RU2160706C1 - Method of production of monosilane and disilane - Google Patents

Abstract

FIELD: production of polycrystalline silicon and semiconductor structures by gas epitaxy methods. SUBSTANCE: monosilane and disilane are produced due to interaction of magnesium with mineral acid in helium atmosphere. Products thus obtained are subjected to cleaning and separation. Fluosilicic acid is used as mineral acid. Concentration of acid ranges from 5 to 39%. Process is conducted at temperature of from 40 to 57 C. Fluosilicic acid is preliminarily treated with helium during 40 to 60 minutes at temperature of from 15 to 40 C. Silanes are cleaned from dropping liquid in water cooler at temperature of from 10 to 12 C. Cleaning from polysilanes and higher silanes is effected at temperature of from minus 76 to minus 80 C. Cleaning from disiloxanes and fluorides is effected on aluminum fluoride and sodium fluoride. Cleaning on sodium fluoride is effected at room temperature and at temperature of from 140 to 150 C in succession. EFFECT: low cost of process due to use of fluosilicic acid instead of hydrochloric or sulfuric acid; high degree of cleaning; possibility of obtaining pure magnesium fluoride; avoidance of wastes. 6 cl, 1 tbl, 1 ex

Description

 The invention relates to the field of chemical technology, in particular to the production of silanes, and can be used in the production of polycrystalline silicon, as well as semiconductor structures by gas epitaxy methods.

 In silane production technologies, monosilane, disilane and higher silanes, as a rule, accompany each other in various proportions.

Known methods for producing silanes by acid methods (Zhigach A.F., Stasinevich D.S. Chemistry of hydrides. - L .: Chemistry, 1969, p. 548-549). Monosilane and higher silanes (Si ₂ H ₆ , Si ₃ H ₈ , Si ₄ H ₁₀ ) are obtained by reacting magnesium silicide with 10-15% hydrochloric acid in an inert atmosphere at 50-65 ^o C. The total yield of silicon contained in silicide, is 25-30%, of which: 37% - SiH ₄ , 30% Si ₂ H ₆ , 15% Si ₃ H ₈ and 10% Si ₄ H ₁₀ .

The maximum yield of silanes (38%) is achieved if the powdered silicon is alloyed with magnesium at 650 ^o C in an inert or reducing atmosphere. An increase in the yield of silanes up to 50% can be achieved by replacing hydrochloric acid with sulfuric acid, raising the temperature to 100 ^o C.

 In the technology for producing semiconductor silicon, monosilane and disilane are mainly used.

A known method of producing monosilane and disilane, based on the reaction of an alloy containing magnesium and silicon, with aqueous solutions of hydrochloric or sulfuric acids in the temperature range 0-90 ^o C (Japan VZ N 60-141613, N 58-246139 from 28.12. 83, MKI C 01 B 33/04). The synthesis proceeds with obtaining mainly monosilane and disilane.

The closest to the achieved result is a method that clarifies the above (Japan c.z. N 60-166216, ac.z. n 59-021892 from 02.10.84, MKI C 01 B 33/04). Its essence is that the preparation of silicon hydrides resulting from the reaction between an alloy of magnesium and silicon treated with 1-50% hydrochloric or sulfuric acid is carried out at 60-100 ^o C. After the reaction, the liquid phase is heated to boiling point, which leads to to the transition of higher hydrides to monosilane and disilane. Gaseous silanes developed by an inert carrier gas are isolated by fractional creogen condensation in accordance with boiling points. Purification from impurities is carried out by rectification and adsorption methods.

The following methods have the following disadvantages:
- low yields of silane and disilane;
- the use of expensive sulfuric and hydrochloric acids (PSA);
- environmentally complex process of purification of silanes from acid fumes;
- significant technological difficulties in the allocation of magnesium chloride or sulfate from solutions for the subsequent regeneration of metallic magnesium.

