JP4774775B2 - Method for producing trialkylgallium - Google Patents

Description

  The present invention relates to a method for producing trialkylgallium useful as a material for forming a compound semiconductor thin film such as GaN by epitaxial crystal growth using a MOCVD (Metal-Organic Chemical Vapor Deposition) method or the like.

  Due to recent advances in mobile phones and optical communication technologies, the demand for compound semiconductors is increasing such as high electron mobility transistors (HEMTs) and heterobipolar transistors (HBTs) used in mobile phones. It is growing rapidly in applications such as high-speed electronic devices, semiconductor lasers used in optical communications and DVDs, and optical devices such as white and blue ultra-high brightness LEDs used in displays.

  In general, as organometallic compounds (MO: Metal Organics) used as raw materials for compound semiconductors, alkyl metal compounds of Group II and III elements of the periodic table, particularly methyl compounds and ethyl compounds are frequently used. Among them, the group III alkylgallium in the periodic table is in great demand as a material for producing a compound semiconductor by MOCVD together with elements of the group V of the periodic table such as nitrogen and arsenic.

As a typical synthesis method of alkyl gallium, a method of synthesizing trialkyl gallium by reaction of gallium halide and alkyl magnesium halide (Grignard reagent) has been reported. For example, Patent Document 1 (US Pat. No. 4,604,473), Patent Document 2 (Japanese Patent Application No. 59-122867), Non-Patent Document 1 (LM Dennis, W. Patnode, J. Am. Chem. Soc). , 54 , 182 (1932)), Non-Patent Document 2 (CA Kraus, FE Toodner, Proc. Natl. Acad. Soc. USA, 19 , 292 (1933)), And Non-Patent Document 3 (J. Cryst. Growth, 68 , 1 (1984)) show that trialkylgallium is produced by reacting gallium trichloride with an alkylmagnesium halide in an ether compound. It has been reported.

  A method of reacting an alkyl halide with a Grignard reagent is generally considered preferable as a method for obtaining high-purity trialkylgallium having industrial quality.

  However, in this method, it is necessary to separately synthesize an alkylmagnesium halide which is an alkylating agent for gallium halide, which is troublesome. In addition, alkylmagnesium halides cannot be stored for a long time because they deteriorate over time. Therefore, in general, the required amount of alkylmagnesium halide is often synthesized immediately before use, which is inefficient.

  An object of the present invention is to provide a simple method by which trialkylgallium can be synthesized by alkylation of gallium halide.

  The present inventors have intensively studied to solve the above problems, and instead of the conventional method using alkylmagnesium halide as a methylating agent for gallium halide, at least one halogen is used in at least one solvent. By directly reacting gallium halide, magnesium, and at least one alkyl halide, and using magnesium that has been vacuum-heated as magnesium, high yield can be obtained without using alkylmagnesium halide. We found that trialkylgallium can be synthesized.

  The present invention has been completed based on the above findings, and provides the following method for producing trialkylgallium.

Item 1. A first step of heating magnesium under vacuum;
A second step of synthesizing trialkylgallium by reacting magnesium, which has been subjected to vacuum heat treatment, at least one alkyl halide, and at least one gallium halide in at least one solvent; A method for producing trialkylgallium containing the same.

  Item 2. Item 2. The method according to Item 1, wherein in the first step, heating under vacuum is performed at a temperature of 60 ° C. or higher at a degree of vacuum of 1000 Pa or lower.

  Item 3. Item 3. The method according to Item 1 or 2, wherein in the first step, heating under vacuum is performed for 1 to 5 hours.

  Item 4. Item 4. The method according to any one of Items 1 to 3, wherein the at least one alkyl halide is at least one alkyl halide selected from the group consisting of alkyl chloride, alkyl bromide, and alkyl iodide.

Item 5. Item 5. The method according to any one of Items 1 to 4, wherein the alkyl halide has an alkyl group having 1 to 10 carbon atoms.
Item 6. Item 6. The method according to any one of Items 1 to 5, wherein the gallium halide is gallium trichloride.

  Item 7. Item 7. The method according to any one of Items 1 to 6, wherein 3 to 6 mol of magnesium is used per 1 mol of gallium halide.

  Item 8. Item 8. The method according to any one of Items 1 to 7, wherein the at least one solvent is at least one solvent selected from the group consisting of an ether compound and an amine compound.

  According to the present invention, the method of synthesizing trialkylgallium by alkylating gallium halide is equivalent to or higher than the method of using alkylmagnesium halide as an alkylating agent without using alkylmagnesium halide. A method was provided that could synthesize trialkylgallium in yield.

  This method eliminates the need for separately synthesizing an alkyl magnesium halide, which is an alkylating agent for gallium halide, simplifies the production process of trialkyl gallium, and greatly improves productivity.

Hereinafter, the present invention will be described in detail.
The method for producing trialkylgallium according to the present invention includes a first step of heating magnesium under vacuum, magnesium that has been vacuum-heated in at least one solvent, at least one gallium halide, and at least And a second step of synthesizing trialkylgallium by reacting with one kind of alkyl halide.
material
<Gallium halide>
As the gallium halide, gallium trichloride, gallium tribromide, gallium triiodide, or the like can be used. Among these, gallium trichloride is preferable because it is widely used.
As gallium trichloride, gallium tribromide, and gallium triiodide, commercially available products having a purity of 99.9% (3N) to 99.999% (5N) can be used.

