Influence of block copolymer feature size on reactive ion etching pattern transfer into silicon

High Aspect Ratio Nanoscale Pores through BCP-Based Metal Oxide Masks and Advanced Dry Etching

The reliable and regular modification of the surface properties of substrates plays a crucial role in material research and the development of functional surfaces. A key aspect of this is the development of the surface pores and topographies. These can confer specific advantages such as high surface area as well as specific functions such as hydrophobic properties. Here, we introduce a combination of nanoscale self-assembled block-copolymer-based metal oxide masks with optimized deep reactive ion etching (DRIE) of silicon to permit the fabrication of porous topographies with aspect ratios of up to 50. Following the evaluation of our procedure and involved parameters using various techniques, such as AFM or SEM, the suitability of our features for applications relying on high light absorption as well as efficient thermal management is explored and discussed in further detail.

Block copolymer self-assembly assisted fabrication of laterally organized- and stacked- nanoarrays

Block copolymer (BCP) self-assembly processes are often seen as reliable techniques for advanced nanopatterning to achieve functional surfaces and create templates for nanofabrication. By taking advantage of the tunability in pitch, diameter and feature-to-feature separation of the self-assembled BCP features, complex, laterally organized- and stacked- multicomponent nanoarrays comprising of gold and polymer have been fabricated. The approaches not only demonstrate nanopatterning of up to two levels of hierarchy but also investigate how a variation in the feature-to-feature gap at the first hierarchy affects the self-assembly of polymer features at the second. Such BCP self-assembly enabled multicomponent nanoarray configurations are rarely achieved by other nanofabrication approaches and are particularly promising for pushing the boundaries of block copolymer lithography and in creating unique surface architectures and complex morphologies at the nanoscale.

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

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.

Hierarchical Order in Dewetted Block Copolymer Thin Films on Chemically Patterned Surfaces

We investigated the dewetting process on flat and chemically patterned surfaces of ultrathin films (thickness between 2 and 15 nm) of a cylinder forming polystyrene- block-poly(methyl methacrylate) (PS- b-PMMA) spin coated on poly(styrene- r-methyl methacrylate) random copolymers (RCPs). When the PS- b-PMMA film dewets on a 2 nm-thick RCP layer, the ordering of the hexagonally packed PMMA cylinders in the dewetted structures extends over distances far exceeding the correlation length obtained in continuous block copolymer (BCP) films. As a result, micrometer-sized circular droplets featuring defectless single grains of self-assembled PS- b-PMMA with PMMA cylinders perpendicularly oriented with respect to the substrate are generated and randomly distributed on the substrate. Additionally, alignment of the droplets along micrometric lines was achieved by performing the dewetting process on large-scale chemically patterned stripes of 2 nm thick RCP films by laser lithography. By properly adjusting the periodicity of the chemical pattern, it was possible to tune and select the geometrical characteristics of the dewetted droplets in terms of maximum thickness, contact angle and diameter while maintaining the defectless single grain perpendicular cylinder morphology of the circular droplets.