Conformal contact and pattern stability of stamps used for soft lithography

Patterning in soft lithography techniques such as microcontact printing or light-coupling mask lithography is mediated by surface topographical patterns of elastomeric stamps: intimate contact with the substrate is achieved locally at the protruding areas, whereas a gap remains between the substrate and recessed zones. This principle challenges the properties of the stamp, especially when printing high-resolution or extreme aspect-ratio patterns with high accuracy. On the one hand, the stamp must be soft enough to enable conformal contact with the substrate, which means that it must adapt elastically without leaving voids created by the natural roughness of the substrate. On the other hand, a precise definition of micropatterns requires a rigid material. In this article, we analyze the conditions of elasticity, roughness, and energy of adhesion to establish conformal contact between an elastomer and the target surface. Furthermore, we address questions of replication accuracy and evaluate local elastic deformation induced by normal forces using model calculations for simple pattern geometries. Pressure applied during contact leads to a sagging or collapse of the unsupported areas. We discuss implications on both material and pattern design that allow spontaneous propagation of conformal contact while inhibiting the spreading of collapse. (C) 2000 American Institute of Physics. [S0021-8979(00)09719-X].