JP3634243B2 - Method for producing group III nitride semiconductor single crystal and method for using group III nitride semiconductor single crystal - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a group III nitride semiconductor single crystal and a method for using a group III nitride semiconductor single crystal, which are expected to be applied to the field of optical information processing and the like.
[0002]
[Prior art]
Currently, a group III nitride semiconductor such as an AlGaN substrate having a relatively low GaN or AlN molar fraction is used for a substrate such as a light receiving element or a light emitting element.
For example, as described in “Applied Physics Letters, 48 (1986) 353”, a GaN substrate is formed by forming a low-temperature AlN buffer layer or a GaN buffer layer on a sapphire substrate, and then crystallizing a GaN semiconductor on the buffer layer. It was made by growing. However, when a short-wavelength light-emitting element or a short-wavelength light-receiving element is manufactured using a GaN substrate, an element that can exhibit sufficient device characteristics cannot be manufactured.
[0003]
On the other hand, a group III nitride semiconductor containing AlN was found to be suitable as a substrate for such a short wavelength device, and various techniques for producing a substrate made of such a nitride semiconductor were studied.
For example, as described in “Japan Journal Applied Physics, 27 (1988) 1156”, a low-temperature buffer layer is formed on a sapphire substrate, and a GaN layer is grown on the low-temperature buffer layer. It is described that an AlGaN semiconductor single crystal is obtained by crystal growth of an AlGaN semiconductor layer.
[0004]
In “MRS internet Nitride Semiconductor. Res. 4S1 (1999) G10.1”, a low-temperature buffer layer is formed on a sapphire substrate, a GaN layer is grown on the buffer layer, and an AlN intermediate layer is further formed. Alternatively, it is described that after an AlGaN intermediate layer is formed, an AlGaN semiconductor layer is grown on the intermediate layer, and this AlGaN semiconductor layer is used as a semiconductor single crystal substrate.
[0005]
However, the AlGaN semiconductor single crystal substrate produced as described above contains a large amount of dislocations due to threading dislocations of 10 ⁸ cm ⁻² or more in the GaN layer. For this reason, the device formed on the substrate produced in this way may not be able to fully exhibit its performance.
[0006]
As a fabrication technique for reducing the dislocation density in a semiconductor, “Japan Journal Applied Physics, 36 (1997) L899” is an ELO technique, “MRS internet Nitride Semiconductor. Res. 4S1, G3. PENDEO epitaxy technology and periodic groove structure technology in “The 46th Autumn Lecture Related to Applied Physics Lecture Proceedings No. 1 (1999) p416” have been proposed.
[0007]
In the ELO technology, after forming a low-temperature buffer layer on a sapphire substrate, a GaN layer is formed on the buffer layer, and a striped layer made of a dielectric material having selectivity such as SiO ₂ is formed on the GaN layer. Form. Thereafter, this is a technique for forming, for example, a GaN semiconductor with low dislocations by selective growth from this layer in the lateral direction.
[0008]
In the PENDEO epitaxy technique, a low-temperature buffer layer is formed on a sapphire substrate, and then a GaN layer is formed on the buffer layer. Then, a recess having a striped bottom surface penetrating to the sapphire substrate is formed in the GaN layer. Then, for example, a GaN semiconductor is formed by lateral growth so as to fill the step of the recess. Then, since the part above the said recessed part of a GaN semiconductor is a low dislocation, this part is used as a board | substrate.
[0009]
Further, in the periodic groove structure technology, after forming a low-temperature buffer layer on the sapphire substrate, a GaN layer is formed on the buffer layer. Then, a stripe-shaped step is formed on the main surface of the GaN layer, and, for example, a GaN semiconductor is formed so as to fill the step. Then, since the part above the level | step difference of a GaN semiconductor is a low dislocation, this part is used as a board | substrate.
[0010]
[Problems to be solved by the invention]
However, in the low dislocation technique as described above, it has been impossible to produce a semiconductor containing AlN in particular.
For example, in the ELO technology, a dielectric material having selectivity for a mixed crystal containing AlN and stable at the crystal growth temperature of the mixed crystal has not been found. Therefore, polycrystalline AlN or a mixed crystal containing it adheres onto the dielectric material, and an AlN-containing semiconductor single crystal that can be used as a substrate cannot be obtained.
[0011]
Also in the PENDEO epitaxy technique, a polycrystalline AlN semiconductor adheres to the main surface of the sapphire substrate exposed in the recess. Furthermore, in the periodic groove structure technique, cracks occur in the AlGaN semiconductor layer due to the instructor mismatch between the stepped GaN layer and the AlGaN semiconductor layer formed thereon. Therefore, even with these techniques, an AlN-containing semiconductor single crystal that can be used as a substrate cannot be obtained.
