Growth Of Cu Thin Films Research Articles

Nucleation-controlled growth of Cu thin films electrodeposited directly on ALD Ru diffusion barrier in additive-free electrolyte for Cu interconnect

Direct Cu electrodeposition on a 3-nm-thick atomic-layer-deposited (ALD) Ru diffusion barrier layer was investigated for Cu interconnect in Si-based microelectronic devices. A Cu-ammonia-citrate (Cu-NH3-Cit) electrolyte was employed with no additives. The nucleation behavior of Cu on Ru was dependent on the cathodic potential applied to ALD Ru/SiO2/Si wafer specimen whether it is instantaneous or progressive. Preferable instantaneous nucleation with a high area density of Cu nuclei on Ru contributed to the formation of uniform Cu thin films. Lastly, direct Cu electrodeposition onto Ru at a constant cathodic potential of −1.0 V filled 30-nm-wide and 120-nm-deep trenches with void-free Cu.

Copper thin films deposited using different ion acceleration strategies in HiPIMS

The growth of Cu thin films by low-energy ion-bombardment using bipolar and conventional HiPIMS pulse configurations to the target in combination with different biasing methods of the substrate were investigated. For bipolar HiPIMS with a substrate at floating potential, XRD measurements indicate minimal ion acceleration and change in the crystal growth when increasing the substrate holder potential to the same level as the applied positive voltage. In contrast, using bipolar HiPIMS with a substrate at ground potential results in a similar ion current profile as in conventional HiPIMS with a synchronized pulsed bias with the same delay and timing as the positive pulse. Furthermore, the trend in crystal growth is the same such that a significant increase in the (200) intensity is observed within an ion acceleration window, 125–175 V. Using conventional HiPIMS with a continuous DC bias also results in Cu films exhibiting significant (200) peaks, but the ion acceleration window is shifted to 175–225 V. The observed differences in the film growth could be explained not only by the energy of the ions but also by the type of ions (working gas vs metal ions) that are accelerated during either the positive pulse or substrate biasing.

Diffusion-controlled growth of Cu thin films electrodeposited directly on atomic-layer-deposited WC diffusion barrier for Cu interconnect

Direct copper (Cu) electrodeposition on a 10-nm atomic-layer-deposited (ALD) tungsten carbide (WC) diffusion barrier layer was investigated for building Cu interconnect in silicon (Si)-based microelectronic devices. The diffusion of Cu reducing species under potentiostatic Cu deposition was characterized according to applied cathodic potential in a neutral electrolyte with a concentration ratio of 1:10 for Cu to iminodiacetic acid (IDA) as a complexing agent. The diffusion-controlled nucleation and growth of Cu thin film on the ALD WC was figured out in relation to diffusion coefficients of Cu reducing species that were calculated from both modified current transient curves and more appropriately electrochemical impedance spectroscopy (EIS) analysis. At the end, the diffusion-controlled Cu fill of trenches with an aspect ratio of 6.3 and 15-nm bottom width was conducted by applying −1.4 V vs Ag/AgCl to an ALD-WC-covered, patterned Si wafer specimen.

Low temperature growth of Cu thin films on TiN(001) templates: Structure and energetics

Synthesis of metal/ceramic interfaces with well-defined structural characteristics is an important step toward understanding the energetics and mechanical response of such interfaces. We used ultra-high-vacuum magnetron sputter deposition to grow elemental Cu thin films onto single crystal TiN(001) thin film templates, grown hetero-epitaxially onto single crystal MgO(001) substrates. Structure of the Cu thin films grown on TiN(001) templates was examined as a function of the growth temperature. At close to room temperature, we observed the previously reported cube-on-cube orientation relationship between Cu and TiN, with Cu(001)//TiN(001). At a slightly elevated temperature, we observed a new Cu-TiN orientation relationship with Cu(110)//TiN(001) that, to the best of our knowledge, is reported here for the first time. Accompanying molecular dynamics simulations with modified embedded atom method potentials newly developed for the Cu-TiN system showed the influence of nanoscale twinning and lattice strain on structure and interfacial energetics of Cu/TiN bicrystals. Controlled growth of metal/ceramic bicrystal thin films offers an opportunity for systematic testing of the mechanical response of metal/ceramic interfaces with better defined structural characteristics.

