Gallium nitride production method, gallium nitride vapor-phase growth device, and gallium nitride substrate

Abstract

Provided is a gallium nitride production method that makes it possible to improve the conductivity of an n-type gallium nitride substrate. The gallium nitride production method uses a vapor-phase growth method in which an organic metal is not used as a gallium raw material. The production method comprises a step for supplying a first raw material gas containing gallium into a reaction container in which a substrate is arranged. The production method further comprises a step for supplying, into the reaction container, a second raw material gas that contains nitrogen and reacts with the first raw material gas. The production method also comprises a step for supplying, into the reaction container, a third raw material gas containing tin. The step for supplying the first raw material gas, the step for supplying the second raw material gas, and the step for supplying the third raw material gas are carried out within a range in which the substrate temperature is from 700°C to 1100°C.

Description

Gallium nitride manufacturing method, gallium nitride vapor phase growth apparatus, and gallium nitride substrate

[0001] This application claims priority from Japanese Patent Application No. 2023-123541, filed on July 28, 2023, the entire contents of which are incorporated herein by reference. This specification discloses techniques relating to a method for producing gallium nitride, a gallium nitride vapor phase growth apparatus, and a gallium nitride substrate.

[0002] There is a demand for improving the conductivity of n-type gallium nitride (GaN) substrates. This is because it is possible to reduce the on-resistance and thereby reduce energy loss. Silicon (Si), germanium (Ge), oxygen (O), etc. are generally used as donors for GaN. Related technology is disclosed in Japanese Patent Application Laid-Open No. 2020-202366.

[0003] When Si or Ge is used as the donor, it is difficult to sufficiently increase the concentration of the impurities incorporated into the GaN crystal. Because the donor concentration cannot be increased, it is difficult to increase the carrier concentration. When O is used as the donor, it is possible to increase the impurity concentration more than with Si or Ge. However, because the donor activation rate of O is low at around 20%, it is difficult to increase the carrier concentration.

[0004] This specification discloses a method for producing gallium nitride using a vapor phase epitaxy method that does not use an organic metal as a gallium source. The method includes a step of supplying a first source gas containing gallium into a reaction vessel in which a substrate is placed. The method also includes a step of supplying a second source gas containing nitrogen that reacts with the first source gas into the reaction vessel. The method also includes a step of supplying a third source gas containing tin into the reaction vessel. The steps of supplying the first source gas, supplying the second source gas, and supplying the third source gas are performed at a substrate temperature in the range of 700°C to 1100°C.

[0005] The inventors have discovered that when tin is used as a donor, the concentration of tin incorporated into GaN crystals can be significantly increased by using a growth temperature lower than that of typical GaN growth temperatures. Furthermore, using a growth temperature lower than that of typical growth temperatures can result in a rough surface with numerous pits, making it difficult to obtain good GaN crystals. However, the inventors have discovered that the surfactant effect of tin can suppress pit formation. As a result, the gallium nitride manufacturing method described herein can achieve both high tin doping and good crystallinity. Tin can have a higher doping concentration than silicon or germanium and a higher activation rate than oxygen, making it possible to form n-type GaN substrates with high carrier concentrations and high conductivity.

[0006] The step of supplying the first source gas, the step of supplying the second source gas, and the step of supplying the third source gas may be performed when the substrate temperature is in the range of 800° C. or more and 950° C. or less.

[0007] The first source gas may be a gas containing gallium chloride, the second source gas may be a gas containing ammonia, and the third source gas may be a gas containing tin chloride.

[0008] The ratio of the molar flow rate of tin chloride contained in the third source gas to the total molar flow rate of gallium chloride contained in the first source gas and tin chloride contained in the third source gas is 1×10 －３ It may be more than that.

[0009] The substrate may be rotated about an axis perpendicular to the surface of the substrate.

[0010] The manufacturing method may further include a step of supplying a fourth source gas containing at least one of silicon and germanium into the reaction chamber simultaneously with the supply of the third source gas.

[0011] One aspect of a gallium nitride vapor phase growth apparatus disclosed herein is a gallium nitride vapor phase growth apparatus used for a vapor phase growth method that does not use an organic metal as a gallium source. The vapor phase growth apparatus includes a reaction vessel, a substrate holder disposed within the reaction vessel, a first source gas supply pipe for supplying a first source gas containing gallium into the reaction vessel, a second source gas supply pipe for supplying a second source gas containing nitrogen that reacts with the first source gas into the reaction vessel, a third source gas supply pipe for supplying a third source gas containing tin into the reaction vessel, and a first heating unit for heating a substrate held by the substrate holder to a temperature in the range of 700°C to 1100°C.

[0012] The third source gas supply pipe may be configured to allow metallic tin to be placed on a supply path thereof. The vapor phase growth apparatus may further include a second heating unit capable of heating the metallic tin placed in the third source gas supply pipe.

