Method for producing epitaxial film, vapor phase growth device and epitaxial film

Abstract

To provide a method for producing an epitaxial film which can suppress mixing of H and C into an epitaxial film and increase in Si concentration distribution, a vapor phase growth device and an epitaxial film.SOLUTION: An n type β-Ga2O3 epitaxial film is grown by using a hot wall MOVPE method using an electric furnace for heating a reaction pipe made of SiO2, using trimethyl gallium (TMGa) as a Ga raw material, O2 gas as an O raw material and tetramethylsilane (TMSi) as a dopant of Si, under the conditions of a growth temperature of 950-1,100°C, and 1.0×10-7 to 1.0×10-3 RSi (wherein, RSi represents (supply amount of TMSi) / ((supply amount of TMSi)+(supply amount of TMGa)) in molar ratio).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing an epitaxial film, a vapor phase growth apparatus, and an epitaxial film. [Background technology]

[0002] β-Ga2O3 has a large bandgap energy (~4.5eV) and is expected to have a high breakdown field strength (>7MV / cm), making it a promising material for next-generation power devices. The fabrication of vertical devices requires the growth of a thick n-type drift layer with controlled conductivity, and halide vapor phase epitaxy (HVPE) has been used to date. Meanwhile, metalorganic vapor phase epitaxy (MOVPE) allows for highly precise film thickness control and alloy growth.

[0003] Patent Document 1 discloses a metalorganic vapor phase epitaxy method for growing an n-type III-V compound semiconductor epitaxial thin film using an organometallic group III source and an organometallic group V source, and using tetramethylsilane (TMSi) and tetraethylsilane (TESi), which are organometallic compounds of Si, as n-type impurities. Non-Patent Document 1 reports that a β-Ga2O3 epitaxial film was formed using the MOVPE method. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 7-130667 [Non-patent literature]

[0005] [Non-Patent Document 1] F. Alema, B. Hertog, A. Osinsky, P. Mukhopadhyay, M. Toporkov, and WVSchoenfeld, Journal of Crystal Growth Vol. 475, pp. 77-82 (2017). Summary of the Invention [Problem to be solved by the invention]

[0006] When growing β-Ga2O3 using organometallic compounds of silicon (Si) as n-type impurities, if the hydrocarbons derived from the organometallic are not completely combusted, hydrogen (H) and carbon (C) will be mixed into the epitaxial film. Furthermore, if the decomposition of the organometallic compound of Si into Si occurs too quickly or too slowly, the Si concentration distribution in the β-Ga2O3 epitaxial film within the substrate surface becomes large. In particular, if the organometallic compound of Si does not completely decompose into Si, Si is not incorporated into the β-Ga2O3 epitaxial film.

[0007] The present invention has been made in view of the above circumstances, and provides a method for manufacturing an epitaxial film, a vapor phase growth apparatus, and an epitaxial film that can suppress the incorporation of H and C into the epitaxial film and the increase in the Si concentration distribution. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention employs the following configuration. [1] In the hot-wall MOVPE method, an electric furnace is used to heat a reaction tube made of quartz (SiO2), and an n-type β-Ga2O3 epitaxial film is grown. The epitaxial film is grown using trimethylgallium (TMGa) as the Ga source, O2 gas as the O source, and TMSi as the Si dopant at a growth temperature of 950-1100°C and a dopant concentration of 1.0 × 10 -7 ~1.0×10 -3 R Si (However, R Si represents the molar ratio (amount of TMSi supplied) / ((amount of TMSi supplied)+(amount of TMGa supplied)). [2] The hot-wall MOVPE method, in which an electric furnace is used to heat a reaction tube made of SiO2, is used to grow n-type β-Ga2O3 epitaxial films. In the vapor phase growth system, TMGa is used as the Ga source, O2 gas is used as the O source, and TMSi is used as the Si dopant. The growth temperature is 950-1100°C, and the dopant is 1.0 × 10 -7 ~1.0×10 -3 R Si This is a vapor phase growth apparatus for growing n-type β-Ga2O3 epitaxial films under the conditions above. [3] An n-type β-Ga2O3 epitaxial film containing Si dopants, in which the value of ((maximum Si concentration) - (minimum Si concentration)) / (average Si concentration) × 100% in the Si concentration distribution within the substrate surface is 0% or more and 2.0% or less. [Effects of the Invention]

