DE1053478B - Process for converting silicon tetrachloride into highly purified silicon - Google Patents

Description

GERMAN

CO1B 33 / 02- -

T 13031 IVa / 12 i

REGISTRATION DAY: DECEMBER 24, 1956

NOTICE
THE REGISTRATION
AND ISSUE OF THE
INTERPRETATION: 2 6 MARCH 1 9 5 9

The invention relates to -a method zir " Manufacture of highly purified silicon, especially used in the manufacture of electrical semiconductor devices suitable is

The extensive consumption of silicon in semiconductor electronic devices has required the manufacture of relatively large quantities of ultra-pure silicon. Contaminants, even as high as 1 part per 10 million parts, are very undesirable and require lengthy, tedious and costly cleaning procedures. ^x

It is known that silicon tetrachloride (SiCl ₄ ) can be reduced with zinc vapor, it being possible, if appropriate, to use hydrogen as the carrier gas. However, the customary reduction of silicon tetrachloride with zinc gives a product which leaves much to be desired in terms of purity. This product usually requires extensive further treatment to remove all traces of zinc and other impurities that may be present in either silicon tetrachloride or zinc.

It is also known to reduce silicon tetrachloride with hydrogen. In a known method, the silicon is allowed to crystallize from a mixture of SiCl ₄ and 2 H., on a 1000 ° C hot carbon or tungsten filament, the filament being kept as a core in the up to 3 mm thick silicon rod. According to another experience, a ratio of silicon tetrachloride to hydrogen of 0.0685 was used in the reduction at a temperature of 1150 ° C. In this case, however, only 12% of the silicon tetrachloride was converted, accordingly only 1.6 ⁰ At of the available hydrogen was used. The production of 1 kg of silicon required the use of 100 cbm of hydrogen and 50 kg of silicon tetrachloride. Even these processes did not lead to a product that met all requirements with regard to purity. Except for the difficult problem of cleaning the source materials. In order to ensure that no perceptible traces of impurities pass into the silicon product, the costs are very high, especially in the case of the last-mentioned process 111; to spend the starting point.

The I ^- JIiIKlUiIg l) i / awakens the overcoming of the disadvantages of the known processes and the creation of a process'- /.ur conversion of Siliciiuntetrachlorid iv hochgcremigu s silicon, in which Siliciunitcti achloi κI ^ ew nhnlielicr Ream n / .i Quality and other chemicals of common reagents that can be used in a silicon ultralemei I lesdiatieiiheit? u ei / eiü'eii

procedure

for the conversion of silicon tetrachloride into highly purified silicon

Applicant:

Texas Instruments Incorporated,
Dallas, Tex. (V. St. A.)

Representative: Dr. E. Wiegand, Munich 9,

and Dipl.-Ing. W. Niemann, Hamburg 1,

Ballindamm 26, patent attorneys

Willis Alfred Adcock and Raymond Charles Sangster,

Dallas, Tex. (V. St. A.),
have been named as inventors

The process according to the invention is characterized in that a mixture of silicon tetrachloride and hydrogen is fed into a reaction zone which is maintained at a temperature so high that a substantial reaction occurs with subsequent deposition of silicon in the zone with the formation of hydrogen chloride, the unreacted silicon tetrachloride and hydrogen as well as withdrawing from the reaction zone the hydrogen chloride InseI / ung formed in the (preferably additional silicon tetrachloride is added to the stripped mixture to replenish the consumed in the reaction material, selectively ( 'borane from the mixture by treatment with evaporated zinc is removed with the formation of hydrogen and zinc chloride, the hydrogen exhaled during the reaction is replaced and the resulting mixture circulates again loudly through the reaction zone.

A silicon tetrachloride is expedient assumed that by mixing with a solvent, such as a halogenated hydrocarbon, and passing through an activated aluminum oxide containing adsorption column as well as anseh.liefciende evaporation of the solvent pre-cleaned word "n is.

What is essential in the Veri'.ihiui according to the invention. dal.'i after the known reduction of

Silicon tetrachloride with hydrogen zinc vapor for selective extraction of hydrogen chloride from the reaction products is used.

It has been found that the hydrogen chloride gas can selectively reduce with zinc vapor to regenerate hydrogen without simultaneously reducing the silicon tetrachloride gas in the mixture to silicon. In the procedure according to the invention is in contrast to the known zinc reduction process of silicon tetrachloride> the initially obtained mixture of unreacted silicon tetrachloride. Hydrogen and formed Hydrogen chloride, which uses zinc vapor to reduce hydrogen chloride to zinc chloride and hydrogen. The zinc chloride formed can be allowed to settle out of the mixture and the mixture can be removed Filter the remaining zinc chloride and other impurities.

