Ingot lifting apparatus with composite exhaust tube and method for selecting the lengths of the lower and upper portions of the exhaust tube.

Abstract

The present invention provides an ingot lifting apparatus that reduces the formation of deposits on the exhaust system of the ingot lifting apparatus, and a method for selecting the length of the lower metal portion of the composite exhaust tube of the ingot lifting apparatus. [Solution] Disclosed is an ingot lifting device having a composite exhaust tube 140 and a method for selecting the lengths of the lower portion 155 and upper portion 147 of the composite exhaust tube. In some embodiments, the upper portion of the composite exhaust tube is made of graphite and the lower portion is made of stainless steel.

Description

Technical Field

[0001] (Cross - reference to Related Applications) This application claims priority based on U.S. Provisional Patent Application No. 63 / 153012, filed on February 24, 2021. The application on which the priority is based is hereby incorporated by reference in its entirety into this application.

[0002] The field of the present disclosure relates to an ingot pulling device having a composite exhaust tube and a method of selecting the lengths of the lower and upper portions of the composite exhaust tube.

Background Art

[0003] Single - crystal silicon ingots may be prepared by the so - called Czochralski method in which a single - crystal silicon seed is contacted with a silicon melt held within a crucible. The single - crystal silicon seed is withdrawn from the melt and a single - crystal silicon ingot is pulled up from the melt. The ingot may be prepared in a batch system in which polycrystalline silicon is first melted within the crucible and the silicon ingot is withdrawn from the melt until the molten silicon within the crucible is depleted. Alternatively, the ingot may be withdrawn by a continuous Czochralski method in which polysilicon is intermittently or continuously added to the melt to replenish the silicon melt during ingot growth.

[0004] Crystal pulling may be performed in the presence of an atmosphere within the housing of the ingot pulling apparatus. In both batch and continuous Czochralski processes, a silicon-inert process gas, such as argon, is continuously introduced into the housing and withdrawn through the puller's exhaust system. As the process gas is withdrawn, compounds (e.g., silicon carbide and silicon oxide compounds) may deposit in the exhaust system, which is colder than the puller chamber. Such deposits are periodically removed from the exhaust system, but this may require shutting down the ingot pulling apparatus, increasing processing costs. Maintaining pressure within the housing is necessary, which is difficult with large cross-sectional area exhaust tubes, making it difficult to increase the size of the exhaust system.

[0005] There is a need for a crystal pulling system that can withstand the environment (e.g., temperature) of an ingot pulling device and is characterized by reducing the formation of deposits on the exhaust system of the ingot pulling device.

[0006] This section is intended to introduce readers to various aspects of the technology that may be relevant to the various aspects of the disclosure described and / or claimed below. This discussion is intended to be useful in providing readers with background information to better understand the various aspects of the disclosure. Therefore, these statements should be read in this context and should not be understood as an admission of prior art. [Overview of the project]

[0007] One aspect of the present disclosure relates to an ingot pulling apparatus for growing a single-crystal silicon ingot from a silicon melt. The apparatus includes a housing that defines a growth chamber. The housing has a bottom and side walls extending from the bottom. A crucible is placed inside the growth chamber to hold the silicon melt. An exhaust tube extends from the growth chamber to the bottom of the housing. The exhaust tube defines an exhaust passage for discharging exhaust gases from the growth chamber. The exhaust tube includes an upper portion made of a first material and a lower portion coupled to the upper portion. The lower portion is made of a second material different from the first material.

[0008] Another aspect of the present disclosure relates to a method for selecting the length of the lower metal portion of a composite exhaust tube of an ingot pulling apparatus. The composite exhaust tube includes an upper portion made of a first material and a lower portion bonded to the upper portion. The lower portion is made of a second material, which is metal. The second material is different from the first material. The composite exhaust tube extends upward from the bottom of the housing through an insulating layer. The method includes determining a threshold temperature for the lower metal portion of the exhaust tube. The radial position of the exhaust tube is determined. The axial temperature profile of the ingot pulling apparatus is determined at the radial position of the exhaust tube during the melting phase of ingot growth. The axial temperature profile decreases from the upper portion of the insulating layer toward the bottom of the housing. The length of the lower metal portion of the exhaust tube is selected such that the upper end of the lower metal portion is at an axial position where the temperature of the lower metal portion is below the threshold temperature during the melting phase of ingot growth.