[0013] The first source gas supply pipe may be configured to allow a solid portion containing gallium to be placed on the supply path. The vapor phase growth apparatus may further include a third heating unit capable of heating the placed solid portion. The heating temperatures of the first heating unit, the second heating unit, and the third heating unit may be equal.

[0014] The distance between the substrate holder and the end positions of the outlet sides of the first and third source gas supply pipes may be greater than the distance between the substrate holder and the end position of the outlet side of the second source gas supply pipe.

[0015] One embodiment of the gallium nitride substrate disclosed in this specification is a gallium nitride substrate that functions as an n-type semiconductor. １９ The tin concentration distribution in the direction perpendicular to the surface of the gallium nitride substrate is approximately constant in the depth direction.

[0016] The activation rate of the doped tin may be 70% or more.

[0017] The tin concentration may vary periodically in the depth direction.

[0018] Satellite peaks reflecting the periodicity of the tin concentration in the depth direction may be present around the reflection peaks obtained in 2θ-ω scanning by X-ray diffraction.

[0019] The gallium nitride substrate has a tin concentration of 1×10 １９ and the resistivity is 1×10 －３ It may be Ω·cm or less.

[0020] The lattice constant calculated based on the main peak angle obtained in 2θ-ω scanning by X-ray diffraction may be 0.05% or more larger than the lattice constant of a gallium nitride crystal that is not doped with tin.

[0021] FIG. 1 is a schematic cross-sectional view of a vapor phase growth apparatus as viewed from the side; FIG. 2 is a graph showing the correspondence relationship between tin concentration and carrier (electron) concentration; FIG. 3 is a graph showing the correspondence relationship between tin concentration and resistivity; FIG. 4 is a graph showing the growth temperature dependence of tin concentration; FIG. 5 is a graph showing the correspondence relationship between tin concentration and tin chloride supply ratio; FIG. 6 is a schematic cross-sectional view of SIMS analysis results and gallium nitride; FIG. 7 is a diagram showing the 2θ-ω scanning results of a GaN (0002) plane; and FIG. 8 is a graph showing the correspondence relationship between tin concentration and lattice constant c.

[0022] <Configuration of Vapor Phase Growth Apparatus> FIG. 1 shows a schematic cross-sectional side view of a vapor phase growth apparatus 1 according to this embodiment. The vapor phase growth apparatus 1 is an example of an apparatus configuration for implementing the HVPE (Halide Vapor Phase Epitaxy) method. The HVPE method is a method for growing crystals from gaseous chloride gas at high temperatures. In other words, the HVPE method is a vapor phase growth method for compound semiconductors that does not use organic metals as the gallium source. The HVPE method can suppress carbon contamination in the grown crystal. Furthermore, the HVPE method has a faster growth rate than other growth methods such as MOVPE, allowing for the growth of thick GaN films. Therefore, it is possible to manufacture GaN freestanding substrates.

[0023] The vapor phase growth apparatus 1 includes a reaction vessel 10, a source gas supply pipe 20, and a gas exhaust pipe 71. The reaction vessel 10 has a cylindrical shape. The reaction vessel 10 may be made of quartz. A wafer holder 11 is disposed inside the reaction vessel 10. A wafer 13 is held on a wafer holding surface of the wafer holder 11. A rotation shaft 14 is connected to the surface of the wafer holder 11 opposite the wafer holding surface. An end of the rotation shaft 14 is connected to a drive mechanism 15. This allows the wafer holder 11 to rotate the wafer 13 around an axis RA perpendicular to the surface of the wafer 13. The wafer holder 11 can also move the wafer 13 left and right (±x direction) within the reaction vessel 10.

[0024] The raw material gas supply pipe section 20 is connected to the reaction vessel 10. The raw material gas supply pipe section 20 includes a first raw material gas supply pipe 21, a second raw material gas supply pipe 22, a third raw material gas supply pipe 23, and specific gas supply pipes 24 and 25. The raw material gas supply pipe section 20 has a cylindrical shape. The specific gas supply pipe 25 has a structure in which the second raw material gas supply pipe 22, the specific gas supply pipe 24, the first raw material gas supply pipe 21, and the third raw material gas supply pipe 23 are arranged in this order inside the specific gas supply pipe 25. A gap between the inner wall of the specific gas supply pipe 25 and the outer wall of the second raw material gas supply pipe 22 forms a supply path for the specific gas supply pipe 25. Similarly, the supply paths for the second raw material gas supply pipe 22 and the specific gas supply pipe 24 are also formed by gaps between the inner and outer walls. The supply paths for the first raw material gas supply pipe 21 and the third raw material gas supply pipe 23 are formed by dividing the interior of the cylinder into upper and lower sections using a partition wall 27.

