KR20010101102A - METHOD FOR THE PRODUCTION OF SINGLE ISOTOPIC SILICON Si-28 - Google Patents

Abstract

FIELD OF THE INVENTION The present invention relates to the field of metallurgy, and in particular, to a method for producing monoisotopic silicon from inorganic compounds, mainly tetrafluoride silicon, concentrated with Si ²⁸ . The method includes reducing tetrafluoride silicon at high temperature, and reducing silane from tetrafluoride silicon by reducing tetrafluoride silicon with calcium hydride at a temperature of 180 ° C. to 200 ° C. It is done. The silane obtained is subjected to high temperature decomposition at a temperature of 800 ° C. to 900 ° C. and the precipitation rate on the base layer of monoisotopic silicon is not greater than 0.5 mm per hour. Precipitation of monoisotopic silicon on the substrate is preferentially controlled by changing the feed rate of silane. Precipitation is influenced by the base layer of preliminarily obtained monoisotopic silicon or in two stages. The precipitate of the first step is in a heat resistant substrate, for example a metal having a melting point higher than the temperature of the silicon precipitate. Then, the obtained monoisotopic silicon bar is separated from the base layer and the precipitation process is continued as obtained in the first step. The final bar undergoes high purification and is preferably by the crucibleless zone melting method.

Description

How to make a single isotopic silicon Si-28 {METHOD FOR THE PRODUCTION OF SINGLE ISOTOPIC SILICON Si-28}

A method for producing monoisotopic silicon Si ²⁸ _, Si ²⁹ , Si ³⁰ by reaction of reducing silicon dioxide with boron is known (SU 1515795, Jan. 7, 1991, C 30 B 29/06). , 23/02). A disadvantage of this method is the limited contamination of the silicon produced by boron and sometimes reduces the actual use of the silicon, which is difficult to remove the boron impurities and affects the electrophysical parameters of the silicon such as resistivity, charge carrier concentration, etc. This is because it has a negative effect.

Also known is a method of producing monoisotopic silicon by reducing silicon dioxide with magnesium at high temperatures. The initial reactant is heated to 1433 ° C. and bound (RU 2036143, May 27, 1995, C 01 B 33/023). One of the drawbacks of the process is that the contaminants of the material appear in the reaction chamber at the high temperatures, and the other is the fact that the resulting mixture contains magnesium oxide, which is insoluble in hydrochloric acid. The use of chemical reactants causes further contamination of the final product.

SU 2137710, September 20, 1999, the method of producing monoanisotopic silicon for the manufacture of electronic devices by C 01 B 33/027, C 22 B 5/00 is the most similar in terms of technical characteristics and efficiency . According to this method, tetrafluoride silicon is produced by reacting with quartzite as a reactant. Here, waste uranium hexafluorine is used as a reactant and the resulting tetrafluoride silicon is isotopically separated and the produced monoisotopic tetrafluoride silicon is ammonia and ammonia at a temperature of 850-900 ° C. to obtain monoisotopic silicon. Reaction and reduced.

Disadvantages of the method are inherently low purity of the monoisotopic silicon produced and also inability to produce silicon in the form of bars. This makes it difficult to produce higher purification and electronic devices.

TECHNICAL FIELD The present invention relates to the field of metallurgy, and in particular, to a method for producing high purity monoisotopic silicon and other stable isotopes Si ²⁹ , Si ³⁰ .

Silicon is used in electronics, for example in the field of integrated circuits and power electronics devices. Monoisotopic silicones have higher thermal conductivity than silicones of natural isotope complexes. For this reason, silicon can reduce the device size of integrated circuits and improve the characteristics of power electronics.

OBJECT OF THE INVENTION The object of the present invention relates to a process for producing monoisotopic silicon Si ²⁸ as at least an additive free semiconductor from a compound enriched with volatile isotopes with the assurance of high yield of product without dilution of the isotope.

The above object is mono iso topic may be obtained by a method of generating a silicon Si ^28, tetrafluoride silicon is generated by the tetrafluoride silicon silane at a high temperature (silane from the inorganic compound mainly tetrafluoride silicon concentration in Si ²⁸ Is reduced to The silane is subjected to high temperature decomposition at a temperature of 800 ° C. to 900 ° C., and the precipitation rate of the monoisotopic silicon on the substrate is not greater than 0.5 mm per hour.

Preferably, the silane is to produce tetrafluoride silicon is reduced with calcium hydride at a temperature of 180 ℃ to 200 ℃.

In order to control the precipitation rate of the silicon, it is desirable to change the feed rate of the silane. According to a more preferred form of carrying out the method, the preliminarily obtained base layer of monoisotopic silicon has an influence on the precipitation. If the base layer is not present, the precipitation of monoisotopic silicon is made in two steps. Precipitation in the first step takes place in a heat resistant base layer of a metal having a melting point higher than the temperature of the silicon precipitate, wherein the layer thickness of Si ²⁸ is grown until it is separated from the base layer. Thereafter, the obtained monoisotopic silicon bar is separated from the base layer and the precipitation process is continued to that obtained in the first step. The silicon layer obtained in the first step of precipitation is separated from the base layer by mechanical or rapid cooling methods.

It is preferable to expose the Si ²⁸ bar for high purification, more preferably by the crucibleless zone melting method.

