Reinforced structural member for high temperature operations and fabrication method

Abstract

A structural member for use in high temperature environments is disclosed. The structural member has a core encased within a shell material. The core material is formed of a strong material having a melting point well above that of the shell material. The disclosed structural member is particularly useful when forming a boat for heating silicon and the like to temperatures between 900 degrees Celsius and 1500 degrees Celsius. In a preferred embodiment the core material is graphite and the shell is fused silica. Even more preferably, the fused silica pneumatically encases the graphite to thereby prevent inadvertent contamination during use of the structural member. A related method for forming the structural member is also disclosed.

1 . A structural frame for use in high temperature environments, said frame having: 
 a structural member having a core material and a shell material;    said core material having a core melting temperature;    said shell material having a shell melting temperature; and,    said core melting temperature is greater than said shell melting temperature.    
   
   
       2 . The structural frame of  claim 1 , wherein the high temperature environment is between 900 degrees Celsius and 1500 degrees Celsius, inclusive.  
   
   
       3 . The structural frame of  claim 1 , wherein said structural frame forms a boat for use in heating silicon wafers.  
   
   
       4 . The structural frame of  claim 1 , wherein said shell material is a member of the SiO2 group.  
   
   
       5 . The structural frame of  claim 4 , wherein said shell material is silica.  
   
   
       6 . The structural frame of  claim 5 , wherein said shell material is fused silica.  
   
   
       7 . The structural frame of  claim 1 , wherein said core material is selected from the group consisting of graphite, carbon, Monocrystalline Silicon, Polycrystalline Silicon, SiC, AlN, Al2O3, Sapphire, ZrO2, and Si3N4.  
   
   
       8 . The structural frame of  claim 1 , wherein said core material is graphite.  
   
   
       9 . The structural frame of  claim 1 , wherein said core material is elongate and has a substantially circular cross-section.  
   
   
       10 . The structural frame of  claim 1 , wherein said core material is elongate and has a substantially rectangular cross-section.  
   
   
       11 . The structural frame of  claim 1 , further including a second core material and said structural member includes said core material and said second core material therein.  
   
   
       12 . The structural frame of  claim 1 , wherein said core material is formed of individual segments.  
   
   
       13 . The structural frame of  claim 1 , wherein said core material is an elongate monolithic structure.  
   
   
       14 . A boat for use in heating silicon to high temperatures, said boat having 
 a rack-type structure formed from a plurality substantially parrallelly aligned elongate structural members joined to an upper member and a lower member,    at least one structural member having a core material having a first melting temperature encased within a shell material having a second melting temperature; and,    said first melting temperature is higher than said second melting temperature.    
   
   
       15 . The boat of  claim 14 , wherein said core material is pneumatically sealed within said shell material.  
   
   
       16 . The boat of  claim 14 , wherein said core material is selected from the group consisting of graphite, carbon, Monocrystalline Silicon, Polycrystalline Silicon, SiC, AlN, Al2O3, Sapphire, ZrO2, and Si3N4.  
   
   
       17 . The boat of  claim 14 , wherein said shell material is material is a member of the SiO2 group.  
   
   
       18 . The boat of  claim 14 , wherein at least one of said upper member and said lower member is formed with said core material encased within said shell material.  
   
   
       19 . The boat of  claim 14 , wherein said plurality of elongate structural members include protrusions for operably holding silicon wafers in a substantially horizontal position within said boat.  
   
   
       20 . The boat of  claim 19 , wherein said protrusions include said core material within said shell material.  
   
   
       21 . A method of forming a support member for a structural frame for use in high temperature environments, said method comprising the steps of: 
 forming a section of core material to a desired cross sectional shape, said core material having a first melting temperature;    inserting the section of core material into a hollow shell material, said shell material having a second melting temperature lower than said first melting temperature;    capping an end of the shell material with a cap of said shell materials; and,    heating said shell material to a temperature above said second melting temperature but below said first melting temperature thereby sealing said shell material around said core material.    
   
   
       22 . The method of forming a support member for a structural frame for use in high temperature environments of  claim 21 , further including: 
 capping the opposite end of said shell material and heating said shell material to seal the core material within said shell material.    
   
   
       23 . The method of forming a support member for a structural frame for use in high temperature environments of  claim 21 , further including: 
 allowing said shell material to cool; and,    machining spaced apart notches into said shell material, said notches not extending to said core material.    
   
   
       24 . The method of forming a support member for a structural frame for use in high temperature environments of  claim 21 , further including: 
 providing an elongate recess within said section of core material;    positioning a plurality of substantially L-shaped segments of core material along said recess thereby defining a plurality of spaced-apart protrusions of said core material;    positioning segments of shell material between said spaced apart protrusions; and    heat sealing said core material and said substantially L-shaped segments within said hollow shell material.