Halogenated polysilane and plasma-chemical process for producing the same

Abstract

The present invention relates to a halogenated polysilane as a pure compound or a mixture of compounds each having at least one direct SiSi bond, whose substituents consist exclusively of halogen or of halogen and hydrogen and in the composition of which the atomic ratio of substituent to silicon is at least 1:1.

Claims

1. A composition comprising a halogenated polysilane having at least one direct SiSi bond, whose substituents consist of halogen or of halogen and hydrogen and in the composition of which the atomic ratio of substituent to silicon is at least 1:1, wherein a) the halogen is chlorine, b) the hydrogen content of the polysilane is less than 2 atom-%, c) the polysilane contains less than 2 mass % short-chain branched chains and rings for which n=2-6, where n is the number of Si atoms bound to each other directly, and the content of branching points of the short-chain fraction relative to the total composition is less than 1 mass %, d) the polysilane has a Raman molecular vibrational spectrum of I.sub.100/I.sub.132>1, where I.sub.100 denotes the Raman intensity at 100 cm.sup.1 and I.sub.132 denotes the Raman intensity at 132 cm.sup.1, and e) the .sup.29Si-NMR spectra of the composition has its significant product signals in the range of chemical shift from +15 ppm to 7 ppm.

2. The composition according to claim 1, wherein the average size of the backbone chain of the halogenated polysilane is [n=]8-20.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows the H-NMR spectrum of the chlorinated polysilane made by Example 1.

(2) FIG. 2 shows the .sup.29Si NMR spectrum of the chlorinated polysilane made by Example 1.

(3) FIG. 3 shows the Raman molecular vibrational spectrum of the chlorinated polysilane made by Example 1.

(4) FIG. 4 shows the H-NMR spectrum of the chlorinated polysilane made by Example 2.

(5) FIG. 5 shows the .sup.29Si NMR spectrum of the chlorinated polysilane made by Example 2.

(6) FIG. 6 shows the H-NMR spectrum of the chlorinated polysilane made by Example 3.

(7) FIG. 7 shows the .sup.29Si NMR spectrum of the chlorinated polysilane made by Example 3.

(8) FIG. 8 shows the H-NMR spectrum of the brominated polysilane made by Example 4.

(9) FIG. 9 shows the .sup.29S NMR spectrum of the brominated polysilane made by Example 4.

(10) FIG. 10 shows the Raman molecular vibrational spectrum of the brominated polysilane made by Example 4.

(11) FIG. 11 shows the H-NMR spectrum of the fluorinated polysilane made by Example 5.

DETAILED DESCRIPTION OF THE INVENTION

Example 1

(12) A mixture of 500 sccm H.sub.2 and 500 sccm SiCl.sub.4 (1:1) is fed into a reactor made of quartz glass, the process pressure being kept constant in the range 1.6-1.8 hPa. Transition of the gas mixture to the plasma state is then effected by a high-frequency discharge, and the chlorinated polysilane that forms is deposited on the cooled (20 C.) quartz glass walls of the reactor. The power input is 400 W. After 2 hours the yellow to orange-yellow product is removed from the reactor by dissolving in a little SiCl.sub.4. After removal of the SiCl.sub.4 under vacuum, 91.1 g polysilane is left behind in the form of an orange-yellow viscous mass.

(13) The average molecular weight is determined by cryoscopy as approx. 1700 g/mol, which for the chlorinated polysilane (SiCl.sub.2).sub.n or Si.sub.nCl.sub.2n+2 corresponds to an average chain length of approx. n=17 for (SiCl.sub.2).sub.n or approx. n=16 for Si.sub.nCl.sub.2n+2.

(14) The ratio of Si to Cl in the product mixture is determined after decomposition by chloride titration according to Mohr as Si:Cl=1:2 (which corresponds to the empirical (analytical) formula SiCl.sub.2).

