WO2006041272A1

WO2006041272A1 - Method of silane production

Info

Publication number: WO2006041272A1
Application number: PCT/KZ2005/000008
Authority: WO
Inventors: Marat Fatykhovich Tamendarov; Bolat Nygmetuly Mukashev; Khabibulla Abdullaevich Abdullin; Zhaksybek Abdrakhmetovich Kulekeev; Nuraly Sultanovich Bekturganov; Boris Anatolievich Beketov
Original assignee: Ministry Of Education And Sciences Of Republic Kazakhstan Republican State Enterprise 'center Of Chemical-Technological Researches'; 'silicon Technologies' Ltd Liability Partnersship
Current assignee: Ministry Of Education And Sciences Of Republic Kazakhstan Republican State Enterprise 'center Of Chemical-Technological Researches'; 'silicon Technologies' Ltd Liability Partnersship
Priority date: 2004-10-12
Filing date: 2005-10-12
Publication date: 2006-04-20
Anticipated expiration: 2007-04-12

Abstract

Suggested method for the production of Silane used for the formation of the thin-film semi-conductor structures by the gas epitaxy technology and manufacture of poly-and monocrystal silicon for various purposes (semi- conductors, solar energy). The process suggested in the present invention includes production of the silicon-containing alloy by aluminothermic reduction of silica obtained from silicon-containing metallurgical wastes, and the interaction of the mentioned silicon-containing alloy with aqueous solution of mineral acid. In this, process the hydrochloric acid has been used as the required mineral acid. Main advantages of the described processes are the following: utilization of inexpensive raw materials, low energy consumption, environmental safety. High yield of Silane in turn decreases the cost of the product allows effective utilization of the industrial wastes. Aluminous cement, which is the byproduct of the mentioned process, can be used in the construction industry.

Description

Method of silane production

The invention relates to the silane production. More particularly, it relates to an improved process of the Silane production for ensuring its lower cost and higher yield, using special alloy, obtained by the aluminothermic reduction of silica in metallurgical slags and by the reaction of the above-mentioned alloy with aqueous solutions of mineral acids.

At present time the demand for polycrystalline silicon as the basic material for semi-conductor electronics and solar power industry will grow and grow. There are several methods for the industrial manufacture of polycrystalline silicon. One of them is the method of thermal decomposition (pyrolysis): monosilane is inserted into the reactor, where it reacts with the surfaces of the heated silicon rods, decomposing and depositing onto them. In the other method the monosilane filled with the fine particles of silicon should be inserted into the fluidized-bed reactor, where Silane is deposited in the form of powdered commodity.

Thus, Silane is used as initial material for the production of polycrystalline silicon. Nowadays there are two standard methods for the production of silane:

(1) using hydrogen reduction of trichlorosilane (SiHCl₃), so-called "Siemens Process" (see O " Mara W.C., Herring R.B., Hunt I.P., Hand book of

Semiconductor SiliconTechnology, pp.33-77, Noyes Publicatins, Park Ridge NJ (1990) and FRG Patent N° 3,311,650 published on October, 13, 1983 ), and its improved version for disproportionation of trichlorosilane for the production of monosilane SiH₄, developed by the Union Carbide Company (see Union Carbide. Base Gas Condition for Use Silane Process. Report DOE/JPL-954343-21, Nat. Tech. Inform. Center, Springfield, VA, 1981);

(2) method for hydrolysis of various binary alloys, such as CaSi, CaSi₂, MgSi and Mg₂Si., among which only magnesium suicide (Mg₂Si) represents real interest for the Silane manufacture (see E. Wiberg, Hydrides, Elsevier N.Y. 1971, p 473).

In Siemens process (1) SiHCl₃ is produced in the reactor with boiling bed as a result of interaction between powdered metallurgical silicon and gaseous HCl. Obtained gas-vapor mixture is separated in filtration and condensation, and HCl and hydrogen return into process (recirculation). Then the condensate should be separated and SiHCl₃ purified in the process of multistage purification. Purified trichlorosilane (SiHCl₃) mixed with the hydrogen (H2) is inserted into the reactor of pyrolysis for the production of polycrystalline silicon.

