Multi-step proportional miniaturization to sub-micron dimensions using pre-stressed polymer films.

The ability to define patterns and fabricate structures at the nanoscale in a scalable manner is crucial not only in integrated circuit fabrication but also in fabrication of nanofluidic devices as well as in nano and micromechanical systems. Top down fabrication at the nanoscale often involves fabrication of a master using a direct write method and then its replication using a variety of methods such as by hot embossing, nanoimprint lithography, or soft lithography. Nevertheless, fabrication of the master is a time consuming and expensive process. One interesting approach is to define patterns at larger dimensions on pre-stressed films using methods such as xurography or lithography which are scalable and heat them to de-stress and shrink which can reduce the size proportionally. Although attractive, suitable fabrication processes that can perform iterative shrinking of patterns over several cycles and into the nanoscale have not been demonstrated. Here, we demonstrate a fabrication process that is capable of accurately producing patterns and features over several cycles of miniaturization and shrinking to achieve resolution in the order of 100 s of nanometers. In this approach, a pattern transfer method is developed by combining soft imprint lithography followed by reactive ion etching, both of which are scalable processes, to transfer the original patterns into a shrinkable polymer film. The patterned shrinkable film is heated to allow thermal shrinking. As a result, the pattern size was decreased by 60% of the original size in a single cycle. This reduced pattern was used as the master for the next cycle and three cycles of miniaturization was demonstrated. Sub-micron patterns of 750 nm were generated by the multi-step miniaturization method, showing approximately 20× reduction in size of the original patterns. Finally, these patterns are transferred into features on a silicon substrate to demonstrate its application in semiconductor microfabrication or its use as a master template for microsystems applications.