Sacrificial materials are often used in the fabrication of devices, such as MEMS (microelectromechanical system) devices. These sacrificial materials are removed in a later stage in a process flow to generate designed empty spaces below or around the devices. This removal process is also commonly called a release process, because the movable parts of a device are released and free to move in at least one dimension after the sacrificial material is removed. The sacrificial material is often removed using chemical processes, such as etching, near the end of wafer fabrication. Since the sacrificial material often occupies space underneath the movable devices, it is frequently difficult to determine when the removal process is complete using standard optical inspection of the wafer.
In the past, it has been difficult to accurately monitor or evaluate the completeness of the release process. In some processes, device structures are scratched or otherwise physically removed to reveal the progress of the release process.