[0009] According to the present invention, it is possible to suppress the incorporation of H and C into the epitaxial film and the widening of the Si concentration distribution. By using the above-mentioned means, hydrocarbons derived from organometallics are completely combusted, and H and C are hardly incorporated into the β-Ga2O3 epitaxial film. In addition, the position of the decomposition of TMSi to Si in the gas flow direction is adjusted, and the Si concentration distribution in the β-Ga2O3 epitaxial film within the substrate surface can be suppressed. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a vertical cross-sectional view of a vapor phase growth apparatus according to an embodiment. [Figure 2] 1 is a horizontal cross-sectional view of a vapor phase growth apparatus according to an embodiment. [Figure 3] 1 is a graph showing the relationship between RSi and the Si concentration and effective carrier density of an epitaxial film. [Figure 4] FIG. 10 is an explanatory diagram showing the Si concentration distribution within the substrate surface when the substrate is not rotated. [Figure 5] FIG. 10 is an explanatory diagram showing the Si concentration distribution in the substrate surface when the substrate is rotated. DETAILED DESCRIPTION OF THE INVENTION

[0011] 1 and 2 are cross-sectional views illustrating a vapor phase growth apparatus according to an embodiment. Fig. 1 shows a cross section along a plane perpendicular to a substrate (a vertical cross section), and Fig. 2 shows a cross section along a plane parallel to the substrate (a horizontal cross section).

[0012] The illustrated vapor phase growth apparatus 100 is a vapor phase growth apparatus that grows an n-type β-Ga2O3 epitaxial film using the hot-wall MOVPE method. This apparatus includes a reaction tube 1 in which a substrate 2 is placed and a zone heater 10 that heats the reaction tube 1. The reaction tube 1 corresponds to a reactor. Examples of materials for the reaction tube 1 include SiO2. The zone heater 10 corresponds to a heating device used to heat the reaction tube 1 and is an electric furnace. The substrate 2 is rotatable around a rotation axis that passes through the center of the substrate. For example, the substrate 2 in the illustrated example is held by a rotatable hanging-type substrate holder 3.

[0013] An upstream flow channel 20, an intermediate flow channel 26, and a downstream flow channel 29 are formed within the reaction tube 1. The upstream flow channel 20 corresponds to a source gas flow path that guides multiple source gases to a joining position. The intermediate flow channel 26 and the downstream flow channel 29 correspond to a mixed gas flow path that guides the mixed gas from the joining position to the substrate surface and then discharges it.

[0014] In the upstream flow channel 20, three flow paths are formed, in order from top to bottom: a top channel 21, a middle channel 22, and a bottom channel 23. The middle channel 22 serves as a source gas flow path for supplying a first source gas G1 to the substrate 2, and the top channel 21 and the bottom channel 23 serve as source gas flow paths for supplying a second source gas G2 to the substrate 2.

[0015] 1 and 2, the vertical cross section of upstream flow channel 20 in this embodiment narrows from upstream to downstream, and the horizontal cross section expands from upstream to downstream. The downstream end of upstream flow channel 20 has a flat shape that expands horizontally. The first source gas G1 flows out from the vertical center, and the second source gas G2 flows out from above and below.

[0016] The intermediate flow channel 26 is connected to the downstream side of the upstream flow channel 20. This connection point, i.e., the upstream end of the intermediate flow channel 26, corresponds to the confluence position where multiple source gases converge. At the confluence position, the first source gas G1 flowing out of the middle channel 22 and the second source gas G2 flowing out of the top channel 21 and the bottom channel 23 converge, and the resulting mixed gas flows through the intermediate flow channel 26.

[0017] An upper opening 27 is formed in the upper pipe wall of the intermediate flow channel 26. A hanging-type substrate holder 3 is fitted into the upper opening 27. The hanging-type substrate holder 3 has a plurality of claws for supporting the substrate 2 on its underside facing the interior of the intermediate flow channel 26. By placing the substrate 2 on this hanging-type substrate holder 3, the lower surface of the substrate 2 is exposed to the mixed gas in the intermediate flow channel 26. By using a so-called face-down type in which the lower surface of the substrate 2 is exposed to the mixed gas, it is easy to avoid unexpected particle adhesion, etc.