[0012]
An object of the present invention is to provide a method for producing a group III nitride semiconductor single crystal that can be used as a semiconductor substrate with low dislocations and excellent crystallinity, and to provide the semiconductor substrate.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides:
Forming a buffer layer by crystal growth on a main surface of a predetermined single crystal substrate;
Forming a base layer on the main surface of the buffer layer by crystal growth;
Etching the main surface of the underlayer to partially remove the underlayer, and forming a first recess having a stepped bottom surface in the underlayer;
Forming an intermediate layer by crystal growth on the entire surface of the foundation layer including the recess , so as to leave the step of the first recess at least on the main surface of the foundation layer;
Forming a first group III nitride semiconductor layer on the intermediate layer by crystal growth from the intermediate layer so as to fill a step caused by the first recess;
In particular, the present invention relates to a method for manufacturing a group III nitride semiconductor single crystal.
[0014]
The present inventors have intensively studied to obtain a group III nitride semiconductor single crystal having low dislocations and excellent crystallinity.
As a result, after a buffer layer is formed on, for example, a sapphire substrate, a base layer is formed on the buffer layer and a recess as described above is formed on the base layer, as in the prior art. It has been found that by forming a semiconductor layer through an intermediate layer so that the step of the concave portion remains , the dislocation density in the semiconductor layer is reduced and excellent crystallinity is exhibited. The inventors have found that a semiconductor single crystal substrate having low dislocations and excellent crystallinity can be obtained by using the semiconductor layer as a substrate.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail based on embodiments of the invention.
FIG. 1 is a diagram showing an assembly configuration obtained by carrying out the manufacturing method of the present invention. The AlGaN semiconductor layer 6 in FIG. 1 corresponds to the semiconductor single crystal that is the object of the present invention and has low dislocations and excellent crystallinity.
Hereinafter, the production method of the present invention will be described in detail in the case of obtaining an AlGaN semiconductor single crystal by configuring the assembly shown in FIG.
[0016]
First, as shown in FIG. 1, the AlN buffer layer 2 is formed on the main surface of the (0001) sapphire substrate 1. The AlN buffer layer 2 is preferably formed by epitaxial growth at a low temperature of 300 to 700 ° C., for example, by an organic metal compound vapor phase growth method. The thickness of the AlN buffer layer 2 is preferably 10 to 100 nm.
[0017]
The semiconductor constituting the buffer layer is not limited to AlN. However, in order to obtain a group III nitride semiconductor single crystal having excellent crystallinity by facilitating crystal growth, it is composed of a nitride semiconductor. It is preferable. In particular, in order to obtain an AlGaN semiconductor single crystal, it is preferably made of AlN as shown in FIG.
[0018]
Next, the GaN foundation layer 3 is formed on the main surface of the AlN buffer layer 2. The GaN foundation layer 3 is preferably formed by epitaxial growth at 800 to 1300 ° C., for example, by an organic metal compound vapor phase growth method. The thickness of the GaN foundation layer 3 is preferably 300 nm or more.
The semiconductor constituting the underlayer is not limited to GaN. However, in order to obtain a group III nitride semiconductor single crystal excellent in crystallinity by facilitating crystal growth, it is composed of a nitride semiconductor. It is preferable.
[0019]
Next, the main surface of the GaN foundation layer 3 is partially removed by etching to form a recess 4 having a stepped bottom surface 4A.
Etching is preferably performed by reactive ion etching using a chlorine-based gas. Since such reactive ion etching is excellent in selectivity, the recess 4 can be formed in a short time, and the step on the bottom surface 4A of the recess 4 can be easily formed.
[0020]
In addition, if the step of 4 A of bottom faces of the recessed part 4 is step shape, it will not specifically limit about the specific shape. However, by forming a stripe-shaped step, it is possible to facilitate crystal growth and obtain a semiconductor single crystal having low dislocations and excellent crystallinity.
Moreover, when producing an AlGaN semiconductor single crystal from an assembly as shown in FIG. 1, the depth d of the recess 4 is preferably 300 nm or more, and the width W is preferably 1 to 20 μm.
[0021]
Next, the AlN intermediate layer 5 is formed on the GaN foundation layer 3 so that the step of the recess 4 remains . The AlN intermediate layer 5 is preferably formed by epitaxial growth at a low temperature of 300 to 700 ° C., for example, by an organic metal compound vapor phase growth method. The thickness of the AlN intermediate layer 5 is preferably 10 to 100 nm.
