JP2013091596A - Method for producing nitride crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the deposition of a low-grade crystal on the surface of a seed crystal or inner wall of a reaction vessel in a temperature increasing stage in the case of producing a nitride single crystal by the ammonothermal process and grow a high-quality nitride single crystal in high raw material use efficiency in the following growth stage.SOLUTION: Melt-back treatment to melt the seed crystal to a thickness of ≥1 μm from the surface is carried out in the temperature increasing stage of the ammonothermal process.

Description

  The present invention relates to a method for producing a nitride single crystal using an ammonothermal method for growing a nitride single crystal.

  The ammonothermal method is a method for producing a desired material by using a raw material dissolution-precipitation reaction using a solvent containing nitrogen such as ammonia in a supercritical state and / or a subcritical state. When applied to crystal growth, crystals are precipitated by generating a supersaturated state due to a temperature difference utilizing the temperature dependence of the raw material solubility in a solvent such as ammonia. In order to grow a single crystal by the ammonothermal method, it is necessary that a sufficient amount of raw material exists in a supersaturated state and precipitates. For this purpose, it is necessary that the raw material for crystal growth is sufficiently dissolved in a solvent. is there. However, for example, nitrides such as gallium nitride have a very low solubility in a solvent such as pure ammonia in a temperature and pressure range that can be employed, and therefore, an amount necessary for practical crystal growth cannot be dissolved. For this reason, a mineralizer that improves the solubility of nitrides such as gallium nitride is generally added to the reaction system. Since the mineralizer can form (solvate) a complex with a nitride, more nitride can be dissolved in a solvent such as ammonia.

  When producing a nitride single crystal by the ammonothermal method, first, a step of heating a raw material, a solvent containing nitrogen, a mineralizer, etc. in a reaction vessel (hereinafter simply referred to as a “temperature raising step”). In some cases, a step of growing a crystal in a supercritical state and / or a subcritical state (hereinafter, simply referred to as a “growth step”) is performed. At this time, crystal growth in the reaction vessel occurs not only in the growth step but also in the temperature raising step. For this reason, in the temperature raising step, a low quality crystal is deposited on the surface of the seed crystal (seed) or the inner wall of the reaction vessel, thereby causing a problem that the growth of the high quality crystal in the growth step is hindered.

In view of such a problem, a method for removing the spontaneous nucleus crystals deposited on the inner wall of the reaction vessel before performing the growth process has been proposed (see Patent Document 1). A region in which the raw material is dissolved in a solvent such as ammonia in the reaction vessel (hereinafter sometimes referred to as “raw material dissolution region”), and a region in which the nitride single crystal is grown on the seed crystal in the reaction vessel (hereinafter referred to as “raw material dissolution region”). And may be referred to as a “crystal growth region”), and by maintaining a temperature difference of less than about 10 ° C. for about 1 minute to 2 hours, the spontaneous nucleus crystals are melted and removed. It is described.
Similarly, it has also been proposed to melt back the surface of the seed crystal by providing a temperature difference between the raw material dissolution region and the crystal growth region (see Patent Document 2). In this document, the surface of the seed crystal is melt-backed by maintaining the temperature difference for 0.1 to 20 minutes so that the nitride is more easily dissolved in the crystal growth region than in the raw material dissolution region. It is described that it is preferable to do this. In the growth process, the temperature difference between the raw material dissolution region and the crystal growth region is reversed, and the nitride single crystal is seeded so that the raw material dissolution region is more easily dissolved than the crystal growth region. It is described to grow on top.
Patent Document 3 also describes that a temperature difference is created between the raw material melting region and the crystal growth region in the temperature raising step. Here, the temperature of the crystal growth region is maintained at a temperature of about 300 ° C., which is lower than that of the raw material dissolution region, and then the temperature is raised. In the growth process, the crystal growth region is maintained at a temperature higher than that of the raw material dissolution region. The growth of nitride single crystals is described.

JP 2006-51322 A International Publication No. WO2010 / 053977 JP 2005-530664 A

As described above, several methods for creating a temperature difference between the raw material melting region and the crystal growth region have been proposed. Even when these methods are actually implemented, a sufficiently high quality single crystal nitride can be efficiently produced. It could not be manufactured. When the present inventors examined the cause, it is thought that there exists a cause in the point that meltback is inadequate in the method described in patent document 1 or patent document 2, for example. Further, the method described in Patent Document 3 has a high probability that meltback itself does not occur. For this reason, even if these methods were adopted, it was found that the damage and contamination of the seed crystal surface could not be sufficiently removed, and high-quality crystals could not be grown in the next growth step. .
Based on such knowledge, the present inventors adopt conditions under which a high-quality nitride single crystal can be obtained, and promote the dissolution of the seed crystal surface to perform high-quality crystal growth. It was considered to carry out a suitable meltback. However, if the meltback is further advanced, there is no confirmation that a crystal of good quality can be grown in the subsequent growth process. Conversely, if dissolution of the seed crystal surface is advanced, There has also been a concern that there is a risk that the seed crystal may be dropped or lost and the crystal cannot be grown.
Under the above circumstances, the present inventors can suppress the deposition of low quality crystals on the seed crystal surface or the inner wall of the reaction vessel in the temperature raising step, and in the subsequent growth step, the raw material use efficiency is reduced. The present inventors have intensively studied for the purpose of providing a method for producing a nitride single crystal capable of producing a high-quality nitride single crystal.

As a result of intensive studies, the present inventors have found that the seed crystal can be appropriately melt-backed and that a high-quality crystal can be obtained, and the present invention described below has been provided.
[1] A method for producing a nitride single crystal in which a nitride single crystal is grown in a solvent containing nitrogen in a supercritical state and / or subcritical state, and at least a preparation for disposing a seed crystal in a reaction vessel A step, a temperature raising step for raising the temperature inside the reaction vessel, and a growth step for growing the nitride single crystal on the seed crystal at a growth temperature in this order,
The method for producing a nitride single crystal, wherein in the temperature raising step, a meltback treatment is performed to dissolve the seed crystal with a thickness of 1 μm or more from the surface.
[2] The method for producing a nitride single crystal according to [1], wherein the meltback treatment is performed for 3 hours or more.
[3] A method for producing a nitride single crystal in which a nitride single crystal is grown in a solvent containing nitrogen in a supercritical state and / or a subcritical state, and at least a temperature raising step for raising the temperature in the reaction vessel And a growth step of growing the nitride single crystal at the growth temperature,
In the temperature raising step, a temperature (T1) of a region where a seed crystal is arranged in the reaction vessel and a nitride single crystal is grown, and a region in which the raw material of the nitride single crystal in the reaction vessel is dissolved in a solvent. A nitride which is subjected to a meltback treatment for 3 hours or more with respect to the seed crystal by reversing the level relationship with the temperature (T2) from the level relationship between the temperature (T1) and the temperature (T2) in the growth step. A method for producing a single crystal.
[4] The method for producing a nitride single crystal according to [3], wherein the temperature (T1) of the region where the seed crystal is arranged and the nitride single crystal is grown in the meltback treatment is 400 ° C. to 700 ° C. .
[5] The method for producing a nitride single crystal according to any one of [1] to [4], wherein a mineralizer having a positive solubility characteristic is used in the growth step.
[6] The method for producing a nitride single crystal according to any one of [1] to [4], wherein a mineralizer having negative solubility characteristics is used in the growth step.
[7] The method for producing a nitride single crystal according to any one of [1] to [6], wherein an acidic mineralizer is used in the growth step.

