Growth Of Copper Films Research Articles

Role of sputtered atom and ion energy distribution in films deposited by physical vapor deposition: A molecular dynamics approach

We present a comparative molecular dynamics simulation study of copper film growth between various physical vapor deposition (PVD) techniques: a constant energy neutral beam, thermal evaporation, dc magnetron sputtering, high-power impulse magnetron sputtering (HiPIMS), and bipolar HiPIMS. Experimentally determined energy distribution functions were utilized to model the deposition processes. Our results indicate significant differences in the film quality, growth rate, and substrate erosion. Bipolar HiPIMS shows the potential for an improved film structure under certain conditions, albeit with increased substrate erosion. Bipolar HiPIMS (+180 V and 10% Cu+ ions) exhibited the best film properties in terms of crystallinity and atomic stress among the PVD processes investigated.

Thickness dependence of the room-temperature ethanol sensor properties of Cu2O polycrystalline films

This study investigates the fabrication process of copper thin films via thermal evaporation, with precise control over film thickness achieved through Z-position adjustment. Analysis of the as-fabricated copper films reveals a discernible relationship between grain size (〈D〉) and Z-position, characterized by a phenomenological equation 〈D〉XRDn(Z)=〈D〉0n1+32rZ2+158rZ4 , which is further supported by a growth exponent (n) of 0.41 obtained from the analysis. This value aligns well with findings in the literature concerning the growth of copper films, thus underlining the validity and reliability of our experimental outcomes. The resulting crystallites, ranging in size from 20 to 26 nm, exhibit a resistivity within the range of 3.3–4.6 μΩ · cm. Upon thermal annealing at 200 °C, cuprite Cu2O thin films are produced, demonstrating crystallite sizes ranging from ∼9 to ∼24 nm with increasing film thickness. The observed monotonic reduction in Cu2O crystallites relative to film thickness is attributed to a recrystallization process, indicating amorphization when oxygen atoms are introduced, followed by the nucleation and growth of newly formed copper oxide phase. Changes in the optical bandgap of the Cu2O films, ranging from 2.31 to 2.07 eV, are attributed mainly to the quantum confinement effect, particularly important in Cu2O with size close than the Bohr exciton diameter (5 nm) of the Cu2O. Additionally, correlations between refractive index and extinction coefficient with film thickness are observed, notably a linear relationship between refractive index and charge carrier density. Electrical measurements confirm the presence of a p-type semiconductor with carrier concentrations of ∼1014 cm−3, showing a slight decrease with film thickness. This phenomenon is likely attributed to escalating film roughness, which introduces supplementary scattering mechanisms for charge carriers, leading to a resistivity increase, especially as the roughness approaches or surpasses the mean free path of charge carriers (8.61 nm). Moreover, ab-initio calculations on the Cu2O crystalline phase to investigate the impact of hydrostatic strain on its electronic and optical properties was conducted. We believe that our findings provide crucial insights that support the elucidation of the experimental results. Notably, thinner cuprite films exhibit heightened sensitivity to ethanol gas at room temperature, indicating potential for highly responsive gas sensors, particularly for ethanol breath testing, with significant implications for portable device applications.

Flexible Plasmonics Using Aluminum and Copper Epitaxial Films on Mica.

We demonstrate here the growth of aluminum (Al), copper (Cu), gold (Au), and silver (Ag) epitaxial films on two-dimensional, layered muscovite mica (Mica) substrates via van der Waals (vdW) heteroepitaxy with controllable film thicknesses from a few to hundreds of nanometers. In this approach, the mica thin sheet acts as a flexible and transparent substrate for vdW heteroepitaxy, which allows for large-area formation of atomically smooth, single-crystalline, and ultrathin plasmonic metals without the issue of film dewetting. The high-quality plasmonic metal films grown on mica enable us to design and fabricate well-controlled Al and Cu plasmonic nanostructures with tunable surface plasmon resonances ranging from visible to the near-infrared spectral region. Using these films, two kinds of plasmonic device applications are reported, including (1) plasmonic sensors with high effective index sensitivities based on surface plasmon interferometers fabricated on the Al/Mica film and (2) Cu/Mica nanoslit arrays for plasmonic color filters in the visible and near-infrared regions. Furthermore, we show that the responses of plasmonic nanostructures fabricated on the Mica substrates remain unaltered under large substrate bending conditions. Therefore, the metal-on-mica vdW heteroepitaxy platform is suitable for flexible plasmonics based on their bendable properties.

