Top seed crystal pulling single crystal growth device
By designing the lifting rod to lift only, the crucible adopts a round barrel shape and is heated from the lower side, which solves the problem of interrupting crystals and large temperature gradients in the existing devices, and improves the reliability and quality of crystal growth.
Patent Information
- Application Number
- CN202510094292.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-01-21
- Publication Date
- 2025-06-24
AI Technical Summary
The existing top seed crystal lifting single crystal growth device is prone to crystal breakage accidents during crystal growth, and the large temperature gradient affects the crystal growth quality.
A single crystal growth device with a top seed crystal lifting is designed. The lifting rod has only a degree of freedom of lifting and lowering and lacks rotational movement; the crucible adopts a barrel-shaped structure with large upper and small upper upper and small lower lower, and is heated from the lower side by a heater. The rotation direction of the crucible and the heater are opposite.
By reducing the rotation load of the pull rod, the probability of crystal breakage is reduced; the circular barrel crucible and the lower side heating design reduce the temperature gradient, improving the reliability and quality of crystal growth.
Smart Images
Figure CN120193326A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to a top seed crystal pulling single crystal growth device, which is also called a Czochralski single crystal growth device. Background Art
[0002] The top seed crystal pulling single crystal growth method is one of the main methods for manufacturing crystal columns. It should be known that the crystal column is the blank before being cut into wafers. Therefore, the growth quality of the crystal column directly determines the quality of the wafer. At present, the crucibles used in most crystal pulling equipment on the market are, for example, cylindrical quartz crucibles, graphite crucibles, etc. The crucibles are mostly heated by induction heating. Specifically, an induction coil is surrounded outside the crucible, and the induction coil is used to heat the material contained in the crucible. Since single crystal silicon is not conductive, it cannot be heated by induction heating, and it is necessary to adapt a conductive crucible for indirect heating, such as a graphite crucible, to heat the graphite crucible through an induction coil, and then heat the single crystal silicon contained in the graphite crucible. The defect of this kind of heating is that there will be a certain temperature gradient in the crucible, resulting in different radial supercooling of the melt, which will affect the crystal growth and reduce the quality of crystal growth.
[0003] In order to reduce the influence of temperature gradient, the lifting rod needs to be able to rotate during the lifting process, that is, it can be pulled upward and rotated at the same time to eliminate or reduce the influence of temperature gradient.
[0004] However, it should be known that there is an accident in this field, which is crystal breakage. Specifically, during the crystal growth process, for example, the seed crystal (also known as the seed crystal) on the pulling rod may suddenly break, causing the crystal column to fall and hit the crucible. The loss caused by this accident ranges from tens of thousands to hundreds of thousands.
[0005] At the same time, it should be known that the diameter of the seed crystal connected to the lower end of the lifting rod is generally much smaller than the diameter of the crystal column. The diameter of the seed crystal is usually 20mm~200mm, and the weight of the crystal column after growth is usually 50 kg~several hundred kg. The effect of simple lifting on the seed crystal is relatively small. If it rotates at the same time, the seed crystal is required to have a higher shear resistance. However, as mentioned above, the current top lifting requires the lifting rod to have two movements, namely rotation and lifting (up and down), which makes the probability of crystal breakage relatively high.
[0006] In addition, regarding the crucible, in the top-seeded Czochralski single-crystal growth method, it usually has a rotational motion. It is required that the rotational motion of the crucible (becoming a rotating pot) is opposite to the rotational motion of the seed crystal (commonly referred to as crystal rotation). In other words, at least the crucible already has a rotational motion. By means of the difference between the rotational motions of the seed crystal and the crucible, one of the purposes is to avoid local overheating or overcooling to ensure the quality of the grown crystal. On the other hand, it is to ensure the orderly growth of the single crystal. The inventor believes that compared with driving the lifting rod to perform rotational and lifting motions, the rotational motion of the crucible is easier to achieve, and the aforementioned relative motion form of the rotating pot and crystal rotation can still obtain the expected relative angular velocity through the single rotation of the crucible. Summary of the Invention
[0007] In view of this, an object of the present invention is to provide a top-seeded Czochralski single-crystal growth device with relatively better reliability.
