JP5626322B2 - Single crystal pulling device - Google Patents

Description

  The present invention relates to an apparatus for producing single crystals such as oxides, fluorides, and metal alloys used for so-called laser optical elements, nonlinear optical elements, medical scintillators, piezoelectric elements, giant magnetostrictive elements, and the like. More specifically, a pulling method for obtaining a desired crystal material while drawing a raw material melt from a hole provided at the lower end of the crucible, particularly a so-called micro pulling (μ-pD) method for obtaining a fiber-like single crystal. The present invention relates to a single crystal pulling apparatus used in a crystal manufacturing method.

  A pull-out hole is formed in the lower end of the crucible holding the heated and melted raw material, crystal nuclei (hereinafter referred to as seeds) are brought into contact with the raw material melt leaked from the hole, and leakage of the raw material from the hole is caused. A so-called pulling-down method (see Patent Documents 1 to 3) is known in which a single crystal that grows using the seed as a nucleus is obtained by pulling down the seed. When compared with a single crystal obtained by a so-called pulling method represented by a conventionally known CZ method, the single crystal obtained by this method has a smaller crystal diameter. However, the time required for crystal growth is short, and it is cheaper than the CZ method, and it is a method that can obtain a single crystal with excellent crystallinity. Application of various single crystals to manufacturing processes has been studied.

  In the pulling-down method, there is a so-called micro-pulling-down method as a method for obtaining a fiber crystal having higher crystallinity and maintaining a high crystal growth rate. Using this method, a fluoride single crystal such as calcium fluoride used for an optical material for excimer laser, or an oxide single crystal such as alumina or calcia, and also a giant magnetostrictive material exemplified by so-called terphenol D Manufacturing conditions for single crystals are being studied.

JP 2003-095783 A JP 11-278994 A JP 2006-206351 A

  In the single crystal pulling apparatus, as described in Patent Document 3, the behavior of a so-called solid-liquid interface (also referred to as a meniscus because of its shape; hereinafter referred to as a meniscus) is constantly observed. In order to correct the pulling direction, the twisting with respect to the pulling shaft, etc. according to the behavior, it is required to appropriately move the member holding the seed. That is, in the current single crystal pulling apparatus, a configuration that enables observation of the meniscus is essential. However, as shown in Patent Document 1 or 3, the meniscus generation region is covered with a cylindrical after-heater, a heat retaining tube, a heat generation tube, or the like, which will be described later, in order to perform temperature control in a space including the region. It has been broken. For this reason, conventionally, an observation hole penetrating from the outside to the inside of the cylinder is provided for these cylindrical components, and a reduction condition for generating a meniscus in an area that can be observed through the observation hole is selected, and the actual reduction is performed. The operation is being performed. However, the presence of such observation holes causes loss of thermal energy such as outflow of a high-temperature atmosphere around the meniscus and leakage of radiant heat, and therefore only deteriorates temperature uniformity in a plane perpendicular to the pull-down axis. It also has an influence on the so-called temperature gradient to be controlled in the pulling-down direction.

  The present invention has been made in view of the above situation, and in the meniscus formation region and the space in the vicinity thereof, improvement in temperature uniformity in a plane parallel to the pull-down axis and temperature change in the pull-down direction, that is, An object of the present invention is to provide a lowering device capable of suitably controlling a temperature gradient.

  In order to solve the above-described problems, a pulling device according to the present invention holds a raw material melt in a crucible, contacts a raw material melt leaked from a lower opening of the crucible, and contacts a predetermined pulling axis. A pulling device for obtaining a single crystal by pulling down the seed, and a seed moving mechanism that holds the seed and can move the seed up and down along the pulling shaft, and is aligned in the pulling direction of the crucible and the pulling shaft. A cylindrical after heater arranged coaxially with the pulling shaft, a cylindrical outer ring arranged coaxially with the crucible and the after heater, and containing the crucible and the after heater, and the crucible, the after heater, and the outer ring are wound. A heating coil capable of conducting high-frequency power and an imaging means for imaging a meniscus generated from the raw material melt. A plurality of first observation windows arranged in a point-symmetrical manner with respect to the lowering axis in a plane orthogonal to the axis, and the outer ring is centered on the lowering axis in a plane orthogonal to the lowering axis A plurality of second observation windows arranged so as to be point-symmetric, and the imaging means images the meniscus through the first observation window and the second observation window.