  The electrical characteristics and optical characteristics of the compound semiconductor produced by MOCVD are greatly influenced by the purity of the organometallic compound as a raw material. Therefore, it is required to synthesize high-purity trialkylgallium also in the method of the present invention. Since the purity of the produced trialkylgallium depends on the purity of the gallium halide that is the raw material, it is desirable that the gallium halide is highly pure.

Although high purity gallium halide exceeding 4N is commercially available, it can be obtained by refining the above-mentioned 3N or 4N purity commercial products by methods such as recrystallization, vacuum sublimation, and fusion purification. In the present invention, the purity of gallium halide is preferably 99.999% (5N) or more, more preferably 99.9999% (6N) or more.
<Magnesium>
A commercially available product having a purity of 99% (2N) to 99.9999% (6N) can be used. However, since magnesium having a purity of 5N or more is very expensive, it is sufficient to use a magnesium having a purity of 2 to 4N purified by vacuum distillation, vacuum sublimation, or the like. The purity of magnesium used in the method of the present invention is preferably 3N or more.

  The shape of magnesium is not particularly limited. For example, ribbons, shavings, chips (scraping smaller than shavings), powders, granules, and the like that are generally used in Grignard reagent synthesis can be used. In the present invention, powdered magnesium refers to magnesium having an average particle size of 500 μm or less. In the present invention, the average particle diameter is a value measured by a laser diffraction method.

  Among these, a shaving shape, a chip shape, a powder shape, and a granular shape that pass through a mesh screen (Japanese Industrial Standard Z8801) having an opening of 2 mm are preferable. Those that cannot pass through the 2 mm mesh screen may be used after being passed through the 2 mm mesh screen in advance by means of pulverization, grinding, or the like before being subjected to the method of the present invention. In the present invention, the term “magnesium that passes through a mesh screen having a mesh opening of 2 mm” refers to magnesium that 99% by weight or more of which passes through this mesh screen. Furthermore, it is more preferable to use a powdered magnesium having an average particle size of 500 μm or less. In the present invention, the average particle diameter is a value measured by a laser diffraction method. By using magnesium of such a size, the reactivity is improved, and thus the yield is improved.

In addition, since the reactivity of magnesium to an alkyl halide is proportional to the specific surface area of magnesium, it is preferable to use powdered magnesium having a specific surface area of 0.1 m ² / g or more, particularly 1 m ² / g or more. The lower limit of the specific surface area is usually about 0.01 m ² / g in order to have appropriate reactivity and facilitate handling. In the present invention, the specific surface area is a value measured by the BET method.
<Solvent>
The solvent should just be an organic compound solvent which does not have active hydrogen, and can use a well-known thing without a restriction | limiting. Of these, ether compound solvents and amine compound solvents are preferred because they are widely used and easy to use.

  Usable ether compounds are not particularly limited, and known ether compounds used for trialkylgallium synthesis may be used. For example, aliphatic ether compounds such as diethyl ether, di-n-propyl ether, diisopropyl ether, di-n-butyl ether, diisobutyl ether, di-sec-butyl ether, diisopentyl ether (diisoamyl ether); anisole, methylanisole Aromatic ether compounds such as benzyl methyl ether, ethyl anisole, dimethyl anisole, isopropyl anisole, and phenetole can be used.

  Since the ether compound forms an adduct with the product trialkylgallium compound, the ether adduct of trialkylgallium is thermally decomposed by distillation as described later after the synthesis step, so that the trialkylgallium is obtained. It is preferred to isolate the compound. For this reason, the ether compound is preferably a compound having a boiling point higher than that of trialkylgallium. Also, when the thermal decomposition temperature of the trialkylgallium ether adduct is higher than the thermal decomposition temperature of the trialkylgallium compound, the decomposition of the trialkylgallium compound also proceeds due to the thermal decomposition of the ether adduct. It is preferable to select an ether compound whose temperature is lower than the decomposition temperature of trialkylgallium.

  The amine compound which can be used is not specifically limited, What is necessary is just to use the well-known amine compound currently used for the synthesis | combination of a trialkyl gallium. As such an amine compound, for example, a tertiary amine compound can be used. Specifically, aliphatic tertiary amine compounds such as trimethylamine, triethylamine, tri-n-propylamine, triisopropylamine, tri-n-butylamine, triisobutylamine, tri-sec-butylamine, tri-tert-butylamine; pyridine And heterocyclic tertiary amine compounds such as pyrrole, pyrimidine, pyrazine, pyridazine, 1,3,5-triazine, and hexahydrotriazine.

  Since the amine compound forms an adduct with the product trialkylgallium compound, after the synthesis reaction, the trialkylgallium compound is pyrolyzed by pyrolyzing the amine adduct of trialkylgallium by distillation as described later. It is preferred to isolate. For this reason, when the thermal decomposition temperature of the amine adduct of trialkylgallium is higher than the thermal decomposition temperature of the trialkylgallium compound, the decomposition of the trialkylgallium compound also proceeds. It is preferable to select an amine compound that is lower than the decomposition temperature.

