阅读说明：本技术 Iii族氮化物结晶的制造方法 (Method for producing group III nitride crystal ) 是由 森勇介 吉村政志 今西正幸 北本启 泷野淳一 隅智亮 于 2020-02-03 设计创作，主要内容包括：本发明提供一种抑制多晶化且提高III族氮化物结晶的品质的III族氮化物结晶的制造方法。III族氮化物结晶的制造方法包括：准备种基板的工序；以及以过饱和比(P<Sup>0</Sup>/P<Sup>e</Sup>)成为大于1且为5以下的方式,供给III族元素氧化物气体和含氮元素的气体,从而使III族氮化物结晶在种基板上生长的工序,P<Sup>0</Sup>为III族氧化物气体的供给分压,P<Sup>e</Sup>为III族氧化物气体的平衡分压。(The invention provides a method for producing a group III nitride crystal, which can inhibit polycrystallization and improve the quality of the group III nitride crystal. The method for producing a group III nitride crystal includes: preparing a seed substrate; and at supersaturation ratio (P) 0 /P e ) A step of growing a group III nitride crystal on the seed substrate by supplying a group III element oxide gas and a nitrogen-containing gas so as to be more than 1 and 5 or less, P 0 Is a supplied partial pressure of a group III oxide gas, P e Is the equilibrium partial pressure of the group III oxide gas.)

1. A method for producing a group III nitride crystal, comprising:

preparing a seed substrate; and

at a supersaturation ratio P⁰/P^eA step of growing a group III nitride crystal on the seed substrate by supplying a group III element oxide gas and a nitrogen-containing gas so as to be more than 1 and 5 or less,

the P is⁰Is a supplied partial pressure of the group III element oxide gas, the P^eIs the equilibrium partial pressure of the group III element oxide gas.

2. The group III-nitride junction of claim 1A method of manufacturing a crystal, further comprising: at the supersaturation ratio P⁰/P^eAnd a step of introducing a group III nitride crystal decomposition inhibiting layer by supplying the group III element oxide gas and the nitrogen element-containing gas from a temperature lower than the substrate temperature in the growth step so as to be greater than 1 and not more than 5.

3. The method for producing a group III nitride crystal according to claim 1 or 2, comprising: at the supersaturation ratio P⁰/P^eAnd a step of growing a group III nitride on the seed substrate by supplying the group III element oxide gas and the nitrogen element-containing gas so as to be 1.3 or more and less than 2.5.

4. The method for producing a group III nitride crystal according to claim 1 or 2, further comprising: at the supersaturation ratio P⁰/P^eAnd a step of introducing a group III nitride crystal decomposition inhibiting layer by supplying the group III element oxide gas and the nitrogen-containing gas from the seed substrate at a substrate temperature of 1050 ℃ or lower so as to be 1.3 or more and less than 2.5.

Technical Field

The present invention relates to a method for producing a group III nitride crystal.

Background

Group III nitride crystals are used in heterojunction high-speed electronic devices such as power semiconductors and optoelectronic devices such as LEDs and lasers. As a method for producing a group III nitride crystal, an oxide vapor phase growth method using a group III oxide as a raw material is considered (for example, see patent document 1). The reaction system in the oxide vapor phase growth method is as follows. First, Ga is heated, and H is introduced in this state₂And (4) O gas. Introduced H₂The O gas reacts with Ga to form Ga₂O gas (formula (I) below). And, introducing NH₃Gas, with the Ga produced₂The O gas reacts to grow a GaN crystal (formula (II) below) on the seed substrate.

2Ga+H₂O→Ga₂O+H₂(I)

Ga₂O+2NH₃→2GaN+H₂O+2H₂(II)

Disclosure of Invention

Problems to be solved by the invention

However, in the conventional production method, when a group III nitride crystal is grown, polycrystallization occurs in which a plane different from the growth plane is oriented, and it is difficult to produce a high-quality crystal uniformly in the growth plane.

Accordingly, an object of the present invention is to provide a method for producing a group III nitride crystal, in which polycrystallization is suppressed and the quality of the group III nitride crystal is improved.

Means for solving the problems

The method for producing a group III nitride crystal according to the present invention comprises:

preparing a seed substrate; and

at a supersaturation ratio (P)⁰/P^e) A step of growing a group III nitride crystal on the seed substrate by supplying a group III element oxide gas and a nitrogen-containing gas so as to be more than 1 and 5 or less,

p is above⁰The partial pressure of the group III element oxide gas supplied, P^eIs the equilibrium partial pressure of the above group III element oxide gas.

