Hikaru Momose

Application of High-Resolution MALDI-TOFMS with a Spiral Ion Trajectory for the Structural Characterization of Free Radical Polymerized Methacrylate Ester Copolymers

The structural characterization of copolymers by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) remains a challenging task, since their random comonomer distribution creates very complicated mass spectra. In this study, a high-resolution TOF mass spectrometer with a spiral ion trajectory was applied to the structural and compositional characterization of free radical copolymerized poly(methyl methacrylate-co-tert-butyl methacrylate), poly(MMA-co-tBMA)s in ethyl lactate acting as a chain transfer agent. Virtually complete peak assignments of the isobaric components within the poly(MMA-co-tBMA)s served to identify the end-group combinations and copolymer compositions of individual copolymer components, allowing the distributions of comonomer compositions and six types of end-group combinations to be evaluated.

Mechanism for low-etching resistance and surface roughness of ArF photoresist during plasma irradiation

ArF excimer laser lithography was introduced to fabricate nanometer-scale devices and uses chemically amplified photoresist polymers including photoacid generators (PAGs). Because plasma-etching processes cause serious problems related to the use of ArF photoresists, such as line-edge roughness and low etching selectivity, we have to understand the interaction between plasma and ArF photoresist polymers. Investigating the effects of surface temperature and the irradiation species from plasma, we have found that ion irradiation by itself did not drastically increase the roughness or etching rate of ArF photoresist films unless it was combined with ultraviolet/vacuum ultraviolet (UV/VUV) photon irradiation. The structures of ArF photoresist polymers were largely unchanged by ion irradiation alone but were destroyed by combinations of ion and UV/VUV-photon irradiation. Our results suggested that PAG-mediated deprotection induced by UV/VUV-photon irradiation was amplified at surface temperatures above 100 °C....

Decisive factors affecting plasma resistance and roughness formation in ArF photoresist

Low plasma resistance and roughness formation in an ArF photoresist are serious issues in plasma processes. To resolve these issues, we investigated several factors that affect the roughness formation and plasma resistance in an ArF photoresist. We used our neutral beam process to categorize the effects of species from the plasma on the ArF photoresist into physical bombardment, chemical reactions and ultraviolet/vacuum ultraviolet (UV/VUV) radiation. The UV/VUV radiation drastically increased the etching rates of the ArF photoresist films, and, in contrast, chemical reactions increased the formation of surface roughness. FTIR analysis indicated that the UV/VUV radiation preferentially dissociates C–H bonds in the ArF photoresist, rather than C=O bonds, because of the dissociation energies of the bonds. This indicated that the etching rates of the ArF photoresist are determined by the UV/VUV radiation because this radiation can break C–H bonds, which account for the majority of structures in the ArF photoresist. In contrast, FTIR analysis showed that chemical species such as radicals and ions were likely to react with C=O bonds, in particular C=O bonds in the lactone groups of the ArF photoresist, due to the structural and electronic effects of the lactone groups. As a result, the etching rates of the ArF photoresist can vary in different bond structures, leading to increased surface roughness in the ArF photoresist.

Effect of end group structures of methacrylate polymers on ArF photoresist performances

The relationship between the sensitivity of ArF photoresist and the end group structures of copolymers consisting of (beta) -hydroxy-(gamma) -butyrolactone methacrylate (HGBMA) and 2-methyl-2-adamantyl methacrylate (MadMA) was investigated. The sensitivity is strongly dependent on the kind and amount of end groups. It has been found that the copolymer with relatively non-polar end group structure has higher sensitivity than that with polar end group structure, and that the sensitivity of copolymer with end groups of methylisobutyrate and 1-octhylthio moieties showed approximately three times higher than that of copolymer with end groups of isobutyronitrile and 2-hydroxyethylthio moieties. The difference of sensitivity among these copolymers has been discussed from the view point of the change of development rate attributed to the amount of carboxylic acid groups formed in the resist film by exposure of 193nm light.

Newly developed acrylic copolymers for ArF photoresist

We have developed novel acrylic copolymers for ArF photoresist which have more etching durability than usual. The excellent one of those copolymers in handling contains 8- or 9- methacryloyloxy-4-oxatricyclo[5.2.1.02,6]decan-3-one (OTDMA) and (gamma) ,(gamma) -dimethyl-(alpha) -methylene-(gamma) -butyrolac tone (DMMB). OTDMA is a new methacrylic ester monomer having a lactone unit with bridged structure. DMMB introduces a lactone structure to the main chain of acrylic copolymers. It was suggested that the solubility of monomers depends on the hindrance of their polar group, and the role of the hydrophilic monomers has been discussed from the standpoint of the position of their hydrophilic parts.

