Structured-illumination microscopy on technical surfaces: 3D metrology with nanometer sensitivity

Structured-illumination microscopy is an incoherent method to measure the microtopography of rough and smooth objects. The principle: A sinusoidal fringe pattern is projected into the focal plane of a microscope. While the object is scanned axially, the contrast evaluation of the observed pattern delivers the 3D topography with a height uncertainty of only a few nanometers. By means of a high aperture the system can measure steep slopes: +/- 50 degrees on smooth objects (NA=0.8) and +/- 80 degrees on rough surfaces are possible. For industrial applications a fast measurement is one of the most desired aspects. We face this demand by exploiting the physical and information-theoretical limits of the sensor, and giving rules for a trade-off between accuracy and efficiency. We further present a new method for data acquisition and evaluation which allows for a fast mechanical scanning without "stop-and-go".