This thesis covers nanofabrication of central stops for application in soft X-ray imaging using electron-beam lithography for pattern definition. Central stops are small scale optical components used in combination with an order sorting aperture to eliminate the higher order and zeroth order of light after diffraction from a Fresnel zone plate. The main objectives of this study were to produce central stops with the desired parameters and to obtain an understanding of the nanofabrication process. A challenge which was encountered during the fabrication of the central stops was uncertainties in electroplating time, resulting in multiple plating rounds and in turn impacting the quality of the nanostructures. Another challenge which presented itself was that the structures disappeared on the chip with an uneven resist layer, suggesting that the resist layer’s smoothness is important. A key consideration when fabricating structures on this small scale is therefore to ensure the smoothness of the resist layer. Despite these challenges, one chip was successfully fabricated and could likely be used in the optical system for the SoftiMAX beamline, a beamline used for X-ray imaging at MAX IV, a fourth generation synchrotron radiation facility in Lund. In summary, recommendations for future replications and research would be to use chips with evenly coated resist, to make sure to only electroplate once and, if working with similar structures and parameters, to electroplate for a longer time than calculations suggest.

Shrinking the feature size of very large scale integrated circuits (VLSI) with advanced lithography has been a holy grail for the semiconductor industry. However, the gap between manufacturing capability and the expectation of design performance becomes critically challenged in sub-16nm technology nodes. To bridge this gap, design for manufacturing (DFM) is a must to co-optimize both design and lithography process at the same time. DFM for advanced lithography could be defined very differently under different circumstances. In general, progress in advanced lithography happens along three different directions: (1) New patterning technique (e.g., layout decomposition for different patterning techniques); (2) New design methodology (e.g., lithography aware standard cell design and physical design); (3) New illumination system (e.g., layout fracturing for EBL system, stencil planning for EBL system). In this dissertation, we present our research results on design for manufacturing (DFM) with multiple patterning lithography (MPL) and electron beam lithography (EBL) addressing these three DFM research directions in advanced lithography. For the research direction of new patterning technique, we study the layout decomposition problems for different patterning technique and explore four important topics: (1) layout decomposition for triple patterning; (2) density balanced layout decomposition for triple patterning; (3) layout decomposition for triple patterning with end-cutting; (4) layout decomposition for quadruple patterning and beyond. We present the proof that triple patterning layout decomposition is NP-hard. Besides, we propose a number of CAD optimization and integration techniques to solve different problems. For the research direction of new design methodology, we will show the limitation of traditional design flow. That is, ignoring triple patterning lithography (TPL) in early stages may limit the potential to resolve all the TPL conflicts. We propose a coherent framework, including standard cell compliance and detailed placement, to enable TPL friendly design. Considering TPL constraints during early design stages, such as standard cell compliance, improves the layout decomposability. With the pre-coloring solutions of standard cells, we present a TPL aware detailed placement where the layout decomposition and placement can be resolved simultaneously. In addition, we propose a linear dynamic programming to solve TPL aware detailed placement with maximum displacement, which can achieve good trade-off in terms of runtime and performance. For the EBL illumination system, we focus on two topics to improve the throughput of the whole EBL system: (1) overlapping aware stencil planning under MCC system; (2) L-shape based layout fracturing for mask preparation. With simulations and experiments, we demonstrate the critical role and effectiveness of DFM techniques for the advanced lithography, as the semiconductor industry marches forward in the deeper sub-micron domain. / text

