Method for producing III-nitride crystals

Abstract

To provide a method for manufacturing a high quality group III nitride crystal.SOLUTION: A method for manufacturing a group III nitride crystal comprises: the preparation step for preparing a seed substrate; the temperature rising step of rising the temperature of the seed substrate arranged in a growing chamber; and the growth step of supplying group III element oxide gas produced a raw material chamber connected to the growing chamber by a connection pipe and nitrogen element containing gas to grow a group III nitride crystal on the seed substrate. In the temperature rising step, the flow rate y of carrier gas supplied to the raw material chamber satisfies the following two relational expressions (I) and (II), y<[1-k×H(Ts)] / [k×H(Ts)-j×H(Tg)] xj×H(Tg)xt (I) and y≥1.58x10-4×(22.4 / 28)SxF(N) / F(T) (II).SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a method for producing Group III nitride crystals. [Background technology]

[0002] Group III nitride crystals such as GaN are expected to be applied to next-generation optical devices such as high-output LEDs (light-emitting diodes) and LDs (laser diodes), and next-generation electronic devices such as high-output power transistors mounted on EVs (electric vehicles) and PHVs (plug-in hybrid vehicles), etc. As a method for producing Group III nitride crystals, an oxide vapor phase epitaxy (OVPE) method using Group III element oxides as raw materials is used (for example, see Patent Document 1).

[0003] An example of a reaction system in the OVPE method is shown below. (1) Ga is heated, and in this state, H2O gas is introduced. The introduced H2O gas reacts with Ga to generate Ga2O gas (represented by the following formula (I)). (2) Then, NH3 gas is introduced and reacted with the generated Ga2O gas to produce GaN crystals on the seed substrate (reaction formula (II) below). 2Ga(l)+H2O(g)→Ga2O(g)+H2(g)...(I) Ga2O(g)+2NH3(g)→2GaN(s)+H2O(g)+2H2(g)...(II) [Prior art documents] [Patent documents]

[0004] [Patent Document 1] WO2015 / 053341A1 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the manufacturing method described in Patent Document 1, in the step of increasing the temperature of the seed substrate, vapor of the Group III metal (Ga) gas, which is a raw material for generating GaO gas, may diffuse from the raw material chamber in which the raw material is placed to the growth chamber in which the seed substrate is placed. In this case, the seed substrate may react with the Group III metal gas, causing the starting point of abnormal growth such as polycrystals or through pits to be generated on the seed substrate.

[0006] On the other hand, in order to suppress the diffusion of the group III metal gas, it is conceivable to reduce the flow rate of the carrier gas in the gas line supplied to the source chamber in which the group III metal is installed. However, when the flow rate of the carrier gas is reduced, the nitrogen-containing gas (NH3) supplied to the growth chamber flows back into the source chamber in which the group III metal is installed, reacts with the group III metal, and group III nitride crystals are generated on the group III metal. In this case, the group III metal is covered with the group III nitride crystals. As a result, even if a reactive gas (H2O) is supplied onto the group III metal in the growth step after the temperature increase step, it becomes difficult to generate the group III element oxide gas (Ga2O) required for crystal growth. Therefore, it is difficult to efficiently generate high-quality group III nitride crystals.

[0007] The present disclosure has been made in view of the above-mentioned problems, and has an object to provide a method for producing high-quality Group III nitride crystals. [Means for solving the problem]

[0008] The method for producing a Group III nitride crystal according to the present disclosure includes a preparation step of preparing a seed substrate, a heating step of raising the temperature of the seed substrate placed in a growth chamber, and a growth step of supplying into the growth chamber a Group III element oxide gas and a nitrogen-containing gas, which are generated in a source chamber connected to the growth chamber by a connecting pipe, to grow a Group III nitride crystal on the seed substrate, wherein in the heating step, the flow rate y of the carrier gas supplied into the source chamber satisfies the following two relational expressions (I) and (II): y<[1-k×H(Ts)] / [k×H(Ts)-j×H(Tg)]×j×H(Tg)×t (I) y ≧ 1.58 × 10 -4 ×(22.4 / 28)S×F(N) / F(T) (II) where k is the rate at which the saturated vapor pressure of the Group III element in the source chamber is reached, Ts is the temperature of the source chamber, Tg is the temperature of the growth chamber, H(Ts) is the saturated vapor pressure of the Group III element at temperature Ts in the source chamber, H(Tg) is the saturated vapor pressure of the Group III element at temperature Tg in the growth chamber, j is a correction coefficient, t is the sum of the gas flow rates flowing into the growth chamber from sources other than the source chamber, S is the cross-sectional area of ​​the connecting pipe, F(N) is the volumetric flow rate of the nitrogen-containing gas supplied to the growth chamber, and F(T) is the sum of the volumetric flow rates of the gases supplied to the growth chamber 111 from sources other than the source chamber. Effect of the Invention

