Nucleation Of Copper Research Articles

Growth of Metal Nucleus on Polyimide Surface with Photochemical Reaction

AbstractCircuit patterned nucleation of copper or nickel atoms onto polyimide surface was demonstrated by using ArF excimer laser (λ=193nm) and copper sulfate aqueous solution (CuSO4.5H2O+nH2O), or nickel sulfate aqueous solution (NiSO4–6H2O+nH2O) in an atmospheric pressure. Photo-excited C-H bonds of the polyimide surface were effectively dehydrated with hydrogen atoms which were photodissociated from the water. The dangling bonds of the dehydrated hydrogen atoms were combined with the oxygen and the copper or nickel atoms that were photodissociated by CuSO4 solution or NiSO4 solution. Thus, C-O-Cu bonds or C-O-Ni bonds were formed on the surface. After this copper and nickel substitution, it was carried out onto the nucleated parts by usual electroless plating at 70 °C. In this process, the conductive circuit patterned copper or nickel thin film was deposited on polyimide surface.

Effects of Seeding Layers on Electroless Copper Deposition

AbstractCopper has been actively pursued as the most promising candidate for replacing the current Al metallization for ULSI interconnection because of its higher electrical conductivity and resistance to electromigration. In this work, we present our experimental results on electroless copper deposition on various seeding layers from a formaldehyde-based solution with EDTA as a complexing agent. For electroless plating, a seeding layer is essential for the initiation of copper deposition. X-ray diffraction analysis revealed a variation in the crystallographic orientation of the electroless deposited copper with different underlying seeding layers. The seeding layer is the key factor affecting copper nucleation and grain growth. The initial nucleation behaviors of electroless copper deposition on palladium and copper seeding layers were investigated. The microstructure of electroless deposited copper blanket films was studied using both SEM and AFM, and the crystallinity was analyzed using XRD. The crystal orientation and surface texture of the electroless deposited copper films could be modified by thermal annealing in vacuum (10E-6 Torr) for 30 min at temperatures ranging from 200°C to 300°C. The ratio of crystal orientation, I(111)/I(200) increased with higher annealing temperature, indicating enhanced growth of the (111) crystal structure.

Nucleation of Trace Copper on the H−Si(111) Surface in Aqueous Fluoride Solutions

The initial nucleation process of trace amounts of copper metal on the H−Si(111)(1 × 1) surface in aqueous fluoride solution was investigated by ex-situ scanning tunneling microscopy. We observed that copper nucleates preferentially along step edges and appears to inhibit the step-flow etching of silicon. The presence of copper species in the fluoride solution also appears to inhibit the formation of terrace etch pits, which are known to be initiated by dissolved oxygen. It is suggested that silicon−dihydroxyl−cuprous ion complexes are formed at dihydroxyl kink sites, resulting in the preferential nucleation of Cu metal at step edges and the inhibition of step-flow etching. Copper ions in solution may act as catalysts for the disproportionation and electrocatalytic reduction of superoxide anion radical formed by the electrochemical reduction of dissolved oxygen at the silicon surface. Such reactions would reduce the rate of etch-pit initiation and may also decrease the rate of deposition of metallic copper on the silicon surface.

Electrochemical characterization of copper deposited on plasma and thermally modified titanium surfaces

Thin oxide films were grown at temperatures from 373 to 1073 K in plasma and in air on commercially pure titanium substrates. It was determined that the color, thickness, composition, phase, and polarization behavior in a copper electrolyte varied with operating conditions: temperature, oxygen partial pressure, and plasma composition. High-temperature and high oxygen partial pressure plasma produced a thick oxide film. The surface film structure transformed from TiO2 (anatase) to TiO2 (rutile) at a temperature of 600 °C. A lower oxide of the form Ti n O2n−1, such as Ti2O3 (which may be porous) or possibly Ti3O5, was formed on a thermally treated sample (400 °C, 80 mtorr O2, 3 hours). This sample exhibited the lowest potential for copper nucleation and gave a very uniform, smooth, and hole-free copper foil.

