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Adhesion/Diffusion Barrier Layers for Copper Integration: Carbon-Silicon Polymer Films and Tantalum Substrates

Description: The Semiconductor Industry Association (SIA) has identified the integration of copper (Cu) with low-dielectric-constant (low-k) materials as a critical goal for future interconnect architectures. A fundamental understanding of the chemical interaction of Cu with various substrates, including diffusion barriers and adhesion promoters, is essential to achieve this goal. The objective of this research is to develop novel organic polymers as Cu/low-k interfacial layers and to investigate popular barrier candidates, such as clean and modified tantalum (Ta) substrates. Carbon-silicon (C-Si) polymeric films have been formed by electron beam bombardment or ultraviolet (UV) radiation of molecularly adsorbed vinyl silane precursors on metal substrates under ultra-high vacuum (UHV) conditions. Temperature programmed desorption (TPD) studies show that polymerization is via the vinyl groups, while Auger electron spectroscopy (AES) results show that the polymerized films have compositions similar to the precursors. Films derived from vinyltrimethyl silane (VTMS) are adherent and stable on Ta substrates until 1100 K. Diffusion of deposited Cu overlayers is not observed below 800 K, with dewetting occurred only above 400 K. Hexafluorobenzene moieties can also be incorporated into the growing film with good thermal stability. Studies on the Ta substrates demonstrate that even sub-monolayer coverages of oxygen or carbide on polycrystalline Ta significantly degrade the strength of Cu/Ta chemical interactions, and affect the kinetics of Cu diffusion into bulk Ta. On clean Ta, monolayer coverages of Cu will de-wet only above 600 K. A partial monolayer of adsorbed oxygen (3L O2 at 300 K) results in a lowering of the de-wetting temperature to 500 K, while saturation oxygen coverage (10 L O2, 300 K) results in de-wetting at 300 K. Carbide formation also lowers the de-wetting temperature to 300 K. Diffusion of Cu into the Ta substrate at 1100 K occurs only after a 5-minute induction period. This induction period increases ...
Date: December 1999
Creator: Chen, Li
Partner: UNT Libraries

Diffusion Barriers/Adhesion Promoters. Surface and Interfacial Studies of Copper and Copper-Aluminum Alloys

Description: The focus of this research is to study the interaction between copper and the diffusion barrier/adhesion promoter. The behavior of copper sputter-deposited onto sputter-cleaned tantalum nitride is investigated. The data show that copper growth on tantalum nitride proceeds with the formation of 3-D islands, indicating poor adhesion characteristics between copper and Ta0.4N. Post-annealing experiments indicate that copper will diffuse into Ta0.4N at 800 K. Although the data suggests that Ta0.4N is effective in preventing copper diffusion, copper's inability to wet Ta0.4N will render this barrier ineffective. The interaction of copper with oxidized tantalum silicon nitride (O/TaSiN) is characterized. The data indicate that initial copper depositions result in the formation a conformal ionic layer followed by Cu(0) formation in subsequent depositions. Post-deposition annealing experiments performed indicate that although diffusion does not occur for temperatures less than 800 K, copper "de-wetting" occurs for temperatures above 500 K. These results indicate that in conditions where the substrate has been oxidized facile de-wetting of copper may occur. The behavior of a sputter-deposited Cu0.6Al0.4 film with SiO2 (Cu0.6Al0.4/SiO2) is investigated. The data indicate that aluminum segregates to the SiO2 interface and becomes oxidized. For copper coverages less than ~ 0.31 ML (based on a Cu/O atomic ratio), only Cu(I) formation is observed. At higher coverages, Cu(0) is observed. These data are in contrast with the observed behavior of copper metal deposited onto SiO2 (Cu/SiO2). The data for Cu/SiO2 show that copper does not wet SiO2 and forms 3-D nuclei. Furthermore, post-annealing experiments performed on Cu0.6Al0.4/SiO2 show that neither de-wetting nor diffusion of copper occurs for temperatures up to 800 K, while Cu diffusion into SiO2 occurs ~ 600 K. These data indicate that aluminum alloyed with copper at the SiO2 interface serves as an effective adhesion promoter and thermal diffusion barrier.
Date: August 2000
Creator: Shepherd, Krupanand Solomon
Partner: UNT Libraries

