Advances in the interconnection technology have played a key role in the continued improvement of the integrated circuit (IC) density, performance and cost. Copper (Cu) metallization, dual damascenes processing and integration of copper with low dielectric constant material are key issues in the IC industries. Chemical mechanical planarization of copper (CuCMP) has emerged as an important process for the manufacturing of ICs. Usually, Cu-CMP process consists of several steps such as the removal of surface layer by mechanical action of the pad and the abrasive particles, the dissolution of the abraded particles in the CMP solution, and the protection of the recess areas. The CMP process occurs at the atomic level at the pad/slurry/wafer interface, and hence, slurries and polishing pads play critical role in its successful implementation. The slurry for the Cu-CMP contains chemical components to facilitate the oxidation and removal of excess Cu as well as passivation of the polished surface. During the process, these slurry chemicals also react with the pad. In the present study, investigations were carried out to understand the effect of hydrogen peroxide (H2O2) as an oxidant and benzotriazole (BTA) as an inhibitor on the CMP of Cu. Interaction of these slurry components on copper has been investigated using electrochemical studies, x-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS). In the presence of 0.1M glycine, Cu removal rate was found to be high in the solution containing 5% H2O2 at pH 2 because of the Cu-glycine complexation reaction. The dissolution rate of the Cu was found to increase due to the formation of highly soluble Cu-glycine complex in the presence of H2O2. Addition of 0.01M BTA in the solution containing 0.1M glycine and 5% H2O2 at pH 2 exhibited a reduction in the Cu removal rate due to the formation of Cu-BTA complex on the surface of the Cu further inhibiting the dissolution. XPS and SIMS investigations revealed the formation of such Cu-glycine complex, which help understand the mechanism of the Cu-oxidant-inhibitor interaction during polishing. Along with the slurry, pads used in the Cu-CMP process have direct influence an overall process. To overcome problems associated with the current pads, new application specific pad (ASP) have been developed in collaboration with PsiloQuest Inc. Using plasma enhanced chemical vapor deposition (PECVD) process; surface of such ASP pads were modified. Plasma treatment of a polymer surface results in the formation of various functional groups and radicals. Post plasma treatment such as chemical reduction or oxidation imparts a more uniform distribution of such functional groups on the surface of the polymer resulting in unique surface properties. The mechanical properties of such coated pad have been investigated using nanoindentation technique in collaboration with Dr. Vaidyanathan’s research group. The surface morphology and the chemistry of the ASP are studied using scanning electron microcopy (SEM), x-ray photoelectron spectroscopy (XPS), and fourier transform infrared spectroscopy (FTIR) to understand the formation of different chemical species on the surface. It is observed that the mechanical and the chemical properties of the pad top surface are a function of the PECVD coating time. Such PECVD treated pads are found to be hydrophilic and do not require being stored in aqueous medium during the not-in-use period. The metal removal rate using such surface modified polishing pad is found to increase linearly with the PECVD coating time. Overall, this thesis is an attempt to optimize the two most important parameters of the Cu-CMP process viz. slurry and pads for enhanced performance and ultimately reduce the cost of ownership (CoO).

Copper (Cu) electrodeposition on ruthenium (Ru) oxides was studied due to important implications in semiconductor industry. Ruthenium, proposed as the copper diffusion barrier/liner material, has higher oxygen affinity to form different oxides. Three different oxides (the native oxide, reversible oxide, and irreversible oxide) were studied. Native oxide can be formed on exposing Ru in atmosphere. The reversible and irreversible oxides can be formed by applying electrochemical potential. Investigation of Cu under potential deposition on these oxides indicates the similarity between native and reversible oxides by its nature of inhibiting Cu deposition. Irreversible oxide formed on Ru surface is rather conductive and interfacial binding between Cu and Ru is greatly enhanced. After deposition, bimetallic corrosion of Cu/Ru in different polyphenols was studied. Polyphenols are widely used as antioxidants in post chemical mechanical planarization (CMP). For this purpose, different trihydroxyl substituted benzenes were used as antioxidants. Ru, with its noble nature enhances bimetallic corrosion of Cu. Gallic acid (3,4,5 - trihydroxybenzoic acid) was chosen as model compound. A mechanism has been proposed and validity of the mechanism was checked with other antioxidants. Results show that understanding the chemical structure of antioxidants is necessary during its course of reaction with Cu.

