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Mitigating re-entrant etch profile undercut in Au etch with an aqua regia variant
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  • Mark Ferguson ,
  • Mohamed Najah ,
  • Frederic Banville ,
  • Mohamed Boucherit ,
  • Naresh Miriyala ,
  • Jacques Renaud ,
  • Luc Frechette ,
  • Francois Boone ,
  • Serge Ecoffey ,
  • Serge Charlebois
Mark Ferguson
University of Sherbrooke

Corresponding Author:[email protected]

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Mohamed Najah
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Frederic Banville
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Mohamed Boucherit
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Naresh Miriyala
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Jacques Renaud
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Luc Frechette
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Francois Boone
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Serge Ecoffey
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Serge Charlebois
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We investigate the re-entrant undercut profile resulting from Au wet etching for patterning micron range thick films using an aqua regia-based solution in comparison with an iodine-iodide-based commercial etchant. Our work discriminates between two undercutting mechanisms: galvanic acceleration of etch rate at the Au adhesion or barrier layer, and delamination-based undercutting. We tracked etch outcomes of feature size reduction from photoresist size, undercut Au in cross-section and lift-off of small (5-10 μm) features. Results indicate that galvanic undercutting is well-mitigated by the aqua regia solution compared to commercial etchant results. Good Au adhesion eliminates undercut for 500 nm-thick Au and mitigates it by ~80% for 1 μm-thick Au. We discuss the electrochemical origin of this mitigated galvanic undercut.
01 Aug 2022Published in Journal of The Electrochemical Society volume 169 issue 8 on pages 083504. 10.1149/1945-7111/ac8769