Stress and stress relief in dielectric thin films - the role of hydrogen

Novel crack propagation modes are reported in amorphous silicon-rich oxide (SiO_x) films deposited onto (1 0 0) silicon substrates and subjected to thermal annealing. These include the formation of straight cracks aligned with 〈0 0 1〉 directions in the underlying Si substrate as well as oscillating cracks aligned with 〈0 1 1〉 directions in the underlying Si substrate. The cracks are shown to form as the result of increasing tensile stress in the film caused by annealing, with the straight cracks forming at lower tensile stress levels than the oscillating cracks. The increase in tensile stress with increasing annealing temperature in the range 400-650 °C is shown to be correlated with the hydrogen content of the films, as measured by heavy-ion elastic recoil detection.