JP3744155B2 - Method for manufacturing gallium nitride compound semiconductor substrate - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a method for obtaining an epitaxial substrate of a gallium nitride compound semiconductor.
[0002]
[Prior art]
The present invention relates to the general formula _{Al x Ga y In 1-xy} N (0 ≦ x ≦ 1,0 ≦ y ≦ 1,0 ≦ x + y ≦ 1) method for producing a gallium nitride compound semiconductor substrate.
[0003]
[Prior art]
Gallium nitride compound semiconductors are direct transition semiconductors whose emission spectrum covers a wide range from ultraviolet to red, and are applied to light-emitting elements such as light-emitting diodes (LEDs) and laser diodes (LDs). The gallium nitride compound semiconductor is usually formed on sapphire.
[0004]
[Problems to be solved by the invention]
However, in the above prior art, when a gallium nitride compound semiconductor is formed on a sapphire substrate, cracks and warpage occur in the semiconductor layer due to a difference in thermal expansion coefficient between sapphire and the gallium nitride compound semiconductor, and dislocation occurs due to a misfoot. For this reason, there is a problem that device characteristics are not good. Furthermore, since sapphire is insulative, it is necessary to form both electrodes on the same surface side with respect to the substrate. For this reason, it is necessary to etch up to the n layer on the side close to the substrate. There is a problem that it is not good. In addition, since both electrodes are formed on the same surface side, the element size increases. In addition, wire bonding is required for both electrodes, and a lateral current path is formed in the n layer and the current path becomes longer, so that the drive voltage slightly increases. In addition, since the substrate and the semiconductor layer are made of different materials, it is difficult to cleave well with a laser diode.
[0005]
Therefore, in view of the above problems, an object of the present invention is to easily obtain a gallium nitride semiconductor substrate having good crystallinity. Further, it is to improve element characteristics by using the high-quality substrate.
[0006]
[Means for solving the problems and effects]
The invention of claim 1, to form a first layer capable of wet etching on the substrate, on the first layer, a lower layer formed by a low temperature growth, good crystallinity first upper layer consisting of gallium nitride-based compound semiconductor A gallium nitride compound semiconductor is formed in a dot-like, stripe-like or lattice- like island state so that the exposed portion of the second layer is scattered on the second layer. A third layer that is not epitaxially grown is formed, epitaxially grown using the exposed portion of the second layer not covered by the third layer as a nucleus, and epitaxially grown in the lateral direction above the third layer, thereby performing the second nitridation. A gallium nitride compound semiconductor substrate is formed by forming a fourth layer made of a gallium compound semiconductor and peeling it from the substrate by wet etching using a solution for etching the first layer. That.
[0007]
Here, the lateral direction means the surface direction of the substrate. When the second gallium nitride compound semiconductor is grown as the fourth layer, it is not epitaxially grown in the upper region of the third layer, and the first gallium nitride compound semiconductor in the exposed region of the second layer is used as the nucleus. And grow laterally. As a result, threading dislocations existing in the first gallium nitride compound semiconductor exist only on the exposed region of the second layer in the second gallium nitride compound semiconductor, and the upper part of the third layer grown in the lateral direction. Then there are no vertical threading dislocations. Therefore, the surface density of the threading dislocations in the vertical direction of the second gallium nitride compound semiconductor is extremely reduced, and the crystallinity is improved. In addition, since the third layer and the second gallium nitride compound semiconductor forming the fourth layer thereon are not chemically bonded, warping of the fourth layer is prevented and stress strain is applied to the layer. Entering is suppressed.
[0008]
In this manner, after the gallium nitride compound semiconductor is formed, the first layer can be removed by wet etching to obtain a gallium nitride compound semiconductor substrate.
The invention described in claim 2 is characterized in that the lower layer of the second layer is in a state where amorphous or microcrystals are mixed.
The invention described in claim 3 is characterized in that the lower layer of the second layer is made of GaInN .
[0009]
The invention of claim 4 is that the first layer is made of zinc oxide (ZnO). Zinc oxide has a lattice constant close to that of sapphire and a gallium nitride compound semiconductor. Therefore, zinc oxide can be formed on the sapphire substrate, and the first gallium nitride compound semiconductor as the second layer having good crystallinity can be formed on the zinc oxide. Further, only zinc oxide can be etched with hydrofluoric acid, and the substrate can be easily peeled off.
