Interdiffusion Of Copper Research Articles

Fire gilding investigation on early medieval copper-based jewellery by focused ion beam (FIB) on FEG-SEM

The study of ancient gilding is often problematic, as the gilding layers are soft and prone to deformation during sample preparation. In this respect, focused ion beam (FIB) milling on a field emission gun scanning electron microscope (FEG-SEM) provides poorly invasive in situ sampling. The operating process is here detailed and applied on gilded medieval copper-based elite jewellery (10th century) from Prague Castle. Obtained cross-sections and slices of gilded samples were investigated up to nanometer scale without gilding layer deformation. By coupling structural observation with elemental X-ray analysis (EDS) and electron beam diffraction (EBSD), FIB FEG-SEM provided new data on the physical–chemical characteristics of the gilded layer. The gilding has a two-layer metallurgical structure containing a quaternary Au (Hg, Cu, Ag) alloy corresponding to the gold solid solution fcc phase, and a submicrometric inner sublayer formed by a Au-Cu phase, relative to the interdiffusion of copper from the substrate during the fire gilding process. The applied temperature for gilding can be estimated at c. 400 °C. Sintering of the mercury-gold amalgam globules during the fire heating is highlighted. The precise characterisation of the gilding layers provided useful comparative parameters for identifying fire gilding skill levels and assessing the overall quality of the archaeological pieces.

The effect of thickness of niobium isolation layer on properties of copper-based Nb3Sn films

Copper-based Nb3Sn film is a promising material for applications in the field of superconducting radio frequency (SRF). However, the interdiffusion of copper (Cu) from the substrates into the Nb3Sn films affects the superconductivity of the samples, and the preparation of Nb3 Sn–Nb–Cu composite films is a good solution. In this paper, the effects of the niobium (Nb) layer thickness on Cu interdiffusion and the critical temperature of Nb3Sn film were investigated. Nb3 Sn–Nb films were deposited on Cu substrates by magnetron sputtering. The obtained samples have been characterized via focused ion beam (FIB), time of flight secondary ion mass spectrometry (TOF-SIMS), and magnetic property measurement system (MPMS). It was found that the thicker the Nb isolation layer, the stronger the hindrance effect on the Cu interdiffusion and the higher the critical temperature. A suitable Nb isolation layer thickness was 2.6μm, which effectively hindered the Cu interdiffusion, corresponding to a critical temperature of 16.6 K for the samples.

L10 ordered phase formation at solid state reactions in Cu/Au and Fe/Pd thin films

To understand the mechanism of mass transfer during solid state reactions and order-disorder transitions the formation processes of CuAuI and L10-FePd ordered structures at solid state reactions in Cu/Au и Fe/Pd bilayer thin films have been carried out using the method of in situ electron diffraction (ED). The value of the long-range order (LRO) parameter has been estimated for the L10 type ordered structures being formed; the order-disorder transition temperatures have been determined. The formation mechanism of the L10 type ordered structures formed at the initial stages of the solid state reaction in the Cu/Au and Fe/Pd thin films has been suggested. In the case of Cu/Au it has been shown that the interdiffusion of copper and gold at the initial stage of the solid state reaction results in the reduced size of the grains of the initial materials, as a result, nanocrystalites of the Cu-Au solid solution are formed, and further, grains of the CuAuI ordered solid solution appear and their growth begins.

Sn-Cu codeposition from a non-aqueous solution based on ethylene glycol for wafer-bonding applications: direct and pulse electroplating

ABSTRACTMetal wafer bonding is being investigated in industry and research fields due to the relatively low process temperatures (T < 500 °C) and, at the same time, to obtain a metallic junction able to offer greater reliability compared with other materials. In this work, electrodeposition of eutectic Sn-Cu alloy, suitable for wafer bonding, was studied using ethylene glycol (EG) as a solvent. The resulting organic electrolyte was used for its promising properties, such as a wider electrochemical window than traditional aqueous electroplating baths. Ethylene glycol solutions containing copper(II) and tin(II) chloride salts were characterised electrochemically by means of cyclic voltammetry (CV) and linear sweep voltammetry (LSV). Deposition was performed both under direct (DC) and pulsed (PC) current conditions and the advantages of the latter are discussed, also in terms of surface morphology as observed by scanning electron microscope (SEM). Wafer bonding was successfully achieved and the interdiffusion of copper and tin species in the bonding region is discussed.

