer preferably has a composition gradient that has a high p-type impurity concentration and a low Al mixed crystal ratio on the conductive substrate side. In this case, the composition gradient may change the composition continuously or may change the composition stepwise in a discontinuous manner. For example, a p-type contact layer is in contact with a p-electrode, a first p-type contact layer having a high p-type impurity concentration and a low Al composition ratio, and a second p-type contact having a low p-type impurity concentration and a high Al composition ratio. It can also consist of layers. Good ohmic contact can be obtained by the first p-type contact layer, and self-absorption can be prevented by the second p-type contact layer.
[0063]
The composition of the first p-type contact layer is Al _g Ga _1-g N (0 ≦ g <0.05) is preferable, and more preferably g is 0 <g <0.01. If the Al composition ratio is within the above range, even if the p-type impurity is doped at a high concentration, the inactivation of the impurity can be prevented and a good ohmic contact can be obtained. The p-type impurity concentration of the first p-type contact layer is preferably 1 × 10. ¹⁹ ~ 1x10 ²² / Cm ³ , More preferably 5 × 10 ²⁰ ~ 5x10 ²¹ / Cm ³ It is. The film thickness of the first p-type contact layer is preferably 100 to 500 mm, more preferably 150 to 300 mm.
[0064]
The composition of the second p-type contact layer is Al _h Ga _1-h N (0 ≦ h <0.1) is preferable, and more preferably, h is 0.1 <h <0.05. If the Al composition ratio is within the above range, self-absorption can be prevented. The p-type impurity concentration of the second p-type contact layer is preferably 1 × 10 ²⁰ / Cm ³ Or less, more preferably 5 × 10 ¹⁸ ~ 5x10 ¹⁹ / Cm ³ It is. The film thickness of the second p-type contact layer is preferably 400 to 1200 mm, more preferably 800 to 1200 mm.
A nitride semiconductor light emitting device having no self-absorption can be obtained by adopting the above-described configuration and removing GaN from the growth substrate, the underlayer, and the high temperature growth layer.
[0065]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples.
Example 1.
The structure of the nitride semiconductor laminate used in this example is shown in FIG. The n-type nitride semiconductor layer 3 is formed on the growth substrate 1 with an underlayer 32 composed of a buffer layer 31a and a high-temperature growth layer 31b, an n-type contact layer 34, an n-type first multilayer film layer 35, and an n-type superlattice multilayer. The film layer 36 is sequentially laminated. The p-type nitride semiconductor layer 5 is formed by sequentially laminating a multilayer p-type cladding layer 51, a p-type lightly doped layer 53, and a p-type contact layer 52 on the active layer 4. Hereinafter, the manufacturing method of this laminated body and the manufacturing method of the LED element using this laminated body are demonstrated with reference to FIGS.
[0066]
(Growth substrate)
The growth substrate 1 made of sapphire (C surface) was set in a MOVPE reaction vessel, and the temperature of the substrate was raised to 1050 ° C. while flowing hydrogen to clean the substrate.
[0067]
(Underlayer)
Buffer layer: Subsequently, the temperature is lowered to 510 ° C., hydrogen is used as the carrier gas, ammonia and TMG (trimethyl gallium) are used as the source gas, and a buffer layer 31a made of AlGaN is grown on the substrate 1 to a thickness of about 200 mm. I let you. The buffer layer grown at a low temperature can be omitted depending on the type of substrate, growth method, and the like.
[0068]
High temperature growth layer: After growing the buffer layer 31a, only TMG was stopped and the temperature was raised to 1050 ° C. When the temperature reached 1050 ° C., TMG and ammonia gas were similarly used as the source gas, and the undoped GaN layer 31b was grown to a thickness of 1.5 μm.
[0069]
(N-type contact layer)
Subsequently, at 1050 ° C., TMG, ammonia gas, and silane gas are used as source gas and silane gas as impurity gas, and Si is 6 × 10 6. ¹⁸ /cm ^Three An n-type contact layer 34 made of doped GaN was grown to a thickness of 1.85 μm.
[0070]
(First multilayer layer)
Next, stop only the silane gas, and use TMG and ammonia gas at 1050 ° C. to grow a lower layer made of undoped GaN with a film thickness of 3000 mm, and then add silane gas at the same temperature to add 6 × 10 Si. ¹⁸ /cm ^Three An intermediate layer made of doped GaN is grown to a thickness of 300 mm, and then only the silane gas is stopped, and an upper layer made of undoped GaN is grown to a thickness of 50 mm at the same temperature, so that the total thickness of 3 layers is 3350 mm. The first multilayer film layer 35 was grown.
