Abstract:
A dopant funnel for loading dopant pellets into a dispenser tube of a dopant dispenser is disclosed. The dopant funnel has a cup connected through a restrictor to a shaft. The cup holds random oriented dopant pellets. The restrictor meters the amount and orientation of dopant pellets being removed from the cup. The shaft is in alignment with the restrictor for delivering dopant pellets from the cup to the dispenser tube.

Description:
CROSS REFERENCE 
       [0001]    This application claims priority to U.S. Provisional Application No. 61/740,809 filed Dec. 21, 2012, the disclosure of which is hereby incorporated by reference in its entirety. 
     
    
     FIELD 
       [0002]    The field relates generally to the preparation of ingots of semiconductor or solar-grade material, more particularly, to methods and devices for loading and dispensing dopant during the production of ingots. 
       BACKGROUND 
       [0003]    Single crystal silicon, which is the starting material for most processes for the fabrication of semiconductor electronic devices and solar cells, is commonly prepared by the so-called Continuous Czochralski (“CCz”) or Czochralski (“Cz”) methods. In these methods, polysilicon in the form of solid feedstock material is charged to a crucible and melted, a seed crystal is brought into contact with the molten silicon or a melt, and a single crystal is grown by slow extraction. 
         [0004]    Dopant may be added to the melt to achieve a desired resistivity in the silicon. Conventionally, the silicon melt is doped by feeding a dopant into the melt from a feed hopper located above the silicon melt. 
         [0005]    The typical loading process of the feed hopper includes individually placing small pellets into a dispenser tube of the dopant dispenser or feed hopper by hand. In some applications, an operator may need to individually position a large number of pellets, e.g., 600 or more pellets, in the dispenser tube. As will be understood, this is a very tedious process. Additionally, handling the pellets may cause contamination, and thereby degrade the quality of the silicon product. In view of the above, it can be seen that a need exists for a simple, cost-effective approach to improve the efficiency associated with loading a dopant dispenser. 
         [0006]    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 
       [0007]    A first aspect is a dopant funnel for loading dopant pellets into a dispenser tube of a dopant dispenser. The dopant funnel includes a cup for holding the dopant pellets, and a shaft. The cup has a restrictor to meter the number of dopant pellets and to orient the dopant pellets. The shaft is in alignment with the restrictor for delivering the dopant pellets from the cup to the dispenser tube. 
         [0008]    Another aspect is a method for loading a dispenser tube of a dopant dispenser for use in a crystal pulling system with a dopant funnel having a cup connected through a restrictor with a shaft. The method includes loading the cup of the dopant funnel with randomly oriented dopant pellets, positioning the shaft in alignment with the dispenser tube, and causing a vibrating movement of the dopant funnel to induce movement of the dopant pellets with respect to the dopant funnel. 
         [0009]    Various refinements exist of the features noted in relation to the above-mentioned aspects. Further features may also be incorporated in the above-mentioned aspects as well. These refinements and additional features may exist individually or in any combination. For instance, various features discussed below in relation to any of the illustrated embodiments may be incorporated into any of the above-described aspects, alone or in any combination. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a front elevation of a dopant funnel in accordance with one embodiment; 
           [0011]      FIG. 2  is a top view of the dopant funnel in accordance with  FIG. 1 ; 
           [0012]      FIG. 3  is a side view of the dopant funnel in accordance with  FIGS. 1-2 ; and 
           [0013]      FIG. 4  is a front perspective view of the dopant funnel in accordance with  FIGS. 1-3 , loading a plurality of dopant pellets into a dispenser tube of a dispenser. 
       
    
    