Electrochemical nucleation on microelectrodes. Theory and experiment for diffusion-controlled growth

This paper describes a general theory for the study of electrochemical nucleation on microelectrodes for the case of diffusion-controlled growth. The starting point is the model of Sluyters-Rechbach (M. Sluyters-Rechbach et al., J. Electroanal. Chem. 236 (1987) 1) which is the most general available at present. This model is combined with the approximate solution of Shoup and Szabo (D. Shoup and A. Szabo, J. Electroanal. Chem. 140 (1982) 237) for a chronoamperometric transient on microelectrodes. In this way a single expression is obtained for the description of electrochemical nucleation and growth on microelectrodes for the case of diffusion-controlled overlap. The resulting equation is more general than the equations of Correia et al. (A.N. Correia et al., J. Electroanal. Chem. 407 (1996) 37) for the case of diffusion-controlled growth on inlaid disk electrodes. These authors presented separate equations for the short and long time limits and consider only the limiting cases of instantaneous and progressive nucleation. The limitations of this model and the conditions of its applicability are critically examined. The theory is illustrated with results obtained for the nucleation of copper from concentrated CuSO4+H2SO4 solutions on platinum microelectrodes in the presence of an organic addition agent (gelatine). Analysis of the experimental transients was performed using a nonlinear least square fitting procedure based on the Levenberg–Marquardt algorithm with the nucleation site density and the nucleation rate constant A as fitting parameters.

Area-selective nucleation of copper on fluorocarbon–resin surface using ArF excimer laser-induced chemical modification

Area-selective nucleation of copper onto fluorocarbon–resin surface was demonstrated by using an ArF excimer laser and copper–sulfate (CuSO4) aqueous solution. Pyramid-typed shaped nuclei of copper were initially formed on even an inert surface of fluorocarbon–resin in the same way as semiconductor or metal surfaces. Interface of copper nuclei and fluorocarbon–resin was chemically bonded through oxygen which was photodissociated from water in copper–sulfate aqueous solution under ArF excimer laser irradiation. The modification cannot be successful without our previous defluorination efforts using ArF excimer laser-induced chemical reaction.

The influence of intermediate particles on the nucleation of copper on polycrystalline platinum

The influences of the Cu adatoms and Cu + ions on the initial stages of copper electrodeposition on polycrystalline Pt in acidified copper sulphate solution have been studied by cyclic voltammetry, potentiostatic current transients, rotating ring-disk electrode ( rrde ), and in situ scanning tunnelling microscopy (STM). It has been established that during the long-time polarization of the platinum electrode, at potentials close to the copper equilibrium potential, the concentration of Cu + ions in the vicinity of the electrode increases and a Cu microdeposit if formed. The dissolution of the microdeposit occurs very slowly and takes several minutes of potential cycling in the range of 0.27–1.25 V. While the microdeposit is present on the platinum, the electrode surface is more active with respect to upd and bulk copper deposition. The combination of electrochemical and in situ STM results indicates that formation of surface alloy occurs during electrodeposition of copper on polycrystalline platinum.

Electrodeposition of copper on thermally oxidized 316 L stainless steel substrates

The effect of thermal oxidation of 316 L stainless steel cathode blanks used in copper electrodeposition was studied. Current and potential step experiments were performed to evaluate electrochemical changes caused by the oxidation treatments. SEM and AES were used to characterize the stainless steel substrates and the deposited copper films. Particular emphasis was given to the initial stages of copper nucleation and growth. The copper electrocrystallization process was strongly influenced by the temperature employed in oxidizing the stainless steel. Dense, uniform and fine copper nuclei were obtained on the stainless steel substrate oxidized in air at 200°C and 300°C for 3h. The copper nucleation density and uniformity decreased considerably on substrates treated at 500°C and 600°C. Attempts were made to identify changes in the mechanism of copper nucleation on the various oxidized stainless steel substrates using models developed by Thirsk and Harrison.