[0025] The first source gas supply pipe 21 is a pipe that supplies a first source gas G1 containing gallium into the reaction vessel 10. The first source gas supply pipe 21 supplies the first source gas G1 so that the flow direction is approximately perpendicular to the surface of the wafer 13. Hydrogen chloride (HCl) gas and nitrogen (N ２) gas is supplied. A quartz boat 41 containing metal gallium 43 is disposed on the path of the first source gas supply pipe 21. A heater 32 is disposed outside the source gas supply pipe 20 so as to surround the metal gallium 43. The heater 32 can heat the metal gallium 43 to a temperature range of 700°C to 1200°C. This generates gallium chloride, which can be supplied as the first source gas G1 from the outlet (gas supply port) into the reaction vessel 10.

[0026] The second source gas supply pipe 22 is a pipe that supplies a second source gas G2, which contains nitrogen and reacts with the first source gas G1, into the reaction chamber 10. The second source gas supply pipe 22 supplies the second source gas G2 so that the flow direction is approximately perpendicular to the surface of the wafer 13. Specifically, the second source gas G2 is ammonia (NH ３ ) and nitrogen-containing gas.

[0027] The third source gas supply pipe 23 is a pipe that supplies a third source gas G3 containing tin (Sn) into the reaction vessel 10. The third source gas supply pipe 23 supplies the third source gas G3 so that the flow direction is approximately perpendicular to the surface of the wafer 13. Hydrogen chloride gas and nitrogen gas are supplied to the inlet of the third source gas supply pipe 23. A quartz boat 45 containing metal tin 47 is disposed on the path of the third source gas supply pipe 23. A heater 31 is disposed outside the source gas supply pipe section 20 so as to surround the metal tin 47. The heater 31 can heat the metal tin 47 to a temperature range of 300°C to 1200°C. This generates tin chloride, which can be supplied into the reaction vessel 10 from the outlet (gas supply port) as the third source gas G3. Tin chloride is produced from tin(II) chloride (SnCl ２ ) or tin(IV) chloride (SnCl ４ The metal tin 47 may be placed in the same region as the metal gallium 43 and heated by the heater 32 at the same time.

[0028] The amount of tin supplied from the third source gas supply pipe 23 can be controlled by various parameters. For example, the amount of tin supplied can be increased by increasing the heating temperature of the metal tin 47, increasing the amount of metal tin 47 placed on the quartz boat 45, or shortening the distance between the outlet of the third source gas supply pipe 23 and the wafer 13.

[0029] The end position on the outlet side (-x direction side) of the partition wall between the first source gas supply pipe 21 and the third source gas supply pipe 23 is defined as end E1. The end position on the outlet side of the second source gas supply pipe 22 is defined as end E2. End E1 is located farther from the wafer 13 than end E2. This allows the first source gas G1 and the third source gas G3 to be mixed together, and then the second source gas G2 to be mixed together. That is, gallium chloride and tin chloride can be mixed together first and then reacted with ammonia. The tin concentration distribution within the surface of the wafer 13 can be made more uniform.

[0030] The first source gas supply pipe 21 and the third source gas supply pipe 23 are configured as separate lines. This allows the flow rate ratio of the first source gas G1 to the third source gas G3 to be freely set. This makes it possible to freely adjust the amount of tin doped into the gallium nitride crystal.

[0031] The specific gas supply pipes 24 and 25 are pipes that supply a specific gas into the reaction vessel 10. The specific gas is a gas that does not contain oxygen and does not react with the first source gas G1 and the second source gas G2. Specific examples of the specific gas include gases that contain at least one of hydrogen, nitrogen, helium, neon, argon, and krypton. In this embodiment, a mixed gas of hydrogen and nitrogen is supplied from the specific gas supply pipe 24. Furthermore, nitrogen gas is supplied from the specific gas supply pipe 25.

[0032] A heater 30 is disposed around the outer periphery of the reaction vessel 10 so as to surround the wafer holder 11. The heater 30 is a device that heats the wafer 13 by a hot wall method. This allows the wafer 13 to be maintained at a temperature (700°C or higher and 1100°C or lower) sufficient for gallium nitride crystal growth. The source gas used for the vapor phase growth of gallium nitride is then exhausted to a vent line via a gas exhaust pipe 71. Note that the temperatures of the wafer 13 and the wafer holder 11 may be measured using a pyrometer or thermocouple (not shown), and the heater may be feedback-controlled based on the measured temperatures.

