JP2001148508A - Nitride semiconductor device and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem, where it is normally difficult for a nitride semiconductor device to meet requirements such as high performance, annealing controllability, and characteristic uniformity at the same time, so as to provide a nitride semiconductor device which possesses an N-type electrode suitable to these requirements and method of manufacturing the same. SOLUTION: An electrode is provided on an N-type conductivity nitride semiconductor for the formation of a nitride semiconductor device, where the electrode is of a four-layered structure composed of a first W-containing layer, a second Al-containing layer, a third Pt-containing layer, and a fourth Au or Pt-containing layer, and the electrode is connected electrically through the fourth layer. With this setup, even if the nitride semiconductor device is possessed of an N-type electrode formed of multilayred thin film, diffusion of elements into the N-type electrode can be controlled easily, and the nitride semiconductor device with an N-type electrode which is high in adhesion and excellent in ohmic properties can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for a light emitting element which can emit red light from ultraviolet light and a light emitting element which can be used for a laser diode, a photodiode, a light receiving element such as a solar cell, and a nitride semiconductor. (General formula I
_{n x Al y Ga 1-xy} N, where, 0 ≦ x ≦ y, x + y ≦
More particularly, the present invention relates to a nitride semiconductor device having an electrode that makes good ohmic contact with a nitride semiconductor having n conductivity and a method for manufacturing the same.

[0002]

2. Description of the Related Art An element using a nitride semiconductor (hereinafter, referred to as a nitride semiconductor element) has an optical recording device such as a light emitting diode and a DVD capable of emitting light of a wavelength from ultraviolet to red due to the characteristics of the semiconductor. Expectations are growing for its application to semiconductor lasers as light sources for increasing the density of media, and even to devices other than light-emitting devices.

[0003] In order to lower the forward voltage of the nitride semiconductor device including such an LED, it is necessary to obtain a preferable ohmic contact between the semiconductor layer and each electrode. Also in the LED having the above-described structure, good ohmic contact is obtained between the p-type nitride semiconductor and the positive electrode (hereinafter, referred to as “p-type electrode”). Similarly, good ohmic contact is obtained with a negative electrode (hereinafter, referred to as “n-type electrode”) in contact with the n-type nitride semiconductor.

However, the physical properties of the N-type nitride semiconductor have not been sufficiently elucidated, and it has been difficult to form a semiconductor device having excellent electrical characteristics and the like and operating under severe operating conditions with good reproducibility.

[0005]

An n-type electrode formed on such a nitride semiconductor having n-type conductivity (hereinafter, referred to as an n-type nitride semiconductor) has a reduced forward voltage and a reduced voltage with the semiconductor. In pursuit of performance improvements such as ohmic properties and adhesion, advanced designs have become necessary. Specifically, the n-type electrode is formed of a multilayer film, and each layer is formed of a thin film in order to reduce the resistance value. However, when such a thin film layer is formed as a multilayer film, it causes reproducibility and variation among element chips within the same wafer during mass production.

Specifically, when the n-type electrode is a multilayer film and most of the constituent layers are thin films having a thickness of several thousand mm or less, the stability of manufacturing, especially the layer structure including the film thickness of each element is considered. Tend to increase. In addition, after laminating each layer as an n-type electrode, heat treatment such as annealing for the purpose of improving the performance of the electrode formed of a multilayer film is performed.
Variations in the annealing effect occur due to the change in the thickness of the layer for each element.

Furthermore, in the electrode of the multilayer film, the diffusion of the elements constituting each layer cannot be ignored, and the diffusion of the elements in each layer based on the variation of the layer configuration of the electrode causes the variation between the elements. It will further increase.