[0018] The downstream flow channel 29 is connected to the downstream side of the intermediate flow channel 26. The mixed gas that has passed through the intermediate flow channel 26 is discharged from the downstream side of the downstream flow channel 29 to the outside of the reaction tube 1. In the reaction tube 1, a gas such as nitrogen may be circulated in the space outside the upstream flow channel 20, the intermediate flow channel 26, and the downstream flow channel 29.

[0019] A source gas supply pipe is connected to the upstream side of the upstream flow channel 20. Specifically, a first source gas supply pipe 31 is connected to the middle channel 22 and supplies a first source gas G1 to the middle channel 22. A second source gas supply pipe 32a is connected to the top channel 21 and supplies a second source gas G2 to the top channel 21. A second source gas supply pipe 32b is connected to the bottom channel 23 and supplies a second source gas G2 to the bottom channel 23.

[0020] The zone heater 10 is provided in an annular shape along the outer wall of the reaction tube 1. The zone heater 10 is composed of an upstream heater 11, an intermediate heater 12, and a downstream heater 13, and the temperatures of the upstream heater 11, the intermediate heater 12, and the downstream heater 13 can be set individually.

[0021] The upstream heater 11 is disposed within the outer wall of the reaction tube 1 around the upstream portion of the intermediate flow channel 26 so as to heat the vicinity of the point where the first source gas G1 and the second source gas G2 join. The intermediate heater 12 is disposed within the outer wall of the reaction tube 1 around the portion surrounding the location where the top surface opening 27 is provided so as to heat the portion of the intermediate flow channel 26 where the substrate 2 is located. The downstream heater 13 is disposed within the outer wall of the reaction tube 1 around the portion surrounding the downstream side of the location where the top surface opening 27 is provided so as to heat the downstream side of the location where the top surface opening 27 is provided in the intermediate flow channel 26 and the downstream flow channel 29.

[0022] To produce an epitaxial film using the vapor phase growth apparatus 100, the substrate 2 is suspended by the hanging-type substrate holder 3, and a mixed gas is brought into contact with the lower surface of the substrate 2 under predetermined heating conditions. Although not shown, the vapor phase growth apparatus 100 may be of a so-called face-up type in which the upper surface of the substrate 2 is exposed to the mixed gas. By forming a lower opening in the lower tubular wall of the intermediate flow channel 26 and fitting an upper-type substrate holder into it, the substrate 2 can be arranged in a face-up position.

[0023] The substrate 2 is not particularly limited as long as it is plate-shaped and can support an epitaxial film, and may be a known substrate. Examples of the substrate include an insulating substrate, a conductive substrate, and a semiconductor substrate. In this embodiment, the substrate 2 is preferably a crystalline substrate.

[0024] The crystalline substrate is not particularly limited as long as it contains a crystalline material as its main component, and examples thereof include an insulating substrate, a conductive substrate, a semiconductor substrate, a single crystal substrate, and a polycrystalline substrate. Examples of semiconductor crystalline substrates include a substrate containing a crystalline material with a corundum structure as its main component, a substrate containing a crystalline material with a β-gallium structure as its main component, and a substrate with a hexagonal crystal structure. The term "main component" refers to a substrate containing 50% or more of the crystalline material, preferably 70% or more, and more preferably 90% or more, of the crystalline material in terms of composition ratio in the substrate.

[0025] Examples of substrates containing a crystalline material having a corundum structure as a main component include sapphire substrates and α-type gallium oxide substrates. Examples of substrates containing a crystalline material having a β-gallium structure as a main component include β-Ga2O3 substrates and mixed crystal substrates containing β-Ga2O3 and Al2O3. Examples of substrates having a hexagonal crystal structure include SiC substrates, ZnO substrates, and GaN substrates. Examples of other crystalline substrates include Si substrates. The thickness of the crystalline substrate is not particularly limited, but is preferably 50 to 2000 μm, and more preferably 200 to 800 μm.

[0026] The mixed gas contains trimethylgallium (TMGa), oxygen (oxygen molecules), and Si dopant vaporized in argon gas. TMGa is the source of gallium atoms (Ga precursor). Oxygen is the source of oxygen atoms (O precursor). Argon is the carrier gas. Tetramethylsilane (TMSi) is used as the Si dopant.

