Fabrication of Quartz Microcapillary Electrophoresis Chips Using Plasma Etching

In order to fabricate microcapillary electrophoresis (µ-CE) chips, high-rate quartz etching with high selectivity over the mask was studied using both C 4 F 8 /Ar and C 4 F 8 /SF 6 high-density plasmas with Cr hard masks. Vertical quartz etching with high etch rate selectivity against the mask was attained using an 85%C 4 F 8 /15%SF 6 inductively coupled plasma, where the quartz etch rate 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 quartz etching technology has been demonstrated by fabricating vertical trench features with 50 µm depth and 20 µm 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 µ-CE chips fabricated using plasma etching were examined and compared with those fabricated 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 become attainable for the first time by deep plasma etching technology, has been shown to be the most suitable for the optical absorption detection commonly used in capillary electrophoresis and liquid chromatography and for the image observation necessary for particle and/or cell electrophoresis. Furthermore, the advantage of pattern transfer with high resolution and high fidelity has been demonstrated by fabricating functional microstructures such as a slit or a filter within a capillary.