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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Now showing 1 - 5 of 5

Dynamic dimension reduction for thin-film deposition reaction network models
(IFAC, 2016-06-06) Adomaitis, Raymond
A prototype thin-film deposition model is developed and subsequently used in a sequence of model reduction procedures, ultimately reducing the dynamic dimension from six to one with essentially no loss in accuracy to the dynamics of the deposition process. The species balance model consists of a singular perturbation problem of nonstandard form which first is numerically solved following the approach of Daoutidis (2015). An alternative strategy then is presented, consisting of a reaction factorization procedure which facilitates the solution of the outer solution of the singular perturbation problem and provides unique physical insight into the conserved quantities (reaction invariants) identified by the elimination of redundant dynamic modes. Further reduction in dynamic dimension then is achieved through a second factorization focused only on the major reaction species. This second reduction procedure identifies pseudo- equilibria of finite-rate properties and introduces an additional level of complexity to the challenges of identifying consistent initial conditions for DAE systems.
Full wafer mapping and response surface modeling techniques for thin ﬁlm deposition processes
(2008-07-25) Leon, Marıa del Pilar; Adomaitis, Raymond
Computational techniques for representing and analyzing full wafer metrology data are developed for chemical vapor deposition and other thin-ﬁlm processing applications. Spatially resolved mea- surement data are used to produce “vir tual wafers” that are subsequently used to create response surface models for predicting the full-wafer thickness, composition, or any other proper ty proﬁle as a function of processing parameters. Statistical analysis tools are developed to assess model prediction accuracy and to compare the relative accuracies of different models created from the same wafer data set. Examples illustrating the use of these techniques for ﬁlm proper ty unifor- mity optimization and for creating intentional ﬁlm-proper ty spatial gradients for combinatorial CVD applications are presented.
Multiscale simulation of atomic layer deposition in a nanoporous material
(2008-08-15) Dwivedi, Vivek; Adomaitis, Raymond
A multiscale simulator for alumina film growth inside a nanoporous material during an atomic layer deposition process is developed. The model combines a continuum description at the macroscopic level of precursor gas transport inside a nanopore during exposure to each of the two precursor species (trimethyaluminum and water) with a lattice Monte Carlo simulation of the film growth on the microscopic scale. Simulation results are presented for both the Monte Carlo simulation and for the multiscale system, the latter illustrating how nonuniform deposition along the nanopore can occur when insufficient precursor exposure levels are used.
Process Modeling of a Wire Saw Operation
(2008) Palathra, Thomas; Adomaitis, Raymond
Multicrystalline (MC) silicon solar cells are manufactured from bread-loaf sized ingots of solar-grade silicon. These ingots are sliced by a multi-wire saw mechanism consisting of a single thin and extremely long stainless steel wire wound on constant-pitch wire grooves. The wire is wound over each groove to create a web consisting of 500-700 parallel wires. The wire is kept at a constant tension using feedback control and the wire speeds typically are 10-15 m/s. A high speed nozzle directs an aqueous slurry of oil and SiC particles to the top of the wire array and the crystal silicon ingot is pushed upwards against the wire array during the cut. In a typical wire saw system MC ingots are sliced with an area of 100x100 square mm and the latest wire saw systems can achieve thicknesses down to 300 microns. What makes this a challenging simulation problem is the wide range of timescales that characterize the overall cutting process. The slowest dynamics are associated with the evolution of the cut, which is described by a spatially dependent differential equation in time and in which the cutting rate is modeled much in the same manner as the Chemical Mechanical Planarization (CMP) process. Cutting rate is a direct function of the distance between the wire and ingot surface. Because the wire dynamics are orders of magnitude faster than cut evolution, the wire deflection is modeled by a static circular beam. The goal of this modeling work is to understand the physical mechanisms that limit how thin the wafers can be cut and to determine the sensitivity of cutting time and cutting rate based on process operating conditions.
Reaction path analysis for atomic layer deposition systems
(FOCAPO/CPC 2017, 2017-01-08) Adomaitis, Raymond
In this paper, we examine the mathematical structure of thin-film deposition process reaction kinetics models with the goal of determining whether a reaction network can guarantee the self-limiting and stable growth inherent in true atomic layer deposition systems. This analysis is based on identifying reaction invariants and interpreting the chemical significance of these conserved modes. A species-reaction graph approach is introduced to aid in distinguishing “proper” from problematic ALD reaction networks.