Electrochemical Deposition Of Cu Research Articles

Recent Advances in Barrier Layer of Cu Interconnects.

The barrier layer in Cu technology is essential to prevent Cu from diffusing into the dielectric layer at high temperatures; therefore, it must have a high stability and good adhesion to both Cu and the dielectric layer. In the past three decades, tantalum/tantalum nitride (Ta/TaN) has been widely used as an inter-layer to separate the dielectric layer and the Cu. However, to fulfill the demand for continuous down-scaling of the Cu technology node, traditional materials and technical processes are being challenged. Direct electrochemical deposition of Cu on top of Ta/TaN is not realistic, due to its high resistivity. Therefore, pre-deposition of a Cu seed layer by physical vapor deposition (PVD) or chemical vapor deposition (CVD) is necessary, but the non-uniformity of the Cu seed layer has a devastating effect on the defect-free fill of modern sub-20 or even sub-10 nm Cu technology nodes. New Cu diffusion barrier materials having ultra-thin size, high resistivity and stability are needed for the successful super-fill of trenches at the nanometer scale. In this review, we briefly summarize recent advances in the development of Cu diffusion-proof materials, including metals, metal alloys, self-assembled molecular layers (SAMs), two-dimensional (2D) materials and high-entropy alloys (HEAs). Also, challenges are highlighted and future research directions are suggested.

Copper Electrodeposition from Deep Eutectic Solvents-Voltammetric Studies Providing Insights into the Role of Substrate: Platinum vs Glassy Carbon.

We report on the effect of the substrate on electrochemical deposition of Cu from deep eutectic solvent ethaline. We investigated the polarization behavior during electrodeposition of Cu on Pt and glassy carbon (GC) from both Cu2+ and Cu+ containing ethaline using cyclic voltammetry (CV). Formation of bulk Cu deposits on both substrates underwent nucleation and growth processes; however, the nucleation was considerably sluggish on GC compared to Pt. While experiments in Cu+ solutions indicated that coalescence of Cu islands on Pt is a slow process and that its surface may not be fully covered by Cu, such determination of Cu coverage could not be made on GC. Cu dissolution is also slower from GC than from Pt. It was observed that CV of Cu deposition on GC is influenced by the surface preparation method. Since ethaline has high chloride concentration, a parallel study in aqueous 3 M NaCl solution was conducted in order to examine the influence of the chloride medium on the electrodeposition process. This revealed that electrodeposition in both media occurred in the same manner but with different charge and mass transfer rates caused by the differences in viscosity and chloride concentrations of the two solutions.

A New Alternative Electrochemical Process for a Pre-Deposited UPD-Mn Mediated the Growth of Cu(Mn) Film by Controlling the Time during the Cu-SLRR

A layer-by-layer deposition is essential for fabricating the Cu interconnects in a nanoscale-sized microelectronics because the gap-filling capability limits the film deposition step coverage on trenches/vias. Conventional layer-by-layer electrochemical deposition of Cu typically works by using two electrolytes, i.e., a sacrificial Pb electrolyte and a Cu electrolyte. However, the use of a Pb electrolyte is known to cause environmental issues. This study presents an Mn monolayer, which mediated the electrochemical growth of Cu(Mn) film through a sequence of alternating an underpotential deposition (UPD) of Mn, replacing the conventionally used UPD-Pb, with a surface-limited redox replacement (SLRR) of Cu. The use of the sacrificial Mn monolayer uniquely provides redox replacement by Cu2+ owing to the standard reductive potential differences. Repeating the sequence of the UPD-Mn followed by the SLRR-Cu enables Cu(Mn) film growth in an atomic layer growth manner. Further, controlling the time of open circuit potential (OCP) during the Cu-SLRR yields a technique to control the content of the resultant Cu(Mn) film. A longer OCP time caused more replacement of the UPD-Mn by the Cu2+, thus resulting in a Cu(Mn) film with a higher Cu concentration. The proposed layer-by-layer growth method offers a wet, chemistry-based deposition capable of fabricating Cu interconnects without the use of the barrier layer and can be of interest in microelectronics.