  According to the method for producing a nitride single crystal of the present invention, it is possible to suppress the deposition of low quality crystals on the surface of the seed crystal or the inner wall of the reaction vessel in the temperature raising step, the raw material use efficiency is high, and high quality nitride Single crystals can be produced.

It is a schematic diagram of the crystal manufacturing apparatus which can be used by this invention.

Below, the manufacturing method of the nitride single crystal of this invention is demonstrated in detail. The description of the constituent elements described below may be made based on typical embodiments of the present invention, but the present invention is not limited to such embodiments.
In addition, a numerical range expressed using “to” in this specification means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.

[Production Method of Nitride Single Crystal of the Present Invention]
The method for producing a nitride single crystal according to the present invention is a method for producing a nitride single crystal using an ammonothermal method, and includes at least a temperature raising step for raising the temperature in a reaction vessel, and the nitriding at the growth temperature. A temperature step (T1) of a region (crystal growth region) in which a seed crystal is arranged in the reaction vessel and grows a nitride single crystal in the temperature raising step, The relationship between the temperature (T2) of the region (raw material dissolution region) where the nitride single crystal raw material is dissolved in the solvent in the reaction vessel is expressed as the temperature (T1) and the temperature (T2) in the growth step. Contrary to the elevation relationship, the seed crystal is melt-backed.
As described above, in the method for producing a nitride single crystal of the present invention, the seed crystal is subjected to a meltback process in the temperature raising step. The meltback treatment is performed so that the relationship between the temperature (T1) of the crystal growth region and the temperature (T2) of the raw material dissolution region in the reaction vessel in the growth step is reversed, that is, in the growth step. The temperature (T1) and the temperature (T2) are set by setting the temperature (T1) and the temperature (T2) in the temperature raising step so that the height relationship between the temperature (T1) and the temperature (T2) is reversed.

According to the method for producing a nitride single crystal of the present invention, as described above, the meltback process is performed by reversing the height relationship between the temperature of the crystal growth region and the temperature of the raw material dissolution region in the temperature raising step with respect to the growth step. It is possible to suppress the deposition of low quality crystals on the surface of the seed crystal or the inner wall of the reaction vessel in the temperature raising step. Thereby, the raw material use efficiency can be increased, and the surface of the seed crystal can be dissolved (melt back) by the melt back treatment. For this reason, since damage and contamination on the seed crystal surface can be sufficiently removed, a high-quality nitride single crystal can be grown on the seed crystal.
The “ammonothermal method” is a method for producing a desired material using a dissolution-precipitation reaction of raw materials using a solvent containing nitrogen such as ammonia in a supercritical state and / or a subcritical state. . When the ammonothermal method is applied to crystal growth, crystals are precipitated by generating a supersaturated state due to a temperature difference utilizing the temperature dependence of the solubility of the raw material in the solvent.
Gallium nitride crystal growth by the ammonothermal method is a reaction under supercritical conditions at high temperature and pressure, and the solubility of gallium nitride in a solvent such as pure ammonia in the supercritical state and / or subcritical state is extremely high. Because it is small, mineralizers are used to improve solubility and promote crystal growth.
In the method for producing a nitride single crystal of the present invention, a temperature and a pressure in a reaction vessel containing a seed crystal, a nitrogen-containing solvent, a raw material, and a mineralizer are set in a supercritical state and / or a subcritical state. A nitride single crystal is grown on the surface of the seed crystal by controlling to be in a state.

[Temperature raising process]
The temperature raising step is a step of raising the temperature in the reaction vessel. The temperature rise is usually performed from room temperature. The temperature reached by the temperature increase is the temperature at which the meltback process is performed. The temperature at which the meltback treatment is performed is preferably the growth temperature in the growth step or a temperature in the vicinity thereof. The specific temperature will be described in detail in the description of the meltback process described later.
(Reaction vessel)
The method for producing a nitride single crystal of the present invention can be carried out in a reaction vessel.
The reaction vessel can be selected from those capable of withstanding high temperature and high pressure conditions when growing a nitride single crystal. Examples of the reaction vessel include those described in JP-T-2003-511326 (International Publication No. 01/024921 pamphlet) and JP-T-2007-509507 (International Publication No. 2005/043638 pamphlet). A mechanism that adjusts the pressure applied to the reaction vessel and its contents from the outside may be provided, or an autoclave that does not have such a mechanism may be used.

The reaction vessel is preferably made of a material having pressure resistance and corrosion resistance. In particular, a Ni-based alloy having excellent corrosion resistance against a solvent such as ammonia, Stellite (registered trademark of Deloro Stellite Company, Inc.) It is preferable to use a Co-based alloy such as More preferably, it is a Ni-based alloy. Specifically, Inconel 625 (Inconel is a registered trademark of Huntington Alloys Canada Limited, the same applies hereinafter), Nimonic 90 (Nimonic is a registered trademark of Special Metals Wiggin Limited, the same applies hereinafter), RENE41 (Teledyne). Allvac, Inc.), Inconel 718 (Inconel is a registered trademark of Huntington Alloys Canada Limited), Hastelloy (registered trademark of Haynes International, Inc.), Waspaloy (registered trademark of United Technologies, Inc.).
The composition ratio of these alloys depends on the temperature and pressure conditions of the solvent in the system, and the reactivity with the mineralizers and their reactants contained in the system and / or the oxidizing power / reducing power, pH conditions, What is necessary is just to select suitably. In order to use these as materials constituting the inner surface of the reaction vessel, the reaction vessel itself may be manufactured using these alloys, and a thin film is formed as an inner cylinder and placed in a pressure resistant vessel as a reaction vessel. Alternatively, the inner surface of any reaction vessel material may be plated.

  In order to further improve the corrosion resistance of the reaction vessel, the inner surface of the reaction vessel may be lined or coated using the excellent corrosion resistance of the noble metal. Moreover, the material of the reaction vessel can be a noble metal. Examples of the noble metal herein include Pt, Au, Ir, Ru, Rh, Pd, Ag, and alloys containing these noble metals as a main component, and among these, it is preferable to use Pt having excellent corrosion resistance and an alloy thereof. .

  A specific example of a crystal production apparatus including a reaction vessel that can be used in the method for producing a nitride single crystal of the present invention is shown in FIG. FIG. 1 is a schematic view of a crystal manufacturing apparatus that can be used in the present invention. In the crystal manufacturing apparatus shown in FIG. 1, crystal growth is performed in a capsule 20 loaded as a reaction vessel in the autoclave 1. The capsule 20 includes a raw material dissolution region 9 for dissolving the raw material and a crystal growth region 6 for growing crystals. A solvent and a mineralizer can be placed in the raw material dissolution region 9 together with the raw material 8, and the seed crystal 7 can be installed in the crystal growth region 6 by suspending it with a wire. Between the raw material melting region 9 and the crystal growth region 6, a baffle plate 5 that partitions the two regions is installed. The baffle plate 5 has a hole area ratio of preferably 2% or more, more preferably 3% or more, more preferably 60% or less, and even more preferably 40% or less. The material of the surface of the baffle plate is preferably the same as the material of the capsule 20 that is a reaction vessel. Further, in order to provide more corrosion resistance and to purify the crystal to be grown, the surface of the baffle plate should be Ni, Ta, Ti, Nb, Pd, Pt, Au, Ir, Mo, W, pBN. Pd, Pt, Au, Ir, Mo, W, and pBN are more preferable, and Pt, Mo, and W are particularly preferable. In the crystal manufacturing apparatus shown in FIG. 1, the gap between the inner wall of the autoclave 1 and the capsule 20 can be filled with the second solvent. Here, ammonia or the like can be filled as the second solvent while filling the nitrogen gas from the nitrogen cylinder 13 through the valve 10 or confirming the flow rate from the ammonia cylinder 12 with the mass flow meter 14. In addition, the vacuum pump 11 can perform necessary pressure reduction. Note that a valve, a mass flow meter, and a conduit do not necessarily have to be installed in the crystal manufacturing apparatus used when the nitride single crystal manufacturing method of the present invention is carried out.

