Ultrahigh-purity graphite thermal field of monocrystalline silicon furnace

Abstract

The invention relates to the technical field of monocrystalline silicon czochralski equipment, in particular to an ultra-pure graphite thermal field of a monocrystalline silicon furnace, which comprises an outer cylinder body, a heat preservation cylinder, a graphite heater, a quartz crucible, a shaft rod driving mechanism and a bottom heating tray structure, therefore, a bottom temperature dead zone in a traditional thermal field is avoided. A composite ceramic stirring assembly composed of a movable rotating strip and a static rotating strip is arranged in the quartz crucible, and the movable rotating strip is eccentrically driven by a crank to generate periodic eccentric motion. The structure can weaken the viscous flow region of the bottom and side wall region of the crucible, improve the uniformity of a melt temperature field and a component field, reduce the fluctuation of a solid-liquid interface, reduce dislocation and thermal stress, and realize the growth of large-size monocrystalline silicon with higher stability. The single crystal silicon furnace is simple and reliable in structure and suitable for upgrading and reconstruction of an existing single crystal silicon furnace and production of high-quality single crystal silicon.

Description

Technical Field

[0001] This invention relates to the field of monocrystalline silicon Czochralski equipment technology, specifically to an ultra-high purity graphite hot zone for a monocrystalline silicon furnace. Background Technology

[0002] When growing monocrystalline silicon using the Czochralski (CZ) method, the polycrystalline silicon raw material is typically placed in a quartz crucible and melted by resistance heating via a graphite heater. A typical thermal structure of existing monocrystalline silicon furnaces generally includes an outer cylinder, an insulating cylinder, a graphite heater, and a quartz crucible, with a crystal pulling mechanism at the top for introducing and pulling the monocrystalline seed crystal. To obtain a stable solid-liquid interface morphology, current technologies primarily rely on radiative heating provided by the graphite heater, creating a top-down heat distribution throughout the crucible. However, because the heaters are often arranged laterally or in a ring shape, a "heating blind zone" is commonly found at the bottom of the quartz crucible. This area has a relatively low temperature and is prone to forming localized cold spots, resulting in an uneven temperature distribution in the melt.

[0003] In existing crystal pulling furnaces, the flow of molten silicon mainly relies on natural convection and melt disturbance caused by the differential rotation between the crucible and the crystal. Natural convection in high-temperature melts often exhibits randomness and uncertainty, especially in the area near the bottom and sidewalls of the crucible, where low-speed stagnant zones are easily formed. These zones have large temperature gradients and slow melt renewal rates. When the bottom of the melt is insufficiently heated, localized undercooling or overheating can occur. Furthermore, due to the lack of an effective forced melt agitation structure, the radial and axial temperature differences of the melt are large, and the distribution of oxygen content and impurities in the melt is uneven, easily causing instability at the solid-liquid interface. This, in turn, leads to problems such as crystal diameter fluctuations, dislocation concentration, and thermal stress accumulation.

[0004] While existing technologies can improve melt convection by adjusting the rotation speed of the crucible and crystal, this method has limited ability to disturb the interior of the melt, failing to create a controllable flow field structure and making it difficult to solve the problems of large temperature differences at the bottom of the crucible and local dead zones. Furthermore, due to the lack of an active stirring mechanism located inside the quartz crucible, the melt flow pattern remains dominated by natural vortices, resulting in low heat and component transfer efficiency within the melt and insufficient thermal uniformity, ultimately affecting the growth quality of the single-crystal silicon.

[0005] Therefore, existing single-crystal silicon furnaces still have significant shortcomings in terms of thermal field heating structure and melt convection control: First, the heating capacity at the bottom of the crucible is insufficient, easily forming a heating dead zone; second, there is a lack of a structure capable of effectively and controllably agitating the molten silicon, making it impossible to significantly improve the uniformity of the internal temperature and composition fields of the melt. These problems directly affect the quality and production stability of single-crystal silicon crystals, necessitating a technical solution that can compensate for weak bottom heating, improve melt flow patterns, and enhance the overall uniformity of the thermal field. Summary of the Invention

