JP2004047764A - Method for manufacturing nitride semiconductor, semiconductor wafer and semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable the dislocation density of a nitride semiconductor formed on a substrate to be reduced significantly. <P>SOLUTION: A high density Si-doped GaN buffer layer 2 having an Si concentration of 4×10<SP>19</SP>cm<SP>-3</SP>or higher is epitaxially grown on a single crystal insulating substrate 1, and the nitride semiconductor layer 3, having a crystal structure of a single crystal is formed by an epitaxially growing method. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a low dislocation nitride semiconductor, a semiconductor wafer using the same, and a semiconductor device.
[0002]
[Prior art]
When trying to obtain a semiconductor epitaxial film, the easiest method is to prepare a single crystal substrate made of the same material as the semiconductor to be grown, and then vapor-phase grow it on it. Successful in materials.
[0003]
However, because it is difficult to obtain a semiconductor single crystal substrate technically like gallium nitride, or because the semiconductor single crystal substrate is expensive, it is not industrially used in terms of cost. There are many situations in which semiconductors must be grown. Representative examples include GaAs on a silicon substrate, GaN on a sapphire and silicon carbide substrate, and II-VI group semiconductor on a GaAs substrate.
[0004]
For example, gallium nitride (GaN) is used as a material for optical devices such as short-wavelength light emitting diodes (LEDs) and semiconductor lasers (LDs) in the blue to ultraviolet range, or for high power field effect transistors (FETs) and high electron mobilities. Although important as a material for an electronic device such as a transistor (HEMT), gallium nitride cannot be used to obtain a bulk single crystal substrate, and thus a sapphire or SiC substrate is used as a substrate material. GaN is grown by a method (VPE method) (including a metal organic chemical vapor deposition method (MOVPE method)).
[0005]
When a semiconductor is grown on such a heterogeneous substrate, a high mismatch occurs in the grown semiconductor epitaxial film due to mismatches in various material-specific characteristics such as lattice mismatch, thermal expansion coefficient mismatch, and surface energy mismatch. Density dislocations are introduced. Since dislocations in semiconductors act as non-radiative recombination centers and scattering centers, the characteristics, stability, and lifetime of optical and electronic devices using semiconductors containing such dislocations are limited to devices containing only a small amount of dislocations. It is extremely inferior.
[0006]
Similarly, GaN, nitride-based compound semiconductors represented by AlGaN, GaInN, and the like are grown on heterogeneous substrates such as sapphire and silicon carbide because a single-crystal substrate cannot be obtained. In, the occurrence of the above-mentioned dislocation has been a serious problem.
[0007]
However, in recent years, this problem has been partially solved by the “two-stage growth method” using the MOVPE method. That is, to grow a low temperature buffer layer made of GaN or AlN at a low temperature of about 500 to 600 ° C. on a sapphire substrate, then, is a method of growing GaN at a temperature of about 1000 ° C. In addition, this by conventional ^{10 10} It has succeeded in suppressing the dislocation density of GaN on sapphire, which was about 10 to 10 ¹¹ cm ^{-2, to the} order of 10 ⁸ to 10 ⁹ cm ^-2 (JP-B-8-8217).
[0008]
[Problems to be solved by the invention]
However, even if the dislocation density in the nitride semiconductor is on the order of 10 ⁸ cm ⁻² , it causes phenomena such as a decrease in the withstand voltage of the nitride semiconductor electronic device and a shortened life of the optical device. It is a major obstacle. That is, it is necessary to further reduce the dislocation density in the nitride semiconductor in order to achieve practical use of the electronic / optical device using the nitride semiconductor. Incidentally, in order to realize a blue-violet laser diode or an ultraviolet LED which is a next-generation product target of a nitride semiconductor, it is required to have a dislocation density of 10 ⁷ cm ⁻² or less.
[0009]
Therefore, an object of the present invention is to solve the above problems and provide a method of manufacturing a nitride semiconductor, a semiconductor wafer, and a structure of a semiconductor device that realize further reduction in dislocation density.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the present invention is configured as follows.