[0033] <Vapor Phase Growth Method> A method for vapor phase growth of gallium nitride crystals on a wafer 13 by HVPE using a vapor phase growth apparatus 1 will be described. Vapor phase growth conditions are listed below. The heating temperature of the wafer 13 must be in the range of 700°C or higher and 1100°C or lower. A more preferable temperature range is 800°C or higher and 950°C or lower. In this example, the temperature was set to 890°C. Furthermore, the "ratio of the molar flow rate of tin chloride contained in the third source gas to the total molar flow rate of gallium chloride contained in the first source gas G1 and tin chloride contained in the third source gas G3" is defined as the "tin chloride supply ratio." The tin chloride supply ratio is 1×10 －３ In this example, the supply ratio of tin chloride is preferably 3.6×10 －３ It was decided.

[0034] The wafer 13 serving as the support substrate was prepared by growing undoped gallium nitride to a thickness of 4.5 μm on the surface of a sapphire substrate. The surface of the undoped gallium nitride was the c-plane (Ga-plane). The following conditions were used: growth time: 30 minutes, growth rate: 20 to 500 μm / h, heating temperature of metal gallium 43: 850° C., heating temperature of metal tin 47: 850° C., hydrogen chloride flow rate in first source gas supply pipe 21: 40 sccm, hydrogen chloride flow rate in third source gas supply pipe 23: 1 sccm, V / III ratio: 100, H ２ / (N ２ +H ２ ) ratio: 0.23.

[0035] By turning on heater 30, wafer 13 is heated to 890°C. Furthermore, by turning on heaters 31 and 32, metal tin 47 and metal gallium 43 are heated to 850°C. Then, supply of first source gas G1, second source gas G2, and specific gas is started. This makes it possible to grow an Sn-doped GaN layer (a gallium nitride crystal layer doped with tin) on wafer 13.

[0036] <Relationship between tin concentration, carrier concentration, and resistivity> Figure 2 shows the relationship between the tin concentration and carrier (electron) concentration of the Sn-doped GaN layer. The horizontal axis represents the tin concentration [cm －３ The vertical axis is the carrier concentration [cm －３ 2, it can be seen that the tin concentration and the carrier concentration are approximately equal. In other words, when tin is used as a donor, it can be seen that almost 100% of the doped tin becomes an active donor. In other words, the activation rate of tin doped into GaN is approximately 100%.

[0037] 3 shows the relationship between the tin concentration and the resistivity of the Sn-doped GaN layer. The horizontal axis represents the tin concentration [cm －３ The vertical axis is resistivity [Ω cm]. As shown in FIG. 3, the resistivity decreases as the tin concentration increases. Here, the resistivity of 1×10 －２ [Ω cm] is defined as a guideline value for producing n-type GaN with sufficient conductivity. １９ [cm －３ ] or more, it can be seen that the target value can be achieved.

[0038] Furthermore, as shown in region R1, the tin concentration is 1×10 ２０ If it is more than 1×10 －３ It can be seen that the resistivity can be reduced to Ω·cm or less. The technique of the present specification makes it possible to produce an Sn-doped GaN layer with such an extremely low resistivity.

[0039] <Control of Tin Concentration> The main parameters for controlling the tin concentration in the Sn-doped GaN layer are the growth temperature and the supply ratio of tin chloride. Figure 4 shows the growth temperature dependence of the tin concentration in the Sn-doped GaN layer. The horizontal axis is the growth temperature. The vertical axis is the tin concentration [cm －３ The tin chloride feed rate is 3.56 x 10 －３ As shown in Fig. 4, it is clear that tin can be incorporated into the GaN crystal if the substrate temperature during growth is within the range of 700°C or higher and 1100°C or lower.

[0040] As mentioned above, the resistivity is 1×10 －２ The target value of the tin concentration to achieve [Ω cm] is 1×10 １９ [cm －３ 4, it can be seen that the tin concentration can be increased to or above the target value by using a growth temperature of 950°C or less. That is, the inventors have discovered that the concentration of tin incorporated into the GaN crystal can be significantly increased by setting the growth temperature of Sn-doped GaN by the HVPE method in the range of 800°C to 950°C. In other words, it is preferable that the growth temperature of Sn-doped GaN by the HVPE method be approximately 100°C to 250°C lower than the growth temperature of ordinary GaN (e.g., undoped GaN, Si-doped GaN, Ge-doped GaN, etc.).

[0041] FIG. 5 shows the relationship between the tin concentration and the supply ratio of tin chloride. The horizontal axis represents the supply ratio of tin chloride as defined above. The vertical axis represents the tin concentration [cm －３ The growth temperature was kept constant at 905° C. As shown in FIG. 5, it can be seen that the tin concentration in the Sn-doped GaN layer can be increased by increasing the supply ratio of tin chloride.

[0042] 6 shows the measurement results of gallium nitride crystals by secondary ion mass spectrometry (SIMS). The growth temperature during sample preparation was 890° C., and the supply ratio of tin chloride was 3.6×10 －３The other conditions were the same as those described above. Fig. 6(A) shows the concentration profile of tin in the depth direction obtained by SIMS. Fig. 6(B) illustrates the structure corresponding to Fig. 6(A). The vertical axis of Fig. 6(A) is the tin concentration [atoms / cm ３ The horizontal axis represents the depth [μm] from the surface 13s of the Sn-doped GaN layer.