Pulsed Galvanostatic Electrodeposition of Copper on Cobalt Using a pH-Neutral Plating Bath and Electroless Seeds

Due to its notable retention of electrical conductivity in nanoscale features, cobalt is a leading material candidate for diffusion barriers in the sub-14 nm node copper interconnects. In this application, Co also facilitates high aspect ratio gap-filling by serving as a substrate for direct electrochemical deposition (ECD) of Cu. However, the Co-Cu ECD system is associated with several technical challenges, which include dissolution of Cu seeds (and Co) in conventional acidic baths, interference of hydrogen evolution, and solution-sensitive nucleation barriers. We investigate here this ECD system by using pulsed galvanostatic ECD in a neutral plating bath of CuSO4, with in situ electroless deposition of Cu seeds. Both seeding and ECD of Cu are enhanced with the use of a carbon based catalytic activator. These observations are explained in terms of a proposed mixed-potential mechanism. Nucleation of the ECD-Cu is detected with voltammetry, and further quantified as an instantaneous step by measuring the associated kinetic parameters with chronoamperometry. Spatially uniform layers of pulse-deposited Cu on Co are detected by electron microscopy, and the deposition rates are determined using energy dispersed X-Ray spectroscopy. Corrosion tests performed in a glycine-based solution for Cu planarization confirm the general CMP compatible electrochemistry of the ECD-Cu.

Enhanced electrocatalytic reduction of aqueous nitrate by modified copper catalyst through electrochemical deposition and annealing treatment

ABSTRACTCopper has been intensively investigated as an electrocatalyst for electrochemical reduction of aqueous nitrate. Here we report preparation of Cu electrocatalyst by electrochemical deposition of Cu on Ni foils, annealing treatment to produce nanograins of Cu oxides and electroreduction to form metallic Cu nanograins to enhance the catalytic activities of nitrate reduction. The prepared Cu electrocatalysts were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. The electrochemical deposition of Cu on Ni substrates produced different sizes and sharp-edged microcrystal of Cu, and the annealing treatment at 300°C transformed these microcrystals into uniform spheroids of Cu oxides in sizes of 150–350 nm. The potentiostatic electrolysis of aqueous nitrate showed that the annealing treatment improved nitrate reduction efficiency by 4.5 times and 20% at −0.8 and −1.4 V versus the saturated calomel electrode, respectively. The rate and Faradaic efficiency for nitrate reduction by modified Cu electrode remained constant within a testing time of 48 h. The results demonstrate that electrochemical deposition on Ni foils and subsequent annealing treatment provide a simple and cost-effective approach to enhance the catalytic activity and stability of a transition metal catalyst.

Fabrication of CNT-based Planar Micro-Coils on Silicon Substrate

Micro-coils are the most popular inductor structures. It is desirable to have high aspect ratio (HAR) planar micro-coils where the “planar” structure ensures less fabrication process steps compared to their 3-D counterparts, and HAR ensures that a lesser area is occupied by the micro-coil as well as low resistance due to larger conductor cross section. Such HAR planar micro-coils are generally realized through electrochemical-deposition (ECD) of metals, generally copper, inside blind HAR trenches in a substrate. However, such an ECD process into HAR trenches is very challenging, resulting into voids and the process is required to be optimized for different aspect ratios, which makes it time consuming and complex. In this paper, we present a novel way of realizing planar micro-coils in silicon using carbon nanotubes (CNTs). The issue of poor electrical conduction between two adjacent CNT bundle is resolved through graphene-deposition and this allows the electrical conduction along the length of the micro-coil (in the plane of the coil), which is necessary for a planar micro-coil structure. Planar micro-coils of an aspect ratio (AR) 3:1 is realized using such graphenic-CNTs and their electrical characterization is reported here. DC and low-frequency electrical characterization of these coils are performed, which shows the micro-coils have a high inductance value compared to the other micro-coils reported in the literature. The process of obtaining such planar micro-coils, using the CNT-graphenic heterostructure reported here, is less complex compared to the conventionally used ECD of Cu, and unlike ECD of Cu inside trenches of different AR will not require any optimization.

