Method for growing single crystals, method for manufacturing semiconductor substrates, and semiconductor substrates

Abstract

To provide a method for growing a gallium oxide based semiconductor single crystal in an oxygen atmosphere, capable of controlling the state of voids in the single crystal in order to suppress influence on the characteristics of a device manufactured using the grown single crystal; a method for manufacturing a semiconductor substrate using the single crystal grown by the growth method; and a semiconductor substrate manufactured by the manufacturing method.SOLUTION: A method for growing a gallium oxide based semiconductor single crystal comprises the step of growing a single crystal in an oxidizing atmosphere from a melt obtained by melting the raw material of the single crystal. The density and average length of voids in the single crystal are controlled by the relative value of Si and Sn concentrations of the single crystal.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to a method for growing a single crystal, a method for manufacturing a semiconductor substrate, and a semiconductor substrate.

Background Art

[0002] Conventionally, a technique for growing a gallium oxide single crystal by the vertical Bridgman method (VB method) has been known (see, for example, Patent Document 1). In general, the growth of a single crystal of a gallium oxide-based semiconductor by the vertical Bridgman method or the vertical gradient freeze (VGF) method is carried out in an oxidizing atmosphere in order to prevent damage to a crucible made of a Pt-based material.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the melt growth of a gallium oxide-based semiconductor, the melt is likely to be decomposed into Ga2O gas and O₂ gas, and when these are incorporated into the growing crystal, voids are formed. In addition, oxygen ejected at the solid-liquid interface due to the difference in the solid solubility limit of oxygen in the melt and in the crystal forms bubbles, and these bubbles may be incorporated into the growing crystal and become voids. When manufacturing a device using the grown crystal of a gallium oxide-based semiconductor, the voids may affect the device characteristics.

[0005] For example, when growing a sapphire crystal, which is the same high melting point oxide as the gallium oxide-based semiconductor, it is known that the density of voids in the crystal can be reduced by using a reducing gas. However, as described above, the growth of a crystal of a gallium oxide-based semiconductor by the VB method or the like needs to be carried out in an oxidizing atmosphere, and it is not possible to reduce the density of voids by using a reducing gas.

[0006] An object of the present invention is to provide a method for growing a single crystal of a gallium oxide-based semiconductor in an oxygen atmosphere, and a method for growing a single crystal capable of controlling the state of voids in the single crystal in order to suppress the influence on the characteristics of a device manufactured using the grown single crystal, a method for manufacturing a semiconductor substrate using the single crystal grown by the growth method, and a semiconductor substrate manufactured by the manufacturing method.

Means for Solving the Problems

[0007] One aspect of the present invention provides the following method for growing a single crystal, method for manufacturing a semiconductor substrate, and semiconductor substrate in order to achieve the above object.

