Effects of layers and vias on continuous-wave laser heating and damage of surface-micromachined structures

Abstract

The response of microsystem components to laser irradiation is relevant to processes and applications such as laser processing, optical diagnostics, and optical microelectromechanical systems (MEMS) device design and performance. The dimensions of MEMS, which are on the order of several micrometers, are on the same order as infrared laser wavelengths, which results in interference phenomena when the parts are partially transparent. Four polycrystalline silicon structures were designed and irradiated with 532 and 808 nm continuous wave laser light to determine the effects of layers, air gaps, and the presence of a substrate via on the threshold laser power for damage. The presence of a substrate via resulted in lower damage thresholds, and a single-layer structure had the highest damage threshold for structures irradiated with infrared light. Structures irradiated with visible wavelength light exhibited less sensitivity to the underlying via. Optical interference calculations are carried out to evaluate the absorptance of these structures as a feasible explanation for the observed results.