As part of an on-going study of electromigration in aluminium interconnect films used in microelectronic applications, 3 single crystal pure aluminium films were investigated using the NanoTest. The films were deposited on 100 nm of thermally grown SiO2.

Since the films were of relatively poor quality, for averaging purposes approximately 60 Depth vs Load hysteresis curves were produced for each specimen. The maximum on-load depth was about 100 nm, and accurate contact areas were determined through the NanoTest automatic diamond geometry calibration program. The maximum load was maintained for 20 s in order to eliminate time-dependent effects.

The hardness values were sorted into ascending order and the resulting 3 sets of data are shown graphically in the figure below. The mean hardness values based on the first 50 points of each set were as follows:

The hardness in the 'flat' sorted region was not related to the film thickness since the thinnest film (100) exhibited the lowest hardness. Also, it is clear that the NanoTest can consistently identify crystallographic variations in aluminium films and could therefore be used for 'mapping' the relatively large grains found in aluminium interconnect metallisations.