[0008] [1] A method for growing a single crystal of a gallium oxide-based semiconductor, including a step of growing the single crystal in an oxidizing atmosphere from a melt in which a raw material of the single crystal is melted, and controlling the density and average length of voids in the single crystal by the relative values of the Si concentration and the Sn concentration in the single crystal. [2] By adjusting the value obtained by subtracting the Sn concentration from the Si concentration within a range of -2.8×10 18 ~3.0×10 18 cm -3 , the density and average length of the voids are controlled within ranges of 56 to 57000 cm -2 , 14 to 85 μm, respectively. The method for growing a single crystal according to [1] above. [3] When the Si concentration is less than 4.0×10 18 cm -3 , and the value obtained by subtracting the Sn concentration from the Si concentration is adjusted within a range of -2.8×10 18 ~3.0×10 18 cm -3 , the density and average length of the voids are controlled within ranges of 56 to 57000 cm -2 , 14 to 85 μm, respectively. The method for growing a single crystal according to [1] above. [4] A method for manufacturing a semiconductor substrate made of a single crystal of a gallium oxide semiconductor, comprising the steps of growing the single crystal from a molten liquid in which the raw materials for the single crystal have molten under an oxidizing atmosphere, and cutting the semiconductor substrate from the single crystal, wherein the density and average length of voids in the single crystal are controlled by the relative values ​​of the Si concentration and Sn concentration of the single crystal. [5] A method for manufacturing a semiconductor substrate according to [4] above, wherein the average length of the void is controlled according to the thickness and surface orientation of the semiconductor substrate in order to prevent the void from penetrating between the two main surfaces of the semiconductor substrate. [6] The value obtained by subtracting the Sn concentration from the Si concentration is -2.8 × 10 18 ~3.0×10 18 cm -3 By adjusting within the range, the density and average length of the void can be set to 56-57000 cm, respectively. -2 A method for manufacturing a semiconductor substrate as described in [4] or [5] above, wherein the thickness is controlled within the range of 14 to 85 μm. [7] The Si concentration is 4.0 × 10 18 cm -3 If less than the Si concentration minus the Sn concentration, the value obtained by subtracting the Sn concentration from the Si concentration is -2.8 × 10 18 ~3.0×10 18 cm -3 By adjusting within the range, the density and average length of the void can be set to 56-57000 cm, respectively. -2 A method for manufacturing a semiconductor substrate as described in [4] or [5] above, wherein the thickness is controlled within the range of 14 to 85 μm. [8] A semiconductor substrate made of a single crystal of a gallium oxide semiconductor, wherein the density and average length are 56 to 57,000 cm² -2 A semiconductor substrate containing voids in the range of 14 to 85 μm. [9] The value obtained by subtracting the Sn concentration from the Si concentration is -2.8 × 10 18 ~3.0×10 18 cm -3 The semiconductor substrate described in [8] above, which is within the range 。 [10 The void does not penetrate between the two main surfaces. [8] or [9] The semiconductor substrate described above. [ 11 The Si concentration is 2 × 10 17 cm -3 If the Sn concentration is higher, then the Sn concentration is 2 × 10 16 cm -3 higher, above [9] The semiconductor substrate described above. [Effects of the Invention]

[0009] According to the present invention, a method for growing a gallium oxide-based semiconductor single crystal in an oxygen atmosphere is provided, which allows for the control of the void state in the single crystal in order to minimize the influence on the properties of a device manufactured using the grown single crystal; a method for manufacturing a semiconductor substrate using the single crystal grown by this method is provided; and a semiconductor substrate manufactured by this manufacturing method is provided. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a vertical cross-sectional view schematically showing the configuration of a single crystal growth apparatus used in the VB method. [Figure 2] Figure 2 is an optical microscope image of a cross-section of a semiconductor substrate with the (010) plane as the main surface according to this embodiment. [Figure 3] Figure 3 shows optical microscope images of cross-sections of four types of semiconductor substrates according to this embodiment. [Figure 4] Figure 4 is a graph showing the relationship between the concentrations of the dopants Si and Sn and the density of voids in the semiconductor substrate. [Figure 5] Figure 5 is a graph showing the relationship between the concentrations of the dopants Si and Sn and the average length of voids in the semiconductor substrate. [Figure 6] Figure 6 is a graph showing the relationship between void density and average length in a semiconductor substrate. [Modes for carrying out the invention]

[0011] A method for growing a single crystal according to an embodiment of the present invention (hereinafter referred to as "this growth method") is a method for growing a single crystal of a gallium oxide semiconductor, comprising the step of growing the single crystal from a molten single crystal raw material under an oxidizing atmosphere, and controlling the density and average length of voids in the single crystal by the relative values ​​of the Si concentration and Sn concentration of the single crystal. Here, gallium oxide semiconductor refers to β-Ga2O3, or β-Ga2O3 containing substitutional impurities such as Al and In, or dopants such as Sn and Si.

[0012] This growth method employs techniques for growing gallium oxide-based semiconductor single crystals in an oxygen atmosphere, such as the vertical Bridgman method (VB method) or the vertical temperature gradient solidification method (VGF method).

[0013] In these methods, under a reducing atmosphere, the melt becomes Ga-rich (high proportion of Ga). Therefore, when using crucibles made of Pt-based materials such as PtRh and PtIr, the crucible and Ga alloy together, lowering the melting point of the crucible. This can lead to the crucible breaking during growth and the melt leaking out.

[0014] In this crystal growth method, since single crystals are grown under an oxygen atmosphere, it is not possible to reduce the density of voids using a reducing gas during growth, as is done with sapphire single crystals. Therefore, after diligent research, the inventors have discovered that the density and average length of voids in a single crystal can be controlled by the relative values ​​of the Si concentration and Sn concentration in the single crystal. This crystal growth method utilizes this technique for controlling the density and length of voids in a single crystal to suppress the adverse effects of voids.

