JP3384700B2 - Gallium nitride based compound semiconductor light emitting device and method of manufacturing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gallium nitride-based compound semiconductor light emitting device that emits blue light or light in a short wavelength region and a method for manufacturing the same.

[0002]

BACKGROUND ART A gallium nitride-based compound semiconductor (Al _x Ga
_1-x N; 0 ≦ x <1, hereinafter also referred to as “GaN”) has attracted attention as a material for a blue light emitting diode or a light emitting element in a short wavelength region.

Since a low resistance p-type crystal has not been obtained for GaN, a light emitting diode using this has a metal electrode (M)-
A so-called MIS type structure having a structure of a semi-insulating GaN layer (I layer) -N type GaN layer (S layer) is adopted. In order to develop such a light emitting diode, it is essential to establish a technique for forming an electrode connected to the lower N-type GaN layer. That is, other III-, such as Al _x Ga _1-x As.
In a light emitting device using a group V compound semiconductor, a lower electrode is formed on the substrate side by using a conductive substrate. However, in the case of GaN, since the substrate sapphire is an insulator, the lower layer This is because it is impossible to form an electrode connected to the N-type GaN layer on the substrate side.

Since GaN is a chemically very stable substance, the I-type GaN layer is partially removed by chemical etching with a chemical to expose the N-type GaN layer, and the exposed surface is exposed. It is also difficult to form electrodes. Further, a method of providing an electrode portion on the side surface of the N-type GaN layer and connecting with a metal wire can be used. However, the thickness of the N-type GaN layer is at most about several μm to several tens of μm, and the reliability as an electrode is improved. Mass productivity is poor. Therefore, the following methods have been reported so far as techniques for forming electrodes on the N-type GaN layer.

The first method is to form a low resistance region in a part of the GaN layer by subjecting the substrate to some kind of processing. That is, as shown in FIG. 5, a scriber or dicer is used in advance to form an uneven region 12 such as a shallow kerf or a scratch (see FIG. 5A) on a part of the sapphire substrate 10 and then epitaxial growth of GaN is performed. As a result, the GaN grown on the concavo-convex region 12 does not become an I-type layer even if it is heavily doped with Zn, and an N-type low resistance region 18 is formed (see FIG. 5B). By forming the N-side electrode 20 on the low resistance region 18, it is possible to make contact with the N-type GaN layer 14 via the N-type low resistance region 18 (see FIG. 5C). Furthermore, the I-side electrode 22 is separated from the N-side electrode 20 on the I-type GaN layer 16.
To form.

Similarly, when the GaN epitaxial growth is performed after depositing a dielectric film such as SiO ₂ , Al ₂ O ₃ or Si ₃ N _{4 on} a part of the sapphire substrate in advance, the concavo-convex region 12 is also formed. As in the case of formation, an N-type low resistance GaN layer is formed on these films, and the N-type GaN layer is formed thereon.
By forming the side electrode, it is possible to make contact with the N-type GaN layer.

The second method is a method of removing the I-type GaN layer by dry etching or the like. That is, as shown in FIG. 6, an opening is formed after depositing the SiO ₂ film 24 on the I-type GaN layer 16 (see FIG. 6A), and CCl ₄ , C
The I-type GaN layer 16 immediately below the opening is removed by dry etching using a gas such as Cl ₂ F ₂ to remove the N-type GaN layer 14.
Is exposed to form a recess (contact hole) 26 (see FIG. 6B), and the N-side electrode 20 is formed in the recess 26, so that the N-type GaN layer 14 can be contacted.

Similarly, after depositing a SiO ₂ film on the I-type GaN layer, an opening is provided, and heat treatment is performed in a hydrogen atmosphere in a mixed gas atmosphere having a mixture ratio of hydrogen chloride and argon of 3: 1. , The I-type GaN layer on the exposed surface is decomposed and removed, and N
It is also possible to expose the type GaN layer and form the N-side electrode there. Further, by scribing with a needle made of diamond, the I-type GaN layer is mechanically removed and the N-type Ga is
There is also a method of forming a recess reaching the N layer and forming an N-side electrode there.

