Method for growing single crystal, method for manufacturing semiconductor substrate, and semiconductor substrate

Abstract

Provided is a method for growing a single crystal of a gallium oxide semiconductor, the method including a step for growing a single crystal in an oxidizing atmosphere from a melt obtained by melting a raw material of the single crystal, and the density and the average length of voids in the single crystal being controlled by the relative value between the Si concentration and the Sn concentration of the single crystal.

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 (for example, refer to Patent Document 1). Generally, in order to prevent breakage of a crucible including a Pt-based material, etc., 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.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2020-164415 Summary of the Invention

[0006] Problems to be Solved by the Invention

[0007] In the melt growth of a gallium oxide-based semiconductor, the melt is liable to decompose into Ga 2 O gas and O 2 gas. If they are taken into the crystal during the growth process, voids will be formed. In addition, there is also a case where oxygen discharged to the solid-liquid interface due to the difference in the solid solubility limit of oxygen in the melt and the crystal forms bubbles, and these bubbles are taken into the crystal that is growing and become voids. When manufacturing a device using the crystal of the gallium oxide-based semiconductor grown, the voids may affect the device characteristics.

[0008] For example, it is known that in the case of growing a crystal of sapphire, which is also a high-melting-point oxide like the gallium oxide-based semiconductor, by using a reducing gas, the density of voids in the crystal can be reduced. However, as described above, the growth of a crystal of a gallium oxide-based semiconductor by the VB method, etc. needs to be carried out in an oxidizing atmosphere, and a reducing gas cannot be used to reduce the density of voids.

[0009] An object of the present invention is to provide a method for growing a single crystal, a method for manufacturing a semiconductor substrate using the single crystal grown by this growth method, and a semiconductor substrate manufactured by this manufacturing method. The method for growing a single crystal is a method for growing a single crystal of a gallium oxide-based semiconductor in an oxygen atmosphere, and can control the state of voids in the single crystal to suppress the influence on the characteristics of a device manufactured using the grown single crystal.

[0010] Solutions to Solve the Problems

[0011] To achieve the above object, one aspect of the present invention provides the following single crystal cultivation method, semiconductor substrate manufacturing method, and semiconductor substrate.

[0012] [1] A method for cultivating a single crystal, which is a method for cultivating a single crystal of a gallium oxide-based semiconductor, includes a step of growing the single crystal from a melt formed by melting the raw material of the single crystal in an oxidizing atmosphere, and controlling the density and average length of voids in the single crystal by the relative value of the Si concentration and the Sn concentration in the single crystal.

[0013] [2] The method for cultivating a single crystal according to the above [1], wherein the value obtained by subtracting the Sn concentration from the Si concentration is adjusted within the range of -2.8×10 18 ~3.0×10 18 cm -3 so as to control the density and average length of the voids within the ranges of 56~57000 cm -2 and 14~85 μm, respectively.

[0014] [3] The method for cultivating a single crystal according to the above [1], wherein the Si concentration is within the range of 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 ~3.0×10 18 cm -3 so as to control the density and average length of the voids within the ranges of 56~57000 cm -2 and 14~85 μm, respectively.

[0015] [4] A method for manufacturing a semiconductor substrate, which is a method for manufacturing a semiconductor substrate including a single crystal of a gallium oxide-based semiconductor, includes: a step of growing the single crystal from a melt formed by melting the raw material of the single crystal in an oxidizing atmosphere; and a step of cutting out the semiconductor substrate from the single crystal, and controlling the density and average length of voids in the single crystal by the relative value of the Si concentration and the Sn concentration in the single crystal.

[0016] [5] The method for manufacturing a semiconductor substrate according to the above [4], wherein in order to suppress the voids from penetrating between the two main surfaces of the semiconductor substrate, the average length of the voids is controlled according to the thickness and plane orientation of the semiconductor substrate.

[0017] [6] The method for manufacturing a semiconductor substrate according to the above [4] or [5], wherein the value obtained by subtracting the Sn concentration from the Si concentration is adjusted within the range of -2.8×10 18 ~3.0×10 18cm -3 within the range of to adjust the density and average length of the voids to be controlled within the ranges of 56 to 57000 cm -2 and 14 to 85 μm, respectively.