[0015] When cutting semiconductor substrates from grown single crystals, it is especially important to avoid voids penetrating between the two main surfaces of the semiconductor substrate (between the front and back surfaces). A high-quality epitaxial film cannot be deposited on areas where voids penetrating between the two main surfaces exist, and abnormal regions in the epitaxial film formed locally by the voids become pathways for leakage current. On the other hand, the higher the density of voids in the single crystal, the greater the impact on the properties of the device manufactured using that single crystal; therefore, a lower void density in the single crystal is preferable.

[0016] In this growth method, for example, the value obtained by subtracting the Sn concentration from the Si concentration of the single crystal is -2.8 × 10⁻⁶. 18 ~3.0×10 18 cm -3 By adjusting within this range, the density and average length of voids in the single crystal can be set to 56-57,000 cm², respectively. -2 It can be controlled within the range of 14 to 85 μm. Note that the value obtained by subtracting the Sn concentration from the Si concentration of the single crystal is -2.8 × 10⁻⁶. 18 ~3.0×10 18 cm -3 To keep it within this range, for example, the concentrations of Si and Sn in the raw materials for the single crystal are adjusted to be within the ranges of 0 to 0.03 atomic percent and 0 to 0.1 atomic percent, respectively, relative to Ga.

[0017] Here, when the density of voids in a single crystal decreases, the length of the voids tends to increase, and conversely, when the length of the voids in a single crystal decreases, the density tends to increase. Therefore, for example, the density and length of voids in a single crystal can be controlled to be as low as possible, within a range where the voids have a length that makes it difficult for them to penetrate between the two main surfaces of the semiconductor substrate cut from the single crystal.

[0018] Voids that occur in a single crystal of gallium oxide semiconductor are needle-shaped voids that extend in the

[0010] direction of the gallium oxide semiconductor crystal. Therefore, when cutting a semiconductor substrate from a single crystal with the (010) plane, where the

[0010] direction is the thickness direction, as the main surface, voids are most likely to penetrate between the two main surfaces. In this case, for example, by controlling the average length of the voids to be smaller than the thickness of the semiconductor substrate, it is possible to suppress voids from penetrating between the two main surfaces.

[0019] When cutting a semiconductor substrate from a single crystal with a main surface having a large inclination from the (010) plane, the inclination from the thickness direction of the semiconductor substrate in the direction in which the void extends becomes large, so the length of the void can be set to be large in order to suppress the void from penetrating between the two main surfaces.

[0020] Thus, in this growth method, in order to suppress voids contained in the semiconductor substrate from penetrating between the two main surfaces of the semiconductor substrate, the relative values ​​of the Si concentration and Sn concentration of the single crystal can be adjusted to control the average length of voids in the single crystal according to the thickness and plane orientation of the semiconductor substrate.

[0021] The following describes a method for growing single crystals using the VB method as an example.

[0022] (Single crystal growth apparatus) Figure 1 is a schematic vertical cross-sectional view showing the configuration of a single crystal growth apparatus 1 used in the VB method. The single crystal growth apparatus 1 comprises a crucible 10, a vertically movable susceptor 11 that supports the crucible 10 from below, a tubular core tube 14 surrounding the crucible 10, the susceptor 11, and the crucible support shaft 12, a heater 13 installed on the outside of the core tube 14, and a housing 15 made of thermal insulation material that houses these components of the single crystal growth apparatus 1.

[0023] The crucible 10 has a seed crystal section 101 for containing seed crystals 20, and a growth crystal section 102 located above the seed crystal section 101 for crystallizing the contained raw material melt 21 and growing a single crystal 22 of gallium oxide semiconductor.

[0024] The growing crystal portion 102 typically comprises a constant diameter portion having a constant inner diameter larger than the inner diameter of the seed crystal portion 101, as shown in Figure 1, and an increasing diameter portion located between the constant diameter portion and the seed crystal portion 101, where the inner diameter increases from the seed crystal portion 101 side toward the constant diameter portion side.

[0025] The crucible 10 has a shape and size corresponding to the shape and size of the single crystal 22 to be grown. For example, when growing a single crystal 22 with a cylindrical diameter section of 2 inches, a crucible 10 with a cylindrical diameter section of 2 inches in the growth crystal section 102 is used. When growing a single crystal 22 with a diameter section of a shape other than cylindrical, such as a rectangular prismatic or hexagonal prismatic shape, a crucible 10 with a rectangular prismatic or hexagonal prismatic diameter section of the growth crystal section 102 is used. A lid may be used to cover the opening of the crucible 10.

