Thermal insulation and single crystal furnace

Abstract

The utility model embodiment provides a kind of heat insulation piece and single crystal furnace, the heat insulation piece is provided with multiple heat conduction holes along its thickness direction through;The area of the side surface of the heat insulation piece in its thickness direction is first area S1, the total area of the multiple heat conduction holes is second area S2, 8%≤S2 / (S1+S2)≤25%.Both can realize reducing the oxygen content in crystal bar, also can consider stability in the process of pulling crystal, reduce the breakage rate, eliminate the adverse effect to single yield.

Description

Technical Field

[0001] This utility model relates to the field of crystal pulling technology, and in particular to a heat insulation component and a single crystal furnace. Background Technology

[0002] The oxygen in the crystal rod mainly originates from the reaction between the quartz crucible and molten silicon, with the chemical reaction formula: SiO2 + Si → SiO. The more intense the heating of the quartz crucible by the heater, the higher the reaction temperature, and the more oxygen is generated. Crystal rod growth generally involves first melting the silicon material in the quartz crucible, and then going through stages such as crystal pulling, shoulder formation, shoulder turning, and constant diameter growth. During the melting process, the bottom of the quartz crucible experiences a higher temperature, generating a large amount of oxygen, which has a significant impact on the oxygen content at the tip of the crystal rod.

[0003] Currently, thermal field devices are designed to block the thermal radiation from the main heater, thereby reducing the thermal radiation from the main heater to the bottom of the quartz crucible and thus lowering the oxygen content at the crystal tip. However, this method has drawbacks: after the thermal field devices are designed to block the radiation, the thermal radiation from the main heater to the bottom of the quartz crucible is drastically reduced, resulting in large temperature fluctuations at the bottom and top of the quartz crucible during crystal pulling. This leads to a significant increase in the breakage rate during crystal growth, severely impacting production capacity. Utility Model Content

[0004] In view of the above problems, embodiments of the present invention are proposed to provide a heat insulation component and a single crystal furnace that overcome or at least partially solve the above problems.

[0005] To address the aforementioned problems, this utility model discloses a heat insulation component, which has an annular structure and is provided with a plurality of heat-conducting holes extending along its thickness direction.

[0006] The area of ​​one side surface of the heat insulation component in its thickness direction is the first area S1, and the total area of ​​the openings of the plurality of heat-conducting holes is the second area S2, where 8% ≤ S2 / (S1+S2) ≤ 25%.

[0007] Secondly, this utility model discloses a single crystal furnace, including a furnace body and a heater, a quartz crucible and the aforementioned heat insulation component disposed in the furnace body;

[0008] The heater and the heat insulation are arranged around the top of the quartz crucible;

[0009] The heat insulation element is disposed below the annular heating zone of the heater.

[0010] The embodiments of this utility model have the following advantages:

[0011] In this embodiment of the invention, heat-conducting holes are formed on the heat insulation component, allowing some of the heat radiated by the main heater to be transferred to the bottom of the quartz crucible through the heat-conducting holes. The area of ​​one side surface of the heat insulation component in its thickness direction is the first area S1, and the sum of the opening areas of the plurality of heat-conducting holes is the second area S2. 8% ≤ S2 / (S1+S2) ≤ 25%, making the proportion of the opening area on the heat insulation component 8%-25%. This allows control of the heat radiation area of ​​the main heater to the bottom of the quartz crucible, effectively balancing the temperature at the bottom of the quartz crucible. This not only reduces the oxygen content in the crystal rod but also ensures stability during the crystal pulling process, reduces the breakage rate, and eliminates adverse effects on yield per unit area. Attached Figure Description

[0012] Figure 1 This is a structural schematic diagram of a heat insulation component according to this utility model;

[0013] Figure 2 This is a schematic diagram of the structure of a heat insulation body according to this utility model;

[0014] Figure 3 This is a schematic diagram of the cross-sectional structure of a single crystal furnace according to this utility model.

