Crystalline silicon ingot heater and method of using the same
By designing a flexible controlled crystalline silicon ingot heater in the polycrystalline silicon ingot casting process, the problem of unbalanced temperature gradient of silicon melt is solved, the crystal growth rate and ingot cycle are optimized, and the production cost and dislocation density are reduced. Improve the quality of polycrystalline silicon ingots.
Patent Information
- Application Number
- CN201811389892.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2018-11-21
- Publication Date
- 2024-12-31
- Estimated Expiration
- 2038-11-21
AI Technical Summary
During the polycrystalline silicon ingot casting process, there is an imbalance in the longitudinal and transverse temperature gradients in the silicon melt, which slows down the crystal growth rate, extends the ingot cycle and time-consuming, and increases production costs.
Design a crystalline silicon ingot heater, including top and side heaters, the side heaters are divided into two parts, upper and lower parts, and the respective heating power is controlled through series unit to optimize heat compensation, and avoid the "cold wall effect" and thermal stress, adjust the temperature gradient and crystal growth rate.
It effectively shortens the time spent in long crystals and ingot cycle, reduces the dislocation density and production energy consumption in silicon ingots, and improves the quality and photoelectric conversion efficiency of polycrystalline silicon ingots.
Smart Images
Figure CN109402734B_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the field of silicon ingot preparation, and in particular to a crystalline silicon ingot heater and a method for using the same. Background Art
[0002] The process of directional crystallization casting polysilicon ingots is simple and easy to industrialize, with large output and relatively low production cost, so cast polysilicon is the most widely used solar material. However, compared with traditional thermal power generation, the cost of solar photovoltaic power generation is still relatively high, so it is still necessary to further optimize the polysilicon ingot casting process, increase production, improve the quality of polysilicon ingots, and improve the photoelectric conversion efficiency, thereby reducing the cost of solar power generation.
[0003] Directional solidification crystal growth is to conduct heat downward through the heat exchange block (DSS block), and at the same time, the heat is compensated by the heating system in the polysilicon ingot furnace, so as to form a longitudinal temperature gradient in the silicon melt and grow columnar polysilicon with different crystal directions. However, in the actual ingot casting process, there is not only a large longitudinal temperature gradient in the silicon melt, but also a relatively obvious transverse temperature gradient. The crystal growth interface is an uneven "W" shape. There are more thermal stresses in the crystal during the ingot casting process, which is also an important reason for the formation of dislocation bundles in polysilicon ingots. The heating system of the polysilicon ingot furnace includes a top heater and a side heater. A small number of ingot furnaces also include a bottom heater. The top and bottom heaters are connected in parallel. During the opening of the insulation cage, the heat is compensated from the top and bottom of the silicon solution. However, as the crystal continues to grow, the silicon melt receives more and more heat radiated by the top and side heaters, and the heat conduction to the outside through the DSS block becomes slower and slower. The longitudinal temperature gradient in the silicon melt decreases, and the crystal growth speed becomes slower and slower, which restricts the crystal growth time and the ingot casting cycle, thereby affecting the ingot casting energy consumption and production cost. Summary of the invention
[0004] Based on this, it is necessary to provide a crystalline silicon ingot heater and a method of using the heater to address the time-consuming crystal growth and long ingot casting cycle.
[0005] A crystalline silicon ingot heater, comprising
[0006] Top heater;
[0007] The side heater comprises an upper side heater and a lower side heater, wherein the upper side heater and the top heater are connected in series to form a series unit, and the series unit and the lower side heater are independently connected to a power source.
[0008] The above-mentioned crystalline silicon ingot heater, the side heater is divided into two parts, one part is independently connected to the power supply, and the other part is connected in series with the top heater, so that the respective heating power can be conveniently controlled during the crystal growth process, so that the side heater can be flexibly controlled to radiate heat to the silicon material, thereby optimizing the crystal growth time and ingot cycle.
[0009] In one embodiment, the series unit is connected to a three-phase AC power source, and the lower side heater is connected to a different three-phase AC power source.
