Growth Of Cu Films Research Articles

Pd nanocubes enclosed by {100} facets for activating electroless Cu deposition on liquid crystal polymer substrates with strong adhesion strength

In this study, we investigate the catalytic performance of palladium (Pd) nanocatalysts with different surface atomic structures for activating electroless copper (Cu) deposition on liquid crystal polymer (LCP) substrates. These nanocatalysts include Pd nanocubes featuring {100} facets of square atomic arrangement as their predominant surface structure and Pd spherical nanoparticles characterized by random atomic arrangements, synthesized using an aqueous method. Our electrochemical measurements reveal that the induction time for the growth of Cu films is significantly shorter when utilizing Pd nanocubes compared to Pd nanospheres. This shorter induction time signifies a quicker initiation of Cu growth, primarily due to the presence of Pd {100} facets. Furthermore, we also develop a surface modification approach involving a crosslinking reaction that utilizes the highly branched polyethylenimine and linear polyvinylpyrrolidone on the Pd nanocubes. This method not only facilitates the adsorption of Pd nanocubes onto the LCP substrates but also achieves a robust peel adhesion strength (630 gf/cm) of the resulting Cu films, exceeding the industrial adhesion goal of 500 gf/cm. Moreover, in-depth synchrotron X-ray photoelectron spectroscopy analysis provides valuable insights into the depth-dependent chemical changes within the Cu films and proves the removal of Cu oxides after the acid treatment.

The Effect of Ultrasonic Agitation on the Seedless Growth of Cu on Ru-W Thin Films.

Ru attracted considerable attention as a candidate to replace TaN as a diffusion barrier layer for Cu interconnect metallisation. The addition of W improves the diffusion barrier properties of Ru but appears to weaken the adhesion strength between the barrier and Cu and the direct (seedless) electroplatability behaviour. Although Cu can be directly electroplated on near equimolar Ru-W thin films, no complete substrate coverage is obtained. The understanding of Cu electrocrystallisation on Ru-W is essential to develop methods of fabricating thin, continuous, and well adherent films for advanced interconnect metallisation, where Ru-W thin films could be used as diffusion barriers. This work studies the effect of ultrasonic agitation on the growth of Cu films electroplated on Ru-W, namely on the impact on substrate coverage. Film structure, morphology and chemical composition were evaluated by digital and scanning and transmission electron microscopies, and X-ray diffraction. The results show that Cu particles decrease with increasing current density, but when no electrolyte agitation is applied, substrate coverage is incomplete in the central region, with openings around larger Cu particles, regardless of current density. Under ultrasonic agitation, substrate coverage is remarkably improved. An active particle detachment mechanism is proposed as responsible for attaining improved substrate coverage, only possible at intermediate current density. Lower current densities promote growth over nucleation, whereas higher currents result in extensive hydrogen reduction/formation. Ultrasonic agitation also enhances a preferential Cu growth along <111> direction.

Energy-dependent film growth of Cu and NiTi from a tilted DC magnetron sputtering source determined by calorimetric probe analysis

Plasma-based processes are key applications in microsystems technology and are mainly used for the deposition and modification of thin films. A strong dependence on used equipment and materials can easily affect plasma processes and results in many differences of process characteristics like energy flow and deposition rates. For a deeper understanding of inclined magnetron-deposited thin films, a passive thermal probe was used to investigate the correlation between the film growth of two commonly used metallic target materials (Cu and Ni 46.8/Ti 53.2) and the energy flow from the plasma to the substrate. The special design of the sputtering system with a fixed angle of 45° between targets and substrate allows homogeneous coating of 200mm wafers with 100mm targets. The passive thermal probe measurements were performed radially across the substrate area for two different magnetron positions. Complementary surface and cross-sectional analysis of the deposited layers by atomic force microscopy, focused ion beam technique, and fracture edge analysis by scanning electron microscopy were performed on thin film samples on silicon substrate to investigate the growth rate and structure of the films. The films deposited in these experiments exhibit randomly oriented crystalline grains and heavily position-dependent change in surface topography and morphology from compact films to columnar growth, for Cu and NiTi respectively.

