HK1176746B

HK1176746B - Apparatus and method for purifying metallurgical silicon for solar cells

Info

Publication number: HK1176746B
Application number: HK13104106.8A
Authority: HK
Inventors: 星野政宏; 高政治
Original assignee: 星野政宏; 高政治
Priority date: 2010-08-16
Filing date: 2011-02-11
Publication date: 2015-10-30

Description

Apparatus and method for purifying metallurgical silicon for solar cells

Cross Reference to Related Applications

The present application claims priority from U.S. application serial No.61/374,213 filed on day 16, 2010, U.S. application serial No.13/023,467 filed on day 8, 2011, 2, 9, 2011, U.S. application serial No.13/024,292 filed on day 2, 9, 2010, taiwan application No.099104551 filed on day 12, 2010, which applications are commonly assigned with the present application, and the contents of which are incorporated herein by reference.

Technical Field

The present invention relates to an apparatus and a method for purifying a material. More particularly, the present invention relates to a method and system for purifying metallurgical silicon ore to produce feedstock suitable for manufacturing monocrystalline and multicrystalline silicon ingots for solar cells at a lower cost. Although the above describes aspects of purifying silicon, the invention may be used in other applications.

Background

Conventional polycrystalline silicon materials for the manufacture of solar cells are usually produced by the so-called Siemens process. This process is complete, stable and produces silicon of a certain quality for the manufacture of solar cells. However, the siemens process has limitations. That is, due to the nature of its manufacturing process, the siemens process is difficult to regulate and cannot meet the rapidly increasing demand over the past years and the demand for lower prices. Furthermore, it involves the use of toxic raw materials such as HCl and SiHCl in the manufacturing process₃And toxic by-product SiCl is produced₄. These materials are also highly explosive. The siemens process is also hazardous and harmful to the environment.

Alternatively, a silicon purification method using a metallurgical method is proposed. However, this purification method has limitations. That is, this method cannot be scaled up. Some other efforts have been made using metallurgical techniques. Unfortunately, the effort to build (scale) instruments for this technology is enormous and therefore the production costs are still high. These and other limitations are overcome by the techniques described throughout the present specification, and more particularly, the following specification.

From the foregoing, there is a great need for improved silicon production techniques.

Disclosure of Invention

The present invention relates to an apparatus and method for purifying a material. More particularly, the present invention relates to a method and system for purifying metallurgical silicon ore to produce feedstock suitable for the manufacture of monocrystalline and multicrystalline silicon ingots for solar cells at a lower cost. Although the above describes aspects of purifying silicon, the invention may be used in other applications.

The above manufacturing method produces silicon having a sufficiently high quality that can be used for solar cells. But with the growing demand for cleaner, more flexible products, lower costs and mass production capacity, the conventional methods have limitations. According to embodiments, one or more of these limitations may be overcome.

In a particular embodiment, the present invention provides a system for forming high quality silicon material (e.g., polysilicon). In a particular embodiment, the molten material includes a silicon material and an impurity, such as a phosphorous species. The system includes a crucible having an interior region. In a particular embodiment, the crucible is made of a suitable material, such as a quartz material or others. The quartz material is capable of withstanding high temperatures of at least 1400 degrees celsius for processing silicon. In certain embodiments, the crucible is configured in a vertical position and has an open area that exposes the molten material. In a particular embodiment, the system has an energy source. The energy source may be an arc heater or other suitable heating device, including multiple heating devices that may be the same or different. An arc heater is disposed above the open region and spaced apart by a gap between the exposed molten material and a spout region of the arc heater to form a determined temperature distribution in the vicinity of a central region of the exposed molten material while maintaining a temperature of an outer region of the molten material below a melting point of the quartz material of the crucible. In a particular embodiment, the system produces a molten material that includes 0.1ppm and less than 0.1ppm of final phosphorus species, which is purified silicon.

In a particular embodiment, the present invention provides a method of forming high quality silicon material (e.g., polysilicon). The method includes conveying a feedstock silicon material in a crucible having an interior region. The crucible is made of a quartz material or other suitable material capable of withstanding a temperature of at least 1400 degrees celsius. The method includes subjecting the raw silicon material in a crucible to thermal energy to melt the raw silicon material into a liquid state to form a molten material at a temperature below about 1400 degrees celsius. Preferably, the molten material has an exposed area bounded by the inner region of the crucible. The method also includes subjecting the exposed inner region of the molten material to an energy source comprising an arc heater disposed above the exposed region and spaced apart by a gap between the exposed region and a spout region of the arc heater to form a defined temperature profile in the vicinity of the exposed inner region of the molten material while maintaining the temperature of the outer region of the molten material below the melting point of the quartz material of the crucible. Preferably, the method removes one or more impurities from the molten material to form a higher purity silicon material in the crucible.

In a particular embodiment, the arc heater is a plasma gun configured to emit an excited argon species to transfer heat to a portion of the molten material. In certain embodiments, the arc heater is configured to face a selected portion of the exposed area of molten material. The arc heater is provided with a heat transfer means to cool the arc heater. In a particular embodiment, the arc heater is capable of being fired by a power source. Preferably, the arc heater includes a power rating of 20kW and above 20kW and is capable of pulsing according to a duty cycle of about 30% to 50% or otherwise. For example, a duty cycle of 30% means 30% on, 70% off, as will be appreciated by those of ordinary skill in the art. In a particular embodiment, the spout region has a maximum dimension of about 0.5 cm to about 2 cm. Of course, there can be other variations, modifications, and alternatives.

In certain embodiments, the temperature profile is determined to achieve certain results. That is, this temperature profile is a maximum temperature profile greater than about 3000 degrees Celsius to remove phosphorus entities from the molten material. In a preferred embodiment, this temperature is important to remove any phosphorus impurities and/or entities from the molten material. In a particular embodiment, the molten mass in the crucible is characterized by convection resulting from a temperature gradient formed by at least the maximum temperature profile and the lower temperature near the edge of the molten material. In certain embodiments, convection causes mixing within the molten material. In certain embodiments, convection is also turbulent to aid in mixing within the molten material.