[0009] Various improvements exist to the features described in relation to the embodiments of this disclosure described above. Similarly, further features may be incorporated into the embodiments of this disclosure described above. These improvements and additional features may exist individually or in any combination. For example, various features described below in relation to any of the illustrated embodiments of this disclosure may be incorporated into any of the embodiments of this disclosure described above, individually or in any combination. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a cross-sectional view of an ingot pulling apparatus having a charge of molten polycrystalline silicon. [Figure 2] Figure 2 is a cross-sectional view of the ingot pulling device after melting and before silicon ingot growth. [Figure 3] Figure 3 is a cross-sectional view of an ingot pulling device during silicon ingot growth. [Figure 4] Figure 4 is a perspective view of the exhaust tube of the ingot lifting device. [Figure 5] Figure 5 is an exploded view of the exhaust tube, showing the upper and lower sections of the exhaust tube.

[0011] Throughout the drawings, corresponding reference numerals indicate corresponding parts. [Modes for carrying out the invention]

[0012] The present disclosure provides an ingot pulling apparatus having a composite exhaust tube and a method for selecting the length of the lower portion of the exhaust tube (e.g., the metal lower portion). The ingot pulling apparatus may be any ingot pulling apparatus configured to pull up single-crystal silicon ingots. An example of an ingot pulling apparatus (or more simply, an ingot puller) is shown as "100" in whole in Figure 1. The ingot pulling apparatus 100 includes a crucible 102 for holding a molten semiconductor or solar-grade material such as silicon (Figure 2), supported by a susceptor 106. The ingot pulling apparatus 100 includes an ingot pulling housing 108 that defines a growth chamber 152 for pulling up a silicon ingot 113 (Figure 3) from the molten material 104 along a pulling axis A. The crucible 102 is located within the growth chamber 152. The ingot pulling apparatus 100 is generally suitable for batch Czochralski growth, which fully grows an ingot from an initial charge of polysilicon 101. In other embodiments, polysilicon is added during ingot growth, such as in a continuous Czochralski process.

[0013] The crucible 102 includes a floor 129 and a side wall 131 extending upward from the floor 129. The side wall 131 is generally vertical. The floor 129 includes a curved portion of the crucible 102 that extends below the side wall 131. Inside the crucible 102 is a silicon melt 104 (Figure 3) having a melt surface 111 (i.e., a melt-ingot interface).

[0014] In some embodiments, the crucible 102 is layered. For example, the crucible 102 may be made of a quartz base layer and a synthetic quartz layer placed on top of the quartz base layer.

[0015] The susceptor 106 is supported by the shaft 105. The susceptor 106, crucible 102, shaft 105, and ingot 113 have a common longitudinal axis A or “pull-up axis” A.

[0016] The ingot lifting housing 108 includes a housing bottom 116 and a housing side wall 121 extending upward from the bottom 116. The ingot lifting device 100 includes an insulating cap 125 to prevent contaminants from entering the growth chamber 152 from the bottom insulating layer 110. The side insulating material 124 extends radially inward from the housing side wall 121.

[0017] The ingot retrieval device 100 includes a retrieval mechanism 114 for growing the ingot 113 (Figure 3) and retrieving it from the molten metal 104. The retrieval mechanism 114 includes a retrieval cable 118, a seed holder or chuck 120 coupled to one end of the retrieval cable 118, and a silicon seed crystal 122 coupled to the seed holder or chuck 120 for initiating crystal growth. One end of the retrieval cable 118 is connected to a pulley (not shown) or drum (not shown), or any other suitable type of lifting mechanism, such as a shaft, and the other end is connected to a chuck 120 that holds the seed crystal 122. During operation, the seed crystal 122 is lowered and comes into contact with the molten metal 104. The retrieval mechanism 114 operates to raise the seed crystal 122. This retrieves the single-crystal ingot 113 (Figure 3) from the molten metal 104.

