RU2551511C1 - Method for producing monosilane and device for implementing it - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention can be used in chemical engineering. A method for producing monosilane involves carrying out a reaction of calcium hydride and silicone tetrafluoride in an eutectic melt of lithium and potassium chlorides at 360-390°C and purifying monosilane. A device for producing monosilane comprises a heated reactor for preparing the eutectic melt of lithium and potassium chlorides and dissolving calcium hydride therein. A monosilane (II) synthesis assembly consists in 10-15 reactors integrated into the same body. Each reactor is connected through a nozzle in its upper part to a dispensing nozzle group and to a common feeder, which is used to introduce the eutectic melt with dissolved calcium hydride. In the lower part, the reactors are provided with nozzles, which are used to connect through a discharge nozzle group to an eutectics filtration unit, whereas silicone tetrafluoride is introduced into each reactor through a flow meter.

EFFECT: invention enables increasing the device effectiveness, as well as producing high-purity monosilane containing the hydrogen fluoride impurity in an amount of less than 1 ppm, and the carbon monoxide, silicone tetrafluoride, methane impurities in the amount of less than 10 ppm.

2 cl, 1 dwg, 1 tbl

Description

The present invention relates to the field of chemical technology for producing monosilane and can be used in the national economy for the production of monosilane on an industrial scale for semiconductor technology. Currently, dozens of methods for producing monosilane are known. The choice of the method for producing monosilane is determined by the raw material base, the purity class of the obtained compounds, the possibility of recycling by-products, and environmental safety. Monosilane is obtained in large volumes using chloride technology (various versions of the Siemens process), but environmental problems make it necessary to search for new technologies. The hydride fluoride technology offered by us eliminates emissions of harmful substances. As a prototype, we have adopted the Russian patent No. 2412902, class. C01B 33/04. The specified method consists in the fact that the reaction is used to obtain monosilane:

SiF ₄ + 2CaH ₂ = SiH ₄ + 2CaF ₂

This reaction takes place in a eutectic melt of lithium and potassium chlorides at a temperature of 360-390 ° C. The described option is designed to conduct the process in a continuous mode, which allows to obtain large batches of monosilane. However, an increase in the productivity of the installation cannot be ensured by an increase in the volume of the apparatus, since it is difficult to organize the sputtering of silicon tetrafluoride with a stable supply of calcium hydride to the reaction zone to obtain monosilane.

The technical result of the invention is to obtain high-purity monosilane and the possibility of a significant increase in plant productivity.

The technical result is achieved by the fact that in the method for producing monosilane, comprising the interaction of calcium hydride with silicon tetrafluoride in a eutectic melt of lithium and potassium chlorides at 360-390 ° C, the preparation of the eutectic melt of lithium and potassium chlorides and dissolution of calcium hydride in it is carried out in a separate apparatus, which allows the prepared eutectic melt to be continuously fed into reactors where the reaction of calcium hydride and silicon tetrafluoride sprayed in the reactor volume takes place.

In the proposed method for producing monosilane, monosilane is purified from H ₂ , O ₂ , N ₂ , CO, CH ₄ impurities by contacting with an adsorbent, and they also analyze impurities by introducing these impurities together with a carrier gas into a gas chromatograph.

In addition, monosilane containing hydrogen fluoride as an impurity is introduced into an optical cell with optical windows of metal halide and hydrogen fluoride and / or silicon tetrafluoride, hexafluorodisiloxane are analyzed by infrared spectrometry.

The monosilane synthesis unit is a vertical structure of 10-15 reactors with a volume of 60 liters, combined in one housing.

The preparation of the eutectic (molten potassium chloride and lithium) and the dissolution of calcium hydride are carried out in a separate apparatus and strictly control the flow of the solution into the reactors.

To maintain the concentration of calcium hydride in the melt at the saturation level, a heated sealed container with a supply of calcium hydride was installed above the reactor. The prepared eutectic melt is continuously fed to the reactors, where the reaction of calcium hydride with silicon tetrafluoride sprayed in the reactor volume takes place. The monosilane thus obtained is withdrawn through the top of the reactors. Calcium fluoride is discharged through a sump installed in the lower part of the reactor. The drawing shows a schematic view of the installation used to implement the method of producing monosilane

according to the present invention. Description of the main units of the device block for producing monosilane using hydride-fluoride technology

1.1. Eutectic preparation and dosing unit (feeder) - pos. I. Designed for the preparation of a solution of eutectic with calcium hydride and its continuous supply to the reactor (monosilane synthesis unit).