In a preferred embodiment, the system and method further have a nozzle region configured to output argon gas to form a dimple region in the vicinity of the central region of the molten material. In one or more embodiments, the nozzle region is a plurality of nozzles or the like. In a particular embodiment, the dimple region is provided with an increased surface area for a gas flow to interact with the molten material, wherein the dimple region has a depth of at least 1 centimeter and greater than 1 centimeter. Preferably, the increased surface area is at least three times greater than the surface area without the dimple area, or more preferably, the increased surface area is at least five times greater than the surface area without the dimple area. Taking silicon as an example, the molten material includes a viscosity of 0.7 pascal-seconds, which may increase or decrease slightly. In a preferred embodiment, the argon has a flow rate of 5L/min to 20L/min. In certain embodiments, the gas impinging on the molten material forms a dimple region characterized by a plurality of recessed regions, each separated by a raised region. In a particular embodiment, the nozzle region coupled to the argon gas source is made of a ceramic material. Preferably, the argon source is capable of operating independently of the operation of the arc tube energy. In a preferred embodiment, the argon source has a purity of 99.99% and greater than 99.99%. In other embodiments, other suitable non-reactive gases may be used. Of course, there can be other variations, modifications, and alternatives.

In a preferred embodiment, the present system and method uses a cover gas or a pressing gas to enclose a substantial portion of the molten material in the crucible. That is, the crucible is subjected to a cover gas to hold the molten material in the crucible. In a preferred embodiment, the crucible is subjected to argon or other suitable inert gas or gases containing a cover gas to maintain the molten material in the crucible. Preferably, the cover gas is adapted to keep the molten material from oxidation or other undesirable conditions. A cover gas is disposed in the cavity and/or the enclosure to enclose the crucible. Of course, there can be other variations, modifications, and alternatives.

In a preferred embodiment, the system and method further comprise a carrier gas configured to return a portion of the vaporized molten material to the molten material. In particular embodiments, the carrier gas may be argon or other inert gas suitable for returning any vaporized molten material composed of silicon entities to the molten material. In a particular embodiment, the system includes a plurality of surface regions configured to cause a substantial portion of the phosphorous species to be depleted while returning a substantial portion of the silicon species to the molten material. Preferably, the surface region comprises a plurality of fin regions configured to cause a substantial portion of the phosphorus species to be depleted while returning a substantial portion of the silicon species to the molten material. Of course, there can be other variations, modifications, and alternatives.

In other embodiments, the invention includes an apparatus for purifying metallurgical silicon that overcomes the limitations of conventional techniques. In certain embodiments, the present methods and systems improve upon conventional single crystal silicon crystal puller equipment, which generally includes a vessel, a crucible support, and a heater. By implementing at least one of the following devices in an existing plant, while utilizing one, some or all of the devices for the purification of metallurgical silicon:

a separate injection device disposed above the crucible for supplying plasma, gas and chemical required for purification to the surface of silicon melt with a high-speed jet, forming a dimple on the surface of silicon melt through its supply tube and in cooperation with a temperature distribution across the silicon melt due to a temperature gradient, facilitating thermal cycling and increasing the cycle inversion radius, and increasing the contact area between the purification gas and chemical and the silicon melt, thereby improving purification efficiency;

a guide member having fins provided thereon, provided above the silicon melt in the crucible in a proper position with respect to the crucible and the purification gas and chemical supply tube, for guiding a flow of the moisture gas raised from the surface of the silicon melt by heating the silicon melt back to the surface of the silicon melt so that the moisture gas effectively contacts the silicon melt, wherein a distance between the guide member and the surface of the silicon melt, a distance between the fins and the silicon melt, and a distance between the inner periphery of the crucible and the fins are critical;

a manipulation device disposed under the container for vertically and horizontally transferring or rotating the crucible with respect to the heater to adjust a solid-liquid interface, thereby obtaining a one-way cooling purification without temperature segregation coefficient management of a concentration of remaining impurities in the silicon melt with respect to a solid-liquid line, thus allowing an effective backflow of a humid gas, and controlling a shallow concave shape formed on a surface of the silicon melt via a jet flow from the injection device by adjusting a distance between the crucible and the guide, wherein a set of valves capable of horizontal transfer are further provided in the manipulation device, so as to reduce a reaction of a carbon portion with oxygen when the crucible is taken out or inserted into the container by opening/closing the container; and

a vacuum pump configured to adjust pressure or vacuum degree in the container and to adapt to evaporation conditions of various impurities.

According to certain embodiments, the present technology overcomes some or all of these limitations by adding simple structures, such as separate gas and chemical injection devices, crucible transfer manipulation devices, gas flow guides, and vacuum pumps to regulate the pressure within the vessel, so that purification efficiency can be improved with these small improvements. At the same time, the apparatus is simple, easy to maintain, provides little modification to existing single crystal silicon crystal puller equipment, and has a short build time, thus allowing cost reduction and mass production. Furthermore, the apparatus of the present technology does not use toxic raw materials and produces non-toxic by-products while ensuring the safety of the purification process.

According to certain embodiments, the present invention provides metallurgical silicon purification apparatus obtained by retrofitting an existing single crystal silicon puller apparatus including a vessel, a crucible support, and a heater. The apparatus comprises one, some or all of the following means for metallurgical silicon purification: a separate injection device disposed above the crucible for supplying plasma, gas and chemicals required for purification to the surface of the silicon melt with a high-speed jet; a guide member disposed at a suitable position above the silicon melt in the crucible for guiding the gas rising from the surface of the silicon melt back to the surface of the silicon melt; a manipulation device disposed under the container for vertically and horizontally transferring and rotating the crucible with respect to the heater and the guide to obtain an optimal purification efficiency; and a vacuum pump for adjusting the pressure or vacuum degree in the container and adapting to the evaporation conditions of various impurities.

Many benefits are achieved by way of the present invention over conventional techniques. For example, the present techniques provide an easy-to-use procedure that relies on conventional techniques. In some embodiments, the methods provide highly purified silicon using a modular approach. In a preferred embodiment, the present method and system uses one or more of the following: (1) a gas nozzle for forming a dimple region in the molten material; (2) a cover gas or environment for holding molten material; and (3) a carrier gas or environment for returning the vaporized molten material to the melt. Further, the method provides a process and system that is compatible with conventional process technologies without requiring substantial modification to conventional instruments and processes. Depending on the embodiment, one or more of these benefits may be achieved. These and other benefits will be described in more detail throughout the specification or in the specific specification that follows.

Various additional objects, features and advantages of the present invention can be more fully understood with reference to the detailed description and accompanying drawings that follow.

