WO2014093419A1

WO2014093419A1 - Production of tri-alkyl compounds of group 3a metals

Info

Publication number: WO2014093419A1
Application number: PCT/US2013/074252
Authority: WO
Inventors: Liam P. SPENCER; Artashes Amamchyan; Deodatta Vinayak Shenai-Khatkhate; James C. Stevens
Original assignee: Dow Global Technologies Llc; Rohm And Haas Electronic Materials Llc
Priority date: 2012-12-12
Filing date: 2013-12-11
Publication date: 2014-06-19

Abstract

Disclosed herein are methods of making compounds of the formula: (R)₃M, where M is gallium, indium or thallium; and each R is independently C₁-C₁₀ alkyl; the methods comprising: combining the metal, M, the trihalide of the metal, MX₃, where X is I, Br or Cl; and a halomethane to form (R)₃M₂X₃; treating the (R)₃M₂X₃with a reducing agent in a solvent to form (R)₃M.

Description

PRODUCTION OF TRI-ALKYL COMPOUNDS OF GROUP 3A METALS

Background of the Invention

[001] Trimethylgallium (TMG) is one of the expensive metal-organic precursors used in the electronics and solar cell industries. It is commonly used in metal-organic chemical vapor deposition (MOCVD) processes, where a gas phase epitaxial surface reaction occurs at high temperatures, and in other deposition processes. In the synthesis of gallium-based

semiconductor materials such as GaN and GaAs, a dilute organogallium precursor, typically TMG is reacted in a controlled fashion with an N- or As-atom source at the surface of a substrate. The product of the reaction decomposes at this surface to provide a thin film with the desired properties.

[002] As is known in the art, ultra-high purity TMG is almost always required because the optoelectronic properties of the final products made from it are extremely sensitive to trace levels of dopants and impurities. So, not only must the reagents used be of ultra-high purity, but certain specific impurities must be rigorously excluded in order to achieve the desired device properties. For example, when making TMG for use in the preparation of semiconductors, it is extremely important to minimize levels of Si and O, as the presence of these impurities (and others) negatively impacts the crystal growth stage and thus, the functionality of the final product.

[003] Fukin, K. K.; Frolov, LA. Tr. Khim. Khim. Tekhnol. 1973, 4, 40, teach a method for making TMG that employs an exchange reaction between GaCl₃ and trimethylaluminum (TMA) (Scheme 1). However, this method suffers from at least two serious defects. First, only one methyl group is transferred from the TMA to the gallium. Consequently, at least three equivalents of TMA, which is an expensive reagent, are required to make one equivalent of TMG. Second, trace impurities in the TMA require a distillation step prior to use which can cause up to 25% loss of the product. Although this route is expensive, it does provide a high purity product after distillation. And since this process occurs in the absence of any ethers or other coordinating solvents, the product is free of oxygen impurities and thus, may be used in MOCVD.

GaCI₃ + 3 Me₃AI ► GaMe₃ + 3 Me₂AICI

toluene

Scheme 1. Direct alkylation of GaCl₃ with TMA.

[004] Another method used to prepare TMG is taught in EP1247813 and employs a ligand- modified exchange reaction that employs TMA as a key reagent (see Scheme 2, below). In this approach, a tri-w-propylamine (TPA) adduct of TMA is first generated, the adduct then reacts with the GaCl₃, and the TMG is then removed via fractional distillation.

MegAI + N Pr₃ Me₃AI(N Pr₃)

2 GaCI₃ + 3 Me₃AI(NPr₃) 2 GaMe₃ + 3 MeAICI₂(NPr₃)

toluene

Scheme 2. Production of TMG from a ligand-modified methyl exchange reaction.

[005] Still another method used to make TMG is described in U.S. Patent No. 4,604,473. This method utilizes ether adducts of Grignard reagents (Scheme 3). Provided that the ether has a high boiling point, this approach yields adduct-free TMG in roughly 68% yields. While this method does not involve TMA, the purity of the TMG remains an issue, due to trace

contamination of the TMG product with the high boiling dialkyls ether solvent. Further purification of the ether-contaminated TMG produced can be achieved by the formation of a TMG-amine or TMG-phosphine adduct, isolation of the adduct, and thermal dissociation of the Lewis acid-base adduct to release TMG. Although this approach successfully yields TMG with sufficient purity, the cost and time associated with the preparation and use of the Grignard reagent and the additional purification efforts needed to purify the resulting TMG render this method uncompetitive, when compared to other TMG manufacturing approaches.

