DE2938670A1 - METHOD AND DEVICE FOR PRODUCING AND POURING LIQUID SILICON - Google Patents

Description

PAT DEALERS

Dipl.-Ing. A. Wasmeier _n Dipl.-Ing. R count

Patent attorneys P.O. Box 382 8400 Regensburg 1

J _{1n the} D-8400 REGENSBURG

German Patent Office Greflinger Strasse 7

Telephone (09 41) 54753

8 Munich 2 Telegram Begpatent Rgb.

Telex 6 5709 repat d Your reference your message Our reference day 2M-, September 1979 Your (M. Your Letter Our Ref. Date y Λτ

C / p 10,026

Applicant: Justice Neale Carman, II30 W. Currie Avenue, Santa Ana, California 92707, USA

Title: "Method and device for producing and pouring of liquid silicon "

Inventor: like applicant

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Accounts: Bayerische Vereinsbank (BLZ 750 200 73) 5 839 300 Jurisdiction Regensburg Post check Munich 89369-801

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"Method and device for the production and casting of liquid silicon".

Summary;

The invention relates to a method and a device for producing liquid silicon of high purity and for Pouring silicon. There are hydrogen and a hydrogenated silane in a gaseous state, preferably with a low Amount of oxygen, mixed in a heated chamber and it is produced liquid silicon, whereby the exhaust gases bubble-shaped emerge from the melt under a baffle. The chamber for the melt of liquid silicon is preferably with silicon dioxide lined. The liquid silicon can be used for the production of high purity vitreous silicon dioxide and also for the production can be used by castings made of silicon. During the manufacture of cast parts, the liquid silicon is stored in a second chamber is accumulated and periodically moved from the second chamber to a third chamber containing the mold for the casting.

The invention relates to a method and a device for producing liquid silicon of high purity, as it is for Use in the manufacture of vitreous. Silicon dioxide according to the patent application P 27 35 516.4 and is suitable for the production of cast parts made of silicon. The poured silicon can the shape of tablets for crystal pullers, the shape of tubes and tubs for use in semiconductor processing equipment, take the form of infrared transmission windows and the like.

Vitreous silica is detailed in the Encyclopedia of Chemical Technology, 2nd Edition, Volume 18 by Kirk-Othmer on pages 73-105. There are different types of Silicon dioxide glass in the article "Properties and Structure of Vitreous Silica" by R. Bruckner in "Journal of Non-Crystalline Solids "5 (1970), pp. 123-175. This article describes

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four types of silica glass according to the type in which they are made and "also refers to a fifth type made in a plasma flame.

The silicon produced by the method and device according to the prior art has various disadvantages, esp. the inadequate purity. The object of the present invention is therefore to provide a method and a device for production of liquid silicon, the purity of which is only limited by the purity of the starting material.

According to the invention it is proposed that a pool of liquid silicon is maintained in a first chamber, the an inner wall made of silicon oxide (silicon dioxide) possesses that hydrogen and at least one halogenated silane in gaseous form State directly above the pool of liquid silicon that the hydrogen and the halogenated are continuously mixed Silane are heated, the reaction producing additional liquid silicon in the pool that the pool of liquid silicon is kept saturated with oxygen and that liquid silicon is continuously withdrawn from the pool.

In a further embodiment of the invention, a device for producing silicon is proposed, which is identified by a device for forming a first chamber for liquid silicon, a device for heating the first Chamber, a device that allows hydrogen and at least one gaseous halogenated silane to flow into the first chamber directed, and a device for removing exhaust gases from the first chamber.

Streams of hydrogen and halogenated silane in gaseous state have been mixed in a heated chamber to make liquid Obtain silicon. The exhaust gases are discharged from the melt under a guide surface in the form of bubbles and the chamber is preferably lined with silicon dioxide.

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The liquid silicon can flow from the first chamber into a second one Chamber to be transferred, in which liquid silicon is accumulated for the purpose of the production of castings, with the liquid Silicon is brought into a mold from the second chamber at periodic intervals. On the other hand, the liquid silicon for the production of high-purity, vitreous silicon oxide are used, as described in the aforementioned earlier application of the Applicant is described.

Further features of the invention are the subject of subclaims.

The single figure of the drawing shows a sectional view of a device for the production and casting of liquid silicon.

The device according to the invention has a source 10 of liquid silicon, preferably the one shown in the drawing Shape on. A container 11 has an outer wall 12 made of a refractory metal such as tungsten or molybdenum, and a inner lining 13 made of quartz glass. The container can thereby be made that quartz glass is brought into the desired configuration and then the metal outer layer by plasma spraying is applied. A pool of liquid silicon 15 is thereby created creates a stream of hydrogen in line 16 and a trichlorosilane be mixed in line 17. The silicon will heated above its melting point of 1685 ° K, e.g. with the aid of an induction heating coil 20, which is arranged above the chamber 11. If desired, silicon tetrachloride can be used in conjunction with or can be used in place of trichlorosilane. Other halogenated Silanes can also be used, but most of them are more expensive or difficult to work with.

The two materials mentioned above are the only two at the moment. known materials that are available in commercial quantities.

