Steven P. Kowalczyk

Adhesion and interface investigation of polyimide on metals

The interface and adhesion of PMDA-ODA and PAA-ethyl ester polyimides to several metals including Cr, Ni, Cu, and Au have been studied by transmission electron microscopy (TEM) and a 90° peel test. The adhesion strength of polyimide on metals is generally very high compared with that of metals on polyimide. The trend in both cases is the same, i.e., Cr has the highest adhesion strength followed by Ni, Cu, and Au. Cross-sectional TEM studies showed that very fine particles were precipitated in the polyimide near the interface in the case of polyimide on Cu (or Ni). The precipitates were not found closer than 80-200 nm from the polyimide/Cu (or Ni) interface. Some large particles were identified as Cu2O (NiO in the case of polyimide/Ni) by scanning transmission electron microscopy and microdiffraction analyses. The formation of these particles was ascribed to a process involving first the reaction of polyamic acid with Cu (or Ni) to form a polyamic acid complex. During subsequent thermal curing, the complex...

Polyimide on copper: The role of solvent in the formation of copper precipitates

The interaction at the polyimide‐copper (oxide) interface has been investigated by means of cross‐sectional transmission electron microscopy. By using a solventless molecular beam epitaxy growth technique, the role of solvent in the aggregation and diffusion of copper‐rich particles into the polyimide film and away from the interface was unambiguously demonstrated. The polyimide on copper growth sequence is contrasted to the copper on polyimide growth sequence, and the reasons for the differences between the two growth interfaces are discussed.

Adhesion enhancement of Cr/polyimide interfaces using RF pre-sputtering of polyimide surfaces

The effects of Ar ion RF pre-sputtering of polyimide surfaces on the adhesion of Cr/polyimide interfaces have been examined by TEM, XPS, and peel test. With Ar pre-sputtering, the peel strength of Cu/Cr to polyimide increases remarkably from 1 g/mm to 130 g/mm and 90 g/mm on PMDA-ODA spun on Si and silica substrates, respectively. The negligible change in the polyimide surface morphology by RF sputtering and the little change in the adhesion strength by a long exposure to the air after the sputtering prior to metal deposition eliminate contributions of mechanical interlocking and surface cleaning effects to this adhesion enhancement. Thus, adhesion enhancement by RF pre-sputtering is mainly attributed to chemical changes of the polyimide surface facilitating bonding with the deposited Cr. Such a surface treatment with RF sputtering was also found to be effective for the retardation of the moisture-induced failure of Cr/polyimide interfaces. It has been observed that cracks develop in both Cr and polyimide...

Adhesion, Reaction and Stability of Metal/Polyimide Interfaces

Interfacial reactions of polyimide with several metals have been investigated by XPS and TEM to determine their effects on adhesion and long term stability. It has been found that the polyimide-on-metal interface and the metal-on-polyimide interface are intrinsically different; in the case of PI-on-metal interface, the precursor of polyimide, polyamic acid, reacts with the metal resulting in a strong chemical bond and therefore, higher adhesion strength than the corresponding metal-on-PI interface. Both interfaces are found susceptible to T/H environment, resulting in significant adhesion loss. The mechanical and electrical properties of polyimide may be altered as a result of the interaction with metals and therefore, great care is necessary to insure a stable interface and the reliability of devices.

Comparison of the selective adsorption and reactivity behavior of WF6 and TaF5 on SiO2 and polyimide surfaces

The initial stages of WF6 and TaF5 adsorption on SiO2 and polyimide surfaces were investigated by photoelectron spectroscopy. WF6 selectively adsorbs on Si relative to SiO2 and polyimide, while TaF5 exhibited nonselective adsorption behavior. This trend is explained by differences in molecular structure and suggests a general basis for predicting selective deposition.

Low‐temperature selective‐area deposition of metals: Chemical vapor deposition of gold from ethyl(trimethylphosphine)gold(I)

Chemical vapor deposition of high purity gold is demonstrated using ethyl(trimethylphosphine)gold(I) at temperatures as low as room temperature. Total selectivity for growth on atomically clean metallic surfaces in the presence of insulating surfaces is found over a ∼200 °C temperature range and confirmed with scanning electron microscopy and x‐ray photoelectron spectroscopy. A key processing parameter is shown to be ultrahigh vacuum, particularly for growth on reactive metals such as chromium. These results suggest low‐temperature selectivity can be extended to other known precursors.

Hydrothermal stability of Cr/polyimide interfaces

The hydrothermal stability of both Cr/polyimide and C75Cr2/polyimide interfaces has been studied using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and peel testing. It was found that RF sputter treatment of the polyimide surface prior to metal deposition leads to an enhancement of adhesion through chemical bonding of the metal with polyimide. Owing to the enhanced chemical bonding at the interface, failure always occurs cohesively in the polyimide. The RF sputter treatment of the polyimide surface also simultaneously modifies the polyimide underneath the surface. The adhesion strength of the Cr/polyimide interface is degraded significantly upon exposure to high temperature and high humidity (85°C/81% relative humidity, T/H) environment. It is suggested that this degradation results from the hydrolysis of polyimide. The hydrolysis is facilitated by the presence of unstable modified polyimide near the interface. This degradation of adhesion strength can be minimiz...

Scanning force microscopy of polyimide surfaces

Abstract Scanning force microscopy was used to study several polyimide surfaces. The effects of r.f.-sputtering in argon and nitrogen atmospheres on the surface morphology of poly-[4,4′-oxydiphenylenepyromellitimide] (PMDA-ODA) and the polyimide (PI) based on the monomers 3,3′,4,4′-biphenyl tetracarboxylic dianhydride (BPDA) and p-phenylene diamine (PDA) were investigated. PI surfaces treated with r.f.-sputtering in nitrogen exhibited morphological features due to redeposited metal from the walls of the sputtering chamber, while no significant morphological change was observed when an argon atmosphere was used, for the same duration of sputtering treatment. It was shown that the enhancement of adhesion of metals on PI surfaces that have been treated with r.f.-sputtering in Ar, is not due to mechanical interlocking but rather due to chemical modification of the surface. The effect of different heat treatments on the surface morphology of co-deposited films of oxydipthalic dianhydride (ODPA) and 1,3-bis-[3-aminophenoxyl] benzene (APB), prepared by molecular beam deposition (MBD), was also studied. Such MBD films exhibited a strong dependence of morphology on the annealing process and environment.

Growth of ODPA-APB polyimide films using molecular beam deposition, and their characterization

Abstract We report the first growth of polyimide ODPA—APB films by the molecular beam deposition (MBD) technique and characterize these films using X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. MBD is a dry, ultra-high vacuum technique based on the co-deposition of monomers from two different sources, followed by a thermally induced polycondensation reaction to form polyimide. This technique is an alternative to standard wet processing techniques involving the use of solvents. Asdeposited films consist largely of low-molecular-weight species. Heat-treated films are chemically indistinguishable from thermally cured, spin-coated films. Different heat treatment conditions are compared.

Low Temperature Selective Area Chemical Vapor Deposition of Gold Films: Growth and Characterization

Substrate-selective, low-temperature chemical vapor deposition of high quality gold filmswas obtained with the new precursor ethyl(trimethylphosphine)gold(I) in an ultrahigh vacuum reactor designed to handle wafers up to 3 inches in diameter. Growth behavior at temperatures as low as room temperature as well as substrate pre-cleaning procedures are presented. Activation energies of 35.1 ± 0.4 kcal mol −1 and 18.3 ± 0.7 kcal mol −1 were found for growth of gold films on gold and copper substrates, respectively.