Leveraging new SEMI standard to reduce waste and improve flow for semicoductor manufacturing

A successful cutting-edge semiconductor manufacturer applies Lean principles with the goal set on perfecting its operation flow. In 2007 SEMI adopted a new standard E94-1107 that breaks the dependency between carrier and lot for processing wafers and formally introduces material redirection, which creates several opportunities for waste reductions and improved WIP handling. As depicted from simulations, the new standard is impacting several KPIs including throughput, cycle time, yield, and Just-In-Time customer response. This paper discusses different lean optimizations leveraging the new standard. Some tools require loading of many wafers simultaneously to achieve a high throughput. Although with reducing lot sizes, takt time can be improved, the sequential nature of these tools become limited by the number of load ports and thus have a negative impact on the equipment effectiveness. Before the new standard implementation, no carrier could be removed from load ports during processing to allow other carriers to load or unload wafers leaving the ports blocked. With this change, we can now remove the carrier from the Load Port after unloading wafers into the tool to allow filling the tool with the optimum number of wafers. Over the years, numerous lean manufacturing studies have been performed in terms of determining the correct lot size (number of wafers in a lot) to meet the Just-In-Time targets. Simulation runs demonstrate that smaller lots have up to 33% and 50% improved cycle time for batch tools and single wafer tools, respectively. Based on fluctuations in demand, there may not only be a need to speed up, but also to slow down production quickly. All these have direct correlation with scheduling of right sized lots (dynamic lot sizing), carefully planned delivery of carriers for processing and improved pull production techniques.     

Molecular simulation study of the structural properties in InxGa1−xAs alloys: Comparison between Valence Force Field and Tersoff potential models

The thermodynamic and structural properties of compound semiconductor alloys have been generally modelled using either the Valence Force Field model or the Tersoff potential model. This work compares the properties, such as lattice constant and bond length, of the In_xGa_1−xAs alloy as predicted by Monte Carlo simulations in the semigrand isothermal isobaric ensemble using both the potential models, with experimental data. The lattice constants are expected to follow the Vegard’s law at any given temperature. Valence Force Field model predicts bond length data which follows the experimentally determined values at 300 K; whereas the Tersoff model forecasts that the virtual crystal approximation will be followed. The VFF model, with its experimentally determined parameters, is found to be better for modelling the alloy at room temperature. The Tersoff model, with its fitted parameters, on the other hand predicts the effect of temperature on the microscopic structure of the alloy better. The parameters of the Tersoff potential characterizing the In–Ga interactions can be further improved to predict bond lengths more accurately.     

Synthesis and Biological Evaluation of Ferrocenylquinoline as a Potential Antileishmanial Agent

The emergence of resistance against antileishmanial drugs in current use necessitates the search for new classes of antileishmanial compounds. Herein we report the design, synthesis, and evaluation of a novel ferrocenylquinoline for activity against Leishmania donovani. 7‐Chloro‐N‐[2‐(1H‐5‐ferrocenyl‐1,2,3‐triazol‐1‐yl)ethyl]quinolin‐4‐amine ( 1 ) was generated by coupling an iron(II) ethynylferrocene species with 4‐(2‐ethylazido)amino‐7‐chloroquinoline using click chemistry. The synthesized compound 1 was tested for its antileishmanial activity using both promastigote and amastigote stages of L. donovani. Compound 1 showed promising anti‐promastigote activity, with an IC₅₀ value of 15.26 μM and no cytotoxicity toward host splenocytes. From the battery of tests conducted in this study, it appears that this compound induces parasite death by promoting oxidative stress and depolarizing the mitochondrial membrane potential, thereby triggering apoptosis. These results suggest that ferrocenylquinoline 1 is a suitable lead for the development of new antileishmanial drugs.     

