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Nanoporous low-dielectric-constant films constitute a class of materials that are
plagued by fracture concerns and are not amenable to traditional fracture
toughness measurement techniques. An indentation fracture toughness
measurement technique has been developed for these materials. The experiment
utilizes nanoindentation in combination with cube-corner indenters which create
flaws are on the scale of the film thickness, about a micrometer. Interpretation of
experimental results are a far-reaching generalization of the traditional Vickers
based indentation test used for ceramics at the mesoscale. Cube-corner
indentation fracture is dominated by crack-wedging effects that are not important
for Vickers indentation. Film-substrate elastic coupling is very important, and is
manifested in three distinct ways. After film-substrate coupling phenomena are
identified, they are combined with acute indentation fracture models to form a
complete thin-film indentation fracture mechanics model. The fracture toughness
of two materials have been measured to be 0.09 MPa m1/2 and 0.05 MPa m1/2.