Browsing by Subject "Nanofabrication"

Now showing 1 - 8 of 8

Fabrication and process optimization for functional 3D periodic nanolattices
(2023-12) Premnath, Vijay Anirudh; Chang, Chih-Hao, Ph. D.
This research focuses on the development and analysis of advanced nanolattices and three-dimensional (3D) nanostructures, showing their significance in nanophotonics, integrated circuits, lasers, optical systems, and various other applications. Nanolattices are characterized by their periodic lattice arrangement, hollow-core, and thin-shell elements, are fabricated using thin-film deposition on 3D polymer templates. These structures offer immense potential in mechanical, optical, and thermal applications, due to their unique properties. However, a major challenge in their fabrication is the residual polymer left within the nanolattice, which can impede their performance. To address this, the study investigates three different polymer template removal techniques, including oxygen plasma etching, solvent dissolution, and thermal desorption, to determine their effectiveness in eliminating residual polymer. The removal rates and effectiveness of each method are quantitatively analyzed using spectroscopic ellipsometry, a technique that precisely measures the effective refractive index and calculates the amount of residual polymer. The findings reveal that thermal treatment is the most effective in template removal, providing a path to enhance nanolattice fabrication for various applications. Additionally, the research utilizes a three-phase Maxwell–Garnett effective medium model to estimate the residual polymer in nanolattices. Parallelly, the research delves into the fabrication of 3D nanostructures, specifically opal structures, which are spatially aligned to an array of holes defined in the photoresist. This approach employs colloidal lithography to pattern a hexagonal array of holes, guiding the assembly of colloidal particles into 3D opal structures. This method ensures the alignment of the 3D opal structures with the 2D hole array, enhancing spatial-phase coherence and minimizing defects. The polymer patterns serve as a sacrificial template for atomic layer deposition, enabling the creation of free-standing nanolattices. These nanolattices are subsequently coated with a thick layer of titanium oxide, demonstrating their mechanical stability. The resulting structures boast high porosity, essential for creating low-index materials in nanophotonics. Additionally, the study incorporates nature-inspired nanostructures, employing biomimetic principles to enhance the functionality and efficiency of these materials. These nature-inspired designs, mimicking the structures found in natural organisms, provide solutions for light manipulation and structural resilience. These nanostructures, with controlled height and precise deposition, are ideal for applications in Bragg reflectors, nanophotonics, and optical multilayers, marking a significant advancement in the field of nanostructured materials. The study's findings on template removal, 3D nanostructure fabrication, and biomimetic design open new avenues for research and development in this rapidly evolving field, promising enhancements in the efficiency and functionality of nanostructured materials and devices.
Fabrication of silicon nanowires with controlled nano-scale shapes using wet anisotropic etching
(2015-08) Yin, Bailey Anderson; Sreenivasan, S. V.; Banerjee, Sanjay K; Bonnecaze, Roger T; Cullinan, Michael A; Li, Wei
Silicon nanowires can enable important applications in energy and healthcare such as biochemical sensors, thermoelectric devices, and ultra-capacitors. In the energy sector, for example, as the need for more efficient energy storage continues to grow for enabling applications such as electric vehicles, high energy storage density capacitors are being explored as a potential replacement to traditional batteries that lack fast charge/discharge rates as well as have shorter life cycles. Silicon nanowire based ultra-capacitors offer increased energy storage density by increasing the surface area per unit projected area of the electrode, thereby allowing more surface “charge” to reside. The motivation behind this dissertation is the study of low-cost techniques for fabrication of high aspect ratio silicon nanowires with controlled geometry with an exemplar application in ultra-capacitors. Controlled transfer of high aspect ratio, nano-scale features into functional device layers requires anisotropic etch techniques. Dry reactive ion etch techniques are commonly used since most solution-based wet etch processes lack anisotropic pattern transfer capability. However, in silicon, anisotropic wet etch processes are available for the fabrication of nano-scale features, but have some constraints in the range of geometry of patterns that they can address. While this lack of geometric and material versatility precludes the use of these processes in applications like integrated circuits, they can be potentially realized for fabricating nanoscale pillars. This dissertation explores the geometric limitations of such inexpensive wet anisotropic etching processes and develops additional methods and geometries for fabrication of controlled nano-scale, high aspect ratio features. Jet and Flash Imprint Lithography (J-FIL™) has been used as the preferred pre-etch patterning process as it enables patterning of sub-50 nm high density features with versatile geometries over large areas. Exemplary anisotropic wet etch processes studied include Crystalline Orientation Dependent Etch (CODE) using potassium hydroxide (KOH) etching of silicon and Metal Assisted Chemical Etching (MACE) using gold as a catalyst to etch silicon. Experiments with CODE indicate that the geometric limitations of the etch process prevent the fabrication of high aspect ratio nanowires without adding a prohibitive number of steps to protect the pillar geometry. On the other hand, MACE offers a relatively simple process for fabricating high aspect ratio pillars with unique cross sections, and has thus been pursued to fabricate fully functional electrostatic capacitors featuring both circular and diamond-shaped nano-pillar electrodes. The capacitance of the diamond-shaped nano-pillar capacitor has been shown to be ~77.9% larger than that of the circular cross section due to the increase in surface area per unit projected area. This increase in capacitance approximately matches the increase calculated using analytical models. Thus, this dissertation provides a framework for the ability to create unique sharp cornered nanowires that can be explored further for a wider variety of cross sections.
