METALORGANIC COMPOUNDS

Abstract: The invention concerns a process for preparing metalorganic compounds and metalorganic amine adducts. A Grignard reagent is prepared and reacted with the metal halide in an amine solvent. The amine used can form a useful adduct with the metalorganic compound produced. Either the metalorganic compound or its amine adduct may be used for growing semiconductor layers by vapor phase epitaxial techniques.

Description: TITLE: Metalorganic compounds DESCRIPTION This invention concerns metalorganic compounds, especially metalorganic compounds used in the growth of semiconductor layers by vapour phase epitaxial techniques, such as by chemical beam epitaxy, MOVPE, or ALE. Metalorganic precursors used in semiconductor growth are generally synthesised by reacting a Grignard reagent such as an alkyl magnesium halide RMgX or an alkyl lithium compound with a metal halide. The formation of the Grignard reagent and its subsequent reaction with a metal halide to form the precursor are carried out in an oxygen containing solvent, typically an ether. Subsequent purification processes are then performed to remove the oxygen containing ether solvent and other impurities from the metalorganic precursor. Unfortunately residual trace amounts of ether can result in oxygen contamination of semi-conductor structures grown using the above prepared precursors. Consequently, there is a deleterious effect on the properties of the semiconductor structures. An object of this invention is to provide a method of preparing metalorganic compounds that avoids the above-mentioned disadvantages. According to this invention there is provided a process for preparing a metalorganic compound by reacting a Grignard reagent with the metal halide, characterised in that said reaction is carried out in an amine solvent. The Grignard reagent for use in the process of the invention is preferably prepared in an amine solvent, especially the amine to be used in preparing the metalorganic compound. The amine is preferably a tertiary amine such as, for example, a tertiary alkyl amine or a tertiary heterocyclic amine. Amines for use in the invention are preferably liquid at room temperature, typically 18 to 20°C. Tertiary alkyl amines for use in the invention preferably have the formula wherein R 1 , R 2 and R 3 are alkyl groups having from 1 to 4 carbon atoms and wherein R 1 , R 2 and R 3 may be the same or two of R 1 , R 2 and R 3 may be the same. Preferred alkyl amines for use in the invention are triethylamine and dimethylethylamine. Suitable heterocylic amines for use in tHe invention may include pyridine, 2H-pyrrole, pyrimidine, pyrazine, pyridazine, 1,3,5-triazine and hexahydro- triazine. The process of the invention may result in novel compounds, which are hereby encompassed by the invention. According to a second aspect of the invention there are provided novel metalorganic amine adducts of the formula MR 3 . A wherein M is a metal, R is an alkyl group and A is a tertiary amine such as a tertiary alkyl amine of the formula R l / N - R 2 wherein R 1 , R 2 and R 3 are as defined above or a tertiary heterocyclic amine. The Grignard reagent may be prepared in any suitable way, typically by reaction of magnesium with an alkyl halide, wherein the alkyl group is that required for the metalorganic compound. Metalorganic compounds that may be prepared in accordance with the invention include alkyl compounds of Group II, Group III and Group V metals. Examples of such compounds include dialkyl zinc, dialkyl cadmium, trialkyl aluminium, trialkyl gallium, trialkyl indium, trialkyl phosphorus, trialkyl arsenic and trialkyl antimony . It is believed that the process of the present invention results in an adduct of the metalorganic compound with the amine. The formation of this adduct permits the removal of volatile metallic and non- metallic microimpurities from the metalorganic compound. Impurities may be readily removed from the adduct by distillation. The adduct may be split by removal of the amine, such as by heating, to provide the metalorganic compound alone for some purposes, such as a precursor for MOVPE or CBE. Alternatively the adduct itself may be used as a precursor for the deposition of, for example Group III-V or II-VI layers, such as gallium arsenide, aluminium gallium arsenide and zinc selenide, by MOVPE, CBE and other vapour phase epitaxy techniques. A preferred process according to the invention includes the following steps: 1. Synthesis of RMgX in NR 3 solvent; 