Uranium-Bearing Copper Deposits Near Guadalupita, Mora County, New Mexico

Description: Abstract: Dark shale and arkosic sandstone south of Guadalupita, Mora County, New Mexico, contain as much as 4 percent copper and 0. 01 percent uranium on the basis of a few samples recently analyzed. The deposits occur primarily in the dark shale which is about 5 feet thick and dips about 900. Potential reserves of this material are very large. Prospecting and further geologic work will be necessary, however, to evaluate possibilities of these large tonnages. If the deposits can be mined for their copper content, the uranium might be recovered as a byproduct. Detailed mapping and possibly some trenching will be undertaken by the Geological Survey in order further to evaluate the deposits.
Date: July 1952
Creator: Bachman, George Odell & Read, Charles B.
Partner: UNT Libraries Government Documents Department

Study of Interactions Between Diffusion Barrier Layers and Low-k Dielectric Materials for Copper/Low-k Integration

Description: The shift to the Cu/low-k interconnect scheme requires the development of diffusion barrier/adhesion promoter materials that provide excellent performance in preventing the diffusion and intermixing of Cu into the adjacent dielectrics. The integration of Cu with low-k materials may decrease RC delays in signal propagation but pose additional problems because such materials are often porous and contain significant amounts of carbon. Therefore barrier metal diffusion into the dielectric and the formation of interfacial carbides and oxides are of significant concern. The objective of the present research is to investigate the fundamental surface interactions between diffusion barriers and various low-k dielectric materials. Two major diffusion barriers¾ tatalum (Ta) and titanium nitride (TiN) are prepared by DC magnetron sputtering and metal-organic chemical vapor deposition (MOCVD), respectively. Surface analytical techniques, such as X-ray photoelectronic spectroscopy (XPS), transmission electron microscopy (TEM), and atomic force microscopy (AFM) are employed. Ta sputter-deposited onto a Si-O-C low dielectric constant substrate forms a reaction layer composed of Ta oxide and TaC. The composition of the reaction layer varies with deposition rate (1 Å-min-1 vs. 2 Å-sec-1), but in both cases, the thickness of the TaC layer is found to be at least 30 Å on the basis of XPS spectra, which is corroborated with cross-sectional TEM data. Sputter-deposited Cu will not wet the TaC layer and displays facile agglomeration, even at 400 K. Deposition for longer time at 2 Å-sec-1 results in formation of a metallic Ta layer. Sputter deposited Cu wets (grows conformally) on the metallic Ta surface at 300 K, and resists significant agglomeration at up to ~ 600 K. Cu diffusion into the substrate is not observed up to 800 K in the UHV environment. Tetrakis(diethylamido) titanium (TDEAT) interactions with SiO2, Cu and a variety of low-k samples in the presence (~ 10-7 Torr or ...
Date: December 2003
Creator: Tong, Jinhong
Partner: UNT Libraries

Cu Electrodeposition on Ru with a Chemisorbed Iodine Surface Layer.

Description: An iodine surface layer has been prepared on Ru(poly) and Ru(0001) electrodes by exposure to iodine vapor in UHV and polarizing in a 0.1 M HClO4/0.005 M KI solution, respectively. A saturation coverage of I on a Ru(poly) electrode passivates the Ru surface against significant hydroxide, chemisorbed oxygen or oxide formation during exposure to water vapor over an electrochemical cell in a UHV-electrochemistry transfer system. Immersion of I-Ru(poly) results in greater hydroxide and chemisorbed oxygen formation than water vapor exposure, but an inhibition of surface oxide formation relative that of the unmodified Ru(poly) surface is still observed. Studies with combined electrochemical and XPS techniques show that the iodine surface adlayer remained on top of the surface after cycles of overpotential electrodeposition/dissolution of copper on both Ru(poly) and Ru(0001) electrodes. These results indicate the potential bifunctionality of iodine layer to both passivate the Ru surface in the microelectronic processing and to act as a surfactant for copper electrodeposition. The electrodeposition of Cu on Ru(0001) or polycrystalline Ru was studied using XPS with combined ultrahigh vacuum/electrochemistry methodology (UHV-EC) in 0.1 M HClO4 with Cu(ClO4)2 concentrations ranging from 0.005 M to 0.0005 M, and on polycrystalline Ru in a 0.05M H2SO4/0.005 M CuSO4/0.001 M NaCl solution. The electrochemical data show well-defined cyclic voltammograms (CV) with a Cu underpotential deposition (UPD) peak and overpotential deposition (OPD) peak. XPS spectra of Ru electrodes emersed from perchloric acid solution at cathodic potentials indicate that ClO4- anions dissociate to yield specifically adsorbed Cl and ClOx species. Subsequent Cu deposition results in the formation of a thin, insoluble Cu(II) film with Cu(I) underneath. In contrast, similar deposition on polycrystalline Ru in the sulfuric acid/Cu sulfate solution with NaCl added yields only Cu(0), indicating that the formation of Cu(II) and Cu(I) involves both Cl and perchlorate interactions with the ...
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Date: August 2005
Creator: Lei, Jipu
Partner: UNT Libraries

