High-definition vertical-scan interferometry
View Patent ↗A broadband interferometric vertical scan of a sample surface is performed to produce interference data in conventional manner. A coarse surface profile of the surface is obtained in real time using a conventional technique, such as a center-of-mass calculation. A fine surface map is obtained concurrently using a quadrature-demodulation algorithm applied in real time to the same interference data used for the coarse surface calculation. The fine surface map is then combined with the coarse surface profile using an unwrapping technique that produces a final surface map with sub-nanometer resolution within a large height range.
1. A method for mapping a sample surface comprising the following steps:
scanning the sample surface in an interferometer at a predetermined scan step to produce a plurality of interference signals registered on a detector;
calculating a coarse map of the sample surface by application of a coherence-peak sensing technique on said interference signals;
calculating a fine map of the sample surface by application of a quadrature-demodulation technique on said interference signals;
subtracting the fine map from the coarse map of the sample surface to produce a noisy fringe map thereof;
rounding said noisy fringe map to values corresponding to an integer number of fringes, thereby producing a noise-free fringe map;
adding the fine map to the noise-free fringe map to obtain a high-definition map of the sample surface; and
processing said high-definition map to produce a visibly perceptible map of the sample surface;
wherein said interference signals are used both in the coherence-peak sensing technique and in the quadrature-demodulation technique; and
wherein said coherence-peak sensing technique and said quadrature demodulation technique are carried out concurrently in real time during said scanning step.
2. The method of claim 1 , wherein said sample surface belongs to a layer with two opposite surfaces and the method is used to map each of said surfaces.
3. The method of claim 2 , further including the step of calculating a thickness of said layer.
4. The method of claim 1 , wherein said coherence-peak sensing technique and said quadrature demodulation technique are carried out concurrently in real time during said scanning step.
5. The method of claim 1 , wherein said coherence-peak sensing technique is a center of mass technique.
6. The method of claim 1 , wherein said coherence-peak sensing technique is a quadrature center of mass technique.
7. The method of claim 1 , wherein said coherence-peak sensing technique is a zero crossing detection technique.
8. The method of claim 1 , wherein said quadrature-demodulation technique is a filter with a phase parameter equal to said scan step.
9. The method of claim 1 , further including the step of correcting said noise-free fringe map with a frame offset.