Determination of Young's modulus and yield strength of porous low-k dielectric films by nanoindentation under complete consideration of the substrate influence

The capabilities of the 'effective indenter method' with respect to the characterisation of porous xerogel thin films have been investigated using samples with porosities ranging from 43% to 57%. Young's modulus of the samples was decreasing from 2.67 GPa to 0.83 GPa with growing porosity. Yield strength was determined using spherical indentation data. With a larger indenter (R = 48 μm) the 'effective indenter method' could be directly applied while for a smaller one (R = 4.2 μm) the 'effective indenter extrapolation method' had to be utilised to account for the larger amount of plastic deformation. Both approaches delivered the same yield strength decreasing from (140 ± 5) MPa to (75 ± 3) MPa with increasing porosity.