Takeshi Okino

Fabrication of 5 Tdot/in.2 bit patterned media with servo pattern using directed self-assembly

The fabrication of an etching template for 5 Td/in.2 bit patterned media using a self-organization material, namely, poly(styrene)-poly(dimethylsiloxane) (PS-PDMS), was investigated. The molecular weight of the PS-PDMS for forming the areal density of 5 Td/in.2 dot pattern was estimated from the polymerization index related to the Flory–Huggins interaction parameter. Annealing was carried out to obtain a fine-order dot pattern. PS-PDMS films were subjected to thermal treatment or solvent annealing. The ordering of the dot array in these films was evaluated by using Voronoi diagrams. The results indicate that the film annealed in N-methylpyrrolidone (NMP) vapor showed finer ordering than did the thermally treated film. This seemed to be attributable to the high solubility parameter of NMP. The soaking of NMP into the PS phase slightly shifted the phase separation energy of the polymer matrix. The lattice spacing of the obtained hexagonal pattern was 11 nm. By using low-molecular-weight PS-PDMS with solvent...

Large Area Fabrication of Moth-Eye Antireflection Structures Using Self-Assembled Nanoparticles in Combination with Nanoimprinting

A moth-eye structure, which suppresses the reflection on a surface, was fabricated on the entire surface of a large silicon wafer by the formation of a self-assembled particle monolayer as a dry-etch mask formed by our embedded particle monolayer (EPM) method. We optimized the shape of moth-eye structures by optical calculation and improved the fabrication procedure to allow formation over a large area. As a result, we succeeded in fabricating a moth-eye structure on the entire surface of a 12-in. silicon wafer and the surface reflectance was reduced to less than 0.8% in the visible light range. A large nickel mold, which is able to transfer the pattern to an 8-in. display, could be formed using the 12-in. silicon substrate as a master. A moth-eye film was fabricated by UV nanoimprinting using the nickel mold and the high antireflection performance was confirmed. The fabrication cost of the moth-eye structure over a large area would be markedly reduced by the use of the self-assembly technique in combination with nanoimprinting.

Advanced materials for 193-nm resists

Acrylate monomers containing alicyclic side chains featuring a series of polar substituent groups were assumed to be model compounds. Solubility parameters were calculated for the corresponding acrylate polymers. These acrylate monomers were synthesized using a novel aerobic oxidation reaction employing N-hydroxyphtalimide (NHPI) as a catalyst, and then polymerized. These reactions were confirmed to be applicable for the mass-production of those compounds. The calculation results agreed with the hydrophilic parameters measured experimentally. Moreover, the relationship between the resist performance and the above-mentioned solubility parameter has been studied. As a result, a correlation between the resist performance and the calculated solubility parameter was observed. Finally, resolution of 0.13-micron patterns, based on the 1G DRAM design rule, could be successfully fabricated by optimizing the solubility parameter and the resist composition.

Evaluation of ordering of directed self-assembly of block copolymers with pre-patterned guides for bit patterned media

Bit patterned media (BPM) is a promising candidate for next-generation magnetic recording media beyond 2.5 Tb/in2. To realize such high-density patterned media, directed self-assembling (DSA) technology is a possible solution to form fine dots. In order to read and write magnetic signals on a magnetic dot of magnetic media, the position of magnetic dots must be controlled. We examined ordering of directed self-assembly of diblock copolymer dots with a variety of prepatterned guides in some conditions and evaluated the ordering of the dots by using Delaunay triangulation and Voronoi diagram. Applying the optimized conditions, we obtained highly controlled dot pattern suitable for magnetic recording media.

Chemically amplified ArF resists based on cleavable alicyclic group and the absorption band shift method

Recent advances in the single-layer resist for forming finer patterns have led us to a search for new resist materials for the ArF excimer laser. We describe a novel, environmentally friendly, single-layer resist based on a menthyl acrylate copolymer protected with a cleavable alicyclic group and the absorption band shift method.

