Characterization of deep wet etching of fused silica glass for single cell and optical sensor deposition (pdf)
The development of a high-throughput single-cell metabolic rate monitoring system relies onthe use of transparent substrate material for a single cell-trapping platform. The high opticaltransparency, high chemical resistance, improved surface quality and compatibility with thesilicon micromachining process of fused silica make it very attractive and desirable for thisapplication. In this paper, we report the results from the development and characterization of ahydrofluoric acid (HF) based deep wet-etch process on fused silica. The pin holes andnotching defects of various single-coated masking layers during the etching are characterizedand the most suitable masking materials are identified for different etch depths. Thedependence of the average etch rate and surface roughness on the etch depth, impurityconcentration and HF composition are also examined. The resulting undercut from the deepHF etch using various masking materials is also investigated. The developed and characterizedprocess techniques have been successfully implemented in the fabrication of micro-well arraysfor single cell trapping and sensor deposition. Up to 60 μm deep micro-wells have beenetched in a fused silica substrate with over 90% process yield and repeatability. To ourknowledge, such etch depth has never been achieved in a fused silica substrate by using anon-diluted HF etchant and a single-coated masking layer at room temperature.