Electroless Copper Films Research Articles

Characterisation of the Oxidation Kinetics of Thin, Low Temperature, Electroless Plated Copper Films

AbstractThe morphology, chemical state and oxidation behaviour of electroless copper films deposited from two different baths were characterised using scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), secondary ion mass spectrometry (SIMS) and spectroscopic ellipsometry (SE). The electroless solutions used were a commercial electroless formaldehyde (HCHO)-based solution (Cupro-Thick 84, Alfachimici) and an electroless solution developed within the NMRC which was based on dimethylamine borane (DMAB). Both methods produced as-deposited copper films with different morphologies. SE analysis of the as-deposited films and those oxidised in a dry synthetic air environment between 75°C–150°C indicated that the freshly deposited films had inherent oxide layers of between 45Å–92Å and that significant growth of these only occurred at temperatures above 100°C within 180 minutes isothermal oxidation periods. XRD analysis confirmed that the oxidation products formed were a mixture of cuprous oxide (Cu2O) and cupric oxide (CuO). Multiple linear regression analysis of the rates of change in oxide layer thicknesses as a function of both time and temperature indicated that mixed rate laws dominated. The application of an oxidation inhibitor was shown to prevent oxidation of the asdeposited commercial copper films when heat treated at 125°C.

Electroless copper films deposited onto laser-activated aluminum nitride and alumina

Metallization of ceramic substrates by laser activation and subsequent electroless deposition has been demonstrated recently in aluminum nitride and alumina. However, the bond strength between the electroless copper and the ceiamic substrate is weak (less than 14 MPa). Low temperature annealing of electroless copper films deposited on substrates activated at low laser energies strongly increases the adhesion strength. The effectiveness of the annealing for improving the metal-ceramic bonding is dependent upon the laser treatment performed on the substrate prior to deposition. Faster deposition kinetics are obtained for both substrates by increasing the laser energy density. On the other hand, an increase in the laser energy density leads to poor adhesion strengths. The dislocation microstructure produced during laser irradiation in aluminum nitride is analyzed as a possible cause of laser activation. Free aluminum produced by laser irradiation of aluminum nitride and of alumina is discussed as another factor of laser activation. The chemical and microstructural changes taking place in the near-surface region as a consequence of laser-induced processes are correlated with adhesion enhancement promoted by the annealing treatment.

Morphological and Chemical Comparisons of Electroless Nickel and Electroless Copper Film Growth

A detailed study was undertaken on one practical system used in electroless plating of ABS plastics. The macroscopic appearances were examined after short and standard etch times, after catalytic and accelerating steps as well as after electroless copper and nickel plating steps. X-ray Photoelectron Spectroscopy was used to examine the chemical status of the surface during different plating steps and Transmission Electron Microscopy was used to analyze polymer-metal interface dependence on etching conditions

無電解銅めっき浴におけるＰｄ（ＩＩ）およびＳｎ（ＩＶ）イオンの作用機構

Electroless copper deposition has been widely used in the manufacture of printed circuit boards with plated through-holes. Intrinsic contaminants originating from the mixed PdCl2/SnCl2 catalyst may be present in the plating bath. In this study, the effects of Pd2+ and Sn4+ ions on the rate of copper deposition and the mechanical properties of the copper films were investigated. An excess of PdCl2 makes the bath unstable, leading to a reduction in the apparent deposition rate, but the appropriate amount of Pd2+ ions not only decreases lattice strain but also improves the elongation of the copper films. In the presence of both Pd2+ and Sn4+ ions, internal stress in the copper films was reduced, and the elongation of copper films was significantly improved by synergism between the two different ion species. Electrochemical analysis of electroless copper deposition elucidates that the presence of Pd2+ and Sn4+ ions not only decreases the amount of the methylene glycol anion adsorbed on the electrode surface but also prevents the inclusion of hydrogen into electroless copper films.

Kinetics of Electroless Copper Plating and Mechanical Properties of Deposits

Electroless copper films were prepared from an EDTA bath in which pH was adjusted with three kinds of alkalis (, , and ). Mechanical properties of the deposits and the kinetics of electroless copper plating were investigated to clarify their mutual relationship. The use of , among the alkalis tested, gave the best result for the mechanical properties. The electrochemical analysis of the electroless copper deposition based on the mixed potential theory indicates that there is an interaction between the partial anodic and cathodic reactions, which is induced by the adsorption of methylene glycol anion. The polarization technique using a quartz crystal microbalance electrode and the AC impedance method disclose that an improvement of the mechanical properties of copper films is achieved when such an interaction is eliminated by preventing the adsorption of methylene glycol anion through utilizing and surfactant such as polyethylene glycol as well as elevating the bath temperature.