[0008] The problems with the n-type electrode as described above are as follows.
In an element required to have high functionality, this may cause serious characteristic deterioration. This also makes it impossible for the performance of the n-type electrode to keep up with the speed of improving the performance of the device itself, which is a serious problem in the application of nitride semiconductor devices.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and is intended to improve the performance and productivity of an n-type electrode by forming a multi-layered n-type electrode with a thin film. To provide a nitride semiconductor device that solves the problem of reduced reproducibility, variation in device characteristics due to a slight change in film thickness of each layer, and reduced controllability of element diffusion due to heat treatment, and a method of manufacturing the same. It is.

That is, the present invention relates to a nitride semiconductor device in which an electrode is provided on a nitride semiconductor having n-type conductivity, wherein the electrode has a first layer having W, A second layer having Al on the layer, Pt on the second layer
A third layer having Au or Pt on the third layer
And the electrodes are electrically connected by the fourth layer. Also,
Between the second layer and the third layer, W, Cr, Ni, M
It has one kind of intermediate layer selected from the group consisting of o and Ti. Further, as a method of manufacturing the nitride semiconductor device, a step of forming a nitride semiconductor having n-type conductivity on a base and a step of forming W on the nitride semiconductor as an electrode are performed.
A first layer having Al, and a second layer having Al on the first layer.
Layer, one kind of intermediate layer selected from the group consisting of W, Cr, Ni, Mo, Ti, and a third layer having Pt on the intermediate layer.
A fourth layer having Au or Pt on the third layer.
And a step of forming a layer of In addition, after the electrode is formed, a first protective film is formed so as to cover almost the entire surface of the electrode, and a second protective film having an insulating property is formed on the first protective film. The first protective film is at least one metal selected from the group consisting of W, Ti, Cr, Ni, Cu, and Al; and the second protective film is silicon oxide or nitrogen oxide. After the formation of the second protective film, an opening is provided from above the electrode to remove part of the first protective film and the second protective film, thereby exposing the fourth layer. .

According to the first aspect of the present invention, a nitride semiconductor device having an n-type electrode having excellent adhesion while making good ohmic contact can be obtained. With the configuration according to claim 2 of the present invention,
Diffusion of the constituent elements of each layer is appropriately suppressed, and a nitride semiconductor device having an n-type electrode with good ohmic contact can be obtained. Further, by adopting the method according to claim 3 of the present invention, a nitride semiconductor device having an n-type electrode excellent in mass productivity and high functionality can be manufactured. By adopting the method according to claim 4 of the present invention, a nitride semiconductor device in which the n-type electrode is highly insulated and adhered can be manufactured. By adopting the method according to claim 5 of the present invention, the n-type electrode is covered with an insulating protective film with excellent adhesion, and a highly reliable nitride semiconductor device can be manufactured. By adopting the method according to claim 6 of the present invention, a nitride semiconductor device having excellent reliability under high mass productivity can be manufactured.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to FIG. FIG. 1 is a schematic cross-sectional view in which a light emitting diode is formed as an element structure by stacking a nitride semiconductor on a base 11. The layer structure is such that the active layer 13 is sandwiched between nitride semiconductor layers 12 and 14 having different conductivity types. Positive and negative electrodes 15 and 16 and an extraction electrode 17 are provided on the same surface side of the base 11.

(N-Type Electrode) The n-type electrode 401 of the present invention, which is an electrode for a nitride semiconductor having n-type conductivity, uses a metal such as tungsten or aluminum or an alloy thereof as a vapor deposition material or a sputter material. It can be formed in a desired place by various methods such as an evaporation method and a sputtering method. In order to form a stacked structure as an n-type electrode, by setting the first layer to W and the second layer to Al, good ohmic contact with the n-type nitride semiconductor can be obtained. W of the first layer, Al of the second layer
May be formed of an alloy. As a specific alloy material, at least one material selected from Al and Si is used for the first layer, and as an alloy material used for the second layer,
At least one material selected from W, Cu, and Si is used. Further, on the first layer and the second layer, a material having a higher melting point than the second layer is used to prevent alloying between the metal material of the second layer and the layer laminated thereon. It is laminated as a third layer or an intermediate layer. Further, a metal having good electrical connection with an external circuit is further laminated on the third layer as a fourth layer. As specific intermediate layers, W, Cr, n
i, Mo, Ti, alloys thereof, and the like, and Pt as the third layer. The fourth layer includes Au and an alloy thereof. Although a plurality of metal multilayer films may be formed as desired, the surface of the n-type electrode electrically connected to an external circuit is preferably a fourth layer.
Still further, the n-type electrode of the present invention is characterized in that Si or / and Ge are used as n-type dopants in an amount of 2 × 10 ¹⁸ / cm ³ to 1
Ohmic contact and adhesion with an n-type nitride semiconductor contained at × 10 ¹⁹ / cm ³ are particularly good. Although the reason is not clear, it is considered that there is some correlation between the first layer and Si and / or Ge contained in the n-type nitride semiconductor.