[0010]
The invention of claim 5 is that the third layer is made of silicon dioxide (SiO ₂ ). In this case, by making the fourth layer a gallium nitride compound semiconductor that does not contain Al, the fourth layer is not epitaxially formed on the third layer, but the fourth layer is made crystalline by lateral epitaxial growth. Can get well.
[0011]
The invention of claim 6 is characterized in that the third layer is made of a metal having a high melting point or amorphous silicon (Si). Even if these layers are used, the second gallium nitride-based compound semiconductor as the fourth layer can be obtained by epitaxial growth in the lateral direction without directly epitaxially growing on the third layer. In addition, since the third layer has conductivity, a current can flow in a direction perpendicular to the surface of the gallium nitride compound semiconductor substrate in which the third layer is left. Therefore, the electrode of the element can be formed on both end faces. The metal having a high melting point is a metal having a melting point of 2000 ° C. or higher, and examples thereof include Nb, Mo, Ru, Hf, Ta, and W.
[0012]
The invention of claim 7 is that the substrate is made of sapphire, silicon, or silicon carbide. The crystallinity of the second gallium nitride compound semiconductor as the fourth layer obtained on the substrate can be improved.
[0013]
The invention of claim 8 is that the thickness of the fourth layer is 50 to 100 μm. With this thickness, dislocations growing in a direction perpendicular to the plane disappear, and dislocation-free crystals can be obtained.
[0014]
According to a ninth aspect of the present invention, a plurality of layers made of a third gallium nitride compound semiconductor forming an element are formed on the fourth layer, and then the first layer is etched to form the element. A substrate is obtained. Thereby, the fourth layer can be used as a base layer, and the layer above the fourth layer can be used as a functional layer, and an element with good crystallinity can be obtained.
[0015]
The inventions of claim 10 and claim 11 use a single substrate by forming each layer on the substrate on both sides of the substrate and removing the first layer formed on both sides of the substrate by etching. Two gallium nitride compound semiconductor substrates are obtained. Since the gallium nitride compound semiconductor is grown on both sides of the substrate, there is no warpage, and two gallium nitride compound semiconductor substrates can be obtained at a time, so that the production efficiency is increased.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described based on specific examples.
1 to 4 are process diagrams showing a method of manufacturing a GaN substrate according to the present invention.
As shown in FIG. 1, a sapphire substrate 1 having a (0001) orientation was prepared, and the sapphire substrate 1 was washed with an organic chemical such as methanol. Thereafter, the sapphire substrate 1 was set in a chamber of an RF sputtering apparatus, and the chamber was evacuated to a vacuum. Thereafter, as shown in FIG. 1, a first layer 2 made of ZnO having a thickness of 100 nm was formed on the upper surface of the sapphire substrate 1 with a mixed gas of argon and oxygen. The first layer 2 had a strong degree of orientation in the c-axis direction.
[0017]
Next, a gallium nitride compound semiconductor was grown on the first layer 2 by the following method. This semiconductor was manufactured by sputtering and metal organic vapor phase epitaxy (hereinafter abbreviated as “MOVPE”). The gases used in MOVPE are ammonia (NH ₃ ), carrier gas (H ₂ , N ₂ ), trimethyl gallium (Ga (CH ₃ ) ₃ ) (hereinafter referred to as “TMG”), trimethyl aluminum (Al (CH _{3 3} ) (hereinafter referred to as “TMA”) and trimethylindium (In (CH ₃ ) ₃ ) (hereinafter referred to as “TMI”).
[0018]
First, after the surface of the first layer 2 is cleaned using a hydrofluoric acid solution (HF: H ₂ O = 1: 1), the substrate 1 is mounted on a susceptor placed in a reaction chamber of the MOVPE apparatus. Next, the first layer 2 was baked at a temperature of 1150 ° C. while flowing H ₂ at normal pressure at a flow rate of ₂ liters / minute for about 10 minutes.
[0019]
Thereafter, the temperature of the substrate 1 is maintained at 500 ° C., N ₂ or H ₂ is 10 liter / min, NH ₃ is 10 liter / min, TMG is 1.0 × 10 ⁻⁴ mol / min, and TMI is 5.0 × 10 ⁻⁴ mol. As shown in FIG. 2, a lower layer 31 of a second layer made of Ga _0.8 In _0.2 N was formed as shown in FIG. This layer functions as a buffer layer in which amorphous or microcrystals are mixed by low-temperature growth, that is, a layer that relaxes the lattice constant of ZnO and GaN.
