CN115198345A - Top heater cable arrangement and electromagnetic stirrer - Google Patents

Abstract

The invention relates to a distribution structure of cables outside a furnace chamber of a top heater, which is used for realizing electromagnetic stirring. The structure of the heater comprises a top heater and a side heater, wherein the top heater and the side heater are respectively provided with n electrodes, and n =3 or 4 is connected with an n-phase alternating power supply; the current of the side heater is fed in from the upper part through the suspension arm; corresponding to each section of the side heater loop, arranging a conductor circuit outside the furnace chamber and close to the furnace wall, wherein the conductor circuit comprises a transverse extension section and downward extension sections at two ends of the transverse extension section; the lower end of the downward extension section at one side is connected to a top-charging power supply, and the lower end of the downward extension section at the other side is connected to a top-charging graphite electrode. The connection of the transformer and the cable is adjusted, so that the current phase in each section of the side loop is approximately the same as the current phase in the adjacent transverse extension section outside the furnace chamber, and the two currents cooperate to obtain larger electromagnetic stirring force. The current of the suspension arm added on the inner side of the furnace is approximately opposite to the current of the downward extending section outside the furnace, and the currents are mutually offset to obtain a more uniform stirring force field, so that a uniform molten silicon flow field is obtained, and the growth of the ingot casting single crystal with high quality is favorably realized.

Description

Top heater cable arrangement and electromagnetic stirrer

Technical Field

The invention relates to the field of crystal growth equipment, in particular to an electromagnetic stirring device with mutually matched current in a furnace chamber and current outside the furnace chamber and a using method thereof.

Background

A directional solidification method crystal silicon ingot casting growing furnace is a key device in the fields of silicon crystal growth and silicon wafer manufacturing. Compared with the growth of the monocrystalline silicon by the Czochralski method, the ingot casting method has the advantages of low energy consumption and low production cost, and has the defects of more impurities, dislocation, grain boundary and the like of the silicon crystal. With the popularization of high-efficiency battery technologies such as back passivation and heterojunction, the difference between the conversion efficiency of the cast polycrystalline silicon battery and the monocrystalline battery is larger and larger. Ingot technology requires improvement in the quality of silicon crystals, which relies on the development of ingot single crystal technology based on seed crystal growth.

In the growth process of the ingot silicon crystal, carbon and nitrogen impurities in the molten silicon generally reach saturated solubility concentrations, and the solid-liquid segregation coefficients of the carbon and nitrogen impurities are respectively 0.07 and less than 0.001, which means that most of the carbon and nitrogen impurities are discharged into the molten silicon in the process of forward pushing of a solid-liquid interface. If the molten silicon has no convection with enough strength, the carbon and nitrogen impurities discharged into the melt cannot be taken away in time, and an impurity enrichment layer is formed at the front edge of the interface to promote nucleation and precipitation of silicon carbide and silicon nitride. This can further lead to three negative effects: firstly, forming point-like impurities and shadow defects of infrared detection, and reducing the yield of cast ingots; secondly, the silicon nitride and the silicon carbide precipitate increase the hardness of the crystal brick, so that the crystal brick is more difficult to slice, and further the slicing cost is increased and the slicing yield (the number of the crystal brick per kilogram) is reduced; finally, for cast single crystals, the impact of impurity precipitation is greater, considering that grains and dislocations are more likely to nucleate at impurity sites, affecting single crystal region yield and cell conversion efficiency. Therefore, convection of molten silicon of sufficient strength is a prerequisite for growth of an ingot single crystal.

Another precondition for ingot single crystal growth is to keep the solid-liquid interface flat, that is, to ensure the uniformity and symmetry of temperature distribution and avoid the asymmetry of cold and hot area distribution. During the crystal growth, the flow velocity of the molten silicon reaches several centimeters per second, and the convection heat transfer is the dominant heat transfer form. Therefore, the thermal symmetry depends not only on the symmetry uniformity of the heating body and the thermal field heat-insulating structure, but also on the uniformity symmetry of the silicon melt flow field, and particularly, the local up-and-down tumble flow of the silicon melt is avoided. The upward flow area of the molten silicon is slightly cold, the interface is inclined inwards, the sidewall nucleation and the invasion of a polycrystalline region are caused, and the single crystal proportion is influenced. In the area where the molten silicon flows downwards, scouring of hot silicon flow can cause heat bias, the outer slope of an interface, high thermal stress and increased dislocation density, so that the efficiency of the battery is reduced.

