METHOD FOR PRODUCING CHLORINATED OLIGOSILANES

Abstract

The present invention relates to a process for preparing chlorinated oligosilanes, wherein chlorinated polysilane having an empirical formula of SiCl.sub.1.0-2.8 and/or a mixture comprising the chlorinated polysilane is reacted with elemental chlorine or a chlorine-containing mixture. Additionally claimed are chlorinated oligosilanes prepared by the process and the use thereof for production of semiconductors and/or hard coatings.

Claims

1. A process for preparing chlorinated oligosilanes comprising reacting chlorinated polysilane having an empirical formula of SiCl.sub.1.0-2.8 and/or a mixture comprising the chlorinated polysilane with elemental chlorine or a chlorine-containing mixture.

2. The process as claimed in claim 1, wherein the chlorinated polysilane having an empirical formula of SiCl.sub.1.0-2.8 is chlorinated polysilane having an empirical formula of SiCl.sub.1.6-2.2.

3. The process of claim 1, wherein the chlorinated polysilane has a mean chain length of n=4 to n=50.

4. The process of claim 1, wherein the reacting is conducted at a temperature of 20° C. to 300° C.

5. The process of claim 4, wherein the reacting is conducted in at least two steps in at least two different temperature ranges.

6. The process of claim 5, wherein the first temperature range is 100° C. to 140° C. and the second temperature range is 145° C. to 175° C.

7. The process as of claim 1, wherein the reacting is conducted within a pressure range from 100 hPa to 2000 hPa.

8. The process of claim 1, wherein the reacting takes place in solution with a diluent which is selected from the group consisting of Si.sub.2Cl.sub.6, Si.sub.3Cl.sub.8, Si.sub.4Cl.sub.10, Si.sub.5Cl.sub.12, and mixtures thereof.

9. The process of claim 1, wherein SiCl.sub.4 is distilled off during the chlorination reaction.

10. The process of claim 9, wherein at least one additional chlorinated oligosilane is distilled off.

11. The process of claim 1, wherein the reacting is effected with full or partial reflux of SiCl.sub.4 or a mixture of SiCl.sub.4 and at least one additional chlorinated oligosilane.

12. The process of claim 1, wherein the reacting is conducted continuously in a column.

13. The process of claim 1, being conducted batchwise.

14. Chlorinated oligosilanes obtainable by the process of claim 1.

15. A process for production of semiconductors and/or hard coatings comprising incorporating chlorinated oligosilanes of claim 1.

Description

WORKING EXAMPLES

Example 1

[0029] 3052.7 g of chlorinated polysilane produced by plasma chemistry are diluted with 1388.7 g of Si.sub.2Cl.sub.6 and introduced into an apparatus equipped with stirrer, reflux condenser and gas inlet tube. The reflux condenser is kept at 60° C. Chlorosilanes that exit from the reaction vessel are condensed in a cold trap at 0° C. The temperature of the reaction mixture is kept between 110° C. and 120° C., and 950 g of chlorine gas are introduced into the reaction mixture with vigorous stirring within 25.5 h. The pressure in the apparatus is kept within the range between 1013 hPa and 1213 hPa. Fractionation of the reaction product gives 760.1 g of SiCl.sub.4, 3354.9 g of Si.sub.2Cl.sub.6 and 861.8 g of Si.sub.3Cl.sub.8. According to .sup.29Si NMR spectroscopy, the 401.7 g of fractionation residue contain, as well as residues of Si.sub.3Cl.sub.8, the compounds i-tetrasilane, neopentasilane and neohexasilane in their perchlorinated form.

Example 2

[0030] To 505.7 g of Si.sub.3Cl.sub.8 are added 100.1 g of a solid having the empirical composition SiCl.sub.0.7 in an apparatus equipped with stirrer and gas inlet tube. The mixture is contacted with about 200 g of chlorine gas while stirring within 30 h. During the addition of chlorine, the temperature of the liquid rises as a result of the exothermic reaction from initially 23° C. to a maximum of 125° C. This maximum temperature is maintained by monitoring the rate of chlorine addition. As soon as the reaction rate decreases, as indicated by reduced chlorine absorption and decreasing temperature, the reaction is continued with external heating to 120° C. Fractionation of the reaction mixture gives 202.4 g of SiCl.sub.4, 362.5 g of Si.sub.2Cl.sub.6 and 181.7 g of Si.sub.3Cl.sub.8. The distillation residue weighs 42.6 g.

