New gap detection method using two lasers optical heterodyne interference for X-ray lithography

A wet-silylated and dry-developed resist process for proximity X-ray and broad-band EUV (13-40nm) lithographies is investigated in order to overcome pattern collapse during wet development and to delineate finepitch and high-aspect-ratio patterns. In addition, the applicability to sub- 0.1-μm patterning is discussed. Imaging experiments for proximity X-ray lithography are performed using a synchrotron radiation (SR) light source from the beamline (BL-A1) at the SORTEC ring, and those for broad-band EUV lithography are performed using 32:1 reduction Schwarzschild optics illuminated with the SR light source from the beamline (BL-D2). The silylation solution consists of B[DMA]DS (bis(dimethylamino)dimethylsilane) or HMCTS (hexamethylcyclotrisilazane) as the silylating agent, MCA (methyl cellosolve acetate) as the diffusion promoter and a solvent xylene. Silylation characterization and determination of the optimum composition of the silylation solution have been performed using Fourier transform infrared spec roscopy (FTIR) measurement. Using the optimal wet-silylation and dry-developed resist system, 0.08-μm lines and spaces of a 0.5-μm-thick resist (aspect ratio=6) in proximity X-ray lithography, and 0.1-μm lines and spaces of a 0.55-μm-thick resist (aspect ratio=5.5) in broad-band EUVL can be successfully delineated. High resolutions of_??_0.1μm show that the silylation process for proximity X-ray and EUV lithographies is applicable to sub-0.1-μm lithography with a single-resist scheme.

Recent progress in synchrotron radiation lithography

Synchrotron radiation (SR)-based techniques provide unique capabilities to address scientific issues underpinning environmental remediation science and have emerged as major research tools in this field. The high intensity of SR sources and x-ray photon-in/photon-out detection allow noninvasive in-situ analysis of dilute, hydrated, and chemically/structurally complex natural samples. SR x-rays can be focused to beams of micron and sub-micron dimension, which allows the study of microstructures, chemical microgradients, and microenvironments such as in biofilms, pore spaces, and around plant roots, that may control the transformation of contaminants in the environment. The utilization of SR techniques in environmental remediation sciences is often frustrated, however, by an ''activation energy barrier'', which is associated with the need to become familiar with an array of data acquisition and analysis techniques, a new technical vocabulary, beam lines, experimental instrumentation, and user facility administrative procedures. Many investigators find it challenging to become sufficiently expert in all of these areas or to maintain their training as techniques evolve. Another challenge is the dearth of facilities for hard x-ray micro-spectroscopy, particularly in the 15 to 23 KeV range, which includes x-ray absorption edges of the priority DOE contaminants Sr, U, Np, Pu, and Tc. Prior to the current program, there were only two (heavily oversubscribed) microprobe facilities in the U.S. that could fully address this energy range (one at each of APS and NSLS); none existed in the Western U.S., in spite of the relatively large number of DOE laboratories in this region.

A new synchrotron radiation exposure station dedicated to deep-UV exposures has been installed at the synchrotron light source at the Center for Advanced Microstructures and Devices (CAMD). It complements the activities in synchrotron-based lithography including X-ray lithography, deep X-ray lithography, and under way, ultra-deep X-ray lithography. The UV station branches out of the X-ray lithography beamline. A retractable Si mirror reflects the incoming synchrotron radiation beam by 90 deg through a CaF<SUB>2</SUB> window. Three insertable bandpass filters allow the selection of broad-band transmission spectra around the wavelengths of two excimer lasers at 248 nm (KrF) and 193 nm (ArF), and at a shorter wavelength of 187 nm. The station allows for exposures under vacuum or in an inert gas atmosphere.