[0043] As shown in FIG. 6A, the average concentration of tin in the direction perpendicular to the surface 13s of the wafer 13 (i.e., the depth direction) is 5.1×10 １９ [cm －３ ] is approximately constant. This is due to the fact that tin is doped by a crystal growth method. For example, when tin is doped by ion implantation, a Gaussian concentration distribution is obtained, making it difficult to make the concentration constant in the depth direction. By making the tin concentration approximately constant in the depth direction, it is possible to make the conductivity in the depth direction approximately constant. This makes it possible to reduce the on-resistance when constructing a vertical device in which current flows in the depth direction.

[0044] It can also be seen that the tin concentration in the depth direction varies periodically with a period T1. The reason for this is explained below. The in-plane distribution of the tin doping concentration in the wafer 13 can be biased with respect to the axis RA. This can be achieved, for example, by eccentrically positioning the outlet of the third source gas supply pipe 23 with respect to the axis RA in FIG. 1 . The crystal is grown while rotating the wafer 13 around the axis RA. Therefore, the tin concentration can be varied periodically depending on the rotation speed. The period T1 can be appropriately adjusted by adjusting the growth rate and rotation speed. For example, when the growth rate is 27 μm / h and the rotation speed is 5 rpm, the period T1 is 90 nm. By varying the tin concentration distribution in the depth direction with the desired period T1, various conduction characteristics can be designed.

[0045] <XRD Analysis Results> Analysis was performed by X-ray diffraction (XRD) to evaluate the orientation of the grown GaN crystals. Figure 7 shows the 2θ-ω scan results of the GaN (0002) plane. Profile P0 is the measurement result for undoped GaN. Profiles P1-P3 are each the measurement result for Sn-doped GaN. The tin doping concentration in the GaN substrate is lowest in profile P1 and highest in profile P3. The carrier concentrations of profiles P1-P3 are each 1.5 x 10 １９ [cm －３ ], 7.8 × 10 １９ [cm －３ ], 2.5 × 10 ２０ [cm －３ ],.

[0046] In profile P0, the main peak angle was detected near 34.56° (see region R10). On the other hand, in profile P2, the main peak angle was detected near 34.54°. In profile P3, the main peak angle was detected near 34.47°. This shows that the higher the carrier concentration (i.e., the higher the tin doping concentration), the lower the main peak angle (see arrow A1). This is because the ionic radius of tin (0.69 [pm]) is larger than the ionic radius of gallium (0.61 [pm]). Furthermore, as the tin doping concentration increases and the amount of gallium substituted with tin increases, the lattice constant becomes larger.

[0047] Furthermore, in profiles P2 and P3, satellite peaks SP are present around the main peak angle. The satellite peaks SP reflect the periodicity of the tin concentration in the depth direction. The satellite peaks SP also appear at equal intervals due to the periodicity of the tin concentration distribution. In other words, by checking whether satellite peaks SP are present in the profile obtained by 2θ-ω scanning, it is possible to determine whether the tin concentration distribution in the depth direction fluctuates periodically.

[0048] FIG. 8 shows the relationship between the tin concentration and the lattice constant c. The horizontal axis represents the tin concentration [cm －３The vertical axis represents the lattice constant c [angstroms] calculated based on the main peak angle obtained in 2θ-ω scanning. In Sn-undoped GaN, the lattice constant c is approximately 5.187 [angstroms] (see region R20). In addition, when the tin concentration is 1×10 －１９ In the above region, it can be seen that the lattice constant c increases as the tin concentration increases (see region R21). ２０ [cm －３ In other words, when the tin concentration is 1×10, the lattice constant c increases to about 5.1905 [angstroms] (see region R22). ２０ [cm －３ ] is found to have a lattice constant c of gallium nitride crystal of 0.05% or more larger.

[0049] <Substrate Surface Morphology> When tin is not doped, using a low growth temperature of 950°C or less can result in a rough surface with numerous pits, making it difficult to obtain good GaN crystals. However, the inventors have discovered that supplying tin can suppress pit formation even when using a growth temperature of 950°C or less. This is due to the surfactant effect of tin. That is, the surface roughness caused by lowering the growth temperature can be complementarily suppressed by the high concentration of tin doped at the lower temperature. This makes it possible to achieve both high concentration tin doping and good crystallinity. Therefore, it is possible to form an n-type GaN substrate with a high carrier concentration and high conductivity.