A solvent can be used individually by 1 type or in mixture of 2 or more types. However, it is preferable to use one type of ether compound or amine compound alone in terms of easy purification of the resulting trialkylgallium.
<Alkyl halide>
As the alkyl halide, an alkyl group having 1 to 10 carbon atoms, preferably 1 to 4 carbon atoms, and more preferably 1 to 3 carbon atoms may be used. The alkyl iodide and alkyl bromide having an alkyl group having the above carbon number are highly reactive, and by using these, trialkylgallium having sufficient volatility as a MOCVD raw material can be obtained.

  Also, any of alkyl chloride, alkyl bromide, and alkyl iodide can be used, but alkyl bromide and alkyl iodide are preferable, and alkyl iodide is more preferable in terms of relatively high reactivity.

  Specific examples of the alkyl halide having an alkyl group having 1 to 4 carbon atoms include methyl chloride, ethyl chloride, n-propyl chloride, isopropyl chloride, n-butyl chloride, isobutyl chloride, sec-butyl chloride, and tert-butyl chloride. Alkyl chlorides such as; bromides such as methyl bromide, ethyl bromide, n-propyl bromide, isopropyl bromide, n-butyl bromide, isobutyl bromide, sec-butyl bromide, tert-butyl bromide Alkyl; alkyl iodides such as methyl iodide, ethyl iodide, n-propyl iodide, isopropyl iodide, n-butyl iodide, isobutyl iodide, sec-butyl iodide, and tert-butyl iodide. .

  Of these, methyl bromide, ethyl bromide, n-propyl bromide, isopropyl bromide, methyl iodide, ethyl iodide, n-propyl iodide, and isopropyl iodide are preferred. Methyl bromide, ethyl bromide, iodine More preferred are methyl iodide and ethyl iodide.

Alkyl halides can be used alone or in combination of two or more. When two or more types are combined, those having different halogen types may be used, or those having different alkyl group types may be used.
Usage ratio The reaction of producing trialkylgallium by the reaction of gallium halide, magnesium and alkyl halide can be represented by the following formula (1): GaX ₃ + 3Mg + 3RX ′ → GaR ₃ + 3MgX′X (1)
(Wherein R represents an alkyl group, and X and X ′ represent a halogen atom)
In the reaction of the formula (1), as shown in the following formula (2), an alkylmagnesium halide (Grignard reagent) is generated in situ by the reaction of magnesium and an alkyl halide, which alkylates the gallium halide. It is thought that.

Mg + RX ′ → MgRX ′ (2)
(Wherein R represents an alkyl group, and X ′ represents a halogen atom)
The usage ratio of gallium and magnesium is preferably about 3 to 6 mol of magnesium, and more preferably about 3 to 4 mol, per 1 mol of gallium. According to Formula (1), 3 mol of magnesium is a stoichiometric composition ratio with respect to 1 mol of gallium. Therefore, the reaction can proceed sufficiently efficiently within the above range of magnesium usage. Further, if the ratio of magnesium used is too large, no further effect can be obtained, the raw material cost only increases, and the post-treatment of magnesium remaining after the completion of the reaction takes time. Such a problem does not occur.

As shown in the formula (2), the reaction required mole number of alkyl halide is 1 mole per 1 mole of magnesium, but usually about 0.8 to 1.5 times mole per mole of magnesium. Alkyl may be used.
First step (magnesium preactivation step)
In general, since the magnesium surface is more or less covered with an oxide film, the reaction induction period becomes longer accordingly. For this reason, when using a low-reactivity alkyl halide, activation such as mechanical stirring, pulverization, addition of a small amount of iodine or bromine, washing with dilute hydrochloric acid, etc. is generally performed on magnesium before the reaction. Has been done. In addition, a companion method of activating magnesium by adding a small amount of methyl iodide, ethyl iodide, 1,2-dibromoethane or the like has been carried out (DE Peason, D. Cowan, JD Beckler, J. Org. Chem., 24 , 504 (1959)).

  However, practically sufficient reactivity cannot be obtained by activation by mechanical stirring, pulverization, or washing with dilute hydrochloric acid. In addition, the method of adding a reaction accelerator such as iodine or 1,2-dibromoethane is effective in promoting the reaction, but it is mixed with the trialkyl gallium from which impurities derived from the reaction accelerator are obtained. Reduce the degree of purification. For this reason, the above-described conventional preactivation method is difficult to produce in order to produce high-purity trialkylgallium used as a raw material for producing a compound semiconductor by MOCVD.

  In the process of the present invention, magnesium is activated by heating under vacuum before reacting with gallium trichloride and an alkyl halide. This preactivation contributes to the removal of moisture on the magnesium surface and the formation of alkylmagnesium halides.

Although the vacuum condition at the time of vacuum heating of magnesium is not particularly limited, it is usually 1000 Pa or less, preferably 100 Pa or less, more preferably 10 Pa or less. If it is the range of the said vacuum degree, the water | moisture content etc. on the magnesium surface will fully be removed, and a trialkyl gallium will be obtained with a sufficiently high yield. The lower limit of the degree of vacuum is usually about 10 ⁻⁶ Pa.

  The temperature during vacuum heating is usually 60 ° C. or higher, preferably 80 ° C. or higher, more preferably 110 ° C. or higher. If it is the said range, the water | moisture content etc. on the magnesium surface can fully be removed.