Maskless, Direct Deposition of Copper onto Aluminum Bond Pads for Flip Chip Applications

ABSTRACTFlip chip interconnection of integrated circuits (IC) for packaging applications such as direct chip attachment use Pb-Sn solders as the connection between the die and the substrate. Underbump metallization is typically used to transition from the non-solderable Al bond pad on the IC to a solderable surface such as copper using traditional blanket metal deposition, photolithography and etching procedures. In this study, we report for the first time the use of a novel process for selectively depositing adherent copper directly onto aluminum thin films, eliminating the need for adhesion promoting transition layers and additional patterning steps. Utilizing copper bearing organic solutions and standard electroless and electrolytic copper plating baths, as-deposited and annealed sputter deposited Al-x%Cu (x = 0 to 2) thin films were coated with metallic copper. An increase in the organically deposited copper nucleation site density was observed with increasing copper concentration in the sputtered aluminum/copper thin films. Preliminary results using focused ion beam microscopy indicated that dissolution of the aluminum oxide surface and subsequent deposition of copper by cementation occurs in the non-conducting organic solution at sub-micron reaction lengths. Qualitative adhesion testing of samples resulted in the majority of films passing the tape test. Demonstration of the process using 50 micron diameter vias in BCB coated flip chip test vehicles from MCNC will be presented.

Influence of processing parameters on the selectivity in a CVD-process of copper using Cu(I)(hfac)(TMVS)

Nucleation behaviour of copper on SiO 2 surface in a CVD process using Cu(I)(hfac)(TMVS) was investigated by EDX and SEM. Removing residues from previous processing steps and passivating the hydroxyl groups at the SiO 2 surface was essential for maintaining selectivity. Temperature is the most critical process parameter with respect to selectivity. Up to 190°C only a few very small nuclei could be detected; at 210°C there were numerous Cu nuclei on the SiO 2 surface. At the chosen set of processing parameters the flow rate of precursor up to 80 mg min −1 had little effect on nucleation of copper; increasing the chamber pressure is the most promising way to get higher deposition rates without loss of selectivity.

Effects of the Partial Pressure of Copper (I) Hexafluoroacetylacetonate Trimethylvinylsilane on the Chemical Vapor Deposition of Copper

The effects of the partial pressure of precursor on the metalorganic chemical vapor deposition of copper were investigated. Copper was deposited using copper (I) hexafluoroacetylacetonate trimethylvinylsilane as a metalorganic precursor on TiN/Ti/Si substrates in a low-pressure warm-wall chemical vapor deposition reactor. The deposition rate of copper film was a constant value at a partial pressure higher than 0.048 Torr and decreased to below the constant value at a partial pressure lower than 0.048 Torr. The incubation time for copper nucleation decreased with increasing partial pressure of the precursor. The resistivity of copper film decreased to 2.00 µ Ω· cm with increasing partial pressure of the precursor. At a partial pressure lower than 0.048 Torr, copper did not nucleate inside the trench so that the step coverage of copper film became very poor.

Effect of substrate surface treatment on the nucleation and crystal growth of electrodeposited copper and copper–indium alloys

Thin films of copper–indium alloy electroplated on molybdenum substrates show different morphologies related to the substrate treatment. An ammonia treatment of the molybdenum electrode can remove a thin oxide layer from the electrode surface, changing the morphological structure of the deposit. The nucleation kinetics of copper were investigated by potentiostatic current–time transients. The deposition process involves instantaneous nucleation for untreated substrates and progressive nucleation for ammonia treated substrates, with diffusion-controlled growth of the three-dimensional nuclei. A higher nucleation density is observed for ammonia-treated molybdenum substrates. The film morphology of the copper–indium alloys can be closely related to the copper nucleation mechanism. On the untreated substrates a low nucleation density together with high adatom mobility lead to the formation of a globular structure. However, when the nucleation density is high and the nuclei are formed continuously during crystal growth, the film evolves towards a porous structure. After the selenization step the film morphology appears related to the precursor structure. © 1997 Elsevier Science S.A. All rights reserved.