[0018] During heating and crystal pulling, the crucible drive unit 107 (e.g., a motor) rotates the crucible 102 and susceptor 106. The lifting mechanism 112 raises and lowers the crucible 102 along the pull axis A during the growth process. For example, as shown in Figure 1, the crucible 102 may be at its lowest position (near the bottom heater 126) where the initial charge 101 of solid-phase polycrystalline silicon pre-added to the crucible 102 is melted. Crystal growth is initiated by bringing the molten silicon 104 into contact with the seed crystal 122 and raising the seed crystal 122 by the pull mechanism 114. As the ingot 113 grows, the silicon molten silicon 104 is consumed, and the height of the silicon molten silicon 104 in the crucible 102 decreases. The crucible 102 and susceptor 106 may be raised to maintain the molten surface 111 in the same position or near the ingot puller 100 (Figure 3).

[0019] A crystal drive unit (not shown) may rotate the pull-up cable 118 and the ingot 113 (Figure 3) in the opposite direction to the direction in which the crucible drive unit 107 rotates the crucible 102 (e.g., reverse rotation). In embodiments using unidirectional rotation, the crystal drive unit may rotate the pull-up cable 118 in the same direction as the direction in which the crucible drive unit 107 rotates the crucible 102. The crystal drive unit may also raise or lower the ingot 113 relative to the molten surface 111 as desired during the growth process.

[0020] The ingot lifting apparatus 100 may include an inert gas system for introducing an inert gas, such as argon, into or out of the growth chamber 152. The ingot lifting apparatus 100 may also include a dopant supply system (not shown) for introducing a dopant into the molten liquid 104.

[0021] According to the Czochralski single crystal growth process, a large amount of solid polycrystalline silicon 101, i.e., polysilicon, is charged into a crucible 102. The initial charge 101 of semiconductor or solar-grade material introduced into the crucible 102 is melted by heat provided by one or more heating elements, forming a silicon melt 104 (Figure 2) within the crucible 102. The ingot pulling device 100 includes a bottom insulation layer 110 and side insulation 124 to maintain heat in the growth chamber 152. Part of the ingot pulling device 100 may be cooled (for example, fluid cooling at the bottom of the device 100). In the illustrated embodiment, the ingot pulling device 100 includes a bottom heater 126 located below the crucible floor 129. As shown in Figure 1, the crucible 102 may be moved to a relatively close position to the bottom heater 126 so that the bottom heater 126 melts the polycrystalline charge 101 within the crucible 102.

[0022] To form the ingot 113 (Figure 3), the seed crystal 122 is brought into contact with the surface 111 of the molten metal 104. A pulling mechanism 114 is operated to pull the seed crystal 122 from the molten metal 104. Referring to Figure 3, the ingot 113 includes a crown portion 142, in which the ingot 113 tapers as it moves outward from the seed crystal 122 to reach a target diameter. The ingot 113 includes a portion 145 or cylindrical "body" of the crystal 113 that grows by increasing the pulling rate. The body 145 of the ingot 113 has a relatively constant diameter. The ingot 113 includes a tail or end cone (not shown) after the body 145, in which the ingot tapers radially. When the diameter is small enough, the ingot 113 is separated from the molten metal 104.

[0023] The ingot lifting device 100 includes a side heater 135 and a susceptor 106 that surrounds the crucible 102 to maintain the temperature of the melt 104 during crystal growth. The side heater 135 is disposed radially outside the side wall 131 of the crucible when the crucible 102 moves vertically along the lifting axis A. The side heater 135 and the bottom heater 126 may be any type of heater operable as described herein for the side heater 135 and the bottom heater 126. In some embodiments, the heaters 135, 126 are resistance heaters. The side heater 135 and the bottom heater 126 may be controlled by a control system (not shown) such that the temperature of the melt 104 is controlled throughout the lifting process. The bottom heater 126 and the side heater 135 are exemplary, and the ingot lifting device 100 may include different arrangements of heaters (e.g., heaters at different positions and / or additional heaters).

[0024] The ingot lifting device 100 may include a thermal shield 151. The thermal shield 151 may surround the ingot 113 and may be partially disposed within the crucible 102 during crystal growth (FIG. 3).