  In the above-described pulling-down device, the first observation window is preferably closed with a transparent high melting point material that can transmit the imaging light of the imaging means. In this case, the first observation window is obtained by closing a slit-like space extending in a horizontal plane with a transparent high melting point material, and the first observation window has a predetermined interval in the pull-down axis direction. More preferably, it is provided in a plurality of horizontal planes that are arranged at an interval. Alternatively, the first observation window is made of a second annular member having an annular shape made of a transparent high melting point material, and the after heater is made of the first annular member having an annular shape made of a conductive material and the second annular member. More preferably, the annular members are stacked. Furthermore, the above-described pulling device preferably further includes an outer ring rotating mechanism that rotates the outer ring about the pulling shaft. In this case, the second observation window is more preferably a slit-like observation window extending in the pulling-down direction. Alternatively, a cylindrical first having a third observation window corresponding to the second observation window of the outer ring, which is disposed between the outer ring and the heating coil or between the outer ring and the crucible and the after heater. It is preferable to further have a second outer ring.

  According to the present invention, rather than providing an observation hole that opens only in a specific direction with respect to the cylindrical after-heater, lateral slits are arranged evenly around the central axis in a horizontal plane perpendicular to the central axis. ing. Therefore, in the after heater, there is no factor that disturbs temperature uniformity at a specific position, and a uniform temperature distribution can be obtained in the horizontal plane. For the outer ring, a plurality of observation vertical slits extending in the axial direction are arranged symmetrically with respect to the central axis. Accordingly, the temperature reduction factor in the horizontal plane due to the vertical slit exists radially and symmetrically about the axis center. By arranging the temperature non-uniformity in the horizontal plane due to the structure of the above-mentioned after-heater and outer ring symmetrically about the axis center, the uniformity in the horizontal plane perpendicular to the pull-down axis is improved with respect to the temperature distribution inside the crucible. Thus, it is possible to suitably form a temperature gradient in the pulling-down axis direction. Therefore, it is possible to achieve both the monitoring of the meniscus generation state and the securing of a soaking state, and it is possible to grow a suitable single crystal.

  Further, according to the present invention, the lateral slit in the after heater is filled with a transparent member such as a quartz plate. Therefore, the high temperature atmosphere does not flow out through the horizontal slit, and it is possible to suppress a temperature drop caused by the observation part made of the transparent member. In addition, by arranging the observation part evenly in the horizontal direction, the temperature drop due to the radiation of heat such as so-called radiation through the observation part also occurs uniformly in the horizontal plane. Therefore, the heat transfer characteristic in the horizontal plane in the after heater becomes uniform, and the presence of the observation part does not become an obstruction factor for the temperature distribution. Therefore, it is possible to observe the generation state of the meniscus through the outer ring and the after heater, and it is possible to perform monitoring under suitable single crystal growth conditions.

  Further, according to the present invention, the outer ring is rotated around the central axis. Accordingly, the position of the observation groove in the outer ring consisting of the vertical slits moves sequentially, and the loss of heat energy due to the high temperature atmosphere or radiant heat flowing out from the observation groove is uniform in the horizontal plane and symmetrical with respect to the central axis. A temperature distribution with excellent properties can be obtained. By combining the effects of the after heater and the outer ring described above, it is possible to suppress variations in temperature distribution in a horizontal plane perpendicular to the pulling direction, and it is possible to obtain suitable single crystal growth conditions. . In addition, although it is suitable to implement together regarding the above-mentioned after-heater and outer ring, depending on growth conditions, such as a single crystal material and the required temperature distribution, the temperature distribution can also be carried out individually. It is possible to improve and obtain suitable growth conditions.

