Fabrication of quartz microcapillary electrophoresis chips using plasma etching

In order to fabricate microcapillary electrophoresis (mu-CE) chips, high-ra te quartz etching with high selectivity over the mask was studied using bot h C4F8/Ar and C4F8/SF6 high-density plasmas with Cr hard masks. Vertical qu artz etching with high etch rate selectivity against the mask was attained using an 85%C4F8/15%SF6 inductively coupled plasma, where the quartz etch r ate was 530 nm/min and the etch rate selectivity against the mask measured at the Cr top surface and the facet were 80 and 27, respectively. Deep quar tz etching technology has been demonstrated by fabricating vertical trench features with 50 mu m depth and 20 mu m width, i.e., the aspect ratio of 2. 5, which cannot be attained by means of the wet chemical etching technology conventionally used. Subsequently, fundamental performances of mu-CE chips fabricated using plasma etching were examined and compared with those fabr icated by conventional wet etching. No significant difference was found in the separation performances between dry-etched and wet-etched chips, while the rectangular cross-sectional feature with high aspect ratio, which has b ecome attainable for the first time by deep plasma etching technology, has been shown to be the most suitable for the optical absorption detection com monly used in capillary electrophoresis and liquid chromatography and for t he image observation necessary for particle and/or cell electrophoresis. Fu rthermore, the advantage of pattern transfer with high resolution and high fidelity has been demonstrated by fabricating functional microstructures su ch as a slit or a filter within a capillary.