  A lining can also be used to provide corrosion resistance by the autoclave. The lining material is preferably at least one metal or element of Pt, Ir, Ag, Pd, Rh, Cu, Au and C, or an alloy or compound containing at least one metal, More preferably, it is an alloy or compound containing at least one or more kinds of metals or elements of Pt, Ag, Cu and C, or at least one kind of metals because they are easily lined. For example, Pt simple substance, Pt-Ir alloy, Ag simple substance, Cu simple substance, graphite, etc. are mentioned.

(Meltback processing)
In the present invention, for example, when a mineralizer having positive solubility characteristics is used, the temperature of the raw material dissolution region (T2 _grow ) is set higher than the temperature of the crystal growth region (T1 _grow ) in the growth process. (I.e., temperature (T1 _grow ) <temperature (T2 _grow )). At this time, the temperature relationship between the crystal growth region and the raw material dissolution region is reversed at least once in the temperature raising step so that the temperature of the crystal growth region (T1 _elev ) is higher than the temperature of the raw material dissolution region (T2 _elev ). (Ie, temperature (T1 _elev )> temperature (T2 _elev )), the seed crystal is subjected to a _meltback treatment. In this case, the difference (ΔT _grow = T2 _grow −T1 _grow ) between the temperature of the raw material dissolution region (T2 _grow ) and the temperature of the crystal growth region (T1 _grow ) in the growth step is a positive value. Is _subjected to a _{meltback treatment so} that the difference (ΔT _elev = T2 _elev −T1 _elev ) between the temperature of the raw material melting region (T2 _elev ) and the temperature of the crystal growth region (T1 _elev ) becomes a negative value.

On the other hand, when a mineralizer having a negative solubility characteristic is used, the temperature of the raw material dissolution region (T2 _grow ) is set lower than the temperature of the crystal growth region (T1 _grow ) in the growth process ( Temperature (T1 _grow )> Temperature (T2 _grow )). At this time, the temperature relationship between the crystal growth region and the raw material dissolution region is reversed at least once in the temperature raising step so that the temperature (T2 _elev ) of the raw material dissolution region is higher than the temperature (T1 _elev ) of the crystal growth region ( That is, the temperature (T1 _elev ) <temperature (T2 _elev ) _makes it possible to subject the seed crystal to a _meltback process. In this case, the difference (ΔT _grow = T2 _grow −T1 _grow ) between the temperature of the raw material dissolution region (T2 _grow ) and the temperature of the crystal growth region (T1 _grow ) in the growth step is a negative value. Is _subjected to a _{meltback process so} that the difference (ΔT _elev = T2 _elev −T1 _elev ) between the temperature of the raw material melting region (T2 _elev ) and the temperature of the crystal growth region (T1 _elev ) becomes a positive value.
Here, the positive solubility characteristic means a characteristic such that the solubility of a solute such as a GaN raw material in a solvent such as ammonia increases with an increase in temperature. On the other hand, the negative solubility characteristic means a characteristic such that the solubility of a solute such as a GaN raw material in a solvent such as ammonia decreases with increasing temperature.

In the growth step, the temperature of the raw material dissolution region (T2 _grow ) is set higher than the temperature of the crystal growth region (T1 _grow ) (temperature (T1 _grow ) <temperature (T2 _grow )). temperature (T1 _elev) the material temperature dissolution zone (T2 _elev) higher than (the temperature (T1 _elev)> temperature (T2 _elev)) and, if subjected to melt-back process to the seed crystal, wherein at the time of melt-back process The temperature (T1 _elev ) of the crystal growth region is preferably 400 ° C. or higher, more preferably 425 ° C. or higher, further preferably 450 ° C. or higher, and 700 ° C. from the viewpoint of the material strength of the pressure vessel and the efficiency of _meltback. The following is preferable, 675 ° C. or lower is more preferable, and 650 ° C. or lower is further preferable. The temperature (T2 _elev ) of the raw material melting region is preferably 400 ° C. or higher, more preferably 425 ° C. or higher, further preferably 450 ° C. or higher, from the viewpoint of the material strength of the pressure vessel and the efficiency of _meltback. 700 ° C. or lower is preferable, 675 ° C. or lower is more preferable, and 650 ° C. or lower is further preferable.
At this time, the difference (ΔT _elev = T2 _elev −T1 _elev ) between the temperature of the raw material melting region (T2 _elev ) and the temperature of the crystal growth region (T1 _elev ) at the time of _{meltback treatment} is the _meltback efficiency and seed crystal From the viewpoint of protection, -200 ° C to 0 ° C is preferable, -150 ° C to 0 ° C is more preferable, -100 ° C to 0 ° C is further preferable, and -50 ° C to -1 ° C is particularly preferable.

In the growth step, the temperature of the raw material dissolution region (T2 _grow ) is set lower than the temperature of the crystal growth region (T1 _grow ) (temperature (T1 _grow )> temperature (T2 _grow )). temperature (T1 _elev) the material temperature dissolution zone (T2 _elev) lower than (the temperature (T1 _elev) <temperature (T2 _elev)) and, if subjected to melt-back process to the seed crystal, wherein at the time of melt-back process The temperature (T1 _elev ) of the crystal growth region is preferably 400 ° C. or higher, more preferably 425 ° C. or higher, further preferably 450 ° C. or higher, and 700 ° C. from the viewpoint of the material strength of the pressure vessel and the efficiency of _meltback. The following is preferable, 675 ° C. or lower is more preferable, and 650 ° C. or lower is further preferable. The temperature (T2 _elev ) of the raw material melting region is preferably 400 ° C. or higher, more preferably 425 ° C. or higher, further preferably 450 ° C. or higher, from the viewpoint of the material strength of the pressure vessel and the efficiency of _meltback. 700 ° C. or lower is preferable, 675 ° C. or lower is more preferable, and 650 ° C. or lower is further preferable.
At this time, the difference (ΔT _elev = T2 _elev −T1 _elev ) between the temperature of the raw material melting region (T2 _elev ) and the temperature of the crystal growth region (T1 _elev ) at the time of _{meltback treatment} is the _meltback efficiency and seed crystal From the viewpoint of protection, 0 ° C to 200 ° C is preferable, 0 ° C to 150 ° C is more preferable, 0 ° C to 100 ° C is further preferable, and 1 ° C to 50 ° C is particularly preferable.