On the premise of ensuring enough convection strength, the circumferential symmetry of convection is kept, and the uniformity of a cold and hot region is improved, so that the method is a core problem to be solved for casting the single crystal. The existing crystal silicon ingot furnace can not meet the two requirements at the same time. About six thousand domestic ingot furnaces are mostly of GT type, and the heater comprises a top heater positioned above the crucible and a side heater positioned on the side surface of the crucibleA heat exchanger. In addition to the top side heater, an independently controlled bottom heater is added below the crucible on large-sized benches for later delivery use. The top, side and bottom heaters are connected to a three-phase AC power supply, respectively. The peak current is typically in the range of 1600 to 2800A at line voltage 25V. The silicon melt is about 10cm from the boom and side heater, and the alternating current generates a magnetic field of 30 to 60 Gauss at the silicon melt surface, which may result in 5 to 10A/cm ² Induced current of (2). Under 50Hz power frequency, the penetration depth (the distance of halving the strength) of the alternating magnetic field at different parts of the molten silicon is approximately within the range of 2 to 4 cm. The induced current is acted by Lorentz force in the magnetic field, and the volume force can reach 10N/m within a few centimeters of the surface of the fused silicon ³ As described above. In the ingot furnace, the rotating magnetic field along the ABC direction causes the rotating flow of the molten silicon in the same direction. Because the current is introduced into the side heater loop from top to bottom through the suspension arm, the current distribution is asymmetric in the vertical direction, so that the molten silicon on the two sides of the electrode is asymmetric in the electromagnetic force in the vertical direction. Taking electrode B as an example, in the vicinity thereof, the silicon melt is pulled upward toward electrode a, and is pushed downward toward electrode C. In the furnace type with low voltage and large current, the electromagnetic stirring force is large, molten silicon convection with enough strength exists, but the molten silicon convection is asymmetric due to the asymmetry of an electromagnetic force field, the distribution of a cold and hot area in the crystal growth process is very uneven, and the high-quality ingot casting single crystal growth cannot be realized.

Besides the electromagnetic stirring force, another driving mechanism of the convection of the molten silicon is thermal convection, namely, buoyancy convection caused by density difference due to temperature difference. The buoyancy is derived from the temperature difference distribution on the same horizontal plane, and the generation of thermal convection is inevitably accompanied by the inclined distribution of the solid-liquid interface. In a flat molten bath, a greater driving force is required to maintain an ordered appropriately strong thermal convection flow field, meaning that in large G7 or G8 size ingots, a greater center-edge solid-liquid interface height difference is required, which can compromise crystal quality. First, an excessively convex interface means a longer edge-growth time, i.e., more severe impurity diffusion, including diffusion of impurities into the silicon ingot in the crucible and back-diffusion of metal impurities segregated and accumulated at the top of the silicon ingot into the interior of the silicon ingot. Secondly, a more convex interface also means that higher stresses will be generated during annealing with temperature homogenization, resulting in a higher dislocation density. Thirdly, in gallium-doped silicon crystal, since the segregation coefficient of gallium is only 0.008, the uneven solid-liquid interface means that low resistance is liable to occur on the upper part of the hot zone crystal brick and the resistivity distribution is not uniform in the same silicon wafer.

Due to the above disadvantages of the over-convex interface, the intensity of the thermal convection can be generally maintained only at a low level under the condition of insufficient electromagnetic stirring force and the need of relying on the thermal convection for impurity removal, and the above weak convection causes the enrichment and precipitation of impurities and various problems related to the impurities. In recent years, at least four crystal silicon ingot casting companies try high-voltage and low-current furnace type design successively. As the electromagnetic stirring force (proportional to the square of the current) is reduced, the convection intensity is reduced, the symmetry of the cold and hot regions of the furnace is automatically and remarkably improved, but the high requirement on the quality of the silicon material is caused after the convection intensity is reduced, the defect of impurity shadow is easy to occur, and the problem that the hardness of crystal bricks is increased and the crystal bricks are difficult to slice is caused, so that several companies are forced to abandon the research and development of the furnace after debugging for several years.

