Typical surface preparation consists of exposure to cleaning chemical to remove contaminants followed by rinsing with ultra-pure water which is followed by drying. Large quantities of water, various chemicals, and energy are used during rinsing and drying processes. Currently there is no in-situ metrology available to determine the cleanliness of micro- and nano-structures as these processes are taking place. This is a major technology gap and leads to over use of resources and adversely affects the throughput.Surface preparation of patterned wafers by batch processing becomes a major challenge as semiconductor fabrication moves deeper in submicron technology nodes. Many fabs have already employed single wafer tools. The main roadblock for single-wafer tools is their lower throughput. This obstacle is eased by introduction of multi chamber tools. To reduce cycle time and resource utilization during rinse and dry processes without sacrificing surface cleanliness and throughput, in-situ metrology is developed and used to compare typical single wafer spinning tools with immersion tools for rinsing of patterned wafers. This novel metrology technology includes both hardware for an in-situ measurement and software for process data analysis. Successful incorporation of this metrology will eliminate dependency on external analysis techniques such as Inductively Coupled Mass Spectroscopy (ICPMS), Scanning Electron Microscope (SEM), and Tunneling Electron Microscope (TEM), and will lead to fast response time.In this study the electro-chemical residue sensor (ECRS) was incorporated in a lab scale single-wafer spinning and single- wafer immersion tool. The ECRS was used to monitor dynamics of rinsing of various cleans such as ammonium peroxide mixture (APM), hydrochloric peroxide mixture (HPM), and sulfuric peroxide mixture (SPM). It was observed that different cleaning chemicals impact the subsequent rinse not only through adsorption and desorption but also through surface charge. The results are analyzed by using a comprehensive process model which takes into account various transport mechanisms such as adsorption, desorption, diffusion, convection, and surface charge. This novel metrology can be used at very low concentration with very high accuracy. It is used to study the effect of the key process parameters such as flow rate, spin rate, temperature, and chemical concentration.

The development of modern digital communication systems has been entered a new era with faster signal transmission and processing capability, called high-speed circuit systems. As their clock frequencies have increased and rise times of signals have decreased, the signal integrity of interconnects in the packaging and printed circuit boards plays a more and more important role. In high-speed circuit systems, the well-designed logic functions most likely will not work well if their interconnects are not taken into account.This dissertation addresses to profoundly understand the signal integrity knowledge, be proficient in calculation, simulation and measurements, and be capable of solving related signal integrity problems. The research mainly emphasizes on three aspects. First of all, the impact of on-wafer calibration methods on the measured results of coplanar waveguide circuits is comprehensively investigated, with their measurement repeatability and accuracy. Furthermore, a method is presented to characterize the physically-consistent broadband material properties for both rigid and flexible dielectric materials. Last but not least, a hybrid method for efficient modeling of three dimensional via structures is developed, in order to simplify the traditional 3D full-length via simulations and dramatically reduce the via build and simulation time and complexity.