[0050] Furthermore, the higher the supply ratio of tin chloride described above, the more likely Sn droplets are generated on the surface of the wafer 13. Sn droplets are formed when excess Sn atoms condense on the substrate surface. However, since Sn droplets are generated only on the substrate surface, they can be removed by cleaning or polishing. Therefore, it is possible to form Sn-doped GaN with good crystallinity.

[0051] Although the embodiments of the present invention have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the specific examples exemplified above.

[0052] The vapor phase growth apparatus 1 may be configured to supply a fourth source gas containing at least one of silicon and germanium into the reaction chamber. For example, the apparatus may further include a fourth source gas supply pipe for supplying the fourth source gas. Alternatively, for example, a solid portion containing silicon or germanium may be disposed together with metallic tin 47 or metallic gallium 43. The supply of the fourth source gas may be performed simultaneously with the supply of the third source gas G3. This allows tin to be co-doped (co-doped) with at least one of silicon and germanium. As described above, the ionic radius of tin is larger than that of gallium. On the other hand, the ionic radius of silicon (0.40 pm) and the ionic radius of germanium (0.53 pm) are smaller than that of gallium. Thus, by co-doping multiple elements having different ionic radius relationships with gallium, a synergistic effect can be achieved, improving the ease of incorporation of the multiple elements into the GaN crystal. Since the doping concentrations of both of the multiple elements can be increased, the resistance of the Sn-doped GaN layer can be further reduced.

[0053] The source of tin is not limited to metallic tin, but may be other tin compounds, or tin may be added to metallic gallium.

[0054] The heating temperatures of the heaters 30, 31, and 32 may be the same. For example, the heating temperatures of the heaters 30, 31, and 32 may be set to a temperature sufficient for gallium nitride crystal growth (700°C or higher and 1100°C or lower). In this case, the heaters 30, 31, and 32 may be integrated into one or two heaters. This makes it possible to simplify the heater structure.

[0055] The flow directions of the first source gas G1, the second source gas G2, and the third source gas G3 relative to the surface of the wafer 13 are not limited to being substantially perpendicular, and may be various. For example, the flow direction may be parallel to the surface of the wafer 13. A flow direction that is closer to parallel can more easily form a rate difference or a concentration difference between upstream and downstream than when the flow direction is perpendicular. This makes it easier to control the fluctuation period of the tin concentration distribution in the depth direction due to the rotation (spin and revolution) of the wafer.

[0056] The gas supplied to the inlets of the first source gas supply pipe 21 and the third source gas supply pipe 23 is not limited to hydrogen chloride (HCl) gas. For example, chlorine (Cl ２ The gas may be a gas containing Cl, such as a fluorine-containing gas, or a gas containing other halogen elements, such as F or Br.

[0057] The scope of application of the technology described in this specification is not limited to gallium nitride. It can be applied to the crystal growth of various compound semiconductors that can use tin as an impurity. For example, it may be applied to AlGaN (aluminum gallium nitride), AlN (aluminum nitride), InN (indium nitride), InGaN (indium gallium nitride), or mixed crystals thereof.

[0058] The number and arrangement of the first source gas supply pipe 21 to the third source gas supply pipe 23 described in this specification are merely examples and are not limited to these. For example, the first source gas supply pipe 21 and the third source gas supply pipe 23 may be integrated.

[0059] The heating temperatures of the wafer 13, the metal gallium 43, and the metal tin 47 are examples.

[0060] Although the first source gas G1 is a gas containing gallium chloride, the present invention is not limited to this. The first source gas G1 may be a gas having any chemical composition as long as it contains gallium. For example, the first source gas G1 may be gallium trichloride (GaCl ３ Alternatively, for example, the first source gas G1 may be a gas containing simple gallium.

[0061] The technical elements described in this specification or drawings may exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technologies illustrated in this specification or drawings may achieve multiple objectives simultaneously, and achieving one of those objectives alone is technically useful.

