JP2012232879A - Silicon core wire holder and method for manufacturing polycrystalline silicon - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polycrystalline silicon manufacturing technique in which mounting of a silicon core wire into a core wire holder is easy, the time required to make the core wire holder hold the silicon core wire with satisfactory strength is shortened, falling is prevented, and it is made possible to shorten growth rate control time in the early stage of deposition reaction of polycrystalline silicon.SOLUTION: A core wire holder 20 has an opening 22 in an upper surface of the body, and a core wire insertion hole 21 is formed facing a lower surface side. In addition, a hole part (securing member insertion hole) is formed in an upper part of the body of the holder 20, and a bolt-shaped member (securing shaft) is made to pass through the hole part. A silicon core wire 5 that is inserted into the core wire insertion hole 21 is secured by fastening an upper part of the body of the holder 20 from a side surface using such a securing member 31 of a bolt and nut type.

Description

  The present invention relates to a core wire holder used for manufacturing polycrystalline silicon and a method for manufacturing polycrystalline silicon using the core wire holder.

  A Siemens method is known as a method for producing polycrystalline silicon which is a raw material of single crystal silicon for semiconductor production or silicon for solar cell production. The Siemens method is a method in which a source gas containing chlorosilane is brought into contact with a heated silicon core wire, and polycrystalline silicon is vapor-phase grown on the surface of the silicon core wire using a CVD (Chemical Vapor Deposition) method.

  When the polycrystalline silicon is vapor-phase grown by the Siemens method, two silicon core wires in the vertical direction and one silicon core wire in the horizontal direction are assembled in a torii type in the reactor of the vapor phase growth apparatus. Then, both ends of the torii type silicon core wire are fixed to a pair of metal electrodes disposed on the base plate via a pair of core wire holders. Such a configuration is disclosed in, for example, JP 2010-235438 A (Patent Document 1).

  The above-mentioned metal electrode penetrates the base plate with an insulator interposed therebetween and is connected to another metal electrode by wiring or connected to a power source arranged outside the reaction furnace. In order to prevent the deposition of polycrystalline silicon during vapor phase growth, the metal electrode, the base plate, and the reactor are cooled using a refrigerant. As a result, the core wire holder fixed to the metal electrode is also cooled by the metal electrode.

  While conducting the current from the metal electrode and heating the silicon core wire to a temperature range of 900 ° C. or higher and 1200 ° C. or lower in a hydrogen atmosphere, a source gas, for example, a mixed gas of trichlorosilane and hydrogen is supplied from the gas nozzle into the reactor. To do. Silicon contained in the source gas is deposited (vapor phase growth) as polycrystalline silicon on the silicon core wire, and a polycrystalline silicon rod having a desired diameter is formed in an inverted U shape.

  Conventionally, it has been recognized as a problem that the polycrystalline silicon rod collapses during or after the vapor phase growth process of polycrystalline silicon. As a measure for preventing such a collapse, for example, Japanese Patent Laid-Open No. 2002-234720 (Patent Document 2) has a thermal conductivity greater than 145 W / m · K and is adapted to the thermal expansion coefficient of silicon. It has been proposed to use a core wire holder having a coefficient of thermal expansion.

  When the polycrystalline silicon is vapor-phase grown by the Siemens method, in order to improve productivity, it is desirable to increase the growth rate by supplying a raw material gas at a high flow rate or a high concentration from the beginning of the growth. However, if the raw material gas is supplied at a large flow rate or high concentration in the early stage of growth, the silicon core wire tends to collapse.

  The collapse of the silicon core wire is likely to occur when the bonding strength between the silicon core wire and the core wire holder is insufficient, but this is in the vicinity of the silicon core wire holding portion (joining portion) of the core wire holder in the early stage of the growth of polycrystalline silicon. This is considered to be caused by non-uniform growth of polycrystalline silicon on the silicon core wire.

  The core wire holder is usually made of graphite, and one end side (upper end side) is formed with a cavity (hole) that is opened to insert and hold the silicon core wire, and the other end side (lower end side) is made of metal. Fixed to the electrode. The current supplied from the metal electrode to the lower end side of the core wire holder flows to the upper end side end of the low resistance core wire holder, and flows into the silicon core wire only in the vicinity of the opening of the cavity.

  FIG. 1 is a schematic cross-sectional view for explaining a state in which a silicon core wire is held by a core wire holder in a conventional manner. The cross section of the silicon core wire 5 is generally rectangular, and in this case, the cross section of the hole 21 formed in the core wire holder 20 is also square. The end portion of the silicon core wire is inserted into the hole having the rectangular cross section, and is pressed and fixed to two adjacent surfaces among the four surfaces of the inner surface of the hole 21 by a rod-like fastening member 40 or the like.

  The current supplied from the metal electrode to the lower end side of the core wire holder 20 flows into the silicon core wire 5 from the two surfaces in close contact with the end of the silicon core wire. Since the current that has flowed into the silicon core wire 5 flows to the upper side of the silicon core wire 5 at the shortest distance, the silicon core wire 5 on the second surface side that is in close contact with the silicon core wire 5 out of the four inner surfaces of the hole 21 of the core wire holder 20 Heat generation at the part is promoted as compared with the part of the silicon core wire 5 on the non-contact two-surface side.