Time‐Resolved Grazing Incidence X‐Ray Absorption Spectroscopy for the In Situ Investigation of the Initial Stages of Sputter‐Deposited Copper Thin Films

The sputter deposition and the growth of thin copper films on float glass substrates are in situ studied using grazing incidence, reflection mode X‐ray absorption fine structure spectroscopy with subsecond time resolution. The experimental data are compared with model calculations, assuming the presence of crystalline, face‐centered cubic metallic Cu nanostructures. From a detailed analysis of the measured spectra, the film thickness as well as the surface roughness is determined, leading to a detailed understanding of the films growth as a function of the sputter deposition time. In particular, different stages of film growth can clearly be distinguished from the fits of the experimental data. The results suggest the formation of isolated, approximately nm‐sized copper clusters in the initial phase of the film deposition for the first few seconds, a coalescence phase with a nominal thickness of ≈1.5−2.8 nm, constant roughness of about 1.4 nm for the subsequent ≈5 s, and finally 3D growth of the Cu crystallites in the film for later stages of film growth. Further prospects of the methodology are given.

Enantioselective recognition of amino acid based on electrochemical deposition and X-ray diffraction technology

Addition of D-Asp in the electrochemical deposition process of Bismuth film resulted the generation of a new diffraction peak in X-ray diffraction (XRD) spectrum. This phenomenon was not observed in the situation of L-Asp. The new diffraction peak might suggest D-Asp could result in the generation of a specific Bismuth structure. Enantioselective recognition of D- and L-Asp can be realized based on this new XRD peak. The limit of detection was determined to be 3.5 × 10−8 and 1.7 × 10−8 mol L−1 for D- and L-Asp, respectively. The XRD spectra of electrodeposited Copper films fabricated in the presence of D- or L-Asp showed different lattice plane diffraction peak intensity ratios. The reason was believed to be chirality induced different binding capabilities of Asp enantiomers that influenced Copper film growth. Therefore, the combination of electrochemical deposition using Copper as metal source and XRD technology can be used to achieve enantioselective recognition of Asp. The limit of detection for D- and L-Asp were determined to be 1.5 × 10−10 and 1.2 × 10−11 mol L−1, respectively.

Effect of Reverse Currents during Electroplating on the ⟨111⟩-Oriented and Nanotwinned Columnar Grain Growth of Copper Films

Nanotwinned copper (nt-Cu) has been attracting a great deal of attention in the past decades due to its excellent mechanical and electrical properties. In this study, a new approach, periodic-rever...

Facile large-scale preparation of high-performance copper electrode materials for BaTiO3 ceramic capacitors

An accessible and cost-effective approach for preparation of copper layers used as electrode materials of ceramic capacitors based on inkjet printing and electroless plating technique has been investigated. An Ag(I) ink was inkjet-printed on the pretreated barium titanate (BaTiO3) ceramics to catalyze the growth of copper film in subsequent electroless plating. The ink concentration was explored to achieve best catalytic effect, as well as the pretreatment time and the copper plating time were investigated to guarantee desirable film morphology and performance. SEM, XRD and sheet resistance test were conducted to analyze the morphological, structural and electrical properties of copper films. By applying this approach, a continuous copper film with high crystallization and fine morphology was obtained, which showed excellent electrical and mechanical performances with a resistivity as low as 3.77 × 10−8 Ω m and a reliable adhesion strength. The copper electrodes could be prepared in large scale, and the ceramic capacitors with such copper layers had been proven to meet the requirements of industrial application as filter components. Easily-achieved mass production and superiority over commercial products in electrical and mechanical performance of the copper electrodes make the approach a better alternative for preparation of electrodes of ceramic capacitors in industrial production.

