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Biodegradable polymers, such as poly(L-lactide) (PLLA), are very useful in many biomedical applications. However, their degradation by-products have been much of a concern as they are the sources of inflammatory reactions in the body. In this work, we suggest a novel composite system composed of PLLA and oligolactide-grafted magnesium hydroxide (Mg-OLA) that can overcome drawbacks caused by poor mechanical properties and inflammatory response of PLLA for biomedical applications. Mg-OLAs were synthesized by ring opening polymerization and the structure, morphology, pH change, thermal, and mechanical properties were analyzed using FTIR, SEM, pH meter, TGA, and UTM. In particular, the tensile strength and modulus of PLLA/Mg80-OLA20 (0–20 wt%) were higher than those of PLLA/magnesium hydroxide. The PLLA/Mg80-OLA20 composite was also very effective in neutralizing the acidic environment caused by the degradable by-product of the PLLA matrix. In vitro cell viability and the expression levels of COX-2 and IL-6 proteins in the PLLA composites were also evaluated. Cell viability increased to around 100% with increasing the amount of Mg80-OLA20 from 0 to 20 wt%. The expression levels of IL-6 and COX-2 were reduced dramatically when increasing the proportion of Mg80-OLA20 from 0 to 50 wt%. As a result, the incorporation of Mg-OLAs into the PLLA matrix could reinforce the mechanical properties as well as reduce the inflammatory response of the hybrid PLLA. Therefore, this hybrid composite system blending oligomer-grafted magnesium hydroxide in biodegradable polymers would be a promising strategy for avoiding current fatal problems in biomedical applications.

Specific biodegradable polymers having shape-memory properties through "polymer-blend" method are investigated and their shape-switching in body temperature (37 °C) is characterized. Poly(L-lactide-co-caprolactone) (PLCL) and poly(L-lactide-co-glycolide) (PLGA) are dissolved in chloroform and the films of several blending ratios of PLCL/PLGA are prepared by solvent casting. The shape-memory properties of films are also examined using dynamic mechanical analysis (DMA). Among the blending ratios, the PLCL50/PLGA50 film shows good performance of shape-fixity and shape-recovery based on glass transition temperature. It displays that the degree of shape recovery is 100% at 37 °C and the shape recovery proceeds within only 15 s. In vitro biocompatibility studies are shown to have good blood compatibility and cytocompatibility for the PLCL50/PLGA50 films. It is expected that this blended biodegradable polymer can be potentially used as a material for blood-contacting medical devices such as a self-expended vascular polymer stents and vascular closure devices in biomedical applications.

In active noise control filter, IIR filter structure which used for control filter assures the stability property. The stability characteristics of IIR filter structure is mainly determined by pole location of control filter within unit disc, so stable selection of the value of control filter coefficient is very important. In this paper, we proposed novel adaptive stabilized Filtered_U LMS algorithms with IIR filter structure which has better convergence speed and less computational burden than conventional FIR structures, for multi-channel active noise control with vehicle enclosure signal case. For better convergence speed in adaptive algorithms, fuzzy LMS algorithms where convergence coefficient computed by a fuzzy PI type controller was proposed.

In active noise control filter, IIR filter structure which used for control filter assures the stability property. The stability characteristics of IIR filter structure is mainly determined by pole location of ����������� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �

Water-droplet adhesiveness was freely controlled on a single platform of superhydrophobic anodized aluminum oxide (AAO) within the range from highly adhesive to self-cleanable. Changing the structure from nanopore to nanopillar arrays at the surface caused a dramatic increase in the receding angle and a decrease in the hysteresis of water contact angles. The presence of dead-end nanopores but not through nanoholes was recognized as one of the main causes of the adhesiveness of superhydrophobic surfaces. The adhesiveness-controllable superhydrophobic AAO can be an excellent platform on which to elucidate the physical nature of the wetting phenomenon related to the nanostructure and has promising potential in technological applications.

