Interferometric Metrology
Method for measuring surface topography by analyzing the interference patterns of light waves involves shifting the phase of a reference beam in known increments. Phase shifting interferometry produces extremely high vertical resolution, making it suitable for characterizing the smoothness of copper foil and the flatness of semiconductor substrates. The technique relies on the interaction between a reflected light wave from the sample and a reference wave to create a map of height variations.
Measurement Precision
Algorithms calculate the height at each pixel by comparing the intensity changes across a series of captured images as the phase is shifted. This process allows phase shifting interferometry to resolve vertical features that are much smaller than the wavelength of the light used. Because it is highly sensitive to vibrations, the equipment is typically housed on anti-vibration tables in a controlled environment.
High-precision manufacturing environments use this data to ensure that surface roughness does not exceed the limits required for high-frequency signal integrity.
Application Domain
Engineers use this technology to verify that the surface finish on a pad is uniform enough for gold wire bonding or fine-pitch flip-chip mounting. Variations in height that are invisible to standard microscopes are easily captured and quantified. This level of detail is necessary for the development of high-speed circuits where surface roughness can influence signal loss.