It is the schematic which shows the axial direction cross section of the after heater and outer ring which concerns on one Embodiment of this invention, and the single crystal pulled down from this crucible. It is a figure which shows an example of the shape of an outer ring. It is a figure which shows typically the cross-sectional shape in the plane orthogonal to the pulling-down axis | shaft of the outer ring shown to FIG. 2A, and arrangement | positioning of a CCD camera. It is a figure which shows the further example of the shape of an outer ring. It is a figure which shows typically the cross-sectional shape in the plane orthogonal to the pulling-down axis | shaft of the outer ring shown to FIG. 3A, and arrangement | positioning of a CCD camera. It is a figure which shows schematic structure of the rotation mechanism of an outer ring. It is a figure which shows schematic structure of the pulling-down apparatus which concerns on one Embodiment of this invention.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram schematically showing main sections of the lowering apparatus according to the present embodiment, which are axial sections of an after heater and an outer ring, a crucible lower end, a seed, a seed holder, and a single crystal to be lowered. is there. In the figure, a crucible 11 has an opening 11a at a lower end surface and holds a raw material melt 9 therein. The raw material melt 9 leaks vertically downward from the opening 11a. The raw material melt 9 becomes a single crystal crystal nucleus at the lower end of the leaked portion and comes into contact with a seed crystal that determines the crystal orientation, the so-called seed 7. The raw material melt 9 changes from a liquid raw material melt 9 to a solid single crystal 9 a. A liquid boundary portion 9b (hereinafter referred to as a meniscus) is formed. The seed 7 is held vertically by a seed holder 8, and the seed holder 8 is pulled down along a vertical axis that is a lowering shaft, thereby lowering the seed 7 and growing a single crystal 9 a in the lowering axis direction. . In the present invention, the afterheater 13 and the outer ring 15 arranged around the meniscus 9b are characterized.

  Hereinafter, these characteristic configurations will be described. In the present embodiment, the after-heater 13 has a cylindrical shape, and is in the vicinity of the opening provided on the lower end surface of the crucible 11 and is located above the lower end surface along the lowering axis (in this embodiment, the vertical axis). Are arranged so as to surround an area defined by the second predetermined distance below. That is, the after-heater 13 is aligned with the crucible 11 in the pull-down direction of the pull-down shaft and is arranged coaxially with the pull-down shaft. The after-heater 13 is usually formed of a cylindrical member made of a conductive material. The member is arranged so that the central axis coincides with the pull-down axis, and induction heat is generated by a so-called high frequency given from a heating coil (not shown), so that the temperature in the space where the meniscus 9b is formed, the soaking area is secured, and the temperature gradient It plays the role of optimization. In this embodiment, the after-heater 13 includes an annular first annular member 13a made of a conductive material, and an annular transparent second annular member 13b made of a light-transmitting material such as quartz. Are stacked so that the center of the ring is alternately aligned on the central axis of the after heater 13. The generation state of the meniscus can be observed from the outside of the after heater 13 through the second annular member 13b. That is, the second annular member 13b constitutes a first observation window in the present invention. Further, by eliminating the space for communicating the inside and the outside of the after heater by the second annular member 13b, at least the temperature inside the after heater 13 is lowered due to the outflow of the high temperature atmosphere, and the existence of the space. It is possible to suppress variations in temperature uniformity within a horizontal plane.

The normal meniscus 9b does not always occur at the same position on the lowering shaft, and does not always occur so as to extend in a horizontal plane perpendicular to the lowering shaft. For example, in a specific material, the meniscus 9b is generated within a range of 0.1 to 0.5 mm in the pulling-down axis direction. In the case of using a conventional hole-like observation window, it is preferable to make the observation window as small as possible in order to obtain the effect of the after heater sufficiently and to ensure the thermal uniformity in the horizontal plane. Such a meniscus 9b It was difficult to cope with fluctuations in the location of the occurrence. However, according to the present embodiment, as shown by the observation points a _{1 to} a ₅ in FIG. 1, it is possible to provide an observation region of a plurality of points in the pull-down axis direction, and cope with fluctuations in the generation position of the meniscus 9b. Becomes easy. In addition to grasping the actual meniscus state at multiple points, it is also possible to give an overview of the state between these points from the state at these points, so that the state of meniscus occurrence can be grasped continuously in space. Is also possible.

  As described above, the second annular member 13b is preferably a transparent member made of a high melting point material such as quartz. Further, from the viewpoint of suppressing the radiation of heat rays, it is more preferable that the material is made of a material that has low permeability in the infrared region, or is made of a composite material with the material. In the present embodiment, the first member 13a for heat generation and the translucent second member 13b for observation are formed by an annular member from the viewpoint of securing the observation point in the pull-down axis direction and facilitating the configuration. It is going to be composed. However, the embodiment of the present invention is not limited to this aspect. That is, for example, the first observation window closed by the second member 13b may have a conventional hole shape, and the hole may be closed by the second member 13b. However, in this case, it is preferable that a plurality of the first observation windows are continuously arranged in the pull-down axis direction. Note that the above-described translucency means that imaging light of a later-described CCD camera serving as imaging means is transmitted, and does not mean that other light such as ultraviolet rays is transmitted. Further, from the viewpoint of heat radiation, it is more preferable that a plurality of elements are arranged in the horizontal plane so as to be point-symmetric with respect to the central axis of the after heater 13. That is, in a preferred embodiment of the present invention, the first observation window is point-symmetric with respect to an intersection point of the pull-down axis and the horizontal plane in a horizontal plane orthogonal to the pull-down axis. Must be placed in.