[0027] It is preferable that the TMGa and oxygen contained in the mixed gas are supplied separately up to the joining point. This prevents the TMGa and oxygen from reacting with each other before the gases join. It is also preferable that the TMGa and TMSi are supplied to the joining point in a pre-mixed state. This allows for stable control of the supply ratio of TMSi to TMGa.

[0028] In this embodiment, a gas containing TMGa and TMSi in argon is used as the first source gas G1, and is supplied to the joining position via the middle channel 22. A gas containing oxygen in argon is used as the second source gas G2, and is supplied to the joining position via the top channel 21 and the bottom channel 23. Argon is preferable as a carrier gas because it does not form donors or acceptors in the film.

[0029] The growth temperature is the temperature of the mixed gas when it comes into contact with the surface of the substrate 2, and is preferably 800 to 1200°C, and more preferably 950 to 1100°C. If the growth temperature is too low, hydrocarbons will not burn completely, resulting in H and C being incorporated into the epitaxial film. Also, TMSi will not completely decompose into Si, resulting in Si not being incorporated into the epitaxial film. If the growth temperature is too high, the decomposition of TMSi will be too rapid, resulting in a peak in Si supply at a position upstream from the substrate, resulting in Si being incorporated only at the edge of the substrate, resulting in a large distribution of Si concentration within the surface.

[0030] The reactor pressure is preferably 2.4 to 3.4 kPa. If the reactor pressure is too low, the gas flow rate becomes too fast, causing TMSi to pass over the substrate without being completely decomposed into Si, and Si is not incorporated into the epitaxial film. If the reactor pressure is too high, the gas phase reaction becomes too intense, producing powder and preventing the growth of an epitaxial film.

[0031] The total gas flow rate is preferably 6.0 to 10.0 L / min. If the total gas flow rate is too low, the gas flow rate becomes too slow, causing the gas phase reaction to become intense, resulting in the generation of powder and preventing the growth of an epitaxial film. If the total gas flow rate is too high, the gas flow rate becomes too fast, causing TMSi to pass over the substrate without being completely decomposed into Si, preventing Si from being incorporated into the epitaxial film.

[0032] The O / Ga supply ratio is preferably 800 to 1200 in molar ratio. If the O / Ga supply ratio is too low, hydrocarbons are not completely combusted, resulting in H and C being incorporated into the epitaxial film. TMSi is not completely decomposed into Si, resulting in Si not being incorporated into the epitaxial film. If the O / Ga supply ratio is too high, the decomposition of TMSi is too rapid, resulting in a peak in Si supply at a position upstream from the substrate, resulting in Si being incorporated only at the edge of the substrate, resulting in a large distribution of the Si concentration within the surface.

[0033] R Si represents the molar ratio (supplied amount of TMSi) / ((supplied amount of TMSi)+(supplied amount of TMGa)), and is 1.0×10 -7 ~1.0×10 -3 It is preferable that R Si Within this range, the Si concentration and effective carrier density (N d -N a ) changes. R Si If R is too low, the desired Si concentration cannot be obtained. Si If it is too high, the Si concentration becomes too high, and the crystallinity of the epitaxial film deteriorates.

[0034] The substrate rotation speed is preferably 1 to 10 rpm (revolutions per minute). If the substrate rotation speed is too low, the gradient of the Si concentration distribution will not be averaged even if the substrate is rotated, resulting in a large distribution of the Si concentration within the surface. If the substrate rotation speed is too high, turbulence will occur, causing the Si flow to become non-uniform and resulting in a large distribution of the Si concentration within the surface.