Mel + Mg ► MeMgl

DIPE

GaCI₃ + 3 MeMgl ► Me₃Ga

DIPE

Scheme3. Preparation of TMG from ether adducts of Grignard reagents.

[006] Another method of making TMG that does not utilize TMA, but does utilize Grignard reagents, is taught in European Patent No. 1,705,719. This method involves the alkylation of alkyl gallium sesquihalide derivatives of the general formula R_mGa₂X6-_m (R = methyl or ethyl and m is an integer from 1 to 5) can be achieved by employing alkyl lithium compounds, alkyl magnesium halides (Scheme 4), trialkylaluminum reagents, and dialkyl zinc compounds. Such reactions yield trialkylgallium products in high yield but has thus far been performed in ethereal solvents. As a result, the utility of this process remains questionable for the reasons described above, especially because of an oxygen-containing solvent.

Scheme 4. Grignard route to TMG.

R_mGa₂X₆__m + 6-m RMgl ► 2 R₃Ga

Ethereal

solvent

[007] Synthetic approaches that do not involve TMA and Grignard reagents have also been reported. Alkylating agents such as MeLi (Kovar, R.A.; Derr, H.; Brandau, D.; Calloway, J.O. Inorg. Chem. 1975, 14, 2809) ZnMe₂ (Kraus, C.A.; Toonder, F.E. Proc. Natl. Acad. Sci. USA 1933, 19, 292), and dialkyl mercury reagents (Coates, G.E., J. Chem. Soc. 1951, page 2003) have been examined, as has the use of Ga/Mg alloys (U.S. Patent No. 5,248,800); however, in our opinion, each of these methods were undesirable, from the standpoints of achieving either the required economic feasibility or the higher purities required in the microelectronics and nanotechnology fields.

[008] In U.S. Patent No. 5,817,847, Giolando teaches the following methods:

In + lnCI₃ + MeCI(g) - lnCI₂Me + lnMe₂CI

In + lnCI₃ ⁺ MeCI(g) ^¹"⁹ > lnMe₃

[009] The first reaction prepares InCl₂Me and InMe₂Cl. The second reaction, which also incorporates the use of a reducing agent, results in the formation of InMe₃. It should be noted that all teachings in Giolando are directed towards the use of gaseous MeCl. Giolando also suggests in "Predictive Example 1" that the second reaction (above) will work when the indium is replaced with gallium, but no data is given.

[0010] These prior- art methods used ethereal solvents to facilitate the formation of trialkylgallium products. While using these solvents typically results in the isolation of products in high yields, the use of an oxygen containing ether solvent is undesirable due to the formation of Lewis acid-base adducts with trialkylgallium or trialkylindium compounds. Although separation techniques such as high temperature distillation have been attempted to release the base-free trialkylgallium species, it has been found that this approach does not result in products that possess a sufficient purity for use in deposition processes, such as MOCVD. The presence of oxygen-containing impurities, which come from the use of oxygenated solvents during the synthesis, impairs the use of these metallo-organic compounds by modifying the desired electronic properties of the resulting semiconductors during the crystal growth stage. In the above examples, elemental gallium or a gallium(III) halide was used as the source of gallium in the alkylgallium products.

[0011] In spite of the above efforts, additional methods of making TMG are needed. Especially those that do not utilize oxygen containing solvents or Grignard reagents.

Summary of the Invention

[0012] Disclosed herein are methods of making trialkyl compounds of the group 13 elements, wherein the alkyl portions may be the same or different.

[0013] In one aspect, the methods comprise making compounds of the formula:

(R)₃M,

where M is a group 13 element (preferably gallium, indium or thallium); and

each R is independently Q-CK) alkyl;

the methods comprising:

i) combining the metal, M, the trihalide of the metal, MX , where each X is independently I, Br or CI; and at least one haloalkane of the formula RZ, where Z is I, Br or CI to form (R)₃M₂X₃; and

ii) treating the (R) M₂X with a reducing agent to form (R)₃M.

[0014] In a second aspect, compounds made according to the above methods are used in vapor deposition processes such as, but not limited to, Metal-Organic Chemical Vapor Deposition (MOCVD), Metal-Organic Vapor Phase Epitaxy (MOVPE), Metal-Organic Molecular Beam Epitaxy (MOMBE), and Atomic Layer Deposition (ALD) processes. Brief Description of the Figures

[0015] Figure 1 is a 400 MHz ¹H NMR spectrum of Me₃Ga₂I₃ in d₈-toluene.

[0016] Figure 2 is a 400 MHz 1H NMR spectrum of Me₃Ga in d₈-toluene.

[0017] Figure 3 is a 100 MHz ¹³C{ 1H} spectrum of Me₃Ga in d₈-toluene.