  The vacuum heating time is not particularly limited, but is usually 1 hour or longer, preferably 3 hours or longer. Moreover, it is sufficient to carry out for about 3 hours.

  Further, magnesium may be allowed to stand or be stirred during vacuum heating. Stirring is preferred for efficient activation. Stirring may be performed by a known method such as stirring with a magnetic stirrer or induction stirring. Stirring can be performed smoothly by adding liquid paraffin, petrolatum oil, etc. to magnesium at the time of stirring. When powdered magnesium, especially powdered magnesium with a large specific surface area is used, it can be sufficiently activated without stirring.

  Magnesium is subjected to vacuum heat treatment in an inert gas atmosphere such as nitrogen, helium, neon, argon, krypton, or xenon. The purity of these inert gases is preferably 99.99% (4N) or more, particularly preferably 99.9999% (6N) or more.

In particular, moisture and oxygen in the atmospheric gas not only reduce the yield of trialkylgallium, but can also cause a decrease in purity, so it is desirable to use atmospheric gas from which moisture and oxygen have been removed as much as possible. The reaction atmosphere gas preferably has a dew point of −80 ° C. or lower and an oxygen concentration of 100 ppb or lower, particularly preferably a dew point of −100 ° C. or lower and an oxygen concentration of 10 ppb or lower. Such a high purity inert gas can be obtained by a membrane separation method, a catalytic reaction method, a liquefaction rectification method, a PSA (Pressure Swing Adsorption) method, or the like.
Second step (synthesis reaction step)
In the synthesis reaction, gallium trichloride, preactivated magnesium, an alkyl halide, and an ether compound are placed in the reaction vessel in the above-described inert gas atmosphere, and mixed and reacted. In order to control the reaction, usually, gallium trichloride, preactivated magnesium, and an ether compound are placed in a reaction vessel, and finally an alkyl halide is slowly introduced into the mixture.

  The amount of ether used is not particularly limited, but at the start of the reaction, both the gallium concentration and the magnesium concentration in the solvent (each means the number of moles relative to 1 L of the solvent; hereinafter the same) are 0.01 to 10 mol / L. The amount which becomes about is preferable, and the amount which becomes about 0.1 to 5 moL / L is more preferable. When the concentration is within the above range, the reactivity and thus the yield of trialkylgallium are sufficiently high, and the reaction can be easily controlled, that is, the reaction proceeds suddenly, or the reaction is in progress due to precipitation of the generated alkylmagnesium halide. It does not end with, and stirring is difficult due to the by-product magnesium halide.

  The reaction temperature may be a temperature at which the reaction proceeds efficiently in consideration of the type of ether compound used and the alkyl halide. After mixing all the materials, the reaction may be carried out by setting the temperature of the reaction solution to usually about 0 to 200 ° C, preferably about 40 to 160 ° C, more preferably about 60 to 120 ° C. Usually, a trialkylgallium is produced by a reaction for about 3 to 30 hours.

The synthesis reaction pressure is not particularly limited, and the synthesis reaction can be performed under atmospheric pressure, reduced pressure, or increased pressure.
The trialkyl gallium obtained after completion of the purification step reaction includes an ether compound and trialkyl gallium to which an alkyl halide is added. Therefore, by distilling the reaction solution, these adducts can be decomposed and the trialkylgallium can be isolated by fractional distillation. The heating temperature is preferably lower than the decomposition temperature of the trialkylgallium and higher than the decomposition temperature of the trialkylgallium ether compound or the adduct of the alkyl halide. Distillation may be performed at normal pressure, but vacuum distillation may be performed.

  Furthermore, by purifying by a method such as precision distillation or sublimation, a trialkylgallium having a purity of 99.999% (5N) or more that can be used as a MOCVD raw material is obtained.

The purification step is also usually performed in an inert gas atmosphere.
Gallium-based compound semiconductor device Using trialkylgallium obtained by the method of the present invention and at least one group III element-containing compound selected from the group consisting of nitrogen-containing compounds, phosphorus-containing compounds, and arsenic-containing compounds as raw materials, for example, MOCVD The gallium-based compound semiconductor thin film of the gallium-based compound semiconductor device can be formed by epitaxial growth. A typical example of the gallium compound semiconductor thin film is a gallium nitride compound semiconductor thin film formed using trialkylgallium and a nitrogen-containing compound such as ammonia as raw materials.

  Examples of the semiconductor structure include a MIS (Metal Insulator Semiconductor) junction, a homostructure having a PIN junction or a pn junction, a heterostructure, or a double heterostructure. Various emission wavelengths can be selected depending on the material of the semiconductor layer and the degree of mixed crystal. In addition, a single quantum well structure or a multiple quantum well structure in which the semiconductor active layer is formed in a thin film in which a quantum effect is generated can be used.

  If the gallium nitride compound semiconductor thin film is described as an example, materials such as sapphire, spinel, SiC, Si, ZnO, and GaN are preferably used for the gallium nitride compound semiconductor substrate. In order to form a nitride semiconductor with good crystallinity with high productivity, it is preferable to use a sapphire substrate. A gallium nitride compound semiconductor can be formed on the sapphire substrate by MOCVD or the like. A buffer layer of GaN, AlN, GaAIN or the like is formed on the sapphire substrate, and a nitride semiconductor having a pn junction is formed thereon.

