The interaction of Al and W in the Si/SiO2/W-Ti/Al thin film system is studied quantitatively by glancing angle x-ray diffraction. The formation of Al-W compounds due to annealing is monitored by the variation of the integrated intensity from a few x-ray diffraction peaks of the corresponding compounds. The annealing was conducted at 400°C, 450°C and 500°C from 1 hour to 300 hours. The kinetics of compound formation is determined using x-ray diffraction data and verified by TEM observations. We will also show the correlation of the compound formation to the change of the electrical properties of these films.

The growth characteristics of magnetron sputtered Co-22%Cr thin films on amorphous glass or carbon substrates have been investigated utilizing transmission electron microscopy,. X-ray diffraction, electrical resisivity and in-plane stress measurements. Results indicate that the initial deposit is “amorphous”, but that isolated islands of small crystallites form before the film reaches 5nm film thickness. By 10nm, well oriented grains with hcp c axis perpendicular to the film plane develop, and by 50nm, a twinned columnar microstructure is evident. As this occurs, the in-plane film stress becomes constant. Also, we have observed a distinct subgrain structure in the thinner films (10–50 nm), and this is reflected in the electrical resistivity. This cannot be accounted for by an “evolutionary selection” growth scenario, but must be related to the low surface mobility of adatoms at these low substrate deposition temperatures.

Interfacial reactions between either copper or titanium and cordierite-based (2MgO.2Al2O3.5SiO2) ceramic substrates are probed using X-ray Photoelectron Spectroscopy (XPS). Room temperature reactions are found to be strongly dependent on interfacial chemistry; while copper reacts weakly with the cordierite surface, titanium strongly reduces the Si-O and Al-O substrate bonds. Behavior during subsequent “in situ” annealing is dependent on substrate morphology. On amorphous cordierite films copper remains nonreactive while titanium dissociates remaining Si-O and Al-O bonds, forming a low valency Ti1+ oxide. On crystalline cordierite substrates copper diffuses rapidly upon annealing while titanium reduces substrate bonds forming a high valency Ti3+ oxide. Furthermore, thin 5Å Ti interlayers prevent copper diffusion at temperatures below 650°C. This study represents the first comprehensive treatment of the interfacial reactions in metal-multicomponent ceramic systems.

Interfacial reactions between Co and GaAs have been studied using bulk diffusion couples of Co (∼0.5 mm thick)/GaAs and thin-film Co(∼-40 nm) on (001)GaAs as well as the epitaxial formation of CoAs and CoGa on (001)GaAs. In addition, phase diagram of Co-Ga-As at 600°C was determined. The thin-film results are rationalized in terms of the phase diagram and bulk diffusion data.

We report on the adhesion characteristics of Low Pressure Chemical Vapor Deposited (LPCVD) WSi2 to doped and undoped polysilicon when used for fabricating silicon discreie and integrated devices. About 3000Å of silicon rich (Si:W atomic ratio of 2.6) LPCVD WSi2 was deposited on 6 kÅ of polysilicon and annealed in nitriding and oxidizing ambients at various temperatures from 1000°C to 1100°C to lower the sheet resistance. Detailed material analyses of as-deposited and annealed polycides were performed using Auger, SIMS, RBS, TEM, and SEM and electrical conductivities of the films were measured using the four point probe. In some samples, the oxide grown on the silicide film was wet etched prior to implanting and diffusing As corresponding to the source/drain diffusions in power FET's. It was observed that polysilicon doping, WSi2 deposition and annealing, oxide or nitride etching, implantation and diffusion of As - all had significant impact on the grain structures of silicide and polysilicon, adhesion of the silicide film to polysilicon, and the electrical conductivity of the silicide. In samples where the oxide grown on the silicide was wet etched, enhanced grain boundary related oxidation of the silicide and polysilicon and seepage of the wet etchant through sequential etching of grain boundary oxide resulted in poor adhesion of WSi2 grains to polysilicon and eventual silicide peeloff. This problem was severe in samples which were not implanted with As but subjected to 900°C, 60 min. source drive.

There are several possible descriptions of the nature of the adhesion between an oxide and a metal substrate, some of which are formally equivalent. These include electrostatic interactions connected with the development of space charge regions, chemical bonding across the interface, van der Waals forces, and mechanical interactions associated with a nonplanar interface. However, the detailed mechanism must also be consistent with the growth process and the associated evolution of the interface for an oxide growing on a metal substrate. The problem is further complicated by the nature of the failure at or near the interface which leads to a phenomenological definition of adhesion which is not necessarily identical to the formal definition, and involves other parameters such as the growth stresses in the oxide, the plasticity of the oxide or the surface metal, and the effect of thermal cycling when the coefficients of thermal expansion of the two phases differ. In this paper, an attempt is made to describe these different aspects of the problem, and to refer to some of the more important ways of modifying the adhesion of an oxide, including the reactive element effect and the segregation of impurities to the interface and the modification of the morphology of the interface.