  Furthermore, in the present embodiment, the cylindrical afterheater 13 is illustrated because it is intended for a columnar single crystal, but various forms of afterheaters such as a cross-sectional frame shape according to the cross-sectional shape of the single crystal, that is, What is necessary is just to be constructed | assembled as a cylindrical afterheater. The after heater 13 is composed of a stack of a first annular member 13a and a second annular member 13b that serves as a first observation window. The first observation window extends in a specific horizontal plane. The slit-shaped space existing may be closed with a translucent high melting point material, and a plurality of the first observation windows may be juxtaposed at a predetermined interval in the pull-down axis direction. In this case, it is preferable that the slit shape is also point-symmetric as described above in order to make the loss of heat energy due to radiation in-plane.

  Next, the outer ring 15 will be described. The outer ring 15 can be made of various materials according to the melting temperature of the single crystal to be obtained. However, the outer ring 15 is arranged so as to surround the crucible 11 and the after-heater 13, and keeps these members and the surrounding space warm. Mainly has a role. In this embodiment, the outer ring 15 has a cylindrical shape, and further includes a vertical slit 15a serving as a second observation window that extends in the pull-down axis direction and communicates from the outside of the cylinder to the inside. . 2A shows an overview of the vicinity of the vertical slit 15a of the outer ring 15, and FIG. 2B shows a schematic diagram of a cross-sectional shape in a plane perpendicular to the central axis of the outer ring 15. As shown in the figure, a plurality of vertical slits 15 a are arranged, and each vertical slit 15 a is arranged so as to be symmetric about the central axis of the outer ring 15. More specifically, the second observation window shown as the vertical slit 15a is arranged so as to be point-symmetric with respect to the intersection of the pull-down axis and the horizontal plane in a horizontal plane orthogonal to the pull-down axis. It must be done. 3A and 3B show a case where eight vertical slits 15a are provided in the same manner as in FIGS. 2A and 2B. By disposing the longitudinal slits 15a symmetrically for this purpose, the high-heat atmosphere leaks evenly in each direction with respect to the pull-down shaft disposed in alignment with the central axis. Therefore, the temperature distribution in the horizontal plane shows an axisymmetric tendency.

  2A or 3B also shows a CCD camera 59 used to actually observe the meniscus 9b. The CCD camera 59 is preferably arranged according to the vertical slit 15a shown in the figure so that the state of the meniscus 9b can be confirmed from all directions. However, as described above, since the state of the meniscus 9b in the pull-down direction can be observed in detail, only one CCD camera 59 may be arranged in the present invention. Further, the imaging means is not limited to the CCD camera 59, and various types of imaging devices can be used as long as the state of the meniscus can be suitably imaged. The extending direction of the vertical slit 15a is parallel to the pulling-down axis, and this can be arranged at the shortest intervals with the observation points in consideration of the arrangement of the second member 13b as the observation window of the after heater 13 described above. It depends. However, in the present invention, the extending direction is not limited to this direction, and the extending direction extends in a direction that can intersect the aligned or extending direction when the second member 13b of the after heater 13 is arranged. It should be. In the crossing direction, it is possible to easily observe the meniscus 9b at a plurality of points. As with the above-described after-heater 13, the outer ring 15 is not limited to a cylindrical shape, and various cylindrical shapes such as a horizontal cross-section having a frame shape depending on the cross-sectional shape of the single crystal to be obtained. Is possible. In this case as well, a plurality of the vertical slits 15a may be arranged so as to satisfy the above-described relationship with respect to the arrangement of the second member 13b and to be symmetrical with respect to the central axis.

  Further, in the present invention, in order to further improve the temperature distribution due to the presence of the vertical slit 15a of the outer ring 15, the outer ring 15 is rotated about the axis. As the outer ring 15 rotates, the vertical slit 15a and the temperature drop region in the horizontal plane due to the vertical slit 15a rotate in the horizontal plane. For this reason, the local temperature drop region does not exist in the temperature distribution in the horizontal plane in the outer ring 15, and the effect of improving the uniformity of the temperature distribution is obtained.