[0006] This invention aims to solve the problems in existing single-crystal silicon pulling furnaces, such as insufficient heating at the bottom of the quartz crucible leading to a heating dead zone, weak natural convection of the melt resulting in uneven temperature and composition, stagnant zones in the bottom and sidewall regions, and poor solid-liquid interface stability. This invention proposes an ultra-high purity graphite thermal field structure for single-crystal silicon furnaces with bottom compensation heating function and radial reciprocating extrusion and stirring capability. Through the coordinated design of composite ceramic stirring components and eccentric drive mechanism, a controllable "radial-axial linkage flow mode" inside the molten silicon is achieved, thereby significantly improving the uniformity of the melt thermal field and the stability of crystal growth.

[0007] The overall solution of this invention is as follows: Based on the traditional CZ single crystal silicon furnace, a thermal field body is constructed consisting of an outer cylinder, an insulation cylinder, a graphite heater, a quartz crucible, and a shaft drive mechanism. Inside the quartz crucible, a composite ceramic stirring mechanism consisting of a moving swirl bar and a stationary swirl bar is arranged. The crank pin is driven by the shaft to achieve eccentric drive, so that the moving swirl bar and the stationary swirl bar generate relative motion. The molten silicon is radially reciprocated and squeezed through the periodically formed variable cavity, while inducing the formation of an axially stable upward flow path, thereby significantly improving the temperature field and composition field distribution of the melt.

[0008] In a preferred example, an insulation cylinder is installed inside the outer cylinder, and a heater is fitted on the outside of the quartz crucible to form the main heating field; the shaft is driven by a bottom motor and connected to the stirring assembly inside the crucible through a crank pin; the furnace plate and the bottom tray form the bottom support structure, and a heating coil is installed on the surface of the bottom tray to provide auxiliary heating to the bottom of the quartz crucible.

[0009] The specific technical effect is as follows: by coordinating the main heating source and the bottom heating source for compensation, the heat field at the bottom of the crucible is effectively filled, avoiding the bottom temperature dead zone generated by the traditional CZ heater structure, and making the temperature gradient of the melt more uniform.

[0010] In a preferred example, a removable crystal pulling cap is installed on the top of the outer cylinder. The crystal pulling cap and the inner side of the outer cylinder are provided with a vacuum insulation layer to prevent external heat loss. The heater is fixedly sleeved on the outside of the quartz crucible and electrically connected to an external power supply through the bottom electrode feet to achieve stable heating.

[0011] The specific technical effects are: reducing heat loss and improving thermal efficiency through the vacuum insulation layer; and ensuring that the heater receives continuous and controllable electrical power through the electrode foot design, thereby achieving stable heating of the melt.

[0012] In a preferred example, an annular groove is formed on the surface of the bottom tray and a heat-conducting ring is placed therein. Multiple through holes are opened at the bottom of the quartz crucible for the crank pin and the heat-conducting ring to pass into the interior of the crucible. The crank pin is inserted into the slide seat to achieve eccentric drive, while the top surface of the heat-conducting ring slides in contact with the bottom surface of the slide seat.

[0013] The specific technical effects are as follows: the bottom heat-conducting ring and the contact area of ​​the inner bottom surface of the crucible can improve the heat transfer efficiency of the bottom of the crucible and ensure that the sliding plate seat maintains stable support during eccentric movement.

[0014] In a preferred example, the moving swivel bar and the slide block seat are integrally formed, and the stationary swivel bar, slide block seat, sealing slip ring and chuck seat are all made of high-temperature resistant composite ceramic material to adapt to the molten silicon environment of up to 1600°C and reduce impurity precipitation.

[0015] The specific technical effects are as follows: by using composite ceramic materials to enhance corrosion resistance, thermal stability and structural strength, reduce chemical reactions with molten silicon, and improve the long-term lifespan of the stirring components at high temperatures.

[0016] In a preferred example, the outer peripheral surface of the sealing slip ring slides against the inner wall of the quartz crucible, and the inner side slides against the outer peripheral surface of the sliding plate seat, forming a radial sliding sealing structure.