[0018] Figure 4 is a 400 MHz 1H NMR spectrum of Me₃Ga₂Cl₃ in d₈-toluene.

[0019] Figure 5 is 400 MHz 1H NMR spectrum of Et₃Ga₂I₃ in d₆-benzene.

Detailed Description

[0020] When conducting the reactions disclosed herein, at least three equivalents of haloalkane should be used. While lesser amounts may be used, the reaction product will be a mixture of mono, bis, and tri-alkylated compounds. Thus it is preferred that at least four equivalents of haloalkane are used. More preferably more than 5 equivalents are used. In one preferred embodiment, at least 8 equivalents are used. In another preferred embodiment, at least 10 equivalents are used. While 20 or more equivalents of haloalkane may be used, it is believed that using such a large excess is not cost effective. In another embodiment, the mole ratio of M to haloalkane is 1:3 to 1:20. More preferably it is 1:3 to 1: 10.

[0021] While the R groups in (R)₃M may be different, it is preferred that they are the same.

[0022] In one embodiment, the haloalkane is a Ci-C4 haloalkane. More preferably, the haloalkane is a haloethane or a halomethane (i.e., R is ethyl or methyl.) Preferred halomethanes include Mel, MeBr and/or MeCl. A particularly preferred halomethane is MeCl.

[0023] When the halomethane is Mel, the first reaction, i), may be performed at room pressure, as Mel is a liquid at atmospheric pressure. But, when EtCl or MeCl or MeBR is used, the reaction should be run at a pressure that is high enough to cause the EtCl or MeCl or MeBr gas to condense and form a liquid.

[0024] As shown in the examples, MeCl gas does not form the desired product (Example 6, no catalyst) or does so slowly (Example 8, with catalyst). Yet, the inventors surprisingly found that when MeCl liquid is used, the reaction occurs effectively (Example 2, with catalyst). Typical pressures when MeCl is used are greater than or equal to 2 MPA and up to 500 MPA. More preferably, the pressure is 2 to 400 MPa. As mentioned above, in a preferred embodiment, the pressure must be high enough to cause the MeCl to condense and form a liquid.

[0025] The first reaction, i) typically occurs at a temperature greater than or equal to 20 °C to 300 °C. More preferably, the temperature is from 25 to 250 °C.

[0026] The first reaction, i) is typically run for 1 to 96 hours. More preferably, it is run for 24-72 hours. The exact time required for the reaction to reach completion is readily determined by one of ordinary skill in the art.

[0027] The formation of the (R)₃M₂X3 and the subsequent reduction may be performed in a single reaction vessel or in separate reaction vessels.

[0028] The use of the MX₃ catalyst is found to facilitate the formation of the (R)₃M₂X₃.

Typically, the metal in the MX is the same as that of the metal, M, that is used when making the (R)₃M.

[0029] In one embodiment, the mole ratio M:MC1₃ is 1:0.01 to 1:2.0. More preferably, the mole ratio M:MC1₃ is 1: 1. Even more preferably, the MC1₃ is used in catalytic amounts, i.e., less than one equivalent. Still more preferably, the mole ratio M:MC1₃ is 1.0:0.01 to 1.0:0.5. Even more preferably, the mole ratio M:MC1₃ is 1.0:0.01 to 1.0:0.25. [0030] Besides the MX₃, other activators may be used to accelerate the formation of the organometallic sesquihalide. These other activators include Cl₂, HC1, InCl₃, FeCl₃, (PtCl₄) ^", PdCl₂. The oxide activators include ln₂0, Ti0₂, Ni0₂, Fe₂0₃. The function of the activator is to react with the metal, M, to generate a sub-valent reactive metal species. Thus, other metal halides or metal oxides that are capable of forming sub-valent metal species in the melt are suitable for use with the methods disclosed herein.

[0031] When making the compounds of formula (R)₃M, it is preferred that the R groups are the same and are C C₄ alkyl. It can be a logical extension of the alkylation concept to use mixtures of alkyl groups to produce heteroleptic or mixed alkyl metal compounds. More preferably, the R groups are C C₂ alkyl. Most preferably, the R groups are methyl.

[0032] When a one pot procedure is conducted, the reducing agent is added to the reaction mixture, along with the RZ and the metal, M. If desired, a solvent may also be added. The final product of the one pot procedure is the (R)₃M compound.

[0033] When conducting a two step reaction sequence, after the (R) M₂X is formed, the pressure in the reaction vessel is released (if MeCl was used, it will gasify upon release of the pressur and then boil off) and a reducing agent and a solvent are added.