[0018] [7] The method for manufacturing a semiconductor substrate according to the above [4] or [5], wherein the Si concentration is adjusted within the range of 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 to adjust the density and average length of the voids to be controlled within the ranges of 56 to 57000 cm -2 and 14 to 85 μm, respectively.

[0019] [8] A semiconductor substrate comprising a single crystal of a gallium oxide-based semiconductor, wherein the value obtained by subtracting the Sn concentration from the Si concentration is in the range of -2.8×10 18 to 3.0×10 18 cm -3 and includes voids having a density and average length in the ranges of 56 to 57000 cm -2 and 14 to 85 μm, respectively.

[0020] [9] The semiconductor substrate according to the above [8], wherein the voids do not penetrate between the two main surfaces.

[0021]

[10] The semiconductor substrate according to the above [8] or [9], wherein the Si concentration is higher than 2×10 17 cm -3 and the Sn concentration is higher than 2×10 16 cm -3 .

[0022] Advantages of the Invention

[0023] According to the present invention, it is possible to provide a method for growing a single crystal, a method for manufacturing a semiconductor substrate using the single crystal grown by the growing method, and a semiconductor substrate manufactured by the manufacturing method. The method for growing a single crystal is a method for growing a single crystal of a gallium oxide-based semiconductor in an oxygen atmosphere, and can control the state of voids in the single crystal to suppress the influence on the characteristics of a device manufactured using the grown single crystal. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a vertical cross-sectional view schematically showing the configuration of a single crystal growth apparatus used in the VB method.

[0025] Figure 2 This is an observation image obtained by observing, through an optical microscope, a cross-section of a semiconductor substrate having a (010) plane as a main plane in the present embodiment.

[0026] Figure 3 These are observation images obtained by observing, through an optical microscope, cross-sections of four types of semiconductor substrates in the present embodiment.

[0027] Figure 4 This is a coordinate diagram showing the relationship between the concentrations of Si and Sn as dopants and the density of voids in a semiconductor substrate.

[0028] Figure 5 This is a coordinate diagram showing the relationship between the concentrations of Si and Sn as dopants and the average length of voids in a semiconductor substrate.

[0029] Figure 6 This is a coordinate diagram showing the relationship between the density and the average length of voids in a semiconductor substrate. Detailed Embodiment

[0030] The 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-based semiconductor, and includes a step of growing the single crystal from a melt obtained by melting a raw material of the single crystal in an oxidizing atmosphere, and controlling the density and the average length of voids in the single crystal by the relative values of the Si concentration and the Sn concentration of the single crystal. Here, the gallium oxide-based semiconductor means β-Ga 2 O 3 or β-Ga containing substitutional impurities such as Al and In or dopants such as Sn and Si 2 O 3 .

[0031] This growth method uses a method for growing a single crystal of a gallium oxide-based semiconductor in an oxygen atmosphere, such as the vertical Bridgman method (VB method) or the vertical gradient freeze method (VGF method).

[0032] In these methods, since the melt becomes a state rich in Ga (high ratio of Ga) in a reducing atmosphere, when using a crucible made of a Pt-based material such as PtRh or PtIr, there is a possibility that the crucible is alloyed with Ga and the melting point of the crucible drops, and the crucible is damaged during the growth process and the melt leaks.

[0033] In this cultivation method, since single crystal cultivation is carried out in an oxygen atmosphere, it is impossible to use a reducing gas during cultivation to reduce the density of voids as in the case of sapphire single crystals. Therefore, the inventors of the present invention conducted intensive research and found that the density and average length of voids in a single crystal can be controlled by the relative values of the Si concentration and the Sn concentration in the single crystal. In this cultivation method, a technique for controlling the density and length of voids in the single crystal is used to suppress the adverse effects caused by the voids.

[0034] When cutting out a semiconductor substrate from the cultivated single crystal, it is particularly important to avoid voids penetrating between the two main surfaces (front and back surfaces) of the semiconductor substrate. High-quality epitaxial films cannot be formed on the part where voids penetrate between the two main surfaces, and abnormal regions locally formed in the epitaxial film due to the voids become paths for leakage current. On the other hand, since the greater the density of voids in the single crystal, the greater the impact on the characteristics of the device manufactured using the single crystal, it is preferable that the density of voids in the single crystal is low.