The self-assembly layer consisting of fusion protein is investigated in molecular-scale for the construction of bioelectronic device. Cytochrome b562 and green fluorescent protein were used as an electron acceptor and a sensitizer in the molecular layer by mimicking the photosynthesis. Self-assembled monolayer of fusion protein was formed on Au coated glass. The formation of fusion protein layer onto the Au substrate was observed by the surface plasmon resonance measurement. The surface of fusion protein layer was observed and analyzed by the scanning tunneling microscopy observation. For embodiment of the molecular electronic device, molecular arrays of fusion protein SA layer were formed by micro contact printing. Surface charge distribution of fusion protein SA layer was measured to confirm an electrical conductivity by electrostatic force microscopy observation.

Specific biodegradable polymers having shape-memory properties through "polymer-blend" method are investigated and their shape-switching in body temperature (37 °C) is characterized. Poly(L-lactide-co-caprolactone) (PLCL) and poly(L-lactide-co-glycolide) (PLGA) are dissolved in chloroform and the films of several blending ratios of PLCL/PLGA are prepared by solvent casting. The shape-memory properties of films are also examined using dynamic mechanical analysis (DMA). Among the blending ratios, the PLCL50/PLGA50 film shows good performance of shape-fixity and shape-recovery based on glass transition temperature. It displays that the degree of shape recovery is 100% at 37 °C and the shape recovery proceeds within only 15 s. In vitro biocompatibility studies are shown to have good blood compatibility and cytocompatibility for the PLCL50/PLGA50 films. It is expected that this blended biodegradable polymer can be potentially used as a material for blood-contacting medical devices such as a self-expended vascular polymer stents and vascular closure devices in biomedical applications.

As an oxidation resistant layer, silicon nitride film has been widely used in semiconductor processes. Normally, silicon nitride deposition induces strong tensile stress on the silicon wafer. This stress also contributes to the wafer warpage. In order to investigate the relationship between this phenomenon and electrical properties of device, we prepared silicon nitride coated wafers with different film thickness. After the silicon nitride deposition on both sides of wafers, we stripped full of the film or half of the film on the backside surface. For each and every wafer, the degree of warpage and the electrical characteristics were measured. In this paper, we reported the warpage trend according to the silicon nitride film thickness and to the area of nitride stripped backside surface. Besides, we observed breakdown voltage difference depending on the degree of warpage.

We discuss a duplicate repairing process for opaque repair by means of a Ga/sup +/ focussed ion beam (FIB) and a blue laser scanning on a MoSiON phase shift mask. We show the pattern fidelity and edge roughness on the wafer and photomask substrates. The aerial images and intensity profiles produced by the AIMS tool show the fine resolution capability. Although somewhat resolved, we must consider the specifications of CD control for next generation devices such as design rules of 0.15 /spl mu/m. We evaluate the printability of the half-tone phase shift mask with i-line and KrF steppers after defect repair. We also confirm the accuracy of edge repair, Ga+ deep implantation effects and the environmental stability of FIB and blue laser repair tools. Finally, we measure the topography of the repaired photomask by AFM and AIMS.

We estimated the process margins of various cell structures and process problems for full chip process under extremeresolution limit of exposure tool. Therefore, optimizing off axis illumination (OAI) condition for various structures obtainedthe fme pattern and wider process margin using simulation and experiment. From our experiment, we should use as highernumerical aperture (NA), smaller R and smaller r as possible to reduce critical dimension (CD) difference between denseand isolated patterns. Process margins are obtained more than 8% exposure latitude (EL) and 0.5 tin depth of focus (DOF)for each cell. However, we can consider using of attenuated phase shift mask (PSM) to improve the exposure and DOFmargin. We fmd that real full chip process induces the critical problems such as isolated line (I/L) and space (L'S) patternvariation due to lens aberration, partial coherence effect, mask error effect, and optical proximity effect. These effects playa role to determine the design rule of cell and periphery structures. In spite of good lens quality, variation of I/L and USpattern for various exposure conditions is almost 4Onm or more compared to line and space (L/S) pattern. These phenomenaare becoming the critical issue to fulfill the full chip process of l3Onm lithography. By optimizing mask error effect,isolated and dense pattern bias (ID bias), and OAI, we can achieve l3Onm technology with 248nm KrF lithography.KEYWORDS : KrF, Design rule, ID bias, OAI, Full chip process, High NA, Process margin