[0034] Preferred reducing agents comprise a group 1 metal, a group 2 metal, a group 3 metal, or a group 12 species. If desired, a group 1 metal- mercury amalgam may be used. But typically, the metal is used as the reducing agent. Preferred group 1 metals include lithium, sodium and potassium, with sodium being particularly preferred. Preferred group 2 metals include magnesium and calcium, with magnesium being preferred. Preferred group 3 metals include aluminum, gallium and indium. Preferred group 12 species include those wherein the metal is Zn, Cd, Hg or combinations thereof. Combinations of one or more group 1, 2, 3, and/or 12 metals may also be used.

[0035] Solvents useful in the reduction reaction include those that do not contain oxygen. And even more preferably, they also are hydrocarbons. Examples of solvents suitable for the reduction reaction include benzene, toluene, xylene, mesitylene, heptane, octane, hexadecane, squalane, and combinations thereof. More preferred are toluene, xylene, mesitylene, octane, hexadecane, squalane, or combinations thereof.

[0036] The reduction reaction is conducted at temperatures between -40 °C to room temperature. More typically, the temperature is -30 °C to 0°C.

[0037] Once the reaction is complete the product is typically isolated by fractional distillation, although other methds such as crystallization or extraction may be used.

[0038] The metal, M, is typically melted or in a high surface area form, such as a particle or powder. Of course, other forms, shot, pellets, etc., may be used, but the reaction rate may be decreased as a result of the lower surface area.

[0039] In one embodiment, M is gallium.

[0040] In another embodiment, M is indium.

[0041] In still another embodiment, M is thallium.

[0042] In one preferred embodiment, the R groups are the same and are methyl; MX₃ is GaCl₃; the haloalkane is Etl, EtCl, Mel or MeCl, the reducing agent is sodium metal, and wherein the temperature of the first reaction, i), is from 25 to 250 °C, and the pressure in the first reaction i) is from 2-400 MPa (when the halomethane is CH₃C1). Examples

Example 1 : Synthesis of Me₃Ga₂l3 Using Mel and a Catalyst

[0043] A 250 ml flask equipped with a magnetic stir bar and a condenser was charged, under nitrogen atmosphere, with 24 g gallium metal, 3 g GaCl₃ and 110 g iodomethane. The flask was heated up to reflux at vigorous stirring. After 2 hours at reflux conditions almost all gallium metal dissolved. Excess iodomethane was removed in vacuum, and clear viscous product was obtained, Me Ga₂I , which was identified by NMR spectroscopy. The yield was almost quantitative.

1H NMR (C₆D₆, 400 MHz): δ 0.55 (s, 6H, -GaCH ), 0.98 (s, 3Η, -GaCH ).

Example 2: Synthesis of Me Ga₂Cl₃ Using Liquid MeCl and a Catalyst

[0044] A Hastelloy accelerating rate calorimetric sphere was charged with Ga metal (1.45 g, 20.8 mmol), GaCl₃ (0.176 g, 1.00 mmol), and CH₃C1 (3.252 g, 64.0 mmol). The sphere was stirred with a Teflon stir bar and heated to 110 °C for 48 hours. After cooling to room temperature, the contents of the flask were examined with 1H NMR spectroscopy which demonstrated conversion to Me Ga₂Cl₃ (1.325 g, 44 % yield).

1H NMR (CD₃C₆D₅, 400 MHz): δ 0.43 (s, 3H, -GaCH ), 0.49 (s, 6Η, -GaCH ).

Example 3: Synthesis of Me Ga from Me Ga₂I

[0045] To a 20 mL high pressure scintillation vial was added Me Ga₂I (1.00 g, 1.77 mmol) and 2 mL d₈-toluene. The flask was cooled to -30 °C and a d₈-toluene suspenions of Na (0.122 g, 5.31 mmol) was added carefully. Upon warming to room temperature, the composition of the sample was investigated with H and C{ H} NMR spectroscopy which demonstrated complete conversion to Me₃Ga.

1H NMR (CD₃C₆D₅, 400 MHz): δ-0.18 (s, 9H, -GaCH ).

¹³C{ ¹H} NMR (CD₃C₆D₅, 100 MHz): δ 1.64 (s, -GaCH₃).

Example 4. Synthesis of Me Ga from Me GaCl₃

[0046] To a 20 mL high pressure scintillation vial was added Me Ga₂Cl₃ (0.200 g, 0.689 mmol) and 2 mL d₈-toluene. The flask was cooled to -30 °C and a d₈-toluene suspenions of Na (0.393 g, 2.06 mmol) was added carefully. Upon warming to room temperature, the composition of the

1 13 1

sample was investigated with H and C{ H} NMR spectroscopy which demonstrated complete conversion to Me Ga.

