Spectral Coherence Interferometry
A Spectral Coherence Interferometer can measure single and multilayer thickness and wafer shape.
A Spectral Coherence Interferometer utilizes an interferometer optics installed on a piezo actuator (the measuring instrument), a superluminescent diode light source and a digital spectrometer equipped with a diffraction grating and a line scan detector. While the piezo actuator is focusing the interferometer on the layer of interest, the line scan detector of the spectrometer receives an interference spectral-domain-signal that contains information of interface reflections at any material transition within the sample. With a Fast Fourier Transformation of the spectral-domain-signal every material interface will be separated and characterized. The difference between the appropriate peak centers, divided by the refractive index of the layer material results the thickness of the layer.
With this technique multilayer thickness of infrared transparent material down to 1 µm can be measured with nanometer resolution.
Measuring instrument StraDex f is used for this technology.