In the present study, we successfully obtained nonstaining blood flow images of a developing fish egg embryo using optical interference caused by the Doppler shift. The spectral distribution of light reflected by moving objects such as the heart and red cells was found to be different from that of the incident light because of the Doppler effect. Interference between different frequency components was observed in an interferogram through heterodyne interaction using an imaging-type two-dimensional Fourier spectroscopic system, and information on the intensities of the spectral components was obtained by Fourier transformation. Beat signals with specific frequencies due to the heart beating and blood flow of the fish egg embryo were detected. When the signals were plotted in two dimensions, the heart part and vessel flows were clearly visualized without staining. In addition, near-infrared (NIR) images were produced using absorbance spectra of the molecular vibrations of O-H and C-H groups included in water, hydrocarbons, and aliphatic compounds. Obtaining nonstaining blood flow images using heterodyne optical interference and images of molecular distribution using molecular vibrational information simultaneously manifests an exciting advance in NIR imaging.

ObjectiveTissue injuries caused by the thermal effects of xenon light microscopes have previously been reported. Due to this, the development of a safe microscope light source became a necessity. A newly developed laser light source is evaluated regarding its effectiveness and safety as an alternative to conventional xenon light source.MethodsWe developed and tested a new laser light source for surgical microscopes. Four experiments were conducted to compare xenon and laser lights: 1) visual luminance comparison, 2) luminous and light chromaticity measurements, 3) examination and analysis of visual fatigue, and 4) comparison of focal temperature elevation due to light source illumination using porcine muscle samples.ResultsResults revealed that the laser light could be used at a lower illumination value than the xenon light (p < 0.01). There was no significant difference in visual fatigue status between the laser light and the xenon light. The laser light was superior to the xenon light regarding luminous intensity and color chromaticity. The focal temperature elevation of the muscle samples was significantly higher when irradiated with xenon light in vitro than with laser light (p < 0.01).ConclusionThe newly developed laser light source is more efficient and safer than a conventional xenon light source. It lacks harmful ultraviolet waves, has a longer lifespan, a lower focal temperature than that of other light sources, a wide range of brightness and color production, and improved safety for the user’s vision. Further clinical trials are necessary to validate the impact of this new light source on the patient’s outcome and prognosis.

Preliminary experience of optical elements fabrication by X-ray lithography

Replicated pattern accuracy was investigated in synchrotron radiation (SR) lithography, using a chemically amplified (CA) negative-type resist and a highly accurate x-ray mask delineated by focused ion beams (FIB). The size of the hole resist pattern which is arranged in a lattice is affected by the proximity gap and the pattern pitch, but that of the dot resist pattern is hardly dependent on these variables. The dot resist pattern, which was replicated with the 0.25- micrometers -square hole mask pattern, became circular with a proximity gap of over 20 micrometers . In order to obtain highly accurate pattern shape as well as pattern size, the proximity gap should be less than 20 micrometers . The resist pattern size and shape depend on the exposure dose. This was confirmed through the simulation of Fresnel diffraction. The resist pattern was influenced considerably by the post-exposure baking (PEB) conditions, temperature and time. The PEB condition dependence of a replicated pattern was investigated. It is effective to extend the PEB time to improve the sensitivity without deforming the pattern shape.

In distributed microwave photonic (MWP) radar systems, the detection performance is highly sensitive to the quality of optical signals transmitted over the long fibers connecting the indoor and outdoor units. In this Letter, we propose an MWP radar system that, in addition to its standard range measurement capability, integrates optical frequency domain reflectometry (OFDR) for distributed vibration sensing along the optical fibers. A carrier-suppressed double-sideband (CS-DSB) optical signal is generated in the indoor unit, which serves as a light source and the local reference for the OFDR, as well as a transmitted signal for the radar transmitter. For radar detection, an echo received from an antenna is sent back to the indoor unit, where it is mixed with the local reference to perform de-chirping. For OFDR, a beat signal is produced by the coherent interference of the backscattered Rayleigh signal with the local reference, which realizes distributed optical fiber sensing. The dual functions of the system are evaluated by an experiment. For range measurement, a resolution of 4.8 cm at a transmitted bandwidth of 4 GHz is obtained. For distributed sensing, a reflection point detection with a resolution of 6.7 cm and a vibration measurement with a spatial resolution of 6 m at a vibration frequency of 4 kHz are demonstrated. The experiment also verified that utilizing OFDR to determine the vibration frequency, its impact on radar detection performance can be mitigated through digital signal processing.

