Abstract:
A system for growing a crystal ingot includes a crucible and a weir. The crucible has a base and a sidewall for the containment of a silicon melt therein. The weir is located along the base of the crucible inward from the sidewall of the crucible. The weir has a body connected with at least a pair of legs disposed to inhibit movement of the silicon melt therebetween.

Description:
CROSS REFERENCE 
     This application claims priority to U.S. Provisional Application No. 61/738,718 filed Dec. 18, 2012, the disclosure of which is hereby incorporated by reference in its entirety. 
    
    
     FIELD 
     This disclosure generally relates to systems and methods for the production of ingots of semiconductor or solar material and more particularly to systems and methods for reducing dislocations in the ingot by limiting or inhibiting movement within a silicon melt. 
     BACKGROUND 
     In the production of single silicon crystals grown by the Czochralski (CZ) method, polycrystalline silicon is first melted within a crucible, such as a quartz crucible, of a crystal pulling device to form a silicon melt. The puller then lowers a seed crystal into the melt and slowly raises the seed crystal out of the melt. To produce a single high quality crystal using this method, the temperature and the stability of the surface of the melt immediately adjacent to the ingot must be maintained substantially constant. Prior systems for accomplishing this goal have not been completely satisfactory. Thus, there exists a need for a more efficient and effective system and method to limit temperature fluctuation and surface disruptions in the melt immediately adjacent to the ingot. 
     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. 
     BRIEF SUMMARY 
     A first aspect is a system for growing a crystal ingot from a silicon melt. The system includes a crucible and a weir. The crucible has a base and a sidewall for containing the silicon melt therein. The weir is located along the base of the crucible at a location inward from the sidewall. The weir has a body and at least a pair of legs for inhibiting movement of the silicon melt therebetween. In some embodiments, the body is formed as a single unit with at least one of the legs. 
     Another aspect is a method for growing a crystal ingot. The method includes providing a crucible with a weir that has an inner leg and an outer leg forming a space therebetween, placing a feedstock material into the crucible at a location that is outward of the weir; melting the feedstock material to form a melt that is able to flow to a location that is inward of the weir; and causing the melt to cool to form a crystal ingot. 
     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 
         FIG. 1  is a side cross sectional view of a crystal growing system in accordance with one embodiment; 
         FIG. 2  is a partial cross sectional view of a weir used in the crystal growing system of  FIG. 1 ; 
         FIG. 3  is a partial cross sectional view of a crystal growing system in accordance with another embodiment; 
         FIG. 4  is a top perspective view of a weir used in the crystal growing system of  FIG. 3 ; 
         FIG. 5  is a bottom perspective view of the weir of  FIG. 4 ; 
         FIG. 6  is a partial cross sectional view of the weir of  FIGS. 4-5 ; 
         FIG. 7  is a top elevation of  FIG. 4-6 ; 
         FIG. 8  is a partial cross sectional view of the crystal growing system of  FIG. 3  illustrating the temperature field and streamlines of the melt; 
         FIG. 9  is a partial cross sectional view of a crystal growing system in accordance with another embodiment; 
         FIG. 10  is a top perspective view of a weir used in the crystal growing system of  FIG. 9 ; 
         FIG. 11  is a top elevation of the weir of  FIG. 10 ; 
         FIG. 12  is cross sectional view of the weir of  FIGS. 10-11 ; 
         FIG. 13  is a side elevation of the weir of  FIGS. 10-12 ; 
         FIG. 14  is a partial cross sectional view of a crystal growing system in accordance with yet another embodiment; and 
         FIG. 15  is a partial cross sectional view of a crystal growing system in accordance with still another embodiment. 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a crystal growing system is shown schematically and is indicated generally at  100 . The crystal growing system  100  is used to produce a large crystal or ingot by the Czochralski method. The crystal growing system  100  includes a crucible  110  that contains a silicon melt  112  from which an ingot  114  is being pulled from the melt by a puller  134 . 
     During the crystal pulling process, a seed crystal  132  is lowered by a puller or puller system  134  into a melt  112  and then slowly raised from the silicon melt. As seed crystal  132  is slowly raised from melt  112 , silicon atoms from the melt align themselves with and attach to the seed crystal to form an ingot  114 . 
     The crucible  110  has a sidewall  136  and a base  138 . The sidewall  136  extends around the circumference of base  138  to form a cavity. Solid feedstock material  116  may be placed into the cavity of crucible  110  from feeder  118  through feed tube  120 . 
     The feedstock material  116  is at a much lower temperature than the surrounding melt  112  and absorbs heat from the melt as the feedstock material&#39;s temperature rises, and as the feedstock material itself melts. As feedstock material  116  (sometimes referred to as “cold feedstock”) absorbs energy from melt  112  the temperature of the surrounding melt falls proportionately. 