The method according to the invention is expediently carried out in three stages, in the first of which Stage a pre-cleaning of the silicon tetrachloride takes place, in the second stage the conversion of the prepurified silicon tetrachloride takes place in an effective manner to ultra-pure silicon and in the third stage of the silicon is removed from the apparatus and converted into ingot form.

The first stage is new in itself and leads to a particularly suitable starting material for the process according to the invention. The second stage forms the core of the method according to the invention and creates a highly effective cycle process for separating the chlorine from the silicon tetrachloride. while at the same time avoiding that the resulting silicon by any impurities, which may be present in the silicon tetrachloride or in the conversion process are introduced is contaminated. The third stage represents a convenient removal of the obtained ultrapure silicon from the apparatus, which conveniently comprises a quartz or silicon dioxide tube, in which the silicon is deposited, which can then be melted into bars or the like.

In the first stage, the silicon tetrachloride to be cleaned is first mixed with a solvent, preferably dichloromethane, trichloromonofluorommerane or trichlorotrifluoroethane. The mixture of silicon tetrachloride and solvent is then passed through an adsorption column. He is filled with activated alumina. The solvent can then be fractionated off and reused. The impurities in the silicon tetrachloride, in particular those which could possibly interfere with the further process according to the invention, are adsorbed by deactivated alumina. Silicon tetrachloride, being non-polar, is not strongly adsorbed, but impurities such as boron trichloride and phosphorus trichloride, which are polar in nature, are adsorbed quite completely.

In the second stage, a mixture of silicon tetrachloride and hydrogen is heated by a Zone passed through in which the reaction to form silicon and hydrogen chloride he follows. Silicon tetrachloride is expediently added to the gas mixture flowing out of the reaction zone added to replenish the material consumed in the reaction zone, the hydrogen chloride and

■ r replenishment of added hydrogen or hydrogen in the mixture can be removed and the Mixture returned to the reaction zone will. By reusing zinc vapors to break down the hydrogen chloride in the exhaust gas from the Reaction zone to replenish the hydrogen in the mixture and form zinc chloride as a N-product it is possible to carry out a cleaning step at the same time that the mixture is on their correct ratio between silicon tetrachloride and hydrogen is brought back. The education of zinc chloride and its subsequent removal,

ίο z. B. by settling and filtering through a Filter material, such as glass wool, also removes incidental impurities from the mixture and ensures that there is no contamination of the end product is avoided. The unused silicon tetrachloride and the hydrogen, which again are fed back, do not add any new impurities, and the «leads to a simplification the task of keeping the system free of contamination Condition.

The third final stage is expediently carried out periodically instead of continuously and consists of that Removing the area on which the silicon has deposited in the reaction zone and the Ent away the silicon from this surface. Usually a quartz tube or a tube that is made of almost pure silica is used for this purpose, and in general it is necessary to do so Breaking the tube to extract the silicon Quartz, which does not separate from the silicon easily let can be separated by leaching with hydrofluoric acid. The silicon is afterwards converted by melting into ingot form or another suitable form.

The invention is exemplified below a representation of a preferred embodiment of the overall method explained in more detail.

Fig. 1 is a flow diagram of the overall process according to the invention;

Fig. 2 is a schematic representation of the distillation and adsorption stage according to the invention; Figure 3 is a flow sheet of the silicon deposition stage of the process according to the invention;

Fig. 4 is a schematic representation of an apparatus for performing the silicon deposition step of FIG Method according to the invention, with certain parts cut away to illustrate the working elements are.

As illustrated in Fig I, silicon tetrachloride, generally reagent grade which is not ultra pure at this point in the process. first led into a distillation and adsorption stage 1, which cleans the silicon tetrachloride and ati ^ removes impurities from him which may later be detrimental to the process could. From this distillation and adsorption stage the silicon tetrachloride goes into a fractionation column, where it is removed from solvent and remaining Ver impurities is separated, and then to a cyclic silicon deposition stage 2, in which also metallic Zinc is introduced, and at this stage of the process the silicon is removed from the silicon tetrachloride separated and deposited in a highly purified form, usually in a quartz or Silica tube. From this stage of the process. " in which zinc chloride is formed as a by-product the highly purified silicon usually trapped in the quartz or silica tube is removed is in which it was cast down. In the final stage 3 of the process, the quartz tube removed from the silicon and the silicon under

carefully regulated conditions to prevent contamination melted together and in Bars or another suitable form for further use.

