Graphite electrode for single crystal furnace

Abstract

The utility model provides a graphite electrode for a single crystal furnace, and relates to the field of monocrystalline silicon production. The graphite electrode for a single crystal furnace comprises: an extension part extending from one end to the other end; the butt joint part is arranged at one end of the extension part; wherein the area of the butt joint surface of the butt joint part and the heater is larger than the sectional area of the extension part in the extension direction, and a transition structure with a gradually-changed sectional area is arranged at the joint of the extension part and the butt joint part, so that the situation that the current density is obviously increased due to sudden change of the sectional area at the joint of the extension part and the butt joint part can be avoided; according to the utility model, the corrosion speed of the contact end of the graphite electrode is reduced, the corrosion of a deposition layer on the heater to a conductive area is slowed down, and the current density is reduced, so that electrical sparks are reduced, and furnace shutdown accidents are avoided.

Description

Technical Field

[0001] The utility model relates to the field of single crystal silicon production, in particular to a graphite electrode for a single crystal furnace. Background Art

[0002] In the single crystal furnace used in the production of single crystal silicon, the electrical spark phenomenon of the heater has always been a problem that has troubled single crystal silicon production companies. Figure 9 As shown in the , conventional heaters include a main heater and a furnace bottom heater. Electrical sparks can occur simultaneously in both heaters; sparks from one heater can trigger further sparks in both heaters; or one heater can continuously spark. Due to the lack of clear research and conclusions on the various causes of electrical sparks in the monocrystalline silicon industry, the heater sparking phenomenon continues to remain unresolved.

[0003] In view of the above situation, how to explore and discover from a fundamental level and solve the problem of heater electrical sparking from a fundamental perspective has become an urgent problem to be solved. At present, the electrical spark phenomenon of heaters in single crystal silicon production is generally believed to have the following causes: 1. Insufficient heating distance; 2. Poor contact; 3. Impurities causing electrical sparks; 4. Direct grounding type electrical spark phenomenon. The heating distance refers to the distance between the heater and other thermal field components. The heating distance falls within the scope of thermal field design and installation operations. The above four items are considered by most companies to be the main causes of electrical sparking. The existing technology can reduce the occurrence of the above four electrical spark phenomena through appropriate methods.

[0004] However, the electrical spark phenomenon at the contact point between the heater and the electrode is a chronic disease in the industry. The monocrystalline silicon industry lacks effective means to solve this type of problem, which creates safety hazards in the use of single crystal furnaces and affects production stability. Utility Model Content

[0005] The utility model aims to solve the problem that in the prior art, there is a lack of effective solution to the electric spark phenomenon at the contact position between the heater and the electrode, which causes safety hazards in the use of single crystal furnaces and affects production stability. The utility model provides a graphite electrode for single crystal furnaces that can avoid electric sparks at the contact position between the graphite electrode and the heater foot plate, thereby improving production safety and stability.

[0006] The technical solution adopted in this utility model is:

[0007] A graphite electrode for a single crystal furnace, comprising:

[0008] an extension extending from one end to the other end; and

[0009] a docking portion, disposed at one end of the extension portion;

[0010] Among them, the area of ​​the docking surface between the docking part and the heater is larger than the cross-sectional area of ​​the extension part in the extension direction, and a cross-sectional area gradient transition structure is provided at the connection between the extension part and the docking part, which can avoid the sudden change of cross-sectional area at the connection between the extension part and the docking part, causing a significant increase in current density.

[0011] Furthermore, a first screw hole and a second screw hole are respectively provided at both ends of the graphite electrode for a single crystal furnace, and at least two ventilation holes are provided on the side of the extension portion, and the ventilation holes are respectively connected to the first screw hole and the second screw hole.

[0012] Furthermore, the area of ​​the butt joint surface between the butt joint portion and the heater is greater than 80% of the cross-sectional area of ​​the extension portion in the extension direction.

[0013] Furthermore, the cross-sectional area gradually changing transition structure is a transition section, the side surface of the transition section is conical, and the entire circumference of the side surface is arc-shaped and concave.

[0014] Furthermore, the ratio of the curvature radius R1 of the arc-shaped concave portion of the transition section side surface to the radial spacing S1 between the cross-section of the butt joint surface and the extension portion is 2:3 to 5:3.

[0015] Furthermore, the cross-sectional area gradually changing transition structure is a transition section, and the side surface of the transition section is a straight cone.

[0016] Furthermore, the cross-sectional area gradual transition structure is in a multi-segment wave shape.