     As discussed herein, the system is described in relation to the Czochralski method of producing single crystal ingots. However, the system disclosed herein may also be used to produce multi-crystalline ingots, such as by a directional solidification process. 
     The amount of feedstock material  116  added is controlled by feeder  118 , which is responsive to activation signals from a controller  122 . The amount of cooling of the melt  112  is precisely determined and controlled by controller  122 . Controller  122  either adds or does not add feedstock material  116  to adjust the temperature and the mass of the melt  112 . The addition of feedstock material  116  may be based on the mass of the silicon in the crucible, e.g., by measuring the weight or measuring liquid height of the melt. As feedstock material  116  is added to melt  112 , the surface of the melt may be disturbed. This disturbance also affects the ability of silicon atoms of the melt  112  to properly align with the silicon atoms of the seed crystal  132 . 
     Heat is provided to crucible  110  by heaters  124 ,  126 , and  128  located at suitable positions about the crucible. Heat from heaters  124 ,  126 , and  128  initially melt the solid feedstock material  116  and then maintains melt  112  in a liquefied state. Heater  124  is generally cylindrical in shape and provides heat to the sides of the crucible  110 , and heaters  126  and  128  provide heat to the bottom of the crucible. In some embodiments, heaters  126  and  128  are generally annular in shape. 
     Heaters  124 ,  126 , and  128  are resistive heaters coupled to controller  122 , which controllably applies electric current to the heaters to alter their temperature. A sensor  130 , such as a pyrometer or like temperature sensor, provides a continuous measurement of the temperature of melt  112  at the crystal/melt interface of the growing single crystal ingot  114 . Sensor  130  also may be directed to measure the temperature of the growing ingot. Sensor  130  is communicatively coupled with controller  122 . Additional temperature sensors may be used to measure and provide temperature feedback to the controller with respect to points that are critical to the growing ingot. While a single communication lead is shown for clarity, one or more temperature sensor(s) may be linked to the controller by multiple leads or a wireless connection, such as by an infra-red data link or another suitable means. 
     The amount of current supplied to each of the heaters  124 ,  126 , and  128  by controller  122  may be separately and independently chosen to optimize the thermal characteristics of melt  112 . In some embodiments, one or more heaters may be disposed around the crucible to provide heat. 
     As discussed above, seed crystal  132  is attached to a portion of puller  134  located over melt  112 . The puller  134  provides movement of seed crystal  132  in a direction perpendicular to the surface of melt  112  allowing the seed crystal to be lowered down toward or into the melt, and raised up or out of the melt. To produce a high quality ingot  114 , the melt  112  in an area adjacent to seed crystal  132 /ingot  114  must be maintained at a substantially constant temperature and surface disruptions must be minimized. 
     To limit the surface disturbances and temperature fluctuations in the area immediately adjacent to seed crystal  132 /ingot  114 , a baffle or weir  150  is placed in the cavity of the crucible  110  to separate the melt  112  into an inner melt portion and an outer melt portion. 
     With additional reference to  FIG. 2 , the weir  150  has a body  152 , an outer leg  154 , and an inner leg  156 . Both outer leg  154  and inner leg  156  extends downward from the upwardly extending body  152  and rest against a top surface of base  138  of crucible  110 . The outer leg  154  and inner leg  156  are separated by a space that forms an intermediate melt portion. The outer melt portion is between sidewall  136  of crucible  110  and weir  150 . The intermediate portion is between the outer leg  154  and the inner leg  156  of weir  150 . The inner melt portion is inward from weir  150  and is adjacent to the seed crystal  132 /ingot  114 . 
     The outer leg  154  and inner leg  156  limit movement of melt  112  between the melt portions. Movement of melt  112  between the melt portions may be permitted through passages  158 ,  160  in a lower section of each the outer leg  154  and inner leg  156 , respectively. 
     The movement of the melt  112  is substantially limited to the location of the passages  158 ,  160 . Placing the passages  158 ,  160  along a lower section of outer leg  154  and inner leg  156 , confines the movement of melt  112  to along the base  138  of the crucible  110 . Any movement of melt  112  into the inner melt portion is at a direct opposite location from the top of the melt, where ingot  114  is being pulled. This confinement of the melt movement limits surface disruptions and temperature fluctuations along the top of the inner melt portion of the melt  112 . 
     The passages  158 ,  160  permit controlled movement of melt  112  between the outer melt portion and the intermediate melt portion and the inner melt portion. Inhibiting or limiting the melt movement between the melt portions allows silicon material in the outer melt portion to heat to a temperature that is approximately equivalent to the temperature of the inner melt portion as the silicon material passes into and through the intermediate melt portion. 
