Semiconductor substrate and method for production thereof

Abstract

Hetero-semiconductor structures possessing an SOI structure containing a silicon-germanium mixed crystal are produced at a low cost and high productivity. The semiconductor substrates comprise a first layer formed of silicon having germanium added thereto, a second layer formed of an oxide and adjoined to the first layer, and a third layer derived from the same source as the first layer, but having an enriched content of germanium as a result of thermal oxidation and thinning of the third layer.

1 . A semiconductor substrate, comprising 
 a germanium doped silicon single crystal substrate having a first concentration of germanium and having a planar surface;    an insulating oxide film formed below the planar surface and dividing said single crystal into a first, germanium doped silicon layer, a second, insulating oxide layer, and a third germanium doped silicon layer, said third layer having a higher concentration of germanium than said first layer.    
   
   
       2 . The semiconductor substrate of  claim 1 , wherein said germanium doped silicon single crystal substrate comprises a wafer processed from a germanium doped silicon single crystal.  
   
   
       3 . The semiconductor substrate of  claim 1 , wherein the first concentration of germanium is in the range of 0.05 to 5 mol percent based on mols of silicon and germanium.  
   
   
       4 . The semiconductor substrate of  claim 1 , wherein the first concentration of germanium is in the range of 0.2 to 1 mol percent based on mols of silicon and germanium.  
   
   
       5 . The semiconductor substrate of  claim 1 , wherein said insulating oxide is a silicon oxide.  
   
   
       6 . The semiconductor substrate of  claim 1 , wherein said second layer has a thickness of 80 nm or more.  
   
   
       7 . The semiconductor substrate of  claim 1 , wherein said third layer is a single crystal.  
   
   
       8 . The semiconductor substrate of  claim 1 , wherein said third layer has a thickness between 1 nm and 50 nm, inclusively.  
   
   
       9 . The semiconductor substrate of  claim 1 , wherein the germanium concentration of said third layer is not less than 15 mol % and up to 100 mol %.  
   
   
       10 . The semiconductor substrate of  claim 1 , wherein said first layer contains no COP.  
   
   
       11 . The semiconductor substrate of  claim 1 , wherein said third layer contains no COP.  
   
   
       12 . The semiconductor substrate of  claim 1 , wherein the dislocation density reaching the surface of said third layer is not more than 1×10 5  pieces/cm 2 .  
   
   
       13 . The semiconductor substrate of  claim 1 , wherein the roughness of said third layer is not more than 5 nm RMS over 40×40 μm.  
   
   
       14 . The semiconductor substrate of  claim 1 , wherein the fluctuation of the thickness of said third layer is not more than 5% or not more than 2.5 nm.  
   
   
       15 . The semiconductor substrate of  claim 1 , wherein the fluctuation of the germanium concentration in said third layer is not more than 5%.  
   
   
       16 . The semiconductor substrate of  claim 1 , further comprising a strained silicon layer formed adjacent said third layer.  
   
   
       17 . The semiconductor substrate of  claim 1 , further comprising a germanium layer formed adjacent said third layer.  
   
   
       18 . A method for the production of a semiconductor substrate, comprising 
 a) providing a wafer processed from a germanium doped silicon single crystal ingot having a first concentration of germanium;    b) implanting oxygen ions into said wafer by ion implantation and heat treating to form a buried oxide film, said buried oxide film separating said wafer into a first layer below said buried oxide film, a second layer comprising said buried oxide film, and a third layer above said buried oxide film; and    c) thinning said third layer by thermal oxidation in an oxidizing atmosphere to enrich the concentration of germanium in said third layer to a second concentration higher than said first concentration.    
   
   
       19 . The method of  claim 18 , wherein prior to step b), the concentration of germanium near the surface of said wafer is increased by oxidizing the wafer in an oxidizing atmosphere at elevated temperature, followed by removal of an oxide film formed thereby.  
   
   
       20 . The process of  claim 19 , wherein the oxidizing atmosphere comprises steam, said elevated temperature is from 900° C. to the melting point of the wafer, and said oxidizing is conducted for a period of minimally 30 minutes.  
   
   
       21 . The process of  claim 19 , wherein said oxide film has a thickness of 1 μm or greater.  
   
   
       22 . The process of  claim 18 , wherein said first concentration of germanium is from 0.05 mol percent to 5 mol percent.  
   
   
       23 . The process of  claim 18 , wherein said first concentration of germanium is from 0.2 mol percent to 1 mol percent.  
   
   
       24 . The method of  claim 18 , further comprising depositing a strained silicon film above said third layer by vapor phase deposition.  
   
   
       25 . The process of  claim 18 , wherein the first concentration of germanium and the amount of thinning are sufficient to provide a germanium concentration in said third layer of 95 mol percent or more, further comprising depositing onto said third layer a germanium film by vapor phase deposition.  
   
   
       26 . A semiconductor device prepared by processing a semiconductor substrate of  claim 1.