The Prospect of the Electroless Atomic Layer Deposition (ALD) for Applications in Semiconductor Technology

The metallic thin films are widely used for in semiconductor technology. Surface morphology, thickness and purity of the film are the key attributes determining its functionality 1 , 2. Recent developments indicate that Cu/liner/TaN structures where liner could be either Co, Ru or Rh and TaN serves as barrier are of particular interest. The electrochemical doping of Zn with liner material to develop barrier-less Cu structures has been demonstrated3. In this talk we demonstrate a protocol to deposit conformal Cu thin film on Co by replacement of Zn overlayer without etching Co. EDTA and BTA are used for corrosion inhibition of Co film once all Zn capping layer is consumed in galvanic displacement with Cu. TEM, XPS and EDS indicate conformal Cu layer deposition Co layer underneath being intact. The second part of the talk focuses on electroless ALD application for deposition of Pt and Rh layers on Cu, Au or Ru substrates. 4 , 5. Surface reflectivity changes during electroless ALD serves as an indicator of surface roughness evolution after each cycle. Surface morphology after 20 electroless ALD cycles is studied by STM and AFM. Cyclic voltammetry illustrates catalytically active Pt and Rh surface after deposition. All electroless ALDs are performed at room temperature in glove box with inert atmosphere. Surface selective, self-terminating deposition and precise control over the film thickness are achieved demonstrating potential of this deposition method for scale up and industrial applications. Ahmadi, K., Wu, D., Dole, N., R. Monteiro, O. & R. Brankovic, S. Tuning Surface Chemoresistivity of Au Ultrathin Films Using Metal Deposition via Surface-Limited Redox Replacement of the Underpotentially Deposited Pb Monolayer. ACS Sensors 4, 2442–2449 (2019).Wu, D. et al. Pb Monolayer Mediated Thin Film Growth of Cu and Co: Exploring Different Concepts. Journal of The Electrochemical Society 166, D3013–D3021 (2019).Kailash Venkatraman, Yezdi Dordi, A. J. Electrochemical doping of thin metal layers employing underpotential deposition and thermal treatment. 1 (2019).Wu, D. et al. Electroless Deposition of Pb Monolayer: A New Process and Application to Surface Selective Atomic Layer Deposition. Langmuir 34, 11384–11394 (2018).Wu, D. et al. Underpotential and Electroless Pb Monolayer Deposition on Ru(0001). Journal of The Electrochemical Society 166, D359–D365 (2019). Figure 1

Role of ionization fraction on the surface roughness, density, and interface mixing of the films deposited by thermal evaporation, dc magnetron sputtering, and HiPIMS: An atomistic simulation

The effect of ionization fraction on the epitaxial growth of Cu film on Cu (111) substrate at room temperature is explored. Three deposition methods, thermal evaporation, dc magnetron sputtering (dcMS), and high power impulse magnetron sputtering (HiPIMS) are compared. Three deposition conditions, i.e., fully neutral, 50% ionized, and 100% ionized flux were considered thermal evaporation, dcMS, and HiPIMS, respectively, for ∼20000 adatoms. It is shown that higher ionization fraction of the deposition flux leads to smoother surfaces by two major mechanisms, i.e., decreasing clustering in the vapor phase and bicollision of high energy ions at the film surface. The bicollision event consists of local amorphization which fills the gaps between islands followed by crystallization due to secondary collisions. The bicollision events are found to be very important to prevent island growth to become dominant and increase the surface roughness. Regardless of the deposition method, epitaxial Cu thin films suffer from stacking fault areas (twin boundaries) in agreement with recent experimental results. Thermal evaporation and dcMS deposition present negligible interface mixing while HiPIMS deposition presents considerable interface mixing.