Morphology and surface properties of Cu thin film on Si (001)

In this work, molecular dynamics simulation was used to expect the effect of incident energy and substrate temperature on the morphology, surface roughness and structure of Cu thin film on Si (001) substrate. Our results indicate that the growth of Cu thin film depend clearly on the incident energy and substrate temperature. It was found that for lower incident energy, the morphology of deposited film is not smooth, and the film mixing is observed and limited to the top layer of substrate, it can be considered as quasi-epitaxial growth mode. Thus, the film-mixing mode is produced when the incident energy increases. In this case, the morphology of deposited film becomes smoother. In addition, the radial distribution function show that with increasing incident energy, the structure of the film deposited changes notably from crystalline structure to an amorphous structure one. As well, the surface roughness and length of film mixing are influenced by the substrate temperature. With the increase of substrate temperature, the surface roughness decreases whereas the length of film mixing increases.

Confined step-flow growth of Cu intercalated between graphene and a Ru(0 0 0 1) surface

By comparing the growth of Cu thin films on bare and graphene-covered Ru(0 0 0 1) surfaces, we demonstrate the role of graphene as a surfactant allowing the formation of flat Cu films. Low-energy electron microscopy, x-ray photoemission electron microscopy and x-ray absorption spectroscopy reveal that depositing Cu at 580 K leads to distinct behaviors on both types of surfaces. On bare Ru, a Stranski–Krastanov growth is observed, with first the formation of an atomically flat and monolayer-thick wetting layer, followed by the nucleation of three-dimensional islands. In sharp contrast, when Cu is deposited on a graphene-covered Ru surface under the very same conditions, Cu intercalates below graphene and grows in a step-flow manner: atomically-high growth fronts of intercalated Cu form at the graphene edges, and extend towards the center of the flakes. Our findings suggest potential routes in metal heteroepitaxy for the control of thin film morphology.

Molecular dynamics simulation of temperature effects on deposition of Cu film on Si by magnetron sputtering

The temperature effects on the growth of Cu thin film on Si (0 0 1) in the context of magnetron sputtering deposition were systematically studied using molecular dynamics (MD) method. To improve the comparability of simulation results at varying temperatures, the initial status data of incident Cu atoms used in all simulations were read from an identical file via LAMMPS-Python interface. In particular, crystalline microstructure, interface mixing and internal stress of Cu thin film deposited at different temperatures were investigated in detail. With raising the substrate temperature, the interspecies mixed volume and the proportion of face-centered cubic (fcc) structure in the deposited film both increased, while the internal compressive stress decreased. It was found that the fcc structure in the deposited Cu thin films was 〈1 1 1〉 oriented, which was reasonably explained by surface energy minimization and the selectivity of bombardment energy to the crystalline planes. The quantified analysis of interface mixing revealed that the diffusion of Cu atoms dominated the interface mixing, and the injection of incident Cu atoms resulted in the densification of phase near the film-substrate interface. More important, the distribution of atomic stress indicated that the compressive stress was mainly originated from the film-substrate interface, which might be attributed to the densification of interfacial phase at the initial stage of film deposition.