     The passages may be aligned to allow controlled flow of the melt from the outer melt portion, through the intermediate melt portion, and into the inner melt portion. In some embodiments, the passages through the outer leg may be unaligned with the passages of the inner leg for further restricting the flow from the outer melt portion, through the intermediate portion, and into the inner melt portion. 
     Referring to  FIGS. 3-8 , a crystal growing system  200  in accordance with another embodiment is shown. The crucible  210  has a sidewall  236  extending around the circumference of a concave base  238  to form a cavity. 
     Heat is provided to crucible  210  from heaters  226  and  228  to initially melt material within the crucible  210  and then to maintain melt  212  in a liquefied state. Heaters  226  and  228  are generally annular in shape and arranged about the base  238  of the crucible  210 . Heaters  226  and  228  may be resistive heaters. 
     As discussed above, a seed crystal is lowered into the melt  212 , and then slowly raised out of the melt. To limit the surface disturbances and temperature fluctuations in the area immediately adjacent to ingot  214 , a weir  250  is placed within the crucible  210  to separate the melt  212  into an inner melt portion and an outer melt portion. 
     The weir  250  has a body  252 , an outer leg  254 , and an inner leg  256 . Both outer leg  254  and inner leg  256  extend downward from the upwardly extending body  252  and rest against an inner surface of crucible  210 . The outer leg  254  and inner leg  256  are separated by a space that forms an intermediate melt portion between the outer leg  254  and the inner leg  256  of weir  250 . The inner melt portion is inward from weir  250 , adjacent to the ingot  214 . 
     Movement of melt  212  between the various melt portions is limited by outer leg  254  and inner leg  256  to the bottom of the melt, along the base  238  of the crucible  210 , directly opposite from ingot  214 . This confinement of the melt movement limits surface disruptions and temperature fluctuations along the top of the inner melt portion of the melt  212 , which is adjacent to the pulled ingot  214 . Inhibiting the melt movement to along base  238 , adjacent heaters  226  and  228 , allows silicon material from the outer melt portion to heat to a temperature that is approximately equivalent to the temperature of the inner melt portion as the silicon material passes through the intermediate melt portion. 
     With specific reference to  FIG. 8 , streamlines and temperature fields during operation are shown for crystal growing system  200 . The outer melt portion is cooler than either the intermediate or inner melt portion. Additional material is added to the outer melt portion during operation of the crystal growing system lowering the temperature of the outer melt portion. As discussed above, the additional material is cooler than the melt and therefore absorbs heat from the surrounding melt when added to the melt. Forcing the cooler melt material to move along the surface of the crucible adjacent to the heaters allow heat to be transferred into the cooler material before the cooler material enters the inner melt portion. 
     Referring to  FIGS. 9-13 , a crystal growing system  300  in accordance with another embodiment is shown. A melt  312  is contained within a crucible  310  that has a sidewall  336  surrounding a concave base  338 . To limit the surface disturbances and temperature fluctuations of the melt  312  in a center area of the crucible  310 , a weir  350 , and a separator  360  are placed within the crucible  310  to separate the melt  312  into an outer melt portion, an intermediate melt portion, and an outer melt portion. The inner melt portion forms the center area that is inward from the weir  350  and separator  360 . 
     The weir  350  is a cylindrical body with an open top and bottom. The bottom  352  of the weir  350  is located adjacent to the inner surface of the crucible  310 . The separator  360  is a circular ring  362  having a convex shape. The diameter of the outer circumference of the separator  360  is less than the diameter of the inner circumference of the weir  350 . The separator  360  may have a radial passage  364  extending along a lower edge. Movement of the melt  312  is permitted through radial passage  364 . 
     The outer melt portion is between sidewall  336  of crucible  310  and weir  350 . The intermediate portion is between weir  350  and separator  360 . The inner melt portion is inward from separator  360 . 
     Movement of melt  312  between the various melt portions is limited to along the inner surface of the crucible  310 . Inhibiting the melt movement between the various melt portions allows silicon material in outer melt portion to heat to a temperature that is approximately equivalent to the temperature of the inner melt portion as the silicon material passes through the intermediate melt portion. 
     The passage  364  in the separator  360  may be aligned with a passage in the weir  350  to allow controlled flow of the melt from the outer melt portion through the intermediate melt portion and into the inner melt portion. In some embodiments, the passage through the body may be unaligned with the passage of the separator for restricting the flow from the outer melt portion through the intermediate portion and into the inner melt portion. 
     In other embodiments, the separator  360  may have a height that is greater than a height of the weir  350 . In still other embodiments, the separator  360  may include a top portion that extends substantially parallel to the weir  350 . 