Interfacial bonding mechanism and annealing effect on Cu-Al joint produced by solid-liquid compound casting

Copper-aluminum (Cu-Al) based lamellar composites were prepared using a solid-liquid compound casting (SLCC) technology. Characterization results showed that the Cu-Al composites were fully-sintered at 700°C under an argon atmosphere using the SLCC technology. Cu-Al interfacial bonding was uniform with a well-defined transitional and inter-diffusion region. Intermetallic compounds and solid solutions of CuAl2, CuAl, Cu9Al4, CuAl3 and Cu3Al2 were detected at the interfacial region. With the increase of annealing temperature, the width of the Cu-Al interfacial region was increased, and the interfacial bonding strength was also increased, whereas the types of the intermediate phases were changed. With the increase of dwelling time at a given annealing temperature, the width of Cu-Al interfacial region was increased, the interfacial bonding strength was decreased and the mesophases were changed. The bonding strength of the as-prepared composite was 30MPa, whereas those of specimens annealed at 200°C for 2h, 300°C for 2h, 400°C for 2h, 300°C for 30min and 300°C for 1h were 59, 39, 74, 56, and 49MPa, respectively. The Cu-Al interfacial bonding mechanisms were identified to be rapid inter-diffusion of copper and aluminum and formation of interfacial and graded microstructures. The formation of copper-aluminum interface is a combined result of inter-atomic diffusion and interfacial chemical reactions, the latter of which is more dominant in the diffusion process.

Demonstration of Copper Co‐Fired (Na, K)NbO3 Multilayer Structures for Piezoelectric Applications

A Li and Ta modified (Na, K)NbO3 piezoelectric ceramic has been successfully co‐fired with inner copper electrodes in a reduced atmosphere. Highly dense NKN ceramics (95% relative density, 4.64 g/cm3) were obtained by sintering the samples in a low oxygen partial pressure (low pO2) atmosphere at 1050°C. The poly(propylene carbonate) binder system was used to permit a clean burnout at low temperature in N2 atmosphere, and also prevent the electrode copper particles from undergoing any oxidation. No interdiffusion of copper, chemical reactions, and/or carbon residues were observed in the grains, grain boundaries, or at the electrode–ceramic interface of the co‐fired samples from a detailed transmission electron microscopy (TEM) analysis. Dielectric and piezoelectric properties were characterized from those co‐fired prototyped samples. The samples displayed high relative dielectric permittivity above 800, with low dielectric loss about 3.6%. A normalized strain coefficient (max. strain/max. electric field) of = 220 pm/V was obtained under unipolar converse electromechanical measurement at 20 kV/cm. This paper presents the feasibility of co‐firing a Cu inner electrode with NKN ceramics toward multilayer lead‐free piezoelectric applications, providing an engineering route to narrow the performance differences between soft lead‐based piezoelectrics and lead‐free materials.

Low temperature solid–liquid interdiffusion wafer and die bonding based on PVD thin Sn/Cu films

Cu–Sn intermetallic diffusion has been studied with thin Sn and Cu films deposited by physical vapor deposition. It was found that annealing time is critical to the interdiffusion of copper and tin, leading to the formation of Cu6Sn5 and Cu3Sn phases at temperatures of interest. Based on this observation, test wafer bonding have been implemented at 320 and 250 °C with sealing pressures of 0.6, 2, 4, 6 and 10 MPa. The experiments emphasized the importance of the sealing pressure and the existence of a sealing pressure threshold for the success of the bonding. When the sealing pressure was superior to that threshold, at 250 °C a thin (<4 µm) bonded Cu/Cu3Sn/Cu joint was obtained, with none of the voiding defects previously reported by using electroplating.