1H NMR (CD₃C₆D₅, 400 MHz): δ-0.18 (s, 9H, -GaCH ).

¹³C{ ¹H} NMR (CD₃C₆D₅, 100 MHz): δ 1.64 (s, -GaCH₃).

Example 5. A theoretical One Pot Synthesis of Me Ga Using Liquid MeCl

[0047] A Hastelloy accelerating rate calorimetric sphere will be charged with Ga metal (1.45 g, 20.8 mmol), GaCl₃ (0.176 g, 1.00 mmol), CH₃C1 (3.252 g, 64.0 mmol) and Na metal (3.014 g, 15.8 mmol). The sphere will be stirred with a Teflon stir bar and heated to 110 °C for 48 hours.

Example 6. Attempted Synthesis of Me Ga₂Cl₃ Using MeCl gas.

[0048] The reaction apparatus consisted of a vertical reactor (OD 30 mm, capacity 50 ml) equipped with fritted gas dispersion tube reaching the bottom of the reactor, thermocouple and side neck connected to a cooled receiver via a U-tube. The reactor was charged under nitrogen atmosphere with 80 grams of gallium metal. The bottom portion of the reactor was equipped with a cable heater connected to a transformer for temperature control. Gallium metal was heated to 120°C under nitrogen flow through the gas dispersion tube. Upon complete melting, nitrogen gas was replaced with chloromethane gas, which was added at a rate of 100 ml/min.

[0049] The reaction temperature of the gallium melt was then increased, by 50°C and the reaction temperature was then held for 20 min. This process was repeated until the

decomposition point of chloromethane (~350°C) was reached. No reaction was observed at any temperature.

Example 7 Synthesis of Me₃Ga₂Cl₃ using MeCl gas and GaCl₃

[0050] The reaction apparatus consisted of a vertical reactor (OD 30 mm, capacity 50 ml) equipped with fritted gas dispersion tube reaching the bottom of the reactor, thermocouple and side neck connected to a cooled receiver via a U-tube. The reactor was charged under nitrogen atmosphere with 80 grams of gallium metal and 10 grams of gallium trichloride. The bottom portion of the reactor was equipped with a cable heater connected to a transformer for temperature control. The Gallium metal and gallium trichloride mixture was heated up to 200°C under slow nitrogen flow through the gas dispersion tube. Two immiscible layers formed with the gallium melt on the bottom. The temperature was increased to 270-290°C, and nitrogen gas was replaced with chloromethane (100 ml/min). Very slow reaction was observed yielding, after 1 hr, 0.5 g of solid product, methylgallium sesquichloride, was obtained. The identity of this solid was determined using 1H NMR spectroscopy.

Example 8 A theoretical method of making Me Ga₂Cl₃ using chloromethane and GaCl₃ gas [0051] The apparatus consists of vertical reactor (OD 30 mm, capacity 50 ml) equipped with fritted gas dispersion tube reaching the bottom of the reactor, thermocouple and side neck connected to a cooled receiver via a U-tube. The reactor is charged under nitrogen atmosphere with 80 grams of gallium metal. The bottom portion of the reactor is equipped with a cable heater connected to a transformer for temperature control. Gallium metal is heated up to 120°C under nitrogen flow through the gas dispersion tube. Upon complete melting, nitrogen gas is replaced with chloromethane-gaseous gallium trichloride mixture which is made by passing chloromethane gas through liquefied gallium trichloride at elevated temperature. Bubbling the above mixture through gallium melt at 270-290°C for 1 hr is expected to generate the desired product, methylgallium sesquichloride (Me₃Ga₂Cl₃).

Example 9 Preparation of Me₃Ga₂I using Etl and GaCl₃

[0052] A 250 ml flask equipped with a magnetic stir bar and a condenser was charged, under nitrogen atmosphere, with 7.0 g gallium metal, 0.5 g GaCl₃ and 35 g iodo-ethane. The flask was heated up to reflux at vigorous stirring. After 5 hours at reflux conditions all gallium metal dissolved. Excess iodo-ethane was pumped out in vacuum, and clear viscous liquid was obtained, Et Ga₂I , which was identified by NMR spectroscopy. The yield was quantitative. See Figure 1 for the 1H NMR of this product.