According to a particular embodiment, the present disclosure provides a method of forming high quality silicon material for a photovoltaic device, the method comprising: conveying a feedstock silicon material in a crucible having an interior region, the crucible being made of a quartz material capable of withstanding a temperature of at least 1400 degrees Celsius; subjecting the raw silicon material in the crucible to thermal energy to melt the raw silicon material into a liquid state to form a molten material at a temperature below about 1400 degrees Celsius, the molten material having an exposed region defined by the interior region of the crucible; subjecting the exposed inner region of the molten material to an energy source comprising an arc heater disposed above the exposed region and spaced apart by a gap between the exposed region and a spout region of the arc heater to form a defined temperature profile in the vicinity of the exposed inner region of the molten material while maintaining the temperature of the outer region of the molten material below the melting point of the quartz material of the crucible; and removing one or more impurities from the molten material to form a higher purity silicon material in the crucible. Further, the method includes outputting an inert gas through the nozzle region to form a dimple region near the central region of the molten material. The inert gas may include argon gas characterized by a flow rate suitable for forming dimples, the dimple areas comprising a plurality of dimple areas, each dimple area separated by a raised area. The nozzle region can be coupled to an argon gas source, the nozzle region comprising a ceramic material. The dimple areas can be provided with an increased surface area to allow gas flow to interact with the molten material, wherein the dimple areas have a depth of at least 1 centimeter and greater than 1 centimeter. The molten material may include a viscosity of 0.7 pascal-seconds. The method may further provide a cover gas to maintain the molten material within the crucible. The method may further provide a carrier gas configured to return a portion of the vaporized molten material to the molten material. The method may further include utilizing a plurality of surface regions such that a substantial portion of the phosphorus species is depleted while a substantial portion of the silicon species is returned to the molten material. The molten material may include a silicon material and a phosphorus species. The molten material may include 0.1ppm and less than 0.1ppm of final phosphorus species.

Drawings

The present invention may be more completely understood in consideration of the following detailed description of preferred embodiments in connection with the accompanying drawings, in which:

FIG. 1 is a cross-sectional view depicting a simplified conventional apparatus for growing a single crystal silicon ingot;

FIG. 2 is a cross-sectional view depicting a first embodiment of the improved apparatus of the present invention;

FIG. 3 is a cross-sectional view depicting a second embodiment of the improved apparatus of the present invention for easily transporting crucibles;

FIG. 4 is a cross-sectional view depicting insertion or removal of a crucible into or from the container of FIG. 3;

fig. 5 is a sectional view depicting a pipe end of the purified material supply system of the present invention;

fig. 6 (including fig. 6A and 6B) is a cross-sectional view depicting a plurality of tubes of a purifier material supply system of the invention;

FIG. 7 is a cross-sectional view depicting the guide of the present invention;

FIG. 8 is a cross-sectional view depicting gas flow of a plasma arc heater in the apparatus of the present invention;

FIG. 9 is a schematic diagram illustrating the dishing and the circulation of silicon melt produced by the plasma arc heater and high pressure gas of the present invention;

FIG. 10 is a schematic view illustrating the positional relationship of the injection device and the guide in the apparatus of the present invention;

FIG. 11 (including FIGS. 11A to 11D) is a schematic diagram illustrating the arrangement of multiple arc heaters of the present invention;

FIG. 12 is a schematic diagram illustrating the position of a plurality of injection devices of the present invention relative to a crucible;

FIG. 13 (comprising FIGS. 13A and 13B) is a schematic diagram illustrating a shallow depression on the center of a silicon melt surface produced by multiple plasma arc heaters of the present invention;

FIG. 14 is a simplified diagram of a crystal puller according to an embodiment of the invention.

Detailed Description

The present invention relates to an apparatus and a method for purifying a material. More particularly, the present invention relates to a method and system for purifying metallurgical silicon ore to produce feedstock suitable for the manufacture of monocrystalline and multicrystalline silicon ingots for solar cells at a lower cost. Although the above describes aspects of purifying silicon, the invention may be used in other applications. Although the foregoing has described aspects of purifying silicon, it may be applied to other applications.

Embodiments of the present invention will now be described using the following examples.

FIG. 1 is a cross-sectional view depicting a simplified apparatus commonly used for growing single crystal silicon ingots. This diagram is merely an example, which should not unduly limit the scope of the claims. Other variations, modifications, and alternatives will occur to those skilled in the art. In the figure, reference numeral 1 denotes a container, 2 denotes a crucible support, 3 denotes a crucible manipulating device, 4 denotes a heater, and 5 denotes a crucible. The quartz crucible 5 in the container 1 is supported by the crucible support 2 made of a low-density thermal material to prevent the crucible 5 from being cracked due to thermal creep in the silicon purification process. The crucible 5 is located in a heater 4, the heater 4 radiating heat and generating a thermal field in the vessel 1 to melt the silicon feedstock in the crucible 5, thereby producing a silicon melt. The silicon melt absorbs heat radiated from the heater 4 and dissipates the heat from the surface thereof or transfers the heat to and from a growing ingot (not shown) via a solid-liquid interface, resulting in a silicon growth phenomenon. The crucible manipulating device 3 transfers the crucible 5 upward or downward to assist silicon growth. This is because during silicon growth, the ingot is slowly rotated upward while the silicon melt surface is lowered so as to keep the liquid surface at a constant height and continuously heat the solid-liquid interface of the silicon material; the crucible 5 must be raised slowly to ensure stability of the silicon growth process.

It should be noted that to avoid oxidation of silicon at high temperatures, it is common to operate in a vessel under an inert argon (Ar) gas atmosphere, wherein Ar gas may be fed through the top of the vessel to facilitate purification by reaction of the moist Ar gas with the silicon melt.

In a preferred embodiment, the present system and method uses a cover gas or a press gas to enclose a substantial portion of the molten material in the crucible. That is, the crucible is subjected to a cover gas to hold the molten material in the crucible. In a preferred embodiment, the crucible is subjected to argon or other suitable inert gas or gases containing a cover gas to retain the molten material in the crucible. Preferably, the cover gas is adapted to keep the molten material from oxidation or other undesirable conditions. The cover gas is disposed in a cavity and/or housing surrounding the crucible. Of course, there can be other variations, modifications, and alternatives.

FIG. 2 is a drawing depicting a first embodiment of a metallurgical silicon purification apparatus modified in accordance with a conventional crystal puller. This diagram is merely an example, which should not unduly limit the scope of the claims. Other variations, modifications, and alternatives will occur to those skilled in the art. In the drawing, reference numeral 10 denotes a container, 10a denotes an upper portion of the container, 10b denotes a container main body, 11 denotes a heater, 12 denotes a pressure reducing pipe, 15 denotes a discharge passage control cap, 20 denotes a crucible, 30 denotes a crucible manipulating device, 61 denotes a chemical and gas supply pipe, 62 denotes a high-pressure gas supply pipe, 70 denotes a gas flow guide, and 100 denotes a silicon melt.