The semiconductor constituting the intermediate layer is not limited to AlN. However, in order to obtain a group III nitride semiconductor single crystal having excellent crystallinity by facilitating crystal growth, it is composed of a nitride semiconductor. It is preferable. Specifically, in addition to AlN, it can be composed of a semiconductor represented by a general formula of Al _a Ga _1-ab In _b N (0 ≦ a ≦ 1, 0 ≦ b ≦ 1).
[0022]
Next, an AlGaN semiconductor layer 6 is formed on the AlN intermediate layer 5 so as to fill a step caused by the recess 4. Also in this case, the AlGaN semiconductor layer 6 is formed at 800 to 1300 ° C. by using, for example, an organic metal compound vapor phase growth method. The AlGaN semiconductor layer 6 is formed to an arbitrary thickness according to the desired thickness of the substrate.
[0023]
FIG. 2 is a view showing another assembly configuration obtained by carrying out the manufacturing method of the present invention. The AlGaN semiconductor layer 16 in FIG. 2 corresponds to a semiconductor single crystal that is an object of the present invention and has low dislocations and excellent crystallinity.
The assembly configuration shown in FIG. 2 is different from the assembly configuration shown in FIG. 1 in that the AlN intermediate layer 15 is formed only on the main surface 3A of the GaN foundation layer 3. Thus, if an AlN intermediate layer is formed on at least the main surface 3A of the GaN foundation layer 3, a semiconductor single crystal targeted by the present invention can be obtained. In this case, since the AlN intermediate layer 15 is not formed in the recess 4, the recess 4 remains as it is.
The other AlN buffer layers are formed in the same manner as in FIG.
[0024]
Although not shown in FIGS. 1 and 2, etching is performed from the main surface 6A or 16A of the AlGaN semiconductor layer 6 or 16 (first group III nitride semiconductor layer) to form the recess 4 (first An additional concave portion (second concave portion) is formed at a position different from the concave portion, and a group III nitride semiconductor layer (second III) such as an AlGaN semiconductor layer is formed on the AlGaN semiconductor layer 6 or 16 so as to fill the concave portion. A group nitride semiconductor layer) can also be formed.
[0025]
Thus, the second group III nitride semiconductor layer formed again through the recess has a dislocation concentration more than that of the first group III nitride semiconductor layer such as the AlGaN semiconductor layer shown in FIGS. descend. Therefore, a semiconductor single crystal having a very low dislocation density can be obtained by such a group III nitride semiconductor layer.
Then, by using the first group III nitride semiconductor layer and the second group III nitride semiconductor layer formed as described above as a substrate, a semiconductor single crystal substrate having low dislocation and excellent crystallinity is obtained. be able to.
[0026]
【Example】
Hereinafter, specific examples in the production method of the present invention will be shown in Examples.
In this example, an assembly as shown in FIG. 1 was constructed, and an AlGaN semiconductor layer was formed.
As the substrate 1, a (0001) sapphire substrate as described above was used. Then, the AlN buffer layer 2 is formed to a thickness of 20 nm on the main surface of the substrate 1 by a metal organic compound vapor deposition method using trimethylammonia (TMA) gas and ammonia (NH ₃ ) gas at a low temperature of 500 ° C. Formed.
Next, the GaN underlayer 3 was formed on the main surface of the AlN buffer layer 2 to a thickness of 1 μm at about 1000 ° C. by an organic metal compound vapor phase growth method using trimethylgallium (TMG) gas and ammonia gas.
[0027]
After that, reactive ion etching using Cl ₂ gas is performed from the main surface of the GaN foundation layer 3 so that the depth d is 5 μm and the width W is 5 μm in the recess 4 having the bottom surface 4A having stripe-shaped steps. Formed.
FIG. 3 is a surface micrograph of the bottom surface 4A of the recess 4 formed in this way. As is apparent from the figure, it can be seen that the bottom surface 4A of the recess 4 has a stripe shape having steps at equal intervals.
[0028]
Then, the entire surface of the GaN underlying layer containing recesses 4, at low temperatures of about 500 ° C., by metal organic vapor phase deposition using trimethylaluminum (TMA) gas and ammonia gas, an AlN intermediate layer 5 in the recess 4 It was formed to a thickness of 20 nm so that the resulting step difference remained .
Next, an AlGaN semiconductor layer 6 containing 0.2 mol percent of AlN was formed on the AlN intermediate layer 5 so as to fill the step caused by the recess 4.
[0029]
A surface micrograph of the AlGaN semiconductor layer 6 is shown in FIG. As can be seen from FIG. 4, the surface of the AlGaN semiconductor layer 6 is extremely flat and smooth, and exhibits good crystallinity without cracks.
Further, FIG. 5 shows a cross-sectional photograph of the assembly thus prepared by a transmission electron microscope. As can be seen from FIG. 5, a portion having a low dislocation concentration in the AlGaN semiconductor layer 6 is formed above the recess 4.
