JPH10178202A - Manufacture of gan-based substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a GaN-based substrate whose quality is high and whose large area can be achieved easily by a method wherein a buffer layer composed of a group II oxide is formed and a cap layer and a thick-film layer whose composition is indicated by a formula are laminated on it in this order. SOLUTION: As a seed substrate, a substrate which is composed of various materials such as sapphire, Si, MnO and the like can be used. As a group II oxide as a constituent material for a buffer layer, ZnO, MgO or the like can be enumerated, and its layer thickness is set at about 0.005 to 5μm, a cap layer and a thick-film layer are constituted of various materials expressed by a formula of InXGaYAZN (wherein 0<=X<=1, 0<=Y<=1, 0<=Z<=1, and X+Y+Z=1), e.g. at least one kind out of GaN, AlN, In0.1 Ga0.9 N and the like. The cap layer and the thick-film layer may be formed of a mutually identical material or of different materials. The cap layer is formed at less than the thermal decomposition temperature of the group II oxide used to form the buffer layer, and its layer thickness is set at about 0.005 to 5μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for manufacturing a GaN-based substrate.

[0002]

2. Description of the Related Art In recent years, there has been a strong demand for easy manufacture of semiconductor devices capable of emitting high-luminance blue light due to the demand for multicolor display in light-emitting displays and the like and the demand for improvement in data density in communication and recording. Has been requested. As a material used for manufacturing a semiconductor element that emits blue light, GaN-based crystals have attracted attention. The GaN-based crystal is a material suitable for a blue light-emitting element that can meet the above requirements because it has a direct transition-type band structure and can emit light with high efficiency and has a large band gap at room temperature. But GaN
Since the system crystal has a high melting point and a high nitrogen vapor pressure near the melting point, it is extremely difficult to grow a bulk crystal from the melt. For this reason, GaN-based crystals are manufactured on a sapphire substrate or on the sapphire substrate by AlN,
At present, a buffer layer made of a material having good lattice matching with a GaN-based material such as ZnO is formed, and a crystal thin film of the GaN-based material is grown thereon.

However, since the sapphire substrate is an insulator, the placement of the electrodes is limited to a specific position, and there is a problem that the degree of freedom in the structural design of the light emitting element is limited as described below. FIG. 1 is an example of a sectional structural view of a conventional LED using a GaN crystal. In the figure, 1 is p
Side electrodes, 2 is an n-side electrode, 4 is an n-type GaN-based semiconductor, and 6 is a p-type GaN-based semiconductor. Since the sapphire substrate S is an insulator, the p-side electrode 1 and the n-side electrode 2 cannot be opposed to each other with the substrate interposed therebetween, as in an LED using a conductive substrate. For this reason, both electrodes have to be provided on the same surface side of the sapphire substrate S, as shown in the figure. The structure for forming these electrodes has various problems in terms of manufacturing and mounting of the light emitting element, and is disadvantageous in terms of the light emitting area. Also, in the case of manufacturing a GaN-based LD, there is a problem similar to that of the LED at the electrode formation position, and there is a disadvantage that sapphire has no cleavage property, so that a resonator surface cannot be formed by cleavage.

In view of the above, the present inventors have paid attention to the fact that GaN-based crystals are conductive and used GaN-based crystals instead of sapphire substrates for the manufacture of light-emitting devices, and A proposal for a method of manufacturing a system crystal substrate was made first. By using a GaN-based crystal as a substrate, a p-side electrode and an n-side electrode are sandwiched from above and below a stacked body composed of the GaN-based crystal substrate and a GaN-based semiconductor epitaxial layer formed thereon. Thus, the various problems described above when using a sapphire substrate can be solved. In addition, a high-quality GaN-based semiconductor layer can be epitaxially formed on the GaN-based crystal substrate because of good lattice matching. Further, the GaN-based crystal substrate has excellent cleavage properties. It is also advantageous for the production of high-performance LDs.

[0005] Regarding a method of manufacturing a GaN-based crystal substrate,
Sapphire or the like is used as a seed substrate, and a thick GaN-based crystal layer is formed thereon. At this time, a sapphire seed substrate is used to reduce lattice mismatch between the seed substrate and the GaN-based crystal layer. A buffer layer made of a Group 2 oxide such as ZnO is formed on the substrate by sputtering, and a GaN-based crystal layer is grown thereon by HVPE or the like.
Finally, the buffer layer is removed by etching to obtain a GaN-based crystal serving as a substrate.