[0009] According to the method for producing Group III nitride crystals according to the present disclosure, high-quality Group III nitride crystals can be produced. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1A is a flowchart showing a chronological manufacturing method of a Group III nitride crystal in accordance with a first embodiment of the present disclosure, and FIG. 1B is a flowchart showing, as steps, each functional unit from upstream to downstream in a manufacturing apparatus used in the manufacturing method. [Diagram 2] 1 is a schematic diagram of a Group III nitride crystal manufacturing apparatus according to a first embodiment of the present disclosure. [Diagram 3] 1 is a graph showing the relationship between temperature and saturated vapor pressure of Ga. [Figure 4] 11 is a graph showing the relationship between the flow rate of gases flowing into the growth chamber from sources other than the source chamber, and the diffusion of Ga vapor and the backflow of NH3 gas relative to the N2 flow rate from the source chamber. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The method for producing a Group III nitride crystal according to the first aspect includes a preparation step of preparing a seed substrate, a heating step of raising the temperature of the seed substrate placed in a growth chamber, and a growth step of supplying into the growth chamber a Group III element oxide gas, generated in a source chamber connected to the growth chamber by a connecting pipe, and a nitrogen-containing gas, to grow a Group III nitride crystal on the seed substrate, wherein in the heating step, the flow rate y of the carrier gas supplied into the source chamber satisfies the following two relational expressions (I) and (II): y<[1-k×H(Ts)] / [k×H(Ts)-j×H(Tg)]×j×H(Tg)×t (I) y ≧ 1.58 × 10 -4 ×(22.4 / 28)S×F(N) / F(T) (II) where k is the rate at which the saturated vapor pressure of the Group III element in the source chamber is reached, Ts is the temperature of the source chamber, Tg is the temperature of the growth chamber, H(Ts) is the saturated vapor pressure of the Group III element at temperature Ts in the source chamber, H(Tg) is the saturated vapor pressure of the Group III element at temperature Tg in the growth chamber, j is a correction coefficient, t is the sum of the gas flow rates flowing into the growth chamber from sources other than the source chamber, S is the cross-sectional area of ​​the connecting pipe, F(N) is the volumetric flow rate of the nitrogen-containing gas supplied to the growth chamber, and F(T) is the sum of the volumetric flow rates of the gases supplied to the growth chamber 111 from sources other than the source chamber.

[0012] A second aspect of the method for producing a Group III nitride crystal is the same as the first aspect, in which the heating step is carried out in a heating process at 500° C. or higher and lower than 1050° C., prior to the growth step.

[0013] A third aspect of the method for producing a Group III nitride crystal is any of the first and second aspects described above, wherein the temperature increasing step may be carried out in a mixed atmosphere of an inert gas and the nitrogen-element-containing gas.

[0014] Hereinafter, a Group III nitride crystal manufacturing apparatus and a Group III nitride crystal manufacturing method according to embodiments will be described with reference to the accompanying drawings, in which substantially identical components are designated by the same reference numerals.

[0015] (Embodiment 1) (Outline of a method for manufacturing a group-III nitride crystal) (The outline of the method for manufacturing a group-III nitride crystal according to Embodiment 1 will be described with reference to the flowchart of FIG. 1 and FIG. 2. FIG. 1(a) shows a time-series flowchart of the method for manufacturing a group-III nitride crystal. FIG. 1(b) shows each functional unit from the upstream to the downstream in the manufacturing apparatus used in this manufacturing method as steps.)

[0016] (As shown in FIG. 1(a), the method for manufacturing a group-III nitride crystal according to Embodiment 1 includes a seed substrate preparation step of preparing a seed substrate, a heating step of heating the seed substrate in an inert gas atmosphere, a decomposition protection heating step of heating the seed substrate in a nitrogen element-containing gas atmosphere, a growth step of supplying a group-III element oxide gas and a nitrogen element-containing gas to grow a group-III nitride crystal on the seed substrate, a step of cooling while suppressing the decomposition of the group-III nitride crystal in a nitrogen element-containing gas atmosphere, a step of cooling the group-III nitride crystal in an inert gas atmosphere, and a step of taking out the group-III nitride crystal.)

[0017] (Seed substrate preparation step) (In the seed substrate preparation step of preparing the seed substrate 116, the seed substrate 116 is placed on the substrate susceptor 117.)

[0018] (Heating step) (In this embodiment, the method for manufacturing a group-III nitride crystal has a heating step. In the heating step, the growth chamber 111 is heated to 100°C or higher and lower than 500°C in an inert gas atmosphere.)

[0019] (Decomposition protection heating step) (In the decomposition protection heating step, the growth chamber 111 is heated to 500°C or higher and lower than 1000°C in an NH3 gas atmosphere.)

