Apparatus and method for the production of ingots

Abstract

Apparatus and method for a crucible-less production of silicon ingots, including a support with a seed layer and a liquid layer is gradually lowered in a temperature field with a vertical gradient to solidify the liquid layer in a controlled way.

What is claimed is: 
     
         1 . A wafer with a monocrystalline structure, the wafer comprising:
 a size of at least 140 mm×140 mm;   striations or other structural and electrical properties, which display a mirror symmetry with respect to one of the diagonals of the wafer only.   
     
     
         2 . A wafer according to  claim 1 , wherein a dislocation density of the wa-fer is smaller than 10 3  cm −2 . 
     
     
         3 . A wafer according to  claim 2 , wherein the dislocation density is at least 1 cm −2 . 
     
     
         4 . A wafer according to  claim 1 , wherein a content of interstitial oxygen is less than 5×10 16  atoms/cm 3 . 
     
     
         5 . A wafer according to  claim 1 , wherein a content of nitrogen is less than 10 15  atoms/cm 3 . 
     
     
         6 . A wafer according to  claim 1 , wherein a variability of a specific resistance across a surface of the wafer is in at least three quarters of the surface less than 5%. 
     
     
         7 . A wafer with a monocrystalline structure, the wafer comprising:
 a size of at least 140 mm×140 mm;   a specific resistance, which in at least three quarters of a surface of the wafer has a variability of less than 5%; and   a mean dislocation density over a surface thereof which is less than 100/cm 2 .   
     
     
         8 . A wafer produced according to a method comprising the following steps:
 providing an apparatus for producing an ingot, the apparatus comprising a chamber to provide a controllable atmosphere and at least one means for controlling a temperature field in a given volume of growth in the chamber, wherein the temperature field has a temperature gradient in a longitudinal direction, the apparatus further comprising a support for a seed layer, the support being movable in the longitudinal direction inside the chamber and a controllable feeding apparatus for providing feedstock,   producing an ingot by:
 providing a seed layer on the support, wherein the seed layer defines a cross-sectional area of an ingot to be produced; 
 moving the support, such that the seed layer is located at a predetermined position within the volume of growth; 
 generating a temperature field with a predetermined vertical temperature gradient and a lateral temperature gradient within the volume of growth, wherein the vertical temperature gradient is in a range of 100 K/m to 10000 K/m and a lateral temperature gradient is at most 1 K/cm; 
 providing feedstock on the seed layer by way of the feeding apparatus, wherein the feeding of feedstock and the temperature field within the volume of growth are controlled such that the entire seed layer is covered with a layer of liquid feedstock; 
 lowering the support while solidifying the layer of liquid feedstock; and 
 adding more liquid feedstock from the feeding apparatus; 
   dividing the ingot into at least four columns, from which the wafer can be cut.