Apparatus for producing polycrystalline silicon

An apparatus for producing polycrystalline silicon which heats a silicon seed rod in a reactor to which a raw material gas is supplied, and deposits polycrystalline silicon on the surface of the silicon seed rod, includes an electrode extending in a vertical direction to hold the silicon seed rod, an electrode holder having a cooling flow passage circulating a cooling medium formed therein, and inserted into a through-hole formed in a bottom plate of the reactor to hold the electrode, and an annular insulating material arranged between an inner peripheral surface of the through-hole and an outer peripheral surface of the electrode holder to electrically insulate the bottom plate and the electrode holder from each other.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus for producing polycrystalline silicon which deposits polycrystalline silicon on the surface of a heated silicon seed rod to produce a polycrystalline silicon rod.

Priority is claimed on Japanese Patent Application No. 2008-164298, filed Jun. 24, 2008, and Japanese Patent Application No. 2009-135831, filed Jun. 5, 2009, the content of which is incorporated herein by reference.

2. Description of Related Art

An apparatus employing Siemens method is known as an apparatus for producing polycrystalline silicon. In the apparatus for producing polycrystalline silicon using the Siemens method, a number of silicon seed rods are arranged in the reactor. The silicon seed rods in the reactor are heated, and raw material gas including mixed gas of chlorosilane gas and hydrogen gas is supplied to the reactor to come into contact with the heated silicon seed rods. On a surface of a silicon seed rod, polycrystalline silicon is produced by a hydrogen reduction reaction and a thermal decomposition reaction of the raw material gas.

In such an apparatus for producing polycrystalline silicon, the silicon seed rods are disposed so as to stand upright on the electrodes arranged at an inner bottom portion of the reactor. Then, an electric current is applied to the silicon seed rods from the electrodes, and the silicon seed rods generate heat by the resistance thereof. At this time, the raw material gas which is jetted from below is come into contact with the surfaces of the silicon seed rods to form polycrystalline silicon rods. A plurality of the electrodes holding the silicon seed rods is provided so as be distributed over almost the whole region of the inner bottom face of the reactor, and as described in Japanese Patent Unexamined Publication No. 2007-107030, is provided in through-holes of a bottom plate of the reactor so as to surrounded by an annular insulating material.

In the apparatus for producing polycrystalline silicon described above, the gas temperature in the reactor becomes elevated to 500 to 600° C. at a maximum. Thus, the electrode holders holding electrodes are cooled by circulating cooling water in the electrode holders. However, since the insulating material provided between the through-holes of a bottom plate of the reactor and the electrode holders cannot be directly cooled, the shape thereof is apt to be damaged due to the heat in the reactor, which is apt to cause deterioration of the insulating function. In this case, if a ceramic-based insulating material is used, there is a possibility that the insulating material will become damaged, since the insulating material is not be capable of absorbing the thermal expansion difference between the bottom plate of the reactor and the electrode holder.

SUMMARY OF THE INVENTION

The present invention was contrived in view of such a problem, and an object of the present invention is to provide an apparatus for producing polycrystalline silicon which can absorb the thermal expansion difference between a bottom plate of a reactor and the electrode holders, and can realize excellent insulation.

The apparatus for producing polycrystalline silicon of the present invention includes a reactor to which a raw material gas is supplied, and a silicon seed rod heated in the reactor, and deposits polycrystalline silicon on the surface of the silicon seed rod. The apparatus for producing polycrystalline silicon of the present invention has an electrode, an electrode holder, and an annular insulating material. The electrode extends in a vertical direction to hold the silicon seed rod. The electrode holder has a cooling flow passage formed therein for circulating a cooling medium, and the electrode holder is inserted into a through-hole formed in a bottom plate of the reactor to hold the electrode. The annular insulating material arranges between an inner peripheral surface of the through-hole and an outer peripheral surface of the electrode holder to electrically insulate the bottom plate and the electrode holder from each other. Furthermore, in the apparatus for producing polycrystalline silicon of the present invention, an outer peripheral surface of the electrode holder is provided with an enlarged diameter portion which contacts at least a portion of a top face of an upper end of the annular insulating material and has a portion of the cooling flow passage formed therein.

