Interfacial diffusivity of moisture along a SiO_2/TiN interface measured using imaging secondary ion mass spectroscopy (SIMS)

摘要

The SiO_2/TiN interface is prone to sub-critical decohesion by crack extension along the interface when exposed to moisture. As with conventional sub-critical crack growth in bulk silica, the rate of decohesion is dependent on both the relative humidity and the strain energy release rate. One of the unusual observations we have noted is that the decohesion velocity of narrow strips is highly sensitive to the exposure time in the humid environment, suggesting that the moisture diffuses into the interface ahead of the propagating decohesion crack, causing a form of hydrolytic weakening of the interface. In seeking to establish the origin of this behavior, we report measurements of moisture diffusion along the SiO_2/TiN interface using Imaging Secondary Ion Mass Spectroscopy (SIMS) after immersion in water containing radioactive tracers, ~2D and ~(18)O. Analysis of images formed using 2~D and ~(18)O revealed that both diffuse along the interface with a diffusivity of (6+-2)x10~9-13) cm~2/sec, a value about 10~4 times faster than the bulk diffusion in the SiO_2 dielectric.