2. Suspension of MCI 3 in pentane; 3. Addition of RMgX to MC1 3 in NR 3 /pentane; 4. Removal of volatiles and isolation of M 3 (NR 3 ) by distillation; 5. Removal of volatile impurities from MR 3 (NR 3 ); 6. Isolation of the adduct or thermal dissociation of MR 3 (NR 3 ) and removal by fractional distillation of the NR 3 ligand. The invention will now be further described by means of the following examples. Each reaction described below was carried out in an atmosphere of dry/oxygen-free dinitrogen using reagents which had been dried and deoxygenated by standard purification methods. Example 1 This example demonstrates the production of triisopropylgallium using triethylamine as solvent. A solution of iso-propyl magnesium bromide, i-PrMgBr, in triethylamine was prepared by the dropwise addition of iso-propyl bromide, i-PrBr (280g, 2.3mol) to a stirred suspension of magnesium metal turnings (60g, 2.5mol) in triethylamine, NEt 3 (1000cm 3 ). This resulted in a vigorous exothermic reaction. It was found that this reaction could be more easily initiated by the addition of a crystal of iodine. After complete addition of the i-PrBr, the reaction mixture was stirred at ambient temperature for 4 hours. A solution of gallium trichloride, GaCl 3 (125g, 0.7mol) in pentane (500cm 3 ) was then added slowly with stirring to the solution of i-PrMgBr in NEt 3 - This led to an exothermic reaction. After complete addition of the GaCl 3 -pentane solution, the reaction mixture was stirred for 4 hours at room temperature to ensure complete reaction. After removal of volatiles by distillation in vacuo. the crude product was isolated by vacuum distillation (100°C) into a receiver cooled in liquid nitrogen (ca - 196°C) . Volatile impurities were removed from the crude product by distillation in vacuo (25- 50°C) and the pure liquid product was obtained by vacuum distillation (80°C) into a cooled receiver (c - 106°C). The metalorganic product was identified using proton NMR spectroscopy as a triethylamine adduct of triisopropylgallium, i-P^Ga(NEt 3 )o. 6 • The proton NMR data are summarised below: (ppm) (Assignment) 0.8 (triplet, 5.4H) NCH 2 CH 3 1.0 (multiplet, 3H) GaCH(CH 3 ) 2 1.4 (doublet, 18H) GaCH(CH 3 ) 2 2.4 (quartet, 3.6H) NCH 2 CH 3 The i-Pr 3 Ga-NEt 3 adduct was further analysed for trace metal impurities using inductively coupled plasma emission spectroscopy (ICP-ES). The only impurities detected were silicon (0.03ppm w.r.t. Ga) and zinc (0.2ppm w.r.t. Ga). Yield i-Pr 3 Ga(NEt 3 ) o.6 = 9 - 4 g« The vapour pressure of the iP^Ga adduct was found to be 0.9mBar ar 13°C. The tri-isopropyl gallium prepared in the above way was used to grow a layer of AlGaAs on a gallium arsenide substrate by chemical beam epitaxy under the following conditions: Substrate temperature 540°C AlGaAs growth rate 1 /hr Group V precursor - thermally cracked arsine Group III precursors - tri-isopropyl gallium triethylamine adduct plus AlH 3 -NMe 2 Et An AlGaAs layer (aluminium composition of 18%) grown in this manner demonstrated oxygen levels of less than 4 x lθ 16 cm -3 (as measured by secondary ion mass spectrometry, SIMS) . This layer is superior to an AlGaAs layer (aluminium composition of 25%) grown using triisopropylgallium synthesised in a conventional manner (i.e. using an ether solvent), and AlH 3 (NMe Et) , in which much higher oxygen levels of 9 x 10 16 cm -3 were detected by SIMS. The AlGaAs layer grown using the triisopropyl gallium-triethylamine adduct was comparable in oxygen content (<4 x 10 16 cm~ 3 ) with the best layers thus far obtained using triethylgallium and AlH 3 (NMe 2 Et) under identical CBE growth conditions. Figures 1 and 2 respectively of the accompanying drawings show comparison of vapour pressures and growth rates of the tri-isopropyl gallium adduct prepared according to this Example and tri-isopropyl gallium prepared in the conventional way. As can be seen the adduct has both higher vapour pressures and growth rates which are advantageous for chemical vapour deposition processes. Example 2 This demonstrates the production of tri- isopropylgallium using dimethylethylamine as solvent. A solution of iso-propylmagnesium bromide, i- PrMgBr, in dimethylethylamine was prepared by the dropwise addition of iso-propylbromide, i-PrBr (166g, 1.4mol) to a stirred suspension of Mg metal turnings (48g, 2.0mol) in dimethylethylamine, NMe 2 Et (500cm 3 ). This resulted in a vigorous exothermic reaction which could be more easily initiated by the addition of a small quantity of iodine. After