Pattern collapse in lithographic nanostructures: quantifying photoresist nanostructure behavior and novel methods for collapse mitigation

The Microelectronics industry has continuously pushed the limit of critical dimensions to sub-20 nm. One of the challenges is pattern collapse, caused by unbalanced capillary forces during the final rinse and drying process. The use of surfactants offers a convenient method to reduce capillary forces but causes another deformation issue. This thesis work focuses on alternative approaches that are compatible with lithographic processes to mitigate pattern collapse. First, an e-beam lithography pattern with a series of varying line and space widths has been specifically designed in order to quantitatively study pattern collapse behavior. This pattern generates increasing stress in the pairs of resist lines as one moves across the pattern array and eventually a sufficiently small space value (critical space, S1c) is reached in each array such that the stress applied to the resist exceeds the critical stress (σc) required for pattern bending and subsequently feature deformation and collapse occurrs. The patterns we designed allow us to qualitatively and quantitatively study pattern collapse and obtain consistent, reproducible results. In the first part of the thesis work, a quick surface crosslink (called a reactive rinse) that involves the strengthening of the resist using crosslinking via carbodiimide chemistry while the resist structures are still in their wet state, has been developed and demonstrated. This technique provides efficient and significant improvement on the pattern collapse issue. In the second part of the thesis work, a triethoxysilane compound, vinyl ether silane (VE), has been successfully synthesized. It can be used to modify the silicon or silicon nitride substrates and form a covalent bond with the resist film instead of manipulating the surface energies using common HMDS. Compared to traditional Hexamethyldisilazane (HMDS) vapor primed surfaces, the implementation of the VE adhesion promoter resulted in a significant improvement in the adhesion and resistance to adhesion based pattern collapse failure in small sub-60 nm resist features. In the third part of the thesis work, the effect of drying rates and drying methods has been systematically studied. SEM analysis and critical stress results showed that fast drying appear to reduce the resist collapse. The line pair orientations in each pattern array with respect to the wafer radius reveal an apparent effect of fluid flow and centrifugal forces on collapse. Finally, a comprehensive pattern collapse model that incorporates adhesion based pattern failure and elastoplastic deformation-based failure, and dimensionally dependent resist modulus properties has been developed. This model provides such an excellent prediction of the experimental data and supports the idea that this level of combined adhesion-failure and elastoplastic-failure based pattern collapse modeling, where one explicitly considers the dimensionally dependent mechanical properties of the resist can be quantitatively predictive and useful for understanding the pattern collapse behavior of polymeric nanostructures.PhDCommittee Chair: Henderson, Clifford; Committee Member: Meredith, J. Carson; Committee Member: Hess, Dennis; Committee Member: Reichmanis, Elsa; Committee Member: Tolbert, Lare

Advanced resist materials for next generation lithography

With the advancement in technology the minimum lithographic feature size decreases more and more for every generation. The development of lithographic techniques and resist materials capable of meeting the requirements for the up- graded technology (resolution, sensitivity, roughness) started to play a trivial role. However, the issue represents a fundamental principle in lithography (the RLS trade-off) and it proves difficult to overcome. Addition of quenchers in chemically amplified resists reduces the acid diffusion length and improves the line edge roughness and increases the resolution of the patterned features, but decreases the sensitivity. The current most commonly researched approach to boost the sensitivity in organic resists is the addition of metals embedded in the molecular structure by covalent bonds. This approach was investigated in this thesis, and an extension towards high-Z organic additive compounds and high-Z cross-linkers was conducted. Furthermore as feature sizes less than 20 nm are routinely required, pattern col- lapse driven by the capillary forces upon development has become a serious limiting factor, independent of the lithography technique involved. Alongside with constantly developing the resist platforms there is also the need to improve the adhesion of the resist material to the silicon substrate, reducing pattern collapse and allowing for ultra high resolution and high aspect ratio patterning. In this thesis I will present the research I have undertaken in order to implement a resist platform suitable for next generation lithography and I will introduce and describe the new multi-trigger mechanism concept developed for this resist system. I will also present a study on active underlayes investigated for improved adhesion between the resist and the substrate

Fabricating microfluidic devices in polymers for bioanalytica applications

The research presented in this document focuses on the fabrication, characterization and application of microfluidic systems fabricated in poly(methyl methacrylate) (PMMA) with the emphasis focused on the fabrication processing steps. Microfluidic devices were produced in PMMA using X-ray lithography. The fabrication methods investigated were sacrificial mask, polyimide membrane mask and embossing techniques. PMMA microfluidic devices fabricated using X-ray lithography were characterized using scanning electron microscopy (SEM) and optical microscopy, while analytical techniques such as electroosmotic flow determination, separations, and fluorescent microscopy were used to characterize fluid transport in these devices. A novel method for the heat annealing of PMMA to PMMA to create a closed system is described. Characterization of this technique was carried out by optical microscopy and scanning electron microscopy. The manufacturing techniques utilized in producing mold inserts for hot embossing and injection molding is discussed as well. Both the mold insert and devices produced from the inserts were characterized using scanning electron microscopy. Devices produced can be used to perform a number of analytical techniques including single molecule detection and fluorescence lifetime monitoring. The primary goal of this research was to develop molding tools consisting of high-aspect-ratio microstructures using robust and reproducible processing steps

