Amorphization of the silicon substrate and stress-relaxation in HfN films bombarded with Au ions

Sputter-deposited HfN films were exposed (after their growth) to a mono-energetic Au-ion beam (E=1, 2.5 and 5 MeV, fluence=1014 cm−2). This treatment resulted in a significant reduction of high internal stresses which arise in transition metal nitride films during the deposition process. The structural changes induced in the ion modified HfN-film/silicon-substrate system were studied by means of scanning and transition electron microscopy. The latter reveals that bombardment with energetic Au ions does not affect either the dislocation arrangement or the crystal structure of HfN films, but causes an amorphization of those parts of the silicon substrate located directly under the top nitride film. The registered stress release is ascribed to a transport of defects within thermal spikes induced by the applied ion treatment, since the amorphous layer is the thicker the smaller the observed stress reduction. Energy considerations of the stress-relaxation process in a multilayer system are used to estimate the possible influence of the amorphization of the substrate on the reduction of intrinsic stresses prevailing in HfN films.