Gas flow guiding device for use in crystal-growing furnace

The present invention relates to a gas flow guiding device for use in a crystal-growing furnace. The gas flow guiding device has an insulation layer enclosing a crucible, a gas inlet mounted in the upper insulation layer, and a gas exit formed in the lateral insulation layer. A plurality of guide plates are radially arranged around the opening of the gas inlet, so that the free surface of the melt is blown by the guided gas flow in such a manner that the gas flow takes the impurity away from the free surface efficiently. As a result, the crystal ingot obtained by solidifying the melt will exhibit a reduced concentration of impurities and an improved crystal quality.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a gas flow guiding device for use in a crystal-growing furnace, and more particularly, to a gas flow guiding device for use in a crystal-growing furnace that is capable of effectively reducing the impurities present in a crystal ingot produced thereby.

2. Description of the Prior Art

It is known in the art that a solar cell is a non-pollutant renewable energy source that can directly generate electric power by virtue of the interactions between the sunlight and chemical materials. Especially, the solar cell will not discharge any undesired waste gas during use, such as CO2, so that the solar cell is promising in helping environmental protection and solving the problem of the earth's greenhouse effect.

A solar cell is a device that is capable of converting the solar energy into electrical power by generating a potential difference at the P-N junction interface of a semiconductor device, rather than by transmission of electrically conductive ions via an electrolyte. The semiconductor device will generate a tremendous amount of electrons when struck by the sunlight, and the movement of the electrons results in a potential difference at the P-N junction.

The modern solar cells are typically made by three types of materials: amorphous materials, mono-crystal materials and poly-crystal materials.FIG. 1illustrates a furnace for producing a silicon crystal ingot, which primarily includes a crucible21for containing a silicon melt11. The crucible21is provided circumferentially with a lateral insulation layer22and an upper insulation layer23, so as to constitute a hot zone, in which a heater24are equipped to provide heat to silicon .

The upper insulation layer23is further provided with a gas inlet25used for introducing an inert gas, whereas the lateral insulation layer22may be formed with a gas exit26. During the process of melting the silicon by heat, a gas is introduced into the furnace at a predetermined flow rate through the gas inlet25to generate a gas flow passing through the hot zone and, thus, carrying the impurity away from the furnace via the gas exit26.

A crystal ingot12may be obtained by reducing the output power of the heater24(casting process), or by moving the lateral insulation layer22upwards to allow radiant cooling of the crucible21(directional solidification system process), to thereby solidify the silicon melt11contained within the crucible21.

Moreover, the crystal ingot12may also be obtained by additionally disposing a support28between the crucible21and a base27, so that the silicon melt11contained within the crucible21can be solidified by lowering the support28to draw the crucible21downwards to a cooling zone (Bridgman process), or by introducing a cooling fluid into the support28(heat exchanger process).

In the conventional furnace described above, however, the gas inlet25of the gas flow guiding device only slightly protrudes into the hot zone beneath the upper insulation layer23. As a consequence, the opening of the gas inlet25is located so far from the free surface of the silicon melt11contained in the crucible21(namely, the interface of the silicon melt and the gas) that the gas flow introduced through the gas inlet25fails to effectively carry the impurities away from the free surface and leads to an unfavorable result that the crystal ingot produced thereby has a high concentration of impurities and a reduced crystal quality.

SUMMARY OF THE INVENTION

Accordingly, an object of the invention is to provide a gas flow guiding device for use in a crystal-growing furnace that is capable of improving the quality of the crystal ingot produced thereby by effectively reducing the impurities present in the crystal ingot.

In order to achieve this object, a gas flow guiding device for use in a crystal-growing furnace is provided, which comprises an insulation layer enclosing a crucible, a gas inlet mounted in the insulation layer, and a gas exit formed in the insulation layer, so that the gas inlet is allowed to introduce a gas at a predetermined flow rate to generate a gas flow passing through the hot zone and carrying the impurity away from the furnace via the gas exit. A plurality of guide plates is radially arranged around the opening of the gas inlet, so that the free surface of the melt is blown by the gas flow guided by the guide plates. As a result, the crystal ingot thus obtained exhibits a reduced concentration of impurities and an improved crystal quality.

Preferably, the gas flow guiding device according to the invention additionally comprises a height-adjusting unit coupled to the gas inlet. The height-adjusting unit allows a precise control of the height of the gas inlet in relation to either the height of crucible or the height of the free surface of the melt during an actual operation, so as to maintain the distance between the opening of the gas inlet and the free surface of the melt contained in the crucible within a predetermined range. As a result, at a given gas flow rate, the impurities can be efficiently taken away from the free surface of the melt by the gas flow.

Preferably, the gas flow guiding device according to the invention additionally comprises an angle-adjusting unit provided between the respective guide plates and the gas inlet, so that the angles of the respective guide plates are adjustable according to the actual operation conditions. As such, the speed of the gas flow can be optimized depending on the growth of the crystal ingot and the quality of the crystal ingot produced can be precisely controlled.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a gas flow guiding device for use in a crystal-growing furnace that is capable of improving the quality of the crystal ingot produced thereby by effectively reducing the impurities present in the crystal ingot. As shown inFIGS. 2 and 3, the furnace according to the invention generally comprises a crucible31for containing a silicon melt41. The crucible31is surrounded circumferentially by an insulation layer32, so as to constitute a hot zone, in which a heater37are equipped to provide heat to silicon.