(15) The hydrogen content is 0.0005 mass-% and accordingly well below 1 mass-% (as well as below 1 atom-%), as can be seen from the following .sup.1H-NMR spectrum (FIG. 1). For this, the integrals of the solvent are compared at =7.15 ppm and of the product at =4.66 ppm. The content of the solvent C.sub.6D.sub.6 is approx. 25 mass-% and its degree of deuteration is 99%.

(16) Typical .sup.29Si-NMR shifts at approx. 3.7 ppm, 0.4 ppm, 4.1 ppm and 6.5 ppm can be seen from the following spectrum (FIG. 2). These signals are within the range of shifts for (1) and (2), which is typical of signals of SiCl.sub.3 end groups (primary Si atoms), and (2), which is typical of signals of SiCl.sub.2 groups (secondary Si atoms), such as they are present for example as connecting links in the region of linear chains.

(17) The low content of short-chain branched compounds, e.g. decachloroisotetrasilane (among others =32 ppm), dodecachloroneopentasilane (among others =80 ppm) can also be seen from the next .sup.29Si-NMR spectrum (FIG. 2). By integration of the .sup.29Si-NMR spectra it can be seen that the content of silicon atoms, which form the branching points of the short-chain fraction, relative to the total product mixture is 0.6 mass-% and so is less than 1 mass-%.

(18) Low-molecular cyclosilanes cannot be detected in the mixtures. In the .sup.29Si-NMR spectra these would show sharp signals at =5.8 ppm (Si.sub.4Cl.sub.8), =1.7 ppm (Si.sub.5Cl.sub.10), =2.5 ppm (Si.sub.8Cl.sub.12), but these are not found.

(19) A typical Raman molecular vibrational spectrum of the chlorinated polysilane is shown below (FIG. 3). The spectrum has an I.sub.100/I.sub.132 ratio greater than 1, i.e. the Raman intensity at 100 cm.sup.1 (I.sub.100) is markedly higher than that at 132 cm.sup.1 (I.sub.132). The spectrum of a thermally produced perchloropolysilane mixture and the calculated spectrum of octachlorocyclotetrasilane (Si.sub.4Cl.sub.8) are given for comparison, and in each case the ratio reverses to I.sub.100/I.sub.132 less than 1.

(20) This diagram also shows, as an example, a section of a theoretical curve. For this, the quantum-chemically calculated modes [Hohenberg P, Kohn W. 1964. Phys. Rev. B 136:864-71; Kohn W, Sham L J. 1965. Phys. Rev. A 140:1133-38, W. Koch and M. C. Holthausen, A Chemist's Guide to Density Functional Theory, Wiley, Weinheim, 2nd edn., 2000] are adjusted with a Multi-Lorentz peak function, which roughly simulates the experimental spectral resolution. With respect to the absolute intensity, the theoretical curve was normalized, so that it fits well in the diagram for viewing. The relative intensities of the peaks in the theory originate directly from the calculation from first principles calculation. This should show that certain intensities are typical of cyclic polysilanes. The data of the Raman spectrum point to a lower content of cyclic polysilanes in the plasma-chemically produced polysilane mixture, which is consistent with the NMR data (see above).

Example 2

(21) A mixture of 300 sccm H.sub.2 and 600 sccm SiCl.sub.4 (1:2) is fed into a reactor made of quartz glass, the process pressure being kept constant in the range 1.5-1.6 hPa. Transition of the gas mixture to the plasma state is then effected by a high-frequency discharge, and the chlorinated polysilane that forms is deposited on the cooled (20 C.) quartz glass walls of the reactor. The power input is 400 W. After 4 hours the orange-yellow product is removed from the reactor by dissolving in a little SiCl.sub.4. After removal of the SiCl.sub.4 under vacuum, 187.7 g of chlorinated polysilane is left behind in the form of an orange-yellow viscous mass.