Benefits of energetic ion bombardment for tailoring stress and microstructural evolution during growth of Cu thin films

We have studied the development of intrinsic stress and microstructure of copper (Cu) films deposited under energetic ion bombardment. Stress evolution during growth of ∼150 nm thick Cu films on Si(001) substrates has been investigated by in situ measurements in a high power impulse magnetron sputtering (HiPIMS) process for different substrate bias voltages (from 0 to −160 V) and benchmarked with conventional direct current magnetron sputtering (DCMS). The microstructure and crystal orientation of the studied films have been examined by various ex situ methods. For HiPIMS, we found that the substrate bias voltage (energy of Cu ions) strongly affects the film continuity during the early growth stages and the compressive stress developed during the post-coalescence stage. Contrarily to common expectations, the stress magnitude can be significantly reduced despite the energy increase of the bombarding particles when using HiPIMS. These results are discussed based on a recent kinetic model taking into account the grain size-dependent defect incorporation due to energetic particle bombardment. Reversible stress relaxations are observed upon growth interrupts, with characteristic time constants of tens of seconds, which suggests that the stress and microstructure development are mainly mediated by surface diffusion processes. In addition, polycrystalline films (111)-textured are obtained for negative bias voltages from 0 to −100 V, while for even higher negative bias voltages (up to −160 V), epitaxial growth of Cu(001) is achieved. For the DCMS samples, there is no significant change in film continuity and crystal orientation when varying the bias voltage.

Influence of additives on Cu thin films electrodeposited directly on Ti diffusion barrier in Cl−-free electrolytes for Cu interconnect

For Cu interconnect in Si-based microelectronic devices, seedless electrodeposition of Cu thin films directly on Ti diffusion barrier was investigated in Cl−-free, citrate (Cit)-based acidic electrolytes with polyethylene glycol (PEG) or Janus Green B (JGB) additive. Both PEG and JGB suppressed Cu electrodeposition on the Ti surface effectively, and even their inhibition against Cu-Cit complex reduction was synergetic. Accordingly they decreased the surface roughness of Cu thin film on the Ti surface considerably. Thus, seedless growth of Cu thin films on Ti was achieved from the synergistic leveling effect of both PEG and JGB in the absence of Cl− because PEG adsorption onto the Ti surface did not accompany PEG complexation with Cl− and Cu+, and CuCl contamination did not occur. 3D nucleation of Cu on the Ti surface became more progressive in more additive-concentrated electrolytes. Good interfacial adhesion between Cu thin film and Ti diffusion barrier was maintained, whereas the sheet resistance of Cu thin films was fairly increased, in spite of adding PEG and JGB.

Comparison of Cu thin films deposited on Si substrates with different surfaces and temperatures

Deposition and growth of Cu thin films on Si(100), Si(110) and Si(111) substrates are studied using molecular dynamics method. The Cu/Si interface diffusion, surface roughness, crystalline structure and growth orientation of Cu thin films are investigated in detail. The effects of substrate surface and temperature are analyzed. Our simulation results show that the number of Cu atoms getting across the substrate surface for Si(111) substrate is the largest, and the number for Si(110) substrate is the smallest. This is caused by the difference of the linear atomic densities and planar atomic densities of Si crystal in different directions and planes. The growth of Cu thin films deposited on Si(100) substrate is 〈100〉 oriented at low temperature, and gradually changes to be 〈111〉 oriented as the increasing of substrate temperature. On the other side, the growth of Cu thin films deposited on Si(110) and Si(111) substrates is always 〈111〉 oriented. Increasing substrate temperature could effectively reduce surface roughness, increase the number of Cu atoms with face-centered cubic (fcc) structure, but meanwhile increase the Cu/Si interface diffusion. Under the same substrate temperature condition, the number of Cu atoms with fcc structure in thin films deposited on Si(110) substrate is larger than that deposited on Si(111) substrate.

Study of Stress Evolution in Cu/Au Systems Using Molecular Dynamics Simulation

Growth of Cu thin film on Au substrate and stress evolution were modeled using molecular dynamics simulation. The Au substrate consists of an unmoved layer and a regular strips as a grains. The interactions in the system are described by embedded atom method. We considered two cases of the substrate: substrate with different lateral correlations, and substrate with different size of grains. For larger distances between strips/grains larger compressive contribution are observed. Thicker deposited film is also needed to stress change in the tensile direction. Moreover, the grain size effect plays an important role in stress generation. For the film thickness of about 1 ML we observed occurring of extreme on the stress curves. Collapse of the direction of stress changes suggests the appearance of a new mechanism for generating tensile stress in the system. Appearance of tensile stresses during the deposition is associated with the coalescence of the copper grains with gold grains during the layer growth.