The distillation and adsorption process is preferably carried out in an apparatus as shown in FIG Type executed This apparatus can consist of quartz in order to increase the purity of the product to enhance. But this is not absolutely necessary. The silicon tetrachloride is in the storage room a separating funnel 10 and goes down through a stopcock 11 of the funnel in a container 12 arranged below. An intermediate part 13 between the stopcock 11 and the ßehäller 12 creates the possibility for the entry of solvents such as dichloromethane, trichloromonofluoromethane or trichlorotrifloroethane which mixes with the silicon tetrachloride in container 12. The mixture then goes further down through a three-way stopcock 14 into an adsorption column 15 which is filled with activated alumina which seeks to adsorb the undesirable impurities from the silicon tetrachloride.

Silicon tetrachloride has a symmetrical molecule with no electric dipole moment with a stable one F. electron structure. that little or no tendency to form additional chemical bonds shows. In contrast, critical impurities, such as boron trichloride and phosphorus trichloride, asymmetrical structures that have perceptible di polmotnente and therefore have these connections a strong tendency to form additional chemical bonds. Hence, these become contaminants attracted and retained by the active surfaces of the alumina, while the silicon tetrachloride passes through. At the lower end of the adsorption column 15 is one with three necks provided bottle 16. which is heated by an electric heating jacket 17, which is equipped with a suitable Energy source (not shown) is connected by lines 18. The bottle contains some pieces of ouarz, UiTi to prevent violent boiling.

The bottle 16 is provided with a conventional thermometer 19 and also has a connection to it a solvent vapor return pipe 20, through which solvent vapor up to a Pair of water-cooled condensers 21 and 22 can occur. The solvent is condensed in these condensers and goes down into the Intermediate part 13 that returns it to the system. Any non-condensable gas entered through the condenser 21 and an acid adsorption pipe 23 with soda lime filling to the outside. When a sufficient circulation of solvent has taken place to remove all of the silicon tetrachloride which the Can process the apparatus in one operation, to clean, the three-way stopcock 14 is turned so, that the solvent runs into a solvent recovery vessel 24. Most of the Solvent is removed from the system in this way. Escaping gas comes out of the system through an acid adsorption tube 24a connected to the solvent recovery vessel 24 in a conventional manner Way is connected. The individual parts of this system are common and therefore do not need to be described in more detail.

The silicon tetrachloride. which remains in the bottle 16 after most of the solvent is evaporated, is transferred to a fractionation column (not shown) and from there the remaining solvent and the remaining impurities are separated. This fractionation column is of conventional design, except that it is preferably made of quartz prevent contamination of the silicon tetracloride by materials such as boron and arsenic which, if glass were used, it could be leached out of it.

The purified silicon tetracloride is in the

ίο second stage of the process shown in FIGS. 3 and t is illustrated is used. A mixture of silicon tetrachloride, hydrogen and hydrogen chloride exits a silicon settling tube 31 continuously. Enough silicon tetrachloride is added to this mixture from a silicon tetrachloride reservoir 30 is added to that consumed in the settling tube 31 to fill up. The mixture, now enriched in silicon tetrachloride, goes into a zinc reaction tube 32, where it is mixed with zinc vapors from a zinc evaporator 33, which is at a temperature of about 900 to about 1100 ° C is maintained. The zinc reaction tube 32 itself is at a temperature held between about 600 and about 800 ° C. The zinc vapors settle in this reaction tube the hydrogen chloride to form zinc chloride and hydrogen. The silicon tetrachloride that Zinc chloride and the hydrogen then go to a cooling and settling chamber 34 which is the largest Part of the zinc chloride and other impurities is removed leaving only silicon tetrachloride and hydrogen going to a filter 35 go. This filter is preferably a glass wool filter and any residual zinc chloride or other solid impurities are removed here. The silicon tetrachloride and the hydrogen go from the filter 35 to a pump 36 and then to the silicon settling tube 31 which is at about 1100 to about 1300 ° C is heated. In the tube 31, part of the hydrogen settles with part of the silicon tetrachloride with the formation of hydrogen chloride and elemental silicon, which is called υ Pipe settles. The initial charge of hydrogen used in the process as well as any for replenishment purposes required hydrogen are introduced into the system before the zinc reaction tube 32.

So that there is no problem of pollution and the tube 31 is designed so that it the necessary Withstands temperatures, it has proven advantageous to use a silicon dioxide or a 96% silica-containing glass to use existing tube. That from the silicon settling pipe 31 emerging material is then, as stated above, mixed with additional silicon tetrachloride.

The preferred temperature for settling tube 31 is 1200 ⁰ C, for zinc evaporator 33 1050 ° C and for the zinc reaction tube 32 650 ° C.