[0017] Furthermore, the connection between the cross-sectional area gradual transition structure and the docking portion is located at the outer edge of the docking portion.

[0018] The beneficial effects of the utility model are:

[0019] 1. The present invention reduces the corrosion rate of the contact end of the graphite electrode by providing a docking portion with an increased docking surface area, slowing down the erosion of the conductive area by the deposited layer on the heater. It also reduces the current density, thereby reducing the generation of electrical sparks and avoiding furnace shutdown accidents. This solves the problem in the prior art of lacking effective solutions to the electrical spark phenomenon at the contact point between the heater and the electrode, which poses a safety hazard in the use of single crystal furnaces and affects production stability.

[0020] 2. The utility model eliminates the high current density at the cross-sectional area mutation point by setting a transition structure with gradual cross-sectional area change, avoids the temperature concentration at the cross-sectional area mutation point where the butt joint and the extension part are connected, and causes rapid corrosion at the contact point of the graphite electrode, thereby slowing down the formation rate of the deposition layer;

[0021] 3. The utility model retains the traditional structure of the single crystal furnace without adding changes to the thermal field structure of other parts. It only improves the structure of the graphite electrode, minimally changing the thermal field structure and saving the cost of thermal field modification. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0023] Figure 1 It is a front view of a graphite electrode in the prior art;

[0024] Figure 2 This is a front view of the graphite electrode of Example 1 of the present utility model;

[0025] Figure 3 This is a three-dimensional schematic diagram of a graphite electrode according to Example 1 of the present utility model;

[0026] Figure 4 This is a three-dimensional perspective view of a graphite electrode according to Example 1 of the present utility model;

[0027] Figure 5 This is a front view of a graphite electrode according to Example 2 of the present utility model;

[0028] Figure 6 This is a three-dimensional schematic diagram of a graphite electrode according to Example 2 of the present utility model;

[0029] Figure 7 This is a front view of a graphite electrode according to Example 3 of the present utility model;

[0030] Figure 8 This is a three-dimensional schematic diagram of a graphite electrode according to Example 3 of the present utility model;

[0031] Figure 9 This is a schematic diagram of the internal structure of a single crystal furnace according to an embodiment of the present utility model;

[0032] Figure 10 for Figure 9 A specific enlarged view of point A in the middle;

[0033] Figure 11 It is a current density simulation diagram of the graphite electrode of the prior art and Example 1 of the utility model;

[0034] Figure 12 It is a temperature simulation diagram of the graphite electrode of the prior art and Example 1 of the present invention.

[0035] Reference numerals: 100 - extension portion, 120 - second screw hole, 130 - vent hole;

[0036] 200- docking portion, 210- first screw hole, 220- transition section, 230- docking surface;

[0037] 300-main heater, 310-heater foot plate;

[0038] 400-bottom heater;

[0039] 500-furnace chassis, 510-quartz sheath;

[0040] 600-quartz crucible;

[0041] 700-furnace cover;

[0042] 800-Secondary room. DETAILED DESCRIPTION

[0043] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation to the present invention.

[0044] The disclosure below provides many different embodiments or examples for realizing different structures of the present invention. In order to simplify the disclosure of the present invention, the components and settings of specific examples are described below. Of course, they are only examples and are not intended to limit the present invention.

[0045] Conventional wisdom holds that sparking at the heater-electrode interface is also caused by poor contact, i.e., a weak contact between the heater's footplate and the graphite electrode in the single crystal furnace. This sparking should be addressed by strengthening contact stability. However, thorough research into the contact between the heater and electrode revealed that the fundamental cause of this poor contact lies in the low conductivity of the deposited layer. The deposited layer forms on the surface of the heater's footplate after the graphite electrode is corroded and melted by the high temperature at the contact point. Traditionally, since the deposited layer is primarily composed of conductive graphite, it is assumed to be conductive.

[0046] Composition analysis and resistance measurements revealed that the deposited layer is primarily composed of silicon carbide, which is non-conductive at room temperature. The measured resistance also indicates that the deposited layer has a very high resistance, indicating that the deposited material is non-conductive at room temperature. Furthermore, over time, the deposited layer gradually covers the contact area between the heater's footplate and the electrode, reducing the effective conductive area at that contact point. When the effective conductive area falls below a certain threshold, current overload at the contact surface inevitably leads to electrical sparking. When electrical sparking occurs, an arc forms at the contact surface. The high temperature of the arc causes the graphite at the contact point to corrode and melt. This melting of the graphite further overloads the contact surface, increasing the melted area. This sparking eventually causes a current overload, exceeding the permitted current and voltage limits of the power equipment, leading to production stoppages and other accidents. The discovery that the deposited layer is non-conductive dispels common misconceptions and expands understanding of the cause of electrical sparking. High temperatures accelerate the corrosion and melting of graphite, creating a deposited layer that reduces the conductive area, causing electrical sparking.

