Claudia Simao

Fabrication of highly ordered sub-20 nm silicon nanopillars by block copolymer lithography combined with resist design

The control of order and orientation of the self-assembly of cylinder-forming poly(styrene-b-dimethylsiloxane) block copolymer is demonstrated. Copolymer thin films are spun-cast onto topographically patterned (well-defined rectangular cross-section channels) polyhedral-silsesquioxane-type resist templates and annealed in solvent vapor. The templates used here are fabricated by UV-curing nanoimprint lithography and the surface properties of the resist are tuned by the ligands coordinated to the resists silsesquioxane cages. Depending on the resists composition and on the surface chemistry at the base of the trench (resist or silicon), various morphologies and orientations of the polydimethylsiloxane cylinders are observed without the use of a brush layer. Some surfaces are demonstrated to be neutral for the copolymer, without any wetting layer and, under favorable conditions, highly ordered features are observed over substrate areas of about 1 cm2 (scalable to larger surfaces). Also, the possibility of using solvents widely accepted in industry for polymer spin-coating and annealing is proved. Due to the high plasma etch resistance of the polydimethylsiloxane block, self-assembled patterns can be transferred to the silicon substrate producing silicon features with aspect ratios up to 2. We demonstrate that the methodology developed here could be integrated into conventional fabrication processes and scaled to wafer production.

Optical and mechanical properties of nanofibrillated cellulose: Toward a robust platform for next-generation green technologies

Nanofibrillated cellulose, a polymer that can be obtained from one of the most abundant biopolymers in nature, is being increasingly explored due to its outstanding properties for packaging and device applications. Still, open challenges in engineering its intrinsic properties remain to address. To elucidate the optical and mechanical stability of nanofibrillated cellulose as a standalone platform, herein we report on three main findings: (i) for the first time an experimental determination of the optical bandgap of nanofibrillated cellulose, important for future modeling purposes, based on the onset of the optical bandgap of the nanofibrillated cellulose film at Eg≈275 nm (4.5 eV), obtained using absorption and cathodoluminescence measurements. In addition, comparing this result with ab-initio calculations of the electronic structure the exciton binding energy is estimated to be Eex≈800 meV; (ii) hydrostatic pressure experiments revealed that nanofibrillated cellulose is structurally stable at least up to 1.2 GPa; and (iii) surface elastic properties with repeatability better than 5% were observed under moisture cycles with changes of the Young modulus as large as 65%. The results obtained show the precise determination of significant properties as elastic properties and interactions that are compared with similar works and, moreover, demonstrate that nanofibrillated cellulose properties can be reversibly controlled, supporting the extended potential of nanofibrillated cellulose as a robust platform for green-technology applications.

Defect analysis and alignment quantification of line arrays prepared by directed self-assembly of a block copolymer

Different linear patterns obtained from the directed self-assembly of the block copolymer (BCP) polystyrene-b-polyethylene oxide (PS-b-PEO) were analysed and compared. The hexagonal phase PS-b-PEO in a thin film exhibits linear pattern morphology, by conventional solvent annealing in an atmosphere saturated in chloroform. The surface energy of the silicon substrates was varied using surface functionalization of a self-assembly monolayer (SAM) and a polymer brush, chosen to investigate the influence of the surface energy on the self-assembly of the BCP. The linear patterns formed were analyzed with innovative image analysis software specifically developed in our laboratory to identify elements and defects of line arrays from block copolymer self-assembly. The technique starts by performing dimensional metrology to calculate the pitch size and estimate the linewidth of the lines. Secondly, the methodology allows identification and quantification of typical defects observable in BCP systems, such as turning points, disclination or branching points, break or lone points and end points. The defect density and the quantification of the alignment were estimated using our technique. The methodology presented here represents a step forward in dimensional metrology and defect analysis of BCP DSA systems and can be readily used to analyze other lithographic or non-lithographic patterns.

Nanoimprint-assisted directed self-assembly of low-molecular weight block copolymers: a route for 3D and multilevel nanostructures

Multilevel controllable nanoimprint driven molecular orientation has been obtained in thin films of block copolymer polystyrene-b-polyethylene oxide( PS-b-PEO) by means of solvent vapours assisted nanoimprint lithography (SAIL). The NIL setup using solvent vapours was capable of imprinting nanoscale features over a large area and simultaneously annealing PS-b-PEO thin films. A line pattern stamp was replicated in the BCP film in over a large area with a high resolution registry, and was also observed that the PS-b-PEO film exhibited microphase segregation in the residual layer exhibits a nanodot array from showing hexagonally packed PEO dots in the PS matrix, with a diameter of 20 nm with 40 nm pitch. The order of the hexagonally arranged nanodot lattice seen in the nanodots array was quantified from SEM images using by the opposite partner method from SEM images analysis and compared with to conventionally solvent annealed BCP films, demonstrating an improvement of the ordering of up to 50%. Grazing-incidence small-angle X-ray scattering (GISAXS) study demonstrates the excellent fidelity of the pattern transfer and confirms the periodicity of the BCP in the mesas. In addition, applying the SAIL methodology to BCP thin films in nanopatterned silsequioxane substrates, it was possible to obtain multilevel structures decorated with the BCP microphase segregation. The SAIL technique is a versatile and robust platform to obtain complex high density periodic nanostructures, particularly for second generation block copolymers directed self-assembly.

