Novel crack propagation in PECVD-deposited dielectric thin films

Silicon-rich silicon oxide (SRSO) films, deposited onto (1 0 0) silicon substrates by plasma-enhanced chemical vapor deposition (PECVD), are shown to develop large tensile stresses during annealing in the temperature range 350-650 °C, a process that has previously been shown to be accompanied by release of hydrogen from the films. Two distinct modes of crack propagation are shown to result from the presence of high tensile stress: linear cracks that propagate along directions parallel to 〈0 0 1〉 directions of the underlying silicon substrate and oscillating cracks that propagate parallel to 〈0 1 1〉 directions of the substrate. In both cases the cracks extend through the deposited thin film and into the underlying silicon, with the latter showing a complex relationship between the in-plane (transverse) crack oscillation and the orientation of the crack extension in the crystalline substrate. Finally, ion-irradiation of the films with 400 keV Si⁺ ions is shown to have a dramatic effect on crack formation, reducing the total density of cracks by as much as an order of magnitude for a fluence of 1 × 10¹⁶ Si/cm². It is speculated that this is a result of stress reduction in the irradiated films.