Browsing by Subject "Nanomanufacturing"

Now showing 1 - 7 of 7

Enabling hybrid process metrology in roll-to-roll nanomanufacturing: design of a tip-based tool for topographic sampling on flexible substrates
(2022-05) Connolly, Liam Glazer; Cullinan, Michael; Sreenivasan, S.V.; Zhou, Lei; Djurdjanovic, Dragan; Sarkar, Neil
This work seeks to demonstrate the efficacy of a novel approach for topography measurement of nano-scale structures fabricated on a flexible substrate in a roll-to-roll (R2R) fashion. R2R manufactured products can be extremely cost competitive compared to more traditional, silicon wafer or glass panel based nanofabrication solutions, in addition to the unique and often desirable mechanical properties inherent to flexible substrates. As such, flexible nanomanufacturing is an area of immense research interest. However, despite the significant potential of these products for a variety of applications, developing manufacturing systems from lab-scale prototypes to pilot- or high volume manufacturing (HVM) has often proven both difficult and infeasibly expensive as research investment and achievable process yield limit advancement. One of the most significant capability gaps in current art, and roadblocks on the path towards adoption of R2R nanomanufacturing, is the lack of high-throughput, nanometer-scale metrology for process development, real-time control, and yield enhancement. This dissertation presents the design of a tip-based measurement tool implementing atomic force microscope (AFM) probes manufactured with a micro-electro-mechanical system (MEMS) approach to the challenge of sub-micron topography measurement which is also compatible with R2R manufacturing on flexible substrates. A proof-of-concept prototype tool with subsystems to regulate a flexible web, isolate and position the atomic force microscope probe, and measure features on the substrate, all coordinated by a real-time embedded control system, was designed and fabricated. The positioning subsystem was evaluated dynamically to ensure initial design requirements were met, and stationery, step-and-scan results were presented. However, to wholly meet this extent need for in-line R2R metrology, a system capable of atomic force microscope scanning despite a continuous, non-zero substrate velocity is required - any regular stoppage of the web in a R2R process all but dooms economically viable production throughput. Refinement and redesign of the proof-of-concept tool was driven by new system requirements to meet this goal, in addition to lessons learned from the initial prototype. Improvements focused on upgrading the web handling spindle design and mechatronics, tool power electronics, moving structures, and control algorithms used for high-speed synchronous positioning of the atomic force microscope and web. The culmination of this work will serve to introduce a new measurement framework which may be used to accelerate and enable future research in R2R manufacturing of nanofeatured products.
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.
Graphene-based gas sensor analysis for disease detection applications
(2020-05-08) Piacente, Nicholas Paul; Cullinan, Michael
This thesis presents an analysis of graphene sensors for the measurement of ultra-low concentrations of volatile organic compounds (VOCs) found in human breath. Adsorption of gas molecules to graphene sensing elements is measured as a function of various conditions, including gas concentration and flow. This analysis is foundational in enabling the use of such sensors for detection of biomarkers within the breath, which could ultimately lead to new, non-invasive detection of diseases such as lung cancer. A method of producing graphene samples for measurement will be discussed, using scalable and cost-effective nanomanufacturing methods. Finally, this thesis will describe the design and fabrication of a test system capable of supplying low parts-per-million (PPM) concentrations of VOC flow across the sensor. The testing system can flow multiple VOCs at a wide range of concentrations, and at sub-atmospheric pressures, to isolate the VOC of interest for highly accurate and sensitive measurements. Preliminary sensitivity data of graphene sensors to acetone will be reported. The test system can be used for future sensor testing of new designs, or sensitivity to different VOCs.
