Abstract:
A reactor ( 10 ) for the production of polycrystalline silicon is disclosed, comprising a reactor floor ( 12 ) exhibiting a plurality of nozzles ( 40 ), through which a gas containing silicon flows into the reactor ( 10 ). On an outer surface ( 33 ) of the reactor floor ( 12 ) a cavity ( 71 ) is circumscribed by this outer surface ( 33 ) and a wall ( 70 ), the cavity ( 71 ) providing for the distribution of the gas containing silicon to at least part of the nozzles ( 40 ).

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This patent application claims priority of German Patent Application No. DE 10 2009 043 950.1 filed on Sep. 4, 2009 which is incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to a reactor for the production of polycrystalline silicon. 
       BACKGROUND OF THE INVENTION 
       [0003]    The principle processes for the production of polycrystalline silicon in a reactor according to the invention are the “Siemens Process” and the “Monosilane Process”. 
         [0004]    In the Siemens Process Trichlorosilane (SiHCl 3 ) is thermally decomposed in the presence of hydrogen on heated rods of high-purity silicon at 1000-1200° C. Elemental silicon therein is growing onto the rods. The hydrogen chloride released therein is fed back into the cycle. The process is conducted at a pressure of about 6.5 bar. 
         [0005]    In the Monosilane Process monosilane (SiH 4 ) is thermally decomposed in the presence of hydrogen on heated rods of high-purity silicon at 850-900° C. Elemental silicon therein is growing onto the rods. The Monosilane Process is conducted at a pressure of about 2 to 2.5 bar. 
         [0006]    In the U.S. Pat. No. 4,179,530 a method for the accretion of pure silicon is disclosed. The reactor used therein is a container with double walls. Cooling water flows in the space between the two walls. The reactor comprises plural thin U-shaped filaments onto which the silicon is deposited. Likewise the clamps of the electrodes are cooled. The gas is supplied and withdrawn through openings in the floor of the reactor. 
         [0007]    The German patent application DE 25 58 387 discloses a method and an apparatus for the production of polycrystalline silicon. The polycrystalline silicon is obtained by hydrogen reduction of compounds containing silicon. Through an infeed nozzle the reactants are supplied to the reaction chamber. Used reactants are withdrawn via a conduit through an outlet. Infeed and outlet are arranged opposite each other. 
         [0008]    The German patent application DE 10 2005 042 753 A1 discloses a method for the production of granular polycrystalline silicon in a fluidised bed reactor. In the method for the production of granular polycrystalline silicon the polycrystalline silicon is deposited from a reaction gas in a fluidised bed reactor exhibiting a hot surface. This occurs at a reaction temperature of about 600 to 1100° C. The particles with deposited silicon are removed from the reactor along with reaction gas which has not reacted and with fluidising gas. 
         [0009]    The U.S. Pat. No. RE 36,936 discloses a method for the production of high-purity polycrystalline silicon. Herein, too, the silicon is obtained by deposition from gas containing silicon. The gas circulating in the chamber precipitates on cooled surfaces provided for this purpose. The circulation of the gas can be augmented by a fan. 
         [0010]    The unpublished German patent application DE 10 2009 003 368 A1 discloses a reactor for the production of polycrystalline silicon comprising a reactor floor exhibiting a plurality of nozzles. Through the nozzles a gas containing silicon is flowing in. Also, plural filament rods are mounted on the reactor floor. Furthermore a gas outlet for supplying used gas containing silicon to an enrichment and/or a preparation is provided. The gas outlet is located at a free end of an inner pipe, wherein the inner pipe is passed through the reactor floor. 
         [0011]    The German patent application DE 28 54 707 A1 discloses an apparatus and a method used for the deposition of pure semiconductor material, in particular silicon, by thermal decomposition gaseous compounds of this semiconductor material. A metallic base plate has nozzles for the provision of reaction gas. Removal of the reaction gases carried out as well via base plate. 
         [0012]    The German patent application DE 29 12 661 A1 relates to a method for the deposition of pure semiconductor material, in particular, silicon, by thermal decomposition of a compound of the semiconductor material, on the surface of a heated carrier element, which carrier element is heated by applying an electrical current thereto, so as to heat the same to the decomposition temperature of the corresponding decomposable compound in a gas-tight, closed reactor. A nozzle design is disclosed, which is used in the process for feeding the decomposable compound. 
