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Scattering techniques are today well controlled to characterize roughnesses of high-precision substrates and coatings, which are around a fraction of a nanometer in the optical bandwidth [1, 2, 3]. All these techniques involve a receiver, sample or beam motion so as to record the whole angular scattering pattern by reflection and transmission. However, in some situations these angular motions are penalising. This is the case when fast roughness-measurements are required (on-line measurements), or when the sample cannot be displaced (case of large pieces), or when only one scattering direction is allowed (case where the sample cannot be separated from a system) … For these reasons we recently proposed proposed [4] an alternative which consisted in using white light so as to cancel any mechanical movement in a scattering system. The resulting system is a one-angle white-light scatterometer with a reduced spatial frequency bandwidth. The principle of this white light scatterometer relies on the wavelength-angle equivalence in the spatial frequency. However additional concepts must be introduced to make the white light scattering to be proportional to roughness. Actually we have to shape the wavelength spectrum of illumination in a specific way given by theory. Two experimental techniques are presented to shape the incident spectrum. The first [4] is based on an interferential filter but suffers some disadvantages, such as the absence of tunability or retroaction. The second technique [5] involves micro-mirror or LCD matrices coupled with gratings, and offers several advantages. Fast retroaction allows to take account of a shift in the source power, and the tunability also offers the opportunity to build quasi-arbitrary filters. This last remark allows to extract a series of roughness moments (not only the roughness), so that the autocorrelation function of the topography can be reconstructed. We will discuss advantages and limits of this new technique.
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