[0020]
After the formation of the layer 31, the temperature of the substrate 1 is set to 1100 ° C. by the MOVPE method on the layer 31, N ₂ or H ₂ is 20 liter / min, NH ₃ is 10 liter / min, TMG is 2.0 × 10 ⁻⁴ mol / min, Silane diluted to 0.86 ppm with H ₂ gas was supplied at 20 × 10 ⁻⁸ mol / min to form GaN, and an upper layer 32 of a second layer having a thickness of about 3 μm was formed. In the present embodiment, the second layer 3 is formed by the two-layer structure of the layer 31 and the layer 32.
[0021]
Next, after SiO ₂ is formed on the layer 32 by sputtering to a film thickness of about 2000 mm, a width a is about 5 μm and the distance b between the exposed regions B is as shown in FIG. 3 by applying a resist and photolithography. A third layer 4 having a stripe shape (FIG. 5) or a lattice shape (FIG. 6) of about 5 μm was formed.
[0022]
Next, a fourth layer 5 made of GaN having a thickness of about 80 μm is formed on the exposed region B of the upper layer 32 of the second layer and the upper region A of the third layer 4. At this time, GaN grows in a direction perpendicular to the surface with GaN in the exposed portion B of the layer 32 as a nucleus. In the upper region A of the third layer 4 of SiO ₂ , GaN grows epitaxially in the lateral direction using GaN grown on the exposed portion B of the layer 32 as a nucleus. In this way, in this embodiment, GaN is epitaxially grown both vertically and laterally with GaN as a nucleus, so that GaN with high crystallinity can be obtained.
[0023]
Next, the sapphire substrate 1 on which each layer was formed in this manner was immersed in a hydrochloric acid-based etchant, and the temperature of the etchant was set to 60 ° C. Then, the first layer 2 was etched using an ultrasonic cleaner for about 10 minutes. As a result, a gallium nitride compound semiconductor substrate mainly composed of the fourth layer 5 of GaN could be obtained.
[0024]
In the above embodiment, the width a of the third layer 4 formed in a stripe shape or a lattice shape is about 5 μm. However, if the width a of the third layer 4 exceeds 10 μm, it takes a long time for the lateral growth. Thus, if the width a of the third layer 4 is less than 1 μm, it will be difficult to remove the SiO ₂ film later with hydrofluoric acid or the like, so the range of 1 to 10 μm is desirable. In the above embodiment, the interval b between the exposed regions B of the upper layer 32 of the second layer is 5 μm. However, if the interval b between the exposed regions B exceeds 10 μm, the probability of dislocation increases, and the interval b between the exposed regions B is increased. If the thickness is less than 1 μm, it becomes difficult to form the fourth layer 5 made of good GaN. Therefore, the range of 1 to 10 μm is desirable. In addition, the width ratio a / b is preferably 1 to 10 in terms of crystallinity of the fourth layer 5.
[0025]
In the above embodiment, it is desirable that the thickness of the fourth layer 5 is 50 to 100 μm because dislocation-free crystals are obtained. The lower layer 31 of the second layer made of Ga _0.8 In _0.2 N is used as a buffer layer by low-temperature growth. Further, on this layer, single-crystal Al _0.15 Ga _0.85 N by high-temperature growth is formed, and the layer is formed. A GaN layer 32 may be formed thereon.
[0026]
In this embodiment, the composition of the lower layer 31 of the second layer is Ga _0.8 In _0.2 N. However, the general formula Al _x Ga _y In _1-xy N (0 ≦ x ≦ 1,0 ≦ y) having an arbitrary composition ratio is used. A gallium nitride compound semiconductor of ≦ 1,0 ≦ x + y ≦ 1) can be used. The upper layer 32 of the second layer is made of GaN, which is also nitrided by the general formula Al _x Ga _y In _1-xy N (0 ≦ x ≦ 1,0 ≦ y ≦ 1,0 ≦ x + y ≦ 1). Gallium-based compound semiconductors can be used. Moreover, although the second layer has a two-layer structure, it may have one layer, three layers or more.