The heating uniformity of the heater is the basis of high-quality crystal growth, the side heater is of an independent control structure in an upper-lower layered mode, the upper layer of the side heater and the top heater are in a parallel connection structure, the top heater and the side heater are designed to achieve local heating amount regulation through thickness change, and the side heater adopts different designs such as a structure that six electrodes share three electrodes with the top heater, and the like, and is disclosed in patents CN107523867, CN107699943 and CN108193266. The structure aims at improving the uniformity of the heating value of the heater, and the problem that the Lorentz force at the suspension arm is not symmetrical cannot be solved. In a large-size ingot, the electromagnetic stirring force plays a leading role, and the problem of asymmetry of a cold and hot region of the ingot cannot be solved only by improving the heating uniformity.

The resistance heater generates heat and uses the current to generate a moving magnetic field to regulate the convection of molten silicon, and the design of the ingot furnace is disclosed in DE102009045680. The side heater is of a multilayer coil structure, although a moving magnetic field in the vertical direction can be generated, the coils of all layers are positioned at different heights, and the external connection electrodes of the coils are not symmetrical on four sides, so that the electromagnetic stirring force field is asymmetrical on four sides. Patent WO2007148988 proposes an ingot furnace structure, wherein a plurality of layers of water-cooling copper coils are arranged between a furnace shell and a heat insulation layer, and alternating currents in different phases are fed in to realize electromagnetic stirring of molten silicon. The structure needs a special power supply unit and coil arrangement, needs additional electric energy consumption and occupies the space in the furnace chamber, which is not beneficial to the upgrading and transformation of the existing ingot furnace. Patent CN111910247 provides an ingot furnace with a rotary crucible, which has the advantages that the problem of asymmetric distribution of a cold area and a hot area can be solved by the rotation of a silicon ingot, but the improvement of a thermal field of the equipment is complex, and the following two defects exist: first, since the average distance between the side heater and the silicon melt is increased by the rotation, the electromagnetic driving force is decreased, and the convection intensity is decreased; secondly, if a nearly circular crucible is used, ingot yield is lost when cutting square tiles, and if a crucible deviating from a circular shape is used, a gap between the crucible and the insulating layer becomes large, resulting in increased power consumption. Patent application 202110144662 provides a side heater design that generates a rotating magnetic field and a uniform upward or downward moving magnetic field around the crucible, achieving better cold and hot zone symmetry under strong electromagnetic stirring. The invention realizes the symmetry of the convection of the molten silicon under strong electromagnetic stirring through the cooperation of the current inside and outside the furnace chamber.

Disclosure of Invention

Aiming at the existing standard side heater structure and aiming at the reason that the electromagnetic force distribution is asymmetric near the suspension arm, the connecting cable of the top heater is arranged outside the furnace chamber, so that the asymmetric distribution of the electromagnetic force field generated by the current structure outside the furnace chamber and the asymmetric distribution of the electromagnetic force field caused by the current of the side heater inside the furnace chamber are opposite in direction and mutually offset and weakened, the internal current and the external current of the furnace chamber are mutually matched, and the symmetry of the convection of the molten silicon under strong electromagnetic stirring is realized, and the detailed characteristics are described as follows.

An electromagnetic stirring device for a crystal growing furnace comprises a top heater, a side heater and a conductor circuit, wherein the top heater is positioned in a furnace chamber, and the conductor circuit is positioned outside the furnace chamber.

The top heater is a loop formed by bending and coiling a graphite heating belt, n electrode access points are approximately and uniformly arranged along the length direction of the top heater, the top heater loop is approximately equally divided into n sections, and n =3 or 4; the n graphite electrodes penetrate through the top heat insulation plate and are connected with a top heater loop at the electrode access point; on the n graphite electrodes, an n-phase alternating voltage is applied, the frequency range of which is 1 to 500Hz, and the voltage range between two adjacent phases is 12V to 72V.

The side heater is a closed loop which is formed by connecting a plurality of sections of heating sections with different shapes end to end in sequence by using bolts and surrounds the crucible for one circle; on the side heating loop, n electrode access points are approximately and uniformly arranged, and the side heater loop is approximately and equally divided into n sections; the n graphite electrodes penetrate through the top or side heat insulation plate above the side heater loop, and are connected with the heater loop at the electrode access point through a suspension arm extending downwards; and applying n-phase alternating voltage to the n graphite electrodes, wherein the frequency of the n-phase alternating voltage is the same as the power supply frequency of the top heater, and the voltage between two adjacent phases ranges from 12V to 72V.