[0010] In one embodiment, the top heater includes two serpentine heaters arranged side by side in the same plane, two S-shaped heaters are respectively arranged on both sides of each serpentine heater, the side upper heaters are evenly distributed at four locations along the circumferential direction, each side upper heater includes two U-shaped heaters arranged side by side, the top heater and the four side upper heaters form two series sub-units, wherein each series sub-unit is formed by connecting four U-shaped heaters arranged in sequence in series by one serpentine heater and two S-shaped heaters on both sides of the serpentine heater, and graphite electrodes are respectively connected to the two S-shaped heaters in the series sub-unit.
[0011] In one of the embodiments, in the series sub-unit, along the circumferential direction, adjacent U-shaped heaters are connected in series in sequence through S-shaped heaters or snake-shaped heaters, wherein both ends of the snake-shaped heater are connected to the U-shaped heater through an adapter plate, and both ends of the S-shaped heater are connected to the U-shaped heater through an adapter plate.
[0012] In one embodiment, the width of the adapter plate to which the S-shaped heater is connected differs from the width of the S-shaped heater by less than 10 mm.
[0013] In one of the embodiments, the inner surface of the upper side heater and the inner surface of the lower side heater are on the same plane.
[0014] In one of the embodiments, the distance between the upper side heater and the lower side heater is 10 mm to 60 mm.
[0015] In one embodiment, the resistance of the lower side heater is not greater than the sum of the resistances of the upper side heater and the top heater in series; the resistance of the upper side heater is less than 1 / 2 of the sum of the resistances of the upper side heater and the top heater in series.
[0016] The method for using the above-mentioned crystalline silicon ingot heater comprises the steps of:
[0017] In the first stage of crystal growth, the heating power of the lower heater on the side is made greater than the heating power of the upper heater on the side;
[0018] In the second stage of crystal growth, the heating power of the lower side heater is gradually reduced or the lower side heater is turned off.
[0019] The above method increases the heating power of the lower side heater in the early stage of crystal growth to avoid the occurrence of "cold wall effect", and reduces or turns off the heating power of the lower side heater in the later stage of crystal growth, and only uses the upper side heater to accelerate the dissipation of heat in the silicon crystal. At the same time, it optimizes the temperature gradient and crystal growth rate in the silicon melt in the later stage of crystal growth, so that the crystal growth rate fluctuates less during the crystal growth process, optimizes the crystal growth time and ingot casting cycle, reduces the dislocation density in the silicon crystal, reduces production energy consumption and cost, and further improves the quality of silicon ingots.
[0020] In one of the embodiments, in the first stage of crystal growth, the ratio of the heating power of the lower side heater to the heating power of the upper side heater is not less than 4.5:2; in the second stage of crystal growth, the ratio of the heating power of the lower side heater to the heating power of the upper side heater is not greater than 1:2. BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Figure 1 It is a schematic diagram of the three-dimensional structure of a heater according to an embodiment of the present invention;
[0022] Figure 2 It is a schematic diagram of assembling a heater and a graphite crucible according to an embodiment of the present invention;
[0023] Figure 3 A schematic diagram of the connection between a top heater and a side heater in a heater according to an embodiment of the present invention;
[0024] Figure 4 for Figure 3 A schematic top view of the structure shown;
[0025] Figure 5 and Figure 6 They are Figure 3 Side schematic diagrams of the structure shown at different angles;
[0026] Figure 7 A schematic diagram of a cross-section PL of a polycrystalline silicon ingot produced by a method for using a heater according to an embodiment of the present invention; and
[0027] Figure 8 FIG. 1 is a diagram of minority carrier lifetime in a cross section of a polycrystalline silicon ingot produced by a method for using a heater according to an embodiment of the present invention. DETAILED DESCRIPTION
[0028] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed below.
[0029] It should be noted that when an element is referred to as being "fixed to" another element, it may be directly on the other element or there may be an intermediate element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be an intermediate element at the same time.