[0009]

The first method, however, utilizes the fact that GaN grown on a portion of the surface of the substrate 10 that has been processed such as forming the concavo-convex region 12 becomes polycrystalline, and N Since the low resistance region 18 is formed, it is difficult to accurately and reproducibly control the carrier concentration of the low resistance region 18 and the low resistance region 18 is formed in the I-type GaN layer 1.
It is formed up to the depth reaching the sapphire substrate 10 from the surface of 6, and the depth cannot be set arbitrarily. In addition, the first method is based on the conventionally used Ga—HCl—NH ₃ system hydride vapor phase growth (HV).
It is a method devised for GaN crystal production by the PE) method, and these methods cannot be used as they are for the crystal production by the metal organic chemical vapor deposition (MOVPE) method. Especially in the MOVPE method, SiO ₂ or Al ₂ O ₃
A polycrystalline GaN layer cannot be uniformly grown on a dielectric thin film such as, and a low resistance region cannot be formed.

Further, the second method requires multi-step and complicated steps such as production of the SiO ₂ layer used as a mask, pattern formation thereof, dry etching or heat treatment, and subsequent electrode formation. In addition, the method of scribing the I-type GaN layer causes stress to be introduced into the GaN layer, induces cracks, deteriorates electrical characteristics, and causes a large reduction in yield in actual device fabrication. .

Therefore, an object of the present invention is to provide a GaN light-emitting element having excellent reliability and mass productivity, which does not require any processing on the substrate, or does not include complicated steps such as the production of contact holes, and a method for manufacturing the same. To provide.

[0012]

In order to achieve the above object, a gallium nitride-based compound semiconductor light emitting device according to claim 1 is a gallium nitride-based compound semiconductor (Al _x Ga).
_1-x N; 0≤x <1), in a semiconductor light emitting device including a semiconductor layer, an electrode formed on the semiconductor layer,
A low resistance region that is continuous with the electrode and is formed by diffusion of a material of the electrode.

In the semiconductor light emitting device having this structure, in addition to the case where a semi-insulating (I-type) GaN layer is formed in the semiconductor layer immediately below the electrode, impurities are different due to the difference in ionization potential between the electrode material and GaN. Even if the high resistance layer is intentionally formed by adhesion, the contact resistance between the semiconductor layer and the electrode can be reduced by forming the low resistance region penetrating these high resistance layers. And, for example,
For example, the N-type low resistance region is formed by the specific heat treatment on the N-side electrode.
Formed by diffusing the material into the GaN layer
It

The electrode can be made of, for example, nickel (Ni) alone, but the first conductive layer made of titanium (Ti) or chromium (Cr) and the second conductive layer made of Ni or an alloy containing Ni. An electrode having a multilayer structure in which at least and are laminated can be preferably used. When the Ni layer is used alone, the adhesion of the Ni layer to the GaN layer is poor. Therefore, by forming an electrode through a thin film of Ti or Cr, the adhesion of the Ni layer-GaN layer can be improved. Also, the ohmic characteristics after heat treatment are improved.

As described above, in the gallium nitride compound semiconductor light emitting device of the present invention, the electrode is taken out through the low resistance region formed continuously with the electrode, and the electrical resistance component of the light emitting device is measured. Can be made smaller.

The gallium nitride-based compound semiconductor light-emitting device according to claim 5 is a gallium nitride-based compound semiconductor (Al _x
Ga _1-x N; a semiconductor light-emitting device including a semiconductor layer of 0 ≦ x <1), the first light-emitting device formed on the semiconductor layer.
Electrode and a low resistance region that is continuous with the first electrode and is formed by diffusion of the material of the electrode, and is formed on the same surface as the first electrode, apart from the first electrode. And a second electrode.

According to a sixth aspect of the present invention, there is provided a method of manufacturing a gallium nitride-based compound semiconductor light emitting device, wherein a gallium nitride-based compound semiconductor (Al _x Ga) is formed on a substrate made of a semiconductor or an insulator.
_1-x N; 0 ≦ x <1) In the method for manufacturing a semiconductor light emitting device, including the step of forming a semiconductor layer, an electrode forming step of forming an electrode on the surface of the semiconductor layer, and a heat treatment, And a step of forming a low resistance region directly under the electrode.

That is, in this manufacturing method, first, for example, GaN is formed on a sapphire substrate by a vapor phase growth method or the like.
A semiconductor layer including layers is formed.

Next, an electrode (first electrode) is formed on the GaN layer by a process well known in semiconductor engineering such as mask vapor deposition or photo etching.