Although a sufficient ohmic contact can be formed without annealing in the nitride semiconductor device of the present invention, annealing may be performed in order to obtain a more stable and high mechanical strength semiconductor device. In this case, the annealing temperature is preferably 350 ° C. or lower so that an annealing effect is generated and the adhesion between the formed n-type electrode and the electrical connection member or the n-type nitride semiconductor is not adversely affected. The temperature is more preferably from 80 ° C to 280 ° C, and still more preferably from 100 ° C to 220 ° C. In addition, it is preferable to perform the annealing in an inert gas such as Ar, He, or N ₂ . At this time, in the present invention, unlike the comparative example 1, since the third layer having Pt is provided, the n-type electrode is excellent in heat treatment,
It is possible to stably realize high-performance electrodes by annealing.

(Nitride Semiconductor) The nitride semiconductor used in the present invention is obtained by a liquid phase growth method, a VPE method (VaporPh method).
case Epitaxy), MOVPE method (Metal
Organic Vapor Phase Epita
xy) and MOCVD (Metal Organic)
Chemical Vapor Deposition
n) and the like. Examples of the structure of the semiconductor element include various structures such as a homo structure having a MIS junction or a PN junction, a hetero structure, a double hetero structure, and a Schottky junction, as desired. The emission wavelength and the reception wavelength can be variously selected from the ultraviolet light to the red region depending on the material of the semiconductor and the degree of mixed crystal thereof. In particular, when the n-type electrode of the present invention is used, an ohmic contact can be obtained without applying an excessive voltage to the nitride semiconductor device, which is particularly effective for a semiconductor device having an extremely thin semiconductor. Specifically, it is particularly useful in a nitride semiconductor device having a structure in which one layer constituting the semiconductor active layer has a quantum effect of 100 Å or less.

The gallium nitride-based compound semiconductor can be formed as a single crystal under high temperature and high pressure, so that the base can be omitted. However, it is preferable to form the gallium nitride on the substrate from the viewpoint of mass productivity. As a substrate on which a nitride semiconductor is formed, a single crystal semiconductor substrate of Si, Ge, SiC, or the like, GaAs, InAs, InP, GaSb, AlN,
III-V compound semiconductor substrates such as GaN, sapphire (Al2O3), spinel (MgAl2O4), quartz (S
iO2), Ti2O, MgO, MgF2, CaF2, SrT
Substrates using a material such as iO3, ZnO or the like can be given. The thickness of the substrate can be variously selected depending on the semiconductor device to be formed and the material of the substrate, but when light is emitted or received through the substrate, the thinner the better, the thinner the light transmittance and the ease of formation as a chip. . On the other hand, the mechanical strength of the substrate is required during the process of forming the element and during the handling. Therefore, as a preferable thickness of the substrate,
It is 0.01 to 3.0 mm. More preferably 0.05
~ 2.0 mm is preferred. Note that a sapphire substrate is preferably used to form a nitride semiconductor with good crystallinity. A light emitting element and a light receiving element can be formed by forming a buffer layer such as GaN or AlN on the sapphire substrate to alleviate lattice mismatch and forming a nitride semiconductor having a PN junction or the like thereon.