[0017] The specific technical effects are: to achieve stable dynamic sealing under eccentric drive, to prevent molten silicon from leaking along the through hole, and to provide radial support to ensure the stable movement trajectory of the moving swivel.

[0018] In a preferred example, both the moving and stationary spiral bars are helical structures and are arranged parallel to each other in the same horizontal plane.

[0019] The specific technical effect is as follows: multiple periodic variable cavities are formed by the spatial changes between the two spiral structures, so that the molten silicon can be continuously sucked in and squeezed between the two, realizing radial reciprocating squeezing and agitation.

[0020] In a preferred example, the chuck seat is a hollow disc with teeth on its surface, which are press-fitted into the grooves on the inner wall of the quartz crucible to ensure that the stationary swirl bar remains fixed in the melt.

[0021] The specific technical effect is: to ensure the stability of the position of the stationary swirl bar under the eccentric motion of the moving swirl bar, and to form a stable flow field structure through the relative motion between the fixed helical surface and the moving helical surface.

[0022] The beneficial effects achieved by this invention are as follows: 1. In this invention, a heater serves as the primary heat source to heat the quartz crucible and its surrounding environment as a whole, while a heating coil on the surface of the bottom tray provides auxiliary heating to the bottom area of ​​the quartz crucible. This effectively compensates for the thermal field at the bottom of the crucible, avoiding the low-temperature dead zone problem present in the bottom area of ​​traditional crystal pulling furnaces. The double-layer heating structure of this invention makes the temperature distribution inside and outside the crucible more uniform, thereby improving the overall heating efficiency and temperature field stability of molten silicon.

[0023] 2. In this invention, multiple sets of periodically changing cavity structures are formed by the relative motion between the moving and stationary swirl bars, allowing the moving swirl bars to apply radial reciprocating extrusion to the molten silicon under eccentric drive. This structure can create significant radial pressure fluctuations inside the melt, causing the molten silicon to be drawn in and extruded multiple times in a short period, achieving continuous radial disturbance and solving the problem of insufficient melt agitation in the traditional natural convection mode.

[0024] 3. In this invention, a composite stirring method combining radial reciprocating extrusion and axial flow guidance is employed. This allows the melt to generate a stable overall flow path along the crucible axis while being subjected to radial extrusion, forming a clear upper and lower laminar flow structure from bottom to top and from center to outward. This controllable composite stirring method effectively weakens the low-speed stagnant zone at the bottom and sidewalls of the crucible, significantly improving problems such as large temperature differences at the melt bottom, localized overheating, and cold spots in traditional CZ processes. This results in more continuous and uniform heat and oxygen transport in the melt. By rationally setting the eccentricity amplitude and stirring frequency, this invention avoids strong vortices disturbing the solid-liquid interface, resulting in a smoother interface morphology. This facilitates control of monocrystalline silicon diameter fluctuations, reduces dislocation density and thermal stress defects, and overall improves the finished product quality and growth stability of monocrystalline silicon. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the overall structure of one embodiment of the present invention; Figure 2 This is a partial cross-sectional structural diagram of an embodiment of the present invention; Figure 3 This is a schematic diagram of the internal structure of a quartz crucible according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the quartz crucible and bottom tray structure according to an embodiment of the present invention; Figure 5 This is a schematic diagram of the cross-sectional structure of a quartz crucible according to an embodiment of the present invention; Figure 6 This is an exploded view of a quartz crucible, a moving swirl bar, and a moving swirl bar according to an embodiment of the present invention; Figure 7 This is a schematic diagram of a heater structure according to an embodiment of the present invention; Figure 8 This is a schematic diagram of a quartz crucible structure according to an embodiment of the present invention; Figure 9 This is a schematic diagram of a moving swirl bar structure according to an embodiment of the present invention. Figure 10 This is a schematic diagram of a static rotary bar structure according to an embodiment of the present invention.

[0026] Figure label: 1. Outer cylinder; 11. Crystal pulling cap; 12. Vacuum insulation layer; 2. Insulation cylinder; 3. Heater; 4. Quartz crucible; 41. Slot; 5. Shaft; 51. Crank pin; 6. Furnace plate; 7. Bottom tray; 71. Heating coil; 8. Moving rotary bar; 81. Sliding plate seat; 82. Sealing slip ring; 9. Stationary rotary bar; 91. Chuck seat. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0028] It should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the invention.

