  A new pyramidal structural defect, 5 to 8 micron wide, has been discovered in
thin films of epitaxial erbium disilicide formed by annealing thin Er films on
Si(001) substrates at temperatures of 500 to 800C. Since these defects form
even upon annealing in vacuum of TiN-capped films their formation is not due to
oxidation. The pyramidal defects are absent when the erbium disilicide forms on
amorphous substrates, which suggests that epitaxial strains play an important
role in their formation. We propose that these defects form as a result of the
separation of the silicide film from the substrate and its buckling in order to
relieve the compressive, biaxial epitaxial stresses. Silicon can then diffuse
through the silicide or along the interface to fully or partially fill the void
between the buckled erbium disilicide film and the substrate.
