Wafer-level screening data taken during the process development and capacity expansion phases of a fabrication line for micro-electromechanical system (MEMS) acceleration sensor elements were analyzed to guide test improvement decisions. The process variation of the mature sensor fabrication line was estimated from several relatively stable periods of production during development and expansion to provide a reference for predicting the usefulness of test improvements.

The screening test system was evaluated using data from two types of reference wafers; zero function standards, and reference wafers whose true functional values were unknown but assumed to be constant and representative. Screening effectiveness was validated by correlation with accelerometer calibration results.

The effects of test interface failures and reference wafer wear-out were identified and removed from the reference wafer measurements to isolate the test system variation. This was used with the estimated stable production variation and the failure data to evaluate test capability and reliability.