[0047] Based on the above findings, the present invention optimizes the traditional straight-cylinder electrode structure (such as Figure 1 As shown in FIG, a new graphite electrode is proposed, which can effectively reduce the occurrence of electrical sparks, increase the service life of the electrode and heater, and reduce the frequency of furnace shutdown accidents. Specific embodiments are shown below.

[0048] Example 1

[0049] See also Figures 1-12 This embodiment provides a graphite electrode for a single crystal furnace, which is used to interface with the heater foot plate 310 of the single crystal furnace's main heater 300 to conduct high-voltage current. In this embodiment, the single crystal furnace structure using this graphite electrode primarily includes: a furnace cover 700, a furnace drum (not shown), a furnace bottom plate 500, an insulation drum (not shown), a heater, a quartz crucible 600, a flow guide drum (not shown), and a secondary chamber 800.

[0050] like Figure 9 、 Figure 10As shown in FIG, the upper furnace cover 700, the central furnace drum, and the lower furnace base 500 together form the main chamber of the single crystal furnace. The secondary chamber 800 is located above the furnace cover 700 and is connected to the main chamber. Within the main chamber, from the outside to the inside, are arranged an insulation cylinder, a heater, and a quartz crucible 600. The insulation cylinder is wrapped in soft felt, providing insulation for the heater and quartz crucible 600 within. The heaters include a main heater 300 and a bottom heater 400, respectively positioned circumferentially outside and below the quartz crucible 600 to uniformly heat the crucible 600. Below the main heater 300 is a heater footplate 310 for connecting to the electrodes for power supply. The quartz crucible 600 is used to melt silicon material, and a guide tube is located above it to guide crystal pulling. Single crystal furnaces have high requirements for internal thermal field distribution. In this embodiment of the single crystal furnace, the insulation cylinder, heater, graphite electrodes, quartz crucible 600, and guide tube are all components that constitute the thermal field.

[0051] The graphite electrode for a single crystal furnace of this embodiment can increase the area of ​​the interface 230 between the graphite electrode and the heater foot plate 310, reduce the rate of deposition, and prevent electrical sparks from occurring between the graphite electrode and the heater foot plate 310 during use of the single crystal furnace. The graphite electrode for a single crystal furnace primarily comprises an extension portion 100 and a docking portion 200.

[0052] The extension portion 100 is the conductive body of the graphite electrode and is mainly used for current conduction. Figure 2-Figure 4 As shown in FIG, the extension portion 100 extends from one end to the other end to form a generally cylindrical shape.

[0053] The docking portion 200 is provided at one end of the extension portion 100 and is used to dock with the heater foot plate 310. The docking portion 200 is cylindrical on the side where it docks with the heater foot plate 310. A transition section 220 is provided on the side where the docking portion 200 is connected to the extension portion 100. The transition section 220 is conical, extending from the side of the extension portion 100 toward the docking portion 200 and expanding outward. In this embodiment, the entire circumference of the side of the transition section 220 is concave in an arc shape. In this embodiment, the area of ​​the docking surface 230 between the docking portion 200 and the heater foot plate 310 is 10,000 mm2, while the cross-sectional area of ​​the extension portion 100 in the extension axis direction is 4,900 mm2, which is an increase of more than 104%. Figure 1As shown in the prior art, the area of ​​the interface 230 between the graphite electrode and the heater foot plate 310 is close to the cross-sectional area of ​​its extended portion, resulting in a high current density at the contact position of the graphite electrode, high heat generation, and rapid temperature rise of the graphite electrode. The high temperature also accelerates its corrosion rate, causing the rapid formation of a deposit layer. At the same time, the small area of ​​the interface 230 will be quickly covered by the deposit layer, ultimately causing continuous electric sparks to be generated, leading to accidents such as production stoppages. In this embodiment, by enlarging the interface 200 of the electrode, firstly, the interface 230 can be enlarged, reducing the current density and preventing current overload; secondly, the temperature near the interface 230 can be reduced, preventing the interface 230 from rapidly corroding the graphite due to excessive temperature, thereby avoiding the generation of electric sparks; thirdly, while increasing the area of ​​the interface 230, the generation and expansion rate of the deposit layer on the heater is slowed down, reducing the deposition area of ​​the deposit layer, further reducing the generation of electric sparks, and avoiding the occurrence of circuit breaker and furnace shutdown accidents. It should be noted that the graphite electrode in this embodiment can be used to connect to the heater foot plate 310 and can also be used to connect to the connection plate of the bottom heater 400.