Growth and properties of Cu thin film deposited on Si(0 0 1) substrate: A molecular dynamics simulation study

Molecular dynamics simulations are used to study the growth and properties of Cu thin film deposited on Si(001) substrate. In particular, growth mode, crystalline structure and orientation, and surface morphology of Cu thin film are investigated in detail. Our simulation results predict that the growth of Cu thin film on Si substrate is three-dimensional island growth mode. In the growth process, interspecies mixing occurs at the interface between Cu film and Si substrate, and the mixing length increases as the increasing of substrate temperature. Based on the common neighbor analysis of atoms, three crystalline structures in the deposited Cu films are indentified. More important, the formed face-centered cubic (fcc) structure of Cu thin film is (001) oriented with a rotation by 45° along 〈001〉 axis when the substrate temperature is 300K, while the fcc structure of Cu thin film becomes to be (111) oriented when the substrate temperature is 900K. The crystalline orientation of deposited film could be explained based on the surface free energy of different crystalline planes as well as the geometrical lattice match rule. In addition, surface roughness of Cu thin film decreases as the increasing of substrate temperature due to the enhancement of surface diffusion.

Growth of Cu Metal Films at Room Temperature Using Catalyzed Reactions

Proposed mechanism of catalytic reaction of pyridine with Cu(hfac)2. The addition of pyridine with H2 initiated immediate growth of Cu thin films even at room temperature.

Martensitic transformation of Cu on Ag(001) and Cu on Au(001) studied with classical molecular dynamics

Received 13 October 2008; revised manuscript received 29 December 2008; published 4 March 2009The growth of Cu thin films on Ag 001 and Au 001 substrates was modeled using molecular dynamicswith classical potentials. We observed that deposited atoms formed an unstable bcc or bcc/body-centered-tetragonal structure, in agreement with previous experiments. We show that the formation of such structures isrelated to film thickness and temperature that was analyzed in the interval from 200 to 600 K. bcc nucleationwas measured by observing the relation between thickness and temperature of the deposited thin film. Themartensitic transformation accompanied by a stripe pattern occurred as a consequence of the distortions causedby the underlying substrate lattice. The stripe patterns were measured as 57 and 61 A for Cu onAg and Cu onAu, respectively. Monolayer spacing and coordination number of atoms were calculated, clearly evidencing theformed structures. Local structures were studied using the Ackland-Jones method, to determine the phases ofthe deposited films.DOI: 10.1103/PhysRevB.79.115404 PACS number s : 68.55. a, 68.35.Ct, 68.35.Rh

In Situ Observation of Initial Nucleation and Growth of Chemical Vapor Deposition of Copper by Surface Reflectivity Measurement

Initial nucleation and growth of Cu thin films on a Ta substrate via chemical vapor deposition (Cu-CVD) for ultra large scale integration (ULSI) interconnects is monitored in situ by irradiating the substrate surface with 635-nm-wavelength laser light and then measuring the change in reflected-light intensity. The effect of injection of water vapor during deposition on initial nucleation and growth is investigated by using X-ray photoelectron spectroscopy (XPS) to measure the surface chemical state of the Ta substrate. Results show that water-vapor injection during Cu-CVD enhances both the nucleation and growth of Cu by introducing adsorbed OH groups onto the substrate surface and yields a smooth, continuous surface morphology. The optimal time at which to inject water vapor before and/or during deposition is also determined using our in situ monitoring technique.

