JP2004006919A - Nitride semiconductor device - Google Patents

Abstract

An object of the present invention is to provide a nitride semiconductor device having a structure from which electrodes can be taken out from above and below.
A first step of bonding a conductive substrate to a nitride semiconductor layer surface of a wafer on which a nitride semiconductor layer having an n-type layer, an active layer, and a p-type layer sequentially grown on an insulating substrate. And a second step of removing a part or all of the insulating substrate of the wafer and exposing the nitride semiconductor layer after bonding the conductive substrate, the exposed nitride semiconductor layer, An electrode facing the substrate is provided. A current confinement layer having an opening is provided on the n-type layer, and a negative electrode is formed in the opening. The current confinement layer is made of sapphire, SiO ₂ or TiO ₂ .
[Selection diagram] FIG.

Description

[0001]
[Industrial applications]
The present invention relates to an element made of a nitride semiconductor (InXAlYGa1-X-YN, 0 ≦ X, 0 ≦ Y, X + Y ≦ 1) used for a light-emitting device such as a light-emitting diode or a laser diode, or a light-receiving device such as a photodiode. .
[0002]
[Prior art]
Nitride semiconductors have attracted attention for various semiconductor devices such as light-emitting elements and light-receiving elements because of their band gap energies from 1.9 eV to 6.0 eV. Recently, blue LEDs and blue-green LEDs using this material have been put to practical use. It has just been transformed.
[0003]
In general, a nitride semiconductor device is obtained by growing a nitride semiconductor having a conductivity type defined as n-type, p-type, or i-type on a substrate by using a vapor phase growth method such as MBE or MOVPE. It is known that, in addition to an insulating substrate such as sapphire, spinel, lithium niobate, and neodymium gallate, a conductive substrate such as silicon carbide, silicon, zinc oxide, and gallium arsenide can be used as the substrate. A substrate that perfectly lattice-matches with a semiconductor has not yet been developed, and at present, blue and blue-green LED devices in which a nitride semiconductor layer is forcibly grown on sapphire having a lattice constant different by 10% or more have been developed. Has been put to practical use.
[0004]
FIG. 6 is a schematic sectional view showing the structure of a conventional blue LED element. The conventional LED element basically has a double hetero structure in which an n-type layer 62 made of a nitride semiconductor, an active layer 63 and a p-type layer 64 are sequentially stacked on a sapphire substrate 61. As described above, sapphire is insulative and an electrode cannot be taken out from the substrate side, so that it is a so-called flip-chip type device in which a positive electrode 65 and a negative electrode 66 are provided on the same nitride semiconductor layer surface. I have.
[0005]
[Problems to be solved by the invention]
However, the conventional flip-chip type device using sapphire as a substrate has various problems. First, since both electrodes are taken out from the same surface side, the chip size becomes large, and a large number of chips cannot be obtained from the wafer. Second, the current flows in the horizontal direction because the negative electrode and the positive electrode are arranged in the horizontal direction. As a result, the current density is locally increased and the chip generates heat. Third, since a very hard and non-cleavable substrate called sapphire is used, a high level of technology is required to make a chip. Further, when realizing an LD, it is very difficult to form a resonance surface because the cleavage surface of the nitride semiconductor using the cleavage property of the substrate cannot be used as the resonance surface.
[0006]
In order to avoid the above problems, attempts have been made to grow a nitride semiconductor on a conductive substrate such as silicon carbide, silicon, zinc oxide, gallium arsenide, and gallium phosphide, as described above. No success has been reported.
[0007]
Accordingly, the present invention has been made in view of such circumstances, and a purpose thereof is to provide a method of manufacturing a nitride semiconductor device having a structure in which electrodes can be mainly taken out from above and below, and a nitride semiconductor device. It is in.