       SUMMARY OF THE INVENTION 
       [0013]    It is an object of the invention to provide a reactor for the production of polycrystalline silicon with a reactor floor designed in such a way that the distribution of the gas containing silicon to the nozzles in the reactor floor occurs in a manner which saves space, is safe and cost-effective, and provides easy access to the further elements on the outside of the reactor floor, for example electrodes and coolant connections. 
         [0014]    The object of the invention is achieved with a reactor for the production of polycrystalline silicon. The reactor has a reactor floor with a plurality of nozzles, wherein each nozzle has a nozzle inlet a nozzle outlet which form an infeed for a silicon containing gas to a reactor interior. At least one wall is of such a shape that it, together with an outer surface of the reactor floor, circumscribes at least one cavity, which provides for a distribution system of the silicon containing gas to at least a portion of the nozzles with which it communicates. The wall is attached to the reactor floor in a gas-tight manner in such a way that at least one surface of contact of the cavity with the outer surface of the reactor floor is restricted to a subregion of the outer surface of the reactor floor. 
         [0015]    According to a preferred embodiment of the invention a gas supply to the reactor floor exhibits a first branch and a second branch, wherein the first branch is a gas supply to the cavity circumscribed by the wall and the outer surface of the reactor floor, and wherein the second branch is a gas supply to a central nozzle. The first and the second branch each comprise a valve, through which the flow of gas in the respective branch is controllable. It is conceivable for the other nozzles to be distributed uniformly about the central nozzle. Preferentially the invention is implemented in such a way that the cavity circumscribed by the wall and the outer surface of the reactor floor has the shape of a closed annulus. However, it is also conceivable that according to another embodiment the cavity circumscribed by the wall and the outer surface of the reactor floor has the shape of an open annulus. In an embodiment of the invention the cavity circumscribed by the wall and the outer surface of the reactor floor exhibits a cross-section which has the shape of a segment of a circle. Preferentially the wall is attached to the outer surface of the reactor floor by at least one continuous welded seam. Due to reasons of manufacture it is particularly advantageous, if the cross-section of the cavity circumscribed by the wall and the outer surface of the reactor floor is a semicircle. In this case the shape of the wall provides particularly easy access for producing the welded seam between the outer surface of the reactor floor and the wall, and also for cleaning the reactor floor. 
         [0016]    According to a further embodiment, the reactor for the production of polycrystalline silicon has a reactor floor with a plurality of nozzles and plurality of nozzles is distributed uniformly about a central nozzle. Each nozzle has a nozzle inlet a nozzle outlet which form an infeed for a silicon containing gas to a reactor interior. At least one wall is of such a shape that it, together with an outer surface of the reactor floor, circumscribes a cavity, which provides for a distribution system of the silicon containing gas to all nozzles with which it communicates. The cavity circumscribed by the wall and the outer surface of the reactor floor has the shape of a closed annulus. The wall is attached to the reactor floor in a gas-tight manner in such a way that at least one surface of contact of the cavity with the outer surface of the reactor floor is restricted to a subregion of the outer surface of the reactor floor. 
         [0017]    A further embodiment of the inventive reactor for the production of polycrystalline silicon shows a reactor floor with a first set of nozzles a second set of nozzles. The first set of nozzles and the second set of nozzles is distributed uniformly about a central nozzle, wherein each nozzle has a nozzle inlet a nozzle outlet which form an infeed for a silicon containing gas to a reactor interior. A wall is of such a shape that it, together with an outer surface of the reactor floor, circumscribes a cavity, wherein an individual cavity is assigned to the first set of nozzles and the second set of nozzles so that a distribution system of the silicon containing gas to the first set of nozzles and the second set of nozzles is defined. Each cavity circumscribed by the wall and the outer surface of the reactor floor has the shape of a closed annulus. The wall is attached to the reactor floor in a gas-tight manner in such a way that at least one surface of contact of the cavity with the outer surface of the reactor floor is restricted to a subregion of the outer surface of the reactor floor. 
         [0018]    It is obvious to a person skilled in the art that further shapes and cross-sections of the cavity circumscribed by the wall and the outer surface of the reactor floor are conceivable without leaving the scope of the invention. Thus for example cross-sections in the shape of a rectangle or of a segment of an ellipse can be conceived of, the cavity could also be shaped like a U or like a meander. 
