Interference Microscopy

An Interference Microscope can measure 3D topography.

An Interference Microscope utilizes a Mirau objective installed on a piezo actuator, a white light source with larger bandwidth or a blue light with smaller bandwidth and a camera to create a stack of images by moving the Mirau objective vertical to the sample. Every pixel of the camera receives an interference signal (one wave packet) for an opaque surface or even 2 in case of a transparent membrane as long as the coherence length of the interference microscope is smaller than the membrane thickness.

The distance between 2 center points of wave packets from adjacent pixels are the vertical heights between those pixels. All pixel together form the topography map of the front side.

For a transparent membrane the backside surface evaluation requires the refractive index of the membrane to calculate the thickness and the backside topography map.

With this technique areas with different size and lateral resolution, according to the objective magnification, can be 3D scanned. The minimum digital-lateral resolution is 0.33 µm while the minimum vertical resolution is in the range of a couple of Angstroms.

Measuring instrument StraDex a is used for this technology.