Projecting outwards from the vertical central line of the furnace chamber, the n electrode access points on the side heater loop approximately equally divide the outer wall of the furnace chamber into n fan-shaped areas, and in each fan-shaped area, a furnace chamber outer conductor circuit is respectively arranged and comprises two parts: one is a transverse extension section spanning the sector and positioned between the height of the lower edge of the side heater loop and the height of the upper surface of the top insulation board; two downward extending sections which are respectively positioned at two ends of the transverse extending section and are close to the suspension arm of the side heater; the lateral extension and the two downward extensions are disposed adjacent to an outer wall of the oven cavity.

The n furnace chamber outer conductor circuits are respectively used as one section of a cable connected to the outside of the top heater and are connected in series with the top heater circuit; the lower end of the downward extension section of one side thereof is connected to an outgoing terminal of the power supply of the top heater, and the lower end of the downward extension section of the other side thereof is connected to a graphite electrode of the top heater.

In any m sectors in the total n sectors, m is not more than n, the outer conductor circuit of the furnace chamber can be of a double-turn structure and comprises two parallel and closely-arranged transverse extension sections A and B, two ends of the transverse extension section A are respectively connected with downward extension sections A1 and A2, two ends of the transverse extension section B are respectively connected with downward extension sections B1 and B2, and the two downward extension sections A1 and B1 are adjacent to each other and are positioned on the same side of the sector where the two downward extension sections A1 and B1 are positioned; connecting the lower end of the downward extension section A1 and the lower end of the downward extension section B2 to form a closed double-turn loop; the lower ends of the remaining two downward extensions A2 and B1 are connected, one to an outlet terminal of the power supply of the top heater and the other to a graphite electrode of the top heater.

Preferably, the top and side heater alternating power supplies are both at power frequency.

Preferably, the lateral extension of the oven cavity outer conductor circuit is located between the side heater loop center level and the top heater level. Preferably, the lateral extension section of the oven cavity outer conductor circuit is formed by combining a plurality of horizontal sections and inclined sections.

Preferably, the length of the downward extension section of the oven cavity outer conductor circuit is not less than 0.3 m, and the deviation angle between the downward extension section and the vertical direction is not more than 60 degrees.

Preferably, the deviation distance between any one downward extending section of the furnace cavity outer conductor circuit and the projection position of the adjacent side heater suspension arm on the furnace cavity outer wall in the horizontal direction is not more than 0.6 m; as a further preference, the offset distance is not more than 0.3 m.

Preferably, the clockwise rotation direction along the central vertical axis of the furnace body is defined as the positive current direction, the current phase in any one of the n sections of side heater loops is approximately the same as the current phase in the adjacent transverse extension section of the outer conductor circuit of the furnace chamber in the same sector, and the absolute value of the phase angle difference between the two currents is not more than 60 degrees.

The material of the furnace chamber of the ingot furnace is 321 or 316 stainless steel, the material is non-ferromagnetic material, the magnetic conductivity is approximate to 1, and the electric conductivity is about 1.3e6S/m at normal temperature. At 50Hz line frequency, the skin depth, i.e., the depth at which the current density is reduced to about 37% of the value at the surface, is about 62 mm. G6 chambers typically have an inner wall thickness of 12 mm and an outer wall thickness of 6mm. G8 size oven chambers typically have an inner wall thickness of up to 16mm and an outer wall thickness of 8mm. The total thickness of the furnace wall is in the range of 18-24 mm, which is significantly less than the skin depth, so that the shielding effect of the furnace chamber is limited. Numerical simulation calculation shows that under the conditions that the total thickness of the furnace wall is 20 mm and the diameter of the furnace chamber is 2 m, a vertically upward flat copper busbar is arranged close to the outer side of the furnace wall, power frequency current is applied, the total induced current induced in the furnace wall is about half of the busbar current, and the phase lags about 140-150 degrees.

In the ingot furnace, the electrodes are led in through the upper insulation board, current enters the side heater loop from the upper part, and the current distribution is asymmetric in the vertical direction, so that the molten silicon on the two sides of the electrodes is asymmetric in the electromagnetic force in the vertical direction. Taking electrode B as an example, in the vicinity thereof, the silicon melt is pulled upward toward electrode a, and is pushed downward toward electrode C. By arranging a current loop outside the furnace chamber, the current direction and phase of the current loop are basically consistent with the current in the side loop, and the two currents cooperate to obtain larger electromagnetic stirring force. The current of the side loop is fed in from the upper part, the current of the external circuit is fed in from the lower part, the asymmetric pulling force or pushing force generated at the two sides of the electrode connection points are opposite in direction and partially offset, a more uniform electromagnetic force field is obtained, a uniform and consistent silicon melt flow field is further obtained, and the realization of high-quality ingot casting single crystal growth is facilitated.

