RU2472875C1 - Method for growing silicon monocrystal from molten metal - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method involves supply of working gas to the chamber with further evacuation of formed gas flow with steam-gas mixture formed above molten metal, which is located in a melting pot; at that, working gas is supplied to the chamber from below, for the meting pot, and steam-gas mixture is evacuated above the melting pot; at that, after gas flow is supplied to the chamber, it is directed along walls of the melting pot through heat-insulating material so that it is heated due to contact with heat insulation and its volume increases, which reduces its flow rate, extracts some part of heat from heat insulation, thus reducing the flow of cooling water and electric power, and when passing above the molten metal surface, it carries over steam-gas mixture in upward direction.

EFFECT: avoiding the action of corrosive steam-gas mixture on elements of heating system, thus considerably increasing its service life.

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Description

The invention relates to a technology for producing semiconductor materials for electronic equipment and photovoltaics, in particular silicon, obtained for these purposes by the Czochralski method.

As you know, the furnace equipment for growing silicon single crystals by the Czochralski method consists of graphite and carbon composite materials: more than 80% of the furnace equipment elements are made from these materials. As a rule, the growing process is carried out in a stream of pure argon using a quartz crucible for melt. A gas stream is formed to create a clean zone above the melt in the crucible and to remove from the crystallization region a vapor-gas mixture of silicon monoxide SiO and carbon monoxide CO, as well as other volatile impurities. In this case, the gas flow is directed both from top to bottom and from bottom to top, along the vertical axis of the melt crucible. In the first case, the vapor-gas mixture of argon with silicon and carbon monoxides is in contact with the elements of the thermal unit, leading to their destruction. However, in this case, the formation of, for example, silicon monoxide is not so intense, since the gas moving from top to bottom “squeezes” the silicon monoxide vapor, reducing the intensity of their formation. In the second case, the elements of the thermal unit are in contact with pure argon and are not destroyed. However, in this case, the gas moving from bottom to top picks up silicon monoxide vapor and the rate of monoxide formation increases, which leads to accelerated destruction of the crucible.

Silicon monoxide SiO is formed mainly as a result of a chemical reaction between molten silicon and a quartz crucible

Si + SiО ₂ ⇔2SiO

CO carbon monoxide is formed as a result of chemical reactions between a graphite support under a crucible and a quartz crucible

3C + SiО ₂ ⇔ SiC + 2CO,

C + SiO ₂ ⇔ SiO + CO,

between oxygen entering the chamber through seals and furnace accessories

2C + O ₂ ⇔ 2CO,

as well as between silicon monoxide SiO and furnace accessories:

2C + SiO⇔SiC + CO.

The formation of a vapor – gas mixture from cold argon, hot SiO monoxide, and carbon monoxide CO and other volatile compounds above the melt leads to their coagulation into microparticles, which are deposited on relatively cold surfaces inside the chamber, and are transferred into the melt surface by convective flows of this vapor – gas mixture in the chamber volume and fall into the crystallization region, which leads to disruption of the dislocation-free growth of a single crystal. Since gas flows constantly carry away silicon monoxide vapor from the surface layer above the melt, the process of their formation is intensive and their evacuation requires a large volume of argon.

A device is known for growing silicon single crystals from a melt (patent RU No. 2102539, IPC ⁷ C30B 15/00, 01/20/1998), in which openings for evacuating the gas stream are made in the lower part of the chamber, below the elements of the thermal unit. The vapor-gas mixture leaving the melt is directed through the hot (800-1500 ° C) elements of the thermal unit to the lower part of the evacuation chamber. In this case, aggressive combined-cycle flows destroy the heater and other graphite elements and lead to pollution of the chamber atmosphere.

The disadvantage of this growing process is the contact of silicon monoxide and other aggressive components of the exhaust gas-vapor mixture with the elements of the thermal unit (heater, screens, thermal insulation), which leads to their destruction and the need to disassemble the thermal unit to clean it after each melting. In addition, the growing process proceeds at high consumption of argon.

