Activation Energy Of Cu Diffusion Research Articles

Anisotropic copper diffusion in olivine: Implications for Cu preservation in olivine and olivine-hosted melt inclusions

The rate of copper diffusion in olivine governs the preservation of copper in olivine and olivine-hosted melt inclusions, but Cu diffusivity in olivine has not been well determined especially regarding its anisotropy. In this study, Cu diffusion in single crystal olivine (Fo91Fa09) cuboid, prepared to comply with the three principle crystallographic axes, was investigated at 1273–1673 K and 1–2.5 GPa in a piston cylinder apparatus, using a diffusion-in approach with Cu or Cu2O as the source. Copper concentration profiles were analyzed by LA-ICP-MS scanning on the recovered samples along multiple directions. We found Cu diffusion in olivine to be appreciably anisotropic, with Cu diffusivity along the c axis being greater than that along the a axis by nearly an order of magnitude (Dc ≈ 3Db ≈ 7.5 Da). The activation energy for Cu diffusion is ∼210 kJ/mol, with little dependence on crystallographic orientation. Cu diffusivity at 2.5 GPa is only slightly lower than that at 1 GPa, yielding a small activation volume of 2.3 cm3/mol. While not being as rapid as the migration of H and interstitial Li, Cu diffusion, especially along the c axis, is significantly faster than the major elements of olivine (Fe-Mg, Si and O). Diffusion modeling indicates that the timescale for re-equilibration of Cu between olivine-hosted melt inclusion and external melt is relatively short (<60 yr at 1000 °C and <3000 yr at 800 °C) compared to the typical lifetime of magma chambers. Cu concentrations in olivine-hosted melt inclusions may therefore have been significantly modified from the pristine values. For Cu profiles preserved in olivine phenocryst, our determined Cu diffusivity can be used to constrain its residence time in magma chamber, and the diffusion anisotropy can provide a cross-check.

Graphene as a diffusion barrier at the interface of Liquid–State low-melting Sn–58Bi alloy and copper foil

Graphene is widely used as a barrier at the solid–solid and gas–solid state interface. However, the use of graphene as a barrier at the liquid–solid interface has been rarely reported, particularly in the case of a liquid-state metal and a solid-state metal interface. Herein, a graphene layer is synthesized on a Cu foil, and single-layer and bilayer graphene is detected via Raman spectroscopy. The interfacial intermetallic compound between eutectic Sn–58Bi alloy with a melting temperature of 138 °C and Cu with a melting temperature of 1085 °C can be significantly suppressed by graphene using different reflow temperatures (180 °C and 300 °C) and reflow times (144–625 s). Cu diffusion through graphene is visible in the Sn–Cu intermetallic compound (IMC) formations in the SB58 solder and at the interface after the reflow processes. We found that the activation energy of Cu diffusion through graphene into the liquid-state graphene is ∼ 32.6 kJ/(mol∙k), which is higher than that attained without graphene. Therefore, the findings of this study show that graphene is a promising diffusion barrier for the liquid–solid interface.

Fabrication and characterization of Cu2O/Cu-WO3 bilayers for lateral programmable metallization cells

Lateral Programmable Metallization Cell (PMC) structures rely on metal electrodeposition in a long channel consisting of a solid electrolyte layer between an anode and a cathode. Integration of these devices with CMOS circuitry demands using materials such as copper and tungsten for the electrodes, and an oxide of tungsten (WO3) doped with Cu for the electrolyte. However, low diffusivity of Cu in WO3 and its high resistivity results in a slow electrodeposition process. Our solution to this problem involves the use of a Cu2O/Cu-WO3 bilayer, formed by oxidation of a thin Cu film on a WO3 layer and a simultaneous diffusion of Cu into the WO3 at moderate temperatures. This creates a Cu-WO3 solid electrolyte with a semiconducting Cu2O coating that brings electrons to where the ions are most abundant and thereby greatly increases the electrodeposition rate. In this paper, an investigation of thin film Cu oxidation is presented along with the diffusion kinetics of Cu in WO3. The Cu was oxidized in air to form Cu2O with an activation energy of 0.70 eV. The diffusion analysis showed activation energy of Cu diffusion in WO3 was 0.74 eV, which we believe is the first time this value has been reported.

Structural and Thermodynamic Factors of Suppressed Interdiffusion Kinetics in Multi-component High-entropy Materials

We report multi-component high-entropy materials as extraordinarily robust diffusion barriers and clarify the highly suppressed interdiffusion kinetics in the multi-component materials from structural and thermodynamic perspectives. The failures of six alloy barriers with different numbers of elements, from unitary Ti to senary TiTaCrZrAlRu, against the interdiffusion of Cu and Si were characterized, and experimental results indicated that, with more elements incorporated, the failure temperature of the barriers increased from 550 to 900°C. The activation energy of Cu diffusion through the alloy barriers was determined to increase from 110 to 163 kJ/mole. Mechanistic analyses suggest that, structurally, severe lattice distortion strains and a high packing density caused by different atom sizes, and, thermodynamically, a strengthened cohesion provide a total increase of 55 kJ/mole in the activation energy of substitutional Cu diffusion, and are believed to be the dominant factors of suppressed interdiffusion kinetics through the multi-component barrier materials.