[0008]
[Means for Solving the Problems]
The method for manufacturing a nitride semiconductor device according to the present invention is directed to a nitride semiconductor device having an n-type layer, an active layer, and a p-type layer in that the n-type layer has a current confinement layer provided with an opening on the n-type layer; A negative electrode is formed in the opening. The current confinement layer is sapphire. The current confinement layer is made of SiO ₂ or TiO ₂ .
The method of manufacturing a nitride semiconductor device according to the present invention includes a first step of bonding a conductive substrate to a nitride semiconductor layer surface of a wafer on which a nitride semiconductor layer is grown on an insulating substrate; And a second step of removing part or all of the insulating substrate of the wafer to expose the nitride semiconductor layer. Further, the nitride semiconductor device of the present invention is characterized in that a conductive substrate and a nitride semiconductor are bonded.
[0009]
In the method of the present invention, sapphire, spinel, lithium niobate, neodymium gallate, or the like is used for the insulating substrate as described above. Preferably, sapphire, a nitride semiconductor grown on spinel has excellent crystallinity. ing. On the other hand, as the conductive substrate to be bonded to the nitride semiconductor, any material may be used as long as it is a conductive substrate material. For example, Si, SiC, GaAs, GaP, InP, ZnSe, ZnS, ZnO, or the like may be used. Can be. However, it is needless to say that the conductive substrate has substantially the same shape as the insulating substrate on which the nitride semiconductor is laminated, and furthermore, a wafer-like substrate having substantially the same area or an area larger than that. Absent.
[0010]
On the other hand, in order to remove the insulating substrate of the wafer on which the nitride semiconductor layers are stacked, for example, techniques such as polishing and etching are used. Normally, the thickness of the insulating substrate is several hundred μm, and the thickness of the nitride semiconductor layer is at most 20 μm or less. May be removed, and then fine portions may be removed by etching to expose a nitride semiconductor surface required for forming an electrode. In the case where an element requiring an insulator as a current confinement layer on the surface of the nitride semiconductor layer such as a laser element is manufactured, the nitride semiconductor layer is exposed by selective etching without removing the entire insulating substrate. It is also possible to remove only the parts necessary for the removal.
[0011]
Further, in the method and the device according to the present invention, the conductive substrate adhered to the nitride semiconductor layer has a cleavage property. For example, GaAs, GaP, InP, SiC, or the like can be preferably used for the conductive substrate having the cleavage.
[0012]
Next, the method and the device according to the present invention are characterized in that the surface of the nitride semiconductor layer and the conductive substrate are bonded to each other via an electrode or a conductive material. This method can be similarly applied to the case where a cleavage substrate is used as the conductive substrate. The bonding method may be a so-called wafer bonding method in which the bonding surface of the conductive substrate and the nitride semiconductor layer surface are mirror surfaces, the mirror surfaces are bonded to each other, and then thermocompression bonding is performed. Bonding can be easily achieved by using a material. As the conductive material, any material can be used as long as it can bond the nitride semiconductor and the conductive substrate. For example, a material such as In, Au, solder, and silver paste can be used.
[0013]
In the bonding method, the electrodes include an ohmic electrode formed on the surface of the nitride semiconductor layer and / or an ohmic electrode formed on the surface of the conductive substrate. Note that an ohmic electrode generally means a thin ohmic electrode formed on the surface of a nitride semiconductor and a thick bonding metal provided on the electrode, for example, a metal such as Au, In, or Al. In this specification, it is defined as an ohmic electrode. As the ohmic electrode material formed on the surface of the nitride semiconductor layer, if the n-type layer is an adhesive surface, for example, at least one of Al, Cr, Ti, and In shown in JP-A-5-291621, Particularly preferably, an electrode having Ti in contact with the n-type layer, and a material containing Ti-Al disclosed in JP-A-7-45867 can be exemplified. If the bonding surface is a p-type layer, at least one of Au, Pt, Ag, and Ni, particularly preferably Ni, described in Japanese Patent Application Laid-Open No. 5-291621, particularly preferably Ni, is used as the side in contact with the p-type layer. Electrodes can be mentioned.