[0015] Explanation of reference numerals in the attached figures:

[0016] 10. Heat insulation component; 11. Heat insulation body; 12. Heat conduction hole; 13. First hole group; 14. Second hole group; 20. Furnace body; 30. Heater; 40. Quartz crucible; 50. Crucible side; 60. Insulation cylinder. Detailed Implementation

[0017] To make the above-mentioned objectives, features and advantages of this utility model more apparent and understandable, the utility model will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0018] The terms "first" and "second" in the specification and claims of this application may explicitly or implicitly include one or more of the features. In the description of this utility model, unless otherwise stated, "a plurality of" means two or more. Furthermore, in the specification and claims, "and / or" indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship.

[0019] In the description of this utility model, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this utility model and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this utility model.

[0020] In the description of this utility model, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances.

[0021] In this embodiment of the invention, the heat insulation component can be applied inside a single crystal furnace. The single crystal furnace operates based on the Czochralski method, where polycrystalline silicon raw material is placed in a quartz crucible 40 and heated to melt by a heater 30. Then, a seed crystal is slowly lowered to the surface of the molten silicon, allowing the seed crystal to contact the molten silicon and melt a small portion. Next, the seed crystal is rotated at a certain speed and pulled upwards, while simultaneously controlling the heating power and furnace temperature, allowing the molten silicon to solidify and grow layer by layer, ultimately forming a single crystal silicon rod.

[0022] Specifically, the heater 30 can be fitted over the outside of the quartz crucible 40. The heater 30 can radiate heat onto the quartz crucible 40 to melt the silicon material inside, thereby achieving the pulling of crystal rods. The more intensely the heater 30 heats the quartz crucible 40, the higher the reaction temperature, and the more oxygen is generated by the reaction between the quartz crucible 40 and the molten silicon. Since the bottom of the quartz crucible has a larger contact area with the melt, the temperature at the bottom of the quartz crucible 40 has a greater impact on the oxygen content of the crystal rod than the temperature at the top of the quartz crucible 40.

[0023] This utility model proposes a heat insulation component. The heat insulation component 10 can be in the form of a ring structure. The heat insulation component 10 is sleeved in the middle position of the quartz crucible 40 and is located below the heater 30. The heat insulation component 10 can adjust the heat radiation area of ​​the heater 30 to the bottom of the quartz crucible 40, thereby adjusting the temperature of the bottom of the quartz crucible 40.

[0024] Specifically, such as Figure 1As shown, the heat insulation component 10 is provided with a plurality of heat-conducting holes 12 extending through its thickness direction; the area of ​​one side surface of the heat insulation component 10 in its thickness direction is the first area S1, and the total opening area of ​​the plurality of heat-conducting holes 12 is the second area S2, where 8% ≤ S2 / (S1+S2) ≤ 25%.

[0025] In this embodiment of the invention, heat-conducting holes 12 are formed on the heat insulation component 10, so that only a portion of the heat radiated by the main heater 30 can be transferred to the bottom of the quartz crucible 40 through the heat-conducting holes 12. The area of ​​one side surface of the heat insulation component 10 in its thickness direction is the first area S1, and the total area of ​​the openings of the multiple heat-conducting holes 12 is the second area S2. 8% ≤ S2 / (S1+S2) ≤ 25%, so that the proportion of the opening area on the heat insulation component 10 is 8%-25%, thereby controlling the heat radiation area of ​​the main heater 30 to the bottom of the quartz crucible 40, effectively balancing the temperature at the bottom of the quartz crucible 40, which can reduce the oxygen content in the crystal rod, and also take into account the stability during the crystal pulling process, reduce the breakage rate, and eliminate the adverse effects on the yield per unit.

[0026] Specifically, the break-through rate refers to the ratio of the number of interruptions in the ingot pulling process to the total number of pulling operations. Break-through rate = Number of interruptions / Total number of pulling operations. The break-through rate is an important indicator for measuring the stability and production efficiency of the ingot pulling process. An excessively high break-through rate means frequent interruptions during ingot pulling, leading to reduced production efficiency, increased production costs, and potentially affecting ingot quality and yield.

