Method of manufacturing epitaxial film, and vapor growth device

Abstract

To provide a method of manufacturing an epitaxial film and a vapor growth device that can suppress organic metal (organic gallium) such as TMGa from being decomposing into carbon hydride and metal (Ga) in an upstream flow channel.SOLUTION: In a hot wall MOVPE method using an electric furnace to heat a reaction pipe 1, a heat insulation box 5 for charging a heat insulator 6 is provided to encircle the circumference of an upstream flow channel 20 arranged in the reaction pipe 1, the heat insulation box 5 is filled with the heat insulator 6, and a β-Ga2O3 epitaxial film is grown under the condition that a lower end part 5a of the heat insulation box 5 is located downstream from an upper end part 10a of the electric furnace.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing an epitaxial film and a vapor phase growth apparatus. [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. A thick n-type drift layer with controlled conductivity is essential for fabricating vertical devices, and halide vapor phase epitaxy (HVPE) has been used to fabricate this. Meanwhile, metalorganic vapor phase epitaxy (MOVPE) allows for highly precise film thickness control and alloy growth.

[0003] In the vapor phase growth apparatus of Patent Document 1, the source gas flow path is cooled by a cooling device to prevent the source gas from forming a film in the flow path before reaching the substrate. Furthermore, in Patent Document 1, the source gas flow path and the vicinity of the substrate are separated by a heat insulating plate to prevent the source gas flow path and the vicinity of the substrate from being heated. Non-Patent Document 1 reports that a β-Ga2O3 epitaxial film was formed by MOVPE. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4542860 [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] Radiant heat from the electric furnace decomposes organometallic compounds (organic gallium compounds) such as TMGa into hydrocarbons and metals (Ga), contaminating the upstream flow channel with deposits of hydrocarbons and Ga.

[0007] The present invention has been made in consideration of the above-mentioned circumstances, and provides a method for producing an epitaxial film and a vapor phase growth apparatus that can suppress decomposition of an organic metal (organic gallium) such as TMGa into hydrocarbons and a metal (Ga) in an upstream flow channel. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention employs the following configuration. [1] A method for producing an epitaxial film, in which an electric furnace is used to heat a reaction tube, an insulating box for filling with insulating material is provided so as to surround an upstream flow channel arranged in the reaction tube, the insulating material is filled in the insulating box, and a β-Ga2O3 epitaxial film is grown under the condition that the lower end of the insulating box is located downstream of the upper end of the electric furnace. [2] A vapor phase growth apparatus for growing a β-Ga2O3 epitaxial film in a hot-wall MOVPE method in which an electric furnace is used to heat a reaction tube, an insulating box for filling with insulating material is provided so as to surround an upstream flow channel arranged in the reaction tube, the insulating material is filled in the insulating box, and the lower end of the insulating box is located downstream of the upper end of the electric furnace. [Effects of the Invention]

[0009] By placing an insulating box around the upstream flow channel, heat radiation from the electric furnace is reduced, which can suppress the decomposition of organometallics (organogallium compounds) such as TMGa into hydrocarbons and metal (Ga) in the upstream flow channel. [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 comparing a comparative example with Example 1. [Figure 4] 1 is a graph comparing Examples 2 to 4. 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 a 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. An example of the material of the reaction tube 1 is SiO2. The zone heater 10 corresponds to a heating device used to heat the reaction tube 1, and an electric furnace is used. The substrate 2 is held by a 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 connects 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 from the middle channel 22 and the second source gas G2 flowing out from the top channel 21 and the bottom channel 23 converge, and the resulting mixed gas flows through the intermediate flow channel 26. Point A shown in the figure (the position indicated by the black circle in the figure) is the center of the confluence position.