Nanoengineering of surfaces to modulate cell behavior : nanofabrication and the influence of nanopatterned features on the behavior of neurons and preadipocytes
(2009-08) Fozdar, David Yash; Chen, Shaochen
Promising strategies for treating diseases and conditions like cancer, tissue necrosis from injury, congenital abnormalities, etc., involve replacing pathologic tissue with healthy tissue. Strategies devoted to the development of tissue to restore, maintain, or improve function is called tissue engineering. Engineering tissue requires three components, cells that can proliferate to form tissue, a microenvironment that nourishes the cells, and a tissue scaffold that provides mechanical stability, controls tissue architecture, and aids in mimicking the cell’s natural extracellular matrix (ECM). Currently, there is much focus on designing scaffolds that recapitulate the topology of cells’ ECM, in vivo, which undoubtedly wields structures with nanoscale dimensions. Although it is widely thought that sub-microscale features in the ECM have the greatest vii impact on cell behavior relative to larger structures, interactions between cells and nanostructures surfaces is not well understood. There have been few comprehensive studies elucidating the effects of both feature dimension and geometry on the initial formation and growth of the axons of individual neurons. Reconnecting the axons of neurons in damaged nerves is vital in restoring function. Understanding how neurons react with nanopatterned surfaces will advance development of optimal biomaterials used for reconnecting neural networks Here, we investigated the effects of micro- and nanostructures of various sizes and shape on neurons at the single cell level. Compulsory to studying interactions between cells and sub-cellular structures is having nanofabrication technologies that enable biomaterials to be patterned at the nanoscale. We also present a novel nanofabrication process, coined Flash Imprint Lithography using a Mask Aligner (FILM), used to pattern nanofeatures in UV-curable biomaterials for tissue engineering applications. Using FILM, we were able to pattern 50 nm lines in polyethylene glycol (PEG). We later used FILM to pattern nanowells in PEG to study the effect of the nanowells on the behavior preadipocytes (PAs). Results of our cell experiments with neurons and PAs suggested that incorporating micro- and nanoscale topography on biomaterial surfaces may enhance biomaterials’ ability to constrain cell development. Moreover, we found the FILM process to be a useful fabrication tool for tissue engineering applications.
Nanofabrication via directed assembly: a computational study of dynamics, design & limits
(2016-08) Arshad, Talha Ali; Bonnecaze, R. T. (Roger T.); Ellison, Christopher J.; Ganesan, Venkat; Sreenivasan, S. V.; Willson, Carlton G.
Three early-stage techniques, for the fabrication of metallic nanostructures, creation of controlled topography in polymer films and precise deposition of nanowires are studied. Mathematical models and computational simulations clarify how interplay of multiple physical processes drives dynamics, provide a rational approach to selecting process parameters targeting specific structures efficiently and identify limits of throughput and resolution for each technique. A topographically patterned membrane resting on a film of nanoparticles suspended in a solvent promotes non-uniform evaporation, driving convection which accumulates particles in regions where the template is thin. Left behind is a deposit of particles the dimensions of which can be controlled through template thickness and topography as well as film thickness and concentration. Particle distribution is shown to be a competition between convection and diffusion represented by the Peclet number. Analytical models yield predictive expressions for bounds within which deposit dimensions and drying time lie. Ambient evaporation is shown to drive convection strong enough to accumulate particles 10 nm in diameter. Features up to 1 µm high with 10 nm residual layers can be deposited in < 3 minutes, making this a promising approach for continuous, single-step deposition of metallic nanostructures on flexible substrates. Selective exposure of a polystyrene film to UV radiation has been shown to result in non-uniform surface energy which drives convection on thermal annealing, forming topography. Film dynamics are shown to be a product of interplay between Marangoni convection, capillary dissipation and diffusion. At short times, secondary peaks form at double the pattern density of the mask, while at long times pattern periodicity follows the mask. Increased temperature, larger surface tension differentials and thick films result in faster dynamics and larger features. Electric fields in conjunction with fluid flow can be used to position semi-conducting nanowires or nanotubes at precise locations on a substrate. Nanowires are captured successfully if they arrive within a region next to the substrate where dielectrophoresis dominates hydrodynamics. Successful assembly is predicated upon a favorable balance of hydrodynamics, dielectrophoresis and diffusion, represented by two dimensionless groups. Nanowires down to 20 nm in length can be assembled successfully.