[0071]
(N-type superlattice multilayer film layer)
Next, a first nitride semiconductor layer made of undoped GaN is grown at 40 ° C. at the same temperature. Next, the temperature is set to 800 ° C., and TMG, TMI, and ammonia are used. _0.02 Ga _0.98 A second nitride semiconductor layer made of N was grown by 20 cm. Then, these operations are repeated, and 10 layers are alternately stacked in the order of 1 + 2, and finally an n-type superstructure composed of a multi-layer film having a superlattice structure in which a first nitride semiconductor layer made of GaN is grown by 40%. The lattice multilayer film layer 36 was grown to a thickness of 640 mm.
[0072]
(Active layer)
Next, a barrier layer made of undoped GaN is grown to a thickness of 200 mm, and subsequently the temperature is set to 800 ° C., and TMG, TMI, and ammonia are used to undoped In _0.4 Ga _0.6 A well layer made of N was grown to a thickness of 30 mm. Then, five barrier layers and four well layers are alternately stacked in the order of barrier + well + barrier + well... + Barrier to grow an active layer 4 having a multiple quantum well structure with a total film thickness of 1120 mm. It was.
[0073]
(Medium-doped multilayer p-type cladding layer)
Next, at a temperature of 1050 ° C., TMG, TMA, ammonia, Cp ₂ Mg (cyclopentadienylmagnesium) is used and Mg is 5 × 10 ¹⁹ / Cm ³ Doped p-type Al _0.2 Ga _0.8 A first nitride semiconductor layer made of N is grown to a thickness of 40 mm, and subsequently the temperature is set to 800 ° C., and TMG, TMI, ammonia, Cp ₂ Mg is used 5 × 10 Mg ¹⁹ / Cm ³ Doped In _0.03 Ga _0.97 A second nitride semiconductor layer made of N was grown to a thickness of 25 mm. Then, by repeating these operations, five layers are alternately stacked in the order of 1 + 2, and finally the p-side made of a multilayer film having a superlattice structure in which the first nitride semiconductor layer is grown to a thickness of 40 mm. A multilayer clad layer 51 was grown to a thickness of 365 mm.
[0074]
(Lightly doped p-type lightly doped layer)
Subsequently, at 1050 ° C., a p-type lightly doped layer 53 made of undoped GaN was grown to a thickness of 2000 mm using TMG and ammonia. This lightly doped layer is grown as undoped during growth, but Mg doped in the medium-doped multi-layer p-type cladding layer 51 diffuses during the growth of the lightly doped layer 53, and further, When the highly doped p-type contact layer 52 is grown, Mg diffuses, and the lightly doped layer exhibits p-type.
The Mg concentration of the lightly doped layer 53 is 2 × 10 at the lowest concentration portion. ¹⁸ / Cm ^Three It becomes. The change in the Mg concentration of the lightly doped layer 53 is substantially the same as the Mg concentration of the p-type cladding layer 51 at the portion in contact with the p-type cladding layer 51, but gradually as the distance from the p-type cladding layer 51 increases. The Mg concentration in the vicinity (immediately before the growth of the p-type contact layer 52) close to the p-type contact layer 52 to be grown later is almost the minimum value.
[0075]
(Highly doped p-type contact layer)
Subsequently, at 1050 ° C., TMG, ammonia, Cp ₂ Mg is used, and Mg is 1 × 10 ²⁰ /cm ^Three A p-type contact layer 52 made of doped GaN is grown to a thickness of 1200 mm.
After the completion of the reaction, the temperature is lowered to room temperature, and the wafer is annealed in a reaction vessel at 700 ° C. in a nitrogen atmosphere to further reduce the resistance of the p-type layer.
[0076]
(P electrode)
After annealing, the wafer was taken out of the reaction vessel, and an Rh / Ir / Pt film was formed on the p-type contact layer 52 at a thickness of 400/500/1000 to form a p-electrode 6. Then, after performing ohmic annealing at 600 ° C., an insulating p-side protective film 20 is formed on the exposed surface other than the p electrode 6 as SiO 2 ₂ Was formed with a film thickness of 0.3 μm.
[0077]
(First bonding layer)
Next, a multilayer film of Ti / Pt / Au / Sn / Au was formed as a first bonding layer 71 on the p-electrode with a film thickness of 1000 mm / 1000 mm / 1000 mm / 30000 mm / 1000 mm. Here, Ti is an adhesion layer, Pt is a barrier layer, Sn is a first eutectic formation layer, and an Au layer between Pt and Sn serves to prevent Sn from diffusing into the barrier layer. The outer Au layer plays a role of improving the adhesion with the second eutectic forming layer. The first bonding layer 71 is formed at least on the p-electrode, and is preferably formed on the entire surface of the bonding laminate on the p-electrode side.