The closest in technical essence is the method of growing a silicon single crystal from a melt (patent RU No. 2241079, IPC ⁷ C30B 15/00, 11/27/2004), where the feed stream of argon is formed above the melt using the upper gas guide screen, captures the vapor-gas mixture from the region crystallization and free space and carries it to the holes for evacuation.

However, this method, although it minimizes, but does not exclude the contact of silicon monoxide and other aggressive components of the exhaust gas-vapor mixture with the elements of the thermal unit. In addition, cold working gas is supplied to the melt zone, which forms turbulent flows, mixing with the hot gas mixture, increasing the gas flow rate and the rate of formation of silicon monoxide, which reduces the service life of the quartz crucible and graphite elements of the thermal unit.

The objective of the invention is the formation of a flow of working gas in such a way as to reduce the consumption of working gas and electricity, as well as to eliminate the effect of aggressive steam-gas mixture on the elements of the thermal unit, which significantly increases its service life.

This object is achieved by the fact that in the method of growing a silicon single crystal from a melt in installations according to the Czochralski method, comprising supplying a working gas to a chamber followed by evacuating the generated gas stream with a vapor-gas mixture formed above the melt located in the crucible, the working gas is supplied to the chamber from below crucible, and the vapor-gas mixture is evacuated from above above the crucible. In this case, after being fed into the chamber, the gas flow is directed along the walls of the crucible, through a heat-insulating material with a developed surface, for example, granular silicon carbide, silicon nitride, silicon oxide or zirconia, so that the gas is heated from contact with thermal insulation, increasing in volume, which reduces it consumption. When warming up, the gas takes part of the heat from the thermal insulation, stabilizing the process thermodynamics in such a way that the excess heat is discharged by the thermal insulation mainly not through the water-cooled walls of the chamber, but by a stream of gaseous argon, reducing the consumption of cooling water and electricity. Hot gas passing above the surface of the melt carries up the vapor-gas mixture. Moreover, the mixing of hot gas with hot silicon monoxide is not accompanied by coagulation of the latter into microparticles, and the rate of gas flow can be controlled by the rate of formation of silicon monoxide, minimizing this process. This possibility arises due to a multiple increase in the volume of gas due to its heating during passage through thermal insulation with a developed surface and the associated increase in gas pressure in the chamber. As a result, the argon consumption is significantly reduced, the possibility of contact between the vapor-gas mixture containing aggressive monoxides and the elements of the thermal unit is excluded, most of the excess heat from the thermal unit is carried away by the argon flow, which greatly simplifies the chamber cooling system and reduces the energy consumption for the process of growing a single crystal.

The figure shows a diagram of the supply of the working gas and the evacuation of the gas mixture in the chamber of the installation for growing silicon single crystal from the melt.

The main advantage of the proposed method is the supply of working gas from below through a heat-insulating material, an increase in gas in the volume and cooling of the thermal insulation with the passing gas.

The implementation of this method is carried out in a plant for growing a single crystal of silicon 1 from melt 2 according to the Czochralski method.

The installation comprises a chamber 3 with several nozzles 4 for pumping out the vapor-gas mixture flow located above the guide well 5, a pan 6 with an opening for supplying the working gas combined with the vacuum inlet of the rod 7 of the crucible 8, a heater 9 located around the crucible 8 and mounted on the current leads 10. The entire space between the heater 9 and the chamber 3, as well as between the bottom of the crucible 8 and the pan 6 is covered with heat-insulating material 11. At the bottom of the chamber 3 there is a switchgear 12. For regulating pressure, speed flow and the formation of working gas flows on the pump nozzles 4 are installed control valves 13, 14.

The method is as follows.

Cold working gas is supplied from below through a gas distributor 12 located in the pallet 6 of the working chamber 3. Moving along the pallet 6 and the chamber 3 through the charge insulation 1 1, the gas is heated, thereby cooling the insulation. Then, the heated working gas leaves the thermal insulation and passes along the guide well 5 and melt 2. The gas reaches its maximum temperature and maximum volume already above the melt. In this case, the gas stream does not cool melt 2, but passes over the surface of melt 2, entraining a certain amount of a vapor-gas mixture of silicon monoxide SiO and carbon monoxide CO and other volatile impurities, rises and is evacuated. The trajectory of movement, the flow rate and the pressure of the working gas is formed by the guide well 5, the gas flow rate and the change in the pumping speed through the different pumping nozzles 4 using the control valves 13, 14.