[0025] The ingot lifting device 100 includes an exhaust tube 140. The exhaust tube 140 passes through the bottom 116 of the housing 108, through the bottom insulation layer 110, through the insulation cap 125, and extends to the growth chamber 152. The exhaust tube 140 includes an upper end 143 that may be aligned with the insulation cap 125 and a lower end 149 that is aligned with the bottom 116 of the housing 108. The exhaust tube 140 has an overall length L140 (FIG. 4) extending from the upper end 143 to the lower end 149. The exhaust tube 140 defines an exhaust flow path 166 (FIG. 1) for discharging exhaust gas from the growth chamber 152. The exhaust tube 140 may be integrated with an exhaust port (not shown). The exhaust port may be connected (e.g., by a flange connection) to an external conduit that directs the exhaust gas to a filtration system and a vacuum pump.

[0026] Although the ingot lifting device 100 is shown with a single exhaust tube 140, the ingot lifting device 100 may include multiple exhaust tubes 140 (and associated exhaust ports), such as at least two, three, four, five, six, or more exhaust tubes 140. In such embodiments, each exhaust tube 140 may be a composite exhaust tube as described herein.

[0027] Referring to Figure 4, the exhaust tube 140 includes an upper portion 147 and a lower portion 155 coupled to the upper portion 147. The upper portion 147 is made of a first material, and the lower portion 155 is made of a second material different from the first material. According to some embodiments of the present disclosure, the first material from which the upper portion 147 is made has a higher melting temperature than the second material from which the lower portion 155 is made. In some embodiments, the first material from which the upper portion 147 of the exhaust tube 140 is made is graphite. The second material from which the lower portion 155 of the exhaust tube 140 is made may be a metal such as stainless steel (for example, the upper portion 147 is graphite and the lower portion 155 is stainless steel).

[0028] It should be noted that the exhaust tube 140 shown in Figure 4-5 is illustrative. For example, the upper portion 147 and / or lower portion 155 may include two or more layers (for example, the upper portion 147 may include a layer of graphite on the inside and a layer of metal on the outside). In some embodiments, the composite exhaust tube 140 includes additional portions made of different materials.

[0029] The upper portion 147 and the lower portion 155 of the exhaust tube 140 may be joined to each other by any known method for connecting two dissimilar materials. For example, as shown in Figure 5, the lower portion 155 includes a collar 158. When the two portions 147,155 are joined to each other, the collar 158 is received in the upper portion 147 (e.g., a counterbore formed in the upper portion 147). The collar 158 may be friction-fitted into the upper portion 147 (e.g., the weight of the upper portion 147 and / or the bore in the bottom insulation layer 110 help maintain the connection).

[0030] The upper portion 147 of the exhaust tube has a length L147 extending from the upper end 154 to the lower end 156. The lower portion 155 has a length L155 extending from the upper end 164 to the lower end 164 (i.e., length L155 includes the collar 158).

[0031] According to some embodiments of the present disclosure (for example, when the lower portion 155 of the exhaust tube 140 is made of a metal such as stainless steel), the length L155 of the lower portion 155 of the exhaust tube 140 may be selected to prevent deformation and / or breakage of the lower portion 155 of the exhaust tube 140. In order to select the length L155 of the lower portion 155 of the exhaust tube 140, a threshold temperature for the lower (e.g., metal) portion of the exhaust tube 140 is determined. The threshold temperature may be related to the melting temperature of the second material of the lower portion 155 of the exhaust tube 140 (for example, 10°C lower than the melting temperature of the second material from which the lower portion 155 of the exhaust tube 140 is made, or 25°C lower than the melting temperature, 50°C lower than the melting temperature, or 100°C lower than the melting temperature of the second material from which the lower portion 155 of the exhaust tube 140 is made). In some embodiments, the threshold temperature is the melting temperature of the second material of the lower portion 155 of the exhaust tube 140.

[0032] In embodiments in which the lower portion 155 is made of stainless steel (for example, 304L stainless steel, which generally has a melting temperature in the range of 1400°C to 1420°C), the threshold temperature may be 1400°C or less, 1375°C or less, or 1330°C or less.