[0078]
(Second bonding layer)
On the other hand, as the conductive substrate 8, a metal substrate having a film thickness of 200 μm and made of a composite of Cu 30% and W 70% is used, and an adhesion layer made of Ti is formed on the surface of the metal substrate as a second bonding layer 72, A barrier layer made of Pt and a second eutectic forming layer made of Au were formed in this order at a film thickness of 1000 Å / 1000 １４/14000 Å.
[0079]
Next, in a state where the first bonding layer 71 and the second bonding layer 72 are opposed to each other, the bonding laminate 2 and the conductive substrate 8 are press-pressed at a heater temperature of 250 ° C. and heated and pressed. . Thereby, the metal of the 1st eutectic formation layer and the 2nd eutectic formation layer was diffused mutually, and the eutectic was formed.
[0080]
(Removal of growth substrate)
Next, with respect to the bonding laminate 2 to which the conductive substrate 8 is bonded, an output of 600 J / cm is applied from the opposite surface of the sapphire substrate on the base layer side using a KrF excimer laser with a wavelength of 248 nm. ² Then, the laser beam was irradiated in the form of a 1 mm × 50 mm line to scan the entire opposite surface. The underlayer nitride semiconductor was decomposed by laser irradiation to remove the sapphire substrate. Further, the buffer layer and the undoped GaN layer are further polished until the n-type contact layer is exposed, and the exposed n-type contact layer is polished with KOH and colloidal silica (K ₂ SiO ₃ ) Was used for chemical polishing to remove surface roughness. The n-type contact layer was polished until the film thickness up to the p-type contact layer was about 3 μm.
[0081]
(Dimple formation)
Next, the exposed surface of the n-type nitride semiconductor layer is formed into an uneven dimple 331 by RIE. In this shape, it is assumed that cylindrical concave portions having a diameter of 4 μm and a depth of 1 μm are regularly arranged.
[0082]
(Laminate separation)
Next, from the n-type contact layer side, the n-type contact layer to the p-type contact layer are etched to expose the p-side protective film, and the laminate made of nitride semiconductor is separated so as to have a desired chip size. To do.
[0083]
(N electrode)
Next, on the exposed n-type contact layer, an n-electrode 9 made of W—Si / Pt / Au is evaporated to a thickness of 200 mm / 2000 mm / 6000 mm to form an n-electrode, and an n-type contact layer other than the n-electrode is formed. As the n-side protective film 21 so as to cover all of the exposed surface and the side surface of the laminated body, SiO ₂ Was AR coated. Here, the composition of the WSi alloy is W _x Si _1-x It is. In this example, the size of the n electrode was 100 μm × 100 μm.
[0084]
(Element isolation)
Then, after polishing the conductive substrate to 100 μm, a multilayer film made of Ti / Pt / Au was formed as a pad electrode for the p electrode on the back surface of the conductive substrate at 1000 mm / 2000 mm / 3000 mm. Next, the element was separated by dicing.
[0085]
The obtained LED element had a size of 250 μm × 250 μm, showed blue light emission of 460 nm at a forward current of 20 mA, and Vf was 3.55V.
[0086]
Comparative Example 1
A device was fabricated under the same conditions as in Example 1 except that a multilayer electrode composed of W / Al / Ti / Pt / Au (film thickness: 100 mm / 2500 mm / 1000 mm / 2000 mm / 6000 mm) was used as the n-electrode. Here, Pt / Au is a pad electrode, and Ti functions as a layer that prevents Al from diffusing into Pt / Au. Conventionally, when an alloy or multilayer film containing Al is used as an ohmic electrode, Al diffusion Ti or the like needs to be formed as a prevention layer.
[0087]
The obtained LED element emitted blue light of 460 nm at a forward current of 20 mA, and Vf was 5.19V.
[0088]
Comparative Example 2
The process is the same as in Example 1 until a heavily doped p-type contact layer is formed and annealed at 700 ° C.
Next, after the highly doped p-type contact layer is formed, the p-type nitride semiconductor layer, the active layer, and a part of the n-type nitride semiconductor layer are etched from the p-type contact layer side to form the n-type contact layer. Exposed. The case where W / Al / Ti / Pt / Au was formed on the exposed surface of the n-type contact layer and the case where W-Si / Pt / Au was formed were examined for the ohmic characteristics of the n-electrode. There was no improvement in ohmic contact due to the use of -Si / Pt / Au. It has been found that the effect of the present invention is not seen when the n-electrode is formed on the (0001) plane of the n-type nitride semiconductor layer.
