Rapid Hierarchical Nanostructures of Lamellar Block Copolymer Thin Films via Microwave Annealing

Block copolymers (BCP) have been long investigated to achieve periodic nanostructures on silicon substrates which have a wide range of applications from the semiconductor industry to nanoelectronics. The nano periodicity of BCP in different shapes such as cylinders, lamella, spheres, and gyroids, is achieved by self-assembly by manipulating BCP composition nd temperature. While these structures can be achieved by thermal annealing (TA), it is a slow process. In contrast, microwave is a fast, effective and intriguing energy source, and a desirable method for heating various materials. We obtain hierarchically ordered lamellar BCP nanostructures in thin films by short-time microwave annealing on boron-doped silicon substrates, chosen for its high microwave absorption. We investigate the fast ordering kinetics of BCP films in as little as 10s compared to hours in TA, with respect to domain spacings (L₀) formation in parallel lamellar BCP morphology, as measured by island and hole formation characteristics on the film surface. An exciting feature is that ½ L₀ plateau form around the holes within a short time of microwave annealing, that is not typically observed in TA. These ½ L₀ relief structures transition to 1 L₀ when further subjected to extended TA. Lastly, we compared the domain spacing and average hole diameters evolution of microwave annealing of the BCP films with that of TA. We conclude that microwave annealing can be effectively used to obtain parallel, both non-traditional ½ L₀ and traditional L₀ lamellar relief topography structures, in very short times, making it suitable for industrial processing.