METHOD FOR PURIFYING HALOGENATED OLIGOSILANES

Abstract

1. The present invention relates to a method for the purification of halogenated oligosilanes as a pure compound or mixture of compounds each having at least one direct Si—Si bond, the substituents thereof being exclusively halogen or halogen and hydrogen, and the composition thereof being an atom ratio of substituent:silicon of at least 3:2, by the action of at least one purification agent on the halogenated oligosilane and isolation of the halogenated oligosilane with improved purity.

2.1. In the prior art, halogenated monosilanes such as HSiCl.sub.3 are purified by treatment with preferably polymeric organic compounds containing amino groups, and are separated out from these mixtures. This method cannot be used for halogenated oligosilanes because of the contained amino groups, since secondary reactions would lead to decomposition of the products. The new method should provide the desired products in high yield and purity without amino groups being used.

2.2. The purification of the halogenated oligosilanes is carried out in the presence of special purification agents, which convert contaminations such as, for example, FeCl.sub.2 into an insoluble and/or less volatile form. A separation of the products of completes the purification This method gives a high yield and avoids the problems associated with the prior art, such as, for example, long distillation times.

2.3. The method is suitable for the purification of, for example, Si.sub.2Cl.sub.6, Si.sub.3Cl.sub.8, Si.sub.4Cl.sub.10, and higher homologs. These find application, for example, in the deposition of silicon nitride layers in CVD processes.

Claims

1. Method for the purification of halogenated oligosilanes Si.sub.nX.sub.2n+2 with n=2 through n=6 as pure compounds or as mixtures of compounds in which the substituents X comprise chlorine or chlorine and hydrogen, characterized in that (a) a fluoride is added to the halogenated oligosilane, wherein said fluoride is in pure form and/or as a fluoride mixture and/or as a fluorine-containing compound and/or preparation and added in an amount, when calculated as F.sup.− in relation to the mass of the halogenated oligosilane, of more than 1 ppb, preferably more than 100 ppb, especially preferably more than 1 ppm, especially more than 10 ppm, (b) at least one processing phase takes place in which at least the fluoride acts upon the halogenated oligosilane, wherein the at least one processing is selected from a group comprising stirring, swirling, shaking, heating to reflux, diffusing, and passing through, preferably at least two processing phases comprising stirring and heating to reflux, (c) at least one separation method for the isolation of the halogenated oligosilane takes place, selected from a group comprising decanting, filtering, distilling, and subliming, (d) the halogenated oligosilane exhibits a reduced metal content after the purification.

2. Method according to claim 1, characterized in that the fluoride is selected from a group comprising alkali metal fluorides, alkaline earth metal fluorides, silicon fluorides Si.sub.nX.sub.oF.sub.p (X=halogen, organyl, siloxanyl and/or hydrogen; o+p=2n+2; n≧1), and zinc fluoride, preferably alkali metal fluorides, especially preferably potassium fluoride.

3. Method according to claim 1, characterized in that a complexing agent is added to the halogenated oligosilane, said complexing agent being selected from a group comprising polyethers, crown ethers, and cryptands, preferably crown ethers, especially preferably 18-crown-6.

4. Method according to claim 1, characterized in that to the halogenated oligosilane and/or fluoride is added before or during the processing phase a solvent that is selected from a group comprising alkanes, cycloalkanes, ethers, aromatics, and chlorinated silanes, preferably cycloalkanes and ethers such as triglyme, diglyme, dioxane, dibutyl ether, THF, and diethyl ether, especially preferably cycloalkanes, especially cyclohexane, wherein the proportion of the solvent in the mixture with the ogenated oligosilanes is at least 0.01 mass %, preferably at least 0.1 mass %, especially preferably at least 1 mass %, especially at least 2 mass %.

5. Method according to claim 1, characterized in that X in Si.sub.nX.sub.2n+2 is more than 95 atom % chlorine, preferably more than 98 atom %, and/or the hydrogen content in Si.sub.nX.sub.2n+2 is less than 5 atom %, preferably less than 2 atom %, especially preferably less than 1 atom %.

6. Method according to claim 1, characterized in that the chlorinated oligosilane contains a diluent selected from a group comprising of Si.sub.2Cl.sub.6, Si.sub.3Cl.sub.8, and Si.sub.4Cl.sub.10, wherein the proportion of the diluent based on the halogenated oligosilane is least 0.001 mass %, preferably at least 0.1 mass %, especially preferably at least 1 mass %, especially at least 10 mass %.