  FIG. 4 is a schematic view schematically showing an outer ring rotating mechanism that is configured to rotate the outer ring 15 described above. The crucible 11 is supported by an after heater 13, and the after heater 13 is supported by a heater stage 21 so as to maintain a predetermined positional relationship with a heating coil (not shown). The outer ring 15 is supported by the ring stage 19 so as to maintain a predetermined positional relationship with respect to the crucible 11 and the after heater 13 in the pulling-down axis direction. The ring stage 19 has a cylindrical shape with an upper portion closed by a disk, and supports the outer ring 15 on the upper surface of the disk. In addition, a through hole is provided in the central portion of the disk, and the cylindrical heater stage 21 extends in the downward axis direction through the through hole. The heater stage 21 is connected to the inner surface of the ring stage 19 via a bearing 25 so as to be relatively movable. The heater stage 21 is further fixed by a non-rotating member 27 so that the after-heater 13 and the crucible 11 do not follow the rotating operation of the outer ring 15. The heater stage 19 is fixed to a wheel 29 that can rotate about its axis at the lower end. The wheel 29 meshes with a worm gear 33 connected to the motor 31 at the outer peripheral gear portion. That is, when the motor 31 rotates the worm gear 33, the wheel 29 meshing with the worm gear 33 rotates about its axis. With the above configuration, when the motor 31 rotates the heater stage 19 about the axis via the worm gear 33 and the wheel 29, the outer ring 15 rotates around the after heater 13. In other words, in the present invention, the outer ring rotating mechanism includes the motor 31, the worm gear 33, the wheel 29, the bearing 25, and the rotation preventing member 27 described above. Note that this mechanism is merely an example, and other known various configurations can be applied as long as the outer ring can be rotated around the pull-down shaft independently of the after heater.

  As a preferred embodiment of the present invention, the outer ring 15 is configured as a single body and rotates around the axis. However, for example, the outer ring 15 can be composed of a plurality of cylindrical bodies so as to be composed of the first and second outer rings. In this case, one outer ring may be made of a light-transmitting material such as quartz, and the other outer ring may have the same structure as the outer ring 15 described above. As a result, the outer ring made of a translucent material suppresses the outflow of the high temperature atmosphere, and the outer ring having the vertical slit 15a suppresses the loss due to the radiation of thermal energy. In this case, a suitable image of the meniscus 9b is obtained due to a decrease in resolution of the image obtained through the second member 13b in the after heater 13 and an increase in image distortion due to the presence of the outer ring made of a light-transmitting material. There is a risk of being lost. Therefore, it is preferable that the translucent outer ring has a polygonal cross section so that the meniscus 9b can be observed through the plane portion.

  Moreover, it is good also as using two or more structures which have the vertical slit 15a similar to the outer ring 15 mentioned above. In this case, by making one of them rotatable, only when the vertical slit 15a is aligned on a line connecting the axis center and the CCD camera 59, outflow of a high temperature atmosphere and loss of heat energy due to radiation occur. Therefore, by shortening the time during which this state is established, it is possible to substantially eliminate the situation that disturbs the temperature uniformity in the horizontal plane. Moreover, when it is set as the structure which arrange | positions the outer ring 15 in multiple numbers as mentioned above, for example, even when it is a case where the above-mentioned after heater is made into the structure which consists of the conventional observation hole, a certain amount of temperature uniformity is obtained in a horizontal surface. It is also possible. In other words, a cylindrical second outer ring having a third observation window that enables the CCD camera 59 to image the meniscus 9b can be arranged corresponding to the second observation window. In this case, the second outer ring may be disposed between the outer ring and the heating coil described above, or between the outer ring, the crucible and the after heater.

  Next, a specific configuration of the pulling device having the above-described characteristic configuration will be described. FIG. 5 schematically shows a schematic configuration of the main part of the pulling-down device 1 according to the embodiment of the present invention. The pulling device 1 includes a crucible 11, an after heater 13, an outer ring 15, a heating coil 17, a tube stage 19, a stage holder 16, a seed holder 8, and a holder chuck 18 around a pulling shaft. Moreover, these structures are arrange | positioned inside the vacuum chamber 43 which can supply pressure reduction and the specific gas with respect to interior space. The heating coil 17 emits a high frequency to the crucible 11 as described above, and causes the crucible 11 and the after heater 13 to generate heat up to a predetermined temperature. In addition, the description regarding the after heater 13 and the outer ring 15 is abbreviate | omitted here. The tube stage 19 supports the crucible 11, the after heater 13, and the outer ring 15 in the vacuum chamber 43. In addition, the stage holder 16 adjusts the height of the tube stage 19 and maintains various configurations supported by the tube stage 19 at predetermined positions (heights) with respect to the heating coil 17. The seed 7 described above is held on the lowering shaft by the seed holder 8 arranged on the lowering shaft. Further, the holder chuck 18 connects the seed holder 8 to a pull-down drive unit described later.