Effects of the invention

The method for producing a group III nitride crystal according to the present invention can improve the quality of the obtained group III nitride crystal.

Drawings

Fig. 1 is a flowchart of a method for producing a group III nitride crystal according to embodiment 1.

Fig. 2 is a schematic view showing the configuration of an apparatus for producing a group III nitride crystal according to embodiment 1.

FIG. 3 is a graph showing the results of experiments relating the supersaturation ratio to the polycrystalline density.

Fig. 4 is a graph showing a temperature increase curve of the substrate temperature.

Fig. 5 is a schematic view of a seed substrate on which a decomposition-inhibiting layer is provided and on which crystal growth is performed.

Fig. 6 (a) is a schematic cross-sectional view showing an example of crystal growth when no decomposition-inhibiting layer is introduced, and fig. 6 (b) is a schematic cross-sectional view showing an example of crystal growth when a decomposition-inhibiting layer is introduced.

Description of the reference numerals

100 raw material chamber

101 raw material reaction chamber

102 first conveying gas supply port

103 reactive gas supply tube

104 raw material boat

105 starting Ga source (starting III group element source)

106 first heater

107 III group oxide gas exhaust

108 group III oxide gas and transport gas exhaust

109 connecting pipe

110 third heater

111 incubation Chamber (grow チャンバ)

112 gas supply port containing nitrogen element

113 an oxidizing gas (acidified ガス) supply port

114 second conveying gas supply port

115 second heater

116 kinds of base plate

117 base plate

118 group III oxide gas and transport gas supply port

119 air outlet

121 decomposition inhibiting layer

123 growth layer

125 abnormal growth source

126 polycrystal

127 pit

Apparatus for producing 150 III group nitride crystal

Detailed Description

The method for producing a group III nitride crystal according to the first aspect includes:

preparing a seed substrate; and

at a supersaturation ratio (P)⁰/P^e) A step of growing a group III nitride crystal on the seed substrate by supplying a group III element oxide gas and a nitrogen-containing gas so as to be more than 1 and 5 or less,

p is above⁰The partial pressure of the group III element oxide gas supplied, P^eIs the equilibrium partial pressure of the above group III element oxide gas.

The method for producing a group III nitride crystal according to the second aspect may further include the step of forming a crystal layer on the substrate according to the first aspect: at the above supersaturation ratio (P)⁰/P^e) And a step of introducing a group III nitride crystal decomposition inhibiting layer by supplying the group III element oxide gas and the nitrogen element-containing gas at a temperature lower than the substrate temperature in the growth step so as to be greater than 1 and not more than 5.

The method for producing a group III nitride crystal according to the third aspect may include, according to the first or second aspect: at the above supersaturation ratio (P)⁰/P^e) And a step of growing a group III nitride on the seed substrate by supplying the group III element oxide gas and the nitrogen-containing gas so as to be 1.3 or more and less than 2.5.

The method for producing a group III nitride crystal according to the fourth aspect may further include, according to any one of the first to third aspects: at the above supersaturation ratio (P)⁰/P^e) And introducing a group III nitride crystal decomposition inhibiting layer by supplying the group III element oxide gas and the nitrogen element-containing gas at a substrate temperature of 1050 ℃ or less of the seed substrate so as to be 1.3 or more and less than 2.5.

< original committee for obtaining the invention >

The method for producing a group III nitride crystal according to the present application comprises: supplying a reactive gas to the starting group III element source; a step of reacting the starting group III element source with the reactive gas to generate an oxide gas of the group III element; supplying the group III element oxide gas into the growth chamber; supplying a nitrogen-containing gas into the incubation chamber; supplying an oxidizable gas into the incubation chamber; a step of reacting the group III element oxide gas with the nitrogen-containing gas in an atmosphere of the oxidizing gas to form a group III nitride crystal; a step of generating an oxide gas by reacting the gas to be oxidized with a substance containing an oxygen element present in the incubation chamber; and discharging the unreacted gas to the outside of the incubation chamber.

In the method for producing a group III nitride crystal, the supersaturation ratio (P) that determines the frequency of crystal nucleus formation on the substrate can be controlled by adjusting the amount of group III element oxide gas produced in the group III element oxide gas production step, adjusting the amount of group III oxide gas to be supplied to the group III nitride production step in the group III element oxide gas supply step, and adjusting the amount of nitrogen-containing gas supplied from the nitrogen-containing gas supply step to the group III nitride crystal production step⁰/P^e). Therefore, the present inventors have found that: by controlling the supersaturation ratio (P)⁰/P^e) The present inventors have found that the quality of group III nitride crystals can be improved while suppressing polycrystallization, which is a problem, and have completed the present invention. In addition, P is⁰Partial pressure of group III oxide gas supplied to determine growth driving force of group III nitride crystal, P^eIs the equilibrium partial pressure of the group III oxide gas.