[0026] The crucible 10 is made of a material that has heat resistance to withstand the temperature of the molten gallium oxide semiconductor (a temperature above the melting point of the gallium oxide semiconductor), which is the raw material molten 21, and is not easily reacted with the molten gallium oxide semiconductor, such as a PtRh alloy.

[0027] The susceptor 11 is a tubular member that surrounds the seed crystal portion 101 of the crucible 10 and supports the crucible 10 from below. The susceptor 11 is made of a material that has heat resistance capable of withstanding the growth temperature of a gallium oxide semiconductor single crystal and does not react with the crucible 10 at that growth temperature, such as zirconia or alumina.

[0028] A crucible support shaft 12 is connected to the lower side of the susceptor 11. By moving the crucible support shaft 12 vertically using a drive mechanism (not shown), the susceptor 11 and the crucible 10 supported by the susceptor 11 can be moved vertically. The crucible support shaft 12 may also be capable of rotation around a vertical axis by the drive mechanism. In this case, the crucible 10 supported by the susceptor 11 can be rotated inside the reactor tube 14.

[0029] The crucible support shaft 12 is typically a tubular member, similar to the susceptor 11. In this case, thermocouples for measuring the temperature of the crucible 10 can be passed inside the susceptor 11 and the crucible support shaft 12. The crucible support shaft 12 is made of a heat-resistant material capable of withstanding the growth temperature of a gallium oxide semiconductor single crystal, such as zirconia or alumina.

[0030] The heater 13 is used to melt the gallium oxide semiconductor raw material contained in the growth crystal section 102 of the crucible 10 to obtain a raw material melt 21. The heater 13 is inserted into the housing 15 through a hole provided in the housing 15 and is connected to an external device (not shown) outside the housing 15 to supply current to the heater 13. The heater 13 is typically a MoSi2 heater, which is a resistance heating element made of MoSi2. MoSi2 heaters have excellent oxidation resistance and heat resistance and can be used in an oxidizing atmosphere at a high temperature of approximately 1800°C, which is necessary for growing single crystals of gallium oxide semiconductors.

[0031] The core tube 14 is used to regulate the heat flow around the crucible 10 and to suppress the intrusion of impurities such as Si and Mo from the heater 13. The core tube 14 is typically cylindrical. Alternatively, as shown in Figure 1, a lid 17 may be installed at the upper opening of the core tube 14. By using the lid 17, the upward escape of heat around the crucible 10 can be suppressed. The core tube 14 and lid 17 are made of a heat-resistant material that can withstand the growth temperature of gallium oxide semiconductor single crystals, such as zirconia or alumina.

[0032] (Single crystal growth process) First, seed crystals 20 of a gallium oxide semiconductor are placed in the seed crystal section 101 of the crucible 10, and raw materials for a single crystal of the gallium oxide semiconductor are placed in the growth crystal section 102. Here, for example, the concentrations of Si and Sn in the raw materials for the single crystal are adjusted to within the range of 0 to 0.03 atomic percent and 0 to 0.1 atomic percent relative to Ga, respectively. As raw materials for the single crystal, for example, a sintered body of Ga2O3 with added Si or Sn can be used, which is obtained by mixing SiO2 powder or SiC powder as a Si raw material, or SnO2 powder as a Sn raw material, with Ga2O3 powder and heating it. Alternatively, a sintered body of Ga2O3, a sintered body of SiO2 or SiC, and a sintered body of SnO2 may be used as raw materials for the single crystal.

[0033] Next, the heater 13 heats the inside of the single crystal growth apparatus 1 (the inside of the housing 15), creating a temperature gradient where the temperature is higher at the top and lower at the bottom, thereby melting the single crystal raw material in the crucible 10 to obtain the raw material melt 21.

[0034] In a typical method, the crucible support shaft 12 is first moved up and down to adjust the height of the crucible 10 so that the temperature of the upper region within the growth crystal section 102 is above the melting point of gallium oxide. This causes a portion of the upper raw material within the growth crystal section 102 to melt. Next, the crucible support shaft 12 is moved upward at a predetermined speed, raising the crucible 10 at a predetermined speed while melting the raw material down to the bottom, ultimately melting the entire raw material and a portion of the seed crystal.