The meltback treatment is performed for 3 hours or more from the viewpoint of sufficiently melting back (dissolving) the surface of the seed crystal and removing the damage and contamination of the surface while suppressing the precipitation of crystals on the inner wall of the reaction vessel. Preferably, it is applied for 6 hours or more, more preferably for 12 hours or more, and particularly preferably for 15 hours or more. The upper limit of the meltback treatment time is preferably 36 hours or less, more preferably 30 hours or less, and particularly preferably 24 hours or less from the viewpoint of productivity and seed crystal protection. Further, in the temperature raising step, the temperature in the reaction vessel may be controlled and the meltback treatment may be performed a plurality of times. In this case, it is preferable to set the total time of the meltback treatment within the above range.
The pressure in the reaction vessel at the time of the meltback treatment is preferably 120 MPa or more, more preferably 150 MPa or more, further preferably 180 MPa or more, and preferably 700 MPa or less, from the viewpoint of the material strength of the pressure vessel and the efficiency of the meltback. 500 MPa or less is more preferable, and 350 MPa or less is more preferable.

  According to the method for producing a nitride single crystal of the present invention, since the seed crystal before crystal growth can be melt-backed, a wafer that has only been sliced (as-sliced) or lapped only after being sliced (as-lapped) ) A wafer can be used. For this reason, a high quality crystal can be grown on the surface of the seed crystal without using an expensive polished substrate subjected to polishing such as CMP. For this reason, it is also possible to reduce the cost from this viewpoint.

In the meltback treatment, the surface of the seed crystal is preferably melt-backed (dissolved) on average by 1 μm or more on average from the viewpoint of sufficiently removing damage and contamination on the surface of the seed crystal, and melt-backed by 10 μm or more. More preferably, it is particularly preferable that the melt back is 15 μm or more. When the surface of the seed crystal is dissolved by 1 μm or more on average, damage and contamination on the surface of the seed crystal are removed. Regarding the thickness to be dissolved, if the absolute value of ΔT _elev at the time of the _meltback process is small, the melted thickness can be increased by increasing the time of the _{meltback process} . When the value is large, the melted thickness can be increased compared with the case where the absolute value of ΔT _elev is small even when the _meltback processing time is shortened. Since the ease of dissolution differs depending on the plane orientation of the main surface, the conditions for the meltback treatment can be appropriately selected by combining temperature and time. In particular, since the seed crystal having the M plane as the main surface is not easily _{melted back} , it is preferable to set the _meltback treatment time to 3 hours or longer, or to _set the absolute value of ΔT _elev to 20 ° C. or higher.

[Growth process]
The growth step is a step of growing the nitride single crystal at the growth temperature. In the method for producing a nitride single crystal of the present invention, the nitride single crystal grows on the seed crystal that has been subjected to the meltback treatment in the temperature raising step. In the growth step, a nitride single crystal is grown in a supercritical state and / or a subcritical state using a solvent containing nitrogen.
In the supercritical state, the viscosity is generally low and it is more easily diffused than the liquid, but has the same solvating power as the liquid. The subcritical state means a liquid state having a density substantially equal to the critical density near the critical temperature. For example, in the raw material melting region, the raw material is melted as a supercritical state, and in the crystal growth part, the temperature is changed so as to be in the subcritical state, and the crystal growth using the difference in solubility between the supercritical state and the subcritical state raw material is also performed. Is possible.

When in the supercritical state, the reaction mixture is generally maintained at a temperature above the critical point of the solvent. When an ammonia solvent is used, the critical point is a critical temperature of 132 ° C. and a critical pressure of 11.35 MPa. However, if the filling rate with respect to the volume of the reaction vessel is high, the pressure far exceeds the critical pressure even at a temperature below the critical temperature. In the present invention, the “supercritical state” includes such a state exceeding the critical pressure. Since the reaction mixture is enclosed in a constant volume reaction vessel, the increase in temperature increases the pressure of the fluid. In general, if T> Tc (critical temperature of one solvent) and P> Pc (critical pressure of one solvent), the fluid is in a supercritical state.
Under supercritical conditions, a sufficient growth rate of the nitride single crystal can be obtained. The reaction time depends in particular on the reactivity of the mineralizer and the thermodynamic parameters, ie temperature and pressure values. During the synthesis or growth of the nitride single crystal, the pressure in the reaction vessel is preferably 120 MPa or more, more preferably 150 MPa or more, and further preferably 180 MPa or more. The pressure in the reaction vessel is preferably 700 MPa or less, more preferably 500 MPa or less, further preferably 350 MPa or less, and particularly preferably 300 MPa or less. The pressure is appropriately determined depending on the filling rate of the solvent volume with respect to the temperature and the volume of the reaction vessel. Originally, the pressure in the reaction vessel is uniquely determined by the temperature and the filling rate of the solvent, but in practice, additives such as raw materials and mineralizers, temperature heterogeneity in the reaction vessel, and It varies slightly depending on the presence of free volume.

(Temperature control)
For example, when a mineralizer having a positive solubility characteristic is used, the raw material dissolution region is set to a high temperature and the crystal growth region is set to a low temperature. In this case, the difference (ΔT _grow = T2 _grow −T1 _grow ) between the temperature of the raw material dissolution region (T2 _grow ) and the temperature of the crystal growth region (T1 _grow ) in the growth process is a positive value (temperature of the raw material dissolution region ( T2 _grow ) can be increased up to the maximum use temperature (Tmax) of a reaction vessel such as an autoclave. Therefore, if the temperature of the raw material dissolution region is set to the maximum use temperature (Tmax) of the reaction vessel, the temperature (T2 _grow ) T1 _grow ) can be expressed by the following equation.
T1 _grow = Tmax-ΔT
The temperature difference ΔT is set so that a certain degree of supersaturation can be secured so that the crystal grows sufficiently. The temperature difference for ensuring a certain degree of supersaturation decreases as the slope of the solubility curve increases. Therefore, according to the present invention, the temperature (T1 _grow ) of the crystal growth region can be set high by appropriately selecting a mineralizer.

  The preferred range of the temperature difference (ΔT) in the growth step varies depending on the mineralizer used, but in general, it is preferably set to 5 ° C. or higher, more preferably set to 10 ° C. or higher, More preferably, the temperature is set to 15 ° C. or higher, more preferably 70 ° C. or lower, more preferably 65 ° C. or lower, and still more preferably 55 ° C. or lower. By growing in such a small temperature difference, the precipitation of microcrystals due to the generation of spontaneous nuclei can be suppressed. Further, since the degree of supersaturation is appropriately controlled, smooth crystal growth proceeds on the seed crystal, and preferable hexagonal gallium nitride in which mixing of cubic gallium nitride is suppressed grows.

In the growth step, the temperature (T1 _grow ) of the crystal growth region is usually set to 400 ° C. or higher, preferably 450 ° C. or higher, more preferably 495 ° C. or higher, and the upper limit is preferably set to 645 ° C. or lower. A temperature of the crystal growth region (T1 _grow ) of 400 ° C. or higher is preferable because the obtained nitride single crystal is likely to be a single-layer hexagonal crystal and has excellent crystallinity. In particular, when the temperature is 495 ° C. or higher, it has been confirmed that cubic crystals are not detected and a single-layer hexagonal crystal is formed. The temperature of the crystal growth region (T1 _grow ) here is the temperature of the region in which the target nitride single crystal is grown. When the nitride single crystal is grown on the seed crystal, the temperature of the seed crystal and the vicinity thereof. It is. The temperature (T2 _grow ) of the raw material dissolution region is usually set to 405 ° C. or higher, preferably 455 ° C. or higher, more preferably 500 ° C. or higher, and the upper limit is preferably set to 650 ° C. or lower. The temperature of the raw material dissolution region (T2 _grow ) here is the temperature of the region where the raw material is dissolved in the solvent, and when it is dissolved in a wide range, it is the temperature of the region where the amount of raw material dissolution is large. Note that the upper limit values of the temperature range of the crystal growth region and the temperature range of the raw material dissolution region mentioned here are those newly developed reactions when a practical reaction vessel having a high maximum use temperature (Tmax) is developed. It can be raised according to the maximum operating temperature of the container.