According to the fact that silanes concentrated with silicon Si ²⁸ can be obtained by reducing tetrafluoride silicon with calcium hydride at temperatures between 180 ° C. and 200 ° C., the highest yield of silane is assured and the loss of monoisotopic silicon Si ²⁸ is reduced. Is prevented. Below 180 ° C., the conversion of tetrafluoride silicon to silane is incomplete and the yield is almost 70%. Above 200 ° C., the partially produced silane decomposes, which also leads to a decrease in the yield, resulting in an unrecoverable loss of monoisotopic silicon.

At temperatures between 800 ° C. and 900 ° C., an important factor in terms of silicon precipitation is pyrolysis of silane and the growth rate of the silane layer is only 0.5 mm per hour. The suggested temperature interval is above 90% as the highest yield of silicon produced. At temperatures below 800 ° C., the silane is incompletely degraded and transported in the reaction zone in the form of non-reactants. If the silane decomposes with the polycrystalline silicon deposited on the substrate at temperatures above 900 ° C., some of the silicon separates into finely divided particles that are discharged with the hydrogen flow produced during the decomposition of the silane. do. In order to separate silicon in the form of a crystal layer, the growth rate of the silicon layer does not exceed 0.5 mm per hour. In this case, the proportion of the amorphous silicon powder is only about 1%. When the growth rate of the silicon layer is 0.5 mm or more per hour, the proportion of amorphous silicon reaches 10% or more, which reduces the yield of the product.

Preferably, the base layer is a refractory material, for example a metal having a melting point higher than the decomposition temperature of silicon. The substrate is made in the form of a band, rod or wire.

The invention can be better understood through the examples.

Powdered calcium hydride is transferred from the flow of helium to the reactor. The stream of tetrafluoride silicon concentrated with Si ²⁸ is then fed to the reactor. The silane synthesis reaction takes place at 180 ° C. and atmospheric pressure. The concentration of silane in the stream of the effluent is determined by gas chromatographic method. The yield of silane relative to tetrafluoride silicon is 90%. Removal of unreacted tetrafluoride silicon from the silane is accomplished by sorption of sodium fluoride at 220 ° C. The produced sodium fluorosilicate is subjected to pyrolysis due to the production of tetrafluoride silicon, which minimizes the loss of silane. The resulting silane is subjected to rectification purification and decomposes to obtain silicon.

A chamber of molybdenum wire, the substrate located therein and a pipeline for supplying gas are discharged and filled with pure argon. The substrate is then heated to a temperature of 800 ° C. through electrical current. After the temperature required for the substrate is reached, the silane is fed from the vessel to the camera. Silicon precipitates on the surface of the substrate at a rate of 0.1 mm per hour. The amount of voltage supplied to the substrate is increased to maintain the temperature of the surface while the thickness of the layer increases. The grown silicon layer is separated from the metal base layer and the obtained monoisotopic silicon is used as the base layer while further decomposition of the silane proceeds.

The yield of the silicon is determined by comparing the weight of the silane passed through the reactor with the weight of precipitated silicon. The yield of the silicon is more than 90%. The silicon obtained after the decomposition of the silane is subjected to purification by a crucibleless melting method. According to the data of laser mass-spectrometry (see Table 1), the main amount of impurities in the obtained monoisotopic silicon does not exceed 10 ^-4 % by weight. The above method is also used to obtain stable isotopes of Si ²⁹ and Si ³⁰ .

The practical use of the monoisotopic silicon obtained by the method according to the invention offers the possibility of opening up the basis of a new generation of computer engineering devices. The possibility of enhancing the technical characteristics of modern computers is essentially exhausted as long as the use of silicon as a natural compound. Registering nuclear molecules, a new generation of devices for power electronics, can be achieved on the basis of pure silicon isotopes. Many practical perspectives will be opened by the practical use and invention of novel materials obtained by neutron strain doping of monoisotopic silicones.

Claims (10)

In the method for producing monoisotopic silicon Si ²⁸ from inorganic compounds mainly concentrated in tetrafluoride, which is concentrated to Si ²⁸ , which is silicon, comprising reducing tetrafluoride silicon at a high temperature, Silane is formed from the tetrafluoride silicon, The silane is preferably subjected to high temperature decomposition at a temperature of 800 ° C to 900 ° C, The precipitation rate on the base layer of the monoisotopic silicone is 0.5 mm or less per hour. The method of claim 1, wherein the silane is produced by reducing tetrafluoride silicon with calcium hydride at a temperature of 180 ° C to 200 ° C. The method of claim 1 or 2, wherein the precipitation rate of the silicon is adjusted primarily by varying the feed rate of the silane. 4. A process according to any one of claims 1 to 3, wherein the precipitation is in the base layer of preliminarily produced monoisotopic silicon. The method of any one of claims 1 to 4, wherein the precipitate of monoisotopic silicon is comprised of two stages, wherein in the first stage the precipitation is in a heat resistant substrate and the resulting monoisotopic silicone is produced in the substrate. Wherein the precipitation process is continued as obtained in the first step. The method of claim 5, wherein a metal having a melting point higher than the precipitation temperature of the silicon is used as the base material in the first step of the silicon precipitation. 6. The method of claim 5, wherein the monoisotopic silicon layer having a thickness allowing separation of the precipitate layer is obtained in the first step of monoisotopic silicon precipitation. 8. The method according to claim 5, wherein the separation of the silicon layer from the base layer obtained in the first step of precipitation is mechanical. 9. 8. The process according to claim 5, wherein the separation of the silicon layer from the base layer obtained in the first step of precipitation is by quenching. 9. 10. The method according to any one of the preceding claims, wherein the final bar is subjected to a high purification, preferably crucibleless zone melting method.