Effects of ion beam treatment on atomic and macroscopic adhesion of copper to different polymer materials

Low-energy ion irradiation of polymer induces different phenomena in the near surface layer, which effect strongly the metal–polymer interface formation and promotes adhesion of polymers to metals. Low-energy argon and oxygen ion beams were used to alter the chemical and physical properties of different polymers (PS (polystyrene), P?MS (poly(?-methylstyrene), BPA-PC (bisphenol-A-polycarbonate) and PMMA (poly(methyl methacrylate)), in order to understand the adhesion phenomena between a deposited Cu layer and the polymers. The resulting changes were investigated by various techniques including X-ray photoelectron spectroscopy, measurements of the metal condensation coefficient and a new technique to measure cross-linking at the polymer surface. Two types of practical adhesion strengths of Cu–polymer systems, measured using 90° peel tests, were observed: (i) peel strength increased at low ion fluences, reached a maximum and then decreased after prolonged treatment and (ii) no improvement in the peel strength on treated polymer surfaces was recorded. The improvement in the metal–polymer adhesion in the ion fluence range of 1013–1015 cm?2 is attributed to the creation of a large density of new adsorption sites resulting in a larger contact area and incorporation of chemically active groups that lead to increased interaction between metal and polymer by metal–oxygen–polymer species formation. XPS analysis of peeled-off surfaces showed that in most cases the failure location changed from interfacial for untreated polymers to cohesive failure in the polymer for treated surfaces. These observations and measurements of the metal condensation coefficients suggest that bonding is improved at the metal–polymer interface for all metal–polymer systems. However, the decrease in the peel strength at high ion fluences is attributed to the formation of a weak boundary layer in polymers. The correlation between sputter rate of polymers and altering in the peel strength for moderate ion fluences was determined. It was observed that the metal–polymer adhesion could be improved for PS and BPA-PC, which have a low sputter rate and preferentially formed cross-links in the treated surface. For degrading polymers, like P?MS and PMMA, chain scission rather than cross-linking dominates, low molecular weight species are formed and no adhesion enhancement is observed

Investigation of the drastic change in the sputter rate of polymers at low ion fluence

The polymer sputter rate dependence on ion fluence and ion chemistry (Ar, N2, O2) at 1 keV energy was investigated using a quartz crystal microbalance (QCM) which allowed to do real time etch rate measurements and to study kinetics of sputtering. The obtained sputter rates differed drastically from polymer to polymer showing, that the chemical structure of polymer is an important factor in the polymer etch yield. A decrease in the sputter rate was observed up to ion fluence of 5 × 1014 to 5 × 1015 cm-2 (depending on the polymer type and ion chemistry) followed by the saturation in the rate at prolonged ion bombardment. Polymer removal was accompanied by the formation of degradation products, cross-linking or branching, modification of the surface chemical structure, which was studied in situ using XPS. The dependence of the surface glass transition temperature, Tgs on the ion fluence was studied using the method based on the embedding of metallic nanoparticles. The correlation between chemical yield data and ablation rate is discussed.<br/

Surface glass transition in bimodal polystyrene mixtures

Using the cluster-embedding method of V. Zaporojchenko et al. (Macromolecules 34, 1125 (2000)), we measured the glass transition temperature T g at the polystyrene/vacuum interface of bimodal mixtures of monodisperse polystyrenes of 3.5k and 1000k. Embedding of ≈ 1 nm Au clusters was monitored in situ by X-ray photoelectron spectroscopy (XPS). The clusters were formed by evaporation of Au onto the polymer surface. Only one glass transition was observed in the mixtures. The surface glass transition temperatures are correlated to but are below the bulk values of the mixtures and obey the Gordon-Taylor equation. The results suggest that the earlier reported molecular-weight dependence of the surface glass transition is not due to segregation of short chains to the surface

Etching rate and structural modification of polymer films during low energy ion irradiation

Various polymers were sputtered with low energy Ar+ ions of 1 keV in order to determine their etching rate. Hydrocarbons, oxygenated, fluorinated and nitrogen-containing glassy polymers with a broad range of the glass transition temperature (Tg) were chosen. The etching rate was measured using a profilometer, and X-ray photoelectron spectroscopy. At the same time the surface chemical modification, and the surface glass transition temperature were studied. Comparing the sputter rate to the various polymer properties a correlation among the Tg, cross-link density, and sputter rate was found. In addition, the sputter rate as a function of the integral ion fluence proved to exhibit a sharp increase in the initial regime of very low fluence. The results are discussed in terms of the characteristics of the polymer

Mechanisms of argon ion-beam surface modification of polystyrene

The surface characteristics of polymers are important factors determining their interfacial properties and their technological performance. Changes in physical and chemical properties of a polymer film may be induced by subjecting the material to a variety of surface modification techniques, one of which is ion-beam modification. In order to understand the underlying mechanisms X-ray photoelectron spectroscopy (XPS) was used to study the alterations of the polystyrene (PS) surface after Ar-ion treatment under well controlled conditions with low ion doses from 1012 to 1016 cm?2. The ion bombardment leads to surface functionalization, loss of aromaticity, and free radical formation. Induced surface cross-linking and the formation of polar groups raised the surface glass transition temperature of PS fil

Controlled growth of nano-size metal clusters on polymers by using VPD method

A completely dry technique (VPD) for the preparation of a metal cluster onto a polymer surface or between two polymer layers opens up very good possibilities to control the two dimensional dispersion of the metal clusters and their size during variation of the deposition parameters or the polymer surface treatment. The kinetics of heterogenous nucleation and the growth of nano-size metal clusters (Ni, Ag, Cu, Au) on polymers with different chemical composition (PMDA-ODA polyimide, polystyrene and Teflon AF) are studied by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). In contrast to preferred nucleation and significantly incomplete condensation on the surface of Teflon AF and PS random nucleation and well defined cluster distribution was observed on PMDA-ODA polyimide. It was shown that cluster size and cluster distribution can be influenced in a wide range (some order of magnitude) by the variation of the preparation parameters. Ar ion beam treatment of polymers with low ion dose (1012–1016 cm?2) as well as predeposition of a trace amount of a reactive metal can be successfully used to prepare a definite cluster structure due to creation of adsorption sites on polymer surface.<br/

Modification of polyethylene powder with an organic precursor in a spiral conveyor by hollow cathode glow discharge

Hexamethyldisiloxane (HMDSO) films were deposited on polyethylene (PE, (C2H4)$_n$) powder by hollow cathode glow discharge. The reactive species in different HMDSO/Ar plasmas were studied by optical emission spectroscopy (OES). Increasing the HMDSO fraction in the gas mixture additional compounds like CH$_x$, OH, SiC and SiO can be identified. After deposition the formed silicon and carbon containing groups (C–O, C=O, SiC and SiO) on the PE powder surface have been analyzed by X-ray photoemission spectroscopy (XPS). Changes in wettability depending on the HMDSO fraction were investigated by contact angle measurements (CAM). The free surface energy of the PE powder decreases with increasing HMDSO fraction in the process gas and encapsulation of the powder particles occurs. An aging effect of the plasma treated PE surface was observed depending on the process gas composition. The higher the HMDSO fraction the less is the aging effect of the plasma treated PE surface