Nondestructive inspection of buried channels and cavities in silicon

Microelectromechanical systems and microfluidic devices feature buried channels, cavities, and other embedded microstructures. These features are usually examined by breaking the wafer and by imaging the revealed cross section. We propose a nondestructive technique to evaluate the shape and surface quality of buried microchannels with submicrometer resolution. The technique relies on infrared light interferometry. We employed the technique to nondestructively examine channels and cavities through a silicon roof. With the proposed technique, we can quantitatively examine the size and shape of microchannels that are hidden to visible light.