That is, the top face of the upper end of the annular insulating material in the state of being inserted into the bottom plate of the reactor is directed to the inside of the reactor. Thus, if the insulating material is kept in the state of being exposed into the reactor from a gap between the inner peripheral surface of the through-hole and the electrode holder, the radiant heat from the silicon seed rod or the like with the reactor will directly act on the upper end of the annular insulating material through the inner peripheral surface of the through-hole and the electrode holder. In this present invention, the electrode holder is provided with the enlarged diameter portion which contacts at least a portion of the top face of the upper end of the annular insulating material, whereby the electrode holder absorbs the radiant heat directed to the top face. Thus, the radiant heat which directly acts on the annular insulating material can be reduced. Moreover, since the cooling medium also circulates through the enlarged diameter portion, the cooling effect on the annular insulating material can be enhanced.

In the apparatus for producing polycrystalline silicon of the present invention, preferably, the enlarged diameter portion covers the whole top face of the upper end of the annular insulating material.

In this case, since the enlarged diameter portion is provided so as to cover the whole top face of the upper end of the annular insulating material whereby the radiant heat from the reactor is interrupted by the enlarged diameter portion, the annular insulating material can be more effectively protected from the radiant heat. Additionally, since the whole top face of the upper end of the annular insulating material is cooled by the enlarged diameter portion, deterioration of the shape and insulating function of the annular insulating material can be more effectively prevented.

In the apparatus for producing polycrystalline silicon of the present invention, preferably, the cooling medium cools the enlarged diameter portion, and then cools the vicinity of the electrode.

In this case, the cooling medium circulating through the inside of the electrode holder cools the enlarged diameter portion of a relatively low temperature, and then cools the vicinity of the electrode of a relatively high temperature, so that the enlarged diameter portion can be maintained at a low temperature. Thus, the temperature of the annular insulating material can be effectively prevented from reaching a high temperature.

In the apparatus for producing polycrystalline silicon of the present invention, preferably, the cooling flow passage has an outer peripheral flow passage through which the cooling medium is circulated at an outer peripheral portion in the electrode holder toward the upper end thereof along the longitudinal direction of the electrode holder, and an inner peripheral flow passage through which the cooling medium is circulated inside the outer peripheral flow passage toward the lower end of the electrode holder along the longitudinal direction, and a portion of the outer peripheral flow passage is formed in the enlarged diameter portion.

In this case, the cooling medium is circulated at the outer peripheral portion in the electrode holder toward the upper end of the electrode holder, and is then circulated inside the outer peripheral flow passage toward the lower end of the electrode holder, so that the electrode holder can be efficiently cooled to the upper end thereof.

In the apparatus for producing polycrystalline silicon of the present invention, preferably, the annular insulating material is made of resin having elasticity. In this case, damage to the annular insulating material caused by the thermal expansion difference between the bottom plate and the electrode holder is prevented, the thermal expansion difference between the bottom plate and the electrode holder is absorbed by an annular insulator, and displacement of the silicon seed rod and damage to deposited polycrystalline silicon are prevented.

According to the apparatus for producing polycrystalline silicon of the present invention, the enlarged diameter portion provided in the electrode holder intercepts the radiant heat from the silicon seed rod to the annular insulating material, and cools the annular insulating material. Thus, the annular insulating material can be effectively protected from the heat at the time of reaction, and the insulation and elasticity of the annular insulating material can be reliably maintained. Accordingly, synthetic resin or the like can be used as the annular insulating material, and the soundness of the whole apparatus can be maintained such that the thermal expansion difference can be absorbed while securing the insulation between the bottom plate and the electrode.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of an apparatus for producing polycrystalline silicon of the present invention will be described below with reference to the drawings.

First Embodiment

FIG. 1is an overall view of the apparatus for producing polycrystalline silicon to which the present invention is applied. A reactor1of the apparatus for producing polycrystalline silicon includes a bottom plate2which constitutes a reactor bottom, and a bell-shaped bell jar3detachably attached on the bottom plate2. The upper face of the bottom plate2is formed on a substantially flat horizontal plane. Since the bell jar3is bell-shaped as a whole, and the ceiling of the bell jar is dome-shaped, the internal space of the bell jar is formed such that the central portion thereof is the highest and the outer peripheral portion thereof is the lowest. Additionally, the bottom plate2and the wall of the bell jar3have a jacket structure (not shown), and are cooled by cooling water.

