Siloxane Polymers for High-Resolution, High-Accuracy Soft Lithography

We report the formulation of siloxane polymers for high-resolution, high-accuracy stamps for soft lithography. With this technique, a molecular, polymeric, or liquid ink is applied to the surface of a stamp and then transferred by conformal contact to a substrate. Stamps for this technique are usually made of a commercial siloxane elastomer with appropriate mechanical properties to achieve conformal contact but are incapable of printing accurate, submicrometer patterns. To formulate better stamp polymers, we used models of rubber-like elasticity as guidelines. Polydimethylsiloxane networks were prepared from vinyl and hydrosilane end-linked polymers and vinyl and hydrosilane copolymers, with varying mass between crosslinks and junction functionality. The polymer formulations were characterized by strain at break as well as compression modulus and surface hardness measurements. This resulted in the identification of polymers having mechanical properties that allow the replication of high-density patterns at the 100-nm scale and that withstand the mechanical constraints during use as a stamp material. We also demonstrate advantageous implementations of the formulated polymers in hybrid stamps that achieve submicrometer
dimensional accuracy over large areas.