The influence of hydrofluoric acid concentration on electroless copper deposition onto silicon

Electroless metal plating is widely used in a variety of applications in the electronic and semiconductor industries such as selectively depositing on patterned substrates [1,2], making ohmic contacts [3-81, filling contact holes and vias in microelectronic devices [9,101, and delineating semiconductor junctions [ll-131. Some of the advantages of electroless deposition over conventional vacuum deposition techniques are its ease of use and low cost. Hence much research has gone into improving and utilizing this plating process. In contrast to the large number of papers dealing with electroless metal deposition on metal surfaces, relatively few papers have been written dealing with electroless metal deposition onto semiconductor surfaces, especially during the initial stages of formation. The advent of scanning probe microscopy, such as scanning tunneling microscopy WI&I) 1141 and atomic force microscopy (AFM) [15], enables the investigation of such processes to be performed simply on the nanometer scale. For example, Osaka and co-workers [16-181 have used STM to study the electroless plating process of magnetic materials (e.g. NiP and CoNiReP) on highly oriented pyrolytic graphite (HOPG). Moffatt Kennedy et al. [19] observed the growth of electroless copper films on Pd-activated HOPG and printed circuit boards. Phaner et al. [20] have reported STM observation of 100-200 nm thick electroless gold deposits on Pd-activated n-GaAs. In the case of electroless metal deposition onto Si, HF solution is occasionally used in the plating bath in place of a reducing agent in order to induce deposition onto the surface. The HF removes any residual oxide on the surface and more importantly aids in metal deposition through direct displacement of the silicon [9,21]. In this note, we

On the Texture of Electroless Copper Films on Epitaxial Cu Seed Layers Grown on Si (100) and Si (111) Substrates

The orientation control of electroless copper films on copper seed layers with different preferential orientations was investigated. Copper films, deposited by electron‐beam evaporation, show an epitaxial relationship with the Si substrates, resulting in (100)‐ and (111)‐oriented Cu films on (100) and (111) Si substrates, respectively. Ion‐channeling, plan‐view and cross‐sectional transmission electron microscopy and x‐ray diffraction have been employed to investigate the orientation dependence of the copper layers on the copper seed layers with (100) and (111) orientations and surface condition between electroless copper and E‐beam copper layers.

Impedance Study of the Electroless Copper Films

The formation of atomic or molecular hydrogen is inevitable due to the oxidation of reducing agents in electroless deposition. The highly mobile atomic hydrogen within the electroless copper layer possibly combines to form voids, which may alter the hydrogen diffusion path. An interstitial diffusion mode, adopted to resolve the movement of atomic hydrogen, resulted in two segments in the Arrhenius plot. It was estimated that the diffusivities of atomic hydrogen in the electroless copper films were in the range of 283–308 K, and in the range of 308–343 K. The threshold temperature for electroless copper to be nucleated on the platinum electrode was estimated at 318 K, correlating to the phase angle drift derived from the fixed frequency impedance technique.

Growth structures of electroless copper films for printed wiring boards

Though a mature process, electroless copper deposition occupies an important economic and technological position in the electronics industry today. Virtually all multilayer circuit boards require the process for through hole connections enabling the miniaturization of the board to keep apace with the total electronics trend to higher densities and smaller components. This trend places more stringent requirements on adhesion of the copper and reliability of the film. The process itself consists of two deposition stages, a surface catalyzation with a palladium colloid followed by deposition of copper. The surface presents a composite substrate of greatly different materials on which adhesion is required: copper, silicate glass, and polymeric resins of diverse compositions. To facilitate study of surface structures, we have used highly oriented pyrolitic graphite as a substrate. Scanning tunneling microscopy (STM) has shown the incipient stages of the palladium catalyst and electroless copper. The results of STM investigations have revealed the nucleation, the microisland formation and the surface growth morphology. The surface composition at each step is identified by scanning tunneling spectroscopy. The surface structures and the defect formation on printed circuit board materials are also investigated by AFM.

On the Texture of Electroless Copper Films

Textures of electroless copper films were investigated as a function of bath parameters and of the plating base. The top surface layer of films deposited on titanium‐seeded glass substrates is (100)‐textured when the baths contain surfactant, and (111)‐textured when they are free of surfactant. In both cases the crystals near the bottom surface are randomly oriented. Cyanide concentration and plating rate only have small effects on textures. The texture of peel‐apart copper foils, the second kind of applied plating base, is of the (110) type. Electroless films on these foils contain an increased number of (100)‐oriented grains; but (110) orientation is still dominating when surfactant‐free baths are used, whereas baths containing surfactant produce (100)‐textured deposits. The results are discussed in terms of the “survival of the slowest” rule. They suggest preferred growth of (100) faces in absence of surfactant causing dominance of (111)‐oriented crystals, and blocking of (100) faces in presence of surfactant causing dominance of (100)‐oriented crystals in the film.

Characterization of electroless nickel and copper coatings: An x-ray photoelectron spectroscopy study

Electroless nickel and copper platings on alumina and gold substrates have been studied by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The composition of the films was analysed using argon ion profiling. The electroless films were found to be mostly metallic and contained almost no phosphorus. In a few cases, some oxygen-containing species were identified. There was an initial unevenness in film formation which was also confirmed by SEM studies. Electroless copper films also showed the presence of oxygen-containing species. A detailed XPS study of the two metals is presented.

Improved electroless process of copper coating ceramics. 1. Some parameters of coating glass substrates

The shortcomings of the available electroless processes, such as scarcity of information on the controlling parameters, bath instability, poor film adhesivity and film contamination are reported. The process described in this paper differs from the conventional process not only in the raw materials used but also in the operational details. The criteria of choice of such materials are discussed. Further, the parameters affecting the quality of electroless copper films are defined and some of them,viz., concentration of bath ingredients and the number of sensitisation-activation treatments needed, are optimised for coating on glass substrates. It has been found that the bath decomposition, a hazard peculiar to an electroless bath can be avoided by maintaining the bath pH below 10.86. The substrate should undergo three sensitisation-activation treatments to receive complete coating. The adhesivity of copper film on glass substrate achieved by this improved process is more than 21.6 kg/cm2 as compared to 7 kg/cm3, which is the adhesivity of evaporated copper film on the same substrate.

Twins in electroless copper films

Twins in electroless copper films