[0089]
Example 2
A device was fabricated in the same manner as in Example 1 except that the n-electrode 9 was a multilayer electrode made of W—Al—Si / Ti / Pt / Au and the film thickness was 200/1000/2000/6000. The obtained device exhibited almost the same characteristics as in Example 1.
[0090]
Example 3
(Growth substrate)
A substrate made of sapphire (C surface) was used as the growth substrate, and the surface was cleaned in a MOCVD reaction vessel at 1050 ° C. in a hydrogen atmosphere.
[0091]
(Underlayer)
Buffer layer: Subsequently, a buffer layer made of GaN was grown to a thickness of about 200 mm on the substrate using ammonia and TMG (trimethylgallium) at 510 ° C. in a hydrogen atmosphere.
[0092]
High-temperature growth layer: After growing the buffer layer, only TMG is stopped, the temperature is raised to 1050 ° C., and when it reaches 1050 ° C., TMG and ammonia are used as source gases, and a high-temperature growth nitride semiconductor made of undoped GaN is 5 μm. The film was grown with a thickness of.
[0093]
(N-type cladding layer)
Next, using MG, TMA, ammonia, and silane at 1050 ° C., Si was 5 × 10 ¹⁷ / Cm ³ Doped n-type Al _0.18 Ga _0.82 An n-type cladding layer made of N was formed with a thickness of 400 mm.
[0094]
(Active layer)
Next, the temperature is set to 800 ° C., TMI (trimethylindium), TMG, and TMA are used as source gases, and Si-doped Al is used. _0.1 Ga _0.9 A barrier layer made of N, on which undoped In _0.03 Al _0.02 Ga _0.95 Well layers made of N were laminated in the order of barrier layer (1) / well layer (1) / barrier layer (2) / well layer (2) / barrier layer (3). At this time, the barrier layer (1) was formed in a thickness of 200, the barrier layers (2) and (3) in a thickness of 40, and the well layers (1) and (2) in a thickness of 70. The active layer has a multiple quantum well structure (MQW) with a total film thickness of about 420 mm.
[0095]
(P-type cladding layer)
Next, in a hydrogen atmosphere at 1050 ° C., TMG, TMA, ammonia, Cp ₂ Mg (cyclopentadienylmagnesium) is used and Mg is 1 × 10 ²⁰ / Cm ³ Doped Al _0.2 Ga _0.8 A p-type cladding layer made of N was grown to a thickness of 600 mm.
[0096]
(P-type contact layer)
Subsequently, TMG, TMA, ammonia, Cp are formed on the p-type cladding layer. ₂ Using Mg, Mg is 1 × 10 ¹⁹ / Cm ³ Doped Al _0.04 Ga _0.96 A second p-type contact layer made of N is grown to a thickness of 0.1 μm, and then the gas flow rate is adjusted to make Mg 2 × 10 ²¹ / Cm ³ Doped Al _0.01 Ga _0.99 A second p-type contact layer made of N was grown to a thickness of 0.02 μm.
[0097]
After completion of the growth, the wafer was annealed in a reaction vessel at 700 ° C. in a nitrogen atmosphere to further reduce the resistance of the p-type layer.
[0098]
(P electrode)
After annealing, the wafer was taken out of the reaction vessel, and a Rh / Ir / Pt film was formed on the p-type contact layer at a thickness of 400/500/1000 to form a p-electrode. Thereafter, ohmic annealing is performed at 600 ° C., and then an insulating p-side protective film 20 is formed on the exposed surface other than the p-electrode. ₂ Was formed with a film thickness of 0.3 μm.
[0099]
(First bonding layer)
Next, a multilayer film of Ti / Pt / Au / Sn / Au was formed as a first bonding layer 71 on the p-electrode with a film thickness of 1000 mm / 1000 mm / 1000 mm / 30000 mm / 1000 mm. Here, Ti is an adhesion layer, Pt is a barrier layer, Sn is a first eutectic formation layer, and an Au layer between Pt and Sn serves to prevent Sn from diffusing into the barrier layer, The outermost Au layer plays a role of improving the adhesion with the second eutectic forming layer. The first bonding layer 71 is formed at least on the p-electrode, and is preferably formed on the entire surface of the bonding laminate on the p-electrode side.