The bottom plate2is provided with a plurality of electrode units5to which silicon seed rods4are attached, a plurality of jet nozzles (gas supply ports)6for jetting a raw material gas including a chlorosilane gas and a hydrogen gas into the reactor, and a plurality of gas discharge ports7for discharging the gas after reaction to the outside of the reactor.

The plurality of the jet nozzles6for the raw material gas are distributed at suitable intervals over most of the upper face of the bottom plate2of the reactor1so that the raw material gas can be uniformly supplied to each of the silicon seed rods4. The jet nozzles6are connected to a raw material gas supply source8outside the reactor1. Additionally, the plurality of gas discharge ports7are set at suitable intervals in a circumferential direction in the vicinity of an outer peripheral portion on the bottom plate2, and are connected to an exhaust gas processing system9. A power supply circuit10is connected to the electrode units5. The bottom plate2has a jacket structure, and the inside thereof is formed with a cooling flow passage (not shown).

The silicon seed rods4are fixed in a state where the lower ends thereof are inserted into the electrode units5, respectively, and thereby extend upward so as to stand upright. One short connecting member12is attached to the upper ends of every two of the silicon seed rods4so as to connect them together as a pair. The connecting member12is also made of the same silicon as the silicon seed rods4. A seed assembly13is assembled by these two silicon seed rods4and the connecting member12connecting these together so as to be substantially H-shaped (inversed U-shaped) as a whole. Since the electrode units5are arranged concentrically from the center of the reactor1, seed assemblies13are arranged substantially concentrically from the center of the reactor1.

Specifically, as shown inFIG. 2, electrode units5A for one silicon seed rod holding one silicon seed rod4and electrode units5B for two silicon seed rods holding two silicon seed rods4are arranged as the electrode units5in the reactor1.

The electrode units5A for one silicon seed rod and the electrode units5B for two silicon seed rods, as shown inFIG. 2, are able to connect three sets of seed assemblies13in series as one unit. At this time, one electrode unit5A for one silicon seed rod, two electrode units5B for two silicon seed rods, and one electrode unit5A for one silicon seed rod are lined up in this order from an end of a unit row. In this case, three sets of seed assemblies13are provided so as to stride over four electrode units5A and5B. Each of silicon seed rods4forming one seed assembly13is held by adjacent different electrode units5, respectively.

That is, one of two silicon seed rods4of the seed assembly13is held at the electrode unit5A for one silicon seed rod, and one silicon seed rod4of each of two sets of seed assemblies13is held at the electrode unit5B for two silicon seed rods. A power cable is connected to the electrode units5A for one silicon seed rod at both ends of the row so that an electric current flows thereto. At this time, in the electrode unit5B for two silicon seed rods, an electric current flows between both electrodes47through an arm portion42(refer toFIG. 4).

As described above, two kinds of electrodes are used, and the electrode unit5A for one silicon seed rod holding one silicon seed rod4, and the electrode unit5B for two silicon seed rods holding every two silicon seed rods4are provided. Thereby, the number of electrode units can be reduced (for example, about ⅔) compared with a case where all silicon rods are held one by one. In a case where the number of electrode units is small, the number of through-holes formed in the bottom plate2of the reactor1can also be reduced, and the bottom plate2can be maintained as a rigid structure. Additionally, since a number of silicon seed rods4can be held by a small number of electrode units, a number of silicon seed rods4can be set into the reactor1, and productivity can be increased. Additionally, since the number of electrode units is reduced, cooling pipes or power cables to be arranged below the bottom plate2can also be reduced, and the maintenance workability thereof improves.

Next, the structure of each electrode unit will be described in detail.

First, the electrode unit5A for one silicon seed rod holding one silicon seed rod4will be described. As shown inFIG. 3, the electrode unit5A includes an electrode holder22and an electrode23. The electrode holder22is provided in the state of being inserted into a through-hole21formed in the bottom plate2of the reactor1, and the electrode23is provided at the upper end of the electrode holder22to hold the silicon seed rod4.

