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Nanoelectrode lithography : : modelling, experimental validation and instrumentation
Get PDFThis thesis was previously held under moratorium from 02/11/20 to 02/11/22Continuous rapid shrinking of feature size made the authorities to seek alternative patterning methods as the conventional photolithography process is reaching its intrinsic resolution limit. In this regard, some promising techniques have been proposed as the next generation lithography (NGL) that have the potentials to achieve both high volume production and very high resolution. Among them, several methods such as Extreme Ultraviolet Lithography (EUVL), Electron Beam lithography (EBL), Nanoimprint Lithography (NIL), Directed Self Assembly (DSA) and Scanning Probe Lithography (SPL) have demonstrated excellent potentials as promising candidates for future industrial nanofabrication. -- However, all these technologies are in their development phases and still need further work to overcome some challenges in terms of flexibility, uniformity, high throughput, high resolution, high reliability, high- efficiency, defectivity, and cost of ownership. On the other hand, nanoelectrode nanolithography (NEL) has been developed in the laboratory and demonstrated as an efficient lithographic tool. It has been strengthened in recent years as one of the most promising methods due to its high reproducibility, low cost, and ability to manufacture nano-sized structures. -- -- This method is based on the spatial confinement of the anodic oxidation between a conductive stamp and the sample surface. However, the non-uniformity issue severely limits the existing nanoelectrode lithography to be applied for large area nanopatterning. Besides, other issues such as stamp lifetime and low-cost stamp fabrication method need to be addressed to make this lithography technique viable for commercial applications. -- A clear and explicit understanding of the mechanism at a molecular level helps to improve this technique. Therefore, this PhD thesis firstly aims to gain an in-depth understanding of nanoscale mechanisms involved in the anodic oxidation process and the parametric influence in nanoelectrode lithography through molecular dynamics (MD) simulations. -- To do this, three-dimensional MD models of oxidation nanocell were developed, and a reactive force field (ReaxFF) was adopted to describe the interactions between atoms. The MD simulations were implemented in LAMMPS software and were performed by using a High-Performance Computing (HPC) service, ARCHIE-WeSt. The simulation results demonstrated two forms of adsorption of water molecules: molecular adsorption and dissociative adsorption. After breaking the adsorbed hydroxyls, the oxygen atoms insert into the substrate to form the Si−O−Si bonds so as to make the surface oxidized. A linear dependency of the electric field intensity on oxidation growth was observed. The relative humidity also showed the same linear behavior after a certain value (40%). The simulation results have been compared qualitatively with the experimental results, and they show in good agreement. -- -- MD simulation results also showed that the crystallographic orientation of the substrate has a great impact on the oxidation process. It was revealed that the thickness of the oxide film and the initial oxygen diffusion rate follow an order of (100) > (110) > (111) at lower electric field intensities. It also confirmed that surfaces with higher surface energy are more reactive at lower electric field intensity. Crossovers occurred at a higher electric field intensity (7 V/nm) under which the thickness of the oxide film yields an order of T(110) > T(100) > T(111). -- -- Atomic force microscope (AFM) oxidation experiments were performed to validate these results, which showed different orders for the (100) and (111) substrates, while (110) remained the largest for the oxide thickness. A good correlation has been found between the oxide growth and the orientation-dependent parameters where the oxide growth is proportional to the areal density of the surfaces. -- The oxide growth also follows the relative order of the activation energies, which could be another controlling factor for the oxide growth. However, the differences between simulation and experimental results probably relate to the empirical potential as well as different time and spatial scales of the process. -- Another objective of this thesis is to develop a new NEL process with a brass stamp that does not require conductive layer deposition. The brass material was chosen as it has high elastic modulus and high breaking strength, which ensures higher life expectancy. Therefore, this thesis reports the feasibility of using brass materials as the conductive stamps for NEL to shorten the process steps and reduce the production cost. The fabrication of nanostructures on the brass stamp was performed on a single point diamond turning (SPDT) machine. Some burrs were formed during the machining process, that prohibit the stamps from achieving a homogeneous contact with the substrates. Oxidation experiments were carried out with a home built NEL system. The results showed that an introduction of a thin layer of polymer (PS-OH) on the silicon substrate could improve the contact uniformity so as the oxidation. -- -- Finally, a rolling nanoelectrode lithography process was proposed, for the first time, to scale up the nanoelectrode lithography technique for large-area nanofabrication. A test-bed was developed to realize uniform pressure distribution over the whole contact area so that the local oxidation process occurs uniformly over a large area of the samples. A brass roller wrapped with a fabricated polycarbonate strip has been used as a stamp to generate nanopatterns