[0027] Yield per unit typically refers to the number of qualified crystal rods produced per unit of time (such as daily, weekly, or monthly). It is a key indicator for measuring production efficiency and capacity. Higher yield per unit means that more crystal rods meeting quality standards can be produced with the same production time and resource input, which helps to reduce the production cost per unit.

[0028] In this embodiment of the invention, the heat insulation element 10 can be used to block heat. The material of the heat insulation element 10 can be solid felt, carbon carbon, graphite, etc. For heat insulation elements 10 made of the same material, increasing the thickness of the heat insulation element 10 can increase the heat transfer path, so that the heat insulation element 10 can more effectively block heat radiation and heat conduction. In this embodiment of the invention, the thickness of the heat insulation element 10 is not specifically limited.

[0029] In some embodiments, the heat insulation element 10 has an annular structure, such as a circular ring or a rectangular ring. The inner wall of the heat insulation element 10 is enclosed to form a through hole so that the heat insulation element 10 can be fitted over the quartz crucible 40. The through hole can be circular or polygonal, etc., and this embodiment of the present invention does not specifically limit it.

[0030] Optionally, the heat insulation element 10 can be a ring structure, which facilitates the adaptation of the shape of the heat insulation element 10 to the quartz crucible 40, thereby improving the convenience of fitting the heat insulation element 10 onto the quartz crucible 40 and the convenience of installing the heat insulation element 10 into the single crystal furnace.

[0031] Specifically, a heat-conducting hole 12 is opened on the heat insulation component 10, and the heat-conducting hole 12 extends through the thickness direction of the heat insulation component 10. In this way, part of the heat generated by the heater 30 can be conducted through the heat-conducting hole 12 to the bottom of the quartz crucible 40, thereby ensuring the stability of the crystal pulling process.

[0032] Furthermore, the heat insulation component 10 may have a first side and a second side along its thickness direction. The area of ​​the first side or the second side is the first area S1, and the sum of the opening areas of the multiple heat-conducting holes 12 is the second area S2. When S2 / (S1+S2) < 8%, the temperature at the bottom of the quartz crucible 40 is unbalanced, resulting in poor crystal pulling and affecting the yield per unit area. When S2 / (S1+S2) > 25%, the oxygen reduction effect is weakened or even non-existent. In this embodiment of the present invention, 8% ≤ S2 / (S1+S2) ≤ 25% is controlled to balance the crystal pulling effect and the oxygen reduction effect.

[0033] Specifically, the opening area of ​​the heat-conducting hole 12 is the cross-sectional area of ​​the heat-conducting hole 12, that is, the area of ​​the cross-section of the heat-conducting hole 12 along the radial direction of the heat insulation component 10. The sum of the opening areas of the multiple heat-conducting holes 12 is the sum of the cross-sectional areas of the multiple heat-conducting holes 12.

[0034] For example, S2 / (S1+S2) can be 8%, 9.8%, 10%, 11.2%, 13%, 15%, 18%, 20%, 23%, 25%, etc.

[0035] Optionally, the shape of the cross section of the heat conduction hole 12 along the radial direction of the heat insulation member 10 includes at least one of the following: circular, elliptical and polygonal, so that the structure of the heat conduction hole 12 is more diverse.

[0036] Specifically, when the cross-sectional shape of the heat-conducting hole 12 along the radial direction of the heat insulation member 10 is circular, the heat-conducting hole 12 is a circular hole; when the cross-sectional shape of the heat-conducting hole 12 along the radial direction of the heat insulation member 10 is elliptical, the heat-conducting hole 12 is an elliptical hole; when the cross-sectional shape of the heat-conducting hole 12 along the radial direction of the heat insulation member 10 is polygonal, the heat-conducting hole 12 is a polygonal hole, such as... Figure 2 As shown in the box, the heat conduction hole 12 can be a triangular hole, a quadrilateral hole, a pentagonal hole, or a hexagonal hole, etc.

