Corrosion susceptibility of thin films
Hernandez, Sandra Emilia
Brotzen, Franz R.
Doctor of Philosophy
The corrosion susceptibility of Al thin-film metallizations in an aqueous solution containing chlorine was measured. DC polarization techniques were used to determine the corrosion behavior of Al thin-film metallizations, Al-alloy thin-film metallizations and Al thin-film metallizations deposited on CVD W and sputtered W-Ti(10%) barrier layers. A galvanic series was developed by listing the stable open-circuit potentials for several metallizations, barrier metals and metallization/barrier-layer couples immersed in a 2000 ppm NH$\sb4$Cl electrolyte. Barrier layers of CVD W and sputtered W-Ti(10%) influenced the corrosion behavior of Al metallizations deposited on their surface. Results were discussed in terms of the galvanic couple formed between the metallization and the barrier layer, as well as the difference in surface topographies of CVD W and sputtered W-Ti(10%). The rough surface inherent on CVD W causes localized variation in metallization thickness and may provide sites where the W layer is exposed to the electrolyte, thereby acting as an efficient cathode. These results were substantiated with SEM photomicrographs. Electrochemical Impedance Spectroscopy (EIS) and DC polarization techniques were used to study the effect of increasing film thickness and grain size on the corrosion behavior of Al thin films. In general, as the film thickness is increased, the overall resistance to corrosion improves. The increase in corrosion resistance is attributed to an enlargement of the grain size, a result of the thin-film deposition process. As the grain size is increased, there is a reduction in the effective grain boundary area, which is the most prominent place were defects can be created or accumulated, thus rendering the oxide layer weak and promoting corrosion. The effect of grain size on the corrosion resistance of the films could not be determined, since the films were pitting upon immersion in the electrolyte.
Engineering; Materials science