Next, for example, S which becomes a protective film is preferable.
After depositing the iO ₂ layer by evaporation or the like, heat treatment is applied to promote the reaction between the electrode and the GaN layer, and the material of the electrode is diffused into the GaN layer to form a low resistance region. For example, heat treatment is applied to separate the N-side electrode and the GaN layer.
Promote reaction and diffuse N-side electrode material into GaN layer
Then, an N-type low resistance region is produced. At this time, the heat treatment temperature is preferably 700 to 1000 ° C, more preferably 800 to 900 ° C. Heat treatment temperature is 1000 ℃
If it exceeds, the whole or part of the GaN layer is deteriorated by heat, which is not preferable, while if it is less than 700 ° C., a good low resistance region cannot be formed. The heat treatment is preferably performed under a nitrogen gas flow, a hydrogen gas flow, or the like. The heat treatment time is preferably about 15 seconds to 1 minute. Further, as a heat treatment apparatus, an infrared heating system capable of rapid heating and rapid cooling is preferable in order to control thermal damage to the GaN layer and diffusion of dopant.

As described above, the electrode can be made of nickel alone, for example, but a first conductive layer made of titanium or chromium and a second conductive layer made of nickel or an alloy containing nickel are laminated. A two-layer structure electrode can be preferably used.

That is, in the electrode forming step,
First, it is preferable that the first conductive layer is formed on the surface of the semiconductor layer by a method such as vapor deposition, and the second conductive layer is formed on the surface of the first conductive layer.

Next, for example, the protective film is removed, and the other electrode (second electrode) is formed by vapor deposition or the like.

In the method for manufacturing the gallium nitride-based compound semiconductor light emitting device, the low resistance region is manufactured by the reaction between the electrode and the GaN layer, and therefore, various operational effects exemplified below are exhibited.

1. Since the low resistance region is formed by diffusion of the material of the electrode by heat treatment, the position of the electrode and the low resistance region are necessarily the same, and the position of the low resistance region or the contact hole position and the electrode which is conventionally required is the same. No need for alignment.

2. The low resistance region of the present invention is formed by a heat treatment process after electrode formation, unlike the case where the low resistance region is formed at the same time when the GaN layer is grown after processing the substrate (the first method of the prior art). To be done. Therefore, the carrier concentration in the low resistance region can be controlled accurately and with good reproducibility by adjusting the heat treatment time and temperature independently of the growth conditions of the GaN layer, and the electrical resistance of the light emitting element can be controlled. The components can be easily reduced, and there is little variation in characteristics among the elements.

In the first method of the prior art, the low resistance region extends from the surface of the GaN layer to the substrate. However, according to the method for manufacturing a gallium nitride-based compound semiconductor light emitting device of the present invention, the condition of the heat treatment step is set. Thus, the depth of the low resistance region can be controlled, and the low resistance region can be formed to an arbitrary depth. Therefore,
A low resistance region can be formed at a desired depth, and the device structure can be optimized.

3. In the case of forming a contact hole (second method of the prior art), it takes many steps and time for forming the SiO ₂ layer used as an etching mask and for the dry etching process, but the gallium nitride compound semiconductor light emission of the present invention is required. According to the element manufacturing method, the process is simplified, and the processing can be performed in a relatively short time, and the economical element manufacturing can be easily performed.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below based on specific embodiments. The present invention is not limited to the embodiments described below.

FIG. 1 is a sectional view schematically showing the structure of a light emitting diode to which the gallium nitride compound semiconductor light emitting device of the present invention is applied.

In FIG. 1, the light emitting diode has a sapphire substrate 30, and an AlN buffer layer 32 having a film thickness of about 50 nm is formed on the sapphire substrate 30. A film thickness of about 2.5 μm is formed on the upper surface of the buffer layer 32.
An N layer 34 made of m N-type GaN is formed. Further, on the upper surface of the N layer 34, an I layer 36 made of semi-insulating GaN having a film thickness of about 0.2 μm is formed. And I
The upper surface of the layer 36 has a metal I
Side electrode 42 and metal N-side electrode 4 connected to N layer 34
0 and 0 are formed in a separated state. An N-type low resistance region 38 that penetrates the I layer 36 and reaches the N layer 34 is formed immediately below the N-side electrode 40.