A suitable analysis device 37 can be connected to the pipeline which carries the pump 36 and the silicon settling tube 31 connects so that a sample is either continuously or intermittently the gases that go to the A ^ bsetzrohr 31 can be taken and analyzed for control purposes. An infrared analysis unit and a heat conduction cell are preferably used for this analysis.

so that both the concentration of silicon tetra-chloride as well as that of the remaining hydrogen chloride can be determined.

From Fig. 4 it can be seen that in the flow diagram 3 schematically illustrated parts are included in a housing 40 with a

Opening 41 is provided, with which a suction fan Can be connected to od any vapors. Like. That can escape, to remove. The details of the analysis and control panel 42 are not shown as they are not part of the invention and can be changed to suit the particular case.

A typical composition of the gas entering the silicon settling tube 31 is 10% silicon tetrachloride, approximately 0.05% hydrogen chloride and the remainder hydrogen. The silicon tetrachloride content of this gas can vary between 5 and 20%, and the hydrogen chloride content of this gas is preferably as low as possible. However, the process also works satisfactorily with a somewhat higher hydrogen chloride content, e.g. B. up to about 0.5%.

A typical composition of the gases "leaving the silicon settling tube 31 would be 9.5% silicon tetrachloride, approximately 2% hydrogen chloride and the remainder hydrogen. The percentage of the Silicon tetrachloride can again fluctuate between 5 and 20%, whereby it is always a little lower is as the percentage of the input charge to silicon settling tube 31 due to settling \ on silicon in this one. A similar change in the percentage of hydrogen chloride can occur in the Outlet gas can be determined.

One of the most important features of the invention is that the silicon tetrachloride is in the star is introduced immediately before the zinc reaction tube 32. Accordingly, the silicon tends to be removed chloride is cleaned by passage through the hot zinc vapor before it hits the precipitation pipe achieved. Impurities are either removed by the zinc or tend to be very resistant «! - capable of preventing deposition in the silicon to be chamber. Therefore, the zinc steam cleans in addition to its main task of regeneration of the hydrogen also continuously both the incoming silicon tetrachloride and the circulating gas stream. In trial runs both pre-purified silicon tetrachloride as well as crude, undistilled silicon tetrachloride silicon very much high purity when the silicon was deposited according to the procedure described iv. Hence can. although pre-cleaning is highly desirable. the silicon deposition stage ain.h are carried out alone in order to To produce silicon, which is gan / /.ti for many purposes t'is satisfactory.

In addition to the characteristic inherent in it η so Self-cleaning, the system has the advantage of being complete Consumption of the silicon tetrachloride supplied to it as well as the advantage that there is very little Requires gas cleaning and delivery or extraction facilities.

The silicon is usually deposited on the inside of a quartz tube. In some cases the silicon has shown a tendency to peel off without having to break the quartz tube!

but in most cases the quartz tube must be destroyed in the process, but this is not a problem A particular problem. A part of the quartz often tries to stay together with the silicon, but this one Part can be leached away with hydrofluoric acid.

Claims (4)

Patent claims: 1. Process for converting silicon tetrachloride into highly purified silicon by means of Reduction by hydrogen, characterized in that a mixture of silicon tetrachloride, which is optionally pre-cleaned, and introducing hydrogen into a reaction zone maintained at a temperature so high that a substantial implementation with a subsequent deposition of silicon in the zone un ter formation of hydrogen chloride takes place, the unreacted silicon tetrachloride from the reaction zone and withdraws both hydrogen and the hydrogen chloride formed during the reaction, preferably additional silicon tetrachloride to the withdrawn mixture for replenishment of the material consumed in the reaction, selectively the hydrogen chloride from the mixture by treatment with vaporized zinc to produce hydrogen and zinc chloride removed, replacing the hydrogen consumed in the reaction and the resulting mixture circulate again through the reaction zone lal.it. 2. The method according to claim 1, characterized in that the zinc chloride formed can settle out of the mixture and the mixture is nitrated to remove residual zinc chloride and other impurities. 3. The method according to claim I or 2, characterized characterized in that the reaction zone is at a temperature between approximately 1 100 and approximately LWO-C is held. 4. The method according to any one of claims 2 and 3, characterized in that implementation of the zinc vapors with the mixture of silicon tetrachloride. W ater stoti and hydrogen chloride in one Ί temperature /. Between about (> () () and about 800 "C he follows. 3. \ experienced according to one of claims 1 to 4. characterized in that silicon tetrachloride that is assumed by doing with a LoMuig.sinitKl. like a halogenate kohlemvas.si r «tort. and performing an AiI containing activated alumina sorptioussaule as well as auschlii-lieiuk evaporation the solvent has been pre-mixed. Printed documents drawn in läetrricht:
Ziitschiifl for auorg chemistry. Vol. 2ü5. P. 143 and 1 sheet of drawings 809 787 502 3.