Improved Diffusion-Resistant Ability of Multicomponent Nitrides: From Unitary TiN to Senary High-Entropy (TiTaCrZrAlRu)N

Multicomponent high-entropy nitrides have been attempted as robust diffusion barrier materials to inhibit the severe interdiffusion of Cu and Si; however, the improvement in their diffusion resistance relative to the abilities of few-component nitrides has actually not been verified. Thus, in this study, nitride barriers with different numbers of components (metallic elements), from unitary TiN to senary high-entropy (TiTaCrZrAlRu)N (with the same face-centered cubic structure and a thickness of 5 nm), were prepared. The failure of these nitride barriers in resisting the interdiffusion of Cu and Si was examined, and the activation energy of Cu diffusion through the nitrides was determined. With more components incorporated, the failure temperature of the nitrides was found to markedly increase from 550°C to 900°C, and the activation energy of Cu diffusion was effectively raised from 107 kJ/mol to 161 kJ/mol. Severe lattice distortions and random cohesions are suggested as the dominant factors for the improved diffusion-resistant ability of the multicomponent high-entropy nitrides.

Atomic Layer Deposited Co(W) Film as a Single-Layered Barrier/Liner for Next-Generation Cu-Interconnects

Cobalt film with tungsten addition [Co(W)] has the potential to be an effective single-layered barrier/liner in interconnects awing to its good adhesion with Cu, a lower resistivity than TaN, and an improved barrier property with respect to cobalt films. Our previous study on chemical-vapor-deposited (CVD) Co(W) using carbonyl precursors clarified, however, that WO3 included in the films increased the resistivity. In this current study, to reduce the resistivity of Co(W), oxygen-free Co(W) films were fabricated from two oxygen-free precursors, bis(cyclopentadienyl)cobalt and bis(cyclopentadienyl)tungstendihydride, by atomic layer deposition (ALD) using NH2 radicals generated using a hot filament. Results revealed that (a) W concentration in ALD-Co(W) could be controlled by adjusting the gas-feed sequences, (b) W addition improved the barrier property of ALD-Co(W) against Cu diffusion, (c) diffusion of Cu into ALD-Co(W) had a high activation energy, 2.0 eV, indicating interstitial diffusion, and (d) ALD-Co(W) consisted mainly of an amorphous-like phase, which is consistent with the high activation energy of Cu diffusion.

Comparative Study of Cu Diffusion in Ru and Ru-C Films for Cu Metallization

In this paper, the diffusivities of copper in 15 nm thick Ru and Ru–C barrier layers are determined experimentally by using sheet resistance and X-ray diffraction measurements with the Cu/barrier/Si samples. By fitting the dependence of diffusivities on temperature, the activation energy for Cu diffusion in Ru–C film is 1.11 eV, which is substantially higher than that in Ru film (0.54 eV). Microstructural analysis by transmission electron microscopy combined with energy-dispersive X-ray suggests that the higher activation energy for Cu diffusion in Ru–C is associated with the stuffing of added carbon atoms on the grain boundaries of the Ru matrix and consequently leading to the superior diffusion barrier performance of the Ru–C film.

Growth Mechanism of a Ternary (Cu,Ni)6Sn5 Compound at the Sn(Cu)/Ni(P) Interface

The growth mechanism of an interfacial (Cu,Ni)6Sn5 compound at the Sn(Cu) solder/Ni(P) interface under thermal aging has been studied in this work. The activation energy for the formation of the (Cu,Ni)6Sn5 compound for cases of Sn-3Cu/Ni(P), Sn-1.8Cu/Ni(P), and Sn-0.7Cu/Ni(P) was calculated to be 28.02 kJ/mol, 28.64 kJ/mol, and 29.97 kJ/mol, respectively. The obtained activation energy for the growth of the (Cu,Ni)6Sn5 compound layer was found to be close to the activation energy for Cu diffusion in Sn (33.02 kJ/mol). Therefore, the controlling step for formation of the ternary (Cu,Ni)6Sn5 layer could be Cu diffusion in the Sn(Cu) solder matrix.

TaCN growth with PDMAT and H 2/Ar plasma by plasma enhanced atomic layer deposition

TaCN films were deposited using atomic layer deposition (ALD) using PDMAT and H 2/Ar plasma. Calculations based on density functional theory (DFT) indicate a high energy barrier and a low reaction energy for reducing the +5 Ta oxidation state in the PDMAT precursor by using pure H radicals. Through the assistance of Ar radicals, low resistivity of TaCN films of 230 μΩ cm could be deposited by using H 2/Ar plasma. By employing in situ X-ray diffraction during annealing, the activation energy for Cu diffusion through the TaCN barrier was evaluated at 1.6 eV.