Pb Monolayer Mediated Thin Film Growth of Cu and Co: Exploring Different Concepts

We present results exploring different concepts for Pb monolayer mediated thin film growth of Cu on Ru(0001) and Co on polycrystalline Cu substrates. Both systems are of considerable importance in microchip fabrication technology and they exhibit a three dimensional growth at room temperature which somewhat limits their application. The Pb monolayer mediation of the growth process is explored by having its role as a surfactant, flux mediator or as a sacrificial layer in deposition via surface limited redox replacement protocol. Electrochemical and STM results suggest that Pb monolayer induces 2D Cu growth on Ru(0001) and the growth mechanism is very dependent on the Pb mediation role. The surfactant properties of electrolessly deposited Pb monolayer are also studied during electroless deposition of Co on polycrystalline Cu. The benefit of Pb monolayer mediation of the Co growth process was manifested by 2D Co thin film morphology, high quality of the grain boundaries, and improved magnetic properties.

Investigation of fcc and hcp island nucleated during homoepitaxial growth of copper by molecular dynamics simulation

We studied thin film growth of Cu on Cu (111) surface by molecular dynamics (MD) simulations using the Embedded Atom Method (EAM) potential and an incidence energy of 0.06 eV at 300 K. At the beginning of the deposition, we observe a coexistence of atoms nucleated on hcp and fcc sites in the first layer. The connection of these islands produces a border zone in rectangular form. The coexistence of fcc and hcp geometries has generated energy competition and eventually transitioned to fcc sites implying a large collective movement of several layers. However, the transition to the coexistence of these two structures, can promote coalescence by linking two large mounds.

Effects of Additives on Electrochemical Growth of Cu Film on Co/SiO2/Si Substrate by Alternating Underpotential Deposition of Pb and Surface-Limited Redox Replacement by Cu

The effects of additives to an acidic electrolyte for electrochemical deposition of copper film to prevent corrosion of the Co/SiO2/Si substrate have been investigated. A sacrificial Pb layer was formed by underpotential deposition (UPD), then a Cu layer was prepared using surface-limited redox replacement (SLRR) to exchange the UPD-Pb layer in an acidic copper electrolyte with trisodium citrate, sodium perchlorate, and ethylenediamine as additives. The additives significantly affected the replacement of UPD-Pb by Cu and prevented galvanic corrosion of the Co/SiO2/Si substrate in the acidic Cu electrolyte. The results showed that both sodium perchlorate and ethylenediamine reduced the corrosion of the Co substrate and resulted in Cu film with low electrical resistivity. However, residual Pb was present in the Cu film when using trisodium citrate, as the citrate ions slowed copper displacement. The proposed sequential UPD-Pb and SLRR-Cu growth method may enable electrochemical deposition for fabrication of Cu interconnects on Co substrate from acidic Cu electrolyte.

Palladium-free electroless deposition of pure copper film on glass substrate using hydrazine as reducing agent

Thin copper films were fabricated on glass substrates by palladium-free electroless deposition, using hydrazine. The effects of modifying the deposition parameters like temperature, initial concentration and pH of electroless bath on the deposition rate and morphology of resulting films were studied and optimized. The film deposition is performed in two simple steps which shortens the pretreatment time and avoids applying expensive components and is environmentally benign. FESEM images show a uniform dispersion of Cu nanoparticles on the glass substrates in the first step. These nanoparticles act as an activator in the growth of homogeneous Cu thin film in the second step. The activation energy for the growth of Cu films was found to be 62kJ/mol. EDX and XRD analysis demonstrates that the composition of the deposits was pure Cu with FCC crystal structure. The Cu films of 260nm thickness showed a resistivity of about 2×10−6Ωcm.

Characteristics and Mechanism of Cu Films Fabricated at Room Temperature by Aerosol Deposition.

