Meandering 'string-like' features observed in an anodic bond

• Published in: Journal of micromechanics and microengineering 2002-09, Vol.12 (5), p.541-547
• Main Authors: Spangler, Glenn E, Kolesar, Edward S
• Format: Article
• Language: English
• Subjects: Anodic polarization; Applied sciences; Electric field effects; Electronics; Etching; Exact sciences and technology; Gas chromatography; Lithography, masks and pattern transfer; Microelectronic fabrication (materials and surfaces technology); Optical microscopy; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Silicon wafers; Viscous flow
• ISSN: 0960-1317; 1361-6439
• DOI: 10.1088/0960-1317/12/5/305

During assembly of the components of a microfabricated gas chromatographic (GC) column with an anodic bond, 'string-like' features were observed in the anodic bond with high-resolution optical microscopy. The 'string-like' features are attributed to boundaries between multiple fronts of viscous fluid flow that occurred during bond formation. The viscous flow is thought to originate from the boric oxide content of the Schott BOROFLOAT glass that was used for the cover-plate, and activated by the negative ion migration created by the large externally applied electric field. The boric oxide appeared to act not only as filler for the anodic bond, but also as a sealer. This latter property allowed the irregular surfaces associated with the etched silicon wafer to be sealed to the flat BOROFLOAT cover-plate. Due to the strong solvent action of boric oxide for silicon oxide, the bond was improved by pre-oxidizing the silicon wafer. (Author)