[0008] According to an embodiment of the present invention, there is provided a top-seeded Czochralski single-crystal growth device, and its basic composition includes: A furnace body; A lifting mechanism, located inside the furnace body and provided with a lifting rod, and the lifting rod only has a lifting degree of freedom; A seed crystal holder, located at the lower end of the lifting rod for mounting the seed crystal; A crucible, located inside the furnace body and directly below the seed crystal holder, and the main body of the crucible is a frustum-shaped barrel with a larger upper part and a smaller lower part; A lifting rotating shaft, located below the crucible; and A heater, installed at the upper end of the lifting rotating shaft to heat the crucible from the lower side.
[0009] Optionally, the bottom diameter of the frustum-shaped barrel of the crucible is larger than the diameter of a predetermined crystal column.
[0010] Optionally, the angle between the generatrix of the frustum-shaped barrel of the crucible and the upper bottom is less than or equal to 18° and greater than or equal to 5°.
[0011] Optionally, the upper end of the frustum-shaped barrel of the crucible has a cylindrical retaining wall.
[0012] Optionally, the height of the retaining wall is not greater than one-fifth of the height of the crucible.
[0013] Optionally, the heater is a disk-shaped electrothermal heating element or a bottomed electrothermal heating element with a conical part; If the heater is a bottomed electrothermal heating element with a conical part, the lower part of the crucible is nested inside the conical part.
[0014] Optionally, the rotational direction of the crucible is opposite to the rotational direction of the heater, and the rotational angular velocities are the same.
[0015] Optionally, an upper dead point constraint is adapted to be provided on the lifting rotating shaft to maintain the non-contact heating of the crucible by the heater.
[0016] Optionally, the lifting rod is a polygonal prism. A corresponding polygonal prism sleeve is provided to provide axial guidance and circumferential constraint for the lifting rod.
[0017] Optionally, the lower end of the seed crystal holder has a seed crystal jacket.
[0018] In an embodiment of the present invention, the lifting mechanism of the top-seeded Czochralski single crystal growth device only retains the lifting freedom degree of the lifting rod, that is, it cannot rotate. Under this condition, due to the reduction of the load of rotational shear, the seed crystal is relatively less likely to have the accident of crystal breakage. In addition, the lifting rod with load has one less degree of freedom and has better reliability. Relatively speaking, the heater is arranged below the crucible to heat the crucible from below instead of from all around. With the rotation of the crucible and the heater, a melt with a relatively small temperature gradient can be obtained. Correspondingly, the crucible is designed as a frustum-shaped barrel. Under the condition of the same height, the volume is easy to ensure, and the thermal utilization rate of the heater is also relatively good. Description of the Drawings
[0019] Figure 1 It is a schematic structural diagram of the top-seeded Czochralski single crystal growth device in an embodiment.
[0020] Figure 2 It is a schematic diagram of the crucible structure in an embodiment.
[0021] In the figure: 1. Lifting rotating shaft, 2. Heater, 3. Crucible, 4. Crystal column, 5. Seed crystal, 6. Seed crystal holder, 7. Lifting rod.
[0022] 31. Cone shell, 32. Cofferdam, 33. Bottom plate. Detailed Embodiments
[0023] It should be known that during the process of growing crystals by the Czochralski method, the air inside the furnace body usually needs to be pumped out by a vacuum pumping device first, so that a certain vacuum degree is reached inside the furnace body to ensure the purity and stability of the crystal growth environment. However, usually, it is not necessary to maintain a relatively low vacuum degree inside the furnace body, but a certain amount of inert gas needs to be filled to ensure the full melting of the raw materials and the high-quality growth of the crystals. In other words, vacuum pumping is actually mainly used to ensure the temperature and atmosphere inside the furnace body to provide suitable conditions for crystal growth, rather than obtaining a very low vacuum degree. Therefore, the conditions for heat convection are still satisfied inside the furnace body.