The electrode holder22, as shown inFIG. 3, is formed in a rod shape, and made of a conductive material, such as stainless steel. The electrode holder22is formed by integrating a straight rod portion24, a hollow disc-like enlarged diameter portion25, and a male thread portion26. The straight rod portion24is inserted into the through-hole21along a vertical direction. The hollow disc-like enlarged diameter portion25is coaxially formed at the upper end of the straight rod portion24, and the enlarged diameter portion25has a diameter larger than that of the rod portion24. A ring-shaped space25ais formed in the enlarged diameter portion25coaxially with the electrode holder22, and the space25ahas an outer diameter larger than the maximum diameter of the rod portion24. The male thread portion26further protrudes upward from the top face of the enlarged diameter portion25. Additionally, below the rod portion24, a male thread portion28is formed at a position where it protrudes from the bottom plate2.

The electrode holder22is formed in a hollow shape. Inside the electrode holder22, an inner tube30which has a smaller external diameter than the internal diameter of the electrode holder22and divides the inside of the electrode holder22into an outer peripheral space and an inner peripheral space (core) is provided coaxially with the electrode holder22. The upper end of the inner tube30abuts on the inner surface of the upper end of the electrode holder22, and this upper end is formed with an opening30awhich allows the inside and outside of the inner tube30to communicate with each other. Thereby, a cooling flow passage27adapted such that an outer peripheral flow passage27A formed between the inner tube30and the electrode holder22and an inner peripheral flow passage27B formed in the inner tube30communicate with each other by the opening30ais formed from the rod portion24to the male thread portion26inside the electrode holder22. A cooling medium circulates through the cooling flow passage27.

A ring plate31is provided at an outer peripheral surface of the inner tube30so as to be substantially orthogonal to the inner tube30at a position corresponding to the space25ain the enlarged diameter portion25. By means of the ring plate31, the circulation direction of the cooling medium which circulates through the outer peripheral flow passage27A is guided into the space25ain the enlarged diameter portion25. A plate-like spacer32which secures the spacing between the inner peripheral surface of the electrode holder22and the outer peripheral surface of the inner tube30at a position corresponding to the male thread portion28is further provided at the outer peripheral surface of the inner tube30so as to extend along the axis direction of the inner tube30.

Meanwhile, the through-hole21of the bottom plate2in a state where the electrode holder22is inserted includes a lower straight portion21A and an upper tapered portion21B whose diameter gradually increased upward. The straight portion21A is formed so as to have a larger internal diameter than the external diameter of the rod portion24of the electrode holder22. Thereby, a ring-shaped space25ais formed around the rod portion24. The tapered portion21B is formed at an inclination angle of, for example, 5° to 15° with respect to a vertical axis. An opening of an upper end of the tapered portion21B is formed with a counterbore33whose diameter further increases than the maximum internal diameter of the tapered portion21B.

An annular insulating material34is provided between the inner peripheral surface of the through-hole21and the rod portion24of the electrode holder22so as to surround the electrode holder22. The annular insulating material34is formed from high-melting point insulating resin having elasticity, such as fluorine-based resin represented by, for example, polytetrafluoroethylene (PTFE) and perfluoroalkoxyalkane (PFA). The annular insulating material34includes two members of a sleeve35with a collar to be inserted into the straight portion21A of the through-hole21, and a cone member36arranged at the tapered portion21B of the through-hole21. For example, PTFE to be used as the material of the annular insulating material34has a melting point (ASTM standard: D792) of 327° C., and a bending elastic modulus (ASTM standard: D790) of 0.55 GPa, a tensile elastic modulus (ASTM standard: D638) of 0.44 GPa to 0.55 GPa, and a linear coefficient of expansion (ASTM standard: D696) of 10×10−5/° C.