[0011]
In the method of manufacturing a nitride semiconductor according to the first aspect of the present invention, when a nitride semiconductor layer is formed on a substrate, a Si-doped GaN buffer layer having a Si concentration of 4 × 10 ¹⁹ cm ⁻³ or more is formed on the substrate. It is characterized by epitaxially growing and forming a nitride semiconductor layer having a single crystal structure on the Si-doped GaN buffer layer by an epitaxial growth method.
[0012]
In the method of manufacturing a nitride semiconductor according to the invention of claim 2, when forming the nitride semiconductor layer on the substrate, a Si-doped GaN buffer layer having a Si concentration of 1 × 10 ²⁰ cm ⁻³ or more is formed on the substrate. It is characterized by epitaxially growing and forming a nitride semiconductor layer having a single crystal structure on the Si-doped GaN buffer layer by an epitaxial growth method.
[0013]
According to a third aspect of the present invention, in the method of manufacturing a nitride semiconductor according to the first or second aspect, the substrate is a sapphire substrate, a SiC substrate, a Si substrate, or a nitride semiconductor layer is grown on these substrates. It is characterized by using a composite substrate.
[0014]
According to a fourth aspect of the present invention, in the method of manufacturing a nitride semiconductor according to any one of the first to third aspects, the mixed crystal semiconductor layer of the buffer layer is grown in a temperature range of 400 to 1200 ° C. .
[0015]
According to a fifth aspect of the present invention, in the method of manufacturing a nitride semiconductor according to any one of the first to fourth aspects, the nitride semiconductor layer is grown in a temperature range of 600 to 1200 ° C. From the viewpoint of reducing the dislocation density, the crystal is grown preferably at a temperature in the range of 950 to 1100 ° C, more preferably 1010 to 1050 ° C.
[0016]
According to a sixth aspect of the present invention, in the method of manufacturing a nitride semiconductor according to any one of the first to fifth aspects, the Si-doped GaN buffer layer is formed with a thickness of 0.1 molecular layer to 1 μm. I do.
[0017]
According to a seventh aspect of the present invention, in the method for manufacturing a nitride semiconductor according to any one of the first to sixth aspects, the thickness of the nitride semiconductor layer is formed to be less than 0.5 to 10 μm. This specifies a part of a range of 0.5 to 500 μm, which is a preferable thickness of the nitride semiconductor layer in the present invention.
[0018]
According to an eighth aspect of the present invention, in the method of manufacturing a nitride semiconductor according to any one of the first to sixth aspects, the nitride semiconductor layer is formed to have a thickness of 10 to 500 μm. This specifies a part of a range of 0.5 to 500 μm, which is a preferable thickness of the nitride semiconductor layer in the present invention.
[0019]
According to a ninth aspect of the present invention, in the semiconductor wafer, a nitride semiconductor is formed by an epitaxial growth method on the nitride semiconductor formed by the method according to any one of the first to eighth aspects to form a stacked structure of the nitride semiconductor. It is characterized by having done. This is because a Si-doped GaN buffer layer having an Si concentration of 4 × 10 ¹⁹ cm ⁻³ or more or a Si concentration of 1 × 10 ²⁰ cm is provided as a buffer layer between a substrate and a nitride semiconductor formed thereon. ³ is a semiconductor wafer having a structure in which a Si-doped GaN buffer layer of ⁻³ or more is formed. As the substrate, any of a sapphire substrate, a SiC substrate, a Si substrate, and a composite substrate obtained by growing a nitride semiconductor layer on these substrates can be used.
[0020]
In this semiconductor wafer, as a laminated structure (device structure) of a nitride semiconductor formed on the Si-doped GaN buffer layer, in addition to the structure of an optical device such as a short-wavelength light emitting diode (LED) and a semiconductor laser (LD), There are electronic device structures such as high power field effect transistors (FETs), high electron mobility transistors (HEMTs), and hetero bipolar transistors (HBTs). Specifically, for example, in the case of manufacturing an LED or an LD, a structure in which AlGaN, InGaN, GaN, or the like is laminated in multiple layers, and a light emitting layer (active layer) is sandwiched between an n-type cladding layer and a p-type cladding layer. Need to be formed. Also in the HBT, it is necessary to form an npn or pnp junction by laminating AlGaN, InGaN, GaN, or the like in multiple layers.
