Abstract:
A tool for harvesting polycrystalline silicon-coated rods from a chemical vapor deposition reactor includes a body including outer walls sized for enclosing the rods within the outer walls. Each outer wall includes a door for allowing access to at least one of the rods.

Description:
CROSS-REFERENCE 
       [0001]    This application claims priority to U.S. Provisional Patent Application No. 61/453,996 filed Mar. 18, 2011, the entire disclosure of which is hereby incorporated by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    Ultrapure polycrystalline silicon used in the electronic and solar industry is often produced through deposition from gaseous reactants via a chemical vapor deposition (CVD) process conducted within a reactor. 
         [0003]      FIGS. 1 and 2  show an arrangement of silicon rods  100  within a CVD reactor (the reactor is omitted for clarity). Individual silicon rods  100  are coupled together in pairs by silicon bridges  102 . The rods  100  are connected to a plate  104 . The plate  104  of rods  100  is disposed within a housing of a CVD reactor. Each pair of coupled rods  100  has a characteristic U-shape. The rods  100  are arranged in three concentric circles. Twelve rods  100  are disposed along the inner circle, 18 rods along the middle circle and 24 rods along the outer circle, for a total of 54 rods. 
         [0004]    One such process used to produce ultrapure polycrystalline silicon in a CVD reactor is referred to as a Siemens process. Silicon is deposited on the surface of the rods  100  in this process and the rods  100  are used as seeds to start the process. Gaseous silicon-containing reactants flow through the reactor and deposit silicon onto the surface of the rods  100 . The gaseous reactants (i.e., gaseous precursors) are silane-containing compounds such as halosilanes or monosilane and are heated to temperatures above 1000° C. Under these conditions the gaseous reactants decompose on the surface of the rods  100  so that silicon is deposited according to the following overall reaction: 
         [0000]      2HSiC 1   3 →Si+2HCl+SiCl 4 .
 
         [0005]    The process is stopped after a layer of silicon having a predetermined thickness has been deposited on the surface of the rods  100 . The silicon rods are then harvested from the CVD reactor for further processing. 
         [0006]    Traditional tools are designed to extract two rods  100  from the CVD reactor in one operation. This tool, commonly known as a “partner”, is lowered around one pair of rods  100  at a time and fastened to a portion of the rods. The tool is then lifted to extract the pair of rods  100  from the reactor. The rods are then removed and stored for processing. 
         [0007]    Several drawbacks are apparent when using the traditional tool to extract the rods  100  from the CVD reactor. First, the harvesting procedure must be performed many times. For a 54 rod reactor, the procedure has to be performed 27 times, resulting in a time-consuming procedure. Second, the tool is cumbersome and difficult to operate within the narrow spans between the rods  100  and neighboring rods can be damaged during removal of adjacent rods from the reactor. Third, after the first pair of rods  100  has been extracted from the reactor, the tool is unavailable for further use until the extracted pair of rods  100  has cooled because the rods cannot be removed from the tool until they have cooled. This cooling time delays the removal of the remaining rods  100 , resulting in a longer shutdown of the reactor. Lastly, it can be difficult to lower the tool along a straight-forward track around the pairs of rods  100  since it cannot be guided easily. 
         [0008]    This Background section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art. 
       SUMMARY 
       [0009]    One aspect is directed to a tool for harvesting polycrystalline silicon-coated rods from a chemical vapor deposition reactor comprising a body including outer walls sized for enclosing the rods within the outer walls. Each outer wall includes a door for allowing access to at least one of the rods. 
         [0010]    Another aspect is directed to a method of harvesting polycrystalline silicon-coated rods from a chemical vapor deposition reactor having a reactor plate. The method comprises positioning a harvesting tool atop the reactor plate, outer walls of tool being disposed outward of the rods. The method further comprises inserting forks into slots of the tool, and holding and detaching the rods form the reactor plate using the forks. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a perspective view of a plurality of pairs of rods connected to a plate; 
           [0012]      FIG. 2  is a top plan view of  FIG. 1 ; 
           [0013]      FIG. 3  is a perspective view of  FIG. 1  showing a tool for removing the rods from a CVD reactor being lowered over the rods; 
           [0014]      FIG. 4  is a side view of tool lowered in place over the rods; 
           [0015]      FIG. 5  is a top plan view of  FIG. 4  with a top portion of the outer shell removed; 
           [0016]      FIG. 6  is a perspective view of an enlarged portion of  FIG. 4 ; 
           [0017]      FIG. 7  is a perspective view of the tool and rods of  FIG. 4  being lowered onto a revolving platform; 
           [0018]      FIG. 8  is a top plan view of tool in a closed configuration; 
           [0019]      FIG. 9  is a top plan view of the tool of  FIG. 8  showing the tool in an open configuration; 
           [0020]      FIG. 10  is a top plan view of the revolving platform of  FIG. 7  in a closed configuration; 
           [0021]      FIG. 11  is a top plan view of the revolving platform of  FIG. 10  in an open configuration; 
           [0022]      FIG. 12  is a perspective view of the tool and revolving platform in an open configuration; and 
           [0023]      FIG. 13  is a perspective view of the tool and revolving platform in a closed configuration; 
       
    
    
