A method for improving the life of a heater for a silicon single crystal pulling furnace

Abstract

The application discloses a method for improving the service life of a heater of a silicon single crystal pulling furnace, which comprises the following steps: (1) making graphite paper rings with geometric shapes suitable for the shapes of electrode columns and heater feet; (2) loading the graphite paper rings with different inner and outer diameters into corresponding connection parts between the heater feet and the electrode columns of a single crystal pulling furnace, and normally operating to pull single crystals; and (3) recording the presence or absence and degree of oxide deposition at the connection parts between the heater feet and the electrode columns of different single crystal pulling furnaces, and obtaining suitable inner and outer diameter parameters of the graphite paper rings which can improve the service life of the heater of the single crystal pulling furnace. The graphite paper rings are in good contact with the graphite electrode columns and the heater feet due to the special geometric shapes of the graphite paper rings, which is beneficial to reducing the deposition of oxides in the single crystal pulling furnace, preventing the hardening of the deposited substances, reducing the gap sparking, enhancing the robustness of the electric connection of the heater and improving the service life of the heater.

Description

Technical Field

[0001] This invention relates to a method for improving the lifespan of heaters in silicon Czochralski furnaces, belonging to the technical field of silicon Czochralski furnaces. Background Technology

[0002] Currently, over 98% of electronic components used in IC manufacturing utilize single-crystal silicon. Single-crystal silicon is prepared using two methods: the Czochralski (CZ) method accounts for over 85%, while the rest are grown using the zone melting (FZ) method. Single crystals grown using the Czochralski (CZ) method are primarily used to produce low-power devices such as DRAM, SRAM, and ASICs; while single crystals grown using the FZ method are mainly used in high-power electronic devices, such as thyristors. This difference stems from the different methods of melting the polycrystalline material. The CZ method requires a quartz crucible as the container for the polycrystalline material, which is then heated and melted by an external graphite electric heater. In the FZ method, the polycrystalline material can be melted in a vacuum by an electric heating coil and then directly falls into the single-crystal growth region. This results in a higher oxygen content and lower resistivity in the CZ method.

[0003] In a Czochralski single crystal furnace, a quartz crucible is used to contain the molten silicon. Due to the superior high-temperature mechanical and thermal conductivity of graphite, a graphite crucible is placed outside the quartz crucible to support the softened quartz crucible at high temperatures. An outer layer is a graphite heater. Quartz is currently the most commonly used crucible material. However, at high temperatures, quartz reacts with the molten silicon in the following reaction: SiO₂ + Si → 2SiO. SiO enters the molten silicon, becoming the main source of oxygen in the Czochralski single crystal rod. On the other hand, some SiO volatilizes from the surface of the molten silicon and reacts with graphite in the thermal field in the following reaction: SiO + 2C → SiC + CO. The SiC produced on the graphite surface gradually alters the electrical and thermal conductivity properties of the graphite.

[0004] The heater's function is to provide a heat source to melt the silicon material. Current large-size Czochralski silicon single crystal furnaces primarily use graphite resistance heaters, whose resistivity increases with repeated use. The graphite heater is connected to the bottom electrode post via graphite bolts. Since the entire thermal environment is filled with dopants and volatiles from the molten silicon, most of these volatiles are discharged into the dust canister via the airflow, while some deposit on the graphite components, forming volatile deposits. During operation, these volatiles gradually accumulate at the joints of the graphite components, forming hard deposits. Especially during operation, the furnace airflow is from top to bottom. When the airflow carrying volatiles impacts the bottom graphite guard plate, it easily creates backflow around the bottom graphite electrodes, where the flow velocity decreases, leading to cooling and obstruction, resulting in deposition. Oxidized volatiles deposit at the connection gap between the heater foot and the electrode post, forming a hard deposit that is difficult to remove by grinding. After the next furnace loading, these hard deposits act as fulcrums, causing gaps in the contact between the heater foot and the graphite electrode. On the other hand, they form sharp discharge points, causing gaps in the electrical connection components, resulting in poor conductivity. Furthermore, with the increase of operating time, gap arcing can lead to serious consequences such as damage to the thermal field.

