Redox buffered hydrofluoric acid etchant for the reduction of galvanic attack during release etching of MEMS devices having noble material films
AssigneeSandia Corporation
InventorMatthew G. Hankins
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Abstract
Etchant solutions comprising a redox buffer can be used during the release etch step to reduce damage to the structural layers of a MEMS device that has noble material films. A preferred redox buffer comprises a soluble thiophosphoric acid, ester, or salt that maintains the electrochemical potential of the etchant solution at a level that prevents oxidation of the structural material. Therefore, the redox buffer preferentially oxidizes in place of the structural material. The sacrificial redox buffer thereby protects the exposed structural layers while permitting the dissolution of sacrificial oxide layers during the release etch.
Claims19
An etchant solution to reduce galvanic attack on a structural material during the release etching of a sacrificial material layer of a MEMS device having a noble material film, comprising:
- an aqueous solution of water and hydrofluoric acid, and
- at least one redox buffer dissolved in the aqueous solution that maintains the redox potential of the etchant solution so that the redox buffer is preferentially oxidized over the structural material, wherein the at least one redox buffer comprises a thio-phosphorous-based compound comprising one or more phosphorous atoms and one or more sulfur atoms bonded to the phosphorous atom.
Dependencies are inferred from the claim text.