The formation of a thick GaN crystal layer on the buffer layer is efficiently performed at a high temperature by HVPE or the like. However, a buffer layer made of a Group 2 oxide such as ZnO tends to thermally decompose at a high temperature,
In some cases, the buffer layer almost disappears during the formation of the GaN crystal layer. When the buffer layer disappears, the above-described separation method of removing the buffer layer by etching cannot be employed in separating the GaN-based crystal layer from the sapphire substrate after the growth of the GaN-based crystal layer. Decrease.

[0007]

SUMMARY OF THE INVENTION The present invention is directed to a thick Ga film.
Even after the formation of the N-based crystal layer, the buffer layer made of Group II oxide does not disappear, or at least the buffer layer does not disappear to a small extent. It is an object of the present invention to provide a method for easily separating a GaN-based crystal substrate from a sapphire substrate and producing a GaN-based crystal substrate at a high yield.

[0008]

The present invention has the following features.
Have. (1) Form a buffer layer made of Group 2 oxide on the seed substrate.
Formed on top of In at a low temperature._XGa_YAl_ZN (here
0 ≦ X ≦ 1, 0 ≦ Y ≦ 1, 0 ≦ Z ≦ 1, X + Y + Z =
1) forming a cap layer, and further forming a thick film thereon
In_XGa_YAl _ZN (where 0 ≦ X ≦ 1, 0 ≦ Y ≦
1, 0 ≦ Z ≦ 1, X + Y + Z = 1) forming a layer
A method for producing a GaN-based substrate, which is characterized by the following. (2) Thick In_XGa_YAl_ZAfter forming the N layer,
After removing the buffer layer, the thick substrate In_XGa_Y
Al_ZThe method of manufacturing a GaN-based substrate according to the above (1), wherein the N layer is separated.
Construction method. (3) The cap layer is formed by using a group II forming a buffer layer.
(1) above or performed at a low temperature below the thermal decomposition temperature of the oxide
(2) The method for manufacturing a GaN substrate according to (2). (4) The cap layer is formed under a non-reducing atmosphere.
The method for producing a GaN-based substrate according to any one of (1) to (3). (5) Thick In_XGa_YAl_ZForm N layer by HVPE method
The GaN-based substrate according to any one of (1) to (4) above,
Production method.

[0009]

A thick film I is formed on a buffer layer made of a group II oxide.
n _X Ga _Y Al _Z N layer (hereinafter referred to as thick GaN-based layer)
Prior to forming the, In _X Ga _Y on the buffer layer
Cap layer made of al _Z N (hereinafter, referred to as a cap GaN-based layer) formed in advance a. Since the cap GaN-based layer is formed at a low temperature, it is possible to form the cap
Unlike the case of forming an aN-based layer, the cap GaN
Thermal decomposition of the buffer layer does not substantially occur in the step of forming the system layer. In the step of forming the thick GaN-based layer performed after the formation of the cap GaN-based layer, the cap GaN-based layer functions as a protective layer of the buffer layer, and functions to prevent or reduce thermal decomposition.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Sapphire, S
iC, GaAs, Si, MgAl ₂ O ₄ , LiGa
Substrates made of various materials such as O ₃ , LiAlO ₃ , and MnO can be used.

Examples of the Group 2 oxide as a constituent material of the buffer layer include ZnO, MgO, CaO and the like, and the layer thickness is about 0.005 to 5 μm, particularly 0.01 to 5 μm.
About 0.5 μm is appropriate.

In the present invention, the cap GaN-based layer and the thick GaN-based layer are represented by the following general formula (1): In _X Ga _Y Al _Z N (1) (where 0 ≦ X ≦ 1, 0 ≦ Y ≦ 1, 0 ≦ Z ≦ 1, X +
Y + Z = 1), for example, GaN, A
1N, In _0.1 Ga _0.9 N, Al _0.2 Ga _0.8 N, etc.
And at least one of them. The cap GaN-based layer and the thick-film GaN-based layer may be made of the same material or different from each other.