complete addition of the i-PrBr the reaction mixture was stirred at room temperature for 4 hours. A solution of GaCl 3 (69g, 0.4mol) in pentane (260cm 3 ) was then added slowly, with stirring, to the solution of i-PrMgBr in NMe 2 Et. This led to a vigorous exothermic reaction. After complete addition of the GaCl 3 -pentane solution, the reaction mixture was stirred for 4 hours at room temperature to ensure complete reaction. After removal of volatiles by atmospheric pressure distillation (60°C), the crude product was isolated by vacuum distillation (100°C) into a cooled receiver (c_a - 196°C) . Volatile impurities were removed from the crude products in vacuo. and the pure liquid product was obtained by reduced pressure distillation (70°C) into a receiver. The metalorganic product was identified using proton NMR spectroscopy as the dimethylethylamine adduct of triisopropylgalliu , i-Pr 3 Ga(NMe 2 Et) . The proton NMR data are summarised below: (ppm) (Assignment) 0.6 (triplet, 3H) NCH 2 CH 3 0.9 (multiplet, 3H) GaCH(CH 3 ) 2 1.4 (doublet, 18H) GaCH(CH 3 ) 2 1.9 (singlet, 6H) NCU 3 2.4 (quartet, 2H) NCH 2 CH 3 The i-Pr 3 Ga-NMe 2 Et adduct was further analysed for trace metal impurities using ICP-ES. The only impurities detected were silicon (0.2ppm w.r.t Ga) and Zinc (4.6ppm w.r.t Ga). Yield i-Pr 3 Ga(NMe 2 Et) = 58.5g Example 3 This example demonstrates the production of tri- isopropylindium using triethylamine as solvent. A solution of i-PrMgBr in NEt 3 was prepared by the dropwise addition of i-PrBr (72g,0.6mol) in NEt 3 (200cm 3 ). This led to a vigorous exothermic reaction. After complete addition of the i-PrBr the reaction mixture was stirred at room temperature for 4 hours. The solution of i-PrMgBr in NEt 3 was added dropwise, with stirring, to a suspension of indium trichloride, InCl 3 (35g, 0.2mol) in NEt 3 (200cm 3 ) . This led to an exothermic reaction. After complete addition of the i-PrMgBr/NEt 3 solution, the reaction mixture was boiled under reflux for 2 hours. After removal of volatiles by distillation in vacuo. the crude product was obtained by vacuum distillation (100°C) into a cooled receiver (ca- 196°C). Volatile impurities were removed from the crude product by distillation in vacuo and the pure liquid product was obtained by vacuum distillation (70°C) into a cooled receiver (ca - 196°C) . The metalorganic product was identified using proton NMR spectroscopy as a triethylamine adduct of triisopropylindium, i-Pr 3 In(NEt 3 ) . The proton NMR data are summarised below: (ppm) (Assignment) 0.8 (triplet, 9H) NCH 2 CH 3 1.1 ( ultiplet, 3H) InCH(CH 3 ) 2 1.6 (doublet, 18H) InCH(CH 3 ) 2 2.4 (quartet, 6H) NCH 2 CH 3 The i-Pr 3 ln-NE 3 adduct was further analysed for trace metal impurities using ICP-ES. The only impurities detected were silicon (0.04ppm w.r.t In) and zinc (3.8ppm w.r.t In). Yield i-Pr 3 In ( NEt 3 ) = 8g . Example 4 This example demonstrates the production of triisopropylindium using dimethylethylamine as solvent. A solution of i-PrMgBr in NMe Et was prepared by the dropwise addition of i-PrBr (192g, 1.6mol) to a stirred suspension of Mg metal turnings (56g, 2.3mol) in NMe 2 Et (400cm 3 ). This resulted in a vigorous exothermic reaction. After complete addition of the i-PrBr the reaction mixture was stirred for 4 hours at room temperature. The solution of i-PrMgBr in NMe 2 Et was added dropwise, with stirring, to a suspension of InCl 3 (72g, 0.3mol) in pentane. This resulted in an exothermic reaction. After complete addition of the i- PrMgBr/NMe 2 Et solution, the reaction mixture was boiled under reflux for 2 hours. After removal of volatiles by atmospheric pressure distillation, (60°C), the crude product was obtained by reduced pressure distillation (85-90°C) into a receiver. Volatile impurities were removed from the crude product by vacuum distillation (25°C). The pure liquid product was obtained by vacuum distillation (85-90°C) into a receiver cooled to approx. -196°C. The straw yellow liquid was identified using proton NMR spectroscopy as the dimethylethylamine adduct of tri-isopropyl indium, iPr 3 In(NMe 2 Et) . The proton NMR data are summarised below: (ppm) (Assignment) 0.8 (triplet, 3H) NCH 2 CE 3 1.0 (multiplet, 3H) InCH(CH 3 ) 2 1.5 (doublet, 18H) InCH(CH 3 ) 2 2.0 (singlet, 6H) NCH 3 2.3 (quartet, 2H) NCH 2 CH 3 The i-Pr 3 In-NMe 2 Et adduct was further analysed for trace metal impurities using ICP-EAS. The only impurities detected were silicon (<lppm) w.r.t In), and Zn(0.12 w.r.t In) . Yield i-Pr 3 In(NMe 2 Et) = 81.7g.