     Referring to  FIG. 14 , a crystal growing system  400  in accordance with another embodiment is shown. The crystal growing system  400  includes a weir  450 . The weir  450  has a body  452 , an outer leg  454 , an inner leg  456 , and an upper leg  470 . The legs  454 ,  456 , and  470  extend from the body  452  to rest against an inner surface of the crucible. Each of the legs  454 ,  456 , and  470  are separated by a space that defines a melt portion. Note that other numbers of legs are contemplated within the scope of the present disclosure. 
     Movement of the melt between the various melt portions is limited by the legs  454 ,  456 , and  470  to the bottom of the melt, along the base of the crucible. This confinement of the melt movement limits surface disruptions and temperature fluctuations along the top of an inner melt portion of the melt, which is adjacent to a pulled ingot. Inhibiting the melt movement to along the base, adjacent to the heaters, allows silicon material from an outer melt portion to heat to a temperature that is approximately equivalent to the temperature of the inner melt portion as the silicon material passes through the intermediate melt portions. 
     Referring to  FIG. 15 , a crystal growing system  500  in accordance with another embodiment is shown. The crystal growing system  500  includes a weir  550 . The weir  550  has a body  552 , an outer leg  554 , an inner leg  556 , an upper leg  570 , and a fourth leg  572 . The legs  554 ,  556 ,  570 , and  572  extend from the body  552  to rest against an inner surface of crucible. Each of the legs  554 ,  556 ,  570 , and  572  are separated by a space that defines a melt portion. 
     Movement of the melt between the various melt portions is limited by the legs  554 ,  556 ,  570 , and  572  to the bottom of the melt, along the base of the crucible. This confinement of the melt movement limits surface disruptions and temperature fluctuations along the top of an inner melt portion of the melt, which is adjacent to a pulled ingot. Inhibiting the melt movement to along the base, adjacent to the heaters, allows silicon material from an outer melt portion to heat to a temperature that is approximately equivalent to the temperature of the inner melt portion as the silicon material passes through the intermediate melt portions. 
     In a method of one embodiment for growing a single crystal ingot, the weir and feedstock material are placed in the crucible. Heaters are placed adjacent to the crucible to provide heat for liquefying or melting the feedstock material, forming a melt. The seed crystal is lowered into and then slowly raised out of the melt to grow the ingot from the seed crystal. As the seed crystal is slowly raised, silicon atoms from the melt align with and attach to the silicon atoms of the seed crystal allowing the ingot to grow larger and larger. 
     The feedstock material may be placed in an area outside of the weir. As the feedstock material outside of the weir melts, the melt is allowed to move from the outer melt portion to the intermediate melt portion and then into the inner melt portion. The movement of the melt between the various melt portions is limited to passages through the outer leg and inner leg of the weir. 
     In other embodiments, the weir does not include passages between legs. In these embodiments movement of the melt from the outer area into the inner area is limited to movement under the weir. 
     Inhibiting movement of the melt between the melt portions to movement along the base allows the melt temperature to increase as the melt passes from the outer melt portion to the intermediate melt portion and then into the inner melt portion. By the time the melt reaches the inner melt portion, the melt is substantially equivalent in temperature to the melt already in the inner melt portion. Raising the temperature of the melt before reaching the inner melt portion reduces the temperature fields within the inner melt portion. The controller may act to maintain a substantially constant temperature within the inner melt portion. 
     Further, inhibiting movement of the melt between the melt portions to movement along the base allows the surface of the inner melt portion to remain relatively undisturbed. The weir substantially prevents disturbances in the outer area from disrupting the surface of the inner melt portion by substantially containing the energy waves produced by the disturbances in the outer melt portion. The disturbances are also inhibited by the location of the passages. The passages are only along the bottom of each leg, which allows movement of the melt into the inner melt portion without disrupting the surface stability of the inner melt portion. 
     In some embodiments, the temperature of the inner melt portion may suitably be measured at a location immediately adjacent the growing ingot by a sensor. The sensor is connected with the controller. The controller adjusts the temperature of the melt by supplying more or less current to the heaters and by supplying more or less feedstock material to the melt. The controller is also capable of simultaneously supplying feedstock material while the seed crystal is raised from the melt and growing the ingot. 
     The presently disclosed systems provide an inner melt portion with a larger surface area than previous two weir systems that included vertically extending, tubular weirs. Thus, the presently disclosed systems provide a high melt-gas surface area near the crystal ingot while maintaining a plurality of melt zones below the surface of the melt. One advantage of the increased melt-gas surface area of the inner melt portion is that it decreases the amount of oxygen in the crystal ingot. Other advantages of the present systems include improvements in the pull rate, dam/crucible ablation rate, heater power, and power requirements. 
     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. 
     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 drawing[s] shall be interpreted as illustrative and not in a inhibiting sense.