Semiconductor film and method for manufacturing the same

Abstract

A semiconductor film comprising a β-Ga2O3 single crystal with few fatal defects and a method thereof are provided. As one embodiment, a method for manufacturing a semiconductor film (12) is provided, comprising: a step of placing a semiconductor substrate (10) comprising a β-Ga2O3 single crystal into a reaction chamber (20) of an HVPE apparatus (2) with its growth substrate surface (11) facing upwards; and a step of flowing Ga chloride gas, oxygen-containing gas, and dopant-containing gas into a space (24) within the reaction chamber (20) where the semiconductor substrate (10) is disposed, and epitaxially growing a semiconductor film (12) comprising a β-Ga2O3 single crystal on the growth substrate surface (11) of the semiconductor substrate (10), wherein the position of the inlet of the dopant-containing gas into the space (24) is higher than the position of the inlet of the oxygen-containing gas into the space (24), and the position of the inlet of the Ga chloride gas into the space (24) is higher than the position of the inlet of the dopant-containing gas into the space (24).

Description

Technical Field

[0001] This invention relates to semiconductor films and their manufacturing methods. Background Technology

[0002] Previously, techniques for growing β-Ga2O3 single-crystal films using HVPE (Halide Vapor Phase Epitaxy) were known (for example, see Patent Document 1). According to the technique described in Patent Document 1, gallium feed gas, oxygen feed gas, and dopant feed gas are flowed into the region of the reaction chamber of the vapor phase growth apparatus where a Ga2O3 substrate is disposed, causing epitaxial growth of a β-Ga2O3 single-crystal film on the Ga2O3 substrate.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent No. 5984069 Summary of the Invention

[0006] The problem the invention aims to solve

[0007] However, when growing β-Ga2O3 single crystal films using the HVPE method, compared to growing other nitride semiconductors such as GaN using the HVPE method, there is a problem that serious defects, namely fatal defects, are more likely to occur, which cause a significant deterioration in device characteristics. Previously, the causes of fatal defects and methods to reduce them were not clear.

[0008] Therefore, the object of the present invention is to provide a semiconductor film comprising β-Ga2O3 single crystal with few fatal defects and a method for manufacturing the same.

[0009] Solution for solving the problem

[0010] In order to achieve the above objectives, one aspect of the present invention provides a method for manufacturing a semiconductor film as described in [1] to [4] below, and a semiconductor film as described in [5] below.

[0011] [1] A method for manufacturing a semiconductor film includes: a step of placing a semiconductor substrate comprising a β-Ga2O3 single crystal into a reaction chamber of an HVPE apparatus with the growth substrate surface facing upward or downward; and a step of flowing Ga chloride gas, oxygen-containing gas, and dopant gas into a space in the reaction chamber where the semiconductor substrate is disposed, and epitaxially growing a semiconductor film comprising a β-Ga2O3 single crystal on the growth substrate surface of the semiconductor substrate, wherein when the semiconductor substrate is placed with the growth substrate surface facing upward, the position of the inlet of the dopant gas into the space is higher than the position of the inlet of the oxygen-containing gas into the space, and the position of the inlet of the Ga chloride gas into the space is higher than the position of the inlet of the dopant gas into the space; and when the semiconductor substrate is placed with the growth substrate surface facing downward, the position of the inlet of the dopant gas into the space is higher than the position of the inlet of the Ga chloride gas into the space, and the position of the inlet of the oxygen-containing gas into the space is higher than the position of the inlet of the dopant gas into the space.

[0012] [2] According to the semiconductor film manufacturing method described in [1] above, the Ga chloride gas is GaCl gas, the oxygen-containing gas is O2 gas, and the dopant-containing gas is SiCl4 gas.

[0013] [3] In the method for manufacturing a semiconductor film according to [1] or [2] above, in the step of setting the semiconductor substrate, the semiconductor substrate is placed in the reaction chamber with the growth substrate surface facing downward.

[0014] [4] According to the semiconductor film manufacturing method described in [3] above, in the process of epitaxially growing the semiconductor film, the Ga chloride gas, the oxygen-containing gas and the dopant-containing gas are flowed into the space at a flow rate of 110 cm / s or more.

[0015] [5] A semiconductor film comprising a β-Ga2O3 single crystal containing Cl, wherein the in-plane density of defects is 10 defects / cm² continuous from the front to the back in the thickness direction. 2 the following.

[0016] Invention Effects

[0017] According to the present invention, a semiconductor film comprising β-Ga2O3 single crystal with few fatal defects and a method thereof can be provided. Attached Figure Description

[0018] Figure 1This is a vertical cross-sectional view of the crystal stacked structure according to the first embodiment of the present invention.

[0019] Figure 2A This is a schematic diagram showing the installation state of the semiconductor substrate 10 and the introduction position of the raw material gas according to the first embodiment of the present invention.