We were successful in growing a dense Cu film on Al2O3 substrates at room temperature using an aerosol deposition (AD) method. The characteristics of Cu films were investigated through electrical resistivity and X-ray photoelectron spectroscopy (XPS). The resistivity of Cu films was low (9.2–12.5 μΩ cm), but it was five to seven times higher than that of bulk copper. The deterioration of the resistivity indicates that a Cu2O phase with CuO occurs due to a particle-to-particle collision. Moreover, the growth of Cu films was investigated by observing their microstructures. At the initial stage in the AD process, the impacted particles were flattened and deformed on a rough Al2O3 substrate. The continuous collision of impacted particles leads to the densification of deposited coating layers due to the plastic deformation of particles. The bonding between the Cu particles and the rough Al2O3 substrate was explained in terms of the adhesive properties on the surface roughness of Al2O3 substrates. It was revealed that the roughness of substrates was considerably associated with the mechanical interlocking between Cu particles and rough Al2O3 substrate.

Effect of grain orientations of Cu seed layers on the growth of -oriented nanotwinned Cu.

We investigate the growth of Cu films on two different Cu seed layers: one with regular <111>-oriented grains and the other with very strong <111>-preferred orientation. It is found that densely-packed nanotwinned Cu (nt-Cu) can be grown by pulsed electroplating on the strong <111>-oriented Cu seed layer without a randomly-oriented transition layer between the nt-Cu and the Cu seed layer. The electroplated nt-Cu grow almost epitaxially on the seed layer and formed <111>-oriented columnar structures. However, with the regular <111>-oriented Cu seed, there is a randomly-oriented transition layer between the nt-Cu and the regular <111>-oriented Cu seed. The results indicate that the seed layer plays a crucial role on the regularity of <111>-oriented nanotwinned Cu.

Plasma enhanced atomic layer deposition of copper: A comparison of precursors

The growth of Cu films by atomic layer deposition using hydrogen plasma has been investigated. To obtain continuous films at sub 5nm thicknesses the two dimensional coalescence of Cu nucleation sites formed at the start of the deposition process must be enhanced in preference to three dimensional island growth. Thermal energy reduction in the growth process is a key parameter. In this work hydrogen plasma is used to allow the reduction of the adsorbed precursor to metallic Cu at a range of low temperatures. Therefore, precursors can be compared at their low temperature limit, which is mainly determined by transport issues due to their relatively low vapor pressures. The structure of the deposited Cu films varies strongly with the substrate material used highlighting the importance of the nucleation mechanisms. On metallic substrates such as Ru and Pd continuous conductive thin films could be obtained, island formation and slow coalescence were observed on Si, TaN and CDO substrates even at temperatures low as 30°C; therefore conductive films could only be obtained for relatively thick deposits.

Molecular Dynamics Simulation of Grain Growth of Cu Film

We investigated the growth process of Cu polycrystalline films on three substrates Si, Ti and Ru during isothermal annealing by the molecular dynamics method. We focused on the influence of the adhesion strength and size mismatch between substrate and Cu on crystallinity and orientational order of the film. The present simulation clarified that Ru is excellent material as substare/barrier metal for Cu wire. Based on the findings, a search plot for replacement material of Ru was proposed.

Molecular Dynamics Simulation of Grain Growth of Cu Film

not Available.

Molecular Dynamics Simulation of Grain Growth of Cu Film &amp;mdash;Effects of Adhesion Strength between Substrate and Cu Atoms&amp;mdash;

The growth process of Cu polycrystal films on Si, Ti, W and Ru substrate during isothermal annealing was studied by the molecular dynamics method. We focused on the influence of the adhesion strength between substrate and Cu on crystallinity and orientational order of the film. After structural relaxation at low temperature (50 K), the movements of individual Cu atoms were calculated for different annealing temperatures using the molecular dynamics method. The crystallinity and orientational order of the film were examined by 2D-Fourier transformation of the atomic structure. We found that the system with strong adhesion strength between substrate and Cu showed higher crystallinity and orientational order for (111) oriented Cu film.