[0062] The aspects of the present technology are listed below. [Aspect 1] A method for producing gallium nitride using a vapor phase epitaxy method that does not use an organic metal as a gallium source, comprising the steps of: supplying a first source gas containing gallium into a reaction vessel in which a substrate is placed; supplying a second source gas containing nitrogen that reacts with the first source gas into the reaction vessel; and supplying a third source gas containing tin into the reaction vessel, wherein the steps of supplying the first source gas, supplying the second source gas, and supplying the third source gas are performed when the temperature of the substrate is in the range of 700°C to 1100°C. [Aspect 2] The method for producing gallium nitride according to Aspect 1, wherein the steps of supplying the first source gas, supplying the second source gas, and supplying the third source gas are performed when the temperature of the substrate is in the range of 800°C to 950°C. [Aspect 3] The method for producing gallium nitride according to Aspect 1 or 2, wherein the first source gas is a gas containing gallium chloride, the second source gas is a gas containing ammonia, and the third source gas is a gas containing tin chloride. [Aspect 4] A ratio of the molar flow rate of the tin chloride contained in the third source gas to the total molar flow rate of the gallium chloride contained in the first source gas and the tin chloride contained in the third source gas is 1×10 －３The method for producing gallium nitride according to Aspect 3 is as described above. [Aspect 5] The method for producing gallium nitride according to any one of Aspects 1 to 4, wherein the substrate is rotated around an axis perpendicular to a surface of the substrate. [Aspect 6] The method for producing gallium nitride according to any one of Aspects 1 to 5, further comprising the step of supplying a fourth source gas containing at least one of silicon and germanium into the reaction vessel simultaneously with the supply of the third source gas. Aspect 7 is a gallium nitride vapor phase growth apparatus used for vapor phase growth that does not use an organic metal as a gallium source, comprising: a reaction vessel; a substrate holder disposed within the reaction vessel; a first source gas supply pipe that supplies a first source gas containing gallium into the reaction vessel; a second source gas supply pipe that supplies a second source gas that contains nitrogen and reacts with the first source gas into the reaction vessel; a third source gas supply pipe that supplies a third source gas that contains tin into the reaction vessel; and a first heating unit that heats the temperature of a substrate held by the substrate holder to a range of 700° C. to 1100° C. Aspect 8 is the gallium nitride vapor phase growth apparatus according to Aspect 7, wherein the first heating unit heats the temperature of the substrate held by the substrate holder to a range of 800° C. to 950° C. Aspect 9: The gallium nitride vapor phase growth apparatus according to Aspect 7 or 8, wherein hydrogen chloride gas or chlorine gas is supplied to the inlets of the first source gas supply pipe and the third source gas supply pipe, the first source gas containing gallium chloride is discharged from the outlet of the first source gas supply pipe, and the third source gas containing tin chloride is discharged from the outlet of the third source gas supply pipe. Aspect 10: The ratio of the molar flow rate of the tin chloride contained in the third source gas to the total molar flow rate of the gallium chloride contained in the first source gas and the tin chloride contained in the third source gas is 1×10 －３The gallium nitride vapor phase growth apparatus according to Aspect 9, wherein the substrate holder is configured to be able to rotate the substrate around an axis perpendicular to the surface of the substrate. [Aspect 11] The gallium nitride vapor phase growth apparatus according to any one of Aspects 7 to 10, wherein the substrate holder is configured to be able to rotate the substrate around an axis perpendicular to the surface of the substrate. [Aspect 12] The gallium nitride vapor phase growth apparatus according to any one of Aspects 7 to 11, wherein the third source gas supply pipe is configured to allow metallic tin to be placed on a supply path, and the apparatus further comprises a second heating unit capable of heating the metallic tin placed on the third source gas supply pipe. [Aspect 13] The gallium nitride vapor phase growth apparatus according to Aspect 12, wherein the first source gas supply pipe is configured to allow a solid portion containing gallium to be placed on a supply path, and the apparatus further comprises a third heating unit capable of heating the placed solid portion, and the heating temperatures by the first heating unit, the second heating unit, and the third heating unit are equivalent. Aspect 14: The gallium nitride vapor phase growth apparatus according to any one of Aspects 7 to 13, wherein the distance between the substrate holder and the end positions of the outlet sides of the first and third source gas supply pipes is greater than the distance between the substrate holder and the end position of the outlet side of the second source gas supply pipe. １９ A gallium nitride substrate as described above, functioning as an n-type semiconductor, wherein the tin concentration distribution in the direction perpendicular to the surface of the gallium nitride substrate is approximately constant in the depth direction. [Aspect 16] The gallium nitride substrate according to Aspect 15, wherein the activation rate of the doped tin is 70% or more. [Aspect 17] The gallium nitride substrate according to Aspect 15 or 16, wherein the tin concentration varies periodically in the depth direction. [Aspect 18] The gallium nitride substrate according to any one of Aspects 15 to 17, wherein satellite peaks reflecting the periodicity of the tin concentration in the depth direction are present around reflection peaks obtained in 2θ-ω scanning by X-ray diffraction. [Aspect 19] The gallium nitride substrate according to any one of Aspects 15 to 17, wherein the tin concentration is 1×10 １９ and the resistivity is 1×10 －３A gallium nitride substrate according to any one of Aspects 15 to 18, having a lattice constant calculated based on a main peak angle obtained in 2θ-ω scanning by X-ray diffraction that is 0.05% or more larger than the lattice constant of a gallium nitride crystal that is not doped with tin.

Claims

1. A method for producing gallium nitride using a vapor phase growth method that does not use an organic metal as a gallium source, comprising the steps of: supplying a first source gas containing gallium into a reaction vessel in which a substrate is placed; supplying a second source gas containing nitrogen that reacts with the first source gas into the reaction vessel; and supplying a third source gas containing tin into the reaction vessel, wherein the steps of supplying the first source gas, supplying the second source gas, and supplying the third source gas are carried out when the temperature of the substrate is in the range of 700°C or higher and 1100°C or lower.