[0024] Meanwhile, the crucible 3 in the furnace body usually adopts a graphite crucible (operating temperature at 2400 °C and below) or a quartz crucible (operating temperature at 1400 °C and below). Among them, the graphite crucible has a higher operating temperature and good thermal conductivity itself. The quartz crucible has relatively poor thermal conductivity, but it can still meet the requirements of heat conduction. Therefore, heating the crucible 3 from the bottom, due to heat conduction, heat convection, and the special structure (frustum barrel shape) of the crucible 3, the temperature gradient of the melt is relatively low.
[0025] In view of the improvement points of the top-seeded Czochralski single-crystal growth device according to the embodiments of the present invention, which are mainly the shape of the crucible 3, the installation position of the heater 2, and the movement form of the pulling rod 7, for the rest, the existing configuration of the top-seeded Czochralski single-crystal growth device can be directly adopted, and no more description will be made for the rest.
[0026] For example, the furnace body, etc., are the inherent configurations of such top-seeded Czochralski single-crystal growth devices, and there is no structural or constructional change due to the changes in the pulling mechanism, crucible 3, and heater 2 in the embodiments of the present invention. Although in some embodiments, the lifting rotating shaft 1 for supporting the heater 2 positions the heater 2 below the crucible 3, it should be known that in known top-seeded Czochralski single-crystal growth devices, there is also a case where the support shaft for supporting the heater 2 adopts the form of a lifting rotating shaft to adjust the heating position according to the required technical conditions. At the same time, it should be known that the required position change amount of the heater 2 is usually very small. Therefore, configuring the heater 2 below the crucible 3 does not cause a substantial change to the furnace body structure.
[0027] Taking the furnace body as an example, for the rest of the configuration of the top-seeded Czochralski single-crystal growth device except for the parts described in detail in the embodiments of the present invention, no more description will be made. Those skilled in the art can obtain it according to the prior art and the technical content recorded in the present invention without creative labor.
[0028] Regarding the pulling mechanism, the traditional pulling mechanism has degrees of freedom of up-and-down movement, that is, the lifting degree of freedom, and also has the degree of freedom of rotation. Therefore, it has relatively high requirements for anti-shear ability. However, for the seed crystal 5, its individual specifications are determined and will not cause crystal breaking accidents because of the improvement of the stiffness of the pulling rod 7. In other words, it has nothing to do with the stiffness of the pulling rod 7.
[0029] In the embodiments of the present invention, the pulling mechanism only needs to provide the lifting degree of freedom, that is, its pulling rod 7 only needs to have the lifting degree of freedom, and circumferential constraints can be further provided to it to improve the overall dynamic stiffness.
[0030] Correspondingly, at least the pulling rod 7 of the pulling mechanism is located in the furnace body.
[0031] The seed crystal holder 6 is in principle part of the lifting rod 7, or can be understood as a fixture installed at the lower end of the lifting rod 7 for clamping the seed crystal 5. This is a general configuration in the art and will not be elaborated here. However, it should also be known that since the lifting rod 7 only has the degree of freedom of lifting and the degree of freedom of rotation is reduced, under the condition of using the same seed crystal holder 6 to clamp the seed crystal 5, the clamping reliability is relatively less likely to fail. Even without considering crystal breakage, the reliability of the top-seed pulling single crystal growth device based on the embodiment of the present invention is relatively good.
