FIGURE 1 Collapse behavior of photoresist structures (Apex-E, pitch = 400 nm, line-width = 200 nm).

In the bulk, the mechanical properties and the glass transition of a material are related; the shear modulus, for example, increases substantially as the temperature is decreased below T_g. It is therefore natural to anticipate similar relations in nanoscopic structures. When the distance between patterned resist structures (or MEMS [microelectromechanical systems] components) decreases, tremendous capillary forces are produced during drying of rinse liquids (e.g., water, after wet chemical processing) (Cao et al., 2000). These forces can cause the structures to collapse (see Figure 1) (Cao et al., 2000; Goldfarb et al., 2000; Namatsu et al., 1999). For arrays of dense (1:1) and semidense (1:2-1:5) lines with widths of 100 to 200 nm and aspect ratios of 3 to 4, we have shown that the susceptibility to collapse is strongly dependent on the aspect ratio and that the critical aspect ratio of collapse is inversely proportional to the distance between structures (Cao et al., 2000). These observations are consistent with models of capillary forces that predict that the force acting on the resist structures is inversely proportional to the distance between structures. They are also consistent with beam-bending models that predict that the maximum deformation of the resist structure in response to the imposed force is proportional to the aspect ratio cubed and is inversely proportional to the stiffness (Young’s modulus).

The focus of our efforts over the last few years has been to fill a serious gap that hinders the development of nanotechnology and to develop a fundamental understanding of the properties of nanostructured polymeric materials. Through a combination of theoretical and experimental work, we have attempted to acquire a fundamental understanding of transport and mechanical properties of nanostructured polymers, because precisely these properties often determine their usefulness in coating, packaging, MEMS, microelectronic, and nanotechnology