Effect of Sputtering Power on the Nucleation and Growth of Cu Films Deposited by Magnetron Sputtering

Cu thin films were deposited on Si(100) substrates using direct current (DC) magnetron sputtering. We focused on the effect of sputtering DC power on the electrical, structural properties, and the nucleation and growth of Cu films during the initial stage of sputtering. The Cu films deposited at higher sputtering power showed strong crystallinity, low electrical resistivity in comparison with the Cu films deposited at lower sputtering power. Concerning the nucleation and growth of Cu films during initial stage of magnetron sputtering, it was found that the progress of the nucleation and growth of the Cu films at higher sputtering is much faster than those of the Cu films at lower sputtering power even though they have a similar nucleation and growth mechanism, and their relation to resultant microstructure was confirmed by atomic force microscopy.

Barrier layer and annealing temperature dependent microstructure evolution of nanocrystalline Cu films

The effects of barrier layers and annealing temperature on texture variation, grain growth and void forming of nanocrystalline Cu films were investigated by X-ray diffraction, transmission electron microscope and scanning electron microscope (SEM). The variation in texture and grain size of Cu films with annealing temperature is different for Cu/Ti and Cu/Ta. The activation energies of grain growth of Cu films on Ti and Ta, respectively, are 19.7 and 23.4 kJ mol −1, which are much closer to that of grain boundary diffusion of Cu. The average diameter of about 400 nm for surface voids of Cu/Ti is larger than that of Cu/Ta structure. Furthermore, both the electrical resistivity measurement and SEM observation imply that Cu/Ti rather than Cu/Ta structure tend to fail easier as annealing temperature exceed 400 °C.

Atomic assembly of Cu/Ta multilayers: Surface roughness, grain structure, misfit dislocations, and amorphization

Molecular dynamics simulations and selected experiments have been carried out to study the growth of Cu films on (010) bcc Ta and the deposition of CuxTa1−x alloy films on (111) fcc Cu. They indicate that fcc Cu films with a (111) texture are always formed when Cu is deposited on Ta surfaces. These films are polycrystalline even when the Ta substrate is single crystalline. The grains have one of two different orientations and are separated by either orientational or misfit dislocations. Periodic misfit dislocations and stacking faults develop within these grains to release structure difference induced misfit strain energy. The Cu film surface roughness was found to decrease with increase in the adatom energy for deposition. When CuxTa1−x is deposited on Ta, the films always have a higher Cu composition than that of the vapor mixture. This arises from a surface segregation phenomenon. When the Cu and Ta fractions in the films are comparable, amorphous structures form. The fundamental origins for the segregation and amorphization phenomena are discussed.

Effect of Negative Substrate Bias Voltage on the Nucleation and Growth of Cu Films during the Initial Stage of Ion Beam Deposition

We focused the effect of a negative substrate bias voltage on the nucleation and growth of Cu films during the initial stage of ion beam deposition. The resultant microstructure of Cu films was observed by atomic force microscopy (AFM). It was found that Cu films with or without a negative substrate bias voltage have a different dependence of nucleation and growth. It was established that the mechanism of nucleation and growth of Cu films is changed to a progressive nucleation and lateral growth by a sufficient migration of adatoms accelerated by applying a negative substrate bias voltage.

Growth of Cu Films on Si(111)-7×7 Surfaces at LowTemperature: A Scanning Tunnelling Microscopy Study

Morphologies of Cu(111) films on Si(111)-7×7 surfaces prepared at lowtemperature are investigated by scanning tunnelling microscopy (STM) andreflection high-energy electron diffraction (RHEED). At the initialgrowth stage, Cu films are flat due to the formation of silicide at theinterface that decreases the mismatch between Cu films and the Sisubstrate. Different from the usual multilayer growth of Cu/Cu(111), onthe silicide layer a layer-by-layer growth is observed. The twodimensional (2D) growth is explained by the enhanced high islanddensity at low deposition temperature. Increasing deposition rateproduces films with different morphologies, which is the result ofOstwald ripening.