  Such unevenness in the heat generation state causes uneven deposition of polycrystalline silicon, and therefore, silicon on the two surfaces that are in close contact with the inner surface of the hole 21 of the core wire holder 20 in the initial stage of the reaction reaction of polycrystalline silicon. The non-uniformity of the polycrystalline silicon shape becomes remarkable at the portion of the silicon core wire 5 on the two surfaces that are not in close contact with the portion of the core wire 5. Further, in the inner region of the hole 21 that is not in close contact with the silicon core wire 5, electric discharge is likely to occur and the silicon core wire 5 is easily damaged.

  FIG. 2 is a schematic cross-sectional view for explaining a state in which the silicon core wire is held by the core wire holder in another conventional mode, but the silicon core wire 5 has a circular cross section and is formed in the core wire holder 20. Even when the cross section of 21 is circular, a non-contact portion with the silicon core wire 5 is formed on the inner surface of the hole 21, and the same problem as described above occurs.

  Since the core wire holder 20 is cooled by the metal electrode, the temperature of the silicon core wire 5 on the core wire holder 20 side is lower than that of the straight body portion of the silicon core wire 5. For this reason, especially in the initial stage of the precipitation reaction of polycrystalline silicon, the difference in the polycrystalline silicon diameter between the core wire holder 20 side where the deposition rate is relatively slow and the straight body portion where the deposition rate is relatively fast becomes significant.

  Thus, particularly in the initial stage of the precipitation reaction, the diameter of the polycrystalline silicon is significantly smaller than that of the straight body portion in the vicinity of the silicon core wire holding portion of the core wire holder, and the shape of the polycrystalline silicon in the region is not good. It is in an even state. When the flow rate and concentration of the source gas are greatly increased in such a state, the silicon core wire is shaken, and the moment concentrates on the holding portion due to the shake. Moreover, as described above, the silicon core wire is easily damaged by the discharge in the holding portion. These causes the silicon core wire to fall down easily.

  In addition, when the flow rate or concentration of the source gas is increased, it is necessary to replenish the amount of heat corresponding to the convective heat transfer of the source gas in order to maintain the temperature of the silicon core wire. Need to increase. Such a sudden increase in supply current means a sudden increase in current density in each part of the silicon core wire, and therefore induces partial silicon melting and fusing in a part having an uneven shape and a part having a small diameter. This also causes the silicon core wire to fall.

  Under these circumstances, conventionally, when vapor-phase growing polycrystalline silicon, polycrystalline silicon is deposited in the entire gap not in contact with the silicon core wire in the hole of the core wire holder, and the silicon core wire is held by the core wire holder. It was necessary to limit the flow rate and concentration of the raw material gas until the required strength was sufficient. As a result, there has been a problem that the deposition rate of polycrystalline silicon has to be reduced while the supply control of the source gas is being performed.

  In addition, WO2010 / 115542 pamphlet (Patent Document 3) discloses a holding portion in which a portion for holding a silicon core wire is divided into three or more symmetrically in order to suppress damage due to initial heating.

  Further, in WO 2010/133386 pamphlet (Patent Document 4), in order to obtain a good contact between the silicon core wire and the core wire holder, silicon to be held by a cap mechanism having a gap provided in a part of the core wire holder and having a taper. A method of tightening the lower end portion of the core wire has been proposed.

  However, with the techniques disclosed in Patent Document 3 and Patent Document 4, it is not always easy to hold the silicon core wire on the core wire holder, and it is difficult to complete the work in a short time. For example, when a cap mechanism as disclosed in Patent Document 4 is used, the work of holding the silicon core wire on the core wire holder is complicated, and it is difficult to adjust the tightening strength.

JP 2010-235438 A JP 2002-234720 A WO2010 / 115542 pamphlet WO2010 / 133386 pamphlet

  The present invention has been made in view of the problems of the prior art as described above, and the object of the present invention is that the silicon core wire can be easily attached to the core wire holder, and the silicon core wire is sufficient for the core wire holder. An object of the present invention is to provide a polycrystalline silicon manufacturing technique that can shorten the growth rate suppression time in the initial stage of the polycrystalline silicon precipitation reaction by shortening the time until the strength is maintained.

  In order to solve such a problem, the silicon core wire holder according to the first aspect of the present invention is a holder for holding a silicon core wire used when manufacturing polycrystalline silicon by the Siemens method, and the main body of the holder Is provided with a core wire insertion hole for inserting the silicon core wire from the upper surface to the lower surface side, and a fixing member insertion hole in a direction perpendicular to the longitudinal section of the holder body. A fixing member that is inserted into the member insertion hole and includes a fixing member that fixes the silicon core wire inserted into the core wire insertion hole by tightening.