(22) The average molecular weight is determined by cryoscopy and is approx. 1400 g/mol, which for the chlorinated polysilane (SiCl.sub.2).sub.n or Si.sub.nCl.sub.2n+2 corresponds to an average chain length of approx. n=14 for (SiCl.sub.2).sub.n or approx. n=13 for Si.sub.nCl.sub.2n+2.

(23) The ratio of Si to Cl in the product mixture is determined after decomposition by chloride titration according to Mohr as Si:Cl=1:1.8 (which corresponds to the empirical (analytical) formula SiCl.sub.1.8).

(24) The hydrogen content is well below 1 mass-% (0.0008%) (also below 1 atom-%), as can be seen from the following .sup.1H-NMR spectrum (FIG. 4). For this, the integrals of the solvent are compared at =7.15 ppm and of the product at =3.75 ppm.

(25) The content of the solvent C.sub.6D.sub.6 is approx. 27 mass-% and its degree of deuteration is 99%.

(26) Typical .sup.29Si-NMR shifts at approx. 10.9 ppm, 3.3 ppm, 1.3 ppm and 4.8 ppm can be seen from the following spectrum (FIG. 5). These signals are within the range of shifts at (1) and (2), which is typical of signals of SiCl.sub.3 end groups (primary Si atoms), and (2), which is typical of signals of SiCl.sub.2 groups (secondary Si atoms), such as they are present for example as connecting links in the region of linear chains.

(27) The low content of short-chain branched compounds, e.g. decachloroisotetrasilane (among others =32 ppm), dodecachloroneopentasilane (among others =80 ppm) (these signals are within the range of shifts at (3), which is typical of signals of SiCl groups (tertiary Si atoms), and (4), which is typical of signals of Si groups with exclusively Si substituents (quaternary Si atoms)), can be seen from the following spectrum (FIG. 5). By integration of the .sup.29Si-NMR spectra it can be seen that the content of silicon atoms, which form said branching points (SiCl groups (tertiary Si atoms) and Si groups with exclusively Si substituents (quaternary Si atoms)) of the short-chain fraction, relative to the total product mixture is 0.3 mass-% and so is less than 1 mass-%.

(28) Low-molecular cyclosilanes could not be detected in the mixtures. These ought to show sharp signals at =5.8 ppm (Si.sub.4Cl.sub.8), =1.7 ppm (Si.sub.6Cl.sub.10), =2.5 ppm (Si.sub.6Cl.sub.12) in the .sup.29Si-NMR spectra, but cannot be identified with certainty in the spectrum, as the spectrum has a large number of signals in this region.

(29) The peak at approx. 20 ppm originates from the solvent SiCl.sub.4.

Example 3

(30) A mixture of 200 sccm H.sub.2 and 600 sccm SiCl.sub.4 vapor (1:3) is fed into a reactor made of quartz glass, the process pressure being kept constant in the range 1.50-1.55 hPa. Transition of the gas mixture to the plasma state is then effected by a high-frequency discharge, and the chlorinated polysilane that forms is deposited on the cooled (20 C.) quartz glass walls of the reactor. The power input is 400 W. After 2 h 9 min the orange-yellow product is removed from the reactor by dissolving in a little SiCl.sub.4. After removal of the SiCl.sub.4 under vacuum, 86.5 g of chlorinated polysilane is left behind in the form of an orange-yellow viscous mass.

(31) The average molecular weight is determined by cryoscopy and is approx. 1300 g/mol, which for the chlorinated polysilane (SiCl.sub.2).sub.n or Si.sub.nCl.sub.2n+2 corresponds to an average chain length of approx. n=13 for (SiCl.sub.2).sub.n or approx. n=12 for Si.sub.nCl.sub.2n+2.

(32) The ratio of Si to Cl in the product mixture is determined after decomposition by chloride titration according to Mohr as Si:Cl=1:1.7 (which corresponds to the empirical (analytical) formula SiCl.sub.1.7).