This thesis addresses nanostructure fabrication techniques based on electron beam lithography, which is the most widely employed nanofabrication techniques for R&D and for the prototyping or production of photo-mask or imprint mold. The focus is on the study of novel resist and development process, as well as pattern transfer procedure after lithography. Specifically, this thesis investigates the following topics that are related to either electron beam resists, their development, or pattern transfer process after electron beam lithography: (1) The dry thermal development (contrary to conventional solvent development) of negative electron beam resists polystyrene (PS) to achieve reasonably high contrast and resolution. (2) The solvent development for polycarbonate electron beam resist, which is more desirable than the usual hot aqueous solution of NaOH developer, to achieve a low contrast that is ideal for grayscale lithography. (3) The fabrication of metal nanostructure by electron beam lithography and dry liftoff (contrary to the conventional liftoff using a strong solvent or aqueous solution), to achieved down to ~50 nm resolution. (4) The study a novel electron beam resist poly(sodium 4-styrenesulfonate) (sodium PSS) that is water soluble and water developable, to fabricate the feature size down to ~ 40 nm. And finally, (5) The fabrication of gold nanostructure on a thin membrane, which will be used as an object for novel x-ray imaging, where we developed the fabrication process for silicon nitride membrane, electroplating of gold, and pattern transfer after electron beam lithography using single layer resist and tri-layer resist stack.

In this study, template-based methods are used for the fabrication of various nanostructures such as nandots, nanorods, nanowires, nanotubes, and core-shell structures. Porous alumina membranes were employed as templates and metal nanostructures were synthesized in the templates by electrodeposition. By using lithography techniques, controlled patterned nanostructures were also fabricated on alumina templates. The magnetic properties of the various metal nanostructures were investigated. The pore size, interpore distance, and pore geometry highly affect magnetic properties of nanostructures grown in the templates. Hexagonally ordered porous alumina templates can be fabricated by two-step anodization. The pore diameters and interpore distances were readily controlled by appropriately changing anodization conditions and pore widening time. Alumina templates with various pore geometries were also successfully synthesized by changing applied voltage, increasing and decreasing, during a third anodization step. To understand magnetic properties of nanostructures with different aspect rations in the form of nanodots, nanorods, or nanowires, Fe nanostructures were fabricated in the templates by controlling of electrodeposition times. The coercivity of nanostructures increased with increasing aspect ratio. The anisotropy of the arrays was governed by the shape anisotropy of the magnetic objects with different aspect ratios. nanowires in mild-hard alumina and conventional alumina templates showed distinct differences in the squareness of hysteresis loops and coercivity both as a function of pore structure and magnetic component. Iron oxide nanotubes with a unique inner-surface were also fabricated by an electrodeposition method. β-FeOOH nanotubes were grown in alumina templates and transformed into hematite and magnetite structures during various heating processes. Hematite nanotubes are composed of small nanoparticles less than 20 nm diameters and the hysteresis loops and FC-ZFC curves show superparamagnetic properties without the Morin transition. In the case of magnetite nanotubes, which consist of slightly larger nanoparticles, hysteresis loops show ferromagnetism with weak coercivity at room temperature while FC-ZFC curves exhibit the Verwey transition at 125 K. For the patterning of nanowires, lithography techniques including nanosphere lithography and e-beam lithography were used. Nanosphere lithography used self-assembled PS spheres as a mask creates holes between spheres and the size of the holes is determined by the size and geometry of ordered PS spheres on the templates. This method can grow patterned nanowires arrays and also produce unique cup-shaped nanostructures with sizes ranging from micrometer down to several nanometers. E-beam lithography was also combined with template-based electrodeposition. Of these two lithographic methods, this one is the most powerful in the fabrication of patterned nanostructures with high aspect ratios. Various features and the sizes of patterned structures can be readily controlled. By the directing the pore diameters and interpore distances of the alumina template, the size and number of patterned nanowires are also adjustable.