The temperature of the crystal growth region (T1 _grow ), the temperature of the raw material dissolution region (T2 _grow ), and the temperature difference (ΔT) can also be defined from another viewpoint. That is, it is preferable that the supersaturation degree (ΔS) of nitride with respect to ammonia is set to 0.03 or more, more preferably set to 0.06 or more, and 0.09 or more. More preferably, it is set to be 0.43 or less, more preferably 0.40 or less, and to be set to 0.33 or less. Further preferred.
For example, by adopting a combination of mineralizers that increase the slope of the solubility curve and reducing the temperature difference (ΔT), temperature unevenness and temperature fluctuation in the crystal growth region can be reduced. As a result, the temperature range optimum for crystal growth is expanded and the time at the optimum temperature for crystal growth is extended, so that stable crystal growth is possible. The smaller the temperature distribution in the crystal growth region, the better. However, it is usually in the range of 0 to 30 ° C, preferably in the range of 0 to 20 ° C, and more preferably in the range of 0 to 10 ° C. preferable.

  The mineralizer, solvent, raw material, and seed crystal used in the method for producing a nitride single crystal of the present invention will be described below.

(Mineralizer)
In the present invention, a mineralizer generally used in the ammonothermal method can be appropriately selected and used. The mineralizer used may be a basic mineralizer or an acidic mineralizer. Basic mineralizers include alkali metals, alkaline earth metals, compounds containing rare earth metals and nitrogen atoms, alkaline earth metal amides, rare earth amides, alkali nitride metals, alkaline earth metal nitrides, azide compounds, and other hydrazines. Class of salts. Preferably, it is an alkali metal amide, and specific examples include sodium amide (NaNH ₂ ), potassium amide (KNH ₂ ), and lithium amide (LiNH ₂ ). The acidic mineralizer is a compound containing a halogen atom, and examples thereof include ammonium halides. For example, ammonium chloride (NH ₄ Cl), ammonium iodide (NH ₄ I), ammonium bromide (NH ₄ Br) , Ammonium fluoride (NH ₄ F). In the present invention, it is preferable to use an acidic mineralizer containing ammonium halide. Moreover, a mineralizer may be used individually by 1 type, and may mix and use multiple types suitably.
When performing the crystal growth, aluminum halide, phosphorus halide, silicon halide, germanium halide, zinc halide, arsenic halide, tin halide, antimony halide, bismuth halide, etc. are used in a reaction vessel. May be present.

  The molar concentration of the halogen element contained in the mineralizer with respect to a solvent such as ammonia is preferably 0.1 mol% or more, more preferably 0.3 mol% or more, and further preferably 0.5 mol% or more. preferable. Further, the molar concentration of the halogen element contained in the mineralizer with respect to a solvent such as ammonia is preferably 30 mol% or less, more preferably 20 mol% or less, and even more preferably 10 mol% or less. If the concentration is too low, the solubility tends to decrease and the growth rate tends to decrease. On the other hand, when the concentration is too high, the solubility tends to be too high and the generation of spontaneous nuclei increases, or the degree of supersaturation becomes too high and control tends to be difficult.

In the present invention, either a mineralizer having a positive solubility characteristic or a mineralizer having a negative solubility characteristic can be used.
Examples of preferable mineralizers having the positive solubility characteristics include ammonium chloride, ammonium bromide, and ammonium iodide.
Examples of preferable mineralizers having the negative solubility characteristic include sodium amide, potassium amide, and ammonium fluoride.

(solvent)
As the solvent used in the ammonothermal method, a solvent containing nitrogen can be used. Examples of the solvent containing nitrogen include a solvent that does not impair the stability of the grown nitride single crystal. Examples of the solvent include ammonia, hydrazine, urea, amines (for example, primary amines such as methylamine, secondary amines such as dimethylamine, tertiary amines such as trimethylamine, and ethylenediamine. Diamine) and melamine. These solvents may be used alone or in combination.
The amount of water or oxygen contained in the solvent is desirably as small as possible, and the content thereof is preferably 1000 ppm or less, more preferably 10 ppm or less, and further preferably 0.1 ppm or less. When ammonia is used as a solvent, the purity is usually 99.9% or more, preferably 99.99% or more, more preferably 99.999% or more, and particularly preferably 99.9999% or more. .

(material)
In the manufacturing method, as the raw material, a raw material usually used for growing a nitride single crystal by an ammonothermal method can be appropriately selected and used. For example, when growing a gallium nitride crystal, metal gallium, gallium nitride, or a mixture thereof can be used as a raw material to be a gallium source.
For other nitride single crystal growth conditions and the like, reference can be made to the column of manufacturing conditions in JP-A-2007-238347.

(Seed crystal)
Although it does not specifically limit as said seed crystal, It is preferable to use the same single crystal as the nitride grown in a growth process. Specific examples of the seed crystal include nitride single crystals such as gallium nitride (GaN) and aluminum nitride (AlN).
The seed crystal can be determined in consideration of solubility in a solvent and reactivity with a mineralizer. For example, as a seed crystal of GaN, a single crystal obtained by crystal growth on a heterogeneous substrate such as sapphire and then peeled off, a single crystal obtained by crystal growth of Na, Li, or Bi from metal Ga as a flux, liquid A single crystal obtained by homoepitaxial growth using a phase epitaxy method (LPE method), a single crystal produced based on a solution growth method, a crystal obtained by cutting them, and the like can be used. The specific method of the crystal growth is not particularly limited, and for example, a hydride vapor deposition method (HVPE) method, a metal organic chemical vapor deposition method (MOCVD method), a liquid phase method, an ammonothermal method, or the like is adopted. can do.

The kind of the main surface of the seed crystal is not particularly limited. It may be a polar surface, a nonpolar surface, or a semipolar surface. The main surface here means a surface having the maximum area among the surfaces constituting the crystal. As the seed crystal, a seed crystal having a C plane as a main surface, a seed crystal having an M plane as a main surface, a seed crystal having an A plane as a main surface, or a seed crystal having a semipolar plane as a main surface is used. it can. These main surfaces may be formed by cleaving. For example, if a seed crystal having an M plane generated by cleavage is used, the quality is higher than that of a crystal grown using a seed crystal having an unpolished M plane or a seed crystal having a precisely polished M plane. This single crystal nitride can be produced at a high growth rate. For example, when the nitride single crystal is a hexagonal crystal and its main surface is represented by (hklm), h, k, l and m are each independently an integer of −3 to 3. Preferably, it is an integer of −2 to 2. Specific examples of the main surface of the nitride single crystal include {10-10} plane, {11-20} plane, [10-11] plane, [10-1-1] plane, [20-21] plane, [20-2-1] plane and the like.
The seed crystal can be pretreated. Examples of the pretreatment include polishing the crystal growth surface of the seed crystal, etching the seed crystal, and washing.