The container 10 is composed of an upper portion 10a and a container body 10 b. In the melting of siliconAbove the surface of object 100 is a separate spraying device consisting of chemical and gas supply pipe 61 and high pressure gas supply pipe 62. Chemicals and gases required for purification, such as soluble compounds of calcium (Ca), silicon (Si) and magnesium (Mg), hydrogen (H) are supplied through the supply pipe 61₂) Gas or oxygen (O)₂) Gas, to the surface of silicon melt 100. At the same time, for example, water vapor (H)₂O) or Ar gas is delivered to the center of the surface of silicon melt 100 through high-pressure gas supply tube 62 via high-pressure jets, thereby forming dimples 90 (see fig. 9) at the surface of silicon melt 100 and, in cooperation with the temperature gradient within silicon melt 100 in crucible 20, thermal circulation and/or mass convection can be achieved. The jet not only aids in the mixing of the silicon melt 100 in the crucible 20, but also increases the contact area between the chemicals/gases and the silicon melt 100, thereby increasing the efficiency of the purification process.

Further, a guide 70 is provided in the crucible 20 at a position above the silicon melt 100 and at a distance from the crucible 20 and the supply tubes 61 and 62. The hot gas rising from the surface of silicon melt 100 is guided back to the surface of silicon melt 100 by guide 70 so that the humid gas is in effective contact with silicon melt 100, thus improving the efficiency of the purification process. The guide 70 is discussed further below.

In a preferred embodiment, the system includes a guide along with a carrier gas configured to return a portion of the vaporized molten material to the molten material. In a particular embodiment, the carrier gas may be argon or other inert gas suitable for returning any evaporated molten material consisting of silicon entities into the molten material. In a particular embodiment, the system includes a plurality of surface regions configured to cause a majority of the phosphorus species to be depleted while returning a majority of the silicon species to the molten material. Preferably, the surface region comprises a plurality of fin-shaped regions configured such that a majority of the phosphorus species is depleted while a majority of the silicon species is returned to the molten material. Of course, there can be other variations, modifications, and alternatives.

In addition, in order to prevent silicon from being oxidized at high temperature and excessively heating silicon melt, the degree of vacuum in the vessel 10 is changed to suit the evaporation conditions of various impurities contained in the raw material silicon, thereby ensuring a safe metallurgical silicon purification process. In particular, a vacuum pump (not shown) and a gas flow valve (not shown) may be used to control the gas and gas flow rate in the vessel 10, wherein the pump regulates the pressure via the pressure reducing pipe 12, which avoids any danger caused by the pressure rise caused by the continuous supply of water vapor (purification material), thereby providing safe and stable metallurgical silicon purification process conditions.

FIGS. 3 and 4 are views depicting a second embodiment of a metallurgical silicon purification apparatus modified in accordance with a conventional crystal puller. In the drawing, reference numeral 10 denotes a container, 11 denotes a heater, 12 denotes a pressure reducing tube, 13 denotes a set of valves and/or ports or load locks, 14 denotes a set of valve manipulation arms, 15 denotes a discharge passage control cap, 20 denotes a crucible, 30 denotes a crucible manipulation device, 31 denotes a crucible manipulation device base, 32 denotes a crucible manipulation device transfer shaft, 33 denotes a crucible manipulation device motor, 40 denotes a crucible transfer device, 41 denotes a crucible conveyor belt, 50 denotes a plasma arc heater, 60 denotes a purification material supply system, 61 denotes a chemical and gas supply tube, 62 denotes a high-pressure gas supply tube, 70 denotes a gas flow guide, and 100 denotes a silicon melt.

Above the surface of silicon melt 100 is a separate injection device consisting of chemical and gas supply tube 61 and high pressure gas supply tube 62. Chemicals and gases required for purification, such as soluble compounds of calcium (Ca), silicon (Si) and magnesium (Mg), hydrogen (H) are supplied through the supply pipe 61₂) Gas or oxygen (O)₂) Gas, is provided to the surface of silicon melt 100. At the same time, for example, water vapor (H)₂O) or Ar gas is supplied to the center of the surface of silicon melt 100 through high-pressure gas supply tube 62 via high-pressure jets, thereby forming dimples 90 (see fig. 9) at the surface of silicon melt 100, the dimples 90 cooperating with the temperature gradient within silicon melt 100 in crucible 20 to enable thermal circulation and/or convection. The jet flow not onlyFacilitates mixing of silicon melt 100 in crucible 20 and also enlarges the contact area between the chemical/gas and silicon melt 100, thereby increasing the efficiency of the purification process. Further, plasma arc heater 50 is disposed above silicon melt 100. The plasma arc heater 50, which forms a separate injection means together with the purifying material supply system 60, intermittently and locally emits plasma toward the surface of the silicon melt 100 in the crucible 20. This produces a reproducible temperature profile across silicon melt 100. At the same time, the hydrogen (H) gas burned supplied by the plasma arc heater 50 is supplied₂) Oxygen (O) is supplied from a high-pressure gas supply pipe 62₂) And oxygen enters the center of the surface of the silicon melt 100 in the crucible 20 and forms water vapor (H) via combustion of hydrogen₂O). The water vapor is further transferred into silicon melt 100 by the force of the high pressure oxygen jet, effectively providing silicon melt 100 with the water vapor required for silicon purification.

Further, in the second embodiment, the crucible manipulating device 30 is disposed under the container 10 to provide elevation/lowering, rotation, and horizontal transfer. The crucible manipulating device 30 includes a crucible manipulating device base 31, a crucible manipulating device transfer shaft 32, and a crucible manipulating device motor 33. Since the present invention does not require a seed ingot (seed ingot) for silicon growth, the surface height of the silicon melt 100 in the crucible 20 does not decrease during the purification process. By means of the crucible manipulating device 30, not only the vertical movement of the crucible 20 within the container 10 can be controlled in order to install or remove the crucible 20, but also the crucible 20 can be transferred in cooperation with the crucible transferring device 40 and the crucible conveyor 41 at the end of the silicon purification process. In addition, the crucible 20 can be controlled to move vertically and rotate by the crucible manipulating device 30, so that the solid-liquid interface of the silicon melt 100 is adjusted relative to the position of the heater 11, thereby realizing unidirectional cooling purification related to the segregation theory without temperature segregation coefficient management of the concentration of the residual impurities in the silicon melt 100 relative to the solid-liquid line. In addition to silicon purification by adjusting the solid-liquid interface of silicon melt 100 by the position of crucible manipulation device 30 relative to heater 11, the distance between crucible 20 and guide 70 may be controlled by crucible manipulation device 30 so that humid gas from the surface may be effectively directed back to silicon melt 100 to assist in supplying water for purification. At the same time, by controlling said distance, it is possible to control the formation of a dimple 90 (see fig. 9) on the surface of silicon melt 100 caused by the direct action of the jet from the spraying device. Further, referring to fig. 3 and 4, a set of valves 13 is disposed under the container 10 in addition to the crucible manipulating device 30, the set of valves 13 may be horizontally closed or opened, and the set of valves 13 is controlled by a set of valve manipulating arms 14 capable of horizontally transferring. When crucible 20 is installed/removed from vessel 10, valve 13 is opened or closed horizontally to reduce the reaction of carbon product in the vessel with oxygen, which affects the purification reaction of silicon melt 100.