[0035] Next, the crucible support shaft 12 is moved downward, and the crucible 10 is lowered at a predetermined speed, allowing the molten raw material 21 to crystallize from the bottom (seed crystal 20 side) and grow a single crystal 22. The above single crystal growth is carried out in an oxidizing atmosphere. After the entire molten raw material 21 has crystallized, the single crystal 22 is removed from the crucible 10.

[0036] Subsequently, the obtained single crystal 22 is sliced ​​in a desired direction and at a desired interval using a multi-wire saw or the like, and the surface is polished to obtain a semiconductor substrate of a desired thickness with a desired surface orientation as the main plane.

[0037] (Evaluation results) The following shows the results of various evaluations performed on semiconductor substrates (hereinafter simply referred to as semiconductor substrates) cut from β-Ga2O3 single crystals obtained by this growth method using the VB method.

[0038] Table 1 shows the concentrations of Si and Sn in the five types of semiconductor substrates manufactured for this evaluation, and the Si and Sn concentrations in the raw materials of the single crystals from which the semiconductor substrates were cut. In Table 1, "Si concentration" and "Sn concentration" refer to the Si concentration and Sn concentration in the raw materials of the single crystal, respectively. "Si-Sn concentration" means the Si concentration minus the Sn concentration. Also, "UID: Unintentional Doped" means that the dopant was not intentionally added.

[0039] JPEG0007867275000001.jpg60170

[0040] In this evaluation, as shown in Table 1, the concentrations of Si and Sn that are not intentionally added are considered to be the concentrations of Si and Sn that inevitably become mixed into the semiconductor substrate, respectively, as 2 × 10⁻⁶. 17 cm -3 and 2 × 10 16 cm -3 The results were as follows:

[0041] According to Table 1, the Si concentration is 2 × 10⁻⁶ 18 cm -3 The sample and Si concentration are 3 × 10 18 cm -3 Although the Si concentration in both samples is the same at 0.03 at%, this is because these two samples were cut from regions of the same single crystal that have different Si concentrations.

[0042] Figure 2 is an optical microscope image of a cross-section of a semiconductor substrate with the (010) plane as the main plane according to this embodiment. The cross-section shown in Figure 2 is the (100) plane, and the vertical direction of the image in Figure 2 is the

[0010] direction of the β-Ga2O3 single crystal. Figure 2 shows that the semiconductor substrate contains multiple needle-shaped voids extending in the

[0010] direction.

[0043] Figure 3 shows optical microscope images of cross-sections of four types of semiconductor substrates according to this embodiment. The upper left image is the same as that shown in Figure 2, and is an image of the (100) cross-section of a semiconductor substrate with the (010) plane as the main surface, in which no dopant has been intentionally added. The upper right image shows a concentration of 3 × 10⁻⁶ 18 cm -3 This is an observation image of the (100) cross-section of a semiconductor substrate whose main surface is the (010) plane containing Si. The observation image in the lower left shows a density of 3 × 10⁻¹⁰ 18 cm -3 This is an observation image of a (100) cross-section of a semiconductor substrate whose main surface is the (011) plane containing Sn. The observation image in the lower right shows a density of 8 × 10⁻¹⁰. 17 cm -3 Si and concentration 3 × 10 18 cm -3 This is an observation image of the (100) cross-section of a semiconductor substrate whose main surface is the (011) plane containing Sn.

[0044] Figure 3 shows that the density and size of voids in the semiconductor substrate differ depending on the type of dopant contained in the semiconductor substrate, i.e., Si, Sn, or both Si and Sn.

[0045] Figure 4 is a graph showing the relationship between the concentrations of the dopants Si and Sn and the density of voids in the semiconductor substrate. The horizontal axis of Figure 4, "Si-Sn concentration," represents the Si concentration minus the Sn concentration. The density of voids in the semiconductor substrate was calculated by measuring the number of voids in a predetermined region of the (100) cross-section. The area of ​​the predetermined region is shown as "Observation Area" in Table 2 below.

[0046] Figure 4 shows that the Si-Sn concentration is at least -2.8 × 10⁻⁶ 18 ~3.0×10 18 cm -3 Within this range, the void density decreases as the Si concentration relative to the Sn concentration increases, and increases as the Sn concentration relative to the Si concentration increases.