(Nitride single crystal)
The main surface of the nitride single crystal produced by the method for producing a nitride single crystal of the present invention preferably coincides with the main surface of the seed crystal from the viewpoint of production efficiency.
The nitride single crystal is preferably a self-supporting crystal. Specifically, the thickness of the crystal itself (m-axis direction or a-axis direction thickness) is preferably 100 μm or more, more preferably 500 μm or more, and further preferably 1 mm or more. The above is particularly preferable. In particular, a nitride single crystal obtained by growing a crystal using a HVPE method on a seed crystal having a nonpolar plane or a semipolar plane as a main plane is a laminated layer inherent in the grown crystal when the thickness exceeds 0.1 mm. The number of defects tends to increase significantly. In contrast, the nitride single crystal of the present invention can increase the number of stacking faults even when the thickness is set to 1 mm or more, so that a high-quality crystal can be enlarged. The thickness and size of the crystal (substrate) can be adjusted within a desired range by adjusting the thickness of the grown crystal and adjusting the processing such as polishing, cutting, and etching.

The nitride single crystal is preferably a group 13 metal nitride single crystal of the periodic table. For example, as the nitride constituting the seed crystal and the growth crystal, gallium nitride, aluminum nitride, indium nitride, a mixed crystal thereof, or the like is preferable, and among these, gallium nitride is more preferable.
When the nitride single crystal is manufactured, a nitride single crystal having a desired shape can be obtained by appropriately selecting the shape of the seed crystal, growth conditions, and the like. For example, by performing ammonothermal crystal growth using a seed crystal having an M-plane as a main surface, a nitride single crystal having a thickness in the m-axis direction can be obtained with higher production efficiency.
The nitride single crystal may be used as it is or after being processed.

(Manufacturing process)
An example of the method for producing a nitride single crystal of the present invention will be described. When carrying out the method for producing a nitride single crystal of the present invention, first, a seed crystal, a nitrogen-containing solvent, a raw material, and a mineralizer are put in a reaction vessel and sealed. Here, as the seed crystal, a nitride crystal grown with the C-plane as the main surface is cut out in a desired direction, whereby a substrate with the main surface being a nonpolar surface or a semipolar surface can be obtained. Thereby, a seed crystal having a nonpolar plane such as an M plane and a semipolar plane such as [10-11] or [20-21] can be obtained. In particular, when a nitride single crystal having a large-diameter C-plane is manufactured, a large-diameter seed crystal can be obtained by cutting in a direction perpendicular to the c-axis.
Prior to introducing the material into the reaction vessel, the reaction vessel may be evacuated. Moreover, you may distribute | circulate inert gas, such as nitrogen gas, at the time of introduction | transduction of material. The seed crystal is usually charged into the reaction vessel at the same time or after the raw material and the mineralizer are charged. The seed crystal is preferably fixed to a noble metal jig similar to the noble metal constituting the inner surface of the reaction vessel. After loading, heat deaeration may be performed as necessary.

For example, when the manufacturing apparatus shown in FIG. 1 is used, the capsule 20 is sealed after putting seed crystals, a nitrogen-containing solvent, a raw material, and a mineralizer in the capsule 20 that is a reaction vessel. (Autoclave) 1 is loaded, and preferably, the space between the pressure-resistant vessel and the reaction vessel is filled with the second solvent to seal the pressure-resistant vessel.
Thereafter, the whole is heated to bring the inside of the reaction vessel into a supercritical state and / or a subcritical state (temperature raising step). In the method for producing a nitride single crystal of the present invention, the above-described meltback treatment is performed on the seed crystal in the temperature raising step.
In order to achieve the temperature range and pressure range in the reaction vessel, the injection rate of the solvent into the reaction vessel, that is, the filling rate is the free volume of the reaction vessel, that is, the polycrystalline raw material and the seed crystal are used in the reaction vessel. In this case, subtract the volume of the seed crystal and the structure where it is installed from the volume of the reaction vessel, and if a baffle plate is installed, subtract the volume of the baffle plate from the volume of the reaction vessel. The liquid density at the boiling point of the remaining volume of the solvent is preferably 20% or more, more preferably 30% or more, still more preferably 40% or more, and preferably 95% or less, more preferably 80% or less. More preferably, it is made 70% or less.

Nitride single crystal growth in a reaction vessel is performed by heating and heating the reaction vessel using an electric furnace having a thermocouple, etc., so that the reaction vessel is subcritical and / or supercritical in a solvent such as ammonia. This is done by maintaining the state. The heating method and the rate of temperature increase to a predetermined reaction temperature are not particularly limited, but are usually performed over several hours to several days. If necessary, the temperature can be raised in multiple stages, or the temperature raising speed can be changed in the temperature range. It can also be heated while being partially cooled.
The “reaction temperature” is measured by a thermocouple provided so as to be in contact with the outer surface of the reaction vessel and / or a thermocouple inserted into a hole having a certain depth from the outer surface. It can be estimated in terms of temperature. The average value of the temperatures measured with these thermocouples is taken as the average temperature.

  The reaction time after reaching a predetermined temperature varies depending on the type of nitride single crystal, the raw material used, the type of mineralizer, and the size and amount of the crystal to be produced, but is usually several hours to several hundred days. can do. During the reaction, the reaction temperature may be constant, or the temperature may be gradually raised or lowered. After a reaction time for producing desired crystals, the temperature is lowered. The temperature lowering method is not particularly limited, but the heating may be stopped while the heating of the heater is stopped and the reaction vessel is installed in the furnace as it is, or the reaction vessel may be removed from the electric furnace and air cooled. If necessary, quenching with a refrigerant is also preferably used.

After the temperature of the outer surface of the reaction vessel or the estimated temperature inside the reaction vessel is below a predetermined temperature, the reaction vessel is opened. The predetermined temperature at this time is not particularly limited, and is preferably −80 ° C. or higher, more preferably −33 ° C. or higher, and preferably 200 ° C. or lower, more preferably 100 ° C. or lower. Here, the valve may be opened by connecting a pipe to the pipe connection port of the valve attached to the reaction vessel, leading to a vessel filled with water or the like. Furthermore, if necessary, the ammonia solvent in the reaction vessel is sufficiently removed by making a vacuum or the like, and then dried, and the nitride single crystal formed by opening the reaction vessel lid, etc. and unreacted raw materials and ores Additives such as an agent can be taken out.
In addition, when manufacturing gallium nitride according to the method for manufacturing a nitride single crystal of the present invention, JP 2009-263229 A can be preferably referred to for details of materials, manufacturing conditions, manufacturing apparatuses, and processes other than those described above. .

(Wafer)
By cutting the nitride single crystal obtained by the manufacturing method of the present invention in a desired direction, a wafer (semiconductor substrate) having an arbitrary crystal orientation can be obtained. When a nitride single crystal having a large and large-diameter M-plane is manufactured by the manufacturing method of the present invention, a large-diameter M-plane wafer can be obtained by cutting in a direction perpendicular to the m-axis. In addition, when a nitride single crystal having a large-diameter semipolar surface is manufactured by the manufacturing method of the present invention, a large-diameter semipolar surface wafer can be obtained by cutting in parallel to the semipolar surface. These wafers are also characterized by being uniform and of high quality.

(device)
The nitride single crystal or wafer obtained by the production method of the present invention is suitably used for devices such as light emitting elements and electronic devices. Examples of the light-emitting element using the nitride single crystal or the wafer include a light-emitting diode, a laser diode, and a light-emitting element combining these with a phosphor. In addition, examples of the electronic device using the nitride single crystal or the wafer include a high frequency element, a high breakdown voltage high output element, and the like. Examples of the high frequency element include a transistor (HEMT, HBT), and an example of the high breakdown voltage high output element includes a thyristor (IGBT). Since the nitride single crystal and the wafer are characterized by being uniform and of high quality, they are suitable for any of the above applications. Especially, it is suitable for the electronic device use for which high uniformity is especially required.

