Asymmetric fluid-structure dynamics in nanoscale imprint lithography

⎛ n ⎞in the FFT that is not indicative of the true signal I ⎜ ⎟ . A method is proposed⎝ λ ⎠for the minimization of the distortion introduced by K () t is described.The intensity is normalized by a reference signal. It was observed thatthe normalization of the intensity spectrum is very sensitive to the referencespectrum. The reference spectrum should be at zero gap or film thickness andthrough a material with the same index of refraction. However, if the referencecannot be taken for these conditions, the Fourier transform of the intensityspectrum will contain a false peak that belongs to the reference signal. This leadsto incorrect detection of the true signal since the magnitude of the reference isdominant in this case.Fortuitously, it was discovered that the intensity signal when the gap isinfinite, or practically speaking when interference is negligible, is identical to thatof zero gap. This allows the fiber optic probes to be placed at the measurementlocations and a reference to be taken through the quartz template. The template ismoved up from the substrate 100 microns and then a reference signal is captured.Without this capability, taking a proper reference is not trivial since the referencemust be taken with the template removed and then the template must be put backinto to place before the experiment can proceed. However, in doing this, thereference has been slightly modified because the index of refraction of quartz isnot unity, the sample placement has changed, and the measurement angle haschanged.Height and angle of the probe also make a difference when obtaining thereference signal. In the case of the reference, its period also changes as a functionof the optical path length. This is affected by the angle and focus of the signal.Changes to these parameters can affect the measured gap thickness or lead tofailure in the FFT. Thus, the reference should be collected at large gap where the96