Systems 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 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 system 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 a level controller 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.   
     
     
         2 . The system as set forth in  claim 1  comprising a plurality of independently controlled heaters continuously disposed adjacent the crucible for establishing corresponding thermal zones through the melt, such that heat is driven uniformly by higher surface area of contact and shorter thermal path into the charge in the crucible, including solid chunks, rods or granules. 
     
     
         3 . The system as set forth in  claim 1  comprising:
 a growth chamber for enclosing an ingot pulled from the seed crystal at a crystal/melt interface; and 
 multiple pull chambers disposed with respect to the growth chamber for pulling the ingot from the melt, such that upon completion of a first ingot, a first pull chamber moves the completed first ingot out of the growth chamber and a successive pull chamber positions a successive seed crystal at the crystal/melt interface. 
 
     
     
         4 . The system as set forth in  claim 1  wherein the system does not include a lifting mechanism for vertical travel of the crucible. 
     
     
         5 . The system as set forth in  claim 1  further comprising:
 one or more individually controlled side wall heaters; 
 one or more sensors for monitoring temperature of each thermal zone and for producing signals representative of sensed temperature; and 
 a heater controller responsive to the sensor signals for activating each side wall heater and an annular heater such that an optimal thermal distribution is established across the melt and at the crystal melt interface. 
 
     
     
         6 . The system as set forth in  claim 1  further comprising a source of dopant connected to the pre melter such that a dopant concentration throughout the ingot is substantially uniform, axially and radially. 
     
     
         7 . The system as set forth in  claim 1  wherein the crucible has an aspect ratio of 4:1 to 10:1. 
     
     
         8 . The system as set forth in  claim 1  wherein the crucible has interior surfaces for containing the molten material coated with alpha or beta sintered silicon carbide or tantalum nitride. 
     
     
         9 . The system as set forth in  claim 1  wherein the crucible comprises alpha or beta sintered silicon carbide or tantalum nitride. 
     
     
         10 . 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 cell 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   a level controller having an input responsive to the load cell 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.   
     
     
         11 . The system as set forth in  claim 10  comprising a plurality of independently controlled heaters continuously disposed adjacent the crucible for establishing corresponding thermal zones through the melt, such that heat is driven uniformly by higher surface area of contact and shorter thermal path into the charge in the crucible, including solid chunks, rods or granules. 
     
     
         12 . The system as set forth in  claim 10  comprising:
 a growth chamber for enclosing an ingot pulled from the seed crystal at a crystal/melt interface; and 
 multiple pull chambers disposed with respect to the growth chamber for pulling the ingot from the melt, such that upon completion of a first ingot, a first pull chamber moves the completed first ingot out of the growth chamber and a successive pull chamber positions a successive seed crystal at the crystal/melt interface. 
 
     
     
         13 . The system as set forth in  claim 10  wherein the system does not include a lifting mechanism for vertical travel of the crucible. 
     
     
         14 . The system as set forth in  claim 10  further comprising:
 one or more individually controlled side wall heaters; 
 one or more sensors for monitoring temperature of each thermal zone and for producing signals representative of sensed temperature; and 
 a heater controller responsive to the sensor signals for activating each side wall heater and an annular heater such that an optimal thermal distribution is established across the melt and at the crystal melt interface. 
 
     
     
         15 . The system as set forth in  claim 10  further comprising a source of dopant connected to the pre melter such that a dopant concentration throughout the ingot is substantially uniform, axially and radially. 
     
     
         16 . The system as set forth in  claim 10  wherein the crucible has an aspect ratio of 4:1 to 10:1. 
     
     
         17 . The system as set forth in  claim 10  wherein the crucible has interior surfaces for containing the molten material coated with alpha or beta sintered silicon carbide or tantalum nitride. 
     
     
         18 . The system as set forth in  claim 10  wherein the crucible comprises alpha or beta sintered silicon carbide or tantalum nitride.