[0005] Although there are various silicon single crystal furnaces still in operation on the market, their thermal field structures are largely similar, and the connection between the heater and the electrode is basically a connection between graphite components. Due to the different sizes of the heater and the electrode column, the geometry of the heater feet after they are connected to the electrode column will change the airflow direction in the furnace thermal field, and particles will generally deposit or even clump together at this point. Summary of the Invention

[0006] In view of the above-mentioned problems in the prior art, the purpose of this invention is to propose a method to improve the lifespan of the heater in a silicon single crystal Czochralski furnace. By fitting a graphite paper ring of appropriate geometry at the connection between the heater foot and the electrode post, good contact and conductivity between the heater and the electrode post are ensured, reducing the deposition of deposits in this critical area, thereby improving the lifespan of the heater.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for improving the lifespan of a silicon single crystal Czochralski furnace heater includes the following steps:

[0009] (1) Fabricate a graphite paper ring with a geometric shape adapted to the shape of the electrode post and heater foot;

[0010] (2) Insert the graphite paper rings with different inner and outer diameters into the corresponding connection parts between the heater feet and the electrode column in the Czochralski single crystal furnace, and pull single crystals under normal operation;

[0011] (3) Record the presence and extent of oxide deposition at the connection points between the heater feet and electrode posts of different single crystal furnaces to obtain suitable inner and outer diameter graphite paper ring parameters that can improve the lifespan of the Czochralski single crystal furnace heater.

[0012] Furthermore, in the connection form where the electrode post area is smaller than the heater foot area, the diameter of the matching graphite paper ring is larger than the electrode post diameter, and the width of the excess portion is ≤5mm, preferably 1-5mm; in the connection form where the electrode post area is larger than the heater foot area, the area of ​​the matching graphite paper ring is larger than the heater foot area, and the width of the excess portion of the graphite paper ring is ≤5mm, preferably 1-5mm; when the electrode post is inserted into the countersunk hole under the heater foot, the diameter of the matching graphite paper ring is larger than the electrode post diameter, and the width of the excess portion is ≤5mm, preferably 1-5mm, and smaller than the diameter of the countersunk hole under the heater foot, and the distance from the outer ring of the graphite paper ring to the edge is ≤5mm, preferably 1-5mm.

[0013] Furthermore, this method uses a cutting and stamping device to produce graphite paper rings. This cutting and stamping device includes functional components such as a vertical guide rail, an upper cutter, a lower ring cutter, and an inner convex cutter, all mounted on a clamping table. The upper cutter is ring-shaped and is clamped by an upper connecting plate, which is connected to the vertical guide rail on the clamping table. The lower ring cutter has a recessed space and is clamped by a lower connecting plate and positioned below the upper cutter. The lower connecting plate is fixed to the clamping table. The inner convex cutter is positioned at the center of the recessed space of the lower ring cutter, and its outer diameter matches the central through hole of the upper cutter.

[0014] Furthermore, the graphite paper ring is assembled into a tooling and stamped using upper cutting blades, lower ring blades, and inner convex blades of different sizes.

[0015] Furthermore, the manufacturing process of the graphite paper ring includes the following steps:

[0016] S1: Measure the diameter of the graphite bolt connecting the heater foot to the electrode post and the outer diameter of the graphite electrode post;

[0017] S2: Based on the results of the graphite bolt diameter and graphite electrode post outer diameter measured in S1, use upper cutters, lower ring cutters, and inner convex cutters of different diameters to assemble a matching tool for cutting graphite paper rings.

[0018] S3: Assemble the upper cutting blade, lower ring blade, and inner convex blade into a tooling to stamp and cut the graphite paper to obtain a graphite paper ring with a suitable geometric shape.

[0019] Preferably, in step S2, matching cutting tools of different diameters selected from xi±1, yi±1; xi±2, yi±2; xi±3, yi±3; xi±4, yi±4; xi±5, yi±5 are manufactured at 1mm intervals.