Drawings

FIG. 1 is a top heater cable arrangement and electromagnetic stirring structure.

1.3, 8-side heater copper electrodes; 2. 6, 7-top heater copper electrode; 4. 10, 36-top heater copper bar terminal; 5. 13, 28-side heater graphite electrodes; 9. 26, 35-top heater graphite electrode; 14. 32, 37-side heater boom; 15. 29-side adding a loop electrode access point; 21. A snake-shaped heating belt is added at the 27 and 33-sides; 24-top heater heating tape; 25-side heater corner connection plate; 12. 23, 34-transverse extending section of the outer conductor circuit of the furnace chamber; 16. 17, 30, 31-a downward extending section of the oven cavity outer conductor circuit; 18. 19, 20-top heater transformer connection terminals; 11. 22-peripheral connection lines between the downwardly extending segments and the transformer terminals.

Detailed Description

In order to make the aforementioned and other features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below.

FIG. 1 is a top heater and side heater loop with three electrode access points, a cable arrangement and an electromagnetic stirring structure driven by two independent three-phase power supplies. The phase voltages of the top and side transformers are both 25V. The side heater graphite electrodes 13, 28,5 are connected on one side to the side heater booms 14, 32, 37, respectively, and on the other side to the copper electrodes 8,1,3, respectively, which are in turn connected to the side-applied transformer connection terminals a, B, C, respectively. Here, according to the conventional, the potential phases of the a-B-C terminals are sequentially decreased by 120 degrees. The top heater graphite electrodes 35,9, 26 are connected to copper electrodes 2,7,6, respectively, which are in turn connected to bus bar copper terminals 36,4, 10, respectively. The horizontally extending sections 12, 23, 34 and the downwardly extending sections 16, 17, 30, 31 of the outer conductor circuit of the oven cavity are active parts of the outer electromagnetic drive circuit of the oven cavity, which are arranged against the outer wall of the oven cavity. Considering the figure too complex, the two downward extensions of the boom 37 adjacent thereto are not indicated in the figure. The copper bar terminal 36 is connected to the top-loading transformer terminal 19 sequentially through the downward extension section 30, the transverse extension section 23 and the downward extension section 17. The copper bar terminal 4 is connected to the top-loading transformer terminal 20 sequentially through the transverse extension section 34, the downward extension section 31 and the peripheral connecting section 22. The copper bar terminal 10 is connected to the top-added transformer terminal 18 sequentially through the downward extension section 16, the transverse extension section 12 and the peripheral connection section 11.

The connecting portion between the copper bar terminal 36 and the downwardly extending section 30 is a non-working section, and in order to avoid interference with convection of molten silicon, the arrangement route thereof is bent to avoid the sections extending laterally and downwardly. Based on the same consideration, the copper bars 11 and 22 connecting the lower end of the downward extension section and the top heater transformer are also arranged close to the periphery as much as possible, so that the interference on the convection of the molten silicon is avoided. Here the three laterally extending sections are at the same level, approximately level with the upper edge of the side heater loop. The length of the six downwardly extending sections is 0.4 meters. The width of the circuit copper bar outside the furnace cavity is 110 mm, and the thickness of the circuit copper bar is 10 mm.

The potential phase of the side-plus transformer terminal a is zero, and the potential phase of the terminal B is-120 degrees. The loop between the side heater electrode access points 15 and 29, including the serpentine heating strips 21, 27 and the corner connection plates 25, is 30 degrees in phase, defining a clockwise direction along the central vertical axis of the furnace as the positive direction of current flow in the side heater loop and the laterally extending section outside the furnace chamber. Similarly, the current in the serpentine heating zone 33 is in-90 degrees phase. The high-side connections of the top-loading transformer are adjusted so that the potential phases of the terminals 19, 20, 18 are 60, -60, 180 degrees, respectively, and correspondingly the current in the lateral extensions 23, 34, 12 is also 60, -60, 180 degrees. It can be found that the current phase in any section of the side heater loop is 30 degrees behind the current phase in the adjacent transverse extension section of the outer conductor circuit of the furnace chamber in the same sector, and the two groups of current phases are close and mutually overlapped, which is beneficial to obtaining larger electromagnetic stirring force.