This dissertation describes the finding that dissolved carbon dioxide is a potent inhibitor of sonoluminescence and describes the implications of the finding in the development of improved megasonic cleaning formulations. Megasonic cleaning, or the removal of contaminants particles from wafer surfaces using sound-irradiated cleaning fluids, has been traditionally used in the semiconductor industry for cleaning of wafers. Recently however, advancing technology and miniaturization has made wafer features increasingly susceptible to damage by megasonic energy. International Technology Roadmap for Semiconductors (ITRS) 2011 predicts the critical particle diameter, critical particle count and killer defect numbers to be 22 nm, 113 #/wafer and 4.3 #/mm², respectively, on a 300 mm wafer for 45 nm technology node. A critical challenge in the field, therefore, is to achieve removal of small particles (22 nm to 200 nm) without causing damage to fine wafer features. The work described here addresses this challenge by identifying sonoluminescence and solution pH as two key factors affecting damage and cleaning efficiency, respectively and establishing novel means to control them using CO₂(aq) release compounds in the presence of acids and bases. Sonoluminescence (SL) behavior of the major dissolved gases such as Ar, Air, N₂, O₂ and CO₂ was determined using a newly designed Cavitation Threshold Cell (CT Cell). SL, which is the phenomenon of release of light in sound-irradiated liquids, is a sensitive indicator of cavitation, primarily transient cavitation. It was found that all the tested dissolved gases such as Ar, Air, N₂ and O₂, generated SL signal efficiently. However, dissolved CO₂ was found to be completely incapable of generating SL signal. Based on this interesting result, gradual suppression of SL signal was demonstrated using CO₂(aq). It was further demonstrated that CO₂(aq) is not only incapable but is also a potent inhibitor of SL. The inhibitory role of CO₂(aq) was established using a novel method of controlled in-situ release of CO₂ from NH₄HCO₃. ~130 ppm CO₂(aq) was shown to be necessary and sufficient for complete suppression of SL generation in air saturated DI water. The method however required acidification of solution for significant release of CO₂, making it unsuitable for the design of cleaning solutions at high pH. Analysis of the underlying ionic equilibria revealed that the loss of released CO₂(aq) upon increase in pH can be compensated by moderate increase in added NH₄HCO₃. Using this method, simultaneous control of SL and solution pH was demonstrated in two systems, NH₄HCO₃/HCl and NH₄OH/CO₂, at two nominal pH values; 5.7 and 7.0. Damage studies were performed on wafer samples with line/space patterns donated by IMEC and FSI International bearing Si/metal/a-Si gate stacks of thickness ~36 nm and Si/Poly-Si gate stacks of thickness ~67 nm, respectively. A single wafer spin cleaning tool MegPie® was used for the generation of megasonic energy for inducing damage to the structures. It was demonstrated that CO₂ dissolution in DI water suppresses damage to the gate stacks in a dose-dependent manner. Together, these studies establish a systematic and strong correlation between CO₂(aq) concentration, SL suppression and damage suppression. Significant damage reduction (~50 % to ~90 %) was observed at [CO₂(aq)] > ~300 ppm. It was also demonstrated that CO₂(aq) suppresses damage under alkaline pH condition too. This demonstration was made possible by the successful design of two new cleaning systems NH₄HCO₃/NH₄OH and CO₂/NH4OH that could generate CO₂(aq) under alkaline conditions. Damage suppressing ability of the newly designed cleaning systems were compared to the standard cleaning system NH₄OH at pH 8.2 and it was found that NH₄HCO₃/NH₄OH and CO₂/NH₄OH systems were 80 % more efficient in suppressing damage compared to the standard NH₄OH cleaning system. Finally, megasonic cleaning studies were conducted in the same single wafer spin cleaning tool MegPie®, using SiO₂ particles (size 185 nm) deposited on 200 mm oxide Si wafers, as the contaminant. It was found that the standard cleaning chemical, NH₄OH, pH 8.2, was effective in achieving > 95 % particle removal for 2 min irradiation of megasonic energy at power densities > 0.7 W/cm². Based on these results, a new system, NH₄HCO₃/NH₄OH, was designed with an aim to release ~300 ppm CO₂ at pH 8.2. It was demonstrated that newly designed system NH₄HCO₃/NH₄OH, allowed significant suppression of damage in comparison to NH₄OH while maintaining > 90 % cleaning efficiency that was comparable to NH₄OH solution, at the same acoustic power densities. Taken together, these studies establish a potent and flexible means for the inhibition of SL generation over a wide pH range and acoustic power densities and demonstrate its use in suppression of wafer damage without compromising megasonic cleaning efficiency.

As the miniaturization keeps decreasing in semiconductor device fabrication, metal contamination on silicon surfaces becomes critical. An investigation of the fundamental mechanism of metal contamination process on silicon surface is therefore important. Kinetics and thermodynamics of the copper out-plating process on silicon surfaces in diluted HF solutions are both evaluated by several analytical methods.