[0020] Preferably, the cutting and stamping device uses a non-metallic material with a flat and rigid surface, and the connection tolerance of each component is <0.5mm.

[0021] The beneficial effects of this invention are as follows:

[0022] This invention utilizes the unique geometry of the graphite paper ring to form good contact with the graphite electrode post and the heater foot, which helps to reduce the deposition of oxides in the silicon Czochralski furnace at the connection of the graphite heater components, prevents the deposits from hardening and agglomerating, reduces gap arcing, and enhances the robustness of the heater's electrical connection, thereby improving the heater's service life.

[0023] The graphite paper rings used in this invention are standardized through a combination of non-metallic materials of various sizes. The resulting graphite paper rings have neat edges without burrs and no breaks in the electrical contact surface. By using graphite paper rings with different inner and outer radii and different numbers of sheets, and applying them to the connection between the heater feet and electrode posts of various Czochralski single crystal furnaces, the severity of oxide deposition at the connection between the graphite heater feet and electrode posts of the single crystal furnace is compared, providing a basis for improving the lifespan of silicon Czochralski single crystal furnace heaters. Attached Figure Description

[0024] Figure 1 This is a perspective view of the cutting and stamping device used in this invention.

[0025] Figure 2 This is a side view of the cutting and stamping device used in this invention.

[0026] Figure 3 for Figure 2 Cross-sectional view along line BB.

[0027] Figure 4 This is a schematic diagram of the graphite paper ring fitting method in a connection configuration where the electrode post area is smaller than the heater foot area.

[0028] Figure 5 This is a schematic diagram of the graphite paper ring fitting method in a connection configuration where the electrode post area is larger than the heater foot area.

[0029] Figure 6 This is a schematic diagram showing the graphite paper ring fitting method in the connection configuration where the electrode post is inserted into the countersunk hole at the heater foot.

[0030] Figure 7 This is a statistical chart showing the number of times the single crystal furnace is ignited during operation and production. Detailed Implementation

[0031] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, but this does not imply a limitation on the scope of protection of the present invention.

[0032] The method of this invention uses a detachable cutting and stamping device to prepare ring-shaped graphite paper (graphite paper rings) of various sizes, which are then applied to the connection between the heater feet and electrode posts of a Czochralski single crystal furnace. For example... Figures 1-3 As shown, the cutting and stamping device includes functional components such as a vertical guide rail 1, an upper cutter 2, a lower ring cutter 3, and an inner convex cutter 4, all mounted on a clamping table. The upper cutter is ring-shaped and is clamped by an upper connecting plate 5, which is connected to the vertical guide rail 1 on the clamping table. The lower ring cutter 3 has a recessed space and is clamped by a lower connecting plate 6 and positioned below the upper cutter 2. The lower connecting plate 6 is fixed to the clamping table. The inner convex cutter 4 is positioned in the center of the recessed space of the lower ring cutter 3, and its outer diameter matches the central through hole of the upper cutter 2.

[0033] When using this cutting and stamping device to make graphite paper rings, one or more sheets of graphite paper are placed between the upper cutter and the lower ring cutter. The upper cutter moves down along the vertical guide rail and enters the concave space of the lower cutter. The inner convex cutter is inserted into the middle through hole of the upper cutter. Under the combined action of the upper cutter, the inner convex cutter and the lower ring cutter, the graphite paper is cut and pressed between the bottom of the concave space of the upper cutter and the lower ring cutter. After the stamping action of the upper cutter and the lower ring cutter, a graphite paper ring without cracks, creases, and with regular edges and no burrs is produced.

[0034] The inner diameter of the produced graphite paper ring is equivalent to the outer diameter of the inner convex knife, and the outer diameter of the graphite paper ring is equivalent to the outer diameter of the upper cutting knife.

[0035] The present invention uses the above-mentioned cutting and stamping device to produce graphite ring paper, and the process of using the produced graphite paper ring in a single crystal furnace includes the following steps:

[0036] S1: Use vernier calipers to measure the diameter of the graphite bolt connecting the heater foot to the electrode post and record it as xi. Use vernier calipers to measure the diameter of the graphite electrode post and record it as yi. According to the different single crystal furnace machines, label the subscripts of x and y to make them correspond one by one.