[0029] The following describes, with reference to the accompanying drawings, some embodiments of the present invention, providing an ultra-high purity graphite hot zone for a single-crystal silicon furnace.

[0030] Combination Figures 1-10 As shown, the present invention provides an ultra-high purity graphite hot zone for a single-crystal silicon furnace, comprising an outer cylinder 1, a crystal pulling cover 11, a vacuum insulation layer 12, a heat insulation cylinder 2, a heater 3, a quartz crucible 4, a shaft 5, a furnace tray 6, and a bottom tray 7. The crystal pulling cover 11 is detachably installed on the top of the outer cylinder 1, and both its inner side and the inner wall of the outer cylinder 1 are provided with a vacuum insulation layer 12 to reduce heat loss from the furnace shell.

[0031] In this embodiment, the insulation cylinder 2 is attached to the inner wall of the outer cylinder 1 to form a stable heat-insulating space. The heater 3 is fitted around the outer periphery of the quartz crucible 4 and is located inside the insulation cylinder 2 to provide the main heat source. The furnace plate 6 is fixed to the bottom of the outer cylinder 1, and the shaft 5 is driven to rotate by a motor arranged on the lower surface of the furnace plate 6.

[0032] In this embodiment, the quartz crucible 4 is installed inside the outer cylinder 1, with its bottom surface in close contact with the upper surface of the bottom tray 7. The surface of the bottom tray 7 is provided with a heating coil 71 for auxiliary heating of the bottom area of ​​the quartz crucible 4, avoiding the formation of a heating dead zone.

[0033] In this embodiment, as Figure 4 and Figure 5 As shown, the bottom surface of the quartz crucible 4 has multiple through holes for the crank pin 51 and the heat-conducting ring 72 to pass into the crucible for driving and support. Several slots 41 are formed on the inner wall of the quartz crucible 4 for locking and positioning the stationary spindle 9.

[0034] In this embodiment, as Figure 6 and Figure 7As shown, the moving bar 8 is an integral spiral bar structure, with a slide plate seat 81 integrally formed on its bottom surface. A sealing slip ring 82 is sleeved on the outer periphery of the slide plate seat 81. The outer surface of the sealing slip ring 82 slides against the inner wall of the quartz crucible 4 to provide dynamic sealing function and support the eccentric movement of the moving bar 8.

[0035] In this embodiment, the bottom surface of the slide block 81 is provided with a pin hole for insertion and connection with the crank pin 51 at the top of the shaft 5. The crank pin 51 is arranged off-center from the central axis of the quartz crucible 4, causing the moving bar 8 to oscillate eccentrically under rotational drive, thereby forming radial reciprocating extrusion in the melt.

[0036] In this embodiment, the surface of the bottom tray 7 is provided with an annular groove, which can hold a heat-conducting ring 72. The top surface of the heat-conducting ring 72 abuts against the bottom surface of the sliding plate seat 81 to enhance the heat conduction effect in the bottom area of ​​the crucible and improve the heating uniformity of the melt at the bottom of the crucible.

[0037] In this embodiment, the stationary rotary bar 9 is spiral-shaped and has the same structure as the moving rotary bar 8, but it does not move with the crank. A chuck seat 91 is provided on the top of the stationary rotary bar 9. The chuck seat 91 is hollowed-out disc-shaped and has teeth on its outer periphery for interference fit with the groove 41 on the inner wall of the quartz crucible 4, so that the stationary rotary bar 9 remains fixed during operation.

[0038] The moving swirl bar 8 and the stationary swirl bar 9 are located in the same horizontal plane. Through the relative movement between the two, multiple variable-volume cavities are formed between the spiral bar structures, causing the molten silicon to form periodic disturbances during pressure and release.

