AU2013224703B2

AU2013224703B2 - Polysilane processing and use

Info

Publication number: AU2013224703B2
Application number: AU2013224703A
Authority: AU
Inventors: Gudrun Annette Auner; Christian Bauch; Rumen Deltschew; Gerd Lippold
Original assignee: Nagarjuna Fertilizers and Chemicals Ltd
Current assignee: Nagarjuna Fertilizers and Chemicals Ltd
Priority date: 2006-07-20
Filing date: 2013-09-05
Publication date: 2016-06-02
Anticipated expiration: 2027-07-20
Also published as: AU2013224703A1

Abstract

Abstract The invention relates to a method for the final product related manufacture of low-molecular, medium-molecular, and high-molecular halogenated polysilanes, the distillation thereof into selected fractions, the direct deposition of 10 silicon from the gas phase or a liquid phase of polysilane mixtures or polysilanes, the hydrogenation or derivatiza tion of halogenated polysilanes, and the processing into final products in an adequate system. (7805457_1):MRR

Description

FlPolysilane Processing and Use

The invention is directed to a method for the final product-related production of halogenated polysilanes, the distillation, hydrogenation or derivatization thereof and the processing into final products in an adequate system.

As polysilanes in the sense of the inventive method chemical compounds are designated which are characterized by at least one direct linkage Si-Si. Polysilanes can contain linear Sin chains and/or Sin rings as well as chain branchings .

Halogenated polysilanes in the sense of the inventive method are polysilanes the substituents of which largely consist of halogens X = F, Cl, Br, I as well as of hydrogen. Halogenated polysilanes in the sense of the inventive method are poor with respect to hydrogen with a ratio H : X < 1 : 5.

Preparation of the polysilanes

The mixture of halogenated polysilanes which can serve, among others, for the production of silicon is produced in a plasma chemical step from S1X4 and H2. This method is described in the patent application of Prof. Dr. Auner "Ver-fahren zur Herstellung von Silizium aus Halogensilanen" with the number PCT/DE2006/00089. The plasma reaction can be carried out, for instance, through continuous stimulation (continuous wave): A H2/S1X4 vapour mixture is stimulated by means of an electric or electromagnetic alternating field and is converted into the plasma-like condition. Dependent on the reaction conditions liquid, semi-solid or solid mixtures of halogen-ated polysilanes are produced.

According to the present understanding polysilanes with 2 to 6 silicon atoms are designated low-molecular polysilanes, polysilanes with 7 to 14 silicon atoms are designated medium-molecular polysilanes and polysilanes with at least 15 silicon atoms are designated high-molecular polysilanes. The selected groups are different with respect to their possibilities of further processing by distillation, hydrogenation or derivatization.

According to the invention it is especially advantageous to control the reaction conditions in the plasma reactor in such a manner that not only any mixture of halogenated polysilanes is produced but the mixture of polysilanes which is most favourable for the further processing.

The specific halogenated polysilanes provided for further processing can be unambiguously determined especially by means of the molecular masses as well as additional suitable determining methods. One can produce low-molecular, medium-molecular and high-molecular halogenated polysilanes and characterize the same wherein cyclically structured polysilanes are also important with respect to the polymerization to obtain long-chain polysilanes.

It is advantageous to provide the plasma source located in the plasma reactor in several stages and to provide all possible measures for the aimed introduction of energy into a space volume as small as possible with a reaction mixture as homogeneous as possible.

This enables a high flow rate of the reaction mixture with largely homogeneous reaction conditions and thus largely homogeneous reaction products either.

It is decisive for a reaction product which is as homogeneous as possible to form the introduction of energy into the reaction plasma which has to be produced as homogeneously as possible and to provide reaction conditions as homogenous as possible in the plasma. Here it is advantageous to provide not only one plasma stimulation but several plasma stimulations which are passed subsequently by the reaction mixture .

In order to obtain an energy introduction into the space volume filled by the reaction mixture which is as uniform as possible it is advantageous to pulse the plasma source in order to obtain a more uniform stimulation of the reaction mixture.

The same object of a more homogeneous stimulation can be obtained by exposing the reaction mixture to an additional electron flow for achieving a more stable plasma or a better plasma ignition.

Additionally, the reaction mixture can be quenched by electromagnetic coils located at the outside of the reactor so that the reaction plasma is exposed to a compression with subsequent expansion. According to the invention it is also provided that the reaction mixture passes through a resonator chamber tuned to the wave length of the stimulation source .

It is advantageous to additionally expose the plasma to radiation of visible or ultraviolet light in order to be able to selectively stimulate ions or molecules in the reaction mixture .

It is decisive for a continuous operation of the system that the product mixture has a liquid (viscous) consistency so that it can flow out from the reactor in order to avoid occlusions .