[0037] S2: Produce matching cutting tools of different diameters selected from xi±1, yi±1; xi±2, yi±2; xi±3, yi±3; xi±4, yi±4; xi±5, yi±5 at 1mm intervals.

[0038] S3: Assemble the upper cutting blade, lower ring blade, and inner convex blade into a tooling to stamp and cut the graphite paper to obtain a graphite paper ring with a suitable geometric shape.

[0039] S4: Based on the graphite paper rings with different inner and outer diameters prepared in S3, when the Czochralski single crystal furnace heater is first assembled, or when the single crystal furnace is being cleaned and unloaded, the graphite paper rings with different inner and outer diameters are applied to the connection between the heater feet and the electrode posts of each Czochralski single crystal furnace, put into production operation, and record the inner and outer diameters of the graphite paper rings applied to each single crystal furnace.

[0040] S5: Based on the record in S4, during each furnace cleaning process when the single crystal furnace is cooled, disconnect the graphite heater foot from the electrode post, compare the presence and degree of oxidation deposition, and determine the appropriate inner and outer diameter graphite paper rings for production.

[0041] Preferably, the specific design of the cutting tool in step S2 should allow the graphite paper ring to be easily and undamagedly removed from the tooling after cutting, as graphite paper is thin and brittle, and creases or even breakage should be avoided during removal. The cutting tool in step S2 should be made of non-metallic materials to avoid metal contamination. In step S4, the age of the heaters in each single crystal furnace should be uniform, and the operating time of the single crystal furnace and the dopant used for pulling the single crystals should be consistent throughout the experiment.

[0042] The method of using the above-mentioned cutting and stamping device to manufacture graphite paper rings and the method of using graphite paper rings have the following advantages:

[0043] 1. A graphite paper ring shape is designed to fit the connection of different heater feet and electrode posts, which effectively prevents the deposition of volatiles.

[0044] 2. By measuring the dimensions of the heater feet and electrode posts of the single crystal furnace used, it is possible to produce annular graphite paper of different shapes and inner and outer diameters.

[0045] 3. Different furnace types have different heater feet and electrode column sizes, and different installation techniques used by workers result in different thermal fields inside the single crystal furnace. Therefore, paper cutting fixtures of different sizes can be designed for experimentation. This facilitates the selection of graphite paper rings suitable for the furnace type, thereby reducing the incidence of gap arcing and improving the lifespan of the single crystal furnace heater.

[0046] 4. Compared to making graphite paper rings by hand, using a defined cutting fixture is more convenient and faster. The finished graphite paper rings have no burrs on the edges and are of uniform size. Compared to providing drawings to manufacturers for machining, using a cutting fixture to process graphite paper is comparable to machining in terms of precision, and greatly reduces production costs.

[0047] 5. A suitable graphite paper ring scheme can be quickly determined through just one round of experiments, which can avoid intermittent arcing during the operation of the single crystal furnace and help improve the life of the heater.

[0048] like Figures 4-6 As shown, three methods for fitting graphite paper rings to the electrode post and heater pins are illustrated. Figure 4As shown, in a connection configuration where the area of ​​electrode post 9 is smaller than the area of ​​heater foot 7, the diameter of the matching graphite paper ring 8 is larger than the diameter of the electrode post, and the width of the excess portion is ≤5mm, preferably 1-5mm; Figure 5 As shown, in a connection configuration where the area of ​​electrode post 9 is larger than the area of ​​heater foot 7, the area of ​​the matching graphite paper ring 8 is larger than the area of ​​heater foot, and the width of the extended portion of the graphite paper ring is ≤5mm, preferably 1-5mm; Figure 6 As shown, the electrode post 9 is inserted into the recessed hole of the heater foot 7. The diameter of the matching graphite paper ring 8 is larger than the diameter of the electrode post, and the width of the excess part is ≤5mm (preferably 1-5mm) and smaller than the diameter of the recessed hole under the heater foot. The distance between the outer ring of the graphite paper ring and the edge is ≤5mm, preferably 1-5mm.