[0032] Under the condition that the lifting rod 7 only has the degree of freedom of lifting, the forward and reverse rotation movement between the crucible 3 and the lifting rod 7 becomes the single rotation movement of the crucible 3. Under this condition, in order to make the melt obtain a relatively small temperature gradient (that is, the temperature uniformity is relatively good), the crucible 3 cannot adopt the traditional crucible shape. The outer contour of the traditional crucible shape for crystal growth is close to a cylindrical shape, and its outer contour is usually a convex curved surface. In the embodiment of the present invention, the crucible 3 with a frustum barrel shape that is larger at the top and smaller at the bottom is adopted. In order to reduce the amount of tailings in the final stage of crystal growth, it is required that the small bottom of the crucible 3, that is, the diameter of the lower bottom, is larger than the diameter of the crystal column to be grown. For example, if the diameter of the crystal column to be grown is an eight-inch crystal column, the diameter of the lower bottom of the crucible 3 is not less than eight inches.
[0033] However, the diameter of the small bottom of the crucible 3 should not be too large, only slightly larger than the diameter of the crystal column to be grown, generally not more than 1.5 times the diameter of the crystal column to be grown.
[0034] In Figure 1 and Figure 2 In the exemplified structure, the crucible 3 can be regarded as a shallow barrel shape. Since the crucible 3 is a typical rotational body structure, based on its generatrix, the angle between the generatrix and the plane where the upper bottom is located is not greater than 18° and not less than 5°. Under this condition, in order to completely hold the material for growing an eight-inch crystal column with a height of three feet (0.914 meters), the diameter of the upper bottom of the crucible 3 is greater than twenty-four inches under this condition, and relatively speaking, a higher requirement is imposed on the diameter of the furnace body. In addition, due to the increase in the overall radial dimension of the crucible 3, the height of the crucible 3 is reduced. In other words, the furnace body can have a relatively small height.
[0035] Since the crucible 3 is relatively shallow, under this condition, the melt is also relatively shallow, and it is easier to ensure the uniformity of heating the material, resulting in a relatively small temperature gradient of the melt.
[0036] Correspondingly, since the crucible 3 is relatively flat as a whole, the heater 2 is arranged below the crucible 3 instead of surrounding the crucible 3. Under this condition, in the top view direction, the heater can have a relatively large area. The heater uses an electrothermal heating element, such as a disk-shaped electric heating wire formed by a double helix arrangement. The diameter of the disk surface of the disk-shaped electric heating wire is larger than the small bottom diameter of the crucible 3 and not larger than the large bottom diameter of the crucible 3.
[0037] In Figure 1 In the illustrated structure, a lifting rotating shaft 1 is provided. On the one hand, the distance between the heater 2 and the crucible 3 is adjusted according to the amount of material, and on the other hand, by rotating, a homogenized heating range is formed on the disk surface of the electric heating wire, for example.
[0038] Correspondingly, the heater 2 is installed at the upper end of the lifting rotating shaft 1. At the same time, it should be known that the configuration of the rotational freedom of the crucible 3 belongs to the conventional configuration in the art. It should be known that in the art, the lifting rod 7 and the crucible 3 can rotate relative to each other, and the rotation directions are opposite. In the embodiment of the present invention, only the rotational freedom of the crucible 3 is retained. The difference from the prior art is that under this condition, due to the loss of the rotational freedom of the lifting rod 7, the relative rotational angular velocity between the crucible 3 and the crystal column 4 needs to be considered. Except for this, other configurations can be exactly the same.
[0039] Regarding the rotation speed of the heater 2, in terms of angular velocity, it can be the same as the rotation speed of the crucible 3.
[0040] Regarding the shape of the electrothermal heating element, for example, a barrel-shaped cover that is geometrically similar to the lower part of the crucible 3 can also be constructed using an electric heating wire, and it has a disk-shaped part and a conical part.
[0041] Correspondingly, if the electrothermal heating element is constructed as a barrel-shaped cover, the lower part of the crucible 3 can be nested into the conical part, and it is not required to incorporate the entire main body of the crucible 3 into it.
