Imprint template advances and surface modification, and defect analysis for step and flash imprint lithography
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Step and flash imprint lithography (SFIL) is a relatively new technique for patterning high-resolution polymer features on planar substrates. This technique has been used to produce features smaller than 30 nm in size through many imprints, pattern a substrate with existing topography, and also to produce functional optical and electric devices. The ultimate manufacturability of SFIL for high-resolution applications depends on the ability to manufacture high-resolution imprint templates, and also to produce imprint fields that are relatively free of defects caused during the imprint process. The primary goal of this work was to investigate the generation and propagation of defects produced during the imprint process, and this involved various material and process development efforts. A process analogous to that used in the photomask manufacturing process has been created for manufacturing imprint templates with features smaller than 30 nm. Using a thin layer of electron beam resist and a thin Cr film resulted in the mitigation of the shift in feature sizes during the etching steps. Additionally, by substituting ITO and deposited SiO2 for the Cr allows similar feature resolution, and the final template possesses charge dissipation capabilities needed for end-of-line inspection. The quality of the surface treatments deposited on the template using a fluoroalkyltrichlorosilane is dependent on the substrate used, and also on the degree of hydration of the substrate. Several materials were tested for compatibility with the current surface treatment, and it was found that deposition of the surface treatment on Si3N4 and SiOxNy resulted in films that possessed coverage and durability similar to that of SiO2, but that films deposited on ITO lacked mechanical wear durability. It was found that exposing a dehydrated SiO2 substrate to water vapor for various times followed by the surface treatment precursor resulted in greater deposition of film species on the surface with increasing water exposure. A defect analysis was performed for SFIL, and it was discovered that the defect trends over time are strongly dependent on photopolymer material properties. Early results indicated that the dominant failure mode during template/substrate separation was that of cohesive polymer failure. By redesigning the etch barrier material blend, the elongation-to-break of the photopolymer was increased by more than one order of magnitude. This material change resulted in the elimination of the cohesive failure mode, and allowed faithful replication of features through more than 400 imprints. It was discovered that imprint film thickness variations can have a dramatic effect on the pattern contrast. This pattern contrast was modeled for various film thickness combinations, and this effect is believed to impact defect detection in optical inspection equipment.