[0049] Example

[0050] Table 1 shows the tooling dimensions required for grouping different bolt diameters and electrode post diameters.

[0051] Table 1

[0052]

[0053] The graphite paper rings were distributed and installed on the corresponding single crystal furnaces No. 1, 2, 3... After 100 hours of operation, the graphite heater feet and graphite electrode posts of each single crystal furnace were disassembled and inspected for deposit adhesion. The results are shown in Table 2.

[0054] Table 2

[0055] 1-1 have 2 1 Full of 1-2 have 2 1 Full of 1-3 have 2 1 Full of 2-1 have 1.8 2 large pieces 2-2 have 1.8 2 large pieces 2-3 none 0 0 Almost no sediment 3-1 none 0 0 Almost no sediment 3-2 none 0 0 Almost no sediment 3-3 have 0.7 4 Scattered moldings with hard texture 4-1 have 0.8 3 Scattered molding 4-2 have 0.7 2 Scattered molding 4-3 have 0.9 4 Scattered molding 5-1 have 1.1 5 Scattered molding 5-2 have 0.9 1 Scattered molding 5-3 have 1.2 2 Loose sediment 6-1 have 0.7 2 Loose sediment 6-2 have 1.5 2 Loose sediment 6-3 have 1.6 4 Loose sediment 7-1 have 1.7 2 Loose sediment 7-2 have 1.8 1 Loose sediment 7-3 none 0 0 Almost no sediment 8-1 none 0 0 Almost no sediment 8-2 none 0 0 Almost no sediment 8-3 none 0 0 Almost no sediment 9-1 have 1.6 2 Scattered moldings with hard texture 9-2 have 1.7 2 Scattered moldings with hard texture 9-3 have 1.2 3 Scattered molding 10-1 have 1.4 2 Loose sediment 10-2 have 1.3 5 Loose sediment 10-3 have 1.7 2 Loose sediment

[0056] A lateral comparison was conducted using graphite paper rings of different sizes to connect the graphite heater feet and graphite electrode posts, selecting the optimal process tooling dimensions to avoid oxide deposition at the connection point and improve heater lifespan. The results are shown in Table 2 above. The results show that comparing the effects of different graphite paper ring sizes on reducing oxide deposition reveals that the inner diameter of the graphite paper ring primarily affects the installation process. If the inner diameter is too small, it can easily cause the graphite paper ring to become eccentric, leading to oxide particles entering and depositing on one side of the electrode post surface through gaps. If the inner diameter is large, the effect is less significant. Regarding the outer diameter of the graphite paper ring, when the outer diameter is exactly 1-5 mm larger than the outer diameter of the graphite electrode post, oxides are less likely to deposit on either the graphite heater feet or the graphite electrode post. The principle is that the larger portion of the graphite paper ring effectively prevents oxides from penetrating the contact surface and also prevents oxides from forming agglomerates on the outside. Furthermore, for connection types where the area of ​​the heater foot is smaller than that of the graphite electrode post, the contact surface between the two is not a concentric circle due to the bending of the heater foot. For this type of connection, graphite paper is adapted to the bending area of ​​the heater foot, and the edge of the graphite paper ring extends 1-5mm beyond the contact portion between the heater foot and the graphite electrode post, thereby further avoiding oxidation deposition.

[0057] Statistical analysis was conducted on ignition events during operation of 60 single crystal furnaces. The time series of heater ignition frequency is as follows: Figure 7 As shown in the figure. The results indicate that the number of ignition attempts significantly decreased after intervention using the above method starting from week 20.

