DEVICE FOR MAKING A POLYSILIZUM ROD

Abstract

Apparatus for producing a polysilicon rod using the Siemens method, the apparatus comprising: a base plate; and a holding body provided on the base plate in such a way that it is movable in a horizontal direction relative to an upper surface of the base plate, and which is electrically connected between a core wire holder and an electrode, wherein the holding body is arranged to hold the core wire holder pivotably at least in a vertical direction with respect to the base plate.

Description

FIELD OF THE INVENTIONThe present invention relates to an apparatus for manufacturing a polysilicon rod by the Siemens method.BACKGROUNDPolysilicon is a starting material for monocrystalline silicon for producing a semiconductor and for silicon for producing a solar cell. As a method for manufacturing polysilicon, the Siemens method is known, and in this method, a silane-based gas is generally brought into contact with a heated silicon core wire to deposit polysilicon on a surface of the silicon core wire by a CVD (chemical vapor deposition) method.In the Siemens method, two silicon core wires are mounted in a vertical direction, and one silicon core wire is mounted in a gate shape (an inverted U-shape) in a horizontal direction, opposite ends of the silicon core wires are respectively connected to core wire holders to fix them to a pair of metal electrodes disposed on a base plate. Generally, a plurality of groups of reverse U-shape silicon core wires are arranged in a reactor.When the silicon core wire of inverted U-shape is electrically heated to a deposition temperature and a mixed gas of, for example, trichlorosilane and hydrogen as a raw material is brought into contact with the silicon core wire, polysilicon is evaporated on the silicon core wire, and a polysilicon rod having a desired diameter and inverted U-shape is formed.The electrode penetrates the base plate via an insulator and is connected to another electrode or a power source disposed outside the reactor. While the polysilicon is deposited, the electrode, the base plate and a bell jar are cooled with a coolant such as water to prevent the polysilicon from being deposited on the electrode and the polysilicon from being contaminated with metals caused by a temperature rise of the electrode during the deposition.FIG. 4 is a schematic diagram for exemplarily explaining an aspect of the related art in which an electrode holder is attached to the electrode for holding a core wire holder 11. In the example shown in FIG. 4, an electrode 14 made of metal and the core wire holder 11 made of carbon are connected via an electrode adapter 13 to suppress wear of the electrode 14, and the electrode adapter 13 is screw-fastened to the electrode 14.A current is supplied from the electrode 14 to the silicon core wire (not illustrated) held on the core wire by the core wire holder 11, and a surface of the silicon core wire is heated to a temperature of about 900° C. to 1200° C. by Joule heat in a hydrogen atmosphere. In this state, for example, high purity silicon is vapor-deposited on the silicon core wire, so that a polysilicon rod is grown by introducing a mixed gas of, for example, trichlorosilane and hydrogen as a raw material into a reactor.During this process, the deposition of the polysilicon on the core wire holder 11 made of carbon occurs with an increase in a diameter of the polysilicon rod, and the polysilicon is gradually integrated with the core wire holder 11. Since the electric resistance decreases with the growth of the polysilicon rod, the current to be supplied is gradually increased to maintain a surface temperature of the polysilicon rod at a temperature suitable for the deposition reaction.Generally, the current to be fed into the polysilicon rod is a high current of 2000 A to 4000 A at the end of the deposition reaction. As the diameter of the polysilicon rod increases, an amount of heat radiation from a rod surface increases. Therefore, an electric energy to be supplied to the polysilicon rod needs to be increased to balance the amount of heat lost when the heat is radiated from the rod surface in order to maintain a temperature required for the deposition reaction (900° C. to 1200° C.).Since polysilicon has a property that its electrical resistivity decreases basically with increasing temperature, most of the current flows in the center of the rod where the temperature is high. Therefore, in a bridge part of the rod, an inside of the inverted U-shape has a high temperature and a maximum current.As causes for this, there are assumed the fact that a distance along an inner side of the rod on an arc as an electric circuit is short, and the fact