[0100]
(Second bonding layer)
On the other hand, as the conductive substrate 8, a metal substrate having a film thickness of 200 μm and made of a composite of Cu 30% and W 70% is used, and an adhesion layer made of Ti is formed on the surface of the metal substrate as a second bonding layer 72, A barrier layer made of Pt and a second eutectic forming layer made of Au were formed in this order at a film thickness of 1000 Å / 1000 １４/14000 Å.
[0101]
Next, in a state where the first bonding layer 71 and the second bonding layer 72 are opposed to each other, the bonding laminate 2 and the conductive substrate 8 are press-pressed at a heater temperature of 250 ° C. and heated and pressed. . Thereby, the metal of the 1st eutectic formation layer and the 2nd eutectic formation layer was diffused mutually, and the eutectic was formed.
[0102]
(Removal of growth substrate)
Next, with respect to the bonding laminate 2 to which the conductive substrate 8 is bonded, an output of 600 J / cm is applied from the opposite surface of the sapphire substrate on the base layer side using a KrF excimer laser with a wavelength of 248 nm. ² Then, the laser beam was irradiated in the form of a 1 mm × 50 mm line to scan the entire opposite surface. The underlayer nitride semiconductor was decomposed by laser irradiation to remove the sapphire substrate. Further, the buffer layer and the undoped GaN layer are further polished until the n-type contact layer is exposed, and the exposed n-type contact layer is polished with KOH and colloidal silica (K ₂ SiO ₃ ) Was used for chemical polishing to remove surface roughness. The n-type contact layer was polished until the film thickness up to the p-type contact layer was about 3 μm.
[0103]
(Dimple formation)
Next, the exposed surface of the n-type nitride semiconductor layer is formed into an uneven dimple 331 by RIE. In this shape, cylindrical concave portions having a diameter of 4 μm and a depth of 1 μm were regularly arranged.
[0104]
(Laminate separation)
Next, from the n-type contact layer side, the n-type contact layer to the p-type contact layer are etched to expose the p-side protective film, and the laminate made of nitride semiconductor is separated so as to have a desired chip size. did.
[0105]
(N electrode)
Next, an n-electrode 9 made of W—Si / Pt / Au was deposited on the n-type cladding layer at a film thickness of 200/2000/6000 to form an n-electrode. As the n-side protective film 21 so as to cover all of the exposed surface of the n-type contact layer other than the n-electrode and the side surface of the laminate, SiO 2 ₂ Was AR coated. Here, the composition of the WSi alloy is W _x Si _1-x Met. In this example, the size of the n electrode was 100 μm × 100 μm.
[0106]
(Element isolation)
Then, after polishing the conductive substrate to 100 μm, a multilayer film made of Ti / Pt / Au was formed as a pad electrode for the p electrode on the back surface of the conductive substrate at 1000 mm / 2000 mm / 3000 mm. Next, the element was separated by dicing.
[0107]
The obtained LED element had a size of 250 μm × 250 μm, showed ultraviolet light emission of 373 nm, and it was confirmed that the n electrode had good ohmic contact with the n-type cladding layer.
[0108]
As described above, the LED element of the present invention has a reduced Vf and improved luminous efficiency compared to the conventional n-electrode. In addition, since the n electrode and the n-type contact layer are in good ohmic contact, the size of the n electrode can be reduced and light emission output can be expected to be improved.
[0109]
Next, a semiconductor laser device using a nitride semiconductor will be described with reference to FIG. 6 as an example. However, the semiconductor device of the present invention is not limited to this, and various semiconductors can be used in the technical idea of the present invention. Needless to say, it can be implemented.
[0110]
Example 4
(Underlayer)
Buffer layer: 2 inches φ, dissimilar substrate made of sapphire with C-plane as the main surface, set as growth substrate in MOVPE reaction vessel, temperature set to 500 ° C., trimethylgallium (TMG), ammonia (NH ₃ ) Was used to grow a buffer layer made of GaN with a film thickness of 200 mm.
[0111]
High temperature growth layer: After forming the buffer layer, the temperature was set to 1050 ° C., and a nitride semiconductor layer made of undoped GaN was grown to a thickness of 4 μm using TMG and ammonia. This layer acts as a substantial underlayer (growth substrate) in the growth of each layer forming the element structure. In addition, when a nitride semiconductor grown by ELOG (Epitaxially Laterally Overgrowth) is used as the underlayer, a growth substrate with good crystallinity can be obtained. As a specific example of the ELOG growth layer, a nitride region is formed on a heterogeneous substrate, a mask region formed by, for example, providing a protective film on which the nitride semiconductor layer is difficult to grow, and a nitride semiconductor A non-mask region to be grown is provided in a stripe shape, and a nitride semiconductor is grown from the non-mask region, so that growth in the lateral direction is achieved in addition to growth in the film thickness direction. Nitride semiconductors were grown and deposited, or nitride semiconductor layers grown on different substrates were provided with openings and laterally grown from the sides of the openings. And the like.