Claims

1. A method for improving the lifespan of a heater in a silicon single crystal Czochralski furnace, characterized in that, Includes the following steps: (1) Fabricate a graphite paper ring with a geometric shape adapted to the shape of the electrode post and heater foot; (2) Insert the graphite paper rings of different inner and outer diameters into the corresponding connection parts between the heater feet and the electrode column in the Czochralski single crystal furnace, and pull the single crystal under normal operation; (3) Record the presence and extent of oxide deposition at the connection points between the heater feet and electrode posts of different single crystal furnaces to obtain suitable inner and outer diameter graphite paper ring parameters that can improve the lifespan of the Czochralski single crystal furnace heater; This method uses a cutting and stamping device to produce graphite paper rings. The cutting and stamping device includes a vertical guide rail, an upper cutter, a lower ring cutter, and an inner convex cutter, all mounted on a clamping table. The upper cutter is ring-shaped and is clamped by an upper connecting plate, which is connected to the vertical guide rail on the clamping table. The lower ring cutter has a recessed space and is clamped by the lower connecting plate and positioned below the upper cutter. The lower connecting plate is fixed to the clamping table. The inner convex cutter is positioned at the center of the recessed space of the lower ring cutter, and its outer diameter matches the central through hole of the upper cutter.

2. The method for improving the lifespan of a silicon single crystal Czochralski furnace heater according to claim 1, characterized in that, In connection configurations where the electrode post area is smaller than the heater foot area, the diameter of the matching graphite paper ring is larger than the electrode post diameter, with the excess width ≤ 5mm; in connection configurations where the electrode post area is larger than the heater foot area, the area of ​​the matching graphite paper ring is larger than the heater foot area, with the excess width ≤ 5mm; when the electrode post is inserted into the countersunk hole under the heater foot, the diameter of the matching graphite paper ring is larger than the electrode post diameter, with the excess width ≤ 5mm and smaller than the countersunk hole diameter under the heater foot, and the distance from the outer ring of the graphite paper ring to the edge ≤ 5mm.

3. The method for improving the lifespan of a silicon single crystal Czochralski furnace heater according to claim 2, characterized in that, In connection configurations where the electrode post area is smaller than the heater foot area, the diameter of the matching graphite paper ring is larger than the electrode post diameter, with the excess width being 1-5 mm. In connection configurations where the electrode post area is larger than the heater foot area, the area of ​​the matching graphite paper ring is larger than the heater foot area, with the excess width being 1-5 mm. When the electrode post is inserted into the countersunk hole under the heater foot, the diameter of the matching graphite paper ring is larger than the electrode post diameter, with the excess width being 1-5 mm and smaller than the countersunk hole diameter under the heater foot, and the outer ring of the graphite paper ring is 1-5 mm from the edge.

4. The method for improving the lifespan of a silicon single crystal Czochralski furnace heater according to claim 1, characterized in that, Graphite paper rings are assembled into tooling and stamped using upper cutting blades, lower ring blades, and inner convex blades of different sizes.

5. The method for improving the lifespan of a silicon single crystal Czochralski furnace heater according to claim 1, characterized in that, The process of manufacturing the graphite paper ring includes the following steps: S1: Measure the diameter of the graphite bolt connecting the heater foot to the electrode post and the outer diameter of the graphite electrode post; S2: Based on the results of the graphite bolt diameter and graphite electrode post outer diameter measured in S1, use upper cutters, lower ring cutters, and inner convex cutters of different diameters to assemble a matching tool for cutting graphite paper rings. S3: Assemble the upper cutting blade, lower ring blade, and inner convex blade into a tooling to stamp and cut the graphite paper to obtain a graphite paper ring with a suitable geometric shape.

6. The method for improving the lifespan of a silicon single crystal Czochralski furnace heater according to claim 5, characterized in that, In step S2, matching cutting tools of different diameters, selected from xi±1, yi±1; xi±2, yi±2; xi±3, yi±3; xi±4, yi±4; xi±5, yi±5, are manufactured at 1mm intervals. The diameter of the graphite bolt is denoted as xi, and the outer diameter of the graphite electrode post is denoted as yi. The subscripts of x and y are labeled according to the different single crystal furnace machines to achieve a one-to-one correspondence.

7. The method for improving the lifespan of a silicon single crystal Czochralski furnace heater according to claim 1, characterized in that, The cutting and stamping device uses a flat and rigid non-metallic material, and the connection tolerance of each component is <0.5mm.

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