Hoyoung Kang

Genomic blueprint of Hahella chejuensis, a marine microbe producing an algicidal agent

Harmful algal blooms, caused by rapid growth and accumulation of certain microalgae in the ocean, pose considerable impacts on marine environments, aquatic industries and even public health. Here, we present the 7.2-megabase genome of the marine bacterium Hahella chejuensis including genes responsible for the biosynthesis of a pigment which has the lytic activity against a red-tide dinoflagellate. H.chejuensis is the first sequenced species in the Oceanospiralles clade, and sequence analysis revealed its distant relationship to the Pseudomonas group. The genome was well equipped with genes for basic metabolic capabilities and contained a large number of genes involved in regulation or transport as well as with characteristics as a marine heterotroph. Sequence analysis also revealed a multitude of genes of functional equivalence or of possible foreign origin. Functions encoded in the genomic islands include biosynthesis of exopolysacchrides, toxins, polyketides or non-ribosomal peptides, iron utilization, motility, type III protein secretion and pigmentation. Molecular structure of the algicidal pigment, which was determined through LC-ESI-MS/MS and NMR analyses, indicated that it is prodigiosin. In conclusion, our work provides new insights into mitigating algal blooms in addition to genetic make-up, physiology, biotic interactions and biological roles in the community of a marine bacterium.

Fission yeast Dna2 is required for generation of the telomeric single-strand overhang

ABSTRACT It has been suggested that the Schizosaccharomyces pombe Rad50 (Rad50-Rad32-Nbs1) complex is required for the resection of the C-rich strand at telomere ends in taz1-d cells. However, the nuclease-deficient Rad32-D25A mutant can still resect the C-rich strand, suggesting the existence of a nuclease that resects the C-rich strand. Here, we demonstrate that a taz1-d dna2-2C double mutant lost the G-rich overhang at a semipermissive temperature. The amount of G-rich overhang in S phase in the dna2-C2 mutant was lower than that in wild-type cells at the semipermissive temperature. Dna2 bound to telomere DNA in a chromatin immunoprecipitation assay. Moreover, telomere length decreased with each generation after shift of the dna2-2C mutant to the semipermissive temperature. These results suggest that Dna2 is involved in the generation of G-rich overhangs in both wild-type cells and taz1-d cells. The dna2-C2 mutant was not gamma ray sensitive at the semipermissive temperature, suggesting that the ability to process double-strand break (DSB) ends was not affected in the dna2-C2 mutant. Our results reveal that DSB ends and telomere ends are processed by different mechanisms.

Measuring flare and its effect on process latitude

In this paper we report on the method of measuring the magnitude of scattered light, flare in a stepper lens and its effect on the overall process latitude. By measuring the required energy to clear large square patterns, it was possible to calculate the amount of scattered light in a lens system. When the size of a square pattern is larger than 10 micrometers , the magnitude of scattered light saturates to be independent on the size. But it gradually increases as the clear to dark area ratio of the mask increases. Simulation result shows that scattered light degrade the MTF of an aerial image and when it becomes larger than 2%, the process latitude start to decrease. Measuring scattered light with different mask opening ratio reveal that it exceed 2% when the mask opening ratio is around 70%. There was no significant difference in scattered light between different DUV scanner tools when the patterns were larger than 10 micrometers , but some difference was observed at the smaller patterns. Overall process latitude were measured with masks with different opening ratio. The exposure latitude decreased as mask opening ratio increase for positive photoresist, depth of focus was not significantly affected at increase of 20 to 50%. But we can observe 0.2 micrometers of focus margin decrease for mask open ratio change from 50 to 80% for both 260 and 240 nm patterns. So if we assume that there is no difference in process performances between positive and negative photoresists, using a negative photoresist will give more process latitude.

Titanium oxide film for the bottom antireflective layer in deep ultraviolet lithography

Titanium oxide thin film, fabricated with tetraisopropyltitanate and oxygen by electron cyclotron resonance-plasma-enhanced chemical vapor deposition, is investigated as a potential candidate for the antireflective layer in KrF excimer laser (248-nm) lithography. The oxygen flow-rate dependence of the optical properties such as the refractive index (n) and the extinction coefficient (k) of the film at the 248-nm wavelength has been characterized, and the films with the expected combinations of n and k values for the antireflective layer have been deposited. Simulation results indicate that reflectance values of less than 4% and as low as 1.2% can be reached at the interface between the photoresist and the film postulating the structures of the photoresist/300-A TiO(x) film/c-Si substrate and the W-Si substrate, respectively, by selected proper combinations of n and k values. Moreover the reflectance can be further reduced to almost zero by changing the film thickness. Thus it is found that titanium oxide thin films can be used as the bottom antireflective layer in KrF excimer laser lithography.

Pattern Displacement Error Under Off-Axis Illumination

Pattern displacement errors under off axis illumination (OAI) are investigated using multiple OAI settings and patterns which simulate a dynamic random access memory (DRAM) device situation. Pattern displacement errors of various systems were observed and aberration effects were simulated. The difficulty in correlating between pattern displacement errors and line width asymmetries is observed from measurement and analyzed with simulation. In order to avoid this problem, use of a larger pole size and grouping of machines which have similar pattern displacement errors are suggested.

