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Diffractive inline optical metrology

The quest for affordable microfluidics manufacturing techniques has led us to consider how micro-/nano-fluidic devices could be monitored on a production line. We need fast methods for determining whether pattern replication is complete. One approach is to imprint process-monitor holograms, customized so that, when illuminated, their far-field diffraction pattern reveals certain processing defects. In preliminary work, we have used simulated annealing to design a set of holograms that, when brought into contact with an imprinted array of nanochannels and illuminated, yield a diffraction pattern that can show the approximate depth of the nanochannels. The use of the holograms allows the diffraction patterns to be interpreted with a series of binary intensity comparisons, making the method simple to execute and applicable where there is spurious ambient light.