Imprint lithography apparatus and method

An imprint apparatus comprising:

• an imprint holder configured to hold an imprint template, the imprint template having a patterned surface to pattern an imprintable liquid medium on a substrate by contact between the patterned surface and the imprintable liquid medium,
• a substrate table configured to hold the substrate,
• a detector configured to generate a signal derived from light emergent from an interface between the imprintable liquid medium and the patterned surface, during a filling period as imprintable liquid medium substantially fills the recesses in the patterned surface, and
• a computer configured to derive data from the signal concerning one or more voids at the interface during the filling period, and to derive an estimated end time for the filling period from a relationship between the data and time.

An imprint apparatus comprising:

• an imprint holder configured to hold an imprint template, the imprint template having a patterned surface to pattern an imprintable liquid medium on a substrate by contact between the patterned surface and the imprintable liquid medium,
• a substrate table configured to hold the substrate,
• a detector configured to collect and measure light emergent from an interface comprising one or more voids between the imprintable liquid medium and the patterned surface and to generate a signal therefrom, and
• a computer configured to calculate an estimated end time required for the imprintable liquid medium to substantially fill the recesses in the patterned surface from data derived from the signal generated by the detector.