GB2295392A - Organometallic complexes of aluminium, gallium and indium - Google Patents

Abstract

Novel organometallic complexes of aluminium, gallium and indium are disclosed, having improved stability and volatility for use in CVD processes. These are donor ligand complexes of the formula ML 3 where M is the metal, and L is a ligand containing an amidine (R'N---C(R')---NR') group, where R is H, alkyl etc.

Description

ORGSNOMETALLIC COMPLEXES OF ALUMINLUM GALLIUM AND INDIUM This invention relates to volatile organometallic complexes of aluminium, gallium and indium.

Volatile organometallic compounds of aluminium, gallium and indium, e.g. the aluminium, gallium and indium alkyls, especially trimethyl gallium and triethyl indium, are of considerable interest as volatile sources of aluminium, gallium and indium metal in CVD (chemical vapour deposition) processes. Of particular interest are CVD processes employing a volatile source of aluminium, gallium or indium in the manufacture, by chemical vapour deposition on the surface of a suitable substrate, of compound semi-conductor materials such as gallium arsenide (GaAs), indium arsenide (InAs), indium phosphide (InP), indium aluminium gallium arsenide (InA1GaAs) or wide bandgap material systems such as aluminium, gallium or indium nitride.

Metal alkyls, such as trimethylaluminium, trimethylgallium and triethylindium, are, however, unstable at elevated temperature, pyrophoric and extremely sensitive to air, and are explosively hydrolytic in contact with moisture. Such materials can, therefore, be manufactured and used only under very stringent conditions.

In accordance with the present invention we have discovered that amidine complexes of aluminium, gallium and indium possess good stability at room temperature, are substantially non-pyrophoric, and show excellent thermal stability in the vapour phase. They are, therefore, of high utility as a volatile source of aluminium, gallium and indium in CVD processes of all kinds.

In accordance with the present invention, therefore, there are provided novel organometallic complexes of the formula I where M is aluminium, gallium or indium; and L is an organic ligand containing a substituted or unsubstituted amidino [R'N---C(R')---NR'] group.

The advantages of the complexes of the present invention are that they are more stable to air and moisture. Moreover, they reduce the levels of residual, unwanted alkyl groups during and after CVD processes.

The reduced alkyl content of the complex of the present invention also reduces significantly the possibility of carbon inclusion in the deposited product.

Furthermore, the complex of the present invention has a distinct advantage over the acetylacetonato analogues which are typically used in MOCVD in that the highly preferred complexes of the present invention contain no oxygen, the presence of which is detrimental to film formation. In this regard, AcAc gives Gaze,.

Preferred amidine ligands are amidines of the formula II: R'N(H)C(R') =NR' II where R' is H, C,-C8 alkyl or haloalkyl, C3-C8 cycloalkyl, optionally including an NH- group in the ring, C3-C8 cycloalkenyl, phenyl or substituted phenyl containing from 1-3 (C,-C8)alkyl or halo-substituents, trimethylsilyl or halogen, the R' groups being the same or different.

Typical amidine ligands within that formula are N,N'-diphenylbenzamidine, N,N'di(p-chlorophenyl)acetamidine, N, N' -diphenylformamidine, N,N'-di(p-fluorophenyl)acetamidine, benzamidine, acetamidine, and N ,N ' -dicyclohexylacetamidine.

Other suitable amidine ligands will be apparent to those skilled in the art, as will be methods for the preparation of such amidines.

The amidine complexes of this invention are prepared by reacting a suitable amount of the trialkylaluminium, trialkylgallium or trialkylindium compounds, e.g.

trimethylaluminium, trimethylgallium or triethylindium with the ligand under anhydrous conditions in vacuo or under an inert atmosphere, preferably, but not necessarily in the presence of an anhydrous hydrocarbon solvent such as toluene or n-hexane. That reaction may be represented as follows: vacuolinert gas

The alkane (RH) evolved during the course of the reaction is removed preferably continuously, following which the product complex can be recovered by removal of the slight excess of aluminium, gallium or indium trialkyl, amidine, and the solvent, if present, preferably by distillation in vacuo.

Whilst the alkyl substituents of the aluminium, gallium or indium triaikyl reactant will usually be the same, trialkyls containing different alkyl groups may be used.