  As an example of a light-emitting element having a pn junction using a gallium nitride compound semiconductor, a first contact layer formed of n-type gallium nitride and a first cladding layer formed of n-type aluminum nitride / gallium on a buffer layer A double hetero structure in which an active layer formed of indium gallium nitride, a second cladding layer formed of p-type aluminum nitride / gallium, and a second contact layer formed of p-type gallium nitride are sequentially stacked. It is done.

The gallium nitride compound semiconductor exhibits n-type conductivity without being doped with impurities. When forming a desired n-type nitride semiconductor, for example, to improve luminous efficiency, it is preferable to appropriately introduce Si, Ge, Se, Te, C, etc. as an n-type dopant. On the other hand, when forming a p-type gallium nitride compound semiconductor, p-type dopants such as Zn, Mg, Be, Ca, Sr, and Ba are doped. Since the gallium nitride compound semiconductor is difficult to be p-type only by being doped with a p-type dopant, it is preferable to lower the resistance by heating in a furnace or plasma irradiation after introducing the p-type dopant. After the electrodes are formed, a light emitting element made of a nitride semiconductor can be obtained by cutting the semiconductor wafer into chips.
EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.
[Example 1] Synthesis of trimethylgallium
Reaction of gallium trichloride, magnesium, and methyl chloride A magnetic stirrer chip is placed in a 200 mL capacity SUS316 autoclave substituted with nitrogen, and a powder having an average particle size of 45 μm (measured using a Marsern Mastersizer 2000) at room temperature. 4.17 g (174 mmoL) of magnesium are introduced. While the autoclave is heated and stirred at 90 ° C., preactivation is performed at a vacuum of 10 Pa for 3 hours.
The temperature in the autoclave is returned to room temperature, and 10.03 g (57 mmol) of gallium trichloride and 60 mL of diisoamyl ether sufficiently dehydrated with molecular sieves are added. Next, 12.32 g (244 mmol) of methyl chloride is slowly introduced into the autoclave, the temperature inside the autoclave is increased to 120 ° C., and the mixture is heated and stirred for 20 hours.

  The purity of gallium trichloride used is 5N, and the purity of magnesium is 3N. Nitrogen has a purity of 6N, a dew point of −110 ° C., and an oxygen concentration of 1 ppb. Further, the gallium trichloride concentration in the solvent at the start of the reaction is 0.95 mol / L, and the magnesium concentration is 2.90 mol / L (respectively, the number of moles relative to 1 liter of solvent, the same applies hereinafter).

  After completion of the reaction, crude trimethylgallium is fractionated using a 30 cm long, 1.5 cm diameter column filled with glass beads from the reaction mixture in a state where diisoamyl ether is boiling.

Determination of gallium with an inductively coupled plasma emission spectrometer (ICP-AES) Inductively Coupled Plasma Atomic Emission Spectrometer yields 2.31 g (35.5% yield in terms of gallium) of crude trimethylgallium.
[Example 2] Synthesis of trimethylgallium
Reaction of gallium trichloride, magnesium, and methyl iodide A magnetic stirrer chip was placed in a 200 mL four-necked flask purged with nitrogen, and an average particle diameter of 45 μm at room temperature (measured using a Mastersizer 2000 manufactured by Marvern) 4.14 g (173 mmol) of powdered magnesium is introduced. While the flask is heated and stirred at 90 ° C., preactivation is performed for 3 hours at a vacuum of 10 Pa.
The temperature in the flask is returned to room temperature, and 10.05 g (57 mmol) of gallium trichloride and 60 mL of diisoamyl ether sufficiently dehydrated with molecular sieves are added. Next, after attaching a dry ice condenser and adjusting the internal temperature to 20 ° C., 25.1 g (177 mmol) of methyl iodide weighed separately is dropped into the solution in the flask over about 1 hour with stirring. After all the methyl iodide has been added, the flask is heated and stirred for 18 hours while maintaining the internal temperature of the flask at 110 ° C.

  The purity of gallium trichloride used is 5N, and the purity of magnesium is 3N. Nitrogen has a purity of 6N, a dew point of −110 ° C., and an oxygen concentration of 1 ppb. Further, the gallium trichloride concentration in the solvent at the start of the reaction is 0.95 moL / L, and the magnesium concentration is 2.88 moL / L.

  After completion of the reaction, a large amount of white magnesium iodide is precipitated. Crude trimethylgallium is fractionated using a 30 cm long, 1.5 cm diameter column filled with glass beads from the reaction mixture while diisoamyl ether is boiling.