that radiation from a straight body and a bridge of the arc is easily absorbed from each other and the straight body and the bridge of the arc are easily heated because the rod has the inverted U shape.OBJECT OF THE INVENTIONTherefore, there is a problem that as the diameter of the rod increases, a temperature difference between the inside and the outside of the bridge part increases and the risk of cracking increases because differences in the elongation of the bridge part during growth and the contraction during cooling become more marked after completion of growth.The cracks during the growth generate forces for opening the inverted U-shape due to the difference between a low temperature on the outside and a high temperature on the inside of the arc of the inverted U-shape rod part. At this time, when the electrodes are attached to the leg at opposite ends of the rod, the rod cannot deform, the stress exceeds a predetermined value, and a crack is thereby generated. Since this growing crack results in a variation of the applied current and also the rod temperature varies, the homogeneity of crystals is negatively affected. As the influence of the crack increases, current can no longer be applied, and the reaction must be interrupted in the middle.On the other hand, since the inside of the sheet contracts most strongly upon cooling after the completion of the growth, a force closing the inverted U-shape is generated. Then, when the rod can no longer deform and the stress exceeds the predetermined value, a crack is generated. Experience has shown that the crack during cooling is larger than the crack during growth and can propagate throughout the rod, resulting in failure of the rod.As set forth above, in the Siemens method, the crack of the rod is generated by the temperature difference between the inside and the outside of the inverted U-shape. Therefore, it can be seen that, in addition to simple expansion and contraction caused by the temperature change of the entire rod, a two-dimensional force including a rotational force with a contact point between the straight main part and the bridge part of the rod as a fulcrum is applied.A major concern is the economic damage in the production of the rod which arises as a result of the crack formation. However, in order to cope with the above two-dimensional force, expansion and contraction and a rotating mechanism are required. In addition, the Siemens method requires a suitable material having a high temperature resistance and a high strength, which is only a low source of impurity. In order to stably maintain the efficiency and quality of the manufacturing process, cleaning and installation between lots must be easy to perform. It is therefore very difficult to solve the above-described problem.A new structure has already been proposed for the electrode adapter.For example, in JP 2006-240 934 A, an apparatus is disclosed in which an electrode and a holder are slidably electrically connected, but the apparatus cannot cope with rotational movement with a contact point between a straight main part and a bridge part of a rod as a fulcrum.In document JP 2 805 457 B2 it is disclosed that horizontal and oblique movements of an electrode holder can be carried out using a spring element. However, cleaning between lots is very difficult and it is almost impossible to keep all surfaces clean because the shape is complex due to the use of the spring elements. In the holding with the spring, there is a problem that a force required for the movement increases as the amount of movement increases, and that a sufficient amount of movement cannot be ensured as the diameter increases more and the amount of movement required increases.US 2012 / 0 222 619 A1 and JP 2013-249 251 A both describe carbon electrodes and devices for producing a polycrystalline silicon rod.As set forth above, the prior art electrode adapter does not have a sufficient degree of freedom for movement, and / or countermeasures for cleaning performed between lots are not sufficient for the electrode adapter. It is therefore an object of the present invention to provide an apparatus for manufacturing polysilicon in which an electrode adapter can be moved in a horizontal direction and rotated, and the polysilicon is easily cleaned.MEANS FOR SOLVING THE PROBLEMPrinciple 1An apparatus for manufacturing a polysilicon rod by the Siemens method may include:a base plate; anda holding body provided on the base plate so as to be movable in a horizontal direction and electrically connected between a core wire holder and an electrode,wherein the support body is configured to rotatably support the core wire holder with respect to the base plate.Principle 2In the