Polymeric Photoacid Generator Research Articles

A new type of sulfonium salt copolymers generating polymeric photoacid: Preparation, properties and application

Photoacid generators (PAGs) are critical components in chemically amplified (CA) photoresists system, among which small molecular sulfonium salts are commonly used but possess inherent incompatibility with polymer matrixes and acid migration during the post exposure baking (PEB) processes. PAG-bound polymers would be better choices for CA photoresists to acquire excellent lithographic performance. In this work, a new and convenient way is designed to prepare polymeric PAGs which generate polymeric photoacids and with this method the existing small molecular sulfonium salts can be transformed into polymeric compounds with convenience. Poly (sodium p-styrenesulfonate-co-tertiary-butyl methacrylate) (p(SSNa-co-t-BMA)) was prepared through free radical polymerization and then was further reacted with various sulfonium halides to give sulfonium salt copolymers. Different molecular weights of the copolymers can be obtained from Mn 5.5 × 103–2.5 × 104 with distribution coefficient between 1.18‐1.88. The ionic copolymers display good solubilities in common resist solvents. The thermal decomposition temperatures (Td) are around 150–155 °C and the glass transition temperatures (Tg) are above 130 °C. After exposed to light, the copolymers can generate polymeric photoacids. The photoacid generation efficiencies are determined around 0.31–0.34. UV spectra show big difference between the polymeric PAGs and the mixture of the corresponding small molecular sulfonium salts and framework polymers and demonstrate much better transparency of polymeric PAGs. Thick film 248-nm CA photoresist can be formed by one of the polymeric PAGs and partly protected poly(4-hydroxystyrene-co- tertiary-butyl methacrylate) (p(4-HS-co-t-BMA)), and display excellent performance with high height/width (H/W) ratio of 5:1 and resolution of 0.35 μm. These polymeric PAGs also have potentiality to be used in CA photoresists for other photolithography technologies such as 193-nm immersion technology.

Novel Polymeric Sulfonium Photoacid Generator and Its Application for Chemically Amplified Photoresists

The polymeric PAGs based resist systems which incorporated the PAG units into the main chain showed improved lithographic performance, such as faster photospeed and higher stability, lower outgassing, and lower LER than corresponding blend resists. In this paper, with poly (4-hydroxylstyrene) (PHS) as raw material, a new type of polymeric photoacid generators (PAGs) was synthesized with sulfonuium triflate groups bonded onto part of the benzene rings. The phenolic hydroxyl group was partly esterified to improve its solubility in common organic solvents for resists. Upon irradiation to light, the sulfonium units in the polymer effectively decomposed to generate sulfonic acid. The properties of the novel polymeric PAGs were investigated. Chemically amplified photorssists can be formed by the polymeric PAG and other film forming material containing acid labile groups.

The preparation of a novel polymeric sulfonium salt photoacid generator and its application for advanced photoresists

With poly(4-hydroxylstyrene) (PHS) as a raw material, a new type of polymeric photoacid generator (PAG) is synthesized with sulfonium perfluoroalkyl sulfonate groups bonded onto part of the benzene rings. The phenolic hydroxyl groups are esterified to increase the solubilities of the polymeric sulfonium salts in organic solvents. Upon irradiation to 254 nm light, the sulfonium units in the polymer effectively decompose to generate sulfonic acid. The photolysis is confirmed by UV spectroscopy and the generation of sulfonic acids which catalyze the decomposition of the t-BOC protection group of the polymeric PAGs. Making use of the polymeric PAGs, positive-tone chemically amplified 248-nm photoresists can be formed by them and ester acetal polymer with high acidolytic activity. The photolithography performance of the photoresist was evaluated using a KrF laser exposure system with high photosensitivity and resolution. This novel kind of polymeric sulfonium salt PAG is applicable for advanced chemically amplified resist materials.

Polymeric photoacid generators for direct photochemical modification of surface

AbstractTo achieve easy spin coating and enhanced efficiency in the photolithographic process for the direct photochemical modification of surface, we incorporated photoacid generator (PAG) into polymer backbone. Bis‐(4‐hydroxy‐phenyl)‐(4‐methoxy‐3,5‐dimethyl‐phenyl)‐sulfonium chloride was synthesized as a monomer, and was polymerized with sebacoyl chloride and terephthaloyl chloride. The resulting polymeric PAG in chloride salt form was converted to the p‐toluenesulfonate and 1‐naphthol‐5‐sulfonate forms with ion‐exchange reactions. By the photolithographic process with the polymeric PAG, the protecting groups of the linker molecules self‐assembled onto a glass plate were micropatterned to produce an amine pattern for the microarray of oligonucleotides. The acids generated from the polymeric PAG effectively deprotect the acid‐labile protecting groups of the linker molecules through a chemical amplification process in the exposed region. After the treatment of the patterned amino groups with a fluorescent dye, the pattern profiles were observed with a fluorescence scanner. The fluorescence image reveals a well‐defined pattern at a micro level, which clearly indicates that the polymeric PAGs have a great potential in photochemical surface modification for the microarray of oligonucleotides. Copyright © 2007 John Wiley & Sons, Ltd.