Aluminium, gallium and indium complexes in accordance with this invention and the preparation thereof will now be described by way of examples, in which reference is made to the following Figures: Figure 1 which shows the x-ray crystal diffraction results for In(PhNCPhNPh)3; and Figure 2 which shows the thermogravimetric analysis curves of the various complexes according to the invention.

In all the Examples, the reactions were carried out on a vacuum line.

Synthesis of ([A1(PhNCPhNPh),) N,N' -Diphenylbenzamidine (1 .70g, 6.25mmol) was suspended in dry degassed hexane (40 mls), cooled to -78 C and a solution of AlMe3, in hexanes (1.1 cm3, 2 M) was added via syringe. The stirred solution was left to warm to room temperature and and the resulting white suspension was heated under reflux for 12 hours, giving a flocculent pale yellow suspension. The solvent was removed under vacuum to give a pale green/yellow solid which was dissolved in a minimum quantity of chloroform and recrystallised by cooling to -35 C, producing a slightly air sensitive pale green powder.

Yield: 62% Found: C, 79.97; H, 5.59; N. 9.55% C57H45N6Al requires C, 80.86; H, 5.55; N, 10.30% 'H NMR (CDCl3) 7.20 (ArH, 3H, t, 7Hz), 7.09 (ArH, 6H, t, 7Hz), 7.00 (ArH, 12H, t, SHz), 6.86 (ArH, 12H, t, 7Hz), 6.64(ArH, 12H, d, 7Hz).

HRMS(EI): calcd for C57H45N6Al (M)+ m/z 840.342112, found m/z 840.352 + 0.0016 MS (EI) m/z 840 (M+, 6%), 56([M-PhNCPhNPh]+,23 %), 272([LH]+, 10%), 180([M-(PhNCPhNPh)2AlNPH)J1, 100%.

Synthesis of {Ga(NPhCPhNPh)3} N,N'Diphenylbenzamidine (0.95g, 3.5 mmol) and monomethylgalliumbis(N,N'diphenylbenzamidine) (2.19g, 3.Smmol) were dissolved in a sealed tube and heated to 200 C for 30 mins, over which time methane (1 mole equivalent) was evolved.

The pale yellow solid was dissolved in chloroform (15cm3), and the solution cooled to -35 C, producing slightly air sensitive pale yellow crystals. These were isolated by removing the solvent by filtration and washed with hexane (2 x 10cm3), and dried in vacuum.

Yield 2.0g (65%) Found: C, 77.10 H, 5.25, N,9.40 C5,H45N6 Ga requires C, 77.47, H,5.13, N, 9.51.

'H NMR (CDCl3) 6.68 (d, 12H, 0-ArH-N), 6.87 (t, 6H, p-ArH-N), 6.94 (d, 6H, o ArH-C), 7.03 (t, 12H, m-ArH-N), 7.13 (t, 6H, m-ArH-C), 7.21 (t, 3H, p-ArH-C).

13C NMR (CDCl3) 166.70 (N-C-N), 144.60 (Ar-N), 130.97 (Ar-C), 129.50 (0-Ar-C), 129.23 (p-Ar-C), 128.27 (m-Ar-C), 127.83 (m-Ar-N), 124-71 (o-Ar-N), 121.78 (p Ar-N).

M.S.(EI) : 882 (M, 7.0), 611 ([M-PhNCPhNPh]+, 26.4), 77(Phl, 100%).

Synthesis of [Ga(PhNCMeNPh)3J This complex was prepared by the same procedure to that used for gallium-tris(N,N1- diphenylbenzamidinato). The product is a colourless solid.

Yield: 1.1 lug (65 %).

C42H39N6Ga requires; C, 72.32; H, 5.64; N, 12.5%.

Found: C, 72.02; H, 5.50; N, 11.80% 'H NMR (CDCl3); 6/ppml.95 (s, 9H, CH3), 6.63 (d, 12H, o-ArH-N), 6.85 (t, 6H, p-ArH-N), 7.00 (t, 12H, m-ArH-N).

Synthesis of [In(PhNCPhNPh)3] N,N1-diphenylbenzamidine (0.55g, 2.02mmol) was reacted with ethylindium-bis N,N'-diphenylbenzamidine) (1.39g, 2.02mmol) as a melt at 1800C, and 1 mole equivalent of ethane was evolved over 0.5 hour. Recrystallisation of the solid from chloroform gave pale a yellow crystals, which isolated by filtration and washed with hexane (2 x 10cm3).

Yield: 1.24g (66%).

