Moisture impact on dielectric reliability in low-k dielectric materials

Moisture impact on dielectric reliability was investigated with intentional moisture uptake and removal from porous low-k dielectric. In our tests, moisture can reduce TDDB lifetimes by 6 orders, while the kinetics is maintained (for both dry and wet samples). Interestingly, moisture from humid atmosphere does not increase the leakage current, but can reduce TDDB lifetimes significantly. So, the leakage current is not a good index to detect moisture-induced TDDB degradation. TDDB tests with various pre-bake conditions show moisture removal is not linear over bake temperatures, indicating multiple moisture states in low-k dielectric. Moisture diffusion, scaled from our test condition, shows moisture can diffuse few micro-meters in one second into low-k dielectric even at room temperature and impact dielectric reliability. To recover from the moisture damage, we recommend a high bake temperature (300°C~350°C).