Chemical composition distribution analysis of photoresist copolymers and influence on ArF lithographic performance

For getting information about the distribution of chemical composition, several model polymers were prepared under different polymerization conditions and were measured by critical adsorption point-liquid chromatography (CAP-LC). In the copolymer system of 8- and 9- (4-oxatricyclo[5.2.1.02,6]decane-3-one) acrylate (OTDA) and 2-ethyl-2-adamantyl methacrylate (EAdMA), the peak shapes of the CAP-LC chromatogram varied according to the polymerization condition although they indicated same molecular weight and averaged chemical composition. The difference of the CAP-LC elution curves was related to the chemical composition distribution of copolymers for CAP-LC measurement combined with proton nuclear magnetic resonance (1H-NMR). The terpolymers consisted of α-hydroxy-γ-butyrolactone methacrylate (GBLMA), 2-methyl-2-adamantyl methacrylate (MAdMA) and 1-hydroxy-3-adamantyl methacrylate (HAdMA) were prepared under various polymerization conditions. In the terpolymer system that had same molecular weight and average chemical composition, the solubility parameter (&dgr;) and the dissolution rate were measured. The &dgr; value and the dissolution rate curve were different among these terpolymers. It was suggested that the &dgr; value and the chemical composition distribution of these terpolymers have a significant influence on the lithographic performance.

Design and development of novel monomers and copolymers for 193-nm lithography

Design and development of novel monomers and copolymers for 193-nm lithography are described. At the present time, 193-nm lithography is required for 65-nm node and below. Novel monomers and copolymers are considered to be candidates for the development of higher performance resist materials. We focused our attention on pattern profile and line edge roughness. In design of novel monomers, molecular orbital calculation was adopted. It was revealed that CN-group has a higher potential than other polar groups. Novel monomers that contain CN-group were designed, synthesized and co-polymerized with traditional acrylate monomers. It is expected that these copolymers could be higher performance resist materials that could be used in 65-nm node and below.

Improving plasma resistance and lowering roughness in an ArF photoresist by adding a chemical reaction inhibitor

Major challenges associated with 193 nm lithography using an ArF photoresist are low plasma resistance and roughness formation in the ArF photoresist during plasma processes. We have previously found decisive factors affecting the plasma resistance and roughness formation in an ArF photoresist: plasma resistance is determined by UV/VUV radiation, and roughness formation is dominated by chemical reactions. In this study, based on our findings on the interaction between plasma radiation species and ArF photoresist polymers, we proposed an ArF photoresist with a chemical reaction inhibitor, which can trap reactive species from the plasma, and characterized the performances of the resultant ArF photoresist through neutral beam experiments. Hindered amine light stabilizers, i.e. 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy (HO-TEMPO), were used as the chemical reaction inhibitor. Etching rates of the ArF photoresist films were not dependent on the HO-TEMPO content in the irradiations without chemical reactions or under UV/VUV radiation. However, in the irradiation with chemical reactions, the etching rates of the ArF photoresist films decreased as the HO-TEMPO content increased. In addition, the surface roughness decreased with the increase in the additive amount of chemical reaction inhibitor. According to FTIR analysis, a chemical reaction inhibitor can inhibit the chemical reactions in ArF photoresist films through plasma radicals. These results indicate that a chemical reaction inhibitor is effective against chemical reactions, resulting in improved plasma resistance and less roughness in an ArF photoresist. These results also support our suggested mechanism of plasma resistance and roughness formation in an ArF photoresist.

Correlations between Chemical Compositions and Retention Times of Methacrylate Random Copolymers Using LC-ESI-MS

Correlations between chemical compositions and chromatographic retention times (Rt) of methacrylate random copolymers were studied by liquid chromatography electrospray ionization mass spectrometry (LC-ESI-MS). Twenty-six different polymers including homopolymers of poly(methyl methacrylate) (PMMA), poly(tert-butyl methacrylate) (PTBMA) and poly(2-hydroxyethyl methacrylate) (PHEMA), and their random copolymers of P(MMA-TBMA) and P(MMA-HEMA) with known chemical compositions were studied. The results indicate that there is close correlations between the chemical compositions of the random copolymers and their Rt of the C8 column in the mass spectral ranges of m/z 1,800-2,000. The LC-ESI-MS analysis showed molecular weights of the copolymers distribute in the mass range of ca. 500-20,000, and the structures of polymer terminals and their monomer units can be identified.