[0020] (Growth step) In the growth process, group III element oxide gas is generated in the raw material chamber 100 and supplied to the growth chamber 111, and a nitrogen element-containing gas is supplied to the growth chamber 111 to form a group III nitride crystal on the seed substrate 116.

[0021] As shown in Fig. 1(b), the growth process includes a reactive gas supply process, a group III element oxide gas generation process, a group III element oxide gas supply process, a nitrogen element-containing gas supply process, a group III nitride crystal generation process, and a residual gas discharge process. Each process included in the growth process may be performed simultaneously in the apparatus for manufacturing a group III nitride crystal. Each process included in the growth process is shown with each functional unit from upstream to downstream in the apparatus for manufacturing a group III nitride crystal shown in Fig. 2 as a process.

[0022] <Reactive gas supply process> In the reactive gas supply process, a reactive gas is supplied to the raw material reaction chamber.

[0023] <Group III element oxide gas generation process> In the group III element oxide gas generation process, a starting group III element source is reacted with a reactive gas (a reducing gas when the starting group III element source is an oxide, and an oxidizing gas when it is a metal) to generate a group III element oxide gas.

[0024] <Group III element oxide gas supply process> In the group III element oxide gas supply process, the group III element oxide gas produced in the group III element oxide gas generation process is supplied to the growth chamber.

[0025] <Nitrogen element-containing gas supply process> In the nitrogen element-containing gas supply process, a nitrogen element-containing gas is supplied to the growth chamber.

[0026] <Group III nitride crystal generation process> In the III-nitride crystal growth process, the III-group element oxide gas supplied into the growth chamber in the III-group element oxide gas supply process is reacted with the nitrogen element-containing gas supplied into the growth chamber in the nitrogen element-containing gas supply process to grow III-nitride crystals on the seed substrate.

[0027] <Residual gas discharge process> In the residual gas discharge process, unreacted gases that do not contribute to the formation of III-nitride crystals are discharged outside the chamber.

[0028] <Decomposition protection and temperature reduction process> In the first embodiment, the method for manufacturing III-nitride crystals has a decomposition protection and temperature reduction process. In the decomposition protection and temperature reduction process, in order to suppress the decomposition of the III-nitride crystals grown on the seed substrate 116, the temperature of the raw material chamber 100 and the growth chamber 111 is reduced to 500 °C while supplying NH3 gas.

[0029] <Temperature reduction process> In the first embodiment, the method for manufacturing III-nitride crystals has a temperature reduction process. In the temperature reduction process, the temperature of the raw material chamber 100 and the growth chamber 111 is reduced to less than 100 °C in an inert gas atmosphere.

[0030] <Taking-out process> In the first embodiment, the method for manufacturing III-nitride crystals has a taking-out process. In the taking-out process, the seed substrate 116 on which III-nitride crystals have grown is taken out from the growth chamber 111.

[0031] <Overview of the manufacturing apparatus for III-nitride crystals> First, an overview of the manufacturing apparatus for III-nitride crystals used in the method for manufacturing III-nitride crystals according to the first embodiment will be described with reference to FIG. 2. In FIG. 2, the sizes, ratios, etc. of the respective components may be different from the actual ones. The manufacturing apparatus for group-III nitride crystals includes a raw material chamber 100 and a growth chamber 111. The raw material chamber 100 generates a group-III element oxide gas. The growth chamber 111 reacts the group-III element oxide gas supplied from the raw material chamber 100 with a nitrogen element-containing gas to generate group-III nitride crystals on a seed substrate. Inside the raw material chamber 100, a raw material reaction chamber 101 is arranged, and a raw material boat 104 on which a starting group-III element source 105 is placed is arranged inside the raw material reaction chamber 101. A reactive gas supply pipe 103 for supplying a gas that reacts with the starting group-III element source 105 is connected to the raw material reaction chamber 101. The raw material reaction chamber 101 has a group-III element oxide gas discharge port 107 for discharging the generated group-III element oxide gas. When the starting group-III source is an oxide, a reducing gas is used as the reactive gas. When the starting group-III source is a metal, an oxidizing gas is used as the reactive gas.

[0032] Also, a first carrier gas supply port 102 for supplying a first carrier gas is connected to the raw material chamber 100. The first carrier gas supplied from the first carrier gas supply port 102 and the group-III element oxide gas discharged from the group-III element oxide gas discharge port 107 flow from the gas discharge port 108 through the connection pipe 109 to the growth chamber 111. That is, the first carrier gas and the group-III element oxide gas are supplied into the growth chamber 111 from a gas supply port 118 connected to the growth chamber 111. The growth chamber 111 has a gas supply port 118, a third carrier gas supply port 112, a nitrogen element-containing gas supply port 113, a second carrier gas supply port 114, and an exhaust port 119. The growth chamber 111 includes a substrate susceptor 117 for installing a seed substrate 116.