[0021]
According to a tenth aspect, in the semiconductor wafer according to the ninth aspect, the laminated structure of the nitride semiconductor is formed on the nitride semiconductor layer formed on the Si-doped GaN buffer layer and on the nitride semiconductor layer. A first cladding layer of the first conductivity type, an active layer formed on the first cladding layer, and a second cladding layer of a second conductivity type formed on the active layer and opposite to the first conductivity type. And two cladding layers. This specifies an optical device such as a short wavelength light emitting diode (LED) or a semiconductor laser (LD).
[0022]
According to an eleventh aspect of the present invention, in the semiconductor wafer according to the ninth aspect, the laminated structure of the nitride semiconductor is formed on the undoped nitride semiconductor layer formed on the Si-doped GaN buffer layer and on the nitride semiconductor layer. And a formed n-type nitride semiconductor layer. This specifies the structure of a GaN-based HEMT wafer.
[0023]
According to a twelfth aspect of the present invention, there is provided a semiconductor device formed using the semiconductor wafer according to any one of the ninth to eleventh aspects. This includes not only optical devices such as LEDs and LDs, but also electronic devices such as FETs, HEMTs, and HBTs.
[0024]
<The gist of the invention>
In order to solve the above-mentioned problems, the present inventors have searched for a new buffer layer material that can replace the AlN and GaN low-temperature buffers, and made intensive research. As a result, as shown in FIG. 1, sapphire, SiC, Si, etc. First, as a buffer layer 2, Si of 4 × 10 ¹⁹ cm ⁻³ or more, preferably 5 × 10 ¹⁹ cm ³ , is formed on a substrate 1 such as a heterosubstrate or a composite substrate in which a nitride semiconductor is grown on the heterogeneous substrate in advance. ^-3 or more, more preferably 1 × 10 ²⁰ cm ⁻³ or more doped high-concentration Si-doped GaN is grown, and the nitride semiconductor layer 3 is grown thereon. It has been found that it is possible to make it smaller than ⁸ cm ⁻² .
[0025]
This is because, as shown in FIG. 2, as a result of doping the substrate 1 with Si at a high concentration, the growth mode of GaN is changed from a normal two-dimensional growth mode to a three-dimensional growth mode as shown in FIG. This is because the mode has changed to the island growth mode. When the buried surface of such an island-shaped structure of the Si-doped GaN layer 2 is planarized by growing the nitride semiconductor 3 as shown in FIG. Since the direction of propagation of the dislocations 30 changes in the lateral direction as shown in FIG. 2C during the burying growth, the density of the dislocations 32 appearing on the outermost surface is greatly reduced as shown in FIG.
[0026]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, an embodiment of a method for manufacturing a nitride semiconductor according to the present invention, and a semiconductor wafer and a semiconductor device manufactured by the method will be described. The following embodiment is an example in which MOVPE growth is used, but similar results are obtained in the case of HVPE growth (hydride vapor phase growth) or MBE growth (molecular beam epitaxy).
[0027]
<Example 1>
In the present embodiment, a sapphire substrate is used as the substrate 1, which is first cleaned at 1100 ° C. in a hydrogen atmosphere, and then a Si-doped GaN buffer layer is formed thereon as a buffer layer 2. The GaN layer is grown in various ways, and a GaN layer of about 3 μm is further grown thereon as the nitride semiconductor layer 3. The pressure, total gas flow rate, and temperature during the growth are all constant throughout the Si-doped GaN buffer layer and the GaN layer, and are 300 Torr, 100 slm, and 1025 ° C., respectively. As a carrier gas, a gas obtained by mixing nitrogen and hydrogen at a ratio of 1: 3 was used. Trimethyl gallium (TMG) and ammonia were used as raw materials of Ga and N for GaN growth, and tetraethylsilane (TESi) was used as a raw material of Si.