7. Method according to claim 1 characterized in that at least one separation process is operated at a pressure less than 1600 hPa, preferably less than 800 hPa, especially preferably less than 80 hPa, and especially less than 1 hPa.

8. Method according to claim 1, characterized in that the at least one processing step and/or one separation process is operated at a temperature of more than 30° C., preferably more than 50° C., especially preferably more than 80° C., and especially more than 100° C.

9. Method according to claim 1, characterized in that a content of 1 ppm each of Al, Fe, and Cu in the halogenated oligosilane will be reduced by purification to less than 100 ppb, preferably below 30 ppb, especially preferably below 5 ppb, and especially less than 1 ppb.

10. Method according to claim 1, characterized in that a siloxane as a pure compound or mixture of compounds preferably selected from the group Cl.sub.3SiOSiCl.sub.3, Cl.sub.3SiOSiCl.sub.2SiCl.sub.3, Cl.sub.3SiOSiCl.sub.2OSiCl.sub.3 is added to the halogenated oligosilane before or during the processing phase, wherein the proportion of the siloxane in the mixture with the halogenated oligosilane is at least 0.001 mass %, preferably at least 0.01 mass %, especially preferably at least 0.1 mass %, especially at least 1 mass %.

11. Method for the purification of halogenated oligosilanes Si.sub.nX.sub.2n+2 with n=2 through n=6 as pure compounds or as mixtures of compounds in which the substituents X comprise chlorine or chlorine and hydrogen, characterized in that (a) a fluoride or fluoride mixture is added to the halogenated oligosilane, wherein fluoride F.sup.− from the specific compound is made available for a reaction, being admixed in an amount of more than 1 ppb calculated as F.sup.− in relation to the mass of the halogenated oligosilane, (b) at least one processing phase takes place in which at least the fluoride acts upon the halogenated oligosilane, wherein the at least one processing is selected from a group comprising stirring, swirling, shaking, heating to reflux, diffusing, and passing through, preferably at least two processing phases comprising stirring and heating to reflux, (c) at least one separation method for the isolation of the halogenated oligosilane takes place, selected from a group comprising decanting, filtering, distilling, and subliming.

12. Method according to claim 11, characterized in that the fluoride is selected from a group comprising alkali metal fluorides, alkaline earth metal fluorides, silicon fluorides Si.sub.nX.sub.oF.sub.p (X=halogen, organyl, siloxanyl and/or hydrogen; o+p=2n+2; n≧1), and zinc fluoride, preferably alkali metal fluorides, especially preferably potassium fluoride.

13. Method according to claim 11, characterized in that a complexing agent is added to the halogenated oligosilane, said complexing agent being selected from a group comprising polyethers, crown ethers, and cryptands, preferably crown ethers, especially preferably 18-crown-6.

14. Method according to claim 11, characterized in that to the halogenated oligosilane and/or fluoride is added before or during the processing phase a solvent that is selected from a group comprising alkanes, cycloalkanes, ethers, aromatics, and chlorinated silanes, preferably cycloalkanes and ethers such as triglyme, diglyme, dioxane, dibutyl ether, THF, and diethyl ether, especially preferably cycloalkanes, particularly cyclohexane, wherein the proportion of the solvent in the mixture with the halogenated oligosilanes is at least 0.01 mass %.

15. Method of claim 11, characterized in that X in Si.sub.nX.sub.2n+2 is more than 95 atom % chlorine, preferably more than 98 atom %, and/or the hydrogen content in Si.sub.nX.sub.2n+2 is less than 5 atomic %, preferably less than 2 atom %, especially preferably less than 1 atom %.

16. Method of claim 11, characterized in that the chlorinated oligosilane contains a diluent selected from a group comprising of SiCl.sub.4, Si.sub.2CI.sub.6, Si.sub.3Cl.sub.8, Si.sub.4Cl.sub.10, wherein the proportion of the diluent based on the halogenated oligosilane is least 0.001 mass %.

17. Method of claim 11, characterized in that at least one separation process is operated at a pressure less than 1600 hPa, preferably less than 800 hPa, especially preferably less than 80 hPa, and especially less than 1 hPa.

18. Method according to claim 11, characterized in that the at least one processing step and/or one separation process is operated at a temperature of higher than 30° C.

19. Method according to claim 11, characterized in that a siloxane as a pure compound or mixture of compounds preferably selected from the group Cl.sub.3SiOSiCl.sub.3, Cl.sub.3SiOSiCl.sub.2SiCl.sub.3, Cl.sub.3SiOSiCl.sub.2OSiCl.sub.3 is added to the halogenated oligosilane before or during the processing phase, wherein the proportion of the siloxane in the mixture with the halogenated oligosilane is at least 0.001 mass %.