Further, a guide 70 is provided in the crucible 20 at a suitable position above the silicon melt 100 with respect to the crucible 20 and the supply pipes 61 and 62. The flow of hot air from the purification gas flow provided to the surface of silicon melt 100 is directed back to the surface of silicon melt 100 by guide 70 so that the humid gas is in effective contact with silicon melt 100, thereby increasing the efficiency of the purification process.

In addition, to prevent oxidation of silicon at high temperatures, the vessel 10 must be maintained at a certain vacuum. In particular, the gas and gas flow rate in the vessel 10 may be controlled using a vacuum pump (not shown) that adjusts the pressure via the pressure reducing pipe 12 and a gas flow valve (not shown), which avoids any danger caused by a pressure rise due to continuous supply of water vapor (purification material), thereby providing safe and stable metallurgical silicon purification process conditions.

Fig. 5 is a schematic view depicting the tube end of the purified material supply system 60 of the present invention depicted in fig. 2, 3 and 4. In order to provide a high-pressure humid gas mixture to form dimple 90 on the center of the surface of silicon melt 100 that increases the contact area and contact time of the purification material with silicon melt 100 and to improve the mixing of silicon melt 100 in crucible 20 for purification, the tube of purification material supply system 60 is designed to have a constricted conical shape to increase the injection pressure and flow rate. The material of this conical tube should be carefully selected to reduce losses when used to supply chemicals and gases and as a heat source. For this purpose, the tube is preferably coated with a material such as quartz.

Fig. 6 is a schematic diagram depicting an embodiment of a stand-alone purifier material supply system 60 of the present invention, purifier material supply system 60 being comprised of a chemical and gas supply line 61 and a high pressure gas supply line 62 depicted in fig. 2, 3, 4. Fig. 6 shows a design of two coaxial tubes for providing different combinations of purification materials (e.g., chemicals, gases, and soluble chemicals), including an outer tube a and an inner tube b. Reference letters/marks a0 and b0 denote outlets of the outer tube a and the inner tube b, respectively. However, the present invention is not limited to these, but may have three or more tubes as long as they provide different combinations of purification materials to the surface of the silicon melt.

Fig. 6(a) and 6(B) are cross-sectional views depicting embodiments of a multi-tube design for supplying a purification material to the surface of silicon melt 100. As shown in fig. 6(a), the inner tube protrudes from the outer tube, wherein an outlet b1 of the inner tube supplies high-pressure humid gas (e.g., Ar) and/or water, and an outlet a1 of the outer tube supplies Ar gas. With this design, high pressure humid gas and/or water may pass through the surface of silicon melt via the center of dimple 90 (see fig. 9), effectively delivering the humid gas and/or water required for silicon purification into silicon melt 100 in crucible 20. As shown in FIG. 6(B), the inner tube is shorter than the outer tube, and the outlet a2 of the outer tube supplies H₂The gas is used for reacting with O₂Reacted to form water, the outlet b2 of the inner tube supplying the O needed to form water should react with the hydrogen of the combustion₂. H supplied through the outlet a2 of the outer tube because the inner tube is shorter than the outer tube₂Can reach the surface of silicon melt 100 by diffusion and burn due to high temperature, and if H burns from outlet b2 of the inner tube₂Is provided with O at the center₂Water vapor is generated. This water vapor and a portion of the unreacted free oxygen effectively reach the surface of silicon melt 100 for purification.

Fig. 7 is a schematic diagram depicting the design of the gas flow guide 70 of the present invention. As described above, in consideration of plasma arc heater 50 and purification material supply system 60, guide 70 is located at a proper distance from silicon melt 100 in crucible 20. Guide 70 redirects the rising hot air back to the surface of silicon melt 100 so that the humid gas is in effective contact with silicon melt 100, thereby increasing the efficiency of the purification process. The guide 70 includes a body 74 and a plurality of fins 71, 72, and 73 extending from a lower edge of the body 74.

Fig. 8 is a schematic diagram depicting the flow of rising hot humid gas. When plasma arc heater 50 irradiates silicon melt 100 in crucible 20, the temperature of silicon melt 100 increases and generates an elevated hot humid gas stream (shown by the dashed line) that diffuses over the surface of silicon melt 100 in crucible 20.

Further, fig. 10 shows the distance and position of the guide 70 relative to the crucible 20 and the surface of the silicon melt 100, and their relative relationship to the rising hot humid gas stream. The following distances and positions are obtained from actual experiments performed by the inventors, which should not be construed as limiting the present invention.

As shown in fig. 10, reference numeral 11 denotes a heater, 50 denotes a plasma arc heater, 60 denotes a purification material supply system, 61 denotes a chemical and gas supply tube, 62 denotes a high-pressure gas supply tube, 70 denotes a gas flow guide, 71 and 72 denote fins, 20 denotes a crucible, 100 denotes silicon melt, h1 denotes a distance between an outlet of the plasma arc heater and a surface of the silicon melt, h2 denotes a distance between fin 71 of guide 70 and a surface of silicon melt 100, h3 is a length of the longest fin 71, h4 is a distance from gas supply tube 61 to an outlet of plasma arc heater 50, s1 is a distance from a hole of guide 70 to plasma arc heater 50, s2 is a distance from plasma arc heater 50 to inner fin 72, and s3 is a space between fins 71 and 72. The distance h4 depends on the injection force of the purification material supply system 60 and the gas flow supply amount (V) through the guide member 70.

Based on the experimental results, when the supply amount (V) was 100-800L/hour, the distance h4 was 10cm, which is the maximum value.

With respect to the distance h1, it is found from the experimental results that the results are the best when the distance h1 reaches 5 cm. A suitable range is from 1cm to 18 cm.

For the first distance s1, it can be seen from the experimental results that the distance s1 should be as short as possible to increase the speed of the airflow. According to the experimental results, in the case where the chemical and gas supply pipe 61 and the high pressure gas supply pipe 62 are lowered to the height of the lower edge of the guide 70, the distance s1 is preferably between 1cm and 6 cm.

