Institute for Systems Research

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Author: search.filters.author.Adomaitis, Raymond A.Subject: search.filters.subject.chemical process control

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Now showing 1 - 5 of 5
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    Influence of Gas Composition on Wafer Temperature Control in a Tungsten Chemical Vapor Deposition Reactor
    (2000) Chang, Hsiao-Yung; Adomaitis, Raymond A.; Kidder, John N., Jr.; Rubloff, Gary W.; ISR
    Experimental measurements of wafer temperature in a single-wafer,lamp-heated CVD system were used to study the wafer temperature responseto gas composition. A physically based simulation procedure for theprocess gas and wafer temperature was developed in which a subset ofparameter values were estimated using a nonlinear, iterative parameteridentification method, producing a validated model with true predictivecapabilities.

    With process heating lamp power held constant, wafertemperature variations of up to 160 degrees K were observed by varying feed gasH_2/N_2 ratio. Heat transfer between the wafer and susceptor wasstudied by shifting the instrumented wafer off the susceptor axis,exposing a portion of the wafer backside to the chamber floor. Modelpredictions and experimental observations both demonstrated that the gasvelocity field had little influence on the observed wafer and predictedgas temperatures.

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    A Collocation/Quadrature-Based Sturm-Liouville Problem Solver
    (1999) Adomaitis, Raymond A.; Lin, Yi-hung; ISR
    We present a computational method for solving a class of boundary-value problemsin Sturm-Liouville form. The algorithms are based on global polynomialcollocation methods and produce discrete representationsof the eigenfunctions. Error control is performed by evaluating theeigenvalue problem residuals generated when the eigenfunctions are interpolatedto a finer discretization grid; eigenfunctions thatproduce residuals exceeding an infinity-norm bound are discarded.Because the computational approach involves the generationof quadrature weights and discrete differentiation operations, our computationalmethods provide a convenient framework for solving boundary-value problemsby eigenfunction expansion and other projection methods.
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    A Computational Framework for Boundary-Value Problem Based Simulations
    (1998) Adomaitis, Raymond A.; Lin, Yi-hung; Chang, Hsiao-Yung; ISR
    A framework is presented for step-by-step implementation of weighted-residualmethods (MWR) for simulations that require the solution ofboundary-value problems. A set of Matlab-based functions ofthe computationally common MWR solution steps has beendeveloped and is used in the application of eigenfunction expansion,collocation, and Galerkin-projection discretizations oftime-dependent, distributed-parameter system models. Fourindustrially relevant examples taken from electronic materialsand chemical processing applications are used to demonstrate thesimulation approach developed.
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    Model Reduction for RTCVD Optimization
    (1996) Theodoropoulou, A.; Adomaitis, Raymond A.; Zafiriou, E.; ISR
    A model of a three-zone Rapid Thermal Chemical Vapor Deposition (RTCVD) system is developed to study the effects of spatial wafer temperature patterns on polysilicon deposition uniformity. A sequence of simulated runs is performed, varying the lamp power profiles so that different wafer temperature modes are excited. The dominant spatial wafer thermal modes are extracted via Proper Orthogonal Decomposition and subsequently used as a set of trial functions to represent both the wafer temperature and deposition thickness. A collocation formulation of Galerkin's method is developed to discretize the original modeling equations, giving a low-order model which looses little of the original, high-order model's fidelity. We make use of the excellent predictive capabilities of the reduced model to optimize power inputs to the lamp banks to achieve a desired polysilicon deposition thickness at the end of a run with minimal deposition spatial nonuniformity.
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    On the Dynamics and Global Stability Characteristics of Adaptive Systems
    (1991) Adomaitis, Raymond A.; Frouzakis, Christos E.; Kevrekidis, Ioannis G.; ISR
    We consider the dynamics of some representative adaptively- controlled systems and focus on situations where the desired operating point is locally, but not globally, stable. Perturbations which drive the system from the set point are quantified by computing the boundaries separating the basin of attraction of the set point from the basins of attraction of the other, undesirable attractors. The basins are found to sometimes consist of complicated, disconnected structures in phase space. This results from the nonunique reverse-time dynamics often exhibited by these systems and can be studied by considering the behavior of the reverse-time map along the basin boundaries. The effect of noninvertibility on the forward-time dynamical behavior is also explored.