[0020] Figure 2B This is a schematic diagram showing the setup state of the semiconductor substrate 10 in the comparative example and the location of the raw material gas introduction.

[0021] Figure 3 This is a schematic diagram showing the installation state of the semiconductor substrate 10 and the introduction position of the raw material gas according to the second embodiment of the present invention.

[0022] Figure 4A This is an emission microscope image of a semiconductor film formed by the method of the second embodiment.

[0023] Figure 4B The image is an emission microscope image of a semiconductor film used as a comparative example, formed using conventional methods.

[0024] Figure 5A This is an optical microscope image of the surface of a semiconductor film formed by the method of the second embodiment, showing etch pits.

[0025] Figure 5B This is an optical microscope image of the surface of a semiconductor film formed using conventional methods as a comparative example, showing etch pits.

[0026] Figure 6 This is a vertical cross-sectional view of a Schottky barrier diode used for evaluating the characteristics of the Schottky barrier diode, which will be discussed later.

[0027] Figure 7A This is a coordinate graph showing the reverse leakage characteristics of a Schottky barrier diode having a semiconductor film formed by the method of the first embodiment.

[0028] Figure 7B This is a coordinate graph showing the reverse leakage characteristics of a Schottky barrier diode having a semiconductor film formed by the method of the second embodiment.

[0029] Figure 8 This is a coordinate graph showing the reverse leakage characteristics of a Schottky barrier diode with a semiconductor film formed by conventional methods as a comparative example.

[0030] Figure 9A This is a diagram showing the distribution of the breakdown voltage characteristics of a Schottky barrier diode in a 2-inch wafer before monolithization of a Schottky barrier diode having a semiconductor film formed by the method of the second embodiment.

[0031] Figure 9B This is a diagram showing the distribution of the breakdown voltage characteristics of a Schottky barrier diode in a 2-inch wafer before monolithization of a Schottky barrier diode having a semiconductor film formed by the method of the second embodiment.

[0032] Figure 9C This is a diagram showing the distribution of the breakdown voltage characteristics of a Schottky barrier diode in a 2-inch wafer before monolithization of a Schottky barrier diode having a semiconductor film formed by the method of the second embodiment.

[0033] Figure 10A This is a coordinate graph showing the reverse characteristics of a Schottky barrier diode having a semiconductor film formed by the method of the second embodiment and a square anode electrode of 2.3 mm.

[0034] Figure 10B This is a coordinate graph showing the forward characteristics of a Schottky barrier diode having a semiconductor film formed by the method of the second embodiment and a 2.3 mm square anode electrode. Detailed Implementation

[0035] In order to investigate the cause of fatal defects in β-Ga2O3 single crystal films grown by the HVPE method, the inventors of this invention used conventional methods of the HVPE method to grow β-Ga2O3 single crystal films, fabricated multiple Schottky barrier diodes with different device sizes, and evaluated their reverse breakdown voltage characteristics.

[0036] As a result, when the size of the device (the size of the circular anode electrode) is less than 400 μm in diameter, a device with near-ideal characteristics and suppressed reverse leakage current is obtained with a yield of about 80%. However, as the device size increases, the number of devices with large reverse leakage current increases, and the yield of devices with a diameter of 1 mm is approximately 0%.

[0037] Thus, since the device characteristics depend on the device size, it is presumed that fatal defects exist in the crystal film. Furthermore, based on the yield and the area of ​​the anode electrode, the fatal defect density in the β-Ga₂O₃ crystal film grown by conventional methods is estimated to be 200 defects / cm². 2 The density of fatal defects directly affects the size of the components that can be manufactured, i.e., the maximum rated current of the device. β-Ga2O3 crystal films manufactured by conventional methods can only produce Schottky barrier diodes with a rated current (the current value when a forward voltage of about 1.5 to 2.5V is applied) of about 1A or less.

[0038] Furthermore, the inventors of this invention conducted intensive research and discovered that the primary cause of fatal defects in β-Ga₂O₃ crystalline films is the formation of Ga oxide particles in the gas phase within the reaction chamber of the HVPE apparatus. During the growth of β-Ga₂O₃ single-crystal films via the HVPE method, the reaction rate between oxygen and Ga chloride gas is extremely fast, resulting in the formation of Ga oxide particles in the gas phase, which then adhere to the Ga₂O₃ substrate. If these Ga oxide particles are incorporated into the epitaxially grown β-Ga₂O₃ single-crystal film, the periodicity of the crystal structure becomes disordered, resulting in numerous fatal defects that can become leakage paths, extending continuously from the front to the back side along the film's thickness direction.

[0039] Furthermore, it has been confirmed that the growth of GaN-based crystalline films via HVPE does not produce as many fatal defects as the growth of β-Ga₂O₃-based crystalline films. This is believed to be due to the relatively slow reaction rate between ammonia and Ga chloride gas, thus minimizing the formation of GaN-based compound particles in the gas phase.

