Plasma dielectric etch process using a long fluorocarbon

Abstract

A process for etching a dielectric layer with an underlying stop layer, particularly in a counterbore process for a dual-damascene interconnect structure. The substrate is formed with a lower stop layer, a lower dielectric layer, an upper stop layer, and an upper dielectric layer. The initial deep via etch includes at least two substeps. A first substep includes a non-selective etch through the upper stop layer followed by a second substep of selectively etching through the lower dielectric layer and stopping on the lower stop layer. The first substep may be preceded by yet another substep including a selective etch part ways through the upper dielectric layer. For the oxide/nitride compositions, the selective etch is based on a fluorocarbon and argon chemistry, preferably with a lean etchant combined with a richer polymer former, and the non-selective etch includes a fluorocarbon or hydrofluorocarbon, argon and an oxygen-containing gas, such as CO.

What is claimed is:  
     
         1 . A multi-level dielectric etch method, comprising the steps of: 
 placing into a plasma reactor a substrate containing a layered structure formed over a substrate and comprising sequentially, from a bottom thereof, a first stop layer, a first dielectric layer, a second stop layer, a second dielectric layer, and a first photomask patterned with at least one first aperture;    a first flowing step of flowing a first gas mixture into said reactor and exciting it into a first plasma, said first plasma being capable of etching both said second dielectric layer and said second stop layer through said at least one first aperture; continuing said first step at least until said second stop layer is etched through; and    a second flowing step, performed without removing said substrate from said reactor after said flowing step, of flowing a second gas mixture into said reactor and exciting it into a second plasma, said second plasma etching said first dielectric layer through said at least one first aperture selectively to said first stop layer;    wherein at least one of said first and second gas mixtures comprise a single-hydrogen fluorocarbon gas and multi-carbon fluorocarbon gas.    
     
     
         2 . The multi-level dielectric etch method of  claim 1 , wherein said single-hydrogen gas has as F/C ratio of 3 or greater.  
     
     
         3 . The multi-level dielectric etch method of  claim 1 , wherein said multi-carbon gas has an F/C ratio of 3 or less.  
     
     
         4 . The multi-level dielectric etch method of  claim 2 , wherein said multi-carbon gas has an F/C ratio of 3 or less.  
     
     
         5 . The multi-level dielectric etch method of  claim 2 , wherein said first gas mixture further comprises CO.  
     
     
         6 . An etching method, comprising the step of: 
 providing a substrate having formed on the surface a sequentially arranged structure comprising a stop layer, a lower dielectric layer, and an upper dielectric layer;    defining a first photomask over said structure having a plurality of first apertures extending from a top most level a bottommost level of said photomask;    placing said substrate defined with said first photomask into a first plasma reactor substrate and powered by RF power supply;    a first step of flowing gas mixture into said reactor and exciting it into a first plasma, said first plasma etching said upper dielectric layer through said first apertures; and    a second step, performed without removing said substrate from said reactor after said first flowing step, of flowing a second gas mixture into said reactor and exciting it into a second plasma, said second plasma etching through said lower dielectric layer selectively to said stop layer until said stop layer is exposed;    wherein at least one of said stop first and second gas mixtures comprise a first single-hydrogen fluorocarbon gas and a first multi-carbon fluorocarbon gas.    
     
     
         7 . The etching method of  claim 6 , wherein said single-hydrogen gas has as F/C ratio of 3 or greater.  
     
     
         8 . The etching method of  claim 7 , wherein said multi-carbon fluorocarbon gas comprises a fluorocarbon having an F/C ratio of 3 or less.  
     
     
         9 . The etching method of  claim 6 , wherein said first multi-carbon fluorocarbon gas comprises a fluorocarbon having an F/C ratio of 3 or less.  
     
     
         10 . The etching method of  claim 9 , wherein said fluorocarbon has at least four carbon atoms.  
     
     
         11 . The etching method of  claim 6 , wherein said first gas mixture further comprises CO.  
     
     
         12 . The etching method of  claim 6 , further comprising: 
 providing a second photomask over said substrate to define a plurality of trenches; and    performing a trench etch comprising the steps of 
 a first trench etch substep of flowing a first trench etch gas mixture into said reactor and exciting it into a plasma so as to etch said upper dielectric layer to thereby define trenches,  
 a first ash step of flowing ashing gas to etch said second photomask, and  
 a second trench etch substep of flowing a second trench etch gas mixture into said reactor and exciting it into a plasma so as to etch said stop layer.  
   
     
     
         13 . The etching method of  claim 12 , wherein at least one of said first trench etch gas mixture and second trench etch gas mixtures comprises a second single-hydrogen fluorocarbon gas and a second multi-carbon fluorocarbon gas.  
     
     
         14 . The etching method of  claim 16 , wherein said second multi-carbon fluorocarbon gas comprises a hydrogen-free fluorocarbon having at least four carbon atoms.  
     
     
         15 . A multi-level dielectric etch method, comprising the steps of: 
 placing into a plasma reactor a substrate containing a layered structure formed over a substrate and comprising sequentially, from a bottom thereof, a first stop layer, a first dielectric layer, a second stop layer, a second dielectric layer, and a first photomask patterned with at least one first aperture;    a first flowing step of flowing a first gas mixture including a first fluorocarbon into said reactor and exciting it into a first plasma, said first plasma being capable of etching both said second dielectric layer and said second stop layer through said at least one first aperture; continuing said first step at least until said second stop layer is etched through; and    a second flowing step, performed without removing said substrate from said reactor after said flowing step, of flowing a second gas mixture including a hydrogen-free second fluorocarbon into said reactor and exciting it into a second plasma, said second plasma etching said first dielectric layer through said at least one first aperture selectively to said first stop layer;    wherein said second fluorocarbon is more heavily polymerizing than said first fluorocarbon.    
     
     
         16 . The method of  claim 15 , wherein said first fluorocarbon is a hydrogen-containing fluorocarbon.  
     
     
         17 . The method of  claim 16 , wherein said second fluorocarbon contains at least 4 carbon atoms.  
     
     
         18 . The method of  claim 17 , wherein said first fluorocarbon comprises CHF 3 .  
     
     
         19 . The method of  claim 16 , wherein said second fluorocarbon contains at least 4 carbon atoms.  
     
     
         20 . The method of  claim 19 , wherein said second gas mixture additionally includes CO.