Hereinafter, a method for producing a group III nitride crystal according to an embodiment will be described with reference to the drawings. In the drawings, substantially the same components are denoted by the same reference numerals.

(embodiment mode 1)

< overview of method for producing group III nitride Crystal >

An outline of the method for producing a group III nitride crystal according to embodiment 1 of the present application will be described with reference to the flowchart of fig. 1. The method for producing a group III nitride crystal according to embodiment 1 includes a reactive gas supply step (S01), a group III element oxide gas generation step (S02), a group III element oxide gas supply step (S03), a nitrogen element-containing gas supply step (S04), an oxidizable gas supply step (S05), a group III nitride crystal generation step (S06), an oxidizable gas reaction step (S07), and a residual gas discharge step (S08).

(1) In the reactive gas supply step, a reactive gas is supplied to the raw material reaction chamber (S01).

(2) In the group III element oxide gas generation step, the starting group III element source is reacted with a reactive gas (the reactive gas is a reducing gas when the starting group III element source is an oxide, and the reactive gas is an oxidizing gas when the starting group III element source is a metal) to generate a group III element oxide gas (S02).

(3) In the group III element oxide gas supply step, the group III element oxide gas produced in the group III element oxide gas production step is supplied to the growth chamber (S03).

(4) In the nitrogen element-containing gas supply step, a nitrogen element-containing gas is supplied to the incubation chamber (S04).

(5) In the oxidizable gas supply step, an oxidizable gas is supplied to the incubation chamber (S05).

(6) In the group III nitride crystal producing step, the group III element oxide gas supplied into the growth chamber in the group III element oxide gas supplying step and the nitrogen element-containing gas supplied into the growth chamber in the nitrogen element-containing gas supplying step are reacted with each other to produce a group III nitride crystal (S06).

(7) In the oxidizing gas reaction step, oxides other than the group III element oxide gas supplied into the growth chamber are reacted with the oxidizing gas to suppress the mixing of oxygen into the group III nitride crystal (S07).

(8) In the residual gas discharge step, unreacted gas that does not contribute to the formation of group III nitride crystals is discharged outside the chamber (S08).

Through the above steps, a group III nitride crystal can be produced on the seed substrate.

< overview of apparatus for producing group III nitride Crystal >

An outline of the apparatus 150 for producing a group III nitride crystal according to embodiment 1 of the present application will be described with reference to a schematic diagram of fig. 2 showing the configuration of the apparatus 150 for producing a group III nitride crystal.

In fig. 2, the sizes, ratios, and the like of the respective components may be different from the actual ones. The apparatus 150 for producing a group III nitride crystal according to embodiment 1 has a raw material reaction chamber 101 disposed in a raw material chamber 100, and a raw material boat 104 having a starting group III element source 105 disposed in the raw material reaction chamber 101. The raw material reaction chamber 101 is connected to a reactive gas supply pipe 103 for supplying a gas that reacts with the starting group III element source 105, and has a group III oxide gas discharge port 107. In the case where the starting group III source is an oxide, a reducing gas is used as the reactive gas, and in the case where the starting group III source is a metal, an oxidizing gas is used as the reactive gas. The material chamber 100 is provided with a first carrier gas supply port 102, and the group III oxide gas and the carrier gas flow from the group III oxide gas and carrier gas discharge port 108 to the growth chamber 111 through a connection pipe 109. The growth chamber 111 has a group III oxide gas and carrier gas supply port 118, an oxidizable gas supply port 113, a nitrogen element-containing gas supply port 112, a second carrier gas supply port 114, and an exhaust port 119, and is provided with a substrate pedestal 117 on which a seed substrate 116 is placed.

< details of the production method and production apparatus >

The method for producing a group III nitride crystal according to embodiment 1 will be described in detail with reference to fig. 2.

Here, a case where metal Ga is used for the starting group III element source 105 will be described.

(1) In the reactive gas supply step, a reactive gas is supplied from the reactive gas supply pipe 103 to the raw material reaction chamber 101.