Previous studies have shown that spectral analysis based on force data can elucidate fundamental physical phenomena during chemical mechanical planarization (CMP). While it has not been literally described elsewhere, such analysis was partly motivated by modern violinmakers and physicists studying Old Italian violins, who were trying to discover spectral relations to sound quality. In this paper, we draw parallels between violins and CMP as far as functionality and spectral characteristics are concerned. Inspired by the de facto standard of violin testing via hammer strikes on the base edge of a violin's bridge, we introduce for the first time, a mobility plot for the polisher by striking the wafer carrier head of a CMP polisher with a hammer. Results show three independent peaks that can indeed be attributed to the polisher's natural resonance. Extending our study to an actual CMP process, similar to hammered and bowed violin tests, at lower frequencies the hammered and polished mobility peaks are somewhat aligned. At higher frequencies, peak alignment becomes less obvious and the peaks become more isolated and defined in the case of the polished wafer spectrum. Lastly, we introduce another parameter from violin testing known as directivity, , which in our case, we define as the ratio of shear force variance to normal force variance acquired during CMP. Results shows that under identical polishing conditions, increases with the polishing removal rate.

In the first part of this dissertation, copper bimetallic corrosion and its inhibition in cleaning processes involved in interconnect fabrication is explored. In microelectronics fabrication, post chemical mechanical polishing (CMP) cleaning is required to remove organic contaminants and particles left on copper interconnects after the CMP process. Use of cleaning solutions, however, causes serious reliability issues due to corrosion and recession of the interconnects. In this study, different azole compounds are explored and pyrazole is found out to be a potentially superior Cu corrosion inhibitor, compared to the most widely used benzotriazole (BTA), for tetramethyl ammonium hydroxide (TMAH)-based post CMP cleaning solutions at pH 14. Micropattern corrosion screening results and electrochemical impedance spectroscopy (EIS) revealed that 1 mM Pyrazole in 8 wt% TMAH solution inhibits Cu corrosion more effectively than 10 mM benzotriazole (BTA) under same conditions. Moreover, water contact angle measurement results also showed that Pyrazole-treated Cu surfaces are relatively hydrophilic compared to those treated with BTA/TMAH. X-ray photoelectron spectroscopy (XPS) analysis supports Cu-Pyrazole complex formation on the Cu surface. Overall Cu corrosion rate in TMAH-based highly alkaline post CMP cleaning solution is shown to be considerably reduced to less than 1Å/min by addition of 1 mM Pyrazole. In the second part, a novel technique built in-house called multiple internal Reflection Infrared Spectroscopy (MIR-IR) was explored as a characterization tool for characterization of different low-k structures.In leading edge integrated circuit manufacturing, reduction of RC time delay by incorporation of porous ultra low-k interlayer dielectrics into Cu interconnect nanostructure continues to pose major integration challenges. The main challenge is that porous structure renders interlayer dielectrics mechanically weak, chemically unstable and more susceptible to the RIE plasma etching damages. Besides the challenge of handling weak porous ultra low-k materials, a lack of sensitive metrology to guide systematic development of plasma etching, restoration and cleaning processes is the major stumbling block. We explored Multiple Internal Reflection Infrared Spectroscopy and associated IR techniques as a sensitive (sub-5 nm) characterization tool to investigate chemical bonding modification across fluorocarbon etch residues and low-k dielectric interface after plasma etching, ashing, UV curing and post-etch cleaning. The new insights on chemical bonding transformation mapping can effectively guide the development of clean-friendly plasma etch for creating ultra low-k dielectric nanostructures with minimal dielectric damages.

Chemical mechanical polishing (CMP) has been used for a long time in the manufacturing of prime silicon wafers for the IC industry. Lately, other substrates, such as silicon-on-insulator has become in use which requires a greater control of the silicon CMP process. CMP is used to planarize oxide interlevel dielectric and to remove excessive tungsten after plug filling in the Al interconnection technology. In Cu interconnection technology, the plugs and wiring are filled in one step and excessive Cu is removed by CMP. In front end processing, CMP is used to realize shallow trench isolation (STI), to planarize trench capacitors in dynamic random access memories (DRAM) and in novel gate concepts. This thesis is focused on CMP for front end processing, which is the processing on the device level and the starting material. The effects of dopants, crystal orientation and process parameters on silicon removal rate are investigated. CMP and silicon wafer bonding is investigated. Also, plasma assisted wafer bonding to form InP MOS structures is investigated. A complexity of using STI in bipolar and BiCMOS processes is the integration of STI with deep trench isolation (DTI). A process module to realize STI/DTI, which introduces a poly CMP step to planarize the deep trench filling, is presented. Another investigated front end application is to remove the overgrowth in selectively epitaxially grown collector for a SiGe heterojunction bipolar transistor. CMP is also investigated for rounding, which could be beneficial for stress reduction or to create microoptical devices, using a pad softer than pads used for planarization. An issue in CMP for planarization is glazing of the pad, which results in a decrease in removal rate. To retain a stable removal rate, the pad needs to be conditioned. This thesis introduces a geometrically defined abrasive surface for pad conditioning.

