Vacancy, dominated, defect-free silicon

Abstract

The present invention relates to single crystal silicon, in ingot or wafer form, which contains an axially symmetric region in which vacancies are the predominant intrinsic point defect and which is substantially free of agglomerated vacancy intrinsic point defects, wherein the first axially symmetric region has a width which is at least about 50% of the length of the radius of the ingot, and a process for the preparation thereof.

What is claimed is:  
     
         1 . A single crystal silicon wafer having a central axis, a front side and a back side which are generally perpendicular to the central axis, a circumferential edge, and a radius extending from the central axis to the circumferential edge of the wafer, the wafer comprising 
 a first axially symmetric region in which vacancies are the predominant intrinsic point defect and which is substantially free of agglomerated vacancy intrinsic point defects wherein the first axially symmetric region has a width of at least about 60% of the radius of the wafer.    
     
     
         2 . The wafer of  claim 1  wherein the wafer comprises a second axially symmetric region in which silicon self-interstitial atoms are the predominant intrinsic point defect and which is substantially free of agglomerated silicon self-interstitial intrinsic point defects.  
     
     
         3 . The wafer of  claim 1  wherein the width of the first axially symmetric region is at least about 80% of the radius.  
     
     
         4 . The wafer of  claim 3  wherein the wafer comprises a second axially symmetric region in which silicon self-interstitial atoms are the predominant intrinsic point defect and which is substantially free of agglomerated silicon self-interstitial intrinsic point defects.  
     
     
         5 . The wafer of  claim 1  wherein the width of the first axially symmetric region is at least about 90% of the radius.  
     
     
         6 . The wafer of  claim 5  wherein the wafer comprises a second axially symmetric region in which silicon self-interstitial atoms are the predominant intrinsic point defect and which is substantially free of agglomerated silicon self-interstitial intrinsic point defects.  
     
     
         7 . The wafer of  claim 1  wherein the width of the first axially symmetric region is about equal to the radius.  
     
     
         8 . The wafer of  claim 1  wherein the wafer has as oxygen content which is less than about 13 PPMA.  
     
     
         9 . The wafer of  claim 1  wherein the wafer has as oxygen content which is less than about 11 PPMA.  
     
     
         10 . The wafer of  claim 1  wherein the wafer has an absence of oxygen precipitate nucleation centers.  
     
     
         11 . The wafer of  claim 1  having an epitaxial layer deposited upon a front side of the wafer.  
     
     
         12 . A single crystal silicon ingot having a central axis, a seed-cone, an end-cone, and a constant diameter portion between the seed-cone and the end-cone having a circumferential edge and a radius extending from the central axis to the circumferential edge, the single crystal silicon ingot being characterized in that after the ingot is grown and cooled from the solidification temperature, the constant diameter portion contains a first axially symmetric region in which vacancies are the predominant intrinsic point defect and which is substantially free of agglomerated intrinsic point defects wherein the first axially symmetric region has a width of at least about 50% of the radius of the ingot and a length as measured along the central axis of at least about 20% of the length of the constant diameter portion of the ingot.  
     
     
         13 . The single crystal silicon ingot of  claim 12  wherein the ingot comprises a second axially symmetric region which is concentric with said first axially symmetric region, the second axially symmetric region containing self-interstitial atoms as the predominant intrinsic point defect and being substantially free of agglomerated silicon self-interstitial intrinsic point defects.  
     
     
         14 . The single crystal silicon ingot of  claim 12  wherein the length of the first axially symmetric region is at least about 40% the length of the constant diameter portion of the ingot.  
     
     
         15 . The single crystal silicon ingot of  claim 14  wherein the ingot comprises a second axially symmetric region which is concentric with said first axially symmetric region, the second axially symmetric region containing self-interstitial atoms as the predominant intrinsic point defect and being substantially free of agglomerated silicon self-interstitial intrinsic point defects.  
     
     
         16 . The single crystal silicon ingot of  claim 12  wherein the length of the first axially symmetric region is at least about 80% the length of the constant diameter portion of the ingot.  
     
     
         17 . The single crystal silicon ingot of  claim 16  wherein the ingot comprises a second axially symmetric region which is concentric with said first axially symmetric region, the second axially symmetric region containing self-interstitial atoms as the predominant intrinsic point defect and being substantially free of agglomerated silicon self-interstitial intrinsic point defects.  
     
     
         18 . The single crystal silicon ingot of  claim 12  wherein the width of the first axially symmetric region is at least about 80% of the radius.  
     
     
         19 . The single crystal silicon ingot of  claim 18  wherein the ingot comprises a second axially symmetric region which is concentric with said first axially symmetric region, the second axially symmetric region containing self-interstitial atoms as the predominant intrinsic point defect and being substantially free of agglomerated silicon self-interstitial intrinsic point defects.  
     
