Yuichi Kurashima

Step and repeat photo-nanoimprint system using active orientation head

In this paper, we have designed a new active orientation head for compliant contact and constructed a new step and repeat photo-nanoimprint system using the orientation head.

Mode-locking nanoporous alumina membrane embedded with carbon nanotube saturable absorber

The saturable absorption effect of semiconducting single-wall carbon nanotubes (SWCNTs) covering the near-infrared region is promising for mode-locking devices of short pulse lasers. However, an issue remains that the heat generated at the SWCNTs would destroy the devices. In this research, we fabricated a nanostructured heat sink in which the SWCNTs are stuffed into specially developed nanopores of heat conductive alumina. Actually, it induced stable mode-locked operation of an Er fiber laser for over 4 months.

Evaluation of Line Edge Roughness in Nanoimprint Lithography Using Photocurable Polymer

To evaluate the ultimate accuracy in nanoimprint replication using photocurable resin, we studied the line edge roughness (LER) of replicated patterns using a mold pattern on a Si (110) substrate produced by anisotropic wet etching. The root mean square (RMS) for the replicated pattern LER was between 0.64 nm and 0.9 nm. This was slightly larger than that for the mold pattern. The RMS for the mold pattern was between 0.48 nm and 0.62 nm. The replicated pattern RMS shows no systematic change when the ultraviolet light exposure dose is increased from 10 mJ/cm2 to 3 J/cm2. Based on the dependence of the RMS for both of the line edge and Ti coated resin surface, we concluded that the increment of the RMS in the replicated pattern is due to the Ti coating which was carried out for scanning electron microscope observation of the replicated pattern.

Fabrication of low line edge roughness mold for photo-nanoimprint

In this paper, we fabricate low LER pattern on Spin On Glass (SOG) by simple nanoimprint process using a Si master mold obtained by anisotropic wet etching.

Reducing Photocurable Polymer Pattern Shrinkage and Roughness during Dry Etching in Photo-Nanoimprint Lithography

When we apply a photocurable polymer to photo-nanoimprint lithography, dry etching is necessary to remove the remaining photocurable polymer after imprinting. During dry etching, it is necessary to achieve pattern profiles with small pattern shrinkage, smooth surface, and low edge roughness. Room-temperature etching resulted in serious pattern shrinkage, but this was markedly reduced by substrate cooling (temperature -120°C). We obtained pattern shrinkage ranging from a maximum of 23 nm to a minimum of 4 nm under optimum etching conditions. We found that the surface of the photocurable polymer became rough and a large amount of polymer residue still remained after removing the remaining photocurable polymer. We obtained a smooth substrate surface by increasing both the RF power and total flow rate of the SF6/O2 gas mixture. Under optimum etching conditions, we obtained fine etch profiles of the photocurable polymer with a surface roughness of 2.5 nm, reduced pattern shrinkage, and a 3 nm line edge roughness.

Wafer-scale layer transfer of GaAs and Ge onto Si wafers using patterned epitaxial lift-off

We have developed a wafer-scale layer-transfer technique for transferring GaAs and Ge onto Si wafers of up to 300 mm in diameter. Lattice-matched GaAs or Ge layers were epitaxially grown on GaAs wafers using an AlAs release layer, which can subsequently be transferred onto a Si handle wafer via direct wafer bonding and patterned epitaxial lift-off (ELO). The crystal properties of the transferred GaAs layers were characterized by X-ray diffraction (XRD), photoluminescence, and the quality of the transferred Ge layers was characterized using Raman spectroscopy. We find that, after bonding and the wet ELO processes, the quality of the transferred GaAs and Ge layers remained the same compared to that of the as-grown epitaxial layers. Furthermore, we realized Ge-on-insulator and GaAs-on-insulator wafers by wafer-scale pattern ELO technique.

Evaluation of surface roughness of Zerodur® substrates machined by Ar+ ion beam with energy of 3–10keV

Ion beam figuring is suitable for the final correction of the surface figure error of aspherical substrates in an extreme ultraviolet lithography apparatus. In ion beam processing, however, the surfaces are considered to become rougher. This paper reports the investigation of the surface roughness of Zerodur® machined with an Ar+ ion beam having an energy of 3–10keV. For an Ar+ ion beam with energies in the range of 3–10keV, the mid-spatial frequency roughness of the surfaces machined to a depth of less than 50nm was comparable to the surface roughness of an unprocessed one. The high-spatial frequency roughness of the unprocessed surface was 0.26nm rms; whereas the high-spatial frequency roughness of the surface machined with energies of 3, 5, 7, and 10keV was 0.46, 0.54, 0.63, and 0.65nm rms, respectively. The HSFR of the machined surface increases with an increase in the energy of the ion beam.

Room temperature wafer direct bonding of smooth Si surfaces recovered by Ne beam surface treatments

We examined the applicability of a Ne fast atom beam (FAB) to surface activated bonding of Si wafers at room temperature. With etching depth more than 1.5 nm, the bonding strength comparable to Si bulk strength was attained. Moreover, we found the improvement of the bonding strength by surface smoothing effect of the Ne FAB. Silicon surface roughness decreased from 0.40 to 0.17 nm rms by applying a Ne FAB of 30 nm etching depth. The bonding strength between surfaces recovered by Ne FAB surface smoothing was largely improved and finally became equivalent to Si bulk strength.

Line Width Reproducibility of Photo-Nanoimprints

Well-shaped patterns were fabricated by photo-nanoimprinting using a spin-on-glass (SOG) mold, the patterns of which were replicated from a Si master mold by the SOG replica method. The line width reproducibility of the photo-nanoimprint was then evaluated using an atomic force microscope (AFM). Pattern widths with a sub-nm resolution were determined by an edge detection program. The obtained widths included errors attributable to the nonlinearity of the AFM piezo scanner; however, a calibration method using pattern pitches was employed to filter out these errors and allow precise evaluation of line widths. Using this method, the standard deviation of differences between averaged values from 5 measurements of two patterns, which were fabricated on different dies by photo-nanoimprinting, was found to be 0.23 nm. High photo-nanoimprint reproducibility was thus confirmed quantitatively.

Fabrication of nanodot array molds for photonanoimprint using anodic porous alumina

This article reports on the fabrication of a transparent nanodot array mold for nanoimprint and so on. In the mold fabrication, the combination of a porous alumina master mold made by anodization of an Al plate and spin on glass replica process is utilized to pattern nanodot array on a transparent mold with large area. Using this method, the authors could obtain transparent nanodot array mold pattern with a pitch of about 100nm and height/depth of 90nm. When this nanodot array mold was used for photonanoimprint, a pitch of the photonanoimprinted pattern was found to be about 100nm. The pitch is considered quite comparable to the pitch of the patterns on the porous alumina master mold.