The cone member36has an outer surface formed in a tapered shape of the same inclination angle as the inner peripheral surface of the tapered portion21B of the through-hole21. The cone member36is inserted into the through-hole21from above the bottom plate2, and is made to abut on the inner surface of the tapered portion21B of the through-hole21. The bottom face of the enlarged diameter portion25of the electrode holder22abuts on the top face of an upper end of the cone member36. The enlarged diameter portion25is set to have an external diameter that is almost equal to the maximum external diameter of the cone member36, i.e., the external diameter of the top face of the upper end of the cone member36, and covers the whole top face of the cone member36(annular insulating material34). When the distance between the enlarged diameter portion25and the side face of the counterbore33is larger enough to avoid the short-circuit between the enlarged diameter portion25and the side face of the counterbore33, it is preferable that the external diameter of the enlarged diameter portion25be slightly larger than the external diameter of the top face of the upper end of the cone member36to enhance the cooling effect on the annular insulating material. When the distance between the enlarged diameter portion25and the side face of the counterbore33is small, it is preferable that the external diameter of the enlarged diameter portion25be slightly smaller than the external diameter of the top face of the upper end of the cone member36to avoid the short-circuit between the enlarged diameter portion25and the side face of the counterbore33.

O rings43are respectively provided at inner peripheral portion of upper end surface and the outer peripheral surface of the cone member36. The airtightness between the cone member36and the electrode holder22, and the airtightness between the cone member36and the bottom plate2, i.e., the airtightness in the through-hole21of the reactor1are maintained by the O rings43.

The sleeve35with a collar is inserted into the straight portion21A so that a collar portion37integrally formed at a lower end thereof abuts on the rear surface of the bottom plate2of the reactor1. The upper face of the collar portion37is pressed against the rear surface of the bottom plate2by a nut38threaded into the male thread portion28of the electrode holder22. Pair of ring washers39aand a disc spring39bare arranged between the lower face of collar portion37and the nut38, the disc spring39bis arranged between the pair of ring washers39a. While the upper face of the collar portion37is pressed against the rear surface of the bottom plate2by a nut38, the press strength is adjusted appropriately by the disc spring39b. It is preferable that the ring washers39abe made of stainless steel (SUS304), and it is preferable that the disc spring39bbe made of stainless steel (SUS631).

Since the distance between the enlarged diameter portion25and the nut38becomes short by fastening the nut38, the electrode holder22is pulled downward with respect to the bottom plate2, and the annular insulated member34is sandwiched between the enlarged diameter portion25and the nut38. Moreover, the outer peripheral surface of the cone member36is pressed against the inner peripheral surface of the tapered portion21B of the through-hole21by the sandwiching force, and the annular insulating material34and the electrode holder22are integrally fixed to the bottom plate2. At this time, while checking the height of the lower face of the enlarged diameter portion25of the electrode holder22from the bottom face of the counterbore33, a lower portion of the enlarged diameter portion25approaches the bottom plate2. At this time, the amount of screwing of the nut38is adjusted to prevent electric short-circuiting between a lower portion of the enlarged diameter portion25and the bottom plate2.

By the elastic deformation of the disc spring39band the annular insulating material34(the sleeve35with a collar and the cone member36made of resin), the relative displacement in the vertical direction between the electrode holder22and the bottom plate2is permitted. Accordingly, the thermal expansion difference between the electrode holder22and the bottom plate2is absorbed.

In this fixed state, the upper end of the cone member36of the annular insulating material34protrude slightly upward from the upper end of the tapered portion21B of the through-hole21, and is made to face the counterbore33. For this reason, the cone member36is set to have a larger external diameter than the maximum external diameter of the tapered portion21B at the upper end thereof so as to protrude from the bottom face of the counterbore33and so as not to protrude upward from the upper end of the counterbore33.

Meanwhile, the electrode23is formed in a columnar shape as a whole and made of carbon or the like. The electrode23has a female thread portion43, which is screwed into the male thread portion26of the electrode holder22, at the lower end thereof, and has a hole23a, which fixes the silicon seed rod4in an inserted state, at the upper end thereof, and the hole23ais formed along an axial center.

The cooling flow passage27formed in the electrode unit5A for one silicon seed rod will be described. As shown inFIG. 3, a cooling medium flows into the outer peripheral flow passage27A through an inlet127A provided at the lower portion of the electrode holder22, and circulates upward. Then, the cooling medium is guided by the ring plate31to circulate through the space25ain the enlarged diameter portion25, and then reaches the inside of the male thread portion26, i.e., the vicinity of the electrode23. When the inside of the outer peripheral flow passage27A is filled with the cooling medium until the cooling medium contacts the inner surface of the upper end of the electrode holder22, the cooling medium flows into the inner tube30from the opening30aprovided at the upper end of the inner tube30. Then, the cooling medium circulates downward through the inside of the inner tube30, i.e., the inner peripheral flow passage27B, and flows to the outside of the electrode holder22from an outlet127B provided at the lower end of the inner tube30. That is, the cooling medium cools the enlarged diameter portion25at a relatively low temperature while circulating through the outer peripheral flow passage27A, and then, cools the vicinity of the electrode23at a relatively high temperature, and is discharged from the electrode holder22through the inner peripheral flow passage27B.

