Browsing by Subject "Photolithography"
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Item AFM-based measurement of the mechanical properties of thin polymer films and determination of the optical path length of nearly index-matched cavities(2008-05) Wieland, Christopher F., 1980-; Shih, Chih-KangTwo technologies, immersion and imprint lithography, represent important stepping stones for the development of the next generation of lithography tools. However, although the two approaches offer important advantages, both pose many significant technological challenges that must be overcome before they can be successfully implemented. For imprint lithography, special care must be taken when choosing an etch barrier because studies have indicated that some physical material properties may be size dependent. Additionally, regarding immersion lithography, proper image focus requires that the optical path length between the lens and substrate be maintained during the entire writing process. The work described in this document was undertaken to address the two challenges described above. A new mathematical model was developed and used in conjunction with AFM nano-indentation techniques to measure the elastic modulus of adhesive, thin polymer films as a function of the film thickness. It was found that the elastic modulus of the polymer tested did not change appreciably from the value determined using bulk measurement techniques in the thickness range probed. Additionally, a method for monitoring and controlling the optical path length within the gap of a nearly index-matching cavity based on coherent broadband interference was developed. In this method, the spectrum reflected for a cavity illuminated with a modelocked Ti:Sapphire laser was collected and analyzed using Fourier techniques. It was found that this method could determine the optical path length of the cavity, quickly and accurately enough to control a servo-based feedback system to correct deviations in the optical path length in real time when coupled with special computation techniques that minimized unnecessary operations.Item Applications of multiphoton-excited photochemistry to microsecond capillary electrophoresis, photolithography, and the development of smart materials(2010-08) Ritschdorff, Eric Thomas; Shear, Jason B.; Holcombe, James A.; Stevenson, Keith J.; Vanden Bout, David A.; Schmidt, ChristineLaser-based techniques have become essential tools for probing biological molecules in systems that demand high spatial and temporal control. This dissertation presents the development of micro-analytical techniques based on multiphoton excitation (MPE) to promote highly localized, three-dimensional (3D) photochemistry of biologically relevant molecules on submicron dimensions. Strategies based on capillary electrophoresis (CE) have been developed for the rapid separation and spectroscopic analysis of short-lived photochemical reaction products. High-speed separation and analysis are achieved through a combination of very high electric fields and a laser-based optical system that uses MPE for both the generation and detection of hydroxyindole photoproducts on the time scale of microseconds. MPE was also used for the development of photolithographic techniques for the creation of microstructured protein-based materials with highly defined three-dimensional (3D) topographies. Specifically, a multiphoton lithographic (MPL) technique was developed that used a low-cost microchip laser for the rapid prototyping of 3D microarchitectures when combined with dynamic optical masking. Furthermore, MPL was used to create novel “smart” biomaterials that reproducibly respond with tunable actuation to changes in the local chemical and thermal environment. The utility of these materials for creating biocompatible cellular microenvironments was demonstrated and presents a novel approach for studying small populations of microorganisms. Finally, through the development of a multifocal approach that used multiple laser beams to promote the photocrosslinking of biological molecules, the speed and versatility of MPL was extended to allow both the parallel fabrication of 3D microstructures and the rapid creation of large-scale biomaterials with highly defined spatial features.Item Applications of photolithographic techniques : materials modeling for double-exposure lithography and development of shape-encoded biosensor arrays(2009-08) Lee, Shao-Chien; Willson, C. G. (C. Grant), 1939-Double-exposure lithography has shown promise as potential resolu- tion enhancement technique that is attractive because it is much cheaper than double-patterning lithography and it can be deployed on existing imaging tools. However, this technology is not possible without the development of new materials with nonlinear response to exposure dose. Several materials have been proposed to implement a nonlinear response to exposure including re- versible contrast enhancement layers (rCELs), two-photon materials, interme- diate state two-photon (ISTP) materials, and optical threshold layers (OTLs). The performance of these materials in double-exposure applications was inves- tigated through computer simulation using a custom simulator. The results from the feasibility studies revealed that the ISTP and OTL types of materials showed much more promise than the rCEL and two-photon types of materi- als. Calculations show that two-photon materials will not be feasible unless achievable laser peak power in exposure tools can be signi¯cantly increased. Although rCEL materials demonstrated nonlinear behavior in double-exposure