A nitride semiconductor shows n-type conductivity without being doped with an impurity.
It is preferable to appropriately introduce Ge, Se, Te, C, Sn and the like. Further, double doping in which an n-type dopant and a small amount of a P-type dopant are doped can also be used. By changing the type and doping amount of these dopants, the carrier density can be controlled and the electric resistance can be reduced. In this case, the carrier density is 1017 c
It is preferably at least m-3, more preferably at least 1018 cm-3. On the other hand, when a P-type nitride semiconductor is formed, Zn, Mg, Be, Ca, S
Doping with r, Ba, etc. The gallium nitride semiconductor is P
Since it is difficult to form a p-type simply by doping the p-type dopant, the p-type may be formed by introducing a low-speed electron beam or annealing by plasma irradiation or the like after the introduction of the p-type dopant.

In order to form different electrodes on the emission observation surface side, each semiconductor is preferably etched into a desired shape. As etching, dry etching,
There is wet etching. Examples of the dry etching include reactive ion etching, ion milling, focused beam etching, and ECR etching.
For wet etching, a mixed acid of nitric acid and phosphoric acid can be used. However, it goes without saying that a mask is formed in a desired shape using a material such as silicon nitride or silicon dioxide before etching. The electrode of the present invention shows sufficient adhesion and electric characteristics even on such an etched surface.

(P-type electrode) The p-type electrode, which is a nitride semiconductor electrode having p-type conductivity, needs to be in ohmic contact with the p-type nitride semiconductor layer to be brought into contact. In the case where light is emitted as a light-emitting element through a p-type electrode, a light-transmitting material formed of a metal thin film or the like (here, light-transmitting means that light passes through the electrode with respect to the wavelength of light emitted from the light-emitting element). Should be used.)

Materials satisfying these conditions include, for example, Au, Ni, Pt, Al, Cr, Mo, W, In, G
Metals such as a, Tl, Ag, and Rh and alloys thereof are included. In addition, ITO as a translucent electrode material,
Metal oxides such as SnO2 and NiO2 are also included. Furthermore, it is also possible to laminate the metal thin film on these. In order to make a metal or the like light-transmitting, it may be formed to be extremely thin using an evaporation method, a sputtering method, or the like. Also,
After a metal is formed by vapor deposition or sputtering, annealing is performed to diffuse the metal into the semiconductor layer having p-type conductivity and to scatter the metal to the outside to obtain a desired film thickness (thickness of the electrode that becomes translucent). ) Can be formed. The thickness of the metal electrode that becomes translucent varies depending on the desired emission wavelength and the type of metal, but is preferably 0.001 to 0.1 μm, more preferably 0.05 to 0.2 μm. is there. Further, when the electrode is made translucent, the p-type electrode can be formed according to the purpose, such as linear or planar. A planar electrode formed on the entire semiconductor layer having p-type conductivity can spread current over the entire surface and emit light over the entire surface.

Furthermore, when the p-type electrode is formed to be extremely thin, if wire bonding is performed directly on the electrode,
Since the ball tends to be hardly connected, it is preferable to form a pedestal electrode for bonding separately from the p-type electrode or to form the p-type electrode in a multilayer structure in order to improve adhesion. Au, Pt, Al, or the like can be used as the material of the pedestal electrode. The thickness of the pedestal electrode is preferably on the order of microns. In the case where at least a part of the p-type electrode has a multilayer structure, the contact electrodes to be brought into contact with the nitride semiconductor include Cr, Mo, W, Ni, Al, In,
A metal selected from Ga, Tl, and Ag or an alloy thereof is preferably used, and a metal such as Al or Au or an alloy thereof is preferably used as a bonding electrode that comes into contact with the bonding. When the semiconductor element is energized,
Since the bonding electrode material may migrate into the p-type electrode, it is particularly preferable to use the bonding electrode Au alone or an Au alloy having a low content of Al and / Cr. In the case of a p-type nitride semiconductor, p
It is preferable to anneal at 400 ° C. or more in order to improve the ohmic characteristics by blending the mold electrode material and the semiconductor material, and to remove hydrogen contained during the formation of the nitride semiconductor. Further, it is preferable to anneal at 1100 ° C. or lower for the purpose of suppressing the decomposition of the gallium nitride semiconductor. Further, by performing the annealing in a nitrogen atmosphere, nitrogen in the gallium nitride-based compound semiconductor can be suppressed from decomposing and leaving, and the crystallinity can be maintained.
In the present invention, when the annealing temperature of the p-type electrode is high, the N-type electrode is preferably formed after the formation of the p-type electrode.