[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.
[0031] refer to Figure 1 One embodiment of the present invention discloses a crystalline silicon ingot heater, comprising a top heater 10 and a side heater 20. The side heater 20 comprises an upper side heater 210 and a lower side heater 220, wherein the upper side heater 210 and the top heater 10 are connected in series to form a series unit, wherein the series unit and the lower side heater 220 are independently connected to a power source. In other words, in this embodiment, dual power supply control is adopted. The electrode installation positions of the top heater 10 and the side heater 20 in the ingot furnace can be consistent with those of the conventional single power supply controlled graphite heater. When dual power supply control is used, the rated total power of the crystalline silicon ingot heater is not less than the rated total power when a single power supply is used.
[0032] The upper side heater 210 and the top heater 10 form a series unit, and the series unit and the lower side heater 220 can be independently controlled in the circuit, so that the heating power of each can be conveniently controlled during the crystal growth process, so that the heat radiated to the silicon material by the side heater 20 can be flexibly controlled, thereby optimizing the crystal growth time and the ingot casting cycle. Specifically, the heating power of the lower side heater 220 can be increased in the early stage of crystal growth to avoid the occurrence of the "cold wall effect", thereby weakening the side nucleation effect; in the late stage of crystal growth, the heating power of the lower side heater 220 is reduced or turned off, and only the upper side heater 210 is used to accelerate the heat dissipation in the silicon crystal, and at the same time optimize the temperature gradient and crystal growth rate in the silicon melt in the late stage of crystal growth, so that the crystal growth rate fluctuates less during the crystal growth process, optimizes the crystal growth time and the ingot casting cycle, reduces the dislocation density in the silicon crystal, reduces production energy consumption and costs, and further improves the quality of silicon ingots. In addition, the side upper heater 210 is connected in series with the top, which can increase the total heat release power of the side, reduce the heating power of the top heater 10 (part of the heating power is distributed to the side upper heater 210), optimize the crystal growth interface, avoid the appearance of microcrystals in the crystal, and reduce the thermal stress in the crystal and reduce the proportion of square cracks in the silicon ingot.
[0033] According to some embodiments of the present invention, the upper side heater 210 and the top heater 10 are connected to a three-phase AC power supply, and the lower side heater 220 is connected to a different three-phase AC power supply, thereby achieving independent control of the circuit. Figure 1 As shown, four first graphite electrodes 110 are connected to the series unit composed of the side upper heater 210 and the top heater 10 for connecting to a three-phase AC power supply.
[0034] According to some embodiments of the present invention, the top heater 10 includes two serpentine heaters 120 arranged side by side in the same plane, and two S-shaped heaters 130 are respectively arranged on both sides of each serpentine heater 120. Four upper side heaters 210 are arranged. Each upper side heater 210 includes two U-shaped heaters 211 arranged side by side. The top heater 10 and the upper side heater 210 form two series sub-units, wherein each series sub-unit is formed by connecting four U-shaped heaters 211 arranged in series by one serpentine heater 120 and two S-shaped heaters 130 on both sides thereof, and the first graphite electrodes 110 are respectively connected to the two S-shaped heaters 130 in the series sub-unit. The lower side heater 220 is arranged in a serpentine shape, and the second graphite electrodes 221 are respectively connected to its two ends.
[0035] Specifically, Figure 1 , Figures 3 to 6 As shown, two serpentine heaters 120 are placed side by side, and two S-shaped heaters 130 are respectively arranged on both sides of each of the two serpentine heaters 120. In this way, the four S-shaped heaters 130 and the two serpentine heaters 120 are arranged along the circumferential direction as a whole and roughly form a rectangle, wherein the four S-shaped heaters 130 form a pair of sides of the rectangle, and the two serpentine heaters 120 form another pair of sides of the rectangle. The eight U-shaped heaters 211 are evenly arranged at the four sides of the rectangle, that is, two U-shaped heaters 211 are arranged side by side on each side. Figure 4 As shown, the serpentine heater 120 on the left side and the two S-shaped heaters 130 on the upper and lower sides of the serpentine heater 120 connect a total of four U-shaped heaters 211 in series to form series sub-units a and b. Figure 1 In the three-dimensional structural schematic diagram shown, two series-connected sub-units a and b are arranged roughly up and down. Figure 4 In the top view shown, two series-connected subunits a and b are arranged side by side.
