WO2012150153A1

WO2012150153A1 - Process for preparing silicon

Info

Publication number: WO2012150153A1
Application number: PCT/EP2012/057501
Authority: WO
Inventors: Markus Fuchs; Paul Fuchs; Günter Seidel
Original assignee: Wacker Chemie Ag
Priority date: 2011-05-04
Filing date: 2012-04-25
Publication date: 2012-11-08
Also published as: DE102011075215A1

Abstract

The invention provides a process for preparing silicon, comprising deposition of silicon in a reactor on a multitude of packings (2) present within a tubular, heated carrier body (1) which heats the packings (2) to a temperature at which silicon is deposited on the packings (2) as a result of thermal decomposition of a silicon-containing gas; and subsequent heating of the tubular carrier body (1), such that the packings (2) are heated to a temperature which corresponds at least to the melting temperature of silicon, and silicon deposited thereby melts away from the packings (2) and flows away into a receiving apparatus (6) for liquid silicon. Apparatus for preparing silicon, comprising a tubular, heatable carrier body (1), the tube containing packings (2) comprising a material selected from the group consisting of graphite, SiC, Si3N and quartz, at least one feed line (7) for reaction gas and at least one offgas line, two electrical connecting elements (3) in order to accomplish heating of the carrier body (1), and an outlet line (5) suitable for conducting liquid silicon out of the apparatus into a receiving apparatus (6).

Description

Process for the production of silicon

The invention relates to a process for the preparation of silicon.

Polycrystalline silicon (polysilicon in short) serves as a starting material in the production of monocrystalline silicon by means of crucible pulling (Czochralski or CZ process) or by zone melting (floatzone or FZ process). This monocrystalline silicon is cut into slices (wafers) and used for a variety of mechanical, chemical and chemo-mechanical processes in the semiconductor industry for the manufacture of electronic components (chips).

In particular, however, polycrystalline silicon is increasingly required for the production of monocrystalline or multicrystalline silicon by means of drawing or casting processes, this monocrystalline or multicrystalline silicon being used to produce solar cells for photovoltaics.

The polycrystalline silicon, often called polysilicon for short, is usually produced by means of the Siemens process. In this process, thin filament rods of silicon are heated in a bell-shaped reactor ("Siemens reactor") by direct current passage, and a reaction gas containing a silicon-containing component and hydrogen is introduced.

In addition, it is also known to suspend small silicon particles in a fluidized bed reactor directly such a reaction gas. The polycrystalline silicon produced in this way is in the form of granules (granular poly).

The silicon-containing component of the reaction gas is usually monosilane or a halosilane of the general composition SiH _n X_ _n (n = 0, 1, 2, 3; X = Cl, Br, I). It is preferably a chlorosilane, more preferably um Trichlorosilane. Mostly SiH ₄ or SiHCl ₃ (trichlorosilane, TCS) is used in admixture with hydrogen.

In the Siemens process, the filament rods are usually placed vertically in electrodes located at the bottom of the reactor, via which the connection to the power supply takes place. Two filament rods each are coupled via a horizontal bridge (also made of silicon) and form a carrier body for the silicon deposition. The bridging coupling produces the typical U-shape of the support bodies, which are also called thin rods.

High-purity polysilicon deposits on the heated rods and the bridge, causing the rod diameter to increase over time (CVD = Chemical Vapor Deposition).

DE 25 33 455 A1 describes a method for the production of silicon by thermal decomposition of a gaseous silicon source and deposition of the silicon on heated deposition rods. In contrast to the Siemens process, the deposition rods (preferably made of graphite with a quartz sheath) are held above the melting point of silicon and the silicon is collected in liquid form. A disadvantage of this method is that make power supply, contacting and power control as extremely difficult and the process is prone to failure.

WO 84/00156 A1 discloses another method for producing molten silicon by thermally reacting a gaseous composition in a reaction chamber, wherein the interior of the reactor chamber is maintained at a first temperature range above the melting point of silicon with a uniform flow of the gaseous composition, wherein unreacted Gas and exhaust gas and molten silicon are discharged from the reactor chamber. As a separation body in this process, an elongated hollow body, such as a hollow cylinder or a tubular body is provided. The depositing silicon drains off to the reactor bottom and is collected.