[0039] Working principle and usage process of this invention: At the start of operation, the outer cylinder 1 already integrates the insulation cylinder 2, heater 3, shaft 5, furnace plate 6, bottom tray 7, and motor structure arranged on the bottom surface of the furnace plate 6. After placing the quartz crucible 4 into the outer cylinder 1, the bottom surface of the quartz crucible 4 is brought into contact with the upper surface of the bottom tray 7. At this time, the crank pin 51 and the heat-conducting ring 72 are exposed inside the crucible through several through holes at the bottom of the quartz crucible 4.

[0040] Subsequently, the moving swivel bar 8 is placed into the quartz crucible 4, so that the pin hole on the bottom surface of the sliding plate seat 81 is inserted into the surface of the crank pin 51, and the bottom surface of the sliding plate seat 81 simultaneously abuts and supports the top surface of the heat-conducting ring 72. Further, the stationary swivel bar 9 is placed through the slot 41 provided on the inner wall of the crucible, so that the chuck seat 91 and the slot 41 are engaged and fixed, keeping the stationary swivel bar 9 in a stable, stationary state.

[0041] After completing the above assembly, the crystal pulling cover 11 is sealed on the top of the outer cylinder 1, and polycrystalline silicon raw material is added into the quartz crucible 4. At the same time, it is connected to the upper crystal pulling device, ready to enter the monocrystalline silicon growth stage.

[0042] During operation, the heater 3 heats the inner cavity of the outer cylinder 1 and the quartz crucible 4 as a whole, and the heating coil 71 on the surface of the bottom tray 7 provides auxiliary heating to the bottom area of ​​the quartz crucible 4 to avoid the formation of a temperature dead zone at the bottom of the crucible in the traditional heater structure.

[0043] The motor drives the shaft 5 to rotate continuously, and the crank pin 51 drives the slide block 81 and the moving swivel bar 8 to produce an eccentric rotational motion. Under the radial support and dynamic sealing of the sealing slip ring 82, the moving swivel bar 8 achieves stable eccentric movement within the quartz crucible 4, preventing molten silicon from leaking or escaping from the bottom. The stationary swivel bar 9 is fixed in place by the chuck seat 91 and the slot 41, keeping it stationary throughout the entire operation.

[0044] The moving swirl bar 8 and the stationary swirl bar 9 are located on the same horizontal plane and are both helical. Through their relative movement, multiple variable cavities are formed between their annular helical structures, which change continuously with the eccentric motion. After molten silicon enters these cavities, driven by the eccentric trajectory of the passive swirl bar 8, a reciprocating extrusion effect is generated in the radial direction through periodic extrusion and release, and an axial flow path is formed from radial to center and from bottom to top under the guidance of the helical path.

[0045] Through the aforementioned processes, molten silicon forms a distinct upper and lower laminar flow structure inside the crucible, transforming the melt temperature and composition fields from a "random vortex type" under traditional natural convection to a "composite type of radial periodic extrusion and axial steady-state flow." This composite flow mode significantly reduces the radial temperature difference and axial temperature gradient of the melt, resulting in a more stable and smooth solid-liquid interface.

[0046] By employing the aforementioned radial-axial linkage stirring method, the low-speed stagnant zone at the bottom and adjacent sidewalls of the crucible can be effectively reduced, improving the problems of large temperature gradients at the melt bottom and the coexistence of local overheating zones and cold spots in the traditional CZ process. This results in a more continuous, uniform, and controllable transport of heat and oxygen content within the melt. By further adjusting the eccentricity and stirring frequency, this invention can avoid interface disturbances caused by strong shearing, thereby maintaining a stable crystal growth interface, reducing crystal diameter fluctuations, and effectively minimizing defects such as dislocations, scratches, and thermal stress. In the description of this specification, the terms "one embodiment," "some embodiments," "specific embodiment," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any suitable manner in one or more embodiments or examples.

[0047] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A single-crystal silicon furnace ultra-high purity graphite thermal field, comprising an outer cylinder (1), an insulation cylinder (2), a heater (3), a quartz crucible (4), and a shaft (5) rotatably mounted inside the outer cylinder (1), characterized in that: A furnace plate (6) is fixedly installed on the inner side of the outer cylinder (1), and a motor for driving the shaft (5) to rotate is provided on the bottom surface of the furnace plate (6); a bottom tray (7) sleeved on the surface of the shaft (5) is fixedly installed on the inner side of the heater (3); a heating coil (71) is provided on the surface of the bottom tray (7) for heating the bottom surface of the quartz crucible (4); a moving swivel bar (8) and a stationary swivel bar (9) are detachably installed on the inner side of the quartz crucible (4), the moving swivel bar (8) and the stationary swivel bar (9) have the same structure and are located in the same horizontal plane.