Orientation and Position Control of Self-Assembled Polymer Pattern for Bit-Patterned Media

Directed self-assembly (DSA) is expected to be a solution for the fabrication process of high-density bit-patterned media. A DSA pattern of polystyrene-b-polydimethylsiloxane diblock copolymer with 20 nm pitch was fabricated on a 2.5 in disk substrate using a postguide. Uniformity of the dot alignment as well as dot-pitch fluctuation and linearity of pseudodot tracks are estimated using image analyses of SEM photographs. Uniformity along the circumferential direction was confirmed. All the SEM images at eight different angles at r=29.4 mm showed single domain. Pitch distribution and linearity error were estimated to be 14% and 7.8%, respectively. Uniformity along the radius direction was estimated with the moiré method. The single-domain region is expected to be 5 mm in width. Margin of the postguide pitch for the single-domain formation is revealed to be more than 15% of the self-assembled dot pitch.

Chemically amplified resists using the absorption band shift method in conjunction with alicyclic compounds for ArF excimer laser lithography

The resist comprising naphthalene rings instead of benzene rings was developed for ArF excimer laser lithography. Naphthalene shows outstanding dry etch resistance, stronger adhesion to silicon surface and low hydrophobicity compared with most alicyclic compounds. Di-tert-butyl 2-[(1- adamanthyl) carbonylmethyl] (ADTB) was developed as an additive to improve the characteristics of development of base polymer. Although ADTB has tert-butyl protective groups, the decomposition temperature is low compared with that of polymer which has a tert-butyl protective group. Moreover, the dry etch resistance of the resist becomes greater as ADTB content increases. 0.133 micrometers L/S patterns were fabricated using Nikons ArF prototype exposure system. Next, in order to improve the adhesion of the resist having the alicyclic frame, introduction of naphthalene in to the resist was attempted. The new resists which has naphthalene frame showed stronger adhesion and 0.15 micrometers L/S patterns were fabricated using the ArF exposure system with the standard developer.

Orientation and position-controlled block copolymer nanolithography for bit-patterned media

Bit-patterned media (BPM) is a candidate for high-density magnetic recording media. Directed self-assembly (DSA) is expected to be a solution for the fabrication process of high-density BPM. A BPM with 20 nm-pitch dot pattern is fabricated. A 100 nm-pitch triangle lattice dot pattern, which is fabricated by EB lithography, is used as a guide post to order PS-PDMS self-assembled diblock co-polymer with 20 nm pitch. Dot-pitch fluctuation and linearity of pseudo dot tracks are estimated. The standard deviation of the dot-pitch variation including the post guide is 8% of the self-assembled dot pitch. The dot-position deviation is estimated to be about 8% of the pseudo dot track pitch. In both cases, variation of the size and pitch of the post guides is found to increase the dot-pitch fluctuation and dot-position deviation from pseudo dot-track.

Dissolution inhibitors for 193-nm chemically amplified resists

Dissolution characteristics and adhesion of 193-nm resists have been investigated by using molecular orbital calculations. The calculation indicated that naphthalene compound had better adhesion than alicyclic compounds by a factor of 1.2. Another calculation result obtained indicated that naphthalene was more hydrophilic than alicyclic compounds. In order to improve the adhesion and dissolution characteristics of the alicyclic resist, introduction of the naphthalene backbone into alicyclic resists was attempted in the form of additives (dissolution inhibitors) or copolymer components. Dissolution inhibitors that have simultaneously a naphthol novolak backbone and a characteristic generate carboxylic acid, such as tetrahydropyranyl ester of naphthol novolak compound condenced with glyoxlic acid (NV4THP), were the most effective dissolution inhibitors increasing dry etch resistance of base polymer by 14% and pattern resolution of original resist by 10%. The naphthalene dissolution inhibitor also largely improves pattern adhesion. These results were consistent with above-mentioned calculation results. 193-nm resists containing vinyl naphthalene in the copolymer structure were also investigated and fundamental resist requirements were satisfied with this polymer by adding adamantane dissolution inhibitor di-tert-butyl 2-((1-adamanthyl)carbonylmethyl) malonate (ADTB).