Institute for Systems Research Technical Reports
Permanent URI for this collectionhttp://hdl.handle.net/1903/4376
This archive contains a collection of reports generated by the faculty and students of the Institute for Systems Research (ISR), a permanent, interdisciplinary research unit in the A. James Clark School of Engineering at the University of Maryland. ISR-based projects are conducted through partnerships with industry and government, bringing together faculty and students from multiple academic departments and colleges across the university.
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Item A Tool Optimization Interface for a Semiconductor Manufacturing System(2000) Thomas, Ryan; Herrmann, Jeffrey W.; ISRThis paper will serve as the documentation for the Tool Optimization codeof the HSE software. The purpose of the software is, simply, to enable auser to optimize a factory's tool selection. This will be added to theexisting Factory Administrator which enables users to understand theeffects of changes in many parts of the manufacturing process (i.e. Temperatures, Pressures, etc.).To accomplish this an interface was designed via the DELPHI programminglanguage that can take inputs from a user as well as factory details froman Excel spreadsheet, run simulations, determine an optimal toolconfiguration, and output this data as easily as possible to the user.
The Interface will guide the Simulation as many times as needed to performits gradient analysis. After the program is complete, it determines a bestcase tool configuration that meets the user's throughput while maintainingto his budget. The interface will output how many of each tool to purchaseas well the best possible tool allocation (usage) for each tool.
Item Sequencing Wafer Handler Moves to Improve the Performance of Hybrid Cluster Tools(2000) Nguyen, Manh-Quan T.; Herrmann, Jeffrey W.; ISRCluster tools are highly integrated machines that can perform a sequence of semiconductor manufacturing processes. The sequence of wafer handler moves affects the total time needed to process a set of wafers.Reducing this time can reduce cycle time, reduce tool utilization, and increase tool capacity. This paper introduces the cluster tool scheduling problem for hybrid cluster tools, which are multiple-stage tools that have at least one stage with two or more parallel chambers.
This paper presents algorithms that can find superior sequences of wafer handler moves. Experimental results show that the tool performance can be improved significantly if the wafer handler follows a cyclic sequence instead of using a dispatching rule.
Item Randomized Difference Two-Timescale Simultaneous Perturbation Stochastic Approximation Algorithms for Simulation Optimization of Hidden Markov Models(2000) Bhatnagar, Shalabh; Fu, Michael C.; Marcus, Steven I.; Bhatnagar, Shashank; Marcus, Steven I.; Fu, Michael C.; ISRWe proposetwo finite difference two-timescale simultaneous perturbationstochastic approximation (SPSA)algorithmsfor simulation optimization ofhidden Markov models. Stability and convergence of both thealgorithms is proved.Numericalexperiments on a queueing model with high-dimensional parameter vectorsdemonstrate orders of magnitude faster convergence using thesealgorithms over related $(N+1)$-Simulation finite difference analoguesand another two-simulation finite difference algorithm that updates incycles.
Item Sequencing Wafer Handler Moves to Improve the Performance of Sequential Cluster Tools(2000) Herrmann, Jeffrey W.; Nguyen, Manh-Quan T.; ISRCluster tools are highly integrated machines that can perform a sequence of semiconductor manufacturing processes. The sequence of wafer handler moves affects the total time needed to process a set of wafers. Reducing this time can reduce cycle time, reduce tool utilization, and increase tool capacity. This paper introduces the cluster tool scheduling problem for sequential cluster tools and describes a branch-and-bound algorithm that can find an optimal sequence of wafer handler moves. In addition, we enumerate the set of 1-unit cyclic sequences for two- and three-stage sequential cluster tools. Experimental results show that the tool performance can be improved significantly if the wafer handler follows a cyclic sequence instead of using a dispatching rule.Item Fixture-Based Design Similarity Measures for Variant Fixture Planning(1999) Balasubramanian, Sundar; Herrmann, Jeffrey W.; ISROne of the important activities in process planning is the design of fixtures to position, locate and secure the workpiece during operations such as machining, assembly and inspection. The proposed approach for variant fixture planning is an essential part of a hybrid process planning methodology.The aim is to retrieve, for a new product design, a useful fixture from a given set of existing designs and their fixtures. Thus, the variant approach exploits this existing knowledge.