[0035] Figure 4 shows the 8.0 x 10 -7 R Si 5 is an explanatory diagram showing the Si concentration distribution in the substrate surface when an n-type β-Ga2O3 epitaxial film is grown without rotating the substrate under the conditions of 8.0 × 10 -7 R Si This figure shows the Si concentration distribution within the substrate surface when an n-type β-Ga2O3 epitaxial film was grown while rotating the substrate under the following conditions. When the growth temperature was 800°C and the substrate was not rotated, TMSi decomposed downstream of the target, resulting in a higher Si concentration at 0 mm (the substrate center) than at the upstream positions of -10 mm and -20 mm and the downstream positions of +10 mm and +20 mm. Conversely, when the growth temperature was 1200°C and the substrate was not rotated, TMSi decomposed upstream of the target, resulting in a Si concentration approaching zero at the downstream positions of +10 mm and +20 mm. As shown in Figure 5, when the growth temperature was 800°C, even with substrate rotation, the Si concentration at 0 mm (the substrate center) was high, resulting in poor in-plane uniformity of the Si concentration. When the growth temperature was 1200°C, even with substrate rotation, the Si concentration was not averaged out, resulting in poor in-plane uniformity of the Si concentration. When the growth temperature is 1000°C, the Si concentration distribution in the gas flow direction is averaged by the rotation of the substrate, resulting in a uniform epitaxial film across the surface.

[0036] The n-type β-Ga2O3 epitaxial film grown in this embodiment contains Si dopant. In the Si concentration distribution within the substrate surface, it is preferable that the value of ((maximum Si concentration) - (minimum Si concentration)) / (average Si concentration) x 100% is 0% or more and 2.0% or less. The Si concentration is expressed in terms of the number of atoms per unit volume (e.g., atoms / cm 3 The difference between the maximum and minimum values ​​of the Si concentration is a non-negative value, and the average value of the Si concentration is a positive value.

[0037] According to this embodiment, it is possible to suppress the incorporation of H and C into the epitaxial film and the widening of the Si concentration distribution. By using the above-mentioned means, hydrocarbons derived from organometallics are completely combusted, and H and C are hardly incorporated into the β-Ga2O3 epitaxial film. In addition, the position of the decomposition of TMSi to Si in the gas flow direction is adjusted, and the Si concentration distribution in the β-Ga2O3 epitaxial film within the substrate surface can be suppressed.

[0038] In the above embodiment, TMGa is used as the Ga source because it has a high decomposition temperature and is not prone to self-thermal decomposition. This suppresses reaction with SiO2 and other materials, reducing the amount of Si unintentionally incorporated into the epitaxial film. Furthermore, because TMGa has a high vapor pressure, it is possible to supply a high concentration of Ga to the reactor, enabling the epitaxial film to grow at a high rate.

[0039] In the above embodiment, TMSi was used as the Si dopant. Generally, when an organic metal is used as a metal source, H and C derived from hydrocarbon groups tend to be incorporated into the epitaxial film. In the above embodiment, by adopting the above-described conditions, the position of the decomposition of TMSi to Si in the gas flow direction was adjusted, and the Si concentration distribution in the β-Ga2O3 epitaxial film within the substrate surface was able to be kept small.

[0040] In this way, in the above embodiment, the amount of H and C unintentionally mixed into the epitaxial film can be reduced, and therefore, by adjusting the supply ratio of TMSi to TMGa, it is possible to stably control the effective carrier density in the epitaxial film.

[0041] The epitaxial film of this embodiment is doped with Si to be n-type. The effective carrier density is 10 16 cm -3 Over 10 19 cm -3It is preferable that the effective carrier density is equal to or less than 1000 . The effective carrier density is the average value of values ​​obtained by measurement using a Hall effect measurement device. The Hall effect measurement method used was ResiTest8300 manufactured by Toyo Corporation.

[0042] The epitaxial film of this embodiment has a mobility of 30 cm 2 / Vs or more is preferable, and 50cm 2 / Vs or more is more preferable, and 100cm 2 / Vs or more is more preferable. High mobility can suppress power loss during operation of the semiconductor device. The thickness of the epitaxial film of this embodiment is preferably 0.5 to 100 μm.