Electrodeposition of copper on plasma and thermally oxidized titanium substrates

The effect of plasma and thermal oxidation of titanium cathode blanks on copper electrodeposition was studied. Polarization, potential and current step experiments were performed to evaluate electrochemical changes caused by the oxidation treatments. Scanning electron microscopy, Auger electron spectroscopy and X-ray diffraction were used to characterize the titanium substrates and the deposited copper films. Particular emphasis was given to the initial stages of copper nucleation and growth. The results showed that copper electrocrystallization was strongly influenced by the condition of the oxidized titanium surface. High density, uniform copper coverage was found on titanium substrates oxidized at 400 and 500 °C for 3 h under plasma or low oxygen pressure (80 m Torr) environments. The copper nucleation density and uniformity decreased considerably on titanium surfaces oxidized at 100 and 200 °C. Attempts were made to identify changes in the mechanism of copper nucleation on the oxidized titanium substrates using models developed by Thirsk and Harrison ( A Guide to the Study of Kinetics, Academic, New York, 1972 , p. 115).

Underpotential – Overpotential Phase Transformation Phenomena in Copper Deposition Processes on Glassy Carbon

ABSTRACTThe initial stages of copper electrodeposition on glassy carbon were studied from a solution of 1 M CuSO4 in 0.5 M H2SO4 by the methods of potentiostatic current transients and pulse experiments. The experimental data were analyzed according to the theory of potentiostatic current transients for three-dimensional multiple nucleation with diffusion controlled growth. The theory was found to be in good agreement with experimental data for instantaneous copper nucleation in the cathodic overpotential range η = −0.18 – −0.40 V. It is shown that in case of progressive nucleation at η ≤ −0.16 V, this theory can be used only for trend analysis of copper nucleation process parameters. An important influence of the initial state of glassy carbon surface on the nucleation rate was found determined by the underpotential. It is shown that the dependence of nucleation rate on the underpotential is inadequate and is determined by cathodic overpotential.

Influence of phosphorous acid on the nucleation and growth of copper

Influence of phosphorous acid on the nucleation and growth of copper

Chemical and electrochemical behaviour of copper ions in the ZnCl 2-2NaCl mixture at 450 °C

To investigate the possibility of selective chlorination to separate copper traces from zinc matrixes, we have determined redox and oxoacidobasic properties of the copper in the molten ZnCl 2-2NaCl. In this way, the stability of copper chlorides and oxides as well as the electrochemical behaviour of Cu(I) have been studied by using voltammetric, chronopotentiometric, chronoamperometric and potentiometric techniques. The experiments were performed in a controlled argon atmosphere cell with safety features. Copper oxidation states I and II have been shown to exist in the mixture and the stability of metallic copper has been confirmed. The standard potential of the redox couple Cu(II) Cu(I) and Cu(I) Cu(0) have been determined by voltammetry ( E Cu(II) Cu(I) 0 = − 0.135 ± 0.016 V vs Cl 2 Cl − ) and by potentiometry ( E Cu(I) Cu(0) 0 = − 1.129 ± 0.030 V vs Cl 2 Cl − ), respectively, finding that Cu(II) ion can oxidize, under certain conditions, the chloride ion of the melt. Moreover, the stability of both Cu(I) and Cu(II) oxides was investigated and the solubility product of CuO was determined, whereas Cu 2O was found to be a hard oxide donor. These results have allowed the construction of E- pO 2− equilibrium diagram. On the other hand, the kinetics of copper electrodeposition and electrocrystallization at a tungsten electrode were studied, and it was demonstrated that the process is quasi-reversible. In the same way, the Cu(II) Cu(I) exchange was found to be quasi-reversible. The values of the kinetic parameters, K 0 and α, were obtained for both reactions. Mass transport towards the electrode is a simple diffusion process, and the diffusion coefficient has been calculated. Chronoamperometric studies indicated instantaneous and three dimensional nucleation and crystal growth of copper.

Scanning probe microscopy studies of Ebonex® electrodes

The porosity of Ebonex® electrodes is known to have a marked affect on their electrochemical properties. Atomic force microscopy (AFM) and scanning tunnelling microscopy (STM) have been used to investigate the topography of porous and fully-hardened (nonporous) Ebonex® at high resolution. AFM has also been used to study the early stages of copper electrodeposition on porous Ebonex® electrodes. Initial copper nucleation and growth were found to occur preferentially at surface pores.

