196,055 research outputs found
Silicon doping techniques using chemical vapor dopant deposition
No full textUltrashallow junctions are essential for the achievement of superior transistor performance, both in MOSFET and bipolar transistors. The stringent demands require state-of-the-art fabrication techniques. At the same time, in a different context, the accurate fabrication of various n type doping profiles by low-temperature Si epitaxy is a challenge due to autodoping. In this thesis, these two, apparently unrelated, problems are both addressed as the layer of CVD surface-deposited dopant atoms is used as a doping source. It is demonstrated that a layer of dopants deposited on the Si surface can be used as a doping source by either thermal or laser drive-in for the fabrication of both deep and ultrashallow defect-free junctions. In low-temperature CVD epitaxy, autodoping is a consequence of dopant surface segregation and doping from the surface layer. This process has been characterized, and consequently excellent controllability is achieved. In addition, new results related to the CVD of dopants itself are obtained, and two theoretical achievements are made: the analytical model of arbitrarily shallow junctions is derived, and a new C-V profiling technique suitable for the characterization of ultrashallow junctions is developed. The analytical model of arbitrarily shallow junctions, presented in Chapter 2, is derived based on the basic transport mechanisms, with the junction depth as a free parameter, allowing the junction to be fully depleted or disappear. In this way, a closed-form model is obtained that unifies the standard p-n junction and Schottky junction models. With such a unified description, the characteristics of extremely shallow diodes that lie at the cross-over between the standard p-n and Schottky diodes are for the first time analytically described, and new phenomena are observed: both forward and reverse characteristics exhibit specific nonidealities. In that respect, this model can be used to predict the onset of nonidealities as a function of the doping levels, junction depth and biasing conditions. The process of dopant CVD is central to the experimental work presented in this thesis, and it is described in detail in Chapter 3, together with other experimental techniques. Particular focus is given to the deposition of As, the deposition dynamics of which have been empirically modeled to enable accurate sub-monolayer deposition at 800 °C, and the ability to achieve substantial deposition has been demonstrated down to 300 °C. The high-temperature step prior to deposition was found to be unnecessary if Marangoni drying is used. Also, techniques for the removal of As have been investigated: thermal desorption and different wet cleaning solutions. With dopant CVD and drive-in, there are two high-temperature steps to which windows in SiO2 to the Si are exposed: first, for surface cleaning before dopant deposition, and second, for dopant drive-in; and both can have detrimental effects on the definition of deposition windows and on the Si surface. The kind and extent of disfiguration that appears in these two processes has been described in Chapter 4. At temperatures above 900 °C, significant lateral widening of deposition windows is observed. At 1100 °C, also micrometer-deep cavities in the Si form. These spikes typically form in the corners or around the edges of deposition windows, and their generation is catalyzed by the presence of dopants. Contrary to the CVD of B, As and P depositions are limited to a maximum of a single monolayer. This is nevertheless a substantial dose, well suited for the ultrashallow junction formation, which has been demonstrated by thermal and laser drive-in, and the results are presented in Chapter 5. Thermal diffusion was characterized in the temperature range from 700 °C to 900 °C. Due to the high concentration gradient, low diffusivity and SiO2 encapsulation, nanometer-shallow junctions are formed, while no defects are introduced. The diffused dose, however, is only a fraction of a monolayer, and the junctions can even be fully depleted, exhibiting characteristics predicted by the model of arbitrarily