Process and apparatus for producing a single crystal of semiconductor material

Abstract

A process for producing a single crystal of semiconductor material, in which fractions of a melt, are kept in liquid form by a pulling coil, solidify on a seed crystal to form the growing single crystal, and granules are melted in order to maintain the growth of the single crystal. The melting granules are passed to the melt after a delay. There is also an apparatus which is suitable for carrying out the process and has a device which delays mixing of the molten granules and of the melt.

What is claimed is:  
     
         1 . A process for producing a single crystal of semiconductor material, comprising 
 maintaining fractions of a melt in a liquid state by a pulling coil;    solidifying said liquid on a seed crystal to form a growing single crystal;    melting granules of semiconductor material in order to maintain growth of the single crystal; and    passing said melting granules to the melt after a delay.    
     
     
         2 . The process as claimed in  claim 1 , comprising 
 passing the melting granules through a system of passages to the melt.    
     
     
         3 . The process as claimed in  claim 2 , 
 wherein the melting granules are passed through a meandering system of passages to the melt.    
     
     
         4 . The process as claimed in  claim 1 , 
 wherein the melting granules have to overcome at least one barrier on the way to the melt.    
     
     
         5 . The process as claimed in  claim 1 , 
 wherein the melting granules travel a distance of at least 25 mm before reaching the melt.    
     
     
         6 . The process as claimed in  claim 1 , comprising 
 completely melting the granules; and then feeding said granules to the melt.    
     
     
         7 . The process as claimed in  claim 1 , comprising 
 effecting the melting of the granules and maintaining of the melt in the liquid state by an inductive energy supply; and    wherein the two operations are inductively decoupled.    
     
     
         8 . The process as claimed in  claim 1 , comprising 
 melting the granules in an outer region of a vessel which is arranged above the growing single crystal; and    passing said granules to a central opening in the vessel and, from there, to the melt.    
     
     
         9 . An apparatus for producing a single crystal, comprising 
 a vessel which is arranged above a growing single crystal;    a conveyor device for feeding granules into the vessel;    a melting coil for melting the granules;    a pulling coil for maintaining a melt on the growing single crystal;    the melting granules passing through openings in the vessel and the pulling coil to the melt, so as to form a melt neck, and solidifying fractions of the melt maintaining growth of the single crystal; and    said vessel having a device which delays mixing of molten granules and of the melt.    
     
     
         10 . The apparatus as claimed in  claim 9 , further comprising 
 a protective shield which separates a space around the vessel in a dustproof manner from a space around the growing single crystal.    
     
     
         11 . The apparatus as claimed in  claim 9 , further comprising 
 covers which are arranged above the melting coil and which the granules strike when they are fed into the vessel.    
     
     
         12 . The apparatus as claimed in  claim 9 , further comprising 
 a device for cooling the vessel.    
     
     
         13 . The apparatus as claimed in  claim 12 , comprising 
 a water-cooled metal plate which is separated from the vessel by a narrow gap, thus effecting radiant and convective cooling.    
     
     
         14 . The apparatus as claimed in  claim 9 , comprising 
 means for mounting the vessel so that it can rotate about an axis of rotation, said vessel consists of quartz and has walls made from quartz which divide the interior of the vessel into concentric regions, these regions being in communication with one another and forming a system of passages which the melting granules have to overcome before they can pass between the opening in the vessel and an ingot of semiconductor material which projects through the opening to reach the melt.    
     
     
         15 . The apparatus as claimed in  claim 14 , 
 wherein the axis of rotation of the vessel is tilted about an angle α.    
     
     
         16 . The apparatus as claimed in  claim 9 , 
 wherein the vessel comprises a coolable plate of semiconductor material and has walls made from quartz which divide the interior of the vessel into concentric regions, these regions being in communication with one another and forming a system of passages which the melting granules have to overcome before they can pass through the opening in the vessel, which is designed as a section of pipe, to the melt, and the apparatus comprising a radiation heating means for heating a surface of the melt neck and the semiconductor material flowing through the section of pipe.    
     
     
         17 . The apparatus as claimed in  claim 9 , 
 wherein the vessel comprises a coolable plate of semiconductor material, which is delimited by an outer edge, and the opening of the vessel is designed as a downwardly directed section of pipe which is connected to a raised inner edge of the plate, the inner edge of the plate forming a barrier which the molten granules have to overcome before they can pass through the opening in the vessel to the melt, and the apparatus comprising a radiation heating means for heating a surface of a melt neck and the semiconductor material flowing through the section of pipe.    
     
     
         18 . The apparatus as claimed in  claim 9 , comprising 
 means for mounting the vessel so that it can rotate about an axis of rotation, and said vessel comprises a coolable plate of semiconductor material and has webs which are constantly remelted under the influence of the heating coil and the rotation of the vessel and divide the interior of the vessel into concentric regions, these regions being in communication with one another and forming a system of passages which the melting granules have to overcome before they can pass through the opening in the vessel, which is designed as a section of pipe, to the melt, and the apparatus comprising a radiation heating means for heating a surface of the melt neck and the semiconductor material flowing through the section of pipe.    
     
     
         19 . A silicon single crystal comprising 
 an oxygen concentration of 3-9*10 17  atoms/cm 3  and grown-in defects with a size of less than 60 nm.    
     
     
         20 . The silicon single crystal as claimed in  claim 19 , further comprising a nitrogen concentration of 1*10 13 -6*10 15  atoms/cm 3 .