18.4 g (92.7% yield in terms of gallium) of crude trimethylgallium is obtained by gallium quantification using an inductively coupled plasma emission spectrometer.
[Example 3] Synthesis of triethylgallium
Reaction of gallium trichloride, magnesium and ethyl iodide Put a magnetic stirrer chip into a 200 mL capacity four-necked flask substituted with nitrogen, and powder having an average particle size of 45 μm (measured using a Marsern Mastersizer 2000) at room temperature Introduce 4.21 g (175 mmol) of magnesium. While the flask is heated and stirred at 90 ° C., preactivation is performed for 3 hours at a vacuum of 10 Pa.
The temperature in the flask is returned to room temperature, and 10.06 g (57 mmol) of gallium trichloride and 60 mL of diethyl ether sufficiently dehydrated with molecular sieves are added. Next, after attaching a dry ice condenser and adjusting the internal temperature to 20 ° C., 27.29 g (175 mmol) of ethyl iodide weighed separately is dropped into the solution in the flask at a speed at which diethyl ether is gently refluxed. The time required for dropping is about 1 hour. After all the ethyl iodide has been added, stir at reflux for 18 hours.

  The purity of gallium trichloride used is 5N, and the purity of magnesium is 3N. Nitrogen has a purity of 6N, a dew point of −110 ° C., and an oxygen concentration of 1 ppb. Further, the gallium trichloride concentration in the solvent at the start of the reaction is 0.95 mol / L, and the magnesium concentration is 2.92 mol / L.

  After completion of the reaction, a large amount of white magnesium iodide is precipitated. After completion of the reaction, diethyl ether is first fractionated at normal pressure using a 30 cm long, 1.5 cm diameter column filled with glass beads from the reaction mixture. Subsequently, crude triethylgallium is fractionally distilled under a reduced pressure of 100 Torr. Trialkylgallium distills at 79-81 ° C.

By gallium quantification using an inductively coupled plasma optical emission spectrometer, 8.17 g (91.5% yield in terms of gallium) of crude triethylgallium is obtained.
[Comparative Example 1] Synthesis of trimethylgallium
(1) Synthesis of methylmagnesium chloride Put a magnetic stirrer chip into a 300 mL capacity four-necked flask purged with nitrogen, and add 4.37 g (180 mmol) of shaved magnesium at room temperature and 70 mL of diisoamyl ether sufficiently dehydrated with molecular sieves. . After attaching a dry ice condenser and adjusting the internal temperature to 20 ° C., 10.2 g (200 mmol) of methyl chloride weighed separately is bubbled into the solution in the flask over about 8 hours and stirred. During this time, the temperature in the flask is adjusted to 20 ° C. After completion of the dropwise addition, the mixture is kept stirring for 12 hours. This magnesium does not pass through a mesh screen (Japanese Industrial Standard Z8801) having an opening of 2 mm. The purity of magnesium is 3N. Nitrogen has a purity of 6N, a dew point of −110 ° C., and an oxygen concentration of 1 ppb.

The reaction mixture was analyzed by Gilman double titration method (H. Gilman, FK Cantledge, J. Organomet. Chem., 2 , 447 (1964)) in 92.0% yield (165 mmol) in methyl magnesium chloride. Is generated.
(2) Reaction process of gallium trichloride and methylmagnesium chloride A solution of 10.05 g (57 mmol) of gallium trichloride dissolved in 30 mL of diisoamyl ether at room temperature is slowly added to a diisoamyl ether solution (165 mmol) of methylmagnesium chloride. Dripping. During this time, the temperature in the flask is adjusted to 20 ° C. After completion of dropping, the mixture is heated and stirred at 110 ° C. for 18 hours. The purity of gallium trichloride is 5N.

  The crude trimethylgallium is fractionated from the reaction mixture in a state where the diisoamyl ether is boiled, using a column having a length of 30 cm and a diameter of 1.5 cm filled with glass beads.

By gallium quantification using an inductively coupled plasma emission spectrometer (ICP-AES) Inductively Coupled Plasma Atomic Emission Spectrometer, 1.51 g (23.0% yield in terms of gallium) of crude trimethylgallium is obtained.
[Comparative Example 2] Synthesis of methylmagnesium iodide
(1) Synthesis of methylmagnesium iodide To a 300 mL four-necked flask purged with nitrogen, 8.04 g (335 mmol) of shaved magnesium and 137 mL of diisoamyl ether sufficiently dehydrated with molecular sieves are added at room temperature. After attaching a dry ice condenser and adjusting the internal temperature to 20 ° C., 55.9 g (394 mmol) of methyl iodide is dropped into the solution in the flask over about 2 hours. During this time, the temperature in the flask is adjusted so as not to exceed 40 ° C. After completion of dropping, the mixture is stirred at room temperature for 12 hours. This magnesium does not pass through a mesh screen (Japanese Industrial Standard Z8801) having an opening of 2 mm. The purity of magnesium is 3N. Nitrogen has a purity of 6N, a dew point of −110 ° C., and an oxygen concentration of 1 ppb.
When the obtained reaction mixture was filtered and analyzed by Gilman double titration method, methylmagnesium iodide was produced in a yield of 97% (325 mmol).
(2) Reaction of gallium trichloride and methylmagnesium iodide In a 300 mL four-necked flask purged with nitrogen, a solution prepared by dissolving 15.51 g (88 mmol) of gallium trichloride in 58 mL of diisoamyl ether at room temperature Slowly add dropwise to a solution of methylmagnesium iodide (325 mmol) in diisoamyl ether. During this time, the temperature in the flask is adjusted to 60 ° C. After completion of dropping, the mixture is heated and stirred at 110 ° C. for 18 hours. The purity of gallium trichloride is 5N.

