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Reliability testing has long served as a method of ensuring that semiconductor devices maintain their desired performance over a given lifetime. As IC manufacturers continue to introduce new and innovative processes with decreasing device geometries, they need to ensure that the additional complexity from these changes doesn't affect the long-term reliability of their ICs. In addition, major technology trends in autonomous driving, cloud-based data storage, and life sciences are forcing IC suppliers to provide higher assurances of product reliability to their customers who work on mission-critical applications.
These two trends are driving semiconductor manufacturers to vastly increase the amount of reliability data they collect and analyze while decreasing the cost of test. When faced with this problem of more data at a lower cost, many reliability engineers find they cannot solve it using traditional reliability solutions. As a result, they're turning toward modular, flexible solutions that can scale to fit their needs (Fig. 1).
RELIABILITY TESTING
Device reliability is typically modeled as failure rate over time, with the highest failure rates occurring immediately after manufacturing and again after the product has exceeded its useful lifetime (Fig. 2).
The left side of the graph shows early failures often caused by defects in the manufacturing process. These types of failures can be screened during production to minimize the number of defective parts sent to customers. However, the functional tests performed during production can neither identify defects that cause the device to prematurely wear out, nor offer insight into the product's usable lifetime. But reliability testing identifies these types of failure mechanisms and estimates the product's usable lifetime.
Reliability testing involves stressing a device at the extreme ends of the device's specifications -- usually voltage and temperature -- to accelerate device wearout and model the usable lifetime against known failure mechanisms. These tests can be performed on a wafer or packaged part. Wafer-level reliability (WLR) provides more data earlier in the manufacturing process without the cost and potential damage associated with cutting and packaging the IC.
WAFER-LEVEL RELIABILITY
WLR is a type of parametric test that extracts information about the device's usable lifetime and long-term reliability. These tests typically aren't performed...