In the present invention, the cap GaN-based layer is formed at a low temperature as described above. Here, the low temperature refers to a low temperature of less than the thermal decomposition temperature (T ° C) of the Group II oxide used for forming the buffer layer, preferably (T-10) ° C or less, and more preferably (T-50) ° C or less. Means The layer thickness is about 0.005 to 5 μm, particularly 0.01 to 0.
About 5 μm is appropriate. The formation of the cap GaN-based layer may be performed in various atmospheres, but in a reducing atmosphere, the Group 2 oxide of the buffer layer may be decomposed by reduction. Therefore, it is preferable to carry out under air, oxygen, nitrogen, argon or other non-reducing atmosphere.

A thick GaN-based layer is formed on the cap GaN-based layer thus formed. Since the thick GaN-based layer itself is used as a substrate, its thickness is set to a thickness suitable for use as a substrate, for example, 10 to 1.
About 000 μm, particularly about 50 to 500 μm is suitable.

After the formation of the thick GaN-based layer, the buffer layer is removed to separate the GaN-based layer from the seed substrate. The removal of the buffer layer at that time can be performed by a method such as wet etching using an acid such as hydrochloric acid, nitric acid, sulfuric acid, or the like. Thus, a GaN-based substrate can be obtained. Although a cap GaN-based layer is attached to one surface of the GaN-based substrate, it is not necessary to remove the cap GaN-based layer, and the GaN-based substrate may be used as a part of the GaN-based substrate.

In the present invention, the method for forming the buffer layer is not particularly limited, and conventionally known methods, for example, sputtering, MOCVD (metal organic chemical vapor deposition), and HVPE (hydride vapor deposition). , MBE
Method (molecular epitaxial method), P-CVD method (plasma-chemical vapor deposition method) and the like. Also cap G
Regarding the method of forming the aN-based layer and the thick GaN-based layer,
For example, the HVPE method, the MOCVD method, the MBE method and the like can be mentioned, and the HVPE method is particularly preferable.

Hereinafter, the present invention will be described in more detail with reference to examples, and the remarkable effects of the present invention will also be shown with reference to comparative examples.

[0018]

【Example】

Example 1 An MgO film as a buffer layer was grown to a thickness of about 0.05 μm on a 2 inch φ sapphire C surface by a sputtering method. At this time, in order to reduce oxygen deficiency of MgO, oxygen gas was introduced in addition to ordinary argon gas introduction. Sapphire seed substrate having MgO film
The apparatus was placed in an OVPE apparatus and heated to 500 ° C. while flowing nitrogen at 20 SLM. Next, ammonia 10SL
A cap layer of GaN having a thickness of 0.1 μm was grown while flowing M, hydrogen 10 SLM, nitrogen 10 SLM, and trimethylgallium 50 μmol / min. The sapphire seed substrate with the cap layer is placed in a normal HVPE apparatus, heated to 800 ° C. while flowing 10 SLM of nitrogen, and reacted with Ga while flowing 1 SLM of hydrogen chloride and 3 SLM of ammonia to form a thick film having a thickness of 100 μm. A GaN crystal was grown. The sapphire seed substrate having the thick-film GaN crystal thus obtained was immersed in hydrochloric acid for 20 minutes to completely remove the MgO film, thereby obtaining a target GaN crystal substrate.

Example 2 A GaN crystal substrate was obtained in the same manner as in Example 1 except that a cap layer was grown at 500 ° C. by the HVPE method.

Example 3 Instead of the MgO film, a buffer layer of about 0.05 μm
A GaN crystal substrate was obtained in the same manner as in Example 1, except that a thick ZnO film was grown on a sapphire seed substrate by a sputtering method.

Example 4 A GaN crystal substrate was obtained in the same manner as in Example 1 except that the growth thickness of the MgO film was about 0.1 μm.

Example 5 A GaN crystal substrate was obtained in the same manner as in Example 1 except that the growth thickness of the GaN cap layer was about 0.05 μm.

Example 6 A GaN crystal substrate was obtained in the same manner as in Example 1 except that the GaN cap layer was grown at 400 ° C.

Comparative Example 1 A method similar to that of Example 1 was performed except that a thick GaN crystal was grown directly on the MgO buffer layer without forming a GaN cap layer. However, since the thermal decomposition of MgO progressed during the growth of the thick-film GaN crystal, a region where the GaN crystal grew directly on the surface of the sapphire seed substrate was generated. In that region, a single crystal film was obtained due to a difference in lattice constant. There were no cracks or cracks in the GaN crystal. Further, even when the remaining small amount of the MgO buffer layer was removed with hydrochloric acid, a thick-film GaN crystal could not be separated from the sapphire seed substrate. For this purpose, a GaN crystal substrate was obtained by mechanical polishing with a diamond paste. The resulting GaN crystal substrate had only a small area of about 2 to 3 mm square due to cracks generated.