A method for producing monosilane and disilane is proposed, including the interaction of magnesium silicide with mineral acid when heated in an inert atmosphere, purification from impurities, separation of products. Silicon fluorosilicic acid with a concentration of 5-39%, at a temperature of 40-57 ^o C, is used as a mineral acid, and helium as an inert medium. Silicon fluorosilicic acid (KFVK) is pre-treated with helium for 40-60 minutes at a temperature of 15-40 ^o C. Purification of silanes from vapors is carried out at a temperature of 10-12 ^o C in a water refrigerator. Silanes are purified from polysilanes and higher silanes at a temperature of minus 76 - minus 80 ^o C. Silanes are purified from disiloxane and fluoride compounds sequentially on aluminum fluoride and sodium fluoride. Purification on sodium fluoride is carried out in two stages: at room temperature and 140-150 ^o C, respectively.

The synthesis of monosilane and disilane proceeds according to the following equations:
Mg ₂ Si + 2H ₂ SiF ₆ = 2MgSiF ₆ + SiH ₄ (1)
2Mg ₂ Si + 4H ₂ SiF ₆ = 4MgSiF ₆ + Si ₂ H ₆ (2)
Using KFVK allows you to get magnesium silicofluoride, which when heated, the salt solution to a temperature of more than 80 ^o C decomposes with the release of magnesium fluoride, silicon dioxide and KFVK. The residue (fluoride and silicon dioxide) is treated with hydrofluoric acid, while silicon dioxide is converted into CPVC by the reaction:
SiO ₂ + 6HF = H ₂ SiF ₆ + 2H ₂ O (3)
KFVK pre-treated with helium. This treatment is performed to remove oxygen dissolved in the acid.

 According to the invention, the method is as follows.

Powdered magnesium silicide through a sealed feeder is periodically fed into the reactor with KFVK. Helium is also fed to the reactor. Mixing is carried out with a magnetic stirrer, as well as by sparging of helium. At the outlet of the reactor, the resulting product is a para-gas mixture containing, in addition to monosilane and disilane, hydrogen and helium, a dropping liquid (water, CPVC), polysilanes and higher silanes, a small amount of hydrogen fluoride and silicon tetrafluoride, disiloxane. This mixture is served in a reflux condenser mounted on the reactor lid, cooled with water to a temperature of 10-12 ^o C, where there is a cleaning of the dropping liquid. Next, the mixture is fed to a condenser, where, at dry ice temperature ((-76) - (-80) ^o C), polysylene and higher silanes are purified, and the mixture enters a sorption column with granular aluminum fluoride. On aluminum fluoride, the disiloxane is purified, and the mixture is purified from hydrogen fluoride and silicon tetrafluoride in two adsorption columns with granular sodium fluoride connected in series. In the first column, cleaning is carried out at room temperature, in the second - at 140-150 ^o C. Next, the gas stream is passed through a diffusion filter (0.01 - 0.03 μm) and a Petryanov filter, where there is cleaning from solid particles (traces of silicon dioxide , sodium fluoride).

 The separation of silanes is carried out on the condensation-evaporation unit of the installation. The gas mixture (monosilane, disilane, hydrogen helium) is cooled at the temperature of liquid nitrogen. Silanes are released into the solid phase at a pressure close to atmospheric, and traces of silanes, hydrogen and helium are removed through a bubble-type afterburning system.

After condensation of a given amount of silanes, the loading of magnesium silicide into the reactor ceases, non-condensable gases (H ₂ , He) are pumped from the condenser into an autonomous vacuum system. Raise the temperature in the condenser to minus 110-120 ^o C. Monosilane is transferred to the receiving cylinder, cooled to the temperature of liquid nitrogen. After separation of the monosilane, the temperature in the condenser is increased to minus 60 - minus 15 ^o C. The disilane is condensed into another receiving cylinder similar to monosilane. The collector of the receiving cylinders is washed with helium and pumped into an autonomous vacuum system, the silane-containing gases are discharged through the afterburner.

 The gas composition before condensation is analyzed on an infrared spectrometer.

 Example.

In a fluoroplast-4 reactor with a magnetic stirrer, 350 ml of CPVC with a concentration of 20.53% were loaded. Performed the processing of the acid solution with helium while heating to 40 ^o C.