Electroless- and Electroplating of Cu(Re) Alloy Films for Self-Forming Ultrathin Re Diffusion Barrier

To inhibit the detrimental diffusion of copper into silicon devices, an effective barrier is strongly demanded. In this study, copper(rhenium) alloy films were successfully electroless- and electroplated on silicon substrates for self-forming an ultrathin rhenium barrier layer. In pure copper films, the interdiffusion of copper and silicon already occurred at 400°C, forming silicides and increasing the electrical resistivity of the films. In comparison, not any silicide formation was observed in the electroless- and electroplated copper(rhenium) alloy films with minor incorporations of rhenium for 0.10 and 0.39 at% until 600 and 500°C, respectively, attributed to the prior segregation of rhenium and the self-formation of rhenium barrier layer at the copper/silicon interface at 400°C. A zero solubility of rhenium in copper and a small solubility in palladium catalysts facilitate the separation of rhenium from copper. The kinetics of rhenium segregation follows uphill diffusion, and the diffusivity of rhenium in copper at 400°C is estimated to be 1.5 × 10−17 cm2/s.

The critical oxide thickness for Pb-free reflow soldering on Cu substrate

Oxidation is an undesirable effect of reflow soldering. Non-wetting occurs when the oxide layer grows above the critical thickness. Characterizing the critical oxide thickness for soldering is challenging due to oxide's nano-scale thickness and irregular topographic surface. In this paper, the critical copper oxide thickness was characterized by Time-of-Flight Secondary Ion Mass Spectrometry, Scanning Electron Microscopy, Energy-Dispersive X-ray spectroscopy, and Transmission Electron Microscopy. Copper substrates were coated with an Organic-Solderable-Preservative (OSP) layer and baked at 150°C and 85% Relative Humidity for different amounts of time. The onset of the non-wetting phenomenon occurred when the oxide thickness reached 18±5nm. As the oxide grew beyond this critical thickness, the percentage of non-wetting solder joint increased exponentially. The growth of the oxide thickness followed a parabolic rate law. The rate constant of oxidation was 0.6×10−15cm2min−1. Oxidation resulted from interdiffusion of copper and oxygen atoms through the OSP and oxide layers. The oxidation mechanism will be presented and discussed.

Effect of phosphorus on the copper diffusion barrier properties of electroless CoWP films

The properties of electroless CoWP barrier films with different phosphorus contents in Cu/CoWP/Si stacked samples were explored. The Cu/CoWP/Si stacked samples with 30 nm CoWP films, contained about 5.7, 8.2 and 10.8 at.% P, were prepared by electroless deposition, and then annealed in a rapid thermal annealer at a temperature between 300 and 700 °C. The effect of phosphorus content in CoWP film on the barrier properties in preventing copper diffusion and the failure of the Cu/CoWP/Si stacked samples after thermal annealing were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectrometer (EDS), Auger electron spectroscopy (AES), and sheet resistance measurement. Increasing the phosphorus content in the electroless CoWP film markedly improves the barrier properties. The failure temperature of Cu/CoWP/Si increased from 500 to 600 °C with the phosphorus content in CoWP film increasing from 5.7 to 10.8 at.%, and the failure of the Cu/CoWP/Si has mainly arisen from the interdiffusion of copper and cobalt during thermal annealing.

3D atom probe investigation of nanocomposite wires

Two kinds of high strength nanocomposite wires produced under heavy plastic deformation were investigated using 3D Atom Probe. First, cold drawn pearlitic steel wires were analysed. Partly dissolved cementite lamellae were mapped out in 3D. The surface to volume ratio of cementite lamellae was correlated to their dissolution rate. Considering the increase of the interfacial energy during drawing, a model based on simple thermodynamical arguments was developed to estimate the global dissolution rate of cementite. Cu/Nb nanocomposite wires were also studied. Their nanoscale cross-section microstructure was revealed for the first time. 3D Atom Probe analysis pointed out a slight inter-diffusion of copper and niobium, and steps in copper channels attributed to tracks of moving dislocations in the (111) Cu plane, along the direction.

