Redox buffered hydrofluoric acid etchant for the reduction of galvanic attack during release etching of MEMS devices having noble material films
| DWPI Title: Etchant solution to reduce galvanic attack during release etching of microelectromechanical system device with noble metal film, comprises aqueous solution of water and hydrofluoric acid, and redox buffer dissolved in the aqueous solution |
| 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. |
| Use: For reducing galvanic attack on a structural material (i.e. silicon, polysilicon, silicon nitride, germanium, carbon, tungsten, molybdenum, hafnium, zirconium, titanium, nickel, metal, non-metal, nitride, oxide, or composite that does not etch quickly in hydrofluoric acid, and where structural material has a lower standard potential than the noble material) during the release etching of a sacrificial material (i.e. silicon dioxide) layer of a microelectromechanical systems (MEMS) device having a noble material (i.e. gold, silver, copper, platinum, palladium, iridium, rhodium, osmium, ruthenium or rhenium) film (all claimed). |
| Advantage: The etchant solution chemistries prevents the degradation of structural layers during the release etch step are highly sought after. The noble material comprises a metal or material that provides a superior electrode surface to the structural material for the reduction of hydrogen ions or other species that can be oxidized. The redox buffer in the etchant solution maintains the electrochemical potential of the etchant solution at a level that prevents oxidation of the structural layers during the release etch of MEMS devices; suppresses unwanted oxidation of an anodic material in a closed circuit with a noble metal; reduces roughening by buffering oxidation on a microscopic scale; and provides adequate buffering capacity at a specific redox potential and preferential oxidation of the redox buffer over the structure is protected. |
| Novelty: An etchant solution (S1) comprises 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 oxidized over the structural material, where the redox buffer comprises a thio-phosphorus-based compound containing at least one phosphorus atoms and sulfur atoms bonded to the phosphorus atom. |
| Filed: 12/20/2004 |
| Application Number: US200417108A |
| Tech ID: SD 7634.0 |
| This invention was made with Government support under Contract No. DE-NA0003525 awarded by the United States Department of Energy/National Nuclear Security Administration. The Government has certain rights in the invention. |
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