[0035] In this cultivation method, for example, by adjusting the value obtained by subtracting the Sn concentration from the Si concentration in the single crystal within the range of -2.8×10 18 ~3.0×10 18 cm -3 , the density and average length of voids in the single crystal can be controlled within the ranges of 56~57000 cm -2 and 14~85 μm, respectively. In addition, in order to make the value obtained by subtracting the Sn concentration from the Si concentration in the single crystal fall within the range of -2.8×10 18 ~3.0×10 18 cm -3 , for example, the addition concentrations of Si and Sn in the raw material of the single crystal are adjusted within the ranges of 0~0.03 atomic % and 0~0.1 atomic % relative to Ga, respectively.

[0036] Here, there is a tendency that when the density of voids in the single crystal becomes low, the length of the voids becomes large, and conversely, when the length of the voids in the single crystal becomes small, the density becomes high. Therefore, for example, the density and length of voids in the single crystal can be controlled in such a way that the density is made as low as possible within the range where the voids have a length such that it is difficult to penetrate between the two main surfaces of the semiconductor substrate cut out from the single crystal.

[0037] The voids generated in the single crystal of the gallium oxide-based semiconductor are needle-shaped voids extending in the

[010] direction of the gallium oxide-based semiconductor crystal. Therefore, in the case of cutting out a semiconductor substrate having the (010) plane as the main plane with the

[010] direction as the thickness direction from the single crystal, the voids are most likely to penetrate between the two main planes. 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 the voids from penetrating between the two main planes.

[0038] In the case of cutting out a semiconductor substrate having a plane with a large inclination with respect to the (010) plane as the main plane from the single crystal, the inclination of the direction in which the voids extend with respect to the thickness direction of the semiconductor substrate becomes larger. Therefore, the length of the voids for suppressing the voids from penetrating between the two main planes can be set large.

[0039] Thus, in this cultivation method, in order to suppress the voids contained in the semiconductor substrate from penetrating between the two main planes of the semiconductor substrate, the relative value of the Si concentration and the Sn concentration of the single crystal can be adjusted, and the average length of the voids in the single crystal can be controlled according to the thickness and the plane orientation of the semiconductor substrate.

[0040] Hereinafter, as an example, a method for cultivating a single crystal by the VB method will be described.

[0041] (Single crystal cultivation apparatus)

[0042] Figure 1 It is a vertical cross-sectional view schematically showing the configuration of a single crystal cultivation apparatus 1 used in the VB method. The single crystal cultivation apparatus 1 includes: a crucible 10; a susceptor 11 that supports the crucible 10 from below and can move in the vertical direction; a tubular furnace core tube 14 that surrounds the crucible 10, the susceptor 11, and the crucible support shaft 12; a heater 13 that is provided outside the furnace core tube 14; and a housing 15 that includes a heat insulating material and houses these constituent members of the single crystal cultivation apparatus 1.

[0043] The crucible 10 has: a seed crystal portion 101 that houses a seed crystal 20; and a growing crystal portion 102 that is located above the seed crystal portion 101 and crystallizes the contained raw material melt 21 to grow a single crystal 22 of a gallium oxide-based semiconductor.

[0044] The growing crystal portion 102 typically has, as Figure 1 shown: a sizing portion having a fixed inner diameter larger than the inner diameter of the seed crystal portion 101; and a diameter increasing portion that is located between the sizing portion and the seed crystal portion 101 and whose inner diameter increases from the seed crystal portion 101 side toward the sizing portion side.

[0045] 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 sizing part having a diameter of 2 inches, a crucible 10 with a cylindrical sizing part having an inner diameter of 2 inches in the crystal growth part 102 is used. In addition, when growing a single crystal 22 with a sizing part having a shape other than cylindrical, such as a quadrangular prism or a hexagonal prism, a crucible 10 with a sizing part having a quadrangular prism or hexagonal prism shape in the crystal growth part 102 is used. In addition, a lid covering the opening of the crucible 10 may also be used.

