Surface plasmons (SPs) are coherent oscillations of conduction electrons on a metal surface excited by electromagnetic radiation at a metal -dielectric interface. The growing field of research on such light -metal interactions is known as ‘plasmonics’. 1-3 This branch of research has attracted much attention due to its potential applications in miniaturized optical devices, sensors, and photonic circuits as well as in medical diagnostics and therapeutics. 4-8

Nanostructured plasmonic sensors.

Nanoimprint lithography (NIL) is a nonconventional lithographic technique for high-throughput patterning of polymer nanostructures at great precision and at low costs. Unlike traditional lithographic approaches, which achieve pattern definition through the use of photons or electrons to modify the chemical and physical properties of the resist, NIL relies on direct mechanical deformation of the resist material and can therefore achieve resolutions beyond the limitations set by light diffraction or beam scattering that are encountered in conventional techniques. This Review covers the basic principles of nanoimprinting, with an emphasis on the requirements on materials for the imprinting mold, surface properties, and resist materials for successful and reliable nanostructure replication.

/pdf/nanoimprint-lithography-methods-and-material-requirements-csc83swyi1.pdf

Nanoimprint Lithography: Methods and Material Requirements**

Beams of electrons and ions are now fairly routinely focused to dimensions in the nanometer range. Since the beams can be used to locally alter material at the point where they are incident on a surface, they represent direct nanofabrication tools. The authors will focus here on direct fabrication rather than lithography, which is indirect in that it uses the intermediary of resist. In the case of both ions and electrons, material addition or removal can be achieved using precursor gases. In addition ions can also alter material by sputtering (milling), by damage, or by implantation. Many material removal and deposition processes employing precursor gases have been developed for numerous practical applications, such as mask repair, circuit restructuring and repair, and sample sectioning. The authors will also discuss structures that are made for research purposes or for demonstration of the processing capabilities. In many cases the minimum dimensions at which these processes can be realized are considerably larger than the beam diameters. The atomic level mechanisms responsible for the precursor gas activation have not been studied in detail in many cases. The authors will review the state of the art and level of understanding of direct ion and electron beam fabrication and point out some of the unsolved problems.

/pdf/gas-assisted-focused-electron-beam-and-ion-beam-processing-2wl9i66zrn.pdf

Gas-assisted focused electron beam and ion beam processing and fabrication

The phase-shifting mask consists of a normal transmission mask that has been coated with a transparent layer patterned to ensure that the optical phases of nearest apertures are opposite. Destructive interference between waves from adjacent apertures cancels some diffraction effects and increases the spatial resolution with which such patterns can be projected. A simple theory predicts a near doubling of resolution for illumination with partial incoherence σ < 0.3, and substantial improvements in resolution for σ < 0.7. Initial results obtained with a phase-shifting mask patterned with typical device structures by electron-beam lithography and exposed using a Mann 4800 10× tool reveals a 40-percent increase in usuable resolution with some structures printed at a resolution of 1000 lines/mm. Phase-shifting mask structures can be used to facilitate proximity printing with larger gaps between mask and wafer. Theory indicates that the increase in resolution is accompanied by a minimal decrease in depth of focus. Thus the phase-shifting mask may be the most desirable device for enhancing optical lithography resolution in the VLSI/VHSIC era.

Improving resolution in photolithography with a phase-shifting mask

Nanoimprint is an emerging lithographic technology that promises high-throughput patterning of nanostructures. Based on the mechanical embossing principle, nanoimprint technique can achieve pattern resolutions beyond the limitations set by the light diffractions or beam scatterings in other conventional techniques. This article reviews the basic principles of nanoimprint technology and some of the recent progress in this field. It also explores a few alternative approaches that are related to nanoimprint as well as additive approaches for patterning polymer structures. Nanoimprint technology can not only create resist patterns as in lithography but can also imprint functional device structures in polymers. This property is exploited in several non-traditional microelectronic applications in the areas of photonics and biotechnology.

https://deepblue.lib.umich.edu/bitstream/handle/2027.42/48920/d4_11_r01.pdf?sequence=2

Recent progress in nanoimprint technology and its applications

Imprinting lithography is the most promising technology in terms of mass-production and low-cost of equipment, but thermal cycle above the glass transition temperature (more than 100/spl deg/C) will worsen positional accuracy in stitching and overlay of patterns. In this paper, we describe the imprinting process using liquid polymer, which is solidified with Ultra-violet (UV) light exposure.

https://iopscience.iop.org/article/10.1143/JJAP.39.7075/pdf

Imprinting characteristics by photo-induced solidification of liquid polymer

This paper details high time-resolution flow field measurements in a micro-pipe made by a micro digital holographic particle tracking velocimetry (micro-DHPTV) method. The system consists of an objective lens, a high-speed camera and a single high-frequency double pulsed laser. The volume of the system is 409.6 µm × 92 µm × 92 µm. It is illuminated by a laser beam with a pulse length of 58 ns, a resolution time of 100 µs and a repetition rate of 1 kHz. 104 velocity vectors could be obtained instantaneously in the micro-pipe. Particle positions in the three-dimensional field are reconstructed by a computer-generated hologram. The time evolution of a three-dimensional water flow in a micro-pipe of 92 µm inner diameter is obtained successfully using the micro-DHPTV system. The error of reconstruction in the z-direction is evaluated by analysing the traverse of particles on a glass plate and obtaining the velocity error in the z-direction by uncertainty analysis.

https://iopscience.iop.org/article/10.1088/0957-0233/17/7/002/pdf

Measurements of 3D flow in a micro-pipe via micro digital holographic particle tracking velocimetry

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.

https://iopscience.iop.org/article/10.1088/0957-4484/13/5/309/pdf

Diamond nanoimprint lithography

A micro digital-holographic particle-tracking velocimetry (micro-DHPTV) method for high time-resolution flow field measurement in a micro-channel is developed. The system consists of an objective lens, a high-speed camera and a single high-frequency double pulsed laser. Particle positions in a three-dimensional field can be reconstructed by a computer-generated hologram. The time evolution of a three-dimensional water flow in a semicircular micro-channel of 100-μm width and 40-μm depth is obtained successfully using this micro-DHPTV system. The three-dimensional measurement volume of the system is 410 × 100 × 40 μm3 and is irradiated by one laser beam with the time resolution of 100 μs and a reputation rate of 1 kHz. Consequently, 130 velocity vectors in the semicircular micro-channel can be obtained instantaneously. A significant aspect of this method is that even though both the laser and camera are located in line and perpendicular to the flow direction, velocity vectors can be obtained by reconstructing the particle positions via the computer hologram and the semicircular cross section shape of the micro-channel can be resolved.

Three-Dimensional Flow Tracking in a Micro Channel with High Time Resolution Using Micro Digital-Holographic Particle-Tracking Velocimetry

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.

https://iopscience.iop.org/article/10.1143/JJAP.41.4173/pdf

Jun Taniguchi

Papers

Imprinting characteristics by photo-induced solidification of liquid polymer

Measurements of 3D flow in a micro-pipe via micro digital holographic particle tracking velocimetry

Diamond nanoimprint lithography

Three-Dimensional Flow Tracking in a Micro Channel with High Time Resolution Using Micro Digital-Holographic Particle-Tracking Velocimetry

Uniformity in patterns imprinted using photo-curable liquid polymer