[0033] <Details of the manufacturing method and manufacturing apparatus for group-III nitride crystals> Referring to FIGS. 1 and 2, the manufacturing method for group-III nitride crystals according to Embodiment 1 will be described in detail. In Embodiment 1, metal Ga is used as the starting group-III element source 105, but it is not limited thereto. For example, Al or In may be used.

[0034] <Seed substrate preparation process> First, prepare the seed substrate 116. For example, gallium nitride, gallium arsenide, silicon, sapphire, silicon carbide, zinc oxide, gallium oxide, and ScAlMgO4 can be used as the seed substrate 116. In this embodiment, gallium nitride is used as the seed substrate 116.

[0035] <Heating process> In the temperature raising step, the temperature of the growth chamber is raised in an inert gas atmosphere to a temperature that does not cause decomposition of the seed substrate 116. In producing Group III nitride crystals by the OVPE method, heating is performed up to about 500° C. in an inert gas (e.g., N2 gas) atmosphere.

[0036] <Decomposition protection temperature increase process> In the decomposition protection heating step, the temperature is raised in a nitrogen-element-containing gas atmosphere while suppressing the decomposition of the seed substrate 116. In the manufacture of Group III nitride crystals by the OVPE method, heating is performed in a state in which an inert gas is mixed with NH3 gas, which is a nitrogen-element-containing gas, up to a temperature of 500° C. or higher and lower than 1050° C. The reason for mixing NH3 is to prevent the seed substrate 116 from decomposing due to the detachment of N atoms.

[0037] In addition, in the decomposition protection heating step, a carrier gas is supplied from the reactive gas supply pipe 103. For example, an inert gas or H2 gas can be used as the carrier gas. The reason for supplying the carrier gas from the reactive gas supply pipe 103 is to suppress the backflow of the nitrogen element-containing gas supplied to the growth chamber 111 to the raw material chamber 100. In this case, if the flow rate of the carrier gas supplied from the reactive gas supply pipe 103 or the supply rate of the first carrier gas supplied from the first carrier gas supply port 102 is large, the amount of evaporation of the metal Ga, which is the starting group III element source 105 installed in the raw material boat 104, increases, and the evaporated metal Ga is likely to move from the raw material chamber 100 to the growth chamber 111. In the decomposition protection heating step, if metal Ga is supplied onto the seed substrate 116 in the growth chamber 111, Ga droplets will be generated on the seed substrate 116 when the vapor pressure of the supplied metal Ga exceeds the saturated vapor pressure of Ga. The generated droplets become a source of abnormal growth such as polycrystals and through pits when growing a group III nitride crystal in the growth step. Therefore, in order to reduce the supply of Ga vapor to the growth chamber 111, it is conceivable to lower the flow rates of the carrier gas and the first carrier gas supplied to the source chamber 100.

[0038] However, if the flow rates of the carrier gas and the first carrier gas are reduced, the nitrogen-containing gas supplied to the growth chamber 111 will flow back into the source chamber 100. When the nitrogen-containing gas NH3 gas flows back into the source chamber 100, Ga and NH3 react on the metal Ga, which is the starting group III element source in the source chamber 100, to generate GaN, which covers the surface of the metal Ga. If the metal Ga is covered with GaN, the reaction between the metal Ga and the reactive gas is prevented in the growth step, even if the reactive gas is supplied to the source chamber 100, and a desired amount of group III element oxide gas cannot be generated. In other words, it is necessary to simultaneously suppress the diffusion of the metal Ga vapor onto the seed substrate 116 and the backflow of the nitrogen-containing gas into the source chamber 100. Here, for ease of understanding, it is assumed that the gas supplied to the source chamber 100 in the decomposition protection heating step is only the carrier gas N2 gas from the reactive gas supply pipe. The pressure is 1 atm.

[0039] First, the suppression of the diffusion of Ga vapor into the seed substrate 116 will be examined. First, consider the volumetric flow rate of Ga vapor in the source chamber 100. If the partial pressure of Ga vapor in the source chamber 100 is x (atm), the volumetric flow rate of N2 carrier gas supplied to the source chamber 100 is y (L / min), and the volumetric flow rate of Ga vapor is z (L / min), the relationship between Ga gas and N2 gas (N2:Ga) in the source chamber 100 is expressed by formula (III). 1 - x:x = y:z (III) When this is modified with respect to z, it is expressed by formula (IV). z = (x × y) / (1 - x) (IV)

[0040] Next, consider the partial pressure of Ga vapor when it is supplied to the growth chamber 111. The flow rate of gas other than Ga vapor supplied to the growth chamber 111 is T (L / min), and the flow rate of gas supplied to the growth chamber 111 from sources other than the raw material chamber 100 is t (L / min). The flow rate of gas other than Ga vapor supplied to the growth chamber 111 means the sum of the flow rate of gas other than Ga vapor supplied from the raw material chamber 100 and the flow rate of gas supplied to the growth chamber 111 from sources other than the raw material chamber 100. In this case, T satisfies the relationship of the following formula (V). T = y + t (V)

