TEM and ellipsometry studies of nanolaminate oxide films prepared using atomic layer deposition

Nanolaminate oxide layers consisting of TiO2 and Al2O3 have been deposited on silicon using atomic layer deposition (ALD). Characterisation of these films has been achieved by use of a range of modern transmission electron microscopy (TEM)- based techniques, including plasmon loss imaging, energy filtered imaging and scanning TEM (STEM) X-ray line profiling. These have shown that the target thickness of the individual layers in the nanolaminate structures (20 nm) has been met with a high degree of accuracy, that the layers are extremely flat and parallel and that the interfaces between the layers are compositionally abrupt. Localised crystallisation within the stacks, and responses to electron beam irradiation point to the presence of a stress gradient within the layers. The performance of ellipsometry in characterising multilayer stacks has been benchmarked against the TEM measurements. Errors in determination of individual layer thicknesses were found to increase with growing stack size, as expected given the increasing number of interfaces incorporated in each model. The most sophisticated model gave maximum deviations of 4 nm from the TEM determined values for the 5- and 10-layer stacks.