Nonlinear optical studies on new conjugated poly{2,2l‐(3,4‐ dialkoxythiophene‐2,5‐diyl) bis[5‐(2‐thienyl)‐1,3,4‐oxadiazole]}s

Three new donor–acceptor type poly{2,2^l‐(3,4‐ dialkoxythiophene‐2,5‐diyl)bis[5‐(2‐thienyl)‐1,3,4‐oxadiazole]}s ( P1, P2, and P3 ) were synthesized starting from thiodiglycolic acid and diethyl oxalate through multistep reactions. The polymerization was carried out using chemical polymerization technique. The optical and charge‐transporting properties of the polymers were investigated by UV‐visible, fluorescence emission spectroscopic and cyclic voltammetric studies. The polymers showed bluish‐green fluorescence in solutions. The electrochemical band gaps were determined to be 2.03, 2.09, and 2.17 eV for P1 , P2, and P3, respectively. The nonlinear optical properties of new polymers were investigated at 532 nm using single beam Z‐scan and degenerate four‐wave mixing (DFWM) techniques with nanosecond laser pulses. The polymers exhibited strong optical limiting behavior due to “effective” three‐photon absorption. Values of the effective three‐photon absorption ( 3PA ) coefficients, third‐order nonlinear susceptibilities (χ⁽³⁾), and figures (F) of merit were calculated. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Microencapsulation of α-Amylase by Carrying Out Complex Coacervation and Drying in a Single Step Using a Novel Three-Fluid Nozzle Spray Drying

The aim of this research was to develop an enzyme encapsulation process in which both the complex coacervation and drying processes are combined into a single step. For this purpose, we used a novel three-fluid nozzle at the atomization step of spray drying. α-Amylase as a model enzyme was encapsulated by coacervation in calcium (Ca) alginate and Ca-alginate + chitosan shell matrices and the powder was obtained in a single step through spray drying. The single-step process was compared to carrying out the complex coacervation and drying processes in two steps using freeze drying, in which α-amylase was encapsulated by carrying out the complexation process in the above-mentioned shell matrices using the same three-fluid atomizer and collecting the coacervates, which were subsequently freeze dried. The results showed that the microcapsules obtained from the single-step encapsulation process (three-fluid nozzle spray drying) had smaller particle sizes, were less porous, and provided better enzyme stability compared to the microcapsules obtained by carrying out the complexation and drying in two steps and the single-step process was faster. It was observed that the egg-box structure was formed in both types of powder particles; however, the complexation with chitosan partially disrupted the formation of this structure. The three-fluid nozzle–based spray drying is a promising technology in which both the complex coacervation and drying processes can be carried out in a single step.     

Fluid flow characterization with tube viscometer data

Pressure gradients and the corresponding mass flow rates of five different non-Newtonian fluid foods: 1% solutions of sodium alginate and CMC, 1.5% CMC solution, two different tomato ketchups, oyster sauce, in four different diameter stainless steel tubes ranging from 7.51 to 16.34 mm i.d. were recorded using a tube viscometer capable of operating in both transient and continuous flow modes. The flow was confined to the laminar flow regime and appreciable slippage occurred in all cases. Power law parameters for the tube flow obtained from the plots of wall shear stress versus apparent wall shear rate are presented for various time-independent fluids in different diameter tubes in original and slip-corrected forms. Such experimental data should prove useful in developing an understanding of flow characterization of non-Newtonian fluids.     

Generalized form of optimal teleportation witnesses

We propose a generalized form of optimal teleportation witness to demonstrate their importance in experimental detection of the larger set of entangled states useful for teleportation in higher dimensional systems. The interesting properties of our witness reveal that teleportation witness can be used to characterize mixed state entanglement using Schmidt numbers. Our results show that while every teleportation witness is also a entanglement witness, the converse is not true. Also, we show that a hermitian operator is a teleportation witness iff it is a decomposable entanglement witness. In addition, we analyze the practical significance of our study by decomposing our teleportation witness in terms of Pauli and Gell-Mann matrices, which are experimentally measurable quantities.     

Kinetics and Reactor Modeling of Hydrogen Production from Glycerol via Steam Reforming Process over Ni/CeO2 Catalysts

As a result of skyrocketing prices, environmental concerns and depletion associated with fossil fuels, renewable fuels are becoming attractive alternatives. In this respect, the demand for biodiesel has increased tremendously in recent years. Increased production of biodiesel has resulted in a glut of glycerol that has reduced the demand for this once valuable commodity. Consequently, finding alternative uses for glycerol is a timely proposition. One alternative is producing renewable hydrogen from this cheap commodity. Only a handful of studies have been conducted on producing hydrogen from glycerol. Previous studies have mainly focused on finding effective catalysts for glycerol steam reforming. This paper extends previous knowledge by presenting kinetic parameters in relation to glycerol steam reforming over Ni/CeO₂ and a reactor modeling. The study found that the activation energy and the reaction order for the glycerol steam reforming reaction over Ni/CeO₂ catalyst were 103.4 kJ/mol and 0.233, respectively.