Student Number ; 9901384G - MPharm dissertation - School of Pharmacy and Pharmacology - Faculty of Health Sciences / A lyophilized polymeric wafer system was formulated for the provision of rapid drug release in the oramucosal region. Lyophilization produced a porous sponge-like matrix which allowed simulated saliva to be rapidly imbibed into the hydrophilic structure. This surge of simulated saliva resulted in rapid disintegration of the wafer. Hydroxypropyl cellulose (HPC) was selected as the polymeric platform based on its low gelation potential. Other excipients incorporated into the system were lactose and mannitol as diluents, and glycine as a collapse protectant. A Face Centred Central Composite Design was chosen to establish the significant effects of the independent formulation variables on the physicochemical and physicomechanical properties of the wafer. The formulation variables investigated were, HPC concentration, type of diluent (lactose, mannitol or mixture), concentration of diluent, quantity of glycine and fill volume. An analysis of these variables elucidated the influential factors that may be controlled to form an ‘ideal’ wafer. The concentration of HPC significantly affected the disintegration rate (p=0.003), influx of simulated saliva (p=0.011) and friability (p=0.023). The quantity of diluent present in the system also had significant effect on matrix tolerance (p=0.029) and friability (p=0.032). Statistical optimization was undertaken using stepwise forward and backward regression, and Artificial Neural Networks to predict the ideal combination of the independent variables that would produce an ideal formulation. This wafer was required to produce a matrix disintegration of 3.33%/s, friability of 0.1% loss and maximum matrix resilience. Formulations manufactured with and without model drug, diphenhydramine hydrochloride, reflected no significant differences in their physicomechanical and physicochemical properties. In an attempt to expand the scope of this technology, a preliminary investigation was undertaken to develop a prolonged release wafer system. This was successfully achieved trough the application of crosslinking technology. It was possible to achieve drug released over a period of 6 hours.

Thin films are used for a variety of applications, which can include electronic devices, optical coatings and decorative parts. They are used for their physical, electrical, magnetic, optical and mechanical properties, and many times these properties are required simultaneously. Obtaining these desired properties starts with the deposition process and they are verified by a number of analysis techniques after deposition. A DC magnetron sputter system was used here to deposit tungsten films, with film thickness and residual stress uniformity being of primary interest. The film thickness was measured to vary by up to 45 % from the center to outer edge of a 4" wafer. Ar pressure was found to influence the thin film residual stress with lower Ar pressures leading to compressive residual stress (-1.5 GPa) and higher Ar pressures leading to tensile residual stress (1 GPa). Residual stress measurements of the tungsten films were made using a wafer curvature technique and X-ray diffraction. The results of the two techniques were compared and found to be within 20 %. Nanoindentation was used to analyze the mechanical properties of several types of thin films that are commonly used in microelectronic devices. Thin film reduced modulus, hardness, interfacial toughness and fracture toughness were some of the mechanical properties measured. Difficulties with performing shallow indents (less than 100 nm) were addressed, with proper calibration procedures for the indentation equipment and tip area function detailed. Pile-up during the indentation of soft films will lead to errors in the indentation contact depth and area, leading to an overestimation of the films' reduced modulus and hardness. A method was developed to account for pile-up in determining the indentation contact depth and calculating a new contact area for improving the analysis of reduced modulus and hardness. Residual stresses in thin films are normally undesired because in extreme cases they may result in thru-film cracking or interfacial film delamination. With the use of lithography techniques to pattern wafers with areas of an adhesion reducing layer, thin film delamination was controlled. The patterned delamination microchannels may be used as an alternative method of creating microchannels for fluid transport in MEMS devices. Delamination morphology was influenced by the amount of residual stress in the film and the critical buckling stress, which was primarily controlled by the width of the adhesion reducing layers.