[0037] Optionally, multiple heat-conducting holes 12 can be spaced apart along the circumference of the heat insulation member 10, so that the heat generated by the heater 30 can radiate along the circumference of the quartz crucible 40 to the bottom end of the quartz crucible 40, so that the bottom end of the quartz crucible 40 can be heated more evenly.

[0038] Specifically, the multiple heat-conducting holes 12 are evenly spaced along the circumference of the heat insulation component 10, which can further improve the uniformity of heating the bottom of the quartz crucible 40 by the heater 30, and is beneficial to improving the stability of the crystal pulling process.

[0039] Specifically, at least two heat-conducting holes 12 may also be arranged radially spaced along the heat insulation member 10, that is, multiple heat-conducting holes 12 may be arranged circumferentially and / or radially spaced along the heat insulation member 10.

[0040] In some alternative embodiments, the plurality of heat-conducting holes 12 include at least two sets of holes, the at least two sets of holes including a first set of holes 13 and a second set of holes 14; the first set of holes 13 and the second set of holes 14 are arranged radially apart along the heat insulation member 10.

[0041] In this embodiment of the present invention, the first hole group 13 and the second hole group 14 are arranged at a distance along the radial direction of the heat insulation member 10, and the multiple heat conduction holes 12 in the first hole group 13 and the second hole group 14 can be arranged at a distance along the circumferential direction of the heat insulation member 10, so that the heat conduction holes 12 can be distributed more evenly, which is convenient to ensure that the temperature at the bottom of the quartz crucible 40 is more balanced.

[0042] In some alternative embodiments, the first hole group 13 is disposed on the side of the second hole group 14 facing the center line of the heat insulation member 10; the opening size of the heat-conducting hole 12 in the first hole group 13 is smaller than the opening size of the heat-conducting hole 12 in the second hole group 14.

[0043] In this embodiment of the present invention, when the heat insulation component 10 is applied in a single crystal furnace, the first hole group 13 is arranged close to the quartz crucible 40. The opening size of the heat conduction hole 12 in the first hole group 13 is designed to be smaller, which can reduce the transmitted heat radiation and achieve a better oxygen reduction effect.

[0044] Specifically, the number of heat-conducting holes 12 in the first hole group 13 can be the same as or different from the number of heat-conducting holes 12 in the second hole group 14.

[0045] Specifically, when the heat insulation component 10 is composed of at least two heat insulation bodies 11 spliced ​​together, the number of heat-conducting holes 12 in the first hole group 13 and the second hole group 14 on each heat insulation body 11 may be the same or different.

[0046] In some embodiments, the heat-conducting holes 12 in the first hole group 13 and the second hole group 14 are alternately arranged along the circumference of the heat insulation member 10, so that the heat-conducting holes 12 on the heat insulation member 10 are arranged more dispersedly, which is beneficial to improving the structural stability of the heat insulation member 10.

[0047] In other embodiments, the heat-conducting holes 12 in the first hole group 13 and the second hole group 14 may also be arranged opposite each other in the radial direction of the heat insulation member 10.

[0048] In some alternative embodiments, the thermal insulation element 10 has a first width in its radial direction, and the thermal conductive hole 12 has a second width in its radial direction, the second width being less than or equal to half of the first width.

[0049] In this embodiment of the invention, the second width is less than or equal to half of the first width, which can prevent the heat conduction hole 12 from being too large and ensure the structural stability of the heat insulation component 10.

[0050] Specifically, when the diameter of the heat-conducting hole 12 is less than 15 mm, the opening area of ​​the heat-conducting hole 12 is small, allowing less heat to radiate to the bottom of the quartz crucible 40. When the diameter of the heat-conducting hole 12 is greater than 35 mm, the opening area of ​​the heat-conducting hole 12 is large, which is not conducive to ensuring the structural strength of the heat insulation component 10. Therefore, in some optional embodiments, the diameter of at least some of the heat-conducting holes 12 is adjusted to 15 mm–35 mm to ensure that sufficient heat can be radiated to the bottom of the quartz crucible 40 through the heat-conducting hole 12, ensuring the stability of the temperature at the bottom of the quartz crucible 40, and also ensuring the structural strength of the heat insulation component 10.