[0040] This invention relates to a method for manufacturing a semiconductor film comprising a β-Ga₂O₃ single crystal, which reduces the amount of Ga oxide particles formed in the gas phase and attached to a Ga₂O₃ substrate within the reaction chamber of an HVPE apparatus, thereby reducing fatal defects. Furthermore, this invention relates to a semiconductor film comprising a β-Ga₂O₃ single crystal with fewer fatal defects manufactured by this method. Embodiments of the invention will be described below.

[0041] [First Embodiment]

[0042] (The composition of crystal layered structures)

[0043] Figure 1 This is a vertical cross-sectional view of the crystal stacked structure 1 according to the first embodiment of the present invention. The crystal stacked structure 1 includes: a semiconductor substrate 10, which includes a β-Ga2O3 single crystal; and a semiconductor film 12, which includes a β-Ga2O3 single crystal, formed on the growth substrate surface 11 of the semiconductor substrate 10 by epitaxial crystal growth.

[0044] Here, β-Ga₂O₃ single crystal refers to a β-Ga₂O₃ single crystal with a β-type crystal structure, or a β-Ga₂O₃ single crystal with added elements such as Al and In. For example, it could be a β-Ga₂O₃ single crystal with added Al and In (Ga₂O₃). x Al y In (1-x-y)The semiconductor substrate 10 can also contain dopants such as Si. The band gap widens with the addition of Al, and narrows with the addition of In.

[0045] The orientation of the growth substrate surface 11 of the semiconductor substrate 10 is, for example, (001), (010), (100), (011), (-201), or (101).

[0046] The semiconductor substrate 10 is formed, for example, by slicing a block crystal of Ga2O3 single crystal grown using melt growth methods such as FZ (Floating Zone) method and EFG (Edge Defined Film Fed Growth) method, and then polishing the surface.

[0047] The semiconductor film 12 contains Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ba, Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Hg, B, Al, In, Tl, C, Si, Ge, Sn, Pb, N, P, As, Sb, Bi, S, Se, Te, etc., as dopants, which are doped in parallel with the crystal growth.

[0048] The concentration of dopants contained in semiconductor film 12 is, for example, 1 × 10⁻⁶. 13 atoms / cm 3 Above, 5×10 20 atoms / cm 3 The preferred value is 6.5 × 10⁻⁶. 15 atoms / cm 3 Above, 2.1×10 20 atoms / cm 3 Below. Additionally, the carrier density generated by the addition of dopant is, for example, 1 × 10⁻⁶. 15 cm -3 Above, 1×10 20 cm -3 the following.

[0049] In addition, the semiconductor film 12 contains a concentration of 5×10 16 atoms / cm 3The following refers to Cl. This is because the semiconductor film 12 is formed using the HVPE method with Cl-containing gas. Typically, when forming β-Ga₂O₃ single-crystal films using methods other than HVPE, since Cl-containing gas is not used, the β-Ga₂O₃ single-crystal film does not contain Cl, at least not 1×10⁻⁶ Cl. 16 cm -3 The above Cl.

[0050] Furthermore, since the semiconductor film 12 is formed using the high-speed HVPE (Halide Vapor Phase Epitaxy) method, it can be formed to a thickness of, for example, 1000 nm or more. Additionally, the growth rate of β-Ga₂O₃ single-crystal films using industrial-grade HVPE is typically 200 μm / h. In this case, a thickness up to 1000 μm can be achieved within a realistic timeframe. That is, semiconductor films 12 with thicknesses of 1000 nm or more but less than 1000 μm can be formed. Furthermore, the crystal growth rate of β-Ga₂O₃ single-crystal films using the MBE method is approximately 120 nm / h, requiring more than 8 hours to form a thickness of 1000 nm or more, which is impractical in production settings.

[0051] Furthermore, according to the manufacturing method of the semiconductor film 12 described later, the in-plane density of fatal defects that are continuous from the front to the back side in the thickness direction of the semiconductor film 12 can be made to be 10 defects / cm². 2 The in-plane density of fatal defects contained in the semiconductor film 12 can be determined by observation using an emission microscope under an anode bias of -200V.

[0052] (Structure of the HVPE device)

[0053] Hereinafter, an example of the structure of the HVPE apparatus used for growing the semiconductor film 12 according to the first embodiment of the present invention will be described.

[0054] The semiconductor film manufacturing method of the first embodiment of the present invention is used in... Figure 2A , Figure 2B The image shows an HVPE apparatus 2 with a vertical cross-section. The HVPE apparatus 2 is a vapor-phase growth apparatus for the HVPE process, comprising: a space 24 in which a semiconductor substrate 10 is disposed; and a reaction chamber 20 having a first gas inlet port 21, a second gas inlet port 22, and a third gas inlet port 23 for introducing a raw material gas for growing a semiconductor film 12 into the space 24. The reaction chamber 20 comprises, for example, quartz glass.