     
         20 . The single crystal silicon ingot of  claim 18  wherein the length of the first axially symmetric region is at least about 40% the length of the constant diameter portion of the ingot.  
     
     
         21 . The single crystal silicon ingot of  claim 20  wherein the ingot comprises a second axially symmetric region which is concentric with said first axially symmetric region, the second axially symmetric region containing self-interstitial atoms as the predominant intrinsic point defect and being substantially free of agglomerated silicon self-interstitial intrinsic point defects.  
     
     
         22 . The single crystal silicon ingot of  claim 18  wherein the length of the first axially symmetric region is at least about 80% the length of the constant diameter portion of the ingot.  
     
     
         23 . The single crystal silicon ingot of  claim 22  wherein the ingot comprises a second axially symmetric region which is concentric with said first axially symmetric region, the second axially symmetric region containing self-interstitial atoms as the predominant intrinsic point defect and being substantially free of agglomerated silicon self-interstitial intrinsic point defects.  
     
     
         24 . The single crystal silicon ingot of  claim 12  wherein the ingot has an oxygen content of less than about 13 PPMA.  
     
     
         25 . The single crystal silicon ingot of  claim 12  wherein the ingot has an oxygen content of less than about 11 PPMA.  
     
     
         26 . The single crystal silicon ingot of  claim 12  wherein the width of the first axially symmetric region is about equal to the radius.  
     
     
         27 . The single crystal silicon ingot of  claim 26  wherein the length of the first axially symmetric region is at least about 40% the length of the constant diameter portion of the ingot.  
     
     
         28 . A process for growing a single crystal silicon ingot in which the ingot comprises a central axis, a seed-cone, an end-cone and a constant diameter portion between the seed-cone and the end-cone having a circumferential edge and a radius extending from the central axis to the circumferential edge, the ingot being grown from a silicon melt and then cooled from the solidification temperature in accordance with the Czochralski method, the process comprising 
 controlling a growth velocity, v, and an average axial temperature gradient, G 0 , during the growth of the constant diameter portion of the crystal over the temperature range from solidification to a temperature of no less than about 1325° C., to cause the formation of a first axially symmetrical region in which vacancies, upon cooling of the ingot from the solidification temperature, are the predominant intrinsic point defect and which is substantially free of agglomerated intrinsic point defects wherein the first axially symmetric region has a width of at least about 50% of the radius of the constant diameter portion of the ingot.    
     
     
         29 . The process of  claim 28  wherein the first axially symmetric region has a length which is at least about 40% the length of the constant diameter portion of the ingot.  
     
     
         30 . The process of  claim 29  wherein the ingot comprises a second axially symmetric region which is concentric with said first axially symmetric region, the second axially symmetric region containing self-interstitial atoms as the predominant intrinsic point defect and being substantially free of agglomerated silicon self-interstitial intrinsic point defects.  
     
     
         31 . The process of  claim 28  wherein the first axially symmetric region has a length which is at least about 80% the length of the constant diameter portion of the ingot.  
     
     
         32 . The process of  claim 31  wherein the ingot comprises a second axially symmetric region which is concentric with said first axially symmetric region, the second axially symmetric region containing self-interstitial atoms as the predominant intrinsic point defect and being substantially free of agglomerated silicon self-interstitial intrinsic point defects.  
     
     
         33 . The process of  claim 28  wherein the first axially symmetric region has a width which is at least about 80% the length of the radius of the constant diameter portion of the ingot.  
     
     
         34 . The process of  claim 33  wherein the first axially symmetric region has a length which is at least about 40% the length of the constant diameter portion of the ingot.  
     
     
         35 . The process of  claim 34  wherein the ingot comprises a second axially symmetric region which is concentric with said first axially symmetric region, the second axially symmetric region containing self-interstitial atoms as the predominant intrinsic point defect and being substantially free of agglomerated silicon self-interstitial intrinsic point defects.  
     
     
         36 . The process of  claim 33  wherein the first axially symmetric region has a length which is at least about 80% the length of the constant diameter portion of the ingot.  
     
     
         37 . The process of  claim 36  wherein the ingot comprises a second axially symmetric region which is concentric with said first axially symmetric region, the second axially symmetric region containing self-interstitial atoms as the predominant intrinsic point defect and being substantially free of agglomerated silicon self-interstitial intrinsic point defects.  
     
     
         38 . The process of  claim 28  wherein the first axially symmetric region has a width which is about equal to the radius of the constant diameter portion of the ingot.  
     
     
         39 . The process of  claim 38  wherein the first axially symmetric region has a length which is at least about 20% the length of the constant diameter portion of the ingot.  
     
     
         40 . The process of  claim 38  wherein the first axially symmetric region has a length which is at least about 40% the length of the constant diameter portion of the ingot.