mode, only marginal image quality and process window improvements were ob- served. Using the results from the simulation work described herein, materials development work is currently ongoing to enable potential ISTP and OTL materials for manufacturing. A new biochip platform named \Mesoscale Unaddressed Functional- ized Features INdexed by Shape" (MUFFINS) was developed in the Willson Research Group at the University of Texas at Austin as a potential method to achieve a new low-cost biosensor system. The platform uses poly(ethylene glycol) hydrogels with bioprobes covalently cross-linked into the matrix for detection. Each sensor is shape-encoded with a unique pattern such that the information of the sensor is associated with the pattern and not its position. Large quantities of individual sensors can be produced separately and then self- assembled to form random arrays. Detection occurs through hybridization of the probes with °uorescently labeled targets. The key designs of the system include parallel batch fabrication using photolithography and self-assembly, in- creased information density using multiplexing, and enhanced shape-encoding with automated pattern recognition. The development of two aspects of the platform { self-assembly mechanics and pattern recognition algorithm, and a demonstration of all the key design elements using a single array are described herein.Item Design and Fabrication of Nanochannel Devices(2010-10-12) Wang, MiaoNanochannel devices have been explored over the years with wide applications in bio/chemical analysis. With a dimension comparable to many bio-samples, such as proteins, viruses and DNA, nanochannels can be used as a platform to manipulate and detect such analytes with unique advantages. As a prerequisite to the development of nanochannel devices, various nanofabrication techniques have been investigated by many researchers for decades. In this dissertation, three different fabrication approaches for nanochannels are discussed, including a novel scanning coaxial electrospinning process, a heat-induced stretching approach and a standard contact photolithography process. The scanning coaxial electrospinning process is established based on conventional electrospinning process. A coaxial jet, with the motor oil as the core and spin-on-glass-coating/PVP solution as the shell, is deposited on the rotating collector as oriented coaxial nanofibers. These nanofibers are then annealed to eliminate the core material and form the hollow interior. Silica nanochannels with an inner diameter as small as 15 nm were obtained. The heat-induced stretching approach includes using commercially available fused silica tubings to create nanochannels by thermal deforming. This method and the electrospinning technique both focus on fabricate one-dimensional nanochannels with a circular opening. Fluorescent dye was used as a testing sample for single molecule detection and electrokinetic analysis in the resultant nanochannels. Another nanochannel device described in this dissertation has a deep-shallow step structure. It was fabricated by standard contact lithography, followed by etching and bonding. This device was applied as a powerful detection platform for surface-enhanced Raman spectroscopy (SERS). The experiment results proved that it is able to highly improve the sensitivity and efficiency of SERS. The SERS enhancement factor obtained from the device is 108. Moreover, the molecule enrichment effect of this device provides an extra 105 enhancement. The detection can be efficiently finished within minutes after simply loading the mixture of analytes solution and gold nanoparticles in the device. The sample consumption is in micro-liter range. Potential applications in diagnostics, prognositics and water pollutants detection could be achieved using this device.Item Design and synthesis of materials for 157 nm photoresists applications(2005) Pinnow, Matthew James; Willson, C. G. (C. Grant), 1939-Item Design, synthesis and testing of materials for 157 nm photolithography(2005) Chambers, Charles Ray; Willson, C. G. (C. Grant), 1939-The microelectronics industries’ ability to keep pace with Moore’s law (the doubling of the number of transistors per integrated circuit every 18 to 24 months) has been due to advances in the photolithographic process. Shrinking the feature sizes that can be printed has been accomplished by decreasing the exposure wavelength which allows higher resolution and thereby more transistors per area. Currently i-line (365 nm) and deep UV (248 nm) are the most frequently used wavelengths for integrated circuit manufacturing. As device geometries shrink below 100 nm, the lithography for critical layers will be performed at an exposure wavelength of 193 nm. The 193 nm technology is being implemented now. Some “next generation” photolithography will be used to print features down to 45 nm. The technology that has investigated the most for printing the 45 nm node is uses 157 nm as the exposure wavelength. As the move is made from one exposure wavelength to the next new photoresist materials are required that have a low absorbance at the lower wavelength. Finding materials for 157 nm photolithography was particularly challenging due to the inherently high absorbance of most materials at this short wavelength. It was discovered that the addition of fluorine into organic molecules greatly increased their transparency at 157 nm. Fluorine or other transparency enhancing moieties were therefore incorporated into analogues of the 193 nm photoresist polymers. New fluoro polymers were prepared by free radical