(33) The hydrogen content is well below 1 mass-% (0.0006%) (also below 1 atom-%), as can be seen from the following .sup.1H-NMR spectrum (FIG. 6). For this, the integrals of the solvent are compared at =7.15 ppm and of the product at =3.74 ppm. The content of the solvent C.sub.6D.sub.6 is approx. 30 mass-% and its degree of deuteration is 99%.

(34) The typical .sup.29Si-NMR shifts at approx. 10.3 ppm, 3.3 ppm, 1.3 ppm and 4.8 ppm and the low content of short-chain branched compounds, e.g. decachloroisotetrasilane (among others =32 ppm), dodecachloroneopentasilane (among others =80 ppm) (these signals are within the range of shifts at (3), which is typical of signals of SiCl groups (tertiary Si atoms), and (4), which is typical of signals of Si groups with exclusively Si substituents (quaternary Si atoms)), can be seen from the following spectrum (FIG. 7).

(35) The low content of short-chain branched compounds, e.g. decachloroisotetrasilane (among others =32 ppm), dodecachloroneopentasilane (among others =80 ppm) (these signals are within the range of shifts at (3), which is typical of signals of SiCl groups (tertiary Si atoms), and (4), which is typical of signals of Si groups with exclusively Si substituents (quaternary Si atoms)), can be seen from the following spectrum (FIG. 7). By integration of the .sup.29Si-NMR spectra it can be seen that the content of silicon atoms, which form the stated branching points (SiCl groups (tertiary Si atoms) and Si groups with exclusively Si substituents (quaternary Si atoms)) of the short-chain fraction, relative to the total product mixture is 0.6 mass-% and so is less than 1 mass-%.

(36) Low-molecular cyclosilanes cannot be detected in the mixtures. These ought to show sharp signals at =5.8 ppm (Si.sub.4Cl.sub.8), =1.7 ppm (Si.sub.5Cl.sub.10), =2.5 ppm (Si.sub.6Cl.sub.12) in the .sup.29Si-NMR spectra, but cannot be identified with certainty in the spectrum, as the spectrum has a large number of signals in this region.

(37) The peak at approx. 20 ppm originates from the solvent SiCl.sub.4.

Example 4

(38) A mixture of 300 sccm H.sub.2 and 240 sccm SiBr.sub.4 vapor is fed into a reactor made of quartz glass, the process pressure being kept constant in the region of 0.8 hPa. Transition of the gas mixture to the plasma state is then effected by a high-frequency discharge, and the brominated polysilane that forms is deposited on the cooled (20 C.) quartz glass walls of the reactor. The power input is 140 W. After 2 hours the colorless product is removed from the reactor by dissolving in benzene. After removal of the benzene under vacuum, 55.2 g of brominated polysilane remains in the form of a white mush of crystals.

(39) The average molecular weight is determined by cryoscopy and is approx. 1680 g/mol, which for the brominated polysilane (SiBr.sub.2).sub.n or Si.sub.nBr.sub.2n+2 corresponds to an average chain length of approx. n=9 for (SiBr.sub.2).sub.n or approx. n=8 for Si.sub.nBr.sub.2n+2.

(40) The ratio of Si to Br in the product mixture is determined after decomposition by bromide titration according to Mohr as Si:Br=1:2.3 (which corresponds to the empirical (analytical) formula SiBr.sub.2.3).

(41) The hydrogen content is well below 1 mass-% (0.01%) (also below 1 atom-%), as can be seen from the following .sup.1H-NMR spectrum (FIG. 8). For this, the integrals of the solvent are compared at =7.15 ppm and of the product at =3.9 ppm. The content of the solvent C.sub.6D.sub.6 is approx. 30 mass-% and its degree of deuteration is 99%.

(42) The typical .sup.29Si-NMR shifts (FIG. 9) appear in the range from 15 ppm to 40 ppm, from 49 ppm to 51 ppm and from 72 ppm to 91 ppm.