[0046] The crucible 10 includes a material such as a PtRh alloy that has heat resistance capable of withstanding the temperature of the melt of the gallium oxide-based semiconductor as the raw material melt 21 (a temperature above the melting point of the gallium oxide-based semiconductor) and is difficult to react with the melt of the gallium oxide-based semiconductor.

[0047] The base 11 is a tubular member that surrounds the seed crystal part 101 of the crucible 10 and supports the crucible 10 from below. The base 11 includes a material such as zirconia or alumina that has heat resistance capable of withstanding the growth temperature of the single crystal of the gallium oxide-based semiconductor and does not react with the crucible 10 at this growth temperature.

[0048] A crucible support shaft 12 is connected to the lower side of the base 11. By moving the crucible support shaft 12 in the vertical direction using a drive mechanism (not shown), the base 11 and the crucible 10 supported by the base 11 can be moved in the vertical direction. In addition, the crucible support shaft 12 can also be rotated about the vertical axis by the above drive mechanism. In this case, the crucible 10 supported by the base 11 can be rotated inside the furnace core tube 14.

[0049] The crucible support shaft 12 is typically a tubular member similar to the base 11. In this case, a thermocouple used to measure the temperature of the crucible 10 can be passed through the inside of the base 11 and the crucible support shaft 12. The crucible support shaft 12 includes a material such as zirconia or alumina that has heat resistance capable of withstanding the growth temperature of the single crystal of the gallium oxide-based semiconductor.

[0050] The heater 13 is a heater for melting the raw material of the gallium oxide-based semiconductor accommodated in the crystal growth part 102 of the crucible 10 to obtain the 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) for supplying current to the heater 13 outside the housing 15. The heater 13 is typically a MoSi 2 heater including a resistance heating element of MoSi 2 heater. MoSi 2The heater has excellent oxidation resistance and heat resistance and can be used even in an oxidizing atmosphere at a high temperature of about 1800 °C required for growing a single crystal of a gallium oxide-based semiconductor.

[0051] The crucible tube 14 is used to adjust the heat flow around the crucible 10 or to suppress the incorporation of impurities such as Si and Mo from the heater 13. The crucible tube 14 is typically cylindrical. In addition, as Figure 1 shown, a lid 17 may be provided at the upper opening of the crucible tube 14. By using the lid 17, heat dissipation around the crucible 10 upward can be suppressed. The crucible tube 14 and the lid 17 are made of a material having heat resistance capable of withstanding the temperature for growing a single crystal of a gallium oxide-based semiconductor, such as zirconia or alumina.

[0052] (Single crystal growth process)

[0053] First, a seed crystal 20 of a gallium oxide-based semiconductor is placed in the seed crystal portion 101 of the crucible 10, and a raw material for a single crystal of a gallium oxide-based semiconductor is placed in the crystal growth portion 102. Here, for example, the addition concentrations of Si and Sn in the raw material for a single crystal are adjusted within the ranges of 0 to 0.03 atomic % and 0 to 0.1 atomic %, respectively, relative to Ga. As the raw material for a single crystal, for example, a sintered body of Ga 2 O 2 to which Si and Sn are added, which is obtained by mixing SiO 2 powder or SiC powder as an Si raw material and SnO 3 powder as an Sn raw material with Ga 2 O 3 powder and heating them, can be used. Alternatively, a sintered body of Ga 2 O 3 , a sintered body of SiO 2 or SiC, and a sintered body of SnO 2 can also be used as the raw material for a single crystal.

[0054] Next, the inside of the single crystal growth apparatus 1 (inside the housing 15) is heated by the heater 13 to form a temperature gradient such that the temperature is higher on the upper side and lower on the lower side, and the raw material for a single crystal in the crucible 10 is melted to obtain a raw material melt 21.

[0055] In a typical method, first, the crucible support shaft 12 is moved up and down to adjust the height of the crucible 10 so that the temperature in the upper region of the crystal growth portion 102 is above the melting point of gallium oxide. As a result, a part of the raw material in the upper side of the crystal growth portion 102 melts. Next, while moving the crucible support shaft 12 upward at a predetermined speed to raise the crucible 10 at a predetermined speed, the raw material is melted to the lower side, and finally all of the raw material and a part of the seed crystal are melted.