A wide variety of tunable physio-chemical properties make ZnO nanowires a promising candidate for functional device applications. Although bottom-up grown nanowires are producible in volume, their high-throughput device integration requires control over dimensions and, more importantly, of precise placement. Thus development of top-down fabrication routes with accurate device positioning is imperative and hence pursued in this thesis. ZnO thin film transistors (TFT) were fabricated using solution based precursor zinc neodecanoate. A range of ZnO thin films were prepared by varying process parameters, such as precursor concentrations and annealing temperatures, and then analysed for their optical and electrical characteristics. ZnO TFTs prepared from a 15 % precursor concentration and annealing at 700 $^\circ$C exhibited best device performance with a saturation mobility of 0.1 cm$^2$/V.s and an on/off ratio of 10$^7$. Trap limited conduction (TLC) transport was found to be dominant in these devices. A direct-write electron beam lithography (EBL) process was developed using zinc naphthenate and zinc neodecanoate precursors for the top-down synthesis of ZnO nanowires. Nanoscale ZnO patterns with a resolution of 50 nm and lengths up to 25 $\mu$m were fabricated. A linear mobility of 0.5 cm$^2$/V.s and an on/off ratio of $\sim$10$^5$ was achieved in the micro-FETs with 50 $\mu$m channel width. Interestingly, on scaling down the ZnO channel width down to 100 nm, almost two orders of magnitude enhancement in the linear mobility was observed, which reached $\sim$33.75 cm$^2$/V.s. Such increment in the device performance was attributed to the formation of larger grains and thus reduction in the grain-boundary scattering. Six volatile organic compounds (VOCs) were sensed at room temperature using the direct-write EBL fabricated ZnO devices under UV sensitisation. As the surface-to-volume ratio increases with the decreasing channel width (from 50 $\mu$m to 100 nm), sensing response of the ZnO devices becomes more significant. Ppm level detection of various VOCs was observed; with a 25 ppm level Anisole detection being the lowest concentration. Additionally, using 100 nm device, detection of 10 ppm NO$_2$ was achieved at room temperature. The sensing response towards NO$_2$ was found to be increased with UV illumination and sensor temperature. This led to exhibit $\sim$171 % sensing response for a 2.5 ppm level of NO$_2$.

We have fabricated nanofuses from thin-film, arc-evaporation carbon for use in permanent data storage. Thin film carbon fuses have fewer fabrication barriers and retain the required resistivity and structural stability to work as a data storage medium. Carbon thin films were characterized for their electrical, microstructural, and chemical bonding properties. Annealing the thin-film carbon in an argon environment at 400°C reduced the resistivity from about 4*10-2 Ω cm as deposited down to about 5*10-4 Ω cm, allowing a lower blowing voltage. Nanofuses with widths ranging from 200 nm down to 60 nm were fabricated and tested. They blow with voltages between 2 V and 5.5 V, and the nanofuses remain stable in both a "1" and a "0" state under a constantly applied read voltage of 1 volt for over 90 hours, corresponding to a cumulative time of >1012 reads.

Magnetic permalloy nanostructures were fabricated onto a silicon wafer using electron beam lithography and a liftoff process. The lithography was performed with a Hitachi SU-70 SEM retrofitted with a Nabity NPGS lithography conversion kit. PMMA of 950kDa molecular weight was used as the photoresist. Features were either nanowires, nanodots, or elliptical or rectangular nanostructures. The nanowires had dimensions of 15µm x 200nm x 40nm, the nanodots had diameters of 145nm and thickness of 12nm, and the ellipses and rectangles had dimensions of 110nm x 50nm x 13nm. Characterization of the nanostructures was performed using the same Hitachi SEM as well as a Digital Instruments DI 3100 Nanoscope IIIa AFM used in magnetic force imaging mode. The SEM was used to measure lateral dimensions of the features and to capture images of features for proper documentation and for external simulation studies. The MFM was used to capture magnetic images of the samples to determine the magnetic state of the nanowires or arrays.

We report on the process parameters of nanoimprint lithography (NIL) for the fabrication of two-dimensional (2-D) photonic crystals. The nickel mould with 2-D photonic crystal patterns covering the area up to 20mm² is produced by electron-beam lithography (EBL) and electroplating. Periodic pillars as high as 200nm to 250nm are produced on the mould with the diameters ranging from 180nm to 400nm. The mould is employed for nanoimprinting on the poly-methyl-methacrylate (PMMA) layer spin-coated on the silicon substrate. Periodic air holes are formed in PMMA above its glass-transition temperature and the patterns on the mould are well transferred. This nanometer-size structure provided by NIL is subjective to further pattern transfer. / Singapore-MIT Alliance (SMA)

