Optimized blocking impurity placement for SiGe HBTs

Abstract

A high performance SiGe HBT that has a SiGe layer with a peak Ge concentration of at least approximately 20% and a boron-doped base region formed therein having a thickness. The base region includes diffusion-limiting impurities substantially throughout its thickness, at a peak concentration below that of boron in the base region. Both the base region and the diffusion-limiting impurities are positioned relative to a peak concentration of Ge in the SiGe layer so as to optimize both performance and yield.

What is claimed is:  
     
         1 . A high performance SiGe HBT that has a SiGe layer with a peak Ge concentration of at least approximately 20% and a boron-doped base region formed therein having a thickness, wherein said base region includes diffusion-limiting impurities throughout said thickness at a concentration below that of boron in said base region, and wherein said diffusion limiting impurities are physically located relative to both said base region and a portion of said SiGe layer having a Ge concentration of 20% to optimize performance and yield of said SiGe HBT.  
     
     
         2 . A high performance SiGe HBT that has a SiGe layer with a peak Ge concentration of at least approximately 20%, a boron-doped base region formed therein having a thickness, and a region of diffusion-limiting impurities at a concentration, thickness, and spacing relative to said base region and a portion of said SiGe layer having said peak concentration of Ge that optimizes both performance and yield of said SiGe HBT.  
     
     
         3 . A method of producing a SiGe layer on a Si substrate, comprising the steps of: 
 introducing germanium atoms during formation of a Si layer, such that at least a portion of said SiGe layer has a peak Ge concentration of at least 20%;    introducing diffusion-limiting impurities and boron atoms during formation of said Si layer, while said germanium atoms are still being introduced; and    terminating both said diffusion-limiting impurities and said boron atoms approximately simultaneously, said diffusion limiting impurities being introduced at a concentration and for a duration that optimizes both performance and yield.    
     
     
         4 . The device of  claim 1 , wherein said SiGe layer is of a thickness of approximately 300-900 A.  
     
     
         5 . The device of  claim 1 , wherein the Ge has a peak concentration thickness of approximately 20-100 angstroms.  
     
     
         6 . The device of  claim 5 , wherein said base region is approximately 10-150 angstroms in thickness.  
     
     
         7 . The device of  claim 6 , wherein the base region has a peak boron concentration of boron of approximately 8.5×10 E 19/cm 3 .  
     
     
         8 . The device of  claim 1 , wherein said diffusion limiting impurity comprises carbon.  
     
     
         9 . The device of  claim 8 , wherein said carbon has a peak concentration between approximately 1×10 e 19/cm 3  and 4×0 e 19/cm 3 .  
     
     
         10 . The device of  claim 8 , wherein said carbon defines a dopant region that is approximately 10-500 angstroms in thickness.  
     
     
         11 . The device of  claim 8 , wherein said carbon has defines a dopant region having an upper bound and a lower bound, wherein said peak concentration thickness of said Ge has an upper bound and a lower bound, and wherein said lower bound of said carbon region is within approximately 150 angstroms of said upper bound of said peak concentration thickness of said Ge.  
     
     
         12 . The device of  claim 10 , wherein said base region is within approximately 200-250 angstroms of said upper bound of said peak concentration thickness of said Ge.  
     
     
         13 . The method of  claim 3 , wherein said diffusion-limiting impurities comprise carbon, and wherein said carbon is first introduced when said Ge reaches a plateau concentration.  
     
     
         14 . The method of  claim 11 , wherein said diffusion-limiting impurities come from a gaseous source.  
     
     
         15 . The method of  claim 12 , wherein said gaseous source comprises ethylene.  
     
     
         16 . The method of  claim 13 , wherein when said germanium atoms are introduced at a peak flow rate of Germane at 28 SCCM, said ethylene is provided at a rate of 40 SCCM.  
     
     
         17 . A SiGe HBT comprising an SiGe layer, a base region, and a diffusion-limiting region, in which said diffusion-limiting region extends substantially throughout said base region and has a dopant concentration less than that of said base region, and wherein both said base region and said diffusion-limiting region are spaced within a given distance of a portion of said SiGe layer having a Ge concentration of at least approximately 20% so as to optimize both performance and yield of said SiGe HBT.  
     
     
         18 . The device of  claim 16 , wherein said base region is within approximately 250 A of said portion of said SiGe layer having a peak Ge concentration.  
     
     
         19 . The device of  claim 17 , wherein said diffusion-limiting region is within approximately 150A of said portion of said SiGe layer having a peak Ge concentration.  
     
     
         20 . The device of  claim 17 , wherein said base region is within approximately 250 A of said portion of said SiGe layer having a peak Ge concentration, and wherein said diffusion-limiting region is within approximately 150A of said portion of said SiGe layer having a peak Ge concentration.