Novel imaging system for measuring microscale curvatures at high temperatures

An innovative system was designed to optically measure the curvature of mic roelectromechanical system at high temperatures. The system takes advantage of the limited numerical aperture of the imaging system to detect the curv ature of cantilever beams. Images of the beam are used to determine beam cu rvature at high temperatures of up to 850 degrees C by analyzing the appare nt change in beam length as seen by the camera during an experimental trial . The system is designed to operate at very high temperatures, which is dif ficult in conventional microscale curvature measurement techniques such as scanning electron microscopy or stylus profilometry due to excess heating o f peripheral equipment. The system can measure curvatures as small as 300 m (-1), which corresponds to tip deflections of 1.5 mu m for a 100 mu m beam. The resolution of the system is limited by the image resolution of the cha rge-coupled device camera, and increases at large curvatures. The maximum c urvature that can be measured by the system is limited by the increase in s ystem resolution, and is estimated to be 4500 m(-1), corresponding to 22 mu m deflection for a 100 mu m beam. The apparatus was demonstrated to measur e the thermally induced curvature of multilayered thin-film cantilever beam s. The beams bend at high temperatures due to mismatch in thermal expansion coefficients between the layers. One innovative application of such curvat ure measurement is the determination of thermophysical properties of thin f ilms at elevated temperatures. This article presents the experimental setup and operational theory of apparatus, as well as curvature measurements obt ained by the system. The thermal expansion coefficient of polycrystalline s ilicon, determined from the curvature measurements, are also discussed. (C) 2000 American Institute of Physics. [S0034-6748(00)04401-4].