Systems and processes for continuous growing of ingots

Abstract

An improved system based on the Czochralski process for continuous growth of a single crystal ingot comprises a low aspect ratio, large diameter, and substantially flat crucible, including an optional weir surrounding the crystal. The low aspect ratio crucible substantially eliminates convection currents and reduces oxygen content in a finished single crystal silicon ingot. A separate level controlled silicon pre-melting chamber provides a continuous source of molten silicon to the growth crucible advantageously eliminating the need for vertical travel and a crucible raising system during the crystal pulling process. A plurality of heaters beneath the crucible establish corresponding thermal zones across the melt. Thermal output of the heaters is individually controlled for providing an optimal thermal distribution across the melt and at the crystal/melt interface for improved crystal growth. Multiple crystal pulling chambers are provided for continuous processing and high throughput.

What is claimed is: 
     
         1 . A process for improved growth of a single crystal ingot from a seed crystal positioned at a crystal/melt interface in a molten material comprising:
 containing the molten material in a low aspect ratio, wide diameter crucible for reducing convection currents and thermal variations in the melt;   melting solid crystalline material in a pre melter for providing a substantially continuous replenishment of molten material to the crucible for maintaining the crystal/melt interface at a desired level in the crucible;   providing a plurality of heaters beneath the crucible for establishing corresponding thermal zones across the melt;   controlling the thermal output of the heaters for providing an optimal thermal distribution across the melt and at the crystal/melt interface for improved crystal growth.   
     
     
         2 . A process according to  claim 1  wherein the step of providing substantially continuous replenishment of molten material to the crucible for maintaining the crystal/melt interface at a desired level further comprises:
 determining the weight of the crucible both empty and with a desired depth of melt in the crucible; 
 sensing the actual weight of the growth crucible during crystal growth; and 
 controlling the output of the pre melter based on a difference between the actual weight of crucible and melt during crystal growth and the determined weight of the crucible with a desired depth of melt by actuating a dispenser for releasing a predetermined amount of solid crystalline feedstock into the pre melter to maintain the desired depth of melt in the crucible. 
 
     
     
         3 . A system for growing an ingot from a crystal positioned at a crystal melt interface in a molten material contained in a crucible having a controlled atmosphere, the improvement comprising:
 a pre melter disposed within the controlled atmosphere of the crucible for providing a continuous source of molten crystalline feedstock to the crucible, such that the crystal melt interface is maintained at a desired level with respect to the growing ingot without vertical travel of the crucible;   the pre melter comprising a melting chamber including a first section having an inlet for receiving the source of solid crystalline feedstock and a second section including an outlet having an exit end positioned substantially at the level of the melt in the crucible for providing perturbation free distribution of the molten feedstock to the crucible; and   a heater provided adjacent the melting chamber for melting the solid crystalline feedstock;   a weir positioned in the melting chamber, for defining the first and second sections, such that the second section is filled upward from the bottom of the first section to thereby prevent any unmelted, solid crystalline feedstock from passing to the crucible.   control means responsive to the level of the crystal melt interface in the crucible and having a connection to the source of solid crystalline feedstock for controllably dispensing the solid crystalline feedstock into the pre melter such that the depth of molten material in the crucible is maintained at a desired level for optimal crystal growth; and   wherein the outlet of the melting chamber comprises a second weir having an inlet and outlet for providing continuous replenishment of molten feedstock into the crucible.   
     
     
         4 . A system for growing an ingot from a crystal, the system comprising:
 a pre melter for providing a continuous flow of molten crystalline feedstock to a crucible for growing an ingot at a crystal melt interface therein comprising:
 a melting chamber having an inlet for receiving a source of solid crystalline feedstock and an outlet having a distal end positioned substantially at the level of the crystal melt interface for providing substantially continuous replenishment of molten crystalline feedstock to the crucible; 
 a heater adjacent the melting chamber for melting the molten crystalline feedstock; and 
 a weir, provided in the melting chamber between the inlet and outlet for directing molten crystalline feedstock to flow downward beneath the weir and upward into the outlet, thereby preventing unwanted solid crystalline feedstock, by virtue of a density lower than molten feedstock, from passing through the outlet to the crucible; 
   a load sensing the weight of molten material in the crucible corresponding to an optimal level of the crystal melt interface with respect to ingot growth; and   control means having an input responsive to the means for sensing and an output lead connected to the source of solid crystalline feedstock for controllably dispensing solid crystalline feedstock to the pre melter, such that optimal ingot growth is maintained in the crucible.