[0036] Furthermore, in the series subunit, adjacent U-shaped heaters 211 are sequentially connected in series along the circumferential direction through the serpentine heater 120 or the S-shaped heater 130, wherein both ends of the serpentine heater 120 are connected to the U-shaped heater 211 through a transfer plate 40, and both ends of the S-shaped heater 130 are connected to the U-shaped heater 211 through a transfer plate 40. Figure 1 , Figure 4 Taking the series subunit a as an example, the two U-shaped heaters 211 in the middle of the four U-shaped heaters 211 in the series subunit a each have an end connected to an adapter plate 40, and the two adapter plates 40 are respectively connected to the two ends of the snake-shaped heater 120. In this way, the snake-shaped heater 120 connects the two middle U-shaped heaters 211 in series. Similarly, the S-shaped heater 130 connects the remaining ends of the two middle U-shaped heaters 211 to the U-shaped heater 211 located on the outside through the adapter plate. In this way, the four U-shaped heaters 211 form a series subunit a through one snake-shaped heater 120 and two S-shaped heaters 130. For the series subunit b, the connection method is similar to that of the series subunit a and will not be repeated.
[0037] Furthermore, the width of the adapter plate 40 connected to the S-shaped heater 130 differs from the width of the S-shaped heater 130 by less than 10 mm. This size can ensure a more uniform distribution of thermal power, while ensuring that the distance between the side heater and the side insulation screen in the ingot furnace is within a safe distance.
[0038] Furthermore, the amplitude of the side lower heater 220 is consistent with the width of the U-shaped heater 211. Figure 1 As shown, the side lower heater 220 is a serpentine heater, and the amplitude (ie, height) of each serpentine heater is consistent with the width of the U-shaped heater 211 constituting the side upper heater 210. This structure allows the radiant heat of the U-shaped heater 211 to be mainly distributed in the middle and upper part of the silicon material.
[0039] In the above embodiment, the top heater 10 includes two types of heaters, S-shaped and U-shaped, and the side upper heater 210 is composed of a U-shaped heater 211. It can be understood that according to the thermal field characteristics of the ingot furnace, heaters of other shapes, such as elliptical or rectangular shapes, can be selected.
[0040] According to some embodiments of the present invention, the inner surface of the upper side heater 210 and the inner surface of the lower side heater 220 are on the same plane, ensuring that the distance between the surface of the side heater composed of the upper side heater 210 and the lower side heater 220 and the crucible is consistent, and the distance between the crucible and the side insulation screen is within a safe distance. The inner surface here refers to the surface of the upper side heater 210 or the lower side heater 220 that is opposite to the graphite crucible 50. Figure 2 As shown, when the side heater 20 is assembled with the graphite crucible 50 , the inner surface of the upper side heater 210 and the inner surface of the lower side heater 220 together constitute the inner wall of the space enclosed by the side heater 20 .
[0041] According to some embodiments of the present invention, the width of the lower side heater 220 is less than 50 mm from the width of the upper side heater 210, ensuring that the radiant heat of the U-shaped heater 211 is distributed in the middle and upper part of the silicon material. The distance between the upper side heater 210 and the lower side heater 220 is 10 mm to 60 mm.
[0042] According to some embodiments of the present invention, the material of the upper side heater 210 and the lower side heater 220 is CC fiberboard or graphite. It can be understood that the material can be determined according to the resistance characteristics of the material itself and the requirements of the ingot furnace thermal field on the heater resistance.