[0028]
Prior to this experiment, a Si-doped GaN layer having a thickness of about 1 μm was grown on a sapphire substrate by a conventional method, and the relationship between the flow rates of TMG and TESi during growth and the Si doping concentration at that time was grasped by SIMS analysis. Note that, as described above, since the high-concentration Si-doped GaN does not grow flat, the above expression of “film thickness” is not appropriate, but here, GaN is used as an index of the amount of TMG supplied for growing GaN. It is simply expressed by the term "film thickness" that the thickness becomes as if it grows flat.
[0029]
FIG. 3 shows the relationship between the doping concentration when the thickness of the Si-doped GaN buffer layer is 1 nm and the dislocation density of the GaN layer grown thereon. When the Si doping concentration is 4 × 10 ¹⁹ cm ⁻³ or more, the dislocation density of the GaN layer starts to decrease from the value obtained by the conventional method, and when the Si doping concentration is 1 × 10 ²⁰ cm ⁻³ or more, the dislocation density becomes 2 × 10 ¹⁹ cm ^−3. It is an extremely low value of ⁷ cm ^-2 or less. Furthermore, when the Si doping concentration is 1.8 × 10 ²⁰ cm ⁻³ , a minimum dislocation density of 1.5 × 10 ⁷ cm ⁻² is obtained within the range of this experiment. That is, by introducing GaN doped with Si at a high concentration between the substrate and the nitride semiconductor layer, the dislocation density of the nitride semiconductor has been significantly reduced.
[0030]
FIG. 4 shows the thickness (nm) of the Si-doped GaN buffer layer and the dislocation of the GaN layer grown thereon when the doping concentration of the Si-doped GaN buffer layer is 1.8 × 10 ²⁰ cm ^−3. It shows the relationship of density (cm ⁻² ). The dislocation density is equal to or less than the dislocation density of GaN according to the conventional method over a wide range of the thickness of the Si-doped GaN buffer layer from about 0.1 molecular layer (0.025 nm) to 1000 nm. In particular, when the thickness of the Si-doped GaN buffer layer is 1 nm, a minimum dislocation density of 1.5 × 10 ⁷ cm ⁻² is obtained. Therefore, the thickness of the Si-doped GaN buffer layer is preferably from 0.1 molecular layer to 1000 nm (1 μm), preferably from 0.1 to 100 nm, and most preferably 1 nm. You can see that.
[0031]
<Example 2>
In this embodiment, a composite substrate in which a GaN layer is grown to about 1 μm on a SiC substrate is used as the substrate 1, and a buffer layer 2 having an Si concentration of 1.8 × is formed on this composite substrate under the same conditions as in the first embodiment. A high-concentration Si doped GaN buffer layer of 10 ²⁰ cm ⁻³ is grown to 1 nm, and Al _0.1 Ga _0.9 N is grown thereon as a nitride semiconductor layer 3 by about 2 μm. As a result, at the stage of the composite substrate, the dislocation density was 1 × 10 ⁹ cm ⁻² on the outermost surface of the GaN layer, but the dislocation density was 5 × 10 ^{9 on} the surface of Al _0.1 Ga _0.9 N. ^It has been reduced to ⁷ cm ^-2 .