Nanoscale investigation of silk proteins using near-field optics
(2018-05) Zhang, Shaoqing; Tao, Hu (doctor of mechanical engineering); Fan, Donglei; Lai, Keji; Li, Wei; Xie, Chong
Recent developments in nanotechnology have led to renewed interest and breakthroughs in structural biopolymers, specifically silk protein, as functional materials. The exceptional mechanical properties and the bio-compatibility of silk has enabled wide range of applications from biomedical devices, optics, electronics, to transient implants. Understanding the mechanisms that underpin the β-sheet formation and deformation as well as the formulation of strategies to control inter- and intramolecular bonds within silk protein matrices is paramount for the control of protein structures and the improvement of material properties. However, conventional imaging techniques that are used to characterize and recapitulate silk structure–function relationships present challenges at the nanoscale given their limitations in chemical sensitivity (for example, electron microscopy and atomic force microscopy (AFM)) or limited spatial resolution (for example, ‘far-field’ infrared (IR) spectroscopy). In this context, my research focuses on the understanding of the conformational transitions of silk fibroin and recombinant spider silk, and the interaction between the protein and energy or other biomolecules at nanoscale using near-field optics. In particular, the complete conformational transition of the silk protein under the electron bombardment have been visualized, guiding the creation of novel 3D nanostructures using Electron Beam Lithography (EBL). Meanwhile, the dual-tone structural formation of silk structures under ion beam irradiation have been thoroughly investigated, resulting in the “Protein Lego” manufacturing paradigm. The UV enabled silk protein cross-linking has also been utilized for scalable manufacturing of bio-structures. The interaction between the silk protein and other types of biological materials (such as cells, bacteria, and virus) has been studied to explore the stabilization capability of the silk matrix. The comprehensive investigation of the interplay between the protein material, energy input, as well as other chemical/biological species will pave the way for the bio-compatible, bio-degradable, and multi-functional platforms, serving as the building blocks of the green bio-manufacturing paradigm
Patternable materials for next-generation lithography
(2017-05) Lane, Austin Patrick; Willson, C. G. (C. Grant), 1939-; Ellison, Christopher J; Bonnecaze, Roger T; Baiz, Carlos; Mack, Chris
One of the salient truths facing the microelectronics industry today is that photolithography tools are unable to meet the resolution requirements for manufacturing next-generation devices. In the past, circuit feature sizes have been minimized by reducing the exposure wavelength used for patterning. However, this strategy failed with the worldwide dereliction of 157 nm lithography in 2003. Extreme ultraviolet (EUV) lithography still faces many technical challenges and is not ready for high volume manufacturing. How will the microelectronics industry continue to innovate without regular advances in photopatterning technology? Regardless of which paradigm is adopted, new materials will probably be required to meet the specific challenges of scaling down feature sizes and satisfying the economic ultimatum of Moore’s Law. In the search for higher resolution patterning tools, device manufacturers have identified block copolymer (BCP) lithography as a possible technique for next-generation nanofabrication. BCP self-assembly offers access to sub-5 nm features in thin films, well beyond the resolution limits of photolithography. However, BCP materials must be carefully designed, synthesized, and processed to create lithographically interesting features with good etch resistance for pattern transfer. In this dissertation, we describe a pattern transfer process for 5 nm BCP lamellae and a directed self-assembly (DSA) process for aligning 5 nm structures in thin films. To achieve defect-free alignment, the interfacial interactions between the BCP and pre-patterned substrate must be precisely controlled. We also discuss a new process for selectively modifying oxidized chromium films using polymer brushes, which could further improve the aforesaid DSA process. To facilitate better pattern transfer of BCP structures, several new BCPs with “self-developing” blocks were synthesized and tested. These materials depolymerize and evaporate in strongly acidic environments, leading to developed BCP features without the need for etching or solvent. “Self-developing” polymers may also be useful materials for traditional photolithography. Chemically amplified resists used in manufacturing today are fundamentally limited by a trade-off between sensitivity and pattern quality. To overcome this problem, we present a new type of photoresist that relies on depolymerization, rather than catalysis, to achieve amplification without producing significant roughness or bias in the final pattern
Platinum assisted chemical etching of single- and poly-crystalline silicon with applications to templated nanomaterials