[0022]

[Example 1] A light emitting device using a nitride semiconductor will be described as one embodiment of the present invention. FIG.
FIG. 2 is a schematic cross-sectional view showing the structure of the light emitting element, and shows a nitride semiconductor layer 1 having n-type conductivity on a sapphire substrate 11.
2. It has a structure in which an active layer 13 and a nitride semiconductor layer having p-type conductivity are sequentially stacked. As shown in FIG. 1, after the respective semiconductor layers are stacked, a part of the p-type conductive nitride semiconductor layer 14, the active layer 13, and a part of the n-type conductive nitride semiconductor layer 12 are removed in predetermined regions. Then, the surface for forming an electrode on the n-type conductive nitride semiconductor layer is exposed, and the following n-type electrode is formed on the surface.

First, after forming a negative resist film,
W is 200 ° as the first layer, and Al is 2 as the second layer.
000 °, W as the intermediate layer, 500 ° as the third layer, Pt as 1000 °, and Au as the fourth layer, 3500 °.

Next, as shown in FIG. 2, as a first protective film, Ni is formed to a thickness of 60 ° so as to cover almost the entire surface and the side surface of the electrode 31 (FIG. 2).
(A)) Then, as the second protective film 33, 3
It is formed with a thickness of 000 mm. At this time, each protective film is formed by a sputtering apparatus, and in order to form a predetermined pattern, unnecessary portions are removed by a lift-off method or the like (FIG. 2B).

After forming the second protective film, as shown in FIG. 2C, a photoresist mask 34 is formed to provide an opening for connecting an external circuit and an electrode in a predetermined shape.
To form Subsequently, the first protective film 32 and the second protective film 33 below the opening of the photoresist mask 34 are removed,
An opening 35 where the electrode 31 is exposed is formed.
(D)). At this time, if a part of the electrode 31 is removed to form a recess in the electrode as well, the fourth layer made of Au can be reliably exposed, which is advantageous for electrical connection with an external circuit, which is preferable. . This is because, in the vicinity of the boundary between the first protective film and the electrode, depending on the material of the protective film and the material of the electrode, alloying may be performed due to diffusion of an element or the like. This is because, by exposing the electrodes, this problem can be avoided, and the electrical connection is reliably established. Preferably, as the electrode to be removed,
This is to remove a part of the fourth layer which is an electrode surface for making an electrical connection with an external circuit, that is, to provide a recess in the fourth layer. Here, the fourth Au
Is removed at a depth of 300 ° from the surface.

In the step of providing this opening 35, S
The first protective film 33 made of iO ₂ is
After the removal using F ₄ gas, the second protective film 32 made of Ni is removed by RIE using a gas obtained by adding an Ar gas to a chlorine-based gas.
The fourth layer (Au) is partially removed to provide an opening.

Further, before forming the first and second protective films of the n-type electrode, a p-type conductive nitride semiconductor layer 14
The light-emitting element as shown in FIG. 1 is obtained by providing the pattern electrode 15 and the p-type extraction electrode 16 and providing the above-mentioned protective film for the n-type electrode also on the p-type electrode.