As the design rule of device shrinks below O.14j.tm, the higher resolution is required for real device application.With smaller feature size below 0. 14.tm, the lower coating thickness of resist is essential because of the patterncollapse issue at the high aspect ratio. However, the lower resist thickness induces the problem of etch selectivitydue to the limited etch resistance of resist. In this study, the method of electron beam stabilization has beenapplied for improving the etch selectivity ofresist patterns having an aspect ratio less than 3 : 1. With applying theelectron beam stabilization, the Deep-UV photoresists based on the chemical structures of Acetal (AS1O6) andEscap (UV82) types have been evaluated in the respect of etch selectivity as the functions of an electron beamdose and etch condition. The metal etch rate reductions of 20 percent and 26 percent have been occurred for theresists of Acetal and Escap type, respectively, at 2OOOtC/cm2. And the thermal and chemical properties werecharacterized before and after electron beam stabilization using DSC, TGA, and FT-JR. The cross-sectionalviews of resist pattern after electron beam processing were also investigated to know the chemical stability ofresist during the electron beam process. Based on the experimental results, the application possibility of electronbeam stabilization for real device fabrication below O.l4prn has been presented in this paper.Key Words : Electron Beam Stabilization, Deep-UV Photoresist, Acetal Type, Escap Type, Aspect Ratio

Photomask quality for the next generation processing such as DUV scanner lithography is critical, but there still are many problems. In this situation, we have to find some keys to solve these problems to accommodate the narrow scope of the process margin and the printing bias control on wafer, as well as coarse lithography margins. Currently, the CD uniformity of the patterned Cr, or PSM features including the repaired mask patterns, is about +/- 0.03um. In next generation photomask production, there are some fundamental difficulties to overcome as; Firstly, there is the inherent physical behavior of DUV laser on quartz substrate, and secondly, there are photomask, defects that invisible to blue laser inspection, but can still be portioned onto the wafer. In order to keep up with photomask product requirements, the next generation inspection systems are being developed with i-line and KrF laser sources. However, issues such as low-level transmission defects and critical line-widths defects have not been solved yet. In part, the Ga+ implantation defect is one of these invisible transmission defects due to the fact that the carried inspection tools use a blue laser, so it is not counted as killing defect of the DUV transmitted types. Although it is captured into a false defect, we have a difficult to classify by ion implantation defect. This paper discusses the process margins of FIB Ga+ ion scanning on the opaque repairing of damaged quartz substrate. It will show the effects of reduced intensity or using the Gas Assisted Etching process. And though it has been solved somewhat, we also have to consider the CD control specifications for the next generation device such as 1G DRAM with DUV lithography. In this experiment, we have evaluated the printability of 4X DUV scanner after both opaque and clear defect repair with a focused ion beam (FIB) system. We also confirmed the accuracy of edge repair, implantation effects of each FIB machine and determined the topography of repair by AFM.