[0041] Here, the partial pressure of Ga gas in the growth chamber 111 is z / (T+z). If the saturated vapor pressure of Ga at the seed substrate 116 is H(Tg)(atm), Ga droplets will form when the Ga gas partial pressure exceeds the Ga saturated vapor pressure. Therefore, in order to suppress the generation of Ga droplets on the seed substrate 116, the Ga gas flow rate z needs to be kept as expressed by the following formula (VI). z / (T+z) <j×H(Tg)···(VI) Here, j is the correction coefficient. The value of j was determined to be 2.25 × 10 -3 Therefore, by substituting formula (IV) and formula (V) into formula (VI), formula (VII) can be obtained. y<(1-x) / [xj×H(Tg)]×j×H(Tg)×t...(VII)

[0042] Furthermore, if the Ga vapor in the source chamber 100 reaches the saturated vapor pressure by (k×100)%, the Ga saturated vapor pressure in the source chamber 100 is H(Ts), and the partial pressure x of the Ga vapor in the source chamber 100 can be expressed as (VIII) below. In this case, k is the ratio of the Ga vapor in the source chamber 100 to the saturated vapor pressure H(Ts). x = k × H(Ts) (VIII) Substituting formula (VIII) into formula (VII) gives formula (IX). y<[1-k×H(Ts)] / [k×H(Ts)-j×H(Tg)]×j×H(Tg)×t...(IX)

[0043] Moreover, H(Ts) and H(Tg) are expressed by the following formula. H(Ts)=EXP[-ΔG(Ts) / (R×Ts)]···(X) H(Tg)=EXP[-ΔG(Tg) / (R×Tg)]...(XI) Here, Ts and Tg are the temperatures of the source chamber 100 and the growth chamber 111, respectively. Furthermore, R is the gas constant, and ΔG is the Gibbs potential of Ga gas determined by the temperatures of the source chamber 100 and the growth chamber 111. Therefore, the volumetric flow rate y of N2 gas supplied to the source chamber 100 may be within a range that satisfies formula (IX) expressed using formulas (X) and (XI). For reference, the relationship between the saturated vapor pressure of Ga and the temperature is shown in FIG. 3.

[0044] Secondly, suppression of backflow of the nitrogen-containing gas NH3 into the source chamber 100 will be considered. The mass flow rate of N2 gas supplied to the source chamber 100 is X (g / min), and the cross-sectional area of ​​the connecting pipe 109 is S (mm 2 ), the volumetric flow rate of the NH3 gas supplied to the growth chamber 111 is F(NH3) (L / min), and the volumetric flow rate of the gas supplied to the growth chamber 111 from a source other than the raw material chamber 100 is F(T) (L / min). The concentration of NH3 gas in the gas supplied to the growth chamber 111 from a source other than the raw material chamber 100 can be expressed as F(NH3) / F(T).

[0045] It is believed that the backflow of NH3, a nitrogen-containing gas, into the raw material chamber 100 is more suppressed as the mass flow rate X (g / min) of N2 gas, a carrier gas supplied to the raw material chamber 100, increases. It is also believed that the backflow of NH3 into the raw material chamber 100 is more suppressed as the cross-sectional area S of the connecting pipe 109 decreases. It is also believed that the backflow of NH3 into the raw material chamber 100 is more suppressed as the inverse of the volumetric flow rate F(NH3) (L / min) of NH3 gas increases. It is also believed that the backflow of NH3 into the raw material chamber 100 is more suppressed as the volumetric flow rate F(T) (L / min) of gas supplied to the growth chamber 111 from outside the raw material chamber 100 increases. From the above relationship, consider the value of A expressed by formula XII) with the mass flow rate X (g / min) of N2 gas and the volumetric flow rate F(T) (L / min) of gas supplied to the growth chamber 111 from outside the source chamber 100, which show a positive correlation with the suppression of the backflow of NH3 into the source chamber 100, as the numerator, and the cross-sectional area S of the connecting pipe 109 and the volumetric flow rate F(NH3) (L / min) of the NH3 gas, which show a negative correlation, as the denominator. This A is a parameter for judging the suppression of the backflow of NH3 gas from the growth chamber 111 to the source chamber 100, and it can be judged that the backflow of NH3 into the source chamber 100 can be suppressed when the numerical value of A is larger than a predetermined value. A=(X / S)×(FT(T) / F(NH3))=(X×FT(T)) / (S×F(NH3))...(XII) The lower limit of A that can suppress the backflow of NH3 into the source chamber 100, which was derived as a result of repeated experimental investigations, is 1.58×10 -4 It was.