       [0024]    Like reference symbols in the various drawings indicate like elements. 
       DETAILED DESCRIPTION 
       [0025]    The disclosure is directed to a tool  150  able to extract and safely handle a set of rods  100  from a CVD reactor (i.e., the total number of rods in the reactor) at the same time. In this embodiment, the tool is capable of handling a full or entire set of rods from the reactor, rather than merely a portion of subset of the rods. As described above, when a silicon deposition process reaches its maximum extent or completion, i.e. the thickness of the layer of deposited silicon cannot be increased any further, the rods  100  are removed (i.e., harvested) from the reactor. 
         [0026]    The tool  150  described herein is able to simultaneously grasp and extract more than one pair of rods  100  from a CVD reactor. In the example embodiment with a CVD reactor having 54 rods, the tool  150  is capable of removing all of the rods  100  from the reactor simultaneously. The new tool  150  thus reduces the amount of time required to remove the rods  100  from the CVD reactor and increases the throughput of the reactor. 
         [0027]    The tool  150  of this embodiment, as shown in  FIGS. 3-5 , comprises a body, e.g., a metallic structure, with a dodecahedral section  152  which is lowered in between the rods until it rests on the reactor plate  104 . The inner metallic walls of the tool  150  are designed to avoid any contact with the silicon bridge  102  coupling each pair of rods  100  while the tool is in motion. 
         [0028]    The internal space  154  of the tool  150  is arranged in three large sections  160 ,  162 ,  164  (best seen in  FIGS. 9 and 12 ), each of which is sized to hold eighteen rods  100 . Each section  160 ,  162 ,  164  comprises two cabinets  165  for the inner circle, one cabinet  165  for the middle circle and four cabinets  165  for the outer circle. 
         [0029]    As shown in  FIGS. 3-5 , the tool  150  has a dodecahedral shape. Each side of the tool is equipped with three panels  170  (“floating” panels), and each panel operates as a door to allow operators to access the harvested rods. All the panels  170  are provided with vents, e.g., narrow slits, to expedite rapid cooling of the rods  100 . 
         [0030]    In order to prevent the tool  150  from bumping into the rods  100  or to avoid misalignments while being lowered the tool is slid along two external shafts  180  ( FIG. 7 ) which guide the tool  150  with respect to the reactor plate  104 . The two external shafts  180  are shown only in  FIG. 7 , where they are also used to guide the tool  150  onto a revolving platform  200 , described in greater detail below. 
         [0031]    As shown in  FIG. 6 , once the tool  150  is positioned atop the reactor plate  104 , forks  190  are inserted in appropriate slots  192  at the bottom of each section  160 ,  162 ,  164  of the tool. The forks  190  detach the rods  100  from the plate  104  and hold the rods while the tool  150  is lifted up from the plate. A total of twelve forks  190  are used in the tool in this embodiment: six forks are designed to hold five rods, whereas the other six forks hold four rods. 
         [0032]    The tool  150  is placed on a revolving platform  200  as shown in  FIG. 7  after the rods  100  have been removed from the CVD reactor with the tool  150 . The first step for harvesting silicon is to open one at a time the outer panels  170  and collect the rods  100  off of the outer ring.  FIGS. 9 ,  11 , and  12  show the tool  150  in this open configuration.  FIGS. 8 ,  10 , and  13  show the tool  150  in the closed configuration. The system of inner walls which keep the rods  100  segregated permits operators to easily break one single rod at a time into ingots of about 5 kilograms instead of handling a whole one. This step is carried out under safe conditions as breakage of adjacent rods  100  is prevented. 
         [0033]    After the removal of the 24 outer rods  100 , the second step is the collection of the eighteen rods through the middle doors. The third step consists in the removal of the inner rods  100 . To facilitate this operation, two sections  160 ,  162 , or  164  of the tool  150  are opened by means of a mechanism or system disposed inside the revolving platform  200 . At the end of the rod  100  extraction, sections  160 ,  162 ,  164  and panels  170  are closed, forks  190  are removed and the tool  150  is ready to harvest another set of rods  100  from a CVD reactor. 
         [0034]    To avoid silicon contamination from metals on the inner surfaces of the tool  150 , the inner surfaces of the tool likely to be in contact with the rods  100  are lined with a polymeric material such as polytetrafluoroethylene (PTFE). Moreover, use of the tool  150  described herein results in the reduced handling of rods  100  compared to known tools. This reduced handling of the rods  100  increases the quality of silicon produced with the CVD reactor as the likelihood of contamination of the silicon is greatly reduced. 
         [0035]    As shown in  FIG. 9 , the operator can enter between the three sections  160 ,  162 ,  164 , open the inner doors and remove the twelve inner rods  100 . This solution results in ergonomic advantages because the distance between the inner rods  100  and the operator&#39;s body as shown in  FIG. 9  is less than the distance between the inner rods and the operator&#39;s body outside the tool  150 . 
         [0036]    Compared to traditional tools, the tool  150  described above achieves several advantages. First, the down time of the reactor is significantly as the rods  100  are removed in one operation, rather than 27 separate steps. Second, the rods  100  can be left to cool inside the tool  150  whereas with traditional tools this operation takes place with the rods still disposed within the reactor. Second, the quality of the silicon produced is greatly increased as the product handling is reduced to a minimal level. Moreover, parts in contact with the silicon are made from or coated with PTFE. Third, the risk of the rods  100  contacting each other during removal from the reactor is greatly reduced or eliminated since all the rods are withdrawn at the same time and held in place with the forks  490 . Fourth, an operator of the tool  150  is able to open the tool and easily access the rods  100  disposed in the center of the tool. 
         [0037]    While the invention has been described in terms of various specific embodiments, it will be recognized that the invention can be practiced with modification within the spirit and scope of the claims. 
         [0038]    When introducing elements of the present invention or the embodiment(s) thereof, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. The use of terms indicating a particular orientation (e.g., “top”, “bottom”, “side”, etc.) is for convenience of description and does not require any particular orientation of the item described. 
         [0039]    As various changes could be made in the above constructions and methods without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.