After that, within two hours, in small portions, 11.8 g of magnesium silicide was fed into the reactor, the content of which in the sample was 95.7%. During the experiment, the temperature of the solution in the reactor did not exceed 50 ^o C, and the gas pressure was 80-100 mm of water. At the end of the process, the CPVC concentration decreased to 12.2%. The solution was filtered and contained magnesium silicofluoride and CPVC. After condensation and separation of the silanes, 1.34 g of disilane and 2.45 g of monosilane were obtained. According to the results of the analysis, it was found that the reaction yield for magnesium (ratio in solution and magnesium silicide) was 77.54% and for silicon 78.5%. The content of silanes in their mixture: 37.26 wt.% Disilane and 62.74% monosilane. The same ratio of silanes and silicon. The filtrate (solution from the reactor) contained 39.71 g of magnesium silicofluoride. The latter was subjected to heating to 100-110 ^o C for 6 hours, which led to the decomposition of salt into magnesium fluoride and silicon dioxide. The precipitate was filtered and treated with 40% hydrofluoric acid. After filtering and drying the precipitate at 200 ^° C., 14 g of magnesium fluoride were obtained, the yield of which was 94.1%. About 6% of magnesium fluoride was in the filtrate in the form of fine crystals. The filtrate (KFVK) was returned to the reactor.

 At the same time, a study was conducted of the effect of the CPVC concentration on the ratio of silanes in their mixture and the total reaction yield for silicon (see table).

 From the above example it follows that the silicon yield of the reactions of magnesium silicide with CPVC is 78-84%. The yield of disilane increased almost 2-3 times. It can be seen from the example that with an increase in the concentration of CPVC from 14 to 39%, the concentration of disilane in the mixture of silanes decreases from 38.5 to 21%, respectively, the concentration of monosilane increases from 64.5 (68.9%) to 78.8%. Acid production is possible up to 5%, and maybe even lower.

The optimal initial working concentration of hydrofluoric acid, providing a high yield of mono- and disilane, is 14-20%. The temperature of the medium in the reactor is 40-57 ^o C. At a temperature in the reactor of less than 40 ^o C, the synthesis of silanes proceeds at a lower rate.

It can be seen from the example that the optimal decomposition temperature of magnesium silicofluoride to fluoride and silicon dioxide in the solution is 100-110 ^o C. Regeneration of CPVC from silicon dioxide makes the proposed technology virtually waste-free.

 The use of CPVC instead of hydrochloric or sulfuric allows you to reduce the cost of the process, because this acid (30-31%) is an order of magnitude cheaper than the aforementioned acids. The synthesis of silane and disilane in the environment of KFVK is also a refining operation: sodium, potassium, rubidium, calcium, barium silicofluorides are slightly soluble; silicofluorides of other metals (copper, silver, magnesium, iron, zinc, cadmium, lead, cobalt, nickel) are soluble; boron is also bound in the form of soluble fluorides, which makes it possible to achieve good purification from impurities.

 Another advantage of the invention is the fact that as a result of additional processing of the solution from the reactor, it is possible to regenerate up to 70-80% hydrofluoric acid, and also to obtain sufficiently pure magnesium fluoride, which can be used to produce special glasses or as a refractory.

 The proposed method for producing silanes is essentially waste-free.

Claims (6)

1. The method of producing monosilane and disilane, including the interaction of magnesium silicide with mineral acid when heated in an inert atmosphere, purification from impurities and separation of products, characterized in that as a mineral acid using hydrofluoric acid with a concentration of 5 - 39%, and the process is conducted at a temperature of 40 - 57 ^o C in a helium atmosphere. 2. The method according to claim 1, characterized in that the hydrofluoric acid is pre-treated with helium for 40-60 minutes at a temperature of 15-40 ^o C. 3. The method according to p. 1, characterized in that the purification of silanes from the dropping liquid is carried out at a temperature of 10 - 12 ^o C in a water refrigerator. 4. The method according to claim 1, characterized in that the purification of silanes from polysilanes and higher silanes is carried out at a temperature of (-76) - (-80) ^o C.  5. The method according to claim 1. characterized in that the purification of silanes from disiloxanes and fluoride compounds is carried out sequentially on granular aluminum fluoride and sodium fluoride. 6. The method according to claim 1 or 5, characterized in that the purification on sodium fluoride is carried out in two stages: at room temperature and 140 - 150 ^o C, respectively.

Images