  The features of the present invention will be described more specifically with reference to examples and comparative examples. The materials, amounts used, ratios, processing details, processing procedures, and the like shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below. In Examples and Comparative Examples described below, an attempt was made to grow a nitride single crystal using the reactor shown in FIG.

<Example 1>
Crystal growth was performed using the RENE41 autoclave 1 as a pressure-resistant container and the Pt-Ir capsule 20 as a reaction container. Polycrystalline GaN particles were placed as the raw material 8 in the capsule lower region (raw material dissolution region 9 in FIG. 1). Next, 99.999% pure NH ₄ I and purity 99.999% GaF ₃ was sufficiently dried as a mineralizer was placed into the capsule, the sum of I and F with respect to the filling amount of NH ₃ is 1. It adjusted so that it might become 1 mol%.
Further, a platinum baffle plate 5 was installed between the lower raw material dissolution region 9 and the upper crystal growth region 6. As the seed crystal 7, a wafer (10 mm × 20 mm × 0.3 mm) having an M surface grown by the HVPE method as a main surface was used. The main surface of the seed crystal was subjected to chemical mechanical polishing (CMP) finishing, and the surface roughness was confirmed to be Rms of 0.5 nm or less by measurement with an atomic force microscope. These seed crystals 7 were hung on a platinum seed crystal support frame by a platinum wire and placed in the crystal growth region 6 above the capsule. Next, a cap made of Pt—Ir was connected to the upper portion of the capsule 20 by TIG welding, and the weight was measured.
A valve similar to the valve 10 in FIG. 1 is connected to the tube attached to the upper part of the cap, the valve is operated so as to pass through the vacuum pump 11 and vacuum deaeration is performed, and then the valve is operated so as to pass through the nitrogen cylinder 13 so that the inside of the capsule is filled with nitrogen. Purge was repeated with gas. Thereafter, heating was performed while connected to a vacuum pump to deaerate moisture and attached gas in the capsule. After naturally cooling the capsule to room temperature, the valve was closed and the capsule was cooled with a dry ice ethanol solvent while maintaining the vacuum state. Subsequently, the valve of the conduit was operated so as to communicate with the NH ₃ cylinder 12, the valve was opened again, NH ₃ was filled without touching the outside air, and then the valve was closed again. The filling amount was confirmed from the difference in weight before and after NH ₃ filling.

Subsequently, after the capsule 20 was inserted into the autoclave 1 to which the valve 10 was attached, the lid was closed and the weight of the autoclave 1 was measured. Subsequently, the conduit was connected to the vacuum pump 11 through the valve 10 attached to the autoclave, and the valve was opened to perform vacuum deaeration. Nitrogen gas purging was performed several times as in the capsule. Thereafter, the autoclave 1 was cooled with a dry ice ethanol solvent while maintaining the vacuum state, and the valve 10 was once closed. Next, after the conduit was operated to lead to the NH ₃ cylinder 12, the valve 10 was opened again, and NH ₃ was filled in the autoclave 1 without continuously touching the outside air, and then the valve 10 was closed again. The temperature of the autoclave 1 was returned to room temperature, the outer surface was sufficiently dried, and the weight of the autoclave 1 was measured. The weight of NH ₃ was calculated from the difference from the weight before filling with NH ₃ to confirm the filling amount.
Subsequently, the autoclave 1 was stored in an electric furnace composed of a plurality of heaters. First, the temperature was raised until the average temperature of the crystal growth region 6 in the autoclave was about 595 ° C. and the temperature of the raw material dissolution region 9 was about 593 ° C., and the temperature was maintained for 6 hours to adhere to the seed crystal and the platinum member. The crystal nuclei were melted back. At this time, the pressure in the autoclave was about 195 MPa.
Further, the temperature was raised until the average temperature of the crystal growth region 6 was about 585 ° C. and the temperature of the raw material dissolution region 9 was about 640 ° C., and then held at that temperature for 10 days. The pressure in the autoclave was about 210 MPa. Further, the variation in the control temperature of the outer surface of the autoclave during the holding was ± 0.3 ° C. or less.

Then, it cooled naturally until the temperature of the outer surface of the autoclave 1 returned to room temperature, the valve 10 attached to the autoclave was opened, and NH ₃ in the autoclave was removed. Thereafter, the autoclave 1 was weighed to confirm the discharge of NH ₃ , the lid of the autoclave was opened, and the capsule 20 was taken out. A hole was made in the tube attached to the upper part of the capsule to remove NH ₃ from the inside of the capsule.
When the inside of the capsule was confirmed, a smooth GaN crystal had grown on the M-plane seed crystal. In addition, several micro cracks were observed inside the crystal, but the crystal surface was a mirror surface, and no deposits or the like due to the generation of natural nuclei were observed.
Furthermore, almost no GaN crystals were found on the inner wall of the capsule growth area, the platinum seed crystal support frame, and the baffle plate. As a result of measuring the rocking curve by X-ray, the half width was 50 seconds or less.

<Example 2>
In the same manner as described in Example 1 above, the raw materials and members were charged into the capsule and then filled with ammonia. Subsequently, the capsule was placed in the autoclave, and then the ammonia was put in the autoclave under the same conditions as in the previous example. Was introduced.
Next, after the autoclave is housed in an electric furnace, the temperature is raised until the average temperature of the crystal growth region 6 inside the autoclave becomes about 605 ° C. and the temperature of the raw material melting region 9 becomes about 585 ° C., and the temperature is maintained for 12 hours. The seed crystal and the crystal nucleus attached to the platinum member were melted back. The pressure in the autoclave was about 210 MPa.
Further, the temperature was raised until the average temperature of the crystal growth region 6 was about 600 ° C. and the temperature of the raw material dissolution region 9 was about 635 ° C., and then held at that temperature for 15 days. The pressure in the autoclave was about 215 MPa. Further, the variation in the control temperature of the outer surface of the autoclave during the holding was ± 0.3 ° C. or less.
Then, it cooled naturally until the temperature of the outer surface of the autoclave 1 returned to room temperature, the valve 10 attached to the autoclave was opened, and NH ₃ in the autoclave was removed. Thereafter, the autoclave 1 was weighed to confirm the discharge of NH ₃ , the lid of the autoclave was opened, and the capsule 20 was taken out. A hole was made in the tube attached to the upper part of the capsule to remove NH ₃ from the inside of the capsule.
When the inside of the capsule was confirmed, a smooth GaN crystal had grown on the M-plane seed crystal. Further, the crystal surface was a mirror surface, and no deposits or the like due to the generation of natural nuclei were observed.
Furthermore, almost no GaN crystals were found on the inner wall of the capsule growth area, the platinum seed crystal support frame, and the baffle plate. As a result of measuring the rocking curve by X-ray, the half width was 50 seconds or less.