  A silicon core wire holder according to a second aspect of the present invention is a holder for holding a silicon core wire used in the production of polycrystalline silicon by the Siemens method, and the main body of the holder has a hole from the upper surface toward the lower surface side. A core wire insertion hole for inserting the silicon core wire, and a fixing member insertion hole provided in a direction passing through a central axis of the core wire insertion hole and perpendicular to a longitudinal section of the holder main body. A fixing member that is inserted from a member insertion hole so as to pass through a through hole provided on a lower end side of the silicon core wire, and that fixes the silicon core wire inserted into the core wire insertion hole by tightening. I have.

  In the silicon core wire holder according to the present invention, the main body of the holder has a slit-like gap located along a virtual plane including the central axis of the core wire insertion hole or a slit located on a plane parallel to the virtual plane. It is possible to adopt an aspect in which a gap portion extending from the core wire insertion hole to the outer surface of the holder body is provided.

  In the silicon core wire holder of the present invention, the fixing member may include a fixed shaft portion having a screw structure, and the fixed shaft portion may be inserted into the fixing member insertion hole. For example, the fixed shaft is a male screw, and the fixing member is tightened by at least one female screw.

  Preferably, the holder body is made of a material having a bending strength of 10 MPa or more and a Shore hardness of 20 or more.

  In the method for producing polycrystalline silicon according to the present invention, the distance between the inner surface of the core wire insertion hole and the surface of the silicon core wire when the silicon core wire is inserted into the core wire insertion hole using the silicon core wire holder according to the present invention. Is 0.3 mm or less.

  If the silicon | silicone core wire holder of this invention is used, a silicon | silicone core wire can be fixed substantially symmetrically from both ends of a core wire insertion hole. For this reason, the thermal environment such as heat conduction and heat radiation becomes uniform from the beginning of the precipitation reaction, and as a result, the shape of the deposited polycrystalline silicon becomes symmetrical with respect to the axis.

  Moreover, the discharge which was easy to generate | occur | produce when the silicon core wire holder of the conventional structure was used is also suppressed, and damage to the core wire holder and silicon core wire of the precipitation reaction initial stage is also suppressed.

  According to the present invention, it is easy to attach the silicon core wire to the core wire holder, and the growth rate suppression time in the initial stage of the precipitation reaction of polycrystalline silicon is shortened by shortening the time until the core wire holder holds the silicon core wire with sufficient strength. There is provided a polycrystalline silicon manufacturing technique capable of shortening the length of the crystal.

It is the cross-sectional schematic for demonstrating the state which hold | maintained the silicon core wire to the core wire holder in the conventional aspect. It is the cross-sectional schematic for demonstrating the state which hold | maintained the silicon | silicone core wire to the core wire holder in the other conventional aspect. It is a figure (side view) for demonstrating the structural example of the silicon | silicone core wire holder of the 1st aspect which concerns on this invention. It is a figure (front view) for demonstrating the structural example of the silicon | silicone core wire holder of the 1st aspect which concerns on this invention. It is a figure (top view) for demonstrating the structural example of the silicon | silicone core wire holder of the 1st aspect which concerns on this invention. It is a figure (top view) for demonstrating the other structural example of the silicon | silicone core wire holder of the 1st aspect which concerns on this invention. It is a figure (sectional drawing) for demonstrating the other structural example of the silicon | silicone core wire holder of the 1st aspect which concerns on this invention. It is a figure (side view) for demonstrating the other structural example of the silicon | silicone core wire holder of the 1st aspect which concerns on this invention. It is a figure (sectional drawing) for demonstrating the structural example of the silicon | silicone core wire holder of the 2nd aspect which concerns on this invention. It is a figure (top view) for demonstrating the structural example of the silicon | silicone core wire holder of the 2nd aspect which concerns on this invention. It is a figure (side view) for demonstrating the structural example of the silicon | silicone core wire holder of the 2nd aspect which concerns on this invention. It is a figure (top view) for demonstrating the structural example of the silicon | silicone core wire holder of the 2nd aspect which concerns on this invention. It is a figure (side view) for demonstrating the structural example of the silicon | silicone core wire holder of the 2nd aspect which concerns on this invention. It is a figure (top view) for demonstrating the structural example of the silicon | silicone core wire holder of the 2nd aspect which concerns on this invention. It is a figure (side view) for demonstrating the structural example of the silicon | silicone core wire holder of the 2nd aspect which concerns on this invention. It is a figure (top view) for demonstrating the structural example of the silicon | silicone core wire holder of the 2nd aspect which concerns on this invention. It is a figure (sectional drawing) for demonstrating the other structural example of the silicon | silicone core wire holder of the 2nd aspect which concerns on this invention. It is a structure top view of the silicon | silicone core wire holder for demonstrating the state using an electroconductive sheet. It is a figure for demonstrating the shape of the polycrystalline silicon at the time of using the holder of the conventional structure. It is a figure for demonstrating the shape of the polycrystalline silicon at the time of using the holder which concerns on this invention. It is a cross-sectional schematic diagram for demonstrating the structure of the vapor phase growth apparatus of a polycrystalline silicon.

  Below, with reference to drawings, the silicon core wire holder and the manufacturing method of polycrystalline silicon of the present invention are explained.

