FIB Process for Selective and Clean Etching of Copper

Abstract

Etch assisting agents for focused ion beam (FIB) etching of copper for circuit editing of integrated circuits both prevent loss of adjacent dielectric due to sputtering by the ion beam, and render sputtered re-deposited copper on adjacent surfaces non-conductive to avoid electrical short circuits. The agents comprise hydrazine and hydrazine derivatives compounds having an N—N (N being Nitrogen) bonding in their molecules, and boiling points between about 70° and 200° C. Preferred agents are either Hydrazine monohydrate or Nitrosodimethylamine, alone or in combination with Nitrogen Tetroxide, and are effective for etching copper in high aspect ratio (deep) holes.

1 . A method of focused ion beam etching of copper in the presence of a dielectric comprising:
 directing a focused ion beam onto the copper to be etched; and   exposing the copper and the dielectric to an etch assisting agent comprising a compound selected from the group of compounds that contain an N—N bonding in their molecules, where N is nitrogen.   
     
     
         2 . The method of  claim 1 , wherein said compound comprises hydrazine and derivatives thereof with boiling points between about 70° C. and 200° C. 
     
     
         3 . The method of  claim 2 , wherein said compound is selected from the group consisting of Hydrazine monohydrate and Nitrosodimethylamine. 
     
     
         4 . The method of  claim 3  wherein said etch assisting agent further comprises Nitrogen Tetroxide in combination with one of said Hydrazine monohydrate and Nitrosodimethylamine. 
     
     
         5 . The method of  claim 1 , further comprising lowering the temperature of the copper and the dielectric to decrease the volatility and increase the sticking coefficient of the agent. 
     
     
         6 . The method of  claim 5 , wherein said lowering the temperature of the copper and the dielectric comprises lowering the temperature to between about −15° C. to +10° C. 
     
     
         7 . The method of  claim 1 , wherein said agent comprises an oxidizer having a low boiling point at or below about 21° C. 
     
     
         8 . The method of  claim 7 , wherein said oxidizer comprises Nitrogen Tetroxide. 
     
     
         9 . The method of  claim 8 , wherein said cooling comprises cooling the copper and dielectric to a temperature of the order of about −12° C. such that the Nitrogen Tetroxide is collected in a solid phase on the surfaces of the dielectric and the copper. 
     
     
         10 . A method of focused ion beam etching of copper in the presence of a dielectric comprising:
 directing a focused ion beam onto a portion of the copper; and   exposing the copper to an etch assisting agent comprising a first compound selected to protect the dielectric from etching and a second compound comprising a strong oxidizer to render sputtered conductive copper non-conductive.   
     
     
         11 . The method of  claim 10 , wherein the first compound is selected to have low to moderate volatility to afford a sufficient residence time on the dielectric to replenish dielectric lost due to ion beam etching. 
     
     
         12 . The method of  claim 11 , wherein said copper is located in a high aspect ratio hole that has first surfaces shadowed from direct exposure to the etch assisting agent, and said first compound is selected to have a volatility such that it bounces from second surfaces on which it impinges directly onto said first surfaces with sufficient flux to oxidize re-deposited copper at said first surfaces. 
     
     
         13 . The method of  claim 10  further comprising adjusting a ratio of copper etching ion beam current to a flux of the etch assisting agent to oxidize substantially completely sputtered copper that is re-deposited onto surfaces in the vicinity of said etching. 
     
     
         14 . The method of  claim 10 , wherein the first compound is selected from the group consisting of compounds that contain an N—N bonding in their molecules, where N is nitrogen. 
     
     
         15 . The method of  claim 14 , wherein said first compound is selected from the group consisting of Hydrazine monohydrate and Nitrosodimethylamine. 
     
     
         16 . The method of  claim 14 , wherein said second compound comprises Nitrogen Tetroxide. 
     
     
         17 . The method of  claim 10 , wherein said dielectric is one of a conventional or an organic dielectric. 
     
     
         18 . A method of focused ion beam etching of copper in the presence of a dielectric comprising:
 cooling the copper and the dielectric to a temperature between about −15° C. to +10° C.;   directing a focused ion beam onto a portion of the copper; and   exposing the copper and the dielectric to an etch assisting agent comprising Nitrogen Tetroxide.   
     
     
         19 . The method of  claim 18  further comprising adjusting a copper etching ion beam current relative to a flux of Nitrogen Tetroxide such that sputtered copper is substantially completely oxidized and dielectric sputtered by the ion beam is substantially replenished. 
     
     
         20 . The method of  claim 19 , wherein the dielectric is one of silicon dioxide or an organic dielectric, and the dielectric is replenished through reaction of Nitrogen with one or both of the dielectric and Gallium from the ion beam.