[0027]
Further, although the fourth layer 5 is made of GaN, GaInN having an arbitrary composition ratio may be used. Since the gallium nitride compound semiconductor containing Al is deposited on the SiO ₂ layer, it is desirable not to contain Al. However, the third layer 4 formed in a stripe shape or a lattice shape may be replaced with SiO ₂ and a high melting point metal such as tungsten (W), amorphous Si, or the like may be used. As described above, since the third layer 4 is made of metal or amorphous Si, a current flows through the third layer 4, so that a current can be more uniformly and uniformly flown in the thickness direction of the GaN compound semiconductor. . Tungsten (W) high melting point metal or the like, in the case of using amorphous Si, the general formula of any composition ratio _{Al x Ga y In 1-xy} N (0 ≦ x ≦ 1,0 ≦ y ≦ 1,0 ≦ Since the gallium nitride compound semiconductor of x + y ≦ 1) is not epitaxially grown thereon, the general formula Al _x Ga _y In _1-xy N can be used as the fourth layer 5. The fourth layer 5 and the second layer 3 may have the same composition ratio or different composition ratios.
[0028]
Further, as shown in FIG. 7, the formation of the layers 4 and 5 may be repeated twice. At this time, the patterns of the lower layer 41 and the upper layer 42 constituting the layer 4 are formed in such a pattern that the layer 32 cannot be seen from above. That is, the layer 42 is formed in the upper region where the layer 41 does not exist. Thereby, in the lower layer 51 constituting the layer 5, the vertical threading dislocation of the portion B1 where the lower layer 41 is not formed is blocked by the upper layer 42 existing above the portion B1, and the upper region A2 of the upper layer 42 is laterally grown. Therefore, there are no longitudinal threading dislocations in the upper layer 52 constituting the layer 5. Further, since the region B2 in which the upper layer 42 of the upper layer 52 does not exist is an extension region of the upper region A1 of the lower layer 41, there is no vertical threading dislocation. Therefore, the threading dislocations in the upper layer 52 are extremely reduced, whereby the crystallinity of the layer 5 can be made dislocation-free crystals, and the crystallinity can be remarkably improved.
It should be noted that the number of repetitions of layer 4 and layer 5 may be any number other than two. At that time, the pattern of the plurality of layers 4 may be shifted so that the layer 32 cannot be seen as a whole when viewed from above. Of course, when the layer 4 is formed in a plurality of stages, a high melting point metal such as tungsten (W), amorphous Si, or the like can be used. Even if the material including SiO ₂ is changed for each stage, the material can be changed. good.
[0029]
In the above embodiment, sapphire is used for the substrate 1, but other substrates such as silicon and silicon carbide can be used. In addition, although each layer is formed only on the upper surface of the substrate 1, it is possible to prevent warping of the substrate by forming each layer symmetrically on both sides of the upper and lower surfaces of the substrate, and two gallium nitride compound semiconductor substrates at a time. As a result, manufacturing efficiency is improved.
[0030]
On the gallium nitride compound semiconductor substrate thus obtained, as well known, a guide layer, a clad layer, and an MQW or SQW structure active layer made of a gallium nitride compound semiconductor are heterojunctioned. A light emitting diode or a laser element may be formed. Each functional layer constituting these elements may be formed on the fourth layer 5 as a base layer, and then the substrate such as the fourth layer 5 may be separated from the substrate 1 by etching the first layer 2. . When a laser diode is formed by such a method, since the base layer of the fourth layer 5 to each functional layer of the element are formed of a gallium nitride compound semiconductor, the end face of the resonator can be easily formed. It can be formed by cleavage. Thereby, the oscillation efficiency of the laser can be improved. Further, by forming the fourth layer 5 to be conductive, current can flow in a direction perpendicular to the substrate surface, the electrode forming process is simplified, and the current path has a large cross-sectional area and length. The driving voltage can be reduced because the driving time is shortened.
[0031]
Further, although ZnO is used as the first layer 2, it is sufficient that a buffer layer of a gallium nitride compound semiconductor can be formed and only the first layer 2 can be etched.
In the above embodiment, the MOVPE method was performed in a normal pressure atmosphere, but may be performed under reduced pressure growth. Moreover, you may carry out by the combination of a normal pressure and pressure reduction. The GaN-based compound semiconductor obtained in the present invention can be used for a light emitting device such as an LED or LD, and can also be used for a light receiving device and an electronic device.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a method for manufacturing a GaN substrate according to a specific embodiment of the present invention.