PRODUCTION OF TRI-ALKYL COMPOUNDS OF GROUP 3A METALS

Background of the Invention

[003] Fukin, K. K.; Frolov, LA. Tr. Khim. Khim. Tekhnol. 1973, 4, 40, teach a method for making TMG that employs an exchange reaction between GaCl₃ and trimethylaluminum (TMA) (Scheme 1). However, this method suffers from at least two serious defects. First, only one methyl group is transferred from the TMA to the gallium. Consequently, at least three equivalents of TMA, which is an expensive reagent, are required to make one equivalent of TMG. Second, trace impurities in the TMA require a distillation step prior to use which can

1 cause up to 25% loss of the product. Although this route is expensive, it does provide a high purity product after distillation. And since this process occurs in the absence of any ethers or other coordinating solvents, the product is free of oxygen impurities and thus, may be used in MOCVD.

GaCI₃ + 3 Me₃AI ► GaMe₃ + 3 Me₂AICI

toluene

Scheme 1. Direct alkylation of GaCl₃ with TMA.

Me₃AI + N Pr₃ >· Me₃AI(N Pr₃)

2 GaCI₃ + 3 M e3AI(NPr₃) >· 2 GaMe₃ + 3 MeAICI₂(NPr₃)

toluene

Scheme 2. Production of TMG from a ligand-modified methyl exchange reaction.

contamination of the TMG product with the high boiling dialkyls ether solvent. Further purification of the ether-contaminated TMG produced can be achieved by the formation of a

2 TMG-amine or TMG-phosphine adduct, isolation of the adduct, and thermal dissociation of the Lewis acid-base adduct to release TMG. Although this approach successfully yields TMG with sufficient purity, the cost and time associated with the preparation and use of the Grignard reagent and the additional purification efforts needed to purify the resulting TMG render this method uncompetitive, when compared to other TMG manufacturing approaches.

Mel + Mg ► MeMgl

DIPE

GaCI₃ + 3 MeMgl ► Me₃Ga

DIPE

Scheme3. Preparation of TMG from ether adducts of Grignard reagents.

Scheme 4. Grignard route to TMG.

R_mGa₂X₆-m + 6-m RMgl ^► 2 R₃Ga

Ethereal

solvent

[007] Synthetic approaches that do not involve TMA and Grignard reagents have also been reported. Alkylating agents such as MeLi (Kovar, R.A.; Derr, H.; Brandau, D.; Calloway, J.O.

3 Inorg. Chem. 1975, 14, 2809) ZnMe₂ (Kraus, C.A.; Toonder, F.E. Proc. Natl. Acad. Sci. USA 1933, 19, 292), and dialkyl mercury reagents (Coates, G.E., J. Chem. Soc. 1951, page 2003) have been examined, as has the use of Ga/Mg alloys (U.S. Patent No. 5,248,800); however, in our opinion, each of these methods were undesirable, from the standpoints of achieving either the required economic feasibility or the higher purities required in the microelectronics and nanotechnology fields.

[008] In U.S. Patent No. 5,817,847, Giolando teaches the following methods:

In + lnCI₃ + MeCI(g) - lnCI₂Me + lnMe₂CI

In + lnCI₃ ⁺ MeCI(g) gucing > lnMe₃

[0010] These prior- art methods used ethereal solvents to facilitate the formation of trialkylgallium products. While using these solvents typically results in the isolation of products in high yields, the use of an oxygen containing ether solvent is undesirable due to the formation of Lewis acid-base adducts with trialkylgallium or trialkylindium compounds. Although separation techniques such as high temperature distillation have been attempted to release the base-free trialkylgallium species, it has been found that this approach does not result in products that possess a sufficient purity for use in deposition processes, such as MOCVD. The presence of oxygen-containing impurities, which come from the use of oxygenated solvents during the synthesis, impairs the use of these metallo-organic compounds by modifying the desired

4 electronic properties of the resulting semiconductors during the crystal growth stage. In the above examples, elemental gallium or a gallium(III) halide was used as the source of gallium in the alkylgallium products.

Summary of the Invention

[0013] In one aspect, the methods comprise making compounds of the formula:

(R)₃M,

where M is a group 13 element (preferably gallium, indium or thallium); and

each R is independently Q-CK) alkyl;

the methods comprising:

ii) treating the (R) M₂X with a reducing agent to form (R)₃M.

[0014] In a second aspect, compounds made according to the above methods are used in vapor deposition processes such as, but not limited to, Metal-Organic Chemical Vapor Deposition (MOCVD), Metal-Organic Vapor Phase Epitaxy (MOVPE), Metal-Organic Molecular Beam Epitaxy (MOMBE), and Atomic Layer Deposition (ALD) processes.

5 Brief Description of the Figures

[0016] Figure 2 is a 400 MHz 1H NMR spectrum of Me₃Ga in d₈-toluene.

