Device for continuous growing of oriented layers of silicon on a carbon fabric

FIELD: devices for growing from a melt of polycrystalline layers of silicon used for production of solar sells.

SUBSTANCE: the invention is pertaining to the field of growing from a melt of polycrystalline layers of silicon and may find application in production of solar cells (photoconverters). The substance of the invention: the device includes a crucible for a melt, a heater, a substrate linked with the gear of its relocation and a capillary feeding mechanism. The substrate is made out of a carbon reticular fabric, the heater consists of two sections of heating: a square section, inside which the crucible is mounted, and a right-angled section located above the substrate. At that the cross-section of the heater components is selected so, that the section of heating of the crucible is overheated in respect to the section of heating of the substrate. For a capillary feeding of the melt of silicon from the crucible use harnesses made out of a carbon filament spooled on a tail-end of the feeding mechanism. For replenishment of the level of the melt in the crucible use a vibrofeeder to feed the crushed silicon. The technical result of the invention is an increased productivity of the device and formation of conditions for production of the orientated coarse-crystalline structure of a silicon layer on the substrate naturally open for making of the rear electrical contact.

EFFECT: the invention ensures an increased productivity of the device, production of the orientated coarse-crystalline structures of the silicon layers on the substrates.

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

A device containing a crucible, a heater, a pull mechanism and a device for maintaining the level of the melt in the crucible at a constant Mason B. application of a silicon film on the ceramic sheet of the substrate. "Electronics", 1979, t, No. 15, p.10-11). This device allows you to grow silicon layers on long ceramic substrates, coated with a layer of carbon to wetting by molten silicon, using zheloboobraznogo quartz crucibles.

However, the known device has several disadvantages. So, maintaining the melt level in the crucible is constant technical challenge. During the process of growing a layer of the required procedure "persecution", consisting in the overflow of the crucible melt using the devices for regulating the level, bringing the substrate into contact with the melt and the formation of a meniscus by raising the substrate to the desired height above the walls of the crucible, which complicates the technology and reduces the performance of the installation. In addition, the ceramic substrate is necessary to punch, because otherwise it is impossible to create the back contact to the grown layer of silicon. This is optional increases the cost of production.

A device for growing oriented crystalline layers on wetted by molten silicon substrates, comprising a crucible for melting installed inside the heater, substrate, connected to the mechanism of its movement, and the feeder vertically located in a crucible made of wetted by the melt plates forming between a capillary channel and having a sharp working edge for supplying the melt to the substrate (U.S. Patent No. 4022652, 01 J 17/18, 1977). This device is intended for growing a crystal layer on a substrate, which is tape the crystal grown from the bottom of the crucible. Plate feeder parallel to the substrate so that the substrate when moving slides on the outer side of the plates of the feeder.

Between the substrate and the plate forms a capillary gap, which when the device will be filled by the melt from the crucible similar to the gap between the plates of the feeder. The disadvantage of this device is the penetration of the melt from the top of the crucible at the bottom, as well as the fact that its upper part is only possible when using a pre-prepared solid substrates, the area of contact of the substrate with the melt, due to its flowing into the gap between the feeder and the substrate is determined by the area of the plates Pete the body, along which runs the substrate.

The significant value of the zone of contact of the melt with the substrate leads to a deterioration in the quality of the grown layer due to contamination of the melt impurities.

A device for growing oriented crystalline layers on a substrate by author. St. USSR №949979 (publ. 1982, Bulletin of inventions and discoveries, No. 45, s), comprising a crucible for melting installed inside the heater, substrate, connected to the mechanism of its movement, and the capillary feeder, vertically located in a crucible made of wetted by the melt plates forming between a capillary channel and having a sharp working edge for supplying the melt to the substrate. The substrate is perpendicular to the plates of the feeder.

The disadvantage of this device is the necessity of using only solid substrates. Upon receipt of the layers of silicon must also be in the substrate openings to allow the back electrical contact to the layer of silicon.

Another disadvantage of the known device is unnecessarily complex design of the feeder. He made teams of the plates and provided with sharp edges to reduce the area of the melt in contact with the substrate. When growing layers of silicon on a carbon mesh fabric must, on the contrary, took the ing the width of the zone of contact of the melt with the substrate, as the limiting stage of the process is the impregnation of the substrate with the melt, followed by conversion of the substrate material in the silicon carbide. The feeder is economically advantageous to perform solid, and the capillary channels, - semi-open.

The known device does not provide for the filing of the charge in the melting pot. Maintaining the melt level in the crucible relative to the level of the substrate provides a gradual crucible is moved up. This limits the performance of the continuous process capacity of the crucible.

The heater of the feeder and the crucible is made symmetrical with respect to the axis of extrusion of the substrate, in the case of growing layers of silicon leads to the formation of unoriented crystalline structure of the material.

The above device closest to the technical nature of the claimed device, therefore, selected as a prototype.

Technical result obtained by carrying out the present invention, is expressed in increasing productivity and creating the conditions for receiving the oriented crystalline structure of the silicon layer on the substrate, naturally open to create a back electrical contact.