Example 3

[0031] 5.710 kg of chlorinated polysilane produced by plasma chemistry and 5.327 kg of fractionation residue from prior chlorination batches, diluted with 19.215 kg of Si.sub.3Cl.sub.8, are introduced into an apparatus equipped with reflux condenser, stirrer and gas inlet tube. The reflux condenser is kept at 150° C. The reaction mixture is heated to 165° C. and, within 36 h, 6.7 kg of chlorine gas are introduced into the liquid with vigorous stirring. The pressure in the apparatus is kept between 1013 hPa and 1113 hPa. During the reaction period, 17.82 kg of a chlorosilane mixture containing mainly SiCl.sub.4 and Si.sub.2Cl.sub.6 and also a small amount of Si.sub.3Cl.sub.8 leave the apparatus via the reflux condenser and are condensed in a second condenser at 12° C. The oligosilanes are concentrated by distilling of the majority of SiCl.sub.4, and the distillation residue is combined with the contents of the chlorination reactor. After fractionation of this liquid, 12.660 kg of Si.sub.2Cl.sub.6 and 3.370 kg of Si.sub.3Cl.sub.8 are isolated, as well as 1.629 kg of mixed fractions. The 5.745 kg of fractionation residue contain, by .sup.29Si NMR spectroscopy, as well as residues of Si.sub.3Cl.sub.8, the compounds i-tetrasilane, neopentasilane and neohexasilane in their perchlorinated form.

Example 4

[0032] 26.27 kg of chlorinated polysilanes produced by plasma chemistry, diluted with 18.20 kg of fractionation residues from prior chlorination batches and 2.50 kg of Si.sub.2Cl.sub.6, are introduced into an apparatus equipped with stirrer, reflux condenser and gas inlet tube. The reflux condenser is kept at 60° C. The temperature of the reaction mixture is at first kept at 120° C., and it is later heated with declining chlorine absorption to 140° and finally to 155° C. 9.5 kg of chlorine gas are introduced with vigorous stirring within 50 h. The pressure within the apparatus is kept between 1013 hPa and 1250 hPa. Within the reaction period, 14.3 kg of chlorinated SiCl.sub.4 are distilled off about every 2 h by pressure reduction and condensed in a second condenser at 12° C. Fractionation of the reactor contents gives 1.12 kg of SiCl.sub.4/Si.sub.2Cl.sub.6 mixture, 20.39 kg of pure Si.sub.2Cl.sub.6 and 0.30 kg of Si.sub.2Cl.sub.6/Si.sub.3Cl.sub.8 mixture. 20.20 kg of fractionation residue remain, containing a mixture of Si.sub.3Cl.sub.8 and the perchlorinated i-tetrasilane, neopentasilane and neohexasilane.

Example 5

[0033] 63.88 g of chlorinated polysilanes produced by plasma chemistry are dissolved in 52.65 g of Si.sub.2Cl.sub.6. The solution is transferred into a dropping funnel at the upper end of a vertical column having random packing (diameter 2.4 cm, length 25 cm), filled with 3 mm Raschig rings. The column is heated to a constant temperature of 90° C. The reaction products are collected in a Schlenk flask at the lower end of the column which is cooled to 0° C. A gentle stream of chlorine gas through the column and the collecting flask is maintained during the reaction time. The solution is introduced dropwise into the column within h and the chlorine gas stream is maintained for a further 30 min until the majority of the liquid has passed through the column. A small amount of product remains in the column. Volatile components of the product mixture are drawn off under reduced pressure at 200° C. (63.37 g) and subsequently subjected to a fractional vacuum distillation (distillation temperatures and yields: 50° C.: 46.28 g; 100° C.: 6.45 g; 130° C.: 1.35 g).

Example 6

Comparative Example

[0034] 223.4 g of PCS produced by plasma chemistry are mixed with 65.4 g of Si.sub.3Cl.sub.8. The solution is transferred into the dropping funnel of the apparatus described in example 5. The column is heated to 155° C. Once a gentle chlorine gas stream through the apparatus has been established, the tap of the dropping funnel is opened slightly. When the chlorosilane mixture meets the column packing, the mixture ignites immediately and burns with local glowing and an orange-red flame which penetrates into the column packing. The experiment is stopped.

Example 7

[0035] The apparatus described in example 5 is supplemented with a further unheated and uninsulated column having random packing (diameter 3 cm, length 25 cm, 3 mm Raschig rings) which is inserted between the dropping funnel and heated column.

[0036] 524.9 g of PCS produced by plasma chemistry are mixed with 153.7 g of Si.sub.3Cl.sub.8 and transferred into the dropping funnel of the apparatus. A gentle chlorine gas stream through both columns having random packing and the collecting flask is established and adjusted in accordance with the gas consumption during the reaction. The chlorosilane mixture is introduced into the upper column having random packing within 13.5 h. The upper half of this column heats up gradually to less than 50° C. The viscosity of the mixture is distinctly reduced as it passes through the upper column and the color of the orange/yellow mixture likewise becomes less intense. Material exiting from the upper column does not ignite on contact with the column packing heated to 155° C. On completion of the addition of liquid, a gentle chlorine gas stream is maintained for a further 30 min. Fractional distillation of the 892.3 g of product mixture under reduced pressure gives 185.2 g of a fraction consisting mainly of SiCl.sub.4 and a little Si.sub.2Cl.sub.6, 354.7 g of a fraction consisting mainly of Si.sub.2Cl.sub.6 and a little Si.sub.3Cl.sub.8, and 223.9 g of a fraction consisting mainly of Si.sub.3Cl.sub.8 and a little Si.sub.2Cl.sub.6. This leaves a residue of 118.5 g.