Evaluation of phase-edge phase-shifting mask for sub-0.18-μm gate patterns in logic devices

The speed of logic device is mainly dependent on gate length. To achieve process margin (DOF, E/T, etc.) and minimize On Chip Variation (OCV) of logic gate with sub 0.18 mm design rule, the need for phase-edge PSM technology that has the advantages of minimum resolution and Critical Dimension (CD) control has been increased. In this paper, performance and feasibility of phase-edge PSM technology were investigated. Using phase-edge PSM and positive resist process at DUV wavelength ((lambda) equals 248 nm), the possibility of 0.10 micrometer logic gate patterning was confirmed and 0.18 micrometer gate lines with DOF larger than 1.0 micrometer and plus or minus 6% CD variation were obtained. And design rules for phase-edge layout generation were extracted. Then the possibility of layout generation by the extracted design rules and layout conversion tool was confirmed. Also, the feasibility of mask CD uniformity and phase uniformity, and alignment between phase-edge mask and normal chrome (Cr) mask was investigated and confirmed. Considering lithographic performance and process feasibility, phase-edge PSM technology is a very promising method for patterning sub 0.18 micrometer gate in logic devices.

New method of tilted illumination using grating mask: advanced tilted illumination on mask

A modified illumination method recently developed is known to improve resolution and depth of focus (DOF) dramatically. But, it requires substantial modification in the optical projection system and has some problems such as low throughput caused by low intensity and poor uniformity. To solve these problems, we developed a new illumination technique, named advanced tilted illumination on mask (ATOM) using phase grating which is the same, in principle, as quadrupole illumination but a very simple approach with little loss of intensity. In our experiments, we obtained the best resolution of 0.28 micrometers and 2.0 micrometers DOF for 0.36 micrometers feature size with an i-line stepper, which is two times as wide as that of a conventional illumination method. We also obtained 0.22 micrometers resolution and 2.0 micrometers DOF for 0.28 micrometers with an 0.45 NA KrF excimer laser stepper. For complex device patterns, a more than 1.5 times wider DOF could be obtained compared to the conventional illumination method. From these results, we conclude that second generation of 64 M DRAM with 0.30 micrometers design rule could be printed well with this technology combined with high NA (> 0.5) i-line steppers. With a KrF excimer laser stepper, a 256 M DRAM with a 0.25 micrometers design rule can be printed with the wide DOF.

Fluorinated silicon nitride film for the bottom antireflective layer in quarter micron optical lithography

Fluorinated silicon nitride thin film as a bottom antireflective layer (BARL) material, being suitable for line-patterning in KrF excimer laser (248 nm) lithography, has been studied by film fabrication/characterization and computer simulation. Three-dimensional reflectance simulation process suggests that the 0% reflectance between photoresist (PR) and BARL can be achieved by selecting proper combinations of film optical properties such as refractive index (n), extinction coefficient (k) and thickness (d). For the PR/300 A BARL/c-Si or PR/300 A BARL/W-Si structure at a wavelength of 248 nm, the simulation process reveals that nearly 0% reflectance could be obtained when the n and k values of the film are 2.109 and 0.68 or 2.052 and 0.592 respectively. The fluorinated silicon nitride films prepared by ICP enhanced CVD have been evaluated with the variations of flow rates under the two conditions of and 3:20 (sccm). The film n and k values at 248 nm vary in the ranges of 1.665 - 2.352 and 0.007 - 0.695 respectively, depending on gas flow ratio. As it is very sensitive to the film thickness, the reflectance could be reduced, using compoter simulation, to almost 0% by changing the film thickness. Furthermore, the ARL performance for line/space processed by the KrF excimer laser stepper and the stripping ability/selectivity show this material to be a superior candidate for deep-UV microlithography applications.

Optical proximity correction using a transmittance-controlled mask (TCM)

When small feature delineation is considered using existing exposure tools, special techniques might be needed such as phase shift mask, oblique illumination, top surface imaging, etc. When different types of patterns exist simultaneously or island patterns exist predominantly, optical proximity effect will become more important to be controlled. In this study, six different mask types were prepared and evaluated in view of a pattern fidelity and process latitude for 256 mega bit DRAMs storage node patterns. The masks used for this experiment were conventional transmission mask, serif patterned mask, square patterned Transmittance Controlled Mask (TCM), horizontally rectangular TCM, vertically rectangular TCM, and cross patterned TCM. The cross patterned TCM had three different transmittance on it and was evaluated also. In view of both pattern fidelity and process latitude, cross-TCM showed the best result. The vert-TCM also showed fairly good result. But the worst results always came from the conventional mask. From plane surface area point of view, once serif mask or TCMs are used, the areas always improved ranging from 120% to 145% at the best focus condition compared to the convention mask. There was not so much difference among three different transmittance in view of pattern fidelity and process latitude. As one of candidates for optical proximity correction, since small serif delineation on mask level is not easy for devices with small features such as 1 giga bit DRAM or beyond, TCM is more promising which has much bigger and easily writable gray area.

Lithography of 180-nm design rule for 1-Gb DRAM

Optical lithography is the most fundamental technology for the development of 1 Gbit DRAM device. As a current status, KrF lithography is a powerful candidate for 180 nm generation because of relatively high cost of ArF lithography and its untimely applicability to mass production. In this paper, we showed that the optimized OAI system with large quadrupole offset and small opening could improve the resolution and process margin in the photo process of 180 nm level DRAM devices. We also demonstrated what the effect of CD amplification factor ((alpha) ) was related to the mask CD control and resist tone under the optimized OAI system. The result shows that the combination of the optimized OAI system and positive tone resist can give rise to the reduction of (alpha) from 4.5 to almost 1 and provide a reasonable margin.