[0046] If y (L / min) is the volumetric flow rate of N2 gas supplied to the raw material chamber 100, the mass flow rate X of N2 gas supplied from the raw material chamber 100 is expressed by formula (XIII) using the standard molar volume of 22.4 L / mol and the molecular weight of N2 gas of 28 g / mol. X = y × (28 / 22.4) (XIII) Substituting formula (XIII) into formula (XII), y≧A×(22.4 / 28)×S×F(NH3) / F(T)...(XIV) Therefore, when substituting the lower limit value of A, y must satisfy the relationship of the following formula (XV). y ≧ 1.58×10 -4 ×(22.4 / 28)S×F(NH3) / F(T) ··· (XV)

[0047] Summarizing the above content, in the decomposition protection heating-up process, the volume flow rate y of the carrier gas supplied to the raw material chamber 100 may be adjusted within the range that simultaneously satisfies formulas (IX) and (XV). Specifically, the gas flow rate F(T) flowing into the growth chamber from outside the raw material chamber and the flow rate of N2 from the raw material chamber may be adjusted within the range above the dotted line and below the dashed-dotted line shown in FIG. 4. Thereby, it becomes possible to suppress the diffusion of Ga vapor supplied from the raw material chamber 100 to the seed substrate 116 and to suppress the backflow of the nitrogen element-containing gas to the raw material chamber 100. In FIG. 4, the flow rate of N2 from the raw material chamber is shown as a volume flow rate, but the volume flow rate and the mass flow rate can be mutually converted.

[0048] <Growth process> In the growth process, a group III element oxide gas is generated in the raw material chamber 100 and supplied to the growth chamber 111, and a nitrogen element-containing gas is supplied to the growth chamber 111 to generate a group III nitride crystal on the seed substrate 116. Specifically, the growth process includes a reactive gas supply process, a group III element oxide gas generation process, a group III element oxide gas supply process, a nitrogen element-containing gas supply process, a group III nitride crystal generation process, and a residual gas discharge process.

[0049] <Reactive gas supply process> In the reactive gas supply process, the reactive gas is supplied from the reactive gas supply pipe 103 to the raw material reaction chamber 101 in the raw material chamber 100. As described above, as the reactive gas, a reducing gas or an oxidizing gas can be used as necessary. In the present embodiment, since metal Ga is used as the group III element source 105, H2O gas is used as the reactive gas.

[0050] <Group III element oxide gas supply process> In the Group III element oxide gas generation step, the reactive gas supplied to the raw material reaction chamber 101 in the reactive gas supply step reacts with Ga, which is the starting Group III element source 105, to generate Ga2O gas, which is a Group III element oxide gas. The generated Ga2O gas is exhausted from the raw material reaction chamber 101 to the raw material chamber 100 via the Group III element oxide gas exhaust port 107. The exhausted Ga2O gas is mixed with the first carrier gas supplied to the raw material chamber from the first carrier gas supply port 102, and supplied to the gas exhaust port 108.

[0051] In this embodiment, the source chamber 100 is heated by the first heater 106. When the source chamber 100 is heated, the temperature of the source chamber 100 is preferably set to 800° C. or higher in view of the boiling point of GaO gas. In addition, the temperature of the source chamber 100 is preferably set to a lower temperature than that of the growth chamber 111. When the growth chamber is heated by the second heater 115 as described below, the temperature of the source chamber 100 is preferably set to less than 1800° C., for example.

[0052] The starting group III element source 105 is placed in a source boat 104 arranged in the source reaction chamber 101. The source boat 104 is preferably shaped to increase the contact area between the reactive gas and the starting group III element source. For example, the source boat 104 is preferably shaped like a multi-stage dish to prevent the starting group III element source 105 and the reactive gas from passing through the source reaction chamber 101 without contacting each other.

[0053] In addition, the methods for generating group III element oxide gas can be broadly classified into a method of reducing the starting group III element source 105 and a method of oxidizing the starting group III element source 105. For example, in the reduction method, an oxide (e.g., Ga2O3) is used as the starting group III element source 105, and a reducing gas (e.g., H2 gas, CO gas, CH4 gas, C2H6 gas, H2S gas, SO2 gas) is used as the reactive gas. On the other hand, in the oxidation method, a non-oxide (e.g., liquid Ga) is used as the starting group III element source 105, and an oxidizing gas (e.g., H2O gas, O2 gas, CO gas, CO2 gas, NO gas, N2O gas, NO2 gas) is used as the reactive gas. In addition to the Ga source as the starting group III element source 105, an In source and an Al source can be adopted as the starting group III elements. As the first carrier gas, an inert gas, H2 gas, etc. can be used.

[0054] In the group III element oxide gas supply step, the Ga2O gas generated in the group III element oxide gas generation step is supplied to the growth chamber 111 via the gas outlet 108, the connecting pipe 109, and the gas supply port 118. When the temperature of the connecting pipe 109 connecting the raw material chamber 100 and the growth chamber 111 is lower than the temperature of the raw material chamber 100, a reverse reaction of the reaction for generating the group III element oxide gas occurs, and the starting group III element source 105 precipitates in the connecting pipe 109. Therefore, the connecting pipe 109 is preferably heated to a temperature higher than that of the first heater 106 by the third heater 110 so as not to be lower than the temperature of the raw material chamber 100.

