Naoto Sugino

Ecofriendly ethanol-developable processes for electron beam lithography using positive-tone dextrin resist material

From the viewpoints of the utilization of agricultural resources and advanced use of biomass, this study is aimed at expanding the resolution limits of ecofriendly ethanol-developable processes for electron-beam lithography using a positive-tone dextrin resist material with high hydrophilicity on a cellulose-based underlayer. The images of 20-nm-hole and 40-nm-line patterns with an exposure dose of approximately 1800 µC/cm2 were provided by ecofriendly ethanol-developable processes instead of the common development processes using tetramethylammonium hydroxide and organic solvents. The CF4 etching selectivity of the positive-tone dextrin resist material was approximately 10% lower than that of the polymethyl methacrylate used as a reference resist material.

Nanoimprint lithography using disposable biomass template

A novel nanoimprint lithography process using disposable biomass template having gas permeability was investigated. It was found that a disposable biomass template derived from cellulose materials shows an excellent gas permeability and decreases transcriptional defects in conventional templates such as quartz, PMDS, DLC that have no gas permeability. We believe that outgasses from imprinted materials are easily removed through the template. The approach to use a cellulose for template material is suitable as the next generation of clean separation technology. It is expected to be one of the defect-less thermal nanoimprint lithographic technologies. It is also expected that volatile materials and solvent including materials become available that often create defects and peelings in conventional temples that have no gas permeability.

Nanoimprint lithography using gas permeable template II

We have been trying to improve nanoimprint lithography performance through modification of template materials. We have reported a biomass based template with gas permeability which decreases transcriptional defects on template materials caused by involved solvents and cracked gasses generated from imprinted materials. (SPIE2016 and 2017) The line patterning results using the biomass based gas permeable template were better to reduce the line pattern failure as compared with that of quartz based template as the standard reference. In this study, we will report a mechanical property improvement of the template by blending cellulose nanofiber (CNF) to the biomass template. The blended template showed improved gas transmission coefficient and mechanical properties than non-blended template. The proposed nanoimprint lithography using biomass based template with gas permeable and gaseous adsorption is one of the most promising processes ready to use for mass-production of nanoscale devices.

Utilization of gas permeable metal plate for the purpose of reduction of transfer defect in MEMS electronic device

The electronic substrate used for the MEMS device is finely processed, and imprint lithography is often used as a processing method. However, in the printing process, gas is caught in the molding material, and transfer failure frequently occurs. Therefore, in this study, a gas permeable metal plate with a gas permeable structure inside was fabricated and imprinted on a material to be transferred containing 50% of volatile material. As a result, no gas pool was observed and imprinting was possible without defective transfer. This not only prevents entrainment of gas at the time of imprinting, but also a transfer material containing a volatile solvent can be used as a material to be transferred. It is greatly expected that the developed gas permeable metal plate becomes a material necessary for MEMS device processing.

Internal structure of metal material with gas permeability function related to MEMS devices

MEMS technology is incorporated into various devices (automobiles, digital cameras, optical devices) indispensable for our daily lives. Semiconductor manufacturing process technology such as photolithography method and ion beam method is mainly used for micropatterning necessary for MEMS and microfabrication of diffraction grating. In photolithography, many transfer defects caused by gas are generated. Therefore, a metal plate having gas permeability was prepared with a 3D printer, and the surface and internal structure of the metal plate was evaluated. Further, the porosity of the metal plate was calculated by measuring the size and weight of the produced metal plate. As a result, it was confirmed that there were numerous holes in the inside of the metallic material, and it was confirmed that the hole having the role of permeating the gas and the hole having the role of temporarily preserving the gas. Furthermore, it was also confirmed that the porosity of the metal plate is about 10%. Metallic materials with gas permeability can be expected to be materials required for MEMS device processing.

