Polymer issues in nanoimprinting technique

We have studied the suitability of poly(methylmethacrylate) (PMMA) of different molecular weight for large area pattern transfer by embossing structures above the glass transition temperature (Tg) of the specific polymer. The molecular weight covers a range of one order of magnitude (Mw approximately 5.0×104-8.1×105). This range was chosen in order to obtain information regarding the flow properties that we expect to depend strongly on the molecular weight at a specific temperature. Large area pattern transfer were tested by applying a stamp with both densely packed and isolated features. The feature size ranged from 100 μm down to 450 nm. At a processing temperature of 90 °C above Tg we found clear indications that flow is sufficient to transfer large, isolated features even into the polymer with the highest Mw. Problems of incomplete material transport can be related to local inhomogeneities of the imprint due to a lack of parallelism between the stamp and the sample. At 50 °C above Tg incomplete flow effects were observed over the whole area and for all molecular weights. This was observed only with large, isolated structures whereas small, periodic features showed a well defined transfer.