Interfacial Electrochemistry and Surface Characterization: Hydrogen Terminated Silicon, Electrolessly Deposited Palladium & Platinum on Pyrolyzed Photoresist Films and Electrodeposited Copper on Iridium

Description: Hydrogen terminated silicon surfaces play an important role in the integrated circuit (IC) industry. Ultra-pure water is extensively used for the cleaning and surface preparation of silicon surfaces. This work studies the effects of ultra-pure water on hydrogen passivated silicon surfaces in a short time frame of 120 minutes using fourier transform infrared spectroscopy – attenuated total reflection techniques. Varying conditions of ultra-pure water are used. This includes dissolved oxygen poor media after nitrogen bubbling and equilibration under nitrogen atmosphere, as well as metal contaminated solutions. Both microscopically rough and ideal monohydride terminated surfaces are examined. Hydrogen terminated silicon is also used as the sensing electrode for a potentiometric sensor for ultra-trace amounts of metal contaminants. Previous studies show the use of this potentiometric electrode sensor in hydrofluoric acid solution. This work is able to shows sensor function in ultra-pure water media without the need for further addition of hydrofluoric acid. This is considered a boon for the sensor due to the hazardous nature of hydrofluoric acid. Thin carbon films can be formed by spin coating photoresist onto silicon substrates and pyrolyzing at 1000 degrees C under reducing conditions. This work also shows that the electroless deposition of palladium and platinum may be accomplished in hydrofluoric acid solutions to attain palladium and platinum nanoparticles on a this film carbon surface for use as an electrode. Catalysis of these substrates is studied using hydrogen evolution in acidic media, cyclic voltammetry, and catalysis of formaldehyde. X-ray diffractometry (XRD) is used to ensure that there is little strain on palladium and platinum particles. Iridium is thought to be a prime candidate for investigation as a new generation copper diffusion barrier for the IC industry. Copper electrodeposition on iridium is studied to address the potential of iridium as a copper diffusion barrier. Copper electrodeposition ...
Date: December 2003
Creator: Chan, Raymond
Partner: UNT Libraries

Influence of copper on resistance of Lumbricus terrestris to bacterial challenge

Description: Earthworms, Lumbricus terrestris, were challenged orally and intracoelomically with two bacterial species, Aeromonas hydrophila and Pseudomonas aeruginosa, and mortality rates were observed. Neither were found to be particularly pathogenic at injected doses of up to 108 bacteria per earthworm. The influence of Cu++ (as CuSO4) on the earthworm's response to bacterial challenge was investigated by exposing earthworms to sublethal levels of Cu++ prior to bacterial challenge. Exposure at sublethal concentrations up to 3 m g/cm2 did not have a pronounced influence on host resistance to challenge as measured by earthworm mortality. Cu++ increased the earthworm's ability to agglutinate rabbit erythrocytes, indicating that Cu++ exposure caused coelomocyte death, autolysis and release of agglutinins into the coelom, possibly explaining resistance to bacterial challenge.
Date: August 2000
Creator: Simmons, Carla Stull
Partner: UNT Libraries

Surface and Interfacial Studies of Metal-Organic Chemical Vapor Deposition of Copper

