High Refractive Index Fluids Research Articles

Designing refractive index fluids using the Kramers-Kronig relations.

For a number of optical applications, it is advantageous to precisely tune the refractive index of a liquid. Here, we harness a well-established concept in optics for this purpose. The Kramers-Kronig relation provides a physical connection between the spectral variation of the (real) refractive index and the absorption coefficient. In particular, a sharp spectral variation of the absorption coefficient gives rise to either an enhancement or reduction of the refractive index in the spectral vicinity of this variation. By using bright commodity dyes that fulfil this absorption requirement, we demonstrate the use of the Kramers-Kronig relation to predictively obtain refractive index values in water solutions that are otherwise only attained with toxic specialised liquids.

Use of Optical Clearing Agents for Imaging Root Surfaces With Optical Coherence Tomography

The diagnosis of root caries and root fractures is of increasing importance due to our aging population. The objective of this study is to show that optical clearing agents can be used to increase the visibility of subsurface structures in tooth roots to aid in the diagnosis of root caries depth and extension and to differentiate from subsurface defects. Previous studies have shown that high refractive index fluids can increase the depth penetration of optical coherence tomography (OCT) for imaging caries lesions on tooth enamel. Extracted teeth with suspected root caries were imaged with (OCT) with and without the addition of water (W), glycerol (G), and propylene glycol (PG). The reflectance was monitored in sound and demineralized areas before and after application of W, G, and PG. The visibility of subsurface root canals was also measured before and after application of the respective fluids. In addition, shrinkage in lesion areas was measured after lesion dehydration to aid in the assessment of lesion activity. This study shows that optical clearing agents can be used to increase the performance of OCT for the diagnosis of root caries and other defects on root surfaces.

Use of an optical clearing agent to enhance the visibility of subsurface structures and lesions from tooth occlusal surfaces.

The purpose of this study is to show that optical clearing agents can be used to increase the visibility of deeply penetrating occlusal lesions that have reached the underlying dentin and spread laterally under the enamel. Previous studies have shown that high refractive index fluids can increase the contrast of caries lesions. Extracted teeth with natural occlusal lesions were imaged with optical coherence tomography (OCT) with and without the addition of a transparent vinyl polysiloxane impression material (VPS) currently used in vivo. The relative intensity of the reflectivity from the underlying lesion area for each sample was measured before and after application of the VPS. Lesion presence was confirmed with polarized light microscopy and microradiography. Application of VPS significantly increased (P < 0.0001) the integrated reflectivity of subsurface dentinal lesions. This study shows that optical clearing agents can be used to increase the optical penetration and the visibility of subsurface lesions and the dentinal–enamel junction under sound and demineralized enamel in OCT images.

Enhancing the detection of hidden occlusal caries lesions with OCT using high index liquids.

In a previous study, we investigated the influence of several high refractive index fluids on the performance of polarization sensitive optical coherence tomography (PS-OCT). That study showed that these liquids can increase the effective imaging depth and lesion contrast. Other in vitro and in vivo studies have shown that OCT can be used to show whether occlusal lesions have penetrated to the dentinal-enamel junction (DEJ) and spread laterally under the enamel. The purpose of this study was to determine if high index fluids can enhance the ability of OCT to detect hidden occlusal lesions and show if these lesions have penetrated through the enamel into the underlying dentin. Ten extracted teeth with occlusal lesions were imaged using OCT after the application of water, glycerol, BABB (33% Benzyl Alcohol + 67% Benzyl Benzoate) and a Cargille Liquid (Cedar Grove, NJ) (hydrogenated terphenyl 1-bromo-naphthalene) with a refractive index of 1.61. The intensity of the reflectance from the underlying lesion area for each sample was compared with the reflectance of the sound tooth surface for each fluid. The use of high index fluids significantly (P< 0.0001) increased the reflectivity of subsurface occlusal lesions under the surrounding sound enamel.

Projection lithography below lambda/7 through deep-ultraviolet evanescent optical imaging

An approach is presented to allow for imaging down to 26 nm using 193 nm projection reduction lithography together with evanescent wave optical effects at the imaging plane. The physical limitations of imaging imposed by the refractive indices of the materials were surpassed through the interference of evanescent waves at near fields. This has allowed for the imaging into photoresist of half-pitch resolution below lambda/7. A special situation where imaging at a system numerical aperture above the resist refractive index is discussed. Lithography results are shown using image media including air, water, and a high refractive index fluid together with a systematic gauge control to determine gap requirements and tolerances to achieve adequate image contrast into the resist. Gauging methods include both optical and mechanical approaches to achieve nanometer level gap control. It is found that gap depths as large as 50 nm can be tolerated using this approach, well beyond the levels associated with alternative high resolution approaches such as those using surface plasmons.