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The gases flowing into the tubes 16, 17 are heated by a further induction heating coil 21; the tube 16 preferably has an inner liner 22 made of tungsten and an outer layer 23 made of quartz glass. The excess gases from the reaction causing the Liquid silicon forms, reach the outside in bubbles around a guide wall 26 and are removed as exhaust gases via the outlet line 27 .

A second chamber 30 is arranged below the chamber 11 and is preferably designed similar to the upper chamber 11, with an outer wall 31 made of heat-resistant material and an inner lining 32 made of quartz glass. The chamber 30 can be heated by a further induction heating coil 33.

A mouth, preferably in an insert 36 at the junction between the upper chamber 11 and the lower chamber 30 » provides a continuous flow of a fine stream of liquid silicon into chamber 30. Typically the insert consists of a high temperature resistant material, e.g. silicon carbide.

The silicon produced in the chamber 11 can be taken directly from the chamber for further use, e.g. for production of vitreous silica to make castings and other uses. When castings are made, is it is convenient to use the chamber 30 to collect a certain amount of the liquid silicon necessary for the desired casting is sufficient, the liquid silicon of the chamber 30 is added from chamber 11 in a continuous stream while it is withdrawn from chamber 30 periodically to fill a mold will.

A shape handling configuration is shown in the drawing. It is desirable to carry out the casting process in an inert atmosphere. This can be achieved by making a mold 40 in a first chamber 41 is inserted through a door 42. When closed Door, the chamber 41 is evacuated via the line 43 and then filled with an inert gas via the line 44. then a sliding door 45 is opened, allowing movement of the mold

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the chamber 41 into another chamber 46 allows the shape is placed under an outlet of the chamber 30.

A mouth, preferably in an insert 50 at the lower end of the Chamber 30 provides a flow of liquid silicon from the chamber into the mold. In particular, the insert consists of a high-temperature resistant one Material, e.g. silicon carbide. An induction heating coil 51 is located around the insert and can be used to control flow through the orifice. Is the heating coil 51 switched off, the silicon solidifies at the mouth and blocks the flow from the chamber 30. When a casting is to be made, the heating coil 51 is turned on, whereby the silicon is liquefied at the mouth and allows the flow of liquid silicon from the chamber 30 into the mold 40. if the mold is filled to the desired level, the electrical energy for the coil 51 is switched off, whereby the silicon in the Muzzle is made to solidify. The mold is now ready to be removed from the chamber 46. You can use the Chamber 41 can be removed, or a different exit chamber may be provided so that an empty mold is inserted over chamber 41 can be, whereby the time interval between castings can be reduced.

The mold is expediently made of titanium because this has a high melting point; the inner surface is preferred

d coated with a layer of silicon oxide that is sprayed on can. However, the mold can also be made of silicon with a silicon dioxide lining exist. As a further alternative, the mold can consist entirely of silicon dioxide, similar to the conventional ones Crucibles used for Czochralski crystal growth. The part of the arrangement near the muzzle outlet including the sleeve 55 and the plate 56 is preferably made of a refractory metal such as tungsten and a water cooling tube 57 may be mounted on the plate 56. Others Parts of the chambers 41, 46 can consist of steel or other metals. The plate 58, which forms the bottom of the chambers 41 and 46, can be cooled by a water cooling pipe 59. The cooling

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the chambers 11 and 30 can be replaced by another water cooling pipe 60, which is received on a sleeve 61 arranged above the chambers, can be achieved.

The chamber 11 is heated so far that the silicon in molten State is maintained, preferably in the range from 1.700 to 1,900 K. It is desirable that the reaction gases be heated beforehand before they are introduced into the chamber 11 to enhance the reaction, and this can be achieved by the induction heating coil 21 will. Other methods of preheating the gas can be used, but the separate ones are preferred Gas flows into the chamber just above the liquid silicon. The incoming gas flows result in a pressure in the chamber 11, the exit of the stream of liquid silicon into the chamber 30 supports.

While the present invention relates to a method and apparatus for producing pure silicon, various modifiers and dopants are used. If the end product is to be an oxide, e.g. silica, are common Hodificators used. Below are some modifiers given as examples. The softening point of molten silicon oxide can be increased by about 100 ° K by adding the The order of magnitude of 0.20 to 0.25% aluminum oxide is added to the silicon dioxide. This can be achieved by using an aluminum halogen, e.g. aluminum chloride, is introduced into the trichlorosilane gas inlet.

The inclusion of about 10% titanium dioxide reduces the thermal expansion coefficient of silicon dioxide from 55 x 10 about zero. Titanium dioxide also prevents the refractive index of

di * ~
Silicon oxide. Titanium dioxide can be added in the form of titanium tetrachloride.

The addition of about 1/4 to 1/2% neodymium oxide results in silicon Dioxide that is suitable for use as laser glass. The neodymium can be introduced as neodynium chloride. All these

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Metallic halogens become gaseous when heated and can easily be handled in the device described here.

If the end product is to be a semiconductor, dopants can be used. Typical dopants are boron, aluminum, Gallium, phosphorus, arsenic and antimony, which are used in conventional amounts for semiconductors. The dopant can can be introduced into the silane gas stream in the form of a gaseous compound; typical compounds are diborane and phosphene and arsenic.