(2) In the group III element oxide gas producing step, the reactive gas supplied to the raw material reaction chamber 101 in the reactive gas supplying step reacts with the metal Ga as the starting group III element source 105 to produce Ga as a group III element oxide gas₂And (4) O gas. Ga produced₂The O gas is discharged from the raw material reaction chamber 101 to the raw material chamber 100 through the group III oxide gas discharge port 107. Ga discharged₂The O gas is mixed with the first carrier gas supplied from the first carrier gas supply port 102 to the raw material chamber, and is supplied to the group III oxide gas and carrier gas discharge port 108. Here, from Ga₂Of the boiling point of O gasFrom the viewpoint of this, the temperature of the first heater 106 is set to 800 ℃ or higher, and is set to less than 1800 ℃ so as to be lower than the temperature of the second heater 115. The starting Ga source is placed in the raw material boat 104. The raw material boat 104 is preferably shaped to increase the contact area of the reactive gas with the starting Ga source.

The methods for generating the group III oxide gas include a method of reducing the starting Ga source 105 and a method of oxidizing the starting Ga source 105. For example, in the reduction method, an oxide (e.g., Ga) is used as the starting Ga source 105₂O₃) A reducing gas (e.g., H) is used as the reactive gas₂Gas, CO gas, CH₄Gas, C₂H₆Gas, H₂S gas, SO₂Gas). On the other hand, in the oxidation method, a non-oxide (e.g., liquid Ga) is used as the starting Ga source 105, and an oxidizing gas (e.g., H) is used as the reactive gas₂O gas, O₂Gas, CO gas). Further, In source, Al source may be employed as the starting group III element In addition to the starting Ga source 105. Here, as the first carrier gas, an inert gas or H may be used₂A gas.

(3) In the group III element oxide gas supply step, Ga produced in the group III element oxide gas production step is supplied₂The O gas is supplied to the incubation chamber 111 through the group III oxide gas and carrier gas discharge port 108, the connection pipe 109, and the group III oxide gas and carrier gas supply port 118. When the temperature of the connection pipe 109 connecting the raw material chamber 100 and the incubation chamber 111 is lower than the temperature of the raw material chamber 100, a reverse reaction of the reaction of generating the group III oxide gas occurs, and the initial Ga source 105 is precipitated in the connection pipe 109. Therefore, the connection pipe 109 is heated to a temperature higher than that of the first heater 106 by the third heater 110 in a manner not lower than the temperature of the raw material chamber 100.

(4) In the nitrogen element-containing gas supply step, a nitrogen element-containing gas is supplied to the incubation chamber 111 from the nitrogen element-containing gas supply port 112. As the gas containing nitrogen element, NH may be used₃Gas, NO₂Gas, N₂O gas, O gas,N₂H₂Gas, N₂H₄Gases, and the like.

(5) In the oxidizable gas supply step, an oxidizable gas is supplied to the growth chamber 111 from the oxidizable gas supply port 113. The oxidizing gas is supplied because the oxidizing gas other than the group III oxide gas is reduced (oxidizing gas reaction step). As the oxidizable gas, B gas, Ga gas, In gas, Tl gas, or the like can be used from the viewpoint of reactivity with an oxide gas other than the Ga source. Further, as the oxidizable gas, CH may be used₄Gas, C₂H₆Gas, C₃H₈Gas, C₄H₁₀Gas, C₂H₄Gas, C₃H₆Gas, C₄H₈Gas, C₂H₂Gas, C₃H₄Gas, HCN gas, etc.

(6) In the group III nitride crystal production step, the raw material gases supplied into the growth chamber through the respective supply steps are synthesized to produce a group III nitride crystal. The temperature of the incubation chamber 111 is raised by the second heater 115 to a temperature at which the group III oxide gas and the nitrogen element-containing gas react with each other. At this time, the temperature of the incubation chamber 111 is heated to be not lower than the temperature of the raw material chamber 100 so that the reverse reaction of the reaction of generating the group III oxide gas does not occur. Therefore, the temperature of the second heater 115 is set to 1000 ℃ or higher and 1800 ℃ or lower. Furthermore, the Ga generated in the raw material chamber 100 is suppressed₂The temperature of the incubation chamber 111 is changed by the O gas and the first transport gas, and the second heater 115 and the 3 rd heater 110 have the same temperature.

By mixing the group III oxide gas supplied to the growth chamber 111 through the group III oxide supply step and the nitrogen element-containing gas supplied to the growth chamber 111 through the nitrogen element-containing gas supply step upstream of the seed substrate 116, the group III nitride crystal can be grown on the seed substrate 116.