2. The method for producing gallium nitride as described in claim 1, wherein the step of supplying the first raw material gas, the step of supplying the second raw material gas, and the step of supplying the third raw material gas are performed when the temperature of the substrate is in the range of 800°C or higher and 950°C or lower.

3. A method for producing gallium nitride as described in claim 2, wherein the first source gas is a gas containing gallium chloride, the second source gas is a gas containing ammonia, and the third source gas is a gas containing tin chloride.

4. The ratio of the molar flow rate of the tin chloride contained in the third source gas to the total molar flow rate of the gallium chloride contained in the first source gas and the tin chloride contained in the third source gas is 1×10 －３ The method for producing gallium nitride according to claim 3 .

5. The method for producing gallium nitride according to claim 4, wherein the substrate is rotated about an axis perpendicular to the surface of the substrate.

6. A method for producing gallium nitride described in any one of claims 1 to 5, further comprising a step of supplying a fourth source gas containing at least one of silicon and germanium into the reaction vessel simultaneously with the supply of the third source gas.

7. A gallium nitride vapor phase growth apparatus used for a vapor phase growth method that does not use an organic metal as a gallium source, comprising: a reaction vessel; a substrate holding unit disposed within the reaction vessel; a first source gas supply pipe for supplying a first source gas containing gallium into the reaction vessel; a second source gas supply pipe for supplying a second source gas containing nitrogen and reacting with the first source gas into the reaction vessel; a third source gas supply pipe for supplying a third source gas containing tin into the reaction vessel; and a first heating unit for heating the temperature of a substrate held by the substrate holding unit to a temperature in the range of 700°C to 1100°C.

8. A gallium nitride vapor phase growth apparatus as set forth in claim 7, wherein said first heating section heats the substrate held by said substrate holder to a temperature in the range of 800°C to 950°C.

9. A gallium nitride vapor phase growth apparatus as described in claim 8, wherein hydrogen chloride gas or chlorine gas is supplied to the inlets of the first raw material gas supply pipe and the third raw material gas supply pipe, the first raw material gas containing gallium chloride is discharged from the outlet of the first raw material gas supply pipe, and the third raw material gas containing tin chloride is discharged from the outlet of the third raw material gas supply pipe.

10. The ratio of the molar flow rate of the tin chloride contained in the third source gas to the total molar flow rate of the gallium chloride contained in the first source gas and the tin chloride contained in the third source gas is 1×10 －３ 10. The vapor phase growth apparatus for gallium nitride according to claim 9.

11. The gallium nitride vapor phase growth apparatus according to claim 10, wherein the substrate holder is configured to be capable of rotating the substrate about an axis perpendicular to a surface of the substrate.

12. The vapor phase growth apparatus for gallium nitride as described in claim 11, wherein the third source gas supply pipe is configured to allow metallic tin to be placed on a supply path, and further comprising a second heating section capable of heating the metallic tin placed in the third source gas supply pipe.

13. A gallium nitride vapor phase growth apparatus as described in claim 12, wherein the first raw material gas supply pipe is configured to allow a solid part containing gallium to be placed on the supply path, and further comprises a third heating part capable of heating the placed solid part, and the heating temperatures by the first heating part, the second heating part and the third heating part are equivalent.

14. A gallium nitride vapor phase growth apparatus as described in claim 7, wherein the distance between the end positions on the outlet side of the first and third source gas supply pipes and the substrate holding part is greater than the distance between the end position on the outlet side of the second source gas supply pipe and the substrate holding part.

15. Tin concentration is 1 x 10 １９ The gallium nitride substrate as described above functions as an n-type semiconductor, wherein a concentration distribution of tin in a direction perpendicular to a surface of the gallium nitride substrate is approximately constant in a depth direction.

16. The gallium nitride substrate according to claim 15, in which the activation rate of the doped tin is 70% or more.

17. The gallium nitride substrate according to claim 16, wherein the tin concentration varies periodically in the depth direction.

18. The gallium nitride substrate according to claim 17, in which satellite peaks reflecting periodicity of tin concentration in the depth direction are present around a reflection peak obtained in 2θ-ω scanning by X-ray diffraction.

19. Tin concentration is 1 x 10 １９ The resistivity is 1×10 or more. －３ The gallium nitride substrate according to claim 15 , having a resistivity of Ω·cm or less.

20. The gallium nitride substrate according to claim 15, wherein the lattice constant calculated based on the main peak angle obtained in 2θ-ω scanning by X-ray diffraction is greater than the lattice constant of a gallium nitride crystal that is not doped with tin by 0.05% or more.

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