Scheduling of multiple in-line steppers for semiconductor wafer fabs

A few prior studies noticed that an in-line stepper (a bottleneck machine in a semiconductor fab) may have a capacity loss while operated in a low-yield scenario. To alleviate such a capacity loss, some meta-heuristic algorithms for scheduling a single in-line stepper were proposed. Yet, in practice, there are multiple in-line steppers to be scheduled in a fab. This article aims to enhance prior algorithms so as to deal with the scheduling for multiple in-line steppers. Compared to prior studies, this research has to additionally consider how to appropriately allocate jobs to various machines. We enhance prior algorithms by developing a chromosome-decoding scheme which can yield a job-allocation decision for any given chromosome (or job sequence). Seven enhanced versions of meta-heuristic algorithms (genetic algorithm, Tabu, GA–Tabu, simulated annealing, M-MMAX, PACO and particle swarm optimisation) were then proposed and tested. Numerical experiments indicate that the GA–Tabu method outperforms the others. In addition, the lower the process yield, the better is the performance of the GA–Tabu algorithm.     

Gas permeation in miscible blends of poly(methyl methacrylate) with bisphenol chloral polycarbonate

The miscibility of poly(methyl methacrylate) (PMMA) with bisphenol chloral polycarbonate (BCPC) has been studied using differential scanning calorimetry (DSC), optical indication of phase separation on heating (i.e., lower critical solution temperature (LCST) behavior), density measurement, and gas permeation. All evidence indicates that PMMA is miscible with BCPC over the whole blend composition range. Single composition-dependent glass transition temperature and LCST behavior have been observed for each blend. The specific volumes of the blends follow closely the simple additivity rule indicating the interaction between PMMA and BCPC is weak. Gas permeability coefficients for He, H₂, O₂, Ar, N₂, CH₄, and CO₂ measured at 35°C under 1 to 2 atm upstream pressure are lower than those calculated from the semilogarithmic additivity rule. The difference between this calculated permeability and the measured one increases with gas molecular size. As a result, the ideal gas separation factors for He/CH₄, CO₂/CH₄, and O₂/N₂ gas pairs estimated from the ratio of pure gas permeabilities are higher than predicted from the semilogarithmic additivity rule. These permeation results were interpreted in terms of the free volume theory and the activated state theory, which have been proposed to describe gas transport behavior in polymer mixtures.     

Exploring heterogeneous information networks and random walk with restart for academic search

In this paper, we explore heterogenous information networks in which each vertex represents one entity and the edges reflect linkage relationships. Heterogenous information networks contain vertices of several entity types, such as papers, authors and terms, and hence can fully reflect multiple linkage relationships among different entities. Such a heterogeneous information network is similar to a mixed media graph (MMG). By representing a bibliographic dataset as an MMG, the performance obtained when searching relevant entities (e.g., papers) can be improved. Furthermore, our academic search enables multiple-entity search, where a variety of entity search results are provided, such as relevant papers, authors and conferences, via a one-time query. Explicitly, given a bibliographic dataset, we propose a Global-MMG, in which a global heterogeneous information network is built. When a user submits a query keyword, we perform a random walk with restart (RWR) to retrieve papers or other types of entity objects. To reduce the query response time, algorithm Net-MMG (standing for NetClus-based MMG) is developed. Algorithm Net-MMG first divides a heterogeneous information network into a collection of sub-networks. Afterward, the Net-MMG performs a RWR on a set of selected relevant sub-networks. We implemented our academic search and conducted extensive experiments using the ACM Digital Library. The experimental results show that by exploring heterogeneous information networks and RWR, both the Global-MMG and Net-MMG achieve better search quality compared with existing academic search services. In addition, the Net-MMG has a shorter query response time while still guaranteeing good quality in search results.     

Identifying cluster number for subspace projected functional data clustering

We propose a new approach, the forward functional testing (FFT) procedure, to cluster number selection for functional data clustering. We present a framework of subspace projected functional data clustering based on the functional multiplicative random-effects model, and propose to perform functional hypothesis tests on equivalence of cluster structures to identify the number of clusters. The aim is to find the maximum number of distinctive clusters while retaining significant differences between cluster structures. The null hypotheses comprise equalities between the cluster mean functions and between the sets of cluster eigenfunctions of the covariance kernels. Bootstrap resampling methods are developed to construct reference distributions of the derived test statistics. We compare several other cluster number selection criteria, extended from methods of multivariate data, with the proposed FFT procedure. The performance of the proposed approaches is examined by simulation studies, with applications to clustering gene expression profiles.     