It is an apparatus with a volume of 1.4 m ³ with a device for loading powdered eutectic components: KCl, LiCl and CaH ₂ . The assembly is purged with an inert gas or N ₂ to prevent moisture from the air entering the eutectic mixture. In the lower part of the apparatus there is access to a dosing comb connected to a monosilane synthesis unit. It contains a device for introducing calcium hydride (HA) into the melt and replenishing the loss of melt when removing a portion of calcium fluoride. The eutectic preparation unit communicates with the solution clarification unit through which the eutectic mixture returns to the apparatus.

1.2. Monosilane synthesis unit (MS) - pos. II

The monosilane synthesis unit is a vertical structure of 10-15 reactors with a volume of 60 liters, combined in one housing. The total volume of the reaction zone is 600 liters. Each reactor through a fitting in the upper part is connected to a metering comb and to a common feeder, from which the eutectic melt is introduced with calcium hydride dissolved in it. In the lower part, the reactors are equipped with fittings by means of which they communicate through the discharge comb with the eutectic filtering unit.

In each reactor, three zones can be distinguished:

- lower, to the level of TPA input, - zone of calcium fluoride sludge;

- medium — reaction zone;

- upper - monosilane collection zone.

The melt level is controlled by 10 level gauges. TFK enters each reactor from a cylinder through a flow meter. If necessary, helium or nitrogen can be mixed into the TFK from the cylinder through the flow meter.

The monosilane synthesis unit is heated with the help of heating elements; in the reaction zone, a temperature of 400 ° C is maintained

1.3. Filtration unit - pos. III

Designed to filter calcium fluoride precipitate removed from reactors. During operation, the filtered calcium fluoride is discharged from the apparatus through a fitting in the side. The filtrate enters through the lower fitting into the sedimentation unit (clarification).

1.4. The unit of sedimentation (clarification) - pos. IV

Designed for clarification of the incoming filtrate, release from suspended particulate matter CaF ₂ . The purified eutectic mixture is returned to the apparatus for preparing the eutectic solution.

1.5. The node for cleaning MS from fluorides - pos. V

It consists of 2 lines connected in parallel to the reactor, each of which consists of three vertical columns connected in series. MS from the reactor enters a heated adsorber filled with granular sodium fluoride. At a temperature of 140 ° C, TFA is absorbed by sodium fluoride to form sodium silicofluoride. The equilibrium concentration of TFA at this temperature is sufficient to reduce its concentration in the MS below 0.0001 vol.%.

Then TFA enters the adsorber heated to 280 ° C, where the MS is purified from traces of hydrogen fluoride and other fluorides. As impurities accumulate in the adsorbers, they are turned off without stopping the process and sent for regeneration, the MS stream from the reactor is sent to a parallel line.

1.6. The unit for cleaning MS from oxygen, nitrogen, carbon oxides, hydrocarbons and moisture - pos. VI

Two parallel connected lines, each of which consists of two columns. The MS purified from fluorides enters the adsorber filled with CaA zeolite and then into the adsorber filled with activated carbon. Both adsorbers are cooled with cold nitrogen to minus 40 ° C. As impurities accumulate in these adsorbers, they are turned off without stopping the process and sent for regeneration, the MS stream from the reactor is sent to a parallel line.

1.7. Capacitor assembly - pos. VII

The condenser is designed to collect MS, remove helium, if used, maintain a given pressure in the MS line and (when heating) fill transport cylinders under pressure up to 20-30 bar.

1.8. Vacuum post - pos. VIII

The vacuum post serves to carry out the preparatory operation of cleaning the entire MS passage line from moisture and air components by alternately pumping and filling the system with pure nitrogen and / or helium. Consists of a vacuum pump and a cryogenic trap.

In the case where monosilane is used to produce elemental silicon (in particular, detector silicon), monosilane with a reduced content of impurities is required and methods for analyzing trace amounts of impurities in monosilane are equally necessary.

Obtaining monosilane with a low content of impurities is implemented using the following procedures:

1. Purification of traces of silicon tetrafluoride by sorption on granular sodium fluoride.

2. Filtration from solid particles larger than 0.1 microns.

3. Preliminary adsorption purification on activated carbon and molecular sieves at low temperatures.

4. Filtration from solid particles larger than 0.01 microns. on filters like Wafergard Mini XL inline Gas Filters.

5. Blowing off monosilane enriched in impurities for discharge through a decomposition furnace.

6. Removal of the monosilane fraction enriched in impurities through a decomposition furnace.

7. Sampling of purified monosilane for analysis.

8. Finishing treatment of heated monosilane with activated carbon of high purity and zeolite at a low temperature (but higher than the boiling point of monosilane).

