The thermal stability of Al-0.5% Cu/barrier/TiSix multilayer structures is investigated. The barriers studied in this work are TiN films prepared by physical vapor deposition (PVD) and TiN-based barrier films prepared by metal-organic chemical vapor deposition (MOCVD) with post-deposition anneal in silane. Sheet resistance, secondary ion mass spectroscopy (SIMS), diode leakage current and high spatial resolution electron microscopy measurements show significantly better thermal stability for structures using the silane-treated MOCVD barrier. Structural and composition differences of the two types of barriers are examined.