The high temperature oxidation behavior of Al, Y and Hf ion-implantation in Ni-25wtCr alloy with dosages ranging from 1015-1017 ions/cm2 has been studied. Results are compared with the unimplanted alloy, a Xe-implanted alloy and alloys with 0.2wt% Y or lwt% Al additions. Oxidation tests were carried out at 1000°C and 1100°C in 1 atm. O2. It is found that the ion-implantation of Y and Hf greatly reduced oxidation rate and improved scale adherence after a critical implantation dosage, ∼ l×1016 ions/cm2, has been reached. The improved scale adhesion is attributed to both a reduction in growth stress and a strengthened scale/alloy interface, which all developed as a result of a modified scale growth process.

A combined experimental/analytical study is being conducted to investigate the fundamental nature of adherence of oxide scales formed on metals during high-temperature oxidation. Isothermal oxidation experiments were conducted on high-purity nickel (Ni 270) specimens in air at temperatures of up to 1200°C. None of the experiments resulted in physical separation of nickel oxide scales from the nickel substrate, even though substantial amounts of porosity were found in scales close to the scale/matal interfaces. The results of numerical and analytical calculations of stresses in the NiO/Ni system suggest that metal and oxide plasticities play a role in the experimental observations.

The surface of a powdered glass has been treated to optimize its performance as a filler in polymer composites cast from solution. The aim has been to enhance acid-base interactions between the functional sites of polymers and the surface sites of the glass particles so as to insure complete coverage of the glass particles by adsorbed polymer molecules, and to thereby enhance both the adhesion and dispersion of the filler. The glass chosen for this study is a magnesium aluminum silicate of very low alkali metal content, and its surface sites have negligible basicity and only moderate acidity, as evidenced by weak adsorption of polymethylmethacrylate and negligible adsorption of chlorinated polyvinylchloride from solution in methylene chloride. Because of the negligible surface basicity of the filler, acidic polymers such as polyvinylbutyral and polyvinyl chloride are not adsorbed sufficiently to promote adhesion or dispersibility, and brittle or weak composites result.

Surface treatments to enhance surface acidity or basicity of the glass particles were evaluated by electrophoresis in organic solvents, in which acidic particles had negative zeta-potentials and basic particles had positive zeta-potentials; untreated glass particles had zero zetapotentials. The most effective treatments were done with silane coupling agents; amino-silanes provided strong negative zeta-potentials and methacryloxy-silanes provided strong positive zeta-potentials. Angleresolved ESCA spectra showed that the adsorbed amino-silanes averaged about a monolayer in thickness and that half of the nitrogens bonded to the surface as ammonium groups and half were in the outer surface as basic amine groups; the carbonyl oxygens of the methacryloxy-silanes appeared to be bonded to the surface.

Heavily-loaded polymer composites were made with the silane-treated and with untreated glass powders, using two acidic binders and a basic binder. The acidic binders were a polyvinylbutyral (PVB) binder cast from solution in a methanol-MIBK mixture, and a post-chlorinated polyvinylchloride (CPVC) binder cast from solution in a mixture of cyclohexane and tetrahydrofuran (THF): the glass transition temperature (Tg) for CPVC is about 140 C, but for PVB it is only about 35 C. The basic polymer (PEHM, polyethyl-hexylmethacrylate) has a Tg well below room temperature. Thus the extension to break in tensile tests was about 1% for CPVC, 10% for PVB, and 20 % for PEHM. About ten stress-strain Instron tests were made on each composite, and the composites with appreciable acid-base interactions between the matrix polymer and the surface sites of the treated glass fillers were in all cases much tougher than those without such acid-base interactions. The brittleness of the polyvinylbutyral composites filled with untreated glass powders was not observed at all on silane-treated glass powders.

The adhesive properties of PET have been enhanced by treatments with alkaline solutions and CF4/02 plasmas. Alkaline solution induce hydrolysis of the polyester and etching, with consequent strong roughening of the surface. Adhesion siemed more related to etching than to surface chemistry modifications, suggesting a prominent role of mechanical interlocking.

CF4/02 plasmas did not induce significant etching, but the surface chemistry was strongly altered. Ester bridges were effectively removed by the plasma, high oxygen mixtures destroyed aromatic rings and introduced oxygen by the hydroperoxide mechanism. Adhesion was worsened by the introduction of fluorocarbon radicals by Low oxygen discharges. The most effective enhancement was obtained with the 30 % discharge, where the aromatic rings are still quite intact, while ester bridges are removed with formation of phenolic end groups.

XPS and static SIMS have been used to characterize the interfaces between squalene or cis-polyisoprene and steel in an attempt to elucidate the mechanism of bonding.

We have investigated the effect of different inorganic substrates on the adhesion of polymer films. We have used crystalline surfaces in an effort to “map” the adhesive interactions that take place through the interface between substrate and polyimide (-arnic acid). Significant differences were found in the adhesion of polyimide films (as measured by peel tests) on substrates varying only in crystalline orientation. Detailed analytical investigations are reported of the interfaces of these substrates after peeling of the film, using angular dependent ESCA. A correlation was found between the chemical nature of the substrate and the adhesion quality. This correlation involves the crystalline matrix of the substrate surface.