[0014]
In the nitride semiconductor, a p-type layer is difficult to obtain, and to obtain a p-type layer, for example, electron beam irradiation as disclosed in JP-A-3-218625 or JP-A-5-183189 A thermal annealing process is performed after the growth, and the outermost p-type layer is reduced in resistance. For this reason, the nitride semiconductor wafer often has a p-type layer as the uppermost layer. Therefore, when bonding the nitride semiconductor wafer to the conductive substrate, it is particularly desirable to bond the nitride semiconductor wafer to the p-type conductive substrate via the ohmic electrode formed on the p-type layer.
[0015]
On the other hand, as the ohmic electrode formed on the conductive substrate on the other bonding surface, for example, if the conductive substrate is n-type GaAs, Ag-Sn, In-Sn, Ni-Sn, Au-Sn, Au-Si, Au-Ge or the like can be used, and for p-type GaAs, Au-Zn, Ag-Zn, Ag-In, or the like can be used. In addition, known ohmic electrode materials can be used for SiC, Si, and the like, but it is particularly desirable to bond a p-type conductive substrate through the ohmic electrode of the conductive substrate as described above.
[0016]
[Action]
In the method and device of the present invention, a conductive substrate is bonded to the nitride semiconductor layer. In other words, in the case of a wafer on which a nitride semiconductor is grown on an insulating substrate, various elements obtained from the nitride semiconductor must be of a flip-chip type. The conductive substrate becomes a substrate on which electrodes are formed by bonding to the substrate. After that, when the insulating substrate is removed, the nitride semiconductor layer is exposed, so that another electrode can be formed on the exposed nitride semiconductor layer surface, and is not a conventional element in which electrodes are arranged in a horizontal direction, An element in which the electrodes face each other can be manufactured.
[0017]
Next, when a material having a cleavage property is selected for the conductive substrate to be bonded, even if the nitride semiconductor is grown on an insulating substrate having no cleavage property, a chip-like material is formed by utilizing the cleavage property of the bonded conductive substrate. Can be divided into Therefore, an element having a small chip size is easily obtained, and a laser element having a cleavage plane of a nitride semiconductor as an optical resonance surface can be manufactured.
[0018]
There is also a method of bonding the surface of the nitride semiconductor layer and the conductive substrate with a technique generally called wafer bonding. In particular, when the bonding is performed via an electrode of the nitride semiconductor layer or an electrode of the conductive substrate, or a conductive material, the conductive layer is electrically conductive. It is preferable because the electrical characteristics between the conductive substrate and the nitride semiconductor layer are also stabilized. Further, if a material capable of reflecting the emission wavelength of the nitride semiconductor such as Au, Al, or Ag is selected as the conductive material, when a light emitting device is manufactured, light coming to the conductive substrate to which the conductive material is adhered is reduced. Since the light is reflected and returned to the nitride semiconductor layer, the light emitting efficiency of the light emitting element is improved.
[0019]
In particular, when an ohmic electrode formed on the surface of the nitride semiconductor layer and / or an ohmic electrode formed on the surface of the conductive substrate is included as an adhesive material, for example, when a light-emitting device such as a light-emitting element is manufactured, the resistance value becomes low. This has the effect of lowering the Vf of the device.
[0020]
【Example】
Hereinafter, the present invention will be described in detail with reference to examples. 1 to 3 are schematic cross-sectional views of a wafer and a conductive substrate for explaining one step of the method of the present invention, and FIG. 4 is a schematic view showing the structure of a nitride semiconductor light-emitting device obtained in Example 1. Embodiment 1 is described below with reference to these drawings.