[0055] Additionally, the HVPE device 2 has a heating unit (not shown) disposed around the reaction chamber 20 for heating the space 24 within the reaction chamber 20. This heating unit is, for example, a resistance heating or radiation heating device.

[0056] In the reaction chamber 20, the raw material gas for growing the semiconductor film 12 is introduced into the space 24 from the first gas inlet port 21, the second gas inlet port 22, and the third gas inlet port 23.

[0057] The heights (positions perpendicular to the growth substrate surface 11 of the semiconductor substrate 10) of the first gas inlet port 21 to the inlet 21a of the space 24, the second gas inlet port 22 to the space 24, and the third gas inlet port 23 to the space 24 are different. An inlet 22a is positioned above the inlet 23a, and an inlet 21a is positioned above the inlet 22a. Furthermore, to prevent deviations in the state of the semiconductor film 12 in the in-plane direction of the growth substrate surface 11, the inlets 21a, 22a, and 23a are positioned in the horizontal direction orthogonal to the direction of travel of the raw material gas. Figure 2A , Figure 2B The positions of the two objects (in the direction perpendicular to the paper) are roughly the same.

[0058] The raw material gas used to grow the semiconductor film 12 includes: a gallium raw material gas, such as GaCl gas, GaCl2 gas, GaCl3 gas, (GaCl3)2 gas, and other Ga chloride gases; an oxygen raw material gas, such as O2 gas, H2O gas, and other oxygen-containing gases; and a dopant raw material gas, such as SiCl4 gas, GeCl4 gas, SnCl4 gas, PbCl2 gas, and other dopant-containing gases.

[0059] Each raw material gas uses inert gases such as Ar and N2 as carrier gases to flow into the reaction chamber 20.

[0060] (Manufacturing method of semiconductor film)

[0061] The method for manufacturing the semiconductor film 12 according to the first embodiment of the present invention includes: a step of placing a semiconductor substrate 10 comprising a β-Ga2O3 single crystal into a reaction chamber 20 of an HVPE apparatus 2; and a step of flowing Ga chloride gas, an oxygen-containing gas and a dopant-containing gas into a space 24 in the reaction chamber 20 where the semiconductor substrate 10 is disposed, and epitaxially growing the semiconductor film 12 comprising a β-Ga2O3 single crystal on a growth substrate surface 11 of the semiconductor substrate 10.

[0062] In this embodiment, the semiconductor substrate 10 is disposed on the bottom surface side of the space 24 within the reaction chamber 20 with the growth substrate surface 11 facing upward. Here, "growth substrate surface 11 facing upward" means that the growth substrate surface 11 faces the opposite side of the ground surface, and the angle between the growth substrate surface 11 and the horizontal plane is in the range of -5 to +5°.

[0063] Ga chloride gas, oxygen-containing gas, and doped gas flowing in from inlets 21a, 22a, and 23a are mixed in space 24. Then, the growth substrate surface 11 of the semiconductor substrate 10 is exposed to the mixed gas, and the semiconductor film 12 undergoes epitaxial growth.

[0064] During the epitaxial growth of the semiconductor film 12, the pressure within the space 24 is maintained, for example, at 1 atm. Furthermore, for the semiconductor film 12 to grow, a growth temperature of 900°C or higher is required. Below 900°C, it may be impossible to obtain a single crystal.

[0065] Here, Ga chloride gas is preferably used as the feed gas for gallium. GaCl gas is the Ga chloride gas that can maintain the growth driving force of Ga2O3 crystals to the highest temperature. In order to obtain high-purity, high-quality Ga2O3 crystals, it is effective to grow at a high growth temperature. Therefore, GaCl gas, which has a high growth driving force at high temperatures, is preferred.

[0066] Furthermore, for the dopant gas used as the feedstock gas, a chloride-based gas is preferred to suppress the unintentional introduction of other impurities. For example, when Si, Ge, Sn, or Pb, which are group 14 elements, are used as dopants as described above, chloride-based gases such as SiCl4, GeCl4, SnCl4, and PbCl2 are used respectively. Additionally, the chloride-based gas is not limited to compounds that react only with chlorine; silane-based gases such as SiHCl3 can also be used.

[0067] Si and other dopants are doped in parallel with the growth of β-Ga2O3 single crystals.

[0068] Furthermore, if hydrogen is present in the atmosphere during the growth of the semiconductor film 12, the surface flatness of the semiconductor film 12 and the crystal growth driving force will decrease. Therefore, it is preferable to use hydrogen-free O2 gas as the oxygen-containing gas as the oxygen feed gas.

[0069] The method for manufacturing the semiconductor film 12 according to the first embodiment of the present invention is characterized in the positional relationship between the inlet of the gallium raw material gas, the oxygen raw material gas, and the dopant raw material gas and the semiconductor substrate 10 within the reaction chamber 20 of the HVPE apparatus 2.