[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] An insulating box 5 is provided to surround the upstream flow channel 20 disposed within the reaction tube 1. The insulating box 5 is filled with a heat insulating material 6. In the illustrated example, the insulating box 5 covers the downstream side (near point A) of the upstream flow channel 20. The insulating box 5 can be constructed, for example, by enclosing an alumina heat insulating material 6 inside a hollow annular box made of quartz (SiO2). The lower end 5a of the insulating box 5 is located downstream of the upper end 10a of the zone heater 10, which serves as an electric furnace. The upper end and lower end are the upstream and downstream ends, respectively. The insulating box 5 reduces heat radiation from the electric furnace. This suppresses decomposition of organometallic compounds (organic gallium compounds) such as TMGa contained in the source gas into hydrocarbons and metals (Ga) within the upstream flow channel 20 and prevents metals such as gallium from adhering to the interior of the upstream flow channel 20. In the illustrated example, the upper end 10a of the electric furnace (zone heater 10) is the upper end of the upstream heater 11. A part of the electric furnace (upstream heater 11 in the illustrated example) is also arranged around the downstream side (near point A) of the upstream flow channel 20, outside the reaction tube 1. The upper end 10a of the zone heater 10 is located upstream of point A, and the lower end 5a of the heat insulating box 5 is located downstream of point A. The electric furnace can heat the range from the upstream side of the confluence point (near point A) where multiple source gases converge to the downstream side of the epitaxial film formation position (position of the substrate 2). The multiple source gases for forming the β-Ga2O3 film include at least a source of gallium atoms and a source of oxygen atoms. The surroundings refers to the surroundings in the direction perpendicular to the gas flow direction.

[0023] The use of the heat insulating box 5 allows the heat insulating box 5 to be moved in the direction of the flow of the source gas while maintaining its overall shape, making it easy to adjust the temperature downstream of the upstream flow channel 20 (near point A). By appropriately adjusting the distance L2 between the heat insulating box 5 and the substrate 2, the temperature distribution within the substrate surface can be reduced. The distance L2 is preferably 50 mm or more.

[0024] 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.

[0025] 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.

[0026] The crystalline substrate is not particularly limited as long as it contains a crystalline material as a 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 the crystalline substrate include a substrate containing a crystalline material with a corundum structure as a main component, a substrate containing a crystalline material with a β-gallium structure as a 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.

[0027] 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.

[0028] The mixed gas contains an organic metal (such as organic gallium) vaporized in argon gas and oxygen gas. For example, trimethylgallium (TMGa) can be used as a source of gallium atoms. Oxygen (oxygen molecules) is the source of oxygen atoms, and argon is the carrier. When doping β-Ga2O3 with silicon as an n-type impurity, monosilane, tetramethylsilane, tetraethylsilane, etc. can be used as the silicon dopant.

[0029] The organic metal (organic gallium, etc.) and oxygen contained in the mixed gas are preferably supplied separately up to the joining point. This prevents the organic metal (organic gallium, etc.) from reacting with oxygen before the gases join. When doping silicon into β-Ga2O3, it is preferable to supply the organic gallium and silicon dopant in a pre-mixed state to the joining point. This allows for stable control of the supply ratio of the organic gallium and silicon dopant.

[0030] In this embodiment, a gas containing TMGa and a silicon dopant 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 because it does not form donors or acceptors in the film.

[0031] The growth temperature, i.e., the temperature of the mixed gas when it contacts the surface of substrate 2, is preferably approximately constant over the entire range of the upstream and downstream surfaces of substrate 2. The temperature of the mixed gas before contacting the surface of substrate 2, including point A, is preferably equal to or lower than the growth temperature, and is preferably lower than the growth temperature. This prevents the mixed gas from thermally decomposing before reaching the surface of substrate 2, and prevents gallium, gallium oxide, and the like from adhering to the interior of upstream flow channel 20 or the upstream side of intermediate flow channel 26. The temperature of the mixed gas from point A until it contacts the most upstream side of the surface of substrate 2 is preferably gradually increased.

[0032] The temperature inside the intermediate flow channel 26, such as at point A, can be confirmed by inserting a thermocouple 4 into the flow path. When measuring the temperature at point A, the tip of the thermocouple 4 is inserted until it reaches the position of point A. When measuring the temperature at point B (the position indicated by the white circle in the figure), the tip of the thermocouple 4 is inserted until it reaches the position of point B. Figures 1 and 2 show the state in which the tip of the thermocouple 4 is retracted slightly downstream of point B.

[0033] However, if the thermocouple 4 is inserted during actual film formation, problems such as the adhesion of a gallium oxide film to the thermocouple 4 may occur. Therefore, it is preferable to flow nitrogen containing neither the source gas nor oxygen during measurement using the thermocouple 4. Then, the thermocouple 4 is pulled out from the reaction tube 1 during film formation.