Description: The nucleation and successful growth of copper (Cu) thin films on diffusion barrier/adhesion promoter substrates during metal-organic chemical vapor deposition (MOCVD) are strongly dependent on the initial Cu precursor-substrate chemistry and surface conditions such as organic contamination and oxidation. This research focuses on the interactions of bis(1,1,1,5,5,5-hexafluoroacetylacetonato)copper(II), [Cu(hfac)2], with polycrystalline tantalum (Ta) and polycrystalline as well as epitaxial titanium nitride (TiN) substrates during Cu MOCVD, under ultra-high vacuum (UHV) conditions and low substrate temperatures (T < 500 K). The results obtained from X-ray photoelectron spectroscopy (XPS), Auger Electron Spectroscopy (AES) and Temperature Programmed Desorption (TPD) measurements indicate substantial differences in the chemical reaction pathways of metallic Cu formation from Cu(hfac)2 on TiN versus Ta surfaces.
Date: December 1997
Creator: Nuesca, Guillermo M.
Partner: UNT Libraries

Tantalum- and ruthenium-based diffusion barriers/adhesion promoters for copper/silicon dioxide and copper/low κ integration.

Description: The TaSiO6 films, ~8Å thick, were formed by sputter deposition of Ta onto ultrathin SiO2 substrates at 300 K, followed by annealing to 600 K in 2 torr O2. X-ray photoelectron spectroscopy (XPS) measurements of the films yielded a Si(2p) binding energy at 102.1 eV and Ta(4f7/2) binding energy at 26.2 eV, indicative of Ta silicate formation. O(1s) spectra indicate that the film is substantially hydroxylated. Annealing the film to > 900 K in UHV resulted in silicate decomposition to SiO2 and Ta2O5. The Ta silicate film is stable in air at 300K. XPS data show that sputter-deposited Cu (300 K) displays conformal growth on Ta silicate surface (TaSiO6) but 3-D growth on the annealed and decomposed silicate surface. Initial Cu/silicate interaction involves Cu charge donation to Ta surface sites, with Cu(I) formation and Ta reduction. The results are similar to those previously reported for air-exposed TaSiN, and indicate that Si-modified Ta barriers should maintain Cu wettability under oxidizing conditions for Cu interconnect applications. XPS has been used to study the reaction of tert-butylimino tris(diethylamino) tantalum (TBTDET) with atomic hydrogen on SiO2 and organosilicate glass (OSG) substrates. The results on both substrates indicate that at 300K, TBTDET partially dissociates, forming Ta-O bonds with some precursor still attached. Subsequent bombardment with atomic hydrogen at 500K results in stoichiometric TaN formation, with a Ta(4f7/2) feature at binding energy 23.2 eV and N(1s) at 396.6 eV, leading to a TaN phase bonded to the substrate by Ta-O interactions. Subsequent depositions of the precursor on the reacted layer on SiO2 and OSG, followed by atomic hydrogen bombardment, result in increased TaN formation. These results indicate that TBTDET and atomic hydrogen may form the basis for a low temperature atomic layer deposition (ALD) process for the formation of ultraconformal TaNx or Ru/TaNx barriers. The interactions ...
Date: December 2004
Creator: Zhao, Xiaopeng
Partner: UNT Libraries

Adherence/Diffusion Barrier Layers for Copper Metallization: Amorphous Carbon:Silicon Polymerized Films