Addition Polymerization Toward the Synthesis of Photoresists for Microlithography with Carbon Dioxide Development

In the drive for smaller image sizes in microelectronic devices, the lithography industry has reached a point where the solvents traditionally used for development are potentially damaging to the images formed. The use of a more gentle solvent, such as supercritical carbon dioxide, has been shown to alleviate this problem. Furthermore, replacement of the solvents in spin-coating and stripping with condensed CO2 could streamline the lithography process as the "wet" solvents would be eliminated. Also, CO2 is an environmentally benign and easily recyclable alternative to the solvents currently used in microlithography for the solvent-intensive steps of processing a photoresist. As next generations of lithographic techniques for imaging a photoresist approach, more stringent requirements are placed on the resist. For 193 nm and 193 nm immersion resists, alicyclic backbones have been shown to impart etch resistance and to elevate glass transition temperatures, while fluorination has been shown to decrease absorbance. As an additional advantage for processing in CO2, fluorination also increases CO2 solubility. Various norbornene-based monomers were synthesized to include fluorinated moieties. Resist materials were synthesized by addition polymerization using allylpalladium chloride dimer. Fluorinated copolymers containing a "chemical switch" have been found to have a significant CO2 solubility difference, as well as a difference in intrinsic viscosities. Dry plasma etching of these polymers has demonstrated moderate etch resistance compared to Novolac. Imaging with an ASML 193 nm scanner has resolved 1 micrometer semidense lines, using CO2 as the developer

Recent Advances on Nanocomposite Resists With Design Functionality for Lithographic Microfabrication

Nanocomposites formed by a phase-dispersed nanomaterial and a polymeric host matrix are highly attractive for nano- and micro-fabrication. The combination of nanoscale and bulk materials aims at achieving an effective interplay between extensive and intensive physical properties. Nanofillers display size-dependent effects, paving the way for the design of tunable functional composites. The matrix, on the other hand, can facilitate or even enhance the applicability of nanomaterials by allowing their easy processing for device manufacturing. In this article, we review the field of polymer-based nanocomposites acting as resist materials, i.e. being patternable through radiation-based lithographic methods. A comprehensive explanation of the synthesis of nanofillers, their functionalization and the physicochemical concepts behind the formulation of nanocomposites resists will be given. We will consider nanocomposites containing different types of fillers, such as metallic, magnetic, ceramic, luminescent and carbon-based nanomaterials. We will outline the role of nanofillers in modifying various properties of the polymer matrix, such as the mechanical strength, the refractive index and their performance during lithography. Also, we will discuss the lithographic techniques employed for transferring 2D patterns and 3D shapes with high spatial resolution. The capabilities of nanocomposites to act as structural and functional materials in novel devices and selected applications in photonics, electronics, magnetism and bioscience will be presented. Finally, we will conclude with a discussion of the current trends in this field and perspectives for its development in the near future.Fil: Martínez, Eduardo David. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia - Nodo Bariloche | Comision Nacional de Energia Atomica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia - Nodo Bariloche.; ArgentinaFil: Prado, A.. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia - Nodo Bariloche | Comision Nacional de Energia Atomica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia - Nodo Bariloche.; ArgentinaFil: Gonzalez, M.. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia - Nodo Bariloche | Comision Nacional de Energia Atomica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia - Nodo Bariloche.; ArgentinaFil: Anguiano, S.. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia - Nodo Bariloche | Comision Nacional de Energia Atomica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia - Nodo Bariloche.; ArgentinaFil: Tosi, Leandro. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia - Nodo Bariloche | Comision Nacional de Energia Atomica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia - Nodo Bariloche.; ArgentinaFil: Salazar Alarcón, Leonardo. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia - Nodo Bariloche | Comision Nacional de Energia Atomica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia - Nodo Bariloche.; ArgentinaFil: Pastoriza, Hernan. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia - Nodo Bariloche | Comision Nacional de Energia Atomica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia - Nodo Bariloche.; Argentin

