Investigating the Efficacy of Hafnium Dioxide Barrier Layers to Halt Copper Oxide Formation in Redistribution Layers for Three- Dimensional (3D) Packaging

HfO2 is investigated for its suitability to act as an oxygen and moisture barrier to
prevent Cu oxidation in redistribution layers (RDLs) in 3D packaging technologies. HfO2
barriers of varying thicknesses were deposited via atomic layer deposition (ALD) on Cu
surfaces and then stressed by (i) high temperature stress and (ii) humidity and thermal stress
for 1000 h to ascertain the optimal thickness to prevent oxidation of the Cu. The thickness of
the ALD HfO2 film was monitored by ellipsometry, while the extent of Cu oxidation was
monitored by focus ion beam prepared SEM cross sections. It is found that ∼9 nm of HfO2 is
sufficient to prevent Cu oxidation.