CPM Seminar
Conforming Surfaces:
Some Mechanics of the Nanoimprint
Forming Process
Graham L. W. Cross
SFI Trinity Nanoscience Laboratory
Trinity College
Nanoimprint and a number of other related techniques are a collection of
surface patterning technologies that involve direct contact of a master
template with the target surface. As such, they are governed by the laws of
contacting bodies, and the mechanics involved can readily be investigated by
recently developed nanoindentation methods or close variants thereof.
Pattern transfer can be achieved by the application of heat and pressure to
the stamp (hot embossing), or solely by the generation of shear stress at the
contact (cold forming.) Among the many demonstrated applications of
nanoimprint, lithographic resist processing has generated considerable
interest due to its unique combination of high resolution patterning - now
pushing towards 10 nm in feature size and pitch - with rapid throughput over
very wide areas.
From a mechanical perspective, the problem of imprint is related to the
classic tribological problem of determining the true area of contact between
two rough surfaces under simple or combined tractions. For lithographic
purposes, the goal of imprint is to establish a complete, stress-free and
permanent conformation of the two surfaces over a wide range of length
scales, but in such a manner that the surfaces can be separated from each
other (ie. a crack propagated) without adhesive forces inducing further
permanent deformation. Further, this conformation must be achieved with a
supply of material that maximizes etch contrast by providing for almost
complete extrusion of material from negative regions when positive regions
become filled. The requirement of near complete extrusion in large aspect
ratio geometries makes for a challenging prospect even in systems with a low
shear strength, and this, in fact, defines the uniquely nanoscopic aspect of
the problem.
In this talk I summarize our experimental findings and conclusions on the
role of important factors influencing the fidelity of the imprint process
including elastic stresses, plastic deformation mechanisms, complexities in
the confined deformation rheology, and choices in the form of applied stress.
These are illustrated by a series of idealized experiments ranging from the
squeeze flow of prepared coupons to the flat punch indentation of thin films
and back extrusion into isolated cavities. A connection between these more
localized experiments and the established findings and requirements of
applications such as wide area lithography and functional polymer patterning
will be made.
Thursday, December 9th 2004, 15:30
Ernest Rutherford Physics Building, R.E. Bell Conference Room (room 103)
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