Aluminum and Al-Cu conductor lines etched with a Cl containing plasma in low-pressure diode systems corroded rapidly upon atmospheric exposure. The mechanisms underlying this corrosion problem were investigated using Auger electron and x-ray photoelectron spectroscopies. Reactive ion etching resulted in a nonprotective oxide layer and thus rendered the etched samples more susceptible to atmospheric corrosion. Factors contributing to the increased reactivity of etched samples includes C and Cl contamination, radiation damage, and for Al-Cu alloys, Cu enrichment. A thermal oxidation treatment at temperatures of ∼300-350 °C and l atm O2 pressure for ≳30-45 min was found to be effective in restoring the protective oxide layer and thus improving the corrosion resistance of etched samples.