Iwao Miyamoto

Measurement of adhesive force between mold and photo-curable resin in imprint technology

Imprint lithography using photocurable resin is the most promising technique compared with other imprint lithography techniques, because it can complete a pattern transfer at room temperature. Thus, it would be able to implement practical mass-production lithography. In a previous report, however, a part of the solidified polymer was ripped away, because of strong adhesive force between the mold and solidified polymer. In order to improve this phenomenon, release coating of quartz mold and development of a photocurable resin are necessary. In this paper, we describe a measurement method of adhesive force between mold and resin using a tensile tester and, furthermore, durability of release coating material.

Diamond nanoimprint lithography

Electron beam (EB) lithography using polymethylmethacrylate (PMMA) and oxygen gas reactive ion etching (RIE) were used to fabricate fine patterns in a diamond mould. To prevent charge-up during EB lithography, thin conductive polymer was spin-coated over the PMMA resist, yielding dented line patterns 2 μ m wide and 270 nm deep. The diamond mould was pressed into PMMA on a silicon substrate heated to 130, 150 and 170oC at 43.6, 65.4 and 87.2 MPa. All transferred PMMA convex line patterns were 2 μ m wide. Imprinted pattern depth increased with rising temperature and pressure. PMMA patterns on diamond were transferred by the diamond mould at 150oC and 65.4 MPa, yielding convex line patterns 2 μ m wide and 200 nm high. Direct aluminium and copper patterns were obtained using the diamond mould at room temperature and 130.8 MPa. The diamond mould is thus useful for replicating patterns on PMMA and metals.

Uniformity in patterns imprinted using photo-curable liquid polymer

Imprint lithography reported by Chou et al (Appl. Phys. Lett. vol. 67, p. 3114, 1995) may become one of the most promising lithographic technologies in terms of mass-production and low equipment cost . In particular, those based on photo-induced solidification (Haisma et al, 1996; Bailey et al, 2000) are very attractive because of elimination of heat-up and cool-down time and the possibility of a step and repeat procedure. We have already reported preliminary results (Komuro et al, Jpn. J. Appl. Phys., vol. 39, p. 7075, 2000) by imprint using liquid polymer curable by ultra-violet (UV) light exposure. The paper shows the pattern fabrication process by imprint using photo-curable liquid polymer. The base layer, which is accompanied with a press process, must be removed by etching. In this paper, we describe uniformity in imprinted patterns and reproducibility of our imprint process.

Focused-ion-beam-assisted etching of diamond in XeF2

Ga focused-ion-beam (FIB)-assisted etching of single-crystal diamond and thin film diamond in XeF2 was studied. The etch yield in FIB-assisted etching of diamond in XeF2 is enhanced some six times over the physical sputtering yield. In the crystal orientation dependence of the etch yield in FIB-assisted etching, the (100) face produced the highest etch yield of the three faces—(100), (110), and (111). Thin film diamond produces the lowest etch yield. A diamond field emitter with a tip radius of less than 100 nm was obtained using Ga FIB spot exposure.

Ion beam machining of single-point diamond tools for nano-precision turning

In order to obtain single-point diamond tools (SPDT) with cutting edges of sharp or small negative land for ultra-precision turning of soft materials, machining of the SPDT by an argon ion beam of 1.0 keV has been investigated. The edge radius of the SPDT was measured using a profile SEM (scanning electron microscope having two secondary electron detectors). By this processing method, mechanically lapped or polished SPDTS which have a mean edge radius of 70 nm were sharpened, and their edge radii became of the order of 20-30 nm. Moreover, is is found that the processing method can be useful for improving the surface topography of the SPDT formed by mechanical lapping removing micro-chippings on the cutting edge of the SPDT, and improving the straightness of the cutting edge of the SPDT. The processing method, also, can result in the formation of a small negative land of sub-micrometer width on the cutting edge of the SPDT.

Preparation of Diamond Mold Using Electron Beam Lithography for Application to Nanoimprint Lithography

Diamond molds were fabricated by two types of fabrication processes, both of which use a conductive intermediate layer between the diamond surface and polymethylmethacrylate (PMMA) resist to prevent surface charge-up. Using a PtPd intermediate layer, electron beam lithography and ion beam etching, a denting line pattern of 600 nm width and 70 nm depth was fabricated. Using a carbon intermediate layer, electron beam lithography, PtPd lift-off and oxygen ion beam etching, a convex line pattern of 600 nm width and 110 nm height was fabricated. These diamond molds were pressed into PMMA on a silicon substrate that was heated to a temperature of 150°C and kept at a pressure of 23.5 MPa until the temperature dropped below 90°C, and then the diamond mold was released from the PMMA. The convex line pattern of 600 nm width and 150 nm height was imprinted using a denting diamond mold. The denting pattern of 1100 nm width and 180 nm height was imprinted using a convex diamond mold. PMMA patterns were transferred well over the imprinted area by the diamond molds.

Improvement of imprinted pattern uniformity using sapphire mold

Imprint lithography is an attractive technology for LSIs era below 40-nm critical dimension from the viewpoints of high-throughput and low-cost equipment. In order to avoid a pattern placement error due to thermal expansion in the conventional thermal imprint process, we have previously attempted to replicate a mold pattern onto a liquid polymer, which was solidified using ultra-violet (UV) light irradiation at room temperature. The imprint technology based on photo-induced solidification has several advantages such as elimination of heat-up and cool-down time and possibility of step and repeat process. However part of the solidified polymer film was remained on the quartz mold surface. In order to improve this problem, in this article we propose to use a sapphire plate as a mold.

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 Three-Dimensional Hydrogen Silsesquioxane Resist Structure using Electron Beam Lithography

We have investigated a process for fabricating three-dimensional (3D) structures using electron beam lithography (EBL), in which such a structure is fabricated from a negative tone resist of hydrogen silsesquioxane (HSQ). The HSQ film for this purpose is coated on a Si wafer and is about 250 nm thick. In electron beam (EB) exposure, the depth of HSQ resist is controlled by the strength of the EB acceleration voltage. After exposing the resist according to a carefully planned scheme, followed by a developing process, a free standing and 3D HSQ structure is fabricated. This structure is a mesh saved in midair, and a line in the structure is 200 nm wide, 100 nm thick, and 1.8 µm long. These samples consisting of a periodic structure are then used as 3D photonic crystals. Fabrication of 3D photonic crystals is a complicated process, but our current work simplifies the task to a great extent.