shallow junctions. Nevertheless, they can be very effective in modulating the effective Schottky barrier height. With laser annealing, at laser energy densities above the Si melt limit, successful drive-in of the complete monolayer is achieved. Thereby, junctions 10 nm to 15 nm deep, with 3 nm/dec or better vertical abruptness, doped above 3x10^20 cm-3, with sheet resistance around 300 ohm/sq indicative of 100% activation are formed in an essentially room-temperature process. Such exceptionally good results are enabled by the fact that the defect-inducing ion implantation is not used, thus no defect annealing steps are needed. While the doping profiles satisfy the ITRS requirements, the low defect density and low processing temperature make this, in combination with As deposition at 300 °C, a promising solution for junction formation after metallization and for backside junction formation in the SOG substrate-transfer technology. For the low-temperature RPCVD Si epitaxy, an empirical model of As surface segregation, adsorption, and incorporation from the surface layer has been developed, and is presented in Chapter 6. Together with the pure As deposition and As wet chemical removal, this model enables very accurate fabrication of doping profiles of nearly arbitrary shape, the most important restriction being that the profiles can be both continuously or discretely increasing in the growth direction, but only discretely decreasing using ex-situ As cleaning. Based on this model, profiles inversely proportional to the square of the doping depth are fabricated for the novel varactor diodes with state-of-the-art linearity. For the purpose of characterization of ultrashallow junctions, beyond the limitations of SIMS resolution, a new C-V profiling technique has been developed and is presented in Chapter 7. It relies on fabricating and measuring two diodes, one Schottky and one p-n diode, both with the same background doping profile, in order to obtain first the background and then the ultrashallow doping profile. It has been demonstrated that this can be achieved if the background profile contains abrupt changes in doping, e.g. in the form of steps, even if it is considerably less abrupt and less highly doped. Using an epitaxially grown step-like background profile, the ultrashallow B profile formed only by pure B CVD has been measured to have the junction depth of 7 nm, and the slope of around 2.5 nm/dec.Microelectronics & Computer EngineeringElectrical Engineering, Mathematics and Computer Scienc
C-V profiling of ultra-shallow junctions using a buried layer with stepped doping
No full textThe paper investigates two-sided capacitance-voltage (C-V) technique for application in doping profile characterization of Si ultra shallow p+-n junctions. Stepped doping profile in the n region is designed for the accurate determination of xn0, a crucial parameter for the extraction of the doping profile in the p region. Medici simulations are carried out for the C-VR relationships of the p+-n and n-Schottky junctions with the same step-like n profile. The xn0 can be determined with an accuracy of 1.7 nm by a criteria developed in this work. And the doping profile in the p+ doped region can finally be extracted and shown to be in good agreement with the Medici simulation results.Electrical Engineering, Mathematics and Computer Scienc
Dr. Duane M. Jackson, Morehouse College, July 2011
No full textThis video is a conversation with Dr. Duane M. Jackson. Dr. Jackson talks about his paper, "Recall and the Serial Position Effect: The Role of Primacy and Recency on Accounting Students' Performance." Jackie Daniel, AUC Woodruff Library, is the interviewer
"Reflections on the subject of Emigration from Europe with a view to Settlement in the United States" By M. Carey.
No full text"Reflections on the subject of Emigration from Europe with a view to Settlement in the United States: containing bried sketches of the moral and political character of those states.
By M. Carey, member of the American philosophical, and of the American Antiquarian Society, and author of The Olive Branch, Cindiciae Hibernicae, essays on banking, on political economy, and on internal improvement.