Therefore, the process (1) allows to obtain high purity Silane, it has several disadvantages, for example, the process should be realized in chemically hostile environment at a high pressure, which requires expensive equipment, made from heat-resistant and chemically inert materials. Presence of chemically aggressive chlorine compounds corrodes equipment, thus contaminating Silane. Moreover, this process is complicated, power consuming and ecologically dangerous. These factors considerably increase the cost of polycrystalline silicon. The Process (2), on the contrary, is very simple, but the yield of Silane doe not exceed 25-30%. This process also requires expensive magnesium suicide, which production in turn requires special equipment. Silane yield can be increased up to 80% owing to the interaction of magnesium suicide with sal ammonia in liquid ammonia. However, this process can be realized only at a high pressure, and requires effective purification of silane from ammonia.

The most closely related method, which has been considered as prototype - is the method for the production of silane, submitted in the US patent the N° 4698218, class MKI C01B33/04. According to the invention, the synthesis of silane can be realized through the effect of mineral acid aqueous solution on the industrial threefold alloys of Al/Ca/Si. The main advantage of this method is the simplicity of technological process, allowing using inexpensive initial materials. However, the present method does not allow synthesizing silane with relatively high yield regarding to the content of silicon in the alloy. Thus, the descried processes for the Silane production do not meet the requirements of its cost and its yield.

Technical purpose of suggested invention is to increase the yield of the finished product while decreasing its manufacturing self-cost.

For these purposes, the suggested method includes hydrolysis of binary alloys (CaSi, CaSi₂, MgSi and Mg₂Si) and hydrolysis of ternary alloys of Al/Ca/Si in aqueous solutions of mineral acids. The present invention stipulates use of highly active silicon containing of variable Ca/Al/Mg/Si content, which includes insignificant concentration of other impurities. This alloy is obtained by the reduction of silica with aluminium in phosphoric slags. Silane can be obtained through interaction of silicon containing in the form of the fine powder with hydrochloric acid at a relative temperature of 50-60⁰C and normal atmospheric pressure with the use of safe chemical agents, resistant in atmospheric air. Silane purification can be achieved by well-known methods, such as low- temperature rectification and by means of absorbents. The process's byproduct - aluminous cement can be used in the construction industry.

The main advantages of the described process are the simplicity of chemical processes, possibility to use inexpensive raw materials, low energy consumption, and higher yield of the finished product. All mentioned above allow using this process in commercial scales with lower self-cost of obtained Silane and effective utilization of industrial wastes.

The purpose of the invention is to create highly effective, wasteless, ecologically clean, and energy-efficient method for the manufacture of semi¬ conductor silicon for photoelectron and microelectronic industry from inexpensive initial raw materials, namely from the phosphoric industry wastes, available in surplus at the phosphoric industry enterprises.

It is known, that manufacture of yellow phosphorus by the electrothermal method, mostly used in the world practice [see H.S. Bryant, N.G. Holloway, A.D. Silber, Industrial and Engineering Chemistry, (1970), vol. 62, No. 4, pp. 8-23] is realized on the basis of the following reaction: 2Ca₃(PO₄)₂+10C+6SiO₂→P₄T+10Cθt+6CaSiO₃. Thus, the yield of the waste products, at phosphorous manufacture makes 10-14 tons per one ton of produced phosphorus. Such methods of production leave millions of tons of phosphorous industry products on the dumps nearby manufacturing enterprises. This silicon-containing alloy can be obtained in the following way: open graphite crucible is filled with phosphorous slag and then heated in the induction furnace at the melting temperature. Than the definite amount of aluminium should be introduced into the phosphorous slag in the reaction chamber. Flame heating, is required mainly when starting up the process and in course of the oxidation- reduction reactions. Because of the exothermic nature of the reaction, the process of interaction of the phosphorous slag with aluminum, can be completed in rather short time interval. It is worth mentioning that the temperature of the liquid melt should be maintained at 1600 ... 1800⁰C. Only when the reaction subsides is it necessary to apply heat again, in order to prevent the temperature dropping below the melting point of the reagents of the reaction mixture and for the complete separation of metal and secondary slag.

