Control Relevant System Identification Using Orthonormal Basis Filter Models

Models are extensively used in advanced process control system design and implementations. Nearly all optimal control design techniques including the widely used model predictive control techniques rely on the use of model of the system to be controlled. There are several linear model structures that are commonly used in control relevant problems in process industries. Some of these model structures are: Auto Regressive with Exogenous Input (ARX), Auto Regressive Moving Average with Exogenous Input (ARMAX), Finite Impulse Response (FIR), Output Error (OE) and Box Jenkins (BJ) models. The selection of the appropriate model structure, among other factors, depend on the consistency of the model parameters, the number of parameters required to describe a system with acceptable accuracy and the computational load in estimating the model parameters. ARX and ARMAX models suffer from inconsistency problem in most open-loop identification problems. Finite Impulse Response (FIR) models require large number of parameters to describe linear systems with acceptable accuracy. BJ, OE and ARMAX models involve nonlinear optimization in estimating their parameters. In addition, all of the above conventional linear models, except FIR, require the time delay of the system to be separately estimated and included in the estimation of the parameters. Orthonormal Basis Filter (OBF) models have several advantages over the other conventional linear models. They are consistent in parameters for most open-loop identification problems. They are parsimonious in parameters if the dominant pole(s) of the system are used in their development. The model parameters are easily estimated using the linear least square method. Moreover, the time delay estimation can be easily integrated in the model development. However, there are several problems that are not yet addressed. Some of the outstanding problems are: (i) Developing parsimonious OBF models when the dominant poles of the system are not known (ii) Obtaining a better estimate of time delay for second or higher order systems (iii) Including an explicit noise model in the framework of OBF model structures and determine the parameters and multi-step ahead predictions (iv) Closed-loop identification problems in this new OBF plus noise model frame work This study presents novel schemes that address the above problems. The first problem is addressed by formulating an iterative scheme where one or two of the dominant pole(s) of the system are estimated and used to develop parsimonious OBF models. A unified scheme is formulated where an OBF-deterministic model and an explicit AR or ARMA stochastic (noise) models are developed to address the second problem. The closed-loop identification problem is addressed by developing schemes based on the direct and indirect approaches using OBF based structures. For all the proposed OBF prediction model structures, the method for estimating the model parameters and multi-step ahead prediction are developed. All the proposed schemes are demonstrated with the help of simulation and real plant case studies. The accuracy of the developed OBF-based models is verified using appropriate validation procedures and residual analysis

Study of Non-Equilibrium Electron Dynamics in Metals

Thermal phenomena, such as heat propagation, lattice melting, and ablation, are the result of energy deposition in metals. A fundamental understanding of the electron dynamics leading to these thermal phenomena would benefit many laser applications, such as laser deposition of thin films and laser processing. In this work, thin metal films were prepared using the resistive heating evaporation technique. High dynamic range autocorrelators were constructed to characterize the different laser systems used in this study. The nonequilibrium electron dynamics in single layer gold films, multi-layer gold-vanadium, and gold-titanium films were studied. The time evolution of the electron temperature was monitored using femtosecond time-resolved thermoreflectivity (ΔR/R) measurements. The validity of the Two-Temperature Model (TTM) in describing ultrafast laser heating processes was checked. The effect of the padding layer on the surface damage threshold was investigated. The experimental results revealed a reduction of the thermoreflectivity signal, ΔRmax, for the multi-layer film that signifies a reduction in the surface electron temperature. Multi-shot damage experiments, in contrast to the thermoreflectivity measurements and the results of Qiu et al., showed no evidence of surface damage in the case of the gold sample, whereas the multi-layer sample experienced an onset of surface damage at the same experimental conditions. The suitability of the Two-Temperature Model (TTM) in describing the transport and relaxation dynamics of hot electrons accurately was verified. A new methodology for the correction of the TTM to account for the internal thermalization of the electron gas and convolution effects was achieved

Real-time feedback for etch rate and sidewall profile control in reactive ion etching.

The purpose of this dissertation is to explore how real-time feedback control may be used to improve the reactive ion etching process. A control strategy was developed based on conceptually decomposing the etching process into a plasma generation process and a wafer etch process. The research was performed on an Applied Materials Precision Etch 8300 using a CF\sb4 chemistry. This etcher was first reconfigured to allow implementation of the real-time control strategy. Several of the actuators and sensors on the etcher were upgraded. This included the addition of an optical emission spectroscopy system to estimate fluorine concentration in the plasma. A data acquisition and control system was also developed to allow the implementation of real-time control algorithms. Control-oriented models of the plasma generation process were developed based on empirical data. These models were then used to develop a real-time controller to regulate plasma characteristics. It was shown that the real-time control strategy was effective in attenuating disturbances to etch rate. Finally, a feasibility study was performed for a sidewall profile control strategy based upon the process decomposition. A method was developed to relate desired sidewall profiles the plasma conditions during the etch. These conditions can then be regulated using the plasma generation process controller. The potential of this strategy was investigated by relating plasma characteristics to a sidewall profile at a single operating point.Ph.D.Applied SciencesElectrical engineeringMechanical engineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/129723/2/9610223.pd