Next, each layer which comprises a laminated body is formed on a high temperature growth layer.
[0112]
(N-type contact layer)
Subsequently, at 1050 ° C., similarly, TMG, ammonia gas, and silane gas are used as source gas and silane gas as impurity gas, and Si is 4.5 × 10 ¹⁸ / Cm ³ An n-type contact layer made of doped GaN was grown to a thickness of 2.25 μm. The film thickness of this n-type contact layer should just be 2-30 micrometers.
[0113]
(Crack prevention layer)
Next, using TMG, TMI (trimethylindium), and ammonia, the temperature is set to 800 ° C. and In _0.06 Ga _0.94 A crack prevention layer made of N was grown to a thickness of 0.15 μm. This crack prevention layer can be omitted.
[0114]
(N-type cladding layer)
Next, the temperature is set to 1050 ° C., TMA (trimethylaluminum), TMG and ammonia are used as source gases, and an A layer made of undoped AlGaN is grown to a thickness of 25 mm, and then TMA is stopped as an impurity gas. Silane is used and Si is 5 × 10 ¹⁸ / Cm ³ A B layer made of doped GaN was grown to a thickness of 25 mm. This operation was repeated 160 times, and the A layer and the B layer were alternately laminated to grow an n-type cladding layer made of a multilayer film (superlattice structure) having a total film thickness of 8000 mm. At this time, if the mixed crystal ratio of Al in the undoped AlGaN is in the range of 0.05 to 0.3, a refractive index difference that sufficiently functions as a cladding layer can be provided.
[0115]
(N-type light guide layer)
Next, TMG and ammonia were used as source gases at the same temperature, and an n-type light guide layer made of undoped GaN was grown to a thickness of 0.1 μm. This layer may be doped with n-type impurities.
[0116]
(Active layer)
Next, the temperature is set to 800 ° C., TMI (trimethylindium), TMG and ammonia are used as raw materials, silane gas is used as impurity gas, and Si is 5 × 10 5. ¹⁸ / Cm ³ Doped In _0.05 Ga _0.95 A barrier layer made of N was grown to a thickness of 100 mm. Subsequently, silane gas was turned off and undoped In _0.1 Ga _0.9 A well layer made of N is grown to a thickness of 50 mm. This operation was repeated three times. Finally, a barrier layer was stacked to grow an active layer having a total quantum film thickness of 550 mm and having a multiple quantum well structure (MQW).
[0117]
(P-type cap layer)
Next, at the same temperature, TMA, TMG, and ammonia are used as source gases, and Cp is used as an impurity gas. ₂ Mg (cyclopentadienylmagnesium) is used and Mg is 1 × 10 ¹⁹ / Cm ³ A p-type electron confinement layer made of doped AlGaN was grown to a thickness of 100 mm.
[0118]
(P-type light guide layer)
Next, the temperature was set to 1050 ° C., TMG and ammonia were used as source gases, and a p-type light guide layer made of undoped GaN was grown to a thickness of 750 mm. The p-type light guide layer is grown as undoped, but may be doped with Mg.
[0119]
(P-type cladding layer)
Subsequently, undoped Al at 1050 ° C. _0.16 Ga _0.84 Grow a layer of N with a thickness of 25 mm, then stop TMG, Cp ₂ A layer made of Mg-doped GaN was grown to a thickness of 25 mm using Mg, and a p-type cladding layer made of a superlattice layer having a total thickness of 0.6 μm was grown. When a p-type cladding layer is made of a superlattice in which at least one nitride semiconductor layer containing Al is included and nitride semiconductor layers having different bandgap energies are stacked, impurities are both highly doped in one layer. Although so-called modulation doping tends to improve the crystallinity, both may be doped in the same manner.
[0120]
(P-type contact layer)
Finally, 1 × 10 5 Mg on the p-type cladding layer at 1050 ° C. ²⁰ / Cm ³ A p-type contact layer made of doped p-type GaN was grown to a thickness of 150 mm. The p-type contact layer is p-type In _x Al _y Ga _1-xy N (x.ltoreq.0, y.ltoreq.0, x + y.ltoreq.1), preferably Mg-doped GaN provides the most preferable ohmic contact with the p-electrode. After completion of the reaction, the wafer was annealed at 700 ° C. in a nitrogen atmosphere in the reaction vessel to further reduce the resistance of the p-type layer.
