RU2258772C1 - Device for continuous grouped growing of oriented layers of silicon on a carbonic fabric - Google Patents

Abstract

FIELD: devices for continuous grouped growing of the orientated layers of silicon on a carbonic fabric.

SUBSTANCE: the invention is pertaining to the field of growing of polycrystallic layers from a melt of silicon and may be used in production of solar cells (photo-converters) Substance of the invention: the device consist of a crucible for a melt mounted inside a heater, a substrates connected to gears of their relocation and a capillary feeding mechanism. The substrates are made out of a carbonic reticulated fabric, and the capillary feeding mechanism consists of two horizontal sections, located to the left and to the right of the crucible, each of which has a tail swathed by harnesses out of a carbonic thread. The crucible is made with the bottom hollow elongated spout supplied with an independent heater, under the crucible there is a tank for a drain of the crucible residue, the inner surface of which is coated by a layer of a hexagonal boron nitride, and above the crucible a vibrating feeder for feeding the ground silicon is mounted.

EFFECT: the invention ensures growing of polycrystallic layers from a melt of silicon.

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Description

The invention relates to the field of growing polycrystalline silicon layers from a melt and may find application in the production of solar cells (photoconverters).

A device containing a crucible, a heater, a pulling mechanism and a device for maintaining the melt level in the crucible constant is known (Mason B. Deposition of a silicon film on ceramic sheet substrates. "Electronics", 1979, v. 52, No. 15, p.10-11) . This device allows you to grow layers of silicon on long ceramic substrates coated with a layer of carbon for wetting with a molten silicon, using horizontal gutter-shaped quartz crucibles.

However, the known device has several disadvantages. Thus, maintaining the melt level in the crucible constant is a difficult technical task. During the process of growing the layer, the process of “seeding” is necessary, which consists in overflowing the crucible with the melt using a level adjusting device, bringing the substrate into contact with the melt and forming the meniscus by raising the substrate to the required height above the crucible walls, which complicates the technology and reduces the installation performance. In addition, the ceramic substrate must be perforated, since otherwise it is impossible to create a back contact to the grown silicon layer. This further increases the cost of production. A device is known for growing oriented crystalline layers on a substrate (according to ed. St. USSR No. 949979, publ. 1982, Bulletin of inventions and discoveries, No. 45, p. 283), including a crucible for the melt mounted inside the heater, a substrate connected with a mechanism for its movement, and a feeder vertically located in the crucible, made of melt-wettable plates forming a capillary channel between themselves, and having sharp working edges for supplying the melt to the substrate. The substrate is perpendicular to the feeder plates.

The disadvantage of this device is the need to use only solid substrates. Upon receipt of the silicon layers, it is necessary to additionally make holes in the substrates for the hole of the back electrical contact to the silicon layer.

Another disadvantage of the known device is the unreasonably complex design of the feeder. It is made of precast graphite plates. It is economically more cost-effective to carry out the feeder monolithic, and capillary channels - half-open.

The known device does not provide for the supply of charge into the melting crucible. Maintaining the level of the melt in the crucible relative to the level of the substrate is provided by the gradual movement of the crucible up. This limits the performance of the continuous crucible tank process.

Another disadvantage of the known device is a single use of the crucible, because after each process, it is destroyed.

The above device is closest in technical essence to the claimed device, therefore, is selected as a prototype.

The technical result obtained by the implementation of the present invention is expressed in increasing the productivity of the device and lowering the material costs of the device due to the group growing of silicon layers on a carbon cloth, the repeated use of the crucible, and the use of a vibrating feeder to supply crushed silicon to the crucible.

The essence of the invention is that in a device for growing oriented crystalline silicon layers, including a melt crucible installed inside the heater, substrates connected to their movement mechanisms, and a capillary feeder, the substrates are made of carbon mesh fabric, the capillary feeder consists of two horizontal sections located to the left and to the right of the crucible, each of which has a shank wrapped in carbon fiber bundles, the crucible is made with a hollow bottom elongated nose An ohm equipped with an independent heater, a container is installed under the crucible for draining the crucible residue, the inner surface of which is covered with a layer of hexagonal boron nitride; a vibrating feeder mounted above it is used to continuously supply crushed silicon to the crucible.

Due to the presence of these features, it is possible to grow silicon layers on the surface of a group of substrates simultaneously. The execution of the capillary feeder in the form of two horizontal sections allows, while ensuring high performance, to use only one crucible with its silicon feeding systems and draining the crucible residue at the end of the process. The capillary channels of both sections of the feeder are connected and the hydrostatic pressure of the melt in them is the same.

A crucible with a hollow, elongated nose can be used an unlimited number of times, provided that the remainder of the melt is drained after completion of the process. The fused crucible residue can also be used as raw material for the following processes.

