Bosch deep silicon etching: improving uniformity and etch rate for advanced MEMS applications

Bosch deep silicon etching is nowadays widely used on inductive coupled plasma equipment. Most inductive plasma sources in the field consist of a coil of one or several turns wound around a dielectric vessel, which is powered by radio frequency to generate a high density plasma. Wafers are placed onto a substrate electrode downstream of the plasma source. RF self-biasing is applied to accelerate ions from the high density plasma towards the wafer. A major drawback of this kind of plasma source is its limited uniformity, which lowers the yield in critical MEMS applications. In this paper, we present an approach to improve etch uniformity by introducing an aperture construction between the plasma source and the wafer. In combination with balanced coil drive, excellent uniformity over 150 mm diameter wafers was achieved even at very high etch-rates.