[0056] Next, while moving the crucible support shaft 12 downward to lower the crucible 10 at a prescribed speed, the raw material melt 21 is crystallized from the lower side (seed crystal 20 side) to grow a single crystal 22. The above-described single crystal growth is carried out in an oxidizing atmosphere. After all of the raw material melt 21 has been crystallized, the single crystal 22 is taken out from the crucible 10.

[0057] Thereafter, the obtained single crystal 22 is sliced at a desired interval in a desired direction using a multi-wire saw or the like and the surface is polished, thereby obtaining a semiconductor substrate having a desired thickness with a desired plane orientation as the main plane.

[0058] (Evaluation results)

[0059] Hereinafter, the results of various evaluations performed on a semiconductor substrate (hereinafter simply referred to as the semiconductor substrate) cut out from a β-Ga 2 O 3 single crystal obtained by the present growth method using the VB method are shown.

[0060] In Table 1 below, the concentrations of Si and Sn contained in five types of semiconductor substrates manufactured for this evaluation, and the addition concentrations of Si and Sn in the raw material of the single crystal from which the semiconductor substrate was cut out are shown. "Si addition concentration" and "Sn addition concentration" in Table 1 are the addition concentrations of Si and Sn in the raw material of the single crystal, respectively. "Si - Sn concentration" is the concentration obtained by subtracting the Sn concentration from the Si concentration. In addition, "UID: Unintentional Doped" means that no dopant has been intentionally added.

[0061] [Table 1]

[0062]

[0063] In this evaluation, as shown in Table 1, the concentrations of Si and Sn that are not intentionally added, which are inevitably mixed into the semiconductor substrate, are 2×10 17 cm -3 and 2×10 16 cm -3 or less.

[0064] In addition, according to Table 1, the Si addition concentrations of the sample with a Si concentration of 2×10 18 cm -3 and the sample with a Si concentration of 3×10 18 cm -3 are both 0.03 at%, but this is because these two samples were cut out from regions with different Si concentrations of the same single crystal.

[0065] Figure 2This is an observation image obtained by optical microscopy of a cross-section of a semiconductor substrate with the (010) plane as the main plane according to this embodiment. Figure 2 The cross-section shown is the (100) plane, Figure 2 and the up-down direction of the image is the

[010] direction of β-Ga 2 O 3 single crystal. According to Figure 2 it can be seen that the semiconductor substrate contains a plurality of needle-shaped voids extending in the

[010] direction.

[0066] Figure 3 These are observation images obtained by optical microscopy of cross-sections of four semiconductor substrates according to this embodiment. The upper-left observation image is the same as the Figure 2 observation image shown, and it is an observation image of the (100) cross-section of a semiconductor substrate with the (010) plane as the main plane without intentionally adding dopants. The upper-right observation image is an observation image of the (100) cross-section of a semiconductor substrate with the (010) plane as the main plane containing Si with a concentration of 3×10 18 cm -3 . The lower-left observation image is an observation image of the (100) cross-section of a semiconductor substrate with the (011) plane as the main plane containing Sn with a concentration of 3×10 18 cm -3 . The lower-right observation image is an observation image of the (100) cross-section of a semiconductor substrate with the (011) plane as the main plane containing Si with a concentration of 8×10 17 cm -3 and Sn with a concentration of 3×10 18 cm -3 .

[0067] From Figure 3 it can be seen that the density and size of the voids in the semiconductor substrate vary depending on the type of dopants contained in the semiconductor substrate, namely Si, Sn, or both Si and Sn.

[0068] Figure 4 This is a coordinate graph showing the relationship between the concentrations of Si and Sn as dopants and the density of voids in the semiconductor substrate. Figure 4 The horizontal axis "Si - Sn concentration" of refers to the concentration obtained by subtracting the Sn concentration from the Si concentration. The density of voids in the semiconductor substrate is calculated by measuring the number of voids in a specified region of the (100) cross-section. The area of the specified region is shown as the "observation area" in Table 2 below.

[0069] Figure 4 It shows that at least when the Si - Sn concentration is from -2.8×10 18 to 3.0×10 18 cm -3Within the range, when the Si concentration becomes higher relative to the Sn concentration, the density of voids becomes smaller, and when the Sn concentration becomes higher relative to the Si concentration, the density of voids becomes larger.