The heat is supplied indirectly via a leading around the outer periphery of the support body resistance heater.

The carrier body consists of graphite, which reacts superficially with the depositing silicon to silicon carbide.

However, especially in view of the high process temperatures, the silicon melt is endangered by impurities with carbon or by other foreign substances originating from the graphite.

According to US 4,265,859 A silicon is deposited by thermal decomposition of a silicon-containing compound on the inner walls of a tubular, multi-walled reactor in solid form and subsequently melted by an increase in temperature at the reactor walls. The deposition of the silicon in solid form allows lower process temperatures and in the case of using, for example, trichlorosilane lower hydrogen partial pressures for the reduction, so that also chlorosilanes can be economically implemented.

As wall materials glassy quartz, silicon carbide or graphite are used. As a result, however, contamination of the silicon produced by foreign substances from the reactor wall remains a problem. Quartz is particularly unfavorable as a wall material because it softens at the deposition temperatures and loses its dimensional stability.

Furthermore, located outside of the reactor, these annular surrounding heating elements can ensure no uniform over the entire separation surface temperature, so that the hotter wall areas near the gas inlet point are occupied much faster with silicon, as the colder, more distant therefrom Abscheideflächen. DE 4127819 AI relates to a method for depositing polycrystalline silicon on a tubular support body by thermal decomposition of a silicon-containing, gaseous compound and subsequent melting of the grown silicon layer, characterized in that the support body is heated by direct passage of current. Likewise disclosed is a device for depositing polycrystalline silicon on a tubular support body by thermal decomposition of a silicon-containing, gaseous compound and subsequent melting of the grown silicon layer, characterized by a support body of silicon which can be heated by direct current passage. WO 2008/134568 A2 describes the use of deposition plates or spiral bodies for the deposition of silicon. The separation bodies are heated by passage of current. After depositing silicon, the temperature of the precipitating bodies is raised above the melting point of silicon to produce liquid silicon.

In both of the last-mentioned methods and devices, the carrier bodies are heated by passage of current and serve in each case for depositing solid silicon, which is later melted off by further increase in the passage of current through the carrier bodies.

Because the carrier bodies have to be electrically conductive, certain materials are not suitable for the carrier bodies. This makes the procedures inflexible.

In addition, the active separation surface (inner surface of the tubular support body, surfaces of plates or spirals) is not optimally designed. In addition, the production of carrier spirals is complex and their use is problematic, since it has been shown that they can break easily. The object of the invention was to avoid the above-mentioned disadvantages of the prior art.

The object of the invention is achieved by a method for the production of silicon, comprising depositing silicon in a reactor on a multiplicity of random packings (2) which are located inside a tubular, heated carrier body (1) containing the fillers (2 ) is heated to a temperature at which silicon is deposited on the packing (2) by thermal decomposition of a silicon-containing gas; and then heating the tubular carrier body (1) such that the filling bodies (2) are heated to a temperature which corresponds at least to the melting temperature of silicon, thereby melting deposited silicon from the filling bodies (2) and into a receiving device ( 6) for liquid silicon.

The object is also achieved by a device for producing silicon, comprising a tubular, aufheizba- ren carrier body (1), wherein within the tube packing (2), comprising a material selected from the group consisting of graphite, Sic, Si3N and Quartz, at least one supply line (7) for reaction gas and at least one exhaust pipe, two electrical connection elements (3) to heat the carrier body (1) to accomplish, and a derivative (5), suitable for liquid silicon from the device in to remove a receiving device (6).

The tubular carrier body is preferably heated by direct passage of current. For this purpose, a power supply of the carrier body is provided. The carrier body must in this case consist of a conductive material.

Preferably, the carrier body for the deposition of silicon on the packing is heated to a temperature of 1300 to 1450 ° C. As a result, in the interior of the carrier body, where the fillers are located, a temperature of about 1050 to Reaches 1150 ° C, at which silicon is deposited on the packing.

The fillers themselves are not heated by passage of current. The heating of the packing to the required deposition temperature is effected by a heat radiation emanating from the carrier body and by convection.

The fillers may consist of both conductive and non-conductive material.

By thermal decomposition of a silicon-containing, gaseous compound, silicon is deposited on the packing. By subsequent melting of the grown silicon layer, liquid silicon can be obtained and removed by means of a receiving device for further processing.