  3A to 3C are views for explaining a configuration example of the silicon core wire holder according to the first aspect of the present invention, and are a side view, a front view, and a top view, respectively.

  The core wire holder 20 is a holder for holding a silicon core wire used in the production of polycrystalline silicon by the Siemens method, and has a hole portion (core wire insertion hole) having an opening 22 on the upper surface of the main body of the holder 20 and facing the lower surface side. ) 21 is formed, and the silicon core wire 5 is inserted into the core wire insertion hole 21. In addition, a slit-like gap 60 is formed along the virtual plane P including the central axis C of the core wire insertion hole 21 (located on the virtual plane). The slit-like gap 60 extends from the core wire insertion hole 21. The gap portion reaches the outer surface of the main body of the holder 20.

  The silicon core wire 5 inserted into the core wire insertion hole 21 is tightened from the side by the upper part of the main body of the holder 20 by the pinch cock type fixing member 31 having a plate-like pressing member 31c, so that the gap 60 is spaced apart. It is tightened and fixed so that it narrows.

  3A to 3C, the slit-shaped gap portion 60 is two-fold symmetric with respect to the center axis C of the core wire insertion hole 21 (360 ° / 180 ° symmetric). It is provided as two slit-like gaps extending to the outer side surfaces S1 and S2 of the holder body 20 in a relationship. However, the present invention is not limited to this aspect, and may be an aspect in which only one slit-like gap is provided. Contrary to this, n (n is an integer of 3 or more) slit-like gaps reaching the outer surface of the holder body 20 that is in a three-fold symmetry or more with respect to the central axis C of the core wire insertion hole 21. May be provided. Further, the “gap part” does not have to be a single slit-like gap part, and a set of a plurality of slit-like gap parts can be considered as a “gap part”. In such a case, even when a two-fold symmetrical “gap part” is provided, the number of slit-like gap parts is 2m (m is an integer of 2 or more). For example, if the “gap part” is composed of a set of two slit-like gap parts, two (two sets) of such “gap parts” are formed, and a total of four “gap parts” are formed. A slit-shaped gap is provided.

  Here, the tightening that narrows the gap 60 is not limited to the pinch cock type fixing member 31 illustrated in FIGS.

  For example, as illustrated in the top view of FIG. 4, a portion that can obtain the same action is formed on the upper portion of the main body of the holder 20 without using the plate-like member 31 c as shown in FIG. 3C. May be. And you may make it use the fixing member 31 of the structure which passes a bolt-shaped member (fixed shaft) through the hole (fixed member insertion hole) provided in the said site | part, and fastens this with a nut-shaped member.

  For example, as illustrated in the cross-sectional view of FIG. 5, a convex portion 31 a that is one of the fixing members 31 is formed in the holder body 20 in a male screw shape, and the convex portion 31 a and the other of the fixing member 31 are formed. The silicon core wire 5 may be fixed by tightening so that the gap 60 is narrowed by a combination of certain nut-like members 31b.

  Furthermore, as illustrated in the side view of FIG. 6, a concave portion 31 a as one of the fixing members 31 is formed in the holder main body 20 and the inner surface thereof is formed into a female screw shape, and the other of the concave portion 31 a and the fixing member 31 is formed. The silicon core wire 5 may be fixed by tightening so that the gap 60 is narrowed by a combination of the bolt-shaped members 31b. The attachment workability of the silicon core wire 5 is high in the aspect shown in FIG.

  In addition, when the fixing member 31 is a bolt / nut system, one male screw part may be one or two female screw parts, but according to the comparison of the present inventors, the latter is preferable. More secure tightening is possible.

  In the embodiment illustrated so far, the lower end (terminal) of the slit-shaped gap portion 60 is located higher than the bottom surface of the holder body 20, and the bottom surface of the holder body 20 is not divided. However, the lower end of the gap 60 may reach the bottom surface of the holder body 20 and the bottom surface of the holder body 20 may be divided.

  7A and 7B are views for explaining a configuration example of the silicon core wire holder according to the second aspect of the present invention, and are a sectional view and a top view, respectively.

  The core wire holder 20 is a holder for holding a silicon core wire used in the production of polycrystalline silicon by the Siemens method, and has a hole portion (core wire insertion hole) having an opening 22 on the upper surface of the main body of the holder 20 and facing the lower surface side. ) 21 is formed, and the silicon core wire 5 is inserted into the core wire insertion hole 21. In addition, a slit-like gap 60 is formed along a virtual plane P including the central axis C of the core wire insertion hole 21, and the slit-like gap 60 extends from the core wire insertion hole 21 to the outer surface of the main body of the holder 20. It is a gap that extends to.

  The holder body 20 is further provided with an insertion hole 30 for the fixing member 31 in a direction passing through the central axis C of the core wire insertion hole 21 and perpendicular to the virtual plane P. A through hole 32 is also formed on the lower end side of the silicon core wire 5, and the fixing member 31 inserted from the insertion hole 30 of the fixing member passes through the through hole 32 and is tightened so that the gap 60 is narrowed. The silicon core wire 5 inserted into the core wire insertion hole 21 is fixed.