apparatus for manufacturing a polysilicon rod according to Principle 1, the holding body may include a foot provided on the base plate so as to be movable in the horizontal direction, the electrode adapter provided so as to be rotatable with respect to the base plate and electrically connected between the core wire holder and the electrode.Principle 3In the apparatus for manufacturing a polysilicon rod according to Principle 2, the foot may have a curved surface part on its upper part, and the electrode adapter may be rotatable along the curved surface part and slidable in the horizontal direction with respect to the electrode.Principle 4The apparatus for manufacturing a polysilicon rod according to Principle 3 may further include a pressing part, the electrode adapter including an electrode adapter main part rotatably provided on the curved surface part, and an electrode adapter slide part extending in the horizontal direction from the electrode adapter main part and contacting the electrode, the electrode may be connected between the electrode adapter slide part and the pressing part.Principle 5In the apparatus for manufacturing a polysilicon rod according to any one of Principles 2 to 4, the base plate, the electrode adapter, and the electrode may each be made only with a planar surface and with a spherical surface or a curved surface having a radius of 5 mm or more.Principle 6In the apparatus for manufacturing a polysilicon rod according to Principle 5, the base plate, the electrode adapter, and the electrode may not have (each) an inner corner part having an angle of less than 90°.Principle 7In the apparatus for manufacturing a polysilicon rod according to any one of the principles 2 to 4, the foot provided on the base plate may be an insulator.According to aspects of the present invention, the electrode adapter can be moved in the horizontal direction and can be rotated; polysilicon that can be easily cleaned can be produced; and the crack on cooling during growth and after growth can be reduced.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1 is a plan view showing a principle of an aspect in which an electrode holder according to an embodiment of the present invention is attached to a metal electrode to hold a core wire holder. FIG. 2 is a side sectional view taken along a line II-II of FIG. 1. FIG. 3 is a plan view corresponding to FIG. 1 and showing a modification example of an embodiment of the present invention. FIG. 4 is a side sectional view showing a principle of an aspect in which a prior art electrode holder is attached to a metal electrode to hold a core wire holder.DETAILED DESCRIPTIONThe embodiment provides an apparatus for manufacturing a polysilicon rod by the Siemens method. As shown in FIGS. 1 and 2, the apparatus for manufacturing a polysilicon rod according to the embodiment includes a holder body 100 that is disposed on a reactor base plate (base plate) 20 so as to be movable in a horizontal direction and that is electrically connected between a core wire holder 1 and a metal electrode (electrode) 4. The holding body 100 is configured to hold the core wire holder 1 rotatably (pivotally) with respect to the reactor base plate 20. The holding body 100 may hold the core wire holder 1 to be rotatable in a vertical direction with respect to the reactor base plate 20, and may hold the core wire holder 1 to be rotatable in a horizontal plane. In FIG. 2, arrows R 1 and R 2 are shown to indicate that the support body 100 rotatably (swingably) supports the core wire holder 1 in the vertical direction with respect to the reactor base plate 20. Also shown in FIG. 2 are arrows S 1 and S 2 intended to indicate that the support body 100 is movable in the horizontal direction with respect to the reactor base plate 20.The holding body 100 may include an adapter base (leg) 3 provided on the reactor base plate 20 so as to be movable in the horizontal direction; and an electrode adapter 2 provided so as to be rotatable (pivotable) with respect to the adapter base 3 and electrically connected between the core wire holder 1 and the metal electrode 4.The adapter base 3 may have a curved surface portion 3a on its upper portion. The electrode adapter 2 may be rotatable along the curved surface part 3 aand may be slidable in the horizontal direction with respect to the metal electrode 4.The electrode adapter 2 may include an electrode adapter main part 2 athat is rotatably provided on the curved surface part 3 aof the leg 3; and an electrode adapter slide part 2 bthat extends from the electrode adapter main part 2 ain the horizontal direction and contacts the metal electrode 4. The electrode adapter main body 2a and the electrode adapter slide body 