Growth behavior of copper metalorganic chemical vapor deposition using the (hfac)Cu(VTMOS) precursor on titanium nitride substrates

Metalorganic chemical vapor deposition of copper using the thermally stable (hfac)Cu(VTMOS) [C10H13O5CuF6Si: 1,1,1,5,5,5-hexafluoro-2,4 pentadionato(vinyltrimethoxysilane) copper (I)] precursor has been carried out on TiN substrates prepared by physical vapor deposition (PVD) and rapid thermal processing (RTP). The apparent activation energies over substrate temperatures ranging from 160 to 220 °C were about 7.5 kcal/mol on the PVD-TiN and 9.7 kcal/mol on the RTP-TiN. The higher growth rate of the copper deposit on the RTP-TiN could be ascribed to the increase in nucleation sites and the higher electron catalytic reactivity, resulting in enhancement of copper nucleation density in the initial stages of film growth. The copper deposits revealed polycrystalline phases with a preferred orientation of (111), and impurities within the films were below the detection limit of Auger electron spectroscopy. As substrate temperature increased, the copper films on the PVD-TiN developed as a columnar structure according to the Volmer–Weber growth mode, and on the RTP-TiN a nearly equiaxed structure was formed presumably by Stranski–Krastanov grain growth. The electrical resistivity of the deposits on the PVD-TiN and the RTP-TiN was in the range 2.8–5.4 μΩ cm for 1500–3100 Å film thicknesses and 4.4–6.2 μΩ cm for 2300–4300 Å film thicknesses, respectively. With increasing film thickness, the electrical resistivity of the copper layers linearly increased on the PVD-TiN, while it gradually decreased on the RTP-TiN. Consequently, the variations in the electrical resistivity of the deposits could be explained by changes in microstructures of the copper films, due to different growth behavior of copper on the two types of substrates.

NUCLEATION REACTIONS AND FILM GROWTH OF COPPER ON TiN USING HEXAFLUOROACETYLACETONATE COPPER(I) TRIMETHYLVINYLSILANE

In this work, the nucleation and film growth of copper on TiN chemically treated with WF6 and air-exposed TiN by chemical vapor deposition(CVD) from hexafluoroacetylacetonate copper1 trimethyl-vinylsilane, (HFA)Cu(TMVS), was studied. Copper grows as islands of poorly connected grains on air-exposed TiN. In contrast, copper grows as a continuous film with well-connected grains on the surface of WF6-treated TiN. The effect of TiN surface condition has been examined using Auger electron spectros-copy(AES), X-ray photoelectron spectroscopy(XPS) and scanning electron microscopy(SEM). On the basis of our experimental observation, and information in the literature, nucleation reaction mechanisms are proposed for the chemical vapor deposition of copper on the two different TiN samples.

Copper precipitation during continuous cooling and isothermal aging of a710-type steels

Precipitation in copper-containing A710 (also referred to as HSLA-80) and modified-A710 steels was investigated by transmission electron microscopy. Isothermal aging of as-quenched specimens at 675 °C produced e-copper precipitates located primarily at α-iron matrix dislocations. The precipitates exhibited multiple variants of an orientation relationship (OR) consistent with that reported by Kurdjumov and Sachs, fine fault formation, and associated streaking in electron diffraction patterns. For reaustenitized and continuously cooled specimens, the primary precipitation event was associated with interphase precipitation of copper at ferrite/austenite interfaces. Interphase precipitates frequently displayed ORs other than that reported by Kurdjumov and Sachs, although a unique crystallographic variant was observed within any one region of interphase precipitation, faults were observed infrequently, and streaking was not observed in diffraction patterns. At high temperatures during cooling, precipitate-free ferrite formed, whereas at lower temperatures, nucleation of copper precipitates occurred at ferrite/austenite interfaces for crystals of polygonal ferrite and Widmanstatten ferrite. This latter feature precludes the formation of Widmanstatten ferritevia a displacive mechanism. Interphase precipitation was not observed for granular ferrite or acicular ferrite. Less-common precipitation events during continuous cooling included the formation of AIN and CuS.