[0054] In this embodiment, the graphite electrode for a single crystal furnace is provided with a docking portion 200 with an enlarged docking surface 230, thereby reducing the corrosion rate of the contact end of the graphite electrode, slowing down the erosion of the conductive area by the deposited layer on the heater, and reducing the current density, thereby reducing the generation of electrical sparks and avoiding furnace shutdown accidents. This solves the problem that the existing technology lacks an effective solution to the electrical spark phenomenon at the contact position between the heater and the electrode, causing safety hazards in the use of single crystal furnaces and affecting production stability.

[0055] Furthermore, the advantage of the graphite electrode for the single crystal furnace of this embodiment is that, while retaining the traditional structure of the single crystal furnace, no changes are made to the thermal field structure of other parts. Improvements are made only by changing the structure of the graphite electrode, which minimizes the change in the thermal field structure and saves the cost of thermal field modification.

[0056] In this embodiment, a first screw hole 210 and a second screw hole 120 for upper and lower fixing are also provided at both ends of the graphite electrode. The first screw hole 210 is provided on the docking surface 230 of the docking portion 200 and is used to fix the graphite electrode and the heater foot plate 310 of the upper main heater 300. The second screw hole 120 is provided on the end surface of the extension portion 100 away from the docking portion 200 and is used to fix the graphite electrode and the lower furnace bottom plate 500. The size of the first screw hole 210 and the second screw hole 120 can be selected according to the setting of the thermal field components. In addition, two ventilation holes 130 are provided on the side of the extension portion 100. The two ventilation holes 130 are provided in an upper and lower manner and respectively connect the first screw hole 210 and the second screw hole 120. The function of the two ventilation holes 130 is to facilitate the discharge of air inside the insulation cylinder when the single crystal furnace thermal field is operating at low pressure.

[0057] At the same time, in this embodiment, a transition section 220 with a circular arc-shaped concave portion is provided at one side of the connecting portion 200 and the extending portion 100, thereby forming a transition structure with a gradually changing cross-sectional area. Figure 11 and Figure 12 As can be seen, the gradual transition structure eliminates high current density at the point of sudden change in cross-sectional area, preventing temperature concentration at the junction of the butt joint 200 and the extension 100, which could cause rapid corrosion and melting of the graphite electrode at the contact point, thereby slowing the formation of the deposited layer. Furthermore, in this embodiment, the junction between the transition section 220 and the butt joint 200 is located at the outer edge of the butt joint 200, thereby fully extending the length of the transition section 220 and enhancing the effect of reducing high current density at the sudden change in cross-sectional area.

[0058] In addition, through experiments, it was found that in one or more other embodiments, the area of ​​the interface 230 between the docking portion 200 and the heater foot plate 310 can be expanded by more than 80% relative to the cross-sectional area of ​​the extension portion 100 in the extension axis direction to effectively reduce the current density and slow down the formation of the deposited layer. It should also be noted that in this embodiment, the diameter of the interface 230 between the docking portion 200 and the heater foot plate 310 is 100 mm, and the cross-sectional diameter of the extension portion 100 is 70 mm. Therefore, the radial spacing S1 between the cross-sectional area of ​​the docking portion 200 and the heater foot plate 310 and the extension portion 100 is 30 mm. In addition, the curvature radius R1 of the arc-shaped concave side of the transition section 220 in this embodiment is 30 mm. Therefore, in this embodiment, the ratio of the curvature radius R1 of the arc-shaped concave side of the transition section 220 to the radial spacing S1 between the cross-sectional area of ​​the docking portion 230 and the extension portion 100 is 1:1. Experiments have also found that in one or more other embodiments, when other conditions remain basically unchanged, the curvature radius R1 of the arc-shaped concave side of the transition section 220 is between 20 mm and 50 mm, which has a better effect in preventing current density concentration. At this time, the ratio of the curvature radius R1 of the arc-shaped concave side of the transition section 220 to the cross-sectional radial spacing S1 between the docking surface 230 and the extension portion 100 is in the range of 2:3 to 5:3.