FIG. 2 is a cross-sectional view showing the same manufacturing process.
FIG. 3 is a sectional view showing the same manufacturing process.
FIG. 4 is a cross-sectional view showing the same manufacturing process.
FIG. 5 is a plan view showing the shape of a third layer.
FIG. 6 is a plan view showing another shape of the third layer.
FIG. 7 is a cross-sectional view showing a manufacturing process according to another embodiment in which the third layer is used a plurality of times.
[Explanation of symbols]
1 ... sapphire substrate 2 ... 1st layer (ZnO)
3 ... Second layer 31 ... Lower layer of second layer (Ga _0.8 In _0.2 N)
32 ... Upper layer of second layer (GaN)
4. Third layer (SiO ₂ )
5 ... Fourth layer (GaN)

Claims (11)

Forming a wet-etchable first layer on the substrate;
On the first layer, a second layer composed of a lower layer formed by low temperature growth and an upper layer made of a first gallium nitride compound semiconductor with good crystallinity is formed,
On the second layer, a third layer in which the gallium nitride compound semiconductor is not epitaxially grown is formed in a dot-like, stripe-like or lattice- like island state so that the exposed portion of the second layer is scattered. ,
Epitaxial growth is performed using the exposed portion of the second layer not covered by the third layer as a nucleus, and a fourth gallium nitride-based compound semiconductor is formed by epitaxial growth in the lateral direction above the third layer. Forming a layer,
A method for producing a gallium nitride-based compound semiconductor substrate, wherein the gallium nitride-based compound semiconductor substrate is formed by peeling from the substrate by wet etching using a solution for etching the first layer. 2. The method for manufacturing a gallium nitride-based compound semiconductor substrate according to claim 1, wherein the lower layer of the second layer is in a state where amorphous or microcrystals are mixed. The lower layer of the second layer is GaInN The method for producing a gallium nitride-based compound semiconductor substrate according to claim 1 or 2, wherein 4. The method for manufacturing a gallium nitride compound semiconductor substrate according to claim 1 , wherein the first layer is zinc oxide (ZnO). 5. The method for manufacturing a gallium nitride-based compound semiconductor substrate according to any one of claims 1 to 4, wherein the third layer is made of silicon dioxide (SiO ₂ ). 5. The gallium nitride compound semiconductor substrate according to claim 1 , wherein the third layer is made of a metal having a high melting point or amorphous silicon (Si). Production method. The method for manufacturing a gallium nitride-based compound semiconductor substrate according to any one of claims 1 to 6 , wherein the substrate is sapphire, silicon, or silicon carbide. The method of manufacturing a gallium nitride-based compound semiconductor substrate according to any one of claims 1 to 7 , wherein the fourth layer has a thickness of 50 to 100 µm. Forming a plurality of layers made of a third gallium nitride compound semiconductor forming an element on the fourth layer, and then etching the first layer to obtain a substrate on which the element is formed; The method for manufacturing a gallium nitride-based compound semiconductor substrate according to any one of claims 1 to 8 . Each of the layers on the substrate is formed on both surfaces of the substrate, and the first layer formed on both surfaces of the substrate is removed by etching, whereby two gallium nitride compound semiconductor substrates are used using one substrate. The method for producing a gallium nitride-based compound semiconductor substrate according to claim 1, wherein: Forming a wet-etchable first layer on the substrate;
Forming a second layer of the first gallium nitride compound semiconductor on the first layer;
On the second layer, a third layer in which the gallium nitride compound semiconductor is not epitaxially grown is formed in a dot-like, stripe-like or lattice-like island state so that the exposed portion of the second layer is scattered. ,
Epitaxial growth is performed using the exposed portion of the second layer not covered by the third layer as a nucleus, and a fourth gallium nitride-based compound semiconductor is formed by epitaxial growth in the lateral direction above the third layer. Forming a layer,
The gallium nitride compound semiconductor substrate is formed by peeling from the substrate by wet etching using a solution for etching the first layer,
Each layer on the substrate is formed on both sides of the substrate, and the first layer formed on both sides of the substrate is etched. A method of manufacturing a gallium nitride compound semiconductor substrate, characterized in that two gallium nitride compound semiconductor substrates are obtained by using a single substrate by removing by ching.

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