Innovative patternable materials for micro- and nano- fabrication

The research activity of this thesis is focused on the development and optimization of new directly patternable organically modified TiO2, Al2O3 and ZrO2 based sol-gel materials whose peculiar characteristics and performances were optimized and exploited for the final specific application. In particular, the main strategy that lies at the basis of all the thesis work is the combination of top down and- bottom up approach for the final device realization. In fact, special attention has been set to materials design and synthesis (bottom up) and subsequently to the micro- and nano- fabrication of patterns on the corresponding film surface with different lithographic techniques (top down) in order to achieve the required properties, according to the final application. As it concerns the bottom up approach, the sol-gel has been assumed as the main synthetic method since, by mixing different organic-inorganic precursors, new materials with unique properties and microstructures can be created. In fact, by using organically modified precursors (such as trimethoxyphenylsilane, 3-glycidoxypropyltrimethoxysilane, 3-(Trimethoxysilyl)propyl methacrylate) or organic monomers it was possible to produce hybrid materials with the organic and inorganic components intimately mixed at a molecular scale, with the twofold effect of obtaining new properties and conferring them the patternability. Moreover, the addition of tetrafunctional precursors (Titanium isopropoxide, Zirconium butoxide, Aluminum-tri-sec-butoxide) allowed to increase the reticulation degree, taking part to the inorganic network formation, to improve the material mechanical properties (such as scratch, abrasion, plasma etching resistance) and to confer particular characteristics to the final materials, i.e. to modulate the refractive index. On the other hand, as it regards the top down approach, different lithographic techniques (photolithography, X-ray lithography, electron beam lithography and nanoimprint lithography) have been exploited in the realization of high refractive index patterns, high selective etching masks features, adaptive-optics devices and stamps for microinjection moulding directly with the synthesized materials. The structural and chemical changes induced inside the material by the interactions with the source used in the lithographic process have been deeply investigated in order to optimize both the synthesis of the best sol-gel systems and the final lithographic procedures. In conclusion the development of all the above mentioned advanced materials and innovative processing was pushed by the main target of improving, simplifying and decreasing costs and time of the overall micro- and nano- fabrication process in order to obtain better final features quality, with respect to traditional lithographic procedures

Advances in sensors: the enabling roles of photocatalysis, polymer brushes and exotic characterization approaches

A transformative advance in the field of sensor technology has been the development of smart sensor systems. One major implication of smart sensor systems is the use of robust and reliable sensing devices. lt could appear to be trivial, but even the most intelligent system is completely useless if its sensing core does not work properly. For this reason, it is of paramount importance to develop highly efficient sensing platforms with self-calibrating, self-healing, self-compensating and selfcleaning properties. This is one of the most challenging and actual field of research, which benefited much from the "nanotechnology revolution", generating high promises especially for the development of miniaturized devices. This broad field crosses many different disciplines ranging from chemistry to physics to materials science, with a major role played by surface science. The scope of this Thesis is to explore three different, although converging, approaches to develop such kind of sensing platforms. The enabling roles of photocatalysis, polymer brushes and of exotic characterization techniques (such as positron annihilation spectroscopy) to reach this goal are discussed. Theoretical as well as highly applicative results are described, as products of a genuine curiosity-driven approach

Nano-scale lithography and microscopy of organic semiconductors

The development of organic electronic and photonic devices increasingly requires the development of micro- and nano-structured morphologies, which in turn require the development of both prototyping and scalable patterning methods. This thesis presents investigations which explore and develop unconventional patterning techniques for a variety of conjugated polymers and organic molecules, using scanning near-field optical lithography (SNOL), scanning thermal lithography (SThL) and molecular self-assembly. Optimised formation of organic nanostructures is demonstrated, at resolutions which equal or better the current state of the art, with patterning resolution for isolated structures below 60nm for SNOL and 30nm for SThL. SThL in particular is demonstrated as a technique which can achieve serial write-speeds of over 100 μm/s, with significant potential for up-scaling. Furthermore, arbitrarily defined two-dimensional large-area nanostructures up to 20 × 20 μm are demonstrated using SNOL while maintaining both high resolution and the integrity of the probe. The nanostructures fabricated in the course of this work, and others, are characterised using both optical and topographic techniques, primarily atomic force microscopy and near-field microscopy. The detailed formation mechanisms for structures fabricated using SNOL via an in-situ conversion route are systematically investigated and contrasted with other formation routes, resulting in a comprehensive account of the factors affecting structure morphology. In addition, the optimised nanostructures achieved in this work are shown, within this context, to be very close to best achievable with an apertured scanning near-field system

Nanoscale Manipulation of Electrokinetic Transport for Iontronic Applications based on Surface Modification

