Method and apparatus for growing silicon carbide crystals

Abstract

A method and apparatus for controlled, extended and repeatable growth of high quality silicon carbide boules of a desired polytype is disclosed which utilizes graphite crucibles coated with a thin coating of a metal carbide and in particular carbides selected from the group consisting of tantalum carbide, hafnium carbide, niobium carbide, titanium carbide, zirconium carbide, tungsten carbide and vanadium carbide.

1 . A seeded SiC crystal growth system for high temperature SiC crystal growth, comprising: 
 a container for receiving a silicon carbide seed crystal, said container comprising:    a first inlet to the interior of said container;    a second inlet to the interior of said container;    a graphite core; and    a coating on said graphite core, said coating being characterized by a melting point above the sublimation temperature of SiC, chemical inertness with respect to silicon and hydrogen at the sublimation temperature of SiC, and a coefficient of thermal expansion sufficiently similar to said graphite core to prevent cracking between said graphite core and said coating during heating and cooling of said container to and from the sublimation temperature of SiC;    a source of silicon connected to said first inlet of said container; and    a source of carbon connected to said second inlet of said container.    
   
   
       2 . The seeded SiC crystal growth system according to  claim 1 , wherein said source of silicon is silane.  
   
   
       3 . A seeded SiC crystal growth system according to  claim 1  wherein said coating comprises a refractory metal compound selected from the group consisting of tantalum carbide, hafnium carbide, niobium carbide, titanium carbide, zirconium carbide, tungsten carbide, vanadium carbide, tantalum nitride, hafnium nitride, niobium nitride, titanium nitride, zirconium nitride, tungsten nitride, vanadium nitride and mixtures thereof.  
   
   
       4 . A seeded SiC crystal growth system according to  claim 1  wherein said coating comprises tantalum carbide.  
   
   
       5 . A seeded SiC crystal growth system according to  claim 1  further comprising: 
 a heating element for heating said container;    a seed holder attached to the interior of said container; and    a seed crystal on said seed holder;    wherein vaporized species containing silicon and carbon enter said system and propagate sublimation growth of silicon carbide on said seed crystal.    
   
   
       6 . A seeded SiC crystal growth system according to  claim 5 , wherein said inlets provide separate pathways for a silicon source gas and a carbon source gas to enter said core.  
   
   
       7 . A seeded SiC crystal growth system, comprising: 
 a graphite enclosure having an inner surface defining a hollow reaction area therein;    a coating on said inner surface, said coating comprising a material characterized by a melting point above the sublimation temperature of silicon carbide;    a first pathway for introducing a silicon source gas to the reaction area;    a second pathway for introducing a carbon source gas to the reaction area;    a heating element for heating the reaction area to a temperature sufficient to allow the silicon source gas and carbon source gas to form vaporized species of silicon carbide in the reaction area; and    a silicon carbide seed crystal positioned in sufficient proximity to said reaction area to allow vaporized species of silicon carbide to deposit on said silicon carbide seed crystal.    
   
   
       8 . A seeded SiC crystal growth system according to  claim 7 , wherein said coating comprises a material characterized by chemical inertness with respect to silicon and hydrogen at the sublimation temperature of silicon carbide, and a coefficient of thermal expansion sufficiently similar to said graphite enclosure to prevent cracking between said graphite enclosure and said coating during heating and cooling of said enclosure to and from the sublimation temperature of SiC.  
   
   
       9 . A seeded SiC crystal growth system according to  claim 7 , wherein said coating comprises a refractory metal compound selected from the group consisting of tantalum carbide, hafnium carbide, niobium carbide, titanium carbide, zirconium carbide, tungsten carbide, vanadium carbide, tantalum nitride, hafnium nitride, niobium nitride, titanium nitride, zirconium nitride, tungsten nitride, vanadium nitride and mixtures thereof.  
   
   
       10 . A seeded SiC crystal growth system according to  claim 7 , wherein said coating has an infrared emissivity ratio between about 0.4 and 0.6.  
   
   
       11 . A seeded SiC crystal growth system according to  claim 7 , further comprising a seed holder for securing said seed crystal proximate the reaction area.  
   
   
       12 . A seeded SiC crystal growth system according to  claim 11 , wherein said seed holder secures said seed crystal sufficiently close to the reaction area of said graphite enclosure to allow vaporized species of SiC to deposit on said seed crystal, and wherein said seed holder secures said seed crystal sufficiently separated from the inner surface of said graphite enclosure and said heating element to maintain said seed crystal at a temperature that is between about 150° C. and 200° C. lower than the temperature of said inner surface of said enclosure.  
   
   
       13 . A seeded silicon carbide growth system according to  claim 7 , comprising a silicon source gas selected from the group consisting of silane, chlorosilane, and methyltrichlorosilane, said silicon source gas being in fluid communication with the reaction area of said graphite enclosure via said first pathway.  
   
   
       14 . A seeded silicon carbide growth system according to  claim 7 , comprising a hydrocarbon source gas in fluid communication with the reaction area of said graphite enclosure via said second pathway.  
   
   
       15 . A seeded silicon carbide growth system according to  claim 7 , wherein said first and second pathways separate the carbon source gas from the silicon source gas until each source gas enters the reaction area.  
   
   
       16 . A seeded silicon carbide growth system according to  claim 7 , wherein said first and second pathways for source gases are inner and outer concentric pathways.  
   