Here, in order to improve the quality of the grown group III nitride crystal, it is necessary to suppress polycrystallization. As a quantitative parameter of the amount of polycrystal produced, an oversaturation ratio (P) can be mentioned⁰/P^e). From the viewpoint of reducing the frequency of nucleus generation for suppressing polycrystallization, it is preferable to set the supply amounts of the group III oxide gas and the nitrogen element-containing gas so that the supersaturation ratio becomes greater than 1 and 5 or less. Further, it is preferably more than 1 and 2.5 or less, and more preferably 1.3 or more and less than 2.5.

Here, P^eIs a group III oxide gas (e.g. Ga)₂Equilibrium partial pressure of O), P⁰Is the supplied partial pressure of the group III oxide gas. P^eThe equilibrium partial pressure of each gas can be calculated by using thermodynamic analysis in the reaction formulae represented by the following formulae (III) and (IV), and obtained as the partial pressure of the group III oxide gas with respect to the total pressure in the equilibrium state. On the other hand, P⁰May be obtained as a ratio of the flow rate of the group III oxide gas relative to the total flow rate of the gas supplied into the incubation chamber. The same applies to the case where the group III oxide gas is a compound of In and Al.

Ga₂O+2NH₃→2GaN+H₂O+2H₂(III)

Ga₂O+H₂→2Ga+H₂O (IV)

Then, the thermal decomposition of the substrate is interfered with (interference する). In the case of considering the use of gallium nitride as the seed substrate, even in the case of a gas containing a nitrogen element (e.g., NH)₃Gas) is suppressed, and thermal decomposition of gallium nitride is likely to occur even at 1050 ℃ or higher in an atmospheric pressure atmosphere. When thermal decomposition occurs, Ga droplets and gallium nitride having a different orientation from the growth surface are generated on the substrate, and become an abnormal growth source such as polycrystallization and pits (fig. 6 (a)).

Therefore, in the case of gallium nitride, it is preferable to start crystal growth from the stage when the substrate temperature reaches 1050 ℃. Further, when considering suppression of an abnormality source due to thermal decomposition on the substrate, it is preferable to grow the crystal from the stage when the substrate temperature reaches 1000 ℃, and it is more preferable to grow the crystal from the stage when the substrate temperature reaches 900 ℃. In addition, when growing the crystal, it is preferable to control the supersaturation ratio as described above from the viewpoint of suppressing polycrystallization.

In this case, in order to suppress the decomposition of the nitrogen-containing gas by the heat from the incubation chamber 111, it is preferable that the nitrogen-containing gas supply port 112 and the outer wall of the incubation chamber 111 be covered with a heat insulating material.

Further, as a problem, parasitic growth of the group III nitride crystal on the furnace wall of the growth chamber 111 and the substrate base 117 may be mentioned. Therefore, by controlling the concentrations of the group III oxide gas and the nitrogen element-containing gas by the carrier gas supplied from the second carrier gas supply port 114 to the growth chamber 111, parasitic growth of the group III nitride crystal on the furnace wall of the growth chamber 111 and the substrate susceptor 117 can be suppressed.

In addition, as the seed substrate 116, gallium nitride, gallium arsenide, silicon, sapphire, silicon carbide, zinc oxide, gallium oxide, and ScAlMgO may be used as an example₄。

As the second transport gas, an inert gas or H may be used₂A gas.

Further, in order to reduce the oxygen concentration of the group III nitride crystal, an oxidizable gas is supplied into the growth chamber 111 through an oxidizable gas supply step. The oxide gas other than the Ga source supplied to the growth chamber 111 through the group III oxide gas generation step and the group III oxide gas supply step is caused by an increase in the oxygen concentration of the group III nitride crystal. Therefore, by reacting an oxide gas other than the Ga source with an oxidizable gas before reaching the seed substrate 116, the mixing of oxygen into the crystal can be suppressed. For example, In gas is used as the oxidizable gas, and H gas, which is an oxide gas other than Ga source, is used together with the In gas₂In gas and H when O reacts₂O gas reacts to form In₂O gas and H₂A gas. In at a growth temperature exceeding 1000 ℃ as In the method for producing a group III nitride crystal according to embodiment 1₂The O gas is very difficult to enter the solid.

The unreacted group III oxide gas, the nitrogen element-containing gas, the oxidizable gas, and the carrier gas are discharged from the exhaust port 119 (residual gas discharge step).