The liquid consistency of the produced mixtures of halogen-ated polysilanes is obtained by operating in the reactor with S1X4 excess and H2 content as low as possible and by holding the temperature of the reactor below room temperature .

Accordingly, it is preferably if the mol concentration of hydrogen in the used gas mixture is smaller than the mol concentration of the S1X4.

The characterization of the prepared polysilanes is made with the example of a mixture of chlorinated polysilanes as follows :

The volumetric determination of the chlorine content (chloride according to Mohr) of a sample solved in an aqueous lye results in the empirical formula SiCl2+x for the mixture of polysilanes wherein x varies between 0 and 1 according to the mean chain length so that one can also speak of a polymer dichlorosilylene consisting of rings (x=0) and chains (0<x<l) wherein the chains are terminated with -S1CI3 groups. The structural formula of the rings is:

SinCl2n and that of the chains is: SinCl2n+2. EDX measurements confirm an atom ratio in the product of about Si:Cl = 1:2. 29Si-NMR measurements show that, dependent on the conditions of production, the product can be a complex mixture of different chlorinated polysilanes. Preferably, linear compounds are present as confirmed by the deficiency of signals of tertiary (Cl-Si/SiR.3) 3) and quaternary (Si(SiR.3)4) silicon atoms. 1H-NMR measurements show that the product contains only traces of hydrogen (Si-H linkages).

The obtained mixtures of halogenated polysilanes are designated low-molecular, medium-molecular and high-molecular polysilanes. The mixture of low-molecular polysilanes consists largely of hexachlorodisilane (Si:Cl = 1:3) and octa-chlorotrisilane S13CI8 (Si:Cl = 1:2.67). These two components can be separated by distillation.

Separation of the mixture of polysilanes:

Individual components or fractions can be obtained from the product mixture, for example by distillation. 1. Hexachlorodisilane escapes at first at a temperature of about 144 °C/1013 hPa wherein it can be already separated in the mixture in a vapour-like condition during the polysilane synthesis and can be condensed (for instance 0 °C) . 2. The next fraction is formed by the lower chlorinated oligosilanes, as for instance the octachloro-trisilane, the decachlorotrisilane and the deca-chloroisotetrasilane. 3. The polysilanes the decomposition temperatures of which are below the boiling points at normal pressure remain as residue.

Other separation methods, as vacuum distillation, sublimation, chromatography, selective crystallisation, selective solving and centrifugation, are also suitable for separating the polysilanes of different molar weights from one another .

Hydrogenation of the polysilanes:

By the hydrogenation of the halogenated polysilanes partly hydrogenated and perhydrogenated compounds can be obtained, i.e. the halogen atoms are partly or completely replaced by hydrogen atoms. The hydrogenation can be carried out in inert solvents, as ethers, toluene etc., wherein as hydrogenation agent preferably metal hydrides and metalloid hydrides are suited. Sodium aluminum hydride and several boron hydrides, as for instance sodium boron hydride, are to be especially mentioned in this connection. During the hydrogenation one should operate at temperatures (RT or lower) as low as possible in order to suppress a decomposition of the formed polysilanes. Preferably, only the desired fractions are hydrogenated so that a product/product mixture as uniform as possible is obtained.

