Method and apparatus for the improvement of material/voltage contrast

Abstract

A method and system for registering a CAD layout to a Focused Ion Beam image for through-the substrate probing, without using an optical image and without requiring biasing, includes an improved method of trench endpointing during the FIB milling operation with a low beam energy. The method further includes removal of Ga at the trench floor using XeF 2 , as well as the deposition of an insulating layer onto the trench floor.

1 . A first method of aligning a voltage contrast (VC) FIB image of an integrated circuit wafer portion having corners to a corresponding Computer-Aided Design (CAD) layout so as to probe a target location on said wafer portion, said target location corresponding to a probe location on said CAD layout, said FIB image being produced by a FIB beam having a beam energy and a beam current, said FIB image having a Field of View, said FIB beam being controlled by a computing device including software, comprising the steps of: 
 performing CAD-IDS OptiFIB 3-point alignment using said corners of said wafer portion;    locally aligning said VC FIB image to said CAD layout by observing said voltage contrast;    placing said target location in the center of said Field of View;    forming a spot mark at the exact center of said wafer portion;    lowering said FIB beam current; and    configuring said software to direct said FIB beam at said target location according to said local alignment.    
   
   
       2 . The method of  claim 1 , wherein: 
 said step of locally aligning said VC FIB image to said CAD layout by observing said voltage contrast is performed at a FIB beam current in the range between 250 pA and 4 nA; and wherein    said step of forming a spot mark at the exact center of said wafer portion is performed by directing said FIB beam at said center with no dynamic deflection for a period of time.    
   
   
       3 . The method of  claim 2 , wherein said period of time is approximately equal to 100 ms.  
   
   
       4 . A second method of aligning a voltage contrast (VC) FIB image of an integrated circuit wafer portion having comers to a corresponding Computer-Aided Design (CAD) layout so as to probe a target location on said wafer portion, said target location corresponding to a probe location on said CAD layout, said FIB image being produced by a FIB beam having a beam energy and a beam current, said FIB image having a Field of View, said FIB beam being controlled by a computing device including software, comprising the steps of: 
 performing CAD-IDS OptiFIB 3-point alignment using said comers of said wafer portion;    aligning on a drawn fiducial mark at a first and a second beam current;    performing local FIB-CAD alignment using VC at high beam current;    switching to low beam current and making a fiducial on the target location;    switching to high beam current a second time, and performing FIB-CAD alignment a second time;    measuring at high beam current the offset between said fiducial mark and said target location;    switching to low beam current a second time; and    configuring said software to direct said FIB beam at said target location according to said measured offset between said fiducial mark and said target location.    
   
   
       5 . The method of  claim 4 , wherein said first beam current is a first high beam current and said second beam current is a first low beam current.  
   
   
       6 . The method of  claim 5 , wherein said first high beam current is in the range between 500 pA and 6 nA, and wherein said first low beam current is approximately equal to 10 pA.  
   
   
       7 . The method of  claim 4 , wherein said step of performing local FIB-CAD alignment using VC at high beam current is performed at a beam current greater than 1 nA.  
   
   
       8 . The method of  claim 4 , wherein said low beam current is in the range between 5 and 50 pA.  
   
   
       9 . The method of  claim 4 , wherein said fiducial mark is a cross.  
   
   
       10 . The method of  claim 4 , wherein said step of configuring said software to direct said FIB beam at said target location according to said measured offset between said fiducial mark and said target location comprises configuring said software to electrically deflect said FIB beam to said target location.