Hyunseop Lee

Adaptive Parallel Decomposition for Multidisciplinary Design

The conceptual design of a rotorcraft system involves many different analysis disciplines. The decomposition of such a system into several subsystems can make analysis and design more efficient in terms of the total computation time. Adaptive parallel decomposition makes the structure of the overall design problem suitable to apply the multidisciplinary design optimization methodologies and it can exploit parallel computing. This study proposes a decomposition method which adaptively determines the number and sequence of analyses in each sub-problem corresponding to the available number of processors in parallel. A rotorcraft design problem is solved and as a result, the adaptive parallel decomposition method shows better performance than other previous methods for the selected design problem.

Electrochemical Analysis of the Slurry Composition for Chemical Mechanical Polishing of Flexible Stainless-Steel Substrates

The surface quality of the stainless steel affects the efficiency of flexible photovoltaics. Chemical mechanical polishing (CMP) is a finishing process that is used to prepare substrates for electronic devices. The CMP slurry composition is an important factor because additives in the slurry generally improve the polishing performance. However, it is limited to find the optimum conditions for the slurry by only experimental approaches. Thus, this study uses electrochemical analysis and friction monitoring to examine the effects of the abrasive, oxidizer, chelating agent, and pH. Electrochemical and monitoring analysis are useful for validating predictions and understanding interactions between the slurry and the stainless steel surface. Good correspondence was found between the predictions and the polishing results in more accurate. The corrosion rate (CR) obtained from the potentiodynamic polarization curve is proportional to the experimental results, as is the behavior of the curve and the coefficient of friction (COF). After only 3 min CMP, the best performing slurry (abrasive 39 wt %, oxalic acid 1 wt %, H2O2 0.03 wt %, pH 1.5) improved the surface quality of 304 stainless steel by 4 nm. As a result, the proposed methods could help reduce the risks involved in stainless steel CMP slurry and these results could provide a reference for optimizing CMP slurry for flexible 304 stainless steel substrates.

A study on swing-arm conditioning for enhancing pad lifetime in CMP

A swing-arm conditioning is generally adopted for chemical mechanical polishing (CMP) system to recover the surface roughness of polishing pad. However, the conditioning process results in uneven pad profile. During conditioning, locally excessive pad wear relates to the pad lifetime in CMP process. In this paper we investigate on the relationship of locally controlled swing condition and maximum pad wear during pad conditioning process.

Development of Green Chemical Mechanical Planarization (CMP) Process using Minimum Quantity Slurry Mist

Extended Abstract Chemical mechanical planarization (CMP) is one of the most powerful process to realize next generation semiconductor devices including 3D heterogeneous structures and several nanometer line width. In CMP industry, reduction of slurry consumption without avoiding the drop in productivity is one of the most important requirements for environmental sustainability on [1], [2], and [3]. In this paper, authors propose a spray slurry nozzle to supply minimum quantity slurry mist, which reduce the slurry consumption and increase the material removal rate (MRR) in SiO2 CMP on [4] and [5]. The spray slurry nozzle is compared with a commonly used tube-type slurry nozzle in terms of MRR, material removal uniformity, friction force, and process temperature. A case study on the greenhouse gas (GHG) emission associated with the slurry consumption is provided by polishing patterned wafers on [6]. Adopting the spray slurry nozzle in CMP process provides higher MRR, higher friction force, and shorter process time than the normal tube-type slurry nozzle. Thus, the spray slurry nozzle will diminish the carbon dioxide equivalent (CDE) of [7] and [8] associated with the slurry and electricity consumptions. Furthermore, authors could find that minimum quantity slurry mist decreases the process temperature and it may be used as a cooling system for the CMP process.

Advanced electrostatic plasma diagnostic using sideband floating harmonic method

Summary form only given. Single Langmuir probe (SLP) is one of the well-known electrostatic diagnostic methods, which can measure various plasma parameters, such as electron temperature, plasma density, and plasma potential. However, the SLP cannot be applied in some plasmas, such as dust plasmas and processing plasmas containing deposition gases or dust particles, without probe tip cleaning. To overcome the weakness of the SLP, a floating harmonic method (FHM) has been recently developed and extended researches based on the FHM have been studied. This FHM measures plasma parameters using the relation between a fundamental frequency current and a second harmonic current, and thus, a careful consideration for the stray current is needed when the FHM is used. In this study, a sideband method (SBM), which is based on the FHM but no consideration of the stray current, is studied and the comparisons of the measured electron temperature and the plasma density from the conventional FHM and the SBM are investigated. The SBM can be helpful to the plasma diagnostics for the large-area plasma reactor or fusion device reactor, which has a long measurement cable length or a large amount of the stray current.