  The crude trimethylgallium is fractionated from the reaction mixture in a state where the diisoamyl ether is boiled, using a column having a length of 30 cm and a diameter of 1.5 cm filled with glass beads.

By gallium quantification using an inductively coupled plasma emission spectrometer, 8.88 g (87.7% yield in terms of gallium) of crude trimethylgallium is obtained.
[Comparative Example 3] Synthesis of trimethylgallium
(1) Synthesis of methylmagnesium chloride (using powdered magnesium)
A magnetic stirrer chip is placed in a four-necked flask with a capacity of 300 mL that is purged with nitrogen, and 4.41 g (181 mmoL) of powdered magnesium having an average particle size of 45 μm at room temperature (measured with a Mastersizer 2000 manufactured by Marvern), diisoamyl sufficiently dehydrated with molecular sieves. Add 70 mL of ether. After attaching a dry ice condenser and adjusting the internal temperature to 20 ° C., 10.2 g (200 mmol) of methyl chloride weighed separately is bubbled into the solution in the flask over about 8 hours and stirred. During this time, the temperature in the flask is adjusted to 20 ° C. After completion of the dropwise addition, the mixture is kept stirred for 3 hours. The purity of magnesium is 3N. Nitrogen has a purity of 6N, a dew point of −110 ° C., and an oxygen concentration of 1 ppb.

The reaction mixture was analyzed by Gilman double titration method (H. Gilman, FK Cantledge, J. Organomet. Chem., 2 , 447 (1964)) in 96.1% yield (174 mmol). Is generated.
(2) Reaction process of gallium trichloride and methylmagnesium chloride A solution prepared by dissolving 10.03 g (57 mmol) of gallium trichloride in 30 mL of diisoamyl ether at room temperature is slowly added to a diisoamyl ether solution (174 mmol) of methylmagnesium chloride. Dripping. During this time, the temperature in the flask is adjusted to 20 ° C. After completion of dropping, the mixture is heated and stirred at 110 ° C. for 18 hours. The purity of gallium trichloride is 5N.

  The crude trimethylgallium is fractionated from the reaction mixture in a state where the diisoamyl ether is boiled, using a column having a length of 30 cm and a diameter of 1.5 cm filled with glass beads.

  1.46 g (22.2% yield in terms of gallium) of crude trimethylgallium is obtained by gallium determination with an inductively coupled plasma emission spectrometer (ICP-AES) Inductively Coupled Plasma Atomic Emission Spectrometer.

In the synthesis of trimethylgallium, the yield of 35.5% is obtained in Example 1 where alkylation of gallium trichloride is performed using magnesium and methyl chloride, but in Comparative Example 1 where alkylation is performed using methylmagnesium chloride. The yield is 23.0%, and even in Comparative Example 3 using powdered magnesium, it is 22.2%, and the yield of Example 1 is higher.

  Further, in the synthesis of trimethylgallium, in Example 2 where alkylation of gallium trichloride is performed using magnesium and methyl iodide, the yield is 92.7%, but the comparison of alkylation using methylmagnesium iodide is performed. In Example 2, the yield is 87.7%, and the yield of Example 2 is higher.

As described above, trialkylgallium can be obtained in a higher yield by alkylating gallium trichloride with vacuum heat-treated magnesium and alkyl halide than alkylating with alkylmagnesium halide. I understand.

[Example 4] Manufacture of gallium nitride compound semiconductor device A substrate made of sapphire (C-plane) was set in a reaction vessel of MOVPE (Metal Organic Vapor Phase Epitaxy), and the temperature of the substrate was increased to 1050 ° C while flowing hydrogen. Raise the substrate and clean the substrate.
(Buffer layer)
Subsequently, the temperature is lowered to 510 ° C., hydrogen is used as a carrier gas, ammonia is used as a source gas, and trimethyl gallium obtained in the above-described Example 1 is further purified. Grow with angstrom thickness. This reaction is represented by the following formula.

