Keithley hci wp free download

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WHITE PA P E R Reduced Test Time for HCI and Electromigration Tests Many reliability "wearout" tests monitor a performance parameter that degrades steadily with the log of the time on stress. In most cases, a time to 10% degradation is measured. The time to 10% degradation is considered a benchmark because many devices are tested at speeds or voltages that are 10% greater than the certified capability of the semiconductor devices. For example, a DRAM might be tested and found to be fully functional with a 45ns access time but then sold as a slower 50ns device. This "guard-banding" allows for a drift of up to 10% in the critical performance parameters without the device falling outside of its specified performance. A reliability test must prove that the device will not experience a critical performance parameter drift of more than 10% over the expected product lifetime (typically ten or 20 years). Accelerated stress levels can be used to obtain a measure of the time to 10% degradation in a shorter period. However, a good knowledge of the failure mechanism is required in order to extrapolate the results to find the time to 10% degradation at the use conditions. In most cases, this will require testing at several different stress conditions to extract the relationship between the stress condition and rate of degradation. This multiplies the cost of the test and limits the test time reduction to what can be obtained using the lowest stress condition. The maximum stress conditions are typically limited by parasitic considerations such as joule heating or source-drain punch-through voltage. Additionally, competing failure mechanisms can cause a change in the tested failure mechanism at higher stress conditions (e.g., the change from grain boundary diffusion to bulk diffusion at higher temperatures for electromigration tests). This limits the acceleration that can be applied to the highest stress condition. Keithley Instruments, Inc. 28775 Aurora Road Cleveland, Ohio 44139 (440) 248-0400 Fax: (440) 248-6168 www.keithley.com