Distance s2 depends on the pressure of purifying material supply system 60 and the gas supply amount (V), i.e., the flow rate of the gas passing through the space. According to the experimental results, in the case of a supply of 100-800L/h, the results were best when the distance s2 was between 2cm and 8 cm.

The distances s2 and s3 also depend on the number of fins 71 and 72. According to the experimental result, when the number of fins is 2, the sum of the distances s2 and s3 is preferably 5mm to 30mm from the distance s 2.

For the distance h2, it is theoretically believed that the smaller the distance, the better the result. However, the distance h2 is preferably between 5mm and 50mm in consideration of the influence of temperature and the like.

Distance h3 is related to distance h2 and the position of guide 70. According to the experimental results, the distance h3 is preferably between 5mm and 30 mm.

For the distance h1, 5cm is suitable in the case of the plasma arc heater 50 used in the experiments. However, the use of the plasma arc heater 50 is potentially dangerous, and therefore good results can be obtained if the distance h1 is between 1cm and 18 cm.

Further, fig. 9 is a schematic diagram depicting dimple 90 formed by irradiation of plasma arc heater 50 and/or circulation in silicon melt 100 caused by purification material supply system 60. When plasma arc heater 50 emits plasma and purification material supply system 60 supplies high-pressure and high-speed jet flow to the center of the surface of silicon melt 100, dimple 90 is formed on the center of the surface of silicon melt 100, and when plasma irradiates dimple 90, the high-temperature area of the surface of silicon melt 100 is expanded. In conjunction with the temperature profile developed across silicon melt 100 in crucible 20 by plasma arc heater 50, a larger inversion radius of thermal cycling is created in silicon melt 100. The thermal cycling redistributes the impurities in silicon melt 100 more evenly. The jet flow facilitates mixing of the silicon melt 100 in the crucible 20 and also enlarges the contact area between the silicon melt 100 and the purification materials (e.g., gases and chemicals), thereby increasing the purification efficiency. In addition, plasma from plasma arc heater 50 may be applied intermittently to prevent overheating of the entire silicon melt 100 and to maintain a suitable temperature profile across silicon melt 100 in crucible 20.

FIGS. 11, 12 and 13 are schematic diagrams depicting the irradiation of the surface of a silicon melt 100 in a crucible 20 with different sets of plasma arc heaters 50.

When a large amount of raw silicon needs to be purified, a plurality of plasma arc heaters 50 may be used to generate higher-energy irradiation. However, when the center of the surface of silicon melt 100 is irradiated simultaneously using a plurality of plasma arc heaters 50, the purification apparatus may be overheated and damaged, for example, the bottom of crucible 20. To overcome this problem, the present invention arranges a plurality of plasma arc heaters 50 at equal angular distances around the center of the surface of silicon melt 100. For example, fig. 11(a) is a schematic drawing depicting three plasma arc heaters 50 around the center a of the surface; FIG. 11(B) depicts four plasma arc heaters 50; fig. 11(C) depicts five plasma arc heaters 50; fig. 11(D) depicts six plasma arc heaters 50. In the above combination of plasma arc heaters 50, the irradiation from multiple plasma arc heaters 50 needs to be focused somewhere below the surface of silicon melt 100 to avoid overheating crucible 20 while ensuring good thermal cycling of silicon melt 100.

Referring to fig. 12, plasma arc heater 50 may be disposed at an angle to the surface of silicon melt 100. The different angles create different shaped dimples 90. The angle should be less than or equal to 90 ° (≦ 90 °). As shown in fig. 12, the plasma arc heaters are disposed at angles α and β above the surface of silicon melt 100, which determine the irradiation focus of the plasma. Generally, the deeper the illumination, the larger the angles α and β. Furthermore, as the angle of the plasma arc heater 50 changes, the temperature distribution of the silicon melt 100 in the crucible 20 will also change. The dimple 90 formed will be different, which means that changing the angle of irradiation causes the evaporation rate of silicon melt 100 to change. As shown in fig. 13(a) and 13(B), when plasma arc heater 50 irradiates the surface of silicon melt 100 at different angles, different dimples 90 are formed. Further, it should be noted that by controlling the position of the plasma arc heater 50 with the crucible manipulation device 30, different locations and temperatures for optimal plasma irradiation can be obtained, and the shape of the dimple 90 depends on the irradiation angles α and β of the plasma arc heater 50.

Preferred embodiments of the present invention will be described in detail below with reference to the foregoing drawings.

The present invention solves the problem of how to efficiently mix refining materials, such as chemicals and gases, into the metallurgical silicon to be refined.

The melting temperature of metallurgical silicon is about 1425 ℃. Due to the circulation of the radiant heat of the silicon melt, the purification material may become misty and depleted before reaching the silicon melt.

In view of this, the conventional art proposes the following method.

The refining material is blown in from the bottom of the crucible. This method is theoretically possible, but practically causes the following problems. A pressure sufficient to resist the viscosity of the liquid silicon melt is required. Furthermore, in order to avoid the back flow, the blowing must be done at a height above the surface of the silicon melt, which lengthens the blowing tube and therefore requires higher pressure. In the case of a temporary drop in pressure, the silicon melt flows back into the tube and solidifies in the low-temperature zone, which can lead to the tube breaking due to the increase in mechanical pressure. Therefore, the tube must be maintained within a certain temperature.

Therefore, this method has the following problems:

a) the impurities are inevitably added, i.e. the product purity is low;

b) the equipment is expensive;

c) and (4) safety problems.

Furthermore, despite the mixing and stirring of the silicon melt by the mechanical stirring device, the material and mechanical strength requirements of the stirring rod result in no easy solution in view of the high temperature and viscous environment.

Another method, the so-called weathering method, is also used for purification.

This purification method is commonly used for the manufacture of iron and aluminum and has proven effective.

The method removes impurities and additives (e.g., magnesium oxide and calcium) by vitrification.

The vitrified impurities float on the surface of the purified metal and, after cooling, they can be removed from the surface by mechanical means to obtain a purified product.

This process has limitations in the purity level of the final product. However, if this method is simultaneously employed with the apparatus of the present invention, the purity can be improved.

The present invention relates to the development of a purification apparatus that can efficiently mix a purification material into a silicon melt.