Description: Semiconductor circuitry feature miniaturization continues in response to Moore 's Law pushing the limits of aluminum and forcing the transition to Cu due to its lower resistivity and electromigration. Copper diffuses into silicon dioxide under thermal and electrical stresses, requiring the use of barriers to inhibit diffusion, adding to the insulator thickness and delay time, or replacement of SiO2 with new insulator materials that can inhibit diffusion while enabling Cu wetting. This study proposes modified amorphous silicon carbon hydrogen (a-Si:C:H) films as possible diffusion barriers and replacements for SiO2 between metal levels, interlevel dielectric (ILD), or between metal lines (IMD), based upon the diffusion inhibition of previous a-Si:C:H species expected lower dielectric constants, acceptable thermal conductivity. Vinyltrimethylsilane (VTMS) precursor was condensed on a titanium substrate at 90 K and bombarded with electron beams to induce crosslinking and form polymerized a-Si:C:H films. Modifications of the films with hydroxyl and nitrogen was accomplished by dosing the condensed VTMS with water or ammonia before electron bombardment producing a-Si:C:H/OH and a-Si:C:H/N and a-Si:C:H/OH/N polymerized films in expectation of developing films that would inhibit copper diffusion and promote Cu adherence, wetting, on the film surface. X-ray Photoelectron Spectroscopy was used to characterize Cu metallization of these a-Si:C:H films. XPS revealed substantial Cu wetting of a-Si:C:H/OH and a-Si:C:H/OH/N films and some wetting of a-Si:C:H/N films, and similar Cu diffusion inhibition to 800 K by all of the a-:S:C:H films. These findings suggest the possible use of a-Si:C:H films as ILD and IMD materials, with the possibility of further tailoring a-Si:C:H films to meet future device requirements.
Date: May 2004
Creator: Pritchett, Merry
Partner: UNT Libraries

Amorphization and De-vitrification in Immiscible Copper-Niobium Alloy Thin Films

Description: While amorphous phases have been reported in immiscible alloy systems, there is still some controversy regarding the reason for the stabilization of these unusual amorphous phases. Direct evidence of nanoscale phase separation within the amorphous phase forming in immiscible Cu-Nb alloy thin films using 3D atom probe tomography has been presented. This evidence clearly indicates that the nanoscale phase separation is responsible for the stabilization of the amorphous phase in such immiscible systems since it substantially reduces the free energy of the undercooled liquid (or amorphous) phase, below that of the competing supersaturated crystalline phases. The devitrification of the immiscible Cu-Nb thin film of composition Cu-45% Nb has been studied in detail with the discussion on the mechanism of phase transformation. The initial phase separation in the amorphous condition seems to play a vital role in the crystallization of the thin film. Detailed analysis has been done using X-ray diffraction, transmission electron microscopy and 3D atom probe tomography.
Date: May 2007
Creator: Puthucode Balakrishnan, Anantharamakrishnan
Partner: UNT Libraries

Copper Electrodeposition on Iridium, Ruthenium and Its Conductive Oxide Substrate

Description: The aim of this thesis was to investigate the physical and electrochemical properties of sub monolayer and monolayer of copper deposition on the polycrystalline iridium, ruthenium and its conductive oxide. The electrochemical methods cyclic voltammetry (CV) and chronocoulometry were used to study the under potential deposition. The electrochemical methods to oxidize the ruthenium metal are presented, and the electrochemical properties of the oxide ruthenium are studied. The full range of CV is presented in this thesis, and the distances between the stripping bulk peak and stripping UPD peak in various concentration of CuSO4 on iridium, ruthenium and its conductive oxide are shown, which yields thermodynamic data on relative difference of bonding strength between Cu-Ru/Ir atoms and Cu-Cu atoms. The monolayer of UPD on ruthenium is about 0.5mL, and on oxidized ruthenium is around 0.9mL to 1.0mL. The conductive oxide ruthenium presents the similar properties of ruthenium metal. The pH effect of stripping bulk peak and stripping UPD peak of copper deposition on ruthenium and oxide ruthenium was investigated. The stripping UPD peak and stripping bulk peak disappeared after the pH ≥ 3 on oxidized ruthenium electrode, and a new peak appeared, which means the condition of pH is very important. The results show that the Cl- , SO42- , Br- will affect the position of stripping bulk peak and stripping UPD peak: the stripping bulk peak will shift and decrease if the concentration of halide ions is increasing, and the monolayer of UPD will increase at the same time.
Date: December 2003
Creator: Huang, Long
Partner: UNT Libraries

Improvement of Homogeneity and Adhesion of Diamond-Like Carbon Films on Copper Substrates

