TRANSIENT, INTERFEROMETRIC IMAGING OF POLYCRYSTALLINE SILICON MEMS DEVICES DURING LASER HEATING

Abstract

To characterize microelectromechanical systems (MEMS) during laser processing, imaging and metrology techniques need to be developed that are capable of visualizing the dynamics of MEMS structures and that are compatible with high power lasers. This study describes a high-speed, interferometric imaging system for measuring out-of-plane deflections of polycrystalline silicon (polysilicon) MEMS structures. A HeNe laser with a wavelength of 632.8 nm illuminates the structures. Since polysilicon is semitransparent at 632.8 nm, interference occurs between light waves reflected from the top of the microstructure and light waves transmitting through the structure and reflecting off the substrate. The interference produces fringes along microstructures that correspond to changes in height. Using a high-speed CCD camera, transient interferometric images of the dynamic motion of MEMS devices are captured. The imaging technique is demonstrated by obtaining the first transient images of the repair of adhered polysilicon microcantilevers, due to Nd:YAG pulsed laser heating. The experimental results clearly show failed structures peeling from the substrate as they are repaired.