(2023-12) Barrera, Crystal; Sreenivasan, S. V.; Hutter, Tanya; Cullinan, Michael; Banerjee, Sanjay; Li, Xiuling
When emerging nanofabrication techniques are explored for improved performance in semiconductor device fabrication, they need to substantially improve in their performance and/or cost relative to incumbent process technologies. These incumbent technologies align themselves to the CMOS (Complimentary Metal Oxide Semiconductor) semiconductor roadmap, which continuously strives towards reduced feature size, increased aspect ratio, and increased fabrication throughput for complex 3D architectures. Metal Assisted Chemical Etching (MacEtch) is an emerging wet etch technique with potential to outperform reactive ion etch (RIE) methods. At nanometer scale patterns, RIE methods have limitations in the quality of high aspect ratio nanoscale structures due to potential for tapered profiles and high side wall roughness. MacEtch is capable of producing anisotropic, high aspect ratio features with atomically smooth, vertical sidewalls in silicon materials with high throughput capability. MacEtch requires a catalyst that enables a reaction just underneath it, which leads to silicon being etched beneath the catalyst. The catalyst that is predominantly reported in the literature is gold (Au). However, Au is an undesirable material choice for CMOS fabrication as it leads to deep level defects in silicon. In the MacEtch research literature non-Au catalysts such as Ruthenium (Ru) and Platinum (Pt) have been recently reported. But these non-Au results could require process steps that are not CMOS friendly (e.g., requiring high temperature annealing) and do not have tunable process quality (non-porous, atomically precise high aspect ratio silicon nanostructures) equivalent to Au-based MacEtch methods. This dissertation demonstrates a MacEtch process that utilizes a Pt catalyst with process steps that do not conflict with CMOS process flows. This process is also capable of wafer-scale process quality that is comparable to Au-based MacEtch. In addition to overcoming catalyst limitations, this work demonstrates MacEtch in both liquid and gas phases with anneal-free Pt catalyst. The gas phase etching has demonstrated the ability to produce >100:1 aspect ratio in silicon. In addition to semiconductor fabrication where silicon etching is valuable, there are a number of applications in areas including medicine, optics, and energy storage that require high-quality nanofabrication methods for non-silicon materials. This work has developed a demonstrated an approach for extending nanoscale precision, high-aspect ratio, and nano-dimensional capability of MacEtch to non-silicon materials by the use of a novel approach enabled by fabrication of silicon templates.
Simulation of UV nanoimprint lithography on rigid and flexible substrates
(2016-12) Jain, Akhilesh; Bonnecaze, R. T. (Roger T.); Sreenivasan, S.V.; Willson, C. Grant; Schunk, P. Randall; Ganesan, Venkat
Nanoimprint lithography (NIL) is a low cost, high throughput process used to replicate sub-20 nm feature from a patterned template to a rigid or flexible substrate. Various configurations for NIL are analyzed and classified based on type of template and substrate. The steps involved in pattern transfer using roller template based NIL are identified and models to study these steps are proposed. Important process parameters such as maximum web speed possible, required UV intensity, minimum droplet size and pitch and required force on the roller are calculated. The advantages, disadvantages and optimal process window for the different configurations are identified. Droplet spreading is simulated in NIL with rigid substrates in order to study the effect of droplet size, droplet placement error, gas diffusion and template pattern on throughput and defectivity. Square arrangement is found to be the optimum arrangement for achieving minimum throughput. Large droplet-free regions on the substrate edge and error in droplet placement error have significant impact on the throughput. A fluid flow model with average flow permeability is presented to account for flow in the template patterns. Optimum droplet dispensing for multi-patterned templates is achieved by distributing droplet volume according to local filling requirements. Non-fill defects in NIL are classified into pocket, edge and channel defects. A model to predict the size of non-fill defects based on imprint time and droplet size is presented. Defect characterization is presented for various pattern-types. A model is presented to determine the time required for the encapsulated gas to diffuse into the resist. The coupled fluid-structure interaction in NIL with flexible substrate is studied by simulating the web deformation as the droplet spreads on the substrate. It is found that the flexible substrate can be modeled as a membrane due to the lack of rigidity. RLT variation reduces as the number of droplets or the web tension increases. For the magnitude of RLT variation, thinner residual layers require higher web tension. The position of the template on the substrate is important and template positioned at the corner of the substrate is found to provide the least RLT variation.