In this case, a device is provided which transports the liquid molten silicon from the interior of the reactor to the receiving device. For this purpose, the system is preferably slightly inclined.

This device may be, for example, a quartz trough.

The invention will be explained below with reference to FIG. 1 in detail. Fig. 1 shows the schematic structure of a device suitable for carrying out the method.

1 shows the tubular carrier body. Carrier body 1 comprises a derivative 5 for liquid silicon.

FIG. 2 shows a multiplicity of random packings which are located inside the carrier body 1. 3 shows a power supply which heats the carrier body 1 by direct passage of current. 8 shows the reactor wall or reactor shell.

Between reactor wall 8 and support body 1 is a lining with graphite (insulation). FIG. 6 shows a device for receiving the liquid silicon, FIG. 7 shows a gas feed line.

Carrier body 1 is lined in the lower part 9 with quartz glass.

The core of the system forms according to FIG. 1, a tubular carrier body. 1

The outer walls of the separation plant (reactor wall 8) are preferably made of double-walled stainless steel and can be cooled, for example, with water.

In addition, Kühlvorrich ^¬ tions are also provided for the power supply lines 3.

The bottom of the device 6 for receiving the liquid silicon is also cooled with water.

Advantageously, the carrier body 1 is provided on its inner surface with a coating of silver in order to minimize energy losses due to heat radiation during operation of the system.

The supplied electric current can be uniformly brought to the carrier body 1 by means of a silver ring.

The process begins with the deposition of silicon on the packing 2 within the tubular carrier body 1. For this purpose, the carrier body 1 heats the filling bodies 2 in the interior to the deposition temperature. The silicon-containing reaction gas supplied via supply line 7 passes over the filling bodies 2 and builds up a solid silicon layer on the surfaces of the filling bodies 2 within the tubular carrier body 1. By supplying a purge gas, it can be prevented that silicon is deposited outside the deposition region.

Support body 1 is heated to a high temperature (about 1300-1450 ° C) for deposition of silicon on the filling bodies 2.

In this case, very little silicon is deposited on the carrier body 1.

The carrier body 1 is preferably made of graphite or CFC (carbon fiber reinforced carbon), a composite consisting of a C-fiber matrix, which is fed with carbon whose surface is preferably coated with SiC. The carrier body 1 is preferably heated by a direct current supply to about 1300-1450 ° C from a DC power supply, so that the inner packing 2 are heated to about 1050-1150 ° C by heat radiation and convection. With increasing deposition, the temperature of support body 1 is lowered in order to achieve optimum deposition rates also on the outer packing 2.

The deposition of silicon can take place until the gas flow is too low and the differential pressure between inlet and outlet of the gas becomes too high. When the growing silicon layer has reached the desired thickness, the deposition is stopped by inhibiting the supply of the reaction gas. After the deposition process, the gas inlet is stopped and the temperature of the carrier body is increased such that silicon melts away from the packing and drains off at the bottom of the carrier body 1 via discharge 5 into the intended receiving device 6, without being too contaminated by the heating tube.

This is done by increasing the current passage through carrier body 1, so that the temperature of the filling body 2 is increased beyond the melting point of the silicon addition.

The tubular design of the carrier body 1 ensures that any existing, local temperature differences on the separation surfaces of the packing 2 due to the radial heat radiation compensate rapidly, so that the silicon melts at the same rates.

Lead 5 is preferably a quartz channel to prevent contamination of the liquid silicon as it drains off.

Receiving device 6 is preferably a collecting trough in the form of a high-walled shell.

Fillers 2 may be fragments or custom molded parts made of graphite, SiC, Si 3 N or quartz-coated molded parts of the aforementioned materials or may consist entirely of quartz.

The effluent silicon is, for example, dripped off in a quartz glass sieve, poured into molds or removed in liquid form. It is particularly advantageous to remove the silicon as molten as possible to the destination of its further processing. When so much or nearly as much material has been melted off as previously grown, the melting phase of the process is terminated. For this purpose, the electric current flow of the power supply 3 is throttled. Briefly dripping silicon falls into the drip pan. 6

When the fillers 2 have reached the intended deposition temperature, the next deposition phase begins with the introduction of reaction gas.

The deposition and melting of silicon are repeated periodically in this way. Particularly advantageous is the simultaneous operation of several such deposition systems.