It should be understood that the metallurgical silicon purification apparatus of the present invention may be obtained by modifying an existing single crystal silicon crystal puller apparatus. The existing apparatus generally includes a container, a crucible support, and a heater. The purification of metallurgical silicon is performed by providing in an existing apparatus at least one of the following devices, while utilizing one, some or all of the devices:

a separate injection device disposed above the crucible for supplying plasma, gas and chemical required for purification to the surface of the silicon melt with a high-speed jet, forming a dimple on the surface of the silicon melt through its supply tube and in cooperation with the temperature distribution across the silicon melt, facilitating thermal cycling and increasing the cycle inversion radius, and increasing the contact area between the purification gas and chemical and the silicon melt, thereby improving purification efficiency;

a guide member having fins provided thereon, disposed above the silicon melt in the crucible in a proper position with respect to the crucible and the supply tube for supplying the purification gas and the chemical, for guiding a flow of the moisture gas rising from the surface of the silicon melt back to the surface of the silicon melt so that the moisture gas effectively contacts the silicon melt, wherein a distance between the guide member and the surface of the silicon melt, a distance between the fins and the silicon melt, and a distance between the inner periphery of the crucible and the fins are critical;

a manipulation device disposed under the container for vertically and horizontally transferring or rotating the crucible with respect to the heater to adjust a solid-liquid interface, thereby obtaining a one-way cooling purification without temperature segregation coefficient management of a concentration of remaining impurities in the silicon melt with respect to a solid-liquid line, and allowing an effective backflow of a humid gas, and controlling a shallow concave shape formed on a surface of the silicon melt via a jet flow from the injection device by adjusting a distance between the crucible and the guide, wherein a set of valves capable of moving horizontally is further provided in the manipulation device so as to reduce a reaction of a carbon portion with oxygen when the crucible is taken out or inserted into the container by opening/closing the valves; and

In summary, the present invention proposes an apparatus for purifying metallurgical silicon used as a raw material in the manufacture of solar cells, obtained by modifying existing equipment, in place of the conventional siemens method.

According to the above embodiments, one or more of the following aspects are included.

1. An apparatus for purifying metallurgical silicon obtained by modifying an existing single crystal silicon crystal puller apparatus comprising a vessel, a crucible support and a heater, and adding one, some or all of the following means for purifying metallurgical silicon:

a separate injection device disposed above the crucible for supplying plasma, gas and chemicals required for purification to the surface of the silicon melt with a high-speed jet and forming a dimple on the surface of the silicon melt by its uniquely designed supply tube;

a guide having fins thereon, disposed above the silicon melt in the crucible at a proper position and distance (h 1) (h 2) (h 3) (h 4) (s 1) (s 2) (s 3) with respect to the crucible and the surface of the silicon melt, for guiding a flow of the moisture gas (caused by heating the surface of the silicon melt) rising from the surface of the silicon melt back to the surface of the silicon melt, so that the moisture gas effectively contacts the silicon melt;

a manipulation device disposed under the container for vertically and horizontally transferring or rotating the crucible with respect to the heater to adjust the solid-liquid interface for purification and further controlling the relative positions of the crucible and the above guide and injection device, thereby obtaining optimal purification efficiency; and

2. The apparatus of claim 1, wherein the injection device comprises separate chemical and gas supply tubes for supplying chemicals, gas and soluble gas to the center of the silicon melt surface for purification.

3. The apparatus of claim 1, wherein the injection device comprises a separate high pressure gas supply tube for supplying the high pressure humid gas mixture to the center of the surface of the silicon melt for purification.

4. The apparatus of claim 1, wherein the injection device comprises a separate purification material supply system comprising a chemical and gas supply tube and a high pressure gas supply tube for supplying a chemical, a gas and a soluble gas, and a high pressure humid gas mixture, respectively, to the center of the surface of the silicon melt for purification.

5. The apparatus of claim 4, wherein the end of the tube in the purified material supply system has a reduced conical shape for increasing the injection pressure and flow rate.

6. The apparatus of claim 5, wherein the material of the tube comprises a quartz-coated material.

7. The apparatus of claim 4, wherein the purifier material supply system has a coaxial multitube design for supplying at least one of chemicals, gases, soluble chemicals, humid gases, and water.

8. The apparatus of claim 7, wherein the plurality of coaxial tubes comprises an inner tube that is longer than an outer tube.

9. The apparatus of claim 8, wherein the outlet of the inner tube supplies at least one of high pressure humid gas and water and the outlet of the outer tube supplies argon.

10. The apparatus of claim 7, wherein the plurality of coaxial tubes comprises an inner tube shorter than an outer tube.

11. The apparatus of claim 10, wherein the outlet of the outer tube supplies hydrogen to react with oxygen to produce water and the outlet of the inner tube supplies oxygen to react with the combusted hydrogen to produce water.

12. The apparatus of claim 1, wherein the injection device comprises at least one plasma arc heater for irradiating the silicon melt surface and injecting chemicals and gases required for purification.

13. The apparatus of claim 12, wherein the plasma is intermittently and locally irradiated on the surface of the silicon melt to establish a reproducible temperature gradient in the silicon melt.

14. The apparatus of claim 12, wherein the plurality of plasma arc heaters are arranged at equal angular distances around a center of the silicon melt surface and are tilted at a predetermined angle relative to a plane of the silicon melt such that the illumination is focused at a point below the silicon melt surface to form different shaped dimples on the silicon melt surface.

15. The apparatus of claim 14, wherein the plasma arc heater is inclined at an angle less than or equal to 90 ° (≦ 90 °) relative to the silicon melt surface.

16. The apparatus of claim 1, wherein the manipulator device comprises a crucible manipulator device base, a crucible manipulator device transfer shaft, and a crucible manipulator device motor for controlling vertical movement of the crucible within the vessel for mounting or dismounting the crucible, and for controlling vertical movement and rotation of the crucible for moving the crucible relative to the heater for adjusting the solid-liquid interface for unidirectional cooling purification, and for controlling the distance between the above silicon melt surface and the guide such that the humid gas generated from the surface can be effectively directed back to the silicon melt to assist in supplying water for purification, and by controlling the distance, controlling the shape of the dimple created on the silicon melt surface by the direct action of the jet from the jet device.

17. The apparatus of claim 16, wherein the handling device further comprises a transfer device for transferring the crucible at the end of the purification process and a crucible conveyor.

18. The apparatus of claim 1, wherein the manipulation device further comprises a set of valves disposed below the vessel that can be horizontally closed or opened by a set of valve manipulation arms, such that in the case of mounting or removing the crucible into or from the vessel, the valves can be horizontally opened and closed to reduce a reaction of a carbon portion in the vessel with oxygen, which reaction affects purification of the silicon melt.

19. The apparatus of claim 1, wherein the guide comprises a body and at least one fin extending from a lower edge of the body.