[0034] 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 MIS and HEMT, TFTs, Schottky barrier diodes using semiconductor-metal junctions, PN or PIN diodes combined with other P layers, and light-emitting and receiving devices. 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, can be used in semiconductor systems using, for example, power supplies. [Example]

[0035] The effects of the present invention will be explained below using examples, but the present invention is not limited to the configurations of the examples. 1 and 2 is an MOVPE apparatus, and includes an insulating box 5 made of SiO2 for filling with insulating material 6 so as to surround an upstream flow channel 20. A zone heater 10 is used as an electric furnace to heat a reaction tube 1 made of SiO2. The length L1 of the insulating box 5 is 150 mm.

[0036] <Comparative Example> As a comparative example, the temperature distribution in the gas flow direction of the vapor phase growth apparatus 100 was confirmed using a thermocouple 4 with the heat insulating box 5 provided in the vapor phase growth apparatus 100 removed. The height and width of the intermediate flow channel 26 were 10 mm and 80 mm, respectively. To confirm the temperature distribution using the thermocouple 4, only N2 was introduced into the apparatus, and the flow rates of N2 supplied from the first source gas supply pipe 31, the second source gas supply pipe 32a, and the second source gas supply pipe 32b were each 3.0 L / min, with a total flow rate of 9.0 L / min, and the reactor pressure was 1.4 kPa.

[0037] In the comparative example, the set temperatures of the upstream heater 11, the intermediate heater 12, and the downstream heater 13 of the zone heater 10 were 960°C, 960°C, and 960°C, respectively.

[0038] Example 1 In Example 1, the temperature distribution in the gas flow direction of the vapor phase growth apparatus 100 was confirmed using a thermocouple 4 with the heat insulating box 5 installed in the vapor phase growth apparatus 100. The height and width of the intermediate flow channel 26 were 10 mm and 80 mm, respectively. To confirm the temperature distribution using the thermocouple 4, only N2 was introduced into the apparatus. The flow rates of N2 supplied from the first source gas supply pipe 31, the second source gas supply pipe 32a, and the second source gas supply pipe 32b were each 3.0 L / min, with a total flow rate of 9.0 L / min, and the reactor pressure was 1.4 kPa.

[0039] In Example 1, with the thermal insulation box 5 installed in the vapor phase growth apparatus 100, temperature measurements were performed at a position where the distance L2 between the thermal insulation box 5 and the substrate 2 was 85 mm. At this time, the distance L3 between the lower end of the upstream heater 11 and the lower end 5a of the thermal insulation box 5 was 0 mm. The set temperatures of the upstream heater 11, intermediate heater 12, and downstream heater 13 of the zone heater 10 were 960°C, 960°C, and 960°C, respectively.

[0040] <Comparison between Comparative Example and Example 1> The temperature distributions shown in FIG. 3 were obtained from the comparative example and Example 1. The horizontal axis in FIG. 3 represents the distance from point A, which is the exit of the flow channel (FC). The temperature at point A was 972°C in the comparative example (without an insulating box) and 939°C in Example 1 (with an insulating box, L2 = 85 mm). By placing the insulating box 5 around the upstream flow channel 20, it was possible to reduce heat radiation from the electric furnace and gradually increase the temperature of the mixed gas from point A until it contacted the most upstream side of the surface of the substrate 2. Furthermore, the temperature distribution within the substrate surface in the gas flow direction (the difference between the maximum and minimum temperatures within the substrate surface) was 1.6°C in the comparative example and 2.0°C in Example 1. By placing the insulating box 5 around the upstream flow channel 20, it was possible to gradually increase the temperature of the mixed gas from point A until it contacted the most upstream side of the surface of the substrate 2 and to reduce the temperature distribution within the substrate surface.

[0041] <Example 2> In Example 2, the temperature distribution in the gas flow direction of the vapor phase growth apparatus 100 was confirmed. This is basically the same as Example 1. Therefore, the differences between the two will be mainly described, and a description of similar parts will be omitted. Parts corresponding to those in Example 1 will be described using the same reference numerals.