[0021]
[Example 1]
A wafer having a nitride semiconductor layer 2 laminated on the surface of a sapphire substrate 1 is prepared. The nitride semiconductor layer 2 includes an n-type layer 21 made of AlXGa1-XN (0 ≦ X ≦ 1) doped with a donor impurity and an active layer made of InYGa1-YN (0 <Y <1) in order from the sapphire substrate 1. 22 and a p-type layer 23 made of AlXGa1-XN (0 ≦ X ≦ 1) doped with an acceptor impurity. The resistance of the uppermost p-type layer 23 is reduced by annealing at 400 ° C. or higher.
[0022]
Next, as shown in FIG. 1, an ohmic electrode 30 containing Ni and Au is formed on almost the entire surface of the nitride semiconductor layer 2 to a thickness of 500 Å. That is, the first ohmic electrode 30 is formed on almost the entire surface of the uppermost p-type layer of the nitride semiconductor layer 2 so as to obtain a preferable ohmic with the p-type layer. Further, an Au thin film having a thickness of 0.1 μm is formed on the ohmic electrode 30 in order to improve the adhesiveness.
[0023]
On the other hand, a p-type GaAs substrate 50 having substantially the same size as the sapphire substrate 1 is prepared as a conductive substrate, and a second ohmic electrode 40 made of Au-Zn is formed on the surface of the p-type GaAs substrate 50 by 500 angstroms. It is formed with a film thickness. Further, on the second ohmic electrode 40, an Au thin film is formed in a thickness of 0.1 μm to improve the adhesiveness.
[0024]
Next, as shown in FIG. 2, the ohmic electrodes of the nitride semiconductor wafer having the first ohmic electrode 30 and the p-type GaAs substrate 50 having the second ohmic electrode 40 are bonded to each other and pressed by heating. However, the sapphire substrate 1 and the p-type GaAs substrate 50 of the wafer at the time of pressure bonding are made parallel. If they are not parallel, a horizontal plane of the exposed nitride semiconductor layer will not be formed in the next step of removing the sapphire substrate. Although Au was used to bond the first ohmic electrode 30 and the second ohmic electrode 40, a conductive material such as indium, tin, solder, or silver paste was used between the electrodes 30 and 40. It is also possible to glue through. Needless to say, when the p-type GaAs substrate 50 is bonded, the cleavage property of the nitride semiconductor layer and the cleavage direction with the substrate 50 are matched.
[0025]
Next, the wafer to which the p-type GaAs substrate 50 has been bonded is placed on a polishing machine, the sapphire substrate 1 is wrapped, the sapphire substrate is removed, and the n-type layer 21 of the nitride semiconductor layer 2 is exposed. In this step, for example, after sapphire substrate 1 is wrapped so as to have a thickness of about several μm, it is also possible to remove the remaining sapphire substrate by etching. FIG. 3 shows the structure of the wafer after removing the sapphire substrate 1.
[0026]
After polishing the surface of the finally exposed n-type layer 21, a negative electrode 25 made of Ti-Al is formed on the n-type layer as an ohmic electrode, while the p-type GaAs substrate 50 is also made of Au- as an ohmic electrode. A positive electrode 55 made of Zn is formed on the entire surface.
[0027]
The wafer on which the positive electrode and the negative electrode are formed as described above is separated into 200 μm square light emitting chips by utilizing the cleavage of the p-type GaAs substrate. FIG. 4 is a schematic cross-sectional view showing the structure of the light emitting chip after separation. This light emitting chip shows the structure of an LED element in which the active layer 22 emits light when electricity is passed between the electrodes 25 and 55. In this light emitting device, the light emitted from the active layer 22 is reflected at the interface between the first ohmic electrode 30 and the p-type layer 23 and is not absorbed by the p-type GaAs substrate 50. The output increased by more than 50%.
[0028]
In this example, the insulating substrate is sapphire, and the conductive substrate is p-type GaAs.However, in addition to sapphire, for example, the above-described spinel, an insulating substrate such as neodymium gallate may be used. Further, a substrate such as Si or ZnO may be used as the conductive substrate.