Comparative Example 2 A method similar to that of Example 1 was performed except that the growth temperature of the GaN cap layer was 800 ° C., which is the thermal decomposition temperature of MgO. However, during the growth of the GaN cap layer, the thermal decomposition of MgO proceeds, and the sapphire seed substrate and the thick Ga
There were places that could not be separated from the N crystals. For this purpose, a GaN crystal substrate was obtained by mechanical polishing with a diamond paste. The resulting GaN crystal substrate had only a small area of about 2 to 3 mm square due to cracks generated.

Comparative Example 3 Example 1 was repeated except that the growth of the MgO buffer layer was omitted.
The same method as described above was performed. As a result, although a GaN film was obtained, it was in an amorphous state to a polycrystalline state due to a difference in lattice constant, and a single crystal GaN film was not obtained.

The features of the GaN crystal substrates obtained from Examples 1 to 5 and Comparative Examples 1 to 3 are shown below. In the following, the unit of the average area is mm square, and the unit of the mobility is V
/ Cm. S and the unit of the X-ray diffraction half width is seconds. Example 1 (average area: 15, mobility: 320, X-ray diffraction half width: 155), Example 2 (average area: 15, mobility: 280, X-ray diffraction half width: 162), Example 3 ( Average area: 15, mobility: 350, X-ray diffraction half width: 14
5), Example 4 (average area: 15, mobility: 327, X
Line diffraction half width: 149), Example 5 (average area: 15,
Mobility: 319, X-ray diffraction half width: 151), Comparative Example 1
(Average area: 2, mobility: 151, X-ray diffraction half width: 4)
50), Comparative Example 2 (average area: 2, mobility: 142, X
X-ray diffraction half width: 497), Comparative Example 3 (average area: 1, mobility: 139, X-ray diffraction half width: 485).

[0028]

According to the present invention, high quality and large area G
An aN-based substrate can be easily manufactured at a high yield. By using this GaN-based substrate, what is performed in a red LD or LED, such as production of a resonance surface by cleavage and installation of p and n electrodes opposite to each other on the front and back surfaces of the substrate, is performed for a blue LD or LED. It can be applied to manufacturing.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a conventional blue LED.

[Explanation of symbols]

 Reference Signs List 1 p-side electrode 2 n-side electrode S sapphire substrate 4 n-type GaN-based semiconductor 6 p-type GaN-based semiconductor

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Kazuyuki Tadomo 4-3 Ikejiri, Itami-shi, Hyogo Mitsubishi Electric Cable Industry Co., Ltd. Itami Works

Claims (5)

[Claims] 1. A buffer layer made of a Group II oxide is formed on a seed substrate, and In _x Ga _Y Al _Z is formed thereon at a low temperature.
N (where 0 ≦ X ≦ 1, 0 ≦ Y ≦ 1, 0 ≦ Z ≦ 1, X +
A cap layer made of Y + Z = 1) is formed thereon, and a thick In _x Ga _Y Al _Z N (where 0 ≦ X ≦ 1, where 0 ≦ X ≦ 1,
0 ≦ Y ≦ 1, 0 ≦ Z ≦ 1, X + Y + Z = 1) A method of manufacturing a GaN-based substrate, characterized by forming a layer. 2. After forming a thick In _x Ga _Y Al _Z N layer, the buffer layer is removed and the thick I _x Ga _Y Al _Z N layer is removed from the seed substrate.
n _X Ga _Y Al _Z N layer GaN according to claim 1, wherein separating the
Method of manufacturing system substrate. 3. The method of manufacturing a GaN substrate according to claim 1, wherein the formation of the cap layer is performed at a low temperature lower than the thermal decomposition temperature of the group II oxide forming the buffer layer. 4. The method for producing a GaN-based substrate according to claim 1, wherein the formation of the cap layer is performed in a non-reducing atmosphere. 5. The method according to claim 1, wherein the thick In _x Ga _Y Al _Z N layer is formed by HVP.
5. The GaN according to claim 1, wherein the GaN is formed by an E method.
Method of manufacturing system substrate.