Mechanistic Studies of CVD Metallization Processes: Reactions of Rhodium and Platinum β-Diketonate Complexes on Copper Surfaces

The hexafluoroacetylacetonate complexes Rh(hfac)(C2H4)2 and Pt(hfac)2 are known to serve as chemical vapor deposition precursors to Rh and Pt thin films. In the absence of a reducing carrier gas, the depositions are surface-selective and occur preferentially on copper, but under these conditions, the metallization processes are unexpectedly inefficient relative to the rapid deposition of Pd on Cu seen for the palladium analogue Pd(hfac)2. Mechanistic studies of the reactions of Rh(hfac)(C 2H4)2 and Pt(hfac)2 on copper surfaces under ultrahigh vacuum conditions have now been performed in order to elucidate the factors responsible for the differences among these surface-selective metallization processes. The studies demonstrate that adsorption of the rhodium complex Rh(hfac)(C2H4)2 on copper surfaces is accompanied by the loss of the coordinated ethylene groups, even at 100 K. At these low temperatures, the adsorbed Rh(hfac) fragments are oriented in several ways with respect to the surface. Heating the substrate above 150 K causes the hfac ligands to realign to a perpendicular orientation relative to the surface. The platinum precursor Pt(hfac) 2 adsorbs molecularly at 100 K with the molecular planes of the hfac ligands oriented parallel to the copper surface. Heating the substrate to temperatures above 150 K again results in a realignment of the hfac ligands to a perpendicular orientation. This reorientation is accompanied by a partial reduction of the Pt centers (as judged from shifts seen in X-ray photoelectron spectroscopy core level data), a result suggesting that the hfac ligands begin to dissociate from the platinum centers near 150 K. At temperatures above 220 K, the transfer of the hfac ligands from both complexes to the copper surface is complete, as signaled by the reduction of the metal centers to the zero-valent state. The copper-bound hfac ligands are further transformed upon heating, either reacting with copper surface atoms to yield Cu(hfac)2 (which desorbs at temperatures above 250 K) or decomposing (with fragments desorbing above 350 K). The presence of platinum on the copper surface promotes the former reaction as judged by the appearance of a new reaction-limited desorption process for Cu(hfac) 2. The presence of rhodium on the copper surface does not promote the formation of Cu(hfac)2, although autocatalysis is noted in the steady-state reactive scattering data. The inability of the Rh and Pt precursors to engage in a sustained transmetalation reaction with the copper surface is attributed to the slow interdiffusion of copper through the Rh/Cu and Pt/Cu alloys that are produced in the near-surface region.

Effect of high pressure on interdiffusion in Cu-Zn alloys at temperatures near the melting point

Interdiffusion of copper and zinc alloys of Cu-28.5 at. pct Zn and Cu-4.9 at. pct Zn has been investigated under pressures from 0.101 to 3240 MPa in the temperature range from 1256 to 1377 K. The diffusion coefficients decrease with increasing pressure. The activation energy for impurity diffusion of zinc in copper increases with pressure. The ratio of the activation volume to the molar volume of copper is between 0.75 and 0.90. It is concluded that the impurity diffusion of zinc in copper occurs predominantly by the monovacancy mechanism at temperatures near the melting point of the alloy.

Interdiffusion in copper–aluminum thin film bilayers. II. Analysis of marker motion during sequential compound formation

Isolated W islands, 150 Å in diameter, have been deposited between Cu and Al thin film bilayers to serve as inert diffusion markers. Marker displacements have been measured consecutively by Rutherford backscattering spectroscopy during the sequential growth of CuAl2, CuAl, and Cu9Al4 intermetallic compounds upon annealing in the temperature range 160–250 °C. The intrinsic interdiffusion coefficients of Al and Cu in each of these compounds have been determined by applying an analysis of marker motion in a binary diffusion couple to the measured displacement data. Moreover, the prefactor and activation energy of the individual diffusivities have been calculated as shown below by measuring the marker motion as a function of temperature. For CuAl2, D0Al =0.4 cm2/s, QAl =1.25±0.05 eV, D0Cu =9.5 cm2/s, QCu =1.40±0.05 eV. For CuAl, D0Al =1.5×10−7 cm2/s, QAl =0.7±0.05 eV, D0Cu =1×10−2 cm2/s, QCu =1.1±0.05 eV. For Cu9Al4, D0Al =1.7×10−3 cm2/s, QAl =1.20±0.05 eV, D0Cu =2.4×10−2 cm2/s, QCu =1.30±0.05 eV. These values agree quite well to those chemical interdiffusion coefficients published in the literature for bulk samples. A discussion on sequential compound formation has been given on the basis of these measured values.