         [0019]    The design of the gas distribution in the case of the reactor according to the invention affords the possibility to give more consideration to further requirements for the setup of the reactor, in particular the accessibility to further elements on the reactor floor, like electrical contacts or coolant connections, can be improved. Furthermore, in particular in the preferred embodiments, welded seams are reduced and connections by screws are redundant. Thereby the risk of leaks is reduced. This increases the operational safety of the reactor, as the gas containing silicon used may cause an explosion if in contact with water (for example the cooling water used in the reactor). Depending on the operational conditions, if the gas and the cooling water are in contact, also deposits may form, which reduce the reliability of the operation of the reactor. By attaching the gas distribution to the reactor floor without an intervening distance furthermore the spatial requirements of the apparatus are reduced. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    Further features, objects and advantages of the present invention are now be explained in greater detail in the following description of a preferred embodiment of the invention, which should not be regarded as limiting the invention and which refers to the accompanying figures. Same reference numbers refer to same figures throughout the various figures and are partially not referred to repeatedly. 
           [0021]      FIG. 1   a  shows a perspective section of a prior art reactor for the production of polycrystalline silicon. 
           [0022]      FIG. 1   b  shows a magnified view of the principle elements of an area around a nozzle, the reactor floor and one fixture of a filament rod of the prior art reactor a shown in  FIG. 1   a.    
           [0023]      FIG. 2  shows a side view of the reactor floor according to the invention with plural incoming and outgoing conduits. 
           [0024]      FIG. 3  shows a top view of the reactor floor according to the invention from below, wherein in this cut-away view the nozzles distributed annularly are visible. 
           [0025]      FIG. 4  shows a sectional view of the reactor floor according to the invention. 
           [0026]      FIG. 5  shows a magnified view of a section of  FIG. 4 , which essentially shows a nozzle for supplying reaction gas to the interior. 
           [0027]      FIG. 6  shows a sectional view of a further embodiment of the reactor floor according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0028]    Identical reference numerals are used for like elements of the invention or elements of like function. Furthermore for the sake of clarity only those reference numerals are shown in the individual figures which are required for the description of the respective figure or for putting a figure into the context of other figures. 
         [0029]      FIG. 1   a  shows a reactor  10  for the production of polycrystalline silicon according to prior art. The reactor floor  12  exhibits a plurality of nozzles  40 , through which the gas containing silicon enters the interior  11  of the reactor  10 . Also mounted on the reactor floor  12  are a plurality of filaments  60 , onto which the polycrystalline silicon is deposited from the gas phase during the process. In the embodiment shown here a gas eduction  20  is furnished with a gas outlet opening  22 , through which used gas is supplied to an enrichment and/or preparation. The reactor wall  18  and the inner pipe  21  are double-walled and thus can be cooled with water. The used gas is supplied to the enrichment and/or preparation via an eduction  20 . Fresh silicon containing gas is supplied to the multi-layered reactor floor  12  via a supply conduit (not shown here). From there the gas is distributed within the reactor floor  12  to the individual nozzles  40  and then enters the interior  11  of the reactor  10 . The nozzles  40  and the filaments  60  set into corresponding fixtures  61  are distributed uniformly about the outlet opening  22 , which is formed in the reactor floor  12 . 
         [0030]      FIG. 1   b  essentially shows a magnified view of a section of the reactor  12  floor as shown in  FIG. 1   a.  The reactor floor  12  is multi-layered, consisting of a first compartment  13  and a second compartment  14 . The first compartment  13  is formed by a board  15  facing the interior  11  of the reactor  10  and a middle board  16 . The second compartment  14  is formed by the middle board  16  and a bottom board  17 . The middle board  16  exhibits openings carrying the nozzles  40  for the gas. The nozzles end in the board  15  facing the reactor interior  11  and thus furnish the outlets for the gas. Consequently the fresh gas containing silicon is supplied to the second compartment  14  and distributes in this second compartment  14 , in order to enter the reactor interior  11  through the nozzles  40 . In the first compartment  13  cooling water is flowing. The supply connections  62  and  63  for the filaments  60  extend below the bottom board. The supply connection  62  is for voltage supply to the filaments  60 . The supply connection  62  is furnished as a high voltage electrode and supplies the filaments  60  with high voltage of about 10,000 Volts. In different embodiments the process can also be conducted with low voltage. The supply connections  63  are connections for cooling water, in order to maintain the fixtures  61  of the filaments  60  at a corresponding process temperature. The filaments  60  consist of a high-purity silicon rod with a diameter of about 8 mm. 
