Nanopatterning with diblock copolymers

There has been an interest in going beyond conventional lithographic techniques in order to make features of ever smaller scale and higher density over large areas. In this paper we discuss progress that has been made over the past decade in using the self-assembly of diblock copolymer films as a template for creating two dimensional patterns (lines and dots) with a characteristic spacing of 20-30 nm. Typically trillions of dots, holes, posts of semiconductors and metals are produced on conventional semiconductor wafers. We describe the basic concept of the pattern formation and the technology of the transfer of the pattern from soft to hard materials. In order to produce and study these nanoscopic patterns we had to develop some new techniques for getting two and three dimensional images. 3D depth profiling with reactive ion etch (RIE) slices of 7 nm thickness alternating with electron microscope pictures proved very effective. We became very interested in the pattern formation and annealing necessary to control the long range order of the arrays and found new ways to follow the ordering. The coarsening was found to obey a t^1/4 power law, (that is the size of the “grains” grew with time with this dependence) and at least for the striped pattern (cylinders lying down in a fingerprint like pattern) we could understand the microscopic origin of this behavior. We studied these phenomena with time lapse AFM microscopy and found that the disorder was dominated by the presence of disclinations and the annealing occurred by the annihilation of disclination multipoles rather than simple disclination – antidisclination, dipole dynamics. We also found that the orientation of the patterns could be controlled by introducing alignment marks, step edges.