Claims: CLAIMS 1. A process for preparing a metalorganic compound by reacting a Grignard reagent with the metal halide, characterized in that the reaction is carried out in an amine solvent. 2. A process as claimed in claim 1, characterized in that the Grignard reagent is prepared in an amine solvent. 3. A process as claimed in claim 2, characterized in that the amine solvent used in preparing the Grignard reagent is the same as that used for the reaction thereof with the metal halide. 4. A process as claimed in claim 1, 2 or 3, characterized in that the amine is a tertiary amine. 5. A process as claimed in any one of claims 1 to 4, characterized in that the amine is selected from tertiary alkyl amines and tertiary heterocyclic amines. 6. A process as claimed in any one of claims 1 to 5, characterized in that the amine is liquid at room temperature. 7. A process as claimed in any one of claims 1 to 6, characterized in that the amine has the following general formula: Rl / N - R 2 X R3 wherein R 1 , R 2 and R 3 are alkyl groups having from 1 to 4 carbon atoms and wherein R 1 , R 2 and R 3 are the same or two of R 1 , R 2 and R 3 are the same. 8. A process as claimed in any one of claims 1 to 7, characterized in that the amine is selected from triethylamine and dimethylethylamine. 9. A process as claimed in any one of claims 1 to 6, characterized in that the amine is selected from pyridine, 2H-pyrrole, pyrimidine, pyrazine, pyridazine, 1,3,5-triazine and hexahydrotriazine. 10. A process as claimed in any one of claims 1 to 9, characterized in that the Grignard reagent is prepared by reaction of magnesium with an alkyl halide, the alkyl group thereof being that required for the metalorganic compound. 11. A process as claimed in any one of claims 1 to 10, characterized in that the metalorganic compound is an alkyl compound of a metal selected from Group II, Group III and Group V metals. 12. A process as claimed in claim 11, characterized in that the metalorganic compound is selected from dialkyl zinc, dialkyl cadmium, trialkyl aluminium, trialkyl gallium, trialkyl indium, trialkyl phosphorus. trialkyl arsenic and trialkyl antimony. 13. A process as claimed in claims 11 or 12, wherein the alkyl groups are isopropyl groups. 14. A process as claimed in any one of claims 1 to 14 characterized in that an adduct of the metalorganic compound with the amine used as solvent is isolated. 15. A process as claimed in claim 14 characterized by the further step of dissociating the metal organic amine adduct to leave the metalorganic compound. 16. A metalorganic compound whenever prepared by a process as claimed in any one of claims 1 to 15. 17. Metalorganic amine adducts of the formula MR 3 . A wherein M is a metal; R is an alkyl group; and A is a tertiary alkyl amine of the formula. R 1 N /- R 2 ^»R 3 wherein R 1 , R 2 , R 3 are alkyl groups having from 1 to 4 carbon atoms and wherein R 1 , R 2 and R 3 are the same or two of R 1 , R 2 and R 3 are the same, or a tertiary heterocyclic amine. 18. An adduct as claimed in claim 17, wherein the alkyl group of the MR 3 is a Cτ__ 5 straight or branched chain alkyl group. 19. An adduct as claimed in claim 18, wherein the alkyl group is an isopropyl group. 20. A process as claimed in claim 1 and substantially as hereinbefore described with reference to any one of the foregoing Examples.

Inventors: FREER RICHARD WILLIAM, JONES ANTHONY COPELAND, MARTIN TREVOR, RUSHWORTH SIMON ANDREW, WHITTAKER TIMOTHY JOHN, FREER, RICHARD, WILLIAM, JONES, ANTHONY, COPELAND, MARTIN, TREVOR, RUSHWORTH, SIMON, ANDREW, WHITTAKER, TIMOTHY, JOHN
Applicants: FREER RICHARD WILLIAM, JONES ANTHONY COPELAND, MARTIN TREVOR, RUSHWORTH SIMON ANDREW, SECR DEFENCE, WHITTAKER TIMOTHY JOHN, FREER, RICHARD, WILLIAM, JONES, ANTHONY, COPELAND, MARTIN, TREVOR, RUSHWORTH, SIMON, ANDREW, SECRETARY OF STATE FOR DEFENCE, ACTING THROUGH HIS, WHITTAKER, TIMOTHY, JOHN
Application year: 1995
Main classification: C07F5
IPC codes: C07F5, C07F9, C23C16, C30B25, C30B29, H01L21