A variety of plasma treatments of polymer surfaces for improved adhesion are reviewed: noble and reactive gas treatment of fluoropolymers; noble and reactive treatment of polyolefins, and plasmainduced amination of polymer fibers. The plasma induced surface chemical and morphological changes are discussed, as are the mechanisms of adhesion to polymeric adhesives, particularly epoxy. Noble gas plasma etching of fluoropolymers produces a partially defluorinated, textured surface. The mechanical interlocking of this textured surface is the primary cause of improved adhesion to epoxy. Reactive gas plasmas also induce defluorination, but oxygen containing gases cause continual ablation of the fluoropolymer surface. Noble and reactive gas (except for hydrogen) etching of polyolefins results in surface oxidation and improved adhesion via hydrogen bonding of these oxygen containing groups across the interface. The introduction of amine groups to a polymer surface by ammonia or amine plasma treatment generally results in improved adhesion to epoxy. However, amine-epoxy ring interactions can be severely effected by steric factors due to chemical groups surrounding the amine.

Irradiation of polytetrafluoroethylene (PTFE) with Mg(Ka) X-rays is shown to protect the surface against the chemical etching steps used to prepare PTFE for adhesion. Pre-irradiated etched samples of PTFE have adhesion strengths of less than 3% of that for non-irradiated etched samples. The major portion of this decrease in adhesion strength occurs for X-ray exposures of less than 10 min (∼4.8×103 mrads) and failure in every case occurs in PTFE and not in the bonded transition region. XPS measurements (20 Å sampling depth) show little difference in F content between irradiated and non-irradiated samples, but thermal desorption shows increasing fluorocarbon desorption with irradiation time. These results are consistent with the known radiation chemistry of PTFE. Irradiation produced free radicals lead to branching and/or cross-linking, and a surface rich in low molecular weight fluorocarbons. The more rigid cross-linked surface is resistant to deep (10,000 Å) chemical attack and the bond formed is with a surface rich in short chain fluorocarbons. Both a thin boundary region and bonding to short chain species is expected to lead to weak adhesive bonding. Electron irradiation is shown to lead to protection against chemical etching comparable to that obtained with X-rays. With electrons one has the capability of rastering the electron beam and drawing low adhesion strength patterns with resolution limited by the beam diameter.

Polyimide(PI) films were modified by O2 reactive ion beam etching(RIBE) to make special surface features which enhance the adhesion of copper films. The top plane and the cross-sectional plane of PI films were changed to a grass-like structure and a plate-like structure, respectively. The reason for these surface morphological changes is presumably due to the structural inhomogeniety of PI. XPS studies show that the O2 RIBE oxygenates the PI, resulting in an increase in oxygen and a decrease in carbon and nitrogen. The adhesion of evaporated copper on the O2 RIBE modified PI was substantially increased. In this study, the maximum peel strength of modified PI, 70 grams/mm, is more than 25 times larger than that of the unmodified PI, 2.5 grams/mm. Two types of failure mechanisms were observed with various ion doses:adhesive failure at the Cu/PI interface and at very large doses cohesive failure at the roots of the thin and long grass blades of PI.

Copper surfaces were derivatized resulting in the formation of Mx[Cu(II)(CN)Fe(II/III)(CN)5] at the interface. Polyimides were spin coated onto the modified metal surfaces and the degree of adhesion measured by the tape pull test. Effects of mechanical interlocking were evident in the case of modified copper samples, due to derivatization by ferricyanide. The chemical bonding and elemental analyses of the interfaces were studied by XPS and SEM.

Static SIMS was used to characterize polypropylene and polystyrene films following exposure to SF 6 and C2F 6 plasmas. The predominant species which are incorporated into the polymer surfaces are fluorine atoms and CF 2 /CF 3 radicals, respectively.

Transmission electron microscope techniques have been applied to the problem of thin film delamination from substrates during film formation. Model systems involving metal films on single crystal silicon substrates have been used and it is found that delamination of the films is initiated by the formation of damage in the substrate. This understanding removes some of the fundamental problems regarding delamination.

The surface chemical changes induced in polystyrene, polypropylene and poly(ethylene terephthalate) (PET) by argon and oxygen rf sputter etching were studied by XPS and infrared reflection absorption spectroscopy (IRRAS). Thin (∼5nm) chemically modified surface layers were observed for all three materials. Polystyrene surfaces were oxidized by sputter etching in both oxygen and argon with differing chemical functionality resulting from etching in the different gases. Polypropylene surfaces, by contrast, were oxidized with similar chemical functionality resulting from etching in either gas. PET surfaces were oxidized slightly by oxygen sputter etching and reduced by argon sputter etching. For the model systems chosen, etch mechanisms are suggested based on trends in the chemical modification behavior.

Auger electron spectroscopy (AES) with depth profiling was used to characterize the fiber/matrix interface of SIC fiber, reaction bonded Si3N4 matrix composite. Depth profiles of the “as received” double coated fiber revealed concentration oscillations which disappeared after annealing the fiber in the environment used to fabricate the composite. After the composite was fractured, the Auger depth profiles indicated that failure occurred in neither the ß-SiC fiber body nor in the Si3N4 matrix but in the fiber coating itself.