Single crystal ingots with reduced dislocation defects and methods for producing such 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 high purity single crystal ingot characterized by reduced dislocation defects and more uniform resistivity or conductivity axially and radially made by the process comprising:
 growing the single crystal ingot from a seed crystal held at a crystal/melt interface in a wide diameter, low aspect ratio crucible for preventing formation of convection currents and minimizing oxygen in the melt, wherein said crucible includes a weir surrounding the crystal;   melting crystalline feedstock and providing dopant such that static thermal conditions are maintained at the crystal/melt interface during replenishment of the melt in the crucible; and   separately controlling a plurality of heaters disposed beneath the crucible for establishing controllable thermal zones across the melt, such that a uniform thermal distribution and is maintained across the radius of the growing ingot.   
     
     
         2 . The high purity single crystal ingot as set forth in  claim 1  wherein melting crystalline feedstock and providing dopant is conducted in a pre-melter communicating with the crucible. 
     
     
         3 . The high purity single crystal ingot as set forth in  claim 1  wherein the weir defines a melting region surrounding the crystal. 
     
     
         4 . The high purity single crystal ingot as set forth in  claim 1  wherein the weir rests on a bottom of the crucible or is supported by support means provided on the inner walls of the crucible, and the top of the weir extends above the surface of the melt. 
     
     
         5 . The high purity single crystal ingot as set forth in  claim 1  wherein apertures are provided in that portion of the weir extending beneath the surface of the melt to enable a desired thermal distribution in the melt. 
     
     
         6 . The high purity single crystal ingot as set forth in  claim 1  wherein providing a plurality of separately controllable heaters beneath the crucible establishes controllable thermal zones at the crystal melt interface. 
     
     
         7 . The high purity single crystal ingot as set forth in  claim 1  wherein the ingot is a silicon ingot. 
     
     
         8 . The high purity single crystal ingot as set forth in  claim 1  wherein the crucible includes an outer sidewall, the weir being disposed interior to the crucible sidewall, the weir being closer to the crystal than to the sidewall during growth of the single crystal ingot. 
     
     
         9 . The high purity single crystal ingot as set forth in  claim 1  wherein a heat shield is disposed above the crucible. 
     
     
         10 . The high purity single crystal ingot as set forth in  claim 1  wherein the crucible has a ratio of its diameter to its height of at least 4:1. 
     
     
         11 . The high purity single crystal ingot as set forth in  claim 1  wherein the crucible has a ratio of its diameter to its height of at least 8:1. 
     
     
         12 . The high purity single crystal ingot as set forth in  claim 1  wherein the crucible is not raised or lowered during growth of the single crystal ingot. 
     
     
         13 . The high purity single crystal ingot as set forth in  claim 1  wherein the ingot is a single crystal silicon ingot, the method comprising melting a charge of granular polysilicon material before the single crystal silicon ingot is grown, the diameter of the granular polysilicon material being less than 1 mm. 
     
     
         14 . The high purity single crystal ingot as set forth in  claim 13  comprising providing melted polysilicon to the crucible and into the charge of granular polysilicon material while melting the charge to wet the granules and provide a large area of thermal contact between granules to accelerate the melting process. 
     
     
         15 . The high purity single crystal ingot as set forth in  claim 1  comprising monitoring an activation time and power consumption of each heater, the thermal output of each heater being controlled based on the activation time and/or power consumption. 
     
     
         16 . The high purity single crystal ingot as set forth in  claim 1  wherein the melt includes a plurality of thermal zones, each thermal zone being produced by a separate heater, the method comprising:
 sensing the temperature of each thermal zone; 
 transmitting a signal related to each sensed temperature to a controller; and 
 controlling the thermal output of each heater based on the sensed temperature of the corresponding thermal zone. 
 
     
     
         17 . A process for producing a high purity single crystal silicon ingot characterized by reduced dislocation defects and more uniform resistivity or conductivity axially and radially, the process comprising:
 growing the single crystal silicon ingot from a seed crystal held at a crystal/melt interface in a wide diameter, low aspect ratio crucible having a ratio of diameter to height of at least 4:1 for preventing formation of convection currents and minimizing oxygen in the melt, the crucible not being raised or lowered during growth of the single crystal silicon ingot, wherein said crucible includes:   an outer sidewall; and   a weir disposed interior to the crucible sidewall and surrounding the crystal, the weir being closer to the ingot than to the sidewall during growth of the ingot;   melting crystalline feedstock and providing dopant such that static thermal conditions are maintained at the crystal/melt interface during replenishment of the melt in the crucible; and   separately controlling a plurality of heaters disposed beneath the crucible for establishing controllable thermal zones across the melt, such that a uniform thermal distribution and is maintained across the radius of the growing ingot.   
     
     
         18 . The process as set forth in  claim 17  wherein a heat shield is disposed above the crucible. 
     
     
         19 . The process as set forth in  claim 17  comprising:
 melting a charge of granular polysilicon material before the single crystal ingot is grown, the diameter of the granular polysilicon material being less than 1 mm; and 
 providing melted polysilicon to the crucible and into the charge of granular polysilicon material while melting the charge to wet the granules and provide a large area of thermal contact between granules to accelerate the melting process. 
 
     
     
         20 . The process as set forth in  claim 17  wherein the melt includes a plurality of thermal zones, each thermal zone being produced by a separate heater, the method comprising:
 sensing the temperature of each thermal zone; 
 transmitting a signal related to each sensed temperature to a controller; and 
 controlling the thermal output of each heater based on the sensed temperature of the corresponding thermal zone.