Thickness and microdomain orientation of asymmetric PS-b-PMMA block copolymer films inside periodic gratings (original) (raw)

ACS Applied Materials & Interfaces, 2015

Abstract

The ordering process of asymmetric PS-b-PMMA block copolymers (BCPs) with molecular weight Mn = 54 kg∙mol-1 is investigated on flat surfaces and on topographically patterned substrates with gratings of ten trenches defined by conventional top down approaches and arranged to form densely packed periodic structures. When the ordering process is accomplished on a flat surface, in a temperature range between 180 and 230 °C, cylindrical nanodomains perpendicularly oriented with respect to the substrate are observed irrespective of annealing temperature. In contrast, when the ordering process occurs on topographically patterned substrates, different phenomena have to be considered. The simultaneous effect of the flow around the gratings and the BCP flux from the zone located between adjacent trenches (mesa) into the inner part of the trenches results in significant thickness variations of the confined BCP film. Therefore, the amount of BCP inside the trenches depends on the width of the mesa region, which acts as a BCP reservoir. Moreover within each trench group, the BCP thickness progressively decreases from the external to the central trenches composing the periodic grating. The thickness variation of the BCP film within the trenches strongly affects the ordering process ultimately leading to different orientation of the microdomains within the trenches. In particular when the annealing temperature is 190 °C a precise confinement of the BCP within the trenches featuring a perpendicular cylinder morphology is observed. At higher temperatures mixed or parallel orientations of the microdomains are obtained depending on the width of the trenches in the periodic grating.

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