Phase filed simulation of dendritic growth of copper films irradiated by ultrashort laser pulses

A phase field model (PFM) is combined with a two-dimensional two-temperature model (TTM) to simulate the evolution of dendritic growth during re-solidification of ultrafast laser-material interaction. The dynamic solidification conditions at different locations of the melting pool obtained from TTM are fed into the quantitative PFM based on the macro-micro coupled method. A series of simulations are executed to investigate the influence of laser parameters, such as laser influence and pulse duration, on melting pool characteristics and local dendrite morphology. Besides, dendrite structures calculated at different areas of the melting pool were discussed based on local solidification conditions, and the simulated dendrite arm spacing (DAS) for various cooling rates was made comparison with previously published experimental data. The simulated results reveal that the maximum temperature gradient has significant influence on the local dendritic competitive growth, while the laser parameters effect the local microstructure distinctly due to the changes of solidification conditions. This work demonstrates the potential application of PFM to predict the microstructure morphology presented in ultrashort laser-material interaction and other industrially relevant conditions with complex solidification conditions.

Effect of substrate temperature on quality of copper film catalyst substrate: A Molecular Dynamics Study

Copper film growth using thermal evaporation methods was studied using molecular dynamics simulations. The AlSiMgCuFe modified embedded atom method potential was used to describe interaction of Cu-Cu, Si-Si and Cu-Si atoms. Our results showed that the variations of substrate temperature affected crystal structure composition and surface roughness of the produced copper film catalyst substrate. In this study, we observed intermixing phenomenon after deposition process. The increasing of substrate temperature affected the increasing of the total silicon atoms had diffusion into copper film.

Effect of copper film catalyst substrate thickness on atomic diffusion time at the initiation of the recrystallization stage: a molecular dynamics study

Copper film growth using thermal evaporation and annealing methods were studied using molecular dynamics simulations. The AlSiMgCuFe modified embedded atom method potential was used to describe the interaction of Cu–Cu, Si–Si and Cu–Si atoms. The annealing process, which was limited to atomic diffusion, repaired the crystal structure of the copper film. Our results showed that the thickness of the copper film catalyst substrate affected the initiation of the recrystallization process. A change of phase transition of copper atoms was observed after annealing. These phenomena were supported by knowledge of the radial distribution function and analysis of the crystal structure.

Surface-initiated growth of copper using isonicotinic acid-functionalized aluminum oxide surfaces

Isonicotinate self-assembled monolayers (SAM) were prepared on alumina surfaces (A) using isonicotinic acid (iNA). These functionalized layers (iNA-A) were used for the seeded growth of copper films (Cu-iNA-A) by hydrazine hydrate-initiated electroless deposition. The films were characterized by scanning electron microscopy (SEM), electron-dispersive X-ray spectroscopy, atomic force microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and advancing contact angle measurements. The films are Cu0 but with surface oxidation, and show a faceted morphology, which is more textured (Rq = 460 ± 90 nm) compared to the SAM (Rq = 2.8 ± 0.5 nm). In contrast, growth of copper films by SnCl2/PdCl2 catalyzed electroless deposition, using formaldehyde (CH2O) as the reducing agent, shows a nodular morphology on top of a relatively smooth surface. No copper films are observed in the absence of the isonicotinate SAM. The binding of Cu2+ to the iNA is proposed to facilitate reduction to Cu0 and create the seed for subsequent growth. The films show good adhesion to the functionalized surface.