Electrodeposition of Cu–Ga precursor layer for CuGaS2 solar energy thin film from alcohol solution

CuGaS2 thin film is fabricated with electrochemical deposition of Cu–Ga alloys from alcohol solution to eliminate the interference of hydrogen evolution reaction (HER). The process involves electrodeposition of Cu–Ga precursor on molybdenum substrate and subsequential annealing in sulfur vapor. The formation of CuGa2 alloy in precursor is observed and pure ternary chalcopyrite CuGaS2 phase in good polycrystalline structure without secondary phase is obtained after thermal treatment. The influence of the applied deposition potential on the crystalline phase, morphology, compositions, and carrier concentration of the films were investigated. The results show that an optimum choice of electrodeposition potential is necessary to obtain a pure crystallized CuGaS2 thin film. A lower absolute deposition potential results in a higher Cu/Ga ratio and the emergence of CuS secondary phase after annealing in sulfur atmosphere. The crystal size of the formed CuGaS2 phase with thermal annealing process increases with the positive shift of deposition potential. Impedance spectroscopy test demonstrates the semiconductor property of the synthesized CuGaS2 polycrystalline thin films are all p-type. The carrier density of the obtained CuGaS2 thin films increases with the negative shift of deposited potential.

One-step electrochemical synthesis of Cu—Zn—Sn—Se precursor thin films from solutions containing lactic acid

The influence of the conditions of electrochemical deposition of Cu—Zn—Sn—Se precursor thin films from solutions containing lactic acid on their optical and electrophysical properties was studied. It was found that an additional annealing step of precursor films in a selenium atmosphere at 550 °C is necessary for the preparation of single-phase polycrystalline photoconducting Cu—Zn—Sn—Se films with a band gap energy equal to ~1 eV. The obtained semiconductor CZTSe materials satisfy the composition and property requirements imposed on absorbing layers in solar panels.

Synthesis of copper nanocone array electrodes and its electrocatalytic properties toward hydrogen peroxide reduction

The copper nanocone (Cu-NC) array electrodes were successfully synthesized by metal sputtering on Al2O3/Al substrate with conical nanopores followed by electrodeposition of Cu. To fabricate the conical pores on aluminum substrate, repeated and alternating anodizations and pore widening treatments were performed. Each anodization step was conducted at 45V in a 0.3M oxalic acid solution at 9°C. After that, the holes were widened by immersion in a 5vol% phosphoric acid solution at 30°C. The effect of different number of alternating anodization-etching cycles on the shape, diameter and height of pores in anodic aluminum oxide (AAO) template was studied. After the electrochemical deposition of Cu, free standing Cu-NC arrays were obtained by chemical etching of Al2O3 templates in dilute phosphoric acid. The dimensions of copper nanocones correspond closely with used Al2O3 templates. The morphology and structural characterization of fabricated Al2O3 templates and Cu-NC arrays were performed. The electrocatalytic activity of the Cu-NC array electrodes toward hydrogen peroxide reduction was investigated.

Facile electrochemical deposition of Cu7Te4 thin films with visible-light driven photocatalytic activity and thermoelectric performance

Excellent photocatalytic and thermoelectric performances by Cu7Te4 thin films synthesised by galvanic deposition.

Electrodeposition of Cu on Nickel Seed Layer/p-Si in Buft Cell

This paper describes the electrochemical deposition of Cu by galvanostatic method on p-Si with high deposition rate. To prevent the diffusion of Cu into Si, a thin layer of Ni is used as a diffusion barrier. A novel bath i.e., high pH Nickel sulphate bath without reducing agent was used for the galvanic reaction to form a Ni seed layer. The SEM images show the thickness of smooth and dense Ni film is in the range of 190-200 nm. Resistance of the Ni-pSi was found to be ~0.28 Ω/sq by four point probe which is lower than the resistance of Si i.e, ~108 Ω/sq. Copper was deposited on this seed layer of Ni by applying a high electric field across the wafer by placing it between a copper plating bath and an acid electrolyte. A high DC voltage was applied between a copper sheet placed in the copper bath and a platinum sheet placed in the acid electrolyte. A deposition rate of about 3.85 um/min of Cu on Ni-pSi was achieved and the film showed good adhesion. This electrochemical reaction involves silicon dissolution from one face and simultaneous copper deposition on the other. SEM images show the compact and smooth Cu film having ~3.85 um thicknesses. This experimental value of the thickness is in agreement with the theoretical value expected for 100% current efficiency. The resistance of electroplated Cu film on Ni/p-Si was measured by four point probe and found to be 0.07 Ω/sq. Fig: a and b: SEM image (Surface and Cross sectional) of Ni/p-Si c and d: SEM image (Surface and Cross sectional) of Cu on Ni-pSi