[0121]
(N-type layer exposure and resonator surface formation)
After the nitride semiconductor is formed as described above, the wafer is taken out of the reaction vessel, and the surface of the uppermost p-type contact layer is made of SiO. ₂ A protective film is formed and SiCl is formed using RIE (reactive ion etching). ₄ Etching was performed with gas to expose the end face of the active layer serving as the resonator surface, and the etched end surface was used as the resonator end surface.
[0122]
(Substrate exposure)
Next, SiO ₂ Is formed on the entire surface of the wafer, a resist film is formed thereon except for the exposed surface of the n-type contact layer, and etching is performed until the substrate is exposed. Since the resist film is also formed on the side surface such as the resonator surface, the side surface (p-type layer 15, active layer 14, and part of n-type layer 13) such as the previously formed resonator surface is formed after etching. And an n-type layer between the resonator surface and the substrate are formed.
[0123]
(Striped convex formation)
Next, in order to form a stripe-shaped waveguide region, a Si oxide (mainly SiO 2) is formed on almost the entire surface of the uppermost p-type contact layer by a CVD apparatus. ₂ ) Is formed to a thickness of 0.5 μm, and then a stripe-shaped mask having a width of 3 μm is put on the protective film, and CF is performed by an RIE apparatus. ₄ SiO2 using gas ₂ And then SiCl ₄ Thus, the nitride semiconductor layer is etched until the p-type guide layer is exposed, and stripe-shaped convex portions are formed above the active layer.
[0124]
(First insulating film)
SiO ₂ With the mask attached, the surface of the p-type semiconductor layer is ZrO ₂ A first insulating film 22 is formed. The first insulating film may be provided with a portion where the insulating film is not formed so as to be easily divided later. After the formation of the first insulating film, the SiO formed on the upper surface of the stripe-shaped convex part by dipping in a buffered solution ₂ Is dissolved and removed by a lift-off method. ₂ ZrO on the p-type contact layer (and on the n-type contact layer) ₂ Remove. Thereby, the upper surface of the stripe-shaped convex part is exposed, and the side surface of the convex part is ZrO. ₂ It becomes a structure covered with.
[0125]
(P electrode)
Next, the p-electrode 16 was formed on the outermost surface of the convex portion on the p-type contact layer. The p electrode is made of Ni / Au. After the electrodes are formed, each is annealed at 600 ° C. in an oxygen / nitrogen ratio of 1:99 to alloy the p-electrode and obtain good ohmic characteristics.
[0126]
(Second insulating film)
Next, Si oxide (mainly SiO ₂ ) And Ti oxide film (TiO ₂ ) Is formed on the etched bottom and side surfaces under the condition of 2 pairs (4 layers) with a film thickness of λ / 4n. At this time, the p-pad electrode is exposed.
[0127]
(P pad electrode)
Next, a p-pad electrode 24 made of Ti / Pt / Au that is electrically connected to the p-electrode on the upper surface of the stripe-shaped convex portion through the first insulating film was formed.
[0128]
(Bonding layer)
Next, a first bonding layer 171 was formed on the p-pad electrode. The first bonding layer of the semiconductor laser device of the present invention is composed of a first eutectic layer, and each layer is formed with a film thickness of 30000 mm / 1000 mm in the order of Sn / Au from the p-type semiconductor layer side.
On the other hand, a conductive substrate is prepared. A second bonding layer 172 was formed in a thickness of 2000 mm / 3000 mm / 12000 mm in the order of Ti / Pt / Au on the surface of a conductive substrate having a film thickness of 200 μm and made of Cu 20% and W 80%.
Next, the first bonding layer 171 and the second bonding layer 172 of the conductive substrate were bonded to each other and bonded together. A press pressure was applied at 240 ° C. Here, a eutectic forming layer is formed. Then, after removing the sapphire substrate by grinding, the exposed n-type contact layer is replaced with KOH and colloidal silica (K ₂ SiO ₃ ) Was used for chemical polishing to eliminate surface roughness.
Next, an n-electrode 19 was formed on the n-type contact layer in the order of W-Si / Pt / Au with a film thickness of 200/2000/6000. Then, after polishing the conductive substrate to 100 μm, Ti / Pt / Au was formed on the back surface of the conductive substrate at 1000/2000/3000, and then dicing was performed to separate the elements.
