The present invention provides a technique for determining characteristics of
substrates, such as the presence of contaminants, shape, as well as the spatial
relationships between spaced-apart substrates. The spatial relationships include
distance and angular orientation, between first and second spaced apart substrates.
The technique includes forming a volume of fluid on the second substrate, with
the volume of fluid having an area associated therewith. The volume of fluid is
compressed between the first and second substrates to effectuate a change in properties
of the area, defining changed properties. The changed properties are sensed, and
the characteristics of the first and second substrates are determined as a function
of the changed properties.