copolymerizations of electron deficient olefins with fluorinated and nonfluorinated norbornenes. Unfortunately the transparency requirements were not fully achieved with the 193 nm photoresist polymer analogues. Highly transparent fluorinated norbornene polymers were prepared using metal catalysts. One such polymer is poly(2-(3,3,3-trifluoro-2-trifuoromethyl-2- hydroxypropyl)bicyclo[2.2.1]hept-5-ene) (PNBHFA). It was discovered that PNBHFA has unique dissolution inhibition properties which are reminiscent of the novolac resin used in two component, non-chemically amplified photoresist system used at 365 nm. A more transparent fluoropolymer (Asahi RS001 polymer) was later introduced. Transparent, highly functionalized additives that could be blended with PNBHFA or the Asahi polymer and used to print high resolution, high aspect ratio images at 157 nm were designed, synthesized and tested.Item Development of photocurable pillar arrays formed via electrohydrodynamic instabilities(2006) Dickey, Michael David; Willson, C. G. (C. Grant), 1939-As photolithography approaches both fundamental and economic barriers, interest in alternative patterning technologies has grown. This thesis focuses on two alternative patterning techniques: nanoimprint lithography (NIL) and electric field assisted assembly. NIL is a high resolution, yet inexpensive contact patterning process. Step and Flash Imprint Lithography (SFIL) is a type of NIL that involves pressing a topographically patterned template onto a substrate covered with a small volume of liquid. The liquid fills the voids of the template and is hardened by UV irradiation. Low viscosity liquids are ideal for rapid patterning. An acrylate material formulation was developed to meet the various processing needs of SFIL. Unfortunately, oxygen inhibits the free radical photopolymerization used to cure the acrylate. The effects of oxygen were characterized using a semi-empirical model that relies on rate coefficients measured by real time IR spectroscopy. The model predicts an inhibition period at the beginning of irradiation as radicals are quenched by oxygen. After the oxygen is consumed, the polymerization proceeds rapidly except at the perimeter of the template, which is subject to oxygen diffusion from the ambient. Electric field assisted assembly is another attractive patterning technique that is capable of forming polymeric pillar arrays. Pillars form by the amplification of thin-film surface instabilities through the application of an electric field normal to the film. Work to date on pillars has focused on glassy polymers that are limited by the requirement of heat to modulate the rheological properties. A focus of this thesis is on developing low viscosity materials for the formation of pillars. Low viscosity materials form pillars orders of magnitude faster than high-melt viscosity polymers. The pillars form at room temperature and are hardened by UV irradiation. In addition to developing and characterizing low viscosity materials, the aspect ratio of the pillars was optimized. The aspect ratio of the pillars was increased by physically stretching the pillars through the development of an active gap tool. Methods to improve long range order were also investigated. Electric field assisted assembly and imprint lithography are promising photolithographic alternatives that benefit considerably from the use of low viscosity materials.Item Development of responsive materials for diffraction-based chemical sensing(2009-05) Kondrachova, Lilia; Stevenson, Keith J.A new sensor technology based on optical diffraction of visible light shows promise for sensing metal ions and other species that employ chemically-responsive metal oxide and conducting polymer grating elements. These materials undergo reversible redox processes upon interaction with a chemical analyte that subsequently induces changes in the materials refractive index. The two key design parameters of this sensing technique involve preparation of micropatterned sensor elements and the evaluation of appropriate wavelengths for detection of diffracted light. Much of the ability to “tune” a desired sensing response is dictated by the understanding of how factors of size, dimension, crystallinity, morphology, porosity, and heterogeneity influence analyte/sensor interactions (i.e., adsorption, binding, and transport). The effect of composition, structure, and morphology of MoO₃, WO₃, Moₓ W₁₋ₓO₃, IrOₓ and polyaniline grating materials on chemical, electrochemical and optical properties of these systems will be examined by a range of spectroscopic and electrochemical techniques. Comprehensive evaluation and correlation of materials’ optical properties to diffraction-based detection will advance understanding of the capabilities and limitations for the diffraction-based sensing methodology. This information can then used to determine optimal sensing parameters to improve detection limits, enhance sensitivity and increase the dynamic range for detection of model analytes.Item Modeling and defect analysis of step and flash imprint lithography and photolithography(2010-08) Chauhan, Siddharth; Bonnecaze, R. T. (Roger T.); Willson, C. G. (C. Grant), 1939-; Somervell, Mark H.; Mack, Chris A.; Edgar, Thomas F.In 1960's Gordon Moore predicted that the increase in the number of components in integrated circuits would exponentially decrease the relative manufacturing cost per component with time. The semiconductor industry has managed to keep that pace for nearly 45 years and one of the main contributors to this phenomenal improvement in technology is