To achieve the technical result in the device for growing oriented the crystalline silicon layers, includes a crucible for melting, heater, substrate, connected to the mechanism of its movement, and capillary crucible, the substrate is made of carbon mesh fabric, the heater has two heating sections: square, inside of which is installed the crucible, and rectangular, placed above the substrate, and the cross section of the heater elements is chosen in such a way that the heating section of the crucible was overheated relative to the sections of the heating substrate; capillary supply of molten silicon from the crucible using the wiring of the carbon filament wound on the shank of the feeder, to replenish the melt level in the crucible using a vibratory feeder feeder crushed silicon.

Due to the presence of these characteristics of the crystalline structure of the silicon layer is formed on a relatively "transparent" to the back metal contact to the substrate. The occupancy degree of the heater above the substrate enables you to create the tilt of the solidification front to the plane of the horizon, through which the front surface of the silicon layer does not inherit the structure of the substrate, and is formed exclusively by thermal conditions of the crystallization process. The result is optimum for solar silicon wafers structure including elongated along the direction of extrusion of grain large enough.

The use of carbon bundles from the Noah fabric for supplying melt to the feeder from the crucible allows you to prevent ingress of micro particles of silicon carbide from the crucible into the growing layer (the most promising form of a cheap mixture of silicon are waste molding silicon contains an inclusion of microcrystalline silicon carbide). In addition, the use of such binders can dramatically reduce the cost of renewal of technological equipment of expensive graphite, is also equipped with special coatings.

The use of vibratory feeder for feeding the crushed silicon in the crucible allows to increase the duration of a continuous process and to reduce energy consumption by reducing the dimensions of the crucible and zone heating.

The proposed device is illustrated in the drawing. Thermal insulation, fasteners and machine parts not listed.

Device for the continuous cultivation of oriented layers of silicon on a carbon mesh fabric contains a heater 1, is made of graphite, the substrate 2 of the carbon mesh fabric wound on a bobbin 3, the feeder 4 from dense graphite, graphite crucible 5, the feeder crushed silicon 6, vibrooccasion roller 7 and the pulling mechanism 8 of the substrate 2. The shank of the feeder wrapped bundles 9 of the carbon filament for capillary feed of the melt. The heater 1 is integral and provided with vertical slots to provide the necessary resistance. The substrate 2 made of mesh carbon-graphite fabric viscose fibres cut-to-length strip is subjected to compaction perople the Odom and thermochemical cleaning Halogens. Bobbin 3 is placed in the growth chamber on the bracket and provided with a brake tension of the substrate. Capillary feeder 4 is made of the dense graphite and optionally subjected to a thermochemical treatment and modification of the pyrocarbon to prevent cracking when in contact with molten silicon.

The crucible 5 is made from high-density graphite and goes to use the same operations. The vibratory feeder 6 is made of fused quartz. The vibrooccasion 7 is placed above the right end of the feeder and is controlled by a voltage source placed outside the growth chamber. The pulling mechanism 8 is placed outside the growth chamber.

The heater 1 includes a square (top view) the furnace crucible and rectangular section to ensure that the temperature in the cultivation layer of silicon on the substrate. The rectangular section is placed above the substrate. The cross section of the heater elements is chosen in such a way that the heating section of the crucible was overheated relative to the heating section of the substrate. This provides almost instantaneous melting of the crushed silicon, continuously coming into the crucible 5 from the feeder 6.

The device operates as follows.

Cut-to-length tape width up to 0.12 m, modified by pyrocarbon and otvergnutaya thermochemical cleaning carbon mesh substrate 2, wound on graphite reel 3, is equipped with a brake for tensioning the substrate is installed inside the growth chamber. In the cavity of a graphite heater 1 is installed graphite crucible 5 on the stand. On the retaining elements associated with insulated from the heater 1 designs, installs capillary feeder 4, the shank of which is wrapped bundles 9 of the carbon filament. On two supports attached to the vibratory feeder 6, loaded with crushed silicon 10. The vibratory feeder 6 connect the vibrooccasion 7. The substrate 2 is output to the exhaust slit growth chamber, which is closed vacuum-tight lid. After pumping chamber includes a heating system and reach temperatures exceeding the melting point of silicon. Then include the vibrooccasion 7 and fill the crucible 5 silicon. Then turn off the pump and fill the growth chamber with argon to atmospheric pressure. Then open the cover of the outlet slit growth chamber, pull the substrate and fill its end between the rollers of the pulling mechanism 8. In the future conduct a continuous flow of argon in the growth chamber. After the tension of the substrate 2 set the rotation speed and the rate of feed of crushed silicon 10. As the substrate with the silicon layer 11, it periodically mechanically breaks off, the process prodolzhaet is up to the exhaustion of the supply of silicon vibratory feeder 6 or the substrate on reel 3.

Device for the continuous cultivation of oriented layers of silicon, comprising a crucible for melting, heater, substrate, connected to the mechanism of its movement, and the capillary feeder, characterized in that the substrate is made of carbon mesh fabric, the heater has two heating sections: square, inside of which is installed the crucible, and rectangular, placed above the substrate, and the cross section of the heater elements is chosen in such a way that the heating section of the crucible was overheated relative to the heating section of the substrate; capillary supply of molten silicon from the crucible using the wiring of the carbon filament wound on the shank of the feeder, to replenish the melt level in the crucible using a vibratory feeder feeder crushed silicon.



 

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