  Note that the configuration of the worm gear 33 and the like shown in FIG. 4 is omitted here for the sake of explanation and illustration. A so-called bellows 43 a is disposed coaxially with the seed holder 8 on the bottom surface of the vacuum chamber 43. The lower end portion of the holder chuck 18 is fixed to the θ table 47 fixed to the lower end of the bellows 43a through the internal space of the bellows 43a. A Y table 49 and an X table 51 are attached to the lower portion of the θ table 47. The Y table 49 and the X table 51 are rotated around the lowering shaft with respect to the seed 7 via the holder chuck 18 and the seed holder 8, and are perpendicular to the lowering axis. The movement in the Y direction and the movement in the X direction perpendicular to the pull-down axis and the Y direction are given. In addition, these components are integrally supported by the Z-axis adjusting mechanism 53 and can be moved minutely in the pull-down axis direction that is the Z-axis. Further, the θ table 47, the Y table 49, and the X table 51 are fixed to be slidable with respect to a pull-down guide 55 that extends in the pull-down axis direction as a unit, and are fixed along the pull-down guide 55 by a pull-down motor 57. The seed 7 can be lowered at a speed. These configurations constitute a seed moving mechanism capable of moving the seed up and down along the pull-down axis. The vacuum chamber 43 is provided with a viewing window (not shown) so that the state of the meniscus 9b can be observed through the viewing window. In the illustrated apparatus, the CCD is placed outside the viewing window so that the central axis of the visual field coincides with the observation axis (the central line passing through the visual field center of the first observation window and the center of the meniscus described above). A camera 59 is arranged.

  By using the pulling device having the above configuration, in the meniscus formation region and the space in the vicinity thereof, the temperature uniformity in the plane parallel to the pulling axis and the temperature change in the pulling direction, that is, the temperature gradient, are suitable. It becomes possible to control to. Therefore, it is possible to easily obtain a high-quality single crystal by always appropriately controlling the growth conditions of the single crystal.

1: Pulling device, 7: Seed, 8: Seed holder, 9: Raw material melt, 11: Crucible, 13: After heater, 15: Outer ring, 16: Stage holder, 18: Holder chuck, 19: Tube stage 21: Heater stage 27: Non-rotating member 29: Wheel 31: Motor 33: Worm gear 43: Vacuum chamber 47: θ table 49: Y table 51: X table 53: Z-axis adjustment mechanism 55: Pull-down guide, 57: Pull-down motor, 59: CCD camera

Claims (3)

A pulling device for holding a raw material melt in a crucible, bringing a seed into contact with the raw material melt leaked from a lower opening of the crucible, and pulling the seed along a predetermined pulling axis to obtain a single crystal Because
A seed moving mechanism that holds the seed and can move the seed up and down along the pull-down axis;
A cylindrical after heater arranged coaxially with the pulling shaft in alignment with the pulling direction of the crucible and the pulling shaft;
A cylindrical outer ring that is arranged coaxially with the crucible and the after heater and accommodates the crucible and the after heater inside;
The crucible, the after-heater, and the outer ring are wound and arranged, a heating coil capable of conducting high-frequency power, and an imaging means for imaging a meniscus generated from the raw material melt,
The after heater in a plane perpendicular to the pull-down axis, having a plurality of first observation window disposed so as to be symmetrical points around the pull-down axis,
The outer ring is in a plane perpendicular to the pull-down axis, having a plurality of second observation window is disposed so as to be symmetrical points around the pull-down axis,
The imaging means images the meniscus through the first observation window and the second observation window,
The pulling device further comprising an outer ring rotating mechanism for continuously rotating the outer ring around the pulling shaft when pulling down the seed .   The pulling-down apparatus according to claim 1, wherein the second observation window is a slit-shaped observation window extending in the pulling-down direction.   A third observation window corresponding to the second observation window of the outer ring, disposed between the outer ring and the heating coil, or between the outer ring and the crucible and the after heater; The pulling-down device according to claim 1, further comprising a cylindrical second outer ring.

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