For this purpose, it is particularly advantageous to connect the systems in series and to provide a common power supply.

This makes it possible to keep switching losses of the regulated power supply much lower than in systems with individual power supply. The reaction gas passes via the supply line 7 directed into the inner reactor space.

The reaction gases and unreacted reaction gas leave the reactor space through an exhaust pipe 10.

The hydrogen is preferably introduced via a separate feed line into the reactor interior.

The invention has a number of advantages over the prior art.

It is particularly advantageous in the method according to the invention that no carrier spirals, which are expensive to produce, are necessary are. In addition, very different materials can be used for the packing in the context of the invention. While in the prior art, the carrier body used

must be electrically conductive, since they are themselves heated by current passage and deposited on these substrates silicon, need not be electrically conductive in the present invention used filler since the heating of the packing is carried out by the tubular support body.

The use of materials such as pure SiC or silicon nitride as deposition surfaces is not possible in the prior art methods and devices because they do not or only slightly conduct the electrical current.

However, just these two materials can be in very high

Purity, which has a positive effect on any contamination of the produced Fiüssigsiliciums.

The fillers, on which silicon is deposited, can thus consist of both conductive and non-conductive material.

It is particularly advantageous that the breakage of individual fillers can not impair the operability of the reactor, since the fillers are not used for power conduction.

It can be used without structural alteration of the reactor any filler (by number and geometric shape). The use of packing allows a much larger active separation area. This leads to a considerable increase in the efficiency.

The fillers are relatively easy to manufacture.

Furthermore, no uncontrolled aborting of the deposited and subsequently melted silicon can occur. There is a risk in the prior art that the carrier plates or spirals slip off and cause short circuits. The filling of the carrier body in the form of packing has a large surface area. Therefore, a comparatively high deposition rate results.

The filling may comprise broken granules or separately prepared fillers (e.g., high surface area tubing) of quartz, SiC or Si 3 N.

The filling is preferably poured into the tubular carrier body made of graphite or CFC. The assembly of the support body is not a great deal of effort. The internals of the reactor as the tubular support body are very robust.

The filling can be reused very often, so it has a long service life, since the filling can practically not be de- fect.

The reactor is preferably placed horizontally with a slight slope towards the outflow of silicon. As a result, there is little contact between the liquid silicon and the packing during defrosting and draining. This leads to a comparatively low contamination of the silicon.

The inner side 9 of at least the lower part of the tubular carrier body is preferably lined with a quartz glass. This reduces the contamination of the silicon as it drains off.

Fillers are only on the inside 9 made of quartz glass. Above this, the filler to the heating tube at a distance of 1 mm can be up to about 20 mm

Claims

claims

A process for the production of silicon comprising depositing silicon in a reactor on a plurality of packing bodies (2) located inside a tubular, heated carrier body (1) which heats the packing bodies (2) to a temperature, wherein silicon is deposited on the packing (2) by thermal decomposition of a silicon-containing gas; and a subsequent heating of the tubular carrier body (1), so that the filling bodies (2) are heated to a temperature which corresponds at least to the melting temperature of silicon, thereby melting deposited silicon from the filling bodies (2) and into a receiving device ( 6) for liquid silicon.

2. The method of claim 1, wherein the tubular support body is heated during the deposition to a temperature of 1300-1450 ° C.

3. The method of claim 1 or claim 2, wherein during the heating of the tubular support body above the melting temperature of silicon no silicon-containing gas is fed into the reactor.

4. The method of claim 1, wherein the tubular support body comprises one or more of the materials selected from the group consisting of graphite, Sic, Si ₃ N, and quartz.

5. A device for producing silicon, comprising a tubular, heatable carrier body (1), wherein inside the tube filler (2) comprising a material selected from the group consisting of graphite, Sic, Si3N and quartz, at least one supply line ( 7) for the reaction gas and at least one exhaust pipe (10), two electrical connection elements (3) to accomplish a heating of the carrier body (1), and a derivative (5) suitable to remove liquid silicon from the device into a receiving device (6).

6. Apparatus according to claim 5, wherein a controllable power supply is connected to the electrical connection elements (3) and the carrier body (1) consists of electrically conductive material, so that the carrier body (1) can be heated by direct current passage.