The role of subtractive defects and grain boundaries in determining early failures in VLSI metal interconnects

Subtractive metal defects which remove more than 50% of the conductor width have an impact on early failures when the grain size is small compared to the feature size. The results of over 300 samples show that for 3 micron wide Al-1%Si conductors with a mean grain size of 0.7 micron, the first failures occur within 10 minutes whilst in the nondefected after 6 hrs. The log normal standard deviation (σ) of the lifetime distribution for the defected stripes is also very large. Defects which remove up to 80% of the metal line width have no effect on early failures in conductors with a grain size of 1.0 micron. These samples exhibit a bamboo structure at the site of the defect. All tests were conducted at 200°C and 1.5×10⁶ Amp/cm²