[0070] Figure 2AThis is a schematic diagram showing the installation state of the semiconductor substrate 10 and the introduction position of the raw material gas according to the first embodiment of the present invention. Figure 2B This is a schematic diagram showing the setup state of the semiconductor substrate 10 in the comparative example and the location of the raw material gas introduction.

[0071] In the first embodiment of the present invention, as Figure 2A As shown, Ga chloride gas and carrier gas (for example, labeled GaCl gas and Ar gas) flow in from the first gas inlet port 21, doped gas and carrier gas (for example, labeled SiCl4 gas and Ar gas) flow in from the second gas inlet port 22, and oxygen gas and carrier gas (for example, labeled O2 gas and Ar gas) flow in from the third gas inlet port 23.

[0072] On the other hand, Figure 2B In the comparative example shown, similar to the conventional HVPE method for growing β-Ga2O3 single crystals, oxygen-containing gas and carrier gas (for example, labeled as O2 gas and Ar gas) flow in from the first gas inlet port 21, dopant gas and carrier gas (for example, labeled as SiCl4 gas and Ar gas) flow in from the second gas inlet port 22, and Ga chloride gas and carrier gas (for example, labeled as GaCl gas and Ar gas) flow in from the third gas inlet port 23.

[0073] The inventors of this invention conducted intensive research and discovered that by setting the introduction position of the raw material gas to... Figure 2A The position shown is the same as the setting. Figure 2B Compared to the situation shown, the number of fatal defects contained in the grown semiconductor film 12 is reduced. This is believed to be because: by making it easiest for oxygen-containing gas to reach the growth substrate 11 and making it least difficult for Ga chloride gas to reach the growth substrate 11, the amount of Ga oxide particles generated in the gas phase and attached to the growth substrate 11 is reduced for some reason.

[0074] That is, when the semiconductor substrate 10 is arranged with the growth substrate surface 11 facing upward, by making the position of the inlet of the doped gas into the space 24 higher than the position of the inlet of the oxygen gas into the space 24, and making the position of the inlet of the Ga chloride gas into the space 24 higher than the position of the inlet of the doped gas into the space 24, the number of fatal defects contained in the grown semiconductor film 12 is reduced.

[0075] [Second Implementation]

[0076] The second embodiment of the present invention differs from the first embodiment in the orientation of the semiconductor substrate 10 disposed within the reaction chamber 20 of the HVPE apparatus 2. Furthermore, descriptions of aspects similar to the first embodiment are sometimes omitted or simplified.

[0077] (Manufacturing method of semiconductor film)

[0078] In the method for manufacturing the semiconductor film 12 according to the second embodiment of the present invention, the semiconductor substrate 10 is disposed on the upper surface side of the space 24 within the reaction chamber 20 with the growth substrate surface 11 facing downward. Here, the growth substrate surface 11 facing downward means that the growth substrate surface 11 faces the ground surface side, and the angle between the growth substrate surface 11 and the horizontal plane is in the range of -5 to +5°.

[0079] Figure 3 This is a schematic diagram showing the installation state of the semiconductor substrate 10 and the introduction position of the raw material gas according to the second embodiment of the present invention.

[0080] In the second embodiment of the present invention, as Figure 3 As shown, the semiconductor substrate 10 is disposed with the growth substrate surface 11 facing downwards. Therefore, oxygen-containing gas and carrier gas (for example, labeled as O2 gas and Ar gas) flow in from the first gas inlet port 21, doped gas and carrier gas (for example, labeled as SiCl4 gas and Ar gas) flow in from the second gas inlet port 22, and Ga chloride gas and carrier gas (for example, labeled as GaCl gas and Ar gas) flow in from the third gas inlet port 23.

[0081] That is, the inlet position of the doped gas into space 24 is higher than the inlet position of the Ga chloride gas into space 24, and the inlet position of the oxygen gas into space 24 is higher than the inlet position of the doped gas into space 24. As a result, the oxygen gas can reach the growth substrate 11 most easily, while the Ga chloride gas is least likely to reach the growth substrate 11, thus reducing the number of fatal defects in the grown semiconductor film 12.

[0082] Furthermore, the Ga oxide particles generated in the gas phase tend to move downwards due to gravity. Therefore, by setting the semiconductor substrate 10 with the growth substrate 11 facing downwards, it is more difficult for the Ga oxide particles to adhere to the growth substrate 11. Thus, according to the semiconductor film manufacturing method of this embodiment, the number of fatal defects contained in the semiconductor film 12 can be further reduced compared to the semiconductor film manufacturing method of the first embodiment.