First steps in the growth of Cu thin films on the five-fold surface of the icosahedral Al–Cu–Fe quasicrystal

The growth of Cu on the five-fold surface of the icosahedral Al–Cu–Fe is investigated by scanning tunneling microscopy. The clean surface exhibits atomically flat terraces separated by steps of different heights. The steps are found to be frequently bunched. For a coverage close to a monolayer, Cu forms a nearly closed film of a height corresponding to a monolayer of Cu. The film, however, does not exhibit long-range order.

Growth of Cu thin films by the successive ionic layer adsorption and reaction (SILAR) method

Copper thin films were grown on reduced indium tin oxide, molybdenum and polymer substrates using successive ionic layer adsorption and reaction (SILAR) method. Copper films were grown sequentially in a controlled way using simple copper salt and basic solution of formaldehyde as precursors. The copper films were polycrystalline with no preferred orientation as characterised by X-ray diffraction. On all substrates, the growth was clearly island growth in the beginning but after the whole surface was covered, the growth was more homogeneous.

Computer simulation of thin-film epitaxy growth

A three-dimensional kinetic Monte-Carlo technique has been developed for simulating the growth of thin Cu films. The model involves incident atom attachments, diffusion of the atoms on the growing surface, and the detachment of the atoms from the growing surface. Related effects due to surface atom diffusion was taken into account. A great improvement was made on calculation of the activation energy for atom diffusion based on a reasonable assumption of interaction potential between atoms. The results showed that as the substrate temperature is raised or the deposited rate decreased, the diffusion of particles causes the particles grouping into islands (more than three atoms). The higher the temperature or the lower the deposition rate, the larger the size of the islands. Also we observed the island shape transition from two-dimensional islands to three-dimensional ones. There exist three optimum growth temperatures at a given deposition rate, namely Tn at which the nucleation rate is maximum, Tr at which the surface roughness minimizes and Td at which the relative density approaches to saturation. They all increase with the increase of substrate temperature, and these variations almost superpose on each other. The simulation results also showed that the relative density decreases with increasing deposition rate. But the nucleation rate is close to a steadiness at a lower temperature while it increases at a higher temperature. The surface roughness increases at a lower temperature while it decreases at a higher temperature.

Kinetic Monte Carlo simulation of Cu thin film growth

A three-dimensional kinetic Monte Carlo technique has been developed for simulating the growth of thin Cu films. The model involves incident atom attachment, surface diffusion of the atoms on the growing surface and atom detachment from the growing surface. A significant improvement in calculation of activation barriers for the surface atom diffusion on the growing film was made. The related effects caused by surface atom diffusion were taken into account. The results showed that there exist a transition temperature T t at a certain deposition rate. When the substrate temperature approaches T t, the growing surface becomes smoother and the relative density of the films increases. The surface roughness minimizes and the relative density saturates at T t. The surface roughness increases with increased substrate temperature when the temperature is higher than T t. T t is a function of the deposition rate. The influence of the deposition rate on the surface roughness is dependent on the substrate temperature. The simulation results also showed that the relative density decreases with increasing deposition rate and average thickness of the film.

Influence of vapor phase pretreatments of epoxy surfaces on the nucleation of MOCVD copper thin films

Vapor phase pretreatments of epoxy composite material reinforced with carbon fibers were carried out prior to the growth of Cu thin films by metal-organic chemical vapor deposition (MOCVD) using Cu (hfa)(COD) as copper precursor. These dry surface oxidation processes include H2O/UV, O2/UV and O2/Plasma treatments. Oxygen plasma method is the most efficient to oxidize the surface and it has the greatest effect to improve the wettability of epoxy samples. As a consequence, the higher hydrophilicity of the plasma-modified epoxy surface induces a higher nucleation density in the Cu film. Furthermore, this treatment reduces drastically the induction period observed for the growth of the metal. Even though the O2/UV pretreatment incorporates almost the same amount of oxygen in the epoxy surface than the plasma treatment, the functional groups are different, as revealed by XPS analyses, and the surface is less hydrophilic. Correlations between oxidation, wettability and nucleation density of the Cu films are discussed.