on a silicon surface. The experimental results indicated that a significant improvement in pattern uniformity compared to the other results was obtained with the conventional NEL process. -- Moreover, the impact of pattern direction has been investigated, which shows no significant variation in the oxide pattern. Lastly, the rolling speed and the applied bias voltage were identified as the primary control parameters for the oxide growth.Continuous rapid shrinking of feature size made the authorities to seek alternative patterning methods as the conventional photolithography process is reaching its intrinsic resolution limit. In this regard, some promising techniques have been proposed as the next generation lithography (NGL) that have the potentials to achieve both high volume production and very high resolution. Among them, several methods such as Extreme Ultraviolet Lithography (EUVL), Electron Beam lithography (EBL), Nanoimprint Lithography (NIL), Directed Self Assembly (DSA) and Scanning Probe Lithography (SPL) have demonstrated excellent potentials as promising candidates for future industrial nanofabrication. -- However, all these technologies are in their development phases and still need further work to overcome some challenges in terms of flexibility, uniformity, high throughput, high resolution, high reliability, high- efficiency, defectivity, and cost of ownership. On the other hand, nanoelectrode nanolithography (NEL) has been developed in the laboratory and demonstrated as an efficient lithographic tool. It has been strengthened in recent years as one of the most promising methods due to its high reproducibility, low cost, and ability to manufacture nano-sized structures. -- -- This method is based on the spatial confinement of the anodic oxidation between a conductive stamp and the sample surface. However, the non-uniformity issue severely limits the existing nanoelectrode lithography to be applied for large area nanopatterning. Besides, other issues such as stamp lifetime and low-cost stamp fabrication method need to be addressed to make this lithography technique viable for commercial applications. -- A clear and explicit understanding of the mechanism at a molecular level helps to improve this technique. Therefore, this PhD thesis firstly aims to gain an in-depth understanding of nanoscale mechanisms involved in the anodic oxidation process and the parametric influence in nanoelectrode lithography through molecular dynamics (MD) simulations. -- To do this, three-dimensional MD models of oxidation nanocell were developed, and a reactive force field (ReaxFF) was adopted to describe the interactions between atoms. The MD simulations were implemented in LAMMPS software and were performed by using a High-Performance Computing (HPC) service, ARCHIE-WeSt. The simulation results demonstrated two forms of adsorption of water molecules: molecular adsorption and dissociative adsorption. After breaking the adsorbed hydroxyls, the oxygen atoms insert into the substrate to form the Si−O−Si bonds so as to make the surface oxidized. A linear dependency of the electric field intensity on oxidation growth was observed. The relative humidity also showed the same linear behavior after a certain value (40%). The simulation results have been compared qualitatively with the experimental results, and they show in good agreement. -- -- MD simulation results also showed that the crystallographic orientation of the substrate has a great impact on the oxidation process. It was revealed that the thickness of the oxide film and the initial oxygen diffusion rate follow an order of (100) > (110) > (111) at lower electric field intensities. It also confirmed that surfaces with higher surface energy are more reactive at lower electric field intensity. Crossovers occurred at a higher electric field intensity (7 V/nm) under which the thickness of the oxide film yields an order of T(110) > T(100) > T(111). -- -- Atomic force microscope (AFM) oxidation experiments were performed to validate these results, which showed different orders for the (100) and (111) substrates, while (110) remained the largest for the oxide thickness. A good correlation has been found between the oxide growth and the orientation-dependent parameters where the oxide growth is proportional to the areal density of the surfaces. -- The oxide growth also follows the relative order of the activation energies, which could be another controlling factor for the oxide growth. However, the differences between simulation and experimental results probably relate to the empirical potential as well as different time and spatial scales of the process. -- Another objective of this thesis is to develop a new NEL process with a brass stamp that does not require conductive layer deposition. The brass material was chosen as it has high elastic modulus and high breaking strength, which ensures higher life expectancy. Therefore, this thesis reports the feasibility of using brass materials as the conductive stamps for NEL to shorten the process steps and reduce the production cost. The fabrication of nanostructures on the brass stamp was performed on a single point diamond turning (SPDT) machine. Some burrs were formed during the machining process, that prohibit the stamps from achieving a homogeneous contact with the substrates. Oxidation experiments were carried out with a home built NEL system. The results showed that an introduction of a thin layer of polymer (PS-OH) on the silicon substrate could improve the contact uniformity so as the oxidation. -- -- Finally, a rolling nanoelectrode lithography process was proposed, for the first time, to scale up the nanoelectrode lithography technique for large-area nanofabrication. A test-bed was developed to realize uniform pressure distribution over the whole contact area so that the local oxidation process occurs uniformly over a large area of the samples. A brass roller wrapped with a fabricated polycarbonate strip has been used as a stamp to generate nanopatterns on a silicon surface. The experimental results indicated that a significant improvement in pattern uniformity compared to the other results was obtained with the conventional NEL process. -- Moreover, the impact of pattern direction has been investigated, which shows no significant variation in the oxide pattern. Lastly, the rolling speed and the applied bias voltage were identified as the primary control parameters for the oxide growth