[0043] According to some embodiments of the present invention, the resistance of the lower side heater 220 is not greater than the sum of the resistances of the upper side heater 210 and the top heater 10 connected in series; the resistance of the upper side heater 210 is less than 1 / 2 of the sum of the resistances of the upper side heater 210 and the top heater 10 connected in series. By regulating the power distribution on the top and the side, the crystal growth interface is made smoother and the crystal growth time consumption is more effectively regulated.
[0044] An embodiment of the present invention further provides a method for using the crystalline silicon ingot heater of the above embodiment. The method includes the following steps.
[0045] S100 , in the first stage of crystal growth, the heating power of the lower side heater 220 is made greater than the heating power of the upper side heater 210 .
[0046] According to the crystal growth rate, crystal growth can be roughly divided into two stages. The first stage is the initial stage of crystal growth, during which the height of the generated crystal generally does not exceed 30% of the crystal height. During this stage, the heating power of the lower heater 220 on the side is made greater than the heating power of the upper heater 210 on the side, thereby avoiding the occurrence of the "cold wall effect", reducing the side nucleation caused by the "cold wall effect", and improving the crystal growth interface.
[0047] S120. In the second stage of crystal growth, gradually reduce or turn off the heating power of the lower side heater 220. The second stage is the middle and late stages of crystal growth. In this stage, by gradually reducing the heating power of the lower side heater 220, the upper side heater 210 is mainly used to radiate heat into the graphite crucible 50; or the lower side heater 220 is turned off, and only the upper side heater 210 is used to radiate heat into the graphite crucible 50. In this way, the heat dissipation in the silicon crystal is accelerated, the crystal growth speed is accelerated, and the purpose of optimizing the temperature gradient and crystal growth rate in the silicon solution in the late stage of crystal growth is achieved. At the same time, the crystal growth rate fluctuates less during the crystal growth process, the residual thermal stress in the silicon crystal is smaller, the dislocation density in the silicon crystal is reduced, the production energy consumption and cost are reduced, and the quality of silicon ingots is further improved.
[0048] According to some embodiments of the present invention, in the first stage of crystal growth, the ratio of the heating power of the lower side heater 220 to the heating power of the upper side heater 210 is not less than 4.5:2; in the second stage of crystal growth, the ratio of the heating power of the lower side heater 220 to the heating power of the upper side heater 210 is not greater than 1:2.
[0049] The crystalline silicon ingot heater and its use method according to an embodiment of the present invention are described below with reference to an embodiment.
[0050] In one embodiment, the crystalline silicon ingot heater includes a top heater 10 and a side heater. The side heater 20 includes a side upper heater 210 and a side lower heater 220. The top heater 10 includes two serpentine heaters 120 arranged side by side in the same plane, and two S-shaped heaters 130 are respectively arranged on both sides of each serpentine heater 120. The side upper heater 210 includes eight U-shaped heaters 211 arranged in a circumferential direction. The top heater 10 and the side upper heater 210 form two series sub-units, wherein each series sub-unit is formed by a serpentine heater 120 and two S-shaped heaters 130 on both sides thereof connecting four U-shaped heaters 211 arranged in series, and the two S-shaped heaters in the series sub-unit are respectively connected to graphite first graphite electrodes. The width of the adapter plate 40 is 70 mm, and the length of the adapter plate at different positions may be different. The width of the serpentine heater 120 and the S-shaped heater 130 is 70 mm.
[0051] The width of the upper side heater 210 is 83 mm and the thickness is 26 mm. However, it should be noted that the line length (i.e., the total length after unfolding) of the upper side heaters at different positions may be different. The resistance of the lower side heater 220 is equal to the sum of the resistances of the top heater 10 and the upper side heater 210, and the resistance ratio of the upper side heater 210 to the top heater 10 is 1:2.
[0052] When the crystalline silicon ingot heater is installed in the ingot furnace, Figure 2 The distance between the lower edge of the side lower heater 220 and the graphite bottom plate is 25 mm, and the safety distance between the upper edge of the side lower heater 220 and the side upper heater 210 is 30 mm. The upper edge of the side upper heater 210 is 20 mm higher than the upper surface of the graphite crucible 50. The inner surface of the side upper heater 210 and the inner surface of the side lower heater 220 are in the same plane.