  7A-B has two slit-like gap portions 60, that is, two-fold symmetry (360 ° / 180 ° symmetry) with respect to the central axis C of the core wire insertion hole 21. It is provided as two slit-like gaps extending to the outer side surfaces S1 and S2 of the holder body 20 in a relationship. However, as already described, the present invention is not limited to this aspect, and may be an aspect in which only one slit-like gap is provided. On the contrary, n (n is an integer of 3 or more) slit-shaped slits reaching the outer surface of the holder body 20 which is in a three-fold symmetry or more with respect to the central axis C of the core wire insertion hole 21. A gap may be provided. As shown in FIGS. 7C and 7D, the fixing member 31 can be obtained by appropriately providing a gap between the core wire insertion hole 21 and the silicon core wire 5 without intentionally providing the slit-shaped gap portion 60. A good contact between the holder body 20 and the silicon core wire 5 may be formed by utilizing the bending of the holder body 20 when tightened by. Further, as shown in FIGS. 7E and 7F, a set of two slit-shaped gaps (60A: 60A1-2, 60B: 60B1-2) is considered as a “gap”, and this “gap” (60A and 60B) are arranged in two-fold symmetry, or as shown in FIGS. 7G and 7H, a set of three slit-like gaps (60A: 60A1-3, 60B: 60B1-3) The “gap part” may be considered and the “gap part” (60A and 60B) may be arranged symmetrically twice. That is, a group of m slit-like gaps may be considered as a “gap part”, and the “gap part” may be arranged symmetrically twice. In this case, the total number of slit-like gaps is 2m (m is an integer of 2 or more).

  Furthermore, the number of the fixing members 31 is not necessarily one (or one set), and for example, as illustrated in the cross-sectional view of FIG. This point is the same as in the first aspect described above, and there are various variations in the aspect of the fixing member 31, as described in the first aspect, and therefore redundant description is omitted. To do.

  In the silicon core wire holder of the present invention, the tightening force in the direction in which the gap 60 is narrowed is substantially symmetric with respect to the silicon core wire 5 inserted into the core wire insertion hole 21 and has asymmetry as in the conventional method. No.

  The main body 20 of the silicon core wire holder is preferably made of a material having a bending strength of 10 MPa and a Shore hardness of 20 or more. Specifically, a carbon material having a high crystallinity by heat-treating a carbon material having a low crystallinity at around 3000 ° C. is preferable. Information on these strengths can be easily obtained from catalog information or the like.

  As shown in FIG. 9, when the silicon core wire 5 is inserted into the core wire insertion hole 21, a conductive sheet 61 having a resistivity of 1500 μΩ-cm or less is provided on the contact surface between the holder body 20 and the silicon core wire 5. It is preferable to reduce the contact resistance by increasing the micro contact area between the holder main body 20 and the silicon core wire 5 when the silicon core wire 5 is sandwiched and energized. Examples of such a conductive sheet 61 include graphite, a composite material such as aluminum-carbon fiber and aluminum-silicon carbide, and a metal such as tungsten carbide. The thickness of such a conductive sheet 61 is, for example, 0.2 to 2 mm.

  Below, the manufacturing procedure of the polycrystalline silicon performed using the silicon | silicone core wire holder of the 2nd aspect which concerns on this invention illustrated to FIG.

  The holder body 20 can be a carbon electrode made of graphite, for example. In the example shown in FIGS. 7A and 7B, one end side has a truncated cone-like slope, and an opening 22 is provided at the end, and a hole for inserting and holding the silicon core wire 5 ( A core wire insertion hole) 21 is formed.

  Here, the cross-sectional shape of the silicon core wire 5 and the cross-sectional shape of the core wire insertion hole 21 do not necessarily have to be rectangular, and both may be circular, triangular or pentagonal. However, when these cross-sectional shapes are rectangular, it is easy to reliably obtain a wide contact area when the fixing member 31 is tightened.

  Polycrystalline silicon is vapor-grown on the surface of the silicon core wire 5 by the Siemens method, and a polycrystalline silicon rod is manufactured. As will be described later, the other end side of the core wire holder 20 serves as a contact portion between a metal electrode for passing a current through the silicon core wire 5 or an adapter provided between the metal electrode and the core wire holder. When there is an adapter on the electrode 2, it is fixed via the adapter.

  An insertion hole 30 for the fixing member 31 penetrating the core wire holder is provided on the truncated cone-shaped slope in the vicinity of the opening 22. The silicon core wire 5 inserted into the core wire insertion hole 21 is provided with a through hole 32 at the same height as the insertion hole 30 provided in the holder body 20.

  A bolt-shaped fixing shaft 31a which is one of the fixing members 31 is passed through an insertion hole 30 provided in the holder body 20 and a through-hole 32 provided in the silicon core wire 5, and a nut which is the other of the fixing parts 31 from both sides thereof. Fix with 31b.