[0029]
[Example 2]
When lapping the sapphire substrate 1 in the first embodiment, lapping is performed so that the sapphire substrate 1 remains with a thickness of 5 μm. Next, a mask having a shape capable of forming a current confinement layer is formed on the surface of the remaining sapphire substrate 1, and the sapphire substrate 1 in the mask opening is removed by etching with an etching apparatus, thereby exposing a part of the n-type layer 21. Let it. After exposure, a negative electrode 25 is formed on the n-type layer and a positive electrode 55 is formed on the p-type GaAs substrate 50 in the same manner.
[0030]
Next, using the cleavage properties of the p-type GaAs substrate 50, it is separated into chips to form a laser device. FIG. 5 is a schematic cross-sectional view showing the structure of the laser element, and the sapphire substrate 1 left intentionally acts as a current confinement layer of the laser element. This example shows an example in which a sapphire substrate is left as a current confinement layer. In addition to this, in order to form a current confinement layer of a laser device, the sapphire substrate 1 is entirely removed as in Example 1, and then, for example, SiO 2, An insulating film such as TiO2 may be formed on the exposed nitride semiconductor layer.
[0031]
【The invention's effect】
As described above, according to the method of the present invention, a nitride semiconductor device having a conductive substrate can be realized, so that a device having a small chip size can be provided. In addition, since the electrodes formed on the device are opposed to each other, the current flows uniformly in the nitride semiconductor layer and the calorific value is reduced, so that a laser device can be realized. Further, the nitride semiconductor can be easily cleaved, and the cleaved surface can be used as a resonator, thereby facilitating the manufacture of a laser device. Furthermore, when a light emitting device is realized, the light emission of the nitride semiconductor layer is reflected on the electrode surface by the electrode in which the nitride semiconductor layer and the conductive substrate are bonded, so that the light emission output can be increased.
[0032]
In a conventional nitride semiconductor LED, as shown in FIG. 6, a positive electrode 65 that transmits light is formed on almost the entire surface of the p-type layer 64. This is because the current in the p-type layer is difficult to spread. 50% or more of the light emitted by the positive electrode 65 was absorbed. However, according to the device of the present invention, the low-resistance n-type layer 21 is the uppermost layer as shown in FIGS. 4 and 5, so that there is no need to provide a full-surface electrode as in the prior art, and a small partial electrode is sufficient. Therefore, the light extraction efficiency from the nitride semiconductor layer side is dramatically improved, and the light emission output is improved. As described above, the present invention has an extremely large industrial value in realizing a device using a nitride semiconductor.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view of a nitride semiconductor wafer for explaining one step of the method of the present invention.
FIG. 2 is a schematic sectional view of a nitride semiconductor wafer for explaining one step of the method of the present invention.
FIG. 3 is a schematic cross-sectional view of a nitride semiconductor wafer for explaining one step of the method of the present invention.
FIG. 4 is a schematic sectional view showing the structure of a nitride semiconductor device according to one embodiment of the present invention.
FIG. 5 is a schematic sectional view showing the structure of a nitride semiconductor device according to another embodiment of the present invention.
FIG. 6 is a schematic sectional view showing the structure of a conventional nitride semiconductor light emitting device.
[Explanation of symbols]
1 sapphire substrate 2 nitride semiconductor layer 21 n-type layer 22 active layer 23 p-type layer 30 first ohmic electrode 40 ... Second ohmic electrode 50... P-type GaAs substrate 25... Negative electrode 55.

Claims (3)

In a nitride semiconductor device having an n-type layer, an active layer, and a p-type layer in order, a current confinement layer having an opening is provided on the n-type layer, and a negative electrode is formed in the opening. A nitride semiconductor device characterized by the above-mentioned. The nitride semiconductor device according to claim 1, wherein the current confinement layer is sapphire. The nitride semiconductor device according to claim 1 wherein the current confinement layer, characterized in that it consists of SiO ₂ or TiO _2.

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