[0032]
<Example 3>
In the present embodiment, the premise is that the high-concentration Si-doped GaN buffer layer of the first embodiment has a Si concentration of 1.8 × 10 ²⁰ cm ⁻³ and a thickness of 1 nm. An experiment was performed in which the growth temperature of the buffer layer 2) was changed in the range of 200 to 1300 ° C. As a result, when the growth temperature of the high-concentration Si-doped GaN buffer layer was in the range of 400 to 1200 ° C., the dislocation density was equal to or less than the conventional GaN dislocation density. In particular, the dislocation density is 5 × 10 ⁷ cm ⁻² or less when the growth temperature is in the range of 800 to 1100 ° C., and the dislocation density is 2 × 10 ⁷ cm ⁻² or less in the range of 1000 to 1050 ° C. Was reduced to
[0033]
<Example 4>
In this embodiment, it is assumed that the high-concentration Si-doped GaN buffer layer in the first embodiment has a Si concentration of 1.8 × 10 ²⁰ cm ⁻³ and a thickness of 1 nm. An experiment was performed in which the growth temperature of the GaN layer (nitride semiconductor layer 3) grown on the layer was changed in the range of 200 to 1300 ° C. As a result, when the growth temperature was in the range of 600 to 1200 ° C., the dislocation density became equal to or less than the dislocation density of GaN according to the conventional method. In particular, the dislocation density is 5 × 10 ⁷ cm ⁻² or less when the growth temperature is in the range of 950 to 1100 ° C., and the dislocation density is 2 × 10 ⁷ cm ⁻² or less in the range of 1010 to 1050 ° C. Was reduced to
[0034]
<Example 5>
In Examples 1 to 4, the thickness of the nitride semiconductor layer is preferably 0.5 μm to 500 μm. When the thickness of the nitride semiconductor layer is less than 0.5 μm, the electrical and optical characteristics of the nitride semiconductor are deteriorated, and when the thickness of the nitride semiconductor layer is 500 μm or more, Growth time is too long. In particular, when the thickness of the nitride semiconductor layer is less than 0.5 μm to 10 μm, it is suitable as a low cost and low dislocation nitride semiconductor epitaxial wafer, and the thickness of the nitride semiconductor layer is 10 μm In the case of ５００500 μm, the wafer cost is slightly higher, but it is suitable as a nitride semiconductor epitaxial wafer having lower dislocation.
[0035]
<Example 6>
FIG. 5 shows an example of a light emitting semiconductor device wafer in which a double hetero (DH) structure of a gallium nitride-based compound semiconductor is grown on a sapphire substrate 11 by MOVPE. This wafer W has a high concentration Si-doped GaN buffer layer 12 formed on a sapphire substrate 11 in a temperature range of 400 to 1200 ° C. with a thickness of 0.1 molecular layer to 1 μm, and then a temperature of 600 to 1200 ° C. An n-type GaN layer 13 for attaching an ohmic electrode in the range is formed, and an n-type AlGaN cladding layer 14 (first cladding layer), an InGaN active layer 15, and a p-type AlGaN cladding layer 16 (second After growing a double heterostructure composed of a p-type GaN contact layer 17, a double hetero structure composed of
[0036]
FIG. 6 shows an example of a semiconductor device formed using the semiconductor wafer. A part of the surface of the wafer W is removed by etching by a reactive ion etching (RIE) method to expose the n-type GaN layer 13, and then titanium (Ti) and aluminum ( An n-type electrode 18 having a laminated structure of Al) and a p-type electrode 19 having a laminated structure of nickel (Ni) and gold (Au) are provided on a part of the surface of the p-type layer. Gallium-based compound semiconductor light emitting semiconductor device).
[0037]
<Example 7>
FIG. 7 shows that a high-concentration Si-doped GaN buffer layer 22 is formed on a sapphire substrate 21 with a thickness of 0.1 molecular layer to 1 μm on a sapphire substrate 21 in a temperature range of 400 to 1200 ° C. This is an example in which an undoped GaN layer 23 is formed in a temperature range of 1200 ° C., and an n-type AlGaN layer 24 is formed thereon to form a HEMT wafer. In the GaN-based HEMT made using this wafer, a steep heterointerface is formed by the function of the GaNSi buffer layer 22, and a high current density can be obtained.
[0038]
【The invention's effect】
As described above, according to the present invention, when forming a nitride semiconductor layer on a single-crystal insulating substrate, the Si concentration between the substrate and the nitride semiconductor layer is 4 × 10 ¹⁹ cm ⁻³ or more. Since the high-concentration Si-doped GaN buffer layer, which is preferably 1 × 10 ²⁰ cm ⁻³ or more, is formed, it is possible to grow a nitride semiconductor having a lower dislocation than before. This means that the dislocation density in the nitride semiconductor layer can be drastically reduced to 10 ⁷ cm ⁻² or less. For this reason, according to the method for manufacturing a nitride semiconductor, the semiconductor wafer, and the semiconductor device of the present invention, it is possible to realize a next-generation blue-violet laser diode or an ultraviolet LED, and withstand the nitride semiconductor electronic device or the optical device. It is possible to obtain an electronic device or an optical device suitable for practical use by improving the life and the like.