Das chemisch-mechanische Planarisieren (CMP) in der Halbleiterindustrie ist ein Prozess mit sehr vielen Einflussgrößen, wobei das Polierergebnis unter anderem von den Eigenschaften der Wechselwirkungskomponenten Wafer, Poliersuspension und Polierpad abhängig ist. Bei der Entwicklung neuer Schaltkreisentwürfe werden die strukturellen Abhängigkeiten der Topografie nach dem CMP häufig im Verlauf von zeit- und kostenintensiven Lernzyklen aufgedeckt und angepasst. Um Dauer und Kosten für die Entwicklung neuer Schaltkreise zu reduzieren, sollte im Rahmen eines BMBF-Projektes ein umfassendes Gesamtmodell, welches den Polierprozess ausführlich beschreibt, entwickelt werden. Für die Umsetzung dieses Vorhabens ist ein umfassendes qualitatives und quantitatives Verständnis der mechanisch-hydrodynamischen und physikalisch-chemischen Mechanismen zu erarbeiten, welche den Materialabtrag und die Planarisierung beim CMP bestimmen. Ziel der vorliegenden Arbeit war es zum einen, mittels direkter Kraftmessung am AFM die Wechselwirkungskräfte zwischen den Festkörperoberflächen von Schleifpartikel und Wafer sowie zwischen den Schleifpartikeln untereinander in CMP-relevanten Flüssigkeiten und ihre Bedeutung für das CMP zu untersuchen. Um die Wechselwirkungskräfte am AFM bestimmen zu können, war zuvor die Entwicklung einer geeigneten Versuchsanordnung nötig. Zur Absicherung der Ergebnisse aus den Kraftmessungen wurde eine Methode erarbeitet, um die zwischenpartikulären Wechselwirkungen mittels rheologischer Untersuchungen indirekt bestimmen zu können. Des Weiteren fanden rheologische Messungen zur Untersuchung der Fließeigenschaften der Poliersuspensionen statt, wobei außerdem der Einfluss anwendungsrelevanter hydrodynamischer Kräfte auf die Stabilität der Poliersuspension zu überprüfen war. Als Poliersuspensionen kamen kommerziell verfügbare Slurries sowie eine Modellslurry zum Einsatz. Neben Systemen mit dispergierten Silica-Partikeln wurde auch eine Slurry mit Ceria-Partikeln als disperse Phase betrachtet. Die kontinuierliche Phase einer Poliersuspension ist ein Mehrkomponentensystem und enthält unterschiedlichste Additive. Untersucht wurde der Einfluss von pH-Wert und Elektrolytkonzentration auf die Wechselwirkungskräfte, das Fließverhalten sowie den Materialabtrag.

Composite materials formed from two or more functionally different materials offer a versatile avenue to create a tailored material with well defined traits. Within this dissertation research, multi-functional composites were synthesized based on organic and inorganic materials. The functionally of these composites was experimentally tested and a semi-empirical model describing the sedimentation behavior of these particles was developed. This first objective involved the fabrication of microcomposites consisting of titanium dioxide (TiO2) nanoparticles confined within porous, microgels of a thermo-responsive polymer for use in the photocatalytic treatment of wastewater. TiO2 has been shown to be an excellent photocatalyst with potential applications in advanced oxidative processes such as wastewater remediation. Upon UV irradiation, short-lived electron-hole pairs are generated, which produce oxidative species that degrade simple organic contaminants. The rapid sedimentation of these microcomposites provided an easy gravimetric separation after remediation. Methyl orange was used as a model organic contaminant to investigate the kinetics of photodegradation under a range of concentrations and pH conditions. Although after prolonged periods of UV irradiation (~8-13 hrs), the titania-microgels also degrade, regeneration of the microcomposites was straightforward via the addition of polymer microgels with no loss in photocatalytic activity of the reformed microcomposites. The second objective within this dissertation involved the systematic development of abrasive microcomposite particles containing well dispersed nanoparticles of ceria in an organic/inorganic hybrid polymeric particle for use in chemical mechanical polishing/planarization (CMP). A challenge in IC fabrication involves the defect-free planarization of silicon oxide films for successful multi-layer deposition. Planarization studies conducted with the microcomposites prepared in this research, yield very smooth, planar surfaces with removal rates that rival those of inorganic oxides slurries typically used in industry. The density and size of these ceria-microgel particles could be controlled by varying the temperature or composition during synthesis, leading to softer or harder polishing when desired.

