The function of common, positive tone photoresist materials is based on radiation-induced modulation of the dissolution rate of phenolic polymer films in aqueous base. The process through which novolac and other low molecular weight phenolic polymers undergo dissolution is examined from a new perspective in which the “average degree of ionization” of the polymer is regarded as the principal factor that determines the rate of dissolution rather than a diffusive, transport process. This perspective has been coupled with a probabilistic model that provides an explanation for the dependence of the dissolution rate on molecular weight, base concentration, added salts, residual casting solvent, and the addition of “dissolution inhibitors”. It predicts the observed minimum base concentration below which dissolution is no longer observed, and it predicts a molecular weight dependence of that phenomenon. A series of experiments was designed to test this predicted molecular weight response. The results of these experiments are in good agreement with the predicted response.

Low viscosity, photocurable liquids are demonstrated as ideal materials for the formation of pillar arrays generated spontaneously by field-assisted assembly. Pillars form spontaneously via electrohydrodynamic instabilities that arise from the force imbalance at a film−air interface generated by an applied electric field. Conventional polymer films form pillars slowly as a result of their relatively large viscosities and are often process-limited by a requirement of heat to modulate rheological properties. In contrast, low viscosity liquids require no heat and form pillars orders of magnitude faster, as predicted by theory. The resulting structures are preserved by photopolymerization, eliminating the lengthy heating−cooling cycle necessary to process most polymers. The combination of nearly instantaneous formation and rapid photocuring at room temperature is ideal for patterning. Epoxy, vinyl ether, acrylate, and thiol-ene systems were evaluated for pillar formation. Relevant material properties were characterized (viscosity, dielectric constant, interfacial energy, kinetics) to explain the phenomenological behavior of each system during electrohydrodynamic patterning. The thiol-ene system formed pillar arrays nearly instantaneously and cured rapidly under ambient conditions. These are nearly ideal characteristics for pillar formation.

Progress in the semiconductor manufacturing industry depends upon continuous improvements in the resolution of lithographic patterning through innovative materials development and frequent retooling with expensive optics and radiation sources. Step and Flash Imprint Lithography is a low-cost, nanoimprint lithography process that generates nanopatterned polymeric films via the photopolymerization of low-viscosity solutions containing cross-linking monomers in a transparent template (mold). The highly cross-linked imprint materials are completely insoluble in all inert solvents, which poses a problem for reworking wafers with faulty imprints and cleaning templates contaminated with cured imprint resist. Degradable cross-linkers provide a means of stripping cross-linked polymer networks. The controlled degradation of polymers containing acetal- and tertiary ester-based cross-linkers is demonstrated herein. The viscosity and dose to cure are presented for several prepolymer formulations, along with imprint resolution and tensile modulus results for the cured polymers. Optimum conditions for de-cross-linking and stripping of the cross-linked polymers are presented, including demonstrations of their utility.

Polymer structure effect on dissolution characteristics and acid diffusion in chemically amplified deep ultraviolet resists J.The microlithographic process is dependent upon the dissolution of acidic polymers in aqueous base. The fundamental mechanism that governs the dissolution of these polymers has been the subject of considerable discussion, and a number of theories have been proposed to explain this behavior. Our research group has presented the critical ionization ͑CI͒ dissolution model to explain the dissolution of phenolic polymers in aqueous base. Specifically, the model proposes that a minimum or critical fraction of ionized sites, f crit , on a given polymer chain must be ionized in order for that chain to dissolve. The main input parameters to this model are the critical fraction of ionized sites, f crit , and the fraction of ionized surface sites, ␣. In this work methods are established for measuring these parameters. A quantitative link between the CI model and experiment has been demonstrated for the dissolution rate and surface roughness dependence on polymer molecular weight. Methods for calculating ␣ are discussed, including a new method that considers the formation of an electrostatic double layer at the resist-developer interface.

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Extraction of small molecule components into water from photoresist materials designed for 193 nm immersion lithography has been observed. Leaching of photoacid generator (PAG) has been monitored using three techniques: liquid scintillation counting (LSC); liquid chromatography mass spectrometry (LCMS); and scanning electrochemical microscopy (SECM). LSC was also used to detect leaching of residual casting solvent (RCS) and base. The amount of PAG leaching from the resist films, 30 -50 ng/cm 2 , was quantified using LSC. Both LSC and LCMS results suggest that PAG and photoacid leach from the film only upon initial contact with water (within 10 seconds) and minimal leaching occurs thereafter for immersion times up to 30 minutes. Exposed films show an increase in the amount of photoacid anion leaching by upwards of 20% relative to unexposed films. Films pre-rinsed with water for 30 seconds showed no further PAG leaching as determined by LSC. No statistically significant amount of residual casting solvent was extracted after 30 minutes of immersion. Base extraction was quantified at 2 ng/cm 2 after 30 seconds. The leaching process is qualitatively described by a model based on the stratigraphy of resist films.