The impact of perceived ease of use on Internet service adoption: The moderating effects of temporal distance and perceived risk

Perceived ease of use is found to affect consumer’s intention toward using an Internet-based service. However, to protect online transaction security, more security verification mechanisms are established which in turn increase the complexity and difficulty of using online services. This study proposed that the importance of perceived ease of use is depending on short- vs. long-term transaction expectation, product type, and whether security concern information is presented. In certain situations buyers or sellers of an Internet service may tolerate the inconvenience of using the Internet-based service. A 2 (verification requirement) × 2 (network externality) × 2 (short vs. long term) between-subject design was conducted on sellers of an auction site and a 2 (verification requirement) × 2 (product type) × 2 (with vs. without security concern information) between-subject design was conducted on buyers of an auction site. The results of two studies suggest that perceived ease of use increases the intention toward using online service when sellers expect that the Internet service usage is only for a short-term transaction or when buyers have no access of the security concern information on the website. In contrast, sellers prefer using an online service which requires a relatively high verification requirement when the purpose of using Internet service is for long-term transaction or when buyers have access of security concern information. The results also showed that perceived network externality positively affect sellers’ intention toward using an auction website.     

Large-scale Internet benchmarking: Technology and application in warehousing operations

Effective benchmarking requires standards for measuring performance across a broad range of organizations. Industry-benchmarking measures the relative performance levels of similar operations, but gathering sufficient data to robustly characterize best performance is the primary hurdle to more widespread implementation. This paper describes the development of an innovative, large-scale benchmarking methodology which employs Internet technology to overcome the data collection problem. We discuss a particular instance of this approach, iDEAs-W—the result of an ongoing collaboration between academia and the warehousing industry. This paper's purpose is to demonstrate the methodology for the warehousing industry and share our insights to allow others to refine the tool for applications in other industries.     

A GA-Tabu algorithm for scheduling in-line steppers in low-yield scenarios

This paper presents a scheduling algorithm for an in-line stepper in low-yield scenarios, which mostly appear in cases when new process/production is introduced. An in-line stepper is a bottleneck machine in a semiconductor fab. Its interior comprises a sequence of chambers, while its exterior is a dock equipped with several ports. The transportation unit for entry of each port is a job (a group of wafers), while that for each chamber is a piece of wafer. This transportation incompatibility may lead to a capacity-loss, in particular in low-yield scenarios. Such a capacity-loss could be alleviated by effective scheduling. The proposed scheduling algorithm, called GA-Tabu, is a combination of a genetic algorithm (GA) and a tabu search technique. Numerical experiments indicate that the GA-Tabu algorithm outperforms seven benchmark ones. In particular, the GA-Tabu algorithm outperforms a prior GA both in solution quality and computation efforts.     

Error concealment algorithm based on sparse optimization

In this paper, an application of sparse optimization in the error concealment area is proposed. The spatial and temporal formulations of the pixels in the current frame and reference frame are proposed to solve the problem. Based on the sparse characteristics of nature images, we form sparse optimization problems for both formulations. The optimization problem is solved by the primal-dual interior point method. The solutions are combined for better results. By solving for a limited numbers of significant predictors using the sparse optimization, our algorithm performs subjectively and objectively better for the concealed result; compared to two state-of-the-art spatial-temporal hybrid error concealment methods, the proposed methods can improve by up to 0.19 dB and 1.12 dB in PSNR (Peak Signal-to-Noise Ratio).     

The social influence of online collaborative community: the moderating effect of achievement

Online collaborative communities become particularly influential in contemporary Internet economy. However, these communities are often characterised by limited liability. Following the perspective of social influence, this study examines the impacts of three social influence modes in online collaborative communities of a famous online game. The moderating role of a player’s game achievement is also explored. Our results show that community identification is the most influential on online game continuance intention, especially for high achievement players. Community value congruence is likely to affect online game continuance intention for low achievement players. The impact of community normative influence on online game continuance intention appears to be curvilinear. This is more obvious for low achievement players. Implications for research and practice are also discussed.     

GaN MSM UV photodetectors with titanium tungsten transparent electrodes

GaN metal-semiconductor-metal (MSM) ultraviolet photodetectors with titanium tungsten (TiW) transparent electrodes were fabricated and characterized. It was found that the 10-nm-thick TiW film deposited with a 300-W RF power can still provide a reasonably high transmittance of 75.1% at 300 nm, a low resistivity of 1.7/spl times/10/sup -3/ /spl Omega//spl middot/cm and an effective Schottky barrier height of 0.773 eV on u-GaN. We also achieved a peak responsivity of 0.192 A/W and a quantum efficiency of 66.4% from the GaN ultraviolet MSM photodetector with TiW electrodes. With a 3-V applied bias, it was found that minimum noise equivalent power and maximum D/sup */ of our detector were 1.987/spl times/10/sup -10/ W and 6.365/spl times/10/sup 9/ cmHz/sup 0.5/W/sup -1/, respectively.