Evaluation of an optical particle sensor to determine the effect of nozzle shape on counting efficiency

The optical particle sensor (OPS), using light scattering from particles, is widely used in clean-rooms and in atmospheric environmental monitoring. However, parameters that affect the particle counting of the OPS have been less explored previously. The present study examines the effect of the nozzle shape on particle counting performance of the OPS. Experiments and simulation studies were carried out for four different nozzle shapes in conjunction with three different particle sizes. The effect of nozzle shape is evaluated not only by experiments analyzing the intensity of scattered light and particle velocity but also by simulation. Fluent was used to simulate the flow field and particle trajectories. We observed that particle velocity and trajectory are strongly dependent on the input nozzle shape, which in turn has an effect on the particle counting performance. Using these results, the design of OPS can be optimized to provide higher counting efficiency.     

Nano-scale stick-slip friction model for the chatter scratch generated by chemical mechanical polishing process

Although Chemical Mechanical Planarization (CMP) process is a still promising technology for the fabrication of the next generation devices, CMP-induced defects tackle further development of CMP process. In particular, even nano-sized scratches generated by CMP process kill the device directly. However mechanism of scratch formation was not clearly understood yet. CMP-induced scratches are classified as razor, chatter mark and skipping scratch. Among them, chatter mark scratch (or chatter scratch) is the most critical defect for the device yield loss. Chatter scratch has a periodic pattern of scars, which is reminiscent of a stick-slip friction pattern. Based on that similarity, stick-slip model was proposed in this paper in order to explain how chatter scratch is formed. And controlling parameters for chatter scratch are defined. During stick period the friction force that exceeds the yield strength of wafer surface makes chatter scratch and the distance between chatter marks is determined by slip period.     

Removal of Nano-sized Particles Using Carbon Dioxide (CO2) Gas Cluster Cleaning without Pattern Damage

As pattern size of semiconductor device becomes less than 20 nm, the removal of particles smaller than 10 nm without pattern damages requires new physical dry cleaning technology. CO₂ gas cluster cleaning is an alternative dry cleaning process to meet these cleaning requirements. To demonstrate gas cluster cleaning performance, particle removal efficiency (PRE) and gate structure pattern damages were evaluated. When pressurized and low temperature CO₂ gas was passed through a convergence–divergence (C–D) nozzle, high energy CO₂ gas clusters were generated at high speed in a vacuum atmosphere. The cleaning force of the CO₂ gas cluster is related to the flow rate of the CO₂ gas. The optimum CO₂ gas flow rate for the particle removal without pattern damage was found to be 6 L/min (LPM). Removal efficiency for 50 nm silica particles was greater than 90%, and no pattern damage was observed on 60 nm poly-Si and a-Si gate line patterns. It was confirmed that the CO₂ gas cluster cleaning force could be controlled by the CO₂ gas flow rate supplied to nozzle.     

Formation of large ordered domains in benzenethiol self-assembled monolayers on Au(1 1 1) observed by scanning tunneling microscopy

Benzenethiol (BT) self-assembled monolayers (SAMs) on Au(1 1 1) were prepared as a function of solution temperature after immersion in a 1 mM ethanol solution for 1 day. The surface structures of BT SAMs were examined by means of scanning tunneling microscopy (STM). Although BT molecules usually form disordered SAMs containing the Au adatom islands at room temperature, we found that they formed two-dimensional ordered SAMs containing a large size domain at a high solution temperature of 50 or 75 °C. High-resolution STM imaging revealed that BT SAMs on Au(1 1 1) formed at 50 °C have a (2×3√2)R23° packing structure. From our STM study, we revealed that two-dimensional ordered BT SAMs on Au(1 1 1) can be obtained by changing the solution temperature.     

Analysis of response‐time compensation for black‐frame insertion

Abstract— An impulsive driving technique has been widely adopted for the elimination of motion blur in LCDs. Although the problem of slow temporal response time is very well known for LCDs, the inherent motion blur of moving objects in hold‐type displays has a more‐serious impact on display performance. It is well known that even very fast LCDs with zero response time still suffer from the motion‐blur artifact due to hold‐type driving effects. However, a fast temporal response is also critical in order to maximize the blur‐reduction effect even in the case of impulsive driving. In this paper, the special behavior of LC molecules in an impulsive driving environment has been analyzed especially for the case of black‐frame insertion, and we propose an effective means to implement optimized response‐time compensation (RTC) for the black‐frame insertion technique.     

Numerical analysis of particle concentration around the air-inlet of a train in a tunnel by using a discrete phase model

Subways are used for public transportation as a commuting medium in Korea. Subway trains operate mainly through tunnels. Fine particles generated by friction between rails and train wheels affect the air quality inside a train because the particles enter the ventilation system of the train passing through a tunnel. The PM₁₀ concentration has been mainly used to evaluate indoor air quality, and the PM_2.5 concentration has measured recently. Therefore, in this study, the concentrations of the particles entering the air-inlet with respect to particle sizes including 0.1, 1, 2.5 and 10 μm were investigated by using numerical analysis with ANSYS FLUENT software. The particle analysis was performed corresponding to 10, 40 and 80 km/h. It is expected that the numerical results would be helpful in studying the effect of particles corresponding to PM_2.5 on the ventilation system, to improve the air quality inside a train passing through a tunnel.     

Comparative study of toxic chlorophenolic compounds generated in various bleaching sequences of wheat straw pulp

This study compared the chlorophenolic compounds generated during the bleaching of wheat straw pulp. The six different bleaching sequences used in present study were: (i) chlorine-extraction-hypo (CEH); (ii) persulphate-peroxide-chlorine-extraction-hypo (Px-P-CEH); (iii) oxygen-chlorine-extraction-hypo (OCEH); (iv) chlorine dioxide-extraction-chlorine dioxide (DED); (v) persulphate-peroxide-chlorine dioxide-extraction-chlorine dioxide (Px-P-DED); and (vi) oxygen-chlorine dioxide-extraction-chlorine dioxide (ODED) bleaching. The concentrations of a large number of identified chlorophenolic compounds often exceed their threshold concentrations in CEH effluent. Therefore, the untreated effluent generated from the CEH bleaching sequence of wheat straw pulp can be considered toxic. Prebleaching (PxP) reduces the generation of chlorophenolic compounds by 36 % in the (PxP)CEH sequence. Oxygen prebleaching reduces the generation of chlorophenolic compounds by 86 % in the OCEH bleaching effluent. The PxP also reduces the generation of chlorophenolic compounds by 46 % in the (PxP)DED bleaching sequence and oxygen delignification substantially reduces the generation of the compounds by 78 %.     

Patterning of various silicon structures via polymer lithography and catalytic chemical etching

We demonstrate a facile fabrication of a rich variety of silicon patterns with different length scales by combining polymer lithography and a metal-assisted chemical etching method. Several types of polymer patterns were fabricated on silicon substrates, and silver layers were deposited on the patterned silicon surfaces and used to etch the silicon beneath. Various silicon patterns including topographic lines, concentric rings, and square arrays were created at a micro-?and nanoscale after etching the silicon and subsequent removal of the patterned polymer masks. Alternatively, the arrays of sub-30?nm silicon nanowires were produced by a chemical etching of the silicon wafer which was covered with highly ordered polystyrene-block-polyvinylpyridine (PS-b-PVP) micellar films. In addition, silicon nanohole arrays were also generated by etching with hexagonally packed silver nanoparticles that were prepared using PS-b-PVP block copolymer templates.