A wafer-level test method for combined friction force and shock stress testing using a MEMS accelerometer based test structure

Micro-Electro-Mechanical Systems (MEMS) are well established across a broad range of markets, including industrial, consumer, and automotive applications. As all markets trend toward further miniaturization, there is a growing demand for devices that maintain high reliability and meet tightening specifications. One of those specifications is the long-term stiction robustness, which is increasingly becoming a crucial point in the development of further miniaturized MEMS. Miniaturization leads to more sensitive springs, which then lead to smaller restoring spring forces, causing stiction failure events. However, due to the complexity of MEMS in terms of manufacturing processes and failure mechanisms, no comprehensive predictive model currently exists that can accurately forecast lifetime by simultaneously considering all reliability-critical parameters, including contact surface tribology and material properties. This situation highlights the necessity for test data to ensure the reliability of MEMS devices. In this context, a wafer-level test (WLT) approach is presented for contact area characterization, enabling the study of coating materials, stopper geometries, and their changes under stress tests. The method reveals a correlation between adhesive and friction forces and detects changes in friction curves over the course of stress testing. The presented WLT method thus provides a comprehensive tool for characterizing the contact area of MEMS sidewalls under friction-affected stress within real chip environments.