[0053] In the early stage of crystal growth, the heating power ratio of the lower heater 220 on the side to the upper heater 210 on the side is 5.5:4.5; in the middle and late stages of crystal growth, the heating power of the lower heater 220 on the side is gradually reduced; in the late stage of crystal growth, the heating power ratio of the lower heater 220 on the side to the upper heater 210 on the side is controlled at 1:4; in the late stage of crystal growth, the lower heater 220 on the side is turned off. Calculations show that the ingot casting cycle is 85 hours, which is 7 hours shorter than the production cycle of 92 hours in the same period. In addition, Figure 7 and Figure 8 As shown, the side nucleation caused by the "cold wall effect" of the polycrystalline silicon crystal cast by the above-mentioned crystalline silicon heater is significantly weakened, the crystal growth interface is slightly convex, no black dislocation bundles appear in the surrounding ingots, and the dislocation distribution of the small square ingot in the middle is consistent with that of a normal silicon ingot.
[0054] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.
Claims
1. A method for using a crystalline silicon ingot heater, characterized in that: The crystalline silicon ingot heater comprises a top heater; a side heater comprises an upper side heater and a lower side heater, wherein the upper side heater and the top heater are connected in series to form a series unit, and the series unit and the lower side heater are independently connected to a power supply, and the method comprises: In the first stage of crystal growth, the heating power of the lower heater on the side is made greater than the heating power of the upper heater on the side; In the second stage of crystal growth, the heating power of the lower side heater is gradually reduced or the lower side heater is turned off.
2. The method according to claim 1, characterized in that In the first stage of crystal growth, the ratio of the heating power of the lower side heater to the heating power of the upper side heater is not less than 4.5:2; in the second stage of crystal growth, the ratio of the heating power of the lower side heater to the heating power of the upper side heater is not greater than 1:
2.
3. The method according to claim 1, characterized in that The series unit is connected to a three-phase AC power source, and the side lower heater is connected to a different three-phase AC power source.
4. The method according to claim 1, characterized in that The top heater includes two serpentine heaters arranged side by side in the same plane, two S-shaped heaters are arranged on both sides of each serpentine heater, and the side upper heaters are evenly distributed at four locations along the circumferential direction, each side upper heater includes two U-shaped heaters arranged side by side. The top heater and the four side upper heaters form two series sub-units, wherein each series sub-unit is formed by connecting four U-shaped heaters arranged in sequence in series, including one serpentine heater and two S-shaped heaters on both sides of the serpentine heater, and graphite electrodes are connected to the two S-shaped heaters in the series sub-unit respectively.
5. The method according to claim 4, characterized in that In the series sub-unit, along the circumferential direction, adjacent U-shaped heaters are connected in series in sequence through S-shaped heaters or snake-shaped heaters, wherein both ends of the snake-shaped heater are connected to the U-shaped heater through an adapter plate, and both ends of the S-shaped heater are connected to the U-shaped heater through an adapter plate.
6. The method according to claim 5, characterized in that The difference between the width of the adapter plate to which the S-shaped heater is connected and the width of the S-shaped heater is less than 10 mm.
7. The method according to claim 4, characterized in that The amplitude of the lower side heater is consistent with the width of the U-shaped heater.
8. The method according to claim 1, characterized in that The inner surface of the upper side heater and the inner surface of the lower side heater are on the same plane.
9. The method according to claim 1, characterized in that: The distance between the upper side heater and the lower side heater is 10 mm to 60 mm.
10. The method according to claim 1, characterized in that The resistance of the lower side heater is not greater than the sum of the resistances of the upper side heater and the top heater connected in series; the resistance of the upper side heater is less than 1 / 2 of the sum of the resistances of the upper side heater and the top heater connected in series.