The N-side electrode 40 may have a multilayer structure in which a single element of nickel, or at least a first electrically conductive layer of titanium or chromium and a second electrically conductive layer of nickel or an alloy containing nickel are laminated. preferable.

Next, a method of manufacturing a light emitting diode having this structure will be described with reference to FIG.

The light emitting diode is manufactured by vapor phase growth by MOVPE.

First, the single crystal sapphire substrate 30 whose main surface is the a-plane, which has been cleaned by organic cleaning and heat treatment, is MO.
It is attached to the susceptor placed in the reaction chamber of the VPE device.
Next, the sapphire substrate 30 was vapor-phase etched at 1200 ° C. for 10 minutes while flowing hydrogen gas into the reaction chamber.

Next, the AlN buffer layer 32 is formed to a thickness of about 50 n.
It was formed to a thickness of m. Subsequently, an N layer 34 made of N-type GaN having a thickness of about 2.5 μm and an I layer 36 made of semi-insulating GaN having a thickness of about 0.2 μm were sequentially formed. In this way, an LED wafer having a multilayer structure as shown in FIG. 2A was obtained (first step).

Next, as shown in FIG. 2B, the I layer 36 is formed.
On the entire upper surface of the Ti electrode layer 40a and Ni by vapor deposition.
The electrode layer 40b has a thickness of about 10 nm and about 300 nm, respectively.
The layers are sequentially formed to have a thickness of nm. Then, a photoresist was applied to the upper surface of the Ni electrode layer 40b, and a pattern was formed by photolithography into a predetermined shape so that the photoresist 44 remained at the formation position of the electrode portion connected to the N layer 34. Next, as shown in FIG. 2C, the exposed portions of the lower Ti electrode layer 40a and the Ni electrode layer 40b are etched using the photoresist 44 as a mask, and the photoresist 44 is further removed to remove the N-side electrode 40. Was produced (second step).

Next, as shown in FIG. 2D, the I layer 36 is formed.
A SiO ₂ layer 46 having a thickness of about 100 nm was formed on the entire upper surface of the N-side electrode 40 by vapor deposition. Then, the sample is heated in an infrared lamp in nitrogen gas, and the system is heated to 900 ° C.
After holding the temperature for 20 seconds or more,
The sample was cooled. Thus, as shown in FIG. 2E, the N-type low resistance region 38 was formed in the GaN layer (third step).

Next, a photoresist is applied to the upper surface of the SiO ₂ layer 46, and the photoresist is patterned into a predetermined shape by photolithography so that portions other than the electrode portions connected to the I layer 36 remain. Subsequently, an Al layer is formed on the entire upper surface of the sample by vapor deposition, and the sample is further covered with SiO ₂
By dipping in the stripping solution to remove the SiO ₂ layer 46,
The photoresist and the Al layer formed directly on the SiO ₂ layer 46 were removed, and the I-side electrode 42 connected to the I layer 36 was formed as shown in FIG. 2F (fourth step). .

In this way, the MIS having the structure shown in FIG.
(Metal-Insulator-Semicond
(uctor) type gallium nitride compound semiconductor light emitting device can be manufactured.

In the manufacturing process described above, the N-type low resistance region 38 is formed by heat treatment in the third process.
It is formed by promoting the reaction between 0 and the GaN layer. In order to confirm this, the following analytical test was conducted.

FIGS. 3 and 4 show the results of Auger electron spectroscopy (AES) analysis of composition changes in the depth direction before and after heat treatment at the N-side electrode 40 portion of the sample. In the analysis results shown in FIGS. 3 and 4,
For ease of understanding, the curves of Ti, O, Ti + N are omitted and only the curves of Ni and Ga are shown.

Comparing FIG. 3 and FIG. 4, it was confirmed that Ni penetrated into the GaN layer and Ga penetrated into the Ni layer after the heat treatment, and due to the interdiffusion between the electrode material of the N-side electrode 40 and GaN. It can be seen that the N-type low resistance region is formed.

The light-emitting diode shown in FIG. 1 manufactured by the above method has a current-voltage characteristic with a rising voltage of 6 V, which is about 3/4 of that of the conventional structure, and the driving voltage is reduced. It was confirmed that it contributed to.