In the vertical direction, defined downwards as the positive direction of current flow, the current phase in the side heater booms 14 and 32 is 0 and-120 degrees, respectively. The potential phase of the top heater transformer terminal 18 is 180 degrees and correspondingly the ground current phase in the downward extension 16 is 180 degrees. The ground potential of the terminal 19 is 60 degrees and correspondingly the ground potential in the downward extension 17 is-120 degrees. The sum current in the two downward extensions 16 and 17 is-150 degrees in phase, which is 150 degrees out of phase with the current in the adjacent side heater boom 14, which is approximately in the opposite direction. Analysis also reveals that the current phases in the downward extensions 30 and 31 are 60 and 120 degrees, respectively, and that the sum of the currents is 90 degrees in phase, which is 150 degrees out of phase with the current in the adjacent boom 32, with the currents being approximately opposite. The mutually opposite vertical direction currents are beneficial to reducing the upward or downward electromagnetic stirring force on the two sides of the suspension arm, so that a more uniform rotating force field is obtained.

The three copper bar terminals and the three top heater copper electrodes can be connected and combined in six independent modes, the current phase outside the furnace cavity can be arranged 30 degrees ahead of the current of the side heater in the above example, and the current phase difference can be obtained by 60, 0, -30 or-60 degrees through selection of a transformer and different wiring modes. Which setting is specifically selected is adjusted accordingly according to the actual requirements for thermal field symmetry and convection strength. The top or side transformer may be selected to have a higher voltage if the convective intensity is sufficient and it is desired to improve the hot and cold zone uniformity during crystal growth. The side heater in the example is a typical snake-shaped periodic structure, and can also be a single-layer or multi-layer parallel carbon-carbon composite straight plate, or a combined structure of the single-layer or multi-layer parallel carbon-carbon composite straight plate, which is determined according to practical conditions such as transformer voltage selection and the like. In the embodiment, the transverse extension section of the circuit outside the furnace cavity is horizontally arranged and can also be arranged in an inclined or step shape, and the downward extension section can be vertically downward or inclined at a certain angle so as to compensate and correct the special cold and hot area distribution near the suspension arm under different side heater structures. The auxiliary connection circuit outside the furnace chamber outside the transverse extending section and the downward extending section can be varied, and the key point is that the auxiliary connection circuit is properly far away from the silicon melt to avoid interference.

In the embodiment, the top heater and the side heater are both connected with a three-phase alternating power supply. The central points of two low-voltage coils of a Scott transformer with a common structure are communicated, and a four-phase alternating power supply with a phase angle difference of 90 degrees can be obtained. The top and side heaters of the four electrodes are connected by two four-phase power supplies, and the conductive structure outside the furnace chamber is correspondingly arranged, so that the three-phase power supply can be directly popularized to the four-phase power supply structure.

The key point of the invention is to arrange a circuit outside the furnace chamber, the phase of the horizontal transverse current of the circuit is basically consistent with the current of the heater inside the furnace, stronger electromagnetic stirring force is obtained by mutual reinforcement, the current in the vertical direction of the circuit is approximately opposite to the current of the suspension arm of the heater inside the furnace, and a more uniform stirring force field is obtained by mutual offset. Numerous modifications and equivalents will occur to those skilled in the art without departing from the spirit of the invention and should be considered as within the scope of the invention and the invention is not limited to the specific embodiments described above.

Claims (10)

1. The utility model provides an electromagnetic stirring device that crystal growth furnace was used, includes the top heater that is located the furnace chamber inside, and lateral part heater and the conductor circuit three part that are located the furnace chamber outside, characterized by:

a. the top heater is a loop formed by bending and coiling a graphite heating belt, n electrode access points are approximately and uniformly arranged along the length direction of the top heater, the top heater loop is approximately divided into n sections, and n =3 or 4; the n graphite electrodes penetrate through the top heat insulation plate and are connected with a top heater loop at the electrode access points; applying n-phase alternating voltage to the n graphite electrodes, wherein the frequency range of the n-phase alternating voltage is 1 to 500Hz, and the voltage range between two adjacent phases is 12V to 72V;