However, since calculating each fixture's feasibility and then determining the necessary modifications for infeasible fixtures would require too much effort, the approach searches quickly for the most promising fixtures based on a surrogate design similarity measure. Then, it evaluates the definitive usefulness metric for those promising fixtures and identifies the best one for the new design.
Item Optimal Multilevel Feedback Policies for ABR Flow Control using Two Timescale SPSA(1999) Bhatnagar, Shalabh; Fu, Michael C.; Marcus, Steven I.; ISROptimal multilevel control policies for rate based flow control in available bit rate (ABR) service in asynchronous transfer mode (ATM) networks are obtained in the presence of information and propagation delays, using a numerically efficient two timescale simultaneous perturbation stochastic approximation (SPSA) algorithm. Numerical experiments demonstrate fast convergence even in the presence of significant delays and a large number of parametrized parameter levels.Item An Internet-Based Work Instructions System(1998) Herrmann, Jeffrey W.; Lin, Edward; Minis, Ioannis; ISRThe Black & Decker factory in Easton, Maryland, uses parallel, off-line assembly lines to produce multiple models in small, infrequent production runs. The University of Maryland and Black & Decker have implemented an Internet-based work instructions system that supports parallel, off-line assembly. Black & Decker personnel create and update easy-to-read paperless work instructions, and each assembly station automatically retrieves the correct paperless work instructions and displays them.Item Locators and Sensors for Automated Coordinate Checking Fixtures(1997) Wang, Yu; Nagarkar, Sanjeev; ISRThis article proposes a systematic method for the optimal design of sensor locations for an automated Coordinate Checking Fixture (CCF). The fixture can be employed for making at-machine assessments of the dimensional accuracy of manufactured components. Coordinate measurements obtained by the sensors built into the fixture can be utilized in estimating geometric parameters of a manufactured part. Two important issues that arise in the design of a CCF are the optimal number of sensors to be used and the best locations for each sensor. The proposed method uses statistical analyses of the Fisher information matrix and the prediction matrix to obtain an optimal set of sensors from an initial candidate set. Sensors are placed at locations that maximize the determinant of the Fisher information matrix for best parameter estimation, while the sensor of the least contribution to the measurement objective is iteratively eliminated. With the benefit of physical insight, the design procedure results in a balanced decision for the ultimate placement of sensors. The developed method also addresses the problem of selection of part locators for part localization in the CCF. Examples are provided for illustration of the developed procedure for automotive space frame extrusion parts.Item Integrated Dynamic Simulation of Rapid Thermal Chemical Vapor Deposition of Polysilicon(1997) Lu, Guangquan; Bora, Monalisa; Tedder, Laura L.; Rubloff, Gary W.; ISRA physically-based dynamic simulator has been constructed to investigate the time-dependent behavior of equipment process, sensor, and control system for rapid thermal chemical vapor deposition (RTCVD) of polysilicon from SiH4. The simulator captures the essential physics and chemistry of mass transport, heat transfer, and chemical kinetics of the RTCVD process as embodied in equipment. In order to complete the system-level description, reduced-order models are also employed to represent processes involving high complexity of physics. Integration of individual simulator elements for equipment, process, sensors, and control systems enables the evaluation of not only the deposition rate and film thickness, but also of a broad range of dynamic system properties such as equipment performance, gas flow conditions, wafer temperature variation, wafer optical properties (absorptivity/emissivity), gas composition in reactor, total process cycle time, consumables volume, and reactant utilization. This makes the simulator directly applicable to the optimization of process recipe and equipment design, to process control strategy, and to fault classification. This case study of polysilicon RTCVD demonstrates (1) that integrated dynamic simulation is a versatile tool for representing system-level dynamics, and (2) that such representation is pivotal in successful application of modeling and simulation for manufacturing optimization and control.Item Process Sensors, Simulation, and Control to Build in Reliability(1997) Rubloff, G.W.; ISRBuilding a reliability is fundamentally difficult because detailed mechanistic origins of reliability failures are not commonly known. Controlled process experiments and sophisticated characterization methods offer hope of revealing mechanisms more broadly. Real-time and in-line sensors present perhaps even more potential in two cases, (1) when their information is correlated with reliability performance, and (2) when used to achieve process control through course correction and/or fault management; the later has special value in difficult situations where the reliability failure emerges from process integration sensitivities. Integrated modeling and simulation structures provide a vehicle for broad knowledge capture, and enabler of design optimization from reliability and other metrics, and a platform for effective process control.