Diffusion of copper into polyimide deposited by ionized cluster beam

Copper was deposited by sputtering on two types of polyimide (PI) films, one is fabricated by ionized cluster beam deposition (ICBD) and the other is Kapton, commercially available from DuPont. Diffusion properties of copper into these two polyimide films were investigated by x-ray photoelectron spectroscopy and Rutherford backscattering spectroscopy. In addition, the packing densities of these PI films were measured by a rotational analyzer type ellipsometer. We found that PI films deposited by ICBD (ICB-PI) have a higher packing density than Kapton. We also found that less copper is diffused into ICB-PI than into Kapton, that is, PI by the ICB method blocks Cu diffusion into PI. The diffusion coefficient of Cu/ICB-PI is 2.45×10−17–2.8×10−15 cm2/s at 300–390 °C, the activation energy of Cu diffusion into ICB-PI is 1.75 eV and D0 for ICB-PI is 1.92×10−1 cm2/s. The Cu atoms diffuse into PI as a form of clusters.

The Interfacial and Diffusion Properties of Copper on Polyimide Deposited by Ionized Cluster Beam

Polyimide (PI) films have been prepared by ionized cluster beam deposition (ICBD), and Kapton, which is the trademark of PI from DuPont, was also prepared. Copper was deposited by sputtering on PI films. We investigated the interfacial properties of these two systems by X-ray photoelectron spectroscopy (XPS), and the diffusion phenomena by Rutherford backscattering spectroscopy (RBS). In addition, the packing densities of these PI films were measured by a rotational analyzer (RA) type ellipsometer. Two Cu/PI systems are compared. We found that PI films deposited by ICBD (ICB-PI) have a higher packing density than Kapton. We found that Cu interacts with pyromellitic dianhydride (PMDA) part of PI in the form of Cu–C–N, Cu–C–O, Cu–N–O complex, and that the interface of Cu/ICB-PI is sharper than Cu/Kapton. We also found that less copper is diffused into ICB-PI than into Kapton. The diffusion coefficient of Cu/ICB-PI is 2.45×10-17–2.8×10-15 cm2/s at 300–390°C, the activation energy of Cu diffusion into ICB-PI is 1.75 eV and D0 for ICB-PI is 1.92 ×10-1 cm2/s. The Cu atoms diffused into PI as a form of Clusters.

Influence of microstructure on the resistivity of Al-Cu-Si thin-film interconnects

The rate of resistivity decay in Al-2Cu-1Si thin-film conductors was studied as a function of temperature and grain size distribution. The decay kinetics were assumed to be governed by the rate of precipitate reconfiguration to grain boundaries. This assumption was confirmed by transmission electron microscopy (TEM) observations of the microstructure during resistance decay, and by studies of lines of two different widths. The results can be explained qualitatively from the microstructure of the lines. In particular, increasing the mean grain size slows the rate of resistivity decay, and establishing a bimodal distribution with a significant population of relatively large grains has the same effect. A simple model was developed to treat these effects quantitatively. The model assumes a cylindrical grain geometry and a uniform initial distribution of Cu and ignores the effect of intragranular precipitation. The model yields reasonable values for the activation energy for Cu diffusion in thin films, and predicts the correct dependence of the decay rate on grain size and grain distribution; however, it appears to overestimate the value of the preexponential factor D0.

Comparative Cu Diffusion Studies in Advanced Metallizations of Cu and Al-Cu Based Thin Films

ABSTRACTAvailability of diffusion data is important in the evaluation of the prospect of substituting Cu for Al-Cu metallization for improving electrical and electromigration performance. Measurements have been made of 67Cu radioactive tracer diffusion in Cu, Cu-0.4Zr and several Al-Cu thin films of commonly used compositions. Grain boundary self diffusion in Cu is described by δDb= 1.5xl0-9 exp( — 0.92eV/kT) cm3/ sec. The activation energy for Cu diffusion in Al, Al-l%Cu and Al-0.5Cu-0.15Ti thin films depends on the amount of Cu present and varies in the 0.4 - 1.0 eV range. The measured diffusion parameters in the two alloy systems are compared and contrasted with those available from electromigration studies.

Phosphosilicate Glass Passivation for ULSI Cu Metallization

Phosphosilicate glass (PSG) passivation for Cu metallization is proposed, and the Cu diffusion rate into Si substrates through various oxide structures is measured quantitatively. Cu diffusion is suppressed effectively by the PSG passivation resulting in reduction of the diffused Cu atoms to about an order of magnitude less than when passivated by nondoped films. The passivation is effective when the annealing temperature is less than 600°C. The apparent activation energy of Cu diffusion for the nondoped substrate and PSG/nondoped is 1.2 and 1.6 eV, respectively. However, most of the diffused Cu precipitates near the oxide/Si substrate interface and the amount of the diffused Cu is comparable to the limit for ordinary device contamination. Thus, further improvement or optimization of the passivation layer structure is desired.