Browsing by Subject "Photoresists"
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Item Advanced lithographic patterning technologies : materials and processes(2007-05) Taylor, James Christopher, 1980-; Willson, C. G. (C. Grant), 1939-Item Advanced lithographic patterning technologies: materials and processes(2007) Taylor, James Christopher; Willson, C. G. (C. Grant), 1939-Item Catalyst diffusion in positive-tone chemically amplified photoresists(2003) Stewart, Michael Dean; Willson, C. G. (C. Grant), 1939-Item Design, synthesis, and evaluation of materials for microelectronics applications(2006) Heath, William Hoy; Willson, C. G. (C. Grant), 1939-The advancement of the microelectronics industry is heavily dependent on the design, synthesis, and integration of new materials. Non-chemically amplified photoresists (NCAR) consist of a base resin and photoactive additive which inhibits the dissolution of the this resin. The robustness of NCARs has made them well suited to the unique material requirements of the photomask making industry for many years. However, smaller feature sizes now require mask makers to move to shorter wavelengths of light and thus a more transparent polymer and photoactive compound are needed for these applications. During the search for 157nm photoresists, it was found that polymers containing the hexafluoroisopropanol functionality are transparent well into the ultraviolet region and possess dissolution characteristics similar to the Novolak resins utilized in NCARs. A suitable photoactive compound (PAC) has been identified; the synthesis of the PAC and transparent polymers, as well as their formulation, dissolution properties, and lithographic evaluation will be presented. Additionally, the base catalyzed imidization of poly(amic acid ethyl ester) (PAETE) provides a good tool for developing a photosensitive polyimide insulator. However few base photogenerators (PBG) exist that absorb at the appropriate wavelength (>400nm) for use in these opaque films. Two sensitized systems were evaluated; their synthesis, photophysical evaluation, and attempted imaging in PAETE will be described. Additionally, the synthesis and photophysical evaluation of a red-shifted thiophene-based PBG will be described. Finally, step and flash imprint lithography exhibits a great promise as a cost effective alternative imaging solution to traditional optical lithography. A strippable resist is needed to preserve the templates used in this process should they become contaminated. The thermal reversibility of urethanes, specifically those derived from aromatic oximes, make them well suited for integration into a thermally degradable diacrylate crosslinker. The synthesis of urethane linked diacrylates, their incorporation into cross-linked polymer networks, and thermal degradation will be described.Item Fabrication of binary phase diffusers for space-variant processing(Texas Tech University, 1983-12) Chase, Scott BTechniques have previously been described for holographically representing space-variant systems. By spatially sampling the input plane and using phase mask diffusers to encode the multiple reference beams, one can sequentially record holograms exhibiting a minimal amount of crosstalk. Gold-coded binary phase masks have been shown to have good correlation properties with known cross-correlation bounds. This thesis describes a technique which generates phase masks using a laser scanner computer generated hologram (CGH) writing f a c i l i t y at a wavelength of 4579A. Methods for determining the proper resist thickness to achieve the necessary 180 degree phase shift between adjacent cells in a mask include analyzing the data taken by an interference microscope and quantitative analysis of the dc component present in the Fourier spectrum of the mask. Comparisons of the effectiveness of the phase masks with that of ground-glass were obtained using two different tests. First, the phase masks were used in a space-variant processor, and the results of the multiplexed holograms were compared to those obtained earlier using a ground-glass diff user. Secondly, computer-generated holograms were made using the phase masks as diffusers and the results were compared with those previously obtained using amplitude masks.Item Monitoring and control of semiconductor manufacturing coating and developing process(Texas Tech University, 1988-08) Pan, Yih-herngNot availableItem Organic materials for microelectronics : 157 nm photoresists and electrooptic liquid crystals(2001-12) Hung, Raymond Jui-pu, 1969-; Willson, C. G. (C. Grant), 1939-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 Top surface imaging for sub-100nm lithography(2004) Jamieson, Andrew Thomas; Willson, C. G. (C. Grant), 1939-Advances in semiconductor microlithography have resulted in reduced transistor dimensions and consequent improvements in chip performance and cost. In the microlithographic process a photoactive material called a photoresist is uniformly spun cast on a substrate and selectively exposed to radiation, causing a chemical change in the exposed areas. The polymer is subsequently removed in either the exposed or unexposed regions, typically using an aqueous base developer. An alternative to the traditional lithographic method is a process called Top Surface Imaging (TSI). TSI has a number of advantages over traditional base-development techniques but is highly susceptible to line edge deformities commonly referred to as line edge roughness (LER). In TSI, the top surface of the photoresist is exposed to radiation, resulting in the generation of reactive sites. A gas phase, silicon-containing compound called a silylation agent reacts with these sites, causing selective incorporation of silicon. The silicon then acts as an etch mask in an anisotropic oxygen etch process. As the industry continues to improve resolution by shifting to shorter wavelengths, TSI’s lax transparency requirements provide it with a distinct advantage over traditional lithographic techniques. In this work, TSI was evaluated for use with three industrially relevant radiation sources, including 157nm light, low-voltage electron beams, and extreme ultraviolet light. An investigation into the origins of low frequency LER in TSI systems showed it to be the result of surface tension induced capillary instabilities (also known as a Rayleigh instability). The polymer contribution to LER was investigated by the synthesis of numerous high-Tg TSI polymers. Although many of these polymers are capable of producing high-resolution features, they all suffer from significant levels of LER. The kinetics of the gas phase reaction of the TSI polymer poly(hydroxystyrene) and the silylation agent dimethylaminodimethylsilane was investigated using variable angle spectroscopic ellipsometry, and was found to be front propagated and reaction limited. It was found that the addition of base quenchers to chemically amplified photoresists greatly minimizes LER, and a theoretical approach to understand this effect is presented. Overall, TSI performs well, but the nature of LER in TSI systems is still not fully understood.Item Understanding fundamental mechanisms of photoresist dissolution(2003) Burns, Sean David; Willson, C. G. (C. Grant), 1939-Fabrication of microelectronic devices relies upon the photolithographic process for patterning devices. A key step in this process is the selective, aqueous base dissolution of exposed regions of a photoresist polymer film, yet this step is not completely understood at a fundamental level. The most successful model for photoresist dissolution has been the critical ionization dissolution model. The basic premise of this model is that a critical fraction of monomer units of a given polymer chain must be deprotonated (ionized) in order to render that chain soluble. This work is an extension of the CI model, in which subtle improvements (such as the inclusion of Coulombic forces) have been made to the lattice based CI dissolution model. The model has been used to investigate formation of surface roughness and surface inhibition during dissolution of photoresists. Surface inhibition has been investigated experimentally to determine the fundamental mechanisms of this phenomenon. A “Halt Development” technique was used to measure concentration gradients in resist films. It was determined that no significant concentration gradients of residual casting solvent, low molecular weight chains, photoactive compound, or polymer density were present, and thus were not responsible for surface inhibition. Several other theories were tested, including interfacial gel layer formation, surface oxidation, and roughness effects. The best explanation for surface inhibition (for the novolac polymer of interest) was derived from the CI model as a combination of roughness and pKa effects. Real time spectroscopic interferometry and ellipsometry were used to characterize photoresist dissolution, with a focus on interfacial gel layer formation. Within the resolution limits of the techniques (10-20 nm), interfacial gel layer formation was not observed in a series of phenolic polymers, suggesting that this assumption of the CI model is valid for most phenolic polymers. Formation of surface roughness during dissolution was characterized by AFM and compared to model predictions.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.