2b may be integrated.As shown in FIG. 2, the electrode adapter main body 2 amay have a quadrangular shape in a plan view, and the electrode adapter slide body 2 bmay also have a quadrangular shape in a plan view. Also, the adapter base 3 may have a quadrangular shape in a plan view. The curved surface part 3 aof the adapter base 3 may have a circular shape in a plan view.In the aspect shown in FIGS. 1 and 2, the metal electrode 4 is fixed to the reactor base plate 20 by an insulator 5, and is made to be a substantially rectangular parallelepiped. The electrode adapter slide part 2 bis in contact with the press part by clamping the metal electrode 4 between the electrode adapter slide part 2 band a pressing part such as a pressing plate 10, and the electrode adapter slide part 2 band the pressing part are fastened with a bolt 9 aand a nut 9 b. The metal electrode 4 can be clamped between the electrode adapter slide 2 band the holding plate 10 within a predetermined distance W of the electrode adapter slide 2 b. By releasing the fastening with the bolt 9 aand the nut 9 b, a position of the electrode adapter 2 with respect to the metal electrode 4 can be shifted in the horizontal direction. The electrode adapter main body 2a has a protruding portion 2a 1, to which the core wire holder 1 can be connected on its upper portion. A lower part of the electrode adapter main body 2 ais connected to the adapter base 3 via the curved surface part 3 a. By using this aspect, the core wire holder 1 can be slid and rotated.A coolant 30 is provided in the metal electrode 4 (see FIG. 2 ), and the metal electrode 4 may be configured to be cooled from inside.In the aspect shown in FIG. 2, a gap G is provided between the electrode adapter main part 2 aand the adapter base 3 in the vertical direction, and in FIG. 2, the electrode adapter main part 2 ais rotatable (pivotable) in the vertical direction (see the arrow R 1 of FIG. 2 ) and movable in the horizontal direction (see the arrow S 1 of FIG. 2 ). When the electrode adapter main body 2 ais rotated in the vertical direction, the electrode adapter slide body 2 bis also rotated in the vertical direction (see the arrow R 2 of FIG. 2 ). When the electrode adapter main body 2 ais moved in the horizontal direction, the electrode adapter slide body 2 bis also moved in the horizontal direction (see the arrow S 2 of FIG. 2 ).As an example, the metal electrode 4 may be fixed so as to be rotatable (pivotable) in the horizontal direction. In this case, the electrode adapter main body 2a is also rotatable in the horizontal direction with respect to the adapter base 3.The electrode adapter 2, the adapter base 3, the metal electrode 4 and the holding plate 10 which are used continuously between the lots can all be manufactured with a flat surface and a simple spherical surface or a curved surface, the simple spherical surface or the curved surface being only slightly curved so as to have a radius of 5 mm or more, and also may have a shape having no inner corner part with an angle smaller than 90°. In this case, for example, manual cleaning with a usual cloth-like cleaning tool such as BEMCOT is easily possible. Since the bolt 9a and the nut 9b are small components, a financial burden is small even if the bolt 9a and the nut 9b are replaced with new components in each lot. In addition, the time is small when two sets of the bolt 9a and the nut 9b are provided, one set being cleaned while the other set is in use. It is preferable not to use an inner corner part having an angle of less than 90°, so that the shape does not have a part that is difficult to clean. When a layer is deposited on an arc part at an acute angle, there is a risk that the layer peels off during deposition (as the voltage of the deposited layer increases, so that the layer becomes thicker, and / or the layer is deposited without maintaining sufficient adhesion to the inner corner part), and that the layer flies upward in a chamber and becomes a source of impurity. However, if an inner corner part having an angle of less than 90° is not used, occurrence of the above-mentioned events can be prevented. More preferably, no inner corner part having an angle of less than 120° is used, since thereby cleaning can be facilitated and the risk of contamination can be reduced. In addition, an inner corner portion having an angle of less than 60° may not be used. In this case, although an effect is low as compared with the effect of not using an inner corner part having an angle of less than 90°, an effect can be obtained to a certain extent insofar as cleaning can be facilitated and the risk of contamination can be reduced. Angles c1in FIG. 1 and c2in FIG. 2 are each 90°, and