1117 光ファイバー型LDVセンサーによる高温・高屈折率流体の局所流速測定(GS-5 計測)

1117 光ファイバー型LDVセンサーによる高温・高屈折率流体の局所流速測定(GS-5 計測)

High Refractive Index Nanocomposite Fluids for Immersion Lithography

The concept of using dispersions of nanoparticles as high refractive index fluids in immersion lithography is examined both from a theoretical and experimental point of view. In the theoretical part we show that gelation and demixing can be controlled in high solid dispersions, needed to achieve a high (refractive) index, by using short stabilizing brushes. We considered both fluid-fluid demixing by using statistical thermodynamics and percolation, computed using liquid-state approaches. Whenever demixing or percolation takes place, the nanoparticle dispersion is unsuited for immersion lithography. The minimum thickness of the stabilizer layer of a stable suspension is estimated assuming particles plus steric stabilizer to act as hard spheres with van der Waals attraction between the cores. Since the van der Waals attraction can be related to the optical properties of the particles and dispersion medium, it is also possible to estimate the refractive index that can be attained with composite immersion fluids. Using materials that are known to be highly transparent in the bulk at a wavelength of 193 nm, indices above 1.8 can be attained. Other materials with higher indices are expected to be transparent at 193 nm due to a blue shift of the UV absorption and enable much higher indices. In the experiment, we show that it is possible to prepare suspensions with particles of about 4 nm diameter that increase the refractive index of the continuous phase with 0.2 at a wavelength of 193 nm. The refractive index and density of such dispersions are proportional to the volume fraction of the disperse phase, and it is shown that the refractive index of the composite fluid can be predicted very well from the optical properties of the components. Furthermore, successful imaging experiments were performed through a dispersion of silica nanoparticles. These findings lead to the conclusion that immersion lithography using nanoparticle dispersions is indeed possible.

A liquid waveguide based evanescent wave sensor integrated onto a microfluidic chip

An evanescent wave sensor based on liquid waveguide is integrated onto a microfluidic chip. The structure of the liquid waveguide consists of three streams with two low refractive index fluids as cladding layers, which envelop a high refractive index fluid as a core layer along a microchannel. Light is coupled into the core layer, and a detected sample is injected into one cladding layer. The profile of the output light modal power is changed by varying the concentration of the sample. The sensor with a sensitivity of 275μm2l∕mol can be used for real-time, low-cost, and label-free measurements in a wide range of applications.

Degradation of Hydrocarbon Fluids in the Immersion Lithography at 193nm

The search for successful generation 3 immersion lithography fluids is focused on high refractive index fluids which are transparent to 193 nm light. This search has led to saturated hydrocarbons which have been shown potential in this field. This paper discusses our observations that many immersion fluid candidates (saturated hydrocarbons and acetonitrile) were observed to polymerize upon irradiation with 193 nm light.

High Refractive Index Fluid Evaluations at 193nm: Fluid Lifetime and Fluid/Resist Interaction Studies

We report on recent studies on two of our leading fluid candidates for high index immersion lithography, designated IF132 and IF169. The most recent fluid radiation durability results are discussed, leading us to define two important parameters, the fluid lifetime factor and the clean window dose related to suppression of window contamination through use of active recycle technology. Results of fluid-resist interactions, with water and high index fluids on four commercial resists, will be shown. These experiments include PAG leaching and contact angle measurements, resist profile and thickness changes due to pre- and post-exposure fluid contact, residues and defects from the fluid and from resist contact, and 36 nm hp imaging on an immersion interference printer.

