Atsuro Nakano

Proton Dynamics in Chemically Amplified Electron Beam Resists

The proton dynamics of poly(4-hydroxystyrene) (PHS) films were investigated using Coumarin 6 (C6). The acid density was 0.022 nm-3 at the exposure dose of 10 µC cm-2 (75 keV electron beam). The absorption intensity of C6 proton adducts was saturated at a certain concentration of C6, indicating an almost complete addition of protons at this C6 concentration. Protons can move in PHS films near C6 molecules even at room temperature. Also, the absorbed dose was estimated using 60Co γ-rays. The acid yield can be well explained by an acid generation model involving the ionization of a base polymer.

Potential cause of inhomogeneous acid distribution in chemically amplified resists for post optical lithography

In chemically amplified resists for ionizing radiation such as an electron beam and EUV, protons of acids are mainly generated by the deprotonation of base polymers. Therefore, the acid generation efficiency depends highly on polymer structure. In recent resist formulas, partially protected poly(4-hydroxystyrene) has often been used as a base polymer. In this work, the effects of protecting groups on acid generation were investigated. We found differences in acid generation efficiency caused by protecting groups. These differences are likely to affect acid distribution.

Acid Generation Mechanism of Poly(4-hydroxystyrene)-Based Chemically Amplified Resists for Post-Optical Lithography: Acid Yield and Deprotonation Behavior of Poly(4-hydroxystyrene) and Poly(4-methoxystyrene)

With the shrinkage of patterns, the elucidation of reaction mechanisms at the molecular level has become essential in resist design. In particular, proton dynamics is one of the most important issues on the sensitivity and resolution of chemically amplified resists. In chemically amplified resists for post-optical lithographies, such as extreme ultraviolet and electron beam lithographies, it has been reported that protons mainly come from not acid generators but polymers. Determining proton sources is a key to understanding reaction mechanisms at the molecular level. In this article, we investigated the deprotonation mechanism of poly(4-hydroxystyrene) and poly(4-methoxystyrene) upon exposure to ionizing radiation. We found that the difference between the proton labilities of polymer radical cations (proton source for acid generation) leads to a difference in acid yield.

Relation between spatial resolution and reaction mechanism of chemically amplified resists for electron beam lithography

The generation of acids in chemically amplified electron beam resists needs the cation radicals of base polymer and electrons, both of which are generated via the ionization of base polymer on the exposure. This leads to the separation of several nanometers between protons and counter anions. The separation deserves special attention from the viewpoint of resolution blur. The distribution of counter anions was examined with a simulation based on the Smoluchowski equation.

Polymer screening method for chemically amplified electron beam and X-ray resists

In this paper, we discuss the dependency of acid generation on polymer structures and a polymer screening method for the development of chemically amplified resists. Convenient screening method is expected to reduce laborious tasks for the selection of base polymers.

Reactivity of Acid Generators for Chemically Amplified Resists with Low-Energy Electrons

In chemically amplified resists for ionizing radiations such as electron beams and extreme ultraviolet (EUV), low-energy electrons play an important role in the pattern formation processes. The reactivity of acid generators with low-energy electrons was evaluated using solvated electrons in tetrahydrofuran, which were generated by a pulsed electron beam. The rate constants of acid generators with the solvated electrons ranged from 0.6 to 1.9 ×1011 M-1 s-1.

Dependence of acid generation efficiency on the protection ratio of hydroxyl groups in chemically amplified electron beam, x-ray and EUV resists

In chemically amplified resists for ionizing radiation such as an electron beam, protons of acids come from not acid generators but base polymers. This means that the modification of base polymers has a great effect on the acid generation efficiency. The relation between relative acid yield and protecting groups of poly(4-hydroxystyrene) was examined. The selection of protecting groups is important for the acid generation efficiency and the acid distribution uniformity.

Pulse Radiolysis Study on Proton and Charge Transfer Reactions in Solid Poly(methyl methacrylate)

Poly(methyl methacrylate) (PMMA) is a good matrix for a case study aimed at understanding reaction mechanisms of electron beam, X-ray and EUV resists. Radiation-induced reactions and proton dynamics of solid PMMA were studied under room temperature by pulse radiolysis. PMMA samples were doped with pyrene (Py), crystal violet lactone (CVL) or an anion scavenger to observe charge and proton transfer reactions in the solid matrix. The time-dependent behavior of ionic radicals was observed with the time resolution of 10 ns. The electron transfer from PMMA anion radicals to the anion scavenger or Py was observed in the time range of several hundred nanoseconds. The dynamics of protons generated in irradiated PMMA was traced using CVL. The growth of optical absorbance attributed to proton adducts of CVL was observed in the time range of several hundreds minutes. Protons derived from PMMA cation radicals have a long lifetime and migrated in the solid PMMA matrix.

Effects of ester groups on proton generation and diffusion in polymethacrylate matrices

In this paper, primary reaction in polymethacrylates were investigated with a pulse radiolysis method. we discuss the difference of proton generation and transfer in polymethacrylates, which is the essential property for polymethylacrylate base chemically amplified electron beam and X-ray resists.

Study on acid generation from polymer

In the fabrication beyond the 32nm node, the uniform distribution of acid generators in a resist matrix is a serious concern. The incorporation of acid generators to polymers via covalent bonds has attracted much attention in order to overcome the compatibility problem of acid generators with polymers. We reported the reaction mechanism of acid generation in typical chemically amplified resists for ionizing radiation, such as electron beam and extreme ultraviolet. The simplest way to induce the same reactions in a single-component resist is the halogenation of polymers. We carried out a case study on the acid generation from polymers using brominated poly(4-hyroxystyrene) (Br-PHS). Br-PHS without an acid generator produced hydrogen bromide with the same amount as acid yield of PHS with 1.2mol% (4.1wt%) triphenylsulfonium-triflate. It was confirmed that Br-PHS with hexamethoxy methyl melamine worked as a chemically amplified resist without any acid generators. From the comparison among the acid yields of B...