KEYWORDS: Optical coherence tomography, Fiber optics, Polarization, Phase modulation, Calibration, Mirrors, In vivo imaging, Birefringence, Signal to noise ratio, Interferometers
A swept source (SS)-based circular-state (CS) polarization-sensitive optical coherence tomography (PS-OCT) constructed entirely with polarization-maintaining fiber optics components is proposed with the experimental verification. By means of the proposed calibration scheme, bulk quarter-wave plates can be replaced by fiber optics polarization controllers to, therefore, realize an all-fiber optics CS SSPS-OCT. We also present a numerical dispersion compensation method, which can not only enhance the axial resolution, but also improve the signal-to-noise ratio of the images. We demonstrate that this compact and portable CS SSPS-OCT system with an accuracy comparable to bulk optics systems requires less stringent lens alignment and can possibly serve as a technology to realize PS-OCT instrument for clinical applications (e.g., endoscopy). The largest deviations in the phase retardation (PR) and fast-axis (FA) angle due to sample probe in the linear scanning and a rotation angle smaller than 65 deg were of the same order as those in stationary probe setups. The influence of fiber bending on the measured PR and FA is also investigated. The largest deviations of the PR were 3.5 deg and the measured FA change by ∼12 to 21 deg. Finally, in vivo imaging of the human fingertip and nail was successfully demonstrated with a linear scanning probe.
Design rules and the design rule check (DRC) utility are conventional approaches to design for manufacturability
(DFM). The DRC utility is based on unsophisticated rules to check the design layout in a simple environment. As the
design dimension shrinks drastically, the introduction of a more powerful DFM utility with model-based layout
patterning check (LPC) becomes mandatory for designers to filter process weak-points before taping out layouts. In this
paper, a system of integrated hotspot scores consisting of three lithography sensitive indexes is proposed to assist
designers to circumvent risky layout patterns in lithography. With the hotspot fixing guideline and the hotspot severity
classification deduced from the scoring system provided in this paper, designers can deliver much more manufacturable
designs.
Accurate simulation of today's devices needs to account for real device geometry
complexities after the lithography and etching processes, especially when the channel
length shrinks to 65-nm and below. The device performance is believed to be quite
different from what designers expect in the conventional IC design flow. The
traditional design lacks consideration of the photolithography effects and pattern
geometrical operations from the manufacturing side. In to order obtain more accurate
prediction on circuits, an efficient approach to estimate nonrectangular MOSFET
devices is proposed. In addition, an electrical hotspot criterion is also proposed to
investigate and verify the manufacturability of devices during patterning processes.
This electrical rule criterion will be performed after the regular Design Rule Check
(DRC) or Design for Manufacturing (DFM) rule check. Photolithography and
industrial-strength SPICE model are taken into consideration to further correlate the
process variation. As a result, the correlation between process-windows and driving
current variation of devices will be discussed explicitly in this paper.
Atherosclerosis is unquestionably the leading cause of morbidity and mortality in developed countries. In the mean time, the worldwide importance of acute vascular syndromes is increasing. Because collagen fiber is a critical component of atherosclerotic lesions; it constitutes up to 60% of the total atherosclerotic plaque protein. The uncontrolled collagen accumulation leads to arterial stenosis, whereas excessive collagen breakdown weakens plaques thereby making them prone to rupture finally. Thus, in this study, we present the first application, to our knowledge, of using polarization-sensitive optical coherence tomography (PS-OCT) in human atherosclerosis. We demonstrate this technique for imaging of intensity, birefringence, and fast-axis orientation simultaneously in atherosclerotic plaques. This in vitro study suggests that the birefringence change in plaque is due to the prominent deposition of collagen according to the correlation of PS-OCT images with histological counterpart. Moreover, we can acquire quantitative criteria based on the change of polarization of incident beam to estimate whether the collagen synthesized is "too much" or "not enough". Thus by combining of high resolution intensity imaging and birefringence detection makes PS-OCT could be a potentially powerful tool for early assessment of atherosclerosis appearance and the prediction of plaque rupture in clinic.
MBE growth of high quality diluted Nitride materials have been investigated. Photoluminescence intensity of high nitrogen content InGaAsN/GaAs SQW can be improved significantly by decreasing the growth temperature due to suppressd phase separation of InGaAsN alloy. The longest room temperature PL peak wavelength obtained in this study is 1.59 μm by increasing the nitrogen composition up to 5.3%. High performance ridge-waveguide InGaAsN/GaAs single quantum well lasers at wavelength 1.3 μm have been demonstrated. Threshold current density of 0.57 KA/cm2 was achieved for the lasers with a 3-μm ridge width and a 2-mm cavity length. Slope efficiencies of 0.67 W/A was obtained with 1 mm cavity length. The cw kink-free output power of wavelength 1.3 μm single lateral mode laser is more than 200 mW, and the maximum total wallplug efficiency of 29% was obtained. Furthermore, monolithic MBE-grown vertical cavity surface emitting lasers (VCSELs) on GaAs substrate with an active region based on InGaAsN/GaAs double quantum wells emitting at 1304 nm with record threshold current density below 2 KA/cm2 also have been demonstrated. The CW output power exceeds 1 mW with an initial slope efficiency of 0.15 W/A. Such low threshold current density indicates the high quality of InGaAsN/GaAs QW active region.