[0055] <Nitrogen element-containing gas supply step> In the nitrogen element-containing gas supply step, the nitrogen element-containing gas is supplied from the nitrogen element-containing gas supply port 113 to the growth chamber 111. Examples of the nitrogen element-containing gas include NH3 gas, NO gas, NO2 gas, N2O gas, N2H2 gas, and N2H4 gas.

[0056] <Group III nitride crystal generation step> In the III-nitride crystal generating process, the source gases supplied into the growth chamber through each supply process are reacted to grow III-nitride crystals on the seed substrate 116. The growth chamber 111 is preferably heated to a temperature at which the III-element oxide gas and the nitrogen-containing gas react with each other by the second heater 115. At this time, the temperature of the growth chamber 111 is preferably controlled so that it does not drop below the temperature of the source chamber 100 in order to prevent a reverse reaction of the reaction generating the III-element oxide gas. The temperature of the growth chamber 111 heated by the second heater 115 is preferably 1000° C. or more and 1800° C. or less. In order to suppress temperature fluctuations in the growth chamber 111 due to the Ga2O gas generated in the source chamber 100 and the first carrier gas, it is preferable that the temperatures of the second heater 115 and the third heater 110 are the same.

[0057] The Group III element oxide gas supplied to the growth chamber 111 through a Group III element oxide supplying step and the nitrogen-containing gas supplied to the growth chamber 111 through a nitrogen-containing gas supplying step are mixed upstream of the seed substrate 116, thereby enabling the growth of a Group III nitride crystal on the seed substrate 116. As the second carrier gas, an inert gas, H2 gas, or the like can be used.

[0058] The reactive gas supplying step, the Group III element oxide gas generating step, the Group III element oxide gas supplying step, the nitrogen-containing gas supplying step, the Group III nitride crystal generating step, and the residual gas discharging step, which are included in the growth step, may be performed simultaneously.

[0059] <Residual gas exhaust process> In the residual gas exhaust process, the unreacted Group III element oxide gas and nitrogen element-containing gas, as well as the first carrier gas, second carrier gas, and third carrier gas, are exhausted from the exhaust port 119 .

[0060] <Decomposition protection temperature cooling process> In the decomposition protection temperature-reducing step, the temperature is reduced in a nitrogen-containing gas atmosphere while suppressing the decomposition of the Group III nitride crystal. In the production of Group III nitride crystals by the OVPE method, the temperature is reduced to 500°C or lower in a state in which an inert gas and a nitrogen-containing gas, NH3 gas, are mixed.

[0061] <Temperature cooling process> In the temperature-lowering step, the temperature is lowered in an inert gas atmosphere to a temperature at which the Group III nitride crystal can be removed from the growth chamber.

[0062] <Removal process> In this embodiment, the seed substrate 116 on which the Group III nitride crystal has grown is removed from the growth chamber 111 after the temperature lowering step. EXAMPLES

[0063] Using the growth furnace shown in Figure 2, an experiment was carried out up to the decomposition protection heating step. Here, it was assumed that GaN was grown as the group III nitride crystal. Liquid Ga was used as the starting group III element source, and NH3 gas was used as the nitrogen element-containing gas. A mixture of H2 gas and N2 gas was used as the first carrier gas and the second carrier gas. The time until the decomposition protection heating step was 85 minutes for verification. A GaN substrate was used as the seed substrate.

[0064] The occurrence of polycrystals and pits originating from Ga droplets due to the diffusion of Ga vapor was evaluated by surface photoluminescence (PL) image observation or atomic force microscope (AFM) observation. The occurrence of GaN on the metallic Ga in the source boat due to the backflow of NH3 gas was confirmed by visual inspection.

[0065] Example 1 The conditions for the decomposition protection heating process were as follows: substrate temperature was heated from 500°C to 1050°C, and source temperature was heated from 500°C to 900°C. The flow rate of N2 gas supplied to the source chamber was 0.25L / min, the flow rate of NH3 gas was 10L / min, and the flow rate of other N2 gas was 35L / min. The substrate was heated to the desired temperature and then cooled down, and the result of evaluating the substrate was that no polycrystals or pits originating from Ga droplets on the crystal surface were confirmed. Furthermore, no GaN was confirmed to be generated on the metallic Ga in the source boat.

[0066] Comparative Example 1 The conditions for the decomposition protection heating process were as follows: substrate temperature was heated from 500°C to 1050°C, and source temperature was heated from 500°C to 900°C. The flow rate of N2 gas supplied to the source chamber was 2L / min, the flow rate of NH3 gas was 10L / min, and the flow rate of other N2 gas was 29L / min. The substrate was heated to the desired temperature and then cooled down, and the occurrence of polycrystals and pits originating from Ga droplets on the crystal surface was confirmed. Furthermore, the occurrence of GaN on the metallic Ga in the source boat was not confirmed.

