Evaluation of copper thin film on SiO2/Si substrates by dynamic ultramicroindentation, SEM and AFM

Chemical-vapour-deposited copper film (250 nm) on 500 nm SiO2/Si substrates was evaluated by dynamic ultramicroindentation, scanning electron microscopy (SEM) and atomic force microscopy (AFM). Surface hardness and roughness measurements provide important parameters for the copper integration process. The objective of this study is to investigate the hardness of copper thin film at the simulated back end of the line packaging processing. The roughness of copper film surfaces after thermal treatment will also be discussed. Dynamic hardness (DH) variation of copper films after thermal simulations of wire-bonding and die-attach adhesive curing were compared to the as-deposited film. The DH of copper films was observed to decrease in the following sequence of specimens: as-deposited > after die-attach adhesive curing > after wire-bonding treatment. The results of a load–unload cyclic test revealed that the extent of plastic deformation of the copper film surface was 95%, 75% and 80% for as-deposited, after wire-bonding treatment and after die-attach adhesive curing, respectively. Surface morphology after hardness tests was examined with SEM and elemental analysis showed that organic films ‘squashed’ out near regions of indentations. Atomic force microscopy at areas of 3µm × 3µm showed that the copper surface roughness (2.4–2.9 nm) was not much affected by the thermal treatments. Copyright © 2000 John Wiley & Sons, Ltd.