Description: Electrodeposition method is used to deposit diamond-like carbon (DLC) films on copper substrates via anodic oxidation at low temperature. These films are characterized using Raman spectroscopy, Fourier transform infrared spectroscopy and scanning electron microscopy. Homogeneity of these films is studied using Raman spectroscopy and scanning electron microscopy. Scotch tape peel tests indicate adherent film on copper substrate. Carbon phase transformation is studied using thermal annealing experiments in conjunction with Raman spectroscopy and scanning electron microscopy. A cathodic electrochemical method is also studied to deposit diamond-like carbon films on copper substrates. However, films deposited by the cathodic route have poor adhesion and quality compared to anodically deposited films. It is also possible to grow diamond phase on copper substrates using acetylene in liquid ammonia via electrodeposition route. An electrochemical method is proposed for boron doping into DLC films.
Date: August 2004
Creator: Vavilala, Suma
Partner: UNT Libraries

FTIR-ATR Characterization of Hydrogel, Polymer Films, Protein Immobilization and Benzotriazole Adsorption on Copper Surface

Description: Plasma polymerization techniques were used to synthesize and deposit hydrogel on silicon (Si) substrate. Hydrogel is a network of polymer chains that are water-insoluble and has a high degree of flexibility. The various fields of applications of hydrogel include drug release, biosensors and tissue engineering etc. Hydrogel synthesized from different monomers possess a common property of moisture absorption. In this work two monomers were used namely 1-amino-2-propanol (1A2P) and 2(ethylamino)ethanol (2EAE) to produce polymer films deposited on Si ATR crystal. Their moisture uptake property was tested using FTIR-ATR technique. This was evident by the decrease in -OH band in increasing N2 purging time of the films. Secondly, two monomer compounds namely vinyl acetic acid and glycidyl methacrylate which have both amine and carboxylic groups are used as solid surface for the immobilization of bovine serum albumin (BSA). Pulsed plasma polymerization was used to polymerize these monomers with different duty cycles. Initial works in this field were all about protein surface adsorption. But more recently, the emphasis is on covalent bonding of protein on to the surface. This immobilization of protein on solid surface has a lot of applications in the field of biochemical studies. The polymerization of vinyl acetic acid and glycidyl methacrylate were shown as successful method to attach protein on them. Chemical mechanical polishing (CMP) of Cu is one of the processes in the integrated chips manufacturing industry. Benzotriazole is one of the constituents of this CMP slurry used as corrosion inhibitor for Cu. Benzotriazole (C6H5N3) is a nitrogen heterocyclic derivative having three nitrogen atoms, each with an unshared pair of electrons, forming five-membered ring structure. This molecule coordinates with Cu atoms by loosing a proton from one of its nitrogen atom and thereby forming a film which is polymeric in nature that prevents further oxidation of Cu. ...
Date: December 2007
Creator: Pillai, Karthikeyan
Partner: UNT Libraries

Interfacial Study of Copper Electrodeposition with the Electrochemical Quartz Crystal Microbalance (EQCM)

Description: The electrochemical quartz crystal microbalance (EQCM) has been proven an effective mean of monitoring up to nano-scale mass changes related to electrode potential variations at its surface. The principles of operation are based on the converse piezoelectric response of quartz crystals to mass variations on the crystal surface. In this work, principles and operations of the EQCM and piezo-electrodes are discussed. A conductive oxide, ruthenium oxide (RuO2) is a promising material to be used as a diffusion barrier for metal interconnects. Characterization of copper underpotential deposition (UPD) on ruthenium and RuO2 electrodes by means of electrochemical methods and other spectroscopic methods is presented. Copper electrodeposition in platinum and ruthenium substrates is investigated at pH values higher than zero. In pH=5 solutions, the rise in local pH caused by the reduction of oxygen leads to the formation of a precipitate, characterized as posnjakite or basic copper sulfate by means of X-ray electron spectroscopy and X-ray diffraction. The mechanism of formation is studied by means of the EQCM, presenting this technique as a powerful in-situ sensing device.
Date: May 2005
Creator: Ojeda Mota, Oscar Ulises
Partner: UNT Libraries

The Revival of Electrochemistry: Electrochemical Deposition of Metals in Semiconductor Related Research