Electrochemical deposition of Cu and Ta from pyrrolidinium based ionic liquid

Electrochemical deposition of Cu and Ta from pyrrolidinium based ionic liquid

Development of seed layer for electrodeposition of copper on carbon nanotube bundles

The reliability of metal filled through silicon vias (TSVs) will determine their suitability in the semiconductor industry. The adoption of this technology will depend strongly on the materials used for filling vias that function as vertical interconnects. Conventional materials for filling TSVs include copper and tungsten. Carbon nanotubes (CNTs) are an excellent candidate to replace or be used in conjunction with these materials due to their superior electrical and mechanical properties. Metallic CNT bundles can allow nearly unhampered transport of electrons, resulting in a low resistance interconnect capable of withstanding high current densities. The growth of CNTs with ethylene and methane precursors by thermal chemical vapor deposition has been investigated using thin films of aluminum oxide and iron as catalysts. Nickel and cobalt were investigated as well with limited success. CNT growth is followed by electrochemical deposition (ECD) of copper. Traditionally, sputtered or evaporated Cu is used as a seed layer for ECD; however, the high temperatures necessary for CNT growth made Cu an unsuitable seed layer due to migration. The authors investigated combinations of ECD seed layers and CNT catalysts on the surface of a silicon wafer to qualify the best materials for the formation of a Cu/CNT matrix. ECD of Cu was studied on as-grown and densified CNTs with a tungsten seed layer. Once the process for covering CNT bundles with copper is optimized, future work will focus on placing the materials system inside cylindrical vias formed using an inductively coupled plasma etch process.

Study of the electrochemical co-reduction of Cu2+ and Zn2+ ions from an alkaline non-cyanide solution containing glycine

The electrochemical deposition of Cu–Zn alloy was studied in weakly alkaline glycine solutions at pH 10.0 and room temperature. This study was realized by cyclic voltammetry, chronoamperometry, scanning electron microscopy, energy dispersive X-rays and atomic absorption spectrometry. Voltammetric studies displayed three cathodic and anodic peaks, respectively, for Cu–Zn alloys. ALSV profiles showed different oxidation peaks for dissolution of the deposits of Cu–Zn alloy and these had shapes which depend on the conditions of electrodeposition. The dissolution peaks do not coincide with peak potential for the dissolution peak of pure copper and zinc. The physical and chemical characterization of these coatings showed to be interrelated, meaning that the chemical composition, cathodic current efficiency and surface morphology of Cu–Zn alloys obtained were found to be depending on the electrolyte composition and applied potential. AAS analysis revealed the presence of mainly copper, which suggests that the process of formation of Cu–Zn alloy can be classified as normal (irregular) solution.

Electrochemical deposition of Cu and Nb from pyrrolidinium based ionic liquid

A study on the electrochemical deposition of Cu/Nb composites is presented in this work.The electrodeposition tests were performed using 1-butyl-1-methylpyrrolidinium bis (trifluoromethylsulphonyl) imide as solvent. The electrochemical behaviour of copper and niobium ions was investigated by cyclic and linear sweep voltammetries, allowing to obtain information on potentials and mechanisms of deposition. Firstly, the electrodeposition of Nb on Cu substrate and of Cu on Nb substrate was investigated; then, the deposition of Cu and Nb in dual bath mode was considered. All the experimental tests were carried out at 125°C under inert atmosphere, in order to avoid interference of water and oxygen. According to the electrochemistry of the metals considered and based on the experimental results, the possible reaction path for the oxidation/reduction was proposed. Deposition tests were carried out at different potentials and the related samples were analysed by scanning electron microscopy and energy dispersive X-ray spectroscopy.Structural and chemical analyses indicate that the obtained deposits cover uniformly the electrode surface and exhibit individual layers with a characteristic size ranging between 50 and 100nm.