The field of Information and Communication Technologies is witnessing a development speed unprecedented in history. Moore’s law proves that the processor speed and memory size are roughly doubling each 18 months, which is expected to continue in the next decade. If photonics is going to play a substantial role in the ICT market, it will have to follow the same dynamics. There are mainly two groups of components that need to be integrated. The active components, including light sources, electro-optic modulators, and detectors, are mostly fabricated in III-V semiconductors. The passive components, such as waveguides, resonators, couplers and splitters, need no power supply and can be realized in silicon-related semiconductors. The prospects of silicon photonics are particularly promising, the fabrication is mostly compatible with standard CMOS technology and the on-chip optical interconnects are expected to increase the speed of microprocessors to the next generation. This thesis starts with designs of various silicon-based devices using finite-difference time-domain simulations. Parallel computation is a powerful tool in the modeling of large-scale photonic circuits. High Q cavities and resonant channel drop filters are designed in photonic crystal platform. Different methods to couple light from a single mode fiber to silicon waveguides are studied by coupled-mode theory and verified using parallel simulations. The performance of waveguide grating coupler for vertical radiation is also studied. The fabrication of silicon-based photonic devices involves material deposition, E-beam or optical lithography for pattern defining, and plasma/wet-chemistry etching for pattern transfer. For nanometer-scaled structures, E-beam lithography is the most critical process. Depending on the structures of the devices, both positive resist (ZEP520A) and negative resist (maN2405) are used. The proximity and stitch issues are addressed by careful dose correction and patches exposure. Some examples are given including photonic crystal surface mode filter, micro-ring resonators and gold grating couplers. In particular, high Q (2.6×105), deep notch (40 dB) and resonance-splitting phenomenon are demonstrated for silicon ring resonators. It is challenging to couple light into photonic integrated circuits directly from a single-mode fiber. The butt-coupled light-injecting method usually causes large insertion loss due to small overlap of the mode profiles and large index mismatch. Practically it is not easy to cleave silicon sample with smooth facet where the waveguide exposes. By adding gold gratings to the waveguides, light can be injected and collected vertically from single-mode fiber. The coupling efficiency is much higher. There is no need to cleave the sample. The access waveguides are much shortened and the stitch problem in E-beam lithography is avoided. In summary, this thesis introduces parallel simulations for the design of modern large-scale photonic devices, addresses various issues with Si-based fabrication, and analyses the data from the characterization. Several novel devices using silicon nanowire waveguides and 2D photonic crystal structures have been demonstrated for the first time. / QC 20100923

Nanopore-based single-molecule analysis of biomolecules such as DNA and proteins is a subject of strong scientific and technological interest. In recent years, solid state nanopores have been demonstrated to possess a number of advantages over biological (e.g., ion channel protein) pores due to the relative ease of tuning the pore dimensions, pore geometry, and surface chemistry. However, solid state fabrication methods have been limited in their scalability, automation, and reproducibility. In this work, a wafer-scale fabrication method is first demonstrated for reproducibly fabricating large arrays of solid-state nanopores. The method couples the high-resolution processes of electron beam lithography (EBL) and atomic layer deposition (ALD). Arrays of nanopores (825 per wafer) are successfully fabricated across a series of 4' wafers, with tunable pore sizes from 50 nm to sub-20 nm. The nanopores are fabricated in silicon nitride films with thicknesses varying from 10 nm to 50 nm. ALD of aluminum oxide is used to tune the nanopore size in the above range. By careful optimization of all the processing steps, a device survival rate of 96% is achieved on a wafer with 50 nm silicon nitride films on 60- 80 micron windows. Furthermore, a significant device survival rate of 88% was obtained for 20 nm silicon nitride films on order 100 micron windows. In order to develop a deeper understanding of nanopore fabrication-structure relationships, a modeling study was conducted to examine the physics of EBL, in particular: to investigate the effects of beam blur, dose, shot pattern, and secondary electrons on internal pore structure. Under the operating conditions used in pore production, the pores were expected to taper to a substantially smaller size than their apparent size in SEM. This finding was supported by preliminary conductance readings from nanopores.