To which are now added the English editor's comments on the subject; together with Important Advice to Emigrants, and Cautions Against Impositions Practiced in the Outports
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Dr. Glendon Swarthout
No full textHosted by Roger M. Busfield, MSU Assistant Professor of Speech and Theater, Meet the Author is designed to introduce a general audience to a contemporary author and their work through in-depth interviews. This episode features a conversation between Dr. Glendon Swarthout, prolific author and English professor at MSU, and assistant professors Sam S. Baskett and Theodore B. Strandness
Simulation of thermal plant optimization and hydraulic aspects of thermal distribution loops for large campuses
No full textFollowing an introduction, the author describes Texas A&M University and its utilities system. After that, the author presents how to construct simulation models for chilled water and heating hot water distribution systems. The simulation model was used in a $2.3 million Ross Street chilled water pipe replacement project at Texas A&M University. A second project conducted at the University of Texas at San Antonio was used as an example to demonstrate how to identify and design an optimal distribution system by using a simulation model. The author found that the minor losses of these closed loop thermal distribution systems are significantly higher than potable water distribution systems. In the second part of the report, the author presents the latest development of software called the Plant Optimization Program, which can simulate cogeneration plant operation, estimate its operation cost and provide optimized operation suggestions. The author also developed detailed simulation models for a gas turbine and heat recovery steam generator and identified significant potential savings. Finally, the author also used a steam turbine as an example to present a multi-regression method on constructing simulation models by using basic statistics and optimization algorithms. This report presents a survey of the author??s working experience at the Energy Systems Laboratory (ESL) at Texas A&M University during the period of January 2002 through March 2004. The purpose of the above work was to allow the author to become familiar with the practice of engineering. The result is that the author knows how to complete a project from start to finish and understands how both technical and nontechnical aspects of a project need to be considered in order to ensure a quality deliverable and bring a project to successful completion. This report concludes that the objectives of the internship were successfully accomplished and that the requirements for the degree of Degree of Engineering have been satisfied
Analytical model of I–V characteristics of arbitrarily shallow p-n junctions
No full textFor the first time, an analytical model of arbitrarily shallow p-n junctions is presented. Depending on the junction depth, electrical characteristics of ultrashallow p-n junctions can vary from the characteristics of standard Schottky diodes to standard deep p-n junctions. This model successfully unifies the standard Schottky and p-n diode expressions. In the crossover region, where the shallow doping region can be totally depleted, electrical characteristics phenomenologically substantially different from typical diode characteristics are predicted. These predictions and the accuracy of the presented model are evaluated by comparison with the MEDICI simulations. Furthermore, ultrashallow n+-p diodes were fabricated, and the anomalous behavior in the crossover regime was experimentally observed.Microelectronics & Computer EngineeringElectrical Engineering, Mathematics and Computer Scienc
Intern experience at CH���M Hill, Inc.: an internship report
No full textIncludes author's vita"Submitted to the College of Engineering of Texas A&M University in partial
fulfillment of the requirement for the degree of Doctor of Engineering."Includes bibliographical referencesA review of the author's internship experience with CH���M HILL, Inc.
during the period September 1975 through May 1976 is presented. During this nine month
internship the author worked as an Engineer II in the Industrial Processes discipline of this
large consulting engineering firm... The author's prime responsibility was as one of three
lead design engineers on the design of a large wastewater treatment facility for a pulp mill
in Hoquiam, Washington owned by ITT Rayonier Inc. The work generally consisted of the design
of individual treatment units and associated piping and pumping. The purpose of the project
was to provide wastewater treatment capabilities that would satisfy the effluent limitations
(standards) imposed upon the mill by the State of Washington Department of Ecology and the
U.S. Environmental Protection Agency. The author's assignment also entailed necessary
interaction with the project manager and other CH���M HILL design engineers and support staff
members, the client's representatives, and representatives of two other consulting engineering
firms working on the project. Thus, the internship position at CH���M HILL provided considerable
experience coordinating the author's work with the work of other engineers, guiding the design
and administrative efforts of a support staff, and interacting regularly with the client and
other consulting firms. This broad exposure to a variety of engineering and organizational
problems provided a valuable educational experience
Transition to turbulence in a qblique shock-wave/boundary-layer interaction at M=15
No full textDirect numerical simulations are carried out for different forcing techniques to trigger transition during the interaction between an oblique shock-wave and a laminar boundary-layer at M = 1.5. Three forcing methods are used: a) forcing of oblique unstable modes, whose shape and behaviour are determined by the local linear stability theory, b) broadband free-stream acoustic disturbances, and c) a cold plasma flow control device. While the oblique-mode breakdown is dominant for low-amplitude forcing, long streaky structures drive the transition process in a high-amplitude disturbance environment. LES are also performed on the experimental setup by the Institute of Theoretical and Applied Mechanics (ITAM) from Novosibirsk State University with cold plasma actuation. As well as the disturbance type, the effect of Reynolds number and forcing amplitude will be investigated
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