Promising lithography techniques for next generation logic devices : a review
Get PDFContinuous rapid shrinking of feature size made the authorities to seek alternative patterning methods as the conventional photolithography comes with its intrinsic resolution limit. In this regard, some promising techniques have been proposed as next generation lithography (NGL) that have the potentials to achieve both high volume production and very high resolution. This article reviews the promising next generation lithography techniques and introduces the challenges and a perspective on future directions of the NGL techniques. Extreme Ultraviolet Lithography (EUVL) is considered as the main candidate for sub-10 nm manufacturing and it could potentially meet the current requirements of the industry. Remarkable progress in EUVL has been made and the tools will be available for commercial operation soon. Maskless lithography techniques are used for patterning in R&D, mask/mold fabrication and low volume chip design. Directed Self Assembly (DSA) has already been realized in laboratory and further effort will be needed to make it as NGL solution. Nanoimprint Lithography has emerged attractively due to its simple process-steps, high-throughput, high-resolution and low-cost and become one of the commercial platforms for nanofabrication. However, a number of challenging issues are waiting ahead and further technological progresses are required to make the techniques significant and reliable to meet the current demand. Finally, a comparative study is presented among these techniques
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Substrate orientation effects on nanoelectrode lithography : ReaxFF molecular dynamics and experimental study
Get PDFThe crystallographic orientation of the substrate is an essential parameter in the kinetic mechanism for the oxidation process. Hence, the choice of substrate surface orientation is crucial in nanofabrication industries. In the present work, we have studied qualitatively the influence of substrate orientation in nanoelectrode lithography using ReaxFF reactive molecular dynamics simulation. We have investigated the oxidation processes on (100), (110) and (111) orientation surfaces of silicon at different electric field intensities. The simulation results show the thickness of the oxide film and the initial oxygen diffusion rate follow an order of (100) > (110) > (111) at lower electric field intensities. It also confirms that surfaces with higher surface energy are more reactive at lower electric field intensity. Crossovers occurred at a higher electric field intensity (7 V nm -1) under which the thickness of the oxide film yields an order of T(110) > T(100) > T(111). These types of anomalous characteristics have previously been observed for thermal oxidation of silicon surfaces. Experimental results show different orders for the (100) and (111) substrate, while (110) remains the largest for the oxide thickness. A good correlation has been found between the oxide growth and the orientation-dependent parameters where the oxide growth is proportional to the areal density of the surfaces. The oxide growth also follows the relative order of the activation energies, which could be another controlling factor for the oxide growth. Less activation energy of the surface allows more oxide growth and vice versa. However, the differences between simulation and experimental results probably relate to the empirical potential as well as different time and spatial scales of the process
ReaxFF molecular dynamics simulation study of nanoelectrode lithography oxidation process on silicon (100) surface
Get PDFThe nanoelectrode lithography has been strengthened in recent years as one of the most promising methods due to its high reproducibility, low cost and ability to manufacture nano-sized structures. In this work, the mechanism and the parametric influence in nanoelectrode lithography have been studied qualitatively in atomic scale using ReaxFF MD simulation. This approach was originally developed by van Duin and co-workers to investigate hydrocarbon chemistry. We have investigated the water adsorption and dissociation processes on Si (100) surface as well as the characteristics (structure, chemical composition, morphology, charge distribution, etc.) of the oxide growth. The simulation results show two forms of adsorption of water molecules: molecular adsorption and dissociative adsorption. After breaking the adsorbed hydroxyls, the oxygen atoms insert into the substrate to form the Si−O−Si bonds so as to make the surface oxidized. The influence of the electric field intensity (1.5 – 7 V/nm) and the relative humidity (20 – 90%) on the oxidation process have also been discussed. Nevertheless, the results obtained from the simulations have been compared qualitatively with the experimental results and they show in good agreements. Variable charge molecular dynamics allowed us to characterize the nanoelectrode lithography process from an atomistic point of view
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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