Description: Adherent Cu films were electrodeposited onto polycrystalline W foils from purged solutions of 0.05 M CuSO4 in H2SO4 supporting electrolyte and 0.025 M CuCO3∙Cu(OH)2 in 0.32 M H3BO3 and corresponding HBF4 supporting electrolyte, both at pH = 1. Films were deposited under constant potential conditions at voltages between -0.6 V and -0.2 V versus Ag/AgCl. All films produced by pulses of 10 s duration were visible to the eye, copper colored, and survived a crude test called "the Scotch tape test", which involves sticking the scotch tape on the sample, then peeling off the tape and observing if the copper film peels off or not. Characterization by scanning electron microscopy (SEM)/energy dispersive X-ray (EDX) and X-ray photon spectroscopy (XPS) confirmed the presence of metallic Cu, with apparent dendritic growth. No sulfur impurity was observable by XPS or EDX. Kinetics measurements indicated that the Cu nucleation process in the sulfuric bath is slower than in the borate bath. In both baths, nucleation kinetics does not correspond to either instantaneous or progressive nucleation. Films deposited from 0.05 M CuSO4/H2SO4 solution at pH > 1 at -0.2 V exhibited poor adhesion and decreased Cu reduction current. In both borate and sulfate baths, small Cu nuclei are observable by SEM upon deposition at higher negative overpotentials, while only large nuclei (~ 1 micron or larger) are observed upon deposition at less negative potentials. Osmium metal has been successfully electrodeposited directly onto p-Si (100) from both Os3+ and Os4+ in both sulfuric and perchloric baths. This electrochemical deposition of osmium metal can provide sufficient amount of osmium which overcome ion beam implantation limitations. The deposited metal can undergo further processing to form osmium silicides, such as Os2Si3, which can be used as optical active materials. The higher osmium concentration results in large deposition currents and ...
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Date: August 2005
Creator: Wang, Chen
Partner: UNT Libraries

Electrodeposition of adherent copper film on unmodified tungsten.

Description: Adherent Cu films were electrodeposited onto polycrystalline W foils from purged solutions of 0.05 M CuSO4 in H2SO4 supporting electrolyte and 0.025 M CuCO3∙Cu(OH)2 in 0.32 M H3BO3 and corresponding HBF4 supporting electrolyte, both at pH = 1. Films were deposited under constant potential conditions at voltages between -0.6 V and -0.2 V vs Ag/AgCl. All films produced by pulses of 10 s duration were visible to the eye, copper colored, and survived a crude test called "the Scotch tape test", which stick the scotch tape on the sample, then peel off the tape and see if the copper film peels off or not. Characterization by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and X-ray photon spectroscopy (XPS) confirmed the presence of metallic Cu, with apparent dendritic growth. No sulfur impurity was observable by XPS or EDX. Kinetics measurements indicate that the Cu nucleation process in the sulfuric bath is slower than in the borate bath. In both baths, nucleation kinetics do not correspond to either instantaneous or progressive nucleation. Films deposited from 0.05 M CuSO4/H2SO4 solution at pH > 1 at -0.2 V exhibited poor adhesion and decreased Cu reduction current. In both borate and sulfate baths, small Cu nuclei are observable by SEM upon deposition at higher negative overpotentials, while only large nuclei (~ 1 micron or larger) are observed upon deposition at less negative potentials.
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Date: May 2004
Creator: Wang, Chen
Partner: UNT Libraries

Process Evaluation and Characterization of Tungsten Nitride as a Diffusion Barrier for Copper Interconnect Technology

