SUBPICOSECOND LASER PROCESSING OF POLYCRYSTALLINE SILICON MICROSTRUCTURES

Ultrashort-pulse lasers are able to recover stiction-failed microelectromechanical systems (MEMS) structures. A possible physical mechanism for this process is an electronic disruption of the bonding between the structure and the substrate, which depends strongly on the peak carrier temperatures. This article presents predicted carrier temperatures for polycrystalline silicon microcantilevers irradiated with ultrashort-pulse lasers. The effects of increased carrier-phonon coupling, reduced thermal conductivity, and increased absorption for polycrystalline silicon as compared to crystalline silicon are determined. An expression for the optimal absorption coefficient is derived for processes in which the excitation is desired at a specified depth into the material.