[0070] Figure 5 is a coordinate graph showing the relationship between the concentrations of Si and Sn as dopants and the average length of voids in a semiconductor substrate. Figure 5 The horizontal axis "Si - Sn concentration" in refers to the concentration obtained by subtracting the Sn concentration from the Si concentration. The average length of voids in the semiconductor substrate is obtained by measuring the lengths of voids in a specified region of the (100) cross-section and taking the average.

[0071] Figure 5 shows that at least within the range of Si - Sn concentration from -2.8×10 18 to 3.0×10 18 cm -3 when the Si concentration becomes higher relative to the Sn concentration, the average length of voids becomes larger, and when the Sn concentration becomes higher relative to the Si concentration, the average length of voids becomes smaller.

[0072] The "Si - Sn concentration" of the evaluated semiconductor substrate, the corresponding density and average length of voids, and the observation area of the cross-section of the semiconductor substrate and the number of observed voids used in the calculation of the density and average length of voids are shown in Table 2 below.

[0073] [Table 2]

[0074]

[0075] Figure 4 , Figure 5 The results shown indicate that the density and average length of voids contained in a single crystal and a semiconductor substrate cut therefrom 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 the semiconductor substrate depends on the total value of the Si concentration and the Sn concentration. Therefore, by intentionally adding both Si and Sn, it is possible to obtain a desired donor concentration and control the density and average length of voids. In addition, when Si and Sn are intentionally added, the concentrations of Si and Sn themselves are higher than the concentrations accidentally mixed in. For example, the Si concentration is higher than 2×10 17 cm -3 , and the Sn concentration is higher than 2×10 16 cm -3 . Specifically, the donor concentration of the single crystal and the semiconductor substrate becomes the value obtained by subtracting the concentration of Fe that compensates for the donor from the total value of the Si concentration and the Sn concentration. This Fe is mixed into the single crystal from the crucible 10 at approximately 1×10 17 cm-3 The following concentrations are present in the single crystal and the semiconductor substrate.

[0076] Figure 6 It is a coordinate diagram showing the relationship between the density and the average length of voids in the semiconductor substrate. Figure 6 It shows that at least in the range where the void density is 56 - 57000 cm -2 and the average void length is 14 - 85 μm, when the void density decreases, the average void length increases, and conversely, when the average void length decreases, the void density increases.

[0077] From the above evaluation results, it can be seen that at least a semiconductor substrate can be manufactured in which the value obtained by subtracting the Sn concentration from the Si concentration is in the range of -2.8×10 18 to 3.0×10 18 cm -3 and which contains voids with a density and an average length respectively in the ranges of 56 - 57000 cm -2 and 14 - 85 μm. In addition, by controlling the average length of voids in the single crystal according to the thickness and the plane orientation of the semiconductor substrate, a semiconductor substrate in which the voids do not penetrate between the two main surfaces can also be obtained.

[0078] In addition, it has been confirmed that when the Si concentration becomes 4.0×10 18 cm -3 or more, there is a tendency that huge voids considered to be formed by the aggregation of multiple voids are generated in the single crystal. Therefore, when the Si concentration becomes 4.0×10 18 cm -3 or more, 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 void length sometimes do not hold. On the other hand, if the Si concentration is within the range shown in Table 1 (3.0×10 18 cm -3 or less), huge voids are not generated 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 void length hold reliably. Therefore, the Si concentration is preferably less than 4.0×10 18 cm -3 , and more preferably 3.0×10 18 cm -3 or less.

[0079] In addition, although the above evaluations are all for β-Ga 2 O 3It is implemented using a semiconductor substrate cut from a single crystal of gallium oxide, but the same results are obtained when evaluating a semiconductor substrate cut from a single crystal of other gallium oxide-based semiconductors. Additionally, the same results are obtained even when evaluating a semiconductor substrate cut from a single crystal grown by a method such as the VGF method other than the VB method in an oxygen atmosphere.