Purification of solid particles with a particle size of more than 0.01 μm on Wafergard Vini XL inline Gas Filters filters.

9. Sampling of the finished product for analysis.

10. The condensation of liquid monosilane in a condenser evaporator and the removal of low-boiling impurities and hydrogen by periodic pumping.

11. Cleaning of exhaust gases after the decomposition furnace from solid particles and discharge through a hydraulic shutter.

12. Regeneration of sorbents by heating the adsorbers and washing with clean dry nitrogen and OHS hydrogen.

13. Periodic flushing of the HFC equipment with hydrogen to the dew point (-90 ° C).

For cooling, liquid nitrogen is used.

As auxiliary gases - OSH hydrogen, argon and dry nitrogen. Before carrying out a series of experiments, the entire chain of VHF apparatuses must be flushed with hydrogen with heating of the units operating at elevated temperatures (to higher than the operating temperature).

Quality control of cleaning is carried out at the dew point of the exhaust hydrogen. In addition, the presence of dust particles with a particle size of more than 0.01 microns is checked in the exhaust hydrogen.

Continuous monitoring of particulate matter after filters is desirable. Components that can be analyzed in monosilane at the level of trace amounts: H ₂ , O ₂ , N ₂ , CO, CH ₄ , HF. The technical result is achieved through the use of a pre-column (stainless steel column with an inner diameter of 3 mm and a length of 1 m) filled with a Poropak-R polymer sorbent with particles 60-100 mesh in size. 2 cm ^{3 of} monosilane are introduced into such a pre-column using a gas valve. The carrier gas used is high-purity helium. Separation of H ₂ , O ₂ , N ₂ , CO, CH ₄ is carried out on a NaX separation column. Separated components are introduced into a pulse discharge detector of a gas chromatograph and their concentration is measured. After the peaks belonging to the impurities H ₂ , O ₂ , N ₂ , CO, CH _{4 are released} , the sample is discharged through the afterburner.

Analysis of hydrogen fluoride (HP) is carried out by infrared spectroscopy with Fourier transform. Measurements of hydrogen fluoride concentration are carried out in a stainless steel gas cell equipped with fluorite optical windows. After purging the cell with a monosilane sample, it is evacuated for 5 minutes, then the background absorption spectrum is taken. Then the cell is filled with a breakdown of monosilane to a pressure at which the peaks of the vibrational-rotational spectrum of hydrogen fluoride (3788, 3834, 3878, 3920, 4000, 4038, 4075, 4109 cm ^-1 ) are available for reliable integration, but not more than 0 6 MPa and register the spectrum of the sample. The partial pressure of the detected impurity of hydrogen fluoride is carried out using known values of the integral absorption coefficient. Table 1 shows data on the content of impurities in 8 batches of monosilane.

Table 1 Parameter Name Units rev. Analysis result Minimum Maximum CH ₄ ppm <10 <10 H ₂ ON ON H ₂ O <0.1 <0.1 O ₂ ON ON CO ON ON N ₂ ON ON Hf <1 5

The set of measures allows you to optimize the process of obtaining monosilane. In the above method, high purity monosilane is obtained.

The plant performance is regulated by the number of segment devices involved.

Claims (2)

1. A method of producing monosilane, comprising the interaction of calcium hydride with silicon tetrafluoride in a eutectic melt of lithium and potassium chlorides at 360-390 ° C, purification of monosilane, characterized in that the preparation of the eutectic melt of lithium and potassium chlorides and dissolution of calcium hydride in it is carried out in a separate the reactor and the prepared eutectic melt are continuously fed into reactors where the reaction of calcium hydride and silicon tetrafluoride sprayed in the reactor volume takes place. 2. A device for producing monosilane, including a heated reactor for preparing a eutectic melt of lithium and potassium chlorides and dissolving calcium hydride in it, characterized in that the monosilane synthesis unit consists of 10-15 reactors combined in one housing, and each reactor through a fitting the upper part is connected to a dosing comb and to a common feeder, from which the eutectic melt is introduced with calcium hydride dissolved in it, in the lower part the reactors are equipped with fittings by which they together through a discharge comb with a eutectic filtering unit, and silicon tetrafluoride enters each reactor through a flow meter.