< decomposition inhibiting layer >

In the method for producing a group III nitride crystal, the decomposition inhibiting layer 121 may be introduced directly above the seed substrate 116. Fig. 4 shows a temperature rise curve of the substrate temperature. As an example, a case where the substrate arrival temperature is 1200 ℃. The above has been described with respect to the thermal decomposition when gallium nitride is used as the seed substrate, but when the substrate temperature is 900 ℃ or more, NH as an N source is supplied thereto₃In the case of a gas, gallium nitride is also thermally decomposed. Therefore, in order to suppress thermal decomposition of gallium nitride, it is preferable to supply a group III oxide gas from the thermal decomposition temperature and start growth of gallium nitride. The layer deposited in the process of increasing from the thermal decomposition temperature to the desired substrate temperature is referred to as a decomposition-inhibiting layer (fig. 5). That is, the decomposition-inhibiting layer 121 is a group III nitride layer grown at a lower temperature than the growth layer 123. The decomposition-suppressing layer 121 is grown so that the lattice mismatch between the decomposition-suppressing layer and the seed substrate 116 does not occur, and the degree of lattice mismatch is controlled to 0.01% or less by controlling the concentration of oxygen mixed into the crystal. In addition, the oxygen concentration in the crystal can be changed by changing Ga₂The amount of the supplied O gas is controlled. Thereby, thermal decomposition of gallium nitride is suppressed, and the origin of pits and abnormal growth is suppressed.

Fig. 6 (a) is a schematic cross-sectional view showing an example of crystal growth when the decomposition-inhibiting layer is not introduced, and fig. 6 (b) is a schematic cross-sectional view showing an example of crystal growth when the decomposition-inhibiting layer 121 is introduced. The effect of the presence or absence of the decomposition-inhibiting layer 121 will be described with reference to fig. 6. That is, as shown in fig. 6 (a), when the decomposition-inhibiting layer 121 is not introduced, thermal decomposition of the substrate 116 occurs at the time of temperature rise of the substrate 116 (900 to 1200 ℃), thereby generating the abnormal growth sources 125. The abnormal growth source 125 is, for example, a droplet of a group III element, a crystal having a different orientation from the growth plane of the group III nitride to be grown, or the like. The abnormal growth source 125 causes polycrystals 126 and pits 127 to be generated during the subsequent growth of the growth layer 123 of the group III nitride crystal at 1200 ℃. On the other hand, as shown in fig. 6 (b), when the decomposition-inhibiting layer 121 is introduced, the decomposition-inhibiting layer 121 functions as a protective layer at the time of temperature rise of the substrate (900 to 1200 ℃), prevents thermal decomposition of the substrate 116, and suppresses generation of the abnormal growth source 125. This makes it possible to suppress the generation of polycrystals 126 and pits 127 even when growing the group III nitride crystal growth layer 123 at 1200 ℃.

In conclusion, polycrystallization of the group III nitride crystal can be suppressed, and the crystal quality can be improved.

(outline of examples and comparative examples)

The growth of the group III nitride crystal is performed using a growth furnace as the group III nitride crystal manufacturing apparatus 150 shown in fig. 2. Here, GaN is grown as a group III nitride crystal. As starting Ga source, use is made of liquid Ga, Ga and H as reactive gas₂Reacting O gas to form Ga₂O gas is used as the Ga source gas. Use of NH as N source₃Gas, using H as carrier gas₂Gas and N₂A gas. In addition, the growth time is 1-3 hours under the condition of verification. Further, the density of polycrystals was observed by an optical microscope on the surface of the grown crystal, and the number of polycrystals per unit area (number/cm) was counted²) To be measured.

(example 1)

As the growth conditions, the substrate temperature was 1200 ℃ and the raw material temperature was 1130 ℃. Further, as the supply partial pressure, Ga₂The partial pressure of O gas is set to 0.0076atm and H₂O gas partial pressure of 0.0152atm and NH₃The gas partial pressure is set to 0.0444atm, H₂The gas partial pressure is set to 0.9022atm, N₂The gas partial pressure was set to 0.0305 atm. As for the supersaturation ratio at this time, Ga estimated from thermodynamic calculation is used₂Equilibrium partial pressure P of O^eAnd Ga₂Partial pressure P of supply of O⁰To be P⁰/P^e1.1. In this example, it is not introducedA decomposition inhibiting layer.

As a result of growing GaN, the polycrystalline density was 537 pieces/cm²The growth rate was 32 μm/h.