       [0014]    Corresponding reference characters indicate corresponding parts throughout the several views of the drawings. 
       DETAILED DESCRIPTION 
       [0015]    Referring to  FIGS. 1 and 2 , a dopant funnel for use in loading dopant is generally indicated at  100 . The funnel  100  is configured for loading dopant pellets into a dispenser tube of a dopant dispenser of a single-crystal pulling system, though other applications of the funnel are contemplated. The dopant funnel  100  is suitably made of a high purity material, such as high purity quartz, to reduce or eliminate possible contamination of the dopant pellets. 
         [0016]    The dopant funnel  100  includes a cup  110  for holding a plurality of dopant pellets  190 , as shown in  FIG. 4 . The cup  110  defines a cavity  112  connected with an opening in the form of a restrictor  114  to aid in alignment of the dopant pellets  190  as the dopant pellets pass from the cup through the restrictor. The restrictor  190  acts to meter the number of dopant pellets exiting the cup  110  during operation of the dopant funnel  100 . 
         [0017]    A shaft  120  is connected with the cup  110  around the restrictor  114  and extends outward therefrom. The shaft  120  has a straight semi-cylindrical body  126  having baffles  122  adjacent each side to aid in the alignment of the dopant pellets  190  with the shaft and prevent unaligned dopant pellets from passing thereby. The lowermost portion of the shaft  120  defines a trough  124  that has a length and a bottom  128  for supporting the dopant pellets as the dopant pellets move along the length of the trough. 
         [0018]    The baffles  122  terminate at a distance that is equal to approximately one pellet diameter length from the bottom  128  of the trough  124 . The baffles  122  are sized and shaped to allow aligned pellets  190  to pass by the baffles  122 , and to prevent unaligned pellets  190  from passing thereby. The shape and size of the baffles  122 , and their relative positions, are based on the dimensions of the pellets  190 . The baffles  122  are spaced from each other along the longitudinal axis of the trough. In other embodiments, the shaft may include at least one baffle that is positioned opposite another baffle. 
         [0019]    Dopant pellets of this embodiment have a standard or specific size and mass or weight, so that the exact amount of dopant being delivered to the crystal pulling system is known. These dopant pellets have a standard pellet diameter or width and standard pellet length. As a result, a constant wafer resistivity can be achieved by dispensing a predetermined number of pellets. During transport or loading the dopant pellets may become broken resulting in a broken dopant pellet that has a diameter or length that is less than the standard unbroken size. 
         [0020]    The shaft  120  includes at least one slot  130  located along the bottom  128  of the trough  124  for removing or extracting broken pellets during the loading process. The slot  130  has a slot length that is less than the standard pellet length and a width that is substantially equivalent to the standard pellet diameter. As the pellets  190  move across the length of the shaft  120  and over the slots  130 , broken pellets are unable to traverse the length of the slot and therefore are dropped downward through the slot  130 . 
         [0021]    With additional reference to  FIG. 4 , the construction described above enables the crystal pulling system  200  to be loaded with a dopant dispenser  202  having a known amount of dopant, which enables the dispenser to dispense a specific amount of dopant during the crystal forming process. Accordingly, the resistivity of the product can be determined by the quantity of loaded dopant in the dispenser tube  202 . 
         [0022]    The shaft  120  terminates in a delivery tube  140 . The delivery tube  140  has a passage  142  terminating in an orifice  144  sized to accept/receive a portion of the dispenser tube  204  therein, and to align the pellets  190  within the trough  124  with a passageway  206  extending through the dispenser tube. The alignment of the delivery tube  140  with the dispenser tube  204  allows the dopant pellets  190  to pass unobstructed from the shaft  120  into the delivery tube. 
         [0023]    To facilitate the movement and subsequent alignment of the pellets  190  with the passageway  206 , the funnel  100  includes a first vibrator  150  and a second vibrator  160 , as shown in  FIG. 3 . The first vibrator  150  is attached to the cup  110  to induce an initial movement of the pellets  190  for alignment and passage through the restrictor  114 . The second vibrator  160  is located along the shaft  120  to facilitate alignment and passage of the pellets  190  through the baffles  122  and along the length of the shaft. In other embodiments, more or less vibrators may be used in the same or other locations along the dopant funnel. 
         [0024]    In some embodiments, a vibrator  150 ,  160  is located adjacent to one of the restrictor  114  and the baffle  122 . 
         [0025]    In operation, an operator loads the cup  110  with randomly oriented pellets  190 . The dopant funnel  100  is aligned with the dispenser tube  204  and the delivery tube  140  is placed over the dispenser tube. The operator then activates the vibrators  150 ,  160 , which causes a vibrating movement. The vibrating movement induces the pellets  190  to move and shift in location relative to the funnel  100 . As the pellets  190  move and shift, some of the pellets are aligned with the restrictor  114  and move out of the cup  110  and down the shaft  120 . As the pellets  190  are moved between the restrictor  114  and the baffles  122  any broken pellets fall out of the funnel  100  through the slots  130 . Any unaligned pellets are then aligned as the pellets  190  pass by the baffles  122 . 
         [0026]    The time required to load the pellets may be decreased using the above method, e.g. from about 30 to 40 minutes to less than approximately 5 minutes. 
         [0027]    Once the pellets  190  are aligned and any broken or chipped pellets are expelled, the pellets pass the length of the shaft  120  and through the delivery tube  140  and into the dispenser tube  202 . 
         [0028]    Use of the above embodiments reduces the contact and thereby the risk of contamination of the dopant. As described above, the operator need not touch the pellets. Because touching with potentially contaminated hands or gloves may contaminate the dopant, reducing the contact reduces the risk of contamination. Additionally, use of the dopant funnel significantly reduces the time required to load the dispenser tubes. This reduction in risk and improved efficiency not only increases the overall production of the crystal forming system, but also lowers overall operational costs. 
         [0029]    When introducing elements of the present disclosure or the embodiments 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. 
         [0030]    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.