Effect of current density during electrodeposition on microstructure and hardness of textured Cu coating in the application of antimicrobial Al touch surface

Copper is a well proven antimicrobial material which can be used in the form of a coating on the touch surfaces. Those coating can offer a good service as touch surface for very long time if only they possess good mechanical properties like scratch resistance and microhardness. In the present work the above mentioned mechanical properties were determined on the electrodeposited copper thin film; deposited on double zincated aluminium. During deposition, current density was varied from 2Adm−2 to 10Adm−2, to produce crystallite size in the range of 33.5nm to 66nm. The crystallite size was calculated from the X-ray peak broadening (Scherrer׳s formula) which were later confirmed by TEM micrographs. The scratch hardness and microhardness of the coating were measured and correlated with the crystallite size in the copper coating. Both characteristic values were found to increase with the reduction in crystallite size. Reduced crystallite size (Hall–Petch effect) and preferred growth of copper films along (111) plane play a significant role on the increase in the hardness of the coating. Further, TEM analysis reveals the presence of nano-twins in the film deposited at higher current density, which contributed to a large extent to the sharp increase of coating hardness compared to the mechanism of Hall–Petch effect. The antimicrobial ability of the coated sample has been evaluated against Escherichia coli bacteria and which is compared with that of commercially available bulk copper using the colony count method. 94% of E. coli cells were died after six hours of exposure to the copper coated surface. The morphology of the copper treated cells was studied using SEM.

Direct, sequential growth of copper film on TaN/Ta barrier substrates by alternation of Pb-UPD and Cu-SLRR

This study uses an electrochemical form of layer-by-layer deposition to grow Cu films on TaN/Ta barriers without the need for a copper seed layer. The process involves sequential underpotential deposition (UPD) of Pb and surface-limited redox replacement (SLRR) of Cu. Additionally, this work elucidates the influence of pH and Pb deposition potential on the growth mechanism and electrical properties of the resulting Cu films on TaN/Ta barriers. The results demonstrate that during Cu-SLRR, the onset of Cu2+ substitution of Pb2+ is delayed when Pb coverage is increased via deposition at a higher Pb-UPD. This is because perchlorate anions are adsorbed on the underlying UPD-deposited Pb adatoms. Cu films formed at a Pb-UPD of −1150mV exhibit the lowest resistivity of 7.6μΩcm in the as-deposited state because these films are formed with the Cu(111) texture. Additionally, the Cu layer remains thermally stable after annealing at 700°C. The results of this study may be of interest for the fabrication of microelectronics, particularly for forming Cu-interconnections.

Epitaxial Growth of Copper Film by MOCVD

Copper thin films were deposited on single crystal sapphire substrate via metal-organic MOCVD using Cu (acac)2 as precursor. X-ray diffraction (XRD) and Scanning Electronic Microscope (SEM) were employed for studying preferred orientation and microstructure. Atomic Force Microscope was utilized in order to characterize roughness of copper thin layer. By calculation of the Gibbs free energy, the reactions have been deeply understood. Depositions were carried out at various substrate temperatures in the rage 473K to 673K. It has been revealed that temperature determined the orientation and microstructure of copper films. At 673K, copper films have exhibited preferred orientation, smooth surface and connected grains, which proved that this copper thin film can act as precursor. Based on the study of epitaxial growth of copper films, a schematic diagram of epitaxial growth relationship is suggested for the step by step depositions processes.

Magnetron sputtering of thin Cu(200) films on Ni(200)/SiO2/Si substrates

The possibility of oriented growth of thin copper films with a (200) texture on a SiO2/Si substrate by magnetron sputtering in medium vacuum is demonstrated for the case when a predeposited nickel layer with a (200) texture serves as an orienting sublayer.

Formation of small volatile complexes during copper film growth by the combined synthesis-transport method

Stable heterogeneous synthesis products in combined synthesis-transport processes for the growth of thin copper films have been studied by ESR, X-ray photoelectron, and IR spectroscopies. The results demonstrate that the synthesized volatile compounds condensed on solid surfaces have the form of formate-like metal complexes of copper(I). We have identified the mechanisms underlying the formation of volatile monomeric metal complexes on the surface of copper-containing precursor particles and the mechanism of the thermal decomposition of metal complexes on a heated substrate.