The gas flow guiding device according to the invention comprises a gas inlet33protruding from the insulation layer32, and a gas exit34formed in the insulation layer32, so that the gas inlet33is allowed to introduce a gas at a predetermined flow rate to generate a gas flow passing through the hot zone and, thus, carrying the impurity away from the furnace via the gas exit34. The gas flow guiding device is characterized by the technical features described below.

The gas inlet33is provided around its opening with a plurality of radially arranged guide plates36for guiding the gas flow from the gas inlet33to the regions surrounding the opening of the gas inlet33, so that the free surface of the melt41is blown by the guided gas flow in such a manner that the gas flow takes impurities away from the free surface at a more rapid rate compared to the prior art. As a result, the crystal ingot obtained by solidifying the melt41will exhibit a reduced concentration of impurities and an improved crystal quality.

The furnace that is equipped with the gas flow guiding device according to the invention may be a furnace designed to solidify the melt41contained within the crucible31by reducing the output power of the heater (casting process), or a furnace designed to solidify the melt41contained within the crucible31by moving the insulation layer32upwards to effect radiant cooling of the crucible31(directional solidification system process).

It is apparent to one having ordinary skill in the art that the furnace which is equipped with the gas flow guiding device according to the invention may be additionally provided with a support38connected to an underside of the crucible31, so that the melt41contained within the crucible31can be solidified by lowering the support38to draw the crucible31downwards to a cooling zone (Bridgman process), or by introducing a cooling fluid into the support38(heat exchanger process). All of the furnaces described herein may be provided with the gas flow guiding device disclosed herein to effectively reduce the concentration of impurities present in the crystal ingot42produced by solidifying the melt41, thereby improving crystal quality of the crystal ingot42.

Preferably, the gas flow guiding device according to the invention additionally includes a height-adjusting unit coupled to the gas inlet33and used to adjust the height of the gas inlet33in relation to the crucible31. The height-adjusting unit includes an internally threaded sleeve35inserted substantially vertically into the insulation layer32. The gas inlet33is provided on its outer surface with a threaded section331for engaging the threaded sleeve35, so that the relative height of the gas inlet33can be adjusted by rotating the gas inlet33in relation to the threaded sleeve35.

By virtue of the arrangement disclosed herein, the inventive gas flow guiding device for use in the furnace allows a precise control of the height of the gas inlet33in relation to the height of crucible31or the height of the free surface of the melt41during an actual operation, so as to maintain the distance between the opening of the gas inlet33and the free surface of the melt41contained in the crucible31within a predetermined range. As a result, at a given gas flow rate, the impurities can be more efficiently taken away from the free surface of the melt41by the gas flow according to the invention disclosed herein as compared to the prior art.

Preferably, the crucible31is configured to have a cuboidal internal contour as shown inFIG. 3or a cylindrical internal contour as shown inFIG. 4. The free ends of the respective guide plates36are kept apart from the internal wall of the crucible31by a predetermined distance. Preferably, in the gas flow guiding device according to the invention, two adjacent ones of the guide plates36are spaced apart at their free ends by a gap smaller than half of the width of the respective guide plates36.

In addition, the gas flow guiding device according to the invention may preferably comprise an angle-adjusting unit provided between the respective guide plates36and the gas inlet, so that the angles of the respective guide plates36are adjustable according to the actual operation conditions. By virtue of this arrangement, the speed of the gas flow can be optimized depending on the growth of the crystal ingot and the quality of the crystal ingot can be precisely controlled.

In actual practice, as shown inFIG. 5, the angle-adjusting unit may include a plurality of rails361, each mounted on the corresponding one of the guide plates36, and a plurality of linkages362, each disposed between the corresponding one of the rails361and the gas inlet33, such that the linkages362cooperate with the rails361to adjust the angle of the guide plates36relative to the gas inlet33. As shown inFIG. 6, the angle-adjusting unit may alternatively include a plurality of hinge elements363, each pivotally connecting the corresponding one of the guide plates36to the gas inlet33in such a manner that the angles of the respective guide plates36are adjustable relative to the gas inlet33, thereby fulfilling the needs of changing the speed of the gas flow. Preferably, the respective guide plates36are positioned at an angle between 8˜160 degree, more preferably at an angle of 90 or 150 degree, relative to the gas inlet33. Preferably, the crucible31is provided above with a cover39formed with a gas exit34.

The gas flow guiding device disclosed herein is tailored to dispose the guide plates36around the opening of the gas inlet33to allow the gas flow introduced through the gas inlet33to be guided by the guide plates36, so that the free surface of the melt41is blown by the guided gas flow in such an effective manner that the crystal ingot thus produced exhibit a reduced concentration of impurities.

In conclusion, the gas flow guiding device for use in a crystal-growing furnace as disclosed herein can achieve the intended objects and effects of the invention by virtue of the structural arrangements described above. While the invention has been described with reference to the preferred embodiments above, it should be recognized that the preferred embodiments are given for the purpose of illustration only and are not intended to limit the scope of the present invention and that various modifications and changes, which will be apparent to those skilled in the relevant art, may be made without departing from the spirit of the invention and the scope thereof as defined in the appended claims.