Practical triggering of early breakdowns in thin oxides

When measuring breakdown distributions it is often necessary to account for both the early non-destructive breakdowns and the final destructive breakdown. Early, non-destructive, breakdowns on thinner oxides are difficult to detect. The early breakdowns, often called extrinsic breakdowns, may be the more important of the two breakdowns, since the early failures probably determine field returns and fabrication yield. However, when attempting to measure the distributions of these two types of failures it is necessary to consume a lot of time making a large number of breakdown measurements, since in modern IC fabrication very few early failures occur. In this paper we describe two techniques for simplifying the measurement of the early failure distributions. In one technique we purposely trigger the hard-to-measure early failures into a thermal, dielectric breakdown by adding more energy to the breakdown path during the triggering of an early breakdown. The added energy heats the dielectric to the point where a stable melted region is formed between the two electrodes. In the second technique a high-speed storage oscilloscope is used to record (a) the times of all early, non-destructive breakdowns, (b) the time of the final, thermal, dielectric breakdown, and (c) the wave shapes of all of the breakdowns. This second measurement technique uses less time and a smaller number of test structures than does the more conventional technique using large numbers of breakdown measurements