Topographic Templating of Islands and Holes in Highly Asymmetric Block Copolymer Films

Abstract

Asymmetric diblock copolymers with a spherical domain structure form islands or holes on the free surface of a thin film when the initial spun-cast film thickness does not match that of an integral number of layers of spheres plus a brush. When this film is cast on a substrate topologically patterned with rectangular, flat bottomed wells as deep as a layer of spheres, the edges of these wells act as sinks for excess material. As a result, we observe the movement of material away from the raised areas (mesas) toward the adjacent wells so that if a mesa surface initially contains holes exposing the underlying layer of spheres or brush, these holes will coalesce and grow until the top layer of spheres forms a bicontinuous structure with the holes, and finally this structure will break up into discrete islands. If the islands exist on top of only a brush layer, their shrinkage is limited by the detachment kinetics of a chain from the island into the brush. If the islands are on top of another layer of spheres, the shrinkage of the islands is much faster than would be expected if it were controlled by the diffusion of chains through the underlying nanodomain structure.

Patterning with block copolymer thin films

“…Heier et al have succeeded in templating surface domain structures on smooth substrates that were chemically patterned by microcontact printing on a scale of 1-16 mm [141]. Similar patterning of island and holes has been shown for sphere-forming [142] and lamellar [143] block copolymers on a topographically patterned substrates. Several more studies have investigated the effect of surface patterning on block copolymer orientation and order and these will be discussed later in this review.…”

“…Initially, islands and holes form on top of the topographically patterned substrate. In a manner similar to that described earlier in this review for sphere-forming block copolymers [142], material flows from the tops of the mesas to fill the channels. In this case, however, transport may take place via a mass flow along the cylinder axis.…”

“…If the island is on top of another layer of spheres, the shrinkage of the islands is much faster than would be expected if it were controlled by the diffusion of chains through the underlying nanodomain structure. This indicates the insertion of entire spheres from the island into the layer below, probably through a defect in the underlying film [142]. This is in contrast to the bulk case in which diffusion does not appear to occur through the diffusion of entire spherical domains and instead occurs through the hopping diffusion of individual chains [165].…”

Square Packing and Structural Arrangement of ABC Triblock Copolymer Spheres in Thin Films

“…30,31,[43][44][45][46][47][48][49] However, for the much faster process of solvent annealing and evaporation under controlled humidity, chains must diffuse and reorganize within a time several orders of magnitude shorter than those used for thermal processing. Under such conditions, the surface and interior reconstruction is unlikely to result in an equilibrium structure.…”

Integration of block-copolymer with nano-imprint lithography : pushing the boundaries of emerging nano-patterning technology.

“…5,8,[23][24][25][26] Several studies have examined the structure and dynamics of defects of BCP thin films on homogeneous surfaces. [27][28][29][30][31][32][33] Structural evolution on chemically patterned surfaces, however, is significantly different from that observed on homogeneous substrates. 26 Welander et al, for example, have shown that annealing at elevated temperatures leads to formation of defect-free structures in a matter of minutes.…”