Electrokinetic transport demonstrates a lot of new physical behaviors in nanofluidic systems due to the high surface-to-volume ratios and interactions between the fluid and walls of nanofluidic systems. The unique properties of electrokinetic transport in nanoscale offer possibilities for applications in many fields, such as biological computing, sensing, and drug delivery. Fundamental studies of electrokinetic transport phenomena in nanoscale have been investigated numerically and experimentally. However, the precise manipulation of electrokinetic transport in nanoscale is still a great challenge. Traditional nanofluidic devices are difficult to achieve practical applications due to their low accuracy and sensitivity. Surface modification is a promising method to develop nanofluidic devices with more functionalities. Up to date, the experimental study of electrokinetic transport in modified nanochannels is still limited. This thesis systematically studies the electrokinetic transport phenomena in surface-modified polydimethylsiloxane (PDMS) nanochannels, as well as applications of chip-scale nanofluidic devices with surface modifications. At the beginning of this thesis, electroosmotic flow (EOF) is measured in pristine PDMS single nanochannels by the current-slope method. This nanochannel is fabricated by using solvent-induced cracking method and used to form a nanofluidic chip. The effects of ion size, ion valence, and pH of electrolyte solutions on the velocity of EOF in the nanochannel are experimentally studied. These results will serve as control data for the following studies of electrokinetic transport phenomena in modified nanochannels. Then two fundamental research projects are conducted in nanochannels modified with DNA and charged polyelectrolytes to study the effects of surface modifications on electrokinetic transport phenomena. Electroosmotic flow is systematically investigated in DNA grafted hard PDMS (h-PDMS) channels with the channel size ranging from 50 nm to 2.5 μm by using the current-slope method. The effects of the DNA types, the incubation time, the pH value, the ionic concentration of electrolyte solutions, and the UV (ultraviolet) illumination on the EOF velocity are experimentally studied. The comparisons between the EOF in pristine nanochannels and DNA grafted nanochannels indicate that the surface modification of nanochannel can significantly affect the electrokinetic transport. Furthermore, the transport of fluid can be regulated by UV illumination in DNA grafted nanochannels. The size and surface charge of nanochannels after the layer-by-layer (LBL) deposition of polyelectrolytes are experimentally measured. The results reveal that the increment of the coated multilayer thickness will be limited in small nanochannels. A minimum size of nanochannel exists when the nanochannel is modified by using LBL deposition of polyelectrolytes. This minimum size depends on the salt additive in the polyelectrolyte solutions. In addition, the surface charge of the modified nanochannels is determined by the outmost coated layer. The EOF can be alternatively reversed in the modified nanochannels by repeatedly coating oppositely charged polyelectrolytes. Based on the results from the fundamental studies, a nanofluidic diode is developed by modifying the surface charge and size of a nanochannel with charged polyelectrolytes. The surface charge-governed electrokinetic transport of mobile ions results in diode-like behaviors of ionic current in the modified nanochannel. The working principle of the nanofluidic diode is explained and experimentally verified. The effects of the operation parameters, including ionic concentration, nanochannel length, and frequency, are systematically investigated. Two applications of the nanofluidic diode are presented in this thesis: improved resistive pulse sensing (RPS) system and iontronic circuits. A nanofluidic diode is fabricated and integrated into a RPS system serving as the sensing gate. A mathematic model for the modified RPS system is developed to evaluate the RPS signals. Nanoparticles with a diameter of 5 nm are also experimentally detected in the modified nanochannel-based RPS system. The experimental results are in good agreement with the numerical simulation results. By comparing the RPS signals in the modified nanochannel with that in the pristine nanochannel, it is found that RPS signals can be enhanced by approximately 50% when a nanofluidic diode is used as the sensing nanochannel. By integrating multiple nanofluidic diodes into a PDMS chip, iontronic circuits are developed. The performances of the iontronic circuits working as bipolar junction transistor and full-wave rectifier are examined and demonstrated. Signal manipulation and current rectification with high accuracy can be achieved by these iontronic circuits. This thesis develops simple methods to modulate electrokinetic transport in nanochannels by surface modifications. The fundamental research in this thesis expands the understanding of electrokinetic transport phenomena in nanochannels with various surface modifications. The iontronic devices fabricated by using modified nanochannels provide new possibilities in the development of nanofluidic systems with more functionalities, toward improved biological computing and sensing

Microelectromechanical Systems and Devices

The advances of microelectromechanical systems (MEMS) and devices have been instrumental in the demonstration of new devices and applications, and even in the creation of new fields of research and development: bioMEMS, actuators, microfluidic devices, RF and optical MEMS. Experience indicates a need for MEMS book covering these materials as well as the most important process steps in bulk micro-machining and modeling. We are very pleased to present this book that contains 18 chapters, written by the experts in the field of MEMS. These chapters are groups into four broad sections of BioMEMS Devices, MEMS characterization and micromachining, RF and Optical MEMS, and MEMS based Actuators. The book starts with the emerging field of bioMEMS, including MEMS coil for retinal prostheses, DNA extraction by micro/bio-fluidics devices and acoustic biosensors. MEMS characterization, micromachining, macromodels, RF and Optical MEMS switches are discussed in next sections. The book concludes with the emphasis on MEMS based actuators