<Example 3>
Except that the average temperature of the crystal growth region 6 inside the autoclave is about 605 ° C., the temperature of the raw material dissolution region 9 is about 585 ° C. and the holding time is 24 hours, and the seed crystal and the crystal nucleus attached to the platinum member are melted back. Crystal growth was performed in the same manner as in Example 2. The pressure in the autoclave was about 210 MPa. However, in addition to the M-plane wafer subjected to the mirror polishing, the M-plane wafer etched with an alkali and an acid without using the mirror polishing after cutting the seed with a multi-wire saw was used as a seed.
Then, it cooled naturally until the temperature of the outer surface of the autoclave 1 returned to room temperature, the valve 10 attached to the autoclave was opened, and NH ₃ in the autoclave was removed. Thereafter, the autoclave 1 was weighed to confirm the discharge of NH ₃ , the lid of the autoclave was opened, and the capsule 20 was taken out. A hole was made in the tube attached to the upper part of the capsule to remove NH ₃ from the inside of the capsule.
When the inside of the capsule was confirmed, a smooth GaN crystal had grown on the M-plane seed crystal. Further, the crystal surface was a mirror surface, and no deposits or the like due to the generation of natural nuclei were observed. Furthermore, almost no GaN crystals were found on the inner wall of the capsule growth area, the platinum seed crystal support frame, and the baffle plate. As a result of measuring the rocking curve by X-ray, the half width was 50 seconds or less. Moreover, it was confirmed that the crystal grown on the seed subjected to the etching process after slicing was equivalent in quality to the crystal grown on the seed subjected to the polishing process.

<Comparative Example 1>
In the same manner as described in Example 1, the raw materials and members were charged into the capsule and then filled with ammonia. Subsequently, after the capsule was placed in the autoclave, ammonia was also introduced into the autoclave under the same conditions as in the previous example. Introduced.
After the autoclave is housed in the electric furnace, the temperature is raised until the average temperature of the crystal growth region 6 inside the autoclave is about 585 ° C. and the temperature of the raw material melting region 9 is about 575 ° C., and the temperature is maintained for 2 hours. The seed crystal and the crystal nucleus adhering to the platinum member were melted back. The pressure in the autoclave was about 180 MPa.
Further, the temperature was raised until the average temperature of the crystal growth region 6 was about 585 ° C. and the temperature of the raw material dissolution region 9 was about 640 ° C., and then held at that temperature for 5 days. The pressure in the autoclave was about 210 MPa. Further, the variation in the control temperature of the outer surface of the autoclave during the holding was ± 0.3 ° C. or less.
Then, it cooled naturally until the temperature of the outer surface of the autoclave 1 returned to room temperature, the valve 10 attached to the autoclave was opened, and NH ₃ in the autoclave was removed. Thereafter, the autoclave 1 was weighed to confirm the discharge of NH ₃ , the lid of the autoclave was opened, and the capsule 20 was taken out. A hole was made in the tube attached to the upper part of the capsule to remove NH ₃ from the inside of the capsule.
When the inside of the capsule was confirmed, a large number of minute cracks were inherent in the GaN crystal grown on the M-plane seed crystal. In addition, a plurality of deposits and cracks that were thought to be due to the generation of natural nuclei were observed on the crystal surface, and the surface was not smooth. Furthermore, deposits of GaN crystals were observed on the inner wall of the capsule growth region, the platinum seed crystal support frame, and the baffle plate. As a result of measuring the rocking curve by X-ray, it was a multi-peak.

<Comparative example 2>
In the same manner as described in Example 1, the raw materials and members were charged into the capsule and then filled with ammonia. Subsequently, after the capsule was placed in the autoclave, ammonia was also introduced into the autoclave under the same conditions as in the previous example. Introduced.
After the autoclave is housed in the electric furnace, the temperature is raised until the average temperature of the crystal growth region 6 becomes about 585 ° C. and the temperature of the raw material melting region 9 becomes about 640 ° C. without performing meltback treatment by temperature reversal. Hold at temperature for 6 days. The pressure in the autoclave was about 240 MPa. Further, the variation in the control temperature of the outer surface of the autoclave during the holding was ± 0.3 ° C. or less.
Then, it cooled naturally until the temperature of the outer surface of the autoclave 1 returned to room temperature, the valve 10 attached to the autoclave was opened, and NH ₃ in the autoclave was removed. Thereafter, the autoclave 1 was weighed to confirm the discharge of NH ₃ , the lid of the autoclave was opened, and the capsule 20 was taken out. A hole was made in the tube attached to the upper part of the capsule to remove NH ₃ from the inside of the capsule.
When the inside of the capsule was confirmed, a large number of minute cracks were inherent in the GaN crystal grown on the M-plane seed crystal. In addition, many deposits and cracks that were thought to be due to the generation of natural nuclei were observed on the crystal surface, and the surface was not smooth. Further, a large amount of GaN crystal deposits were found on the inner wall of the capsule growth area, the platinum seed crystal support frame, and the baffle plate. As a result of measuring the rocking curve by X-ray, it was a multi-peak.

As can be seen from the results in Table 2, in the temperature raising step, the meltback treatment is performed for 6 hours or more in a temperature range set so that the temperature relationship between the crystal region and the raw material melting region in the growth step is reversed. In the examples, the surface of the obtained nitride was smooth and specular, and no deposits were observed. From this, in Examples 1-3, it is guessed that the thickness of 1 micrometer or more was melt | dissolved from the surface with respect to the seed crystal.
In contrast, in Comparative Example 1 in which ΔT _elev was melt-backed for 2 hours at −10 ° C., a large number of minute cracks were observed on the surface, and adhesion of crystal grains was observed. From this, it can be inferred that the meltback treatment conditions of Comparative Example 1 were only dissolved in the seed crystal at a thickness of less than 1 μm from the surface.

DESCRIPTION OF SYMBOLS 1 Autoclave 2 Autoclave inner surface 5 Baffle plate 6 Crystal growth region 7 Seed crystal 8 Raw material 9 Raw material melting region 10 Valve 11 Vacuum pump 12 Ammonia cylinder 13 Nitrogen cylinder 14 Mass flow meter 20 Capsule 21 Inner surface of capsule

Claims (7)

A method for producing a nitride single crystal in which a nitride single crystal is grown in a solvent containing nitrogen in a supercritical state and / or a subcritical state, wherein at least a preparation step of arranging a seed crystal in a reaction vessel, A heating step for raising the temperature inside the reaction vessel, and a growth step for growing the nitride single crystal on the seed crystal at the growth temperature in this order,
The method for producing a nitride single crystal, wherein in the temperature raising step, a meltback treatment is performed to dissolve the seed crystal with a thickness of 1 μm or more from the surface.   The method for producing a nitride single crystal according to claim 1, wherein the meltback treatment is performed for 3 hours or more. A method for producing a nitride single crystal in which a nitride single crystal is grown in a solvent containing nitrogen in a supercritical state and / or subcritical state, at least a temperature raising step for raising the temperature in a reaction vessel, Growing the nitride single crystal at a growth temperature, and
In the temperature raising step, a temperature (T1) of a region where a seed crystal is arranged in the reaction vessel and a nitride single crystal is grown, and a region in which the raw material of the nitride single crystal in the reaction vessel is dissolved in a solvent. A nitride which is subjected to a meltback treatment for 3 hours or more with respect to the seed crystal by reversing the level relationship with the temperature (T2) from the level relationship between the temperature (T1) and the temperature (T2) in the growth step. A method for producing a single crystal.   The method for producing a nitride single crystal according to claim 3, wherein a temperature (T1) of a region in which the seed crystal is arranged and the nitride single crystal is grown in the meltback treatment is 400 ° C to 700 ° C.   The manufacturing method of the nitride single crystal of any one of Claims 1-4 which uses the mineralizer which has a positive solubility characteristic in the said growth process.   The manufacturing method of the nitride single crystal of any one of Claims 1-4 which uses the mineralizer which has a negative solubility characteristic in the said growth process.   The method for producing a nitride single crystal according to any one of claims 1 to 6, wherein an acidic mineralizer is used in the growth step.