FIGS. 3 and 4 show the distribution of each element in the depth direction from the surface after the light emitting devices obtained in Example 1 and Comparative Example 1 were subjected to heat treatment at 550 ° C. and 500 ° C., respectively. It is. In FIG. 3, although element diffusion due to the heat treatment is observed near the boundary between the layers, the elements of the layers from the first layer to the fourth layer have a clear layer structure, and the annealing is performed with good reproducibility in the heat treatment. Understand. On the other hand, in FIG. 4, which is the n-type electrode of the comparative example, it can be seen that the diffusion of the layer made of Al reaches the entire thickness of the n-type electrode, and the multilayer film structure is broken. This indicates that, in the light-emitting element of the comparative example, there is a risk that the functionality of the n-type electrode may be lost even in the heat treatment at a relatively low temperature. Some elements lead to instability of element diffusion, and as a result, the diffusion degrades device characteristics.

[Comparative Example 1] W having a thickness of 200 ° and a thickness of 20
00Å Al, 200Å W, 3000３ A
A light emitting element is obtained in the same manner as in Example 1, except that n is stacked in order to form an n-type electrode.

[0030]

As described above, the nitride semiconductor device of the present invention has excellent adhesiveness,
Despite its high performance with excellent ohmic contact, it has excellent reproducibility and can be used in harsh environments such as high temperatures.

Further, according to the manufacturing method of the present invention, even if a multilayer film is formed by a thin film, an n-type electrode having excellent reproducibility and annealing, little variation in element characteristics, and excellent mass productivity is provided. A nitride semiconductor device can be manufactured.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view illustrating one embodiment of the present invention.

FIG. 2 is a schematic sectional view illustrating a manufacturing method of the present invention.

FIG. 3 is a diagram illustrating a layer configuration after heat treatment of an n-type electrode according to one embodiment of the present invention.

FIG. 4 is a diagram illustrating a layer configuration after heat treatment of an n-type electrode according to a comparative example of the present invention.

[Description of Signs] 11 ··· Base 12 ···· N-type nitride semiconductor 13 ···· Active layer 14 ···· P-type nitride semiconductor 15 ····· P-type electrode 16 ··· · Extraction electrode 17 ··· N electrode 18 ··· Second protective film 23 ··· Ball (bonding member) 30 ··· n-type nitride semiconductor 31 ··· n-type electrode 32 ··· ... First protective film 33 ... Second protective film

Claims (6)

[Claims] 1. A nitride semiconductor device in which an electrode is provided on a nitride semiconductor having n-type conductivity, wherein the electrode is formed on a first layer having W, and on the first layer. A second layer having Al, a third layer having Pt on the second layer,
A nitride semiconductor device, comprising: a fourth layer having Au or Pt on the third layer, wherein the electrodes are electrically connected by the fourth layer. 2. A method according to claim 1, wherein W, C are provided between said second layer and said third layer.
2. The nitride semiconductor device according to claim 1, comprising one kind of intermediate layer selected from the group consisting of r, Ni, Mo, and Ti. 3. A step of forming a nitride semiconductor having n-type conductivity on a base, and forming an electrode on the nitride semiconductor as an electrode.
A first layer having W, a second layer having Al on the first layer, one kind of intermediate layer selected from the group consisting of W, Cr, Ni, Mo, and Ti; Forming a third layer having Pt thereon and a fourth layer having Au or Pt on the third layer. . 4. After forming the electrode, a first protective film is formed so as to cover substantially the entire surface of the electrode, and a second protective film having an insulating property is formed on the first protective film. 4. The method for manufacturing a nitride semiconductor device according to claim 3, wherein 5. The method according to claim 1, wherein the first protective film is made of W, Ti, Cr, N
at least one selected from the group consisting of i, Cu, Al
5. The method according to claim 3, wherein the second protective film is made of one of silicon and nitrogen oxide. 6. 6. After the formation of the second protective film, an opening is provided from above the electrode to remove part of the first protective film and the second protective film, thereby exposing the fourth layer. 6. The method for manufacturing a nitride semiconductor device according to claim 4, wherein said method is performed.