The proposed device is illustrated in the drawing. Thermal insulation, fasteners and mechanism parts are not shown on it.

A device for continuous batch growth of oriented silicon layers on a carbon fabric comprises a left heater 1 made of graphite, a carbon mesh fabric substrate 2 wound on a bobbin 3, a left section of a capillary feeder 4, a graphite crucible 5, a crucible heater 6 mounted above the crucible 5 vibration feeder of crushed silicon 7 with vibrodrive 8, crucible nose heater 9, reservoir 5, tank for draining crucible residue 10, right heater 11, right section of capillary feeder 12, left roller mechanism pulling 13 and the right mechanism - 14. The shank of each of the feeders is wrapped with carbon fiber bundles 15 for capillary melt supply. Carbon mesh substrate 2 is cut into measuring strips, densified with pyrocarbon and thermochemical cleaning with halogens. The bobbin 3 is placed in the growth chamber or beyond and is equipped with a brake for tensioning the substrates. Sections of capillary feeders 4 and 12 are made of dense graphite and are additionally subjected to thermochemical cleaning and compaction with pyrocarbon.

The inner surface of the vessel 10 for draining the crucible residue is protected by a layer of hexagonal boron hydride to prevent wetting with molten silicon and subsequent destruction after crystallization and cooling. The layer can be applied by rubbing boron nitride powder into the surface of graphite or by spraying from a BN suspension.

The crucible 5 is made of high-density graphite and goes through the same operations before use. Vibratory feeder 7 is made of fused silica (graphite, steel). The vibrodrive 8 is located above the housing of the vibrating feeder and is controlled by a voltage source located outside the growth chamber. The mechanisms 13 and 14 are also located outside the growth chamber and include pairs of rubberized horizontal rollers, gearboxes and electric drives with their control systems.

The device operates as follows.

Carbon mesh substrate 2 cut into measuring tapes, modified with pyrocarbon and thermochemically cleaned, wound on a graphite bobbin 3, equipped with a brake for tensioning the substrate, is installed inside the growth chamber or in a separate housing connected with it by vacuum-tight flanges. A graphite crucible 5 is installed in the cavity of the graphite heater 6. On the electrically isolated fasteners, the left 4 and right 12 sections of the capillary feeder are installed. The shanks of each section are wrapped with carbon fiber tows 15. Vibratory feeder 7 is loaded with purified crushed silicon. A vibrating actuator 8 is connected to the vibration feeder 7. The substrates 2 are discharged to the outlet slots of the growth chamber, which are closed by vacuum-tight covers. After pumping, the chambers turn on the heating system and reach a temperature exceeding the melting point of silicon. Then include a vibrator 8 and fill the crucible 5 with molten silicon. At the same time, crystalline silicon plug 16 is formed in the bottom hollow elongated nose of the crucible, which prevents the melt from draining. After that, the pumpdown is turned off and the growth chamber is filled with pure argon to atmospheric pressure. Then the covers of the outlet slots of the growth chamber are opened, the substrates are pulled, and their ends are tucked between the rollers of the traction mechanisms 13 and 14. Subsequently, argon is supplied at a flow rate that prevents the oxidation of molten silicon. After tensioning the substrates 2, the speed of their movement and the feed rate of crushed silicon are set. As products 17 (substrates with a silicon layer) are released, they are mechanically broken off, and the process continues until the silicon stock in the vibrating feeder 7 or substrates on the bobbin 3 is exhausted.

After the process is completed, the pulling mechanisms 13 and 14 are turned off, the grown substrates with a silicon layer are mechanically broken off to a level that allows closing the outlet slots of the growth chamber. The slots are closed with vacuum-tight covers, the flow of argon is stopped and pumping is turned on. Upon reaching a vacuum, the crucible nozzle heater 9 is turned on, after which the plug 16 is melted and the crucible residue is drained into the receiving tank 10.

Then all heating elements are turned off. After cooling the growth chamber, the crucible residue is removed from the receiving vessel 10. The crucible 5 remains intact and can be used in an unlimited number of cycles described.

Claims (1)

A device for continuous group growing of oriented silicon layers, including a melt crucible installed inside the heater, substrates connected to their movement mechanisms, and a capillary feeder, characterized in that the substrates are made of carbon mesh fabric, the capillary feeder consists of two horizontal sections placed to the left and to the right of the crucible, each of which has a shank wrapped in carbon fiber bundles, the crucible is made with a bottom hollow elongated nose equipped with independent a heater installed under the crucible vessel for draining residue crucible whose inner surface is coated with a layer of hexagonal boron nitride, and above the crucible is set vibrating feeder for feeding the crushed silicon.