advancement in the field of lithography. However, the technical challenges ahead are severe and the future roadmap laid by the International Technology Roadmap for Semiconductors looks mostly red (i.e. no solution has been found to specific problem). There are efforts in the industry and academia directed toward development of newer, alternative lithographic techniques. Step and Flash Imprint Lithography (SFIL) has recently emerged as one of the most promising alternatives, capable of producing high resolution patterns. While it has numerous advantages over conventional photolithography, several engineering challenges must be overcome to eliminate defects due to the nature of contact imprinting if SFIL is to be a viable alternative technique for manufacturing tomorrow's integrated circuits. The complete filling of template features is vital in order for the SFIL imprint process to truly replicate the template features. The feature filling phenomena for SFIL was analyzed by studying diffusion of a gas, entrapped in the features, through liquid imprint resist. A simulation of the dynamics of feature filling for different pattern configurations and process conditions during the SFIL imprint step is presented. Simulations show that initial filling is pressure-controlled and very rapid; while the rest of the feature filling is diffusion-controlled, but fast enough that diffusion of entrapped gas is not a cause for non-filling of features. A theory describing pinning of an air-liquid interface at the feature edge of a template during the SFIL imprint step was developed, which shows that pinning is the main cause of non-filling of features. Pinning occurs when the pressure at the air-liquid interface reaches the pressure of the bulk liquid. At this condition, there is no pressure gradient or driving force to move the liquid and fill the feature. The effect of several parameters on pinning was examined. A SFIL process window was established and template modifications are proposed that minimize the pinning at the feature edge while still preventing any extrusion along the mesa (pattern containing area on the template) edge. Part of semiconductor manufacturing community believes that optical lithography has the capability to drive this industry further and is committed to the continuous improvement of current optical patterning approaches. Some of the major challenges with shrinking critical dimensions (CDs) in coming years are the control of line-edge roughness (LER) and other related defects. The current CDs are such that the presence or absence of even a single polymer molecule can have a considerable impact on LER. Therefore molecular level understanding of each step in the patterning process is required. Computer simulations are a cost-effective approach to explore the huge process space. Mesoscale modeling is one promising approach to simulations because it captures the stochastic phenomena at a molecular level within reasonable computational time. The modeling and simulation of the post-exposure bake (PEB) and the photoresist dissolution steps are presented. The new simulator enables efficient exploration of the statistical excursions that lead to LER and the formation of insoluble residues during the dissolution process. The relative contributions of the PEB and the dissolution step to the LER have also been examined in the low/high frequency domain. The simulations were also used to assess the commonly proposed measures to reduce LER. The goal of the work was to achieve quantification of the effect of changes in resist composition, developer concentration, and process variables on LER and the associated defectivity.Item Process parameters governing deep ultraviolet (DUV) data buffer yield(Texas Tech University, 2002-05) Janakiraman, PraveenaTimely identification of causes for low quality of devices is a primary key to the profit of a semiconductor industry. There are various methods to aid the identification and rectification of defects arising from the wafer manufacturing process. Parametric data analysis is a key method to extract process related information about the wafers. Parameters like idrives, leakage currents, threshold voltages, oxide thickness, critical dimension measurements provide a wealth of details about the manufactured wafers. This thesis aims at addressing the root cause of the problem of low quality of Deep Ultra Violet data buffers after an analysis of process parameters. On finding the cause, a solution to achieving a required quality level is suggested and verified.Item Synthesis, copolymerization studies and 157 nm photolithography applications of 2-trifluoromethylacrylates(2003) Trinque, Brian C.; Willson, C. G. (C. Grant), 1939-Advances in microelectronic devices have relied heavily on improved photolithographic imaging capabilities. The resolution limit of optical lithography can be improved by lowering the wavelength of exposure light. The latest reduction in exposure wavelength is from 193 nm to 157 nm. The focus of this work is the synthesis, copolymerization studies and lithographic imaging capabilities of 2-trifluoromethylacrylates. Model calculations and gas phase absorbance measurements of model compounds first suggested that these materials would provide suitable transparency at the 157 nm wavelength. Methyl 2-trifluoromethylacrylate was synthesized and aniocically polymerized and variable angle spectroscopic ellipsometry showed that this material had an absorbance that was 1,000 times more transparent than its non-fluorinated analogue. A variety of relatively transparent resist materials based on