Nanoimprint lithography using gas permeable template

Cracked gasses generated from imprinted materials and/or involved solvents cause transcriptional defects on template materials and insufficient filling of imprinted materials in nanoimprint lithography. This study aims to create the novel gas permeable nanoimprint template materials to prevent such defects caused by cracked gasses and involved solvents. A biomass based template was investigated in thermal and UV nanoimprint lithography instead of the conventional template such as quartz, PMDS, DLC, block copolymers. The line patterning results using the biomass based gas permeable template in nanoimprint lithography were better to reduce the line pattern failure compared with that of quartz based template as a reference. Gas transmission coefficient was evaluated for template materials having thermal crosslinkable urethane groups. The proposed nanoimprint lithography using biomass based gas permeable template is one of the most promising processes ready to be investigated for mass-production of fine device applications.

Temperature dependence of viscoelasticity of crystalline cellulose with different molecular weights added to silicone elastomer

Silicone elastomers ( polydimethylsiloxane _ PDMS) are widely used in the field of imprint lithography and microcontactprinting (μCP). When performing microcontactprinting, the mechanical properties of the PCMS as a base material have a great influence on the performance of the device. Cellulose nanofibers having features of high strength, high elasticity and low coefficient of linear expansion have attracted attention in recent years due to their characteristics. Therefore, three types of crystalline cellulose having different molecular weights were added to PDMS to prepare a composite material, and dynamic viscoelasticity was measured using a rheometer. The PDMS with the highest molecular weight crystalline cellulose added exhibited smaller storage modulus than PDMS with other molecular weight added in all temperature ranges. Furthermore, when comparing PDMS to which crystalline cellulose was added and PDMS which is not added, the storage modulus of PDMS to which cellulose was added in the low temperature region was higher than that of PDMS to which it was not added, but it was reversed in the high temperature region It was a result. When used in a low temperature range (less than 150 ° C.), it can be said that cellulose can function as a reinforcing material for PDMS.

Organic-inorganic hybrid resist materials in advanced lithography

Advanced nano-imprint lithography appears as a simple, cost reduction in manufacturing, fast operation, develop-less patterning application compatible with conventional pattern transfer techniques such as ultraviolet and electron beam lithography. However, defects generated in nano-imprint lithography present challenges that must be resolved in order to mass-produce advanced devices. The nano-imprint lithography requires the clean separation of a quartz template from a resist material, and the force required to create this separation must be minimized to prevent the resist pattern collapse and defects. This procedure is proven to be suitable for material design and the process conditions of organic-inorganic hybrid resist materials on photo-reactive underlayer material for the defect reduction by mold contamination when the mold was removed from the organic-inorganic hybrid resist materials after ultraviolet irradiation. The developed organic-inorganic hybrid resist material with ultraviolet crosslinking groups produced high resolutions nano-patterning of 50 nm line and excellent etch properties for semiconductor memory, MEMS, NEMS, biosensors, and medical devices.

Temperature dependency of mechanical properties for crystalline cellulose added to silicone elastomer

A chemical cross-linked transparent film was got by a silicon compound to crystalline cellulose. Temperature dependency for the elasticity modulus of a provided film was measured. The shear elastic modulus was obtained the value of 2 x 106 [Pa] at room temperature. The sample decreases in 190 [deg. C] for the elasticity modulus at the room temperature as 60%, but approximately 10% recover when temperature rises up to 200 [deg. C] or more.

High resolution patterning of ultraviolet cross-linked resins using gas permeable mold derived from cellulose in nanoimprint lithography

A cellulose-based gas permeable mold having thermal crosslinking group for nanoimprint lithography has been developed to prevent transcriptional defects by volatile solvents from nanoimprinting materials. 3 wt.% of thermal initiator was required for producing the cellulose-based gas permeable mold. The void on 10 μm line structure of imprinted UV crosslinked resin with acetone as volatile solvents in nanoimprint lithography process using non-gas permeable mold was significantly removed using the cellulose-based gas permeable mold due to its high oxygen gas permeability. The cellulosebased gas permeable mold allows the employment of solvent including imprinting materials such as compounds and alloy particle.