[0067] Comparative Example 2 The conditions for the decomposition protection heating process were as follows: substrate temperature was heated from 500°C to 1050°C, and source temperature was heated from 500°C to 900°C. The flow rate of N2 gas supplied to the source chamber was less than 0.01L / min, the flow rate of NH3 gas was 15L / min, and the flow rate of other N2 gas was 75L / min. The substrate was heated to the desired temperature and then cooled down, and the result of evaluating the substrate was that no polycrystals or pits originating from Ga droplets on the crystal surface were confirmed. In addition, the generation of GaN on the metallic Ga in the source boat was confirmed.

[0068] (Summary of Examples and Comparative Examples) Fig. 4 shows the evaluation results of the examples and comparative examples. The upper and lower limit values of the N2 flow rate that can be supplied into the raw material chamber described in <Method and Apparatus for Manufacturing Group III Nitride Crystals> are also shown. Since Example 1 is within the desired region, it simultaneously satisfies the suppression of Ga vapor diffusion and the suppression of NH3 gas backflow. No polycrystals or pits originating from Ga droplets on the seed substrate were confirmed, and furthermore, the generation of GaN on the metallic Ga in the raw material boat was not confirmed either.

[0069] On the other hand, in the case of Comparative Example 1, since it exceeds the lower limit value for suppressing the backflow of NH3, the generation of GaN on the metallic Ga in the raw material boat was not confirmed. However, since it exceeds the upper limit value for suppressing the diffusion of Ga vapor onto the seed substrate, the generation of polycrystals and pits originating from Ga droplets on the seed substrate was confirmed. In the case of Comparative Example 2, since it did not exceed the upper limit value for suppressing the diffusion of Ga vapor onto the seed substrate, the generation of polycrystals and pits originating from Ga droplets on the seed substrate was not confirmed. However, since it was below the lower limit value for suppressing the backflow of NH3, the generation of GaN on the metallic Ga in the raw material boat was confirmed.

[0070] Note that in the present disclosure, it includes appropriately combining any of the various embodiments and / or examples described above, and the effects possessed by each embodiment and / or example can be achieved.

Description of Reference Numerals

[0071] 100 Raw material chamber 101 Raw material reaction chamber 102 First carrier gas supply port 103 Reactive gas supply pipe 104 Raw material boat 105 Starting group III element source 106 First heater 107 Group III element oxide gas discharge port 108 Gas discharge port 109 Connecting pipe 110 Third heater 111 Growth chamber 112 Third carrier gas supply port 113 Nitrogen-containing gas supply port 114 Second carrier gas supply port 115 Second heater 116 species substrate 117 Substrate susceptor 118 Gas supply port 119 Exhaust vent

Claims

1. A preparation step of preparing a seed substrate; a temperature increasing step of increasing the temperature of the seed substrate disposed in a growth chamber; a growth step of supplying into the growth chamber a Group III element oxide gas generated in a source chamber connected to the growth chamber by a connecting pipe, and a nitrogen-containing gas, to grow a Group III nitride crystal on the seed substrate; Including, In the heating step, a flow rate y (L / min) of the carrier gas supplied into the raw material chamber satisfies the following two relational expressions (I) and (II), y<[1-k×H(Ts)] / [k×H(Ts)-j×H(Tg)]×j×H(Tg)×t (I) y≧!)･00 －４ × ((). k is the rate at which the saturated vapor pressure of the group III element in the source chamber is reached, Ts (° C.) is the temperature of the source chamber; Tg (°C) is the temperature of the growth chamber; H(Ts) (atm) is the saturated vapor pressure of the Group III element at temperature Ts in the source chamber. H(Tg) (atm) is the saturated vapor pressure of the Group III element at the temperature Tg in the growth chamber. j is a correction factor having a value of 2.25×10 −3 ; t (L / min) is the sum of the gas flow rates flowing into the growth chamber from sources other than the source chamber, S (mm 2 ) is the cross-sectional area of ​​the connecting pipe, F (N) (L / min) is the volumetric flow rate of the nitrogen-containing gas supplied to the growth chamber, F(T) (L / min) represents the sum of the volumetric flow rates of gases supplied to the growth chamber from sources other than the source chamber; A method for producing a Group III nitride crystal.

2. The temperature rise step is carried out in a temperature rise process of 500 ° C. or more and less than 1050 ° C. before the growth step. A method for producing a Group III nitride crystal according to claim 1.

3. The temperature increasing step is carried out in a mixed atmosphere of an inert gas and the nitrogen element-containing gas. A method for producing a Group III nitride crystal according to claim 1 or 2.

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