Development of Ordered, Porous (Sub-25 nm Dimensions) Surface Membrane Structures Using a Block Copolymer Approach

Abstract

In an effort to develop block copolymer lithography to create high aspect vertical pore arrangements in a substrate surface we have used a microphase separated poly(ethylene oxide) -b- polystyrene (PEO-b-PS) block copolymer (BCP) thin film where (and most unusually) PS not PEO is the cylinder forming phase and PEO is the majority block. Compared to previous work, we can amplify etch contrast by inclusion of hard mask material into the matrix block allowing the cylinder polymer to be removed and the exposed substrate subject to deep etching thereby generating uniform, arranged, sub-25 nm cylindrical nanopore arrays. Briefly, selective metal ion inclusion into the PEO matrix and subsequent processing (etch/modification) was applied for creating iron oxide nanohole arrays. The oxide nanoholes (22 nm diameter) were cylindrical, uniform diameter and mimics the original BCP nanopatterns. The oxide nanohole network is demonstrated as a resistant mask to fabricate ultra dense, well ordered, good sidewall profile silicon nanopore arrays on substrate surface through the pattern transfer approach. The Si nanopores have uniform diameter and smooth sidewalls throughout their depth. The depth of the porous structure can be controlled via the etch process.

Structural Evolution of Nanophase Separated Block Copolymer Patterns in Supercritical CO2

“…Figure 7 a shows parallel orientation of PS cylinders inside PEO matrix with an average cylinder to cylinders spacing of 50 nm and cylinder diameter of 20 nm. The self-assembly was realised at a lower temperature (40 °C) compared to those achieved by solvent annealing process (60 °C) [ 39 ]. A mixed orientation (parallel and perpendicular to the substrate surface) of PDMS cylinders inside the PS matrix is observed for scCO 2 annealing with similar conditions ( Figure 7 b).…”

Large-Area Fabrication of Vertical Silicon Nanotube Arrays via Toroidal Micelle Self-Assembly

“…Block copolymer (BCP) self-assembly provides an avenue for the formation of a myriad of nano-scale morphologies, with applications such as optoelectronics, biosensing, filtration, bioactive surfaces, surface coatings, and magnetic applications, among others. − More usual microphase separated self-assembled architectures include lamellar, cylindrical, spherical, and gyroidal structures as well as various micellar-based morphologies such as helices, tubes, disks, and toroids. − Micelle formation is defined as the self-assembly of an amphiphilic BCP in a solvent medium to form a structure typically with a core and corona. , Of the myriad of available micellar structures, toroidal micelles, in particular, have garnered interest owing to their proven applicability in synthesizing unique nanostructured materials with unique plasmonic and magnetic properties. , Such structures are typically fabricated via incorporating various metals and metal oxides, which upon removal of the polymer matrix produce metallic toroidal or nanoring structures . These metal/metal oxide structures have also been utilized as hard masks for patterning underlying silicon substrates, yielding high aspect ratio nanotube arrays. , Nonetheless, one notable drawback of toroidal micelles obtained via BCP or triblock copolymer self-assembly is that the size distributions of the structure are often too small for optoelectronic applications …”

“…In this work, we describe a novel strategy to address this issue by controlling the formation of large toroidal structures via water vapor annealing (WVA) of a polystyrene- b -poly­(ethylene oxide) (PS- b -PEO) diblock copolymer system atop a PS-modified substrate. Vapor annealing is a common technique employed to direct BCP self-assembly via polymer swelling. , Solvent vapor can selectively swell one or more blocks (thereby affecting the morphology) and the propensity of swelling can be estimated by the Flory–Huggins interaction parameter χ. , The solvent vapor-driven swelling creates free volume, increasing the chain mobility . This is also described as plasticization and results in effective reduction of the glass-transition temperature and effective χ parameter .…”

Deep learning-based estimation of Flory–Huggins parameter of A–B block copolymers from cross-sectional images of phase-separated structures

“…Concerning DSA 67 – 70 , regular lamellar and cylindrical structures were required for line/space arrangements and contact-hole patterning, respectively. The implementation of DSAs on substrates has involved a rigorous study of nanoimprinting lithography 71 , electron beam lithography 72 , 73 , and solvent-vapor annealing 74 – 76 . Solvent-vapor annealing requires effective interactions among polymers, substrates, and solvents 74 – 76 .…”

“…The implementation of DSAs on substrates has involved a rigorous study of nanoimprinting lithography 71 , electron beam lithography 72 , 73 , and solvent-vapor annealing 74 – 76 . Solvent-vapor annealing requires effective interactions among polymers, substrates, and solvents 74 – 76 . To achieve sub-20 nm periods, the control of high χ parameters with custom chemical synthesis is important 77 , 78 .…”