Silica has a solubility in molten silicon on the order of 1 to 10 parts per million. If so a silica liner is used for a molten silicon containing chamber, e.g., chamber 11, has that molten silicon has a tendency to erode the wall over a prolonged period of time. This erosion effect can thereby reduced or eliminated so that the molten silicon is kept saturated with oxygen,

In the embodiment described here, this can be achieved can be achieved that the hydrogen streams a small amount of Water vapor is added. Preferably, a silicon dioxide lining is provided within the tungsten 22 of the tube 16 in order to to protect the metal against the oxidizing effect of water vapor.

In an alternative embodiment, a small amount of oxysilane, on the order of 1 to 10 ppm, is added to the halogenated Silane is used so that the oxygen for the silicon is present.

The optimal amount of oxygen source material is best determined experimentally with the special facility.

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L e r s e i t e

Claims (18)

9/24/1979 W / He - * T- C / p 10,026 claims: 1. A method for producing silicon, characterized in that a pool (15) of liquid silicon is maintained in a first chamber (11) which has an inner wall made of silicon oxide (silicon dioxide), that hydrogen and at least one halogenated silane (10, 17 ) are continuously mixed in the gaseous state directly above the pool of liquid silicon, that the hydrogen and the halogenated silane (10, 17) are heated, the reaction producing additional liquid silicon in the pool (15) that the pool (15) of liquid silicon is kept saturated with oxygen, and that liquid silicon is continuously withdrawn from the pool (15), 2. The method according to claim 1, wherein the reaction generates exhaust gases, characterized in that the level of the pool (15) is liquid Silicon is held above the lower edge of an exhaust baffle (26) which has a gas outlet (27) from the reaction section the first chamber (11) separates, so that the exhaust gases from the pool (15) of liquid silicon under the baffle (26) in the Sasauslaß (27) emerge in the form of bubbles. 3. The method according to claim 2, characterized in that liquid Silicon from the pool (15) in. The first chamber (11) into a second chamber (50) is transferred at a speed at that the level of the pool in the first chamber (11) is maintained above the lower edge of the baffle (26), and liquid silicon is accumulated in the second chamber (50), and that the silicon is heated in the second chamber (30) to keep it in a liquid state. 4. The method according to claim 3, characterized in that liquid Silicon is periodically transferred from the second chamber (30) into a mold for producing a silicon casting. 130014/0677 9/24/1979 W / He - 2 - C / p 10.026 5. The method according to claim 3 »characterized in that the Steps of mixing and accumulating are carried out in chambers, which are lined with silicon dioxide. 6. The method according to claim 1, characterized in that the oxygen is added in that a small amount of oxysilane is introduced into the halogenated silane. 7. The method according to claim 1, characterized in that the Silane is at least trichlorosilane or silicon tetrachloride. 8. The method according to claim 1, characterized in that the mixing process is carried out in a chamber filled with silicon dioxide is lined. 9. The method according to claim 1, characterized in that the Oxygen is added by introducing a small amount of water vapor into the hydrogen. 10. Device for the production of silicon, characterized by a device (11) for forming a first chamber for liquid silicon, a device (20) for heating the first chamber (11), a device (16, 17), the currents of Hydrogen and at least one gaseous halogenated Silane is directed into the first chamber (11), and a device (27) for removing exhaust gases from the first chamber (11). 11. Device according to claim 10, characterized by a divider (26) extending from the upper surface of the first chamber (11) runs downwards and separates the incoming streams and the exhaust gases. 12. Device according to claim 10, characterized by a device. That oxygen in the first chamber (11) with a of the streams of hydrogen (16) and hemogenized silane (17) directs. 1300U / 0677 copy 9/24/1979 W / He - 3 - C / p 10.026 293867Q 13. Device according to claim 10, characterized in that the first chamber (11) has an outer metal jacket (12) and an inner one Has lining (13) made of silicon dioxide. 14. Device according to claim 10, characterized in that a second chamber (30) is provided which accumulates liquid silicon, and that a device (36) the first and second Chambers (11, 30) for the flow of liquid silicon from the first chamber (11) into the second chamber (50) connects. 15. Device according to claim 14, characterized in that the first and second chambers (11, 30) have an outer metal jacket (12, 31) and an inner lining (13, 32) made of silicon dioxide own. 16. Device according to Claiml4, characterized in that a third, the mold (40) receiving chamber (41) below the second Chamber (30) is arranged, and that a device (50) is provided which connects the second chamber (30) with the third chamber (41) connects for the flow of liquid silicon from the second chamber into the third chamber. 17. Device according to claim 10, characterized in that the Device (16, 17) <directs the currents into the first chamber (11), Has metal pipes (16, 17) with a silicon dioxide lining (22), and that an induction heating coil (21) over the pipes (16, 17) is arranged. 18. Device according to claim 17, characterized in that one of the tubes (16 or 17) is arranged within the other (17 or 16) of the tubes and that a spiral heating coil (21) over the Pipes is arranged. 130014/0677 COPY