[0129]
FIG. 6 is a schematic cross-sectional view showing the structure of the obtained nitride semiconductor laser device.
The element is formed on a conductive substrate 18, a bonding layer 17, a p-pad electrode 24 electrically connected to the p-electrode 16 through the first insulating film 22, a p-electrode 16, a laminate 12 made of a nitride semiconductor, The n electrode 19 is sequentially stacked, and the p electrode 16 and the n electrode 19 are disposed so as to face each other. Furthermore, the laminated body 12 has the 2nd insulating film 23 which forms a mirror on the etched side surface. Note that the bonding layer 17 plays a role of bonding the conductive substrate 18 and the stacked body 12, and the first bonding layer 171 and the second bonding layer 172 are integrally formed.
[0130]
The nitride semiconductor laser device obtained as described above has a lower threshold voltage than when Ti / Al / Ti / Pt / Au is used for the conventional n electrode, and the n electrode is an n-type contact layer. It was confirmed that good ohmic contact was obtained.
[0131]
【The invention's effect】
As described above, the nitride semiconductor device of the present invention has a structure in which a p-electrode and an n-electrode are arranged to face each other, and includes an n-electrode having an alloy layer containing an n-type impurity. Since the n-electrode is formed so as to be in contact with the (000-1) plane of the nitride semiconductor layer and good ohmic contact can be obtained with the (000-1) plane, the device can be miniaturized and the heat dissipation performance can be reduced. It is possible to provide an element that is excellent in light emission and has a high light emission output.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing an example of the structure of a nitride semiconductor device according to the present invention.
FIG. 2 is a schematic cross-sectional view (1) showing an example of a method for manufacturing a nitride semiconductor device according to the present invention.
FIG. 3 is a schematic cross-sectional view (2) showing an example of a method for manufacturing a nitride semiconductor device according to the present invention.
FIG. 4 is a schematic cross-sectional view (3) showing an example of a method for manufacturing a nitride semiconductor device according to the present invention.
FIG. 5 is a schematic cross-sectional view showing an example of a structure of a nitride semiconductor laminate used for manufacturing a nitride semiconductor device according to the present invention.
FIG. 6 is a schematic cross-sectional view showing an example of the structure of a nitride semiconductor laser device according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Growth substrate, 2,12 laminated body, 3,13 n-type nitride semiconductor layer, 31a buffer layer, 31b High temperature growth layer, 32 Underlayer, 33 n-type clad layer, 331 dimple, 34 n-type contact layer, 35 n-type first multilayer film layer, 36 n-type superlattice multilayer film layer, 4,14 active layer, 5,15 p-type nitride semiconductor layer, 51p-type cladding layer, 52p-type contact layer, 53p-type lightly doped Layer, 6, 16 p electrode, 7, 17 bonding layer, 71, 171 first bonding layer, 72, 172 second bonding layer, 8, 18 conductive substrate, 9, 19 n electrode, 10 separation groove, 20 p-side protective film, 21 n-side protective film, 22 first insulating film, 23 second insulating film, 24 p-pad electrode.

Claims (6)

A nitride semiconductor device in which a p-electrode is formed on one main surface of a laminate made of a nitride semiconductor, an n-electrode is formed on the other main surface, and both electrodes are arranged opposite to each other.
The above other main surface is (000-1) plane of the n-type nitride semiconductor layer, the n electrode, possess an alloy layer containing Si as n-type impurity in contact with the (000-1) plane, The nitride semiconductor device, wherein the metal constituting the alloy layer is at least one metal selected from the group consisting of Al, Ag, Ti, Mo, Nb, Ta, Hf, Pt, and W. The alloy layer is W _x Si _1-x The nitride semiconductor device according to claim 1, wherein (0.3 ≦ x <1). 3. The nitride semiconductor device according to claim 1, wherein the n electrode and the p electrode are disposed so as to face each other so as not to overlap each other when viewed from the stacking direction of the nitride semiconductor. 4. The nitride semiconductor device according to claim 1, wherein the n-electrode is a multilayer film in which one or more metal layers are further laminated on an alloy layer. 5. The nitride semiconductor device according to claim 1, wherein the n-type nitride semiconductor layer has an exposed surface on a surface on which an n electrode is formed, and the exposed surface has irregularities. The n-type nitride semiconductor layer is made of SiO so as to cover an exposed surface other than the n-electrode. ₂ , Al ₂ O ₃ , ZrO ₂ TiO ₂ , Si ₂ N ₄ , MgF ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ The nitride semiconductor device according to claim 1, further comprising an insulating protective film selected from the group consisting of:

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