         [0031]      FIG. 2  shows a side view of the reactor floor  12  according to the invention. It comprises, in the embodiment shown, a first wall  31  and a second wall  32 , which delimit a compartment  34 . A coolant flows in the compartment  34 . The first wall  31  delimits the compartment  34  against the reactor interior  11 . A first outer surface  33  of the reactor floor together with a wall  70  furnishes a cavity  71 , which provides for the distribution of the gas containing silicon to the nozzles  40  (see  FIG. 3 ). In the embodiment shown a pipe  50  is a gas supply to the reactor floor; the pipe  50  branches into a first branch  51  and a second branch  52 . The first branch  51  leads to the cavity  71 , the second branch  52  to a central nozzle  41  (see  FIG. 3 ), which does not communicate with the cavity  71 . In the first branch there is provided a valve  53 , and in the second branch a valve  54 . The gas supply to the cavity  71  is controllable by the valve  53  in the first branch  51 , the gas supply to the central nozzle  41  is controllable by the valve  54  in the second branch  52 . In the embodiment shown the central nozzle  41  is located at the centre of the reactor floor  12 . In the embodiment shown a gas eduction  20  from the reactor  10  comprises a pipe  23 . 
         [0032]      FIG. 3  is a top view of the bottom side of the reactor floor  12  according to the invention. The wall  70  is shown in a cut-away view and shows the nozzles  40  communicating with the cavity  71 . As already mentioned in the context of  FIG. 2 , in the embodiment shown a central nozzle  41  is located at the centre of the reactor floor  12 . Furthermore in this embodiment on the reactor floor  12  also the fixtures  61  of the filaments  60  are shown, which in the reactor interior  11  serve for the deposition of silicon from the gas phase during the process. In the embodiment shown the cavity  71  furnished by the wall  70  and the outer surface  33  has the shape of a closed annulus, which does not limit the scope of the invention. Further elements with reference numerals in this figure have already been described in the context of  FIG. 2 . 
         [0033]      FIG. 4  is a side view of the reactor floor  12 . In particular there are shown the central nozzle  41  and several of the nozzles  40  for which the distribution of the silicon containing gas is provided by the cavity  71  circumscribed by the wall  70  and the outer surface  33  of the reactor floor  12 . The central nozzle  41 , which in the embodiment shown is located at the centre of the reactor floor  12 , is supplied with silicon containing gas via the second branch  52  (not shown here, see  FIG. 2 ). Further elements with reference numerals in this figure have already been described in the context of  FIG. 2  or  3 . 
         [0034]      FIG. 5  shows a magnified view of a section of  FIG. 4 . In particular one of the nozzles  40  is shown which furnish the supply of the silicon containing gas from the cavity  71  circumscribed by the wall  70  and an outer surface  33  of the reactor floor  12  into the reactor interior  11 . For the supply of gas to the reactor interior  11  the silicon containing gas enters the nozzle  40  through a nozzle inlet  42  and from there reaches the reactor interior  11  through a nozzle outlet  43 . While passing the nozzle  40  the gas is separated by the nozzle wall  44  from a coolant (for example cooling water) flowing, in the embodiment shown, in the compartment  34  delimited by the first wall  31  and the second wall  32 . The wall  70  is attached to the outer surface  33  of the reactor floor  12  by a welded seam  80  in a gas-tight manner. 
         [0035]      FIG. 6  is a side view of a further embodiment of the reactor floor  12 . In particular there are shown the central nozzle  41  and a first set  40   1  of several of the nozzles  40  and a second set  40   2  of several of the nozzles  40 , wherein a the distribution of the silicon containing gas is provided to the first set  40   1  of nozzles  40  and the second set  40   2  of nozzles  40  by an individual cavity  71  circumscribed by the wall  70  and the outer surface  33  of the reactor floor  12 . The central nozzle  41 , which in the embodiment shown is located at the centre of the reactor floor  12 , is supplied with silicon containing gas via the second branch  52  (not shown here, see  FIG. 2 ). The first set  40   1  of nozzles  40  and the second set  40   2  of nozzles  40  are distributed uniformly about the central nozzle  41 . In the embodiment shown here, two individual cavities  71  are provided. The wall  70  is of such a shape that each cavity  70  is circumscribed by the wall and the outer surface  33  of the reactor floor  12 . It is particularly advantageous if the cross-section of the cavity has the shape of a segment of a circle which is equal or less than a semicircle. This shape of the cross-section makes the welding process easier to carry out and to control. 
         [0036]    The invention has been described with reference to preferred embodiments. It is obvious to a person skilled in the art, however, that modifications of the construction and alterations can be made without leaving the scope of the subsequent claims. In particular, in the figures the cavity  71  was shown as having the shape of an annulus and a semicircular cross-section. This in no way constitutes a limitation of the invention, other shapes and cross-sections can be conceived of, too, like for example U-shaped with rectangular cross-section.