[0083] Furthermore, as mentioned above, when growing GaN-based crystalline films using the HVPE method, the reaction rate between ammonia and Ga chloride gas is relatively slow, so the formation of GaN-based compound particles in the gas phase is almost negligible. Therefore, when growing GaN-based crystalline films, the generation of many fatal defects is not as significant as in the growth of β-Ga₂O₃-based crystalline films. Additionally, there is essentially no effect on reducing fatal defects by oriented the growth substrate surface downwards. Although the technique of growing GaN-based crystalline films using the HVPE method with the growth substrate surface facing downwards is known (Japanese Patent No. 3376809), its purpose is to suppress thermal convection of the raw material gas near the substrate to grow a uniform thin film.

[0084] Furthermore, it has been confirmed that when the semiconductor substrate 10 is disposed with the growth substrate 11 facing downwards, the dopant absorption rate is higher compared to when the semiconductor substrate 10 is disposed with the growth substrate 11 facing upwards. By disposing the semiconductor substrate 10 with the growth substrate 11 facing downwards, the donor concentration in the semiconductor film 12 becomes approximately equal to the amount of dopant added, thus making it easier to control the donor concentration.

[0085] In addition, by increasing the flow rate of Ga chloride gas, oxygen-containing gas and dopant-containing gas, these raw material gases can easily wash away the Ga oxide particles generated in the gas phase, thereby reducing the amount of Ga oxide particles adhering to the growth substrate 11.

[0086] For example, when a semiconductor film 12 is grown on a circular semiconductor substrate 10 with a diameter of 2 inches, the number of fatal defects contained in the semiconductor film 12 can be significantly reduced by allowing Ga chloride gas, oxygen-containing gas and dopant gas to flow into the space 24 at a flow rate of 110 cm / s or more. Furthermore, the number of fatal defects contained in the semiconductor film 12 can be further reduced by allowing Ga chloride gas, oxygen-containing gas and dopant gas to flow into the space 24 at a flow rate of 165 cm / s or more.

[0087] (Effects of the implementation method)

[0088] According to the above embodiment, the amount of Ga oxide particles formed in the gas phase and attached to the semiconductor substrate 10 in the reaction chamber of the HVPE device can be reduced, thereby reducing fatal defects in the semiconductor film 12, including β-Ga2O3 single crystals. By using the semiconductor film 12 with fewer fatal defects, semiconductor devices with excellent characteristics, such as Schottky barrier diodes with excellent forward current characteristics or reverse leakage current characteristics, can be manufactured with high yield.

[0089] Example

[0090] Figure 4A Through Figure 3 An emission microscope image of the semiconductor film 12 formed by the method of the second embodiment described herein. Figure 4B Through Figure 2B The image shows an emission microscope observation of a semiconductor film formed using a conventional method as a comparative example.

[0091] Figure 4A , Figure 4B The emission microscopy image is formed on the surface of the semiconductor film 12 and the surface of the semiconductor substrate 10 in a non-overlapping manner with anode and cathode electrodes. The image is obtained by taking a picture of the area where the anode electrode is formed from the semiconductor substrate 10 side using a CCD camera. The image is formed by superimposing the pattern image of the circular anode electrode with a diameter of 500μm, which is taken when light is irradiated without applying a voltage between the two electrodes, and the luminescent image taken when a reverse voltage of 200V is applied between the two electrodes (the voltage is positive on the cathode electrode side and negative on the anode electrode side).

[0092] Figure 4B The black dots visible within the circle represent leakage paths that emit light when a reverse voltage is applied, indicating the location of the fatal defect that becomes a leakage path. Figure 4A In the emission microscope image, it is not possible to observe such as Figure 4B Emission microscopy was used to observe such prominent luminescent spots, and the density of these spots was estimated using multiple anodic electrodes, yielding a result of 10 spots / cm³. 2 The density of fatal defects in the semiconductor film 12 of the second embodiment is 10 defects / cm². 2 the following.

[0093] Figure 5A Through Figure 3 An optical microscope image of the surface of the semiconductor film 12 formed by the method of the second embodiment described herein, showing the presence of etch pits. Figure 5B Through Figure 2B The image described is an optical microscope image of the surface of a semiconductor film with etch pits formed by a conventional method, which is used as a comparative example.

[0094] Etching pits are depressions that are formed when the surface of a crystal is etched due to the difference in etching rate between the defective part and other parts. By observing the etching pits, the location and density of the defect can be determined. Figure 5A , Figure 5B The etching pits are formed by immersing the semiconductor film 12 grown on the semiconductor substrate 10 in hot phosphoric acid for 1 hour.

[0095] according to Figure 5B The observed image shows that the etch pit density of the comparative example semiconductor film is approximately 10,000 / cm².2 On the other hand, according to Figure 5A The observed image shows that the etch pit density of the semiconductor film 12 is approximately 2500 / cm². 2 Compared to the etch pit density of the semiconductor film in the comparative example, it is approximately 1 / 4.