20. The apparatus according to claim 1, 2, 3, 12 or 19, wherein the distance h4 from the gas supply tube of the injection device to the plasma arc heater outlet is 10cm, which is the maximum value, in the case of a gas flow rate (V) through the guide of 100-800L/h; the distance h1 from the plasma arc heater outlet to the silicon melt surface ranges between 1cm and 18cm, preferably 5 cm; in the case where the chemical and gas supply tubes and the high-pressure gas supply tube are lowered to the height of the guide, the distance s1 from the plasma arc heater to the hole of the guide is preferably between 1cm and 6 cm; in the case where the supply amount (V) is 100-800L/hr, the distance s2 from the plasma arc heater to the inner fin of the guide member is preferably between 2cm and 8cm depending on the pressure of the injection device and the gas supply amount (V) (i.e., the flow rate of the gas passing through the space); the distance s2 and the distance s3 between the fins of the guide also depend on the number of fins provided, so that when the number of fins is 2, the sum of the distances s2 and s3 is preferably the distance s2 plus 5mm to 30 mm; the distance h2 from the fin to the silicon melt surface is preferably between 5mm and 50 mm; and the longest fin h3 in the guide is preferably between 5mm and 30 mm.

21. The apparatus of claim 1, wherein the gas and gas flow rates in the vessel are controlled using a vacuum pump and a gas flow valve, wherein the pump adjusts the pressure via a pressure reducing tube to avoid any danger caused by a pressure rise due to continuous supply of water vapor to accommodate evaporation conditions of various impurities contained in the raw silicon and to prevent overheating of the silicon melt, thereby ensuring a safe metallurgical silicon purification process.

It is also understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the purview and spirit of this application and scope of the appended claims.

Example (c):

to demonstrate the principle and operation of the present invention, we performed some experiments. We performed polysilicon purification experiments using several generations of modified conventional monocrystalline silicon ingot pullers. Such crystal pullers include small and conventional crystal pullers (loaded with about 20Kg of silicon at a time) to medium-sized crystal pullers (loaded with about 80Kg of silicon at a time). We retain a crucible apparatus and control apparatus that is modified to operate in a manner consistent with the present sample silicon purification apparatus configured to purify metallurgical silicon. By introducing metallurgical silicon, treating this silicon and purifying this silicon according to the present example, we obtain a purification result of 6N-7N (e.g., silicon purity of 99.9999 to 99.99999), reaching the required specifications for solar cell applications. The actual purification unit of this trial was modified from a large conventional crystal puller (loaded with about 140Kg of silicon at a time). See, for example, fig. 14. Of course, there can be other variations, modifications, and alternatives.

Claims

1. A system for forming high quality silicon material for a photovoltaic device, the system comprising:

a crucible having an interior region, the crucible being made of a quartz material capable of withstanding a temperature of at least 1400 degrees Celsius, the crucible being configured in a vertical position and having an open region exposing molten material;

an energy source including an arc heater disposed above the open region and spaced apart by a gap between the exposed molten material and a spout region of the arc heater to form a determined temperature distribution in the vicinity of a central region of the exposed molten material while maintaining a temperature of an outer region of the molten material below a melting point of the quartz material of the crucible; and

a carrier gas configured to return a portion of the vaporized molten material to the molten material.

2. The system of claim 1, wherein the arc heater is a plasma gun configured to emit an excited argon species to transfer heat to a portion of the molten material, the arc heater configured with a heat transfer device to cool the arc heater.

3. The system of claim 1, wherein the arc heater is ignitable by a power source.

4. The system of claim 1, wherein the arc heater comprises a power rating of 20kW or greater and is capable of generating pulses according to a duty cycle.

5. The system of claim 1, wherein the spout region has a maximum dimension of 0.5 cm to 2 cm.

6. The system of claim 1, wherein the determined temperature profile is greater than 3000 degrees celsius to remove phosphorus entities from the molten material.

7. The system of claim 1, wherein the molten substance includes convection caused by a temperature gradient formed by at least the determined temperature profile.

8. The system of claim 7, wherein the convection causes mixing within the molten material.

9. A system for forming high quality silicon material for solar cells, the system comprising:

a nozzle region configured to output argon gas to form a dimple region in a vicinity of the central region of the molten material.

10. The system of claim 9, wherein the argon gas has a flow rate suitable for forming the dimple region, the dimple region comprising a plurality of recessed regions, each separated by a raised region.

11. The system of claim 9, wherein the nozzle region is coupled to an argon gas source, the nozzle region comprising a ceramic material.

12. The system of claim 11, wherein the argon gas source is operable independently of an arc tube, wherein the molten material comprises a viscosity of 0.7 pascal-seconds, and wherein the argon gas source has a purity of 99.99% or greater.

13. The system of claim 9, wherein the dimple region is provided with an increased surface area to allow gas flow to interact with the molten material, wherein the dimple region has a depth of at least 1 centimeter.

14. The system of claim 13, wherein the increased surface area is at least three times greater than a surface area without the dimple area.

15. The system of claim 13, wherein the increased surface area is at least five times greater than a surface area without the dimple areas, wherein the molten material is characterized by turbulent flow, and wherein the arc heaters are configured to face selected portions of the exposed areas of the molten material.

16. The system of claim 1, wherein the crucible is subjected to a cover gas to hold the molten material within the crucible.

17. The system of claim 1, wherein the crucible is subjected to a cover gas comprising argon to maintain the molten material in the crucible, the cover gas adapted to keep the molten material from being oxidized.

18. The system of claim 1, further comprising a plurality of surface regions configured to cause a substantial portion of phosphorus species to be depleted while returning a substantial portion of silicon species to the molten material.

19. The system of claim 1, further comprising a plurality of fin regions configured to cause a substantial portion of a phosphorous species to be depleted while a substantial portion of a silicon species is returned to the molten material, wherein the molten material comprises a silicon material and a phosphorous species, and wherein the molten material comprises 0.1ppm and less than 0.1ppm of a final phosphorous species.

20. A method for forming high quality silicon material for a photovoltaic device, the method comprising:

conveying a feedstock silicon material in a crucible having an interior region, the crucible being made of a quartz material capable of withstanding a temperature of at least 1400 degrees Celsius;

subjecting the raw silicon material in the crucible to thermal energy to melt the raw silicon material into a liquid state to form a molten material at a temperature below 1400 degrees Celsius, the molten material having an exposed region defined by the interior region of the crucible;

subjecting the exposed inner region of the molten material to an energy source comprising an arc heater disposed above the exposed region and spaced apart by a gap between the exposed region and a spout region of the arc heater to form a defined temperature profile in the vicinity of the exposed inner region of the molten material while maintaining the temperature of the outer region of the molten material below the melting point of the quartz material of the crucible; and

removing one or more impurities from the molten material to form a higher purity silicon material in the crucible;

wherein the method further comprises providing a carrier gas that returns a portion of the vaporized molten material to the molten material.