[0017] Figure 3 is a 100 MHz ¹³C{ 1H} spectrum of Me₃Ga in d₈-toluene.

[0019] Figure 5 is 400 MHz 1H NMR spectrum of Et₃Ga₂I₃ in d₆-benzene.

Detailed Description

[0023] When the halomethane is Mel, the first reaction, i), may be performed at room pressure, as Mel is a liquid at atmospheric pressure. But, when EtCl or MeCl or MeBR is used, the

6 reaction should be run at a pressure that is high enough to cause the EtCl or MeCl or MeBr gas to condense and form a liquid.

[0029] In one embodiment, the mole ratio M:MC1₃ is 1:0.01 to 1:2.0. More preferably, the mole ratio M:MC1₃ is 1: 1. Even more preferably, the MC1₃ is used in catalytic amounts, i.e., less than one equivalent. Still more preferably, the mole ratio M:MC1₃ is 1.0:0.01 to 1.0:0.5. Even more preferably, the mole ratio M:MC1₃ is 1.0:0.01 to 1.0:0.25.

7 [0030] Besides the MX₃, other activators may be used to accelerate the formation of the organometallic sesquihalide. These other activators include Cl₂, HC1, InCl₃, FeCl₃, (PtCl₄) ^", PdCl₂. The oxide activators include ln₂0, Ti0₂, Ni0₂, Fe₂0₃. The function of the activator is to react with the metal, M, to generate a sub-valent reactive metal species. Thus, other metal halides or metal oxides that are capable of forming sub-valent metal species in the melt are suitable for use with the methods disclosed herein.

[0034] Preferred reducing agents comprise a group 1 metal, a group 2 metal, a group 3 metal, or a group 12 species. If desired, a group 1 metal- mercury amalgam may be used. But typically, the metal is used as the reducing agent. Preferred group 1 metals include lithium, sodium and potassium, with sodium being particularly preferred. Preferred group 2 metals include magnesium and calcium, with magnesium being preferred. Preferred group 3 metals include aluminum, gallium and indium. Preferred group 12 species include those wherein the metal is

8 Zn, Cd, Hg or combinations thereof. Combinations of one or more group 1, 2, 3, and/or 12 metals may also be used.

[0039] In one embodiment, M is gallium.

[0040] In another embodiment, M is indium.

[0041] In still another embodiment, M is thallium.

[0042] In one preferred embodiment, the R groups are the same and are methyl; MX₃ is GaCl₃; the haloalkane is Etl, EtCl, Mel or MeCl, the reducing agent is sodium metal, and wherein the temperature of the first reaction, i), is from 25 to 250 °C, and the pressure in the first reaction i) is from 2-400 MPa (when the halomethane is CH₃C1).

9 Examples

Example 1 : Synthesis of Me₃Ga₂l3 Using Mel and a Catalyst

1H NMR (C₆D₆, 400 MHz): δ 0.55 (s, 6H, -GaCH ), 0.98 (s, 3Η, -GaCH ).

Example 2: Synthesis of Me Ga₂Cl₃ Using Liquid MeCl and a Catalyst

Example 3: Synthesis of Me Ga from Me Ga₂I

[0045] To a 20 mL high pressure scintillation vial was added Me Ga₂I (1.00 g, 1.77 mmol) and 2 mL d₈-toluene. The flask was cooled to -30 °C and a d₈-toluene suspenions of Na (0.122 g, 5.31 mmol) was added carefully. Upon warming to room temperature, the composition of the

1 0 1 13 1

sample was investigated with H and C{ H} NMR spectroscopy which demonstrated complete conversion to Me₃Ga.

1H NMR (CD₃C₆D₅, 400 MHz): δ-0.18 (s, 9H, -GaCH ).

¹³C{ ¹H} NMR (CD₃C₆D₅, 100 MHz): δ 1.64 (s, -GaCH₃).

Example 4. Synthesis of Me Ga from Me GaCl₃

1 13 1

1H NMR (CD₃C₆D₅, 400 MHz): δ-0.18 (s, 9H, -GaCH ).

¹³C{ ¹H} NMR (CD₃C₆D₅, 100 MHz): δ 1.64 (s, -GaCH₃).

Example 5. A theoretical One Pot Synthesis of Me Ga Using Liquid MeCl

Example 6. Attempted Synthesis of Me Ga₂Cl₃ Using MeCl gas.