[0080] (Effects of the Embodiment)

[0081] According to the above-described embodiment of the present invention, in a method of growing a single crystal in an oxygen atmosphere where the void density cannot be reduced by a reducing gas, it is possible to control the density and length of voids contained in the single crystal of the gallium oxide-based semiconductor to be grown, and suppress the influence of the voids on the characteristics of devices manufactured using a semiconductor substrate cut from the single crystal.

[0082] The above describes the embodiments of the present invention, but the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the invention. Additionally, the constituent elements of the above embodiments can be arbitrarily combined without departing from the gist of the invention. Additionally, the above-described embodiments do not limit the invention recited in the claims. Additionally, it should be noted that not all combinations of the features described in the embodiments are essential for the solution to the problems of the invention.

[0083] Industrial Applicability

[0084] Provided is a method for growing a single crystal, a method for manufacturing a semiconductor substrate using the single crystal grown by this growth method, and a semiconductor substrate manufactured by this manufacturing method. The method for growing a single crystal is a method for growing a single crystal of a gallium oxide-based semiconductor in an oxygen atmosphere, and can control the state of voids in the single crystal to suppress the influence on the characteristics of devices manufactured using the grown single crystal.

[0085] Explanation of Reference Numerals

[0086] 1... Single crystal growth apparatus, 10... Crucible, 101... Seed crystal part, 102... Growing crystal part, 11... Base, 13... Heater, 20... Seed crystal, 21... Raw material melt, 22... Single crystal.

Claims

1. A method for cultivating a single crystal, which is a method for cultivating a single crystal of a gallium oxide-based semiconductor, characterized in that, it includes a step of growing the single crystal from a melt formed by melting the raw material of the single crystal in 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 the Sn concentration of the single crystal.

2. The method for cultivating a single crystal according to claim 1, wherein, By adjusting the value obtained by subtracting the Sn concentration from the Si concentration within the range of -2.8×10 18 ~3.0×10 18 cm -3 the density and average length of the voids are respectively controlled within the ranges of 56~57000 cm -2 and 14~85 μm.

3. The method for cultivating a single crystal according to claim 1, wherein, By setting the Si concentration within the range lower than 4.0×10 18 cm -3 and adjusting the value obtained by subtracting the Sn concentration from the Si concentration within the range of -2.8×10 18 to 3.0×10 18 cm -3 , 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.

4. A method for manufacturing a semiconductor substrate, which is a method for manufacturing a semiconductor substrate including a single crystal of a gallium oxide-based semiconductor, characterized in that, it includes: a step of growing the single crystal from a melt formed by melting the raw material of the single crystal in an oxidizing atmosphere; and a step of cutting out the semiconductor substrate from the single crystal, 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 of the single crystal.

5. The method for manufacturing a semiconductor substrate according to claim 4, wherein, in order to suppress the voids from penetrating between the two main surfaces of the semiconductor substrate, the average length of the voids is controlled according to the thickness and plane orientation of the semiconductor substrate.

6. The method for manufacturing a semiconductor substrate according to claim 4 or 5, wherein, By adjusting the value obtained by subtracting the Sn concentration from the Si concentration within the range of -2.8×10 18 to 3.0×10 18 cm -3 the density and average length of the voids are respectively controlled within the ranges of 56 to 57000 cm -2 and 14 to 85 μm.

7. The method for manufacturing a semiconductor substrate according to claim 4 or 5, wherein, By setting the Si concentration within the range lower than 4.0×10 18 cm -3 and adjusting the value obtained by subtracting the Sn concentration from the Si concentration within the range of -2.8×10 18 to 3.0×10 18 cm -3 , 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.

8. A semiconductor substrate, which is a semiconductor substrate including a single crystal of a gallium oxide-based semiconductor, characterized in that, The value obtained by subtracting the Sn concentration from the Si concentration is in the range of -2.8×10 18 to 3.0×10 18 cm -3 . containing voids with a density and an average length in the ranges of 56 to 57000 cm -2 and 14 to 85 μm, respectively.

9. The semiconductor substrate according to claim 8, wherein, the voids do not penetrate between the two main surfaces.

10. The semiconductor substrate according to claim 8 or 9, wherein, The Si concentration is higher than 2×10 17 cm -3 , and the Sn concentration is higher than 2×10 16 cm -3 .

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