(43) The peak at approx. 90 ppm originates from the educt SiBr.sub.4.

(44) A typical Raman molecular vibrational spectrum of the brominated polysilane is shown below (FIG. 10). The spectrum has typical Raman intensities at approx. 110 cm.sup.1 to 130 cm.sup.1, at 170 cm.sup.1 to 230 cm.sup.1, at 450 cm.sup.1 to 550 cm.sup.1 and at 940 cm.sup.1 to 1000 cm.sup.1.

Example 5

(45) A mixture of 100 sccm H.sub.2 and 50 sccm SiF.sub.4 gas is fed into a plasma reactor, the process pressure being kept constant in the region of 1.2 hPa. Transition of the gas mixture to the plasma state is then effected by a high-frequency discharge, and the fluorinated polysilane that forms is deposited on the cooled (20 C.) walls of the reactor. The power input is 100 W. After 2 h the colorless to yellowish-beige-white product is removed from the reactor by dissolving in cyclohexane. After removal of the solvent under vacuum, 0.8 g of fluorinated polysilane remains in the form of a white to yellowish-beige solid.

(46) The average molecular weight is determined by cryoscopy and is approx. 2500 g/mol, which for the fluorinated polysilane (SiF.sub.2).sub.n (M=66.08) or Si.sub.nF.sub.2n+2 corresponds to an average chain length of approx. n=38 for (SiF.sub.2).sub.n or approx. n=37 for Si.sub.nF.sub.2n+2.

(47) The hydrogen content is well below 1 mass-% (also under atom-%), as can be seen from the following .sup.1H-NMR spectrum (FIG. 11).

(48) The typical .sup.29Si-NMR shifts of the fluorinated polysilane appear in the range from 4 ppm to 25 ppm and/or from 50 ppm to 80 ppm.

(49) A Raman molecular vibrational spectrum of the fluorinated polysilane has typical Raman intensities at approx. 183 cm.sup.1 to 221 cm.sup.1, at approx. 497 cm.sup.1 to 542 cm.sup.1 and at approx. 900 cm.sup.1 to 920 cm.sup.1.

Example 6

(50) A mixture of 60 sccm H.sub.2 and 60 sccm SiI.sub.4 vapor is fed into a reactor made of quartz glass, the process pressure being kept constant in the region of 0.6 hPa. Transition of the gas mixture to the plasma state is then effected by a high-frequency discharge, and the iodated polysilane that forms is deposited on the cooled (20 C.) quartz glass walls of the reactor. The power input is 100 W. After 2 h the reddish-yellow product is removed from the reactor by dissolving in cyclohexane. After removal of the cyclohexane under vacuum, 8 g of iodated polysilane remains in the form of a reddish-yellow to brownish solid.

(51) The average molecular weight is determined by cryoscopy and is approx. 2450 g/mol, which for the iodated polysilane (SiI.sub.2), or Si.sub.nI.sub.2n+2 corresponds to an average chain length of approx. n=9 for (SiI.sub.2).sub.n or approx. n=8 for Si.sub.nI.sub.2n+2.

(52) The ratio of Si to I in the product mixture is determined as Si:I=1:2.3 (which corresponds to the empirical (analytical) formula SiI.sub.2.3).

(53) The hydrogen content is well below 1 mass-% (also under <1 atom-%).

(54) The typical .sup.29Si-NMR shifts of the iodated polysilane appear in the range from 28 ppm to 52 ppm, from 70 ppm to 95 ppm and/or from 138 ppm to 170 ppm.

(55) A typical Raman molecular vibrational spectrum of the iodated polysilane has typical Raman intensities at approx. 98 cm.sup.1 to 116 cm.sup.1, at 132 cm.sup.1 to 138 cm.sup.1, at 325 cm.sup.1 to 350 cm.sup.1 and at 490 cm.sup.1 to 510 cm.sup.1.