[0048] The reaction apparatus consisted of a vertical reactor (OD 30 mm, capacity 50 ml) equipped with fritted gas dispersion tube reaching the bottom of the reactor, thermocouple and side neck connected to a cooled receiver via a U-tube. The reactor was charged under nitrogen

1 1 atmosphere with 80 grams of gallium metal. The bottom portion of the reactor was equipped with a cable heater connected to a transformer for temperature control. Gallium metal was heated to 120°C under nitrogen flow through the gas dispersion tube. Upon complete melting, nitrogen gas was replaced with chloromethane gas, which was added at a rate of 100 ml/min.

Example 7 Synthesis of Me₃Ga₂Cl₃ using MeCl gas and GaCl₃

Example 8 A theoretical method of making Me Ga₂Cl₃ using chloromethane and GaCl₃ gas

1 2 [0051] The apparatus consists of vertical reactor (OD 30 mm, capacity 50 ml) equipped with fritted gas dispersion tube reaching the bottom of the reactor, thermocouple and side neck connected to a cooled receiver via a U-tube. The reactor is charged under nitrogen atmosphere with 80 grams of gallium metal. The bottom portion of the reactor is equipped with a cable heater connected to a transformer for temperature control. Gallium metal is heated up to 120°C under nitrogen flow through the gas dispersion tube. Upon complete melting, nitrogen gas is replaced with chloromethane-gaseous gallium trichloride mixture which is made by passing chloromethane gas through liquefied gallium trichloride at elevated temperature. Bubbling the above mixture through gallium melt at 270-290°C for 1 hr is expected to generate the desired product, methylgallium sesquichloride (Me₃Ga₂Cl₃).

Example 9 Preparation of Me₃Ga₂I using Etl and GaCl₃

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Claims

What is claimed is:

1. Methods of making compounds of the formula:

a. (R)₃M,

b. where M is gallium, indium or thallium; and

c. each R is independently Q-Qo alkyl;

d. the methods comprising:

2. combining the metal, M, the trihalide of the metal, MX , where X is I, Br or CI; and a haloalkane to form (R) M₂X₃; and

3. treating the (R) M₂X with a reducing agent in a solvent to form (R)₃M.

4. Methods according to claim 1, wherein the haloalkane comprises Mel, MeBr or MeCl.

5. Methods according to claims 1-2, wherein the mole ratio M:MC1₃ is 1:0.01 to 1:0.25.

6. Methods according to claims 1-3, wherein the mole ratio of M to haloalkane is 1:3 to 1: 10.

7. Methods according to claims 1-4, wherein the reducing reagent comprises a group 1 metal, a group 2 metal, or a group 12 species.

8. Methods according to claims 1-5, wherein the R groups are the same and are Ci-C₄ alkyl.

9. Methods according to claims 1-6, wherein R is methyl or ethyl.

10. Methods according to claims 1-7, wherein the solvent is toluene, xylene, mesitylene, octane, hexadecane, or squalane.

11. Methods according to claims 1-8, wherein M is gallium and X is CI.

1 4

2. Methods according to claims 1-9, wherein the R groups are the same and are methyl; MX₃ is GaCl₃; the haloalkane is CH I or CH C1, the reducing agent is sodium metal, and wherein the temperature of the first reaction, i), is from 25 to 250 °C.

15 What is claimed is:

1. Methods of making compounds of the formula:

(R)₃M,

where M is gallium, indium or thallium; and

each R is independently Q-Qo alkyl;

the methods comprising:

combining the metal, M, the trihalide of the metal, MX₃, where X is I, Br or CI; and a haloalkane to form (R) M₂X₃; and

treating the (R) M₂X with a reducing agent in a solvent to form (R)₃M.

2. Methods according to claim 1, wherein the haloalkane comprises Mel, MeBr or MeCl.

3. Methods according to claims 1-2, wherein the mole ratio M:MC1₃ is 1:0.01 to 1:0.25.

4. Methods according to claims 1-3, wherein the mole ratio of M to haloalkane is 1:3 to 1: 10.

5. Methods according to claims 1-4, wherein the reducing reagent comprises a group 1 metal, a group 2 metal, or a group 12 species.

6. Methods according to claims 1-5, wherein the R groups are the same and are Ci-C₄ alkyl.

7. Methods according to claims 1-6, wherein R is methyl or ethyl.

8. Methods according to claims 1-7, wherein the solvent is toluene, xylene, mesitylene, octane, hexadecane, or squalane.

9. Methods according to claims 1-8, wherein M is gallium and X is CI.

1 4

0. Methods according to claims 1-9, wherein the R groups are the same and are methyl; MX₃ is GaCl₃; the haloalkane is CH I or CH C1, the reducing agent is sodium metal, and wherein the temperature of the first reaction, i), is from 25 to 250 °C.

15