[Brief description of the drawings]
FIG. 1 is a diagram showing a structure of a nitride semiconductor of the present invention.
FIG. 2 is a diagram for explaining the principle of dislocation reduction by a Si-doped GaN buffer layer in the present invention.
FIG. 3 is a diagram showing a relationship between a doping concentration and a dislocation density of a GaN layer grown thereon when the thickness of a Si-doped GaN buffer layer is 1 nm in the present invention.
FIG. 4 shows the relationship between the thickness of the buffer layer and the dislocation density of the GaN layer grown thereon when the doping concentration of the Si-doped GaN buffer layer is 1.8 × 10 ²⁰ cm ^{−3 in} the present invention. FIG.
FIG. 5 is a sectional view showing a structure of an optical device wafer prepared according to the present invention.
FIG. 6 is a cross-sectional view showing a structure of an optical device manufactured by using the wafer of FIG. 4 according to the present invention.
FIG. 7 is a sectional view showing a structure of a GaN-based HEMT wafer prepared according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Substrate 2 Buffer layer 3 Nitride semiconductor layer

Claims (12)

In forming a nitride semiconductor layer on a substrate,
A Si-doped GaN buffer layer having a Si concentration of 4 × 10 ¹⁹ cm ⁻³ or more is epitaxially grown on the substrate,
A method for manufacturing a nitride semiconductor, comprising forming a nitride semiconductor layer having a single crystal structure by epitaxial growth on the Si-doped GaN buffer layer. In forming a nitride semiconductor layer on a substrate,
A Si-doped GaN buffer layer having a Si concentration of 1 × 10 ²⁰ cm ⁻³ or more is epitaxially grown on the substrate,
A method for manufacturing a nitride semiconductor, comprising forming a nitride semiconductor layer having a single crystal structure by epitaxial growth on the Si-doped GaN buffer layer. 3. The method for manufacturing a nitride semiconductor according to claim 1, wherein a sapphire substrate, a SiC substrate, a Si substrate, or a composite substrate obtained by growing a nitride semiconductor layer on these substrates is used as the substrate. . The method for manufacturing a nitride semiconductor according to claim 1, wherein the Si-doped GaN buffer layer is grown in a temperature range of 400 to 1200 ° C. 5. The method for manufacturing a nitride semiconductor according to any one of claims 1 to 4, wherein the nitride semiconductor layer is grown in a temperature range of 600 to 1200C. The method according to any one of claims 1 to 5, wherein the Si-doped GaN buffer layer is formed with a thickness of 0.1 molecular layer to 1 µm. The method for producing a nitride semiconductor according to claim 1, wherein the thickness of the nitride semiconductor layer is formed to be less than 0.5 to 10 μm. The method for manufacturing a nitride semiconductor according to claim 1, wherein the thickness of the nitride semiconductor layer is formed to be 10 to 500 μm. A semiconductor wafer comprising a nitride semiconductor formed by an epitaxial growth method on the nitride semiconductor formed by the method according to claim 1, thereby forming a nitride semiconductor laminated structure. The laminated structure of the nitride semiconductor includes a nitride semiconductor layer formed on the Si-doped GaN buffer layer, a first conductive type first cladding layer formed on the nitride semiconductor layer, 10. The semiconductor device according to claim 9, further comprising: an active layer formed on the clad layer, and a second clad layer formed on the active layer and having a second conductivity type opposite to the first conductivity type. Semiconductor wafer. The stacked structure of the nitride semiconductor includes an undoped nitride semiconductor layer formed on the Si-doped GaN buffer layer and an n-type nitride semiconductor layer formed on the nitride semiconductor layer. The semiconductor wafer according to claim 9. A semiconductor device formed using the semiconductor wafer according to claim 9.

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