A Corner Cube Retro-reflector (CCR) is a device that can be used as transmitters in wireless free space optical communication systems, or remote sensing instruments. A novel approach to fabricate the CCR is developed, where almost 100% of the planar chip area acts as the CCR compared to the maximum of 33% in the prior MEMS CCRs. Unlike the conventional micro machined CCRs that have two planes (mirrors of the CCR) normal to the surface of the wafer, our approach yields all the mirrors within the bulk of the wafer, ensuring very high packing densities and wide acceptance angles. The crystallography of single crystal silicon wafer along with different micromachining and wafer bonding techniques are used to fabricate and assemble the CCR. The solid models of both the active and passive CCRs were built using Coventorware simulation software. In the active CCRs, one of the mirror was electrostatically actuated; this is simulated using the software. The results which show a three fold decrease in the pull-in voltage as compared to surface micromachined cantilevers with the same dimensions as presented. Fabrication of the passive CCR along with various fabrication and assembling processes used are discussed. Experimental results are presented and then discussed.

Zugl.: Aachen, Techn. Hochsch., Diss., 2007.

<p>Direct semiconductor wafer bonding has emerged as a technology to meet the demand foradditional flexibility in materials integration. The applications are found in microelectronics, optoelectronics and micromechanics. For instance, wafer bonding is used to produce silicon-on-insulator (SOI) wafers. Wafer bonding is also interesting to use for combining dissimilar semiconductors, such as Si and InP, with different dictated optical, electronic and mechanicalproperties. This enables a completely new freedom in the design of components and systems, e.g. for high performance optoelectronic integrated circuits (OEIC). Although wafer bonding has proved to be a useful and versatile tool, the high temperature annealing that is needed to achieve reliable properties sometimes hampers its applicability. Therefore, low temperature wafer bonding procedures may further qualify this technology.</p><p>In the present thesis, low temperature wafer bonding procedures using oxygen plasma surface activation have been studied. A specially designed fixture was adopted enabling <i>in situ </i>oxygen plasma wafer bonding. Oxygen plasma surface activation was seen to indeed yield high Si-Si bonding-strength at low temperatures. Here, the optimisation of the plasma parameters was shown to be the key to improved results. Furthermore, dependence of wafer bonded Si p-n junctions on the annealing temperature was investigated. InP-to-Si wafer bonding is also presented within this thesis. High temperature annealing was seen to induce severe material degradation. However, using oxygen plasma assisted wafer bonding reliable InP-to-Si integration was achieved already at low temperature, thereby circumventing the problems associated with the lattice and thermal mismatch that exist between these materials. As a result, low temperature InP-based epitaxial-layer transferring to Si could be presented. Finally, high-quality SiO2 insulator on InP and Si was realised at low temperatures.</p><p>It is concluded that low temperature oxygen plasma assisted wafer bonding is an interesting approach to integrate dissimilar materials, for a wide range of applications.</p>

A research synopsis is presented summarizing work with integration of Ge and III-V semiconductors and optical devices with Si. III-V GaAs/AlGaAs quantum well lasers and GaAs/AlGaAs optical circuit structures have been fabricated on Si using Ge/GeSi/Si virtual substrates. The lasers fabricated on bulk GaAs showed similar output characteristics as those on Si. The GaAs/AlGaAs lasers fabricated on Si emitted at 858nm and had room temperature cw lifetimes of ~4hours. Straight optical links integrating an LED emitter, waveguide and detector exhibited losses of approximately 144dB/cm. A process for fabrication of a novel CMOS-compatible platform that integrates III-V or Ge layers with Si is demonstrated. Thin Ge layers have been transferred from Ge/GeSi/Si virtual substrates to bulk Si utilizing wafer bonding and an epitaxial Si CMP layer to facilitate virtual substrate planarization. A unique CMP-less method for removal of Ge exfoliation damage induced by the SmartCut™ process is also presented. / Singapore-MIT Alliance (SMA)