  As described with reference to FIGS. 1 and 2, the core wire insertion hole provided in the core wire holder 20 in the conventional mode in which the hole portion through which the common fixing shaft 31 a can be passed through the core wire holder body 20 and the silicon core wire 5 is not provided. The contact state between the silicon core wire 5 inserted into the core wire insertion hole 21 and the core wire insertion hole 21 is significantly asymmetric with respect to the central axis of the silicon core wire 5. When energization is performed in such a state, the temperature of the silicon core wire 5 becomes remarkably asymmetric with respect to the central axis thereof, so the shape of the deposited polycrystalline silicon 6 is not uniform as shown in FIG. It will be a thing.

  On the other hand, when the silicon core wire holder of the present invention is used, since the silicon core wire 5 can be positioned at the center in the core wire insertion hole 21, it is inserted into the core wire insertion hole 21 and the core wire insertion hole 21. The contact state with the silicon core wire 5 can be made substantially symmetric with respect to the central axis of the silicon core wire 5.

  When energization is performed in such a state, the temperature of the silicon core wire 5 becomes substantially symmetric with respect to the central axis thereof, so that the shape of the deposited polycrystalline silicon 6 is uniform as shown in FIG. It will be a thing.

  As described with reference to FIG. 9, when the silicon core wire 5 is inserted into the core wire insertion hole 21, a conductive sheet having a resistivity of 1500 μΩ-cm or less is applied to the contact surface between the holder body 20 and the silicon core wire 5. When sandwiched, the holder body 20 and the silicon core wire 5 are not only fixed more reliably, but also the contact resistance is lowered, so that the uniformity of the initial shape of the polycrystalline silicon precipitation reaction is further increased.

  Thus, when the silicon core wire holder according to the present invention is used, not only the silicon core wire 5 is firmly held in the core wire holder 20 and the overturn is prevented, but also the growth rate in the initial stage of the precipitation reaction of polycrystalline silicon. As a result of the reduction of the suppression period, productivity is also increased.

  According to the study by the present inventors, in order to obtain a good contact state between the core wire holder 20 and the silicon core wire 5, the silicon core wire 5 and the core wire when the silicon core wire 5 is inserted into the core wire insertion hole 21 of the core wire holder 20. The gap with the inner surface of the insertion hole 21 is preferably 0.3 mm or less before being tightened by the fixing member 31.

  When the gap between the silicon core wire 5 and the inner surface of the core wire insertion hole 21 exceeds 0.3 mm, cracks or the like are likely to occur in the tightened portion of the holder body 20 when the fixing member 31 is tightened. In order to avoid such an inconvenience, the holder body 20 needs to have high strength, and the holder body 20 preferably has a Shore hardness of 20 or more and a bending strength of 10 Mpa or more. .

  When the fixing member 31 is of a bolt / nut type, it is preferable to manage the tightening torque to be constant.

  FIG. 12 is a schematic explanatory view showing an example of a vapor phase growth apparatus 100 in which the present invention is used. The vapor phase growth apparatus 100 is an apparatus for vapor growth of polycrystalline silicon 6 on the surface of the silicon core wire 5 by the Siemens method, and is roughly constituted by the base plate 1 and the reaction furnace 10. Here, the core wire holder 20 is a carbon electrode made of graphite.

  The base plate 1 is provided with a metal electrode 2 for supplying a current to the silicon core wire 5, a gas nozzle 3 for supplying a process gas such as nitrogen gas, hydrogen gas and trichlorosilane gas, and an exhaust port 4 for discharging exhaust gas. .

  The metal electrode 2 penetrates the base plate 1 with the insulator 7 interposed therebetween, and is connected to another metal electrode through wiring or connected to a power source arranged outside the reaction furnace. The metal electrode 2, the base plate 1, and the reaction furnace 10 are cooled using a refrigerant.

  As shown in FIG. 12, when the polycrystalline silicon 6 is vapor-phase grown, the silicon core wire 5 is assembled into a torii type with two vertical directions and one horizontal direction in the reaction furnace 10, and the torii type silicon core wire 5 is assembled. Are fixed to a pair of metal electrodes 2 disposed on the base plate 1 via a pair of core wire holders 20.

  The core wire holder 20 is made of graphite having a Shore hardness of 20 or more, a bending strength of 10 Mpa or more, and a thermal conductivity of 145 W / m · K or less, and has one end side (upper end side) having a truncated cone-like slope. ) Is formed with a cavity (core wire insertion hole) 21 opened to insert and hold the silicon core wire 5, and the other end side (lower end side) is fixed to the metal electrode 2.

  The reason why the heat conduction is 145 W / m · K or less depends on the results of the study by the present inventors. However, the lower the thermal conductivity of the core wire holder 20 itself, the lower the amount of heat that escapes to the metal electrode 2, thereby This is because the effect works and the temperature of the upper part of the core wire holder 20 can be kept high. If the temperature of the upper part of the core wire holder 20 can be kept high, the temperature of the lower part of the silicon core wire at the time of energization can be kept high, so that the applied voltage can be lowered and damage at the time of energization can be suppressed. Also, the deposition rate of polycrystalline silicon at the initial stage of the reaction at this portion can be increased.