Potential uses of the prepared polysilanes: 1. The complete pyrolysis of the product mixture or of individual components (halogenated polysilanes) results in the formation of silicon which, for instance, can be used for photovoltaic or microelectronic purposes if correspondingly pure starting compounds are used for the production of the polysilane . 2. After the distillative separation of the product mixture the components with high vapour pressure can be used for the separation of silicon layers (for instance a-Si, monocrystalline or polycrystalline silicon) from the gaseous phase on heated substrates wherein a heat treatment can be carried out inductively or by infrared radiation depending on the carrier material. 3. For this, for instance, the hexachlorodisilane and the lower oligosilanes are suited wherein silicon layers can be already deposited from temperatures of 400-500 °C not only in the presence of H2 but also without H2. For this, the substances are passed in a vapour-like condition, also in a mixture with a carrier gas (for instance H2) , over the heated substrate. 4. The components with low vapour pressure can be also used for the layer deposition of silicon from the product mixture or after separation of the fractions with higher vapour pressure if they are applied to a heatable substrate in substance or as solution and are pyrolyzed. 5. The deposition of silicon on the surfaces of substrates or the heat aftertreatment of a silicon layer produced on a substrate can be used for the formation of a compound with the substrate. So, for instance, the surface of metal substrates can be modified by the production of a metal silicide layer in order to obtain an increased abrasion resistance, a higher hardness or another surface treatment. 6. By the hydrogenation of the product mixture or of individual components completely or partly hydrogenated polysilanes can be obtained which are especially suited for the deposition of silicon layers or substrates at low temperature, for instance (SiH2)n -> n Si + n H2. Hereby, the volatile hydrogenated oligosilanes can be used for depositions from the gaseous phase. Then the less volatile hydrogenated polysilanes can be applied onto a carrier in an undiluted manner or as solution in inert solvents (for instance toluene) and can be decomposed by suitable measures (for instance heating, ultraviolet light etc.) so that a silicon layer is formed. 7. By the derivatization of the product mixture or of individual components organopolysilanes can be obtained, as for instance partly methylated or per-methylated compounds of the general formula SinXaMeb (a + b = 2n) and SinXcMed (c + d = 2n +2) . Then the organopolysilanes can be introduced into polymers, for instance by suitable coupling reactions (for instance Wurtz-couplings) or can be grafted onto existing polymers in order to use the special optical or electronical characteristics of the polysilane chain. In the inorganic synthetic chemistry different methods for the chemical conversion of differently substituted polysilanes by chain splitting or ring opening as well as the partial replacement of substituents by, for instance, halogens are known. These methods can be applied to the primary polysilane mixture, to individual fractions after a separation, to separated pure compounds or to daughter products of the partly or complete substitution of the halogen atoms in the corresponding polysilanes. So, for instance, completely organo-substituted cyclic silanes can be converted by ring opening into chains which have halogen substituents only at the ends or at completely organosubstituted cyclosilanes only one or two substituents can be replaced by halogens under adapted conditions so that the ring system is maintained. A direct use of suitably derivatisized polysilanes, for instance in the form of thin layers on suitable substrates, is possible. The manufacture of LED's is a possible use of the organopolysilanes. 8. Polysilanes having individual or several hydrogen substituents can be added to C-C multiple bonds by hydrosilylation so that, dependent on the reaction partners and the reaction conditions, hydrogen can be replaced by organosubstituents or copolymers with organic compounds as well as polysilane side chains at organic polymers can be produced. 9. Suitable C-substituted polysilanes produce silicon carbide if they are used as precursors and suitable nitrogen-substituted polysilanes produce silicon nitride when used as precursors. In this manner layers of silicon carbide or silicon nitride are accessible after an adapted processing of the precursors . 10. After separation (for instance distillatively) the halogenated polysilanes can be also used as fine chemicals for syntheses. So, for instance, hexa-chlorodisilane which, dependent on the plasma processing, is a main component of the product mixture can be used for deoxygenation reactions in the synthetic chemistry.

The inventive method for the use of polysilanes is shown in 5 drawings .

Drawing 1 shows the complete method scheme for processing.

Drawing 2 shows the use of the method scheme for the deposition of bulk silicon from halogenated polysilanes of small molar weight, as for instance hexachlorodisilane.

Drawing 3 shows the use of the method scheme for the hydrogenation and the deposition of thin layer silicon from hydrogenated polysilanes of small molar weight, as for instance disilane.

Drawing 4 shows the use of the method scheme for the partial methylation of halogenated polysilanes of medium molar weight, as for instance decachlorotetrasilane, and the further processing of these organochloropolysilanes by the Wurtz-coupling of these organopolysilanes to long-chain polymers when the low-molecular and high-molecular halogenated polysilanes are reconducted from the distillation into the store tank for low-molecular/high-molecular polysilanes and the high-molecular distillation residue is directed to the direct separation of silicon.

Drawing 5 shows the use of the method for the separation of high-molecular halogenated polysilanes, their methylation and subsequent processing to obtain organopolysilanes when the low-molecular and medium-molecular distillates are reconducted into the respective store tanks.