High-throughput, tip-based in-line nanometrology in semiconductor and nano-featured manufacturing
(2018-08) Yao, Tsung-Fu; Cullinan, Michael; Djurdjanovic, Dragan; Sreenivasan, S.V.; Sarkar , Neil
A high-throughput, tip-based, in-line nanometrology system that can be helpful for developing closed-loop process control in nanomanufacturing of semiconductor industries. One of the most significant barriers stands in the path to in-line inspection in nanomanufacturing is sample-preparation. After the beforehand inspection process detecting regions that have higher chance to be failed, known as “hotspots,” the operator may need to spend much time to position a high-resolution probe to there because small field-of-view (FOV) makes it hard to recognize its position from target. The other barrier to developing in-line inspection is the resolution limitation of conventional metrology technique, a.k.a. optical and e-beam inspections. Especially for technology nodes beyond 10-nm, the critical dimension is going close to resolving capability. As a result, the in-line inspection requires a higher resolution imaging technique with fast and precision method to position the probe. The methodology developed in this study overcomes those barriers by passive alignment methods and a state-of-the-art single-chip atomic force microscopy system. Instead of those prevalent active methods, the passive alignment uses kinematic method providing the wafer adequately constraint to limit degree of freedoms in place. Once the wafer sit into site, a preload applied then a sub-micron precision can be achieved. The passive mechanism almost instantaneously finishes alignment, so no time budget should be counted. Compared with AFM’s FOV, the sub-micron positioning precision guarantees the same location on wafer-by-wafer inspection. To enhance the metrology throughput, the proposed system uses multiple AFM chips distributed over the wafer footprint in order to image on multiple hotspots simultaneously. On the other hand, a flexure-based XY stage which is able to make nm-precision and mm-range is implemented to position AFM probe. The proposed system takes a serial of images neighboring to each other, image-stitching programmatically mosaic all images to generate a large area FOV measurement. This system applies several concepts to thoroughly enhance the throughput of advanced nanometrology and make it compatible with an in-line inspection methodology in the nanomanufacturing process. By the enhanced throughput of metrology, the nanomanufacturing will have a great potential to develop a feedback, process control and improve product’s quality and yield.
Low temperature area-selective atomic layer deposition of NiO, Ni and Pd for next-generation nanomanufacturing
(2022-08-12) Nallan Chakravarthula, Himamshu; Ekerdt, John G.; Bonnecaze, Roger T; Milliron, Delia J; Zhou, Jianshi
Nickel, nickel oxide and palladium are used within various device heterostructures for chemical sensing, solar cells, batteries, etc. There is increasing interest in realizing flexible, low-cost, wearable electronics to enable ubiquitous sensors, next-generation displays, and improved human-machine interfaces. A major hurdle for flexible technology is the development of low temperature fabrication processes for the integration of inorganic devices with polymeric substrates. Here we investigate area-selective atomic layer deposition of NiO performed at 100 °C using bis(N,N'-di-tert-butylacetamidinato)nickel(II) and water on SiO₂ and polystyrene. NiO grows two dimensionally and without nucleation delay on oxide substrates but not on SiN [subscript x] or polystyrene, which require surface treatments such as an Al₂O₃ buffer layer or O₂ plasma treatment to promote NiO nucleation. Additionally, pre-patterned sp² carbon-rich resists inhibit the nucleation of NiO. This way, carbon-free NiO may be patterned. A NiO grid pattern is fabricated as a demonstration. Additionally, thermal reduction of NiO to Ni was explored using H₂ (50-300 mTorr) and thermally generated H-atoms (3×10⁻⁵ Torr chamber pressure). Due to the relatively high free surface energy of metals, Ni films undergo dewetting at elevated temperatures when solid-state transport is enabled. Reduction of NiO to Ni is demonstrated at 100 °C and below using atomic hydrogen, a temperature low enough to be compatible with organic substrate temperature constraints as well as to avoid significant dewetting. Finally, the area-selective atomic layer deposition of Pd by area-activation is studied. Thermal atomic layer deposition of Pd can only proceed at low temperatures on surfaces that can dissociate the coreactant, H₂. Prepatterned Ni functions to catalyze the nucleation of Pd at 100 °C. H-atom reduction of NiO grown by atomic layer deposition can generate an atomically smooth Ni surface, which allows the growth of void-free Pd films. Finally, the area-selective atomic layer deposition of Pd on patterned Ni grid lines is explored.
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.
