Effects of ion irradiation on the residual stresses in Cr thin films

Cr films sputtered onto {100} Si substrates at room temperature were found to be under residual tension, as revealed by wafer curvature measurements. A 150 nm thick Cr film was bombarded with 300 keV Ar ions after deposition. The intrinsic residual tensile stress increased slightly and then decreased with further increase in the ion dose. For ion doses ${\text{>1×10}}^{15}\hspace{0.17em}{\mathrm{ions/cm}}^{\mathrm{2}},$ the stress in the film became compressive and increased with increasing dose. Transmission electron microscopy revealed that the grain boundaries in as-deposited Cr have columnar porosity. A Cr film, ion irradiated to a dose of ${\text{5×10}}^{15}\hspace{0.17em}{\mathrm{ions/cm}}^{\mathrm{2}},$ showed no grain boundary porosity. The changes in the residual stress during ion irradiation are explained by considering Ar incorporation in the film and the manner in which irradiation may change the interatomic distances and forces.