Therefore, by using such a low dislocation concentration portion as a substrate, an AlGaN semiconductor single crystal substrate having low dislocations and excellent crystallinity can be provided.
[0030]
For comparison, an AlGaN semiconductor layer was formed directly on the GaN foundation layer 3 without forming the AlN intermediate layer 5 in FIG. FIG. 6 is a surface micrograph of the AlGaN semiconductor layer thus formed. As is apparent from the figure, in this case, a large number of cracks occur in the AlGaN semiconductor layer, and it is understood that the crystallinity is inferior compared with the case where the AlGaN semiconductor layer is manufactured by the method of the present invention.
[0031]
As described above, the present invention has been described in detail based on the embodiments of the present invention with specific examples. However, the present invention is not limited to the above contents, and all modifications and changes can be made without departing from the scope of the present invention. It can be changed.
For example, in FIGS. 1 and 2, the recess 4 is formed so that the lower portion of the GaN foundation layer 3 remains, but the main surface of the sapphire substrate is exposed through the GaN foundation layer 3 and the AlN buffer layer 2. It can also be formed.
In addition, conductivity can be imparted by adding donor impurities such as Si and Ge or acceptor impurities such as Mg to the AlGaN semiconductor layer 6 or 16 as necessary.
[0032]
【The invention's effect】
As described above, according to the manufacturing method of the present invention, a group III nitride semiconductor single crystal that has low dislocations and excellent crystallinity and can be used as a semiconductor substrate can be manufactured.
[Brief description of the drawings]
FIG. 1 shows an assembly obtained by carrying out the production method of the present invention.
FIG. 2 is a view showing another assembly obtained by carrying out the manufacturing method of the present invention.
FIG. 3 is a surface micrograph of a bottom surface of a recess formed in a GaN underlayer.
FIG. 4 is a surface micrograph of an AlGaN semiconductor layer obtained by the manufacturing method of the present invention.
FIG. 5 is a cross-sectional photograph taken by a transmission electron microscope in an assembly obtained by carrying out the manufacturing method of the present invention.
FIG. 6 is a surface micrograph of an AlGaN semiconductor layer formed directly on a GaN underlayer without forming an AlN intermediate layer.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 (0001) Sapphire substrate 2 AlN buffer layer 3 GaN foundation layer 4 Recess 5, 15 AlN intermediate layer 6, 16 AlGaN semiconductor layer

Claims (9)

Forming a buffer layer by crystal growth on a main surface of a predetermined single crystal substrate;
Forming a base layer on the main surface of the buffer layer by crystal growth;
Etching the main surface of the underlayer to partially remove the underlayer, and forming a first recess having a stepped bottom surface in the underlayer;
Forming an intermediate layer by crystal growth on the entire surface of the foundation layer including the recess , so as to leave the step of the first recess at least on the main surface of the foundation layer;
Forming a first group III nitride semiconductor layer on the intermediate layer by crystal growth from the intermediate layer so as to fill a step caused by the first recess;
A method for producing a group III nitride semiconductor single crystal, comprising: 2. The method for producing a group III nitride semiconductor single crystal according to claim 1 , wherein the buffer layer is made of a nitride semiconductor epitaxially grown at a low temperature of 300 to 700 ° C. 3. The underlying layer is characterized by comprising the nitride semiconductor epitaxially grown at 800 to 1300 ° C., III group method for manufacturing a nitride semiconductor single crystal according to claim 1 or 2. The method for producing a group III nitride semiconductor single crystal according to any one of claims 1 to 3 , wherein the etching removal of the underlayer is performed by reactive ion etching using a chlorine-based gas. The bottom surface of the first recess and having a stripe-shaped step, a method for manufacturing a Group III nitride semiconductor single crystal according to any one of claims 1-4. The method for producing a group III nitride semiconductor single crystal according to any one of claims 1 to 5 , wherein the intermediate layer is made of a nitride semiconductor epitaxially grown at a low temperature of 300 to 700 ° C. An additional step of forming a second recess at a position different from the first recess formed in the underlayer by etching from the main surface of the first group III nitride semiconductor;
An additional step of forming a second group III nitride semiconductor layer on the first group III nitride semiconductor so as to fill the second recess;
Characterized in that it comprises a, III-nitride semiconductor manufacturing method as claimed in any one of claims 1-6. A method for using a group III nitride semiconductor, wherein the first group III nitride semiconductor formed by the method according to any one of claims 1 to 7 is used as a semiconductor single crystal substrate. A method for using a group III nitride semiconductor, wherein the second group III nitride semiconductor formed by the method according to claim 8 is used as a semiconductor single crystal substrate.

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