The effect of random copolymer on the characteristic dimensions of cylinder-forming PS-b-PMMA thin films

Abstract

The block copolymer self-assembly approach has received great attention in recent years as apossible way to overcome the limits of conventional lithography and to fabricate sub-22 nmstructures. At this level, precise nanometric control is crucial for technological applications andthe search for a flexible and reproducible protocol is a great challenge. The polystyrene-b-poly(methylmethacrylate)(PS-b-PMMA) system, with a styrene fraction of 0.71, spontaneously separates into a periodicarray of hexagonally packed PMMA cylinders embedded in a matrix of PS and, undersuitable processing conditions, this is perpendicularly oriented with respect to theunderlying substrate. The selective removal of the PMMA allows us to obtain ananoporous PS matrix with well-defined pore dimensions. Perpendicular orientation ofthe PMMA cylinders requires surface neutralization by means of a suitable PS-r-PMMA random copolymer. The choice of the random copolymer is not trivial, because different PS-r-PMMA copolymers strongly affect the characteristics of the PS-b-PMMA film deposited on it. In this paper the effects of the selected PS-r-PMMA on the arrangement as well as on the peculiar dimensions (pore diameter, pore topore distance) of the final nanoporous PS thin film are studied. Reliable protocols for thefabrication of a disposable polymeric mask are proposed in view of its application inadvanced lithographic processes.