[0033] An embodiment of the method for selecting the length L155 of the lower portion 155 of the exhaust tube 140 includes determining the axial temperature profile of the ingot puller 100 (i.e., the temperature inside the ingot puller along the length L140 of the exhaust tube 140) at the radial position R140 (Figure 1) of the exhaust tube 140 during the melting phase of ingot growth. In an existing ingot puller 100 in which the composite exhaust tube 140 is retrofitted to a conventional exhaust tube, the radial position 140 (Figure 1) of the exhaust tube 140 is simply the position of the tube in the ingot puller 100. In a new ingot puller 100, the radial position R140 is set by determining the position where the exhaust tube 140 is positioned when designing the new ingot puller 100.

[0034] The axial temperature profile at the radial position of the exhaust tube 140 is determined by measuring the temperature inside the ingot retrieval device 100 during the melting phase of ingot growth (for example, by measuring the actual temperature inside the ingot retrieval device 100 having one or more temperature sensors). In some embodiments, the axial temperature profile at the radial position of the exhaust tube 140 is determined by modeling the temperature inside the ingot retrieval device 100 during the melting phase. The temperature profile of the ingot retrieval device 100 during melting may be modeled using commercially available tools such as CrysVun (CrysVun software from the Crystal Growth Laboratory of the Fraunhofer Institute IISB (Erlangen, Germany)), COMSOL (COSMOL multiphysics software from COSMOL Inc. (Burlington, Massachusetts, USA)), Fluent (commercial software managed by Ansys (Canonsburg, Pennsylvania, USA)), and CGSim (CGSim software commercialized by STR Group Inc. (Saint Petersburg, Russia)). These tools are illustrative, and other software code (e.g., 2D simulations of arbitrary steady states) may be used to model heat transfer in a molten puller.

[0035] According to embodiments of the present disclosure, the temperature profile of the ingot pulling device 100 is determined during the melting phase in which the initial charge 101 (Figure 1) of solid-phase polycrystalline silicon added to the crucible 102 melts. During melting, the crucible 102 is typically lowered to the lowest position closest to the bottom heater (or multiple heaters) 126. During melting, the exhaust tube 140 may reach the highest temperature, with the lower portion 155 approaching the threshold temperature. The axial temperature profile of the exhaust tube 140 at the radial position R140 generally shows a decrease in temperature from the upper end 143 to the lower end 149.

[0036] Once the temperature profile of the ingot pulling device 100 at the radial position of the exhaust tube 140 is determined during melting, the length L155 of the lower metal portion 155 of the exhaust tube 140 is selected. The length L155 of the lower metal portion 155 of the exhaust tube 140 is selected such that the upper end 164 (Figure 5) of the lower metal portion 155 is in an axial position where the temperature of the entire lower metal portion 155 is below the threshold temperature during the melting phase of ingot growth (i.e., when the silicon charge 101 (Figure 1) is melting). In this regard, it should be noted that the length L155 of the lower portion 155 of the exhaust tube may include a collar 158 to ensure that the entire lower portion 155 of the exhaust tube 140 remains below the threshold temperature.

[0037] It should be noted that since the length L140 of the exhaust tube 140 (Figure 4) is relatively fixed by the thickness of the bottom insulation layer 110, the length L147 of the upper portion 147 of the exhaust tube 140 is determined by selecting the length of the lower portion 155 of the exhaust tube (i.e., in embodiments where the composite exhaust tube 140 includes only two portions and the height of the collar 158 is fixed).

[0038] In some embodiments, a second threshold temperature is set for the upper portion 147 of the exhaust tube 140 (i.e., the threshold temperature described above is the first threshold temperature). In such embodiments, the length L155 of the lower portion 155 of the exhaust tube may be shortened to ensure that the upper end 164 of the lower portion 155 is below the first threshold temperature, while the length L155 may be selected such that the bottom 155 is sufficiently long to allow the entire length L147 of the upper portion 147 of the exhaust tube 140 to be above the second threshold temperature. For example, the second threshold temperature may be the maximum temperature at which at least some deposits are formed on the upper portion 147 of the exhaust tube 140 (i.e., the second threshold temperature may be a temperature at which such deposits are not formed above the second threshold temperature). Examples of deposits include silicon oxide (SiOx), silicon (e.g., by silicon condensation), and silicon carbide (SiC) (including composites of SiC and SiOx). In embodiments in which the upper portion 147 is made of graphite, the upper portion 147 is maintained at a temperature higher than the second threshold temperature (i.e., by making the lower portion 155 of sufficient length L155 so that the entire upper portion 147 is maintained in the hotter portion of the bottom insulation layer 110), and the second threshold temperature may be 1200°C.