2. The ultra-high purity graphite hot zone for a single-crystal silicon furnace according to claim 1, characterized in that: The top surface of the outer cylinder (1) is provided with a detachable crystal pulling cover (11); the inner sides of the outer cylinder (1) and the crystal pulling cover (11) are provided with a vacuum insulation layer (12); the heat insulation cylinder (2) is a high temperature resistant heat insulation material component and is attached to the inner wall surface of the outer cylinder (1) for heat preservation.

3. The ultra-high purity graphite hot zone for a single-crystal silicon furnace according to claim 1, characterized in that: The heater (3) is fixedly sleeved on the outside of the quartz crucible (4) and located inside the insulation cylinder (2); the bottom end of the heater (3) is provided with electrode feet for contacting an external power source to heat the environment inside the insulation cylinder (2) and the quartz crucible (4).

4. The ultra-high purity graphite hot zone for a single-crystal silicon furnace according to claim 1, characterized in that: The bottom surface of the moving swivel bar (8) is provided with a sliding plate seat (81), and a sealing slip ring (82) that slides against the inner wall of the quartz crucible (4) is sleeved on the outer periphery of the sliding plate seat (81); a chuck seat (91) is fixedly installed on the top surface of the stationary swivel bar (9); a slot (41) is opened on the inner side of the quartz crucible (4), and the end of the stationary swivel bar (9) is fixed by engaging with the inner side of the slot (41).

5. The ultra-high purity graphite hot zone for a single-crystal silicon furnace according to claim 4, characterized in that: The top end of the shaft (5) is provided with a crank pin (51) for inserting and connecting with the bottom surface of the slide block (81).

6. The ultra-high purity graphite hot zone for a single-crystal silicon furnace according to claim 5, characterized in that: The bottom tray (7) has an annular groove on its surface, and a heat-conducting ring (72) is placed in the annular groove; the bottom surface of the quartz crucible (4) has several through holes for the crank pin (51) and the heat-conducting ring (72) to pass through respectively; the top surface of the heat-conducting ring (72) slides against the bottom surface of the slide plate seat (81); the bottom surface of the slide plate seat (81) has a pin hole located at the central axis for insertion and connection with the crank pin (51).

7. The ultra-high purity graphite hot zone for a single-crystal silicon furnace according to claim 4, characterized in that: The moving swivel bar (8) and the slide plate seat (81) are integrally formed structures; the moving swivel bar (8), the stationary swivel bar (9), the slide plate seat (81), the sealing slip ring (82) and the chuck seat (91) are all made of high temperature resistant composite ceramic material, and the center of the outer circumference of the slide plate seat (81) is eccentrically arranged relative to the axis of the quartz crucible (4).

8. The ultra-high purity graphite hot zone for a single-crystal silicon furnace according to claim 4, characterized in that: The sealing slip ring (82) has an annular structure, with its outer circumferential surface coaxial with the quartz crucible (4) and slidingly abutting against the inner wall of the quartz crucible (4); the inner circumferential surface of the sealing slip ring (82) is coaxial with the slide plate seat (81) and slidesly abutting against the outer circumference of the slide plate seat (81), and is used to realize the rotational support and dynamic sealing of the slide plate seat (81) through the sealing slip ring (82).

9. The ultra-high purity graphite hot zone for a single-crystal silicon furnace according to claim 4, characterized in that: The chuck seat (91) has a hollow disc-shaped structure and its surface is provided with several teeth for interlocking and fixing with the inner side of the chuck groove (41).

10. The ultra-high purity graphite hot zone for a single-crystal silicon furnace according to claim 1, characterized in that: Both the moving swivel bar (8) and the stationary swivel bar (9) have a spiral structure and are arranged in the same horizontal plane corresponding to each other.

Images