Spectral imaging for high-throughput metrology of large-area nanostructure arrays
(2019-12-16) Gawlik, Brian Matthew; Sreenivasan, S. V.; Yu, Edward T.; Labrake, Dwayne; Djurdjanovic, Dragan; Wang, Yaguo
Modern high-throughput nanopatterning techniques such as nanoimprint lithography make it possible to fabricate arrays of nanostructures (features with dimensions on the 10’s to 100’s of nm scale) over large area substrates (in² to m² scale) such as Si wafers, glass sheets, and flexible roll-to-roll webs. The ability to make such large area nanostructure arrays, or “LNAs” as we will call them, gives birth to an extensive design space enabling a wide array of applications. For instance, LNAs exhibit nanophotonic properties enabling optical devices like wire-grid polarizers (WGPs), transparent conducting metal mesh grids (MMGs), color filters, perfect mirrors, and anti-reflection surfaces. LNAs can also be utilized for increasing surface area as well as generally creating large arrays of discrete features to be utilized as building blocks for electronic components in memory storage devices, sensors, and microprocessors. These unique properties make LNAs immediately attractive to certain industries such as the display and photovoltaic industries. As fabrication methods for LNAs are becoming viable, various industries are becoming interested in pursuing high-volume manufacturing of LNAs for these applications. Unfortunately, metrology methods are currently rudimentary outside of the silicon integrated circuits industry, impeding manufacturing scalability in applications such as displays and photovoltaics. Metrology is essential in the manufacturing context, because it provides invaluable feedback on the success of the fabrication process, both during new process development and large-scale production by tracking of device quality metrics, including performance and reliability metrics, and enables classification of defects that cause devices to not achieve desired quality metrics. Traditional nanometrology methods have fundamental issues which make their applicability to LNA manufacturing difficult. In particular, their low throughput is a major deal-breaker. Fortunately, the nanophotonic properties of LNAs offer a convenient basis for metrology which offers the potential to bridge the gap between the macro and nano scales. This is because the nanophotonic properties of LNAs are inherently geometry dependent, meaning that the optical effects observed from LNAs on the macroscale give direct insight into what is happening on the nanoscale. These optical properties can be characterized using spectral imaging methods such as RGB color imaging, multispectral imaging, and hyperspectral imaging. The throughput of these systems can be extremely high relative to traditional metrology approaches. For instance, a hyperspectral imaging system, when optimized, can achieve throughput of 2.6 m²/hr with 61 spectral bands (wavelength centers of 400 to 700 nm in steps of 5 nm) and a resolution of 10 x 10 µm. An RGB imaging system can achieve an even higher throughput of 15.3 m²/hr. The 10 x 10 µm lateral resolution is often adequate for display and photovoltaic applications. The high throughput makes this approach is incredibly attractive. In this dissertation, we show how spectral imaging techniques can be applied to metrology characterization tasks including defect detection and classification as well as providing a geometric measurement capability via a technique called optical critical dimension (OCD) scatterometry. In this work, we utilize exemplar manufacturing methods, namely JFIL nanoimprint lithography, to create a variety of exemplar LNAs on which we demonstrate the various metrology capabilities of spectral imaging. These LNAs include plasma etched vertical Si nanopillar arrays, metal assisted chemical etching (MACE) vertical Si nanowire arrays, WGPs, and MMGs. Each of these devices has unique manufacturing processes, and we show how the various manufacturing process steps can create a variety of different defects. Naturally, many of the defects originate in the nanoimprint process which lithographically defines the features. We show how defects like particle contamination, non-filling, residual layer thickness (RLT) variations, and adhesion failure uniquely manifest as changes in the optical signatures of the LNAs and use this principle to provide a basis for defect detection. Then, we show how image processing methods can be used to classify what types of defects have occurred over large areas such as wafer scale. Furthermore, we demonstrate that spectral imaging can be used as a geometric metrology using the OCD method, and show how hyperspectral imaging, in particular, can provide geometric measurement on wafer scale areas. The large field of view (FOV), high spatial resolution, and high speed offered by the spectral imaging approach allows for identification of a variety of interesting defect signatures that would be difficult, or nearly impossible, to observe using other metrology approaches. Finally, we discuss ongoing development of a spectral imaging system for roll-to-roll (R2R) LNA manufacturing. Construction of this system will begin in the months following this dissertation and will primarily be applied to manufacturing of WGPs and MMGs on R2R. In summary, these demonstrations are intended to serve as a demonstration of the use of spectral imaging wherever possible in LNA manufacturing. Naturally, this requires that the LNAs being manufacturing exhibit significant enough optical effects for the approach to work, but when this is the case, the advantages of the approach appear outstanding and thus have the potential to be utilized in volume manufacturing of LNAs.