Advanced materials for 193 nm immersion lithography

AbstractRecently 193 nm immersion lithography is considered the most promising next generation technology which will enable a 45 nm and below node device to be manufactured. This will lead to not only depth of focus (DOF) enlargement, but immersion lithography enables the use of a hyper numerical aperture (NA) larger than 1.0 and achieve higher resolution capability. For 193 nm lithography, water is an ideal immersion fluid, providing suitable refractive index and transmission properties. Furthermore the higher refractive index fluid is expected to provide a potential extension of optical lithography to the 32 nm node. This paper describes the critical issues of the water immersion lithography process, such as photoresist component leaching into water, defectivity etc. Leaching materials were analyzed by liquid chromatography‐mass spectrometry (LC‐MS) and were found to be composed of the photoacid generator (PAG) and its decomposed chemicals. The leaching amount is in the order of 10−12 mol/cm2 with a normal 193 nm photoresist. An other issue to be studied is the water‐mark defect caused by small waters droplets left on the exposed wafer. These undesirable phenomenons could be prevented by applying a topcoat material onto the photoresist film. Material design for the topcoat material and its physical and lithographic properties are discussed in detail. Development of a high refractive index fluid is also discussed in this paper. A promising high refractive index fluid HIL‐001 was developed which has a higher refractive index (n = 1.64) than water and high transparency (98%/mm) at 193 nm wavelength. Immersion exposure experiments using high refractive index fluid with and without topcoat material was carried out and 32 nm L/S imaging capability was demonstrated by using a two‐beam interferometric exposure tool. Copyright © 2006 John Wiley &amp; Sons, Ltd.

A study of 193-nm immersion lithography using novel high refractive index fluids

In search for the next 193-nm immersion lithography fluid, research and development continue to focus on low absorbance fluids with a refractive index n higher than 1.6. In this paper, the properties of a newly developed high refractive index fluid of low absorption coefficient named ‘Delphi’ will be discussed. The refractive index of ‘Delphi’ at 193.39 nm was 1.63 and absorption coefficient was 0.08/cm as evaluated using a spectroscopic ellipsometer. Thirty two nanometer lines and spaces patterns imaging of excellent rectangular profiles were achieved with this fluid using a 193-nm two-beam interferometric exposure tool. The physical characteristics of ‘Delphi’ were also proven as feasible for application with possible future 193-nm high refractive index immersion lithography systems.

High Refractive Index Fluid for Next Generation ArF Immersion Lithography

ArF immersion lithography using a high-refractive-index fluid (HIF) is considered to be one of the most promising candidates for hp38nm or below. We have developed JSR HIL-001 and HIL-002 as new immersion fluids, the refractive index and transmittance of which are 1.64, >98%/mm and 1.65, >99%/mm (193.4nm, 23&deg:C), respectively. Using HIL-001 immersion and a two-beam interferometric exposure tool, hp30nm imaging has been demonstrated. However, despite the remarkable advances of recent HIF research, there is still a lot of issue about whether an organic fluid can be used in immersion lithography, since optical and photochemical behaviors of organic fluids at ArF wavelength have not been well understood so far. Besides, cost and disposal issues will be encountered when the organic immersion fluid is substituted for water. In this paper, we will address such problems by reporting our updated results on research of JSR HILs.

Optical Lithography for the 32nm Node

The 32nm lithography node is the next major target for optical lithography on the Semiconductor Industry Roadmap. The recently developed water-based immersion lithography using ArF illumination will be able to provide an optical solution for lithography at the 45nm node, but it cannot achieve the 32nm node as currently defined. EUV is the main solution for the 32nm node, but the evolution of immersion lithography does represent an opportunity to extend ArF lithography down to the 32nm node.This paper reports progress towards achieving 32nm lithography using immersion lithography. To achieve this next lithographic node will require new, very high refractive index fluids to replace the water used in current immersion systems.Testing and experiments to develop key technology for the 32nm node are reported. These experiments were run using interference immersion lithography.Interference imaging printers have been available for years, and with the advent of immersion lithography have a new use. Interference immersion image printing offers the user a rapid, cost-effective way to develop immersion lithography, particularly at extremely high resolutions. Although it can never replace classical lens-based lithography systems for semiconductor device production, it does offer a way to develop resist and fluid technology at a relatively low cost. Its simple, image-forming format offers easy access to the basic physics of advanced imaging. Issues such as: fluid/resist interaction during exposure; topcoat film performance; line edge roughness of resists at extremely high resolutions; and the polarization of the image-forming light rays can all be readily studied.Experiments are described and results are provided for work on: 32nm imaging tests; high refractive index fluid testing using ArF wavelength at resolutions well beyond current lens-based system capabilities; and polarization configuration testing on both 32nm and 45nm L/S features.