Description: The integration of copper (Cu) and dielectric materials has been outlined in the International Technology Roadmap for Semiconductors (ITRS) as a critical goal for future microelectronic devices. A necessity toward achieving this goal is the development of diffusion barriers that resolve the Cu and dielectric incompatibility. The focus of this research examines the potential use of tungsten nitride as a diffusion barrier by characterizing the interfacial properties with Cu and evaluating its process capability for industrial use. Tungsten nitride (β-W2N) development has been carried out using a plasma enhanced chemical vapor deposition (PECVD) technique that utilizes tungsten hexafluoride (WF6), nitrogen (N2), hydrogen (H2), and argon (Ar). Two design of experiments (DOE) were performed to optimize the process with respect to film stoichiometry, resistivity and uniformity across a 200 mm diameter Si wafer. Auger depth profiling showed a 2:1 W:N ratio. X-ray diffraction (XRD) showed a broad peak centered on the β-W2N phase. Film resistivity was 270 mohm-cm and film uniformity < 3 %. The step coverage (film thickness variance) across a structured etched dielectric (SiO2, 0.35 mm, 3:1 aspect ratio) was > 44 %. Secondary ion mass spectroscopy (SIMS) measurements showed good barrier performance for W2N between Cu and SiO2 with no intermixing of the Cu and silicon when annealed to 390o C for 3 hours. Cu nucleation behavior and thermal stability on clean and nitrided tungsten foil (WxN = δ-WN and β-W2N phases) have been characterized by Auger electron spectroscopy (AES) and thermal desorption spectroscopy (TDS) under controlled ultra high vacuum (UHV) conditions. At room temperature, the Auger intensity ratio vs. time plots demonstrates layer by layer Cu growth for the clean tungsten (W) surface and three-dimensional nucleation for the nitride overlayer. Auger intensity ratio vs. temperature measurements for the Cu/W system indicates a stable interface up to 1000 ...
Date: August 2005
Creator: Ekstrom, Bradley Mitsuharu
Partner: UNT Libraries

Study of Ruthenium and Ruthenium Oxide's Electrochemical Properties and Application as a Copper Diffusion Barrier

Description: As a very promising material of copper diffusion barrier for next generation microelectronics, Ru has already obtained a considerable attention recently. In this dissertation, we investigated ruthenium and ruthenium oxide electrochemical properties and the application as a copper diffusion barrier. Cu under potential deposition (UPD) on the RuOx formed electrochemically was first observed. Strong binding interaction, manifesting by the observed Cu UPD process, exists between Cu and Ru as well as its conductive ruthenium oxide. Since UPD can be conformally formed on the electrode surface, which enable Ru and RuOx has a potential application in the next generation anode. The [Cl-] and pH dependent experiment were conducted, both of them will affect UPD Cu on Ru oxide. We also found the Cu deposition is thermodynamically favored on RuOx formed electrochemically. We have studied the Ru thin film (5nm) as a copper diffusion barrier. It can successfully block Cu diffusion annealed at 300 oC for 10min under vacuum, and fail at 450 oC. We think the silicidation process at the interface between Ru and Si. PVD Cu/Ru/Si and ECP Cu/Ru/Si were compared each other during copper diffusion study. It was observed that ECP Cu is easy to diffuse through Ru barrier. The function of RuOx in diffusion study on Cu/Ru/Si stack was discussed. In pH 5 Cu2+ solution, Ru and Pt electrochemical behavior were investigated. A sharp difference was observed compared to low pH value. The mechanism in pH 5 Cu2+ solution was interpreted. An interesting compound (posnjakite) was obtained during the electrochemical process. An appropriate formation mechanism was proposed. Also Cu2O was formed in the process. We found oxygen reduction reaction is a key factor to cause this phenomenon.
Date: August 2005
Creator: Zhang, Yibin
Partner: UNT Libraries

Effects of Cyclic Stains on Transport Properties of a Superconducting Composite : Phase I, Degradation of Electrical Conductivity in Copper at 4.2 K

Description: The effects of cyclic strains at 4.2 K on the electrical resistivity of copper have been investigated as Phase I of a program to determine the overall effects on monolithic superconducting composites. This work is a direct application to the design of large superconducting magnets that are subject to several different modes of cyclic strain during assembly and normal operations.
Date: August 1977
Creator: Fisher, E. S.; Kim, S. H.; Linz, R. J. & Turner, A. P. L.
Partner: UNT Libraries Government Documents Department

Copper: A Materials Survey

Description: Report issued by the U.S. Bureau of Mines discussing surveys conducted on copper. Physicality, mineral properties, history, geology, production methods, and uses of copper are presented. This report includes maps, tables, illustrations, and photographs.
Date: 1965
Creator: McMahon, A. D.
Partner: UNT Libraries Government Documents Department

Methods for Producing Secondary Copper

Description: Report issued by the U.S. Bureau of Mines discussing production of secondary copper. As stated in the introduction, "the purpose of this report is to present a complete collection of information on secondary copper in a single publication" (p. 1-2). This report includes tables, illustrations, and photographs.
Date: 1961
Creator: Spendlove, Max J.
Partner: UNT Libraries Government Documents Department