[0042] In Example 2, with the thermal insulation box 5 installed in the vapor phase growth apparatus 100, temperature measurements were performed at a position where the distance L2 between the thermal insulation box 5 and the substrate 2 was 85 mm. At this time, the distance L3 between the lower end of the upstream heater 11 and the lower end 5a of the thermal insulation box 5 was 0 mm. The set temperatures of the upstream heater 11, intermediate heater 12, and downstream heater 13 of the zone heater 10 were 600°C, 960°C, and 960°C, respectively.

[0043] Example 3 As Example 3, the temperature distribution in the gas flow direction of the vapor phase growth apparatus 100 was confirmed. This is basically the same as Example 1. Therefore, the differences between the two will be mainly described, and a description of similar parts will be omitted. Parts corresponding to those in Example 1 will be described using the same reference numerals.

[0044] In Example 3, with the insulating box 5 installed in the vapor phase growth apparatus 100, temperature measurements were performed at a position where the distance L2 between the insulating box 5 and the substrate 2 was 65 mm. At this time, the distance L3 between the lower end of the upstream heater 11 and the lower end 5a of the insulating box 5 was 20 mm. The set temperatures of the upstream heater 11, intermediate heater 12, and downstream heater 13 of the zone heater 10 were 600°C, 960°C, and 960°C, respectively.

[0045] Example 4 As Example 4, the temperature distribution in the gas flow direction of the vapor phase growth apparatus 100 was confirmed. This is basically the same as Example 1. Therefore, the differences between the two will be mainly described, and a description of similar parts will be omitted. Parts corresponding to those in Example 1 will be described using the same reference numerals.

[0046] In Example 4, with the thermal insulation box 5 installed in the vapor phase growth apparatus 100, temperature measurements were performed at a position where the distance L2 between the thermal insulation box 5 and the substrate 2 was 50 mm. At this time, the distance L3 between the lower end of the upstream heater 11 and the lower end 5a of the thermal insulation box 5 was 35 mm. The set temperatures of the upstream heater 11, intermediate heater 12, and downstream heater 13 of the zone heater 10 were 600°C, 960°C, and 960°C, respectively.

[0047] <Comparison of Examples 2 to 4> The temperature distributions shown in FIG. 4 were obtained from Examples 2 to 4. The horizontal axis in FIG. 4 represents the distance from point A, which is the outlet of the flow channel (FC). The temperature at point A was 923°C in Example 2 (L2 = 85 mm), 899°C in Example 3 (L2 = 65 mm), and 864°C in Example 4 (L2 = 50 mm). In all Examples, the temperature of the mixed gas was gradually increased from point A until it contacted the most upstream side of the surface of the substrate 2. Furthermore, the temperature distribution within the substrate surface in the gas flow direction (the difference between the maximum and minimum temperatures within the substrate surface) was 4.0°C in Example 2 (L2 = 85 mm), 4.1°C in Example 3 (L2 = 65 mm), and 5.4°C in Example 4 (L2 = 50 mm). In all cases, by appropriately adjusting the distance L2 between the insulating box 5 and the substrate 2, the temperature of the mixed gas was gradually increased from point A until it contacted the most upstream side of the surface of the substrate 2, and the temperature distribution within the substrate surface was reduced. [Explanation of symbols]

[0048] G1 First source gas G2 Second source gas L1 Length of the insulation box L2: Distance between the insulation box and the board L3 Distance between the bottom of the upstream heater and the bottom of the insulation box 1 reaction tube 2 boards 3 Hanging type PCB holder 4 thermocouples 5. Insulated box 5a Bottom end of the insulation box 6. Insulation 10 Zone Heater 10a Top of 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 1] In a hot wall MOVPE method using an electric furnace to heat a reaction tube, an insulating box for filling with a heat insulating material is provided so as to surround an upstream flow channel arranged in the reaction tube, and the insulating material is filled in the insulating box, and β-Ga is heated under the condition that the lower end of the insulating box is located downstream of the upper end of the electric furnace. ２ O ３ A method for producing an epitaxial film, which grows an epitaxial film. Request 2 In a hot wall MOVPE method using an electric furnace to heat a reaction tube, an insulating box for filling with a heat insulating material is provided so as to surround an upstream flow channel arranged in the reaction tube, and the insulating material is filled in the insulating box, and β-Ga is heated under the condition that the lower end of the insulating box is located downstream of the upper end of the electric furnace. ２ O ３ Vapor phase growth equipment for growing epitaxial films.

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