[0039] Compared to conventional ingot lifting equipment, the ingot lifting equipment of this disclosure offers several advantages. By using a composite exhaust tube, the exhaust tube can be adapted to reduce the accumulation of deposits formed in the exhaust tube. In embodiments where the upper portion is made from graphite, the upper portion is relatively simple and inexpensive to manufacture. Graphite is a relatively inexpensive material. In such embodiments, graphite is limited to the upper portion of the exhaust tube, where temperatures are relatively high and deposit formation is less likely. In embodiments where the lower portion of the exhaust tube is made from stainless steel, stainless steel is resistant to deposit formation, which is beneficial in the lower portion of the exhaust tube, where temperatures are lower and deposit formation is more likely. Reducing deposits allows for a longer runtime of the ingot lifting equipment, thereby improving productivity. A longer runtime allows for more stable processing (which improves yield) and reduces damage to the hot zone because the frequency of hot zone decomposition is reduced. Furthermore, the frequency of exhaust tube replacement can be reduced, thereby lowering operating costs. By modeling the temperature of the ingot pulling device, the length of the lower portion of the tube may be selected such that the upper portion of the exhaust tube is at a threshold temperature below which the material of the lower portion (e.g., stainless steel) begins to deform or melt. Alternatively or additionally, the length of the lower portion of the tube may be selected so that the length of the upper portion of the tube is sufficiently short to ensure that the temperature of the upper portion of the tube is higher than the temperature at which deposits are formed on the material on which the upper portion of the tube is made (e.g., higher than 1200°C for graphite).

[0040] (Examples) The processes described herein are further illustrated by the following embodiments, which should not be taken as limiting. Example 1: Use of composite exhaust tube

[0041] A composite exhaust tube was used in an ingot pulling apparatus similar to the ingot pulling apparatus 100 shown in Figures 1 to 3. The exhaust tube consisted of an upper portion made of graphite and a lower portion made of stainless steel. During ingot growth, the upper portion of the stainless steel lower portion of the exhaust tube melted. The temperature profile of the ingot pulling apparatus was modeled using conventional tools. The boundary between the molten portion of the stainless steel part of the tube and the unmolten portion below it generally corresponded to the position of the 1330°C contour line in the temperature profile of the ingot pulling apparatus (i.e., the contour line where melting actually occurred may be used as the maximum threshold temperature of the lower metal portion of the exhaust tube).

[0042] A second exhaust tube, consisting of an upper section made of graphite and a lower section made of stainless steel, was used in the ingot pulling device. The length of the stainless steel lower section of the second exhaust tube was shortened (and the length of the corresponding graphite upper section was lengthened) so that the entire stainless steel section was located below the 1330°C contour line of the modeled temperature profile of the ingot pulling device. The stainless steel section did not melt during ingot growth. In the exhaust tube, excessive deposit formation did not occur in the upper graphite section, and deposit formation was minimal in the lower stainless steel section.

[0043] As used herein, the terms “about,” “substantially,” “essentially,” and “approximately,” when used in relation to a range of dimensions, density, temperature, or other physical or chemical properties or characteristics, mean to include any variations that may exist at the upper and / or lower limits of the range of the property or characteristic. Such variations include, for example, variations resulting from rounding, measurement methods, or other statistical variations.

[0044] When describing elements of this disclosure or embodiments thereof, the articles “a,” “an,” “the,” and “said” are intended to indicate that there is one or more elements. The terms “comprising,” “including,” “containing,” and “having” are intended to indicate comprehensiveness and that additional elements other than those listed may exist. The use of terms indicating specific orientations (e.g., “top,” “bottom,” “side”) is for explanatory convenience and does not require a specific orientation of the described article.