  The silicon core wire 5 having the insertion hole 32 aligned with the insertion hole 30 is inserted into the core wire insertion hole 21 of the core wire holder 20 having the hole (insertion hole) 30 in the truncated cone-shaped slope on the upper end side, and the bolt 31a And using a nut 31b. As described above, it is desirable to manage the torque for tightening the nut 31b.

  The bolt 31a may be a machine bolt type. In this case, the nut 31b is tightened only from one side. When the bolt 31a is a stat bolt type, the nut 31b is tightened from both sides. According to the study by the present inventors, the bolt 30a is preferably a stat bolt type.

  Next, the silicon core wire 5 is preheated to a temperature of 250 ° C. or higher by using a heater (not shown) so that the silicon core wire 5 becomes conductive enough to allow current to flow efficiently. Subsequently, a current is supplied from the metal electrode 2 to the silicon core wire 5 via the core wire holder 20 to heat the silicon core wire 5 to 900 ° C. or higher.

According to the study of the present invention, it is preferable that a current of about 60 to 70 A is supplied at the time of ignition, and then a current of about 100 A is supplied to set the core wire surface temperature to 900 ° C. or higher to start the polycrystalline silicon precipitation reaction. Therefore, after ignition, while supplying a current of about 100 A, trichlorosilane gas is supplied together with hydrogen gas as a raw material gas at a low flow rate, and vapor phase growth is started. At this time, the cross-sectional current density of the current flowing through the silicon core wire 5 fixed to the graphite core wire holder 20 is 0.13 A / mm ² or more and 4.9 A / mm ² or less.

  When energization to the silicon core wire 5 is started and vapor phase growth of the polycrystalline silicon 6 is started, the upper end side of the core wire holder 20 is heated by receiving conduction heat and radiant heat from the silicon core wire 5 and the polycrystalline silicon 6. As described above, in the present invention, since the silicon core wire 5 and the core wire holder 20 are in contact with each other so as to be substantially axially symmetric, the contact surface between the upper end side of the core wire holder 20 and the silicon core wire 5 is uniform (axis (Symmetrically) and heated, the deposition of polycrystalline silicon 6 becomes uniform.

  As described above, the uniformly deposited polycrystalline silicon not only strengthens the fixing of the silicon core wire 5 by the core wire holder 20, but is abnormal because the shape of the polycrystalline silicon of the portion is axisymmetric. No stress is applied.

  In the conventional method, in order to make the silicon core wire 5 fixed by the core wire holder 20 sufficiently strong, the silicon rod diameter has to reach about 35 mm. However, the silicon core wire holder of the present invention is used. In such a case, it was found that a sufficiently strong fixation was realized when the diameter of the silicon rod reached about 15 mm.

  After sufficiently fixing the silicon core wire 5 by the core wire holder 20, the polycrystalline silicon 6 is placed on the silicon core wire 5 while further increasing the supply amount of hydrogen gas and trichlorosilane gas and the current supply amount of the source gas. Vapor phase growth is performed in a temperature range of 900 ° C. or higher and 1200 ° C. or lower. Unreacted gas and by-product gas are discharged from the exhaust port 4.

  Then, after the polycrystalline silicon 6 has grown to a desired diameter (for example, 120 mm), the supply of the source gas is stopped, the temperature in the reaction furnace 10 is lowered, and the atmosphere in the reaction furnace is replaced with hydrogen from nitrogen, The reactor 10 is opened to the atmosphere.

[Example 1]
An insertion hole 30 of a 4 mm screw toward the core wire insertion hole 21 is formed on the inclined surface of the truncated cone 10 mm away from the opening 22 of the core wire insertion hole 21 at the upper end side. A graphite core wire holder 20 having a slit 60 is used.

  Further, when the silicon core wire 5 is inserted to the bottom of the core wire insertion hole 21, the through hole 32 is opened so that the bolt 31 a which is a common fixed shaft passes through the through hole 32 of the core wire holder and the insertion hole 30 of the silicon core wire 5. A silicon core wire 5 was used.

  Further, a conductive sheet material 61 having a specific resistance equivalent to that of the core wire holder 20 was inserted into the inner surface of the core wire insertion hole 21 and the contact surface of the silicon core wire 5, and fixed with bolts 31a and solid nuts 31b.

  Here, a 3.7 mm stat type screw made of carbon graphite was used for the bolt 31a, which is a common fixed shaft, and was tightened from both ends using a nut 31b.

  When trichlorosilane gas is supplied as a source gas together with hydrogen gas while heating the silicon core wire 5 at 1063 ° C., the upper end side of the core wire holder 20 is deposited with polycrystalline silicon 6 in a growth rate suppression period of 15 hours after the start of vapor phase growth. Was evenly coated. At that time, the polycrystalline silicon 6 had a diameter of 16 mm and a current value of 230 A. From this point of time, the supply gas amount started to increase, and then the current value was increased with the growth of the diameter of the polycrystalline silicon rod, and 122 mm diameter polycrystalline silicon could be obtained in 68 hours.