[0096] Figure 6 This is a vertical cross-sectional view of the Schottky barrier diode 3, used for evaluating the characteristics of the Schottky barrier diode as described later.

[0097] Schottky barrier diode 3 comprises: a semiconductor substrate 10, which includes a β-Ga2O3 single crystal, and an effective carrier concentration (from donor concentration N) d Subtract the acceptor concentration N a The obtained value is approximately 1 × 10 18 / cm 3 The thickness is approximately 600 μm; the semiconductor film 12 comprises a β-Ga₂O₃ single crystal with an effective carrier concentration of approximately 1 × 10⁻⁶. 16 / cm 3 The thickness is approximately 6 μm; the anode electrode 31 is formed on the surface of the semiconductor film 12 and has a Ni / Au stacked structure; and the cathode electrode 32 is formed on the entire surface of the semiconductor substrate 10 and has a Ti / Ni / Au stacked structure.

[0098] Figure 7A It shows that it has the capability to pass Figure 2A A coordinate graph showing the reverse leakage characteristics of the Schottky barrier diode 3 of the semiconductor film 12 formed by the method of the first embodiment described herein. Figure 7B It shows that it has the capability to pass Figure 3 A coordinate graph showing the reverse leakage characteristics of the Schottky barrier diode 3 of the semiconductor film 12 formed by the method of the second embodiment described herein. Figure 8 It shows that it has the capability to pass Figure 2B The diagram illustrates the reverse leakage characteristics of a Schottky barrier diode 3, which is a comparative example of a semiconductor film formed by a conventional method to replace semiconductor film 12.

[0099] These Figure 7A , Figure 7B , Figure 8 The anode electrode 31 of the Schottky barrier diode 3 is a circular electrode with a diameter of 500 μm.

[0100] exist Figure 7A , Figure 7B , Figure 8 In the above scenario, when a voltage of -200V is applied to the anode electrode, if the leakage current is 1×10⁻⁶... -4 A / cm 2The following is considered "good"; if it exceeds 1×10 -4 A / cm 2 If it is, then it is indicated as "inferior".

[0101] If the proportion of "good" products out of the total is defined as the yield rate, then it has the capability to pass... Figure 2A The Schottky barrier diode 3 formed by the method of the first embodiment described herein has a yield of 78%, and is capable of passing through... Figure 3 The Schottky barrier diode 3 formed by the method of the second embodiment described herein has a yield of 89%, and is capable of passing through... Figure 2B The yield of the Schottky barrier diode 3, which is a comparative example of a semiconductor film formed by the conventional method described herein, is 11%.

[0102] Figures 9A to 9C This indicates that it will have the capability to pass Figure 3 The diagram illustrates the distribution of the breakdown voltage characteristics of the Schottky barrier diode 3 in a 2-inch wafer (a crystal stack structure 1 having multiple anode electrodes 31 and cathode electrodes 32) before the monolithization of the Schottky barrier diode 3 formed by the method of the second embodiment described herein.

[0103] Figures 9A to 9C This diagram shows the semiconductor film 12 of the wafer viewed from vertical above. The values ​​shown indicate the breakdown voltage (voltage when a leakage current of 1 μA flows) of the Schottky barrier diode 3 at that location; negative values ​​indicate the reverse voltage. Furthermore, since the limit for breakdown voltage measurement is -200V, the breakdown voltage of the Schottky barrier diode 3 at the "-200" location in the diagram is below -200V. It can be determined that the Schottky barrier diode 3 at the "-200" location in the diagram has sufficient breakdown voltage.

[0104] Figure 9A The semiconductor film 12 is grown by allowing raw material gases (Ga chloride gas, oxygen-containing gas, and dopant-containing gas) to flow into space 24 at a flow rate of 55 cm / s. Figure 9B The semiconductor film 12 is grown by allowing the raw material gas to flow into the space 24 at a flow rate of 110 cm / s. Figure 9C The semiconductor film 12 is grown by allowing the raw material gas to flow into the space 24 at a flow rate of 165 cm / s. The direction of the arrow in the figure indicates the flow direction of the raw material gas.

[0105] Figures 9A to 9CIt is shown that the higher the flow rate of the raw material gas, the greater the area within the wafer where a Schottky barrier diode 3 with excellent withstand voltage can be obtained. This can be attributed to the following reason: the higher the flow rate of the raw material gas, the easier it is to wash away the Ga oxide particles generated in the gas phase. Therefore, the amount of Ga oxide particles adhering to the growth substrate 11 is reduced, and the fatal defects of the semiconductor film 12 are reduced.

[0106] Furthermore, according to Figures 9A to 9C It is known that when the diameter of the wafer is 2 inches, by allowing the raw material gas to flow into the space 24 at a flow rate of 110 cm / s or more, the number of fatal defects contained in the semiconductor film 12 can be significantly reduced, and by allowing the raw material gas to flow into the space 24 at a flow rate of 165 cm / s or more, the number of fatal defects contained in the semiconductor film 12 can be further reduced.