We experimentally demonstrate simulation of two entangled quantum bits using classical fields of two frequencies and two polarizations. Multiplication of optical heterodyne beat signals from two spatially separated regions simulates coincidence detection of two particles. The product signal so obtained contains several frequency components, one of which can be selected by bandpass frequency filtering. The bandpassed signal contains two indistinguishable, interfering contributions, permitting simulation of four polarization-entangled Bell-like states. These classical field methods may be useful in small scale simulations of quantum logic operations that require multiparticle entanglement without collapse.

Optical manifestations of the Aharonov-Bohm effect by ion interferometry

In recent years X-ray synchrotron radiation and pulsed neutron radiation have been used in the study of organic crystal systems. In this paper we shall describe one such study with X-rays (cimetidine) and two studies with neutrons (fullerene and 4-methyl pyridine oxide). All three studies were carried out on powdered samples and gave results which demonstrate the power of high-resolution instruments in solving structural problems in organic crystal chemistry.

Generation of optical pulses at repetition rates in 10s-100s GHz range beyond the limits of conventional electronics can be achieved using all optical passive techniques. Here, we report a 60 GHz soliton pulse source utilizing all optical fibre technology. The principle of operation is based on the use of dual frequency beating as a source of periodic optical signal and the transformation of the beat half-periods into optical pulses using nonlinear propagation in a novel optical fibre design which we call a Comblike Dispersion Profiled Fibre (CDPF). This fibre consists of many alternating segments of two fibre types with high anomalous dispersion and minimum absolute dispersion at the operational wavelength. In fact, the dispersion-length profile of this fibre has a comb-like shape. Previously, transformation of the optical beat signal into pulse train was demonstrated in a Dispersion Decreasing Fibre (DDF) [1]. However, the implementation of CDPF has a number of advantages: CDPF can provide significant suppression of Stimulated Brillouin Scattering (SBS) enabling the use of a narrow linewidth, low phase noise beat signal; it can provide pulse train generation over a much wider range of repetition rates and a reduction of the necessary input power; and a CDPF can be accurately produced with in advance determined properties using conventional standard types of optical fibres - Standard Telecommunication (STF) and Dispersion Shifted Fibres (DSF) and thus does not require any special technology.

This paper reports the results of analyzing the proximity effect on the patterning characteristics for plural neighboring hole patterns in synchrotron radiation lithography. Fresnel diffraction simulation was used and pattern replication experiments were performed with pattern pitch, proximity gap, and mask contrast as parameters. Even when the pattern pitch (hole:space) is 1:1, pattern sizes down to 0.2 µ m can be replicated with a large dose margin under a large proximity gap condition up to 40 µ m, irrespective of the mask contrast. A low-contrast (2.5) mask has an advantage over the conventional-contrast (7) mask in that it allows the use of a larger proximity gap when replicating hole patterns with a size of 0.1–0.2 µ m. Moreover, the phase-shifting mask we previously proposed improves the exposure latitude and widens the proximity gap, so that it is possible to use a 20-µ m gap to replicate 0.1-µ m hole patterns for a pitch of 1:1 and to use a 30-µ m gap for a pitch of 1:2.

Interference caused by the multiple optical carriers in the broadband passive optical network (BPON) is reduced. This is achieved by modulating each multilongitudinal-mode laser diode with a strong sine wave to broaden optical spectral width. The results show that optical interference can be reduced to be minor, even when the optical spectra of all laser diodes overlap. Thus, the number of the optical carriers in the BPON system can be greatly extended. © 1997 John Wiley & Sons, Inc. Microwave Opt Technol Lett 14: 255–258, 1997.