State of the Art MEMS testing
MEMS are today tested on the wafer level using a serial approach, which means that the inspection system is scanned from structure to structure over the whole wafer. In production line mostly the testing of passive parameters are carried out.
MEMS are produced on a large scale for e.g. hard disk heads, RF antennas, displays and sensor applications. The testing of MEMS in industrial production lines is today mainly limited to dimension control and electrical functionality.
The most important optical technique for the static inspection of MEMS is microscopy (size of MEMS structures is typically 1-1000µm). Fault detection and measurements of lateral dimensions of MEMS structures are the most important applications for MEMS measurement techniques.
Passive MEMS-testing (i.e. x-y-(z) dimensions) is often based on such a microscope system connected with a camera. Image processing is utilised for the detection of the x- and y-dimensions. For many producers this is the only test approach. Some suppliers offer confocal techniques or interferometry to measure the z-direction. The shape of the object can thus be measured.
Active MEMS-testing (e.g. resonance frequencies, displacements) is typically carried out using interferometers and vibrometers.