Integrated 3D Hydrogel Waveguide Out-Coupler by Step-and-Repeat Thermal Nanoimprint Lithography: A Promising Sensor Device for Water and pH

Hydrogel materials offer many advantages for chemical and biological sensoring due to their response to a small change in their environment with a related change in volume. Several designs have been outlined in the literature in the specific field of hydrogel-based optical sensors, reporting a large number of steps for their fabrication. In this work we present a three-dimensional, hydrogel-based sensor the structure of which is fabricated in a single step using thermal nanoimprint lithography. The sensor is based on a waveguide with a grating readout section. A specific hydrogel formulation, based on a combination of PEGDMA (Poly(Ethylene Glycol DiMethAcrylate)), NIPAAm (N-IsoPropylAcrylAmide), and AA (Acrylic Acid), was developed. This stimulus-responsive hydrogel is sensitive to pH and to water. Moreover, the hydrogel has been modified to be suitable for fabrication by thermal nanoimprint lithography. Once stimulated, the hydrogel-based sensor changes its topography, which is characterised physically by AFM and SEM, and optically using a specific optical set-up.

Self-Assembled Nanofeatures in Complex Three-Dimensional Topographies via Nanoimprint and Block Copolymer Lithography Methods

Achieving ultrasmall dimensions of materials and retaining high throughput are critical fabrication considerations for nanotechnology use. This article demonstrates an integrated approach for developing isolated sub-20 nm silicon oxide features through combined “top-down” and “bottom-up” methods: nanoimprint lithography (NIL) and block copolymer (BCP) lithography. Although techniques like those demonstrated here have been developed for nanolithographic application in the microelectronics processing industry, similar approaches could be utilized for sensor, fluidic, and optical-based devices. Thus, this article centers on looking at the possibility of generating isolated silica structures on substrates. NIL was used to create intriguing three-dimensional (3-D) polyhedral oligomeric silsesquioxane (POSS) topographical arrays that guided and confined polystyrene-block-poly(dimethylsiloxane) (PS-b-PDMS) BCP nanofeatures in isolated regions. A cylinder forming PS-b-PDMS BCP system was successfully etched using a one-step etching process to create line-space arrays with a period of 35 nm in confined POSS arrays. We highlight large-area (>6 μm) coverage of line-space arrays in 3-D topographies that could potentially be utilized, for example, in nanofluidic systems. Aligned features for directed self-assembly application are also demonstrated. The high-density, confined silicon oxide nanofeatures in soft lithographic templates over macroscopic areas illustrate the advantages of integrating distinct lithographic methods for attaining discrete features in the deep nanoscale regime.

Mapping self-assembled dots and line arrays by image analysis for quantification of defect density and alignment

Bottom-up alternative lithographic masks from directed self-assembly systems have been extending the limits of critical dimensions in a cost-effective manner although great challenges in controlling defectivity remain open. Particularly, defectivity and dimensional metrology are two main challenges in lithography due to the increasing miniaturisation of circuits. To gain insights about the percentage of alignment, defectivity and order quantification, directed self-assembly block copolymer fingerprints were investigated via an image analysis methodology. Here we present the analysis of hexagonal phase of polystyrene-b-polydimethylsiloxane (PS-b-PDMS) forming linear patterns in topological substrates. From our methodology, we have performed dimensional metrology estimating pitch size and error, and the linewidth of the lines was estimated. In parallel, the methodology allowed us identification and quantification of typical defects observable in self-assembly, such as turning points, disclination or branching points, break or lone points and end points. The methodology presented here yields high volume statistical data useful for advancing dimensional metrology and defect analysis of self- and directed assembly systems.

Order and defectivity nanometrology by image processing and analysis of sub-20 nm BCPs features for lithographic applications

The line patterns obtained by the self-assembly of the block copolymer (BCP) polystyrene-b-polyethylene oxide (PS-b-PEO) was investigated. The hexagonal PS-b-PEO 42k-11.5k in a thin film was solvent annealed in a chlorophorm saturated atmosphere for three different annealing times. The microphase segregation of this BCP returned 18nm cylinders of PEO through the PS matrix, with an approximately 40 n periodicity, as expected. Under chlorophorm vapours, the PEO cylinders oriented perpendicular to the silicon substrate while increasing the annealing time. These cylinders formed linear patterns with different alignment. To achieve insights about the percentage of alignment, defect type pareto and density, and order quantification to compare the three annealing recipes, the samples were analysed with innovative image analysis software specifically developed in our laboratory to identify elements and defects of line arrays from block copolymer self-assembly. From this technique, it was extracted dimensional metrology estimating pitch size and placement error, and the line-width of the lines was estimated. Secondly, the methodology allows identification and quantification of typical defects observable in BCP systems, such as turning points, disclination or branching points, break or lone points and end points. The defect density and the quantification of the alignment were estimated using our technique. The methodology presented here represents a step forward in dimensional metrology and defect analysis of BCP DSA systems and can be readily used to analyze other lithographic or non-lithographic patterns.