a 2- trifluoromethylacrylate backbone were synthesized by anionic polymerization, and these materials were successfully imaged at 157 nm. While 2- trifluoromethylacrylates do not undergo homopolymerization with radical initiators, they do radically copolymerize with various norbornenes. Interestingly, these materials exhibit a 2:1 (2-trifluromethacrylate:norbornene) monomer incorporation. This phenomenon was exploited to produce a number of relatively transparent materials that produced positive-tone structures when imaged at the 157 nm wavelength. Kinetic studies were performed to show that the copolymerizations of 2-trifluormethacrylates and norbornene derivatives deviate from the terminal model and follow the penultimate model. Competitive reaction studies using the “mercury method” were performed to demonstrate that substitution of a trifluoromethyl group can indeed effect the reactivity of a propagating radical, lending support to the proposed penultimate model. The structure of the 2-trifluoromethylacrylate propagating radical will also be investigated by electron spin resonance spectroscopy.Item Understanding molecular scale effects during photoresist processing(2003-05) Schmid, Gerard Michael; Willson, C. G. (C. Grant), 1939-The dimensional tolerances of photoresist features are now at the nanometer scale, where effects of individual molecules are important. In recognition of the industrial need for a molecular-scale understanding of photoresist performance, mechanistic models have been developed for each of the several photolithography processes that are used with positive-tone, chemically amplified photoresists: film creation, exposure, post exposure bake, and development. These models are based on experimental studies that have clarified details of photoresist function including the photochemical quantum efficiency of photoresist exposure, the reaction-diffusion properties of exposure photoproducts, and the complex dissolution behavior of phenolic homopolymers and copolymers in aqueous base. A dynamic Monte Carlo simulation has been developed to test the experimentally derived models and further examine the underlying physical processes relevant to photoresist patterning. This mesoscale simulation consists of distinct modules for each processing step, each of which captures the appropriate chemical and physical phenomena at the molecular scale. The several simulation modules have yielded results that are qualitatively correct for every major resist processing step. The inputs to the simulation are fundamental and measurable material and processing parameters and empirical calibrations are not required. The chemical detail included in the models enables investigation of the wide formulation variable space. Furthermore, the mesoscale nature of the simulation offers the unique ability to study the stochastic processes that contribute to resist feature roughness. This simulation thus provides a useful predictive tool to guide the rational design of new photoresist materials and the optimization of photolithography processes.Item Vacuum ultraviolet directed design, synthesis and development of 157nm photoresist materials(2004) Osborn, Brian Philip; Willson, C. G. (C. Grant), 1939-The design of 157 nm materials for photolithography presented many challenges, stemming from the inherently strong absorbance of the majority of organic compounds in the vacuum ultraviolet (V-UV). A spectrophotometer designed to operate in the vacuum was utilized to screen a multitude of materials for high transparency at 157 nm. These hydrogenated monomers served as model compounds for the repeat units in polymers. A variety of fluorinated, hydrogenated norbornanes were found to be transparent for use at 157 nm, and empirical evidence showed that the position and amount of fluorine incorporation mattered significantly in norbornene systems. The best of these are geminally substituted but, unfortunately, geminally disubstituted norbornenes do not polymerize to any significant degree using transition metal addition catalysts such as palladium or nickel. A variety of different methods were used to incorporate fluorinated and transparent monomers into polymers. Dinorbornene monomers were used in conjunction with the Grubbs second-generation catalyst to produce polymers using ring-opening metathesis polymerization (ROMP), but these compounds were found to be too strongly absorbing for use at 157 nm. Tricyclononene analogues of the norbornene materials were synthesized, found to be transparent in the V-UV and can be polymerized via addition polymerization. The absorbance of these materials matched the absorbance trends first seen in the gas phase spectra of the monomers, which bolstered the case for screening materials in the vacuum UV first. Vicinal cis-exo-norbornane diols were also synthesized of these fluorinated, geminally disubstituted norbornenes for use as condensation polymer precursors. Attempts to form polycarbonates and polyethers from these diols proved unsuccessful, because of the propensity for the cis-exo-norbornane diols to form cyclic carbonates. The final, optimized photoresist that gave the best results in imaging experiments at 157 nm employed poly(2-(3,3,3-trifluoro-2-trifuoromethyl-2- hydroxypropyl)bicyclo[2.2.1]heptane-5-ene) (PNBHFA) or the Asahi Glass RS001 fluoropolymer in conjunction with a variety of oligomeric dissolution inhibitors. These formulations allowed us to print high resolution, high aspect ratio images at 157 nm. The vacuum ultraviolet spectroscopy, polymer synthesis and imaging of 157 nm materials are presented.