Modification of block copolymer lithography masks by O₂/Ar plasma treatment: insights from lift-off experiments, nanopore etching and free membranes

Abstract

Block copolymer lithography allows for the large-area patterning of surfaces with self-assembled nanoscale features. The created nanostructured polymer films can be applied as masks in common lithography processing steps, such as lift-off and etching for pattern replication and transfer. In this work, we discuss an approach to improve the pattern replication efficiency by modification of the polymer mask prior to lithographical use by means of an O2/Ar plasma treatment. We present a much better quality of pattern replication without loss of features, along with a precise tunability of feature sizes, that can be achieved by short mask treatment. We point out a correlation between nanopore position within the ordered arrays, expressed by its coordination number, the nanopore shape and the replication efficiency. Our experimental strategy to explain these correlations combines the indirect investigation of patterns replicated from the modified polymer masks and direct investigation of the mask top and bottom. Pattern replication is performed either in the form of gold nanodot arrays created via lift-off or nanopores transferred into a SiO2 substrate by reactive ion etching. The direct analysis of free polymer membranes released from the substrate reveals the nanopore shape at the mask top and bottom surfaces.

High‐Resolution Study of Changes in Morphology and Chemistry of Cylindrical PS‐b‐PMMA Block Copolymer Nanomasks during Mask Development

“…For further utilization in subsequent lithography processes, one polymer type can be selectively removed to use the remaining nanostructure as a shadow mask for, e.g., lift-off or etching processes. [13][14][15][16][17][18][19] To enhance the hardness of thin nanomasks in these etching processes, one polymer species can be selectively infiltrated with organometallic precursors prior to etching. [20] PS-b-PMMA is the most commonly used polymer in BCP lithography, where the chemically less stable PMMA domains are usually selectively removed to create a PS shadow mask.…”

Nanoscale Block Copolymer Self‐Assembly and Microscale Polymer Film Dewetting: Progress in Understanding the Role of Interfacial Energies in the Formation of Hierarchical Nanostructures

“…Since block copolymer self‐assembly was found suitable for lithography purposes large effort was invested to control the orientation of polymer domains with respect to the substrate because only perpendicular orientations of polymer cylinders, gyroids, or lamellae allow for their use as shadow masks during lithography processing . It was shown before that the orientation can be controlled by adjustment of the film thickness, minimizing the total free surface energy by optimization of interfacial areas due to polymer geometry.…”

“…One crucial issue in advancing BCP lithography to its next technological level, i.e., rendering the technique applicable for versatile device integration, is the fundamental understanding of the self‐assembly process enabling control of the pattern formation and its guiding into desired surface architectures. In particular, interactions between the polymer and solid surfaces determine the morphology of nanostructures: polymer wetting behavior, nanopattern orientation, nanopattern uniformity through a thin film, and defect density in BCP thin films are fundamentally investigated by research groups contributing with insights from chemistry, physics, and material science.…”

Macroscopic Alignment of Block Copolymers on Silicon Substrates by Laser Annealing

“…g ., high-performance elastomers, 2 their anticipated potential lies in solution-based 3 and thin-film applications. 4 − 7 As thin films, these periodic nanostructures can be utilized as filtration 8 − 10 and ion-conducting membranes, 11 − 13 lithography masks, 14 − 18 and electronic 5 , 6 and photovoltaic materials. 19 − 21 Despite numerous efforts, reaching the point when practical implementation of BCP self-assembly can compete with conventional top-down fabrication remains a challenge.…”

“…While BCPs have found use as bulk heterogeneous materials, e . g ., high-performance elastomers, their anticipated potential lies in solution-based and thin-film applications. − As thin films, these periodic nanostructures can be utilized as filtration − and ion-conducting membranes, − lithography masks, − and electronic , and photovoltaic materials. − Despite numerous efforts, reaching the point when practical implementation of BCP self-assembly can compete with conventional top-down fabrication remains a challenge. It is primarily hindered by impractically slow self-assembly kinetics caused by high viscosity of these materials and by high density of kinetically trapped structural defects present in spontaneously ordered films. , Typically, spontaneous self-assembly yields only short-range ordered BCP morphologies with grain size not exceeding several repeats of the spacing between the microdomains .…”