Abstract
Numerous processes, e.g. in semiconductor and optics producing industries require film thickness observation.
These measuring systems depend on different working principles, e.g. spectral reflectometry or ellipsometry. The
spectral reflectometry interrogation method can be evaluated by various algorithms depending on resolution and
measuring range demanded. All methods require a broad spectral distribution of the light source in order to
sample the signal sufficiently for parameter extraction. Spectral sampling is often realized using a spectroscope,
which produces equidistant sampling points in frequency space. In contrast to conventional spectrally broad
light sources, the one employed here emits several spectral lines, which are non-equidistantly distributed. It also
introduces problems like variations of intensity in the output spectrum and narrow wavelength bands, in which
the reflected spectrum can be investigated. Non-equidistant sampling points additionally imply problems in
conventional analysis algorithms, e.g. a FFT anticipates equidistant sampling points. Narrow wavelength bands
imply little information to interrogate at the same spectral resolution of the interrogator. Strong variations
of intensity lead to high noise levels at wavelengths with low intensities. Therewith, accuracy, resolution and
measuring range are limited. An interrogator based on a Hg-Ar light source, a fiber coupler and a commercial
spectroscope is described in this work. Both, accuracy and measuring range, are investigated by simulation and
are experimentally proven on a glass on silicon demonstrator. Introducing an advanced algorithm, uncertainties
invoked by the source's spectral and intensity distribution are minimized and resolution as well as measuring
range are increased.