Details of thermodynamic calculations are described below. The gas species considered is Ga₂O、NH₃、H₂O、H₂、Ga、N₂These 6 types of solid species are 1 type of GaN. The activity of GaN as a solid species is considered to be approximately 1. The partial pressures of these molecular species in the equilibrium state are obtained by solving the following 6 equations (V) to (X) simultaneously.

K1＝(P^e _H2o·P^e _HH2)/(P^e _Ga2O·P^e _NH3)²(V)

K2＝((P^e _Ga)²·P^e _H2)/(P^e _Ga2O·P^e _H2) (VI)

∑Pi＝P^e _Ga2o+P^e _NH3+P^e _H2o+P^e _H2+P^e _Ga+P^e _N2(VII)

0.5(P⁰ _Ga2o-P^e _Ga2o)+(P⁰ _Ga-P^e _Ga)＝P⁰ _NH3-P^e _NH3(VIII)

F＝(1.5P^e _NH3+P^e _H2O+P^e _H2)/(1.5P^e _NH3+P^e _H2O+P^e _H2+P^e _N2) (IX)

A＝(P^e _Ga2O+P^e _H2O)/(P^e _Ga2O+P^e _H2O+P^e _N2) (X)

K＝exp(ΔG/R·T) (XI)

The formulae (V) and (VI) are formulae of equilibrium constants of the formulae (III) and (IV). The values of the equilibrium constants K1 and K2 were calculated based on the gibbs potentials of the respective atoms and molecular species described in non-patent document 1. The equilibrium constant can be represented by formula (XI). Δ G is the difference between gibbs potentials before and after the reaction of each reaction formula, R is the gas constant, and T is the reaction temperature.

The formula (VII) is a formula in which the total pressure in the system is constant. In this system, 1atm is considered.

Formula (VIII) is a stoichiometric formula. The atomic ratio of Ga to N in GaN was calculated assuming that it was 1: 1.

The formula (IX) represents the number of hydrogen atoms relative to the hydrogen and inert gas N in the system₂The ratio of the two components is shown in the formula. The hydrogen atom is assumed not to enter the solid phase and is constant in the system. The value of F can be uniquely calculated by determining the value of the supply partial pressure.

The formula (X) represents the number of oxygen atoms relative to the oxygen in the system and the inert gas N₂The ratio of the two components is shown in the formula. Assuming that the oxygen atom does not enter the solid phase, it is constant in the system. The value of a can be uniquely calculated by determining the value of the supply partial pressure.

The supply partial pressure of each gas species is calculated as a ratio of each gas flow rate to the total gas flow rate flowing into the system. Regarding the supply partial pressure, the total pressure in the system is also considered as "latm". For example, in the case where the total flow rate of Xslm is flowed into the system and the gas flow rate Yslm of the gas Y is flowed, the partial pressure of the gas Y can be represented as (Y/X) atm.

(example 2)

As the growth conditions, the substrate temperature was 1200 ℃ and the raw material temperature was 1130 ℃. In addition, Ga is₂The partial pressure of O gas was set to 0.0076atm and H was added₂O partial pressure of 0.0152atm and NH₃The gas partial pressure was set to 0.0444atm and H was added₂The partial pressure of the gas was 0.8067atm and N was₂The gas partial pressure was set at 0.1261 atm. As for the supersaturation ratio at this time, Ga estimated from thermodynamic calculation is used₂Equilibrium partial pressure P of O^eAnd Ga₂Partial pressure P of supply of O⁰To be P⁰/P^e1.3. In example 2, no decomposition inhibiting layer was introduced.

As a result of growing GaN, the polycrystalline density was 4 pieces/cm²Growth rate ofThe degree was 43 μm/h.

(example 3)

As the growth conditions, the substrate temperature was 1200 ℃ and the raw material temperature was 1130 ℃. In addition, Ga is₂The partial pressure of O gas was set to 0.0076atm and H was added₂O partial pressure of 0.0152atm and NH₃The gas partial pressure was set to 0.0444atm and H was added₂The partial pressure of the gas was set to 0.4578atm and N was added₂The gas partial pressure was set at 0.4750 atm. As for the supersaturation ratio at this time, Ga estimated from thermodynamic calculation is used₂Equilibrium partial pressure P of O^eAnd Ga₂Partial pressure P of supply of O⁰To be P⁰/P^e3.4. In example 3, no decomposition inhibiting layer was introduced.

As a result of growing GaN, the polycrystalline density was 896 grains/cm²The growth rate was 61 μm/h.