Metallic Nanostructure Formation Limited by the Surface Hydrogen on Silicon

Constant miniaturization of electronic devices and interfaces needed to make them functional requires an understanding of the initial stages of metal growth at the molecular level. The use of metal-organic precursors for metal deposition allows for some control of the deposition process, but the ligands of these precursor molecules often pose substantial contamination problems. One of the ways to alleviate the contamination problem with common copper deposition precursors, such as copper(I) (hexafluoroacetylacetonato) vinyltrimethylsilane, Cu(hfac)VTMS, is a gas-phase reduction with molecular hydrogen. Here we present an alternative method to copper film and nanostructure growth using the well-defined silicon surface. Nearly ideal hydrogen termination of silicon single-crystalline substrates achievable by modern surface modification methods provides a limited supply of a reducing agent at the surface during the initial stages of metal deposition. Spectroscopic evidence shows that the Cu(hfac) fragment is present upon room-temperature adsorption and reacts with H-terminated Si(100) and Si(111) surfaces to deposit metallic copper. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) are used to follow the initial stages of copper nucleation and the formation of copper nanoparticles, and X-ray energy dispersive spectroscopy (XEDS) confirms the presence of hfac fragments on the surfaces of nanoparticles. As the surface hydrogen is consumed, copper nanoparticles are formed; however, this growth stops as the accessible hydrogen is reacted away at room temperature. This reaction sets a reference for using other solid substrates that can act as reducing agents in nanoparticle growth and metal deposition.

Coupling effect of the electric and temperature fields on the growth of nanocrystalline copper films

The effect of an external static electric field on the grain growth in nanocrystalline Cu films was studied at different annealing temperatures. Transmission electron microscopy and x-ray diffraction indicate that the grain growth in Cu films is accelerated with various rates by an external electric field at different annealing temperatures. It is found that there is a coupling effect from the external electric and temperature fields on grain growth in Cu films during annealing. The growth rate is accelerated proportional to a factor $f(E)\ensuremath{\cdot}{\ensuremath{\mu}}^{T/100\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}}$, which is determined from the theoretical derivation. The analysis indicates that the enhanced grain growth is achieved by the effect of the electric field on the vacancies migration and dislocation climb along grain boundaries.

Seedless Copper Electrodeposition onto Tantalum Diffusion Barrier by Two-Step Deposition Process

Copper was electrodeposited directly onto a 5 nm thick physical vapor deposited tantalum (Ta) diffusion barrier layer in a copper-ammonium-citrate (Cu-NH 3 -Cit) bath. An anodic potential was applied to Ta in a saturated KOH solution to remove native Ta oxide before seedless copper deposition on Ta. The dense growth of copper films with sufficient wetting and adhesion on Ta was made possible by a two-step potentiostatic deposition at -1.26 V vs saturated calomel electrode (SCE) for Cu 2 (Cit) 2 OH 3- ion reduction and then at -0.58 V vs SCE for cupric ion reduction.

Uptake of Copper Acetamidinate ALD Precursors on Nickel Surfaces

The adsorption and thermal activation of copper(I)-N,N′-di-sec-butylacetamidinate on a Ni(110) single-crystal surface were characterized in connection with the use of that compound as a precursor for the growth of copper films via atomic layer deposition (ALD) processes. Studies were carried out under ultrahigh vacuum (UHV) conditions by using a combination of X-ray photoelectron spectroscopy (XPS), low-energy ion scattering (LEIS), and temperature-programmed desorption (TPD). A temperature window between approximately 350 and 450 K was identified for the clean deposition of the precursor on the surface: lower temperatures are insufficient for activation of the dissociative adsorption, and higher temperatures lead to continuous decomposition beyond Cu monolayer saturation. Approximately three ALD-like cycles are required to reach full Cu monolayer saturation, the equivalent of a film growth rate of approximately 0.75 A/cycle. Preadsorption of hydrogen on the surface does not modify any of this behavior be...