[0107] However, the higher the flow rate of the raw gas, the more raw gas flows away without contributing to the growth of the semiconductor film 12. As a result, the efficiency of raw gas utilization decreases, and consequently, the manufacturing cost of the semiconductor film 12 increases. Therefore, it is preferable to set the flow rate to an upper limit, such that a Schottky barrier diode 3 with excellent withstand voltage can be obtained in the entire area within the wafer.

[0108] Furthermore, by increasing the size of the wafer from which the Schottky barrier diode 3 is cut, the area where the Schottky barrier diode 3 with excellent withstand voltage can be ensured to be larger by further increasing the flow rate of the raw material gas. For example, when forming a wafer with a diameter of 4 inches, it is sufficient to set the flow rate of the raw material gas to twice that when forming a wafer with a diameter of 2 inches. By allowing the raw material gas to flow into the space 24 at a flow rate of 220 cm / s or more, the number of fatal defects contained in the semiconductor film 12 can be significantly reduced. By allowing the raw material gas to flow into the space 24 at a flow rate of 330 cm / s or more, the number of fatal defects contained in the semiconductor film 12 can be further reduced.

[0109] Figure 10A , Figure 10B They respectively show that they have the capability to pass Figure 3 The diagram shows the reverse and forward characteristics of the Schottky barrier diode 3 formed by the semiconductor film 12 and the 2.3 mm square anode electrode 31 according to the method of the second embodiment described in the text. Figure 10A The dashed line represents the measurement limit. Additionally, Figure 10B The positive characteristic was measured by applying a pulse voltage with a pulse width of 1ms.

[0110] according to Figure 10A It can be seen that even when a voltage of -460V is applied, the leakage current is less than 1μA, demonstrating excellent reverse leakage characteristics. Furthermore, according to... Figure 10B It can be seen that when the applied voltage is above 2.1V, a current of more than 10A flows, resulting in excellent high current characteristics.

[0111] The above describes the embodiments and examples of the present invention. However, the present invention is not limited to the above embodiments and examples, and various modifications can be made without departing from the spirit of the invention. Furthermore, the constituent elements of the above embodiments and examples can be arbitrarily combined without departing from the spirit of the invention.

[0112] Furthermore, the embodiments and examples described above do not limit the invention as defined in the claims. It should also be noted that not all combinations of features described in the embodiments and examples are essential for solving the problems of the invention.

[0113] Industrial availability

[0114] This invention provides semiconductor films with few fatal defects, including β-Ga2O3 single crystals, and methods for their fabrication.

[0115] Explanation of reference numerals in the attached figures

[0116] 1… Crystal stacked structure, 2… HVPE device, 3… Schottky barrier diode, 10… Semiconductor substrate, 11… Growth substrate surface, 12… Semiconductor film, 20… Reaction chamber, 21… First gas inlet port, 22… Second gas inlet port, 23… Third gas inlet port, 24… Space, 31… Anode electrode, 32… Cathode electrode.

Claims

1. A method for manufacturing a semiconductor film, characterized by, Comprising: a process of disposing a semiconductor substrate including a β-Ga2O3-based single crystal into a reaction chamber of an HVPE device with a growth substrate surface facing upward or downward; and a process of flowing a Ga chloride gas, an oxygen-containing gas, and a dopant-containing gas into a space in the reaction chamber in which the semiconductor substrate is disposed, and epitaxially growing a semiconductor film including a β-Ga2O3-based single crystal on a growth substrate surface of the semiconductor substrate, in a case where the semiconductor substrate is disposed with the growth substrate surface facing upward, making a position of a flow inlet of the dopant-containing gas to the space higher than a position of a flow inlet of the oxygen-containing gas to the space, and making a position of a flow inlet of the Ga chloride gas to the space higher than the position of the flow inlet of the dopant-containing gas to the space, in a case where the semiconductor substrate is disposed with the growth substrate surface facing downward, making a position of a flow inlet of the dopant-containing gas to the space higher than a position of a flow inlet of the Ga chloride gas to the space, and making a position of a flow inlet of the oxygen-containing gas to the space higher than the position of the flow inlet of the dopant-containing gas to the space, in the process of disposing the semiconductor substrate, disposing the semiconductor substrate into the reaction chamber with the growth substrate surface facing downward.

2. The method of manufacturing a semiconductor film according to claim 1, wherein the Ga chloride gas is a GaCl gas, the oxygen-containing gas is an O2 gas, the dopant-containing gas is a SiCl4 gas.

3. The method of manufacturing a semiconductor film according to claim 1, wherein in the process of epitaxially growing the semiconductor film, the Ga chloride gas, the oxygen-containing gas, and the dopant-containing gas are flowed into the space at a flow rate of 110 cm / s or more.

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