[Example 2]
A graphite core wire holder 20 of the same type as in Example 1 was used, and trichlorosilane gas was supplied as a raw material gas together with hydrogen gas while heating the silicon core wire 5 held by the core wire holder 20 to 1050 ° C. In the growth rate suppression period of 13 hours after the start of vapor phase growth, the first end side of the core wire holder 20 was evenly coated by the deposition of polycrystalline silicon 6. At that time, the polycrystalline silicon 6 had a diameter of 15 mm and a current value of 205A. From this point of time, the supply gas amount started to increase, and then the current value increased with the growth of the diameter of the polycrystalline silicon rod, and a 119 mm diameter polycrystal could be obtained in 65 hours.

[Comparative Example 1]
A conventional core wire holder 20 made of the same material as in Example 1 and having the structure shown in FIG. 1 was used. While heating the silicon core wire 5 held by the core wire holder 20 to 1055 ° C., trichlorosilane gas was supplied as a raw material gas together with hydrogen gas. In the growth rate suppression period of 16 hours after the start of vapor phase growth, the polycrystalline silicon 6 had a diameter of 18 mm and a current value of 240 A. As in Examples 1 and 2, the current value started to increase after starting the supply gas amount increase. At this time, the precipitation shape of the polycrystalline silicon 6 on the upper end side of the core wire holder 20 is already shown in FIG. As shown, it was uneven. After that, when the growth was continued with a current value of 514 A, the polycrystalline silicon rod fell down when the diameter of the polycrystalline silicon 6 reached 36 mm, and the reaction could not be continued.

[Comparative Example 2]
In the same manner as in Comparative Example 1, the initial reaction conditions were controlled to deposit polycrystalline silicon. When the diameter of the polycrystalline silicon 6 became 35 mm in 33 hours, the deposition of the polycrystalline silicon 6 on the upper end side of the core wire holder 20 became uniform. Thereafter, the supply gas amount started to increase and the current value started to increase. A polycrystalline silicon rod having a diameter of 121 mm could be obtained after 87 hours of precipitation.

  As described above, according to the present invention, since polycrystalline silicon can be uniformly deposited in the vicinity of the upper end of the core wire holder, it is difficult for tilting due to local growth of polycrystalline silicon to occur. For this reason, the start time of the supply gas amount increase can be greatly advanced, and the productivity can be greatly increased.

  According to the present invention, it is easy to attach the silicon core wire to the core wire holder, shorten the time until the core wire holder holds the silicon core wire with sufficient strength, prevent overturning, and at the initial stage of the precipitation reaction of polycrystalline silicon Provided is a polycrystalline silicon manufacturing technique that can shorten the growth rate suppression time.

DESCRIPTION OF SYMBOLS 1 Base plate 2 Metal electrode 3 Gas nozzle 4 Exhaust port 5 Silicon core wire 6 Polycrystalline silicon 7 Insulator 10 Reactor 20 Core wire holder 21 Core wire insertion hole 22 Opening 30 Fixing member insertion hole 31 Fixing member 32 Through hole 40 Bar-shaped tightening Member 60 Slit-like gap portion 61 Conductive sheet 100 Vapor growth apparatus

Claims (7)

A holder for holding a silicon core wire used in the production of polycrystalline silicon by the Siemens method,
The holder main body is provided with a core wire insertion hole for inserting the silicon core wire from the upper surface to the lower surface side, and a fixing member insertion hole in a direction perpendicular to the longitudinal section of the holder main body. And
A silicon core wire holder, comprising: a fixing member that is inserted into the fixing member insertion hole and that fixes the silicon core wire inserted into the core wire insertion hole by tightening. A holder for holding a silicon core wire used in the production of polycrystalline silicon by the Siemens method,
The main body of the holder has a hole portion extending from the upper surface to the lower surface side for inserting the silicon core wire, and passes through the central axis of the core wire insertion hole and perpendicular to the longitudinal section of the holder main body. A fixing member insertion hole is provided in the direction,
A fixing member inserted from the fixing member insertion hole so as to pass through a through hole provided on the lower end side of the silicon core wire, and fixing the silicon core wire inserted into the core wire insertion hole by tightening A silicon core wire holder provided with a member.   The holder body has a slit-like gap portion located on a virtual plane including a central axis of the core wire insertion hole or a slit-like gap portion located on a plane parallel to the virtual plane, and the core wire is inserted. The silicon | silicone core wire holder of Claim 1 or 2 with which the clearance gap from the hole to the outer surface of the said holder main body is provided.   The silicon core wire holder according to claim 1, wherein the fixing member includes a fixing shaft portion having a screw structure, and the fixing shaft portion is inserted into the fixing member insertion hole.   The silicon core wire holder according to claim 4, wherein the fixed shaft is a male screw, and the fixing member is tightened by at least one female screw.   The silicon core wire holder according to any one of claims 1 to 5, wherein the holder body is made of a material having a bending strength of 10 MPa or more and a Shore hardness of 20 or more. A method for producing polycrystalline silicon using the silicon core wire holder according to any one of claims 1 to 6,
A method for producing polycrystalline silicon, wherein an interval between an inner surface of the core wire insertion hole and a surface of the silicon core wire when the silicon core wire is inserted into the core wire insertion hole is 0.3 mm or less.

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