This paper describes the phase shift mask (PSM) effects in view of production using i-line lithography. For the PSM technology, it was hard to control process because the process condition was limited by the exposure tool. To fabricate the 256MB DRAM with 0.25 micrometers minimum feature size (MFS), we evaluated the PSM including attenuated type for conventional patterns and a 0.25 micrometers cell array using positive and negative tone phase shift mask for actual process. Furthermore, we applied various approaches to get a sufficient depth of focus (DOF) and high resolution using an i-line system with 0.57 NA, an off-axis illumination system, low partial coherence factor, and process in cases of alternating, subresolution, and attenuated type of phase shift mask. As a result, even if pattern delineation was possible, we should optimize design, topology structure, and process to get enough DOF margin, good uniformity, and high repeatability for device fabrication.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Phase-shifting mask allows remarkable improvement of the resolution and depth of focus than is possible with conventional mask. In this paper, we examine the optimum coherence factor ((sigma) ) and numerical aperture (NA) by considering the process margins of conventional and alternating shifter L&S patterns on high NA i-line stepper and next we investigate the possibility to apply this optimum parameter in real devices of 0.25 micrometers - 0.35 micrometers design rules. We evaluate the process window, line and space duty ratio, CD difference by proximity effect, illumination uniformity, and neighboring linewidth variation with experimental and simulations including resist profile as well as aerial image. In this experiment, we obtained the DOF of 2.0 micrometers for 0.25 micrometers alternating shifter L&S with an optimum coherence factor on high NA i-line stepper and we can conclude that 256 Mb DRAM with 0.25 micrometers design rule could be printed with large DOF.

As the design rule of devices continues to shrink, the overlay margin of layer to layer continues to become smaller. Inter-field error of overlay can be compensated by alignment parameters of the exposure system, but intra-field error of overlay is very difficult to change within a field. This paper discusses the intra-field overlay error, especially that caused by oxidation and deposition processes of a metal-oxide-silicon (MOS) integrated circuit device. In an experiment, to analyze process induced affects on the intra-field overlay error of device, we monitored thermal process, film deposition, oxidation, lithography, etching, and implantation process and pursued the trend and sources of intra-field overlay error generated in wafer process. We analyzed the affects of film stress and thermal process by measuring box and box overlay marks using the KLA metrology system at the etch process step.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Single level dry developable resist process based on gas phase silylation has great promise for sub-halfmicron pattern imaging due to shallow exposure, which leads to a thin silicon incorporation layer during silylation process in the top exposed region. In this paper the influence of process key parameters on the lithographic performance characterization has been investigated. For this experiment, two kinds of commercial i-line photoresists based upon novolac-diazoquinone and tetramethyldisilazane as a silylation agent were used for analyzing the process properties. As a result, it was observed that the ultimate resolution of 0.30 micrometers with vertical profiles, projected with an i-line of 0.54 NA lens, was obtained. However, it was found that CD linearity characteristics strongly depend on the compositions and the structure of photoresist, independent of other process parameters. Selectivity of dry development with a range of 13 - 15 was achieved using the oxygen/argon mixtures at 5 mTorr with MERIE. Major factors affect on the resist pattern profile were proven to be dry development parameters as well as the latent image formation of silylation. In particular, lower power and higher magnetic field conditions at low pressure allowed a good resist pattern profile without sidewall roughness and residues. And effects of silylation parameters on process latitudes has also been studied by comparing resolution capability, DOF, and exposure latitude, respectively.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Phase shift mask ( PSM ) is a useful technique to higher the resolution and focus margin in the lithography process with sub-half micron range, which is limited by currently used process tools. PSM with i-line stepper is one of the leading candidates for mass production of 64M Bit Dram. In this study, in order to obtain the information about the basic trend and process limitation of PSM, we evaluated the PSM technique by simulation and lithographic experiment. However several difficulties were encountered when attempting to use the PSM in real process. These difficulties were mainly due to the process margin and variation in munufacturing a real device. We simulated PSM by changing numerical aperture, patial coherence, focus, and pattern size for g-line and i-line. Intensity profiles of patterns were monitored for both conventional and phase shift mask ( alternating t>ye ). With those simulation results, we first analyzed the aerial image and studied the trend and limitation of PSM technology. Then we compared these results with experimental results of g-line and i-line process. Although the simulation and the experimental results showed that definable resolution limit and the resolution with depth of focus ( DOF ) margin were significantly increased by PSM technology, it was hard to control the process due to the errors occuring in manufacturing PSM. The study for resolution limit with marginal depth of focus led us to optimize the method how to approach the PSM from simulation. In addition, the process limitation and lithographic trend of PSM were investigated as well.