b. the side heater is a closed loop which is formed by connecting a plurality of sections of heating sections with different shapes end to end in sequence by using bolts and surrounds the crucible for one circle; on the side heating loop, n electrode access points are approximately and uniformly arranged, and the side heating loop is approximately and uniformly divided into n sections; the n graphite electrodes are arranged above the side heater loop, firstly penetrate through the top or side heat insulation plate, and then are respectively connected with the heater loop at the electrode access point through a suspension arm extending downwards; applying n-phase alternating voltage on the n graphite electrodes, wherein the frequency of the n-phase alternating voltage is the same as the power supply frequency of the top heater, and the range of the voltage between two adjacent phases is 12V to 72V;

c. projecting outwards from the vertical central line of the furnace chamber, the n electrode access points on the side heater loop approximately equally divide the outer wall of the furnace chamber into n fan-shaped areas, and in each fan-shaped area, a furnace chamber outer conductor circuit is respectively arranged and comprises two parts: one is a transverse extension section spanning the sector and positioned between the height of the lower edge of the side heater loop and the height of the upper surface of the top insulation board; two downward extending sections which are respectively positioned at two ends of the transverse extending section and are close to the suspension arm of the side heater; the transverse extending section and the two downward extending sections are arranged close to the outer wall of the furnace cavity;

d. the n furnace chamber outer conductor circuits are respectively used as one section of a cable connected to the outside of the top heater and are connected in series with the top heater circuit; the lower end of one side of the downward extending section is connected to an outgoing terminal of a top heater power supply, and the lower end of the other side of the downward extending section is connected to a top heater graphite electrode.

2. The electromagnetic stirring device of claim 1, wherein m is not greater than n in any m sectors out of the total n sectors, the conductive circuit outside the oven cavity may be a double-turn structure including two parallel and closely-arranged laterally extending sections a and B, two ends of the laterally extending section a are respectively connected to the downwardly extending sections A1 and A2, two ends of the laterally extending section B are respectively connected to the downwardly extending sections B1 and B2, and two downwardly extending sections A1 and B1 are adjacent to each other and located on the same side of the sector; connecting the lower end of the downward extension section A1 with the lower end of the downward extension section B2 to form a closed double-turn loop; the lower ends of the remaining two downward extensions A2 and B1 are connected, one to an outgoing terminal of the power supply of the top heater and the other to a graphite electrode of the top heater.

3. The electromagnetic stirring device of claims 1-2, wherein the top and side heater alternating power supplies are power frequency.

4. The electromagnetic stirring device of claims 1-3, wherein the lateral extension of the oven cavity outer conductor circuit is located between the side heater loop center height and the top heater height.

5. The electromagnetic stirring device of claims 1-4, wherein the lateral extension of the outer conductor circuit of the oven cavity is formed by a combination of a plurality of horizontal sections and inclined sections.

6. The electromagnetic stirring device as set forth in claims 1-5, wherein the length of the downward extension of the outer conductor circuit of the oven cavity is not less than 0.3 m, and the deviation angle from the vertical direction is not more than 60 degrees.

7. The electromagnetic stirring device of claims 1-6, wherein the horizontal deviation distance between any downward extension of the outer conductor circuit of the furnace chamber and the projected position of the adjacent heater boom on the outer wall of the furnace chamber is not greater than 0.6 m.

8. The electromagnetic stirring apparatus of claims 1-6 wherein any downward extending section of the outer conductor circuit of the furnace chamber is horizontally offset from the projected position of the adjacent heater boom on the outer wall of the furnace chamber by no more than 0.3 m.

9. The electromagnetic stirring apparatus as set forth in claim 1 to 8, wherein the clockwise direction of rotation along the central vertical axis of the furnace body is defined as the positive direction of current flow, the phase of current flow in any one of the n-stage side heater loops is substantially the same as the phase of current flow in the adjacent laterally extending stage of the outer conductor circuit of the furnace chamber located in the same sector, and the absolute value of the phase angle difference between the two currents is not more than 60 degrees.

10. A crystalline silicon ingot furnace, comprising a furnace body, wherein a heat-insulating layer cage body is arranged in the furnace body, a directional solidification heat exchange block is arranged in the heat-insulating layer cage body, a crucible is arranged above the heat exchange block, and the crystalline silicon ingot furnace is characterized in that an electromagnetic stirring device as set forth in any one of claims 1-9 is also arranged in the furnace body.

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