Interdiffusion in copper–aluminum thin film bilayers. I. Structure and kinetics of sequential compound formation

Interdiffusion in Cu–Al thin film bilayers at temperatures between 160 and 300 °C has been studied by a combination of glancing-incidence x-ray diffraction, Rutherford backscattering spectroscopy, and transmission electron diffraction and microscopy. A sequential intermetallic compound formation was observed in samples with an excess amount of Cu with θ-CuAl2 forming first, followed by η2-CuAl, and γ2-Cu9Al4. In samples with excess Al, the θ-CuAl2 is the first and the last phase formed. The thickening of these compounds was found to obey a parabolic relationship with time, and especially the thickening of θ-CuAl2 can be described by a prefactor of 7.4 cm2/s and an activation energy of 1.31 eV.

Annealing effects in plated-wire memory elements, part I: Interdiffusion of copper and permalloy

Results of investigations using X-ray diffraction and electron-beam microprobe techniques have shown that copper and Permalloy platings interdiffuse at low temperatures (in the range 180-230°C) when plated-wire memory elements are annealed for times as short as 50 h. Measurable interdiffusion between Permalloy platings and gold substrates does not occur in similar conditions. Both magnetic and compositional changes during aging are found to occur by a thermally activated process with activation energies around 38 kcal/mol. It is shown, however, that copper-diffusion and magnetic-dispersion changes during aging are merely concurrent processes, neither being the other's cause.

Interdiffusion in dilute aluminium-copper solid solutions

A study has been made of the interdiffusion of copper from an α solid solution into aluminium with special attention to minimizing experimental and computational errors. The form of the concentration-distance curves obtained showed that interdiffusion was independent of concentration within the range 0–0.5 wt.% copper. The activation energy calculated from the slope of a log e D ̃ versus T −1 plot was 31.12 ± 1.54 kcal/ g and the frequency factor D ̃ 0 was 0.29 −0.17 +0.43 cm 2/sec. It is concluded that the data obtained are closely related to the tracer diffusion of copper in aluminium.

金屬粉の擴散現象に就て

金屬粉の擴散現象に就て

X-ray study of the inter-diffusion of copper and zinc

Since the publication of Roberts-Austen's classical paper describing extensive investigations on the inter-diffusion of metals and alloys, several methods have been employed to study the phenomenon. A comprehensive survey of these has recently been published by Hevesy and Seith. Only a few investigations have been recorded in which X-ray analysis has been applied to the problem, as it is only during the last few years that X-ray measurements and technique have attained the necessary precision to enable the phenomenon to be examined by this method. The present paper describes an attempt to develop the X-ray method for the investigation of the phenomenon of inter-diffusion in metals. When a mixture of silver and zinc filings, or copper and zinc filings is heated in vacuo , inter-diffusion takes place. The heated mixture, when cool, can be broken up and then used to produce X-ray reflections in the precision camera. In the photographs, the reflection lines from each phase present in the sample are usually well separated and can be studied independently, so that the composition of each phase can be determined from standard parameter-composition curves. The method therefore provides a means of studying any change which occurs in the composition of each phase with time and with change of temperature, and thus it differs from such methods as chemical analysis, zone measurements or electrical resistance, where usually a mean effect is measured. Since 0·01 mm of copper absorbs about 36% of the K α radiation from copper, the reflected beams registered on the photographic film are produced by the surface layers of the particles, so that as diffusion proceeds, the photographs indicate the changing conditions in the outermost layers only.