C42H39N6 In requires C, 73.71; H, 4.88; N,9.05%.

Found: C, 74.44; H, 4.81; N, 8.83%.

'H NMR (CDCl3): b/ppm 6.56 (d, 12H, o-ArH-N), 6.80 (t, 6H, p-ArH-N), 6.94 (t, 12H, m-ArH-N),m 7.01-7.05 (d, 6H, p-ArH-C), 7.11-7.26 (m, 9H, o-ArH-C, m ArH-C).

Crystals of this compound suitable for x-ray diffraction were grown and characterisation by x-ray crystallography establishes the structure of the complex to be monomeric and to contain three bidentate amidinato groups, as shown in Figure 1 of the accompanying drawings.

Synthesis of [A1(PhNCMeNPh)J This complex was prepared using the same procedure as used for aluminium-tris(N,Ndiphnylbenzamidinato). A solution of Al2Me6 in hexanes (0.79cm3, 0.79mmol) was added to a suspension of N,N'-diphenylacetamidine (1 .0g, 4.76mmol) in hexane. The product is a colourless crystalline solid.

Yield: 0.82g (79%).

C42H39N6 Al requires C, 77.04; H, 6.00; N, 12.83%.

Found: C, 76.56; H, 6.09; N, 12.62%.

'H NMR (CDCl3); 6/pom 2.00 (s, 9H, CH3), 6.73 (d, 12H, o-ArH-N), 6.99 (t, 6H, p-ArH-N), 7. 18 (t, 12H, m-ArH-N).

Synthesis of {In(PhNCMeNPh)3} N, N l-Diphenylacetamidine (0.53g, 2.52mmol) was reacted with ethylindum-bis(N ,N diphenylacetamidinato) (1.42g, 2.25mmol) in a sealed tube at 1800C and the product washed with hexane (2 x 10cm3). The product is a colourless solid.

Yield: 1.57g (84%).

C42H39N6In requires; C, 67.93; H, 5.29; N, 11.32%.

Found: C, 68.29; H. 4.77; N, 11.40%.

'H NMR (CDCl3); 6/pom. 1.94 (s, 9H, CH3), 6.63 (d, 12H, o-ArH-N), 6.85 (t, 6H, p-ArH-N). 7.02 (t, 12H, m-ArH-N).

The (TGA) thermogravimetric analysis curves of various complexes according to the present invention are shown in Figure 2 and show the complexes to be thermally stable to at least 200"C. (e.g. curve A) allowing ease of handling at ambient and moderately elevated temperatures. The following key applies: A: Al(N,N'diphenylacetamidato)3 B: In(N, N ldiphenylbenzamidato)3 Thus the complexes may be readily volatalised intact, and have a useful thermal stability range; both of which properties make them useful metal precursors in metal CVD operations. Further, observation of parent ions in the mass-spectra of these complexes may be thought indicative of the thermal-stability-volatility of such complexes under vacuo and thermal load.

Other modifications to the complexes of the present invention will be apparent to those skilled in the art.

Claims (5)

CLAIMS:

1. Organometallic aluminium, gallium and indium complexes of the formula I: ML3 wherein M is aluminium, gallium or indium; and L is an amidino group of the formula II R'N---C(R') --NR' II wherein R' is H, C,-C8 alkyl or haloalkyl, C3-C8 cycloalkyl optionally including an NH- group in the ring, C3-C8 cycloalkyl, phenyl, substituted phenyl containing from 1-3 (C,-C5) alkyl or halo-substituents, trimethylsilyl or halogen, the R' groups being the same or different.

2. Organometallic aluminium, gallium and indium complexes according to claim 1 wherein the amidine group is derived from any one of the following: acetamidine, benzamidine, N, N' -diphenylbenzamidine, N,N' -di(p-chlorophenyl)-acetamidine, N, N ' -diphenylformamidine ,N, N' -diphenylacetamidine,N ,N '-di(p-tolyl)benzamidine, N, N '-di(p-fluorophenyl)acetamidine, and N, N' -dicyclohexylacetamidine.

3. A method for the chemical vapour phase deposition of aluminium, gallium or indium on a substrate which comprises contacting the substrate with a volatile organometallic gallium or indium in the vapour phase, wherein there is used an organometallic aluminium, gallium or indium complex according to claim 1 or claim 2.

4. A compound substantially as described herein.

5. A

substantially as described herein.