Diffusivity measurements in polymers: IV. Acid diffusion in chemically amplified resists (original) (raw)
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Microelectronic Engineering, 1996
A new method for the measurement of acid diffusion in chemically amplified resists is introduced. It is based on the measurement of the diameter of lithographic features (pillars for negative resists) obtained from single pixei e-beam exposures to determine the proximity function in a wide range of doses and PEB times. The method is applied in the measurement of the diffusion coefficients of two negative chemically amplified resists, the commercial resist SAL-601 (Shipley) and a prototype epoxy novolac based resist (EPR) developed at IMEL. The method directly provides proximity effect correction parameters for chemically amplified resists.
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 1995
The effect of the remaining solvent on the diffusion of the catalytically active acid within the chemical amplification resists is discussed. A range of solvents was investigated from the viewpoint of sensitivity, diffusion, and resolution. The solvent remaining after the coating and baking processes is thought to one of the most probable factors among the several possible causes in the determination of the performance of the resists. It is also considered to result in the environmental instability which is currently one of the most serious problems in the use of the resists of this type. The remaining solvent drastically enhances the thermal diffusion of acid generated from photo-acid generators upon photoanalysis. The log of the diffusion range of the acid is found to be proportional to the concentration of the remaining solvent. This phenomenon may be described by a theory which combines the hole theory of liquids and the free volume theory of polymers and was also found to be the correlation energy between resin, solvent, and acid. In practice, this enhancement of diffusion range by remaining solvent does not result in higher sensitivity but rather degrades the performance of the resists.
Lithographic importance of base diffusion in chemically amplified photoresists
Microelectronic Engineering, 2009
Mesoscopic (i.e., discrete and stochastic) models are applied to study the impact of photoresist processing and material conditions on process performance. The modeling approach includes all exposure, postexposure bake, and development related parameters for chemically amplified resists. Resist process performance is evaluated in terms of required exposure dose (i.e., sensitivity), dose latitude (i.e., resolution), and line-edge roughness (LER). There exists a well-known trade-off between sensitivity, resolution, and LER. Theoretical models have concluded that optimization of any one or two of these properties go at the expense of the other properties. This paper shows that the effects of base diffusion, which have not been taken into account in previous studies, allow a simultaneous improvement of photoresist sensitivity, resolution, and LER. A putative explanation is given about the mechanism how the coupled diffusion of acid and base can allow a simultaneous improvement of all three process properties.
Acid diffusion in chemically amplified resist might limit the ultimate minimum half-pitch that can be achieved with high sensitivity resists unless diffusion length is reduced until new methods of sensitizing resists are found. Precise knowledge of molecular dynamics of resist materials and advanced techniques need to be developed actively for this issue. In this sense, computer simulations have become a valuable tool in terms of reducing time and costs. However, simulations are generally based on continuum or mesoscale models, which are unable to predict accurately variations at the molecular level. Deeper understanding and investigation of the coupled reaction-diffusion kinetics at the molecular scale during the post exposure bake (PEB) become crucial to achieve nanoscale features with good critical dimension (CD) control and good line-edge roughness (LER). In this work we have developed a molecular level approach for understanding of the coupled acid-catalyzed diffusion process in chemically amplified resist (CAR) systems. Here, the molecules of photoacid generator (PAG) are selected as the building blocks of a three-dimensional grid. Reaction and diffusion of the photoconverted acid molecules during the PEB step will produce resist volumes of cleaved polymers. After a certain PEB time τ, these created volumes produced by adjacent acids will almost contact each other, enabling the subsequent development of the polymer. We also determine this parameter τ by means of experiments with real resist systems and investigate the influence of the process conditions on it.
Polymers for Advanced Technologies, 2013
A simple, quick and novel method for the determination of diffusion properties through polymer films, based on Quantum Resistive Sensors made of Conductive Polymer nanoComposites is presented. The integral time lag method is employed for the calculation of diffusion coefficient, and the results are compared simultaneously with that of Fourier transform infrared spectroscopy and sorption method. Two model polymers, a semi-crystalline poly(lactic acid) and an amorphous poly(isobutylene-co-isoprene), are used to validate the study. A good correlation is established between the diffusion coefficient values derived from all techniques demonstrating the interest of such reliable, simple and cheap nanosensors for the quick determination (several minutes) of diffusion properties in polymer films. Our first results suggest that this technique is meaningful for the determination of barrier properties in nanocomposite membranes filled with platelets of graphene or clay.
Diffusivity of small molecules in polymers: Carboxylic acids in polystyrene
Polymer, 2012
Gravimetry was used to study the diffusion of a homologous series of linear carboxylic acids (C n , with n ¼ 2, 6e16) in amorphous polystyrene at temperatures from 35 C to 165 C, that is, both below and above the polymer glass transition temperature of 100 C. All the mass uptake results are well described by a simple Fickian model (for t < t 1/2 ) and were used to calculate the corresponding diffusion coefficients using the thin-film approximation. Acetic acid exhibits a peculiar diffusion rate: its diffusion coefficients in polystyrene do not follow the same trend of all the remaining acids, being smaller than those of hexanoic acid at the same temperatures. Polystyrene swells at a higher rate in hexanoic and octanoic acids than in acetic acid, at the same temperature. This peculiarity is confirmed using NMR spectroscopy for acetic and hexanoic acids. For all the carboxylic acids considered, the temperature dependence of the diffusion coefficients is non-Arrhenius in character. For each liquid penetrant, its log(D) increases linearly with the decrease in liquid viscosity associated with an increase in temperature. Plots of log(n 2 D) versus n suggest that higher-n carboxylic acids diffuse through a reptation-like mechanism at higher temperatures.