[0042] Regarding the relationship between the crucible 3 and the electrothermal heating element, a non-contact heating method should be adopted, and the distance is not less than 5 mm and not more than 20 mm.
[0043] As mentioned above, the large bottom of the crucible 3 is much larger than the small bottom. The overly large large bottom will generate a relatively large moment of inertia during the rotation of the crucible 3, and under the condition of the same angular velocity, the melt on the centrifugal side will generate a relatively large centrifugal force, which easily causes a relatively typical concave surface on the upper surface of the melt. And the depth of the concave surface is positively correlated with the angular velocity of the crucible 3 and the diameter of the large bottom. In view of this, in order to minimize the depth of the concave surface, the upper end of the frustum barrel-shaped crucible 3 has a cylindrical cofferdam 32, so as to increase the overall volume and reduce the radial size of the crucible 3.
[0044] However, the height of the cofferdam 32 should not be too large, otherwise the significance of using the frustum bucket-shaped structure will be lost. Therefore, the height of the cofferdam 32 is not greater than one-fifth of the height of the crucible 3.
[0045] Regarding the lifting rod 7, the traditional lifting rod 7 is generally a round rod. In the embodiments of the present invention, since there is no need to consider its rotational freedom, there are more choices. For the convenience of guiding and limiting, the lifting rod 7 is a multi-prism; a multi-prism sleeve is correspondingly provided to provide axial guidance and circumferential constraint for the lifting rod 7. The circumferential constraint is similar to the profile connection and has a good limiting effect.
Claims
1. A top seed crystal pulling single crystal growth device, characterized in that: include: Furnace body; A lifting mechanism, located in the furnace body and provided with a lifting rod, the lifting rod only has the degree of freedom of lifting and lowering; The seed crystal holder is located at the lower end of the lifting rod and is used to install the seed crystal; The crucible is located in the furnace body and directly below the seed crystal holder, and the main body of the crucible is a frustum barrel shape with a larger top and a smaller bottom; A lifting shaft is located below the crucible; as well as A heater is installed at the upper end of the lifting shaft to heat the crucible from the bottom.
2. The top seed crystal pulling single crystal growth device according to claim 1, characterized in that: The bottom diameter of the truncated cone barrel-shaped crucible is larger than the predetermined diameter of the crystal column.
3. The top seed crystal pulling single crystal growth device according to claim 1 or 2, characterized in that: The included angle between the generatrix of the truncated cone barrel-shaped crucible and the upper bottom is less than or equal to 18° and greater than or equal to 5°.
4. The top seed crystal pulling single crystal growth device according to claim 3, characterized in that: The upper end of the truncated cone barrel-shaped crucible is provided with a cylindrical cofferdam.
5. The top seed crystal pulling single crystal growth device according to claim 4, characterized in that: The height of the cofferdam shall not be greater than one fifth of the height of the crucible.
6. The top seed crystal pulling single crystal growth device according to claim 1, characterized in that: The heater is a disc-shaped electric heating element or a bottom-mounted electric heating element with a tapered portion; If the heater is an electric heating element with a bottom and a tapered portion, the lower portion of the crucible is located and nested in the tapered portion.
7. The top seed crystal pulling single crystal growth device according to claim 1 or 6, characterized in that: The crucible rotates in the opposite direction to the heater and at the same angular velocity.
8. The top seed crystal pulling single crystal growth device according to claim 1, characterized in that: The lifting shaft is adapted to be provided with an upper dead point constraint to maintain non-contact heating of the crucible by the heater.
9. The top seed crystal pulling single crystal growth device according to claim 1, characterized in that: The lifting rod is a polygonal column; A polygonal column sleeve is provided accordingly to provide axial guidance and circumferential constraint to the lifting rod.
10. The top seed crystal pulling single crystal growth device according to claim 1, characterized in that: The lower end of the seed crystal holder is provided with a seed crystal jacket.