Real-time scanner-nonlinearity error correction for HDVSI
View Patent ↗An error correction for scanner position is implemented by adjusting the filter parameters of the quadrature demodulation module of an HDVSI algorithm using a reference signal from an independent position measurement device (PMD). The step size generated by the PMD at each scanner step is substituted for the nominal scanner step in the quadrature demodulation algorithm calculating phase and in the coherent envelope algorithm calculating peak. This substitution eliminates all errors produced by scanner nonlinearities. Furthermore, over the large number of steps carried out during a normal scanning range, random scanner-position errors (such as produced by vibration and other system noise) are automatically corrected by integration over their normal distribution around the noise-free position value. Therefore, a complete correction of scanner-position error may be achieved using the reference signal.
1. A method for producing a height map of a sample with correction of errors produced by scanner nonlinearities, the method comprising the following steps:
producing a plurality of signals from a fringe pattern; and
calculating the map of the sample by application of a quadrature-demodulation technique on said signals;
wherein said quadrature-demodulation technique utilizes a phase parameter equal to a scan step produced by a reference signal.
2. A method for producing a height map of a sample with correction of errors produced by scanner nonlinearities, the method comprising the following steps:
producing a plurality of signals from a fringe pattern;
calculating a coarse map of the sample by application of a coherence-peak sensing technique on said signals;
calculating a fine map of the sample surface by application of a quadrature-demodulation technique on said signals; and
combining the coarse map and the fine map to produce a high-definition map of the sample;
wherein said quadrature-demodulation technique utilizes a phase parameter equal to a scan step produced by a reference signal.
3. The method of claim 2 , wherein said coherence-peak sensing technique and said quadrature-demodulation technique are carried out concurrently in real time during said scan step.
4. The method of claim 2 , wherein said coherence-peak sensing technique utilizes a phase parameter equal to said scan step produced by the reference signal.
5. The method of claim 4 , wherein said coherence-peak sensing technique and said quadrature-demodulation technique are carried out concurrently in real time during said scan step.
6. Apparatus for producing a height map of a sample surface with correction of errors produced by scanner nonlinearities, the apparatus comprising:
means for scanning the sample surface at a predetermined scan step to produce a plurality of signals registered on a detector from a fringe pattern;
means for calculating a coarse map of the sample surface by application of a coherence-peak sensing technique on said signals;
means for calculating a fine map of the sample surface by application of a quadrature-demodulation technique on the signals; and
means for combining the coarse map and the fine map to produce a high-definition map of the sample surface;
wherein said quadrature-demodulation technique utilizes a phase parameter equal to a scan step produced by a reference signal.
7. The apparatus of claim 6 , wherein said means for calculating a coarse map and said means for calculating a fine map of the sample surface are operated concurrently in real time.
8. The apparatus of claim 6 , wherein said coherence-peak sensing technique utilizes a phase parameter equal to said scan step produced by the reference signal.
9. The apparatus of claim 8 , wherein said means for calculating a coarse map and said means for calculating a fine map of the sample surface are operated concurrently in real time.