Markus Biebl

Acceleration sensor and method for manufacturing same

An acceleration sensor has a proof mass attached by resilient elements, in the form of micromechanical components, in a monocrystalline silicon layer of an SOI (silicon-on-insulator) substrate, the insulator layer of the substrate being removed under the structure which is susceptible to acceleration, in order to enable free mobility of the micromechanical components. Piezoresistors are provided for detecting movement of the proof mass, the piezoresistors supplying electrical signals to an evaluation circuit.

Micromechanics compatible with an 0.8 μm CMOS process

Results on a new approach for the monolithic integration of micromechanics and electronics are presented. The same process steps and layers can be used for both the mechanical and the electronic elements. This is a promising process concept for integrated microelectromechanical systems with a minimum of additional costs compared to the standard electronics process. Results on the fabrication of micromechanical structures using the process steps of a 0.8 μm CMOS process are given. The sublimation technique is used to dry the released surface-micromachined structures and different sublimating chemicals are compared. The influences of polycrystalline and amorphous deposition as well as diffusion doping and ion implantation on the strain gradients of the structural layers are presented. A fabricated electrostatically deflectable and capacitively detectable cantilever is presented and the dependence of the capacitance on the drive voltage is shown. By using the presented theory and fitting calculations to the measured non-linear characteristic, a value of 170 GPa for Youngs modulus of the polysilicon film is extracted.

Ultrashallow Emitter-Base Profiles by Double Diffusion

The diffusion of boron out of polysilicon was investigated. Diffusion and segregation coefficients were determined for furnace annealing and rapid thermal processing. Double polysilicon self-aligned npn bipolar transistors with sub 100 nm base widths were obtained, using the double diffusion technique. Calculations for the optimization of the base pinch resistance are presented. It is shown that base widths as low as 50 nm can be obtained with the double diffusion technique.