Aluminum/polyimide interface formation: An x-ray photoelectron spectroscopy study of selective chemical bonding

Abstract

High-resolution x-ray photoelectron spectroscopy has been used to study the formation of the aluminum/polyimide (Al/PI) interface at room temperature. Aluminum films up to 80 Å thick were vapor deposited onto cured polyimide in situ. Our results show that Al is chemically active for coverages below ∼20 Å. Preferential aluminum bonding with PI occurs at carbonyl sites, as evidenced by the rapid attenuation of the carbonyl C 1s core level photoemission intensity. In the initial reaction stage (1–2 Å), Al preferentially occupies planar imide rings. These adatoms transfer charge to carbonyl carbon atoms via oxygen and this resonance hybrid state of C–O–Al weakens, but does not break, carbonyl bonds. With increasing Al coverage, the formation of strong Al–O bonds is observed and is attributed to a C–O–Al complex compound. Metallic Al is observed at a nominal coverage of 2 to 5 Å. The Al/PI interface exhibits the attenuation behavior characteristic of cluster growth through both reacted and unreacted regions. Annealing the 80-Å Al/PI interface at 300 °C results in extended reaction with less selective chemical interaction of Al with PI.

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