We report our results on InGaNAs/GaAs vertical-cavity surface-emitting lasers (VCSELs) for fiber-optic applications in the 1.3 μm range. The epitaxial structures were grown on (100) GaAs substrates by MBE or MOCVD. The nitrogen composition of the InGaNAs/GaAs quantum-well (QW) active region is 0 to 0.02. Long-wavelength (up to 1.3 μm) room-temperature continuous-wave (RT CW) lasing operation was achieved for MBE and MOCVD-grown VCELs. For MOCVD-grown devices with n- and p-doped distributed Bragg reflectors (DBRs), a maximum optical output power of 0.74 mW was measured for In0.36Ga0.64N0.006As0.994/GaAs VCSELs. The MBE-grown devices were made with intracavity structure. Top-emitting multi-mode 1.3 μm In0.35Ga0.65N0.02As0.98/GaAs VCSELs with 1mW output power have been achieved under RT CW operation. Emission characteristics of InGaNAs/GaAs VCSELs were measured and analyzed.
The ripple patterns induced by the lithography process will lead to unpredictable necking or bridging risks on circuit patterns. This phenomenon is particularly severe while using the attenuated-phase-shifting mask combined with the strong off-axis illumination. The CD variation induced by the ripple effect is difficult to be accurately corrected by conventional OPC approaches. In this paper, ripples on patterning for the 65nm node have been studied and their problems solved. One of the dominant root causes of ripples is the optical side-lobes from the surrounding patterns. On the L-shape patterns for example, the ripples that occur on the horizontal lines are induced by the side-lobes of the vertical lines. Based on this study of the ripple effect, the layout types resulting in ripple patterns can be classified and predicted. An advanced OPC approach by the segmentation analysis on polygons as well as the correction algorithm optimization has been developed and applied to solve this ripple problem.
A simple graphic analysis technique named the illumination chart method is introduced to aid the customization of the illumination aperture filter for synergistic combination with a high transmission rim-type attenuated phase-shifting mask (PSM) for deep submicron contact hole printing. This graphic method gives direct visualization of the relationship between the interference condition in the pupil and the incident angle of illumination. The working ranges of oblique illuminations with different numbers of diffraction beams taking part in imaging can be easily clarified by this graphic method, which explains the dependence of depth of focus (DOF) on pattern duty. A customized illumination aperture filter (CIF) is synthesized by collecting the effective source elements for every pattern pitch to remedy the inability of the attenuated PSM for dense patterns. To preserve the merits of off-axis illumination to dense patterns and on-axis illuminations to sparse patterns in a single exposure, the illumination chart suggests a zeroth-order-reduction mask design for dense hole pattern. We applied this integrated resolution enhancement technique to 0.17 μm contact hole printing in 248 nm wavelength, 0.55 numerical aperture optics. The experimental results show our CIF illumination not only balances the DOF enhancement throughout the pattern pitches but also suppresses the best focus shift due to spherical aberration.
A newly installed molecular beam epitaxy system has been used to grow GaN epifilms on c-sapphire. Initial efforts are on the nitridation and the low-temperature buffer layer growth. Considerable nitridation with a high V/III flux ratio results in pure near-bandgap (NBG) transition without the usual yellow emission in photoluminescence spectra. Spotty reflection high-energy electron diffraction patterns and field emission scanning electron microscopy show that the surface is rough. No or less nitridation with a lower V/III flux ratio gives a streaky reflection high-energy electron diffraction patterns and a smooth surface. Photoluminescence measurements yield a narrower NBG emission with certain yellow emission. The images of transmission electron microscopy ensure the thickness of the low temperature GaN buffer layer to be around 200 Angstroms, and the diffraction patterns indicate increasing better quality of the GaN epifilm away from the buffer layer and a single crystal near the surface. Both van der Pauw and capacitance-voltage measurements reveal that the undoped GaN epilayers are natively n-type. X-ray diffraction in (theta) /2(theta) mode is performed, which gives a sharp GaN (0002) peak with a full-width-at-half-maximum of 150 arcsec. Other details on the growth and characterizations are discussed.
Several super resolution techniques, such as phase-shifting mask (PSM) and off-axis illumination (OAI), have been reported to extend the resolution limit and increase the depth-of-focus (DOF) of optical lithography. However, these techniques provide less immunity to spherical aberration than the conventional approaches like chrome binary mask and low coherent illumination. Best focus position shift is the most well known anomalous phenomenon resulted from spherical aberration. In this paper, the origin of best focus shift is explained in pictorial and analytical forms. The phenomenon is evaluated by observing the exposure-defocus windows of sub-0.2micrometers hole patterns from an 18% transmission rim-type attenuated PSM combined with several types of illumination. Under high coherent illumination, severe focus shift was observed in sparse patterns as strong phase-shifting effect is applied. For dense hole patterns, OAI results in abrupt focus position variation at specific pattern pitch. The experimental results show that spherical aberration would induce best focus shift, distortion of process windows, loss of DOF, and shrinkage of iso/dense process window overlap. Two approaches were proposed to suppress the impact of spherical aberration. One is introducing proper amount of phase bias in attenuated PSM to adjust the wave aberration in the lens. The other more feasible method is using a customized illumination. A synthesized illumination aperture was proposed to compensate the focus shift. Excellent lithographic performance was obtained in the experiment from this method.