c3is more than 90°.The adapter base 3 should preferably be an insulator to avoid the current being applied to the reactor base plate 20. However, the present invention is not limited thereto, and a conductive member may also be used as the adapter base 3. In this case, the intended function is achieved by using a material having high sliding property and placing a flat plate made of an insulator between the adapter base 3 and the reactor base plate 20.A cover 40 functioning as a stopper may be provided on the metal electrode 4 so that the electrode adapter slide part 2 bis not accidentally separated from the metal electrode 4 (see FIG. 3 ).As shown in FIG. 3, the adapter base 3 may be provided on a guide part 50 extending in the horizontal direction, the adapter base 3 being movable in the horizontal direction along the guide part 50. In the aspect shown in FIG. 3, in a plan view, the guide part 50 extends in the same direction as the electrode adapter slide part 2 b.In addition, a cover for protecting the metal electrode 4 and a movable part of the electrode adapter sliding part 2 bmay be provided, and a carbon layer for assisting the application of the current and the sliding of a contact part may be provided therebetween.Example:With the Siemens method, a reaction for growing a polysilicon rod each having five lots was performed until the diameter φ of the polysilicon rod was about 160 mm, and a cracking speed was determined. In the most common metal solid electrode and the most common prior art solid electrode adapter corresponding to FIG. 4, current variation due to growth cracking was detected in two lots, a crack upon cooling was detected in all five lots, and a rod failure was detected in one of the five lots. On the other hand, in the configuration according to the embodiment shown in FIGS. 1 and 2, no current variation presumably caused by cracking during growth was observed, and in three lots, a crack upon cooling was observed, but there was no failure of the rod.LIST OF REFERENCE SYMBOLS1 Core wire holder 2 Electrode adapter 2 aElectrode adapter main part 2 bElectrode adapter slide part 3 Adapter base (leg) 4 Metal electrode (electrode) 5 Insulator 9 aScrew 9 b Mutter 10 Holder plate 20 Reactor base plate (base plate) 30 Coolant 100 Holder body S 1, S 2 Sliding direction R 1, R 2 Rotating direction (pivoting direction)

Claims

An apparatus for manufacturing a polysilicon rod by the Siemens method, the apparatus comprising: a base plate; and a support body provided on the base plate so as to be movable in a horizontal direction relative to an upper surface of the base plate and electrically connected between a core wire holder and an electrode, wherein the support body is configured to support the core wire holder to be pivotable at least in a vertical direction with respect to the base plate.The apparatus for manufacturing a polysilicon rod according to claim 1, wherein the holding body has a leg provided on the base plate so as to be movable in the horizontal direction, and an electrode adapter is provided so as to be pivotable at least in the vertical direction with respect to the base plate, and is electrically connected between the core wire holder and the electrode.The apparatus for manufacturing a polysilicon rod according to claim 2, wherein the foot has a curved surface part on its upper part, and the electrode adapter is pivotable along the curved surface part at least in a vertical direction and slidable in the horizontal direction with respect to the electrode.The apparatus for manufacturing a polysilicon rod according to claim 3, further comprising a pressing part, wherein the electrode adapter comprises an electrode adapter main part provided on the curved surface part to be pivotable at least in a vertical direction, and an electrode adapter slide part extending in the horizontal direction from the electrode adapter main part and contacting the electrode, and the electrode is connected between the electrode adapter slide part and the pressing part.The apparatus for manufacturing a polysilicon rod according to any one of claims 2 to 4, wherein the base plate, the electrode adapter, and the electrode are each made only with a planar surface and with a spherical surface or a curved surface having a radius of 5 mm or more.The apparatus for manufacturing a polysilicon rod according to claim 5, wherein the base plate, the electrode adapter, and the electrode each do not have an inner corner part having an angle of less than 90°.The apparatus for manufacturing a polysilicon rod according to any one of claims 2 to 5, wherein the foot provided on the base plate is an insulator.

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