Photolithographic Patterning of a Conductive Polymer Using a Polymeric Photoacid Generator and a Traceless Removable Group

AbstractSummary: In the present communication we describe a photolithographic method to produce polyaniline (PANI) patterns using PANI modified with a traceless removable functional group (nitrosated polyaniline, PANI‐NO) and external inexpensive polymeric photoacid generators (poly(vinyl chloride), PVC). Therefore, residual sub‐products created by irradiation of the plate do not remain occluded in the polymeric films. The borders of the patterns are better defined than in the case of chemical lithography using inorganic acids as the hydrolyzing agent. magnified image

Patterning of Single-Wall Carbon Nanotubes via a Combined Technique (Chemical Anchoring and Photolithography) on Patterned Substrates

Single-walled carbon nanotubes (SWNTs) have been chemically attached with high density onto a patterned substrate. To form the SWNT pattern, the substrate was treated with acid-labile group protected amine, and an amine prepattern was formed using a photolithographic process with a novel polymeric photoacid generator (PAG). The polymeric PAG contains a triphenylsulfonium salt on its backbone and was synthesized to obtain a PAG with enhanced efficiency and ease of spin-coating onto the amine-modified glass substrate. The SWNT monolayer pattern was then formed through the amidation reaction between the carboxylic acid groups of carboxylated SWNTs (ca-SWNTs) and the prepatterned amino groups. A high-density multilayer was fabricated via further repeated reaction between the carboxylic acid groups of the ca-SWNTs and the amino groups of the linker with the aid of a condensation agent. The formation of covalent amide bonding was confirmed by X-ray photoelectron spectroscopy (XPS) analysis. Scanning electron microscopy and UV-vis-near-IR results show that the patterned SWNT films have uniform coverage with high surface density. Unlike previously reported patterned SWNT arrays, this ca-SWNT patterned layer has high surface density and excellent surface adhesion due to its direct chemical bonding to the substrate.

Patterning of Single-Walled Carbon Nanotubes Using Wet Chemical Self-Assembling and Photolithographic Technique

AbstractSingle-walled carbon nanotubes (SWNTs) have been chemically attached with high density onto a patterned substrate. To form the SWNT pattern, the substrate was treated with acid-labile group protected amine, and an amine prepattern was formed using a photolithographic process with a polymeric photo acid generator. The SWNT monolayer pattern was then formed through the amidation reaction between the carboxylic acid groups of carboxylated SWNTs (ca-SWNTs) and the prepatterned amino groups. A high-density multilayer was fabricated via further repeated reaction between the carboxylic acid groups of the ca-SWNTs and the amino groups of the linker with the aid of a condensation agent. Scanning electron microscopy results show that the patterned SWNT films have uniform coverage with high surface density.

Acid catalyst mobility in resist resins

In a chemically amplified resist absorbed photons generate stable catalyst molecules instead of directly switching resist solubility via photochemical reaction. This allows for much lower exposure doses to be used in imaging. Some catalyst mobility is necessary to achieve amplification since the catalyst must move from reaction site to reaction site, but a mobile catalyst can blur the deposited aerial image. Catalyst molecules that are free to move in exposed regions are also free to move into adjacent unexposed regions. Understanding acid catalyst diffusion in photoresist resins is complicated by the constantly changing chemical environment the diffusing catalyst experiences as the resist undergoes chemical reactions. The diffusing catalyst promotes chemical reactions which change the properties of its surrounding resin. In addition, it is possible a transient material state is generated by volatile reaction byproducts and their desorption from the film. In most photoresist systems it is impossible to separate reaction and diffusion effects. This work describes studies of acid diffusion in polymers that are close structural analogs to reactive photoresist resins but do not react with the diffusing acidic catalyst. The purpose of this study into nonreactive polymer is to gain insight into the more complex, reactive systems. In addition, experiments with polymeric photoacid generators are reported. These materials provide added insight into acid transport in photoresist materials.

Terpolymers of tosyloxymaleimide for application as a polymeric photoacid generator in single-component resists.

Terpolymers of sulfonyloxymaleimides have been prepared as a new class of polymeric photoacid generator and their photochemical and thermal properties were investigated. The styrenic copolymers of N-tosyloxymaleimide (TsOMI) produced p-toluenesulfonic acid (TsOH) in solid state by deep UV irradiation and the amount of generated acid was determined by using a colorimetric method. Two terpolymers of TsOMI and p-(t-butyloxycarbonyloxy)styrene showed the capability of a single-component, chemically amplified resist system in deep UV region. Positive- and negative-tone images were obtained with sensitivity of 50mJ/cm2.