Study of acid transport using IR spectroscopy and SEM (original) (raw)
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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.
The formation of acid diffusion wells in acid catalyzed photoresists
Microelectronic Engineering, 1997
This paper describes the use of two step post-exposure-bakes for improving the lithographic performance of the chemically amplified resist, UVIIHS TM from the Shipley Company. With this process, postexposure-baking at a low temperature allows the deprotection reaction to go to completion, with minimal acid diffusion into unexposed portions of the resist; and the high temperature PEB makes it possible to average out the standing waves. This study examines various two step post-exposure-bakes and provides evidence for the existence of the formation of a diffusion well. For 250nm nominal features, conventional single bake processes yield +40nm for the isolated to grouped line bias and in excess of -20nm for the isofocal region bias. Using a double PEB, processes were found that reduced both the isolated line to grouped line bias and the isofocal region bias to 0nm. Finally the kinetics of the double PEB process is studied using FTIR.
Macromolecules, 2006
Neutron reflectivity and Fourier transform infrared spectroscopy measurements are used to profile the deprotection reaction-diffusion front with nanometer resolution in a model photoresist polymer using three perfluoroalkane-based photoacid generators (PAG) with varying chain lengths. As expected, the spatial extent of the deprotection reaction front increases with decreasing PAG size. Although the total extent of deprotection increases with increasing postexposure bake time for each PAG, the reaction-diffusion of deprotection does not propagate continuously into the photoresist polymer. The form of the deprotection reaction front changes because the diffusion process is affected by the changing polymer composition. The data are well described by a reactiondiffusion model that includes a simple acid-trapping term and does not require a varying PAG diffusivity. This high-resolution profiling, together with modeling, illustrates details of the coupled diffusion and deprotection reaction processes that affect lithographic performance.
2010
A soft-contact film transfer method was developed to prepare multilayer photoresist thin films that enable high-resolution spectroscopic and reflectivity measurements for determining the reaction-diffusion kinetic parameters and photoacid diffusion length. Infrared reflectance absorption spectroscopy was applied to follow, quantitatively, the reaction-diffusion kinetics during the post-exposure bake (PEB) step; the time evolution of the average deprotection level across a bilayer film with model photoresists is described by a kinetics model with three parameters: a reaction rate constant (k P), the phenomenological photoacid trapping constant (k T), and the photoacid diffusion constant (D H). A polymeric and molecular resist for next-generation extreme ultraviolet (EUV) lithography with chemically analogous structure was studied with this methodology. The three kinetic parameters follow an Arrhenius dependence but show quantitative differences between these two photoresists at a given PEB temperature. Further it was demonstrated that the photoacid diffusion length is not a simple function of diffusion coefficient; instead, it is dictated by all three kinetics parameters jointly in addition to the deprotection level at which the resist becomes soluble in an aqueous developer solution. These observations qualitatively explain the experimentally observed shorter photoacid diffusion length of the molecular resist in comparison to its polymeric counterpart.
Diffusivity measurements in polymers: IV. Acid diffusion in chemically amplified resists
Advances in Resist Technology and Processing XIV, 1997
Many of the strategies for sub 0.25 µm lithography depend on chemically amplified resists to provide sensitivity. For example, glass damage limits the dose that can be delivered at 193 nm, and source brightness limits the dose that can be delivered in the EUV. However, acid diffusion, an integral part of the chemical amplification process, dramatically affects the lithographic performance of chemically amplified resists [1]. The transport properties of Brønsted acids in glassy polymers have been estimated from a variety of indirect measurements [1]. We have, for the first time, directly measured the diffusion coefficients of acids in polymer films. A Quartz Crystal Microbalance (QCM) was used to make the measurements. The QCM can detect small changes in mass which is indicated by a shift in the resonant frequency of the piezoelectric quartz crystal (see the accompanying paper "Diffusivity Measurements in Polymers, Part III: Quartz Crystal Microbalance Techniques"). The experiments were conducted at different temperatures in order to establish the dependence of the diffusion coefficient on temperature. Acid diffusion in poly(hydroxystyrene) will be discussed.
Mechanistic Studies of the Acidolysis Reactions Occurring in Silicon-Containing Bilayer Photoresists
Chemistry of Materials, 2002
As the feature sizes of semiconductor devices continue to shrink, there is an increasing interest in thin film imaging approaches such as silicon-based bilayer resists. We have developed such a resist based on a copolymer of 4-hydroxystyrene with a silicon-containing monomer, which functions simultaneously as the acid-sensitive component and a source of O 2 etch resistance. In an attempt to understand the reactions that occur in the photoresist film, the acidolysis reactions of the 2-[tris(trimethylsilyl)silyl]ethyl moiety have been studied in solution. Acid-catalyzed cleavage of the model 2-trimethylsilylethyl acetate in solution proceeds via a nucleophilic attack on the silicon atom of the protonated acetate. Protonation of 2-[tris(trimethylsilyl)silyl]ethyl acetate is postulated to lead to a bridged siliconium cation, which reacts with nucleophiles along three pathways and yields products in which a nucleophile is attached to a silicon atom. This mechanism is consistent with the silylation of phenolic hydroxyl groups in the photoresist film consisting of a copolymer of 4-hydroxystyrene with 2-[tris(trimethylsilyl)silyl]ethyl methacrylate, observed during photolithographic processing.
On-wafer photoacid determination and imaging technique for chemically amplified photoresists
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 1998
A fundamental task of chemically amplified photoresists is to record the incident radiation by generating catalyst concentration gradients within the film. In many resists, the catalyst is a strong Brönsted acid which yields a latent image of pH within the exposed film. A number of mechanistic questions remain about acid generator efficiency and its mobility once generated and heated. We have developed a technique in which a pH-dependent fluorophore is incorporated into the resist ͑an undyed version of SAL 605 from the Shipley Company and similar formulations͒. The localized acid concentrations generated by exposure to x-rays are analyzed and imaged using fluorescence spectroscopy and microscopy. Initial experiments, the spectroscopic apparatus, and initial far-field imaging are reported elsewhere ͓S.