Das chemisch-mechanische Planarisieren (CMP) in der Halbleiterindustrie ist ein Prozess mit sehr vielen Einflussgrößen, wobei das Polierergebnis unter anderem von den Eigenschaften der Wechselwirkungskomponenten Wafer, Poliersuspension und Polierpad abhängig ist. Bei der Entwicklung neuer Schaltkreisentwürfe werden die strukturellen Abhängigkeiten der Topografie nach dem CMP häufig im Verlauf von zeit- und kostenintensiven Lernzyklen aufgedeckt und angepasst. Um Dauer und Kosten für die Entwicklung neuer Schaltkreise zu reduzieren, sollte im Rahmen eines BMBF-Projektes ein umfassendes Gesamtmodell, welches den Polierprozess ausführlich beschreibt, entwickelt werden. Für die Umsetzung dieses Vorhabens ist ein umfassendes qualitatives und quantitatives Verständnis der mechanisch-hydrodynamischen und physikalisch-chemischen Mechanismen zu erarbeiten, welche den Materialabtrag und die Planarisierung beim CMP bestimmen. Ziel der vorliegenden Arbeit war es zum einen, mittels direkter Kraftmessung am AFM die Wechselwirkungskräfte zwischen den Festkörperoberflächen von Schleifpartikel und Wafer sowie zwischen den Schleifpartikeln untereinander in CMP-relevanten Flüssigkeiten und ihre Bedeutung für das CMP zu untersuchen. Um die Wechselwirkungskräfte am AFM bestimmen zu können, war zuvor die Entwicklung einer geeigneten Versuchsanordnung nötig. Zur Absicherung der Ergebnisse aus den Kraftmessungen wurde eine Methode erarbeitet, um die zwischenpartikulären Wechselwirkungen mittels rheologischer Untersuchungen indirekt bestimmen zu können. Des Weiteren fanden rheologische Messungen zur Untersuchung der Fließeigenschaften der Poliersuspensionen statt, wobei außerdem der Einfluss anwendungsrelevanter hydrodynamischer Kräfte auf die Stabilität der Poliersuspension zu überprüfen war. Als Poliersuspensionen kamen kommerziell verfügbare Slurries sowie eine Modellslurry zum Einsatz. Neben Systemen mit dispergierten Silica-Partikeln wurde auch eine Slurry mit Ceria-Partikeln als disperse Phase betrachtet. Die kontinuierliche Phase einer Poliersuspension ist ein Mehrkomponentensystem und enthält unterschiedlichste Additive. Untersucht wurde der Einfluss von pH-Wert und Elektrolytkonzentration auf die Wechselwirkungskräfte, das Fließverhalten sowie den Materialabtrag.

<p>III-V nanowire (NW) ensemble devices were fabricated using novel approaches to address key NW optoelectronic issues concerning electrical contacts, doping, surface effects and underlying electrostatics physics.</p> <p>NWs were first embedded in a filling medium, thus achieving low sheet resistance front contacts while preventing shunts. Various filling materials were assessed for porosity, surface roughness and thermal stability, giving Cyclotene as an ideal filing material. Sonication was also introduced as a novel method to achieve perfect planarization.</p> <p>The presence of the Cyclotene also enabled the NWs to be characterized precisely and easily by secondary ion mass spectrometry (SIMS) to give the NW dopant concentration with excellent spatial resolution. Additionally, SIMS characterization demonstrated the ability to characterize the height uniformity of individual segments in a heterostructure NW ensemble.</p> <p>The focus of the work shifted towards surface effects on NW device performance. Therefore, Poisson's equation was solved to provide a comprehensive model of NW surface depletion as a function of interface state density, NW radius and doping density. Underlying physics was examined where surface depletion was found to significantly reduce the conductivity of thin NWs, leading to carrier inversion for some.</p> <p>This model was then applied in conjunction with a transport model to fit current-voltage curves of an AlInP-passivated GaAs NW ensemble device. A 55% decrease in surface state density was achieved upon passivation, corresponding to an impressive four order of magnitude increase in the effective carrier concentration. Additionally, conventional and time-resolved photoluminescence measurements showed intensity and carrier lifetime improvement greater than 20x upon passivation.</p> <p>Finally, the model was extended to describe radial pn junction NWs with surface depletion to give radial energy band profiles for any arbitrary set of NW parameters. Specific cases were analyzed to extract pertinent underlying physics, while the built-in potential was optimized for the design for an optimal device.</p> / Doctor of Philosophy (PhD)