[0059] Example 2

[0060] Based on Example 1, a variation is proposed.

[0061] See also Figure 5 、 Figure 6 The main difference between Example 2 and Example 1 is that the transition section 220 in Example 2 is a cone with straight sides, and also expands outward when extending from the side of the extension portion 100 to the docking portion 200.

[0062] In this embodiment, the junction between the transition section 220 and the butt joint 200 is also located at the outer edge of the butt joint 200. The flat, tapered transition section 220 also reduces current density concentration. Functionally, this embodiment differs from Example 1 in that the transition section 220 of the graphite electrode for a single crystal furnace in this embodiment is more easily machined and formed. However, the cross-sectional area of ​​the transition section 220 at the junction with the extension 100 in this embodiment changes rapidly, resulting in a less smooth transition and a slight current density concentration at the junction.

[0063] Example 3

[0064] Based on Example 1, a variation is proposed.

[0065] See also Figure 7 、 Figure 8 The main difference between Example 3 and Example 1 is that the connection between the docking portion 200 and the extension portion 100 in Example 3 adopts a multi-segment wavy transition structure with a gradually changing cross-sectional area. The multi-segment wavy transition structure extends from the side of the extension portion 100 toward the docking portion 200, maintaining an overall outward expansion trend. The connection between the multi-segment wavy transition structure and the docking portion 200 is also located at the outer edge of the docking portion 200.

[0066] This embodiment differs from Example 1 in its functionality in that the outer side of the graphite electrode for a single crystal furnace in this embodiment, with its gradually changing cross-sectional area, can be clipped onto the quartz sheath 510 attached to the furnace bottom chassis, preventing slippage and providing more stable installation. Furthermore, the outer surface of the graphite electrode for a single crystal furnace in this embodiment provides a larger heat dissipation area, aiding in cooling. However, the curvature radius of each segment of the multi-segment structure in this embodiment is relatively small, resulting in a less smooth transition between the segments and a slight concentration of current density.

[0067] The above shows and describes the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely preferred examples of the present invention and are not intended to limit the present invention. Various changes and improvements may be made to the present invention without departing from the spirit and scope of the present invention, and such changes and improvements fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A graphite electrode for a single crystal furnace, characterized in that: Include: an extension portion (100) extending from one end to the other end; and a docking portion (200) provided at one end of the extension portion (100); The area of ​​the docking surface (230) between the docking portion (200) and the heater is larger than the cross-sectional area of ​​the extension portion (100) in the extension direction, and a cross-sectional area gradient transition structure is provided at the connection between the extension portion (100) and the docking portion (200), thereby preventing a sudden change in the cross-sectional area at the connection between the extension portion (100) and the docking portion (200) from significantly increasing the current density.

2. The graphite electrode for single crystal furnace according to claim 1, characterized in that A first screw hole (210) and a second screw hole (120) are respectively provided at both ends, and at least two vent holes (130) are provided on the side of the extension portion (100), and the vent holes (130) are respectively communicated with the first screw hole (210) and the second screw hole (120).

3. The graphite electrode for a single crystal furnace according to claim 1, wherein: The area of ​​the docking surface (230) of the docking portion (200) and the heater is greater than 80% of the cross-sectional area of ​​the extension portion (100) in the extension direction.

4. The graphite electrode for a single crystal furnace according to claim 1, wherein The cross-sectional area gradually changing transition structure is a transition section (220), the side surface of the transition section (220) is conical, and the entire circumference of the side surface is arc-shaped and concave.

5. The graphite electrode for a single crystal furnace according to claim 4, characterized in that: The ratio of the curvature radius R1 of the arc-shaped concave side surface of the transition section (220) and the radial spacing S1 between the cross-section of the butt joint surface (230) and the extension portion (100) is 2:3 to 5:

3.

6. The graphite electrode for a single crystal furnace according to claim 1, wherein: The cross-sectional area gradually changing transition structure is a transition section (220), and the side surface of the transition section (220) is in the shape of a straight cone.

7. The graphite electrode for a single crystal furnace according to claim 1, wherein: The cross-sectional area gradually changing transition structure is in a multi-segment wave shape.

8. The graphite electrode for a single crystal furnace according to claim 1, wherein: The connection between the cross-sectional area gradual transition structure and the docking portion (200) is located at the outer edge of the docking portion (200).

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