[0043] The epitaxial film of this embodiment is particularly suitable for use in semiconductor devices, and is particularly useful in power devices. Examples of semiconductor devices formed using the epitaxial film of this embodiment include transistors such as MOS and HEMT, TFTs, Schottky barrier diodes using semiconductor-metal junctions, PN or PIN diodes combined with other P layers, and light-emitting and receiving elements. The epitaxial film of this embodiment may be used in semiconductor devices as is, as formed on a substrate, or may be peeled off from the substrate using known means before application to a semiconductor device. The semiconductor device can be further used as a power module, inverter, or converter using known means, and further, for example, as a semiconductor system using a power supply device. [Example]

[0044] <Substrate> The following substrates were used in the following experimental examples: Substrate: (010) surface, 0.50 mm thick, Fe-doped semi-insulating Ga2O3 substrate (Novel Crystal Technology Co., Ltd.). <Raw materials> The following raw materials were used in the following experimental examples: TMGa: Trimethylgallium (manufactured by Taiyo Nippon Sanso Corporation). O2: Oxygen (manufactured by Taiyo Nippon Sanso Corporation). Ar: Argon (manufactured by Taiyo Nippon Sanso Corporation). TMSi: tetramethylsilane (manufactured by Taiyo Nippon Sanso Corporation).

[0045] The n-type β-Ga2O3 epitaxial film was grown using a hot-wall MOVPE system in which an electric furnace was used to heat the SiO2 reactor tube. TMGa was used as the Ga source, O2 gas was used as the O source, and TMSi was used as the Si dopant. The growth temperature was 1000°C, the reactor pressure was 3.4 kPa, the total gas flow rate was 8.4 L / min, the O / Ga supply ratio was 1000, and the SiO2 / TMSi ratio was 9.8 × 10 -8 ~8.0×10 -4 R Si N-type β-Ga2O3 epitaxial films were grown on β-Ga2O3 substrates under the conditions of (TMSi / (TMSi+TMGa)) and a substrate rotation speed of 1 rpm. The concentrations of H, C, and Si in the n-type β-Ga2O3 epitaxial films were measured by secondary ion mass spectrometry (SIMS).

[0046] As shown in Figure 3, R Si As the concentration increased, the Si concentration and effective carrier density of the n-type β-Ga2O3 epitaxial film changed (increased) linearly. In addition, the H and C concentrations of each sample were all below the SIMS background level (3.0 × 10 16 atoms / cm 3 ) or less. Furthermore, as shown in Figure 5, the Si concentration distribution ((maximum value - minimum value) / average value) within the substrate surface of the n-type β-Ga2O3 epitaxial film was within 1.5%. [Explanation of symbols]

[0047] G1 First source gas G2 Second source gas 1 reaction tube 2 boards 3 Hanging type PCB holder 10 Zone Heater 11 Upstream heating heater 12 Intermediate heating heater 13 Downstream heating heater 20 Upstream Flow Channel 21 Top Channel 22 Middle Channel 23 Bottom Channel 26 Intermediate Flow Channel 27 Top opening 29 Downstream Flow Channel 31 First raw material gas supply pipe 32a, 32b Second source gas supply pipe 100 Vapor phase growth equipment

Claims

【Request Item 1】 The material is SiO ２ n-type β-Ga was grown using a hot-wall MOVPE method in which an electric furnace was used to heat the reaction tube. ２ O ３ In a method for producing an epitaxial film, trimethylgallium (TMGa) is used as a Ga source and O is used as an O source. ２ The growth temperature was 950 to 1100°C, and the concentration was 1.0 × 10 －７ ~1.0 x 10 －３ R Ｓｉ (However, R Ｓｉ represents the molar ratio (the amount of TMSi supplied) / ((the amount of TMSi supplied)+(the amount of TMGa supplied)). ２ O ３ A method for producing an epitaxial film, which grows an epitaxial film. 【Request Item 2】 The material is SiO ２ n-type β-Ga was grown using a hot-wall MOVPE method in which an electric furnace was used to heat the reaction tube. ２ O ３ In a vapor phase growth apparatus for growing an epitaxial film, trimethylgallium (TMGa) is used as a Ga source and O is used as an O source. ２ The growth temperature was 950 to 1100°C, and the concentration was 1.0 × 10 －７ ~1.0 x 10 －３ R Ｓｉ (However, R Ｓｉ represents the molar ratio (the amount of TMSi supplied) / ((the amount of TMSi supplied)+(the amount of TMGa supplied)). ２ O ３ Vapor phase growth equipment for growing epitaxial films. 【Request Item 3】 n-type β-Ga containing Si dopant ２ O ３ An epitaxial film, wherein the value of ((maximum Si concentration) - (minimum Si concentration)) / (average Si concentration) x 100% in the Si concentration distribution within the substrate surface is 0% or more and 2.0% or less.

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