List of reference numbers 1. Plasma reactor

2. electromagnetic radio frequency generator I

3. electromagnetic radio frequency generator II

4. electromagnetic radio frequency generator III 5. removal of predominantly low-molecular halogenated polysilanes 6. removal of predominantly medium-molecular halogenated polysilanes 7. removal of predominantly high-molecular halogenated polysilanes 8. distillation of predominantly low-molecular halogenated polysilanes 9. distillation of predominantly medium-molecular halogenated polysilanes 10. distillation of predominantly high-molecular halogenated polysilanes 11. removal of undistilled low-molecular halogenated polysilanes 12. removal of distillation residues 13. removal of distillation residues 14. removal of distillation residues 15. removal of low-molecular distillates 16. removal of undistilled medium-molecular halogenated polysilanes 17. removal of distillation residues 18. removal of distillation residues 19. removal of distillation residues 20. removal of distillation residues 21. removal of distillation residues 22. removal of medium-molecular distillates 23. removal of undistilled high-molecular halogenated polysilanes 24. removal of distillation residues 25. removal of distillation residues 26. removal of distillation residues 27. removal of distillation residues 28. removal of distillation residues 29. removal of high-molecular distillates 30. store tank of low-molecular halogenated polysilanes 31. store tank of medium-molecular halogenated polysilanes 32. store tank of high-molecular halogenated polysilanes 33. store tank of predominantly low-molecular halogenated polysilane mixtures 34. deposition device for silicon from low-molecular polysilane mixtures 35. deposition device for silicon layers from gaseous low-molecular hydrogenated polysilanes 36. hydrogenation reactor 37. store tank of liquid low-molecular hydrogenated polysilanes 38. methylation reactor 39. store tank of low-molecular organopolysilanes 40. store tank of predominantly medium-molecular halogenated polysilane mixtures 41. deposition device for silicon from medium-molecular polysilane mixtures 42. hydrogenation reactor 43. deposition device for silicon layers from gaseous medium-molecular hydrogenated polysilanes 44. store tank of medium-molecular organopolysilanes 45. methylation reactor 46. deposition device for silicon from high-molecular polysilane mixtures 47. store tank of predominantly high-molecular halogen-ated polysilane mixtures 48. deposition device for silicon layers from gaseous high-molecular hydrogenated polysilanes 49. hydrogenation reactor 50. store tank of liquid high-molecular hydrogenated polysilanes 51. store tank of gaseous high-molecular organopolysilanes 52. methylation reactor 53. store tank of liquid high-molecular organopolysilanes

Claims

CLAIMS:

1. Method for the production and subsequent processing of a mixture of halogenated poly silanes for the generation of silicon or silicon-based products, wherein the mixture of halogenated polysilanes is produced plasma-chemically in a plasma reactor which comprises more than one plasma source from the reaction between S1X4 and H2, wherein X is selected from the group consisting of F, Cl, Br, I, and H, and wherein the more than one plasma sources to be used in the plasma reactor are pulsed and/or a plasma in the plasma reactor is periodically quenched by an additional electromagnetic field or lead through a resonator chamber which is tuned to a microwave source, wherein the produced halogenated polysilanes have a ratio of H:X <1:5 and are predominantly low, medium or high molecular weight, depending upon the number of plasma sources used, and wherein said predominantly low, medium or high molecular weight halogenated polysilane mixtures are separated by distillation or other separation methods for further processing.
2. The method according to claim 1, wherein the plasma in the plasma reactor is periodically quenched by an additional electromagnetic alternating field or passes a resonator chamber tuned to the microwave source.
3. The method according to claim 1 or claim 2, wherein plasma pulsing and/or additional electrical discharge and/or plasma quenching alternate in the plasma reactor.
4. The method according to any one of claims 1 to 3, wherein the plasma in the plasma reactor is additionally radiated with infrared light, visible light or ultraviolet light.
5. The method according to any one of claims 1 to 4, wherein the predominantly high-molecular weight halogenated polysilane mixtures are further exposed to the separation method of size-selective chromatography to obtain poly silane fractions with high and medium molecular weights.
6. The method according to any one of claims 1 to 5, wherein a separation fraction with predominantly low or medium molecular weights is led to direct further processing or into another distillation column.
7. The method according to any one of claims 1 to 6, wherein the halogenated polysilane mixtures with low, medium or high molecular weights obtained after the distillation or other separation methods are hydrogenated and partly hydrogenated or perhydrogenated compounds are obtained.
8. The method according to any one of claims 1 to 6, wherein the halogenated polysilane mixtures with low, medium or high molecular weights obtained after the distillation or other separation methods are methylated and partly methylated or permethylated organopolysilanes of the formula SinXaMeb (a+b=2n) and SinXcMed (c+d=2n+2).
9. The method according to any one of claims 1 to 6, wherein a mixture of low-molecular weight halogenated polysilanes is directed over a heated surface directly from the gaseous phase for deposition of silicon and is pyrolytically decomposed there.
10. The method according to any one of claims 1 to 6, wherein a liquid halogenated polysilane mixture or its solution is applied in a suitable solvent onto a deposition surface and is decomposed there by pyrolysis wherein silicon is deposited there.
11. The method according to claim 7, wherein a hydrogenated polysilane with a high purity of a selected molecular weight is directed over a heated surface in the gaseous phase and silicon is deposited on this surface by pyrolysis.
12. The method according to claim 7, wherein a hydrogenated polysilane of a selected molecular weight is applied onto a suitable surface in the liquid phase or in solution and is decomposed by heating whereby silicon is deposited on this surface.
13. The method according to any one of claims 9 to 12, wherein silicon is deposited as a layer of any thickness from mixtures of halogenated polysilanes above 400 °C or hydrogenated poly silanes above 200 °C.
14. The method according to any one of claims 9 to 13, wherein the deposited silicon layers are exposed to a heat aftertreatment. Spawnt Private S.a.r.l. Patent Attorneys for the Applicant/Nominated Person SPRUSON & FERGUSON