Thus, the proposed method allows to reduce the consumption of working gas and cooling water and to save the graphite base of the heater from destruction, by eliminating the chemical effect of silicon monoxide on graphite at high temperature. The heater and the graphite parts of the thermal unit are always in an inert gas atmosphere, which in itself increases their service life. At the same time, the qualitative characteristics of the grown single crystals are improved by eliminating the source of additional pollution of the chamber atmosphere by the interaction products of the aggressive gas-vapor mixture with the elements of the heat unit.

Example 1. The growth of a single crystal of silicon in an argon flow with a heat-insulating filling of silicon carbide.

Silicon carbide crystals with a fraction size of 0.8 to 5 mm are used as thermal insulation in the furnace.

Initial silicon is loaded into crucible 8, the chamber is closed, pumped out to a pressure not higher than 0.01 Torr. Then the heating is turned on. Argon is also supplied from below from a distribution device 12. Argon consumption can be changed. Argon passes through a heat-insulating filling 11 along the pallet 6 and the chamber 3, heats up, thereby cooling the thermal insulation. Then the heated working gas exits the insulation and passes along the guide well 5 and the melt 2. Gas is pumped out through the nozzles 13, 14 at the same time.

The control valves 13, 14 are fully open. The gas pressure in the chamber is determined by the gas flow rate at the inlet.

Example 2. The growth of a silicon single crystal in an argon flow while maintaining a predetermined pressure above the melt with a heat-insulating filling of silicon carbide.

Silicon carbide crystals are used in the furnace as thermal insulation, with a particle size of 0.8 to 5 mm.

Initial silicon is loaded into crucible 8, the chamber is closed, pumped out to a pressure not higher than 0.01 Torr. Then the heating is turned on. Argon is also supplied from below from a distribution device 12. The argon flow rate is set constant, for example 30 l / min. Argon passes through a heat-insulating filling 1 1 along the pallet 6 and the chamber 3, heats up, thereby cooling the thermal insulation. Then the heated working gas exits the insulation and passes along the guide well 5 and the melt 2. Gas is pumped out through the nozzles 13, 14 at the same time.

The control valves 13, 14 are opened so as to provide a predetermined pressure in the chamber, for example 50 Torr. The gas pressure in the chamber is determined by the bore of the valves 13, 14.

Example 3. The growth of a single crystal of silicon in a minimum flow of argon while maintaining a predetermined pressure above the melt with a heat-insulating filling of silicon nitride.

In the furnace, crystals of silicon nitride are used as thermal insulation with a particle size of 0.8 to 5 mm.

Initial silicon is loaded into crucible 8, the chamber is closed, pumped out to a pressure not higher than 0.01 Torr. Then the heating is turned on. Also through the switchgear 12, argon is supplied from below. The argon flow rate is set constant, for example 5 l / min. Argon passes through a heat-insulating filling 11 along the pallet 6 and the chamber 3, heats up, thereby cooling the thermal insulation. Then, the heated working gas leaves the insulation and passes along the guide well 5 and melt 2. Gas is pumped out through only one pipe with a control valve 14.

The control valve 14 is opened so as to provide a predetermined pressure in the chamber, for example 50 Torr. The control valve 13 is closed. The gas pressure in the chamber is determined by the bore of the valve 14.

Claims (1)

A method of growing a silicon single crystal from a melt in installations according to the Czochralski method, comprising supplying a working gas to the chamber followed by evacuating the generated gas stream with a vapor-gas mixture formed above the melt located in the crucible, characterized in that the working gas is supplied to the chamber from below under the crucible, and the gas-vapor mixture is evacuated from above above the crucible, and after being fed into the chamber, the gas flow is directed along the walls of the crucible through the heat-insulating material so that, passing over the surface of the melt, it is heated gas carries up the gas-vapor mixture.

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