(example 4)

As the growth conditions, the substrate temperature was 1200 ℃ and the raw material temperature was 1130 ℃. In addition, Ga is₂O partial pressure was set to 0.0004atm and H was added₂O partial pressure of 0.0004atm and NH₃The gas partial pressure was set to 0.030atm and H₂The partial pressure of the gas was 0.3793atm and N was₂The gas partial pressure was set at 0.5899 atm. As for the supersaturation ratio at this time, Ga estimated from thermodynamic calculation is used₂Equilibrium partial pressure P of O^eAnd Ga₂Partial pressure P of supply of O⁰To be P⁰/P^e4.5. In example 4, the decomposition-inhibiting layer was introduced. The decomposition-inhibiting layer is introduced at a temperature of 1050 ℃ and within a supersaturation ratio of 1.3 or more and less than 2.5 to prevent polycrystallization.

As a result of growing GaN, the polycrystalline density was 5 pieces/cm²The growth rate was 60 μm/h. According to the figure, when the crystal is grown at a supersaturation ratio of 4.5, the polycrystalline density is 920, but the decomposition-inhibiting layer can be optimized to about 100 times.

Comparative example 1

As the growth conditions, the substrate temperature was 1200 ℃ and the raw material temperature was 1130 DEG C. In addition, Ga is₂The partial pressure of O gas was set to 0.0076atm and H was added₂O partial pressure of 0.0152atm and NH₃The partial pressure of the gas was set to 0.1111atm and H was added₂The partial pressure of the gas was set to 0.4578atm and N was added₂The gas partial pressure was set at 0.4083 atm. As for the supersaturation ratio at this time, Ga estimated from thermodynamic calculation is used₂Equilibrium partial pressure P of O^eAnd Ga₂Partial pressure P of supply of O⁰To be P⁰/P^e19. In comparative example 1, no decomposition inhibiting layer was introduced.

As a result of growing GaN, the polycrystalline density was 1792 grains/cm²The growth rate was 71 μm/h.

(summary of examples and comparative examples)

Fig. 3 shows a graph showing the relationship between supersaturation ratio and whether or not a decomposition inhibiting layer is introduced, and polycrystallization (polycrystalline density). The present graph was obtained by plotting the values of the polycrystal degree and the supersaturation ratio obtained in each example and connecting them with a straight line. As shown by the results, the polycrystalline density of 896 grains/cm was achieved at a supersaturation ratio of 3.4²The polycrystal density was achieved at a supersaturation ratio of 1.3 of 4/cm²Further, a polycrystalline density of 537/cm was achieved at a supersaturation ratio of 1.1². Here, for example, when considering a pn junction diode as an electronic device, the diameter of the electrode size is preferably 50 μm or more in consideration of the applied current density. When the polycrystalline density is 1019/cm considering the electrode size of 50 μm²When the number of the particles is converted to 50 μm, the number of the particles is 0.02. In other words, the probability that the electrode portion and the polycrystalline region match each other is 2%, which is a good value. In this case, according to the drawing, when the supersaturation ratio is 5 or less, the polycrystalline density is 1019/cm². If the polycrystalline density is 509 pieces/cm²When the number of the particles is converted to 50 μm, the number of the particles is 0.01. In other words, the probability that the electrode portion and the polycrystalline region coincide with each other is 1%, which is a more preferable value. In this case, according to the drawing, when the supersaturation ratio is 2.5 or less, the polycrystalline density of 509 pieces/cm can be achieved². If the polycrystalline density is 4/cm²The value is a more favorable value. In this case, according to the figure, at the supersaturation ratioIn the case of 1.3, a polycrystalline density of 4 pieces/cm can be achieved²。

When the supersaturation ratio is 1, the crystal does not grow theoretically.

When these are summarized, 1019 particles/cm can be realized by setting the supersaturation ratio to more than 1 and 5 or less²The polycrystalline density is as follows, and furthermore, 509 pieces/cm can be realized by setting the supersaturation ratio to be more than 1 and 2.5 or less²The polycrystalline density below can be 4 pieces/cm by setting the supersaturation ratio to 1.3 or more and less than 2.5²More than 509/cm²Polycrystalline density of (2).

Further, by introducing the decomposition inhibiting layer, the polycrystalline density can be about 1/100 according to the drawing.

The present application includes a combination of any of the above-described various embodiments and/or examples as appropriate, and the effects of the various embodiments and/or examples can be exhibited.

Industrial applicability

According to the method for producing a group III nitride crystal of the present invention, the supersaturation ratio (P) is controlled⁰/P^e) The polycrystallization is suppressed and the quality of the obtained group III nitride crystal is improved.