In the manufacturing example described above, an electrode having a two-layer structure of Ti and Ni is used as the N-side electrode 40, but an electrode having a two-layer structure of Cr and Ni or an electrode having only one Ni layer may be used.

[0046]

[Brief description of drawings]

FIG. 1 is a sectional view schematically showing an example of a light emitting diode to which a gallium nitride-based compound semiconductor light emitting device of the present invention is applied.

2A to 2F are sectional views schematically showing a manufacturing process of the light emitting diode shown in FIG.

FIG. 3 is a diagram showing Auger electron spectroscopic analysis results before heat treatment for confirming that a low resistance region is formed.

FIG. 4 is a diagram showing Auger electron spectroscopic analysis results after heat treatment for confirming that a low resistance region is formed.

5A to 5C are cross-sectional views schematically showing a production example of a conventional gallium nitride-based compound semiconductor device.

6A to 6C are cross-sectional views schematically showing a production example of another conventional gallium nitride-based compound semiconductor element.

[Explanation of symbols]

30 sapphire substrate 32 buffer layer 34 N layer 36 I layer 38 N type low resistance region 40 N side electrode 42 I side electrode

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Takahiro Ozawa               Aichi Prefecture Aichi District Nagakute Town               Address 1 Toyota Central Research Institute Co., Ltd.

Claims (11)

(57) [Claims] 1. A gallium nitride-based compound semiconductor (Al _x G
a _1-x N; 0 ≦ x <1), wherein a semiconductor light emitting device includes a semiconductor layer, and a first metal layer laminated on the semiconductor layer;
An electrode including a second metal layer laminated on the metal layer, and a low resistance region that is continuous with the electrode and is formed by diffusion of a material forming the second metal layer. A characteristic gallium nitride-based compound semiconductor light emitting device. 2. The gallium nitride-based compound semiconductor light emitting device according to claim 1, wherein the second metal layer is nickel. 3. The gallium nitride-based compound semiconductor light emitting device according to claim 2, wherein the first metal layer is made of titanium or chromium. 4. A gallium nitride-based compound semiconductor (Al _x G
a _1-x N; 0 ≦ x <1), wherein a semiconductor light emitting device includes a semiconductor layer, and a first metal layer laminated on the semiconductor layer;
A first electrode including a second metal layer laminated on the metal layer, and a low resistance region which is continuous with the first electrode and is formed by diffusion of a material forming the second metal layer. And a second electrode formed on the same surface as the first electrode and spaced apart from the first electrode, and a gallium nitride-based compound semiconductor light emitting device. 5. A substrate made of a semiconductor or an insulator,
Gallium nitride compound semiconductor (Al _x Ga _1-x N; 0 ≦ x
In a method for manufacturing a semiconductor light emitting device, including the step of forming a semiconductor layer consisting of <1), a first metal layer laminated on a surface of the semiconductor layer, and a second metal layer laminated on the first metal layer. And an electrode forming step of forming an electrode including the metal layer, and a step of performing a heat treatment to form a low resistance region directly under the electrode by diffusing a material forming the second metal layer. A method for manufacturing a gallium nitride-based compound semiconductor light emitting device, comprising: 6. The method for manufacturing a gallium nitride-based compound semiconductor light emitting device according to claim 5, wherein the temperature of the heat treatment is 700 to 1000 ° C. 7. The method for manufacturing a gallium nitride-based compound semiconductor light emitting device according to claim 5, wherein the heat treatment is performed by heating with infrared rays. 8. The method for manufacturing a gallium nitride-based compound semiconductor light emitting device according to claim 5, wherein the second metal layer is made of nickel. 9. The method for manufacturing a gallium nitride-based compound semiconductor light emitting device according to claim 5, wherein the material forming the first metal layer is titanium or chromium. 10. The semiconductor layer according to claim 1, wherein the semiconductor layer includes at least an N layer made of an N-type gallium nitride-based compound semiconductor (Al _x Ga _1-x N; 0 ≦ x <1). A gallium nitride based semiconductor light emitting device characterized by the above. 11. The semiconductor layer according to claim 5, wherein the semiconductor layer includes at least an N layer made of an N-type gallium nitride-based compound semiconductor (Al _x Ga _1-x N; 0 ≦ x <1). A method for manufacturing a gallium nitride-based semiconductor light emitting device, comprising: