Thesis (Ph. D.)--University of Oregon, 2000. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 168-174). Also available for download via the World Wide Web; free to University of Oregon users.

Thesis (M.S.)--Brigham Young University. Dept. of Mechanical Engineering, 2003. / Includes bibliographical references (p. 109-110).

Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, September 2003. / Thesis advisor(s): Todd R. Weatherford, Andrew A. Parker. Includes bibliographical references (p. 39). Also available online.

Thesis (Ph. D.)--University of Hong Kong, 2002. / Includes bibliographical references (leaves 68-71).

Thesis (M.S.)--Youngstown State University, 2009. / Includes bibliographical references (leaves 65-67). Also available via the World Wide Web in PDF format.

With the decrease in feature size in semiconductor manufacturing, molecular contamination problems are increased significantly. In order to optimize the yields in wafer fabrication units there is a need for process modeling that addresses the details of wafer contamination. Wafer contamination and cleaning is a complex process that covers various length and time scale events and phenomena. At the largest scales, there is the availability and transport of specific species within the fabrication unit and subsequent contamination of the wafer surface either through processing steps or through simple ambient transport processes. To limit wafer contaminant levels and/or to decontaminate them, wafers in the semiconductor fabrication unit are often cleaned and transported in a closed enclosure called Front Opening Unified Pod (FOUP) and purged with an inert gas like nitrogen. For the FOUP geometry, I analyze the large scale process modeling approaches to cleaning wafers. At smaller scales, the specific molecular configuration of the contaminant species impacts the kinetic chemical-physical cleaning mechanisms. To determine, from a fundamental perspective, the mechanisms contributing to wafer cleaning requires different scale tools from transport tools aimed at characterizing equipment scale (e.g., FOUP) contamination issues. I use molecular dynamics models and optimization techniques to infer physicochemical rates for molecular desorption on wafer surfaces. This dissertation considers these problems from a common perspective. The objective of this study has been to characterize the multi-scale problem of wafer cleaning with the objective of developing appropriate tools and models at different scales to best predict the dynamics of contaminant removal from wafer surfaces. A standardized method has been presented to extract kinetic rate parameters using molecular dynamics simulation (smaller-scale) and optimization for use in a larger-scale model of wafer decontamination using computational fluid dynamics (CFD). Also, by using available experimental data and CFD analysis an optimized FOUP purging recipe for better decontamination is presented and the relative magnitude of the time scales associated with surface kinetics and FOUP purging have been estimated. / text

Semiconductor manufacturing is complex. Companies strive to lead in the markets by delivering timely chips which are bug (a.k.a defect) free and have very low power consumption. The new research drives new features in chips. The case study research reported here is about the usability and productivity of the silicon debug software tools. Silicon debug software tools are a set of software used to find bugs before delivering chips to the customer. The study has an objective to improve usability and productivity of the tools, by introducing metrics. The results of the measurements drive a concrete plan of action. The GQM (Goal, Questions, Metrics) methodology was used to define and gather data for the measurements. The project was developed in two parts or phases. We took the measurements using the method over the two phases of the tool development. The findings from phase one improved the tool usability in the second phase. The lesson learnt is that tool usability is a complex measurement. Improving usability means that the user will use less of the tool help button; the user will have less downtime and will not input incorrect data. Even though for this study the focus was on three important tools, the same usability metrics can be applied to the remaining five tools. For defining productivity metrics, we also used the GQM methodology. A productivity measurement using historic data was done to establish a baseline. The baseline measurements identified some existing bottlenecks in the overall silicon debug process. We link productivity to time it takes for a debug tool user to complete the assigned task(s). The total time taken for using all the tools does not give us any actionable items for improving productivity. We will need to measure the time it takes for use of each tool in the debug process to give us actionable items. This is identified as future work. To improve usability we recommend making tools that are more robust to error handling and having good help features. To improve productivity we recommend getting data on where the user is spending most of the debug time. Then, we can focus on improving that time-consuming part of debug to make the users more productive. / text

Block copolymers are an ideal solution for a wide variety of nanolithographic opportunities due to their tendency to self-assemble on nanoscopic length scales. High etch selectivity and thin-film orientation are crucial to the success of this technology. Most conventional block copolymers have poor etch selectivity; however, incorporating silicon into one block produces the desired etch selectivity. A positive side effect of the silicon addition is that the χ value (a block-to-block interaction parameter) of the block copolymer increases. This decreases the critical dimension of potential features. Unfortunately, one negative side effect is the increase in the surface energy difference between the blocks. Incorporating silicon decreases the surface energy of that block. Typically, annealing is used to induce the chain mobility that is required for the block copolymer to reach its minimum thermodynamic energy state. Thermal annealing is the easiest annealing technique; however, if the glass transition temperature (Tg) of one block is above the thermal decomposition temperature of the other block, the latter will degrade before the former can reorient. In addition, annealing silicon-containing block copolymers usually results in a wetting layer and parallel orientation since the lower surface energy block favors the air interface, minimizing the free energy. Solvent annealing replaces the air interface with a solvent, thereby changing the surface energy. The solvent plasticizes the block copolymer, effectively decreasing the Tgs of both blocks. Another benefit is the ability to reversibly alter the orientation by changing the solvent or solvent concentration. The challenge with solvent annealing is that it depends on a number of parameters including: solvent selection, annealing time, and vapor concentration, which generate a very large variable space that must be searched to find optimum screening conditions. / text

Directional microphones, which suppress noise coming from unwanted directions while preserving sound signals arriving from a desired direction, are essential to hearing aid technology. The device presented in this paper abandons the principles of standard pressure sensor microphones, dual port microphones, and multi-chip array systems and instead employs a new method of operation. The proposed device uses a lightweight silicon micromachined structure that becomes “entrained” in the oscillatory motion of air vibrations, and thus maintains the vector component of the air velocity. The mechanical structures are made as compliant as possible so that the motion of the diaphragm directly replicates the motion of the sound wave as it travels through air. The microphone discussed in this paper achieves the bi-directionality seen in a ribbon microphone but is built using standard semiconductor fabrication techniques and utilizes piezoelectric readout of a circular diaphragm suspended on compliant silicon springs. Finite element analysis and lumped element modeling have been performed to aid in structural design and device verification. The proposed microphone was successfully fabricated in a cleanroom facility at The University of Texas at Austin. Testing procedures verified that the resonant frequency of the microphone, as expected, was much lower than in traditional microphones. This report discusses the theory, modeling, fabrication and testing of the microphone. / text

Silicon nanocrystals (NCs), especially Si NCs embedded in SiO₂, have been studied intensely for decades for their potential application in silicon photonics, especially as efficient room temperature light emitters. Despite progress in fabricating photonic devices from Si NCs, the origin of the efficient photoluminescence (PL), the electronic and microscopic structure of the nanocrystals, and the structure of the elusive NC/SiO₂ interfaces for the oxide-embedded nanocrystals, remain controversial. Optical spectroscopy provides a powerful noninvasive tool for probing the structure of the Si NCs, including the active buried NC/SiO₂ interfaces of embedded particles. In this thesis work, oxide-embedded and free-standing alkyl-passivated silicon nanocrystals, prepared by different techniques, have been studied by linear and nonlinear optical spectroscopies. Cross-polarized 2-beam second-harmonic and sum-frequency generation (XP2-SHG/SFG) has been applied spectroscopically to study oxide embedded Si NCs of different sizes (3 to 5 nm diameter) and interface chemistries. The SHG/SFG spectra of silicon nanocrystals (Si NCs) prepared by implanting Si ions uniformly into silica substrates, then annealing, are compared and contrasted to their spectroscopic ellipsometric (SE) and photoluminescence excitation (PLE) spectra. Three resonances--two close in energy to E₁ (3.4 eV) and E2 (4.27 eV) critical-point resonances of crystalline silicon (c-Si), and a broad resonance intermediate in energy between E₁ and E₂--are observed in all three types of spectra. These features are observed in conjunction with a sharp 520 cm⁻¹ Raman peak characteristic of c-Si and an a-Si tail in the Raman spectra. The appearance of bulk-like CP resonances in the parallel PLE, SE and SHG/SFG spectra from Si NCs suggests the basic electronic structure of the bulk c-Si is preserved in nano-particles as small as 3 nm in diameter, albeit with significant size-dependent modification. At the same time, the prominence of a non-bulk-like resonance intermediate in energy between E₁ and E₂ CPs in all three types of spectra demonstrates the important contribution of nano-interfaces to the electronic structure.We also applied Raman spectroscopy to study oxide-embedded and oxide-free alkyl-passivated Si NCs with diameters ranging from 3 nm to greater than 10 nm synthesized by thermal decomposition of hydrogen silsesquioxane (HSQ). While oxide matrix complicates the size-dependence of the Raman peak shift for oxide-embedded nanocrystals, the Raman peak of the free-standing alkyl-passivated Si NCs shifts monotonically with NC size. / text