Second Embodiment

The electrode unit5B for two silicon seed rods will be described. The electrode unit5B for two silicon seed rods is shown in an enlarged manner inFIG. 4. The electrode unit5B for two silicon seed rods has the same configuration as the electrode unit5A for one silicon seed rod in that it includes an electrode holder46provided in the state of being inserted into the through-hole21formed at the bottom plate2of the reactor1, and an electrode47provided at the upper end of the electrode holder46. The electrode unit5B for two silicon seed rods is different from the electrode unit5A for one silicon seed rod in that the electrode holder46is bifurcated at the upper end thereof, and the electrodes47are respectively provided at both ends of the electrode holder46.

The electrode holder46of the electrode unit5B is configured such that a rod-shaped rod portion41, and an arm portion42orthogonal to an upper end of the rod portion41are integrally formed. The electrode holder46is made of a conductive material, such as stainless steel. A hollow annular enlarged diameter portion45is attached to a longitudinal midway position of the rod portion41. Additionally, the same male thread portion46aas the male thread portion28in the first embodiment is formed at the position of the rod portion41protruding from the bottom face of the bottom plate2.

Since the through-hole21(the straight portion21A and the tapered portion21B) of the bottom plate2in a state where the electrode holder46is inserted, the counterbore33formed at the opening of the upper end of the tapered portion21B, the annular insulating material34(the sleeve35with a collar and the cone member36) provided between the inner peripheral surface of the through-hole21and the rod portion41of the electrode holder46, the nut member38screwed to the male thread portion46aof the rod portion41, the ring washers39a, etc. have the same configuration and effects as the electrode unit5A for one silicon seed rod, their description thereof will be omitted.

The arm portions42of the electrode holder46extends horizontally in right and left directions from the upper end of the rod portion41, and the electrode holder46is formed to be T-shaped. The arm portion42is formed with female thread holes42awhich pass through both the right and left ends in a vertical direction. The electrodes47are screwed to the female thread holes42a, and are exposed to upper portions of the arm portion42. Nut members44are attached to base of the electrodes47on the arm portion42. The nut members44are formed in a columnar shape, and the inner peripheral portions thereof are formed with female thread portions into which the electrodes47are screwed. It is preferable that the nut members44be made of carbon or the like.

The arm portion42is formed with a straight inner space42bwhich extends in right and left directions, and a circular inner space42cwhich surrounds the outer periphery of the female thread holes42ain a C-shape, and communicates with the straight inner space42b. The straight inner space42bis partitioned into upper and lower portions by a third partition plate48C.

The upper space of the rod portion41of the electrode holder46is partitioned into a left space41cand a right space41dby a second partition plate48B to be connected to the third partition plate48C. A disc-like first partition plate48A which partitions the inside of the rod portion41into upper and lower portions in a direction substantially orthogonal to the axis direction of the rod portion41is connected to a lower end of the second partition plate48B. The first partition plate48A is formed with a through-hole148A opened only to the right of the second partition plate48B. Moreover, the rod portion41is formed with a first opening41aprovided below the first partition plate48A, and a second opening41bprovided above the first partition plate48A and opposite to the first opening41aby 180° with the axis of the rod portion41therebetween.

The enlarged diameter portion45is an annular member which fits to an outer peripheral surface of the rod portion41and thereby forms an annular space45bat the outer peripheral surface of the rod portion41. The annular space45bin the enlarged diameter portion45communicates with the inside of the rod portion41through the first opening41aopened below the first partition plate48A and the second opening41bopened above the first partition plate48A. Additionally, the outer peripheral portion of the top face of the enlarged diameter portion45is formed with a peripheral wall portion45a.