Description

Embodiment 1

[0046] 70 kg hexachlorodisilane was treated with a suspension of 18 g 18-crown-6 and 2.7 g KF in 50 mL cyclohexane. The mixture was stirred for 2 h and then was fractionally distilled. A main run of 62 kg HCDS was obtained after 10 h. In the course of this purification, the original aluminum content of 3.8 ppm and iron content of 1.3 ppm were thus respectively reduced to below 30 ppb.

Embodiment 2

[0047] 60 kg hexachlorodisilane was treated with a suspension of 50 g 18-crown-6 and 5 g KF in 150 mL triglyme. The mixture was stirred overnight and then was fractionally distilled. A main run of 45 kg HCDS was obtained after 9 h. In the course of this purification, the original aluminum content of 800 ppb, iron content of 75 ppb, and magnesium content of 180 ppb were thus respectively reduced to below 5 ppb.

Embodiment 3

[0048] 8 kg octachlorotrisilane was treated with a suspension of 0.5 g NaF and 4.5 g 15-crown-5 in 30 mL dichloromethane. The mixture was stirred at rt overnight and then was decanted from the undissolved solids. The OCTS was then quickly distilled off under vacuum (approx. 10 hPa) through a short column, and was then fractionally distilled under vacuum (approx. 10 hPa) A main run of 5 kg OCTS was obtained over 8 h. The content values in ppb for the exemplary trace contaminants before and after purification are shown in the following table.

TABLE-US-00002 OCTS Al Cr Mn Cu Fe Mg K Na Ti Ca Crude 920 <30 <30 58 46 110 160 120 <30 750 Purified <30 <30 <30 <30 <30 <30 <50 <50 <30 <50

Embodiment 4

[0049] 1.5 kg of a mixture of approx. 90% of a tetrachlorodisilane isomer mixture and 10% pentachlorodisilane was treated with a suspension of 0.1 g NaF and 1 g 12-crown-4 in 20 mL dichloromethane. The mixture was stirred at rt for 2 h and then overnight at 0° C. The liquid phase was decanted from the undissolved solids, filtered through a fitted glass filter (D3), and then rapidly recondensed through a short column under vacuum (approx. 10 hPa). The condensate was then fractionally distilled under vacuum (approx. 10 hPa). A main run of 1.2 kg oligosilane mixture was obtained over 14 h. The content values in ppb for the exemplary trace contaminants before and after purification are shown in the following table.

TABLE-US-00003 TCDS/PCDS Al Cr Mn Cu Fe Mg K Na Ti Ca Purified <30 <30 <30 <30 <30 <30 <50 <50 <30 <50

Embodiment 5

[0050] 35 kg hexachlorodisilane was treated with a suspension of 3 g KF, 12 g 15-crown-5 and 15 g 18-crown-6 in 120 mL dichloromethane. The mixture was heated to reflux for approx. 2 h, and then was fractionally distilled. A main run of 28 kg HCDS was obtained over 8 h.

[0051] The content values in ppb for the exemplary trace contaminants before and after purification are shown in the following table.

TABLE-US-00004 HCDS Al B Sb Cu Fe Mg K Na Ti Ca Crude 112 420 0.7 5.2 848 11 78 49 734 125 Purified 25 23 0.1 0.8 13 7 6.6 2.2 27 26

Embodiment 6

[0052] 40 kg hexachlorodisilane was treated with a suspension of 3.5 g KF, 14 g 15-crown-5 and 17 g 18-crown-6 in 140 mL dichloromethane. The mixture was heated to reflux for approx. 2 h, and then was fractionally distilled. A main run of 32 kg HCDS was obtained over 10 h. From this, 26 kg HCDS was treated with a suspension of 2.2 g KF, 11 g 18-crown-6, and 10 g 12-crown-4 in 100 mL dichloromethane, and then again fractionally distilled. A main run of 20 kg HCDS was obtained after 9 h. The content values in ppb for the exemplary trace contaminants before and after purification are shown in the following table.

TABLE-US-00005 HCDS Al B Sb Cu Fe Mg K Na Ti Ca Crude 55 57 0.9 4.5 21 8.1 39 133 342 77 Purified 3.5 2.4 0.1 0.1 1.6 0.8 0.07 0.9 2.8 6.5