[0047] Figure 5 is a graph showing the relationship between the concentrations of the dopants Si and Sn and the average length of voids in the semiconductor substrate. The horizontal axis of Figure 5, "Si-Sn concentration," represents the Si concentration minus the Sn concentration. The average length of voids in the semiconductor substrate was obtained by measuring the length of voids within a predetermined region of the (100) cross-section and taking the average value.

[0048] Figure 5 shows that the Si-Sn concentration is at least -2.8 × 10⁻⁶ 18 ~3.0×10 18 cm -3 Within this range, it is shown that as the Si concentration relative to the Sn concentration increases, the average length of the voids increases, and as the Sn concentration relative to the Si concentration increases, the average length of the voids decreases.

[0049] Table 2 shows the Si-Sn concentration of the evaluated semiconductor substrate, the corresponding void density and average length, and the observation area of ​​the semiconductor substrate cross-section used to calculate the void density and average length, as well as the number of voids observed.

[0050] JPEG0007867275000002.jpg122170

[0051] The results shown in Figures 4 and 5 demonstrate that the density and average length of voids contained in the single crystal and the semiconductor substrate cut from it can be controlled by the magnitude of the value obtained by subtracting the Sn concentration from the Si concentration. On the other hand, the donor concentration of the single crystal and semiconductor substrate depends on the sum of the Si and Sn concentrations. Therefore, by intentionally adding both Si and Sn, it is possible to control the density and average length of voids while obtaining the desired donor concentration. Note that when Si and Sn are intentionally added, the concentrations of Si and Sn, respectively, are higher than the concentrations that would occur if they were unintentionally mixed in; for example, the Si concentration is 2 × 10⁻⁶ 17 cm -3 The Sn concentration is 2 × 10 16 cm -3It will become even higher. Specifically, the donor concentration of single crystals and semiconductor substrates is the sum of the Si and Sn concentrations minus the Fe concentration that compensates for the donor. This Fe is mixed into the single crystal from crucible 10, and approximately 1 × 10⁻⁶ Fe is present in the single crystal and semiconductor substrate. 17 cm -3 It exists at the following concentrations.

[0052] Figure 6 is a graph showing the relationship between void density and average length in a semiconductor substrate. Figure 6 shows the relationship between void density of at least 56-57000 cm². -2 This indicates that, within the range of 14 to 85 μm for the average void length, a decrease in void density leads to a larger average void length, and conversely, a decrease in average void length leads to a larger void density.

[0053] According to the evaluation results above, at least the value obtained by subtracting the Sn concentration from the Si concentration is -2.8 × 10⁻⁶. 18 ~3.0×10 18 cm -3 It is within the range of 56-57,000 cm², with density and average length being 56-57,000 cm². -2 It is possible to manufacture semiconductor substrates containing voids in the range of 14 to 85 μm. Furthermore, by controlling the average length of voids in the single crystal according to the thickness and plane orientation of the semiconductor substrate, it is also possible to obtain a semiconductor substrate in which voids do not penetrate between the two main planes.

[0054] Note that the Si concentration is 4.0 × 10 18 cm -3 At this level, it has been observed that large voids, which are thought to be densely packed voids, tend to form in the single crystal. Therefore, when the Si concentration is 4.0 × 10⁻⁶ 18 cm -3 Beyond this point, the relationship between the value obtained by subtracting the Sn concentration from the Si concentration and the void density, and the relationship between the value obtained by subtracting the Sn concentration from the Si concentration and the average length of the voids, may no longer hold true. On the other hand, if the Si concentration is within the range shown in Table 1 (3.0 × 10⁻⁶ 18 cm -3If the following conditions are met, then large voids will not occur in the single crystal, and the relationship between the value obtained by subtracting the Sn concentration from the Si concentration and the void density, and the relationship between the value obtained by subtracting the Sn concentration from the Si concentration and the average length of the voids will definitely hold true. Therefore, the Si concentration is 4.0 × 10 18 cm -3 Smaller is preferable, 3.0 × 10 18 cm -3 The following is more preferable:

[0055] The above evaluations were performed on semiconductor substrates cut from single crystals of β-Ga2O3, a typical example of a gallium oxide-based semiconductor. However, similar results can be obtained when evaluating semiconductor substrates cut from single crystals of other gallium oxide-based semiconductors. Furthermore, similar results can be obtained when evaluating semiconductor substrates cut from single crystals grown using methods other than the VB method, such as the VGF method, which involves growing single crystals in an oxygen atmosphere.

