Systematic Characterization of DRIE-Based Fabrication Process of Silicon Microneedles
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1052-DD07-07
Systematic Characterization of DRIE-Based Fabrication Process of Silicon Microneedles Jochen Held1, Joao Gaspar1, Patrick Ruther1, Matthias Hagner2, Andreas Cismak3, Andreas Heilmann3, and Oliver Paul1 1 Department of Microsystems Engineering (IMTEK), University of Freiburg, Georges-KoehlerAllee 103, Freiburg, D-79110, Germany 2 Department of Physics, University of Konstanz, Universitätsstr. 10, Konstanz, D-78457, Germany 3 Department of Biological materials and interfaces, Fraunhofer Institute for Mechanics of Materials Hal, Walter-Hülse-Strafle 1, Halle (Saale), D-06120, Germany ABSTRACT This paper reports on the systematic characterization of a deep reactive ion etching based process for the fabrication of silicon microneedles. The possibility of using such microneedles as protruding microelectrodes enabling to electroporate adherently growing cells and to record intracellular potentials motivated the systematic analysis of the influence of etching parameters on the needle shape. The microneedles are fabricated using dry etching of silicon performed in three steps. A first isotropic step defines the tip of the needle. Next, an anisotropic etch increases the height of the needle. Finally, an isotropic etch step thins the microneedles and sharpens their tip. In total, 13 process parameters characterizing this etching sequence are varied systematically. Microneedles with diameters in the sub-micron range and heights below 10 µm are obtained. The resulting geometry of the fabricated microneedles is extracted from scanning electron micrographs of focused ion beam cross sections. The process analysis is based on design-ofexperiment methods to find the dominant etch parameters. The dependence of the needle profiles on process settings are presented and interpolation procedures of the geometry with processing conditions are proposed and discussed. INTRODUCTION For drug development and disease studies, electrical recording of cells is a fundamental method. However, the classical patch-clamp methods available for intracellular measurements are time-consuming and require experienced staff [1]. On the other hand, methods like patch-onchip systems enable the parallel examination of a larger number of cells [1]. However, the patchon-chip method is restricted to cells in suspension, as the cells have to be positioned and fixed through small holes in the measurement chip. So far, cell monitoring chips with adherent cell cultures have allowed the detection of extra-cellular potentials only [2]. To provide a method that enables the measurement of intracellular cell potentials of adherently growing cells, a novel cell chip design comprising microneedle-based electrodes has been developed [3,4]. The cells are cultured on these electrodes which are introduced into the cytoplasm using electroporation [4]. Due to the low radius of curvature of the electrodes below 1 µm, a voltage pulse on the order of a few hundred millivolts up to a few volts is sufficient for this purpose [4]. The profile of the needles is important for
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