[0051] For example, the diameter of some of the heat conduction holes 12 can be 15mm, 18mm, 20mm, 25mm, 29mm, 30mm, 32mm or 35mm, etc.

[0052] In some alternative embodiments, the insulation 10 includes at least two insulation bodies 11 connected end to end.

[0053] In this embodiment of the utility model, the heat insulation component 10 can be spliced ​​together from at least two heat insulation bodies 11. During the installation process, the heat insulation component 10 can be installed into the single crystal furnace in sections, which can reduce the installation difficulty of the heat insulation component 10 and improve the installation convenience of the heat insulation component 10.

[0054] Specifically, the number of heat insulation elements 11 can be two, three, or four, etc. The specific number of heat insulation elements 11 is not limited in this embodiment of the present invention.

[0055] Specifically, two adjacent heat insulation bodies 11 can abut against each other, or two adjacent heat insulation bodies 11 can be spaced apart. In this case, there can also be a heat conduction space between two adjacent heat insulation bodies 11, so that the heat radiated by the heater 30 can be conducted from the heat conduction space to the bottom of the quartz crucible 40.

[0056] Specifically, Example 1 uses the heat insulation component 10 described in this invention, while Comparative Example 1 does not use the heat insulation component 10. The average oxygen content at the tip of the crystal rods in Comparative Example 1 is 9.15 ppma, while the average oxygen content at the tip of the crystal rods in Example 1 is 8.25 ppma. Compared to Comparative Example 1, the oxygen content at the tip of the crystal rods in Example 1 is reduced by 0.9 ppma. Furthermore, compared to Comparative Example 1, Example 1 shows a 4.7% reduction in breakage rate, an increase of 0.14 kg / h in the output of 7 furnaces, and stable crystal pulling has no negative impact on the output per furnace.

[0057] The heat insulation component 10 described in this embodiment of the present invention has at least the following advantages:

[0058] In this embodiment of the invention, heat-conducting holes 12 are formed on the heat insulation component 10, so that only a portion of the heat radiated by the main heater 30 can be transferred to the bottom of the quartz crucible 40 through the heat-conducting holes 12. The area of ​​one side surface of the heat insulation component 10 in its thickness direction is the first area S1, and the sum of the opening areas of the plurality of heat-conducting holes 12 is the second area S2, where 8% ≤ S2 / (S1+S2) ≤ 25%, so that the proportion of the opening area on the heat insulation component 10 is 8%-25%. This allows control of the heat radiation area of ​​the main heater 30 to the bottom of the quartz crucible 40, effectively balancing the temperature at the bottom of the quartz crucible 40. This not only reduces the oxygen content in the crystal rod but also ensures stability during the crystal pulling process, reduces the breakage rate, and eliminates adverse effects on single-yield production.

[0059] Secondly, in this embodiment of the invention, a single crystal furnace is also disclosed, such as... Figure 3 As shown, it includes a furnace body 20 and a heater 30, a quartz crucible 40 and the aforementioned heat insulation component 10 disposed within the furnace body 20; the heater 30 and the heat insulation component 10 are arranged around the quartz crucible 40; the heat insulation component 10 is disposed below the annular heating area of ​​the heater 30, that is, the heat insulation component 10 can surround the middle area or the lower middle area of ​​the quartz crucible 40.

[0060] In this embodiment of the utility model, the heat insulation component 10 can block the heat radiation of the heater 30. Part of the heat radiated by the heater 30 is radiated from the heat conduction hole 12 on the heat insulation component 10 to the bottom of the quartz crucible 40. This can not only prevent the bottom temperature of the quartz crucible 40 from being too high and effectively reduce the oxygen content in the crystal rod, but also effectively balance the temperature at the bottom of the quartz crucible 40. This can reduce the oxygen content in the crystal rod and also take into account the stability of the crystal pulling process, reduce the breakage rate, and eliminate the adverse effects on the yield per unit.