Ga (CH ₃ ) ₃ + NH ₃ → GaN + 3CH ₄
(Undoped GaN layer)
After growing the buffer layer, only trimethylgallium is stopped and the temperature is raised to 1050 ° C. When the temperature reaches 1050 ° C., trimethylgallium and ammonia gas are similarly used as source gases, and an undoped GaN layer is grown to a thickness of 1.5 μm.
(N-side contact layer)
Subsequently, at 1050 ° C., an n-side contact layer made of GaN doped with 4.5 × 10 ¹⁸ / cm ^{3 of} Si is used, using trimethyl gallium, ammonia gas as source gas, and silane gas as impurity gas, and a film thickness of 2.25 μm. Grow in.
(N-side first multilayer film layer)
Next, the silane gas alone was stopped, and an undoped GaN layer was grown to a thickness of 75 Å at 1050 ° C. using trimethyl gallium and ammonia gas. Subsequently, silane gas was added at the same temperature to add Si to 4.5 × 10 ^18. A / cm ³ -doped GaN layer is grown to a thickness of 25 Å. In this way, a pair consisting of an A layer composed of an undoped GaN layer of 75 angstroms and a 25 angstrom B layer having an Si doped GaN layer is grown. Then, 25 pairs are stacked to have a thickness of 2500 Å, and an n-side first multilayer film made of a multilayer film having a superlattice structure is grown.
(N-side second multilayer film layer)
Next, a second nitride semiconductor layer made of undoped GaN is grown at a similar temperature by 40 Å, and then at a temperature of 800 ° C., using trimethylgallium, trimethylindium, and ammonia, and using undoped In _0.13 Ga. _A first nitride semiconductor layer made of _0.87 N is grown by 20 Å. Then, these operations are repeated, and 10 layers are alternately stacked in the order of 2 + 1 and finally, the n-side formed of a multi-layer film having a superlattice structure in which a second nitride semiconductor layer made of GaN is grown by 40 angstroms. A second multilayer layer is grown to a thickness of 640 angstroms.
(Active layer)
Next, a barrier layer made of undoped GaN is grown to a thickness of 200 angstroms, followed by a temperature of 800 ° C. and a well made of undoped In _0.4 Ga _0.6 N using trimethylgallium, trimethylindium, and ammonia. The layer is grown to a thickness of 30 angstroms. Then, an active layer having a multiple quantum well structure with a total film thickness of 1120 angstroms is formed by alternately laminating five barrier layers and four well layers in the order of barrier + well + barrier + well. Grow.
(P-side multilayer clad layer)
Next, a ^{third layer of} p-type Al _0.2 Ga _0.8 N doped with 1 × 10 ²⁰ / cm ^{3 of} Mg using trimethyl gallium, trimethyl aluminum, ammonia, biscyclopentadienyl magnesium at a temperature of 1050 ° C. The nitride semiconductor layer is grown to a thickness of 40 Å, and then the temperature is set to 800 ° C., and Mg is doped with 1 × 10 ²⁰ / cm ³ using trimethylgallium, trimethylindium, ammonia, and biscyclopentadienylmagnesium. A fourth nitride semiconductor layer made of In _0.03 Ga _0.97 N is grown to a thickness of 25 Å. Then, these operations are repeated, and 5 layers are alternately stacked in the order of 3 + 4, and finally, the third nitride semiconductor layer is grown to a thickness of 40 angstroms and is formed of a superlattice multilayer film. A side multilayer cladding layer is grown to a film thickness of 365 angstroms.
(P-side GaN contact layer)
Subsequently, at 1050 ° C., a p-side contact layer made of p-type GaN doped with 1 × 10 ²⁰ / cm ^{3 of} Mg is grown to a thickness of 700 Å using trimethylgallium, ammonia, and biscyclopentadienylmagnesium.

  After completion of the reaction, the temperature is lowered to room temperature, and the wafer is annealed in a reaction vessel at 700 ° C. in a nitrogen atmosphere to further reduce the resistance of the p-type layer.

  After annealing, the wafer is taken out of the reaction vessel, a mask having a predetermined shape is formed on the surface of the uppermost p-side contact layer, and etching is performed from the p-side contact layer side with a reactive ion etching (RIE) apparatus. To expose the surface of the n-side contact layer.

  After etching, a translucent p-electrode 10 containing Ni and Au having a thickness of 200 angstroms is formed on almost the entire surface of the p-side contact layer on the uppermost layer, and a p-pad electrode made of Au for bonding is formed on the p-electrode. It is formed with a film thickness of 0.5 μm. On the other hand, an n-electrode containing W and Al is formed on the surface of the n-side contact layer exposed by etching to form a gallium nitride compound semiconductor device.

  This gallium nitride-based compound semiconductor device emits pure green light of 520 nm at a forward current of 20 mA.

Trimethylgallium can also be used for a gallium nitride compound semiconductor device having another configuration. For example, ammonia and trimethyl gallium are used as source gases, and a buffer layer made of GaN is grown on the substrate. On the first buffer layer made of GaN, a second buffer layer made of undoped GaN, an n-side contact layer made of Si-doped GaN, an active layer made of a multiple quantum well structure, a single Mg-doped Al _{0. For example, a 1} Ga _0.9 N layer and a p-side contact layer made of Mg-doped GaN are sequentially stacked.

The trialkylgallium obtained by the method of the present invention can be suitably used as a raw material for forming a gallium compound semiconductor thin film by epitaxial crystal growth.

Claims (8)

A first step of heating magnesium under vacuum;
A second step of synthesizing trialkylgallium by reacting magnesium, which has been subjected to vacuum heat treatment, at least one alkyl halide, and at least one gallium halide in at least one solvent; A method for producing trialkylgallium containing the same.   The method according to claim 1, wherein in the first step, heating under vacuum is performed at a temperature of 60 ° C. or higher at a degree of vacuum of 1000 Pa or lower.   The method of Claim 1 or 2 which heats in a vacuum for 1 to 5 hours in a 1st process.   The method according to claim 1, wherein the at least one alkyl halide is at least one alkyl halide selected from the group consisting of alkyl chloride, alkyl bromide, and alkyl iodide.   The method according to any one of claims 1 to 4, wherein the halogenated alkyl has an alkyl group having 1 to 10 carbon atoms.   The method according to claim 1, wherein the gallium halide is gallium trichloride.   The method according to any one of claims 1 to 6, wherein 3 to 6 mol of magnesium is used per 1 mol of gallium halide.   The method according to any one of claims 1 to 7, wherein the at least one solvent is at least one solvent selected from the group consisting of an ether compound and an amine compound.