Stiction-Induced Sealing of Surface Micromachined Channels

Abstract

We established a technique to achieve low temperature hermetic sealing of surface micromachined channels by exploiting stiction. Using a wing-shaped structural layer, microchannels automatically seal during the drying step that follows the sacrificial etch. This avoids the need of plugging layers to close the apertures of the sacrificial etch. To demonstrate the technique, we designed a surface micromachined channel with a structural layer made of polycrystalline silicon carbide (poly-SiC). This layer integrates an array of anchored pillars to achieve long and wide microchannels (5.4 mm × 0.43 mm × 0.001 mm). To dimension the sealing-wing, we estimate the minimum adhesion energy between the poly-SiC and silicon. This is done by analytical modeling and experimental characterization of test structures in the shape of centrally-supported circular plates. The bending and adhesion of the sealing-wing is followed in situ by optical microscopy. The closed microchannels are annealed at 100 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C. Some structures are exposed to thermal stress at 760 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C. The results are inspected by white light interferometry, scanning electron microscopy, and helium leak testing. Microchannels result hermetically sealed showing leak rates below the detection limit (4×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> Pa·m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> /s). The seal is effective to at least 600 kPa.