The amount of aluminium in the charge should exceed its required calculated amount to the extent of complete reduction of silica in the phosphorus slag by 10-60%, preferably by 40%. However, this process does not require insertion of highly purified reducing agents. The use of the aluminium scrap is admissible.

When the oxidation-reduction reaction has completed and the metal and secondary slag separated, they should be discharged from the crucible in separate moulds. Obtained secondary slag represents itself aluminous cement of a high quality and can be used for the needs of the construction industry.

Insertion of powdered siliceous alloys into mineral acids, for example into hydrochloric acid, results in generation of gas, which includes mixture of hydrogen, silane (SiH₄), disilane (Si₂H₆), and trisilane (Si₃Hg). There are no special limitations for the used particles of alloy, but it is desirable to use fine particles and even powder, if possible. However, due to the economic reasons and considering easier practical handling of the powder, it is recommended using silicon powder with the particle sizes less than 100 microns.

The process, suggested in the present invention can be fully described in the following example: Three weight parts of phosphoric slag were mixed with one weight part of granulated aluminium. Open graphite crucible was filled with the mixture and then heated in the induction furnace prior to the beginning of aluminothermic reaction. The process is characterized with high speed of oxidation-reduction reactions and considerable heat evolution. Reaction time is 15-20 minutes at the liquid melt's final temperature beyond 1600⁰C. When the separation of the metal from the secondary slag has finished, the alloy was separately discharged into the mould and cooled on the atmospheric air. . After that, the alloy was crushed, milled an sawed into fractions with the particle sizes less than 100 microns. Experiments on the synthesis of Silane have been carried out on the laboratory-scale plant consisting of reactor with hydrochloric acid, gas burette and aspiration system.

One (1) gram of obtained powder was added into the 5-20 % hydrochloric acid (preferably 10 %) at preferable temperature of 50-60⁰C and normal atmospheric pressure. Obtained gas has been collected into the special reservoir for further analysis.

Repeated experiments have shown that the average volume of generated gas, identified as Silane in recalculation for one kilogram of alloy has made 356 liters or 513 grams of Silane.

Thus, suggested method allows obtaining one kilogram of Silane from two kilograms of silicon-containing alloy.

For comparison of considered method for the production of Silane with the method, suggested in the US patent N° 4698218 and method, which uses Al/Ca/Si alloys we have realized similar experiments with ternary alloys (33%A1, 18%Ca and 40%Si). This method allows obtaining one kilogram of Silane fromlO kilograms of such ternary alloys.

Considering all mentioned above, this invention has the following main advantages: (1) higher yield of Silane, (2) simple technological operations, which allow decreasing Silane self-cost, and (3) effective utilization of industrial wastes.

Claims

1. The method for the Silane production by the acid hydrolysis of the silicon-containing alloy, which includes the reaction between silicon-containing alloy and 5-20% hydrochloric acid solution at a temperature of 50-60⁰C₅ carried out by its addition into the acid in the form of the powder differs as it requires the use of silicon-containing alloy obtained by the reduction of silica with aluminium in phosphorous slags, considering that the amount of aluminium should quantitatively exceed required stoichiometric amounts by 10-60%,

2. The present method differs in the item 1, as it realization requires using silicon-containing alloy of variable structures Ca/Al/Si/Mg, including insignificant concentration of other impurities.

3. The present method differs in the item 2, as it realization requires using silicon-containing alloy of the following structure: Al 30-38 %; Cal5-25 %; Si 35-45 %; Mg 2-3 %; rare earth elements 0.1-0.3 %.

4. The present method differs in the item 1, as it realization requires using silicon-containing alloy with average size of the particles size less than 100 micrometers.

5. The present method differs in the item 1, as it realization requires using preferably 10-12% hydrochloric acid solutions.

6. The present method differs in the item 1, as the amounts of aluminium in the charge should exceed its required calculated amount to the extent of complete reduction of silica in the phosphorus slag by 10-60%, preferably by 40%.