Increasing capabilities in precision manufacturing and micro technology are accompanied by increasing demands of high
precision industrial metrology systems. Especially for measuring functional surfaces, areal optical principles are widely
used. If, in addition, nanometer height resolution is needed interferometers seem to be the most promising instruments.
First, this contribution focuses on the transfer characteristics of white-light interferometers with microscopic field of
view. In general, microscopic instruments suffer from their limited lateral resolution capabilities. Hence, the transfer
function of these instruments is typically assumed to show a linear low-pass characteristic. We studied the transfer
characteristics of white-light interferometers by theoretical simulations and experimental investigations. Our results show
that in most practical cases these instruments behave nonlinear, i.e. the output surface profile cannot be obtained from the
input profile by a simple linear filter operation.
Although they are well-established, there are some further limitations of white-light interferometers if they are used to
measure micro or even sub-microstructures. If edges, steeper slopes or abrupt slope changes are present on a measuring
object characteristic errors such as batwings occur. Furthermore, a high effort concerning the correction of chromatic
aberration is necessary in order to avoid dispersion effects. Otherwise, there will be systematic discrepancies between
profiles obtained from evaluation of the coherence peak and those resulting from the phase of the interference signals.
These may lead to 2π phase jumps if the fringe order is obtained from the position of the coherence peak. Finally,
measurement artifacts may also result if the measured micro-structure shows discontinuities of the surface slope.
This contribution analyses the different phenomena and discusses approaches to overcome existing limitations.