Andrea Schilp

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.

A surface micromachined silicon gyroscope using a thick polysilicon layer

A new silicon gyroscope is presented in this paper. It has a measuring range of /spl plusmn/100/spl deg//s and a resolution of 1.26/spl deg//s at 10 Hz bandwidth. The mechanical sensor structure consists of polysilicon and its lateral extension is 1600 /spl mu/m. The gyro element is 11 /spl mu/m thick and less than 19 /spl mu/g in weight. This structure is suspended in its centre of gravity with a thin tether beam. The tether beam is shaped in a way that the sensor structure can be tilted around its three axes. The gyroscope is fabricated using silicon surface micromachining technology incorporating several new process steps. These new steps are mainly thick polysilicon deposited in an epitaxy reactor, the deep silicon etching and a new stiction free release etch. The gyro structure is electrostatically driven in an in-plane torsional dithering motion. In response to an external angular rate the drive motion is coupled into an out-of-plane motion which is measured capacitively.

Experimental characterization of dynamic micromechanical transducers

This paper starts with a short review on interferometric methods for optical analysis of resonant structures. Three important types of resonant sensor elements are then discussed: a piezoelectrically driven beam as the strain sensitive element of a bulk micromachined force-sensor, electrothermally driven/piezoresistively detected single and triple beams as the sensing elements of a bulk micromachined resonant accelerometer, and an electrostatically driven capacitively detected torsional resonator in surface micromachining technology, the key element of a (pseudo-) vibrating gyroscope. We present optical and electrical measurements and discuss the importance of crosstalk in the electric pickup signal. The dynamic behaviour of the resonant accelerometer in closed-loop undamping circuitry is analyzed by external excitation on a shaker table.