[0061] Specifically, the heat insulation component 10 is sleeved outside the quartz crucible 40, and the gap width between the inner diameter of the heat insulation component 10 and the outer wall of the quartz crucible 40 is greater than or equal to 20mm, so as to ensure a safe distance between the heat insulation component 10 and the quartz crucible 40 and avoid collisions between the heat insulation component 10 and the quartz crucible 40 caused by processing errors.

[0062] Furthermore, the single crystal furnace also includes a crucible side 50, and a quartz crucible 40 can be installed inside the crucible side 50. In this case, the heat insulation element 10 is sleeved outside the crucible side 50, and the gap width between the inner diameter of the heat insulation element 10 and the outer wall of the crucible side 50 is greater than or equal to 20 mm.

[0063] Specifically, the single crystal furnace also includes a heat insulation cylinder 60 disposed within the furnace body 20, and the heat insulation component 10 can be disposed within the heat insulation cylinder 60 and connected to the heat insulation cylinder 60.

[0064] Although preferred embodiments of the present invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the present invention.

[0065] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or terminal device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or terminal device. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or terminal device that includes said element.

[0066] The above provides a detailed description of the heat insulation component and single crystal furnace provided by this utility model. Specific examples have been used to illustrate the principle and implementation of this utility model. The description of the above embodiments is only for the purpose of helping to understand the method and core idea of ​​this utility model. At the same time, for those skilled in the art, there will be changes in the specific implementation and application scope based on the idea of ​​this utility model. Therefore, the content of this specification should not be construed as a limitation of this utility model.

Claims

1. A heat insulation component, characterized in that, The heat insulation component (10) has an annular structure; the heat insulation component (10) is provided with a plurality of heat-conducting holes (12) that penetrate along its thickness direction; The area of ​​one side surface of the heat insulation component (10) in its thickness direction is the first area S1, and the total area of ​​the openings of the plurality of heat-conducting holes (12) is the second area S2, where 8% ≤ S2 / (S1+S2) ≤ 25%.

2. The heat insulation component according to claim 1, characterized in that, The plurality of heat-conducting holes (12) are arranged at intervals along the circumference of the heat insulation member (10).

3. The heat insulation component according to claim 1, characterized in that, The plurality of heat-conducting holes (12) include at least two sets of holes, wherein the at least two sets of holes include a first set of holes (13) and a second set of holes (14); The first hole group (13) and the second hole group (14) are arranged radially apart along the heat insulation member (10).

4. The heat insulation component according to claim 3, characterized in that, The first hole group (13) is disposed on the side of the second hole group (14) facing the center line of the heat insulation member (10); The opening size of the heat-conducting hole (12) in the first hole group (13) is smaller than the opening size of the heat-conducting hole (12) in the second hole group (14).

5. The heat insulation component according to claim 3, characterized in that, The heat-conducting holes (12) in the first hole group (13) and the second hole group (14) are alternately arranged along the circumference of the heat insulation member (10).

6. The heat insulation component according to claim 1, characterized in that, The thermal insulation element (10) has a first width in its radial direction, and the thermal conductive hole (12) has a second width in its radial direction, wherein the second width is less than or equal to half of the first width.

7. The heat insulation component according to claim 1, characterized in that, At least some of the heat-conducting holes (12) have a diameter of 15-35 mm.

8. The heat insulation component according to claim 1, characterized in that, The insulation element (10) includes at least two insulation bodies (11) connected end to end.

9. The heat insulation component according to claim 1, characterized in that, The shape of the cross section of the heat-conducting hole (12) along the radial direction of the heat insulation member (10) includes at least one of the following: circular, elliptical, and polygonal.

10. A single crystal furnace, characterized in that, It includes a furnace body (20) and a heater (30), a quartz crucible (40) disposed within the furnace body (20) and a heat insulation element (10) as described in any one of claims 1-9; The heater (30) and the heat insulation element (10) are arranged around the quartz crucible (40); The heat insulation element (10) is disposed below the annular heating zone of the heater (30).

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