A new plasma-etching technique for micromechanical structuring of quartz

Abstract A plasma-etching technique is presented for the micromechanical structuring of single-crystal quartz wafers that are used for the fabrication of piezoelectric bulk wave resonators. The glow discharge is r.f. powered (27 MHz) and the feed gas is CF 4 . The structuring principle is based on a specially designed electrode system in which the substrates are closely integrated. A patterned carbon plate at floating potential and small r.f. electrode heads provide for the confinement of the plasma onto the substrate areas that are to be etched. The achieved etch profiles are due to the plasma structure and correspond qualitatively to the radial charge carrier as well as the excited-species distribution known from hollow-cathode measurements. Plane-parallel, convex and concave etching profiles in the lateral millimetre range are possible. The etch rate of AT-cut single-crystal quartz amounts to more than 2.5 times the value of common diode-etch systems under similar discharge conditions and reaches about 4 μ/min. Total etch depths are 50 – 100 μ. Surface studies indicate almost no changes of the roughness of polished quartz samples during the described etch processes.