   
       17 . A seeded silicon carbide growth system according to  claim 16 , wherein said inner concentric pathway supplies a silicon source gas to the reaction area and said outer concentric pathway supplies a carbon source gas to the reaction area.  
   
   
       18 . A SiC crystal growth system for seeded growth, said system comprising: 
 a crucible comprising a bottom, a hollow outer cylinder extending from said bottom and a hollow inner cylinder positioned inside said outer cylinder, said inner cylinder extending from said bottom to a height less than the height of said outer cylinder,    a lid attached to said outer cylinder and enclosing said inner and outer cylinders, wherein the lid and said outer cylinder define a reaction area inside said crucible above said inner cylinder;    wherein said hollow inner cylinder defines an inner pathway from said bottom to said reaction area, and wherein the inner wall of said outer cylinder and the outer wall of said inner cylinder define an outer pathway between said inner and outer cylinders, said outer pathway extending from said bottom to said reaction area, said inner and outer pathways providing points of entry from outside said crucible into the reaction area;    a seed crystal holder secured to the underside of said lid in the reaction area of said crucible;    a seed crystal secured within the reaction area by said seed crystal holder;    a silicon gas source in fluid communication with said inner pathway through said bottom;    a carbon gas source in fluid communication with said outer pathway through said bottom;    a heating element outside said crucible for heating the reaction area to a temperature sufficient to allow the silicon source gas and carbon source gas to deposit vaporized species of silicon carbide onto said seed crystal in the reaction area.    
   
   
       19 . A SiC crystal growth system according to  claim 18 , wherein said silicon gas source is selected from the group consisting of silane, chlorosilane, and methyltrichlorosilane.  
   
   
       20 . A SiC crystal growth system according to  claim 18 , wherein said carbon source gas is a hydrocarbon.  
   
   
       21 . A SiC crystal growth system according to  claim 18 , wherein said crucible, said lid, and said seed crystal holder comprise graphite.  
   
   
       22 . A SiC crystal growth system according to  claim 21 , wherein said crucible, said lid and said seed crystal holder are coated with a material characterized by a melting point above the sublimation temperature of silicon carbide.  
   
   
       23 . A SiC crystal growth system according to  claim 22 , wherein said coating comprises a material characterized by chemical inertness with respect to silicon and hydrogen at the sublimation temperature, and a coefficient of thermal expansion sufficiently similar to said graphite enclosure to prevent cracking between said graphite enclosure and said coating during heating and cooling of said enclosure to and from the sublimation temperature of SiC.  
   
   
       24 . A SiC crystal growth system according to  claim 22 , wherein said coating comprises a refractory metal compound selected from the group consisting of tantalum carbide, hafnium carbide, niobium carbide, titanium carbide, zirconium carbide, tungsten carbide and vanadium carbide; and tantalum nitride, hafnium nitride, niobium nitride, titanium nitride, zirconium nitride, tungsten nitride and vanadium nitride and mixtures thereof.  
   
   
       25 . A SiC crystal growth system according to  claim 22 , wherein said coating comprises tantalum carbide.  
   
   
       26 . A SiC crystal growth system according to  claim 22 , wherein said coating has an infrared emissivity ratio between about 0.4 and 0.6.  
   
   
       27 . A SiC crystal growth system according to  claim 18 , wherein said seed holder secures said seed crystal sufficiently close to the reaction area of said crucible to allow vaporized species of SiC to deposit on said seed crystal, and wherein said seed holder secures said seed crystal sufficiently separated from said heating element to maintain said seed crystal at a temperature that is between about 150° C. and 200° C. lower than the temperature of said inner and outer cylinders.  
   
   
       28 . A SiC crystal growth system according to  claim 27 , wherein said outer cylinder comprises a spacer ring extending from the top of said outer cylinder to said lid, thereby increasing the height of said reaction area in said crucible.  
   
   
       29 . A SiC crystal growth system according to  claim 18 , comprising a gas outlet port extending from said reaction area and through said lid, said gas outlet port providing a passage for evacuating gas from said reaction area.  
   
   
       30 . A SiC crystal growth system according to  claim 18 , wherein said seed holder is secured by a graphite rod extending through said lid into said reaction area.  
   
   
       31 . A SiC crystal growth system for high temperature seeded SiC crystal growth, said system comprising a container for receiving a silicon carbide seed crystal, a source of silicon and a source of carbon, wherein said container comprises: 
 a graphite core;    a coating on said graphite core for penetrating the pores of said graphite core and sufficiently reinforcing the graphite grain boundaries to keep said graphite intact even after a portion of said coating has been removed from said core;    said coating being characterized by a melting point above the sublimation temperature of SiC, chemical inertness with respect to silicon and hydrogen at the sublimation temperature, and a coefficient of thermal expansion sufficiently similar to said graphite core to prevent cracking between said graphite core and said coating during heating and cooling of said container to and from the sublimation temperature of SiC.    
   
   
       32 . A SiC crystal growth system according to  claim 31  wherein said coating comprises a refractory metal compound selected from the group consisting of tantalum carbide, hafnium carbide, niobium carbide, titanium carbide, zirconium carbide, tungsten carbide and vanadium carbide; and tantalum nitride, hafnium nitride, niobium nitride, titanium nitride, zirconium nitride, tungsten nitride and vanadium nitride and mixtures thereof.  
   
   
       33 . A SiC crystal growth system according to  claim 32  wherein said refractory metal compound is tantalum caride.