Improvement in the adhesion of thin films to semiconductors and oxides using electron and photon irradiation

The adhesion enhancement of evaporated metal films on silicon and silicon dioxide substrates following electron and photon irradiation has been investigated. It is shown that an electric field applied across the metal-oxide-semiconductor interface during electron irradiation has a dramatic influence on adhesion enhancement. For photon irradiation, comparative adhesion measurements were undertaken as a function of increasing metal film thickness and different irradiation doses, for photon energies <4, <6 and 10.2 eV. Metal-oxide-semiconductor structures were also biased during photon irradiation to indicate the role of secondary processes such as charge flow to the interface from the oxide. Results indicate that adhesion enhancement can be significant even if the metal film thickness exceeds the photon penetration depth, supporting the view that low-energy secondary excitations are responsible for the stronger bonding configurations. It was also concluded that both electron and photon irradiation give rise not only to increased adhesion but also to increased cohesion within the metal film.