High NA illumination system and off-axis illumination (OAI) have been shown as two of the most practical resolution enhancement techniques (RET) available for micro-lithography. However, these two illumination approaches may reduce the DOF of iso-patterns. To overcome this problem, scattering bar (SB) assignment has been wildly used. In this paper, the discussions are focused on SB variables of iso-features. The most important variable of SB usage is where is the suitable assignment position. A simply efficient rule has been found to easily catch the optimal position of SB assignment. For OAI illumination, the optimal SB position is exactly the same with the defocus side-lobe position of iso-line. The effect of the secondary pair of SB is also discussed in this paper, and it is found that if the secondary SB pair was not at the optimal position, the process window would be reduced. Another major topic in this paper is the specification of SB width. Here we design a test pattern to target the specification of SB width. The experimental results might give us a clear specification of SB width.
A great deal of progress has been made in the design of dual damascene process, including via first, trench first, and self-aligned. For overlay, via-first process provides the largest process tolerance to misalignment. However, the positive tone resist face to some difficulties in dual damascene via first approach of photo process, because the 0.18micrometers positive tone trench resist can not be exposed and removed in the 0.20micrometers via hole, observed residues from the SEM cross section profiles after development. In contrast, the negative tone resist show s great advantage in the via first process and producing desired patterns without resist residues in the via hole. In this paper, the design of dual damascene photo process using commercial N702Y (JSR) negative tone resist on DUV43 (Brewer Sc.) Bottom anti reflective coating is evaluated. To improve the depth of focus (DOF) of negative tone resist process, the different resolution enhancement techniques (RET) are investigated fro dense and isolated trench patterns: off-axis illumination (annular ½), attenuated phase shift mask (halftone 6%) with 248nm (NA 0.55) exposure technology, and experimental results regarding to its process performance are presented.
Heterocyclic aromatic polymer poly(p- phenylenebenzobisthiazole), PBT, is a rigid-rod polymer having a fully conjugated backbone as well as excellent dimensional, thermo-oxidative, and solvent stabilities. A PBT polymer with intrinsic viscosity of 18.0 dL/g was dissolved in methanesulfonic acid or Lewis acid. The PBT solution was spin- coated, doctor-bladed or extruded for freestanding films or onto an indium-tin-oxide (ITO) substrate. The acid was removed via coagulation resulted in PBT films of about 80 nm in thickness on the ITO substrate as determined by scanning electron microscopy. X-ray scattering demonstrated that the extruded freestanding films were uniaxial while the others were isotropic without long-range order. Both temperature and excitation power dependences of the photoluminescence measurements were performed. The laser excitation power dependence of the emission intensity is fitted well with a bimolecular recombination model. Light-emitting devices were fabricated with a structure of Al(Mg)/PBT/ITO/glass, and gave out green-yellow light. A threshold voltage as low as 1 V was achieved. Electroluminescence spectra showed a blue-shift with increasing voltage, which is ascribed to the band-filling effect. Vibrational structure emerged in the photoluminescence spectra at low temperatures, and was observed in the electroluminescence spectra at high voltages, which gives a vibrational mode spacing of 186 meV for the lowest levels.
A completely new concept for designing the illumination aperture filter is suggested. From experimental or simulative methods, we have extracted the performance of every individual beam component on the illumination plane. The optimal apertures are then obtained by superimposing the best components that meet the requirements demanded by the specific photo process. Different kinds of optimal apertures were successfully implanted to deal with different process problems. Therefore, it is called the customized illumination aperture filter (CIF). The zero 1D OPE CIF, as a proof of concept, was designed to eliminate the OPE of low k1 process. Without any OPC, 0.6micrometers DOF of the common ED window was obtained, where k1 equals 0.39 for our NA equals 0.55 stepper to print. 0.18 micrometers line patterns, T push to smaller k1, another CIF was designed to maximize the individual DOF and overcome the reduced power problem accompanied with the typical aggressive OAI. Using this CIF, we achieved 1.1 micrometers common DOF with 7 percent EL for 0.18 micrometers lien patterns. The CIF doubles the power of the Nikon's strong quadrupole, shrine. An ultimate resolution limit of 0.11 micrometers line pattern was reached as well with the CIF. Finally, a contact/via CIF was designed combined with a halt-tone PSM. The CIF gives about 0.8 micrometers common DOF with 7 percent EL for 0.2 micrometers holes and 0.7 micrometers DOF for 0.17 holes using thinner resist. The CIF approach is, therefore, proven to be a cost effective and relatively easy realizable alternative to the alternating PSM for extremely low k1 process applications.
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