[0056] (Effects of the embodiment) According to the above embodiment of the present invention, in a method for growing a single crystal in an oxygen atmosphere where void density cannot be reduced by a reducing gas, it is possible to control the density and length of voids contained in the gallium oxide-based semiconductor single crystal being grown, thereby suppressing the influence of voids on the characteristics of devices manufactured using semiconductor substrates cut from the single crystal.

[0057] Although embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the invention. Furthermore, the components of the above embodiments can be arbitrarily combined without departing from the spirit of the invention. Moreover, the embodiments described above do not limit the invention as claimed. It should also be noted that not all combinations of features described in the embodiments are necessarily essential for solving the problem of the invention. [Explanation of Symbols]

[0058] 1...Single crystal growth apparatus, 10...Crucible, 101...Seed crystal section, 102...Growing crystal section, 11...Susceptor, 13...Heater, 20...Seed crystal, 21...Melting raw material, 22...Single crystal

Claims

1. A method for growing single crystals of gallium oxide semiconductors, The process includes growing the single crystal from a molten liquid containing the raw materials for the single crystal under an oxidizing atmosphere. The density and average length of voids in the single crystal are controlled by the relative values ​​of the Si concentration and Sn concentration of the single crystal. Methods for growing single crystals.

2. The value obtained by subtracting the Sn concentration from the Si concentration is -2.8 × 10 １８ ~3.0 x 10 １８ cm －３ By adjusting within the range, the density and average length of the void can be set to 56 to 57,000 cm². －２ , controlled within the range of 14 to 85 μm. A method for growing a single crystal according to claim 1.

3. The Si concentration is less than 4.0×10 １８ cm －３ and the value obtained by subtracting the Sn concentration from the Si concentration is adjusted within the range of -2.8×10 １８ to 3.0×10 １８ cm －３ so that the density and average length of the voids are controlled within the ranges of 56 to 57000 cm －２ and 14 to 85 μm, respectively. A method for growing a single crystal according to claim 1.

4. A method for manufacturing a semiconductor substrate made of a single crystal of a gallium oxide semiconductor, The process involves growing the single crystal from a molten liquid containing the raw materials for the single crystal under an oxidizing atmosphere, A step of cutting the semiconductor substrate from the single crystal, Includes, The density and average length of voids in the single crystal are controlled by the relative values ​​of the Si concentration and Sn concentration of the single crystal. A method for manufacturing semiconductor substrates.

5. In order to prevent the void from penetrating between the two main surfaces of the semiconductor substrate, the average length of the void is controlled according to the thickness and surface orientation of the semiconductor substrate. A method for manufacturing a semiconductor substrate according to claim 4.

6. The value obtained by subtracting the Sn concentration from the Si concentration is -2.8 × 10 １８ ~3.0 x 10 １８ cm －３ By adjusting within the range, the density and average length of the void can be set to 56 to 57,000 cm². －２ , controlled within the range of 14 to 85 μm. A method for manufacturing a semiconductor substrate according to claim 4 or 5.

7. The aforementioned Si concentration is 4.0 × 10 １８ cm －３ If less than the Si concentration minus the Sn concentration, the value obtained by subtracting the Sn concentration from the Si concentration is -2.8 × 10 １８ ~3.0 x 10 １８ cm －３ By adjusting within the range, the density and average length of the void can be set to 56 to 57,000 cm². －２ , controlled within the range of 14 to 85 μm. A method for manufacturing a semiconductor substrate according to claim 4 or 5.

8. A semiconductor substrate made of a single crystal of a gallium oxide-based semiconductor, Density and average length are 56 to 57,000 cm², respectively. －２ , containing voids in the range of 14 to 85 μm, Semiconductor substrate.

9. The value obtained by subtracting the Sn concentration from the Si concentration is -2.8 × 10⁻⁶. １８ ~3.0 x 10 １８ cm －３ Within the range, The semiconductor substrate according to claim 8.

10. The void does not penetrate between the two main surfaces. The semiconductor substrate according to claim 8 or 9.

11. The Si concentration is 2 × 10 １７ cm －３ If the Sn concentration is higher, then the Sn concentration is 2 × 10 １６ cm －３ higher, The semiconductor substrate according to claim 9.

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