Additionally, the inner tube49which communicates with the right space41dthrough the through-hole148A is attached to the bottom face of the first partition plate48A substantially coaxially with the rod portion41. The inner tube49divides the inside of the rod portion41into an outer peripheral space (outer peripheral flow passage40A) and an inner peripheral space (inner peripheral flow passage40B) below the first partition plate48A.

By configuring the electrode unit5B for two silicon seed rods in this way, a cooling flow passage40is formed inside the electrode holder46by the outer peripheral flow passage40A and inner peripheral flow passage40B at the lower portion of the rod portion41, the annular space45bof the enlarged diameter portion45, the left space41cand right space41dat the upper portion of the rod portion41, and the straight space42band circular space42cof the arm portion42.

In the cooling flow passage40, a cooling medium flows into the outer peripheral flow passage40A formed between the outer peripheral surface of the inner tube49and the inner peripheral surface of the rod portion41from the lower end of the electrode holder46, and circulates upward. When the cooling medium reaches the first partition plate48A, the cooling medium is interrupted by the first partition plate48A, flows into the annular space45bin the enlarged diameter portion45through the first opening41a, and cools the enlarged diameter portion45. Then, the cooling medium circulates to the upper side of the first partition plate48A and the left side of the second partition plate48B, i.e., to the left space41cthrough the second opening41b.

After the cooling medium which has flowed into the left space41cis guided to the left circular inner space42cfrom a lower left portion of the straight inner space42bof the arm portion42by the second partition plate48B and the third partition plate48C. Then, the cooling medium circulates above the third partition plate48C in the straight inner space42b, and is guided to a lower right portion of the straight inner space42bthrough the right circular inner space42c. In this period, the cooling medium cools the vicinity of the electrode47. Then, when the cooling medium circulates through the right space41dalong the second partition plate48B and reaches the first partition plate48A, the cooling medium flows into the inner peripheral flow passage40B in the inner tube49through the through-hole148A, and is discharged from the electrode holder46.

In the apparatus for producing polycrystalline silicon configured in this way, an electric current is applied to the silicon seed rod4from each electrode unit5(the electrode unit5A, the electrode unit5B), bringing the silicon seed rod4into a resistance heating state. Additionally, even among the silicon seed rods4, a silicon seed rod4receives radiant heat from an adjacent silicon seed rod4, and is heated, and thereby, these silicon seed rods4are brought into a high-temperature state by a synergetic effect. As a result, the raw material gas which has contacted the surface of the silicon seed rod4in a high-temperature state reacts to deposit polycrystalline silicon.

Since the radiant heat from the silicon seed rods4acts also on each electrode unit5A or electrode unit5B on the bottom plate2of the reactor1and a portion of the upper end of the annular insulating material34which is weak to heat is also exposed in the counterbore33, the influence of heat is concerned. However, as shown inFIGS. 3 and 4, since the enlarged diameter portion25of the electrode holder22and the enlarged diameter portion45of the electrode holder46are arranged on the top face of the upper end of the annular insulating material34so that they are covered, the radiant heat which directly acts on the upper end surface decreases. Moreover, since the electrode holder22or the electrode holder46is cooled by the cooling medium circulating therethrough, the annular insulating material34is also effectively cooled. In particular, the annular insulating material34is effectively cooled as the cooling medium circulates through the space provided inside the enlarged diameter portion25or the enlarged diameter portion45which covers the top face of the upper end thereof.

As such, since deformation, deterioration, etc. of the annular insulating material34caused by a high temperature are suppressed, and the elasticity thereof is maintained even in the hot reactor1, the thermal deformation of each member can be absorbed, the action of stress can be suppressed, and the function of a facility is suitably maintained.

In addition, the present invention is not limited to the configuration of the above embodiment, but in the detailed configuration various modifications can be made without departing from the spirit and scope of the invention.

For example, the enlarged diameter portion of the electrode holder may be provided so as to cover at least a portion of the top face to such a degree that deformation, deterioration, etc. of the annular insulating material can be prevented. The enlarged diameter portion of the electrode holder does not necessarily cover the whole top face of the upper end surface of the annular insulating material.

Additionally, although a cooling flow passage of only one system is provided in the above embodiment, a cooling flow passage for cooling the enlarged diameter portion and a cooling flow passage for cooling the vicinity of an electrode may be provided independently.