Electrochemical activation of carbon–halogen bonds: Electrocatalysis at silver/copper nanoparticles

Cu nanoparticles (NPs) of average dimension of 20–30nm were deposited following a double step potential deposition on glassy carbon (GC). Cu NPs morphology, shape, dimension and distribution were investigated by scanning electron microscopy (SEM). According to SEM the electrochemical deposition of Cu produces two different type of NPs (spherical and polyhedral), which result randomly distributed all over the GC support. In a second step, Ag was deposited over Cu NPs by displacement deposition giving a Cu nanostructured electrode decorated with very small Ag NPs (hereafter Ag/Cu). The electrodes were fully characterized by X-ray photoemission spectroscopy and energy dispersive X-ray spectroscopy, which provided the surface and bulk chemical composition of the electrodes.The reductive cleavage of a series of organic chlorides, including chloroaromatics, benzyl chlorides, trichloroethylene and polychloromethanes, was investigated both at Cu and Ag/Cu NPs in DMF+0.1M (C2H5)4NBF4. Cu and Ag/Cu NPs electrodes have shown remarkable electrocatalytic reduction properties for the halides following concerted dissociative electron transfer. The peak potentials recorded at Cu and Ag/Cu NPs electrodes at v=0.2Vs−1 are positively shifted by 0.3–0.5V with respect to the reduction potentials measured at a non-catalytic electrode such as GC and in some cases the catalytic effect is even better than bulk Ag and Cu.

Enhancement of Cu Filling into p-Type Macro-Porous Silicon by Pore Wall Thinning, Oxide Deposition and Back Side Illumination

Electrochemical deposition of Cu on structured silicon including groves and pores is critical for several applications such as microelectronics, sensors, and energy applications. In the case of Cu filling of porous Si, the silicon skeleton can be either etched to produce free nano- or micro-structured Cu or can be left to form a nano- or micro-composite of Si/Cu. Deposition of metals into n-type porous Si is a relatively straight-forward process, due to the availability of electrons at the conduction band to reduce Cu cations. Cu deposition into p-type porous Si requires illumination, unfortunately, it enhances the growth on pore walls and results in either non-conformal growth or plug-in which lead to voids. In this work, it is shown that illuminating the back side of the wafer combined with insulating the pore walls and pore top leads to conformal growth of Cu from the pore-tip to the pore-top. Two approaches have been tested: wall thinning by chemical etching and SiO2 coating on the pore top. Massive wires have been obtained by completely and conformally filling porous Si without leaving gaps in the case of SiO2-coated samples. The conformal filling of p-type Si was obtained without using additives and without seed layer.

Synthesis of nanoporous Cu films by dealloying of electrochemically deposited Cu–Zn alloy films

Crack-free nanoporous Cu films were synthesized by electrochemical deposition of Cu–Zn alloy films by chronoamperometry (CA) at −0.5V(Ag/AgCl), followed by a two-step chemical dealloying process. Various nanoporous structures were successfully created with very low concentration of less-noble element (3–4at.% Zn), by a wet-chemical process. In addition to the Zn, less noble constituent, it is believed that Cu oxide formed during the electrochemical deposition might act as less-noble constituent as well.

Through-Silicon-Via (TSV) Filling By the Electro-Chemical Deposition of Cu With Modified Microstructures By Ultra-Fast Pulsed Current

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Copper nanocones grown in polymer ion-track membranes as field emitters

Field emission (FE) properties of unstructured and patch-structured cathodes with randomly distributed and vertically aligned copper nanocones (Cu-NCs) are reported. The cones of ~28 μ m height, 2.4 μ m base diameter and 95–220 nm tip radius were fabricated by electrochemical deposition of Cu into conical channels of heavy-ion-irradiated and asymmetrically etched polycarbonate membranes. FE measurements of the unstructured cathodes with slowly-grown Cu-NCs of high number density (10 7 cm −2 ) and excellent mechanical stability yield stable currents up to 280 μ A from an emission spot of 30 μ m. For the structured cathodes with a triangular patch array of less dense Cu-NCs ( 6 cm −2 ), well-aligned FE with ~90% efficiency is reproducibly achieved. A trade-off between low onset field (~22 V/ μ m) for sparsely grown Cu-NCs with sharp tips and high current limit (~100 μ A) for densely grown ones with broader tips is observed. Possibilities for further optimization of such field emitters for cold cathode applications are discussed.