[0045] Because various modifications are possible in the above-described structure and method without departing from the scope of this disclosure, all matters included in the above description and shown in the accompanying drawings are intended to be interpreted as illustrative rather than restrictive.

Claims

1. An ingot pulling apparatus for growing single-crystal silicon from a silicon melt, A housing defining a growth chamber, the housing having a bottom and side walls extending from the bottom, A vessel placed inside the growth chamber to hold the aforementioned silicon melt, An exhaust tube extending from the growth chamber to the bottom of the housing, wherein the exhaust tube defines an exhaust passage for discharging exhaust gas from the growth chamber, and Equipped with, The exhaust tube is The upper part made from the first material, The upper portion is joined to the lower portion which is made of a second material different from the first material. An ingot lifting device equipped with [a specific feature].

2. The ingot pulling apparatus according to claim 1, wherein the first material is graphite.

3. The ingot pulling apparatus according to claim 1 or 2, wherein the second material is a metal.

4. The ingot pulling apparatus according to claim 3, wherein the second material is stainless steel.

5. The ingot pulling apparatus according to claim 1, wherein the first material is graphite and the second material is stainless steel.

6. The ingot pulling apparatus according to any one of claims 1 to 6, wherein the first material has a melting temperature higher than the melting temperature of the second material.

7. The lower portion includes a collar that is received by the upper portion. The ingot pulling device according to any one of claims 1 to 6, wherein the collar is friction-fitted within the upper portion.

8. The ingot lifting device is equipped with multiple exhaust tubes, Each exhaust tube is, The upper part made from the first material, The upper portion is joined to the lower portion made of the second material. An ingot lifting device according to any one of claims 1 to 7, comprising:

9. A method for selecting the length of the lower metal portion of a composite exhaust tube of an ingot lifting device, wherein the composite exhaust tube comprises an upper portion made of a first material and a lower portion made of a second material which is metal and is coupled to the upper portion, the second material being different from the first material, and the composite exhaust tube extends upward from the bottom of the housing through an insulating layer. The aforementioned method, Determine the threshold temperature for the lower metal portion of the exhaust tube. Determine the radial position of the exhaust tube, The axial temperature profile of the ingot pulling device at the radial position of the exhaust tube during the melting phase of ingot growth is determined, and the axial temperature profile decreases from the upper portion of the insulating layer toward the bottom of the housing. The length of the lower metal portion of the exhaust tube is selected such that the upper end of the lower metal portion is in an axial position where the temperature of the lower metal portion is lower than the threshold temperature during the melting phase of ingot growth. A method that includes doing so.

10. The method according to claim 9, wherein the axial temperature profile at the radial position of the exhaust tube is determined by measuring the temperature in the ingot pulling device during the melting phase.

11. The method according to claim 9, wherein the axial temperature profile at the radial position of the exhaust tube is determined by modeling the temperature in the ingot pulling device during the melting phase.

12. The method according to any one of claims 9 to 11, wherein the threshold temperature is related to the melting temperature of the second material of the lower metal portion of the exhaust tube.

13. The method according to any one of claims 9 to 11, wherein the threshold temperature is the melting temperature of the second material of the lower metal portion of the exhaust tube.

14. The threshold temperature is the first threshold temperature, The method according to any one of claims 9 to 13, wherein the length of the lower metal portion of the exhaust tube is selected such that the total length of the upper portion of the exhaust tube exceeds the second threshold temperature.

15. The method according to claim 14, wherein the second threshold temperature is the highest temperature at which at least some deposits are formed on the upper portion of the exhaust tube.

16. The method according to claim 15, wherein the deposit is at least silicon oxide, silicon, and silicon carbide.

17. The method according to any one of claims 14 to 16, wherein the first material from which the upper portion is made is graphite, and the second threshold temperature is 1200°C.

18. The method according to any one of claims 9 to 17, wherein the second material from which the lower portion is made is stainless steel.

19. The method according to any one of claims 9 to 18, wherein the first material from which the upper portion is made is graphite.

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